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Appelo, Sophia Aletta. "Structural optimisation via genetic algorithms." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71907.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The design of steel structures needs to incorporate some optimisation procedure that evolves the initial design into a more economic nal design, where this nal design must still satisfy all the initial design criteria. A candidate optimisation technique suggested by this research is the genetic algorithm. The genetic algorithm (GA) is an optimisation technique that was inspired by evolutionary principles, such as the survival of the ttest (also known as natural selection). The GA operates by generating a population of individuals which 'compete' with one another in order to survive, or di erently stated, in order to make it into the next generation. Each individual presents a solution to the problem. Surviving solutions which propagate through to the next generation are typically 'better' or ' tter' than the ones that had died o , hence suggesting a process of optimisation. This process continues until a de ned convergence criteria is met (e.g. speci ed maximum number of generations is reached), where after the best individual in the population serves as the ultimate solution to the problem. This study thoroughly investigates the inner workings that drive the algorithm, after which an algorithm is presented to face the challenges of structural optimisation. This algorithm will be concerned only with sizing optimisation; geometry, topology and shape optimisation is outside the scope of this research. The objective of this optimising problem will be to minimise the weight of the structure, it is assumed that the weight is inversely propotional to the cost of the structure. The motive behind using a genetic algorithm in this study is largely due to its ability to handle discrete search spaces; classical search methods are typically limited to some form of gradient search technique for which the search space must be continuous. The algorithm is also preferred due to its ability to e ciently search through vast search spaces, which is typically the case for a structural optimisation problem. The genetic algorithm's performance will be examined through the use of bench-marking problems. Benchmarking is done for both planar and space trusses; the 10 - and 25 bar truss problems. Such problems are typically analysed with stress and displacement constraints. After the performance of the algorithm is validated, the study commences towards solving real life practical problems. The rst step towards solving such problems would be to investigate the 160 bar truss benchmarking problem. This problem will be slightly adapted by applying South African design standards to the design, SANS (2005). This approach is more realistic, when compared to simply specifying stress and displacement constraints due to the fact that an element cannot simply be assigned the same stress constraint for tension and compression; slenderness and buckling e ects need to be taken into account. For this case, the search space will no longer simply be some sample search space, but will consist of real sections taken from the Southern African Steel Construction Handbook, SAISC (2008). Finally, the research will investigate what is needed to optimise a proper real life structure, the Eskom Self-Supporting Suspension 518H Tower. It will address a wide variety of topics, such as modelling the structure as realistically as possible, to investigating key aspects that might make the problem di erent from standard benchmarking problems and what kind of steps can be taken to over-come possible issues and errors. The algorithm runs in parallel with a nite element method program, provided by Dr G.C. van Rooyen, which analyses the solutions obtained from the algorithm and ensures structural feasibility.
AFRIKAANSE OPSOMMING: Die ontwerp van staal strukture moet 'n sekere optimalisasie proses in sluit wat die aanvanklike ontwerp ontwikkel na 'n meer ekonomiese nale ontwerp, terwyl die nuwe ontwerp nog steeds aan al die aanvanklike ontwerp kriteria voldoen. 'n Kandidaat optimeringstegniek wat voorgestel word deur hierdie navorsing is die genetiese algoritme. Die genetiese algoritme (GA) is 'n optimaliserings tegniek wat ge- ïnspireer was deur evolusionêre beginsels soos die oorlewing van die sterkste (ook bekend as natuurlike seleksie). Dit werk deur die skep van 'n bevolking van individue wat 'kompeteer' met mekaar om dit te maak na die volgende generasie. Elke individu bied 'n oplossing vir die probleem. Oorlewende oplossings wat voortplant deur middel van die volgende generasie is tipies 'beter' of ' kser' as die individue wat uitgesterf het, dus word 'n proses van optimalisering word saamgestel. Hierdie proses gaan voort totdat 'n bepaalde konvergensie kriteria voldoen is (bv. 'n gespesi seerde aantal generasies), waar na die beste individu in die bevolking dien as die uiteindelike oplossing vir die probleem. Hierdie studie ondersoek die genetiese algoritme, waarna 'n algoritme aangebied word om die uitdagings van strukturele optimalisering aan te spreek. Hierdie algoritme het alleenlik te doen met snit optimalisering; meetkunde, topologie en vorm optimalisering is buite die bestek van hierdie navorsing. Die motief agter die gebruik van 'n genetiese algoritme in hierdie studie is grootliks te danke aan sy vermoë om diskrete soek ruimtes te hanteer; klassieke soek metodes word gewoonlik beperk tot 'n vorm van 'n helling tegniek waarvoor die soektog ruimte deurlopende moet wees. Die algoritme is ook gekies as gevolg van sy vermoë om doeltre end deur groot soektog ruimtes te soek, wat gewoonlik die geval vir 'n strukturele probleem met optimering is. Die genetiese algoritme se prestasie sal ondersoek word deur die gebruik van standaarde toetse. Standarde toetse word gedoen vir beide vlak en ruimte kappe, die 10 - en 25 element vakwerk. Sulke probleme word tipies met spanning en verplasing beperkings ontleed. Na a oop van die bekragtiging van die algoritme, word praktiese probleme hanteer. Die eerste stap in die rigting sou wees om die 160 element vakwerk toets probleem te ondersoek. Hierdie probleem sal e ens aangepas word deur die toepassing van die Suid-Afrikaanse ontwerp standaarde, SANS (2005) aan die ontwerp. Dit is 'n meer realistiese benadering in vergelyking met net gespesi seerde spanning en verplasing beperkings as gevolg van die feit dat 'n element nie net eenvoudig dieselfde spanning beperking vir spanning en druk toegeken kan word nie; slankheid en knik e ekte moet ook in ag geneem word. In hierdie geval sal die soek ruimte nie meer net meer eenvoudig 'n sekere teoretiese soek ruimte wees nie, maar sal bestaan uit ware snitte wat uit die Suid Afrikaanse Konstruksie Handboek kom, SAISC (2008). Ten slotte sal die navorsing ondersoek instel na 'n standaard Eskom Transmissie toring en dit sal 'n wye verskeidenheid van onderwerpe aanspreek, soos om die modellering van die struktuur so realisties as moontlik te maak, tot die ondersoek van sleutelaspekte wat die probleem verskillend van standaard toets probleme maak en ook watter soort stappe geneem kan word om moontlike probleme te oor-kom. Die algoritme werk in parallel met 'n eindige element metode program, wat deur Dr GC van Rooyen verskaf is, wat die oplossings ontleed van die algoritme en verseker dat die struktuur lewensvatbaar is.
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Barry, Mamadou Aliou. "Optimisation des structures nanophotoniques pour le photovoltaïque." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC096/document.
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Ce manuscrit s'attache au problème du design en photonique, à savoir déterminer la meilleure façon d'agencer des éléments nanométriques pour obtenir la réponse optique que l'on désire. Différents algorithmes sont testés. Un algorithme en particulier semble adapté à ce type de problème, et permet de retrouver des structures photoniques présentes dans la nature sur les carapaces de certains insectes ou les ailes de certains papillons. Appliqué à l'anti-reflet d'une cellule photovoltaïque, l'algorithme a permis de trouver une structure contre-intuitive mais particulièrement efficace, ce qui montre tout le potentiel de cette techniqueThe present manuscript deals with the problem of the design in photonics, i.e. to determine which is the best way to assemble nanometric elements to reach a desired optical response. Different algorithms are tested. One algorithm in particular seems well adapted to this kind of problem, and allows to retrieve the most emblematic photonic structures which a present in nature on the tegument of insects or on the wings of butterflies. Applied to the case of an anti-reflective coating for a photovoltaic device, the algorithm has produced a particularly counter intuivite but efficient structure. This clearly demonstrates the potential of such an approach
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Laamiri, Hassan. "Optimisation methods in structural systems reliability." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46878.
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Pritchard, Thomas J. "Novel techniques in structural layout optimisation." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419635.
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Buckney, Neil. "Optimisation of wind turbine blade structural topology." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633206.
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Wind turbines become more cost effective as they grow larger; however the blade mass increases at a greater rate than the power. For a continued size increase, reducing the mass of the blades is necessary. Additionally, lighter blades lower overall turbine costs because the loads on the rest of the structure are decreased. Therefore, the use of lightweight blades can have a significant impact on the cost of wind energy. To achieve blade mass reductions, an alternative structural layout is generated using topology optimisation. The result is a topology which varies along the blade length, transitioning from a structure with trailing edge reinforcement to one with offset spar caps. An alternative beam topology optimisation method is developed that enabled a buckling constraint to be applied. The structural efficiency of the topologically optimised blade is then assessed using shape factors and performance indices, measures which have been expanded to account for asymmetric bending of beams with multiple materials. The utility of shape factors is first demonstrated on six example beam sections before being applied to the blade. To demonstrate application to a more refined design, the performance of a 100m wind turbine blade is assessed , using maps to visualise the structural efficiency. The effect of using carbon fibre and offsetting the spar caps is evaluated, providing a greater understanding of the improved designs. Overall , the results show that wind turbine blades can be improved with structural layouts that take advantage of favourable bend-bend coupling between the out-of-plane and in-plane directions. Because traditional design concepts do not account for bending coupling, a missed opportunity for further mass reduction exists. To this day, the structural topology of the blades has remained fixed despite increasing length and changing loads. Topology optimisation and structural efficiency analysis are shown as methods used to challenge this design convention and reduce blade mass, thereby lowering the cost of wind energy.
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Wood, Derren Wesley. "Dual sequential approximation methods in structural optimisation." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20033.
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Thesis (PhD)--Stellenbosch University, 2012ENGLISH ABSTRACT: This dissertation addresses a number of topics that arise from the use of a dual method of sequential approximate optimisation (SAO) to solve structural optimisation problems. Said approach is widely used because it allows relatively large problems to be solved efficiently by minimising the number of expensive structural analyses required. Some extensions to traditional implementations are suggested that can serve to increase the efficacy of such algorithms. The work presented herein is concerned primarily with three topics: the use of nonconvex functions in the definition of SAO subproblems, the global convergence of the method, and the application of the dual SAO approach to large-scale problems. Additionally, a chapter is presented that focuses on the interpretation of Sigmund’s mesh independence sensitivity filter in topology optimisation. It is standard practice to formulate the approximate subproblems as strictly convex, since strict convexity is a sufficient condition to ensure that the solution of the dual problem corresponds with the unique stationary point of the primal. The incorporation of nonconvex functions in the definition of the subproblems is rarely attempted. However, many problems exhibit nonconvex behaviour that is easily represented by simple nonconvex functions. It is demonstrated herein that, under certain conditions, such functions can be fruitfully incorporated into the definition of the approximate subproblems without destroying the correspondence or uniqueness of the primal and dual solutions. Global convergence of dual SAO algorithms is examined within the context of the CCSA method, which relies on the use and manipulation of conservative convex and separable approximations. This method currently requires that a given problem and each of its subproblems be relaxed to ensure that the sequence of iterates that is produced remains feasible. A novel method, called the bounded dual, is presented as an alternative to relaxation. Infeasibility is catered for in the solution of the dual, and no relaxation-like modification is required. It is shown that when infeasibility is encountered, maximising the dual subproblem is equivalent to minimising a penalised linear combination of its constraint infeasibilities. Upon iteration, a restorative series of iterates is produced that gains feasibility, after which convergence to a feasible local minimum is assured. Two instances of the dual SAO solution of large-scale problems are addressed herein. The first is a discrete problem regarding the selection of the point-wise optimal fibre orientation in the two-dimensional minimum compliance design for fibre-reinforced composite plates. It is solved by means of the discrete dual approach, and the formulation employed gives rise to a partially separable dual problem. The second instance involves the solution of planar material distribution problems subject to local stress constraints. These are solved in a continuous sense using a sparse solver. The complexity and dimensionality of the dual is controlled by employing a constraint selection strategy in tandem with a mechanism by which inconsequential elements of the Jacobian of the active constraints are omitted. In this way, both the size of the dual and the amount of information that needs to be stored in order to define the dual are reduced.
AFRIKAANSE OPSOMMING: Hierdie proefskrif spreek ’n aantal onderwerpe aan wat spruit uit die gebruik van ’n duale metode van sekwensi¨ele benaderde optimering (SBO; sequential approximate optimisation (SAO)) om strukturele optimeringsprobleme op te los. Hierdie benadering word breedvoerig gebruik omdat dit die moontlikheid skep dat relatief groot probleme doeltreffend opgelos kan word deur die aantal duur strukturele analises wat vereis word, te minimeer. Sommige uitbreidings op tradisionele implementerings word voorgestel wat kan dien om die doeltreffendheid van sulke algoritmes te verhoog. Die werk wat hierin aangebied word, het hoofsaaklik betrekking op drie onderwerpe: die gebruik van nie-konvekse funksies in die defini¨ering van SBO-subprobleme, die globale konvergensie van die metode, en die toepassing van die duale SBO-benadering op grootskaalse probleme. Daarbenewens word ’n hoofstuk aangebied wat fokus op die interpretasie van Sigmund se maasonafhanklike sensitiwiteitsfilter (mesh independence sensitivity filter) in topologie-optimering. Dit is standaard praktyk om die benaderde subprobleme as streng konveks te formuleer, aangesien streng konveksiteit ’n voldoende voorwaarde is om te verseker dat die oplossing van die duale probleem ooreenstem met die unieke stasionˆere punt van die primaal. Die insluiting van niekonvekse funksies in die definisie van die subprobleme word selde gepoog. Baie probleme toon egter nie-konvekse gedrag wat maklik deur eenvoudige nie-konvekse funksies voorgestel kan word. In hierdie werk word daar gedemonstreer dat sulke funksies onder sekere voorwaardes met vrug in die definisie van die benaderde subprobleme inkorporeer kan word sonder om die korrespondensie of uniekheid van die primale en duale oplossings te vernietig. Globale konvergensie van duale SBO-algoritmes word ondersoek binne die konteks van die CCSAmetode, wat afhanklik is van die gebruik en manipulering van konserwatiewe konvekse en skeibare benaderings. Hierdie metode vereis tans dat ’n gegewe probleem en elk van sy subprobleme verslap word om te verseker dat die sekwensie van iterasies wat geproduseer word, toelaatbaar bly. ’n Nuwe metode, wat die begrensde duaal genoem word, word aangebied as ’n alternatief tot verslapping. Daar word vir ontoelaatbaarheid voorsiening gemaak in die oplossing van die duaal, en geen verslappings-tipe wysiging word benodig nie. Daar word gewys dat wanneer ontoelaatbaarheid te¨engekom word, maksimering van die duaal-subprobleem ekwivalent is aan minimering van sy begrensingsontoelaatbaarhede (constraint infeasibilities). Met iterasie word ’n herstellende reeks iterasies geproduseer wat toelaatbaarheid bereik, waarna konvergensie tot ’n plaaslike KKT-punt verseker word. Twee gevalle van die duale SBO-oplossing van grootskaalse probleme word hierin aangespreek. Die eerste geval is ’n diskrete probleem betreffende die seleksie van die puntsgewyse optimale veselori¨entasie in die tweedimensionele minimum meegeefbaarheidsontwerp vir veselversterkte saamgestelde plate. Dit word opgelos deur middel van die diskrete duale benadering, en die formulering wat gebruik word, gee aanleiding tot ’n gedeeltelik skeibare duale probleem. Die tweede geval behels die oplossing van in-vlak materiaalverspredingsprobleme onderworpe aan plaaslike spanningsbegrensings. Hulle word in ’n kontinue sin opgelos met die gebruik van ’n yl oplosser. Die kompleksiteit en dimensionaliteit van die duaal word beheer deur gebruik te maak van ’n strategie om begrensings te selekteer tesame met ’n meganisme waardeur onbelangrike elemente van die Jacobiaan van die aktiewe begrensings uitgelaat word. Op hierdie wyse word beide die grootte van die duaal en die hoeveelheid inligting wat gestoor moet word om die duaal te definieer, verminder.
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Qian, Connie Cheng. "Structural optimisation of discontinuous carbon fibre composites." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14542/.
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There has been a growing interest in using discontinuous carbon fibre composites for semi-structural applications within the automotive industry. The main advantages of discontinuous fibres are low material costs, low wastage and low touch labour compared with processes using carbon fibre textiles. Directed Carbon Fibre Preforming (DCFP) is an automated process for producing complex 3D preforms for liquid moulding. DCFP offers the potential for producing highly optimised structures, with local control over tow size, fibre length and volume fraction within the component. The execution of this is challenging however, as confidence in the current library of material properties is low and existing structural optimisation packages only consider a very limited number of design variables, which are restricted to more conventional composite materials. This thesis aims to establish a structural design tool to exploit the design freedom offered by the DCFP process. A large number of parameters associated with the fibre architecture can be controlled to meet a range of design criterions such as performance, weight and cost. The optimisation tool is capable of generating locally varied fibre areal mass and thickness maps that are suitable for manufacture by the robot controlled process. The developed model adopts a multi-scaled finite element approach. Meso-scale simulations are performed to establish size effects in discontinuous fibre composites, to quantify the level of stochastic variability and to determine the representative volume element for a given fibre architecture. A DCFP material database is generated to facilitate macro-scale modelling at the component level. The macro-scale model iteratively redistributes material in order to minimise the total strain energy of the model under prescribed loading conditions. The optimised model is segmented into areas of uniform areal mass, where the zone geometries are tailored to achieve representative material properties according to the meso-scale results, whilst ensuring the design is fit for manufacture. An automotive spare wheel well has been chosen as a demonstrator component, enabling two DCFP architectures to be compared against a continuous glass/carbon fibre NCF design. The first case offers a high performance (high specific stiffness) solution and the second offers a low cost option using high filament count tows. Following optimisation, results suggest that a 3K 25mm fibre length DCFP option can achieve a specific stiffness 52% higher than the glass/carbon baseline design, but for 1.33 times higher material cost. Alternatively, the specific stiffness of a 24K 50mm fibre length DCFP is marginally lower than the first option, but still out-performs the baseline for just 67% of the material cost. The structural optimisation method demonstrates that discontinuous fibre composites can compete against continuous fibre counterparts for semi-structural applications.
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Uthman, Zana. "Configurational forces in structural and continuum optimisation." Thesis, University of Sheffield, 2008. http://etheses.whiterose.ac.uk/91/.
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This thesis deals with optimisation using the principles of continuum mechanics. Both shape and mesh optimisation will be covered. A unified approach will be introduced to obtain shape and mesh optimisation for hyperelastic, hyperelastodynamic and hyperelastoplastic settings. The approach makes use of the generated material force method in mesh optimisation and the so-called imposed material force method in shape optimisation. To this end, the appropriate spatial and material continuum mechanic Equations will be developed in hyperelastic, hyperelastodynamic and hyperelastoplastic settings. A summary of the four main parts is as follows. The first part begins with structural optimisation in hyperelastic setting. After introducing the necessary Equations, the effectiveness of the material force method to obtain global optimised solutions for truss structures will be demonstrated. The implementation produces the global optimised undeformed configuration and the global optimised deformed configuration. The shape and mesh optimisation will be tested for two and three dimensional truss structures under small and large deformations. In addition, these formulations will be extended to obtain constrained optimised solutions. The penalty method is used to realise optimised truss structures within certain design criteria. The second part develops a new Arbitrary Lagrangian Eulerian (ALE) hyperelastic setting in rate form. It will deal with two systems of partial differential Equations, namely the spatial and the material momentum Equation. Both are discretised with the finite element method. The spatial Equation will then be linearised by taking the material time derivative while the material Equation will be linearised by taking the spatial time derivative. The solution defines the optimal spatial and material configuration in the context of energy minimisation in hyperelastic setting. The implemented examples will illustrate shape optimisation under the effect of mesh refinement The third part provides the formulation and implementation details of ALE hyperelastodynamic problem classes. This ALE formulation is based on the dual balance of momentum in terms of both spatial and material forces. The balance of spatial momentum results in the usual Equation of motion, whereas the balance of the material momentum indicates deficiencies in the nodal positions, hence providing an objective criterion to optimise the finite element mesh. The main difference with traditional ALE approaches is that the combination of the Lagrangian and Eulerian description is no longer arbitrary. In other words the mesh motion is no longer user defined but completely embedded within the formulation. This presents a discretisation and linearisation for a recently developed variational arbitrary Lagrangian Eulerian framework in hyperelastodynamics setting. The spatial and material variational Equations will be discretised to obtain the weak form of the momentum and continuity Equations. The discretised ALE Hamiltonian Equations of the spatial motion problem introduces the balance of the discretised spatial momentum and the discretised spatial continuity Equation while the corresponding material motion problem defines the balance of the discretised material (or configurational) momentum and the discretised material continuity Equation. We will deal with two systems of partial differential Equations: the scalar continuity Equation and the vector balance of momentum Equation. The momentum and continuity Equations will then be linearised. The time integration of both the spatial and the material Equations is performed with Newmark scheme. A monolithic solution strategy solving both the spatial and the material momentum Equations has been carried out while updating of the spatial and the material densities were attained through solving the spatial and material continuity Equations (mass conservation). The concept of generated material force has been implemented to optimise the mesh and consequently the wave propagation. The solution defines the optimal spatial and material configuration in the context of energy minimisation. The fourth part provides the framework and implementational details of ALE hyperelastoplasticity problem classes. This ALE formulation is based on the dual balance of momentum in terms of spatial forces (the well-known Newtonian forces) as well as material forces (also known as configurational forces). The balance of spatial momentum results in the usual Equation of motion, whereas the balance of the material momentum indicates deficiencies in the nodal positions, hence providing an objective criterion to optimise the shape or the finite element mesh. The earlier developed ALE hyperelastic setting will provide the platform to extend the formulation to include plasticity. The new ALE hyperelastoplasticity setting will be developed at finite strain. In ALE hyperelastoplastic formulation additional Equations are required to update the stresses. The principle of maximum plastic dissipation as well as the consistency conditions in spatial and material setting will introduce the spatial and material plastic parameters and rate form of the stress-strain relations. The solution defines the optimal spatial and material configuration in the context of energy minimisation in hyperelastoplasticity setting. The concepts of imposed and generated material force are implemented to provide improvements over Lagrangian solutions.
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Liu, Jing-Sheng. "Integrated structural and electromagnetic optimisation of large terrestrial and space antenna structures." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/843480/.
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In this study, a novel multi-parameter overall situation optimisation method and mathematical model has been developed for use with terrestrial and space reflector antenna electro-mechanical systems and other metallic and polymer composite civil engineering structures. To satisfy extremely high design requirements, the proposed approach incorporates the objectives from various structural and electromagnetic (EM) performances of the system such as structural frequency, weight, stiffness, strength, reflector surface accuracy, antenna EM efficiency (gain), and radiation patterns at many working/loading cases simultaneously. The optimisation involves geometric and material design variables, and integrated design of composites and structural systems. Various terrestrial, launch and orbital working environments and loading cases which affect antenna performances have been included in the optimisation. These involve self-weight at different elevation attitudes, wind loading, random/dynamic loads and temperature distributions. Both truss and sandwich parabolic reflector panels with honeycomb core and carbon fibre laminate skins stiffened with composite ribs have been optimised. The effects of structural deformation on antenna EM performances have been investigated, modelled and repeatedly analysed in the iterative optimum-seeking procedure. Optical ray tracing, spline function aperture field interpolation, geometric optics aperture integration, Zernike modes analysis and FFT techniques have been used to analyse the EM performances of distorted reflector antennas. An important aspect of the work was the establishment of evaluation criteria in optimising engineering systems. A new method is presented, which can be used as a design review tool to assess the design quality of engineering systems. This systematic method quantitatively evaluates a design from multi-discipline and numerous points of view simultaneously for Pareto optimisation. A general purpose optimisation program MOST (Multifactor Optimisation of Structures Technique) has been developed to implement the proposed approach. MOST has the ability to utilise ABAQUS as an analysis routine for linear and non-linear, static and dynamic structural analysis in the optimisation procedures. Examples are presented to demonstrate the capabilities of the optimisation methodology and MOST program system. These examples are: an 8m Cassegrain antenna system, a 3.6x2.6m composite space deployable reflector antenna structure, and two 4m low side-lobe off-set antenna systems (with composite structures). The optimisation results for these antennas show that the optimisation procedures succeed in that at all the working/loading cases the antenna performances have been greatly improved.
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Proos, Kaarel. "Evolutionary structural optimisation as a robust and reliable design tool." Connect to full text, 2002. http://hdl.handle.net/2123/519.
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Thesis (Ph. D.)--University of Sydney, 2002.Title from title screen (viewed Apr. 28, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Aeronautical, Mechatronic and Mechanical Engineering. Includes bibliographical references. Also available in print form.
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Kuzjatkin, Juri. "Structural Weight Optimisation of a Carbon Fibre Ferry." Thesis, KTH, Marina system, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163696.
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The Damen Ferry department is developing a concept of fast ferries (DFFe) built of composite materials. Based on the previous experience in composite shipbuilding of Damen modular waterbuses (DWBu) and Water Taxies the Ferry department tries to utilize the existing experience and use it in production of larger vessels that are capable to develop higher speeds and carry more passengers. The key objective is the weight saving - that results in a lighter and therefore more sustainable craft that consumes less fuel and is capable to carry more payload. The expectations are at least 30 per cent of weight saving comparing to the aluminium version of the craft. A general structural plan of the vessel is the basis of this thesis. The structural design is as much as possible defined based on the regulations according to classification society Det Norske Veritas. Three global load cases are considered: longitudinal bending, transverse bending and torsional bending. Besides, five local load cases are considered: sea pressure on the hull, impact pressure on the bottom of the hull, wet deck slamming, deck loads and superstructure loads. Lightweight is one of the important reasons to develop the vessel in composite materials. The material combination of carbon fibre (CF) and vinyl ester (VE) resin is chosen for this vessel. This combination of materials has superior mechanical properties but is considered relatively expensive comparing with glass fibre (GF). The preference is given to CF due to its high strength-to-weight and stiffness-to-weight ratios, which give possibility to obtain the same strength and higher stiffness with lower weight and better mechanical properties than GF. All structural members except the wheelhouse that is not included in this thesis will be sandwich construction because of the much increased strength and stiffness regarding weight. As core material cross-linked PVC will be used. The vessel will be produced with vacuum infusion, which enables relatively fast production and ensures good and consistent material properties. The material properties and safety factors for strength are determined according to Bureau Veritas. Robustness of the laminates is defined by describing minimum laminate thicknesses. Based on the analytical considerations and design requirements a set of optimisation tools has been developed to optimise various composite structures in order to achieve a lightweight solution for the composite craft. The approach used for the development of the tools is fully analytical and can be called as Simple FEA Approach giving the possibility to mesh the analysed structural members in order to get a full picture of the responses due to the applied loads. The developed tools are relatively easy to handle, yet some knowledge in composite structures is needed in order to be able to give critical judgement upon the design of the craft. The tools can be used not only for the preliminary design of the craft and weight estimation needed for the proposal documents provided to the client but also for later design stages when the final scantlings of the craft are estimated. The validation of the developed tools and global analysis of the vessel is performed using Siemens NX. A CAD model is created and linked to a Finite Element environment where different load cases can be evaluated. Adjustments of the material definition could be necessary depending on the results of the Finite Element Analysis.
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Jarmo, Söderman. "Structural and operational optimisation - applications in energy systems /." Åbo : Åbo Akademi University, 2007. http://catalogue.bnf.fr/ark:/12148/cb41224358g.
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Jiang, Haihui Joy. "Structural Design of Ionic Liquids for Process Optimisation." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19001.
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Ionic liquids (ILs) are designer solvents with tuneable cationic and anionic structures. We propose structural factors that are key to realising the designer solvent promise of ILs. We highlight their potential for translation to new generations of low-cost and environmentally sustainable cation and anion motifs for large-scale applications. Starting from a comparison among primary and secondary ammonium ILs, the unusual liquid nanostructure of pyrrolidinium ILs explains its versatile solvent properties. In the context of biomass processing, we present a framework for the design of IL structure to minimize competition and to enhance driving forces for aromatic extraction. Choline amino-acid ILs and their water mixtures show great promise as low-cost biocompatible solvents. ILs as solvents have the rare ability to promote amphiphilic self-assembly of molecules, such as n-alkanols, that are not conventionally considered as amphiphilic surfactants in water. We investigate the structure of complex solutions using a combination of small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), invariant analysis, and neutron diffraction combined with Empirical Potential Structural Refinement (EPSR) simulation technique. We rationalise how IL-supported self-assembly can be controlled over solute polarity, packing geometry and formulation. The design of ILs as solvents is not restricted to pure ionic species. We demonstrate new categories of ILs based on molecular complexation around metal cations. Non-ionic surfactants self-assemble in inorganic salts as they do in ILs or water, with predictable phase behaviours rationalised by the surfactant packing parameter. Further, we show mixtures of paramagnetic salts and low-volatile solvents as magnetic ionic liquids. Our structural understanding of ILs and their mixtures creates opportunities for formulating new types of nanomaterials and facilitates the design of future solvents for process optimisation.
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Baldock, Robert David. "Structural optimisation in building design practice : case-studies in topology optimisation of bracing systems." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612227.
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Tandon, Vijay Lakshmi. "Computer based optimisation techniques in design methodology." Thesis, University of Wolverhampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335754.
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McCafferty, R. "Optimisation of the design of structures using sensitivity analysis." Thesis, University of Wolverhampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370176.
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The increasing demands placed upon design engineers to evolve optimal solutions to prescribed problem specifications necessitates more definitive analysis of system response to modifications.Traditional solution techniques including discretised methods are required to be repeatedly evaluated in multiple re-analysis solution environments in the search for optimal behavioural response. Modern developments in sequential linear programming techniques in both unconstrained and constrained environments have enabled the methods of optimisation to be applied in a structural context.Such advances are now being limited by the present state of solution to criterion and constraint functions. The state of the art in structural optimisation is reviewed and the application of current methods in the presence of discontinuities examined.The extension of such methods to the discretised problem is advocated.The search for an effective and economical re-solution vehicle is described with reference to the classical formulation of sensi tivi ties defined in a discretised context. The development of a solution technique based on sensitivity is described and limitations examined.The extension of sensitivities into the clearly defined non-linear state with large design variable changes is discussed and the development of a residual correction technique to linearise the sensitivities documented.Utilising residual correction the sensitivity method is extended into the concept of adjoint structures and predictive solution models for design variable changes. Quantitative and qualitative techniques for design performance assessment are evolved and an interactive program developed to graphically display the effect of design variable changes on design parameter response. A new design philosophy based upon design system syntheais is advocated and demonstrated wi th reference to particular design problems.Exploratory work is discussed with reference to the general application and the interfacing of the developed software system with alternate systems.
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Crewe, Adam J. "The characterisation and optimisation of earthquake shaking table performance." Thesis, University of Bristol, 1998. http://hdl.handle.net/1983/47c8d984-04b8-4c21-9491-e74829e561ed.
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Schmidt, Martin-Pierre. "Computational generation and optimization of mechanical structures On structural topology optimization using graded porosity control Structural topology optimization with smoothly varying fiber orientations." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR01.
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Cette thèse étudie et développe des méthodes de modélisation mathématique, analyse et optimisation numérique appliquées à la génération d’objets 3D. Les approches proposées sont utilisées pour la génération de structures lattices et de structure continue par optimisation topologiqueThis thesis studies and develops methods for mathematical modeling, numerical analysis and optimization applied to the generation of 3D objects. The proposed approaches are used to generate lattice structures and continuum structures with topology optimization
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Salah, Maher Jawad Younis. "Optimum plastic design of structures by generalized inverse theory and quadratic programming." Thesis, Queen Mary, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337445.
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Proos, Kaarel Andres. "Evolutionary structural optimisation as a robust and reliable design tool." Thesis, The University of Sydney, 2002. http://hdl.handle.net/2123/519.
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Evolutionary Structural Optimisation (ESO) is a relatively new design tool used to improve and optimise the design of structures. It is a heuristic method where a few elements of an initial design domain of finite elements are iteratively removed. Such a process is carried out repeatedly until an optimum design is achieved, or until a desired given area or volume is reached. There have been many contributions to the ESO procedure since its conception back in 1992. For example, a provision known as Bi-Directional ESO (BESO) has now been incorporated where elements may not only be removed, but added. Also, rather than deal with elements where they are either present or not, the designer now has the option to change the element's properties in a progressive fashion. This includes the modulus of elasticity, the density of the material and the thickness of plate elements, and is known as Morphing ESO. In addition to the algorithmic aspects of ESO, a large preference exists to optimise a structure based on a selection of criteria for various physical processes. Such examples include stress minimisation, buckling and electromagnetic problems. In a changing world that demands the enhancement of design tools and methods that incorporate optimisation, the development of methods like ESO to accommodate this demand is called for. It is this demand that this thesis seeks to satisfy. This thesis develops and examines the concept of multicriteria optimisation in the ESO process. Taking into account the optimisation of numerous criteria simultaneously, Multicriteria ESO allows a more realistic and accurate approach to optimising a model in any given environment. Two traditional methods � the Weighting method and the Global Criterion (Min-max) method have been used, as has two unconventional methods � the Logical AND method and the Logical OR method. These four methods have been examined for different combinations of Finite Element Analysis (FEA) solver types. This has included linear static FEA solver, the natural frequency FEA solver and a recently developed inertia FE solver. Mean compliance minimisation (stiffness maximisation), frequency maximisation and moment of inertia maximisation are an assortment of the specific objectives incorporated. Such a study has provided a platform to use many other criteria and multiple combinations of criteria. In extending the features of ESO, and hence its practical capabilities as a design tool, the creation of another optimisation method based on ESO has been ushered in. This method concerns the betterment of the bending and rotational performance of cross-sectional areas and is known as Evolutionary Moment of Inertia Optimisation (EMIO). Again founded upon a domain of finite elements, the EMIO method seeks to either minimise or maximise the rectangular, product and polar moments of inertia. This dissertation then goes one step further to include the EMIO method as one of the objectives considered in Multicriteria ESO as mentioned above. Most structures, (if not all) in reality are not homogenous as assumed by many structural optimisation methods. In fact, many structures (particularly biological ones) are composed of different materials or the same material with continually varying properties. In this thesis, a new feature called Constant Width Layer (CWL) ESO is developed, in which a distinct layer of material evolves with the developing boundary. During the optimisation process, the width of the outer surrounding material remains constant and is defined by the user. Finally, in verifying its usefulness to the practical aspect of design, the work presented herein applies the CWL ESO and the ESO methods to two dental case studies. They concern the optimisation of an anterior (front of the mouth) ceramic dental bridge and the optimisation of a posterior (back of the mouth) ceramic dental bridge. Comparisons of these optimised models are then made to those developed by other methods.
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Proos, Kaarel Andres. "Evolutionary structural optimisation as a robust and reliable design tool." University of Sydney. Aerospace, 2002. http://hdl.handle.net/2123/519.
Full textAbstract:
Evolutionary Structural Optimisation (ESO) is a relatively new design tool used to improve and optimise the design of structures. It is a heuristic method where a few elements of an initial design domain of finite elements are iteratively removed. Such a process is carried out repeatedly until an optimum design is achieved, or until a desired given area or volume is reached. There have been many contributions to the ESO procedure since its conception back in 1992. For example, a provision known as Bi-Directional ESO (BESO) has now been incorporated where elements may not only be removed, but added. Also, rather than deal with elements where they are either present or not, the designer now has the option to change the element's properties in a progressive fashion. This includes the modulus of elasticity, the density of the material and the thickness of plate elements, and is known as Morphing ESO. In addition to the algorithmic aspects of ESO, a large preference exists to optimise a structure based on a selection of criteria for various physical processes. Such examples include stress minimisation, buckling and electromagnetic problems. In a changing world that demands the enhancement of design tools and methods that incorporate optimisation, the development of methods like ESO to accommodate this demand is called for. It is this demand that this thesis seeks to satisfy. This thesis develops and examines the concept of multicriteria optimisation in the ESO process. Taking into account the optimisation of numerous criteria simultaneously, Multicriteria ESO allows a more realistic and accurate approach to optimising a model in any given environment. Two traditional methods � the Weighting method and the Global Criterion (Min-max) method have been used, as has two unconventional methods � the Logical AND method and the Logical OR method. These four methods have been examined for different combinations of Finite Element Analysis (FEA) solver types. This has included linear static FEA solver, the natural frequency FEA solver and a recently developed inertia FE solver. Mean compliance minimisation (stiffness maximisation), frequency maximisation and moment of inertia maximisation are an assortment of the specific objectives incorporated. Such a study has provided a platform to use many other criteria and multiple combinations of criteria. In extending the features of ESO, and hence its practical capabilities as a design tool, the creation of another optimisation method based on ESO has been ushered in. This method concerns the betterment of the bending and rotational performance of cross-sectional areas and is known as Evolutionary Moment of Inertia Optimisation (EMIO). Again founded upon a domain of finite elements, the EMIO method seeks to either minimise or maximise the rectangular, product and polar moments of inertia. This dissertation then goes one step further to include the EMIO method as one of the objectives considered in Multicriteria ESO as mentioned above. Most structures, (if not all) in reality are not homogenous as assumed by many structural optimisation methods. In fact, many structures (particularly biological ones) are composed of different materials or the same material with continually varying properties. In this thesis, a new feature called Constant Width Layer (CWL) ESO is developed, in which a distinct layer of material evolves with the developing boundary. During the optimisation process, the width of the outer surrounding material remains constant and is defined by the user. Finally, in verifying its usefulness to the practical aspect of design, the work presented herein applies the CWL ESO and the ESO methods to two dental case studies. They concern the optimisation of an anterior (front of the mouth) ceramic dental bridge and the optimisation of a posterior (back of the mouth) ceramic dental bridge. Comparisons of these optimised models are then made to those developed by other methods.
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Gil, Lorenzo Saleta. "Structural behaviour of concrete segmental lining tunnels : towards design optimisation." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/286292.
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The deployment of engineering models and design methods divorced from the effect that mechanised shield tunnelling with tunnel boring machines (TBMs) has on concrete segmental linings (CSLs) can lead to either material waste or structural damage within the tunnel design life. Most research to date on CSL behaviour during construction neglects the sequential ring loading and TBM-lining transverse interactions, which this thesis proved to be key in the short and long term behaviour of CSLs and whose study is essential if the design and maintenance of CSL structures is ever to be optimised. This thesis investigates the longitudinal and transverse behaviour of CSL structures simultaneously backfilled with bicomponent grouts (BGs) during tunnelling, and how this early response influences long term behaviour. The research work is drawn on three pillars that enable cross-validation of conclusions: analytical models, three-dimensional numerical simulations and the interpretation of the Crossrail's Thames tunnel (CTT) field data, which included distributed fibre optic strain (DFOS) data. A theoretical framework ranging from construction loading scenarios to the mechanisms underlying structural damage is described for the future development of limit state design methods. Analytical models of longitudinal behaviour are also proposed. The study of joint geometries, temporary spear bolts and DFOS sensing in CSL construction monitoring is included as ancillary research. The solution developed for a sequential elastic rod subjected to a trilinear temperature profile and in shear interaction with the elastic ground predicts accurately the early tunnel pre-stressing relaxation caused by grout hardening, e.g. ≈50% in the CTT. The proposed sequential elastic beam model, which incorporates the effects of stage-varying net TBM moments, transverse loads and lining pressure gradients within the tunnel unsupported length, estimates satisfactorily the history of tunnel beam response during construction for a realistic expression of the lining stiffness. A potential damage assessment method for the early detection of tunnel sections prone to ring joint damage was proposed. The TBM-lining transverse interaction determines the CSL ring behaviour at the early stages of tunnelling. The ring response resultant from this interaction is irrecoverable and contributes to the long term total deformations and internal forces; in tunnels excavated in grounds with Ko≈1, it becomes the major source of ring distortion. The main transverse actions are the sealing pressures, which are inversely related to the tail clearance, and the transverse load of oblique hydraulic jacks. When the non-bedded rings are eccentric with respect to the shield tail, the ring distortion increases the risk of cracking near the rear corners and spalling at the ram pad interspaces of constrained segments. The ring distortion is directly related to the pressure gradients, the unsupported length and the ring flexibility. When individual segments rotate outwards under the action of transverse ram loads, e.g. the outer springline segment during pronounced TBM steering around a horizontal curve, the localised action of the sealing pressures can result in longitudinal cracking at the intrados of the segment front. This study represents a qualitative leap towards the optimisation of CSL design, shifting the attention of researchers and designers to TBM-lining transverse interactions as the most determinant factor of structural response during construction in CSLs simultaneously backfilled with BGs.
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Dunning, Peter. "Introducing loading uncertainty in level set-based structural topology optimisation." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538137.
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Structural topology optimisation aims to provide solutions that are independent of the initial layout, allowing the greatest opportunity to find the best design. Recent developments have seen increased interest in level set based optimisation, as the solutions obtained possess smooth boundaries and are free of numerical instabilities that affect traditional element based methods. The direct level set based structural topology optimisation method has been successful in solving a range of problems. However, it does suffer from some drawbacks and limitations. Two of the main issues with the direct level set method are accurate and efficient sensitivity computation on the boundary and initial design dependent solutions for two dimensional problems. These issues are addressed in this thesis by investigating and improving the efficient area-weighted fixed grid method and creating a novel hole creation method for two dimensional problems based on a pseudo third dimension. Uncertainty is important to include during design and optimisation to produce structures that are reliable and robust. Loading magnitude and direction uncertainty is introduced into the minimisation of compliance problem by considering the robust expected compliance objective. An efficient formulation is derived using an analytical approach where uncertainties are normally distributed. The robust problem is then extended to include compliance variance and sensitivities are derived using the adjoint method.
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Bothma, André Smith. "A computational implementation of design sensitivity analysis and structural optimisation." Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/16106.
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Bibliography: pages 118-121.In the field of computational mechanics, increases in computing power and enhancements in material and kinematic models have enhanced the feasibility of performing structural design optimisation for a wide range of applications. The work presented here was motivated by the current groundswell of research effort in computational optimisation. Design Sensitivity Analysis (DSA) crucially underpins much of structural optimisation and, as such, is focussed on more intently than the optimisation theory itself: various approaches to the Direct Differentiation Method (DDM) DSA procedure are investigated and computationally implemented. The procedures implemented were chosen so as to involve a range of important issues in computational sensitivity analysis, particularly * Shape and non-shape sensitivity analysis, * Total and Updated Lagrange-based DSA, * DSA of displacement and non-displacement based response functionals, * Multiparameter DSA. * DSA for large strain behaviour The primary objectives of this thesis are: I. Development of a design sensitivity formulation which, when discretised, resembles the standard displacement based kinematic element formulation, thus enabling the implementation of design sensitivity analysis in established Finite Element Analysis (FEA) codes as a 'pseudo'-element routine. II. lmplemention of several design sensitivity formulations and structural optimisation into the FEA code ABAQUS as a verification of the first objective. Numerical results provided in this work demonstrate the successful completion of the above-mentioned objectives. The discretised DSA formulations presented, as well as the 'pseudo'-element approach adopted, particularly in the case of shape DSA are entirely original. To the best of the author's knowledge, DSA and DSA-based structural optimisation had never before been attempted with ABAQUS. The research conducted here lays the foundation for potentially very fruitful future work.
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Ugail, Hassan. "Parametric design and optimisation of thin-walled structures for food packaging." Springer, 2003. http://hdl.handle.net/10454/2647.
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In this paper the parametric design and functional optimisation of thin-walled structures made from plastics for food packaging is considered. These objects are produced in such vast numbers each year that one important task in the design of these objects is to minimise the amount of plastic used, subject to functional constraints, to reduce the costs of production and to conserve raw materials. By means of performing an automated optimisation on the possible shapes of the food containers, where the geometry is parametrised succinctly, a strategy to create the optimal design of the containers subject to a given set of functional constraints is demonstrated.
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Kelly, Liam. "Reducing design time : the impact of evolutionary structural optimisation on structural trade studies during preliminary design." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/380508/.
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Aircraft design is an inherently multi-disciplinary decision making process. In many design processes, the vehicle configuration is selected based on aerodynamic considerations in the concept design stage, before the structural layout is considered during preliminary design. Selection of the best vehicle configuration relies on an estimate of weight to determine the required lift of the aircraft. Structural topology optimisation is an efficient method for automatically generating a structural design layout that fits within a given design space and meets a given set of design criteria. By comparison to parametric structural optimisation approaches, topology optimisation permits a much greater design freedom. Though often difficult to manufacture using conventional methods, this design freedom can be exploited by using additive manufacture. In this thesis, an integrated concept and preliminary aerostructural design framework is proposed, which incorporates topology optimisation as a means of structural layout generation and weight estimation. The framework is utilised to optimise the wing geometry of an unmanned air vehicle, while generating a fuselage structure, intended for construction using additive manufacture, which satisfies a von Mises stress constraint. By comparison to an equivalent shell thickness optimisation study, the topology optimisation approach is shown to generate much lighter structural designs for the same aerodynamic efficiency.
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Wong, Kin Ming. "Evolutionary structural form optimisation for lateral stiffness design of tall buildings /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20WONGK.
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Wegert, Zach. "Analysis and optimisation of periodic piezoelectric materials." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232770/1/Zachary_Wegert_Thesis.pdf.
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This project developed computational tools to analyse and design novel piezoelectric materials that have the potential to be utilised in next-generation electromechanical devices. The thesis demonstrates how such architectured materials can be used in the design of multi-functional robotic ‘pain’ sensors.
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Mesnil, Romain. "Explorations structurelles de domaines de formes constructibles pour l’architecture non-standard." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1151/document.
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Les dernières décennies ont vu l’émergence de formes architecturales non standard. Les concepteurs se retrouvent généralement démunis face à la complexité géométrique de ces objets, dont la fabrication rime souvent avec complication. De plus, les outils utilisés dissocient forme et fonctionnement structurel,ce qui complexifie le processus de décision pour ingénieurs et architectes. Ce mémoire prend un point de vue fondé sur la notion d’invariance par transformation géométrique et étudie plusieurs strategies de génération de formes naturellement constructibles pour remédier à ces manques. Trois contraintes constructives ont été identifiées et correspondent à trois contributions indépendantes de cette thèse.La répétition des noeuds d’assemblage est étudiée via les transformations par maillages parallèles. Ces dernières sont utilisées pour créer une généralisation des surfaces de révolution. On retrouve par là un paramétrage particulier des surfaces moulures de Monge avec une grande répétition d’éléments, et notamment de noeuds d’assemblage.Les réseaux de cyclides sont ensuite utilisés pour dessiner des formes parametrées par leurs lignes de courbures. Cela permet la couverture par panneaux plans ainsi que l’offset des éléments structurels sans excentricité. L’apport de cette thèse est l’implémentation de plusieurs améliorations, notamment l’introduction de plis à double courbure, un algorithme permettant de généraliser les réseaux de cyclides à des topologies quelconques, et la génération de surfaces généralisant les surfaces canal à partir de deux courbes rail et une courbe profil.Finalement, une méthode innovante inspirée de la géométrie descriptive permettant la génération de formes courbes couvertes par des quadrilatères plans est proposée. La méthode, baptisée méthode marionnette, réduit ce problème à un système linéaire, ce qui permet une manipulation de ces forms constructibles en temps réel. Une étude comparative montre que cette technique peut être utilisée pour paramétrer des problèmes d’optimisation de forme de coques sans perte de performance par rapport aux paramétrages utilisés de façon classique. L’intégration des contraintes de fabrication dans le processus d’optimisation structurelle ouvre de nouvelles possibilités d’applications, comme des résilles gauches et des coques plissées. La pertinence de ces nouvelles solutions est démontrée par de multiples études de casThe last decades have seen the emergence of non-standard architectural shapes. Designers find often themselves helpless with the geometrical complexity of these objects. Furthermore, the available tools dissociate shape and structural behaviour, which adds another complication. This dissertation takes the point of view based on invariance under geometrical transformations, and studies several strategies for fabrication-aware shape modelling. Three technological constraints have been identified and correspond to three independent contributions of this thesis.The repetition of nodes is studied via transformations by parallelism. They are used to generalise surfaces of revolution. A special parametrisation of moulding surfaces is found with this method. The resulting structure has a high node congruence.Cyclidic nets are then used to model shapes parametrised by their lines of curvature. This guarantees meshing by planar panels and torsion-free beam layout. The contribution of this dissertation is the implementation of several improvements, like doubly-curved creases, a hole-filling strategy that allows the extension of cyclidic nets to complex topologies, and the generation of a generalisation of canal surfaces from two rail curves and one profile curves.Finally, an innovative method inspired by descriptive geometry is proposed to generate doubly-curved shapes covered with planar facets. The method, called marionette technique, reduces the problem to a linear problem, which can be solved in real-time. A comparative study shows that this technique can be used to parametrise shape optimisation of shell structures without loss of performance compared to usual modelling technique. The handling of fabrication constraints in shape optimisation opens new possibilities for its practical application, like gridshells or plated shell structures. The relevance of those solutions is demonstrated through multiple case-studies
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Ainul, Azmel. "Structural and aeroelastic multidisciplinary optimisation of a joined-type sensorcraft wing." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494600.
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Classical criteria of aircraft design involve adding a multiplier to the structure's inertial load to cater for various flight circumstances. The value of this multiplier depends on the type of aircraft designed, for example a high value is used in acrobatic variants to cater for their high g manoeuvres, as compared to a lower value in light non-acrobatic versions.
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Allen, Jonathan George. "A framework for hyper-heuristic optimisation of conceptual aircraft structural designs." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/10741/.
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Conceptual aircraft structural design concerns the generation of an airframe that will provide sufficient strength under the loads encountered during the operation of the aircraft. In providing such strength, the airframe greatly contributes to the mass of the vehicle, where an excessively heavy design can penalise the performance and cost of the aircraft. Structural mass optimisation aims to minimise the airframe weight whilst maintaining adequate resistance to load. The traditional approach to such optimisation applies a single optimisation technique within a static process, which prevents adaptation of the optimisation process to react to changes in the problem. Hyper-heuristic optimisation is an evolving field of research wherein the optimisation process is evaluated and modified in an attempt to improve its performance, and thus the quality of solutions generated. Due to its relative infancy, hyper-heuristics have not been applied to the problem of aircraft structural design optimisation. It is the thesis of this research that hyper-heuristics can be employed within a framework to improve the quality of airframe designs generated without incurring additional computational cost. A framework has been developed to perform hyper-heuristic structural optimisation of a conceptual aircraft design. Four aspects of hyper-heuristics are included within the framework to promote improved process performance and subsequent solution quality. These aspects select multiple optimisation techniques to apply to the problem, analyse the solution space neighbouring good designs and adapt the process based on its performance. The framework has been evaluated through its implementation as a purpose-built computational tool called AStrO. The results of this evaluation have shown that significantly lighter airframe designs can be generated using hyper-heuristics than are obtainable by traditional optimisation approaches. Moreover, this is possible without penalising airframe strength or necessarily increasing computational costs. Furthermore, improvements are possible over the existing aircraft designs currently in production and operation.
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Nasuf, A. "An automated shape grammar approach to structural design description and optimisation." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/359741/.
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The main objective of this research is to develop and evaluate an automated design description and optimisation framework based on the Shape Grammar (SG) syntax. In particular, an algorithmic methodology to automate the SG syntax using evolutionary intelligence is proposed. The proposed automation of SG is achieved by mapping the genetic information provided by a Genetic Algorithm (GA) to context-free grammar rules by a means of Backus-Naur Form (BNF) syntax known as Grammatical Evolution (GE). GE is an efficient optimisation tool, which can be used in a variety of optimisation problems. First, its use in single and multi-objective optimisation of mathematical functions is demonstrated. Several techniques for synthesis of variables using specific BNF syntaxes are proposed. The results obtained from numerical experiments are compared with those obtained using a standard GA. Interestingly, the results show a notable improvement in the convergence speed over the standard GA for the functions tested. This observation surpassed expectations, since the GE is based on the GA. The use of GE is then extended to automate the SG syntax by deriving a grammar based design shape description and optimisation framework. To evaluate its efficacy and to demonstrate the concept, this framework is applied to two distinctive classes of problems frequently encountered in engineering practice. The first class of problems is related to shape descriptions and optimisation aspects of structural design. A specific BNF syntax is developed for planar shapes which makes use of four SG rules with arc primitives of variable size given by a radius and an angle of rotation. These SG rules are then used in the synthesis of piecewise parametric curves for the shape description and optimisation of a planar crane hook. The experimental results show superiority in convergence speed when compared to shape optimisation of the same problem based on Non-Uniform Rational B-Spline (NURBS) combined with a GA search strategy. The second class of problems considered here relates to the topology description and optimisation of planar trusses. Several BNF syntaxes are developed to achieve simultaneous topology, size and configuration optimisation. The experimental results thus obtained show good agreement with the results reported in the literature using an alternative truss optimisation method based on GA. Furthermore, by using the proposed truss description and optimisation method the computational expense is significantly reduced. The proposed design description and optimisation framework based on the SG syntax is a fast and efficient design exploration tool. The successful application of this proposed framework combining SG with design exploration in a range of structural problems validates the proposed idea.
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Ngim, Da-Zhe (Bertrand). "A two-stage structural optimisation and thermal discretisation of non-convective structured insulators : applications in granular-solid structures by additive manufacturing technology." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/33992.
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A systematic design procedure for characterising the strength and insulation requirements of a modular unit structure from additive manufacturing has been presented. The proposed 'two-stage' method consists of structural optimisation and thermal 'discretisation', through use of the Metamorphic Development (MD) and Discretisation by Partitioning Method (DbPM), respectively. A structural layout optimisation method of a consolidated granular-solid structure for strength requirements is demonstrated. The reliability of the layout optimized design solution tested using experiments and finite element analysis (PEA) are reproduced with reasonable accuracy. Layout optimisation yielded 40% savings in build material, whilst satisfying the targeted deflection.
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Ollar, Jonathan. "A multidisciplinary design optimisation framework for structural problems with disparate variable dependence." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24715.
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Multidisciplinary design optimisation incorporates several disciplines in one integrated optimisation problem. The benefi t of considering all requirements at once rather than in individual optimisations is that synergies between disciplines can be exploited to fi nd superior designs to what would otherwise be possible. The main obstacle for the use of multidisciplinary design optimisation in an industrial setting is the related computational cost which may become prohibitively large. This work is focused on the development of a multidisciplinary design optimisation framework that extends the existing trust-region based optimisation method known as the mid-range approximation method. The main novel contribution is an approach to solving multidisciplinary design optimisation problems using metamodels built in sub-spaces of the design variable space. Each metamodel is built in the sub-space relevant to the corresponding discipline while the optimisation problem is solved in the full design variable space. Since the metamodels are built in a space of reduced dimensionality, the computational budget for building them can be reduced without compromising their quality. Furthermore, a method for efficiently building kriging metamodels is proposed. This is done by means of a two-step hyper parameter tuning strategy. The fi rst step is a line search where the set of tuning parameters is treated as a single variable. The solution of the fi rst step is used in the second step, a gradient based hyper parameter optimisation where partial derivatives are obtained using the adjoint method. The framework is demonstrated on two examples, a multidisciplinary design optimisation of a thin-walled beam section subject to static and impact requirements, and a multidisciplinary design optimisation of an aircraft wing subject to static and bird strike requirements. In both cases the developed technique demonstrates a reduced computational effort compared to what would typically be achieved by existing methods.
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Gerzen, Nikolai [Verfasser]. "Analysis and Applications of Variational Sensitivity Information in Structural Optimisation / Nikolai Gerzen." Aachen : Shaker, 2014. http://d-nb.info/1060623048/34.
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Thein, Chung Ket. "An effective optimisation method for multifactor and reliability-related structural design problems." Thesis, University of Hull, 2011. http://hydra.hull.ac.uk/resources/hull:5338.
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This thesis first presents a systematic design procedure which satisfies the required strength and stiffness, and structural mass for conceptual engineering structural designs. The procedure employs a multi-objective and multi-disciplinary (MO–MD) optimisation method (multifactor optimisation of structure techniques, MOST) which is coupled with finite element analysis (FEA) as an analysis tool for seeking the optimum design. The effectiveness of the MOST technique is demonstrated in two case studies. Next, a reliability-related multi-factor optimisation method is proposed and developed, representing a combination of MOST (as a method of multi-factor optimisation) and the reliability-loading case index (RLI) (as a method of calculating the reliability index). The RLI is developed based on a well-known reliability method: the first-order reliability method (FORM). The effectiveness and robustness of the proposed methodology are demonstrated in two case studies in which the method is used to simultaneously consider multi-objective, multi-disciplinary, and multi-loading-case problems. The optimised designs meet the targeted performance criteria under various loading conditions. The results show that the attributes of the proposed optimisation methods can be used to address engineering design problems which require simultaneous consideration of multi-disciplinary problems. An important contribution of this study is the development of a conceptual MO–MD design optimisation method, in which multi-factor structural and reliability design problems can be simultaneously considered.
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Zavvos, Aristeidis. "Structural optimisation of permanent magnet direct drive generators for 5MW wind turbines." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8299.
Full textAbstract:
This thesis focuses on permanent magnet "direct drive" electrical generators for wind turbines with large power output. A variety of such generator topologies is reviewed, tested and optimised in an attempt to increase their potential as commercial concepts for the wind industry. Direct drive electrical generators offer a reliable alternative to gearbox drivetrains. This novel technology reduces energy loses thus allowing more energy to be yield from the wind and decreases the maintenance cost at the same time. A fundamental issue for these generators is their large size which makes them difficult to manufacture, transport and assembly. A number of structural designs have been suggested in the literature in an attempt to minimise this attribute. A set of design tools are set out in an attempt to investigate the structural stiffness of the different permanent magnet direct drive generator topologies against a number of structural stresses that apply to such wind turbine energy converters. Optimisation techniques, both analytical and structural, are also developed for minimising the total mass of a variety of "directly driven" machines with power output of 5MW or greater. Conventional and promising generator designs are modelled and optimised with the use of these optimisation techniques. The topologies under examination are then compared in terms of structural mass, stiffness and cost. As the number of wind turbine manufactures who adopt the direct drive concept increases, it is important to outline the unique characteristics of the different topologies and increase their manufacturing potential. Discussions and conclusions will provide an indication of the design solutions that could help decrease the mass and cost of such machines.
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Cervera, Eva. "Evolutionary structural optimisation based on boundary element representation of B-spline geometry." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/2004/.
Full textAbstract:
Evolutionary Structural Optimisation (ESO) has become a well-established technique for determining the optimum shape and topology of a structure given a set of loads and constraints. The basic ESO concept that the optimum topology design evolves by slow removal and addition of material has matured over the last ten years. Nevertheless, the development of the method has almost exclusively considered finite elements (FE) as the approach for providing stress solutions. This thesis presents an ESO approach based on the boundary element method. Non-uniform rational B-splines (NURBS) are used to define the geometry of the component and, since the shape of these splines is governed by a set of control points, use can be made of the locations of these control points as design variables. The developed algorithm creates internal cavities to accomplish topology changes. Cavities are also described by NURBS and so they have similar behaviour to the outside boundary. Therefore, both outside and inside are optimised at the same time. The optimum topologies evolve allowing cavities to merge between each other and to their closest outer boundary. Two-dimensional structural optimisation is investigated in detail exploring multi-load case and multi-criteria optimisation. The algorithm is also extended to three-dimensional optimisation, in which promising preliminary results are obtained. It is shown that this approach overcomes some of the drawbacks inherent in traditional FE-based approaches, and naturally provides accurate stress solutions on smooth boundary representations at each iteration.
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Scanlan, M. J. "The application of ab initio structural optimisation to contemporary problems in biochemistry." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356432.
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Calvi, Adriano. "Finite element model updating in structural dynamics using design sensitivity and optimisation." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/10507.
Full textAbstract:
Model
updating is an important issue in engineering. In fact a well-correlated model
provides for accurate evaluation of the structure loads and responses. The main
objectives of the study were to exploit available optimisation programs to create an
error localisation and
updating procedure of nite element models that minimises
the "error" between
experimental and analytical modal data, addressing in particular
the
updating of large scale nite element models with severe requirements on the
mode
shapes correlation.
A new
methodology and procedure that allows the semi-automatic adjustment of a
large nite element dynamic model of a structure to better represent the dynamic
characteristics of an actual structure was developed. The key aspect of the procedure
is a "two
steps" optimisation process to achieve a complete correlation of the modal
data.
Eigenfrequency deviations and mode shapes cross-othogonality (CO) and/or
modal assurance criterion (MAC) are used in the objective functions for the
estimation
problem of the updating parameters, that are the variables for tuning the
analytical model. Theoretical aspects and practical implementation conceming CO
and MAC, and their derivatives, have been fully developed and the advantages of
using these mode correlation indices in the objective function have been largely
commented.
The selection of the updating parameters is a complex issue and can be still
considered a
partially open point. In the new procedure the suggested automated
selection of the
updating parameters by means of a preliminary calculation of the
element modal strain energy and eigenvalue sensitivities is adequate for the
reduction of the
frequency deviations but could not be to improve the correlation
indices of the mode shapes.
The new
procedure was successfully applied four times: to a cantilever beam model,
the Garteur model, the Spacehab dynamic model and the Mini-Pressurised Logistics
Module model. The last application was a real life application on a large scale
structural mathematical model and in this case the procedure was mainly used for
error localisation
purposes. The developed procedure is robust, effective and
efficient, thus the original objectives of the study were largely met.
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Ullah, Baseer. "Structural topology optimisation based on the boundary element and level set methods." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/10659/.
Full textAbstract:
The research work presented in this thesis is related to the development of structural optimisation algorithms based on the boundary element and level set methods for two and three-dimensional linear elastic problems. In the initial implementation, a stress based evolutionary structural optimisation (ESO) approach has been used to add and remove material simultaneously for the solution of two-dimensional optimisation problems. The level set method (LSM) is used to provide an implicit description of the structural geometry, which is also capable of automatically handling topological changes, i.e. holes merging with each other or with the boundary. The classical level set based optimisation methods are dependent on initial designs with pre-existing holes. However, the proposed method automatically introduces internal cavities utilising a stress based hole insertion criteria, and thereby eliminates the use of initial designs with pre-existing holes. A detailed study has also been carried out to investigate the relationship between a stress and topological derivative based hole insertion criteria within a boundary element method (BEM) and LSM framework. The evolving structural geometry (i.e. the zero level set contours) is represented by non-uniform rational b-splines (NURBS), providing a smooth geometry throughout the optimisation process and completely eliminating jagged edges. The BEM and LSM are further combined with a shape sensitivity approach for the solution of minimum compliance problems in two-dimensions. The proposed sensitivity based method is capable of automatically inserting holes during the optimisation process using a topological derivative approach. In order to investigate the associated advantages and disadvantages of the evolutionary and sensitivity based optimisation methods a comparative study has also been carried out. There are two advantages associated with the use of LSM in three-dimensional topology optimisation. Firstly, the LSM may readily be applied to three-dimensional space, and it is shown how this can be linked to a 3D BEM solver. Secondly, the holes appear automatically through the intersection of two surfaces moving towards each other. Therefore, the use of LSM eliminates the need for an additional hole insertion mechanism as both shape and topology optimisation can be performed at the same time. A complete algorithm is proposed and tested for BEM and LSM based topology optimisation in three-dimensions. Optimal geometries compare well against those in the literature for a range of benchmark examples.
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Ghurbal, Ehsan. "Un-weighted multi-criteria mesh and structural optimisation method with finite element analysis." Thesis, University of Huddersfield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273718.
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Brodie, Robert Neil. "Development of controllability and robustness methodologies for Bi-directional Evolutionary Structural Optimisation (BESO)." Thesis, University of Leeds, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486156.
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Plouraboué, Thibaud. "Optimisation des propriétés thermomécaniques d’adhésifs polyépoxydes structuraux en conditions extrêmes : relation structure-propriétés." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0413.
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La démocratisation des technologies du collage dans le domaine aérospatial amène les industriels à exiger des adhésifs toujours plus performants. L’objectif de cette thèse est d’optimiser les propriétés thermomécaniques d’un adhésif polyépoxyde bi-composant qui devra présenter des propriétés structurales entre -150°C et +150°C, tout en respectant des exigences de mise en oeuvre.L’analyse de la littérature et des expériences préliminaires a permis de sélectionner le système polyépoxyde modèle binaire le plus pertinent en termes de réactivité à l’ambiante et de propriétés sur assemblage collé. Pour optimiser la résistance en température élevée de ce système, deux voies ont été explorées : l’incorporation d’époxydes multi-fonctionnalisés pour augmenter la densité de réticulation, et l’utilisation d’amines cycliques qui accroit la rigidité des segments macromoléculaires. Pour améliorer les propriétés de résistance à la propagation de fissure à basse température, les additifs de renforcement montrent un intérêt certain pour la formulation d’adhésifs structuraux polymérisés à température ambiante. Sur la base de ces résultats, plusieurs formulations complexes ont pu être élaborées. Des phénomènes de synergie et d’inhibition entre les différents éléments des formulations ont été constatés, sans pouvoir être totalement compris ce qui met en lumière la difficulté de prévoir le comportement d’adhésifs complexes, à l’image des formulations commerciales.Ces travaux de thèse ont permis de développer un adhésif structural répondant aux exigences strictes du secteur aérospatial, et de dégager une stratégie de formulation qui pourra être appliquée à d’autres secteurs d’activitésThe democratisation of bonding technologies in aerospace field leads industrials to demand more and more efficient adhesives. The aim of this thesis is to optimise thermomechanical properties of two-component epoxy adhesives which need to preserve structural properties on a large scale of temperature (from -150°C to +150°C) and observing application process requirements.The analysis of scientific literature and preliminary experiments enable to select the most relevant binary epoxy system in terms of reactivity and bonding mechanical properties. To optimise high temperature resistance of this epoxy system, two approaches have been explored: addition of multi-functionalised epoxy resin to extend the crosslink density, and use of cycloaliphatic amines which increase the rigidity of macromolecular segments. To improve crack propagation resistance in low temperature, tougheners reveal an interest to formulate room temperature structural adhesives. On the basis of these results, complex formulations have been developed. Synergy and inhibition phenomenon between the formulation blends have been observed without being able to fully understand them which highlight the difficulty to predict the behaviour of complex adhesives such as commercial formulations.This thesis works allowed to develop a two-component epoxy adhesive formulation which meets aerospace requirements, and to bring about a formulation strategy which could be adapted to others sectors activities
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Frabolot, Ferdinand. "Optimisation de forme avec détection automatique de paramètres." Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2182/document.
Full textAbstract:
L’objectif de ce travail de thèse est de pouvoir intégrer totalement l’optimisation de forme des raidisseurs de capot dans un processus de conception industrielle et cela afin d’optimiser la forme et la distribution des raidisseurs dans un contexte multi-objectif (voire multi-disciplinaire) d’une structure 3D surfacique. Pour ce faire, nous avons tout d’abord établi un aperçu de l’état de l’art dans l’optimisation de forme des structures en classifiant les différentes méthodes de paramétrage de forme, en trois catégories ; les méthodes basées sur la géométrie (telle la paramétrisation d’un modèle de type CAO), les méthodes basées sur une grille fixe (telles que les méthodes d’optimisation topologique) et les méthodes basées sur le maillage (telles que les méthodes de régularisation du maillage). Toutefois, aucune de ces méthodes ne satisfait pleinement aux objectifs posés. Nous introduisons ainsi dans cette thèse la méthode FEM-CsG : Finite Element Mesh - Constructive surface Geometry. Imprégnée d’un fort contexte industriel, cette méthode propose une réponse à des contraintes telles que la possibilité de représenter la solution optimale par un ensemble de paramètres CAO, la possibilité d’adapter le modèle EF à l’analyse souhaitée et la garantie d’une représentation géométrique et d’un maillage robuste. En proposant d’intégrer des formes élémentaires paramétrées et prémaillées issues d’une bibliothèque de formes dans une structure coque 3D maillée par l’utilisation des variables issues de la CAO, la méthode FEM-CsG permet une évolution constante de la topologie guidée par l’optimisation. Ainsi, même si la topologie est modifiée la forme résultante reste conforme avec une représentation CAO par construction, correspondant davantage à la réalité des optimisations réalisées en avant-projet. La méthode FEM-CsG a été validée sur deux études de cas, de complexité variable, permettant de mettre en avant la robustesse de cette dernière. Ainsi, avec un choix intelligent et cohérent des variables de formes, les problèmes d’optimisation peuvent avec un nombre restreint de variables explorer un nombre important de topologies ou de formes. Les changements de topologies s’effectuent de manière continue, validant ainsi la méthode à tout type d’analyse souhaitéeThe objective of this thesis work is to be able to completely integrate shape optimization of car inner hood stiffeners in a complex industrial process, in order to fully optimize the shape and distribution of the stiffeners in a multi-objective approach (or even multi-disciplinary) of a 3D surfacic structure. To this end, we established, at the outset, an insight of the state-of-the-art in shape optimization of structures by classifying the different shape parametrizations in three distinct categories : geometry-based methods (a shape parametrization such as a CAD model), grid-based methods (such as topology optimization methods) and mesh-based methods (such as morphing methods or mesh regulation). However, none of these methods fully satisfies the set objectives. Thus, we will introduce in this work the FEM-CsG method : Finite Element Mesh - Constructive surface Geometry. Bolstered by its strong industrial context, this method offers a response to such constraints, i.e. the possibility to represent the optimal solution by a system of CAD parameters, the possibility to adapt the FE model to the wanted analysis and the guarantee of a robust geometrical representation and mesh stability. We offer to incorporate premeshed parameterized elementary forms into a 3D sheet meshed structures. Hence, these forms are arising from a CAD parameterized elementary form library. Furthermore, the FEM-CsG method uses a set of operators acting on the mesh allowing a constant evolution of the topology guided by optimization. Therefore, even if the topology may vary, the resulting shapes comply with CAD representations by construction, a solution better reflecting the reality of optimizations performed during the preliminary development stage. The FEM-CsG method has been validated on two simple case studies in order to bring forward its reliability. Thus, with an intelligent and coherent choice of the design variables, shape optimization issues may, with a restrictive number of variables, explore an important number of shapes and topologies. Topology changes are accomplished in a continuous manner, therefore validating the FEM-CsG method to any desired analysis
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Roets, Philip J. "Development of a hybrid light alloy - carbon fibre aerospace structural panel." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4151.
Full textAbstract:
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The development of light and sti aerospace structural panels is very important in the aerospace industry, e.g. a lighter satellite requires less fuel to launch it into space which in turn saves money for the owner of the satellite. This thesis describes the design, optimisation, manufacturing and testing of a ribbed light alloy core - carbon bre face sheets, sandwich-type, satellite panel operating at launch loading conditions (115 m/s2 accelerations and requiring a minimum structural natural frequency of 90 Hz) to determine the optimum sti ness per mass ratio of the panel. The panel layout was based on a satellite panel designed by SunSpace and Information Systems for the Sumbandila satellite. Only the black box mounting positions of the original panel were used in the optimisation of the new panel. The core of the evaluation panel was manufactured from aluminium (6082-T6). The carbon bre skins were manufactured from unidirectional high modulus carbon bre (K63712) in a [0/90/0] wet layup with the 0± direction in the longitudinal direction of the panel. A three-dimensional model of the panel consisting of 3D wedge elements and containing all the boundary conditions was modelled with the use of the nite element software MSC Patran. The model was optimised with the use of optimisation software Genesis to locate the rib positions. Genesis removes all the elements containing the least amount of stress; only 30% of the core elements were kept while restricting the elements to form an extruded con guration (for milling machining) throughout the thickness of the panel. The rib elements remaining were replaced in MSC Patran by shell elements and the shell element thicknesses were optimised with the use of Genesis to ensure the lightest and sti est possible structure. The optimised rib thicknesses were imported into MSC Patran and the numerically optimised model could then be analysed with MSC Nastran. The numerical model was converted into a manufacturable structure and the core was machined from a solid aluminium sheet. The ribs were machined in the shape of an Ibeam to allow for minimum weight and a su cient bonding area for the two carbon bre face sheets. Elevated circular surfaces, protruding through the carbon bre sheets, were machined in the position of the black box mountings to allow for better heat transfer away from the black boxes. The carbon bre face sheets were bonded to the metal core (3M Scotch-Weld 9323 B/A). The nished panel was put through various tests to determine whether it is suitable for use in the aviation industry. The tests included modal testing, random vibration testing and temperature testing to determine if the structure is durable enough for use in satellites. The test results are promising and show that a substantive amount of money can be saved by reducing the mass on the structure. By using optimisation software and ribbed light alloy - carbon bre face sheets sandwich structures the performance of the structures can be improved without adding mass to the structure.
AFRIKAANSE OPSOMMING: Die ontwikkeling van ligter en stywer lugvaartstruktuur panele is baie belangrik in die lugvaart-industrie, bv. 'n ligter satelliet benodig minder brandstof om tot in 'n wentelbaan lanseer te word. Dit bespaar sodoende lanseerkostes vir die eienaar van die satelliet. In die verslag word die ontwerp, optimering, vervaardiging en toets van 'n gewebde, ligte allooi kern - koolstofveselvel, saamgestelde materiaal, satelliet struktuurpaneel wat onderwerp word aan lanseer belastingstoestande van ongeveer 115 m/s2 versnellings ondersoek. Die tegnieke word gebruik om die optimale styfheid per eenheidsmassa-verhouding te bepaal. Die paneel benodig 'n minimum strukturele eerste natuurlike frekwensie van 90 Hz. Die basiese paneel uitleg is verkry vanaf 'n satellietpaneel wat deur SunSpace and Information Systems ontwerp is vir die basisplaat van die Sumbandila satelliet. Die enigste geometrie wat van die oorspronklike struktuur behou is om die nuwe struktuur te optimeer is die vashegtingspunt-posisies van die swart-kassies. Die kern van die ge-optimeerde struktuur is vervaardig uit gemasjieneerde aluminium (6082-T6). Die koolstofvesel-velle is vervaardig uit enkelrigting hoë-modulus koolstofvesel-doek (K63712). Die oplegging is gedoen met 'n nat-opleggingsproses waar die drie lae van elke vel 'n [0/90/0] oriëntasie het met, die 0± lae in die langsrigting van die paneel. 'n Drie-dimensionele eindige element model van die paneel is geskep met behulp van die MSC Patran sagteware pakket met die model hoofsaaklik opgebou uit 3D wig-elemente. Al die lanseertuig vashegtingsrandwaardes is in die eindige element model ingebou. Om die web posisies te bepaal is die Genesis optimeringsagteware pakket gebruik. Verskeie ontwerpsvoorwaardes is gespesi seer waaraan die optimeringsproses moes voldoen. Slegs 30% van die wig-elemente mag behoue bly in die optimeringsproses en al die elemente deur die dikte van die paneel moet of behou of verwyder word. Dit verseker dat die resultaat masjieneerbaar is met 'n freesmasjien. Die oorblywende wig-elemente is in MSC Patran vervang met dop-elemente. Die dopelemente se diktes is ge-optimeer met Genesis om die ligste en styfste struktuur moontlik te kry. Die ge-optimeerde dop-element diktes is in die MSC Patran model ingetrek. Die numeries ge-optimeerde model is daarna met behulp van MSC Nastran ge-analiseer. Nadat die numeriese model omgeskakel is in 'n vervaardigbare struktuur is die kern gemasjieneer uit 'n soliede blok aluminium. Die webbe is ontwerp en vervaardig in 'n I-balk vorm. Dit laat toe dat die webbe 'n minimum gewig en genoegsame area het waarop die koolstofvesel velle geheg kan word. Verhewe vlakke is gemasjieneer op die aluminium kern in die posisies van die swart-kassie vashegtingpunte. Hierdie verhewe vlakke steek deur die koolstofvesel-vel aan die kant waar die swart-kassies vasgeheg word. Dit verseker 'n metaal-op-metaal verbinding tussen die kern en die swart-kassies vir beter hittegeleiding. 3M Scotch-Weld 9323 B/A epoksie is gebruik om die koolstofvesel-velle aan die aluminium kern te heg. Die voltooide struktuur is aan 'n reeks toetse onderwerp om te bepaal of dit geskik is om in die ruimtevaart-industrie gebruik te kan word. Dit sluit modale toetse, lukrake vibrasie toetse en temperatuursverandering toetse in. Die toetsresultate sal bepaal of die struktuur duursaam genoeg is om in satelliete gebruik te word. Die toetsresultate is belowend en dui daarop dat deur massa te bespaar op die struktuur, 'n aansienlike bedrag op satelliet lanseer-kostes bespaar kan word. Deur optimeringsagteware tesame met gewebde ligte allooi kern - koolstofvesel vel, saamgestelde materiaal strukture te gebruik kan die werksverrigting van die strukture verbeter sonder dat massa bygevoeg word.
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Agyei, Eugene Osei. "Groundwater modeling and management using the finite element method and evolutionary optimisation techniques /." Title page, synopsis and contents only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09pha284.pdf.
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Shah, Darshil Upendra. "Characterisation and optimisation of the mechanical performance of plant fibre composites for structural applications." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13510/.
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Plant fibres, perceived as environmentally sustainable substitutes to E-glass, are increasingly being employed as reinforcements in polymer matrix composites. However, despite the promising technical properties of cellulose-based fibres and the historic use of plant fibre composites (PFRPs) in load-bearing components, the industrial uptake of PFRPs in structural applications has been limited. In developing PFRPs whose mechanical properties are well-characterised, optimised and well-predicted, this thesis addresses the question: Can PFRPs replace E-glass composites (GFRPs) in structural applications? Ensuring that the highest reinforcement potential is exploited, this research examines the mechanical properties of aligned PFRPs based on bast fibre yarns/rovings and thermoset matrices. Although aligned GFRPs are found to outperform aligned PFRPs in terms of absolute mechanical properties, PFRPs reinforced with flax rovings exhibit exceptional properties, with a back-calculated fibre tensile modulus of up to 75 GPa and fibre tensile strength of about 800 MPa. To identify the processing window which produces composites with useful properties, the minimum, critical and maximum fibre volume fraction of PFRPs have been determined, and compared to that of synthetic fibre reinforced composites. The effect of fibre volume fraction on the physical and tensile properties of aligned PFRPs has also been investigated. Furthermore, micro-mechanical models have been developed and experimentally validated, to reliably predict the effect of (mis)orientation, in the forms of yarn twist/construction and off-axis loading, on the tensile properties of aligned PFRPs. To provide a complete set of fatigue data on aligned PFRPs, the effect of various composite parameters on PFRP cyclic-loading behaviour has been illustrated through S-N lifetime diagrams. A constant-life diagram has also been generated to enable the fatigue design and life prediction of a PFRP component. At each stage, the fatigue performance of PFRPs has been compared to that of GFRPs. Finally, in directly addressing the main theme, this thesis adopts a novel comparative case study approach to investigate the manufacture and mechanical testing of full-scale 3.5-meter composite rotor blades (suitable for 11 kW turbines) built from flax/polyester and E-glass/polyester. The study claims that under current market conditions, optimised plant fibre reinforcements are a structural, but not low-cost or sustainable, alternative to conventional E-glass reinforcements.
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Yao, Na. "Towards cost-based structural optimisation : cost modelling and feature recognition for injection moulded components." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612480.
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Yazdanpanah, Moghadam Peyman. "Optimisation de transducteurs piézoélectriques pour la génération d'ondes guidées." Thèse, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/8172.
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Résumé : Les systèmes de surveillance de santé structurale sont proposés pour la détection d’endommagement dans les infrastructures qui dépassent leur durée de vie en utilisant les ondes guidées (GW). Les ondes guidées peuvent parcourir de longues distances et sont sensibles à une variété d’imperfections. Les transducteurs piézoélectriques sont communément utilisés pour générer et mesurer les ondes guidées dans des structures minces. Comme la détection du défaut et sa localisation sont souhaitées, la nature de la génération des ondes guidées sous forme de plusieurs modes implique une complexité supérieure dans le traitement du signal. Pour remédier à cette limitation, une nouvelle méthode est présentée ici pour la génération des ondes guidées par sélection de mode, et un nouveau transducteur piézoélectrique est ensuite conçu, fabriqué et testé.
Tout d'abord, la génération des ondes guidées par optimisation systématique du profil interfacial de la contrainte de cisaillement en mode sélectif est étudiée. En utilisant le principe de superposition, une méthode d'analyse est d'abord développée pour la modélisation de la génération des ondes guidées par un nombre fini de segments de contrainte de cisaillement uniforme, chacun contribuant à un profil élémentaire d’une contrainte constante de cisaillement. Sur cette base, deux fonctions coût sont définies afin de minimiser les modes indésirables et amplifier le mode sélectionné et le problème d'optimisation est résolu avec un cadre d'optimisation d’algorithme génétique parallèle. Les avantages de cette méthode par rapport à d'autres approches de conception de transducteurs classiques sont (1) la contrainte de cisaillement peut être explicitement optimisée à la fois pour exciter un mode et supprimer d'autres modes indésirables, (2) la taille de la zone d'excitation n’est pas limitée et l’excitation en mode sélectif est toujours possible, même si la largeur d'excitation est inférieure à toutes les longueurs d'onde excitées, et (3) la sélectivité est accrue et la largeur de bande est étendue.
La méthode analytique et les fonctions coût sont ensuite développées pour concevoir un transducteur piézoélectrique à éléments multiples (MEPT) simple et performant. Une méthode numérique est tout d'abord mise au point pour extraire la contrainte interfaciale entre un seul élément piézocéramique et une structure d'accueil et ensuite utilisée comme entrée d'un modèle analytique pour prédire la propagation des ondes guidées à travers l'épaisseur d'une plaque isotrope. Deux nouvelles fonctions coût sont proposées pour optimiser la contrainte de cisaillement interfaciale pour supprimer le(s) mode(s) indésirable(s) et maximiser un mode désiré. Simplicité et faible coût de fabrication sont deux principales cibles visées dan la conception du MEPT. Un prototype TPEM est ensuite fabriqué à l'aide de micro-usinage laser. Une procédure expérimentale est présentée afin de valider les performances de la TPEM comme une nouvelle solution pour la génération des ondes guidées en mode sélectif. Des essais expérimentaux illustrent la forte capacité du TPEM pour la génération des ondes guidées en mode sélectif, puisque le mode indésirable est supprimé par un facteur allant jusqu'à 170 fois par rapport aux résultats obtenus avec un seul piézocéramique.Abstract : Structural Health Monitoring (SHM) systems are being proposed for damage detection of infrastructures that exceed their life using ultrasonic Guided waves (GWs). GWs can travel over long distances and are sensitive to variety of defects. Piezoelectric transducers (PZTs) are commonly used to generate and measure GWs in plate-like structures. As damage detection and localization is sought, the multi-mode nature of GW generation involves higher complexity in signal processing. To overcome this limitation, a new method is presented here for modeselective GW generation, and a novel mode-selective PZT is then designed, manufactured and tested. First, mode-selective generation of GWs by systematic optimization of the interfacial shear stress profile is investigated. Using the superposition principle, an analytical method is first developed for modeling GWs generation by a finite number of uniform shear stress segments, each contributing with a constant elementary shear stress profile. Based on this, two cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel Genetic Algorithm (GA) optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The analytical method and objective functions are then developed to design a novel and costeffective multi-element piezoelectric transducer (MEPT). A numerical method is first developed to extract the interfacial stress between a single piezoceramic element and a host structure and then used as the input of an analytical model to predict the GW propagation through the thickness of an isotropic plate. Two novel objective functions are proposed to optimize the interfacial shear stress for both suppressing unwanted mode(s) and maximizing a desired mode. Simplicity and low manufacturing cost are two main targets driving the design of the MEPT. A prototype MEPT is then manufactured using laser micro-machining. An experimental procedure is presented to validate the performances of the MEPT as a new solution for mode-selective GW generation. Experimental tests illustrate the high capability of the MEPT for mode-selective GW generation, as unwanted mode is suppressed by a factor up to 170 times compared with the results obtained with a single piezoceramic.