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1
Rallo, Ayerbe Marta. "Impact sur structure composite sandwich architecturée : application aux pales d'avions". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES088.
Testo completoAbstract (sommario):
La sécurité constitue un aspect essentiel au développement des pièces et assemblages aéronautiques. Pour un avion à hélices, les pales assurent la propulsion de l'appareil, et garantissent sa portance. Elles sont essentielles. C'est pourquoi des essais de certification à l'impact oiseau sont nécessaires afin de garantir la capacité de l'avion à se poser en mode dégradé. Ces essais ont lieu à la fin de la phase de développement. Une caractérisation du comportement à l'impact en amont est nécessaire afin d'éviter d'éventuels coûts supplémentaires liés aux mauvais résultats de ces tests Les pales d'avion étudiées sont des structures composites sandwiches complexes, composées d'une âme en mousse polymère et de plusieurs couches parmi lesquelles on trouve des tresses composites, des plis composites unidirectionnels, de la mousse polymère, des renforts métalliques, des interfaces collées et autres constituants spécifiques (protection foudre, peinture...). De nombreux matériaux sont donc à considérer pour l'étape de caractérisation. A cela s'ajoute la conciliation de phénomènes à des échelles microscopiques et macroscopiques. Le travail de recherche s'attachera dans un premier temps à comprendre et à caractériser les phénomènes d'endommagement dans les conditions de certification d'impact oiseau. Cette première étape doit permettre de hiérarchiser les phénomènes physiques afin de guider le développement d'un modèle de pré-dimensionnement. Dans un second temps, une campagne d'essais de caractérisation sera menée sur les éléments constitutifs de la pale pour alimenter le modèle. Enfin, dans un troisième temps, des essais sur une éprouvette représentative d'un tronçon de pale seront menés ainsi qu'une étude de sensibilité pour mettre en évidence la capacité du modèle à représenter le phénomène étudiéSafety is a crucial aspect in the development of aeronautical parts and assemblies. For a propeller aircraft, the blades ensure the propulsion of the aircraft and guarantee its lift. They are essential. This is why bird strike certification tests are necessary to ensure the aircraft's ability to land in a degraded mode. These tests take place at the end of the development phase. An upstream characterization of impact behavior is necessary to avoid potential additional costs associated with poor test results. The aircraft blades studied are complex sandwich composite structures, consisting of a polymer foam core and several layers, including composite braids, unidirectional composite plies, polymer foam, metallic reinforcements, bonded interfaces, and other specific components (lightning protection, paint, etc.). Therefore, numerous materials need to be considered during the characterization phase. Additionally, it is necessary to reconcile phenomena at both microscopic and macroscopic scales. The research work will initially focus on understanding and characterizing damage phenomena under bird strike certification conditions. This first step should allow the prioritization of physical phenomena to guide the development of a preliminary sizing model. In the second phase, a characterization test campaign will be conducted on the constituent elements of the blade to feed the model. Finally, in the third phase, tests on a representative specimen of a blade section will be conducted, as well as a sensitivity study to highlight the model's ability to represent the studied phenomenon
2
Banihashemi, Seyed Parsa. "Parallel explicit FEM algorithms using GPU's". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54391.
Testo completoAbstract (sommario):
The Explicit Finite Element Method is a powerful tool in nonlinear dynamic finite element analysis. Recent major developments in computational devices, in particular, General Purpose Graphical Processing Units (GPGPU's) now make it possible to increase the performance of the explicit FEM.
This dissertation investigates existing explicit finite element method algorithms which are then redesigned for GPU's and implemented. The performance of these algorithms is assessed and a new asynchronous variational integrator spatial decomposition (AVISD) algorithm is developed which is flexible and encompasses all other methods and can be tuned based for a user-defined problem and the performance of the user's computer.
The mesh-aware performance of the proposed explicit finite element algorithm is studied and verified by implementation. The current research also introduces the use of a Particle Swarm Optimization method to tune the performance of the proposed algorithm automatically given a finite element mesh and the performance characteristics of a user's computer. For this purpose, a time performance model is developed which depends on the finite element mesh and the machine performance. This time performance model is then used as an objective function to minimize the run-time cost.
Also, based on the performance model provided in this research and predictions about the changes in GPU's in the near future, the performance of the AVISD method is predicted for future machines. Finally, suggestions and insights based on these results are proposed to help facilitate future explicit FEM development.
3
Vražina, Lukáš. "Parametrická studie absorpčního prvku zadní části vozidla". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241228.
Testo completoAbstract (sommario):
In 1995 was published a regulation from RCAR company which determines rules for crash tests in maximum speed of 15 km/h on vehicles lighter than 2,5 ton. The main reason was to reduce costs for car reparation in case of crash in low speed. My diploma thesis is focused on the modifications of deformation part in the car alias absorption part of the vehicle. In the first part of my diploma thesis has been done a research about organisations doing basic car crashes as well as topic focused on nonlinear mechanics and description of explicit FEM. In the second part of my work are settled conditions for crash simulation of a barrier into the car. There is an evaluation of critical force on the stringer. Afterwards the calculating simulation simplified on loading of absorption part and there are some material and form adjustments. In the final part of my diploma thesis is done a result comparison and development of the absorption part.
4
Kyrre, Anette Wester. "Quasi-static Analyses of Slender Structures with Complex Cross-Sections using Explicit FEM Codes". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23661.
Testo completoAbstract (sommario):
It has previously been done analyses to find global stiffness values of an umbilical cable, with mixed results or no results at all when subjected to bending. There have also been difficulties in finding a distinct stick-slip point during bending. In this thesis, several models have been examined to get a step closer to resolve these particular issues. To begin with, a very simple flexible cable has been tested to see if the program ANSYS LS-Dyna can provide good global stiffness values, then of course with the use of an explicit scheme. When this first analysis gave good results, it was possible to conclude that the program could handle analyzing long slender structures with good accuracy. Further it was also developed a model with the aim of predicting the stick-slip phenomenon during bending. Results from this model could imply that there existed a stick-slip point, only a short time after the bending started. Finally, a last model was developed, including two armour layers wound around a cover of polyethylene. Other analyses have had problems with the behavior of the tendons during bending, that is they have been spreading, and not been following a loxodromic curve. Different cable lengths were tested, showing relative good results for the axial- and bending stiffness, but not so good results for the torsional stiffness. In addition to be able to develop models that could give realistic global stiffness values, focus have been on reducing the CPU time as much as possible. Therefore, much time has been spent on modeling the models right, and choosing the right path and length of loading.
5
Rek, Václav. "Využití paralelizace při numerickém řešení úloh nelineární dynamiky". Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-392279.
Testo completoAbstract (sommario):
The main aim of this thesis is the exploration of the potential use of the parallelism of numerical computations in the field of nonlinear dynamics. In the last decade the dramatic onset of multicore and multi-processor systems in combination with the possibilities which now provide modern computer networks has risen. The complexity and size of the investigated models are constantly increasing due to the high computational complexity of computational tasks in dynamics and statics of structures, mainly because of the nonlinear character of the solved models. Any possibility to speed up such calculation procedures is more than desirable. This is a relatively new branch of science, therefore specific algorithms and parallel implementation are still in the stage of research and development which is attributed to the latest advances in computer hardware, which is growing rapidly. More questions are raised on how best to utilize the available computing power. The proposed parallel model is based on the explicit form of the finite element method, which naturaly provides the possibility of efficient parallelization. The possibilities of multicore processors, as well as parallel hybrid model combining both the possibilities of multicore processors, and the form of the parallelism on a computer network are investigated. The designed approaches are then examined in addressing of the numerical analysis regarding contact/impact phenomena of shell structures.
6
Wahlström, Catarina, e Gustaf Sellin. "Den dolda kompetensen : en longitudinell undersökning mellan åren 2007 - 2009 av fem gotländska småföretag". Thesis, Gotland University, Department of Business Administration, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hgo:diva-100.
Testo completoAbstract (sommario):
In this thesis we will discuss the importance of human resource development in smaller companies and if it will change from when the Swedish economy was in an economic boom and later on came to be in a recession. We choose to use a more qualitative approach for this research in order to conduct a more in-depth study of five smaller sized companies located on Gotland, Sweden. In order to limit our research we had as an ambition to answer these following questions:
• What obstacles are there when it comes to human resource development and knowledge transference within smaller sized companies?
• What can simplify or enable human resource development and knowledge transference within smaller sized companies?
• Does the teaching process change to a more tacit human resource development between co-workers when there is less room for conventional human resource development?
The result of the research came to show that the biggest barrier, when it comes to competence development within smaller companies, is time. However, our research also showed that a majority of the companies has changed from a more external educational plan to a more internal educational plan which focuses on keeping the human resource development within the company. This in turn makes it easier for the companies to manage time and integrate the learning process into a usual workday for employees.
7
Hermansson, Michaela. "Är explicit undervisning nyckeln till ökad läsförståelse? : En kvalitativ intervjustudie om hur fem lärare i F–3 beskriver sin undervisning i läsförståelse och lässtrategier". Thesis, Högskolan Dalarna, Pedagogiskt arbete, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:du-21495.
Testo completoAbstract (sommario):
Resultaten av de senaste PIRLS-undersökningarna visar att svenska elevers läsförståelse har försämrats under senare år. Enligt forskning bör undervisningen vara inriktad på lässtrategier för att elever ska utveckla läsförståelse. För att eleverna ska lära sig använda olika lässtrategier självständigt när de tolkar text och skapar mening behöver de undervisas explicit. Undervisningen bör vara strukturerad och varierad samtidigt som läraren stöttar eleverna och anpassar undervisningen efter deras individuella behov. Syftet med studien har varit att undersöka hur lärare i F–3 undervisar i läsförståelse och lässtrategier för att se vilka förtjänster och brister som finns. Studiens metod är kvalitativ och för att samla in material har fem halvstrukturerade intervjuer genomförts med fem verksamma lärare, fyra klasslärare och en specialpedagog, fördelade på fyra olika skolor. Resultaten visar att lärare använder sig av olika undervisningsmetoder när de undervisar i läsförståelse, såsom en läsande klass, think-aloud, cirkelmodellen och Chambers modell för boksamtal. Det som tycks genomsyra lärarnas undervisning i läsförståelse är kommunikation, vilket är nära sammankopplat med studiens teoretiska utgångspunkt, det sociokulturella perspektivet. Enligt lärarna samtalar de mycket med eleverna om texter, och de verkar försöka anpassa undervisningen efter elevernas individuella behov genom att välja texter som eleverna har förkunskaper i och om. När de undervisar explicit tycks lärarna diskutera olika lässtrategiers nyttoanvändning genom att samtala om hur och varför olika lässtrategier är lämpliga att använda i olika sammanhang. Enligt lärarna erbjuds eleverna undervisning i olika gruppkonstellationer såsom arbete i helklass, halvklass, mindre grupper, parvis och enskilt. Lärarna tycks vara tydliga i sin undervisning för att eleverna ska bli medvetna om i vilket syfte de ska läsa.Svenska
8
Raffai, Peter. "Vytvoření a validace výpočtového FEM modelu kliky dveří pro crashové výpočty". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230249.
Testo completoAbstract (sommario):
The aim of this master’s thesis was to create a component model of a door handle stiffener used by the Volkswagen concern, which can be used for crash computations. Also to tune its parameters the way, its behavior corresponds the most to the real part’s. In the theoretical part the current regulations of the Euro NCAP are presented, concerning the testing and evaluation of the passive safety of new vehicles. Attention is focused on the evaluation of the side impact barrier tests, where the effect of the door handle stiffener’s damage is reflected the most. Shown are the reasons for the effort to simulate the real behavior of the stiffener, the factors, which initialized the born of the studied problem. The practical part starts with the creation of the FEM mesh of the part based on its 3D CAD model, also describes the requirements for the mesh quality, as well as the used tools and methods. Further on investigated are the characters of real damages of the door handle area during side impacts, based on which the component tests are proposed for the validation of the simulation model. Experimental research consists of the stiffener’s testing for simple bend and twist loads, three specimens each. After the execution of the tests the results get compared with the corresponding simulations. Modifications are made on the model according to the acquired results: refinement of the FEM mesh, new material model usage with failure for shell elements and definition of real material characteristics for the used thermoplastics. The latest obtained simulation dependencies are compared with the measured values again, the results are evaluated at last.
9
Nedělka, Pavel. "Deformační a napjatostní analýza nárazníkové částí automobilu při rázovém zatěžování". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229650.
Testo completoAbstract (sommario):
The master thesis deals with a stress-strain analysis of the front crash structure of a race car by using the finite element method. The structure is loaded by an impact loading. This type of analysis belongs to the transient analysis so the explicit formulation of the finite element method is used. The LS-DYNA software was used for calculations. The goal of this thesis is to express the influence of the crash structure to the change of the car's kinetic energy as well as the amount of absorbed energy in case of frontal impact.
10
Vaněčková, Adéla. "Implicitní a explicitní metoda v nelineární dynamice". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265572.
Testo completoAbstract (sommario):
The final thesis „Explicit and Implicit methods in nonlinear dynamics“ deals with the issue of geometrical and physical nonlinear analysis of structures exposed to seismic loading by the methods of direct integration of equations of motion. Solution by the explicit and the implicit method is compared for three material models. While the differences between the results of the explicit method and the implicit Newmark method are small as expected, the differences are substantial between the results of different material models. However, these differences are explained and they are in full concordance with the theoretical assumptions for the pertinent material models. The conclusion of the final thesis is check of correctness of the results of the new module of the program system RFEM for both tested numerical methods and all three analyzed material models. (linear elastic, plastic Drucker-Prager and the Mazars damage model). With sufficient precision of results, both explicit and implicit numerical methods showed to be suitable for seismic analysis. The implicit method can provide several times faster calculation than the explicit one, but the determination of the optimal time step is problematic and time consuming, so the suitability of use of both methods for seismic analysis is comparable.
11
Stráník, Radim. "Parametrická studie absorpčního prvku přední části vozidla z hlediska bezpečnosti posádky vozidla při čelní kolizi". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241128.
Testo completoAbstract (sommario):
The main subject of this master thesis is the computational modeling of stress-strain analysis of the loaded front part of Toyota Yaris from the year 2010 using an explicit finite element method (FEM). The aim of this thesis is the assessment of resistance of the front part of the car (longeron) at the impact stress. This thesis describes the selection, editing, and creation of the computational model of longeron and simulation of the barrier collision. The objective of the thesis is to use a real vehicle, suggest modified longerons to be implemented in it, test various shape and material versions of the longeron and make their comparison.
12
Guo, Siyu. "New encapsulation concept for robot controller cabinet". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281711.
Testo completoAbstract (sommario):
Robot controller cabinets are specified with interfaces which make it possible to connect different modules for completing numerous tasks that are chosen for the robot manipulators. Different interfaces will be utilized depend on the kind of tasks and settings that are chosen. Thus not every interface will be put into use in a controller cabinet, some are left behind. In order to fulfill the encapsulation standards of electrical enclosures, the unoccupied interfaces are covered and sealed with on-screwed cover plates and gaskets during the assembly of the cabinet. However, a new method for encapsulation hope to be investigated and introduced to improve the current solution with respect to the encapsulation requirements from ABB. The introduced new solution is a knockout concept. The detailed design is investigated with the help of finite element analysis with the explicit dynamics method used for simulating the punching processes of the knockout designs. Where three different design variables are put into consideration for finding the most optimum knockout design. The results show that, for the particular steel plate provided by ABB, a V-grooved knockout design with a grooving angle of 90 degrees and an unaffected thickness of 0.1 mm has the best performance in terms of smoothness at edges and the amount of plastic strain occurred in the material. Traditional manufacturing methods to manufacture the obtained knockout design appear to be extremely time consuming and thus not profitable for mass production. However, a type of fairly recent developed grooving machines, the so called V-grooving machine, is believed to be able to solve the manufacturing problem.Robot styrskåp är specificerad med mängder gränssnitt vilket gör det möjligt för anslutning av olika moduler till att kunna fullborda de uppgifterna valda för robot manipulatorerna. Olika gränssnitt utnyttjas beroende på den typ av arbetsuppgift och inställningar valda just för den. Därför kommer inte alla gränssnitt att kunna tas i bruk i ett styrskåp, vissa lämnas kvar. För att kunna uppfylla inkapslingsstandarden för elektriska kapslingar är dessa obesatta gränssnitt täckt och förseglat med påskruvad täckplåtar och packningar under montering av styrskåp. En ny inkapslingsmetod hoppas att kunna utredas och introduceras till att förbättra den nuvarande lösningen med avseende på de inkapslingskraven från ABB. Den introducerade lösningen är ett knockout koncept. En detaljerad konstruktion undersöks med hjälp av finita element analys med explicit dynamik som grunden till att simulera knockout processer. Där tre olika design parametrar tas i beaktande för att hitta den mest optimala knockout konstruktionen. Resultaten visar sig att, för den här särskilda stålplåten som tillhandahålls av ABB, en V-spårad knockout konstruktion med en spårvinkel på 90 grader och en tjocklek på 0.1 mm har den mest tillfredställande prestandan med avseende på jämnhet, d.v.s. reduceringen av vassa kanter, och mängder av plastiska töjningar som inträffas i materialet efter knockout processen. Traditionella tillverkningsmetoder till att tillverka en sådan knockout konstruktion visar sig vara väldigt tidsödande och anses därför inte vara lönsamt för massproduktion. Emellertid upptäcks det en typ av relativt nyutvecklad spårmaskin, så kallad V-grooving machine, som tros att kunna lösa tillverkningsproblemet.
13
Nazari, Amir, e Behrouz Nourozi. "Behavioral Analysis of Volvo Cars Instrument Panel During Airbag Deployment". Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-132375.
Testo completoAbstract (sommario):
Airbags are a passive safety technology, required to function with zero failure rate. Advances in Computer Aided Engineering have allowed vehicle manufacturers to predict material and system behavior in the event of a crash. The sudden and rapid nature of a vehicle frontal crash, together with strict requirements put on safety make this a sensitive task. This thesis focuses on the front passenger airbag deployment and the instrument panel’s response. Various airbag modelling techniques are studied and presented in this document. This work is part of a larger-scale attempt to model a generic-sled that is physically representative of a real vehicle. Various component tests are to be performed in the sled environment, as opposed to a real vehicle, to save costs. Various modules are added to the sled once their behavior is verified by testing and in simulations. Software are advanced enough to identify location and magnitude of stress concentrations that develop during crash. LS-DYNA is used for explicit finite element simulations of the instrument panel (IP) in question with different airbag models. Verification has been achieved by design of experiment (DOE); with tests conducted to capture both the movements of the airbag housing and IP movements in response. These movements are broken down in various phases, facilitating implementation in the sled environment. Simplifications are made both to the computer models as well as the physical testing environment. The effects of these simplifications are quantified and discussed. Theoretical background is provided where fit while assumptions are justified wherever made. DYNAmore recommendations regarding costeffective calculations as well as result verification are followed. The obtained results show that the FE models replicate the real event with acceptable precision. The findings in this work can, by minor tweaks, be implemented on other IP models in the Volvo Cars range, leading to cost-saving solutions. This thesis provides the necessary information for sled implementations as well as future improvement suggestions.Krockkudde är en s.k. passiv säkerhetsteknik som krävs att fungera felfritt. Framsteg inom Computer Aided Engineering har tillåtit biltillverkare att förutsäga material och systembeteende i samband med krock. Den plötsliga karaktären av krock, tillsammans med höga säkerhetskrav, gör detta till en känslig uppgift. Denna avhandling fokuserar på passagerarsidans krockkudde och instrumentbrädans (IP) respons under uppblåsning. Olika metoder för modellering av krockkuddar har studerats och presenteras i detta dokument. Arbetet är en del av en större skala försök att modellera en generisk-släde som är fysiskt representativ av en riktig bil; där olika komponent-tester skall utföras för att minska kostnader. När olika modulers beteende verifieras läggs de till släden. Denna verifiering sker genom finita element (FE) simuleringar så väl som fysiska tester. FE mjukvara är idag tillräckligt avancerad för att identifiera samt visualisera spänningskoncentrationer som uppstår i en konstruktion vid krock. LS-DYNA används i detta arbete för explicita FE simuleringar av en Volvo XC90 IP, lastad med olika krockkudde-modeller. Modell verifiering har uppnåtts genom försöksplanering (DOE); med tester utförda för att fånga rörelser av IP så väl som krockkudde-behållaren. Dessa rörelser är sedan uppdelade i olika faser för enklare genomförande i släde miljön. Förenklingar och antaganden görs både till FE modeller och fysiska testmiljön. Effekter av dessa har kvantifierats och relevant teoretisk bakgrund har inkluderats. Dokumentet innehåller även diskussion kring val av mätutrustning samt förbättringsförslag för fortsatt arbete. DYNAmore rekommendationer gällande kostnadseffektiva beräkningar och verifiering av simulerings-resultat har följts. Under arbetet visade sig att FE modellerna kan återskapa händelsen med hög noggrannhet; dessa trotts svårigheter i modellering av plast material. Möjligtvis kan man, genom mindre modifieringar, relatera slutsatserna i detta arbete till olika IP modeller i företagets produktkatalog vilket förmodligen leder till ytterligare kostnadsbesparingar. Denna avhandling ger den information som behövs för genomföranden i den generiska miljön.
14
Hoang, Hue, e Matilda Widerström. "Simulation of distributed windings using the insert technique". Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-17430.
Testo completoAbstract (sommario):
During the insert process when the windings of an electric motor are pushed into the stator slots, some detrimental phenomena can occur that affect the efficiency and life of the motor. To detect these phenomena and optimize the process, a simulation would be useful. An investigation of the possibility to perform a simulation, using an appropriate numerical method for the insert process of distributed windings in a permanent magnet synchronous motor, was performed. During the project, a literature study was carried out to investigate existing methods and key-parameters for the simulation of the process. Explicit finite element method has been shown to be a suitable numerical method for simulating another winding process. An explicit finite element analysis was performed with a simplified model of the stator, the wires, the transmission tool and the needles by using the software Abaqus/CAE. In order to reduce the computational time, beam elements were used to model the wires and the other parts as rigid bodies. The model accounted for example contact and provided numerical results. The result was a suitable model. However, it needs to be developed further.
15
Kottravel, Sathish. "GPU accelerated Nonlinear Soft Tissue Deformation". Thesis, Linköpings universitet, Medie- och Informationsteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-76895.
Testo completoAbstract (sommario):
There are two types of structures in human body, solid organs and hollow membrane like organs. Brain, liver and other soft tissues such as tendons, muscles, cartilage etc., are examples of solid organs. Colon and blood vessels are examples of hollow organs. They greatly differ in structure and mechanical behavior. Deformation of these types of structures is an important phenomena during the process of medical simulation. The primary focus of this project is on deformation of soft tissues. These kind of soft tissues usually undergo large deformation. Deformation of an organ can be considered as mechanical response of that organ during medical simulation. This can be modeled using continuum mechanics and FEM. The primary goal of any system, irrespective of methods and models chosen, it must provide real-time response to obtain sufficient realism and accurate information. One such example is medical training system using haptic feedback. In the past two decades many models were developed and very few considered the non-linear nature in material and geometry of the solid organs. TLED is one among them. A finite element formulation proposed by Miller in 2007, known as total Lagrangian explicit dynamics (TLED) algorithm, will be discussed with respect to implementation point of view and deploying GPU acceleration (because of its parallel nature to some extent) for both pre-processing and actual computation.
16
Chlebek, David. "Simulation of ultrasonic time of flight in bolted joints". Thesis, KTH, Hållfasthetslära, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298342.
Testo completoAbstract (sommario):
Ultrasonic measurements of the preload in bolted joints is a very accurate method since it does not depend on the friction and other factors which cause difficulties for common methods. The ultrasonic method works by emitting an ultrasonic pulse into the bolt which is reflected at the end and returned to the transducer, the change in the time of flight (TOF) can be related to the elongation of the bolt and therefore the preload. One must account for the acoustoelastic effect which is the change in sound speed due to an initial stress state. The goal of this thesis project was to implement a Murnaghan hyperelastic material model in order to account for the acoustoelastic effect when conducting a numerical simulation using the finite element method (FEM). An experiment was also performed to validate the numerical simulation. The DeltaTOF as a function of a tensile force was obtained for an M8 and M10 test piece from the experiment. The material model was implemented by creating a user subroutine written in Fortran for the explicit solver Radioss. Hypermesh was used to set-up the numerical simulation. The material model has shown an expected behavior with an increased sound speed with compressive stresses and a decreased speed with tensile stresses. The numerical simulation showed a good correspondence to the experimental results.Ultraljudsmätning av klämklraften i skruvförband är en väldigt noggrann metod eftersom att metoden inte påverkas av friktion eller andra faktorer som innebär svårigheter för vanliga metoder. Ultraljudsmetoden fungerar genom att skicka in en ultraljudsvåg i skruven som reflekteras i botten och återvänder tillbaka till sensorn. Skillnaden i tiden för ekot att återvända kan relateras till förlängningen av skruven och därmed klämkraften. Det är viktigt att ta hänsyn till den akustoelastiska effekten, som är fenomenet där ljudhastigheten av en våg i en solid förändras med spänningstillståndet. Målet med det här arbetet är att implementera en hyperelastisk Murnaghan modell som tar hänsyn till den akustoelastiska effekten med FEM simuleringar. Ett experiment har också genomförts för att validera beräkningsmodellen. Tidsfördröjningen som en funktion av förspänningskraften togs fram för ett M8 och M10 provobjekt. Murnaghans hyperelastiska materialmodell implementerades genom att skapa ett användar material skriven i programmeringsspråket Fortran för den explicita lösaren Radioss. Hypermesh användes för att ställa upp FEM simuleringen. Materialmodellen har visat ett väntat beteende med en ökad ljudhastighet med tryckspänningar och minskad ljudhastighet med dragspänningar. Beräkningsmodellen visade en god överenstämmelse med resultatet från experimentet.
17
Bucňák, Ondřej. "Návrh demonstrátoru konstrukce z kompozitních materiálů pro kalibraci simulace pohlcení energie". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254336.
Testo completoAbstract (sommario):
This master thesis focuses on a scaled fuselage design made from composite material. The first part deals with a description of composite materials and used material models in an explicit FEM simulation. Two types of scaled structures were designed that were subjected to drop test. Test results were compared with FEM simulation. Finally the calibration of models was carried out.
18
Holmberg, Erik. "Analysmetoder för rörsystem". Thesis, Linköping University, Department of Management and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15678.
Testo completoAbstract (sommario):
The purpose of this thesis work is to evaluate how the physical behaviour of a pipe bend is affected by the pipe bending procedure. Effects such as initial ovalization, thinning, thickening and plastic hardening from the bending procedure are examined and the mechanical properties of pipe bends containing these effects are investigated.
This has been evaluated by creating a detailed Finite Element model of a pipe that is being bent. Then the differences compared to a bent tube in a virgin state, so called Elbow elements and an analytical in-house program have been evaluated. The virgin state refers to a model of a pipe that is bent from the beginning, thus having a homogeneous thickness and not containing any plastic hardening. The Elbow element is a calculationally cheap element, specially developed for accurate calculations of pipe bends in an initially virgin state.
The goal with the thesis work is to get a better picture of what happens to a pipe as it is being bent, how this affects the mechanical properties and to evaluate the possibility to develop an easy method for taking these effects into account when using the Elbow element.
This report describes the layout of the work and how the detailed FE-model has been constructed. One step to being able to use the Elbow element with respect to changes in shape and plastic hardening from the manufacturing process has been presented, the differences are though considered being too big to be able to use the Elbow elements with enough confidence in the results. The problems that remain are presented and discussed and proposals for further work are presented.
19
Portugal, André Fernandes Vaz. "Validation of a FEM-based tool and implementation of tyres' dry and wet braking prediction". Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/22755.
Testo completoAbstract (sommario):
Mestrado em Engenharia MecânicaIn the present document, a new explicit FEM-based software developed to optimize tyre pattern geometry is presented. The new software calculates forces and displacements in tyre tread components after applying a load and a longitudinal shear displacement. To overcome long meshing and calculation times, simplifications are made. In this work, the usability of the simplifications is checked and the new software is adjusted and validated through the use of other FEM-based software in the market (Abaqus). To perform the validation, models are created, reproducing tyre tread blocks with different geometries, and the same simulation is reproduced in Abaqus. A set of simulations is run in both software. The results of the simulations are compared regarding the final shape, reaction forces and displacements in the nodes of the models. Finally, simple friction formulations are proposed and implemented in the new software, as well as a slip parameter and a water height level in the tyre footprint, in order to simulate braking performance in dry and wet surfaces. The results are then compared with experimental tests.
No presente documento, um novo software baseado no Método dos Elementos Finitos (MEF) explícito, desenvolvido para otimizar a geometria do padrão de pneus é apresentado. O novo software calcula forças e deslocamentos em componentes do piso dos pneus após a aplicação de uma carga e um deslocamento longitudinal. Para superar longos tempos de geração de malha e de cálculo, simplificações são feitas. Neste trabalho, a viabilidade para a utilização das simplificações é verificada e o novo software é ajustado e validado através da utilização de outro software baseado no MEF no mercado (Abaqus). Para executar a validação, modelos são criados, reproduzindo blocos do piso do pneu com diferentes geometrias, e a mesma simulação é reproduzida no Abaqus. Um conjunto de simulações é executado em ambos os softwares. Os resultados das simulações são comparados em relação à forma final, às forças de reação e deslocamentos nos nós dos modelos. Finalmente, simples formulações de fricção são propostas e implementadas no novo software, bem como um parametro de deslizamento e nível da altura da camada de água na pegada do pneu, a fim de simular o desempenho de travagem em piso seco e molhado. Os resultados são, então, comparados com testes experimentais.
20
Profota, Martin. "Pevnostní návrh ostruhy letadla". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318638.
Testo completoAbstract (sommario):
This master thesis deals with computational stress-strain analysis of the tailskid of airplane L410 NG with main focus firstly the check current design of the tailskid and then the design another design solution with the able to absorb as much as possible the deformation energy. Solution of this problem is performed using computational modeling utilizing numerical simulation of quasi-static and crash deformation load of the tailskid with using explicit Finite Element Method (FEM) in program ABAQUS v6.14. After the introduction with problem situation and tailskid assembly introductory part is devoted to the research study of various designs of the tailskid for different types of airplanes. There follows these theoretical general principles of thin-walled structures and buckling of them. Before the creating of the computational model itself, the explicit form of the Finite Element Method is better described. The conclusion of this thesis deals with the mutual comparison of the most advantageous design variants of the tailskid and the selection of the most suitable one of them for the airplane L410 NG.
21
Onder, Erkan Ismail. "Assessment Of Sheet Metal Forming Processes By Numerical Experiments". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606159/index.pdf.
Testo completoAbstract (sommario):
iv
Sheet metal forming technologies are challenged especially by the improvements in
the automotive industry in the last decades. To fulfill the customer expectations,
safety requirements and market competitions, new production technologies have
been implemented. This study focuses on the assessment of conventional and new
sheet metal forming technologies by performing a systematic analysis. A geometry
spectrum consisting of six different circular, elliptic, quad cross-sections are
selected for the assessment of conventional deep drawing, hydro-mechanical deep
drawing and high-pressure sheet metal forming. Within each cross-section, three
different equivalent drawing ratios are used as a variant. More than 200 numerical
experiments are performed to predict the forming limits of three competing
processes. St14 stainless steel is used as the material throughout the assessment
study. The deformation behavior is described by an elasto-plastic material model
and all numerical simulations are carried out by using dynamic-explicit commercial
The process validation is done by interpreting the strain results of numerical
experiment. Therefore, the reliability of predictions in the assessment study highly
depends on the quality of simulations. The precision of numerical experiments are
verified by comparing to NUMISHEET benchmarks, analytical formulation, and
experiments to increase the assets of the assessment study.
The analyses revealed that depending on the workpiece geometry and dimensional
properties certain processes are more preferable for obtaining satisfactory products.
The process limits for each process are established based on the analyzed crosssections
of the spectrum. This data is expected to be useful for predicting the
formability limits and for selecting the appropriate production process according to
a given workpiece geometry.Dynamic-explicit FEM, Deep drawing, Hydroforming, Forming limits,
Process evaluation
22
Warnert, Steven Paul. "Design and Analysis of the Impact Diffusion Helmet Through a Finite Element Analysis Approach". DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1669.
Testo completoAbstract (sommario):
By applying the finite element approach to the design and analysis of the impact diffusion helmet, many helmet configurations were able to be analyzed. Initially it was important to determine what design variables had an influence on the impact reducing abilities of the helmet design. The helmet was run through a series of Abaqus simulations that determined that a design with two oval shaped channels running along the length of the helmet was best. Next, these options were optimized to generate the helmet that produced the greatest impact reduction. The optimization simulations determined that a helmet that pushed the channels as far from the impact zone as possible reported the lowest acceleration. This indicated that removing the channels from play was most advantageous from an impact reduction perspective. Finally, a 3-D printed experimental helmet was impact tested and compared to a 3-D printed control helmet. The experimental helmet brought the channels back into the impact zone in order to judge if they had a physical effect on the acceleration. Both the simulations and the subsequent physical testing indicated that the Impact Diffusion Helmet design has a negative influence on the concussion reducing properties of a football helmet.
23
Wohllebe, Malte. "Svenska elevers språkkänsla för det engelska språket : Vikten av intuition i elevers språkliga problemlösning". Thesis, Umeå universitet, Institutionen för språkstudier, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-136260.
Testo completoAbstract (sommario):
The purpose of this study was to examine if and in which cases Swedish students rely on their intuition when being confronted with English and how efficiently their language intuition, or sprachgefühl, functions. To study these questions a task was developed in which Swedish students of upper secondary level were asked to identify and correct various kinds of mistakes that were hidden in an English text. They were also asked to give an explanation for the changes they made, based on grammatical rules or feeling for linguistical correctness, to determine if they used their analytical capacity or their intuition in the process. The results showed that the students mainly relied on their intuition when making linguistical choices. Furthermore, the students were able to successfully solve the problems they identified in 77,5% of the cases they relied on their language intuition. However, they were still more successful, to be specific in 92% of the cases, when using their analytical system. This could either point to a lack of knowledge in grammar and deficient focus on teaching grammar in Swedish schools, or to the fact that language intuition is a dominant system in human language learning and should therefore be put in focus of language research.
24
Bezrouková, Martina. "Simulace válečkování pomocí explicitní MKP". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230340.
Testo completoAbstract (sommario):
The purpose of this work is to introduce explicit finite element method (FEM) and to familiarize with commercial software tools witch are capable to perform simulations. The technological conditions and the scope of application of roller burnishing are described in subsequent part. The simulation model of roller burnishing was created. Software ANSYS LS-DYNA was used to make computations. The results of simulation and technical and economical benefits of roller burnishing are presented in the conclusion.
25
Chaloupka, Ondrej. "Modelling evolution of anisotropy in metals using crystal plasticity". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8435.
Testo completoAbstract (sommario):
Many metals used in modern engineering exhibit anisotropy. A common
assumption when modelling anisotropic metals is that the level of anisotropy is
fixed throughout the calculation. As it is well understood that processes such as
cold rolling, forging or shock loading change the level of anisotropy, it is clear
that this assumption is not accurate when dealing with large deformations.
The aim of this project was to develop a tool capable to predict large
deformations of a single crystal or crystalline aggregate of a metal of interest
and able to trace an evolution of anisotropy within the material.
The outcome of this project is a verified computational tool capable of predicting
large deformations in metals. This computational tool is built on the Crystal
Plasticity Finite Element Method (CPFEM). The CPFEM in this project is an
implementation of an existing constitutive model, based on the crystal plasticity
theory (the single crystal strength model), into the framework of the FEA
software DYNA3D® .
Accuracy of the new tool was validated for a large deformation of a single
crystal of an annealed OFHC copper at room temperature. The implementation
was also tested for a large deformation of a polycrystalline aggregate comprised
of 512 crystals of an annealed anisotropic OFHC copper in a uniaxial
compression and tension test. Here sufficient agreement with the experimental
data was not achieved and further investigation was proposed in order to find
out the cause of the discrepancy. Moreover, the behaviour of anisotropic metals
during a large deformation was modelled and it was demonstrated that this tool
is able to trace the evolution of anisotropy.
The main benefit of having this computational tool lies in virtual material testing.
This testing has the advantage over experiments in time and cost expenses.
This tool and its future improvements, which were proposed, will allow studying
evolution of anisotropy in FCC and BCC materials during dynamic finite
deformations, which can lead to current material models improvement.
26
Nytra, Michal. "Simulace zápustkového kování pomocí metody konečných prvků". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400519.
Testo completoAbstract (sommario):
Tato diplomová práce se zabývá výpočtovým modelováním zápustkového kování, které patří do metod objemového tváření zatepla. Cílem je změnit běžnou praxi tvorby výpočtových modelů ve specializovaných softwarech na bázi metody konečných prvků (MKP) a sestavit výpočtový model v MKP softwaru Abaqus. Pro výpočet jsou zde použity deformační varianta MKP a explicitní algoritmus. Řešenou součástí je ozubené kolo automobilové převodovky. V rámci práce je vytvořena rešerše z oblasti objemového tváření včetně specializovaných programů pro simulace procesů tváření. Dále jsou v práci uvedeny všechny konstitutivní vztahy pro popis elasto-plastického modelu materiálu s tvárným porušením. Následuje teorie přenosu tepla, jsou popsány všechny způsoby jeho realizace s jejich matematickými formulacemi včetně metod řešení. Klíčovou je kapitola popisující postup tvorby výpočtového modelu v softwaru Abaqus od tvorby geometrie až po okrajové podmínky. Následuje analýza dosažených výsledků a práce je zakončena výhledem na možné pokračování v tomto tématu.
27
Andersson, Daniel, e Fredrik Saliba. "Virtual testing of self-piercing rivet connections". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79405.
Testo completoAbstract (sommario):
The automotive industry is currently trying to replace the conventional steels to lightweight materials such as aluminum or carbon fiber to meet all stricter emission targets. When using such materials, traditional joining methods, such as spot welds, could be difficult to use. Therefore, more focus has been put on self-piercing rivets (SPR).In whole car models used in crash simulations, substitution models are used to model SPR joints. It is important to calibrate these models for different load cases. Volvo Cars Corporation (VCC) are currently calibrating using time-consuming physical tests where the SPR joint is subjected to loads in different directions. To save time, a way of virtually evaluating the SPR joint strength is therefore sought after. To do this, a method was developed using non-linear FEM in LS-DYNA. The method was then used to perform sensitivity studies concerning friction, sheet thickness and rivet geometry.The method developed can be divided into three parts. The process simulation, where the rivet insertion was simulated. A springback analysis, where the material is allowed to springback, closer resembling the real behaviour. Finally, the three destructive tests, lap-shear, cross-tension and KS2, were built using the geometry and initial values from the springback.For the process simulation, an explicit solution was used. To handle the large deformations present during the event, r-adaptivity was used together with a kill-element-method to describe failure, based on CrachFEM or Gissmo. The following springback analysis was then performed using one implicit step.For the destructive tests, a solid element representation of the SPR joint was created using the geometry and initial values from the springback. A shell-solid hybrid model was used to keep the computational time low.Using the method, a good correlation was found both for the process- and the destructive test simulations when compared to experiments. Furthermore, it could be concluded that friction, sheet thickness and rivet geometry affects the SPR joint strength and characteristics.
28
Rudraraju, Venkata Sai Krishna Varma, e Arjun Valishetty. "Thermal Analysis of a Park Lock System in a DCT Transmission". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-15708.
Testo completoAbstract (sommario):
A park lock is a mechanism used to prevent unintentional movement of the vehicle. A failure in the proper function of this mechanism can lead to the safety concerns of an automobile. The main focus of this thesis is to understand the reason behind the failure of the park lock mechanism by FEM analysis in ANSA. For this, temperature build up during the park lock engagement has been studied in a dynamic explicit analysis. The FE results are compared to results from experiments on park lock. The modelling has been done in ANSA, ABAQUS was used as a solver for simulation and the results have been studied in META. The results indicate that there is a rise in the temperature. This is due to the friction between the contact surfaces and the oscillations generated in the vehicle. Based on the observations, discussions and conclusions are formulated and the research questions are answered.
29
Jakel, Roland. "Lineare und nichtlineare Analyse hochdynamischer Einschlagvorgänge mit Creo Simulate und Abaqus/Explicit". Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-171812.
Testo completoAbstract (sommario):
Der Vortrag beschreibt wie sich mittels der unterschiedlichen Berechnungsverfahren zur Lösung dynamischer Strukturpobleme der Einschlag eines idealisierten Bruchstücks in eine Schutzwand berechnen lässt. Dies wird mittels zweier kommerzieller FEM-Programme beschrieben: a.) Creo Simulate nutzt zur Lösung die Methode der modalen Superposition, d.h., es können nur lineare dynamische Systeme mit rein modaler Dämpfung berechnet werden. Kontakt zwischen zwei Bauteilen lässt sich damit nicht erfassen. Die unbekannte Kraft-Zeit-Funktion des Einschlagvorganges muss also geeignet abgeschätzt und als äußere Last auf die Schutzwand aufgebracht werden. Je dynamischer der Einschlagvorgang, desto eher wird der Gültigkeitsbereich des zugrunde liegenden linearen Modells verlassen. b.) Abaqus/Explicit nutzt ein direktes Zeitintegrationsverfahren zur schrittweisen Lösung der zugrunde liegenden Differentialgleichung, die keine tangentiale Steifigkeitsmatrix benötigt. Damit können sowohl Materialnichtlinearitäten als auch Kontakt geeignet erfasst und damit die Kraft-Zeit-Funktion des Einschlages ermittelt werden. Auch bei extrem hochdynamischen Vorgängen liefert diese Methode ein gutes Ergebnis. Es müssen dafür jedoch weit mehr Werkstoffdaten bekannt sein, um das nichtlineare elasto-plastische Materialverhalten mit Schädigungseffekten korrekt zu beschreiben. Die Schwierigkeiten der Werkstoffdatenbestimmung werden in den Grundlagen erläutertThe presentation describes how to analyze the impact of an idealized fragment into a stell protective panel with different dynamic analysis methods. Two different commercial Finite Element codes are used for this: a.) Creo Simulate: This code uses the method of modal superposition for analyzing the dynamic response of linear dynamic systems. Therefore, only modal damping and no contact can be used. The unknown force-vs.-time curve of the impact event cannot be computed, but must be assumed and applied as external force to the steel protective panel. As more dynamic the impact, as sooner the range of validity of the underlying linear model is left. b.) Abaqus/Explicit: This code uses a direct integration method for an incremental (step by step) solution of the underlying differential equation, which does not need a tangential stiffness matrix. In this way, matieral nonlinearities as well as contact can be obtained as one result of the FEM analysis. Even for extremely high-dynamic impacts, good results can be obtained. But, the nonlinear elasto-plastic material behavior with damage initiation and damage evolution must be characterized with a lot of effort. The principal difficulties of the material characterization are described
30
Singh, Subrat, e Shreedhara Sreehari Veditherakal. "CAE modelling of cast aluminium in automotive structures". Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-162190.
Testo completoAbstract (sommario):
In the automobile industry, there is a big push for the automotive car manufacturers to base engineering decisions on the results of Computer Aided Engineering (CAE) solutions, and to transform the prototyping and testing, from a costly iterative process to a final verification and validation step. The variability in components material properties and environmental conditions together with the lack of knowledge about the underlying physics of complex systems often make it impractical to make reliable predictions based on only deterministic CAE models. One such area is the CAE modelling of cast aluminium components. These cast aluminium components have gained a huge relevance in the automobile industries due to their commendable mechanical properties. The advantage of the cast aluminium alloys are being a well-established alloy system in manufacturing processes, their functional integrity and relatively low weight. However, the presence of pores and micro-voids obtained during the manufacturing process constitutes a specific material behaviour and establishes a challenge in modelling of the cast materials. Furthermore, the low ductility of the materialdemands for the advanced numerical model to predict the failure. The main focus of this master thesis work is to investigate modelling technique of a cast aluminium alloy component, a spring tower, for a drop tower test and validate the predicted behaviour with the physical test results. Volvo Car Corporation currently uses a material model provided by MATFEM for cast aluminium parts which are explored in this thesis work, to validate the material model for component level testing. The methodology used to achieve this objective was to develop a boundary condition to perform component level tests in the drop tower and to correlate these with the obtained results found by using various modelling techniques in the explicit solver LS-DYNA. Therefore, precise and realistic modelling of the drop tower is crucial because the simulation results can be influenced by major design changes. A detailed finite element model for the spring tower has been developed from the observations made during the physical testing. The refined model showed good agreement with the existing model for the spring tower and observations from physical tests.
31
Kohestani, Tamim, e Ali Zeaiter. "FE based method for simulation of rock-loading on a truck". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18274.
Testo completoAbstract (sommario):
Volvos trucks are used to carry boulders of varying sizes from different mining sites or construction sites. These boulders are loaded onto the dumper of the truck by a wheel-loader which drops the boulders from various heights causing an impulse like force which distributes throughout the frame and to the rest of the truck. Depending on the size and what height the boulders are being dropped from, the distributed forces can cause damage to important parts of the truck. An experiment done by Volvo has shown that a two-ton weight dropped from 3.5 meters caused some truck components to crack, such as flywheel housing. Since this is alerting and it is costly to do the experiment on all trucks that Volvo manufactures it is our objective to come up with a method based on Finite Element which would evaluate the rock loading case. By using ANSA as the pre-processor which helps set up the model before running a simulation, and Nastran and LS-DYNA as the FEM solvers, a result was obtained that is somewhat comparable with the measurements. In the Nastran model, no non-linearities such as contact were considered, while in LS-DYNA nonlinear contact between the weight and the dumper body was defined, which improved the results considerably. The key conclusion from the two results was that the contact definition used in LS-DYNA is necessary if accurate results are important. Since LS-DYNA uses an explicit numerical method the model can be made more complicated by including more nonlinearities in the model and it would not affect the computation to much or at all. Hence the method would be future proof.
32
Kamberoglu, Murat. "Improvement Of Impact Resistance Of Aluminum And Zinc Based Die Cast Parts By Means Of Tool Steel Inserts". Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613905/index.pdf.
Testo completoAbstract (sommario):
High Pressure Die Casting (HPDC) is low-cost technique for the mass production of complex, non-ferrous parts. Despite its benefits such as dimensional accuracy, surface quality and high production ratesome mechanical drawbacks limit use of HPDC in production of critical parts especially under dynamical loads. This study aims to improve impact resistance and surface hardness of die cast parts by means of tool steel inserts. These inserts act as a barrier between the impactor and die casting alloy, in order to avoid surface deformation and reduce stress localization which leads crack formation. Except the impact surface, whole insert is embedded into the die casting alloy by placing them on specially machined die casting molds prior to the metal injection. The mentioned method was evaluated by mechanical test and micro-examinations which were applied on AISI D2 tool steel inserted A518.0, A413.2 and Zamak5 alloy samples. To see the effect of inserts on energy absorbance under single destructive loads, both monolithic (conventional) and inserted (produced by mentioned technique) samples were subjected to Charpy impact test. In order to observe its behavior under non-destructive, cyclic, low velocity impacts
a dedicated real rifle part was produced by this method and tested in the real service loads. Explicit Finite Elemental Analysis was also carried out to understand how the inserts increases the energy absorbance and protect the die cast body by simulating both destructive and non-destructive impact loads. In addition to these, micro-examinations were also conducted especially on insert-die casting alloy interface for chemical and physical interactions, defects and stability. In regards of experimental findings, mechanical feasibility of the method was achieved. It was proved that steel inserts improve energy absorbance, stress distribution and impact-surface hardness of die cast products.
33
Hůlka, Jiří. "Aplikace modelů tvárného porušování při výpočtové simulaci technologických operací". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-227954.
Testo completoAbstract (sommario):
This diploma thesis is an introduction to the ductile fracture under large plastic deformations and is focused to numerical simulation of this type of problems. Explicit finite element method (FEM) is discussed in theoretical introduction as the most powerful tool for numerical calculations in this area. Actual state of research and possibilities of ductile fracture simulations are presented. Applicable fracture criteria are collected in a summary sheet and the most important ones are selected and commented in detail. The problem of implementation of selected criteria into commercial FEM packages is discussed, too. Main part of the work is presented in chapters 7÷9 where two ductile fracture criteria (Equivalent Fracture Strain and Johnson-Cook) are applied to numerical simulation of material cutting. All results were obtained with ABAQUS/Explicit 6.5.1 and their verification was realized by experimental measurement.
34
James, Aricatt John, e Devarajan Velmurugan. "Determination of stresses and forces acting on a Granulator knife by using FE simulation". Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-28297.
Testo completoAbstract (sommario):
Recycling of plastics always plays an important role in keeping our environment better and safe. With the rise in usage of plastics and industrialization, the need for recycling the plastics has become a big business and is getting bigger. This thesis work was done for a company called Rapid Granulator AB, which works with the recycling of plastics as a big trade in Sweden. Like all the industries across the globe are trying to be economical in every way, Rapid Granulator AB wanted to develop an economical design of their high quality granulating knife. For achieving the economical design, they wanted to study the behaviour of the rotating knife during the process of producing plastic granules. The granulator cutting process was simulated and numerical analysis was done on the rotating knife of a plastic granulator machine by using the finite element code ABAQUS with 3D stress elements to find out the critical stresses and forces acting on the rotating knife. The bolt preload was applied by Abaqus/Standard, and the results of implicit analysis were imported to Abaqus/Explicit for the impact analysis where the flow of stresses on the rotating knife during the impact with materials were simulated and studied. The study was done on knife models of different thickness to see if the thickness of the current knife model can be reduced. Analysis were done also on a knife model assembly with a double sided cutting edge knife to see if the knife model can be used to its full extent. The simulation models and analysis results were given to the company to develop a more economical knife model.
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Hauquin, Thomas. "La rupture brutale des piliers conditionne-t-elle les effondrements miniers ? : approches énergétiques par modélisation numérique". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0164/document.
Testo completoAbstract (sommario):
A différents endroits du monde, on observe que la méthode d’exploitation minière par chambres et piliers est associée à deux aléas de grande ampleur se manifestant en surface : les affaissements progressifs et les effondrements brutaux. Le bassin ferrifère lorrain est sujet à ces deux types d’aléas notamment depuis la fermeture massive des mines à partir des années 1960. Les effondrements étant plus dangereux que les affaissements, des chercheurs ont développé des méthodes statistiques pour distinguer les zones à risque d’effondrement de celles à risque d’affaissement. L’objectif de cette thèse est de développer des indicateurs mécaniques capables de faire la même distinction, afin d’améliorer la compréhension physique des phénomènes mis en jeux et de valider les indicateurs statistiques. Nous faisons l’hypothèse que les effondrements et affaissements sont tous deux causés par un endommagement des piliers en profondeur. Le Chapitre 1 est consacré à une étude bibliographique qui synthétise les connaissances relatives au comportement mécanique des piliers. Nous constatons que les piliers sont caractérisés par deux critères : le facteur de sécurité (résistance en compression/contrainte verticale moyenne) qui détermine s’ils sont susceptibles de se rompre, et un critère de stabilité des piliers en cas de rupture qui s’exprime comme la raideur relative des piliers par rapport à celle de la roche encaissante. Deux limites des approches actuelles sont identifiées : 1) la question de la contrainte verticale moyenne des piliers (dénominateur du facteur de sécurité) a été relativement peu étudiée pour les piliers aux dimensions irrégulières, caractéristiques des anciennes mines ; 2) l’instabilité de la rupture des piliers est évaluée par un modèle 1D proposé dans les années 1960-1970, se basant sur des considérations énergétiques. Ce modèle très courant n’a toutefois fait l’objet que de peu de développements dans des configurations géomécaniques plus réalistes que celle du modèle de départ. Le Chapitre 2 développe une nouvelle méthode permettant de prendre en compte l’irrégularité géométrique des piliers pour estimer leur contrainte verticale et donc d’avoir une meilleure précision sur l’estimation du facteur de sécurité. Nous introduisons le concept du taux de défruitement relatif et montrons sur la base de résultats de modélisation numérique, qu’une fonction quadratique de ce terme procure une meilleure estimation de la contrainte verticale moyenne que la méthode traditionnelle de l’aire tributaire. Le Chapitre 3 porte sur l’application d’une méthode originale de modélisation explicite de l’instabilité des piliers, basée l’énergie cinétique. Nous montrons que nos résultats de modélisation en 2D sont compatibles avec le modèle 1D traditionnel. La procédure de modélisation employée permet également de localiser et de quantifier les excès d’énergie cinétique lors de l’instabilité. Les quantités d’énergie cinétique modélisées sont du même ordre de grandeur que les magnitudes de Richter d’énergie sismique typiques des ruptures brutales de piliers réels. Nous traitons dans le Chapitre 4 la problématique des effondrements du bassin ferrifère lorrain. Nous montrons sur la base de modélisations 3D que les critères de rupture et d’instabilité des piliers permettent de bien y distinguer les zones affaissées et les zones effondrées. Les secteurs affaissés et effondrés sont caractérisés par un facteur de sécurité moyen des piliers inférieur à 1 du point de vue de leur limite d’élasticité. Cependant, les secteurs effondrés se distinguent des secteurs affaissés par un facteur de sécurité moyen des piliers également inférieur à 1 du point de vue de leur pic de résistance. Ceci est confirmé par des modèles numériques simples en 2D, suggérant par ailleurs que les caractéristiques du recouvrement ont peu d’effet sur l’occurrence des effondrements. Certaines études fournissant des conclusions contraires, nous avançons des arguments pour en discuterAt different locations around the world, the room-and-pillar mining method truns out to be associated with two major types of hazards affecting the surface: the continuous subsidence and the sudden collapse. The Lorraine iron basin (France) have known on many occasions both continuous subsidences and sudden collapses, notably since the decline of the French mining activity in the 1960’s. The collapses are more dangerous than the continuous subsidences. This is why researchers and engineers developed statistical methods capable of distinguishing between the sectors subjected to a collapse hazard and those subjected to a continuous subsidence hazard. The objective of that study if to develop indicators capable of making the same distinction but on the basis of mechanical criteria, for the purpose of improving the understanding of the collapse mechanism and for validating the statistical indicators. The main assumption of this work is that both the continuous subsidences and the collapses are caused by damage of the pillars within the mines. Chapter 1 presents a literature review concerning the actual knowledge about the pillars mechanical behaviour. We notice that pillars are traditionally characterized by two criteria: the factor of safety (pic compressive resistance/average vertical stress), which determines whether or not pillars are susceptible to fail, and a criterion of stability in case of a failure, which consists of comparing the flexural stiffness of the surrounding rock to the pillars axial stiffness in the post-pic domain of their behaviour. We identify two limits regarding the traditional approaches: i) The question of the average vertical stress has only been little studied in the case of pillars with irregular geometry, which is often the case in old mines; ii) The model allowing to estimate whether or not an instability is susceptible to occur comes from a 1D model proposed in the 1960’s and that has never been developed furthermore for being applied to real configurations in various geomechanical conditions. In Chapter 2, we develop a new method for taking the irregularity of the pillars dimensions into account in estimating their average vertical stress, for the purpose of having a better precision in the factor of safety calculation. We introduce the concept of relative extraction ratio and show, on the basis on numerical modelling, that a quadratic function of this ratio is more precise in estimating the average pillar stress than the classical tributary area method.Chapter 3 is devoted to the development and the application of an original explicit method for modelling pillar instability based on the kinetic energy. We show that the numerical results obtained in 2D configurations are compatible with the traditional 1D model of pillar instability. Moreover, we show how the modelling method we are using helps to locate and to quantify the kinetic energy in excess induced by the instability. The magnitudes of modelled kinetic energies are similar to Richter magnitudes of typical seismic energies recorded during real pillar bursts. The problem of the Lorraine iron basin collapses is treated in Chapter 4. Based on 3D modelling results, we show that pillar failure and instability criteria are capable of well distinguishing between the sectors affected by collapses and those affected by continuous subsidences in the iron basin. Both the sectors subjected to collapses and continuous subsidences are characterized by a factor of safety lower than one regarding the limit of elasticity. But the collapsed sectors are distinguished by a factor of safety also lower than one regarding the pic compressive resistance. This observation is confirmed by simplified 2D modelling, which suggests, furthermore, that the properties of the overburden have no effect on the occurrence of the collapses. Some studies provide contrary conclusions. So, we propose some points to be discussed
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Ščerba, Bořek. "Vliv nastavení a konfigurace rovnačky na výsledky simulace kosoúhlého rovnání". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-418209.
Testo completoAbstract (sommario):
Analytical methods or implicit finite element method (FEM) with beam elements to model straightened bar were used to analyze straightening process in multi-staggered cross-roll straighteners up to now. These are effective but require certain simplifications. Aim of this thesis is to create an explicit FEM model allowing usage of solid elements for circular bar without disproportional increase of computational time. This may lead to deeper understanding of the straightening process. The model is to be verified using straightening tables and then used to quantify influence of rollers configuration on results of the straightening process.
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Liu, Chih-Hsing. "A finite element based dynamic modeling method for design analysis of flexible multibody systems". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39605.
Testo completoAbstract (sommario):
This thesis develops a finite element based dynamic modeling method for design and analysis of compliant mechanisms which transfer input force, displacement and energy through elastic deformations. Most published analyses have largely based on quasi-static and lump-parameter models neglecting the effects of damping, torsion, complex geometry, and nonlinearity of deformable contacts. For applications such as handling of objects by the robotic hands with multiple high-damped compliant fingers, there is a need for a dynamic model capable of analyzing the flexible multibody system. This research begins with the formulation of the explicit dynamic finite element method (FEM) which takes into account the effects of damping, complex geometry and contact nonlinearity. The numerical stability is considered by evaluating the critical time step in terms of material properties and mesh quality. A general framework incorporating explicit dynamic FEM, topology optimization, modal analysis, and damping identification has been developed. Unlike previous studies commonly focusing on geometry optimization, this research considers both geometric and operating parameters for evaluation where the dynamic performance and trajectory of the multibody motion are particularly interested. The dynamic response and contact behavior of the rotating fingers acting on the fixed and moving objects are validated by comparing against published experimental results. The effectiveness of the dynamic modeling method, which relaxes the quasi-static assumption, has been demonstrated in the analyses of developing an automated transfer system involved grasping and handling objects by the compliant robotic hands. This FEM based dynamic model offers a more realistic simulation and a better understanding of the multibody motion for improving future design. It is expected that the method presented here can be applied to a spectrum of engineering applications where flexible multibody dynamics plays a significant role.
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Nie, Zifeng. "Advanced Mesomechanical Modeling of Triaxially Braided Composites for Dynamic Impact Analysis with Failure". University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1407129124.
Testo completo
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Bringmann, Philipp. "Adaptive least-squares finite element method with optimal convergence rates". Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22350.
Testo completoAbstract (sommario):
Die Least-Squares Finite-Elemente-Methoden (LSFEMn) basieren auf der Minimierung des Least-Squares-Funktionals, das aus quadrierten Normen der Residuen eines Systems von partiellen Differentialgleichungen erster Ordnung besteht. Dieses Funktional liefert einen a posteriori Fehlerschätzer und ermöglicht die adaptive Verfeinerung des zugrundeliegenden Netzes. Aus zwei Gründen versagen die gängigen Methoden zum Beweis optimaler Konvergenzraten, wie sie in Carstensen, Feischl, Page und Praetorius (Comp. Math. Appl., 67(6), 2014) zusammengefasst werden. Erstens scheinen fehlende Vorfaktoren proportional zur Netzweite den Beweis einer schrittweisen Reduktion der Least-Squares-Schätzerterme zu verhindern. Zweitens kontrolliert das Least-Squares-Funktional den Fehler der Fluss- beziehungsweise Spannungsvariablen in der H(div)-Norm, wodurch ein Datenapproximationsfehler der rechten Seite f auftritt. Diese Schwierigkeiten führten zu einem zweifachen Paradigmenwechsel in der Konvergenzanalyse adaptiver LSFEMn in Carstensen und Park (SIAM J. Numer. Anal., 53(1), 2015) für das 2D-Poisson-Modellproblem mit Diskretisierung niedrigster Ordnung und homogenen Dirichlet-Randdaten. Ein neuartiger expliziter residuenbasierter Fehlerschätzer ermöglicht den Beweis der Reduktionseigenschaft. Durch separiertes Markieren im adaptiven Algorithmus wird zudem der Datenapproximationsfehler reduziert.
Die vorliegende Arbeit verallgemeinert diese Techniken auf die drei linearen Modellprobleme das Poisson-Problem, die Stokes-Gleichungen und das lineare Elastizitätsproblem. Die Axiome der Adaptivität mit separiertem Markieren nach Carstensen und Rabus (SIAM J. Numer. Anal., 55(6), 2017) werden in drei Raumdimensionen nachgewiesen. Die Analysis umfasst Diskretisierungen mit beliebigem Polynomgrad sowie inhomogene Dirichlet- und Neumann-Randbedingungen. Abschließend bestätigen numerische Experimente mit dem h-adaptiven Algorithmus die theoretisch bewiesenen optimalen Konvergenzraten.The least-squares finite element methods (LSFEMs) base on the minimisation of the least-squares functional consisting of the squared norms of the residuals of first-order systems of partial differential equations. This functional provides a reliable and efficient built-in a posteriori error estimator and allows for adaptive mesh-refinement. The established convergence analysis with rates for adaptive algorithms, as summarised in the axiomatic framework by Carstensen, Feischl, Page, and Praetorius (Comp. Math. Appl., 67(6), 2014), fails for two reasons. First, the least-squares estimator lacks prefactors in terms of the mesh-size, what seemingly prevents a reduction under mesh-refinement. Second, the first-order divergence LSFEMs measure the flux or stress errors in the H(div) norm and, thus, involve a data resolution error of the right-hand side f. These difficulties led to a twofold paradigm shift in the convergence analysis with rates for adaptive LSFEMs in Carstensen and Park (SIAM J. Numer. Anal., 53(1), 2015) for the lowest-order discretisation of the 2D Poisson model problem with homogeneous Dirichlet boundary conditions. Accordingly, some novel explicit residual-based a posteriori error estimator accomplishes the reduction property. Furthermore, a separate marking strategy in the adaptive algorithm ensures the sufficient data resolution. This thesis presents the generalisation of these techniques to three linear model problems, namely, the Poisson problem, the Stokes equations, and the linear elasticity problem. It verifies the axioms of adaptivity with separate marking by Carstensen and Rabus (SIAM J. Numer. Anal., 55(6), 2017) in three spatial dimensions. The analysis covers discretisations with arbitrary polynomial degree and inhomogeneous Dirichlet and Neumann boundary conditions. Numerical experiments confirm the theoretically proven optimal convergence rates of the h-adaptive algorithm.
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Abdijalilov, Kahkhor. "Hybrid explicit-implicit FDTD-FEM time-domain solver for electromagnetic problems". Thesis, 2005. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2005-017.
Testo completo
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Chang, Chia-Jung, e 張家榮. "A study on the dynamic-explicit FEM analysis in the upsetting process". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/32451004691495423897.
Testo completoAbstract (sommario):
碩士清雲科技大學
機械工程研究所
94
In the past decade, the researches of metal forming focus on the upsetting process still a popular and common topic. Since the shape of billet is easy to model, and the control parameters are obtained quickly, make the numerical simulation of upsetting process as a useful case studying. The dynamic FEM code, LS-DYNA, is used in this study. Attention on applications of the velocity and mass factor techniques for the A6061-T6 aluminum square billet in the upsetting process are modeled. The predicted load, the material distortion, the stress distribution, and the computing time of computer are presented, the usage of these factors at proper time also discussed. In the investigations of the upsetting process by the dynamic-explicit FEM analysis, detail discussions in the simulation with variations of relative parameters, such as velocity, mass density, and mesh size etc. are assessed. The fully history of deformation states and some defects in the simulations are observed, then, the modified and available model is suggested. Finally, it is through the verification of the experiment, the comparisons between the numerical simulation and the experiment show a reasonable tendency. Goal of this research, is hope to set up a basic simulation modeling for the numerical analysis, and then apply to the other complicated metal forming problems, the benefits of reducing the analysis cost, and saving the design time of manufacturing process are dramatic.
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Santos, Abel Dias dos. "Tool descriptions and contact strategies used in the static explicit FEM code ITAS3D for simulation of 3-D sheet metal forming processes". Doctoral thesis, 1993. http://hdl.handle.net/10216/11599.
Testo completo
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Santos, Abel Dias dos. "Tool descriptions and contact strategies used in the static explicit FEM code ITAS3D for simulation of 3-D sheet metal forming processes". Tese, 1993. http://hdl.handle.net/10216/11599.
Testo completo
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Shehni, Alaleh. "Modeling of Strain-Hardening Cement-based Composites (SHCC): A Finite Element Method using the Strong Discontinuity Approach (SDA) with Explicit Representation of Fibers". 2020. https://tud.qucosa.de/id/qucosa%3A74170.
Testo completoAbstract (sommario):
Concrete is a predominant construction material due to several advantages; however, the pure cementitious composites have shown quasi-brittle behavior with undesirable typical large cracks under tensile loading conditions. Thus, the addition of a small volume of short fibers is a well-known strategy to increase the ductility and toughness of cementitious matrices besides optimization of the crack opening. Strain-hardening cement-based composites (SHCCs) is a particular class of fiber-reinforced concretes (FRCC) that can develop controlled multiple cracks while subjected to incremental tensile loading conditions. However, a proper composition design, especially concerning fiber and bond properties, still follows a trial and error approach.
This work presents a newly developed model to simulate SHCC at the meso-scale level. This model is based on Finite-Element-Method and allows for nonlinear behavior for cement matrix, fiber material, and bond laws. Concerning three complexities of target FRCC, i.e., crack formation in the cement matrix, a large number of explicit fibers with arbitrary random distribution, and fibers’ interaction with the cement matrix via the bond, extra features are added to standard FE consist of:
• Further development of the Strong Discontinuity Approach (SDA) to model discrete cracking of continuum elements on the element level
• Discretization of single fibers by truss elements with truss nodes independently placed of continuum nodes
• Connecting SDA elements to explicit truss elements by particular bond elements.
In this research study, first, theoretical basics and special implementation issues were described. Later, this newly developed model was calibrated with several simple configurations. The bond law utilized in the simulation was derived from single fiber pullout test and calibrated with several analyses. In the next step, 2D SHCC dumbbell specimens under tensile loading condition were simulated, and a series of numerical case studies were performed to assess the quality, credibility, and limitations of the numerical model. It should be noted that cracking patterns could not be directly compared to experimental cracking patterns as the simulation model’s current state is deterministic by random material properties that influence the experimental specimen behavior. Taking the effect of random field and other simplifying assumptions into account, the simulation model seems to describe enumerated SHCC behavior at an acceptable level.
In summary, a further base is given for the target-oriented design of FRCC material composition to reach the given objectives of material properties. The concepts and methods presented in this study can simulate short and thin polymer fibers in a random position and steel fibers and structures with long reinforcement in a regular arrangement.