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Hay, Neil Conway. "The simulation of random environments for structural dynamics testing." Thesis, Edinburgh Napier University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328063.
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Bonnet, Paul A. "The development of multi-axis real-time substructure testing." Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:39730635-b112-4775-9956-73d26d964178.
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Real-time substructure is a novel hybrid method for the dynamic testing of structures. During an experiment, the structure of interest is divided into two entities. The crucial parts for the project undertaken are physically replicated and loaded dynamically through powerful actuators while the rest is numerically modelled and solved via real-time software. The dynamics of both substructures must be accurately reproduced, as well as their mutual interaction. The applications are multiple but that of earthquake engineering is primarily considered in this research. Beyond the accurate modelling of both substructures, three main issues are crucial to the validity of a real-time hybrid simulation. Firstly, the loading equipment must be capable of imposing large loads and accurate displacements on the laboratory specimen. The behaviour of this loading system must be consistent and predictable over a wide range of frequencies and velocities. Secondly, the computational solver employed to emulate the numerical model dynamics requires stability, computational efficiency and accuracy. It must be able to deal with non-linear multi-degree of freedom systems. Thirdly, the interaction between the two substructures must be reliably emulated by a set of communication devices. The reciprocal boundary conditions must be imposed on the interface of each substructure. This notably implies quasi-instantaneous measurement and application of physical forces and displacements. The two substructures have to be solved simultaneously and in real-time. The three areas mentioned above have been investigated in this research. Initially, the laboratory installations of the hardware and software were focussed on. The servo-controlled hydraulic actuation system was optimised and a development rig was designed and constructed. It was found that hardware settings could greatly improve the general actuator performance, even though some particular situations could compromise it. This work was then complemented by an extensive study of the necessary actuation compensation. Numerous algorithms – either previously published or developed in the course of this research – were implemented and formally compared through a set of real-time experiments. Particularly, some challenging multi-axis experiments with a high level of actuator coupling were conducted. Direct extrapolation coupled with adaptive delay estimation was found to be the most effective approach to ensure synchronisation of the substructures. Attention was then given to the integration algorithms used to solve the numerical substructure problem and output the actuator demand on a real-time basis. Both explicit and implicit schemes were considered, even though an explicit formulation is required for this hybrid application. Computationally simple schemes are more suitable and several were shown to satisfy the necessary accuracy and stability requirements. Successful realtime hybrid tests were carried out with fifty degrees of freedom in the numerical substructure, including non-linear force/displacement relationships and using integration time-steps proving unconditional stability of the algorithms used. Finally, a realistic earthquake engineering application of the real-time substructure method was conducted. A steel column was tested physically as part of 20-storey building structure subject to the 1940 El Centro earthquake. To further display the usefulness of the method, an energy dissipative device was also integrated in the numerical model and its effect on the building response was shown.
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Dancila, Dragos Stefan. "Energy-dissipating tensile composite members with progressive failure." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12474.
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Valdés, Julio R. "Simultaneous determination of frequency dependent modulus and damping from resonant column tests." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/20169.
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De, Villiers Pieter Jacobus. "Imposed loads for inaccessible roofs of light industrial steel buildings." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53460.
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Thesis (MScEng)--Stellenbosch University, 2003.Some digitised pages may appear illegible due to the condition of the original hard copy.
ENGLISH ABSTRACT: A critical evaluation of provisions for imposed loads in the South African Loading Code for design of structures, SABS 0160-1989 (SABS), by comparison with other codes was performed earlier. The evaluation revealed the SABS loading code to be generally non-conservative in its provisions for imposed loads for a range of general and specialist occupancy classes. The SABS provision for imposed loads for inaccessible roofs was found to be substantially non-conservative in comparison with the other codes. An investigation into the imposed load for inaccessible roofs is subsequently performed in order to establish a scientific rationale through which the codified design values may be measured effectively. Due to the lack of information and the large uncertainties involved in the imposed roof load, stochastic treatment of the loads is implemented. This is in line with the stochastic modelling of loads as implemented in general. The approach applied is to select a type of building that can be regarded as a generic example of buildings to which these loads apply, and to discretisize the load into the various sub-mechanisms that translate into the imposed roof load. The probabilistic models for the load mechanisms are then quantified, either through physical load surveys, or through conducting an expert survey for those variables which are not observable. The use of expert opinion as a resource for information is not readily accessible in terms of yielding scientifically defendable results. Therefore, the expert survey is performed as a calibrated experiment whereby weights were calculated for the individual experts' opinions and their opinions combined accordingly. The probabilistic models for the load mechanisms are then translated into load effects by taking into account the physical process resulting in the load effects. By applying these mechanisms in such a way as to maximise the said load effects, equivalent uniformly distributed loads (EUDL's) were calculated for each mechanism. The probabilistic models obtained in terms of the EUDL's pose an easily accessible format through which existing load models and codified provisions can be evaluated. These load models are then utilised to evaluate the SABS provisions in terms of the level of reliability catered for by SABS ultimate limit-state design criteria. It is concluded that the SABS conservatively provides for maintenance loads on the roof, while the reliability for construction loads is non-conservative for large tributary areas and highly non-conservative for small areas. The load models so obtained can further be applied for structural reliability assessment.
AFRIKAANSE OPSOMMING: "n Kritiese evaluasie van die voorskrifte vir opgelegde belastings in die Suid- Afrikaanse Selastingskode vir die ontwerp van strukture, SASS 0160-1989 (SASS) deur 'n vergelyking met ander kodes is vroeër uitgevoer. Die evaluasie het getoon dat die SASS in die algemeen onkonserwatief is in sy voorsiening vir opgelegde belastings oor 'n bereik van algemene en spesialis okkupasie tipes. Die SASS voorskrif vir opgelegde belastings vir ontoeganklike dakke is hoogs onkonserwatief in vergelyking met die ander kodes. 'n Ondersoek na die opgelegde belasting vir ontoeganklike dakke word gevolglik uitgevoer met die doelom 'n wetenskaplike rasionaal daar te stel waardeur die gekodifiseerde voorskrifte effektief gemeet kan word. As gevolg van die gebrek aan inligting en groot onsekerhede betrokke by die opgelegde dakbelasting word stogastiese modellering geimplimenteer. Die aanslag wat gevolg is, is om 'n tipe gebou te selekteer wat beskou kan word as verteenwoordigend van die geboue waarvoor hierdie belastings van toepassing is, en om die belasting te diskretiseer in die verskeie lasmeganismes wat die opgelegde dakbelasting voortbring. Die waarskynlikheidsmodelle vir die lasmeganismes word dan gekwantifiseer, óf deur fisiese opnames, óf deur die uitvoering van 'n ekspertopname vir daardie veranderlikes wat nie waarneembaar is nie. Die gebruik van ekspert opinie as "n bron van inligting is nie maklik toeganklik in terme daarvan om wetenskaplik verdedigbare resultate te lewer nie. Daarom is die ekspert-opname uitgevoer soos 'n gekalibreerde eksperiment waardeur relatiewe gewigte bereken word vir die individuele eksperts en hulopinies daarvolgens gekombineer word. Die waarskynlikheidsmodelle vir die lasmeganismes word dan omgeskakel in laseffekte deur in agneming van die fisiese proses wat die las-effek voortbring. Deur die lasmeganismes op só 'n manier toe te pas dat die betrokke las-effekte gemaksimeer word, word ekwivalent uniforme belastings (EUS's) bepaal. Die waarskynlikheidsmodelle in terme van EUS's bied "n maklik toeganklike formaat waardeur bestaande lasmodelle en gekodifiseerde voorskrifte evalueer kan word. Die lasmodelle word gevolglik gebruik om die SASS voorskrifte te evalueer in terme van die vlak van betroubaarheid wat gehandhaaf word deur SASS limiet-staat ontwerp kriteria. Dit is bepaal dat die SASS konserwatief voorsiening maak vir onderhoudslaste op die dak, maar onkonserwatief tot hoogs-onkonserwatief is vir konstruksie laste. Die bepaalde lasmodelle kan verder toegepas word in strukturele betroubaarheids analise.
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Werner, Carl Scott. "Cyclic Behavior of Screen Grid Insulated Concrete Form Components." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/364.
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The principle of sustainability in the built environment has become much more significant in the past decade, resulting in a push to develop building systems that are more energy efficient, durable, and use fewer natural resources. For residential and light commercial buildings, insulated concrete forms (ICF) have enjoyed increasing popularity for their ability to meet these new demands. ICFs are a stay-in-place concrete formwork system for building structural walls that are also highly insulated, among other benefits. Screen-grid ICFs (SGICF) are a small subset of ICFs that tend to use less concrete than standard ICFs and are sometimes made of recycled materials. These traits make SGICFs attractive, but there is a lack of understanding of their structural characteristics due to their irregular internal concrete structure. Because of this, structures using SGICFs are limited to heights no higher than two stories. Further study should show whether SGICFs structures can safely built to greater heights. This investigation studied two types of SGICFs at a component level in order to gain understanding of their lateral force and drift ratio capacities under cyclic loading. Several variables, including steel reinforcement details, the type of concrete, and the presence of the forms, were altered to measure their impact on the performance of the systems. Test results suggested that the ICF formwork increased lateral strength by up to 100% and lateral deformation capacity by up 60% when compared to identical specimens tested with the formwork removed. Results also showed that confinement of the cement, either by mesh hoops, spiral wire, or fiber-reinforced concrete improved the drift ratio at failure up to 500% when compared to specimens with no confinement material. Computer models were created to gauge their ability to replicate the behavior of the experimental test results. The models typically overestimated the lateral load resistance of the samples by 50-100%, and even more in some cases, depending on the reinforcement. The models were not reliable in determining the drift ratio at which the sample was considered to have failed. In some cases the model failed at 50% lower lateral deformations than the test specimen, while in others the model did not fail at all. Future studies should explore refinements of the models to increase their accuracy and usefulness, as well as accounting for the contributions do to the form material. Future studies should also include using spiral wires, mesh hoops, or fiber reinforced concrete in full-scale walls to verify their efficacy in improving overall wall performance.
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Elgazzar, Hesham. "End-Shield Bridges for High-Speed Railway : Full scale dynamic testing and numerical simulations." Licentiate thesis, KTH, Bro- och stålbyggnad, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204774.
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The increasing need for High-Speed Railway (HSR) to reduce the travelling time requires increasing research within this field. Bridges are main components of any railway network, including HSR networks, and the optimization of their design for this purpose would contribute to a faster and more cost effective development of the HSR network. The initial investment, the running and maintenance costs of the bridges can be decreased through better understanding of the their dynamic behaviour. This thesis studies the dynamic behaviour of end-shield railway bridges under HSR operation. 2D beam analysis is used to study the effect of the distribution of the train’s axle load. Relatively accurate 3D FE-models are developed to study the effect of Soil-Structure Interaction (SSI) and the dynamic response of the bridges. Modelling alternatives are studied to develop an accurate model. A full scale test of a simply supported Bridge with end-shields using load-controlled forced excitation was performed and the results were used to verify the theoretical models. A manual model updating process of the material properties of the 3D FE-model is performed using FRFs from the field measurements. A Simple 2D model is also developed, where a spring/dashpot system is implemented to simplify SSI, and updated to reproduce the field measured responses. The conclusions of the project emphasize the importance of SSI effects in the dynamic analysis of end-shield bridges for predicting their dynamic behaviour. The conclusions also show that the modelling of the surrounding soil and the assumption of the soil material parameters have significant effect on the dynamic response. Even the boundary conditions, bedrock level and the ballast on the railway track affects the response. The results also show that the bridge’s concrete section behaves as uncracked section under the studied dynamic loading.QC 20170403
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Tarazaga, Pablo Alberto. "Dynamics and Control of a Pressurized Optical Membranes." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28727.
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Optical membranes are currently pursued for their ability to replace the conventional mirrors that are used to correct wave front aberration and space-based telescopes. Among some of the many benefits of using optical membranes, is their ability to considerably reduce the weight of the structure. As a secondary effect, the cost of transportation, which is of great interest in space applications, is reduced as well. Given the low density of these thin-film membranes, the lower end dynamics play a greater significant role than their rigid plate-like counterparts in achieving functional mirrors. Space-based mirrors are subjected to a series of disturbances. Among those encountered are thermal radiation, debris impact, and slewing maneuvers. Thus, dynamic control is essential for the adequate performance of thin-film membrane mirrors.
With this in mind, the work described herein aims to improve the performance of optical membranes with an innovative, acoustical control approach to suppress vibration of optical membranes backed by an air cavity. This is achieved by using a centralized acoustic source in the cavity as the method of actuation. The acoustic actuation is of great interest since it does not mass load the membrane in the conventional way, as most methods of actuation would.
To achieve this end goal, two structural-acoustic coupled models are developed to describe the dynamics of a pressurized optical membrane system. This is done through an impedance based modeling approach where the subsystems are modeled individually, and then coupled at the interface. The control of the membrane is implemented using a positive position feedback approach. The theory is also extended to positive velocity and positive acceleration feedback.
Three experiments are carried out to validate the models previously mentioned. Successful implementation of a control experiment is also accomplished leading to considerable attenuations in the coupled membraneâ s dynamics.Ph. D.
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Demharter, Samuel. "Novel applications for hierarchical natural move Monte Carlo simulations : from proteins to nucleic acids." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:c0ef3ba5-4fe0-4684-a0ce-202003cd79a5.
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Biological molecules often undergo large structural changes to perform their function. Computational methods can provide a fine-grained description at the atomistic scale. Without sufficient approximations to accelerate the simulations, however, the time-scale on which functional motions often occur is out of reach for many traditional methods. Natural Move Monte Carlo belongs to a class of methods that were introduced to bridge this gap. I present three novel applications for Natural Move Monte Carlo, two on proteins and one on DNA epigenetics. In the second part of this thesis I introduce a new protocol for the testing of hypotheses regarding the functional motions of biological systems, named customised Natural Move Monte Carlo. Two different case studies are presented aimed at demonstrating the feasibility of customised Natural Move Monte Carlo.
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Garth, John Stuart. "Experimental Investigation of Lateral Cyclic Behavior of Wood-Based Screen-Grid Insulated Concrete Form Walls." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1857.
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Insulated concrete forms (ICFs) are green building components that are primarily used for residential wall construction. Unlike most polystyrene based ICF variants, the Faswall ICFs used in these experiments were significantly denser because they were made from recycled wood particles and cement. The current design approach for structures constructed with this type of wall form only allows the designer to consider the contribution of the reinforced concrete cores. Previous research has shown that this approach may be conservative. This project experimentally evaluated the lateral structural response of these types of grid ICF walls under increasing amplitude of in-plane cyclic loading. Two different height-to-length (aspect) ratios (approximately 2:1 and 1:1) were investigated, as was the effect of simultaneous gravity load. Furthermore, the reinforced concrete grid was exposed for each aspect ratio in order to examine the contribution of the ICF blocks to the lateral response. Analyses of hysteretic behaviors and failure modes indicated conservatism in the current design approach for estimating lateral strength and ignoring the beneficial contribution of the ICF blocks to overall performance. The presence of the wall forms increased the lateral shear capacity of the walls by an average of 42% (compared to the walls with forms removed), while also increasing the deformation capacity by an average of 102%. Furthermore, by considering an additional gravity load of 10 kips-per-lineal-foot (klf), the shear resistance of the walls increased by 32% (versus walls only subjected to self-weight), on average, and the deformation capacity of the walls increased by an average of 19%. Comparisons of the experimental results to several design equations led to the recommendation of a design equation that was previously accepted for another type of ICF system.
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Fu, Tuan-Chun. "Development of Effective Approaches to the Large-Scale Aerodynamic Testing of Low-Rise Building." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/986.
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Low-rise buildings are often subjected to high wind loads during hurricanes that lead to severe damage and cause water intrusion. It is therefore important to estimate accurate wind pressures for design purposes to reduce losses. Wind loads on low-rise buildings can differ significantly depending upon the laboratory in which they were measured. The differences are due in large part to inadequate simulations of the low-frequency content of atmospheric velocity fluctuations in the laboratory and to the small scale of the models used for the measurements. A new partial turbulence simulation methodology was developed for simulating the effect of low-frequency flow fluctuations on low-rise buildings more effectively from the point of view of testing accuracy and repeatability than is currently the case. The methodology was validated by comparing aerodynamic pressure data for building models obtained in the open-jet 12-Fan Wall of Wind (WOW) facility against their counterparts in a boundary-layer wind tunnel. Field measurements of pressures on Texas Tech University building and Silsoe building were also used for validation purposes. The tests in partial simulation are freed of integral length scale constraints, meaning that model length scales in such testing are only limited by blockage considerations. Thus the partial simulation methodology can be used to produce aerodynamic data for low-rise buildings by using large-scale models in wind tunnels and WOW-like facilities. This is a major advantage, because large-scale models allow for accurate modeling of architectural details, testing at higher Reynolds number, using greater spatial resolution of the pressure taps in high pressure zones, and assessing the performance of aerodynamic devices to reduce wind effects. The technique eliminates a major cause of discrepancies among measurements conducted in different laboratories and can help to standardize flow simulations for testing residential homes as well as significantly improving testing accuracy and repeatability. Partial turbulence simulation was used in the WOW to determine the performance of discontinuous perforated parapets in mitigating roof pressures. The comparisons of pressures with and without parapets showed significant reductions in pressure coefficients in the zones with high suctions. This demonstrated the potential of such aerodynamic add-on devices to reduce uplift forces.
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Uliana, David A. "The effects of earthquake excitations on reticulated domes." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45667.
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Comparisons were made on the behavior of two full-sized reticulated domes subjected to uniform static loads only and uniform static loads with earthquake excitations. Space truss elements were used in the dome models. The stiffness matrix of the space truss element allows for the nonlinear strain-displacement behavior and the stress-strain behavior of the material is modeled with a bilinear approximation. The nonlinear solution technique is the Newton-Raphson method while the direct integration technique is the Newmark- Beta method.
The joint displacements for the static and the dynamic analyses were compared for both domes along with the axial stresses in all members. The percentage increases in the axial stresses of the dynamic analyses as compared to those of the static analyses were determined.
The reticulated domes used in the study were found to bet capable of withstanding the earthquake excitations when subjected to various uniform loads without failure.
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Liu, Wenjie. "Structural dynamic analysis and testing of coupled structures." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246801.
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Chen, Yousheng. "Model calibration methods for mechanical systems with local nonlinearities." Doctoral thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-57638.
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Most modern product development utilizes computational models. With increasing demands on reducing the product development lead-time, it becomes more important to improve the accuracy and efficiency of simulations. In addition, to improve product performance, a lot of products are designed to be lighter and more flexible, thus more prone to nonlinear behaviour. Linear finite element (FE) models, which still form the basis of numerical models used to represent mechanical structures, may not be able to predict structural behaviour with necessary accuracy when nonlinear effects are significant. Nonlinearities are often localized to joints or boundary conditions. Including nonlinear behaviour in FE-models introduces more sources of uncertainty and it is often necessary to calibrate the models with the use of experimental data. This research work presents a model calibration method that is suitable for mechanical systems with structural nonlinearities. The methodology concerns pre-test planning, parameterization, simulation methods, vibrational testing and optimization. The selection of parameters for the calibration requires physical insights together with analyses of the structure; the latter can be achieved by use of simulations. Traditional simulation methods may be computationally expensive when dealing with nonlinear systems; therefore an efficient fixed-step state-space based simulation method was developed. To gain knowledge of the accuracy of different simulation methods, the bias errors for the proposed method as well as other widespread simulation methods were studied and compared. The proposed method performs well in comparison to other simulation methods. To obtain precise estimates of the parameters, the test data should be informative of the parameters chosen and the parameters should be identifiable. Test data informativeness and parameter identifiability are coupled and they can be assessed by the Fisher information matrix (FIM). To optimize the informativeness of test data, a FIM based pre-test planning method was developed and a multi-sinusoidal excitation was designed. The steady-state responses at the side harmonics were shown to contain valuable information for model calibration of FE-models representing mechanical systems with structural nonlinearities. In this work, model calibration was made by minimizing the difference between predicted and measured multi-harmonic frequency response functions using an efficient optimization routine. The steady-state responses were calculated using the extended multi-harmonic balance method. When the parameters were calibrated, a k-fold cross validation was used to obtain parameter uncertainty. The proposed model calibration method was validated using two test-rigs, one with a geometrical nonlinearity and one with a clearance type of nonlinearity. To attain high quality data efficiently, the amplitude of the forcing harmonics was controlled at each frequency step by an off-line force feedback algorithm. The applied force was then measured and used in the numerical simulations of the responses. It was shown in the validation results that the predictions from the calibrated models agree well with the experimental results. In summary, the presented methodology concerns both theoretical and experimental aspects as it includes methods for pre-test planning, simulations, testing, calibration and validation. As such, this research work offers a complete framework and contributes to more effective and efficient analyses on mechanical systems with structural nonlinearities.
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Pandiya, Nimish. "Design and Validation of a MIMO Nonlinear Vibration Test Rig with Hardening Stiffness Characteristics in Multiple Degrees of Freedom." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1504879018436068.
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Brizard, Denis. "Contrôle des vibrations de charge utile sur lanceur spatial." Thesis, Ecully, Ecole centrale de Lyon, 2011. http://www.theses.fr/2011ECDL0041/document.
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Les lanceurs spatiaux sont soumis à un certain nombre d’excitations complexes durant les différentes phases de vie du produit. Ces excitations sont transmises à la charge utile par voie solidienne ou aérienne. Pour assurer la protection de la charge utile, l’architecture du lanceur étant figée au début du projet, l’amélioration des comportements dynamiques passe par l’introduction de systèmes secondaires. La partie essentielle des travaux de thèse est donc consacrée à l’implantation optimale de systèmes capables de diminuer les réponses vibratoires en utilisant des modèles adaptés. C’est pourquoi une méthode de double synthèse modale est mise en place, permettant ainsi de calculer la réponse vibratoire de la structure à l’aide de bases réduites et offrant des performances améliorées par rapport aux méthodes classiques. L’ajout d’un dispositif amortissant local nécessite la prise en compte d’une ou plusieurs modifications structurales dans le modèle, une méthode dédiée est alors développée. Le choix du dissipateur se porte sur un dissipateur frottant. Un prototype est conçu et réalisé. Il est dans un premier temps caractérisé seul et le modèle de comportement identifié est un modèle constitué d’un ressort en série avec un patin ; la loi de frottement adaptée est une loi de Coulomb simple. En parallèle, une maquette représentative du dernier étage d’un lanceur est dimensionnée et réalisée. Le frotteur est alors monté en pied de propulseur de la maquette et permet une diminution significative des vibrations de la charge utile au passage du mode de propulseurSpace launchers undergo a certain amount of complex excitations during their lifecycle. These excitations are transmitted to the payload in a structure-born or air-born way. To improve the dynamic behaviour and thus ensure the protection of the payload, secondary systems must be added to the launcher – indeed, the architecture of the launcher is fixed at the beginning of the project. The essential part of this thesis work is dedicated to the optimal fitting of a system capable of reducing the vibration response of the payload, using appropriate models. Therefore a double modal synthesis method is implemented, allowing to calculate the vibrational response of the structure with reduced bases and offering improved performances over conventional methods. The addition of a local damping device requires the consideration of one or more structural modifications in the model, a dedicated method is thus developped along with a specific continuation algorithm. A friction damper is retained, a prototype is designed and built. It is first characterized alone ; the identified behaviour is that of a spring in series with a dry friction element, a simple Coulomb friction law enables to reproduce the experimental curves. A scale model of the launcher’s last stage is designed and built. The friction device is then mounted inside the scale model and leads to a significant reduction of the payload vibration levels
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Daborn, Philip Matthew. "Smarter dynamic testing of critical structures." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683391.
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Critical structures, such as are found in many aerospace applications, are those whose failure in service could be catastrophic, leading to multiple loss of life and/ or unacceptable financial and reputational damage. The safety and performance of these structures are regularly qualified using laboratory-based environmental tests, the aim of which is to simulate the in-service environments. The methodology behind these environmental tests was developed during the 1960s and 1970s and with only minor advances since then, there is a wealth of anecdotal evidence that suggests this situation leads to serious limitations with current practice. The aims of this research are (i) to conduct an objective assessment of current environmental test practice, (ii) to reveal any deficiencies and (iii) to propose a new technology which could offer significant enhancements. Numerical and practical case studies are presented which highlight that current practice often leads to tests which offer poor simulations of the intended environment. This results from inadequate matching of the boundary conditions, ignorance of the load-path and the prevalence of single-axis excitation techniques. The structure is often' over-tested' to such a degree that unrealistic failures occur in the laboratory, resulting in lengthy and costly delays to certification programmes. Equally, the research found clear examples of significant under-testing and revealed an alarming characteristic of current practice - namely, a wholly unjustifiable perceived conservatism. A new technology has been developed as part of this research - specifically, the Impedance-Matched Multi-Axis Test (IMMAT) technology - which has been designed to overcome the issues identified with current practice. The IMMAT technology offers far superior tests and can help to ensure that critical structures are subjected to realistic excitation conditions in the laboratory. It is hoped that industry will embrace it, thereby ensuring critical structures are adequately qualified in future certification programmes in a scientific and efficient manner.
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Gopalakrishnamurthy, Sharath H. "Structural integrity inspection using dynamic responses /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418023.
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Simmons, Martin Christopher. "Safety through novel dynamic pressure testing of aircraft structural panels." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417174.
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Negro, P. "Combined experiment and computation for dynamic testing of structures." Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638308.
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The purpose of this study is to demonstrate the effectiveness of an approach which combines experiment and calculation in addressing structural dynamics problems. Calculation is generally not sufficient to solve the problem, since our knowledge of the nonlinear cyclic behaviour of materials is not sufficiently accurate. On the other hand, the availability of an effective and robust experimental technique does not yield per se the solution to any structural problem, due to the necessarily limited number of specimens which can be tested. Experimental results must be used to calibrate the available computer models, so that the computer models can be applied to any structure and/or any kind of dynamic action. The effectiveness of the approach is demonstrated with reference to the experimental programmes for which the author was responsible at the European Laboratory of Structural Assessment (ELSA). This includes the testing activity on a four-storey reinforced concrete frame building, and that on the same building equipped with nonstructural masonry infills regularly and irregularly distributed along the frame elevation. The approach is also applied to the tests conducted on large-scale models of reinforced concrete bridges, in which the author participated. For each experimental programme, the information which has been derived is described in the necessary detail. The experimental framework is represented by the pseudodynamic test method. For this reason, the activities carried out at ELSA for the verification of the method, to which the author contributed, are also presented. In addition, a new formulation of the method, capable of taking into account the presence of distributed masses, is introduced. The most important outcome of this work is the calibration of simple numerical models for reinforced concrete structures. It is expected that these models will be extensively used in the parametric analyses in support of the final drafting of Eurocode 8.
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Karar, Sayed Shehata. "Adaptive force control of hydraulic actuator systems for dynamic structural testing." Thesis, University of Sheffield, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299026.
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Kurt, Efe Gokce. "Investigation Of Strenghthening Techniques Using Pseudo-dynamic Testing." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612181/index.pdf.
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Pseudo-dynamic testing was employed to observe the seismic performance of three different retrofit methods on two story three bay reinforced concrete frame structures. The three test frames have hollow clay tile (HCT) infills in the central bay. All of the test frames represent the seismic deficiencies of the Turkish construction practice such as use of plain reinforcing bars, low strength concrete and insufficient confining steel. Two non-invasive and occupant friendly retrofit schemes suggested in the Turkish Earthquake Code, namely use of Fiber Reinforced Polymers and precast concrete panels integrated on the HCT infills and traditional approach of adding concrete infill wall were employed. Specimens were subjected to three different scale levels of North-South component of Duzce ground motion. Reference specimen experienced severe damage at 100% scale level and reached collapse stage due to the loss of integrity of the infill wall and significant damage on the boundary columns. The retrofitted test structures were able to survive the highest level 140% Duzce ground motion. Test results confirmed the success of the retrofit methods for simulated earthquake loads.
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Silva, Andre Espozel Pinheiro da. "Testing dynamic agency predictions to corporate finance." reponame:Repositório Institucional do FGV, 2017. http://hdl.handle.net/10438/18243.
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This papers tests theoretical predictions concerning to agent compensation, debt structure and investment in the models of dynamic agency in DeMarzo and Fishman (2007), DeMarzo and Sannikov (2006) and DeMarzo, Fishman, He and Wang (2012). The results related to agent compensation are consistent with the patterns predicted in the models, indicating that the firm-years that the models would have as more likely to pay dividends are indeed the ones more likely to pay; also, among firms that pay dividends, more profits generate higher dividend payments and higher executive compensation, as predicted in the models. The prediction that firms that go well and reach a payment threshold present marginal q equal to average q, and thus after controlling for average q cash flows would not explain investment is also supported by the tests in here. On the other hand, predictions related to the role of the credit line and to the debt structure are not compatible with the results in here. The credit line doesn’t seem to be the provider of financial slack that protects the firm from low cash flows and also doesn’t seem to have the dynamics of being paid when profits are high and being more used when profits are low.
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Thölken, Denise. "Efeito da rigidez de pilar parede no comportamento sísmico de edifício de concreto armado." Universidade Tecnológica Federal do Paraná, 2013. http://repositorio.utfpr.edu.br/jspui/handle/1/962.
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Este trabalho tem como objeto o estudo do efeito da rigidez de pilar parede no comportamento estrutural de edifícios de concreto armado submetidos a sismos. Foram consideradas as premissas da norma brasileira ABNT NBR15421:2006, que apresenta os critérios para projeto de estruturas resistentes a sismo. A análise linear com emprego dos métodos da norma - método das forças horizontais equivalentes, método espectral e histórico de aceleração no tempo - foi aplicada em edifícios com dois tipos de sistemas estruturais, sendo eles pórtico de concreto e sistema dual pórtico de concreto e pilar parede. Os resultados foram analisados nos pórticos de extremidade das estruturas nos sentidos longitudinal (x) e transversal (y), comparando-se os deslocamentos de cada pavimento e esforços cortantes, momento fletor e normal nas bases dos pilares. A comparação foi realizada entre os três métodos aplicados e os sistemas estruturais analisados.The aim of this work is to study the stiffness effect of wall columns on structural behavior of reinforced concrete buildings subjected to seismic action. The premises of the Brazilian standard ABNT NBR14521:2006 were considered, which presents criteria for earthquake resistant design of structures. The linear analysis employed the methods of the Brazilian standard - equivalent static load method, response spectrum analysis and time history method - were applied to buildings with two types of structural systems, namely concrete frame and dual system concrete frame and wall columns. The results were analyzed in edge frames structures in the longitudinal and transverse directions, comparing the displacement of each floor and shear, bending moment and axial forces on the bases of the columns. A comparison was made between the three methods applied and the structural systems analyzed.
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Macdonald, John Hugh George. "Identification of the dynamic behaviour of a cable-stayed bridge from full scale testing during and after construction." Thesis, University of Bristol, 2000. http://hdl.handle.net/1983/68b3c36f-6f7a-44ab-845d-8f5599d863b6.
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Williams, David Michael. "Numerical modelling of real-time sub-structure testing." Thesis, University of Oxford, 2000. http://ora.ox.ac.uk/objects/uuid:c2c9ff13-887f-4065-9ce6-1969375099c7.
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Current dynamic testing methods can prove unrealistic due to the scale at which test components are modelled, the rate at which they are loaded or the boundary conditions to which they are subjected. A new test method, termed "Real-Time Sub-Structure Testing" seeks to provide a more realistic testing environment for energy dissipative components. The method tests structural components at full or large scale and in real-time. The physical test interacts with a computer model of the structure surrounding the test component. In this way, the in-situ behaviour of the test component is evaluated in relation to the overall structural response. The testing method requires fast and realistic modelling of the surrounding structure and a rapid interaction with the physical test specimen. For these reasons, a new non-linear finite element method has been proposed in order to model the surrounding structure behaviour efficiently. The method uses the Central Difference Method time stepping integration scheme together with a newly devised basis. The proposed basis consists of the structure’s elastic modes and additional Ritz vectors, which are calculated from the inelastic static displacement shapes of the structure. The displacement shapes correspond to the same static spatial distribution of loading as the intended dynamic excitation, and are intended to characterise the inelastic behaviour of the structure. The method has been validated against a Newmark event to event algorithm as well as Drain2DX. The non-linear dynamic response of a propped cantilever beam and portal frame structure was investigated. The response evaluated by the algorithm agrees closely with both validation analyses. The new algorithm was also shown to be faster than the Newmark procedure in simple benchmark tests. In addition, a numerical model of the testing apparatus has been developed in order to simulate complete tests for the purposes of testing procedure development and validation. The model is developed using Matlab Simulink. Parameters for the model are deduced from published data, experimental component tests and open loop step response calibrations. The model behaviour was found to be very sensitive to the parameters used. However, after calibration against open loop tests the model reproduces the observed laboratory behaviour to a good degree of accuracy. In an attempt to predict the behaviour of an actual test, the laboratory model has been coupled with the new structural solution algorithm to simulate a virtual test. The simulated results compare well with experimentally observed data demonstrating the usefulness of the overall simulation as a test modelling tool.
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Chin, Victor B. L. "The dynamic response of pile-soil interfaces during pile driving and dynamic testing events." Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9421.
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Araiza, Garaygordobil Juan Carlos. "Dynamic assessment of structural building components." Doctoral thesis, Universitat Politècnica de Catalunya, 2003. http://hdl.handle.net/10803/6154.
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The development of methods that correlate the measure of dynamic parameters with the condition of the structure has received a considerable attention from the engineering community in the last few years. In the field of structural assessment of buildings, dynamic testing can be used to extend the inspection to every structural component, covering the gaps left by other more complex techniques (such as core extraction or load testing). The information obtained by the dynamic means is not restricted only (as traditional methods are) to the location in which the tests is developed while the use of a low number of sensors and simple excitation devices helps to reduce dramatically the cost of implementation.The general objective of the thesis consists on the demonstration of the usefulness of dynamic assessment on building components (such as masonry walls, stone piers or RC beams and slabs) using a simple-layout experiment but based intensively in numerical simulation.
The methodology to achieve the objective include tasks such as:
- The study the influence of different parameters on dynamic behavior of structures. This process -also known as parametrical study- recognizes the influence of the variables when performing a model updating.
- A series of laboratory campaigns to identify the influence of different structural damages on dynamic parameters. Studied damage-influence include: Stiffness deterioration by cracking on supported or suspended beams, carbonation of concrete, sulfate attack on concrete and rebars, chloride attack on concrete and axial load on masonry walls and piers.
- The application of a simple-layout method of dynamic assessment in real-life buildings. In some of those cases, static load test (direct identification method) is also developed to compare the reliability of the dynamic approach.
Experimental works and field studies carried out in this investigation have permitted to conclude that a combined implementation of a simple dynamic testing and numerical modeling is able to characterize the current structural conditions of a building component. The proposed dynamic assessment layout has conduced to the identification of characteristics such as boundary conditions, cracking levels, geometry properties or levels of axial loading. By comparing systematically the experimental and the numerical frequencies, it can also be concluded that a detailed model is able to predict the dynamic behavior of a building component. This prediction was accurate not only for undamaged conditions, but also for different damage scenarios. The present research has contributed to ascertain that dynamic testing is a valuable tool to assess the structural conditions of single concrete or masonry building elements such as concrete beams, RC or prestressed slabs, masonry walls or stone piers.
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Lestari, Wahyu. "Damage of composite structures : detection technique, dynamic response and residual strength." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12072.
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Rigby, Douglas Bertrand. "Testing and constitutive modelling of saturated interfaces in dynamic soil-structure interaction." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187454.
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Cyclic direct and simple-shear experiments are conducted on remolded clay-steel interfaces under undrained conditions and a constant normal stress. Also, a constitutive model for the stress-strain-pore-pressure behavior of cohesive soil interfaces under dynamic loading is developed using the new unified disturbed state concept (DSC). The model is based on elasto-plasticity theory as defined by the hierarchical single surface (HISS) plasticity model. The proposed model is calibrated with laboratory tests and is shown to capture the complex strain-softening, degradation, and pore pressure behavior observed in cyclic loading of piles in saturated clay. Understanding of the mechanical behavior of saturated interfaces between structural and geologic materials and joints in rock, subjected to cyclic loading is important for safe and improved analysis and design of many geotechnical structures. Appropriate testing is vital for the determination of parameters in constitutive models to characterize the mechanical response in terms of stress-strain and failure behavior. A unique laboratory testing device for investigating the dynamic loading effects at the interfaces and joints of materials is described. This new device known as the cyclic multi-degree-of-freedom device with pore fluid pressure effects (CYMDOF-P), can automatically load and test various combinations of material interfaces with dry or saturated conditions and in a direct-shear or simple-shear mode. Based on field observations of instrumented piles it is proposed that there is a thin interface zone of clay between the moving pile and clay mass in which significant shear deformations and generation of pore pressure occur. To explore this behavior, a test program using Gulf of Mexico marine clay is carried out with the CYMDOF-P device. Important behavioral aspects are identified and incorporated as part of the new disturbed-state interface model. Laboratory test results are used for the determination of parameters for the model, and for verification of the model. The model predictions, in general, were found to provide satisfactory correlation with the observations. The procedure to find material parameters for the interface model is described. The model is simple enough to be easily implemented in numerical techniques such as the finite element method, and this implementation is briefly discussed.
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Han, Tai Chun. "Effects of geometric variation and residual stress on the dynamic response of multilayerd thin membrane structures." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Summer2007/T_Han_080107.pdf.
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Tan, Hock Chuan. "Load-induced damage evaluation in reinforced concrete structures using dynamic response signatures." Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602019.
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The purpose of this thesis is to assess and develop a non-destructive evaluation (NDE) procedure for evaluating the integrity of rectangular and square reinforced concrete (RC) slabs. This procedure employs both dynamic frequency and deformation response signatures to track changes in the slab following dynamic excitation. Such a procedure could provide a good basis for practising engineers to conduct nondestructive testing (NDT) and evaluation of general RC structures. The response of RC floor slabs to dynamic excitation have been experimentally studied at 1/3rd scale for two aspect ratios (square and rectangular), three concrete grades, and with and without cement replacement under clamped edge conditions. The model slabs were subjected to series of quasi-static loading and unloading sequences, to increasing load levels until failure was reached. At the unloaded part of each load cycle, the slabs were subjected to dynamic excitations, alternately using a hand-held, Bruel and Kjaer (B and K) impact hammer, and broad-band burst chirp shaker excitation. For the larger square slabs, at each unloaded part of the load cycle, a 265 gm steel ball bearing dropped from a fixed, standard height to provide more robust impulse excitation. All of the slabs were instrumented with optimally located accelerometers and strain gauges to capture the slab responses. The acceleration, deflection and strain readings resulting from the dynamic excitation were recorded at incremental load steps, from the initial unloaded state up to failure, and subsequently evaluated and analysed. The results show that the changes resulting from damage are readily observable, in the fundamental and higher modes of vibration and in the load-deflection and strain responses. These changes have been examined and analysed in both the time and frequency domains, and using other techniques, to establish the viability of this approach in evaluating the integrity of RC and other complex structures.
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Mukalay, J. N. "Structural bond behaviour of ribbed GFRP rebars in concrete beams under dynamic loading." Thesis, Vaal University of Technology, 2019. http://hdl.handle.net/10352/461.
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M.Tech. (Department of Civil Engineering, Faculty of Engineering and Technology), Vaal University of TechnologyThis research investigated the structural bond strength of GFRP rebars in concrete beams under dynamic loading with the aim to characterize the structural bond behaviour and evaluate the limitations of the GFRP rebars under dynamic loading. The dynamic loading in this study was set at 500 repeating cycles to simulate a more realistic dynamic loading scenario such as earthquake since most dynamic loading studies are carried under ten repeating cycles. The experimental work was divided into 2 main tests which were firstly, the tensile tests of the GFRP rebars in order to evaluate the tensile strength of the rebars and characterize their properties. Secondly, the flexural tests of GFRP and steel reinforced concrete beams in order to evaluate the bond strength of GFRP and steel rebars, to characterize the average bond strength of GFRP and steel reinforced concrete beams under dynamic loading and finally to compare the average bond strength of GFRP rebars to Steel rebars in both dynamic and static loadings. The tensile tests were carried out using a Universal Testing Machine (UTM) and the results of the tensile tests of the GFRP rebars showed that the average experimental tensile strength of GFRP rebars was only 56.65% of the nominal tensile strength provided on the supplier data sheet. As for flexural tests, they were carried out through a four-point bending test using a UTM in conjunction with a universal dynamic shaker to create the dynamic loading set up. Steel reinforced concrete beams were used as control beams during the tests and factors such as the tensile strength of the GFRP rebars, the slip of the rebars, the load-deflection relationship and the stress-strain relationship were investigated. The results of the tests showed that the tensile strength of the GFRP rebar is strongly proportional to the maximum beam load bearing capacity and the maximum stresses of GFRP reinforced concrete beams. The results also showed that the average bond strength of GFRP rebars in static loading (8.44 MPa) was only 80% of the average bond strength in dynamic loading (10.95 MPa). Moreover, the experimental work showed that the failure of GFRP reinforced concrete beams depicted large deflections (19 mm) and slips (5 mm to 12.5 mm) when compared to steel reinforced concrete beams (for which the maximum deflection was 9.66 mm at failure and slippage values of 2 mm to 10 mm). Based on that it could be stipulated that the tensile strength of GFRP rebars is one determinant factor to the bond strength behaviour of GFRP rebars in concrete. Hence, the structural bond behaviour of GFRP rebars could be well-defined if more studies were done on the bond behaviour of GFRP rebars in concrete beams under dynamic loading using another type of GFRP rebars that would consist of a relatively high tensile strength as compared to the ones used in this study and different surface texture.
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Martin, Kipp Alan. "BEHAVIOR AND DESIGN OF MONOTUBE SIGN SUPPORT STRUCTURES (VORTEX SHEDDING, DYNAMIC FORCES, STRAIN GAGE, FIELD TESTING, COMPUTER MODEL)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291193.
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Hammond, Lloyd Charles 1961. "The structural response of submerged air-backed plates to underwater explosions." Monash University, Dept. of Civil Engineering, 2000. http://arrow.monash.edu.au/hdl/1959.1/9244.
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Hedric, Andrew C. "Dynamic Behaviors of Historical Wrought Iron Truss Bridges – a Field Testing Case Study." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc822751/.
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Civil infrastructure throughout the world serves as main arteries for commerce and transportation, commonly forming the backbone of many societies. Bridges have been and remain a crucial part of the success of these civil networks. However, the crucial elements have been built over centuries and have been subject to generations of use. Many current bridges have outlived their intended service life or have been retrofitted to carry additional loads over their original design. A large number of these historic bridges are still in everyday use and their condition needs to be monitored for public safety. Transportation infrastructure authorities have implemented various inspection and management programs throughout the world, mainly visual inspections. However, careful visual inspections can provide valuable information but it has limitations in that it provides no actual stress-strain information to determine structural soundness. Structural Health Monitoring (SHM) has been a growing area of research as officials need to asses and triage the aging infrastructure with methods that provide measurable response information to determine the health of the structure. A rapid improvement in technology has allowed researchers to start using new sensors and algorithms to understand the structural parameters of tested structures due to known and unknown loading scenarios. One of the most promising methods involves the use of wireless sensor nodes to measure structural responses to loads in real time. The structural responses can be processed to help understand the modal parameters, determine the health of the structure, and potentially identify damage. For example, modal parameters of structures are typically used when designing the lateral system of a structure. A better understanding of these parameters can lead to better and more efficient designs. Usually engineers rely on a finite element analysis to identify these parameters. By observing the actual parameters displayed during field testing, the theoretical FE models can be validated for accuracy. This paper will present the field testing of a historic wrought iron truss bridge, in a case study, to establish a repeatable procedure to be used as reference for the testing of other similar structures.
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Hallak, Yanina Soledad. "DESIGN, MANUFACTURE, DYNAMIC TESTING, AND FINITE ELEMENT ANALYSIS OF A COMPOSITE 6U CUBESAT." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1572.
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CubeSats, specially the 6U standard, is nowadays the tendency where many developers point towards. The upscaling size of the standard and payloads entail the increase of the satellite overall mass. Composite materials have demonstrated the ability to fulfill expectations like reducing structural masses, having been applied to different types of spacecraft, including small satellites.
This Thesis is focused on designing, manufacturing, and dynamic testing of a 6U CubeSat made of carbon fiber, fiberglass, and aluminum.
The main objective of this study was obtaining a mass reduction of a 6U CubeSat structure, maintaining the stiffness and strength. Considering the thermal effects of the used materials an outgassing test of the used materials was performed and the experimental results are presented.
The CubeSat structure was entirely manufactured and tested at Cal Poly Aerospace Engineering Department facilities. A mechanical shock test and random vibration test were performed using a shock table and a shake table respectively. Results of both tests are presented. A correlation between the Experimental data and the Finite Element Model of the satellite was carried out. Finally, a comparison between 6U structure studied and aluminum 6U structures available in the market is presented.
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Pearce, Garth Morgan Kendall Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "High strain-rate behaviour of bolted joints in carbon fibre composite structures." Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44593.
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An investigation is presented into the behaviour of carbon fibre composite joints subjected to dynamic loading rates in the range of 0.1 m/s to 10 m/s. The research is focused on the response of single fastener joints and more complex structural arrangements involving multiple fasteners and complex loads. Fasteners play a crucial role in the joining of aerospace components due to their ease of installation and inspection and their resistance to creep and environmental degradation. A consequence of the operating environment of aircraft is that many critical load cases involve impact and crash. These loading events are characterised by high loading rates, high kinetic energy and possibly loads well above the static design case. The properties of composite materials change with loading rate, so it is likely that the behaviour of bolted composite joints may also vary significantly. Dynamic behaviour of bolted joints is an area of research that has been given little attention to date. The few available papers on the topic are limited to the investigation of ideal bearing loads and include some contradictory results. The research developed a detailed understanding of the behaviour of bolted joints in composite structures through a combined numerical and experimental investigation. A set of quasi-static and dynamic single fastener joint tests was conducted to develop an understanding of the complex failure mechanisms present in bolted composite joints. Simple structural tests were developed to investigate the interaction of multiple bolts in a joint. High speed camera footage, full-field strain measurement and CT scanning techniques were all used to develop an understanding of the changes in the failure process with increased loading rate. Finite element analyses used implicit and explicit dynamic algorithms to model the tests. The finite element analysis contributed to the understanding of the experimental results as well as providing a predictive tool to minimise the need for further testing. A method of incorporating detailed information about bolt failure into large scale structural models was investigated and developed. The original contributions of this thesis involve novel dynamic joint testing including dynamic pull-through and structural tests. CT Scanning was utilised in a novel way to investigate the complex failure modes within a bolted joint. Novel finite element techniques were developed for modelling bolted joints at both a detailed level and a simplified level for structural analyses. These contributions significantly improve the current understanding of bolted joint failure, both quasi-statically and dynamically, and will allow for more efficient design of bolted composite structures for crash and impact loads.
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Hu, Shanshan. "AFFECT, MOTIVATION, AND ENGAGEMENT IN THE CONTEXT OF MATHEMATICS EDUCATION: TESTING A DYNAMIC MODEL OF INTERACTIVE RELATIONSHIPS." UKnowledge, 2018. https://uknowledge.uky.edu/edp_etds/71.
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The present study tested the interactive model of affect, motivation, and engagement (Linnenbrink, 2007) in mathematics education with a nationally representative sample. Self-efficacy, self-concept, and anxiety were indicators of pleasant and unpleasant affect. Intrinsic and extrinsic motivation were indicators of mastery and performance approach. Persistence and cognitive activation were indicators of behavioral and cognitive engagement. The 2012 Programme for International Student Assessment (PISA) supplied a sample of 4,978 students from the United States for structural equation modeling. The results indicated that PISA data overall supported the interactive model. Specifically, PISA data completely supported the specification of the relationship between motivation and affect, largely supported the specification of the relationship between affect and engagement, but failed to support the specification of the relationship between motivation and engagement. Finally, PISA data largely supported the specification of the mediation effects of affect on the relationship between motivation and engagement.
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Coussa, Fabien. "Du comportement dynamique de matériaux composites tissés à matrice polyamide." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM063/document.
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Contraint de respecter les réglementations environnementales concernant les émissions de CO2, les industriels du secteur automobile se doivent de lever certains verrous technologiques associés à l’allègement des structures au sein de leur véhicule. L’introduction des matériaux composites dans le développement et la production de pièces structurantes est envisagée comme étant une des solutions les plus efficaces à moyen et long terme. L’optimisation des coûts matière, caractéristique de cette industrie de masse, nécessite de maîtriser le comportement physique de matériaux composites à matrice thermoplastique et à fibres de verre continues tissées. En termes de coût et de variétés d’applications, ces derniers sont considérés aujourd’hui comme une alternative pertinente aux onéreux composites utilisés dans l’aéronautique. Un renfort de porte pour crash latéral a été ainsi développé et les travaux présentés dans cette thèse sont une contribution à la compréhension, la caractérisation et à la prédiction numérique du comportement jusqu’à rupture de cette pièce, qui lors d’un crash est soumise à de forts gradients de vitesses. Au regard de l’absence de normalisation ou de consensus liés aux essais dynamiques sur matériaux composites, nous proposons une procédure expérimentale robuste, garantissant la représentativité de la caractérisation du comportement sur un spectre de vitesses quasi-statiques et dynamiques. La validation des étapes de la procédure et l’utilisation d’un montage d’essais dynamiques développé dans ces travaux permettent d’aboutir à une base de données riche, et utile à une procédure d’identification des paramètres d’un modèle phénoménologique prenant en compte l’influence de la vitesse sur l’évolution des phénomènes dissipatifs jusqu’à rupture. Fort d’une identification majoritairement directe, la précision de la réponse numérique issue de la loi de comportement identifiée est évaluée et validée à l’aide de calculs de structures faisant intervenir d’importants gradients matériels et structurelsCar manufacturers are looking for solutions to lighten their vehicles in order to meet pollutant emission requirements – for thermal engines – or to extend their range – for electric vehicles. Composite materials, among other solutions, offer excellent strength and durability. However increased per unit cost and manufacturing time are among the main drawbacks material producers have to overcome in order to make composite solutions viable for mass-market production. In that prospect, woven glass fibers and thermoplastic matrices respectively are more serious contenders than aeronautic-grade composites. The objective application is a door reinforcement module, whose main function is to act as a safety net, adding its own stiffness and strength to that of the steel door and preventing any foreign object from entering the passenger compartment. A main preoccupation is therefore the constitutive behavior of that material under strain rates varying from 10-3 s-1 to approximately 50 s-1. The study objective is to develop a physically-based constitutive law modelling in order to take into account strain-rate sensitivity on behavior. A new and consistent experimental procedure aiming at capturing the influence of speed solicitation on non-linear internal mechanisms is developed and allows identifying non-linear constitutive law parameters over a wide range of strain rates until failure. Resulting mainly from direct evaluations and direct identification procedure, the accuracy of the implemented constitutive law is guaranteed through numerical computations involving effects of material and structural heterogeneities
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Ouellette, Jeffrey Alan. "Modeling and Scaling of a Flexible Subscale Aircraft for Flight Control Development and Testing in the Presence of Aeroservoelastic Interactions." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/51819.
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The interaction of an aircraft's structure and the flight dynamics can degrade the performance of a controller designed only considering the rigid body flight dynamics. These concerns are greater for the next generation adaptive controls. These interactions lead to an increase in the tracking error, instabilities in the control parameters, and significant structural excitations. To improve the understanding of these issues the interactions have been examined using simulation as well as flight testing of a subscale aircraft. The scaling required for such a subscale aircraft has also been examined. For the simulation a coordinate system where the non-linear flight dynamics are orthogonal to the linear structural dynamics was defined. The orthogonality allows the use of separates models for the aerodynamics. For the non-linear flight dynamics, preexisting table lookups with extended vortex lattice are used to determine the aerodynamic forces. Strip theory is then used to determine the smaller, but still important, unsteady aerodynamic forces due to the flexible motion. Because the orientation of the engines is dependent on the structural deformations, the propulsive force is modeled as a non-conservative follower force. The simulation of the integrated dynamics is then used to examine the effects of the aircraft flexibility and resultant ASE interactions on the performance of adaptive controls. For the scaling, the complete similitude of a flexible aircraft was examined. However, this complete similitude is unfeasible for an actual model, so partial similitude is investigated using two approaches. First, the classical approximations of the flight dynamic modes are used to reduce the order of the coupled model, and consequently the number of scaling parameters required to maintain the physics of the system. The second approach uses sensitivity of the response to errors in the aircraft's nondimensional parameters. Both methods give a consistent set of nondimensional parameters which do not have significant influence on the aeroservoelastic interaction. These parameters do not need to be scaled, thus leading to a viable scaled model. A subscale vehicle has been designed which shows significant coupling between the flight dynamics and structural dynamics. This vehicle was used to validate the results of the scaling theory. Output error system identification was used to identify a model from the flight test data. This identified model provides the frequency of the short-period mode, and the effects of the Froude number on the flexibility.Ph. D.
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Elshesheny, Ahmed. "Dynamic soil-structure interaction of reinforced concrete buried structures under the effect of dynamic loads using soil reinforcement new technologies. Soil-structure interaction of buried rigid and flexible pipes under geogrid-reinforced soil subjected to cyclic loads." Thesis, University of Bradford, 2019. http://hdl.handle.net/10454/18312.
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Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary.
In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically.
The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain.Government of Egypt
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Ozerkan, Taner. "Instrumented Monitoring And Dynamic Testing Of Metu Cable Stayed Pedestrian Bridge And Comparisons Against The Analytical Model Simulations." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606335/index.pdf.
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This study includes structural instrumentation and monitoring of a 48.5 meters long cable-stayed pedestrian bridge located on EskiSehir road near METU campus. The objectives of the study are (1) to monitor the bridge responses during erection and operation stages so that the strain changes are determined during important events such as transportation, lifting, cabling, mid-support removal, slab concrete pouring and tile placement, (2) to determine existing cable forces using vibration frequencies, and (3) comparison of the experimental and analytical results for model updating.
A total of 10 vibrating wire type strain gages were used for strain readings in steel members. The readings are taken at various stages of construction at every 10 to 30 minutes intervals. The bridge responses were monitored about three months and large strain changes in the order of 300 to 500 micro-strain were recorded during important events (e.g., transportation, lifting, cabling, mid-support removal, deck cover placement).
The deck and tower natural vibration frequency measurements are conducted in two main directions. Two different FE models are constructed using two levels of complexity. FEM analysis results are compared against measured natural frequencies of the bridge and tower.
Simplistic analytical model is modified to include temporary support removal in order to perform staged construction simulation and investigate cable force variations. Actual cable tensile forces are obtained using measured cable natural vibration frequencies. The cable frequencies are measured using a CR10X data logger and a PCB 393C accelerometer. Existing cable forces are compared against analytical simulations and symmetrically placed cables
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Calanni, Fraccone Giorgio M. "Bayesian networks for uncertainty estimation in the response of dynamic structures." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24714.
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Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Vitali Volovoi; Committee Co-Chair: Dr. Massimo Ruzzene; Committee Member: Dr. Andrew Makeev; Committee Member: Dr. Dewey Hodges; Committee Member: Dr. Peter Cento
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Kahraman, Engin. "Investigation Of The Dynamic Properties Of Plate-like Structures." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613703/index.pdf.
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This study presents the investigation and the verification of the modal parameters of a plate-like structure by using different modal analysis methods. A fin-like structure which is generally used in aircraft is selected as a subcategory of a plate-like test structure.
In the first part of the thesis, the natural frequencies and the corresponding mode shapes of the fin are extracted by Finite Element Analysis method. Classical Modal Analysis and Testing methods comprising both impact hammer and modal shaker applications are then applied in order to obtain the modal parameters such asresonance frequencies, mode shapes and damping ratios. In the second part, a recent modal analysis technique, Operational Modal Analysis, is also applied in the laboratory environment. Since Operational Modal Analysis method does not require any information of input forcing, the fin structure is tested under both mechanical and acoustical types of excitations without measuring the given input forces. Finally, Operational Modal Analysis and Testing is also performed under various flow conditions generated in the wind tunnel which may simulate the real operating environment for the fin structure. The modal parameters extracted under these flow conditions are then compared with the previously obtained Finite Element, Classical and Operational Modal Analyses results.
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Shepenkov, Valeriy. "Vibration Modal Analysis of a Deployable Boom Integrated to a CubeSat." Thesis, KTH, Strukturmekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122076.
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CubeSat or Cubic Satellite is an effective method to study the space aroundthe Earth thanks to its low cost, easy maintenance and short lead time. However, a great challenge of small satellites lies in achieving technicaland scientific requirements during the design stage. In the present workprimary focus is given to dynamic characterization of the deployable tapespringboom in order to verify and study the boom deployment dynamiceffects on the satellite. The deployed boom dynamic characteristics werestudied through simulations and experimental testing. The gravity offloadingsystem was used to simulate weightlessness environment in theexperimental testing and simulations showed that the deployment of thesystem influence the results in a different way depending on the vibrationmode shape.En CubeSat eller kubisk satellit är effektivt för att studera rymden runtjorden på grund av dess låga kostnad, enkla underhåll och korta ledtid. Enstor utmaningen i utformningen av små satelliter är att uppnå de tekniskaoch vetenskapliga kraven. Detta arbete har analyserat de dynamiska egenskapernahos en utfällbar band-fjäder bom i syfte att verifera och för attstudera bommens utfällningsdynamiska effekter på satellitens bana och attityd.Den utfällda bommens dynamiska egenskaper har studerats genomsimuleringar och experimentella tester. Ett tyngdkraftskompenserande systemhar använts för att simulera tyngdlöshet i de experimentella testernaoch simuleringar visar att utformningen av detta system påverkar resultatenolika beroende på svängingsmodens form.
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Brackus, Travis R. "Destructive Testing and Finite-Element Modeling of Full-Scale Bridge Sections Containing Precast Deck Panels." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/861.
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Full-depth, precast panel deck systems are becoming more common in bridge installation and repair. The objective of these systems is to achieve the performance of cast-in-place systems while simultaneously saving time and money. The structural behavior of these systems has been the subject of scrutiny in recent research. The Utah Department of Transportation demolished a steel I-girder bridge containing a precast panel deck system and provided two full-scale specimens for this project. Destructive testing was performed at Utah State University on the specimens to investigate three failure modes: flexural, beam shear, and punching shear. Finite-element models were created using ANSYS software to replicate experimental behavior. Overall, it was found that the elastic, post-elastic, and ultimate behavior of the full-scale bridge sections containing precast panel deck systems can be accurately predicted in analytical models.
Another aspect of this project was to investigate changes in dynamic behavior as the system was subjected to flexural yield and failure. Point loads were applied and removed in increments, and dynamic testing was conducted at each load level. It was found that significant damage is somewhat noticeable by monitoring the changes in natural frequencies.
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Mutlu, Mehmet Basar. "Numerical Simulations Of Reinforced Concrete Frames Tested Using Pseudo-dynamic Method." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614460/index.pdf.
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Considering the deficiencies frequently observed in the existing reinforced concrete buildings, detailed assessment and rehabilitation must be conducted to avoid significant life and value loss in seismic zones. In this sense, performance based evaluation methods suggested in the regulations and codes must be examined and revised through experimental and analytical research to provide safe and economical rehabilitation solutions.
In this study, seismic behavior of three reinforced concrete frames built and tested in Middle East Technical University Structural Mechanics Laboratory is examined. The specimens are extracted from a typical interior frame of 3-story 3-bay reinforced concrete structure. One of the specimens has compliant design according to Turkish Earthquake Code (2007) and each of the other two specimens represents different types of deficiencies in terms of material strength and detailing. The test specimens were modeled using different modeling approaches and nonlinear dynamic analyses were conducted on the numerical models. Results of continuous pseudo-dynamic testing of three ground motions are presented and compared with the numerical simulations on models. Calibrated finite element models were used for evaluation of performance assessment procedure of Turkish Earthquake Code (2007) and further investigation on local deformation components in light of experimental findings and observations. Deformation sources of columns and joints were studied in terms of their interaction and contributions to the total drift. Estimated plastic hinge lengths of columns were compared with the experimental observations and the proposed expressions in the literature.
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Kahle, Matthew Gilbert. "Partially restrained composite connections : design and analysis of a prototype structure." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20830.
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Uddin, Gazi Salah. "Nonlinear and Nonparametric Dynamical Methods in Economics and Finance." Doctoral thesis, Linköpings universitet, Nationalekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-127340.
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The objectives of the thesis - which comprises six parts – can be summarized in i) implementing linear and nonlinear/nonparametric approaches toward detecting, measuring and analyzing the nature and directionality of causal relationships in financial markets, ii) elaborating on modern topics in financial investment analysis, iii) probing into the role of commodity futures in constructing optimal portfolios as well as iv) investigating growth dynamics via aggregated and disaggregated indices. The first paper named “Analyzing causal interactions between sectoral equity returns and commodity futures returns in the aftermath of the global financial crisis: The case of the US and EU equity returns”, aims to explore and compare the dependence and co-movement structure between commodity and various asset classes’ returns including the USA and EU stock markets via the use of linear and non-linear causality testing in a comparative context with the additional adjustment for cointegration and conditional heteroscedasticity. The findings provide important implications for optimal asset allocation and portfolio diversification with respect to various market conditions, namely both in “good” and “bad” (crisis) times. The second paper is entitled “On the time scale behaviour of Equity-Commodity links: Implications for Portfolio Management”, and has been published in the Journal of International Financial Markets, Institutions and Money (2016). The study is co-authored with Professors S. Bekiros, D.K. Nguyen, and B. Sjö. It develops a holistic framework for the investigation of the multi-horizon and intra-frequency causal directionalities of various asset classes, by means of multi-resolution analysis. The results verify the assumption that financial markets exhibit time-varying co-movement patterns, which are fundamentally important in a) generating profitable trading strategies according to different investor horizon expectations and b) decoding the financialization mechanism across various asset classes. The third paper entitled “Business Cycle (de) Synchronization in the aftermath of the Global Financial Crisis: Implications for the Euro Area”, was published at Studies in Nonlinear Dynamics and Econometrics (2015) and is co-authored with S. Bekiros, D.K Nguyen and B. Sjö. In this work, the scale-dependent time-varying (de)synchronization effects between the Eurozone and the broad Euro area business cycles are revealed, before and after the global financial crisis. The results, which point towards an increased observed comovement during the crisis period for the Euro area, could be catalytic for the introduction of a more efficient monetary policy by EU institutions and in particular by the European Central Bank. In the fourth paper, “Do financial stress and policy uncertainty have an impact on the energy and metals markets? A quantile regression approach”, which was published in the International Review of Economics and Finance (2016) and co-authored with J.C. Reboredo, the financial and policy uncertainty is investigated in relation to the price dynamics of energy and metal commodity futures’ markets. This work lead to the analysis of the asymmetric interrelationships with respect to changes in the perceptions of various risk measures, covering various periods, i.e., “normal” vs. “turbulent” such as upward or downward market episodes. The fifth paper, co-authored with P. Andreasson, S. Bekiros and D.K. Nguyen, is entitled “The impact of speculation and economic uncertainty on commodity markets”, and is published in the International Review of Financial Analysis (2016). This paper attempts a novel methodological approach to measuring speculation in commodity markets, in particular whether market speculation drives agricultural commodity prices or viceversa. The assessment of the empirical analysis demonstrates that agricultural prices are not affected by speculation. Finally, the sixth paper “Energy and Output Dynamics in Bangladesh”, co-authored with B.P. Paul, was published in Energy Economics (2011) and explores the relationship between energy utilization and economic growth in Bangladesh. Specifically, it deals with the important issue of whether energy consumption can be reduced without affecting economic growth while at the same time implicitly may lead to poverty reduction. The findings substantiate the fact that a) energy usage has become more efficient in recent times, as well as indicate that b) fluctuations in energy consumption did not have a significant impact on economic output.