Dissertations / Theses on the topic 'Motor vehicles - Dynamics - Computer simulation'

The expense of high fidelity computational fluid dynamics, in terms of time and amount of computing resources required, excludes such methods from the early stages of aircraft design. It is only in the early, conceptual, stage of aircraft development where a wide range of designs are considered and global, rather than local, optimisation can play a key role. This thesis deals with methods which may allow high cost computer simulations to be used within a global optimisation design process. The first half of the thesis concentrates on the use of surrogate modeling of the optimisation design space, which allows cheap approximations to be used in lieu of expensive computer simulations. The process is automated and present statistical methods are modified to accommodate problems associated with the simulation of fluid flow and uncertainty within an automated system. The re-interpolation of a regression model of noisy data is presented as a method of improving convergence towards a global optimum. The second half of the thesis develops methods of using partially converged computational fluid dynamics simulations within a surrogate modelling optimisation process. Significant time savings are made possible by reducing computational effort directed at producing a surrogate for regions of poor designs and concentrating resources on modelling regions of promising designs.

This work presents an investigation into the parameter estimation of suspension components and the vertical motions of wheeled vehicles from experimental data. The estimation problems considered were for suspension dampers, a single wheel station and a full vehicle. Using conventional methods (gradient-based (GB), Downhill Simplex (DS)) and stochastic methods (Genetic Algorithm (GA) and Differential Evolution (DE)), three major problems were encountered. These were concerned with the ability and consistency of finding the global optimum solution, time consumption in the estimation process, and the difficulties in setting the algorithm's control parameters. To overcome these problems, a new technique named the discrete variable Hybrid Differential Evolution (dvHDE) method is presented. The new dvHDE method employs an integer-encoding technique and treats all parameters involved in the same unified way as discrete variables, and embeds two mechanisms that can be used to deal with convergence difficulties and reduce the time consumed in the optimisation process. The dvHDE algorithm has been validated against the conventional GB, DS and DE techniques and was shown to be more efficient and effective in all but the simplest cases. Its robustness was demonstrated by its application to a number of vehicle related problems of increasing complexity. These include case studies involving parameter estimation using experimental data from tests on automotive dampers, a single wheel station and a full vehicle. The investigation has shown that the proposed dvHDE method, when compared to the other methods, was the best for finding the global optimum solutions in a short time. It is recommended for nonlinear vehicle suspension models and other similar systems.

This work presents an investigation into the parameter estimation of suspension components and the vertical motions of wheeled vehicles from experimental data. The estimation problems considered were for suspension dampers, a single wheel station and a full vehicle. Using conventional methods (gradient-based (GB), Downhill Simplex (DS)) and stochastic methods (Genetic Algorithm (GA) and Differential Evolution (DE)), three major problems were encountered. These were concerned with the ability and consistency of finding the global optimum solution, time consumption in the estimation process, and the difficulties in setting the algorithm's control parameters. To overcome these problems, a new technique named the discrete variable Hybrid Differential Evolution (dvHDE) method is presented. The new dvHDE method employs an integer-encoding technique and treats all parameters involved in the same unified way as discrete variables, and embeds two mechanisms that can be used to deal with convergence difficulties and reduce the time consumed in the optimisation process. The dvHDE algorithm has been validated against the conventional GB, DS and DE techniques and was shown to be more efficient and effective in all but the simplest cases. Its robustness was demonstrated by its application to a number of vehicle related problems of increasing complexity. These include case studies involving parameter estimation using experimental data from tests on automotive dampers, a single wheel station and a full vehicle. The investigation has shown that the proposed dvHDE method, when compared to the other methods, was the best for finding the global optimum solutions in a short time. It is recommended for nonlinear vehicle suspension models and other similar systems.

The Climatic Wind Tunnel (CWT) is a facility used by the motor industry to test vehicles under climatic extremes without the need for expensive overseas test programs. This work focuses on the application of computer simulation to the Heating Ventilation and Air Conditioning (HVAC) plant that makes up a CWT facility. The objective being to reduce its operational costs through the identification of energy saving operational strategies. When in operation the CWT has a peak power consumption of 3MW. The implementation of any measures that would reduce this peak load would give rise to considerable savings in the operating costs of the facility. Computer simulation is an accepted technique for the study of systems operating under varying load conditions. Simulation allows rapid analysis of different strategies for operating plant and the effectiveness of achieving the desired effect without compromising the buildings performance. Models for the components of the CWT have been developed and coded in Neutral Model Format. These models have then been linked together in a modular simulation environment to give a model of the complete plant. The CWT plant naturally decomposesin to four major subsystems these being the test chamber, the soakroom, air make-up and refrigeration system. Models of all the primary and secondary HVAC plant are described as is how they constitute the systems that make up the CWT. Validation tests for individual components as well as for the systems have been carried out. To illustrate the potential of the application of computer simulation into finding improved modes of operation that would reduce the energy consumption of the facility, four studies have been carried out. The studies involve the possibility of scheduling the operation of condenser fans as a function of refrigeration load and outside ambient temperature, methods for the pre-test conditioning of a vehicle, a reduction in the secondary refrigerant flow temperature and an increase in the thickness of the insulated panels from which the facility is constructed. The studies carried out showed that there was potential for moderate energy savings to be made in the operation of the facility and that extended simulation runs would allow for the in-depth assessment of a large range of possible modes of plant operation in order to identify the areas where the greatest savings are possible.

Reacting flows interacting with liquid droplets are of practical and scientific importance due to their appearance in a multiplicity of industrial and domestic applications such as fire suppression systems and humidified gas turbines. Experimental measurements are usually limited to global quantities or local quantities at limited spatial locations, which provide little detailed information for fundamental understanding of complex interactions. Numerical simulations can overcome these limitations, but are restricted by the available computer capacity. Therefore, most previous simulations in the field employ simplifications such as a two-dimensional configuration, the Eulerian description of the dispersed phase, or the Reynolds averaged Navier-Stokes (RANS) methodology, etc. Such simplified methods are not appropriate for scrutinizing the local, unsteady interactions embedded in the realistic multiphase reacting flows from the first principle. To this end, systematic understanding of the multilateral, multiscale and multiphysics interactions among turbulent flow, chemical reaction and dispersing droplets is still far from being achieved. Recently, the rapid development of the supercomputer hardware and software technologies enables the application of high fidelity numerical techniques, i.e., direct numerical simulation (DNS) and large eddy simulation (LES), to such complex flows. In the present study, a hybrid Eulerian-Lagrangian methodology is developed and implemented to investigate the multiphysics interactions. The well-designed parallel algorithms enable us to look at both canonical and practical configurations, including a temporal reacting shear layer, a turbulent reactive jet diluted with droplets and a simplified small-scale domestic fire suppression system. All these configurations are characterised by nonuniform droplet loading in the computational domain, fully three-dimensional simulation and the Lagrangian description for droplets. The number of traced droplets reaches the magnitude of 106 in some cases. DNS results with various physical parameters have been obtained, showing self-consistency and correct trends. In LES, to avoid arbitrary tuning of subgrid model coefficients, fully dynamic procedures have been designed following the Germano procedure and implemented for the main six subgrid models. LES of a heated plane jet, a reacting jet diluted with evaporating droplets and a simplified fire suppression system has been performed and analysed. Droplet effects on turbulence and combustion are quantified through examining the transport equations for the kinetic energy and internal energy of the reacting flow.

As roads become busier and automotive technology improves, there is considerable potential for driver assistance systems to improve the safety of road users. Longitudinal collision warning and collision avoidance systems are starting to appear on production cars to assist drivers when required to stop in an emergency. Many luxury cars are also equipped with stability augmentation systems that prevent the car from spinning out of control during aggressive lateral manoeuvres. Combining these concepts, there is a natural progression to systems that could assist in aiding or performing lateral collision avoidance manoeuvres. A successful automatic lateral collision avoidance system would require convergent development of many fields of technology, from sensors and instrumentation to aid environmental awareness through to improvements in driver vehicle interfaces so that a degree of control can be smoothly and safely transferred between the driver and vehicle computer. A fundamental requirement of any collision avoidance system is determination of a feasible path that avoids obstacles and a means of causing the vehicle to follow that trajectory. This research focuses on feasible trajectory generation and development of an automatic obstacle avoidance controller that integrates steering and braking action. A controller is developed to cause a specially modified car (a Mercedes `S' class with steer-by-wire and brake-by-wire capability) to perform an ISO 3888-2 emergency obstacle avoidance manoeuvre. A nonlinear two-track vehicle model is developed and used to derive optimal controller parameters using a series of simulations. Feedforward and feedback control is used to track a feasible reference trajectory. The feedforward control loops use inverse models of the vehicle dynamics. The feedback control loops are implemented as linear proportional controllers with a force allocation matrix used to apportion braking effort between redundant actuators. Two trajectory generation routines are developed: a geometric method, for steering a vehicle at its physical limits; and an optimal method, which integrates steering and braking action to make full use of available traction. The optimal trajectory is obtained using a multi-stage convex optimisation procedure. The overall controller performance is validated by simulation using a complex proprietary model of the vehicle that is reported to have been validated and calibrated against experimental data over several years of use in an industrial environment.

Walking is healthy, environmentally beneficial and sustainable to human society. Travellers increasingly are being encouraged to walk more. However, pedestrians’ interaction with motorised vehicles is a major constraint to their movement. Many innovative treatments have been developed to balance the two modes. Proper methods are required to evaluate and compare performances of different treatments to support decision making. Micro-simulation is a useful supplementary tool for such evaluation and comparison studies for its cost-effectiveness and non-intrusiveness. However, there is a significant gap between capabilities of existing simulation models and practical needs. New understandings of the Pedestrian-Vehicle Interaction (PVI) behaviour and corresponding micro-simulation models are required to conduct micro-simulation studies of the interaction process between the two modes to derive new knowledge of the mixed traffic. This dissertation presents the development and application of a micro-simulation model, PVISIM (Pedestrian-Vehicle Interaction SIMulation), to study PVI behaviour in a range of circumstances in an urban street environment. Key contributions relate to the collection of a substantial data base, development and validation of the model, an appreciation of the value of the approach and new understandings of PVI behaviour. A series of studies to measure behaviour based on the data collected in Beijing, China have been detailed. Intra vehicle and pedestrian behaviour models were developed and validated separately, incorporating the best available understandings from existing published studies and in accordance with the specific local data. The two modes were integrated by interpreting new findings from the study of microscopic interaction behaviour of the two modes. The complete model was validated against field data independent of those used in model development, covering a number of typical scenarios, including both unsignalised and signalised situations. The validated model was applied to study a typical unsignalised scenario by analysing system performances under different combinations of vehicular traffic and pedestrian crossing demand, in terms of efficiency, safety and environmental impact. Also, operations of different treatments including no-control, Zebra crossing, fixed-time signal crossing and Puffin crossing at two typical types of locations were compared. Interpretations and recommendations were given for each application. The results can be used to supplement existing guidelines for pedestrian related problems, and also contribute to the knowledge base to incorporate pedestrians into current micro-simulation tools in a more realistic way.

Orientador: Franco Giuseppe Dedini
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Dinâmica veicular é o estudo das interações entre o veículo, condutor e o ambiente bem como as reações de carga, sendo esta dividida em 3 grandes áreas: dinâmica longitudinal, vertical e lateral. Existem variações entre os métodos propostos pela literatura para o cálculo da dinâmica longitudinal do veículo, sendo que o objetivo deste trabalho é, por meio de simulações, compararem os resultados obtidos pelas diversas metodologias. Por meio de um modelo gerado com auxílio do programa de análise dinâmica de multicorpos Adams®, juntamente com o Simulink Matlab®, foram implementados os métodos de cálculo propostos pela literatura de forma a simular o comportamento de um veículo em função de uma demanda de potência gerada por meio do padrão de velocidades imposto pelos ciclos das normas brasileiras NBR6601 e NBR7024. Os resultados encontrados foram comparados por meio da correlação linear entre as curvas de torque resultantes do modelo dinâmico, possibilitando uma avaliação entre os resultados encontrados pelos diferentes métodos. Também foram avaliados o consumo de combustível, a influência da variação da massa do veículo e da estratégia de condução no comportamento dinâmico do veículo, bem como modelos complementares referentes a veículos híbridos e o efeito da adição de um modelo de embreagem no conjunto simulado
Abstract: Vehicular dynamics is the study of interactions between vehicle, driver and load reactions. The vehicular dynamics is divided into three areas: longitudinal, vertical and lateral. There are variations between the methods proposed in the literature to calculate the longitudinal dynamics of the vehicle. The purpose of this study is, through simulations; compare the results obtained by different methods. By means of a model generated by Adams® (Software of Multibody Dynamics Analysis) together with Simulink Matlab® were implemented the calculation methods proposed by literature to simulate the behavior of a vehicle according to a power demand resulting from the default speeds cycles required by Brazilian Standards NBR6601 and NBR7024. The results were compared using linear correlation between the couple curves resulting from the dynamic model, allowing an evaluation of the results reported by different methods. Were also evaluated: the fuel consumption and the influence of the mass vehicle variation, the driving strategy in the vehicle dynamic behavior, some complementary models of hybrid vehicles and the effect of add a clutch model
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

This thesis initially presents the work carried out on the research hypothesis –agent-based simulation is better than traditional discrete-event modelling. To test this assertion, a comparison of these two modelling approaches is made by way of a case study. The scenario, a global repair operation of a fleet of civil jet engines, is a real lifecycle costing example which involves logistics and is typical of problems commonly modelled using either of these paradigms. To carry out the comparison, the method involved building a discrete-event model which matched the functions of an existing agent-based model as closely as possible. Rigorous control was applied during its implementation phase by way of formal code walkthroughs and model dynamic testing. Among the internal metrics, lines of code provided an estimate for model size while the McCabe Cyclomatic Number measured structural complexity. The external software quality of maintainability was derived from these metrics and estimated by modelling experts through Delphi sessions. The dynamic performance of each model was determined by the execution times of successfully completed simulation runs over a range of engine fleet sizes. This research went on to develop a hybrid approach (which is currently the subject of a Rolls-Royce patent application) which draws on the strengths of both agent and discrete-event paradigms. In order to combine agent roles and discrete event processes, a new model was implemented using a three-layered architecture. A full fleet simulation was developed using this hybrid approach. Although the code size is slightly larger and run times slightly longer than the conventional model, the thesis argues that, crucially, it is more maintainable as it reduces the conceptual gap between problem and model.

Optimal control for multicopters is difficult in part due to the low processing power available, and the instability inherent to multicopters. Deep imitation learning is a method for approximating an expert control policy with a neural network, and has the potential of improving control for multicopters. We investigate the performance and reliability of deep imitation learning with trajectory optimization as the expert policy by first defining a dynamics model for multicopters and applying a trajectory optimization algorithm to it. Our investigation shows that network architecture plays an important role in the characteristics of both the learning process and the resulting control policy, and that in particular trajectory optimization can be leveraged to improve convergence times for imitation learning. Finally, we identify some limitations and future areas of study and development for the technology.
Optimal kontroll för multikoptrar är ett svårt problem delvis på grund av den vanligtvis låga processorkraft som styrdatorn har, samt att multikoptrar är synnerligen instabila system. Djup imitationsinlärning är en metod där en beräkningstung expert approximeras med ett neuralt nätverk, och gör det därigenom möjligt att köra dessa tunga experter som realtidskontroll för multikoptrar. I detta arbete undersöks prestandan och pålitligheten hos djup imitationsinlärning med banoptimering som expert genom att först definiera en dynamisk modell för multikoptrar, sedan applicera en välkänd banoptimeringsmetod på denna modell, och till sist approximera denna expert med imitationsinlärning. Vår undersökning visar att nätverksarkitekturen spelar en avgörande roll för karakteristiken hos både inlärningsprocessens konvergenstid, såväl som den resulterande kontrollpolicyn, och att särskilt banoptimering kan nyttjas för att förbättra konvergenstiden hos imitationsinlärningen. Till sist påpekar vi några begränsningar hos metoden och identifierar särskilt intressanta områden för framtida studier.

A supercavitating vehicle, a next-generation underwater vehicle capable of changing the paradigm of modern marine warfare, exploits supercavitation as a means to reduce drag and achieve extremely high submerged speeds. In supercavitating flows, a low-density gaseous cavity entirely envelops the vehicle and as a result the vehicle is in contact with liquid water only at its nose and partially over the afterbody. Hence, the vehicle experiences a substantially reduced skin drag and can achieve much higher speed than conventional vehicles. The development of a controllable and maneuvering supercavitating vehicle has been confronted with various challenging problems such as the potential instability of the vehicle, the unsteady nature of cavity dynamics, the complex and non-linear nature of the interaction between vehicle and cavity. Furthermore, major questions still need to be resolved regarding the basic configuration of the vehicle itself, including its control surfaces, the control system, and the cavity dynamics. In order to answer these fundamental questions, together with many similar ones, this dissertation develops an integrated simulation-based design tool to optimize the vehicle configuration subjected to operational design requirements, while predicting the complex coupled behavior of the vehicle for each design configuration. Particularly, this research attempts to include maneuvering flight as well as various operating trim conditions directly in the vehicle configurational optimization. This integrated approach provides significant improvement in performance in the preliminary design phase and indicates that trade-offs between various performance indexes are required due to their conflicting requirements. This dissertation also investigates trim conditions and dynamic characteristics of supercavitating vehicles through a full 6 DOF model. The influence of operating conditions, and cavity models and their memory effects on trim is analyzed and discussed. Unique characteristics are identified, e.g. the cavity memory effects introduce a favorable stabilizing effect by providing restoring fins and planing forces. Furthermore, this research investigates the flight envelope of a supercavitating vehicle, which is significantly different from that of a conventional vehicle due to different hydrodynamic coefficients as well as unique operational conditions.

Orientador: Milton Dias Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O resumo poderá ser visualizado no texto completo da tese digital
Abstract: The abstract is available with the full electronic document
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

This thesis concerns with the design and development of automatic flight controller strategies for the autonomous landing of fixed wing unmanned aircraft subject to severe environmental conditions. The Tactical Unmanned Aerial Vehicle (TUAV) designed at the Middle East Technical University (METU) is used as the subject platform. In the first part of this thesis, a dynamic model of the TUAV is developed in FORTRAN environment. The dynamic model is used to establish the stability characteristics of the TUAV. The simulation model also incorporates ground reaction and atmospheric models. Based on this model, the landing trajectory that provides shortest landing distance and smallest approach time is determined. Then, an automatic flight control system is designed for the autonomous landing of the TUAV. The controller uses a model inversion approach based on the dynamic model characteristics. Feed forward and mixing terms are added to increase performance of the autopilot. Landing strategies are developed under adverse atmospheric conditions and performance of three different classical controllers are compared. Finally, simulation results are presented to demonstrate the effectiveness of the design. Simulation cases include landing under crosswind, head wind, tail wind, wind shear and turbulence.

Orientador: Milton Dias Júnior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O desenvolvimento de novas tecnologias na área automotiva e as restrições cada vez mais apertadas com relação a emissões culminaram em veículos cada vez mais leves, silenciosos e potentes. Por este motivo, os trens de potência atuais são cada vez mais susceptíveis a fenômenos de NVH. Além disso, pelo fato de os motores atuais emitirem menor nível de ruído, alguns destes fenômenos tornam-se mais perceptíveis. Neste contexto se encaixa o trabalho atual. Sabe-se que muitos problemas desta área são solucionados realizando alterações no disco de embreagem, e por isto, neste trabalho estuda-se a influência dos parâmetros de seu pré amortecedor nos fenômenos de shuffle e clunk. São feitas análises do trem de potência linearizado, por este ser um procedimento muito comum na área de desenvolvimento deste sistema. Após isso, analisa-se o mesmo sistema, através de simulações numéricas, porém considerando não linearidades no disco de embreagem e nos engrenamentos, onde foi considerado o impact damping. Identifica-se os pares engrenados que mais contribuem para o surgimento do fenômeno de clunk, e a influência dos parâmetros do pré-amortecedor sobre ambos os fenômenos
Abstract: The development of new technologies on automotive engineering and the toughening emissions laws led to the design of lighter, more silent and more powerful vehicles. For this reason, today's powertrains are more prone to NVH phenomena. Furthermore, the noticeability of those phenomena is increased since newer engines produce lower noise levels. This is the subject in which this work fits into. It is known that many of the NVH phenomena can be attenuated by performing changes on the parameters of the clutch disc, and because of it, the influence of the parameters of the clutch damper on shuffle and clonk is studied in this work. For being a widely used procedure on the development of drivelines, a inear analysis is performed on a linearized model of a powertrain. After that, using umerical integration methods, further analyses are performed on a nonlinear model of the driveline, considering that the clutch disc and the gear meshes are nonlinearities. The latter's energy loss is modeled used impact damping. The geared pairs that contribute most for the clunk phenomenon are identified, and finally the influence of the parameters of the clutch damper on both phenomena are stated
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

Orientador: Robson Pederiva
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O objetivo deste trabalho é apresentar uma forma computacional eficaz de manipular a curva que representa o perfil dos camos, objetivando a sua aplicação em simulações computacionais e rotinas de otimização de um trem de válvulas. Ao longo dos anos, os motores de combustão interna têm sido pesquisados e aprimorados, seja na busca de maior potência, seja na busca de menor consumo de combustível. Um subsistema automotivo que afeta diretamente o desempenho dos motores é o sistema de acionamento de válvulas, que permite controlar a entrada e saída dos gases da câmara de combustão. Diversos pesquisadores têm estudado a cinemática e dinâmica do sistema de acionamento de válvulas para melhorar o desempenho do motor, focando nas características construtivas do perfil dos camos: ele tem ação preponderante sobre a dinâmica do sistema. Neste trabalho foi aplicado o método de otimização da evolução diferencial de modo a otimizar a resposta dinâmica da válvula de exaustão de um motor Diesel, modelada por um sistema de cinco graus de liberdade, utilizando o perfil do camo como variável de projeto. Em um dos estudos de caso obteve-se redução de aproximadamente 60% nos picos de aceleração no fechamento da válvula. Em outro estudo de caso a área sob a curva de aceleração foi maximizada, aumentando aproximadamente 9%. Também Foi demonstrado um artifício matemático para que fossem considerados dois objetivos na otimização, já que os esforços para maximizar a área sob a curva de aceleração e minimizar a aceleração mostraram-se antagônicos. Por fim, mostrou-se que o perfil ótimo do camo varia com a rotação do motor
Abstract: The objective of this work is to present an efficient computational way to manipulate the curve representing the cam profile, aiming their application in computer simulations and optimization routines for a valvetrain. Over the years internal combustion engines have been researched and improved, be it in the search for more power or be it in the search for lower fuel consumption. An automotive subsystem that directly affects the performance of the engine is the valvetrain system. This system allows the control of the admittance and release of gases from the combustion chamber. Several researchers have studied the kinematics and dynamics of the valve actuation system to improve engine performance focusing in the design characteristics of the profile of the cams: it has a predominant action on the dynamics of the system. In this work the optimization method of differential evolution was applied to optimize a Diesel engine exhaust valve's dynamic response using the cam profile as a design variable. In one case of study the acceleration peak had a 60% reduction. In another case of study the area under the valve's displacement curve was increased by 9%. A mathematical scheme was demonstrated to consider tow objectives for the parameters acceleration and area showed to be ambivalent. In addition, it was also demonstrated that the optimal cam profile varies with the engine speed
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

Increasing interest in renewable energy sources for electricity production complying with stricter environmental policies has greatly contributed to further optimisation of existing devices and the development of novel renewable energy generation systems. The research and development of these advanced systems is tightly bound to the use of reliable design methods, which enable accurate and efficient design. Reynolds-averaged Navier-Stokes Computational Fluid Dynamics is one of the design methods that may be used to accurately analyse complex flows past current and forthcoming renewable energy fluid machinery such as wind turbines and oscillating wings for marine power generation. The use of this simulation technology offers a deeper insight into the complex flow physics of renewable energy machines than the lower-fidelity methods widely used in industry. The complex flows past these devices, which are characterised by highly unsteady and, often, predominantly periodic behaviour, can significantly affect power production and structural loads. Therefore, such flows need to be accurately predicted. The research work presented in this thesis deals with the development of a novel, accurate, scalable, massively parallel CFD research code COSA for general fluid-based renewable energy applications. The research work also demonstrates the capabilities of newly developed solvers of COSA by investigating complex three-dimensional unsteady periodic flows past oscillating wings and horizontal-axis wind turbines. Oscillating wings for the extraction of energy from an oncoming water or air stream, feature highly unsteady hydrodynamics. The flow past oscillating wings may feature dynamic stall and leading edge vortex shedding, and is significantly three-dimensional due to finite-wing effects. Detailed understanding of these phenomena is essential for maximising the power generation efficiency. Most of the knowledge on oscillating wing hydrodynamics is based on two-dimensional low-Reynolds number computational fluid dynamics studies and experimental testing. However, real installations are expected to feature Reynolds numbers of the order of 1 million and strong finite-wing-induced losses. This research investigates the impact of finite wing effects on the hydrodynamics of a realistic aspect ratio 10 oscillating wing device in a stream with Reynolds number of 1.5 million, for two high-energy extraction operating regimes. The benefits of using endplates in order to reduce finite-wing-induced losses are also analyzed. Three-dimensional time-accurate Reynolds-averaged Navier-Stokes simulations using Menter's shear stress transport turbulence model and a 30-million-cell grid are performed. Detailed comparative hydrodynamic analyses of the finite and infinite wings highlight that the power generation efficiency of the finite wing with sharp tips for the considered high energy-extraction regimes decreases by up to 20 %, whereas the maximum power drop is 15 % at most when using the endplates. Horizontal-axis wind turbines may experience strong unsteady periodic flow regimes, such as those associated with the yawed wind condition. Reynolds-averaged Navier-Stokes CFD has been demonstrated to predict horizontal-axis wind turbine unsteady flows with accuracy suitable for reliable turbine design. The major drawback of conventional Reynolds-averaged Navier-Stokes CFD is its high computational cost. A time-step-independent time-domain simulation of horizontal-axis wind turbine periodic flows requires long runtimes, as several rotor revolutions have to be simulated before the periodic state is achieved. Runtimes can be significantly reduced by using the frequency-domain harmonic balance method for solving the unsteady Reynolds-averaged Navier-Stokes equations. This research has demonstrated that this promising technology can be efficiently used for the analyses of complex three-dimensional horizontal-axis wind turbine periodic flows, and has a vast potential for rapid wind turbine design. The three-dimensional simulations of the periodic flow past the blade of the NREL 5-MW baseline horizontal-axis wind turbine in yawed wind have been selected for the demonstration of the effectiveness of the developed technology. The comparative assessment is based on thorough parametric time-domain and harmonic balance analyses. Presented results highlight that horizontal-axis wind turbine periodic flows can be computed by the harmonic balance solver about fifty times more rapidly than by the conventional time-domain analysis, with accuracy comparable to that of the time-domain solver.

Le Contrôle Global du Châssis (CGC) est une tâche cruciale dans les véhicules intelligents. Il consiste à assister le conducteur par l'intermédiaire de plusieurs fonctionnalités automatisées, notamment à des fins de sécurité active et de confort. Etant donné que les dynamiques de ces fonctionnalités sont interconnectées, les performances attendues sont parfois contradictoires. Par conséquent, le CGC consiste à coordonner les différents systèmes ADAS « Advanced Driving Assistance Systems » afin de créer des synergies entre les dynamiques interconnectées pour améliorer les performances globales du véhicule. Plusieurs stratégies de coordination puissantes ont déjà été développées, soit dans le monde académique, soit dans le monde industriel pour gérer ces interconnexions. Du fait que les besoins en matière de sécurité active augmentent d'un côté et que la technologie pouvant être intégrée dans les véhicules évolue, une intense activité de recherche et développement est toujours en cours dans le domaine du contrôle global du châssis. Cette thèse analyse différentes interconnexions dynamiques et développe des nouvelles stratégies CGC dans lesquelles le braquage actif avant, le freinage différentiel actif et les suspensions actives sont coordonnés - tous ensemble ou partiellement afin d'améliorer les performances globales du véhicule, à savoir l'évitement du renversement, la stabilité latérale, le confort de conduite (manœuvrabilité) et confort des passagers. Plusieurs architectures multicouches formées par trois couches hiérarchiques sont proposées. La couche inférieure représente les actionneurs implémentés dans le véhicule qui génèrent leurs entrées de commande en fonction des ordres envoyés depuis la couche intermédiaire. La couche intermédiaire est la couche de contrôle qui est chargée de générer les entrées de contrôle qui minimisent les erreurs entre les variables d'état souhaitées et réelles du véhicule, à savoir les mouvements de lacet, de dérapage, de roulis, de tangage et de soulèvement, quelle que soit la situation de conduite. La couche supérieure est la couche de prise de décision. Elle surveille instantanément la dynamique du véhicule selon différents critères, puis génère des paramètres de pondération pour adapter les performances des contrôleurs en fonction des conditions de conduite, c'est-à-dire pour améliorer la manœuvrabilité, la stabilité latérale, l'évitement du renversement et le confort de conduite du véhicule. Les architectures proposées se diffèrent dans les couches de contrôle et de décision en fonction des actionneurs intégrés proposés. Par exemple, les couches de décisions se diffèrent par les critères qui surveillent la dynamique du véhicule et la manière dont la décision est prise (logique floue ou relations explicites). Les couches de contrôle se diffèrent par leurs structures, où des contrôleurs centralisés et décentralisés sont développés. Dans l'architecture centralisée, un seul contrôleur optimal MEMS Multi-Entrées-Multi-Sorties génère les entrées de commande optimales basées sur la technique de commande LPV/H∞. Dans l'architecture décentralisée, les contrôleurs sont découplés. La technique STSM (Super-Twisting Sliding Mode) est appliquée pour déduire chaque entrée de commande. Les architectures proposées sont testées et validées sur le simulateur professionnel SCANeR Studio et sur un modèle complexe non linéaire du véhicule. La simulation montre que toutes les architectures sont pertinentes pour le contrôle global du châssis. Celle centralisée est optimale, complexe et garantit la stabilité globale, tandis que celle décentralisée ne garantit pas la stabilité globale, mais elle est intuitive, simple et robuste
Global Chassis Control (GCC) is crucial task in intelligent vehicles. It consists of assisting the driver by several automated functionalities especially for active safety and comfort purposes. Due to the fact that the dynamics of these functionalities are interconnected, thus the awaited performances are sometimes contradictory. Hence, the main task in GCC field is to coordinate the different Advanced Driving Assistance Systems (ADAS) to create synergies between the interconnected dynamics in order to improve the overall vehicle performance. Several powerful coordination strategies have already been developed either in the academic world or in the industrial one to manage these interconnections. Because the active safety needs are increasing from one side, and the technology that can be embedded into vehicles is evolving, an intense research and development is still involved in the field of global chassis control. This thesis analyzes di_erent dynamics interconnections and develops new several GCC strategies where the Active Front Steering, Active Differential Braking, and the Active Suspensions are coordinated - all together or partially - to improve the vehicle overall performance i.e. the rollover avoidance, the lateral stability, the driving comfort (maneuverability), and the ride comfort. Several multilayer architectures formed by three hierarchical layers are proposed. The lower layer represents the actuators implemented into the vehicle which generate their control inputs based on the orders sent from the middle layer. The middle layer is the control layer which is responsible to generate the control inputs that minimize the errors between the desired and actual vehicle state variables i.e. the yaw, side-slip, roll, pitch, and heave motions, regardless of the driving situation. The higher layer is the decision making layer. It instantly monitors the vehicle dynamics by di_erent criteria, then, it generates weighting parameters to adapt the controllers performances according to the driving conditions i.e. to improve the vehicle's maneuverability, lateral stability, rollover avoidance, and ride comfort. The proposed architectures di_er in the control and decision layers depending on the proposed embedded actuators. For instance, the decision layers di_er in the monitored criteria and the way the decision is taken (fuzzy logic or explicit relations). The control layers di_er in structure, where centralized and decentralized controllers are developed. In the centralized architecture, one single Multi-Input-Multi-Output optimal controller generates the optimal control inputs based on the Linear Parameter Varying (LPV)/H-infinity control technique. In the decentralized architecture, the controllers are decoupled, where the Super-Twisting Sliding Mode (STSM) technique is applied to derive each control input apart. The proposed architectures are tested and validated on the professional simulator « SCANeR Studio » and on a Full vehicle nonlinear complex model. Simulation shows that all architectures are relevant to the global chassis control. The centralized one is optimal, complex and overall stability is guaranteed, while the decentralized one does not guarantee the overall stability, but it is intuitive, simple, and robust

A driving simulator reproduces the essential features of a vehicle and provides an interface for direct human operation. It provides a safe and less expensive way of training people how to drive. Against the backdrop of a comprehensive literature survey on driving simulators and their applications, this thesis endeavours to make five unique contributions. Many of the military armoured vehicles have eight wheels, are able to cross trenches of approximately two meters, and can climb steps of as high as one meter. Available research, however, focuses primarily on the vehicle dynamics modelling of commercial four wheel vehicles. In this thesis, a mathematical model is given for simulating the vehicle dynamics of an eight wheel vehicle over rough terrain, taking into account the limitations of real-time driving simulation. A discussion of the model by Janse van Rensburg et al. is contained in a paper which is currently under review by the International Journal of Modern Physics C (IJMPC). To prove the validity of a vehicle model, it is necessary to provide a method of testing the model. Detail about the vehicle dynamics model used is not always available when developed by a third party. This thesis describes a “black box” testing method for the verification of a vehicle dynamics model. An article regarding this matter by Janse van Rensburg et al. has been submitted to the IJMPC and is currently under review. Normally, the focus on driving simulators is on the modelling of realistic vehicle dynamics models. However, the design of a realistic simulation environment is of equal importance. A human driver usually steers one vehicle, but the rest of the vehicles used in the simulation should be managed by a computer program. An automatic driver model is described to be used within the simulation environment. The current presentation is based on the published paper [86] by Janse van Rensburg et al. (IJMPC, 16(6):895-908, 2005). An understanding of three-dimensional coordinate system transformations is one of the most important parts of a flight or driving simulator. Although the procedure of using Euler angles for coordinate system transformations is nothing new, almost no literature is available of how it can be applied on more complex situations. This thesis supplies more information on how a program language such as C++ could be used to apply more complex coordinate transformations in real-life situations. Results appeared in the published paper by Janse van Rensburg et al. (IJMPC, 16(6):909-920, 2005). Finally the use of vocoders is proposed for the modelling of engine sound. For a driving simulator which should be an exact replica of a certain vehicle, an accurate sound model is of extreme importance. By using vocoders, a technique used for the manipulation of voice, a higher level of accuracy and realism can be obtained than with the methods currently discussed in literature. A paper on this matter, compiled by Janse van Rensburg et al. is currently under review by the IJMPC.
Prof. M. A. van Wyk

In this dissertation, a group of vehicle dynamics simulation tools is developed with two primary goals: to accurately represent vehicle behavior and to provide insight that improves the understanding of vehicle performance. Three tools are developed that focus on tire modeling, vehicle modeling and lap time simulation. Tire modeling is based on Nondimensional Tire Theory, which is extended to provide a flexible model structure that allows arbitrary inputs to be included. For example, rim width is incorporated as a continuous variable in addition to vertical load, inclination angle and inflation pressure. Model order is determined statistically and only significant effects are included. The fitting process is shown to provide satisfactory fits while fit parameters clearly demonstrate characteristic behavior of the tire. To represent the behavior of a complete vehicle, a Nondimensional Tire Model is used, along with a three degree of freedom vehicle model, to create Milliken Moment Diagrams (MMD) at different speeds, longitudinal accelerations, and under various yaw rate conditions. In addition to the normal utility of MMDs for understanding vehicle performance, they are used to develop Limit Acceleration Surfaces that represent the longitudinal, lateral and yaw acceleration limits of the vehicle. Quasi-transient lap time simulation is developed that simulates the performance of a vehicle on a predetermined path based on the Limit Acceleration Surfaces described above. The method improves on the quasi-static simulation method by representing yaw dynamics and indicating the vehicle's stability and controllability over the lap. These improvements are accomplished while maintaining the simplicity and computational efficiency of the two degree of freedom method.
Graduation date: 2013

Investigates ride dynamic aspects of high mobility wheeled/tracked off-road vehicles through comprehensive computer modeling of the vehicle-terrain dynamical system and field validation of the computer model predictions.

In the modem automotive industry product times to market are being increasingly compressed. In the earthmoving and construction machine industry this is also true with the manufacturer having to respond to new customer requirements quickly and decisively. Virtual prototyping is a vital tool in the vehicle engineer's armoury, allowing a large portion of developmental investigation to be done on the virtual model with the attendant savings in time and cost and allowing often dangerous manoeuvres to be predicted and investigated prior to actual physical prototype testing. The University of Natal BELL Equipment collaborative effort involves the vehicle dynamics modelling and model validation of a BELL Equipment manufactured B40C Articulated Dump Truck (ADT). The modelling was completed using the multibody system (MBS) simulation software package, ADAMS. Initial modelling and simulation results are presented with specific attention paid to the introduction of valid data for compliant joints in the MBS as well as modelling of the tire. The physical testing of the ADT is also presented as well as a discussion of the data acquisition system. Key results from the physical testing of the ADT are also presented and discussed.
Thesis (M.Sc.Eng.)-University of Natal,Durban, 2003.