The life of railway wheels and rails has been decreasing in recent years. This is mainly caused by more traffic and running at higher vehicle speed. A higher speed usually generates higher forces, unless compensated by improved track and vehicle designs, in the wheel-rail contact, resulting in more wear and rolling contact fatigue (RCF) damage to the wheels and rails. As recently as 15 years ago, RCF was not recognised as a serious problem. Nowadays it is a serious problem in many countries and ''artificial wear'' is being used to control the growth of cracks by preventive re-profiling and grinding of, respectively, the wheels and rails.  This can be used because a competition exists between wear and surface initiated RCF: At a high wear rate, RCF does not have the opportunity to develop further. Initiated cracks are in this case worn off and will not be able to propagate deep beneath the surface of the rail or wheel. When wheel-rail damage in terms of wear and RCF can be predicted, measures can be taken to decrease it. For example, the combination of wheel and rail profiles, or the combination of vehicle and track, can be optimised to control the damage. Not only can this lead to lower maintenance costs, but also to a safer system since high potential risks can be detected in advance. This thesis describes the development of a wheel-rail life prediction tool with regard to both wear and surface-initiated RCF. The main goal of this PhD work was to develop such a tool where vehicle-track dynamics simulations are implemented. This way, many different wheel-rail contact conditions which a wheel or a rail will encounter in reality can be taken into account. The wear prediction part of the tool had already been successfully developed by others to be used in combination with multibody simulations. The crack prediction part, however, was more difficult to be used in combination with multibody simulations since crack propagation models are time-consuming. Therefore, more concessions had to be made in the crack propagation part of the tool, since time-consuming detailed modelling of the crack, for example in Finite Elements models, was not an option. The use of simple and fast, but less accurate, crack propagation models is the first step in the development of a wheel-rail life prediction model. Another goal of this work was to verify the wheel-rail prediction tool against measurements of profile and crack development. For this purpose, the wheel profiles of trains running on the Stockholm commuter network have been measured together with the crack development on these wheels. Three train units were selected and their wheels have been measured over a period of more than a year. The maximum running distance for these wheels was 230,000 km. A chosen fatigue model was calibrated against crack and wear measurements of rails to determine two unknown parameters.  The verification of the prediction tool against the wheel measurements, however, showed that one of the calibrated parameters was not valid to predict RCF on wheels. It could be concluded that wheels experience relatively less RCF damage than rails. Once the two parameters were calibrated against the wheel measurements, the prediction tool showed promising results for predicting both wear and RCF and their trade-off. The predicted position of the damage on the tread of the wheel also agreed well with the position found in the measurements. / <p>QC 20150526</p>

O uso de simulações computacionais no campo da engenharia vem se tornando cada vez mais freqüente. Este trabalho aplica diferentes tipos de análise, Método Multicorpos e Método dos Elementos Finitos, para estudos dinâmicos e estruturais, como ferramenta de auxílio no desenvolvimento de veículos terrestres. Através de métodos de integração numérica e posteriormente a utilização do método dos multicorpos, uma suspensão independente dianteira de um veículo foi isolada, considerada como um conjunto de corpos unidos por juntas, movidos por forças e restringidos por batentes. O comportamento dinâmico do sistema foi determinado submetendo o modelo a entradas provenientes do pavimento. O Método dos Elementos Finitos já é considerado como ferramenta potente para o cálculo estrutural. Para abordar tal tema, foi construído um modelo discretizado em Elementos Finitos de um veículo comercial completo. Este modelo foi submetido a simulações de situações de situações reais quasi-estáticas e dinâmicas, utilizando algoritmos implícito e explícito, dependendo do fenômeno considerado. A partir destes, puderam ser verificadas a performance estrutural e a segurança passiva do veículo arremessado a obstáculos cotidianos. O último estudo retrata que com a fusão dos métodos é possível, através de programas dedicados, prever a dinâmica de um modelo encriptado de um boneco tipo HYBRIDIII, quando submetido a um pulso de desaceleração no interior de um veículo com e sem bolsa de segurança(airbag). Todos os resultados obtidos foram comparados à realidade ou \"benchmark\". Os obstáculos enfrentados permitiram definir qual ferramenta melhor se encaixa num contexto de desenvolvimento dentro de uma corporação. / The use of computational tools in various engineering fields has increased over the last years. Mathematical modelling is identified as being the most adequate tool for simulating real service conditions along several product development phases. This work investigates different dynamic and structural analysis used for ground vehicle development tools. By numerical integration using the Multibody system method, an independent suspension was isolated from the car and considered as bodies connected by joints, moved by forces and constrained by stoppers. The dynamic behaviour of the systems was predicted when submitted to input exclusively from the ground. The Finite Element Method is already considered a very powerful simulation tool. In order to study the method, a full vehicle model was built and submitted to quasi-static and dynamic inputs. Both implicit and explicit methods were used to simulate different situations. The vehicle had its structural performance analysed related to durability and safety aspects. The last analysis that shows the fusion of methods is possible using dedicated computational tools to simulate the passenger kinematics by using an encrypted dummy and an airbag model under a deceleration pulse as input. AlI the results were compared to experimental and benchmark results. Also the difficulties emerged from each tool were pointed out in order to define which is the most appropriate within the development context.

A capacidade de simulação nos atributos de dinâmica veicular tem crescido nos últimos anos, especialmente para os atributos de handling (manobrabilidade e estabilidade) e steering (dirigibilidade). Entretanto, as simulações de ride (em especial dos fenômenos de ride secundário) continuam muito dependentes de modelos sofisticados de pneus. Tais modelos devem ser capazes de simular fenômenos de freqüência mais alta tais como impacto e transmissibilidade de aspereza em três direções. Este trabalho apresenta uma abordagem semi-analítica para o problema de simulação de fenômenos de ride, através do uso de dados de medição em pista gerados através de transdutores de força (wheel force transducers, WFTs). Tais transdutores são tipicamente usados para fins de cascateamento de cargas e durabilidade. Através do uso de tais carregamentos, é possível simular fenômenos de ride em toda a faixa de frequência de estudo (até 8 Hz para ride primário e até 100 Hz para ride secundário) sem a necessidade de um modelo específico de pneu. Usando um modelo de veículo completo construído no software ADAMS, são apresentados dados de correlação com o veículo real e um estudo de caso através da alteração de propriedades de elementos tais como amortecedores, coxins e buchas de suspensão. / Vehicle dynamics CAE capabilities has increased in the past few years, specially, for handling and steering attributes. However, secondary ride simulations are still highly depended on the tire model. Such tire model must be capable to simulate high order phenomenon such as impact and harshness transmissibility in three directions. This dissertation presents a semi-analytical approach to the ride phenomena simulation problem, using data gathered via wheel force transducers (WFTs) that are typically used for load cascading and durability purposes. Using such load histories, it becomes possible to simulate ride phenomena through the whole typical ride frequency range (up to 8 Hz for primary ride and up to 100 Hz for secondary ride) without the necessity of using a special tire model. The results obtained from this approach using a complete car model developed using ADAMS software showed a very good correlation between measured data and simulations. Then on this work a case study using different properties for components such as shock abosrbers, engine mounts and suspension bushings is conducted in order to show the method\'s potential for ride optimization.

A numerical scheme to simulate time-domain motion responses of multibody floating systems has been successfully proposed. This scheme is integrated into a time-domain simulation tool, with fully coupled hydrodynamic coefficients obtained from the hydrodynamic software - WAMIT which solves the Boundary Value Problem (BVP). The equations of motion are transformed into standard state-space format, using the constant coefficient approximation and the impulse response function method. Thus the Ordinary Differential Equation (ODE) solvers in MATLAB can be directly employed. The time-domain responses of a single spar at sea are initially obtained. The optimal Linear Quadratic Regulator (LQR) controller is further applied to this single spar, by assuming that the Dynamic Positioning (DP) system can provide the optimized thruster forces. Various factors that affect the controlling efficiency, e.g., the time steps ∆τ and ∆t, the weighting factors(Q,R), are further investigated in detail. Next, a two-body floating system is studied. The response amplitude operators (RAOs) of each body are calculated and compared with the single body case. Then the effects of the body-to-body interaction coefficients on the time-domain responses are further investigated. Moreover, the mean drift force is incorporated in the DP system to further mitigate the motion responses of each body. Finally, this tool is extended to a three-body floating system, with the relative motions between them derived.

Modelling mechanical systems using symbolic equations can provide many advantages over the more widely-used numerical methods of modelling these systems. The use of symbolic equations produces more efficient models, which can be used for many purposes such as real-time simulation and control. However, the number, complexity, and computational efficiency of these equations is highly dependent on which coordinate set was used to model the system. One method of modelling a mechanism's topology and formulating its symbolic equations is to model the system using a graph-theoretical approach. This approach models mechanisms using a linear graph, from which spanning trees can be used to define a mechanism's coordinate set. This report develops two tree selection algorithms capable of estimating the tree set, and hence coordinate set, that produces models having the fastest forward dynamic simulation times. The first tree selection algorithm is a heuristic-based algorithm that tries to find the coordinate set containing the minimal possible number of modelling variables. Most of this algorithm's heuristics are based on tree selection criteria found in the literature and on observations of a series of benchmark problems. It uses the topology information provided by a system's graph to find the coordinates set for the given system that produce very low simulation times of the system. The second tree selection algorithm developed in this report also uses graph theory. It bases most of its heuristics on observations of one of the methods developed to obtain a mechanical system's symbolic equations using graph theory. This second algorithm also makes use of, and improves upon, a few of the heuristics developed in the first tree selection algorithm. A series of examples for both algorithms will demonstrate the computational efficiency obtained by using the modelling variables found by the automated tree selection algorithms that are proposed in this report.

Modelling mechanical systems using symbolic equations can provide many advantages over the more widely-used numerical methods of modelling these systems. The use of symbolic equations produces more efficient models, which can be used for many purposes such as real-time simulation and control. However, the number, complexity, and computational efficiency of these equations is highly dependent on which coordinate set was used to model the system. One method of modelling a mechanism's topology and formulating its symbolic equations is to model the system using a graph-theoretical approach. This approach models mechanisms using a linear graph, from which spanning trees can be used to define a mechanism's coordinate set. This report develops two tree selection algorithms capable of estimating the tree set, and hence coordinate set, that produces models having the fastest forward dynamic simulation times. The first tree selection algorithm is a heuristic-based algorithm that tries to find the coordinate set containing the minimal possible number of modelling variables. Most of this algorithm's heuristics are based on tree selection criteria found in the literature and on observations of a series of benchmark problems. It uses the topology information provided by a system's graph to find the coordinates set for the given system that produce very low simulation times of the system. The second tree selection algorithm developed in this report also uses graph theory. It bases most of its heuristics on observations of one of the methods developed to obtain a mechanical system's symbolic equations using graph theory. This second algorithm also makes use of, and improves upon, a few of the heuristics developed in the first tree selection algorithm. A series of examples for both algorithms will demonstrate the computational efficiency obtained by using the modelling variables found by the automated tree selection algorithms that are proposed in this report.

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A co-simulation methodology is explored whereby a finite element code and a multi-body dynamics code featuring flexible cantilevered beams can be coupled and interactively executed. The floating frame of reference formulation is used to develop the equations of motion. The floating frame is fixed at the blade root. Such a formulation results in ordinary differential equations without added algebraic constraints. A variety of loose coupling and tight coupling schemes are examined for this problem. To synchronize the coupling variables, a Gauss-Seidel type iterative algorithm is used. The resulting fixed-point iterations are accelerated using Aitken’s adaptive relaxation technique. The methodology is evaluated for FAST, a wind turbine aeroelastic simulation code developed by NREL. As with FAST, many multi-body codes which can model flexibility employ modal methods. A proposed addition for FAST to simulate flexible effects using a finite element method module offers a potential to include a variety of non-linearities and also provides possibilities for using a high-fidelity aerodynamics module. The coupling schemes are compared and their applicability and limitations for different scenarios are pointed out. Results validating the approach are provided.

This licentiate thesis deals with effective simulation of multibody dynamic systems in the product development process. Previous work to make simulation more effective has concentrated on developing faster calculation methods. Instead, this approach is to make the process of multibody dynamics simulation more effective by structuring of products, simulation models and their usage. Efforts have been made to clarify how computer tools are used in product development in industry today. Insight into the two domains of product development and multibody dynamics is given. These domains have traditionally been separated but the introduction of concurrent engineering and faster computers puts new demands on the integration of computer support and analysis in the development process. A proposal for performing the multibody dynamics methodology in a modular way in the product development process is given based on the performed work.

O objetivo do trabalho é melhorar o controle do comportamento dinâmico sob excitação vertical de um modelo veicular completo levando em consideração os três movimentos principais, de elevação (heave), balanço (pitch) e de rolagem (roll), em termos de aceleração. Com essa finalidade desenvolve-se a programação necessária para implementação de um modelo de veículo completo de 7 GDL no programa MATLAB® que interage com o sistema de controle ativo desenvolvido em diagrama de blocos no programa Simulink®. Em seguida, o desempenho do modelo é avaliado através de programas desenvolvidos de excitações de estrada com perfil senoidal e randômico. Os resultados obtidos mostram que o movimento da massa suspensa, em termos de aceleração, acima e abaixo do valor da frequência natural da roda pode ser diminuído pela filtragem dos coeficientes de mola e amortecimento através de um laço de controle interno, mais a utilização de amortecimento skyhook das velocidades de elevação, balanço e rolagem com um laço de controle externo. A atenuação das constantes de mola abaixo da frequência do corpo do veículo reduz as perturbações da estrada, mas podem bater nos limitadores do percurso da suspensão. / The aim of this work is to improve the control of the dynamic behavior under vertical excitation of a full vehicular model whilst taking into consideration the three main movements of heave, pitch and roll in terms of acceleration. With this goal in mind, the necessary programming was carried out for the implementation of a full vehicular model of 7 DOF using the software MATLAB® which interacts with the active control system developed via blocks diagram using the software Simulink®. Following on from that, the performance of the model is evaluated by means of programmes developed from road excitations with a sinusoidal and random profile. The results show that the motion of the sprung mass, in terms of acceleration, above and below the natural frequency of the wheel can be reduced by filtering the spring and damping coefficients through an internal control loop, plus the usage of skyhook damping of heave, pitch and roll velocities with an external control loop. The mitigation of the spring constants below the frequency of the body of the vehicle reduces the excitations of the road, but may strike against the path limiters of the suspension.