The diploma thesis deals with vehicle movement dynamics and defining a theoretical model for software simulation of vehicle passing a given trajectory, while main aim is time minimization driving mode. Simulation (algorithm for computing speed profile) is then applicated for passing experimental vehicle along Masaryk circuit in Brno. At the end, we optimize chosen vehicle parameters with derivate-free algorithms Multilevel Coordinate Search and Particle Swarm.

With an increasing need for accurate full vehicle models, a sensitivity analysis of the modelling of tyres depending on their age and wear was conducted. This included a sensitivity analysis into the accuracy of acquiring the tyre stiffnesses on a static test setup. An FTire model is developed with the aim to update this model with basic tests to give a more accurate representation of the aged or worn tyre. A well-researched and documented method is used to artificially age the tyres. During the aging process the tyre was statically tested to monitor the potential changes in characteristics. Tyres were also worn on a dynamic test setup and periodically tested to monitor the property changes. These tests included both static and dynamic measurements. The results indicate that the vertical and longitudinal stiffnesses of the tyre have convincing dependencies on the age and wear of the tyre. While the aging process was a trustworthy method, the wear process created irregular wear across and around the tyre subsequently skewing the results. Simple methods of updating the FTire tyre model without re-parameterising the model completely, was found to be effective in accounting for age and wear. / Dissertation (MEng)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

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Mechanical systems always operate under some degree of uncertainty, which can be due to the inherent properties of the system parameters, to random inputs or external excitations, to poorly known parameters in the interface between different systems, or to inadequate knowledge of the dynamic process. Also, mechanical systems are large and highly nonlinear, while the magnitude of uncertainties may be very large. This dissertation addresses the critical need for understanding of the stochastic nature of mechanical system, especially vehicle and terramechanics systems, and need for developing efficient computational tools to model mechanical systems in the presence of parametric and external uncertainty. This dissertation investigates the influence of parametric and external uncertainties on vehicle dynamics and terramechanics. The uncertainties studied include parametric uncertainties, stochastic external excitations, and random variables between vehicle-terrain and vehicle-soil/snow interface. The methodology developed has been illustrated on a stochastic vehicle-terrain interaction model, a stochastic vehicle-soil interaction model, two stochastic tire-snow interaction models, and two stochastic tire-force relations. The uncertainties are quantified and propagated through vehicle and terramechanics systems using a polynomial chaos approach. Algorithms which can predict the geometry of the contact patch and the interfacial forces and torques on the vehicle-soil interfaces are developed. All stochastic models and algorithms are simulated for various scenarios and maneuvers. Numerical results are analyzed from the computational effort point of view, or from the angle of vehicle dynamics and terramechanics, and provide a deeper understanding of the evolution of stochastic vehicle and terramechanics systems. They can also be used in guiding vehicle design and development. This dissertation represents a pioneer study on stochastic vehicle dynamics and terramechanics. Moreover, the methodology developed is not limited to such systems. Any mechanical system with uncertainties can be treated using the polynomial chaos approach presented, considering their specific characteristics. / Ph. D.

The tire is one of the most complex subsystems of the vehicle. It is, however, the least understood of all the components of a car. Without a good tire model, the vehicle simulation handling response will not be realistic, especially for maneuvers that require a combination of braking/traction and cornering. Most of the simplified theoretical developments in tire modeling, however, have been limited to on-road tire models. With the availability of powerful computers, it can be noted that majority of the work done in the development of off-road tire models have mostly been focused on creating better Finite Element, Discrete Element, or Boundary Element models. The research conducted in this study deals with the development of a simplified tire brush-based tire model for on-road simulation, together with a simplified off-road wheel/tire model that has the capability to revert back to on-road trend of behavior on firmer soils. The on-road tire model is developed based on observations and insight of empirical data collected by NHSTA throughout the years, while the off-road tire model is developed based on observations of experimental data and photographic evidence collected by various terramechanics researchers within the last few decades. The tire model was developed to be used in vehicle dynamics simulations for engineering mobility analysis. Vehicle-terrain interaction is a complex phenomena governed by soil mechanical behavior and tire deformation. The theoretical analysis involved in the development of the wheel/ tire model relies on application of existing soil mechanics theories based on strip loads to determine the tangential and radial stresses on the soil-wheel interface. Using theoretical analysis and empirical data, the tire deformation geometry is determined to establish the tractive forces in off-road operation. To illustrate the capabilities of the models developed, a rigid wheel and a flexible tire on deformable terrain is implemented and output of the model was computed for different types of soils; a very loose and deformable sandy terrain and a very firm and cohesive Yolo loam terrain. The behavior of the wheel/tire model on the two types of soil is discussed. The outcome of this work shows results that correlate well with the insight from experimental data collected by various terramechanics researchers throughout the years, which is an indication that the model presented can be used as a subsystem in the modeling of vehicle-terrain interaction to acquire more insight into the coupling between the tire and the terrain. / Ph. D.

Effectively modeling the acceleration behavior of vehicles is an important consideration in a variety of transportation engineering applications. The acceleration profiles of vehicles are important in the geometric design of roadways and are used to model vehicle behavior in simulation software packages. The acceleration profile of the vehicle is also a critical parameter in fuel consumption and emissions models. This paper develops and validates a vehicle dynamics model to predict the maximum acceleration rates of passenger vehicles. The model is shown to be superior to other similar models in that it accurately predicts speed and acceleration profiles in all domains and for a variety of vehicle types. The paper also modifies the model by introducing a reduction factor, which enables the model to predict the typical acceleration patterns for different driver types. The reduction factors for the driving population are shown to follow a normal distribution with a mean of 0.60 and a standard deviation of 0.08. The paper also provides new data sets containing maximum and typical acceleration profiles for thirteen different vehicles and twenty different drivers. / Master of Science

Multibody dynamics simulations are currently widely accepted as valuable means for dynamic performance analysis of mechanical systems. The evolution of theoretical and computational aspects of the multibody dynamics discipline make it conducive these days for other types of applications, in addition to pure simulations. One very important such application is design optimization for multibody systems. Sensitivity analysis of multibody system dynamics, which is performed before optimization or in parallel, is essential for optimization. Current sensitivity approaches have limitations in terms of efficiently performing sensitivity analysis for complex systems with respect to multiple design parameters. Thus, we bring new contributions to the state-of-the-art in analytical sensitivity approaches in this study. A direct differentiation method is developed for multibody dynamic models that employ Maggi's formulation. An adjoint variable method is developed for explicit and implicit first order Maggi's formulations, second order Maggi's formulation, and first and second order penalty formulations. The resulting sensitivities are employed to perform optimization of different multibody systems case studies. The collection of benchmark problems includes a five-bar mechanism, a full vehicle model, and a passive dynamic robot. The five-bar mechanism is used to test and validate the sensitivity approaches derived in this paper by comparing them with other sensitivity approaches. The full vehicle system is used to demonstrate the capability of the adjoint variable method based on the penalty formulation to perform sensitivity analysis and optimization for large and complex multibody systems with respect to multiple design parameters with high efficiency. In addition, a new multibody dynamics software library MBSVT (Multibody Systems at Virginia Tech) is developed in Fortran 2003, with forward kinematics and dynamics, sensitivity analysis, and optimization capabilities. Several different contact and friction models, which can be used to model point contact and surface contact, are developed and included in MBSVT. Finally, this study employs reference point coordinates and the penalty formulation to perform dynamic analysis for the passive dynamic robot, simplifying the modeling stage and making the robotic system more stable. The passive dynamic robot is also used to test and validate all the point contact and surface contact models developed in MBSVT. / Ph. D.

For decades vehicle control has been extensively studied to investigate and improve vehicle stability and performance. Such controllers are designed to improve driving safety while the driver is still in control of the vehicle. It is known that human drivers are capable to learn and adapt to their built-in vehicle controller in order to improve their control actions based on their past driving experiences with the same vehicle controller. Although the learning curve varies for different human drivers, it results in a more constructive cooperation between the human driver and the computer-based vehicle controller, leading to globally optimal vehicle stability. The main intent of this research is to develop a novel cooperative interaction model between the human driver and vehicle controller in order to obtain globally optimal vehicle steering and lateral control. Considering the vehicle driver-controller interactions as a common two-player game problem where both players attempt to improve their payoffs, i.e., minimize their objective functions, the Game Theory approach is applied to obtain the optimal driver's steering inputs and controller's corrective yaw moment. Extending this interaction model to include more realistic scenarios, the model is discretized and a road preview model is added to account for the driver's preview-time characteristic. Also, a robust interaction model is developed to stabilize the vehicle performance while taking bounded uncertainty effects in driver's steering behavior into consideration using the Integral Sliding Mode control methodology. For evaluation purposes, a nonlinear vehicle dynamics model is developed that captures nonlinear tire characteristics and includes driver steering controllability and vehicle speed control systems such as cruise control, differential braking, and anti-lock braking systems. A graphical user interface (GUI) is developed in MATLAB to ease the use of the vehicle model and hopefully encourage its widespread application in the future. Simulation results indicate that the proposed cooperative interaction model, which is the end-product of human driver's and vehicle controller's mutual understanding of each other's objective and performance quality, results in more optimal and stable vehicle performance in lateral and yaw motions compared to the existing LQR controllers that tend to independently optimize the driver and vehicle controller inputs. / Ph. D.

The research focuses on developing a methodology for modeling a pneumatic bias-ply tire with the finite element method for vehicle dynamics simulation. The tire as a load-carrying member in a vehicle system deserves emphasized formulation especially for the contact patch because its representation of mechanics in the contact patch directly impacts the handling and ride performance of a vehicle. On the other hand, the load transfer from the contact patch to the wheel hub is necessary for determining the inputs to a chassis. A finite element (FE) tire model has strong capability to handle these two issues. However, the high cost of computing resources restrains its application mainly in the tire design domain. This research aims to investigate how to balance the complexity of a simplified FE tire model without diminishing its capability towards representing the load transmission for vehicle dynamics simulation. The traditional FE tire model developed by tire suppliers usually consists of an extremely large number of elements, which makes it impossible to be included in a full-vehicle dynamics simulation. The material properties required by tire companies' FE tire models are protected. The car companies have an increasing need for a physical-based tire model to understand more about the interaction between the tire and chassis. A gap between the two sides occurs because the model used for tire design cannot directly help car companies for their purpose. All of these reasons motivate the current research to provide a solution to narrow this gap. Other modern tire models for vehicle dynamics, e.g. FTire or TAME, require a series of full-tire tests to calibrate their model parameters, which is expensive and time-consuming. One great merit of the proposed simplified FE tire model is that determining model inputs only requires small-scale specimen tests instead of full-tire tests. Because much of the usability of a model hinges on whether its input parameters are easily determined, this feature makes the current model low cost and easily accessible in the absence of proprietary information from the tire supplier. A Hoosier LC0 racing tire was selected as a proof of modeling concept. All modeling work was carried out using the general purpose commercial software Abaqus. The developed model was validated through static load-deflection test data together with Digital Image Correlation (DIC) data. The finite element models were further evaluated by predicting the traction/braking and cornering tire forces against Tire Test Consortium (TTC) data from the Calspan flat-track test facility. The emphasis was put on modeling techniques for the transient response due to the lack of available test data. The in-plane and out-of-plane performance of the Hoosier tire on the full-tire test data is used for model validation, not for "calibrating" the model. The agreement between model prediction and physical tests demonstrate the effectiveness of the proposed methodology. / PHD / This research aims to develop a method to build a physically-based tire model less relying on the information of products from tire providers for the purpose of vehicle dynamics simulation. The tire model is a mathematical description of the behavior of tires under various operational conditions. The model is said to be ‘physically-based’ if it is derived from physical laws. In contrast, if the model is termed ‘semi-empirical,’ it means that the model is mainly based on tire measurement data. A physically-based model usually gives more insights to and a better understanding of tire mechanics than a semi-empirical tire model. The tire as a load-carrying member in a vehicle system deserves emphasized formulation especially for the tire-road contact patch because its representation of mechanics in the contact patch directly impacts the handling and ride performance of a vehicle. Therefore, a physically-based tire model is preferred. One kind of physically-based models are developed through the multi-body dynamics (MBD) approach. Various full tire tests are required to identify the parameters associated with the model. Since full tire tests should be conducted on professional tire test machines, the high-cost prevents many users to have a tire model of such kind. The other kind of physically-based models are developed through the finite-element method (FEM). The FEM has strong capability to describe the mechanism of tire-road contact and deformation of the tire body. Also, parameters needed by a finite element tire model are basic material properties of different components of the tire structure, which implies the possibility to acquire parameters through small-scale sample tests instead of full tire tests. However, most of FE tire models are developed for tire design with high complexity, not good for vehicle simulation. This research made efforts to degrade the complexity of the FE tire model and tailor the FE modeling technique suitable for the purpose of vehicle simulation. In addition, the process was designed and implemented for obtaining the necessary parameters associated with the model. A Hoosier LC0 racing tire was selected as a proof of modeling concept without any tire property data provided by tire producers. This research has a practical meaning on building tire models independent of tire companies and at low cost.

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.