Vehicle dynamic simulations form a significant part of the design and development process of vehicles. These simulations are used to study and improve the vehicle’s durability, ride comfort and handling capabilities. All forces acting on the vehicle are either generated in the tyre-road interface or are due to aerodynamic effects, where at low speeds the latter one can be ignored. The accuracy of the tyre model describing the forces on the tyre-road interface is thus of exceptional importance. It ensures that the simulation model is an accurate representation of the actual vehicle. Various approaches are adopted when developing mathematical tyre models. Many of these models are developed to study the handling capabilities of passenger cars over a smooth road. Passenger car tyres are the focal point as larger tyres introduce some difficulties due to their size and load rating. Off-road truck tyres also differ in their construction which will influence force and moment generation of the tyre. Research efforts are increasing to meet the need of tyre models that can describe the behaviour of the tyre over uneven terrain with sufficient accuracy. This thesis addresses the question of whether existing mathematical tyre models can accurately describe the forces and moments generated by a large off-road tyre while driving over rough terrain. The complexity of different mathematical tyre models varies greatly, as does the parameterisation efforts required to obtain the model parameters. The parameterization of most tyre models relies on some experimental test data that is used to extract the necessary information to fit model parameters. The selection of a suitable tyre model for a simulation is often dependent on the availability of such experimental data and the effort to identify the required parameters. In this study the parameterisation process for four different tyre models, are discussed in detail to highlight the difficulties in acquiring the test data and the effort to parameterize the model. The models considered are the One Point Contact, 3D Equivalent Volume contact, 3D Enveloping Contact and FTire model. Experimental measurements are conducted on a 16.00R20 Michelin XZL tyre. Laboratory tests, as well as field tests, over discrete obstacles and uneven hard surfaces are used for parameterisation and validation purposes. Simulation results are compared to experimental test data to determine whether the models could be used to describe the tyre road interactions with sufficient accuracy. Recommendations are made for tyre model selection and model accuracy for simulations over rough off-road surfaces. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Mechanical and Aeronautical Engineering / unrestricted

Problems associated with traffic, such as traffic congestionand pollution, have occurred in major urban areas in particulardue to the increased use of cars. One possible way to reducethe use of cars is to replace commuter trips by car with othermodes of transport, such as a combination of car and publictransport called Park&amp;Ride. The aim of this thesis was tounderstand more about factors influencing the choice of modeand to find measures that could attract car drivers to Park&amp;Ride. A stated preference survey has been conducted inorder to quantify some standard factors. The factors used inthis stated choice experiment were: security at the lot,availability of spaces at the parking lot, costs at the parkinglot and walking distances between the parking space and thestation. The results indicate that security at the Park&amp;Ride facility is important. Both sexes assign a high value tosecure parking, but women are more willing to pay for lights atan unguarded parking lot. The results reveal that parkingfacilities, such as free parking and short distance betweenparking place and work at work, influence people’s choiceof mode. A general conclusion is that there is potential forincreasing the use of Park&amp;Ride facilities, especiallyamong women and respondents over 30 years. Key words:Mode choice, valuation, traffic reduction,stated preference, factors, Park&amp;Ride / <p>NR 20140805</p>

Existing studies on the formulation of regulations for online ride-hailing platforms merely see the process as a struggle between interest groups. They do not address how policymakers perceive this struggle and act on their own initiative to govern these platforms. This study supplements existing studies by exploring how the metropolitan governments of two Chinese cities, Beijing and Shanghai, perceived conflicts between contending forms of chauffeur businesses and brought in regulations for new platform ventures. This thesis employs a policy change approach in the Chinese authoritarian context and reaches three conclusions. Firstly, it explains that the "special interests" of taxi entities institutionalized by the old regulatory regimes for taxi businesses incentivized the two metropolitan governments to protect taxi entities. Thus, even if Beijing and Shanghai had different first responses towards platforms with one initially emphasizing "cracking-down" and the other working on a "loose" regulatory approach, they adopted similar platform-capping policies. Secondly, this thesis finds that the two metropolitan governments cautiously disobeyed the central government's "loose" directives for platforms by combining their capping policies with selectively implementing a central directive of differentiating the markets of ride-hailing platforms and taxi operators. Thirdly, this thesis addresses obstructions to the establishment of "new regulation" that respects the business logic of platforms, which is proposed by the platform coalition. It argues that the interaction between the vested "special interests" and the fragmentation of authority makes local governments resistant to this "new regulation." / Graduate

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The increased integration of distributed and renewable energy resources (DERs) has motivated the evolution of new standards in grid interconnection requirements. New standards have the requirement for the DERs to remain connected during the transient grid fault conditions and to offer support to the grid. This requirement is known as the fault ride-through (FRT) capability of the inverter-based DERs and is an increasingly important issue. This dissertation presents the FRT capability of the DERs that employ a voltage control strategy in their control systems. The voltage control strategy is increasingly replacing the current control strategy in the DERs due to the fact that it provides direct voltage support. However, the voltage control technique limits the ability of direct control over the inverter current. This presents a challenge in addressing the FRT capability where the problem is originally formulated in terms of the current control. This dissertation develops a solution for the FRT capability of inverters that use a voltage control strategy. The proposed controller enables the inverter to ride through the grid faults and support the grid by injecting a balanced current with completely controlled real and reactive power components. The proposed controller is flexible and can be used in connection with various voltage control strategies. Stability analysis of the proposed control structure is performed based on a new linear time-invariant model developed in this dissertation. This model significantly facilitates the stability and design of such control loops. Detailed simulation, real-time and experimental results are presented to evaluate the performance of the proposed control strategy in various operating conditions. Desirable transient and steady-state responses of the proposed controller are observed. Furthermore, the newly established German and Danish grid fault ride-through standards are implemented in this research as two application examples and the effectiveness of the dissertation results are illustrated in the context of those two examples.

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An essential tool in the truck development process is the ability to quantify and grade vehicle dynamic behavior. Today this is performed either through subjective or objective tests. Subjective tests have the disadvantage that numerous factors influence test drivers’ opinions while objective measures have the advantage of repeatability. However, objective methods of today are often only able to provide a rough grading of vehicles. The main objective with this thesis is to develop more sensitive objective methods for ride comfort evaluation. An effective test procedure to measure driver perception sensitivity to small differences in vehicle ride is suggested and utilized. The driver sensitivity is tested on dynamic behavior that is typically graded in vehicle development. Cab motions from a truck are first measured and then recreated in a simulator where a test driver is seated. The perception threshold for small changes in typical vehicle motion is established in this way for each test person. The perception sensitivity tests indicate that humans are quite sensitive to transients in vehicle motion. One problem with many common vehicle ride measures is that the impact of transient behavior is small due to the averaging used to condense the measurement data into scalar measures. A new evaluation method for ride comfort, with influences from the well known handling diagram, is suggested. This method has four main advantages: it is fairly simple to interpret, it shows the absolute vibration level, it considers transient events separately and it shows changes in vehicle character with increasing excitation. Promising results from both measurements and simulations are derived. New technology has made it possible to vary vehicle suspension parameters during vehicle ride. In order to prescribe different damping for different vehicle modes, modal motion estimates are needed. A system identification approach is suggested. It yields improved estimates of vehicle modal motion compared to previous work. / QC 20101221

While semi-active suspensions help improve the ride comfort and road holding capacity of the vehicle, they tend to be reactive in nature and thus leave a lot of room for improvement. Incorporating road preview data allows these suspensions to become more proactive rather than reactive and helps achieve a higher level of performance. A lot of preview-based control algorithms in literature tend to require high computational effort to arrive at the optimal parameters thus making it difficult to implement in real time. Other algorithms tend to be based upon lookup tables which classify the road input into different categories and hence lose their effectiveness when mixed types of road profiles are encountered that are difficult to classify. Thus a novel control algorithm is developed which is easy to implement online and more responsive to the varying road profiles that are encountered by the vehicle. A numerical methods-based semi-active suspension control algorithm and a Model Predictive Control(MPC)-based semi-active suspension control algorithm are developed that can leverage the data from the upcoming road profile to increase the ride comfort of the vehicle. The numerical methods-based algorithm is developed for the sole purpose of determining the maximum possible ride comfort that can be achieved using semi-active dampers capable of altering their damping characteristics every 0.01 seconds. The MPC-based algorithm is a more realistic algorithm that can be implemented in real-time and achieves on average 70% of the ride comfort that the numerical methods-based algorithm can with minimal computational effort. / Master of Science / Semi-active suspensions help cars ride more smoothly and handle better on the road. However, they often react to bumps and potholes only after hitting them, which means there's room for improvement. By using information about the road ahead, these suspensions can adjust before reaching rough spots, making the ride even better. To make this work, a new control system was developed. This system includes two parts. The first part uses detailed calculations to find the best possible comfort level, adjusting the suspension every 0.01 seconds. This method shows the highest comfort that can be achieved but is too complex for everyday use. The second part uses a simpler method called Model Predictive Control (MPC). This part is practical for real-time driving and achieves about 70% of the best possible comfort. It doesn't need as much computing power and can quickly adapt to different road conditions, making it ideal for normal driving. This new system improves driving comfort and safety by making suspensions smarter and more efficient.