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Sensitivity analysis methods are investigated for the optimal design of multibody systems. In order to overcome the shortcomings inherent in existing methods, a "mixed" method is developed. The beneficial features of the finite difference and the direct differentiation methods, and equations of motion in the joint coordinates are employed in this method. As a realistic application of the sensitivity analysis, a Four-Wheel-Steering vehicle with complete suspension systems and comprehensive analytical tire model is implemented. This model keeps full nonlinearity in the governing equations of motion for accuracy, and it is simulated using an existing general-purpose multibody dynamics simulation package. However, by using the transient dynamic analysis of the nonlinear model, optimal design parameters are dependent on driving scenarios. Therefore, the transient behavior of the system is represented by a series of steady state configurations. Hence, a steady state analysis procedure which finds a steady state configuration from an arbitrary initial condition is developed. By using the steady state analysis and the sensitivity analysis, the optimal steering ratios between the angles of the front and the rear wheels are obtained over various driving conditions. A steering control strategy is developed for the vehicle simulation to follow a prescribed path. Finally, the simulation results using the optimal steering ratio are compared against the results of the conventional two-wheel steering and the steering ratio based on the linear bicycle model.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (MTech (Industrial Design))--Cape Peninsula University of Technology, 2016. / This paper is positioned within the broader context of public transportation systems, with specific focus on the development of urban micro first and last mile mobility solutions, and what it could mean for individuals and the economy. Globally, urban problems such as traffic congestion, poor public transport integration, and carbon emissions are forcing us to rethink traditional means of transport. Large fossil-fuelled vehicles and limited public transport infrastructure characterize South Africa’s transport market. Despite the growth in car use, public transport and walking are still the predominant “lifeline” forms of mobility for the vast majority of South Africans in order to access work, schools and services. Moreover, the lack of public transport services in key economic corridors and rural areas of South Africa, the role of the metered taxi industry which is currently effectively limited to serving only the needs of the tourist market due to high charging regimes, and finally, the absence of an effective inner city transport system endorses the lack of first and last mile transportation solutions, and the integration thereof with other transport mediums. This adds to the conflict commuter’s face on a daily basis in obtaining a seamless distribution of transport services. 80% of trips in urban areas are less than 3km, placing urban micro mobility vehicles in an ideal position as a solution to transportation. This describes the investigation conducted into micro-mobility trends within South Africa to identify a key mode of transport that would comply with the stated requirements, and allow accessibility to commuters within the city and to the surrounding communities. In 2014, Mellowcabs, which are electric public transport vehicles that provide first and last mile transport services, was identified as a promising candidate within the local micro-mobility vehicle context. They were in need of a design input for their immediate next requirement, which thus describes the development of a good protective side door system that would isolate passengers in adverse weather conditions, whilst similarly affording comfort and safety features found in normal passenger vehicles. The design process is focused on creating a new side door, however, at the same time the product should be, elegant, smart, fashionable, comfortable, economical, maneuverable and safe. In addition, the virtual product lifecycle management tool, CATIA, allows the design team to get feedback in terms of physical-based data that correspond to how the door could hinder the passengers interaction while they ingress and egress the vehicle. This enables us to try various designs to perform a comparative study without building a single physical prototype.