- PostA report on Objective Development of Damper Specification(2018)Damping of the sprung and un-sprung masses of a vehicle through a suspension damper is crucial to obtain good comfort and handling characteristics. Damper tuning, which is predominantly based on subjective feedback and experience from engineers takes up a large amount of time and resources. Preliminary knowledge of the influence of dampers in different operating regions can provide a good starting point in the damper tuning process. This research thesis aims to develop objective metrics related to the response of simplified vehicle models and could provide information regarding the modifications in the damper specifications to achieve the desired response. Quarter-car models with linear, asymmetric and non-linear damper curves are simulated in the Matlab environment for step and swept sine inputs. The responses are further investigated to identify metrics of interest, by which the behaviour of the vehicle can be understood. For linear damper models, the poles of the system are analyzed and pole placement method is used to understand the behaviour of sprung and un-sprung masses when suspension parameters are varied. For asymmetric dampers, metrics which could help decide the required degree of asymmetricity between compression and rebound damping are presented. Finally, for non-linear dampers, the effect of damping force in different regions of operation is studied. A sensitivity analysis (Design of Experiments) is performed to identify the most influential variables corresponding to these metrics. With these results, the response of the model is studied to obtain the metrics of interest which can be attributed to the behaviour of the vehicle. Comparisons are presented to visualize the effects of different damper specifications by which an initial prediction could be made for the damper specifications. This outcome can potentially enhance the preliminary knowledge of the effects of damper tuning and thereby providing a better starting point for the damper development process.
- PostEffects of electron trapping and ion collisions on electrostatic shocks(2018)Electrostatic shocks in plasmas have been observed to be able to accelerate particles to twice the shock velocity with a very low energy spread. Shock phenomena are often modeled as exactly collisionless, which is a very good approximation for astrophysical shocks. However, collisions might play a role in shocks created in laboratory plasmas, since very sharp features of the ion distribution function develop due to ions being reflected at the shock front; this ion reflection results in empty regions of phase space with discontinuities at their boundaries. In this thesis the effects of a weak but finite ion collisionality are considered in a time dependent, semi-analytical treatment. The amplitude of the downstream potential oscillation is found to increase approximately as the square root of time as particles are scattered into the originally empty regions of phase space. The corresponding changes in the electrostatic potential lead to an increased size of the trapping regions in the ion phase space. This thesis also studies the effect of electron trapping in the potential oscillations downstream of the shockfront. Two model electron distributions, which are flat in the trapped regions of phase space, are considered. The two models only differ in where the potential threshold for trapping is set; one model allows for trapping at a freely set threshold in order to emulate the effects of far downstream behavior of the shock, while the other model only allows for trapping inside the downstream potential oscillation. In general the effects of electron trapping are to reduce the maximum electrostatic potential, but at the same time increase the range of shock propagation speeds for which electrostatic shock solutions exist. The second electron trapping model also exhibits multiple shock solutions for the same temperature ratio and Mach number in certain parameter regions.