Thesis (M.S.)--University of Wisconsin--Madison, 1937. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 93).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-129).

Thèse--Nancy.

Thesis (Ph. D.)--University of Chicago, 1920. / Caption title: The orientation of molecules in surfaces. VI ... "Private edition distributed by the University of Chicago libraries, Chicago, Illinois, 1921." "Reprinted from the Journal of the American chemical society, vol. XLIII, no. 1, January, 1921." Also available on the Internet.

Thesis (MScIng)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Chicago, 1916. / Vita. "Private edition, distributed by the University of Chicago Libraries, Chicago, Illinois." Also available on the Internet. Also issued online.

The necessity to reduce climate related emissions is driving the electrication of transportation. As well as reducing emissions Electric Vehicles (EV) have the capability of improving traction and vehicle stability. Unlike a conventional vehicle that uses a single Internal Combustion Engine (ICE) to drive one or both axles, an EV can have an electric machine driving each of the wheels independently. This opens up the possibility of using the electric machines as an actuator for traction control. In conventional vehicles the hydraulic brakes together with the ICE are used to actuate traction control. The advantages of electric machines over hydraulic brakes are precise measurable torque, higher bandwidth, bidirectional torque and kinetic energy recovery. A review of the literature shows that a wide range of control methods is used for traction control of EVs. These are mainly focused on control of an individual wheel, with only a minority being advanced to the experimental stage of verication. Integrated approaches to the control of multiple wheels are generally lacking, as well as verication that tests the vehicle's directional stability. A large body of the literature uses the slip ratio of the wheel as the key control variable. A signicant challenge for slip-based traction control is the detection of vehicle velocity together with the calculation of slip around zero vehicle velocity. A traction control method that does not depend upon vehicle velocity detection or slip ratio is Maximum Transmissible Torque Estimation (MTTE), after Yin et al. (2009). In this thesis an MTTE based method is developed for a full size electric vehicle with independently driven rear wheels. The original MTTE method for a single wheel is analysed using a simple quarter vehicle model. The simulation results of Yin et al. (2009) are in general reproducible although a lack of data in the original research prevents a quantitative comparison. A modication is proposed to the rate compensation term. Simulation results show that the proposed modication ensures that the torque demand is delivered to the wheel under normal driving conditions, this includes negative torque demand which is not possible for MTTE, Yin et al. (2009). Enabling negative torque demands means that the proposed traction control is compatible with higher level stability control such as torque vectoring. The performance of the controller is veried through a combination of simulation and vehicle based experiments. Compared with experiments, simulations are fast and inexpensive and can provide greater insight as all of the variables are observable. To simulate the controller a high delity vehicle model is required. To achieve this it is necessary to initially validate the model against experimental data. Simulation verication using a validated vehicle model is lacking in the literature. A full vehicle model is developed for this thesis using Dymola, a multi-body system software tool. The model includes the full suspension geometry of the vehicle. Pacejka's "Magic Formula" is used for the tyre model. The model is validated using Delta Motorsport's E4 coupe. The two Wheel Independent Drive (2WID) MTTE-based traction controller is derived from the equations of motion for the vehicle. This shows that the maximum transmissible torque for one driven wheel is dependent on the friction force of both driven wheels, which has not been shown before. An equal torque strategy is proposed to maintain vehicle directional stability on mixed-μ roads. For verication the 2WID-MTTE controller is simulated on the validated vehicle model described above. The proposed 2WID-MTTE controller is benchmarked against a similar method without the equal torque strategy, termed Independent MTTE, as well as a method combining Direct Yaw Control (DYC) and Independent MTTE. The three controllers are simulated for a vehicle accelerating onto a split-μ road. The results show that the proposed 2WID-MTTE controller prevents the vehicle spinning o the road when compared to Independent MTTE. 2WID-MTTE is found to be as eective as DYC+Independent MTTE but is simpler in design and requires fewer sensors. The proposed 2WID-MTTE controller is also simulated for a vehicle accelerating from a low- to high-μ road. This is done to assess the controller's ability to return to normal operation after a traction event, and because there are no simulations of this type for MTTE control on a high delity vehicle model in the literature. The results show that oscillations in the tyre-road friction force as the wheel transitions across the change in μ somewhat impede the return of the controller's output torque to the torque demand. The 2WID-MTTE controller is implemented on Delta Motorsport's E4 coupe by integrating it into the vehicle's Powertrain Control Module (PCM). This is experimentally tested for the vehicle accelerating across a range of surfaces at the MIRA proving ground. The experimental tests include high- to low-μ, low- to high-μ and split-μ roads. The results for the high- to low-μ road tests show that 2WID-MTTE control prevents the vehicle spinning when compared to no control. Similar to the simulation, the results of the low- to high-μ road experiment show that the controller output torque is also impeded from returning to the demand torque. Observation of the estimated friction force together with the on-board accelerometers conrm that this is due to tyre friction oscillating after the transition. This justies the use of a tyre model with transient dynamics. The proposed 2WID-MTTE controller uses wheel velocity and torque feedback to estimate friction torque. These signals are obtained from the vehicle's motor controllers via a Controlled Area Network (CAN) bus. The 2WID-MTTE controller is benchmarked against Independent MTTE that uses wheel velocity measured directly from the wheel hub sensors and the torque demand to estimate friction torque. The results show that the delays introduced by the CAN bus increase wheel slip for the 2WID-MTTE controller. However, the equal torque strategy means that 2WID-MTTE controller maintains greater vehicle directional stability, which is more important than the pursuit of greater acceleration.

With the increase of the computational power over the last decades, computational solid dynamics has become a major field of interest in many industrial applications (as for example aerospace, automotive industry, biomedical engineering or manufacturing). Traditionally, these types of simulations have been carried out using the Finite Element Method (FEM) in conjunction with displacement based formulations, where the displacements are treated as the main problem variables. In the context of solid mechanics, the use of low order (linear) tetrahedral (or triangular) elements is always preferred, primarily due to the complexity of the constitutive models involved (i.e., the number of evaluations needs to be kept as low as possible) as well as the automatic tetrahedral (or triangular) mesh generators available. However, the combination of low order elements with FEM displacement based formulations presents a series of shortcomings, namely: one order of accuracy less for stresses (or strains) than for displacements (or velocities), poor behaviour in bending dominated scenarios, volumetric and shear locking or the appearance of spurious pressure modes. Furthermore, the time integration is usually performed using Newmark integrators, which tend to introduce high frequency noise in the vicinity of sharp gradients. Recently, a new Lagrangian mixed methodology has been presented for the simulation of fast transient dynamics problems. This methodology is in the form of a system of first order conservation laws, where the linear momentum, p, and the deformation gradient tensor, F, are regarded as the two main conservation variables. When thermo-mechanical constitutive models are involved, the formulation is complemented with the first law of thermodynamics (conservation of energy). It has been proven that this formulation circumvents the drawbacks of the low order displacement based FEM methodologies mentioned above. The formulation, presented as a set of conservation laws, allows for standard Computational Fluid Dynamcis (CFD) spatial discretisations. So far, successful implementations have been carried out using cell centred upwind Finite Volume method, two-step Taylor Galerkin, Finite Element Petrov Galerkin (PG), and Hybridizable Discontinuous Galerkin (HDG). The objective of this thesis is to present a new spatial discretisation in order to solve large scale real life problems. To do so, the Jameson-Schmidt-Turkel (JST) scheme, widely know within the CFD community, will be chosen. The JST scheme is a vertex centred finite volume, that combines the use of central differences with an artificial dissipation term. The scheme obtains second order spatial accuracy without the need of linear reconstruction. Furthermore, the artificial dissipation term includes a shock capturing sensor, very suitable in the context of fast dynamics. The scheme can be implemented in an edge-based framework, which combined with the vertex centred storage of the variables results into a computationally efficient scheme. The JST spatial discretisation will be combined with a Total Variation Diminishing (TVD) two-stage Runge-Kutta time integrator. These spatial and temporal discretisations will be adapted to the problem at hand. Specifically, compatibility conditions (involutions) will have to be satisfied by the discrete scheme. Furthermore, numerical corrections will be introduced in order to ensure the conservation of linear and angular momenta. The framework results in a low order computationally efficient solver for solid dynamics, which proves to be very competitive in nearly incompressible scenarios and bending dominated applications. The thesis will present numerical results for one dimension, two dimensions (triangular meshes) and three dimensions (tetrahedral meshes). The problems are chosen in order to prove the order of accuracy, robustness and conservation properties of the algorithm.

Friction factors have been determined experimentally for longitudinal flow of water and various aqueous solutions of polyethylene glycol between regular enclosed arrays of cylinders. Two different geometries were investigated: a 4 × 4 square array enclosed by a square duct and a 19-rod equilateral triangular array enclosed by a hexagonal duct. Four different pitch-to-diameter ratios were studied in each geometry. These covered a range of 1.07 to 2.00 in the square array and 1.11 to 2.06 in the triangular array. No spacers were used in the rod bundle. The Reynolds number range investigated was approximately 2.5 to 40,000 (equivalent diameter based on total wetted perimeter). The fully developed friction factors for all eight arrays were correlated by the Nikuradse equation for smooth round tubes when the Reynolds number exceeded 10,000 and when the equivalent diameter, used in both the Reynolds number and the friction factor, was taken as four times the hydraulic raduis based on total wetted perimeter. In laminar flow no equivalent diameter was found that would consolidate the results of all eight arrays. Deviations from the laminar flow theory of Sparrow and Loeffler for infinite arrays could be consistently accounted for by the wall effect in the present study. The critical Reynolds number for each array ranged between 90 and 450 (equivalent diameter based on total perimeter) and the transition from laminar to turbulent flow appeared to extend over a large Reynolds number range. Friction factors in both laminar and turbulent flow were apparently established in a very short distance from the entrance to the rod bundle, since no entrance effect was detected, even as close as 9.6 total equivalent diameters from the entrance. Local friction factors were also measured in the entrance and fully developed region of a round smooth tube with a sharp-edged entrance. The Reynolds number range covered was 394 to 77,000. The inside tube diameter, determined by forcing the fully developed laminar flow friction factors to fit Poiseuille's equation, was in excellent agreement with the measured diameter, and the fully developed turbulent flow friction factor results, based on the computed diameter, were in good agreement with Nikuradse's equation for a smooth round tube. The Newtonian behavior of the polyethylene glycol solutions over all rates of shear encountered in the present study was thus established. Good agreement was also obtained between the local laminar flow friction factors, measured in the entrance region of the tube, and those predicted theoretically by Langhaar for a rounded entrance. In turbulent flow, the friction factor became fully developed within 50 tube diameters of the entrance. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

This thesis describes the investigation of hydrodynamic properties of pure superfluid flow in liquid helium II by observing the motion of suspended particles in a special experimental arrangement called 'Superfluid Wind Tunnel'. The flow properties of pure superfluid in different velocity regions have been investigated by using particles made with a suitable mixture of hydrogen and deuterium gases as indicators. Two critical velocities, Vp,c and Vs,c, corresponding to 0c and 0t of the oscillating sphere experiments (Benson and Hallett (1956)) have been found. Below Vp,c, the superfluid flow is a perfect potential flow of zero viscosity. Above Vp,c quantized vortex lines are created, therefore the pure superfluid flow breaks down. On the other hand in the vicinity of Ys,c, the starting point of fully developed turbulence, the magnitude of turbulent fluctuations has a maximum which confirms Feynman's prediction (1955) about critical velocity. A rough calculation shows that the velocities of a particle, which obtains energy from a segment of quantized vortex line, are of the same order as that of experimental values. This suggests that by this way, other than Vinen's (1961) vibrating wire experiment, the quantization of superfluid circulation in units of h/m might be verified by visual observations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate