Computationally-efficient Finite-element-based Thermal and Electromagnetic Models of Electric Machines.

With the modern trend of transportation electrification, electric machines are a key component of electric/hybrid electric vehicle (EV/HEV) powertrains. It is therefore important that vehicle powertrain-level and system-level designers and control engineers have access to accurate yet computationally-efficient (CE), physics-based modeling tools of the thermal and electromagnetic (EM) behavior of electric machines. In this dissertation, CE yet accurate thermal and EM models for electric machines, which are suitable for use in vehicle powertrain design, optimization, and control, are developed. This includes not only creating fast and accurate thermal and EM models for specific machine designs, but also the ability to quickly generate and determine the performance of new machine designs through the application of scaling techniques to existing designs. With the developed techniques, the thermal and EM performance can be accurately and efficiently estimated. Furthermore, powertrain or system designers can easily and quickly adjust the characteristics and the performance of the machine in ways that are favorable to the overall vehicle performance.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113497/1/kanzhou_1.pd

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations

Magellan/Galileo solder joint failure analysis and recommendations

On or about November 10, 1988 an open circuit solder joint was discovered in the Magellan Radar digital unit (DFU) during integration testing at Kennedy Space Center (KSC). A detailed analysis of the cause of the failure was conducted at the Jet Propulsion Laboratory leading to the successful repair of many pieces of affected electronic hardware on both the Magellan and Galileo spacecraft. The problem was caused by the presence of high thermal coefficient of expansion heat sink and conformal coating materials located in the large (0.055 inch) gap between Dual Inline Packages (DIPS) and the printed wiring board. The details of the observed problems are described and recommendations are made for improved design and testing activities in the future

Accretion Disc Theory: From the Standard Model Until Advection

Accretion disc theory was first developed as a theory with the local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disc. One of the most important new invention of this theory was a phenomenological treatment of the turbulent viscosity, known as ''alpha'' prescription, when the (r$\phi$) component of the stress tensor was approximated by ($\alpha$ P) with a unknown constant $\alpha$. This prescription played the role in the accretion disc theory as well important as the mixing-length theory of convection for stellar evolution. Sources of turbulence in the accretion disc are discussed, including nonlinear hydrodynamical turbulence, convection and magnetic field role. In parallel to the optically thick geometrically thin accretion disc models, a new branch of the optically thin accretion disc models was discovered, with a larger thickness for the same total luminosity. The choice between these solutions should be done of the base of a stability analysis. The ideas underlying the necessity to include advection into the accretion disc theory are presented and first models with advection are reviewed. The present status of the solution for a low-luminous optically thin accretion disc model with advection is discussed and the limits for an advection dominated accretion flows (ADAF) imposed by the presence of magnetic field are analysed.Comment: Roceeding of the Int. Workshop "Observational Evidence for Black Holes in the Universe". Calcutta, 11-17 January 1998. Kluwer Acad. Pu

COMPREHENSIVE THERMAL MODELING OF POWER SPLIT HYBRID POWER-TRAIN AND ELECTRONICS

Hybrid electric vehicle (HEV) uses both internal combustion engine (ICE) with an electric system. The combination of the electric power train with the ICE is intended to achieve both better fuel economies than the conventional vehicles and better performance. Several types of HEV exist with different layouts. Recent HEVs\u27 make use of regenerative braking, which converts the vehicles\u27 kinetic energy into electric energy instead of wasting it as heat as conventional brakes do. A hybrid-electric is more fuel efficient than ICE and has less environmental impact. The new HEV with its new Key Characteristics and Configurations (i.e. Mechanical complexity, Multiple driving modes, Multiple prime movers, ... etc) inflict an interference with the existed thermal management system of the conventional vehicles, which leads to a new thermal management issues that should be addressed to enhance the performance of such systems. There is no complete knowledge in the open literature about the thermal management issues of HEV yet. This dissertation introduces Comprehensive Thermal Modeling of Hybrid Vehicular systems to assist monitoring the added-on of hybrid modules into the vehicle thermal management system. The model proposes a combined experimental and finite differencing nodal net work simulation modeling approach; using Thermography detectors calibrated for emissivity to capture 2-D spatial and transient temperature measurements. The Thermographic detectors were deployed through dual band thermography to neutralize the emissivity and to provide different dynamic ranges to iii achieve accurate temperature measurements. A thermocouples network was installed to provide a reference signal. A new comprehensive 3-D thermal model was developed by generating 3-D surface description for a complete hybrid electric vehicle from 3-D scans of an actual vehicle to guarantee the quality of the surface geometry, and break down the surfaces of the model into finite elements to improve the accuracy for better thermal analysis. The boundary conditions from a vehicle under different driving modes and load scenarios were deployed into the finite differencing simulation which was performed using finite differencing code capable of solving a sophisticated thermal/fluid systems with minimal user interaction (RadTherm) to provide a 3-D Thermal predictions and an Image Viewer (wireframe and animated thermal display). The 3-D model assisted monitoring the adding of Hybrid modules into the vehicle thermal management system and was used to analyze packaging considerations and integrating different modules for Hybrid Vehicles. In addition to the design of alternative materials for hybrid modules and Battery Packs for better thermal management; the model assisted studying the influence of applying different cooling methodologies and evaluate its effect on the thermal performance of the HEVs\u27 power trains. A spatial and a transient temperature profiles obtained from the simulation for different components were compared with experimental results in order to validate the complete thermal model

Microchannel Heat Sinks For Cooling High Heat Flux Electronic Devices―analysis With Single And Two Phase Flows

Microchannel heat sinks constitute an innovative cooling technology for the efficient dissipation of the large amounts of heat from the very small and constrained areas of the high heat flux microelectronic chips and circuits. Penyerap haba saluran mikro menjadikan sebuah teknologi penyejukan berinovatif bagi lesapan berkesan jumlah haba yang besar daripada kawasan yang amat kecil dan terhad bagi cip dan litar elektronik mikro fluks haba yang tinggi