Comparison of POD reduced order strategies for the nonlinear 2D Shallow Water Equations

This paper introduces tensorial calculus techniques in the framework of Proper Orthogonal Decomposition (POD) to reduce the computational complexity of the reduced nonlinear terms. The resulting method, named tensorial POD, can be applied to polynomial nonlinearities of any degree $p$. Such nonlinear terms have an on-line complexity of $\mathcal{O}(k^{p+1})$, where $k$ is the dimension of POD basis, and therefore is independent of full space dimension. However it is efficient only for quadratic nonlinear terms since for higher nonlinearities standard POD proves to be less time consuming once the POD basis dimension $k$ is increased. Numerical experiments are carried out with a two dimensional shallow water equation (SWE) test problem to compare the performance of tensorial POD, standard POD, and POD/Discrete Empirical Interpolation Method (DEIM). Numerical results show that tensorial POD decreases by $76\times$ times the computational cost of the on-line stage of standard POD for configurations using more than $300,000$ model variables. The tensorial POD SWE model was only $2-8\times$ slower than the POD/DEIM SWE model but the implementation effort is considerably increased. Tensorial calculus was again employed to construct a new algorithm allowing POD/DEIM shallow water equation model to compute its off-line stage faster than the standard and tensorial POD approaches.Comment: 23 pages, 8 figures, 5 table

Projection-Based Reduced Order Modeling for Spacecraft Thermal Analysis

This paper presents a mathematically rigorous, subspace projection-based reduced order modeling (ROM) methodology and an integrated framework to automatically generate reduced order models for spacecraft thermal analysis. Two key steps in the reduced order modeling procedure are described: (1) the acquisition of a full-scale spacecraft model in the ordinary differential equation (ODE) and differential algebraic equation (DAE) form to resolve its dynamic thermal behavior; and (2) the ROM to markedly reduce the dimension of the full-scale model. Specifically, proper orthogonal decomposition (POD) in conjunction with discrete empirical interpolation method (DEIM) and trajectory piece-wise linear (TPWL) methods are developed to address the strong nonlinear thermal effects due to coupled conductive and radiative heat transfer in the spacecraft environment. Case studies using NASA-relevant satellite models are undertaken to verify the capability and to assess the computational performance of the ROM technique in terms of speed-up and error relative to the full-scale model. ROM exhibits excellent agreement in spatiotemporal thermal profiles (<0.5% relative error in pertinent time scales) along with salient computational acceleration (up to two orders of magnitude speed-up) over the full-scale analysis. These findings establish the feasibility of ROM to perform rational and computationally affordable thermal analysis, develop reliable thermal control strategies for spacecraft, and greatly reduce the development cycle times and costs

Novel Test Fixture for Characterizing Microcontacts: Performance and Reliability

Engineers have attempted to improve reliability and lifecycle performance using novel micro-contact metals, unique mechanical designs and packaging. Contact resistance can evolve over the lifetime of the micro-switch by increasing until failure. This work shows the fabrication of micro-contact support structures and test fixture which allow for micro-contact testing, with an emphasis on the fixture\u27s design to allow the determination and analysis of the appropriate failure mode. The other effort of this investigation is the development of a micro-contact test fixture which can measure contact force and resistance directly and perform initial micro-contact characterization, and two forms of lifecycle testing for micro-contacts at rates up to 3kHz. In this work, two different designs of micro-contact structures are fabricated and tested, with each providing advantages for studying micro-contact physics. After fabrication was refined, three functioning fixed-fixed Au micro-contact support structures with contact radii of 4, 6, and 10 µm and two functioning fixed-fixed Ag micro-contacts were tested using the µN force sensor at cycle rates up to 3 kHz. Comparing the PolyMUMPs micro-contact support structure to the fixed-fixed micro-contact support structure, it was determined that the fixed-fixed micro-contact support structure is the best structure for studying the evolution of micro-contact resistance

Air Force Institute of Technology Research Report 2012

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems and Engineering Management, Operational Sciences, Mathematics, Statistics and Engineering Physics

Air Force Institute of Technology Research Report 2003

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems and Engineering Management, Operational Sciences, and Engineering Physics

MICRO HEAT EXCHANGER TO COOL CEREBROSPINAL FLUID FOR BRAIN INJURY TREATMENT

Hypothermia is accepted as a method to preserve cells and tissue. Clinical evidence shows that administration of hypothermia could lead to neuroprotection after cardiac arrest. Non-invasive methods such as surface cooling devices, drugs and cold liquid ventilation are available to induce hypothermia. These approaches for achieving hypothermia have not been optimized yet. The surface cooling methods are generally slow and may lead to additional thermal shock to the body. Here, we propose a rapid, selective cooling method for the brain using a micro heat exchanger to cool the cerebrospinal fluids (CSF). We designed and 3D printed a U-type heat exchanger utilizing UV resin as the material for the heat exchanger as it has good mechanical and thermal properties. The heat exchanger has the inlet and outlet at the centre on both ends. There are seven channels for fluid flow and eight fins around the channels. The heat exchanger is placed on a Peltier component to keep the temperature constant across the heat exchanger. A syringe filled with CSF was utilized, which was placed on a syringe pump to provide the fluid at the inlet through the tube connections. To test the heat exchanger\u27s efficiency, an artificial CSF was allowed to flow through it, and the surface and the outlet temperature were captured. Various parameters were optimized, such as the flow rate, the initial CSF temperature at the inlet, the voltage to be supplied to run the Peltier. This report presents theoretical and experimental results for Micro Heat Exchanger. Fluid flow behavior was investigated analytically as well as using a CFD code (ANSYS Fluent). The theoretical results were validated with the experimental results by measuring the surface and fluid temperature of the heat exchanger at specific locations. Overall, we saw a close agreement between the simulated and experimental results for the surface and outlet temperature. The U-type heat exchanger micromodel will improve the understanding of complex flow patterns in 3D and open a new approach for treating brain injuries in humans and animals with small form factors

Numerical investigation of model combustors for efficiency improvement and miniature applications

Non-premixed combustion process is an important subject in most applications of combustion. Understanding of this phenomenon is crucial in the design of reliable, efficient, economical power generation systems. Microfabrication technologies in the development of power micro electro-mechanical systems is also becoming an increasing trend nowadays and the complete understanding of microfluid dynamics and non-premixed micro-combustion phenomena will lead the success in this field. In recent years numerical simulations have become an essential tool to understand combustion process to overcome experimental problems without losing accuracy. In this study, two numerical simulations were performed on the analysis of the effect of injection on the turbulent mixing quality in a simple combustor and on the dynamics non-premixed flame street in a mesoscale channel using the commercial software Fluent®. The effect of inlet geometries were first investigated for a Lockwood-type combustor in terms of combustion and energy efficiency and an efficient design configuration is deduced. The effect of wall temperature and flow velocities on the dynamics of non-premixed flame in a scaled combustion channel was investigated in the second part of this study. The results suggest that the two main parameters affecting the development of a non-premixed flame street in a mesoscale channel are the heat transfer to and from the wall and the diffusion time of the flow. The analysis of numerical details such as grid resolution, turbulent and chemistry models is emphasized throughout the study to understand the influence of these numerical parameters on the simulated phenomenon by comparing with experimental observations