Papers by Andrzej Przekwas
The packaging trends for the latter part of the 1990’s appear to suggest that advanced computing ... more The packaging trends for the latter part of the 1990’s appear to suggest that advanced computing and military application multi-chip modules (MCMs) will generate tremendous heat loads. Advanced, accurate design tools will be needed to evaluate new cooling concepts entailing complex geometries and complex physics, and which are capable of solving large scale numerical problems. This paper presents a high resolution computational model for thermal design of high density electronic packages. Details of numerical model for strongly implicit conjugate heat transfer are discussed. A novel high accuracy numerical wall scheme has been presented to resolve near wall shear stresses and wall heat fluxes. Three electronics cooling problems have been selected to validate the computer code on complex geometry configurations. These configurations are: an SMT module with fully resolved leadframe, 256 pin heat sink and a 20 module MCM with 74 fin heat sink. Results of the computational study are compared with available experimental data. In all three cases very good agreement with experiment has been achieved.
In recent years, a number of new shock-capturing finite difference schemes, often called high res... more In recent years, a number of new shock-capturing finite difference schemes, often called high resolution schemes, have been proposed. We considered several variations of the TVD scheme, EN0 scheme, FCT scheme, and geometrical schemes such as MUSCL and PPM. Only essential features of the schemes are described and much of the mathematical theory is omitted, but a key source reference list is provided. In this paper we present a comparative study of these schemes applied to the Burgers' equation. The objective is to assess their performance for problems involving formation and propagation of shocks, shock collisions, and expansion of discontinuities. A similar study for gas dynamic equation systems and resonant flow problems is reported in a separate paper.
Proceedings of SPIE, Apr 10, 2000
Simulation and design of microfluidic systems requires various level models: high-fidelity models... more Simulation and design of microfluidic systems requires various level models: high-fidelity models for design and optimization of particular elements and devices as well as system-level models allowing for VLSI-scale simulation of such systems. For the latter purpose, reduced or compact models are necessary to make such system simulations computationally feasible. In this paper, we present a design methodology and practical approach for generation of compact models of microfluidic elements. In this procedure we use high-fidelity 3D simulations of the microfluidic devices to extract their characteristics for compact models, and subsequently, to validate the compact model behavior in various regimes of operation. The compact models are generated automatically in the formats that can be directly used in SPICE or SABER. As an example of a nonlinear fluidic device, the generation of compact model for 'Tesla valve' is described in detail. Tesla valve is one of the no-moving- parts valves used in micropumps in MEMS. Its principle of operation is based on the rectification of the fluid, so it may be considered as a 'fluidic diode'.
NASA STI/Recon Technical Report N, May 1, 1995
The computation of flows within interconnected, multiple-disk cavities shows strong interaction b... more The computation of flows within interconnected, multiple-disk cavities shows strong interaction between the cavities and the power stream. For this reason, simulations of single cavities in such cases are not realistic; the complete, linked configuration must be considered. Unsteady flow fields affect engine stability and can engender power-stream-driven secondary flows that produce local hot spotting or general cavity beating. Further, a concentric whirling rotor produces a circumferential pressure wave, but a statically eccentric whirling rotor produces a radial wave; both waves affect cavity ingestion and the stability of the entire engine. It is strongly suggested that seals be used to enhance turbojet engine stability. Simple devices, such as swirl brakes, honeycomb inserts, and new seal configurations, should be considered. The cost effectiveness of the NASA Lewis Research Center seals program can be expressed in terms of program goals (e.g., the Integrated High-Pressuref[emperature Engine Technology (llIPTET) cannot be achieved without such a program), cost (savings to $250 million/I-percent decrease in specific fuel consumption), and indirect benefits (reduction of atmospheric NO x and CO 2 and reduction of powerplant downtime).
Final Report, Dec 1, 1991
ABSTRACT
Proceedings of SPIE, Jul 7, 1998
ABSTRACT An integrated device and package 3D model is developed to computationally investigate th... more ABSTRACT An integrated device and package 3D model is developed to computationally investigate the thermal crosstalk in arrays of proton-implanted top-surface emitting lasers. A self- consistent electro-thermo-opto model is employed for the device. The anisotropic thermal property is considered for the package model. Temperature dependency of critical device and material properties is included, as well as multiple heat generation mechanisms. Effects of spacing on lasing performance and non-uniformity of VCSEL arrays are found significant. Thermal crosstalk becomes worse for increased sizes and packaging densities of laser arrays. Degraded laser performance is found due to the thermal crosstalk, especially for the lasers closest to the center of the array package.
TechConnect Briefs, Mar 19, 2001
Drug Discovery Today, Sep 1, 2018
Proceedings of SPIE, Feb 9, 2006
The response of the biological cells to optical manipulation in the bio-microfluidic devices is s... more The response of the biological cells to optical manipulation in the bio-microfluidic devices is strongly influenced by the flow and motion inertia. There is a variety of microfluidic architectures in which both the cell-fluid interaction and the optical field are driving forces for segregation and manipulation of the cells. We developed a computational tool for analysis/optimization of these devices. The tool consists of two parts: an optical force library generator and the computational fluid dynamics solver with coupled optical force field. The optical force library can be computed for spherical and non-spherical objects of rotational symmetry and for complex optical fields. The basic idea of our method is to a) represent an incident optical field at the biological cell location as an angular spectrum of plane waves; b) compute the scattered field, being a coherent superposition of the scattered fields coming from each of the incident plane waves, with the powerful T-matrix method used to compute the amplitude matrix; c) use the incident and computed scattered fields to build a spatial map of optical forces exerted on biological cells at different locations in the optical beam coordinate system, and d) apply the library of optical forces to compute laser beam manipulation in microfluidic devices. The position and intensity of the optical field in the microfluidic device may be dynamic, thus optical forces in microfluidic device are based on the instantaneous relative location of the cell in the beam coordinate system. The cell is simulated by the macroparticle that undergoes mutual interactions with the fluid. We will present the exemplary applications of the code.
Proceedings of SPIE, Aug 6, 1999
Thermally induced failures in semiconductor laser diode arrays have been a serious issue in therm... more Thermally induced failures in semiconductor laser diode arrays have been a serious issue in thermal and mechanical design of such an optoelectronic system. Highly localized heating and CTE mismatch of materials have adverse effects on laser operations both at the levels of individual devices and their arrays, and also impact on the alignment required for laser diode arrays for optical coupling. A multi-scale thermal/flow/stress solver CFD-ACE+ package is employed in the present design study of an array of laser diodes cooled by microchannels using heat spreaders. Very good agreement between the simulated results and the published experimental data is achieved for the three dimensional simulations. Prominent temperature peaks are observed for the high power density diode arrays. More than 20% enhancement of cooling using diamond for heat sinks is found over silicon. Thermal stresses induced in the soldering process are investigated for various substrate materials. Coupled flow, thermal and stress analyses are also conducted for the microchannel design.
Three-dimensional integrated circuits (3D IC) are fabricated by vertically stacking a number of t... more Three-dimensional integrated circuits (3D IC) are fabricated by vertically stacking a number of thinned dies on top of each other with interconnects between them. 3D IC can significantly improve circuit performance and offer the promise of integrating various technologies (memory, logic, RF, mixed-signal, optoelectronics) within a single block. This high-density integration however, causes severe thermal management problems. New cooling concepts and novel design tools are needed to accelerate the transition of 3D IC technology from research labs to the commercial market. The objective of this paper is two fold: to present novel multiphysics modeling tools CFD-ACE+ for 3D ICs, and to demonstrate how these tools have been used to design a new concept of thermoelectric-fluidic active cooling device for refrigerative thermal management of 3D IC.
CPT: pharmacometrics & systems pharmacology, Dec 20, 2022
In silico mechanistic modeling approaches have been designed by various stakeholders with the goa... more In silico mechanistic modeling approaches have been designed by various stakeholders with the goal of supporting development and approval of generic orally inhaled drug products in the United States. This review summarizes the presentations and panel discussion that comprised a workshop session concentrated on the use of in silico models to predict various outcomes following orally inhaled drug product administration, including the status of such models and how model credibility may be effectively established.
SAE technical paper series, Feb 24, 1997
SAE technical paper series, Oct 1, 1992
SAE technical paper series, Mar 1, 1993
Proceedings of SPIE, Apr 10, 2000
In this work, a new fully automated geometrical modeling and meshing tool is described. It import... more In this work, a new fully automated geometrical modeling and meshing tool is described. It imports standard layout formats (CIF, GDSII, DXF), images (GIF, JPG), and 3D boundary representations (STL). A 3D model is then generated by simulating 3D operations (etching, deposition, insertion, etc.) specified by the process data or the user. A 3D finite element mesh with tagged boundary and volume conditions is then automatically created. The automatic generation of 3D model and mesh takes typically a couple of minutes on a current PC machine. The paper will present the geometry/meshing engines, user interfaces, and will demonstrate them on a range of microsystem applications.
Electron Technology, 1999
Proceedings of SPIE, Feb 9, 2006
The application of the frequency domain and steady-state diffusive optical spectroscopy (DOS) and... more The application of the frequency domain and steady-state diffusive optical spectroscopy (DOS) and steady-state near infrared spectroscopy (NIRS) to diagnosis of the human lung injury challenges many elements of these techniques. These include the DOS/NIRS instrument performance and accurate models of light transport in heterogeneous thorax tissue. The thorax tissue not only consists of different media (e.g. chest wall with ribs, lungs) but its optical properties also vary with time due to respiration and changes in thorax geometry with contusion (e.g. pneumothorax or hemothorax). This paper presents a finite volume solver developed to model photon migration in the diffusion approximation in heterogeneous complex 3D tissues. The code applies boundary conditions that account for Fresnel reflections. We propose an effective diffusion coefficient for the void volumes (pneumothorax) based on the assumption of the Lambertian diffusion of photons entering the pleural cavity and accounting for the local pleural cavity thickness. The code has been validated using the MCML Monte Carlo code as a benchmark. The code environment enables a semi-automatic preparation of 3D computational geometry from medical images and its rapid automatic meshing. We present the application of the code to analysis/optimization of the hybrid DOS/NIRS/ultrasound technique in which ultrasound provides data on the localization of thorax tissue boundaries. The code effectiveness (3D complex case computation takes 1 second) enables its use to quantitatively relate detected light signal to absorption and reduced scattering coefficients that are indicators of the pulmonary physiologic state (hemoglobin concentration and oxygenation).
Elsevier eBooks, 2020
Abstract The current drug discovery and development process involves costly, slow, and risk-laden... more Abstract The current drug discovery and development process involves costly, slow, and risk-laden preclinical in vitro and animal studies and semiempirical protocols for extrapolation of preclinical data to humans. Because of considerable differences in anatomy and physiology between animals and humans, direct extrapolation from animals to human remains very controversial. Similarly, in vitro static cell culture methods cannot mimic the complex in vivo biological and physiological microenvironments. Microfluidics-enabled cell culture technologies paved the way for organ-on-a-chip (OoC) devices and their linking created the prospect for human-on-a-chip systems that emulate in vivo physiological functions and pharmacological responses. Most OoC devices have been designed by trial and error. Advanced physics- and biology-based computational models are required for designing these systems, analyzing experimental data, and translating in vitro data to human responses. This chapter reviews recent achievements and identifies new directions for application of multiscale computational methods in OoC research.
Journal of Computational Physics, 2015
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Papers by Andrzej Przekwas