Publications

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A streamline upwind Petrov-Galerkin finite element method is presented for the case of a reacting mixture of thermally-perfect gases, using chemical non-equilibrium. Details of the stabilization scheme and nonlinear solution are presented. The authors have independently implemented the proposed algorithm in two separate codes, for both single temperature and and two temperature models. Example problems invoving a cylinder in Mach 20 crossflow, as well as a three-dimensional blunt nosetip are shown and compared to established codes.

The peridynamic theory of mechanics attempts to unite the mathematical modeling of continuous media, cracks, and particles within a single framework. It does this by replacing the partial differential equations of the classical theory of solid mechanics with integral or integro-differential equations. These equations are based on a model of internal forces within a body in which material points interact with each other directly over finite distances. The classical theory of solid mechanics is based on the assumption of a continuous distribution of mass within a body. It further assumes that all internal forces are contact forces that act across zero distance. The mathematical description of a solid that follows from these assumptions relies on partial differential equations that additionally assume sufficient smoothness of the deformation for the PDEs to make sense in either their strong or weak forms. The classical theory has been demonstrated to provide a good approximation to the response of real materials down to small length scales, particularly in single crystals, provided these assumptions are met. Nevertheless, technology increasingly involves the design and fabrication of devices at smaller and smaller length scales, even interatomic dimensions. Therefore, it is worthwhile to investigate whether the classical theory can be extended to permit relaxed assumptions of continuity, to include the modeling of discrete particles such as atoms, and to allow the explicit modeling of nonlocal forces that are known to strongly influence the behavior of real materials.

This paper applies a pragmatic approach to validation of a fire-dynamics model involving computational fluid dynamics, combustion, participating-media radiation, and heat transfer. The validation problem involves experimental and predicted steady-state temperatures of a calorimeter in a wind-driven hydrocarbon pool fire. Significant aleatory and epistemic sources of uncertainty in the experiments and simulations exist and are transformed to a common basis of interval uncertainty for aggregation and comparison purposes. The validation comparison of experimental and simulation results, and corresponding criteria and procedures for model substantiation or refutation, take place in "real space" as opposed to "transform space" where various transform measuresof discrepancy between experiment and simulation results are calculated and assessed. The versatile model validation approach handles difficulties associated with representing and aggregating aleatory and epistemic uncertainties (discrete and continuous) from multiple correlated and uncorrelated source types, including 1) experimental variability from multiple repeat experiments, 2) uncertainty of experimental inputs, 3) experimental output measurement uncertainties, 4) uncertainties that arise in data processing and inference from raw simulation and experiment outputs, 5) parameter and model-form uncertainties intrinsictothe model, and 6) numerical solution uncertainty from model discretization effects. Copyright Clearance Center, Inc.

In this work we describe a new parallel lattice (PL) filter topology for electrically coupled AlN microresonator based filters. While 4th order, narrow percent bandwidth (0.03%) parallel filters based on high impedance (11 kΩ) resonators have been previously demonstrated at 20 MHz [1], in this work we realize low insertion loss PL filters at 400-500 MHz with termination impedances from 50 to 150 Ω and much wider percent bandwidths, up to 5.3%. Obtaining high percent bandwidth is a major challenge in microresonator based filters given the relatively low piezoelectric coupling coefficients, kt2, when compared to bulk (BAW) and surface (SAW) acoustic wave filter materials.

Linear systems are good approximations of the input-output relationship for many real systems. In practice, ensembles of nominally identical systems can seldom be adequately represented by a single linear system. Some accommodation needs to be made for representing inherent ensemble randomness. One approach would be to use a parameterized model of the system, with the random nature captured in discrete parameters of the parameterized model. Another approach is to use data measured from each system in the ensemble to represent the random nature of the ensemble in a non-parametric form. This is the approach described in this paper. There are several different types of data that could be collected from each system in the ensemble, each type capable of capturing the input-output behavior of the linear system: input-output time domain data, perhaps with specific excitation sequences [1,2]; Markov parameters [2,3]; and Frequency Response Functions (FRFs) [2] to name a few. We choose to work with FRF data because many system attributes can be easily interpreted by inspection of the FRF [4]. FRF data can also be used directly for control design [5,6,7]. This paper develops a Karhunen-Loeve expansion [8] representation for linear system behavior based on FRF data to develop a compact representation of the uncertainty inherent in an ensemble of systems. This non-parametric, compact, representation of the distribution of linear systems can then be used to characterize the performance and stability of a given feedback control law, as well as for control law design [5,6,7]. © 2010 AACC.

We demonstrate 5Gbs and10Gbs error free operation of silicon photonic microdisk resonant modulators to a distance of 70km, measure dispersion power penalties and compare the experimental results with theoretically derived values. ©2009 Optical Society of America.

We are concerned with transportation accidents and the subsequent fire. Progress is currently being made on a unique capability to model these very challenging events. We have identified Smoothed Particle Hydrodynamics (SPH) as a good method to employ for the impact dynamics of the fluid. SPH is capable of modeling viscous and inertial effects for these impacts for short times. We have also identified our fire code Lagrangian/Eulerian (L/E) particle capability as an excellent method for fuel transport and spray modeling. This fire code can also model the subsequent fire, including details of the heat and mass transfer necessary for thermal environment predictions. These two methods (SPH and L/E) employ disparate but complimentary length and timescales for the calculation, and are suited for coupling given adequate attention to relevant details. Length and timescale interactions are important considerations when joining the two capabilities. Coupling methodologies have been shown to be important to the model accuracy. Focusing on the transfer methods and spatial resolution, a notional impact problem is examined. The outcome helps to quantify the importance of various methods and to better understand the behavior of these modeling methods in a representative environment.

Motivated by the needs of seismic inversion and building on our prior experience for fluid-dynamics systems, we present a high-order discontinuous Galerkin (DG) Runge-Kutta method applied to isotropic, linearized elasto-dynamics. Unlike other DG methods recently presented in the literature, our method allows for inhomogeneous material variations within each element that enables representation of realistic earth models — a feature critical for future use in seismic inversion. Likewise, our method supports curved elements and hybrid meshes that include both simplicial and nonsimplicial elements. We demonstrate the capabilities of this method through a series of numerical experiments including hybrid mesh discretizations of the Marmousi2 model as well as a modified Marmousi2 model with a oscillatory ocean bottom that is exactly captured by our discretization.

Archimedes’ genius was derived in no small part from his ability to effortlessly interpret problems in both geometric and mechanical ways. We explore, in a modern context, the application of mechanical reasoning to geometric problem solving. The general form of this inherently Archimedean approach is described and it’s specific use is demonstrated with regard to the problem of finding the geodesics of a surface. Archimedes’ approach to thinking about problems may be his greatest contribution, and in that spirit we present some work related to teaching Archimedes’ ideas at an elementary level. The aim is to cultivate the same sort of creative problem solving employed by Archimedes, in young students with nascent mechanical reasoning skills.

The author of a popular book on risk and decision analysis made the statement that "The revolutionary idea that defines the boundary between modern times and the past is the mastery of risk: the notion that the future is more than a whim of the gods and that men and women are not passive before nature." (Bernstein 1998, 1) While this book was written primarily from the perspective of economics and finances, the premise that the tools for making a reasoned prediction of the future, based on past experience and present decisions, goes to the heart of what it means to "do" systems engineering. This paper examines the nature of uncertainty, risk and decision analysis, particularly as understood within the historical context and the continuing development of the "art and science of decision." © 2010 by Mark J. De Spain.

To study the rebound of a sphere colliding against a flat wall, a test setup was developed where the sphere is suspended with strings as a pendulum, elevated, and gravity-released to impact the wall. The motion of the sphere was recorded with a highspeed camera and traced with an image-processing program. From the speed of the sphere before and after each collision, the coefficient of restitution was computed, and shown to be a function of impact speed as predicted analytically.

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Elastic averaging is introduced as a methodology for the fabrication and assembly of multi-element, micro-optic arrays. Its performance and use is evaluated in the demonstration of a high efficiency, photovoltaic tracking system. © 2010 Optical Society of America.

The working of induced voltage alteration (IVA) techniques and its major developments in areas of hardware for analysis, electrical biasing, detection advances, resolution improvements, and future possibilities, is discussed. IVA technique uses either a scanning electron microscope's (SEM) electron beam or a scanning optical microscope's (SOM) laser beam as the external stimulus. The other IVA techniques were developed using different localized stimuli, with the same sensitive biasing approach. The IVA techniques takes advantage of the strong signal response of CMOS devices when operated as current-to-voltage converters. To improve the biasing approach, externally induced voltage alterations (XIVA) was introduced, in which an ac choke circuit acts as a constant-voltage source. Synchronization with device operation also allows specific vectors to be analyzed using local photocurrent and thermal stimulus.

Attitudes play a significant role in determining how individuals process information and behave. In this paper we have developed a new computational model of population wide attitude change that captures the social level: how individuals interact and communicate information, and the cognitive level: how attitudes and concept interact with each other. The model captures the cognitive aspect by representing each individuals as a parallel constraint satisfaction network. The dynamics of this model are explored through a simple attitude change experiment where we vary the social network and distribution of attitudes in a population. Copyright © 2010, Association for the Advancement of Artificial Intelligence. All rights reserved.

This paper presents object-oriented design patterns in the context of object construction and destruction. The examples leverage the newly supported object-oriented features of Fortran 2003. We describe from the client perspective two patterns articulated by Gamma et al. [1]: ABSTRACT FACTORY and FACTORY METHOD. We also describe from the implementation perspective one new pattern: the OBJECT pattern. We apply the Gamma et al. patterns to solve a partial differential equation, and we discuss applying the new pattern to a quantum vortex dynamics code. Finally, we address consequences and describe the use of the patterns in two open-source software projects: ForTrilinos and Morfeus.

Thermal boundary resistance dominates the thermal resistance in nanosystems since material length scales are comparable to material mean free paths. The primary scattering mechanism in nanosystems is interface scattering, and the structure and composition around these interfaces can affect scattering rates and, therefore, device thermal resistances. In this work, the thermal boundary conductance (the inverse of the thermal boundary resistance) is measured using a pump-probe thermoreflectance technique on aluminum films grown on silicon substrates that are subjected to various pre-Al-deposition surface treatments. The Si surfaces are characterized with Atomic Force Microscopy (AFM) to determine mean surface roughness. The measured thermal boundary conductance decreases as Si surface roughness increases. In addition, stripping the native oxide layer on the surface of the Si substrate immediately prior to Al film deposition causes the thermal boundary conductance to increase. The measured data are then compared to an extension of the diffuse mismatch model that accounts for interfacial mixing and structure around the interface. © 2010 by ASME.

To study the rebound of a sphere colliding against a flat wall, a test setup was developed where the sphere is suspended with strings as a pendulum, elevated, and gravity-released to impact the wall. The motion of the sphere was recorded with a highspeed camera and traced with an image-processing program. From the speed of the sphere before and after each collision, the coefficient of restitution was computed, and shown to be a function of impact speed as predicted analytically.

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