Recent Submissions

  • Runtime Abstraction for Autonomous Adaptive Systems on Reconfigurable Hardware

    Bucknall, Alex R.; Fahmy, Suhaib A. (IEEE, 2021-02-01) [Conference Paper]
    Autonomous systems increasingly rely on on-board computation to avoid the latency overheads of offloading to more powerful remote computing. This requires the integration of hardware accelerators to handle the complex computations demanded by date-intensive sensors. FPGAs offer hardware acceleration with ample flexibility and interfacing capabilities when paired with general purpose processors, with the ability to reconfigure at runtime using partial reconfiguration. Managing dynamic hardware is complex and has been left to designers to address in an ad-hoc manner without first-class integration in autonomous software frameworks. This paper presents an abstracted runtime for managing adaptation of FPGA accelerators, including partial reconfiguration and parametric changes, that presents as a typical interface used in autonomous software systems. We present a demonstration using the Robot Operating System (ROS), showing negligible latency overhead as a result of the abstraction.
  • A Visual Analytics Based Decision Making Environment for COVID-19 Modeling and Visualization

    Afzal, Shehzad; Ghani, Sohaib; Jenkins-Smith, Hank C.; Ebert, David S.; Hadwiger, Markus; Hoteit, Ibrahim (IEEE, 2021-02-01) [Conference Paper]
    Public health officials dealing with pandemics like COVID-19 have to evaluate and prepare response plans. This planning phase requires not only looking into the spatiotemporal dynamics and impact of the pandemic using simulation models, but they also need to plan and ensure the availability of resources under different spread scenarios. To this end, we have developed a visual analytics environment that enables public health officials to model, simulate, and explore the spread of COVID-19 by supplying county-level information such as population, demographics, and hospital beds. This environment facilitates users to explore spatiotemporal model simulation data relevant to COVID-19 through a geospatial map with linked statistical views, apply different decision measures at different points in time, and understand their potential impact. Users can drill-down to county-level details such as the number of sicknesses, deaths, needs for hospitalization, and variations in these statistics over time. We demonstrate the usefulness of this environment through a use case study and also provide feedback from domain experts. We also provide details about future extensions and potential applications of this work.
  • DOA Estimation with a Rank-deficient Covariance matrix: A Regularized Least-squares approach

    Ali, Hussain; Ballal, Tarig; Al-Naffouri, Tareq Y.; Sharawi, Mohammad S. (IEEE, 2021-01-18) [Conference Paper]
    DOA estimation in the presence of coherent sources using a small number of snapshots faces the challenge of rank deficiency of the received signal covariance matrix. When the covariance matrix is rank deficient, only the pseudo inverse of the covariance matrix can be computed, which can give undesirable results. Traditionally, regularized least-squares (RLS) algorithms are used to tackle estimation problems in systems with ill-conditioned or rank deficient matrices. In this work, we combine the Capon beamformer with the RLS framework to develop a DOA estimation method for scenarios with rank deficient covariance matrices. Simulation results demonstrate the effectiveness of the proposed approach.
  • A Machine Learning-Based Microwave Device Model for Fully Printed VO2 RF Switches

    Yang, Shuai; Khusro, Ahmad; Li, Weiwei; Vaseem, Mohammad; Hashmi, Mohammad; Shamim, Atif (IEEE, 2021-01-12) [Conference Paper]
    Fully printed vanadium dioxide (VO2) based Radio Frequency (RF) switches have been recently developed for advanced frequency-reconfigurable RF electronics. A reliable and versatile model for the VO2 switches is required for design and simulations in the modern Computer-Aided Design (CAD) tools. This paper proposes a machine learning (ML) based model for VO2 RF switches, which is much more time and resource efficient as compared to the traditional device models. The computational efficiency, accuracy and robustness of the proposed model over a frequency range of 30 GHz is demonstrated through an excellent agreement between the modelled and measured results. The comparison between the measured and modelled results demonstrate a mean-square error (MSE) of lower than 5 x 10-4 and 5 x10-3 for the magnitude and phase values over the complete frequency range.
  • Volume of fluid based model of heavy fuel oil droplet evaporation and combustion

    Guida, Paolo; Saxena, Saumitra; Roberts, William L. (American Society of Mechanical Engineers, 2021-01-11) [Conference Paper]
    Modern CFD simulations of combustion resolve simplified sub-models for droplet evaporation and combustion within a Lagrangian framework. Break-up effects like puffing and micro-explosions are usually neglected but, they eventually influence the evaporation and combustion behaviour of heavy fuel sprays. We are developing a Volume of Fluid (VoF)-based CFD solver that allows us to model single droplet differential evaporation with the break-up effects. Puffing/micro-explosion and droplet ejection proceed in three steps: nucleation of a bubble of a light component within the droplet, expansion/coalescence of the bubbles and finally eruption with sub-droplets formation. Our goal is to individually model each event and then combine them in a composite simulation. Henceforth we can get data in realistic conditions to be used in Lagrangian spray simulations. We identified three relevant features that are necessary to create a reliable representation: interface tracking, differential evaporation, and compressibility effect. The solver is based on the Volume of Fluid (VoF) technique and coded within the open-source OpenFOAM framework. VoF technique consists of transporting the volume fraction of one of the two phases (liquid or gas). The Navier-Stokes equations are solved for a single-phase but adapting the physical properties to the volume fraction value. A state-of-the-art method called iso-Advector was adopted to reconstruct the interface from the volume fraction field. The evaporation was implemented as a source term in the volume fraction equation, and the conservation equations were modified accordingly. In order to calculate the vapour and liquid physical properties, RKS equation of state (EOS) was implemented. The droplet was assumed to have 2 phases: light and heavy, having physical properties comparable to water and heavy fuel oil (HFO), respectively. The pressure closure equation was modified to handle large pressure differences during the internal evaporation of light components. The validation of the solver was performed through benchmark cases as multiphase shock-tube, droplet oscillation and boiling interface either with experimental works and analytical solutions. A single suspended droplet experiment was performed to measure the velocity of an ejected micro-droplet during puffing using a shadowgraphy technique. The code is able to predict ejection velocity within a 15% error, which seems to be promising. The present article documents part of the algorithm development and its validation. In particular, the step describing the ejection of the inner vapours is described.
  • Feasibility of innovative solar-thermo-acoustic power conversion cycles

    Behar, Omar; Saxena, Saumitra; Roberts, William L. (American Society of Mechanical Engineers, 2021-01-11) [Conference Paper]
    The techno-economic assessment of the concentrating solar power thermo-acoustic power conversion systems is carried out to identify the optimum conditions, under-which the solar thermo-acoustic might be competitive to the current commercial solar thermal power technologies. The thermal and economic performance of a thermo-acoustic engine integrated to five different solar collectors including Compound Parabolic Collector, Linear Fresnel, Parabolic Trough, Central receiver, and Solar Dish is compared to the current commercial solar thermal power technologies as well as to their corresponding Carnot-cycle. To do so, a modular modeling approach is used to consider all the available commercial technologies, through combining a modular energy model with a simplified economic model. Jeddah city (Saudi Arabia) has been chosen as a reference site for the present study. The results indicate that the integration of compound and dish solar collectors to a thermo-acoustic engine mightoffer competitive solutions. Compound collectors might be more suitable for integration with the thermo-acoustic engine than linear Fresnel collectors, if the exergy efficiency of the engine reaches 40%. Besides, dish-thermo-acoustic system becomes more competitive than current dish-mechanical Stirling engine, if the investment costs of the thermo-acoustic engine arereduced to 3500 $/kWe, but the operating temperature should be above 700°C. Improving the exergy efficiency of the thermos-acoustic engines, from 35% to 40%, could make the dish-thermo-acoustic system more competitive than current dish-mechanical Stirling engines at a working temperature of 500°C. The study concludes that more efforts must be focused on reducing the costs of the TA devices rather than on improving efficiency.
  • Entropy–Stable No–Slip Wall Boundary Conditions for the Eulerian Model for Viscous and Heat Conducting Compressible Flows

    Sayyari, Mohammed; Dalcin, Lisandro; Parsani, Matteo (American Institute of Aeronautics and Astronautics, 2021-01-11) [Conference Paper]
    Nonlinear (entropy) stability analysis is used to derive entropy–stable no–slip wall boundary conditions at the continuous and semi–discrete levels for the Eulerian model proposed by Svärd in 2018 (Physica A: Statistical Mechanics and its Applications, 2018). The spatial discretization is based on discontinuous Galerkin summation-by-parts operators of any order for unstructured grids. We provide a set of two–dimensional numerical results for laminar and turbulent flows simulated with both the Eulerian and classical Navier–Stokes models. These results are computed with a high-performance ℎ–entropy–stable solver, that also features explicit and implicit entropy–stable time integration schemes.
  • Design optimization of a multi-kW thermoacoustic electric generator using deltaec model

    Somu, Srinath; Lacoste, Deanna; Saxena, Saumitra; Roberts, William L.; Keolian, Robert M. (American Society of Mechanical Engineers, 2021-01-11) [Conference Paper]
    Waste heat recovery from power plants and industries requires a new type of electricity generators and related technological developments. The current research work is aimed at the design of a multi-kilowatt thermoacoustic electric generator, which can be employed as the bottoming cycle of a gas-turbine power plant or for industrial waste heat recovery. The proposed device converts thermal energy into acoustic power and subsequently uses a piezoelectric alternator to convert acoustic power into electricity. The challenge in designing such a device is that it has to be acoustically balanced and the performance of the device is greatly affected by numerous parameters such as frequency of the traveling acoustic wave, heat exchanger parameters, regenerator dimensions, acoustic feedback loop, etc. The proposed device is a lab-scale demonstration targeted to produce a few kilowatts of electric power from a 20 kWth heat source. To achieve the acoustically balanced configuration of the device, DeltaEC software is used. The DeltaEC model outcomes are used to arrive at the optimized design of the device and its components. The analytical method, the optimized geometrical dimensions of thermoacoustic components and the minimum required conditions of heat source input are presented in this paper.
  • Towards Analyzing Semantic Robustness of Deep Neural Networks

    Hamdi, Abdullah; Ghanem, Bernard (Springer International Publishing, 2021-01-10) [Conference Paper]
    Despite the impressive performance of Deep Neural Networks (DNNs) on various vision tasks, they still exhibit erroneous high sensitivity toward semantic primitives (e.g. object pose). We propose a theoretically grounded analysis for DNN robustness in the semantic space. We qualitatively analyze different DNNs’ semantic robustness by visualizing the DNN global behavior as semantic maps and observe interesting behavior of some DNNs. Since generating these semantic maps does not scale well with the dimensionality of the semantic space, we develop a bottom-up approach to detect robust regions of DNNs. To achieve this, we formalize the problem of finding robust semantic regions of the network as optimizing integral bounds and we develop expressions for update directions of the region bounds. We use our developed formulations to quantitatively evaluate the semantic robustness of different popular network architectures. We show through extensive experimentation that several networks, while trained on the same dataset and enjoying comparable accuracy, do not necessarily perform similarly in semantic robustness. For example, InceptionV3 is more accurate despite being less semantically robust than ResNet50. We hope that this tool will serve as a milestone towards understanding the semantic robustness of DNNs.
  • A Comparison of Parallel Profiling Tools for Programs utilizing the FFT

    Leu, Brian; Aseeri, Samar; Muite, Benson (ACM, 2021-01-06) [Conference Paper]
    Performance monitoring is an important component of code optimization. Performance monitoring is also important for the beginning user, but can be difficult to configure appropriately. The overhead of the performance monitoring tools Craypat, FPMP, mpiP, Scalasca and TAU, are measured using default configurations likely to be choosen by a novice user and shown to be small when profiling Fast Fourier Transform based solvers for the Klein Gordon equation based on 2decomp&FFT and on FFTE. Performance measurements help explain that despite FFTE having a more efficient parallel algorithm, it is not always faster than 2decom&FFT because the complied single core FFT is not as fast as that in FFTW which is used in 2decomp&FFT.
  • A robust explicit asynchronous time integration method for hyperbolic conservation laws

    Messahel, R.; Boutsikakis, A.; Grondin, G.; Gressier, J.; Parsani, Matteo; Boukharfane, Radouan (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    Hyperbolic conservation laws are of great practical importance as they model diverse multiscale phenomena (highly turbulent flows, combustion, etc.). To solve these equations, explicit time integration methods are used, for which the Courant–Friedrichs–Lewy (CFL) condition has to be satisfied everywhere in the computational domain. Therefore, the global time step will be dictated by the cells that require the smallest time step, resulting in an unnecessarily expensive computational approach. To overcome this difficulty, a conservative asynchronous method for explicit time integration schemes is developed and implemented for flux-based spatial schemes. The concept of the developed method is using dynamically variable time steps for classes of cells, while ensuring the time coherence of the time integration and flux conservation. In this paper, we present the classification of computational cells in classes based on their local stability criterion. Two versions of the (asynchronous) synchronization sequence are proposed, which are designed regardless of equation model and spatial scheme. In the context of hyperbolic conservation laws, we numerically investigate the conservation, accuracy and stability properties of the proposed method for one-dimensional linear convection and Euler equations. We show that the proposed asynchronous approach can be more accurate than its synchronous counterpart through the limitation of the diffusion errors by locally increasing the CFL number and thus, the local time step.
  • Optimized explicit runge–kutta schemes for entropy stable discontinuous collocated methods applied to the euler and navier–stokes equations

    Al Jahdali, R.; Boukharfane, Radouan; Dalcin, Lisandro; Parsani, Matteo (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    In this work, we design a new set of optimized explicit Runge–Kutta schemes for the integration of systems of ordinary differential equations arising from the spatial discretization of wave propagation problems with entropy stable collocated discontinuous Galerkin methods. The optimization of the new time integration schemes is based on the spectrum of the discrete spatial operator for the advection equation. To demonstrate the efficiency and accuracy of the new schemes compared to some widely used classic explicit Runge–Kutta methods, we report the wall-clock time versus the error for the simulation of the two-dimensional advection equation and the propagation of an isentropic vortex with the compressible Euler equations. The efficiency and robustness of the proposed optimized schemes for more complex flow problems are presented for the three-dimensional Taylor–Green vortex at a Reynolds number of Re = 1.6 × 103 and Mach number Ma = 0.1, and the flow past two identical spheres in tandem at a Reynolds number of Re = 3.9 × 103 and Mach number Ma = 0.1.
  • A numerical study on soot formation and evolution in pressurized turbulent sooting flames

    Zhou, Dezhi; Vaage, Anders; Yang, Suo; Boyette, Wesley; Guiberti, Thibault; Roberts, William L. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    Understandings on soot formation and evolution in pressurized flames are of significant interest due to the increasing operating pressures in different combustors and the accompanying increased soot emissions. In this study, a series of pressurized turbulent sooting flames at 1 bar, 3 bar and 5 bar, are simulated to study the pressure effect on the soot formation and evolution. The inflow conditions are chosen such that the Reynolds number at different pressures keep constant. Via a Radiation Flamelet Progress Variable (RFPV) approach with a conditional soot sub-filter Probability Density Function (PDF) to consider the turbulence-chemistry-soot interaction, quantitatively good agreements (e.g., maximum discrepancy within one order of magnitude) are achieved for soot volume fraction predictions compared with the experimental data at different pressures. Soot volume fraction source terms are then discussed to show the pressure effect on nucleaion, condensation, surface growth and oxidation at different axial positions in these flames.
  • LES Study of Active Valve Resonant Pulse Combustor

    Lisanti, Joel; Zhu, Xuren; Guiberti, Thibault; Roberts, William L. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    This work describes the methodology and progress towards numerical simulation of an active valve resonant pulse combustor. The study is being conducted using a reacting, large eddy simulation with dynamic mesh capability to handle the valve motion. To date results have not reached full resonant operation but preliminary analysis suggest that the simulation is moving towards a resonant state. Pressure oscillations within the simulated combustor are shown to shift in phase towards resonance for each of the three most recently completed cycles. Phasing of reverse flow into the exit plane of the combustor is consistent with the wave structure of resonant operation and the location and phasing of heat release is also shifting towards the expectations for resonance. Future work will include validating the simulated operation with experimental results, calculation of the device Rayleigh efficiency, and analysis of the cycle to cycle flame re-ignition.
  • Large eddy simulation with flamelet progress variable approach combined with artificial neural network acceleration

    Angelilli, Lorenzo; Ciottoli, Pietro Paolo; Malpica Galassi, Riccardo; Hernandez Perez, Francisco; Soldan, Mattia; Lu, Zhen; Valorani, Mauro; Im, Hong G. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    In the context of large eddy simulation of turbulent reacting flows, flamelet-based models are key to affordable simulations of large and complex systems. However, as the complexity of the problem increases, higher-dimensional look-up tables are required, rendering the conventional look-up procedure too demanding. This work focuses on accelerating the estimation of flamelet- based data for the flamelet/progress variable model via an artificial neural network. The neural network hyper-parameters are defined by a Bayesian optimization and two different architectures are selected for comparison against the classical look-up procedure on the well known Sandia flame D. The performance in terms of execution time and accuracy are analyzed, showing that the neural network model reduces the computational time by 30%, as compared to the traditional table look-up, while retaining comparable accuracy.
  • Effects of differential diffusion and stratification characteristic length-scale on the propagation of a spherical methane-air flame kernel

    Er-Raiy, Aimad; Boukharfane, Radouan; Parsani, Matteo (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    Early flame kernel development and propagation in globally lean stratified fuel--air mixtures is of importance in various practical devices such as internal combustion engines. In this work, three-dimensional direct numerical simulation (DNS) is used to study the influence of the differential diffusion effects in a globally lean methane--air mixtures in presence of mixture heterogeneities with the goal of understanding the flame kernel behavior in such conditions. The DNS typical configuration corresponds to a homogeneous isotropic flow with an expanding spherical flame kernel. The local forced ignition of the kernel is performed by appending as source term in the sensible enthalpy transport equation that emulates spark ignition by energy deposit for a prescribed duration. The combustion chemistry is described with a skeletal methane-air mechanism, which i) features 14 species and 38 reactions, and ii) uses a multicomponent approach to evaluate transport coefficients. To assess the joint effects of differential diffusion and the stratification characteristic length-scale $L_{\Phi}$ on the flame kernel development, we considered cases with constant (unitary) and variable fuel Lewis number, both with different values for $L_{\Phi}$.
  • An Assessment of Unmanned Aircraft System Operations with the Extensible Trajectory Optimization Library

    Sanni, Olatunde B.; Khamvilai, Thanakorn; Puntawuttiwong, Teppatat; Feron, E. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    In the not too distant future, Unmanned Aircraft Systems (UAS) will be a source of economic power in urban environments. These systems will be used for package delivery, building inspections, filming, and many other tasks. However, economic benefits should not outweigh public safety. These systems must not collide into buildings, and they must maintain a safe separation distance from neighboring systems. In other words, UAS operations should be assessed for safety. This paper assesses how safety requirements in the urban environment influence UAS operations. It presents a novel way of performing this assessment by using the Extensible Trajectory Optimization Library (ETOL) to continuously solve a vehicle guidance problem (VGP) in a multi-agent robot simulator. This paper introduces the common structure of a VGP, along with a VGP formulation for a UAS in an urban environment. In addition, a platform for safety assessments is presented, along with recommendations for improving the safety of UAS operations.
  • Simulation of Turbulent Flows Using a Fully Discrete Explicit hp-nonconforming Entropy Stable Solver of Any Order on Unstructured Grids

    Parsani, Matteo; Boukharfane, Radouan; Reyna Nolasco, Irving E.; Dalcin, Lisandro; Keyes, David E. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    We report the numerical solution of two challenging turbulent flow test cases simulated with the SSDC framework, a compressible, fully discrete hp-nonconforming entropy stable solver based on the summation-by-parts discontinuous collocation Galerkin discretizations and the relaxation Runge—Kutta methods. The algorithms at the core of the solver are systematically designed with mimetic and structure-preserving techniques that transfer fundamental properties from the continuous level to the discrete one. We aim at providing numerical evidence of the robustness and maturity of these entropy stable scale-resolving methods for the new generation of adaptive unstructured computational fluid dynamics tools. The two selected turbulent flows are i) the flow past two spheres in tandem at a Reynolds number based on the sphere diameter of ReD = 3.9 × 103 and 104, and a Mach number of Ma∞ = 0.1, and ii) the NASA junction flow experiment at a Reynolds number based on the crank chord length of Reℓ = 2.4×106 and Ma∞ = 0.189.
  • Compressibility effects on homogeneous isotropic turbulence using Schur decomposition of the velocity gradient tensor.

    Boukharfane, Radouan; Er-Raiy, Aimad; Parsani, Matteo (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    The study of compressibility effects on the dynamics and the structure of turbulence is an important, but difficult, topic in turbulence modeling. Taking advantage of a recently proposed Schur decomposition approach (Keylock, C. J., The Schur decomposition of the velocity gradient tensor for turbulent flows, Journal of Fluid Mechanics, 2018) to decompose the velocity gradient tensor into its normal and non-normal parts, here we evaluate the influence of the compressibility on some statistical properties of the turbulent structures. We perform a set of direct numerical simulations of decaying compressible turbulence at six turbulent Mach numbers between Mt = 0.12 and Mt = 0.89 and a Reynolds number based on the Taylor micro-scale of Ret = 100. All the simulations have been carried out using an improved seventh-order accurate WENO scheme to discretize the non-linear advective terms and an eight-order accurate centered finite difference scheme is retained for the diffusive terms. In the double decomposition, the normal parts of the velocity gradient tensor (represented by the eigenvalues) are separated explicitly from non-normal components. The two-dimensional space defined by the second and third invariants of the velocity gradient tensor is subdivided into six regions and the contribution of each regional term to the Schur decomposition of the velocity gradient tensor is analyzed. Our preliminary findings show the difficulty of understanding the non-local effects without taking into account both the normal contribution (represented by the eigenvalues) and the non-normal component computed with of the Schur decomposition.
  • A Computational Study of Ammonia Combustion in MILD Conditions

    Khamedov, Ruslan; Song, Wonsik; Hernandez Perez, Francisco; Im, Hong G. (American Institute of Aeronautics and Astronautics, 2021-01-04) [Conference Paper]
    o provide fundamental insights into the heat release and emission characteristics of ammonia flames in moderate or intense low-oxygen dilution (MILD) conditions, numerical simulations in one-dimensional laminar and two-dimensional turbulent flame configurations are conducted. The analysis shows that for the ammonia MILD flame, lower NOx emissions can be achieved while improving flame stability characteristics. In addition, the propagation of ammonia flames into forced turbulent flows in a channel is examined in terms of turbulent flame speed and surface area enhancement. The normalized flame speed and flame surface area are well correlated and show qualitatively similar behavior for the MILD and non-MILD flames.

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