Scholarly Materials And Research @ Georgia Tech

    FPGA prototyping of custom GPGPUs

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    Prototyping new systems on hardware is a time-consuming task with limited scope for architectural exploration. The aim of this work was to perform fast prototyping of general-purpose graphics processing units (GPGPUs) on field programmable gate arrays (FPGAs) using a novel tool chain. This hardware flow combined with the higher level simulation flow using the same source code allowed us to create a whole tool chain to study and build future architectures using new technologies. It also gave us enough flexibility at different granularities to make architectural decisions. We will also discuss some example systems that were built using this tool chain along with some results.M.S

    Bayesian Paradigm to Assess Rock Compression Damage Models

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    Copyright © 2014 ICE PublishingDOI: http://dx.doi.org/10.1680/envgeo.13.00039Energy extraction and waste storage in geological formations raise interest in developing systematic and reliable calibration methods to assess performance of rock models. A methodology is proposed to improve damage prediction in sandstone, based on finite element simulations coupled with the Bayesian paradigm. To illustrate this methodology, we defined parameters of a continuum damage mechanics model as random variables. (1) Probability density functions are formulated for each parameter (expert’s judgement) and sampled later independently to simulate likely random sandstone responses during a triaxial compression test (forward problem). (2) Experimental data are introduced (new evidence available), which allow updating the probability distributions depicting the model parameters (inverse problem). Results show that it is possible to quantify the impact of experimental evidence into the rock characterisation and that correlations between all rock damage parameters can be retrieved. Mechanically speaking, this means that (a) similar accuracy in the prediction of damage might be achievable with less model parameters, (b) and the input of energy released to initiate crack propagation is contingent on conditions external to the model (e.g., initial texture of the rock). Results from this investigation provide promising applications of the probabilistic calibration approach to damage models in multiphase porous medium

    Thermo-Hydro-Mechanical Modeling of Damage in Unsaturated Porous Media: Theoretical Framework and Numerical Study of the EDZ

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    Copyright © 2011 John Wiley & Sons, Ltd.DOI: dx.doi.org/10.1002/nag.1005The damage model presented in this article (named ‘THHMD’ model) is dedicated to non-isothermal unsaturated porous media. It is formulated by means of three independent strain state variables, which are the thermodynamic conjugates of net stress, suction and thermal stress. The damage variable is a second-order tensor. Stress/strain relationships are derived from Helmholtz free energy, which is assumed to be the sum of damaged elastic potentials and ‘crack-closure energies’. Damage is assumed to grow with tensile strains due to net stress, with pore shrinkage due to suction and with thermal dilatation. Specific conductivities are introduced to account for the effects of cracking on the intensification and on the orientation of liquid water and vapor flows. These conductivities depend on damage and internal length parameters. The mechanical aspects of the THHMD model are validated by comparing the results of a triaxial compression test with experimental measurements found in the literature. Parametric studies of damage are performed on three different heating problems related to nuclear waste disposals. Several types of loading and boundary conditions are investigated. The thermal damage potential is thoroughly studied. The THHMD model is expected to be a useful tool in the assessment of the Excavation Damaged Zone, especially in the vicinity of nuclear waste repositories

    Site-specific Spectral Response of Seismic Movement due to Geometrical and Geotechnical Characteristics of Sites

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    Copyright © 2009 Elsevier Ltd.DOI: dx.doi.org/10.1016/j.soildyn.2008.01.015It is well-known that the response of a site to a seismic solicitation depends on local topographical and geotechnical characteristics. Many aspects of seismic site effect still need to be studied in more detail and they can be incorporated in the seismic norms after quantification. The purpose of this paper is to contribute to establishment of a simple method to include complex site effects in a building code. Horizontal ground movements in various points of two-dimensional (2D) irregular configurations subjected to synthetic SV waves of vertical incidence are calculated. The parametric studies are achieved by means of HYBRID program combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The results are shown in the form of pseudo-acceleration response spectra. For the empty valleys, we can classify the spectral response according to a unique geometric criterion: the “surface/angle” ratio, where surface is the area of the valley opening, and angle denotes the angle between the slope and horizontal line in the above corner. To assess the influence of the 2D effect on the spectral response of filled valleys, the response of alluvial basins are compared with the response of one-dimensional columns of soil. Finally, an offset criterion is proposed to choose a relevant computation method for the spectral acceleration at the surface of alluvial basins

    Seismic site effects by an optimized 2D BE/FE method. II. Quantification of site effects in two-dimensional sedimentary valleys

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    Copyright © 2007 Elsevier Ltd.DOI: http://dx.doi.org/10.1016/j.soildyn.2007.09.002This paper deals with the evaluation of seismic site effects due to the local topographical and geotechnical characteristics. The amplification of surface motions is calculated by a numerical method combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The numerical technique is improved by time truncation. In the first part of this article, the accuracy and the relevance of this optimized method are presented. Moreover, parametric studies are done on slopes, ridges and canyons to characterize topographical site effects. The second part deals with sedimentary valleys. The complexity of the combination of geometrical and sedimentary effects is underlined. Extensive parametrical studies are done to discriminate the topographical and geotechnical effects on seismic ground movement amplifications in two-dimensional irregular configurations. Characteristic coefficients are defined to predict the amplifications of horizontal displacements. The accuracy of this quantitative evaluation technique is tested and discussed

    A model of damage and healing coupling halite thermo-mechanical behavior to microstructure evolution

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    Copyright © 2014 Springer-VerlagCreep processes in halite (salt rock) include glide, cross-slip, diffusion and dynamic recrystallization. Diffusive Mass Transfer (DMT) can result in crack rebonding, and mechanical stiffness recovery. Crack rebonding driven by DMT occurs within a few days at room temperature and low pressure. DMT is enhanced at higher temperatures, which could be beneficial for the sustainabilty of geological storage facilities in salt mines. On the one hand, visco-plastic laws relating creep microscopic processes to microstructure changes are empirical. On the other hand, theoretical models of damage and healing disconnect thermodynamic variables from their physical meaning. The proposed model enriches the framework of Continuum Damage Mechanics (CDM) with fabric descriptors. In order to infer the form of fabric tensors from microstructure observation, creep tests were carried out on granular salt under constant stress and humidity conditions. The evolution of net damage is governed by a diffusion equation, in which the characteristic time scales with the typical size of halite crystals, and the diffusion coefficient is a function of temperature. A stress path comprising a tensile loading, a compressive unloading, a creep healing stage and a reloading was simulated. Macroscopic and microscopic model predictions highlight the increased efficiency of healing with time and temperature. The model presented in this paper is expected to improve the fundamental understanding of damage and healing in rocks at both macroscopic and microscopic levels, and the long-term assessment of geological storage facilities

    Mobile Sonification for Athletes: A Case Study in Commercialization of Sonification

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    Presented at the 20th International Conference on Auditory Display (ICAD2014), June 22-25, 2014, New York, NY.Several companies, including Under Armour, Nike and Adidas, are taking advantage of advances in sensor technology to sell wearable systems that measure, record, and analyze the motion of athletes. To date, these systems make little, if any use of sonification. Therefore, there is an opportunity for sonification methods in this domain, including the potential to reach a mass market. In the fall of 2013, Under Armour and NineSigma created the Armour39 Challenge, an open call for proposals to build new technology for the Armour39, Under Armour’s wearable motion and heart-rate sensor. The authors of this paper responded to the challenge, proposing novel sonification systems to exploit the data from the Armour39. This paper presents these systems, including issues, solutions, and tools for sonification performed on a mobile device with a wearable sensor. The sonifications are rhythmic, exploiting the periodicity of human motion, and are demonstrated by sonifying athletic performance metrics in real-time for speed skating and running

    Panel Discussion [Matter Thinks! Symposium]

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    Presented on March 29, 2014 in the Clough Undergraduate Learning Commons room 152 from 12:00 p.m. to 6:00 p.m.Runtime: 52:07 minute

    Introduction [Great Buildings & Structures that Made a Difference: The Crystal Palace, London, 1851]

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    Presented as part of the "Great Buildings & Structures that Made a Difference: The Crystal Palace, London, 1851" Symposium on September 3, 2014 in the Reinsch-Pierce Auditorium in the College of Architecture from 4:30 pm - 8:00 pm.Runtime: 15:20 minutesSymposium introduction by the Dean of the College of Architecture, Steve French. "Great Exhibition of the Works of Industry of All Nations", brief overview of the 1851 World's Fair exhibition, presented by Laura Hollengreen

    Intellectual Property 101

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    Clark Wilson is an intellectual property attorney who focuses on matters of patent and trademark law. He has particular experience working with medical device innovators as both in-house and outside patent counsel.Presented as part of the iCorps 2014 Southeast Regional Life Sciences Startup Accelerator on September 11, 2014 at 12:00pm in the Centergy One Building, Hodges Room.Runtime: 59:11 minute
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