Evaluating kernels on Xeon Phi to accelerate Gysela application

This work describes the challenges presented by porting parts ofthe Gysela code to the Intel Xeon Phi coprocessor, as well as techniques used for optimization, vectorization and tuning that can be applied to other applications. We evaluate the performance of somegeneric micro-benchmark on Phi versus Intel Sandy Bridge. Several interpolation kernels useful for the Gysela application are analyzed and the performance are shown. Some memory-bound and compute-bound kernels are accelerated by a factor 2 on the Phi device compared to Sandy architecture. Nevertheless, it is hard, if not impossible, to reach a large fraction of the peek performance on the Phi device,especially for real-life applications as Gysela. A collateral benefit of this optimization and tuning work is that the execution time of Gysela (using 4D advections) has decreased on a standard architecture such as Intel Sandy Bridge.Comment: submitted to ESAIM proceedings for CEMRACS 2014 summer school version reviewe

On the Fundamentals of Stochastic Spatial Modeling and Analysis of Wireless Networks and its Impact to Channel Losses

With the rapid evolution of wireless networking, it becomes vital to ensure transmission reliability, enhanced connectivity, and efficient resource utilization. One possible pathway for gaining insight into these critical requirements would be to explore the spatial geometry of the network. However, tractably characterizing the actual position of nodes for large wireless networks (LWNs) is technically unfeasible. Thus, stochastical spatial modeling is commonly considered for emulating the random pattern of mobile users. As a result, the concept of random geometry is gaining attention in the field of cellular systems in order to analytically extract hidden features and properties useful for assessing the performance of networks. Meanwhile, the large-scale fading between interacting nodes is the most fundamental element in radio communications, responsible for weakening the propagation, and thus worsening the service quality. Given the importance of channel losses in general, and the inevitability of random networks in real-life situations, it was then natural to merge these two paradigms together in order to obtain an improved stochastical model for the large-scale fading. Therefore, in exact closed-form notation, we generically derived the large-scale fading distributions between a reference base-station and an arbitrary node for uni-cellular (UCN), multi-cellular (MCN), and Gaussian random network models. In fact, we for the first time provided explicit formulations that considered at once: the lattice profile, the users’ random geometry, the spatial intensity, the effect of the far-field phenomenon, the path-loss behavior, and the stochastic impact of channel scatters. Overall, the results can be useful for analyzing and designing LWNs through the evaluation of performance indicators. Moreover, we conceptualized a straightforward and flexible approach for random spatial inhomogeneity by proposing the area-specific deployment (ASD) principle, which takes into account the clustering tendency of users. In fact, the ASD method has the advantage of achieving a more realistic deployment based on limited planning inputs, while still preserving the stochastic character of users’ position. We then applied this inhomogeneous technique to different circumstances, and thus developed three spatial-level network simulator algorithms for: controlled/uncontrolled UCN, and MCN deployments

Constitutive modeling of the thermo-mechanics associated with crystallizable shape memory polymers

This research addresses issues central to material modeling and process simulations. Here, issues related for developing constitutive model for crystallizable shape memory polymers are addressed in details. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Crystallizable shape memory polymers are called crystallizable because the temporary shape is fixed by a crystalline phase, while return to the original shape is due to the melting of this crystalline phase. A set of constitutive equations has been developed to model the thermomechanical behavior of crystallizable shape memory polymers using elements of thermodynamics, continuum mechanics and polymer science. Models are developed for the original amorphous phase, the temporary semi-crystalline phase and transition between these phases. Modeling of the crystallization process is done using a framework that was developed recently for studying crystallization in polymers and is based on the theory of multiple natural configurations. Using the same frame work, the melting of the crystalline phase to capture the return of the polymer to its original shape is also modeled. The developed models are used to simulate a range of boundary value problems commonly encountered in the use of these materials. Predictions of the model are verified against experimental data available in literature and the agreement between theory and experiments are good. The model is able to accurately capture the drop in stress observed on cooling and the return to the original shape on heating. To solve complex boundary value problems in realistic geometries a user material subroutine (UMAT) for this model has been developed for use in conjunction with the commercial finite element software ABAQUS. The accuracy of the UMAT has been verified by testing it against problems for which the results are known. The UMAT was then used to solve complex 2-D and 3-D boundary value problems of practical interest

A Finite Element Implementation of a Coupled Diffusion-Deformation Theory for Elastomeric Gels

The theory of Chester and Anand (2011) for fluid diffusion and large deformations of elastomeric gels is implemented as a user-defined element (UEL) subroutine in the commercial finite element software package ABAQUS. A specialized form of the constitutive equations and the governing partial differential equations of the theory are summarized, and the numerical implementation is described in detail. To demonstrate the robustness of the numerical implementation a few illustrative numerical simulation examples for axisymmetric, plane strain, and three-dimensional geometries are shown. For educational purposes, and also to facilitate the numerical implementation of other coupled multiphysics theories, the source code for the UEL is provided as an online supplement to this paper.National Science Foundation (U.S.) (NSF CMMI-1063626

Orbit-spectrum sharing between the fixed-satellite and broadcasting-satellite services with applications to 12 GHz domestic systems

A systematic, tutorial analysis of the general problem of orbit-spectrum sharing among inhomogeneous satellite system is presented. Emphasis is placed on extrapolating and applying the available data on rain attenuation and on reconciling differences in the results of various measurements of the subjective effects of interference on television picture quality. An analytic method is presented for determining the approximate values of the intersatellite spacings required to keep mutual interference levels within prescribed limits when many dissimilar satellites share the orbit. A computer model was developed for assessing the interference compatibility of arbitrary configurations of large numbers of geostationary satellite systems. It is concluded that the band from 11.7 c GHz can be shared effectively by broadcasting-satellite and fixed-satellite systems. Recommendations for future study are included

ENGINEERING VISCOELASTIC BEHAVIOR OF CARBON FIBER REINFORCED POLYMER COMPOSITES WITH NANOPARTICLES FOR CONTROLLING DEPLOYMENT OF AEROSPACE STRUCTURES

The United States Air Force is focused on reducing mass and power consumption of spacecraft to increase their capabilities for space missions. Low mass and power consumption can be achieved by using composites with low density and high stiffness and utilizing few satellite components. One way to achieve reduced mass is by eliminating attendant deployment mechanisms consuming valuable power and mass allocations on spacecraft with deployable structures. Secondary systems are typically used to assist deployable space structures to ensure 100% success. A passively deployed space structure would be of great value to the Department of Defense and the commercial marketplace. Attaining a passively deployed space structure that is reliable, predictable and controllable to tailored design applications would serve this objective. The research presented herein was experimentally focused and involved incorporation of alumina nanoparticles (ANPs) dispersed into a three-ply composite laminate tape spring structure. The FlexLam composite was designed and fabricated for this class of tape spring deployable structures. A total of 51 tape springs were structurally tested on a unique, custom-designed test fixture with methodology to analyze their stress relaxation behavior in a coiled state for lengths of time varying from 1 hour to 6 months. A finite element model (FEM) with a Fortran subroutine was built and simulations were correlated with the structural deployment testing of 26 control tape springs and 25 ANP tape springs. The FEM simulation-predicted results correlated within 5% of the experimental testing structural results. A total of 5 epoxy samples (3 neat epoxy and 2 ANP epoxy) were fabricated and cut into 29 coupons for Dynamic Mechanical Analyzation (DMA) tests and Scanning Electron Microscope with Energy Dispersive X-ray Spectroscopy (SEM/EDS) examinations were also performed on 4 test coupons (3 ANP and 1 control) to characterize the microstructure of the composites, including the ANP dispersion and agglomeration. It was shown the ANP tape spring structures were able to retain 55% more tip force and experience less stress relaxation compared to the control tape springs. Future work is recommended in optimization of the composite and further development of the FEM simulation for improving structural behavior prediction