Simulation of the degradation of a concrete/clay interface:influence of temperature, unsaturated conditions and porosityvariations

For long-lived intermediate-level radioactive waste, the useof concrete as engineering barrier and Callovian-Oxfordian clay asgeological barrier at a depth of 500 m is considered in the Frenchdisposal concept (ANDRA, 2005). Upon emplacement, initially unsaturatedconcrete is expected to experience coupled processes involving heating,re-saturation with groundwater from the clay formation, gas exchanges andgeochemical reactions. After an early period of re-saturation, solutetransport is supposed to be diffusion-controlled because of the extremelylow permeability of the two media. These coupled processes may lead tochanges in the porosity of the concrete or clay barriers. In the presentpaper, a fully coupled Thermo-Hydro-Chemical (THC) response of atwo-phase (gas and solution) mass-transfer model was evaluated and testedby a sensitivity analysis. This study is an extension of a previous modelapplied to an isothermal and fully saturated concrete/clay interface(Burnol et al., 2005); it investigated the coupled effect of temperatureand unsaturated conditions assuming no production of H2(g). The systemwas simulated for a 2000-year period, which covers the most predominantthermal perturbation

Simulation of the degradation of a concrete/clay interface: influence of temperature, unsaturated conditions and porosity variations

For long-lived intermediate-level radioactive waste, the use of concrete as engineering barrier and Callovian-Oxfordian clay as geological barrier at a depth of 500 m is considered in the French disposal concept (ANDRA, 2005). Upon emplacement, initially unsaturated concrete is expected to experience coupled processes involving heating, re-saturation with groundwater from the clay formation, gas exchanges and geochemical reactions. After an early period of re-saturation, solute transport is supposed to be diffusion-controlled because of the extremely low permeability of the two media. These coupled processes may lead to changes in the porosity of the concrete or clay barriers. In the present paper, a fully coupled Thermo-Hydro-Chemical (THC) response of a two-phase (gas and solution) mass-transfer model was evaluated and tested by a sensitivity analysis. This study is an extension of a previous model applied to an isothermal and fully saturated concrete/clay interface (Burnol et al., 2005); it investigated the coupled effect of temperature and unsaturated conditions assuming no production of H2(g). The system was simulated for a 2000-year period, which covers the most predominant thermal perturbation

On The Energy Efficiency And Performance Of Irregular Application Executions On Multicore, Numa And Manycore Platforms

Until the last decade, performance of HPC architectures has been almost exclusively quantified by their processing power. However, energy efficiency is being recently considered as important as raw performance and has become a critical aspect to the development of scalable systems. These strict energy constraints guided the development of a new class of so-called light-weight manycore processors. This study evaluates the computing and energy performance of two well-known irregular NP-hard problems-the Traveling-Salesman Problem (TSP) and K-Means clustering-and a numerical seismic wave propagation simulation kernel-Ondes3D-on multicore, NUMA, and manycore platforms. First, we concentrate on the nontrivial task of adapting these applications to a manycore, specifically the novel MPPA-256 manycore processor. Then, we analyze their performance and energy consumption on those different machines. Our results show that applications able to fully use the resources of a manycore can have better performance and may consume from 3.8 × to 13 × less energy when compared to low-power and general-purpose multicore processors, respectively.763248Andreolli, C., Thierry, P., Borges, L., Yount, C., Skinner, G., Genetic algorithm based auto-tuning of seismic applications on multi and manycore computers (2014) EAGE Workshop on High Performance Computing for Upstream, Amsterdam, Netherlands, , http://dx.doi.org/10.3997/2214-4609.20141920, SeptemberAochi, H., Ulrich, T., Ducellier, A., Dupros, F., Michea, D., Finite difference simulations of seismic wave propagation for understanding earthquake physics and predicting ground motions: Advances and challenges (2013) J. Phys.: Conf. Ser., 454, p. 012010Aubry, P., Beaucamps, P.-E., Blanc, F., Bobin, B., Carpov, S., Cudennec, L., David, V., Sirdey, R., Extended cyclostatic dataflow program compilation and execution for an integrated manycore processor (2013) International Conference on Computational Science, ICCS, Vol. 18, pp. 1624-1633. , Elsevier Barcelona, SpainBoillot, L., Barucq, H., Calandra, H., Diaz, J., (Portable) task-based programming model for elastodynamics EAGE Workshop on HPC for Upstream, , Chania, GreeceBrooks, D., Bose, P., Schuster, S.E., Power-aware microarchitecture: Design and modeling challenges for next-generation microprocessors (2000) IEEE Micro, 20, pp. 26-44Castro, M., Francesquini, E., Nguélé, T.M., Méhaut, J.-F., Analysis of computing and energy performance of multicore, NUMA, and manycore platforms for an irregular application (2013) Workshop on Irregular Applications: Architectures & Algorithms (IA3) - Supercomputing Conference (SC), , ACM Denver, EUA p. 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Ho, Lecture Notes in Computer Science Springer Berlin, HeidelbergDupros, F., Aochi, H., Ducellier, A., Komatitsch, D., Roman, J., Exploiting intensive multithreading for the efficient simulation of 3D seismic wave propagation International Conference on Computational Science and Engineering, pp. 253-260. , São Paulo, BrazilDupros, F., Do, H.-T., Aochi, H., On scalability issues of the elastodynamics equations on multicore platforms (2013) International Conference on Computational Science, ICCS, 18, pp. 1226-1234. , Procedia Computer Science Elsevier Barcelona, SpainDupros, F., Pousa, C., Carissimi, A., Méhaut, J.-F., Parallel simulations of seismic wave propagation on NUMA architectures (2010) International Parallel Computing Conference, ParCo, 19, pp. 67-74. , Advances in Parallel Computing IOS Press Lyon, FranceFleig, T., Mattes, O., Karl, W., Evaluation of adaptive memory management techniques on the Tilera TILE-Gx platform (2014) International Conference on Architecture of Computing Systems, ARCS, pp. 88-96. , VDE Verlag Luebeck, DeutschlandFurumura, T., Chen, L., Parallel simulation of strong ground motions during recent and historical damaging earthquakes in Tokyo, Japan (2005) Parallel Comput., 31, pp. 149-165. , Parallel Graphics and VisualizationGharaibeh, A., Santos-Neto, E., Costa, L.B.A., Ripeanu, M., The energy case for graph processing on hybrid CPU and GPU systems (2013) Proceedings of the 3rd Workshop on Irregular Applications: Architectures and Algorithms, pp. 21-28. , IA3'13 ACM New York, NY, USAGöddeke, D., Komatitsch, D., Geveler, M., Ribbrock, D., Rajovic, N., Puzovic, N., Ramirez, A., Energy efficiency vs. Performance of the numerical solution of PDEs: An application study on a low-Power ARM-Based cluster (2013) J. Comput. Phys., 237, pp. 132-150Gursoy, A., Data decomposition for parallel k-means clustering (2004) Parallel Processing and Applied Mathematics, 3019, pp. 241-248. , R. Wyrzykowski, J. Dongarra, M. Paprzycki, J. Was̈niewski, Lecture Notes in Computer Science Springer Berlin, HeidelbergHähnel, M., Döbel, B., Völp, M., Härtig, H., Measuring energy consumption for short code paths using RAPL (2012) ACM SIGMETRICS Perform. Eval. Rev., 40, pp. 13-17Jain, A.K., Dubes, R.C., (1988) Algorithms for Clustering Data, , Prentice-Hall, Inc. Upper Saddle River, NJ, USAKanungo, T., Mount, D., Netanyahu, N., Piatko, C., Silverman, R., Wu, A., An efficient k-means clustering algorithm: Analysis and implementation (2002) IEEE Trans. Pattern Anal. Mach. Intell., 24, pp. 881-892Kaufman, L., Rousseeuw, P.J., (1990) Finding Groups in Data: An Introduction to Cluster Analysis, , John Wiley and Sons New YorkLaporte, G., The traveling salesman problem: An overview of exact and approximate algorithms (1992) European J. Oper. Res., 59, pp. 231-247Larus, J., Spending Moore's dividend (2009) Commun. ACM, 52, pp. 62-69De Dinechin, B.D., De Massas, P.G., Lager, G., Léger, C., Orgogozo, B., Reybert, J., Strudel, T., A distributed run-time environment for the Kalray MPPA-256 integrated manycore processor (2013) Intl. 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Using Simulation to Evaluate and Tune the Performance of Dynamic Load Balancing of an Over-decomposed Geophysics Application

Finite difference methods are, in general, well suited to execution on parallel machines and are thus commonplace in High Performance Computing. Yet, despite their apparent regularity, they often exhibit load imbalance that damages their efficiency. In this article, we first characterize the spatial and temporal load imbalance of Ondes3D, a seismic wave propagation simulator used to conduct regional scale risk assessment. Our analysis reveals that this imbalance originates from the structure of the input data and from low-level CPU optimizations. Such dynamic imbalance should, therefore, be quite common and can not be solved by any static approach or classical code reorganization. An effective solution for such scenarios, incurring minimal code modification, is to use AMPI/CHARM++. By over-decomposing the application, the CHARM++ runtime can dynamically rebalance the load by migrating data and computation at the granularity of an MPI rank. We show that this approach is effective to balance the spatial/temporal dynamic load of the application, thus drastically reducing its execution time. However, this approach requires a careful selection of the load balancing algorithm, its activation frequency, and of the over-decomposition level. These choices are, unfortunately, quite dependent on application structure and platform characteristics. Therefore, we propose a methodology that leverages the capabilities of the SimGrid simulation framework and allows to conduct such study at low experimental cost. Our approach relies on a combination of emulation, simulation, and application modeling that requires minimal code modification and yet manages to capture both spatial and temporal load imbalance and to faithfully predict the performance of dynamic load balancing. We evaluate the quality of our simulation by systematically comparing simulation results with the outcome of real executions and demonstrate how this approach can be used to quickly find the optimal load balancing configuration for a given application/hardware configuration.Les méthodes aux différences finies sont en général bien adaptées au machines parallèles et donc assez courantes dans le domaine du calcul à haute performance. Pourtant, en dépit de leurs apparentes régularités, il n'est pas rare qu'elles souffrent d'un déséquilibre de charge dommageable. Dans cet article, nous commençons par caractériser le déséquilibre de charge spatial et temporel d'Ondes3D, une application de simulation de propagation d'ondes sismiques utilisée pour faire de l'évaluation de risque sismique à l'échelle régionale. Notre analyse révèle que ce déséquilibre provient de la nature même des données d'entrées et d'optimisations bas niveau du CPU. Ce type de déséquilibre dynamique est donc a priori relativement courant et ne peut être résolu par des approches statiques ou par des réorganisations de code classiques. Une approche pragmatique et ne nécessitant que des modifications mineures du code consiste à utiliser AMPI/CHARM++. En sur-décomposant l'application, le runtime CHARM++ peut rééquilibrer dynamiquement la charge en migrant les données et les calculs à la granularité du processus MPI. Nous montrons que cette approche permet effectivement de résoudre le problème de déséquilibre spatial et temporel de charge et ainsi de réduire drastiquement le temps d'exécution total. Cependant, cette approche nécessite a priori une sélection minutieuse de l'algorithme d'équilibrage de charge, de la fréquence d'activation ou du niveau de sur-décomposition. Ces choix sont hélas en général assez dépendants de la structure de l'application et des caractéristiques de la plate-forme (\ie le nombre de processeurs et leur vitesse, la topologie et la vitesse du réseau). Nous proposons donc une méthodologie se basant sur l'environnement de simulation SimGrid et permettant de réaliser ce type d'étude à faible coût. Notre approche repose sur une combinaison d'émulation, de simulation et de modélisation d'application qui ne nécessite que des modifications minimes du code d'origine et permet à la fois de capturer le déséquilibre spatial et temporel et de prédire de façon fiable les performances de l'équilibrage de charge. Nous évaluons la qualité de notre proposition en comparant de façon systématique les résultats de notre simulation avec ceux d'expériences réelles. Nous montrons ensuite comment cette approche peut être utilisée pour déterminer rapidement les paramètres optimaux d'équilibrage de charge pour une configuration applicative/matérielle donnée

Influential parameters on 3-D synthetic ground motions in a sedimentary basin derived from global sensitivity analysis

International audienceSUMMARY Which physical parameters are the most influential when predicting earthquake ground motions in a 3-D sedimentary basin? We answer quantitatively by doing a global sensitivity analysis of two quantities of interest: the peak ground motions (PGMs) and a time–frequency representation (the S transform) of ground motions resulting from the synthetic anelastic responses of the EUROSEISTEST. This domain of interest is modeled by two layers with uncertain depth-dependent mechanical properties and is illuminated by a plane S-wave propagating vertically upward in an uncertain homogeneous elastic bedrock. The global sensitivity analysis is conducted on 800+ physics-based simulations of the EUROSEISTEST requiring 8+ million core-hours (i.e. ≈ 900 yr of mono-core computation). The analysis of the PGMs at the free surface displays the spatial influence of the uncertain input parameters over the entire basin scale, while the analysis of the time–frequency representation shows their influence at a specific location inside the basin. The global sensitivity analysis done on the PGMs points out that their most influential parameter in the middle of the basin is the quality factor QS (it controls up to 80 per cent of the PGMs in certain locations where the sediments thickness is larger than 200 m). On the other hand, the geological layering configuration (here represented by the depth of a geological interface controlling the geological layering) strongly influences the PGMs close to the basin edges, up to 90 per cent. We also found that the shear wave velocity at the free surface of the basin and the one of the bedrock underlying the basin are to be considered on an equal footing, both influencing the PGMs in the middle of the basin and close to its edges. We highlight that the bedrock to basin amplification of the PGMs shows a clear increase with respect to the thickness of the sediments, but this amplification saturates from 200 m of sediments around the value of three and is frequency dependent. This PGMs amplification starts from about one tenth of the mean S-wavelength propagating in the basin. The global sensitivity analysis done on the S transform of the ground motions shows that (i) the own effect of the parameters fully controls the first S-wave train and mostly controls the direct arrival of the basin-induced surfaces waves, (ii) the quality factor QS controls 40–60 per cent of the decay of amplitude of coda waves, the remaining part being mainly controlled by interaction effects due to the coupling effect of several parameters and (iii) the interaction effects between the parameters increases with time, suggesting under the hypotheses of our study that the own effects control the ballistic wave propagation while the interaction effects control the diffusive wave propagation