A Pure Java Parallel Flow Solver

In this paper an overview is given on the "Have Java" project to attain a pure Java parallel Navier-Stokes flow solver (JParNSS) based on the thread concept and remote method invocation (RMI). The goal of this project is to produce an industrial flow solver running on an arbitrary sequential or parallel architecture, utilizing the Internet, capable of handling the most complex 3D geometries as well as flow physics, and also linking to codes in other areas such as aeroelasticity etc. Since Java is completely object-oriented the code has been written in an object-oriented programming (OOP) style. The code also includes a graphics user interface (GUI) as well as an interactive steering package for the parallel architecture. The Java OOP approach provides profoundly improved software productivity, robustness, and security as well as reusability and maintainability. OOP allows code construction similar to the aerodynamic design process because objects can be software coded and integrated, reflecting actual design procedures. In addition, Java is the programming language of the Internet and thus Java is the programming language of the Internet and thus Java objects on disparate machines or even separate networks can be connected. We explain the motivation for the design of JParNSS along with its capabilities that set it apart from other solvers. In the first two sections we present a discussion of the Java language as the programming tool for aerospace applications. In section three the objectives of the Have Java project are presented. In the next section the layer structures of JParNSS are discussed with emphasis on the parallelization and client-server (RMI) layers. JParNSS, like its predecessor ParNSS (ANSI-C), is based on the multiblock idea, and allows for arbitrarily complex topologies. Grids are accepted in GridPro property settings, grids of any size or block number can be directly read by JParNSS without any further modifications, requiring no additional preparation time for the solver input. In the last section, computational results are presented, with emphasis on multiprocessor Pentium and Sun parallel systems run by the Solaris operating system (OS)

First spacecraft demise workshop - Test case description and results

International audienceIn order to assess the ground risk of spacecraft operations that should comply with national and international space law regulations, a large number of spacecraft demise tools have recently been developed. In order to treat the complexity of the physical processes involved, different approaches are followed, from low fidelity "object oriented" tools, to higher fidelity "spacecraft oriented" tools. The lack of experimental data and the multidisciplinary aspect of the process make the validation and verification a challenging task. Many codes are based on simplified methods, often a heritage of research performed in the '60s for nuclear missile re-entry. However at that time, the uncertainty margins applied were such to favour a safe entry. For spacecraft risk assessment the uncertainty margins however should be the opposite. Todays computational means allow techniques such as computational fluid dynamics and thermal analysis codes to verify the models used in current tools. In the current paper we present an initiative to enlarge the available data for validation and verification of spacecraft demise software. A collaborative initiative in the form of a workshop, common practice in the aeronautical industry (drag prediction workshop, SPICES, etc), is proposed. The initiative allows comparing between different tools and to assess the uncertainties between different codes and different disciplines for incorporation by a statistical approach. The various disciplines involved have been separated in three groups: integration, where we compare between different codes the complete process of entry; thermal, where we study the thermal time evolutions for imposed heat fluxes, and aerothermal, where we study the heat fluxes and aerodynamic coefficients for a fixed reentry condition. At later stages those disciplines could be extended by, for example, ablation or flight mechanics test cases. The present paper describes the proposed test cases for the different disciplines, and presents a comparison of the main results obtained by the different participants to the first spacecraft demise workshop

Monte-carlo analysis of object reentry in earth's atmosphere based on taguchi method

International audienceThe risk of space debris is now perceived as primordial by governments and international space agencies. Since the last decade, international space agencies have developed tools simulate the re-entry of satellites and orbital stations in order to assess casualty risk on the ground. Nevertheless, all current tools provide deterministic solutions, though models include various parameters that are not well known. Therefore, the provided results are strongly dependent on the assumptions made. One solution to obtain relevant and exploitable results would be to include uncertainties around those parameters in order to perform Monte-Carlo analysis. But such a study is very time consuming due to the large parameter space to explore (that necessitate hundreds of thousands simulations). To reduce the parameter search space, we present an application of the Taguchi Method, to model spacecraft debris re-entry in Earth's atmosphere. The Taguchi Method is a statistical analysis method that permits one to determine the parameters uncertainty that have the biggest impact on the results of the numerical simulation. We show how to use this method so as to restrain the quantity of parameters to consider for a Monte-Carlo analysis. Finally, we present the new object-oriented re-entry tool Calima developed by R.Tech. This new tool features three degree of freedom model, featuring also the perturbation of initial parameters of a numerical simulation in order to perform automatized Monte-Carlo Analysis. Calima is accelerated via Graphics Processing Unit (GPU) devices which have many cores architecture and that consume less energy than classical CPUs

Monte-carlo analysis of object reentry in earth's atmosphere based on taguchi method

International audienceThe risk of space debris is now perceived as primordial by governments and international space agencies. Since the last decade, international space agencies have developed tools simulate the re-entry of satellites and orbital stations in order to assess casualty risk on the ground. Nevertheless, all current tools provide deterministic solutions, though models include various parameters that are not well known. Therefore, the provided results are strongly dependent on the assumptions made. One solution to obtain relevant and exploitable results would be to include uncertainties around those parameters in order to perform Monte-Carlo analysis. But such a study is very time consuming due to the large parameter space to explore (that necessitate hundreds of thousands simulations). To reduce the parameter search space, we present an application of the Taguchi Method, to model spacecraft debris re-entry in Earth's atmosphere. The Taguchi Method is a statistical analysis method that permits one to determine the parameters uncertainty that have the biggest impact on the results of the numerical simulation. We show how to use this method so as to restrain the quantity of parameters to consider for a Monte-Carlo analysis. Finally, we present the new object-oriented re-entry tool Calima developed by R.Tech. This new tool features three degree of freedom model, featuring also the perturbation of initial parameters of a numerical simulation in order to perform automatized Monte-Carlo Analysis. Calima is accelerated via Graphics Processing Unit (GPU) devices which have many cores architecture and that consume less energy than classical CPUs

Parallel Monte-Carlo Simulations on GPU and Xeon Phi for Stratospheric Balloon Envelope Drift Descent Analysis

International audienceA performance evaluation of parallel Monte-Carlo simulations on GPU and MIC is presented and the application to stratospheric balloon envelope drift descent is considered. The experiments show that GPU and MIC permit one to decrease computing time by a factor of 4 and 2, respectively, as compared to a parallel code implemented on a two sockets CPU (E5-2680-v2) which allows us to use these devices in operational conditions

SIMD Monte-Carlo Numerical Simulations Accelerated on GPU and Xeon Phi

International audienceThe efficiency of a pleasingly parallel application is studied for several computing platforms. A real world problem, i.e., Monte-Carlo numerical simulations of stratospheric balloon envelope drift descent is considered. We detail the optimization of the SIMD parallel codes on the K40 and K80 GPUs as well as on the Intel Xeon Phi. We emphasize on loop and task parallelism, multi-threading and vectorization, respectively. The experiments show that GPU and MIC permit one to decrease computing time by non negligeable factors, as compared to a parallel code implemented on a two sockets CPU (E5-2680-v2) which finally allows us to use these devices in operational condition

Rebuilding of ICOTOM radiometer data during the Schiaparelli Martian entry

International audienceIn spite of the crash of Schiaparelli, the Exomars Descent Module in October 2016, following a nevertheless successful aerothermodynamic entry, data from the infrared radiometers ICOTOM embedded of the COMARS modules was sent to the orbiter before and after the blackout phase. Three pairs of radiometers were located in line on the back shield of the probe in order to monitor the infrared radiation received by the thermal protection system from CO and CO2 molecules. Within a pair, one ICOTOM (B1) was dedicated to the range 4,17-5 µm (2000-2400 cm-1) and the other one (B2) was dedicated to the range 2,6-3,36 µm (2950-3850 cm-1) in order to collect cold and CO2 bands as well as CO rovibrational radiation. Flight data provided radiative heat flux densities in both ranges for three locations in the shield, especially at the end of the hot phase. Lower housing temperatures than expected led to recalibration of the ICOTOM depending on the incoming flux and on the sensor own temperatures.In order to derive of maximum of information about the thermodynamic status of the gas behind the spacecraft, CNES gathered laboratories and companies to rebuild the aerodynamic field, the chemical composition, the non-equilibrium status and the radiative transfer within the back body plasma from numerical simulation and on-ground experiments.The main purpose is to obtain a comprehensive numerical tool able to recover the flight measurements and to deal with similar entry situations in the future. Only few hypotheses were made especially about the equilibrium status of the plasma and about the angle of attack of the probe. Then the implicit-in-time code has been developed for 3D geometry and includes partial state-to-state chemistry. Kinetic chemical models developed for 0D and 1D geometry were reduced in order to make them compatible with reasonable computation times. However, a full (vibrational and electronic) model is used along lines in the flow with a Lagrangian approach. A specific scheme has been established to describe the vibrational structure of CO2. That model has been made compatible with chemical and radiative calculations. Solving the radiative transfer equation within the back body plasma implies to take into account possible non-equilibrium effect in CO2 vibrational populations. Following a line-by-line model working out of equilibrium, a statistical narrow-band model was developed in order to reduce the time cost of calculations involving aerodynamics, chemistry and radiation. However, radiation transfer calculations were not coupled to the aerothermochemistry calculations and are carried out as a post-treatment on the fields of densities and temperatures (when applicable).Another important part of the project consists of ground tests of ICOTOM radiometers on plasmas close to those encountered by Schiaparelli. That experimental approach is to confront the signals given by the ICOTOM radiometers and the heat flux densities derived from them with laboratory measurements obtained by optical and laser spectroscopy and interferometry. Ground plasma flows are then used as test cases both for ICOTOM measurements and for numerical simulation. Various facilities such as ICP and arc-jet plasmas were used within that study