Possibilities of parallel calculations in solving gas dynamics problems in the CFD environment of FLUENT software

The results of studying an incompressible gas flow field in a periodic element of the porous structure made up of the same radius spheres are presented; the studies were based on the solution of the Navier-Stokes equations using FLUENT software. The possibilities to accelerate the solution process with the use of parallel calculations are investigated and the calculation results under changes of pressure differential in the periodic element are given.     

Planetary protection considerations for MarsNet and Mars sample return missions.

The ESA MarsNet mission proposal consists most probably of a trio of Mars landers. These landers each contain a variety of scientific equipment. The network of stations demands for a definition of its planetary protection requirements. With respect to the MarsNet mission only forward contamination problems will be considered. Future involvement of European efforts in planetary exploration including sample returns will also raise the problem of back contamination. A tradeoff study for the overall scientific benefit with respect to the approximative cost is necessary. Planetary protection guide-lines will be proposed by an interdisciplinary and international board of experts working in the fields of both biology and planetary science. These guide-lines will have to be flexible in order to be modified with respect to new research results, e.g. on adaptation of microorganisms to extreme (space) conditions. Experiments on the survival of microorganisms at conditions of simulated Mars surface and subsurface will have to be conducted in order to obtain a baseline data collection as a reference standard for future guide-lines.     

The J-MASS Marketplace: a new way for DoD to do business

It is current DoD policy to use commercial off-the-shelf software whenever it meets DoD requirements. The application of this policy to modeling and simulation has resulted in the concept of “The Joint Modeling and Simulation System (J-MASS) Marketplace.” J-MASS is designed as an Open Systems Architecture with the capability for the Simulation Support Environment (SSE) to be expanded by the addition of site specific software. In the “J-MASS Marketplace” industry will build commercial tools to work with J-MASS and individual organizations will license what they need for their particular site. The J-MASS SSE is a framework or backplane into which everything else plugs. A J-MASS product release would have the core capabilities, but the unique needs of various organizations would be satisfied by industry. This paper addresses how the J-MASS Marketplace could work and how compliance can be defined. It will outline opportunities for industry in both building software for the Marketplace and in defining the Marketplace concept     

Multiwavelength monitoring of active galactic nuclei

Recent multiwavelength monitoring of active galactic nuclei (AGN), particularly with the IUE satellite, has produced extraordinary advances in our understanding of the energy-generation mechanism(s) in the central engine and of the structure of the surrounding material. Examples discussed here include both ordinary AGN and blazars (the collective name for highly variable, radio-loud AGN like BL Lac objects and Optically Violently Variable quasars). In the last decade, efforts to obtain single-epoch multiwavelength spectra led to fundamentally new models for the structure of AGN, involving accretion disks for AGN and relativistic jets for blazars. Recent extensions of multiwavelength spectroscopy into the temporal domain have shown that while these general pictures may be correct, the details were probably wrong. Campaigns to monitor Seyfert 1 galaxies like NGC 4151, NGC 5548 and Fairall 9 at infrared, optical, ultraviolet and X-ray wavelengths indicate that broad-emission line regions are stratified by ionization, density, and velocity; argue against a standard thin accretion disk model; and suggest that X-rays represent primary rather than reprocessed radiation. For blazars, years of radio monitoring indicated emission from an inhomogeneous synchrotron-emitting plasma, which could also produce at least some of the shorter-wavelength emission. The recent month-long campaign to observe the BL Lac object PKS 2155-304 has revealed remarkably rapid variability that extends from the infrared through the X-ray with similar amplitude and little or no discernible lag. This lends strong support to relativistic jet models and rules out the proposed accretion disk model for the ultraviolet-X-ray continuum.     

Space Shuttle UHF communications performance evaluation

Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances.     

TMA from bearings and multipath time delays

A novel approach for target motion analysis (TMA), which uses conventional passive bearing together with multipath time-delay measurements is examined. This so-called "Multipath TMA" offers two tactical advantages over the classical bearings-only TMA: no requirement for any ownship maneuver, and a good performance in terms of estimation error achieved in a shorter time. Both known and unknown multipath cases are addressed. Finally, Monte-Carlo simulations and at-sea trials demonstrate the practical efficiency of such a multipath TMA.     

Analysis of queuing behavior of automatic ESM systems

Radar electronic support measures (ESM) systems detect active emitters in a given area and determine their identities and bearings. The high arrival rate of radar pulses in dense emitter environments demands fast automatic processing of arriving pulses so that the ESM system can fulfill its functions properly in real time. Yet, the performance analysis of automatic ESM system in real life Is difficult since both pulse arrivals and widths can be specified only probabilistically. The success of queuing theory in many applications such as computer communication networks and flow-control has encouraged designers to utilize queuing theory in qualifying and judging the performance of automatic ESM systems in dense emitter environments. The queuing behavior of these systems is analytically evaluated under different service disciplines and elaborate computer simulations validate the results. The analysis involves statistical modeling of arrival and departure processes as well as distribution of service times. It permits estimating the blocking probability due to high arrival rates of intercepted radar pulses or due to limited speed of the deinterleaver processor. Queuing analysis is shown to be quite useful to quantitatively assess tradeoffs in ESM systems design     

Time-dependent thermal X-ray afterglows from GRBS

Time-dependent thermal X-ray spectra are calculated from physically plausible conditions around GRB. It is shown that account for time-dependent ionization processes strongly affects the observed spectra of hot rarefied plasma. These calculations may provide an alternative explanation to the observed X-ray lines of early GRBs afterglows (such as GRB 011211). Our technique will allow one to obtain independent constraints on the GRB collimation angle and on the clumpiness of circumstellar matter.     

Power anomaly effects and costs in low-voltage mobile power systems

Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales.     

Modelling of Spall in an Anisotropic Aluminium Alloy

Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using a number of spall models. The Hugoniot elastic limit and spall strength have been studied as a function of orientation, and compared to experimental results.