Effects of shock strength on shock turbulence interaction

Direct numerical simulation (DNS) and linear analysis (LIA) of isotropic turbulence interacting with a shock wave are performed for several upstream shock normal Mach numbers (M(sub 1)). Turbulence kinetic energy (TKE) is amplified across the shock wave, but this amplification tends to saturate beyond M(sub 1) = 3.0. TKE amplification and Reynolds stress anisotropy obtained in DNS are consistent with LIA predictions. Rapid evolution of TKE immediate downstream of the shock wave persists for all shock strengths and is attributed to the transfer between kinetic and potential modes of turbulence energy through acoustic fluctuations. Changes in energy spectra and various length scales across the shock wave are predicted by LIA, which is consistent with DNS results. Most turbulence length scales decrease across the shock. Dissipation length scale (rho-bar q(exp 3) / epsilon), however, increases slightly for shock waves with M(sub 1) less than 1.65. Fluctuations in thermodynamic variables behind the shock wave stay nearly isentropic for M(sub 1) less than 1.2 and deviate significantly from isentropy for the stronger shock waves due to large entropy fluctuation generated through the interaction

Large eddy simulation of shock turbulence interaction

A nonconservative formulation of the energy equation (solving for internal energy) was used to perform large eddy simulations of compressible turbulence in Moin et al. due to its simplicity in implementing SGS models compared to the conservative formulation (solving for total energy). In problems with shocks in the domain, however, the total energy formulation is preferred due to its conservative nature. A conservative set of equations for the LES were derived from the nonconservative equations derived by Moin et al. Performance of the conservative formulation was compared with the experiment on decaying grid-generated turbulence as well as with the filtered DNS field. Various shock-capturing schemes were tested, and an ENO shock-capturing scheme of Shu and Osher was chosen for the simulation of shock/turbulence interaction. The scheme was tested and validated against the data base generated by DNS of weak shock waves. The results obtained with the essentially nonoscillatory (ENO) scheme were within 5 percent from the DNS results, and used less than 25 percent of the CPU time used in the DNS

Dynamics of fullerene coalescence

Fullerene coalescence experimentally found in fullerene-embedded single-wall nanotubes under electron-beam irradiation or heat treatment is simulated by minimizing the classical action for many atom systems. The dynamical trajectory for forming a (5,5) C$_{120}$ nanocapsule from two C$_{60}$ fullerene molecules consists of thermal motions around potential basins and ten successive Stone-Wales-type bond rotations after the initial cage-opening process for which energy cost is about 8 eV. Dynamical paths for forming large-diameter nanocapsules with (10,0), (6,6), and (12,0) chiral indexes have more bond rotations than 25 with the transition barriers in a range of 10--12 eV.Comment: 4 pages, 2 figures, 1 supplementary movie at http://dielc.kaist.ac.kr/yonghyun/coal.mpeg. To be published in Physical Review Letter

Magnetic anisotropy of an extended double exchange model for layered manganites: A Monte Carlo study

The magnetic ground state properties of layered manganites are investigated on the basis of an anisotropic double exchange model using a Monte Carlo technique. The temperature dependence of magnetization and spin-spin correlations are calculated in a highly anisotropic hopping integral $t_c/t_{ab}$ regime. The ferromagnetic ordering temperature (Tc) is suppressed by introducing $t_c/t_{ab}$, and eventually a layered ferromagnetic structure appears along the c-axis, but there are block-walls. The significant change of magnetic anisotropy is also observed for the antiferromagnetic superexchange integral $J_c/t_{ab}$. We discuss the connection of these results to the magnetic anisotropy observed in the La1.4Sr1.6Mn2O7

Kaiki tanteio burakku hakase kochu himitsu no maki

Tapping Sound Analysis is a new NDE method, which determines the existence of subsurface defects by comparing the tapping sound of test structure and original healthy structure. The tapping sound of original healthy structure is named sound print of the structure and is obtained through high precision computation. Because many tapping points are required to obtain the exact sound print data, many times of tapping sound simulation are required. The simulation of tapping sound requires complicated numerical procedures. Departmental Computing GRID system was utilized to run numerical simulations. Three cluster systems and one PC-farm system comprise DCG system. Tapping sound simulations were launched and monitored through Globus and CONDOR. A total of 160 Tera floating-point (double-precision) operations was performed and the elapsed time was 41,880 sec. From the numerical experiments, Grid computing technology reduced the necessary time to make sound print database and made TSA a feasible and practical methodology. GGGGGGGGGGGGGGGGGGGGGGGGGGGGGG GGGGGGGGGGGGGG 0-7695-1524-X/02 $17.00 (c) 2002 IEEE Professor, San 56-1, Shilliom-dong Kwanak-gue, Seoul, 151-742, Korea, E-mail: [email protected] Graduated Student, * Director, Korean Institute of Science and Technology Information, Taejon 305-333, Korea 1

A Grid-based Flow Analysis and Investigation of Load Balance in Heterogeneous Computing Environment

According to Moores law, computer speed doubles in every 18 months. In accordance with the development of computational environment, the problem size in CFD(Computational Fluid Dynamics) has been enormously expanded. However, even now, a lot of problems require too huge computational power to be analyzed using local computing resources. As an alternative proposal, the concept Grid was planned and is on research now. It is obvious that the Grid enables a researcher to analyze a huge-sized problem(e.g. an integral analysis and flow analysis of an airplane). However, diverse communication speed among computing resources and heterogeneity of computing resources can reduce parallel efficiency in the Grid. Therefore, the present research focuses on the effective flow calculation in the Grid. As an analysis of a huge-sized problem, flowfield around a launch vehicle with two strap-on boosters including base region is analyzed. For an efficient load distribution, performances of all computing resources in the Grid are investigated and, on the basis of performance test results, the whole job is distributed explicitly. As an investigation of load balance in the Grid, a simple load balance algorithm is proposed and applied to the flow calculation around a tangent ogive-cylinder. The proposed algorithm distributes the whole job considering the performance of each processor and communication speed between processors. And the application shows a validity of proposed algorithm