Integrated Rocket Simulation of Internal and External Flow Dynamics in an e-Science Environment

The internal and external flowfield variation of a launch vehicle has been simulated in an e-Science environment. To analyze the igniting process of a solid-rocket propellant, a fluid-structure interaction code has been developed using an ALE (arbitrary Lagrangian Eulerian) kinematical description and a staggered fluid-structure interaction algorithm. Also, unsteady motion of a detached rocket booster has been predicted by using an external flow analysis with an aerodynamic-dynamic coupled solver. A Korean e-Science environment designed for aerospace engineering, e-AIRS [15], supplies a user-friendly interface for such individual work and it can advance to an integrated rocket simulation of internal combustion and external flow variation by controlling the execution and data flow of two flow solvers. As a consequence, e-Science facilitates multi-disciplinary collaborative research, and makes individual work more convenient.The current work is a product of the Korea National e-Science project. The authors are grateful to the Korea Institute of Science and Technology Information for their financial support. Also, the authors appreciate the financial supports provided by NSL(National Space Lab.) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (Grant 20090091724) and the authors are grateful to the Agency for Defence Development for financial support on solid-rocket propellant research.OAIID:oai:osos.snu.ac.kr:snu2009-01/102/0000004648/4SEQ:4PERF_CD:SNU2009-01EVAL_ITEM_CD:102USER_ID:0000004648ADJUST_YN:YEMP_ID:A001138DEPT_CD:446CITE_RATE:1.2FILENAME:article.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:YCONFIRM:

A Comparative Study on the Efficacy of Covered Metal Stent and Plastic Stent in Unresectable Malignant Biliary Obstruction

Background/AimsThe placement of self expandable metal stent (SEMS) is one of the palliative therapeutic options for patients with unresectable malignant biliary obstruction. The aim of this study was to compare the effectiveness of a covered SEMS versus the conventional plastic stent.MethodsWe retrospectively evaluated 44 patients with unresectable malignant biliary obstruction who were treated with a covered SEMS (21 patients) or a plastic stent (10 Fr, 23 patients). We analyzed the technical success rate, functional success rate, early complications, late complications, stent patency and survival rate.ResultsThere was one case in the covered SEMS group that had failed technically, but was corrected successfully using lasso. Functional success rates were 90.5% in the covered SEMS group and 91.3% in the plastic stent group. There was no difference in early complications between the two groups. Median patency of the stent was significantly prolonged in patients who had a covered SEMS (233.6 days) compared with those who had a plastic stent (94.6 days) (p=0.006). During the follow-up period, stent occlusion occurred in 11 patients of the covered SEMS group. Mean survival showed no significant difference between the two groups (covered SEMS group, 236.9 days; plastic stent group, 222.3 days; p=0.182).ConclusionsThe patency of the covered SEMS was longer than that of the plastic stent and the lasso of the covered SEMS was available for repositioning of the stent

Separation Motion of Strap-On Boosters with Base Flow and Turbulence Effects

A numerical investigation is conducted around a multistage launch vehicle to examine the influence of the base region and turbulence. A Reynolds-averaged Navier–Stokes flow solver coupled with rigid body dynamics, because of resultant aerodynamic forces and gravity, is developed to simulate the detachment motion of strap-on boosters. An overset mesh technique is adopted to achieve maximal efficiency in simulating the relative motion of launch vehicles, and various turbulence models are implemented to accurately predict aerodynamic forces in high Reynolds number flows. The flow solver is validated by comparing the computed pressure coefficients of the Titan-IV launch vehicle with the experimental data. In addition, some preliminary studies are conducted to examine the influence of the base flow and turbulence effect in the accurate simulation of detachment motion. Finally, the separation behavior of the KSR-III, a three-stage sounding rocket developed in Korea, is numerically investigated. It is observed that the afterbody flowfield strongly affects the separation motion of strap-on boosters. The negative pitching moment of a strap-on at the initial stage of a detachment motion is gradually recovered and the final result is a safe separation, whereas forebody-only analysis yields a collision scenario between the core rocket and the booster. Only a slight difference in vehicle trajectory is observed from the comparison between inviscid and turbulent analyses. Change of the separation trajectory due to viscous effects is just a few percentage points and, therefore, inviscid analysis seems to be sufficient for the simulation of separation motion if the study focuses on the movement of strap-ons.The authors would like to acknowledge the computing support of the Korea Institute of Science and Technology Information (KISTI) under The Sixth Strategic Supercomputing Support Program, with Kum Won Cho as the technical supporter. Also, the authors would like to acknowledge the financial support of the Bain Korea-21 program for the School of Mechanical and Aerospace Engineering Research at Seoul National University and the Korea National e- Science project

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

CACTUS CFD Toolkit: Combination of Aerodynamic Solver with Advanced Computing Technologies

Cactus[1] is a general-purpose, modular PSE(Problem Solving Environment) designed for scientists and engineers. Since 1995, the base framework has been developed and mainly applied for large scale astrophysics simulations[2]. From those researches, Cactus proved to be a valuable tool for scientific and engineering applications that are tightly coupled, have regular space decomposition, and huge memory and processor time requirements. Currently, Cactus is under the progress of being applied to various studies including CFD(Computational Fluid Dynamics)[3], quantum relativity, chemical reaction and EHD(Electro-Hydro-Dynamics). Especially for CFD simulations, aerodynamicists at 'Seoul National University', 'KISTI Supercomputing Center' and 'KAIST' have been collaborating to make a compressible CFD toolkit working on the Cactus framework. Present paper introduces the current status of a CFD toolkit on the Cactus

Separation Analysis of Strap-ons in the Multi-stage Launch Vehicle Using the Grid Computing Technique

A numerical technique for simulating the separation dynamics of strap-on boosters is presented. Six degree of freedom rigid body equations of motion are integrated into the three-dimensional unsteady Navier-Stokes solution procedure to determine the dynamic motions of strap-ons. An automated Chimera overset mesh technique is introduced to achieve maximum efficiency for the relative motion of multiple bodies and each mesh is constructed as multi-block mesh for the representation of the after-body flow. Additionally, a new computing concept, called the Grid computing technique[1,2], is adopted to guarantee sufficient computing resources and a simple load balancing technique is proposed for an efficient computation in the Grid. As a validation of Chimera mesh technique implementation, computed results around the Titan IV launch vehicle is compared with experimental data and, as a validation of base flow analysis, the aerodynamic coefficients of a strap-on booster of KSR-III is analyzed numerically. The complete analysis process is then applied to the KSR-III, a three-stage sounding rocket researched in Korea. From the analyses, the base flow effect on separation motions of strap-on boosters are investigated and the different aerodynamic characteristics of inviscid and viscous flows at every time interval are examined. In addition, a guidance map of the jettisoning forces and moments for a safe separation is presented from various simulations of separation phenomena with different jettisoning conditions.The authors would like to acknowledge the support from KISTI (Korea Institute of Science and Technology Information) under `The Sixth Strategic Supercomputing Support Program' with Dr. Cho as the technical supporter

Load Balancing for CFD Applications in Grid Computing Environment

The Grid is a communication service that collaborates dispersed high performance computers so that those can be shared and worked together. It enables the analysis of large-scale problem with the reduction of computation time by collaborating high performance computing resources in dispersed organizations. Thus, the present paper focuses on the efficient flow calculation using the Grid. To increase parallel efficiency, a simple load balance algorithm for the Grid computing is proposed and applied to various aerodynamic problems.OAIID:oai:osos.snu.ac.kr:snu2004-01/102/0000004648/1SEQ:1PERF_CD:SNU2004-01EVAL_ITEM_CD:102USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:Load_Balancing_for_CFD_Applications_in_Grid_Computing_Environment.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Use of e-AIRS Computing Service on CFD Education and Research

e-AIRS[1,2], an abbreviation of e-Science Aerospace Integrated Research System, is a virtual organization designed to support the aerospace engineering processes on the e-Science environment. Through the collaborative work between aerospace researchers and computer scientists, e-AIRS web portal with the full services on aerodynamic research process is devised. Currently, e-AIRS supports CFD simulations, remote experimental service, and collaborative and integrative study between computation and experiment. Of these supports, CFD (Computational Fluid Dynamics) service is composed is of mesh generation, CFD analysis and result visualization, and enables users to conduct the full simulation process on the web. This characteristic makes e-AIRS to be a good system for both education and research. In this paper, details on e-AIRS computing service and, the use of this system to fluid dynamic lectures on universities and integrative launch vehicle simulation are to be described.OAIID:oai:osos.snu.ac.kr:snu2008-01/104/0000004648/3SEQ:3PERF_CD:SNU2008-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:Use of e-AIRS Computing Service on CFD Education and Research.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Numerical Analysis on Separation Dynamics of Strap-On Boosters in the Dense Atmosphere

A numerical technique for simulating the separation dynamics of strap-on boosters jettisoned in the dense atmosphere is presented. Six degree of freedom rigid body equations of motion are integrated into the three-dimensional unsteady Navier-Stokes solution procedure to determine the dynamic motions of strap-ons. An automated Chimera overlaid grid technique is introduced to achieve maximum efficiency for multi-body dynamic motion and a domain division technique is implemented in order to reduce the computational cost required to find interpolation points in the Chimera grids. The flow solver is validated by comparing the computed results around the Titan N launch vehicle with experimental data. The complete analysis process is then applied to the H- II launch vehicle, the central rocket in japans space program, the CZ-3C launch vehicle developed in China and the KSR-m, a three-stage sounding rocket being developed in Korea. From the analyses, separation trajectories of strap-on boosters are predicted and aerodynamic characteristics around the vehicles at every time interval are examined. In addition, separation-impulse devices generally introduced for safe separation of strap-ons are properly modeled in the present paper and the jettisoning force requirements are examined quantitatively.OAIID:oai:osos.snu.ac.kr:snu2001-01/102/0000004648/26SEQ:26PERF_CD:SNU2001-01EVAL_ITEM_CD:102USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:Numerical_Analysis_on_Separation_Dynamics.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]: