• Title/Summary/Keyword: Lagrangian Code

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Performance Comparison of CEALM and NPSOL

  • Seok, Hong-Young;Jea, Tahk-Min
    • 제어로봇시스템학회:학술대회논문집
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    • 2001.10a
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    • pp.169.4-169
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    • 2001
  • Conventional methods to solve the nonlinear programming problem range from augmented Lagrangian methods to sequential quadratic programming (SQP) methods. NPSOL, which is a SQP code, has been widely used to solve various optimization problems but is still subject to many numerical problems such as convergence to local optima, difficulties in initialization and in handling non-smooth cost functions. Recently, many evolutionary methods have been developed for constrained optimization. Among them, CEALM (Co-Evolutionary Augmented Lagrangian Method) shows excellent performance in the following aspects: global optimization capability, low sensitivity to the initial parameter guessing, and excellent constraint handling capability due to the benefit of the augmented Lagrangian function. This algorithm is ...

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Development of Numerical Code for Interior Ballistics and Analysis of Two-phase Flow according to Drag Models (강내탄도 전산해석 코드 개발과 항력 모델에 따른 이상유동 분석)

  • Sung, Hyung-Gun;Jang, Jin-Sung;Yoo, Seung-Young;Roh, Tae-Seong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.6
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    • pp.38-46
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    • 2011
  • In order to simulate the ignition-gas injection in the interior ballistics, a two-dimensional analytic code for two-phase flows has been developed. The Eulerian-Lagrangian approach and the low-dissipation simple high-resolution upwind scheme(LSHUS) have been adopted in the numerical code for the propellant combustion of the gun propelling charges. The ghost-cell extrapolation method has been used for the moving boundary in the chamber with the projectile movement. The calculation results of the developed code have been compared and verified through those of the dimensionless IBHVG2 code and the previous one-dimensional code. In comparison with the two-phase flows according to the drag models, the numerical analysis of the muzzle velocity has been affected by the drag model.

Simulation of dynamic fracture and fluid-structure interaction in solid propellant rockets : Part 1 (theoretical aspects) (고체추진로켓 내부에서 발생하는 동적 파괴 현상과 유체-고체 상호작용의 시뮬레이션 - Part 1 (이론적 측면))

  • Hwang, Chan-Gyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.9 no.2
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    • pp.286-290
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    • 2008
  • This paper summarizes the components of an explicit aeroelastic solver developed especially for the simulation of dynamic fracture events occurring during the flight of solid propellant rockets. The numerical method combines an explicit Arbitrary Lagrangian Eulerian (ALE) version of the Cohesive Volumetric Finite Element (CVFE) scheme, used to simulate the spontaneous motion of one or more cracks propagating dynamically through a domain with regressing boundaries, and an explicit unstructured finite volume Euler code to follow the flow field during the failure event. A key feature of the algorithm is the ability to adaptively repair and expand the fluid mesh to handle the large geometrical changes associated with grain deformation and crack motion.

Development of 3-Dim FEM Multi-Material Hydrocode (3차원 FEM 다중물질 하이드로코드 개발 현황)

  • Lee, Min-Hyung
    • Journal of the Korea Institute of Military Science and Technology
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    • v.11 no.5
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    • pp.116-123
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    • 2008
  • Hydrocodes are large computer programs that can be used to solve a wide variety of highly transient problems such as high-speed impact and explosion events. This paper describes the recent activity to develop a Multi-material hydrocode in Korea. The code consists of two stages; Lagrangian, and remap stages. Although a sophisticated contact algorithm has been developed for Lagrangian calculations, a relatively simple mechanics at the interfaces of materials are used in the multi-material Eulerian code. Volume of fluid interface reconstruction methods are used to resolve the interfaces between different materials. For the advection stage of the cell centered properties, one-dimensional hyperbolic equation is used. Test problems demonstrated here are the high-speed impact/penetration and explosion problems.

A study on the effect of yield stress in long-rod penetration (긴 관통자 관통에서 항복 응력의 영향에 대한 연구)

  • Hwang, Chan;Chung, Dong-Teak;Lee, Heon-Joo;Oh, Soo-Ik
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.248-253
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    • 2000
  • This paper presents parametric study of long-rod penetration. Influences of yield stress of penetrator and target material on the penetration results such as crater size and penetrator residual length are contemplated. Numerical experiments are carried out with varying the value of static yield stress of materials. Lagrangian explicit code NET2D was used to perform parametric study. Element eroding algorithm was used to properly simulate long-rod penetration. Analytic and empirical model of long-rod penetration and Taylor test are used to explain the relationships of parameter and simulation results.

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Reduction of Grid Size Dependency in DME Spray Modeling with Gas-jet Model (가스 제트 모델을 이용한 DME 분무 해석의 격자 의존성 저감)

  • Oh, Yun-Jung;Kim, Sa-Yop;Lee, Chang-Sik;Park, Sung-Wook
    • Journal of ILASS-Korea
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    • v.15 no.4
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    • pp.170-176
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    • 2010
  • This paper describes the grid-size dependency of the conventional Eulerian-Lagrangian method to spray characteristics such as spray penetration and SMD in modeling DME sprays. In addition, the reduction of the grid-size dependency of the present Gas-jet model was investigated. The calculations were performed using the KIVA code and the calculated results were compared to those of experimental result. The results showed that the conventional Eulerian-Laglangian model predicts shorter spray penetration for large cell because of inaccurate calculation of momentum exchange between liquid and gas phase. However, it was shown that the gas-jet model reduced grid-size dependency to spray penetration by calculating relative velocity between liquid and ambient gas based on gas jet velocity.

Parallel Computing of Large Scale FE Model based on Explicit Lagrangian FEM (외연 Lagrangian 유한요소법 기반의 대규모 유한요소 모델 병렬처리)

  • 백승훈;김승조;이민형
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.8
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    • pp.33-40
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    • 2006
  • A parallel computing strategy for finite element(FE) processing is described and implemented in nonlinear explicit FE code and its parallel performances are evaluated. A self-made linux-cluster supercomputer with 520 CPUs is used as a bench mark test bed. It is observed that speed-up is increased almost idealy even up to 256 CPUs for a large scale model. A communication over head and its effect on the parallel performance is also examined. Parallel performance is compare with the commercial code and developed code shows superior performance as the number of CPUs used are increased.

Estimation of Acceleration Response of Freefall Lifeboat using FSI Analysis Technique of LS-DYNA Code (LS-DYNA 코드의 유체-구조 연성해석 기법을 이용한 자유낙하식 구명정의 가속도 응답 추정)

  • Bae, Dong-Myung;Zakki, A.F.;Kim, Hag-Soo;Kim, Joo-Gon
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.5
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    • pp.681-688
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    • 2010
  • During certification of freefall lifeboats, it is necessary to estimate the injury potential of the impact loads exerted on the occupants during water entry. This paper focused on the numerical simulation to predict the acceleration response during the impact of freefall lifeboats on the water using FSI(Fluid-Structure Interaction) analysis technique of LS-DYNA code. FSI problems could be conveniently simulated by the overlapping capability using Arbitrary Lagrangian Eulerian(ALE) formulation and Euler-Lagrange coupling algorithm of LS-DYNA code. Through this study, it could be found that simulation results were in relatively good agreement with experimental ones in the acceleration peak values, and that the loading conditions were very sensitive to the acceleration responses by the experimental and simulation results.

Prediction of Pressure Drop in Venturi Scrubber Using the Eulerian - Lagrangian Method (오일러-라그랑지 방법을 이용한 벤튜리 스크라버의 압력강하 계산)

  • Pak S, I.;Moon Y. W.;Chang K. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.03a
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    • pp.190-195
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    • 2004
  • The pressure drop in a Venturi Scrubber is predicted using the Eulerian-Lagrangian Method, which is one of the numerical methods to solve the dispersed two-phase flow. KIVA-3V Code is modified to solve the coupled gas-liquid two-phase flow field. The liquid is assumed to be injected through the nozzles with the Rosin-Rammler drop size distribution. The computational results shows good agreement with the experimental data.

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A Study on Relation of Needle-Nozzle Flow of Piezo-driven Injector by using Eulerian-Lagrangian Multi-phase Method (Eulerian-Lagrangian 다상 유동해석법에 의한 피에조인젝터의 니들-노즐유동 상관성 연구)

  • Lee, Jin-Wook;Min, Kyoung-Doug
    • Transactions of the Korean Society of Automotive Engineers
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    • v.18 no.5
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    • pp.108-114
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    • 2010
  • The injection nozzle of an electro-hydraulic injector is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the effects of needle movement in a piezo-driven injector on unsteady cavitating flows behavior inside nozzle were investigated by cavitation numerical model based on the Eulerian-Lagrangian approach. Aimed at simulating the 3-D two-phase flow behavior, the three dimensional geometry model along the central cross-section regarding of one injection hole with real design data of a piezo-driven diesel injector has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. As this research results, we found that it could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle.