• Title/Summary/Keyword: Coupled-Time Integration Method

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Numerical Study of Normal Start and Unstart Processes In a Superdetonative Speed Ram Accelerator (초폭굉속도 램가속기의 정상발진과 불발과정에 대한 수치해석)

  • Moon, Guee-Won;Jeung, In-Seuck;Choi, Jeong-Yeol;Seiler, Friedrich;Patz, Gunther;Smeets, Gunter;Srulijes, Julio
    • 한국연소학회:학술대회논문집
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    • 2002.06a
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    • pp.123-132
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    • 2002
  • A numerical study was conducted to investigate the combustion phenomena of normal start and unstart processes based on ISL's RAMAC 30 experiments with different diluent amounts and fill pressures in a ram accelerator. The initial projectile launching speed was 1.8 km/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with 5 $CO_2$ or 4 $CO_2$. Experiments with same condition except for projectile surface material demonstrated that ignition was successful with an aluminum projectile, but no combustion was observed in case of a steel projectile. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1.8 km/s, as was found in the experiments using a steel projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the normal start and unstart processes found in the experiments with an aluminum projectile. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baldwin-Lomax turbulence model and detailed chemistry reaction equations of $H_2/O_2/CO_2$ suitable for high-pressure gaseous combustion were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. The numerical results matched almost exactly to the experimental results. As a result, it was found that the normal start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

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Transonic Flutter Characteristics of Supercritical Airfoils Considering Shockwave and Flow Separation Effects (충격파 및 유동박리 효과를 고려한 초임계 에어포일의 천음속 플러터 특성)

  • Kim, Dong-Hyun;Kim, Yu-Sung;Kim, Yo-Han;Kim, Seok-Soo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.11a
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    • pp.167-174
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    • 2008
  • In this study, flutter analyses for supercritical airfoil have been conducted in transonic region. Advanced computational analysis system based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) has been developed in order to investigate detailed static and dynamic responses of supercritical airfoil. Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras (S-A) and SST ${\kappa}-{\omega}$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of cascades for fluid-structure interaction (FSI) problems. Also, flow-induced vibration (FIV) analyses for various supercritical airfoil models have been conducted. Detailed flutter responses for supercritical are presented to show the physical performance and vibration characteristics in various angle of attack.

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Analysis of Flexible Media Using ALE Finite Element Method (ALE 유한요소법을 이용한 유연매체의 거동해석)

  • Jee, Jung-Geun;Jang, Yong-Hoon;Park, No-Cheol;Park, Young-Pil
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.247-250
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    • 2007
  • Flexible media such as the paper, the film, etc. are thin, light and very flexible. They behave in geometrically nonlinear. Any of small force makes large deformation. So we must including aerodynamic effect when its behavior is predicted. Thus, it becomes fully coupled fluid-structure interaction(FSI) problem. In FSI problems, where the fluid mesh near the structure undergoes large deformations and becomes unacceptably distorted, which drive the time step to a very small value for explicit calculations, the arbitrary Lagrangian-Eulerian(ALE) methods or rezoning are used to create a new undistorted mesh for the fluid domain, which allows the calculations to continue. In this paper, FE sheet model considering geometric nonlinearity is formulated to simulate the behavior of the flexible media. Aerodynamic force to the media by surrounding air is calculated by solving the incompressible Navier-Stokes equations. Q2Q1(Taylor-Hood) element which means biquadratic for velocity and bilinear for pressure is used for fluid domain. Q2Q1 element satisfies LBB condition and any stabilization technique is not needed. In this paper, cantilevered sheet in the viscous incompressible Navier-Stokes flow is simulated to check the mesh motion and numerical integration scheme, and then falling paper in the air is simulated and the effects of some representative parameters are investigated.

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Lock-in and drag amplification effects in slender line-like structures through CFD

  • Belver, Ali Vasallo;Iban, Antolin Lorenzana;Rossi, Riccardo
    • Wind and Structures
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    • v.15 no.3
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    • pp.189-208
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    • 2012
  • Lock-in and drag amplification phenomena are studied for a flexible cantilever using a simplified fluid-structure interaction approach. Instead of solving the 3D domain, a simplified setup is devised, in which 2D flow problems are solved on a number of planes parallel to the wind direction and transversal to the structure. On such planes, the incompressible Navier-Stokes equations are solved to estimate the fluid action at different positions of the line-like structure. The fluid flow on each plane is coupled with the structural deformation at the corresponding position, affecting the dynamic behaviour of the system. An Arbitrary Lagrangian-Eulerian (ALE) approach is used to take in account the deformation of the domain, and a fractional-step scheme is used to solve the fluid field. The stabilization of incompressibility and convection is achieved through orthogonal quasi-static subscales, an approach that is believed to provide a first step towards turbulence modelling. In order to model the structural problem, a special one-dimensional element for thin walled cross-section beam is implemented. The standard second-order Bossak method is used for the time integration of the structural problem.

Aeroelastic Response Analysis of 3D Wind Turbine Blade Considering Rotating and Flow Separation Effects (회전과 유동박리효과를 고려한 3차원 풍력발전 터빈 블레이드의 공탄성 응답 해석)

  • Kim, Dong-Hyun;Kim, Yo-Han;Kim, Dong-Man;Kim, Yu-Sung;Hwang, Mi-Hyun
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.04a
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    • pp.68-75
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    • 2009
  • In this study, aeroelastic response analyses have been conducted for a 3D wind turbine blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responsed of wind turbine blade. Vibration analyses of rotating wind-turbine blade have been conducted using the general nonlinear finite element program, SAMCEF (Ver.6.3). Reynolds-averaged Navier-Stokes (RANS)equations with spalart-allmaras turbulence model are solved for unsteady flow problems of the rotating turbine blade model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D turbine blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous Mach contour on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating wind-turbine blade model.

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Flow-Induced Vibration (FIV) Analysis of a 3D Axial Compressor Blade (3차원 축류압축기 블레이드의 유체유발진동 해석)

  • Kim, Dong-Hyun;Kim, Yu-Sung;Yang, Guo Wei;Jung, Kyu-Kang;Kim, Kyung-Hee;Min, Dae-Gee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.04a
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    • pp.652-653
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    • 2009
  • In this study, flow-induced vibration (FIV) analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) has been developed in order to investigate detailed dynamic responses of designed compressor blades. Fluid domains are modeled using the computational grid system with local grid deforming and remeshing techniques. Reynolds-averaged Navier-Stokes equations with $\kappa-\varepsilon$ turbulence model are solved for unsteady flow problems of the rotating compressor model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

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Molecular Dynamic Simulation for Penetration of Carbon Nanotubes into an Array of Carbon Nnantotubes

  • Jang, Ilkwang;Jang, Yong Hoon
    • Tribology and Lubricants
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    • v.36 no.5
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    • pp.290-296
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    • 2020
  • When two layers of carbon nanotube (CNT) arrays are loaded to mate, the free ends of individual CNTs come into contact at the interface of the two layers. This leads to a higher contact resistance due to a smaller contact region. However, when the free CNT ends of one array penetrate into the mating array, the contact region increases, effectively lowering the contact resistance. To explore the penetration of mating CNTs, we perform molecular dynamic simulations of a simple unit cell model, incorporating four CNTs in the lower array layer coupled with a single moving CNT on the upper layer. The interaction with neighboring CNTs is modelled by long-range carbon bond order potential (LCBOP I). The model structure is optimized by energy minimization through the conjugate gradient method. A NVT ensemble is used for maintain a room temperature during simulation. The time integration is performed through the velocity-Verlet algorithm. A significant vibrational motion of CNTs is captured when penetration is not available, resulting in a specific vibration mode with a high frequency. Due to this vibrational behavior, the random behaviors of CNT motion for predicting the penetration are confirmed under the specific gap distances between CNTs. Thus, the probability of penetration is examined according to the gap distance between CNTs in the lower array and the aspect ratio of CNTs. The penetration is significantly affected by the vibration mode due to the van der Waals forces between CNTs.

Flow-induced Vibration(FIV) Analysis of a 3D Axial Compressor Blade (3차원 축류압축기 블레이드의 유체유발진동 해석)

  • Kim, Dong-Hyun;Kim, Yu-Sung;Yang, Guo Wei;Jung, Kyu-Kang;Kim, Kyung-Hee;Min, Dae-Gee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.6
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    • pp.551-559
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    • 2009
  • In this study, flow-induced vibration(FIV) analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responses of designed compressor blades. Fluid domains are modeled using the computational grid system with local grid deforming and remeshing techniques. Reynolds-averaged Navier-Stokes equations with $\kappa-\epsilon$ turbulence model are solved for unsteady flow problems of the rotating compressor model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction(FSI) problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

Vibration Analysis of a Turbo-Machinery Blade Considering Rotating and Flow Effect (회전 및 유동효과를 고려한 터보기계 블레이드의 진동해석)

  • Joung, Kyu-Kang;Shin, Seung-Hoon;Park, Hee-Yong;Kim, Dong-Hyun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.11a
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    • pp.519-522
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    • 2010
  • Flow-induced vibration analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics has been developed in order to investigate detailed dynamic responses of designed compressor blades. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

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Aerodynamic and Structural Design of 6kW Class Vertical-Axis Wind Turbine (공탄성 변형효과를 고려한 5MW급 풍력발전 블레이드의 피치각에 따른 성능해석)

  • Kim, Yo-Han;Kim, Dong-Hyun;Hwang, Mi-Hyun;Kim, Kyung-Hee;Hwang, Byung-Sun;Hong, Un-Sung
    • The KSFM Journal of Fluid Machinery
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    • v.14 no.3
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    • pp.39-44
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    • 2011
  • In this study, performance analyses have been conducted for a 5MW class wind turbine blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responsed of wind turbine blade. Reynolds-averaged Navier-Stokes (RANS) equations with K-${\epsilon}$ turbulence model are solved for unsteady flow problems of the rotating turbine blade model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D turbine blade for fluid-structure interaction (FSI) problems. Predicted aerodynamic performance considering structural deformation effect of the blade show different results compared to the case of rigid blade model.