• Title/Summary/Keyword: Fixed Grid System

Search Result 121, Processing Time 0.031 seconds

Numerical Analysis on Flow and Heat Transfer in Twin-Roll Strip Casting Using an Unstructured Fixed-Grid System (비정렬 고정격자계를 이용한 쌍롤 박판주조에서의 유동장 및 열전달 해석)

  • Lee, Jun-Sik;Lee, Ju-Myeong;Jeong, Jae-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.26 no.5
    • /
    • pp.648-657
    • /
    • 2002
  • This paper presents a numerical analysis on the solidification characteristics in twin-roll strip casting. Unstructured fixed-grid system was employed to deal with phase change. Melting of pure gallium was analyzed to confirm the validity of present program in both structured and unstructured grid systems. An algorithm for simultaneous calculation of the temperature in the roll and the molten metal pool was developed. The flow field in the pool and heat transfer features between pool and roll were shown. The effect of process parameters was also studied. Since the geometry of the molten metal Pool significantly deforms along the casting direction, unstructured grid system is more efficient. The unstructured grid system gives almost the same accuracy, even though the number of grids is only 60% of the structure done.

Numerical Analysis of Free Surface Flows Using Adaptable Surface Particle Method based on Grid System (격자기반 적합 표면입자법을 이용한 자유표면유동 수치해석)

  • Shin, Young-Seop
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.54 no.1
    • /
    • pp.26-33
    • /
    • 2017
  • In this study, the surface marker method, one of the particle tracking methods, used to track the free surface is extended to cover the more general cases easily including the collision and separation of the free surface. In surface particle method to redistribute particles effectively using the grid system, the free surface is composed of the sum of quadrilaterals having four curves where fixed markers are placed at ends of each curve. Fixed markers are used to know how curves are connected to each other. The position of fixed markers can move as the free surface deforms but all fixed markers cannot be deleted during all time of simulation to keep informations of curve connection. In the case of the collision or separtion of the free surface where several curves can be intersected disorderly, severe difficulties can occur to define newly states of curve connection. In this study, the adaptable surface parTicle method without fixed markers is introduced. Intersection markers instead of the fixed markers are used to define quadrilaterals. The position of the intersection markers is defined to be the intersection point between the free surface and the edge of the grid and it can be added or deleted during the time of simulation to allow more flexibilities. To verify numerical schemes, two flow cases are simulated and the numerical results are compared with other's one and shown to be valid.

Seawater Exchange and Residence Time in Gamak Bay Determined by Numerical Experiments

  • Lee, Moon-Ock;Kim, Byeong-Kuk
    • Fisheries and Aquatic Sciences
    • /
    • v.14 no.4
    • /
    • pp.421-428
    • /
    • 2011
  • We conducted modeling experiments to evaluate the residence times and exchange rates of seawater in Gamak Bay, located on the southern coast of the Korean Peninsula. The results revealed that pollutants are more quickly dispersed in a fixed grid rather than in a variable grid system. Pollutant concentrations decayed exponentially with time after release near the mouth of the bay, whereas no exponential variations were seen at the northwest end of the bay. The mean exchange rate of the seawater was 1.58% per day in the variable grid system, and the residence time of pollutants was greater than 288 days in Gamak Bay. Conversely, the exchange rate of seawater in Gamak Bay, as revealed by the particle tracking method, was 65% over a 50-day simulation. The results suggest that the seawater exchange in Gamak Bay is so low that pollutants are likely to remain in the bay indefinitely.

Effects of Natural Independent Visual Background for Reducing Simulator Sickness (자연형 IVB(Independent Visual Background)의 Simulator Sickness 감소효과)

  • 김도회;임정위
    • Journal of Korean Society of Industrial and Systems Engineering
    • /
    • v.25 no.3
    • /
    • pp.28-33
    • /
    • 2002
  • Several studies indicated that an independent visual background (IVB) reduced simulator sickness (SS) and balance disturbance associated with exposure to virtual environments (VEs) and motion simulators. A recent study showed that an IVB comprised of an earth-fixed grid was less effective in a complex driving simulator than in a simple VE. Subjects' post-experiment reports indicated that the VE motion "induced" motion of the earth-fixed grid m. This led to the suggestion that an IVB comprised of clouds would be less subject to induced motion and therefore would alleviate nausea more effectively than a grid IVB. Clouds are "natural" and are usually perceived as relatively stable, whereas a grid has no inherent stability. 12 subjects were exposed to complex motion through a simulated environment in a driving simulator under 3 IVB conditions: grid, less clouds, many clouds. They reported less nausea when the many-cloud IVB was used relative to the grid IVB condition. grid IVB condition.

A numerical simulation method for the flow around floating bodies in regular waves using a three-dimensional rectilinear grid system

  • Jeong, Kwang-Leol;Lee, Young-Gill
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.8 no.3
    • /
    • pp.277-300
    • /
    • 2016
  • The motion of a floating body and the free surface flow are the most important design considerations for ships and offshore platforms. In the present research, a numerical method is developed to simulate the motion of a floating body and the free surface using a fixed rectilinear grid system. The governing equations are the continuity equation and Naviere-Stokes equations. The boundary of a moving body is defined by the interaction points of the body surface and the centerline of a grid. To simulate the free surface the Modified Marker-Density method is implemented. Ships advancing in regular waves, the interaction of waves by a fixed circular cylinder array and the response amplitude operators of an offshore platform are simulated and the results are compared with published research data to check the applicability. The numerical method developed in this research gives results good enough for application to the initial design stage.

Fixed speed wind power generation system modeling and transient state stabilization method using PSCAD/EMTDC (PSCAD/EMTDC를 이용한 고정속 풍력발전시스템 모델링 및 과도상태 안정화기법)

  • Kim, Young-Ju;Park, Dae-Jin;Ali, Mohd Hasan;Park, Min-Won;Yu, In-Keun
    • Proceedings of the KIEE Conference
    • /
    • 2008.07a
    • /
    • pp.1178-1179
    • /
    • 2008
  • This paper describes a modeling of fixed speed wind power generation system which comprise of wind turbine, generator and grid. The wind turbine is based on MOD-2, which is IEEE standard wind turbine, and includes a component using wind turbine characteristic equation. Fixed speed induction generator is directly connected to grid, so the variation of wind speed has effects on the electrical torque and electrical output power. Therefore the power control mode pitch control system is necessary for aerodynamic control of the blades. But the power control mode does not operate at the fault condition. So it is required some methods to control the rotor speed at transient state for stabilization of wind power system. In this paper, simulation model of a fixed speed wind power generation system based on the PSCAD/EMTDC is presented and implemented under the real weather conditions. Also, a new pitch control system is proposed to stabilize the wind power system at the fault condition. The validity of the stabilization method is demonstrated with the results produced through sets of simulation.

  • PDF

A NUMERICAL SIMULATION METHOD FOR FREE SURFACE FLOWS NEAR MOVING BODIES IN A FIXED RECTANGULAR GRID SYSTEM (고정된 직사각형 격자계에서 움직이는 물체주위 자유수면유동 계산을 위한 수치기법의 개발)

  • Jeong, K.L.;Lee, Y.G.;Ha, Y.J.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2011.05a
    • /
    • pp.395-406
    • /
    • 2011
  • In this research a numerical simulation method is developed for moving body in free surface flows using fixed staggered rectangular grid system. The non-linear free surface near the body is defined by marker-density method. The body boundary is defined by line segment connecting the points where the body surface and grid line meet. Continuity equation and Navier-Stokes equations are used as governing equations and the equations are coupled with two-step projection method. The velocities and pressures of body boundary and free surface cells are calculated with simultaneous iterative method. To treat a body movement in a fixed grid system, the volume displaced by moving body is added to the divergence of the body boundary cell. For the verification of the present numerical method. vortex shedding period of advancing cylinder is calculated and the period is compared with existing experiment results. Moreover, added mass and damping coefficients of a vertically excited box are calculated and the computed results are compared with published experiment results. Impulsive pressure and water level variation due to sloshing phenomenon are simulated and the results are compared with published experiment results. Varying the plunger shape, the waves generated by plunging type wave maker are compared with the 2nd order Stokes wave theory The plunger shape generating the wave that shows the best agreement with the theory is represented.

  • PDF

Kinetic energy conservative algorithm in moving grid system using segregated finite element formulation (이동격자계에서 분리유한요소법에 의한 운동에너지 보존 알고리듬)

  • Seong, Jae-Yong;Choe, Hyeong-Gwon;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.21 no.11
    • /
    • pp.1538-1551
    • /
    • 1997
  • Kinetic energy conservation for fixed and moving grids is examined in time-accurate finite element computation of fully unsteady inviscid flows. As numerical algorithms, fractional step method (FSM) and modified SIMPLE are used. To simulate the flow in moving grid system, arbitrary Lagrangian-Eulerian (ALE) method is adopted. In the present study, the energy conserving time integration rule for finite element algorithm is proposed and discussed schematically. It is shown that the discretization by Crank-Nicolson in time and Galerkin (central difference) in space must be used to ensure energy conservation. The developed code has been tested for a standing vortex in fixed or moving grid system, sloshing in a tank and propagation of a solitary wave, and has been shown to be a completely energy conserving algorithm.

Numerical simulations of two-dimensional floating breakwaters in regular waves using fixed cartesian grid

  • Jeong, Kwang-Leol;Lee, Young-Gill
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.6 no.2
    • /
    • pp.206-218
    • /
    • 2014
  • The wave attenuation by floating breakwaters in high amplitude waves, which can lead to wave overtopping and breaking, is examined by numerical simulations. The governing equations, the Navier-Stokes equations and the continuity equation, are calculated in a fixed Cartesian grid system. The body boundaries are defined by the line segment connecting the points where the grid line and body surface meet. No-slip and divergence free conditions are satisfied at the body boundary cell. The nonlinear waves near the moving body is defined using the modified marker-density method. To verify the present numerical method, vortex induced vibration on an elastically mounted cylinder and free roll decay are numerically simulated and the results are compared with those reported in the literature. Using the present numerical method, the wave attenuations by three kinds of floating breakwaters are simulated numerically in a regular wave to compare the performance.

Design of Fuzzy Observer for Nonlinear System using Dynamic Rule Insertion (비선형 시스템에 대한 동적인 규칙 삽입을 이용한 퍼지 관측기 설계)

  • Seo, Ho-Joon;Park, Jang-Hyun;Seo, Sam-Jun;Kim, Dong-Sik;Park, Gwi-Tae
    • Proceedings of the KIEE Conference
    • /
    • 2001.07d
    • /
    • pp.2308-2310
    • /
    • 2001
  • In the adaptive fuzzy sliding mode control, from a set of a fuzzy IF-THEN rules adaptive fuzzy sliding mode control whose parameters are adjusted on-line according to some adaptation laws is constructed for the purpose of controlling the plant to track a desired trajectory. Most of the research works in nonlinear controller design using fuzzy systems consider the affine system with fixed grid-rule structure based on system state availability. The fixed grid-rule structure makes the order of the controller big unnecessarily, hence the on-line fuzzy rule structure and fuzzy observer based adaptive fuzzy sliding mode controller is proposed to solve system state availability problems. Therefore, adaptive laws of fuzzy parameters for state observer and fuzzy rule structure are established implying whole system stability in the sense of Lyapunov.

  • PDF