• Title, Summary, Keyword: Overset mesh method

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Application of the Overset Grid Scheme (Suggar++) for Flow Analysis around a Ship (선박의 유동해석 문제에 대한 중첩격자기법(Suggar++)의 활용)

  • Kim, Yoo-Chul;Kim, Yoonsik;Kim, Jin;Kim, Kwang-Soo
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.1
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    • pp.47-57
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    • 2019
  • Recent CFD solvers in engineering have to treat geometrically complex domains and moving body problems. In ship hydrodynamics, flow around the stern and ship motions in waves are examples of such cases mentioned before. The unstructured grid scheme is successfully applied for these problems, but it has weakness of inefficient memory usage and intensive computational time as compared to the structured grid method. Overset grid scheme is one of the alternatives for structured grid system taking advantage of fast and memory efficiency. Overset grid scheme is especially useful for moving body problem because there is no need to re-mesh around the body. In this paper, we adopted the Suggar++, the grid connectivity and interpolation utility for the overlapping grid, to WAVIS which is the in-house flow solver of KRISO. Then we introduced some applications using the overset grid method for flow analysis around the ships. The computed results show that WAVIS with Suggar++ is practically feasible and has an advantages for moving geometry cases.

Development of an Unstructured Parallel Overset Mesh Technique for Unsteady Flow Simulations around bodies with Relative Motion (상대운동이 있는 물체주위의 비정상 유동해석을 위한 병렬화된 비정렬 중첩격자기법 개발)

  • Jung, Mun-Seung;Kwon, Oh-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.2
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    • pp.1-10
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    • 2005
  • An unstructured parallel overset mesh method has been developed for the simulation of unsteady flows around multiple bodies in relative motion. For this purpose, an efficient and robust search method is proposed for the unstructured grid system. A new data-structure is also proposed to handle the variable number of data on parallel sub-domain boundary. The interpolation boundary is defined for data communication between grid systems. An interpolation method to retain second-order spatial accuracy and to treat the points inside the neighboring solid bodies are also suggested. A single store separating from the Eglin/Pylon configuration is calculated and the result is compared with experimental data for validation. Simulation of unsteady flows around multiple bodies in relative motion is also performed.

VISCOUS FLOW CALCULATIONS OF HELICOPTER MAIN ROTOR SYSTEM IN FORWARD FLIGHT (전진 비행하는 헬리콥터 주로터 시스템의 점성 유동 해석)

  • Jung, M.S.;Kwon, O.J.;Kang, H.J.
    • 한국전산유체공학회:학술대회논문집
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    • pp.31-38
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    • 2009
  • In the present study, viscous flow calculations of helicopter main rotor system in forward flight were made by using an unstructured hybrid mesh solver. Each rotating blade relative to the cartesian frame was simulated independently by adopting unstructured overset mesh technique. For the validation of the present method, calculations for the Caradonna-Tung non-lifting forward flight and the AH-1G main rotor system in forward flight were made. Additional computation was made for the UH-60A rotor in forward flight. Reasonable agreements were obtained between the present results and the experiment.

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Prediction of Resistance and Planing Attitude for Prismatic Planing Hull using OpenFOAM (OpenFOAM을 이용한 주형체 활주선의 저항 및 항주자세 추정)

  • Shi, XiangYu;Zhang, Yang;Yum, Deuk-joon
    • Journal of Ocean Engineering and Technology
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    • v.33 no.4
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    • pp.313-321
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    • 2019
  • The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.

A numerical study on ship-ship interaction in shallow and restricted waterway

  • Lee, Sungwook
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.7 no.5
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    • pp.920-938
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    • 2015
  • In the present study, a numerical prediction method on the hydrodynamic interaction force and moment between two ships in shallow and restricted waterway is presented. Especially, the present study proposes a methodology to overcome the limitation of the two dimensional perturbation method which is related to the moored-passing ship interaction. The validation study was performed and compared with the experiment, firstly. Afterward, in order to propose a methodology in terms with the moored-passing ship interaction, further studies were performed for the moored-passing ship case with a Reynolds Averaged Navier-Stokes (RANS) calculation which is using OpenFOAM with Arbitrary Coupled Mesh Interface (ACMI) technique and compared with the experiment result. Finally, the present study proposes a guide to apply the two dimensional perturbation method to the moored-passing ship interaction. In addition, it presents a possibility that the RANS calculation with ACMI can applied to the ship-ship interaction without using a overset moving grid technique.

Analysis of Resistance Performance of a Ship having a Large Attitude based on CFD (CFD에 의한 자세변화가 큰 선박의 저항성능 해석)

  • Kim, Hyun-Soo;Park, Dong-Woo;Yang, Young-Jun
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.25 no.7
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    • pp.961-967
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    • 2019
  • This research presents an efficient method based on computational fluid dynamics (CFD) for estimating the resistance performance of a ship with a large settlement amount and a dynamic trim. The settlement of the inviscid flow analysis and the results of dynamic trim were used to set a large attitude for the ship prior to performing a viscous flow analysis; a viscous flow analysis was subsequently performed by Dynamic Fluid Body Interaction (DFBI). This method is termed as method I, in which a simple grating system can be used without employing the overset mesh technique by setting many attitudes before interpretation. Thus, method I is advantageous in reducing calculation time and improving calculation accuracy. The viscous flow analysis was performed using a commercial CFD code STAR-CCM+. Compared with the final convergence result, the first viscous flow analysis result of method I exhibited a variation of less than 1 % of resistance. The result was obtained by changing the gratings each time an attitude is changed at each calculation stage, based on the DFBI method provided to STAR-CCM+ using a simple grating system, which is not a superposed grating. This method is termed as method II. Compared with method II of resistance, method I exhibited a dif erence of 0.03-0.6 % for linear velocity. The results of method I were confirmed to be qualitatively and quantitatively appropriate through comparison with several trillion simulations.

VIV simulation of riser-conductor systems including nonlinear soil-structure interactions

  • Ye, Maokun;Chen, Hamn-Ching
    • Ocean Systems Engineering
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    • v.9 no.3
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    • pp.241-259
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    • 2019
  • This paper presents a fully three-dimensional numerical approach for analyzing deepwater drilling riser-conductor system vortex-induced vibrations (VIV) including nonlinear soil-structure interactions (SSI). The drilling riser-conductor system is modeled as a tensioned beam with linearly distributed tension and is solved by a fully implicit discretization scheme. The fluid field around the riser-conductor system is obtained by Finite-Analytic Navier-Stokes (FANS) code, which numerically solves the unsteady Navier-Stokes equations. The SSI is considered by modeling the lateral soil resistance force according to nonlinear p-y curves. Overset grid method is adopted to mesh the fluid domain. A partitioned fluid-structure interaction (FSI) method is achieved by communication between the fluid solver and riser motion solver. A riser-conductor system VIV simulation without SSI is firstly presented and served as a benchmark case for the subsequent simulations. Two SSI models based on a nonlinear p-y curve are then applied to the VIV simulations. Also, the effects of two key soil properties on the VIV simulations of riser-conductor systems are studied.

CFD prediction of vortex induced vibrations and fatigue assessment for deepwater marine risers

  • Kamble, Chetna;Chen, Hamn-Ching
    • Ocean Systems Engineering
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    • v.6 no.4
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    • pp.325-344
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    • 2016
  • Using 3D computational fluid dynamics techniques in recent years have shed significant light on the Vortex Induced Vibrations (VIV) encountered by deep-water marine risers. The fatigue damage accumulated due to these vibrations has posed a great concern to the offshore industry. This paper aims to present an algorithm to predict the crossflow and inline fatigue damage for very long (L/D > $10^3$) marine risers using a Finite-Analytical Navier-Stokes (FANS) technique coupled with a tensioned beam motion solver and rainflow counting fatigue module. Large Eddy Simulation (LES) method has been used to simulate the turbulence in the flow. An overset grid system is employed to mesh the riser geometry and the wake field around the riser. Risers from NDP (2003) and Miami (2006) experiments are used for simulation with uniform, linearly sheared and non-uniform (non-linearly sheared) current profiles. The simulation results including inline and crossflow motion, modal decomposition, spectral densities and fatigue damage rate are compared to the experimental data and useful conclusions are drawn.

Numerical Analysis of Flowfield around Multicopter for the Analysis of Air Data Sensor Installation (대기자료센서 장착위치 분석을 위한 멀티콥터 주변 유동장 수치해석)

  • Park, Young Min;Lee, Chang Ho;Lee, Yung Gyo
    • Journal of Aerospace System Engineering
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    • v.11 no.5
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    • pp.20-27
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    • 2017
  • The present paper describes the flow analysis of the flows around the multicopter for the selection of optimal position of air data sensor. For the flow analysis, the commercial fluid dynamics solver, STAR-CCM+ was used with polygon mesh and k-w SST turbulence modeling options. For the simulation of each rotating 4 propellers, unstructured overset mesh method was used. Hovering, forward flight, ascending and descending flight conditions are selected for the analysis and airspeed and flow angle errors were investigated using the CFD results. Through the flow field analysis, sensor location above one propeller diameter distance from the propeller rotating plane showed airspeed error less than 1m/s within the typical flight conditions of multicopter except descending.

Study on Roll Motion Characteristics of a Rectangular Floating Structure in Regular Waves (규칙파 중 사각형 부유식 구조물의 횡동요 운동특성에 대한 연구)

  • Kim, Min-Gyu;Jung, Kwang-Hyo;Park, Sung-Boo;Lee, Gang-Nam;Park, Il-Ryong;Suh, Sung-Bu
    • Journal of Ocean Engineering and Technology
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    • v.33 no.2
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    • pp.131-138
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    • 2019
  • This study focused on the roll motion characteristics of a two-dimensional (2D) rectangular floating structure under regular beam sea conditions. An experiment was conducted in a 2D wave tank for a roll free decay test in calm water and the roll motion in a range of regular waves with and without heave motion to investigate the motion response and heave influence on the roll motion. A numerical study was carried out using Reynolds-averaged Navier Stokes (RANS)-based CFD simulations. A grid convergence test was conducted to accurately capture the wave condition on the free surface based on the overset mesh and wave forcing method. It was found in the roll free decay test that the numerical results agreed well with the experimental results for the natural roll period and roll damping coefficient. It was also observed that the heave motion had an impact on the roll motion, and the responses of the heave and roll motion from the CFD simulations were in reasonable agreement with those from the experiment.