• Journal of Korea Water Resources Association
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• v.56 no.10
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• pp.603-617
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• 2023

This study aims to provide a better understanding of the turbulent flow characteristics in swash zone. A double dam-break method is employed to generate the swash zone flow. Comparing with the conventional single dam-break method, a delay between two gate opening can be controlled to reproduce various interactions between uprush and backwash. For numerical simulations, overInterDyMFoam based on OpenFOAM is adopted. Using overInterDyMFoam, interface between two immiscible fluids having different densities (i.e., air and water phases) can be tracked in a moving mesh with multiple layers. Two-dimensional Reynolds-Averaged Navier-Stokes equations are solved with a standard 𝜅-𝜖 turbulence model for momentum and continuity. Numerical model results are validated with laboratory experiment data for the time series of water depth and streamwise velocity. Turbulent kinetic energy distribution is further investigated to identify the turbulence evolution for each flow regime (i.e., uprush, backwash, and swash-swash interaction).

• Journal of Korea Multimedia Society
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• v.9 no.11
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• pp.1483-1495
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• 2006

The navigation mesh represents a terrain as a set of triangles on which characters may move around. The navigation mesh cab be generated automatically, and it is more flexible in representing 3D surface. The number of triangles to represent a terrain may vary according to the structure of the terrain. As characters are moving around on a navigation mesh, the path planning can be performed more easily by projecting the 3D surfaces into 2D space. However, when the terrain is represented with an elaborated mesh of large number of triangles to achieve more realistic movements, the path finding can be very inefficient because there are too many states(triangles) to be searched. In this paper, we propose an efficient method of path finding in 3D games where the terrain is represented by navigation meshes. Our method uses the visibility tests. When the graph-based search is applied to elaborated polygonal meshes for detailed terrain representation, the path finding can be very inefficient because there are too many states(polygons) to be searched. In our method, we reduce the search space by using visibility tests so that the search can be fast even on the detailed terrain with large number of polygons. First we find the visible vertices of the obstacles, and define the heuristic function as the distance to the goal through those vertices. By doing that, the number of states that the graph-based search visits can be substantially reduced compared to the plane search with straight-line distance heuristic.

• New & Renewable Energy
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• v.8 no.3
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• pp.6-13
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• 2012

This paper describes unsteady internal flow characteristics of a cathode air blower, used for the 1 kW fuel cell system. The cathode air blower considered in the present study is a diaphragm type blower. To analyze the flow field inside the diaphragm cavity, compressible unsteady numerical simulation is performed. Moving mesh system is applied to the numerical analysis for describing the volume change of the diaphragm cavity in time. Throughout a numerical simulation by modeling the inlet and outlet valves in a diaphragm cavity, unsteady nature of an internal flow is successfully analyzed. Variations of mass flow rate, force and pressure on the lower moving plate of a diaphragm cavity are evaluated in time. The computed mass flow rate at the same pressure and rotating frequency of a motor has a maximum of 5 percent error with the experimental data. It is found that flow pattern at the suction process is more complex compared to that at the discharge process. Unsteady nature of internal flow in the cathode air blower is analyzed in detail.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.689-697
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• 2023

The high-pressure hydrogen valve is intended to supply hydrogen charged at high pressure in the hydrogen tank to the fuel cell stack, which decompresses high-pressure hydrogen gas to low pressure and primarily limits the excessive flow. It consists of a pilot valve, a main valve, and a excessive flow valve to operate in a wide pressure range from 2 to 70 MPa of charging pressure. The opening characteristics of the valve were confirmed by computation fluid dynamics applying the moving grid technique. The behavior of the valve was predicted by predicting the force acting on the valve over time. In addition, the difference in behavior according to supply pressure was compared.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.17-26
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• 2014

This paper presents a dynamic crack propagation algorithm based on the Moving Least Squares(MLS) difference method. The derivative approximation for the MLS difference method is derived by Taylor expansion and moving least squares procedure. The method can analyze dynamic crack problems using only node model, which is completely free from the constraint of grid or mesh structure. The dynamic equilibrium equation is integrated by the Newmark method. When a crack propagates, the MLS difference method does not need the reconstruction of mode model at every time step, instead, partial revision of nodal arrangement near the new crack tip is carried out. A crack is modeled by the visibility criterion and dynamic energy release rate is evaluated to decide the onset of crack growth together with the corresponding growth angle. Mode I and mixed mode crack propagation problems are numerically simulated and the accuracy and stability of the proposed algorithm are successfully verified through the comparison with the analytical solutions and the Element-Free Galerkin method results.

• Wind and Structures
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• v.22 no.2
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• pp.211-234
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• 2016

Super long-span bridges provide people with great convenience, but they also bring traffic safety problems caused by strong wind owing to their high decks. In this paper, the large eddy simulation together with dynamic mesh technology in computational fluid dynamics (CFD) is used to explore the mechanism of a moving vehicle's transient aerodynamic force in crosswind, the regularity and mechanism of the vehicle's aerodynamic forces when it passes through a bridge tower's wake zone in crosswind. By comparing the calculated results and those from wind tunnel tests, the reliability of the methods used in the paper is verified on a moving vehicle's aerodynamic forces in a bridge tower's wake region. A vehicle's aerodynamic force coefficient decreases sharply when it enters into the wake region, and reaches its minimum on the leeward of the bridge tower where exists a backflow region. When a vehicle moves on the outermost lane on the windward direction and just passes through the backflow region, it will suffer from negative lateral aerodynamic force and yaw moment in the bridge tower's wake zone. And the vehicle's passing ruins the original vortex structure there, resulting in that the lateral wind on the right side of the bridge tower does not change its direction but directly impact on the vehicle's windward. So when the vehicle leaves from the backflow region, it will suffer stronger aerodynamic than that borne by the vehicle when it just enters into the region. Other cases of vehicle moving on different lane and different directions were also discussed thoroughly. The results show that the vehicle's pneumatic safety performance is evidently better than that of a vehicle on the outermost lane on the windward.

• Journal of computational fluids engineering
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• v.4 no.3
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• pp.52-62
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• 1999

The development of a parallelized aerodynamic simulation process involving moving bodies is presented. The implementation of this process is demonstrated using a fully systemized Chimera methodology for steady and unsteady problems. This methodology consists of a Chimera hole-cutting, a new cut-paste algorithm for optimal mesh interface generation and a two-step search method for donor cell identification. It is fully automated and requires minimal user input. All procedures of the Chimera technique are parallelized on the Cray T3E using the MPI library. Two and three-dimensional examples are chosen to demonstrate the effectiveness and parallel performance of this procedure.

• New & Renewable Energy
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• v.7 no.3
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• pp.29-35
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• 2011

This paper describes an internal flow characteristics of a fuel pressurized blower, used for 1kW domestic fuel cell system. To analyze the flow field inside the diaphragm cavity, compressible unsteady numerical simulation is introduced. SST model with scalable wall function is employed to estimate the eddy viscosity. Moving mesh system is applied to the numerical analysis for describing the volume change of a diaphragm cavity in time. Throughout numerical simulation with the modeling of the inlet and outlet valves in a diaphragm cavity, unsteady nature of an internal flow is successfully analyzed. Force variations on the lower plate of a diaphragm cavity are evaluated in time. It is found that the driving force at the suction stage of a diaphragm cavity is more necessary than that at the discharging stage.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1099-1100
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• 2011

This study deals with the dynamic characteristics analysis of Linear Induction Motor (LIM) using finite element method in which the moving mesh technique is considered. The focus of this paper is to show the appropriate of on-line observer system for position sensorless control of a LIM under the phase asymmetry, saturation and iron loss. Comparisons are given with angle of the observer and that of proposed FEA method of linear induction motor, respectively. The position sensorless control system is realized, and the effective of the observer system is verified by experimental results.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.47-54
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• 2011

A rotating propeller of turboprop aircraft gives much effect on the aerodynamic characteristics of wing such as lift, moment and stall. Specially propeller effect on the wing surface is much more dominant when aircrafts are in landing or take-off conditions. In the present paper, three dimensional Navier-Stokes simulations for the interaction of propeller and wing were carried out for medium sized turboprop aircraft. For rotating propeller, unsteady sliding mesh method was used to simulate a relative motion between moving and static bodies. For the power effect analysis in landing and take off configurations, double slotted flap was also considered and the aerodynamic characteristics were investigated. It was shown that the propeller slipstream enhanced the lift slope including maximum lift by eliminating local flow separation region and this enhancement was more dominant with high lift device.