• Journal of Advanced Marine Engineering and Technology
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• v.22 no.6
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• pp.935-941
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• 1998

Experiments were carried out for a cubic cavity flow. Contrinuous shear stress is supplied by driven flow for high Reynolds number and three kinds of aspect ratios. Velocity vectors are obtained by PIV and they are used as velocity components for Poisson equation for pressure, Related boundary conditions and no-slip condition at solid wall and the linear velocity extrapolation on the upper side of cavity are well examined for the present study. For calculation of pressure resolution of grid is basically $40{\times}40$ and 2-dimensional uniform mesh using MSC staggered grid is adopted. The flow field within the cavity maintains a forced-vortex formation and almost of the shear stress from the driving inflow is transformed into rotating flow energy and the size of the distorted forced-vortex increases with increment of Reynolds number

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.345-348
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• 2008

The subcavity passive control technique is used in present study. Cavity-induced pressure oscillation has been investigated numerically for a supersonic three-dimensional flow over rectangular cavities at Mach number 1.83 at the cavity entrance. The three-dimensional, compressible Navier-stokes equations are numerically solved based on a fully implicit finite volume scheme. The results showed that the resultant amount of attenuation of cavity-induced pressure oscillations was dependent on the length and thickness of the flat plate.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.1-9
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• 2019

In this study, both 2D and 3D failure shapes of rock mass above the water-filled cavity are put forward when the surrounding rock mass cannot bear the pressure caused by the water-filled cavity. Based on the analytical expressions derived by kinematic approach, the profiles of active and passive failure patterns are plotted. The sensitivity analysis is conducted to explore the influences of different rock parameters on the failure profiles. During the excavation of the deep tunnels above the karst cavity, the water table always changes because of progressive failure of cavity roof. Therefore, it is meaningful to discuss the effects of varying water level on the failure patterns of horizontal rock layers. The changing laws of the scope of the failure pattern obtained in this work show good consistency with the fact, which could be used to provide a guide in engineering.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.843-846
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• 2004

Cavity tone is generated due to the feedback between flow and acoustic wave. It is recognized that the period is determined by the time required for the flow convection in one direction, the time required for the acoustic propagation in the other direction and the time for phase shift depending on the flows and mode. Most of the phenomena have been investigated by experiments and a simple but fundamental theory. But the cause of the phase shift and the correctness of the theory have not been clearly explained so far. In this paper, the phenomena are calculated numerically to obtain detail information of flow and acoustic wave to explain the mechanism including the phase. High order high resolution scheme of optimized high order compact is used to resolve the small acoustic quantities and large flow quantities at the same time. The data are reduced using cross correlation function in space and time and cross spectral density function which has phase information. Abrupt change in pressure near corner in cavity is observed and is relate to phase variation. The time required for the feedback between the flow and acoustic wave is calculated after the numerical simulation f3r various modes. The periods based on the time calculated using the above method and direct observation from the acoustic waves generated and propagated in the numerical simulation are compared. It is found that no phase shift is required if we examine the time required carefully. Rossiter's formula for the cavity tone used for quick estimation needs to be modified far some modes.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.377-386
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• 2011

During stamping processes, the air trapped between sheet metal and the die cavity can be highly compressed and ultimately reduce the shape accuracy of formed panels. To prevent this problem, vent holes and passages are sometimes drilled into the based on expert experience and know-how. CAE can be also used for analyzing the air behavior in die cavity during stamping process, incorporating both elasto-plastic behavior of sheet metal and the fluid dynamic behavior of air. This study presents sheet metal forming simulation combined simultaneously with simulation of air behavior in the die cavity. There are three approaches in modeling of air behavior. One is a simple assumption of the bulk modulus having a constant pressure depending on volume change. The next is the use of the ideal gas law having uniform pressure and temperature in air domain. The third is FPM (Finite point method) having non-uniform pressure in air domain. This approach enables direct coupling of mechanical behavior of solid sheet metal and the fluid behavior of air in sheet metal forming simulation, and its result provides the first-hand idea for the location, size and number of the vent holes. In this study, commercial software, PAM-$STAMP^{TM}$ and PAM-$SAFE^{TM}$, were used.

• Nuclear Engineering and Technology
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• v.48 no.1
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• pp.72-86
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• 2016

A steam explosion may occur during a severe accident, when the molten core comes into contact with water. The pressurized water reactor and boiling water reactor ex-vessel steam explosion study, which was carried out with the multicomponent three-dimensional Eulerian fuel-coolant interaction code under the conditions of the Organisation for Economic Co-operation and Development (OECD) Steam Explosion Resolution for Nuclear Applications project reactor exercise, is presented and discussed. In reactor calculations, the largest uncertainties in the prediction of the steam explosion strength are expected to be caused by the large uncertainties related to the jet breakup. To obtain some insight into these uncertainties, premixing simulations were performed with both available jet breakup models, i.e., the global and the local models. The simulations revealed that weaker explosions are predicted by the local model, compared to the global model, due to the predicted smaller melt droplet size, resulting in increased melt solidification and increased void buildup, both reducing the explosion strength. Despite the lower active melt mass predicted for the pressurized water reactor case, pressure loads at the cavity walls are typically higher than that for the boiling water reactor case. This is because of the significantly larger boiling water reactor cavity, where the explosion pressure wave originating from the premixture in the center of the cavity has already been significantly weakened on reaching the distant cavity wall.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.5
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• pp.77-83
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• 2016

A considerable amount of researches has been performed to investigate the flow characteristics produced in the cavity system over straight wall. However, many practical applications of the cavity flows are found on curved walls, which are strongly subject to the centrifugal force effects. No work has been made on the cavity flows on the curved wall to date. In the present study, a computational fluid dynamics method has been applied to investigate the cavity flows over curved walls at Mach numbers in range of 0.4 to 0.8. The aspect ratio of the cavity was fixed at L/H=3, but the radius of curvature of the curved wall is changed in considering the real engineering practice. The results reveal that the pressure oscillations in the curved walls are stronger than those in the straight wall. It is found that the ratio of curvature of the curved wall significantly affects the unsteady flow characteristics inside the cavity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.54-57
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• 2004

Almost all injection molds have multi-cavity runner for mass production, which are designed with geometrically balanced runner system in order to minimize filling imbalance between cavity to cavity during processing. However, even though geometrically balanced runner is used, filling imbalances have sometimes been observed. These filling imbalances have historically been considered as result of uneven mold temperature and mold deflection, but it actually results from non-symmetrically shear, pressure, temperature distribution within melt material as it flows through the runner system. Filling imbalance could be decreased by modifying processing conditions that are related to shear, pressure, temperature such as injection rate, mold temperature, injection pressure, melt temperature. In this study, a series of experiment was conducted using Taguchi method to determine which processing condition influence as the primary cause of filling imbalance in geometrically balanced runner system. As a result of experiments, this paper could present an optimal processing condition to minimize variable that brings about filling imbalance geometrically balanced runner system

• Journal of Hydrospace Technology
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• v.2 no.2
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• pp.44-56
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• 1996

The effects of the air on the reductions in resistance when supplied under the bottom of a semi-planing ship with a step are investigated in the present study. A 1.275m long FRP model is constructed and the pressure and viscous tangential stresses over the planing surface of the hull with and without air supply are measured through measuring holes carefully selected at the towing tank of Seoul National University. Locations of holes most suitable for air injection are surveyed in front of the planing surface of the model with careful examinations of the limiting streamlines and pressure distributions measured without air supply. At those locations, found to be just front of the step, air has been supplied into a wake region to form an air filled cavity of fixed type. Flow rates and pressure of the supplied air as well as the local pressure and shear stress distributions on the hull surface are measured to understand the physics involved as well as to determine the conditions most effective in resistance reduction at the design speed. It has been found that total resistance of the stepped semi-planing hull can be considerably reduced if an air cavity generated by an adequate air injection at the bottom of the hull near the step. After the cavity optimized at the given speed, air bubbles also have been generated right behind the point where dividing streamlines re-attach to further reduce the frictional resistance but found to be not so effective as the air cavity in resistance reductions.