• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.136-145
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• 1996

The theory is based on two thermodynamic equations for the air mass in the air column and bydrodynamic equation for the relation between the response of the air in the water column and the incident wave. The numerical model is experimented in a two dimensional water tank and the caisson model with sloped front wall is tested in the large towing tank.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.10 s.241
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• pp.1101-1110
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• 2005

In this paper we present the numerical results of the behavior of the horizontal vortex generated by ejecting a liquid vertically upward from an orifice into the bulk fluid above the orifice. The numerical calculation has been performed for the axi-symmetric Navier-Stokes equation. A simple flow-visualization experiment was also conducted to qualitatively verify the numerical solutions. Three cases of the flow configurations studied in this paper are; firstly, the vortex was generated without any background rotation, secondly, the vortex was made under a full background rotation, and thirdly, the vortex was made during the spin-up process such that only the region adjacent to the side wall was set into motion viewed in the inertial frame of reference. It was shown that the swirl flow at the inlet boundary affects considerably the formation and development of the vortex for the second case. In the third case, it was remarkable to see that the vortex cannot penetrate into the region near to the side wall of the tank, because of the strong swirl flow and corresponding high pressure gradient in the region.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.989-997
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• 2017

We study opening transient responses of a self-sustainable poppet valve, which is usually used for the main oxidizer shut-off valve of liquid rocket engines. In order to perform numerical analysis, a pneumatic supply system was simulated as an orifice with a diameter of 3.2 mm and the equations of motion of valve moving part were derived. For the validation of the study, a comparison of numerical predictions and experimental results has been done. As one of the practical applications of this study, the employment of an orifice in a high pneumatic pressure has been presented to control the valve opening time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.881-887
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• 2006

The objective of this study are to analyze the flow characteristics of R22 flowing through EEVs and to develop an empirical correlation to predict the refrigerant flow rate. The mass flow rates of EEVs with different geometries were measured at various condensing temperatures, subcoolings, and EEV openings. Based on the experimental data, an empirical correlation for mass flow predictions in EEVs was developed by modifying the orifice equation. The correlation showed good agreement with the measured data for R22 with average and standard deviations of 1.4% and 6.1%, respectively. Approximately 90% of the measured data were within ${\pm}10%$ of the predictions.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.232-238
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• 1997

In this paper, a theoretical method is presented to design a hydraulic control valve system that consist of an important component in the hydraulic snubber. The hydraulic snubber is used essentially to support the piping systems at power plants. To calculate the force due to pressure drop and flow rate in the valve orifice and by-pass hole, Bernoulli equation is used. The Reynolds equation are numerically analyzed in the clearance gap between the valve cone and valve seat to estimate the friction force and leakage flow rate. Based on the detailed theoretical data, we developed successfully the hydraulic snubber for power plants.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.82-91
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• 2003

Experiments to investigate the mixing performance of unlike doublet impinging jets are conducted. Reynolds number of simulants used in this study rages from 1.0 to 1.5 Cold flow test is performed to investigate the hydrodynamic effect and spray of the impinging jets are collected locally and calculated by using Rupe's mixing efficiency equation. Momentum exchanges and relative velocity ratio between two jets are taken as the main parameter to represent the effect of enlargement of the orifice diameter. As diameter ratio increases, the corresponding momentum ratio where maximum mixing efficiency occurs and relative velocity at the maximum mixing efficiency ranges 0.6 to 0.7, respectively. Penetration depth can be taken as a prominent parameter to estimate the mixing efficiency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.939-950
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• 2017

In this work, mathematical models are newly presented for three types of double-acting oleo-pneumatic shock absorbers as the first part of a comparative study on the several types of double-acting oleo-pneumatic shock absorbers. After a typical single-acting shock absorber model is presented for the sake of completeness, mathematical models of three types of double-acting shock absorbers are proposed. To derive the models, Bernoulli equation and orifice discharge coefficient are utilized along with the assumptions of incompressibility and poly-tropic process. The proposed models are expected to be used for investigation of the salient features of several types of double-acting oleo-pneumatic shock absorbers.

• Transactions of Materials Processing
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• v.5 no.3
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• pp.239-255
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• 1996

A new forming technology has been developed to fabricate near-net shape products using light metal. A semi-solid forming technology has some advantages compared with the conventional forming processes such as die casting squeeze casting and hot/cold forging. In this study the numerical analysis of semi-solid filling for a straight die shape and orifice die shape in gate pattern is studied on semi-solid materials(SSM) of solid fraction fs =30% in A356 aluminum alloy. The finite difference program of Navier-Stokes equation coupled with heat transfer and solidification has been developed to predict a filling pattern and the temperature distribution of SSM. The programdeveloped in this study gives die filling patterns of SSM and final solidifica-tion region.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.5
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• pp.127-134
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• 2000

This paper presents the development of a semi-active seat damper using MR fluids and the performance analysis of seat suspension system with a MR seat damper. An annular orifice type MR seat damper is proposed for a seat suspension of a commercial vehicle. After formulating the governing equation of motion, then an appropriate size of the seat damper is designed and manufactured. Following the evaluation of field-dependant damping force characteristics, the controllability of the damping force is experimentally demonstrated in time domain by adopting PID controller. A semi-active seat suspension with the proposed MR damper is constructed and its dynamic model is established. Subsequently, vibration control capability of the semi-active suspension system is investigated by employing the sky-hook controller.

• Transactions of The Korea Fluid Power Systems Society
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• v.5 no.1
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• pp.20-26
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• 2008

Various types of hydraulic shock absorbers are widely used in many fields because of its numerous advantages. However, in order to design adequate damping characteristics, accurate flow data near the orifices are required essentially. In this paper, a commercial computational fluid dynamics(CFD) code, FLUENT is adopted to investigate the flow characteristics near orifices of a shock absorber. Static pressure and velocity vector distributions, fluid path lines are presented for compression/tension strokes and various piston speeds. In order to validate the result of analysis, the numerically obtained damping forces are compared with those of analytical estimations obtained by modified Bernoulli equation. The results reported herein will provide better understanding of the detailed flow fields within shock absorber, and the CFD analysis method proposed in this paper can be used in the design of other types of hydraulic shock absorber.