• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.51-59
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• 2001

An evaluation of one zero-equation and two one-equation eddy viscosity-transport turbulence closure models as implemented CFDS(Characteristic Flux Difference Splitting ) code is presented herein. Comparisons of Baldwin-Lomax model as zero-equation and Baldwin-Barth and Spalart-Allmaras model as one-equation are presented for three test cases, first inlvolving the 3 dimensional supersonic flow at M=1.98 over tangent ogive cylinder, second involving the 2 dimensional transonic flow at M=0.79 over RAE 2822 airfoil, third involving the 3 dimensional transonic flow at M=0.84 over ONERA M6 wing. The numerical results of CFDS code will also examined through direct comparison with experimental data.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.192-200
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• 1999

This paper describes experimental investigations of helium-air exchange flow through parti-tioned opening. Such exchange flow may occur following rupture accident of stand pipe in high temperature gas cooled reactor. A test vessel with a opening on top of test cylinder is used for experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Flow measurements are made with partitioned opening for parti-tion rations $H_p/H_1$ in the range 0 to 1 where $H_p$ and $H_1$ are partition length and height of the open-ing respecticely. In the case of $H_p/H_1$ of 0 flow passages of upward flow of the helium and down-ward flow of the air within the opening are unseparated (bidirectional) and the two flows interact exchange flow rate is minimum through range of the partition ratios, Two flow zones i.e. separat-ed(unidirectional)flow zone and unseparated(bidirectional) flow zone exist with increasing the partition. length, The exchange flow rate increases with increasing the separated flow zone. It is found that a maximum exchange flow rate exists at $H_p/H_1$ of 1. As a result fo comparison of the exchange flow rates by changing the partition ration the fluids interaction in the unseparated zone is found to be an important factor on the helium-air exchange flow rate.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.76-83
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• 2010

The Characteristics of the flow field through cylinders with in-line and staggered arrangements were calculated by vortex method. Vortex distributions and velocity profiles around the cylinders with in-line and staggered arrangements were simulated at the pitch ratio of Pt/D=1.25~2.0 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^4$. As the results the vortices of clockwise at the upper separation point cylinder and the vortices of anticlockwise at the lower separation point of each cylinder were generated at both in-line and staggered arrangements. The generation of the reverse flow in the rear region of the cylinders was caused by the pitch ratio and Reynolds number, the boundary region was at the pitch ratio of Pt/D=1.5 and Reynolds number of Re=$4.0{\times}10^2{\sim}4.0{\times}10^3$ in case of in-line arrangement and was at the pitch ratio of Pt/D=1.4 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^2$ in case of staggered arrangement.

• Journal of Biosystems Engineering
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• v.27 no.2
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• pp.79-88
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• 2002

This study was conducted to develop system for high speed rice transplanting machines. The control system includes a sensor detecting the tilt angle of the seedling bed, a micro-controller and a hydraulic system consisting of a double acting cylinder, a four-way three-position solenoid valve, a relief valve and a hydraulic pump. The levelling system shared the pump with the existing steering control, resulting in a tandem center circuit for the steering and levelling control systems. Using the input signal from the sensor, the micro-controller determined and generated the output signal to control the cylinder through the solenoid valve to keep the seedling bed always parallel to the water surface regardless of soil unevenness during the transplanting operations. Both an ON/OFF and a PWM control schemes were tested. When the flow rate was more than 1 ι/min in the ON/OFF control, the system showed unstable rolling. However, in the PWM control, the system worked stably although the flow rate was more than 1 ι/min. The PWM control showed a better performance when a large difference between the angle and the dead band of the control system occurred. The characteristics of tile system response to given tilt angles were predicted by a computer simulation. Both the ON/OFF and the PWM control systems worked well providing that the operating and waiting times were properly adjusted.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1928-1939
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• 1992

In this study, a computer program has been developed which predicts the variation of the volumetric efficiency with the change of design of the intake system effectively by the analysis of the flow in each part of a multi-cylinder compression ignition engine. For the calculation of the flow in the intake and exhaust systems, the method of characteristics has been used, and the double Wiebe's function has been adopted for the calculation of the heat release rate in the cylinders. The accuracy of presented method has been proved through the comparison between the simulation and experimental results over the various engine speeds and intake pipe lengths.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.67-75
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• 2002

A study to investigate the influence of combustion chamber shape, especially piston top face configuration, on the combustion stability is presented with CFD analysis and single cylinder GDI engine test. Initial configuration of the piston bowl was designed with CFD analysis and further parametric studies of the design factors on the piston top face were carried out through the single cylinder GDI engine test. It was found that both the geometry of piston top face and the compression ratio have great influences on the combustion stability. Of interest is that the design factors of the GDI piston to prevent mixture diffusion out of the piston bowl have important roles for the stable combustion at the stratified mixture condition. Also the relationship between spray impingement and flow pattern in a GDI piston bowl should be considered to design an optimal bowl configuration for stable stratified combustion.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.110-120
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• 1996

The purpose of this study is to build up the control scheme that promptly controls the pressure in a hydraulic cylinder having small control volume, using a PCV(proportional control valve) and a digital computer. Object pressure control system has the character to be unstable easily, because the displacement-flow gain of the PCV is so large considering comparatively small volume of the hydraulic cylinder and the time delay of response of PCV is long. Considering the above-mentioned characteristics of the object pressure control system, in this study, a control system is designed with two degree of freedom scheme that is composed by adding a feed-forward control path to I-PD control system, and the reference model is used to decide control parameters. And through some experiments on FF-I-PD, the validity of this control method is confirmed.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.975-985
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• 2002

This paper deals with theoretical model developed for analyzing the heat transfer of automotive cooling systems. The model has a modular structure which links various cooling system submodels. From the model, heat transfer rate of automotive cooling systems can be predicted, providing useful information at the early stages of the design and development. The aim of the study is to develop a simulation program for automotive cooling system analysis and a performance analysis program for analyzing heat exchanger. Heat release rate from combustion gas to coolant through the cylinder wall in engine cylinder was analysed by using an engine cycle simulation program. In this paper, details of each submodel are described together with the overall structure of the vehicle model.

• Journal of the Korean Society of Industry Convergence
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• v.19 no.3
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• pp.144-153
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• 2016

In this research performed on a pneumatic actuator, the air flow entering and exiting the cylinder, and the motion and deformation characteristics of the piston during operation of the actuator, were predicted. This was carried out by utilizing an FSI(Fluid-Structural Interaction) analysis technique that incorporates principles in computational fluid dynamics and structural stress analysis, and potential performance degradation factors were examined. Analysis results indicated that performance improvements could be made through design modifications. These include adding an inlet and outlet on the upper and lower sections of the cylinder in the conventional model, and increasing the number of sites for piston guide bars from three to four.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.27-30
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• 2007

In recent years, scientific community has found renewed interest in hypersonic flight research. These hypersonic vehicles undergo severe aero-thermal environments during their flight regimes. One of the most important topics of research in hypersonic aerodynamics is to find a reasonable way of calculating either the surface temperature or the heat flux to surface when its temperature is held fixed. This requires modeling of physical and chemical processes. Hyperbolic system of equations with stiff relaxation method are being identified in recent literature as a novel method of predicting long time behavior of systems such as gas at high temperatures. In present work, Energy Relaxation Method (ERM) has been considered to simulate the real gas flow over a 2-D cylinder. Present heat flux results over the cylinder compared well with the experiment. Thus, real gas effects in hypersonic flows can be modeled through energy relaxation method.