• Journal of the Korean Solar Energy Society
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• v.23 no.3
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• pp.55-61
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• 2003

This paper represents the effect of rotor geometry on the performance of a small-scale Wells turbine for wave energy conversion. In this study, four kinds of blade profile were selected from previous studies with regard to the blade profile of the Wells turbine. The experimental investigations have been performed for two solidities by model testing under steady flow conditions, and then the effect of blade profile on the running and starting characteristics under sinusoidal flow conditions have been investigated by a numerical simulation using a quasi-steady analysis. In addition, the effect of sweep on the turbine characteristics has been investigated for the cases of CA9 and HSIM 15-262123-1576. As a result, a suitable choice of these design factors has been suggested.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.99-105
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• 2003

This paper presents the effect of rotor geometry on the performance of a small-scale Wells turbine for wave energy conversion. In this study, four kinds the Wells turbine of blade profile were selected from previous studies. The types of blade profile included in the papers are as follows: NACA0020 ; NACA0015; CA9; and HSIM 15-262123-1576. The experimental investigations have been performed for two solidities by testing model under steady flow conditions. The effect of blade profile on the running and starting characteristics under sinusoidal flow conditions have also been investigated by a numerical simulation based on a quasi-steady analysis. In addition, the effect of sweep on the turbine characteristics has been studied for the cases of CA9 and HSIM 15-262123-1576. Based on the evaluation, a suitable choice of these design factors has been suggested. As a result, it seems that a suitable choice of the sweep ratio of 0.35 for the blade profile of the Wells turbine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.5763-5768
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• 2015

A relief valve is a mechanical element to keep safety by controlling high pressure. Usually, the high pressure is relieved by using the spring force and letting the fluid to flow from another way out of system. When its normal pressure is reached, the relief valve can return to initial state. The relief valve should be designed for smooth operation and should satisfy the structural safety requirement under operating condition. The commercial software ANSYS/WORKBENCH is utilized for flow and structural analysis. Very high pressure may cause structural problem due to severe stress. The study suggests the design satisfying the structural design requirement

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.19-21
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• 2002

Recently, it has become more competitive to take larger market share among domestic companies manufacturing high-power apparatus. Unfortunately, the size of total market in this field is being smaller than before because the business of transmission and distribution of electric power is being shifted from government control to private management. To save this situation, we are trying to develop new high-voltage Gas Insulated Switchgear for export such as 245kV GIS and 300kV GIS. It is very important to make GIS compact size to have international competitiveness against European companies. By reducing GIS's dimensions same as 170kV class, we expect to launch abroad successfully. Many factors should be considered to achieve good performance during short-circuit making-breaking. Analysis on cold gas flow is one method widely used to evaluate small-current interruption. Through this analysis, we can examine the dielectric characteristics at the weak points in the circuit-breaker. In this paper, we describe the results of cold-gas flow analyses on 245kV and 300kV circuit-breakers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.89-93
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• 2008

The effect of pintle shapes and position to the thrust performance of Solid Rocket Motor was studied by experimental-aided Computational Fluid Dynamic(CFD). Among the turbulent models for RANS in Fluent, Spalart-Allmaras model was better agreement with the nozzle wall pressure distribution attained by cold-flow test than other models. When nozzle throat area was decreased, magnitude of thrust was increased. The bigger pintle size was, the more thrust of pintle tip pressure was obtained. Meanwhile the more thrust of nozzle and chamber pressure decreased. Hence, total thrust of big pintle was less than a small pintle under same throat area condition.

• Wind and Structures
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• v.32 no.5
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• pp.509-520
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• 2021

The streamlined box is a common type of girders for long-span suspension bridges. Spanning deep canyons, long-span bridges are frequently attacked by strong winds with large angles of attack. In this situation, the flow field around the streamlined box changes significantly, leading to reduction of the flutter performance. The wind fairings have different effects on the flutter performance. Therefore, this study examines the flutter performance of box girders with different wind fairings at large angles of attack. Computational fluid dynamics (CFD) simulations were carried out to extract the flutter derivatives, and the critical flutter state of a long-span bridge was determined. Further comparisons of the wind fairings were investigated by a rapid method which is related to the input energy by the aerodynamic force. The results show that a reasonable type of wind fairings could improve the flutter performance of long-span bridges at large angles of attack. For the torsional flutter instability, the wind fairings weaken the adverse effect of the vortex attaching to the girder, and a sharper one could achieve a better result. According to the input energies on the girder with different wind fairings, the symmetrical wind fairings are more beneficial to the flutter performance

• Journal of Hydrogen and New Energy
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• v.32 no.4
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• pp.277-284
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• 2021

This paper deals with multi-objective optimization using response surface method to improve the hydraulic performances of a 2 vane pump for wastewater treatment. For analyzing the internal flow field in the pump, steady Reynolds-averaged Navier-Stokes equations were solved with the shear stress transport turbulence model as a turbulence closure model. The impeller and volute variables were defined in the shape of the 2 vane pump. The objective functions were set to satisfy the total head at the design flow rate as well as to improve the efficiency. The hydraulic performance of the optimally designed shape was verified by numerical analysis results.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.11-19
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• 2024

We performed numerical simulations on a C-type liquid hydrogen (LH2) storage tank for commercial vehicles to reduce evaporation rates by manipulating vortical structures. Owing to external heat, natural convection occurs inside the tank, leading to the enhanced evaporation of LH2. We observed that the regions of high magnitude vorticity correlate with those of high evaporation rates. Specifically, vortical structures in the side section area show higher vorticity magnitude and evaporation rates compared to those in the midsection area. To suppress these vortical motions, we installed an array of ribs at intervals corresponding to the mean diameter of the vortical structures. As a result, the area occupied by vortical structures in the side section area decreased, leading to a reduction in evaporation speed by approximately 2.3 times. This study elucidates the internal evaporation mechanism in storage tanks from the perspective of flow structures and potentially contributes to minimizing the boil-off rate in cryogenic storage tanks.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.95-101
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• 2014

In this study, an ISM (immersed solid method) was used for investigating the mass flow rate and efficiency of an involute-gear pump featuring very high rotational speed. For considering circulation flow at the gear pump and housing, fluid flow was assumed as turbulent, and the rotational speed of the gear pump increased under the condition of constant pressure at both the inlet and outlet. The efficiency and mass flow rate of the gear pump were studied by varying its rotational speed and the clearance between the gear tip and the housing. In the simulation results, as the rotational speed were increased, the average mass flow rate and efficiency increased. Furthermore, as the clearance between the gear tip and the housing was increased, the average mass flow rate and efficiency decreased. The efficiency was 85.11, 90.94, and 93.62 at rotational speeds of 6,000 rpm, 8,000 rpm, and 10,000 rpm, respectively, under the condition that there was no clearance. In addition, the efficiency was 93.62, 93.29, and 92.74 at clearances of 0 m, 0.00001 m, and 0.00003 m respectively.

• Clean Technology
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• v.13 no.3
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• pp.195-200
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• 2007

This study investigated the flow rate changes of the heterogeneous rectangular microchannels which have different hydrophilic property on the bottom surface. The heterogeneous rectangular microchannel has three native PDMS (poly-dimethyl siloxane) surfaces which were patterned by the soft lithography. PDMS bottom surface was treated by the argon plasma and coated by the allyl alcohol (99%). The channel length was 10, 20 and 30 mm and the channel width was 100, 200 and $300\;{\mu}m$, respectively. Several external voltages were applied to make the fluid flow by the electroosmosis in the microchannel. For the same electric field strength and hydrophilicity of the bottom surface, the flow rate is almost same. This result is matched to the theoretical expectation and confirms that the experimental system is reliable. With increasing the channel width, the flow rate increased for the same hydrophilicity of the bottom surface. The flow rate of the microchannel of higher hydrophilicity was larger than that of the microchannel of lower hydrophilicity. This result implies that the hydrophilicity change of the bottom surface could be applied to control the flow rate in the microchannel.