• Korean Journal of Fisheries and Aquatic Sciences
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• v.12 no.1
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• pp.1-6
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• 1979

본연구에서는 그물어구의 상사를 지배하는 무차원수 K를 $$K=\frac{{\nu}^n\rho_wv^{2-n}}{{d^{1+n}(\rho-\rho_w)}$$ d, p: 재료의 직경 및 밀도 $\nu,\rho_w,v$: 물의 동점성계수, 밀도 및 속도으로 정하고, 여기에서의 직경의 비를 결정하는 방법에 따라 실물과 모형과의 상사를 완전하게 그리고 근사적으로 만족시키는 조건들을 구하였다. 즉, 원전한 상사한 경우는 직경의 비를 축척비와 같게 하고, 나아가서 다른 모든 치수의 비도 축척비와 같게 함으로써 만족된다고 하였으며, 측사적 상사의 경우느 직경의 비가 축척비 $(\frac{\lambda_2}{\lambda_1})$와 같지 않아도 된다고 하여, 그물실의 직경 d, 코의 크기 $\iota$ 및 콧수 N의 비를 $$\frac{d_2}{d_1}=\frac{\iota_2}{\iota_1}=\frac{\lambda_2}{\lambda_1}{\cdot}\frac{N_1}{N_2}$$ 으로, 줄의 직경 d', 길이 $\iota'$ 및 밀도 $\rho'$의 비를 $$\frac{d_2'}{d_1'}=\sqrt{{\frac{\lambda_2}{\lambda_1}}\cdot{\frac{d_2}{d_1}}\cdot{\frac{\rho_2-\rho_{w2}}{\rho_1-\rho_{w1}}\cdot{\frac{\rho_1'-\rho_{w1}}{\rho_2'-\rho_{w2}}}}$$, $\frac{\iota_2'}{\iota_1'}=\frac{\lambda_2}{\lambda_1}$로, 부속구의 치경 $d'$, 밀도 $\rho'$ 및 수 $N'$의 비를 $$\frac{N_2'}{N_1'}=(\frac{\lambda_2}{\lambda_1})^2(\frac{d_2}{d_1})(\frac{d_1'}{d_2'})\frac{(\rho_2-\rho_{w2})}{(\rho_1-\rho_{w1})}\frac{(\rho_1'-\rho_{w1})}{(\rho_2'-\rho_{w2})}$$으로 정하였다. 이렇게 정해진 모형어구에 대해 유속 v의 비느 $K_1=K_2$로부터 $$(\frac{u_2}{u_1})^{2-n}=(\frac{\nu_2}{\nu_1})^{-n}\;(\frac{\rho_{w1}}{\rho_{w2}})\;(\frac{\rho_2-\rho_{w2}}{\rho_1-\rho_{w1}})\;(\frac{d_2}{d_1})^{1+n}$$으로 주어지므로, 이를 이용하여 어구저항 D 및 그물감의 다리에서의 장력 $\tau$의 비를 $$\frac{D_2}{D_1}=\frac{d_2(\rho_2-\rho_{w2})}{d_1(\rho_1-\rho_{w1})}(\frac{\lambda_2}{\lambda_1})^2$$ $${\frac{\tau_2}{\tau_1}=\frac{d_2\iota_2(\rho_2-\rho_{w2})}{d_1\iota_1(\rho_1-\rho_{w1})}\;{\cdot}\frac{\lambda_2}{\lambda_1}$$로 정하였다.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1085-1091
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• 2011

The dynamic stability of railway vehicle has been one of the important issues in railway safety. The dynamic simulator has been used in the study about the dynamic stability of railway vehicle and wheel/rail interface. Especially, a small scale simulator has been widely used in the fundamental study in the laboratory instead of full scale roller rig which is not cost effective and inconvenient to achieve diverse design parameters. But the technique for the design of the small scale simulator for the fundamental study about the dynamic characteristics of the wheel-rail system and the bogie system has not been well developed in Korea. Therefore, the research about the development of the small scale simulator and the bogie has been conducted. This paper presents the design of the small-scaled derailment simulator and the example design case of a small scale bogie. The simulator could be used in the study about the effect of diverse parameters such as attack angle, wheelbase and cant on dynamic behavior of the bogie and the safety parameter such as derailment coefficient and critical speed.

• Journal of the Korean Geosynthetics Society
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• v.17 no.3
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• pp.33-46
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• 2018

This study presents the experimental results on the performance of deep excavation by using image processing technique particle image velocimetry (PIV). The purpose of present study is to be checked the application of PIV for the successive ground deformation during deep excavation. To meet the objectives of concern study, a series of reduce scale model test box experiments were performed by considering the wall stiffness, ground water table effect and ground relative density. The results were presented in form of contours and vector plot and further based on PIV analysis wall and ground displacement profile were drawn. The results of present study, indicate that, the PIV technique is useful to demonstrate the ground deformation zone during the successive ground excavation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.113-124
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• 1997

This work is performed to investigate the pressure drop and heat transfer characteristics in the air side of finned-tube heat exchanger for air conditioner. Experimental apparatus and method are described to simulate the heat exchanger performance by using the three times enlarged model. The pressure drop and heat transfer coefficient were measured and compared for the heat exchangers with a plane fin and a commercial strip fin. The measured data for the strip fin agree well with those of prototype within a few percentages. For the plane fin, the measured data had similar trend to Gray & Webb's correlation at high air velocity, however a new correlation is needed to give more accurate prediction at low air velocity. It is found that most heat was transferred around the front row of the two-row heat exchanger, and the ratio of thermal load at the front tube row was increased for decreasing air velocity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.9
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• pp.620-626
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• 2011

The purpose of this study is to evaluate a simulation model of a stacking guidance system (SGS) with a roller guide applicable to the mobile harbor. The study used a small-scale model (1/20) made of wood with rollers in order to compare the dynamic analysis with experiment results. The law of similarity was applied for the validation of the scaled model. In order to construct a more realistic simulation model, the damping coefficient of the dynamic model was adjusted to 0.5 Ns/mm for the wood-to-wood contact condition based on the experimental results. Using this validated model, dynamic simulations were also carried out for containers of 20, 30, and 40 tons. The results showed that the reaction force of the roller guide was increased from 74.7 kN to 91.2 kN as the weight of container increased. For the design of a roller guide for SGS, the results obtained in this study can be used to reduce the reaction force by employing a rubber roller or a highly damped rotational joint.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.172-176
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• 2011

최근 들어 생활수준의 향상과 친수 환경에 대한 인식이 높아지면서 하천환경의 보전과 개선에 대한 필요성이 증대되고 과거 이수 또는 치수 목저으로 정비되었던 하천을 자연형 하천으로 탈바꿈 시키려는 움직임이 많이 일어 나고 있다. 자연형 하천 공법의 연구는 1990년대부터 점차 이루어 지고 있으나, 호안의 식생 공법 연구 및 수리 실험을 이루어 지지 않는 실정이다. 이제 본 연구에서는 자연형 하천 정비의 대표적인 방법인 호안 사면 처리 공법 중 지오셀 식생 매트에 대한 수리모형 실험을 실시하였다. 고정상 실험을 통하여 활착된 지오셀 식생 매트가 허용할 수 있는 유속과 수위를 정하는데 목적을 두었고, 상사법칙 이론을 도입하여 수행된 실험결과를 정리 분석하였다. 분석된 실험치를 왜곡모형에 적용하여 실제 규모로 환산한 결과 현재 설계시 허용되는 유속에도 지오셀 식생 매트의 안정성이 확보되는 것을 확인할 수 있었다. 따라서 호안의 지오셀 식생매트의 적용이 가능 할 것으로 보이나, 제한적인 실험결과에 의해 왜곡모형을 이용하여 현장조건을 추정한 것이므로 적용 및 해석에 있어서는 실제 설치되는 하천의 복잡한 수리 수문학적인 변수가 충분히 고려되어야 할 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.39-45
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• 2005

The aim of this research is to predict the thickness and loading noise of the round-tip shaped Hartzell propeller currently used in the general aviation aircraft. Before implementing the noise analysis, the pressure distribution on the propeller was obtained by using the free wake panel method and unsteady Bernoulli's equation. The noise signal at observer position can be obtained by using the FW-H equation. The noise prediction results for the propeller indicates that the thickness noise has s symmetric directivity pattern with respect to the tip path plane, while the noise due to loading shows higher noise directivity toward downstream than the upstream direction from the rotor plane. The loading noise is dominant rather than the thickness noise in normal operating condition.

• Journal of the Korean Geosynthetics Society
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• v.3 no.4
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• pp.13-19
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• 2004

This paper presents the results of an investigation on the failure mechanism of geosynthetic-reinforced segmental retaining walls in tiered arrangement using reduced-scale model tests. In this laboratory model tests, a reduced scale model of the full-scale geosynthetic-reinforced wall which was constructed in Geotechnical Experimental Site at Sungkyunkwan University was used to perform a study on the failure mechanism. In order to a high degree of realism, the geometry of the wall and the material properties were selected applying Similitude Laws was used to perform laboratory model tests. And contrary to the previous failure tests with various surcharge pressures, the failure by the tired wall weight was observed. Primary variables considered in the model tests include the different offset distance between the tiers and the different reinforcement length in the lower tier and as a result of the parametric study, a different failure pattern was observed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.3
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• pp.23-27
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• 2012

A seawater pumps in the nuclear power plant is responsible for providing cooling water to other components all the time. Because of the depreciation, the seawater pump with current impeller consumes too much power for maintaining the total head. Therefore the objective of this study is to reduce power with maintaining certain the total head by cutting the current impeller. By using a commercial CFD code, FLUENT, the overall performance of seawater pump with current and modified impeller was simulated. Also Affinity law was applied at pumps with various impeller diameter and evaluated the validity of the affinity law. The numerical results show that the pump efficiency is quite irrelevant to the diameters of the impellers and the pump efficiency becomes worse over the designed flow rate. And affinity law result and numerical one show good agreements at small change of impeller diameter. One of the impeller diameters was decided to modify and was applied to the nuclear power plant with the numerical study above.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.545-552
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• 2006

Small-scale models have been frequently used for seismic performance tests because of limited testing facilities and economic reasons. However, there are not also enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry similitude is not well consistent in their inelastic seismic behaviors. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to aggregate size. Therefore, it is desirable to use different materials for small-scale model. In our recent study, a modified similitude law was derived depending on geometric scale factor, equivalent modulus ratio and ultimate strain ratio. And quasi-static and pseudo-dynamic tests on the specimens are carried out using constant and variable modulus ratios, and correlation between prototype and small-scale model is investigated based on their test results. In this study, tests on scaled model of different concrete compressive strength aye carried out. In shaking table tests, added mass can not be varied. Thus, constant added mass on expected maximum displacement was applied and the validity was verified in shaking table tests. And shaking table tests on non-artificial mass model is carried out to settle a limitation of acceleration and the validity was verified in shanking table tests.