• The Journal of the Acoustical Society of Korea
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• 제16권1E호
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• pp.49-56
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• 1997

Ultrasonic cleaning at high frequency around 1 MHz, called megasonic cleaning, is commonly used to remove particles less than 1 ㎛ by generating high frequency accelerations on the cleaning objects. Cleaning is performed in an ultrasonically-excited liquid contained in a double-structured container. Ultrasonic waves generated by piezoelectric transducers propagate in the outer container and are transmitted through the inner container. The bottom of the inner container is inclined to make oblique incidence of the ultrasonic wave in order to raise the efficiency of the transmission through the bottom plate. This work deals with the efficiency of the transmission, which directly affects the cleaning performance. The transmission characteristics of the ultrasonic wave in the megasonic cleaner have been obtained analytically and numerically for the variations of some parameters, such as the thickness and inclined angle of the bottom plate of the inner container and the chemical ratio and temperature of the cleaning liquid. The calculated results have yielded the optimum cleaning condition in terms of the sound power transmitted into the cleaning liquid.

• 한국해양공학회지
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• 제21권1호
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• pp.45-50
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• 2007

For a long partially-filled membrane container on an incline, the analytic solution of the similarity shape is studied. The nonlinear equation is solved and its solution is expressed as elliptic integrals, which include an unknown at the point of inflection. The point of inflection is determined by using the boundary condition at the upper separating point. Some characteristic values of the universal shape are evaluated, as the functions of inclination angle and shapes are illustrated for some cases.

• Ocean Systems Engineering
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• 제12권4호
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• pp.385-402
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• 2022

This paper deals with the study of hydrodynamic pressure in reservoir adjacent to the concrete gravity dam subjected to dynamic excitation. Widely famous finite element method is used to discretize the reservoir domain for modelling purpose. Pressure is considered as nodal variable following Eulerian approach. A suitable nonreflecting boundary condition is applied at truncated face of reservoir to make the infinite reservoir to finite one for saving the computational cost. Thorough studies have been done on generation of hydrodynamic pressure in reservoir with variation of different geometrical properties. Velocity profile and hydrodynamic pressure are observed due to harmonic excitation for variation of inclination angle of dam reservoir interface. Effect of bottom slope angle and inclined length of reservoir bottom on hydrodynamic pressure coefficient of reservoir are also observed. There is significant increase in hydrodynamic pressure and distinct changes in velocity profile of reservoir are noticeable for change in inclination angle of dam reservoir interface. Change of bottom slope and inclined length of reservoir bottom are also governing factor for variation of hydrodynamic pressure in reservoir subjected to dynamic excitation.

• 한국지반공학회논문집
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• 제33권3호
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• pp.29-36
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• 2017

NATM 공법에서 터널을 확대하거나 피난갱과 같이 좁은 단면에 록볼트를 설치하는 경우에는 록볼트를 경사지게 설치하거나 또는 짧은 볼트를 연결하여 시공할 수밖에 없다. 국내외에서 실시된 경사 록볼트에 대한 연구는 아직 미흡한 실정이며 실제 현장에 적용하기 위해서는 경사 록볼트의 거동특성에 대한 연구가 필요하다고 사료된다. 본 연구에서는 3차원 유한요소해석을 사용하여 경사 록볼트 시공 시 록볼트의 설치각도와 설치길이에 따른 최대 중립점 발생위치의 변화를 확인하고 이에 따른 록볼트에 의한 원지반 아치형성영역의 두께 변화를 비교 분석하여 지반보강효과에 대해 확인하였다. 해석결과 표준지보패턴(설치길이 4m)에선 설치각도가 감소할수록 터널 주변지반의 변형범위는 증가하여 지반보강효과가 감소하는 것을 알 수 있었다. 또한, 설치길이가 증가함에 따라 설치각도에 의한 영향을 적게 받은 것으로 나타났으며 설치각도 $45^{\circ}$ 이하에서는 설치길이의 영향을 받지 않는 것으로 나타났다. 이러한 결과로부터 경사록볼트의 설치각도는 $45^{\circ}$이상으로 하여 아칭영역을 확보하도록 하여야 하며, 설치각도 $75^{\circ}$이상인 경우 직각으로 설치하는 경우와의 보강효과의 차이가 크지 않음을 확인하였다. 또한 추가적인 상세 검토를 통하여 NATM 터널에서의 경사록볼트 설계지침을 제시하고자 하였다.

• 한국안전학회지
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• 제29권3호
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• pp.14-19
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• 2014

The global demand for reduction in the weight of automobiles has led many countries to focus on the development of hybrid, eco-friendly, and electric cars. Reduction in the weight of materials can both increase fuel efficiency and maximize automobile performance. Therefore, the design of automobile should be inclined towards the safety aspects. but at the same time, it also consider reducing the structural weight of an automobile. In this study, CFRP side members with circular and double hat shaped section was manufactured. The impact collapse tests performed with change of the stacking condition, such as variation of interface number and outerlayer angle. The impact collapse load and absorbed energy were quantitatively analyzed according to the changes in section shapes and stacking condition. This analysis was performed to obtain design data that can be applied in the development of optimum lightweight members for automobiles.

• 터널과지하공간
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• 제33권5호
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• pp.339-347
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• 2023

TBM 추진잭이 경사면에 접촉하거나 편심하중이 발생할 때 추진잭의 페데스탈 및 로드 부위에 횡하중에 의한 휨변형이 발생할 수 있다. 이는 추진잭 모듈의 고장을 유발할 우려가 있으므로, 추진잭 모듈 전체에 대한 좌굴 안정성을 검증할 필요가 있다. 본 연구는 추진잭 좌굴 안정성 분석을 위한 좌굴 압축시험방법을 조사하고, 압축시험 시스템을 구성하였다. 추진잭의 전체 부품을 모델링하여 수치해석을 통해 응력집중 파트를 분석하였다. 경사도 0도 조건에서 최대하중을 가압하여 압축시험을 수행하였다. 로드의 변형과 씰의 누유는 관측되지 않아서 0도 조건에서 추진잭의 좌굴 안정성을 검증하였다.

• Korean Chemical Engineering Research
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• 제60권2호
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• pp.229-236
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• 2022

동일 분체특성의 분진이 평균입경, 농도, 분진조건(부유 또는 퇴적) 변화에 따른 화재폭발 위험성을 조사하였다. 이를 위해 20L분진폭발시험장치, 열중량분석장치, 연소속도시험장치(UN시험법)를 사용하였다. 4종 분진(Sugar, Mg, Al, Zr)의 입경이 서로 다른 8개 분진 시료에 대하여 부유 분진의 폭발특성과 화염전파속도(FPV), 그리고 퇴적분진의 화염확산속도(FSV)를 조사하였다. 부유 분진 조건에서 Mg 및 Al 분진은 입경이 감소하면 폭발 위험성이 증가하였지만, Sugar는 입경 변화에 따른 폭발 위험성의 영향이 거의 나타나지 않았다. 부유 분진의 화염전파속도(FPV)는 마이크로 범위에서의 입경 변화보다 마이크로에서 나노로 입경이 감소하면 크게 증가하였다. 퇴적층의 화염확산속도(FSV)는 수평면(기울기 0°)보다 경사면(기울기 30°)에서 증가하는 경향을 나타냈으며, 경사면(기울기 30°) 퇴적층 조건에서는 상방 전파가 하방 전파보다 높게 나타났다.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.497-518
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• 2021

In this study, a new method for treating the wall boundary in smoothed particle hydrodynamics (SPH) is proposed to simulate free surface flows effectively. Unlike conventional methods of wall boundary treatment through boundary particles, in the proposed method, the wall boundary condition is directly imposed by adding boundary truncation terms to the mass and momentum conservation equations. Thus, boundary particles are not used in boundary modeling. Doing so, the wall boundary condition is accurately imposed, boundary modeling is simplified, and computation is made efficient without losing stability in SPH. Performance of the proposed method is demonstrated through several numerical examples: dam break, dam break with a wedge, sloshing, inclined bed, cross-lever rotation, pulsating tank and sloshing with a flexible baffle. These results are compared with available experimental results, analytical solutions, and results obtained using the boundary particle method.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.235-236
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• 2022

In the present study, the effect of horizontal vent position on fire phenomena in the enclosure with vertical and horizontal vents was examined using numerical simulation. Case 1 indicates the condition that the horizontal vent is in the center of the ceiling. Case 3 indicates the condition that the horizontal vent is far away from the vertical vent. Case 2 indicates the condition that the horizontal vent is installed between Case 1 and Case 3. The temperature distribution, smoke layer temperature, velocity distribution, and mass flow rate of horizontal vent flow were analyzed. In Case 2, the temperatures were lowest and the mass flow rate through the horizontal vent was largest. This is because the flame is inclined by the inflow through the vertical vent. Hence, to determine the proper horizontal vent location for the high smoke ventilation performance, the inflow through the vertical vent and its effect on flame behavior should be considered.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2005년도 추계학술대회 논문집
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• pp.74-79
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• 2005

The tribrachial flame in laminar coflow jet has been investigated experimentally with unsteady propagating condition. With adopting various visualization techniques, including OH-PLIF, Rayleigh Scattering technique, it was confirmed that the location of tribrachial point is on the inclined surface of flame and the propagation speed of tribrachial flame was significantly affected by the velocity gradient.