• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.205-210
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• 2006

The impact forces of the highly nonlinear waves are one of the important factors in designing the ocean structures. The impact forces are very difficult to analyze numerically and experimentally because they are impulsive in magnitude and occur instantaneously. In this study the numerical program based on N.S. equations are used to investigate the impact forces of steep waves where the waves are gene rated by the wave maker in the numerical wave basin. The arbitrary steep waves are generated by the superposition of waves of single frequency and the impact forces on vertical cylinder are simulated on the multiblock grids. V.O.F. and the local height function methods are used to track the free surfaces. To validate the numerical analysis the numerical results are compared with the experimental ones and the acceptable agreements are found. It is thought that more studies on the simulations of the incoming breaking waves and the impact forces on the vertical cylinder should be made to obtain the useful results to be applied in the offshore design.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.299-304
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• 2013

초음속 조건에서 Busemann biplane은 충격파의 중첩에 의해 항력 감소가 일어난다. 그러나 받음각이 증가 할 경우, 앞전에서 궁형 충격파가 발생하여 항력이 급격하게 증가한다. 이에 본 연구에서는 busemann biplane에 플랩을 주어 궁형 충격파를 감소시킬 수 있는 flap biplane의 플랩 길이와 각도의 변화에 따른 공력 성능의 변화를 분석하였다. Flap biplane의 공력성능을 기본 biplane형상 및 diamond airfoil과 비교한 결과, 동일한 양력 조건에서 항력은 diamond airfoil에 비해 약 75%정도 감소함을 확인하였다. 그리고 플랩의 길이와 양항비는 선형의 관계가 있음을 확인하였고, 특정한 플랩의 각도에서 최대 양항비가 도출된다는 사실을 확인하였다. 마지막으로 전압력의 감소를 충격파의 강도로 정의하고, 이를 비교한 결과 flap biplane의 전압력 감소가 diamond airfoil에 비해 약 25%정도가 더 작게 나타난 사실로 부터 flap biplane의 소음 감소 효과를 유추할 수 있었다. flap biplane은 초음속 영역에서 항력과 소음의 감소에 효율적인 익형임을 확인하였다.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.152-172
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• 1992

The ship sailing among waves are suffered the various wave loads that comes from its motion throughout its life. Because there are dynamic, the analysis of ship structure must be considered as the dynamic problem precisely. In the rationally-based design, the dynamic structural analysis is carried out using dynamic wave loads provided from the results of the ship mouton calculation as the rigid body. This method is based on the linear theory assumed low wave height and small amplitude of motion. But at the rough sea condition, high wave height, relatively ship's depth, is induced the large ship motion, so the ship section configulation below water line is rapidly changed at each time. This results in non-linear problem. Considering above situation in this paper, the strength analysis method is introduced for the hull glider among waves considering non-linear hydrodynamic forces. This paper considers that the overall or primary level of the ship structural dynamic loading and dynamic response provided from the non-linear wave forces, and bottom and bow flare impact forces estimated by momentum slamming theory, in which the ship is idealized as a hollow thin-walled box beam using thin-walled beam theory and the finite element method. This method is applied to 40,000 Ton Double-Skin Tanker and attention is paid to the influence of the response of ship speed, wave length and wave height compared with linear strip theory.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.25.1-25.1
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• 2009

Pattern 웨이퍼 상의 오염입자 제거는 반도체 산업의 주된 과제 중 하나이다. Pattern의 선폭이 좁아짐에 따라 Pattern에 손상을 가하지 않고 오염입자를 제거 하는 것은 더욱 어려워지고 있다. 그뿐만 아니라 기존 습식세정 공정에서의 화학액에 의한 환경오염 및 박막의 손실도 문제가 되기 시작했다. 이러한 문제를 해결하기 위해 기존 세정공정에서 화학액의 농도를 낮추고 Megasonic 등을 이용하여 세정력을 보완하는 방법들이 연구되고 있다. 하지만 습식세정의 경우 강한 화학작용으로 인한 표면 손상 및 물 반점의 문제는 여전히 이슈가 되고 있다. 이러한 단점을 극복하기 위하여 건식 세정법이 제시되고 있으며 이 중 레이저 충격파는 레이저를 집속시켜 발생된 충격파를 이용하여 입자를 제거하기 때문에 국부적인 세정이 가능하며 세정력 조절이 가능하여 손상이 세정을 할 수 있다. 그러나 Pattern의 구조에 의해 전되는 세정력의 차이가 발생하고 Trench 내부의 오염입자제거 문제점이 발생할 수 있다. 시편은 Si STI Pattern을 100 nm PSL Particle (Red Fluorescence, Duke Scientific, USA) 을 50ppm 농도로 희석시킨 IPA에 dipping 하여 오염시킨 후 N2 Gas를 이용하여 건조하여 준비하였다. 그리고 레이저 충격파 세정 시스템은 최대 에너지 1.8 J까지 가능한 레이저를 발생하는 1,064 nm Nd:YAG 레이저를 이용하여 실험하였다. 레이져 충격파 실험은 충격파와 시편사이의 거리, gap distance와 에너지를 변환하여 세정효율을 관찰하였다. 세정효율은 세정 전후의 입자 감소량을 현광현미경 (LV-150, Nikon, Japan)를 이용하여 측정하였다. 그 결과, Trench 내부의 오염입자의 경우 Trench 밖의 오염입자에 비해 세정효율이 떨어지는 것으로 나타났으나 시편과 레이저 초점과의 거리가 가까워짐에 따라 Trench 내부의 오염입자에 대한 세정 효율을 증가시킬 수 있었다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.195-201
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• 2006

The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as freak wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.33-39
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• 2008

To improve the mixing efficiency and to reduce the pressure loss, it is needed to develope a new mixing device for supersonic combustion. The vent mixer is introduced as the new supersonic fuel-air mixer. Computational analyses, that include pressure profile, density contour, and streamline tracing, have been carried out. The expansion wave generates at the end of the extended upper wall of the mixer. And it reduces the shock wave from the hole. Incoming air flow through the hole makes several recirculation regions which increase the mixing efficiency, and the separation region at the downward wall expends the boundary layer which reduces the pressure loss.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.9-19
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• 1989

The impact stress and wave propagation of graphite/epoxy and glass/epoxy laminates subjected to the transverse low-velocity impact of steel balls are investigated theoretically. A plate finite element model based on Whitney and Pagano's theory for the analysis of heterogeneous and anisotropic plates taking into account of the transverse shear deformation is used for the theoretical investigation. This model is in conjuction with static contact laws. The basic element is a four-node quadrilateral with the five degrees-of-freedom per node. The reduced integration technique is used for shear locking associated with low-order function in application to thin plates. These two materials are composed of [0.deg./45.deg./0.deg./-45.deg./0.deg.]$_{2S}$ and [90.deg./45.deg./90.deg./-45.deg./90.deg.]$_{2S}$ stacking sequences and have clamped-clamped boundary conditions. Finally, the present results are compared with an existing solution and wave propagation theory and then impact stress and wave propagation phenomena are investigated.gated.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.8-15
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• 2004

Supersonic jets impinging on $60^{\cire}$ wedge were investigated to obtain fundamental design data for jet deflector It was of interest to study flow phenomena such as shock interaction and separation induced by shear layer. Experiments using supersonic cold flow system were conducted for Schlieren flow visualization and measurement of surface pressure. Numerical results were compared with the experimental results. The major parameters are underexpansion ratio, distance from nozzle to apex and design Mach number. Flow conditions were obtained for the wedge shock to attach on or detach from the wedge. The dominant feature of flow-field is shock pattern induced by the Interaction between the wedge shock and the barrel shock.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.287-296
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• 2020

The wave-impact load on offshore structures can be divided into green-water and wave-slamming impact loads. These wave impact loads are known to have strong nonlinear characteristics. Although the wave impact loads are dealt with in the current classification rules in the shipping industry, their strong nonlinear characteristics are not considered in detail. Therefore, to investigate these characteristics, wave-impact loads induced by a breaking wave on a circular cylinder were analyzed. A model test was carried out to measure the wave-impact loads due to breaking waves in a two-dimensional (2D) wave tank. To generate a breaking wave, the focusing wave method was applied. A series of 2D tank tests under a horizontal wave impact was carried out to investigate the structural responses of the cylindrical structure, which were obtained from the measured model test data. According to the results, we proposed a structural damage-estimation procedure of an offshore tubular member due to a wave impact load. Furthermore, a recommended wave-impact load is suggested that considers the minimum required thickness of each member. From the experimental results, we found that the required minimum thickness is dependent on the impact pressure located in a three-dimensional space on the surface of a tubular member.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.4
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• pp.187-192
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• 2007

Impact on cylindrical surface caused by plunging breaking waves is investigated experimentally. The breaking waves are generated in a wave flume by decreasing the wave maker frequencies linearly and focusing the generated wave components at one specific location. The breaking wave packets are based on constant wave steepness spectrum. Three inclination angles of cylinder are applied to examine the effect of contact angle between cylinder and front surface of breaking waves. Also, the effect of cylinder diameter on pressure distribution and its peak value is investigated by adopting three cylinders with different diameters. The longitudinal location of cylinder is slightly moved in eight different points to find out a probable maximum value of impact pressure. The pressures and total force on cylinder surface are measured by piezo-electric pressure sensors and 3-components load cell with 30kHz sampling rate. The variation of peak impact pressures and forces is analyzed in terms of cylinder diameter, inclination angle and location. Also, the pressure distribution on cylindrical surface is examined. The cylinder location and surface position are more important parameters that govern the magnitude and shape of peak pressures, while the cylinder diameter and inclined angle are relatively insignificant. In a certain conditions, the impact phenomenon becomes very unstable which results in a large variation of measured valves in repeated runs.