• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.1
• /
• pp.1-8
• /
• 2002

When a body enters waters, its original kinetic energy or momentum is distributed among the body and surrounding water in the form of added mass. Due to the transfer of the energy or momentum, the bode is subjected to the hydrodynamic impact forces and acceleration. This impact behavior can be an important criterion of submersible vehicle launched to the air. In this paper, based on Life-boat model, an approximate method is proposed for the evaluation of the forces and responses of cylindrical rigid bode by water entry impact. The impact forces are calculated by yon Karman's momentum theory and motion responses the body, especially acceleration, are calculated by a numerical integration of the motion equations derived by hydrodynamic force equilibrium. The proposed method is expected to be a simple but efficient tool lot the preliminary design or motion analysis of a body subjected to water entry impact.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.2
• /
• pp.77-87
• /
• 2000

The water entry forces acting on an air-dropped torpedo are of the restrictions on launch speed and launch altitude, because it could cause the structural damage to components of torpedo. Therefore, it is necessary to estimate the water entry forces with confidence according to launch conditions. In this study, an approximation method for water entry forces is presented, and the results using this approximation are compared with those of other numerical methods. The magnitude and duration of impact forces estimated by the present approximation agree with those of impact by the analysis of ideal or viscous flow. This method can give useful tools to select the launch in initial design stage.

• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.560-565
• /
• 2016

최근 대형 컨테이너선의 개발이 지속적으로 이루어짐에 따라 슬래밍에 의한 선수 및 선미의 구조안정성 문제가 대두되고 있지만 설계 단계에서 슬래밍에 대해 고려하기에는 현상의 복잡성으로 인해 어려움이 많았다. 이를 위해 KRISO에서 시행된 WILS JIP의 선수 단면 형상 및 선미 단면인 쐐기 형상으로 격자를 생성하여 EDISON CFD 다상유동 해석자를 통해 수치해석을 시도하였다. 기존 방식과 달리 계산 시간 절감을 위하여 격자 변형 기법을 적용하지 않고 모형 시험결과를 기반으로 한 유입류 조건을 설정하여 입수 충격 문제를 해석해보았다. 그 결과, 선미 형상의 경우 선행연구와 유사하게 실험 결과에 근접한 유체 충격력을 정량적으로 얻어낼 수 있었다. 선수 형상의 경우에서는 구상 선수로 인해 파생되는 센서 위치별 충격력의 변화를 확인할 수 있었으며, 실제 유동에 가까운 유동 형상과 슬래밍에 의한 충격력을 개략적으로 구할 수 있었다.

• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.2
• /
• pp.78-85
• /
• 1994

Impact forces are acting on the fore part of a body entering water and those are function o the shape of the fore part and entrance angle. In this paper, impact forces are computed for the flat faced body with arbitrary entrance angle The geometric characteristics of the wetted surface of the body are complicated. The surface is divided into several smooth parts and each of them is represented by a bi-cubic B-spline. The free surface condition, $\phi=0$, is applied at the undisturbed free surface and he boundary value problem is analized by using Green's function.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.13 no.6
• /
• pp.1026-1033
• /
• 2010

The analysis of water-entry impact forces acting on the fin shaft of high speed water-entry body is described. During the entry of high speed body into water, the physical phenomenon and flow properties are analyzed. A proper analysis model is established and the method to estimate the flow force which causes impact torque at the fin shaft is described. It is assumed that the fin shaft is damaged by the force which is induced by contacting with cavity wall. The pressure distribution of fin and the maximum torque are estimated and compared with breaking force. Conclusively, it is hard to resist water-entry impact force in terms of the reinforcement of fin shaft. Additionally safe equipment is essentially required.

• Journal of computational fluids engineering
• /
• v.4 no.1
• /
• pp.1-7
• /
• 1999

The numerical methodology for computing tile impact forces and water entry behaviors of high speed water entry bodies was been developed. Since the present method assumed the impact occurs within a very short time interval. the viscous effects do not have enough time to play a significant role in the impact forces, that is, the flow around a water-entry object was assumed as an incompressible potential flow and is solved by the source panel method. The elements fully submerged into the water are routinely treated, but the elements intersected by the effective planar free surface are redefined and reorganized to be amenable to the source panel method. To validate the present code, it was applied to disk, cone and ogive model and compared with experimental data. Good agreement was obtained. The water entry behavior such as the bouncing phenomena from the free surface was also simulated using the impact forces and two degree of freedom dynamic equation. Physically acceptable results were obtained.

• Journal of Ocean Engineering and Technology
• /
• v.28 no.3
• /
• pp.209-217
• /
• 2014

In the present study, the water impact loads on two-dimensional symmetric and asymmetric wedges were mainly studied. The impact pressure and force were measured during a vertical drop of the symmetric and asymmetric wedges. The measured pressure was compared with analytic solutions. The measured force at a local area of the wedge was compared with the integrated pressures and analytic solutions. Some findings on symmetric and asymmetrical wedge drops are presented, and the reliability of the force sensor used for the measurement of the local impact force is discussed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.8
• /
• pp.3374-3383
• /
• 2011

In this study, numerical analyses for slamming impact phenomena have been carried out using a 2-dimensional wedge shaped structure having finite deadrise angles. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct(or PLIC-VOF) scheme is used for the tracking of the deforming free surface. Numerical analyses are carried out for the deadrise angles of $10^{\circ}$, $20^{\circ}$ and $30^{\circ}$. For each deadrise angle, variations are made for the grid size on the wedge bottom and for the entry speed. The magnitude and the location of impact pressure and the total drag force, which is the summation of pressure distributed at the bottom of the structure, are analyzed. Results of the analyses are compared with the results of the Dobrovol'skaya similarity solutions, the asymptotic solution based on the Wagner method and the solution of Boundary Element Method(BEM).

• The Journal of the Acoustical Society of Korea
• /
• v.33 no.1
• /
• pp.10-20
• /
• 2014

To study the water-entry impact noise, on-board experiment using a small launcher firing various objects was performed in the Yellow Sea. As the launcher fires a cylindrical object from the ship vertically, generated noise is measured with a hydrophone on the starboard of Chung-hae, Marine surveyor. Three types of cylindrical objects, which have noses of flat-faced, conical, and hemisphere, were used during the experiment. The measured noise exhibits a time-dependency which can be divided into three phases: (1) initial impact phase, (2) open cavity flow phase, (3) cavity collapse and bubble oscillation phase. In most cases, the waveform of bubble oscillation phase is dominant rather than that of initial impact phase. Pinch-off time, where a cavity begins to collapse, occurs at 0.18 ~ 0.2 second and the average lasting time of bubble was 0.9 ~ 1.3 second. The energy of water-entry impact noise is focused in the frequency region lower than 100 Hz, and the generated noise is influenced by the nose shapes, object mass, and launching velocity. As a result, energy spectral density on the bubble frequency is higher in the order of flat-faced, conical, hemisphere nose, and the increase of initial energy raises the energy spectral density on the bubble frequency in the cylinder body of same shape. Finally, we compare the measurements with the simulated signals and spectrum based on the bubble explosion physics, and obtain satisfactory agreements between them.

• Vending industry
• /
• v.7 no.2 s.20
• /
• pp.54-58
• /
• 2007

지난 7월 10일 MBC뉴스 데스크는 가짜 지폐도 입수하는 '눈먼 자판기' 실태를 고발 취재해 큰 반향을 불러 일으켰다. 지폐식별기의 생명이 품질 신뢰성인데 위폐에 뻥뻥 뚫리는 제품들이 유동되고 있다는 사실은 충격적이었다. 이같은 현상은 자판기에 대한 큰 불신을 초래할 뿐만 아니라 모방범죄 및 조직적 위폐 확산을 불러일으킬 가능성이 크다는 점에서 심각한 문제가 아닐 수 없다. 그 동안 지폐식별기 분야가 품질에 대한 신뢰성을 철저히 검증하지 못하고 양적인 시장 확대에만 매달린 폐단이 비로소 나타나고 있는 것이다. 그나마 다행이라면 위폐문제가 일찌감치 공론화가 되어 산업계가 품질에 대해 경각심을 가질 수 있게 되었다는 점이다. 제품이 우후죽순처럼 깔린 상항에서 문제가 불거지면 걷잡을 수 없는 상황에 빠질 수 있지만, 산업계는 이제라도 적극적인 대책을 마련한다면 전화위복의 기회로 삼을 수가 있다. 협회에서도 사태의 심각성을 반영, 산업계의 현명하고도 신속한 대응을 위해 자판기 관련 업체를 대상으로 "신권용 지폐식별기 '위변조 지폐 사용 확산방지'를 위한 협조 요청" 공문을 발송했다. 산업계가 위변조 지폐 입수 사태에 대해 적극적인 대응책을 모색하려면 현재의 문제점에 대한 엄밀히 진단하는 것이 우선시되어야 한다. 불거진 위변조 지폐 입수 실태의 면면을 살펴보고, 산업계가 어떠한 대책을 마련해야 하는 지를 진단했다.