Effect of Free Surface Based on Submergence Depth of Underwater Vehicle

Taek-Geun Youn,Min-Jae Kim,Moon-Chan Kim,Jin-Gu Kang 한국해양공학회 2022 韓國海洋工學會誌 Vol.36 No.2

This paper presents the minimum submergence depth of an underwater vehicle that can remove the effect of free surface on the resistance of the underwater vehicle. The total resistance of the underwater vehicle in fully submerged modes comprises only viscous pressure and friction resistances, and no wave resistance should be present, based on the free surface effect. In a model test performed in this study, the resistance is measured in the range of 2 to 10 kn (1.03–5.14 m/s) under depth conditions of 850 mm (2.6D) and 1250 mm (3.8D), respectively, and the residual resistance coefficients are compared. Subsequently, resistance analysis is performed via computational fluid dynamics (CFD) simulation to investigate the free surface effect based on various submergence depths. First, the numerical analysis results in the absence of free surface conditions and the model test results are compared to show the tendency of the resistance coefficients and the reliability of the CFD simulation results. Subsequently, numerical analysis results of submergence depth presented in a reference paper are compared with the model test results. These two sets of results confirm that the resistance increased due to the free surface effect as the high speed and depth approach the free surface. Therefore, to identify a fully submerged depth that is not affected by the free surface effect, case studies for various depths are conducted via numerical analysis, and a correlation for the fully submerged depth based on the Froude number of an underwater vehicle is derived.

천해역에 수표면 및 수중방류된 사각형제트의 흐름 거동

김대근,김동옥 대한상하수도학회 2011 상하수도학회지 Vol.25 No.5

In the present study, the flow behaviors of square jets surface discharged and submerged discharged into shallow water were each simulated using computational fluid dynamics, and the results were compared. As for the verification of the models, the results of the hydraulic experiment conducted by Sankar, et al. (2009) were used. According to the results of the verification, the present application of computational fluid dynamics to the flow analysis of square jets discharged into shallow water was valid. As for the wall jet, which is one form of submerged discharges, at the bottom wall boundary, the peak velocity of the jet rapidly moved from the center of the jet to the bottom wall boundary due to the restriction of jet entrainment and the no-slip condition of the bottom wall boundary, and, as for the surface discharge, because jet entrainment is limited on the free water surface, the peak velocity of the jet moved from the center of the jet to the free water surface. This is because jet entrainment is restricted at the bottom wall boundary and the surface so that the momentum of the central core of the jet is preserved for considerable time at the bottom wall boundary and the surface. In addition, due to the effect of the bottom wall boundary and the free water surface, the jet discharged into shallow water had a smaller velocity diminution rate near the discharge outlet than did the free jet; at a location where it was so distant from the discharge outlet that the vertical profile of the velocity was nearly equal (b/x =20~30), moreover, it had a far smaller velocity diminution rate than did the free jet due to the effect of the finite depth.

Experimental and Numerical Study on the Characteristics of Free Surface Waves by the Movement of a Circular Cylinder-Shaped Submerged Body in a Single Fluid Layer

김준범,민은홍,구원철 한국해양공학회 2023 韓國海洋工學會誌 Vol.37 No.3

Analyzing the interactions of free surface waves caused by a submerged-body movement is important as a fundamental study of submerged-body motion. In this study, a two-dimensional mini-towing tank was used to tow an underwater body for analyzing the generation and propagation characteristics of free surface waves. The magnitude of the maximum wave height generated by the underwater body motion increased with the body velocity at shallow submerged depths but did not increase further when the generated wave steepness corresponded to a breaking wave condition. Long-period waves were generated in the forward direction as the body moved initially, and then short-period waves were measured when the body moved at a constant velocity. In numerical simulations based on potential flow, the fluid pressure changes caused by the submerged-body motion were implemented, and the maximum wave height was accurately predicted; however, the complex physical phenomena caused by fluid viscosity and wave breaking in the downstream direction were difficult to implement. This research provides a fundamental understanding of the changes in the free surface caused by a moving underwater body.

부력 제어식 가두리 모형의 부침 특성 및 안정성 해석

이건호 ( Gun Ho Lee ),차봉진 ( Bong Jin Cha ),정성재 ( Seong Jae Jeong ) 한국어업기술학회 2012 수산해양기술연구 Vol.48 No.1

This study aims to analyze the performance of a submersible fish cage which was designed for developing an economical cage system can be applied in korean aquaculture environment easily. To analyze the performance of the designed cage a model test was carried out. In the test, inclination changes of the upper frame and mooring tensions of model cage were measured during the submerging and surfacing motion in still water and wave condition (period: 2s, wave height: 0.1, 0.2, 0.3m). As a result, in the still water condition the model cage kept horizontal balance and inclination degree of the upper frame was about 1。. In the wave condition, the model cage showed bilateral symmetric up-and-down motion but the average inclination degree of the upper frame was about 0 。. When the model cage reached at a depth of 1m, the upand- down motion of the cage was decreased by 12% compared with that of at the surface (period 2s, height 0.3m). In the same wave condition, the maximum and average line tension under the bottom position were about 8% and 11% respectively compared with that of at surface.

Composite Overlapping Meshes for the Solution of Radiation Forces on Submerged-Plate

Kong, Gil-Young,Lee, Sang-Min,Lee, Yun-Sok The Korean Society of Mechanical Engineers 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.7

The purpose of this study is to predict and understand the hydrodynamic forces and their nonlinear behaviors of fluid motion around the submerged plate oscillating near a free surface. To achieve this objective, we have developed a composite grid method for the solution of a radiation problem. The domain is divided into two different grids; one is a moving grid system and the other is a fixed grid system. The moving grid is employed for the body fitted coordinate system and moves with the body. This numerical method is applied to calculation of radiation forces generated by the submerged plate oscillating near a free surface. In order to investigate the characteristics of the radiation forces, the forced heaving tests have been performed with several amplitudes and different submergences near a free surface. These experimental results are compared with the numerical ones obtained by the present method and a linear potential theory. As a result, we can confirm the accuracy of the present method. Finally, the effect of nonlinear and viscous damping has been evaluated on the hydrodynamic forces acting on the submerged plate.

이종재료 접착제 접합부의 환경 피로강도 평가

임재규,이중삼,윤호철,유성철 대한용접접합학회 2002 대한용접·접합학회지 Vol.20 No.5

One of the important advantage of adhesive bonded joint can combine the different materials. The joint that bonded by structural adhesive bond must keep a large force and its strength is affected by some environmental factors such as temperature and submergence time in water. In order to advance the fatigue strength of adhesive bonded joint, mostly put a surface treatment on the surface. This study was researched the effect of air temperature, submergence time, submergence temperature and surface treatment on the fatigue strength. We found that submergence temperature has the most effect and low plasma treatment specimens have the most fatigue strength.

Computation of Water and Air Flow with Submerged Hydrofoil by Interface Capturing Method

Kwag, Seung-Hyun The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.7

Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell wise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.

몰수평판에 작용하는 Radiation 유체력에 관한 연구

이상민(Sang-Min Lee),김순갑(Soon-Kap Kim),공길영(Gil-Young Kong),김철승(Chol-Seong Kim) 한국항해항만학회 2003 한국항해항만학회 학술대회논문집 Vol.3 No.-

라디에이션(radiation) 문제를 해결하기 위해서 중합격자법을 개발하였다. 중합격자계는 이동격자계와 고정격자계로 이루어져 있으며 이동격자계는 운동하는 물체에 적용되어 운동하는 물체와 동시에 이동된다. 이러한 수치계산법은 자유표면 부근에서 운동하는 몰수평판에 작용하는 라디에이션 유체력을 계산하는데 응용되었다. 현재의 수치계산법에 의한 결과는 실험값 및 선형포텐샬 이론에 의한 결과와 상호 비교하였으며, 수치계산의 신뢰성을 확인하였다. 그리고, 몰수평판에 작용하는 비선형 점성감쇄효과에 대하여 평가하였다. We have developed a composite grid method for the solution of the radiation problem. We divide the domain into two different grids; one is a moving grid system and the other is a fixed grid system. This numerical method is applied to calculation of the radiation forces generated by the submerged plate oscillating near a free surface. The experimental data are compared with the numerical ones obtained by the present method and a linear potential theory. As a result we can confirm the accuracy of the present method. Finally, we have evaluated the effect of nonlinear and viscous damping on the hydrodynamic forces acting on the submerged plate.

몰수평판에 작용하는 Radiation 유체력에 관한연구

이상민(Sang-Min Lee),공길영(Gil-Young Kong),김철승(Chol-Seong Kim) 한국항해항만학회 2004 한국항해항만학회지 Vol.28 No.3

라디에이션(radiation) 문제를 해결하기 위해서 중합격자법을 개발하였다. 중합격자계는 이동격자계와 고정격자계로 이루어져 있으며, 이동격자계는 운동하는 물체에 적용되어 운동하는 물체와 동시에 이동된다. 이러한 수치계산법은 자유표면 부근에서 운동하는 몰수평판에 작용하는 라디에이션 유체력을 계산하는데 응용되었다. 현재의 수치계산법에 의한 결과는 실험값 및 선형포텐셜 이론에 의한 결과와 상호 비교하였으며, 수치계산의 신뢰성을 확인하였다. 그리고, 몰수평판에 작용하는 비선형 점성감쇄효과에 대하여 평가하였다. We have developed a composite grid method for the solution of the radiation problem. We divide the domain into two different grids; one is a moving grid system and the other is a fixed grid system. This numerical method is applied to calculation of the radiation forces generated by the submerged plate oscillating near a free surface. The experimental data are compared with the numerical ones obtained by the present method and a linear potential theory. As a result, we can confirm the accuracy of the present method. Finally we have evaluated the effect of nonlinear and viscous damping on the hydrodynamic forces acting on the submerged plate.

Motion of a submerged body in a near-surface water environment

Zemlyak Vitaly,Pogorelova Alexandra,Kozin Victor 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

This study considered the motion of a submerged body near the free surface of a liquid and a liquid covered with ice cover, both theoretically and experimentally. Mathematically, the body was modelled using the sourceesink system. The ice cover was modelled as a thin elastic plate floating on the surface of the liquid. We analysed the influence of the ice cover thickness and the motion of a submerged body on the wave resistance of the body, its lift force, and ice deflections. The relationship between the vertical displacement and speed of movement of the submerged body, as well as the effect on the investigated parameters of the ice cover, were established. The parameters of flexuralegravity waves generated from the motion of the body near the lower ice surface were determined.