• Title/Summary/Keyword: Heaving Oscillation

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Numercal Simulation of Unsteady Performance for 20D Surface Effect Airfoils (2차원 해면효과익의 비정상 성능에 대한 수치적 시뮬레이션)

  • Park, Il-Ryong;Jeon, Ho-Hwan
    • Journal of Ocean Engineering and Technology
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    • v.9 no.2
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    • pp.71-74
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    • 1995
  • A numerical model capable of simulating a 2-D airfoil flying over in the vicinity of the waves is discussed. Instead of treating the problem as a heaving oscillation one above the rigid flat wall, sources are distributed on the prescribed wave profile. The wave deformation due to the airfoil is assumed to be negligible and treated as a rigid undulated wall. The source and vortex are distributed on the surface of the foil. It is found that the variation of $C_L$ with wave steepness in severe and that the lift variation due to waves decreases as the wing height above the water surface increases.

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On The Added Mass and Damping of Chine Sections in Heaving Oscillation -Comparisons with Equivalent Lewis Section- (배골형단면주상체(背骨型斷面柱狀體)의 상하동요(上下動搖)에 있어서의 부가질량(附加質量)과 감쇠력(減衰力)에 관(關)하여)

  • J.H.,Hwang;Yoon-Ho,Kim
    • Bulletin of the Society of Naval Architects of Korea
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    • v.10 no.1
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    • pp.33-44
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    • 1973
  • Chine형 선체단면 주상체의 자유표면에서의 상하운동에 수반되는 부가질량과 감쇠력을 Ursell-Tasai 방법에 의하여 계산하였다. Chine형에서 구하여진 결과는 같은 선체단면적 계수와 반폭흘수비를 갖는 등가 Lewis형의 결과와 비교하였고 선체단면의 형상이 부가질량 및 감쇠력에 미치는 영향을 고찰하였다. Chine형과 등가 Lewis형 선체단면 주상체에 파고가 일정한 횡파가 입사할 때의 상하운동을 고찰하였다. 이상과 같은 계산 및 고찰을 통하여 다음 결과를 얻었다. 1) 자유표면이 부가질량에 미치는 영향은 chine형이 등가 Lewis형단면보다 큰 값을 갖는다. 2) 선체단면적계수와 반폭흘수비가 같은 경우에 감쇠력의 크기는 Lewis form, single chine, double chine순서이다. 3) 선체단면계수와 반폭흘수비는 상하운동에 가장 큰 영향을 미치는 것으로 생각되며, 선체단면의 기하학적인 변형이 운동에 미치는 영향은 중요한 요소가 되질 못한다. 4) 감쇠력계수와 선체단면계수와의 관계는 간단한 관계를 유지한다.

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Investigation of the Effect of Water Depths on Two-dimensional Hydrodynamic Coefficients for Twin-hull Sections (쌍동체(雙胴體)에 작용(作用)하는 2차원 유체력계수(流體力係數)의 수심(水深)의 변화(變化)에 따른 영향(影響)에 관한 고찰(考察))

  • K.P.,Rhee
    • Bulletin of the Society of Naval Architects of Korea
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    • v.19 no.4
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    • pp.39-45
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    • 1982
  • A floating rig, which has been used to develop the ocean resources has a common characteristics with the catamaran ship that it is composed of the two simple hulls. So the motion responses of the floating rig can be predicted theoretically with the aid of the strip method as those of the catamaran. And for the strip method, the two-dimensional hydrodynamic coefficients are the most important inputs to predict the results accurately. In this report, a theoretical method is proposed for calculating two-dimensional hydrodynamic forces and moments acting upon arbitrary shaped twin-hull cylinders, which are forced to make a heaving, swaying and rolling oscillation about their mean position on the free surface of a finite depth water. The theoretical results by making use of the singularity distribution method are presented. The accuracy of the coefficients was confirmed to be reasonable by the comparison with the Ohkusu's results for two circular cylinders in an infinite depth water. The depth effects on two-dimensional hydrodynamic coefficients for two circular cylinders are also checked. In some range of wave numbers, large differences in the behavior of hydrodynamic coefficients between for a finite depth and for an infinite depth are shown.

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