• 대한조선학회논문집
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• 제44권2호
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• pp.74-82
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• 2007

Recently, the erosion due to cavitation frequently occurs on a horn-type rudder of a high-speed large container carrier. It is necessary to understand the flow characteristics around a rudder in fully wetted and cavitating flow condition, and the process of generation and collapse of cavitation for a rudder design to minimize the cavity-induced erosion. The flow characteristics around a two-dimensional hydrofoil(NACA66) are investigated through the computational method utilizing a viscous flow theory applied to a cavitation model. The computational results from the viscous flow theory are verified by the comparison with the experimental results, and are compared with those from the potential flow theory. The effects of angle of attack, Reynolds number, cavitation number, and thickness ratio on the cavitating flow are also investigated.

• 대한조선학회논문집
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• 제43권2호
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• pp.177-185
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• 2006

Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.

• 한국지반공학회논문집
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• 제21권1호
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• pp.43-50
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• 2005

고압분사주입공법은 지반개량, 차수벽, 흙막이벽, 기초 보강말뚝 등에 사용되고 있다. 고압분사주입공법은 사질토지반에 대해서는 지수목적으로, 연약한 점성토 지반에서는 지반강화를 위하여 사용되고 있다. 그러나 현재 국내에 적용되고 있는 경우의 대부분은 지반조건에 따른 강도증가 효과를 경험적으로 파악하여 설계에 적용하고 있는 실정이고 이에 대한 많은 연구가 진행되고 있다. 본 연구에서는 고압분사주입공법의 지반교란에의 효율성을 증대시킬 목적으로 공동현상(cavitation) 이론을 응용하고자 하였다. 그리고 이를 정량적으로 분석하기 위하여 공동현상(cavitation)을 적용한 경우와 적용하지 않은 경우에 대해 지반조건, 주입압력 및 주입시간 등을 변화시켜가며 점성토 및 사질토 모형지반에 대하여 그라우팅을 실시하였다. 시험결과 공동현상(cavitation)을 적용한 경우 점성토 및 사질토 지반 모두 좋은 결과를 보여, 실제 공법에 적용가능성이 높은 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2929-2934
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• 2007

Prediction methods for cavitation noise are presented. At first, direct numerical simulation of cavitating flow noise has been performed, and acoustic analogy equation based on the cavitation noise modeling is derived. For the direct numerical simulation, a density based homogenous equilibrium model is employed to simulate cavitating two-phase flow and the governing equations are solved with high-order numerical schemes to resolve cavitation noise. The compressible Navier-Stokes equations for mixture fluids are discretized with a sixth-order central compact scheme, and the steep gradient of flow variables and supersonic regions are treated with the selective spatial filtering technique. The direct simulation of cavitating flow noise is performed for a 2D circular cylinder at cavitation number 0.7 and 1. The far-field noise is also predicted with the derived analogy equation. Noise spectrum predicted with the equation is well compared with the result of direct numerical simulation and also agree well with the theory.

• 대한조선학회논문집
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• 제46권2호
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• pp.105-113
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• 2009

A theoretical study on the pressure fluctuation induced by a propeller was carried out in this study. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller sheet cavitation. To analyze the pressure fluctuation induced by propeller sheet cavitation, modern acoustic theory was applied. Governing equation of pressure fluctuation induced by sheet cavitation was derived using Ffowcs Williams proposed time domain acoustic approaches. Several factors affecting pressure fluctuation were analyzed based on the derived governing equation. Pressure fluctuation result was represented by combined results of the far field term and near field term. Finally, the physical mechanism of pressure fluctuation at the blade rate frequency was analyzed using numerically generated cavitation volume variation.

• 대한조선학회논문집
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• 제44권2호
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• pp.101-110
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• 2007

Recently, rudder erosion due to cavitation frequently has occurred at large high speed container carriers. Especially, in the case of a horn-type rudder, the rudder erosion is severe around a gap. The gap-flow characteristics are investigated through a computational method to understand the effects of a gap on the cavitation and rudder efficiency. A viscous flow theory utilizing a cavitation model is applied to calculate the flow around idealized 2-dimensional rudder sections in a full scale. The effects of gap clearance and flow-control projection are also investigated. From the computational results, the mass flow rate through a gap is found to be one of the important parameters to affect the cavitation and rudder efficiency.

• Journal of Ship and Ocean Technology
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• 제12권2호
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• pp.32-40
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• 2008

This paper deals with the pressure fluctuation induced by propeller cavitation. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller cavitation. To analyze the source mechanism of the pressure fluctuation, modem acoustic theory is applied. The governing equation of the pressure fluctuation induced by propeller is derived using Ffowcs Williams-Hawkings proposed time domain acoustic method. The physical mechanism of pressure fluctuation at the blade rate frequency is analyzed using numerically generated cavitation volume variation. Finally the characteristics of the pressure fluctuation induced by a propeller are presented.

• 대한조선학회논문집
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• 제41권2호
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• pp.12-20
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• 2004

In this study, a linearized super-cavitation theory was applied in order to analyse the performance of the 2-dimensional foils. For flat plate with non-thickness, the numerical results correlated very well with Nishiyama's theoretical results for closed cavitation model. For plano-convex section, the numerical results correlated very well with Wade's experimental data. The new lifting surface procedure, developed and validated in this study, is generally considered applicable to the performance analyses of the super-cavitating propeller and trans-cavitating propeller.

• 대한조선학회논문집
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• 제50권6호
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• pp.436-449
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• 2013

In this paper, a numerical analysis is carried out to study the characteristics of supercavitating flows and the drag of relatively simple two-dimensional and axisymmetric bodies which can be used for supercavity generation device, cavitator, of a high-speed underwater vehicle. In order to investigate the suitability of numerical models, cavity flows around the hemispherical head form and two-dimensional wedge are calculated with combinations of three turbulence models(standard $k-{\epsilon}$, realizable $k-{\epsilon}$, Reynolds stress) and two cavitation models(Schnerr-Sauer, Zwart-Gerber-Belamri). From the results, it is confirmed that the calculated cavity flow is more affected by the turbulence model than the cavitation model. For the calculation of steady state cavity flows, the convergence in case of the realizable $k-{\epsilon}$ model is better than the other turbulence models. The numerical result of the Schnerr-Sauer cavitation model is changed less by turbulence model and more robust than the Zwart-Gerber-Belamri model. Thus the realizable $k-{\epsilon}$ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate supercavitating flows around disks, two dimensional $10^{\circ}$ and $30^{\circ}$ wedges. In case of the disk, the cavitation number dependences of the cavity size and the drag coefficient predicted are similar to either experimental data or Reichardt's semi-empirical equations, but the drag coefficient is overestimated about 3% higher than the Reichardt's equation. In case of the wedges, the cavitation number dependences of the cavity size are similar to experimental data and Newman's linear theory, and the agreement of the cavity length predicted and Newman's linear theory becomes better as decreasing cavitation number. However, the drag coefficients of wedges agree more with experimental data than those of Newman's analytic solution. The cavitation number dependences of the drag coefficients of both the disk and the wedge appear linear and simple formula for estimating the drag of supercavitating disks and wedges are suggested. Consequently, the CFD scheme of this study can be applied for numerical analysis of supercavitating flows of the cavitator and the cavitator design.

• Journal of Advanced Marine Engineering and Technology
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• 제34권5호
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• pp.718-724
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• 2010

공동수조와 예인수조에서의 프로펠러 단독특성 차이를 보정할 수 있는 위벽효과 연구를 수행하였다. 우선 공동수조의 실험에서 프로펠러의 상류가 아닌 작동 평면 위치에서 계측된 유속을 프로펠러 전진속도로 정의할 경우, 위벽효과의 수정 량 및 단독특성차이가 현저히 줄어드는 것을 확인하였다. 다음으로 양력판 이론에 의한 단독특성 계산을 통해, 프로펠러 평면에서의 위벽효과를 구하고 앞의 결과에 추가적인 보정을 수행하였다. 그 결과, 예인수조에서의 단독특성과 더욱 더 좋은 일치를 보여 주는 것을 확인하였다.