Gun-Do Kim

Application of High Order Panel Method for Improvement of Prediction of Marine Propeller Performance

A higher order panel method based on B-spline representation for both the geometry and the solution is developed for the analysis of steady flow around marine propellers. The self-influence functions due to the normal dipole and the source are desingularized through the quadratic transformation, and then shown to be evaluated using conventional numerical quadrature. By selecting a proper order for numerical quadratur e, the accuracy of the present method can be increased to the machine limit. The far- and near-field influences are shown to be evaluated based on the same far-field approximation, but the near-field solution requires subdividing the panels into smaller subpanels continuously, which can be effectively implemented due to the B-spline representation of t he geometry. A null pressure jump Kutta condition at the trailing edge is found to be effect ive in stabilizing the solution process and in predicting the correct solution. Numerical experiments indicate that the present method is robust and predicts the pressure distribution on the blade surface, including very close to the tip and trailing edge regions, with far fewer panels than existing low order panel methods. ※Keywords: B-spline(B-스플라인), High order panel method(고차패널법), Desingularization(비 특이화), Sub-division method(부분 분할법)

Numerical Calculation and Validation for Rudder Cavitation of a Large Container Ship

With the increase of ship size and speed, the loading on the propeller is increasing, which in turn increases the rotational speed in the propeller slipstream. The rudder placed in the propeller slip stream is therefore subject to severe cavitation with the increased angle of attack due to the increased rotational induction speed of the propeller. In the present paper the surface panel method, which has been proved useful in predicting the sheet cavitation on the propeller blade, is applied to solve the cavity boundary value problem on the rudder. The problem is then solved numerically by discretizing the rudder and cavity surface elements of the quadrilateral panels with constant strengths of sources and dipoles. The strengths of the singularities are determined satisfying the boundary conditions on the rudder and cavity surfaces. The extent of the cavity, which is unknown a priori, is determined by iterative procedure. Series of numerical experiments are performed increasing the degree of complexity of the rudder geometry and oncoming flows from the simple hydrofoil case to the real rudder in the circumferentially averaged propeller slipstream. Numerical results are presented with experimental results.

Development of the Driving Pump for the Low Noise Large Cavitation Tunnel

AbstractIt is reported to develop the driving pump for the Low Noise La rge Cavitation Tunnel(LOCAT) which is under construction at Maritime & Ocean E ngineering Research Institute(MOERI). For low background noise condition of the LO CAT, it is crucial not only the best pump efficiency but also no cavity occurrence at any operating conditions. Design condition of the pump is determined by considering the required pump headrise, flow quantity, shaft rotation velocity and pump diameter. Performanc e analysis of the pump is conducted using commercial CFD codes (BladeGen + , CFX-10), and the predicted results are verified by a series of model tests. Cavity was not observe d at any operating condition in the model test, which were conducted at the midium cavitation tunnel of MOERI. The optimum pump for LOCAT, named as LP-11, was successfully developed through a series of pump design processes composed of blade design, perfo rmance analysis and model test. ※Keywords: Driving pump(구동펌프), Low noise(저소음), Cavitation(캐비테이션), Required headrise(요구양정)

Wake Roll-up Modeling and Steady Hydrodynamic Analysis of Marine Propellers Using a B-Spline Based Higher-Order Panel Method

AbstractA numerical model for the analysis of the marine propeller incl uding wake roll-up is presented. In this study, we apply a higher-order panel method, which is based on a B-spine representation for both generations of the propeller ge ometry and hydrodynamic solutions, to predict the flow around the propeller blades. The present model is validated by comparison of the experimental measurements. The results show that the present method is able to predict the improved pressure distributions on the blad e surface, especially very close to propeller tip regions, where other panel methods witho ut the wake roll-up model give erroneous results. ※Keywords: B-spline(B-스플라인), Higher-order panel method(고차패널법), Propeller steady flow(프로펠러 정상유동), Propeller wake(프로펠러 후류), Wake roll-up(후류감김) 1. 서 론 Hess and Smith(1964)의 선구적인 연구 이후프로펠러 유동을 해석하기 위해 많은 종류의 포텐 접수일: 2008년 2월 19일, 승인일: 2008년 6월 19일✝교신저자: csleepro@cnu.ac.kr, 042-821-6623 셜 유동 해석법이 개발되어 널리 사용되고 있으며 현재 대부분의 해석법들은 속도 포텐셜을 기저로한 패널법을 사용하고 있다. Kerwin and Lee(1978), Hoshino (1989), Kim et al.(1993)은 정상 상태의 프로펠러 문제에 적용하였으며, Hsin(1990), Moon et al.(1994)은 비정상 프로펠

Noise Localization Method for Model Tests in a Large Cavitation Tunnel Using a Hydrophone Array

Model tests are performed in order to predict the noise level of a full ship and to control its noise signature. Localizing noise sources in the model test is therefore an important research subject along with measuring noise levels. In this paper, a noise localization method using a hydrophone array in a large cavitation tunnel is presented. The 45-channel hydrophone array was designed using a global optimization technique for noise measurement. A set of noise experiments was performed in the KRISO (Korea Research Institute of Ships & Ocean Engineering) large cavitation tunnel using scaled models, including a ship with a single propeller, a ship with twin propellers and an underwater vehicle. The incoherent broadband processors defined based on the Bartlett and the minimum variance (MV) processors were applied to the measured data. The results of data analysis and localization are presented in the paper. Finally, it is shown that the mechanical noise, as well as the propeller noise can be successfully localized using the proposed localization method.

A Study on Hydrophone Array Design Optimization for Cavitation Tunnel Noise Measurements

This paper proposes a hydrophone array design optimization technique for cavitation tunnel noise measurements. The optimization technique comprises of design parameters, an objective function and an optimization algorithm. The design parameters are defined for circular, spiral and multi-spiral arrays. The objective function is defined so as to consider the mainlobe beamwidth and the maximum sidelobe level simultaneously. A global optimization scheme is applied to the array design using very fast simulated reannealing (VFSR). After applying the optimization technique to arrays respectively, the peak sidelobe level and the mainlobe beamwidth of optimum arrays are analyzed. Finally the array patterns considering multiple reflections in the cavitation tunnel are evaluated to validate the proposed method.

PIV Measurements of Rudder Inflow Induced by Propeller Revolution in Hull Wake

In the present study, the flow fields in between the propeller and the semi-spade rudder are investigated by using PIV technique to find out the influences of both simulated hull wake and propeller wake on the incident flow to the rudder. The velocity fields are measured at the propeller rotation angle of and the rudder deflection angles of . Flow fields measured at each rudder deflection angle are analyzed in terms of angle-of-attack against the rudder leading edge. The hull wake increases the angle-of-attack more than that in the uniform inflow condition, forming the angle-of-attack of about at 0.7R(R

Numerical Analysis of Unsteady Cavitating Vortex around Two-dimensional Wedge-shaped Submerged Body

Unlike a slender body, vortices are shed off alternately in the wake of a blunt body. In the case of liquid flows, when the pressure falls below the vapor pressure, cavitation occurs in the vortex core and affects the formation of the vortex street. This phenomenon is of major importance in many practical cases because the alternate shedding of vortices creates imbalanced forces on the body. Hence, it is very important to determine the shedding frequency of cavitating vortices. In this paper, the unsteady cavitating flow around a two-dimensional wedge-shaped submerged body was simulated using the commercial code STAR-CCM+. A numerical investigation of the structure of cavitating vortices was performed for a model with an apex angle of 20°. The results were validated by comparing them with experimental measurements carried out at a cavitation tunnel of Chungnam National University (CNU-CT). It was found that the shedding frequency of the vortex increased by up to 18%, which was strongly affected by the development of cavitation. Received 19 December 2017, revised 18 January 2018, accepted 1 February 2018 Corresponding author Byoung-Kwon Ahn: +82-42-821-6625, bkahn@cnu.ac.kr, ORCID: https://orcid.org/0000-0002-0339-6069 It is noted that this paper is revised edition based on proceedings of SNAK 2017 in Yeosu c 2018, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Comparative Study of Full-Scale Propeller Cavitation Test and LCT Model Test for MR Tanker

선박의 대형화 및 고속화로 인한 추진기 및 방향타의 부하 증 가로 캐비테이션 발생량 증가, 이로 인한 효율감소, 선속 저하, 선체 기진력인 변동압력 증가, 추진기 및 타 표면 침식 증가, 수 중방사소음의 증가 등 고부가가치 선박개발에 복합적인 애로 기 술들이 나타나고 있다. 이러한 애로 기술을 해결하기 위해서는 축적된 경험과 정도 높은 실험자료를 기반으로 한 성능시험 평가 기법이 개발되어야 하며, 모형선-실선 상관관계를 파악할 수 있 는 선종별 실선 캐비테이션 실험 결과가 요구된다. 정도 높은 모형시험법 정립은 우선 정도 높은 실험자료 취득 이 필수적으로 요구되는 바, 모형선,추진기, 방향타, 부가물 등이 모두 설치되어 실선과 유사한 3차원 반류 재현이 가능한 대형캐 비테이션터널에서의 모형 실험이 필수적으로 요구된다. 선박해양 플랜트연구소(KRISO)가 보유한 ‘저소음 대형 캐비테이션터 널’(Low Noise Large Cavitation Tunnel, 이하 ‘LCT’로 칭함)은 지난 2009년도 후반기에 제작.설치 및 시운전이 완료되어 (Kim et al. 2009) 모형시험 단계에서 정도높은 실선성능 예측을 위한 시험기법 개발을 수행해 왔으며, 컨테이너선 및 LNG선 등의 실 선 변동압력 계측자료를 확보하여 모형선-실선 상관관계 정립을 위한 연구를 수행한 바 있다 (Kim et al. 2013, 2010). 모형선-실선 상관관계 정립을 위해 컨테이너선 및 LNG선 외 에 다른 선종의 실선 캐비테이션 시험 자료 확보가 요구된 바, 국내 조선소에서 건조중이었던 MR Tanker선을 대상으로 실선 캐비테이션관찰, 변동압력 계측 및 수중방사소음을 계측하였다. 실선프로펠러 캐비테이션 시험을 위한 관련 기술인 관측창 선정 을 위한 3차원 선체형상 분석기술, 관련 치구 설계 및 제작기술, 캐비테이션 촬영 및 변동압력 계측기술 등은 함정 프로펠러를 대 상으로 개발이 된 바 있으며(Ahn et al. 2012), 개발된 기술을 대 상선에 적용하여 일련의 실선 캐비테이션 실험을 수행하였다. 또 한 모형선을 제작하여 LCT에 설치하고 실선 캐비테이션 시험을 pISSN:1225-1143, Vol. 53, No. 3, pp. 171-179, June 2016

Performance Trial-Test of the Full-Scale Driving Pump for the Large Cavitation Tunnel(LCT)

The objective of the present study is to analyze the results of the trial-test for the full-scale driving pump, which is arranged in the LCT (Large Cavitation Tunnel). Firstly, the reasons of selecting the final design pump are introduced in terms of the performance analysis in model tests. The trial-test items for the full-scale driving pump are measurements of output current/voltage at the inverter of the main motor and the flow velocity in the LCT test section. The test results show the increase in flow rate of about 10.7% and the decrease in pump head of about 26%, compared with those of final design-pump specification. The motor power has the margin of about 22%. The performance analysis for the full-scale pump is conducted using the commercial code (CFX-10). The delivered power calculated with CFX-10 shows good agreement with that extracted from the full-scale pump test. It is found that CFX-10 is useful to analyze a full-scale pump.