Kyong-Hwan Kim

Development of panel generation system for seakeeping analysis

Abstract In this paper, a panel generation system for analyzing seakeeping performance of a ship is developed. Given a set of offset data representing the ship hull, the system first creates a surface model of the ship. From the surface model, the wetted part of the ship is obtained by computing the intersection between the water surface and the hull, which is then processed to generate quadrilateral panels for the hull and the water surface. The system is designed to handle various kinds of ships such as ships with a mono-skeg, a twin-skeg and/or a bulbous bow in either an automatic or an interactive manner. Moreover, it can generate input panels for three different seakeeping analysis methods. Examples are provided to demonstrate the capabilities of the system.

Numerical Analysis of Added Resistance on Ships by a Time-domain Rankine Panel Method

Abstract This paper considers the numerical computation of added resistance on ships in the presence of incident waves. As a method of solution, a higher-o rder Rankine panel method is applied in time domain. The added resistance is evalu ated by integrating the second-order pressure on the body surface. Computational result s are validated by comparing with experimental data and other computational results on a hemi-sphere, a barge, Wigley hull models, and Series 60 hull, showing very fair agreements. The study is extended to the comparison between Neumann-Kelvin and double-body linearization approaches, and their differences are discussed. ※Keywords: Aedded resistance(부가저항), Time-domain analysis(시간영역해법), Rankine panel method(랜킨패널법) 1. 서론 선박은 정수 중에서의 조파저항과 점성저항 외 에도 바람이나 파랑 등으로 인해 실제 해상에서 추가적으로 부가저항을 받으며 운행한다. 갑판 위 구조물이 크지 않은 대부분의 상선들은 접수일: 2009년 11월 5일, 승인일: 2010년 5월 7일 교신저자: yhwankim@snu.ac.kr, 02-880-9226 주로 파랑에 의한 부가저항을 크게 받는데, 부가저항은 경우에 따라 선박이 정수 중 운행 하는 경우의 저항보다 15~30%까지 커지는 경우도 있어 선박의 추진장치 설계를 위해 이를 정확히 예측하는 것은 상당히 중요하다. 부가저항에 대한 연구는 오래 전부터 수행되었는데, Storm-Tejsen et al.(1973)과 Journee(1992) et al.은 파랑 중 Wigley 선박이나 Series 60 선박에 대한 부가저항 측정 실험을 수행한 적이 있다. 해석적 방법은

Comparative Study on Added Resistance for Different Hull Forms by using Weakly-Nonlinear Seakeeping Formulations

Recently, the design of commercial ships with less green-house gas is one of great interests in naval architecture fields. Ship designers are asked to find optimum hull forms with minimum resistance in ocean waves. The accurate computation of added resistance, therefore, is getting more important for the prediction of power increase in random ocean waves. This study focuses on the numerical computation of added resistance on ships with Ax-bow shapes which are designed to reduce added resistance. To this end, the time-domain Rankine panel methods based on weakly-nonlinear and weak-scatterer approaches are applied, which can reflect the influence of above-still-water bow shape. As computational models, KCS and KVLCC2 hull forms are considered. Each ship is combined with the three types of Ax-bow shape, and computational results are compared each other.

Detent Force Minimization of Permanent Magnet Linear Synchronous Machines Using Subdomain Analytical Method Considering Auxiliary Teeth Configuration

This paper presents electromagnetic modeling and analysis of the detent force in a permanent magnet linear synchronous machine (PMLSM) according to auxiliary teeth configuration. Analytical solutions for magnetic fields generated by PMs are derived based on the Maxwell equation in terms of a 2-D Cartesian coordinate system. The magnetic vector potential of each subdomain (PM, air-gap, slot, and end region) is derived, and the field solution is obtained by applying the boundary and interface conditions between the subdomains. Based on the analytical solution, the magnetic force is derived by using the Maxwell stress tensor. All the analytical results were extensively validated using nonlinear finite-element analysis and experimental results. Using the proposed method, we investigated the influence of the machine parameters on the detent force. Therefore, the proposed method can be very useful in the initial design and optimization process of PMLSM for detent force analysis.

Statistical analysis of sloshing-induced random impact pressures

This article presents the statistical analysis of sloshing-induced random impact pressure. To obtain the pressure signal, three-dimensional sloshing model tests were conducted at two different filling depths. Several different methods were applied to identify sloshing peaks and to define the rise and decay times of the peak pressure signals. Statistical properties acquired from these methods were compared, and their consistency and/or discrepancy were observed. In addition, 200-h duration test data were acquired by running forty 5-h tests under each test condition. Based on the long-duration test data, the uncertainty of the test results with respect to the test duration was studied using the bootstrap method.

Study on the Effect of Density Ratio of Gas and Liquid in Sloshing Experiment

This paper presents the results of sloshing experiments having different fluids in model tanks with various density ratios. The experimental model consisting water and air at ambient, which has been commonly used, is not consistent in density ratio with that of an actual LNG cargo tank. Therefore, an advanced experimental scheme is developed to consider the same density ratio of LNG and NG by using a mixed gas of sulfur hexafluoride () and nitrogen (). For experimental observation, a two-dimensional model tank of 1/40 scale and a three-dimensional model tank of 1/50 scale have been manufactured and tested at various conditions. Two different fillings with various excitation frequencies under regular motions have been considered for the two-dimensional model tank, and three different filling levels under irregular motions have been imposed for the three-dimensional model tank. The density ratio between gas and liquid varies from the ratio of the ambient air and water to that of the actual LNG cargo container, and the different composition of gas is used for this variation. Based on the present experimental results, it is found that the decrease of sloshing pressure is predicted when the density ratio increases.

Analysis of Added Resistance: Comparative Study on Different Methodologies

This paper considers the comparative study on added resistance for different methodologies. An accurate prediction of added resistance and resultant power increase becomes an important issue in greenship design. There are several methodologies for the prediction of added resistance, and most of them are based on frequency domain approaches such as slender-body theory or wave Green-function approach. As the time-domain approaches becomes an alternative method for seakeeping analysis, the time-domain approaches are also applicable for added resistance prediction.In this paper, a few approaches have been applied for the prediction of added resistance on different hull forms. The methods to be considered in this study are (i) slender-body method, (ii) Rankine panel methods, (iii) Cartesian-grid-based Euler solver, and (iv) short-wave approximations. Both the far- and near-field formations are considered in the slender-body and Rankine panel methods, while the direct pressure integration is applied for the CFD method. The computational results are validated by comparing them with experimental data on Wigley hull, Series 60 hull, and S175 containership, showing reasonable agreements for all models. The study is extended to the analysis of added resistance in short wavelengths.© 2013 ASME

Time-Domain Analysis on Motion Response of Adjacent Multiple-Bodies in Waves

AbstractThis study considers the motion response of multiple adjacent f loating bodies in waves. As a method of solution, a three-dimensional Rankine panel method is adopted in time domain. For the validation of the developed numerical method, the motions of two adjacent Series 60 hulls and ship-barge model are estimated. The computa tional results are compared with other numerical and experimental analyses, showin g favorable agreement. ※Keywords: Multiple-body problem(다중 물체 문제), Rankine panel method(랜킨 패널법), Time domain(시간 영역), Ship motion problem(선박 운동 문제) 1. 서 론 다중 물체 문제는 해상 상태에서 근접하여 운동하는 여러 물체에 대하여 각 물체에 작용하는 힘과 운동을 다루는 문제를 말한다. 이러한 문제는 특히 해양 분야에서 다중 물체로 이루어진 구조물이나 근접한 위치에 있는 해양구조물과 선박의 운동과 관련하여 연구가 이루어져 왔다. 최근에는 석유의 대체 에너지로서 천연가스의 개발과 더불어 액화천연가스 부유식 생산저장하역설비(LNG-FPSO) 등이 개발되면서 생산설비로부터 접수일: 2007년 6월 3일, 승인일: 2007년 12월 26일✝교신저자 : yhwankim@snu.ac.kr, 02-880-9226 액화천연가스 운반선으로의 하역 시에 생산설비와 운반선 사이의 운동이 중요한 문제로 부각되었고 이와 관련한 연구들이 진행되고 있다.다중 물체 문제는 2차원 다중 실린더 물체에 대한 연구로부터 시작되었다(Ohkusu 1974). 초기의 연구는 주로 스트립 이론(strip theory)에 근거한 해석이 이루어졌으며 바지선과 선박 사이의 운동을 계측하는 실험 등이 수행되었다(Kodan 1984, Fang and Kim 1986). 컴퓨터 계산 용량이 늘어나면서 파랑그린함수(wave Green function, WGF)나 통합 이론(unified theory)을 이용하여 선박과 선박 사이의 운동을 계산하는 연구가 수행되었으며(Ahn and Rhee 1987, Fang and Chen 2002, Choi and Hong 2002, Kim and Ha 2002,

Numerical stability of Rankine panel method for steady ship waves

Abstract This article considers the stability of the Rankine panel method associated with ship resistance problem. This method has been widely applied for the prediction of resistance on ships. This study explains the sensitivities of computational parameters, particularly desingularized height and the distance of collocation-point shift, on the computation of wave pattern around ships and the effects on ship resistance. The computations were carried out for three different ship models: Wigley hull, Series 60 hull, and trimarans. This study shows that the stability analysis introduced by Kim and Yue for uniform panels without a body is also valid for wave patterns around ships, predicted using non-uniform panels. The wave patterns obtained using constant panel method show a significant sensitivity to the computational parameters. In general, the use of constant singularity panel predicts wavelengths shorter than exact solution, and desingularization can mitigate such problem. The upstream shift of collocation points results in numerical damping. Despite the success of the analytic explanation of wave patterns, the effect on wave resistance seems more complicated and dependent on ships. It is obvious that ship resistance is very sensitive to the computational parameter.

A Study on the Numerical Methodologies of Hydroelasticity Analysis for Ship Springing Problem

Abstract Numerical methodology to solve ship springing problem, which is basically fluid-structure interaction problem, was explored in this study. Solution of this hydroelasticity problem was sought by coupling higher order B-spline Rankine panel method and finite element method in time domain, each of which is introduced for fluid and structure domain respectively. Even though varieties of different combinations in terms of numerical scheme are possible and have been tried by many researchers to solve the problem, no systematic study regarding the characteristics of each scheme has been don e so far. Here, extensive case studies have been done on the numerical schemes especially focusing on the iteration method, FE analysis of beam-like structure, handling of forward speed problem and so on. Two different iteration scheme, Newton style one and fixed point iteration, were tried in this study and results were compared between the two. For the solution of the FE- based equation of motion, direct integration and modal superposition method were compared with each other from the viewpoint of its efficiency a nd accuracy. Finally, calculation of second derivative of basis potential, which is d ifficult to obtain with accuracy within grid-based method like BEM was discussed.