Dong-Min Park

Systematic Experimental and Numerical Analyses on Added Resistance in Waves

국제적으로 친환경에 대한 관심이 증가하고, 국제해사기구 (International Maritime Organization, IMO)가 선박의 온실가스 방출을 규제하기 위해서 2013년부터 선박연비제조지수 (Energy Efficiency Design Index, EEDI)를 도입하면서 조선 및 해운업계 에서는 선박의 운항 효율이 주요 관심사가 되었다. 선박의 운항 효율을 향상시키기 위한 많은 방법 중에 하나로 파랑 중 저항을 감소시키는 방법이 고려되고 있다. 부가저항이란 선박이 실제 해 상에서 운항하는 경우 바람이나 파랑에 의해 정수 중 저항보다 증가하는 저항을 말하며, 이러한 부가저항은 선박에 따라서 정수 중에서 운항하는 경우의 저항보다 15~30%까지 커지는 경우도 있다. 따라서 부가저항을 정확히 예측하고 이를 효과적으로 감소 시키고자 하는 연구들이 수행되고 있다. 본 논문에서는 최근 수행되었던 부가저항의 예측을 위한 수조 실험 및 수치계산 기법에 대한 연구들에 대하여 체계적으로 살펴 보고, 그 결과들을 비교하여 여러 기법들에 대한 검증과 장단점, 그리고 실선 적용에 대한 활용성 등을 다루고자 한다. 파랑 중 부가저항의 추정을 위해 실험 및 수치적 연구는 1970~1980년대에 많이 수행이 되었으나 한동안 주목을 받지 못 하다가 최근 그린쉽에 대한 관심이 고조되며 근래들어 여러 연구 들이 수행되고 있다. 부가저항의 초기 연구는 실험에 기반하여 진행되었다. 부가저항 실험은 1970년대부터 Series 60 선형 (Gerritsma & Beukelman, 1972; Storm-Tejsen, et al., 1973), S175 컨테이너선 모델 (Fujii & Takahashi, 1975; Nakamura & Naito, 1977), Wigley 모델 (Journee, 1992) 등에 대한 연구가 진행되었다. 최근 Kuroda, et al. (2011)은 컨테이너선 기본선형 을 기준으로 선수부의 형상을 다양하게 변화시켜가면서 이에 따 른 부가저항 변화를 살펴보았다. 또한, Lee, et al. (2013)도 최 pISSN:1225-1143, Vol. 51, No. 6, pp. 459-479, December 2014

Quantitative and qualitative analyses of parametric roll for ship design and operational guidance

This article presents a procedure for quantitatively analyzing the susceptibility of a ship to parametric roll for use in designing a ship against this phenomenon. Due to the nonergodic characteristics of parametric roll motion, numerous direct time-domain simulations are needed to obtain a stable long-term distribution of parametric rolls. To avoid such heavy computational demand and to accelerate numerical simulations, a 1-degree-of-freedom computational model for parametric roll prediction is developed for both regular- and irregular-wave excitations, adopting the approximated righting arm ( GZ ) curve. In this model, the concept of transfer functions is introduced for the mean and the first harmonic component of metacentric height ( GM ), which is introduced to approximate GM fluctuation. The simulation results obtained by using this model are compared to those of a three-dimensional weakly nonlinear simulation program. The sensitivity of the simulation results to the initial value, time window, and number of simulations is investigated, and their proper values are proposed. Using the proposed model, the long-term predictions of parametric roll are carried out for typical post-Panamax container ships and a very large crude oil carrier by applying Monte Carlo simulation. Based on the simulation results, the susceptibility of each ship to parametric roll is evaluated, and the influence of still-water GM on the susceptibility is investigated. This study extends to the development of an operational guidance for the ship crew’s decision-support system, as one of countermeasures of a severe parametric roll. Particularly, a procedure for qualitatively developing an operational guidance is proposed. In this study, numerical simulations are carried out by using an impulse–response function approach. As an example model, a typical 10,000 TEU container ship is considered, and the results are discussed with respect to its operation.

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.

Experimental investigation on the added resistance of modified KVLCC2 hull forms with different bow shapes

The effect of different bow shapes on the added resistance in waves was observed through a series of model tests. To this end, three different hull forms of KRISO Very Large Crude Carrier 2 were considered: an original hull form and two modified hulls with different bow shapes, called ax-bow and leadge-bow. The model tests were conducted for a wide range of wavelengths with two wave amplitudes in a regular head-sea condition at the design speed. Each test condition was imposed at least twice in order to check the repeatability of measurement, considering the uncertainties in model test and the nonlinear nature of the added resistance. This article introduces a preliminary study on the effects of surge motion, amplitude of incident wave, and green-water allowance around bow region. This article briefly includes the uncertainty analysis of recent study regarding the performance of the original hull. Based on the results of the experimental study for three different bow shapes, the parameters which influence the added resistance and motion responses are discussed.

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

Effect of internal sloshing on added resistance of ship

The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This means the added resistance in waves may change when sloshing occurs inside the tank of the ship. In this study, the motion responses and added resistance of a ship, coupled with the sloshing-induced internal forces and moments are considered by using the linear potential theory. The three-dimensional Rankine panel method, in which the physical quantities are represented by using B-spline basis function, is applied. The sloshing flow of inner tanks is also simulated by using the Rankine panel method and linearized boundary value problem. To study the added resistance, a near-field method, which integrates the second-order pressure on a body surface, is applied. The model ship is a blunt modified Wigley model with two inner tanks. Numerical results obtained without inner tanks are compared with the experimental data, and then the effect of filling ratio of inner tanks on ship motion and added resistance are observed. The components that induce added resistance are examined, and the effects of surge motion on sloshing flow and added resistance are briefly considered. This study shows that the sloshing flow inside the inner tanks may significantly influence not only the motion responses, but also added resistance, especially, when the incident wave frequency approaches the resonance frequency of the sloshing flow.

Load mapping for seamless interface between hydrodynamics and structural analyses

Abstract This paper addresses the problem of a seamless interface between hydrodynamics and structural analyses. A pressure distribution on a hydro model computed from seakeeping analysis needs to be transferred to a structural model for evaluating structural strength and its integrity. However, due to the differences in the computation and representation methods for both analyses, the load on the hydro model may not be correctly transferred to the structural model, leading to a different load distribution on the structural model and resulting in some unbalanced force and moment components. In this paper, a method is proposed to solve this problem. A pressure distribution on the hydro model is mapped on the structural model through projection, and force and moment imbalances on the structural model are eliminated through optimization of the nodal forces on the structural model. Moreover, a viscous force distribution along the center of each member of the hydro model is transferred to the nodal forces on the structural model based on the minimum distance measure with resolving any force and moment imbalance. Examples are presented to demonstrate the validity of the proposed method.

Study on Numerical Sensitivity and Uncertainty in the Analysis of Parametric Roll

This study considers the numerical analysis on parametric roll for container ships. As a method of numerical simulation, an impulse-response-function approach is applied in time domain. A systematic study is carried out for the parametric roll of two container ships, particularly observing the sensitivity of computational results to some parameters which can affect the analysis of parametric roll. The parameters to be considered are metacentric height (GM), simulation time window, and the discretization of wave spectrum. Based on the result of parametric roll simulation, numerical sensitivity and uncertainty in computational analysis are discussed.This study considers the numerical analysis on parametric roll for container ships. As a method of numerical simulation, an impulse-response-function approach is applied in time domain. A systematic study is carried out for the parametric roll of two container ships, particularly observing the sensitivity of computational results to some parameters which can affect the analysis of parametric roll. The parameters to be considered are metacentric height (GM), simulation time window, and the discretization of wave spectrum. Based on the result of parametric roll simulation, numerical sensitivity and uncertainty in computational analysis are discussed.