Stern Hull Form Research Articles

Development of a small-sized tanker with reduced greenhouse gas emission under in-service condition based on CFD simulation

In the present study, the hull form and appendage of a 6.5 k DWT tanker was improved to reduce greenhouse gas emissions in the in-service navigation condition. The conventional hull form of the 6.5 k DWT tanker has been designed in terms of performance in the ideal condition of a calm-sea. On the contrary, the performance of a ship in the in-service condition should take the added resistance due to wind and waves in the real sea into consideration. In order to reduce the added resistance due to waves, the bow hull form was modified to have a sharper entrance with increased length between perpendiculars. This was intended to ensure that the waves follow the curved bow surface more smoothly, thereby reducing the added resistance due to waves. The stern hull form was also modified to have V-shaped section shapes to reduce viscous pressure resistance. In addition, the flow control fins were optimized in terms of position and angle of attack. The added resistance of the resulting hull form was then analyzed numerically in regular wave with a varying wavelength ratio λ/Lpp=0.5∼2.0. The added resistance in regular waves was subsequently integrated with respect to the wavelength to obtain the added resistance in irregular waves. Finally, by combining it with the sea state occurrence probability, the daily fuel oil consumption (DFOC) was able to be calculated for the actual in-service routes for the tanker. The entire process of hull form modification and evaluation was conducted with free-surface CFD simulation in the presence of regular waves. A series of model tests was undertaken to confirm the improvements of the optimal hull form over the original in terms of performance in waves as well as calm-sea performance. The resulting DFOC and daily CO2 emissions for the optimal hull form in the in-service conditions was found to be reduced by 14.8%. Furthermore, the calm-sea DFOC and CO2 emissions were also improved by 15.6%.

Investigating the Performance of a Ship by Matching the Stern Hull Form to Propeller and Engine Power

Designing the form of the ship stern hull could have some impacts on the efficiency of ship propeller and the requirement of the ship speed. Therefore, stern hull form of a ship matched to its propeller and engine power is important consideration in preliminary ship design stage. The main objective of this study is to investigate ship performance by matching the stern hull shape to the propeller diameter and engine power toward high speed. This study was conducted by free running model test and Maxsurf Resistance application. The stern forms were employed U-shape and V-shape. In addition, the fixed pitch propeller (FPP) with three blades was used and the diameter is varied into three sizes 0.032 m, 0.040 m, and 0.048 m. The results show the increase of propeller diameter increases model’s speed for both U-shape and V-shape stern and the effect of the propeller diameter on the speed could be described by using the equations of second-order polynomial. The optimum propeller diameter could be determined taking into account stern hull form, stern shape, tip clearance, and proper speed where then propeller diameter related to draft is given by 0.79T with tip clearance 10%Dp for both U-shape and V-shape. The ship resistances of U-shape stern at Fr 0.221 and V-shape at 0.208 are obtained approximately 89.797 KN and 77.10 KN respectively. Furthermore, the powers of ship for both U-shape and V-shape at those Fr are obtained 904,374 KW and 726,807 KW respectively. Finally, the best stern hull form matched to propeller diameter and engine power is selected and given by U-shape stern.

Hydrodynamic Design Study on Ship Bow and Stern Hull Form Synchronous Optimization Covering Whole Speeds Range

The main objective of this article is to describe an innovative methodology of synchronous local optimization which considers the whole ship speed range being presented for a KRISO Container Ship (KCS). Parametric form approaches are adopted by employing a fairing B‐spline curve in order to generate variants of the bow and stern of forms using form design parameters modified, resulting in an optimization system based on NSGA‐II. The total resistance is calculated by the Rankine source panel method and the empirical formula which agrees well with the corresponding experimental data and further acquires validation with the overall error of 2.0%. Accordingly, the ship forepart and stern form have been optimized under conditions of the single design speed and whole speeds range based on the considerations of generally distributed and variable operational speeds for the operating characteristics of modern container ships synchronously. The optimized result presents well‐balanced drag reduction benefits which averagely remain above 4.0% of ship resistance decrease. Compared to the traditional optimization process which is based on a specific design speed, the newly developed method is more practical and effective in both automation and integration.

Prediction Method for Linear Maneuvering Hydrodynamic Derivatives Using Slender Body Theory Based on RANS

It is important to predict the hydrodynamic maneuvering derivatives, which consist of the forces and moment acting on a hull during a maneuvering motion, when estimating the maneuverability of a ship. The estimation of the maneuverability of a ship with a change in the stern hull form is often performed at the initial design stage. In this situation, a method that can reflect the change in the hull form is necessary in the prediction of the maneuverability of the ship. In particular, the linear hydrodynamics maneuvering derivatives affect the yaw checking motion as the key factors. In the present study, static drift calculations were performed using Computational Fluid Dynamics (CFD) based on Reynolds Average Navier-Stokes (RANS) for a 40-segment hull. A prediction method for the linear hydrodynamic maneuvering derivatives was proposed using the slender body theory from the distribution of the lateral force acting on each segment of the hull. Moreover, the results of a comparison study to the model experiment for KVLCC1 performed by KRISO are presented in order to verify the accuracy of the static drift calculation. Finally, the linear hydrodynamic maneuvering derivatives obtained from both the model test and calculation are compared and presented to verity the usefulness of the method proposed in this study.

An Optimization Method of Stern Hull Form to Minimize Brake Horse Power (2nd Report)

This is the second report of hull form optimization to minimize Brake Horse Power (BHP). In the previous report, two hull form optimization techniques, Sequential Quadratic Programming (SQP) and Surrogated-Based Optimization (SBO), for minimizing BHP were proposed, and it was shown that the optimization methods are effective for obtaining high performance hull forms. Recently most of ships are equipped Energy Saving Device (ESD) to improve their performance. Some ESDs have energy saving effect of over 5%. However their effect is strongly dependent of a shape of a main hull. Similarly dimensions of a propeller are dependent of a shape of a main hull. Therefore hull form optimization considering ESD effect and propeller design is necessary for total BHP reduction.

BHP最小化を目的とした船尾船型最適化手法（第1報）

BHP最小化を目的とした船尾船型最適化手法（第1報）

Study on the Manoeuvrability as Function of Stern Hull Form in Shallow Water

A numerical simulation studies were performed to investigate a manoeuvring characteristics as function of stern hull form with the mathematical model. In order to consider the effect of the stern hull form and obtain the manoeuvring characteristics, a parameter( ) which is aft. water plane area coefficient is modified. Because modifying  (± ) means that the stern hull form is modified to V-type or U-type, the numerical simulation was performed with this modified  . A changing trend for the manoeuvring characteristics not only in deep water but also in shallow water such as directional stability, turning and zig-zag was investigated and presented as the results. Present study showed that the manoeuvrability in shallow water largely changed when the draught and water depth ratio(=d/H) become 0.5, and the stern hull form can affect to the manoeuvrability of a vessel navigating in restricted water depth. In addition, it showed that approaching the stern hull to U-type makes the advance and tactical diameter of turning motion large and the overshoot angle of zig-zag motions small. Otherwise, it showed approaching the stern hull form to V-type makes the advance and tactical diameter of turning motion small and the overshoot angle of zig-zag motions large in the present study.

Hull-form optimization of KSUEZMAX to enhance resistance performance

This paper deploys optimization techniques to obtain the optimum hull form of KSUEZMAX at the conditions of full-load draft and design speed. The processes have been carried out using a RaPID-HOP program. The bow and the stern hull-forms are optimized separately without altering neither, and the resulting versions of the two are then combined. Objective functions are the minimum values of wave-making and viscous pressure resistance coefficients for the bow and stern. Parametric modification functions for the bow hull-form variation are SAC shape, section shape (U-Vtype, DLWL type), bulb shape (bulb height and size); and those for the stern are SAC and section shape (U-Vtype, DLWL type). WAVIS version 1.3 code is usedfor the potential and the viscous-flow solver. Prior to the optimization, a parametric study has been conducted to observe the effects of design parameters on the objective functions. SQP has been applied for the optimization algorithm. The model tests have been conducted at a towing tank to evaluate the resistance performance of the optimized hull-form. It has been noted that the optimized hull-form brings 2.4% and 6.8% reduction in total and residual resistance coefficients compared to those of the original hull-form. The propulsive efficiency increases by 2.0% and the delivered power is reduced 3.7%, whereas the propeller rotating speed increases slightly by 0.41 rpm.

Design practice for the stern hull form of a twin-skeg ship

Hydrodynamic standards have been derived for the improvement of propulsive performance of twin-skeg hull forms. Three important physical observations were used in the optimization of design practice for the stern hull form of twin-skeg ships: limiting streamline pattern on the inner and outer skeg surface of a stern skeg, the balance between the flow intensity over the inner and outer skeg surface of a stern skeg and nominal wake distribution in the propeller plane. Numerical calculations and model tests have been compared to validate a CFD code used in the current work. Based on the stern flow analysis for the evaluation of self-propulsion performance, effects of stern skeg arrangement on the propulsion efficiency, i.e. the distance between skegs and the angle of the skeg with respect to shaft centerline, were intensively investigated. An optimized hull form design for a twin-skeg ship was developed using the design practice derived in this work.

쌍축 컨테이너선의 선미선형 변화에 따른 유동 특성에 대한 수치해석

Numerical analysis for flow characteristics of a twin skeg container ship was carried out according to skeg vertical angles(<TEX>$0^{\circ}$</TEX>, <TEX>$10^{\circ}$</TEX>, <TEX>$20^{\circ}$</TEX>) and skeg distances(16m, 20m, 24m) by using a commercial CFD code, FLUENT. Computed: pressure distributions, wake distributions and resistance coefficients have been compared with experimental and WAVIS results carried out by MOERI. Flow characteristics from numerical analysis such as nominal wake fractions, wake distribution and directions of the transverse vectors give good agreement with WAVIS results, even though there are quantitative discrepancy comparing with experimental measurements at the propeller plane. It is found that the better resistance performance can be obtained with the increase of the skeg vertical angle and the decrease of the skeg distance, which are mainly caused by viscous pressure resistance due to the skeg form and pressure recovery around the skeg. In addition, a vertical angle of the skeg gives more effect to the resistance coefficient comparing with the skeg distance. On the basis of results of the present study, it shows that numerical analysis using the commercial code, FLUENT, is useful and efficient tool for the evaluation of the complex stern hull form with twin-skegs.

뉴로퍼지시스템에 의한 반류분포 추정에 관한 연구

프로펠러 회전면에서의 반류분포는 주로 모형시험에 의해서 규명되어 왔다. 이렇게 축적된 데이터베이스를 통해 선박의 기하학적 형상정보와 반류분포 사이의 입출력관계를 모델링할 수 있다면 선박 초기설계시 유사선종의 설계에 도움이 된다. 뉴로퍼지시스템은 예측, 분류, 진단 등의 매우 복잡한 문제를 해결하는 기법으로 다양한 공학분야에서 응용되고 있다. 본 연구에서는 이들 입출력 사이의 관계를 뉴로퍼지시스템으로 모델링하고 학습한 후 새로운 입력에 대한 출력값의 검토를 통해 그 유용성을 확인한다. 3차원 선미형상을 입력으로 하고 선체 모형시험으로 얻어진 프로펠러 회전면에서의 반류분포 값을 출력으로 사용하여 학습 및 추론을 해 보았다. 이를 통해 뉴로퍼지시스템을 초기 선박설계 단계에서 특히 선미형상을 결정할 때 유용한 것을 확인하였다. Wake distribution data of stem flow fields have been accumulated systematically by model tests. If the correlation between geometrical hull information and wake distribution is grasped through the accumulated data, this correlation can be helpful to designing similar ships. In this paper, Neuro-Fuzzy system that is emerging as a new knowledge over a wide range of fields nowadays is tried to estimate the wake distribution on the propeller plan. Neuro-Fuzzy system is well known as one of prospective and representative analysis method for prediction, classification, diagnosis of real complicated world problem, and it is widely applied even in the engineering fields. For this study three-dimensional stern hull forms and nominal wake values from a model test ate structured as processing elements of input and output layer, respectively. The proposed method is proved as an useful technique in ship design by comparing measured wake distribution with predicted wake distribution.

Wake distribution prediction on the propeller plane in ship design using artificial intelligence

In this study, a new neuro-fuzzy technique is applied to estimate the wake field distribution on propeller plane of ship. The wake distribution data of stern flow fields have been collected systematically by model tests of ship. When a correlation between geometrical hull information and wake distribution of ship is grasped through the collected data, the obtained correlation can be helpful in designing similar kinds of ships. Characteristics of the wake distribution by the change of stern hull form can be figured out easily by using a neuro-fuzzy system with the collected data. The neuro-fuzzy technique is applied to the ship designing, which is well known as one of the prospective methods for prediction, classification and diagnosis of real complicated problems. To prove the proposed method, three-dimensional stern hull forms and nominal wake values from a model test are structured as processing elements of input and output layers, respectively. In order to embody three-dimensional hull forms in a neuro-fuzzy system at the same time to avoid excessive increase in the input data, angle values of certain points of the hull form are used to avoid excessive increase in the input data and simultaneously in order to embody three-dimensional hull form in a neuro-fuzzy system. This method proved satisfactory in obtaining safe predictive results. The results from this study may give advanced information to hull form designers for evaluation and optimization of stern hull form by predicting a ship wake distribution at the initial designing stage.

Studies on the optimization of stern hull form based on a potential flow solver

A hypothesis of the minimum energy of secondary flow, suggested by Bessho, is introduced here. According to this hypothesis, it can be expected that hull forms having frame lines with a minimum energy of secondary flow show less form drag. In the first part of this article, secondary flow energy is evaluated for the cases with and without a free-surface effect, and Bessho’s hypothesis is confirmed for practical hull forms. Then optimization methods for the stern hull form are suggested, in which a nonlinear optimization technique is introduced. Numerical examples are given for a practical tanker hull form and a practical container hull form. From these studies, the suggested optimization method can be confirmed as a simplified and practical design method to the select frame lines of stern hull forms.

Wave Resistance Prediction Of A CatamaranBy Linearised Theory

The far field wave system and far field wave coefficients (Eggers coefficients) of a Kelvin source are presented using linearised theory including the effects of a canal depth and width. The wave resistance due to the distribution of such sources is derived using a far field wave energy approach. The trim and sinkage effects of the hull have been included by supplying the dynamic hull surface in the calculation scheme. The effect of transom stem has also been investigated by alternative methods. The developed code has been tested on a mathematically defined hull form and a series of high speed transom stern hull forms. Catamarans with separation ratios of 0.2 to 0.5 are used in the comparisons of the method with experimental results.

A short account of the theory of lubrication. III. dimensional theory, with applications

This paper deploys optimization techniques to obtain the optimum hull form of KSUEZMAX at the conditions of full-load draft and design speed. The processes have been carried out using a RaPID-HOP program. The bow and the stern hull-forms are optimized separately without altering neither, and the resulting versions of the two are then combined. Objective functions are the minimum values of wave-making and viscous pressure resistance coefficients for the bow and stern. Parametric modification functions for the bow hull-form variation are SAC shape, section shape (U-Vtype, DLWL type), bulb shape (bulb height and size); and those for the stern are SAC and section shape (U-Vtype, DLWL type). WAVIS version 1.3 code is usedfor the potential and the viscous-flow solver. Prior to the optimization, a parametric study has been conducted to observe the effects of design parameters on the objective functions. SQP has been applied for the optimization algorithm. The model tests have been conducted at a towing tank to evaluate the resistance performance of the optimized hull-form. It has been noted that the optimized hull-form brings 2.4% and 6.8% reduction in total and residual resistance coefficients compared to those of the original hull-form. The propulsive efficiency increases by 2.0% and the delivered power is reduced 3.7%, whereas the propeller rotating speed increases slightly by 0.41 rpm.