Original Hull Form Research Articles

Study on the Manoeuvring Performance of a Fishing Vessel Based on CFD Simulation of the Hull Forms and Rudder Shapes

To evaluate manoeuvring performance of merchant ships, the mathematical modeling group (MMG) or computational fluid dynamics (CFD) simulations are used. However, it is difficult to use the MMG to evaluate the manoeuvring performance of fishing vessels, thus research using CFD simulations is necessary. Also, since the course-changing and turning ability is crucial in fishing operations, a rudder design suitable for fishing vessels is necessary. This study designs a rudder using National Advisory Committee for Aeronautics (NACA) airfoil sections and evaluates its manoeuvring performance. A CFD model is used to evaluate the manoeuvring performance of the fishing vessel, and turning and zig-zag tests are conducted. The effectiveness of using CFD simulations based on Reynolds averaged Navier-Stokes equations to assess the manoeuvring performance of fishing vessels was validated. No significant difference was found in the manoeuvring performance for hull forms and rudder designs for course-changing ability. However, the original hull form showed superior turning performance. Among five rudders with varying aspect ratios and shapes, the rudder with 5.5% aspect ratio had the best turning performance. Regarding the rudder design for fishing vessels, NACA airfoil was employed, and a rudder aspect ratio of 5.5% based on the immersed hull side area is recommended.

Hull form optimization design of SWATH with combination evaluations of resistance and seakeeping performance

With the rapid development of the marine economy, marine operations are gradually diversified. To improve the hydrodynamic performance of SWATH in offshore working conditions, a design optimization method for Small Water-plane Area Twin Hull (SWATH) considering the resistance and seakeeping performance is proposed. The automatic optimization design of SWATH hull form with minimum resistance at different speeds is carried out to obtain a set of Pareto optimal solutions. Then the seakeeping performance of the original and the Pareto optimal solution set are predicted. On this basis, a comprehensive evaluation method based on the composite weight factor of SWATH resistance and seakeeping performance is provided. The results show that the method can obtain a hull form scheme with better hydrodynamic performance than the original hull form. In addition, it can guide the hull form optimization design of SWATH.

Sonar Dome Geometry Design Using CFD to Reduce Ship Resistance at Cruise Speed.

The objective of this study is to design the hull-mounted sonar dome of a ship. The goal is to reduce the ship total resistance and improve the flow field around the sonar dome for the ship design speed. OpenFOAM 6 was applied to analyze the viscous flow around the ship bow and then optimize the sonar dome geometry. The length, width and depth of the original geometry were maintained. Only the local geometry was fine-tuned considering the back slope and front tip by using Rhinoceros 6. The verification and validation was performed for the original hull form against towing tank resistance data. The grid independence was checked for the optimal design in different design stages. To ensure less influence on the interior equipment installation and to be able to re-use the non-steel dome part, the best resistance reduction is almost 2%. With a larger allowance of shape deformation, the maximal reduction could reach slightly higher than 3%. The flow field is improved for smaller flow separation and vortex, and less fluid nose in sonar detection is expected. The main reason of the resistance reduction is the decrease of the pressure component. In conclusion, a sonar dome design procedure is proposed, and an optimal geometry is suggested.

Hull Form Optimization Study Based on Multiple Parametric Modification Curves and Free Surface Reynolds-Averaged Navier–Stokes (RANS) Solver

In this study, the hull form optimization process to minimize resistance of KCS (KRISO containership) at Fn=0.26 is described. The bow hull form of KCS was modified by varying such design parameters as sectional area curve (SAC), section shape, bulb breadth, and bulb height using multiple parametric modification curves devised by the authors. The resistance performances of modified hull forms were analysed by the viscous flow Reynolds-Averaged Navier–Stokes (RANS) solver of WAVIS ver.2.2. With a view to saving computational time during iterative analyses in the optimization process, the sinkage and trim were set to the fixed values which had been obtained for the original hull form with free condition. The validity of such constant sinkage/trim was then verified by conducting analysis for the optimal hull form with free condition. Optimization to minimize the cost function of the total resistance coefficient of model CTM was performed by sequential quadratic programming (SQP), which is one of the gradient-based local optimization methods. Utilization of parallel computing led to the simultaneous calculation of the gradient, thereby speeding up the whole optimization process. At the design speed of 24 knots, the optimal hull yielded CTM reduction by 1.8%, which is extrapolated to 3.1% reduction of effective power PE in full scale.

Hydrodynamic investigation of wet swimming platform problem for semi-planning motor yachts

One of the main optimization problems for the performance and comfort of yachts is the wet swimming platform problem, also known as the rooster-tail phenomena .And this research presents an investigation using Computational Fluid Dynamics (CFD) method for a real case of an 88 ft. semi-planning motor yacht hull form that encountered this phenomena. First of all, the original hull form was analyzed to define the problem at cruising and maximum speeds, 14 knots, and 24 knots respectively. To solve this problem, modifications to the stern form of the hull were made in a two-step iteration. Initially, the size of the current interceptor was increased with a tunnel wedge. Results of the CFD analysis show that this modification eliminated the wet platform problem and increased the top speed of the yacht. Since the applicability of the wedge to mount is complex and costly, a second analysis with only enlarged interceptors was performed. As a result, the wet platform problem is solved, however, the resistance reduction was slightly lower.

Scenario-based optimization design of icebreaking bow for polar navigation

Global warming and ice extent reduction in Arctic makes commercial shipping through Arctic waters be promising in the near future. The fuel consumption and emission from ships on the Arctic shipping routes, which mainly depends on the ship resistance, is key factor to determine if it is more cost-effective comparing to traditional shipping route. The shipping route in Arctic water include open water and ice-covered water areas. The polar ships traveling through Arctic water need to have ice-strengthened hull to have ice-breaking capability to proceed safely in ice-covered water. Usually the bow hull form with good ice-breaking capability have high resistance in open water, while the bow form with good open-water efficiency (such as bulbous bow) may not have ice-breaking capability. This paper is to develop a methodology for optimized hull form design so that the minimum overall resistance in open-water and ice-covered water can be achieved, while maintaining desired level of ice-breaking capability for considered shipping route with expected ice conditions. The methodology proposed in this paper is based on the ship's desired route with historic ice data to define its typical operation profile. For the test example of this methodology, based on the desired route, the historic ice data are extracted from public available data source to determine the sections of open-water and ice-covered water, as well as the ice-thickness distribution along the route. The ship's resistance in open-water is calculated based on Rankine source method, while the ice resistance is calculated by Lindqvist formula. The overall resistance is weight-averaged based on the route's sections of open-water and ice-covered water. The ice-breaking capability is measured by the ice loads giving by the IACS Polar UR, which serves as the constraint during the optimization process. The parametric model is established for the optimization process. With an ice-breaking bow base design, the optimized bow hull form is achieved on the specified shipping route with historic ice condition. The result shows that the overall resistance is reduced by 5.42% while maintaining enough ice-breaking capability for the considered sample ship. Discrete Element Method is used to verify the optimized hull form's ice-breaking performance compatible with original hull form. It is shown that the methodology developed in this paper can be generally applied to polar ship hull form design for different shipping route and ice conditions.

CFD Simulation on Workability of a Seaweed Harvesting Boat Due to Wake-Wash

In the present study, a 2-ton class seaweed harvesting boat was optimized by employing a W-shape hull form to reduce roll motion due to wake-wash from passing boats. A series of numerical simulations were conducted using Star-CCM+, a commercial CFD (computational fluid dynamics) software, to improve workability by optimizing the hull form from the conventional design (original hull form). The 2-dimensional roll decay motion of various hull forms with W-shape midsection were simulated and the hull form with the best performance in free roll decay test was selected. To evaluate stability of each hull in wake-wash, the original or optimized hull was alternately located at the middle of a computational domain as a target ship while an advancing ship (original hull) moved forward generating Kelvin waves which impact the original or optimized boat. Two kinds of working conditions, i.e., ballast and full loading conditions, of the target ship were considered with and without initial roll angle. It was observed through the comparison of motion between the original and optimized hulls a decrement of roll motion for the optimized ship demonstrating the effectiveness of the W-shape hull. Decrement of roll motion was observed for both working conditions. Additionally, the optimized W-shape hull showed an extraordinary performance under the ballast condition without initial roll angle.

Application of the Design of Experiments and Computational Fluid Dynamics to Bow Design Improvement

Techniques of the design of experiments (DOE) and computational fluid dynamics (CFD) were applied for improving the bow shape of a tanker hull. Through this, a hull that could reduce the added resistance in waves was derived. The key design elements of the bow shape were selected as parameters for design optimization and added resistance in the short-wavelength region was interpreted through CFD considering the operational condition of the full scale ship. For design parameter changes, the number of analyses was minimized by applying DOE. The regression equation for calculating added resistance was derived using bow-shape design parameters by applying the response surface method and regression analysis to obtain the optimal hull with minimal added resistance was derived. The methodology was applied to an Aframax tanker hull form, and the derived added resistance regression equation and the added resistance value obtained through CFD analysis showed a difference of approximately 1%. The model test results of the improved hull form showed that the added resistance was reduced by 52% in comparison to that obtained for the original hull form.

A wake field design system utilizing a database analysis to enhance the performance of energy saving devices and propeller

The purpose of this paper is to propose the wake field design system which outputs a bare hull form generating a desired input wake distribution, and to demonstrate capability and effectiveness of this system through a practical hull form design project considering the interference effect of ESD and propeller. Our proposed wake field design system outputs a hull form which achieves desired input wake distribution utilizing hull form and wake field database. In the system, the database is analyzed by a method for the first time proposed in the present study, that is, a scheme using the Euclidean distance and hull form blending (morphing). To validate our system, the one-leave-out cross validation is performed, which is widely used for the validation of the database analysis. There, it is confirmed that the proposed method has practical accuracy. A practical demonstration is also performed in this paper, where a 749 gross tonnage cargo ship is selected as object ship. The initial (original) hull form in this research was developed in a project of the Japan society of naval architects and ocean engineers as a considerably promising bare hull form. This hull form is defined as the original design in this study, then we try to further modify the design to reduce delivered horse power in a condition of hull with duct type ESD. Importantly, we design a new hull form to improve wake field suitable for the duct along with the consideration of reduction of cavitation. To confirm the effectiveness of our proposed system, the towing tank test is conducted to measure the wake distribution, using 2 model ships (original and new design) with 6.8 m ship length. It is proved that our proposed system is capable to efficiently design desired wake field for the given hull form without trial and error, and provide equivalent to or more precise results than the expert designer’ design. Additionally, we also confirm that the propulsive performance of the new design hull form is improved. In our careful comparison of the effectiveness of the ESD, it is indicated that the new design shows 2.2% reduction of horsepower compared to the original hull form both for ESD installed case.

Pentamaran configuration design with modeling hull form for resistance minimization

Multi-hull ship had characteristics with complex geometry configurations. In the early stage design, multi-hull ship with proper configurations can be producing both minimum resistance and power consumption. Increasing number of hull as in pentamaran will increase frictional resistance, but total resistance can be reducing by decreasing wave making resistance with a slender hull form. With CFD tool used to examine minimum resistance with modified modelling of chine hull form on variation i.e. deadrise angles, waterline section of entrance angle and longitudinal section of stem angle. All simulations were conducted with fix separation on S/L 3/16 and Froude number up to 0.7. Comparison with the original hull form, chine hull form C35 II in deadrise 35° and angle of entrance 15° more advantageous with maximum resistance drag reduction 20.38%. The results of the study had been displayed in table and charts of chine pentamaran which having the smallest total resistance expressed in coefficient of friction and wave resistance.

The Naples warped hard chine hulls systematic series

An experimental study was carried out to evaluate still water performance of a Systematic Series of hard chine hulls in planing and semiplaning speed range. Models of the Naples Systematic Series (NSS) were of varying length-to-beam ratios of the parent hull. The parent hull, shaped with warped bottoms, was derived from a pre-existing hull extensively tested in a towing tank. This hull was validated by many work boats built in the last fifteen years. To simplify the construction of vessels with rigid panels (aluminium alloy, plywood or steel) the original hull form was transformed to obtain developable hull surfaces. The models were tested at Re>3.5×106, in speed ranges Fr=0.5−1.6 and Fr∇=1.1−4.3. The series studies the influence of LP/BC and Ⓜ ratios that vary respectively in the ranges of 3.45–6.25 and 4.83–7.49, for two positions of CG. All the models were tested both with and without interceptors. To enable model-ship correlation following the ITTC recommendations, in addition to the resistance coefficients of the models, dynamic wetted lengths and surfaces were provided as tables. To facilitate the implementation of Velocity Predict Programs, all the data (resistances, lengths and surfaces) were also furnished in polynomial form. In addition to the use of series in the design field, this study was done to provide data to improve the numerical simulations of a planing craft. With this aim, in addition to the resistance data, the wave profiles, obtained by wave cuts, were provided to carry out validation procedures.

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.

어선원 복지공간 확보를 위한 5톤급 쌍동형 연안어선 선형개발에 관한 연구

This paper reports the hull form development and resistance performance of a 5-ton-class catamaran-type coastal fishing boat. The weight estimation and preliminary design were basically extracted from existing coastal fishing vessels. In addition, the resistance performance was investigated using a model test in a high-speed circulating water channel and was analyzed in comparison to an existing catamaran fishing vessel. As a result, the modified hull achieved an approximately 30% reduction in resistance compared to the previous hull. The stability or boarding sensitivity of the modified hull form was more stable or comfortable than the original hull form based on a trim and sinkage comparison between the two boats.

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.

マシウ関数を用いた級数展開法による制約条件下における最適横截面積曲線について

When a high speed vessel is designed, it is important how we make her sectional area curve effectively on purpose to minimize the hull resistance. But on a sectional area curve, there are, in general, some constraints caused by the requirement of ship arrangement and we cannot reject them simply because we must build not only a small resistance ship but also an easily operable ship. A sectional area curve under these constraints is usually made from the experience of designers by referring one of a type ship, but we don't think we can get a true optimal curve easily only by the experience.In this report, we introduce the linear wave-making resistance theory into the optimal problem and Series 64 model 4793 is chosen as the object for analysis. The sectional area curve of Series 64 model 4793 is expanded into Mathieu function series and the performance is evaluated from the viewpoint of the wave-making resistance. Then we make the optimal curve for the improved hull form theoretically using calculus of variation under some constraints which are established artificially by us.Finally, we carry out resistance experiment of the improved hull form to evaluate our optimal method and it shows good result that the residual resistance of improved hull form becomes around the half of that of the original hull form.

저항최소화 소형 어선선형의 선수파 특성에 관한 연구

This paper presents the analysis of resistance performance and bow waves for the resistance-minimized hull form of small fishing boat by using numerical simulations and model tests. The resistance-minimized hull form is developed from an original hull form which is selected from existing small fisher boats in our country. In order to estimate the resistance performance for the original and the developed hull form, several numerical simulations and model tests are carried out. Marker and Cell(MAC) method and Marker-Density method are adopted to simulate the free-surface bow waves around advancing hull surface. The results of numerical simulations are compared with the model tests in towing tank. The results show that the resistance performance of the resistance-minimized hull form is improved than that of the original hull form. The results of this study will be a good guide to the hull form development of small fishing boats in future.

A case study for the effect of a flow improvement device (a partial wake equalizing duct) on ship powering characteristics

A case study for the energy saving in the powering characteristics of a river going general cargo ship has been carried out. Two different hull forms were generated from the original hull form of the vessel to optimise the stern flow of the vessel. A possible energy saving concept, such as partial wake equalizing duct was investigated in this manner. Resistance, self-propulsion and flow visualization measurements were performed with the hull models to explore the effect of partial wake equalizing ducts on the powering characteristics of the hull form. Analysis of the results indicates that the partial wake equalizing duct concept with an appropriate stern design affect not only the flow characteristics at aft-end, but also the propulsion characteristics. In order to identify effect of each component (partial wake equalizing duct and stern form) a further investigation is needed.

An inverse hull design approach in minimizing the ship wave

The Levenberg–Marquardt Method (LMM) and a panel code for solving the wave-making problem are utilized in an inverse hull design problem for minimizing the wave of ships. A typical catamaran is selected as the example ship for the present study. The hull form of the catamaran is described by the B-spline surface method so that the shape of the hull can be completely specified using only a small number of parameters (i.e. control points). The technique of parameter estimation for the inverse design problem is thus chosen. The LMM of parameter estimation, which is the combination of steepest descent and Newton’s methods, has been proven to be a powerful tool for the inverse shape design problem. For this reason it is adopted in the present study. In the present studies, the inverse hull design method can not only be applied to estimate the hull form based on the known wave data of the target ship but can also be applied to estimate the unknown hull form based on the reduced wave height. The optimal hull forms of minimizing wave for a typical catamaran in deep water at service speed and at the critical speed of shallow water are estimated, respectively. Moreover, a new hull form with the combining feature of the optimal hull forms for deep water and shallow water is performing well under both conditions. The numerical simulation indicates that the hull form designed by inverse hull design method can reduce the ship wave significantly in comparison with the original hull form.

On the Principal Particulars of Ship Hull Form and Wave Pattern Resistance (II)

Series tests were performed for eleven mathematical hull forms to investigate the relationship of the principal particulars and wave resistance, by wave pattern analysis. In the previous paper, the results of wave resistance, residual resistance, dipping and form factor on the frictional resistance were mainly presented for these models, and some consequences were compared with the results of linearized theory. In this paper, from the different angle than the previous one, directly measured wave resistance is firstly compared with calculated wave resistance by Michell's theory, and also the experimental results are shown for the amplitude functions and spectra of ship waves, which are compared with the results calculated by Michell's theory and by the method of source distribution on the hull surface.Some examinations are made how closely the principle of linear superposition of free waves is realized. Further, the comparisons in the amplitude functions and spectra are shown for two thin ships, one is added to the fore part and the other to the after part of an original hull form respectively.

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.