Hull Form Research Articles

Study on resistance performance of hexagonal hull form with variation of angle of attack, deadrise, and stern for flat-sided catamaran vessel

Abstract The flat-sided hull vessel was designed with the purpose of simplifying hull production by eliminating the requirement for fairing, bending, and assembly of curved panel lines. Nevertheless, implementing the flat hull concept may marginally increase the hull resistance. The objective of the study is to investigate the impact of the hexagonal hull concept on resistance characteristics when altering the deadrise angle, angle of attack, and stern angle. Additionally, the resistance performances of the proposed hexagonal hulls were compared to evaluate the influence of the hull design geometry parameter. The contribution of this work is to identify the configuration of the design parameters to achieve an ideal level of resistance in a hexagonal catamaran hull design. The findings indicate that a greater angle of attack could potentially enhance wave generation and increase the resistance. Despite the increase in the wave resistance coefficient caused by the increment in deadrise angle, the overall resistance was reduced due to the significant reduction in wetted surface area resulting from the greater deadrise angle. As a result, the decrease in friction resistance was more pronounced than the increase in wave resistance. At last, the stern angle can cause a substantial oscillation in the curved line, resulting in a large increase in wave generation and overall resistance, particularly at high speeds.

Hydrodynamic Performance Improvement of a Tirhandil Yacht by Stern Form Modifications

This paper presents a comprehensive investigation to improve the hydrodynamic performance of a Tirhandil hull form by modification efforts on the stern region. The form improvement approach combines computational fluid dynamics (CFD) methods with computer-aided design (CAD) systems. The design process for the reference and modified models was carried out by using CAD systems. The hydrodynamic characteristics of the reference hull form were evaluated by employing CFD methods and it was determined that form improvements should be concentrated on the stern region. The modification process was conducted by considering constraints on the design variables in the stern region and the main dimensions of the reference model. A grid independence study was performed to evaluate various grid structures to determine the optimal mesh configuration for the numerical analyses. The SST k-Omega turbulence model was used for the numerical analyses to simulate turbulence structure around the hull form. Achieving around a 13.4% reduction in the total resistance coefficient, the modified model also exhibited decreased wave amplitudes, smoother wave transitions, and a significant reduction or cancellation of shoulder and stern waves.

Reinforcement Learning-Based Optimal Hull Form Design with Variations in Fore and Aft Parts

Abstract With recent advancements in artificial intelligence technology, various studies are being conducted in the shipbuilding industry. Traditionally, hull form variation methods have relied on the intuition and expertise of designers, leading to inconsistent results and unintended changes in the ship's main dimensions depending on the designer's competence. Moreover, the iterative process of design variation and analysis to derive the optimal hull form is both costly and time-consuming. To address these issues, this study proposes an optimal hull design technique utilizing reinforcement learning, a type of unsupervised learning in machine learning. Reinforcement learning allows the model to learn from past policies by recording and accumulating the rewards associated with various actions taken by an agent in a specific environment. In this study, after calculating the main parameters of the ship, the agent defines a state representing hull information and performs local transformations of the bow and stern. The reward of reinforcement learning is defined as the change in total resistance due to the hull deformation, constrained by limiting the tolerance of the ship's prismatic coefficient (CP) and longitudinal center of buoyancy (LCB). In this study, the problem is solved by comparing the proximal policy optimization (PPO) algorithm and the deep deterministic policy gradient (DDPG) algorithm to find the best deep reinforcement learning (DRL) model for the hull optimization problem. The results were compared with the genetic algorithm and speed-constrained multi-objective particle swarm optimization (SMPSO), and the optimal hull resistance values were less different, but the time of the reinforcement learning model was five times shorter.

Automatic Optimal Design Method for Minimum Total Resistance Hull Based on Enhanced FFD Method

Hull optimization plays a crucial role in enhancing ship performance and efficiency. This study aimed to improve ship performance, particularly by reducing total resistance, through automated optimization methods. To this end, an integrated, fully automated optimization program was developed based on Python, incorporating Enhanced Free-Form Deformation (FFD) technology, scripted CFD numerical evaluation, and the Particle Swarm Optimization (PSO) algorithm. This program allowed precise control of hull form, improving efficiency while reducing costs. The KCS hull, known for its excellent resistance performance, was chosen as the optimization target, with the goal of minimizing total resistance by adjusting the bulbous bow line plan. The research results indicated that the optimized scheme exhibited lower resistance characteristics compared to the original design while satisfying design constraints. This study not only provides a new optimization strategy for ship design but also lays a foundation for future hull optimization research.

Effects of steady flow and side hull layouts on motions and added resistance of a trimaran sailing in waves

As a high-performance ship, the trimaran holds significant potential in military and civilian fields. This study proposes a novel numerical method based on the Rankine panel method for predicting the time domain motion and wave loads of trimarans navigating in waves. This approach incorporates a more accurate steady flow model for trimarans and meticulously derives the boundary value problem for the unsteady disturbance potential, while retaining the steady terms related to steady flow throughout the process. This approach ensures a comprehensive consideration of the impacts of speed effect and ship wave. The method was innovatively validated using the trimaran hull form, and its accuracy and reliability were confirmed through comparisons with experimental data. Then, the influence of steady flow on time domain motions and added resistance of trimarans was thoroughly investigated. Comparative analysis of different steady flow models demonstrates that the steady flow model for trimaran proposed provides high precision and advantages in predicting the time domain motions of high-speed trimarans in waves. Furthermore, a systematic investigation into the effects of ship speed and side hull layouts on trimaran's motion and added resistance in waves has been conducted, offering crucial technical support for trimarans' seakeeping optimal solution selection.

A benchmark study on the energy efficiency and environmental impacts of alternative fuels in gulet-type sailing yachts

Gulet-type yachts are one of the symbols of maritime culture with their unique hull forms and schooner or ketch-type riggings. In parallel with the targets aiming for decarbonization in the maritime industry, energy efficiency and emission control are on the agenda for these types of yachts. Driven by this motivation, a novel benchmark study for the gulet-type yachts is conducted to evaluate the energy efficiency and environmental impacts associated with the adoption of LNG or methanol as primary fuel alternatives to MDO. The benchmark study is constructed in two steps: Presenting the design and propulsion characteristics of existing gulets, followed by a detailed analysis of the energy efficiency and environmental impacts of using alternative fuels. Therefore, 57 gulets with round and transom sterns whose hull forms are analyzed, modeled and general characteristics are presented. After modeling, the resistance and effective power of hull forms are predicted using the Holtrop-Mennen method and CFD. The flow characteristics around the hulls are obtained and the results are validated using the previous experimental studies in the first step. Then, installed and computed engine capacities are compared, and the Annual Emission Ratio and Energy Efficiency Index (EEI) are calculated for environmental impact assessments. Finally, the applicability of using LNG or MeOH-fueled propulsion systems for gulet-type yachts is discussed considering energy efficiency and design. According to the results, transitioning to alternative fuels can increase the Energy Efficiency Index of gulet-type yachts by over 20%.

Direct prismatic coefficient variation to hull form surface

The initial ship design process aims to optimize the hull form to enhance ship efficiency. During this phase, hull form variations are executed based on a reference ship to meet shipowner requirements, such as altering the CP (prismatic coefficient) to adjust the section lines. Once these variations are made, a surface is generated. However, this iterative process can be time-consuming as the surface creation must be done manually each time. Thus, we propose a method to directly apply CP variation onto the hull form surface, setting the variated section line as a constraint. In this study, the proposed method is employed to modify the hull form surface to meet CP requirements. The section lines of the modified surface are then extracted to validate the results. This streamlines in the initial hull form design, reduces the overall design time, and yields high-quality hull form surfaces efficiently.

Research progress on intelligent optimization techniques for energy-efficient design of ship hull forms

Research progress on intelligent optimization techniques for energy-efficient design of ship hull forms

6DoF CFD Analysis for High-Speed Small Craft in Free Running Conditions

ABSTRACT CFD simulations of a high-speed small craft are performed with 6DoF motions. The hull form and propulsor are scaled to match a deep V fishing boat (DVFB). The on water experimental data of the DVFB was used for qualitative validation. Many captive and free running conditions are considered including some most critical conditions, such as 2DoF captive motion, free running self-propulsion, turning circles in calm water and waves, acceleration, and avoidance line tests. The present work is the first known CFD study for the free running of high-speed small craft with 6DoF motions and is exploratory in nature. The accuracy and performance of the gear case and propeller models are evaluated with the issues identified. Other issues are also discussed including the optimum grid sizes, submerged depth of the gear case, and instabilities. All of these can be provided as recommendations for the future research improvements.

Investigation on Calm Water Resistance of Wind Turbine Installation Vessels with a Type of T-BOW

Given the typical characteristics of self-propulsion and jack-up wind turbine installation vessels (WTIVs), including their full and blunt hull form and complex appendages, this paper combines the model test method with the RANS-based CFD numerical prediction method to experimentally and numerically study the resistance of the optimized hull at different spudcan retraction positions. The calm water resistance components and their mechanisms of WTIVs based on T-BOW were obtained. Furthermore, using the multivariate nonlinear least squares method, an empirical formula for rapid resistance estimation based on the Holtrop method was derived, and its prediction accuracy and applicability were validated with a full-scale ship case. This study indicates that the primary resistance components of such low-speed vessels are viscous pressure resistance, followed by frictional resistance and wave-making resistance. Notably, the spudcan retraction well area, as a unique appendage of WTIVs, exhibits a significant “moonpool additional resistance” effect. Different spudcan retraction positions affect the total calm water resistance by approximately 20% to 30%. Therefore, in the resistance optimization design of WTIVs, special attention should be paid to the matching design of the spudcan structure and the hull shell plate lines in the spudcan retraction well area.

Research on Hull Form Design and Numerical Simulation of Sinkage and Trim for a New Shallow-Water Seismic Survey Vessel

Research on Hull Form Design and Numerical Simulation of Sinkage and Trim for a New Shallow-Water Seismic Survey Vessel

Multi-objective hull form optimization utilizing sequential sampling optimization method

With advancements in computer technology, Computational fluid dynamics (CFD) theory provides a numerical tool for evaluating the comprehensive hydrodynamic performance of ships. On this basis, the Simulation-based design (SBD) technology based on the static sampling method (SSM) which is termed as SBD-SSM in this paper is recognized as a hull form optimization method with significant advantages. However, in the SBD-SSM method, the excessive pursuit of the global accuracy of the surrogate model leads to the need for more CFD evaluations. Consequently, this demands the substantiality of computing resources and diminishes optimization efficiency. We apply a novel hull form optimization method based on the Sequential Sampling-based Optimization (SBO) method to address this challenge. Furthermore, to strike an appropriate balance between prediction value and uncertainty while finding optimal solutions, we employ the adaptive sampling method known as Pseudo Expected Improvement Matrix (PEIM). By integrating SBO with PEIM, we introduce the SBO-PEIM optimization method, initially applied through mathematical optimization functions to verify its feasibility in optimization. Subsequently, we apply this method to optimize the total resistance and wake performance of the KCS ship. Our findings demonstrate that the SBO-PEIM method achieves higher prediction accuracy in near-optimal solutions than the SBD-SSM method, enhancing optimization efficiency by at least 17.5%. It validates the efficacy of the SBO-PEIM approach in addressing real-world engineering optimization challenges.

Bulbous Bow Shapes Effect on Ship Characteristics: A Review

Abstract Hydrodynamic optimization is an effective and robust design method that is indispensable in ship hull form performance. Marine engineering and naval architecture have displayed significant interest in integrating bulbous bows on combatant ships. This review aims to gather and assess the existing knowledge regarding the effects of bulbous bow shapes on the hydrodynamic characteristics of combatant ships in terms of historical background, design principles, and impacts of bulbous bow shapes on ship resistance, ship motion in seaways, squat, and seakeeping performance. The review evaluates the effects of bulbous bow shapes on hull hydrodynamics using computational fluid dynamics (CFD), model testing, and full-scale experiments. The text delves into the complexities of improving hull shape and how the bulbous bow design interacts with many operational factors like draft, speed, and sea conditions. This research offers scholars, naval architects, and marine engineers a comprehensive insight into the intricate effects of bulbous bow shapes on combatant ship performance. It aims to consolidate current material to enhance our comprehension of ship design and operation by identifying knowledge gaps and suggesting future research areas.

The effect of main dimensions on the preliminary design of motor yachts

The design process of motor yachts mainly relies on the experience of designers, who have confidence in the knowledge acquired from designing units with similar hull-form characteristics. However, once a new concept needs to be developed, the acquired experience on a standard platform is no longer sufficient to achieve in a short time a successful design. The design of a motor yacht implies considering multiple aspects of ship hydrodynamics: resistance, propulsion, seakeeping, and manoeuvring. Such factors have been widely discussed individually on different kinds of ships, but an appropriate joint investigation of hulls like motor yachts is missing in the open literature. Therefore, the present paper intends to cover this gap, providing guidelines for the design of motor yachts in a length range between 20 and 40 meters. As a preliminary study, a series of 15 yacht hulls has been developed, starting from a reference hull form. Seakeeping, manoeuvring, and propulsive performances have been evaluated at a reference environmental condition and speeds according to the ISO 22834:2022 guidelines. Such calculations allow for developing response surfaces of the hydrodynamic properties for the series of yachts as a function of the hull's main dimensions. As a final result, the obtained responses allow for identifying the best compromise solutions for the main dimension selection of a new motor yacht in the length range of 20-40 meters.

Experimental analysis of self-propelled characteristics with uncertainty analysis of ONR tumblehome hull

In this paper, the self-propelled characteristics of the benchmark ONRT hull were studied experimentally at both Froude numbers, Fr = 0.20 and Fr = 0.30. The assessments were conducted under free-running conditions using a fully appended Office of Naval Research Tumblehome (ONRT), model 5613, scaled at 48.9, a customary proportion in academic research. To demonstrate the reliability of self-propulsion experiments conducted at the Istanbul Technical University, Ata Nutku Ship Model Testing Laboratory (ITU-AN), an uncertainty analysis method was applied to the ONRT results. The self-propulsion points from the studies in literature at both Fr = 0.20 and Fr = 0.30, were compared with the present test results. Based on the analysis results at self-propulsion points, it was noted that there was a high level of both intra-laboratory repeatability and inter-laboratory reproducibility characteristics. Through repeated tests, it was discerned that the uncertainties impacting essential parameters were, in descending magnitude, thrust, torque, and rotational rate. Consequently, this investigation enhances the precision and reliability of results by presenting the thrust and torque characteristics of the ONRT hull form, along with associated uncertainties for these Fr numbers.

Multi-objective optimisation research of ship form in waves based on Kernel principal component analysis

ABSTRACT In the process of multi-objective optimisation design of ship forms, subjective weighting methods rely on experts’ experience and have a certain impact on the scientificity of results. The objective weighting method can effectively solve this drawback and reduce the interference of human factors. Therefore, this paper proposes a multi-objective optimisation design programme for ship forms based on KPCA method, and constructs a multi-objective optimisation design framework. In this paper, the KPCA method is used to calculate the contribution rate of each indicator for objective weighting, give the comprehensive evaluation score of the optimal solution set and make decisions, solve the technical drawbacks of subjective weighting, and obtain a satisfactory optimal hull form. The results show that the automatic multi-objective optimisation design method proposed in this paper has certain engineering application value, and can provide theoretical basis and technical support for green design and manufacturing of ships.

Enhancing hull form design for robust efficiency: A data-enhanced simulation-based design approach

This paper presents a design approach that integrates machine learning techniques with traditional physics based simulations/models to enhance the ship design process with robust efficiency. While generative machine learning methods, which can directly produce design outputs such as the 3D hull form, have the potential to transform the design strategy, ship design inherently involves a decision-making process that requires consensus among stakeholders based on a foundation in physics-based simulations/models. This paper proposes a practical design strategy that positions physics-based simulations/models at the core of the design process, augmented by data-driven models. The paper first classifies hybrid types of the two models and integrates them into a practical design process. Finally, it demonstrates the effectiveness of the proposed design approach by showcasing the impact of data circulation, which accumulates and reinforces data in day-to-day design operations, on improving design outcomes.

Application of Sampling Methods for Constrained Space in Hull Form Optimization

Use of approximation models instead of direct application of CFD tools plays a crucial role in hull form optimization to enhance efficiency. The selection of sample points directly impacts the accuracy and cost of approximation models, and the effectiveness of hull form optimization. This paper presents a sampling method based on constrained space. The distribution pattern of the constrained space is initially analyzed, and its boundary is subsequently extracted by the Support Vector Machine (SVM), providing guidance for the subsequent sample selection. To ensure effective sampling within the constrained space, the maximum minimum distance criterion is employed. The proposed methodology is validated via a case study involving a 13,000DWT inland twin-screw bulk carrier. The Kriging approximation model is constructed to optimize the hull form while adhering to specific constraint conditions, thereby demonstrating the feasibility and efficacy of the proposed approach.

Numerical Simulation Flow Around the Containership by using CFD Method

Predict accurately resistance of the ship and flow around ship hull form is extremely important as these are input parameters for optimizing ship hull form, designing the ship propulsion system. This paper focuses on the numerical simulation of the flow around the Container Ship Fortune Freighter in calm water condition at different ship speeds by using CFD method. The results of impact of ship speed on components of ship resistance, wave patterns, volume fraction of air, the distribution of pressure, and wall shear stress on the ship's hull surface, as well as the nominal wake field are provided and analysed in this paper.

Planing Hull Hydrodynamic Performance Prediction Using LincoSim Virtual Towing Tank

This work shows the performance of LincoSim, a web-based virtual towing tank enabling automated and standardized calm water computational fluid dynamics (CFD) data sampling, extending previous published applications to the case of a high-speed hull. The calculations are performed for a 1:10 scale model of a 43 ft powerboat hull form in the Froude number range from 0.3 to 2.0. The counterpart physical model is the experimental fluid dynamics (EFD) campaign performed at the University of Naples Federico II, where the resistance, sinkage and trim data have been measured. The EFD/CFD data comparison is performed and shown with a discussion of the spotted differences. The average percentage differences between the EFD and CFD data for the whole speed range are 1.84, 6.87 and 6.94 for the resistance, dynamic trim, and sinkage, respectively. These results confirm the maturity of the standardized and automated CFD modeling for calm water hydrodynamic analysis included in LincoSim, even at very high Froude numbers. The wetted length of the keel and chine and the wetted surface are calculated from numerical data using the advanced post-processing. Finally, as a work in progress, we test a first comparison for the same hull of the EFD and CFD data, considering two seakeeping conditions for head waves at a given wavelength for two velocity conditions. Also, this kind of analysis confirms the tight correlation between the measured and computed outcomes. This synergic interplay of EFD and CFD can link the advantages of both methods to support hull design but also requires experiment planning and final data analysis to obtain physical parameters not easily measurable in laboratory, such as the wetted surface, wetted lengths, proper viscous contribution, and pressure distribution both in calm water and in waves.