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An automated practical multi-objective optimisation scheme is proposed for ship hull modification. A shift transformation and a self-blending method are sequentially performed based on resistance objectives at multi-design speeds. The Lackenby variation alters hull forms and produces initial designs. Subsequently, self-blending method combines obtained ships to cover design space. All processes are automated by MATLAB coding that connects the ©Maxsurf modeller and ©Maxsurf Resistance in the case of panel method resistance calculation. After whole shape optimisation, the platform defines ship portions in the stern and bow regions. Particularly, an approximation modelling Least-Square approach is investigated to construct a surrogate model. Optimisation results indicate 11.26% cost function reduction contributes to 16.23% resistance reduction at lower speed and 6.12% resistance reduction at higher speed for a passenger catamaran boat. Thus, the developed in-house optimisation code provides an optimal and cost-effective solution for hydrodynamic optimisation in the preliminary stage of ship design. [ABSTRACT FROM AUTHOR]

The resistance of a large Pure Car Truck Carrier (PCTC) with a bulbous bow and a transom stern is evaluated in the present paper. Several cases at nine different ship speeds in calm water are simulated and results are compared with the experimental measurements. The maximum relative error is 0.93% at a Froude number (Fr) of 0.209. The total resistance coefficient of the ship in calm water shows a parabolic trend with increasing Fr, and it reaches a minimum value at Fr = 0.1794. Furthermore, the cases of the ship in regular waves with six different wavelengths and three wave heights are simulated. It is observed that the total resistance exhibits a quadratic relationship with the wavelength when the wave height is fixed. The wave-making resistance increases with the increase in wave height at any fixed wavelength, and it reaches a maximum value when the wave-length is 1.2 times the ship length (Lpp). Additionally, we also investigated the resistance in three different sea states at four different speeds. When the significant wave height of irregular waves is the same as regular waves, the wave-making resistance under irregular waves is much smaller than that of the regular waves. All of these results indicate that the bulbous bow and transom stern can reduce the wave-making and residuary resistances, which can provide a useful reference for the subsequent design and manufacturing of related ships. [ABSTRACT FROM AUTHOR]

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Ship-hull design is a complex process because the any slight local alteration in ship hull structure may significantly change the hydrostatic and hydrodynamic performances of a ship. To find the optimum hull shape under the design requirements, the state-of-art of ship hull design combines computational fluid dynamics computation with geometric modeling. However, this process is very computationally intensive, which is only suitable at the final stage of the design process. To narrow down the design parameter space, in this work, we have developed an AI-based deep learning neural network to realize a real-time prediction of the total resistance of the ship-hull structure in its initial design process. In this work, we have demonstrated how to use the developed DNN model to carry out the initial ship hull design. The validation results showed that the deep learning model could accurately predict the ship hull’s total resistance accurately after being trained, where the average error of all samples in the testing dataset is lower than 4%. Simultaneously, the trained deep learning model can predict the hip’s performances in real-time by inputting geometric modification parameters without tedious preprocessing and calculation processes. The machine learning approach in ship hull design proposed in this work is the first step towards the artificial intelligence-aided design in naval architectures.

Numerical optimization of an inverted-bow trimaran is carried out through three simulation-based design (SBD) frameworks. Different positions of the trimaran's side hull are investigated based on a computational fluid dynamics solver using the non-dominated sorting genetic algorithm-III (NSGA-III), simultaneous hybrid exploration that is robust, progressive and adaptive (SHERPA) and response surface (RS) multi-objective optimization for resistance at cruise and sprint speeds. The aims are to create and develop a convenient tool for optimization and investigate the appropriate position of the side hull. An automated, low-cost optimization platform is achieved that can be implemented in other maritime projects. A 10.5% drag reduction for cruise speed and 6.6% reduction for sprint are obtained, corresponding to lower longitudinal and large transversal distances of the side hull. SHERPA and NSGA-III produce the same results, but SHERPA is 2.5 times faster than NSGA-III. RS obtains less desirable results, but in the lowest central processing unit time. [ABSTRACT FROM AUTHOR]

The resistance of a large Pure Car Truck Carrier (PCTC) with a bulbous bow and a transom stern is evaluated in the present paper. Several cases at nine different ship speeds in calm water are simulated and results are compared with the experimental measurements. The maximum relative error is 0.93% at a Froude number (Fr) of 0.209. The total resistance coefficient of the ship in calm water shows a parabolic trend with increasing Fr, and it reaches a minimum value at Fr = 0.1794. Furthermore, the cases of the ship in regular waves with six different wavelengths and three wave heights are simulated. It is observed that the total resistance exhibits a quadratic relationship with the wavelength when the wave height is fixed. The wave-making resistance increases with the increase in wave height at any fixed wavelength, and it reaches a maximum value when the wave-length is 1.2 times the ship length (Lpp). Additionally, we also investigated the resistance in three different sea states at four different speeds. When the significant wave height of irregular waves is the same as regular waves, the wave-making resistance under irregular waves is much smaller than that of the regular waves. All of these results indicate that the bulbous bow and transom stern can reduce the wave-making and residuary resistances, which can provide a useful reference for the subsequent design and manufacturing of related ships.

Ship resistance is an important characteristic to predict in the preliminary design stage. Proper prediction of ship resistance implies the fulfillment of the required speed and power of a ship. The assumed body characteristics of a ship model should also be properly considered when investigating ship resistance. In the present study, the assumption of a hydroelastic body for a ship model was used in an experiment on total ship resistance and added resistance in calm water and waves. Two hydroelastic models were used: a hydroelastic body with a bulbous bow (HB) and a hydroelastic body without a bulbous bow (HWB). The wavelength considered ranged from 0.5 L to 1.3 L, and the Froude number (Fn) considered ranged from 0.058 to 0.232. In the presented results, the total resistance coefficient of the HWB was higher than that of a rigid body without a bulbous bow (RWB). The average difference of magnitude between the HWB and RWB was 30.49% for calm water conditions and 30.37% for overall wave conditions. The total resistance of the HB was higher than that of the rigid body with a bulbous bow (RB), and the difference of magnitude was approximately 31.47% for calm water conditions and 31.68% for overall wave conditions. The added resistance coefficient of the HWB tended to increase with an increase in the wavelength, from 0.5 L to 1.1 L, and then decrease until 1.5 L. The overall tendency of the added resistance coefficient of the HB was significantly different from the other numerical results. Although the tendencies were different, most of the presented results were in the same range as the other numerical results.

This paper presents an efficient optimisation method to improve the main hull of a trimaran ship, whilst proposing a computational fluid dynamics-based automated approach to reduce total resistance. A mesh-based method is introduced to modify a wave-piercing bow trimaran hull at two cruise and sprint speeds. Therefore, the problem pertains to a hydrodynamic multi-objective optimisation problem. Radial basis function-based mesh-morphing tool is implemented to alter the geometry at the mesh level. Mesh-morphing tool leads to elimination of geometry and mesh regeneration steps that consequently provides a shortcut for the designer's extrication from optimisation time and complexity of geometry modification. Ten global parameters accomplish expansion and contraction of the 10 sections, which are known as Magnification Factor. Optimisation results and design comparison illustrate the applicability and efficiency of the proposed technique. The results demonstrate 6.77% reduction in total resistance at cruise speed and 1.55% at sprint speed. [ABSTRACT FROM AUTHOR]

This paper demonstrates the feasibility of Computational Fluid Dynamics (CFD) to predict the motion responses of the damaged ship and the total resistance in calm water and regular head waves. The head waves are described with a fifth-order Stokes scheme. Two benchmarking studies are done to respectively validate the accuracy of the applied numerical approach in predicting the total resistance and ship's motions. By comparing the total resistance of the intact ship with motions and the damaged ship, it can be obtained that the increased total resistance due to the flooding flow almost comes from the viscous pressure resistance. Moreover, added resistance generated by head waves is a considerable factor affecting the resistance performance of the ship. The increased value can be several times even more than ten times that of the upright-floating intact ship in calm water. [ABSTRACT FROM AUTHOR]

The study aims to theoretically determine the total resistance forces acting on bottom trawls used in the commercial trawl fishery around the Turkish Peninsula. For this purpose, a total of 14 (2 for Black Sea, 2 for Sea of Marmara, 6 for Aegean Sea and 4 Mediterranean Sea) trawl gears were ex-amined during the study representing all types of the bottom trawl fishery (e.g., fish targeted, shrimp targeted and mix) in Turkey. The calculation of the hydrodynamic forces of the gears was based on the determination of each gear component; net, floaters, sweep, door, warp and the friction force caused by footrope, sweep and door. The total resistance of trawl gears was calculated according to different towing speeds and warp lengths. Average resistance values of the examined nets with a 500 m warp length indicated that the frictional force of the trawl door composed more than 41.3% of the total resistance, followed by net (39.4%), both doors (6.3%), footrope friction (6.1%), sweep frictions (3.1%) and the rest belonged to sweeps, warps and floaters (totally 3.8%). It was determined that resistance caused by friction including sweeps, footrope and doors constituted more than 50% of the total resistance. Among the examined gears, the greatest resistance values were determined for the 600 meshes tailored-traditional Mediterranean type trawl gear.

The compaction apparatus is used in this study to measure the total resistance of particles during the compressibility process for approaching the real resistance of the particles in the ball mill and to simulate the grinding in an actual ball mill in order to be used for design purposes. The apparatus consists of two punches and a large die which a single punch pressing. The size reduction is measured because it gives an indication to the total resistance and the grinding product of the coarse particles of white cement clinker manufacture by Alkhomes refractory. The effect of the compaction applied pressure and compaction velocity are studied. Results indicated that the high total resistance (Tr) occurred at high compaction speed, low applied pressure and at increase the weight of a compacted material.

Marine industrial engineering face crucial challenges because of environmental footprint of vehicles, global recession, construction, and operation cost. Meanwhile, Shape optimization is the key feature to improve ship efficiency and ascertain better design. Accordingly, the present paper proposes an automated optimization framework for ship hullform modification to reduce total resistance at two cruise and sprint speeds. The case study is a bow shape of a wave-piercing bow trimaran hull. To this end, a multi-objective hydrodynamic problem needs to be solved. A combined optimization strategy using CFD hullform optimization is presented using the software tools STAR-CCM+ and SHERPA algorithm as optimizer. Furthermore, a comparison is made between CAD-based and Mesh-based parametrization techniques. Comparison between geometry regeneration methods is performed to present a practical and efficient parametrization tool. Design variables are control points of FreeForm Deformation (FFD) for CAD-based method and Radial Basis Function (RBF) for Mesh-based method. The optimization results show a 4.77% and 2.47% reduction in the total resistance at cruise and sprint speed, respectively. [ABSTRACT FROM AUTHOR]

The study aims to theoretically determine the total resistance forces acting on bottom trawls used in the commercial trawl fishery around the Turkish Peninsula. For this purpose, a total of 14 (2 for Black Sea, 2 for Sea of Marmara, 6 for Aegean Sea and 4 Mediterranean Sea) trawl gears were examined during the study representing all types of the bottom trawl fishery (e.g., fish targeted, shrimp targeted and mix) in Turkiye. The calculation of the hydrodynamic forces of the gears was based on the determination of each gear component; net, floaters, sweep, door, warp and the friction force caused by footrope, sweep and door. The total resistance of trawl gears was calculated according to different towing speeds and warp lengths. Average resistance values of the examined nets with a 500 m warp length indicated that the frictional force of the trawl door composed more than 41.3% of the total resistance, followed by net (39.4%), both doors (6.3%), footrope friction (6.1%), sweep frictions (3.1%) and the rest belonged to sweeps, warps and floaters (totally 3.8%). It was determined that resistance caused by friction including sweeps, footrope and doors constituted more than 50% of the total resistance. Among the examined gears, the greatest resistance values were determined for the 600 meshes tailored-traditional Mediterranean type trawl gear. [ABSTRACT FROM AUTHOR]

Ship resistance is an important characteristic to predict in the preliminary design stage. Proper prediction of ship resistance implies the fulfillment of the required speed and power of a ship. The assumed body characteristics of a ship model should also be properly considered when investigating ship resistance. In the present study, the assumption of a hydroelastic body for a ship model was used in an experiment on total ship resistance and added resistance in calm water and waves. Two hydroelastic models were used: a hydroelastic body with a bulbous bow (HB) and a hydroelastic body without a bulbous bow (HWB). The wavelength considered ranged from 0.5 L to 1.3 L, and the Froude number (Fn) considered ranged from 0.058 to 0.232. In the presented results, the total resistance coefficient of the HWB was higher than that of a rigid body without a bulbous bow (RWB). The average difference of magnitude between the HWB and RWB was 30.49% for calm water conditions and 30.37% for overall wave conditions. The total resistance of the HB was higher than that of the rigid body with a bulbous bow (RB), and the difference of magnitude was approximately 31.47% for calm water conditions and 31.68% for overall wave conditions. The added resistance coefficient of the HWB tended to increase with an increase in the wavelength, from 0.5 L to 1.1 L, and then decrease until 1.5 L. The overall tendency of the added resistance coefficient of the HB was significantly different from the other numerical results. Although the tendencies were different, most of the presented results were in the same range as the other numerical results. [ABSTRACT FROM AUTHOR]

One of the main goals of the ship design process is the reduction of the total resistance, which is nowadays even more highlighted due to increasingly stringent rules related to ship energy efficiency. In this paper, the investigation of the impact of the bow on the total resistance of a yacht is carried out for three models by towing tank tests and numerical simulations. The verification and validation studies are performed, and satisfactory agreement is achieved. Also, a comparison of three turbulence models for the prediction of the total resistance of a yacht is made. The flow around the models of the yacht is analysed and it is demonstrated that bulbous bow causes the reduction of wave elevations. Experimental and numerical results indicate that the decrease in the total resistance due to bulbous bow can be up to 7%. Finally, the applicability of CFD within the ship design process is presented.

In the conventional process of parametric ship optimization, the selection of design variables mostly relies on design experience. The lack of a clear and quantitative method of parameter selection leads to a certain degree of blindness and inefficiency. In this article, a parametric hull modeling method is proposed. The sensitivity analysis based on orthogonal experimental design is performed to select the design variables of optimization. Through variance and range analysis, the parameters that have a significant influence on the optimization objective are selected as the design variables. A combination of Sobol and tangent search method is applied during the optimization. The shape optimization of a fishing boat with minimum resistance is taken as an example. The optimization result proves the efficiency of the proposed parametric modeling method and the sensitivity analysis, which are significant for the shape optimization of a fishing boat. [ABSTRACT FROM AUTHOR]

In order to investigate the fouling mechanism in dynamic membrane (DM) formation, and filtration performance in domestic sewage treatment at an ambient temperature ranging from 24°C to 36°C, an anaerobic dynamic membrane bioreactor (AnDMBR) was monitored. Hydraulic retention times applied were 8 and 12 h, under permeate fluxes of 1,755 and 1,170 L m–2 h–2 in phases I and II, respectively. In both phases, after a 10% reduction in permeate flux, backwashing was performed. This allowed a prolonged filtration of 84 d for phase I and 76 d for phase II. The total resistance to filtration was in the magnitude of 1011 m–1, implying excellent filterability by the DM, and energy- saving potential for the AnDMBR system. The system had good treatment performance, achieving average volatile fatty acid reduction of 53%, total chemical oxygen demand (COD) removal efficiencies of 84%, soluble COD of 72%, and color of 80%; being able to remove 94% of suspended solids, and producing an effluent with low turbidity (17 NTU). The biogas measured in the system was 154 N mL g–1 COD removed, which represents 35% of its theoretical value, which means that most of it left in dissolved form with the effluent due to supersaturation. The predominant fouling mechanism in DM formation in all permeates fluxes tested was cake filtration, with the main cause being the concentration of inoculum sludge. This confirms the prominence of DM formation during filtration and high solid–liquid separation. [ABSTRACT FROM AUTHOR]

Abstract Purpose The World Health Organization (WHO) in 2017 classified some carbapenem-resistant Gram-negative bacteria into a critical criterial group for research and development. This study reviews the need to prioritize the water matrices as hotspot in the development and transfer of antibiotic resistance determinants, where future total resistant superbug may emerge. Methods Published articles on Google Scholars, PubMed/Medline Search and other search tools were selected, with special interest in articles published in indexed journals. Search criteria were based on antibiotic resistance, antibiotic resistance determinants and emerging trend in the reported trend of antibiotic resistance among bacteria from water matrices. Results Research reports around the globe have identified carbapenem-resistant Gram-negative bacteria (CRGNB) in water matrices. These CRGNB have also been found to be resistant to other antibiotics in the last line of defence. Molecular typing of some carbapenem-resistant Enterobacteriaceae (CRE) in the environment through pulsed-field electrophoresis showed them to be the same as those in the hospital settings. CRGNB from various water matrices have been reported to harbour carbapenem resistance genes with phenotypic expression of carbapenemases’ production. Water habitat provides a conducive environment for the development and spread of carbapenem resistance. Factors like residual antibiotics (RAbs), metals, biocide and water-borne mutagens aid the emergence of the resistance in water matrices. Irrespective of where it was contacted, carbapenem-resistant bacteria have poor prognosis. This is exemplified by resistance to 26 different antibiotics recently in the USA. The human health risk associated with the use of water harbouring these pathogens for irrigating fruits and vegetables may be alarming. Conclusion The reports of the rising trend of antibiotic resistance also necessitate prioritizing water matrices when addressing the problems from the reservoir. Surveillance and strict isolation, education and enlightenment, strict compliance with multiple barrier approach of the WHO and more search for more potent antibiotics remain some of the antidotes against the development and spread of resistance through the water matrices as discussed in this article.

A high−accuracy objective function evaluation method is crucial in ship hull form optimization. This study proposes a novel approximate ship hull form optimization framework using the deep learning technology, deep belief network algorithm. To illustrate the advantages of using the deep belief network algorithm in the prediction of total resistance, two traditional surrogate models (ELMAN and RBF neural networks) are also employed in this study to predict total resistance for different modified ship models. It can be seen from the results that the deep belief network algorithm is more suitable for forecasting total resistance of a DTMB5512 ship model than the traditional surrogate models. Following this, two design variables are selected to alter the bow geometry of the DTMB5512 ship model. The total resistance for different modified ship hulls is estimated using the deep belief network algorithm. Furthermore, an optimal solution with minimum total resistance in a two−dimensional space is obtained using the particle swarm optimization algorithm. The optimization results indicate that the optimization framework using the deep belief network algorithm can obtain an optimal solution with the smallest total resistance for different ship speeds.

This paper investigates the improvement of the bow region of the trimaran ship hull, and proposes a Computational Fluid Dynamics (CFD)-based automated method to reduce total resistance. The main objectives pursued in the present study include: 1) to create and develop a useful optimization platform to modify the ship hull and 2) to investigate the effect of different inverted bow on the hydrodynamic performance of trimaran ship. A wave-piercing bow trimaran hull was taken as the baseline design. The ship bow has been redesigned using Arbitrary Shape Deformation (ASD) technique, which defines the input variables for the optimization process. The objective function was the drag force, and this study is conducted at cruise speed. To accomplish this task, two optimization methods were sequentially applied. A Latin Hypercube Sampling tool distributes design points and an Radial Basis Function (RBF)-based surrogate model is constructed to investigate system behavior. The final optimum design of Design Of Experiment (DOE) study was introduced to the direct optimization SHERPA algorithm as a baseline design. The integration of CFD solver, geometric parameterization and optimizer tools is managed by the HEEDS MDO software package using a multi-connection method. The optimization results show that the optimization was successfully carried out and the resistance was reduced by 10.2%. The comparison between the initial hull and the optimized hull shows that the proposed optimization platform can be used for ship hull optimization in industrial application and significantly reduces the computational time and workload. [ABSTRACT FROM AUTHOR]

One of the main goals of the ship design process is the reduction of the total resistance, which is nowadays even more highlighted due to increasingly stringent rules related to ship energy efficiency. In this paper, the investigation of the impact of the bow on the total resistance of a yacht is carried out for three models by towing tank tests and numerical simulations. The verification and validation studies are performed, and satisfactory agreement is achieved. Also, a comparison of three turbulence models for the prediction of the total resistance of a yacht is made. The flow around the models of the yacht is analysed and it is demonstrated that bulbous bow causes the reduction of wave elevations. Experimental and numerical results indicate that the decrease in the total resistance due to bulbous bow can be up to 7%. Finally, the applicability of CFD within the ship design process is presented. [ABSTRACT FROM AUTHOR]

Prediction of the total resistance of a pusher-barge system has become enormous complexity involving nonlinear-hydrodynamic flow behaviour around their hull forms. Both empirical and simplified numerical solutions may still lead to inaccurate results due to the presence of nonlinear characteristics of the pressure and viscous resistances. The use of a more sophisticated method would obviously necessitate solving the above problem. This paper presents a Computational Fluid Dynamics (CFD) approach to predict the total resistance of a pusher-barge system at various barge configurations. To achieve such an objective, four different configurations of the barge models incorporated with various Froude numbers have been taken into account in the computational simulation. In general, the results revealed that the increase of Froude number (Fr = 0.182 to 0.312) was proportional to the magnitude of RT, RP, and RV. Regardless of the various Froude number, the pusher-barge system with a 13BP configuration provides the highest resistance compared to the 12BP and 11BP. In addition, the arrangement of barges in the longitudinal (12BP) and lateral (21BP) configurations produced a significant effect with increases in RT, RP, and RV values of 110%, 167.5%, and 77.6%, respectively. The possible reason for this is that the increase of the total wetted surface area for 21BP has produced a proportionally higher amount of pressure and viscous resistance. Finally, the numerical results were presented and analyzed based on some aspects involving the total resistance and resistance coefficient in terms of pressure and viscous resistance of the pusher-barge system. This analysis provides very valuable information on selecting a proper arrangement of the pusher-barge system, which results in less total resistance. [ABSTRACT FROM AUTHOR]

Purpose: The World Health Organization (WHO) in 2017 classified some carbapenem-resistant Gram-negative bacteria into a critical criterial group for research and development. This study reviews the need to prioritize the water matrices as hotspot in the development and transfer of antibiotic resistance determinants, where future total resistant superbug may emerge. Methods: Published articles on Google Scholars, PubMed/Medline Search and other search tools were selected, with special interest in articles published in indexed journals. Search criteria were based on antibiotic resistance, antibiotic resistance determinants and emerging trend in the reported trend of antibiotic resistance among bacteria from water matrices. Results: Research reports around the globe have identified carbapenem-resistant Gram-negative bacteria (CRGNB) in water matrices. These CRGNB have also been found to be resistant to other antibiotics in the last line of defence. Molecular typing of some carbapenem-resistant Enterobacteriaceae (CRE) in the environment through pulsed-field electrophoresis showed them to be the same as those in the hospital settings. CRGNB from various water matrices have been reported to harbour carbapenem resistance genes with phenotypic expression of carbapenemases’ production. Water habitat provides a conducive environment for the development and spread of carbapenem resistance. Factors like residual antibiotics (RAbs), metals, biocide and water-borne mutagens aid the emergence of the resistance in water matrices. Irrespective of where it was contacted, carbapenem-resistant bacteria have poor prognosis. This is exemplified by resistance to 26 different antibiotics recently in the USA. The human health risk associated with the use of water harbouring these pathogens for irrigating fruits and vegetables may be alarming. Conclusion: The reports of the rising trend of antibiotic resistance also necessitate prioritizing water matrices when addressing the problems from the reservoir. Surveillance and strict isolation, education and enlightenment, strict compliance with multiple barrier approach of the WHO and more search for more potent antibiotics remain some of the antidotes against the development and spread of resistance through the water matrices as discussed in this article. [ABSTRACT FROM AUTHOR]

The article presents regression formulas for calculating the friction resistance RF and the total resistance RT of ship models in the 2.0-10.0 m range. The method for calculating the total resistance is novel and applies to the design models of an unmanned surface vessel (USV) for experimental testing of autonomous control. For both regression models (RF and RT), statistical and substantive tests were performed (the results of the calculations were compared with the experimental measurements). In both cases, convincing results were obtained, which have confirmed the possibility of their use at the preliminary design stage of unmanned ship models. [ABSTRACT FROM AUTHOR]

Model tests are often conducted by researchers in a real or a numerical towing tank to calculate residuary resistance of a ship with the aid of Froude similarity. Common ITTC-1957 formula is usually employed to calculate frictional resistance. As computer technologies develop over time, CFD tools are used for calculating total resistance of a ship at full scale without establishing any dynamic similarities. In this paper, both Froude and Reynolds similarities are numerically implemented to four different model scales by using virtual fluids. The total resistance at different Fr numbers calculated by the numerical study is validated against the experimental data of DTMB 5512 (L=3.048 m) model hull. The results show that establishing Froude and Reynolds similarities together in numerical simulation is possible in principle. To determine whether it has advantages for prediction of full-scale ship total resistance by employing this method, it is also examined the model scale with the same number of elements and Reynolds number of the full-scale ship. Results show that numerical calculation of total resistance for a full-scale ship in a model scale by defining virtual fluids has only slight advantages on the prediction of residuary resistance. Additionally, no advantage in the calculation of frictional resistance is observed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to show how the improvement of the hydrodynamics performance of a ship can be achieved by solving a shape optimization design problem at different speeds using the Simulation-Based Design (SBD) technique. The SBD technique has been realized by integrating advanced CFD codes, global optimization algorithms and geometry modification methods, which offers a new way for hullform optimization design and configuration innovation. Multiple speeds integrated optimization has been a challenge for hullform design. In this paper, an example of the technique application for a fishing ship hullform optimization at different speeds is demonstrated. In this process, Free-form Deformation method is applied to automatically modify the geometry of ship, and the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm is adopted for exploring the design space. Two objective functions, the total resistances at two different speeds (12kn and 14kn) are assessed by RANS solvers. The optimization results show that the decrease of total resistance is significant for the optimization case at the two speeds, with a reduction of 5.0% and 11.2% respectively. Finally, dedicated experimental campaigns for the design model and the optimized model are carried out to validate the computations and the optimization processes. At the two speeds, the reduction of the total resistance in model scale is about 6.0% and 11.8% for the optimized case. These are a valuable result considering the small modifications allowed and the good initial performances of the original model. The given practical example demonstrates the feasibility and superiority of the proposed SBD technique for multiple speeds integrated optimization problem. [ABSTRACT FROM AUTHOR]

This study proposes a novel approach for reducing the total resistance and mitigating motion in regular head waves of trimarans. Instead of the traditional method of optimising the side hull layout, we investigated the effects of a T-foil and bulbous bow configuration on the trimaran's performance. Through model tests, we studied the impact of T-foils with various aspect ratios and their combination with a bulbous bow on the motion in regular head waves of a trimaran. We observed that the T-foils can reduce the resistance and mitigate the motion of trimarans in regular waves. This effect is more pronounced at high speeds than at low speeds. T-foils with the same projected areas but different aspect ratios have a similar influence on the motion of the trimaran; however, those with large aspect ratios are more effective in reducing resistance. Furthermore, the combination of a T-foil and bulbous bow can simultaneously reduce the total resistance and mitigate the motion in regular head waves of the trimaran. The configuration with a T-foil with a large aspect ratio is particularly effective in mitigating the heave and pitch motions and reducing the total resistance to waves. This study provides a new approach to enhancing the hydrodynamic performance of trimarans. • The resistance and motion of the trimaran can be reduced by the T-foils and their combination with a bulbous bow. • The effect of the T-foils and the multi-appendage is more obvious at high speed than that at low speed. • T-foil with larger aspect ratio is more effective in reducing the resistance. • The influence of the bulbous bow on the heave and pitch motion is more significant than that on the total resistance. [ABSTRACT FROM AUTHOR]

The main objective of this article is to describe an innovative methodology for the hydrodynamic optimization of a ship bulbous bow which considers multiple operating conditions. The proposed method is more practical and effective than the traditional optimization process, which is only based on contractually specified design condition. Parametric form approaches are adopted by employing an F-spline curve in order to generate variants of the hull bulbous bow forms using form design parameters modified, resulting in an optimization system based on improved genetic algorithms. The Rankine source panel method is used for the hydrodynamic evaluation, wherein non-linear free surface conditions and the trim and sinkage of the ship are taken into consideration. The validity and effectiveness of the proposed methodology for a large container ship is investigated by comparing the computational results with experimental data, which demonstrates that the proposed methodology can engage well in the automation process and improve hydrodynamic performance during actual ship design practices.

In order to reduce the resistance and improve the hydrodynamic performance of a ship, two hull form design methods are proposed based on the potential flow theory and viscous flow theory. The flow fields are meshed using body-fitted mesh and structured grids. The parameters of the hull modification function are the design variables. A three-dimensional modeling method is used to alter the geometry. The Non-Linear Programming (NLP) method is utilized to optimize a David Taylor Model Basin (DTMB) model 5415 ship under the constraints, including the displacement constraint. The optimization results show an effective reduction of the resistance. The two hull form design methods developed in this study can provide technical support and theoretical basis for designing green ships. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation of viscous flow around a tanker model was carried out utilizing software package STAR-CCM+. A mathematical model based on Reynolds Averaged Navier-Stokes equations, a k-ε turbulence model and Volume of Fluid method for describing the motion of two-phase media are given. Necessary boundary conditions for the mathematical model and the method of discretization are also described. The effect of grid density on the numerical results for the total resistance of the tanker model was investigated using three different grid densities. Two different types of the k-ε turbulence model were implemented and deviations in the numerical results are highlighted. The results for the total resistance of the tanker model, obtained by numerical simulations, were validated against the experimental results. The experiments were performed in the towing tank of the Brodarski Institute for a wide range of Froude numbers. It was shown that for all three grid densities and for both types of the k-ε turbulence model satisfactory agreement with the experimental results can be achieved for the whole range of Froude numbers. The scale effects were investigated by a Computational Fluid Dynamics study for the same tanker model in three different scales. Numerically calculated scale effects on wave resistance are reviewed. [ABSTRACT FROM AUTHOR]