The hydrodynamic analysis of a new semi-small waterplane area twin hull(SWATH) suitable for various applicationssuch as small and medium size passenger ferries is presented. This may be an attractive crossover configuration resulting from the merging of two classical shapes:a conventional SWATH and a fast catamaran. The final hull design exhibits a wedge-like waterline shapewith the maximum beam at the stern;the hullends with a very narrow entrance angle, has a prominent bulbous bow typical of SWATH vessels, and features full stern to arrange waterjet propellers. Our analysis aims to perform a preliminary assessment of the hydrodynamic performance of a hull with such a complex shapeboth in terms of resistanceof the hull in calm water and seakeeping capability in regular head waves and compare the performancewith that of a conventional SWATH. The analysis is performed usinga boundary element method that waspreliminarily validated on a conventional SWATH vessel.

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.

The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics(CFD) method.A moving mesh method was used to more realistically simulate propulsor working conditions, and the thrust, torque, and lateral force coefficients of both propulsors were compared and analyzed. Forces acting on different parts of the propulsors along with the flow field distribution of steady and unsteady results at different advance coefficients were compared.Moreover, the change of the lateral force and the difference between the abovementioned two methods were mainly analyzed.It was shown that the thrust and torque results of both methods were similar, with the lateral force results having the highest deviation.

Multihull ships are widely used for sea transportation, and those with four hulls are known as quadramarans.Hull position configurations of a quadramaran include the diamond, tetra, and slice.In general, multihull vessels traveling at high speeds have better hydrodynamic efficiency than monohull ships.This study aims to identify possible effects of various quadramaran hull position configurations on ship resistance for hull dimensions of 2 m length, 0.21 m breadth, and 0.045 m thickness.We conducted a towing test in which we varied the hull spacing and speed at Fr values between 0.08 and 0.62 and measured the total resistance using a load cell transducer.The experimental results reveal that the lowest total resistance was achieved with a diamond quadramaran configuration at Fr=0.1-0.6 and an effective interference factor of up to 0.35 with S/L=3/10 and R/L=1/2 at Fr=0.62.

This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves.To perform this investigation, a series of free-running tests was conducted in regular waves using an experimental model of a multipurpose cargo ship to quantify the amount of shipping water.The tests were performed on five bow overhang variants with several combinations of wavelength and ship speed conditions.It was observed that the quantity of shipping water was affected by some parameters such as wavelength, ship speed, and bow shape in terms of an overhang extension.The results show the significant influence of an overhang extension, which is associated with the bow flare shape, on the occurrence of water shipping.These results involve the combined incoming regular waves and model speed.

In this paper, we present a comprehensive numerical simulation of a point wave absorber in deep water.Analyses are performed in both the frequency and time domains.The converter is a two-body floating-point absorber(FPA) with one degree of freedom in the heave direction.Its two parts are connected by a linear mass-spring-damper system.The commercial ANSYS-AQWA software used in this study performs well in considering validations.The velocity potential is obtained by assuming incompressible and irrotational flow.As such, we investigated the effects of wave characteristics on energy conversion and device efficiency, including wave height and wave period, as well as the device diameter, draft, geometry, and damping coefficient.To validate the model, we compared our numerical results with those from similar experiments.Our study results can clearly help to maximize the converter’s efficiency when considering specific conditions.

The effect of the mass ratio on the flow-induced vibration(FIV) of a flexible circular cylinder is experimentally investigated in a towing tank.A Tygon tube with outer and inner diameters of 7.9 mm and 4.8 mm, respectively, was employed for the study.The tube was connected to a carriage and towed from rest to a steady speed up to 1.6 m/s before slowing down to rest again over a distance of 1.6 m in still water.Reynolds number based on the cylinder’s outer diameter was 800-13, 000, and the reduced velocity(velocity normalized by the cylinder’s natural frequency and outer diameter) spanned from 2 to 25.When connected, the cylinder was elongated from 420 mm to 460 mm under an axial pre-tension of 11 N.Based on the cylinder’s elongated length, the aspect ratio(ratio of the cylinder’s length to outer diameter) was calculated as 58.Three mass ratios(ratio of the cylinder’s structural mass to displaced fluid mass, m^*) of 0.7, 1.0, and 3.4 were determined by filling the cylinder’s interior with air, water, and alloy powder(nickel-chromium-boron matrix alloy), respectively. An optical method was adopted for response measurements. Multi-frequency vibrations were observed in both in-line(IL) and cross-flow(CF) responses;at high Reynolds number, vibration modes up to the 3^rd one were identified in the CF response.The mode transition was found to occur at a lower reduced velocity for the highest tested mass ratio.The vibration amplitude and frequency were quantified and expressed with respect to the reduced velocity.A significant reduced vibration amplitude was found in the IL response with increasing mass ratios, and only initial and upper branches existed in the IL and CF response amplitudes.The normalized response frequencies were revealed to linearly increase with respect to the reduced velocity, and slopes for linear relations were found to be identical for the three cases tested.

In the present analysis, several parameters used in a numerical simulation are investigated in an integrated study to obtain their influence on the process and results of this simulation. The parameters studied are element formulation, friction coefficient, and material model.Numerical simulations using the non-linear finite element method are conducted to produce virtual experimental data for several collision scenarios.Pattern and size damages caused by collision in a real accident case are assumed as real experimental data, and these are used to validate the method. The element model study performed indicates that the Belytschko-Tsay element formulation should be recommended for use in virtual experiments.It is recommended that the real value of the friction coefficient for materials involved is applied in simulations.For the study of the material model, the application of materials with high yield strength is recommended for use in the side hull structure.

This study presents a simplified analytical model for predicting the structural responses of double-bottom ships in a shoal grounding scenario.This solution is based on a series of analytical models developed from elastic-plastic mechanism theories for different structural components, including bottom girders, floors, bottom plating, and attached stiffeners.We verify this simplified analytical model by numerical simulation, and establish finite element models for a typical tanker hold and a rigid indenter representing seabed obstacles.Employing the LS-DYNA finite element solver, we conduct numerical simulations for shoal-grounding cases with a wide range of slope angles and indentation depths.In comparison with numerical simulations, we verify the proposed simplified analytical model with respect to the total energy dissipation and the horizontal grounding resistance.We also investigate the interaction effect of deformation patterns between bottom structure components.Our results show that the total energy dissipation and resistances predicted by the analytical model agree well with those from numerical simulations.

The present paper investigated and analyzed swirler material consisting of mild steel which was subjected to service for the period of one year in a 30 MW marine boiler.Due to the presence of high temperatures in the furnace coupled with the corrosive marine environment swirler material showed accelerated degradation and material wastage.An investigation into the feasibility of manufacturing the existing swirler with an alternate material or coating the swirler material with a thermal barrier coating was undertaken.Based on their properties and performance, SS 304 and SS 316 were proposed as the replacement materials for the swirler.The other alternative of coating the existing swirlers with a form thermal barrier coating to observe for any improvement in their performance at elevated temperatures was also tested. Stellite, which is a Ni-Co based coating, was carried out on the MS samples and the same were exposed to same temperatures mentioned above.The performance of the available options was evaluated with respect to the grain structure of the material, the hardness value of the materials and deterioration at elevated temperatures.Investigation showed the proposed materials/coatings like SS 304, SS 316 and Stellite coating revealed that SS 316 is the material best suited for high temperature application.

The marine shipping industry faces challenges to reduce engine exhaust emissions and greenhouse gases(GHGs) from ships, and in particular, carbon dioxide.International regulatory bodies such as the International Maritime Organization and National Environmental Agencies of many countries have issued rules and regulations to drastically reduce GHG and emissions emanating from marine sources.This study investigates the possibility of using natural gas and hydrogen as alternative fuels to diesel oil for marine gas turbines and uses a mathematical model to assess the effect of these alternative fuels on gas turbine thermodynamic performance.Results show that since natural gas is categorized as a hydrocarbon fuel, the thermodynamic performance of the gas turbine cycle using natural gas was close to that of the diesel case. However, the gas turbine thermal efficiency was found to be slightly lower for natural gas and hydrogen fuels compared to diesel fuel.