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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.

One of the most well-known strategies to eliminate or reduce the longitudinal instabilities in planing hull, is to reduce the trim of the craft. In the current study, porpoising is controlled through creating a transverse step, and the combination of adding a wedge to the stern and transverse step in the vessel. Usually, performance of stepped boats is not suitable in pre-planing regime. However, through the proposed method, stepped model performance can be improved prior to the planing regime. The investigated craft is a 2.56 m long monohull high speed model with speed range of 1,3,5,7 and 9 m/s. The obtained results indicate that best performance is acquired by the step and wedge model at the beginning of the planing regime. From 3 to 7 m/s, drag of stepped and wedged models has the lowest value and above 7 m/s and at 9 m/s, the stepped model has the lowest resistance. Among the investigated methods, using combined step and wedge indicates largest reduction in trim angle (At speeds of 3 to 9 m/s). It can therefore be concluded that model equipped by combination of wedge and step improves the poor performance of the stepped models prior to the planing regime.

The present paper focuses on the assessment of turbulent effects on the impact force, spray, and secondary impact force of the wedge water entry. For this purpose, a finite element based finite volume method code coupled with volume of fluid has been developed. The k-e method has also been implemented to model the turbulence effects. The developed code is validated against experimental data with good accordance and is then used to model the water entry of wedges with deadrise angles ranging from 10 to 60 degrees at different velocities of 1 and 2 m/s with laminar and turbulent assumptions. Subsequently, the resulting forces and free surfaces are compared for three critical instances of “Peak”, “Hollow”, and “2nd impact”. It is illustrated that turbulence has negligible effects on the force and free surface in the main water entry process. However, turbulent effects rise up to 14.23% for the secondary impact forces.

Emulsi ed fuel is one of the main strategies to substitute the conventional fossil fuel for the purpose of emission control and enhancement of fuel e ciency. Accordingly, non-reacting spray characteristics of water-in-Heavy Fuel Oil (HFO) emulsion are numerically investigated in the present study via CFD analysis. Three di erent volumetric percentages of water in HFO are investigated and compared with pure HFO. E ects of four di erent injection pressures on injected fuel spray characteristics are studied. Moreover, in fluences of three di erent ambient back pressures and two ambient temperatures are considered. For these purposes, the characteristics of spray penetration, cone angle, volume, and SMD are evaluated through the analyses of non-dimensional numbers. For modeling the interaction of the fuel discrete phase and the gaseous continuous phase, Eulerian- Lagrangian multiphase formulation in OpenFOAM CFD toolbox is implemented. Fuel droplet tracking in Lagrangian scheme is applied by Lagrangian Particle Tracking method. Also, KH-RT as a hybrid breakup model for liquid fuel core breakup and standard model of k ???? " in RANS for turbulence modeling are utilized. Numerical results are validated against existing experimental data with suitable accordance. Longer spray penetration length, larger cone angle, and greater spray volume are achieved for the emulsi ed fuels.

In this article, non-evaporating and non-reacting diesel spray is modeled under ultra-high injection pressure using an Eulerian-Lagrangian scheme. This is accomplished in order to probe into the effects of injection pressure, nozzle diameter, and ambient density on spray characteristics. An advanced hybrid breakup model that takes into consideration the transient processes during spray injection has been added to the open source code OpenFOAM. Reynolds-Average Navier-Stokes (RANS) equations are solved using standard turbulence model and fuel droplet is tracked by a Lagrangian scheme. Published experimental data have been used for validation of spray characteristics at 15 kg/m3 ambient density and injection pressures of 100, 200 and 300MPa. Also, three nozzle diameters of 0.08, 0.12 and 0.16mm have been implemented for investigating the effect of this parameter on spray formation. Computed spray shape, jet penetration, spray volume, equivalent ratio along the injector axis and Sauter Mean Diameter (SMD) illustrate good agreement with experimental data of single hole nozzle and symmetric spray. The effects of fuel injection pressure, nozzle hole diameter and ambient density on main spray parameters are presented. It is concluded that numerical model presented here is quite suitable for accurately predicting diesel spray shapes under ultra-high injection pressures.

In this paper, effects of a wedge on the performance of planing craft in calm water are experimentally investigated. Experiments are carried out on three different cases distinguished by the wedge type. The model, built of fiberglass, is a prismatic planing hull with deadrise angle of 24 degrees. Towing tests are conducted at different Froude numbers ranging from 0.21 to 2.1. The total trim angle, resistance, rise up at the CG as well as stern and bow, keel wetted length, chine wetted length, stagnation angle, and the length of stagnation line are measured. They are used to study the effect of installing a wedge on the performance as well as the effect of height on the hydrodynamic characteristics. Based on the observations made, it is concluded that, when the wedge is applied to the hull, the risk of model exhibiting instability diminishes, while total trim angle largely decreases, keel wetted length is enlarged, wetted surface becomes thinner, CG rise up is lowered, and the resistance is reduced. Moreover, experimental measurements and theoretical 2D+T theory are combined to bring deeper insight about physics of the flow and pressure distribution when a wedge is installed on the bottom of a planing hull.

In the current paper, numerical simulations of Fluid structure interaction (FSI) of a SP (Surface Piercing) hydrofoil are conducted in order to study the influence of elasticity on the initial water entry ventilation. Using ANSYS multi physics solvers, two-way FSI analyses are conducted by the implicit coupled URANS (Unsteady Reynolds averaged Navier–Stokes) equations and finite element method. Numerical result is validated by the well known rigid and elastic wedge water entry problems. Subsequently, computational results are presented for different velocity ratios range [0.38, 0.64] and elasticity factor range [0, 4]. Similar to the Surface Piercing Propeller (SPP), performance curves of a wedge water entry are defined. The obtained similar trend of propeller and wedge performance curves in fully ventilated, transition, and partially cavitated operation modes shows that the adopted approach (2D-study) can be appropriate for future related studies. FSI simulation results indicate that structural deformation can highly affect the location of transition point and shifts it toward the fully ventilated part at high Froude number and elasticity factor. The overall efficiency loss due to increase of foil elasticity is observed and overshoot time of the foil deformation related to the variation of Froude number and elasticity factor, is evaluated.

The use of ferrofluids as shapeable external appendage to a submerged body and as a mean of vortex flow induction is studied in this paper. Ansys-CFX numerical results are validated against analytical problems and used to analyze the ferrofluid free surface shape affected by gravity, different magnets and different densities of the surrounding non-magnetic fluids. It is demonstrated that the height, width, and curvature of ferrofluid can be controlled by magnet size and strength. It is also observed that ferrofluid mass loss may occur due to gravity which should be addressed in designing a fluid appendage. Subsequently, vortex production inside the ferrofluid is investigated via a shear flow on the magnet. It is shown that ferrofluid can contain complex vortices while being shaped by the magnetic field, gravity, and the vortices. It is also observed that vortices inside the ferrofluid affect the flow of the surrounding fluid. Additionally, the effects of surface tension and viscosity are briefly analyzed to roughly show the importance of these parameters for further works. Overall, it is concluded that using ferrofluids as appendages for shaping and controlling fluid flow around submerged bodies seem to be practical and needs further attention.