computational fluid dynamics

In this study, the total resistance and effects of different parameters on the hydrodynamic behavior of a twin-hull unmanned surface vessel have been investigated using the numerical method (CFD) using STAR-CCM+ and the experimental method (towing tank test) in Kowsar towing tank (KTT). Hull has been tested in two tonnages and at four different speeds. The comparison of the results of both methods shows an eligible match between the results of experimental and numerical analysis. Finally, it was found that vessel weight increasing to its maximum value at the operating speed will only increase the total resistance by 17%. Also, during the experiments, it was found that despite the vessel's design for low operating speeds, it is possible to achieve planning speeds or higher. Still, due to a lack of hydrodynamic lift generation at high speeds, hydrodynamic resistance will increase significantly. An increase of 4 kg in hull mass will increase the pitch angle up to 9%, the maximum pressure on the body up to 12%, and the wave height near the body up to 9%.

The ever-increasing expansion of marine recreation using water recreational equipment is one of the important fields of attention in the marine industry. Optimizing and upgrading the appropriate propulsion system for this type of marine device is one of the most important factors of updating and innovation, which leads to the strengthening of the marine economy and related engineering services. Motorized surfboard or so-called jet surf is one of these devices. The water jet is the most important part of the jet surf propulsion system. Limited research has been done on the design and analysis of the water jet system. In this research, the modeling and optimal design of the rotor and stator of the waterjet system related to the propulsion of the motorized surfboard are discussed. According to the limitations of engine selection, rotational speed, and engine design conditions, the appropriate rotor and stator were selected for the waterjet system. Also, the appropriate shape and dimensions of the system inlet channel were modeled in 4000 rounds. The relevant model was tested and the optimization results led to the maximum functional efficiency of Jet Surf being selected for the design. Their results and analysis show that in the 8-blade rotor and 10-blade stator, more thrust force is produced at 3500 rpm, but less torque is needed in the 6-blade rotor and 8-blade stator. Also, by using the trust diagram obtained for the system, it was determined that the ratio of the trust factor to the rotor revolution for this designed waterjet is about 15 and the efficiency of the whole system was 54%.

This study deals with the numerical modeling of symmetrical water entry of tunneled sections. In this study, firstly, the water entry problem of a wedge section without tunnel in four different deadrise angles was numerically modeled. The obtained results related to the pressure distribution on these sections and the maximum pressure have been compared with the experiment results. In the next step, the numerical simulation of the water entry problem with the tunnel section has been done. For this purpose, a tunneled section was created by adding a tunnel to a simple wedge section. Finally, the effects of changing the deadrise angle and also changing the radius of the tunnel section have been modeled. In this study, the viscous Navier-Stokes (N-S) equations are used to simulate water flow around the section and also a Volume of Fluid (VOF)-type method, is employed to capture the free surface. The results of pressure changes and maximum pressure in three different areas of the tunnel section have been obtained. These three areas include the area before the tunnel, in the tunnel area and the area after the tunnel. The results of this research indicate the occurrence of severe pressure changes in the tunnel area. Also, with the increase of the radius of the tunnel, it was observed that the amount of pressure on the section also increases. The results of this study can be used in the hydrodynamic analysis of tunneled vessels.

The use of step at the bottom of the hull is one of the effective factors in reducing the resistance and increasing the stability of the Planning hull. The presence of step at the bottom of this type of hulls creates a separation in the flow, which reduces the wet surface on the hull, thus reducing the drag on the body, as well as reducing the dynamic trim. In this study, a design space was created by making changes to the three input parameters. Input parameters include the linear speed of the hull, the distance from the step from the transom and the change in the step height across the hull. The present study was carried out using the Computational Fluid Dynamics (CFD) coupled with Response Surface Method (RSM). The Computational Fluid Dynamics simulation was done by StarCCM+ software. The design of experiments and the Box–Behnken design method were used to select samples and the Kriging model for the Response Surface Method was used. Genetic Algorithm and screening method were also used to find optimal points. Output parameters include Drag and Lift force on the hull, the total hull trim. The results of the sensitivity analysis on the input parameters show that the hulling speed is the most influential parameter on the value of the output parameter.

In the present paper, the turbulent flow around the propeller model 4381 under the sinusoidal flow wake is investigated. Numerical analysis is performed by finite volume method, which first performs numerical simulations of fluid flow around the propeller, and characteristic curves of the hydrodynamic performance of the propeller under open water conditions for different progress coefficients. For the extracted data, validation was performed with experimental values, the maximum and minimum error percentages being 2% and 1.4% for the thrust coefficient and for the propeller torque coefficient of 7.1% and 4.7%, respectively. In the results obtained for sinusoidal flow wake, the rate of change of the thrust coefficient in the progress coefficients of 0.6 and 0.8, respectively, 2.04% and 3.75% and also the rate of change of the torque coefficient for the progress coefficients of 0.6 and 0.8, respectively 15 It is 7.7% and 1.79%. The results show that the sinusoidal flow wake increases the length and width of the vortex produced in the hub and also reduces the velocity and pressure in the area farther from the propeller disc than the free water flow mode, which in turn It can be effective in reducing the thrust force produced by the propeller.

One of the most important issues in the design of a vessel structure is the vibrations of the structure and its effect on the comfort of the crew and the life of the equipment. The most important factor about the comfort of the crew in a vessel is the range of free and forced vibrations under various internal and external factors in the structure of the vessel. One of the serious factors in stimulation of vibrations in the hull vessel is the propeller. Excessive vibrations as well as the being the structure in the frequency range of propeller excitation, cause fatigue, components exhaustion, and also the resonance phenomenon. Resonance and vibration of the components are the structural design challenges, so in this paper, vibrations caused by a five-bladed propeller KP505 excitation were investigated using numerical simulation on a container vessel (KCS). First, the free vibrations of the hull vessel in wet mode were investigated. Then, to investigate the forced vibrations caused by the propeller excitation, the pressure distribution on the hull in self-propulsion mode was obtained from the numerical solution of the fluid flow by computational fluid dynamics. To validate the results, the natural frequencies obtained in free vibrations were compared with empirical formulas. Comparing the values of the first, second and, third bending frequencies with the empirical values, showed that the analysis error was 5.5, 26, and 26.6, respectively, which explain the accuracy of the analysis. Comparing the results of forced vibrations with the standard allowable range, it was shown that the vibrations are within the allowable range. Also, the structure has not being within the range of the excitation frequency of the propeller. As a result, the resonance phenomenon has not occurred.

The acoustic performance of ship propellers is an important issue in ship design. Noise generated by the ship's propeller is one of the most important sources of noise when ship moving in seaway which has a higher frequency range and level than other noise sources. In this study, the fluid field around the DTMB 4119 marine propeller was simulated by the finite volume method and then by the FW-H integral method, the sound pressure level was estimated and validated with the experimental results. In the following, a standard Series B propeller in two different advanced coefficients simulated. its hydrodynamic properties investigated by velocity triangles and extracted vortex structure of the flow. The Steady and unsteady states were used to evaluate the acoustic performance of this propeller. In the steady-state condition, the noise level was lower at high frequencies, while in the unsteady state, noise levels were around 10 dB higher, which be due to ignored unsteady terms. For extrapolation of the result of acoustic noise levels from the model scale to a full scale of the propeller, the ITTC87 method was used.

One of the important issues in evaluating the numerical analysis of ship resistance by the computational fluid dynamics method is to investigate its uncertainty, which includes verification and validation studies. In this study, the KCS container Ship in calm water was simulated numerically at the design speed, equivalent of Froude number 0.26. The finite volume method was used to discretize the Navier Stokes equations and the turbulence model of shear stress transfer. The free surface was modeled by the fluid volume and inertia of the ship motions using the coupled rigid-body coupling equations with fluid. Uncertainty values were assessed for verification and validation studies. The verification study was investigated by three simulation solutions with different mesh resolution . The numerical method uncertainty was less than 5.76% after the study and in the validation study, considering the uncertainty of the model test, the uncertainty was 5.84%. The results showed good accuracy of the method used and gridding.

In this study, a wave-energy converter based on the Oscillating Water Column is simulated using numerical method. Reynolds averaged Navier-Stokes equations are solved by applying a numerical method based on computational fluid dynamics and using an open source OpenFOAM code. A suitable solver for considering the effects of free surface as well as the effects of turbulence is chosen. Numerical validation was performed based on the published experimental results and for a 2D problem. The changes in the water free surface inside the converter, the air pressure as well as the converter efficiency were presented and the effects of the wave parameters on the hydrodynamic performance of the converter were evaluated. Also, the forces acting on the OWC in different conditions are presenterd and can be used in the design of coastal structures. Using the current method and generating regular waves in a numerical tank, and accurately simulating the hydrodynamic characteristics of the converter, and examining the exact parameters of fluid that is not measurable in the experimental analysis, provides a precise and appropriate solution for achieving the best dimensions and location of the converter in terms of the real sea conditions. The accurate results of numerical simulation against the available experimental data and the possibility of detail analysis of flow characteristics versus experimental measurements are highlights of this study.