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Numerical simulation of transom stern flow has proven to be an interesting topic, but a complicated task in the hydrodynamic field of research. In this paper, a three-dimensional numerical simulation is presented using Ansys-CFX to survey the free surface flow, downstream of the transom stern. To this end, finite volume method coupled with volume of fluid is utilised and k-e turbulent model is applied. The numerical solutions are validated by comparing the findings against the results of empirical formula available in the literature. In order to conduct a parametric study, four different Froude numbers, four trim angles, and two deadrise angles are considered and the effect of each of these parameters is studied.

Water impact phenomenon in the case of a circular cylinder is an important issue in offshore industry where cross members may be in the splash zone of the incident wave. An analytical method as well as a numerical solution are employed to study the water entry problem of a circular section. The procedure for derivation of the analytical formulas is demonstrated step by step. The volume of fluid (VOF) simulation of the water entry problem is also performed to offer comparison of the results of the linearized analytical solution with a fully nonlinear and viscous fluid flow solution. To achieve this, the FLOW-3D code is utilized. Some consideration has also been given to the points of intersection of the free surface and the body, where the singularities exist in the free surface deformation and velocities, as predicted by the linear theory. These singularities appear to be avoided in the real fluid by the formation of jets which quickly break up into sprays under the action of surface tension. Slamming force, free surface profile, impact force, pressure distribution and evolution of intersection points are also presented and comparisons of the obtained results against the results of previous studies illustrate favorable agreements.

In this paper, diffraction problem of a floating vertical circular cylinder is studied. Detailed analytical solution for the boundary value problem to evaluate the wave loads for the cylinder with heave and pitch motions in water of finite depth in the presence of an incident wave, has been presented. Accordingly, diffraction problem for a truncated vertical circular cylinder of radius in water of finite depth has been considered. Incident wave used in this problem, is assumed to be linear with amplitude . In order to calculate the added mass and damping coefficients of the pitch motion of the body, strip theory is applied. For the heave motion, the hydrodynamic coefficients are found by the submerged disk method. Parametric studies of the effects of the wave excitation force on the floating cylinder have been performed for two different cases: 1) constant draft of the cylinder with varying water depth and 2) varying draft of the cylinder with constant water depth.

Fin stabilizers are very effective devices for controlling the ship roll motion against external wave-generated moments. Lift forces due to flow around fin with an angle of attack produce anti - roll moment. Therefore control of attack angle plays important role in reducing roll of ships. This paper presents results of using a combined neural network and PID for roll control of ship with small draught. Numerical results are given of around-fin flow analysis with considering free surface effect modelled by neural network and imposed to controlling loop. Hydraulic machinery constraints are also considered in the modelling. The obtained results show good performance of the controller in reducing roll amplitude in random seas. The approach can be used for any irregular sea conditions.

Two versions of a model for the thermal behavior of the lubricant film in the cavitation region of a journal bearing are presented and incorporated into a solution algorithm for the operating characteristics of an axially grooved bearing. The model is based on an approximation of the flow as two parts: Couette-like streamers plus uniform velocity portions adhered to the journal. One version (CH) results from assuming a constant ratio between the cavity height and the local gap height. The other (FH), results from assuming a constant thickness of the adhered fluid layer. An approximate energy equation is derived for the rupture zone and applied to the calculation of the bearing wall temperature. Parametric studies of the effects of the choice of cavity dimensions indicate that for appropriate choices the agreement between theory and published experiment is significantly better for the new methods. Agreement is lightly better for the FH model that for the CH model, and because of physical arguments the FH m...

Fin stabilizers are very important device for controlling the ship roll motion against the external moments due to wave. This paper presents numerical results for flow field simulation and the hydrodynamic performance of fin stabilizer attached to a ship hull with free surface effects. Combination of CFD and RANS method has been used for this study. The fin is non-rectangular NACA0015 profile section with a finite aspect ratio. The numerical results include pressure distributions and flow field around the fin which are used to calculate lift coefficients and free surface elevation as the main interest. Some results are compared with available experimental and numerical data in literature and they show good agreement.Copyright © 2009 by ASME

Any harbor should be protected from incoming waves. However, these waves are always diffracted at the entrance of the harbor and a fraction of the waves enters the harbor area. In the present paper, by the use of Boussinesq equations solved by Mike21 numerical software, a parametric study on the length of entrance of a simple harbor has been conducted and the diffraction of waves after passing the harbor entrance has been analyzed. As a result, the effects of the length of the entrance have been investigated on the safe zone behind the breakwaters of the harbor. To this end, a parameter called angle of safety is defined as a representative of the safe zone. Finally, an equation is presented to describe the behavior of the safe zone with respect to the length of the entrance. It has been observed that the angle of safety has a minimum of 57.5 degrees which increases with respect to the length of entrance which consequently increases the safe area behind the breakwaters.

Depending on different design parameters and limitations, optimization of sound absorbers has always been a challenge in the field of acoustic engineering. Various methods of optimization have evolved in the past decades with innovative method of evolution strategy gaining more attention in the recent years. Based on their simplicity and straightforward mathematical representations, single-layer absorbers have been widely used in both engineering and industrial applications and an optimized design for these absorbers has become vital. In the present study, the method of evolution strategy algorithm is used for optimization of a single-layer absorber at both a particular frequency and an arbitrary frequency band. Results of the optimization have been compared against different methods of genetic algorithm and penalty functions which are proved to be favorable in both effectiveness and accuracy. Finally, a single-layer absorber is optimized in a desired range of frequencies that is the main goal of an industrial and engineering optimization process.

Numerical simulation of fluid flow phenomena, including complicated free surface deformation, has been a main research interest for many authors. In this context, using mesh based methods has been a common choice in the past decades. However, in the recent years, Smoothed Particle Hydrodynamics (SPH) as a Lagrangian meshless method has been utilized in many of applications. In the present article, a two dimensional solitary wave on a beach is generated and the effect of various wave heights to water depth ratios on solitary wave generation are studied. Furthermore, condition in which wave breaking occurs is also considered. Finally, the results of SPH simulations are compared against the available results in the literature and it is shown that Solitary wave profile simulated by SPH is in good agreement with experimental data.

Through the use of perturbation theory, Kuo has previously introduced a joint surface roughness/volumetric model in order to characterize bubbly sea surface reverberation based on volumetric wave spectra, surface roughness wave spectrum, and correlation of volumetric wave spectrum and surface roughness wave spectrum. Due to the lack of undetermined volumetric scattered wave number Kv, Kuo obtained backscattering strengths using only Pierson-Moskwitz wave spectrum. In this paper, the reformed integral equation of authentic Helmholtz-Kirchhoff-Fresnel is discussed in which volumetric scattering is involved. By applying the reformed Helmholtz-Kirchhoff-Fresnel, volumetric scattered acoustic pressure field Pv is obtained. Using Helmholtz wave equation and the obtained pressure field Pv, the wave number vector of volumetric scattered field Kv is calculated, and this used to compute the volumetric wave spectrum and the joint surface roughness/volumetric wave spectrum. The obtained spectra are then used to compute scattering strengths. Comparison of the obtained results against the results of experimental Critical Sea Tests shows good agreement. Finally, a parametric study is conducted to examine the effects of wind speeds, grazing angles, and frequencies on the scattering strengths.