Wave Kinematics and Seakeeping Calculation With Varying Bathymetry (original) (raw)
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Applied Ocean Research, 2011
The daily productivity of two solar stills (SSs) was investigated experimentally and numerically. Two modifications were done to increase the daily productivity of the conventional SS which include the embedment of mirrors on two side walls and perforated-suspended plate (SP) with various depths. The perforated-SP was placed inside the basin water with different bed depths. The left and right sides were fabricated in double glass with a gap distance to avoid more heat losses from the side walls and simultaneously to place a mirror according to the daytime. The theoretical model was solved numerically by utilizing the fourth-order Runge-Kutta method and the program was written by FORTRAN. The experimental results of conventional SS were verified by the numerical method. The maximum productivity was obtained 4.24 kg/m 2 /day where the mirror was placed in sides and the suspend plate was placed at 0.7 cm in the basin water with a depth of 2.6 cm. The daily productivity was increased by 43% compared to the conventional type. In addition, the thermal efficiency of SS increased 28% in comparison to the conventional SS. The results of the experimental study illustrate that utilizing mirror in sides and suspend plate on the basin water has obvious enhancement in the daily productivity.
Hydrodynamic Analysis of Floating Bodies in General Bathymetry
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2, 2005
A hybrid technique, based on the coupled-mode theory developed by Athanassoulis & Belibassakis (1999) and extended to 3D by Belibassakis et al (2001) and Belibassakis & Athanassoulis (2004), which is free of any mild-slope assumption, is used, in conjunction with a boundary integral representation of the near field in the vicinity of the body, to treat the problem of hydrodynamic analysis of floating bodies in the presence of variable bathymetry. Numerical results are presented concerning floating bodies of simple geometry lying over sloping seabeds. With the aid of systematic comparisons, the effects of bottom slope on the hydrodynamic characteristics (hydrodynamic coefficients and responses) are illustrated and discussed.
Coastal Engineering 1994, 1995
A numerical method has been developed for the analysis of ship motions in a harbor with arbitrary bathymetry. A BEM-based 3-D model, applied partially to a near-field surrounding a ship, is combined with a FEM-based 2-D model, utilized in the remainder of harbor domain. This combination may achieve an efficient computation of the ship motions with taking into account of wave deformation in a harbor. Preliminary examinations have been performed to investigate appropriate location of a matching boundary where these two models are coupled. It is found that, for reliable prediction, (2 ~ 3)ft (h: water depth) is required for the distance between the matching boundary and a body. The numerical results of added mass and damping coefficients for a rectangular floating body in a rectangular basin are then compared with those obtained from a conventional numerical model. Favorable agreement between the results verifies the present numerical method. Ship motions in a harbor with slowly varying depth are also demonstrated.
Applied Ocean Research, 2019
Analysis of a craft with two degrees of freedom (2DOF) consumes time more than simulation of a craft with a fixed trim condition; therefore in most of the previous researches fixed trim condition is taken into account to analyze the flow field around a craft in shallow water and head sea wave conditions. In this paper numerical simulation of Reynolds Average Naiver Stokes (RANS) equations are used to analyze the motion of DTMB 62 model 4667-1 planing vessel in calm water and head sea waves in both deep and shallow water with two degrees of freedom (heave and pitch). For this purpose, a finite volume ANSYS-FLUENT code is used to solve the Navier-Stokes equations for the simulation of the flow field around the vessel. In addition, an explicit VOF scheme and SST k-ω model is used with dynamic mesh scheme to capture the interface of a two-phase flow and to model the turbulence respectively in the 2DOF model. Regarding the results, reducing the wavelength and also the depth of the water can increase the drag force. Also comparing the results of a fixed trim vessel with the results of a free to sink and trim one in calm water shows a difference of approximately 50% in the drag force in shallow water.
Hydroelastic Analysis of Very Large Floating Bodies Over Variable Bathymetry Regions
The coupled-mode model developed by Belibassakis & Athanassoulis (2005) is extended and applied to the hydroelastic analysis of three-dimensional large floating bodies of shallow draft or ice sheets of small thickness, lying over variable bathymetry regions. A general bathymetry is assumed, characterised by a continuous depth function, joining two regions of constant, but possibly different, depth. Following previous works for the propagation and diffraction of water waves over three-dimensional bathymetric terrains (Belibassakis et al 2001, Gerostathis et al 2008), we consider the scattering problem of harmonic incident surface waves, under the combined effects of variable bathymetry and a floating elastic plate of orthogonal planform shape. Under the assumption of small-amplitude waves and small plate deflections, the hydroelastic problem is formulated within the context of linearised water-wave and thin elastic-plate theory. In order to consistently treat the wave field beneath the elastic floating plate, down to the sloping bottom boundary, a complete, local, hydroelastic-mode series expansion of the wave field is used, enhanced by an appropriate sloping-bottom mode. The latter enables the consistent satisfaction of the Neumann bottom-boundary condition on a general topography. Numerical results concerning floating structures over flat and inhomogeneous seabeds are presented, and the effects of wave direction, bottom slope and bottom corrugations on the hydroelastic response are discussed.
Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation, 2009
A non-linear coupled-mode system of horizontal equations has been derived with the aid of variational principle, modelling the evolution of nonlinear water waves in intermediate depth and over a general bathymetry . Following previous work by the authors in the case of linearised water waves (Athanassoulis & Belibassakis 1999), the vertical structure of the wave field is exactly represented by means of a local-mode series expansion of the wave potential. This series contains the usual propagating and evanescent modes, plus two additional modes, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The coupled-mode system fully accounts for the effects of non-linearity and dispersion. The main feature of this approach that a small number of modes (of the order of 5-6) are enough for the precise numerical solution, provided that the two new modes (the free-surface and the sloping-bottom ones) are included in the local-mode series. The consistent coupled-mode system has been applied to numerical investigation of families of steady nonlinear travelling wave solutions in constant depth showing good agreement with known solutions both in the Stokes and the cnoidal wave regimes. In the present work we focus on the hydroelastic analysis of floating bodies lying over variable bathymetry regions, with application to the non-linear scattering of water waves by large floating structures (of VLFS type or ice sheets) characterised by variable thickness (draft), flexural rigidity and mass distributions, modelled as thin plates of variable thickness, extending previous approaches (see, e.g., .
Numerical Investigation of Motion Response of Two Model Ships in Regular Waves
In this paper, the sea keeping performances of two model ships in regular waves are studied by our in-house solver naoe-FOAM-SJTU based on OpenFOAM code package. Volume of Fluid (VOF) method is used to capture the free interface and Finite Volume Method (FVM) is adopted as the discretization scheme. Different wave conditions are set by the wave generation and damping module in the solver. The heave and pitch are simulated, and green water is found during the ship motion. The function of bulbous bow for that is discussed.
The Quest for a Three-Dimensional Theory of Ship-Wave Interactions [and Discussion]
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1991
The radiation and diffraction of water waves by ships can be analysed in classical terms from potential theory. The linearized formulation is well studied, but robust numerical implementations have been achieved only in cases where the vessel is stationary or oscillating about a fixed mean position. Slender-body approximations have been used to rationalize and extend the strip theory of ship motions, providing analytic solutions and guidance in the development of more general numerical methods. The governing equations are reviewed, with emphasis on the interactions between the steady-state velocity field due to the ship’s forward translation and the perturbations due to its unsteady motions in waves. Recent computations based on the boundary-integral-equation method are described, and encouraging results are noted. There is growing evidence that the influence of the steady-state velocity field is important, and the degree of completeness required to account for the steady field depe...
Energies
In this paper, a novel model based on the boundary element method (BEM) is presented for the hydrodynamic analysis of floating twin-hull structures carrying photovoltaic panels, supporting the study of wave responses and their effects on power performance in variable bathymetry regions. The analysis is restricted to two spatial dimensions for simplicity. The method is free of any mild-slope assumptions. A boundary integral representation is applied for the near field in the vicinity of the floating body, which involved simple (Rankine) sources, while the far field is modeled using complete (normal-mode) series expansions that are derived using separation of variables in the constant depth half-strips on either side of the middle, non-uniform domain, where the depth exhibited a general variation, overcoming a mild bottom-slope assumption. The numerical solution is obtained by means of a low-order panel method. Numerical results are presented concerning twin-hull floating bodies of si...
COMPUTATION OF WAVE-MAKING RESISTANCE OF TETRAMARAN HULL IN UNBOUNDED WATER
buet.ac.bd
This paper investigates the analysis of potential flow around the tetramaran hull moving with a uniform velocity in unbounded water using a surface panel method. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The pressure Kutta condition is imposed at the trailing edge of the lifting body to determine the dipole distribution, which generates required circulation on the lifting part. The effects of hull separation and the hull stagger on the wave making resistance of the tetramaran hull are analyzed.