A novel numerical method for the hydrodynamic analysis of floating bodies over a sloping bottom

Tuna can change the area and shape of the median fins, including the first dorsal, second dorsal, and anal fins. The morphing median fins have the ability of adjusting the hydrodynamic forces, thereby affecting the yaw mobility of tuna to a certain extent. In this paper, the hydrodynamic analysis of the median fins under different morphing states is carried out by the numerical method, so as to clarify the influence of the erected median fins on the yaw maneuvers. By comparing the two morphing states of erected and depressed, it can be concluded that the erected median fins can increase their own hydrodynamic forces during the yaw movement. However, the second dorsal and anal fins have limited influence on the yaw maneuverability, and they tend to maintain the stability of tuna. The first dorsal fin has more lift increment in the erection state, which can obviously affect the hydrodynamic performance of tuna. Moreover, as the median fins are erected, the hydrodynamic forces of the tuna’s body increase synchronously due to the interaction between the body and the median fins, which is also very beneficial to the yaw motion. This study indicates that tuna can use the morphing median fins to adjust its mobility and stability, which provides a new idea for the design of robotic fish.

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Hydrodynamic Analysis of Twin-Hull Structures Supporting Floating PV Systems in Offshore and Coastal Regions

Energies ◽

10.3390/en14185979 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5979

Author(s):

Alexandros Magkouris ◽

Kostas Belibassakis ◽

Eugen Rusu

Keyword(s):

Separation Of Variables ◽

Near Field ◽

Boundary Integral ◽

Floating Body ◽

Hydrodynamic Characteristics ◽

Uniform Domain ◽

Bottom Slope ◽

Power Performance ◽

Floating Bodies ◽

Hydrodynamic Analysis

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 simple geometry lying over uniform and sloping seabeds. With the aid of systematic comparisons, the effects of the bottom slope and curvature on the hydrodynamic characteristics (hydrodynamic coefficients and responses) of the floating bodies are illustrated and discussed. Finally, the effects of waves on the floating PV performance are presented, indicating significant variations of the performance index ranging from 0 to 15% depending on the sea state.

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A Parametric Study on the Innovative Coupling Arm Connecting the Coupled TAD-TLP

MATEC Web of Conferences ◽

10.1051/matecconf/201820301017 ◽

2018 ◽

Vol 203 ◽

pp. 01017 ◽

Cited By ~ 1

Author(s):

Xiangbo Liu ◽

Allan Ross Magee ◽

Aziz Merchant ◽

Anis Hussain ◽

Ankit Choudhary ◽

...

Keyword(s):

Parametric Study ◽

Hydrodynamic Interactions ◽

Floating Bodies ◽

Tension Leg Platform ◽

Commercial Software ◽

Hydrodynamic Analysis ◽

Marine Systems ◽

Connection System ◽

Rigid Connection ◽

Two Bodies

Two body marine systems, like a Tender Assisted Drilling (TAD) vessel coupled with a floating Dry-Tree Unit (DTU), have become very common in offshore operations. One of the unavoidable challenge we have to cope with is the connection between the TAD and DTU should make sure the TAD does not drift away from the platform and also avoid the possible collision in case of a harsher environment. The objective of this study is to understand the hydrodynamic interactions between the two coupled floating bodies and improve the devising of the innovative connection system. In this study, an innovative rigid connection system, the coupling arm is applied to connect the TAD and a DTU, in this case, a Tension Leg Platform (TLP). The whole system is modelled by the commercial software HARP. A comprehensive parametric study on the pretension and the nominal length of the coupling arm is carried out. The hydrodynamic analysis of the coupled TAD-TLP system elucidates the interactions between the two bodies. The chosen combination of the coupling arm pretension and the nominal length will determine the required stroke range and maximum forces needed to design the innovative coupling arm for safe operations.

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Hydrodynamic Analysis of Floating Bodies in General Bathymetry

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2 ◽

10.1115/omae2005-67041 ◽

2005 ◽

Cited By ~ 3

Author(s):

K. A. Belibassakis

Keyword(s):

Near Field ◽

Boundary Integral ◽

The Body ◽

Hydrodynamic Characteristics ◽

Hybrid Technique ◽

Floating Bodies ◽

Hydrodynamic Analysis ◽

Coupled Mode ◽

Simple Geometry ◽

Boundary Integral Representation

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.

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Validation of a New Hydroelastic Code for Flexible Floating Structures Moored in Waves

Volume 1: Offshore Technology ◽

10.1115/omae2009-79989 ◽

2009 ◽

Cited By ~ 1

Author(s):

J. L. F. van Kessel

Keyword(s):

Wave Spectrum ◽

Three Dimensional ◽

Numerical Results ◽

Floating Bodies ◽

Hydrodynamic Analysis ◽

Floating Structures ◽

University Of Technology ◽

Deformable Bodies ◽

Elastic Modes ◽

Experimental Values

Natural periods of elastic modes can be in the range of the wave spectrum for relatively long and slender floating bodies. As a result elastic body deformations such as vertical bending, horizontal bending and torsion may be significant and need to be taken into account in the hydrodynamic analysis of very large floating structures. The behavior of flexible floating bodies in waves has been studied at Delft University of Technology. For this purpose the existing linear three dimensional diffraction code DELFRAC was modified to take into account the fluid-structure interaction of deformable bodies at zero forward speed in waves. This paper focuses on the validation of the new hydroelastic code for flexible floating structures moored in waves. Numerical results are validated by model experiments of a flexible barge in waves from different headings. In addition, the obtained results are compared with results from other existing hydroelastic programs. In general it is shown that numerical results show good agreement with experimental values.

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A Fast Convergent Modal-Expansion of the Wave Potential With Application to the Hydrodynamic and Hydroelastic Analysis of Floating Bodies in General Bathymetry

Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation ◽

10.1115/omae2009-79681 ◽

2009 ◽

Cited By ~ 1

Author(s):

K. A. Belibassakis ◽

G. A. Athanassoulis

Keyword(s):

Free Surface ◽

Variable Thickness ◽

Water Waves ◽

Local Mode ◽

Floating Bodies ◽

Coupled Mode ◽

Wave Potential ◽

Non Linear ◽

Hydroelastic Analysis ◽

Sloping Bottom

A non-linear coupled-mode system of horizontal equations has been derived with the aid of Luke’s (1967) variational principle, modelling the evolution of nonlinear water waves in intermediate depth and over a general bathymetry Athanassoulis & Belibassakis (2002, 2008). 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 (Athanassoulis & Belibassakis 2007) 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., Porter & Porter 2004, Belibassakis & Athanassoulis 2005, 2006, Bennets et al 2007). Numerical examples are presented, showing that useful results can be obtained for the analysis of large floating elastic bodies or structures very efficiently by keeping only a few terms in the expansion. Ideas for extending our approach to 3D are also discussed.

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