scholarly journals Research on Wave Attenuation Performance of Floating Breakwater

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8316
Author(s):  
Hao Li ◽  
Junhua Chen ◽  
Lingjie Bao ◽  
Chuhua Jiang
Keyword(s):  
Wave Attenuation ◽  
Performance Testing ◽  
Line Tension ◽  
Wave Theory ◽  
Hydrodynamic Theory ◽  
Hydrodynamic Characteristics ◽  
Mooring Line ◽  
Linear Wave ◽  
Relative Spacing ◽  
Floating Breakwater

In this study, a new type of double-pontoon floating breakwater was designed to improve the wave attenuation performance through the addition of suspended Savonius propeller-blade. Its hydrodynamic characteristics were studied through numerical simulations and performance-testing experiment. The following investigations were performed in this study: Firstly, wave theory and hydrodynamic theory were combined to calculate the wave attenuation performance and motion response of double-pontoon floating breakwater under linear wave conditions. The numerical results showed that the wave attenuation performance was better under a specific wave period and height, the transmission coefficient reached a relatively small value, and the mooring line tension responded periodically and satisfied the condition of maximum breaking force. Secondly, three key geometric parameters of breakwater were researched, including the relative spacing of pontoons, the relative spacing between pontoons and blades, and the height–diameter ratio of Savonius blades. The calculation results showed that the pontoon spacing was closer to the wavelength and the breakwater wave attenuation performance was better. Lastly, experimental tests were also performed on the new double-pontoon floating breakwater and the results showed that the wave attenuation performance and numerical projections were basically the same, which verified the validity and effectiveness of the design method.

scholarly journals MECHANICALLY COUPLED BUOYANT FLAPS: THEORY AND EXPERIMENT

1986 ◽  
Vol 1 (20) ◽  
pp. 180
Author(s):  
Charles K. Sollitt ◽  
Chung-Pan Lee ◽  
William G. McDougal ◽  
Thomas J. Perry
Keyword(s):  
Coupled System ◽  
Line Tension ◽  
Wave Theory ◽  
Mooring Line ◽  
Linear Wave ◽  
Mooring Lines ◽  
Sea Floor ◽  
Transmitted Waves ◽  
Parallel Tube ◽  
Incident Waves

A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring lines is modeled analytically and experimentally. The system behavior is described theoretically utilizing an eigenseries representation of linear wave theory in the vicinity of the breakwater. The structure dynamics are modeled in terms of structure weight, inertia, buoyancy, damping, mooring line tension and the wave pressure field. The mechanically coupled system provides shelter by reflecting incident waves and by attenuating wave energy through structural and viscous damping. The structure can be tuned to minimize wave transmission within a particular frequency range by changing the flap spacing and adjusting the mass and equilibrium position of the mooring line weights. The theory is validated with experimental results for models fabricated from inflatable, parallel-tube membranes. Buoyancy and inertia are changed by filling tubes with air and/or water. Single and double flaps are examined with and without mooring lines. Incident, reflected, and transmitted waves are measured as well as flap motion. Theoretical results are corroborated by the experiments and the importance of including damping in the model is demonstrated.

A Finite Element Model for Efficiency of a Moored Floating OWC Device in Regular Waves

2011 ◽  
Author(s):  
Jean-Roch Nader ◽  
Song-Ping Zhu ◽  
Paul Cooper ◽  
Brad Stappenbelt
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Wave Theory ◽  
Element Model ◽  
Energy Output ◽  
Chamber Pressure ◽  
Hydrodynamic Characteristics ◽  
Linear Wave ◽  
Regular Waves ◽  
Restoring Force

Hydrodynamic characteristics of floating OWC can be quite difficult to predict especially when a strong coupling is present between the chamber pressure and the device movements. Mooring properties, and air pressure inside the chamber can also considerably influence the motion of the device and therefore the energy output. A newly developed 3D finite element model based on the linear wave theory has been applied to a cylindrical type OWC device. The study focused principally on the effects of the mooring restoring force and pressure pneumatic damping in the chamber total volume flux and energy conversion of the device. Results show that properly chosen parameters could effectively increase the efficiency band width of such devices.

scholarly journals Numerical Study on the Hydrodynamic Characteristics of a Double-Row Floating Breakwater Composed of a Pontoon and an Airbag

2021 ◽  
Vol 9 (9) ◽  
pp. 983
Author(s):  
Xiaofei Cheng ◽  
Chang Liu ◽  
Qilong Zhang ◽  
Ming He ◽  
Xifeng Gao
Keyword(s):  
Numerical Model ◽  
Wave Attenuation ◽  
Separation Distance ◽  
Hydrodynamic Characteristics ◽  
Leeward Side ◽  
Solid Boundary ◽  
Lumped Mass ◽  
Double Row ◽  
Wave Regime ◽  
Floating Breakwater

By adding a cylindrical airbag on the leeward side of a cuboid pontoon, a new-type double-row floating breakwater is designed to improve the wave attenuation performance, and its hydrodynamic characteristics are studied through numerical simulations. First, based on the smoothed particle hydrodynamics (SPH) method, a numerical model used to simulate the interaction between waves and moored floating bodies is built. The fluid motion is governed by the Navier–Stokes equations. The motion of the floating body is computed according to Newton’s second law. The modified dynamic boundary condition is employed to treat the solid boundary. The lumped-mass method is adopted to implement the mooring system. Then, two physical model experiments on waves interaction with cuboid and dual cylindrical floating pontoons are reproduced. By comparing the experimental and numerical wave transmission coefficients, wave reflection coefficients, response amplitude operators and mooring force, the reliability of the numerical model is validated. Finally, the validated numerical model is applied to study the influence of separation distance and wave parameters on the hydrodynamic characteristics of the double-row floating breakwater. The results indicate that the optimal separation distance between pontoon and airbag is 0.75 times the wavelength. At such separation distance and within the concerned 1–4 m wave heights and 4–7 s wave periods, the pontoon-airbag system presents better wave attenuation performance than a single pontoon. This improvement weakens as wave height increases while it strengthens as the wave period increases. In addition, the double-row floating breakwater is more effective in a high-wave regime than in a low-wave regime. In the case of short waves, attention should be paid to the stability and mooring reliability of the seaward pontoon, while in the case of long waves, care needs to be taken of the leeward airbag.

Numerical Analysis of Submersible Mussel Raft for Exposed Marine Environment

2017 ◽  
Author(s):  
Xinxin Wang ◽  
Fenfang Zhao ◽  
Yanli Tang ◽  
Liuyi Huang ◽  
Rong Wan ◽  
...  
Keyword(s):  
Finite Element ◽  
Marine Environment ◽  
Line Tension ◽  
Hydrodynamic Characteristics ◽  
Mooring Line ◽  
Mooring Lines ◽  
Finite Element Program ◽  
Wave Condition ◽  
Waves And Currents ◽  
Submergence Depth

To study the hydrodynamic characteristics of the submersible mussel raft in waves and currents, the numerical model of the submersible raft was established based on the finite element method and kinematics theory. The finite element program Aqua-FE™ was applied to simulate the impacts of waves and currents on the hydrodynamic responses of the surface and submerged rafts, respectively. Morison Equation was applied to compute the tension of the mooring lines. Apart from the wave condition, the flow has a significant effect on the mooring line tension of the submersible raft. The submerged raft is useful for reducing the mooring loads. The submergence depth of the mussel raft can be adjusted depending on the marine environment. The results show that the submerged raft wave response was found to be reduced relative to the surface raft. The vertical motion of mussel rope connection points was significantly reduced by submergence, resulting in reduced potential for mussel drop-off. Compared the performance of the submerged raft in the same condition, the motion amplitude of the framework of the raft decreased significantly while increasing the submergence depth. At the same period, the trend of the decrease followed by levelling off with an increasing wave height. However, the submergence depth had no significant effect on the mooring line tension.

scholarly journals Theoretical Hydrodynamic Analysis of a Surface-Piercing Porous Cylindrical Body

Fluids ◽  
2021 ◽  
Vol 6 (9) ◽  
pp. 320
Author(s):  
Dimitrios N. Konispoliatis ◽  
Ioannis K. Chatjigeorgiou ◽  
Spyridon A. Mavrakos
Keyword(s):  
Water Waves ◽  
Wave Attenuation ◽  
Three Dimensional ◽  
Cylindrical Body ◽  
Expansion Method ◽  
Wave Theory ◽  
Linear Wave ◽  
Wave Loads ◽  
Dimensional Solution ◽  
Eigenfunction Expansion Method

In the present study, the diffraction and the radiation problems of water waves by a surface-piercing porous cylindrical body are considered. The idea conceived is based on the capability of porous structures to dissipate the wave energy and to minimize the environmental impact, developing wave attenuation and protection. In the context of linear wave theory, a three-dimensional solution based on the eigenfunction expansion method is developed for the determination of the velocity potential of the flow field around the cylindrical body. Numerical results are presented and discussed concerning the wave elevation and the hydrodynamic forces on the examined body for various values of porosity coefficients. The results revealed that porosity plays a key role in reducing/controlling the wave loads on the structure and the wave run-up, hence porous barriers can be set up to protect a marine structure against wave attack.

scholarly journals Representative Transmission Coefficient for Evaluating the Wave Attenuation Performance of 3D Floating Breakwaters in Regular and Irregular Waves

2021 ◽  
Vol 9 (4) ◽  
pp. 388
Author(s):  
Huu Phu Nguyen ◽  
Jeong Cheol Park ◽  
Mengmeng Han ◽  
Chien Ming Wang ◽  
Nagi Abdussamie ◽  
...  
Keyword(s):  
Transmission Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Transmitted Wave ◽  
Irregular Waves ◽  
Hydrodynamic Analysis ◽  
Evaluation Approach ◽  
Floating Breakwater ◽  
Floating Breakwaters ◽  
Evaluation Approaches

Wave attenuation performance is the prime consideration when designing any floating breakwater. For a 2D hydrodynamic analysis of a floating breakwater, the wave attenuation performance is evaluated by the transmission coefficient, which is defined as the ratio between the transmitted wave height and the incident wave height. For a 3D breakwater, some researchers still adopted this evaluation approach with the transmitted wave height taken at a surface point, while others used the mean transmission coefficient within a surface area. This paper aims to first examine the rationality of these two evaluation approaches via verified numerical simulations of 3D heave-only floating breakwaters in regular and irregular waves. A new index—a representative transmission coefficient—is then presented for one to easily compare the wave attenuation performances of different 3D floating breakwater designs.

A Second Order Lagrangian Model for Irregular Ocean Waves

2005 ◽  
Vol 128 (3) ◽  
pp. 177-183 ◽  
Author(s):  
Sébastien Fouques ◽  
Harald E. Krogstad ◽  
Dag Myrhaug
Keyword(s):  
Specular Reflection ◽  
Fluid Velocity ◽  
Equations Of Motion ◽  
Wave Theory ◽  
Ocean Waves ◽  
Second Order ◽  
Lagrangian Model ◽  
Lagrangian Description ◽  
Linear Wave ◽  
Irregular Solution

Synthetic aperture radar (SAR) imaging of ocean waves involves both the geometry and the kinematics of the sea surface. However, the traditional linear wave theory fails to describe steep waves, which are likely to bring about specular reflection of the radar beam, and it may overestimate the surface fluid velocity that causes the so-called velocity bunching effect. Recently, the interest for a Lagrangian description of ocean gravity waves has increased. Such an approach considers the motion of individual labeled fluid particles and the free surface elevation is derived from the surface particles positions. The first order regular solution to the Lagrangian equations of motion for an inviscid and incompressible fluid is the so-called Gerstner wave. It shows realistic features such as sharper crests and broader troughs as the wave steepness increases. This paper proposes a second order irregular solution to these equations. The general features of the first and second order waves are described, and some statistical properties of various surface parameters such as the orbital velocity, slope, and mean curvature are studied.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

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