scholarly journals THE INTERACTION OF OBLIQUE WAVES WITH A PARTIALLY IMMERSED WAVE ABSORBING BREAKWATER

2011 ◽  
Vol 1 (32) ◽  
pp. 56 ◽  
Author(s):  
Yong Liu ◽  
Yucheng Li
Keyword(s):  
Hydrodynamic Performance ◽  
Design Stage ◽  
Wave Forces ◽  
Linear Potential ◽  
Transmission Coefficients ◽  
Present Solution ◽  
Preliminary Design Stage ◽  
Practical Engineering ◽  
Linear Potential Theory ◽  
Incident Waves

By considering obliquely incident waves, the hydrodynamic performance of a partially immersed wave absorbing breakwater is examined in this study. The breakwater consists of a perforated front barrier and a solid rear barrier. The two barriers are both partially immersed with the same draft. An analytical solution based on the linear potential theory is developed to calculate the reflection and transmission coefficients of the breakwater and the wave forces acting on the barriers. Some useful results are presented according to numerical examples. The present solution may be used at a preliminary design stage in practical engineering.

scholarly journals Analytical Study on an Oscillating Buoy Wave Energy Converter Integrated into a Fixed Box-Type Breakwater

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Xuanlie Zhao ◽  
Dezhi Ning ◽  
Chongwei Zhang ◽  
Yingyi Liu ◽  
Haigui Kang
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Hydrodynamic Performance ◽  
Maximum Efficiency ◽  
Width Ratio ◽  
Geometrical Parameters ◽  
Linear Potential ◽  
Energy Converter ◽  
Transmission Coefficients ◽  
Incident Waves

An oscillating buoy wave energy converter (WEC) integrated to an existing box-type breakwater is introduced in this study. The buoy is installed on the existing breakwater and designed to be much smaller than the breakwater in scale, aiming to reduce the construction cost of the WEC. The oscillating buoy works as a heave-type WEC in front of the breakwater towards the incident waves. A power take-off (PTO) system is installed on the topside of the breakwater to harvest the kinetic energy (in heave mode) of the floating buoy. The hydrodynamic performance of this system is studied analytically based on linear potential-flow theory. Effects of the geometrical parameters on the reflection and transmission coefficients and the capture width ratio (CWR) of the system are investigated. Results show that the maximum efficiency of the energy extraction can reach 80% or even higher. Compared with the isolated box-type breakwater, the reflection coefficient can be effectively decreased by using this oscillating buoy WEC, with unchanged transmission coefficient. Thus, the possibility of capturing the wave energy with the oscillating buoy WEC integrated into breakwaters is shown.

Wave Scattering From Multiple Horizontal Plates as a Breakwater

2009 ◽  
Author(s):  
Guoyu Wang ◽  
Yongxue Wang
Keyword(s):  
Water Depth ◽  
Plate Thickness ◽  
Wave Theory ◽  
Linear Potential ◽  
Antisymmetric Part ◽  
Transmission Coefficients ◽  
Present Solution ◽  
Relative Water ◽  
Constant Coefficients ◽  
Finite Water Depth

The multiple horizontal plates breakwater is proposed in this article, which mainly consists of several horizontal plates. The regular wave test results demonstrate that it has good performance of dissipating waves. Based on the linear potential wave theory, the scattering of waves normally incident on the multiple horizontal plates in a channel of finite water depth is investigated. The velocity potential is split to the symmetric and antisymmetric part, and the method of eigenfunction expansions is used to obtain the unknown constant coefficients determined from the matching conditions. The thickness of the plates is considered in the theoretical analysis. The present solution is compared with the existing theoretical, numerical and experimental results with good agreements. The parameters such as the relative water depth, relative plate width, relative plate thickness and number of plates, those identified with the performance of the breakwater are investigated and discussed. The variation of reflection and transmission coefficients alone with the above mentioned parameters are also presented.

Research on Resonant Fluid Behaviors and Induced Violent Slamming Effects in a Stepped Moonpool Under Wave Excitations With Ship Forward Speed

2020 ◽  
Author(s):  
Hongguan Lyu ◽  
Jiayang Gu ◽  
Yanwu Tao ◽  
Zhongyu Zhang
Keyword(s):  
Natural Frequencies ◽  
Structural Strength ◽  
Nonlinear Effects ◽  
Hydrodynamic Performance ◽  
Linear Potential ◽  
Water Effects ◽  
Practical Engineering ◽  
Moon Pool ◽  
Piston Mode ◽  
External Wave

Abstract Moonpools on drilling vessels are structures located at the mid-ship position to facilitate drilling and other marine operations. The existence of the moonpools is prone to result in intense resonant fluid behaviors even other unexpected violent nonlinear impact on the flow system under external excitations, especially for those types with one or more recesses. The present study focuses on the resonant fluid behaviors and the induced violent nonlinear effects so-called slamming in a moonpool with a recess within the frameworks of both theoretical and numerical investigations. The natural frequencies of the piston mode and the first-three modes of the studied moonpool are approximated based on the theoretical formulas extracted from the linear potential flow theory. Furthermore, the calculated frequency of piston mode are carried out as the external wave excitations combined with varying current velocity to investigate the slamming effects at the typical locations such as the wall of the moonpool and the bottom of the recess. Finally, the characteristics of the slamming pressure both in space and time are discussed in detail based on the RANS-based numerical simulations. The result shows that the resonant fluid behaviors under the wave-current interactions are greatly different from the wave-only excitations. Moreover, intense slamming occur in a moon-pool with a recess under some particular wave-current interactions due to the shallow water effects in the recess region and the phenomenon of energy transfer. The phenomenon of slamming must be treated with special cautions in practical engineering because of the fact that some induced adverse effects could weaken the hydrodynamic performance of the drilling vessel, as well as the structural strength of the moonpool.

On the Interaction of Waves With Intake/Discharge Flows Originating From a Freely-Floating Body

2002 ◽  
Author(s):  
B. Padmanabhan ◽  
R. C. Ertekin
Keyword(s):  
Free Surface ◽  
Surface Condition ◽  
Floating Body ◽  
Wave Forces ◽  
Linear Potential ◽  
Rankine Source ◽  
Total Potential ◽  
Low Froude Number ◽  
Linear Potential Theory ◽  
Steady Potential

This work is motivated by the many instances of intake/discharge flows from openings on floating or submerged ocean vessels and structures that may affect the wave field around them. Damaged vessels may release oil, or water may enter these vessels through openings. In oil skimming operations, for example, a very thin layer of oil must be skimmed off a large surface area, and therefore, oil skimming vessels require large intakes. Floating OTEC plants also require large intake and discharge volumes to sustain their operations. A linear theory is developed to obtain the motions of a 2-dimensional, freely floating body (from which steady intake/discharge flows originate) that encounters incoming waves. The boundary-value problem is formulated within the assumptions of linear potential theory by decomposing the total potential into its oscillatory and steady components. The steady potential is further decomposed into the double-model and perturbation potentials. The time-harmonic potential is coupled with the steady potential through the free-surface condition. The potentials are obtained by use of the quadratic boundary-element method based on the Rankine source. The effect of the steady intake/discharge flows on the diffraction loads, hydrodynamic force coefficients, as well as the motions of a 2-dimensional prismatic body floating on the free surface are presented. It is shown that the exciting wave forces and the hydrodynamic coefficients other than the damping coefficients are not appreciably affected by the intake/discharge flows of low Froude number for a 100MW floating OTEC plant.

Study of Motion Performance of a Floating System With Four Moonpools and a VAWT

2021 ◽  
Author(s):  
Lei Tan ◽  
Satsuya Moritsu ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Potential Theory ◽  
Theoretical Calculations ◽  
Model Tests ◽  
Hydrodynamic Performance ◽  
Linear Potential ◽  
Gyroscopic Effect ◽  
Floating Foundation ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions. The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.

Sloshing in a Cylindrical Liquid Storage Tank With a Floating Roof Under Seismic Excitation

2006 ◽  
Author(s):  
Tetsuya Matsui
Keyword(s):  
Storage Tank ◽  
Expansion Method ◽  
Seismic Excitation ◽  
Design Stage ◽  
Linear Potential ◽  
Early Design Stage ◽  
Liquid Storage ◽  
Preliminary Study ◽  
Liquid Storage Tank ◽  
Linear Potential Theory

An analytical solution is presented to predict the sloshing response of a cylindrical liquid storage tank with a floating roof under seismic excitation. The contained liquid is assumed to be inviscid, incompressible and irrotational, while the floating roof is idealized as an isotropic elastic plate with uniform stiffness and mass. The dynamic interaction between the floating roof and the liquid is taken into account exactly within the framework of linear potential theory. By expanding the response of the floating roof into free vibration modes in air and employing the Fourier-Bessel expansion method in cylindrical coordinates, the solution is obtained in an explicit form which is useful for parametric understanding of the sloshing behavior and preliminary study in the early design stage. Numerical results are also provided to investigate the effect of the stiffness and mass of the floating roof on the sloshing response.

Analytical study of oblique wave scattering by a submerged pile–rock breakwater

2017 ◽  
Vol 233 (1) ◽  
pp. 41-54 ◽  
Author(s):  
Ai-jun Li ◽  
Hua-jun Li ◽  
Yong Liu
Keyword(s):  
Energy Dissipation ◽  
Analytical Solution ◽  
Wave Energy ◽  
Structural Parameters ◽  
Domain Boundary ◽  
Linear Potential ◽  
Wave Energy Dissipation ◽  
Special Cases ◽  
Linear Potential Theory ◽  
Incident Waves

This study examines the scattering of obliquely incident waves by a submerged pile–rock breakwater, which consists of two rows of closely spaced piles and a rock core between them. Based on linear potential theory, a closed-form analytical solution for the present problem is developed using matched eigenfunction expansions. The analytical solution is novel because of the new submerged pile–rock-type breakwater. The analytical solution is confirmed by an independently developed multi-domain boundary element method solution. The analytical solution is also compared with experimental data for three special cases of the present breakwater. Numerical examples are presented to investigate the effects of structural parameters and wave parameters on the reflection, transmission and energy loss coefficients of the breakwater. It is found that the wave energy dissipation by the submerged pile–rock breakwater is mainly contributed by the rock core, and only a small part of wave energy dissipation is due to the closely spaced piles.

scholarly journals Hydrodynamic study of the influence of bulbous bow design for an Offshore Patrol Vessel using Computational Fluid Dynamics

2018 ◽  
Vol 11 (22) ◽  
pp. 29
Author(s):  
Luis Leal ◽  
Edison Flores ◽  
David Fuentes ◽  
Bharat Verma
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Hydrodynamic Performance ◽  
Design Stage ◽  
Hull Form ◽  
Preliminary Design Stage ◽  
Hydrodynamic Study ◽  
Resistance Curves ◽  
Design Speed ◽  
Bulbous Bow

The resistance of a ship is of vital importance in giving greater viability to the development of a design project, since at lower ship resistance, the power demand to achieve a desired design speed will be lower which will reduce the amount of power to be installed in the ship resulting in lower fuel consumption. The use of computational fluid dynamics to analyze and optimize hull form and its appendages permits the hydrodynamic performance of the ship to be improved from the early design stages, allowing improvements to the hull shape and appendages. This paper shows a qualitative analysis which was performed to reduce the resistance of the OPVMKII (Second Generation Offshore Patrol Vessel) in its preliminary design stage by means of designing and integrating three types of bulbous bow with the ship´s hull and analyzing the resistance curves obtained using computational fluid dynamics.

scholarly journals Theoretical Analysis of a Vertical Cylindrical Floater in Front of an Orthogonal Breakwater

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 135
Author(s):  
Dimitrios N. Konispoliatis ◽  
Spyridon A. Mavrakos
Keyword(s):  
Hydrodynamic Interaction ◽  
Velocity Potential ◽  
Cylindrical Body ◽  
The Body ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Linear Potential ◽  
Method Of Images ◽  
Linear Potential Theory ◽  
Exciting Wave

This study investigates the effect of an orthogonal-shaped reflecting breakwater on the hydrodynamic characteristics of a vertical cylindrical body. The reflecting walls are placed behind the body, which can be conceived as a floater for wave energy absorption. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding the floater. The hydrodynamic interaction phenomena between the body and the adjacent breakwaters are exactly taken into account by using the method of images. Results are presented and discussed concerning the exciting wave forces on the floater and its hydrodynamic coefficients, concluding that the hydrodynamics of a vertical cylindrical body in front of an orthogonally shaped breakwater differ from those in unbounded waters.

On the Interaction of Waves With Intake/Discharge Flows Originating From a Freely-Floating Body

2003 ◽  
Vol 125 (1) ◽  
pp. 41-47 ◽  
Author(s):  
B. Padmanabhan ◽  
R. C. Ertekin
Keyword(s):  
Free Surface ◽  
Surface Condition ◽  
Floating Body ◽  
Wave Forces ◽  
Linear Potential ◽  
Two Dimensional ◽  
Rankine Source ◽  
Total Potential ◽  
Linear Potential Theory ◽  
Steady Potential

A linear theory is developed to obtain the motions of a two-dimensional, freely floating body (from which steady intake/discharge flows originate) that encounters incoming waves. The boundary-value problem is formulated within the assumptions of linear potential theory by decomposing the total potential into its oscillatory and steady components. The steady potential is further decomposed into the double-model and perturbation potentials. The time-harmonic potential is coupled with the steady potential through the free-surface condition. The potentials are obtained by use of the quadratic boundary-element method based on the Rankine source. The effect of the steady intake/discharge flows on the diffraction loads, hydrodynamic force coefficients, as well as the motions of a two-dimensional prismatic body floating on the free surface are presented. It is shown that the exciting wave forces and the hydrodynamic coefficients other than the damping coefficients are not appreciably affected in the case of low intake/discharge Froude numbers that are estimated, for example, for a 100 MW floating OTEC plant.

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