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.

scholarly journals Theoretical modeling of hydrodynamic characteristics of a compound column-plate structure based on a novel derivation of mean drift force formulation

2018 ◽  
Vol 233 (4) ◽  
pp. 1022-1036 ◽  
Author(s):  
Peiwen Cong ◽  
Yingyi Liu ◽  
Ying Gou ◽  
Bin Teng
Keyword(s):  
Theoretical Model ◽  
Velocity Potential ◽  
Wave Force ◽  
The Body ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Wave Runup ◽  
Plate Structure ◽  
The Mean ◽  
Drift Force

To improve the seakeeping capability, some devices, such as submerged plates, are often installed on floating structures. The attached plate can not only suppress the motion response but also provide an additional immersed body surface that receives fluid action, aggravating the wave loads. In this study, a theoretical model is developed within the context of linear potential theory to study the hydrodynamic characteristics of a floating column with a submerged plate attached at the bottom. The eigenfunction expansion matching method is applied to obtain the velocity potential, based on which the linear wave force and wave runup can be found immediately. A novel derivation of the mean drift force formulation is developed via the application of Green’s second identity to the velocity potential and its derivative in finite fluid volume surrounding the body. Mean drift force formulation that involves control surfaces is then obtained. With the availability of the velocity potential, semi-analytical solution of the mean drift force on the compound column-plate structure is developed based on, respectively, the derived and the classic far-field formulations. After conducting convergence tests and validating the theoretical model, detailed numerical analysis is performed thereafter based on the theoretical model. The influence of the plate size, such as the radius and height, on the wave force and the associated wave runup is assessed.

scholarly journals Theoretical Evaluation of the Hydrodynamic Characteristics of Arrays of Vertical Axisymmetric Floaters of Arbitrary Shape in front of a Vertical Breakwater

2020 ◽  
Vol 8 (1) ◽  
pp. 62 ◽  
Author(s):  
Dimitrios N. Konispoliatis ◽  
Spyridon A. Mavrakos ◽  
Georgios M. Katsaounis
Keyword(s):  
Arbitrary Shape ◽  
Velocity Potential ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Theoretical Evaluation ◽  
Vertical Breakwater ◽  
Axisymmetric Bodies ◽  
Theoretical Results ◽  
Exciting Wave ◽  
Made In

The present paper deals with the analytical evaluation of the hydrodynamic characteristics of an array of vertical axisymmetric bodies of arbitrary shape, placed in front of a reflecting vertical breakwater, which can be conceived as floaters for wave power absorption. At the first part of the paper, the hydrodynamic interactions between the floaters and the adjacent breakwater are exactly taken into account using the method of images, whereas, the interaction phenomena between the floaters of the array are estimated using the multiple scattering approach. For the solution of the problem, the flow field around each floater of the array is subdivided into ring-shaped fluid regions, in each of which axisymmetric eigenfunction expansions for the velocity potential are made. In the second part of the paper, extensive theoretical results are presented concerning the exciting wave forces and the hydrodynamic coefficients for various arrays’ arrangements of axisymmetric floaters. The aim of the study is to show parametrically the effect that the vertical breakwater has on the hydrodynamic characteristics of each particular floater.

Effect of Floaters’ Geometry on the Performance Characteristics of Tightly Moored Wave Energy Converters

2009 ◽  
Author(s):  
Spyros A. Mavrakos ◽  
Georgios M. Katsaounis ◽  
Michalis S. Apostolidis
Keyword(s):  
Wave Energy ◽  
Cylindrical Body ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Diffraction Radiation ◽  
Wave Energy Converters ◽  
Internal Cone ◽  
Constant Displacement ◽  
Energy Converters

The paper deals with the investigation of the effect that floaters’ hydrodynamics has on the performance characteristics of tightly moored vertical axisymmetric wave energy converters. Several geometries of WEC’s floaters have been examined by assuming that they have constant displacement. Specifically, a cylindrical body with and without vertical and horizontal skirts at its bottom, a cone and a two–body, piston–like arrangement, which consists of an internal cone and an exterior torus, have been investigated and comparatively assessed. The WEC’s first-order hydrodynamic characteristics, i.e. their exciting wave forces and the correspondent hydrodynamic parameters, are evaluated using a linearized diffraction–radiation semi-analytical method. A dynamical model for evaluating of the floaters’ performance in time domain is developed that properly accounts for the floaters hydrodynamic behavior, the modeling of the hydraulic system and of the power take–off mechanism. The effect of the floaters geometry on the efficiency of the converter is analyzed through the results for the power absorption, under the excitation of several sea states.

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.

scholarly journals Wave forces on three-dimensional floating bodies with small forward speed

1991 ◽  
Vol 227 ◽  
pp. 135-160 ◽  
Author(s):  
Jan Nossen ◽  
John Grue ◽  
Enok Palm
Keyword(s):  
Velocity Potential ◽  
The Body ◽  
Wave Forces ◽  
Forward Speed ◽  
Floating Bodies ◽  
Wave Drift ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Wave Drift Damping ◽  
The Mean

A boundary-integral method is developed for computing first-order and mean second-order wave forces on floating bodies with small forward speed in three dimensions. The method is based on applying Green's theorem and linearizing the Green function and velocity potential in the forward speed. The velocity potential on the wetted body surface is then given as the solution of two sets of integral equations with unknowns only on the body. The equations contain no water-line integral, and the free-surface integral decays rapidly. The Timman-Newman symmetry relations for the added mass and damping coefficients are extended to the case when the double-body flow around the body is included in the free-surface condition. The linear wave exciting forces are found both by pressure integration and by a generalized far-field form of the Haskind relations. The mean drift force is found by far-field analysis. All the derivations are made for an arbitrary wave heading. A boundary-element program utilizing the new method has been developed. Numerical results and convergence tests are presented for several body geometries. It is found that the wave exciting forces and the mean drift forces are most influenced by a small forward speed. Values of the wave drift damping coefficient are computed. It is found that interference phenomena may lead to negative wave drift damping for bodies of complicated shape.

Parametric Evaluation of the Performance Characteristics of Tight Moored Wave Energy Converters

2005 ◽  
Author(s):  
Spyridon A. Mavrakos ◽  
Georgios M. Katsaounis
Keyword(s):  
Wave Energy ◽  
Wave Climate ◽  
The Body ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Diffraction Radiation ◽  
Climate Conditions ◽  
Wave Energy Converters ◽  
Energy Converters

The paper aims at presenting a numerical model to predict performance characteristics of tight moored vertical axisymmetric wave energy converters that are allowed to move in heave, pitch and sway modes of motion. The hydrodynamic characteristics (exciting wave forces, hydrodynamic parameters) of the floats are evaluated using a linearized diffraction–radiation method of analysis that is suited for the type of bodies under consideration. According to this method matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain. Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account. The floating WEC is connected to an underwater piston that feeds a hydraulic system with pressurized fluid. Numerical results showing parametrically the performance characteristics in terms of the expected power production for several types of floats that are exposed to the wave climate conditions commonly encountered in the Mediterranean area are presented and discussed.

scholarly journals Hydrodynamics of a Free Floating Vertical Axisymmetric Oscillating Water Column Device

2012 ◽  
Vol 2012 ◽  
pp. 1-27 ◽  
Author(s):  
S. A. Mavrakos ◽  
D. N. Konispoliatis
Keyword(s):  
Water Column ◽  
Wave Motion ◽  
Velocity Potential ◽  
Wave Forces ◽  
Oscillating Water Column ◽  
Rolling Moment ◽  
First Order ◽  
Absorbed Power ◽  
Efficiency Rate ◽  
Exciting Wave

This paper aims at presenting a general formulation of the hydrodynamic problem of a floating or restrained oscillating water column device. Three types of first-order boundary value problems are investigated in order to calculate the velocity potential of the flow field around the device. The horizontal and vertical exciting wave forces, the rolling moment, the hydrodynamic parameters, the volume flows, and the drift forces are obtained in order to find the loads on the structure. The efficiency rate of the device is calculated in connection with the absorbed power and the capture length of energy absorption. Finally, the resulting wave motion inside and outside the device and the inner air pressure are examined.

Wave Elevation Between Elliptical Structures

2009 ◽  
Author(s):  
Ioannis K. Chatjigeorgiou ◽  
Spyros A. Mavrakos
Keyword(s):  
Hydrodynamic Interaction ◽  
Solution Method ◽  
Addition Theorem ◽  
Linear Potential ◽  
Mathieu Functions ◽  
Wave Elevation ◽  
Efficient Calculation ◽  
Close Proximity ◽  
Linear Potential Theory ◽  
Elliptical Cylinders

The hydrodynamic interaction of waves with arrays of vertical elliptical cylinders is considered. The present paper aims at developing of an efficient calculation method for predicting the extreme elevation of the free surface, in the fluid domain between ship-shaped structures in close proximity. Linear potential theory is employed and the solution method is based on the semi-analytical formulation of the various velocity potentials in elliptical coordinates, using series expansions of Mathieu functions and the so-called addition theorem for Mathieu functions.

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.

Hydrodynamics of Tandem Planning Surfaces

2013 ◽  
Author(s):  
Konstantic I. Matveev
Keyword(s):  
Boundary Conditions ◽  
Horizontal Plane ◽  
Water Surface ◽  
Hydrodynamic Interaction ◽  
Velocity Potential ◽  
Pressure Coefficient ◽  
Hydrodynamic Characteristics ◽  
Two Dimensional ◽  
Flow Approximation ◽  
Optimal Configurations

This study addresses Hydrodynamic interaction of two planning surfaces in the two dimensional, inviscid, steady flow approximation. The velocity potential is found by disturbing hydrodynamic sources on the horizontal plane and satisfying linearized boundary conditions for the water flow at finite Froude numbers. Hydrodynamic characteristics of tandem planning plates, including lift coefficients, centers of pressure, lift-drag ratios and wetted lengths, are determined as functions of the spacing between the plates and compared to properties of a single planning surface. The water surface elevations and the pressure coefficient distributions are presented for several cases. Obtained results can be used as initial guidance for selecting optimal configurations of stepped hulls and fast multi-hulls and fast multi-hulls and predicting hydrodynamic interaction between planning boats moving in tandem arrangement.

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