scholarly journals WAVE INTERCEPTION BY SEA-BALLOON BREAKWATER

1986 ◽  
Vol 1 (20) ◽  
pp. 173 ◽  
Author(s):  
Takahiko Uwatoko ◽  
Takeshi Ijima ◽  
Yukimitsu Ushifusa ◽  
Haruyuki Kojima
Keyword(s):  
Incident Wave ◽  
Fluid Motion ◽  
Fluid Pressure ◽  
Vertical Axis ◽  
Boundary Integral ◽  
Long Waves ◽  
Boundary Integral Method ◽  
Wave Crest ◽  
Airflow Resistance ◽  
Incident Waves

When a submerged, flexible bag is filled with air about 60~T0 % of its full volume ( it is called " sea-balloon " ), it has a stable shape with vertical axis of symmetry, on which several vertical wrinkles appear with folds of membrane. If two or more such sea-balloons are arranged to the direction of wave travel and connected pneumatically, balloons are deformed periodically and the air flows reciprocally in connecting pipe, following to the fluid pressure fluctuation due to incident waves. Such a system of sea-balloon intercepts incident waves effectively ( it is called " sea-balloon breakwater "). The wave interception by the breakwater is analyzed numerically by three-dimensional boundary integral method, assuming that the fluid motions both in- and out-side of the balloon are potential and that the tension in balloon membrane is proportional to the apparent elongation of membrane with virtual elastic constant. After analysis and experiments, it is made clear that in relatively long waves the incident wave is canceled by the radiation wave which is generated by volumetric change of sea-balloons, being affected by airflow resistance in connecting pipe. In short waves, sea-balloons seem to behave like as rigid piles and the incident wave is absorbed by airflow resistance in pipe and by the turbulence of fluid motion around balloons. Moreover, the effect of gaps between sea-balloons along wave crest on wave interception for relatively long waves is expressed by a simple empirical formula, by which the transmission coefficients at various types of sea-balloon breakwater is easily estimated by twodimensional computation. For the improvement of wave interception effect and from the point of practical use, the effects of other sea-balloon breakwater system are investigated by two-dimensional computation and experiments.

Reflection of a high-amplitude solitary wave at a vertical wall

1997 ◽  
Vol 342 ◽  
pp. 141-158 ◽  
Author(s):  
M. J. COOKER ◽  
P. D. WEIDMAN ◽  
D. S. BALE
Keyword(s):  
Solitary Wave ◽  
Residence Time ◽  
Vertical Wall ◽  
High Amplitude ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Wave Crest ◽  
Asymptotic Formulae ◽  
Cine Film ◽  
Run Up

The collision of a solitary wave, travelling over a horizontal bed, with a vertical wall is investigated using a boundary-integral method to compute the potential fluid flow described by the Euler equations. We concentrate on reporting new results for that part of the motion when the wave is near the wall. The wall residence time, i.e. the time the wave crest remains attached to the wall, is introduced. It is shown that the wall residence time provides an unambiguous characterization of the phase shift incurred during reflection for waves of both small and large amplitude. Numerically computed attachment and detachment times and amplitudes are compared with asymptotic formulae developed using the perturbation results of Su & Mirie (1980). Other features of the flow, including the maximum run-up and the instantaneous wall force, are also presented. The numerically determined residence times are in good agreement with measurements taken from a cine film of solitary wave reflection experiments conducted by Maxworthy (1976).

Diffraction and radiation loads on open cylinders of thin and arbitrary shapes

2015 ◽  
Vol 772 ◽  
pp. 649-677 ◽  
Author(s):  
Mohamed Hariri Nokob ◽  
Ronald W. Yeung
Keyword(s):  
Wave Field ◽  
Vertical Cylinder ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Linear Potential ◽  
Wave Loads ◽  
Hydrodynamic Properties ◽  
Cross Sectional ◽  
Sectional Shape ◽  
Incident Waves

We study the effects of having an opening in a vertical cylinder of an arbitrary cross-sectional shape when subjected to incident waves from the outside field. Both the diffraction and radiation problems of linear potential-flow theory are addressed. The cylinders considered are bottom-mounted with vanishing thickness and the problem is formulated as a hypersingular boundary-integral method. A simple higher-order procedure is presented to handle the strong singularity. Comparisons are made between the hydrodynamic properties of open and closed cylinders, and the effects of increasing the opening size are discussed and explained. Results for square, circular and elliptical open cylindrical shells, presented as examples, indicate that wave loads on the structures could be dramatically decreased to zero (effectively) at certain frequencies and opening sizes. This leads to the surprising conclusion that directing an open structure into the incident-wave field results in lower loads on the structure. A model of an open harbour with a frontal breakwater in a wave field, inspired by the idea of the Portunus Project, is also analysed.

A comparison of numerical predictions and experimental measurements of the internal kinematics of a deep-water plunging wave

1996 ◽  
Vol 315 ◽  
pp. 51-64 ◽  
Author(s):  
David Skyner
Keyword(s):  
Numerical Model ◽  
Deep Water ◽  
Numerical Data ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Wave Crest ◽  
Breaking Wave ◽  
Small Shift ◽  
Wave Flume ◽  
Numerical Predictions

A deep-water long-crested breaking wave is generated from a time-stepping numerical model, then replicated in a wave flume. The numerical model is based on the boundary integral method and measurements of the internal kinematics are made during the breaking process with Particle Image Velocimetry (PIV). Velocity measurements are obtained throughout the wave crest, including the plunging spout. After a small shift of the numerical data to match the surface profiles, the predicted and measured kinematics are found to be in good agreement, within the limits of experimental error.

Influence of internal viscosity on the large deformation and buckling of a spherical capsule in a simple shear flow

2011 ◽  
Vol 672 ◽  
pp. 477-486 ◽  
Author(s):  
É. FOESSEL ◽  
J. WALTER ◽  
A.-V. SALSAC ◽  
D. BARTHÈS-BIESEL
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Viscosity Ratio ◽  
Fluid Motion ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Simple Shear Flow ◽  
Flow Strength ◽  
Capsule Deformation ◽  
Internal Viscosity

The motion and deformation of a spherical elastic capsule freely suspended in a simple shear flow is studied numerically, focusing on the effect of the internal-to-external viscosity ratio. The three-dimensional fluid–structure interactions are modelled coupling a boundary integral method (for the internal and external fluid motion) with a finite element method (for the membrane deformation). For low viscosity ratios, the internal viscosity affect the capsule deformation. Conversely, for large viscosity ratios, the slowing effect of the internal motion lowers the overall capsule deformation; the deformation is asymptotically independent of the flow strength and membrane behaviour. An important result is that increasing the internal viscosity leads to membrane compression and possibly buckling. Above a critical value of the viscosity ratio, compression zones are found on the capsule membrane for all flow strengths. This shows that very viscous capsules tend to buckle easily.

scholarly journals SOLITARY WAVES PASSING OVER SUBMERGED BREAKWATERS

1988 ◽  
Vol 1 (21) ◽  
pp. 45
Author(s):  
Mark Cooker ◽  
Howell Peregrine
Keyword(s):  
Solitary Waves ◽  
Integral Method ◽  
Velocity Potential ◽  
Fluid Motion ◽  
Unsteady Motion ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Two Dimensional ◽  
Sea Bed ◽  
Exact Boundary

A method is described for the computation of the two-dimensional unsteady motion of a solitary wave passing over submerged breakwaters. Far from the breakwater the fluid is assumed static and the sea bed is level. The fluid motion is assumed to be irrotational, incompressible and inviscid. The exact boundary conditions at the free surface and the impermeable bed are satisfied. Laplace's equation for the velocity potential is solved using a boundary integral method. Numerical results are reported which show the variety of ways in which solitary waves are distorted when they encounter submerged breakwaters.

Time-Domain Simulation of Motions of Large Structures in Nonlinear Waves

2002 ◽  
Author(s):  
Debabrata Sen
Keyword(s):  
Incident Wave ◽  
Time Domain ◽  
Nonlinear Waves ◽  
Large Amplitude ◽  
Time Integration ◽  
Offshore Structures ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Computational Scheme ◽  
Irregular Waves

In this paper, we discuss development of a time-domain motion simulation method for studying the interaction of nonlinear waves with large offshore structures. The computational algorithm follows a simplified numerical wave-tank approach based upon a boundary-integral method and time-integration of boundary conditions. The simplifying approximations include linearization of the interaction hydrodynamic effects (radiation and diffraction) while the incident wave effects are considered in full. The main aim is to develop a method that will consider all important nonlinear effects associated with a large-amplitude incident wave, and yet practical enough to be applied routinely by the industry. In the time-integration of motion equations, numerical instabilities usually arise if difference rules are applied for determining pressures, due to coupling between forces and motions. To avoid this, an algorithm has been developed for the pressure evaluation. The resulting computational scheme is numerically stable for all conditions. The method can incorporate effects of other forces such as Morison forces, forces from mooring lines etc. which can be nonlinear. After providing a description of computational scheme, force and motion results for the interaction of large amplitude regular waves as well as irregular waves with two practical semisubmersible configurations are presented.

scholarly journals Nonlinear two-dimensional free surface solutions of flow exiting a pipe and impacting a wedge

2021 ◽  
Vol 126 (1) ◽  
Author(s):  
Alex Doak ◽  
Jean-Marc Vanden-Broeck
Keyword(s):  
Surface Tension ◽  
Integral Equation ◽  
Free Surface ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Two Dimensional ◽  
Numerical Schemes ◽  
Additional Advantage ◽  
Infinite Wedge ◽  
Good Agreement

AbstractThis paper concerns the flow of fluid exiting a two-dimensional pipe and impacting an infinite wedge. Where the flow leaves the pipe there is a free surface between the fluid and a passive gas. The model is a generalisation of both plane bubbles and flow impacting a flat plate. In the absence of gravity and surface tension, an exact free streamline solution is derived. We also construct two numerical schemes to compute solutions with the inclusion of surface tension and gravity. The first method involves mapping the flow to the lower half-plane, where an integral equation concerning only boundary values is derived. This integral equation is solved numerically. The second method involves conformally mapping the flow domain onto a unit disc in the s-plane. The unknowns are then expressed as a power series in s. The series is truncated, and the coefficients are solved numerically. The boundary integral method has the additional advantage that it allows for solutions with waves in the far-field, as discussed later. Good agreement between the two numerical methods and the exact free streamline solution provides a check on the numerical schemes.

Sign in / Sign up

Export Citation Format

Share Document