Scattering of Water Waves by a Pair of Semi-Infinite Barriers

1975 ◽  
Vol 42 (4) ◽  
pp. 777-779 ◽  
Author(s):  
P. L.-F. Liu
Keyword(s):  
Transmission Coefficient ◽  
Incident Wave ◽  
Water Waves ◽  
Asymptotic Theory ◽  
Three Dimensional ◽  
Incident Wavelength ◽  
Water Motion ◽  
Incident Wave Angle ◽  
Progressive Waves ◽  
Wave Angle

Three-dimensional water waves are incident upon a pair of semi-infinite parallel vertical thin barriers. Assuming that the opening between the barriers is small compared with the incident wavelength, an asymptotic theory is developed for the resulting water motion. Between the barriers uniform progressive waves propagate into the channel. The transmission coefficient is found to be insensitive to the incident wave angle and the separation between the barriers.

Interaction of water waves with three-dimensional periodic topography

2001 ◽  
Vol 434 ◽  
pp. 301-335 ◽  
Author(s):  
R. PORTER ◽  
D. PORTER
Keyword(s):  
Incident Wave ◽  
Water Waves ◽  
Homogeneous Problem ◽  
Scattering Problem ◽  
Three Dimensional ◽  
Trapped Waves ◽  
Trapped Mode ◽  
Bed Elevation ◽  
Input Mode ◽  
Incident Waves

The scattering and trapping of water waves by three-dimensional submerged topography, infinite and periodic in one horizontal coordinate and of finite extent in the other, is considered under the assumptions of linearized theory. The mild-slope approximation is used to reduce the governing boundary value problem to one involving a form of the Helmholtz equation in which the coefficient depends on the topography and is therefore spatially varying.Two problems are considered: the scattering by the topography of parallel-crested obliquely incident waves and the propagation of trapping modes along the periodic topography. Both problems are formulated in terms of ‘domain’ integral equations which are solved numerically.Trapped waves are found to exist over any periodic topography which is ‘sufficiently’ elevated above the unperturbed bed level. In particular, every periodic topography wholly elevated above that level supports trapped waves. Fundamental differences are shown to exist between these trapped waves and the analogous Rayleigh–Bloch waves which exist on periodic gratings in acoustic theory.Results computed for the scattering problem show that, remarkably, there exist zeros of transmission at discrete wavenumbers for any periodic bed elevation and for all incident wave angles. One implication of this property is that total reflection of an incident wave of a particular frequency will occur in a channel with a single symmetric elevation on the bed. The zeros of transmission in the scattering problem are shown to be related to the presence of a ‘nearly trapped’ mode in the corresponding homogeneous problem.The scattering of waves by multiple rows of periodic topography is also considered and it is shown how Bragg resonance – well-established in scattering of waves by two-dimensional ripple beds – occurs in modes other than the input mode.

scholarly journals Hydrodynamic Sensitivity of Moored and Articulated Multibody Offshore Structures in Waves

2021 ◽  
Vol 9 (9) ◽  
pp. 1028
Author(s):  
Changqing Jiang ◽  
Ould el Moctar ◽  
Thomas E. Schellin
Keyword(s):  
Incident Wave ◽  
Critical Phenomenon ◽  
Building Blocks ◽  
Offshore Structures ◽  
Hydrodynamic Characteristics ◽  
Mooring Line ◽  
Mooring Lines ◽  
Weakly Nonlinear ◽  
Incident Wave Angle ◽  
Wave Angle

Within the framework of Space@Sea project, an articulated modular floating structurewas developed to serve as building blocks for artificial islands. The modularity was one of the keyelements, intended to provide the desired flexibility of additional deck space at sea. Consequently, the layout of a modular floating concept may change, depending on its functionality and environmental condition. Employing a potential-flow-based numerical model (i.e., weakly nonlinear Green function solver AQWA), this paper studied the hydrodynamic sensitivity of such multibody structures to the number of modules, to the arrangement of these modules, and to the incident wave angle. Results showed that for most wave frequencies, their hydrodynamic characteristics were similar although the floating platforms consisted of a different number of modules. Only translational horizontal motions, i.e., surge and sway, were sensitive to the incident wave angle. The most critical phenomenon occurred at head seas, where waves traveled perpendicularly to the rotation axes of hinged joints, and the hinge forces were largest. Hydrodynamic characteristics of modules attached behind the forth module hardly changed. The highest mooring line tensions arose at low wave frequencies, and they were caused by second-order mean drift forces. First-order forces acting on the mooring lines were relatively small. Apart from the motion responses and mooring tensions, forces acting on the hinge joints governed the system’s design. The associated results contribute to design of optimal configurations of moored and articulated multibody floating islands. 

scholarly journals Dynamicity of multi-channel rip currents induced by rhythmic sandbars

2020 ◽  
Author(s):  
Yao Zhang ◽  
Xiao Hong ◽  
GuoDong Xu ◽  
Xunan Liu ◽  
Xinping Chen ◽  
...  
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Probabilistic Models ◽  
Numerical Study ◽  
Expected Improvement ◽  
Rip Current ◽  
Rip Currents ◽  
Empirical Formulas ◽  
Incident Wave Angle ◽  
Wave Angle

Abstract. In response to frequent fatal beach drownings, China's first operational attempt on the rip current hazard investigation was made by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches were found developing rip currents interlaced with rhythmic sandbars, varying by season and location evidenced by satellite images and morphodynamic calculation. Considering insufficient understanding of the multi-channel rip system, case analysis and numerical study were conducted to explore its dynamicity and circulation characteristics under various wave climates in present work. The strength of rip currents was generally proportional to wave height and channel width under certain limits. Increasing wave height was not always a promotion and could even weaken the rip current due to the strong wave-current shear. Interesting pump and feed interactions between adjacent rip currents in the multi-channel system were observed. The rip current might be totally absent in narrow channels when the majority of water flows through neighboring broader pathways. The rip current was highly sensitive to the incident wave angle. Alongshore currents prevailed over the rip current when the wave angle reached 11 degrees to shore normal, which was not favorable to the existence of channeled sandbars. Vortices appeared around the edge of the bar owing to nonuniform wave breaking over rapid-varying bathymetry. The setup water was created shoreward by the sandbar array and substantially increased as the wave deviated from the normal incidence. The water surface depression in the rip channel was not observed as the wave angle increased, which fundamentally explained why the rip current could not persist when the incident wave became slightly oblique. In future, incident wave angle should be further incorporated into empirical formulas or probabilistic models to predict the rip current for expected improvement in accuracy.

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