Time Histories Of Surface Elevation Research Articles

Experimental study on the interaction of solitary wave with elastic submerged plate

This study aimed to understand the effect of stiffness under the interaction of a thin plate with a solitary wave. For this purpose, two-dimensional experiments were carried out with three different plates. Surface elevation, elastic plate motion, velocity field, and turbulence field were measured using the particle image velocimetry (PIV) technique. We first illustrated the evolution of the flow fields. Furthermore, a comparison study of different materials was carried out which showed that the more rigid plate could generate the larger velocity magnitude around the core, but the smaller velocity magnitude at the bottom in the end. By comparing the time histories of surface elevation, the x direction displacement at the upper-left corner of the plate, and the acting force on the plate, it was found that the maximum force occurred first, and the maximum deformation of the plate occurred last. The result showed the higher stiffness the greater wave attenuation behind the plate. Interestingly, it was also seen that the force varied linearly with the wave nonlinearity for different elastic plates. Not only can the detailed flow hydrodynamics and motion of elastic plate be obtained and analyzed, but the newly measured data can be used for validating numerical models.

Numerical Modeling and Experimentation of the Dam-Overtopping Process of Landslide-Generated Waves in an Idealized Mountainous Reservoir

AbstractA two-dimensional coupled solid-fluid numerical model was modified and applied to simulate the dam-overtopping event of landslide-generated waves in an idealized reservoir. The model employed was based on the two-dimensional Reynolds-Averaged Navier-Stokes (RANS) in a vertical plane with the k−e equations for turbulence closure. The motion of the solid landslide was modeled using the equation of motion for rigid body, and the free surface was tracked using volume of fluid (VOF) method. For model validation, experiments were conducted for the case of dam overtopping in an open channel. Particle image velocimetry (PIV) was used to measure velocity variations of the first wave during dam overtopping in one field of view (FOV), and wave gauges were used to record variations of the free-surface elevation at three selected locations in the open channel. The calculated and measured data comparisons were performed for time histories of surface elevation, surface profile, and vertical velocity distribution...

A STUDY OF WAVE AMPLIFICATION IN THE VENETIAN HARBOR OF CHANIA, CRETE

We studied resonance in the Venetian Port of Chania, a 14th century historic monument, which frequently exhibits large wave motions in its basin with flooding of its docks. We measured time histories of surface elevation and currents off the harbor for a period of two years and also measured wave elevations at one location inside the Port. Offshore, we recorded maximum Hs= 4.1m with Ts =9.2s. We employed a Boussinesq-type model COULWAVE to explore resonance and determined the resonant frequencies for the entire basin. We also examined the effect of a past proposed breakwater extension design on the resonant frequencies and respective modes. We conclude that the overtopping observed under storm conditions may not be the result of harbor resonance but the little protection of the existing breakwater sheltering the entrance.

Free surface simulation of a two-layer fluid by boundary element method

A two-layer fluid with free surface is simulated in the time domain by a two-dimensional potential-based Numerical Wave Tank (NWT). The developed NWT is based on the boundary element method and a leap-frog time integration scheme. A whole domain scheme including interaction terms between two layers is applied to solve the boundary integral equation. The time histories of surface elevations on both fluid layers in the respective wave modes are verified with analytic results. The amplitude ratios of upper to lower elevation for various density ratios and water depths are also compared.

Infragravity Wave Motions and Runup over Shallow Fringing Reefs

This paper presents the results of a combined laboratory and numerical investigation into the role of infragravity motions in the wave runup process over fringing coral reefs. Laboratory experiments were performed with a reef profile typical of fringing reef systems along the southeast coast of Guam. Spectral analysis of the measured time histories of surface elevation over the reef face and flats show significant changes to the wave energy spectrum shoreward of the break point. Most of the wave energy in the incident wave frequency band is dissipated within a few wavelengths of the reef face with the wave motions over the reef flat and shoreline dominated by oscillations at infragravity periods [O(100s) prototype]. The infragravity wave energy is minimum at the reef crest and increases as waves propagate shoreward over the reef flat and also with increasing water level on the reef. The dominant infragravity mode is the first reef oscillation mode with a wavelength approximately equal to four times the wi...

Optimizing deployment of sponge zone on numerical wave channel

In this study, we used the boundary element method to simulate a two‐dimensional wave tank with an absorbing boundary. The absorbing boundary, which consists of a sponge zone, is further divided into an area with a smoothly varied absorption coefficient μ and an area of constant μ. Both solitary, as well as periodic, waves are used in this study. Time histories of surface elevations are measured by a pseudo wave gage. The optimal combination of the absorption coefficient and sponge length to minimize wave reflection is investigated by studying these time series. The efficiency of the absorption zone is demonstrated by the attenuation rate of the wave energy, which for cases can reach a value of 100%. Based upon the present results, it is recommended that in simulating solitary waves, a value of μ 0=0.5 for the absorption coefficient with a sponge length of 15∼25 times the water depth is ideal, whereas a value of μ 0=1.0 in combination with a sponge length 20 times the water depth should be used for periodic waves.

Runup of solitary waves on a circular Island

This is a study of the interactions of solitary waves climbing up a circular island. A series of large-scale laboratory experiments with waves of different incident height-to-depth ratios and different crest lengths is described. Detailed two-dimensional run-up height measurements and time histories of surface elevations around the island are presented. A numerical model based on the two-dimensional shallow-water wave equations including runup calculations was developed. Numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope. Under certain conditions, enhanced runup and wave trapping on the lee side of the island were observed, suggesting a possible explanation for the devastation reported by field surveys in Babi Island off Flores, Indonesia, and in Okushiri Island, Japan.

Breaking invariants in shoaling waves

The inability of present theory to describe correctly the shoaling transformation of surface gravity waves is well recognized. It owes, at least in part, to the lack of experimental information on internal flow fields. This paper describes a portion of the results from laboratory experiments in which the time histories of surface elevation, crest speed, and horizontal subsurface flow velocities in trains of uniform waves were measured at a plurality of stations before and after breaking, as functions of (uniform) beach slope and wave frequency. It was found that over gentle slopes, wave breaking is characterized by invariancy of crest profiles and kinematics and that most important breaking parameters can be expressed in terms of period and breaker height, the latter of which appears to be related simply to deepwater height and steepness.

Deterministic Response to Free-Surface Waves

The relative importance and method of application of the impulse response technique for predicting motions, forces, etc., due to free-surface wave effects on water-borne vehicles, has been discussed by several authors. Controversy exists over the applicability of the law of causality when there is more than one independent variable; that is, the free surface and the body whose response is desired are distributed in space and vary in time. It is shown in this paper that impulse response operators for systems with free-surface wave inputs, in principle, do not satisfy the law of causality. However, by properly positioning the wave input point, the contribution from negative time can be made small. Nomenclature g = gravitational constant h(t) = time history of surface elevation at origin p(x, y, t) = pressure field t = time x, y = orthogonal Cartesian coordinate system f = complex Fourier transform parameter, f = « + iar)(x, t) = free-surface elevation p = fluid density (x} y, 0 = velocity potential E FFECTIVE operation of marine vehicles in the unsteady ocean environment requires analytical methods to predict motions, accelerations, deck wetness, forefoot emergence, etc. Two equivalent approaches have been described for such predictions. St. Denis and Pierson1 presented methods for determining the probabilistic description of the behavior of a vehicle in a random seaway. The complementary procedure presented by Cummins 2 and exploited by Wehausen 3 yields the deterministic evaluation of a vehicle's reponse to a specified time history of the sea surface. This approach was extended by Henry 4 to the prediction of the rigid body and elastic response of hydrofoil craft. Either method has advantages in attaining effective designs for marine vehicles. This paper is concerned with the deterministic approach and, in particular, with the requirement that the impulse response functions satisfy the law of causality, which states that no physical system can respond to future causes, i.e., the cause must always precede the effect. The deterministic approach to calculating response of physical systems has been highly developed in the field of control theory5 which deals with systems described by ordinary differential equations, i.e., with inputs and outputs functions of one independent variable, time. For stable, linear, timeinvariant systems, it is well known that the output y(t) of a so-called dynamical system can be predicted from the previous history of the input rj(r), T < t by the convolution integral