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Experiments by Invited Researchers

 

Long wave dynamics and statistics of the shoreline motion: influence of the asymmetry and nonlinearity of incoming waves

Project acronym: HyIV-FZK-03
Name of Group Leader: Dr. Ira Didenkulova
User-Project Title: Long wave dynamics and statistics of the shoreline motion: influence of the asymmetry and nonlinearity of incoming waves
Facility: Large Wave Channel (GWK)
Proceedings TA Project: LONG WAVES CLIMBING THE SLOPES OF DIFFERENT ROUGHNESS: RUN-UP HEIGHT AND THE LOAD ON INDIVIDUAL ROUGHNESS ELEMENTS
Data Management Report: Report

User-Project Objectives

The main goal of the project is to study the role of the asymmetry and nonlinearity of long regular and irregular waves approaching the coast and its influence on the characteristics of wave runup on a beach. The asymmetric profile of the wave will be achieved in laboratory experiment by the nonlinear deformation of the wave during its propagation along the basin of constant depth. Waves of larger amplitudes propagating the same distance are more nonlinear and asymmetric. The wave runup on the beach will be studied with respect to the face-back slope asymmetry of the wave, when it reaches the foot of the sloping profile. In addition to verification of purely inviscid models, we plan to study dependence of the runup on the bed roughness and to record velocity statistics in the near-bed boundary layer in the view to shore erosion applications.

Short description of the work carried out

(1) Data recorded were according to the data collection plan. (2) A range of incident wave fields, regular, narrow band, and wide band, have been tested. (3) Runup on the smooth slope and the slope with affixed roughness elements, 50x50 logs, has been studied. (4) The water depth of 3.5m was used for all tests. (5) The incident wave field was measured by an array of resistance gauges spread along the flume. (6) The runup height was measured with a capacitance gauge consisting of two isolated wires suspended at 10mm above the slope. (7) Two components of water velocity have been measured in the near-bottom boundary layer using UVP probes. (8) Force exerted by the waves on selected roughness elements has been measured with load cells. (9) Water profile in the swash zone was measured by video-recording lasersheet reflected from the surface. (10) For calibration purposes, swash zone has been video-recorded. The main disadvantage of the runup gauge is that it only provides reliable results at the run-up stage, while at the backwash stage the residual water layer which covers the wires, distorts gauge readings. Hence, processing of video data is required to recover statistics of the shoreline position.

Highlights of important research results

(1) The strong influence of the wave front steepness on the runup characteristics of the long waves previously found theoretically was also approved experimentally. Among waves of a fixed amplitude and frequency (length), the steepest wave penetrates inland to the largest distance. Consequently, the least dangerous are symmetric sinusoidal waves. (2) The study of the spectrum width influence on the runup maxima distribution showed that the band width influence is weak and Rayleigh distribution describes distribution of maximum runup heights fairly well not only for narrow band spectrum but also when deltaf~f0, which agrees with previous theoretical results. (3) The narrow band incident wave fields result in greater significant runup height than the wider band ones of similar amplitudes of incident waves. (4) Higher loss of the wave energy is found to occur when incident waves have the narrow band spectrum. (5) The comprehensive set of measurement data provides extensive material for code validation.

Publications
P. Denissenko, I. Didenkulova, A. Rodin, M. Listak, E. Pelinovsky Experimental statistics of long wave runup on a plane beach , 2013 Journal of Coastal Research SI 65, 195-200
I. Didenkulova, P. Denissenko, A. Rodin, E. Pelinovsky Effect of asymmetry of incident wave on the maximum runup height , 2013 Journal of Coastal Research SI 65, 207-212

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