Students Info.


2024/03/26 14:00 Prof. Chang Lin(Department of Civil Engineering, NCHU)

Poster:Post date:2024-03-22
NCU IHOS Seminar Announcement

Title:Characteristics of Velocity Field in Swash Front of Solitary Wave Propagating on Very Steep Sloping Beach


Speaker:Prof. Chang Lin

Department of Civil Engineering, NCHU


Place:S-325, Science Building 1

  One of the key issues in coastal engineering and fluid dynamics is the evolution of high free-surface flows near shoreline when the incident perturbations of considerable water masses caused by natural disasters, such as tsunami, tidal waves and bores, can eventually lead to great destructions and casualties. When tsunami or long waves transverse the ocean from deep water to nearshore, wave height increases significantly and wave energy accumulates. After breaking around the shoreline, the subsequent wave run-up forms strong surge and brings a large amount of momentum invading inland, thus resulting in nearshore inundation and structure damages. Most of the casualties are related to the long wave run-up and swash front impact around shoreline. So understanding the feature of flow structure during run-up process in the swash zone is very important and critical. Such kind of studies can help in improving analytical/numerical models for predicting the propogation of long wave over beaches, for determining the maximum run-up height, for estimating the basal resistance/bed shear stress as well as impact force around the swash tip, for evaluating the sediment transport rate, and for any sort of mitigation effort.
  The experiments were conducted in a wave flume at the Department of Civil Engineering, National Chung Hsing University. The wave flume is 14.00 m long, 0.25 m wide and 0.50 m deep, equipped with a horizontal glass-bottom and two vertical glass-sidewalls. A piston-type wave maker driven by a precision servo-motor is installed at one end of the flume. The solitary waves can be satisfactorily generated and highly repeatable by the movement of the programmable wave maker, actuated accurately following the wave-plate trajectory as proposed by Goring (1978). A beach model was made of smooth acrylic sheet (with a dimension of 70.0 cm long and 24.5 cm wide and 2.0 cm thick), having a slope of 1:1 with the toe of the sloping beach located at 650.0 cm from the wave maker at rest. The range of the wave-height to water-depth ratio (H0/h0) of the incident wave varies from 0.171 to 0.363. The free surface elevations were mainly measured by using two capacitance-type gauges and two laser-beam gauges. The first, second and third gauges were located at x = −250.0, −150.0 and 0 cm, respectively. To explore the spatio-temporal variation of the velocity field right on and underlying the free surface of solitary waves, the particle trajectory method and HSPIV were used in this study.
  In the present study, the characteristics of the detailed velocity fields, including free surface boundary layer flow, internal flow, boundary layer flow and very fine structure near the tip of swash front, generated by non-breaking solitary waves traveling over the 1:1 sloping beach, are presented. New findings of the characteristics of detailed velocity fields include (1) Similarity curve of non-dimensional celerity at swash tip; (2) Free surface boundary layer flow (with curving corridor connecting bottom boundary layer flow); (3) Internal flow with spatio-temporal variation in flow demarcation curves (DFCs); (4) Bottom boundary layer flow with strong flow reversal and strong vortex structures; and (5) Very fine structure near the tip of swash front generated by non-breaking solitary waves.
Last modification time:2024-03-22 AM 11:06

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