Long Wave Flow Interaction with a Single Square Structure on a Sloping Beach

Gian Bremm,Torsten Schlurmann,Ioan Nistor,Nils Goseberg

doi:10.3390/jmse3030821

Abstract

In the context of dam breaks, tsunami, and flash floods, it is paramount to quantify the time-history of forces by the rapidly transient flow to vertical structures and the characteristics of the induced flow patterns. To resemble on-land tsunami-induced flow, a free-surface-piercing structure is exposed to long leading depression waves in a tsunami flume where long waves run up and down a 1:40 smooth and impermeable sloping beach after its generation by a volume-driven wave maker. The structure and its surrounding were monitored with force transducers, pressure gauges and cameras. Preparatory steady-state experiments were accomplished to determine the drag force coefficient of the square cylinder at various water depths. The flow during wave run-up and draw-down acting on the structure resulted in distinct flow pattern which were characteristic for the type of flow-structure interaction. Besides bow wave propagating upstream, a standing or partially-standing wave was observed in front of the structure together with a wake formation downstream, while a von Kármán vortex street developed during the deceleration phase of the flow motion and during draw-down. Force measurements indicated a sudden increase in the stream-wise total force starting with the arrival of the flow front during initial run-up. Lateral velocities showed significant oscillations in correlation with the von Kármán vortex street development. A comparison of the total measured base force with the analytically-calculated share of the drag force revealed that forces were prevailingly drag-dominated.

Highlights

This paper focuses on an accurate assessment of drag force which occur during the interaction with a transient flow which can be described by the following equations
A power-law was fitted to determine the CD values corresponding to the Reynolds number which were further used for the computation of the analytical drag forces during the transient flow process
This research work concerns flow-structure interaction processes between a single structure mounted on a 1:40 sloping beach with leading depression long waves having different periods and amplitudes

Summary

Introduction

This paper addresses the interaction of a transient flow with a surface-piercing height-finite structure and presents new detailed laboratory data. It includes the description of the spatio-temporal evolution of the flow fields around the structure and the resulting time series of the induced stream-wise forces. After the 2011 Great East Japan Earthquake and Tsunami which claimed the lives of thousands and caused unprecedented damage to coastal infrastructure, it is of vital importance to deepen the understanding of the interaction of rapidly advancing flow and the induced forces. The approaching flow caused by water-related phenomena such as dam-breaks or tsunami are transient in nature

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