Experimental study of force, pressure, and fluid velocity on a simplified coastal building under tsunami bore impact

Abstract

The present study experimentally investigated the flow kinematics and hydrodynamic pressures and forces on a simplified coastal building under tsunami bore impact. A rectangular structure sitting on a 1/10 sloping beach at four different headings, at 0°, 15°, 30° and 45°, was considered under bore impacts. The input wave condition was designed to generate a tsunami bore traveling at high speed on a sloping beach. The interaction between bore and structure (oriented at four different headings) was investigated using the nonintrusive bubble image velocimetry technique that enables the quantitative visualization of the full-field flow behavior. Simultaneous measurements of forces and pressures during the impacts were correlated with the measured flow velocities. As the tsunami bore is highly turbulent, ensemble averages from repeated tests were obtained for the investigation. To model the interaction, the validity of a dam break solution for a sloping bed as a suitable representation was examined, while the initial water depth was approximated using wave properties and calibrated with measured bore celerity. The study found that the profile of peak impact pressures is similar to a hydrostatic distribution for each heading, but one order of magnitude greater than the hydrostatic pressure. Similar linear distribution is also found in the correlation between peak impact pressure and angle of heading. By correlating the peak impact pressures with the impact velocity, the impact coefficient was estimated as 0.55. The measured pressures were further applied to model the surge force. By examining the peak surge forces against the heading angle, the lowest magnitude occurred when the structure was orientated at 30°.