School of Mechanical Engineering Anatoli Hayat

School of Mechanical Engineering Seminar
Monday, June 11, 2018 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Application of the Boundary Element Method for investigation of nonlinear surface gravity waves in laboratory conditions

Anatoliy Khait, PhD
 

Water Waves Research Laboratory

School of Mechanical Engineering
Tel-Aviv University, Israel

Experimental investigation of surface gravity waves is a complicated task even under controlled laboratory conditions. Application of numerical models in parallel with the experiments may lead to a better understanding of the physical processes provided that the simulations are executed at the conditions that allow direct comparison between the numerical and experimental results. To this end, actual boundary conditions at the walls of the experimental wave flume should be taken into account in the numerical model, including those due to the motion of the wavemaker. For that purpose, Numerical Wave Tank (NWT) based on Boundary Element Method (BEM) was developed and applied to a number of problems related to the mechanically generated water waves.

We first validate the accuracy of the NWT by carrying out detailed comparison of numerical and experimental results. We then consider the phenomenon of the wave breaking. The main outcome of this part is verification of the kinematic criterion of the wave breaking in the formulation that states that breaking occurs when horizontal velocity of a fluid particle at the tip of the wave crest exceeds the crest propagation speed. Application of BEM allowed detailed analysis of the wave crest kinematics with a very fine temporal resolution. The actual motion of the wavemaker as recorded in experiments was introduced to the BEM as a boundary condition, the numerical results were compared against measurements.

We then consider the problem of the mechanical generation of the nonlinear steep waves. Application of the existing theories of the wave generation leads to significant errors (more that 10-20%) even for the 1st order harmonics. Theoretical analysis of the wave generation process together with the numerical simulations utilizing BEM allowed improvement of the wave generation accuracy. The results of the BEM simulations were verified experimentally in the laboratory wave flume.