Original scientific paper
https://doi.org/10.31534/engmod.2020.3-4.ri.03a
Boussinesq Modelling of Waves and Currents in the Presence of Submerged Detached/Discontinuous Breakwaters
Mohammad Barzegar
; Texas A&M University-Corpus Christi, Coastal and Marine System Science, 6300 Ocean Drive, Corpus Christi, TX 78412, USA
Mohammad J. Ketabdari
; Amirkabir University of Technology, Hafez Avenue, Tehran, IRAN
Kourosh Kayhan
; DHI Technical and Marketing Manager, Tehran, IRAN
D. Palaniappan
orcid.org/0000-0003-3490-7914
; Texas A&M University-Corpus Christi, Department of Mathematics & Statistics, 6300 Ocean Drive, Corpus Christi, TX 78412, USA
Abstract
The effect of beach configurations with the main focus on the detached submerged breakwater on shoreline currents is investigated numerically. The Boussinesq equations are used to model the beach with a constant slope, continuous submerged breakwater, and discontinuous/detached submerged breakwater. Our numerical simulation results show that the transient rip currents are generated near the shoreline at the beach with constant slope while the continuous submerged breakwater structure creates a calm beach area along the shoreline. The presence of the gap in submerged breakwater changes the currents along the shoreline by generating rip currents with two pairs of vortices. One pair of vorticities, located around the gap, damage the breakwater by transmitting sediments along the breakwater foundation and eroding its surface. The second pair, created near the shoreline, erodes the shoreline due to sediment transportation and leads to a dangerous and unsafe situation for swimmers. The rip current creates five main critical areas with the maximum velocity towards the shoreline and offshore. The first set of three areas (numbered 1, 2, 3) has an approximately average velocity of 1-1.25 m/s towards the shoreline. One of these areas (numbered 2) is located close to the shoreline and the other two (numbered 1 and 3) are found to occur near the edge of the detached part of the breakwater. The second set of the two areas (numbered by 4 and 5) has the average velocity that is higher than 2.1 m/s towards the offshore and is located at the beginning part of the rip neck. An approximately linear relationship between the returning velocity and the gap length is observed. As the gap length decreases the location of the areas (numbered 4 and 5) gets closer to the center of the gap. Our simulations indicate that the return velocity towards the offshore increases at the gap center while the gap length decreases. Furthermore, the velocity profiles have a sharp jump for gap length that is approximately smaller than 80 m. Also, the return velocity at the gap center is related to the height of the breakwater. The breakwater that is higher (the breakwater height d = 4.2 m) damps wave energy more than shorter breakwater and the return velocity decreases for this structure. For smaller heights (d = 3.7 and 3.2) damping is nearly the same and the returning flow varies depending on the available space through the gap. Specifically, the return velocity for d = 3.7 is higher than that for d = 3.2. The numerical results presented herein suggest that aggressive rip currents are generated in the case of detached submerged breakwater beach configurations.
Keywords
detached submerged breakwater; rip current; Boussinesq equations; surf zone; numerical modelling
Hrčak ID:
247774
URI
Publication date:
14.12.2020.
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