Author(s): Jeremy D. Bricker; Hiroshi Takagi; Jun Mitsui
Linked Author(s):
Keywords: Tsunami; Breakwater; Overtopping; Bearing stress; Turbulence
Abstract: Numerical simulations are used to investigate the mechanisms of failure of the Kamaishi breakwater during the 2011 tsunami. Delft 3D is used to simulate the propagation of the tsunami as a shallow water wave into Kamaishi Bay, in order to estimate the time progression of water levels on each side of the breakwater. OpenFOAM's InterFOAM VOF solver with RANS k-ε turbulence is then used to simulate the unsteady overtopping of a solid breakwater caisson atop a porous rubble mound, and to calculate the total forces exerted on the breakwater by the flow. Interestingly, the simulated overtopping flow is sensitive to the turbulence model used. In comparison with experiments, the standard OpenFOAM k-ε turbulence model predicts too much entrainment of air below the overtopping jet into the fluid, thus pulling the jet quite close to the landward wall of the breakwater. For better agreement with experimental results, reduction of the turbulent eddy viscosity near the air-water interface proves necessary. Results of the simulations indicate that failure of the breakwater due to sliding or toppling was unlikely. However, the bearing stress at the heel of the caisson increased above its allowable limit due to both the water level difference across the breakwater, and due to the overtopping jet pulling away from the landward side of the caisson as the surcharge height above the caisson increased. In addition to the scour-induced failure of the rubble-mound foundation reported by other researchers, the present research indicates that measures to prevent geotechnical punching failure are also necessary to ensure integrity of the structure during overtopping events.
Year: 2013