ANALYSIS OF DAM BREAK FLOW

Abstract

Abrupt and gradual dam- and levee-break analyses were implemented by laboratory experiments and numerical simulations. Some small scale laboratory studies for the dam- or levee-break problems have been performed for verifying an accuracy of the numerical model, but there were few researches from the large scale laboratory that can reproduce the inundation flow close to the natural phenomena. Especially, all of the small scale laboratory studies were performed in a laboratory channel. Therefore the inundation flow was influenced by reflective wave and friction from the both sides of the wall. Finally, those results are not enough to give suitable data for verifying the accuracy of the dam- and levee-break numerical model. This study was performed in a large scale model to increase the accuracy of the model and tested on the flat inundation area large enough to avoid the reflective wave from the wall. Also the laboratory conditions were simplified to decrease the uncertainty could be taken place in the numerical simulation. Based on the results of the abrupt and gradual levee-break laboratory experiments, even though they were somewhat different just after initial breaking, the water depth profiles for all depth gauges were converged gradually. In the inundation test (case 1) without the idealized city, the hydraulic jump was observed on the inundation area, and it moved from the outside to inside as time. In the idealized city tests (case 2 and case 3), the measured water depths were significantly different from those of the Soares-Fraz?o and Zech (2008). A numerical solver of the shallow water equations, include the horizontal eddy viscosity, was developed to solve the dam- and levee-break flow. An intercell flux was reconstructed with the Harten, Lax and van leer (HLLC) approximate Riemann solver which is a modification on the basic HLL scheme. Also, a TVD version of the WAF scheme with SUPERBEE type limiter is applied to control the numerical oscillations in the vicinity of large gradients with second-order numerical accuracy. The Smagorinsky eddy viscosity model was adopted, to consider the horizontal turbulence effects. In order to verify the accuracy of the developed dam- and levee-break solver, idealized one-dimensional dam-break, periodic free oscillation in a frictionless and flat square tank and partial dam-break tests were adopted, and several cases of the dam-break test were implemented. Finally, developed numerical model was applied to the experiments from this study. The results of the present numerical model showed reasonable agreement with those of the experimental data. However, even if the numerical schemes effectively replicated the trends of the observed water depth for the first shock, there were little differences for the second shock. In addition, even though the model considers the Smagorinsky horizontal eddy viscosity, the location and height of the hydraulic jump in the numerical simulation were not in good agreement with experimental measurements. This shows the shallow water equation solver has a limitation which does not exactly reproduce the energy dissipation due to the hydraulic jump. As mentioned above, from the levee-break experiment, the measured water depths were used for verifying the accuracy of the two-dimensional numerical solver developed in this study, and the results of numerical model showed reasonable agreement with experimental results except for the hydraulic jump.