Experiments of dam-break flow in the presence of obstacles

摘要: Dam-break flows are likely to occur in area that not subject more common floods. Also, the importance of wave might be such flow route is no directed by thalweg river. The whole valley involved, and roads, bridges urban buildings become obstacles flow. purpose paper study influence an obstacle on a dam-break wave, being idealized representation single building. experimental set-up consists channel with rectangular shaped obstacle, representing building, placed immediately downstream from dam. building centred channel, aligned direction. Flow observation shows after violent impact forced change its direction pass This implies formation hydraulic jumps consequence water level locally important than without Behind wake zone observed. Then, further downstream, slowly recovers structure it would have Several measurement devices were used characterize evolution was measured at five different locations means gauges. At each gauging point, velocity acoustic Doppler velocimeter. surface field obtained using digital imaging techniques. part IMPACT European project which aims investigating extreme flood processes uncertainty. data set presented here benchmarking programme, as validation for numerical models. way minimum C2, corresponding critical stage, higher uniform condition standard section (Fig. 2b). results control constricted development supercritical profile, returns normal conditions through jump. Figure 2: Water profiles along bridge piers mild-slope cases A similar behavior may observed steepslope conditions, where generally supercritical. In these situations, profile presents two configurations 3. 3: steep-slope If constriction limited, only close disturbed effect will extend farther upstream. becomes significant, possible energy too high reached immediately. specific thus needs increase upstream reach, subcritical flow, requiring resulting extends over short distance. above description obstruction caused presence based one-dimensional modeling. important, two-dimensional aspects predominate significantly location shape discontinuities. second concerns nonlinear alignment, rather complex. flows, transverse superelevation arise near outer bank (or obstacle). case, wall, turns inward produce oblique jump positive front, while inner away develop negative both forming cross waves 4). 4: Cross alignment (after Chow, 1959) When unsteady, all severe transient situations (damor dike break example), this already complex even complicated. now induces reflected turn reflect against banks or other obstacles. Few descriptions phenomena available. However, they could great interest modeling dambreak Above evaluate extension space time limit accurate refined computations really needed. large scale real event, always distinguish between features Therefore, decided design experiment limits parameters involved Through appropriate measurements identify features. program (Soares Frazao et al., 2003). research project, addresses assessment reduction risks flooding natural events failure dams defense structures (Morris, 2002; Morris Vaskinn, 2002) has also special focus floods areas 2 EXPERIMENTAL SET-UP experiments carried out laboratory Civil Engineering Department Universite catholique de Louvain (UCL) Belgium. sketched Figures 5-7. 5: Experimental (dimensions meters) 6: Location dimensions (in 7: Channel (a) reservoir main (b) dam It total length 35.80 m 3.60 wide. 6.90 long. trapezoidal bed 7a). represented gate located solid blocks; cross-section 1.00 wide 7b). To simulate break, pulled up rapidly. 3.40 dam, block 0.80 x 0.40 m. makes angle 64° axis 6). After Manning friction coefficient n = 0.01 s closed wall end. boundary weir chute, but during test duration, 30 s. initial consist thin layer channel. 3 GENERAL FLOW DESCRIPTION rapid opening gate, strong reflects almost submerging it, separates, series shock crossing other. can identified just surrounded waves. rapidly reaches steady state decreasing discharge due emptying reservoir. re-circulation zones walls. illustrated figures computed (Noel 8 free-surface elevation t 1 s, spreading wave. 8: Computed image reflection occurred 9). circular front side walls lateral formed. 10 s: empties formed migrates separation around identified. 9: 10: