Abstract

The development of more and more potent computers and the recent research in the field of hidroinformatics makes possible the free surface flow modelling in two dimensions caused by earthen dam failures. In this paper, the results obtained by uni-dimensional model (HEC-RAS) and two-dimensional model (CARPA) are compared. The use of the HEC-RAS software assumes the hypothesis of unidimensionality to be true, no infiltration and existence of a minimal initial flow. The comparison is made by analyzing the effect of these hypothesis in the downstream flow hydrographs. The used models reproduce the water discharge generated by a possible failure of dam number 1 of the 5th District of the Segarra-Garrigues Irrigation Project in the Ebro river basin in Spain.

Abstract

In this paper, the effects of different widths and lengths of collar around bridge abutment on local scour depth are studied numerically and experimentally. Numerical simulation of scour hole evolution at bridge abutment is more convenient than the experimental modeling, because the computational cost and time have significantly decreased. The numerical model solves 3-D Navier–Stokes equations and bed load conservation equation. The k–ε turbulence model is used to solve the Reynolds-stress term. The simulated results are verified using the laboratory experiments. In addition, the multiple linear regressions are applied to correlate the maximum local scour depth with the other independent parameters. It was found that the relative length of collar 0.73 around bridge abutment reduces the maximum scour depth by 69% compared to no-collar case. Moreover, the results of 3-D numerical model and regression models agree well with the experimental data.

Abstract

In 2006, a work plan was conceived tor the development of a mud transport model tor the Scheldt estuary in the framework of LTV (Long Term Vision) (Winterwerp and De Kok. 2006). The purpose of this model is to support managers of the Scheldt estuary with the solution of a number of managerial issues. Also in 2006, the first two phascs were initiated. Thc present report discusses the actlvities that have been carried out during 2007, i.e. further improvement of the hydrodynarnic and mud transport model and lirst applicarion of the mud model to the release of fine sediment dredged from Sloe harbour, Vlissingen. At a technical level, all model improvements scheduled tor 2007 have been implemenred. The most important developments are: longer hydrodynarnic simulation period (3 month), more accurate concenration boundary condition, variable wave effects and biological effects. The hydrodynarnic sirnulation demonstrates realistic values for water levels, salinities and residual currents. Upstream of Antwerpen. the propagation of the tidal wave is modelled less accurately. Regarding the mud transport simulations, the following is concluded:"br" 1. A minor shift of two dumping locations near Antwerp rnuch improves the proper modelling of the ETM."br" 2. New concentration BC at sea result in more realistic SPM concentrations and longshore SPM fluxes at sea."br" 3. The difference between simulations with 5 and 10 horizontal layers is only minor."br" 4 . Variable waves temporarily enhance the concenrations in the western part of the Western Scheldt during storrns."br" 5. The biological impact on large-scale SPM concentrations in the Scheldt estuary appears to be minor."br" 6. The SPM levels appear to be rather sensitive to the volume of harbour siltation and dumping."br" 7. The model cornputes an unrealistically high residual sediment flux towards the North Sea (about 2 MT/y)."br" If sediment dumping is in equilibrium with harbour siltation, this net export results in too low equilibrium SPM levels. Application of the model to the dumping of sediment dredged from Sloe harbour shows that a shift of the release location in western direction may be favourable because of a small reduction in local SPM levels and siltation rates. Document type: Book

Abstract

This work presents a coupling between two numerical models, one for mesh generation and the other for heat transfer analysis, used to characterize the tree trunk thermal behaviour located in a forest fire environment. The geometry of the tree trunk is developed, using adaptive mesh generation, to evaluate the view factors, used to calculate the heat exchanges by radiation, between the virtual trunk tree and a fire front. The fire front represents the existing forest fire. The trunk tree thermal behavior numerical model is based on energy equations. The energy balance integral and differential equations consider the heat exchange by conduction inside the trunk tree, the heat exchange by convection between the trunk tree external surfaces and the environment and the heat exchanges by radiation between the trunk tree external surfaces and the environment and fire front. The numerical simulation is characterized by the propagation of a fire front at a constant fire spread rate of 0.01 m/s from a distance of 5 m upstream of the tree trunk. With an irregular shape, the tree trunk has a height of 2 m and an external diameter of 0.2 m. The fire front has a tilt angle of 45º, 10 m wide and 2 m high. The temperature distribution in the tree trunk was obtained for a wind speed of 0.1 m/s, an average flame temperature of 500ºC, an environmental air temperature of 20ºC and an air relative humidity around the trunk tree of 50%. The temperature distribution obtained allows to identify the areas of the tree trunk tissues that were most affected by the passage of fire.