Numerical Simulation of the Sedimentation Process in a Trailing Suction Hopper Dredge

摘要

In the last decades large areas of land were reclaimed using trailing suction hopper dredgers, and large reclamation projects will be executed in the near future, especially in the Far East. During the overflow phase of the loading stage of the dredging cycle a part of the dredged volume of sand will not settle in the hopper but is transported with the overflow discharge overboard. For production, sand quality and environmental reasons it is important to predict the amount of this so-called overflow loss. Both the total volume of losses as the influence on the loaded (and lost) particle size distribution (PSD) is important. In 1997 a research program was started to get more under-standing of the sedimentation process onboard a hopper dredge. The goal of the programme was to develop a numerical model that can be used to predict the influence of the relevant parameters as hopper geometry, sand, discharge and concentration on the overflow losses (and which fractions of the PSD will be lost) . The research programme consists of three parts: laboratory experiments, development of numerical models and full-scale validation of the models. In the paper the results of the laboratory tests and the developed 1DV numerical model will be presented. The 1DV-model is one-dimensional, but in contrary to most existing models in the vertical direction: The influence of the PSD distribution is modelled using a coupled system of transport equations (convection-diffusion) for the different grain sizes. The numerical results will be compared with the experiments. Good agreement is achieved in prediction of the overflow losses as function of the loading time with constant and varying inflowing sandflux.