A SENSITIVITY ANALYSIS ON THE EFFECTS OF DIMENSIONS AND GEOMETRY OF TRAILING SUCTION HOPPER DREDGES

摘要

In the past two decades the size of TSHD's has tripled and there are plans for TSHD's in the range of 50,000 m~3. When enlarging hoppers, there are some limitations like the draught of the vessel and the line velocity in the suction lines. It's interesting to compare the influences of length, width, height ratio's, flow capacity and some other parameters on the production and the overflow losses of TSHD's. To do so, mathematical models have been developed to simulate the sedimentation process in the hopper. Two models will be used and compared, first the model of Vlasblom/Miedema (1995) and Miedema/Vlasblom (1996) and second the more sophisticated 2DV model of vaa Rhee (2002) which is verified and validated with model and prototype tests. Both models are explained briefly. With the two models 3 cases are analyzed, a 2316 m~3, a 21579 m~3 and a 36842 m~3 hopper. The results of the case studies give the following conclusions and recommendations:rn1. The two models give the same magnitude for the overflow losses, but the shape of the curves is different due to the differences in the physical modeling of the processes.rn2. Due to the lower losses the computed optimal loading time will be shorter for die Vlasblom /Miedema approach.rn3. The strong point of the van Rhee model is the accurate physical modeling, giving the possibility to model the geometry of the hopper in great detail, but also describing the physical processes in more detail.rn4. The van Rhee model is verified and validated with model and prototype tests and can be considered a reference model for other models.rn5. The strong point of the Miedema/Vlasblom model is the simplicity, giving a transparent model where result and cause are easily related.rn6. The Miedema/Vlasblom model can be extended with a number of features that do not really influence the simplicity of the model. One can think of:rn1.1 Implementing the layer thickness of the layer of water above overflow level.rn2.1 Implementing a horizontal velocity distribution in the hopper that will result in a more gradualrninfluence of the scour effect during the loading process. 3.1 Implementing a storage effect.rn4.1 Implementing a starting volume of water when the loading process starts, 5.1 Implementing a varying inflow and density of mixture.