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    05-A sensitivity analysis of the scaling of TSHDs. (611)

For the estimation of the sedimentation process in TSHD’s a number of models have been developed. The oldest model used is the Camp (1946) model which was developed for sewage and water treatment tanks. Camp and Dobbins added the influence of turbulence based on the two-dimensional advection-diffusion equation, resulting in rather complicated equations. Groot (1981) added the effects of hindered settling. Miedema & Vlasblom (1996) simplified the Camp equations by means of regression and included a rising sediment zone, as well as hindered settling and erosion and an adjustable overflow. Van Rhee (2001) modified the implementation of erosion in the Camp model, but concluded that the influence is small due to the characteristics of the model. Ooijens added the time effect, since the previous models assume an instantaneous response of the settling efficiency on the inflow of mixture. Yagi (1970) developed a new model based on the concentration distribution in open channel flow. Lately Miedema & van Rhee (2007) made a comparison between the Camp model and the sophisticated 2DV model of van Rhee (2002) which showed that especially the overflow losses match. In 2008 Miedema added non-linear effects to the Camp model, such as the behavior of the layer of water above the overflow and an analytical model to determine scour.
The loading process of TSHD’s contains a number of non-linearity’s:
1. The real hopper load parameter will vary during the loading process.
2. The turbulence settling efficiency.
3. The behavior of the layer of water above the overflow.
4. The behavior of hindered settling.
5. The effective concentration in the hopper.
6. The so called storage effect.
Based on all these non-linearity’s it is not expected that TSHD’s can be scaled easily, however the research in this paper shows that with the right choice of scale laws the TSHD’s can be scaled rather well.
4 TSHD’s are chosen, derived from Miedema & van Rhee (2007), but adapted to the scale laws. With each of these TSHD’s simulations are carried out in 4 types of sand, 400 μm, 250 μm, 150 μm and 100 μm sand.

Reference:

Miedema, S.A., "A Sensitivity Analysis Of The Scaling Of TSHD's". WEDA XXIX & Texas A&M 40. Phoenix Arizona, USA, June 14-17 2009.



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