Browsing Department of Applied Mathematics by browse.metadata.advisor "Diedericks, Hardus"
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- ItemIncipient motion of shells and shell fragments(Stellenbosch : Stellenbosch University, 2015-12) Troch, Christophe Nicolas Aimé; Smit, Francois; Diedericks, Hardus; Stellenbosch University. Faculty of Science. Department Mathematical Sciences (Applied Mathematics)ENGLISH ABSTRACT : In the present study, the erosion characteristics of shells and shell fragments are investigated. When shells settle, they settle like leaves, where the biggest cross section is exposed to the drag, unlike when they are flat on the bed, where the smaller cross section is exposed to the direction of flow. The settling velocity of shells is thus lower than the velocity required to make them erode. A model is presented to determine the critical bed shear stress of various shells at incipient motion lying flat on a horizontal sand bed. This model makes use of the hydrodynamical forces, where drag and lift forces are taken into consideration. The mussel and limpet shells are investigated, as well as various shapes of fossilized shells and fragments, in their dirty and clean states. These results are compared to results found in literature. Experiments were conducted in an open channel to determine critical bed shear stresses for incipient motion of the shells using Vanoni's side-wall correction. The lift and drag forces of the mussel and limpet shells are also determined under the flow of water using a strain gauge. The experimental data is compared to the data obtained by the analytical model. The Shields parameter is used in an attempt to relate the erosion characteristics of the shells to non-uniform sand grains on a bed.