Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


L. Donnelson Wright


An aggregation model which allows specification of primary particle size, density, and fractal dimension for two different particle types was written. Three stickiness values are used, the stickiness of each particle type to itself and the stickiness between particle types. Aggregation mechanisms considered include differential settling and turbulent shear. The model is used in three forms. In its simplest form, it operates on a closed system with aggregates breaking up when their size approaches the Kolmogorov scale. If the system begins with two types of primary particles, larger aggregates have uniform composition. A second version of the model includes removal of aggregates by settling. In this mode, the stickiness parameters dominate aggregate characteristics. Stickiness between similar particles controls the ratio of the particle type, whereas interparticle stickiness controls the particle removal rate. In the third form, three aggregation models are connected by a Rouse type suspended sediment model. This version models aggregate dynamics in the water column. Comparison of model results with total suspended sediment data and particulate organic carbon data from a site near the Poquoson River suggests that organic and inorganic constituents of suspended sediment do not stick together well. The dissertation also describes a new type of aggregation device called the rotating oscillating grid turbulent aggregation chamber (ROGTAC). This device combines the advantages of two types of aggregation devices which are commonly used, the oscillating grid device and the rolling cylinder device. Oscillating grid turbulence generators are preferred for creating uniform isotropic turbulence. However, when particles more dense than the fluid are placed in them, the particles settle out. Rotating cylinder devices are effective at keeping particles in suspension. They do this by keeping the fluid in them in solid body rotation, but in this mode the fluid is not experiencing shear. ROGTAC places an oscillating grid in one end of a rotating cylinder. The hydrodynamic characteristics were investigated using laser Doppler velocimetry. Turbulent energy dissipation rates calculated from LDV data agreed well with energy input calculated by applying the quadratic drag law to the grid.



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