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Improvements to the Modeling of Average Floc Size in Turbulent Suspensions of Mud

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dc.contributor.authorKuprenas, Rachel Leahen
dc.contributor.committeechairStrom, Kyle Brenten
dc.contributor.committeememberWeiss, Roberten
dc.contributor.committeememberStark, Ninaen
dc.contributor.departmentCivil and Environmental Engineeringen
dc.date.accessioned2018-06-26T08:01:00Zen
dc.date.available2018-06-26T08:01:00Zen
dc.date.issued2018-06-25en
dc.description.abstractThe accuracy of sediment transport models depends on identifying an appropriate sediment settling velocity. Determining this value for mud suspensions can be difficult because cohesive mud particles can aggregate, forming flocs whose sizes are a function of hydrodynamic and physiochemical conditions of the suspension. Here we present a new model refining the predicted floc size based on hydrodynamic conditions and inherited floc sizes, as well as on the salinity of the fluid environment. The improvements come from modifications made to the Winterwerp (1998) (W98) model. These improvements include: limiting floc size to the Kolmogorov microscale and including an initial salinity dependence. Limiting floc size in this way brings the model predictions more in line with flocculation theory and experimental observations. The salinity dependence was introduced based on a preliminary set of experiments that were conducted to examine floc growth rate and equilibrium size under different salinity conditions. In these experiments, increasing salinity from 2.5 to 10 PSU did not affect equilibrium floc size. However, the increases in salinity did result in longer times to equilibrium and an apparent increase in floc density or fractal dimension. The modified W98 model allows calibrated aggregation and breakup coefficients obtained under one set of concentration values (for both sediment and salinity) to be used to predict floc size under other concentration conditions. Comparing the modified W98 model with laboratory data shows more accurate predictive values, indicating that the modified W98 equation is a promising tool for incorporation into larger sediment transport models.en
dc.description.abstractgeneralIn order to assist in efforts to improve the environments of rivers, oceans, and estuaries, it is essential for scientists to have the ability to model all of the processes involved. One of the more difficult processes to model is sediment transport, specifically, cohesive sediment transport. How quickly a particle settles out of the water, and thus, how far a particle travels, is related to the density, size, and shape of the particle. With non-cohesive particles, this results in a relatively simple model as the particles stay the same size, shape, and density throughout time and space; however, cohesive particles are constantly changing as they can grow and shrink depending on the properties of the water at any given time. This process is called flocculation, and resulting particles are called flocs. This study aims to improve the modeling of cohesive sediment in the water column. Using existing data from [Tran et al., 2018], improvements were made to the existing Winterwerp [1998] model to account for the dependency of the particle size on sediment concentration. Tests were then run to collect data on how salinity impacts flocculation. This data was then used to further modify the Winterwerp [1998] model in order to account for salinity. These modifications resulted in predictions that better matched laboratory data, indicating that the modified Winterwerp [1998] equation is a promising tool for incorporation into larger sediment transport models.en
dc.description.degreeMaster of Scienceen
dc.format.mediumETDen
dc.identifier.othervt_gsexam:15954en
dc.identifier.urihttp://hdl.handle.net/10919/83764en
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectCohesive Sedimenten
dc.subjectFlocculationen
dc.subjectFloc-size Modelingen
dc.titleImprovements to the Modeling of Average Floc Size in Turbulent Suspensions of Muden
dc.typeThesisen
thesis.degree.disciplineCivil Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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