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postgraduate thesis: Mixing and deposition of sedimentladen buoyant jets
Title  Mixing and deposition of sedimentladen buoyant jets 

Authors  
Advisors  Advisor(s):Lam, KM 
Issue Date  2013 
Publisher  The University of Hong Kong (Pokfulam, Hong Kong) 
Citation  Chan, S. [陳樹寧]. (2013). Mixing and deposition of sedimentladen buoyant jets. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5060572 
Abstract  Sedimentladen turbulent buoyant jets are commonly encountered in the natural and manmade environments. Examples of sedimentladen buoyant jets include volcanic eruptions, deep ocean hydrothermal vents (“black smokers”), ocean dumping of dredged spoils and sludge, and submarine discharge of wastewater effluent. It is important to understand the fluid mechanics of sediment jets for environmental impact assessment, and yet there is currently no general model for predicting the mixing of sedimentladen jets. This study reports a theoretical and experimental investigation the sediment mixing, fallout and deposition from sedimentladen buoyant jets.
It is well known that turbulence generates fluctuations to the particle motion, modulating the particle settling velocity. A general threedimensional (3D) stochastic particle tracking model is developed to predict the particle settling out and deposition from a sedimentladen jet. Particle velocity fluctuations are modelled by a Lagrangian velocity autocorrelation function that accounts for the loitering and trapping of sediment particles in turbulent eddies which results in the reduction of settling velocity. The model is validated against results of independent experimental studies. Consistent with basic experiments using gridgenerated turbulence, the model predicts that the apparent settling velocity can be reduced by as much as 30% of the stillwater settling velocity.
The mixing and deposition of sedimentladen horizontal momentum jets are studied using laboratory experiments and 3D computational fluid dynamics (CFD) modelling. It is shown that there is a significant settling velocity reduction up to about 2535%, dependent on jet turbulent fluctuations and particle properties. The CFD approach necessitates an ad hoc adjustment/reduction on settling velocity and lacks generality. Using classical solutions of mean velocity, and turbulent fluctuation and dissipation rate profiles derived from CFD solutions, 3D particle tracking model predictions of sediment deposition and concentration profiles are in excellent agreement with measured data over a wide range of jet flow and particle properties. Unlike CFD calculations, the present method does not require any a priori adjustment of particle settling velocity.
A general particle tracking model for predicting sediment fallout and deposition from an arbitrarily inclined buoyant jets in stagnant ambient is successfully developed. The model incorporates the three flow regimes affecting the sediment dynamics in a buoyant jet, namely turbulent jet flow, jet entrainmentinduced external flow and surface spreading current. The jet mean flow velocity is determined using a wellvalidated jet integral model. The external jetinduced irrotational flow field is computed by a distribution of point sinks along the jet trajectory. The surface spreading current is predicted using an integral model accounting for the interfacial shear. The model is validated against experimental data of sediment deposition from vertical and horizontal sedimentladen buoyant jets. 
Degree  Doctor of Philosophy 
Subject  Sediment transport  Mathematical models. Suspended sediments  Mathematical models. Waste disposal in the ocean  Mathematical models. Jets  Fluid dynamics. 
Dept/Program  Civil Engineering 
Persistent Identifier  http://hdl.handle.net/10722/188746 
DC Field  Value  Language 

dc.contributor.advisor  Lam, KM   
dc.contributor.author  Chan, Shuning.   
dc.contributor.author  陳樹寧.   
dc.date.accessioned  20130908T15:07:53Z   
dc.date.available  20130908T15:07:53Z   
dc.date.issued  2013   
dc.identifier.citation  Chan, S. [陳樹寧]. (2013). Mixing and deposition of sedimentladen buoyant jets. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5060572   
dc.identifier.uri  http://hdl.handle.net/10722/188746   
dc.description.abstract  Sedimentladen turbulent buoyant jets are commonly encountered in the natural and manmade environments. Examples of sedimentladen buoyant jets include volcanic eruptions, deep ocean hydrothermal vents (“black smokers”), ocean dumping of dredged spoils and sludge, and submarine discharge of wastewater effluent. It is important to understand the fluid mechanics of sediment jets for environmental impact assessment, and yet there is currently no general model for predicting the mixing of sedimentladen jets. This study reports a theoretical and experimental investigation the sediment mixing, fallout and deposition from sedimentladen buoyant jets. It is well known that turbulence generates fluctuations to the particle motion, modulating the particle settling velocity. A general threedimensional (3D) stochastic particle tracking model is developed to predict the particle settling out and deposition from a sedimentladen jet. Particle velocity fluctuations are modelled by a Lagrangian velocity autocorrelation function that accounts for the loitering and trapping of sediment particles in turbulent eddies which results in the reduction of settling velocity. The model is validated against results of independent experimental studies. Consistent with basic experiments using gridgenerated turbulence, the model predicts that the apparent settling velocity can be reduced by as much as 30% of the stillwater settling velocity. The mixing and deposition of sedimentladen horizontal momentum jets are studied using laboratory experiments and 3D computational fluid dynamics (CFD) modelling. It is shown that there is a significant settling velocity reduction up to about 2535%, dependent on jet turbulent fluctuations and particle properties. The CFD approach necessitates an ad hoc adjustment/reduction on settling velocity and lacks generality. Using classical solutions of mean velocity, and turbulent fluctuation and dissipation rate profiles derived from CFD solutions, 3D particle tracking model predictions of sediment deposition and concentration profiles are in excellent agreement with measured data over a wide range of jet flow and particle properties. Unlike CFD calculations, the present method does not require any a priori adjustment of particle settling velocity. A general particle tracking model for predicting sediment fallout and deposition from an arbitrarily inclined buoyant jets in stagnant ambient is successfully developed. The model incorporates the three flow regimes affecting the sediment dynamics in a buoyant jet, namely turbulent jet flow, jet entrainmentinduced external flow and surface spreading current. The jet mean flow velocity is determined using a wellvalidated jet integral model. The external jetinduced irrotational flow field is computed by a distribution of point sinks along the jet trajectory. The surface spreading current is predicted using an integral model accounting for the interfacial shear. The model is validated against experimental data of sediment deposition from vertical and horizontal sedimentladen buoyant jets.   
dc.language  eng   
dc.publisher  The University of Hong Kong (Pokfulam, Hong Kong)   
dc.relation.ispartof  HKU Theses Online (HKUTO)   
dc.rights  The author retains all proprietary rights, (such as patent rights) and the right to use in future works.   
dc.rights  Creative Commons: Attribution 3.0 Hong Kong License   
dc.source.uri  http://hub.hku.hk/bib/B50605720   
dc.subject.lcsh  Sediment transport  Mathematical models.   
dc.subject.lcsh  Suspended sediments  Mathematical models.   
dc.subject.lcsh  Waste disposal in the ocean  Mathematical models.   
dc.subject.lcsh  Jets  Fluid dynamics.   
dc.title  Mixing and deposition of sedimentladen buoyant jets   
dc.type  PG_Thesis   
dc.identifier.hkul  b5060572   
dc.description.thesisname  Doctor of Philosophy   
dc.description.thesislevel  Doctoral   
dc.description.thesisdiscipline  Civil Engineering   
dc.description.nature  published_or_final_version   
dc.identifier.doi  10.5353/th_b5060572   
dc.date.hkucongregation  2013   