| Research Abstract |
It is found, from theoretical as well as experimental studies, that the maximun half width H, average buoyancy forceB and falling velocity V of both saline and particle clouds falling in quiescent waters have the following relationships ; against falling distance z H = KィイD21ィエD2z, V = KィイD22ィエD2zィイD1-1/2ィエD1 B = KィイD23ィエD2zィイD1-2ィエD1 initial total buoyancy WィイD20ィエD2 H = CィイD21ィエD2, B = CィイD22ィエD2WィイD20ィエD2, and V = CィイD23ィエD2WィイD31/2(/)0ィエD3. KィイD21ィエD2 for H, B and V in saline clouds become constant although their values are different. On the other hand, KィイD21ィエD2 in particle cloud clouds are function of particle Reynolds number Rp and their dependence on Rp are different for H, B and V. Similar relationships are also true for CィイD21ィエD2. Both saline and particle clouds falling in flowing waters also follows the same relationships against z and WィイD20ィエD2 as the case of quiescent waters although the buoyant clouds advect at the speed of ambient water flow velocity U. But ambient wa
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ter flow alters the values of KィイD21ィエD2. The functional relationships for KィイD21ィエD2 expressed in terms of Rp and U are reduced from extensive experimental study.
It is found experimental that major flow characteristics of both saline and particle clouds before and after impingement on the bottom boundary are not dependent on both initial total buoyancy force WィイD20ィエD2 and ambient water depth h.
Major flow characteristics of buoyant clouds traveling along bottom boundary after impingement can be distinguished into two regions ; transitional and gravity-current-like regions. Based on careful experimental work, we developed the functional relationships, that are able to adequately describe major flow characteristics of buoyant clouds in each region.
A new numerical simulation model for high concentration turbidity clouds is developed, utilizing Large Eddy Simulation (LES) and one-fluid model, coupled with a newly developed CCS scheme for advective-diffusion equation as well as the modified Smagorinsky model for SGS model. Model constants are determined by comparing with experimental results in the falling stage. Using the model constants, it is demonstrated that the proposed numerical model can well simulate both the motion of particle clouds and depositional profile of particles. Capability of the model is demonstrated further through numerical simulations in the presence of a silt fence. Less
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