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intro story DELWAQ

DELWAQ

DELWAQ is the engine of the D-Water Quality and D-Ecology programmes of the Delft3D suite. It is based on a rich library from which relevant substances and processes can be selected to quickly put water and sediment quality models together.

The processes library covers many aspects of water quality and ecology, from basic tracers, dissolved oxygen, nutrients, organic matter, inorganic suspended matter, heavy metals, bacteria and organic micro-pollutants, to complex algae and macrophyte dynamics. High performance solvers enable the simulation of long periods, often required to capture the full cycles of the processes being modelled.

The finite volume approach underlying DELWAQ allows it to be coupled to both the structured grid hydrodynamics of the current Delft3D-FLOW engine and the upcoming D-Flow Flexible Mesh engine (1D-2D-3D) of the Delft3D Flexible Mesh Suite (or even other models such as TELEMAC).

'DELWAQ in open source' is our invitation to all leading experts to collaborate in further development and research in the field of water quality, ecology and morphology using Delft3D. Feel free to post your DELWAQ related questions or comments in this dedicated forum space. If you are new to DELWAQ, the tutorial (in the user manual) is a good place to start. A list of DELWAQ related publications is available here.

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Sub groups
D-Flow Flexible Mesh
DELWAQ

Cohesive sediments & muddy systems

 


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Delwaq: ambient shear stress?

GS
Gholamreza Shiravani, modified 7 Months ago.

Delwaq: ambient shear stress?

Padawan Posts: 54 Join Date: 6/25/16 Recent Posts

Hi,

Could you tell me the difference between ambient shear stress and bed shear stress in Delwaq? How the ambient shear stress will be calculated for IM(Inorganic Matter)? Is it the shear stress of momentum equations (i.e. Tij=(v+vt)(dui/dxj+duj/dxi))? If yes, is the ambient shear stress the value of the shear stress Tensor? How is  the ambient shear stress for each cell in a 3D-mesh by Delwaq calculated?

AM
Arjen Markus, modified 7 Months ago.

RE: Delwaq: ambient shear stress?

Jedi Knight Posts: 222 Join Date: 1/26/11 Recent Posts

I had to search the manual for "ambient shear stress" and it seems I am responsible for this text. A slip of the pen, I am afraid - bottom shear stress is meant, nothing else. In most cases the shear stress can be picked up directly from the hydrodynamics. Otherwise it is calculated from the flow velocity and a user-defined value of the Chézy coefficient, as described in the manual. For DELWAQ the shear stress is not treated as a tensor, it is simply considered a scalar (or an isotropic tensor if you like).

GS
Gholamreza Shiravani, modified 7 Months ago.

RE: Delwaq: ambient shear stress?

Padawan Posts: 54 Join Date: 6/25/16 Recent Posts

Thank a lot Arjen. This term (ambient shear stress) is written in new Manual (published on December 22, 2018) in page 358. I have still  two questions about IM :):

1- How can I use IM for materials with smaller density than water (Floating or colloide material)? If not, do you know a better substance for Floating/sub-Floating (Floating in water columne) contaminants in water? How can I consider their densities (apart from settling velocity)?

2-How can I increase the number of IM from 3 to 6 or larger?

 

AM
Arjen Markus, modified 7 Months ago.

RE: Delwaq: ambient shear stress?

Jedi Knight Posts: 222 Join Date: 1/26/11 Recent Posts

Ad 1.

Truly floating material is a bit tricky - but you can specify a negative settling velocity. Then the material will rise to the surface instead of sink to the bottom. As it is still under the influence of vertical diffusion/mixing, it will be spread over the vertical, but as long as the mixing due to vertical diffusion is small in comparison with the rising due to the negative settling velocity, it shoudl concentrate at the surface.

The thing that will be missing is the influence of the wind at the surface. Most floating materials will feel the wind. It is possible to define an additional velocity per substance, but with a curvilinear or even unstructured grid that is a lot of work.

 

Ad 2.

You may try to do that with so-called fractions. The manual is fairly terse about it, but check section 1.5.1 in the description of the input file. Mind you: it has limitations. The three ordinary sediment types IM1, IM2 and IM3 (and IM1S1, IM2S1, IM3S1) are subject to "processes" like composition of sediment in the bottom - necessary for properly taking care of resuspension and the like - and the use of fractions may give slightly wrong results (I have never tried it in this way myself).

The safer way to do this is by splitting up the calculation into two parts.