Eddy3D - Buildings level of accuracy, trees and Z0

Hello Patrick and Timur,

I write you about three main questions relative to modeling for CFD simulations using Eddy3D: 1) building refinement (level of accuracy), 2) trees and 3) Z0.

1
I already have some experience in working with OpenFOAM in GH so it is quite easy to understand how the refinement works in Eddy3D, though not all the input are clear.
AccFeatures and AccGround are clear. But what I get using AccBuilding and AccBBox? Did some test but didn’t get any visible difference in the mesh.
About building refinement my main question is: is it possible to use different refinements for different buildings? I have a large number of modeled buildings in the domain,
So I would like to use 2 or maybe 3 different refinement levels depending on the vicinity of the buildings to the areas of interest, where I will probe the wind velocities.

As you can see from the following image, all the buildings have a refinement of 4, but for example I would like to get a refinement of 4 only for the 3 buildings closer the
area of interest, the red horizontal surface, and then I would like to assign a refinement of 2 to the other 5 buildings closer the ground perimeter (white surface that Eddy3D creates automatically).
I have created the area of interest, the red horizontal surface, using a plane at 1cm from the ground. It works, though the edges are not perfect, but I think it is not a problem.
I create this area of interest to have an area where I can assign a refinement level higher than the ground.
So is possible to assign different refinement levels?

2
As you can see from the second image, I am going to simulate wind velocities in different areas in our university campus (the red patches in the image)
where I will locate the horizontal planes to increase the mesh accuracy level.
The campus is surrounded by large tree areas. 4 of these areas are very close the areas where I want to analyze wind velocities. How do you suggest to include these large patches of trees in the simulations?
From the third image you can see the type of tree. They are a type of pine tree, they are not deciduous trees, with different crown size.
I have seen that in Eddy3D there is a Tree component that I understand do not create an object in the mesh but it is used only for speed variation calculations.
Can I use this component? If yes, then I have two more questions:

  • do I need to model a large number of simple 3D objects like thick cylinders or ellipsoids supported by thin cylinders, or I can model just one large extruded polyline for each of the 4 tree areas?
  • If I can model just 4 extruded polylines, do I need to model the trunks that support the extruded polylines, or they can float representing the crown without the need to model the trunks?

3
As you can see from the 4th, larger scale, image, the areas surrounding the university are very different.
So I need to use different Z0. The question is: can I use in Eddy3D one specific Z0 for every wind direction when using the cylindrical wind tunnel?

Thank you for the moment.

Best,
Francesco

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Hi Francesco,

But what I get using AccBuilding and AccBBox?

AccBuilding sets the accuracy for the buildings geometries, AccBBox sets the accuracy with in the bounding box that encloses the building geometries.

About building refinement my main question is: is it possible to use different refinements for different buildings? I have a large number of modeled buildings in the domain,
So I would like to use 2 or maybe 3 different refinement levels depending on the vicinity of the buildings to the areas of interest, where I will probe the wind velocities.

Not possible currently.

From the third image you can see the type of tree. They are a type of pine tree, they are not deciduous trees, with different crown size.
I have seen that in Eddy3D there is a Tree component that I understand do not create an object in the mesh but it is used only for speed variation calculations.
Can I use this component?

Yes, however this is not trivial. You will have to compute the Darcy-Forchheimer coefficients for each tree object.

  • do I need to model a large number of simple 3D objects like thick cylinders or ellipsoids supported by thin cylinders, or I can model just one large extruded polyline for each of the 4 tree areas?

See this video for further explanation. In short, you can do both but you will have to adjust your coefficient accordingly.

If I can model just 4 extruded polylines, do I need to model the trunks that support the extruded polylines, or they can float representing the crown without the need to model the trunks?

You could model the trunks as a porous model with very small permeability, so high values for D and F.

As you can see from the 4th, larger scale, image, the areas surrounding the university are very different.
So I need to use different Z0. The question is: can I use in Eddy3D one specific Z0 for every wind direction when using the cylindrical wind tunnel?

This is currently not supported but it is on my todo list and I will implement it into a future release.

Best,

Patrick

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Thank you for the clarifications Patrick!

Best,
Francesco

1 Like