Learning Forum

[Islam Rashid]

Any help would be appreciated- it is urgent

Basically, I am performing a CFD analysis of a tree with a solid trunk, and a porous crown. I have the inertial resistance coefficient of 200 m^-1, but when I input it, my crown is way too porous (it should be 96% porous). As a result my pressures are not quite correct. I have experimented and used random values, and the pressures now are plausible:

Furthermore, I need to import those pressures and apply it onto one side of the tree in a static structural analysis, however, (I think?) my stresses outputted are a bit too low:

 

 

 

 I think it may be to do with my named selections for which I apply the pressure loads to (I have selected all the faces of the tree):

 

 

Many Thanks,

Islam

[Islam Rashid]

also, what's the best way of modelling the porous crown of the tree in the structural analysis? I have reduced its density as well as its Young's modulus

[Rob]

I have no idea about the structural part.

However, for a tree you need to consider what is going on in the leafy bit. A tree is optically thick (you can't see through it), has a range of flexible and solid parts (leaves, twigs and branches) and may be mostly air. This makes estimating resistance coefficients to be quite difficult, and also consider if leaves move do those coefficients vary with wind speed. Luckily some work has been done in this area, and that included dragging lumps of tree into a wind tunnel. So, I advise doing a literature review for more data, and maybe searching for porous tree on here. 

[Islam Rashid]

Brilliant, thank you.

For the structural part though, do you recommend assigning both the crown and trunk as wood, but make the crown have a much lower young's modulus (96% less due to 96% porosity)? Or should I change the density?

Thanks again

[Islam Rashid]

also, since my porosity is 96%, should I put under the 'Porosity' box as 0.96? I have left the viscous coefficient as standard while keeping the inertial coefficient as 0

[Rob]

Read what the porosity does - it's mainly for thermal models. 

Re the structural part, I really don't know. Can you assume a tree canopy is a single material? There are a couple of sections in the Fluent 24R1 beta manual regarding FSI and porous zones; those may be worth reviewing.