WEng scripts stalls

[HPJ]

Hi

I've made a script for WEng that provides me with speed and TI for each turbine/sector/height that has been specified in the workspace.

However... After some time it stalls. I've tried reducing the resolution and after reducing it enough the script runs to the end. What's going on? It seems like it's either a calculation issue or a memory issue?

I'll happily send the script so you can check it.

- Hans Peter

[Morten]

Hans Peter and I have discussed this at technical support. Scripts activating both the flow- and turbulence-model for many turbines/sectors/heights can run into different types of problems. When the calculation simply no longer progress, the usual reason is the turbulence model having difficulties with integrals involving velocity gradients upwind of the site, see equations 14 and 17 in the paper by Jakob Mann, Journal of Wind Engineering and Industrial Aerodynamics, vol. 88 (2000) p. 153-169. That turbulence-model problem could be provoked by a faulty flow solution, which in turn could be caused by problems related to the elevation or roughness map. So, if anyone runs into problems like this, it a good idea to inspect the flow and velocity gradients in the field view for the direction causing problems. Look out for strange velocities directly upwind of the site giving problems.

There is also a memory limitation, like HPJ suggests. WEng attempts to store about 20 different 2D fields with various flow properties in memory, and it is doing so for all the wind directions you calculate in a session. WEng is a Win 32bit program, which means that it can only work with 1½ GB memory, and thus the limitations of about 512x512 sized grids for twelve directions. Our main programmer, Duncan, made an experimental version, where flow solutions were stored as temporary files. With this we could work with 1024x1024 sized domains and have as many of them as we liked in a session. The file operations did not slow down the program significantly. The plan it to provide this feature for the users later.

I should say that by 512x512 sized grid, I mean grids including a buffer zone, which WEng adds to the specified domain in order to work with FFT and thereby with cyclic boundary conditions. If you want a 15% buffer zone you should specify something like 460x460 grid points in the domain editor.