Autodesk Cfd Wind

[Miss Ruhnke]

Hi,

Thank you for the link.

The wind analysis is failing because the terrain is too steep. This usually happens if the terrain is too steep at the edge of the wind tunnel, or the overall difference in altitude across the whole tunnel is too large. The size of the wind tunnel is 1000m*1000m with a center at the center of the wind circle. You can see if you can smoothen or flatten terrain in the steep areas within that boundary to try to get a running wind analysis.

When analyzing the wind, I cant find out where I can edit the size of the circle. With bigger projects, the small analysis area is pretty useless. Also the detailed Wind analysis doesnt work for some reason.

Best, David

The detailed wind analysis did work in the end. I just checked the Classic version again and there you could use a wind analysis circle with a radius of 350m compared to only 150m in standard, which made it alot more useful, since microclimate is also depended on wind analysis. thanks for the consideration, david

i actually posted this very same topic in another forum thread. Spacemaker in its previous incarnation had more capability in this aspect. Small round wind and thermal comfort study areas dont work. Having to generate many of these circles to get an overview for a large masterplan defeats the purpose of these environmental tools. Sadly i feel that the previous versions offered more than the current one. Hope you can remedy this is future updates of Forma.

Also the detailed summary ouputs (% of different categories) of the environmental tools have been lost in the latest version. Again, for me its a step back rather than forward with regards the functionality as an urban designer.

Pleasantly surprised with the update (around October 20) that the analysis circles can now be set from 150 to 350 meters, that the roofs are now also included in the calculation (for roof terraces, etc.) ...

This paper presents an interactive design interface for three-dimensional free-form musical wind instruments. The sound of a wind instrument is governed by the acoustic resonance as a result of complicated interactions of sound waves and internal geometries of the instrument. Thus, creating an original free-form wind instrument by manual methods is a challenging problem. Our interface provides interactive sound simulation feedback as the user edits, allowing exploration of original wind instrument designs. Sound simulation of a three dimensional wind musical instrument is known to be computationally expensive. To overcome this problem, we present a novel fast resonance frequency prediction method based on the boundary element method. Specifically, we formulate the resonance problem as an minimum eigenvalue problem of a nonlinear matrix. Furthermore, we can efficiently compute an approximate resonance frequency using a new technique based on a generalized eigenvalue problem. The designs can be fabricated using a 3D printer, thus we call the results print-wind instrumentsu0022 in association with woodwind instruments. We demonstrate our approach with examples of unconventional shapes performing familiar songs.

We are happy to announce an exciting update for our iOS client. We continue to invest in leveraging our unique and powerful cloud solutions to building performance analysis tools to FormIt. We started at Autodesk University last year with the Energy Cost Range. Now, we are happy to announce that the same rich weather data that is available in Revit and Vasari is now available in FormIt on iOS. When you access the map interface to set location, you will now see weather stations populate your map! Just tap on a station to view the prevailing wind and annual temperature graphs. The Building Performance Analysis blog has some more detail on what is under the hood. This functionality is coming to the web and Android clients soon. And for all of you Android users out there, we have not forgotten about you! We have a new update almost ready to go. Just a few more bugs to squash first. Stay tuned!

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I am comparing results from Butterfly with those from Autodesk CFD. I created a simple urban wind model and ran both simulations with a base wind speed of 5 m/s. The buildings range in height from 10-20m. The results are displayed on a 3x3m grid, with a coloured mesh showing wind speed and white arrows showing direction.

I would suggest to try and align all parameters between the model, mesh type, mesh size and refinement, wind tunnel dimensions, ground roughness, boundary conditions, incoming wind profile, turbulence model, and so on.

As @TheodorosGalanos and @AbrahamYezioro noted Butterfly takes the input wind speed at a specific height (10 meters by default) and generates the wind profile. It makes sense to have a lower wind speed in a lower height. It seems in your study Autodesk CFD generates an inlet with a uniform wind speed.

What I am most interested in is how in Butterfly, the wind speed increases a lot towards the exit of the wind tunnel (see image below). Does this behaviour seem reasonable to you for this scenario (the terrain is totally flat)? @TheodorosGalanos @AbrahamYezioro @mostapha

Hi @nicholas Thanks for sharing all this. A uniform inlet will not do, certainly not for an urban case. If there is a way to script the logarithmic profile in Autodesk I would look for that (much like one can script it in StarCCM+).

Concerning the results, firstly we should note that the ground is not really flat. We are inputting a ground roughness to the model, most likely 1.0 which reflects a city area. This kind of creates a ground that is not considered flat even though there is no obstacle in the way.

As for the specific accelertion I think Abraham covered it nicely. You generally want to allow for a large extension on the leeward side (after the wind hits the area of interest), I would input a number between 10-15 in the leeward extension on BF windTunnelParameters component. This is because when we construct any CFD model, at least with our default settings in BF, we make an assumption. We assume that the pressure in the outlet is 0 (you can validate that by checking the boundary condition of the outlet patch in the p file, inside the 0 folder). To achieve that therefore, we allow a large extension that lets the freestream converge. A nicely converged study will always show that, a pressure that is near 0 close (and not only at) the outlet boundary.

Also you generally want to allow for a side extension, although the one you have now seems ok. You can try extending it a bit, maybe try 6 in the side extension input. I have a habit from the days of hand calculating grid expansion values to use the same number (6 in this case) for windward and side extensions but any number (usually equal or smaller than that) will do for your case. I think a best practice is somewhere around 3-4.

If your model gets too big from the choices above, you can try playing around with the blockMesh grading component. It can allow you to put a lot of refinement near your region and much less at the edges of your mesh. I typically have values like 200m even for individual cells near the end of my tunnel for example. My typical grading mesh settings is to set a blockMesh cell size of 1-2m at my region of interest and an expansion of 1.2 (max) from there to the edges (sides and outlet). For the inlet, I make sure the initial cell size is not too large. A value of 10m for the first cell would be good.

I also tried to match the wind profile (visible on the mesh above), by approximating a logarithmic distribution with the same ground roughness as in Butterfly. I had to use Excel to generate values for every 0.5m height in order to input the profile to Autodesk CFD (not pretty, but better than a uniform inlet).

In the Job Preferences dialog box, in the left panel, click the + sign to expand the Design Codes area, and then click Loads. The Code combinations, Snow/wind loads, and Seismic loads for the current project are displayed as shown below.

Three windows open containing the various calculation notes for the Wind Loads, Results for the Wind, and the Structure Dimensions and Wind Data as shown in part below. Calculation notes enable you to inspect all of the parameters of the loads that have been generated.

Is there software into which I can export my model of an urban development to do a wind/airflow analysis? Better yet - is there an extension/ruby, etc. that is available for SketchUp that would allow me to model/illustrate airflow/wind through a collection of buildings?

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Falcon technology is extremely geometry tolerant and easy to use, enabling you to begin seeing and understanding air flow behaviour within seconds of starting the application. Results update almost in real-time in response to changes in wind-direction and speed that you specify. Visualization tools available within the Falcon family of applications include 2D and 3D flow lines, shaded result planes, vector plots, and surface pressure shading. Quantified outputs include velocity, pressure, drag force, and drag coefficient. Project Falcon uses a revolutionary automatic meshing technology that can handle flow around any geometry at any stage of design. This technology is coupled with a transient, incompressible fluid flow solver and LES turbulence model in a way that delivers quick results and requires very little setup on behalf of the user.

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