cfd: Hurricane Irma

A subforum specific to the development of the OpenFoam-based workbenches ( Cfd https://github.com/qingfengxia/Cfd and CfdOF https://github.com/jaheyns/CfdOF )

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thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

cfd: Hurricane Irma

Postby thschrader » Sat Sep 09, 2017 4:08 pm

Given:
A little house 9x9 m wide, 6 m high. Wind speed 250 km/h.
openFOAM/paraview calculates a resulting drag force of 370 kN (37 tons),
resulting lifting force 250 kN (25 tons). solver: simpleFoam.
If you check back the results with a"thumb-rule" (area 6x9 m, pressure at 250 km/h = 3 kN/m^2, shape factor 1,4)
you will get 226 kN drag force. I am not sure if the openFOAM-model fits better to reality,
but if so the florida folks should better visit an air-raid shelter.
Thomas
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ulrich1a
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Joined: Sun Jul 07, 2013 12:08 pm

Re: cfd: Hurricane Irma

Postby ulrich1a » Sat Sep 09, 2017 4:49 pm

Would it be useful to make a hole in the roof, in order to avoid the pressure difference that causes the lifting force?
thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: cfd: Hurricane Irma

Postby thschrader » Sat Sep 09, 2017 5:06 pm

ulrich1a wrote:
Sat Sep 09, 2017 4:49 pm
Would it be useful to make a hole in the roof, in order to avoid the pressure difference that causes the lifting force?
Mmmh...thats like opening a window. But in general you are right, avoid pressure differences.
What about the drag?
Thomas
ulrich1a
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Re: cfd: Hurricane Irma

Postby ulrich1a » Sat Sep 09, 2017 6:06 pm

thschrader wrote:
Sat Sep 09, 2017 5:06 pm
What about the drag?
You need a stable house with heavy walls. I have no idea to avoid the drag.
In the north see isles, they used timber framed houses. A flood did remove the wall out of the timber frame, but the upper floors stayed untouched. I do not think this is an option for a hurricane.

Ulrich
Worufu
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Location: Italy

Re: cfd: Hurricane Irma

Postby Worufu » Sun Sep 10, 2017 9:44 am

Good simulation :D A solution can be the rounded edges on the roof, it is not a cheap solution, but can help to not detach the streamlines from the roof and reduces a lot the trail turbolence. Also the vortex generator at the base of the roof (all around to prevent every wind direction), helps again this effect, but I think in this case the mesh grid need a lot of resolution and calculation time.

Can you print a 3D view with streamline around the house?
thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: cfd: Hurricane Irma

Postby thschrader » Sun Sep 10, 2017 11:08 am

Worufu wrote:
Sun Sep 10, 2017 9:44 am
Can you print a 3D view with streamline around the house?
Hello Worufu,
I am not familiar with paraview, but I hope you mean the pic below.
Just started with doing some tutorials from
https://www.youtube.com/user/kehoste/videos
https://www.youtube.com/watch?v=J944HOj_4b0

For the calculation of the house I used a 60x20x0,5 m "wind-tunnel".
Fluid is water with 0,001 m^2/s viscosity / 1000 kg/m^3 density, inlet speed is 2,45 m/s.
This gives the same pressure like air at 250 km/h with 1,25 kg/m^3 density.
If you use the real windspeed you need a much finer mesh and excessive calculation time. Too hard stuff for
my steam-driven laptop. I have done the same with a wind-tunnel of 6x2x0,1 m simulating the
aerodynamic forces on a cylinder (D=400 mm). The viscosity is 0,001 m^2/s, density 1000 kg/m^3, inlet speed 1,5 m/s.
This gives the same pressure as air at 150 km/h. The theoretical correct result is 360 N/m drag-force
according to german DIN-manuals. I get the best results with GMSH (325 N/m), no refinement. cfmesh nearly
computes the double force. All simulations are "steady" (simpleFoam) without turbulence.
I am interested in calculating the aerodynamic forces on antenna-masts.
regards Thomas
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chrisb
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Re: cfd: Hurricane Irma

Postby chrisb » Sun Sep 10, 2017 4:10 pm

Your coloured picture of the house is really impressive, thank you!
thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: cfd: Hurricane Irma

Postby thschrader » Tue Sep 12, 2017 10:35 pm

chrisb wrote:
Sun Sep 10, 2017 4:10 pm
Your coloured picture of the house is really impressive, thank you!
Yes, the cfd-wb is really impressive. FC becomes a real engineering-tool.
I did a 3D-calculation of the house. The cool thing is, that
you can adress multiple processors via cfd-wb for using parallel computing.
Speeds up the calculation a lot.
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Worufu
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Location: Italy

Re: cfd: Hurricane Irma

Postby Worufu » Wed Sep 13, 2017 7:55 pm

oooh good, I was trying the 3D version too of this model, but I get a lot of problem, pressure "explosion" at certain moment.
Do you use transient or steady? Does you pressure converge or remains at high value? (0.5-0.3)
GeneFC
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Location: Punta Gorda, FL

Re: cfd: Hurricane Irma

Postby GeneFC » Wed Sep 13, 2017 8:20 pm

I know very little about FEM and CFD, but I do know a thing or two about hurricanes.

In South Florida all houses must now be designed and constructed to withstand 250 km/h winds.

We had surprisingly little impact from Irma even though the eye was only 20 km from us. In 2004 our house was at the exact center of Charley. We saw 230 km/h winds with no structural damage at all.

It is more expensive to design and build for those winds, but it can be done.

Gene