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Force surface goal on deactivated component

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Old   January 12, 2017, 05:01
Default Force surface goal on deactivated component
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Florian
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Hello everybody,

I'm trying to investigate the flow force acting on surfaces using Solidworks Flow Simulation.
Is it possible to assign a force surface goal to a part which is deactivated in the component control? For me, assigning goals to deactivated surfaces works fine for any variables other than force variables.

Thanks for your answers.
Florian
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Old   January 17, 2017, 06:00
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Boris Marovic
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Hi Florian,

no, something that is not there can also have no forces acting on it.
That's why it was never realized.
Can you explain why you want to do that?

Regards,
Boris
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Old   January 20, 2017, 03:04
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Florian
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Hi Boris,

thanks for your reply. Yes, this sounds reasonable. Nevertheless, I'm interested in the force the flow would (approximately) apply to some surfaces if they were existent at different locations. For this reason, I don't want to solve multiple models but get a guess from one single simulation.

Now I approached the problem by equation goals using surface goals from the mentioned deactivated components.

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Florian
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Old   January 20, 2017, 03:26
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Boris Marovic
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Hi Florian,

I understand your point, but since the forces depend on the flow reacting on the bodies shape also, it is very hard to predict anything from such a simulation you are planning.
For example take a round flat plate, the forces on that flat plate alone are higher than the forces on such a plate with a cone in front of it which makes the flow go around the flat plate much better. Also, see the examples in the link below. It is already a big difference if you use a half-sphere, a cone, a cube or a short cylinder. They might all have the same frontal surface area but the way the flow is disturbed by them and creates vortices and a wake behind the object can change the amount of forces acting on them massively.

I hope this helps to understand why it is basically a good idea to try to find an easier way but it wouldn't work out correctly.

I mean by placing a deactivated object like a cube and simply wanting to get the normal forces on it which are the forces created by pressure on the surfaces, you can do that by using a surface goal on this body for the pressure but the forces are created by the pressure difference between the one side of the object and the opposite side of it and therefore creating a high and low pressure which then defines the force direction and amount as you might know. If you have a deactivated cube in the flow, then the flow is completely undisturbed and the pressure before and after the cube is the same, so no forces. But depending on the actual shape of the body (for example aerodynamically shaped) you could create a much lower pressure drop behind the body than with a blunt body of the same cross section. I mean simply take the long and short cylinder example in the link. They have the same cross section area but different lengths which influences the flow and its separation and therefore the pressure behind the cylinder as well as the frictional forces on the cylinder surface.

https://en.wikipedia.org/wiki/Drag_coefficient

I hope this helps.

Boris
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