# trying to find the center of pressure of stratosail

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December 30, 2014, 11:17
trying to find the center of pressure of stratosail
#1
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Hi guys,

I want to calculate the center of pressure of a stratosail body at different angles of attack. I have read through some of the posts, but I cant seem to get a clear step by step guide on this.

Is it possible to print the coordinates of the centre of pressure? I have tried setting x=0 and then printing the other 2 coordinates. But, I do not understand this method.

Alternatively, how can I calculate the moment due to the resultant drag force about the center of mass? The manual says that you will need a moment center and a moment axis. I guess the moment center will be the center of mass of the sail. But, why do you need a moment axis?

Rgds
Jay
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December 30, 2014, 14:20
#2
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Lucky
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Quote:
 Originally Posted by Jayakanth Alternatively, how can I calculate the moment due to the resultant drag force about the center of mass? The manual says that you will need a moment center and a moment axis. I guess the moment center will be the center of mass of the sail. But, why do you need a moment axis?
Moments are always about an axis. A center (location) alone does not define the axis about which the moment is considered. The question is why you would think you can have a moment without any axis?

If the center is at the origin. Your moment axis could still be any axis, (x,y,z, or any other axis). You must also specify what is the axis with respect to which you are going to define your moment. In other words, you need a point (a location) and a direction vector to define the axis and only after that is fully defined can you consider any moment.

December 31, 2014, 05:58
#3
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Quote:
 Originally Posted by LuckyTran Moments are always about an axis. A center (location) alone does not define the axis about which the moment is considered. The question is why you would think you can have a moment without any axis? If the center is at the origin. Your moment axis could still be any axis, (x,y,z, or any other axis). You must also specify what is the axis with respect to which you are going to define your moment. In other words, you need a point (a location) and a direction vector to define the axis and only after that is fully defined can you consider any moment.
So specifying the moment axis tells fluent to compute the moment along that specified axis. So, if the moment had components of x,y and z, then if i specified the moment axis as (1 0 0), it would compute the moment along the x-axis?

What about printing the coordinates of the center of pressure? What are the steps for that?

Rgds
Jay

January 2, 2015, 06:37
#4
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Quote:
 Originally Posted by Jayakanth So specifying the moment axis tells fluent to compute the moment along that specified axis. So, if the moment had components of x,y and z, then if i specified the moment axis as (1 0 0), it would compute the moment along the x-axis? What about printing the coordinates of the center of pressure? What are the steps for that? Rgds Jay
Anyone can verify this?

Rgds
Jay