# Reaction Forces Wind on Hypar with springs

Hey, i’m moddeling a hypar (with different parameters) and would like to find the forces on the edges (different structure) caused by the wind function. So far so good. I generared extra points besides the hypar. Springs with given stifness are between the extra points and the hypar mesh. I calculated the displacement of the hypar mesh boundarys. Force on the structure = Stiffness spring x displacement. There are some problems.

1: the result mesh is very edgy and the mesh/sail is not a smooth one.
2: the calculation of the force (in excel) is not consisent. When I take stifness = 100 or stiffnes = 1000, the displacements don’t follow up (factor 10), so I get other force results. (Is something wrong with the springs? Does the kangaroo engine do something I don’t understand?)
3: Are there other possible ways to find the forces acting on the other structure (where the hypar is attached to)?

I really hope you can help me, because I have been struggeling in my thesis for days.

HyparKangarooEndForcesForum.gh (52.6 KB)

Hi Lukas,

Is this a fabric structure that you want to form-find?
If so, it probably makes sense to separate the form-finding step from the wind load analysis.

Also, if you are form-finding a tensile structure like this, there is no need to create the saddle geometry before putting it into Kangaroo - you can just start from a flat mesh and move a pair of opposing corner points up, and the saddle will form as it relaxes.

Hi Daniel

I’m not really trying to formfind a mesh. I really just have to know the forces (x,y,z in N) that are working on the anchorpoints (which is the steel structure). Later on i’m going to use these forces to calculate the dimensions of my steel structure.

You might consider implementing K2Engineering (see Cecilie’s thesis documenting it here).

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Seems like a good start! Thanks.
But how do i implement this plugin? How can i get the functions in my grasshopper. I downloaded K2Engineering, but i don’t know in which folder i have to put it…

Ah yes sorry, GitHub can a be a bit confusing with releases if you’re not used to it. You simply download the `K2Engineering.gha` file here and install it like any other plugin.

You can also do this with just Kangaroo.
Here’s an indication of how to get started setting this up and showing some reaction forces.

Hi Daniel

Looks awesome, thanks!

But what exactly represent the strenght and 0.1 (green)?
The resultforces are the ones shown in the panel (green), because they change when i change the strenght. Are they in Newton?

Now i’m going to try to add more anchorpoints.

Hi Lukas,

Yes, the easiest unit system to use here is N, m and Pa.
The multiplier of 0.1 I included was just to scale the arrows down for visibility.

For the strength input of the MeshEdges component you would use EA/L, where E is Young’s modulus in Pa, A is cross section area in m^2 and L is rest length in m.
The length of the vector input to the wind component is the pressure in PA in that direction applied to each mesh face.

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Hi Daniel

I made a lot of progress, thanks!
But it’s still not clear to me what the difference is between those two strengths (green)? They are both characteristics of the mesh/sail?

How can i retrieve these ‘numbers’ from a kind of material? What are cummon value’s for tentsails?

Thanks!