## self weight

About the development of the FEM module/workbench.
bernd
Posts: 3856
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### self weight

see topic viewtopic.php?f=3&t=16655

I could not resist:
https://github.com/berndhahnebach/FreeC ... selfweight

We just need an icon for it! Any help is appreciated!
sgrogan
Posts: 2969
Joined: Wed Oct 22, 2014 5:02 pm

### Re: self weight

gravity.PNG (22.67 KiB) Viewed 444 times
fem-constraint-gravity.svg

First thought. The blue lines of the mesh are left over from the pressure constraint. All the mesh lines should be green to imply gravity and that the constraint is volume distributed. Just learning inkscape. Is the idea worth pursuing? The main idea is to modify an existing constraint icon to stay consistent.

bernd wrote:I could not resist:

I haven't tested your branch yet, I will soon. Is the constraint gravity specific? Being able to specify the direction vector immediately generalizes the constraint to acceleration.
sgrogan
Posts: 2969
Joined: Wed Oct 22, 2014 5:02 pm

### Re: self weight

Slightly improved
gravity2.PNG (65.31 KiB) Viewed 437 times

fem-constraint-gravity2.svg

I may be wrong but I think it's a bouncy constraint

Code: Select all

`+            f.write('Eall,GRAV,9810,0,0,1\n')`
makkemal
Posts: 320
Joined: Wed Apr 29, 2015 12:41 pm

### Re: self weight

I think the user need to be able to specify in which direction gravity is, even if it only allows the 3 axis x,y,z
bernd
Posts: 3856
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: self weight

sgrogan wrote:I may be wrong but I think it's a bouncy constraint

Code: Select all

`+            f.write('Eall,GRAV,9810,0,0,1\n')`
What do you mean by bouncy?

sgrogan wrote:Is the constraint gravity specific? Being able to specify the direction vector immediately generalizes the constraint to acceleration.
The current version only applies self weight in z-direction and only for the earth. But this could be changed in the input file easely. If it is a needed feature we could change the constraint in this regard later if someone needs it.

I like the green one.
bernd
Posts: 3856
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: self weight

makkemal wrote:I think the user need to be able to specify in which direction gravity is, even if it only allows the 3 axis x,y,z
If the direction and the vector could be changed by the user we would need a nice task panel to change all this. I do not need it. I'm structural engineer. All my buildings have self weight in z-direction and the NASA is not one of our customer. Means we only have buildings on the earth. If someone needs it he could do the implementation. As stated, this could be easely changed in the input file and could be easily added later on.
bernd
Posts: 3856
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: self weight

sgrogan wrote:I may be wrong but I think it's a bouncy constraint

Code: Select all

`+            f.write('Eall,GRAV,9810,0,0,1\n')`
YEAH it is jumping up !!!
bernd
Posts: 3856
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: self weight

updated https://github.com/berndhahnebach/FreeC ... selfweight

A few other minor changes I have been collecting over the last few days are included as well. Thanks sgrogan for the icon and the jumping info. From my point of view a PullRequest could be made. But I'm waiting of sgrogan to report back.

results for FEM examples:
2D --> 2.29491 mm
3D --> 2.24684 mm

cheers bernd
Jee-Bee
Posts: 611
Joined: Tue Jun 16, 2015 10:32 am
Location: Netherlands

### Re: self weight

bernd wrote:
makkemal wrote:I think the user need to be able to specify in which direction gravity is, even if it only allows the 3 axis x,y,z
If the direction and the vector could be changed by the user we would need a nice task panel to change all this. I do not need it. I'm structural engineer. All my buildings have self weight in z-direction and the NASA is not one of our customer. Means we only have buildings on the earth. If someone needs it he could do the implementation. As stated, this could be easely changed in the input file and could be easily added later on.

On assembly level you're right. at least as long users don't have other directions preferred… for instance the y direction.
and second reason i like to see a direction setting is that on component/part level this goes sometimes wrong. that working directory is not same as building direction… a beam on an angle
sgrogan
Posts: 2969
Joined: Wed Oct 22, 2014 5:02 pm

### Re: self weight

bernd wrote:] YEAH it is jumping up !!!

I meant Buoyancy
Changing the vector and the acceleration by editing the file is fine for now.
The use case I have in mind is using this in combination with the results of a frequency analysis using Miles Equation to calculate "equivalent" static loads due to random vibration.
I think a pull request would be great. Thanks for this