s-ale mesh motion

[Ron Michaelis]

hi
I am trying to simulate the launch and flight of an arrow using s-ale, to analyze effect of wing geometry and material on pitch and yaw

for that, using *ALE_STRUCTURED_MESH_MOTION with the cover_lag option

the mesh moves with and around the arrow in y and z, but in x direction it only stretches from the origin, that leads to distortion of the ALE elements...

i checked for constrained nodes or so, but the arrow flies freely.

and the mesh moves freely in y and z, for some reason just x is "locked"

x is the main velocity direction of the arrow

[l...@schwer.net]

I have never used *ALE_STRUCTURED_MESH_MOTION.

Reading the User Manual Volume I description of this keyword, the parameter NODCEN Caught my eye:

 

NODCEN -- Optional node ID used as the center of mesh expansion

 

Assuming you did not specify a SALE** node ID, it seems the expansion of the mesh is ill defined? As the default value of the expansion coefficient FRCPAD=0.1 is likely active.

 

My suggestion is to specify a SALE** node ID in the center of your SALE mesh. Or possibly set the parameter FRCPAD=0.

 

                                --len

 

**It is unclear to be if they want a SALE mesh node ID [How does one do that?] or a node ID on the Lagrange part.

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[Ron Michaelis]

thank you Len

I have tried your suggestion for both a node from the arrow and then for a node from the S-ALE mesh
what it does is that the mesh will start stretching from this node and farther as the arrow flies

for instance, the defined nodcen is at (10,0,0) so the mesh up to x=10 will stay constant and as the arrow goes further in x, the mesh from x=10 and beyond will stretch to include the complete arrow in it.

i tried giving the arrow a Y velocity, it does the same in the y direction.

if i give both x and y velocity, it will stretch in x and y directions...

how do i make it translate around the arrow without stretching?

ב-יום שלישי, 23 בדצמבר 2025 בשעה 18:46:49 UTC+2, leonarder...@gmail.com כתב/ה:

[l...@schwer.net]

Did you try my second suggestion:

“Or possibly set the parameter FRCPAD=0.”?

 

Also, consider using a non-SALE Eulerian mesh and using the keyword

*ALE_REFERENCE_SYSTEM_GROUP

 

                                --len

To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/2c640eaf-588f-49f7-89ee-c88ec720f3efn%40googlegroups.com.

[Ron Michaelis]

Yes

Frcpad=0  didn't help

I'll try a non s-ale mesh

And use   *ALE_REFERENCE_SYSTEM_GROUP

Which PRTYPE would you reccomend? 1 or 9? 

Is there a relevant example for such a card?

Thanks

בתאריך יום ד׳, 24 בדצמ׳ 2025, 15:58, מאת ‏<l...@schwer.net>: