Code to provide the correct Lay Length value relative to the unit cell

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FabianeGommes

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Hello,

I know that the Lay Length (WeaveGeo) parameter needs to be a multiple of the unit cell, but there are difficulties entering the correct value. Every time you enter a value, the software changes that value to a new value. So I want to create code (phyton) to perform this transformation, can you help me with this code construction?

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Anne Blumer

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Re: Code to provide the correct Lay Length value relative to the unit cell
« Reply #1 on: September 13, 2023, 01:14:22 PM »
Dear Fabiane Gommes,

you say that the Lay Length (or Length of Lay as it is called in GeoDict) has to be a multiple of the unit cell length. This is not correct. In the WeaveGeo User Guide it is stated the other way around.
When setting Length of Lay to the length of the unit cell, exactly one twist (360° rotation) of the thread is performed inside the unit cell. If the unit cell is, e.g., four times larger than the Length of Lay, then four full rotations are performed. The reason behind is, that the resulting structure in the unit cell must be periodically.

However, it is possible to enter a lay length that is larger than the unit cell length. Then, only a part of the full 360° rotation is done in the unit cell. But it depends on the geometry of the thread and its filaments which values for Length of Lay are allowed to get periodic weaves. For example, for a 1x4 rope 90° rotations are allowed, which means you can enter a lay length that is four times the unit cell length.
If a Length of Lay is entered that does not fit to an allowed rotation, the value is corrected to next feasible value. Then a warning message pops up, which I think you have received.

So, in your case, I suppose you entered a value that does not lead to a periodic structure. What you can do to find feasible values is to first create the thread without twist and see the basic geometry (how the filaments are arranged). Then you can identify which rotations lead to a periodic structure and in this way can derive feasible inputs for Length of Lay.

Attached to this post please find some slides which explain the use of Length of Lay. They also contain an example for a 1x19 rope.
Please note that in the current GeoDict version (Service Pack 3) there is a bug with the 1x19 and 7x19 rope types, where wrong rotations are allowed. This bug is already fixed and will be available with Service Pack 4 that will be released in the next weeks.

Best regards,
Anne