Learning Forum

[Chelsea Yu]

I would like to use a "changes cable length" winch to pull the block in the picture up to the water surface. However, when I set the final length of the winch to be shorter than the length of the cable, the error shown in the picture occurs, such as "solution diverged on structure." Here are my settings: 

1. The cable is connected between the fixed point and the connection point on the block, and the unstretched length is the distance between the two points, which is 35cm.
2. In the analysis settings of the time domain analysis, I set the simulation to be 10 seconds. 
3. The final length of the winch is 25cm, and the speed is -1m/s.

Additionally, I want to know what to consider if I want to lower the block from the water surface (i.e., make the cable longer) in reverse. Thank you, everyone!

[Shuangxing Du]

As the messages issued, your time step interval of 0.1 second may be too large. Please try to use smaller value.

I guess that the winding in speed is -1 cm/s instead of -1m/s.

Please also check if the mooring attachment point is along the vertical line acrossing the structural COG. It may be pssoble to deactivate all DOFs motion except heave.

To lower the block from the water surface, the paying out speed should be positive, and the final length should be larger than the initial length.

[Ingrid M]

Hello, 

The time integration diverging in a context including cables could be due to too much cable stiffness which, especially for low mass objects, leads to very high natural frequencies.

The general rule is that is the corresponding period is smaller than the time step, the time integration scheme won't be able to capture the dynamic of the system and cause the calculation to diverge rapidly.

Also, the winding up speed is very high.

Good luck,

Ingrid