July 4, 2024 at 3:08 pm
Yu Bi
Ansys Employee

Hi, there, it looks like there are some unstable natural mode results, and for unstable cases, the critical damping percentage is negative. See Aqwa theory manual section 11.4 equation 11.19 for more information. 

There could be a lot of reasons for an unstable natural mode. From the cable settings you shared, what could be improved is the maximum expected tension, which may be too large compared to the initial tension. The maximum expected tension is not a material property like ultimate tensile strength but defines the furthest point in the 2D quasi-static cable database. Talking about the cable database, the negative/positive dZ range settings are relative distances from the initial position, so 50 meters/60 meters seem to be a bit too large if this is not the relative distance you expect your structure to move in the vertical direction. However, if you use cable dynamics, these parameters won't matter as they won't be used.

I would suggest you adjust those settings and solve them again or try cable dynamics.

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