Learning Forum

[Bushra Rasheed]

Hi! 

I'm doing HD and HR analysis of a TLP in aqwa. For tendons, I have defined a linear catenary section and entered the stiffness and unstretched length values in HR. However, in the Hydrodynamic response time domain analysis, I'm getting positive and negative range of values for tensions ( whole cable force). I don't get why am I getting negative tension values, if the cable is slack, it's tension should be zero. Can anyone help? 

[Shuangxing Du]

If you use the Aqwa quasi-static composite catenary mooring line configuration, the mooring line database will be generated before the time domain anlayis, then the mooring tension at each time step will be interpolated from this database.  Please check if the magnitude of the negative tension value is very small comparing to the positive tension values. If it is negative but its absolute value is very samll, it may be caused by the numerical error during the database interpolation. Please try to adjust the Negative/Positive dZ range of Expected Connection Point Vertical Motion and Number of Vertical Partitions and Number of X Coordiantes (see Aqwa User's Manual, Section 5.8.1.4 Nonlinear Catenary) for your cable setting to make the mooring line database to be more accurate for your analysis case. Or just ignore the small negative tension results.  If it is not the case, please give us more detailed information of your mooring configurations, we can do further investigation.

If you use the dynamic cable configuration, the finite element approach will be used in the Aqwa time domain analysis for this mooring, the negative value of tension/compression with small magnitude may occur.

Happy new year.