Learning Forum

[xinyuan.shao]

Hi!

I am confused with the definition of the section force and whole cable force - Tension in the aqwa workbench. 

My questions are:

1) In the dynamic cable analysis, the mooring is divided into many elements, but there are no options to choose which element's section tension to display. Then, which is the default element for the displayed section tension?

2) Similarly, where is the default mooring element for the displayed whole cable force-tension? 

3) It shows that for the same mooring, the section force and the whole cable force-Tension are different. Why?

 

Thank you!

Xinyuan

 

 

[Shuangxing Du]

The dynamic cable is a special case of the composite catenary mooring line. As shown below, in Aqwa a composite mooring line can consist of several (upto 10) sections, each section can have its own cable properties, and the intermediate buoy or clumped weight can be defined between sections.  The sections' properties are input starting from the section near the anchor to the section near the fairlead point on the structure. The tension at the upper end of each section along a dynamic cable could be output. 

In the Aqwa dynamic cable analysis, up to 250 elements along the whole cable will be automatically created, the sizes of the elements between different cable sections may not be exactly the same but kept to be similar if possible; no element is across the cable sections.

If you really want to have the tension result at a particular location along a dynamic cable, you can define this point as a sectional end of the cable, then the results at this sectional end will be output.

[xinyuan.shao]

Hi!

Thank you for your answer!

I still have one question. In the following figure, the whole cable forces-Tension and section tension have different values for the same mooring section. Why? What is the definition of whole cable forces -tension?

 

Xinyuan

[Shuangxing Du]

I am sorry I made a mistake. The tension at the STARTING end of each section along a dynamic cable could be output as the section tension. For example, the tension at Section#1 is the tension at the anchor. 

 

[xinyuan.shao]

Thank you. 

What is the output of the whole cable force then? Is it the tension of the start position of each cable?

 

[xinyuan.shao]

I have another question. What if a floater connects two sections? There will be a discontinuation in the connecting point. Then what is the value of the section tension there? Is it the average value of the section tension from both sides?

Thank you!

[Shuangxing Du]

The whole cable force is the force at the end of each cable (a cable starting from the section near the anchor). 

From Equation (9.54) in the Aqwa theory manual 9.7. Dynamic Composite Catenary Mooring Line (ansys.com), if a buoy/clump weight is at the element Node#j, half of its weight (as well as buoyancy) will be applied on the Node#j for the Element#j which has the element ends of Node#j and Node#(j+1).