Learning Forum

[NVN NAMMA]

In ANSYS AQWA: I had difficulty in modelling a flooded pipe. The actual volumetric displacement and equivalent volumetric displacement differed by 50%. Is it required to give the water weight by distributed mass?

[NVN NAMMA]

 

I have modelled a long vertical pipe as a line body, which is free at the bottom and fixed to a floating structure at top. In the model tree it is modelled as floodable. Do I need to create an internal tank inside the flooded pipe . During the time domain simulations, it is floating on the surface.  Kindly give assistance

 

This is the hydrostatic result.

 

[Shuangxing Du]

There is no need to use internal tank to define the water inside the floodable circular tube.

In your model, the equivalent volumetric dispalcement is the structure mass dividing the water density, which is 48e5/1025=4682 m^3.

It seems that the actual volumetric displacement result is questionable.  Please check (your project)\dp0\AQW\Analysis\Analysis.dat, which should be similar to 

(1)  in Data Category 2, TUBE elements instead of STUB elements (see 6.3. Element Topology Data Record) are defined.

(2) in Data Category 4,  TUBE geometry's diameter, thickness and indicator of floodable (=1) are defined properly. (8.3. Geometric Property Data Record)

[NVN NAMMA]

Thanks Shuangxing Du for attending my query. 

(1) They are tube elements 

That is also there. The disc element was not there initially, so I tried giving it a try to see if there were any changes. In the data file shared, there were two tube elements. I have only one tube element. is it reason for the change. The weight of the pipe is 4800 t, actual displacement is matching with the same. but the equivalent displacement is of volume displaced, which is different. Do I need to add a point mass corresponding to the difference in weight? The material of the pipe is not steel.

2.

This is how my tube definition comes

 

when we click on the part line body

This is the problem. 

[Shuangxing Du]

The cross sectional area of the tube is A=pi/4*(10.5^2-10.0^2) = 8m^2. The length of the tube could be L=4800t/7.8/A=77m.  The displaced volumn of the foodable tube should be about A*L=616m^3. Is the total displaced volume of 8050^3 mainly contributed by the floating structure?

 

[NVN NAMMA]

 

The length of the pipe is fixed as 1000 m

 

 

 

[Shuangxing Du]

Great. Please use the formulae I used to estimate the displaced volumn of the tube by hand.