Learning Forum

[NVN NAMMA]

Hi 

I have simulated a hollow cylinder for hydrodynamic analysis. I did physical experiments on the same model. calculated viscous damping and gave as an additional damping in aqwa. when i tried to validate the experimental and numerical results, the trend is seen with actual acceleration and the magnitude is matching with rao based acceleration. how to handle this . Any explanation will be highly useful.

2. when i calculated displacement from acceleration using fft code it was not matching with the aqwa displacements.

3. how aqwa calculates actual response?

4. how displacements and accelerations are related in aqwa?

 

 

 

[Shuangxing Du]

(1) Please see Aqwa theory manual, Section 13.5.3 Motions at Drift and Wave Frequency, the RAO based motion, velocity and acceleration are given by

 

in which the irregular waves are represented by 

 

(2) For actual acceleration calculation, the predictor-corrector algorithm is employed, and the raditation forces is caluclated by the impulse function convolution,

the velocity and position is then calculated by

 

[NVN NAMMA]

Thank you so much  sxdu for the reply.

 I saw the documentation on RAO based and actual acceleration and motion parameters.

What is the major difference in the RAO based and actual acceleration? .

For an experimental validation which one should i consider?  I had kept a sensor on the top of the model with moonpool. I used nodal displacement after creating a connection point and fixed point on the top.. The RAO based values are matching with the magnitude and actual shows the trend.

2. For a regular wave analysis in aqwa naut, why small irregularities are seen in the result'

This is from the user manual.  Can i have more explanation on the high lighted part

NB. model is in moored condition with cables