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Question about Hydrodynamic drag forces
Dear David,
I have doubts about NP Water Vel. and NP Water Acc. I am not sure what they mean. If they represent the speed and acceleration of wave propagation, why does NP Water Vel have periodic zero values? Moreover, I don’t understand why the Morison drag force calculated here is not a standard sinusoidal form. Its time domain curve has a linear part and the spectrum has a high-frequency component of the wave.
BR,
AsIlll
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Hi AsIlll,
when water velocities and accelerations are requested from the neutral point (NP) of the substructure, these values are defined only if the NP is located below the water surface. If the NP is positioned above the water, both velocity and acceleration are recorded as zero.
The same principle applies to Morison elements, with the difference that these elements have a length and can be partially submerged. What you are observing as “linear regions” in your data corresponds to the effects of surface-piercing elements. For partially submerged elements, the velocity is evaluated at the center of the submerged portion of the element. Additionally, only the submerged length contributes to the drag force. For the graphs, this drag force is normalized by the total length of the element (expressed as N/m). This “linear taper” effect, is probably responsible for the patterns you are seeing in your graphs.
BR,
David
