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January 29, 2024 at 4:12 amNurhalim Dwi PutraSubscriber
Hello everyone !
I want to analyze the motion response of floating structures in a coupled manner (Heave-Pitch motion equations are solved simultaneously), but I am confused about which Ansys program to use? Is Hydrodynamic Diffraction possible? I found the result in the form of RAO viewed through the frequency domain, like the picture below? is this suitable and suitable? Or is it only viewed uncoupled but only the curves are combined?
Â
Do I need to do it again in Hydrodynamic Response? but I saw the analysis there using the time domain, I'm more confused here?
someone please give me an answer, can ansys aqwa do simultaneous coupled motion response analysis? Thank You
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January 29, 2024 at 4:24 pmShuangxing DuAnsys Employee
Both Hydrodynamic Diffraction and Hydrodynamic Reponse solve the coupled motions simutantaneously.
In Hydrodynamic Diffraction, the structure mass matrix, hydrostatic stiffness matrix, added mass matrix and hydrodynamic dmaping for a single structure are of 6x6 matrix form, the off-diagonal elements may not be zero, so that the motions, such as heave and pitch, are couplied. If several structures (n structures for example) are in a hydrodynamic interaction group, the added mass matrix and hydrodynamic dmaping matrix are of 6nx6n matrix form, all the rigid motions of all the structures in this group will be couplied. The above figure shows the RAOs of the heave and pitch motions, these motions are normally coupled through the motion equations in the frequency domain.
In the Hydrodynamic Response analysis, the matrices of the added mass/hydrodynamic damping for a hydrodynamic interaction group of n structures are of 6nx6n matrix form, together with the moorings and joints defined between structures, all the motions of the structures in the model may be coupled.
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January 31, 2024 at 8:33 pmNurhalim Dwi PutraSubscriber
Thanks for your explain, I want to ask, what is the name of the equation used by the Ansys Aqwa software to complete the response analysis in RAO form in a coupled motion? I have read the aqwa theory manual, and found an explanation as below.
Â
Â
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Meanwhile, in another journal, I read the equation for completing coupled motion response analysis has the form as below. Thank you
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February 1, 2024 at 9:30 amShuangxing DuAnsys Employee
Equation (4.49) is the matrix form of the motion equations in frequency domain. This matrix form equation not only covers the coupling effects between heave and pitch, but also may include all couplying effects between all the rigid body 6 degree of freedom motions.Â
In frequency domain, the acceleration RAO, a, is -omage**2 *x, the velocity RAO, v, is -i*omega*x, where x is the motion response RAO (could be heave z or pitch angle). Substituting these expressions into the equations (1) and (2) in the journal you cited, they will be similar to Equation (4.49). I guess that in equation (2) A is the sum of the pitch-pitch moment of inertia and the pitch-pitch added mass.
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