Dear all,
First of all, I thank you for the possibility to use such a great tool as FAST.
I spent many weeks looking into the manuals and into the blog topics for an answer to my question but I couldn’t find it and for this I need to ask what I hope it’s not a stupid question.
I’m a civil engineer currently working on his MSc thesis regarding integrated analysis of offshore wind turbines on the OC4 deep water jacket substructure founded on suction bucket foundation. The thesis is focused on the effect of the soil-structure interaction.
In order to study this I worked with the commercial software DIANA FEA with a specified subroutine to model the foundation as a lumped node.
Now, as DIANA FEA environment doesn’t allow me to define wave and current loads in a specific way such FAST, I decided to try and use FAST in order somehow to extract a time-history at each node of the jacket substructure and, hence, apply these time-histories to DIANA as lumped loads.
I saw there is a function in the HydroDyn module that allows to do so, but I am not getting realistic results. More specifically I defined a sea state with waves acting in one direction ( x direction ) with a JONSWAP/Pierson-Moskowitz spectrum. After that I gave to the axial coefficient standard values :
---------------------- AXIAL COEFFICIENTS --------------------------------------
1 NAxCoef - Number of axial coefficients (-)
AxCoefID AxCd AxCa AxCp
(-) (-) (-) (-)
1 1.00 1.00 1.00[/code]
My idea, from reading the HydroDyn manual, was to take every component of the total lumped force vector and sum it on by one.
What I have in output is, however, strange as I have same values for components X and Y of drag and inertia forces when I was expecting a dominant x component.
In the next block codes I want show you a few second of the output of my simulation. I printed here just the components of the Viscous-drag force, fluid-inertia force and hydrodynamic added-mass forces at J3 node ( I don't think is really relevant the node position but of course is under the MSL ).
[code]Time J3FDxi J3FDyi J3FDzi J3FIxi J3FIyi J3FIzi J3FAMxi J3FAMyi
(s) (N) (N) (N) (N) (N) (N) (N) (N)
20.0000 -3.239E-01 -3.239E-01 -1.069E-02 1.383E+02 1.383E+02 4.565E+00 -6.792E-02 -6.792E-02
20.0500 -3.212E-01 -3.212E-01 -1.060E-02 1.370E+02 1.370E+02 4.524E+00 -1.690E-02 -1.690E-02
20.1000 -3.182E-01 -3.182E-01 -1.051E-02 1.358E+02 1.358E+02 4.482E+00 -3.404E-03 -3.404E-03
20.1500 -3.157E-01 -3.157E-01 -1.042E-02 1.345E+02 1.345E+02 4.441E+00 -6.688E-02 -6.688E-02
20.2000 -3.136E-01 -3.136E-01 -1.035E-02 1.333E+02 1.333E+02 4.400E+00 -1.035E-01 -1.035E-01
20.2500 -3.116E-01 -3.116E-01 -1.029E-02 1.320E+02 1.320E+02 4.359E+00 -5.906E-02 -5.906E-02
20.3000 -3.052E-01 -3.052E-01 -1.008E-02 1.299E+02 1.299E+02 4.290E+00 -1.017E-02 -1.017E-02
20.3500 -2.981E-01 -2.981E-01 -9.840E-03 1.278E+02 1.278E+02 4.220E+00 4.455E-02 4.455E-02
20.4000 -2.905E-01 -2.905E-01 -9.591E-03 1.257E+02 1.257E+02 4.151E+00 9.582E-02 9.582E-02
20.4500 -2.830E-01 -2.830E-01 -9.343E-03 1.236E+02 1.236E+02 4.081E+00 6.951E-02 6.951E-02
20.5000 -2.759E-01 -2.759E-01 -9.109E-03 1.215E+02 1.215E+02 4.011E+00 1.144E-02 1.144E-02
20.5500 -2.658E-01 -2.658E-01 -8.776E-03 1.186E+02 1.186E+02 3.914E+00 -7.265E-03 -7.265E-03
20.6000 -2.559E-01 -2.559E-01 -8.450E-03 1.156E+02 1.156E+02 3.817E+00 1.748E-02 1.748E-02
20.6500 -2.456E-01 -2.456E-01 -8.108E-03 1.127E+02 1.127E+02 3.720E+00 8.522E-02 8.522E-02
20.7000 -2.350E-01 -2.350E-01 -7.759E-03 1.097E+02 1.097E+02 3.623E+00 1.154E-01 1.154E-01
20.7500 -2.250E-01 -2.250E-01 -7.428E-03 1.068E+02 1.068E+02 3.525E+00 2.380E-02 2.380E-02
20.8000 -2.129E-01 -2.129E-01 -7.029E-03 1.030E+02 1.030E+02 3.401E+00 -7.488E-02 -7.488E-02
20.8500 -2.018E-01 -2.018E-01 -6.663E-03 9.928E+01 9.928E+01 3.277E+00 -1.019E-01 -1.019E-01
20.9000 -1.911E-01 -1.911E-01 -6.308E-03 9.552E+01 9.552E+01 3.154E+00 -6.864E-02 -6.864E-02
20.9500 -1.800E-01 -1.800E-01 -5.943E-03 9.177E+01 9.177E+01 3.030E+00 -5.695E-03 -5.695E-03
21.0000 -1.690E-01 -1.690E-01 -5.580E-03 8.802E+01 8.802E+01 2.906E+00 -4.497E-03 -4.497E-03
21.0500 -1.562E-01 -1.562E-01 -5.157E-03 8.353E+01 8.353E+01 2.758E+00 -7.620E-02 -7.620E-02
21.1000 -1.443E-01 -1.443E-01 -4.765E-03 7.904E+01 7.904E+01 2.609E+00 -1.058E-01 -1.058E-01
21.1500 -1.328E-01 -1.328E-01 -4.383E-03 7.455E+01 7.455E+01 2.461E+00 -2.881E-02 -2.881E-02
21.2000 -1.210E-01 -1.210E-01 -3.996E-03 7.006E+01 7.006E+01 2.313E+00 5.650E-02 5.650E-02
21.2500 -1.095E-01 -1.095E-01 -3.616E-03 6.557E+01 6.557E+01 2.165E+00 4.818E-02 4.818E-02
21.3000 -9.701E-02 -9.701E-02 -3.203E-03 6.043E+01 6.043E+01 1.995E+00 2.931E-02 2.931E-02
21.3500 -8.534E-02 -8.534E-02 -2.817E-03 5.529E+01 5.529E+01 1.825E+00 3.050E-02 3.050E-02
21.4000 -7.419E-02 -7.419E-02 -2.449E-03 5.015E+01 5.015E+01 1.656E+00 7.628E-02 7.628E-02
21.4500 -6.372E-02 -6.372E-02 -2.104E-03 4.501E+01 4.501E+01 1.486E+00 8.891E-02 8.891E-02
21.5000 -5.415E-02 -5.415E-02 -1.788E-03 3.987E+01 3.987E+01 1.316E+00 2.786E-02 2.786E-02
21.5500 -4.451E-02 -4.451E-02 -1.469E-03 3.419E+01 3.419E+01 1.129E+00 1.264E-03 1.264E-03
21.6000 -3.591E-02 -3.591E-02 -1.185E-03 2.852E+01 2.852E+01 9.414E-01 1.286E-02 1.286E-02
21.6500 -2.818E-02 -2.818E-02 -9.304E-04 2.284E+01 2.284E+01 7.541E-01 1.344E-02 1.344E-02
21.7000 -2.136E-02 -2.136E-02 -7.050E-04 1.717E+01 1.717E+01 5.667E-01 -1.088E-03 -1.088E-03
21.7500 -1.562E-02 -1.562E-02 -5.158E-04 1.149E+01 1.149E+01 3.793E-01 -6.504E-02 -6.504E-02
21.8000 -1.056E-02 -1.056E-02 -3.485E-04 5.416E+00 5.416E+00 1.788E-01 -1.349E-01 -1.349E-01
21.8500 -6.484E-03 -6.484E-03 -2.140E-04 -6.601E-01 -6.601E-01 -2.179E-02 -9.712E-02 -9.712E-02
21.9000 -3.332E-03 -3.332E-03 -1.100E-04 -6.736E+00 -6.736E+00 -2.224E-01 -1.177E-02 -1.177E-02
21.9500 -1.182E-03 -1.182E-03 -3.902E-05 -1.281E+01 -1.281E+01 -4.229E-01 6.748E-03 6.748E-03
22.0000 -1.213E-04 -1.213E-04 -4.005E-06 -1.889E+01 -1.889E+01 -6.235E-01 -2.190E-02 -2.190E-02
22.0500 1.805E-04 1.805E-04 5.960E-06 -2.521E+01 -2.521E+01 -8.323E-01 -6.351E-03 -6.351E-03
I do not belive this is the best way to do so, and if you have any suggestion I would be really grateful.
Please find attached the setting of my hydrodyn input file which was taken from the testing folder, test21 regarding OC4 deep-water jacket substructure, and then slightly modified.
I tried to be as clear as I could to explain my problem. Thanks you all for your time and consideration.
Best regard,
Davide Moretti
NRELOffshrBsline5MW_OC4Jacket_HydroDyn.txt (31.7 KB)