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sacs query - wave load calculation

sacs query - wave load calculation

sacs query - wave load calculation


I was calculating the wave load on a vertical pipe (OD=1.0m, Cd=1.0) using linear static analysis option in SACS.

Wave parameters : Water depth= 26.6m, Wave ht = 3.486m, Tassociated =13.33s (stoke 5th order wave)

I took the sacs output for horizontal velocity (at phase =0deg) and calculated the wave drag loading(sacs files, excel are attached to this email), I got the figure as 15.50kN, however, sacs reports 16.465kN, What could be reason for this difference of 5%.

For phase = 0deg, Total wave load is due to Drag force
Drag force/m = Fd = ½ * Cd* D * 1.028* Velo2 = 0.514 * Velo2 (Cd = 1.0, D = 1.0)

I did independent calculation using fine divisions (calculated horizontal particle velocity at every 0.1m for entire 26.6m water depth) and then calculated drag force/m, used curve fitting to get the quadratic polynomial , integrated it, and the load thus calculated was 15.59kN which is close to what I got from below excel.

I have attached the sacs files and excels used for calculation. is sacs having a different algorithm to deal with the portion of water depth near MSWL?

Also, the wave crest elevation is 28.53m, however, the horizontal particle velocity is reported a zero in the output.

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