I want to perform free span detail fatigue analysis in line with DNV-RP-F105 (Feb 2006) (all the below sec references are made to F105). I understand that for each wave state (Hs,Tp, Teta) the design life should be calculated for Response Model and Force Model. To apply current scatter for each wave state on the model I am confused, and I think it should be a method more/less as follows:
-Histogram: to apply current scatter (velocity and direction, and relevant probability) and as such for each wave state to calculate design life based on probability of current. I understand this is the meaning of integration over current velocity histogram, OR
-Weibull: based on 3 parameter Weibull distribution(sec 3.5, 3.6), and to use formula of F105 Sec. 4.2.1 (and 4.2.2), but I am not sure if my calculation is correct because I do not realize exactly the meaning of integration over the long term distribution for current velocity represented by Weibull distribution (or Histogram). I have attached a typical calculation on the Weibull current velocity, I would appreciate if somebody advise if it is correct.
Any comment / advice on the subject (detail fatigue analysis) is welcomed. Of course provision of any sample calculation is highly appreciated.
In addition, regarding specific DNV software FatFree (I do not access to this software), I think the input of the program is only the bottom roughness analysis results plus dynamic soil stiffness. Please advise if otherwise.
In the interim, for analytical calculation of frequency, static bending/deflection as per sec. 6.7, it is quoted “bar buckling does not influence the response if effective axial force (Seff) is higher than half critical bar buckling (Pcr)”. I understand the minimum value of Seff/Pcr (analytical calculation) is -0.5. Kindly advise.
-Histogram: to apply current scatter (velocity and direction, and relevant probability) and as such for each wave state to calculate design life based on probability of current. I understand this is the meaning of integration over current velocity histogram, OR
-Weibull: based on 3 parameter Weibull distribution(sec 3.5, 3.6), and to use formula of F105 Sec. 4.2.1 (and 4.2.2), but I am not sure if my calculation is correct because I do not realize exactly the meaning of integration over the long term distribution for current velocity represented by Weibull distribution (or Histogram). I have attached a typical calculation on the Weibull current velocity, I would appreciate if somebody advise if it is correct.
Any comment / advice on the subject (detail fatigue analysis) is welcomed. Of course provision of any sample calculation is highly appreciated.
In addition, regarding specific DNV software FatFree (I do not access to this software), I think the input of the program is only the bottom roughness analysis results plus dynamic soil stiffness. Please advise if otherwise.
In the interim, for analytical calculation of frequency, static bending/deflection as per sec. 6.7, it is quoted “bar buckling does not influence the response if effective axial force (Seff) is higher than half critical bar buckling (Pcr)”. I understand the minimum value of Seff/Pcr (analytical calculation) is -0.5. Kindly advise.
