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Fatigue analysis: Analysis data |
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Fatigue analysis: Analysis data |
The analysis data page contains data specifying the parts of the line to be analysed.
As well as the positions on the line to consider, the histograms analysis method must also define the result for which histograms are to be calculated:
Histograms are presented for equally-spaced bins of the given size. This bin size is interpreted as having the units of the specified histogram variable.
This sets a warning level: if the total damage at any fatigue point exceeds this value, then that damage figure will be highlighted in the results. This facility is not available for histogram collation.
The number of points around the pipe circumference, at which fatigue analysis will be performed. There will be $n$ of these fatigue points uniformly distributed at $360\degree/n$ intervals around the pipe circumference; by convention, the symbol $\theta$ (theta) is used to represent their circumferential position, hence the name number of thetas. A larger number of thetas gives a more comprehensive analysis, but one which takes a little longer.
This value is not available for mooring and SHEAR7 fatigue, neither of which use $\theta$. For histogram collation, the value is required only if the selected histogram variable depends on the circumferential position within the cross section.
Defines the length of the line being considered by the SHEAR7 analysis. This value has no bearing on the calculation, it is implemented solely to provide some convenience to results reporting. A value of ~ results in arc lengths being reported as non-dimensional $x/L$ values, the native form for SHEAR7. If a value is given here for the line length, then the reported arc lengths are re-dimensionalised using this value.
You define the parts of the line to be analysed by specifying a number of arc length intervals in the form of from and to arc length values, $z_\textrm{from}$ and $z_\textrm{to}$ respectively. OrcaFlex will analyse cross sections at each line end and mid-segment whose arc length $z$ is in the range $z_\textrm{from} \leq z \leq z_\textrm{to}$.
For simple cases you can use just one arc length interval covering the whole line. However it is often clear which part, or parts, of the line are liable to fatigue problems: if calculation time is important, it can be reduced by analysing only those parts of the line.
| Warning: | The included arc lengths must be the same in each load case, so the line to be analysed should have the same number and distribution of segments in each of the load case simulations. |
The arc length intervals may overlap. For example, this would be desirable if you wished to calculate damage for both inner and outer fibres of a homogeneous pipe.
Specifies whether the fatigue analysis is performed at the inner, outer, or mid-wall point of the pipe.
This value is only required for homogeneous pipe stresses, or for histogram variables that depend on the radial position within the cross section.
When stress ranges are used with the S-N curve to calculate damage, the stress ranges are scaled by the stress concentration factor (SCF) and the thickness correction factor before calculating damage.
If no stress correction is required then these factors should both be set to 1.
| Note: | To use different stress correction factors for different parts of the line, you will need to specify separate arc length intervals for those parts. |
Specifies which S-N curve is used for damage calculations in the given arc length interval.
Specifies which T-N curve is used for damage calculations in the given arc length interval.