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Pressurised: the bend moment is calculated from the curvature by simple interpolation of the bend stiffness table.The choice of statics model controls the interpretation of the nonlinear bend stiffness table during the statics calculation. This difference may be significant if the bend stiffness is significantly nonlinear over the range of curvatures involved. If the bend stiffness is hysteretic then the mid-segment curvature cannot be derived in this way (due to possible hysteresis effects) so the mid-segment curvature reported is the mean of the curvatures at the ends of the segment. If the bend stiffness is not hysteretic then the mid-segment curvature reported is the curvature that corresponds to the mid-segment bend moment (which is the mean of the bend moments at either end of the segment). If you are using nonlinear bend stiffness, then the mid-segment curvature results reported depend on whether the bend stiffness is specified to be hysteretic or not. You might be able to speed up the simulation, without significantly affecting accuracy, by removing superfluous rows in areas where the curve is very close to linear.
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If you use the hysteretic bending model then the simulation speed may be significantly slowed if your table of bend moment against curvature has a large number of rows. It is not suitable for modelling rate-dependent effects it is intended for modelling hysteresis due to persisting effects, such as yield of material or slippage of one part of a composite line structure relative to another part. You must check that the hysteretic model is appropriate for the line type being modelled. Note that if the hysteretic model is used, then the line must include torsion effects. Hysteretic means the bend moment includes hysteresis effects, so that the bend moment depends on the history of curvature applied as well as on the current curvature.No hysteresis effects are included and the bend moment magnitude is entirely determined by the given function of the current curvature magnitude. Non-hysteretic means that the nonlinear stiffness is elastic.In the case of nonlinear bend stiffness, you must also specify whether the hysteretic bending model should be used. For homogeneous pipes the plasticity wizard may be useful to help set up the table. The bend moment must be zero at zero curvature. OrcaFlex uses linear interpolation within this table, and linear extrapolation for curvature values beyond those given. Nonlinear bend stiffnessįor nonlinear behaviour, use variable data to specify a table of bend moment magnitude against curvature magnitude. The bend stiffness represents the bend moment required to bend the line to a curvature of 1 radian per unit length. This slope is the equivalent $EI$ value for the line, where $E$ is Young's modulus and $I$ the second moment of area of the cross section.
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Linear bend stiffnessįor normal simple linear behaviour, specify the bend stiffness to be the constant slope of the bend moment-curvature relationship. See calculating bend moments for further details of the bending model used. You can specify the bend stiffness to be linear, elastic nonlinear, hysteretic nonlinear or externally calculated, as follows. The $x$ and $y$ values will often be the same, and this can be indicated by setting the $y$-value to '~', meaning "same as $x$-value". The bend stiffness is the slope of the bend moment-curvature curve. Note however that the axial and torsional stiffnesses are still assumed to be linear.