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#How to calculate damage orcaflex software#
#How to calculate damage orcaflex free#

Thermal and pressure induced stress cycles

#How to calculate damage orcaflex software#

Fatigue damage for each sea state can be calculated based on the calculated stress range, number of stress cycles during the sea state and the selected S-N curveįorce based models also can be used utilizing software like OrcaFlex.

Consequently, fatigue damage for each sea state (Hs, Tp, and 𝜃) will be calculated by integration over the long-term current velocity distribution.

VIV stress ranges and number of cycles can be calculated based on DNVGL-RP-F105 response model.

For each span calculate the effective velocity using the following equation. Where, Lspan is the span length, and U(z) is the water particle velocity along the riser span.

This can be done either by simplified analytical method or by finite element analysis.

#How to calculate damage orcaflex free#

Determine natural frequencies of riser free spans.

In such cases this RP will predict both in-line and cross-flow VIV provided that the natural frequencies are calculated based on relevant boundary conditions.”Ī procedure to conduct VIV analysis for rigid risers based on DNVGL-RP-F105 is as follows

For short risers the lowest eigen modes are typically excited. According to Section C.2.2 of this recommended practice, “for short riser span lengths, typical for steel risers supported by a jacket structure and when the current is uniform, the response models given in Sec.4 of this RP can be applied. For detailed information regarding response based model, DNVGL-RP-F204 refers to DNVGL-RP-F105 (Section 4.1.3 of DNVGL-RP-F204).ĭNVGL-RP-F105, is mainly applicable to free spanning pipelines. It is particularly suited for risers responding at mode no. In Appendix C of DNVGL-RP-F204, a simplified response model assessment method has been provided, which is mainly applicable to top tensioned risers with uniform cross-section in unidirectional current-dominated flow conditions. When required, effect of stress concentration factor shall be considered in gross structural discontinuities, e.g. The difference between longitudinal stresses will be the stress range. Maximum longitudinal stress at each section of the riser shall be calculated for two cases with same riser operating pressure, temperature, and pipeline expansion but with different platform deflection directions. To calculate stress range due to platform motion, the riser shall be modeled in a finite element software. The short term fatigue capacity, (and subsequently fatigue damage) for each riser span against direct wave actions for a single sea state can be calculated using the frequency-domain solution for in-line wave load direction described in Section 5.2 of DNVGL-RPF105, or when the wave period is larger than the natural vibration period of the span, using the simplified fatigue assessment method as described in Section 5.3 of DNVGLRP-F105.

Direct wave loads and associated platform motion Direct Wave loads

Thermal and pressure induced stress cyclesįollowing headings summarize fatigue damage assessment method for these cyclic loadings.

Direct wave loads and associated platform motions.

According to this recommended practice, a typical procedure for fatigue assessment should be based on the following steps įor a rigid riser applicable cyclic loadings are as follows Its principles is also applicable to rigid riser systems. DNVGL-RP-F204 has been developed to address fatigue design of all types of risers.