Page 181 - Pipelines and Risers

154 Chapter IO

6. The fatigue is calculated at 51 points along the pipe span. The computer program predicts
fatigue damages reasonably close to those predicted by Fyrileiv (1998).

A general free span may be described in terms of the natural frequencies, modes shapes,
damping and modal mass. Beams with spring boundary conditions are considered in this
chapter. However, the developed formulation may be easily used to post-process the modal
analysis results from in-place finite element models of a pipeline which models the seabed
and in-service conditions accurately. The FATIGUE program may then be used to validate the
more detailed models, which have been developed as part of the DTA (Design Through
Analysis) by JP Kenny A/S (Bai and Damsleth, (1998)).

10.6 References
1. Bai, Y. and Damsleth, P.A., (1998) ”Design Through Analysis Applying Limit-state
Concepts and Reliability Methods”, Plenary paper for ISOPE’98.
2. Bai, Y., Lauridsen, B., Xu, T. and Damsleth P.A., (1998) “Force Model and In-line
Fatigue of Free-Spanning Pipelines in Waves”, Proc. of OMAE’98.
3. Blevins, R.D., (1994) “Flow-Znduced Vibration”, Krieger Publishing Company.
4. Det Norske Veritas (1998). Guidelines No. 14, “Free Spanning Pipelines”.
5. Fyrileiv, 0. et al., (1998) “Fatigue Calculations Using Frequency Domain Approach”, Fax
dated 30” Jan. 1998.
6. M@rk, K.J., Vitali, L. and Verley, R., (1997) ‘THE MULTISPAN Project: Design
Guideline for Free Spanning Pipelines”, Proceedings of OMAE’97.
7. Sumer, M. B. and Freds@e Jergen. (1997). “Hydrodynamics Around Cylindrical
Structures”, Advanced Series on Ocean Engineering - Vol 12, Published by World
Scientific, Singapore.
8. Tura, F., Bryndum, M.B. and Nielsen, N.J.R., (1994). “Guideline for free Spanning
Piplines: Outstanding Items and Technological Innovations”, Proceedings of Conference
on Advances in Subsea Pipeline Engineering and Technology, Aberdeen.
9. Verley, R., (1992) ”Gudesp - Hydrodynamic Force Model, in-line”, Memo dated 19”
June 1992.
10. Xu, T., Lauridsen, B. and Bai, Y. (1999) “Wave-induced Fatigue of Multi-span Pipelines”
Journal of Marine Structures, Vol. 12, pp. 83-106.