1. Classification: Statoil Internal Status: Draft Summary of lectures 2007 SH-part of Design of Offshore Structures Sverre Haver, Statoil, Trondheim, April 30

2. 2 Lecture February 19: Motivation and Rules and Regulations on the Norwegian Continental shelf Limit states: FLS (Fatigue limit state) ULS (Ultimate Load Limit state): Loads corresponding to an annual excedance probability of 10 -2. ALS (Accidental Load Limit State): Loads cooresponding to an annual exceedance probability of 10 -4. Hierarchy between regulations: Top regulation: Framework regulation Thereafter: Management regulation, Information regulation, Facilities Regulation, Operation Regulation Next levels: Guidelines to regulation, national and international standards, e.g NORSOK standards, ISO standards Last level: Company requirements

3. 3 Lecture February 19 Purpose of regulations: Ensure a high level of health, environment and safety in the petroleum activity. Principles of risk reduction: ALARP: After fulfilling requirements, the level shall be improved as much as is realistically possible. BAT: Best availale technology shall be used Precautionary principle: Use the solution with the smallest uncertainties related to the solution. Substitution principle: Factors which may cause harm to environment and safety shall be replaced with factors with less potential for harms. Barriers (Management regulation): A barrier is anything that can stop a hazardous event between the initian of a hazord and the victim.

4. 4 Lecture February 19 Self-control principle: * The operator is responsible for for ensuring that his petroleum activities are in agreement with the PSA regulations! * A high level of safety is the intention of the regulation. * The safety level shall be continuously improved. * In connection with major modifications the agreement with the lates versions of the rules and regualtions shall be ensured by the operator. In this connection the best available informations are to be used. Limit state control (N-003) (see e.g Ch. 3 of Torgeir Moan kompendium for examples of various load types):

5. 5 Lecture February 19 Curiculum: Ch. 1 and Ch. 2, SH_lectures week 8 – 2007 Lecture notes: SH-lecture_February 19th T. Moan: ”Design of Offshore structures”, Ch. 3.1, Ch. 3.2, Ch. 3.3 and 3.4

6. 6 Lecture February 20 Classification of structural problems First level of classification Linear mechanical system versus non-linear mechanical system. Linear response problem = linear mechanical system plus linear loading and Gaussian sea, ( i.e. linear wave theory) The deterministic structure is described by the transfer function. Stochastic response analysis is conveniently done in the frequency domain, s resp () = RAO() 2 * s wave (). Long term response analysis for obtaining 10 -2 and 10 -4 loads is more or less straight forward.

7. 7 Lecture February 20 Drag load governed response (jacket and jack-up structures) a) Quasistatic analysis (inertial and damping force can be neglected) OK if natural period is lower than – say – 2s. Design wave analysis is convenient. Statistical methods used to find H q, q=10 -2 or 10 -4. Usually Stoke 5th order wave is used in practical work when design wave method is used for drag governed structures.

8. 8 Lecture February 20 Curiculum Chs.3 and 4, SH_lectures week 8 – 2007 Lecture notes. T. Moan: ”Design of Offshore structures”, Chs. 3.6.3 and 3.64, Chs. 5.1.7 and 5.1.8

9. 9 Lecture March 12 Time domain solutions, higher order forcing and design wave method Dynamically sensitive drag governed structures: Short term solution by solving equation of motion in time domain. The various steps of a time domain analysis were pointed out. The aimed results of the time domain approach were discussed. Higher order forcing: Example showing the forces experienced by a fixed pile was reviewed for a sinusoidal wave and a modulated wave. For the modulated wave we saw that the drift force varied slowly as compared to the wave frequency. Design waves – linear or non-linear waves?

10. 10 Design waves Calculation of design response using Stokes Procedure (100-year response): 0) Determine 100-year wave profile. i) Response is calculateded for the given wave position. ii) Wave is stepped some meters forward, and the response is calculated for the new position. iii) Step ii) is repeated until wave has passed structure. iv) Highest response is taken as characteristic design response. H 100 T(H 100 )

11. 11 Lecture March 12 Slamming type load

12. 12 Lecture March 12 Results – dynamic amplification of impulse type loading. (Useful when giving guidance without calculations.)

13. 13 Lecture March 12 Curiculum Ch. 5 and 6, SH-lectures_week 11 -2007 SH_lecture TMR 4195, Monday March 12 2007 Lecture notes Supporting litearture: T. Moan: ”Design of Offshore structures”, Ch. 3.6.4, Chs. 5.1.1 – 5.1.5

14. 14 Lecture March 13 Long term response analysis Ocean waves as a stochastic process. (Linear waves, second order waves and freak waves). Long term analysis – all sea state approach Long term analysis – random storm approach

15. 15 Lecture March 13 Curiculum Ch. 7.1 (except 7.1.4.3) and 7.2, SH-lectures week 12 – 2007 Lecture notes Support litterature: T. Moan: ”Design of Offshore structures”, Ch. 3.6

16. 16 Lecture March 19 Closing remarks on random storm approach, example random storm, reliability methods for long term analysis, environmental contours How one could account for non-observed storms was shown. Example of random storm approach was presented. Importance of including the short term variability of the storm maximum was demonstrated. Important to understand. Long term analysis using reliability methods was presented by using these methods for obtaining an environmental contour. Again the importance of including the short term variability was demonstrated.

17. 17 Lecture March 19 Curiculum Appendix 7A_Week 12 (Meant to be appendic SH_lectures_week 12 – 2007) Lecture notes Ch. 7.1.4.3, SH_lectures_week 12 - 2007

18. 18 Lecture March 20 Environmental contour lines, Mooring and Model Testing Environmental contour lines were introduced for hs, tp and 3-hour maximum response. Sources of variability were pointed out. The importance and consequences of including short term variability was demonstrated. Methods involved in designing mooring line loads were briefly discussed. Model testing was mentioned as a good alternative for complex systems. Some advice was given how to use model tests for direct design application (contour lines and target percentile of 3-hour extreme value distribution for the wors sea states)

19. 19 Lecture March 20 Curiculum Ch. 7.1.4.3, 7.3, 7.4,and 5.4, SH_lectures_week 12-2007 Motions and Mooring Lines of Floaters Lecture notes