Response-based analysis of FPSO systems for squall loadings

Transcription

1 Response-based analysis of FPSO systems for squall loadings OMAE212 Rio de Janeiro July 3 rd 212 OMAE Joerik Minnebo - Amir Izadparast - Arun Duggal - René Huijsmans 1

2 Introduction (1 min avg) wind speed [m/s] original squall scaled squall time [s] 2

3 Research goals Presentation outline Characterize the available squalls Influence of the individual squall parameters Compare the current design practice to a response based method 3

4 Squall characterization wind speed [m/s] time [s] Rising slope Peak wind speed Decay (half life) time OMAE OMAE

5 Squall characterization Correlations and distributions Offset [m] Current Practice Design Value Sample Distribution GPD fit 58 Unscaled Squalls p (u ) Peak wind speed u [m/s] p(s r ) Rising slope s (m/s 2 ) r year return values 1 3 p( ) Decay halflife time [min] Probability of Exceedance P E OMAE

6 Spread Mooring Analysis OMAE

7 Spread Mooring Analysis Response Characteristics 1 1 normalized offset normalized offset rising slope s [m/s 2 ] r peak wind speed u [m/s] normalized offset decay haf life time [min] 7

8 Spread Mooring Analysis Response Characteristics y st CwA 2k y u 2 C st u 2 Offset [m] y dyn y st wind speed u y dyn y time [s] st y dyn / y st time [s] Step Response Tn = 1s Tn = 13s Tn = 16s Tn = 19s Tn = 22s Tn = 25s Tn = 28s Tn = 31s Tn = 34s Tn = 37s Tn = 4s

9 Spread Mooring Analysis Response Characteristics y dyn / y st y dyn / y st Step Response =.2 =.3 =.4 =.5 Tn = 1s Tn = 13s Tn = 16s Tn = 19s Tn = 22s Tn = 25s Tn = 28s Tn = 31s Tn = 34s Tn = 37s Tn = 4s [min] s [m/s 2 ] r 9

10 Design Value Estimation The 1 year event Current Design Practice Response Based Methods Spread moored FPSO 8m water depth Tn = 29s =.4 1

11 Design Value Estimation Current Design Practice (1 min avg) wind speed [m/s] u 1 original squall scaled squall time [s] u m / s 11

12 Design Value Estimation Current Design Practice number of events number of events Unscaled squalls Scaled squalls rising slope s [m/s 2 ] r offset [m] y m 12

13 Design Value Estimation Response based on dynamic amplification y st 4 35 offset [m] C w 2k A y u 2 2 Cstu. 42 u 2 2 offset =.413 * u 2 static =.42 *u peak wind speed u [m/s]

14 Design Value Estimation Peak wind speed relation and dynamic amplification E s r,

15 Design Value Estimation Peak wind speed relation and dynamic amplification y dyn y ( u C u st ) st 2 offset [m] offset =.413 * u 2 static =.42 *u 2 Peak wind speed [m/s] Estimated Probability Distribution Sample Distribution Extreme Values 1 year 1 year 1 year 1 year peak wind speed u [m/s] Probability of Exceedance P E

16 Design Value Estimation Peak wind speed relation and dynamic amplification Case I Case II Case III Expected Values Maximum Observed Values 1 Year Return Values 16

17 Design Value Estimation Peak wind speed relation and dynamic amplification Offset [m] Current Practice Design Value Case I: Expected Values Case II: Max. Observed Values Case III: 1 Year Return Values Static Values Step Response 1 year return values Probability of Exceedance P E α = 1.24 α = 1.11 α =

18 Conclusions Characterized the squall events Found the governing response characteristics Compared the different DVE methods CDP for spread moored is highly conservative Best method is based on response knowledge wind speed [m/s] offset [m] offset =.413 * u 2 static =.42 *u 2 Offset [m] Sample Distribution Current Design Practice Static Offset Values PWS relation = 1.27 Step Response = Direct Extrapolation Monte Carlo Simulations 1 year return values time [s] peak wind speed u [m/s] Probability of Exceedance P E

19 Thank you for your attention! 19

20 14 Bachelor Programs 38 Master Programs 16,4 students Master Program Offshore Engineering Partly Civil Engineering Partly Mechanical Engineering Partly Maritime Engineering 2

21 21

22 Introduction 22

23 Design Value Estimation Direct Extrapolation Offset [m] unscaled squalls Current Design Practice 58 unscaled squalls Estimated Probability Distribution 95% confidence intervals year return values 1 3 Probability of Exceedance P E y m 23

24 Design Value Estimation Monte Carlo Simulations 8 Offset [m] Current Practice Design Value Sample Distribution GPD fit 58 Unscaled Squalls year return values Probability of Exceedance P E y1 3. m 24

25 Design Value Estimation Peak wind speed relation and dynamic amplification Offset [m] Sample Distribution Current Design Practice Static Offset Values PWS relation = = 1.27 Step Response = Direct Extrapolation Monte Carlo Simulations 2 1 year return values Probability of Exceedance P E 25

26 Turret Mooring 26

27 Turret Mooring Response characteristics wind speed u time [s] Y offset [m] degrees 45 degrees 9 degrees 135 degrees 18 degrees X offset [m] 27

28 Turret Mooring Response characteristics 25 Offset [m] deg 45 deg 9 deg 135 deg 18 deg peak wind speed [m/s] 28

29 Turret Mooring Response characteristics 29

30 Turret Mooring Current Design Practice Y offset [m] deg 18 deg 36 deg 54 deg 72 deg 9 deg 18 deg 126 deg 144 deg 162 deg 18 deg X offset [m] y m 3

31 Turret Mooring Dynamic Amplification limitations α 2.6 α

32 Turret Mooring Dynamic Amplification limitations Offset [m] deg 45 deg 9 deg 135 deg 18 deg Static Max observed DA 1 year return DA Max DA peak wind speed [m/s] 32

33 Turret Mooring Dynamic Amplification limitations Offset [m] Current Practice Design Value Static Response Maximum DA Maximum Observed DA 1 year return DA 1 1 year return values Probability of Exceedance P E 33