浮式平台二_海洋平台疲劳强度设计分析概要.ppt

Zone Classification Target Fatigue Lives Assume structure life is 20 years Target fatigue lives and safety factors Area Safety Factor Target Fatigue Life Deck to Column connection 5 100 years Hull Interior (accessible) 5 100 years Hull Interior (inaccessible) 10 200 years Hull Exterior 10 200 years Major joint connection 10 200 years Tendon/mooring porch 10 200 years Fatigue Life Calculation Example Stress range: Obtained from FEA analysis: stress amplitude, the maximum stress at the evaluation location 17.265 ksi Stress range: 2 x stress amplitude 34.53 ksi Plate thickness: from design 1.5 inches Fatigue Life Calculation Example (cont.) S-N curve: Obtained based on the welding detail at the investigate location DoE (The U.S. Department of Energy) E-A curve – CJP (Complete Joint Penetration) welding, air condition slope m=3K = 3.173 E+09 SCF = 1 Reference thickness = 0.8661 inch N = 3.40 E+08 Weibull Parameter: 0.5725 Fatigue Life Calculation Example (cont.) Thickness correction needed: 1.5/0.8661 = 1.732 Target fatigue life: 5 x 20 = 100 years Calculated fatigue life: FL = 495 years Fatigue Life Calculation Example (cont.) Given conditions: Same Weibull parameter Same welding detail Same environment Same reference thickness Same plate thickness Same fatigue requirement Same stress level Fatigue Life Calculation Example (cont.) If the location is in sea water with cathodic protection: Slope m remain the same K = 1.855 E+09 SCF = 1.14 Calculated fatigue life: FL = 195 years Fatigue life comparison: A 2.54 times reduction for the structure in sea water comparing to the life in air Design condition/Location Duration Hard Tank Truss Truss/Hard Tank Connection Hard Tank/ Topsides Connection Dry Transport from Finland to AGM 30 days X ? ? ? Dry tow from AGM to platform site 5 days X X X ? Temporary installation phase with temporary Deck 6 months X X X ? Inplace with initial SCRs* 20 ye