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Analytical Formulations for Ship-Offshore Wind Turbine Collisions
30/01/2015JING-RU HSIEH
SUPERVISOR: PROF. LE SOURNE
CONTENTS Introduction ObjectiveAnalytical formulas development Numerical validation Conclusions Future works
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INTRODUCTION Green energy is taken seriously
nowadays. Ship collision is one of the major
hazards of jacket foundation. Rapid assessment of crashworthiness
is necessary.
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[1]
[2]
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OBJECTIVE Energy dissipation
impacted leg ≈ 60% rear leg ≈ 15% other legs/braces ≈ 25 %
New super-element for punching phenomenon.
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ANALYTICAL FORMULAS DEVELOPMENT
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DEFORMATION PATTERN Punching phenomena is obvious while one
or two junctions are collided by the stem or bulb.
The punching indentation occurs only in x direction of rear leg local coordinate system.
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CRUSHING PROCESS
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[Local mode]-Energy rate
[Local mode]-Crushing resistance
[Global mode]-Crushing resistance
[Global mode]-Energy rate
If local resistance exceed threshold or not?
yes
No
Next δ
Next δ
VIRTUAL WORK
퐸 = 퐸
퐸 = 푃훿
퐸 = ∭ 휎 휖 푑푉
푃 =
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Crushing energy rate of ring
퐸 = 퐸 푎 +
퐸 = 2푀 + − 푉 + ∫ 휅 푑푙 + ∫ 휅 푑푙
M0: fully plastic bending moment
VB VC : tangential velocity of plastic hinge
휅 , 휅 : change of curvature of C1 and C2
LOCAL ENERGY RATE-RING
DISPLACEMENT FIELD-RING [4]
푅 = 푅 + ( )( )
푅 = 푅 − ( )( )
퐴퐵 = 푅 − 푅 푠푖푛 휓
푤 휃, 훿 = 푥 − 푥 + 푧 − 푧
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DISPLACEMENT FIELD-RING
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휓 = 휓 + ( 휋 − 휓 )
휓 = 휋
LOCAL ENERGY RATE-GENERATOR Crushing energy rate of generator
퐸 = ∫ 퐸 푑푙 = + 퐸′
퐸 휃, 훿 = 푛 ∫ 휖 휃, 훿, 푦 푑푦 = 푛 푤 휃, 훿 훿 +
n0 : fully plastic membrane force per unit
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휖 휃, 훿, 푦 ==axial extension rate
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DISPLACEMENT FIELD-GENERATOR
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푊 휃, 훿, 푦 = 푤 휃, 훿 1 − for 푦 ∈ 푎 ; 휉
푊 휃, 훿, 푦 = 푤 휃, 훿 for 푦 ∈ −푎 ; 푎
푊 휃, 훿, 푦 = 푤 휃, 훿 1 − for 푦 ∈ −휉 ; −푎
LOCAL CRUSHING RESISTANCE Total energy rate
퐸 = 퐸 + 퐸 = 퐸 푎 + + 퐸′ +
Evaluation of 휉 and 휉
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TRANSITION OF CRUSHING MODE& GLOBAL CRUSHING RESISTANCE
4 plastic hinges mechanism
휉 훿 = − 1 − 2
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TRANSITION OF CRUSHING MODE& GLOBAL CRUSHING RESISTANCE
Threshold
Global resistance
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NUMERICAL VALIDATION-SIMPLE TUBE JOINT
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MODEL DESCRIPTION● Jacket-like cylinder dimension Material and prescribed displacement
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MESH SIZE CONVERGENCE STUDY● Mesh size: 100mm => 25mm
Smallestmesh size
Number of element
Discrepancy of energy
Discrepancy of force
Simulation time
100 mm 7040 -- -- 67 s
50 mm 7630 ≈3.5% ≈8% 111 s
25 mm 16320 ≈6% ≈12% 298 s
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DIFFERENT β RATIOSInternal energy Crushing resistance
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DIFFERENT β RATIOS β=0.32 (small brace diameter) d=0,2~0,4m => 35% discrepancy
푫풊풔풄풓풆풑풂풏풄풚 =푬풔풖풑풆풓 풆풍풆풎풆풏풕 − 푬푳푺 푫풀푵푨
푬푳푺 푫풀푵푨
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DIFFERENT β RATIOS β=0.48 (jacket-like) d≈0,37m => 8% discrepancy
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DIFFERENT β RATIOS β=1 (large brace diameter, DB=DL) d≈1,8m => -14,7% discrepancy
DIFFERENT SPANInternal energy Crushing resistance
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DIFFERENT SPAN L=23,5 m d≈0,8m => -3% discrepancy
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TWO JOINTS WITH GAP L=17 m (L1=7,5m, L2=9,5m) d≈0,36m => -9,6% discrepancy
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NUMERICAL VALIDATION-REAL JACKET FOUNDATION
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JACKET PUNCHING SCENARIOS
The rear leg is punched by 1 brace(upper brace).
The rear leg is punched by upper brace, and restrained by lower brace.
The rear leg is punched by 2 bracesimultaneously.
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CASE 1: 90˚-SCENARIO I
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● L1: 9m, L2: 14,5m Buckling of braces at d=0,6m
CASE 1: 90˚-SCENARIO I
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CASE 2: 90˚-SCENARIO II
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● L1: 9m, L2: 1,5m● Buckling of braces at d=0,23m
CASE 3: 90˚-SCENARIO III● L1: 10m, L2: 13,5m, gap=0,82m● Abrupt global movement at d=0,23m ● Bulcking of braces at d=0,46m
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CASE 4: 60˚-SCENARIO I
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● L1: 9m, L2: 14,5m● Buckling of brace 558 at d=0,61m
CONCLUSIONS &FUTURE WORKS
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CONCLUSIONS Scenario II should be improved. Energy obtained by super-elements
Bow ≈ 20%Bulb ≈ 23%Punching 1 ≈ 6%Punching 2 ≈ 5%Punching 3 ≈ 15%
≈ 26%
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CONCLUSIONSCollided Leg Rear Leg
Shearing effect => 30% of rear leg energy Punching 3 => overestimated
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CONTRIBUTIONS OF THIS STUDY● Development of a new super-element for punching● Validation of the super-element for different β● Validation of the super-element on real jacket model for
different scenarios
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Programming the new super-element in C++ . Calculation of jacket nodes displacement. Another pattern of punching scenario
(to be more accurate). Buckling of the braces and shearing
near the mudline. Energy absorbed by other legs/braces
(20%).
FUTURE WORKS
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Thank you for your attention
WWW.EMSHIP.EU
REFERENCE[1] http://www.4coffshore.com/windfarms/jacket-or-lattice-structures-aid271.html[2] http://maritime-connector.com/wiki/offshore-vessels/[3] Hervé Le Sourne, Andres Barrera, Jose Babu Maliakel, 2015. “Numerical crashworthiness analysis of
an offshore wind turbine jacket impacted by a ship”. [4] Loïc Buldgen, Hervé Le Sourne and Timothée Pire, 2014. Extension of the super-elements method to
the analysis of a jacket impacted by a ship. Marine structure, 38(2014), 44-71.[5] M. Zeinoddini, J.E. Harding, G.A.R. Parke, 1999. Contribution of ring resistance in the behavior of steel
tubes subjected to a lateral impact. International Journal of Mechanical Sciences, 42(2000), 2303-2320.[6] Standards Norway, 2004. NORSOK Standard-Design of steel structures (Rev.2). Available from:
www.standard.no/pagefiles/1145/n-004.pdf [7] T. Wierzbicki, M.S. Suh, 1988. Indentation of tubes under combined loading. International Journal Mechanical
Sciences, Vol. 30, No.3/4, 229-248.
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