ssc-367 - Ship Structure Committee

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v= flow velocity normal to the cylinder axis fn = fundamental frequency of the member (H) d= diameter of the member Susceptibilityof a member to VIV in air is different than in water due to the density of air flowing around the member being different than the density of water. Susceptibility of a member is defined for in-line and cross-flow oscillations in both environments. In-line VIVmay occur when: l*2svr
8.2.2 VIV Response and Stresses A strategy based on avoidance of VIV is quite feasible for most marine structures. Primarystructuralmembers are usually designed to be sturdy enough that they are not susceptible toVIV. However, some secondary or non-structuralmembers may be susceptible to VIV in water and in air. An empirical approach proposed by DnV (Reference 8.7) does not account for the nonlinear relationship betweenresponseanddamping,therebyyielding conservativeresponse amplitudes and stresses. To predict response amplitudes more reliably an approach based on Hallam et at (Reference 8.9) is recommended. Cross-flow oscillations due to wind action may not always be preventable, requiring the members to have sufficient resistance. An empirical formulation based on a procedure by Engineering Sciences Data’ Unit ESDU (Reference 8.6) that accounts for interaction between vortices shed and forces induced is recommended. This procedure and the basis for estimating maximum bending stresses for different boundaryconditions are discussed in Sections D.4 andD.5 of Appendix D. 8.3 FATIGUE DAMAGE ASSESSMENT All members susceptible to VIV should be assessed for fatigue damage. First, the fatigue damage due to VIV is calculated. Then a global fatigue analyses is performed and fatigue determined for all critical members. The total fatigue damage is equal to the sum of local (VIV) and global fatigue damage on each member. Step-by-step determination of both local and global fatigue damage is discussed further in Section D.6 of Appendix D. Application of the procedurecould indicatethat the fatigue life is expended after relatively small number of oscillations, requiring corrective measures to be taken either in the design process or during fabrication (devices,spoilers, etc.). 8-5
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SSC-367 - FATIGUE TECHNOLOGY ASSESS
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SHIP STRUCTURF COMMllTFF The SHIP S
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—.--— 1. Report No. 2. Gowotnmr
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FATIGUE TECHNOLOGY Assessment AND D
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6. FATIGUE STRESS HISTORY MODELS 6,
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APPENDICES A. REVIEW OF OCEAN ENVIR
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D. VORTEX SHEDDING AVOIDANCE AND FA
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LIST OF FIGURES (cent.) FIGURE TITL
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HOT-SPOT STRESS . The hot-spot stre
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QA/Qc : Quality Assurance/QualityCo
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1. INTRODUCTION 1.1 BACKGROUND The
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general assessmentof fatiguewhile t
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2. OVERVIEW OF FATIGUE 2.1 FATIGUE
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2.2 FATIGUE ANALYSIS 2.2.1 Anal.vsi
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● Loads generated as affected by
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A deterministic method is sometimes
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1 APPLICATION OF NUMEROUS CYCLIC ST
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I MOBiLEANDSTATIONARY MARWE STRUCTU
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3. FATIGUE DESIGN AND ANALYSIS PARA
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and in-plane/out-of-planeangles,and
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the general quality of fabrication,
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3.2 REVIEW OF FATIGUE ANALYSIS PARA
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frequencies of interest, requiring
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● Reqular Waves in FrecjuencvDoma
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The finite element models of increa
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The stressmodel parametersdiscussed
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While API S-N curves are applicable
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DESIGN Osn40H rAnNsirsR8 FAMcA~ M P
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Primarily Affect .--------+’ & In
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MOTIONS MODEL — .—. ● ;LOADS
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loa 1 10 -— — — -t-i-nT 1[ -t
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4. GLOBAL REVIEW OF FATIGUE 4.1 APP
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An allowable stress method, also co
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esults of work covering assessment
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location. Thus, the method should b
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1. SDectral FaticlueAnalvsis Althou
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2. Weibull AtIDroach The Weibull sh
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energy about the central direction
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Although considered to be an emergi
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many design rules implement this ap
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Detailed Anal.vsisMethods The detai
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The DnV X-curve and the DEn Guidanc
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ending restrictions. Cruciform and
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period, are also designed tomeet th
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incorporates inspection-strategy(Re
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‘Thereare numerous finite element
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LOCATIONs oF FATIGUE CMCKS Figure 4
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TW=’T ——— ———___ __ r
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1 —. — — — — -.. - .. - .
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TOP[C U.K.DEPARTMENTOF ENERGY(OEn)
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:1 U.K.DEPARTMENTOF ENERGY(DEn) AME
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TOPIC U.K.DEPARTMENJOFEIWRGV(oEn) O
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5. FATIGUE STRESS MODELS 5.1 REVIEW
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● The water particle kinematicsar
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“radiation pressure” of waves,
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influence on the applied loading. H
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their function, selecting appropria
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hydrostatic stiffness is introduced
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structure is unique and an allowabl
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loads directly. Since the diffracti
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typically from 0.6 to 0.8 and 1.5 t
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therefore be defined uniformly alon
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load analysisof adetailed three-dim
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esponsesare required , or where con
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either multiple stick elements (for
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Braces may have stubs or cones, whi
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Whatever the basis for an empirical
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The SCF equations currently in use
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life. During the comprehensive desi
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?.s I z - ]LEvE~ ~ 1,5 \ i i+ 11 Is
Page 142 and 143: -. Figure 5-5 Comparison of Detaile
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Page 146 and 147: SMEDLEY-WORDSWORTH 0 d =— = D 600
Page 148 and 149: Wave Records Older wave and wind in
Page 150 and 151: In many cases wind informationmay b
Page 152 and 153: q = 3.3 s = 0.07, for f< fm s = 0.0
Page 154 and 155: Seasonal Variation The annual wave
Page 156 and 157: 4. ~arpkaya spreading. (Reference 6
Page 158 and 159: ~. \“ life of a structure,cannot
Page 160 and 161: 6.3 TIME-DOMAIN ANALYSES Nonlinear
Page 162 and 163: The wave environmentdefinitionsbase
Page 164 and 165: .,..,, ....- ., ;., .. .... .- .. .
Page 166 and 167: ● Fatiguetest data should be care
Page 168 and 169: assessmentis typically identifiedas
Page 170 and 171: damage accumulation similar to that
Page 172 and 173: “FabricationRestrictions Fabricat
Page 174 and 175: Fatigue strength of a tubular joint
Page 176 and 177: Current recommendations,rules and s
Page 178 and 179: n NB=T 1 [p=+pi Ei . ‘c where: NB
Page 180 and 181: (2) Damage computation does not acc
Page 182 and 183: DNB = (f. T/K) (2/2 U)m r (f+ 1) wh
Page 184 and 185: interactionof multiple fatigue crac
Page 186 and 187: amplitude loading and loading seque
Page 188 and 189: n“ CAP PASSES ROOT = * { A A 4 I
Page 190 and 191: It should be pointed out that the e
Page 194 and 195: 8.4 METHODS OF MINIMIZING VORTEX SH
Page 196 and 197: Ra < S REGIME OF UNSE?ARATE~ FLOW 5
Page 198 and 199: ages. The designer has no control o
Page 200 and 201: failure data on various structures,
Page 202 and 203: connections, knife edge crossings,
Page 204 and 205: 9.3.1 Fabrication Effects The fatig
Page 206 and 207: ● Controlled Erosion An alternate
Page 208 and 209: after a given number of stress cycl
Page 210 and 211: A second pass with polishingdisc is
Page 212 and 213: others. Extensive analytical and ex
Page 214 and 215: d) Stress SDectrum Hot-spot stresse
Page 216 and 217: Cumulativefatiguedamagecomputations
Page 218 and 219: as a parametric study intended to i
Page 220 and 221: Additional areas requiring further
Page 222 and 223: GROUP Modification of Weld Profile
Page 224 and 225: 400 ‘,, . . 350 - I I 300r [ ~ ,0
Page 226 and 227: TOPIC SUBJECT INVESTIGATOR COMPLETI
Page 228 and 229: 3.1 Soyak, J. F., Caldwell, J. W.,
Page 230 and 231: 4.12 Daidola, J.C., and Basar, N.S.
Page 232 and 233: 5.4 Papanikolaou,A. and Zaraphoniti
Page 234 and 235: 5.21 -”’ ” ”---”---”
Page 236 and 237: “7.2 Jordan, C.R., and Cochran, C
Page 238 and 239: 7.19 Niemi, E.J., “FatigueTests o
Page 240 and 241: 9.1 Skaar, K.T., “ContributingFac
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COMMllTEE ON MARINE STRUCTURES Comm
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U.S.Department of Transportation Un
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Member Agencies: United States Coas
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‘ METRIC CONVERSION FACTORS Appro
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APPENDIX A REVIEW OF OCEAN ENVIRONM
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The most distinctive feature-of a r
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s(w) = 2*(4*112) - For a “height
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common probability distributions, t
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T: v. Visually Observed Period, or
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The characteristic wave heights of
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H~ is the significantwave height, a
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a = 0.09, for UJ>wm The U value of
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H~ is the significant height, ‘m
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If the wind duration is less than t
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Sample Wave scatter Diagram s 12 +.
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Nm is the total number of waves in
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turbulence largely a function of te
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Applied Wind Speed Vz(t) ft/s (m/s)
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A.1O REFERENCES A*I Mechanics of Wa
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APPENDIX B REVIEW OF LINEAR SYSTEM
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Awhite noise function-may be used t
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Multiplication of the wave spectrum
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B.2.2.2 Response Amplitude Operator
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0.2.3 Wave Spectra The wave spectru
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9 is the acceleration of gravity in
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The following is..a. sample...of..a
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is the damping ratio,..the ratio of
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the set of extreme conditions, and
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A response scatter diagram could be
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2.4 2.2 2 1 ‘Sen &-”Swull$p~ctr
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L ‘2
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o Kuang (ReferenceCl) “ o Wordswo
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C.2 STRESS CONCENTRATION FACTOR EQU
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C.3 PARAMETRIC STUDY RESULTS . C.3.
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30. 2s , 20. 15. 10. 5. & wORDSWORT
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ChordSide Brace Side K-Joints SCFU
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Definition of Parameters, Validitv
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-, l— I + ?1 -— I . 4> a ,- I I
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Kuang SCF Computdion 1 L u UI \ f-
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., I , 1- out— FIano SCF m tg n I
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— 6 Smedley-Wordswoti SCF Computa
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T ln— Plan- SCF CrOwn POsltlon o
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C.3.l(C) Kuang Chord SCF’S for T-
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5 Kuang SCF Computation 4 IL u M 3
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C.3.l(d) Smedley-WordsworthChord SC
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. ,i 5 Smedley-Wordsworth SCF Compu
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I I K Out— Plan= SCF —— Saddl
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- 10 Smedley-Wordsworth SCFComputat
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‘\, ?v x out— Plan- SCF ——
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C.3.2(a) Kuang Chord SCF’S for T-
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KuwqSE _im T-joint In%neW UrrdSicko
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C.3.2(b) Smedley-HordsworthChord SC
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T-joint Axial SF Saddle Posiiim
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-— T-joint CtkuHlane ELFSaddlePci
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I 1 1 1 1 ~. l~o ~ ha= 1s0 : ~. ~J
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1 ! ! O.fi ;0.762 %841 0,769 O,= !0
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Ikrdwth-kdlw SF l%quiaiifm K-joint
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hdsmthqwdhy W Camputatim l-joint Ax
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Ejrnnt flkf+lane SF SaddlePmitim ~,
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MAXIMUM PRINCIPAL STRESS SCF = ----
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‘-W, .\ I Ill I : II m -,, !) .
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’ \./ ““’ w~”mm m ““-
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. . I Column L’ Longitudinal Gird
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C.8 Underwater Engineering Group,
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APPENDIX D VORTEX SHEDDING AVOIDANC
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a an b d f“ f ar f~ ‘bmax f~ fn
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D. VORTEX SHEDDING 0.1. INTRODUCTIO
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Vortex Shedding Frequency (f”) fv
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waves. When only isolated members u
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member’s nominal diameter and thi
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\Lf-! of cycles. Thus, the reduced
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s ; J steady current, by substituti
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Step 3: Obtain a new valueof 1/10 b
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vortex shedding will occur, i.e., V
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h. The fatigue life may -be modifie
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NOTE: The relationship given is bas
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CELL C7: KINEMATIC VISCOSITY = U CE
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COLUMN N: THE STRESS AMPLITUDE IS C
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D.8.3 Devices and Spoilers Devices
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D*9 REFERENCES D.1 King, R., “A R
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Fint Insmbility Rtgion I !%mmd Inat
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.—____ *U.S. E.P.O. :1993-343-273
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COMMllTEE ON MARINE STRUCTURES Comm
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4!! . ,—.-.,
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