ssc-367 - Ship Structure Committee

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amplitude loading and loading sequence on fatigue life is a valid concern. The results obtainedfrom a substantialnumber of specimenssubjected to variable amplitude loading show that Miner’s rule is appropriate and generally conservative. Dobson et al (Reference 7.26) studied loading histories of containershipsbased on recorded service data. When the stress intensity ranges were expressed as the root-meansquare, the crack growth of laboratory specimens subjected to constant-amplitude loading history compared quite well with those specimens subjected to constant amplitude loading. Fatigue damage computation is based on stress ranges and number of cycles and does not account for stress sequence. Since welded structure fatigue lives are largely expended in crack propagation, applicationof sufficientnumber of large stress amplitudes early in fatigue life is likely to accelerate crack propagation and overpredictingof fatigue life. The uncertainty of stress sequence, aside, the use of rainflowcounting procedure, based on counting the reversals in accordancewith the material stress-strainresponse,may enhance accuracy of damage computation. However, improvement in accuracy is significantonly for wide band stress histories with an irregularity factor equal to or less than 0.5. When the structure response yields narrow-banded stress cycles, the choice of counting method is innnaterial. Even for moderately wide band stress cycle histories,the variouscycle countingmethods produce similar fatigue damage predictions. Although further research is necessary, especially on the effect of stress sequence, the use of S-N curves and Miner’s cumulative fatigue damage rule is appropriate. 7-22
:Ilo I Cn 80 to 40 . 20 T- m 10 m -k 8 u A. c * .-i- 4, 1“ ,. z ȯnaxxs HLL SICKI S “ $lReSs nrwct I oa— x + Figure 7-I S-N Curve for a Transverse Butt Weld and Test Data #’+’7, — I 13 20 30 Lo 50 ThiCkn@SS. s mm Figure 7-2 Theoretical Thickness Effect for a Cruciform Joint (From Reference 7.9) .,
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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
Page 136 and 137: The SCF equations currently in use
Page 138 and 139: life. During the comprehensive desi
Page 140 and 141: ?.s I z - ]LEvE~ ~ 1,5 \ i i+ 11 Is
Page 142 and 143: -. Figure 5-5 Comparison of Detaile
Page 144 and 145: ( -t ) ( T-JOINT Y-JOINT ( \ I / K-
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 188 and 189: n“ CAP PASSES ROOT = * { A A 4 I
Page 190 and 191: It should be pointed out that the e
Page 192 and 193: v= flow velocity normal to the cyli
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
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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 -”’ ” ”---”---”
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“7.2 Jordan, C.R., and Cochran, C
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7.19 Niemi, E.J., “FatigueTests o
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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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