ssc-367 - Ship Structure Committee

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n NB=T 1 [p=+pi Ei . ‘c where: NB. = predicted life in blocks NC = constant amplitude life at SmaX NEI = i = number of cycles per block 2 ‘i ‘max lton This product rule can be compared to Miner’s NB=~ ‘c x Pi ni 1 where m is the slope of the S-N curve expressed as SmN - constant K It should be noted that Gurney’s rule may also result in underprediction of fatigue damage. Study of spectrum shape and block length (Reference7.22) indicatesthat for long block lengths Gurney’s rule may be unsafe. 7.4 STRESS HISTORY AND UPGRADED MINER’S RULE 7.4.1 Background Miner’s linear cumulativedamage rule can be used safely, provided some of the wave environment uncertainties (including counting of cycles and evaluatingthe stress ranges compatible with cycles) are properly accounted for. 7“14
Typically, the sea state represented by joint probabilities of significant wave heights and characteristic periods (scatter diagram) is applied to the transfer function to produce the stress range spectrum. Integration of the spectra provides a number of statistical parameters, such as the bandwidth, the zero-uncrossing frequency, etc., allowing development of short-term probability density functions. The short-term probabilitydensity function of the stress range for each significant wave height and its characteristic period is generally defined by using a Rayleigh distribution. For this assumption to be valid, (1) a large number of sea states must be used, and (2) the stress cycles can be considered narrow-banded. Individualstress cycles are considerednarrow-bandedwhen they are readily identifiable and there is no ambiguity in counting the stress cycles. The wide-banded loadings exhibit smaller stress cycles interspersed among larger stress cycles. Because it is difficult to define the stress cycles, different cycle counting methods result in different fatigue damage predictions. Rainflow counting is the name of a large class of stress cycle counting methods, including the original rainflow method, Hayes method, range-pair counting, range-pair-range counting, ordered overall range counting, racetrack counting and hysteresis loop counting. Rainflow counting and other alternatives are briefly discussed in Sections 7.4.2 and 7.4.3, respectively, to illustrate the options availableto upgradeMiner’s rule. However, it should be noted that two very important variables affecting fatigue life computation should be addressed in any attempt to upgrade Miner’s rule: (1) S-N curves are based on constant amplitude stress blocks and should be compared against variable amplitude results. 7-15
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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
Page 128 and 129: esponsesare required , or where con
Page 130 and 131: either multiple stick elements (for
Page 132 and 133: Braces may have stubs or cones, whi
Page 134 and 135: 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 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 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
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
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Page 226 and 227: TOPIC SUBJECT INVESTIGATOR COMPLETI
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3.1 Soyak, J. F., Caldwell, J. W.,
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4.12 Daidola, J.C., and Basar, N.S.
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5.4 Papanikolaou,A. and Zaraphoniti
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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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ssc-367 - Ship Structure Committee

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