ssc-367 - Ship Structure Committee

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life. During the comprehensive design the best parameter to increase is brace thickness while keeping t/T constant. Further improvementsin fatiguelivesmaybe obtained by determining the SCF through the use of finite elements analysis or models tests. Another alternative to lower the SCF is to stiffen the joints with rings and thus reduce the SCFS to the lower bound values. However, considering the increased fabrication costs of stiffened joints, the use of rings should be considered the least desirable option to lower the SCFS and improve the fatigue lives. The validity of SCF equations and their sensitivities to various geometric parameters are illustrated in Appendix C. It is recommended that the tables and figures provided are studied to determine an acceptable approach compatible with the specific problem on hand. A finite element study results are also included in Appendix C to illustratethe range of SCFS for a typical complex joint. Since empirical equations are applicable for only simple joints, a FEA is recommended for determination of complex joint SCFS. 5-34
-“ 30 Calculation l.iaoas 6 Beck (1905) Exserlment, Gerritsma & Beukelman 11964) \ $trln Theory 1 30 Calculation Inglis and Price (79B21 I -, , -, * JO calculation Chang [lg77] =zl=~ \ \ “$ ‘\ ---- -. - . . - . .- ‘-”-””” Figure 5-1 Comparison of Heave Added Mass and Oamping coefficients Based on Different Methods (From Reference 5.2) Im lm- 140- 120- lM - w- m- 40- 20- 1 0 2 18 a2 2s Figure 5-2 Comparison of Wave Loading Based Conventional and Consistent Methods (From Reference 5.8)
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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
Page 88 and 89: period, are also designed tomeet th
Page 90 and 91: incorporates inspection-strategy(Re
Page 92 and 93: ‘Thereare numerous finite element
Page 94 and 95: LOCATIONs oF FATIGUE CMCKS Figure 4
Page 96 and 97: TW=’T ——— ———___ __ r
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Page 100 and 101: TOP[C U.K.DEPARTMENTOF ENERGY(OEn)
Page 102 and 103: :1 U.K.DEPARTMENTOF ENERGY(DEn) AME
Page 104 and 105: TOPIC U.K.DEPARTMENJOFEIWRGV(oEn) O
Page 106 and 107: 5. FATIGUE STRESS MODELS 5.1 REVIEW
Page 108 and 109: ● The water particle kinematicsar
Page 110 and 111: “radiation pressure” of waves,
Page 112 and 113: influence on the applied loading. H
Page 114 and 115: their function, selecting appropria
Page 116 and 117: hydrostatic stiffness is introduced
Page 118 and 119: structure is unique and an allowabl
Page 120 and 121: loads directly. Since the diffracti
Page 122 and 123: typically from 0.6 to 0.8 and 1.5 t
Page 124 and 125: therefore be defined uniformly alon
Page 126 and 127: 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 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 186 and 187: amplitude loading and loading seque
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n“ CAP PASSES ROOT = * { A A 4 I
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It should be pointed out that the e
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v= flow velocity normal to the cyli
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8.4 METHODS OF MINIMIZING VORTEX SH
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Ra < S REGIME OF UNSE?ARATE~ FLOW 5
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ages. The designer has no control o
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failure data on various structures,
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connections, knife edge crossings,
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9.3.1 Fabrication Effects The fatig
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● Controlled Erosion An alternate
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after a given number of stress cycl
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A second pass with polishingdisc is
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others. Extensive analytical and ex
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d) Stress SDectrum Hot-spot stresse
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Cumulativefatiguedamagecomputations
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as a parametric study intended to i
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Additional areas requiring further
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GROUP Modification of Weld Profile
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400 ‘,, . . 350 - I I 300r [ ~ ,0
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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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