ssc-367 - Ship Structure Committee

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H~ is the significant height, ‘m = 3.15*T-l+&Wl*T-2, T is the characteristic period of the waves. The timis the frequency of the peak unfortunately, the period, T, used in the correspond to any of the mathematical spectrum. The equation for ~mwas derived data. spectral energy, but equation for ~mdoes not characteristics of the as a curve fit to real The Scott-Wiegel spectrum is a Scott spectrum modification that was proposed by Wiegel (Reference A.8). The constants are adjusted to match the equation to a “100-year storm” wave condition. The new equation is as follows. S(UJ) = 0.300* (H~)*exp[-(w-wm)4/ {0.0.353* (M-WM+0.26) } ] The umin equation. this equation is 1.125 times that specified for the Scott A.4 SELECTING A WAVE SPECTRUM Information about the random sea characteristics in a particular area is derived by either ‘wave hindcasting’ or by direct wave measurement. For many areas of the world’s oceans, the only data available is measured wind speeds and visually estimated wave heights. Sometimes the estimated wave heights are supplemented by estimated wave periods. For afew areas of intense oil development, such as the North Sea, direct wave measurement projects have produced detailed wave spectra information. A-16
A.4.1 Wave Hindcastinq Wave hindcasting is a term used to describe the process of estimating the random sea characteristics of an area based upon meteorological or wind data. Various researchers (ReferencesA.2, A.4, A.6, A.7 and A.8) have attempted to derive a relationship between the wind speed over a recent period of time and the spectrum of the random sea generated by the particular wind. The wind speed data is usually qualified by two additional parameters, the duration that the wind has been blowing at that speed and the fetch or distance over open ocean that the wind has been blowing. A set of equations as derived by Bretschneider (ReferenceA.2), which relate wind speed, duration and fetch are as follows. g*H# = 0.283*tanh[0..125*(g*F/Uz)””42] g*Ts / (2r*U) = 1.2*tanh[0.077*(gF/U2)””42 ... g*t minl” = 6.5882*exp{[0.161*A2-0.3692*h+2.024]% + O.8798*A} where u is the wind speed, F is the fetch, A = ln[g*F/U2], t min is the minimum duration for which the fetch will determine the significant height and period, and tanh is the hyperbolic tangent. A-17 -) s“
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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
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-. Figure 5-5 Comparison of Detaile
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( -t ) ( T-JOINT Y-JOINT ( \ I / K-
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SMEDLEY-WORDSWORTH 0 d =— = D 600
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Wave Records Older wave and wind in
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In many cases wind informationmay b
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q = 3.3 s = 0.07, for f< fm s = 0.0
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Seasonal Variation The annual wave
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4. ~arpkaya spreading. (Reference 6
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~. \“ life of a structure,cannot
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6.3 TIME-DOMAIN ANALYSES Nonlinear
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The wave environmentdefinitionsbase
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.,..,, ....- ., ;., .. .... .- .. .
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● Fatiguetest data should be care
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assessmentis typically identifiedas
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damage accumulation similar to that
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“FabricationRestrictions Fabricat
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Fatigue strength of a tubular joint
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Current recommendations,rules and s
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n NB=T 1 [p=+pi Ei . ‘c where: NB
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(2) Damage computation does not acc
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DNB = (f. T/K) (2/2 U)m r (f+ 1) wh
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interactionof multiple fatigue crac
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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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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
Page 242 and 243: COMMllTEE ON MARINE STRUCTURES Comm
Page 244 and 245: U.S.Department of Transportation Un
Page 246 and 247: Member Agencies: United States Coas
Page 248 and 249: ‘ METRIC CONVERSION FACTORS Appro
Page 250 and 251: APPENDIX A REVIEW OF OCEAN ENVIRONM
Page 252 and 253: The most distinctive feature-of a r
Page 254 and 255: s(w) = 2*(4*112) - For a “height
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Page 258 and 259: T: v. Visually Observed Period, or
Page 260 and 261: The characteristic wave heights of
Page 262 and 263: H~ is the significantwave height, a
Page 264 and 265: a = 0.09, for UJ>wm The U value of
Page 268 and 269: If the wind duration is less than t
Page 270 and 271: Sample Wave scatter Diagram s 12 +.
Page 272 and 273: Nm is the total number of waves in
Page 274 and 275: turbulence largely a function of te
Page 276 and 277: Applied Wind Speed Vz(t) ft/s (m/s)
Page 278 and 279: A.1O REFERENCES A*I Mechanics of Wa
Page 280: APPENDIX B REVIEW OF LINEAR SYSTEM
Page 283 and 284: Awhite noise function-may be used t
Page 285 and 286: Multiplication of the wave spectrum
Page 287 and 288: B.2.2.2 Response Amplitude Operator
Page 289 and 290: 0.2.3 Wave Spectra The wave spectru
Page 291 and 292: 9 is the acceleration of gravity in
Page 293 and 294: The following is..a. sample...of..a
Page 295 and 296: is the damping ratio,..the ratio of
Page 297 and 298: the set of extreme conditions, and
Page 299 and 300: A response scatter diagram could be
Page 301 and 302: 2.4 2.2 2 1 ‘Sen &-”Swull$p~ctr
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Page 305 and 306: o Kuang (ReferenceCl) “ o Wordswo
Page 307 and 308: C.2 STRESS CONCENTRATION FACTOR EQU
Page 309 and 310: C.3 PARAMETRIC STUDY RESULTS . C.3.
Page 311: 30. 2s , 20. 15. 10. 5. & wORDSWORT
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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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