ssc-367 - Ship Structure Committee

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Step 3: Obtain a new valueof 1/10 based on initial amplitude. Step 4: Recompute the amplitude based on the new value of l/l.. Step 5: Repeat Steps 3 and 4 until convergence. 0.5. STRESSES DUE TO VORTEXSHEDDING Once the amplitude of vibration has been calculated, stresses can be computed according to the support conditions. For a simply supported beam with a uniform load w, the midspan deflection Y, and the midspan bending stress fb are given as follows: w Y a = 5 WL41 m “T*T = 384 EIY T“ ~ ~ax = WL2= 384 EIY T m— ~2 Md EDY ‘bmax = ~*~=4”8~ at midspan Expressing fbmax = K . EDY ~ The K value varies with support conditions and location as shown on Table D-1. Fixity Mid-Span Ends Fix Fix 8.0 16.0 Fix Pin 6.5 11.6 Pin Pin 4.8 0 Fix Free N.A. 2.0 Table D-1 K Values Based on Fixity and Location D-13
The vortex shedding bending stress is combined with the member axial and bending stresses due to global deformation of the marine structure. 0.6. FATIGUE LIFE EVALUATION The fatigue life evaluation can be carried out in a conservative twostep process. First, the fatigue damage due to the vortex-induced oscillations is calculated as D1. Second, a deterministic fatigue analysis is performed by computer analysis. Hot spot stress range vs wave height (or wind velocity) for the loading directions considered is determined from the computer analysis. The critical direction is determined and a plot is made. From the plot of hot spot stress range vs wave height (or wind velocity), the stress ranges for the fatigue waves are determined. The maximum vortex-induced stress ranges for the fatigue environment are added to the deterministic fatigue stress ranges. Then, the standard deterministic fatigue analysis is performed using the increased stress range. The fatigue damage calculated in this second step is D2. Therefore the total fattgue damage is equal to the sum of D1 and D2, or Dtot = 01 + 02. The fatigue life fin Years is therefore calculated as l/Btot. A typical fatigue life evaluation procedure is given below: Step 1: a. Calculate the natural frequency fn (Hz) of the member. b. Calculate the stability parameter of the member. K5=~ pd2 c. Determine the minimum Vr required for vibrations based on Ks in Figure D-1. d. Calculate Vmin, the minimum velocity at which current- or wind- 0-14
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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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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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Page 342 and 343: C.3.2(a) Kuang Chord SCF’S for T-
Page 344 and 345: KuwqSE _im T-joint In%neW UrrdSicko
Page 346 and 347: C.3.2(b) Smedley-HordsworthChord SC
Page 348 and 349: T-joint Axial SF Saddle Posiiim
Page 350 and 351: -— T-joint CtkuHlane ELFSaddlePci
Page 352 and 353: I 1 1 1 1 ~. l~o ~ ha= 1s0 : ~. ~J
Page 354 and 355: 1 ! ! O.fi ;0.762 %841 0,769 O,= !0
Page 356 and 357: Ikrdwth-kdlw SF l%quiaiifm K-joint
Page 358 and 359: hdsmthqwdhy W Camputatim l-joint Ax
Page 360 and 361: Ejrnnt flkf+lane SF SaddlePmitim ~,
Page 362 and 363: MAXIMUM PRINCIPAL STRESS SCF = ----
Page 364 and 365: ‘-W, .\ I Ill I : II m -,, !) .
Page 366 and 367: ’ \./ ““’ w~”mm m ““-
Page 368 and 369: . . I Column L’ Longitudinal Gird
Page 370 and 371: C.8 Underwater Engineering Group,
Page 372 and 373: APPENDIX D VORTEX SHEDDING AVOIDANC
Page 374 and 375: a an b d f“ f ar f~ ‘bmax f~ fn
Page 376 and 377: D. VORTEX SHEDDING 0.1. INTRODUCTIO
Page 378 and 379: Vortex Shedding Frequency (f”) fv
Page 380 and 381: waves. When only isolated members u
Page 382 and 383: member’s nominal diameter and thi
Page 384 and 385: \Lf-! of cycles. Thus, the reduced
Page 386 and 387: s ; J steady current, by substituti
Page 390 and 391: vortex shedding will occur, i.e., V
Page 392 and 393: h. The fatigue life may -be modifie
Page 394 and 395: NOTE: The relationship given is bas
Page 396 and 397: CELL C7: KINEMATIC VISCOSITY = U CE
Page 398 and 399: COLUMN N: THE STRESS AMPLITUDE IS C
Page 400 and 401: D.8.3 Devices and Spoilers Devices
Page 402 and 403: D*9 REFERENCES D.1 King, R., “A R
Page 404 and 405: Fint Insmbility Rtgion I !%mmd Inat
Page 406 and 407: .—____ *U.S. E.P.O. :1993-343-273
Page 410 and 411: COMMllTEE ON MARINE STRUCTURES Comm
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