ssc-367 - Ship Structure Committee

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loads directly. Since the diffraction effects are strongly dependent on frequency, a wide range of frequenciesmust be used. The response of the floating structure to applied wave loadings depends on its own geometry, stiffness and mass properties. Water plane area and its distribution (i.e., hydrostatic-stiffness)and mass properties directly affect the natural periods and the heave, pitch and roll response amplitudes. For a tethered structure,such as a TLP, tether stiffnesswill predominate hydrostatic stiffness. Tether pretensionswill control surge and sway natural periods and response amplitudes. The primary damping is due to wave radiation and viscous effects. It is recommended that the “consistent approach” discussed in Section 5.2.2 is used to accuratelygenerate hydrodynamicloads. A finite element model of the structure can be used to obtain the solution to the motions analysis and determine the stress distributions. As an alternate,a stickmodel maybe used to obtain solutions to the equations of motion and to define global deformations and forces. Then, additionalfinite element models of various interfaces will be necessary to determine local stress distributions accurately. The boundary conditions for the finite element models will be the stick model deformations. 5.3 BOTTOM-SUPPORTEDMARINE STRUCTURES This section discusses bottom-supportedmarine structures that are represented by three-dimensional space frames and composed of cylindrical shells. The dynamics of a large gravity-type bottom supported structure dynamics are somewhat similar to those of a fixed platform. However, the characteristicsof excitationalloads on gravity structureshave more in common with floating structures. 5.3.1 Load or HydrodynamicsModel A wave force acting on a single stationary element is due to both the accelerationof water particles (inertialforce) and the kinetic 5-16
energy of the water particle (drag force). These forces are given by Morison’s equation as: 5-2 where: F = hydrodynamicforce vector per unit length acting normal to the axis of the member F,&FD= inertia and drag components of F P = density of water cm ‘ inertia force coefficient cd = drag force coefficient D= diameter of a tubular u“ = duw component of the velocity vector of the water normal to the axis of the member = component of the accelerationvector of the water normal to the axis of the member liw=— dt II = denotes absolute value An appropriateapproachto estimatethe wave forces with reasonable accuracy is to assess the load model in its entirety, and for its component elements. The element diameter should reflect any geometric variations, including marine growth. The Cd and Cm values applied may range 5-17
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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
Page 70 and 71: location. Thus, the method should b
Page 72 and 73: 1. SDectral FaticlueAnalvsis Althou
Page 74 and 75: 2. Weibull AtIDroach The Weibull sh
Page 76 and 77: energy about the central direction
Page 78 and 79: Although considered to be an emergi
Page 80 and 81: many design rules implement this ap
Page 82 and 83: Detailed Anal.vsisMethods The detai
Page 84 and 85: The DnV X-curve and the DEn Guidanc
Page 86 and 87: 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
Page 98 and 99: 1 —. — — — — -.. - .. - .
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 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 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
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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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- 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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