1. VIV fatigue analysis 1.1. Data group identifier, one input line VIVResponse FATIgue DAMAge 1.2. Control data, one input line IOPFAT NSECT NPCS IOPPR TSIOPPR CHTSPRN IOPFAT: integer, default: 0: Option for fatigue calculation IOPFAT = 0: Determined by parameter IOPTSH in VIV response analysis. For IOPTSH = 0, concurrent response frequencies, the default is 1, rain-flow counting. For IOPTSH = 1, consecutive response frequencies, the default is 2, Rayleigh distributed stress cycles IOPFAT = 1: Fatigue calculated in time domain using rain-flow counting. Currently not available for IOPTSH = 1. IOPFAT = 2: Fatigue calculated in frequency domain using Rayleigh distributed stress cycles. Currently not available for IOPTSH = 0. May only be used for SN curves with a single straight line and bilinear SN curves. IOPFAT = 3: Fatigue calculated directly from constant stress amplitude. Not available for IRSTYP = 3 or IOPTSH = 0 and multiple response frequencies. NSECT: integer, default: 0: Number of cross-sections to be specified below NSECT = 0: All elements NSECT > 0: Additional data is given in the end of this subsection. NPCS: integer, default: 8: Number of points around cross-section where fatigue is calculated, 1 ≤ NPCS ≤ 16, see Illustration of points around the cross-section. For definition of local axis, see RIFLEX User Guide. IOPPR: integer, default: 0: Print option for fatigue results IOPPR = 0: Print fatigue results only for most critical point in the cross-section. If TSIOPPR >0, time series is printed for one of two concurrent element ends. IOPPR > 0: Print fatigue results for all NPCS points. If TSIOPPR >0, time series is printed for all elements and both element ends. TSIOPPR: integer, default: 0: Time series print switch. Dummy if IOPTSH = 1. TSIOPPR = 0: No print of tension, y- and z- curvature time series to file TSIOPPR = 1: Print of tension, y- and z- curvature time series to file TSIOPPR = -1: Print of tension, y- and z- curvature time series to file, skip fatigue calculation. CHTSPRN: character(256): Time series file name For NSECT > 0 and IOPFAT = 1, Rain-flow counting method, fatigue damage will be calculated at the specified cross sections only. Otherwise, fatigue damage will be calculated for alle elements. The cross section specification may e used to specify stress concentration factors (SCFs) that differ from the default values (DSCFA, DSCFY and DSCFZ) given below Tension and curvature time series are printed for the NSECT specified elements or for all elements if NSECT = 0. The format of the time series file is given in Appendix B: Format of Time Series File. the two input lines of subsection SN curve data must be given below even if NSECT > 0. 1.3. Stress time series data, one input line. Given if IOPFAT = 0 or IOPFAT = 1. TSLEN DT IRSNO TSLEN: real, default: 0: Length of stress time series to be generated for fatigue calculation \(\mathrm {[T]}\). Minimum length is 60. DT: real, default: 0: Time step to be used in the stress time series \(\mathrm {[T]}\). IRSNO: integer, default: 31415: Seed for generating random phase angles. The time unit is usually seconds. A warning will be written if the user specifies a time step DT which is larger than\(\mathrm {\frac{2\pi }{\omega _{max}\times 20}}\), wheer \(\mathrm {\omega _{max}}\) is the largest of the discrete response frequencies. If default TSLEN and DT are used, TSLEN and DT are calculated by VIVANA. DT will be set to 1/30 of the shortest cross-flow response period with significant response. TSLEN will be set to 200 times the period of the highest ranked cross-flow response frequency, multiplied by the shortest cross-flow response period with significant response divided by the longest cross-flow response period with significant response. 1.4. Cross-sectional data, one input line DSCFA DSCFY DSCFZ ASI WSTI THI RFACT DSCFA: real, default: 1: Default stress concentration factor for axial force contribution. DSCFY: real, default: 1: Default stress concentration factor for bending about Yaxis. DSCFZ: real, default: 1: Default stress concentration factor for bending about Zaxis. ASI: real, default: 0: Optional cross-section area. = 0.0: Use the values specified in or derived from the cross section properties given in INPMOD WSTI: real, default: 0: Optional section modulus. = 0.0: Use the values specified in or derived from the cross section properties given in INPMOD THI: real, default: 0: Optional wall thickness. = 0.0: Use the values specified in or derived from the cross section properties given in INPMOD RFACT: real, default: 0.001: Factor between the stress unit \(\mathrm {[S]}\) used to define the SN curve and the force and length units \(\mathrm {[F]}\) and \(\mathrm {[L]}\) chosen in INPMOD. \(\mathrm {S\times RFACT=\frac{F}{L^2}}\) If \(\mathrm {kN}\) and \(\mathrm {m}\) were chosen as force and length units while the SN curve is given in \(\mathrm {MPa}\), RFACT should be set to 0.001. If the SI units \(\mathrm {N}\) and \(\mathrm {m}\) were chosen for force and length and the SN curve is in \(\mathrm {MPa}\), RFACT should be set to 1.0E-6. the stress concentration factors are included in the reported stress distributions. 1.5. SN curve data, two input lines NSNCRV RELDUR NSNCRV: integer > 0: Number of selected SN curves RELDUR: real, default: 0.0`: Relative duration / probability of the current condition. 0.0 ≤ RELDUR ≤ 1.0. If RELDUR > 0.0, the fatigue damage contributions, the calculated fatigue damage scaled by RELDUR, will be written to the _vivana.mpf file. CHIDSNi...CHIDSNnsncrv CHIDSNi: character(6): Identification of selected SN curve i, i = 1, …,NSNCRV 1.6. Cross-section specification, NSECT input lines. CHILIN ISEG IEL IEND SCFA SCFY SCFZ CHILIN: character(8): Line identifier ISEG: integer/character: Segment number in line. ISEG > 0: Local segment in the specified line ISEG = 'ALL': All segments in the specified line. IEL must then also be `ALL'. IEL: integer/character: Local element number in specified segment. IEL > 0: Local element in the specified line and segment IEL = 'ALL': All elements in the specified segment(s). IEL must be AL if ISEG is ALL. IEND: integer: IEND = 1: Cross-section at end with smallest node number checked. IEND = 2: Cross-section at end with largest node number checked. SCFA: real, default: DSCFA: Stress concentration factor for axial force contribution. SCFY: real, default: DSCFY: Stress concentration factor for bending about Yaxis. SCFZ: real, default: DSCFZ: Stress concentration factor for bending about Zaxis. This input is used to specify lines / segments / elements and stress concentration factors (SCFs) that differ from the default values (DSCFA, DSCFY and DSCFZ) given above. If SCFs are given several times for the one element, the last one given is used. the stress concentration factors are included in the reported stress distributions. 1.7. SN curve properties NOFC NOFC: integer: Number of SN curves 1.8. SN curve, 2xNOFC input lines CHIDSN NOSL LIMIND FATLIM TREF KEXP CHIDSN: character(6): Identification of SN curve NOSL: integer ≤ 5: Number of straight lines defining the SN curve. LIMIND: integer, default: 0: Fatigue limit indicator LIMIND < 0: Fatigue limit in terms of stress cycles is specified. LIMIND = 0: No fatigue limit. LIMIND > 0: Fatigue limit in terms of stress range is specified. FATLIM: real, default: 0: Fatigue limit, interpretation dependent on LIMIND. LIMIND < 0: Logarithm of number of stress cycles for which the SN curve becomes horizontal. LIMIND = 0: FATLIM is dummy. LIMIND > 0: Stress range level for which the SN curve becomes horizonal. TREF: real, default: 0: Reference thickness for thickness correction TREF = 0: No thickness correction KEXP: real, default: 0: Exponent for thickness correction. KEXP = 0: No thickness correction TREF and KEXP must either both be zero, no thickness correction, or both positive, thickness correction included. 1.9. Fatigue capacity curve constants RM1 RC1 RMi RNCi RM1: real: Slope of the SN curve. First curve segment for NOSL > 1 Total curve for NOSL = 1. RC1: real: Constant defining the SN curve. First segment or total curve. RMi: real: Slope of curve segment i, i = 2, …, NOSL RNCi: real: Transition point between curve segment (i-1), and i, i =2, …, NOSL. The transition point is given as the logaritmic value, see Figure 2. Figure 1. llustration of points around the cross-section where fatigue is calculated Figure 2. Illustration of input data for fatigue capacity curve definition. The SN curves defined by the input parameters are always assumed to relate the stress range, \(\mathrm {\Delta S}\), to the number of cycles before failure, N. A straight-lined SN curve in log-log scale is in general defined as \(\mathrm {N=C\times (\Delta S(\frac{t}{t_{ref}})^k)^m_{}}\) or \(\mathrm {\log N=\log C+m\log (\Delta S(\frac{t}{t_{ref}})^k)_{}}\) where: \(\mathrm {N}\): Number of cycles to failure \(\mathrm {\Delta S}\): Stress range \(\mathrm {t}\): Cross section thickness \(\mathrm {t_{ref}}\): Reference thickness \(\mathrm {k_{}}\): Exponent for thickness correction The two input parameters used to define SN curves are directly found in the equation above, namely. \(\mathrm {RC=\log C\quad }\) (always positive) \(\mathrm {RM=m\quad \quad }\) (always negative) If the user has a SN curve without having these parameters explicitly defined, they can be calculated as follows; see also Calculation of SN curve parameters. Figure 3. Calculation of SN curve parameters. Using the two points A and B on Calculation of SN curve parameters to define the straight line, we have \(\mathrm {\log N=\frac{\log N_2-\log N_1}{\log\Delta S_2-\log\Delta S_1}\times \log\Delta S-\frac{\log N_2-\log N_1}{\log\Delta S_2-\log\Delta S_1}\times \log\Delta S_1+\log N_1}\) Hence \(\mathrm {RM=\frac{\log N_2-\log N_1}{\log\Delta S_2-\log\Delta S_1}\quad }\) (always negative) \(\mathrm {RC=-RM\times \log\Delta S_1+\log N_1\quad }\) (always positive) The relation between these parameters specified for different unit systems is easily found from the equations above. VIV response analysis VIVANA print flags