SHEAR7 Data Specification |
 
|
SHEAR7 Data Specification |
|
Flexcom provides a number of keywords to allow you the flexibility to change any model input, calculation option, and output option as you see fit. While it may seem like a large number of options to control the SHEAR7 analysis, there are only a few required keywords: *Restart, *Current,*S-N Curve and *Fatigue Data.
While not required, the keywords *Version, *Folder Option, and *Zones are commonly used to facilitate more control over the analysis.
Additionally, there are a variety of other keywords to control other inputs; these include *Section Coefficients, *Section Parameters, *Fatigue Options, *Output Files, *Power Ratio Exponent, *Cutoff Modes, *Damping Ratio, *Response, *HIGHER HARMONICS, *REFERENCE DIAMETER and *non-orthogonal DAMPING. The various inputs and their significance are outlined below.
For further information on all Shear7 inputs, refer to the Shear7 User Guide which is available for download from the Shear7 Support web page.
•Set Name. The name of the section (i.e. the element set name) whose properties are being defined. Note that any Set Name referenced under the Environmental category must have section properties defined here.
•Modes File Name. The location of the modal analysis that has been performed prior to the SHEAR7 analysis. This can be referenced as the path\filename, or the path\filename with the keyword extension.
•Probability of Occurrence. The current’s annual probability of occurrence. This defines the current profile’s probability in one year. In SHEAR7 this value is multiplied by the computed damage.
•Profile ID. This value is the number reported by SHEAR7 in the output file to help you keep track of which current profile is being used.
•Current Option. The current option allows you to specify which format you wish to define the current. The options are ascending, descending or x/L. Current values are converted to x/L format before being writing to the SHEAR7 input file. The Flexcom output file presents the original and converted current profiles to facilitate inspection of the conversion process. If you not fully satisfied with the in-built conversion process in Flexcom, you can choose the x/L current definition option instead. This transfers the user specified data directly to Shear7, with no conversion process applied.
•Elevation and Velocity. The current elevation and current velocities.
•Elevation is converted to SHEAR7 x/L format. A minimum of two points are required to define a current profile.
•VIV is only considered to be caused by flow that is normal to the riser. While the consideration of this is not generally an issue for TTRs because they can be seen to be vertical or mostly vertical and there is no specific vertical plane flow, this consideration has a heavy impact for in-plane current flow which excites out-of-plane modes for SCR and SLWR configurations. SHEAR7 only provides functionality whereby you can specify the normal flow velocity not taking into account the directionality. This may pose a problem in the modelling of SLWRs as the flow is actually reversed in the hog-bend. While it is not completely accurate to consider the flow all being in the same direction, this is the only way the SHEAR7 currently allows it, therefore it is generally an acceptable approach as it is typically more conservative. If you wish to use your own methodology for the application of current, an option has been reserved for explicit definition in terms of x/L as mentioned above.
•For TTRs and SCRs (or user-defined structures) analysed for in-plane VIV, the current conversion process simply uses linear interpolation based on nodal elevation to find the relevant current velocity at each x/L location.
•For SCRs (or user-defined structures) analysed for out-of-plane VIV, the current conversion process also uses linear interpolation in the same manner, but includes an additional adjustment to compute the current velocity normal to the structure. Specifically, it computes a local orientation based on the Euler angles in DOFs 5 & 6, combines these into a (resultant) local inclination angle, and then factors the current velocity by the cosine of this angle at each x/L location.
•Curve Name. The name of the S-N curve.
•Endurance Limit. The stress range at which the number of cycles to failure is unlimited. SHEAR7 refers to this value as the cutoff stress range.
•Stress Range. The stress value that corresponds to the number of cycles to failure. In SHEAR7 as many as ten segments or 11 data pairs can be used to define an S-N curve. On a log-log plot the S-N curve is assumed to be linear between these points. The stress range for the different points must be in increasing order.
•Cycles to Failure. The number of cycles to failure at the reference stress range.
•Global SCF. The stress concentration factor to be applied to the entire structure. The stress computed by SHEAR7 for the entire structure is multiplied by this value before the damage rate is computed.
•Fatigue Set. The set which will correspond to defined S-N curves. If a set is not assigned an S-N curve, the first S-N curve defined will be assigned to the set.
•S-N Curve. The curve name as defined in the S-N Curve keyword. This curve will be assigned to the element set defined.
•SHEAR7 Installation Path. The location of the SHEAR7 executable path.
•SHEAR7 Version. The version of SHEAR7 to be used. Versions between 4.6 and 4.12 (default) are supported.
•CL Path. SHEAR7 provides lift tables to be used in the SHEAR7 analysis. The file is generally located in the SHEAR7 installation directory.
•Folder. The folder where the SHEAR7 analysis will be performed. The common.mds, and common.CL files will be moved to this location and the SHEAR7 input file will be generated.
•Element Set. This defines a set of elements that will be assigned consistent structural properties for the purpose of the SHEAR7 model. SHEAR7 recommends not trying to model too much detail in zones. Conversely, Flexcom will capture small geometric changes in the model to provide the most accurate model possible. This can prove to be problematic in areas such as tapered sections or detailed casing models where small geometric changes may lead to infinitesimal zone size generation. Zones allows you to have more control over the zone which is generated.
•Element Set. The element set which the coefficients should correspond to.
•Added Mass Coefficient. The normal added mass coefficient for the element set. If this value is left blank these values will default to the added mass coefficients specified in the static file.
•Damping Coefficient 0. The Reynolds still water damping coefficient assigned to the element set. This is only used in SHEAR7 4.8 onwards.
•Damping Coefficient 1. The A/D still water damping coefficient assigned to the element set.
•Damping Coefficient 2. The low relative velocity region damping coefficient assigned to the element set.
•Damping Coefficient 3. The high relative velocity region damping coefficient assigned to the element set.
•Damping Coefficient 4. The axial flow region damping coefficient assigned to the element set. This is only used in SHEAR7 4.8 onwards.
•Element Set. The element set which the parameters should correspond to.
•Reduced Velocity Bandwidth. The reduced velocity bandwidth for the set. This parameter is the width of the band expressed as a fraction of the critical relative velocity that will be used to define which possible modes could lock-in. This value will likely change depending on whether the riser is bare, straked, or faired.
•Strouhal Number. The strouhal number for this set. The strouhal number is a dimensionless parameters that describes the relationship between vortex shedding frequency, characteristic length and the flow velocity. This value will likely change depending on whether the riser is bare, straked, or faired.
•CL Reduction Factor. The lift coefficient reduction factor for the set. The life coefficient (CL) reduction factor allows you to modify the lift coefficient iteration scheme. The lift coefficient reduction factor is multiplied by the CL value in the CL tables.
•Zone CL Type. The lift coefficient table for the set. The lift coefficient (CL) table specifies which CL table from the common.CL table will be used. This value will likely change depending on whether the riser is bare, straked, or faired.
•Animation Flag. The option to output a MATLAB animation.
•Debugging Flag. The option to output additional debug information.
•Damages Flag. The option to output Rayleigh fatigue damage rate per year for all resonant modes at each node.
•Fatigue Flag. The option to output the total response amplitude and phase angles at every node for every resonant frequency.
•RMS Stress Flag. The option to output the RMS stress for each participating mode. This option is not available for SHEAR7 4.6.
•Additional Output Flags. The option to output additional information. There is no option to suppress the basic output which contains input echoes and results summaries. Additional output files include lift coefficients for each mode and resonant modes for all nodes of the structure.
•Power Ratio Exponent Type. The option for determining time sharing probabilities when multiple modes are predicted to be excited.
•Power Cutoff. The power cut-off level controls how many modal power-in regions there are. The lower the number, the more possible excited modes are included. The closer the number is to one, the higher the likelihood of a single frequency lock-in.
•Primary Zone Amplitude Limit. The response definition is the resolution by which the solution is summarized in the SHEAR7 output file. This output option has no bearing on the results.
•Structural Damping Ratio. The structural damping ratio in terms of critical damping.
•Response Definition. The response definition is the resolution by which the solution is summarised in the SHEAR7 output file. This output option has no bearing on the results.
•Amplification Factor. Higher Harmonics amplification factor.
•Threshold. Higher Harmonics threshold, above which a Higher Harmonics amplification factor gets applied.
•Reference Diameter. Reference diameter for Af* calculation. The diameter provided is used in calculating the non-dimensional parameters Af* and cf*.
•Af* is defined as the flexible cylinder equivalent dimensionless response amplitude. The goal of Af* is to provide a single number that characterizes the response for the entire flexible cylinder by using the average of the RMS response in the power-in region.
•cf* is defined as the flexible cylinder equivalent damping parameter and improves on the previous c* parameter by capturing the role of damping in the determination of the VIV of flexible cylinders in sheared flow.
•If the diameter is specified appropriately, the product of Af* and cf* represents the lift coefficient of the riser.
•Flag to account for non-orthogonal damping when calculating the VIV response. Using this flag activates a significant improvement to the modelling of spatially varying damping, resulting in a more accurate response prediction, particularly in regions outside of the excitation zone. When using non-orthogonal damping the beta control number should be set to a non-zero value.
•*CURRENT is used to specify the current to be considered in the SHEAR7 analysis.
•*CUTTOFF MODES is used to define the SHEAR7 parameters “Power Cutoff” and “Primary Zone Amplitude Limit”. These parameters are applicable to SHEAR7 4.5 and later. The SHEAR7 User Manual provides a detailed description of these parameters.
•*DAMPING RATIO is used to define the SHEAR7 structural damping ratio.
•*FATIGUE DATA is used to assign fatigue data to SHEAR7 sets.
•*FATIGUE OPTIONS is used to specify fatigue calculation options for SHEAR7 in Block 5.
•*FOLDER OPTIONS is used to indicate where the SHEAR7 input files will be generated and run.
•*NAME is used to specify a title for SHEAR7 analysis run.
•*OUTPUT FILES is used to request output file types from SHEAR7. The available output file extensions are *.anm, *.scr, *.dmg, *.fat, *.str, *.out, *.out1, and *.out2. Refer to the SHEAR7 User Manual for further information on the output file generation options. The output file options can vary between versions of SHEAR7.
•*POWER RATIO EXPONENT is used to define the type of the Power Ratio Exponent for SHEAR7.
•*RESPONSE is used to define the SHEAR7 response definition/resolution to be used in the output file.
•*RESTART is used to indicate which modal analysis should be used in order to generate the SHEAR7 model.
•*SECTION COEFFICIENTS is used to assign SHEAR7 coefficients to element sets.
•*SECTION PARAMETERS is used to assign SHEAR7 parameters to element sets.
•*S-N CURVE is used to define S-N curves to be used in SHEAR7 analysis.
•*VERSION is used to provide Flexcom with basic SHEAR7 interface information.
•*ZONES is used to define element sets that will be used as one zone in SHEAR7.