SHEAR7 data file

To use SHEAR7 from OrcaFlex, or export a SHEAR7 data file, you must first provide extra data specific to SHEAR7 which are not needed by OrcaFlex. This is done on the SHEAR7 data form which can be opened from the model browser or the line data form. Note that your model must include at least one line for the SHEAR7 data form to be available.

To create a SHEAR7 data file, and any other input files, click on the export input files button. The model must be in statics complete state when you export the SHEAR7 input files, but you should be aware that data on the SHEAR7 data form are editable while in this state. To see the SHEAR7 input data without creating any files, click the view input files button.

A more convenient way to work is to use the SHEAR7 interface which can automatically save the required SHEAR7 input files, run SHEAR7, extract drag amplification factors and perform a coupled static analysis.

Include SHEAR7 data in text data file

By default, data specific to SHEAR7 are not included in OrcaFlex text data files. This option allows you to override that default.

If you are using the SHEAR7 interface, then the SHEAR7 data are always included in text data files irrespective of this setting.

SHEAR7 data

The majority of the required SHEAR7 data can be derived automatically by OrcaFlex from its line data. However, there are a number of other values which SHEAR7 needs and these are documented below. Mostly, we have named these values to correspond to their SHEAR7 names. For full details on how they are used, please refer to the SHEAR7 documentation.

SHEAR7 version

Different versions of SHEAR7 use slightly different data file formats. This value specifies which version of the data file is produced by OrcaFlex.

Output options

These options instruct SHEAR7 to output (or not) anm, dmg fat, str, curv, zeta-hyst and sth files (SHEAR7 version 4.5 and later; str files require version 4.7 or later; curv, zeta-hyst and sth files require version 4.11 or later).

Note: For SHEAR7 4.11 and later, all file extensions are prefixed with s7. So .anm becomes .s7anm, .dmg becomes .s7dmg, etc.

Out file selection (SHEAR7 version 4.6 and later)

Specifies which out files (out, out1, out2) are generated

Note: For SHEAR7 4.11 and later, all file extensions are prefixed with s7. So .out becomes .s7out, .out1 becomes .s7out1, etc.

Line

Selects the OrcaFlex line to be described in the SHEAR7 data file.

Output summary locations

These data specify the locations at which a summary of the response is given in the SHEAR7 .out file. A value of '~' for arc length range start means 'end A'; likewise, '~' for arc length range end means 'end B'.

Bending stress curvature load factor (SHEAR7 version 4.7 and later)

Corresponds to the SHEAR7 data item of the same name. If this value is set to '~' SHEAR7 will use its own internally calculated values.

Reduced velocity bandwidths

For SHEAR7 version 4.3/4.4, specify the single-mode and multi-mode reduced velocity bandwidth.

For SHEAR7 version 4.5, specify a single value for reduced velocity bandwidth.

For SHEAR7 version 4.6 and later, a value for reduced velocity bandwidth is required for each section.

Structural damping ratio

Corresponds to the SHEAR7 data item of the same name.

Power ratio cutoff level

Corresponds to the SHEAR7 data item of the same name. In SHEAR7 version 4.4 and earlier this data item was named cutoff level.

Primary zone amplitude limit (SHEAR7 version 4.5 and later)

Corresponds to the SHEAR7 data item of the same name.

Non-orthogonal damping (SHEAR7 version 4.10 and later)

Corresponds to the SHEAR7 data item of the same name. When using non-orthogonal damping the beta control number should be greater than zero.

Beta control number (SHEAR7 version 4.8 and later)

Corresponds to the SHEAR7 data item of the same name.

Fatigue calculation radial position (SHEAR7 version 4.8 and later)

Specifies whether the outer or inner diameter should be used for calculating fatigue damage.

Higher harmonics factor and threshold (SHEAR7 version 4.9 and later)

The amplification factor and RMS threshold for the higher harmonic correction. If the amplication factor is set to zero then no higher harmonic correction is applied.

Number of lift coefficient tables (SHEAR7 version 4.3/4.4 only)

The number of tables you want SHEAR7 to read from the common.cl file.

Current profile

The discretisation of the output current profile. One per node gives one value for each node in the line. This may give rise to numerical problems in SHEAR7, especially for finely segmented models, in which case you should discretise the current more coarsely using regular spacing.

You also specify the probability of occurrence (a number between 0 and 1) and the ID of the flow profile.

The current speed is exported as zero for any part of the line which uses a P-y model. This allows for hydrodynamic damping, using the still water coefficient, but excludes any excitation due to current.

Young's modulus

Young's modulus for the strength member. SHEAR7 uses this for computing stress and damage rate. For SHEAR7 versions 4.6 and later, this value is per section; for earlier versions, a single global value.

Include gravity for tilt contamination estimation

Controls whether the acceleration due to gravity will be output to the SHEAR7 data file. If unchecked, a value of zero is output. When gravity is provided, the slope values in the SHEAR7 modes file are used to include the effect of tilt in the SHEAR7 RMS acceleration results. The SHEAR7 user guide notes that this is intended only for comparison between SHEAR7 and instrumented vertical risers.

Power ratio exponent (SHEAR7 version 4.5 and later)

Corresponds to the SHEAR7 data item of the same name.

Fatigue calculation method (SHEAR7 version 4.7 and later)

Corresponds to the SHEAR7 data item of the same name.

Response (SHEAR7 version 4.7 and later)

The type of VIV response to analyse, either transverse or inline.

S-N curves

The S-N curves to be used by SHEAR7 for its fatigue calculations. An endurance limit can be specified – this is called the "cutoff stress range" in the SHEAR7 documentation.

For SHEAR7 version 4.6 onwards, you can define multiple S-N curves, each with an endurance limit, and then select which one to use on a section by section basis. For earlier versions, you define a single S-N curve and endurance limit to apply to the entire line.

Stress concentration factors

A global stress concentration factor for the line and, optionally, a number of local stress concentration factors.

VIV Diameter

The VIV diameter specifies the diameter used by the VIV model. Separate values can be specified for each section. The value specified is used for all nodes in that section. For a node at the intersection of two sections the VIV diameter of the following section is used. The VIV Diameter can be set to '~', which is taken to mean 'same as the section normal drag diameter'.

Stick-slip hysteresis (SHEAR7 version 4.11 and later)

Stick-slip hysteresis can be optionally included in the SHEAR7 analysis to account for structural damping in structures such as umbilicals, power cables and unbonded flexible risers. If stick-slip hysteresis is modelled then you must also specify a convergence tolerance and the bending hysteresis curves.

Stress time history output (SHEAR7 version 4.11 and later)

Options to control how the stress time history output (if selected) is generated. These options are documented in the SHEAR7 user guide for block 7 of the data file. Leave blank to use default values chosen by SHEAR7.

Strouhal type, Strouhal number

The Strouhal type and number define the relationship of flow velocity and cylinder diameter to the local vortex shedding frequency. Strouhal type can be rough cylinder or user specified. Rough cylinder corresponds to the SHEAR7 Strouhal code 200. If user-specified is chosen then you must also specify a Strouhal number.

Lift coefficient table, lift coefficient factor

The lift coefficient table identifies which table in the SHEAR7 lift file is to be used.

Lift coefficient factor corresponds to SHEAR7's lift coefficient reduction factor.

Hydrodynamic damping coefficients

The SHEAR7 hydrodynamic damping coefficients.

SHEAR7 structural zones

When OrcaFlex generates the SHEAR7 data file it assumes a one-to-one mapping between OrcaFlex line sections and SHEAR7 structural zones. This has some implications for how you create your OrcaFlex model. Essentially, anywhere on your line where you need SHEAR7 structural zone data to change you must ensure that there is an OrcaFlex section boundary.

SHEAR7 structural zone data comprise

Since most of these properties are constant within an OrcaFlex section you will naturally introduce section boundaries at the locations where they change. However, there are a few exceptions.

Lift coefficient, Strouhal number and hydrodynamic damping coefficients are SHEAR7-specific data, defined by OrcaFlex on the section data page of the SHEAR7 data form. You may need to introduce OrcaFlex section boundaries which coincide with the locations where these properties change.

Area moment of inertia and tension variation are used by SHEAR7 to calculate modal frequencies. However, since OrcaFlex produces a modes file which is more accurate than the internal SHEAR7 modal calculations, these parameters are not usually used.

Mass per unit length is used by SHEAR7 to compute damping ratio. Now, for almost all situations in OrcaFlex the mass per unit length is constant along a section, so this is of no concern. An exception to this, however, is a free-flooding line with a section which spans the water surface. A free-flooding line has greater mass below the water surface (because it is full of water): to represent the mass of this whole section to SHEAR7 as a single value, the mass is effectively smeared across the section. Quite often this is not of any significance, but if you wish you can avoid it by arranging that your OrcaFlex model has a section boundary at the water surface. Similar issues arise with the slug flow contents method.

The other modelling choice in OrcaFlex that leads to properties varying along the length of a section is when profiled line types (e.g. stress joints) are used. Although it may be tempting to use many structural zones to represent the variation of properties the SHEAR7 manual strongly recommends not doing so. Accordingly OrcaFlex outputs a single structural zone for a profiled line type section which has the effect of smearing properties and we believe that this is the correct approach to take in the vast majority of cases.