The steel wire SWIR facility allows modeling of the nonlinear properties of a new steel wire rope. However it is possible to model steel wire using linear (LINE) or nonlinear (NLIN) lines.
This data record defines a nonlinear property of a mooring line. In order to use these defined values, one or more NLIN data records must follow. The maximum number of nonlinear properties that may be defined is 50.
2 5 7 31 41
- --- -- ---- -------------------- --------- ---------
|X| | |SWIR|XXXXXXXXXXXXXXXXXXXX| | |
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| | | | |_(2) Asymptotic Offset (F10.0)
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| | | |_(1) Asymptotic Stiffness (E10.0)
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| | |_Compulsory Data Record Keyword (A4)
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| |_Optional User Identifier (A2)
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|_Compulsory END on last data record in Data Category (A3)
(1)-(2) These fields contain the values of the two constants in the equation defining the tension of the line as a function of the extension (see below). Values must be specified for both fields.
This facility enables the user to input the physical properties (constants defining the tension/extension curve) of a steel wire mooring line. Note that this data record does not define any mooring lines having these properties. This information must be supplied on following NLIN data records.
The mooring line properties defined on the SWIR data record will apply to all NLIN data records that follow until another nonlinear property data record is input. (Note that POLY is also a nonlinear property data record.)
Tension in a steel wire mooring line is given by:
T = k (x - d (tanh(x/d)))
where
x = extension of mooring line
k = asymptotic stiffness (constant)
d = asymptotic offset (constant)
The names of the constants k and d arise from the fact that, at large values of extension, tanh(x/d) tends to unity and the equation tends to the asymptotic form:
T = k (x - d)