1. Stress time series calculated from the time domain analysis

This option allows for calculation of stresses in circular metallic homogeneous risers.

The stress time series are calculated based on the stored force time series from DYNMOD and the component properties specified in INPMOD. Stresses may only be calculated for CRS1 and CRS0 components.

Stress time series are calculated for specified points on the tube circumference.

1.1. Data group identifier

STREss TIME SERIes

1.2. Output options, one input line

IOP IDOF IT1 NTS ISUBST NNELC

  • IOP: integer: Code for type of output

    • IOP = 1: Time series

    • IOP = 2: Time series statistics

    • IOP = 3: Spectral analysis

    • IOP = 1 in present version

  • IDOF: integer: Stress components type 1

    • IDOF = 1/11: Axial stress at end 1/2

    • IDOF = 2/12: Torsional stress at end 1/2

    • IDOF = 3/13: Bending stress at end 1/2

    • IDOF = 4/14: Axial + bending stress at end 1/2

    • IDOF = 5/15: Shear stress at end 1/2

    • IDOF = 6/16: Shear stress + torsional stress at end 1/2

    • IDOF = 7/17: Equivalent stress at end 1/2

    • IDOF = 8/18: Hoop stress at end 1/2

    • IDOF = 9/19: Radial stress at end 1/2

    • IDOF = 21/22: External pressure at end 1/2

    • IDOF = 23/24: Internal pressure at end 1/2

  • IT1: integer: First stored time step to be included

  • NTS: integer: Number of stored time steps to be included (from IT1).

    • A large number includes the remaining time steps

  • ISUBST: integer, default: 0: Code for subtracting the static stress contributions

    • ISUBST = 0: Total stresses calculated

    • ISUBST = 1: Static stress is subtracted

  • NNELC: integer: Number of lines used for element specification

1.3. Point for stress calculation, one input line

THETA INEX IOPPRE

  • THETA: real, default: 0.0: Angle from local y-axis for stress calculation \(\mathrm {[Deg]}\)

  • INEX: integer, default: 2: Stress location switch

    • INEX = 1: Inner wall

    • INEX = 2: Outer wall

  • IOPPRE: integer, default: 1: Code for updating inner and outer pressure values.

    • |IOPPRE| = 1: Static inner and outer pressure used.

      • Outer pressure is calculated as hydrostatic pressure from MWL.

    • |IOPPRE| = 2: Updated inner and outer pressure used.

      • Outer pressure is calculated as hydrostatic pressure from MWL.

    • IOPPRE < 0: Wall forces calculated using outer area given by the pipe diameter or the alternative cross section diameter.

      • Corresponds to evenly distributed shear forces between buoyancy material and pipe.

      • Warning: This option is under development!

Nonlinear time domain analysis only.

In the present version, the external pressure is calculated as a hydrostatic pressure from the MWL. The external pressure is updated for all structural elements.

The internal pressure is updated for all elements that are part of a Main Riser Line.

1.4. Element specification, NNELC input lines

LINE-ID ISEG IELM

  • LINE-ID: character(8): Line identifier.

    • You may specify ALL to include all lines

  • ISEG: integer/character: Segment number.

    • You may specify ALL to include all segments.

    • ENDS includes the end segments on the line

  • IELM: integer/character: Element number.

    • ALL includes all elements, and

    • ENDS includes end elements on the above specified segment

Stresses may only be calculated for elements for which forces are stored, see data group File storage for internal forces for storage information. If the user specifies elements for which forces are not stored, these elements are ignored.

1.5. Options for the output distribution functions of the stress time series statistics, one input line

This input line is given only if IOP=2.

 NCL XCMIN XCMAX

  • NCL: integer: No of classes in the output distribution functions (i.e. no of points on the abscissa axis)

    • 0<NCL<41

  • XCMIN: real: Range of argument values for output distribution functions is XCMIN*sx(1) - XCMAX*sx(1) in which sx(1) is the standard deviation of x estimated from the first sequence.

  • XCMAX: real:

1.6. Spectrum smoothing parameter for the spectral analysis of the stress time series, one input line

This input line is given only if IOP=3.

MSM

  • MSM: integer, default: 0: Smoothing parameter

    • MSM=0: No smoothing

    • MSM>0: Smoothing by averaging over 2*MSM+1 values.