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*Riser Type |
 
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*Riser Type
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*Riser Type |
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To specify the riser type and other parameters relating to the Modes facility for generating output for subsequent input to SHEAR7.
Refer to SHEAR7 Interface for further information on this feature.
A block of three or more lines. The format of the third and subsequent lines depends on the riser type, which is specified on the first line of the keyword.
A block of two lines defining the riser type, element set and VIV option
TYPE=Riser Type [, VIV=VIV Option][, TOLERANCE=SCR Plane Tolerance]
[SET=Set Name]
For TTRs and SCRs, a third and final line is used to specify the number of segments, the number of modes, and a SHEAR7 damping ratio.
No. of Segments, No. of Modes [, SHEAR7 Damping Ratio]
For the User riser type option, a third line is used to specify the number of segments and a SHEAR7 damping ratio. This may be followed by two types of lines that may be mixed and/or repeated as often as necessary.
Line to specify the number of segments and a SHEAR7 damping ratio:
No. of Segments [, SHEAR7 Damping Ratio]
Line requesting a single mode:
Mode Number
Line requesting a list of modes:
GEN=Start Mode, End Mode [, Mode Increment]
Riser Type can be SCR, TTR or USER. VIV Option is only relevant to SCRs, and may be either IN-PLANE (default) or OUT-OF-PLANE. SCR Plane Tolerance is only relevant to SCRs and defaults to 1x10-5. Set Name defaults to all elements (set ALL). SHEAR7 Damping Ratio is only relevant to wake interference analyses, and defaults to zero. Mode Increment defaults to 1.
To specify the riser type relating to the Modes facility for generating output for subsequent input to SHEAR7.
Input: |
Description |
Riser Type: |
The options are SCR (the default), TTR and User. |
To specify various parameters relating to the Modes facility for generating output for subsequent input to SHEAR7.
Input: |
Description |
No. of Modes: |
The number of the natural frequencies/mode shapes calculated by Modes to be considered for SHEAR7 output. The default value of 0 signifies that all of the natural frequencies and mode shapes are to be considered, otherwise, the lowest No. of Modes natural frequencies/mode shapes are considered. |
No. of Segments: |
The number of equally spaced segments into which the riser element set is to be divided. A non-zero positive integer value is required. |
Set Name: |
The set of elements to include in the SHEAR7 output. This input is optional, and can be omitted. See Notes (a) and (b). |
SHEAR7 Damping Ratio: |
A damping ratio for use with a subsequent SHEAR7 analysis. This input is optional, and can be omitted. See Note (c). |
Modes for VIV Analysis: |
The SCR modes to be considered for subsequent SHEAR7 analysis. The options are In-Plane (the default) and Out-of-Plane. See Note (d). |
SCR Plane Tolerance: |
The tolerance value used to determine whether nodal displacements lie in the plane of the SCR (or at 90° to it). This entry has a default value of 1x10-5. See Note (e). |
(a)The element set you specify in the Set Name entry can be defined as part of your Modes input data, using the Define Element Sets table. Alternatively, it can have been previously defined as part of your Flexcom data.
(b)If you do not specify an element set, the composition of the default set depends on the Riser Type under consideration. If the riser is a top tensioned riser (TTR) or a user-defined riser type, then the default is all elements of the finite element mesh. If the riser type is a catenary riser (SCR), then the default is all elements which are not wholly on the seabed, starting at that element whose first node is the SCR touchdown point.
(c)This input is only relevant to wake interference analyses, where Flexcom can automatically run a SHEAR7 analysis to compute enhanced drag and lift coefficients.
(d)This input is only relevant to SCRs. Modes routes SCR SHEAR7 data to two files, named common.inp (for in-plane modes) and common.out (for the out-of-plane modes). The reason is that the two sets of modes will be excited by different current distributions and so will typically be considered in separate SHEAR7 runs. When doing your SHEAR7 analysis, you will need to rename one or other common.mds as appropriate. You can also use the Modes for VIV Analysis input to specify whether you are interested in in-plane or out-of-plane modes, in which case the relevant common file will be renamed automatically for you.
(e)The SCR Plane Tolerance input is only relevant to SCRs. When determining whether a mode is In-Plane, Out-of-Plane or Unknown, Modes first determines modal displacements relative to the local SCR axis system. This axis system is defined such that (i) the SCR local X-axis is aligned with the global X-axis, and (ii) the SCR local Y-axis represents the intersection of the horizontal plane with a vertical plane which contains the end points of the SCR. The next step is a normalisation of the local modal displacement vectors at each finite element node. Three conditions are then possible:
i.If all three components of the modal displacement vector (at any finite element node) are larger than the SCR Plane Tolerance value, then the mode is deemed to be Mixed/Unknown.
ii.If all local X and Y displacements are less than the SCR Plane Tolerance value, then the mode is deemed to be Out-of-Plane.
iii.If all local Z displacements are less that the SCR Plane Tolerance value then the mode is deemed to be In-Plane.
To specify various parameters relating to the Modes facility for generating output for subsequent input to SHEAR7.
Input: |
Description |
No. of Segments: |
The number of equally spaced segments into which the riser element set is to be divided. A non-zero positive integer value is required. |
Set Name: |
The set of elements to include in the SHEAR7 output. This input is optional, and can be omitted. See Notes (a) and (b). |
SHEAR7 Damping Ratio: |
A damping ratio for use with a subsequent SHEAR7 analysis. This input is optional, and can be omitted. See Note (c). |
(a)The element set you specify in the Set Name entry can be defined as part of your Modes input data, using the Define Element Sets table. Alternatively, it can have been previously defined as part of your Flexcom data.
(b)If you do not specify an element set, the composition of the default set depends on the Riser Type under consideration. If the riser is a top tensioned riser (TTR) or a user-defined riser type, then the default is all elements of the finite element mesh. If the riser type is a catenary riser (SCR), then the default is all elements which are not wholly on the seabed, starting at that element whose first node is the SCR touchdown point.
(c)This input is only relevant to wake interference analyses, where Flexcom can automatically run a SHEAR7 analysis to compute enhanced drag and lift coefficients.
To request a single mode to be included in the SHEAR7 output modes.
Input: |
Description |
Mode Number: |
The requested mode number. |
To request multiple modes to be included in the SHEAR7 output modes.
Input: |
Description |
Start Mode: |
The number of the first mode in the series. |
End Mode: |
The number of the last mode in the series. |
Increment: |
The mode number increment to be used in assigning numbers to the generated modes. This input defaults to a value of 1, which will apply in the majority of cases. |
(a)Mode numbers are assigned by repeatedly adding the specified or default increment to the previous number (obviously starting at the start mode) until the end mode number is reached or exceeded. So for example, the specification Start Mode - 1, End Mode - 11, Increment - 2 will result in 6 modes, numbered 1, 3, 5, 7, 9 and 11.