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*Properties |
 
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*Properties
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*Properties |
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To assign effective structural properties to hot spot sets for use in calculating stresses.
Refer to Stress Properties for further information on this feature.
A block of two lines repeated as often as necessary. Each property specified on the second line can be omitted, in which case a default value will be used for stress calculations:
SET=Set Name
Do, Di, A, Iyy, Izz
The properties specified here are used in calculating stresses during fatigue analysis. This keyword is optional and may be ignored if you wish to use the actual properties (e.g. via the *GEOMETRIC SETS keyword in the $MODEL section), or properties explicitly specified for stress computations (i.e. via the corresponding *PROPERTIES keyword in the $MODEL section), as the values specified in the model definition are carried through to LifeTime (assuming you have requested database output storage).
If any of the parameters A, Iyy or Izz are omitted, default values are computed based on the specified (or default) values of Do and Di.
Input: |
Description |
Set Name: |
The name of the element set to which the stress properties are to be assigned. This defaults to all elements. |
Do: |
The effective outside diameter for the elements of the set. The default depends on the format used to specify geometric data. If you used the Flexible Riser format, then the default is the drag diameter for the elements of the set. If you used the Rigid Riser or Mooring Line formats, then Do here defaults to Do input in the properties data. |
Di: |
The effective internal diameter for the elements of the set. The default is the internal diameter specified in the geometric data. |
A: |
The effective cross-sectional area for the elements of the set. The default is given by:
where Do and Di are the inputs described above, default or otherwise. |
Iyy: |
The second moment of area about the local y-axis for the elements of the set. The default is given by:
where Do and Di are the inputs described above, default or otherwise. |
Izz: |
The second moment of area about the local z axis for the elements of the set. The default is Iyy above. |
(a)This table is identical to the Properties – Stress table of the main $MODEL section. If you use the table in $MODEL to specify stress properties, then these automatically carry through to LifeTime (assuming you have requested database output storage) and you do not need to repeat the specification here. Refer to Stress Properties for a detailed discussion of the various parameters above.
(b)It may seem curious that in general you need to specify diameter, cross-section area and moment of inertia values for hot spots although these values have already been input to Flexcom. The reason is because Flexcom does not echo this data to timetrace output files, and by default only Flexcom timetrace output is required as input to LifeTime. Flexcom does however output the external and internal diameter for each element to database output files. So if Flexcom database output is available, then LifeTime can read the required structural data from that source, thus eliminating the need for a repeat specification of this data. LifeTime reads the name of each Flexcom analysis from the Seastate File – Specify data and opens the appropriate timetrace output files for that analysis. The program also checks for the existence of a database output file from the analysis. If a database exists, the program retrieves the external and internal diameter values for each hot spot from that file, and then uses these values to calculate cross-section areas and moments of inertia.
(c)There are a number of important points to note with regard to this facility:
•Only one database needs to exist, and it can correspond to any analysis in your list.
•LifeTime reads database output once only, regardless of how many database files exist. Once it has retrieved the required structural properties from a database file, the program does not check for the existence of database output from any subsequent analysis in the seastate file.
•The database file need not contain very much actual results output. The inputs required by LifeTime are written by default to a header block at the start of the database file at the time of the first output to the database. So in fact database output at only one time is sufficient, and the actual amount of output can be minimised accordingly.
•If database output exists but you specify structural properties for some or all hot spot sets, the values you input in LifeTime take precedence over the values in the database.
