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*RAO |
 
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*RAO
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*RAO |
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To request the creation of RAO plots.
Refer to Computation of RAOs for further information on this feature.
The keyword begins with a line defining miscellaneous parameters for all the RAO plots. This is followed by an optional line to specify the independent variable to be used. This is then followed by blocks of lines repeated as often as necessary to request the actual RAO plots.
Line defining miscellaneous parameters:
[PLOT=YES/NO] [STEP=Time Step], ENSEMBLES=No. of Ensembles [, START=Start Time] [, CUTOFF=Cut-off Frequency]
Optional line defining independent variable:
[OPTION=Independent Variable]
Block requesting motion RAOs. Lines 2 and 3 can be repeated as often as necessary. Line 3 is optional.
TYPE=MOTION
Node (Number or Label), DOF [, Scale] [, PHASE=YES/NO] [, UNITS=Unit]
[TITLE=Figure Title]
Block requesting force RAOs. Lines 2 and 3 can be repeated as often as necessary. Line 3 is optional.
TYPE=FORCE
Element (Number or Label), Local Node, Variable [, Scale] [, PHASE=YES/NO] [, LOCATION=Location] [, UNITS=Unit]
[TITLE=Figure Title]
Refer to Force Variable Input for further information on acceptable Variable values. Refer to Location Parameter Input for further information on the significance of the Location input. The significance of the Local Node Input used during postprocessing depends on whether element based outputs are stored on a node or integration point basis.
Block requesting reaction RAOs. Lines 2 and 3 can be repeated as often as necessary. Line 3 is optional.
TYPE=REACTION
Node (Number or Label), DOF [, Scale] [, PHASE=YES/NO] [, UNITS=Unit]
[TITLE=Figure Title]
Block requesting floating body motion RAOs. Lines 2 and 3 can be repeated as often as necessary. Line 3 is optional.
TYPE=MOTION
FLOATING BODY=Body Name, DOF [, Scale] [, PHASE=YES/NO] [, UNITS=Unit]
[TITLE=Figure Title]
A Time Step value is required in a random sea dynamic analysis with a variable time-step; it is ignored in the case of an analysis with a fixed step. No. of Ensembles is a required input which must be greater than 1. Start Time defaults to the analysis start time. If no Cut-off Frequency is specified, Flexcom calculates a suitable default based on the analysis time variables. Independent Variable can be S (seconds, the default), H (Hertz), or R (radians/second). If you specify a node/element label rather than a node/element number, it must be enclosed in {} brackets. Scale defaults to 1. The Unit entry defaults to base units. Figure Title defaults to blank.
To define a number of parameters relating to the calculation of RAOs.
Input: |
Description |
Start Time: |
The start time for the calculation of RAOs. Flexcom excludes any values before this time. Use this entry to exclude initial transients from RAO calculations. |
Ensembles: |
The number of ensembles to be used in calculating RAOs. See Note (a). |
Time Step: |
The time step to be used when calculating RAOs from the results of a random sea dynamic analysis with a variable time step. See Note (b). If the analysis used a fixed time step then this entry is not required, and any value you might specify is ignored. |
Cut-off Frequency: |
The RAO cut off frequency in Hz. Flexcom truncates all output at this frequency. This entry is optional; by default, Flexcom calculates an appropriate value from the simulation length and the number of ensembles you specify. |
Independent Variable: |
This option allows you to select the independent variable (that is, the variable on the plot X axis) for RAO plots. The options are Period (seconds) which is the default, Frequency (Hz) and Circular Frequency (radians/s). |
Plot Files: |
This option allows you to request the creation of RAO plot files. The options are Yes (the default) and No. |
(a)The procedure used by Flexcom in calculating spectra is as follows. Firstly, the output timetrace is divided equally into a number of smaller timetraces or ensembles. A spectrum for each ensemble is then calculated using the Fast Fourier Transform (FFT) algorithm. Finally, the actual spectrum to be output is found as an average of the spectra calculated for each ensemble. This standard procedure minimises the statistical error associated with the FFT process. You specify the number of ensembles to be used in this process using the Ensembles entry above. This value should always be greater than 1.
(b)The FFT algorithm requires a record with a fixed time step. When you perform a variable step analysis, obviously such a record is not available, and so Flexcom must synthesise one by interpolating from the variable step record. The Time Step entry tells Flexcom what time step to use in the synthesised record.
(c)The procedure followed by the software for the computation of RAOs depends on whether the relevant analysis involved regular or irregular wave loading. Refer to Computation of RAOs for further details.
To request plots of RAOs of motion.
Input: |
Description |
Node: |
The node (number or label) for which the motion RAO is required. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global degree of freedom (DOF) for which the plot is required. Specify a value of 1 for the global X-direction, 2 for the global Y-direction, or 3 for the global Z-direction; 4, 5 or 6 for the components of the rotation vector in the global X, Y and Z axes respectively. |
Scale: |
A scale factor to apply to the data. This entry is optional, and defaults to a value of 1. |
Unit: |
The units to be used for the vertical axis of the plot. This entry is optional, and defaults to the base units for this output type. See Note (a). |
Phase: |
This option allows you to specify if you want a plot of phase angle as well as RAO. The default option is No, which specifies that no plot of phase angle is produced. Whatever option you specify here is of course immaterial if you specify that no output plots are to be created. |
Fig. Title: |
A descriptive title to be associated with the output. This entry is optional. |
(a)The units entry explicitly specifies what units are to be assigned to the vertical axis of the plot. This entry is optional, and if omitted, Flexcom simply assigns suitable units depending on the base units for the particular output type. If you do explicitly specify a unit, then it must be consistent with the dimension of the output type. For example, force can be specified in Newtons, Kips etc. The program is quite flexible in terms of accepting unit descriptions – e.g. Newtons, Newton, N etc. are all equally valid. For a list of the units accepted by Flexcom, refer to Units Reference Guide.
To request plots of RAOs of element restoring forces.
Input: |
Description |
Element: |
The element (number or label) for which the force RAO is required. If you specify an element label rather than an element number, it must be enclosed in {} brackets. |
Local Node: |
This option allows you to choose between three locations on the specified element. The significance of the Local Node Input used during postprocessing depends on whether element based outputs are stored on a node or integration point basis. |
Variable: |
This list allows you to select a relevant output parameter. The entries are largely self-explanatory. See Note (a). |
Scale: |
A scale factor to apply to the data. This entry is optional, and defaults to a value of 1. |
Unit: |
The units to be used for the vertical axis of the plot. This entry is optional, and defaults to the base units for this output type. See Note (b). |
Phase: |
This option allows you to specify if you want a plot of phase angle as well as RAO. The default option is No, which specifies that no plot of phase angle is produced. Whatever option you specify here is of course immaterial if you specify that no output plots are to be created. |
Location: |
This parameter identifies the circumferential or radial location on the element. See Note (c). |
Fig. Title: |
A descriptive title to be associated with the output. This entry is optional. |
Notes
(a)Refer to Force Variable Input for further information on acceptable Variable values.
(b)The units entry explicitly specifies what units are to be assigned to the vertical axis of the plot. This entry is optional, and if omitted, Flexcom simply assigns suitable units depending on the base units for the particular output type. If you do explicitly specify a unit, then it must be consistent with the dimension of the output type. For example, force can be specified in Newtons, Kips etc. The program is quite flexible in terms of accepting unit descriptions – e.g. Newtons, Newton, N etc. are all equally valid. For a list of the units accepted by Flexcom, refer to Units Reference Guide.
(c)Refer to Location Parameter Input for further information on the significance of the Location input.
To request plots of RAOs of reaction at specified restrained nodes.
Input: |
Description |
Node: |
The node (number or label) for which the reaction RAO is required. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global degree of freedom (DOF) for which the plot is required. Specify a value of 1 for the global X-direction, 2 for the global Y-direction, or 3 for the global Z-direction; 4, 5 or 6 for moments about the global X, Y and Z axes respectively. |
Scale: |
A scale factor to apply to the data. This entry is optional, and defaults to a value of 1. |
Unit: |
The units to be used for the vertical axis of the plot. This entry is optional, and defaults to the base units for this output type. See Note (a). |
Phase: |
This option allows you to specify if you want a plot of phase angle as well as RAO. The default option is No, which specifies that no plot of phase angle is produced. Whatever option you specify here is of course immaterial if you specify that no output plots are to be created. |
Fig. Title: |
A descriptive title to be associated with the output. This entry is optional. |
(a)The units entry explicitly specifies what units are to be assigned to the vertical axis of the plot. This entry is optional, and if omitted, Flexcom simply assigns suitable units depending on the base units for the particular output type. If you do explicitly specify a unit, then it must be consistent with the dimension of the output type. For example, force can be specified in Newtons, Kips etc. The program is quite flexible in terms of accepting unit descriptions – e.g. Newtons, Newton, N etc. are all equally valid. For a list of the units accepted by Flexcom, refer to Units Reference Guide.
To request RAO motion plots for floating bodies, in the floating body local axes.
Input: |
Description |
Floating Body: |
The name of the floating body for which the motion RAO is requested. |
DOF: |
The degree of freedom in the local floating body axis system for which the motion RAO is requested. The options are Heave, Surge, Sway, Yaw, Roll and Pitch. |
Scale: |
A scale factor to apply to the data. This entry is optional, and defaults to a value of 1. |
Unit: |
The units to be used for the vertical axis of the plot. This entry is optional, and defaults to the base units for this output type. See Note (a). |
Phase: |
This option allows you to specify if you want a plot of phase angle as well as RAO. The default option is No, which specifies that no plot of phase angle is produced. Whatever option you specify here is of course immaterial if you specify that no output plots are to be created. |
Fig. Title: |
A descriptive title to be associated with the output. This entry is optional. |
(a)The units entry explicitly specifies what units are to be assigned to the vertical axis of the plot. This entry is optional, and if omitted, Flexcom simply assigns suitable units depending on the base units for the particular output type. If you do explicitly specify a unit, then it must be consistent with the dimension of the output type. For example, force can be specified in Newtons, Kips etc. The program is quite flexible in terms of accepting unit descriptions – e.g. Newtons, Newton, N etc. are all equally valid. For a list of the units accepted by Flexcom, refer to Units Reference Guide.