*Boundary
To define boundary conditions.
Refer to Boundary Conditions for further information on this feature.
Boundary condition data is specified in blocks, with each block beginning with a TYPE= line defining the boundary condition type. This is then followed by as many lines as necessary to specify the boundary conditions of that type, and this in turn is then followed as necessary by data for other types. Data for the different boundary condition types can be specified in any order, and indeed types can be repeated in the same *BOUNDARY specification.
To define constant or time invariant boundary conditions.
Block defining constant boundary conditions:
TYPE=CONSTANT
Line defining a single boundary condition:
Node (Number or Label), DOF [, Displacement] [, FIXATION=RELATIVE]
Line generating similar boundary conditions at multiple nodes:
GEN=Start Node (Number or Label), End Node (Number or Label) [, Node Increment], DOF [, Displacement] [, FIXATION=RELATIVE]
If you specify a node label rather than a node number, it must be enclosed in {} brackets. Node Increment defaults to 1. Displacement defaults to 0. If the relative fixation option is invoked, the node is fixed with respect to the position at the end of the preceding analysis, rather than the initial position.
Input: |
Description |
Node: |
The node (number or label) at which the constant boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X - direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Notes (b) and (c). |
Displacement: |
The magnitude of the applied boundary condition at this node. This defaults to a value of 0. Rotational boundary conditions are specified in degrees. |
Fixation: |
This option allows you to select whether the boundary condition is Absolute or Relative. If you select Absolute (the default), the node is fixed with respect to the initial position. If you select Relative, the node is fixed with respect to the position at the end of the preceding analysis, rather than the initial position. |
Input: |
Description |
Start Node: |
The node (number or label) at which the first constant boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
End Node: |
The node (number or label) at which the last constant boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
Increment: |
The increment to be used in assigning boundary conditions to the range of nodes. This input defaults to a value of 1, which will apply in the majority of cases. To specify a decrement value, simply input a negative number. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X - direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (b). |
Displacement: |
The magnitude of the applied boundary condition at this node. This defaults to a value of 0. Rotational boundary conditions are specified in degrees. |
Fixation: |
This option allows you to select whether the boundary condition is Absolute or Relative. If you select Absolute (the default), the node is fixed with respect to the initial position. If you select Relative, the node is fixed with respect to the position at the end of the preceding analysis, rather than the initial position. |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
To identify those nodes on the structure whose motions are defined from the motions of an attached vessel.
Line defining a user subroutine for vessel motions:
USER_VESSEL=File Name
Block defining vessel boundary conditions:
TYPE=VESSEL, VESSEL=Vessel Name
Line defining a single vessel boundary condition:
Node (Number or Label), DOF [, Displacement]
If any drift motions are defined using a user subroutine, then the USER_VESSEL=option is mandatory. If you specify a node label rather than a node number, it must be enclosed in {} brackets. Node Increment defaults to 1. Displacement defaults to 0. Data for any Vessel Name specified here must be input under *VESSEL.
Input: |
Description |
Subroutine File: |
The name of the DLL file containing the drift user-subroutine. |
Input: |
Description |
Vessel: |
The name of the attached vessel. See Note (b). |
Node: |
The node (number or label) at which the vessel boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X - direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (c). |
Displacement: |
The magnitude of the offset applied to connect the riser to the vessel in its reference position. The default value is 0. Refer to Note (d). |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)More than one attached vessel can be included in a Flexcom analysis. You distinguish between connected vessels by giving each a unique name. The name you choose is then used in this Boundary - Vessel table to identify the vessel whose motions define the response at a particular node. The actual name of course has no significance other than as a label to distinguish between vessels. You use the name again in the other tables, such as those used to specify the vessel initial position, offset, RAO file name, drift motions etc.
(c)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
(d)A full discussion of the calculation of vessel motions and corresponding structural displacements is given in Vessels and Vessel Motions.
(e)Refer to Arbitrary Boundary Conditions for a detailed discussion of the drift user-subroutine facility.
To identify those nodes on the structure whose boundary conditions vary sinusoidally with time.
Block defining sinusoidal boundary conditions:
TYPE=SINUSOIDAL
Node (Number or Label), DOF, Amplitude, Phase [, Period]
If you specify a node label rather than a node number, it must be enclosed in {} brackets. The period of a sinusoidal boundary condition defaults to the wave period if a single regular wave is specified, otherwise a period must be specified. Sinusoidal boundary conditions are not relevant for frequency domain analysis.
Input: |
Description |
Node: |
The node (number or label) at which the sinusoidal boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X - direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (c). |
Amplitude: |
The amplitude of the sinusoidal function defining the motion. |
Phase: |
The phase of the sinusoidal function relative to the wave datum. |
Period: |
The period of the sinusoidal function defining the motion. If a (single) regular wave is used in the analysis, this input defaults to the period of the wave. There is no default value for multiple regular waves or irregular waves. |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)More than one sinusoidal boundary condition may be imposed at a particular Node-DOF combination.
(c)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
(d)Where structure displacements are specified using the Boundary - Sinusoidal option, any other boundary condition may also be applied at the same degree of freedom and at the same node. This can be used, for example, where vessel drift is specified using the Boundary - Sinusoidal option, and high frequency vessel motion is specified using the Boundary - Vessel option.
(e)This sinusoidal boundary condition option was provided originally for modelling the effect of vessel drift. However more comprehensive and accurate drift modelling capabilities are now provided, and you may prefer to use those now for that purpose. Sinusoidal boundary conditions are retained for compatibility with earlier versions, and you are of course perfectly entitled to use them as required.
To identify the nodes on the structure whose time-varying displacements are to be read from an ASCII data file, and to input the name of that file.
Block defining timetrace file boundary conditions:
TYPE=FILE, USER=File Name
Node (Number or Label), DOF
File Name should include the entire path of the boundary condition file with its extension. If the file name or any part of its path contains spaces then it should be enclosed in double quotation marks. If you specify a node label rather than a node number, it must be enclosed in {} brackets.
Input: |
Description |
Displacement File: |
The name of the ASCII data file containing the timetrace of displacement to be applied. This should ideally include the entire path of the file, including extension. If the file name or any part of its path contains spaces, the full name should be enclosed in double quotation marks (" "). |
Node: |
The node (number or label) at which the boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X-direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (b). |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
(c)Refer to Displacement Boundary Conditions for further information on this feature.
To identify the nodes on the structure whose time-varying motions are to be calculated from the motion of a so-called reference point, and to specify the name of the file containing the motions of this reference point.
Block defining reference point timetrace file boundary conditions:
TYPE=REFERENCE, USER=File Name
Node (Number or Label), DOF [, Displacement]
File Name should include the entire path of the boundary condition file with its extension. If the file name or any part of its path contains spaces then it should be enclosed in double quotation marks. If you specify a node label rather than a node number, it must be enclosed in {} brackets.
Input: |
Description |
Reference Point File: |
The name of the ASCII data file containing the timetrace of reference point motion. This should ideally include the entire path of the file, including extension. If the file name or any part of its path contains spaces, the full name should be enclosed in double quotation marks (" "). |
Node: |
The node (number or label) at which the boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X-direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (b). |
Displacement: |
The magnitude of the static offset applied to the node before connection to the nominal reference point. |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
(c)Refer to Reference Point Boundary Conditions for further information on this feature.
To identify nodes on the structure whose boundary conditions are defined via a user-subroutine.
Line defining a user subroutine for boundary conditions:
USER_BOUNDARY=File Name
Block defining user subroutine boundary conditions:
TYPE=SUBROUTINE
Node (Number or Label), DOF
The USER_BOUNDARY entry is only relevant if (at least one) boundary condition is defined in a user subroutine. File Name should include the entire path of the boundary condition file with its extension. If the file name or any part of its path contains spaces then it should be enclosed in double quotation marks. If you specify a node label rather than a node number, it must be enclosed in {} brackets.
Input: |
Description |
Node: |
The node (number or label) at which the boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X - direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. Refer to Note (b). |
Input: |
Description |
Subroutine File: |
The name of the DLL file containing the boundary condition user-subroutine. |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Preliminary Note on Rotational Constraints for further information.
(c)Further details regarding the use of the boundary condition user-subroutine facility are contained in Arbitrary Boundary Conditions. You must specify a boundary condition subroutine file name using the Boundary - Subroutine Files table if you invoke the Boundary - Subroutine option.
To identify nodes on the structure whose motions vary harmonically in a frequency domain regular wave analysis, and to specify the parameters relating to this harmonic variation.
Block defining harmonic boundary conditions:
TYPE=HARMONIC
Node (Number or Label), DOF [, Static Displacement] [, Harmonic Displacement] [, Phase Lag]
If you specify a node label rather than a node number, it must be enclosed in {} brackets. Static Displacement, Phase Lag and Harmonic Displacement default to 0. Harmonic boundary conditions are not relevant for time domain analysis.
Input: |
Description |
Node: |
The node (number or label) at which the boundary condition is to be applied. If you specify a node label rather than a node number, it must be enclosed in {} brackets. |
DOF: |
The global DOF in which the boundary condition is applied at this node. For translations, specify a value of 1 for the global X-direction, 2 for the global Y-direction or 3 for the global Z-direction. DOFs 4, 5 and 6 refer to the components of the rotation vector at the node. See Note (b). |
Static Displacement: |
The mean static displacement (defaulting to zero) about which the harmonic motion takes place. |
Harmonic Displacement: |
The amplitude of the harmonic displacement (defaulting to zero). |
Phase Lag: |
The phase lag relative to the regular wave input in degrees (defaulting to zero). See Note (c). |
(a)The specification of boundary conditions is optional, and by default no constraints are applied. This allows free-falling objects, for example, to be analysed. However, most problems will require some boundary conditions to be specified.
(b)It is important if specifying displacements in DOFs 4-6 to understand the significance of these degrees of freedom. Refer to Application of Rotational Constraints for further information.
(c)The phase angle is relative to the wave at the static offset position. By convention, a positive phase angle implies a phase lag, whereas a negative phase angle implies a phase lead.