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Command(s): SAVE

GUI: Utility Menu> File> Save as Jobname.db

Start solution calculations using one of these methods:

Command(s): SOLVE

GUI: Main Menu> Solution> Solve> Current LS Output from the solution consists of the superelement matrix file, Sename.SUB, where Sename is the name assigned as an analysis option [SEOPT] or the jobname [/FILNAME]. The matrix file includes a load vector calculated based on the applied loads. (The load vector will be zero if no loads are defined.)

Repeat for additional load steps (that is, to generate additional load vectors) The load vectors are numbered sequentially (starting from 1) and appended to the same superelement matrix file. See Loading in the Basic Analysis Guide for other methods for multiple load steps.

Leave SOLUTION using one of these methods

Command(s): FINISH

GUI: Main Menu> Finish

10.2.2. Step 2: Use Pass (Using the Superelement)

The use pass is where you use the superelement in an analysis by making it part of the model. The entire model may be a superelement or, as in the plate example, the superelement may be connected to

other nonsuperelements (see Figure 10.2: Example of a Substructuring Application (p. 264)). The solution from the use pass consists only of the reduced solution for the superelement (that is, the degree of freedom solution only at the master DOF) and complete solution for nonsuperelements.

The use pass can involve any analysis type (except an explicit dynamics analysis). The only difference

is that one or more of the elements in the model is a superelement that has been previously generated. The individual analysis guides contain detailed descriptions about performing various analyses. In this section, we will concentrate on the steps you need to make the superelement a part of your model.

10.2.2.1. Clear the Database and Specify a New Jobname

The use pass consists of a new model and new loads. Therefore, the first step is to clear the existing database. This has the same effect as leaving and re-entering the program. To clear the database, use one of these methods:

Command(s): /CLEAR

GUI: Utility Menu> File> Clear & Start New

By default, clearing the database causes the START.ANS file to be reread. (You can change this setting if you so desire.)

Caution

If you are using the command input method to clear the database, additional commands may not be stacked on the same line (using the $ delimiter) as the /CLEAR command.

Be sure to define a jobname that is different from the one used for the generation pass. This way, you can ensure that no generation pass files will be overwritten. To define a jobname, use one of these methods:

Command(s): /FILNAME

GUI: Utility Menu >File> Change Jobname

 

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Using Substructuring

10.2.2.2. Build the Model

This step is performed in PREP7 and consists of the following tasks:

1.Define MATRIX50 (the superelement) as one of the element types. Use one of these methods:

Command(s): ET

GUI: Main Menu> Preprocessor> Element Type> Add/Edit/Delete

2.Define other element types for any nonsuperelements. Nonlinear behavior may or may not be allowed, depending on the type of analysis to be performed.

3.Define element real constants and material properties for the nonsuperelements. Nonlinear properties may or may not be allowed, depending on the type of analysis to be performed.

4.Define the geometry of the nonsuperelements. Take special care in defining the interfaces where the nonsuperelements connect to the superelements. The interface node locations must exactly match the locations of the corresponding master nodes on the superelements (see Figure 10.3: Node Loca- tions (p. 271)).

There are three ways to ensure connectivity at these interfaces:

Use the same node numbers as the ones in the generation pass.

Use the same node number increment (or offset) between interface nodes in the generation pass and interface nodes in the use pass. (Use SETRAN, as described below in step 5b.)

Couple the two sets of nodes in all degrees of freedom using the CP family of commands [CP, CPINTF, etc.]. This method is helpful if you cannot use one of the above two methods. For example, to define a set of coupled degrees of freedom use one of the following:

Command(s): CP

GUI: Main Menu> Preprocessor> Coupling/Ceqn> Couple DOFs

If the superelement is not connected to any other elements, you do not need to define any nodes in the use pass.

Figure 10.3: Node Locations

Interface nodes between superelement and nonsuperelement must exactly match the master node locations.

5.Define the superelement by pointing to the proper element type reference number and reading in the superelement matrix. To point to the element type:

Command(s): TYPE

GUI: Main Menu> Preprocessor> Modeling> Create> Elements> Elem Attributes

Now read in the superelement matrix using one of these methods (you may first need to use other commands to modify the matrix, as explained below):

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Command(s): SE

GUI: Main Menu> Preprocessor> Modeling> Create> Elements> Superelements> From .SUB

File

a.If there are no nonsuperelements in the model, or if there are nonsuperelements and the interface nodes have the exact same node numbers as the master nodes on the superelement, then simply read in the superelement using the SE command:

TYPE,...! Element type reference number

SE,GEN! Reads in superelement from file GEN.SUB

The Sename field on the SE command shown above identifies the name of the superelement matrix file. The extension .SUB is assumed, so the complete file name is Sename.SUB (GEN.SUB in the above example). The superelement is given the next available element number.

b.If there are nonsuperelements in the model and the interface nodes have a constant node number offset from the master nodes, you must first create a new superelement matrix with new node numbers and then read in the new matrix.

To create a new superelement matrix, use one of these methods:

Command(s): SETRAN

GUI: Main Menu> Preprocessor> Modeling> Create> Elements> Superelements> By CS Transfer

Main Menu> Preprocessor> Modeling> Create> Elements> Superelements> By Geom Offset

To read in the new matrix, use one of these methods:

Command(s): SE

GUI: Main Menu> Preprocessor> Modeling> Create> Elements> Superelements> From

.SUB File

For example, given an existing superelement matrix file GEN.SUB and a node number offset of 2000, the commands would be:

SETRAN,GEN,,2000,GEN2,SUB

! Creates new superelement GEN2.SUB with

 

!

node offset = 2000

TYPE,...

! Element type

reference number

SE,GEN2

!

Reads in new

superelement from file GEN2.SUB

c.If there are nonsuperelements in the model and the interface nodes have no relationship with the master nodes (as would be the case with automatically meshed models), first observe the following caution.

Caution

It is quite likely that the node numbers of the master nodes from the generation pass overlap with node numbers in the use pass model. In such cases, reading in the superelement [SE] will cause existing use pass nodes to be overwritten by the superelement's master nodes. To avoid overwriting existing nodes, use a node number offset [SETRAN] before reading in the superelement. In any case, save the database [SAVE] before issuing the SE command.

Thus you should first save the database [SAVE], use the SETRAN command to create a new superelement matrix with a node number offset, and then use the SE command to read in

 

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Using Substructuring

the new matrix. The CPINTF command (Main Menu> Preprocessor> Coupling/Ceqn> Coincident Nodes) can then be used to connect the pairs of nodes at the interface. For example, given a superelement matrix file called GEN.SUB:

*GET,MAXNOD,NODE,,NUM,MAX

! MAXNOD

= maximum node number

SETRAN,GEN,,MAXNOD,GEN2,SUB

! Creates

new superelement with

 

!

node

offset = MAXNOD, name = GEN2.SUB

SE,GEN2

! Reads in new superelement

NSEL,...

! Select

all nodes at the interface

CPINTF,ALL

! Couples

each pair of interface nodes in

 

! all DOF

 

NSEL,ALL

 

 

 

d.If the superelement is to be transformed - moved or copied to a different position, or symmetrically reflected - you must first use the SETRAN command or SESYMM command (Main Menu> Preprocessor> Modeling> Create> Elements> Superelements> By Reflection), with the appropriate node number offsets, to create new superelement matrix files and then use SE to read in the new matrices. Connecting the superelements to the nonsuperelements is done the same way as above - by using common node numbers, a constant node number offset, or the CPINTF command.

Note

If you use SETRAN to transfer the superelement to a different coordinate system,

the superelement's master nodes are rotated with it by default. This is typically useful if the original superelement's master nodes are rotated, into a cylindrical system for example. (In this case, the transfer does not effect the superelement stiffness matrix.) If the original superelement has no rotated nodes, it is likely that the transferred superelement will not need rotated nodes either. You can prevent node rotation in such cases by setting the NOROT field on SETRAN to 1. (The superelement stiffness matrix and load vector are modified by the program for this type of transfer.)

6.Verify the location of the superelement using graphics displays and listings. Superelements are represented by an edge outline display, the data for which are written to the matrix file in the generation pass. To produce a graphics display:

Command(s): EPLOT

GUI: Utility Menu> Plot> Elements

To produce a listing:

Command(s): SELIST

GUI: Utility Menu> List> Other> Superelem Data

7.Save the complete model database:

Command(s): SAVE

GUI: Utility Menu> File> Save as Jobname.db

Leave PREP7 using one of these methods:

Command(s): FINISH GUI: Main Menu> Finish

10.2.2.3. Apply Loads and Obtain the Solution

This step is performed during the solution phase of the analysis. The procedure to obtain the use-pass solution depends on the analysis type. As mentioned earlier, you can subject a superelement to any

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type of analysis. You should, of course, have the appropriate matrices generated during the generation pass. For example, if you intend to do a structural dynamic analysis, the mass matrix must be available. The procedure is as follows:

1.Enter SOLUTION using one of these methods:

Command(s): /SOLU

GUI: Main Menu> Solution

2.Define the analysis type and analysis options.

For large rotation analyses - turn large deformation effects on [NLGEOM,ON], and define the proper number of substeps for the nonlinear analysis.

3.Apply loads on the nonsuperelements. These may consist of DOF constraints and symmetry conditions [D family of commands], force loads [F family], surface loads [SF family], body loads [BF family], and inertia loads [ACEL, etc.]. Remember that inertia loads will affect the superelement only if its mass matrix was generated in the generation pass.

Note

For large rotation analyses, be sure to apply the proper constraints in this step.

4.Apply superelement load vectors (if any) using one of these methods:

Command(s): SFE

GUI: Main Menu> Solution> Define Loads> Apply> Load Vector> For Superelement

One load vector per load step (created during the generation pass) is available on the superelement matrix file, and is identified by its reference number:

SFE,63,1,SELV,0,0.75

applies, on element number 63, load vector number 1, with the load applied as a real load and with a scale factor of 0.75. Thus the ELEM field represents the element number of the superelement, LKEY represents the load vector number (default = 1), Lab is SELV, KVAL is for a real or imaginary load vector, and VAL1 represents the scale factor (default = 0.0). (See the SFE command description for more information.)

Note

The load vector orientation is fixed (frozen) to the superelement, so if the superelement is used in a rotated position, the load vector rotates with it. The same applies to the degree of freedom directions (UX, UY, ROTY, etc.). They too are fixed to the superelement and will rotate with the superelement if it is rotated (unless NOROT = 1 on the SETRAN command, in which case the nodal coordinate systems will not be rotated).

5.Specify load step options that are appropriate for the analysis type. Use the EQSLV command to select an appropriate equation solver based on the chosen analysis type and the physics of the problem.

6.Initiate the solution:

 

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