vk.com/club152685050Substructuring | vk.com/id446425943

The following figure shows the data flow for a complete substructure analysis and some of the files involved.

Figure 10.1: Applicable Solvers in a Typical Substructuring Analysis

10.2.1. Step 1: Generation Pass (Creating the Superelement)

The generation pass is where you condense a group of "regular" finite elements into a single superelement. The condensation is done by identifying a set of master degrees of freedom, used mainly to define the interface between the superelement and other elements and to capture dynamic characteristics for dynamic analyses. Figure 10.2: Example of a Substructuring Application (p. 264) shows a plate-like

structure that is to be analyzed with contact (interface) elements. Since the contact elements require an iterative solution, substructuring the plate portion can result in a significant savings in computer time. The master DOF required in this case are the degrees of freedom that connect the plate to the contact elements.

Figure 10.2: Example of a Substructuring Application

Generating a superelement involves two primary tasks: 10.2.1.1. Building the Model

10.2.1.2. Applying Loads and Creating the Superelement Matrices

10.2.1.1. Building the Model

In this step, you specify the jobname and analysis title and then use /PREP7 to define the element types, element real constants, material properties, and the model geometry. These tasks are common to most analyses and are described in the Basic Analysis Guide. For the generation pass, you should keep in mind the following additional points:

Jobname-This takes on special significance in a substructure analysis. By using jobnames effectively, you can eliminate much of the file handling inherent in a three-pass analysis.

Use one of these methods to specify the jobname:

Command(s): /FILNAME

GUI: Utility Menu> File> Change Jobname

For example,

/FILNAME,GEN

gives the jobname GEN to all files produced by the generation pass. The default jobname is file or whatever name was specified while entering the program.

Element Types - Most element types can be used to generate a substructure. In general, the only restriction is that elements within the superelement are assumed to be linear and cannot use Lagrange multipliers. If you include bilinear elements, they will be treated as linear elements (in their initial state).

Caution

Coupled-field elements used in a direct method coupled-field analysis with load vector coupling are not valid in a substructure analysis. Other elements in the same shape family should be used instead. See the Coupled-Field Analysis Guide for details. In addition, elements with Lagrange multipliers cannot be used in substructuring. These type of elements include MPC184, CONTA171, CONTA172, CONTA173, CONTA174, CONTA175, CONTA176, CONTA177, and CONTA178 with appropriate KEYOPT(2) setting, and elements PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, SOLID272, SOLID273, and SOLID285 when using KEYOPT(6) > 0.

Material Properties - Define all necessary material properties. For example, if the mass matrix is to be generated, density (DENS) (or mass in some form) must be defined; if the specific heat matrix is to be generated, the specific heat (C) must be defined; and so on. Again, because a superelement is linear, any nonlinear material properties will be ignored.

Model Generation - In the generation pass, you are mainly concerned with creating the superelement portion of the model. The nonsuperelement portion, if any, is defined later in the use pass. However, you should plan the modeling approach for both portions before you start building the model. In particular, decide on how you want to connect the superelement to the other elements. To ensure the connection, use the same node numbers at the interface. (Other methods requiring less effort on your part are discussed in the use pass section later in this chapter.)

Edge Outline - Adjust the edge outline used to plot the superelement in the use pass [/EDGE]. A smaller angle will produce more edges.