Creating 1D elements and defining cross-section to 1D elements in a mesh

Objective

The objective of this project is to extract the mid-surface of the component & generate a mesh for that. The next objective is to deploy the 1D elements on that & defining the cross-section to the 1D elements and assigning the property to them.
For this purpose, we are given the following CAD model & we need to create 1D elements on this component with the following given cross-section and DOF (a,b,c,d,e,f on the model refers to the respective element at that position).

a. Rod element:- with only translational DOF and RBE2 link

Cross-Section: 'BOX'- Dimension a= 12 mm

                              dimension b=10 mm

                              Thickness t= 0.75 mm

b. Beam element:- with all DOF and RBE3 link

Cross-Section: 'I' Section- Dimension a= 8 mm

                                     Dimension b= 10 mm

                                     Dimension c= 8.5 mm

                                     Thickness t1= 0.75 mm

                                     Thickness t2= .6 mm

                                     Thickness t3= .6 mm

c. Bar element:-  with only x and y DOFs With RBE3 link

Cross-section: 'CROSS' section- Dimension DIM1= 5 mm

                                             Thickness DIM2= 1.2 mm

                                             Dimension DIM3= 10 mm

                                             Thickness DIM4= 1.2mm

d. & e. apply the mass of magnitude 10 with the 'RBE2' link

f. Join the two components with 'Spring' elements.

Procedure

First, the given 'PARALLEL_BRACKET.IGS' model is imported as geometry into the Hyperworks Optistruct workspace.

Now, to generate a mesh for FEA for this model, we first need to extract the mid-surface of this component. Midsurface modeling is a technique for creating a simplified shell representation of a solid model. It is beneficial to use midsurface meshing when the thickness of the component is small compared to the other two dimensions. And if the thickness is constant or can be approximated to a constant value. Midsurface modeling helps to reduce the computational expense of analyzing a complete solid model when a shell model with a defined thickness and fewer details is suitable for the analysis.

Here we are going to extract the midsurface for the upper part & lower part separately as two different components, i.e., midsurface_1 & midsurface_2, respectively.
To extract the midsurface, go to midsurface & select auto midsurface for surfs & closed solid. Under extract options, change to skin offset, to extract a more accurate midsurface in this case. Then select the upper bracket & extract. Repeat the same for the lower bracket.

The next step is to assign the property (thickness) & material to these two components created. Material (steel) is created by right-clicking in the model tree & selecting 'create>material'. Similarly, by choosing 'create>property', a property is created, named as 'bracket'.
Under 'bracket' parameters, the thickness is changed to 2.5mm, the material is specified as 'Steel' & all other parameters are kept default.

Now, under the model tree, 'midsurface_1' is selected, and 'bracket' is assigned as the property & material automatically changes to 'Steel'. Similarly, the same property is assigned to the 'midsurface_2'.

The next step is to create the 2D mesh for both surfaces. Before meshing, a washer split of 5mm is added to all the circular holes, so as to capture the geometry accurately in meshing.

Next, under the 2D toolbar, automesh is selected. Element size is specified as 5, mesh type is selected as mixed & both surfaces are selected. Next, the number of nodes are adjusted around circular holes, to generate the final mesh, shown below.

Next, we need to add the 1D elements as specified. Before doing that, let's first create the property & sections for Rod, Bar, & Beam element & assign the created sections to the respective property.

To create the sections for rod, bar & beam elements, we need to switch to the Hyperbeam view, which can be done either by going to '1D>Hyperbeam>standard section>create' or by simply clicking on the 'Hyperbeam view' button in the model tree panel on left.

First, the box section is created by 'right click>create>standard section>Hypermesh>Thinwalled box' & the given dimensions are specified as the parameters, to generate the required section as shown below & is renamed to 'box_rod'.

Similarly, the I section is created by 'right click>create>standard section>Hypermesh>Standard I section' & the given dimensions are specified as the parameters, to generate the required section as shown below & is renamed to 'I_beam'.

Similarly, the cross section is created by 'right click>create>standard section>OptiStruct>CROSS' & the given dimensions are specified as the parameters, to generate the required section as shown below & is renamed to 'cross_bar'.

Next, three properties are created, namely, cross_bar, box_rod, & I_beam. For property cross_bar, the card image is changed to PBAR & cross_bar is specified as the beam section. Similarly, for property box_rod & I_beam, card image is changed to PROD & PBEAM, respectively, & box_rod & I_beam respectively are assigned as the beam section.

Next, RBE2 & RBE3 links are deployed for the positions a,b,c,d,e shown in the first figure above.
The difference between RBE2 & RBE3 links is that the RBE2 link is a rigid link of infinite stiffness & will distribute the load equally on each element. On the other hand, the RBE3 link distributes the load proportional to the distance of the element.
1D elements can be created by going to the 1D toolbar at the bottom & selecting the type of element required.

For position 'a' the RBE2/rigids link is selected & node selection is changed to multiple nodes > calculate node. Element type is set to RBE2. And, for the translational degree of freedom dof1, dof2, & dof3 are marked checked.
Similarly, for position 'b' the RBE3 link is selected & node selection is changed to multiple nodes > calculate node. Element type is set to RBE3. And, for all degrees of freedom dof1, dof2, dof3, dof4, dof5, & dof6 are marked checked.
For position 'c' the RBE3 link is selected & node selection is changed to multiple nodes > calculate node. Element type is set to RBE3. And, for x & y degree of freedom dof1 & dof2 are marked checked.
And, for position 'c' the RBE2/rigids link is selected & node selection is changed to multiple nodes > calculate node. Element type is set to RBE2 & all other parameters are kept default.

Next, mass is applied at the position 'd' & 'e' by selecting '1D>masses'. Corresponding nodes are selected, the element type is changed to CMASS1 & mass is assigned a magnitude of 10.
Also, spring element is added to the position 'f' by selecting '1D>springs'. Corresponding nodes are selected, the element type is changed to HMSPRING.

Next, rod element is deployed at position 'a' by selecting '1d>rods'. Corresponding nodes are selected, the element type is changed to CROD & for property 'box_rod' is selected.
Similarly, beam element is deployed at position 'b' by selecting '1d>bars'. Corresponding nodes are selected, the element type is changed to CBEAM & for property 'I_beam' is selected.
And, bar element is deployed at position 'c' by selecting '1d>bars'. Corresponding nodes are selected, the element type is changed to CBAR & for property 'cross_bar' is selected.

And, the final meshed model is obtained, as shown below.