Organizing a Model
Organizing model data can be beneficial when creating a valid solver input file. Basic tasks used to organize model data such as placing elements and loads into groups (collectors), organizing collectors into assemblies, renaming, deleting, reordering, and renumbering are discussed in the exercise for this module.
Model organization is at the heart of a quality Finite Element Analysis. The model can be organized in a multitude of different ways as desired by the user, but below are the basics for model organization.
Collectors - The basis for model organization is the collector. HyperMesh has 10 different types of collectors;
- Component – Contains Elements and Geometry
- Multibody – Contains Ellipsoids, Mbjoints, Mbplanes and Sensors.
- Assembly – Contains Components, Multibodies and Assemblies.
- Load – Contains Loads and Constraints.
- Property* – Used to define the properties assigned to elements or Component Collectors
- Material* - Used to define the material values Property Collectors
- System – Contains user defined systems.
- Vector – Contains vectors.
- Beam Section – Contains beam sections.
*NOTE: Property and Material collectors do not “contain” any entities and are used to define material and physical properties in the model. They are called collectors for uniformity.
To learn more about collectors, select one of the topics below.
Collectors can be created in a number of ways. All of the methods outlined will provide the same result. The preferred method is to use the Model Browser to create the collectors.
Model Browser
Right Clicking in the Model Browser opens a menu from which the selection of Create allows for creation of any type of collector.
The Right click menu in the Model Browser also allows you to edit, rename, and delete collectors as well.
Pull down Menus
Selecting the Collectors menu in the menu bar and then selecting Create will provide the ability to create any of the non material and property collectors.
Material and Property Collectors can be created in a similar manner using the Material and Property menus from the menu bar.
Icon Toolbars
The Collector toolbar is found below the Graphics Area. Unlike the Model Browser and menu bar options, the toolbar will open the panels instead of the dialog box for collector creation. Mouse over the icons in the toolbar to see a short description of each.
The Systems Collector icon also contains additional icons in that can be selected. Mouse over the icons below to see a short description of each.
The Current Collector determines which collector new entities are placed in. In the Model Browser the Current collector will be in BOLD.
Note: The mid2 collector is in a bold font and thus is the Current collector.
The Current Collector can be assigned by right clicking on a collector which opens a menu that will allow it to be made current.
Organize is a tool that can be used to move entities to different collectors. It can be accessed on the Tool page and will open the panel shown below. Mouse over the different options to see a short description of each.
In their simplest form, groups and components are containers for entities. Groups can contain geometry, nodes, elements, systems etc. HyperMesh further breaks this down by entity type. Geometry (points, lines, surfaces, solids) and elements go into component collectors. Loads (SPC, forces, grav card etc) go into load collectors. HyperMesh also has system, cross-section, property (pshell, psolid etc), and material (mat 1 etc) collectors. One of the big differences between groups and collectors is that an entity can only reside in one collector at a time in HyperMesh but can exist in many groups in Patran. While this intially may sound like a limitation, it actually turns out to be a strength as described in the following sections.
Component Collectors
As the model is built, the elements are organized into components that make sense to the user. Typically elements are turned on and off by component, so a well organized model is very helpful. This is in addition to masking of individual entities. Geometry and elements are turned on/off separately from each other using the Model Browser. There is an icon for each as shown below. Click on the appropriate icon to toggle the entities on and off.
This concept of an entity existing in only one component can be difficult for Aero models since typically many groups would exist that would allow the model to be displayed appropriately. An example for a wing might be a group with the upper skin, lower skin, spar, leading edge, and frames components. In HyperMesh, to turn the “wing” on, the components would need to be clicked one by one. That’s where the concept of assemblies are used as a component can exist in many assemblies at once.
Components can be dragged and dropped into assemblies in the Model Browser. Click on a component and then drag it into the assembly. Turn on and off entire assemblies using the appropriate icons in the assembly tree.
Why is this method of organization effective?
If an element exists in a component, and that component exists in many assemblies, any change to the element is automatically propagated up the chain. If an element was split in half, the two new elements would then be in the original component and automatically the assemblies are updated as well because the assemblies contain the components. There is no need to then add the new elements to all of the other assemblies to maintain the model organization like you would in Patran.
Lots of colors can be used when setting up components and assemblies. HyperMesh colors all the elements by component (by default) so by seeing the color, it is automatically known which component the element resides in. It can make models that look like a patchwork quilt, but a useful one. The colors can be changed at anytime using the Model Browser to set a new color to a collector. The color is changed by clicking the right mouse button on the color swatch in the Color column of the Model Browser for the collector.
Property Association
Another big difference between groups and components is that a component can take on a property association. In Patran the property function is opened and then you either add geometry or elements to the properties that exist. This assigns the property directly to the element. In HyperMesh, the property can be assigned to the component or the element directly. If it’s applied to the component, then by the simple fact that the element exists in the component it automatically gets a property. The rules for property assignment are as follows:
Properties are assigned to elements or components using the following rules in order:
- If a property is assigned directly to an element, then that property is the elements property regardless of any other property assignments. Properties are assigned directly to elements on the properties:assign sub-panel.
- If there is no property assigned directly to an element, then the property assigned to the component the element is organized into becomes the elements property. Properties are assigned to components on the components:assign sub-panel.
- If there is no property assigned to the component, then the element has no property assignment.
The benefit of assigning properties to components is that any modification to an element doesn’t result in a property loss. Going back to splitting an element in two, in Patran if the element is split, the property has to be re-assigned to the new elements. In HyperMesh if the component has the property, any change to elements makes no difference because simply residing in the component gives them a property.