Mass Properties
In the Definitions toolbar, select Physics Utilities and click to add a Mass Properties () node and compute the variables for mass, volume, center of gravity, and moment of inertia. Under a Component you can also right-click Definitions to add this feature from the Physics Utilities submenu.
The Settings window for a Mass Properties node includes the following sections:
Source Selection
The source selection defines the source for the mass property variables — the part of the geometry over which the program computes the measurement variables and to which the density contribution is limited. You can add other density contributions by right-clicking the Mass Properties node and choosing Mass Contributions (); see Mass Contributions.
From the Geometric entity level list, select Domain (the default), Boundary, Edge (3D only), or Point. Select Manual or All domains (the default), All boundaries, All edges, or All points from the Selection list. If Manual is selected, select geometric entities in the Graphics window.
Density
In this section you define the source of the density values used for computing some of the mass properties using the Density source list:
•
Choose User defined (the default), to define a value or expression for the density in the Density expression field (SI unit: kg/m3). For example, material.rho, which is a variable for the density from the materials in the model. Use the Density input frame list to specify the frame in which the density is given. The default Material frame indicates that the given density expression is not a function of the strain; Spatial frame indicates that the density expression is an instantaneous value dependent on the material strain. Note that the actual coordinate names — typically (x, y, z) or (X, Y, Z) in 3D — are displayed for each frame.
•
Choose From physics interface to take the density from an active physics interface in the geometry. Not all physics interfaces define such density variables. If there are two or more physics interfaces that provide a density in the same domain, the density used can be from any of the physics interfaces (but the density is then typically the same in those physics interfaces). The Include adjacent entities of lower dimension check box is selected by default to include the density also on adjacent boundaries, edges, and points.
•
Choose From specified physics interface to take the density from a physics interface that you choose from the Physics list. The Include adjacent entities of lower dimension check box is selected by default to include the density also on adjacent boundaries, edges, and points.
Variables
In this section, select the variables to create and which body shape they should refer to. From the Frame list, choose the coordinates to use in the definition of the mass properties. For example, selecting the Material frame means that the center of mass is computed for the undeformed shape; selecting the Spatial frame returns the center of mass in the deformed configuration. In these cases, the density is transformed to the selected frame before integration. Choosing the Geometry frame has a slightly different meaning: the density in the geometry frame is assumed to be the same as in the material frame. That is, the difference between the geometry and material frames do not imply any material strain. Note that the actual coordinate names — typically (x, y, z) or (X, Y, Z) in 3D — are displayed for each frame.
The following check boxes are selected by default to create and compute the corresponding mass property:
•
Create volume variable to create a variable for the volume of the selected geometric entities.
•
Create mass variable to create a variable for the mass of the selected geometric entities.
•
Create center of mass variables to create variables for the center of mass of the selected geometric entities.
•
Create moment of inertia variables to create variables for the moment of inertia of the selected geometric entities.
•
Create principal moment of inertia variables to create variables for the principal moment of inertia of the selected geometric entities.
These variables are available in, for example, a Global Evaluation node under Results>Derived Values. Click the Insert Expression () or Replace Expression () button to choose one of the mass property values such as Model>Component1>Definitions>Mass Properties1>Center of mass>mass1.CMY for the Y-component of the center of mass.
Integration Settings
Specify the integration order of the integration used to compute the output variables (see integration order in the Glossary). The default in the Integration order field is 4 (which typically is twice the order of the shape order function for the physics).