Weight and Center of Gravity Calculator


The Weight and Center of Gravity Calculator can be accessed from the "Tools: Weight and Center of Gravity..." command. The requirements for this tool are as follows:

  1. You must have a mass density assigned for the material for each part in your model.

  2. You must have performed the "Analysis: Check Model" command.

  3. If you do not assign a value for gravity in the "Analysis Parameters" dialog, you will be prompted to enter one before the calculations are performed. The value is entered using the Model Units.

Once the results are calculated, the "Model Information" section at the top of the dialog will list the volume, weight, center of gravity, mass moment of inertia and mass product of inertia values for the entire assembly. The spreadsheet section will list these values for each individual part of the assembly. All results use the Model Units.

 

An HTML report of these values can be created by pressing the "HTML" button. A csv file, which can be opened in a spreadsheet program, can be created by pressing the "Export" button. In addition, two text files are created by the processor. Use a text editor (such as NotePad or Word) to open these statistics (.LG9) and summary (.WCG) files.

 

Tip

When creating an HTML report, the default ALGOR logo can be replaced with a custom logo. Use the "Tools: Options: Reporting" tab to specify the custom logo.

 

The mass moment of inertia is by default calculated about the axes passing through the origin (0,0,0). Use the parallel axis theorem and a hand-calculation to calculate the mass moment of inertia about a different axis.

 

Caution

The mass moment of inertia about the longitudinal axis, I1 is not calculated for line elements (beams, trusses, etc.). Only the m×R2 effect is considered, where R is the distance from the reference point to the element. The mass moment of inertia about the other axes, I2 and I3, are calculated based on the slender rod formula (I2 = I3 = M×L2/12).

 

 

If the model includes parts created from 2-D elements, the statistics (.LG9) and summary (.WCG) files contain the area and area moment of inertia of the 2-D cross section. Similar results can be obtained for cross sections drawn in a sketch. See the page "Meshing Overview: Creating and Modifying Geometry in the FEA Editor: Drawing Planes".

 

Caution

The results for 2-D axisymmetric elements are based on a full revolution, not 1 radian.

 

Tip

Another result of the Weight and Center of Gravity calculator is the ability to display the volume of each element in the Results environment ("Results: Element Properties: Volume"). The volume can also be used in custom calculations ("Results Options:Custom Results"). Note: the file that contains the volume results is deleted whenever any analysis is performed; thus, it may be necessary to re-run the weight and center of gravity calculator in order to display the volume results.  

 

Note

Nodal forces and moments have no effect on the weight and center of gravity results.

 

Note

Lumped masses and lumped mass moments of inertia may or may not be included in the weight and center of gravity calculation depending on the analysis type. Also, the results with masses of different values in the X, Y, and Z directions may be based on the X mass only. Refer to the weight and center of gravity summary file (.WCG) to see how it is treated for each situation.