FEA | FEA Model Updating

FEA Model Updating changes the Properties of selected FEA Objects on an FEA model so that its modal parameters more closely match a set of experimental (EMA) modal parameters.

To perform FEA Model Updating, the following items are required,

  1. Mode shapes of the FEA structure corresponding to its current FEA properties

  2. FEA structure model containing the FEA Objects with properties to be updated

  3. EMA modal parameters

This command repeated executes the SDM command to solve for new mode shapes using FEA properties from a user-defined solution space of FEA Properties

FEA | Point Matching is only required if MAC values between the FEA, Solution, and EMA mode shapes are desired.

Difference Between SDM and FEA Model Updating

FEA Model Updating can be focused on portions of the structure to be updated, and FEA-EMA mode pairs to be used for ordering the solutions from best to worst. You can,

Solution Order

The FEA Model Updating solutions are ordered from best to worst based on the values of an Error function.

Command Requirements

Before this command can be executed, several items are required,

  1. A structure model with FEA Objects attached to it

  2. A Shape Table containing FEA mode shapes that display animate correctly of the FEA model.

  3. A Shape Table containing EMA mode shapes

To initiate an FEA Model Updating calculation,

Shape Table Selection Dialog Box.

The FEA Model Updating window will open, as shown below.

FEA Model Updating Window Showing One Selected Mode Pair &One Selected Property for Updating.

Upper Spreadsheet

The Upper spreadsheet list the modal frequencies and MAC values of all matching FEA-EMA mode pairs.  Each FEA-EMA mode pair is the pair with the maximum MAC value between all pairs of FEA and EMA mode shapes.

If FEA-EMA mode pairs are selected, only those pairs are used for calculating the Error function.  In none are selected, all pairs will be used for calculating the Error function.

Lower Spreadsheet

The lower spreadsheet lists the FEA Properties of all visible FEA Objects on the structure model.

If properties are selected, only those properties are used to define the solution space.  In none are selected, all properties will be used to define the solution space.

FEA Properties That Can Be Updated

Below is a Table of the Properties that can be updated using FEA Model Updating.


FEA Object

Property to Update






cross sectional area,
material (Elasticity, Poisson's ratio, Density)


cross sectional area & inertias
material (Elasticity, Poisson's ratio, Density)


material (Elasticity, Poisson's ratio, Density)


material (Elasticity, Poisson's ratio, Density)

FEA Properties That Can Be Updated Using FEA Model Updating.

Solution Space

Each Property to be used on the lower spreadsheet has a Minimum, Maximum & Steps column.  These three columns together define the solution space for the Property.

The Minimum, Maximum, & Steps of all (or selected) Properties in the lower spreadsheet define the solution space over which solutions are calculated.

Solution Space Example

Calculation Process

Error Function

To order the solutions, an Error function is calculated for each solution.  The Error function is equal to the summation of the error between the frequencies of each selected FEA & EMA pair, as shown above.  If Include MAC is also depressed for a selected mode  pair, a second term (1 - MAC) is added to the Error function, as shown below 

The use of mode shape MAC values is optional for calculating the Error function.

The formula for the Error function is:


Fup = Updated FEA frequency

Fema = EMA frequency

MACup = MAC value between each Updated FEA & EMA mode shape pair.

As the solution calculation progresses through the solution space, the current minimum Error function is listed in the Error box on the Toolbar.

Before Starting a Calculation

Only the modal parameters of the selected mode pairs will be used to calculate the Error function.

If no Target modal parameters are entered for a selected mode pair, that pair will be excluded from the Error function calculation

If no properties are selected, the Minimum, Maximum & Step of all FEA Properties in the lower spreadsheet will be used to define the solution space.

FEA Model Updating Window After Solutions are Calculated.

Solution | Calculate

Calculates the solutions for all (or selected) FEA Properties in the solution space defined in the lower spreadsheet.

Solution | Stop Calculation

This command is enabled after Solution | Calculate has been executed.

Solution Scroll Bar

After the calculation process is completed or stopped, the Solution scroll bar is enabled on the right hand side of the window.

Display | Split

Toggles the spreadsheet display between Upper/Lower and Left/Right format.

Display | Spreadsheets

When this command is checked, the solutions are displayed using two spreadsheets.

Display | Bar Graphics

When this command is checked, the solutions are displayed graphically, as shown below.

Bar Charts

The upper left bar graph shows two bars for each mode pair.

The upper right bar graph displays MAC values using two bars for each mode pair.

The lower bar graph displays the Current & Solution values of the FEA Properties.

Bar Chart Display.

Solution | Save Solution Mode Shapes

Saves the mode shapes into a Shape Table that result from the current FEA Properties in the lower spreadsheet.

Before executing this command scroll the Solution Scroll Bar on the right hand side to display the desired solution.