SDM | Modal Sensitivity

Modal Sensitivity calculates and orders multiple SDM solutions over a user-defined solution space of physical properties.

This command shows you how much physical modification is necessary to change the modal properties of a structure so that they match Target values.

The following Table lists the FEA properties that can be used to define a solution space for this command.


FEA Object


Target Modal Parameter









frequency, damping


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

frequency, damping


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

frequency, damping


(Elasticity, Poisson's ratio, Density)

frequency, damping


(Elasticity, Poisson's ratio, Density)

frequency, damping

FEA Properties and Target Modal Parameters.

Material properties are Young's Modulus of Elasticity, Poisson's ratio, and Density

When this command is executed, the Shape Table selection dialog box will open.

The UMM mode shapes must animate correctly on the structure model before using them with this command.

Modal Sensitivity Spreadsheets  (in Upper/Lower Display format).

Upper Spreadsheet

The upper spreadsheet lists the current, target & solution modal parameters.

If one or more mode pairs are selected, then only those solution parameters are compared with target modal parameters.
If no target modal parameters are entered, the SDM solutions are listed in the order calculated.

Lower Spreadsheet

The lower spreadsheet lists the current and solution values of the Properties of all visible FEA Objects on the structure model.

Solution Space

Each Property on the lower spreadsheet has a Minimum, Maximum and Steps column.  These three columns together define the solution space for each Property.

The Minimum, Maximum, and Steps of all or selected Properties define the solution space. SDM solutions are calculated for all values in the solution space.

Solution Space Example

Error Function

If mode pairs are selected in the upper spreadsheet, an Error function is calculated, and used to order the solutions from best to worst.

The error is a summation of terms, one for each non-zero Target & Solution frequency and/or damping pair in the upper spreadsheet.


Fs = solution frequency,  Ft = target frequency

Ds = solution damping,  Dt = target damping

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.

Best Solution Shown in the Spreadsheets.

Solution | Calculate

Calculates all SDM solutions for all or selected FEA Properties in the user-defined solution space in the lower spreadsheet

Solution | Stop Calculation

Stops the SDM calculation process and displays the solutions that have already been calculated

Solution Scroll Bar

When the SDM calculation is completed or stopped, a Solution Scroll Bar will be enabled on the right side of the Modal Sensitivity window.

Display | Split

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

Display | Spreadsheets

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

Display | Bar Graphics

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

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.