Defining trim variables

You use the Trim Variables Manager command to define the trim conditions for a trim analysis.

The Trim Variables Manager command lets you:

• Work more efficiently because you can define all of the aerodynamic parameters and trim variables for the trim analysis from a single dialog box.

• Avoid creating inconsistencies in the definitions of the AELINK, AESTAT, and TRIM bulk entries.Note: AELINK, AESTAT, and TRIM are the Simcenter Nastran bulk entries that the software creates directly from the Trim Variables Manager dialog box.

From the Trim Variables Manager dialog box, you can do the following:

• Define the trim properties such as Mach number, dynamic pressure, and trim analysis type.

• Specify the standard and user-defined trim variables.

• Assign values to the trim variables.Note: In the table, Free indicates that no value is assigned to a trim variable. Thus, the trim variable is unconstrained.

• Link the motion of the trim variables to one another.

Specifying trim properties

When you perform a trim analysis, the software requires values for Mach number and dynamic pressure. You specify the Mach number in the Trim Variables Manager dialog box, in the Mach Number column of the table. The value for dynamic pressure that the software uses depends on how you define the values in the Pressure Altitude and Dynamic Pressure columns.

• If you specify a value in the Dynamic Pressure column and leave the corresponding cell in the Pressure Altitude column blank, the software uses the value in the Dynamic Pressure column.

• If you specify a value in the Pressure Altitude column, the software calculates the value for the dynamic pressure from the Mach number value and the density of air corresponding to the pressure altitude value. The software uses the International Standard Atmosphere (ISA) definition to obtain the density for a given pressure altitude. The software displays the calculated dynamic pressure value in the Dynamic Pressure column.

Linking trim variables

In a trim analysis, you may want to relate the motion of a trim variable to the motion of other trim variables. You can accomplish this by linking the trim variables. When you link trim variables, you create a constraint equation that is a linear combination of the trim variables.

For example, suppose that you want to specify the angular deflection of an elevator to be twice the angular deflection of an aileron and in the same direction. Assuming that the positive sense of both angular deflections are the same, the constraint equation would be as follows:

Elevator + \left( { - 2.0} \right)Aileron = 0

where Elevator and Aileron are the angular deflections of the elevator and aileron, respectively.

You use the Trim Variables Manager command to link trim variables as follows:

1. In the Trim Variables Manager dialog box, right-click the cell of a trim variable that you want to include in the constraint equation and choose Edit.

2. In the Edit Trim Variable dialog box, from the Constraint list, select Linked.

3. In the Coefficients column, in the cells of the other trim variables that you want to include in the constraint equation, type the values for the coefficients in the constraint equation.In the example, assuming that you are linking the aileron motion to the elevator motion, in the Coefficients column, in the cell for the aileron, type -2.0.After you enter the coefficients, the software displays the constraint equation in the Edit Trim Variable dialog box, in the Coefficients box.In the Trim Variables Manager dialog box, in the table, the software displays Linked in the cells of trim variables to which other trim variables are linked.

Where do I find it?

Application	Pre/Post
Prerequisites	An open SimulationAn active SOL 144 solution
Simulation Navigator	Right-click the solution node→Trim Variables Manager

How do I

Assign a modeling object to a solution or solution subcase

Define an aerodynamic control surface

Create a static aeroelastic subcase

Define aerodynamic divergence data

Create an aerodynamic divergence subcase

Create a fictitious support

Plot trim conditions

Learn more

Static aeroelastic response analysis (SOL 144)

Aeroelastic divergence analysis workflow (SOL 144)

Aeroelastic trim analysis workflow (SOL 144)

Constraints in trim analysis

Post-processing aeroelastic trim analysis results

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Defining trim variables, Simcenter 3D 2021.1 Series

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