Analyze

The Analyze function performs a virtual test on a set of bushing parameters to characterize the set's stiffness and loss angle behavior. In order to do this, Analyze requires a model that you select, a test specification, and a set of bushing parameters. The test specification is contained in the input .spd file. The bushing parameters are contained in the input .gbs file. For each test case in the input .spd file, Analyze computes the dynamic stiffness and loss angle for the selected model and parameters.

Bound,

  Lower

Specifies the smallest possible value for a parameter.

Bound,

  Upper

Specifies the largest possible value for a parameter.

Bushing Model,

  Hydromount

A mathematical model for a hydromount bushing developed by Altair. The model consists of a set of non-linear differential equations that describe the rubber and fluid dynamics associated with rubber deflection and the movement of the fluid in the decoupler membrane and in the inertia track of the bushing. The model can fit multiple frequencies as well as multiple amplitudes with one set of coefficients. See: Bushing Damping Models.

Bushing Model,

  Rubber

A mathematical model for a rubber bushing developed by Altair. The model consists of a set of non-linear differential equations that describes rubber behavior and the friction effects within the rubber of the bushing. The model can fit multiple frequencies as well as multiple amplitudes with one set of coefficients. Bushing Damping Models.

Dynamic Stiffness

Dynamic stiffness is the frequency-dependent ratio between a dynamic force and the resulting dynamic displacement. The force can have two components: a displacement dependent, or spring force, component and a velocity dependent, or damping force, component. See: Steady State Response of Nonlinear Systems.

File,

  GBS

This is a TeimOrbit file that contains the parameters for all bushing models. The .gbs file is used as an input to the simulation model.

File,

 OPT

This is a TeimOrbit file that contains the parameters to be used in the fitting process. The .opt file is used as an input to the fitting algorithm.

File,

  SPD

This is a TeimOrbit file containing data that characterizes bushing behavior for one direction that has been tested. Test directions can be FX, FY, FZ, TX, TY and TZ. Both static and dynamic test results are included for each direction. For static testing, a Force vs. Displacement curve is specified.  For dynamic testing, dynamic stiffness and loss angle are specified for various combinations of the following:

Note: One .spd file contains data for one direction only.

File,

  SPD Input

This is a .spd file containing experimental measurements.

File,

  SPD Output

This is a .spd file, generated by the MIT, that contains the model response to the same tests that were specified in the Input .spd file.

Fit

Fit is an optimization process that uses analytical methods to identify model parameter values that minimize the difference in behavior between the measured physical system and the mathematical representation of the physical system. See: MIT and the Fitting Process.

Fit Score

A Fit Score is a quantitative comparison between actual and calculated outputs.  The optimizer uses mean-squared error as the cost function to minimize. In order to indicate the quality of a fit, and the ability of a model to predict system behavior, you can use the Sprague-Geers Fit Metric and the Maximum Deviation FIT Metric.

Loss Angle

The loss angle is defined as the phase angle between displacement and force. This phase difference is caused by the presence of damping forces. The ratio of a damping force to a spring force is often called a loss tangent, which is the tangent of a loss angle.

Model

A model is a mathematical representation of a physical system.  The model could be a set of differential equations, algebraic equations or differential-algebraic equations that describe the relationship between the inputs to and outputs from a system.

Parameters

A mathematical model consists of equations in terms of inputs, a set of internal states, and a set of unknown coefficients. These coefficients represent design variables known as parameters.

System

A system is a physical entity that if acted upon by well-defined inputs, then generates well-defined outputs. A mathematical model approximates a system.