# Reference: FrequencyInput

Model ElementA Reference_FrequencyInput defines the input to the frequency response analysis.

## Description

The frequency response analysis calculates the response of the system to steady-state oscillatory excitation. The frequency input is characterized by magnitude and phase_angle. You can specify the frequency input on any marker based on forces, displacements, velocity, and acceleration.

## Format

<Reference_FrequencyInput
id          = "integer"
amplitude   = { "real" | "expression" }
phase_angle = { "real" | "expression" }
type        = { "FORCE" | "DISPLACEMENT" | "VELOCITY" | "ACCELERATION" }
marker_id   = "integer"
dof         = "integer"
rm          = "integer"
/>

## Attributes

id
Element identification number (integer>0). This number is unique among all Reference_FrequencyInput elements.
amplitude
Amplitude of the sinusoidal input. amplitude can be a constant or an expression based on frequency using FREQ or OMEGA.
phase_angle
Phase angle of the sinusoidal input. phase_angle can be a constant or an expression based on frequency using FREQ or OMEGA.
type
Specify the type of frequency input from Force, Displacement, Velocity, or Acceleration.
marker_id
Specify the Reference_Marker at which the frequency excitation is to be applied.
dof
Specify the direction of excitation 1-6 for x,y,z, b1, b2, and b3. Multiple direction combinations are allowed.
rm
Specify the Reference_Marker whose coordinate system is used as the basis for defining the components of the frequency input.
This attribute is optional.
When not specified, it defaults to the ground coordinate system.

## Example

Consider a quarter car suspension. Assume that you interested in the frequency response of a vehicle body with respect to the frequency input at the wheel hub in the x, y, z directions, with a amplitude of 1 and a phase_angle of 0.
<Reference_FrequencyInput
id = "1"
amplitude = "1"
type = "DISPLACEMENT"
marker_id = "30102010"
dof = "123"
/>

<Reference_FrequencyInput
id = "2"
amplitude = "STEP(FREQ,0.01,1,10,100)-STEP(FREQ,10,0,20,99)"
type = "DISPLACEMENT"
marker_id = "30102010"
dof = "123"
/>