/ACCEL

Block Format Keyword Defines accelerometers using a node and skew system.

Format

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/ACCEL/accel_ID/unit_ID
accel_title
node_ID Skew_ID Fcut

Definition

Field Contents SI Unit Example
accel_ID Accelerometer identifier

(Integer, maximum 10 digits)
unit_ID Unit identifier

(Integer, maximum 10 digits)
accel_title Accelerometer title

(Character, maximum 100 characters)
node_ID Node identifier

(Integer)
Skew_ID Skew identifier

(Integer)
Fcut Cutoff frequency

(Real)

 [Hz]

Comments

  1. The accelerometer option computes a filtered acceleration in a skew system.
  2. These filtered accelerations provided by an accelerometer are used in either the Sensor option or in post-processing acceleration Time History without aliasing problems.
  3. A 4-pole Butterworth filter is used.
  4. The recommended value for Fcut is 1650 Hz (1.65 ms-1) to obtain a class 1000 SAE filtering.
  5. In addition to these filtered accelerations, the accelerometer also allows output to Time History, the integrals of X, Y and Z raw accelerations projected onto the skew. These quantities are not used by Sensor.
  6. If the skew is moving, the integrals of X, Y and Z raw accelerations projected onto the skew are not the same as the velocities projected onto the skew, as described in Time Histories. But these integrals in derivating Time History post-processor allows to retrieve the accelerations projected to skew without aliasing problems (Integration / Derivation acting like another filter than the 4-pole Butterworth).