/ACCEL

Block Format Keyword

/ACCEL - Accelerometers

Description

Defines accelerometers using a node and skew system.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/ACCEL/accel_ID/unit_ID
accel_title
node_ID	skew_ID		Fcut

Field	Contents	SI Unit Example
accel_ID	Accelerometer identifier (Integer, maximum 10 digits)
unit_ID	Optional 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)

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.

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 /TH. 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).