/TH/ACCEL

Block Format Keyword Describes the time history for accelerometers.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/TH/ACCEL/thgroup_ID
thgroup_name
var_ID1 var_ID2 var_ID3 var_ID4 var_ID5 var_ID6 var_ID7 var_ID8 var_ID9 var_ID10
Obj_ID1 Obj_ID2 Obj_ID3 Obj_ID4 Obj_ID5 Obj_ID6 Obj_ID7 Obj_ID8 Obj_ID9 Obj_ID10

Definitions

Field Contents SI Unit Example
thgroup_ID TH group identifier

(Integer, maximum 10 digits)

  
thgroup_name TH group name

(Character, maximum 100 characters)

  
var_ID1, ...n Variables saved for TH (see table below)

(Character, maximum 8 characters)

  
Obj_ID1, ...n Identifiers of the objects to be saved

(Integer)

  

TH Output Keyword & Variables

Keyword Object Saved Variables
ACCEL Accelerometer AX, AY, AZ, WX, WY, WZ

Table of Available Variables - Part 2

Keyword Variable Group Saved TH Variables
ACCEL DEF W AX, AY, AZ, WX, WY, WZ

Output for Accelerometer

  • AX: acceleration in direction X
  • AY: acceleration in direction Y
  • AZ: acceleration in direction Z
  • WX: integral of acceleration in direction X
  • WY: integral of acceleration in direction Y
  • WZ: integral of acceleration in direction Z
  • Let γ g the nodal acceleration vector with laboratory expressed in the global skew system, γ s the nodal acceleration vector with laboratory projected onto the moving skew.

Let ν g the nodal velocity vector with laboratory expressed in the global skew system, ν s the nodal velocity vector with laboratory projected onto the moving skew.

Let R ( t ) the orientation matrix of the skew at time t, so that: (1)
γ s = R ( t ) ⋅ γ g
(2)
v s = R ( t ) ⋅ v g
Derivating ν s versus time leads to:(3)
d v s dt = dR dt v g +R d v g dt = dR dt v g +R γ g = dR dt v g + γ s

This shows that derivating the nodal velocity with laboratory projected onto the moving skew, ν s does not give as a result the nodal acceleration with laboratory projected onto the moving skew, γ s .

The vector WX, WY, and WZ available for output in the accelerometer is:(4)
w = ∫ 0 t γ s ( u ) d u

Derivating to this output will give a value of γ s nodal acceleration with laboratory projected onto the moving skew, the integration-derivation acting as another filter other than the 4-pole Butterworth, which is used in the accelerometer and computes the filtered accelerations AX, AY, and AZ.

Comments

  1. Available names are listed in the two tables above.

    In the first table, TH-variables are listed. If a TH-variable is requested, this variable is written.

    In the second table, variable groups are listed. If a variable group is requested, all the associated TH-variables are written at once.