/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

Definition

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

Available Variables - Part 2

Keyword Variable Group Saved TH Variables
ACCEL DEF AX, AY, AZ
W 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 ${\gamma }_{g}$ = the nodal acceleration vector expressed in the global skew system, ${\gamma }_{s}$ the nodal acceleration vector projected onto the moving skew.

Let ${\nu }_{g}$ = the nodal velocity vector expressed in the global skew system, ${\nu }_{s}$ the nodal velocity vector projected onto the moving skew.

Let $R\left(t\right)$ = the orientation matrix of the skew at time $t$ , so that: (1)
${\gamma }_{s}=R\left(t\right)\cdot {\gamma }_{g}$
(2)
${v}_{s}=R\left(t\right)\cdot {v}_{g}$
Derivating ${\nu }_{s}$ versus time leads to:(3)
$\frac{d{v}_{s}}{dt}=\frac{dR}{dt}{v}_{g}+R\frac{d{v}_{g}}{dt}=\frac{dR}{dt}{v}_{g}+R{\gamma }_{g}=\frac{dR}{dt}{v}_{g}+{\gamma }_{s}$

This shows that derivating the nodal velocity projected onto the moving skew, ${\nu }_{s}$ does not give an equivalent result to the nodal acceleration projected onto the moving skew, ${\gamma }_{s}$ .

The vector WX, WY, and WZ available for output in the accelerometer is:(4)
$w=\underset{0}{\overset{t}{\int }}{\gamma }_{s}\left(u\right)du$

Derivating this output will give a value of ${\gamma }_{s}$ nodal acceleration 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.