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(‘lateral turbulence’), and its time-derivative,
WDRYD1 generates the turbulence velocity component along the ZB-axis of the aircraft
(‘vertical turbulence’), and its time-derivative.
Inputs
None.
Outputs
uwind = [ ug vg wg u˙ g v˙g w˙ g ]T wind velocity vector (turbulence only), uwind
Note: the outputvector from Turbulence Group 1 has been named uwind, because it has the
same structure as the input vector uwind for the aircraft model. However, in the case of the
aircraft model, this vector is meant to take into account deterministic wind components,
as well as stochastic turbulence.
Parameters
Turbulence Group 1 does not require any workspace parameters to be specified. The user
must specify the scale lengths Lug,vg,wg , the standard deviations sug,vg,wg , and the estimated
mean value of the true airspeed for which the motions are evaluated for each of
the three blocks UDRYD1, VDRYD1, and WDRYD1; double-click these blocks to open the
mask-dialogs that allow you to define these block parameters.
Connections
in: no connections.
out: uwind can be connected to the input-side of the aircraft model (see the description of
Beaver Level 1 in chapter 8). If simulations involve deterministic wind components,
the wind components need to be added to the outputs from this subsystem first,
before entering the aircraft model.
Type browse turb1 at the command-line for on-line help.
9.1. The wind and turbulence blocklibrary 171
Turbulence Group 2 Main library / Wind & turbulence / Atmosph. turb. models / Turbulence Group 2
Wind and turbulence library / Atmospheric turbulence models / Turbulence Group 2
Type
Non-masked subsystem.
Description
The subsystem Turbulence Group 2 determines longitudinal, lateral, and vertical turbulence
velocity components along the body-axes of the aircraft, plus their time-derivatives,
using Dryden filters with airspeed-dependent coefficients. The user must specify the scale
length and standard deviation in each of the Dryden filters from this subsystem (longitudinal,
lateral, and vertical). Variations of the filter coefficients are computed ‘on-the-fly’,
as a function of the airspeed. Since the resulting variations in filter characteristics are usually
relatively small, the turbulence library also offers a simplified subsystem Turbulence
Group 1, which uses constant filter coefficients.
Subsystems and/or blocks
The subsystem Turbulence Group 2 contains three blocks:
UDRYD2 generates the turbulence velocity component along the XB-axis of the aircraft
(‘longitudinal turbulence’), and its time-derivative,
VDRYD2 generates the turbulence velocity component along the YB-axis of the aircraft
(‘lateral turbulence’), and its time-derivative,
WDRYD2 generates the turbulence velocity component along the ZB-axis of the aircraft
(‘vertical turbulence’), and its time-derivative.
Inputs
V true airspeed of the aircraft, V
Outputs
uwind = [ ug vg wg u˙ g v˙g w˙ g ]T wind velocity vector (turbulence only), uwind
Note: the outputvector from Turbulence Group 2 has been named uwind, because it has the
same structure as the input vector uwind for the aircraft model. However, in the case of the
aircraft model this vector is meant to take into account deterministic wind components,
as well as stochastic turbulence.
Parameters
Turbulence Group 2 does not require any workspace parameters to be specified. The user
must specify the scale lengths Lug,vg,wg and the standard deviations sug,vg,wg for each of
the three blocks UDRYD2, VDRYD2, and WDRYD2; double-click these blocks to open the
mask-dialogs that allow you to define these block parameters.
Connections
in: the airspeed V is usually extracted from the state vector x of the nonlinear aircraft
model.
out: uwind can be connected to the input-side of the aircraft model (see the description of
Beaver Level 1 in chapter 8). If simulations involve deterministic wind components,
the wind components need to be added to the outputs from this subsystem first,
before entering the aircraft model.
Type browse turb2 at the command-line for on-line help.
172 Chapter 9. Wind and turbulence block reference
UDRYD1 Main FDC library / Wind and turbulence / Atmospheric turbulence models / UDRYD1
Wind and turbulence library / Atmospheric turbulence models / UDRYD1
Type
Masked subsystem block.
Description
The block UDRYD1 computes the longitudinal turbulence velocity component, which is
aligned along the XB-axis of the aircraft, together with its time-derivative, using a longitudinal
Dryden filter with constant coefficients. The user must specify the longitudinal
　
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