The masked subsystem block VDRYD2, which is contained in the library WINDLIB, implements a lateral Dryden filter with coefficients that vary with the true airspeed V.
The user must specify the scale lenght L_vg and the standard deviation sigma_vg. The airspeed V is used as inputsignal to the block VDRYD2. Often, the changes in V due to atmospheric turbulence are not very large, which means that it may be more straightforward to use a Dryden filter with constant coefficients, computed under the assumption that V is constant and equal to a user-specified value. The block VDRYD1 contains such a filter for lateral turbulence.
The lateral gust velocity vg is obtained by passing white noise through a Dryden filter, which is defined by the following transfer function:
b0 + b1*s a0 = (V/Lvg)^2 Hvg = --------------- a1 = 2*(V/Lvg) s^2 + a1*s + a0 b0 = sigma_vg*sqrt(Lvg/V)*(V/Lvg)^2 b1 = sigma_vg*sqrt(3*Lvg/V)*(V/Lvg)where:
V : true airspeed [m/s] sigma_vg: standard deviation of lateral gust velocity [m/s] Lvg : scale length for lateral gust [m]
Here, V is the input signal to the masked subsystem block. V itself has to be obtained from the aircraft model considered, e.g., V may be an outputsignal from the Beaver model, which uses the turbulence velocity ug and its time-derivative as inputsignals!
V : true airspeed [m/s]
vg : lateral gust velocity [m/s] d(vg)/dt: time derivative of vg [m/s^2]
The following parameters can be specified after double-clicking the block VDRYD2:
Lvg = scale length for lateral turbulence [m] sigma_vg = standard deviation for lateral turbulence [m/s]
While VDRYD1 and VDRYD2 contain lateral Dryden filters, the blocks UDRYD1, UDRYD2, WDRYD1, and WDRYD2 can be used to determine longitudinal and vertical turbulence (the suffix 1 denotes filters with constant coefficients and 2 denotes filters with velocity-dependent coefficients).
These Dryden filters have been combined in the subsystems Turbulence Group 1 and Turbulence Group 2. Those subsystems combine the turbulence velocity-components and their time-derivatives into a single vector uwind, which can be connected to the Beaver model.
All wind and turbulence systems have been gathered in the blocklibrary WINDLIB.