The masked subsystem block UDRYD2, which is contained in the library WINDLIB, implements a longitudinal Dryden filter with coefficients that vary with the true airspeed V.
The user must specify the scale lenght L_ug and the standard deviation sigma_ug. The airspeed V is used as inputsignal to the block UDRYD2. 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 UDRYD1 contains such a filter for longitudinal turbulence.
The longitudinal gust velocity ug is obtained by passing white noise through a Dryden filter, which is defined by the following transfer function:
K Hug = ----------- K = sigma_ug * sqrt(2*Lug/V) 1 + tau*s tau = Lug/Vwhere:
V : true airspeed [m/s] sigma_ug: standard deviation of longitudinal gust velocity [m/s] Lug : scale length for longitudinal 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 non-linear aircraft model (such as the Beaver model), which uses the turbulence velocity ug and its time-derivative as inputsignals!
V : true airspeed [m/s]
ug : longitudinal gust velocity [m/s] d(ug)/dt: time derivative of ug [m/s^2]
The following parameters can be specified after double-clicking the block UDRYD2:
Lug = scale length for longitudinal turbulence [m] sigma_ug = standard deviation for longitudinal turbulence [m/s]
While UDRYD1 and UDRYD2 contain longitudinal Dryden filters, the blocks VDRYD1, VDRYD2, WDRYD1, and WDRYD2 can be used to determine lateral 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.