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FDC help: Turbulence Group 1
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<h2>
The turbulence block <i>Turbulence Group 1</i>
</h2>
<p><i>Turbulence Group 1</i> is a Simulink subsystem which is contained in the Atmospheric
Turbulence sublibrary of the library <i><a href=
"windlib.htm">WINDLIB</a></i>. It contains the Dryden filters <i><a href=
"udryd1.htm">UDRYD1</a></i>, <i><a href="vdryd1.htm">VDRYD1</a></i>, and
<i><a href="wdryd1.htm">WDRYD1</a></i> for longitudinal, lateral and
vertical turbulence, respectively.</p>
<p>The filters have been implemented in
masked subsystem blocks, in which the user must specify the scale lengths
<i>L_u<sub>g</sub></i>, <i>L_v<sub>g</sub></i>, and <i>L_w<sub>g</sub></i>,
the standard deviations <i>sigma_u<sub>g</sub></i>,
<i>sigma_v<sub>g</sub></i>, and <i>sigma_w<sub>g</sub></i>, and the
velocity <i>V</i> (for each of the three masked subsystem blocks!). The
coefficients of the Dryden filters are determined for the value of the
airspeed <i>V</i> which is specified in the dialog boxes from the blocks
<i>UDRYD1</i>, <i>VDRYD1</i>, and <i>WDRYD1</i>, i.e., <i>V</i> is assumed
to be constant during the simulations.</p>
<p>In cases where the airspeed changes over a very large range, it is
recommended to use the <i><a href="Turb2.htm">Turbulence Group 2</a></i> instead,
because it takes into account variations of the filter coefficients due to
changes in the true airspeed <i>V</i> during the simulations (using the
more sophisticated <i><a href="udryd2.htm">UDRYD2</a></i>, <i><a href=
"vdryd2.htm">VDRYD2</a></i>, and <i><a href="wdryd2.htm">WDRYD2</a></i>
Dryden filter implementations).</p>
<h3>
Outputvector
</h3>
<pre>
uwind = [uw vw ww uwdot vwdot wwdot]'
</pre>
<p>(Actually, this vector should have been called <code>ugust = [ug vg wg
ugdot vgdot wgdot]'</code>, since the wind velocities and their
time-derivatives from the subsystem <i>Turbulence Group 1</i> represent gust-velocities
only; contributions due to steady wind or windshear still have to be added to
this vector! See <i><a href="cwind.htm">Cwind</a></i> and <i><a href=
"blwind.htm">BLwind</a></i> for more information on the implementation of
constant wind and a wind-profile in the Earth's boundary layer,
respectively.)</p>
<pre>
uw : wind (gust-) velocity along XB-axis of aircraft [m/s]
vw : wind (gust-) velocity along YB-axis of aircraft [m/s]
ww : wind (gust-) velocity along ZB-axis of aircraft [m/s]
uwdot: time-derivative of uw [m/s^2]
vwdot: time-derivative of vw [m/s^2]
wwdot: time-derivative of ww [m/s^2]
</pre>
<i>Turbulence Group 1</i> does not have any input signals.
<h3>
Block parameters
</h3>
Before starting a simulation of a system in which the subsystem
<i>Turbulence Group 1</i> is involved, the parameters of the masked subsystem blocks
<i><a href="udryd1.htm">UDRYD1</a></i>, <i><a href=
"vdryd1.htm">VDRYD1</a></i>, and <i><a href="wdryd1.htm">WDRYD1</a></i>
have to be defined by double-clicking these blocks and entering the correct
values in their dialog-boxes. These parameters are:<br>
<br>
<i>UDRYD1</i>:
<pre>
Lug = scale length for longitudinal turbulence [m]
sigma_ug = standard deviation for longitudinal
turbulence [m/s]
V = value of airspeed, used to determine filter
coefficients for longitudinal turbulence [m/s]
</pre>
<i>VDRYD1</i>:
<pre>
Lvg = scale length for lateral turbulence [m]
sigma_vg = standard deviation for lateral turbulence [m/s]
V = value of airspeed, used to determine filter
coefficients for lateral turbulence [m/s]
</pre>
<i>WDRYD1</i>:
<pre>
Lwg = scale length for vertical turbulence [m]
sigma_wg = standard deviation for vertical turbulence [m/s]
V = value of airspeed, used to determine filter
coefficients for vertical turbulence [m/s]
</pre>
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