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FDC help: UDRYD1
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<h2>
<i>UDRYD1</i>: Longitudinal Dryden filter with constant coefficients
</h2>
<p>The block <i>UDRYD1</i> is contained in the block-library
<i><a href="windlib.htm">WINDLIB</a></i>. It implements a longitudinal
Dryden filter with constant coefficients.</p>
<p>The user must specify the scale
lenght <i>L_u<sub>g</sub></i>, the standard deviation
<i>sigma_u<sub>g</sub></i> and the airspeed <i>V</i>. In reality, <i>V</i>
will not be constant, which results in non-constant filter coefficients, but in practice the influence of the change in airspeed upon the
gust velocities can often be neglected. Use <i><a href=
"udryd2.htm">UDRYD2</a></i> instead of <i>UDRYD1</i> if the airspeed varies
so much that the filter coefficients cannot be held constant anymore.</p>
<p>The longitudinal gust velocity <i>u<sub>g</sub></i> is obtained by passing
white noise through a Dryden filter, which is defined by the following
transfer function: </p>
<pre>
K
Hug = ----------- K = sigma_ug * sqrt(2*Lug/V)
1 + tau*s tau = Lug/V
</pre>
where:
<pre>
V : true airspeed [m/s]
sigma_ug: standard deviation of longitudinal gust
velocity [m/s]
Lug : scale length for longitudinal gust [m]
</pre>
In this case, <i>V</i> must be pre-specified by the user in the
dialog-boxes from the block <i>UDRYD1</i>.
<h3>
Outputs from the block <i>UDRYD1</i>
</h3>
<pre>
ug : longitudinal gust velocity [m/s]
d(ug)/dt: time derivative of ug [m/s^2]
</pre>
<p><i>UDRYD1</i> has no inputs.</p>
<h3>
Block parameters
</h3>
<p>The following parameters can be specified after double-clicking the block <i>UDRYD1</i>:</p>
<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>
<h3>
More information
</h3>
<p>While <i>UDRYD1</i> and <i>UDRYD2</i> contain longitudinal Dryden filters,
the blocks <i><a href="vdryd1.htm">VDRYD1</a></i>, <i><a href=
"vdryd2.htm">VDRYD2</a></i>, <i><a href="wdryd1.htm">WDRYD1</a></i>, and
<i><a href="wdryd2.htm">WDRYD2</a></i> 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).</p>
<p>These Dryden
filters have been combined in the subsystems <i><a href="turb1.htm">Turbulence Group 1</a></i>
and <i><a href="turb2.htm">Turbulence Group 2</a></i>. Those subsystems combine the
turbulence velocity-components and their time-derivatives into a single vector
<i>uwind</i>, which can be connected to the <i><a
href="beaver.htm">Beaver</a></i> model.</p>
<p>All wind and turbulence systems have been gathered in the blocklibrary
<i><a href="windlib.htm">WINDLIB</a></i>.</p>
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