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<H2><I><FONT FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I>: Vertical Dryden filter with constant coefficients</H2>
The masked subsystem block <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I> is contained in the block-library <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="windlib.htm">WINDLIB</A></FONT></I>. It implements a vertical Dryden filter with constant coefficients. The user must specify the scale lenght <I>L<SUB>w<SUB>g</SUB></SUB></I>, the standard deviation <I>sigma_w<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. However, for most purposes the influence of the change in airspeed upon the gust velocities may be neglected. Use <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="wdryd2.htm">WDRYD2</A></FONT></I> instead of <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I> if the airspeed varies so much that the filter coefficients cannot be held constant anymore.<BR>
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The vertical gust velocity <I>w<SUB>g</SUB></I> is obtained by passing white noise through a Dryden filter, which is defined by the following transfer function:
<PRE> b0 + b1*s a0 = (V/Lwg)^2
Hwg = ----------------- a1 = 2*(V/Lwg)
s^2 + a1*s + a0 b0 = sigma_wg*sqrt(Lwg/V)*(V/Lwg)^2
b1 = sigma_wg*sqrt(3*Lwg/V)*(V/Lwg)
</PRE>
where:
<PRE> V : true airspeed [m/s]
sigma_wg: standard deviation of vertical gust velocity [m/s]
Lwg : scale length for vertical gust [m]
</PRE>
In this case, <I>V</I> must be pre-specified by the user in the dialog-boxes from the block <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I>.
<H3>Outputs from the block <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I></H3>
<PRE> wg : vertical gust velocity [m/s]
d(wg)/dt: time derivative of wg [m/s^2]
</PRE>
<I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I> has no inputs.<BR><BR>
<H3>More information</H3>
While <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD1</FONT></I> and <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">WDRYD2</FONT></I> contain vertical Dryden filters, the blocks <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="udryd1.htm">UDRYD1</A></FONT></I>, <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="udryd2.htm">UDRYD2</A></FONT></I>, <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="vdryd1.htm">VDRYD1</A></FONT></I>, and <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="vdryd2.htm">VDRYD2</A></FONT></I> can be used to determine longitudinal and lateral turbulence (the suffix 1 denotes filters with constant coefficients and 2 denotes filters with velocity-dependent coefficients). Practical combinations of the longitudinal, lateral, and vertical Dryden filters can be found in the subsystems <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="turb1.htm">Turb1</A></FONT></I> and <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="turb2.htm">Turb2</A></FONT></I>. Those subsystems combine the turbulence velocity-components and their time-derivatives in a vector <I>uwind</I>, which can be connected to the non-linear aircraft model <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="beaver.htm">Beaver</A></FONT></I>.<BR>
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<B>Note:</B> the vector <I>uwind</I> that leaves <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">Turb1</FONT></I> and <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif">Turb2</FONT></I> does not contain deterministic wind velocity components. Add this vector to the outputs from <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="blwind.htm">BLwind</A></FONT></I> or <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="cwind.htm">Cwind</A></FONT></I> if you want to take into account those components as well.<BR>
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All wind and turbulence systems have been gathered in the blocklibrary <I><FONT SIZE=2 FACE="Arial","Helvetica","Sans Serif"><A HREF="windlib.htm">WINDLIB</A></FONT></I>.
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