Discrete Wind Gust Model

Generate discrete wind gust

• Library:

• Aerospace Blockset / Environment / Wind

• 

Description

The Discrete Wind Gust Model block implements a wind gust of the standard “1-cosine” shape. This block implements the mathematical representation in the Military Specification MIL-F-8785C [1]. The gust is applied to each axis individually, or to all three axes at once. You specify the gust amplitude (the increase in wind speed generated by the gust), the gust length (length, in meters, over which the gust builds up) and the gust start time. For more information on the gust shape, see Algorithms.

The Discrete Wind Gust Model block can represent the wind speed in units of feet per second, meters per second, or knots.

Ports

Input

V — Air speed

scalar

Airspeed, specified as a scalar, in selected units.

Data Types: double

Output

Vwind — Wind speed

scalar

Wind speed, returned as a scalar, in selected units.

Data Types: double

Parameters

Units — Units

Metric (MKS) (default) | English (Velocity in ft/s) | English (Velocity in kts)

Units of wind gust, specified as:

Units	Wind	Altitude
Metric (MKS)	Meters/second	Meters
English (Velocity in ft/s)	Feet/second	Feet
English (Velocity in kts)	Knots	Feet

Programmatic Use

Block Parameter: units

Type: character vector

Values: 'Metric (MKS)' | 'English (Velocity in ft/s)' | 'English (Velocity in kts)'

Default: 'Metric (MKS)'

Gust in u-axis — Wind gust to u-axis

on (default) | off

To apply a wind gust to the u-axis in the body frame, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: Gx

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Gust in v-axis — Wind gust to v-axis

on (default) | off

To apply a wind gust to the v-axis in the body frame, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: Gy

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Gust in w-axis — Wind gust to w-axis

on (default) | off

To apply a wind gust to the w-axis in the body frame, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: Gz

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Gust start time (sec) — Gust start time

5 (default) | scalar

Model time, specified as a scalar, at which the gust begins, in seconds.

Programmatic Use

Block Parameter: t_0

Type: character vector

Values: scalar

Default: '5'

Gust length [dx dy dz] (m) — Gust length

[120 120 80] (default)

The length, in meters or feet (depending on the choice of units), over which the gust builds up in each axis. These values must be positive.

Programmatic Use

Block Parameter: d_m

Type: character vector

Values: vector

Default: '[120 120 80]'

Gust amplitude [ug vg wg] (m/s) — Gust amplitude

[3.5 3.5 3.0] (default)

The magnitude of the increase in wind speed caused by the gust in each axis. These values may be positive or negative.

Programmatic Use

Block Parameter: d_m

Type: character vector

Values: vector

Default: '[3.5 3.5 3.0]'

Algorithms

This figure shows the shape of the gust with a start time of zero. The parameters that govern the gust shape are indicated on the diagram.

To assess airplane response to large wind disturbances, you can use the discrete gust singly or in multiples.

The mathematical representation of the discrete gust is:

$$V_{wind}=\{\begin{array}{lll}0\hfill & x<0\hfill & \hfill \\ \frac{V_m}{2}\left(1-\cos \left(\frac{\pi x}{d_m}\right)\right)\hfill & 0\le x\le d_m\hfill & \hfill \\ V_m\hfill & x>d_m\hfill & \hfill \end{array}$$

where V_m is the gust amplitude, d_m is the gust length, x is the distance traveled, and V_wind is the resultant wind velocity in the body axis frame.

References

[1] U.S. Military Specification MIL-F-8785C, November 5, 1980.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.