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rotorpy/wind/dryden_winds.py

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+import numpy as np
+import os
+import sys
+
+# The Dryden Gust model is implemented using this package: 
+# https://github.com/goromal/wind-dynamics
+# If using the package directly, make sure the package is installed and the file ./wind-dynamics/python/wind_dynamics.so 
+# exists. It may be named slightly differently depending on your system. 
+# wind_path = os.path.join(os.path.dirname(__file__),'wind-dynamics/python')
+# sys.path.insert(1, wind_path) # if your script is not in the wind-dynamics/python directory
+# from wind_dynamics import DrydenWind
+
+from rotorpy.wind.dryden_utils import *
+
+class DrydenGust(object):
+    """
+    The Dryden Wind Turbulence model is governed by a pink noise process that is parameterized by 
+    an average (mean) windspeed and standard deviation. This class is a wrapper on an 
+    existing external package: https://github.com/goromal/wind-dynamics 
+    The Dryden model is accepted by the DoD in design, characterization, and testing of aircraft
+    in simulation. https://en.wikipedia.org/wiki/Dryden_Wind_Turbulence_Model
+    """
+
+    def __init__(self, dt=1/500, 
+                    avg_wind=np.array([0,0,0]), sig_wind=np.array([1,1,1]),
+                    altitude=2.0):
+        """
+        Inputs:
+            dt := time discretization, s, should match the simulator
+            avg_wind := mean windspeed on each axis, m/s
+            sig_wind := turbulence intensity in windspeed on each axis, m/s
+            altitude := expected operating altitude
+        """
+        self.dt = dt
+
+        self.wind = DrydenWind(avg_wind[0], avg_wind[1], avg_wind[2], sig_wind[0], sig_wind[1], sig_wind[2], altitude)
+
+    def update(self, t, position):
+        """
+        Given the present time and position of the multirotor, return the
+        current wind speed on all three axes. 
+        
+        The wind should be expressed in the world coordinates. 
+        """
+        return self.wind.getWind(self.dt)
+
+class DrydenGustLP(object):
+    """
+    This is another wrapper on an existing external package: https://github.com/goromal/wind-dynamics 
+    The Dryden model is accepted by the DoD in design, characterization, and testing of aircraft
+    in simulation. https://en.wikipedia.org/wiki/Dryden_Wind_Turbulence_Model
+
+    The difference between this model and DrydenGust is that we add an additional low pass filter governed by 
+    a cutoff frequency, 1/tau in order to generate smoother varying winds. 
+    """
+
+    def __init__(self, dt=1/500, 
+                    avg_wind=np.array([0,0,0]), sig_wind=np.array([1,1,1]),
+                    altitude=2.0,
+                    tau=0.1):
+        """
+        Inputs:
+            dt := time discretization, s, should match the simulator
+            avg_wind := mean windspeed on each axis, m/s
+            sig_wind := turbulence intensity (denoted sigma) in windspeed on each axis, m/s
+            altitude := expected operating altitude
+            tau      := cutoff frequency of the low pass filter (s)
+        """
+        self.dt = dt
+
+        self.tau = tau
+
+        self.wind = DrydenWind(avg_wind[0], avg_wind[1], avg_wind[2], sig_wind[0], sig_wind[1], sig_wind[2], altitude)
+        self.prev_wind = self.wind.getWind(self.dt)
+
+    def update(self, t, position):
+        """
+        Given the present time and position of the multirotor, return the
+        current wind speed on all three axes. 
+        
+        The wind should be expressed in the world coordinates. 
+        """
+        wind = (1-self.dt/self.tau)*self.prev_wind + self.dt/self.tau*self.wind.getWind(self.dt)
+        self.prev_wind = wind
+        return wind