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| # -*- coding:Utf-8 -*-
#-----------------------------------------------------------------------
# MODULE IMPORTATION
#-----------------------------------------------------------------------
import numpy as np
from math import cos
import random
import time
#-----------------------------------------------------------------------
# SPECTRUM DEFINITIONS
#-----------------------------------------------------------------------
def HarrisDNV(meanSpeed, Wmin, Wmax, N):
""" Harris - DNV Spectrum """
# Frequencies in rad/s
W = linspace(Wmin,Wmax,N)
# Surface drag coefficient
C = 0.0015
# Spectrum
Spectrum = [(7200/(2*np.pi))*C*meanSpeed*(2+(286.0*W[i]/meanSpeed)**2)**(-5.0/6.0) for i in range(len(W))]
return W,Spectrum
#-----------------------------------------------------------------------
# RANDOM TIME SERIE GENERATOR
#-----------------------------------------------------------------------
def WindGen(Npoints, SampleTime, MaxFreq, Nlags, meanSpeed, Spec=2, Seed=None):
""" Build a time serie of the wind velocity
This function generate a random time serie of wind speed based on
the following wind spectrum:
1- Ochi-Shin
2- Harris-DNV (default)
3- Wills or Modified Harris
4- API
5- NPD
--------------------------------------------------------------------
INPUTS:
--------------------------------------------------------------------
Npoints : Number of points in the time serie (integer)
SampleTime : Sample time (sec) (integer)
MaxFreq : Max frequency for spectrum (float)
Nlags : Number of random phases (integer)
meanSpeed : Mean wind velocity (float)
Spec : Spectrum type (integer)
--------------------------------------------------------------------
OUTPUTS
--------------------------------------------------------------------
liste containing:
- time
- wind velocities
"""
#
# GENERATING WIND SPECTRUM
#
if Spec == 1:
print 'OchiShin'
W,S = OchiShin(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
elif Spec == 2:
print 'HarrisDNV'
W,S = HarrisDNV(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
elif Spec == 3:
print 'Wills'
W,S = Wills(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
elif Spec == 4:
print 'API'
W,S = API(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
elif Spec == 5:
print 'NPD'
W,S = NPD(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
else:
print 'Unvalide choice, default spectrum have been selected (Harris)'
print 'The following spectrum are available:'
print '\t' + '1- Ochi-Shin'
print '\t' + '2- Harris-DNV (default)'
print '\t' + '3- Wills or Modified Harris'
print '\t' + '4- API'
print '\t' + '5- NPD'
print ''
W,S = HarrisDNV(meanSpeed, Wmin=0., Wmax=MaxFreq, N=Nlags)
#
# GENERATING TIME SERIES
#
if Seed: random.seed(Seed)
T = [t for t in range(Npoints)]
A = [(2*(S[i+1]+S[i])/2*(W[i+1]-W[i]))**0.5 for i in range(Nlags-1)]
A.append(0.0)
P = [random.uniform(0.0,2*np.pi) for i in range(Nlags)]
t0 = time.clock()
WindVelocities = [sum([A[i]*cos(W[i]*t + P[i]) for i in range(Nlags)]) + meanSpeed for t in range(Npoints)]
print 'Time serie generated in ' + str(round(time.clock()-t0,4)) + 's'
return T, WindVelocities
if __name__=="__main__":
import numpy as np
from pylab import *
from math import cos
import random
import time
t, WindVelocities = WindGen(Npoints = 3600,
SampleTime = 1,
MaxFreq = 2*np.pi/4,
Nlags = 1000,
meanSpeed = 1.0,
Spec=2,
Seed=145468)
plot(t[100:300],WindVelocities[100:300],'blue')
legend(('Random Wind velocities'),'best')
ylabel('Wind Velocity in m/s')
xlabel('Time in s')
tight_layout()
show() |
