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fitData_Cantera.py
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fitData_Cantera.py
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import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import cantera as ct
import numpy as np
import math
# reference about fitting thermo data: https://github.com/Upstream-Applied-Science/canteraJanaf
# reference about writing thermo file: https://github.com/jiweiqi/Cantera2Chemkin/blob/master/soln2ck.py
def build_nasa(nasa_coeffs, row):
"""
Creates string of nasa polynomial coefficients
:param nasa_coeffs
cantera species thermo coefficients object
:param row
which row to write coefficients in
"""
line_coeffs = ''
lines = [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, 13, 14]]
line_index = lines[row-2]
for ix, c in enumerate(nasa_coeffs):
if ix in line_index:
if c >= 0:
line_coeffs += ' '
line_coeffs += str('{:.8e}'.format(c))
return line_coeffs
def write(gas, thermo_fileName_new, plot):
"""Function to write cantera gas object to inp file.
:param gas:
gas: Cantera gas object,
thermo_fileName_new: Name of converted thermo file
plot: whether plot or not
"""
with open(thermo_fileName_new, 'w+') as f:
#f.write('THERMO ALL' + '\n' +
# ' 300.000 1000.000 5000.000' +'\n')
Tlow = 300
Tcommon = 1000
Thigh = 5000
deltaT = 100
T_low = np.arange(Tlow,Tcommon+deltaT,deltaT)
T_high = np.arange(Tcommon,Thigh+deltaT,deltaT)
temp_rangeAll = '{0:10.3f}'.format(Tlow) + '{0:10.3f}'.format(Tcommon) + '{0:10.3f}'.format(Thigh)
f.write('THERMO ALL' + '\n' + temp_rangeAll + '\n')
#write data for each species in the Solution object
for sp_index in range(len(gas.species_names)):
species = gas.species(sp_index)
species_name = gas.species_name(sp_index)
molecular_weight = gas.molecular_weights[sp_index]
nasa_coeffs = species.thermo.coeffs # orininal coeffs, size = 15, [0]=Tcommon, [1-7] is high coeffs, [8-14] is low coeffs
temp_range = '{:<10}'.format(Tlow) + '{:<10}'.format(Thigh) + '{:<8}'.format(Tcommon)
if (nasa_coeffs[0] != Tcommon):
print("fitting species: %s"%(species_name), "from ",nasa_coeffs[0], "to ",Tcommon)
cp_low = [species.thermo.cp(T)/molecular_weight for T in T_low] # [J/(kmol·K)] / [kg/kmol] = [J/(kg·K)]
cp_high = [species.thermo.cp(T)/molecular_weight for T in T_high] # [J/(kmol·K)] / [kg/kmol] = [J/(kg·K)]
cp_low_polynomials = np.polyfit(T_low, cp_low, 4)
cp_high_polynomials = np.polyfit(T_high, cp_high, 4)
R = ct.gas_constant/molecular_weight # [J/(kmol·K)] / [kg/kmol] = [J/(kg·K)]
#reverse order and divide by R (np.ployfit has calculated coeffs*R so we must divide by R to get just the coeffs)
a1_a5_low = np.flip(cp_low_polynomials,0)/R
a1_a5_high = np.flip(cp_high_polynomials,0)/R
T_ref = 298.15
h = species.thermo.h(T_ref)/molecular_weight # [J/kmol] / [kg/kmol] = [J/kg]
s = species.thermo.s(T_ref)/molecular_weight # [J/kmol/K] / [kg/kmol] = [J/(kg·K)]
a6_low = h/R - np.sum(np.array([a1_a5_low[i]*T_ref**(i+1)/(i+1) for i in range(5)]))
a6_high = h/R - np.sum(np.array([a1_a5_high[i]*T_ref**(i+1)/(i+1) for i in range(5)]))
a7_low = s/R - np.sum(np.array([a1_a5_low[i]*T_ref**(i)/(i) for i in range(1,5)]))-a1_a5_low[0]*math.log(T_ref)
a7_high = s/R - np.sum(np.array([a1_a5_high[i]*T_ref**(i)/(i) for i in range(1,5)]))-a1_a5_high[0]*math.log(T_ref)
nasa_coeffs = np.concatenate([[Tcommon], a1_a5_high, [a6_high], [a7_high], a1_a5_low, [a6_low], [a7_low]])
if plot:
Tlist = np.concatenate([T_low, T_high])
cp = [species.thermo.cp(T)/molecular_weight for T in Tlist] # [J/(kg·K)]
cp_fit_low = [ np.sum(np.array([a1_a5_low[i]*T**(i) for i in range(5)])) for T in T_low] # cp/R
cp_fit_high = [ np.sum(np.array([a1_a5_high[i]*T**(i) for i in range(5)])) for T in T_high] # cp/R
cp_fit = np.concatenate([cp_fit_low, cp_fit_high])*R
a1_a5_org_low = species.thermo.coeffs[8:13]
a1_a5_org_high = species.thermo.coeffs[1:6]
cp_bad_low = [ np.sum(np.array([a1_a5_org_low[i]*T**(i) for i in range(5)])) for T in T_low] # cp/R
cp_bad_high = [ np.sum(np.array([a1_a5_org_high[i]*T**(i) for i in range(5)])) for T in T_high] # cp/R
cp_bad = np.concatenate([cp_bad_low, cp_bad_high])*R
enthalpy = [species.thermo.h(T)/molecular_weight for T in Tlist] # J/kg
enthalpy_fit_low = [ a6_low + np.sum(np.array([a1_a5_low[i]*T**(i+1)/(i+1) for i in range(5)])) for T in T_low] # h/R
enthalpy_fit_high = [ a6_high + np.sum(np.array([a1_a5_high[i]*T**(i+1)/(i+1) for i in range(5)])) for T in T_high] # h/R
enthalpy_fit = np.concatenate([enthalpy_fit_low, enthalpy_fit_high])*R
fig = plt.figure()
ax1 = fig.add_subplot()
ax1.scatter(Tlist, cp, c='blue', label="cp_org, Tcommon=%d"%(species.thermo.coeffs[0]))
ax1.plot(Tlist, cp_fit, c='red', label="cp_fit, Tcommon=1000")
ax1.plot(Tlist, cp_bad, c='purple', label="cp_bad")
ax1.set_xlabel("T [K]")
ax1.set_ylabel("cp [J/kg]")
ax2 = plt.twinx()
ax2.scatter(Tlist, enthalpy, c='black', label="h_org, Tcommon=%d"%(species.thermo.coeffs[0]))
ax2.plot(Tlist, enthalpy_fit, c='green', label="h_fit, Tcommon=1000")
ax2.set_ylabel("h [J/kg]")
fig.legend(loc="lower right", bbox_to_anchor=(1,0), bbox_transform=ax1.transAxes)
plt.savefig("%s.png"%(species_name), dpi=500, bbox_inches='tight', pad_inches=0.1)
plt.close()
species_comp = ''
for atom in species.composition:
species_comp += '{:<3}'.format(atom.upper())
species_comp += '{:<2}'.format(str(int(species.composition[atom])))
species_phase = 'G'
# Ref: Table 3. Summary of the Rules for Thermo Data
# https://shepherd.caltech.edu/EDL/PublicResources/sdt/formats/chemkin.html#:~:text=The%20Chemkin%20thermo%20file%20format,%2C%20Sandia%20Report%20SAND89%2D8009.
line_1 = (
'{:<18}'.format(species_name) +
'{:<6}'.format(' ') +
'{:<20}'.format(species_comp) +
'{:<1}'.format(species_phase) +
'{:<28}'.format(temp_range) +
'{:<5}'.format(' ') +
'{:<1}'.format(' ') +
'{:<1}'.format('1') +
'\n')
f.write(line_1)
line_2_coeffs = build_nasa(nasa_coeffs, 2)
line_2 = line_2_coeffs + ' 2\n'
f.write(line_2)
line_3_coeffs = build_nasa(nasa_coeffs, 3)
line_3 = line_3_coeffs + ' 3\n'
f.write(line_3)
line_4_coeffs = build_nasa(nasa_coeffs, 4)
line_4 = line_4_coeffs + ' 4\n'
f.write(line_4)
f.write('END\n')
if __name__ == '__main__':
mech='mech.cti'
gas = ct.Solution(mech)
thermo_fileName_new = 'thermoCorrected.dat'
print(thermo_fileName_new)
plot=True # True or False
write(gas, thermo_fileName_new, plot)