Source code for burnman.eos.modified_tait

# This file is part of BurnMan - a thermoelastic and thermodynamic toolkit for the Earth and Planetary Sciences
# Copyright (C) 2012 - 2017 by the BurnMan team, released under the GNU
# GPL v2 or later.

from __future__ import absolute_import

import warnings
import numpy as np

from . import equation_of_state as eos

def tait_constants(params):
"""
returns parameters for the modified Tait equation of state
derived from K_T and its two first pressure derivatives
EQ 4 from Holland and Powell, 2011
"""
a = (1. + params['Kprime_0']) / (
1. + params['Kprime_0'] + params['K_0'] * params['Kdprime_0'])
b = params['Kprime_0'] / params['K_0'] - \
params['Kdprime_0'] / (1. + params['Kprime_0'])
c = (1. + params['Kprime_0'] + params['K_0'] * params['Kdprime_0']) / (
params['Kprime_0'] * params['Kprime_0'] + params['Kprime_0'] - params['K_0'] * params['Kdprime_0'])
return a, b, c

def modified_tait(x, params):
"""
equation for the modified Tait equation of state, returns
pressure in the same units that are supplied for the reference bulk
modulus (params['K_0'])
EQ 2 from Holland and Powell, 2011
"""
a, b, c = tait_constants(params)
return (np.power((x + a - 1.) / a, -1. / c) - 1.) / b + params['P_0']

def volume(pressure, params):
"""
Returns volume [m^3] as a function of pressure [Pa] and temperature [K]
EQ 12
"""
a, b, c = tait_constants(params)
x = 1 - a * \
(1. - np.power((1. + b * (pressure - params['P_0'])), -1.0 * c))
return x * params['V_0']

def bulk_modulus(pressure, params):
"""
Returns isothermal bulk modulus :math:K_T of the mineral. :math:[Pa].
EQ 13+2
"""
a, b, c = tait_constants(params)
return params['K_0'] * (1. + b * (pressure - params['P_0'])) * (a + (1. - a) * np.power((1. + b * (pressure - params['P_0'])), c))

def intVdP(pressure, params):
"""
Returns the integral of VdP for the mineral. :math:[J].
EQ 13
"""
a, b, c = tait_constants(params)
psubpth = pressure - params['P_0']

if pressure != params['P_0']:
intVdP = ((pressure - params['P_0'])
* params['V_0']
* (1. - a + (a * (1. - np.power((1. + b * (psubpth)), 1. - c))
/ (b * (c - 1.)
* (pressure - params['P_0'])))))
else:
intVdP = 0.
return intVdP

[docs]class MT(eos.EquationOfState):

"""
Base class for the generic modified Tait equation of state.
References for this can be found in :cite:HC1974
and :cite:HP2011 (followed here).

An instance "m" of a Mineral can be assigned this
equation of state with the command m.set_method('mt')
(or by initialising the class with the param
equation_of_state = 'mt').
"""

[docs]    def volume(self, pressure, temperature, params):
"""
Returns volume :math:[m^3] as a function of pressure :math:[Pa].
"""
return volume(pressure, params)

[docs]    def pressure(self, temperature, volume, params):
"""
Returns pressure [Pa] as a function of temperature [K] and volume[m^3]
"""
return modified_tait(params['V_0'] / volume, params)

[docs]    def isothermal_bulk_modulus(self, pressure, temperature, volume, params):
"""
Returns isothermal bulk modulus :math:K_T of the mineral. :math:[Pa].
"""
return bulk_modulus(pressure, params)

[docs]    def adiabatic_bulk_modulus(self, pressure, temperature, volume, params):
"""
Since this equation of state does not contain temperature effects, simply return a very large number. :math:[Pa]
"""
return 1.e99

[docs]    def shear_modulus(self, pressure, temperature, volume, params):
"""
Not implemented in the Modified Tait EoS. :math:[Pa]
Returns 0.
Could potentially apply a fixed Poissons ratio as a rough estimate.
"""
return 0.

[docs]    def entropy(self, pressure, temperature, volume, params):
"""
Returns the molar entropy :math:\mathcal{S} of the mineral. :math:[J/K/mol]
"""
return 0.

[docs]    def molar_internal_energy(self, pressure, temperature, volume, params):
"""
Returns the internal energy :math:\mathcal{E} of the mineral. :math:[J/mol]
"""

return self.gibbs_free_energy(pressure, temperature, volume, params) - volume*pressure

[docs]    def gibbs_free_energy(self, pressure, temperature, volume, params):
"""
Returns the Gibbs free energy :math:\mathcal{G} of the mineral. :math:[J/mol]
"""
# G = int VdP = [PV] - int PdV = E + PV
a, b, c = tait_constants(params)

intVdP = params['V_0']*( a/(b*(1. - c)) *
(np.power(b*(pressure - params['P_0']) + 1.,
1. - c) - 1.) +
(1. - a)*(pressure - params['P_0']))

return intVdP + params['E_0'] + params['V_0']*params['P_0']

[docs]    def molar_heat_capacity_v(self, pressure, temperature, volume, params):
"""
Since this equation of state does not contain temperature effects, simply return a very large number. :math:[J/K/mol]
"""
return 1.e99

[docs]    def molar_heat_capacity_p(self, pressure, temperature, volume, params):
"""
Since this equation of state does not contain temperature effects, simply return a very large number. :math:[J/K/mol]
"""
return 1.e99

[docs]    def thermal_expansivity(self, pressure, temperature, volume, params):
"""
Since this equation of state does not contain temperature effects, simply return zero. :math:[1/K]
"""
return 0.

[docs]    def grueneisen_parameter(self, pressure, temperature, volume, params):
"""
Since this equation of state does not contain temperature effects, simply return zero. :math:[unitless]
"""
return 0.

[docs]    def validate_parameters(self, params):
"""
Check for existence and validity of the parameters
"""

if 'E_0' not in params:
params['E_0'] = 0.
if 'P_0' not in params:
params['P_0'] = 1.e5

# G and Gprime are not defined in this equation of state,
# We can model density and bulk modulus just fine without them,
# so just add them to the dictionary as nans
if 'G_0' not in params:
params['G_0'] = float('nan')
if 'Gprime_0' not in params:
params['Gprime_0'] = float('nan')

# Check that all the required keys are in the dictionary
expected_keys = [
'V_0', 'K_0', 'Kprime_0', 'Kdprime_0', 'G_0', 'Gprime_0']
for k in expected_keys:
if k not in params:
raise KeyError('params object missing parameter : ' + k)

# Finally, check that the values are reasonable.
if params['P_0'] < 0.:
warnings.warn('Unusual value for P_0', stacklevel=2)
if params['V_0'] < 1.e-7 or params['V_0'] > 1.e-2:
warnings.warn('Unusual value for V_0', stacklevel=2)
if params['K_0'] < 1.e9 or params['K_0'] > 1.e13:
warnings.warn('Unusual value for K_0', stacklevel=2)
if params['Kprime_0'] < 0. or params['Kprime_0'] > 40.:
warnings.warn('Unusual value for Kprime_0', stacklevel=2)
if params['G_0'] < 0.0 or params['G_0'] > 1.e13:
warnings.warn('Unusual value for G_0', stacklevel=2)
if params['Gprime_0'] < -5. or params['Gprime_0'] > 10.:
warnings.warn('Unusual value for Gprime_0', stacklevel=2)