viscosity.py Source File

#
#  viscosity.py
#  This file is part of ISOFT.
#  
#  Copyright 2018 Chris MacMackin <cmacmackin@gmail.com>
#  
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 3 of the License, or
#  (at your option) any later version.
#  
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#  
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#  MA 02110-1301, USA.
#  

'''Contains classes for calculating the viscosity of the ice
using different parameterisations.
'''

import numpy as np
import calculus

class NewtonianViscosity(object):
    '''A class representing Newtonian viscosity.

    value
        The viscosity value of the ice
    '''

    def __init__(this, value=1.0):
        this.val = value

    def __call__(this, uvec, temperature=-15.0, time=0):
        return this.val*np.ones_like(uvec[0,...])


class GlensLaw(object):
    '''A class using Glen's Law to represent viscosity. It treats
    viscosity as a power law for strain.

    size
        The number of Chebyshev modes in the field
    lower
        The lower boundary of the field domain
    upper
        The upper boundary of the field domain
    coef
        The coefficient by which Glen's Law is scaled
    index
        The index of the power law
    '''

    def __init__(this, size, lower=0.0, upper=1.0, coef=1.0, index=3):
        this.diff = calculus.Differentiator(size, lower, upper)
        this.coef = coef
        this.index = float(index)

    def __call__(this, uvec, temperature=-15.0, time=0):
        if (uvec.ndim > 2):
            raise NotImplementedError('GlensLaw only implemented for 1-D '
                                      'velocity field.')
        return 0.5*this.coef*abs(this.diff(uvec[:,0]))**(1./this.index - 1.)