Computational Infrastructure for Geodynamics

Parameter file syntax change for strain weakening behavior

jbnaliboff September 23, 2019, 5:46pm 1

Hello all,

Those of you following the ASPECT github page have likely noticed that the development group is working on simplifying the material model structure by creating very specific rheology (and equation of state) “components”, which are then accesses by the material model.

One example of these components is “strain dependent” rheological behavior, which was implemented in the ViscoPlastic material model in order to simulate brittle or viscous strain-weakening behavior.

In moving the strain weakening portions of code to a new StrainDependent class (pull request #3219), we decided it was a reasonable time to remove backwards compatibility for an older syntax used to prescribe strain weakening.

If you are using the ASPECT master branch and have updated to include pull request (#3223, merged on September 23rd) the parameter syntax for strain weakening will no longer work.

Our normal procedure is to provide an update script that will automatically convert parameters to use the new syntax, but in this case it would have been overly complicated and we decided to use a forum announcement instead.

The old strain weakening syntax required specifying one or multiple parameters:
Use strain weakening
Use plastic strain weakening
Use viscous strain weakening
Use finite strain tensor

An earlier pull request changed this syntax to require only one input parameter (Strain weakening mechanism) to specify the type of strain weakening mechanism.

Examples of how to use the new syntax can be found in the following ASPECT tests:

github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_plastic_strain_weakening.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 0
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_plastic_strain_weakening
set Timing output frequency                = 1
    
subsection Solver parameters
  subsection Stokes solver parameters
    set Number of cheap Stokes solver steps = 0
  end
end

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box
  subsection Box

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github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_plastic_viscous_strain_weakening.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 0
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_plastic_viscous_strain_weakening
set Timing output frequency                = 1

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box
  subsection Box
    set X repetitions = 10
    set Y repetitions = 10
    set X extent      = 100e3
    set Y extent      = 100e3
  end
end

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github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_strain_weakening_full_strain_tensor.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 1e2
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_strain_weakening_full_strain_tensor
set Timing output frequency                = 1

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box
  subsection Box
    set X repetitions = 10
    set Y repetitions = 10
    set X extent      = 100e3
    set Y extent      = 100e3
  end
end

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github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_strain_weakening.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 1
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_strain_weakening
set Timing output frequency                = 1

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box
  subsection Box
    set X repetitions = 10
    set Y repetitions = 10
    set X extent      = 100e3
    set Y extent      = 100e3
  end
end

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github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_viscous_strain_weakening_particles.prm

include $ASPECT_SOURCE_DIR/tests/visco_plastic_yield_viscous_strain_weakening.prm

# Particles mapped to the Compositional fields used to track finite strain invariant
subsection Compositional fields

  set Compositional field methods = particles
  set Mapped particle properties =  viscous_strain:viscous_strain
end

# Post processing
# named additional outputs includes the weakened cohesions and friction angles
subsection Postprocess
  set List of postprocessors = velocity statistics, mass flux statistics, visualization, particles
  
  subsection Particles
    set Number of particles = 1e5
    set Time between data output = 0
    set Data output format = none
    set List of particle properties = viscoplastic strain invariants
    set Particle generator name = random uniform

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github.com

geodynamics/aspect/blob/master/tests/visco_plastic_yield_viscous_strain_weakening.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 0
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_viscous_strain_weakening
set Timing output frequency                = 1

subsection Solver parameters
  subsection Stokes solver parameters
    set Number of cheap Stokes solver steps = 0
  end
end

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box
  subsection Box

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If you have any questions about these changes or how to update your parameter file, please let us know!

Cheers,
John

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