bootstrap_impl define_model_state_impl diagnostics_impl finish_initialization init_impl m_delta m_till_phi max_timestep_impl MohrCoulombYieldStress restart_impl set_till_friction_angle till_friction_angle till_friction_angle update_impl write_model_state_impl ~MohrCoulombYieldStress

update_impl() void pism::MohrCoulombYieldStress::update_impl ( const YieldStressInputs &  inputs, double  t, double  dt  ) protectedvirtual Update the till yield stress for use in the pseudo-plastic till basal stress model. See also IceBasalResistancePlasticLaw. Updates yield stress $\tau_c$ based on modeled till water layer thickness from a Hydrology object. We implement the Mohr-Coulomb criterion allowing a (typically small) till cohesion $c_0$ and by expressing the coefficient as the tangent of a till friction angle $\varphi$ : $$\tau_c = c_0 + (\tan \varphi) N_{till}.$$ See [Paterson] table 8.1 regarding values. The effective pressure on the till is empirically-related to the amount of water in the till. We use this formula derived from [Tulaczyketal2000] and documented in [BuelervanPeltDRAFT]: $$N_{till} = \min\left\{P_o, N_0 \left(\frac{\delta P_o}{N_0}\right)^s 10^{(e_0/C_c) (1 - s)}\right\}$$ where $s = W_{till} / W_{till}^{max}$, $W_{till}^{max}$ =hydrology_tillwat_max, $\delta$ =basal_yield_stress.mohr_coulomb.till_effective_fraction_overburden, $P_o$ is the overburden pressure, $N_0$ =basal_yield_stress.mohr_coulomb.till_reference_effective_pressure is a reference effective pressure, $e_0$ =basal_yield_stress.mohr_coulomb.till_reference_void_ratio is the void ratio at the reference effective pressure, and $C_c$ =basal_yield_stress.mohr_coulomb.till_compressibility_coefficient is the coefficient of compressibility of the till. Constants $N_0, e_0, C_c$ are found by [Tulaczyketal2000] from laboratory experiments on samples of till. If basal_yield_stress.add_transportable_water is yes then $s$ in the above formula becomes $s = (W + W_{till}) / W_{till}^{max}$, that is, the water amount is the sum $W+W_{till}$. Implements pism::YieldStress. Reimplemented in pism::OptTillphiYieldStress. Definition at line 265 of file MohrCoulombYieldStress.cc. References pism::array::Array2D< T >::add(), pism::Geometry::bed_elevation, pism::Geometry::cell_type, pism::YieldStressInputs::geometry, pism::Geometry::ice_thickness, pism::YieldStress::m_basal_yield_stress, pism::Component::m_config, m_delta, pism::Component::m_grid, m_till_phi, pism::Geometry::sea_level_elevation, pism::YieldStressInputs::subglacial_water_thickness, pism::YieldStressInputs::till_water_thickness, pism::array::Array::update_ghosts(), and pism::MohrCoulombPointwise::yield_stress(). Referenced by pism::OptTillphiYieldStress::update_impl().