bootstrap_impl define_model_state_impl diagnostics_impl init_impl init_t_last init_usurf_target m_dhdt_min m_dphi_max m_dphi_min m_dphi_scale m_mask m_phi0_max m_phi0_min m_phi_max m_t_eps m_t_last m_time_name m_topg_max m_topg_min m_update_interval m_usurf_difference m_usurf_target max_timestep_impl OptTillphiYieldStress restart_impl update_impl update_tillphi write_model_state_impl ~OptTillphiYieldStress

update_impl() void pism::OptTillphiYieldStress::update_impl ( const YieldStressInputs &  inputs, double  t, double  dt  ) privatevirtual 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 $W+W_{till}$. Reimplemented from pism::MohrCoulombYieldStress. Definition at line 198 of file OptTillphiYieldStress.cc. References pism::Geometry::bed_elevation, pism::Geometry::cell_type, pism::YieldStressInputs::geometry, pism::Geometry::ice_surface_elevation, m_t_eps, m_t_last, m_update_interval, PISM_ERROR_LOCATION, pism::MohrCoulombYieldStress::update_impl(), and update_tillphi().