Constitutive models¶

numgeo-ACT can calibrate eleven constitutive models, spanning the hypoplastic, IGS, ISA, SANISAND, high-cycle-accumulation and Ta-Ger families. Every model is a Python class in ACT.models and exposes the same interface, so switching models in a calibration is a one-line change.

Supported models¶

Model	Class	`name` string	Free parameters	Family / use
Hypoplasticity	`hypoplasticity`	`Hypoplasticity`	14	Classical sand hypoplasticity (von Wolffersdorff) with intergranular strain
Hypo-ISA	`hypoplasticity_isa`	`Hypo-ISA`	16	Hypoplasticity with Intergranular Strain Anisotropy — small-strain & cyclic
Hypo-IGS	`hypoplasticity_igs`	`Hypo-IGS`	13	Hypoplasticity with intergranular strain — small-strain & cyclic
ISA-SAND	`ISA`	`ISA-SAND`	21	ISA-based sand model
HCA-Sand	`HCA_sand`	`HCA_sand`	15	High-cycle accumulation (explicit) model
Sanisand	`sanisand`	`Sanisand`	17	SANISAND critical-state bounding-surface model
Sanisand-2	`sanisand2`	`Sanisand-2`	16	SANISAND variant
Sanisand-F	`sanisand_f`	`Sanisand-F`	18	SANISAND with fabric / memory-surface extension
Sanisand-MSf	`sanisand_msf`	`Sanisand-MSf`	29	SANISAND with semifluidized-state extension
Ta-Ger	`ta_ger`	`Ta-Ger`	11	Ta-Ger sand model
Mod-Ta-Ger	`mod_ta_ger`	`Mod-Ta-Ger`	14	Ta-Ger with fabric extension (inherits Ta-Ger)

The free parameters column gives how many parameters can be optimized (i.e. have a search bound). You choose which subset to actually optimize via the Free_parameter list in globals.setup; the rest stay fixed at the values you set.

Models map to numgeo

Each model's name string corresponds to the constitutive model implementation in numgeo. When numgeo-ACT writes the numgeo material for a simulation, it uses this name — so the calibration reflects the same model you will use in your boundary-value problems. See the numgeo material reference for the model formulations.

The common model interface¶

Every model class provides the same methods:

Method	Purpose
`set(...)`	assign parameter values (initial / fixed)
`set_bounds(...)`	override the lower/upper search interval of individual parameters
`update(parameter, value)`	set a single parameter by name
`get_parameter(parameter)`	read a single parameter by name
`list_parameter_all()`	list every parameter of the model
`list_parameter_optimize(free)`	list the parameters being optimized
`list_parameter_fixed(free)`	list the parameters held fixed
`parameter_bounds(free_parameter)`	the bounds of the free parameters
`write_numgeo_material(...)`	write the numgeo material definition
`write_numgeo_initial_state_variables(...)`	write the initial state variables

The constructor of every model accepts three output directories (with sensible defaults):

model = hypoplasticity_isa(
    out_dir="./results/",     # final results
    out_dir2="./run_tmp/",    # temporary run files
    out_dir3="./run_final/",  # final run files
)

Typical use in a calibration¶

from ACT.models import sanisand2

model = sanisand2()                       # defaults + default bounds are pre-set
model.set(G0=120, Mc=1.30, lambdac=0.03)  # initial / fixed values
model.set_bounds(G0=[80, 160], Mc=[1.1, 1.5])  # narrow some search intervals

# read / write single parameters
model.update("nb", 1.2)
print(model.get_parameter("nb"))

Then list the free parameters in setup:

globals.setup(
    Model=model,
    Free_parameter=["G0", "Mc", "lambdac", "nb", "h0", "cz"],
    ...,
)

Choosing a model¶

Each model page documents the model's purpose, its default search bounds, the exact arguments of set / set_bounds, and the parameters available for optimization:

Hypoplastic family¶

Hypoplasticity · Hypo-IGS · Hypo-ISA · ISA-SAND — incrementally nonlinear models with intergranular-strain / ISA extensions for small-strain and cyclic behaviour.

Critical-state-line helper¶

Critical-state-line calibration — Bauer and Li-Wang CSL fitting from direct \(p\)-\(e\) data, oedometric compression data or Bolton-generated points.

SANISAND family¶

Sanisand · Sanisand-2 · Sanisand-F · Sanisand-MSf — critical-state bounding-surface plasticity for sands, including fabric and semifluidized extensions for liquefaction.

High-cycle accumulation¶

HCA-Sand — explicit accumulation model for very large numbers of load cycles, calibrated against HCA tests.

Ta-Ger family¶

Ta-Ger · Mod-Ta-Ger — the Ta-Ger sand model and its fabric-extended variant.