12 January 2017

Soil model interface in Anura3D

Dr Alexander Rohe

Dynamic equilibrium liquid

Dynamic equilibrium mixture

Mass balance liquid

Constitutive equation

( )ll l l s l

npkg

r r= Ñ - - +v v v g&

( )1 s s l ln nr r r- + = Ñ × +v v σ g& &

(1 ) vol volls l

Kp n nn

e eé ù= - +ë û& &&

=σ D εg& &g

soil skeleton velocity

liquid velocity

porosity

solid density

liquid density

density of the mixture

liquid pressure

total stress tensor

strain tensor

tangent stiffness tensor

liquid bulk modulus

gravity vector

lvsv

nsr

lrr

pσεD

lKg

MPM is acontinuum-based

method

Governing equations (coupled 2-phase problem)

strain [-]

0

100

200

300

400

500

600

700

0 0.1 0.2 0.3 0.4 0.5 0.6

Relative density = 80%

Relative density = 63%

Relative density = 30%

s1–s2

[kPa

]

0.1 0.2 0.3 0.4 0.5 0.6

advanced material models can depend on:plastic strain, stress and strain rates, density, …

handling the history of state parameters is essential

triaxialconditions

1s

1s

2s2s

Constitutive model

Current constitutive models in Anura3D

• Linear Elasticity• Mohr-Coulomb Elasto-Plasticity• Mohr-Coulomb Elasto-Plasticity (Teunissen)• Mohr-Coulomb Strain-Softening• Mohr-Coulomb Suction Dependent• Isotropic Cone Hardening• Hypoplasticity Sand (Von Wolffersdorff)• Original Cam-Clay (Schofield and Wroth)• Modified Cam-Clay (Burland)• Nor-Sand (Jefferies)• Unsaturated Nor-Sand (Fern)• SANISAND (Dafalias and Manzari)• User-defined soil model (UMAT/VUMAT)

at different levels of:availability,validation,

testing,documentation,

robustness,reliability,

applicability,…

General constitutive model

Approach for user-defined soil model:

• external library (DLL) containing constitutive model

• standardised user-defined soil model interface (UMAT format)

• standardised material parameter input

• can be used in several environments (e.g. Abaqus, Plaxis, Tochnog, …)

Benefits

• standardised software interface (UMAT format)• modular set-up, well-documented• transferable to other (commercial) software products• development is software independent

• validation and testing possibilities• by e.g. using in other software, also single-element test

• straightforward implementation (using Fortran)• no specific Anura3D code knowledge necessary

• straightforward input of material parameters• standard interface in GiD available

• includable in material models database• automated testing and documentation

UMAT/VUMAT interface

www.soilmodels.infoUMAT+VUMAT routines,

open source database of models, documentation

UMAT à used in Abaqus/StandardVUMAT à used in Abaqus/Explicità for differences and interface: Bienen et al., 2014

Full definitions of the UMAT and VUMATrequirements and conventions are detailedin the Abaqus User Subroutines ReferenceManual v6.12 (Dassault Systèmes, 2012)

Example UMAT

Provide DLL for Anura3D

To use the external user-defined soil model, copy the DLLUMAT_mymodel.dll into the calculation directory together with theexecutable of Anura3D and the input files (CPS_001 and GOM)

`

Interface for user-defined soil model

`

`

Input file in ASCII format

automatically generatedwhen selecting “User-defined Soil Model”as “Material model solid” in pre-processor GiD

name of the external DLLcontaining the

user-defined soil model

array of 50 valuesspecifying the material

properties

Triaxial Test Simulation

Linear Elasticity

Triaxial Test Simulation

Mohr-Coulomb

Summary

• user-defined soil model interface available in Anura3D

• develop models in UMAT/VUMAT format

• test and compare UMAT with other (FE) software