The input_data.json format

AMPSSIE drives every analysis from a single JSON file, named input_data.json. The file is one JSON object whose top-level keys correspond to the components of the model: the Mesh, the Initial GIMP distribution, the Boundary conditions, the Material properties and models, the Rigid body, the Solver and the Output data.

This page describes each of the sections in turn and gives a description of each of the options available for each section. This page is designed to act as a reference for constructing your own simulations, however for worked examples please see the tutorial page.

Overall file format

The input_data.json file is split into seven section provided in the table below:

Key	Type	Purpose	Required
"Mesh"	object	Domain extents and the background-grid element size.	Yes
"Initial GIMP distribution"	object	Extent of the initial material-point fill.	Yes
"Boundary conditions"	object	Per-face kinematic conditions and optional per-DOF fixes.	Yes
"Material"	object	Constitutive type and properties for each soil layer.	Yes
"Rigid body"	object	Geometry, kinematics and contact parameters for the rigid body.	Optional
"Solver"	object	Solve type, load type and the number of increments.	Yes
"Output Data"	object	VTU / VTK switches and a stem string for text output.	Yes

These appear as headings in the JSON file:

"Mesh":
{
    ...
},
"Initial GIMP distribution":
{
...
},
"Boundary conditions":
{
...
},
"Material":
{
...
},
"Rigid body":
{
...
},
"Solver":
{
    ...
},
"Output Data":
{
    ...
}

where the ... indicates text.

Mesh

The Mesh object sets the size of the background grid and the element size.

Example:

"Mesh": {
    "domain size x": 0.8,
    "domain size y": 0.8,
    "domain size z": 0.8,
    "dx refined": 0.4
}

Field	Type	Description
"domain size x", "domain size y", "domain size z"	number (m)	Length of the computational domain along each axis.
"dx refined"	number (m)	Element size, uniform in \(x\), \(y\) and \(z\).

Initial GIMP distribution

Specifies the volume in which material points are initially placed. Each element contains a \(2 \times 2 \times 2\) grid of GIMPs by default.

Example:

"Initial GIMP distribution": {
    "Initial GIMP distribution x": 0.8,
    "Initial GIMP distribution y": 0.8,
    "Initial GIMP distribution z": 0.8
}

Field	Type	Default	Description
"Initial GIMP distribution x", "Initial GIMP distribution y", "Initial GIMP distribution z"	number (m)		Extent of the GIMP-filled volume along each axis.
"number GIMP"	number	2	Optional, defines the number of GIMPs in each direction per element.

Boundary conditions

Mesh face and DOF boundary conditions. If the faces or DOFs are not listed, the default for both is "free".

Example:

"Boundary conditions": {
    "neg x-plane": "roller",
    "neg y-plane": "roller",
    "neg z-plane": "free",
    "pos x-plane": "roller",
    "pos y-plane": "roller",
    "pos z-plane": "fixed",
    "x dof": "fixed",
    "y dof": "fixed",
    "z dof": "free"
}

Field	Type	Options	Default	Description
"neg x-plane", "neg y-plane", "neg z-plane"	string	"roller", "free", "fixed"	"free"	Optional condition on each negative mesh face; the face location is set by the domain size x/y/z extents in Mesh.
"pos x-plane", "pos y-plane", "pos z-plane"	string	"roller", "free", "fixed"	"free"	Optional condition on each positive mesh face. Faces default to "free" if omitted from the JSON.
"x dof", "y dof", "z dof"	string	"fixed", "free"	"free"	Optional global DOF constraint applied to every node. Useful for keeping the problem one-dimensional in compression.

Material

Specifies how many soil layers the model contains and, for each layer, the constitutive type and properties.

Example:

"Material": {
    "number of layers": 1,
    "layers": [
        {
            "type": "Elastic",
            "empirical data": "homogeneous elastic",
            "assigned material properties": {"E": 1000.0, "nu": 0.0, "rho": 50.0}
        }
    ]
}

Field	Type	Description
"number of layers"	integer	Number of distinct material layers.
"layers"	array of objects	One object per layer; the sub-fields below apply to each entry.
"type"	string	Constitutive model.
"empirical data"	string	Preset that supplies any empirically-calibrated parameters not listed below.
"assigned material properties.E"	number (Pa)	Young's modulus. (Pa)
"assigned material properties.nu"	number	Poisson's ratio.
"assigned material properties.rho"	number (kg/m³)	Density (kg/m\(^3\)).

Rigid body

Optional. Describes the geometry, position and contact parameters of a rigid body.

Example:

"Rigid body": {
    "geometry": "cube.stl",
    "initial position z": 0.8,
    "prescribed displacement z": -0.2,
    "normal penalty factor": 1000
}

Field	Type	Default	Description
"geometry"	string		.stl file name, relative to the top-level AMPPSIE folder.
"initial position min x", "initial position min y", "initial position min z"	number (m)	.stl file location	Initial x/y/z-position of the rigid body's lowest point in the \(x\), \(y\) and \(z\) direction.
"prescribed displacement x", "prescribed displacement y", "prescribed displacement z"	number (m)		Total vertical displacement applied over Solver.number of increments steps.
"normal penalty factor"	number		Penalty stiffness scaling that enforces non-penetration.

Solver

Selects the solve type, how the loading is applied and the number of load increments.

"Solver": {
    "solve type": "static",
    "load type": "rigid body displacement",
    "number of increments": 20
}

Field	Type	Options	Description
"solve type"	string	"static"	Turns on and off interia terms
"load type"	string	"force","displacement"	How the load is applied.
"number of increments"	integer		Number of pseudo-time / load increments.

Output Data

Switches the supported output streams on or off and supplies a stem string used to name text-output files.

"Output Data": {
    "vtu data": "yes",
    "vtk data": "yes",
    "text data": "contact cube"
}

Field	Type	Options	Description
"vtu data"	string	"yes", "no"	Set to "yes" to write VTU files.
"vtk data"	string	"yes", "no"	Set to "yes" to write VTK files.
"text data"	string	"contact cube", "self-weight column"	Stem used for tabulated text output. Tutorial 1: "column validation". Tutorial 2: "contact cube".