Using Higher Order Basis Functions - geomechanics/mpm GitHub Wiki

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Quadratic BSpline

To run a quadratic BSpline elements: ED2Q4P2B (2D) and ED3H8P2B (3D), additional settings should be added in the main .json file.

"mesh": {
          "cell_type": "ED3H8P2B",
          "nonlocal_mesh_properties": {
			"type": "BSPLINE",
			"node_types": [
				{
					"nset_id": 0,
					"dir": 0,
					"type": 1
				},
                               {...}
                         ]
          }
}

In the "nonlocal_mesh_properties" section the following settings are required:

• "type" should be "BSPLINE".
• "node_types" should be defined for each direction {0, 1, 2} for {x, y, z} following this convention:

  //! Regular = 0 //Default
  //! LowerBoundary = 1
  //! LowerIntermediate = 2
  //! UpperIntermediate = 3
  //! UpperBoundary = 4

Reference:

• Steffen, M., Kirby, R. M., & Berzins, M. (2008). Analysis and reduction of quadrature errors in the material point method (MPM). International journal for numerical methods in engineering, 76(6), 922-948.

Local Maximum Entropy (LME)

To run the Local Maximum Entropy (LME) elements: ED2T3L, ED2Q4L (2D), and ED3H8L (3D), additional settings should be added to the main .json file.

"mesh": {
          "cell_type": "ED2Q4L",
          "nonlocal_mesh_properties": {
			"type": "LME",
			"gamma": XX,
			"anisotropy": true, //optional default is false
                        "mesh_size": YY, //optional (if it is not given, an automatic computation will be done)
                        "support_tolerance": ZZ //optional default is 1e-6
          }
}

In the "nonlocal_mesh_properties" section the following settings are required:

• "type" should be "LME".
• "gamma" is a non-dimensional thermalization parameter.
• "anisotropy" boolean to shift the metric tensor within the LME computation.
• "mesh_size" is the average mesh size, which is assumed to be constant in the current case.
• "support_tolerance" is the threshold magnitude of the shape function value.

Reference:

• Arroyo, M., & Ortiz, M. (2006). Local maximum‐entropy approximation schemes: a seamless bridge between finite elements and meshfree methods. International journal for numerical methods in engineering, 65(13), 2167-2202.