Multimaterial MPM - Revision history

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-29T18:03:16Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 18:03, 29 March 2026
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	** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.		** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.
	** <tt>linreg</tt> (or 5) - use linear regression. Logistic regression<ref name="logreg"/> make an initial guess by linear regression and then refines the norm by further calculations. Choosing linear regression simply stops with the initial guess of the the preferred logistic regression methods.		** <tt>linreg</tt> (or 5) - use linear regression. Logistic regression<ref name="logreg"/> make an initial guess by linear regression and then refines the norm by further calculations. Choosing linear regression simply stops with the initial guess of the the preferred logistic regression methods.
	** <tt>avggrad</tt> (or 2) - the normal is found from the volume-weighted mean volume gradient. When contact is all non-rigid materials, it averages the gradient of one material with the net gradient of all other materials. When a rigid material is involved, it averages each material with the one rigid material ~~(<tt>avggrad</tt> is the default normals option)~~.		** <tt>avggrad</tt> (or 2) - the normal is found from the volume-weighted mean volume gradient. When contact is all non-rigid materials, it averages the gradient of one material with the net gradient of all other materials. When a rigid material is involved, it averages each material with the one rigid material.
	** <tt>specify</tt> (or 4) - use a single, specified normal defined by the provided azimuth and polar angles. The specified normal is used for all contact calculations and it should point from the lower-numbered field into the higher-numbered field. The field number is the order the materials are added to the simulated object (see "FULL MASS MATRIX" section of output for field number used by each material). For contact with rigid materials, the normal vector should point from the non-rigid material into the rigid material.		** <tt>specify</tt> (or 4) - use a single, specified normal defined by the provided azimuth and polar angles. The specified normal is used for all contact calculations and it should point from the lower-numbered field into the higher-numbered field. The field number is the order the materials are added to the simulated object (see "FULL MASS MATRIX" section of output for field number used by each material). For contact with rigid materials, the normal vector should point from the non-rigid material into the rigid material.
	** <tt>maxgrad</tt> (or 0) - the normal is found from the one material at the node that has the largest magnitude of its volume gradient.		** <tt>maxgrad</tt> (or 0) - the normal is found from the one material at the node that has the largest magnitude of its volume gradient.

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-29T18:02:38Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 18:02, 29 March 2026
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	* <tt>(normals)</tt> - the method for calculation of [[Surface Normals#Multimaterial Normal Vector Options\|normal vectors]]. The options are as follows (<tt>XML</tt> files must use numeric value):		* <tt>(normals)</tt> - the method for calculation of [[Surface Normals#Multimaterial Normal Vector Options\|normal vectors]]. The options are as follows (<tt>XML</tt> files must use numeric value):
	** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.		** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.
	** <tt>linreg</tt> (or 5) - use linear regression.		** <tt>linreg</tt> (or 5) - use linear regression. Logistic regression<ref name="logreg"/> make an initial guess by linear regression and then refines the norm by further calculations. Choosing linear regression simply stops with the initial guess of the the preferred logistic regression methods.
	** <tt>avggrad</tt> (or 2) - the normal is found from the volume-weighted mean volume gradient. When contact is all non-rigid materials, it averages the gradient of one material with the net gradient of all other materials. When a rigid material is involved, it averages each material with the one rigid material (<tt>avggrad</tt> is the default normals option).		** <tt>avggrad</tt> (or 2) - the normal is found from the volume-weighted mean volume gradient. When contact is all non-rigid materials, it averages the gradient of one material with the net gradient of all other materials. When a rigid material is involved, it averages each material with the one rigid material (<tt>avggrad</tt> is the default normals option).
	** <tt>specify</tt> (or 4) - use a single, specified normal defined by the provided azimuth and polar angles. The specified normal is used for all contact calculations and it should point from the lower-numbered field into the higher-numbered field. The field number is the order the materials are added to the simulated object (see "FULL MASS MATRIX" section of output for field number used by each material). For contact with rigid materials, the normal vector should point from the non-rigid material into the rigid material.		** <tt>specify</tt> (or 4) - use a single, specified normal defined by the provided azimuth and polar angles. The specified normal is used for all contact calculations and it should point from the lower-numbered field into the higher-numbered field. The field number is the order the materials are added to the simulated object (see "FULL MASS MATRIX" section of output for field number used by each material). For contact with rigid materials, the normal vector should point from the non-rigid material into the rigid material.

Nairnj: /* References */

2026-03-29T16:55:51Z

References

← Older revision		Revision as of 16:55, 29 March 2026
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	<ref name="Nairn">J.A. Nairn, "Modeling Imperfect Interfaces in the Material Point Method using Multimaterial Methods," ''Computer Modeling in Eng. & Sci.'', '''92''', 271-299 (2013). ([https://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MMInterfaces.pdf See PDF])</ref>		<ref name="Nairn">J.A. Nairn, "Modeling Imperfect Interfaces in the Material Point Method using Multimaterial Methods," ''Computer Modeling in Eng. & Sci.'', '''92''', 271-299 (2013). ([https://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MMInterfaces.pdf See PDF])</ref>

	<ref name="gencontact">J. A. Nairn, S. G. Bardenhagen, and G. S. Smith, "Generalized contact and improved frictional heating in the material point method.=," ''Computational Particle Mechanics'', '''5''', 285–296 (2018)</ref>		<ref name="gencontact">J. A. Nairn, S. G. Bardenhagen, and G. S. Smith, "Generalized contact and improved frictional heating in the material point method.=," ''Computational Particle Mechanics'', '''5''', 285–296 (2018) ([https://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MPMContactLawsSV.pdf See PDF])</ref>

	<ref name="logreg">J. A. Nairn, C. C. Hammerquist, and G. Smith, "New material point method contact algorithms for improved accuracy, large-deformation problems, and proper null-space filtering," ''Computer Methods in Applied Mechanics and Engineering'', '''362''', 112859 (2020). ([http://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MPMContactRevisited.pdf See PDF])</ref>		<ref name="logreg">J. A. Nairn, C. C. Hammerquist, and G. Smith, "New material point method contact algorithms for improved accuracy, large-deformation problems, and proper null-space filtering," ''Computer Methods in Applied Mechanics and Engineering'', '''362''', 112859 (2020). ([http://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MPMContactRevisited.pdf See PDF])</ref>

Nairnj: /* References */

2026-03-29T16:54:53Z

References

← Older revision		Revision as of 16:54, 29 March 2026
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	<ref name="Lemiale">V. Lemiale, A. Hurmane, and J. A. Nairn, "Material Point Method Simulation of Equal Channel Angular Pressing Involving Large Plastic Strain and Contact Through Sharp Corners," <i>Computer Modeling in Eng. & Sci.</i>, <b>70(1)</b>, 41-66, (2010).</ref>		<ref name="Lemiale">V. Lemiale, A. Hurmane, and J. A. Nairn, "Material Point Method Simulation of Equal Channel Angular Pressing Involving Large Plastic Strain and Contact Through Sharp Corners," <i>Computer Modeling in Eng. & Sci.</i>, <b>70(1)</b>, 41-66, (2010).</ref>

	<ref name="Nairn">J.A. Nairn, "Modeling Imperfect Interfaces in the Material Point Method using Multimaterial Methods," ''Computer Modeling in Eng. & Sci.'', '''92''', 271-299 (2013).</ref>		<ref name="Nairn">J.A. Nairn, "Modeling Imperfect Interfaces in the Material Point Method using Multimaterial Methods," ''Computer Modeling in Eng. & Sci.'', '''92''', 271-299 (2013). ([https://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MMInterfaces.pdf See PDF])</ref>

	<ref name="gencontact">J. A. Nairn, S. G. Bardenhagen, and G. S. Smith, "Generalized contact and improved frictional heating in the material point method.=," ''Computational Particle Mechanics'', '''5''', 285–296 (2018)</ref>		<ref name="gencontact">J. A. Nairn, S. G. Bardenhagen, and G. S. Smith, "Generalized contact and improved frictional heating in the material point method.=," ''Computational Particle Mechanics'', '''5''', 285–296 (2018)</ref>

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-29T16:52:47Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 16:52, 29 March 2026
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	(commands to set default contact properties)		(commands to set default contact properties)

	A deprecated [[#Deprecated Multimaterial Mode Command\|<tt>MultimaterialMode</tt>]] command still works and may be found in old input files or might be needed in older versions of [[NairnFEAMPM]] or [[~~NairnFEAMPMVia~~]]. In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:		A deprecated [[#Deprecated Multimaterial Mode Command\|<tt>MultimaterialMode</tt>]] command still works and may be found in old input files or might be needed in older versions of [[NairnFEAMPM]] or [[NairnFEAMPMViz]]. In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:

	<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>		<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-29T16:52:36Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 16:52, 29 March 2026
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	(commands to set default contact properties)		(commands to set default contact properties)

	A deprecated [[#Deprecated Multimaterial Mode Command\|<tt>MultimaterialMode</tt>]] command still works and may be found in old input files ~~and~~ be ~~need~~ in older ~~version~~ of [[NairnFEAMPM]] or [[NairnFEAMPMVia]]. In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:		A deprecated [[#Deprecated Multimaterial Mode Command\|<tt>MultimaterialMode</tt>]] command still works and may be found in old input files or might be needed in older versions of [[NairnFEAMPM]] or [[NairnFEAMPMVia]]. In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:

	<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>		<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>

Nairnj at 16:52, 29 March 2026

2026-03-29T16:52:03Z

← Older revision		Revision as of 16:52, 29 March 2026
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	* <tt>(cutoff)</tt> - this optional parameter sets the displacement cutoff (relative to cell size) used to [[Detecting Contact\|detect multimaterial contact]] and normal separation. The [[Detecting Contact#Selecting ContactPosition Options\|<tt>ContactPosition</tt> command]] should be omitted when modeling internal material interfaces that start out initially in contact. It must be included for problems where contact surfaces start out separated but move into contact during the simulation. It is not used when finding normal by <tt>linreg</tt> or <tt>logreg</tt> (unless they have rigid contact and have set <tt>(rigidBiasOrAzimuth)</tt>≥10), but would still be used when finding tangential displacement (See [[Detecting Contact#Imperfect Interface Extrapolations\|detecting contact]] for why this option should not be used when modeling [[Imperfect Interfaces\|imperfect interfaces]]).		* <tt>(cutoff)</tt> - this optional parameter sets the displacement cutoff (relative to cell size) used to [[Detecting Contact\|detect multimaterial contact]] and normal separation. The [[Detecting Contact#Selecting ContactPosition Options\|<tt>ContactPosition</tt> command]] should be omitted when modeling internal material interfaces that start out initially in contact. It must be included for problems where contact surfaces start out separated but move into contact during the simulation. It is not used when finding normal by <tt>linreg</tt> or <tt>logreg</tt> (unless they have rigid contact and have set <tt>(rigidBiasOrAzimuth)</tt>≥10), but would still be used when finding tangential displacement (See [[Detecting Contact#Imperfect Interface Extrapolations\|detecting contact]] for why this option should not be used when modeling [[Imperfect Interfaces\|imperfect interfaces]]).
	* <tt> (commands to set default contact properties)</tt> - set default [[Friction\|contact]] or [[Imperfect Interfaces\|imperfect interface]] properties for multimaterial contact. Note that when more than two materials are present, you can use [[Material Models\|material]] properties for [[Common Material Properties#Contact Properties\|friction and interface]] to override the default settings and thereby set custom contact between any specific pair of materials.		* <tt> (commands to set default contact properties)</tt> - set default [[Friction\|contact]] or [[Imperfect Interfaces\|imperfect interface]] properties for multimaterial contact. Note that when more than two materials are present, you can use [[Material Models\|material]] properties for [[Common Material Properties#Contact Properties\|friction and interface]] to override the default settings and thereby set custom contact between any specific pair of materials.

			== Deprecated Multimaterial Mode Command ==

			Multimaterial MPM can also be activated with the deprecated command:

			MultimaterialMode (arg1),(arg2),(normals),<(rigidBiasOrAzimuth)>,<(polar)>

			where <tt>(arg1)</tt> and <tt>(arg2)</tt> are not used (they should be set to 0 and 1, respectively, to avoid any issues in very old code). If this command is used in current software, delete the first two arguments and change command name to <tt>MultimaterialMPM</tt>.

	== References ==		== References ==

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-29T16:48:43Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 16:48, 29 March 2026
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	(commands to set default contact properties)		(commands to set default contact properties)

	In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:		A deprecated [[#Deprecated Multimaterial Mode Command\|<tt>MultimaterialMode</tt>]] command still works and may be found in old input files and be need in older version of [[NairnFEAMPM]] or [[NairnFEAMPMVia]]. In <tt>XML</tt> files, multimaterial mode MPM is activated with the following block with the [[MPM Input Files#MPM Header\|<tt><MPMHeader></tt> element]]:

	<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>		<MultiMaterialMode Normals='(normals)' RigidBias='(rigidBias)' Azimuth='(azimuth)' Polar='(polar)'>

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-28T00:00:25Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 00:00, 28 March 2026
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	* <tt>(rigidBiasOrAzimuth)</tt> or <tt>(rigidBias)</tt> - when <tt>(normals)</tt> is <tt>maxgrad</tt> or <tt>avggrad</tt>, this parameter means to trust [[Surface Normals\|normals]] calculated from rigid materials more than those from non-rigid materials. The entered number means to use the rigid material's volume gradient unless the normal by the <tt>maxgrad</tt> or <tt>avggrad</tt> method is the entered factor larger in magnitude. For <tt>linreg</tt> and <tt>logreg</tt>, a value ≥10 means to use rigid normal with contacting with rigid materials; otherwise use regression methods to get the normal. See help on [[Surface Normals#Rigid Material Bias Option\|calculating normals]] for more details (default is 1).		* <tt>(rigidBiasOrAzimuth)</tt> or <tt>(rigidBias)</tt> - when <tt>(normals)</tt> is <tt>maxgrad</tt> or <tt>avggrad</tt>, this parameter means to trust [[Surface Normals\|normals]] calculated from rigid materials more than those from non-rigid materials. The entered number means to use the rigid material's volume gradient unless the normal by the <tt>maxgrad</tt> or <tt>avggrad</tt> method is the entered factor larger in magnitude. For <tt>linreg</tt> and <tt>logreg</tt>, a value ≥10 means to use rigid normal with contacting with rigid materials; otherwise use regression methods to get the normal. See help on [[Surface Normals#Rigid Material Bias Option\|calculating normals]] for more details (default is 1).
	* <tt>(azimuth)</tt> (or <tt>(rigidBiasOrAzimuth)</tt>) and <tt>(polar)</tt> - when <tt>(normals)</tt> is <tt>specify</tt>, these two parameters set the azimuth angle (or φ) and polar angle (θ) in degrees for the specified normal vector. The resulting normal is (cos φ sin θ, sin φ sin θ, cos θ). For 2D calculations, the <tt>(polar)</tt> setting is ignored and the 2D normal vector is (cos φ, sin φ). The default values are φ=0 and θ=0 for 3D, which is normal along the z axis, and φ=0 for 2D, which is normal along the x axis.		* <tt>(azimuth)</tt> (or <tt>(rigidBiasOrAzimuth)</tt>) and <tt>(polar)</tt> - when <tt>(normals)</tt> is <tt>specify</tt>, these two parameters set the azimuth angle (or φ) and polar angle (θ) in degrees for the specified normal vector. The resulting normal is (cos φ sin θ, sin φ sin θ, cos θ). For 2D calculations, the <tt>(polar)</tt> setting is ignored and the 2D normal vector is (cos φ, sin φ). The default values are φ=0 and θ=0 for 3D, which is normal along the z axis, and φ=0 for 2D, which is normal along the x axis.
	* <tt>(cutoff)</tt> - this optional parameter sets the displacement cutoff (relative to cell size) used to [[Detecting Contact\|detect multimaterial contact]]. The [[Detecting Contact#Selecting ContactPosition Options\|<tt>ContactPosition</tt> command]] should be omitted when modeling internal material interfaces that start out initially in contact. It must be included for problems where contact surfaces start out separated but move into contact during the simulation. It is not used when finding normal by <tt>linreg</tt> or <tt>logreg</tt> (unless they have rigid contact and have set <tt>(rigidBiasOrAzimuth)</tt>≥10), but would still be used when finding tangential displacement (See [[Detecting Contact#Imperfect Interface Extrapolations\|detecting contact]] for why this option should not be used when modeling [[Imperfect Interfaces\|imperfect interfaces]]).		* <tt>(cutoff)</tt> - this optional parameter sets the displacement cutoff (relative to cell size) used to [[Detecting Contact\|detect multimaterial contact]] and normal separation. The [[Detecting Contact#Selecting ContactPosition Options\|<tt>ContactPosition</tt> command]] should be omitted when modeling internal material interfaces that start out initially in contact. It must be included for problems where contact surfaces start out separated but move into contact during the simulation. It is not used when finding normal by <tt>linreg</tt> or <tt>logreg</tt> (unless they have rigid contact and have set <tt>(rigidBiasOrAzimuth)</tt>≥10), but would still be used when finding tangential displacement (See [[Detecting Contact#Imperfect Interface Extrapolations\|detecting contact]] for why this option should not be used when modeling [[Imperfect Interfaces\|imperfect interfaces]]).
	* <tt> (commands to set default contact properties)</tt> - set default [[Friction\|contact]] or [[Imperfect Interfaces\|imperfect interface]] properties for multimaterial contact. Note that when more than two materials are present, you can use [[Material Models\|material]] properties for [[Common Material Properties#Contact Properties\|friction and interface]] to override the default settings and thereby set custom contact between any specific pair of materials.		* <tt> (commands to set default contact properties)</tt> - set default [[Friction\|contact]] or [[Imperfect Interfaces\|imperfect interface]] properties for multimaterial contact. Note that when more than two materials are present, you can use [[Material Models\|material]] properties for [[Common Material Properties#Contact Properties\|friction and interface]] to override the default settings and thereby set custom contact between any specific pair of materials.

Nairnj: /* Multimaterial Mode Input Commands */

2026-03-27T23:58:24Z

Multimaterial Mode Input Commands

← Older revision		Revision as of 23:58, 27 March 2026
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	In scripted input files, multimaterial mode MPM is activated and customized with the following commands:		In scripted input files, multimaterial mode MPM is activated and customized with the following commands:

	~~MultimaterialMode (res1),(res2),~~(normals),<(rigidBiasOrAzimuth)>,<(polar)>		MultimaterialMPM (normals),<(rigidBiasOrAzimuth)>,<(polar)>
	ContactPosition (cutoff)		ContactPosition (cutoff)
	(commands to set default contact properties)		(commands to set default contact properties)
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	The settings are:		The settings are:

	* <tt>(res1)</tt> and <tt>(res2)</tt> - these options reserved for future use, but they must be specified for parameter alignment in the <tt>MultiMaterialMode</tt> script command. To make sure old versions are using the currently recommended methods, the unused parameters should be set to <tt>(res1)=0</tt> and <tt>(res2)=1</tt>.
	* <tt>(normals)</tt> - the method for calculation of [[Surface Normals#Multimaterial Normal Vector Options\|normal vectors]]. The options are as follows (<tt>XML</tt> files must use numeric value):		* <tt>(normals)</tt> - the method for calculation of [[Surface Normals#Multimaterial Normal Vector Options\|normal vectors]]. The options are as follows (<tt>XML</tt> files must use numeric value):
	** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.		** <tt>logreg</tt> (or 6) - use logistic regression. This is state-of-the-art, default option.<ref name="logreg"/> Other methods should only be for unusual conditions (''e.g.'' when you can <tt>specify</tt> the normal) or for calculation comparisons.