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--- doc:user:elements:contact:rigid_matrices [2013/07/10 17:01] – joris
+++ doc:user:elements:contact:rigid_matrices [2016/03/30 15:23] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+====== Rigid matrices ======
+===== Defining rigid matrices =====
+In Metafor, any geometric entity can be defined as rigid [[doc:user:general:glossaire#Contact Matrices]]. No additional definition is required.
+However, the orientation of the entity is relevant. It defines the area considered as the die, where a penetrating node will experience a contact force. By convention, the normal vector is pointing inside the die.
+<note>DESSIN</note>
+This normal $\boldsymbol{n}$ is defined as stated below.
+    * **In 2D:** The convention states that the cross product $\boldsymbol{t} \wedge \boldsymbol{n} = (0,0,1)$. This is equivalent in saying that the contact matrix is defined with its //**area to the left**// (when following the line defining the matrix, any node trying to penetrate in the aerea to the left will experience a contact force).
+          * The orientation of a ''[[doc:user:geometry:user:courbes|Curve]]'' (''Line'', ''Arc'', etc) is defined by its tangent (which can be displayed in the graphical interface). By default, it is defined by its points, from the first one to the last one.
+          * The orientation of a''[[doc:user:geometry:user:contours|Wire]]'' is defined by the succession of its lines, from the first to the last, and not by their vertices. When a wire is defined by only one curve, the orientation of the wire is the orientation of the curve.
+    * **In 3D:** The normal of a ''[[doc:user:geometry:user:faces|Side]]'' is defined as the normal of the corresponding ''[[doc:user:geometry:user:surfaces|Surface]]'' (which can be displayed in the graphical interface). Concerning a ''[[doc:user:geometry:user:peaux|Skin]]'', nowadays the ''Sides'' must be defined in a way guaranteeing consistency of the whole. To define a planar contact matrix, a ''Plane'' surface  must be defined and associated to a ''Side''.
+For rigid-defo contact, when ''Sides'' or ''Curves'' are used to define contact matrices, contact can be detected outside of the matrix boundary because lines and surfaces are 10% extrapolated. To avoid this issue, a ''Skin'' or ''Wire'' must be defined instead. The orientation of a '''Curve'' or ''Wire'' is easy to modify using ''curve.reverse''. This command is not yet available for surfaces, so consistency of ''Sides'' must be done manually.
+It is also possible to reverse the convention defining where the surface matrix is, changing the value of ''TYPE_CONT'' from the default ''UNILATERAL_POSITIF'' to ''UNILATERAL_NEGATIF''.
+===== Contact - motion of matrices =====
+In Metafor, moving contact matrices is done by moving geometric entities in the contact interaction with a ''Loading'' (see [[doc:user:conditions:displacements]]).