Explicit Grid Boundary Conditions

Introduction

If needed, velocity boundary conditions can be explicitly assigned to numbered nodes by using <fix> elements within the single <DisplacementBCs> element. This approach can only be used in XML input files and is rarely used, except perhaps in separate software or scripts that create an XML input file automatically. The more common way to create boundary conditions on nodes is to use shape commands.

Explicit Velocity Conditions

An explicit velocity is assigned to one node with a <fix> element:

<fix node='(node)' dof='(dir)' style='(style)' time='(time)' id='(id)'>(velocity)</fix>

where the text of the <fix> tag (i.e., (velocity)) is the value of the fixed velocity in velocity units. The attributes of the <fix> element are:

• dof determines if the x direction ((dir)=1), the y direction ((dir)=2), the z direction ((dir)=3), the R direction when axisymetric ((dir)=1), or the Z direction when axisymmetric ((dir)=2) will have the specified velocity. You can also set velocity in a direction that is not along an axis. For details see help on skewed velocity conditions, which modifies the dof attribute and adds angle and angle2 attibutes to define the skew angle.
• (style) specifies the style of the applied velocity. Each velocity depends on two parameters specified by arguments (velocity) and (time). If either argument is not supplied, they are set to zero. The standard units are velocity units for (velocity) and alt time units for (time) (but the units may change depending on the (style) setting). When using an arbitrary function (see (style)=6) the(velocity) text should be the a user-defined function of t (in alt time units) that evaluates to velocity in velocity units. If this attribute is omitted, it is assumed to be 1 (or a constant velocity).
• (id) - this attribute specifies and ID for the boundary condition.