Difference between revisions of "Explicit Grid Boundary Conditions"
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== Introduction == | == Introduction == | ||
If needed, velocity boundary conditions can be explicitly assigned to numbered nodes by using <tt><fix></tt> elements within the single <tt><DisplacementBCs></tt> element. This approach can only be used in <tt>XML</tt> input files and is rarely used, except perhaps in separate software or scripts that create an <tt>XML</tt> input file automatically. The more common way to | If needed, velocity boundary conditions can be explicitly assigned to numbered nodes by using <tt><fix></tt> elements within the single <tt><DisplacementBCs></tt> element. This approach can only be used in <tt>XML</tt> input files and is rarely used, except perhaps in separate software or scripts that create an <tt>XML</tt> input file automatically. The more common way it to assign [[Grid-Based Boundary Conditions|boundary conditions to block of nodes]] suing shapes. | ||
== Explicit Velocity Conditions == | == Explicit Velocity Conditions == | ||
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<fix node='(node)' dof='(dir)' style='(style)' time='(time)' id='(id)'>(velocity)</fix> | <fix node='(node)' dof='(dir)' style='(style)' time='(time)' id='(id)'>(velocity)</fix> | ||
where the text of the <tt><fix></tt> tag (i.e., <tt>(velocity)</tt>) is the value of the fixed velocity | where the text of the <tt><fix></tt> tag (i.e., <tt>(velocity)</tt>) is the value of the fixed velocity in [[ConsistentUnits Command#Legacy and Consistent Units|velocity units]]. The attributes of the <tt><fix></tt> element are: | ||
* <tt>dof</tt> 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 [[Setting Velocity | * <tt>dof</tt> 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 [[Setting Velocity and Transport Values#Skewed Velocity Conditions|skewed velocity conditions]], which modifies the <tt>dof</tt> attribute and adds <tt>angle</tt> and <tt>angle2</tt> attibutes to define the [[Setting Velocity and Transport Values#Skewed Velocity Conditions|skew angle]]. | ||
* <tt>(style)</tt> specifies the [[ | * <tt>(style)</tt> specifies the [[Boundary Condition Styles|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 [[ConsistentUnits Command#Legacy and Consistent Units|velocity units]] for (velocity) and [[ConsistentUnits Command#Legacy and Consistent Units|alt time units]] for (time) (but the units may change depending on the [[Boundary Condition Styles|<tt>(style)</tt> setting]]). When using an arbitrary function (see [[Boundary Condition Styles|<tt>(style)</tt>=6]]) the<tt>(velocity)</tt> text should be the a user-defined function of t (in [[ConsistentUnits Command#Legacy and Consistent Units|alt time units]]) that evaluates to velocity in [[ConsistentUnits Command#Legacy and Consistent Units|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. | * <tt>(id)</tt> - this attribute specifies and ID for the boundary condition. | ||
Latest revision as of 10:40, 20 September 2017
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 it to assign boundary conditions to block of nodes suing shapes.
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.