PATRAN FAQ（Loads/Boundary Conditions）
作者：cad 提交日期：2009-7-4| 分类: | 访问量：
PATRAN FAQ（Loads/Boundary Conditions）
7. Loads/Boundary Conditions
Q7.1 : How do I display the icons (markers) denoting loads and displacement
fixities for checking?
Choose Display from the pull-down menu and then Load / BC / Elem Props.... In
the form that pops up look for a button marked Show on FEM only and click on it
to set it. Also click on Show All. Then click on the Apply and Cancel buttons
respectively.
Click on the radio button Loads/BCs and change the `Action' to Plot Markers.
Under the heading marked Assigned Load/BC Sets select the boundary conditions
and loadings you want to be displayed. In the Select Groups category select the
groups which has
the finite element entities. Then click on the Apply button.
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Q7.2 : How do I remove the icons (markers) denoting loads and displacement
fixities from display?
Choose Display from the pull-down menu and then Load / BC / Elem Props.... In
the form that pops up look for a button marked Show on FEM only and click on it
to unset it. Then click on the button marked Hide All. Finally click on the
Apply and Cancel
buttons respectively.
This should erase the markers. If not click on the Reset graphics icon in the
top right hand corner. It is the 3rd icon.
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Q7.3 : How do I fix a node in the y direction only i.e. it is free to move in
the x direction?
Enter < , 0 > in the box marked Translations .
The first , (comma) indicates that the degree of freedom in direction 1 is free.
If this was a 3-dimensional example then the 3rd degree of freedom is also free
becuase it has not been specified. In the above example the 2nd degree of
freedom is fixed
at 0.
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Q7.4 : I have created a series of surfaces and then trying to apply uniform
pressure (u.d.l.) to one side of these surfaces but in some surfaces it is
directed in the wrong direction?
Check the Normal directions to these surfaces using the answer to Q3.2 above.
The applied positive pressures are directed in the direction of the positive
normal. Applying a negative pressure will be in the direction opposite to it.
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Q7.5 : I want to apply self-weight of the elements as loading. How do I do that?
Create a set of material properties in the usual manner. Make sure you specify
the density.
Click on the radio button Loads/BCs and and in the form make the following
selection :
Action : Create
Object : Inertial Load
Type : Element Uniform
New Set Name : Enter a appropriate name - example : self-wt
Target Element Type : 2D or 3D (Make the appropriate choice)
Click on the button Input Data... and in the new form in the box marked Trans
accel enter < , -1. , > asssuming the gravity is acting in the negative Y
direction. Click on OK in that form.
In the orinial form click on the button Select Application Region... and in the
new form select the radio button Geometry or FEM for the `Geometry filter'. Then
select the elements or surfaces/bodies. Click on Add and then finally on the OK
button.
In the original form click on Apply. This should display yellow arrows pointing
in the direction in which the gravity is acting and the magnitude (for this
example it will be 1).
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Q7.6 : How do I apply a line load?
It is not possible to apply line loads along curves/lines directly.
The user may have to calcualte the equivalent set of point loads for the
individual nodes and specify these as point loads.
If the element sides are 2 noded then the line load is split equally between the
2 nodes. If there are a series of sides then mutiply the line load by the length
of the side and apply half to each node. Interior nodes will take contribution
from the
sides at either side.
If the elements are 3 noded then the total load (line load multiplied by length)
is split in the ratio of 1 : 4 : 1 between the nodes. The centre node taking 2/3
rd of the total load and the end nodes 1/6 th of the total load. Again sum the
contribution from either sides for end nodes in the interior.
For higher order elements similar factors can be calculated using the shape
functions and the principle of virtual work (see any standard book on finite
elements).
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Q7.7 : Is it acceptable to assign boundary conditions on curves/lines not used
in specifying the geometry?
No. If you are assigning boundary conditions on the geometry then you have to
assign it on curves/lines used in specifying the geometry.
Consider the situation where lines L1 ans l2 form part of the surfaces which
define the geometry (in the figure below). Assume that you also have defined a
line L3 which connects points 1 and 3.
Consider the situation where the vertical side between points 1 and 3 is to be
retstrained from moving in the horizontal direction. Then this boundary
condition should be specified on lines L1 and L2 but not L3 (as a short cut).
the reason is when the
finite element mesh is created lines L1 ansd l2 are associated with the nodes
that are created. Line L3 is not associated with these nodes.
If you attempt to specify the boundary condition on L3 only the nodes at points
1 and 2 will be asssigned that boundary conditions. All the intermediate nodes
between points 1 and 3 will not be assigned the boundary condition.
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Q7.8 : How can I specify the Load Proportionality Factor for a RIKS analysis
step?
In the Analysis form make the following selections :
Action : Analyze
Object : Entire Model
Method : Full Run
Click on Step Creation.... In the new form set
Solution Type : Nonlinear Static
Then click on Solution Parameters.... In the new form set
Riks Method = ON
Stopping conditions : max Load Multiplier
Max Load Multiplier : 1.0
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Q7.9 : How can I specify a triangular pressure distribution?
You need to create relationship (variation) using the FIELD form.
This is illustrated with an example :
First of all choose the following settings :
Action / Object / Method : Create / Spatial / PCL Function
Field Name : < Enter an appropriate name here> Example : pressure
Field Type : <> Scalar <> Vector
Choose Vector for prescribed displacement specification. Choose Scalar for
pressure variation.
Co-ordinate System Type : <> Real <> Parametric
Choose REAL if using the co-ordinates of the new system.
Here the default co-ordinate system (Co-ord 0) which is halfway up the side is
not suitable for specifying the pressure variation. It is simpler to create a
co-ordinate system with origin coinciding with the base of the side. Lets call
this Co-ord 1.
Co-ordinate System : Change the default (co-ord 0) to co-ord 1.
Since the pressure variation is scalar enter the relationship in the box marked
"Scalar Function".
Example : p = ( 10. - 'Y ) * ( 150. / 10. )
= ( 10. - 'Y ) * 15.
Here click on the appropriate independent variable ('Y) from the box of the same
name whenever you want to use one of this variable in the equation.
Now click on APPLY to complete creation of the field.
Then open the LOADs/BCs form and give the pressure distribution a name and
choose 3D for "Element Type". Then click on the Input Data.... In the new form
the name of the previously specified pressure relationship (press) will be
listed under the
heading Field.
Click on the box marked "Uniform Pressure" and then click on "pressure" entry
from the "field" section. Then click on OK and complete the form in the usual
manner.
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Q7.10 : How does one deal with the interface conditions between parts (of an
assembly) imported from Pro/ENGINEER?
One can use contact pair option to identify the two surfaces in contact and then
specify the interfcae conditions (smooth, frictional or bonded/tied).
Use the Loads/BCs form and choose : Action / Object / Type = Create / Contact /
Element Uniform. Then choose Deform-Deform for "option" for contact between two
deformable bodies.
Enter a meaningful name for the contact pair you are about to define, in the box
marked New set name.
Click on Input Data... and in the new form choose the contact type to be either
General or Tied. Enter appropriate values of Frictional coefficient and limiting
shear stress if General was chosen. Initial adjustment tolerance also needs to
be specified
for both types of contact. Choose a value of about 1% of the largest dimension
for this. This is the amount the position of the nodes on either sides can be
adjusted to establish contact. Click on OK on this form and then in the main
form click on
Select Application REgions....
In the new form leave both master and slave surfaces at solid Face if dealing
with 3-dimensional solids. If shell elements are involved then it can be set to
shell surface.
Set active region to master and then choose the contact surface on the master
component. If components of different materials are coming into contact then in
general the stiffer of the two is selected as the master.
Similarly set active region to slave and then choose the surface which comes
into contact on the slave component. Note that "master" can penetrate into
"slave". Also the slave surface should have a more finer mesh. Once both sets of
surfaces have been
identified click on OK and then in the main form click on Apply.
In a complex assembly with several components there will be several sets of
contact pairs needs defining. Repeat this procedure for each pair of such
contacts.
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Q7.11 : Given the choice of specifying the boundary conditions either on the
geometry or on the finite elements which is preferrable?
In general it is preferrable to specify the boundary conditions on the geometry.
This way if you decide to chnage the mesh at a later stage then the boundary
conditions need not be re-specified.
However there are situations where there is no choice but to deal with the
f.e.mesh. For example consider the situation where a point load is to be applied
to node which is coincident with a point which has been used in the generation
of the geometry.
Then you need to create the mesh and then apply the load to the node in
question. Alternatively create the geometry which will give a coincident point
where the concentrated load is to be applied apply it the point
Here is a different example : Equal bending moment has to be applied to all the
nodes on a particular face. Here the total bending moment is to be equally
divided amongst all the nodes. Here one needs to work out how many nodes there
is ging to be.
Then apply the bending moment divided by the number of the nodes to the
geometry.
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Q7.12 : I need to apply a radial pressure to a circular hole in a plate for an
imported mesh. Is there a simple way of selecting all the nodes along the
circular hole?
Click on Tools and then choose List / Create. In the Create List Form set Model
/ Object / Method = FEM / Node / Attribute. Then choose the Coord value for
Attribute. The box marked Refer. Coordinate Frame will have Coord 0 by default.
If the default
coordinate system's origin is at the center of the circular whole then the
default is OK. If not create a coordinate system (called Coord 1) at the centre
of the circular hole using the Geometry form and the settings : Action / Object
/ Method = Create
/ Coord / Axis. Choose a cylindrical co-ordinate system.
In the list form chnage the cordinate system to : Coord 1. Select x and this
will display a new box for x value. In cylindrical co-ordinate system x would
represent the (first) radial co-odrinate. So set the X value to be the same as
the radius of the
circular hole. Also set the TOL-XYZ to an appropriate value so that only the
nodes along the circular hole will be selected. Check that the radio button for
Target List is set to A. Now click on Apply. Now click on Add to Group... in the
'List A' form.
The 'lista' contents should hopefully have all the nodes along the circular
hole. These nodes can be highlighted and cut and pasted into any Select
Application Region for nodes for applying a radial load in the Loads/BCs form.
*本文摘自：http://www.jxcad.com.cn/read.php?tid=183948&fpage=43
