lecture 13.pdf
TRANSCRIPT
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JT ME 741: Loads & BC
ME 741
Energy & Variational Methods in
Mechanics I
Instructor:
Dr. Jagadeep Thota
Lecture 13:
Loads & Boundary Conditions
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JT ME 741: Loads & BC
Load Collector
In the previous lectures we looked at 3 important
collectors:
Component
Material
Property
Today, we are going to look at the last important
collector in HyperMesh
Load Collector: this collector houses the loads and boundary conditions (supports, constraints, etc.) applied
to a finite element (FE) model
The above 4 collectors are important, because in
order to process any FE model in HyperMesh
(Radioss), these 4 collectors have to be defined
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JT ME 741: Loads & BC
Types of Load Collectors
Load collectors can be broadly classified into
two types:
Loads
Forces, Moments, Pressures & Temperatures
Boundary Condition (BC)
Constraints, Flux
In this lecture we will look at creating structural
load collectors; forces, moments, pressures and
constraints
Unlike Material and Property collectors, Load
collectors is not coupled with the Component
collector
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JT ME 741: Loads & BC
HyperMesh
The load collector icon is located next to the
property collector icon in the collector toolbar
The load & BC commands can be obtained from
the Analysis menu
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JT ME 741: Loads & BC
Creating Load Collector
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JT ME 741: Loads & BC
Load Collector
Creating a load collector is similar and simpler than the other collectors we
have dealt with till now
The user has to just define an unique name for creation of a load collector
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JT ME 741: Loads & BC
Load Collector
Give any unique name This is the only input required
for creating a load collector
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JT ME 741: Loads & BC
Load Collector
A card image is not needed for the Load collector due to the following 2 reasons:
The properties of the loads are already defined in their individual commands
This collector does not need to be coupled with the Component collector
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JT ME 741: Loads & BC
Load Collector
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JT ME 741: Loads & BC
Load Collector
The created Load collector is visible
in the model tree or tab area
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JT ME 741: Loads & BC
Creating Loads
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JT ME 741: Loads & BC
Create a Meshed Model Create a rectangle
Top/bottom lengths = 6 units
Side lengths = 2 units
Mesh the area enclosed by the rectangle (shell elements)
Top/bottom lengths = 6 elements
Side lengths = 2 elements
Delete any temporary nodes which were created for drawing the geometry
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JT ME 741: Loads & BC
Force/Load Create a force/load of 10 units acting in the ve y-direction at the top right corner
Force/load can only be applied to nodes
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JT ME 741: Loads & BC
Force/Load
(1)
(2)
(3)
(4)
Enter the magnitude of the force/load The negative sign indicates the force
is acting in the negative direction
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JT ME 741: Loads & BC
Force/Load
Choose the direction the force/load is acting
(1)
(2)
(3)
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JT ME 741: Loads & BC
Force/Load
This represents a force/load of 10
units is applied at this location and
in the shown direction
The applied force will be stored in
this Load collector as it is the active
or current collector
The current or active Component
collector is shown in this window
The current or active Load collector
is shown in this window
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JT ME 741: Loads & BC
Moment Create a moment of 20 units about the +ve z-direction on the top right corner
Moments can only be applied to nodes
Before creating the moment, the user has to create a Load collector for the moment
If not then both the force and the moment will share only one collector which will lead to errors during simulation
Create a new Load collector labeled moment
Created a new Load
collector for the moment
(1)
(2)
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JT ME 741: Loads & BC
Moment
The only differnce between creating a force and moment is:
Force is applied along a direction
Moment is applied about a direction
(1)
(3)
(4)
(2)
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JT ME 741: Loads & BC
Moment
The moment is represented
by a double arrow head
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JT ME 741: Loads & BC
Moment
(1)
(2)
(3)
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JT ME 741: Loads & BC
Pressure Apply a pressure of 30 units along the ve z-direction on the top right element
Pressure can be applied only on an element along the elements normal
How to check the direction of the elements normal? Follow the initial few slides
(2)
(1)
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JT ME 741: Loads & BC
Element Normals
(2)
(1)
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JT ME 741: Loads & BC
Element Normals
(1)
(2)
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JT ME 741: Loads & BC
Element Normals
The white arrows on the face of each element shows the +ve direction of the
element normal
An applied +ve pressure will follow the direction of the normal
The user can reverse the direction of the
element normal by hitting this button
(1)
(2)
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JT ME 741: Loads & BC
Pressure
(1)
(2)
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JT ME 741: Loads & BC
Pressure
(1)
(2)
(3)
(4)
Select the element(s) on which
the pressure is to be applied
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JT ME 741: Loads & BC
Pressure
(1)
(2)
Select the nodes enclosing
the selected element(s)
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JT ME 741: Loads & BC
Load Collector We have forgotten to create one important entity
A Load collector for the pressure!
There is no need to panic, we can still create a Load collector for the pressure if you havent hit the create button and come out of the pressure command
So before you hit the create button, create a new Load collector labeled pressure
A new Load collector is
created for the pressure
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JT ME 741: Loads & BC
Pressure Now, lets continue with the pressure command
(1)
(2)
The pressure is applied on the center of the element or at the normal location
The direction of the +ve pressure is along the direction of the normal
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JT ME 741: Loads & BC
Creating Constraints
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JT ME 741: Loads & BC
Constraints
Constraints are the boundary conditions applied
to the nodes to depict either a homogenous or
non-homogenous boundary condition
Basically, a constraint lets the user to restrict or
define the degrees of freedom of the selected
node(s)
By defining a constraint the user can define a
support or a fixed portion of the component
Constraints can be only applied to nodes
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JT ME 741: Loads & BC
Constraints
Create a Load collector labeled constraints
Assume the left portion of the rectangular plate is fixed
The following constraints slides explains how to depict this boundary condition on the FE model
The constraints Load
collector is created
(1)
(2)
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JT ME 741: Loads & BC
Constraints
(2)
(1)
Select the nodes
which are to be fixed
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JT ME 741: Loads & BC
Degree of Freedom (dof)
Translation in the x-direction
Translation in the y-direction
Translation in the z-direction
Rotation in the x-direction
Rotation in the y-direction
Rotation in the z-direction
If a dof is checked, it means that checked dof is fixed for the selected node(s)
If a particular dof is unchecked it means that particular dof is free to move/rotate in
the direction corresponding to the
unchecked dof for the selected node(s)
This would mean that the selected node(s) Translation is fixed in the y & z-directions Rotation is fixed in the x, y & z-directions Will move 2 units in the +ve x-direction
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JT ME 741: Loads & BC
Constraints
Given that the left portion of the rectangular plate is fixed
Hence, all the nodes on the left portion of the FE model are completely fixed, i.e., all
the dof rows in the constraints command are checked
(1)
(2)
(3)
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JT ME 741: Loads & BC
Constraints
The constraints are represented as
triangles on the FE model
The numbers indicates the dofs
constrained for the node
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JT ME 741: Loads & BC
Next Finite Element Class
Conduct FE analysis of a truss assembly
through HyperMesh/Radioss
Compare the simulated results with the
theoretical values
Students should be prepared to create
Geometry
1D elements
Component, Material, Property & Load Collectors
I will grade the students performance in the creation of the FE model as an Inclass
assignment