Lecture 13.pdf

JT ME 741: Loads & BC

ME 741

Energy & Variational Methods in

Mechanics I

Instructor:

Dr. Jagadeep Thota

Lecture 13:

Loads & Boundary Conditions


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


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


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


Creating Load Collector


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


Load Collector

Give any unique name This is the only input required

for creating a load collector


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


Load Collector


Load Collector

The created Load collector is visible

in the model tree or tab area


Creating Loads


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


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


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


Force/Load

Choose the direction the force/load is acting

(1)

(2)

(3)


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


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)


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)


Moment

The moment is represented

by a double arrow head


Moment

(1)

(2)

(3)


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)


Element Normals

(2)

(1)


Element Normals

(1)

(2)


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)


Pressure

(1)

(2)


Pressure

(1)

(2)

(3)

(4)

Select the element(s) on which

the pressure is to be applied


Pressure

(1)

(2)

Select the nodes enclosing

the selected element(s)


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


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


Creating Constraints


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


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)


Constraints

(2)

(1)

Select the nodes

which are to be fixed


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


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)


Constraints

The constraints are represented as

triangles on the FE model

The numbers indicates the dofs

constrained for the node


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

Lecture 13.pdf

Documents

Transcript of Lecture 13.pdf