Lec-01

The Department of Aeronautics & Astronautics Institute of Space Technology, Islamabad

Computational Mechanics/BE-09/A & A 1 9/29/2013


Computational Mechanics (0-2) Seniors

Lecture-01

Faculty

Mr. Adnan Munir

Mr. Raees Fida Swati


Sequence of Presentation

o Theory of FEM

o Analytical Solution to a simplified Problem

o Introduction to Ansys 13.0

o Ansys Modules

o Overview of Ansys Parametic Design Language (APDL)

o Overview of GUI

o Preprocessing, Modeling & Post processing

o Cantilever beam Problem/Tutorial



Scope of Problem

The purpose of this problem is to demonstrate how to solve the displacements and stresses of a homogeneous cantilever beam using ANSYS.

To develop an approach towards relatively complex problems & to understand the flow of steps in ANSYS 13.0



Problem descriptions

Solve a 1-D stress analysis of the cantilever beam shown below:

Computational Mechanics/BE-09/A & A 5

500mm

100N

d = 25 mm

t = 2 mm

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Starting ANSYS

From your desktop:

Click on: START > All

Programs >

ANSYS >

ANSYS

Product Launcher.

Here we will set our Working Directory and the Graphics Manager



ANSYS GUI Overview

• This is ANSYS’s Graphical User Interface window.



Changing Title

• To change title go to file and choose change title.



Give the simplified version a title such as Verification

Model.



Preferences

Go to preferences and choose structural and leave the h method as the

discipline options.



PREPROCESSING

Developing the startup requirements



Element Type

It is important to define the element type for the beam. For this problem

we will use pipe elastic straight 16. PIPE16 is a uniaxial element with

tension-compression, torsion, and bending capabilities. The element has

six degrees of freedom at two nodes: translations in the nodal x, y, and z

directions and rotations about the nodal x, y, and z axes. This element is

based on the 3-D beam element (BEAM4), and includes simplifications

due to its symmetry and standard pipe geometry. To chose this element

type click: preprocessor



Element Type


Preprocessor/Element type/Add/Edit/Delete/Pipe/Elastic straight 16

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Real constants

• To define the geometric properties we select real constants. The real

constant are the dimensions that must remain constant during the

design. These constants are: diameters, thickness, among others.

• For the outside diameter write OD:25 mm and for the wall thickness

TKWALL:2 mm.

To chose the real constants click:

Processor/Real Constants/Add/Edit/Delete



Pre-Processor/Real Constants/Add/Edit/Delete



Material properties

• To define the element material properties we choose material models.

Our material will have a Modulus of Elasticity of 70,000 (MPa) and a

Poisson’s ratio of 0.33

• To add material properties click:

Preprocessor/Material Props/Structural/Elastic/Isotropic



Preprocessor/Material Props/Structural/Elastic/Isotropic



Geometry of the Cantilever Beam

• Now let us build the geometry in ANSYS. The strategy to create the

desired geometry is by first creating the key points where the loads

will be applied and then uniting these key points with lines.

• To create keypoints click:

Preprocessor/Modeling/Create/Keypoints/In Active Cs



Preprocessor/Modeling/Create/Keypoints/In Active Cs

Enter the values for keypoint 1: (0,0,0) and for keypoint 2: (500,0,0).



Now we connect the keypoints to form the bar. To do this click:

Preprocessor/Modeling/Create/Lines/Lines

A pop up window will appear and now you should pick the first

keypoint and then the second and hit the OK button.



The line will look like this:



Element size

• To define the element size of the line we use size controls. To do this click:

Preprocessor/Meshing/Size cntrls/Manual size/Lines/All Lines

When the pop up window appears, write 20 for the element edge length



Meshing

To make the finite element analysis we must first divide the object into small elements, this is called meshing.

Now let us make the mesh using the mesh tool.

On the Main Menu window, select

Preprocessor \ Meshing \ MeshTool

Select mesh lines. After the pop up windows appears click the button that says pick all in that same pop up window. Then hit the OK button.



Preprocessor / Meshing /MeshTool/Mesh Lines/Pick All



Boundary conditions

For keypoint 1: constraint all DOF’s (displacement value = 0)

To apply the Boundary Conditions click:

Preprocessor/Loads/Define Loads/Apply/Structural/Displacement/On keypoints

When the pop up windows appears select the first keypoint and hit the ok button.



Preprocessor/Loads/Define Loads/Apply/Structural/Displacement/On keypoints


Pick this

keypoint

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In order to make it a cantilever beam we must constraint all degrees of freedom to the first key point.


Type 0

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Loads

• The next step is to apply the load vertically downward with a force of

100 N to keypoint 2. To apply the load click:

Preprocessor/Loads/Define Loads/Apply/Structural/Force/Moment/

keypoints



We must apply the load in the negative Y direction. That’s the reason we will enter a negative sign before the force value in the pop up window


Type -100

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The load will look like this:



SOLUTION



To start the solution phase it is important to set the type

of analysis.

We will perform a static analysis since we only want stresses and

deflections. To select analysis type click:

Solution/Analysis Type/New Analysis/ Static/Ok



Solve

• Now we proceed to solve the problem. To do this click:

Solution/ Solve/Current LS

Note: When the pop up windows appear click the OK button.



A pop up window that says: “Solution is done” will appear after ANSYS

finishes solving the problem. Click close



POST PROCESSING



FEM Solution & Plotting Results

• Now we already developed the geometry, Loads & Displacements and the meshing. We will start with the finite element analysis and obtain the displacements and stresses on the key points.

• After make the FEM solution we are able to plot the results, in this case the displacements and stresses.



To see the results of the deflection we use the nodal

solution. Click:

General postproc/Plot results/Contour plot/Nodal Solution



The plot will look like this:



View stress results

• To plot the stresses of the beam under the applied load we choose define table under element table. To do this click:

• General postproc/Element table


Chose Von

Misses

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To view stress results click:

General postproc/Plot Elem Table

The plot will look like this:



Practice Problem/assignment Simply supported beam - Surface Load Objective

This problem will familiarize you with the beam finite elements you are now learning in class. By comparing the ANSYS solution with simple beam theory, you will be able to understand the accuracy of your model.

9/29/2013 Computational Mechanics/BE-09/A & A 41


Simply supported beam - Surface Load

A schematic of a statically determinate beam with distributed load is shown below:



Hints

Element type

using the ANSYS element Beam3, and it will be referred to as element type 1 in your model.

To find out more about this element, consult the online manual.



Practice Problem 3D Space Frame Example

Problem Description

The problem to be modeled in this example is a simple bicycle frame shown in the following figure. The frame is to be built of hollow aluminum tubing having an outside diameter of 25mm and a wall thickness of 2mm for the main part of the frame. For the rear forks, the tubing will be 12mm outside diameter and 1mm wall thickness.



Figure


Lec-01

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