analytical modelling ( ansys )

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1.1 Creat the FE Model of the suspension system

Figure 1: FE model of Suspension system using Solidworks.

Figure 2: FE model of Suspension system using ANSYS

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1.2 Explain the steps used for creating FE model in your tool

The following steps are used in creating the FE model in figure 2 above:

1.2.1 ELEMENT TYPE SELECTION

ANSYSMainMenu → Preprocessor → Element Type → Add/Edit/Delete

o Then the window Element Types, as shown in Figure 3 is opened.

o Click add. Then the window Library of Element Types, as shown in Figure 4 opens.

o Select Shell in the table of Library of Element Types and, then, select C Elastic

8node 93.

o Element type reference number is set to 1. Click OK button to close the window

Library of Element Types.

o Click Close button in the window of Figure 5

Figure 3: Window Element Types

Figure 4: Window Library of Element Types

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Figure 5: Window Element Types

1.2.2 REAL CONSTANTS FOR BEAM ELEMENT

ANSYSMainMenu→Preprocessor→Real Constants→Add/Edit/ Delete→Add

o The window Real Constants opens (Figure 6). Click add button, and the window

Element Type for Real Constants appears in which the name of element type selected

is listed as shown in Figure 7.

o Click OK button to input the values of real constants and the window Real Constant

Set Number1, for Shell opens (Figure 8).

o Input the following values in Figure 8, shell thickness at nodes I, J, K, and L = 0.05e3.

Click OK button to close the window, after inputting these values.

o Click Close button in the window of Real Constants (Figure 9).

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Figure 6: Window of Real Constants. Figure 7: Window of Real Constants.

Figure 8: Window of Real Constants Set Number 1, for Shell.

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Figure 9: Window of Real Constants.

1.2.3 MATERIAL PROPERTIES

ANSYSMainMenu → Preprocessor → Material Props → Material Models

o Click the above buttons in order and the window Define Material Model Behaviour,

as shown in Figure 10 opens.

o Double click the following terms in the window: Structural → linear → Elastic →

Isotropic Then the window of Linear Isotropic Properties for Material Number 1

opens.

o Input Young’s modulus of 208e9 to EX box and Poisson ratio of 0.3 to PRXY box.

Then click OK button (Figure 11).

Next, define the value of density of material.

o Double click the term Density and the window Density for Material Number 1opens

(Figure 12).

o Input the value of Density, 7800 to DENS box and click OK button (Figure 12).

Finally close the window Define Material Model Behaviour by clicking X mark at

the upper right end.

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Figure 10: Windows of Linear Isotropic Property for material Number 1

Figure 11: Windows of Linear Isotropic Property for material Number.1

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Figure 12: Windows of Density for Material Number

1.2.4 CREATE KEYPOINTS

To draw a suspension for the analysis, the method of keypoints is described in this section.

ANSYS Main Menu → Preprocessor → Modeling → Create → Keypoints → In

Active CS

o The window Create Keypoints inactive Coordinate System opens (Figure 13).

o Input (0,-0.0006, 0) to X, Y, Z Location in active CS box, and then click Apply

button. Do not click OK button at this stage. If a figure is not inputted into NPT Key

Point number box, the number of keypoint is automatically assigned in order.

o In the same window, input the values as shown in Table 1 in order. When all values

are inputted, click OK button.

o All inputted keypoints appear on ANSYS Graphics window as shown in Figure 13.

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Figure 13: Window Create Keypoints inactive Coordinate System

Table 1: X, Y, and Z Co-ordinates of keypoints for suspension

Keypoint No. X -co-ordinate Y- co-ordinate Z- co-ordinate

1 0.0000 -0.0006 0.0000

2 0.0083 -0.00215 0.0000

3 0.0083 -0.0014 0.0000

4 0.0135 -0.0014 0.0000

5 0.0135 0.0014 0.0000

6 0.0083 0.0014 0.0000

7 0.0083 0.00215 0.0000

8 0.0000 0.0006 0.0000

9 0.0083 -0.0008 0.0000

10 0.0105 -0.0008 0.0000

11 0.0105 0.0008 0.0000

12 0.0083 0.0008 0.0000

13 0.0000 -0.0006 0.0003

14 0.0083 -0.00215 0.0003

15 0.0083 0.00215 0.0003

16 0.0000 0.0006 0.0003

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Figure 13: ANSYS Graphics Window

1.2.5 CREATE AREAS FOR SUSPENSION

Areas are created from keypoints by performing the following steps:

ANSYSMainMenu→Preprocessor→Modeling→Create→Areas→Arbitrary→Through

KPs

The window Create Area thru KPs opens (Figure 14).

Pick the keypoints, 9, 10, 11, and 12 in order and click Apply button in Figure 14. An

area is created on the window as shown in Figure 15.

By performing the same steps, other areas are made on the window. Click keypoints

listed in Table 2 and make other areas. When you make area No. 3 and 4, you have to

rotate the drawing of suspension, using PlotCtrls—Pan-Zoom-Rotate in Utility

Menu.

When all areas are made on the window, click OK button in Figure 14

Then the drawing of the suspension in Figure 18 appears.

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Figure 14: Window Create Area Thru Kps C B


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Table 2: Keypoint numbers for making areas of the suspension

Area No. Key point Number.

1 9,10, 11, 12

2 1,2,3,4,5,6,7,8

3 1,2,14,13

4 8,7,15,16


ANSYSMainMenu→ Preprocessor → Modeling →Create→Areas→Circle→Solid Circle

The window Solid Circle Area opens, Figure 17. Input the values of (12.0e−3,0, 0.6e−3) to

X, Y and Radius boxes as shown in Figure 17, respectively, and click OK button.

Then the solid circle is made in the drawing of suspension as shown in Figure 18.

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Figure 17: Window Solid Circle Area


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1.2.6 BOOLEAN OPERATION

In order to make a spring region and the fixed region of the suspension, the rectangular and

circular areas in the suspension are subtracted by Boolean operation.

ANSYS Main Menu → Preprocessor → Modelling → Operate → Booleans →

Subtract → Areas.

The window Subtract Areas opens.

Click the area of the suspension in ANSYS Window and OK, and then click

rectangular and circular areas as shown in Figure 19 and OK button.

Next is to glue the for analysis using the COMMAND

ANSYS Main Menu→Preprocessor→Modeling → Operate →Booleans→Glue→Areas


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Figure 21: The FE Model of the Suspension system.

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1.3 Explain real constants, material model and element chosen for the

analysis.

1.3.1 REAL CONSTANTS

This brings up the Element Type for Real Constants menu. It is used to define the

element constant (SHEL 93) and the element thickness (Refer to Figure 6, 7 and 8

above).

For this analysis the shell thickness at node I, J, K and L of the suspension is 5e-005m

or 0.00005m.

Figure 8: Window of Real Constants Set Number 1, for Shell. (As shown above)

1.3.2 MATERIAL PROPERTIES

This defines the material properties of shell element.

For this analysis the material to be used is Structural Linear Isotropic material (Steel)

with the following properties Modulus of Elasticity of 208 GPa, Poisson ratio of 0.3

and Weight Density of 7800Kg/m3

Refer to figure 10, 11 and 12 for details of the steps.

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1.3.3 ELEMENT TYPE

The element type selected in this analysis is SHELL93-8nodes which belongs to the

3D Shell Elements.

The element has 6 DOF at each node (Translations in the x, y, and z plane and as well

as rotations about the x, y and z axis)

The element has plasticity, stress stiffening, large deflection, and large strain

capabilities.

This element is particularly suitable for model curved shells (Ansys Release 12.0

Documentation for Ansys).

Figure 22, below shows the geometry of the shell 93-8node structural shell element.

Figure 22: Geometry of the SHELL 93-8node Structural shell element

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Table 3: Summary of SHELL 93-8 node Structural SHELL element

Element Name SHELL93

Nodes I, J, K, L, M, N, O, P

Degrees of Freedom UX, UY, UZ, ROTX, ROTY, ROTZ

Real Constants TK(I), TK(J), TK(K), TK(L), THETA, ADMSUA

Material Properties EX, EY, EZ, ALPX, ALPY, ALPZ, (PRXY, PRYZ, PRXZ or

NUXY, NUYZ, NUXZ), DENS, GXY, GYZ, GXZ, DAMP

Surface Loads Pressures:

face 1 (I-J-K-L) (bottom, in +Z direction),

face 2 (I-J-K-L) (top, in -Z direction), face 3 (J-I), face 4 (K-J),

face 5 (L-K), face 6 (I-L)

Body Loads Temperature:

T1, T2, T3, T4, T5, T6, T7, T8






T1, T2, T3, T4, T5, T6, T7, T8






T1, T2, T3, T4, T5, T6, T7, T8

Special Features Plasticity, Stress stiffening, Large deflection, Large strain,

Birth and death, Adaptive descent

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1.4 Justify the Selection of your element It is a surface type element.

It has no restriction in the X-Y plane like a 2D solid element since it has 6 DOF

(Translations in the x, y, and z plane and as well as rotations about the x, y and z axis).

It is used in cases where the thickness of the model is very small compared to the

other dimensions of the part and

It is a Quadratic version of SHELL63 hence it produces a better result.

It can be used to analyze Large deflection as in this case, and as well Plasticity, Stress

stiffening, Large deflection, Large strain, Birth and death, Adaptive descent.

It can carry in-plane loads (also called membrane loads) and also out-of-plane bending

moments and twisting.

It can be located anywhere in three-dimensional space.

1.5 Explain the type of meshing used for the analysis

I applied a control mesh size of 0.0002m or 2mm in this analysis, which implies that the areas

are divided by meshes of edge length of 0.0002m.

Below are the procedure followed in creating the mesh in area.

Step 1: ANSYSMainMenu → Preprocessor → Meshing → Size Cntrls → Manual Size

→ Areas → All Areas

Figure 23: Window of Element Sizes on All Selected Areas.

Input 0.0002 to SIZE box and Click OK button and close the window.

Step 2: ANSYSMainMenu → Preprocessor → Meshing → Mesh → Areas → Free

Click PickALL and then OK button to finish dividing the areas.

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1.6 Present meshed FE model and discuss does it require refining

Figure 25: Meshed FE Model

This model does not necessarily require refining since the control mesh size used is very

small (0.0002m or 2mm). Also the aim or object of this assignment is not to determine the

stress or strain distribution along the suspension but to determine the natural frequency

distribution using the modal analysis in order to know where the suspension will experience

resonance, meaning the point with the

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1.7 Explain the boundary conditions used for the mode analysis

All freedoms are constrained at the edge of a hole formed in the suspension. (From figure 26,

ALL 6DOF’s - Translation axis UX, UY, UZ and Rotation axis ROTX, ROTY and ROTZ are

arrested that mean both).

This is the procedure used in applying the boundary condition

ANSYS Main Menu → Solution → Define Loads → Apply → Structural →

Displacement → On Lines

Figure 26: Applying the boundary condition

Figure 27: Showing the Suspension with Boundary Condition.

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1.8 Present your post processing results in textual and graphical form.

In this section, I consider only 3 mode shapes (Showing the Deformed Mode Shapes and the

Nodal Mode Shapes).

Figure 28: First Modal Deformed Plot

Figure 29: First Modal Nodal Plot

From the plot above it can be observed that the Frequency in the first modal plot is

259.225rad/s and the maximum displacement is 543.358m.

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Figure 30: Second Modal Deformed Plot

Figure 31: Second Modal Nodal Plot

From the plot above it can be observed that the Frequency in the second Modal plot is

1959rad/s and the maximum displacement is 584.586m.

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Figure 32: Third Modal Deformed Plot

Figure 33: Third Nodal Modal Nodal Plot

From the plot above it can be observed that the Frequency in the second Modal plot is

2781rad/s and the maximum displacement is 529.354m.

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Figure 34: Post – Processing Result in Textual Form.

The Post – Processing Result in Textual Form above, shows the summary of the 3 Post-

Processing result (Modal Plots) of the Suspension.

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1.9 Explain when this suspension will get failure.

When a dynamic system is subjected to a steady-state harmonic excitation, it is forced to

vibrate at the same frequency as that of the excitation. The harmonic excitation can be given

in many ways like with constant frequency and variable frequency or a swept-sine frequency,

in which the frequency changes from the initial to final values of frequencies with a given

time-rate (ramp).

Based on the Summary of the Post – Processing Result in Textual Form in figure 34 above,

If the frequency of excitation coincides with one of the natural frequencies of the

suspension system, a condition of resonance is encountered and dangerously large

oscillations may result, which results in failure of the suspension system.

Hence, the natural frequency of the system is the frequency at which the resonance occurs. At

the point of resonance the displacement of the system is a maximum.

From observation the First natural frequency is the most critical since it’s the lowest value,

meaning it will be easier for the excited frequency to get to that point.

It is also important to know that the analytical calculation of natural frequencies is of major

importance in the study of vibrations. Because of friction & other resistances vibrating

systems are subjected to damping to some degree due to dissipation of energy.

Thus the validation of the result obtained from the numerical method using ANSYS 12.0 will

be performed analytically in Task 1.11

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1.10 Discuss the solver used for this analysis

In this assignment I have applied the FCG Lanczos Solver as Modal solver the reasons or

justification for using FCG Lanczos Solver is stated below.

The PCG Lanczos eigensolver uses the Lanczos algorithm to compute eigenvalues and

eigenvectors (frequencies and mode shapes) for modal analyses, but replaces matrix

factorization and multiple solves with multiple iterative solves.

It uses the iterative Lanczor algorithm which is faster when compare with the matrix

factorization although it takes a longer time.

PCG Lanczos solver replaces the direct sparse solver but it since uses the same

Lanczos algorithm because the PCG is particularly suitable for this application (modal

analysis).

In ANSYS 12.0 software improves upon its extensive selection of these tools with a

new eigensolver that combines the speed and memory savings of the ANSYS PCG

iterative solver with the robustness of the Lanczos algorithm.

This powerful combination allows users to solve for the natural frequencies and mode

shapes their model using fewer computational resources, often in shorter total elapsed

times than other eigensolvers.

CONDITIONS FOR THE PCG LANCZOS EIGENSOLVER TO WORK The following conditions must be met for the PCG Lanczos eigensolver to be most efficient:

The model would be a good candidate for using the PCG solver in a similar static or

full transient analysis.

The number of modes to extract should be less than 100 in this case it is only 3 modes.

The beginning frequency input on the MODOPT command is zero or close to zero (As

shown in Figure 32).

In this analysis, all these conditions have been met thus the PCG LANCZOS can be applied.

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Figure 35: Window of New Analysis.

Figure 36: Selection of PCG Lanczos Solver (Modal Solver)

Figure 37: Window of PCG Lanczos Solver Analysis

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REFERENCE ANYS User’s Manual: Commands, Vol.2, Swanson Analysis System, Inc

Meirovitch, L., 1967, Analytical Methods in Vibration, Collier-MacMillan Ltd., London.

Saeed Moaveni. 2008, Finite Element Analysis: Theory and application with ANSYS, 3rd

ed.,

USR, Pearson Prentice Hall.

Segrlind, L.1984, Applied Finite Element Analysis, 2nd

ed., New York, John Wiley and Sons

Tirupathi R. Chandrupathla,.1997,Introduction to Finite Element in Engineering,2nd

Edition,

Prentice-Hall,Inc.

T. Stolarski .Y. Nakasone, S.,2006, Engineering Analysis with Ansys Software, 2nd

Edi.

Jordan Hill, Oxford OX28DP.

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Table of Contents 1.1 Creat the FE Model of the suspension system ................................................................ 1

1.2 Explain the steps used for creating FE model in your tool .................................................. 2

1.2.1 ELEMENT TYPE SELECTION ............................................................................. 2

1.2.2 REAL CONSTANTS FOR BEAM ELEMENT ..................................................... 3

1.2.3 MATERIAL PROPERTIES .................................................................................... 5

1.2.4 CREATE KEYPOINTS ........................................................................................... 7

1.2.5 CREATE AREAS FOR SUSPENSION .................................................................. 9

1.2.6 BOOLEAN OPERATION ..................................................................................... 13

1.3 Explain real constants, material model and element chosen for the analysis. ................... 15

1.3.1 REAL CONSTANTS ............................................................................................. 15

1.3.2 MATERIAL PROPERTIES .................................................................................. 15

1.3.3 ELEMENT TYPE ....................................................................................................... 16

1.4 Justify the Selection of your element ............................................................................ 18

1.5 Explain the type of meshing used for the analysis ........................................................ 18

1.6 Present meshed FE model and discuss does it require refining ......................................... 19

1.7 Explain the boundary conditions used for the mode analysis ....................................... 20

1.8 Present your post processing results in textual and graphical form. .................................. 21

1.9 Explain when this suspension will get failure. ................................................................... 25

1.10 Discuss the solver used for this analysis .......................................................................... 26

CONDITIONS FOR THE PCG LANCZOS EIGENSOLVER TO WORK........................ 26

REFERENCE ........................................................................................................................... 28

analytical modelling ( ansys )

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