Finite Element Analysis, Harmonic Analysis and Modal Analysis of the Car Floor by using with and Without Stiffener

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1332
Finite Element Analysis, Harmonic Analysis and Modal Analysis of the
Car Floor by Using With and Without Stiffener
Mohan Kumar G R
Assistant Professor,
Department of Automobile Engineering,
New Horizon College of Engineering,
Bangalore, Karnataka, India
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - This project is concerned with the finite element
modal analysis and experimental modal analysis of an
automotive car floor. To improve ride quality and comfort
zone for the passengers and to extend fatigue life of car floor
component under study condition. The main objective is to
determine and compare the vibration characteristics like
frequencies, mode shapes and damping factors of an
automotive car floor using both FEM and FFT analyzer
techniques. The development of an automotive car floor
structure under the constraint of vibration behavior is
explored by using FEM and FFT analyzer method.
First, car floor geometry is modeled in CATIA and meshed in
HYPERMESH software. Then, afree-freemodalanalysis isdone
by using Optistruct as a solver. To get results of frequencies
and mode shapes.
Second, modal analysis is done experimentally through FFT
analyzer to obtain the results of frequencies, mode shapesand
damping factor.
Third, to control the vibration one of the methods used to
changing frequency of the system by adding stiffener to
automotive floor structure, again free-free modal analysis is
done in both FEM and FFT analyzer method with stiffener
condition. And compare the results obtained.
Key Words: FEM, FFT Analyzer,Hyper-mesh,carfloor,free
-free modal analysis
1. INTRODUCTION
Now a day’s vibration concept was involved in human
activities in one form or other. In recent technology and
development we have seen many engineering applications
regarding with vibration like design of machines and
machine components, foundations, structures, engines,
turbines and control systems.
Most of the machines have vibration difficulties due to
unbalance faulty designs and poor manufacturing. Due to
this reason the machine component subjected to vibration
can fail because of material fatigue resulting from the cyclic
variation of the induced stress.
Vibration causes more wear and tear of machine parts such
as bearings and gears and also creates an excessive noise.
Although the frequency of vibrationofa machineormachine
structure coincides with the frequency of the external
excitation it occur a resonance which results to excessive
deflections and failure of a structure.
2. METHODOLOGY
The methodology of experimentation of flow chart is shown
in figure.1.
Figure.1.Methodology flow chart

GEOMETRIC MODEL
Catia V5 software is used to create the geometric model of
floor of a car as shown in Figure.2
Figure.2. 3D view of geometric model of the floor of a car
FINITE ELEMENT MODEL
Meshing is carried out in Hyper- meshsoftware.Themeshed
or FE model is as shown in Figure.3
Figure.3. Meshed or FE model of the floor of a car
Table.1. General Statistics of meshed car floor
Sl.
No.
Type of
element
No of element
1 CQUAD4 18989
2 CTRIA3 893
Total 19882
Nodes(Grids) 19862
Elements 19882
Mesh Type P-SHELL
Analysis Type Free un-damped
vibration Analysis
LOADS AND BOUNDARY CONDITIONS
In the free - free analysis there are no loads and boundary
conditions.
EXISTING MODEL
The modal analysis is done for floor component in terms of
without stiffener and with stiffener to study the maximum
displacement, minimumdisplacementandfrequencyoccurs.
The Figure.4 shows the floor component having free free
condition and without stiffener.
Figure.4. meshed floor component in free - free
condition and without stiffener
Figure.5. Mode 7th for free -free boundary condition
without stiffener
Figure.6. Mode 8th for free - free boundary condition
without stiffener

Table.2. The frequencies and displacement of without
stiffener condition
The floor component having free- free condition and with
stiffener material used in the component is steel and having
thickness of 10mm with welded at all four ends of the
component.
Figure.7. Mode 7th for free - free boundary condition with
stiffener
Figure.8. Mode 8th for free - free boundary condition with
stiffener
Table.3. The frequencies and displacement of with
stiffener condition
Mode No
FE Method
With stiffener
Frequency in
Hz
Maximum
displacement in mm
7 25.69 39.4
8 43.89 22.2
9 50.73 317
10 56.82 206
11 79.38 131
3. EXPERIMENTAL MODAL ANAYSIS
Figure.9. The floor component of a car hanged freely
i. To prepare the test specimen of automotive car
floor first to measure the lengthandbreadthoffloor
structure and divided into 50mm x 50mm grids
with a total number of node points from 1 to 155.
The floor is hanged or suspended by 7 elastic ropes
for free- free analysis condition. The accelerometer
is located into the right location point for the set of
FRFs dimension. The accelerometer is attached to
the second channel of the signal analyzerinorderto
trace the response of the floor structure. The
accelerometer is fixed to floor at node 7.
Mode No
FE Method
Without stiffener
Frequency in
Hz
Maximum
displacement in mm
7 19.83 387
8 25.24 110
9 31.58 236
10 33.14 349
11 50.74 52.8

ii. Care should be taken to make connections of the
signal analyzer, laptop, accelerometer and impact
hammer.
iii. Switch on the power supply, open the ME’ Scope
software give the required inputs and required
settings in the software. Ensure that there is proper
supply and interactions between the devices are
connected.
iv. We have given impacts by the impact hammer on
the nodes marked on the floor structure onebyone.
Accelerometer is connected at node 7. Hits all the
points from 1 to 155. Signals from the impact
hammer and accelerometer is transferred to the
dynamic signal analyzer for each impact given one
by one and will be compared and analyzed by the
ME’ Scope software. The software generates the
frequency response function to find thefrequencies
of the floor structure. Observe the graph marking
frequencies corresponding to the peaks. The peaks
correspond to the frequencies.
Figure.10. The arrangement of experimental analysis
Figure.11. The nodes applied or marked on the surface of
floor component
Figure.12. The combination of all frequencies occurred at
different points
Figure.13. The floor component hanged freely using
hangers without stiffener
Figure.14.Mode 7th on free - free condition without
stiffener

Table.4.The frequencies of without stiffener condition
Mode No
Experimental analysis
without stiffener
Frequency in
Hz
7 18.6
8 21.7
9 26.4
10 31.3
11 33.9
Figure.15.The floor component with stiffener
Figure.16. Mode 7th on free - free condition with stiffener
Table.5.The frequencies of with stiffener condition
4. RESULT AND DISCUSSION
Table.6.The comparison of FE Method and experimental
modal analysis with stiffener
Table.7.The comparison of FE Method and experimental
modal analysis of without stiffener
Mode No
With stiffener
Frequency in
Hz
7 22.82
8 42.7
9 47.3
10 54.7
11 78.2
Mode No
FEM Experimental
Frequency in Hz Frequency in Hz
7 25.69 22.82
8 43.89 42.7
9 50.73 47.3
10 56.82 54.7
11 79.38 78.2
Mode No
FEM Experimental
Frequency in Hz Frequency in Hz
7 19.83 18.6
8 25.24 21.7
9 31.58 26.4
10 33.14 31.3
11 50.74 33.9

Table.8.The comparison of with and without stiffener of
FE Method
Mode No
FE Method
Without
stiffener
With stiffener
7 19.83 25.69
8 25.24 43.89
9 31.58 50.73
10 33.14 56.82
11 50.74 79.38
Table.9.The comparison of with and without stiffener of
experimental modal analysis
Mode No
Without
stiffener
With stiffener
7 18.6 22.82
8 21.7 42.7
9 26.4 47.3
10 31.3 54.7
11 33.9 78.2
Fixed –fixed mode without stiffener
Figure.17. Mode 1st for fixed boundary condition without
stiffener
Table.10. The frequency values of fixed - fixed mode
without stiffener
Mode No Fixed - fixed mode
without stiffener
Frequency
in Hz
Displacement
in mm
1 32.06 289
2 43.81 196
3 55.47 106
4 72.63 26
5 79.04 26.3
6 81.60 62.9
Fixed - fixed mode with stiffener
Figure.18. Mode 1st for fixed boundary condition with
stiffener
Table.11. The frequency values of fixed - fixed mode with
stiffener
Mode No Fixed - fixed mode
With stiffener
Frequency
in Hz
Displacement
in mm
1 59.89 92.7
2 71.37 191
3 82.39 120
4 102.05 32.5
5 106.75 65.6
6 113.27 66
Harmonic Analysis
Harmonic response analysis gives the ability to predict the
sustained dynamic behavior of structures,thusitenabling to
verify whether or not designs will successfully overcome
resonance, fatigue and other harmful effects of forced
vibrations.

Simple harmonic motion is the movement of a simple
harmonic oscillator; the action is intermittent, as it repeats
itself at regular intervals in a definite manner-described as
being sinusoidal, with regular amplitude. The harmonic
analysis is carried out by means of MSC Nastran which is
described by its amplitude, its period which is the time for a
single fluctuation, its frequency which is the number of
cycles per unit time, and its phase, which decided the initial
position on the sine wave. In words simple harmonicmotion
is “movement where the acceleration of a body is relative to,
and reverses in direction to the displacement from its
equilibrium position”. Simple harmonic motion can provide
as a numerical form of a variety of motions and provides the
foundation of the description of more difficult motions
through the techniques of Fourier analysis.
Figure.19. Image of Harmonic analysis for with stiffener
condition
Figure.20. Simple harmonic analysis is performed in
fixed- fixed modes with stiffener
Displacement Vs Frequency
Table.12.Displacement and Frequency
The simple harmonic analysis chart evaluatesthefixed-fixed
mode shape frequency values. The key material properties
that are relevant to safeguarding cost and structural
performances are density, young’s modulus and poison’s
ratio.
5. CONCLUSIONS
The structural vibration excitations of automotive vehicle
are caused by many different sources. Inour projectwehave
consider one of the key element of automotive vehiclethatis
automotive floor model vibration excitation under free
condition. Firstly the modeling is accomplished for the
automotive floor model in CATIA and meshed in
HYPERMESH then the FEM modal analysis were carried out
using optistruct as a solver. And experimental modal
analysis was conducted using FFT analyzer. To obtained the
results of modal parameters by FEM and FFT analysis of
without stiffener condition. To validate the FEMresultswith
FFT analysis results. To improve the modal parameters by
adding stiffener in the form T-section are welded on the
deterministicsupplementary vibrationfloorarea.Againboth
FEM and FFT analysis was conducted of with stiffener
condition. Finally obtained the results and it’s validated. In
addition to this fixed or clamped modal analysis is done by
Optistruct and harmonic analysis is done by MSC NASTRAN.
REFERENCES
[01] Vibration Analysis of Vehicle Floor Panel Using
HybridMethod of FEM and SEA-Kazuhito Misaji1, Yusuke
Suzuki1, Ayumi Takahashi1, Fumihiko Ide2 and Théophane
Courtois3
[02] Modal Sensitivities of Automotive Vehicle Floor Panels
John G. Chemg,,Tim Akin.
[03]NVH analysis and improvement of a vehicle body
structure using DOE method †Shahram Azadi1, Mohammad
Azadi2,* and Farshad Zahedi1 (Manuscript Received
September 16, 2008; Revised March 4, 2009; Accepted April
15, 2009)
[04] Material vibration propagation in floor pan-R. Burdzik*
Received 22.11.2012; published in revised form 01.01.2013
[05] FEM and Experimental modal analysis of computer
mount-Vishwajit M. Ghatge, David Looper
[06]“Experimental Modal Analysis of Automotive Exhaust
Muffler Using Fem and FFT Analyzer” -Sunil1, Dr Suresh P
M2 International Journal of Recent Development in
Engineering andTechnology Website:www.ijrdet.com(ISSN
2347-6435(Online) Volume 3, Issue 1, July 2014)
With stiffener
Frequency (Hz) 59.89
Displacement (mm) 92.7

Finite Element Analysis, Harmonic Analysis and Modal Analysis of the Car Floor by using with and Without Stiffener

More Related Content

Similar to Finite Element Analysis, Harmonic Analysis and Modal Analysis of the Car Floor by using with and Without Stiffener (20)

More from IRJET Journal (20)

Recently uploaded (20)

Finite Element Analysis, Harmonic Analysis and Modal Analysis of the Car Floor by using with and Without Stiffener