PSD Analysis of automobile dash panel- Dr N V srinivasulu

1. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
PSD Analysis of an Automobile Dash Panel
Dr. N.V.Srinivasulu, S.Jaikrishna, A.Navatha
Abstract:-In this paper, PSD analysis of an automobile used dash panel are the steering wheel and the instrument
dash panel is performed in order to reduce the vibrations that cluster. An instrument cluster includes instrument gauges
occur when force is given as input by keeping a damping such as a speedometer, tachometer, and oil indicator, etc.
material between the panel and a doubler sheet. Modal The top of a dash panel usually contains speakers for the
analysis and Spectrum Analysis of the finite element modal is
audio system, and vents for the heating and A/C system.
performed. By doing this we are comparing the results
obtained with the images and data given .In the initial study A glove box is often found on the passenger side. We
we are trying to compare with the bare dash panel and further look at the dash panel more than any other area of our
study the effect of the Permacel double damp material. Mode cars interior. It makes sense, therefore, that we should
shapes from the modal analysis of this FE model were give it some special attention. The dash panel and the
compared with the transfer function obtained from the Laser deck under the rear window also take the brunt of damage
Vibrometer Test. Tried to identify peaks in the transfer from sun exposure. In order to keep your used dash panel
function graph to the natural frequencies and velocity from from cracking and fading, regular treatment is necessary.
the spectrum analysis of the panel.
II. PROBLEM DESCRIPTION
I. INTRODUCTION
PSD analysis is a probabilistic approach used in Here in this project we consider two cases .In case 1,
random vibration analysis. PSD i.e. the power spectral PSD analysis of the bare dash panel is performed and in
density is the magnitude of the random input. Random case 2, a damper is kept between the dash panel and
Vibration Analysis uses Power spectral density to doubler sheet. In PSD analysis of the bare dash panel, the
quantify the loading. PSD is a statistical measure defined vibrations that occur are high, so in order to reduce the
as the limiting mean-square value of a random variable. It noise or the vibrations we use a damping material. To
is used in random vibration analyses in which the measure the vibrations, a setup is made i.e. the car body
instantaneous magnitudes of the response can be specified or in other words the front part i.e. the dash panel part is
only by probability distribution functions that show the kept on a rod where the excitations are created. These
probability of the magnitude taking a particular value. It excitations are measured practically by placing a laser
is a graph of the PSD value versus frequency, where the vibrometer on that rod. Mode shapes from the modal
PSD may be a displacement PSD, velocity PSD, analysis of this finite element (FE) model are compared
acceleration PSD, or force PSD. Mathematically, the area with the transfer function obtained from the Laser
under a PSD-versus-frequency curve is equal to the Vibrometer Test (practically) and also the vibrations
variance (square of the standard deviation of the produced in case of bare dash panel analysis and the dash
response).The term Power in Power Spectral Density panel with a damper (permacel) is compared.
seems to come from the fact that when random vibration
measurements were taken, they were actually recorded
electronically and so the power levels were used in the
calculations. This type of analysis is basically used for
vibration and noise reduction and control, acoustic
analysis and it is a type of spectrum analysis.
Dash panels are panels under the windshield of a
vehicle, containing indicator dials, compartments, and
sometimes control instruments. It is necessary that a
careful examination should be made of the complete dash
panel and dash areas . It is of vital importance as it keeps
engine fumes, dust and water out of the passenger
compartment. Used dash panel should be checked for a
tight fit around all wires, conduits, and controls.
Particular attention should be paid to the possible
omission of the radio antenna wire grommet in the right
side of the used dash panel. This area is not readily
visible and is commonly overlooked as a possible dust
and water leak source.Many different things are mounted
on dash panels. The most important items located on the
1

2. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
III. THE DASH PANEL
The model as generated from the IGES data.
Fig.1. PSD Analysis of the Bare Dash Panel
Fig.2.Actual Model.
The model of the dash panel is imported to ANSYS.
For the dash panel shell99 element type is used as it is FE Model
generally used for layered applications of a structural Bare
shell model. While SHELL99 is an eight nodded element FE Model for the bare dash panel is as shown below.
and does not have some of the nonlinear capabilities of
SHELL 91, it usually has a smaller element formulation
time. SHELL99 allows up to 250 layers. If more than 250
layers are required, a user-input constitutive matrix is
available. The element has six degrees of freedom at each
node: translations in the nodal x, y, and z directions and
rotations about the nodal x, y, and z-axes. The point
where the excitations are created is taken as the mass21
element which is a point element having six degrees of
freedom i.e. the translations in nodal X,Y,Z directions Fig.3 .Bare
and rotations about the nodal X,Y,Z axes. Dash panel
In this case (bare dash panel) there is only one material After obtaining the mode shapes, spectrum analysis
used i.e. steel, which has the following material option is chosen and also the type of spectrum analysis
properties... i.e. the PSD analysis option is chosen. The number of
Table 1 modes from the modal analysis to include in the PSD
Young’s modulus (Pa) 2.07 e11 analysis is specified. The type of response spectrum
(force spectrum) is chosen. Then the PSD vs frequency
Poisson’s ratio 0.29 graph values are entered in a table and the graph is plot.
Density (kg/m3) 7850 The base PSD excitation node i.e. the mass element is
chosen and the excitation direction (Uy) is given. Now
One set of real constants are defined with thickness of the the participation factor (PF) for the specified PSD table is
layer as 0.8mm. The model is then meshed freely and calculated and the calculation controls are set. Then it is
then the boundary conditions are applied to the dash panel solved for the random vibration solution. After this
and the mass model. Then the modal analysis is solution is obtained the mode combination is set and then
performed and the mode shapes are obtained. In modal the mode combinations and the 1 sigma response are
analysis modal extraction method i.e. the Block element. calculated. Finally the results are read and the response
The mass element is constrained in all degrees of freedom PSD graph is plotted.
and, master and slaves constraints are given to the mass PSD analysis of the dash panel with damper
element and the dash panel Lanczos method is chosen and The model of a 3 layered dash panel i.e. the panel, the
number of modes to extract and number of modes to damping material (permacel) and the doubler sheet is
expand are given. imported and shell99 element type is used for the panel
and the point on the rod is taken as a mass21 element
2

3. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
which is a point element having six degrees of freedom.
In this case two materials are used and the material
properties are defined for both the materials. Steel for
panel and doubler sheet Permacel as a damping material
Table 2. Material Properties:
Material Young’s Poisson’s Density
Modulus Ratio (Kg/m3)
(Pa)
Dash panel 2.07 E11 0.29 7850 Dash Doubler Permacel
& Doubler Sheet material
Sheet panel
Permacel 1.836 E8 0.35 560 Fig.5.FE Model for the model with Doubler and Permacel
The Poisson’s ratio for Permacel is an approximate After obtaining the mode shapes, spectrum analysis
value. option is chosen and also the type of spectrum analysis
Three sets of real constants are defined with thickness i.e. the PSD analysis option is chosen. The number of
of the first layer (panel) as 0.8mm, second layer modes from the modal analysis to include in the PSD
(permacel) as 0.7mm and third layer (doubler sheet) as analysis is specified. The type of response spectrum
0.8mm. The model is then meshed freely and then the (force spectrum) is chosen. Then the PSD vs frequency
boundary conditions are applied to the dash panel and the graph values are entered in a table and the graph is plot.
mass model. Then the modal analysis is performed and The base PSD excitation node i.e. the mass element is
the mode shapes are obtained. In modal analysis modal chosen and the excitation direction (Uy) is given. Now
extraction method i.e. the Block element. The mass the participation factor (PF) for the specified PSD table is
element is constrained in all degrees of freedom and, calculated and the calculation controls are set. Then it is
master and slaves constraints are given to the mass solved for the random vibration solution. After this
element and the dash panel Lanczos method is chosen and solution is obtained the mode combination is set and then
number of modes to extract and number of modes to the mode combinations and the 1 sigma response are
expand are given. calculated. Finally the results are read and the response
PSD graph is plotted.
IV. RESULTS
Modal Analysis Results
Given below are the natural frequencies of the bare dash
panel model, which coincide with the peaks as shown in
the transfer function, obtained from the vibrometer test.
Fig.4. Doubler sheet with damping treatment
sandwiched between the steel sheets
Permacel
The FE Model for the model with Doubler and Permacel
is as shown below. Fig.6. Bare dash panel
3

4. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Natural Natural
VI. CONCLUSION
Peaks from Peaks from
Frequencies Frequencies
Tested Tested
from from Form the analysis it is concluded that…
Transfer Transfer
Analytical Analytical
Functions Functions
Study Study
 In case of the single layered dash panel the first
73.33 75.00 432.91 435.00
92.80 96.25 440.80 438.75
natural frequency obtained is 73.33 Hz.
136.83 137.50 445.63 451.25  In case of the three layered sandwiched dash
144.00 141.25 457.08 468.75 panel, the first natural frequency is 77.5 Hz.
153.37 156.25 492.65 475.00 Here the natural frequency is increased and
178.66 167.50 499.13 493.75 hence the vibrations are reduced by 5.38%
183.34 177.50 507.89 508.75 which is safe and noise controlling. The
194.49 198.75 526.18 527.50 damping material (permacel) used absorbs
209.25 212.50 541.49 546.25 vibrations and prevent them from reaching the
220.58 223.75 551.78 552.50 passenger’s end.
251.02 238.75 573.60 567.50  So, such type of dash panels which are
262.44 256.25 595.36 595.00 sandwiched with a damping material are noise
267.25 270.00 626.44 621.25 controlling and safe to use.
276.94 278.75 654.70 652.50
300.81 297.50 672.66 672.50
305.55 308.75 679.05 682.50
339.85 342.50 685.52 688.75
373.19 345.00 700.49 700.00
377.42 362.50 729.12 726.25
387.37 388.75 763.81 762.50
401.27 403.75 776.82 771.25
418.64 416.25 782.41 780.00
425.78 425.00 798.25 796.25
Fig.8. 1 sigma displacement
Fig.7. Modal results at first natural frequency in Ux and Uy Fig.9.1 sigma velocity
at first natural frequency
V. SPECTRUM ANALYSIS RESULTS
In spectrum analysis the 1 sigma displacement, 1sigma
velocity, 1 sigma acceleration and 1 sigma unit static
solutions are obtained. 1σ results are typically used for
Fatigue calculations. Based on the premise that the stress
level is at or below 1σ 68.2% of the time, between
1σ=and 2σ 27.2% of the time (95.4-68.2), and between
2σ=and 3σ 4.3% of the time (99.7-95.4), and above
Fig.10. 1 sigma acceleration with and without
3σ=less than .3% of the time.
4

5. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Fig.11. 1 sigma displacement AND 1 sigma velocity
Given below are the natural frequencies of the dash panel
with damper model, which coincide with the peaks as
shown in the transfer function, obtained from the
vibrometer test.
Dash panel with damper (permacel)
Natural Natural
Peaks from Peaks from
Frequencies Frequencies
Tested Tested
from from
Transfer Transfer
Analytical Analytical
Functions Functions
Study Study
77.75 75.00 456.86 435.00
106.74 96.25 465.14 438.75
123.82 137.50 484.19 451.25
146.32 141.25 492.13 468.75
158.62 156.25 492.95 475.00
177.59 167.50 499.67 493.75
205.84 177.50 508.13 508.75
220.05 198.75 523.09 527.50
232.23 212.50 542.03 546.25
252.73 223.75 549.28 552.50
263.37 238.75 567.69 567.50
266.88 256.25 582.57 595.00
270.65 270.00 620.55 621.25
281.13 278.75 649.97 652.50
297.34 297.50 673.89 672.50
314.35 308.75 680.40 682.50
338.76 342.50 685.15 688.75
353.87 3450 700.23 700.00
369.65 362.5 720.44 726.25
381.21 388.75 757.70 762.5
400.72 403.75 772.15 771.25
418.57 416.25 781.56 780.00
425.69 425.00 795.67 796.25
5