psd analysis ijeit

ISSN: 2277-3754 ISO 9001:2008 Certified

International Journal of Engineering and Innovative Technology (IJEIT)

Volume 2, Issue 1, July 2012

1

PSD Analysis of an Automobile Dash Panel

Dr. N.V.Srinivasulu, S.Jaikrishna, A.Navatha

Abstract:-In this paper, PSD analysis of an automobile

dash panel is performed in order to reduce the vibrations that

occur when force is given as input by keeping a damping

material between the panel and a doubler sheet. Modal

analysis and Spectrum Analysis of the finite element modal is

performed. By doing this we are comparing the results

obtained with the images and data given .In the initial study

we are trying to compare with the bare dash panel and further

study the effect of the Permacel double damp material. Mode

shapes from the modal analysis of this FE model were

compared with the transfer function obtained from the Laser

Vibrometer Test. Tried to identify peaks in the transfer

function graph to the natural frequencies and velocity from

the spectrum analysis of the panel.

I. INTRODUCTION

PSD analysis is a probabilistic approach used in

random vibration analysis. PSD i.e. the power spectral

density is the magnitude of the random input. Random

Vibration Analysis uses Power spectral density to

quantify the loading. PSD is a statistical measure defined

as the limiting mean-square value of a random variable. It

is used in random vibration analyses in which the

instantaneous magnitudes of the response can be specified

only by probability distribution functions that show the

probability of the magnitude taking a particular value. It

is a graph of the PSD value versus frequency, where the

PSD may be a displacement PSD, velocity PSD,

acceleration PSD, or force PSD. Mathematically, the area

under a PSD-versus-frequency curve is equal to the

variance (square of the standard deviation of the

response).The term Power in Power Spectral Density

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

used dash panel are the steering wheel and the instrument

cluster. An instrument cluster includes instrument gauges

such as a speedometer, tachometer, and oil indicator, etc.

The top of a dash panel usually contains speakers for the

audio system, and vents for the heating and A/C system.

A glove box is often found on the passenger side. We

look at the dash panel more than any other area of our

cars interior. It makes sense, therefore, that we should

give it some special attention. The dash panel and the

deck under the rear window also take the brunt of damage

from sun exposure. In order to keep your used dash panel

from cracking and fading, regular treatment is necessary.

II. PROBLEM DESCRIPTION

Here in this project we consider two cases .In case 1,

PSD analysis of the bare dash panel is performed and in

case 2, a damper is kept between the dash panel and

doubler sheet. In PSD analysis of the bare dash panel, the

vibrations that occur are high, so in order to reduce the

noise or the vibrations we use a damping material. To

measure the vibrations, a setup is made i.e. the car body

or in other words the front part i.e. the dash panel part is

kept on a rod where the excitations are created. These

excitations are measured practically by placing a laser

vibrometer on that rod. Mode shapes from the modal

analysis of this finite element (FE) model are compared

with the transfer function obtained from the Laser

Vibrometer Test (practically) and also the vibrations

produced in case of bare dash panel analysis and the dash

panel with a damper (permacel) is compared.




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Fig.1. PSD Analysis of the Bare Dash Panel

The model of the dash panel is imported to ANSYS.

For the dash panel shell99 element type is used as it is

generally used for layered applications of a structural

shell model. While SHELL99 is an eight nodded element

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

and rotations about the nodal X,Y,Z axes.

In this case (bare dash panel) there is only one material

used i.e. steel, which has the following material

properties... Table 1

Young’s modulus (Pa) 2.07 e11

Poisson’s ratio 0.29

Density (kg/m3) 7850

One set of real constants are defined with thickness of the

layer as 0.8mm. The model is then meshed freely and

then the boundary conditions are applied to the dash panel

and the mass model. Then the modal analysis is

performed and the mode shapes are obtained. In modal

analysis modal extraction method i.e. the Block element.

The mass element is constrained in all degrees of freedom

and, master and slaves constraints are given to the mass

element and the dash panel Lanczos method is chosen and

number of modes to extract and number of modes to

expand are given.

III. THE DASH PANEL

The model as generated from the IGES data.

Fig.2.Actual Model.

FE Model

Bare

FE Model for the bare dash panel is as shown below.

Fig.3 .Bare

Dash panel

After obtaining the mode shapes, spectrum analysis

option is chosen and also the type of spectrum analysis

i.e. the PSD analysis option is chosen. The number of

modes from the modal analysis to include in the PSD

analysis is specified. The type of response spectrum

(force spectrum) is chosen. Then the PSD vs frequency

graph values are entered in a table and the graph is plot.

The base PSD excitation node i.e. the mass element is

chosen and the excitation direction (Uy) is given. Now

the participation factor (PF) for the specified PSD table is

calculated and the calculation controls are set. Then it is

solved for the random vibration solution. After this

solution is obtained the mode combination is set and then

the mode combinations and the 1 sigma response are

calculated. Finally the results are read and the response

PSD graph is plotted.

PSD analysis of the dash panel with damper

The model of a 3 layered dash panel i.e. the panel, the

damping material (permacel) and the doubler sheet is

imported and shell99 element type is used for the panel

and the point on the rod is taken as a mass21 element




3

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

Modulus

(Pa)

Poisson’s

Ratio

Density

(Kg/m3)

Dash panel

& Doubler

Sheet

2.07 E11 0.29 7850

Permacel 1.836 E8 0.35 560

The Poisson’s ratio for Permacel is an approximate

value.

Three sets of real constants are defined with thickness

of the first layer (panel) as 0.8mm, second layer

(permacel) as 0.7mm and third layer (doubler sheet) as

0.8mm. The model is then meshed freely and then the

boundary conditions are applied to the dash panel and the

mass model. Then the modal analysis is performed and

the mode shapes are obtained. In modal analysis modal

extraction method i.e. the Block element. The mass

element is constrained in all degrees of freedom and,

master and slaves constraints are given to the mass

element and the dash panel Lanczos method is chosen and

number of modes to extract and number of modes to

expand are given.

Fig.4.

Permacel

The FE Model for the model with Doubler and Permacel

is as shown below.

Fig.5.FE Model for the model with Doubler and Permacel

After obtaining the mode shapes, spectrum analysis

option is chosen and also the type of spectrum analysis

i.e. the PSD analysis option is chosen. The number of

modes from the modal analysis to include in the PSD

analysis is specified. The type of response spectrum

(force spectrum) is chosen. Then the PSD vs frequency

graph values are entered in a table and the graph is plot.

The base PSD excitation node i.e. the mass element is

chosen and the excitation direction (Uy) is given. Now

the participation factor (PF) for the specified PSD table is

calculated and the calculation controls are set. Then it is

solved for the random vibration solution. After this

solution is obtained the mode combination is set and then

the mode combinations and the 1 sigma response are

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.6. Bare dash panel

Doubler sheet with damping treatment

sandwiched between the steel sheets

Dash

panel

Doubler

Sheet

Permacel

material




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Fig.7. Modal results at first natural frequency in Ux and Uy

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

3σ=less than .3% of the time.

VI. CONCLUSION

Form the analysis it is concluded that…

In case of the single layered dash panel the first

natural frequency obtained is 73.33 Hz.

In case of the three layered sandwiched dash

panel, the first natural frequency is 77.5 Hz.

Here the natural frequency is increased and

hence the vibrations are reduced by 5.38%

which is safe and noise controlling. The

damping material (permacel) used absorbs vibrations and prevent them from reaching the

passenger’s end.

So, such type of dash panels which are

sandwiched with a damping material are noise

controlling and safe to use.

Fig.8. 1 sigma displacement

Fig.9.1 sigma velocity

Fig.10. 1 sigma acceleration with and without

Natural

Frequencies

from

Analytical

Study

Peaks from

Tested

Transfer

Functions

Natural

Frequencies

from

Analytical

Study

Peaks from

Tested

Transfer

Functions

73.33 75.00 432.91 435.00

92.80 96.25 440.80 438.75

136.83 137.50 445.63 451.25

144.00 141.25 457.08 468.75

153.37 156.25 492.65 475.00

178.66 167.50 499.13 493.75

183.34 177.50 507.89 508.75

194.49 198.75 526.18 527.50

209.25 212.50 541.49 546.25

220.58 223.75 551.78 552.50

251.02 238.75 573.60 567.50

262.44 256.25 595.36 595.00

267.25 270.00 626.44 621.25

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




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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

Frequencies

from

Analytical

Study

Peaks from

Tested

Transfer

Functions

Natural

Frequencies

from

Analytical

Study

Peaks from

Tested

Transfer

Functions

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