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

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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 the modal analysis of this FE model were compared with the transfer function obtained the Laser Vibrometer Test. Tried to identify peaks in the transfer function graph to the natural frequencies and velocity 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 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 sun exposure. In order to keep your used dash panel 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 the modal analysis of this finite element (FE) model are compared with the transfer function obtained 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. 1

2 III. THE DASH PANEL The model as generated the IGES data. 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. 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 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 2

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 Material Dash panel & Doubler Sheet Table 2. Material Properties: Young s Poisson s Modulus Ratio (Pa) Density (Kg/m 3 ) 2.07 E Permacel E 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. Dash panel Doubler Sheet Permacel material 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 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 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: Peaks Peaks VI. CONCLUSION Form the analysis it is concluded that In case of the single layered dash panel the first natural frequency obtained is 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 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.7. Modal results at first natural frequency in Ux and Uy at first natural frequency Fig.9.1 sigma velocity 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 ( ), and between 2σ=and 3σ 4.3% of the time ( ), and above 3σ=less than.3% of the time. Fig sigma acceleration with and without 4

5 Fig 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 the vibrometer test. Dash panel with damper (permacel) Peaks Peaks