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Finite Element and Experimental Modal Analysis of Car Roof with and without damper
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 11237–11244
www.materialstoday.com/proceedings
AMMMT 2016
Finite Element and Experimental Modal Analysis of Car Roof with and without damper Chandru B T1, Dr. Suresh P M2 1
EWIT, Bangalore, 2 ACS college of Engineering, Bangalore.
Abstract Noise Vibration and Harshness (NVH) is a common phenomenon when vehicle is in motion, the vibration reduction analysis was carried out, using both Finite Element Analysis and Experimental Analysis. The roof model was created by CATIA-V5, and the F.E analysis was done by Hyper mesh and analysis was done by using solver ABAQUS for Free-Free conditions. The experimental modal analysis was carried out with and without dampers for the roof and the validation of results was carried out. The results of Finite Element and Experimental analysis were agreeing with each other.
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016) Keywords:NVH, FE Analysis, Experimental analysis, modal Analysis, model.
1. Introduction: Recent development in Automotive and Aeronautical industries resulted in manufacturing the vehicles which produce less Noise and Vibrations by its body panels. The Noise, Vibration & Harshness (NVH) generated by the vehicle for many more reasons such as rpm of the engine and road surface conditions. The Researchers worked extensively to meet the requirements of the customer’s needs and developed the vehicle accordingly. The different components are selected for NVH characteristics were door, engine hood, floor and roof. In this present work the roof was analyzed for NVH characteristics. Noise and Vibration is a general phenomenon which will occur generally in any automobiles which is in motion, experimental modal analysis was carried out for Free- Free conditions at excitations on different points of the component for different frequencies. The vibrations can be minimized by adding the dampers [1], changing stiffeners or by changing the material of the components [2]. In this work an attempt has been made to reduce the NVH characteristics by adopting vibration dampers.
2214-7853© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016).
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
2. Literature review Fredo, C, et al., [1] developed a method of panel embossing optimization with respect to NVH for a truck cab floor. Selection of embossing shape functions from the mode shapes helped to control the natural frequencies of noise, further noise transmission peaks are shifted to an acceptable RPM. The weight of optimized floor substantially reduced. C J Cameron et al., [2] designed and optimized the weight of a multifunctional vehicle automotive body panel, which integrates the components requirements present in a traditional roof system within a single module. The acoustic properties of two configurations of novel panel were examined using numerical methods including advance poro-elastic module tools compatible with Nastran, and was compared with Numerical results of finite element model of the existing construction.A reduction in mass of more than 80% was achieved compared to the conventional configuration for both sandwich configurations while still fulfilling static and dynamic stiffness constraints. Results of the optimization yielded a broad design space for future structural and acoustic improvements regarding the materials and configuration of the structural components and the acoustic treatment. David Wennberg [3] focussed on reducing the weight of the vehicles by simplifying the construction to reduce manufacturing costs and assembly time, they developed methods for structural stiffness design of light weight, load carrying, and sandwich panels for high speed rail vehicles, Pooja Doke et al., [4] presented a concept modelling method for a sedan car; the model represented the major structural dynamic characteristics of the body and enabled the designer to optimize the structure in terms of the performances and mass in early design phase. The application of advanced computer aided engineering (CAE) allowed vehicle designer to reduce weight considerable and improve the structural performance of the vehicle body. Feng Pan et al., [5] suggested design optimization of vehicle roof structures using multiple surrogates like kriging, radial basis function, vector regression. Use of multiple surrogates eliminated the surrogate dependency optimization showing potential for surrogate based design optimization of non-linear problems. Suresh PM et al., [6] analysed conventional and sandwich constructed car roof. The sandwich constructed roof was done by adding adhesive material – mastics. The sandwich constructed roof revealed better NVH characteristics than the conventional one. Neelappa G Jagali et al., [7] performed the numerical and experimental analysis of car door. Finite Element analysis was carried out for normal door and also for the door by incorporating with dampers. The experimental analysis was done for the door with and without dampers for free-free conditions. Both the analysis revealed improved performance for doors with dampers. 3. Methodology 3.1Flow chart
Figure 1: Flow chart
The flow chart shown in Figure1, reveals the methodology to carryout both experimental and numerical methods.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
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4. Finite Element Analysis 4.1Modelling The primary requirement of the FEA is the geometry of the part which is generated by using the software CATIA V5 R20, CATIA is as multiplatform CAD/CAM/CAE software suite developed by the modelling software company. This software helps in the creation of the geometry very accurately with the user friendly commands for the better model. After the modelling, this model is meshing software for the next process called meshing. The below figure shows the CATIA model of the car roof is shown in Figure 2.
Figure 2: Model of car Roof 4.2Meshing The approximation of geometry domain in the form polygonal form or polyhedral mesh is known as mesh generation is shown in figure 3. In 3-D meshing, the elements are tetrahedral, pyramids, prisms or hexahedral. Meshing can be defined as discretisation for 1-D, 2-D and 3-D isometric. The HYPERMESH tool is used for meshing of roof. The total number of elements, nodes generated after meshing the model is 19882.
Figure 3: Meshed model of car roof 5. Materials 5.1 Material properties Material and material properties plays an important role for the analysis of any component. Material properties are the characteristics or specification of the material which includes young’s modulus, Poisson’s ratio and density which are necessary for the analysis. Table1 shows the material property of SCGA (Steel cold rolled galvanised annealed) which is used for the manufacturing of car roof. Table 1: Material properties PROPERTIES Young’s modulus Density Poisson’s ratio Thickness
Units 2.1E3 N/mm2 7.9E-9 Kg/mm3 0.3 1.5 mm
6. Numerical analysis The Finite Element method is numerical method that can be used to find accurate solution of complex mathematical and structural problems, this method is the actual structure replaced by several pieces or element. Each element is inter connected at certain point called as joints or node, it is very difficult to find the exact solution of the original structure under specified loads during the solution process, the equilibrium forces at the joints and
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
displacements of compatibility between the elements are satisfied and entire structure is made to behave as a single component, the equilibrium for external vibration which is excreted on the structure deforms the structure which can be described by the method known as modal analysis [3]. The deformation of the structure is in the form of number of well deformed wave like shapes or of the form of modes. Each mode exhibits its own frequency, mode shape and damping factor. Dynamic factors or characteristics of the structure like mode shape, frequencies are known by the methods finite element method and experimental method [4]. For both the above condition we have to deal with damper and without damper. Ultimately we have to compare the results of Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA) for the optimization [5]. 6.1 Finite Element results of the car roof for free-free condition without damper The Finite Element analysis of the car roof is shown in Figure 4. The first 6 six modes are rigid modes and have nil frequency (zero), hence the 7th mode will be the first natural frequency of the roof without damper [6].
Figure 4: 7th mode shape for Free-free analysis without damper for car roof. Table 2: Frequency response of the car roof for free free condition without damper Mode number 7 8 9 10 11 12
Frequency(HZ) 45.89 59.55 101.23 130.21 150.31 168.48
Frequency response for the different modes is tabulated in Table 2 for the car roof without damper.
6.2 Finite Element results of the car roof for free-free condition with damper Finite Element analysis of car roof for Free-free conditions for 7th mode with damper is shown in Figure 5. The first six modes are rigid body motions hence they have nil frequency. The 7th mode is the first natural frequency of the damper.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
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Figure 5: 7th mode shape for Free-free analysis with damper for car roof. Table 3: Frequency response of the car roof for free free condition with damper Mode shape number 7 8 9 10 11 12
Frequency(Hz) 43.41 57.62 98.73 128.54 147.98 165.11
The frequencies of the car roof for Free-Free conditions with damper are shown in Table 3. 6.3 Comparison of FE results of car roof with and without dampers for free free condition Table 4 shows the comparison of frequencies of the car roof with and without dampers for different modes. It reveals that the frequencies of the car roof are reduced after incorporating the dampers for all the modes. Table 4 Comparisons of FE results of car roof with and without dampers for free free condition Mode values 7 8 9 10 11 12
Frequency without dampers(Hz) 45.89 59.55 101.23 130.21 150.31 168.48
Frequency with dampers(Hz) 43.41 57.62 98.73 128.54 147.98 165.11
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
7. Experimental modal analysis
Figure 6 Experimental set-up Experimental modal analysis was carried out using impact hammer, accelerometer and Fast Fourier Transformation (FFT) analyser for the car roof with and without dampers for Free-free conditions. Figure 6 shows the experimental setup of the modal analysis, the procedure for carrying out the experimental modal analysis is as follows; Prepare the component individually by marking around the component by marker, suspend it free in the air, there are no forces acting on the component, fix the accelerometer on the roof appropriately using some adhesives. Using impact hammer hit the roof on marked point with a force of 1 Newton three times [7], repeat the process on all points component, natural frequencies obtained in the form of graphs which are generated by FFT analyser in combined form. 7.1 Experimental modal results Experimental results are evaluated for Free-free conditions for car roof without dampers and are tabulated from the 7th mode which is shown in Table 5. Table 5: Experimental modal analysis frequencies for Free-Free conditions of car roof without dampers Mode numbers 7 8 9 10 11 12
Frequency (Hz) 43 54.9 95 127 146 163
7.2 Experimental mode shapes for free-free condition of car roof without damper After conducting experimental analysis, modes are generated by analyser. 7th mode shape which is obtained from the experimental modal analysis is as shown in figure 7.
Figure 7: Experimental result for 7th mode of car roof without damper
Experimental results are evaluated for Free-free conditions car roof with dampers are tabulated from the 7th mode which is shown in Table 6.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
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Table 6: Experimental modal analysis frequencies for Free-Free conditions of car roof with dampers Mode numbers 7 8 9 10 11 12
Frequency(Hz) 42.8 54.8 94.7 126 145 162
7.3 Experimental mode shapes of free-free condition of car roof with damper After conducting experimental analysis, modes are generated by analyser. 7th mode shape which is obtained from the experimental modal analysis is as shown in figure 8.
Figure 8: Experimental results showing 7th mode of the car roof with damper for free free condition
7.4 Comparison of the results of Experimental analysis of car roof with and without dampers for Free-Free condition Table 7 shows the natural frequencies of the car roof with and without dampers by experimental modal analysis, the frequencies of the car roof with dampers are shown. Table 7: Comparison of frequencies of car roof with and without dampers for free-free conditions Mode numbers 7 8 9 10 11 12
Without Damper Frequency(Hz) 53.9 91.1 109 141 166 188
With Damper Frequency(Hz) 50.6 90.9 108 139 163 186
7.5 Comparison of Finite Element and Experimental modal analysis frequencies of car roof with and without damper for free condition The comparison of Finite Element and Experimental modal analysis frequencies of car roof with and without damper for frees free condition results are tabulated in Table 8. The frequencies of both the Finite element and experimental modal analysis are agreeing with each other for the car roof with and without dampers respectively
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244 Table 8: comparison of Finite Element and Experimental frequencies of car roof with and without dampers for free condition Mode numbers 7 8 9 10 11 12
Finite element results Without damper in Hz With damper in Hz 45.89 43.41 89.55 87.62 101.23 98.73 130.21 128.54 150.31 147.98 168.48 165.11
Experimental results Without damper in Hz With damper in Hz 53.9 50.6 91.1 90.9 109 108 141 139 166 163 188 186
8 Conclusions Comparing the results of Finite Element and Experimental modal analysis from table 8, the following conclusions can be made; 1. The FEM and Experimental results for the car roof for free free condition without damper are closer to each other. 2. The FEM and Experimental results for the car roof for free free condition with damper are agreeing with each other. 3. Comparing the result of Finite Element and Experimental result analysis, it is observed that the frequency obtained for both Finite element and Experimental modal analysis have lesser frequencies for the car roof with damper when compared with the car roof without damper, hence it can be concluded that the NVH characteristics have been improved for the car roof with damper in both the cases. References [1] Freddo, C and Hedlund “NVH optimization of truck cab floor panel embossing pattern” SAE technical paper 2005-01-2342, 2005 [2] C J Cameron, Per Wenhage and Peter Goransson. “Structural-acoustic Design of a multi-functional sandwich panel in an automotive context” Journal of sandwich structures and materials, SAGE publication, 12(6):684-708 · November 2010. [3] David Wennberg. “Light-weighting methodology in rail vehicle design through introduction of load carrying sandwich panels” Thesis TRITA AVE 2011:36, ISSN 1651-7660, ISBN 978-91-7501-002-1, 2011; 36. [4] Pooja Doke, Mohammed Fard, Reza Jazar. “Vehicle concept Modelling: A new technology for structures weight reduction” Elsevier procedia Engineering, 49 (2012) 287-293. [5] Feng Pan and Ping Zhu, “Design optimisation of vehicle roof structures: benefits of using multiple surrogate” International Journal of Crashworthiness, Volume 16, Issue 1, 2011, 85-95. [6] Suresh P M, C S Venkatesha, Guruprasad N C, Basavraj Noolvi, “Modal Analysis of conventional and Sandwich Constructed Passenger Car Roof” International Journal of Applied Engineering Research, ISSN 0973-4562,Volume 6, No. 5, 2011, Research India Publications. [7] Neelappagowda Jagali, Chandru B T, Dr. Maruthi B H, Dr. Suresh P M “Evaluation of natural Frequency of Car Door with and without Damper using Experimental Method and Validate using Numerical Method” International Journal of Advanced and Innovative Research ISSN 2278-7844/#36, Volume 5, Issue 6, June 2016, PP 36-40.
ScienceDirect Materials Today: Proceedings 4 (2017) 11237–11244
www.materialstoday.com/proceedings
AMMMT 2016
Finite Element and Experimental Modal Analysis of Car Roof with and without damper Chandru B T1, Dr. Suresh P M2 1
EWIT, Bangalore, 2 ACS college of Engineering, Bangalore.
Abstract Noise Vibration and Harshness (NVH) is a common phenomenon when vehicle is in motion, the vibration reduction analysis was carried out, using both Finite Element Analysis and Experimental Analysis. The roof model was created by CATIA-V5, and the F.E analysis was done by Hyper mesh and analysis was done by using solver ABAQUS for Free-Free conditions. The experimental modal analysis was carried out with and without dampers for the roof and the validation of results was carried out. The results of Finite Element and Experimental analysis were agreeing with each other.
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016) Keywords:NVH, FE Analysis, Experimental analysis, modal Analysis, model.
1. Introduction: Recent development in Automotive and Aeronautical industries resulted in manufacturing the vehicles which produce less Noise and Vibrations by its body panels. The Noise, Vibration & Harshness (NVH) generated by the vehicle for many more reasons such as rpm of the engine and road surface conditions. The Researchers worked extensively to meet the requirements of the customer’s needs and developed the vehicle accordingly. The different components are selected for NVH characteristics were door, engine hood, floor and roof. In this present work the roof was analyzed for NVH characteristics. Noise and Vibration is a general phenomenon which will occur generally in any automobiles which is in motion, experimental modal analysis was carried out for Free- Free conditions at excitations on different points of the component for different frequencies. The vibrations can be minimized by adding the dampers [1], changing stiffeners or by changing the material of the components [2]. In this work an attempt has been made to reduce the NVH characteristics by adopting vibration dampers.
2214-7853© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016).
11238
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
2. Literature review Fredo, C, et al., [1] developed a method of panel embossing optimization with respect to NVH for a truck cab floor. Selection of embossing shape functions from the mode shapes helped to control the natural frequencies of noise, further noise transmission peaks are shifted to an acceptable RPM. The weight of optimized floor substantially reduced. C J Cameron et al., [2] designed and optimized the weight of a multifunctional vehicle automotive body panel, which integrates the components requirements present in a traditional roof system within a single module. The acoustic properties of two configurations of novel panel were examined using numerical methods including advance poro-elastic module tools compatible with Nastran, and was compared with Numerical results of finite element model of the existing construction.A reduction in mass of more than 80% was achieved compared to the conventional configuration for both sandwich configurations while still fulfilling static and dynamic stiffness constraints. Results of the optimization yielded a broad design space for future structural and acoustic improvements regarding the materials and configuration of the structural components and the acoustic treatment. David Wennberg [3] focussed on reducing the weight of the vehicles by simplifying the construction to reduce manufacturing costs and assembly time, they developed methods for structural stiffness design of light weight, load carrying, and sandwich panels for high speed rail vehicles, Pooja Doke et al., [4] presented a concept modelling method for a sedan car; the model represented the major structural dynamic characteristics of the body and enabled the designer to optimize the structure in terms of the performances and mass in early design phase. The application of advanced computer aided engineering (CAE) allowed vehicle designer to reduce weight considerable and improve the structural performance of the vehicle body. Feng Pan et al., [5] suggested design optimization of vehicle roof structures using multiple surrogates like kriging, radial basis function, vector regression. Use of multiple surrogates eliminated the surrogate dependency optimization showing potential for surrogate based design optimization of non-linear problems. Suresh PM et al., [6] analysed conventional and sandwich constructed car roof. The sandwich constructed roof was done by adding adhesive material – mastics. The sandwich constructed roof revealed better NVH characteristics than the conventional one. Neelappa G Jagali et al., [7] performed the numerical and experimental analysis of car door. Finite Element analysis was carried out for normal door and also for the door by incorporating with dampers. The experimental analysis was done for the door with and without dampers for free-free conditions. Both the analysis revealed improved performance for doors with dampers. 3. Methodology 3.1Flow chart
Figure 1: Flow chart
The flow chart shown in Figure1, reveals the methodology to carryout both experimental and numerical methods.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
11239
4. Finite Element Analysis 4.1Modelling The primary requirement of the FEA is the geometry of the part which is generated by using the software CATIA V5 R20, CATIA is as multiplatform CAD/CAM/CAE software suite developed by the modelling software company. This software helps in the creation of the geometry very accurately with the user friendly commands for the better model. After the modelling, this model is meshing software for the next process called meshing. The below figure shows the CATIA model of the car roof is shown in Figure 2.
Figure 2: Model of car Roof 4.2Meshing The approximation of geometry domain in the form polygonal form or polyhedral mesh is known as mesh generation is shown in figure 3. In 3-D meshing, the elements are tetrahedral, pyramids, prisms or hexahedral. Meshing can be defined as discretisation for 1-D, 2-D and 3-D isometric. The HYPERMESH tool is used for meshing of roof. The total number of elements, nodes generated after meshing the model is 19882.
Figure 3: Meshed model of car roof 5. Materials 5.1 Material properties Material and material properties plays an important role for the analysis of any component. Material properties are the characteristics or specification of the material which includes young’s modulus, Poisson’s ratio and density which are necessary for the analysis. Table1 shows the material property of SCGA (Steel cold rolled galvanised annealed) which is used for the manufacturing of car roof. Table 1: Material properties PROPERTIES Young’s modulus Density Poisson’s ratio Thickness
Units 2.1E3 N/mm2 7.9E-9 Kg/mm3 0.3 1.5 mm
6. Numerical analysis The Finite Element method is numerical method that can be used to find accurate solution of complex mathematical and structural problems, this method is the actual structure replaced by several pieces or element. Each element is inter connected at certain point called as joints or node, it is very difficult to find the exact solution of the original structure under specified loads during the solution process, the equilibrium forces at the joints and
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
displacements of compatibility between the elements are satisfied and entire structure is made to behave as a single component, the equilibrium for external vibration which is excreted on the structure deforms the structure which can be described by the method known as modal analysis [3]. The deformation of the structure is in the form of number of well deformed wave like shapes or of the form of modes. Each mode exhibits its own frequency, mode shape and damping factor. Dynamic factors or characteristics of the structure like mode shape, frequencies are known by the methods finite element method and experimental method [4]. For both the above condition we have to deal with damper and without damper. Ultimately we have to compare the results of Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA) for the optimization [5]. 6.1 Finite Element results of the car roof for free-free condition without damper The Finite Element analysis of the car roof is shown in Figure 4. The first 6 six modes are rigid modes and have nil frequency (zero), hence the 7th mode will be the first natural frequency of the roof without damper [6].
Figure 4: 7th mode shape for Free-free analysis without damper for car roof. Table 2: Frequency response of the car roof for free free condition without damper Mode number 7 8 9 10 11 12
Frequency(HZ) 45.89 59.55 101.23 130.21 150.31 168.48
Frequency response for the different modes is tabulated in Table 2 for the car roof without damper.
6.2 Finite Element results of the car roof for free-free condition with damper Finite Element analysis of car roof for Free-free conditions for 7th mode with damper is shown in Figure 5. The first six modes are rigid body motions hence they have nil frequency. The 7th mode is the first natural frequency of the damper.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
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Figure 5: 7th mode shape for Free-free analysis with damper for car roof. Table 3: Frequency response of the car roof for free free condition with damper Mode shape number 7 8 9 10 11 12
Frequency(Hz) 43.41 57.62 98.73 128.54 147.98 165.11
The frequencies of the car roof for Free-Free conditions with damper are shown in Table 3. 6.3 Comparison of FE results of car roof with and without dampers for free free condition Table 4 shows the comparison of frequencies of the car roof with and without dampers for different modes. It reveals that the frequencies of the car roof are reduced after incorporating the dampers for all the modes. Table 4 Comparisons of FE results of car roof with and without dampers for free free condition Mode values 7 8 9 10 11 12
Frequency without dampers(Hz) 45.89 59.55 101.23 130.21 150.31 168.48
Frequency with dampers(Hz) 43.41 57.62 98.73 128.54 147.98 165.11
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
7. Experimental modal analysis
Figure 6 Experimental set-up Experimental modal analysis was carried out using impact hammer, accelerometer and Fast Fourier Transformation (FFT) analyser for the car roof with and without dampers for Free-free conditions. Figure 6 shows the experimental setup of the modal analysis, the procedure for carrying out the experimental modal analysis is as follows; Prepare the component individually by marking around the component by marker, suspend it free in the air, there are no forces acting on the component, fix the accelerometer on the roof appropriately using some adhesives. Using impact hammer hit the roof on marked point with a force of 1 Newton three times [7], repeat the process on all points component, natural frequencies obtained in the form of graphs which are generated by FFT analyser in combined form. 7.1 Experimental modal results Experimental results are evaluated for Free-free conditions for car roof without dampers and are tabulated from the 7th mode which is shown in Table 5. Table 5: Experimental modal analysis frequencies for Free-Free conditions of car roof without dampers Mode numbers 7 8 9 10 11 12
Frequency (Hz) 43 54.9 95 127 146 163
7.2 Experimental mode shapes for free-free condition of car roof without damper After conducting experimental analysis, modes are generated by analyser. 7th mode shape which is obtained from the experimental modal analysis is as shown in figure 7.
Figure 7: Experimental result for 7th mode of car roof without damper
Experimental results are evaluated for Free-free conditions car roof with dampers are tabulated from the 7th mode which is shown in Table 6.
Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244
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Table 6: Experimental modal analysis frequencies for Free-Free conditions of car roof with dampers Mode numbers 7 8 9 10 11 12
Frequency(Hz) 42.8 54.8 94.7 126 145 162
7.3 Experimental mode shapes of free-free condition of car roof with damper After conducting experimental analysis, modes are generated by analyser. 7th mode shape which is obtained from the experimental modal analysis is as shown in figure 8.
Figure 8: Experimental results showing 7th mode of the car roof with damper for free free condition
7.4 Comparison of the results of Experimental analysis of car roof with and without dampers for Free-Free condition Table 7 shows the natural frequencies of the car roof with and without dampers by experimental modal analysis, the frequencies of the car roof with dampers are shown. Table 7: Comparison of frequencies of car roof with and without dampers for free-free conditions Mode numbers 7 8 9 10 11 12
Without Damper Frequency(Hz) 53.9 91.1 109 141 166 188
With Damper Frequency(Hz) 50.6 90.9 108 139 163 186
7.5 Comparison of Finite Element and Experimental modal analysis frequencies of car roof with and without damper for free condition The comparison of Finite Element and Experimental modal analysis frequencies of car roof with and without damper for frees free condition results are tabulated in Table 8. The frequencies of both the Finite element and experimental modal analysis are agreeing with each other for the car roof with and without dampers respectively
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Chandru B T et al. / Materials Today: Proceedings 4 (2017) 11237–11244 Table 8: comparison of Finite Element and Experimental frequencies of car roof with and without dampers for free condition Mode numbers 7 8 9 10 11 12
Finite element results Without damper in Hz With damper in Hz 45.89 43.41 89.55 87.62 101.23 98.73 130.21 128.54 150.31 147.98 168.48 165.11
Experimental results Without damper in Hz With damper in Hz 53.9 50.6 91.1 90.9 109 108 141 139 166 163 188 186
8 Conclusions Comparing the results of Finite Element and Experimental modal analysis from table 8, the following conclusions can be made; 1. The FEM and Experimental results for the car roof for free free condition without damper are closer to each other. 2. The FEM and Experimental results for the car roof for free free condition with damper are agreeing with each other. 3. Comparing the result of Finite Element and Experimental result analysis, it is observed that the frequency obtained for both Finite element and Experimental modal analysis have lesser frequencies for the car roof with damper when compared with the car roof without damper, hence it can be concluded that the NVH characteristics have been improved for the car roof with damper in both the cases. References [1] Freddo, C and Hedlund “NVH optimization of truck cab floor panel embossing pattern” SAE technical paper 2005-01-2342, 2005 [2] C J Cameron, Per Wenhage and Peter Goransson. “Structural-acoustic Design of a multi-functional sandwich panel in an automotive context” Journal of sandwich structures and materials, SAGE publication, 12(6):684-708 · November 2010. [3] David Wennberg. “Light-weighting methodology in rail vehicle design through introduction of load carrying sandwich panels” Thesis TRITA AVE 2011:36, ISSN 1651-7660, ISBN 978-91-7501-002-1, 2011; 36. [4] Pooja Doke, Mohammed Fard, Reza Jazar. “Vehicle concept Modelling: A new technology for structures weight reduction” Elsevier procedia Engineering, 49 (2012) 287-293. [5] Feng Pan and Ping Zhu, “Design optimisation of vehicle roof structures: benefits of using multiple surrogate” International Journal of Crashworthiness, Volume 16, Issue 1, 2011, 85-95. [6] Suresh P M, C S Venkatesha, Guruprasad N C, Basavraj Noolvi, “Modal Analysis of conventional and Sandwich Constructed Passenger Car Roof” International Journal of Applied Engineering Research, ISSN 0973-4562,Volume 6, No. 5, 2011, Research India Publications. [7] Neelappagowda Jagali, Chandru B T, Dr. Maruthi B H, Dr. Suresh P M “Evaluation of natural Frequency of Car Door with and without Damper using Experimental Method and Validate using Numerical Method” International Journal of Advanced and Innovative Research ISSN 2278-7844/#36, Volume 5, Issue 6, June 2016, PP 36-40.