Natural Frequency Analysis of Automotive Seating System by using fem software
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F. Check the Free-Free Run for Natural Frequencies It is the very important meshing check for assembly of components for Natural frequency calculations without applying any constraints. Any single object allowed to vibrate freely, should show first 6 modes as rigid (natural frequencies = 0) & 7 modes onward deformable modes with positive value of natural frequency. Any number of zero frequency modes greater than 6 means that the model has free connections. G. Boundary Conditions Once the CAD geometry is meshed (i.e. approximated by finite elements), then assembled with each other. Material and property information linked to the elements and constraints are assigned. H. Solution with NASTRAN The free-free run is complete then export the mesh file in NASTRAN format for post processing. The FEM model is consisting of nodes, elements, material properties and constraints. I. Post Processing Natural frequency and mode shape are plotted and examined to see how the part responded to the various loading conditions. Based on the results, modifications may be made to the part and a new analysis may be run to observe how the modifications affected the part. The modal analysis in structural mechanics is to determine the natural mode shapes and frequencies of an object. It is a basic design property. Natural frequency information is useful for avoiding resonance.
Seat is continuous system so it has infinite frequency only find out critical frequency it is very close to human body. A. Natural Frequency of Seat for Steel Material The analysis of seat we use the steel material for whole assembly of seat and find out the critical natural frequency of seat.  
Fig. 2 : Natural frequency of seat for steel material Fig2 shows that the forth natural frequency of seat we can see that the maximum of the deformation is taking place at the arm rest component of seat. This is due to the fact that vibration is going to act on this part of the seat. The frequency of the vibration for this particular mode of the seat is 35.07Hz.
Table .3 : Natural frequency of steel material The engine frequency (35Hz) of the vehicle and 4th natural frequency (35.07Hz) of seat is same then resonance occurs in the seat. The 4th (35.07Hz) and 5th (43.01 Hz) natural frequency of arm rest is match with the natural frequency ranges of human hand of the body(30-50 Hz) so the resonance occurs in this region.
Table. 4 : Comparison of human body part and components for steel material B. Cast iron material for seat components From previous analysis resonance in seat assembly then it requires change natural frequencies of seat for the analysis of seat we use the cast iron material for whole assembly of seat.  
Fig.3 : Natural frequency of cast iron material for seat Fig3 shows that the maximum value of the displacement is taking place at the arm rest component of seat. This is due to the fact that vibration is going to act on this part of the seat. This mode shows that this is the natural frequency of the arm rest. The frequency of the vibration for this particular mode of the seat is 44.21Hz. The engine frequency of the vehicle is near to the natural frequency of head rest of seat then resonance may be occurs in the seat assembly. The natural frequency of arm rest is 44.21Hz match with the natural frequency ranges of human hand of the body (30-50 Hz) so the resonance occurs in this region. Directory: journal ijmer -> pdf pdf -> International Journal on Mechanical Engineering and Robotics (ijmer) Download 420.47 Kb. Share with your friends:
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