Natural Frequency Analysis of Automotive Seating System by using fem software
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- Siddha Uttam Y. Kumbhar Samir B.
- Keywords - Finite element analysis, Natural frequency, Noise vibration Harshness, Whole body vibration
- Spinal column diseases
- Cardiovascular system effects
Abstract - Seat is one of the most suited components for the tactile response, as the passengers and driver is in contact directly with the seat. From NVH (Noise vibration Harshness) point of view in an automobile structure Seats are the most important part. The vibration sensation is a common man-made non-natural surrounding with which humans have a restricted acceptance to survive due to their body dynamics. The design achieved for the seating system to protect the human body in a vibration surroundings. Finite element analysis is being latest regularly to calculate vibration and response to understand the nature of ride vibration and its effect on perceived human comfort. The aim of this paper is to analyze an automotive seating system for Vibration concern and to check whether it meets the final OEM’s (original equipment manufacturer) requirements of modal frequency management. In this paper prepare a Finite element model of the seat and analyze it for the natural frequencies from the Modal management point of view find out critical natural frequencies and isolate it from the range of other automotive component and human body frequency ranges for avoiding the resonance occurrence. Keywords - Finite element analysis, Natural frequency, Noise vibration Harshness, Whole body vibration I. INTRODUCTION Vibration generated from other sources like engine, road surface, tires, exhaust, etc. should be taken careful in the design of an automotive body. These vibrations pass through systems (body, drive train, suspension, etc.) to the seats, steering wheel and further areas where it is detected by the human body in the vehicle [1].Whole body vibration experienced throughout travelling is extremely perceived like a source of discomfort. The seat investigation is necessary to know the characteristic of a seat and to design the seat vibration controller for most important interface between passengers and the vehicle. Finite element analysis is a commanding method to simulate the mechanical behavior of a system. II. WHY FE ANALYSIS IS REQUIRED FOR SEATING SYSTEM The FEA technique has developed to a point where design, meshing, analysis and post processing are greatly built-in and automatic. The automotive seating system is mesh in detail by FEM basics and is simulated for a variety of load cases. Once, a logical level of assurance was gained, the design is accepted to the seat system. Reducing development costs and time, even as delivering high superiority products is one of the main challenges for automotive OEMs and their suppliers. The growth of new automobile seats is extremely time uncontrollable and expensive since it is classically based on experimental evaluation by means of prototypes. FEA models of the human-seat interaction may possibly speed up this development. III. VIBRATION DESIGN ISSUES OF NEW AUTOMOTIVE SEATING SYSTEM The automotive vehicle is travelling on all kinds of road. Roads are characterized by surface roughness profile. The road excitation cause the vehicle to response and the response for human is called as the ride behavior. The Automotive vehicles consist of a number of components made up of other assemblies such as steering column, doors and engine vibration. Different components will have to be adjusted for different frequencies. . The natural frequency of this component must be separated from each other otherwise these will lead to extremely embracing condition thus find out all critical natural frequencies of seating system and separate it from the range of further automotive component frequencies for avoiding the resonance occurrence. International Standard Organization (ISO) presents an accepted and helpful standard concerning ride comfort (ISO 2631). It belonging to vibrations on the human, classify the vibrations between 0.5 and 80 Hz according to frequencies that cause the tire, human health problem, discomfort, and it also classifies the vibrations between 0.1 and 0.5 Hz effect with motion disease [3]. The mainly reason of this case is a resonance condition that exists from the coincidence of the natural frequencies of human body structures and the vibration frequencies comes from the automotive vehicle. Vibration transmissibility, mainly in the vertical direction, is one of the majorities considered point measures of automotive seat comfort. The passengers, due to the most important flexion mode of the trunk, demonstrate a resonance in vertical vibration between 4 and 8Hz. This is difficult because automotive vehicle seats have a tendency to create a resonance in the same range. Thus particular aspects have to be measured and organize to care for the human body. For this motivation of improving the ride comfort, it is needed either to maintain the Frequencies upper at about 8 Hz or to keep the frequencies lesser than 4 Hz [2].
The Vibration acting on the human body are called human vibration and may be of the following 1) Motion sickness, classically initiate in vehicle with extremely flexible suspension and these take place in the frequency range 0.1 to 0.63Hz. 2) Whole body vibration (WBV) in automotive vehicle taking place in the frequency range 1 to 80Hz. One of the mainly significant parts of the human body which extremely responsive to vibration and shocks is the stomach with resonance in the vertical direction happening in the 4 to 8 Hz and vibration range 2.5 to 5 Hz make strong resonance in the spinal column. The transmission of vibration to the human body at the natural frequency of the human body as a total or of its individual parts will cause resonance phenomenon. This embracing situation occurs in which the total human body or individual parts will vibrate at a level greater than the applied vibration environments. WBV is normally due to vibration in the frequency range 0.5 to 80 Hz to which the human body responds considerably. Vibration gets transfer from pedals and seat of a running automotive vehicle to the driver or passenger. The major effect on comfort, human health and task performance due to Whole body vibration are explained below.
Vehicle ride comfort is one of the most important factors touching the purchase choice and customer fulfillment. Gathering the purchaser comfort requirements, this is an accepted issue, acting a central role in terms of vehicle selling. It was recognized that vary in the discomfort is proportion to a change in amount of vibration that is a doubling in vibration amount cause a doubling of discomfort. Discomfort is also strongly associated to vibration frequencies at low frequencies (1to2Hz), Overall discomfort caused because of Vibration is transmitted without magnification to the human body at a little higher frequency a range of body resonances tends to increase the motion. B. Effect on Health Spinal column diseases: There are the most common diseases related with long term experience to WBV, as the spinal column is particularly responsive to the frequency range 4-12Hz Digestive system diseases: These are observed in persons exposed to WBV over a long period of time and are related with the resonant movement of the stomach at frequencies between 4 and 5Hz. Cardiovascular system effects: Expanded experience to WBV at frequencies below 20Hz could result in hyperventilation, increase in heart rate, pulmonary ventilation and respiratory. Effects of task performance: Some of the WBV effects may result in injury or health damage, but can cause problem performing difficult task. The Natural frequency of human body parts are show in the following table.
Table 1: Natural frequency of human body parts C. Understand Factors Affecting Automotive Seat Comfort There are numerous factors that concern automobile seat comfort. Then stiffness, contour, geometry and styling are considered as seat factors. Stiffness refers to the resiliency of the seating system. Geometry defines seat shape in terms of length, width and height, whereas contour deal with the profile of the seated surface .The seat’s geometry and contour related with the anthropometric variability of the target population. Styling must be integrated as a seat factor because visual superiority may affect perceptions of comfort.
The reciprocating parts of the engine may cause vibration in vehicle due to the periodic disturbances. The engine of the vehicle is running at the 2100rpm i.e.35Hz. The main difficulty is the resonance, where response levels under dynamic loading can be 10 or 100 times more than the magnitude resulting as of static loading of the equal amount. Mechanical vibration of a vehicle is caused by the vibrating components of the vehicle. Every moving component has a definite frequency related with its movement so, the generally vibration transmitted to a human body in contact with the seat is made up of different frequencies of vibration happening simultaneously. This is a significant fact to get into consideration when measuring human vibration because the human body part is not equally sensitive to all frequencies of vibration. VI. INPUT DATA FOR ANALYSIS BY FEM A. Geometry Requirement A seat assembly consists of the components: Seat tracks, Seat back rest, Headrest, arm rest, reclining bracket, front cross member, pivot bracket, cushion tube and rear hook. B. Material properties all components 
Table 2 : Material properties C. Pre-Processing Any FE analysis process starts with the import of the components CAD geometry (IGES Format) into pre-processor i.e. Hypermesh Meshing is the core step in the finite element analysis as the quality of the mesh directly reflects on the quality of the results obtained. Deciding the element type and generating the mesh using manual or special meshing operations. Shell element is used for thin wall part having small thickness. It is the most commonly used plate element. It is a 4-noded flat plate element It is capable of resisting both, in-plane and out-of-plane loads. D. Requirement for Meshing Acceptance criteria of seat model quality are considered acceptable when meets the body mesh model Quality check list concerning the various mesh quality parameters such as length , aspect ratio, min and max angles of tria and quad along with percentage of trias in the mesh and the mainly essential parameter, the Jacobian or distortion of the mesh from an ideal shape . E. Assembly of Seat Components Analysis of seat for the natural frequency it is required to be meshed with elements to get the component mesh. When all the parts in the assembly are meshed, they are all connected as one using suitable fastening elements such as Rigid (RBE2). 
Fig 1: Assembly of seat 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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