COMPARATIVE STUDY OF MODAL ANALYSIS ON FLYWHEEL FOR AUTOMOTIVES Aswin Inbaraj Jaison A 1*, Manoj Kumar G 2 12 PG Scholar, Department of Mechanical Engineering, Regional Centre of Anna University, Tirunelveli, Tamil Nadu, India. 1 aswininbaraj@gmail.com Abstract The main concept of work is to reduce the damping effects and weight of automotive flywheel with the utilization of composite material. Composite materials have been used in automotive components because of their properties such as low weight, high specific stiffness, corrosion free, ability to produce complex shapes, high specific strength and high impact energy absorption etc. As the automotive flywheel is a very important component of vehicle. The modeling of the flywheel has done using Creo software. A shaft has to be designed to meet the stringent design requirements for automotives. In present work an attempt has been to estimate natural frequencies of flywheel using Finite element analysis. Modal analysis is done to determine the number of mode shapes for flywheel. Analysis is done for three materials Gray Cast Iron, S-Glass Epoxy and Carbon Epoxy to compare the results. Finally the analysis optimized with the objective on minimizing the vibration of composite flywheel for automotives. Keywords Flywheel, Composites, Finite element analysis, vibration. I. INTRODUCTION A flywheel is a mechanical device with a significant moment of inertia used as a storage device for rotational energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft when a fluctuating torque is exerted on it by its power source such as a piston-based (reciprocating) engine, or when an intermittent load, such as a piston pump, is placed on it. Flywheels can be used to produce very high power pulses for experiments, where drawing the power from the public network would produce unacceptable spikes. A small motor can accelerate the flywheel between the pulses. Recently, flywheels have become the subject of extensive research as power storage devices for uses in vehicles and power plants. A good design solution can be delivered only when the function of the component being designed, is known before hand with proper working condition specifications. Ability of different methodologies in solving for these conditions can be appreciated based on the complexity of the problem, though. Presently, the specifications of the composite flywheel to be designed are considered to be same as that of an optimally designed cast iron flywheel. Comparison is made between the composite and the conventional type for the optimization of numerical analysis. Modal analysis is carried out to study the variation in natural frequency by changing the material of the component [1]. Researchers have proposed, to counter the requirement of smoothing out the large oscillations in velocity during a cycle of a I.C. Engine, a flywheel is designed, and analyzed by using FEA technique and also calculated the stresses inside the flywheel and compared the Design and analysis result with existing flywheel [2-4]. In addition Authors have proposed, a computer-aided-designs of software for flywheels using object-oriented programming approach of Visual Basic. The various configurations of flywheels (rimmed or solid) formed the basis for the development of the software. The software s graphical features were used to give a visual interpretation of the solutions [5, 6]. The software s effectiveness was tested on a number of numerical examples, some of which are outlined in this work. 70
The FEA model is described to achieve a better understanding of the mesh type, mesh size and boundary conditions applied to complete an effective FEA model [7]. Algorithms based on dynamic analysis of crank shaft for designing flywheel for I.C.engine, torsional vibration analysis result by AVL\EXCITE is compared with the angular displacement of a desire free head of crank shaft, also consideration of fatigue for fatigue analysis of flywheel are given [8]. The importance of the flywheel geometry design selection and its contribution in the energy storage performance. This contribution is demonstrated on example cross-sections using computer aided analysis and optimization procedure. Computer aided analysis and optimization procedure results show that smart design of flywheel geometry could both have a significant effect on the Specific Energy performance and reduce the operational loads exerted on the shaft/bearings due to reduced mass at high rotational speeds [9]. The mass of the flywheel is minimized subject to constraints of required moment of inertia and admissible stresses. The theory of the rotating disks of uniform thickness and density is applied to each the disk and the rim independently with suitable matching condition at the junction. Suitable boundary conditions on the centrifugal stresses are applied and the dimensional ratios are obtained for minimum weight [10]. It is proved that the required design is very close to the disk with uniform thickness. A. Geometry It controls the Specific Energy, in other words, kinetic energy storage capability of the flywheel. Any optimization effort of flywheel cross-section may contribute substantial improvements in kinetic energy storage capability thus reducing both overall shaft/bearing loads and material failure occurrences. To improve the quality of the product and in order to have safe and reliable design, it is necessary to investigate the stresses induced in the component during working condition. Fig.1 Factors affecting flywheel performance B. Functions of flywheel The main function of a fly wheel is to smoothen out variations in the speed of a shaft caused by torque fluctuations. If the source of the driving torque or load torque is fluctuating in nature, then a flywheel is usually called for. Many machines have load patterns that cause the torque time function to vary over the cycle. 71
Fig.2 Flywheel function graph II. MODELING OF FLYWHEEL A. Design Approach There are two stages to the design of a flywheel. The amount of energy required for the desired degree of smoothening must be found and the (mass) moment of inertia needed to absorb that energy determined. Flywheel geometry must be defined that caters the required moment of inertia in a reasonably sized package and is safe against failure at the designed speeds of operation. Fig.3 Schematic showing power flow in FES system B. Geometrical Dimension of Flywheel Flywheel used in the thresher machine is solid disk. Dimensions of flywheel are provided below. This flywheel is designed and analyzed. Mass of flywheel (m) = 60kg. Outer diameter of flywheel (d o ) = 500mm. Inner diameter of flywheel (d i ) = 50mm. Speed (n) = 750 Rpm. C. Materials Used S Glass Epoxy 72
Carbon Epoxy Cast Iron D. Model of Flywheel The geometry of a flywheel may be as simple as a cylindrical disc of solid material, or may be of spoke construction like conventional wheels with a hub and rim connected by spokes or arms Small fly wheels are solid discs of hollow circular cross section. Fig.4 Flywheel model As the energy requirements and size of the flywheel increases the geometry changes to disc of central hub and peripheral rim connected by webs and to hollow wheels with multiple arms. Mass at largest radius contributes much more since the mass moment of inertia is proportional to mr 2. Finally model of the flywheel is done with the help of Creo software and it is analyzed numerically Fig.5 3D model of Flywheel III. NUMERICAL ANALYSIS A. Finite Element Analysis There are generally two types of analysis that are used in industry: 2-D modeling, and3-d modeling. While 2-D modeling conserves simplicity and allows the analysis to be run on a relatively normal computer, it tends to yield less accurate results. 3-D modeling, however, produces more accurate results while sacrificing the ability to run on all but the fastest computers 73
effectively. The ANSYS CAE (Computer-Aided Engineering) software program was used in conjunction with 3-D CAD (Computer-Aided Design) solid geometry to simulate the behavior of mechanical bodies under thermal/structural loading conditions. B. Element Type Based on the consideration of rotational deformations in the flywheel, the elementsoilid72, a 3-D 4-node tetrahedral structural solid with rotations, is used to model meshes. The element is defined by 4-nodes with 6DOFs at each node and well suitable to create irregular meshes. It also has stress stiffening capability. C. Meshing Method Free mesh with smart element sizing is adopted to automatically and flexibly mesh the model. Compared to mapped mesh, which is restricted to only quadrilateral (area) or only hexahedron (volume) elements; free mesh has no restrictions in terms of element shapes. Smart sizing gives the mesh a greater opportunity to create reasonably shaped element during automatic element generation. D. Meshed Flywheel Model Various Solid model are designed on the CATIA software. And then they are imported into ANSYS for further analysis. Meshed flywheel model of various types are to be considered and then they are imported into ANSYS. Meshing is carried out generally based on the fine meshing of the solid model. Fig.6 Meshed Flywheel Model B. Modal analysis of s glass epoxy 74
(a) Mode shapes 1 and 2 (b) Mode shapes 3 and 4 (c) Mode shapes 5 and 6 Fig.7 The vibration modes of S-Glass epoxy Fly Wheel 75
Fig.7 shows the various mode shapes of flywheel which has analysed with the properties of g-glass epoxy. Totally six mode shapes are obtained and the frequency range varies with the individual modes due to its strength of the material. C. Modal analysis of carbon epoxy (a) Mode shapes 1 and 2 (b) Mode shapes 3 and 4 (c) Mode shapes 5 and 6 Fig.8 The vibration modes of Carbon epoxy Fly Wheel 76
Fig.6 shows the various mode shapes of flywheel which has analysed with the properties of Carbon epoxy. D. Modal analysis of cast iron (a) Mode shapes 1 and 2 (b) Mode shapes 3 and 4 (c) Mode shapes 5 and 6 Fig.9 The vibration modes of gray Cast Iron Fly Wheel 77
Fig.8 shows the various mode shapes of flywheel which has analysed with the properties of g-glass epoxy. Vibrations compared to flywheel which is designed with composite material is less than the materials of cast iron. IV RESULTS AND DISCUSSION From numerical analysis, mode shapes are obtained to compare the natural frequencies of the flywheel which is made of three different materials such as s-glass epoxy, carbon epoxy and cast iron. Fig.10 Frequency of s-glass epoxy flywheel Fig.11 Frequency of carbon epoxy flywheel 78
Fig.12 Frequency of gray cast iron flywheel Finally six mode shape frequencies are compared with the three different materials to optimize the material. Figure 13 shows the comparison of natural frequency against different materials. The dynamic behaviour of the flywheel could be easily identified through the numerical modal analysis and this is optimized with the help of different materials like s-glass epoxy, carbon epoxy and cast iron. Fig.13 Comparison of frequencies of flywheel designed by three different materials From the above figure, maximum vibration is observed in flywheel designed with gray cast iron material compared to s- glass epoxy and carbon epoxy. By compared to carbon epoxy and gray cast iron materials, s-glass epoxy produce lesser frequency due to the asset of the material. IV. CONCLUSIONS As the aim of the work is to reduce the damping effects of the flywheel, the major sources used for this purpose are composite materials. By using three different kind of composite materials steel, carbon epoxy, E-glass epoxy and gray cast iron the study has been carried out. For controlling the damping effects by using passive materials which reduces these damping of 79
flywheel. Component is analyzed using Numerical method in ANSYS software which utilizes finite element method technologies. Dynamic analysis is done for observing the loading conditions. The results have shown that the flywheel with composite material has less damping effects when compared with flywheel with gray cast iron material. The results have clearly proved that the deflection of flywheel and frequencies are less with the s-glass epoxy material and carbon epoxy material compared to gray cast iron. For the purpose of dynamic loading conditions and for determining natural frequencies, mode shapes modal analysis is also done. ACKNOWLEDGEMENTS The authors would like to be obliged to Anna University for providing laboratory facilities and computer assistance under project. References [1] Autar K. Kaw, Mechanics of Materials, CRC Press, 1997. [2] Akshay P. Punde, G.K.Gattani "Analysis of Flywheel" International Journal of Modern Engineering Research (IJMER) Vol.3, Issue.2. [3] Bawane G Analysis and optimization of Flywheel ijmerr/vol.1/no.2/july2012, pp272-276. [4] Vipul Arora, Satish C. Sharma Integration and Performance Analysis of Flywheel Energy Storage System in an ELPH Vehicle International Journal of Recent Trends in Engineering, Vol. 1, No. 5, May 2009. [5] Bolund B, Bernhoff H, Leijon M -Flywheel energy and power storage systems / Renewable and Sustainable Energy Reviews 11 (2007) 235 258. [6] M. M. Flynn, J. J. Zierer and R. C. Thompson Performance Testing of a Vehicular Flywheel Energy System Center for Electro mechanics, The University of Texas at Austin, SAE technical paper series. [7] Bitterly G, Flywheel technology: past, present, and 21st century projections, IEEE Aerospace and Electronic SystemsMagazine, vol. 13, no. 8, pp. 13 16, 1998. [8] J.D. Herbst, S.M. Manifold, B.T. Murphy, J.H. Price Design, Fabrication, and Testing of 10 MJ Composite Flywheel Energy Storage Rotors SAE technical paper series. [9] Carlos M. Roithmayr International Space Station Attitude Control and Energy Storage Experiment: Effects of Flywheel Torque NASA/TM 1999 209100. [10] Sudipta S Computer aided design & analysis on flywheel for greater efficiency IJAERS/Vol. I/ Issue II/299-301. 80