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Harmonic Analysis of a two cylinder crankshaft using ANSYS Basavaraj Talikoti Research Scholar Mechanical Engineering Department, Dr. K. M. Vasudevan Pillai College of Engg media studies and research, New Panvel , Maharashtra, India Dr. S. N. Kurbet Prof. and Head of Mechanical Engg. Department, Mechanical Engg. dept Basveshwar College of Engg , Bagalkot, Karnataka, India Dr. V. V. Kuppast Prof in Mechanical Engg. dept. , Mechanical Engg. Department, Basveshwar College of Engg, Bagalkot, Karnataka, India Prof. Arvind M. Yadwad Associate Prof. Department of Mechanical Engineering, The National Institute of Engineering Mysore-570008, Karnataka, India AbstractCrankshafts play a pivotal role in the automobile industry as it is the primary part of the internal combustion engines. There is a strong necessity for its stable and dependable operation in the market as failure of the crankshaft results in huge losses. Harmonic analysis helps us to determine the behavior of the crankshaft when subjected to different time varying loads. This will be useful to obtain optimal design of the crankshafts so that it can be durable and hence advantageous for the engine. Keywordscrankshaft; vibration; ANSYS; harmonic analysis; stress; deformation I.INTRODUCTION The primary purpose of the crankshaft is to obtain rotary motion from reciprocating motion. The crankshaft in its entire operating life undergoes both torsional as well as bending vibrations and stresses as it is subjected to continuous load of the components attached to it and stress due to combustion of the gases. The rise in climate pollution and habitat related issues such as noise, there is a constant pressure on the designers to produce lightweight components for the engine to produce low NVH levels. Also, with modernization comes the necessity of high speed engines. Thus, the designers have to deal with the trade-off between speed, weight, efficiency and develop a crankshaft for an engine. Harmonic analysis of a structure facilitates in finding the different positions in the geometry of the structure that get affected due to stress caused by harmonically varying load. The frequency analysis is obtained using which the peaks at different frequencies can be obtained along with the stresses and deformations and the dangerous vibrational frequencies can be obtained. In this way, the crankshaft can be protected from harmful vibrations and hence damage. Harmonic analysis can be performed using three methods: full, reduced and mode superposition, the latter one is the most useful of the three as it can be used for further complex transient dynamic analysis also 1-12. II. LITERATURE REVIEW Harmonic analysis can be brought to advantage when used for stress calculation 15. In 16, harmonic analysis was carried out to evaluate the dynamic twisting moments of the model under test. The transient study of the crankshaft was done to supervise the harmonic response of the structure for torsional deformation 17. The inertia torque harmonics of the crankshaft under test were analyzed for the study of torsional deformation 18. In engines having longer crankshafts, the higher harmonics can reach the torsional frequencies, resulting in faults in the crankshafts 19. In 20, mode superposition method has been used to perform transient dynamic analysis on plates. The steady state values of total deformation, stress, stiffness can be calculated using harmonic analysis 20. Mode superposition method is more preferable than full mode as the number of number of assumptions are less and it takes less time to execute 20. The effects of other components attached to the crankshaft such as the flywheel can also be found out by harmonic analysis. III. PROCESS The process of harmonic analysis is primarily followed by modal analysis; the geometry and the data related to the structure can be directly imported for harmonic analysis after the completion of modal analysis. The harmonic analysis will basically give the frequency response which will alert the user about the range of frequencies at which the crankshaft must be operated and the analysis will also describe the behaviour of the crankshaft at harmonically varying loads. Figure 1. Project schematic A. Import Geometry The geometry of the crankshaft is imported to ANSYS workbench 2. The details for the structure of crankshaft as fed as per the requirements. Figure 2. Imported geometry of the crankshaft Figure 3. Details of the structure as seen in the ANSYS workbench The values of youngs modulus and bulk modulus should be given as the input with proper care as it decides how flexible the structure will be considered. Thus, material of the crankshaft also plays an important role here, as the properties shown in figure 3. will change, which in turn will affect the amount of deformation produced in the crankshaft. B. Meshing After the geometry is imported it is meshed, so that the analysis can be performed on each mesh. Meshing is basically finite element analysis where the given geometry is broken into a number of finite number of elements and each element is analyzed distinctively for all the vibrational parameters like stresses, deformations in the form of displacements etc. Figure 4. Meshed structure The number of elements for the structure are 28874 and the number of nodes are 50281, further details are depicted in the chart shown in figure below. Figure 5. Details of the mesh as seen in the ANSYS workbench C. Modal - Boundary Conditions Before starting the harmonic analysis, the primary step is the modal analysis which has to performed, for which the boundary conditions are assumed as shown in figure 6. Figure 6. Boundary conditions assigned to the crankshaft D. Modal Analysis Results- Total Deformation The result of modal analysis shows the total deformation for 10 modes at 10 distinct frequencies. At these frequencies there is a considerable amount of stress and deformation at different parts of the crankshaft. Figure 7. Chart showing different modes with frequencies as seen in ANSYS workbench Figure 8. Graph of mode versus frequency E. Harmonic Response- Analysis Settings After the execution of the modal analysis, the harmonic response of the structure can be calculated for harmonically time varying load. The analysis settings define the type of harmonic analysis method used; i.e., Mode superposition. Also the boundary conditions are defined which represent the forces acting at different load points. Figure 9. The analysis settings as seen in ANSYS workbench Figure 10. Boundary conditions assigned showing different forces acting (in red) F. Harmonic Analysis Results- Total Deformation and equivalent stress The results of harmonic analysis show that maximum deformation and stress is seen at the centre of the crankpin where the load of the connecting rod and the piston cylinders is maximum. Figure 11. Total deformation in crankshaft Figure 12. Details of deformation as shown in ANSYS workbench Figure 13. Equivalent stress in crankshaft The equivalent stress generated on the crankshaft structure is seen to be more in the centre of the crankpin. Also the deformation is maximum at 66 Hz with maximum displacement. The von mises stress is also calculated which gives the criteria for deciding if the material will result in failure or not. Figure 14. Chart showing details of stress as seen in ANSYS Workbench G. Harmonic Analysis Results- Directional Deformation Figure 15. Directional deformation in crankshaft Figure 16. Details of total deformation, stress as seen in ANSYS Workbench H. Harmonic Analysis Results- Frequency Response The frequency response decides which frequency is harmful to the crankshaft structure; as if the crankshaft vibrates at that frequency it is liable to breakage. Figure 17. Frequency Response I.Harmonic Analysis Results- Phase Response The phase response shows change in phase as soon as the maximum vibrational frequency is obtained. This is thus, matching with characteristic of vibration that is a type of oscillation wherein, after reaching the peak value the oscillation falls with change in phase and again rise with change in phase to reach the peak value. Figure 18. Phase response Figure 19. Phase response including response of force IV. CONCLUSION Thus, Harmonic analysis can be used to analyze the behavior of the crankshaft using the frequency response obtained and from the results of total deformation and stress obtained. The frequencies obtained in the frequency response are the critical frequencies, if the crankshaft is incessantly operated at these frequencies, it will result in the failure of the crankshaft as continuous deformation will result in breaking of the crankshaft. Further, this work can be improved by the use of transient dynamic analysis which is the next stage for harmonic analysis. REFERENCES 1Zissimos P. Mourelatos, “A crankshaft system model for structural dynamic analysis of internal combustion engines“, Vehicle Analysis and Dynamics Lab, Elsevier Science Ltd., June 2001. 2Tata Motors Limited, Mahindra and Mahindra Ltd. 3Priya. D. Shah, Prof. Kiran. K. 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Rao, “Mechanical Vibrations“, Fifth Edition, Copyright 2011, 2004 Pearson Education, Inc., publishing as Prentice Hall. 6Wojciech Homik, “Diagnostics, maintenance and regeneration of torsional vibration dampers for crankshafts of ship diesel engines“, Polish Maritime Research 1(64) Vol 17, 2010, PP. 62-68. 7Rinkle Garg, Sunil Baghla, “Finite element analysis and optimization of crankshaft”, International Journal of Engineering and Management Reaserch, vol-2 Issue-6, December 2012, PP. 26-31. 8Gu Yingkui, Zhou Zhibo, “Strength Analysis of Diesel Engine Crankshaft Based on PRO/E and ANSYS”, Third International Conference on Measuring Technology and Mechatronics Automation, 2011. 9Jaimin Brahmbhatt, Prof. Abhishek Choubey, “Design and analysis of crankshaft for single cylinder 4-stroke deisel engine“, International Journal of Advanced Engineering Research and Studies, Vol. 1 Issue 4, July-Sept 2012, PP. 88-90. 10 R.J Deshbhratar, Y.R Suple, “ Analysis and optimization of Crankshaft using FEM”, International Journal of Modern Engineering Reasearch, vol-2, issue-5, ISSN:2249-6645, pages:3086-3088, SeptOct 2012. 11 Jian Meng, Yongqi Liu, Ruixiang Liu, “Finite element analysis of 4- cylinder diesel crankshaft“, I.J. 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