نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی مکانیک بیوسیستم، دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد، ایران

2 گروه مهندسی مکانیک بیوسیستم دانشگاه شهرکرد، شهرکرد ایران

3 گروه مهندسی مکانیک ، دانشکده مکانیک، دانشگاه کاشان، کاشان ایران

4 مهندسی مکانیک بیوسیستم، دانشکده کشاورزی، دانشگاه اراک، اراک، ایراان

چکیده

در این تحقیق پارامترهایمودالکوبنده کمبایندرشرایطکاری واقعی تحت بار محیطی با استفاده از آنالیز مودال عملیاتی به شیوه غیر پارامتریک و به روش تجزیه فرکانس تخمین زده شد. کمباینبهوسیلهموتوروارتعاشاتناشیاز قسمت‌هایکاریمختلفتحریکشد و سیگنال‌های شتاب با استفاده از سنسور شتاب سنج در شش سرعت مختلف کوبنده جمع آوری شد. با بررسی پارامترهای سیگنال شامل میانگین، فاکتور ضربه، جذر میانگین مربعات، انرژی و انتروپی در دورهای مختلف کوبنده مشخص شد این پارامترها در دورrpm 1000 نسبت به دیگر دورها بطور معناداری مقادیر بالاتری  دارند. که وجود اغتشاش در این دور را تایید می‌کرد. بنابراین  به بررسی پارامترهایمودالسازهبه روش تجزیه فرکانس در دورrpm 1000 پرداخته شد و مدل اجزای­محدود از کوبنده طراحی و با اطلاعات به‌دست آمده از آنالیز مودال تطبیق داده شد. بابررسیمحدودهفرکانس‌هایطبیعیوفرکانس هایتحریکواحدکوبنده یکفرکانسرزونانسبرایموداولسازه موردنظریافتشد کهعمده ترینعاملایجادارتعاشدرواحدکوبنده تشخیص داده شد. فراینداصلاحسازهبا اضافه کردن دو میله با قطر یک سانتی‌متر بین دو فلنچ میانی کوبنده انجام گرفت و مشاهده شد موقعیتفرکانسطبیعی مود اول به 08/32 هرتز تغییر یافت. با فاصله گرفتن از فرکانس طبیعی از فرکانس تحریک،شرایطایجاد پدیده رزونانسودر نتیجهارتعاشات کوبندهکاهش یافت.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Vibration modelling the thresher unit of john deere (955) combine harvester using operational modal analysis

نویسندگان [English]

  • Hamed Ghafarzadeh Zare 1
  • Ali Maleki 2
  • Mohsen Irani Rahaghi 3
  • majid Lashgari 4

1 Department of Mechanical Engineering of Biosystems, Shahrekord University, Shahrekord, Iran

2 Department of Mechanical Engineering of Bio Systems. Shahrekord University, Iran

3 Department of Mechanical Engineering, Kashan University, Kashan, Iran

4 Department of Mechanical Engineering of Biosystems, Arak University, Iran.

چکیده [English]

Introduction An important process in grain harvesting with the combine harvester is threshing the materials using the thresher unit. An ideal thresher is one that carries out complete threshing with maximum crop input and best grain separation while saves the shape and quality of the grain and minimizes grain loss. The vibrations of this unit cause the threshing action to fail and combine harvester loss to increase; therefore, it is highly important to study the vibration produced in the threshing unit. Since measuring the vibration in all working conditions on the farm is expensive, one of the ways to achieve the mentioned objectives is to use a vibration model by the simulation methods in order to examine the effects of vibration on the machine’s and the operator’s performance. Using vibration modeling and dynamic analysis of the structure through a mathematical model, finite element, and modal analysis, the causes and effects of the vibration in different working conditions can be examined with minimum cost. The present study was aimed to carry out the dynamic analysis of combine harvester using operational modal analysis. Therefore, the nonparametric and frequency decomposition methods were used in order to extract values of natural frequencies and damping coefficients, and the information obtained from the modal analysis was utilized to design and update the finite element model of the thresher. Afterward, the vibration of the thresher was adjusted as much as possible by modifying the structure through the weight modification method.
Materials and Methods To measure the vibration of the thresher in practical conditions, a piezoelectric accelerometer sensor DYTRAN/MODEL3255A2, an analyzer device, and a signal processing software MEscopeVES were employed. In order to carry out the analysis, the combine harvester was started in its normal conditions and all parts were set in operation. Due to the geometry of the structure, four points were chosen on the bearings of the threshing drum.
Afterward, de-noising signals used in MATLAB were utilized to calculate the response power spectral matrix, and singular values decomposition method was applied to it. Finally, by drawing each singular value, resonance peaks of the system were determined with respect to different frequencies, and the system’s damping was estimated.
In order to carry out the geometric modeling and the simulation of the thresher by finite element method, ABAQUS finite element software was employed.
In order to compare the analytical and the experimental results of NFD value, the predicted and measured natural frequencies were calculated.
Modifying the structure as one of the applications of the modal analysis is a technique to consider the effect of physical parameters of a structure on its dynamic properties, i.e. natural frequencies and mode shape in order to improve the structure’s dynamic behavior. In the present study, therefore, modification of the threshing unit was aimed to decrease its vibrations by changing the natural frequency. Due to its complexity, the process of modifying the structure can be carried out by changing the mass and hardness. As presented in the study, modification of the structure was conducted by changing the mass on the finite element model.
Results and Discussion The purpose of this study is to determine the vibration characteristics and present a vibration model of the thresher. The vibration responses of the thresher were recorded in working conditions on the bearings of the thresher. Through investigating signal parameters, including root mean square, energy, and entropy in different speeds of the thresher, it was specified that these parameters had significantly higher values in the rotation speed of 1000 rpm compared to other speeds, which proved the disturbance in the rotation speed of 1000 rpm.
By examining the range of the natural and excitation frequencies of the threshing unit and also considering the diagram obtained from decomposing the singular values of the power spectral density matrix and Campbell diagram, a resonance frequency was found for the given structure, which is the major cause of vibration in the thresher. Moreover, the speed of 1000 rpm was determined as the critical speed of the thresher.
In order to reduce the level of vibrations, the thresher’s excitation frequency should be far enough from the natural frequency; therefore, the process of modifying the structure is carried out by changing the mass applied to the finite element model, and it was observed that the natural frequency of the first mode changed from 16.98 Hz to 12.4 Hz.

کلیدواژه‌ها [English]

  • Frequency analysis Method
  • Structural modification
  • Finite element model
  1. Aenlle, M.L. and Brincker, R. 2013. Modal scaling in operational modal analysis using a finite element model. International Journal of Mechanical Sciences, 76 : 86– 101.
  2. Brandt, A. 2011. Noise and Vibration Analysis: Signal Analysis and Experimental Procedures , First ed., John Wiley and Sons.
  3. Brincker, R., Zhang, L., and Andersen, P. 2001. Modal identification of output only systems using frequency domain decomposition. Journal of Smart Materials and Structures, 10: 441- 445.
  4. Chen, Q.W., Han, Z.D., and Cui, J.W. 2015. Development state and trend current situation of self-propelled combine harvester. Journal of Agricultural Science and Technology, 17: 109–114.
  5. Christof, D., Gert, D., and Patrick, G. 2010. An operational modal analysis approach based on parametrically identified multivariable transmissibilities. Mechanical Systems and Signal Processing, 24: 1250-1259.
  6. Ebrahimi, R., Esfahanian, M., and Ziaei-Rad, S. 2013. Vibration modeling and modification of cutting platform in a harvest combine by means of operational modal analysis(OMA). Measurement, 46: 3959–3967.
  7. Ebrahimi, E. and Mollazadeh, K. 2010. Intelligent Fault Classification of a Tractor Starter Motor Using Vibration Monitoring and Adaptive Neuro-Fuzzy Inference System. Insight - Non-Destructive Testing and Condition Monitoring, 52: 561-566.
  8. Hanson, D. 2006. Operational Modal Analysis and Model Updating with a Cyclostationary Input, PhD Thesis, University of New South Wales, Australia.
  9. Hostens, I. and Ramon, H. 2003. Descriptive analysis of combine cabin vibrations and their effect on the human body, Journal of Sound and Vibration, 266: 453–464.
  10. Jamshidi, E., Ashory, M.R., and Daeean, H. 2008. Application of Modal Testing in Model Updating of Structures. Journal of Modeling in Engineering, 1(15): 71-81.(In Persian)
  11. Khatibi, M.M., Ashory, M.R., and Albooyeh, A.R. 2010. Numerical and experimental consideration of frequency domain decomposition method for modal parameters identification of structure. Journal of Modeling in Engineering, 8(21): 83-95. (In Persian)
  12. Khazaee, M., Banakar, A., Ghobadian, B., Mirsalim, S.M., Jafari, S.M., and Javan, S. 2013. Diagnosis and classification of effective abnormal environmental conditions on timing belt performance based on vibration signals. The Journal of Engine Research, 31: 33-41. (In Persian)
  13. Kyprianou, A., Mottershead, J.E., and Ouyang, H. 2005. Structural modification. Part 2: assignment of natural frequencies and antiresonances by an added beam. Journal of Sound and Vibration, 284: 267–281.
  14. Mazhab Jafari, M.H., Hajnayeb, A., and Masoumi, Gh. H. 2015. Study of the causes of excessive vibrations in air fans and proposing practical solutions for decreasing the vibration level. Modares Mechanical Engineering, 51(3): 181-188. (In Persian)
  15. Mirzazadeh, A., Abdollah Pour, S.H.A., Moghaddam, M., and Mohammadi, K.H.O. 2011. Combine cleaning system losses control by using of MOG feed rate through concave. Sustain Agriculture , 22: 113-118,. (In Persian)
  16. Miu, PI. Mathematical modeling of material other than grain separation in threshing units. 1999. ASAE Meeting Presentation, ASAE/CSAE Annual International Meeting, Toronto, Ontario, Canada, pp . 993208.
  17. Miu, P.I. and Kutzbach, H.D. 2008. Modeling and simulation of grain threshing and separation in threshing units, Part I. Journal of Computer and Electronics in Agriculture, 60: 96-104.
  18. Mohanty, P. and Rixen, D.J. 2004. A modified Ibrahim time domain algorithm for operational modal analysis including harmonic excitation. Journal of Sound and Vibration, 275: 375-390.
  19. Moosavian, S.A., Najafi, G., Ghobadian, B., Jafari, S.M., Sakhaei, B., and Khazaee, M. 2012. Fault diagnosis in engine spark plug by vibration analysis using neural Network. The Journal of Engine Research, 28: 21-29. (In Persian)
  20. Nozarpour, M. and Rahi, A. 2012. Study of the effects of lacing rods location on natural frequencies in last stage blades of a steam turbine. Journal of Solid Mechanics in Engineering, 5(2): 37-43. (In Persian) 125
  21. Park, Y.H. and Park,Y.S. 2000. Structural modification based on measured frequency resonse function: an exact eigenproperties reallocation. Journal of Sound and vibration, 237: 411-426.
  22. Parloo, E., Verboven, P., Guillaume, P., and Van Overmeire, M. 2002. Sensitivity based operational mode shape normalization. Mechanical Systems and Signal Processing,16: 757-767.
  23. Ramsey, K. February 1983. Experimental modal analysis, structural modifications and FEM Analysis on a Desktop Computer. Journal of Sound and Vibration. 1-10.
  24. Randal, R. B. 2004. State of the art in monitoring rotating machinery. Journal of Sound and Vibration, 38(5): 10-17.
  25. Randall, R.B., Coats, M.D., and Smith,W.A. 2016. Repressing the effects of variable speed harmonic orders in operational modal analysis. Mechanical Systems and Signal Processing,79:3–15.
  26. Rahmatalla, S., Hudson, K., and Liu, Y. 2013. Finite element modal analysis and vibration-waveforms in health inspection of old bridges. Journal of Finite Elements in Analysis and Design, 78: 40-46.
  27. Sinha, J.K. 2007. Quantification of faults in rotating machines, Noise & Vibration Worldwide, 38(9): 20-29. 28. Tang, Z,. Haotian, Z., and Yuepeng, Z.2018.Unbalanced vibration identification of tangential threshing cylinder induced by rice threshing process, Shock and Vibration, 4708730, 14 pages.
  28. Udom S. 2017. Development of a cutter bar driver for reduction of vibration for a rice combine harvester. Asia-Pacific Journal of Science and Technology, 15: 572–580.
  29. Wenzel, H. and Pichler, D. 2005.Ambient Vibration Monitoring, First ed., John Wiley and Sons. 31. Yao,Y.C., Song, Z.H., Du,Y.F., Zhao, X.Y., Mao, E.R., and Liu, F. 2017. Analysis of vibration characteristics and its major influenced factors of header for corn combine harvesting machine. Transactions of the Chinese Society of Agricultural Engineering, 33: 40–49.
  30. Zhang, G., Ma, J., Chen, Z., and Wang, R. 2014. Automated eigensystem realisation algorithm for operational modal analysis. Journal of Sound and Vibration, 333: 3550– 3563.