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R. B. Sharma, Vikas Sharma & Yogendra S. Rajput / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.com

Vol. 3, Issue 4, Jul-Aug 2013, pp.640-647

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Harmonic Analysis Of Engine Crankshaft As A Fixed Beam

R. B. Sharma 1, Vikas Sharma 2 & Yogendra S. Rajput 2 Asst. Prof. & Head, Mech. Engg., Dept., RustamJi Institute of Technology, Tekanpur, Gwalior, Madhya

Pradesh, India 1 Research Scholar, M.Tech. Automobile Engineering, RustamJi Institute of Technology, BSF Academy,

Tekanpur, Gwalior, Madhya Pradesh, India 2

AbstractThis stu dy examines the behaviour of the

crankshaft under the complex load functions i.e.,the real and the imaginary loads of a force vector.Crankshaft being a very crucial part of theengine for providing the adequate brake powerby sustaining all the pressure and various loadsof the product of combustion. Here in this paper,the harmonic behaviour of the single cylinder SIengine crankshaft is investigated under thedynamic force of piston transferred to crankshaftthrough connecting rod and gudgeon pin. Theresults has been shown in the term of graphsbetween the amplitude and the frequency of thevarious quantities like displacement and stresslevels using finite element method in ANSYS WBplatform .

Keywords: complex load functions, harmonic behaviour, dynamic loads, amplitude, frequency,finite element method.

I. IntroductionIn current times, the rotor bearing systems

utilized for modelling rotating machinery and their supporting structures are of very high importance, asexcessive vibration could harm the mounting pointsor may produce high were and tear thereby

producing sound and wearing out of material. The bearing material is generally of very soft type, likeBabbitt, chrome steel or in conjunction with copper

bushes. The rotor bearing is a very important systemto absorb thrust and vibrations during continuous runfor long operations. The various types of rotor

bearing system are exampled as, electric motors,turbo machinery, transmission shafts, propellers, etc. Now, out these types of rotor bearing, crankshaftengaged with the bearing is one of the importanttypes. In such type of lower pair the one part has to

be remaining fix as the bearing where as thecrankshaft turns inside it. The speed of thecrankshaft depends on the throttling opening and theamount of the charge burned inside the chamber. For a general class single cylinder SI engine, it variesfrom 0 rpm to 10,000 rpm respectively.

When running at such large speeds, severevibrations are observed which could be very severe

for the engine performance. Hence to predict the behaviour of such class of vibration effects majorlyare commonly analyzed by the finite element

method. The forces applied by the pistons are periodic as they repeats after every 2 nd revolution or we can say after 720 revolution of crankshaft. So, if we consider a motion of the type

,Here, ω is the natural frequency and the

motion will be repeated after 2 π /ω time, and X1 & A1 be the displacement. The harmonic motion isrepresented in terms of circular sine and cosinefunctions.

The velocity and the acceleration are x` 1 ==A1 ω cos ω t and x 1`` = - ω

2x1. Thus, theacceleration in a simple harmonic motion is always

proportional to its displacement and directed towardsa fixed particular point. Computations of harmonicamplitude and frequencies for deformations andstresses, responses play important roles in thedesign, identification, diagnosis, and control of crankshaft systems. Thus, an accurate prediction for the dynamic characteristics of a rotor bearing system

using FEM is essential for modern equipment.

II. Literature ReviewThe crankshaft is very important in high-

power drilling pump. The information on thevibration mode and frequency response is critical for the crankshaft to work normally in drilling pump.ANSYS finite element analysis software was used toimplement the modal analysis of the crankshaft thusobtaining characteristic frequency and thecorresponding vibration mode and then by theharmonic response analysis which was carried out

based on the modal analysis, dynamic response of

the crankshaft was obtained. The result shows thatthe working speed of crankshaft can avoid the regionof sympathetic vibration effectively, no resonancewill happen. The strength and fatigue life of crankshaft are also checked according to the stressresults. The analysis also makes a base for theoptimized design of dynamic performance of thecrankshaft [1].

The development and application of atechnique for the steady-state and transient analysesof diesel engine crankshaft torsional vibrations is

presented in this paper. Crankshafts in emergencydiesel generators undergo torsional vibrations due to

the effect of cylinder firing pressure and the inertiaof the reciprocating parts. A diesel engine crankshaft

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is subjected to steady-state loads during normalengine operation (constant speed and constant load)and to transients during start-ups, coast downs, andload changes. Often the transients may result intorsional stresses that far exceed those normally

designed for at constant speed and constant load [2].Crankshafts developed wide applications even

before methods to design them got evolved. Initially,they were assumed to be made up of beam segments.Since, the length to width ratios of the segments areof the order of one, these methods were noteffective. Therefore, till recently they were designed

based mostly on in-house experience and by usingempirical formulae. Of late, with the advent of

powerful computers, analysis based on finiteelement method has come into use for crankshaftdesign. In this work, we generate, fromfundamentals, a systematic procedure to designcrankshafts for finite life [3].

III. MethodologyFor the present work on the crankshaft, first

of all the crankshaft has to be modelled in the design

modeller tool of the Ansys Workbench. The stiffnessof the material of the crankshaft is considered asflexible. This crankshaft modelled here is of singlethrow type also. The maximum permissible pressuredepends on gas pressure, journal velocity, amount

and method of lubrication. Most crankshaft failuresare caused by progressive fracture due to repeatedloading. Since the failure of the crankshaft is likelyto cause a serious engine destruction. Hence, high

priority analyses of all types are used. Consideringthis crankshaft is developed after making anallowance for all the parameters of centre typecrankshaft with applied load of pressure of 12MPawhich acts during the whole cycle operation knownas the mean effective pressure during the cycle.Figure 1 represents the geometric model of crankshaft of single cylinder SI Engine.

Later on the model is meshed as shown infigure 2 using the solid element mesh of tetrahedrontype with physical preference of Mechanical andrelevance of 29. The smoothing is kept medium andtransition fast with coarse span angle centre andminimum edge length of 2.4770mm respectively.

Figure 1, Geometric model of crankshaft of single cylinder SI Engine

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Figure 2, FE Model of Crankshaft of Single Cylinder SI EngineAfter the meshing of the model, the boundary conditions and the constraint have to apply in order to get theoutcome. So for the boundary conditions the crankshaft has to be made fix or we can say by keeping all DOF=0;so that analogically, it will behave like a fixed beam conditions and pressure has been applied to the crankpinend of the crankshaft as shown in figure 3. The applied load is of pressure of 12 MPa.

Figure 3, Point of application of Pressure

IV. ResultsThe results represent the various contours

under the applied load of the pressure for theharmonic analysis. The first figure represents the allvalues of deformation in various parts of crankshaftas projected in figure4. The output in this diagram

figures the maximum deformation of 7.5548e-004mm at a frequency phase angle.Amplitude and the frequency diagram depict thevarious peak points of amplitude at differentfrequency points. The magnitude of amplitude of harmonic vibrations goes on changing at small

small intervals of frequency. The range of frequency starts from 100Hz and lasts to 1000 Hz.

The amplitude hikes at 300 Hz and 600 Hz becomeslowers at 700 Hz.

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Figure 4, Total deformation

Figure 5, Amplitude vs. Frequency for deformation

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Figure 6, Equivalent Elastic Strain

Figure 7, Amplitude vs. Frequency for Strain

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Figure 8, Equivalent Von-mises stress

Figure 9, Amplitude vs. Frequency for Stress

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Figure 10, Amplitude vs. Frequency for Acceleration

V. ConclusionThe marks characterize the various form of

the under the applied load of the pressure in the caseof harmonic analysis. With study of harmonicanalysis we identified the major and criticallocations of a crankshaft where failure can arise. Thevarious values of deformation, stress, strain for thecrankshaft have been shown in the results withcontours. The various graphs plotted represent the

behaviour of the crankshaft under a speed of 9550rpm of the engine. this work is helpful to find outvarious critical positions involved in crankshaft sothat after this study some suitable amendments may

be performed on the design of crankshaft accordingto constraints and boundary conditions.

References [1] Yifei, Y. and Bing, S.; Modal and Harmonic

Analysis of Crankshaft for High-Power Drilling Pump; MAXWELL SciencePublications; 2013, Vol. 5, Issue: 01.

[2] Johnston, P. and Shusto, L., "Analysis of Diesel Engine Crankshaft TorsionalVibrations," SAE Technical Paper 872540,1987.

[3] Prakash, V., Aprameyan, K., and Shrinivasa,U., "An FEM Based Approach to CrankshaftDynamics and Life Estimation," SAE

Technical Paper 980565, 1998.[4] http://en.wikibooks.org/wiki/Mechanical_Vibration

[5] Jacob Pieter Den Hartog , “ Mec an calV bra n”, Fourth Edition, Courier Dover Publications, 1956

[6] Lalane, C.; Mechanical Vibration & Shock Analysis, Volume 2, John Wiley & SonsPublication, USA 2009.

[7] Schmitz, L. T. and Smith, S. K.; MechanicalVibrations: Modelling & Measurement

[8] G. GENTA 0877 Journal of Sound and Vibration 124, 27-53. Whirling of unsymmetrical rotors a finite elementapproach based on complex co-ordinates.

[9] Singh, V. P..; Mechanical Vibrations, ThirdEdition, Dhanpat Rai & Co. (Pvt). Ltd., India2012.

[10] Khurmi, R. S. and Gupta, J. K,; MachineDesign, Eurasia Publishing House, NewDelhi, 2011

[11] Chandrupatla, T.R. and Belegundu, A. D.,;Introduction to Finite Element inEng neer ng”, T rd Ed n, Pren ce -Hall of India Private Limited, New-Delhi, 2008.

[12] Ansys element reference library, Ansys14

http://en.wikibooks.org/wiki/Mechanical_Vibration





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