Study on Bifurcation and Chaotic Motion of a Strongly Nonlinear Torsional Vibration System under Combination Harmonic Excitations

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1 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): Study on Bifurcation and Chaotic Motion of a Strongly Nonlinear Torsional Vibration System under Combination Harmonic Ecitations Wenming Zhang Bohua Wang Shuangshuang Zhao and Shuang Liu Key Lab of Industrial Computer Control Engineering of Hebei Province Yanshan University Qinhuangdao Hebei / China Abstract By using dissipative system Lagrange equation the strongly nonlinear dynamic equation of torsional vibration system is deduced which contains a class of square and cube nonlinear rigidity and combination harmonic ecitations. Bifurcation characteristics of the strongly nonlinear system are analyzed in the autonomous and non-autonomous situations by means of singular point stability theory and singularity theory respectively. The bifurcation diagram of system response corresponding to the change of torsional rigidity is derived by using numerical simulations and evolution process of period period doubling and chaotic motions is studied. Finally chaotic motion is further verified by the maimum Lyapunov eponent phase trajectory and Poincare map. Keywords: Strongly Nonlinear Torsional Vibration Bifurcations Chaos. Introduction Torsional vibration system eists widely in rotating machinery equipment such as turbine generator rolling mill and steam turbine. Torsional vibration may be due to torque fluctuations or due to unbalanced rotating parts or other mechanical reasons. Such vibrations if not controlled may cause damage or destruction to the rotating shafts or their accessories. Torsional vibration has great influence on performance and the reliability of mechanical drive system. Therefore torsional vibration instability mechanism and dynamics behaviors are the key issues to optimal design and vibration monitoring of system. A lot of research on nonlinear torsional vibration system has been done in recent years [-]. The equilibrium stability bifurcation and chaotic characteristics of several This work is supported by National Science Foundation of China(Grant No. ) and Natural Science Foundation Steel and Iron Foundation of Hebei Province (Grant No. E9) typical torsional vibration system were studied in[-]. Zhou [7] analysed the nonlinear gear meshing based on dynamics of gear system and the Hertz elastic theory and the torsional vibration of the transmission system under speeding-up condition and comparisons with a real vehicle results were studied. M.S.tehrani et al [] established the measurement model of cold tandem mill coupled torsional vibration system and researched the influence of tension and rolling speed fluctuation of strip between frame on rolling mill drive system. Östman et al [9] studied the active torsional vibration control of reciprocating engines and balanced the cylinder-wise torque contributions by utilizing the measured angular speeds of the crankshaft system. Jiang [] developed a linear mathematical model of coupled drive system with multi-rotor and analyzed the vibration characteristics of multi-stage centrifugal pump. In [] the authors studied the local dynamics near the Hopf bifurcation points with a direct linear time-delayed velocity feedback and the stability of trivial equilibrium is eamined with the change of counting multiplicity of eigenvalue with positive real part. With precise symbolic computation and a completely mathematical analysis Zhang [] applied the normal form theory to investigate the Hopf bifurcation of the four dimensional autonomous hyperchaos and chaos system with whole parameter space completely. Above papers better eplained the vibration mechanism and dynamic characteristics of nonlinear system under the condition of weak nonlinear. However the strongly nonlinear torsional vibration system is widespread in engineering and its dynamic characteristics including bifurcation and chaos have received less attention. In this paper the dynamics equation of strongly nonlinear torsional vibration system with a class of quadratic and cubic nonlinear rigidity and eternal ecitation is established according to dissipative Lagrange equation. The bifurcation structures and chaotic behaviors of strongly nonlinear torsional vibration system are studied by theoretical analysis and numerical simulation. Some dynamical behaviors including period-m orbits period-doubling and chaos are ehibited by bifurcation Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

2 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): diagram maimum Lyapunov eponent phase trajectory and Poincare map. The paper provides a theoretical basis for further study of comple nonlinear dynamics behaviors and improving dynamic nature of mechanical drive systems..nonlinear Dynamic Equation of Torsional Vibration System Torsional vibration system is widespread in engineering drive system. Considering a class of quadratic and cubic nonlinear rigidity the kinetic and potential energy of twomass system can be epressed as E = J & θ + J & θ () U = a( θ θ) + a( θ θ) + a( θ θ) () Generalized damping force is c F ) = c( & θ & θ c F = c( & θ & θ ) Generalized moment is i θi Qj = Fi q i= j ( j = ) Where J i is inertia moment of concentrated mass θ i & θ i are rotation angle and angular velocity of concentrated mass a is linear torsional rigidity a a are nonlinear torsional rigidity c is linear damping i c coefficient. Fi = Fi + Fi where Fi is generalized eternal c force Fi is generalized damping force q is generalized coordinate. Substituting Eq. ()and Eq. () into Eq. ()yields generalized moment c θ c θ Q = ( F + F ) + ( F + F ) = F c( & θ & θ) θ θ () c θ c θ Q = ( F + F ) + ( F + F ) = F c( & θ & θ) θ θ (7) () () () d E E U + = Q dt q q q j & j j j ( = j ) yields J && θ + a( θ θ ) + a( θ θ ) + a( θ θ ) + c( & θ & θ ) = F () (9) J && θ+ a( θ θ) + a( θ θ) + a( θ θ) + c( & θ & θ) = F () Considering the variation of relative rotation angle in practical engineering Eq.(9) minus Eq. () yields && J + J J J θ - && θ + a ( θ θ ) + a ( θ θ ) () J + J J + J + a( θ θ ) + c( & θ & θ ) = ( J F JF ) J J J J J J J + J J a J = ω a = k Suppose = θ θ J+ J J a k + J = c = μ ( J F JF ) = F() t Eq. () can be simplified as && + ω + k + k + μ & = F ( t) () Eq. () is nonlinear dynamics equation of torsional vibration system which is the basis for further study of dynamic behavior of torsional vibration system..bifurcation Characteristics of Strongly Nonlinear Torsional Vibration System For the study of bifurcation characteristics of strongly nonlinear torsional vibration system parameter ε is introduced and ε is not be limited to a small parameter then Eq. () can be written as && + ω + εk + εk + εμ& = εf t () () Eq. () is a strongly nonlinear dynamics equation of torsional vibration system for ε is not a small parameter. Below bifurcation analysis is carried out of autonomous system and nonautonomous system respectively. Then substituting Eq. () and Eq. (7) into Lagrange equation Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

3 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): Bifurcation Characteristics of Autonomous System εμ = stable; when unstable to stable. system stability changes from According to Eq.() when Ft () = autonomous equa tion of torsional vibration system is && + ω+ εk + εk + εμ& = () Eq. () can be reduced order for first-order equation & = y y & = ω εk εk εμ y () Then Eq. () can be linearized as λ + εμλ+ ω = () = y =.The at this point singular point of system is derivative operator of singular point is epressed as = ω εμ then characteristic equation is λ + εμλ+ ω = and characteristic values are εμ ± ε μ ω λ = (7) () (9) According to singularity stability theory Eq.() eists the following structures: () When ε μ > ω ω < characteristic values are two real roots of opposite sign and singular point of system is saddle point. () When ε μ > ω ω > characteristic εμ < values are two real roots of the same sign. If characteristic values are two positive real roots and εμ > singular point of system is unstable node; If characteristic values are two negative real roots and singular point of system is stable node. () When ε μ < ω characteristic values are two εμ < comple roots. If real part of characteristic value is positive and singular point of system is unstable focus; εμ > when real part of characteristic value is negative singular point of system is stable focus. () When ε μ < ω εμ = characteristic values are two pure imaginary roots and singular point of system is origin. at this time oscillation curve is appeared and Hopf bifurcation is occurred. From the above stability analysis of singular points when εμ < system is unstable; when εμ > system is. Bifurcation Characteristics of Nonautonomous System Suppose eternal disturbance ecitation is a class of combination harmonic F() t = fcos( Ω t) + fcos( Ω t) then nonautonomous equation of torsional vibration system can be written as && + ω+ εk + εk + εμ& =εfcos( Ω t) + εfcos( Ω t) () Below MLP method is employed for bifurcation analysis of nonautonomous system. Introducing a new variable τ = Ω t () substitu ting Eq.() into Eq.() yields Ω + ω+ εk + εk + εω μ = ε fcos( τ) + ε fcos( τ) () where = d / dτ = d / dτ Ω can be epand as power series of ε Ω = ω + εω+ ε ω +L () a new parameter is defined εω σ = ω + εω () such that ωσ ε = ω ( σ ) () and ω Ω = ( + δσ + δσ + L) σ () δ Ω= ω + σ + σ + + L (7) Epanding into power series of σ then substituting into Eq. () comparing the coefficience of σ and eliminating the secular term one can obtain ( ) k a b μω a b a f ω = + + a b a b () where a is the initial condition of Eq.( ) () = aand b is decided by the following equation μωb fb+ μωa = (9) Therefore the new parameter σ will enable a strongly nonlinear system corresponding to ε be transformed into a Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

4 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): small parameter system with respect to σ. Substituting Eq. ()-(7) into Eq. () one can yield ω ωσk ωσk ( + δσ + δσ + L) + ω+ + + σ ω ( σ) ω ( σ) ωσ δ ωσ ωσ ωμ σ σ cosτ ω ( σ + + ) + + L = + ω ( σ) ω ( σ) f fcosτ () To study bifurcation characteristics of Eq.() we use multiple scales method. Let be epanded into power series of small parameter σ namely = ( T T) +σ ( T T) () where T = τ T = στ. Suppose Ω=ω substituting Eq.() into Eq.() then perturbation equations in this case are D + = () k k μω f f D+ = DD+ D+ cost+ cost ω ω ω ω ω The solution of Eq. () is it i = AT e + AT e where T ( ) ( ) A( T ) is the comple conjugate of ( ) A T. () () Substituting equation () into () one can yield k μω f it D + = ida + A AA i A+ e + NST ω ω ω () where NST indicates the other items which do not produce secular term. Eliminating the secular term one can obtain k μω f ida + A A A i A+ = ω ω ω () ( i ( ) ) T A = r T e φ Setting and substituting it into Eq.() and then separating real part and imaginary part one can get average equations under polar coordinate dr μω f = r sinφ dt ω ω (7) dφ r k f r = + r cosφ dt ω ω () dr dφ = = dt Under stable condition we set dt namely f μω sinφ = r ω ω f k cosφ = r+ ω ω eliminating sinφ and cosφ one can yield r (9) μω k f r + r r = ω ω ω () Eq.() is the bifurcation response equation of torsional vibration system under nonautonomous condition. ( ) ω μ ω + ω f p = q = s = k 9k Setting 9ω Eq. () can be simplified to 7 Grspq ( ) = r + pr + qr sr= () According to singularity theory taking germ g () r s = r 7 sr one can prove Grspq ( ) is a 7 universal unfolding of germ g () r s = r sr with unfolding parameters p q and codimension is. To study the bifurcation topological structure of Eq. () and discuss the effect of unfolding parameters p q on bifurcation diagram we use transition set to decide qualitative behavior of bifurcation diagram when Grspq ( ) is under small perturbation. According to the definition of transition set one can obtain Gr = 7r + pr + qr s G s = r Grr = r + pr + qr.when G = Gr = Gs = system B( Z) = ϕ has a bifurcation point set (empty set) B( Z) = ϕ (empty set) ; when G = Gr = Grr = system H has a lag point set ( Z) = { q= } H( Z ) = { q= p / p } ; at the same time system has a double limit point set DZ ( ) = { q= p / p } and transition set Σ= BUBUHUHU D..Numerical study of chaotic motion In order to study the chaotic motion evolution process of strongly nonlinear torsional vibration system different kinds of numerical methods are applied such as bifurcation diagram maimum Lyapunov eponent phase trajectory and Poincare map. These methods are all very useful tools Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

5 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): for eaming chaotic properties and eploring chaotic attractors. Fourth-order Runge-Kutta method is employed to numerical study of torsional vibration system. We fi ω = Ω= μ =. ε = k =. f = f = and let k change in a wide range. The bifurcation diagram of Eq.() in ( k ) plane is shown in Fig.(a) and the maimum Lyapunov eponent corresponding to Fig.(a) is shown in Fig.(b). From Fig.(a) we can see that strongly nonlinear torsional vibration system ehibits periodic and chaotic behaviors when k changes. The maimum Lyapunov eponent given by Fig.(b) can be convince of occurrence of chaotic motion chaotic motion interval occur with the increase of torsional rigidity. In order to further describe chaotic characteristics of torsional vibration system phase trajectory and chaotic attractors are shown in Fig. Fig. and Fig. under k =... respectively. We can see that Phase trajectory repeatedly winding in enclosed area but not closed and Poincare section has the obvious fractal structure. ' (a) Phase trajectory. k (a) Bifurcation diagram '. - λ ma (b) Poincare map Fig. Phase trajectory and Poincare map when k = k (b) Maimum Lyapunov eponent Fig. Bifurcation diagram and Maimum Lyapunov eponent In Fig. periodic and chaotic motion are clearly visible. When torsional rigidity k is small system response is period- motion. With the increase of torsional rigidity system jumps into chaotic motion. When k =. system response is period- motion and then system jumps into chaotic motion. With further increase of torsional rigidity system finally enters chaotic state after period-doubling bifurcation. From Fig. we can see that periodic and ' (a) Phase trajectory Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

6 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): ' (b) Poincare map Fig. Phase trajectory and Poincare map when k =. phase trajectory for m closed curves and poincare map for m fied points. ' (a) Period- motion ' ' ' (a) Phase trajectory ' (b) Period- motion (c) Period motion Fig. Phase trajectory of period doubling (b) Poincare map Fig. Phase trajectory and Poincare map when k =. It can be seen from Fig. that system finally enters chaotic motion usually through period doubling while period doubling is the most commonly known route to chaos at present. Phase trajectory and Poincare map are applied to depict the period doubling bifurcation motion in Fig. and Fig. respectively. When response is period-m motion ' (a) Period- motion Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.

7 IJCSI International Journal of Computer Science Issues Vol. Issue No March ISSN (Print): 9 ISSN (Online): ' ' Conclusion (b) Period- motion -... (c) Period motion Fig. Poincare map of period doubling Torsional vibration characteristics are important information for rotating machinery design and control. In this paper the dynamic performance of nonlinear torsional vibration system has been studied by theoretical analysis and numerical simulation. The results are as follows: () The strongly nonlinear dynamic equation of torsional vibration system is deduced by using dissipative system Lagrange equation which contains a class of square and cube nonlinear rigidity and combination harmonic ecitations. () Bifurcation characteristics of the strongly nonlinear torsional vibration system are analyzed in the autonomous and nonautonomous situations and bifurcation conditions of torsional vibration system are given. () When system parameters and initial conditions are appropriately chosen system bifurcation diagram is made by fourth-order Runge-Kutta method. It is found that with the increase of torsional rigidity periodic motion and chaotic motion intervals occurs in torsional vibration system and ultimately system enters into chaos after period-doubling bifurcation. Different shapes of chaotic attractors and period-doubling bifurcation motions are obtained by using phase trajectory and Poincare map. These results provide a reference for further studying comple nonlinear dynamics behaviors and improving dynamic nature of mechanical drive systems. References [] E.J.Sapountzakis V.J.Tsipiras Nonlinear nonuniform torsional vibrations of bars by the boundary element method Journal of Sound and Vibration 9():7. [] D. J. Ewins Control of vibration and resonance in aero engines and rotating machinery An overview International Journal of Pressure Vessels and Piping 7(9):. [] Attilio Maccari Vibration amplitude control for a van der Pol Duffing oscillator with time delay Journal of Sound and Vibration 7(-):-9. [] Liu Shuang Liu Bin Zhang Yekuan Wen Yan. Hopf bifurcation and stability of periodic solutions in a nonlinear relative rotation dynamical system with time delay ACTA Physica Sinica 9 (): -. [] Liu Shuang Liu Bin Shi Peiming. Nonlinear feedback control of Hopf bifurcation in a relative rotation dynamical system ACTA Physica Sinica 9 (7): 9. [] Shi Peiming LiuBin Hou Dongiao. Chaotic motion of some relative rotation nonlinear dynamic system ACTA Physica Sinica 7 () :. [7] Zhou Lin Zheng Sifa Lian Xiaomin. Modeling and research on torsional vibration of transmission system under speeding up condition. Journal of vibration engineering ():. [] M.S.Tehrani P.Hartley H.M.Naeini Localosed edge bucking in cold rool forming of symmetric channek section Thin-walled structure ():-9. [9] Östman Fredrik Toivonen Hannu T Active torsional vibration control of reciprocating engines Control Engineering Practice ():7. [] JIANG Qinglei WU Dazhuan TAN Shanguang et al Development and application of a model for coupling geared rotors system Journal of Vibration Engineering ():9. [] L.F. Lu Y.F.Wang X.R.Liu Y.X.Liu Delay-induced dynamics of an aially moving string with direct timedelayed velocity feedback Journal of Sound and Vibration 9():. [] Kangming Zhang Qigui Yang Hopf bifurcation analysis in a D hyperchaotic system Journal of systems and science & compleity ():7-7. Wenming Zhang was born in 979. He received the M.Sc. and Ph.D. degrees in Instrument Science and Technology from Yanshan University China in and respectively. He is currently an instructor in the Electrical Engineering Department at the Yanshan University China. His research interests include nonlinear system vision and dynamics. Bohua Wang was born in 9. He received his M.Sc. degree in Electrical Engineering from the Yanshan University China in. His current research interests include nonlinear system dynamics. Copyright (c) International Journal of Computer Science Issues. All Rights Reserved.