Parametric vibrations in offset printing units

Vibrations of offset printing presses are serious problem, which cause many difficulties while printing and impair quality of the prints. The biggest problem lies in construction of printing unit. It mainly consists of three cylinders, but two of them are in a direct contact generate undesired vibrations. Construction of the cylinders makes that stiffness of the unit varies periodically while printing. In this paper model of offset printing unit is presented. The model is described by the system of two parametric differential equations. Computer simulations of the behaviour of the printing unit have been performed. Conditions in which parametric resonance appears are also appointed here.

Nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine,the investigations on the mechanical responses of the pipes have attracted considerable attention.The fluid-structure interaction(FSI)between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes,especially when the pipe is highly flexible and usually undergoes large deformations.In this work,the geometrically exact model(GEM)for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton's principle.The stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid flow.Specific attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid,which is often encountered in practical engineering.By constructing bifurcation diagrams,oscillating shapes,phase portraits,time traces,and Poincarémaps,the dynamic responses of the curved pipe under various system parameters are revealed.The mean flow velocity of the pulsating fluid is chosen to be either subcritical or supercritical.The numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors,including periodic and quasi-periodic motions.It is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second mode.For a moderate value of the mass ratio,however,a third-mode flutter may occur,which is quite different from that of a straight pipe system.

Parametric Vibration of Submerged Floating Tunnel Tether Under Random Excitation

For the study of the parametric vibration response of submerged floating tunnel tether under random excitation, a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up. Subsequently, vibration response of tether in the tether-tube system is analyzed by Monte Carlo method. It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation, the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether; the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases; owing to the damping force of water, the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air; increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether; the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.

Parametric Vibration Analysis of Submerged Floating Tunnel Tension Legs

According to the characteristics of submerged floating tunnel anchored by tension legs,simplifying the tube as point mass and assuming that the tension leg is a nonlinear beam model hinged at both ends,the nonlinear vibration equation of the tension leg is derived.The equation is solved by the Galerkin method and Runge Kutta method.Subsequently,numerical analysis of typical submerged floating tunnel tension leg is carried out.It is shown that,the parametric vibration response of the submerged floating tunnel tension leg is related to the amplitude and frequency of the end excitation.Without considering axial resonance and transverse resonance,it is reasonable that higher order modes are abandoned and only the first three modes are considered.The axial resonance amplitude of the second or third order mode is equivalent to the first order mode axial resonance amplitude,which should not be ignored.

Parametrically excited oscillation of stay cable and its control in cable-stayed bridges＂

This paper presents a nonlinear dynamic model for simulation and analysis of a kind of parametrically excited vibration of stay cable caused by support motion in cable-stayed bridges. The sag, inclination angle of the stay cable are considered in the model, based on which, the oscillation mechanism and dynamic response characteristics of this kind of vibration are analyzed through numerical calculation. It is noted that parametrically excited oscillation of a stay cable with certain sag, inclination angle and initial static tension force may occur in cable-stayed bridges due to deck vibration under the condition that the natural frequency of a cable approaches to about half of the first model frequency of the bridge deck system. A new vibration control system installed on the cable anchorage is proposed as a possible damping system to suppress the cable parametric oscillation. The numerical calculation results showed that with the use of this damping system, the cable oscillation due to the vibration of the deck and/or towers will be considerably reduced.

Semiactive variable stiffness control for parametric vibration of cables

In this paper, a semiactive variable stiffness （SVS） device is used to decrease cable oscillations caused by parametric excitation, and the equation of motion of the parametric vibration of the cable with this SVS device is presented. The ON/OFF control algorithm is used to operate the SVS control device. The vibration response of the cable with the SVS device is numerically studied for a variety of additional stiffness combinations in both the frequency and time domains and for both parametric and classical resonance vibration conditions. The numerical studies further consider the cable sag effect. From the numerical results, it is shown that the SVS device effectively suppresses the cable resonance vibration response, and as the stiffness of the device increases, the device achieves greater suppression of vibration. Moreover, it was shown that the SVS device increases the critical axial displacement of the excitation under cable parametric vibration conditions.

Parametric vibration stability and active control of nonlinear beams

The vibration stability and the active control of the parametrically excited nonlinear beam structures are studied by using the piezoelectric material. The velocity feedback control algorithm is used to obtain the active damping. The cubic aonlineax equation of motion with damping is established by employing Hamilton＇s principle. The multiple-scale method is used to solve the equation of motion, and the stable region is obtained. The effects of the control gain and the amplitude of the external force on the stable region and the amplitude-frequency curve axe analyzed numerically. From the numerical results, it is seen that, with the increase in the feedback control gain, the axial force, to which the structure can be subjected, is increased, and in a certain scope, the structural active damping ratio is also increased. With the increase in the control gain, the response amplitude decreases gradually, but the required control voltage exists a peak value.

Parametric Vibration and Vibration Reduction of Cables in Cable-stayed Space Latticed Structure

Mechanical model and vibration equation of a cable in cable-stayed space latticed structure (CSLS) under external axial excitation were founded.Determination of the mass lumps and natural frequencies sup- plied by the space latticed structure (SLS) was analyzed.Multiple scales method (MSM) was introduced to analyze the characteristics of cable's parametric vibration,and the precise time-integration method (PTIM) was used to solve vibration equation.The vibration behavior of a cable is closely relative to the frequency ratio of the cable and SLS.The cable's parametric vibration caused by the external axial excitation easily occurs if the frequency ratio of the cable and SLS is in a certain range,and the cable's vibration amplitude varies greatly even if the initial disturbance supplied by SLS changes a little.Furthermore,the mechanical model and vibration equation of the composite cable system consisting of main cables and assistant cables were studied. The parametric analysis such as the pre-tension level and arrangement of the assistant cables was carried out. Due to the assistant cables,the single-cable vibration mode can be transferred to the global vibration mode, and the stiffness and damping of the cable system are enhanced.The natural frequencies of the composite cable system with the curve line arrangement of assistant cables are higher than those with the straight-line arrangement and the former is more effective than the latter on the cable's vibration suppression.

Nonlinear parametrically excited vibration and active control of gear pair system with time-varying characteristic

In the present work, we investigate the nonlinear parametrically excited vibration and active control of a gear pair system involving backlash, time-varying meshing stiffness and static transmission error. Firstly, a gear pair model is established in a strongly nonlinear form, and its nonlinear vibration characteristics are systematically investigated through different approaches. Several complicated phenomena such as period doubling bifurcation, anti period doubling bifurcation and chaos can be observed under the internal parametric excitation. Then, an active compensation controller is designed to suppress the vibration, including the chaos. Finally, the effectiveness of the proposed controller is verified numerically.

PARAMETRIC MATCHING SELECTION OF MULTI-MEDIUM COUPLING SHOCK ABSORBER

To achieve the dual demand of resisting violent impact and attenuating vibration in vibration-impact-safety of protection for precision equipment such as MEMS packaging system, a theo- retical mathematical model of multi-medium coupling shock absorber is presented. The coupling of quadratic damping, linear damping, Coulomb damping and nonlinear spring are considered in the model. The approximate theoretical calculating formulae are deduced by introducing transformation-tactics. The contrasts between the analytical results and numerical integration results are developed. The resisting impact characteristics of the model are also analyzed in progress. In the meantime, the optimum model of the parameters matching selection for design of the shock absorber is built. The example design is illustrated to confirm the validity of the modeling method and the theoretical solution.

Hill Instability Analysis of TLP Tether Subjected to Combined Platform Surge and Heave Motions

This paper presents the Hill instability analysis of Tension keg Platform （TLP） tether in deep sea. The 2-D nonlinear beanl model, which is undergoing coupled axial and transverse vibrations, is applied. The governing equations are reduced to nonlinear Hill equation by use of the Galerkin＇ s method and the modes superposition principle. The Hill instability charted up to large parameters is obtained. An important parameter M is defined and can be expressed as the functions of tether length, the platform surge and heave motion amplitudes. Some example studies are performed for various envirotnnental conditions. The results demonstrate that the nonlinear coupling between the axial and transverse vibrations has a significant effect on the response of structure. It needs to be considered for the accurate dynamic analysis of long TI2 tether subjected to the combined platfolna surge and heave motions.

Nonlinear dynamic response of stay cables under axial harmonic excitation

This paper proposes a new numerical simulation method for analyzing the parametric vibration of stay cables based on the theory of nonlinear dynamic response of structures under the asynchronous support excitation. The effects of important pa- rameters related to parametric vibration of cables, i.e., characteristics of structure, excitation frequency, excitation amplitude, damping effect of the air and the viscous damping coefficient of the cables, were investigated by using the proposed method for the cables with significant length difference as examples. The analysis results show that nonlinear finite element method is a powerful technique in analyzing the parametric vibration of cables, the behavior of parametric vibration of the two cables with different Irvine parameters has similar properties, the amplitudes of parametric vibration of cables are related to the frequency and amplitude of harmonic support excitations and the effect of distributed viscous damping on parametric vibration of the cables is very small.

Investigation for Electromechanical Coupling Unstability of Rolling Mill

The unsteady condition of rolling Mill vibration that was caused by flexural vibration of strip was investigated. The parametric flexural vibration equation of rolled strip was established. The parametric flexural vibration stability of rolled strip was studied and region of stability and unstability was determined based on Floquet theory and perturbation method. The flexural-vibration of strip was unstable if the frequency of variable tension was twice as the natural frequency of flexural-vibration strip. The characteristics of electric current in a temp driving motor’s main loop was studied and tested, and approved that there were 6 humorous current ponderance and 12 humorous current ponderance in main circuit of driving motor. Vertical vibration of working roller was tested, the test approved that there were running unsteady caused by parametric vibration. It attached importance to the parametric vibration of rolling mill.

Nonlinear Dynamic Reliability of Coupled Stay Cables and Bridge Tower

Nonlinear vibration can cause serious problems in long span cable-stayed bridges.When the internal resonance threshold is reached between the excitation frequency and natural frequency,large amplitudes occur in the cable.Based on the current situation of lacking corresponding constraint criteria,a model was presented for analyzing the dynamic reliability of coupling oscillation between the cable and tower in a cable-stayed bridge.First of all,in the case of cable sag,the d'Alembert principle is applied to studying the nonlinear dynamic behavior of the structure,and resonance failure interval of parametric oscillation is calculated accordingly.Then the dynamic reliability model is set up using the JC method.An application of this model has been developed for the preliminary design of one cable-stayed bridge located on Hai River in Tianjin,and time histories analysis as well as reliability indexes have been obtained.When frequency ratio between the cable and tower is approaching 1∶2,the reliability index is 0.98,indicating high failure probability.And this is consistent with theoretical derivation and experimental results in reference.This model,which is capable of computing the reliability index of resonance failure,provides theoretical basis for the establishment of corresponding rule.

ANALYSIS OF DYNAMICAL BUCKLING AND POST BUCKLING FOR BEAMS BY FINITE SEGMENT METHOD

Based on the multi-rigid body discretization model, namely, finite segment model,a chain multi-rigid-body-hinge-spring system model of a beam was presented, then a nonlinear parametrically exacted vibration equation of multi-degrees of freedom system was established using the coordination transformation method, and its resonance fields were derived by the restriction parameter method, that is, the dynamical buckling analysis of the beam. Because the deformation of a beam is not restricted by the discrete model and dynamic equation, the post buckling analysis can be done in above math model. The numerical solutions of a few examples were obtained by direct integrated method, which shows that the mechanical and math model gotten is correct.

Stability and Nonlinear Response Analysis of Parametric Vibration for Elastically Constrained Pipes Conveying Pulsating Fluid

Usually,the stability analysis of pipes with pulsating flow velocities is for rigidly constrained pipes or cantilevered pipes.In this paper,the effects of elastic constraints on pipe stability and nonlinear responses under pulsating velocities are investigated.A mechanical model of a fluid-conveying pipe under the constraints of elastic clamps is established.A partial differentialintegral nonlinear equation governing the lateral vibration of the pipe is derived.The natural frequencies and mode functions of the pipe are obtained.Moreover,the stable boundary and nonlinear steady-state responses of the parametric vibration for the pipe are established approximately.Furthermore,the analytical solutions are verified numerically.The results of this work reveal some interesting conclusions.It is found that the elastic constraint stiffness in the direction perpendicular to the axis of the pipe does not affect the critical flow velocity of the pipe.However,the constraint stiffness has a significant effect on the instability boundary of the pipe with pulsating flow velocities.Interestingly,an increase in the stiffness of the constraint increases the instable region of the pipe under parametric excitation.However,when the constraint stiffness is increased,the steady-state response amplitude of the nonlinear vibration for the pipe is significantly reduced.Therefore,the effects of the constraint stiffness on the instable region and vibration responses of the fluid-conveying pipe are different when the flow velocity is pulsating.

ParametricVibration Analysis of Pipes Conveying Fluid by Nonlinear Normal Modes and a Numerical Iterative Approach

Nonlinear normal modes and a numerical iterative approach are applied to study the parametric vibrations of pipes conveying pulsating fluid as an example of gyroscopic continua.The nonlinear non-autonomous governing equations are transformed into a set of pseudo-autonomous ones by employing the harmonic balance method.The nonlinear normal modes are constructed by the invariant manifold method on the state space and a numerical iterative approach is adopted to obtain numerical solutions,in which two types of initial conditions for the modal coefficients are employed.The results show that both initial conditions can lead to fast convergence.The frequency-amplitude responses with some modal motions in phase space are obtained by the present iterative method.Quadrature phase difference and traveling waves are found in the time-domain complex modal analysis.

Parametric oscillation of cables and aerodynamic effect

This paper addresses the aerodynamic effect on the nonlinear oscillation,particularly parametric vibration of cables in cable-stayed bridges.A simplified 2-DOF model,including a beam and a stayed cable,is formulated first.Response of the cable under global harmonic excitation which is associated with wind speed is obtained using the multiple scales method.Via numerical analysis,the stability condition of the cable in terms of wind speed is derived.The method is applied to a numerical example and a long-span bridge to analyze its all stay cables.It is demonstrated that very large vibration at one of the longest cables in the middle span of the bridge can be parametrically excited when the wind speed is over around 210 km/h(58.5 m/s).

Nonlinear Fractional-Order Dynamic Stability of Fluid-Conveying Pipes Constituted by the Viscoelastic Materials with Time-Dependent Velocity

Considering that the fluid-conveying pipes made of fractional-order viscoelastic material such as polymeric materials with pulsatile flow are widely applied in engineering,we focus on the stability and bifurcation behaviors in parametric resonance of a viscoelastic pipe resting on an elastic foundation.The Riemann–Liouville fractional-order constitutive equation is used to accurately describe the viscoelastic property.Based on this,the nonlinear governing equations are established according to the Euler–Bernoulli beam theory and von Karman’s nonlinearity,with using the generalized Hamilton’s principle.The stability boundaries and steady-state responses undergoing parametric excitations are determined with the aid of the direct multiple-scale method.Some numerical examples are carried out to show the effects of fractional order and viscoelastic coefficient on the stability region and nonlinear bifurcation behaviors.It is noticeable that the fractional-order viscoelastic property can effectively reconstruct the dynamic behaviors,indicating that the stability of the pipes can be conspicuously enhanced by designing and tuning the fractional order of viscoelastic materials.