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The purpose of this paper is to study the effect of lateral wind excitation on the transversal vibration of orchard chain ropeway system. The proposed chain system has been proved to be flexible and efficient, which can meet the demands of cargo transportation in mountainous orchards. The axially moving chains always work in a non-steady state and inevitably produce periodic transversal vibrations. The wind excitation exerted on the moving chain makes the transversal vibrations more complex. The transversal vibrations affect the safety and reliability of the moving chain system, and even lead to a disaster with high-amplitude vibrations. It is necessary to find an effective method for reducing wind-induced vibrations to an acceptable level imposed by the boundary conditions. In this paper, the Hamilton principle was applied to develop the dynamic differential functions of one-span moving chain under the lateral wind excitation. Mean lift and drag coefficients were used to characterize the susceptibility of moving chain to the galloping effect since the wind velocity was not normal to the chain axis. Long-span chain system may be subjected to the vortex-induced vibration seriously. The differential equations of axially moving chain system were proposed and discretized, which were based on the force equilibrium considering the chain boundary conditions with polygon effect. The formulation of transversal vibration subjected to the wind excitation was valid for the entire range of chain speeds and all points of the chain span. The solution of the differential equation governing the motion of the moving chain was obtained by using the Crank-Nicolson method and fourth order Ronge-Kutta method. The accuracy of the solution depended on the taken number of terms for the wind-induced chains. The time-history of wind speed was simulated by using harmonic superposition method, and the vibration properties of the axially moving chain with different mean wind speeds were numerically simulated. An experiment set-up was built for wind excitation test and 2 high speed cameras were used to capture the transversal vibration of the moving chain system. The LabWindows/CVI program was designed to process the captured vibration images. The wind speeds were simultaneously measured under different wind excitations generated by the experiment set-up. The wind speed profiles of mean wind speed with additional turbulence components were adopted. The turbulence component could be treated as a stationary random process with a mean value of zero. The equations describing the wind in the atmospheric boundary layer were represented by the proposed wind profile. The results of simulations and experiments showed that the lower mean wind speed could result in the decreasing of the amplitude of transversal vibration, which had a good aerodynamic stability for the moving chain system. At very high mean wind speeds, the negative damping effect would be exerted on the moving chain and cause the vibration to have considerable divergence and instability. This finding is useful for the development of active wind-induced vibration controller considering the chain polygon effect. This study can provide a reference for the transversal vibration control of the axially moving chain or string system under the lateral wind excitation. [ABSTRACT FROM AUTHOR]

To suppress the transverse vibration of an axially moving chain system with concentrated inertial masses in hilly orchard, the important factors affecting frequency characteristic of moving chain and their interaction are required to be studied. Based on the string theory and dynamics of chain transmission, the differential equation of transverse vibration was developed in the Laplace domain and the critical transport velocity was obtained in this paper. The stable condition for transport velocity corresponding to resonance was determined by considering the polygon effect causing speed variation when the moving chain link engaging with supporting end. With solutions for the second-order homogeneous partial differential equation, the effects of initial tension, transport velocity and load mass on the frequency of transverse vibration were numerically and experimentally analyzed. The difference between measured data and calculated data yielded values from 1.4% to 27.6% for various transport velocities, from 6.1% to 14.2% for various load masses, and from 14.7% to 24.3% for various initial tensions. The results show that the frequency of transverse vibration of axially moving chain increases with the increase in initial tension. The negative effect of transport velocity and load mass on vibration frequency in the case of forced nonlinear vibration is found. The proposed differential equation is proved valid to predict the effects of operation parameters on vibration frequency. It is conformed that this approach to transverse vibration of an axially moving chain can be used for parameter optimization under a certain constraint condition. The solution provides the theoretical basis for the vibration analysis and stability control of moving chain by consideration of wind-induced and rain-induced effects. [ABSTRACT FROM AUTHOR]