Journal of Engineering and Thermal Sciences
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A weak solution for free vibration of multi-span beams with general elastic boundary and coupling conditions
Get PDFA weak solution of free vibration is developed for multi-span beams, which can adapt general elastic boundary and coupling conditions. Firstly, create the energy functional of the multi-span beam system based on the small deformation theory. Then, adopt the modified Fourier series method to rewrite the displacement functions. Compared with the traditional Fourier series method, the present series representations provide a solution for general elastic restrains. Lastly, combined with the Rayleigh-Ritz technique, all the series expansion coefficients can be obtained as the generalized coordinates. Numerical results demonstrate that the current weak solution has good convergence and high accuracy compared with the existing results in literature and FEM results
Dynamic coupled vibration analysis of a large wind turbine gearbox transmission system
Get PDFA lumped-parameter coupled nonlinear dynamic model for one large multi-stage wind turbine gearbox transmission system is established comprehensively including wind varying load, mesh stiffness, dynamic transmission error, gravity, and bearing nonlinear characteristics to obtain the gearbox dynamic response. The vibration differential equations of the drive-train are deduced through the Lagrange’s equation. On the basis of that, the dynamics of wind turbine gearbox is investigated by a Runge-Kutta numerical method that includes simultaneous internal and external excitations. The results show that the dynamic response of the partial component is mainly superposed by high-frequency component caused by the internal excitation and low-frequency component caused by the external excitation. In medium-speed stage and high-speed stage, the vibration amplitude has obvious fluctuation, and the multiple frequency and random frequency components become increasingly obvious with increasing rotational speed and eccentricity at gear and bearing positions. Axial vibrations of the system also have some fluctuation. The bearing has self-variable stiffness frequency, which should be avoided in engineering design stage. The study results provide a theoretical foundation for dynamical characteristics evaluation and dynamic optimization of a large wind turbine gearbox transmission system
Nonlinear modelling and transient dynamics analysis of a hoist equipped with a two-stage planetary gear transmission system
Get PDFA system-level nonlinear dynamic model for a two-stage planetary gear transmission system of a hoist is established with the consideration of time-varying meshing stiffness, backlash, damping, and bearing stiffness. Vibrational test results are also presented in accordance with simulation results computed from the dynamic model, and engagement-impacting dynamic simulations are achieved by adapting a dynamic explicit algorithm based on this model. Accordingly, variation in the contact state in relation to the engaging position is obtained together with vibration characteristics of the transmission system. This study provides a theoretical basis for the reduction of vibration and noise for the transmission system
Destructive energy impact to the myocard damage: between technological advantages and risk
Get PDFBackground: The aim of the study was to evaluate and compare destruction effect to different heart structures using RF, cryo and laser methodology in animal (pig) model. Methods: Ablation procedure was performed on right and left pulmonary veins area, free wall of right and left atrias, and free wall of ventricles positioning ablation electrode from endocardial side. Ablation electrodes were inserted through an incision in right/left auricle. The effects of ablation were observed visually and using thermography for temperature control. Results: Standard recommended parameters for both of used destruction energies were possible to evoke quick critical scar formation and rupture. Temperature in cardiac surface differs from 34.5 till 70.2 °C, and directly depends from electrode compression level, time of application and energy power. We express dissent from the general view, what destruction in cardiac structures is point like. We observed enough high range of temperature dispersion, especially in ventricles. Conclusions: Usage of thermography enable to estimate peculiarities and borders of destruction site, optimize parameters of ablation, allows us to avoid or minimize undesirable effects, save structures and improve clinical outcomes
Finite element modeling and active vibration control of high-speed spinning flexible beam
Get PDFFinite element modeling and active vibration control of a high-speed spinning flexible coupled electromechanical beam is investigated using a first-order approximation coupling (FOAC) model. Due to centrifugal forces caused by eccentricity in a spinning flexible beam, there exists coupling between axial and transverse vibration modes. The partial differential equations of motion of the beam governing this coupling are derived using Hamilton’s principle based on an FOAC model, and a finite element method for discretization is given. It is observed that the zero-order approximate coupling (ZOAC) model is valid for dynamic description of the flexible beam spinning at low speeds, but no longer valid at high speeds. However, the validity of FOAC model is confirmed at different speeds. Piezoelectric elements for active vibration control of the spinning flexible beam are analyzed and a velocity feedback controller is proposed. Simulation results demonstrate good performance of the proposed velocity feedback controller
A method for analyzing sensitivity of multi-stage planetary gear coupled modes to modal parameters
Get PDFThis paper proposes a method of analyzing distinct modal characteristics to obtain accurate sensitivity of natural frequencies and coupled modes to system parameters of multi-stage planetary gears. A purely rotational dynamic model of multi-stage planetary gear system with general descriptions is established based on the lumped mass method. The vibration modes of multi-stage planetary gears are classified into overall and planet modes with unique properties. According to the modal energy distributions in multi-stage planetary gears, the natural frequencies are clustered by each dominant vibration stage. The modal properties of each cluster in the multi-stage planetary system are similar to the single-stage planetary gear system established by the associated dominant vibration stage. It is shown that, variation of gear parameters in one planet stage mainly affects the natural frequencies in the cluster associated with the same stage, while the coupling shaft parameters significantly impact the natural frequencies corresponding to the planet stage which contains the connected sun gear
Damage identification using singular value feature of continuous wavelet coefficients
Get PDFA hybrid soft computing approach is developed with the aim of identifying multiple damage in beam-type structures. This approach is formulated based on integration of two renowned soft computing methods: a wavelet transform and a singular value decomposition. The integration features the creation of a sophisticated damage indicator: mode shape’ continuous wavelet transform-singular value decomposition component (MWSC).The MWSC has inherent capabilities of immunity to noise and sensitivity to multiple damage of beam-like structures. The effectiveness of the MWSC is numerically verified by identifying multiple cracks in cantilever beams, with particular emphasis on its ability of locating multiple damages in noisy environments
Coupled vibration of a concrete pipe pile with saturated soil due to longitudinal loading
Get PDFThis paper considers the longitudinal coupled vibration of an elastic bearing concrete pipe pile with the saturated soil. The outer and inner saturated soil are governed by the dynamic consolidation theory originally presented by Biot. The governing equations of soil are transferred to ordinary differential equations by Laplace transform. The volumetric strain and pore pressure of soil are obtained by directly solving the coupling equations of soil without introducing potential functions. The analytical expressions of the displacements and shear stresses of the soil are then obtained. The pile response is derived on the basis of 1D elastic theory and the perfect contacts between the pile and soils. The displacement and velocity of the pile in time domain are obtained by using numerical inverse transformation. Selected numerical results are presented to portray the influence of the existences of soils, pile geometry and dynamic permeability coefficients of soils on the vibration characteristics of the pipe pile. At last, the displacement response between a pipe pile and solid pile are compared
PD control for global stabilization of an n-TORA system
Get PDFThis paper concerns a global stabilization problem for an n-TORA (Translational Oscillator with a Rotational Actuator) system which consists of n carts connected to the fixed walls and each other by n+1 linear springs with each cart having an eccentric rotational proof-mass actuator moving in the horizontal plane. First, this paper derives the motion equation of the n-TORA system. Then, by using Lyapunov stability theory and physical properties of mechanical parameters of the n-TORA system, this paper proves that the global stabilization of the n-TORA system can be achieved by the PD control of the angle of the rotational proof-mass of each TORA. This paper presents numerical simulation results for 2- and 3-TORA systems to validate the result of the global stabilization
Stability analysis of the rolling mill multiple-modal-coupling vibration under nonlinear friction
Get PDFConsidering the unstable oscillation in the rolling process caused by the lubrication conditions change, a dynamic rolling process model considering the nonlinear friction is built using the Bland-Ford-Hill rolling force model. In addition, based on the structure model which can characterize the coupling vibration of rolling mill, and taking the dynamic variations of rolling force and rolling torque as the feedback excitation, the rolling mill vertical-torsional-horizontal coupled dynamic model under nonlinear friction is established. On this basis, the system Hopf bifurcation points at different rolling speeds are calculated by Hurwitz algebraic criterion. And the system stability domain is determined by analyzing the eigenvalue of the system. Finally, using the parameters of a 2030 cold rolling mill, the correctness of the bifurcation point calculation and the stability domain analysis are verified by numerical simulation. The results show that the system stability domain is enclosed by the instability critical lines of vertical vibration modal, torsional vibration modal and horizontal vibration modal. And under different conditions, the system Hopf bifurcation induced by the variation of the friction coefficient can cause system instability with different vibration modals. The study can help to optimize the rolling process, and achieve a reasonable dynamic modification strategy of the rolling mill structure as well