Free vibration analysis of thin-walled rectangular box beams based on generalized coordinates

An eight degree-of-freedom dynamic theory is presented for the free vibration analysis of thin-walled rectangular box beams. With the newly proposed parameters to prescribe the cross-section deformations, governing differential equations of the thin-walled rectangular beam are deduced using the principle of minimum potential energy. For the finite element implementation, two different displacement fields are constructed with generalized coordinates to formulate the stiffness matrix and the mass matrix, respectively. Dynamic equations of motion are deduced with Hamilton’s principle, and approximated with C0 continuous interpolation functions. The validity of this study is confirmed both by published literature and by extensive finite element solutions from MSC/NASTRAN

Dynamic responses of axially moving telescopic mechanism for truss structure bridge inspection vehicle under moving mass

Dynamic responses of a telescopic mechanism for truss structure bridge inspection vehicle under moving mass are investigated under the assumption of Euler-Bernoulli beam theory. Equations of motion for the telescopic mechanism are derived using the Hamilton’s principle. The equations are transformed into discretized equations by employing the Galerkin’s method. The eigenfunctions of the beams are derived based on the kinetic and dynamic boundary conditions. The time-dependent features of the eigenfunctions are taken into account. The discretized equations are solved utilizing the Newmark-β method. Numerical results are presented to explore the influence of the moving mass on the dynamic responses of the telescopic mechanism and find appropriate mass-moving strategy to avoid large vibration. The results show that the vibrations when the mass doesn’t move synchronously with the telescopic beam are not always the minimum; on the other hand, the mass moving in the same direction of the telescopic beam will bring in stronger vibration

Decoupling the aliased spectra of rolling bearing with multispeed multiple frequency correlation

A multispeed multiple frequency correlation method for decoupling aliased spectra when defect frequencies are approximate to integral multiple of the shaft speed is proposed for fault diagnosis of rolling bearing. Firstly, multiple frequencies at various shaft rotation speeds are obtained using the fast Fourier transform (FFT). Secondly, the correlation coefficients between the amplitude growth trend of the multiple frequencies and the expected trend are calculated. Thirdly, correlation coefficients of assumed inner and outer race fault multiple frequencies are acquired by averaging correlation coefficients of possible aliased multiple frequencies for each bearing failure state. Finally, the correlation coefficient curves of different assumed fault multiple frequencies are compared, enabling operational assessment of the rolling bearing. The experimental results show that the multispeed multiple frequency correlation method is an effective tool for decoupling aliased spectra and diagnosing bearing faults

Influence of ventilation on flow-induced vibration of rope-guided conveyance

The behavior of rope-guided conveyances is so complicated that the rope-guided hoisting system hasn’t been understood thoroughly so far. In this paper, with user-defined functions loaded, ANSYS FLUENT 14.5 was employed to simulate the flow-induced vibration of rope-guided conveyances under different ventilation air speed. With rope-guided mine cages taken into account, results show that the ventilation affects the lateral displacement of conveyance greatly. With the increase of ventilation air speed, the maximum lateral and side displacements of ascending conveyances also increase, while those of descending conveyances don’t always increase, because the ventilation air flows downcast. With the thrust bearings equipped with the hoist rope attachment and the tail rope attachment, the rotation of conveyance about vertical axis is very small

Dynamic behaviors of 2-DOF axially telescopic mechanism for truss structure bridge inspection vehicle

Dynamic behaviors of the 2-DOF axially telescopic mechanism for truss structure bridge inspection vehicle is investigated. The telescopic mechanism is a combination of one vertical beam that can move axially, one constant beam perpendicularly fixed at the end of the vertical beam and one telescopic beam that can move along the axial direction of the constant beam during work. The Euler-Bernoulli beam theory is utilized to simplify the beams. The Lagrangian description is adopted to account for the coordinate for the telescopic mechanism. The equations of motion are derived using the Hamilton’s principle and decomposed into a set of ordinary differential equations by employing the Galerkin’s method. The eigenfunctions are acquired based on the boundary conditions by adopting the dichotomy method. The solutions to the equations are acquired using the Newmark-β method. Experiments are carried out to prove the validity of the theoretical model. Numerical examples are simulated to explore whether the vertical beam and telescopic beam can extend or retract synchronously and obtain appropriate beam moving strategy. The results prove that synchronous motion of the vertical beam and telescopic beam will not always lead to pronounced stronger vibration than the separate ones. On the other hand, the beam moving strategies that the telescopic beam moving before the vertical beam when they all extend out or retract back and moving after the vertical beam when one extends out and the other retracts back will effectively reduce the vibration compared with otherwise

Experimental investigation of feedforward inverse control with disturbance observer for acceleration tracking of electro-hydraulic shake table

Electro-hydraulic shake tables (EHSTs) are indispensable equipments in laboratory for evaluating structural performance subject to vibration environment. A novel feedforward inverse control with disturbance observer strategy is proposed in this paper in order to improve the acceleration tracking performance of the EHST system. The EHST system is firstly controlled by the three variable controller (TVC) to obtain a coarse time waveform replication accuracy, and then the parametric transfer function of the TVC controlled EHST system is identified with the H1 estimation method and complex curving fitting technology. Next, the zero magnitude error tracking control technology is employed to deal with the estimated non-minimum phase transfer function so as to design a stable and casual inverse model, and the proposed controller comprised of feedforward inverse controller and disturbance observer is further established based on the designed inverse model. Therefore, the proposed algorithm combines the virtues of feedforward inverse control and disturbance observer. The proposed algorithm is firstly programmed by MATLAB/Simulink software and then is compiled to an Advantech computer with real-time operating system for implementation. Finally, experiments are carried out on a unidirectional EHST system and the results demonstrate that a better acceleration tracking performance is achieved with the proposed controller than with the other conventional controllers

Fault diagnosis of rotating machinery based on time-frequency decomposition and envelope spectrum analysis

In order to raise the working reliability of rotating machinery in real applications and reduce the loss caused by unintended breakdowns, a new method based on improved ensemble empirical mode decomposition (EEMD) and envelope spectrum analysis is proposed for fault diagnosis in this paper. First, the collected vibration signals are decomposed into a series of intrinsic mode functions (IMFs) by the improved EEMD (IEEMD). Then, the envelope spectrums of the selected decompositions of IEEMD are analyzed to calculate the energy values within the frequency bands around speed and bearing fault characteristic frequencies (CDFs) as features for fault diagnosis based on support vector machine (SVM). Experiments are carried out to test the effectiveness of the proposed method. Experimental results show that the proposed method can effectively extract fault characteristics and accurately realize classification of bearing under normal, inner race fault, ball fault and outer race fault

Simulation of the lateral oscillation of rope-guided conveyance based on fluid-structure interaction

How to define the clearance between rope-guided conveyances and shaft wall reasonably has confused peers for more than one hundred years. In this paper, the fluid-structure interaction approach was used to simulate the lateral oscillations of rope-guided conveyances. With Yaoqiao vertical production shaft taken into account to validate this approach, user-defined functions coupled with ANSYS FLUENT were employed to conduct the two-dimensional numerical simulation, and the simulation results show that the lateral aerodynamic buffeting force when two conveyances pass each other is much larger than Coriolis force. What’s more important, with the lateral acceleration, velocity and displacement of the conveyances obtained, the simulation results can explain how the lateral aerodynamic buffeting force to oscillate the conveyance laterally successfully. This approach can be easily extended to three-dimensional simulations, to be more reasonable