Journal of Vibroengineering
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Dynamic analysis of hook block for polar crane in nuclear power plant
Get PDFA systematic method to analyze the trajectory of hook block for polar crane in nuclear power plant (NPP) is proposed, in which dynamic equations of the system and the compatibility conditions for drum parameters are presented. Properties and formulations of the variables involved in these equations are studied in detail. A method to describe the rope-pulley system is given and a numerical method is derived to solve the positions and velocities of the common tangents that consistent with the reeving ropes between spatial pulleys. Based on these displacements and velocities, the angular speeds of pulleys are given to solve the difficulty to confirm the rotating directions of pulleys in some rope-pulley systems. A numerical example contrasting the dynamic model with corresponding static model is demonstrated to validate the systematic method. The proposed method is largely universal and can be a reference for designing and analyzing of polar cranes in NPP
Numerical optimization and analysis on vibration characteristics of bicycles based on the novel CA-PSO algorithm
Get PDFRegarding the published researches on bicycles, they fail to design fatigue characteristics of the bicycle. In addition, dynamics and fatigue characteristics are not further improved by using advanced optimization algorithms. Aiming at these questions, this paper tries to optimize dynamics and fatigue characteristics of the bicycle through combining finite element model with advanced algorithms. The advanced algorithm applies ideas of cellular automation (CA) to Particle Swarm Optimization (PSO), and then a hybrid CA-PSO algorithm is proposed. Moreover, the finite element model is also validated by experimental test. Computational results show that: the maximum stress of bicycles is mainly distributed on the frame, especially on joints of different round pipes at different moments mainly because a dead corner is at the joint, and the dead corner can easily cause stress concentration. Under alternating forces, the stress concentration at joints will cause fatigue damage. Therefore, the service life of this position will be the shortest. As a result, the dynamics and fatigue characteristics of the joint position are taken as the optimized objective. In order to verify the optimized effectiveness of the proposed CA-PSO algorithm in the paper, the widely used PSO algorithm and PSO-GA algorithm are also used to optimize the bicycle. When the traditional PSO algorithm is used to optimize the bicycle, the root-mean-square value and maximum difference of vibration accelerations are decreased by 11.9 % and 14.3 %. When the PSO-GA algorithm is used to optimize the bicycle, the root-mean-square value and maximum difference of vibration accelerations are decreased by 20.3 % and 12.9 %. When the proposed CA-PSO algorithm is used to optimize the bicycle, the root-mean-square value and maximum difference of vibration accelerations are decreased by 27.1 % and 18.6 %. Compared with other two kinds of PSO algorithms, optimized effects of vibration accelerations are very obvious. In addition, the fatigue life of the original structure is 5 years, while the fatigue life of the optimized bicycle is 7 years. Therefore, the fatigue life is improved obviously
Characteristic analysis of vibration isolation system based on high-static-low-dynamic stiffness
Get PDFThe purpose of this study is to investigate the characteristics of vibration isolation system with a single degree-of-freedom (SDOF) and a two-degree-of-freedom (2DOF) respectively based on the high-static-low-dynamic-stiffness (HSLDS). This model consists of a simple configuration connecting a vertical spring and a pair of oblique springs. The restoring force of the isolation system is approximated to linear and cubic stiffness by applying the Maclaurin series expansion. The dynamic equations of the SDOF and 2DOF are established for the harmonic force excitation. The frequency-amplitude response equation of the SDOF is obtained by employing the harmonic balance method (HBM) and is demonstrated in the classical Runge-Kutta method. The solution stability is ensured by applying the Floquet theory. Effects on the frequency response curves (FRCs) for the damping ratio and excitation amplitude are explored and discussed. The force transmissibility (FT) is defined to evaluate the vibration suppression capability. Effects on the FT of the SDOF and 2DOF for the excitation amplitude, mass ratio, and damping ratio are investigated. An experimental investigation of the SDOF is carried out to evaluate the actual attenuation performance in comparison with the equivalent linear system (ELS). The simulation and experimental results show that the HSLDS system with harmonic force excitation demonstrates hardening stiffness with multi-valued solutions. The occurrence of jump phenomenon is observed and explained by the stiffness variation. The system response and resonance frequency are affected by the excitation amplitude and damping ratio. The HSLDS system outperforms the ELS in a low frequency range if an appropriate mass is mounted. It is excited by a proper force and owns a suitable damper, which offers a theoretical guidance for the design and application of a novel HSLDS isolator
Rotating machinery fault diagnosis for imbalanced data based on decision tree and fast clustering algorithm
Get PDFTo diagnose rotating machinery fault for imbalanced data, a kind of method based on fast clustering algorithm and decision tree is proposed. Combined with wavelet packet decomposition and isometric mapping (Isomap), sensitive features of different faults can be obtained so the imbalanced fault sample set is constituted. Then the fast clustering algorithm is applied to search core samples from the majority data of the imbalanced fault sample set. Consequently, the balanced fault sample set consisted of the clustered data and the minority data is built. After that, decision tree is trained with the balanced fault sample set to get the fault diagnosis model. Finally, gearbox fault data set and rolling bearing fault data set are used to test the fault diagnosis model. The experiment results show that proposed fault diagnosis model could accurately diagnose the rotating machinery fault for imbalanced data
Ultrasound spectral analysis-based assessment of macular areas in patients with age related macular degeneration
Get PDFAge-related macular degeneration (AMD) is the leading cause of irreversible vision loss in people aged 50 and older in the developed world. Early detection and treatment of AMD play the key role in helping patients at high risk for developing exudative to maintain their vision or slow down the progression of the disease. In this paper, the new technique for AMD evaluation using ultrasound spectral analysis is presented. Our aim was to compare B scan ultrasound signals backscattered from healthy tissues of macular area with signals from nonexudative and exudative AMD areas. In case-control study of 64 patients (144 tissues) we compared 82 cases of healthy tissue of macular area (I group) with 35 cases of nonexudative AMD (II group) and 30 cases of exudative AMD (III group) using B scan ultrasound. Estimated results showed that B scan amplitude and spectral intercept are informative to distinguish healthy tissues of macular area from AMD and spectral slope spectral, momentary bandwidth allow us to distinguish forms of AMD (nonexudative and exudative).We suggest that ultrasound spectral analysis is noninvasive, widely available, easy-to-use and less expensive method which can be used as an additional diagnostic tool in AMD detecting and differentiating when there are no possibilities to use more specific examination
Research of the induced voltage’s varying law of the pipe-type energy harvester tumbleweed rover
Get PDFThis paper introduces a novel tumbleweed rover design that employs a pipe-type energy harvester system to harvest electrical power from the wind indirectly. The critical parameters law of electromagnetic induction is studied firstly and then propose a preliminary model of the layout of harvesters. Simulates the motion of the harvester inside a spherical shell to achieve the performance of voltage generation and summarize the varying rules of induced voltage. Given the effect of centrifugal force, we further propose spring as a solution to support magnet to recover reciprocating motion in harvester. Finally, the experiments are implemented based on the simulated model to verify the dependability of the energy harvester and the validity of induced voltages’ varying rules
Modeling and analysis of stick-slip vibration and bit bounce in drillstrings
Get PDFBit bounce and stick-slip vibration are detrimental to the service life of drillstring and down-hole equipment. A two degrees-of-freedom lumped parameters model is employed to account for bit-rock interaction and coupled vibration. Qualitative analysis to system parameters is performed through analyzing the influence of the angular speed of the rotary table and the length of drillstring on stick-slip vibration and bit bounce. After that, the suppression methods of stick-slip vibration and bit bounce are also given. The nonlinear motions predicted by the model are in agreement with the experimental observations. The study shows that increasing the weight-on-bit(WOB) and the angular speed of the rotary table effectively suppresses bit bounce and stick-slip vibration. What’s more, the posterior models can suppress stick-slip vibration. At the same time, bit bounce can be reduced through applying the models in the middle. When the drillstring is in a higher-length, the stick-slip frequency is at a lower level. However, the intensity of bit bounce is extremely high
Features of dynamics of mechanical system with self-synchronizing vibroexciters near resonance
Get PDFThe paper describes some features of behavior of a mechanical system with self-synchronizing vibroexciters. The influence of friction torque in the bearings of vibroexciters rotors on their self-synchronization has been established by means of experimental research and mathematical simulation. Both the causes and frequency ranges of gaps in frequency responses has been found out. Further modification of the previously proposed algorithm for resonant tuning has expanded working regimes limits of the control system and improved resonant tuning stability
The stability loss of the rotor-slide bearings system under random load variations
Get PDFThe article presents how the system equipped with a rotor supported by slide bearings loses stability, operating under random load conditions. The computer simulations were applied for the analysis of the rotating machinery (using in-house developed codes). The MESWIR software is presented herein that can be used to assess dynamic performance of machines of this type. A special algorithm for the randomisation of loads was implemented and discussed in detail on the basis of a representative example. The rotor model was subjected to randomly-generated transverse forces during its operation. It exhibited unstable behaviour manifesting itself in the form of oil whirl or oil whip. The system operation was analysed both under constant and random load
Dynamic analysis of reciprocating compressor with clearance and subsidence
Get PDFIn this paper, the reciprocating compressor with clearance and subsidence of the crosshead is studied, considering the varying cylinder pressure. To investigate the nonlinear dynamical behaviors of the reciprocating compressor precisely, a novel dynamic model of the reciprocating compressor of single cylinder with clearance and subsidence for the varying cylinder pressure is established based on the Lagrangian approach. It is demonstrated that different clearance sizes, subsidence sizes and crankshaft angular velocities can affect the dynamic response of the crosshead in the horizontal direction, respectively. The analysis results of dynamic response illustrate that with the increase of clearance sizes and subsidence sizes, the influence of crosshead displacement, velocity and acceleration increase, but the effect of clearance is much stronger than subsidence. Fast Fourier transformation is also applied to analyze the frequency spectrum of the system response. Moreover, the stability of the motion is studied using phase trajectories, maximum Lyapunov exponents and Poincaré sections. Numerical solution results show that clearance sizes, subsidence sizes and crankshaft angular velocities change the dynamical behavior of the system. Through calculation of the maximum Lyapunov exponents and Poincaré portraits, the results reveal that the reciprocating compressor system is characterized by chaotic behavior with the faults of clearance and subsidence. Furthermore, with the increase of the clearance sizes and the crankshaft angular velocities, the shapes of chaotic phase trajectories have changed greatly, and varied inconspicuously with the increase of subsidence sizes in reciprocating compressor system