Journal of Engineering and Thermal Sciences
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Modal analysis of the certain membrane disc coupling
Get PDFThe membrane disc coupling has the ability to transmit higher power under high-speed rotation. It also has the ability of compensation angular and radial displacement. The finite element model of the coupling was established and vibrational characteristics were analyzed. The modal experiments were carried out with hammering method, the modal parameters were obtained and the correct of the simulations was verified under the same constraints with the FEM model. The results showed that simulating results agreed well with that of the experiments
An experimental methodology for evaluating the energy cost and comfort during cycling: a case study for analyzing tire pressure influence
Get PDFMultiple parameters affect energy cost and comfort during cycling, and for some of them there is a trade-off between both phenomena. The aim of this paper is to present a methodology to evaluate the influence of different cycling conditions on energy cost and cyclist’s comfort. The proposed methodology is based on on-road tests where power on pedals and vertical accelerations are measured. The experimental data is used to calculate energy cost and comfort indices to compare different cycling conditions. A case study of the tire pressure influence on energy cost and comfort is presented
An experiment to assess vibration reduction ability of the rubber floating-slab tracks with different supporting forms
Get PDFThe rubber floating-slab track is one of the best methods to isolate vibration induced by the interaction of the train and the rails. In order to improve its vibration reduction ability, three kinds of supporting forms, i.e. full-surface supporting, linear supporting and point-like supporting, were discussed by laboratory tests. Through time history analysis and frequency spectrum analysis, we found that the linear supporting form and the point-like supporting form have the smaller first resonant frequency than the full-surface supporting form, which is induced by the weakened supporting stiffness. Because of this reason, the maximum values of vibration acceleration of the floating slab for the linear supporting form and the point-like supporting form increase in the time domain and the frequency domain. However, the point-like supporting form has the smallest transfer ratio of vibration acceleration from the floating slab to the tunnel wall compared with the linear supporting form and the full-surface supporting form
Seismic signal segmentation procedure using time-frequency decomposition and statistical modelling
Get PDFIn the paper a novel automatic seismic signal segmentation procedure is proposed. This procedure is motivated by analysis of real seismic vibration signals acquired in an underground mine. During regular mining activities in the underground mine one can expect some seismic events which appear just after the mining activity, e.g. blasting procedures, provoked relaxation of rock and some events that are unexpected, like natural rock burst. It often happens that, during one signal realization, several shocks (events) appear. Apart from two main sources of events (i.e. rock burst and blasting), other activities in the mine might also initiate seismic signal recording procedure (for example machine moving nearby the sensor). Obviously, significance of each type of recorded signal is very different, its shape in time domain, energy and frequency structure (i.e. spectrum of the signal) are different. In order to recognize these events automatically, recorded observation should be pre-processed in order to isolate a single event. The problem of signal segmentation is investigated in literature, several application domains might be found. Although, there are just a few works on seismic signal segmentation. In this paper we propose to use a time-frequency decomposition of the signal and model each sub-signal at every frequency bin using statistical methods. Narrowband components are much easier to search for so called structural breakpoint, i.e. time instance when properties of signal significantly change. It is obvious that simple energy-based methods applied to raw signal fail when one event begins before the previous one relaxed. In order to find beginning and end of a single event we propose to use measures based on empirical quantiles estimated for each sub-signal and, finally, aggregate 2D array into 1D probability vector which indicates location where statistical features has switched from one regime to another one. The proposed procedure can be applied in order to improve time domain isolation of single event for the case, when duration of signal acquisition is longer than duration of the event or to isolate single event from sequence of events (recorded for example during blasting)
A vibration-based damage identification technique free of structural baseline information: experimental validation in multi-component plane structure
Get PDFA vibration-based method for damage identification was established based on the “weak” formulation of Pseudo-excitation (PE) technique. The method can be effectively conducted without any prior knowledge of structural baseline parameters, e.g., Young’s Modulus, and is capable of detecting multi-damage in both one- and two-dimensional structural components. Moreover, relying on point-wise examination of structural dynamic equilibrium conditions, the baseline parameters of inspected structure can be inversely estimated in a statistical way, showing promising potential in engineering practices. As a proof-of-concept investigation, multi-damage in a plane structure, containing both beam and plate components, were identified experimentally using the proposed method
Axial vibration analysis of cracked nanorods with arbitrary boundary conditions
Get PDFThe axial vibration of cracked nanorods (carbon nanotubes) with arbitrary boundary conditions is studied. The nonlocal elasticity theory is used, and the crack severity is modeled by an axial spring representing the discontinuity in the axial displacement. The present model is set up by dividing the nanorod into two segments connected by an axial spring located at the cracked section. The axial displacement functions are sought as the combination of two Fourier sine series and Stokes’ transformation. Vibration frequencies of a nanorod for variant crack positions under different boundary conditions are calculated by means of the proposed method. The purpose of this study is mainly to present a general analytical method for the dynamical analysis of cracked nanorods with arbitrary boundary conditions (rigid or restrained) rather than to investigate a specific problem
Smartphone based public participant emergency rescue information platform for earthquake zone – “E-Explorer”
Get PDFDevastating earthquake can often cause the disaster area communication interrupt, traffic paralysis, etc. It is difficult for the emergency rescue force to get the disaster area in time. Therefore, active local participation in the quake-hit areas to aid each other appeals extremely important. The paper is based on a self-developed smartphone software called “E-Explorer”, study its significance and its working methods to help the public participate in the earthquake rescue actively when external network are cut off. “E-Explorer” can help deliver important information for personal survival, let rescue workers locate the positions of survivors trapped, creating an efficient self-help and mutual rescue platform for the earthquake-stricken people
Rolling element bearings fault diagnosis based on correlated kurtosis kurtogram
Get PDFFind optimum frequency band which contains strong impulsive signal is very critical for bearing fault diagnosis. Recently developed kurtogram method is an effective method to determine optimum frequency band for envelope analysis. However, most of kurtograms and its improvements are based on kurtosis criteria. A limitation of kurtosis is that high kurtosis value will be acquired even if the signal has only a single impulse. This will lead to error frequency band selection when the signal contains some impulse like noise. So, this paper uses correlated kurtosis as a criterion to construct kurtogram. Correlated kurtosis is superior to traditional kurtosis for detecting the periodic impulses produced by bearing fault. Finally, a real bearing outer race fault experiment is used to demonstrate the method’s effectiveness
Multirate input based quasi-sliding mode control for permanent magnet synchronous motor
Get PDFPermanent magnet synchronous motor field oriented control system often uses dual-loop (speed and current) cascade structure, and the dynamics speeds of the two loops mismatch. The motor’s mechanical and electrical subsystems have the typical multirate characteristics. Based on the multirate control theory, this paper proposes multirate input quasi-sliding mode algorithm for the speed control loop. Under the situation of the output data loss, the proposed algorithm builds the extended input vector with the output prediction information. Due to the extended input vector, the proposed algorithm reduces the system steady state chatterring, and then improves the performance of the whole system. Simulation and experimental results demonstrate the effectiveness of the proposed algorithm
Development of spherical ultrasonic motor for space. Evaluations of durability under high temperature environment
Get PDFThe purpose of this research is to develop the spherical ultrasonic motor (SUSM) for space. The SUSM is a small multi-DOF motor. The various performances are requested of the motor for space. The experiments under the high temperature environment were carried out to check the durability to the radiant heat from the sun this time. Our experimental results showed that SUSM for space also maintains the drive performance under the high temperature environment. The material of piezoelectric elements and adhesives which influence the performances of SUSM for space will be reported in detail