Journal of Vibroengineering
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Dynamic characteristics analysis on shearer drum in condition of cutting coal with different distributed rocks
Get PDFDynamic characteristics analysis on shearer drum is an important aspect in shearer design and a well-structured shearer drum provides better performance in vibration reduction and service life extension. To make reference for structure improvement, many researchers have focused on the dynamic analysis on cutting pick. However, the simplified model such as single pick, linear motion and continuous coal in the previous study made it divorced from actual situations underground. On basis of this, the model of shearer drum with several arranged picks and the coal model with some distributed rock have been set up in order to consist with the real working conditions. Through simulation, it can be found that the mean force in X-direction is little influenced by rock distribution, but the peak force in X-direction fluctuates greatly under different rock distribution. During the analysis on the peak force, it can be found that this kind of force could be cut down effectively when the rock was distributed on the top of the shearer cutting range. Based on these conclusions, we can program the cutting strategy to lower the influence of cutting forces on the shearer and its drum in the future
Research on compressive mechanical properties of metal rubber and its constitutive relation model
Get PDFThe static compression test of metal rubber components was carried out by using the control variable method. Influences of technological parameters such as relative density and metal wire diameter as well as structural parameters such as height and bearing area on mechanical properties of metal rubber material were studied. Based on micro-element infinitesimal spring theory, one-dimensional (1D) constitutive model of metal rubber material bearing compressive load was established, and it was found by comparing with experimental data that the curve fitted well and the model was reliable, could accurately describe the mechanical behaviors of metal rubber component when bearing load. The model provides theoretical basis for further study of mechanical properties of metal rubber material. It also guides design and manufacture of metal rubber products as well as its engineering application
Vibration model and frequency characteristics of the piezoelectric transducer in airflow-induced acoustic generator
Get PDFPiezoelectric transducers, which convert airflow induced vibrational energy into electrical energy, can be applied to self-powered supply and auxiliary power supply for various aircraft electronic systems. Micro-ringtone airflow piezoelectric generator, designed by the principle of airflow induced acoustic, is one kind among them. The vibrating piezoelectric generator, is usually mounted on the aircraft during the flight. The incoming airflow produces hydrodynamic acoustic source, which is the vibration source of the piezoelectric generator, actively vibrates the piezoelectric plate to convert energy. According to the vibration theory, a one-dimensional vibration model of piezoelectric generator with fixed peripheral pressure, under hydrodynamic excitation is established. The vibration and frequency characteristics of the piezoelectric transducers are analyzed by measuring the sound pressure and the piezoelectric generator voltage. Theoretical analysis and experimental results show that the frequency of hydrodynamic acoustic source is slightly lower than that of piezoelectric generator’s natural frequency. Maximum output power is obtained when the inflow speed is in the range of 128 m/s-148 m/s, the corresponding hydrodynamic acoustic source frequency is 6.9 %-8.7 % lower than the natural frequency of the piezoelectric generator. Excitation force Fex and the displacements of piezoelectric plate are in same frequency. But Fex is ahead of phase angle ψ than the displacement of piezoelectric plate
Direct force control of upper-limb exoskeleton based on fuzzy adaptive algorithm
Get PDFIn order to synchronize human and machine positions and minimize human-machine interaction forces in exoskeleton control, we present a two-degree-of-freedom (2-DOF) upper-limb exoskeleton model with power enhancement and direct force control strategy based on fuzzy adaptive algorithm. The conventional PD controller is widely used in exoskeleton control because it is model independent and its gains can be easily tuned. However, the speed of movement of the operator and the mass of external load are uncertain in practice; hence, the parameters of a conventional PD controller have to be adjusted according to the velocity of the motion and external loads to ensure the effectiveness of trajectory tracking. Additionally, there is a lag in the response time when the operator starts to move or changes direction suddenly. Therefore, this study proposes the use of an adaptive controller combining the fuzzy set techniques and PD controller to improve trajectory tracking. Robustness testing of the fuzzy PD controller for the external load uncertainty and motion velocity change are also investigated. The simulation results clearly indicate the superior performance of the fuzzy adaptive PD controller over the conventional one for tracking performance with external load uncertainty and motion velocity variance
Bidirectional three port converter for power flow management of PV/Battery-Fed elevator system
Get PDFThe Bidirectional Three Port Converter (BTPC) proposed in this research work is addressed for an elevator application that is driven from a BLDC motor in all four quadrants sourced from solar Photovoltaic (PV). The converter design of a PV based system necessitates constant output voltage with high power density and efficiency. The Proposed BTPC tracks the maximum power, maintains constant output voltage and also deals with the bidirectional power flow management whenever there is a change in applied torque when the machine is switched from motoring to regenerating mode. Furthermore, single stage power conversion is achieved with power transfer from PV to dc link or battery to dc link based on the load requirement and surplus power is directly stored in the battery. Closed loop control ensures adjusting the duty cycle of the proposed converter switches thereby maintaining the bidirectional power flow management. The proposed converter is analysed in detail with operating principle, design considerations and verified in terms of simulation and through experimental results
Republished Paper. Multiple damage detection and localization in beam-like and complex structures using co-ordinate modal assurance criterion combined with firefly and genetic algorithms
Get PDFDamage detection and localization in civil engineering constructions using dynamic analysis has become an important topic in recent years. This paper presents a methodology based on non-destructive detection, localization and quantification of multiple damages in simple and continuous beams, and a more complex structure, namely two-dimensional frame structure. The proposed methodology makes used of Firefly Algorithm and Genetic Algorithm as optimization tools and the Coordinate Modal Assurance Criterion as an objective function. The results show that the proposed combination of Coordinate Modal Assurance Criterion and Firefly Algorithm or Genetic Algorithm can be easily used to identify multiple local structural damages in complex structures. However, the convergence rate becomes slower for the case of multiple damages compared to the case of single damage. The effect of noise on the algorithm is further investigated. It is found that the proposed technique is able to detect the damage location and its severity with high accuracy in the presence of noise, although the convergence rate became slower than in the case when no noise is present. It is also found that the convergence rate of Firefly Algorithm is much faster than that of Genetic Algorithm
Novel bearing fault diagnosis model integrated with dual-tree complex wavelet transform, permutation entropy and optimized FCM
Get PDFIn order to enhance the capability of feature extraction and fault classification of bearings, this study proposes a feature extraction approach based on dual-tree complex wavelet transform (DTCWT) and permutation entropy (PE), using the fuzzy c means clustering (FCM) to identify fault types. The vibration signal of bearings can be decomposed into several wavelet components with DTCWT which can describe the local characteristics of vibration signals accurately. And the PE of each wavelet component, which can describe the complexity of a time series, is calculated to be regarded as the fault features. Then forming the standard clustering centers by the FCM, we defined a standard using the Hamming approach degree to evaluate the classification results in the FCM. In order to verify the effectiveness of the proposed approach, compared with two other typical signal analysis methods: ensemble empirical mode decomposition (EEMD) and variational mode decomposition (VMD), through extracting fault features, it required to identify the fault types and severities under variable operating conditions. The experimental results demonstrate that the proposed approach has a better accuracy and performance to diagnose a bearing fault under different fault severities and variable operating conditions. The proposed approach is suitable for a fault diagnosis due to its good ability to the feature extraction and fault classification
Base-isolation design of single-tower cable-stayed bridges: a case study in meizoseismal area
Get PDFThe single-tower cable-stayed bridge is one of the most popular types of bridges. Seismic design for this type of bridge, however, is rather difficult. When subjected to longitudinal earthquakes, the tower stands as the weakest part of all the bridge components. To solve this problem, a base-isolation design was developed and adopted for a practical single-tower cable-stayed bridge. In this design, laminated elastomeric bearings (EB) and liquid viscous dampers (LVD) were installed to serve as a base-isolation layer inside the tower cap. Numerical analysis was then conducted to investigate the variations of dynamic characteristics and seismic responses between conventional designs and base-isolation designs. LVD were used on the top of the transition pier to optimize the seismic system of the bridge. It was found that: i) the seismic loads acting on the bridge component were reduced as the seismic displacements increased. This was the result of amplification of the bridge vibration period by the EB in the base-isolation layer; ii) the seismic displacements were restrained by the LVD in the base-isolation layer, but the seismic forces increased due to improper parameter values; and iii) the seismic response decreased further by the transition pier’s LVD
Rolling element bearings localized fault diagnosis using signal differencing and median filtration
Get PDFWith the increase complexity of bearings’ processing algorithms and the growing trend of using computationally demanding algorithms, it is advantageous to provide analysts with a simple to use and implement algorithm. In this spirit, this paper combines simple functions to provide machine condition analysts with the capacity to diagnose bearing faults without all the complexity and jargon that comes with existing methods. The paper proposes a simplified surveillance and diagnostic algorithm for diagnosing localized faults in rolling element bearings using measured raw vibration signals. The proposed algorithm is based on analyzing the frequency content obtained from applying a median filter on the squared derivative signal (first or higher derivatives) of the vibration signal. The combination of signal differencing and median filters provides a squared envelope signal, which can be used directly to diagnose faults. Signal differencing gives a measure of jerk forces and lifts the high frequency content of the signal. To select the optimum order of differentiation, Kurtosis and maximum correlated kurtosis (MCK) are proposed. Median filter usage represents a better alternative of normal low pass filtration. This completely suppresses impulses with large magnitudes, which may interfere with the diagnosis. The length of the median filter (odd number 3, 5, 7 etc.) is selected as such to include the first 10 harmonics of the defect frequency. Simulated signals are used to demonstrate the efficiency of the proposed algorithm and give insights into the choices of the differentiation and smoothening orders. The proposed processing algorithm gives a first measure (surveillance) for detecting localized faults in rolling element bearings in a very simple way and can be employed in online learning and diagnosis systems. Results obtained from applying the algorithm on complex vibration signals from two types of gearboxes are compared with a well-established semi-automated technique with good correspondence