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Influence of friction coefficient on rubbing behavior of oil bearing rotor system
Get PDFThe failure occurred frequently when rubbing, especially when the rotating machinery worked in abnormal conditions. The research of friction coefficient on rubbing behavior was not much. The model of rubbing rotor system was established. The rubbing characteristics of the different friction coefficient were compared and analyzed. The results showed the friction coefficient had no effect on motion of period 1, period 2 and period-doubling bifurcation, when rotating speed was low. With the increase of the friction coefficient, the chaotic motion transformed into quasi-periodic, and period N motion when rotating speed was in 760-820 rad/s. The chaotic motion disappeared when rotating speed was in 1260-1400 rad/s, and the zone of quasi-periodic motion was expanding
Study of experimental modal analysis method of machine tool spindle system
Get PDFDynamic properties of the machine tools especially the spindle systems contribute greatly to the reliability of the machine tools. The increasing use of modal analysis as a standard tool to estimate the dynamic modal parameters means that both experienced and inexperienced analysts are faced with new challenges: uncertainty about the accuracy of results. Therefore, the key requirement for experimental modal analysis is a reliable, efficient and accurate experimental method in spindle system analysis. Several processes, such as reference and response selection in modal test however would make the system identification process for structural dynamics inaccurate. To investigate the results accuracy when applying experimental modal analysis on machine tool spindle, this work hence further studied the experimental setup itself based on the reference and response selection. The reference selection and reference optimization method is developed for the accuracy and efficiency improving purpose. First, by comparing results from different reference quantity and direction test, the method to select reference points is studied. Then the modal parameters are verified by the complex mode indicator functions and finite element analysis to study the influence of the reference on the modal analysis accuracy. Next, improved algorithm of response points optimization is developed based on the MAC matrix to minimize the number and location of measuring response points. Lastly, the general standard and method to select the reference and response points are put forward. The approach setting-up the experimental impact test provides reliable and accurate results and can reduce the testing time at the same time
Hysteretic behavior simulation of novel rhombic mild steel dampers
Get PDFStructural vibration control technique is an appropriate and acceptable method to control structural vibration condition and dissipate structural vibration energy during severe earthquakes and violent winds. Metallic dampers are verified to be stable and effective for passive control by many scholars and engineers. Low-yield-point (LYP) steel provides a promising prospect for energy dissipation dampers widely applied in structural engineering practice. Experimental study was conducted on a novel rhombic steel plate damper in former research and numerical simulation of the hysteretic behavior of rhombic dampers was performed in this study. Mechanical performance and implementation of the novel rhombic steel plate damper is briefly introduced in this paper. The hysteretic behavior of the novel rhombic steel plate dampers made of three types of steel was investigated by testing and finite element method. It is concluded that the yield strength enhancement of the rhombic steel damper made of LYP steel is substantial. The numerical simulation results of the hysteretic behavior of the rhombic steel plate damper are similar to the experimental results for these three types of steel. The energy dissipation capability of rhombic LYP steel dampers is excellent and adequate to be used in passive control strategy for civil engineering structures
Time-dependent reliability analysis for a herringbone planetary gear set with failure dependency under random loads
Get PDFA gear-bearing coupling dynamic model that includes bearing stiffness, mesh stiffness and mesh errors for a herringbone planetary gear set (HPGS) is proposed. The proposed model is used to predict the random stress process of the gears and bearings along with Monte Carlo simulation, when the effects of tooth surface wear on meshing errors are considered. A calculation model for the random strength process is derived by applying the linear fatigue damage criterion and regarding the Poisson random process as a counting process of the random stress. Assuming that the stress and strength are random processes, a time-dependent reliability model for HPGS with failure dependency is proposed to predict the time-dependent reliability of HPGS based on the failure mode groups that are obtained by the correlation coefficient. The results show that, the meshing errors caused by the tooth surface wear, make the dynamic loads and failure dependency of the parts of HPGS gradually increase over service time. At the same time the fatigue damage, which is caused by the load action, makes the strength of parts of HPGS gradually decrease over service time. Therefore the reliability of HPGS quickly decreases over service time. If the shafts of the planets and sun gear are free in their axial direction, the failure dependency of the parts will significantly decrease, and the reliability of a herringbone planetary gear set will significantly be improved
Sliding mode control based on improved virtual reference model for damping adjustable hydro-pneumatic suspension systems
Get PDFThis paper proposed an improved virtual reference model for semi-active suspension to coordinate the ride comfort and handling stability of a vehicle. The reference model combines the virtues of sky-hook and ground-hook control logic, and the hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the handling stability especially in high speed condition. The full scale vehicle model considering the heave-pitch-roll motion is presented, and the theory of hydro-pneumatic suspension with continuous adjustable damper is also illustrated. A sliding mode controller is designed to track the states of the reference model. The stability of the sliding mode control strategy is analyzed by means of Lyapunov function approach taking into account of the nonlinear damper characteristics and sprung mass variation of the vehicle. Finally, the performances of the controller are validated under three typical working conditions: the random road, speed bump road and sharp acceleration and braking. The simulation results indicated that, compared with the traditional passive suspension, the proposed control algorithm can offer a good coordination between ride comfort and handling stability of a vehicle. The designed controller could be commercially implemented in semi-active suspension systems
Numerical calculation of transmission noise for the magnesium alloy cylinder head cover
Get PDFTransmission noise of the magnesium alloy cylinder head cover was researched in this paper. Firstly, the numerical calculation mode of a cylinder head cover was compared with the experimental one. Results showed that the numerical calculation model had a relatively high accuracy, and it could be used in subsequent analysis. Secondly, sound pressure inside the cylinder head cover was extracted through the four-load method and taken as the sound source. Then, it was applied in a simulation model in order to simulate transmission noise of the actual situations. Afterwards, transmission noise of the magnesium alloy cylinder head cover was compared with the aluminum alloy one. It was shown that relatively low transmission noise was generated from the magnesium alloy cylinder head cover. Meanwhile, its mass was only 0.65 times of that of the aluminum alloy one. Therefore, the requirement for low noise and light weight was achieved by the magnesium alloy cylinder head cover. Then, dynamic stresses of cylinder head covers for two materials were compared. Results showed that dynamic stress of the magnesium alloy cylinder head cover was slightly smaller than that of the aluminum alloy one. The magnesium alloy cylinder head cover satisfied the requirement for strength and had a relatively prominent comprehensive performances. Finally, sound absorption coefficient of a porous material was calculated by using the numerical simulation technology. It was also laid inside the magnesium alloy cylinder head cover to constitute a composite cylinder head cover. Transmission noise of such composite cylinder head cover was much smaller than that of the original structure. This researches provided a method for low noise and light weight design of the cylinder head cover
DC modulation controller parameters tuning based on improved multi-signal Prony algorithm
Get PDFTo aim at the puzzle of DC modulation controller parameters tuning in large-scale AC/DC interconnected power systems, in this paper a multi-signal Prony algorithm is proposed which can simultaneously extracts oscillation modes from multiple signals compared with traditional Prony analysis method. In the algorithm, current setting value increment at rectifier side serves as system input, and AC liaison transmission line active power increment acts as the resulting output under consideration of systems initialization state. Through the improved multi-signal Prony identification on the output time-domain response data under specified input, an equivalent linear model with order reduced is obtained. Based on the identified results, the adjustments are then implemented on the controller parameters using the pole placement method. Through theoretical analysis and IEEE four generators system tests, the simulation results show that to add the DC modulation controller with parameters tuned by the improved Prony algorithm can significantly increase the oscillation damping of AC/DC interconnected systems, and improve the systems operation stability
Forecasting research of overpressure of explosive blast in subway tunnels
Get PDFIn case of an explosion happening inside the subway tunnel, blast waves interacts with the structure in an enclosed space. Both the overpressure and duration of blast increase. On the basis of experimental research, we establish a calculation model of blast effects in a tunnel. Its applicability has been verified by comparing the numerical results and the experimental findings. Then the blast effects in subway tunnel have been analyzed. It has been found out such factors as the tunnel shape, charge position, and distance to the explosion center all have a great influence on blast effects. The overpressure of blast in the subway tunnel is summarized and the formula is proposed. Compared to data of explosion tests at home and abroad, the formula has been proven to have some applicability. It may be provide some reference to the design of antiknock loads of subways and evaluation of casualties
Detection and identification of mechanical faults by Kalman filtering in electric machines
Get PDFKalman filtering technique is applied on vibration signals to detect eccentricity fault and bearing fault in induction motor. The vibration signals are acquired during load performance tests of healthy and faulty cases of induction motor. The state space equations needed for Kalman filter structure are constructed based on autoregressive model of the signals. The harmonics of fault related frequencies are identified from the spectrum of innovation signal, which is provided from the Kalman filter response, for vibration signal and also it is seen that Kalman filter reduce the noise level
Preventive maintenance optimization policy based on a three-stage failure process in finite time horizon
Get PDFIn this paper, a preventive maintenance optimization policy based on a three-stage failure process in finite time horizon is proposed. The lifetime of system is divided into three stages by the concept of three-stage failure process, which is corresponding to the three color scheme commonly used in industry. The subsequent inspection interval is halved when the minor defective stage is identified. Once identifying the severe defective stage, maintenance action is carried out. A numerical example is presented to demonstrate the efficiency of the proposed models