Journal of Engineering and Thermal Sciences
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Experimental study on high frequency chatter attenuation in 2-D vibration assisted micro milling process
Get PDFRegenerative chatter is an unstable form of self-excited vibration in the machining process, and it is one of the main obstacles which limit the productivity and the surface quality of the component. This paper investigates the effect of 2-D vibration assistance on high frequency regenerative chatter in the micro milling process. External vibration is applied on the workpiece in a range of frequencies and amplitudes using the piezoelectric actuators. The chatter vibration is monitored using the sound pressure signal measured by the microphone. The chatter amplitude with vibration assistance in 1-D (feed or normal direction) and 2-D is studied. The effect of the frequency and amplitude of the vibration assistance on chatter amplitude is analyzed. It is concluded that the vibration assistance is able to effectively attenuate the high frequency chatter by modifying the dynamic chip thickness and adding process damping in the micro milling process
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
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
Multiple-input multiple-output proportional-integral-proportional-derivative type fuzzy logic controller design for a twin rotor system
Get PDFA new multiple-input multiple-output (MIMO) proportional-integral-proportional-derivative (PIPD) type fuzzy logic controller (FLC) is proposed for pitch and yaw motion control of a twin rotor system in this study. A fuzzy feedforward compensator for gravity effects on pitch motion of the twin rotor is also designed. Fuzzy logic was preferred for controller design since it can be applied to nonlinear systems and do not require the mathematical model of the system. The twin rotor system is a highly nonlinear system that includes coupling effects between pitch and yaw motions and has similar dynamics to that of a helicopter in certain aspects. Experimental results demonstrate that the proposed controller is able to stabilize the system along with good trajectory tracking performance
A new machinery diagnosis method based on complex bilateral spectrum
Get PDFIn view of the turbo molecular pump high-speed rotating parts, this paper presents a new machinery diagnosis method based on complex bilateral spectrum. At first, the vertical and horizontal vibration signals are directly combined into complex signals in time-domain; and then the complex bilateral spectrum is obtained by fast Fourier transform (FFT). Furthermore, the holospectrum, which can fast find machinery faults, can be obtained using the amplitude and phase at some special frequencies. At the same time, the equivalence of holospectrum technique and the proposed method is verified. Finally, a case study shows the effectiveness of the proposed method
Seismic performance of tuned mass damper on Shazand Railway Bridge induced by train
Get PDFShazand Railway Bridge is located in Markazi province, Iran in north to south-west railway. The bridge consists of ten spans. In 1984, during Iran-Iraq war, that’s main span, which has a length of 72 m, was attacked and severely damaged. Eight month later, damaged span replaced with a steel deck. The deck is straight in plan, but the railway is curved and this causes eccentricity. Excessive vibration was observed during the train passage. Although the bridge was retrofitted in two stages, the problem has not been solved yet, and the trains’ speed should be reduced to around 10 km/h in order to avoid excessive vibration. The present study addressed the effectiveness of tuned mass damper (TMD) in reducing train-induced vibrations of Shazand Railway Bridge. A three dimensional finite-element model of the bridge is developed and dynamic time history analyses under train passage in both as-built and passively controlled with TMD are conducted. Sensitivity analyses are performed to demonstrate the effects of the damper parameters on structural response. The results show that considerable reduction in acceleration response of the bridge can be achieved by employing proper TMD
Study on wheel-rail interaction based on rail roughness
Get PDFEnvironmental vibration and noise pollution caused by the operation of subway is a hot topic of concern at home and abroad. There is a need to research dynamic interaction between trains and track in order to solve environmental vibration and noise pollution caused by the operation of train. As an excitation source of the train vibration, rail surface roughness has significant impact on the wheel-rail interaction. In order to study the effect of rail roughness on the wheel-rail vibration load, the wheel-rail interaction model is established based on excitation of rail surface roughness in this paper. The effect of rail roughness on train vibration load is calculated by this model according to the measured rail roughness data in Beijing subway in the MATLAB program. Wheel-rail force in the most adverse situations is also calculated. The property of wheel-rail force under different conditions such as track forms, driving speed and curve radius is also analyzed in this paper
Simulation of dynamic vehicle load on road pavement
Get PDFNumerical simulation approach has recently grown in popularity due to its wide range of applications in the solving of random vehicle-pavement interaction (VPI). This study proposes a framework to simulate the dynamic vehicle load process due to a quarter-truck vehicle model moving along a rough road surface. A procedure used to generate artificial time histories of dynamic vehicle load on road pavement was developed. Example application of the proposed framework is presented and a comparison of calculated and experimental values demonstrates the effectiveness of the framework. To elucidate the relationship between dynamic vehicle load and road roughness, this study normalized the average maximum dynamic vehicle loads on road surfaces of different grades using standard deviation of dynamic vehicle load. Numerical results indicate that the normalized average maximum dynamic vehicle load is not associated with road roughness
Application review on underwater radiated noise measurement by using a vessel’s own towed array
Get PDFCompared with the traditional fixed test and auxiliary measurement ship, the measurement of the underwater radiated noise by using a vessel’s own towed array has many advantages, such as flexible, convenient, low cost, and so on. In this paper, the previous researches on this method are summarized. From the view of implementing this technique, the method has been divided into four aspects: towed array design, U-turn manoeuvre, underwater sound propagation and towed array signal processing. Overall, this technology is practical and feasible, and has a good application prospect. Next, combined with a large number of experiments, further study on the selected principle of the towed array and U-turn technical indicators will be done