Experimental research on dynamic characteristics of gas bearing-rotor with different radial clearances

The test rig of gas bearing-rotor system was established. The rotor was composed of turbine, compressor and four disks, it was supported by hydrostatic gas bearings. With this test rig, the dynamics of rotor bearing system with different bearing radial clearances were researched. Rotating speed of shaft could be higher with large bearing clearance, but speed soaring and low frequency oscillation occurred were dangerous to the shaft; with small bearing clearance, the speed soaring and low frequency oscillation could be eliminated and the dynamic characteristic was good, but rubbing deceleration was more likely to happen. Make a contrast of the dynamics with different radial clearances, it could be found that the dynamic characteristic of small radial clearance was good, but the threshold of safe amplitude was small, which limited the maximum speed

Experimental research on instability fault of high-speed aerostatic bearing-rotor system

The experimental research on high-speed aerostatic bearing-rotor system with one compressor, one turbine and coaxial four discs was developed. The gas bearing-rotor system stability under different bearing supply pressure plans was studied by experiments. The paper also presents fault features of gas film whip instability, power frequency rubbing and low frequency rubbing, which provides experimental data for gas bearing-rotor system stability study

Influence of friction coefficient on rubbing behavior of oil bearing rotor system

The 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

Dynamics of multi-disk shafting supported on journal bearing

For permanent magnet disc motor-impeller shafting, the dynamic model was established to calculate principle modes and nonlinear dynamic responses. The influences of eccentric magnitude, dynamic viscosity, bearing clearance on nonlinear dynamics were discussed. The results show the shafting have conical mode, translational mode, the first and second bending mode. Two critical speeds were corresponding to conical and translational modes. The shafting has period N and quasi-periodicity characteristics by effect of nonlinear oil film force. When other basic parameters were unchanged, the increasing eccentric magnitude made compressor vibration be larger firstly and then smaller. The larger oil viscosity and smaller bearing clearance increase the stability of motion. The conclusions of the paper provide a theoretical reference for dynamic design and fault diagnosis of the shafting

Precursory characteristics and disaster prevention of rock burst in roadway excavation in steeply inclined extra-thick coal seam

With the gradual coal mining of deep rock burst mine, the impact accompanying roadway excavation becomes more and more intense. Aiming at the problem of effective prevention and control of rock burst in roadway excavation, taking the steep seam mine in the Wudong Coal Mine as an example, the temporal and spatial precursor characteristics of rock burst in roadway excavation were analyzed by microseismic monitoring. Combined with the numerical simulation analysis of stress and energy changes in roadway excavation, the mechanism of rock burst in roadway excavation was revealed, and the prevention and control strategy of rock burst in steeply inclined extra-thick coal seam roadway was put forward, which was verified by field engineering practice. The results show that the total energy of microseisms is extremely low for 2−5 days or there is an energy latency of at least 4 days before the rock burst occurs due to roadway excavation in steeply inclined extra-thick coal seam. Within 5 days before rock burst occurs, there is a high-frequency fluctuation period of maximum energy ratio for more than 3 days. There is an obvious lack of earthquake before the rock burst occurs, and the occurrence position is concentrated in the range of minimum value of microseismic energy near the heading face, or in the range of minimum value of microseismic frequency near the extreme value of microseismic energy, and the rock burst event is located in the area with high impact deformation energy index. The hard overburden structure of horizontal sublevel fully mechanized caving mining in steeply inclined extra-thick coal seam is not easy to break, which makes the stress concentration on both sides of upper horizontal goaf exist in roadway excavation. The stress between the front of the heading face and the bottom of the roadway squeezed by the roof and floor strata is concentrated and the energy accumulation is remarkable. With the increase of the heading depth of the roadway, the stress concentration and energy accumulation are further enhanced, which is easy to induce dynamic disasters such as rock burst. The prevention and control strategies of rock burst was established through comprehensive analysis, which consist of face blasting pressure relief, roadway drilling pressure relief and reinforcement support, and scaffolding in complex areas. Combined with the temporal and spatial precursory anomalies of rock burst, it provides an opportunity to strengthen the unloading pressure in time. Through the pressure relief of working face and roadway, the accumulated microseismic energy of more than 1×105 J per day did not occur during the excavation. After the support was optimized and the complex area was protected, the daily average microseismic energy of roadway excavation decreased to 2.2 kJ, and the proportion of microseismic events above 1 kJ decreased, and the overall section of roadway was flat

Temporal and spatial evolution law of microseisms and induced impact mechanism in complex spatial structure area of steep and extremely thick coal seam

The occurrence of coal mine rock burst disasters is closely related to the spatial structure, especially in the complex spatial structure area. It is of great significance to master the law of coal and rock catastrophe and reveal its mechanism in the complex spatial structure area of coal seam mining for the prevention and control of rock burst. Taking the Wudong Coal Mine as the research background, using numerical simulation, micro-seismic monitoring, theoretical analysis and other methods, the abnormal size effect of rock pillar stress is studied, the temporal and spatial evolution law of microseisms in the complex spatial structure area is analyzed, the mechanism of rock burst under the complex spatial structure is revealed, and the impact risk in the different areas of coal mining is evaluated. The research results show that: ① The steeply inclined rock pillar with narrower thickness and higher exposed height has stronger prying effect, and the abnormal stress of rock thickness variation forms five divisions. ② The area with narrower rock pillar thickness has more micro-seismic frequency, higher energy, stronger spatio-temporal activity and higher dispersion. The high stress region, the stress gradient region and the stress plateau region show the micro-seismic response characteristics of “low frequency-high energy”, “high frequency-high energy” and “low frequency-low energy” in turn. ③ The micro-seismic events in special spatial structure area are clustered and the energy level increases, and the temporal and spatial activity and dispersion increase sharply. This feature is more obvious especially at the edge of the structure, the energy accumulation and release rate increases, and the probability and intensity of rock burst are higher. The micro-seismic activity of special spatial structures located in the narrower area of rock pillars is more acute. ④ The narrower the thickness of rock pillar (the greater the height of coal pillar), the faster the growth rate of bending moment and energy in the depth of rock pillar, and the higher the impact risk. According to the strength effect of structural plane, it is inferred that the fault zone has slip and dislocation, and fault zone is the dominant area for energy accumulation and release. It is revealed that the mechanism of rock burst is the joint action of high static load and low critical load. The impact risk in the different areas of coal mining is evaluated based on stress concentration characteristics

Control of a Tilting Hexacopter under Wind Disturbance

Multicopters are well suited for executing fast maneuvers with high velocity, but they are still affected by the external atmospheric environment because attitude and position cannot be independently controlled. In this paper, we present a novel hexacopter which improves the wind resistance and strong coupling between attitude control and position control. The copter is designed such that the rotor sections can tilt around their respective arm axes. We present the aerodynamic methods to analyze the system dynamics model in windy environments. The entire system is decomposed into six loops based on the model, and the presented flight controller uses the ADRC method to consider both the attitude and the position. The controller introduces the extended state observer to estimate the white noise and wind disturbance. We use the nonlinear state error feedback law to control the output with disturbance compensation. Finally, we linearize the control allocation matrix that the controllers output directly mapped to the rotor velocities and tilting angles. The new theoretical results are thoroughly validated through comparative experiments

Distributed Fixed-Time Attitude Consensus Tracking Control for Multiple Rigid-Bodies Subject to Unknown Uncertainties

This paper investigates the problem of fixed-time attitude consensus tracking control for a team of multiple rigid-bodies in the presence of unknown uncertainties. A robust exact distributed fixed-time observer is presented to estimate velocity state of the virtual-leader for the followers that could not directly access information of the virtual-leader. Subsequently, a novel distributed fixed-time consensus tracking control law is proposed, by which consensus tracking for a team of multiple rigid-bodies could be achieved in a fixed-time regardless of any initial system state. When the proposed control scheme is applied, effects of time-varying disturbances acting on each follower could drastically be attenuated. Analysis on stability of the closed-loop system is rigorously given and effectiveness of the proposed control scheme is verified by numerical simulations

Distributed Fixed-Time Attitude Consensus Tracking Control for Multiple Rigid-Bodies Subject to Unknown Uncertainties

This paper investigates the problem of fixed-time attitude consensus tracking control for a team of multiple rigid-bodies in the presence of unknown uncertainties. A robust exact distributed fixed-time observer is presented to estimate velocity state of the virtual-leader for the followers that could not directly access information of the virtual-leader. Subsequently, a novel distributed fixed-time consensus tracking control law is proposed, by which consensus tracking for a team of multiple rigid-bodies could be achieved in a fixed-time regardless of any initial system state. When the proposed control scheme is applied, effects of time-varying disturbances acting on each follower could drastically be attenuated. Analysis on stability of the closed-loop system is rigorously given and effectiveness of the proposed control scheme is verified by numerical simulations

Bearing-based localization for leader-follower formation control

<div><p>The observability of the leader robot system and the leader-follower formation control are studied. First, the nonlinear observability is studied for when the leader robot observes landmarks. Second, the system is shown to be completely observable when the leader robot observes two different landmarks. When the leader robot system is observable, multi-robots can rapidly form and maintain a formation based on the bearing-only information that the follower robots observe from the leader robot. Finally, simulations confirm the effectiveness of the proposed formation control.</p></div