As the mileage of subway is increasing rapidly, there is an urgent need for automatic subway tunnel inspection equipment to ensure the efficiency and frequency of daily tunnel inspection. The subway tunnel environment is complex, it cannot receive GPS and other satellite signals, a variety of positioning sensors cannot be used. Besides, there are random interference, wheel and rail idling and creep. All the above results in poor performance of conventional speed tracking and positioning methods. In this paper, a multi-sensor motion control system is proposed for the subway tunnel inspection robot. At the same time, a trapezoidal speed planning and a speed tracking algorithm based on MPC (Model Predictive Control) are proposed, which simplify longitudinal dynamics model to overcome the complex and variable nonlinear problems in the operation of the maintenance robot. The optimal function of speed, acceleration and jerk constraint is designed to make the tunnel inspection robot achieve efficient and stable speed control in the subway tunnel environment. In this paper, the "INS (inertial navigation system) + Odometer" positioning method is proposed. The difference between the displacement measured by the inertial navigation system and the displacement calculated by the odometer is taken as the measurement value, which reduces the dimension of the conventional algorithm. The closed-loop Kalman filter is used to establish the combined positioning model, and the system error can be corrected in real time with higher accuracy. The algorithms were verified on the test line. The displacement target was set to be 1 km and the limit speed was 60 km/h. The overshooting error of the speed tracking algorithm based on trapezoidal velocity planning and MPC was 0.89%, and the stability error was 0.32%. It improved the accuracy and stability of the speed following, and was much better than the PID speed tracking algorithm. At the speed of 40 km/h, the maximum positioning error of the robot within 2 km is 0.15%, and the average error is 0.08%. It is verified that the multi-sensor fusion positioning algorithm has significantly improved the accuracy compared with the single-odometer positioning algorithm, and can effectively make up for the position error caused by wheel-rail creep and sensor error.
Abstract Classical bow echoes (CBEs) normally develop due to rear‐inflow jets, while merger‐formation bow echoes (MFBEs) evolve from the merger between linear systems and preline convection. MFBEs are rarely documented before, and the key processes remain unclear because of the small‐scale and fast‐evolving merging processes. Using radar observations during 2015–2019, this study examines the characteristics of these two types of bow echoes over South China. Eighteen MFBEs and 11 CBEs are identified, accounting for 62% and 38% of the total 29 bow echoes, respectively. MFBEs commonly occur over coastal regions in the afternoon, where southerly sea breezes provide favorable thermodynamic conditions. About half CBEs develop over mountainous areas in the morning, and northerly winds enhance the local baroclinity and kinematic convergence. A new Merger‐Classical index is proposed to distinguish the environments for the development of two types of bow echoes, disclosing the more favorable near‐surface thermal conditions for MFBEs. In addition, more severe weather occurs in metropolitan area near the Pearl River Delta region during MFBEs, in which the accumulated precipitation is about 2.5 times higher than that during CBEs. This study reveals the discrepancies between MFBEs and CBEs over South China, emphasizing the MFBEs account for more than half of the total bow echoes and cause more high‐impact weather in the metropolitan area. This study proposes a new perspective on the environment in which bow echo forms by merger process over South China, urging for more research to explore the underlying processes.
Four-switch three-phase inverters (FSTPIs) have been proposed to be used in low-cost applications because of the reduced number of semiconductor devices, and space vector pulse width modulation (SVPWM) techniques have also been introduced to control FSTPIs. However, high-performance controllers are needed to implement complicated SVPWM algorithms, which limits their low-cost applications. To simplify algorithms and reduce the cost of implementation, an equivalent scalar method for SVPWM of FSTPIs is proposed. SVPWM for FSTPIs is actually a sine PWM by modulating two sine waves of 60° phase difference with a triangle wave, so such a special sine PWM can be used to control FSTPIs. The simulation and experimental results demonstrate the validity of the proposed method.
Typhoon Vicente (2012) underwent an extreme rapid intensification (RI) over the northern South China Sea just before its landfall in south China. The extreme RI, the sudden track deflection, and the inner- and outer-core structures of Vicente were reasonably reproduced in an Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model simulation. The evolutions of the axisymmetric inner-core radar reflectivity and the primary circulation of the simulated Vicente before its landfall were verified against the Doppler radar observations. Two intensification stages were identified: 1) the asymmetric intensification stage (i.e., RI onset), represented by a relatively slow intensification rate accompanied by a distinct eyewall contraction; and 2) the axisymmetric RI stage with very slow eyewall contraction. Results from a storm-scale tangential wind tendency budget indicated that the primary spinup mechanism during the first stage was the radial eddy momentum transport, which was beneficial to accelerate primary circulation inside the radius of maximum wind (RMW) and thus conducive to eyewall contraction. In contrast, the principal spinup mechanism during the second stage was mainly ascribed to the forced secondary circulation in response to diabatic heating in the eyewall and boundary layer friction, which efficiently transported the absolute angular momentum radially inward and vertically upward to increase the primary circulation in the eyewall region throughout the troposphere. Further analysis revealed that the interaction between the monsoon circulation and storm-scale vorticity anomalies played an important role in erecting the tilted vortex and spinning up the midtropospheric TC circulation during the first stage.
Radial velocity (Vr) and reflectivity (Z) data from eight coastal operational radars of mainland China and Taiwan are assimilated for the first time using the ARPS 3DVAR and cloud analysis package for Pacific Typhoon Meranti of 2010. It is shown that the vortex‐scale circulations of Meranti can be adequately established after only 2 hourly assimilation cycles while additional cycles provide more details for subvortex‐scale structures. Subsequent 12 h forecasts of typhoon structure, intensity, track, and precipitation are greatly improved over the one without radar data assimilation. Vr data lead to a larger improvement to the intensity and track forecasts than Z data, while additional Z data further improve the precipitation forecast. Overall, assimilating both Vr and Z data from multiple radars gives the best forecasts. In that case, three local rainfall maxima related to typhoon circulations and their interactions with the complex terrain in the southeast China coastal region are also captured. Assimilating radar data at a lower 3 or 6 hourly frequency leads to a weaker typhoon with larger track forecast errors compared to hourly frequency. An attempt to assimilate additional best track minimum sea level pressure data is also made; it results in more accurate surface pressure analyses, but the benefit is mostly lost within the first hour of forecast. Assimilating data from a single Doppler radar with a good coverage of the typhoon inner core region is also quite effective, but it takes one more cycle to establish circulation analyses of similar quality. The forecasts using multiple radars are still the best.
According to the anti-control principle of chaos, a combined control method is proposed based on a class of asymptotically stable linear systems with multiple controllers. A higher-dimensional hyperchaotic system is investigated by the Lyapunov exponents method and equilibrium points analysis, and it exists the largest number of positive Lyapunov exponents. The chaotic pseudo-random sequences of the higher-dimensional hyperchaotic system can pass all NIST tests after preprocess-ing, and behave better chaotic characteristics. Meanwhile, a new encryption algorithm of image information with position scrambling, sequential diffusion and reverse diffusion is designed based on the chaotic pseudo-random sequences. The experiments of image information are given to verify the effectiveness and feasibility of the encryption algorithm. Finally, the security analyses are also discussed by the key sensitivity, differential attack and statistical analysis. It is shown that the encryption algorithm has large enough key space and can be applied to secure communication.
Abstract The drag coefficient is a crucial parameter in the interaction between the Earth's surface and the atmosphere because it directly determines the momentum flux. This study examines the variation in the drag coefficient with wind speed over the land surface using observations from two typhoon cases and one cold front case. The analysis shows a significant decrease in the drag coefficient, roughness length, and zero plane displacement when the wind speed is greater than approximately 15 m s −1 . The drag coefficient is proven to be positively related to the coherence of the turbulent structures. The momentum transport modes changed at 15 m s −1 . By regarding the large eddies as scales larger than observation height, it is found that large‐scale coherent structures dominate the momentum transfer in strong wind conditions, while small eddies contribute significantly in low to moderate wind conditions. Momentum transport in such large coherent eddies is inefficient, leading to the reduction of the surface drag. The results suggest that the formation of inefficient large coherent eddies is likely due to the existence of inverse energy cascade.
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