Synchronous System Research Articles

Two-dimensional spanwise flow regime influenced by tip vortex around a ground-mounted square cylinder in low turbulence uniform flow

The time series data of the lift force acting on a ground-mounted square cylinder in low-turbulence uniform flow reveal a distinctive pattern characterized by a predominant high-amplitude process modulated by intermittent low-amplitude fluctuations. This behavior arises from the intricate interplay between tip and Kármán vortices. However, conflicting interpretations persist, with some findings even presenting contradictory conclusions, particularly regarding the presence of symmetric shedding in the fluctuating lift force process with low amplitude. Furthermore, a clear consensus regarding the mechanism governing the interaction between the tip vortex and the spanwise vortex remains elusive. This study aims to elucidate the two-dimensional flow regime in the spanwise direction influenced by the tip vortex of a ground-mounted square cylinder in low-turbulence uniform flow through experimental investigation. Multiple-point synchronous pressure measurement and particle image velocimetry systems are utilized to measure wind pressure on the side walls and the corresponding flow field at 2/3 of the cylinder's height. The analysis confirms the presence of two distinct types of lift force coefficient behavior: low-amplitude fluctuation (LAF) characterized by longer durations and high-amplitude fluctuation (HAF) occurring in shorter intervals. Subsequently, the flow regime in the near wake corresponding to each mode of the lift force coefficient is discussed. It is observed that the LAF regime corresponds to symmetrical vortex shedding with a prolonged shear layer, maintaining nearly constant curvature. Conversely, for HAF, a pronounced Kármán vortex street is evident. This study conclusively demonstrates the existence of symmetrical vortex shedding, which predominantly contributes to the LAF component of the lift force.

Speed regulation system based on proportional resonance self-coupling PI control

In this paper, an improved self-coupled PI control dual-loop control strategy is proposed for the vector control of permanent magnet synchronous electric speed control system, to improve the poor motor control effect caused by the dead zone of the inverter, the presence of harmonics in the motor magnetic field distribution, and the error in the sampling process of the current. In order to reduce the tracking error of the signal, an acceleration feed-forward method is adopted, and the self-coupled PI controller with an additional Levant differentiator is introduced into the speed loop of the permanent magnet synchronous motor to ensure the accurate derivation of the input signal containing noise to improve the robustness of the system. In addition, this strategy combines the proportional term of the autotuned PI control structure with the standard resonator to form a proportional resonant autotuned PI in the current loop, so that the permanent magnet synchronous motor can better compensate the current in the current loop control to achieve the effect of current harmonic suppression. Finally, the control mechanism of the servo system analyzed, and based on the mathematical model of the controlled object PMSM, the design method of the improved self-coupling PI control structure is given. The experimental results show that the proposed control strategy can reduce the impact of the motor's own parameter changes on the system performance and has a good current harmonic suppression in the low-speed domain, which verifies the effectiveness of the designed improved self-coupled PI controller.

Permanent Magnet Synchronous Motor Speed Control System Based on Fractional Order Integral Sliding Mode Control

Permanent Magnet Synchronous Motor Speed Control System Based on Fractional Order Integral Sliding Mode Control

An air-ground integrated flight test technical framework based on flight simulation

In the modern civil transport aircraft flight test, flight test practitioners need to constantly improve the ability and reduce flight test cycle as much as possible, considering the relationship between flight test efficiency and flight test safety. In order to improve the real-time safety assessment ability of flight test monitoring personnel and reduce the increased test tasks due to safety considerations, a technical framework of air-ground integrated flight test according to the simulation results was proposed. Based on the conventional flight test monitoring system, the technical framework adds the flight test safety assessment model, air-ground data synchronization system and flight test telemetry data real-time processing functions. The overall framework is suitable for most flight test subjects, but the flight test safety assessment models need to carry out simulation requirements capture, scene analysis and model verification according to the flight test subjects requirements. Finally, taking crosswind landing flight test as an example, the basic application of air-ground integrated flight test technology is illustrated, which can provide reference for promoting the air-ground integrated flight test technology.

Effect of conversion time on the stability of mixed-flow pump in rotating speed conversion

The rotating speed conversion strategy has a significant impact on the stability of the variable speed operation of the mixed flow pump. Taking a mixed-flow pump as the research object, this paper collects the shaft vibration, pressure pulsation, and external characteristic parameters under different conversion times based on the synchronous acquisition system, and analyzes the influence of conversion time on these parameters. Finally, based on the improved TOPSIS evaluation method, the influence of different conversion time on the stability of the mixed-flow pump is evaluated. The results indicate that the conversion time is positively correlated with the amplitude of shaft vibration and pressure pulsation in the pump during the transition of rotating speed reduction. The local rubbing of the shaft can induce the vibration component corresponding to the high harmonics frequencies such as 2 f n, 3 f n, and 4 f n. The high correlation frequency band of the impeller outlet pressure pulsation and shaft vibration is located between 64 Hz and 120 Hz. And this frequency band is not affected by the conversion time. According to the TOPSIS evaluation results, in the transition process of speed reduction, the longer the rotating speed conversion time, the worse the stability of the mixed-flow pump during the conversion process.

An experimental study of thermoacoustic instabilities in a RP-3 fueled multi-swirl stabilized lean direct injection combustor

An investigation of self-excited combustion instabilities in a RP-3 fueled, multi-swirl stabilized, lean direct injection (LDI) combustor was performed and investigated with different operating conditions (inlet Reynolds number and fuel–air ratio (FAR)). Pressure fluctuation and heat release data were simultaneously collected using a 3-channel synchronous acquisition system. The results show that as the FAR increases, combustion transitions from a low oscillation mode to a high oscillation mode. During the modal transition, the oscillating flame structure, formed by vortex shedding in the shear layer and the recirculation zone, is then transformed into contraction and expansion movements from the front of the central recirculation zone towards the downstream and radial directions of the combustor. When combustion is in a low oscillation mode, the driving capability of the flame is relatively low. Upon entering a high oscillation mode, the overall driving energy of the flame can maintain combustion in a limit cycle oscillation state.

Parameter fuzzy rectification for sliding mode control of five-phase permanent magnet synchronous motor speed control system

Introduction: Nowadays, five-phase permanent magnet synchronous motors have been widely used in the industrial and transportation fields, and the existing sliding mode control methods for speed control systems can no longer meet the requirements such as fast response and good stability.Methods: In light of the aforementioned considerations, the study initially employs mathematical modeling to elucidate the five-phase permanent magnet synchronous motor. Secondly, on the basis of proportional-integral-derivative sliding mode control, radial basis function and Takagi-Sugeno-Kang fuzzy model are introduced for parameter identification and optimization and regulation. Finally, a new neural network regulation algorithm and speed control strategy are proposed.Results and Discussion: The experimental results demonstrated that the expected parameter optimization rate of the regulation algorithm can reach 90%, and the overshooting amount under small inertia working condition is only 3%, and the adjustment time is 0.02 s. The new control algorithm can be used to control the motor speed with the lowest speed fluctuation and the fastest recovery time. In addition, when affected by the load torque, the motor speed controlled by the new strategy fluctuated the least, with a speed drop of only 1% and the fastest recovery time of 0.02 s. It exhibited the lowest control error of 3.7% and the lowest overshooting amount of 5.9%.Conclusion: In summary, the suggested approach has the potential to significantly enhance the speed control system’s control performance while maintaining strong resilience and anti-interference capabilities. The method has certain guiding significance for the practical application of five-phase permanent magnet synchronous motor speed control system.

A real-time performance improvement method for composite time scale

Abstract The composite time scale (CTS) provides a stable, accurate, and reliable time scale for modern society. The improvement of CTS’s real-time performance will improve its stability, which strengths related applications’ performance. Aiming at this goal, a method achieved by determining the optimal calculation interval and accelerating adjustment stage is proposed in this paper. The determinants of the CTS’s calculation interval (characteristics of the clock ensemble, the measurement noise, the time and frequency synchronization system’s noise and the auxiliary output generator noise floor) are studied and the optimal calculation interval is obtained. We also investigate the effect of ensemble algorithm’s initial parameters on the CTS’s adjustment stage. A strategy to get the reasonable initial parameters of ensemble algorithm is designed. The results show that the adjustment stage can be finished rapidly or even can be shorten to zero with reasonable initial parameters. On this basis, we experimentally generate a distributed CTS with a calculation interval of 500 s and its stability outperforms those of the member clocks when the averaging time is longer than ∼1700 s. The experimental result proves that the CTS’s real-time performance is significantly improved.

Effects Of Wing Elasticity On Tip Vortex: 3D Deformation And 2D3C Flow Field Measurements

As aircraft embrace broader applications, the flexible wing presents a promising avenue to enhance aircraft performance across a wide range of flight conditions. Although the aerodynamic benefits of wing deformation are widely recognized, the present understanding of the tip vortex is relatively limited. This work experimentally examines the effects of wing deformation on the tip vortex of a simplified aircraft model with two kinds of elastic wings and a rigid wing. The 3D deformations and 2D3C flow fields are measured using a synchronous measurement system, which includes the high accuracy deformation measurement (HADM) method and the stereoscopic particle image velocimetry (SPIV). It is shown that increased wing elasticity leads to greater bending, with the wing tip moving along the streamwise, vertically upward, and spanwise inward directions. These deformations are closely linked to aerodynamic forces and influence the tip vortex positions. The more elastic wing, EW2, exhibits the highest vortex core position, more than 0.5 times the length of the wing root, while the other one, EW1, shows the strongest vortex in the lift-increased regime. In the early wakes, the tip vortex of the elastic wing is elongated along the spanwise direction, resulting in an asymmetric shape. As it convects downstream, the vortex core disperses via viscous diffusion, resulting in a relatively more circular shape with decreased vorticity.

Takagi-Sugeno fuzzy sampled-data observer design for nonlinear permanent magnet synchronous generator-based wind turbine systems using auxiliary function-based integral inequality technique

This study focuses on designing the fuzzy sampled-data observer (FSDO) scheme for nonlinear permanent magnet synchronous generator (PMSG)-based wind turbine systems (WTS). The primary objective of this problem is to solve an unmeasurable state problem under the mismatched premise variables conditions among system, observer, and controller, respectively. To do this, firstly, the proposed wind turbine model is described in a Takagi-Sugeno fuzzy model due to the complex nonlinearities in PMSG-based WTS. Next, based on the measured output signals and sampled estimated states, the FSDO is designed to understand some unmeasurable state variables of the studied system. Then, a novel auxiliary function-based integral inequality (AFBII) is presented to approximate the integral quadratic terms related to sampling information. Thanks to the proposed AFBII technique and the introduction of slack variables, several new and less conservative stability requirements are derived in the formulations of linear matrix inequalities (LMIs) using the looped Lyapunov function. Finally, the simulation studies for the considered wind turbine model are validated numerically, and then some comparative results are provided to show the superiority and applicability of the theoretical observations.

Sliding Mode Speed Control for PMSM Based on Model Predictive Current

To enhance the dynamic performance and disturbance rejection capability of the permanent magnet synchronous motor speed control system, a novel speed control method based on a novel sliding mode control (NSMC) and load torque observer is proposed on the basis of model predictive current control (MPCC) with a sliding mode disturbance observer. First, on the basis of MPCC, the influence of parameters such as resistance, inductance, and flux linkage on MPCC is analyzed. To address the aggregated disturbance caused by parameter mismatches, a piecewise square-root switching function sliding mode disturbance observer (SMDO) is designed to enhance the robustness of the parameters. To address the poor dynamic performance and inadequate robustness resulting from the proportional-integral-controller (PI) velocity loop control in the MPCC, a novel NSMC velocity control method is proposed. This method utilizes the hyperbolic sine function and fractional-order integral sliding mode surface, resolving the dilemma faced by traditional slide mode controllers (SMC) in balancing fast response and reduced vibration. Additionally, to enhance the system’s disturbance rejection capability, a sliding mode torque observer (SMTO) is designed to continuously update the observed load torque value into the NSMC controller, achieving speed compensation control. Finally, through comparative experiments among the proportional integral controller (PI), SMC, NSMC, and NSMC + SMTO, the results indicate that the proposed NSMC + SMTO exhibits the best speed response, steady-state characteristics, and disturbance rejection capability.

Performance study of the JadePix-3 telescope from a beam test

We present the results of a beam test conducted on a telescope using the JadePix-3 pixel sensor, developed with TowerJazz 180 nm CMOS imaging technology. The telescope is composed of five planes, each equipped with a JadePix-3 sensor with pitches of 26 × 16 µm2 and 23.11×16 µm2. In addition, it features an FPGA-based synchronous readout system. The telescope underwent testing using an electron beam with energy ranging from 4 to 6GeV. At an electron energy of 5.4GeV, the telescope demonstrated superior spatial resolutions of 2.6 and 2.3µm in two dimensions. By designating the central plane as the device under test, we evaluated the JadePix-3 sensor’s spatial resolutions as 5.2 and 4.6µm in two dimensions, achieving a detection efficiency of over 99.0%.

Observers for hyperbolic systems with multiple delays in the nonlocal boundary condition and its application to secure image encryption

In this article, we propose a step-by-step observer design for a first-order linear hyperbolic system with multiple delays in the nonlocal boundary condition. In the proposed approach inspired by the backstepping methodology, the observer gains are obtained following seven successive steps. Next, we present the application of this observer design in the context of image encryption. We consider a system where a local nonlinear term causing a chaotic vibration is added to the nonlocal boundary condition with time lags. A synchronization system for this chaotic system can be constructed using the same observer design method. The chaotic states generated by both systems can be used to encrypt and decrypt image data. The time lags, and weight functions included in the nonlocal boundary condition play the role of common encryption keys. By considering a system that includes arbitrarily many delays, this approach allows for a significant increase in the number of common encryption keys compared to conventional methods, resulting in greatly improved communication security.

Optimal position collaborative control of dual permanent magnet synchronous motor system

In order to improve the control accuracy and synchronous performance of the multi-motor control system, this paper proposes an optimal position collaborative control strategy for dual permanent magnet synchronous motor system. Firstly, based on the mathematical model of permanent magnet synchronous motor, an incremental predictive model is established to suppress constant and slow time-varying disturbances caused by changes in rotational inertia and load torque. Afterwards, the predicted compensation amount after multi-step prediction is obtained by minimizing the cost function which contains the synchronous error and tracking error simultaneously, and compensated to the given current loop in advance without changing the original dual motor system structure. Then the controllability and observability of the system are analyzed, and it can be proved that the system is asymptotically stable based on the optimal control theory. Secondly, considering the constraints such as maximum voltage and current limits, the optimal solution under the constraints is output to obtain the reference currents i q1 and i q2. Finally, it is demonstrated through the experiments that the proposed control strategy can achieve advance prediction compensation control of synchronous error, and the dynamic response speed is improved, while ensuring its steady-state performance remains unchanged.

Dynamic Validation of Calibration Accuracy and Structural Robustness of a Multi-Sensor Mobile Robot.

For mobile robots, the high-precision integrated calibration and structural robustness of multi-sensor systems are important prerequisites for ensuring healthy operations in the later stage. Currently, there is no well-established validation method for the calibration accuracy and structural robustness of multi-sensor systems, especially for dynamic traveling situations. This paper presents a novel validation method for the calibration accuracy and structural robustness of a multi-sensor mobile robot. The method employs a ground-object-air cooperation mechanism, termed the "ground surface simulation field (GSSF)-mobile robot -photoelectric transmitter station (PTS)". Firstly, a static high-precision GSSF is established with the true north datum as a unified reference. Secondly, a rotatable synchronous tracking system (PTS) is assembled to conduct real-time pose measurements for a mobile vehicle. The relationship between each sensor and the vehicle body is utilized to measure the dynamic pose of each sensor. Finally, the calibration accuracy and structural robustness of the sensors are dynamically evaluated. In this context, epipolar line alignment is employed to assess the accuracy of the evaluation of relative orientation calibration of binocular cameras. Point cloud projection and superposition are utilized to realize the evaluation of absolute calibration accuracy and structural robustness of individual sensors, including the navigation camera (Navcam), hazard avoidance camera (Hazcam), multispectral camera, time-of-flight depth camera (TOF), and light detection and ranging (LiDAR), with respect to the vehicle body. The experimental results demonstrate that the proposed method offers a reliable means of dynamic validation for the testing phase of a mobile robot.

Analysis of arc stability of plasma main arc and inter-wire arc in skew-coupling arc welding

By adjusting the inter-wire arc (IWA) posture, the skew-coupling arc (SCA) is proposed to address the polar effect in the cross arc, enabling decoupling control of heat, force, and mass transfer. Despite the advancement, the arc stabilization mechanism in the SCA remains poorly understood, hindering its application as a heat source in welding or additive manufacturing. To elucidate this mechanism, various influencing factors such as power supply characteristics, shielding gas composition, IWA posture, and plasma main arc (PMA) were analyzed. An electrical signal and high-speed camera synchronous acquisition system was utilized to analyze current-voltage waveforms and arc shapes. The results indicate that the arc stability of the SCA can be enhanced by ensuring specific external conditions. Constant voltage power supply enhances the self-regulating effect of the IWA, maintaining the IWA and the PMA in a hybrid state at all times. Introducing an oxidizing gas to the shielding gas can effectively suppress cathode spot climbing and stabilize the IWA. The vertical spacing between wires directly impacts the PMA deflection, while the wire horizontal angle has a lesser effect. The heat-regulating effect of the PMA column boosts the arc length regulation by the IWA. The current and the ion gas flow rate in the PMA minimally influence the SCA stability. These findings can provide a solid foundation for further applications of the SCA as heat source.

Consensus-Based Formation Control with Time Synchronization for a Decentralized Group of Mobile Robots.

The development and study of an optimal control method for the problem of controlling the formation of a group of mobile robots is still a current and popular theme of work. However, there are few works that take into account the issues of time synchronization of units in a decentralized group. The motivation for taking up this topic was the possibility of improving the accuracy of the movement of a group of robots by including dynamic time synchronization in the control algorithm. The aim of this work was to develop a two-layer synchronous motion control system for a decentralized group of mobile robots. The system consists of a master layer and a sublayer. The sublayer of the control system performs the task of tracking the reference trajectory using a single robot with a kinematic and dynamic controller. In this layer, the input and output signals are linear and angular velocity. The master layer realizes the maintenance of the desired group formation and synchronization of robots during movement. Consensus tracking and virtual structure algorithms were used to implement this level of control. To verify the correctness of operation and evaluate the quality of control for the proposed proprietary approach, simulation studies were conducted in the MATLAB/Simulink environment, followed by laboratory tests using real robots under ROS. The developed system can successfully find application in transportation and logistics tasks in both civilian and military areas.

Hybrid fiber-based time synchronization and vibration detection system.

We propose a hybrid fiber-based time synchronization and vibration detection system. The vibration is detected by exploring the idle light of the time synchronization system, i.e., the Rayleigh backscattering of the timing pulse disseminated in the fiber link. The addition of a sensing function does not affect the performance of time synchronization. In the multiuser experimental demonstration, time deviation results are 3.6 ps at τ = 1 s and 1.4 ps at τ = 104 s on the 40-km fiber link. Meanwhile, the hybrid system can accurately detect and locate vibrations occurring on the link. This method enables multiple functions of the optical fiber network without occupying extra optical channels. Moreover, it gives a possible solution for enhancing the security of the time synchronization network through vibration detection.

Designing a Motion-Onset Visual-Evoked Potential-Based Brain–Computer Interface to Control a Computer Game

Brain-computer interface (BCI) establishes an alternative direct communication channel between the brain and computer or other external devices. Motion-onset visual evoked potential (mVEP) related to the individual perception of movement is among synchronous BCI system that utilizes external stimulus. mVEPs stimulation paradigm is like an oddball stimulation paradigm. Researchers have recently been investigating mVEPs to control a computer game. To control a computer game, they used translation stimulus to evoke these potentials in EEG brain signals. In this study, we examine designing a computer game with four different types of stimuli, including translation, contraction, expansion, and rotation. We also used time-domain and wavelet coefficients for the feature extraction. Also, we used different types of linear discriminant analysis (LDA) classification methods, including least absolute shrinkage and selection operator (LASSO), stepwise LDA (SWLDA); moreover, and spatial-temporal discriminant analysis (STDA) for detecting the target stimulus. Our results demonstrate that contraction, expansion, and rotation stimuli, as well as translation, could be employed to control a BCI game. Our results showed that subjects got higher scores, game accuracy control, and information transfer rate using the rotation stimulus with SWLDA/STDA classification methods.

Experimental investigation into lock-in characteristics of the composite hydrofoils

Abstract This study experimentally investigates the lock-in characteristics of structural vibration of hydrofoils made of CFRP composite material. The synchronous experimental measurement system constituted of high-speed framing camera, LDV, velocity and pressure regulation systems are set up. It can be found that the Com+45° hydrofoil accelerates the cavitation inception, and the Com-45° hydrofoil defers it. The evolution of the dominant vibration frequency and cloud cavity shedding frequency are semblable. As the cavitation evolution gradually develops, the larger dominant frequency reduces, while the lower frequency remains unchanged. The scope of frequency lock-in meets the magnitude relationship Com+45° hydrofoil> Com-45° hydrofoil> Com0° hydrofoil. The wavelet transformation of structural vibration displacement and non-dimensional cavity area shows that both f shed and f shed,lock-in exist in the lock-in condition.