This paper investigates the problem of nonlinear path following control of underactuated marine vehicles in the horizontal plane. Firstly, appropriate kinematic and dynamic models are established, ...where the kinematic model is developed in terms of the relative velocity with respect to the ocean current disturbances, and the dynamic model is developed to include the effects of wind and wave disturbances. Based on the time delay control method and the reduced-order linear extended state observer (LESOs) technique, an improved compound line-of-sight (CLOS) guidance law is first proposed which can estimate the unknown sideslip angle and can compensate for the effects of time-varying ocean currents. Secondly, the control law is decomposed into the kinematic and dynamic controllers by the back-stepping technique. The high-order tracking differentiator is applied to construct derivatives of desired yaw angle, which are calculated by the CLOS guidance law. This approach resolves the problem of computational complexity inherent in the traditional back-stepping method and simplifies the overall controller. The lumped disturbances caused by waves and wind are estimated and compensated by the reduced-order LESOs. Finally, stability analysis of the closed-loop system is performed. The simulation results and comparative analysis validate the effectiveness and robustness of the proposed control approach.
This paper investigates the problem of spatial curvilinear path following control of underactuated autonomous underwater vehicles (AUVs) with multiple uncertainties. Firstly, in order to design the ...appropriate controller, path following error dynamics model is constructed in a moving Serret–Frenet frame, and the five degrees of freedom (DOFs) dynamic model with multiple uncertainties is established. Secondly, the proposed control law is separated into kinematic controller and dynamic controller via back-stepping technique. In the case of kinematic controller, to overcome the drawback of dependence on the accurate vehicle model that are present in a number of path following control strategies described in the literature, the unknown side-slip angular velocity and attack angular velocity are treated as uncertainties. Whereas in the case of dynamic controller, the model parameters perturbations, unknown external environmental disturbances and the nonlinear hydrodynamic damping terms are treated as lumped uncertainties. Both kinematic and dynamic uncertainties are estimated and compensated by designed reduced-order linear extended state observes (LESOs). Thirdly, feedback linearization (FL) based control law is implemented for the control model using the estimates generated by reduced-order LESOs. For handling the problem of computational complexity inherent in the conventional back-stepping method, nonlinear tracking differentiators (NTDs) are applied to construct derivatives of the virtual control commands. Finally, the closed loop stability for the overall system is established. Simulation and comparative analysis demonstrate that the proposed controller exhibits enhanced performance in the presence of internal parameter variations, external unknown disturbances, unmodeled nonlinear damping terms, and measurement noises.
•A robust controller for spatial curvilinear path following problem of underacutated AUV is proposed.•This is the first trial to tackle the unknown terms ̇α and ̇β in kinematic model as uncertainties.•The proposed controller is not dependent on accurate model and precise parameters estimation.•The nominal performance can be retained in the presence of multiple uncertainties.
The inductive debris detection is an effective method for monitoring mechanical wear, and could be used to prevent serious accidents. However, debris detection during early phase of mechanical wear, ...when small debris (<100um) is generated, requires that the sensor has high sensitivity with respect to background noise. In order to detect smaller debris by existing sensors, this paper presents a hybrid method which combines Band Pass Filter and Correlation Algorithm to improve sensor signal-to-noise ratio (SNR). The simulation results indicate that the SNR will be improved at least 2.67 times after signal processing. In other words, this method ensures debris identification when the sensor’s SNR is bigger than −3dB. Thus, smaller debris will be detected in the same SNR. Finally, effectiveness of the proposed method is experimentally validated.
•We build correlation model to study interference elimination for debris sensors.•We present a hybrid method to improve debris sensor capacity.•The SNR will be improved to at least 2.67 times by this method.•Smaller debris can be detected by this method in same initial SNR.
In order to meet the increasing reliability requirements of actuation system for large civil aircraft, the novel distributed dissimilar redundant actuation system composed of one hydraulic actuator ...(HA) and one electro-hydrostatic actuator (EHA) has been applied to the design of advanced aircraft. This configuration can greatly improve the system reliability and effectively avoid potential common-mode/common-cause (CM/CC) failure. However, this actuation configuration can exhibit force fighting problem between HA and EHA due to their different driving mechanisms and rigid coupling when they operate in the active/active mode, which may even cause damage to the control surface. To resolve this problem, an adaptive decoupling synchronous controller (ADSC) is proposed in this study. The coupling effect between HA and EHA is taken into account, and an adaptive decoupling controller is designed to eliminate the coupling term. Parameter adaption law is designed for the parametric uncertainties. In addition, a feed-forward compensator is proposed to compensate for the difference between HA and EHA by accelerating the dynamic response of EHA. Finally, the comparative simulation results indicate that the proposed ADSC controller has high speed/high robustness performances and can effectively reduce the force fighting between HA and EHA.
Although the six-ligament chiral structure has many unique properties, due to its special structure, the stress concentration is prone to defects. In addition, additive manufacturing is also prone to ...defects. This paper studies the effect of defects, which is helpful for the better application of the six-ligament chiral structure. Several new six-ligament chiral structures with random and concentrated defects were designed to explore the effects of the defects on the in-plane dynamic properties. The structures were studied with the finite element ANSYS/LSDYNA numerical simulation and experimental methods. According to the defect-free six-ligament chiral structures exhibiting different deformation modes at different impact velocities, the effects of the defect rate and type (concentrated and random defects) on the six-ligament chiral structure, the in-plane impact deformation mode and energy absorption characteristics are discussed. The research results show that the defect rate and type reduce the energy absorption characteristics of the chiral structure to varying degrees, and the impact deformation mode also changes under medium- and low-speed impact. With the increase in speed, the influence of the defects on the deformation mode weakens. Moreover, the effects of the concentrated and random defects on the platform stress are different. When the defect rate is low, the effect of the random defects is more significant, and as the defect rate increases, the effect of the concentrated defects is more obvious. The study can provide guidance for structural design, predict the failure form of structures containing defects when they are impacted, and realize material recycling.
Accelerated life test (ALT) is commonly used to assess lifetime of mission critical and expensive products. Accurate ALT requires realistic load sequence representative of the actual and/or expected ...work conditions. A novel method, using the Markov information matrix, is proposed in this paper to produce the load sequence to be applied in the ALT. The proposed method provides several advantages, including improved efficiency as well as capturing dynamic characteristics of the loading conditions, such as transition frequency and cumulative time effect of the load. This paper presents the Markov method for analyzing the load sequence, in which the Markov information matrix is modified by taking into account the cumulative effect of each load level. The model is then applied to the ALT of hydraulic piston pumps, which are widely used in aircraft, in order to perform analysis of the cumulative damage. Considering the actual aircraft operation, hidden Markov model is used to generate the equivalent accelerated load sequence of a pump. The load sequence can be easily applied on a test bench for the verification and approval of pumps. Finally, an accelerated sequence design method is proposed to guide the ALT. The method ensures the consistency of the transfer frequency and the cumulative damage caused by the load, which provides an equivalent sequence for the ALT.
A high-speed gearbox is special equipment used in industrial and aerospace application. The rotational speeds of these gearboxes can exceed 50,000 rpm, and any defect in the gears could result in ...catastrophic failure under such high speed. Hence, it is imperative to detect faults as early as possible. There are number of different methods applied in fault detection with various levels of success. In this paper, a condition monitoring for a high-speed gearbox based on the machine learning method is applied to classify evolutionary multi-faults of high-speed gearbox. The types of faults considered in this paper include pitting, pitting on alternate teeth, and tooth breakage. The rotational speed of a high-speed gearbox in this paper is in excess of 10,000 rpm. Face width of the pinion is about 15.28 mm, and the pitting is about 1.5 mm. Although it is easy to recognize serious faults such as tooth breakage, it is difficult to identify indicators for early fault initiation and growth. In this paper, feature extraction of combined time and frequency domains is proposed, including time-domain amplitudes and frequency-domain peaks from the 1st to the 8th harmonic, as well as the individual harmonic sideband values based on the signal’s power spectral density (PSD). Data normalization is applied to make data uniform, and backpropagation algorithm is used to reduce errors. The proposed machine learning method resulted in the training accuracy and testing accuracy of 100% and 98.75%, respectively. The method presented in this paper can provide early detection and recognition of the tooth health status in a high-speed gearbox.
The importance measure is a crucial method to identify and evaluate the system weak link. It is widely used in the optimization design and maintenance decision of aviation, aerospace, nuclear energy ...and other systems. The dissimilar redundancy actuation system (DRAS) is a key aircraft control subsystem which performs aircraft attitude and flight trajectory control. Its performance and reliability directly affect the aircraft flight quality and flight safety. This paper considers the influence of the Birnbaum importance measure (BIM) and integrated importance measure (IIM) on the reliability changes of key components in DRAS. The differences of physical fault characteristics of different components due to performance degradation and power mismatch, are first considered. The reliability of each component in the system is then estimated by assuming that the stochastic degradation process of the DRAS components follows an inverse Gaussian (IG) process. Finally, the weak links of the system are identified using BIM and IIM, so that the resources can be reasonably allocated to the weak links during the maintenance period. The proposed method can provide a technical support for personnel maintenance, in order to improve the system reliability with a minimal lifecycle cost.
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•Niobium’s SEE properties are of significant importance to the performance of accelerator cavities.•Accurate SEY measurements under different incident angles represent a technical ...challenge.•Positioning system allows for precise sample orientation and handling during experiment.•Measurement by mechatronic provides more accurate sample positioning.
Accurate measurement of Secondary Electron Emission (SEE) in scientific experiments provides better insight and understanding of field emission and multipacting properties in accelerator cavities. SEE properties of Niobium (Nb) are of significant importance to the performance and operation of accelerator cavities. Additionally, accurate Secondary Electron Yield (SEY) measurements from primary electrons generated from samples measured under different incident angles represent a technical challenge. For that purpose, the sample positioning system presented in this article is a design that allows for precise sample orientation and handling during single pump-down of the vacuum system in the experimental setup. Measurement techniques supported by a mechatronic system provide the means for acquisition of large quantities of data and at the same time reduce the experimental errors related to sample positioning. The authors describe a sample manipulation system and method for controlling the position of samples used for the measurement of SEY.
In recent years, the band gap characteristics of multiple ligament chiral structures have been a research hotspot. When the elastic wave is propagating, if the vibration frequency is within the band ...gap range, the vibration will be attenuated or suppressed to play the role of vibration reduction. In this paper, by introducing ligament defects and cell defects at different positions, the effect of defect types and positions on the vibration attenuation characteristics of the chiral structure is studied, and the results are obtained through numerical simulation. The results show that when the defects exist in the middle position, it has little effect on the band gap, and a lighter multi-ligament structure can be designed by introducing the form of the defects. When defects exist at the two ends, they have a greater impact on the band gap, and severely cause structural failure. This research can guide the application of chiral structures in engineering.
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