472 research outputs found
Formation control and collision avoidance for a class of multi-agent systems
No full textAbstract Not AvailableYutong Liu, Hongjun Yu, Peng Shi, Cheng-Chew Li
Seismic vibrations attenuation via damped layered periodic foundations
No full textIn recent years, a new type of seismic isolation system which exploits the filtering effect of bandgaps, named Periodic Foundation, has been proposed to isolate the upper structure from ground motion. To date, several works have been conducted to validate the feasibility and efficiency of this new isolation system. However, these works focused on the filtering effect related to the foundation periodicity, while energy dissipation due to materials absorption was ignored. To fill this gap, in this paper we investigate the effect of material damping on the performance of layered periodic foundations. Both the dispersion (related to the periodicity of the periodic foundation) and dissipation (related to the material damping of the periodic foundation) attenuation mechanisms, as well as their interaction, are investigated. First, the complex dispersion relation of a damped layered periodic foundation is formulated to assess the influence of material damping on the dispersive properties of the infinite periodic system. Second, the Riccati-transfer matrix method is used to calculate the dynamic transfer function of the damped layered periodic foundation, from which the energy dispersion and dissipation properties of the system are studied. Third, seismic responses of six-story shear-type buildings equipped with a solid foundation (fixed base), a traditional base isolation (i.e., equivalent of a layered periodic foundation with one unit-cell) and a layered periodic foundation with three unit-cells, are studied and compared. In more detail, the pseudo-excitation method is used to deal with non-classical damped systems under seismic accelerations for different soil conditions. Results show that, thanks to the filtering effect of the layered periodic foundation, the seismic responses of the upper structure are significantly mitigated within the expected frequency attenuation zone. Furthermore, including material damping leads to a further reduction of the upper structure seismic response, within the pass bands. Overall, the seismic performance of the upper structure under ground motions in different site conditions is improved by employing a damped layered periodic foundation with more than one unit cell
Shi ji en yuan Xu Beihong yu Liu Haisu
No full textJin dai Zhongguo she hui de yunjue bo gui, jue ding le Zhongguo jin xian dai mei shu xing ge de fu za duo bian. Zhe yi xing ge duo duo shao shao ye ti xian zai jin xian dai mei shu jia shen shang. Xing zou yu si, huo wei zheng zhi qiang quan suo po, hou wei ming li suo huo, huo qu cong yu shang ye gu zhu, huo hun ji yu mou ge yi shu chao liu, zai zhe yang fu za hun luan de li shi yu jing zhong, mei shu jia neng cong duo da cheng du shang zhang kong zi ji de ming yun
Event-triggered probability-driven adaptive formation control for multiple elliptical agents
No full textIn this article, an event-triggered control scheme is proposed for a group of elliptical agents to achieve a predefined formation. The agents are assumed to have the same dynamics, and the control law for each agent is only updated at its event sequence based on its own minimum collision time and deviation time. The probability-driven controller is designed to prevent the stuck problem among agents. Mapping-adaptive strategy and angle-adaptive scheme based on the minimum collision distance are also developed. Two examples are presented to analyze and demonstrate the effectiveness and potential of the new eventtriggered adaptive control algorithm.Yutong Liu, Peng Shi, Hongjun Yu, and Cheng-Chew Li
A new approach of formation control formulti-agent systems with environmental changes
No full textIn this paper, a two-stage reconfiguration strategy is proposed for a group of agents to find their specially designated formation, which can be seen as a transition from the current states to the predefined formations. The specially designated formation occurs during the inter-task idle time in order to minimize the reconfiguration time. The basic specially designated formation is designed for dotted agents based on the optimal mapping relationships and current probabilities of the predefined formations. Then, the reconfiguration schemes are developed with the agents modeled as circles or ellipses to account for their physical shapes, and the problem of agent overlapping during the formation is addressed. Examples and simulation results are presented to analyze and demonstrate the effectiveness and potential of the new design techniques.Yutong Liu, Peng Shi, Cheng-Chew Lim, Hongjun Y
Adsorption of low cross-linking density hydrogel OMMT/acid hydrolysis lignin grafted polyacrylic acid for Cd (II)
No full text(M=Cd, Ni, and Mn) Janus Atomic Junctions for Plasmonic Energy Upconversion Boosted Multi‐Functional Photocatalysis
No full textRational design/synthesis of atomic-level-engineered Janus junctions for sunlight-impelled high-performance photocatalytic generation of clean fuels (e.g., H2O2 and H2) and valuable chemicals are of great significance. Especially, it is appealing but challenging to acquire accurately-engineered Janus atomic junctions (JAJs) for simultaneously realizing the plasmonic energy upconversion with near-infrared (NIR) light and direct Z-scheme charge transfer with visible light. Here, a range of new Cu7S4/MxSy (M=Cd, Ni, and Mn) JAJs are designed/synthesized via a cation-exchange route using Cu7S4 hexagonal nanodisks as templates. All Cu7S4/MxSy JAJs show apparently-enhanced photocatalytic H2O2 evolution compared to Cu7S4 in pure water. Notably, optimized Cu7S4/CdS (CCS) JAJ exhibits the outstanding H2O2 evolution rate (2.93 mmol g−1 h−1) in benzyl alcohol aqueous solution, due to the following factors: i) NIR light-impelled plasmonic energy upconversion induced H2O2 evolution, revealed by ultrafast transient absorption spectroscopy; ii) visible-light-driven direct Z-scheme charge migration, confirmed by in situ X-ray photoelectron spectroscopy. Besides, three different reaction pathways for H2O2 evolution are disclosed by in situ electron spin resonance spectroscopy and quenching experiments. Finally, CCS JAJ also exhibits super-high rates on H2 and benzaldehyde co-generation using visible-NIR light or NIR light. This work highlights the significance of atomic-scale interface engineering for solar-to-chemical conversion.Meijun Guo, Amin Talebian-Kiakalaieh, Bingquan Xia, Yiyang Hu, Hongjun Chen, Jingrun Ran, and Shi-Zhang Qia
Modelling the Dynamics of a CNC Spindle for Tool Condition Identification Based on On-Rotor Sensing
No full textCutting tool plays an important role in modern manufacturing industry, however, tool wear is unavoidable during machining which could reduce the efficiency. Aiming at studying an appropriate and efficient tool condition monitoring method to improve the accuracy of finished parts, the roughness of the turned surface, a novel On-Rotor Sensing (ORS) is installed on the rotating workpiece to obtain vibration signals. To get an in-depth understand of the vibration data, a multi-degree-of-freedom (MDOF) system consisted of spindle, chuck and workpiece is established and its multi-mode natural frequency is obtained by finite element model (FEM) method. It is found that the dynamic response of the spindle rotor determines machining accuracy in the turning process and shows that the first several modes in the frequency range within 2000 Hz are the main responses of the system, which can be effectively captured by the ORS. Especially, the spring stiffness is calibrated based on the FEM results and the accuracy of the dynamic modal responses of this model are verified when the mass of the workpiece decreases during the turning process. According to the results, two frequency bands are advocated for ORS based online monitoring of tool wear conditions.</p
Formation Control of Localised and Decentralised Robotic Swarms
No full textRobot swarms consist of multiple autonomous robots, which detect and interact with their local environments. The fundamental intelligence is observed when a chaotic swarm reaches a stable and orderly objective formation. The process is important because the objective formation is designed such that the swarm achieves more than the sum of its individuals. A formation is a set of positions or tasks, and intelligent swarms are capable of self-organising and task allocating. Given an objective formation, individuals of a swarm reach different objective positions and perform different tasks. This implies task allocation in different possible choices. For each individual, the path to its objective position is regarded as the efort to take, and the inclination to different objective tasks means different eforts. The challenge is that it needs to choose wisely in the interaction with its neighbourhood. Changes of choices are compromises and each progress to the objective position imposes in uence on its neighbourhood. The collective intelligence comes from series of individual decisions in the process. In this thesis, we consider four problems that arise with the challenge. We use techniques from graph theory and agent-based design to address them. Formation control algorithms should not impose heavy burden in the communication network. Thus, to start with, limited sensing and communication are assumed, and the robots have minimal access to each other's identity through locally established channels. The control strategy is proposed based on local optimisation and multi-object mapping for a team of robots. Robots are able to make mapping decisions based on local information. To achieve the local optimal mapping decisions for each robot, two novel multi-object mapping protocols are designed. The first protocol performs confict locating and resolving, and the second adopts a most-neighbour mapping strategy. The formation problem is further addressed for a scalable team of robots subject to limited sensing with no communication. The robots themselves are fully independent with no designated roles. Scalable objective formation design is proposed such that the robot formation is scalable. Under the assumption that the data transmission among the robots is not available, a novel controller and a protocol are designed that do not rely on communication. As the controller only drives the robots to a partially desired formation, a distributed coordination protocol is proposed to resolve the imperfections. The case is investigated where the objective formations are arbitrary and have fixed sizes. Multi-objective mapping is proposed for the individual robots to identify their positions in the objective formation. The fixed formation size induces mapping loops, and to avoid local optimum traps, an evaluation method imposes a weak restriction on the predened formation, rendering it almost arbitrary. To enhance the robustness, the minimal local topology is proposed, and to reduce the computation burden and avoid the infnite trajectory loop, the coordination protocol is modifed by introducing probability. The practical problem of collision avoidance is also studied. The leaderfollower scheme is implemented on a multi-robot platform. On the premise of coordinated control laws, globally desired formation is achieved. The same problem in the path-planning perspective is considered on a global scale. Disc obstacles are filtered and clusters are identified based on their intersections. The path planning algorithm is designed based on obstacle clusters.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 201
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