Distributed cooperative control for multiple quadrotor systems via dynamic surface control

This paper addresses the cooperative control problems of multiple quadrotor systems under fixed directed communication topologies. Dynamic surface control (DSC) is utilized to design nonlinear consensus controllers to make multiple quadrotors construct and keep a formation during flying. The control scheme is distributed so that each quadrotor updates the values of its information states based on the information states of its neighbors and its own states. Moreover, the leader–follower case is also discussed. In this case, distributed continuous schemes are also proposed with distributed sliding-mode observers, whose function is to estimate two linear combinations of the leader’s velocity and acceleration accurately in finite time. Finally, the effectiveness of the theoretical results is demonstrated via two examples.     

Bounded consensus tracking of second-order multi-agent systems using rectangular impulsive control

Nonlinear Dynamics - In this paper, the problem of bounded consensus tracking for second-order multi-agent systems is addressed with fixed and randomly switching directed topologies, wherein the...     

Group consensus of discrete-time multi-agent systems with fixed and stochastic switching topologies

This paper investigates the group consensus problem for discrete-time multi-agent systems with a fixed topology and stochastic switching topologies. The stochastic switching topologies are assumed to be governed by a finite-time Markov chain. The group consensus problem of the multi-agent systems is converted into the stability problem of the error systems by a model transformation. Based on matrix theory and linear system theory, we obtain two necessary and sufficient conditions of couple-group consensus for the case of fixed topology, and one necessary and sufficient condition of mean-square couple-group consensus for the case of stochastic switching topologies. Algorithms are provided to design the feasible control gains. Then, the results are extended to the case of multi-group consensus. Finally, simulation examples are given to show the effectiveness of the proposed results.     

双导弹拦截角度协同的微分对策制导律

为提高命中高价值目标的概率,基于线性二次型微分对策理论,对两枚导弹协同拦截单个目标的制导律进行了研究。单枚导弹在最小化自身脱靶量的同时,与另一枚导弹实现拦截角度上的协同,从而构成特定的拦截态势,以提高拦截机动目标的性能和末制导尾端对目标的可观测性。所推导的微分对策制导律考虑到了对策三方的控制系统动态,且具有解析解,形式上为零控脱靶量和零控协同拦截角误差的线性组合。基于推导结果完成了微分对策制导律的制导增益和对策空间分析,给出了鞍点解的存在条件,并进行了分析。非线性系统仿真结果表明由于导弹间存在显式的协同关系,拦截目标所需的加速度较低,且在设定的协同拦截角度收敛后,加速度会进一步减小。     

Event-based secure consensus of multiple AUVs under DoS attacks

In this paper, the event-based triggering method is adopted to investigate the secure consensus issue of multiple autonomous underwater vehicles (AUVs) under denial-of-service (DoS) attacks. DoS attack is a form of time-sequence-based cyber attack, which can destroy the normal service of the control target or network. First, based on an event-triggered mechanism, a novel secure control protocol is proposed. Second, the upper bounds of attack duration and attack frequency are given to ensure that multiple AUVs under DoS attacks can reach consensus. Third, an event-triggered mechanism with exponential variables is developed to avoid the continuous update of the controller, thereby reducing the burdens of communication and calculation. Zeno behavior can be strictly ruled out for each AUV under this triggering mechanism. Finally, the simulation results illustrate the feasibility of the proposed scheme.

     

采用捷联惯导系统的反辐射导弹抗关机制导方案研究

本文提出了一种基于被动雷达导引头＋捷联惯导系统的空地反辐射导弹复合制导方案。在此主制导方案的基础上，设计了“目标视线角优化估计”抗关机制导方案，建立了反辐射导弹抗关机性能评估准则，最后通过数学仿真，验证了本文所述方案的有效性。关键词     

Second-order consensus of nonlinear multi-agent systems with restricted switching topology and time delay

In this paper, a distributed protocol based on only relative position information is proposed for consensus of second-order multi-agent systems with inherent nonlinear dynamics and communication time delay. Compared with previous works, the distinguished feature of the paper lies in the directed interaction topology that is switching according to average dwell time (ADT) switching signals. Under the proposed protocol, we not only present sufficient conditions for ensuring consensus, but also explicitly give the lower bound of ADT for admissible switching signals. Numerical examples are provided to illustrate the performance of the proposed consensus algorithm.     

Sensor attack reconstruction for mobile robots via a switching Kalman fusion mechanism

Due to the poor security level in current industrial network, the control performance of robots may be severely affected by cyber attacks. This paper studies the sensor attack reconstruction problem of mobile robots, where a switching Kalman fusion mechanism is proposed to reconstruct the sensor attacks online. It is shown that the proposed mechanism is better than the existing extended state observer and event-triggered sensor attack reconstruction strategy. The experiment test demonstrates the effectiveness and superiority of the proposed method.

     

On the existence of periodic orbits and KAM tori in the Sprott A system: a special case of the Nosé–Hoover oscillator

The emergence of collective decision in swarming systems underscores the central role played by information transmission. Using network-control- and information-theoretic elements applied to a group of topologically interacting agents seeking consensus under switching topologies, the effects of constraints in the information capacity of the communication channel are investigated. This particular system requires us to contend with constantly reconfigurable and spatially embedded interaction networks. We find a sufficient condition on the information data rate guaranteeing the stability of the consensus process in the noiseless case. This result highlights the profound connection with the topological structure of the underlying interaction network, thus having far-reaching implications in the nascent field of swarm robotics. Furthermore, we analyze the more complex case of combined effect of noise and limited data rate. We find that the consensus process is degraded when decreasing the data rate. Moreover, the relationship between critical noise and data rate is found to be in good agreement with information-theoretic predictions. Lastly, we prove that with not-too-large time-delays, our system of topologically interacting agents is stable, provided the underlying interaction network is strongly connected. Using Lyapunov techniques, the maximum allowed time-delay is determined in terms of linear-matrix inequalities.     

Virtual target approach-based optimal guidance law with both impact time and terminal angle constraints

Nonlinear Dynamics - To attack a stationary target with both impact time and angle constraints, a novel two-stage guidance strategy is proposed based on the virtual target approach. A moving...     

Finite-time consensus of nonlinear multi-agent systems via impulsive time window theory: a two-stage control strategy

This paper concentrates on the finite-time consensus problem faced by nonlinear multi-agent systems (MASs) via impulsive time window theory with a two-stage control (TSC) strategy. The TSC strategy divides the whole control period into two parts: a variable impulsive control stage and a finite-time consensus control stage. Different from general single-stage control, TSC can dynamically adjust the time periods of impulsive control and finite-time control according to practical application requirements. Variable impulsive control is also discussed in this paper. Compared with the sampling based on traditional fixed impulsive theory, impulsive sampling in the TSC strategy occurs randomly within an impulsive time window and provides much more flexibility. In addition, a switching topology scheme is introduced in this paper to strengthen the stability of MASs. Finally, two numerical simulation examples (one leaderless case and one leader-following case) are used for the theoretical analysis.

     

Opinion Consensus with Delay When the Zero Eigenvalue of the Connection Matrix is Semi-simple

Two or more groups with different initial opinions can develop into a consensus with appropriate inter- and intra group interactions and communication delay. Here we consider the case when zero is a semi-simple eigenvalue of the normalized connection matrix, and we expand the concept of consensus where opinions of all individual agents must converge to the common (consensus) value to the weak consensus where opinions are clustered and the consensus value is no longer a scalar constant but a vector in a certain consensus subspace. The linearity of the system enables us to adopt an argument of Atay, using the phase space decomposition in terms of the standard bilinear form for functional differential equations, to derive sharp conditions for the system to reach a weak consensus, and to calculate the consensus vector. This calculation also informs how the consensus value of the coupled systems depends on the consensus of the subgroups, initial conditions and communication delay. We also point out the challenge of extending these results to nonlinear versions of the opinion dynamical systems with delay.     

Input-and-measurement event-triggered control for flexible air-breathing hypersonic vehicles with asymmetric partial-state constraints

In this paper, an input-and-measurement event-triggered control scheme considering asymmetric partial-state constraints is proposed for flexible air-breathing hypersonic vehicles (FAHV) subject to lumped disturbances and limited resources. To realize a precise disturbance rejection with decreased communication burden in sensor-to-control channels, intermittent measurement-based extended state observers using switching threshold samplers are developed in altitude and velocity subsystems, while the quantitative relationship between the upper bounds of observation errors and the design parameters of switching triggering mechanism is derived. Subsequently, to ensure the angle of attack (AoA) well within the allowable operational region and simultaneously achieve a reference tracking with expected characteristic, asymmetric constraints imposed on partial states including AoA, velocity, and altitude are embedded in design process, while a one-to-one nonlinear mapping is designed to avoid the violation of state constraint of AoA without enforcing feasibility conditions on virtual control laws, and a modified prescribed performance control is constructed to govern the output constraints of velocity and altitude, releasing the demand on the precise knowledge of initial states. Next, to maintain the resources occupation (energy and communication in controller-to-actuator channel) at low levels and ensure a desirable tracking precision, robust control laws based on switching event-triggered mechanisms are designed for FAHV to circumvent Zeno phenomena and compensate for the sampling error induced by event-triggered conditions. The simulation results and comparisons validate the effectiveness of the proposed scheme.

     

Leader-following formation control for second-order multiagent systems with time-varying delay and nonlinear dynamics

In this paper, the leader-following formation control problem for second-order multiagent systems with time-varying delay and nonlinear dynamics is considered. Two different cases of coupling topologies, fixed topology and switching topology, are analyzed. Based on the Lyapunov theory combined with the linear matrix inequality (LMI) method, sufficient conditions in terms of LMIs are given to ensure the multiagent systems can reach and maintain the desired formation. The simulation results are provided to demonstrate the effectiveness of the obtained theory results.     

Second-order consensus seeking in directed networks of multi-agent dynamical systems via generalized linear local interaction protocols

This paper focuses on the analytical study of final consensus convergence state of multi-agent dynamical systems by using a kind of generalized linear local interaction protocols. All the agents in the fixed directed network topology are governed by double-integrator dynamics. Almost all the existing linear local interaction consensus protocols can be considered as special cases of the present paper. By combining the algebraic graph theory and the matrix theory, some necessary and sufficient conditions are derived for reaching the second-order consensus. Moreover, the finial consensus convergence states of all agents are also be analytically determined. According to the obtained results, it is found that both the linear gains and the eigenvalues of the Laplacian matrix associated with the directed network topology play key roles in reaching consensus. Finally, the effectiveness and correctness of our theoretical findings are demonstrated by some numerical examples.     

Cryptanalysis and improvement of a three-party key agreement protocol using enhanced Chebyshev polynomials

Three-party key agreement protocol is an important cryptographic mechanism for secure communication, which allows two parties authenticate each other with the help of a trusted server. Very recently, Lai et al.’s proposed a novel three-party key agreement protocol using the enhanced Chebyshev chaotic map and claimed their protocol could withstand various attacks. Unfortunately, in this paper, we will show their protocol is vulnerable to the privileged insider attack and the off-line password guessing attack. To solve the problems, we propose an improved three-party key agreement protocol using the enhanced Chebyshev chaotic map. Security analysis and performance analysis show our protocol not only could withstand various attacks, but also has similar performance. Therefore, it is very suitable for practical applications.     

Quasi-static analysis of forces and stress for a novel two-step movable tooth drive

For sine movable tooth drive, the movable tooth number must be increased to obtain large speed ratio of the drive which increases largely radial size of the drive. Here, a novel two-step movable tooth drive is proposed. The drive can realize small size and large speed ratio simultaneously. For the two-step movable tooth drive, 3D design was done; the forces and the contact stress in the drive system were investigated; results show that the maximum force on the second step drive depends on radius of the movable teeth, size parameters of the second step drive, and radius of the sine ball track in the first step drive; the contact stresses between the meshing elements change periodically, the contact stress between the movable teeth and cap end is the maximum which can be taken as design factor for the load-carrying ability of the drive system.     

拦截高超声速飞行器的三维有限时间制导律设计

由于高超声速飞行器具有飞行速度快、机动能力强等特点,因此,传统的制导方式难以保证拦截弹拦截高超声速飞行器时的制导精度。为了减小弹目相对速度,降低对拦截弹的过载能力要求,按照前向制导方式,设计了有限时间收敛的三维前向滑模制导律。该制导律采用了连续的快速双幂次趋近律,不仅保证收敛速度快,同时削弱了传统制导律中存在的抖振现象。在此基础上为了处理系统扰动的上界未知的问题,又设计了自适应滑模制导律,该制导律既可以处理未知上界的外部扰动又可以保证第一种制导律所具有的良好特性。运用李雅普诺夫稳定性理论对所设计的滑模制导律进行了理论证明,最后,通过数值仿真验证了所设计制导律的有效性及优越性。     

A technique for digital steganography using chaotic maps

Chaos has been applied extensively in secure communication over the last decade, but most of the chaotic security protocols defined, are cryptographically weak or slow to compute. Also, study of chaotic phenomena as application in security area is not discussed in detail. In this paper, we have intensely studied chaos, their influence in secure communications and proposed a steganography technique in spatial domain for digital images based upon chaotic maps. By applying chaos effectively in secure communication, the strength of the overall anticipated algorithm has been increased to a significant level. In addition, few security statistical analyses such as correlation, entropy, energy, contrast, homogeneity, peak signal to noise ratio, and mean square error have also been carried out and shown that it can survive against various differential attacks such as the known message attack, known cover attack, known stego attack, and stego only attack.     

On the structure of the group g1 appearing in hyperelasticity

In the representation theorem for the stored energy function of a hyperelastic material, it is necessary to determine a subgroup g^*₁ of the symmetry group g of the stress tensor. It is the purpose of this note to study the construction of g^*₁ and its relation to the other subgroups ot g, viz. the commutator subgroup g_c and the orthogonal subgroup g₀.