Subsonic flutter suppression using self-straining actuators

Analytical (rather than purely computational) study, using full continuum models of bending-torsion wing flutter in inviscid subsonic aerodynamics. Performance evaluation of self-straining actuators for flutter suppression. Time domain analysis — unsteady aerodynamics — using the theory of semigroups of operators. Root locus of aeroelastic modes and precise operational definition of flutter speed. Analytical relationship of flutter speed to structure parameters too complex. Numerical results for the Goland wing model with torsion mode flutter. Finding: while effective in increasing structure damping prior to flutter, self-straining controllers have little or no effect on the flutter speed.     

Flutter analysis of an articulated high aspect ratio wing in subsonic airflow

We present a methodology for calculating flutter speeds of a high aspect ratio flying wing articulated with point masses in inviscid air flow. This highly flexible wing configuration typically models a HALE (High Altitude Long Endurance) UAV (Unmanned Aerial Vehicle) type aircraft. To demonstrate the procedure, we perform flutter analysis on an actual articulated wing model and we investigate the dependence of the flutter speed on the number of loads mounted onto the structure and the number of panels comprising the flying wing for both varying and constant span. The results show that the flutter speed decreases as more panels and point masses are incorporated into the flying wing. On the other hand, the number of point masses mounted onto the structure has a small effect on the flutter speed if the wing span is kept constant.     

Operational space consensus of multiple heterogeneous robots without velocity measurements

This paper proposes a control algorithm for networks of multiple heterogeneous robot manipulators, which solves the leader–follower and the leaderless consensus problems in the operational space. In the leader–follower scenario, the controller ensures that all the robots in the network asymptotically reach a given leader pose (position and orientation), provided that, at least, one follower robot has access to the leader pose. Without a leader pose, in the leaderless problem, the robots asymptotically reach a pose of consensus. The controller is a simple distributed proportional plus damping injection (P+d) scheme which does not require velocity measurements. A singularity-free representation, unit quaternions, is used to describe the orientation of each manipulator. The paper presents some simulations, with a network of six 6-Degrees-of-Freedom (DoF) manipulators, and experiments, with a network of three 6-DoF manipulators, to show the effectiveness of the proposed controller.     

Distributed fuzzy learning sliding mode cooperative control for non-affine nonlinear multi-missile guidance systems via a prescribed performance observer

This paper focuses on the distributed fuzzy learning sliding mode cooperative control issue for non-affine nonlinear multi-missile guidance systems. The dynamics of each follower is non-affine form with unknown lumped factor. To estimate the unknown lumped factor, a generalized fuzzy hyperbolic model (GFHM) based prescribed performance observer (PPO) is proposed. Different from the traditional disturbance observers, a residual set of error transient behavior is incorporated additionally so that the peak phenomenon can be avoided. Meanwhile, an auxiliary system is employed to convert the system of each follower to augmented affine form. Then, a distributed fuzzy learning sliding mode cooperative control approach is designed which consists of two parts. The adaptive sliding mode control (SMC) part is designed to force the states to move along the predefined integral sliding surface. For the equivalent sliding dynamics, the distributed optimal control part with GFHM is developed to minimize the cooperative performance function. Thus, the stability and the optimality of the closed-loop system are guaranteed synchronously. Finally, all signals of closed-loop system are rigorously proved bounded and the multi-missile cooperative guidance scenario is applied to verify the effectiveness of proposed method.     

Active structural control for load mitigation of wind turbines via adaptive sliding-mode approach

This paper studies the load mitigation problem for wind turbines by using active tuned mass dampers. A state space model for the tower/nacelle system is established with the consideration of tower/blade interaction. The uncertainties that appear in the damping matrix and natural frequencies are also considered in the controller design. External loads acting on the tower including the drag force induced by winds and the absolute base shear induced by the rotating blades are involved, and shaping filters for online generating these loads are proposed which can be easily implemented in numerical simulations. An adaptive sliding-mode controller is proposed to handle the system uncertainties, external disturbances and hard constraint, and also to improve the overall performance of the wind turbine system. Numerical simulations are performed to demonstrate the effectiveness of the proposed control law.     

Structural control to minimize the dynamic response of Mindlin—Timoshenko plates

The problem of damping out the vibrations of a thick plate is solved using the optimal control theory of distributed parameter systems. The plate is modelled as a Mindlin- Timoshenko plate to include shear effects and may exhibit viscous damping. The dynamic response of the structure comprises the displacement and velocity components which are combined with the amount of force expended in controlling the motion in a multiobjective cost functional. This functional is minimized with respect to distributed controls. A maximum principle is formulated to relate the control forces to adjoint variables, the use of which leads to the explicit solution of the title problem. The control over the plate is exercised by distributed moment and transverse forces which are in practice applied by means of torque and force actuators.     

Robust active suppression for body-freedom flutter of a flying-wing unmanned aerial vehicle

Flying-wing unmanned aerial vehicles have received extensive attention over the past decade because of their excellent aerodynamic and stealth performance. However, the aeroelastic interaction problems among unsteady aerodynamics, flight dynamics, and structural dynamics, such as the body-freedom flutter, are still open. This paper presents the study of a robust control scheme for active body-freedom flutter suppression of a flexible flying-wing unmanned aerial vehicle. The control objective is to expand the boundary of body-freedom flutter and to enhance the control robustness to external unknown disturbance simultaneously. The paper begins with the modeling procedure of a parameter-varying aeroservoelastic plant for the design of control law. Then, it presents how to synthesize a robust controller so as to suppress the flutter instability for a wide flight range of dynamic pressures. Afterwards, the paper shows how to analyze the flutter stability of the closed-loop system and the robustness of the controller, respectively. The numerical results demonstrate that the proposed robust controller can not only expand the flutter boundary of the unmanned aerial vehicle by 30%, but also exhibit the strong robustness to external disturbance.     

考虑摩擦与刹车制动力作用时的车桥耦合振动数值分析

为了研究车辆在桥面上行驰过程中突然刹车对桥梁产生的冲击振动的影响,考虑了车轮处的摩擦力与刹车制动力共同作用时移动质量模型对车桥的耦合振动现象进行数值模拟。对于工程中常用的变截面箱梁,推导了平面内呈线性和抛物线形变化时的质量阵,采用Romberg数值积分方法得到刚度矩阵中的系数项。对于变速行驰在桥面上的车辆出现紧急刹车的现象,考虑了车轮与桥面间的摩擦并引入冲击系数模拟刹车力对桥面的作用,探讨了摩擦系数与冲击系数对车桥耦合振动的影响。     

The transonic dip in aeroelastic divergence speed—An explicit formula

Using continuum models we develop a closed form analytical formula for the divergence speed as a function of the Mach number and in particular its dependence on wing camber. There is a transonic dip even when the angle of attack is zero and it depends on the wing thickness ratio. For nonzero camber the angle of attack in fact plays a lesser role. The main analytical tool is the Possio integral equation which is shown to have an explicit solution. Neither CFD nor FEM is employed.     

Modal analysis of turborotors using planar modes—theory

The generalized dynamic equations of motion have been obtained by the direct stiffness method for multimass flexible rotor bearing systems including the effects of gyroscopic moments, disc skew, and rotor acceleration. A set of undamped critical speed mode shapes calculated from the average horizontal and vertical bearing stiffness is used to transform the equations of motion into a set of coupled modal equations of motion. The modal equations are coupled by the generalized bearing coefficients and the gyroscopic moments. An analysis using only undamped critical speeds or decoupled modal analysis assuming proportional damping may lead to erroneous results. This paper presents a rapid method of calculating rotor resonance speeds with their corresponding amplification factors, stability and unbalance response of turborotors. Examples of the application of this modal approach are presented and results are compared to those of other methods such as matrix transfer analysis.     

非生产性企业技术授权的对象选择问题

本文建立了一个经济学模型,其中一个非生产性的技术研发企业决定如何向两个生产性企业转让降低成本的技术,两个生产性企业在产品市场上进行Stackelberg竞争。本文的研究表明,技术拥有企业的最优决策不仅取决于其技术创新的程度而且取决于技术转让的合同形式。在固定收费合同下,如果新技术的创新程度较低(高),那么技术拥有者偏好向先(后)进入市场的企业转让其技术;在特许权收费合同下,技术拥有企业会向两个企业同时授权其技术;但是在双重收费合同下,技术拥有者的最优策略是只向跟随企业转让其技术。三种合同相比,双重收费合同不仅会使技术拥有者的授权利润达到最大,而且会使社会福利水平达到最高,从而实现了企业个体目标与社会整体目标的完美一致。     

标准化技术许可中技术后进者的研发策略研究

在技术标准化的实施中,普遍存在着技术领先者对后进者的技术溢出,所以,后进者试图通过专利技术许可实现自身的技术积累和创新。在合约理论的框架内研究了标准化技术许可的演进:采用一个双边序贯投资模型,刻画了许可双方在单向许可下的得益和投资激励,并导致了劫持的后果。而后,基于后进者对核心技术进行局部改进的假设,引入回馈许可机制,并分别考察这一制度下许可双方的收益和研发状况。研究指出:(1)由于后进者谈判力的提升,领先者愿意与之进行交叉许可;(2)上述劫持被克服,后进者的投资和研发激励均得到提高。最后,对后进者提出了进一步的政策建议。     

Adaptive tracking control for nonlinear heterogeneous multi-agent systems with unknown dynamics

This paper is concerned with the tracking control problem for nonlinear heterogeneous multi-agent systems with a static leader, where the leader’s state is only available to a small portion of follower agents. The considered multi-agent system is composed of first- and second-order follower agents with unknown nonlinearities and unknown disturbances, and the communication graph of follower agents is fixed and directed. A robust adaptive neural network controller is designed for each follower agent. By applying the Lyapunov theory with the singular value analysis method, it is shown that all follower agents will synchronize to the leader agent with bounded residual errors. A numerical example is presented to demonstrate the effectiveness of the theoretical findings.     

Containment control of singular heterogeneous multi-agent systems

In this paper, we first consider the containment control problem of singular heterogeneous multi-agent systems, where all the followers converge to the convex hull spanned by the leaders. To solve this problem, we propose two distributed control laws: one is based on the state feedback control framework, which is suitable for the case that the full state information of each follower is accessible; and the other is based on the output regulation framework, where each follower only can access to its output. Furthermore, the distributed observers are designed for every follower to estimate the convex combination of the leader states which is determined by the communication graph. It should be noted that our results can also regard the non-singular multi-agent systems’ containment control problem as a special case. Finally, simulation results corroborate the effectiveness of our analytical results.     

模型翼拍动中动态柔性变形效应的数值研究

本文利用数值求解二维不可压缩Navier-Stokes方程，研究了在两种拍动基元运动中，模型翼动态柔性变形对其气动性能的影响。由柔性翼和刚性翼的结果比较发现，附加惯性效应是动态变形影响气动性能的主要原因，变形加速率决定了瞬时气动性能改变量的大小，相比之下，动态变形对气动性能时均值的影响则弱得多。     

车辆对不平整路面的随机动压力分析

采用双自由度四分之一车辆模型,以路面不平整和车辆发动机振动为激励,运用随机过程理论分析了车辆对不平整路面的随机动压力,得到了车辆动压系数的概率分布以及最大动压系数与路面不平整度、车速、悬挂质量以及悬挂系统与非悬挂系统特性之间的关系。算例分析表明,引起车辆振动的路面不平整波形的频率范围主要集中在0.04～2.0之间,最大动压系数随路面不平整度、车速、悬挂与非悬挂系统刚度的增大而增大,随着悬挂质量以及悬挂系统阻尼的增大而减少,而轮胎阻尼对车辆动荷载的影响并不显著。     

Distributed cruise control of high-speed trains

In this work, the cruise control problem of high-speed trains’ movements is investigated. Both cases of a single high-speed train and multiple high-speed trains are under consideration. Different with most existing studies where the centralized control or the decentralized control methods are adopted based on a single point mass model of the train, in this paper, a distributed control mechanism is proposed by virtue of the graph theory, and the high-speed train’s model is built as a cascade of point masses connected by flexible couplers. For a single high-speed train, the neighboring cars interact through the coupling force with each other, which can be described by a connected topological graph by regarding each car as a node. Besides, the speed information communication among the cars is considered to be described by another directed topological graph. A distributed control strategy is then developed, with which all the cars of a train track a desired speed asymptotically and the neighboring cars keep a safety distance from each other. For the multiple high-speed trains running on a railway line, the in-train force interaction topology and the speed information communication topology of all the trains are more complex than those of a single train. A new cluster consensus technique is developed, by which a distributed control law is designed. Under the control law, the trains can track the desired speeds asymptotically, the headway distance between adjacent trains and the distance between the neighboring cars of a train can be kept in appropriate ranges. Finally, simulations are provided to illustrate the effectiveness of the obtained theoretical results.     

高校科研团队领导语言框架与成员创新行为研究

与以往领导影响下属创新行为的研究多从正向促进视角切入不同，本研究探讨了高校科研团队中领导者积极/消极语言框架对科研人员创新行为的促进/抑制双向影响路径。通过采用三阶段式问卷调查法对高校科研团队中228位科研人员及其直接领导进行实证调研，回归分析结果显示：领导者积极语言框架与科研人员创新行为显著正相关，领导消极语言框架与科研人员创新行为显著负相关；同时，科研人员认知评价中介了领导者语言框架与科研人员创新行为间的关系；而且，领导—下属交换关系正向调节领导者积极语言框架对下属挑战性评价的影响作用。本研究对阐释高校科研团队中，领导者影响（促进/抑制）科研人员创新行为的心理机制具有重要的意义。     

Leader–follower decentralized optimal control for large population hexarotors with tilted propellers: A Stackelberg game approach

In this paper, we consider leader–follower decentralized optimal control for a hexarotor group with one leader and large population followers. Our hexarotor is modeled based on the quaternion framework to resolve singularity of the rotation matrix represented by Euler angles, and has 6-DoF due to six tilted propellers, which allows to control its translation and attitude simultaneously. In our problem setup, the leader hexarotor is coupled with the follower hexarotors through the followers’ average behavior (mean field), and the followers are coupled with each other through their average behavior and the leader’s arbitrary control. By using the mean field Stackelberg game framework, we obtain a set of decentralized optimal controls for the leader and N follower hexarotors when N is arbitrarily large, where each control is a function of its local information. We show that the corresponding decentralized optimal controls constitute an ϵ-Stackelberg equilibrium for the leader and N followers, where ϵ → 0 as N → ∞. Through simulations with two different operating scenarios, we show that the leader–follower hexarotors follow their desired position and attitude references, and the followers are controlled by the leader while effectively tracking their approximated average behavior. Furthermore, we show the nonsingularity and 6-DoF control performance of the leader–follower hexarotor group due to the novel modeling technique of the hexarotor presented in the paper.     

Can the inerter be a successful shock-absorber? The case of a ball-screw inerter with a variable thread lead

This paper investigates an application of a ball-screw inerter for mitigation of impact loadings. The problem of impact absorption is to provide a minimum reaction force that optimally decelerates and eventually stops an impacting object within the available absorber stroke. It significantly differs from vibration mitigation problems which are typical application of inerters. The paper demonstrates that the optimum absorption can be achieved by fully passive means. For known values of the object mass and inerter parameters, the obtained solution is independent of the impact velocity. The optimum passive absorption is achieved by employing a variable thread lead. As a result, two force components emerge, the typical inertance-related force and a damping-like term, and sum up to provide the optimum constant deceleration force. This result is relatively unique: conventional absorbers do not provide a constant force even with complex active control systems. Finally, an optimization problem is formulated to reduce the influence of process uncertainties (range of possible mass values, unknown friction). The results are verified and analyzed in a numerical example.