Robust design of multiple trailing edge flaps for helicopter vibration reduction: A multi-objective bat algorithm approach

The objective of this study is to determine an optimal trailing edge flap configuration and flap location to achieve minimum hub vibration levels and flap actuation power simultaneously. An aeroelastic analysis of a soft in-plane four-bladed rotor is performed in conjunction with optimal control. A second-order polynomial response surface based on an orthogonal array (OA) with 3-level design describes both the objectives adequately. Two new orthogonal arrays called MGB2P-OA and MGB4P-OA are proposed to generate nonlinear response surfaces with all interaction terms for two and four parameters, respectively. A multi-objective bat algorithm (MOBA) approach is used to obtain the optimal design point for the mutually conflicting objectives. MOBA is a recently developed nature-inspired metaheuristic optimization algorithm that is based on the echolocation behaviour of bats. It is found that MOBA inspired Pareto optimal trailing edge flap design reduces vibration levels by 73% and flap actuation power by 27% in comparison with the baseline design.     

后缘小翼智能旋翼减振效果影响因素分析

建立了带后缘小翼智能旋翼气动弹性载荷计算模型及减振优化分析方法。模型考虑刚体后缘小翼的气动力与惯性力对弹性桨叶系统的影响,使用粘性涡粒子法结合翼型查表法计算旋翼气动载荷,采用力积分法计算桨叶与桨毂载荷,构造了包含桨叶根部扭转及桨毂振动载荷为目标函数的优化问题,基于最速下降-黄金分割组合优化算法寻找最佳小翼偏转规律。研究发现,建立的后缘小翼载荷控制方法有效,可降低振动目标函数70%。桨叶的弹性扭转使后缘小翼能有效实施减振,但弹性扭转对小翼气动力矩的放大作用使减振时通常伴随着桨叶扭转载荷增大的现象。     

直升机结构响应主动控制作动器优化设计研究

采用子结构综合法建立考虑作动器动特性与其相互影响的直升机机身／多作动器耦合系统频域数学模型，研究了直升机结构响应主动控制中采用作动器位置序号进行编码的遗传算法对多作动器位置进行优选，以及与电磁式惯性型作动器参数优化的综合优化问题，进行了结构响应主动控制试验研究，验证了多作动器减振的有效性和所提出的作动器位置优选方法的正确性。     

Non‐linear random response of laminated composite shallow shells using finite element modal method

This paper investigates the large‐amplitude multi‐mode random response of thin shallow shells with rectangular planform at elevated temperatures using a finite element non‐linear modal formulation. A thin laminated composite shallow shell element and the system equations of motion are developed. The system equations in structural node degrees‐of‐freedom (DOF) are transformed into modal co‐ordinates, and the non‐linear stiffness matrices are transformed into non‐linear modal stiffness matrices. The number of modal equations is much smaller than the number of equations in structural node DOF. A numerical integration is employed to determine the random response. Thermal buckling deflections are obtained to explain the intermittent snap‐through phenomenon. The natural frequencies of the infinitesimal vibration about the thermally buckled equilibrium positions (BEPs) are studied, and it is found that there is great difference between the frequencies about the primary (positive) and the secondary (negative) BEPs. All three types of motion: (i) linear random vibration about the primary BEP, (ii) intermittent snap‐through between the two BEPs, and (iii) non‐linear large‐amplitude random vibration over the two BEPs, can be predicted. Copyright © 2006 John Wiley & Sons, Ltd.     

A new simple asymmetric hysteresis operator and its application to inverse control of piezoelectric actuators

Piezoelectric actuators (PEAs) are commonly used as micropositioning devices due to their high resolution, high stiffness, and fast frequency response. Because piezoceramic materials are ferroelectric, they fundamentally exhibit hysteresis behavior in their response to an applied electric field. The positioning precision can be significantly reduced due to nonlinear hysteresis effects when PEAs are used in relatively long range applications. This paper describes a new, precise, and simple asymmetric hysteresis operator dedicated to PEAs. The complex hysteretic transfer characteristic has been considered in a purely phenomenological way, without taking into account the underlying physics. This operator is based on two curves. The first curve corresponds to the main ascending branch and is modeled by the function f1. The second curve corresponds to the main reversal branch and is modeled by the function g2. The functions f(1) and g(2) are two very simple hyperbola functions with only three parameters. Particular ascending and reversal branches are deduced from appropriate translations of f(1) and g(2). The efficiency and precision of the proposed approach is demonstrated, in practice, by a real-time inverse feed-forward controller for piezoelectric actuators. Advantages and drawbacks of the proposed approach compared with classical hysteresis operators are discussed.     

Numerical analysis of aerodynamic performance of rotors with leading edge slats

A three dimensional compressible Navier-Stokes analysis capable of computing flows around wings and rotors with partial-span flaps or slats is described. This analysis is cast in a moving body-fitted coordinate system permitting arbitrary motion of the solid surfaces to be directly modeled. This methodology is validated through several single and multi-element rotor and wing configurations. The analysis is subsequently applied to two helicopter rotors. The effects of leading edge slats on the aerodynamic performance of these rotors in hover is studied. It is demonstrated that leading edge slats can significantly improve the hover performance at high pitch settings, with an increase in thrust and a reduction in torque. At low pitch settings, the slats were found to be detrimental to the rotor performance. Many practical issues such as surface imperfections, proper sealing of the slat during retraction, control loads and other implementation aspects should be carefully evaluated in the event of a practical design of a slat. However, in the present study only the aerodynamic effects of slats are addressed and no practical issues are considered.This work was supported by the U.S. Army Research Office under the Center of Excellence in Rotorcraft Technology (CERT) program. Dr. Thomas Doligalski was the technical monitor.     

基于迟滞观测器的压电堆补偿控制

压电堆具有反应速度快、能量密度高等特点被广泛应用于精密仪器的作动装置。然而,压电堆输出位移与驱动电压之间存在的迟滞效应会严重影响控制精度。为了补偿迟滞效应带来的影响,提升控制效果,提出了一种基于滑模变结构理论的类Luenberger迟滞观测器,观测器的设计不仅考虑到了模型中的不确定因素,还可在一定程度上减小外部扰动带来的影响。根据反步滑模控制理论设计了一个基于迟滞补偿系统的跟踪控制器,控制器在设计过程中考虑到了观测器的迟滞补偿误差,且具有一定的鲁棒性。通过仿真及试验验证,证明了所设计的控制系统能够良好地对压电堆实施跟踪控制,且控制效果优于传统控制器。     

Finite element modelling and vibration control study of active plate with debonded piezoelectric actuators

A finite element model for a piezoelectric plate with edge debonded actuators is presented. This model is employed to investigate the effect of edge debonding on actuation authority, natural frequencies and vibration control performance. The regions of the plate with the piezoelectric patches are modelled such that each layer undergoes rotation due to shear deformation independently. The necessary constraints for continuity of displacements at the interfaces of the layers are imposed. The plate with edge debonded actuators is idealized by dividing it into debonded regions and healthy regions. A finite element procedure for imposing the constraints regarding continuity of displacements at the interfaces of the adjacent regions is developed and is implemented using MATLAB. Experiments are conducted for finding the actuation authority and natural frequencies of the plate with debonded actuators. It has been found that the developed model has predicted the mechanics of actuator debonding properly. The investigations have revealed the fact that the edge debonding of actuators will result in considerable degradation in actuation authority and vibration control performance.     

直升机结构响应主动控制飞行试验

为验证结构响应主动控制方法在直升机振动控制中的有效性,以某轻型直升机为验证机,基于具有在线识别功能的时域自适应控制算法,进行了直升机结构响应主动控制飞行试验研究。给出了飞行试验方法、试验系统组成、试验内容及其过程。通过对飞行试验数据的处理分析,对减振效果进行了评估。试飞结果表明:ACSR(Active Control of Structure Response)系统对各测点的垂向振动均有减振效果,各速度状态下的全机垂向减振效率在30%～66%之间,巡航速度状态下具有最佳的减振效率;此外,各测点的侧向振动水平也有一定程度的减小。     

Optimization of composite plates with piezoelectric stiffener-actuators under in-plane compressive loads

Stiffeners which are used to strengthen a plate can be constructed of piezoceramic materials and subsequently used as piezo actuators to improve the load carrying capacity of the plate. In the present study, a fibre composite plate with initial imperfections and under in-plane compressive loads is studied with a view towards minimizing its deflection using the piezo actuators and the fibre orientations. Piezoceramic stiffeners are bonded symmetrically on the top and bottom of the plate and deployed as actuators. Two cases of electric fields, namely, the in-phase and out-of-phase voltages are applied to the actuators. The presence of initial deflections leads to deformation under the in-plane compressive loads which should be less than the critical buckling load. Two cases of initial imperfections are considered, and the first one is the deterministic initial deflections which are known a priori and as such they are given as input parameters for the problem. In the second case the initial deflections are uncertain and they have to be obtained according to a given criterion. In the present study they are determined to produce the least favourable initial deflection (largest deflection) at a given point and the solution is obtained by convex modelling. The effect of the actuators, the ply angles and the voltage are studied and their effects on the transverse deflection are investigated. A performance index involving the L₂ norm of the deflections is minimized using the piezo effect and as well as the ply angles the optimal values of which are determined for various problem parameters.     

Piezo patch sensor/actuator control of the vibrations of a cantilever under axial load

The effect of axial force in the vibration control of beams is studied by means of an integral equation formulation, which facilitates the numerical solution of the problem of finding the eigenfrequencies and eigenfunctions of a freely vibrating beam controlled by piezo patch sensors and actuators. The basic formulation of the problem is given in terms of a differential equation which is converted to an equivalent integral equation formulation by introducing an explicit Green’s function. After approximating the kernel of the integral equation in terms of Fourier series based on the eigenfrequencies of the host structure, a method of solution is outlined which consists of expressing the integral equation as an infinite series of linear equations and using a finite of number of these equations in the numerical solution. Numerical results are obtained for different values of the gain, the axial load and for three patch sizes. The first three vibration frequencies of the controlled and uncontrolled beam are given. The tip deflections of the beam for different axial loads are also plotted to compare transient behaviour.     

Non‐linear finite element modal approach for the large amplitude free vibration of symmetric and unsymmetric composite plates

A theoretical analysis is presented for the large amplitude vibration of symmetric and unsymmetric composite plates using the non‐linear finite element modal reduction method. The problem is first reduced to a set of Duffing‐type modal equations using the finite element modal reduction method. The main advantage of the proposed approach is that no updating of the non‐linear stiffness matrices is needed. Without loss of generality, accurate frequency ratios for the fundamental mode and the higher modes of a composite plate at various values of maximum deflection are then determined by using the Runge–Kutta numerical integration scheme. The procedure for obtaining proper initial conditions for the periodic plate motions is very time consuming. Thus, an alternative scheme (the harmonic balance method) is adopted and assessed, as it was employed to formulate the large amplitude free vibration of beams in a previous study, and the results agreed well with the elliptic solution. The numerical results that are obtained with the harmonic balance method agree reasonably well with those obtained with the Runge–Kutta method. The contribution of each linear mode to the maximum deflection of a plate can also be obtained. The frequency ratios for isotropic and composite plates at various maximum deflections are presented, and convergence of frequencies with the number of finite elements, number of linear modes, and number of harmonic terms is also studied. Copyright © 2005 John Wiley & Sons, Ltd.     

羽翼形隔水管涡激振动抑制装置实验研究

基于鸟类翅膀尾缘锯齿外形的仿生学研究,提出了一种带有双羽翼形飘带结构的海洋钻井隔水管涡激振动抑制装置。对裸圆柱模型和带有不同尾缘外形、不同长度双飘带结构的圆柱模型进行水流模拟实验,应用粒子图像测速技术测量模型的尾迹流场,得到相应的尾迹流线图和涡量图。通过比较分析得:双飘带结构能有效减少水流中圆柱模型后方的旋涡,且飘带尾缘外形能影响圆柱周围的流场,尾缘锯齿形飘带可使旋涡的产生滞后。飘带长度为圆柱直径四倍左右时对旋涡的抑制效果较好。因此,羽翼形涡激振动抑制装置能有效抑制水下隔水管的涡激振动。     

Effect of warping-pretwist coupling on the natural vibration of torsionally clamped-pinned thin-walled open-profile bars

Exact natural frequencies are determined for the torsional vibration of pretwisted thin-walled open-profile bars having torsionally clamped and pinned end restraints. The equation of motion and boundary conditions are derived from a multifilament model of a pretwisted thin-walled bar undergoing warp deformation and a moderately large twist about the elastic axis. Closed-form torsional frequencies and mode shapes are derived from the linear terms of the resulting non-linear equations. As the length-to-leg ratio (L/b) and leg-to-thickness ratio (b/t) of typical open-profile bars are varied, the individual and collective effects of warping and pretwist on the non-dimensional torsional frequencies are demarcated. In addition, the closed-form solutions offered here reveal considerable destiffening of the torsional frequencies due to warping-pretwist coupling present in thin-walled bars having pretwisted, unsymmetrical, open-profiles and torsionally clamped and pinned end restraints. This coupling effect, which have been ignored in thin-walled bar vibration theories hitherto, is brought out by the Wagner effect and warping shear stresses acting on the profiles.     

穿孔损伤大小和方向对复合材料桨叶振动特性的影响

通过建立的全桨叶有限元模型, 研究了穿孔损伤的大小和方向对桨叶振动特性的影响。以桨叶根部z=50mm处矩形剖面和中部z=835mm处翼型剖面为研究对象, 分别在前缘、 翼盒和后缘模拟不同口径的穿孔损伤, 得到振动特性与穿孔损伤大小的关系, 并通过改变前缘的穿孔损伤方向, 得到振动特性与穿孔损伤方向的关系。结果表明, 穿孔损伤一般不会引起各阶振动模态的改变, 但会使各阶振动频率发生变化。随着损伤口径的增大, 各阶振动频率都降低。损伤发生在前缘和后缘, 摆振频率降低最多, 发生在翼盒, 扭转频率降低最多。穿孔方向对各阶振动频率的影响不仅与损伤的位置和结构有关, 还与损伤剖面的几何形状有关。对于根部矩形剖面, 穿孔方向与剖面弦向夹角为75°和105°对摆振频率影响最大, 对于中部翼型剖面, 夹角接近0°(180°)对摆振频率影响最大。      

变距/摆振耦合对直升机空中共振稳定性的影响

采用多桨叶坐标转换和复数坐标 变换等方法,研究了变距/摆振耦合对直升 机空中共振的影响;推导出完全引入变距/ 摆振耦合的直升机空中共振分析公式,建立 了相应的分析模型和计算程序。利用系统的 特征值研究了直升机空中共振的动不稳定性, 得出变距/摆振耦合对直升机空中共振的影响 ;通过系统的特征向量与各自由度之间的相互 作用（能量关系）的研究,揭示了空中共振机理 ,以某型直升机为例进行了计算分析。研究表明 ：正的变距/摆振耦合可以抑制旋翼/机体耦合 系统的动不稳定性,在同时存在挥舞/摆振耦合 和正的变距/摆振耦合时,直升机的旋翼/机体 耦合系统为绝对稳定。     

基于变弯度技术和协同射流的混合流动控制技术研究

现代飞机强调高速巡航特性且兼顾隐身特性,因此翼型往往采用厚度较小,前缘半径不大,弯度不大的薄翼型。这类翼型的低速气动性能较差,容易失速,限制了这类飞机的短距起降特性和载重能力,因此需要借助流动控制技术来改善低速特性。该文讨论新型的协同射流主动流动控制技术,同变弯度技术包括后缘变弯和前缘下垂技术等被动流动控制技术相结合,探索混合流动控制技术的流动控制机理和控制效果。基于数值模拟的结果发现:仅采用单一的流动控制技术在薄翼型上得到的控制效果有限,而将协同射流同变弯度技术结合的混合流动控制技术可同时发挥不同流动控制技术的优点(例如协同射流引起的后缘失速的推迟,下垂前缘带来的前缘失速推迟,后缘襟翼带来的零升迎角减小)。该文提供的混合流动控制方案可以将薄翼型的最大升力系数提升至C_Lmax=3.3127,相对原始构型提升了96%,具有广阔的工程应用前景。     

Boundary element simulation of inviscid flow around an oscillatory foil with vortex sheet

The dynamic performance of a rigid foil with harmonic vertical and rotational motions in fluid flow has been studied through velocity potential theory. A boundary element based time stepping scheme is introduced to simulate the flow around the foil and the vortex wake. The body surface condition is satisfied on the exact foil surface and the motion and deformation of the wake sheet shed at the trailing edge is tracked. Kelvin condition is satisfied and a Kutta condition for the unsteady motion is proposed to circumvent the singularity at the trailing edge. Point vortex, which is reduced from wake vortex dipole, is introduced to approximate the vorticity. The performance of foil NACA0012 with harmonic vertical and rotational motions are studied extensively; the propulsion/swimming mode, energy harvesting mode and the flying mode are analysed in detail.     

Shock Resistance of a Disk-Drive Assembly Using Piezoelectric Actuators With Passive Damping

Current dual-stage actuator design uses piezoelectric patches only, without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. Because they incorporate passive damping, the proposed actuators will improve the existing dual-stage actuators, giving them higher precision and better shock resistance. We report finite-element analyses of different types of piezoelectric actuators in a disk arm assembly under external shock and vibration. We modeled the viscoelastic damping layers in the hybrid actuators with the Prony series, whose parameters we determined from the dynamic frequency data of a nomograph. In the analyses, a shock impulse (175 g, 1 ms half sine) and a vibration impulse (350 g and 1 ms full sine) are applied at one end of the base, while the other end of the base is fixed. We evaluated and compared the responses of the disk arm assembly with different configurations of the piezoelectric actuators. The simulation results show that the enhanced active-passive hybrid actuator design would reduce the residual in-plane vibration induced during the shock, resist liftoff motion, and reduce the impact damage when the head slaps.     

Genetic algorithm based optimal design for vibration control of composite shell structures using piezoelectric sensors and actuators

The present article deals with the design of optimal vibration control of smart fiber reinforced polymer (FRP) composite shell structures using genetic algorithm (GA) based linear quadratic regulator (LQR) and layered shell coupled electro-mechanical finite element analysis. Open loop procedure has been used for optimal placement of actuators considering the control spillover of the higher modes to prevent closed loop instability. An improved real coded GA based LQR control scheme has been developed for designing an optimal controller in order to maximize the closed loop damping ratio while keeping actuators voltages within limit. Results show that increased closed loop-damping has been achieved with a large reduction of control effort considering control spillover.