Optimized structural sandwich panels with minimum delamination hazards

Structural sandwich panels with two-dimensional cellular core are subject to an increased delamination hazard. This effect is caused by an incompatibility in the modes of deformation associated with the cellular core and the homogeneous face sheets. The aim of the present study is the minimization of the delamination hazard induced by this deformation incompatibility. The delamination hazard is assessed by means of an energetic criterion based on the additional strain energy stored in the cell walls next to the face sheets. This strain energy is minimized by a variation of the core geometry using a sequential quadratic programming method while constraints with respect to the geometry and the global structural performance are applied. In two examples, a significant optimization potential with respect to the delamination hazard is made accessible without any loss in global structural performance and overall weight.     

Process for design optimization of honeycomb core sandwich panels for blast load mitigation

A general process for optimization of a sandwich panel to minimize the effects of air blast loading is presented here. The panel geometry consists of two metal face plates with a crushable honeycomb or other type of core. Optimization is necessary as there is strong coupling between the several variables and the physics, which makes parametric studies relatively ineffective. Virtual testing is used to develop a homogenized model for the stress–strain curve of the honeycomb core, which can be readily applied to other types of cellular core. The homogenized model has been validated by comparison to existing results as well as to results from detailed finite element (FE) models. A design of experiments (DOE) based response surface optimization method in combination with LS-DYNA is used to minimize dynamic deflection or acceleration of the back face plate. Constraints on total mass and on plastic strain in the face plates are imposed. The mechanism of lowering the backface deflection is by increasing front face plate thickness which effectively distributes the blast load to a larger area of the core and avoids local concave deformation of the front face plate. Further, core depth is increased which increases panel stiffness. For acceleration minimization, results again produce a stiffer front face plate, but accompanied by a sufficiently soft core. The mechanism of lowering the backface acceleration is by absorbing energy with low transmitted stress. A clear cut comparison between monolithic metal plates and sandwich plates, for the same loading and failure criteria, is presented here.     

Optimum core design to improve noise attenuation performance and stiffness of sandwich panels used for high-speed railway vehicles

Structural and Multidisciplinary Optimization - In this study, we optimally design the core of a metal sandwich panel used in high-speed railway vehicles to minimize the amount of metal solid in...     

热防护系统的无线温度监测技术发展

阐述了温度无线传感技术在热防护系统健康监测中应用的发展与现状;概括地阐明了被动式SensorTag这种无线微传感装置的工作原理和特点,分析了该装置在高温下的工作能力和设计方面存在的问题;总结了主动式无线传感装置的发展与试验测试,比较分析了被动式和主动式无线传感装置的相同点和不同点,指出了各自的优点和不足,并总结了高温无线温度微传感装置今后努力的方向。     

A computational methodology to select the best material combinations and optimally design composite sandwich panels for minimum cost

A procedure to select the best material combination and optimally design sandwich laminates with fibre reinforced skins and low density cores for minimum cost is described. Sandwich constructions generally provide improved stiffness/mass ratios and provide more tailoring opportunities than monolithics, and thus greater chance of satisfying design constraints. The objective of the optimisation is to minimise the laminate cost by selecting the skin and core material combination, layer thicknesses and skin fibre angles optimally, subject to load and mass constraints. As the optimisation problem contains a number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The methodology and its benefits are demonstrated using graphite, glass or kevlar/epoxy facings, and balsa or PVC cores.     

Dynamic output feedback integral sliding mode control design for uncertain systems

This paper addresses the problem of designing a dynamic output feedback sliding mode control algorithm for linear MIMO systems with mismatched parameter uncertainties along with disturbances and matched nonlinear perturbations. Once the system is in the sliding mode, the proposed output‐dependent integral sliding surface can robustly stabilize the closed‐loop system and obtain the desired system performance. Two types of mismatched disturbances are considered and their effects on the sliding mode are explored. By introducing an additional dynamics into the controller design, the developed control law can guarantee that the system globally reaches and is maintained on the sliding surface in finite time. Finally, the feasibility of the proposed method is illustrated by numerical examples. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis and design of integral sliding manifolds for systems with unmatched perturbations

The robustness properties of integral sliding-mode controllers are studied. This note shows how to select the projection matrix in such a way that the euclidean norm of the resulting perturbation is minimal. It is also shown that when the minimum is attained, the resulting perturbation is not amplified. This selection is particularly useful if integral sliding-mode control is to be combined with other methods to further robustify against unmatched perturbations. H/sub /spl infin// is taken as a special case. Simulations support the general analysis and show the effectiveness of this particular combination.     

Efficient simulation of low-velocity impacts on composite sandwich panels

For efficiently simulating the damage resistance of sandwich panels subjected to low-velocity impacts, the finite element based damage tolerance tool CODAC has been enhanced. While sandwich structures are very weight efficient and provide integrated acoustic and thermal insulation, impact damage can provoke a significant strength and stability reduction. Therefore, the objective of CODAC is to provide methodologies which reliably simulate impact events and predict impact damage sizes. Since frequent design loops require a quick analysis, efficient deformation and failure models are desired. To achieve a rapid and accurate stress analysis, a recently developed three-layered finite shell element is applied. Failure analysis is based on a progressive damage mechanics approach: Damage initiation is detected by stress-based failure criteria. Material resistance is reduced by appropriate, step-wise linear degradation models. An experimental impact test program on honeycomb sandwich panels is used to validate the impact simulation of the FE-tool CODAC. Comparisons between impact tests and simulations showed that CODAC is capable of accurately and rapidly simulating impact events, which induce barely visible damage. Furthermore, the onset of clearly visible damage is correctly predicted.     

Experimental and numerical characterization of honeycomb sandwich composite panels

In this paper, an experimental investigation, an analytical analysis and a numerical model of a typical four-point bending test on a honeycomb sandwich panel are proposed. The honeycomb core is modelled as a single solid layer of equivalent material properties. Analytical and numerical (finite element) homogenization approaches are used to compute the effective properties of the honeycomb core. A general kinematic model (unified formulation) has been adopted and used for the modelling of honeycomb sandwich panel submitted to the bending test. A comparative study of major classes of representative theories has been considered. Qualitative and quantitative assessments of displacement, stress have been presented and discussed.     

Unified parametric approaches for high-order integral observer design for matrix second-order linear systems

A type of high-order integral observers for matrix second-order linear systems is proposed on the basis of generalized eigenstructure assignment via unified parametric approaches. Through establishing two general parametric solutions to this type of generalized matrix second-order Sylvester matrix equations, two unified complete parametric methods for the proposed observer design problem are presented. Both methods give simple complete parametric expressions for the observer gain matrices. The first one mainly depends on a series of singular value decompositions, and is thus numerically simple and reliable; the second one utilizes the right factorization of the system, and allows eigenvalues of the error system to be set undetermined and sought via certain optimization procedures. A spring-mass-dashpot system is utilized to illustrate the design procedure and show the effect of the proposed approach.     

Unified parametric approaches for high-order integral observer design for matrix second-order linear systems

A type of high-order integral observers for matrix second-order linear systems is proposed on the basis of generalized eigenstructure assignment via unified parametric approaches. Through establishing two general parametric solutions to this type of generalized matrix second-order Sylvester matrix equations, two unified complete parametric methods for the proposed observer design problem are presented. Both methods give simple complete parametric expressions for the observer gain matrices. The first one mainly depends on a series of singular value decompositions, and is thus numerically simple and reliable; the second one utilizes the right factorization of the system, and allows eigenvalues of the error system to be set undetermined and sought via certain optimization procedures. A spring-mass-dashpot system is utilized to illustrate the design procedure and show the effect of the proposed approach.     

Controller design for parabolic distributed parameter systems using finite integral transform techniques

A procedure is presented for designing a control system for distributed parameter systems of parabolic type based on the reduced-order decoupled state-space model obtained by a finite integral-transform technique. A Kalman filter is used as an observer to estimate the state variables, and state feedback control is performed. The method was applied to a one-dimensional heat conduction process and a moving bed adsorber. Both state estimation and control performances were satisfactory in spite of the model and parameter uncertainties. Following this controller design approach, the searching algorithms for the optimal sensors' and the optimal actuators' allocation problems were solved. These algorithms were applied to a one-dimensional heat conduction process in order to confirm the state estimator and controller performance. The fastest state estimation could be achieved by assigning the sensors at the optimal locations and the desired state distribution was realized with a few actuators located at the optimal positions.     

高速列车司机室三明治板的耐碰撞性能仿真

为验证高速列车司机室三明治板的被动安全设计是否符合要求,参照UIC 651标准运用MSC Dytran软件对某高速列车司机室三明治板的耐碰撞性能进行仿真,分析碰撞后三明治板的变形、应力、能量吸收以及弹头的速度曲线,表明司机室三明治板的耐碰撞结构能满足设计要求.     

基于PCL的折叠式夹层板结构参数化建模

折叠式夹层板具有优越的力学性能,在有限元分析中,由于夹层板结构复杂,建模工作量大.针对这些问题,基于PCL对Patran进行二次开发,通过输入夹层板尺寸和网格数量等参数实现V形折叠式夹层板结构的参数化建模.编制折叠式夹层板建模界面,实现夹层板结构有限元分析参数化,提高建模效率,为夹层板结构设计提供支撑.     

片上网络路由节点优化设计

针对虚输出队列结构的路由节点所构成的片上网络(NoC),提出了一种定制化路由节点中各个虚拟通道缓存大小的方法,以提高片上网络的整体通信性能。在有限的片上缓存资源约束下,分析各个虚输入队列中缓存大小对数据通过片上网络的平均延迟的影响,并在此基础上提出一种缓存资源配置方法,以便将缓存资源分配到片上网络通信瓶颈处,从而在不增加缓存资源开销的情况下提高片上网络的通信性能。最后通过仿真验证了路由节点优化设计对提高片上网络性能的可行性,并同未优化的路由节点构成的片上网络性能进行了比较。     

Sensitivity integral relations and design trade-offs in linearmultivariable feedback systems

The purpose of this paper is to develop integral relations regarding the singular values of the sensitivity function in linear multivariable feedback systems. The main utility of these integrals is that they can be used to quantify the fundamental limitations in feedback design which arise due to system characteristics such as open-loop unstable poles and nonminimum phase zeros and to such fundamental design requirements as stability and bandwidth constraints. We present extensions to both the classical Bode sensitivity integral relation and Poisson integral formula. These extended integral relations exhibit important insights toward trade-offs that must be performed between sensitivity reduction and sensitivity increase due to the aforementioned system characteristics and design constraints. Most importantly, these results display new phenomena concerning design limitations in multivariable systems which have no analog in single-input single-output systems     

Two-step design of critical control systems using disturbance cancellation integral controllers

An efficient critical control system design is proposed in this paper. The key idea is to decompose the design problem into two simpler design steps by the technique used in the classical loop transfer recovery method (LTR). The disturbance cancellation integral controller is used as a basic controller. Since the standard loop transfer recovery method cannot be applied to the disturbance cancellation controller, the nonstandard version recently found is used for the decomposition. Exogenous inputs with constraints both on the amplitude and rate of change are considered. The majorant approach is taken to obtain the analytical sufficient matching conditions. A numerical design example is presented to illustrate the effectiveness of the proposed design.     

基于非光滑观测器的带死区三明治系统状态估计

在控制工程实际中,许多含有死区的系统可以用带死区的三明治系统描述．本文针对带死区的三明治系统特点,构建了一种非光滑观测器以对系统状态进行估计．首先根据带死区三明治系统的特点,由分离原理,建立了描述系统特性的非光滑状态空间方程．据此构造了能够随系统工作区间变化而自动切换的非光滑观测器,给出了相应的收敛定理及其证明．最后通过仿真,分别比较了非光滑观测器和传统的观测器对状态的跟踪效果,比较结果表明非光滑观测器对于带死区三明治系统状态变量估计的准确性要优于传统的观测器．     

基于非光滑观测器的间隙三明治系统状态估计

在工业领域, 机械传动系统、液压系统等往往含有间隙特性, 这类系统可以用带间隙的三明治系统描述. 本文针对带间隙的三明治系统特点, 构建了一种非光滑观测器以对系统状态进行估计. 首先根据带间隙三明治系统的特点, 采用分离原理, 建立了描述系统特性的非光滑状态空间方程. 据此构造了能够随系统工作区间变化而自动切换的非光滑观测器, 给出了相应的收敛定理及其证明. 最后通过伺服液压系统的例子, 分别比较了非光滑观测器和传统的观测器对状态的跟踪效果, 比较结果表明非光滑观测器对于带间隙三明治系统状态变量估计的准确性要优于传统的观测器.