A new decentralized stabilization design for large‐scale systems

Abstract

A decentralized stabilization problem for a large‐scale system composed of a number of subsystems is investigated. Using Lyapunov stability and the bounds of the solution of the Lyapunov equation, we derive two main results. The first result (Theorem 1) requires checking the negativity of a matrix containing two free parameters to test the decentralized stabilizability of the whole system. The second result (Theorem 2) determines the ranges of two free parameters to satisfy Theorem 1 such that the decentralized local state feedbacks guarantee the whole large‐scale system is stabilized. The matching condition for each subsystem is not necessary in this paper. The results are also summarized using a flow chart which represents the algorithm for decentralized stabilization.     

An efficient multilevel solution scheme for large scale non-linear systems

We present a new approach for the fast, efficient solution of large systems of non-linear equations arising from the finite element discretization. The proposed non-linear solver builds on the advantages of the popular methods of solution that are currently being employed, while eliminating most of their undesirable features. It combines the well-known BFGS method with the FAS version of the multigrid method, introduced by Brandt,¹ to form a fast, efficient solution method for non-linear problems. We present numerical performance studies that are indicative of the convergence properties as well as the stability of the new method.     

Efficient model reduction of large scale systems using Krylov-subspace iterative methods

In this work, the use of Krylov-subspace iterative methods is examined to obtain low-rank approximate solutions of Lyapunov equations for use in contol-oriented model reduction of large space structures. In particular, we examine the application of these methods to the approximate component cost analysis (CCA) of large scale systems. It is shown that using the proposed methods approximate CCA reduced-order models can be obtained with a significant reduction in the computational effort and time. In addition, we derive closed-form expressions for approximate cost-equivalent, cost-decoupled and covariance-equivalent realizations using the proposed Krylov-subspace solutions.     

Preparation of yttria-stabilized zirconia nanoplatelets using vacuum roll coating

Roll-to-roll vacuum coating on moving plastic substrates and the subsequent comminuting of the film into a flake or platelet with microscale lateral and thickness dimensions is an industrially mature technology utilized to produce clean, consistent material with high throughput. In this study, we describe the novel preparation of nanoplatelets by top-down vacuum evaporation of yttria-stabilized zirconium dioxides (YSZ) on a nanoembossed, moveable substrate for the purposes of making nanoplatelets. Microscopy and particle size analysis of the resulting YSZ nanoplatelets revealed that use of the nanoembossed substrate results in significant narrowing of the particle size distribution. However, while the YSZ coatings were conformal and successfully replicated the nanopattern of the underlying substrate, the stress in the film was inadequate to fracture the film into platelets that replicated the nanometer dimensions of the underlying pattern. It was determined that this is due to the inherent fracture toughness of the nanoplatelets and the augmented adhesion forces along the increased length scale of nanoparticle contacts. The nanoplatelets were further reduced in average size and size distribution by post-processing techniques of sonication, ball milling, and centrifugation. The nanoplatelet’s stoichiometry and crystallinity were modified by manipulating the source material, deposition parameters, and post-processing steps.     

Applying RCM in large scale systems: a case study with railway networks

In 2000, the European Union founded a project named ‘RAIL: Reliability centered maintenance approach for the infrastructure and logistics of railway operation’ aimed to study the application of Reliability centered maintenance (RCM) techniques to the railway infrastructure. In this paper, we present the results obtained into the RAIL project, including a RCM methodology adapted to large infrastructure networks and a RCM toolkit to perform the RCM analysis, including cost aspects and maintenance planning guidance. This paper addresses the problem of applying RCM to large scale railway infrastructure networks to achieve an efficient and effective maintenance concept. Railways use nowadays very traditional preventive maintenance (PM) techniques, relying mostly on ‘blind’ periodic inspection and the ‘know-how’ of maintenance staff. RCM was seen as a promising technique from the beginning of the RAIL project because of several factors. First, technical insights obtained were better than the existing, so that several maintenance processes could be revised and adjusted. Second, the interdisciplinary approach used to make the analysis was very enriching and very encouraging for maintenance staff consulted. Third, using the RCM structured approach allowed to achieve well-documented analysis and clear decision diagrams. Our methodology includes some new features to overcome the problems of RCM observed in other projects. As a whole, our methodology and Computerized Maintenance Management Systems have produced two short-term benefits: reduction of time and paperwork because databases and tools are accessible through Internet, and creation of a permanent, accurate, and better collection of information. It will also have some long-term benefits: better PM will increase equipment life and will help to reduce corrective maintenance costs; Production will increase as unscheduled downtime decreases; purchase costs of parts and materials will be reduced; more effective and up-to-date record of inventory/stores reports; and better knowledge of the systems to help the company to chose those systems with the best LCC. The results have been corroborated with the application of our methodology to signal equipment in several railway network sections, as shown in this paper. Because of the successful conclusion of the project, the Spanish railway company (RENFE) and the German railway company (DB A.G.), not only decided to adopt RCM to enhance PM, but they have started a large project to implement Total Preventive Maintenance relying on the implantation of the RCM methodology.     

大中型空分设备空气预冷系统

介绍了空气预冷系统的不同流程以及喷淋式、塔板式、填料式冷却塔 ,分析了其优缺点 ;最后 ,指出空冷系统使用中需注意的两个方面。     

Roll‐to‐roll coating of flexible glass

Flexible glass is a relatively new kind of substrate with a unique combination of properties that are, in different aspects, ideal for numerous applications. The material has aroused significant interest and has prompted activities in R&D communities dedicated to topics such as flexible electronics, flexible OLED and flexible PV. As a result, device demonstrators of considerable maturity have been created, some of which were even manufactured using a roll‐to‐roll (R2R) process. So far, these activities have not resulted in marketable final products that are produced in an industrial context. The key prerequisite for a widespread industrial adoption of R2R processing of flexible glass substrates is the availability of suitable and proven manufacturing equipment. The tools need to be able to handle and process this delicate material, taking into account its mechanical properties, which differ significantly from the typical flexible substrates such as paper, polymer film, or metal foil. This article discusses specific equipment aspects that need to be considered in the R2R handling of flexible glass, both in general and by taking the example of a roll‐to‐roll lab coating system. This tool has been designed specifically for handling flexible glass and will be available to the interested community from October 2016. Furthermore, it is shown how different processes such as R2R sputtering, evaporation, and flash lamp annealing can be used for potential flexible glass applications in flexible electronics, architecture, and energy conversion devices. Beyond that, related layer stacks deposited by vacuum coating will be discussed.     

Chemomechanical effects in optical coating systems

The major in-service failure mechanisms of modern optical coatings for architectural glass can be mechanical (e.g. scratch damage). Many of these coatings are multilayer structures of less than 100 nm thickness and different coating architectures are possible (i.e. different layer materials, thickness and stacking order). These coatings are exposed to different types of climatic conditions. In such circumstances it has been shown that chemomechanical effects can lead to changes in the hardness as well as the fracture resistance of bulk oxides. High performance glass is coated with anti-reflection coatings (e.g. ZnO, SnO₂) and barrier layers (e.g. TiO_xN_y) which are also expected to suffer from such chemomechanical effects. In this study we have demonstrated the chemomechanical behaviour of a range of optical coatings exposed to water. Water exposure tends to reduce the hardness and increase the fracture resistance of the coating making it more vulnerable to plastic deformation during scratching. The susceptibility of different coatings to chemomechanical effects is discussed.     

Structural coloring in large scale core-shell nanowires

We demonstrated two complementary size-dependent structural coloring mechanisms, interference and scattering, in indefinitely long core-shell nanowire arrays. The unusual nanostructures are comprised of an amorphous semiconducting core and a polymer shell layer with disparate refractive indices but with similar thermomechanical properties. Core-shell nanowires are mass produced from a macroscopic semiconductor rod by using a new top-to-bottom fabrication approach based on thermal size reduction. Nanostructures with diameters from 30 to 200 nm result in coloration that spans the whole visible spectrum via resonant Mie scattering. Nanoshell coloration based on thin film interference is proposed as a structural coloration mechanism which becomes dominant for nanowires having 700-1200 nm diameter. Controlled color generation in any part of visible and infrared spectral regions can be achieved by the simple scaling down procedure. Spectral color generation in mass-produced uniform core-shell nanowire arrays paves the way for applications such as spectral authentication at nanoscale, light-scattering ingredients in paints and cosmetics, large-area devices, and infrared shielding.     

Behaviour of surface oxide scale before roll bite in hot rolling of steel

Abstract

Hot stalling rolling tests using mild steel slabs with thin and thick scale layers, and cold stalling rolling simulation tests using lead slabs coated with brittle lacquer layers, have been conducted to investigate the behaviour of the surface oxide scales before hot rolling. The effects of rolling reduction, temperature, scale thickness and structure, and slab geometry were examined. The experimental results indicate that the oxide scale can either adhere and deform with the parent steel, or delaminate from the parent steel, or suffer from cracking before hot rolling, depending on the hot strength of the scale and the stress status in the scale, which depend on rolling reduction and temperature, and scale thickness and structure. Therefore, the cracks observed in the oxide scales on the steel slab after hot rolling are generally the combined results of cracking before rolling and further cracking in the roll gap. On the basis of comparative analysis, the prerolling behaviour of the oxide scales in a laboratory scale rolling mill and in an industrial hot strip mill is discussed.     

Microcrack nucleation in thermal barrier coating systems

Crack nucleation in thermal-barrier coating (TBC) systems subjected to a monotonic cooling process is studied. The TBC system is modeled using the finite element method, where cracks are represented as discrete discontinuities across continuum elements using the partition-of-unity method. The numerical implementation used for crack nucleation is based on an algorithm where, at insertion of a discontinuity, the traction response is derived from a cohesive zone model that has been modified to (i) behave like an initially rigid cohesive model, and to (ii) ensure smoothness of the traction-separation law at zero crack opening. Accordingly, an adequate convergence behavior of the numerical formulation can be warranted in boundary value problems of systems with relatively complex geometries. In the present numerical study, a comparison is made between TBC systems composed of different constitutive models. The fracture patterns and evolutions of the overall crack growth resulting from the simulations clearly illustrate the importance of accounting for the effects of plasticity in the bond coating and anisotropy in the top coating. The computed fracture profile is in good correspondence with experimental observations reported in the literature.     

Generation of large scale circulation in turbulent convection

In a horizontal layer of fluid heated below and cooled above, cellular convection with horizontal length scale comparable to the layer depth occurs in a certain range of Rayleigh numbers. As the Rayleigh number is increased, cellular flow disappears and is replaced by a random array of transient plumes. Upon further increase, these plumes drift in one direction near the bottom and in the opposite direction near the top of the layer with the axes of the plumes tilted in such a way that horizontal momentum is transported upwardsvia the Reynolds stress. With the onset of this large-scale horizontal flow, the largest scale of motion increases from a scale comparable to the layer depth to a scale comparable to the layer width. The conditions for the occurrence and the determination of the direction of this largescale circulation are described in this paper. A simple mathematical model is also described which, like the experiment, has the feature of spontaneous generation of a large-scale horizontal flow,u. A truncated Fourier representation of the streamfunction and temperature field is taken, which allows the possibility of a large-scale flow. The bifurcations of the resulting equations have been studied. The first bifurcation is from the conduction state to steady cellular convection. The second is from steady cellular convection to a steady tilted cell convection which has an Eulerian (but not Lagrangian) horizontal mean velocity,u. The third bifurcation is from steady tilted cells to an oscillatory flow, which may be described as consisting of transient, drifting, tilted plumes. The flow in this regime does have a net Lagrangian horizontal mean velocity. Embedded in this regime are also regions of hysteretic and other regions of chaotic flow. A qualitative similarity to the observed flows is noted.     

Pulsating combustion in large systems

A characteristic equation is derived for the excitation of pulsating combustion in equipment of blast-furnace air-heater type with two-pipe fuel and air supply.     

大口径镀膜机均匀性的研究

对于大口径镀膜机的均匀性特性进行了研究,得到了一组厚度分布曲线,并对曲线进行了分析;利用这些实验结果,运用新理论设计出了具有实用性的修正挡板,均匀性可稳定的达到3‰.     

Sea ice fracturing on the large scale

This paper reviews observational and theoretical work on deformation and lead formation in Arctic pack ice on the geophysical scale. The observational overview includes some discussion of stress measurements in pack ice. The theoretical development focuses on isotropic and anisotropic fracture based models of pack ice and discusses the general level of strength in pack ice in terms of the energy needed to build pressure ridges. Particular emphasis is placed on the development of a class of scale independent fracture based models that can apply on all scales. Results from mechanistic idealized and basin wide simulations which yield oriented failure patterns are also presented.     

Very large scale simulations of materials failure

With present-day supercomputers, simulation is becoming a powerful tool for providing immediate insights into the nature of fracture dynamics. Atomistic simulations yield ab initio information about crack-tip formation and deformation at length-scales unattainable by experimental measurement and unpredictable by continuum elasticity theory. We will describe several atomistic dynamics studies concerning brittle fracture and ductile deformation.     

Multifilamentary superconducting materials for large scale applications

The February 1971 edition of this journal carried a ten page article by the author and his colleagues reviewing the then ‘state of the art’ in multifilamentary superconducting composites.¹ At the time we attempted to cover in a fairly comprehensive manner the first decade of development of these materials since the construction of the first high field superconducting magnet.² Now more than another decade of development has passed and obviously the field can no longer be reviewed comprehensively in the same few pages. This article will attempt to give a brief overview of these materials from the point of view of one engaged in their development and supply for large applications. Hopefully, the references to books,^3,4 review articles,^5,6 and the proceedings of the various conferences^7–11 will serve as a source of further information for those who require more details.     

再制造大型热轧支承辊的堆焊层开裂失效分析

针对再制造大型热轧支承辊堆焊层的服役早期开裂现象,通过检测分析堆焊层硬度、显微组织和断口形貌,确定堆焊层开裂失效机制是低周接触疲劳破坏.由于堆焊层内残余奥氏体含量过多,马氏体相含量相对不足,堆焊金属低硬度、低强度,降低了再制造热轧支承辊面堆焊层的抗接触疲劳性能.通过高温回火热处理促使堆焊层残余奥氏体向马氏体转变,调控辊...     

NDI of interfaces in coating systems using digital interferometry

This paper describes a new application of two laser interferometry techniques to the non-destructive inspection (NDI) of coated surfaces. The purpose is to detect interfacial disbond between the coating and the substrate. Debonding is detected by properly exciting the surface of the object under inspection in such a way that the interference fringe pattern is modified rendering the disbond readily visible. The fringe patterns resulting from the associated images were captured using electronic speckle pattern interferometry (ESPI) and shearography. Image processing techniques are applied to enhance the detection and better definition of the debonded layer. Some results and discussions are presented to illustrate the applicability of these two optical techniques to thermal barrier coatings.