Modelling the dependency of the Smith–Watson–Topper parameter on the cycles‐to‐failure using serial hybrid neural networks

Calculating the fatigue damage with a strain‐based approach requires an ?–N durability curve that links the strain amplitude to the corresponding number of cycles‐to‐failure. This ?–N curve is usually modelled by the Coffin–Manson relationship. If a loading mean‐level also needs to be considered, the original Coffin–Manson relationship is modified using a Smith–Watson–Topper parameter. In this article a methodology for modelling the dependence of the Smith–Watson–Topper parameter on the number of cycles‐to‐failure is presented. The core of the presented methodology represents a multilayer perceptron neural network combined with the Smith–Watson–Topper analytical model. The article presents the theoretical background of the methodology, which is applied for the case of the experimental fatigue data. The results show that it is possible to model ?–N curves for different influential parameters, such as the specimen's diameter and the testing temperature. The results further show that it is possible to predict ?–N curves even for those combinations of the influential parameters for which no experimental data about the material endurance is available. This fact makes the presented model very suitable for the application in an R&D process when a durability of a product should be estimated on the basis of a very limited set of experimental data about the material endurance characteristics.     

An anomaly detection technique based on a chi‐square statistic for detecting intrusions into information systems

An intrusion into an information system compromises its security (e.g. availability, integrity and confidentiality) through a series of events in the information system. Intrusive events often show departures (anomalies) from normal events in an information system. This paper presents an anomaly detection technique based on a chi‐square statistic. This technique builds a profile of normal events in an information system—a norm profile computes the departure of events in the recent past from the norm profile and detects a large departure as an anomaly—a likely intrusion. This technique was tested for its performance in distinguishing normal events from intrusive events in an information system. The test results demonstrated the promising performance of this technique for intrusion detection in terms of a low false alarm rate and a high detection rate. Intrusive events were detected at a very early stage. Copyright © 2001 John Wiley & Sons, Ltd.     

Robustness of Chi‐square and Canberra distance metrics for computer intrusion detection

Intrusion detection complements intrusion prevention mechanisms, such as firewalls, cryptography, and authentication, to capture intrusions into an information system while they are acting on the information system. We develop two multivariate quality control techniques based on chi‐square and Canberra distance metrics, respectively, to detect intrusions by building a long‐term profile of normal activities in the information system (norm profile) and using the norm profile to detect anomalies. We investigate the robustness of these two distance metrics by comparing their performance on a number of data sets involving different noise levels in data. The performance results indicate that the Chi‐square distance metric is much more robust to noises than the Canberra distance metric. Copyright © 2002 John Wiley & Sons, Ltd.     

Scalable Chi‐Square Distance versus Conventional Statistical Distance for Process Monitoring with Uncorrelated Data Variables

Multivariate statistical process control charts are often used for process monitoring to detect out‐of‐control anomalies. However, multivariate control charts based on conventional statistical distance measures, such as the one used in the Hotelling's control chart, cannot scale up to large amounts of complex process data, e.g. data with a large number of variables and a high rate of data sampling. In our previous work we developed a multivariate statistical process monitoring procedure based on a more scalable chi‐square distance measure and tested this procedure for detecting out‐of control anomalies—intrusions—in a computer process using computer audit data. The testing results demonstrated the comparable performance of the scalable chi‐square procedure to that of Hotelling's control chart. To establish the chi‐square procedure as a generic, viable multivariate statistical processing monitoring procedure, we conduct a series of further studies to understand the detection power and limitations of the chi‐square procedure for processes with various kinds of data and various types of out‐of‐control anomalies in addition to the scalability and demonstrated performance of the chi‐square procedure for computer intrusion detection. This paper reports on one of these studies that investigates the effectiveness of the scalable chi‐square procedure in detecting out‐of‐control anomalies in processes with uncorrelated data variables, each of which has a normal probability distribution. The results of this study indicate that the chi‐square procedure is at least as effective as Hotelling's control chart for monitoring processes with uncorrelated data variables. Copyright © 2003 John Wiley & Sons, Ltd.     

Dynamics and pattern formation in thermally induced phase separation of polymer–solvent system

In this paper, the characteristic dynamics and pattern formation of polymer–solvent system, undergoing thermal induced phase separation (spinodal decomposition), have been studied using non-linear simulations. The modified Cahn–Hilliard equation with the incorporation of the Flory–Huggins free energy model is used. The development of a wide variety of initial and intermediate stage morphology is feasible either by introducing sharp/continuous spatial temperature variation or by altering the initial mean solvent concentration (C_o) in the vicinity of the minima (C_m) of the spinodal parameter (second derivative of excess Gibbs free energy w.r.t concentration). For C_o < C_m initial stage of phase separation proceeds by the formation of columns/island of the solvent rich phase dispersed in polymer rich continuous phase. On the contrary, C_o > C_m, phase separation leads to formation of holes of polymer rich phase dispersed in the continuous solvent rich phase. For an intermediate mean concentration very close to C_m inter-connecting structures are evolved. A continuous variation of spatial temperature leads to the directional (rather than random) evolution of phase separated pattern. The initial stage of evolution always propagates from the lowest to the highest temperature regime. A spatial step variation of temperature leads to formation of localized novel phase separated patterns. For a flow system, the dynamics and pattern formation can be controlled by tuning the different timescales: timescale of convection, de-mixing and coalescence.     

Airflow‐induced high‐speed separation method for stacked paper labels and its mechanism

An airflow‐induced separation method for stacked paper labels is proposed with a stream of compressed air used to jet vertically onto the side of the stacked labels and force constraints applied to the two ends of the labels. Its mechanism is revealed that the viscous force caused by airflow is the main driving force for the initial separation of labels and the vertical force is the main factor for the formation of successive separation channels. Theoretical and experimental analyses are implemented to ensure the effects of airflow velocity, label characteristics, label stress, and other factors on label separation and show that a stable separation gap can be generated with separation efficiency of more than 3600 sheets per minute and reliability of 99.99%. A complete airflow‐induced label separation device is designed, which can be integrated into the existing packaging machine, and the physical feasibility of the stack label separation method is verified by experiments.     

Robust and provably second‐order explicit–explicit and implicit–explicit staggered time‐integrators for highly non‐linear compressible fluid–structure interaction problems

An explicit–explicit staggered time‐integration algorithm and an implicit–explicit counterpart are presented for the solution of non‐linear transient fluid–structure interaction problems in the Arbitrary Lagrangian–Eulerian (ALE) setting. In the explicit–explicit case where the usually desirable simultaneous updating of the fluid and structural states is both natural and trivial, staggering is shown to improve numerical stability. Using rigorous ALE extensions of the two‐stage explicit Runge–Kutta and three‐point backward difference methods for the fluid, and in both cases the explicit central difference scheme for the structure, second‐order time‐accuracy is achieved for the coupled explicit–explicit and implicit–explicit fluid–structure time‐integration methods, respectively, via suitable predictors and careful stagings of the computational steps. The robustness of both methods and their proven second‐order time‐accuracy are verified for sample application problems. Their potential for the solution of highly non‐linear fluid–structure interaction problems is demonstrated and validated with the simulation of the dynamic collapse of a cylindrical shell submerged in water. The obtained numerical results demonstrate that, even for fluid–structure applications with strong added mass effects, a carefully designed staggered and subiteration‐free time‐integrator can achieve numerical stability and robustness with respect to the slenderness of the structure, as long as the fluid is justifiably modeled as a compressible medium. Copyright © 2010 John Wiley & Sons, Ltd.     

Elasto–acoustic and acoustic–acoustic coupling on non‐matching grids

Flexible discretization techniques for the approximative solution of coupled wave propagation problems are investigated, focussing on aero–acoustic and elasto–acoustic coupling. In particular, the advantages of using non‐matching grids are presented, when one subregion has to be resolved by a substantially finer grid than the other subregion. For the elasto–acoustic coupling, the problem formulation remains essentially the same as for the matching situation, while for the aero–acoustic coupling, the formulation is enhanced with Lagrange multipliers within the framework of mortar finite element methods. Several numerical examples are presented to demonstrate the flexibility and applicability of the approach. Copyright © 2006 John Wiley & Sons, Ltd.     

Highly Efficient and Recyclable Carbon‐Nanofiber‐Based Aerogels for Ionic Liquid–Water Separation and Ionic Liquid Dehydration in Flow‐Through Conditions

Ionic liquids (ILs) are being widely used in many diverse areas of social interest, including catalysis, electrochemistry, etc. However, issues related to hygroscopicity of many ILs and the toxic and/or nonbiodegradable features of some of them limit their practical use. Developing materials capable of IL recovery from aqueous media and dehydration, thus allowing their recycling and subsequent reutilization, in a single and efficient process still poses a major challenge. Herein, electrically conductive aerogels composed of carbon nanofibers (CNFs) with remarkable superhydrophobic features are prepared. CNF‐based 3D aerogels are prepared through a cryogenic process, so called ice‐segregation‐induced self‐assembly (ISISA) consisting of the unidirectional immersion of an aqueous chitosan (CHI) solution also containing CNFs in suspension into a liquid nitrogen bath, and subsequent freeze‐drying. The CNF‐based 3D aerogels prove effective for absorption of ILs from aqueous biphasic systems and recovery with quite low water contents just through a single process of filtration. Moreover, the electrical conductivity of CNF‐based 3D aerogels is particularly interesting to treat highly viscous ILs because the Joule effect allows not only shortening of the absorption process but also enhancement of the flux rate when operating in flow‐through conditions.     

Interface‐reduction for the Craig–Bampton and Rubin method applied to FE–BE coupling with a large fluid–structure interface

Component mode‐based model‐order reduction (MOR) methods like the Craig–Bampton method or the Rubin method are known to be limited to structures with small coupling interfaces. This paper investigates two interface‐reduction methods for application of MOR to systems with large coupling interfaces: for the Craig–Bampton method a direct reduction method based on strain energy considerations is investigated. Additionally, for the Rubin method an iterative reduction scheme is proposed, which incrementally constructs the reduction basis. Hereby, attachment modes are tested if they sufficiently enlarge the spanned subspace of the current reduction basis. If so, the m‐orthogonal part is used to augment the basis. The methods are applied to FE–BE coupled systems in order to predict the vibro‐acoustic behavior of structures, which are partly immersed in water. Hereby, a strong coupling scheme is employed, since for dense fluids the feedback of the acoustic pressure onto the structure is not negligible. For two example structures, the efficiency of the reduction methods with respect to numerical effort, memory consumption and computation time is compared with the exact full‐order solution. Copyright © 2008 John Wiley & Sons, Ltd.     

Dual‐Layer Superamphiphobic/Superhydrophobic‐Oleophilic Nanofibrous Membranes with Unidirectional Oil‐Transport Ability and Strengthened Oil–Water Separation Performance

Thin porous membranes with unidirectional oil‐transport capacity offer great opportunities for intelligent manipulation of oil fluids and development of advanced membrane technologies. However, directional oil‐transport membranes and their unique membrane properties have seldom been reported in research literature. Here, it is proven that a dual‐layer nanofibrous membrane comprising a layer of superamphiphobic nanofibers and a layer of superhydrophobic oleophilic nanofibers has an unexpected directional oil‐transport ability, but is highly superhydrophobic to liquid water. This novel fibrous membrane is prepared by a layered electrospinning technique using poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP), PVDP‐HFP containing well‐dispersed FD‐POSS (fluorinated decyl polyhedral oligomeric silsesquioxanes), and FAS (fluorinated alkyl silane) as materials. The directional oil‐transport is selective only to oil fluids with a surface tension in the range of 23.8–34.0 mN m^–1. By using a mixture of diesel and water, it is further proven that this dual‐layer nanofibrous membrane has a higher diesel–water separation ability than the single‐layer nanofiber membranes. This novel nanofibrous membrane and the incredible oil‐transport ability may lead to the development of intelligent membrane materials and advanced oil–water separation technologies for diverse applications in daily life and industry.     

A new energy‐based isothermal and thermo‐mechanical fatigue lifetime prediction model for aluminium–silicon–magnesium alloy

In this paper, a new fatigue lifetime prediction model is presented for the aluminium–silicon–magnesium alloy, A356.0. This model is based on the plastic strain energy density per cycle including two correction factors in order to consider the effect of the mean stress and the maximum temperature. The thermal term considers creep and oxidation damages in A356.0 alloy. To calibrate the model, isothermal fatigue and out‐of‐phase thermo‐mechanical fatigue (TMF) tests were conducted on the A356.0 alloy. Results showed an improvement in predicting fatigue lifetimes by the present model in comparison with classical theories and also the plastic strain energy density (without any correction factors). Therefore, this model is applicable for TMF, low cycle fatigue (LCF) and both TMF/LCF lifetimes of the A356.0 alloy. Furthermore, this model can be easily used for the estimation of thermo‐mechanical conditions in components such as cylinder heads.     

A TLM method for steady‐state convection–diffusion: Some additions and refinements

A recent paper introduced a novel and efficient scheme, based on the transmission line modelling (TLM) method, for solving steady‐state convection–diffusion problems. This paper shows how this one‐dimensional scheme can be adapted to include reaction and source terms and how it can be implemented with non‐equidistant nodes. It introduces new ways of calculating the necessary model parameters which can improve the accuracy of the scheme, shows how steady‐state solutions can be obtained directly, and compares results with those from two finite difference (FD) methods. While the cost of implementation is higher than for the FD schemes, the new TLM scheme can be significantly more accurate, especially when convection dominates. Copyright © 2008 John Wiley & Sons, Ltd.     

A new stabilized finite element method for reaction–diffusion problems: The source‐stabilized Petrov–Galerkin method

This paper proposes a new stabilized finite element method to solve singular diffusion problems described by the modified Helmholtz operator. The Galerkin method is known to produce spurious oscillations for low diffusion and various alternatives were proposed to improve the accuracy of the solution. The mostly used methods are the well‐known Galerkin least squares and Galerkin gradient least squares (GGLS). The GGLS method yields the exact nodal solution in the one‐dimensional case and for a uniform mesh. However, the behavior of the method deteriorates slightly in the multi‐dimensional case and for non‐uniform meshes. In this work we propose a new stabilized finite element method that leads to improved accuracy for multi‐dimensional problems. For the one‐dimensional case, the new method leads to the same results as the GGLS method and hence provides exact nodal solutions to the problem on uniform meshes. The proposed method is a Galerkin discretization used to solve a modified equation that includes a term depending on the gradient of the original partial differential equation. Copyright © 2008 John Wiley & Sons, Ltd.     

Co@Co3O4 Core–Shell Three‐Dimensional Nano‐Network for High‐Performance Electrochemical Energy Storage

An alternative routine is presented by constructing a novel architecture, conductive metal/transition oxide (Co@Co₃O₄) core–shell three‐dimensional nano‐network (3DN) by surface oxidating Co 3DN in situ, for high‐performance electrochemical capacitors. It is found that the Co@Co₃O₄ core–shell 3DN consists of petal‐like nanosheets with thickness of <10 nm interconnected forming a 3D porous nanostructure, which preserves the original morphology of Co 3DN well. X‐ray photoelectron spectroscopy by polishing the specimen layer by layer reveals that the Co@Co₃O₄ nano‐network is core–shell‐like structure. In the application of electrochemical capacitors, the electrodes exhibit a high specific capacitance of 1049 F g^?1 at scan rate of 2 mV/s with capacitance retention of ～52.05% (546 F g^?1 at scan rate of 100 mV) and relative high areal mass density of 850 F g^?1 at areal mass of 3.52 mg/cm². It is believed that the good electrochemical behaviors mainly originate from its extremely high specific surface area and underneath core‐Co “conductive network”. The high specific surface area enables more electroactive sites for efficient Faradaic redox reactions and thus enhances ion and electron diffusion. The underneath core‐Co “conductive network” enables an ultrafast electron transport.     

An optimal weighted upwinding covolume method on non‐standard grids for convection–diffusion problems in 2D

In this paper we develop an optimal weighted upwinding covolume method on non‐standard covolume grids for convection–diffusion problems in two dimensions. The novel feature of our method is that we construct the non‐standard covolume grid in which the nodes of covolumes vary in the interior of different volumes of primary grid depending on the local weighted factors and further on the local Peclet's numbers. A simple method of finding the local optimal weighted factors is also derived from a non‐linear function of local Peclet's numbers. The developed method leads to a totally new scheme for convection–diffusion problems, which overcomes numerical oscillation, avoids numerical dispersion, and has high‐order accuracy. Some theoretical analyses are given and numerical experiments are presented to illustrate the performance of the method. Copyright © 2006 John Wiley & Sons, Ltd.     

The fixed‐mesh ALE approach applied to solid mechanics and fluid–structure interaction problems

In this paper we propose a method to solve Solid Mechanics and fluid–structure interaction problems using always a fixed background mesh for the spatial discretization. The main feature of the method is that it properly accounts for the advection of information as the domain boundary evolves. To achieve this, we use an Arbitrary Lagrangian–Eulerian (ALE) framework, the distinctive characteristic being that at each time step results are projected onto a fixed, background mesh. For solid mechanics problems subject to large strains, the fixed‐mesh (FM)‐ALE method avoids the element stretching found in fully Lagrangian approaches. For FSI problems, FM‐ALE allows for the use of a single background mesh to solve both the fluid and the structure. Copyright © 2009 John Wiley & Sons, Ltd.