Design of local fuzzy models using evolutionary algorithms

The application of local fuzzy models to determine the remaining life of a unit in a fleet of vehicles is described. Instead of developing individual models based on the track history of each unit or developing a global model based on the collective track history of the fleet, local fuzzy models are used based on clusters of peers—similar units with comparable utilization and performance characteristics. A local fuzzy performance model is created for each cluster of peers. This is combined with an evolutionary framework to maintain the models. A process has been defined to generate a collection of competing models, evaluate their performance in light of the currently available data, refine the best models using evolutionary search, and select the best one after a finite number of iterations. This process is repeated periodically to automatically update and improve the overall model. To illustrate this methodology an asset selection problem has been identified: given a fleet of industrial vehicles (diesel electric locomotives), select the best subset for mission-critical utilization. To this end, the remaining life of each unit in the fleet is predicted. The fleet is then sorted using this prediction and the highest ranked units are selected. A series of experiments using data from locomotive operations was conducted and the results from an initial validation exercise are presented. The approach of constructing local predictive models using fuzzy similarity with neighboring points along appropriate dimensions is not specific to any asset type and may be applied to any problem where the premise of similarity along chosen attribute dimensions implies similarity in predicted future behavior.     

EXPERIMENTAL INVESTIGATION OF HYDRAULIC AND SINGLE-PHASE HEAT TRANSFER IN 0.130-MM CAPILLARY TUBE

The objective of the present study is to investigate the hydraulic characteristics and single-phase thermal behaviour of a capillary tube with internal diameter of 130 w m. As the Reynolds number varies in the range from 100 up to 8,000 in the experiments, and flow regimes from laminar to turbulent are thoroughly investigated. The laminar-to-turbulent flow transition is studied in depth. Experiments show that laminar-to-turbulent flow transition occurs for Reynolds number in the range 1,880-2,480, while heat transfer correlations in laminar and turbulent regimes, developed for conventional tubes, are not adequate for calculation of heat transfer coefficient in microtubes.     

Discussion: Fuzzy Logic Control Technology: A Personal Perspective

The conditional variance function in a heteroscedastic, nonparametric regression model is estimated by linear smoothing of squared residuals. Attention is focused on local polynomial smoothers. Both the mean and variance functions are assumed to be smooth, but neither is assumed to be in a parametric family. The biasing effect of preliminary estimation of the mean is studied, and a degrees-of-freedom correction of bias is proposed. The corrected method is shown to be adaptive in the sense that the variance function can be estimated with the same asymptotic mean and variance as if the mean function were known. A proposal is made for using standard bandwidth selectors for estimating both the mean and variance functions. The proposal is illustrated with data from the LIDAR method of measuring atmospheric pollutants and from turbulence-model computations.     

Optimal dimensioning of the WDM unidirectional ECOFRAME optical packet ring

To efficiently support the high rate and the high dynamicity of the traffic in metro networks, an optical packet-switched WDM ring, named ECOFRAME, is proposed. The key features of the proposed ring are optical transparency and statistical multiplexing of optical packets on parallel WDM channels. Such features can be exploited by properly allocating wavelengths and receivers. This paper aims to optimally dimension the unidirectional ECOFRAME rings. The dimensioning at minimum cost (i.e., for wavelengths and receivers) is modeled with an mixed-integer linear programming formulation. An heuristic algorithm is also proposed, and its performance is compared against the optimal solutions and bounds. When considering the receiver and wavelength cost, results indicate that trading the wavelengths for receivers allows cost saving of up to 75% with respect to WDM optical packet rings with a single dedicated wavelength per node (i.e., single receiver at each node).     

A model of the dynamics of a fluidized bed combustor burning biomass

A dynamical model of an atmospheric, bubbling, fluidized bed combustor of biomass is presented. The model, based on one previously developed for the steady combustion of high-volatile solids, accounts for the fragmentation and attrition of fuel particles, the segregation and postcombustion of volatile matter above the bed, as well as thermal feedback from the splashing region to the bed. The model was used to assess how the dynamic behavior of the combustor varies with some of the operating parameters. To this end, a bifurcation analysis was first used to study the influence of selected parameters on the number and quality of steady state solutions. Moreover, direct integration of the governing equations provided a simulation of the dynamic behavior of the combustor after perturbing the parameters. Results of the bifurcation analysis indicated that extinction may take place through limit point bifurcations when varying the moisture content of the biomass and the flow rates of feed or air. Dynamic simulations showed that the bed temperature changes slowly when a stepwise change is imposed on one of the parameters. Either a new steady state or extinction eventually results, depending on the stepwise change. While relaxation of the bed temperature occurs rather slowly, the dynamics of the splashing region and of the freeboard are much faster, due to the shorter time-scales associated with homogeneous oxidation reactions. The relaxation time of the bed is determined by the heat capacity of the fluidized solids and by the fraction of the heat released recycling to the bed as thermal feedback.     

Primary fragmentation of limestone under oxy-firing conditions in a bubbling fluidized bed

Primary fragmentation of two limestones was studied in a lab-scale bubbling fluidized bed under simulated oxy-firing conditions and, for comparison, under traditional air-firing conditions. The influence of bed temperature, particle size and simultaneous occurrence of sulphation reaction was tested. Additional experiments in a heated strip apparatus were performed to determine if primary fragmentation occurred under high heating rate conditions, but in the absence of particle collisions.Results of the experiments show that only limited fragmentation occurred to both limestones tested under all operating conditions. Under oxy-firing conditions primary fragmentation was significantly reduced with respect to air-fired operation, most likely because of the absence of limestone calcination under high CO₂ atmospheres. Thermal shock upon limestone injection in the hot bed appears not to be able to induce significant particle fragmentation by its own.Particle size, bed temperature and simultaneous occurrence of sulphation reaction were found not to influence significantly the limestone primary fragmentation extent under both oxy-firing and air-firing conditions. On the contrary, the limestone type was found to be a more important variable with respect to the fragmentation tendency.     

Advances in modelling of biomimetic fluid flow at different scales

The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed.     

Unified theory for confinement of RC solid and hollow circular columns

Hollow bridge piers are incorporated in tall bridges to maximize the structural efficiency of the strength-mass and stiffness-mass ratios. Column jacketing with fiber reinforced polymer (FRP) composite materials has been extensively studied in recent years but it is uncertain how FRP jackets may perform when retrofitting hollow concrete columns since the topic has been little researched.A confinement model for circular hollow sections is proposed which can be extended to the case of solid sections. The model is able to estimate confinement effectiveness and to plot stress–strain relationships, which are different in the case of solid and hollow sections.     

Hydration products of FBC wastes as SO2 sorbents: comparison between ettringite and calcium hydroxide

Fluidized bed combustion (FBC) enables the in situ capture of SO₂, but generates large amounts of wastes whose composition and physico-chemical properties make both landfilling and reuse in traditional fields of application (e.g., cement and concrete industries) problematic. Reactivation by water hydration of the desulphurizing ability of these residues is considered a viable mean for their recycling: besides Ca(OH)₂, this process can generate other hydration products, such as ettringite. This paper is devoted to a comparison between the behaviour of Ca(OH)₂ and ettringite as SO₂ sorbents. To this end, synthetic preparations (in the particle size range 0.4–0.6 mm) of the two materials were dehydrated and then sulphated in a lab-scale fluidized bed reactor. Sulphation tests were carried out at 850 °C by fluidizing the bed with an SO₂–N₂–O₂ mixture (1800 ppm SO₂) at 0.8 m/s. Calcium conversion degree and fines elutriation rate were evaluated as a function of sulphation time. The propensity of the sorbents to undergo fragmentation was also estimated by particle sizing of in-bed exhausted sorbent particles, with the aid of laser granulometry. Mercury intrusion porosimetry of samples was directed to the assessment of the influence of sorbent dehydration and subsequent sulphation on pore size distribution and porosimetric texture. X-ray diffraction and differential thermal analysis on the synthetic sorbents complemented the characterization. Results showed that dehydration/thermal decomposition brought about a significant increase of the overall porosity for both sorbents, more extensive than it is commonly observed with calcined commercial limestones. Upon sulphation, the two sorbents showed satisfactory degrees of calcium conversion, larger than those usually observed with limestones. Sulphation resulted into a decrease of particle voidage (that of the Ca(OH)₂-based sorbent was negligible after the process). Ettringite was more prone to attrition/fragmentation than calcium hydroxide. Results are discussed with a focus on differences between calcium hydroxide and ettringite and on key-parameters affecting the performance of the two materials as sorbents.     

Multigate transcranial Doppler ultrasound system with real-time embolic signal identification and archival

An integrated system for acquisition and processing of intracranial and extracranial Doppler signals and automatic embolic signal detection has been developed. The hardware basis of the system is a purpose-built acquisition/processing board that includes a multigate Doppler unit controlled through a computer. The signal-processing engine of the system contains a fast Fourier transform (FFT)-based, spectral-analysis unit and an embolic signal-detection unit using expert system reasoning theory. The system is designed so that up to four receive gates from a single transducer can be used to provide useful reasoning information to the embolic signal-detection unit. Alternatively, two transducers can be used simultaneously, either for bilateral transcranial Doppler (TCD) investigations or for simultaneous intra- and extracranial investigation of different arteries. The structure of the software will allow the future implementation of embolus detection algorithms that use the information from all four channels when a single transducer is used, or of independent embolus detection in two sets of two channels when two transducers are used. The user-friendly system has been tested in-vitro, and it has demonstrated a 93.6% sensitivity for micro-embolic signal (MES) identification. Preliminary in-vivo results also are encouraging.