Stability and H ∞ Performance Analysis of Switched Stochastic Neutral Systems

This paper is concerned with the problems of stability and H _∞ performance for a class of switched stochastic neutral delay systems. By applying the average dwell time method, sufficient condition is first derived to guarantee the mean-square exponential stability of the switched stochastic neutral system. Then, the condition on a weighted H _∞ performance is proposed. The corresponding results are all formulated in terms of linear matrix inequalities (LMIs). Finally, a numerical example is provided to illustrate the effectiveness of the proposed approach.     

Stabilization of Interconnected Discrete Systems with Quantization and Overflow Nonlinearities

In this paper, we address the problem of decentralized feedback control design for a class of linear interconnected discrete-time systems subject to quantization and overflow nonlinearities and unknown-but-bounded couplings. A decentralized quantized state feedback controller is designed at the subsystem level to render the closed-loop system asymptotically stable. When the local output measurements are available, a decentralized output-feedback quantized controller is developed attain similar asymptotic stability and guaranteed performance of the closed-loop quantized system. Several special cases of interest are derived and simulation results are provided.     

A Radon-Multiwavelet Based OFDM System Design and Simulation Under Different Channel Conditions

Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of sub-carriers, it is non sensitive to channel parameters variations, and has a small constellation energy compared with conventional fast Fourier transform (FFT) based orthogonal frequency division multiplexing (OFDM). It is also able to work as a good interleaver which significantly reduces the bit error rate (BER). Due to its good orthogonality, discrete Multiwavelet transform (DMWT) is attractive for implementation in OFDM systems which reduces inter-symbol interference (ISI) and inter-carrier interference (ICI) and eliminates the need for cyclic prefix and increases the spectral efficiency of the design. In this paper both FRAT and DMWT are implemented in a new design for OFDM. The new structure was tested and compared with conventional FFT-based OFDM, Radon-based OFDM, and DMWT-based OFDM for additive white Gaussian noise channel, flat fading channel, and multi-path selective fading channel. Simulation tests were generated for different channels parameters values. The obtained results showed that proposed system has increased spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems.     

Dye sorption characters of gamma irradiated foamed ethylene propylene diene monomer (EPDM) rubber/clay composites

Composites based on gamma irradiated ethylene propylene diene monomer rubber in foam structure, loaded with different types of clays were used as adsorbents for different classes of dyestuffs (basic, acid, reactive and disperse) from aqueous solutions. The clays under investigation were Aswan clay (ASC) and sodium montmorillonite (Na-MMT). The effect of adsorbent composition, irradiation dose, pH and contact time on dye sorption was studied. It was found that the rubber composites loaded by Na-MMT gave maximum adsorption of the basic dye (～42%) in aqueous solution, while the rubber composites loaded by AS clay gave maximum adsorption (～28%) of the acidic dye. On the other hand, both type of clays did not show no affinity toward reactive and disperse dyes. The efficiency of dye removal was found to increase with increasing the pH and contact time. It was also observed that the irradiation dose (50 kGy) was the optimum dose for the removal of dyes for all rubber composites.     

Tanlock loop noise reduction using an optimised phase detector

This article proposes a time-delay digital tanlock loop (TDTL), which uses a new phase detector (PD) design that is optimised for noise reduction making it amenable for applications that require wide lock range without sacrificing the level of noise immunity. The proposed system uses an improved phase detector design which uses two phase detectors; one PD is used to optimise the noise immunity whilst the other is used to control the acquisition time of the TDTL system. Using the modified phase detector it is possible to reduce the second- and higher-order harmonics by at least 50% compared with the conventional TDTL system. The proposed system was simulated and tested using MATLAB/Simulink using frequency step inputs and inputs corrupted with varying levels of harmonic distortion. A hardware prototype of the system was implemented using a field programmable gate array (FPGA). The practical and simulation results indicate considerable improvement in the noise performance of the proposed system over the conventional TDTL architecture.     

Exploring the effects of symmetrical and asymmetrical relative humidity on the performance of H2/air PEM fuel cell at different temperatures

This article is dedicated to study the interlinked effects of symmetric relative humidity (RH), and asymmetric RH on the performance of H₂/air PEM fuel cell at different temperatures. The symmetric and asymmetric RH were achieved by setting the cathode relative humidity (RHC) and anode relative humidity (RHA) as equal and unequal values, respectively. The cell performance was evaluated by collecting polarization curves of the cell at different RH, RHC and RHA and at different cell temperatures (T_cell). The polarization curves along with the measured internal cell resistance (membrane resistance) were discussed in the light of the present fuel cell theory. The results showed that symmetric relative humidity has different impacts depending on the cell temperature. While at RH of 35% the cell can show considerable performance at T_cell = 70 °C, it is not so at T_cell = 90 °C. At T_cell = 70 °C, the cell potential increases with RH at lower and medium current densities but decreases with RH at higher currents. This was attributed to the different controlling processes at higher and lower current densities. This trend at 70 °C is completely destroyed at 90 °C. Operating our PEM fuel cell at dry H₂ gas conditions (RHA = 0%) is not detrimental as operating the cell at dry Air (O₂) conditions (RHC = 0%). At RHA = 0% and humidified air, water transport by back diffusion from the cathode to the anode at the employed experimental conditions can support reasonable rehydration of the membrane and catalysts. At RHA = 0, a possible minimum RHC for considerable cell operation is temperature dependent. At RHC = 0 conditions, the cell can operate only at RHA = 100% with a loss that depends on T_cell. It was found that the internal cell resistance depends on RH, RHA, RHC and T_cell and it is consistent with the observed cell performance.     

Production planning and performance optimization of reconfigurable manufacturing systems using genetic algorithm

To stay competitive in the new dynamic market having large fluctuations in product demand, manufacturing companies must use systems that not only produce their goods with high productivity but also allow for rapid response to market changes. Reconfigurable manufacturing system (RMS) is a new paradigm that enables manufacturing systems to respond quickly and cost effectively to market demand. In other words, RMS is a system designed from the outset, for rapid changes in both hardware and software components, in order to quickly adjust its production capacity to fluctuations in market demand and adapt its functionality to new products. The effectiveness of an RMS depends on implementing its key characteristics and capabilities in the design as well as utilization stage. This paper focuses on the utilization stage of an RMS and introduces a methodology to effectively adjust scalable production capacities and the system functionalities to market demands. It is supposed that arrival orders of product families follow the Poisson distribution. The orders are lost if they are not met immediately. Considering these assumptions, a mixed integer nonlinear programming model is developed to determine optimum sequence of production tasks, corresponding configurations, and batch sizes. A genetic algorithm-based procedure is used to solve the model. The model is also applied to make decision on how to improve the performance of an RMS. Since there is no practical RMS, a numerical example is used to validate the results of the proposed model and its solution procedure.     

Behavior of a viscoelastic composite plates under transient load

An efficient numerical algorithm for analyzing dynamic response of orthotropic viscoelastic composite laminates has been developed in the time domain. The integral form of the constitutive laws is exploited. Generalized Wiechert model is adopted to simulate the viscoelasticity of the structure Mindlin-Reissner plate theory is utilized in finite element formulation employing the consistent mass matrix. The proposed algorithm is incorporated in the framework of the finite element based on the displacement model. Newmark Constant average acceleration method is used for integration equation of motion. The developed recurrence formula permits the new time solutions to be evaluated using only previous time values. The developed solution technique is applied to orthotropic plate under two types of force, which are the step-pulse and sin-pulse force.     

Integrating physical and virtual environments to conserve energy in buildings

Fundamental understandings of how energy is consumed, monitored, and controlled are key prerequisites for an energy conservation process. Users who know exactly when energy consumption occurs and where it takes place are able to make more informed decisions about how to lower their energy consumption. Energy conservation projects in the U.S. have reported a 2-11% savings when users are presented with information on energy consumption. Engineers are increasingly turning to virtual environments to improve system design and development and optimize performance and increase efficiency during operation. A bottom-up approach to real-time energy monitoring by integrating virtual and physical domains to increase user awareness on where, when, how and why aspect of energy to make inform decisions regarding energy consumption, optimization and conservation is proposed. A virtual 3-D environment is developed to display actual space/zone/building real-time power consumption information and to allow users to easily locate equipment/loads that are in standby/inefficient and causing energy waste in the real/physical environment. The proposed system is demonstrated via a prototype board that is virtually integrated with an actual Zero Net Energy Test House (ZNETH) as part of future Net-Zero Energy buildings research. The results establish a promising tool in this filed.     

Application of exceedance probability based on wind kinetic energy to evaluate the pedestrian level wind in dense urban areas

In the present study, assessment of wind environment within the pedestrian level domains of highly populated areas is carried out. Three typical models of a dense urban area are considered and numerically simulated in order to examine the effects of the geometry of such models on wind flow characteristics within the pedestrian domain of a street canyon located within this area. The calculated flow fields are employed to estimate the exceedance probabilities within the study domain using a new approach: average wind kinetic energy. The study is applied to Tokyo, Japan; based on its mean wind velocity data. The results demonstrate that the exceedance probability analysis of the pedestrian wind environment could be a valuable tool for assessing urban areas. Also, the calculated probabilities demonstrate substantial dependence on both the geometry of building arrays and the wind conditions of the considered domain.