Equivalent Modeling Method Research Articles

Influence of Microstructure on the Electrochemical Behavior of LSC Cathodes for Intermediate Temperature SOFC

The complex relationships between the microstructure of the mixed ionic-electronic conductor La0.6Sr0.4CoO3−δ (LSC) and the electrode performance have been investigated on a quantitative level. Symmetric half cells and single cells with various LSC microstructures were synthesized using series of raw cathode powders with different particle size distributions. The dual beam FIB-SEM method was used to perform a 3-D analysis of microstructure to obtain quantitative data such as the surface area, volume fractions, pore size distribution, triple phase boundary length and tortuosity factor. Microstructural data were correlated with data from the ac impedance spectroscopy and the cyclic voltammetry measurement. The impedance responses at different electrode potentials of the half cell and the single cell setups were analyzed by using the equivalent circuit modeling method. The characteristic time constants for the cathode and anode processes obtained from the single cell setup are very similar and the exact separation of the anode and cathode processes characteristics is complicated. Because of that most of the impedance analyze have been done for data accrued from the half cell measurements. It was found that for symmetrical half cell configuration the LSC microstructure, especially the surface area, influences drastically the electrode polarization resistance. The power density was also noticeably affected by the cathode microstructure of the anode supported single cells.

A survey of control strategies for simultaneous vibration suppression and energy harvesting via piezoceramics

This article presents a summary of passive, semipassive, semiactive, and active control methods for schemes using harvested energy as the main source of energy to suppress vibrations via piezoelectric materials. This concept grew out of the fact that energy dissipation effects resulting from energy harvesting can cause structural damping. First, the existing equivalent electromechanical modeling methods are reviewed for vibration-based energy harvesters using piezoelectric transducers. Modeling of base excitation cantilever beam ranges from lumped to distributed parameter formulations. The commonly used electrical power conditioning circuits and their optimization are also summarized and discussed. The energy dissipation from harvesting induces structural damping, and this leads to the concept of purely passive shunt damping. This article reviews the literature on vibration control laws along the lines of purely passive, semipassive, semiactive, and active control. The classification of pervious results is built on whether external power is supplied to the piezoelectric transducers. The focus is placed on recent articles investigating semipassive and semiactive control strategies derived from synchronized switching damping. However, whether or not the harvested energy is large enough to satisfy a vibration suppression requirement has become an important topic of research but has not yet specifically been addressed in previous studies. Hence, this survey also reviews the possible control methods aiming for less control energy consumption and addresses the potential application for simultaneous vibration control and energy harvesting.

Comparison of Site Periods Derived from Different Evaluation Methods

Abstract As a part of our microzonation research activities for the city of Ottawa, the fundamental site period, T 0 , was investigated based on different methods, including (1) the horizontal-to-vertical spectral ratio (HVSR) using microtremor ambient-noise measurements; (2) equivalent single-layer (ESL) modeling, as noted in the current National Building Code of Canada (2005); (3) earthquake weak motion observations; (4) multilayer soil modeling; and (5) finite element modeling for linear and nonlinear soil. The differences between these methods are discussed. We have discovered that T 0 based on the HVSR method systematically deviated from T 0 based on the equivalent single-layer modeling method. The variance was more than 30% for periods longer than 2 s, corresponding to impedance boundary depths of more than 75 m in the study area. The effect of the shear-wave velocity gradient on T 0 was investigated by applying multilayer soil modeling, which confirms that the actual velocity-depth gradient shifts the evaluated T 0 to shorter periods compared to equivalent single-layer modeling. The effects of soil nonlinearity on T 0 were examined using a finite element method analysis. The dependency of T 0 on the level of shaking is well defined at higher levels of shaking when the peak ground acceleration (PGA) exceeds 80 Gal because the soft soil behaves nonlinearly. It has been concluded that, for the case of nonlinear soil response, damping plays an important role in reducing the fundamental frequency. These findings will be used in our future research activities directed at providing fundamental period maps for the city of Ottawa, including fundamental period maps for the strong motion design earthquake.

Research on SOC Estimation of LiFePO4 Battery in HEV

For power distribution between engines and electric motors and the dynamic battery management SOC of the dynamic battery in HEV is an important parameter. To estimate SOC accurately LiFePO4 Battery was taken as study object in this paper and based on the characteristic experiments of the LiFePO4 Battery a new combining algorithm of estimating SOC has been put forward which combined Ah counting method, equivalent circuit model and open circuit voltage method. The simulation model of SOC algorithm in MATLAB was created in the paper and the results of simulation have indicated that the new strategy of estimating SOC was feasible and accurate.

Study on Hoist Force Calculation of Hydraulic Lifting System Used in Pressure Balance Workover Rig

Abstract. Pressure balance workover is an advanced downhole operation technique. It can hoist the strings of the tube or put it down under certain pressure. The research on pressure balance workover rig has become a hotspot in both domestic and overseas. Pressure balance workover operation technique has been widely used oversea. At the present time, relevant studies have been developed in China. In this paper, domestic and international technology status is fully analyzed, working principle of hydraulic lifting system is studied, then equivalent calculation model and calculation method of hoist force are put forward, calculation program of hoist force was compiled for the different oil pipe depth, curve and charts changing with the oil pipe depth are given, It provides a theory reference to field operation.

Galvanotactic Migration of EA.Hy926 Endothelial Cells in a Novel Designed Electric Field Bioreactor

Endogenous direct current electric fields (dcEFs) play a significant role in major biological processes such as embryogenesis, wound healing, and tissue regeneration. In this study, the galvanotaxis of human umbilical vein endothelial cell line EA.Hy926 was investigated by using a novel designed bioreactor. The physical features of the bioreactor were discussed and analyzed by both numerical simulation method and equivalent circuit model method. EA.Hy926 cells were cultured in the bioreactor for 10-24 h under 50-250 mV/mm dcEFs. Cell migration direction, distance, and velocity were recorded under an online time-lapse microscope. The effects of serum and growth factor on cell galvanotatic migration were investigated. To further explore the role of dcEFs in regulating endothelial cells, we analyzed the endothelial cell proliferation and secretion of nitric oxide (NO), endothelin-1 (ET-1) in response to dcEFs of physiological strength. Our results showed that EA.Hy926 cells had an obvious directional migration to the cathode, and the EF-directed migration was voltage dependent. The results also showed dcEFs did not affect cell proliferation, but affected the productions of NO and ET-1. Our study also showed the novel bioreactor, with a compact and planar style, makes it more convenient and more reasonable for EF stimulation experiments than earlier chamber designs.

A modified beam modeling method considering dynamic characteristics for curved flexible pipes

When a curved or flexible pipe is modeled with straight beam elements, its flexibility, especially in bending behavior, is underestimated compared to its actual value. In this study, we present an equivalent beam modeling method for predicting the dynamic characteristics of curved flexible pipes, which can be applied similarly to curved pipes. To reflect rationally the increased flexibility of curved flexible pipes due to curvature, we introduce a strain energy concept into the proposed beam model. The validity of the proposed beam modeling method is verified through comparison with results by shell modeling and dynamic experiments.

Statistical analysis of dead‐time system using a deterministic equivalent modeling method

AbstractTo increase precision and reliability of automatic control systems, random factors affecting the control system have to be taken into account. In this article, the deterministic equivalent modeling method (DEMM) is used for statistical analysis of time delay systems with random parameters. The proposed method is compared with several existing methods such as the Monte Carlo, Latin‐Hypercube, and Quasi Monte Carlo method, to demonstrate its validity and effectiveness. The result shows that the proposed DEMM‐based approach drastically reduces computational time with a desired accuracy over traditional methods. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Optimum Design of the Launch Vehicle Composite Cross Beam Structure Based on Equivalent Model

The iterative optimization method of using equivalent model is used to design launch vehicle payload bearing structure—composite cross beam. The strategy is based on the idea of the substitution of equivalent models for detailed models. Using the engineering software Patran/Nastran, optimization finds geometry of cross-sectional with a minimum weight and stacking sequences satisfying laminate design rules. Equivalent model method can decrease numbers of design variable as well as ensures reliability of result. The strategy showed weight savings of 38% compared with the initial design with little computational effort. This has demonstrated that the strategy appears efficient, reliable and extendable into the cross beam structure.

Small Signal Equivalent Circuit Modeling for AlGaN/GaN HFET: Hybrid Extraction Method for Determining Circuit Elements of AlGaN/GaN HFET

The developments in AlGaN/GaN heterojunction field effect transistors (HFETs) are beginning to allow harnessing of the great potential of this technology in high-power radio-frequency (RF) applications. However, the integration of HFET into a circuit environment requires accurate small and large signal modeling of the device operating under various biasing conditions. The conventional small signal equivalent circuit modeling methods consist of “cold” measurements for extracting parasitic elements, and on-bias measurements in determining the intrinsic device circuit elements. Also, the optimization routines are often explored directly using the “hot” measurement data to minimize errors. In this paper, an 18-element small signal equivalent circuit model for AlGaN/GaN HFET is proposed and implemented, and contrasted to various de-embedding methods. Among the methods treated, the hot-FET optimization extraction based on the parasitic capacitances obtained from cold measurements leads to the smallest error between the simulated S-parameters and the measured ones at all bias points employed, with an average error of about 5%. This hybrid extraction algorithm is strengthened by imposing constraints to avoid any nonphysical convergence. We note that the extrinsic parasitics determined by this method differ considerably from the values obtained by cold-FET measurements, which implies that the assumption on the bias independency for extrinsic parameters in the latter method might be questionable for AlGaN/GaN HFET.

Incorporation of uncertainty analysis in modeling of integrated reforming combined cycle

A systematic approach to quantify uncertainties in an integrated reforming combined cycle (IRCC) process model employing CO 2 capture is presented. IRCC involves reforming of natural gas into a hydrogen-rich fuel which is then used as gas turbine fuel. Included in an IRCC plant is also a steam bottoming cycle. The analysis treats uncertain parameters as random variables whose probability distributions are estimated from limited existing information using entropy maximization. Uncertainties of model parameters were propagated through the process model using the deterministic equivalent modeling method as a computationally efficient alternative to Monte Carlo simulations. The method also quantifies the effect of each parameter on the total uncertainty of model outputs. The IRCC process model was evaluated in terms of four performance metrics: (1) net plant power output, (2) net plant efficiency, (3) CO 2 capture rate, and (4) CO 2 emitted per kWh of generated electricity. Simulation results showed that there was considerable uncertainty in the predicted net power output whereas the other three variables were less affected by input uncertainties. The IRCC plant was predicted to have a median net plant efficiency of 43.4% with a standard deviation of 0.5%, representing a loss of approximately 13%-points compared to a natural gas combined cycle plant without CO 2 capture. Results also indicated that the probability of meeting the requirement of at least 85% CO 2 capture rate for the plant was approximately 95%. Parameters with the largest impact on uncertainties of power output and efficiency predictions proved to be gas turbine inlet temperature, and compressor and turbine efficiencies. For the CO 2 emissions, the equipment pressure drop and the steam-to-carbon ratio proved important. Therefore, the focus of future work should be to reduce uncertainties in these parameters in order to improve the confidence of the IRCC model.

Numerical Simulations of Backward-to-Forward Leaky-Wave Antenna with Composite Right/Left-Handed Coplanar Waveguide

A composite right / left-handed (CRLH) coplanar waveguide (CPW) structure and its leaky-wave antenna (LWA) with continuous backward-to-forward scanning applications are proposed. The structure of the CRLH transmission line (TL) is composed of split-ring resonators (SRRs) for left-handed (LH) series capacitance and short-circuited stubs connected between the CPW central signal line and the ground for LH shunt inductance, while the unavoidable right-handed (RH) parasitic effects series inductance and shunt capacitance are generated by wave propagation through the host transmission line. The dispersion relations are calculated and compared with the equivalent circuit model method and 3D full-wave simulations, which can be used to determine the physical dimensions of the CRLH-CPW, such as in the balanced CRLH-TL case. As a main example, a CRLH-CPW-LWA operating from 1.67 GHz to 1.80 GHz with the dispersion characteristics of the balanced CRLH-TL case shows continuous leakage frequency band (fast wave region) from LH (phase constant β < 0, 1.67 < f < 1.74 GHz) to BH (β > 0, 1.74 < f < 1.80 GHz) state through the transition frequency point (β = 0, f = 1.74 GHz), whereas conventional LWAs operated in RH state only provide forward scanning capabilities (β > 0).

Electrochemical and gas phase parameters of cathodes for intermediate temperature solid oxide fuel cells

A series of cyclic voltammetry, chronoamperometry and electrochemical impedance experiments have been carried out in order to investigate the effect of cathode composition and porosity on the electrochemical characteristics of strontium-doped lanthanum, praseodymium and gadolinium cobaltite cathodes. The impedance responses at different electrode potentials of the half cell and symmetric single cell setups are compared and analyzed by the equivalent circuit modeling method. The deconvolution of impedance spectra for single cell cathode and anode reactions contributions based on the results of simultaneous analysis of half cells and symmetric single cells has been made by differential impedance real part vs. ac frequency plot analysis method. Noticeable influence of cathode chemical composition, meso-porosity and macro-porosity on the electrochemical activity of the oxygen electroreduction has been demonstrated. Seeming activation energy values have been calculated and discussed.

RETRACTED: Design and analytical modeling of folded waveguide traveling wave tube

We are developing a simple analytical model for the design of the folded waveguide traveling wave tube (FWTWT). Numerical software does exist for the design of FWTWT but requires large computer run time, is costly and does not provide the physical view for rapid design optimization of the FWTWT. In this paper, the design and analysis of the FWTWT using the spatial harmonics method of the TE 10 mode of the EM wave are presented. An X-band FWTWT is used to verify this method. The normalized dispersion and beam line equations are used to simplify the design process so that the FWTWT can be designed to operate at any desired frequency. Both the S parameter-ABCD-S parameter conversion method and the equivalent circuit model method using Marcuvitz theorem are used for deriving the S parameters and for the analysis of dispersion curve of the 90 sharp-cornered bend of the FWTWT. The analysis is developed by considering the straight and curved portions of the structure supporting the TE 10 mode of the EM wave.

Medium Temperature Solid Oxide Fuel Cells Based on the Micro-Meso-Macro-Porous Cathodes and Anodes

A series of electrochemical impedance experiments have been carried out in order to investigate the effect of cell chemical composition on the determination of electrochemical characteristics of strontium-doped rare earth cobaltite cathodes. The impedance responses at different electrode potentials of the half-cell and symmetric single-cell setups are compared and analyzed by the equivalent circuit modeling method. The deconvolution of impedance spectra for single cells has been achieved by differential derivative of impedance real part versus ac frequency plot analysis method. The performance of electrolyte-supported Ni/Ce0.9Gd0.1O2-δ|Ce0.9Gd0.1O2-δ|Ln0.6Sr0.4CoO3-δ symmetric single-cells has been optimized for anode diffusion layer porosity, anode functional layer starting powder specific surface area (SBET,powder), and cobaltite-based cathode material composition in a single designed experiment according to the so-called response surface methodology. The combination of electrochemical impedance spectroscopy, equivalent circuit fitting, and mathematical statistics methods proved to be a powerful tool for interpreting solid oxide fuel cell data.

System-Level Modeling of Piezoelectric Energy Harvesters

Accurate modeling and computer aided simulation is advantageous during the design stage of a piezoelectric energy harvesting system. In this paper, system-level finite element modeling (FEM) of a cantilevered piezoelectric energy harvester with a resistor is conducted using ANSYS. Considering that practical energy harvesting circuit includes nonlinear electrical elements, which is beyond the modeling capability of ANSYS, an equivalent circuit modeling (ECM) method is proposed to address the problem. After the parameters of equivalent circuit are identified, system-level simulation is conducted in SPICE software.

A simple prediction method for composite rectangular microcantilevers with equal width and the dimensional optimization

Resonant frequency is a key parameter in designing a resonant transducer with high sensitivity. Eigen-frequency calculation of a composite-layer microcantilever is quite useful for the design of a microcantilever resonant sensor. However, simple methods for predicting the resonant frequency of composite rectangular microcantilevers are poorly developed and invite further research. This paper presents a simple and accurate analytical method called “equivalent model method” to predict the fundamental resonant frequency of composite rectangular microcantilevers with equal width (CRMEW). This novel method, which is much more convenient for practical applications, is then confirmed by both experimental results and simulation results, and presents a strong potential to be used in the design and optimization of micromachined transducers.

다이폴 모델링 기법을 이용한 수중 전기장 신호 특성 예측 기법 연구

본 논문에서는 함정 선체의 갈바닉 부식 전류에 의해 발생되는 수중 전기장 신호를 경계요소 해석 도구인 FNREMUS 소프트웨어를 이용하여 예측하고, 예측된 신호로부터 함정 전기장 신호 특성을 특이치 분해(singular value decomposition) 방법을 이용하여 등가적으로 다이폴 모델링하는 방법에 대해 기술하고 있다. 제안...

Effect of Cell Geometry on the Electrochemical Parameters of Solid Oxide Fuel Cell Cathodes

A series of electrochemical impedance experiments has been carried out in order to investigate the effect of cell composition and geometry on the determination of electrochemical characteristics of strontium-doped lanthanum cobaltite cathodes. The impedance responses at different electrode potentials of the half-cell and symmetric single-cell setups are compared and analyzed by the equivalent circuit modeling method. The deconvolution of impedance spectra for single cells has been achieved by a differential impedance real part vs ac frequency plot analysis method. The results indicate that the three-electrode half-cell configuration is more suitable for fundamental research of material parameters at different electrode potentials (measured vs reference electrode), whereas the simpler two-electrode single-cell setup allows the estimation of cathode performance in approximate working conditions.

ANALYTICAL AND NUMERICAL MODELING METHODS FOR IMPEDANCE ANALYSIS OF SINGLE CELLS ON-CHIP

Electrical impedance spectroscopy (EIS) is a noninvasive method for characterizing the dielectric properties of biological particles. The technique can differentiate between cell types and provide information on cell properties through measurement of the permittivity and conductivity of the cell membrane and cytoplasm. In terms of lab-on-a-chip (LOC) technology, cells pass sequentially through the microfluidic channel at high speed and are analyzed individually, rather than as traditionally done on a mixture of particles in suspension. This paper describes the analytical and numerical modeling methods for EIS of single cell analysis in a microfluidic cytometer. The presented modeling methods include Maxwell's mixture theory, equivalent circuit model and finite element method. The difference and advantages of these methods have been discussed. The modeling work has covered the static case — an immobilized cell in suspension and the dynamic case — a moving cell in the channel.