Simple Equivalent Model Research Articles

An electrochemical impedance model for integrated bacterial biofilms

Bacterial cells attachment onto solid surfaces and the following growth into mature microbial biofilms may result in highly antibiotic resistant biofilms. Such biofilms may be incidentally formed on tissues or implanted devices, or intentionally formed by directed deposition of microbial sensors on whole-cell bio-chip surface. A new method for electrical characterization of the later on-chip microbial biofilm buildup is presented in this paper. Measurement of impedance vs. frequency in the range of 100 mHz to 400 kHz of Escherichia coli cells attachment to indium-tin-oxide-coated electrodes was carried out while using optical microscopy estimating the electrode area coverage. We show that impedance spectroscopy measurements can be interpreted by a simple electrical equivalent model characterizing both attachment and growth of the biofilm. The correlation of extracted equivalent electrical lumped components with the visual biofilm parameters and their dependence on the attachment and growth phases is confirmed.

Level-0 trigger algorithms for the ALICE PHOS detector

The PHOS level-0 trigger provides a minimum bias trigger for p–p collisions and information for a level-1 trigger at both p–p and Pb–Pb collisions. There are two level-0 trigger generating algorithms under consideration: the Direct Comparison algorithm and the Weighted Sum algorithm. In order to study trigger algorithms via simulation, a simplified equivalent model is extracted from the trigger electronics to derive the waveform function of the Analog-or signal as input to the trigger algorithms. Simulations shown that the Weighted Sum algorithm can achieve higher trigger efficiency and provide more precise single channel energy information than the direct compare algorithm. An energy resolution of 9.75 MeV can be achieved with the Weighted Sum algorithm at a sampling rate of 40 Msps (mega samples per second) at 1 GeV. The timing performance at a sampling rate of 40 Msps with the Weighted Sum algorithm is better than that at a sampling rate of 20 Msps with both algorithms. The level-0 trigger can be delivered to ALICE CTP within 800 ns with a timing uncertainty of 2 LHC bunch crossing cycles.

Modelling transformer core joints using Gaussian models for the magnetic flux density and permeability

Simple equivalent permeability and reluctance models are obtained for the transformer core joints from the analysis of the magnetic flux. It is shown that the flux variations in the joint zone can be fitted with simple Gaussian expressions suitable for transformer design purposes. These models are derived from 2D and 3D finite element simulations. The magnetic flux distribution in the transformer core joints is studied for wound cores and stacked-lamination cores with step-lap configurations. The models of the study properly account for the effects of core design parameters such as length of air gaps, number of laminations per step and overlap length. The proposed models, which include saturation and anisotropy, are applied to grain-oriented silicon steel (GOSS) and super GOSS. The new models are intended to estimate, right from the design phase, the magnetic flux density, permeability and the reluctance in the joints. The maximum differences between the Gaussian models of this study and finite element simulations are under 6%. The models of this study can be used to improve core designs with the aim of reducing core losses and magnetising current. A comparison of the total losses computed with the model of the study and measurements on a wound core distribution transformer showed differences of about 2.5%.

Flow and Heat Transfer Characteristics of Supercritical Helium for Magnet Cooling

Supercritical Helium (SHe) is frequently used for the large-scale magnet cooling in many applications. In the present study, the flow and heat transfer characteristics of SHe in the mini-tubes of about 1.0-2.0 mm in diameters are numerically investigated to provide the useful information for the design of the cooling configuration of Cable-in-Conduits Conductors (CICCs) and the related. And a simplified equivalent model is also proposed to estimate the flow and heat transfer characteristics of SHe in the complicated configuration of CICCs.

Vibration absorbers for a rotating flexible structure with cyclic symmetry: nonlinear path design

This paper analytically investigates the nonlinear dynamics of order-tuned vibration absorbers applied to cyclic rotating flexible structures under traveling wave (TW) engine-order excitation. The primary cyclic structure is assumed to be governed by linear vibrations and the nonlinear absorber response arises from large amplitude kinematic effects. These dynamics are captured by a lumped-parameter model that consists of N blades with one blade mode and one absorber per blade, which are arranged with cyclic symmetry on a rotating disk. The governing equations of motion are formulated for arbitrary absorber paths to allow investigation of the absorber path design for nonlinear response. This paper extends previous work by the authors, which considered the linearized blade and absorber dynamics of a similar system. Several intriguing features of the dynamics were uncovered, most notably the existence of an absorber tuning range that avoids resonance at any rotation speed. Of particular interest is the existence and stability of the steady-state TW response to TW excitation, as experienced in turbomachinery, and how these are affected by selection of the absorber paths, which fix the linear and nonlinear tuning characteristics. It is shown that the TW response, which is unique for the linearized system, also exists for the weakly nonlinear model and can be captured by an equivalent two degree of freedom model obtained using the symmetry of the excitation and system response. The forced response exhibits the usual characteristics of a weakly nonlinear system, specifically, bistability and the attendant hysteresis near resonance. More significantly, it does not experience any additional instabilities associated with the symmetry. That is, the desired TW response is robust to nonlinear effects in the absorber, which allows use of the simple equivalent model for selection of absorber tuning parameters. For good performance and robustness, the linear absorber tuning should be in the “no-resonance zone” described by the linear theory and the absorber paths should have a slightly softening nonlinear characteristic.

A Novel TDR-Based Coaxial Cable Sensor for Crack/Strain Sensing in Reinforced Concrete Structures

Novel coaxial cable sensors that feature high sensitivity and high spatial resolution are developed for health monitoring of concrete structures using a time-domain reflectometry (TDR). The new sensor was designed based on the topology change of its outer conductor, which was fabricated with tightly wrapped commercial tin-plated steel spiral covered with solder. The cracks that developed within concrete structures will lead to out-of-contact of local steel spirals. This topology change results in a large impedance discontinuity that can be measured with a TDR. A simplified equivalent transmission line model and numerical full-wave simulations using finite-difference time-domain techniques were used to optimize the sensor design. The sensors under test demonstrated high sensitivity and the capability of multiple-crack detection. A plasma-sprayed coating technique was employed to improve sensor uniformity. Engineering implementation issues, e.g., signal loss, signal postprocessing, and sensor design optimization, were also addressed.

An Examination of the Validity of the Mean Raindrop-Shape Model for Dual-Polarization Radar Rainfall Retrievals

Information about the shape of raindrops is critical for the retrieval of rainfall rate from dual-polarization radar measurements. As described in the literature, the relation describing drop oblateness as a function of its equivolumetric diameter is nonlinear. There are several relations that express the shape-size dependence as a nonlinear fourth-order polynomial that has five coefficients or 5 DOF. While these are important for studying raindrop shape, it is not clear that they are needed to estimate an integral quantity such as rainfall rate. This paper examines the validity of using a simple equivalent linear shape-size model based on the principle of the mean-value theorem for estimating rain from dual-polarization radar measurements. Assuming Rayleigh-Gans scattering for spheroids to describe raindrop scattering and drop oblateness described by a linear relation between axis ratio and equivolumetric diameter, a general self-consistency equation relating reflectivity factor, differential reflectivity, specific differential phase shift, and slope of the shape-size relation is obtained for each radar operating frequency. In this 4-D space, relations for estimating rainfall rate without requiring an assumption of a specific drop-shape model from polarimetric radar measurements were obtained. To study all the implications arising from electromagnetic and microphysical aspects, reconstructed rain and radar measurement profiles obtained from real radar observations were used to test the performance of the proposed rain estimation procedure. The performance is compared with algorithms derived assuming specific a priori fixed drop-shape-size relations expressed by a fourth-order polynomial. Results show that, in general, the proposed rain algorithms perform better or at least equal to the algorithms derived assuming a priori fixed shape-size models, demonstrating that the prevailing model directly derived from data is suitable for rainfall retrieval purposes.

Wind Farms Modeling for Short-Circuit Level Calculations in Large Power Systems

This paper presents a methodology to evaluate the contribution of wind farms (WFs) to the short-circuit level of high-voltage substations. The method relies on simplified equivalent WF models suitable for integration in commercial network-analysis software platforms. The developed WF models are especially suitable for integration in PSS/E and they can be incorporated in models of large power systems. The methodology can be applied to all kinds of WFs regardless of the type of the wind turbines used. Finally, the proposed models are verified through detailed simulations and a case study concerning short-circuit level calculation at all 150-kV and 400-kV buses of the Greek power system is presented. The relevant results are presented and general conclusions are extracted.

Estimation of Real-Time Equivalent of Power System for Distribution System

Distribution power flow methods by and large consider the substation voltage to be known and fixed. This type of model is not suitable for stressed system conditions. Although some power flow software may allow an equivalent representation of the transmission and sub-transmission system, the procedure for the determination of such an equivalent is not available in literature. Hence, this paper presents a very simple three-phase power system equivalent model, which can be obtained with negligible computational effort from real time measurements, for an unbalanced operating system. The validity of the proposed model is demonstrated through studies for two sample systems.

Analyzing Charge-pump Inverter Circuit for Induction-coil Type Electrodeless Lamp

A charge-pump inverter circuit is useful for an induction-coil type electrodeless lamp system, and the input AC current harmonics can be reduced by using an additional diode and a small capacitance. However, the circuit operation is too complicated to understand because of the correlation between the load characteristics of the electrodeless lamp and the involved resonant circuits. This paper analyzes the circuit operation of this inverter circuit and derives some equations that are effective for improving the input AC current waveform near the zero-crossing points of the source voltage. Furthermore, two simplified equivalent models for the involved resonant circuits were assumed for an optimal design of the circuit parameters. The analytical waveforms were experimentally verified, and the input-current harmonics were reduced by the optimized circuit parameters so as to meet the IEC class C regulation.

Elastic cylinder with helicoidal orthotropy: Theory and applications

The elasticity equations are derived for a helicoidally symmetric cylinder. An isotropic cylinder in the center is wrapped by a thick layer of a material with helicoidal anisotropy formed by spiraling of fibers around the core. Such structures are seen in springs, armored cables, trusses, composites, and biostructures. Structure under axial loading and pure bending are considered. The analytical expressions for displacements are obtained from equations of three-dimensional elasticity. The results are verified numerically via the finite element method. The stiffness matrix for an equivalent simplified model that links the displacements of the ends with the applied force and momentum is formulated. A coupling effect is revealed: the bar twists and elongates when axially loaded. The developed technique is used to explain an evolution of structure in nature. A pine trunk with spiralling grain is investigated from an optimization of a mechanical construction viewpoint. We model the trunk as an anisotropic cylinder with helicoidal symmetry and compute the displacements and stresses using nonlinear finite element model. An optimized spiralling angle of the grains accounts for a composite failure, transverse deflection, and fluid transportation. We suggest a combined criterion that could explain this spiralling morphology.

Analytical model of traveling-wave type ultrasonic motor based on the energy equivalent method

The analytical model was proposed to analyse the steady-state characteristics of the traveling-wave type ultrasonic motor (TWUSM) based on the energy equivalent method. Firstly, the simplified equivalent composite beam model of the piezoelectric stator was presented with the energy equivalent principle. By involving the rotary inertia and the shearing deformation of the piezoelectric stator, the equation describing the frequency and the amplitude of transverse vibration of the stator were obtained according to the Timoshinko beam theory. Then the force transfer model and the efficiency of the contact surface between the stator and the rotor were derived with the elastic contact theory. And the mechanical performance expression and the output power of the TWUSM were defined by regarding the friction loss of the contact surface and the output power of the rotor as one of parts of the equivalent damp loss of the stator vibration. Finally, all factors, such as the physical demension, the material parameters, the preload, the driving frequency and the friction layer characteristics, influence the vibration characteristics and the mechanical characteristics were analyzed, and the accuracy of the analytical model was verified by comparison with the experimental results.

Simple Model of Frequency-Dependent Impedance Functions in Soil-Structure Interaction Using Frequency-Independent Elements

This study presents a methodology to make a simple equivalent model of frequency-dependent impedance functions of soil-structure interactions using a frequency-independent spring and dashpot, together with a proposed element called “gyromass.” The gyromass is frequency independent and is defined as a unit system that generates a reaction force due to the relative acceleration of the nodes between which the gyromass is placed. It is found that a model consisting of a spring, dashpot, and gyromass may generate various types of frequency-dependent impedance characteristics. This study proposes two types of simple models that express typical frequency-independent impedance functions of soil-structure interactions by using the gyromass. The advantage of these models is that the frequency-dependent characteristics can easily be expressed by a small number of elements and degrees of freedom. Moreover, they can be applied directly to conventional time-history analyses, even beyond the elastic region of the structural members. An example in which a simple model is applied to the time-history analysis of a soil-pile-superstructure system with an inelastic structural member when subjected to an earthquake wave is illustrated.

Practical Equivalent Continuum Model for Simulation of Jointed Rock Mass Using FLAC3D

A simple practical equivalent continuum numerical model for simulating the behavior of jointed rock mass has been extended to three-dimensional using FLAC3D. This model estimates the properties of jointed rock mass from the properties of intact rock and a joint factor ( Jf ) , which is the integration of the properties of joints to take care of the effects of frequency, orientation, and strength of joint. A new FISH function has been written in FLAC3D specifically for modeling jointed rocks using the Duncan and Chang hyperbolic model. This model has been validated first with simple element tests at different confining pressures for different rocks with different joint configurations. Explicit modeling of the joints has also been done in element tests and results obtained compare well with the results of equivalent continuum model and also with experimental results. Further, this has been applied for a case study of a large underground power house cavern in the Himalayas. The analysis has been done under v...

Non-invasive VHF injected signal monitoring in atmospheric pressure plasma and axial DC magnetron

A universal non-invasive real-time frequency domain reflectometry plasma process measurement that is independent of impedance matching network is described. The measurement is deployed on the main power transmission line of the plasma tool to detect both hardware and reflections form plasma. An illustration for atmospheric pressure plasma and axial DC magnetron plasma is given. Power handling capability is 20 (2 A×10 V) and 100 W (250 mA×400 V), respectively. Four simple equivalent electrical models in terms of transmission-line theory and frequency dependent reflection modulus (gain) are employed to analyze the DC magnetron measurement results. It is shown that the electrical length between the directional device measurement plane and the plane at which the transmission line is termination by the hardware and plasma determines the frequency response signal. The strength of the signal (depth of the zero) is found to be inversely related to the termination resistance. Information on hardware, and dynamic process-induced changes due to physical sputtering/erosion are accessible.

Estimation of the minimum integration time for determining the equivalent continuous sound level with a given level of uncertainty considering some statistical hypotheses for road traffic

In this work a relation is obtained for calculating the minimum time necessary for measuring the hourly equivalent level, with preset uncertainty on the L eq in the case of noise produced by road traffic under different statistical hypotheses for vehicular flow. A simple equivalent level prediction model is used as reference. Some specific relations between acoustic power and vehicle speed are implemented in this model. Through the application of the classic theory of errors, the expression for the uncertainty on the L eq is obtained with reference, in particular, to various vehicle distributions: uniform (rectangular), triangular, normal and Poisson that, according to the available information, can be applied for describing traffic flow. Uncertainties over the distance source/receiver and speed of the vehicles are also taken into consideration in the calculation of uncertainty on L eq . The minimum measurement time is obtained from the expression of the error associated with the L eq , according to the hourly number of vehicles, so that the uncertainty on the L eq stays within a preset value. In this case too, the determination of the minimum time refers to the various previously mentioned hypotheses with respect to vehicle distribution. It is shown that it is possible to obtain a correct description of road traffic noise, within a predetermined uncertainty on the hourly L eq , by measuring over times considerably shorter than an hour.

Application of High Current and Current Zero Simulations of High‐Voltage Circuit Breakers

AbstractThis paper reports on the use of computational fluid dynamic (CFD) simulations to predict the interruption behaviour of high‐voltage circuit breakers (HV‐CB) using the self‐blast principle. Two different levels of accuracy of the arc model are proven to be sufficiently accurate for simulating the high‐current phase and the period around current zero (CZ). For the high‐current phase, a simplified equivalent model of the arc is implemented to predict the pressure build‐up, and even more important to accurately trace the hot gas from the arcing zone into the exhausts and the heating volume. A detailed analysis of the gas mixing in the heating volume for different arcing times and current amplitudes showed the optimum geometrical design of the heating volume. For the CZ phase, a more detailed arc model is needed including the effects of ohmic heating, radiative energy transfer, and turbulent cooling fully resolved in space and time. The validation with experiments was done and shows good agreement which justifies the use of the implemented model. With it, scaling laws varying only one parameter at a time (pressure and applied current slope) were derived and confirm previously found empirical laws. This is of particular interest, as it is very difficult to derive such scaling laws from experiments where the scatter is always very large and where it is impossible to vary only one parameter at a time. The influence of the most important geometrical parameters of the nozzle on the interruption performance is shown. In addition to previous experimental indications of this, the simulation reveals that turbulent cooling on the arc edge is the main reason for the difference in interruption performance. Moreover, the exact spatio‐temporal build‐up of arc resistance and with it the detailed understanding of the arc interruption process is possible and shown here for the first time. These simulations enable us to predict HV‐CB performance and to minimise the number of development tests and are routinely used in new development projects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fundamental Properties and Optimization of Broadside Radiation From Uniform Leaky-Wave Antennas

In this paper, radiation at broadside is studied for a general class of leaky-wave antennas (LWAs) comprised of a grounded slab covered with a partially reflecting surface, on the basis of a simple transverse equivalent network model of the structure. The analysis of the one-dimensional (1-D) version of such a LWA excited by a line source shows that a central role in establishing the features of broadside radiation is played by the condition that the phase and attenuation constants of the leaky mode responsible for radiation are equal. When this happens, a beam with a single peak at broadside is on the verge of splitting into two distinct peaks, and maximum power density is radiated at broadside. Design formulas to achieve such an optimized condition, as well as approximate expressions for the frequency bandwidth and pattern beamwidth of the antenna and for the leaky-wave phase and attenuation constants are derived, both in the absence and in the presence of losses; in addition, an optimal-beamwidth condition (which gives the narrowest broadside beam) is derived. Finally, all the results are extended to the practical case of a 2-D LWA excited by a horizontal dipole

CMUTS with dual electrode structure for improved transmit and receive performance

In this paper, we introduce capacitive micro-machined ultrasonic transducers (CMUTs) with electrically isolated multiple electrodes embedded in the same silicon nitride CMUT membrane. Some of the advantages of this structure are demonstrated using a dual-electrode CMUT with separate transmit and receive electrodes as an example. By locating the transmit electrodes near the edges of a rectangular CMUT membrane, the stable displacement range, hence the maximum pressure amplitude during transmit mode is increased without collapsing the membrane when operated within static collapse voltage range. In the receive mode, the center receive electrode is brought closer to the substrate by biasing the side electrodes, and a higher electromechanical transformer ratio is obtained at low direct current (DC) bias. Therefore, dual-electrode CMUT has an effectively larger gap as compared to conventional CMUT during transmit, and it has an effectively smaller gap during receive. Demonstrative experiments are performed on dual-electrode CMUTs with rectangular membranes with different side and center electrode sizes for transmit and receive measurements. By using the two 4-microm wide side electrodes and an 8-microm wide center electrode on a 20-microm wide membrane, a 6.8 dB increase in maximum output pressure is obtained with side electrode excitation as compared to conventional center electrode. Similarly, the receive performance improvement was demonstrated while reducing the DC bias requirements. Simple finite-element and equivalent circuit-based models were developed to successfully model the behavior of dual-electrode CMUTs. Simulations show that, with simple modifications, more than 10 dB overall sensitivity improvement is feasible with dual-electrode CMUTs with rectangular membranes.

General formulas for 2-D leaky-wave antennas

General formulas for a two-dimensional (2-D) leaky-wave antenna (LWA) are obtained, which are applicable to any general class of 2-D leaky-wave antenna that consists of a partially reflecting surface that is mounted on top of a grounded substrate, and excited by a simple source. Closed-form expressions are obtained for the radiated fields, the field peak values in the E- and H-planes, the beamwidths in the E- and H-planes, and the pattern bandwidth. The formulas are obtained from a simple transverse equivalent network model of the structure. An accurate formula for the substrate thickness necessary to give a beam at any desired angle is also obtained.