Comprehensive Analytical Model Research Articles

Modeling of turbulent cross flow microfiltration of pomegranate juice using hollow fiber membranes

A mathematical analysis of the permeate flux decline during microfiltration of fruit juice with hollow fibers under turbulent flow is presented. Impact of complex fluid flow phenomena on mass transfer is analyzed. A comprehensive analytical model for developing concentration boundary layer was formulated from first principles using integral method. Attempts to model the system considering constant boundary layer thickness (film theory) is inaccurate for developing boundary layer. Gel resistance parameter depending on juice characteristics has significant impact on permeate flux. Specific gel layer concentration has insignificant effect on system performance under total recycle mode but important for batch mode. Theoretical results were compared with experiments in clarification of pomegranate juice with poly(ether ether ketone) and polysulfone hollow fiber membranes. The physical parameters of complex mixture were evaluated by optimizing of the flux profiles in total recycle mode of operation and were successfully applied for prediction of batch mode performance. © 2014 American Institute of Chemical Engineers AIChE J 60: 4279–4291, 2014

Seismic Fragility Study of Fire Sprinkler Piping Systems with Grooved Fit Joints

AbstractA comprehensive analytical model is developed for a pressurized fire sprinkler piping system of a hospital building. A suite of ninety-six artificial triaxial floor acceleration histories is used to generate seismic fragility parameters of the sprinkler piping system. The analytical model accounts for the inelastic behavior of braces, hangers, and wire restrainers. It incorporates an experimentally validated hysteresis model developed, as part of this study, for the moment-rotation relationship of grooved fitted joints. Component fragility parameters were obtained for lateral restrainers, hangers, and pipe joints. Three system-level damage states were defined based on the level of functionality of fire sprinkler systems and severity of leakage after a seismic event and a joint probabilistic model were utilized to obtain system-level fragility parameters. Finally, the seismic fragility of fire sprinkler systems with grooved fit joints is compared to that of a piping system with threaded joints.

Dimensional analysis of thermal stratification in a suppression pool

Due to complexity of direct contact condensation (DCC), it is difficult to predict the thermal hydraulic phenomenon in a suppression pool (SP) of LWRs. Especially, the momentum, induced at condensation interfaces, depends on several interrelated parameters such as the steam mass flux, subcooling, and the diameter of the injection nozzle. Complicated interaction of those parameters creates difficulties in developing a comprehensive analytical model, which applicable to various conditions. To investigate the criteria of thermal stratification created by DCC, experiments were performed using a downsized suppression pool. Time resolved temperatures were acquired by vertically aligned thermocouples. Additionally, steam bubbles were visualized by a high speed camera in order to examine bubble shapes according to the mass flux and subcooling. Both steam bubble frequency and amplitude were analyzed for different DCC regimes. Finally, Richardson number was chosen as a suitable parameter for the dimensional analysis of experimental results. Corresponding velocity at far field in synthetic jet theory was employed to calculate Richardson number. The criteria for the occurrence of the thermal stratification were clearly determined according to the Richardson number.

Predictive Electromechanical Model for Energy Scavengers Using Patterned Piezoelectric Layers

AbstractThe piezoelectric transduction mechanism is widely used in passive sensing, health monitoring, and energy harvesting. Plate-type energy harvesters are usually discouraged; however, piezoelectric layers on a substrate in a certain pattern were found to be suitable for harvesting energy from a wider band of frequencies. However, to understand the theoretical behavior of the harvesters with any arbitrarily shaped piezo patch, a detailed mathematical model is lacking. This paper proposes a comprehensive analytical model to calculate the frequency response function (FRF) from simply patterned piezoelectric layers. A generalized mathematical form is presented for an arbitrary rectangular piezoelectric patch placed on a host plate. The strain-rate damping mechanism is incorporated for better and more accurate results. First, a comparative study on the strain-rate damping effect is presented by placing the piezoelectric layer on the entire plate. Without strain-rate damping, the model incorrectly estimate...

Analysis and Comprehensive Analytical Modeling of Statistical Variations in Subthreshold MOSFET's High Frequency Characteristics

In this research, the analysis of statistical variations in subthreshold MOSFET's high frequency characteristics defined in terms of gate capacitance and transition frequency, have been shown and the resulting comprehensive analytical models of such variations in terms of their variances have been proposed. Major imperfection in the physical level properties including random dopant fluctuation and effects of variations in MOSFET's manufacturing process, have been taken into account in the proposed analysis and modeling. The up to dated comprehensive analytical model of statistical variation in MOSFET's parameter has been used as the basis of analysis and modeling. The resulting models have been found to be both analytic and comprehensive as they are the precise mathematical expressions in terms of physical level variables of MOSFET. Furthermore, they have been verified at the nanometer level by using 65~nm level BSIM4 based benchmarks and have been found to be very accurate with smaller than 5 % average percentages of errors. Hence, the performed analysis gives the resulting models which have been found to be the potential mathematical tool for the statistical and variability aware analysis and design of subthreshold MOSFET based VHF circuits, systems and applications.

A Wind Turbine System Model using a Doubly-Fed Induction Generator (DFIG)

The ever growing interest in developing green energy worldwide has led to the development of hybrid energy system. Many hybrid energy systems do involve wind systems due to the availability and easy access of wind resource. This paper works on the development and the simulation of a wind farm adaptable to high voltage transmission network. It also implements a control of pitch angle using a PID controller, in order to stabilize rotor speed. Firstly a comprehensive analytical model of wind turbine has been presented and this was followed by the modeling of the wind farm under SimPowerSystem of Simulink. The simulated wind turbine system uses a Doubly Fed Induction Generator (DFIG) having a capacity of six (6) MW that supplies a distribution system at 33 KV. A load is connected at the end of the distribution network through a 20 km, 33 KV feeder. PID control system has been implemented to regulate the speed of the rotor vis-avis the wind speed variations. Results show that the speed regulation was very good. In permanent regime, the variation of rotor speed was almost insignificant despite the continuous variation of the wind speed within the interval of 12 to 15 m/s. At the same time, the active and reactive power obtained were in agreement with the simulation pre-set values. General Terms Modeling, Simulation, Wind Turbine, Wind Farm, Speed Control, pitch angle

Optical power of semiconductor lasers with a low-dimensional active region

A comprehensive analytical model for the operating characteristics of semiconductor lasers with a low-dimensional active region is developed. Particular emphasis is given to the effect of capture delay of both electrons and holes from a bulk optical confinement region into a quantum-confined active region and an extended set of rate equations is used. We derive a closed-form expression for the internal quantum efficiency as an explicit function of the injection current and parameters of a laser structure. Due to either electron or hole capture delay, the internal efficiency decreases with increasing injection current above the lasing threshold thus causing sublinearity of the light-current characteristic of a laser.

The influence of the lubricant viscosity on the rolling friction torque

Authors propose a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing, operating in mixed and full film lubrication conditions.The friction torque was measured at low loads and large Λ parameter range using a spin-down method.A comprehensive analytical bearing torque model is described using elastic rolling resistance, curvature effects, inertia forces, disc-air resistance and ball-races hydrodynamic rolling forces, the latter explaining 98% of the final bearing torque. Several sets of hydrodynamic rolling force relationships respecting the transition from IVR to EHL lubrication regime were tested. Final numerical results are shown to be very close to the experimental ones in both full film and mixed lubrication conditions.

The naked toy model of a jumping ring

We present a comprehensive analytical model of the well-known jumping ring—in fact an improved version of that system-–as well as the experimental results that validate the model. Particular attention is paid to the magnetic driving force, whose explicit dependences upon the phase, amplitude and frequency of the exciting current we manage to separate experimentally and plot, so that it becomes evident how the magnetic force on the ring actually arises and evolves in time. We are able to measure not only the large Foucault currents that arise in the ring, but also the magnetic field generated by the ring itself in spite of the presence of the comparable magnetic field in which the ring moves.

Modeling and assessing the influence of linear energy transfer on multiple bit upset susceptibility

The influence of the metric of linear energy transfer (LET) on single event upset (SEU), particularly multiple bit upset (MBU) in a hypothetical 90-nm static random access memory (SRAM) is explored. To explain the odd point of higher LET incident ion but induced lower cross section in the curve of SEU cross section, MBUs induced by incident ions 132Xe and 209Bi with the same LET but different energies at oblique incidence are investigated using multi-functional package for single event effect analysis (MUFPSA). In addition, a comprehensive analytical model of the radial track structure is incorporated into MUFPSA, which is a complementation for assessing and interpreting MBU susceptibility of SRAM. The results show that (i) with the increase of incident angle, MBU multiplicity and probability each present an increasing trend; (ii) due to the higher ion relative velocity and longer range of δ electrons, higher energy ions trigger the MBU with less probability than lower energy ions.

Mobile Data Offloading With Policy and Charging Control in 3GPP Core Network

The Third-Generation Partnership Project (3GPP) has recently standardized the policy and charging control (PCC) system to provide dynamic policy enforcement for network resource allocation combined with real-time charging. The upward trend in smartphone use and the subsequent explosion of data traffic on third-generation (3G) networks have pressed carriers to offload the data traffic from the cellular domain. One key challenge is to elaborate on PCC functionality and mobility management for offloading sessions. This paper proposes an enhanced Wi-Fi offloading model to bring mobile Internet Protocol (IP) integration to a core network with PCC. Specifically, we develop a comprehensive analytical model to quantify the performance of data offloading concerning the amount of 3G resources saved by offloading and the deadline assurance for measuring the quality of user experience with PCC support. Numerical results demonstrate that deadline assurance can be satisfied while saving a significant amount of 3G resources in many situations.

Surface and Thermal Effects on the Pull-In Behavior of Doubly-Clamped Graphene Nanoribbons Under Electrostatic and Casimir Loads

In this study, a comprehensive analytical model is established based on Euler–Bernoulli beam theory with von Kármán geometric nonlinearity to investigate the effect of residual surface tension, surface elasticity, and temperature on the static pull-in voltages of multilayer graphene nanoribbon (MLGNR) doubly-clamped beams under electrostatic and Casimir forces and axial residual stress. An explicit closed-form analytical solution to the governing fourth-order nonlinear differential equation of variable coefficients is presented for the static pull-in behavior of electrostatic nanoactuators using a Fredholm integral equation of the first kind. The high accuracy of the present analytical model is validated for some special cases through comparison with other existing numerical, analytical, and experimental models. The effects of the number of graphene nanoribbons (GNRs), temperature, surface tension, and surface elasticity on the pull-in voltage and displacement of MLGNR electrostatic nanoactuaotrs are investigated. Results indicate that the thermal effect on the pull-in voltage is significant especially when a smaller number of GNRs are used. It is found that the surface effects become more dominant as the number of GNRs decreases. It is also demonstrated that the residual surface tension exerts a greater influence on the pull-in voltage in comparison with the surface elasticity.

Assessing the phase retardation in corneal tissues using a femtosecond laser

We developed and validated a versatile test method for precise quantification of phase retardation in corneal tissues using a femtosecond laser. It is based on an experimental system for direct measurement of corneal phase rotation due to corneal birefringence effects using a dual-polarizer, computer-controlled, femtosecond laser design. It also includes a comprehensive analytical model using Jones matrices. The test method presented is used for quantification of phase retardation in corneal tissues by employing the experimental data obtained from corneal phase rotation measurements and using analytical model assessments. The experimental and theoretical results obtained, and thus, the system's high accuracy and repeatability potential for assessing the corneal phase retardation are validated using control phase retardation evaluation.

Threshold voltage control by gate oxide thickness in fluorinated GaN metal-oxide-semiconductor high-electron-mobility transistors

This paper demonstrates the compensation of the intrinsic positive charges in Al2O3 gate dielectric by fluorine ions in GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs). Negatively-charged fluorine ions diffused into the oxide from the AlGaN barrier during the 250 °C atomic layer deposition compensate the intrinsic positive charge present in the Al2O3. This compensation is key to control the threshold voltage (Vth) of enhancement-mode (E-mode) transistors. A comprehensive analytical model for the Vth of fluorinated MOS-HEMTs was established and verified by experimental data. This model allows the calculation of the different charge components in order to optimize the transistor structure for E-mode operation. Using the proposed charge compensation, the Vth increases with gate dielectric thickness, exceeding 3.5 V for gate dielectrics 25 nm thick.

Toward an economic and energy‐aware cloud cost model

SUMMARYThis paper represents an economic cost model for cloud computing aiming at comprising all kinds of cost of a commercial environment. To extend conventional state‐of‐the‐art models considering only fixed cost, we developed a concise but comprehensive analytical model, which includes also variable cost allowing for the development and evaluation of business strategies for cloud environments. These strategies can be used for both cloud providers and cloud consumers. The major goal of our model is to comprise all important economic fundamentals and methods. Thus, this new model supports the decision‐making process to be applied with business cases and enables cloud consumers and cloud providers to define their own business strategies and to analyze the respective impact on their business. On the basis of this model, also, the energy efficiency of cloud systems can be evaluated according to chosen business models. Copyright © 2013 John Wiley & Sons, Ltd.

Control of Threshold Voltage in GaN Based Metal–Oxide–Semiconductor High-Electron Mobility Transistors towards the Normally-Off Operation

The effect of defect charges on a threshold voltage (Vth) of the GaN/AlGaN/GaN metal–oxide–semiconductor heterostructures (MOS-Hs) with the gate stack thickness scaling was investigated by using capacitance–voltage measurements and a comprehensive analytical model [M. Ťapajna and J. Kuzmík: Appl. Phys. Lett. 100 (2012) 113509]. Using the MOS-Hs with Al2O3 and HfO2 dielectrics grown by plasma-enhanced atomic layer deposition, a high density (∼1013 cm-2) of negative fixed oxide charge (Nox) was extracted for Al2O3 layers, while an order of magnitude lower density (∼1012 cm-2) of positive Nox was extracted for HfO2 films. Consequently, despite similar dielectric constant of Al2O3 to that of (Al)GaN, it is advisable to attain normally-off operation by scaling the AlGaN layer thickness rather than the oxide thickness, taking advantage of the negative Nox offsetting Vth towards the positive voltages. Scaling of the AlGaN layer thickness is found to be effective also in the case of HfO2 dielectric, however, due to a positive Nox in HfO2, AlGaN layer needs to be scaled to a similar thickness (e.g., ∼3 nm) to obtain a positive Vth for the same oxide thickness of HfO2 and Al2O3 (∼5 nm). On the other hand, scaling of the GaN cap has no effect on Vth. Further, our analysis suggests that for MOS-Hs with both Al2O3 and HfO2 gate dielectric, the Fermi level position at the oxide/barrier interface in equilibrium is located within donor-like interface traps. Therefore, the oxide/GaN cap interface trap charge in MOS-Hs with the given structure parameters should lead to a negative Vth shift.

Visible-light optical coherence tomography for retinal oximetry

We applied a visible-light spectroscopic optical coherence tomography (vis-OCT) for in vivo retinal oximetry. To extract hemoglobin oxygen saturation (sO(2)) in individual retinal vessels, we established a comprehensive analytical model to describe optical absorption, optical scattering, and blood cell packing factor in the whole blood and fit the acquired vis-OCT signals from the bottom of each imaged vessel. We found that averaged sO(2) values in arterial and venous bloods were 95% and 72%, respectively.

Comprehensive Analytical Probabilistic Model of the Random Variation in Subthreshold MOSFET's High Frequency Performance

Comprehensive Analytical Probabilistic Model of the Random Variation in Subthreshold MOSFET's High Frequency Performance

A weak-scattering model for turbine-tone haystacking

Noise and emissions are critical technical issues in the development of aircraft engines. This necessitates the development of accurate models to predict the noise radiated from aero-engines. Turbine tones radiated from the exhaust nozzle of a turbofan engine propagate through turbulent jet shear layers which causes scattering of sound. In the far-field, measurements of the tones may exhibit spectral broadening, where owing to scattering, the tones are no longer narrow band peaks in the spectrum. This effect is known colloquially as ‘haystacking’. In this article a comprehensive analytical model to predict spectral broadening for a tone radiated through a circular jet, for an observer in the far field, is presented. This model extends previous work by the authors which considered the prediction of spectral broadening at far-field observer locations outside the cone of silence. The modelling uses high-frequency asymptotic methods and a weak-scattering assumption. A realistic shear layer velocity profile and turbulence characteristics are included in the model. The mathematical formulation which details the spectral broadening, or haystacking, of a single-frequency, single azimuthal order turbine tone is outlined. In order to validate the model, predictions are compared with experimental results, albeit only at polar angle equal to 90°. A range of source frequencies from 4 to 20kHz, and jet velocities from 20 to 60ms−1, are examined for validation purposes. The model correctly predicts how the spectral broadening is affected when the source frequency and jet velocity are varied.

Investigation of UH-60A Rotor Performance and Loads at High Advance Ratios

Wind tunnel measurements of the performance, airloads, and structural loads of a full-scale UH-60A Black Hawk main rotor operating at high advance ratios (up to 1.0) are compared with calculations obtained using the comprehensive rotorcraft analysis Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics II to understand physics and quantify this comprehensive code’s accuracy and reliability in the prediction of rotor performance and loads at high advance ratios. Detailed comparisons are made on rotor thrust, control angles, power, and section loads to illustrate and understand unique aeromechanics phenomena in this regime. The analysis correctly predicts the thrust reversal with collective at high advance ratios. Rotor induced plus profile power is also reasonably well predicted with proper modeling of the shank. Airloads and structural loads correlation is fair. A significant underprediction of 2-per-revolution structural loads is observed.