Field Quantities Research Articles

Refined Green–Lindsay Model for the Response of Skin Tissue under a Ramp-Type Heating

Based on Green–Lindsay generalized thermoelasticity theory, this paper presents a new refined higher-order time-derivative thermoelasticity model. Thinner one-dimensional skin tissue is considered when its inner surface is free of traction and does not show any temperature increase. The skin tissue’s bounding surface has been heated by ramp-type heating. The classical thermoelastic theories are obtained from the present general formula. The governing equations of the present model are obtained. To move the system into a space state, the Laplace transform is used. The inverse of the Laplace transform is also used with Tzuo’s method to solve the problem. As a result, the field quantities are obtained numerically, and the results of the current model are graphically represented with a comparison to two different theories of thermoelasticity. The effects of various parameters on thermomechanical waves through the skin tissue are analyzed. The theory notes a vibrational behavior in heat transfer and a different effect on the parameters discussed in this article.

Experimental study of instantaneous sound intensities in rectangular enclosures

Instantaneous and time-averaged intensities are relevant field quantities in architectural acoustics investigations. Modeling of intensity flows in coupled volumes and the effect of absorptive material on its trajectory in reverberation chambers have been studied recently. This work focuses on vortical energy flows with a derivation of instantaneous intensity in enclosed spaces and an experimental effort for investigating the changes over time in all field quantities of interest—instantaneous intensity, pressure, and velocity simultaneously. In this study, the scale modeling technique is applied to investigate instantaneous intensity flows experimentally measured using pressure-3D velocity sensors in a rectangular room. Experimental results suggest the presence of vortical intensity modes at specific frequencies correlated to the room dimensions. The resulting simulation of intensity vortices has potential applications in the acoustical design and analysis of complex room geometries where sound energy flows play a major role in the acoustics of the space such as that of coupled-volume spaces and small rooms for critical listening.

Particle image velocimetry of supersonic jets with micro vortex generators

The flow field of supersonic jets with micro vortex generators (MVGs) is investigated using Particle Image Velocimetry (PIV) to shed light on the noise reduction mechanisms associated with such devices. Recently, MVG nozzles have been developed as a new noise reduction technology through the collaboration between the University of Cincinnati and the Naval Research Laboratory. MVGs were implemented on model scale nozzles representative of GE F404 engine nozzles, and noise reductions up to −6 dB have been observed in both microphone measurements and LES simulations. The PIV measurements of the flow field reveal that the MVGs alter the shock cell spacing and strengths in the jet plume and substantially reduce the mean axial velocity at the jet axis. In addition, streamwise vortices generated by MVGs enhance shear layer mixing and redistributes turbulence along the shear layer to narrower regions. The measured flow field quantities are extracted to explain flow field changes on the noise reductions observed in the acoustic far field.

A Machine Learning Enabled Image‐data‐driven End‐to‐end Mechanical Field Predictor For Dual‐Phase Steel

AbstractThis contribution presents convolutional neural nets (CNN) based surrogate models for prediction of von Mises stress and equivalent plastic strain fields of commonly used Dual‐Phase (DP) steels in automotive applications. The models predict field quantities in an end‐to‐end manner, driven by segmented phase images from real experimental scanning electron micrographs as inputs and FEM calculations as outputs. Hereby, we train CNN models with the U‐net neural network structure based on around 900 elastoplastic FEM simulations of various DP steel microstructure samples under tensile test. The trained CNN models are validated and tested on 250 and 50 samples, respectively. Thereby CNN models are employed sequentially for different tasks , from the real micrographs to segmented phase maps, then from segmented phase maps to stress, strain field predictions, in an end‐to‐end manner. The field predictor model results show good agreement with the test data and convincing performance on unseen microstructural dataset. This work demonstrates the large potential of a Machine Learning model to make accumulatively use of the physics‐based simulation data of large number of boundary value problems with varying microstructure. It recaptures not only the physics, implied in each simulation training data obtained from the partial different governing equations of mechanics, but also the overarching correlation between the microstructure and the stress and strain field responses.

Simulation of the Electromagnetic Waves Propagation in Conductive Media Using Analytical Formulae

Abstract The paper aims to investigate the electromagnetic waves behavior in conductive media using analytical formulae. An example of a very long vertical conductive wall of given thickness placed in front of a vertically polarized electromagnetic wave is considered. The variation of the electromagnetic field quantities inside the conductive wall are detailed using analytic formulae. The numerical example considered was aimed to easily understand the important properties of the field behavior inside the conductive wall. The main conclusions end the paper.

The Electric-Thermal Uneven Characteristics Simulation of Wide Mg Alloy Strip and Electroplastic Rolling Experiment

In order to solve the problem of wide magnesium strip uneven deformation in electroplastic rolling, an uneven field measurement device was designed. The device simulates the actual electro-thermal characteristics and provides as even and constant field conditions as possible for high-efficiency wide Mg strip rolling. Firstly, the effect of electrode position and distance on the electric field unevenness of magnesium strip is observed by setting the electric rolling condition, to provide the optimal electrical-thermal field quantity coupling conditions required by electric rolling. Secondly, in order to reveal the changing trend of the transient field in the actual rolling, the three-dimensional electric field of wide magnesium strip are simulated by the finite element method. The results show that the even temperature field and stable stress field required by the EPR of a wide Mg strip can be guaranteed to the greatest extent by setting electric field parameter Online. The case proves that the continuous EPR of Mg strip with a thickness of less than 0.13 mm without heat treatment can be realized by fine control of the EPR process.

Impact of the implementation of the new radiation quantities recommended by ICRU/ICRP for practical use in interventional radiology: a Monte Carlo study

The International Commission on Radiation Units and Measurements (ICRU) proposed a new set of operational quantities for radiation protection for external radiation in its Report Committee 26 (ICRU 95). The new proposal aims to improve the coherence between the operational quantities and the definitions of the protection quantities in the recommendations of the International Commission on Radiological Protection set out in 2007 (Ann. ICRP 37). It is expected that this change in operational quantities will impact current dosimeter designs. Although for many photon energies, the conversion coefficients from physical field quantities to the new operational quantities will change relatively little, for radiation fields with low energy photon components, such as medical x-ray applications, there will be a significant decrease in the values of the conversion coefficients. This means that the numerical values of the new operational quantities will be much lower for the same radiation field. These values will be closer to the effective dose, but this change can still cause confusion for medical staff. It is important to examine the effect of the new set of dose conversion coefficients on the personal dose in realistic radiation fields. We performed a study to assess the effect of changing the definition of the operational quantity, personal dose equivalent (), in realistic radiation fields in interventional radiology (IR) workplaces. The x-ray tube kilovoltage peak (kVp) in IR ranges between 60 and 120 kV. The medical staff is exposed to the scattered photons which have a wide range of energies depending on the beam configuration and the patient size. The objective of this study is to ‘quantitatively’ estimate the impact of implementing the new ICRU quantities of Report 95 in IR radiation fields using Monte Carlo simulations. Simulations of 560 different configurations in IR were performed using MCNPX to calculate fluence binned per energy and angle of incidence. and were then calculated for each configuration using dose conversion coefficients from fluence given by ICRU Reports 95 and 57, respectively. The results show that the mean of the ratio, , is 1.6 for all simulated scenarios. This reduction will correct the current overestimation of the effective dose and should result in better compliance with the dose limits in IR. However, it may also have negative consequences on the safety culture among the medical staff. Special care will be needed when interpreting these lower doses.

Two-dimensional analysis on the magnetic field adjusted electrical behaviors in composite semiconductor structures

To explore the exact electric properties and reveal the intrinsic interaction mechanisms among multi-fields in composite magneto-electric-semiconductor structures, two-dimensional analyses are performed based on the coupled field theory. Expanding the basic physical quantities to Fourier series along the length, the governing equations are simplified. And then, the discrete solutions are derived by utilizing differential quadrature method. As applications, three composite structures are designed via considering different poling directions. Respectively, the extension, piecewise deformation and bending are realized. Before analysis, the convergence and correctness of adopted method are discussed systematically. In numerical calculation, the effect of material proportion on the perturbation carrier density is investigated. It is found the variation rule of perturbation carrier density is controlled by material proportion and deformation form simultaneously. Importantly, there are optimal material proportion ranges producing the carriers, nevertheless, the ranges are different for three structures. Additionally, two-dimensional distributions of perturbation carrier density, electric field, electric displacement and polarization are discussed. Along the thickness, the field quantities are symmetric for extension and piecewise deformation, but is antisymmetric for bending. Specially, in the structure with piecewise deformation, the potential barriers are realized. This work could be the guidance designing magneto-electric devices.

Numerical procedure for prechamber transfer from a single-cylinder engine to a rapid compression machine

This paper presents a method for transferring a prechamber from a single-cylinder engine (SCE) to a rapid compression machine (RCM) as a pre-step for carrying out optical experiments. The overall objective of the transfer procedure is to achieve similar flow field conditions in the prechamber which is mounted on an RCM as compared to the same prechamber mounted on an SCE. Computational fluid dynamics (CFD) simulations of a large-bore natural gas SCE were carried out up to ignition timing which serve as the basis for the transfer procedure. The mass-flow rate in the prechamber neck, pressure difference between the main chamber and prechamber, prechamber pressure and mass in the prechamber were defined as the governing thermodynamic quantities which affect the evolution of the flow field in the prechamber during the compression stroke. All of these quantities in an RCM are largely influenced by operating piston speed and compression ratio for given initial conditions. The RCM operation parameters for each governing quantity were estimated with the help of 0D simulations. CFD simulations of RCM were performed for the determined RCM operation parameters, and the evolution of the velocity field and turbulent quantities in the prechamber were evaluated. The procedure has been applied to two prechambers of different shape and size and a good agreement between the RCM and corresponding SCE CFD simulations was achieved for the flow field conditions in both of the prechambers near the ignition timing. It was found that mass-flow rate in the prechamber neck is the most important quantity which influences the prechamber flow field. Overall this numerical procedure provided a flexible and computationally feasible approach to adjusting RCM operation parameters for transferring a prechamber from the SCE to RCM.

Mathematical Study of the Perturbation of Magnetic Fields Caused by Erythrocytes.

The purpose of this chapter is the mathematical study of the perturbation of a homogeneous static magnetic field caused by the embedding of a red blood cell. Analytical expressions for the magnetic potential and the magnetic strength vector are derived. From the obtained results, it emerges that the magnetic field inside the red blood cell is not uniform and the magnitude depends on the orientation of the erythrocyte. The expressions for the magnetic field quantities are significant in applications such as the magnetic resonance imaging and in the magnetic resonance spectroscopy.

Конструирование релятивистской гидродинамики простой жидкости в классе теорий второго порядка. 2. Метод релятивистской расширенной необратимой термодинамики

In this paper we constructed thermo-hydrodynamics for relativistic fluid (taking into account the second order of deviation from equilibrium for dissipative heat and viscosity flows) on the basis of extended irreversible thermodynamics (RNT). RNT formalism, providing adequate modeling of systems close to the equilibrium state, goes beyond the local equilibrium hypothesis by expanding the number of basic independent variables (including dissipative flows), as well as by modifying such conceptual concepts as entropy, temperature and pressure. The evolutionary laws for the main nonequilibrium field quantities of the relativistic system are postulated: 4-vector particle flux, 4-vector energy-momentum and 4-vector entropy flux. In order to derive the constitutive equations, a nonlocal Gibbs covariance relation and a nonlocal form of the second principle of thermodynamics with a source of entropy due to additional variables-dissipative flows-were obtained. The defining equations of the hyperbolic type, forbidding superluminal velocities, modified by relaxation terms, have been obtained. The construction of relativistic thermodynamics is carried out using the hydrodynamic 4-speed defined by Eckart. The constructed relativistic hydrodynamics has its applications in such important fields of science as nuclear physics, astrophysics and cosmology.

Toward the construction of relativistic thermo-hydrodynamics of an ideal fluid by the method of extended irreversible thermodynamics

In this paper we constructed thermo-hydrodynamics for relativistic fluid (taking into account the second order of deviation from equilibrium for dissipative heat and viscosity flows) on the basis of extended irreversible thermodynamics. EIT formalism, providing adequate mod-eling of systems close to the equilibrium state, goes beyond the local equilibrium hypothesis by expanding the number of basic independent variables (including dissipative flows), as well as by modifying such conceptual concepts as entropy, temperature and pressure. The evolutionary laws for the main nonequilibrium field quantities of the relativistic system are postulated: 4-vector particle flux, 4-vector energy-momentum and 4-vector entropy flux. In order to derive the consti-tutive equations, a nonlocal Gibbs covariance relation and a nonlocal form of the second princi-ple of thermodynamics with a source of entropy due to additional variables-dissipative flows-were obtained. The defining equations of the hyperbolic type, forbidding superluminal velocities, modified by relaxation terms, have been obtained. The construction of relativistic thermodynam-ics is carried out using the hydrodynamic 4-speed defined by Eckart. The constructed relativistic hydrodynamics has its applications in such important fields of science as nuclear physics, astro-physics and cosmology.

Double-diffusive convection in viscous flow over a rotating porous and moving disk

This paper presents the double-diffusive convection in the flow of viscous fluid over a heated, rotating, porous and moving disk. All the field quantities, defined at the surface of such disk, are nonuniform and nonlinear, therefore, the boundary conditions of the simulated problem are nonhomogeneous and variable. A set of new variables is found and it has simplified the system of six PDE's along with the boundary conditions into a system of coupled ODE's of boundary value type. The system of nonlinear, coupled and boundary value ODE's has some nine dimensionless parameters, whereas, effects of these numbers have been seen on all field variables, tangential and surface shear stresses and rates of heat and mass transfer. The present simulations have generalized the concept of rotating disk flows in the sense that the three components of velocity, associated with the disk, are taken nonuniform and nonlinear, whereas, the other thermodynamic properties, specified at the surface of the disk, also have the nonlinear nature. In this investigation, we focused on weak and strong assisting and opposing flows of liquids and gases over a rotating disk in the presence of stretching, shrinking, injection and suction velocities. Each component of velocity is effectively (slightly) enhanced with the variation of and in case of assisting (opposing) flow in the presence of stretching/shrinking and injection/suction. Moreover, similar behavior of the other field variables and quantities of physical interests has been noticed. Thin momentum, thermal and concentration boundary layers are appeared in some cases, which are clearly demonstrated in graphs in special situations.

An Analysis of the Photo-Thermoelastic Waves Due to the Interaction between Electrons and Holes in Semiconductor Materials under Laser Pulses

In this paper, the interaction between holes and electrons in semiconductor media is analyzed based on the existing mathematical–physical model. The elasto-thermodiffusion (ETD) theory, according to photothermal (PT) transport processes, has been used to study the model under the impact of the non-Gaussian laser pulse. A one-dimensional (1D) electronic/thermoelastic deformation is described, in detail, by the governing field equations. The governing field equations are taken in non-dimensional forms. The governing equations are established based on coupled elasticity theory, plasma diffusion equations, and moving equations. To determine the physical field quantities in this problem analytically in the Laplace domain, some boundary conditions are taken at the free surface of the semiconductor medium. The inversion of the Laplace transform is implemented using a numerical method to obtain the complete solutions in the time domain for the basic physical fields involved. The effects of the phase lag (relaxation time) of the temperature gradient, phase lag of the heat flux, and laser pulses are graphically obtained and discussed in comparison to silicon and germanium semiconductor materials. The wave behavior of the main fields in the semiconductors, according to optoelectronics and the thermoelastic processes, is obtained and graphically represented.

A Modified Two-Relaxation Thermoelastic Model for a Thermal Shock of Rotating Infinite Medium.

A unified form of thermoelasticity theory that contains three familiar generalized thermoelasticity. The Lord-Shulman theory, Green-Lindsay theory, and the classical one can be outlined in this form. The field quantities of a rotating/non-rotating half-space with and without the effect of the decay parameter can be obtained due to the unified thermoelasticity theory. The present medium is subjected to a time-dependent thermal shock taking into account that the magnitude of the thermal shock wave is not totally fixed but decaying over time. A special case of a thermal shock waveform with constant magnitude may be considered. The field quantities such as temperature, displacements, and stresses of the present problem are analytically obtained. Some plots of these field variables are presented in two- and three-dimensional illustrations in the context of refined theories.

Evolution of the grain structure of metals and alloys under severe plastic deformation: continuum models

Products made of metals and alloys with a fine-grained structure, which have high physical, mechanical and operational characteristics, are becoming increasingly in demand in many technical and technological fields. The most common and efficient technologies for the production of parts from this class of materials are various processes of severe plastic deformation (SPD) (in general practice, at low homologous temperatures). At the same time, to achieve high degrees of deformation, a significant part of metals and alloys require increased processing temperatures, undergo significant heating during deformation processes, which may be accompanied by changes in the grain and subgrain structure due to recovery and recrystallization processes. An empirical approach to the development of SPD modes that ensure the formation of the necessary grain structure requires huge time and financial costs, and therefore considerable attention is paid by researchers in the field of solid mechanics and metal forming to approaches and methods of mathematical modeling. In connection with the foregoing, the number of publications on this subject has been intensively growing in recent years. The currently known models differ significantly in their approaches, the depth of penetration into the physics of processes, and the scope of consideration. The proposed brief review is focused on a qualitative analysis of works on this topic, a preliminary classification of existing models according to their purpose, versatility, and functionality. It seems possible to single out the two most common approaches to describing the change in the grain structure in the processes of thermomechanical processing of metals and alloys: continual (in most cases, single-level) and multilevel, based on the introduction of internal variables and physical theories. This review is devoted to the consideration of publications focused on the first of these approaches. Until now, the most common are macrophenomenological continuum models based on the analysis of experimental data conducted both in laboratories on macrosamples and in real production conditions. Models of this class are usually formulated in the form of operator relations over field quantities, they are relatively easy to implement due to their easy “embedding” into widely used commercial software packages, but they require significant costs for experiments to identify models, they are characterized by a low degree of versatility. Continuous theories are relatively less common, but still often used. These theories are based on the description of physical mechanisms and the evolution of the structure of metals and alloys in terms of continuum variables.

Effect of Hydrostatic Initial Stress on a Rotating Half-Space in the Context of a Two-Relaxation Power-Law Model

The simple and refined Lord–Shulman theories, the simple and refined Green–Lindsay theories as well as the coupled thermoelasticity theory were all employed to investigate the deformation of a rotating thermoelastic half-space. The present medium is subjected to initial pressure, bounded by hydrostatic initial stress and rotation. A unified heat conduction equation is presented. The normal mode strategy is applied to get all analytical expressions of temperature, stresses, and displacements. Some outcomes are tabulated to validate the present refined theories with the simple and classical thermoelasticity theories. The effect of hydrostatic initial stress was investigated on all field quantities of the rotating thermoelastic half-space with and without initial pressure. Two- and three-dimensional plots are illustrated in the context of refined theories to discuss the behaviors of all variables through the coordinate axes. Some particular cases of special interest have been deduced from the present investigation.

Head on collision of ion–acoustic shock waves in weakly relativistic electron–positron–ion quantum plasma

In this work, we explore analytically the head on collision (HoC) of two ion acoustic shock wave in relativistic quantum plasma. Extended Poincaré Lighthill Kuo(PLK) method has been applied in this problem in a fruitful manner to study the HoC of waves which are rare in literature. Introducing the strained coordinates and expanding the field quantities into the parameter ϵ, a set of differential equations is obtained. Tangent Hyperbolic method is also used while investigating nonlinear interaction of this mode. These techniques are proven to be efficient enough to extract the essence of physics. Our major focus is to study the influence of plasma characteristics on shock wave phase shifts upon a head-on collision. The effects of the ratio of electrons to positron temperature, fractional concentration of positrons, quantum parameter, kinematic viscosity on the phase shift are studied. The findings suggest that shock interactions are distinct from those of solitons. It is also observed that the dispersion and dissipation of the colliding nonlinear structure have a combined role in the occurrence and modification of trajectory variations. The results of this work might be beneficial in studying the propagation and interaction of quantum ion–acoustic shock waves in dense astrophysical plasma systems (white dwarf star) and intense laser-solid density plasma investigations.

A Hybrid, Runtime Coupled Incompressible CFD-CAA Method for Analysis of Thermoacoustic Instabilities

Abstract Thermoacoustic instabilities in gas turbine engines are of increasing interest for design of future low-emission technology combustors. Numerical methods used to predict thermoacoustic instabilities often employ either fully compressible resource-intense computational fluid dynamics (CFD) simulations, or two-step approaches where source terms extracted from CFD simulations are supplied to subsequent computational aeroacoustics (CAA) simulations. This work demonstrates an analysis of self-excited thermoacoustic instabilities using a hybrid method based on runtime coupling of incompressible CFD and CAA simulations. A prior implementation for the computation of combustion noise through one-way coupling of CFD and CAA solvers has been extended to a two-way coupling that allows acoustics to influence the flow field. The resulting hybrid method couples acoustic and convective physical phenomena by using mean flow field quantities and the thermoacoustic energy source term obtained from the solution of the Navier–Stokes equations in the low Mach number limit as an input for the acoustic perturbation equations (APEs). The fluctuating acoustic quantities pressure and velocity obtained from the solution of the APE are in turn included in the solution of the low Mach number Navier–Stokes equations, influencing the convective dynamics of the flow field. The suitability of the present implementation to capture thermoacoustic feedback is demonstrated through analysis of the well-known self-excited instability observed in a Rijke tube. The results are presented and discussed in comparison with a fully compressible reference solution.

Transient analysis on surface heated piezoelectric semiconductor plate lying on rigid substrate

Based on the thermo-electro-elastic coupling theory, the mathematical model for a surface heated piezoelectric semiconductor (PS) plate is developed in the time domain. Applying the direct and inverse Laplace transformations to the established model, the mechanical and electrical responses are investigated. The comparison between the analytical solution and the finite element method (FEM) is conducted, which illustrates the validity of the derivation. The calculated results show that the maximum values of the mechanical and electrical fields appear at the heating surface. Importantly, the perturbation carriers tend to concentrate in the zone near the heating surface under the given boundary conditions. It can also be observed that the heating induced elastic wave leads to jumps for the electric potential and perturbation carrier density at the wavefront. When the thermal relaxation time is introduced, all the field quantities become smaller because of the thermal lagging effect. Meanwhile, it can be found that the thermal relaxation time can describe the smooth variation at the jump position. Besides, for a plate with P-N junction, the effect of the interface position on the electrical response is studied. The effects of the initial carrier density on the electrical properties are discussed in detail. The conclusions in this article can be the guidance for the design of PS devices serving in thermal environment.