Non-ideal Region Research Articles

Efficient knowledge model for whale optimization algorithm to solve large-scale problems

In the process of digital transformation and development in various industries, there are more and more large-scale optimization problems. Currently, swarm intelligence optimization algorithms are the best method to solve such problems. However, previous experimental research has found that there is still room for improvement in the performance of using existing swarm intelligence optimization algorithms to solve such problems. To obtain the high-precision optimal value of whale optimization algorithm (WOA) for solving large-scale optimization problems, the optimization problem knowledge model is studied to guide the iterative process of WOA algorithm, and a novel whale optimization algorithm based on knowledge model guidance (KMGWOA) is proposed. First, a population update strategy based on multiple elite individuals is proposed to reduce the impact of the local optimal values, and the knowledge model to guide population update is constructed by combining the proposed population update strategy with the population update strategy based on global optimal individual. Second, a collaborative reverse learning knowledge model with multiple elite and poor individuals in the solution space is proposed to prevent long-term non-ideal region search. The above two knowledge models guide the iterative process of WOA algorithm in solving large-scale optimization problems. The performance of the KMGWOA algorithm guided by the proposed knowledge models is tested through the well-known classical test functions. The results demonstrate that the proposed KMGWOA algorithm not only has good search ability for the theoretical optimal value, but also achieves higher accuracy in obtaining the optimal value when it is difficult to obtain the theoretical optimal value. Moreover, KMGWOA algorithm has fast convergence speed and high effective iteration percentage.

Experimental and Numerical Study on the Residence Time Distribution in a Stirred Membrane Reactor

The residence time distribution (RTD) of a reactor is a key factor related to the actual reaction time of reactants, by which the mixing in a reactor can be judged indirectly. Though many efforts have been made to study RTD in stirred tank reactors (STs) or membrane modules, research on RTD in a stirred membrane reactor (SMR) is still lacking. For this purpose, we investigated the influence of operating conditions on mixing in the SMR through experiments, obtained non-ideal mixing region by mathematical model fitting, and analyzed the flow field combined with CFD simulation. The critical value of the ratio of the discharge of impeller to the flow rate is 13.13 designed to reach ideal mixing in the SMR and that of the ratio of the mean residence time to the mixing time is 10 correspondingly. In addition, the RTD is independent of membrane permeability resistance.

Numerical simulation of ideal and non-ideal under-expanded supersonic jets with adaptive grids

This paper numerically investigates the effect of flow non-ideality on the Mach disk pattern occurring in axisymmetric under-expanded supersonic jets. The explored conditions are found in the non-ideal gas region close to the liquid–vapor saturation curve and the critical point, where involved thermodynamics cannot be accurately described by the ideal gas law. Numerical simulations of steady inviscid compressible flows are carried out by adopting the polytropic ideal gas model and improved Peng–Robinson thermodynamic model, via the open-source computational fluid dynamics code SU2. To properly resolve the Mach disk position and radius, a mesh adaptation procedure is used. An assessment of the most suitable mesh adaptation criteria for the considered ideal and non-ideal flow configurations is carried out, considering isotropic and anisotropic mesh adaptation criteria. The best mesh adaptation criterion for ideal and non-ideal under-expanded jets results to be the anisotropic criterion based on the Hessian of the density and Mach number field. Then, the effects of the flow non-ideality on the Mach disk are investigated by simulating different operating conditions of under-expanded nozzle jets of five different vapors. For nitrogen, oxygen, carbon dioxide, the Mach disk moves downstream and has a smaller radius with a higher level of non-ideality. Conversely, for siloxanes MM and MDM, the Mach disk moves upstream and has a larger radius as the non-ideality of the flows increases.

Nonideal Fields Solve the Injection Problem in Relativistic Reconnection.

Magnetic reconnection in relativistic plasmas is well established as a fast and efficient particle accelerator, capable of explaining the most dramatic astrophysical flares. With particle-in-cell simulations, we demonstrate the importance of nonideal fields for the early stages ("injection") of particle acceleration. Most of the particles ending up with high energies (near or above the mean magnetic energy per particle) must have passed through nonideal regions where the assumptions of ideal magnetohydrodynamics are broken (i.e., regions with E>B or nonzero E_{∥}=E·B/B), whereas most of the particles that do not experience nonideal fields end up with Lorentz factors of order unity. Thus, injection by nonideal fields is a necessary prerequisite for further acceleration. Our results have important implications for the origin of nonthermal particles in high-energy astrophysical sources.

Development and validation of a Riemann solver in OpenFOAM® for non-ideal compressible fluid dynamics

ABSTRACT Recently, there is an increased interest in supercritical CO2 and organic Rankine cycles (ORC) for their ability to achieve higher thermodynamic efficiency. However, the non-ideal gas thermodynamic in these cycles may affect the flow properties critically, necessitating the research of non-ideal compressible fluid dynamics (NICFD). Thus, simulation tools that can accurately predict fluid flows with NICFD are significant. This study presents a new approximation Riemann solver in OpenFOAM for NICFD. The new solver uses a real-gas (look-up table based) approximate Riemann flux calculator (modified from HLLC ALE flux calculator) through adding a new thermodynamic library tightly coupled with the OpenFOAM®. To validate the solver, three cases are presented, including a NASA transonic nozzle operating with air, to confirm the ability to correctly simulate the transonic flow phenomena and the shock waves; the VKI 2D cascade operated with MDM to assess the ability in simulating non-ideal gas flows typically to industrial applications; and the dense gas flow (MD4M) passing a backward ramp to illustrate the ability of the flux calculator and look-up table mechanism that can work well in the non-ideal region of fluid properties. This study can benefit future engineering applications of computational fluid mechanics of NICFD and the OpenFOAM community.

Three-dimensional unsteady stator-rotor interactions in high-expansion organic Rankine cycle turbines

Organic Rankine cycle (ORC) systems are a readily available technology to convert thermal energy from renewable- and waste heat sources into electricity. However, their thermal performance is relatively low due to the low temperature of the available heat sources, but more importantly, due to the low efficiency of the employed expander. Designing the turboexpander is exceptionally challenging, because the flow field is highly supersonic and unsteady, and since the expansion takes place in the highly non-ideal dense-vapor region. In this work, we perform unprecedented three-dimensional unsteady simulations of several high-expansion cantilever ORC turbines to highlight distinctive loss mechanisms. The simulations indicate strong unsteady effects in the rotor blade passage, as a result of unsteady propagating shock waves interacting with viscous wakes and boundary layers. Moreover, the flow field in the rotor blade passage is strongly affected by three-dimensional secondary flow features and a sharp expansion in the shroud region at the inlet of the rotor blade. These span-wise mechanisms and unsteady flow interactions introduce irreversible losses which must be taken into account for designing highly efficient ORC expanders.

Magnetic Reconnection in the Absence of Three-Dimension Null Point

In this study, a numerical examination is portrayed which explores the idea of 3D reconnection, in the absence of magnetic null points focuses, at a segregated non-ideal region. We center around the subsequent conduct of the magnetic flux, which has been appeared D.I. Pontin et al. (2004), to be on a very basic level diverse in the kinematic routine from the natural two-dimensional conduct. The point of this numerical investigation is to test whether the new properties of 3D kinematic reconnection, depicted by D.I. Pontin et al. (2004) finish to the dynamical routine, where magnetohydrodynamics equations are unraveled. We point likewise specifically to check (or something else) the arrangement by G. Hornig and E.R. Priest (2003) for kinematic 3D reconnection without an magnetic null point.

Observations of a Kinetic‐Scale Magnetic Hole in a Reconnection Diffusion Region

AbstractMagnetic holes have been widely observed in various space plasma systems. The origin of magnetic holes and their influence to background plasma are under debate. In this paper, we show a kinetic‐scale electron vortex magnetic hole in a nonideal region of an active X line, which was observed by the Magnetospheric Multiscale mission at the dayside magnetopause. Intense current and nonideal electric field in the electron frame were observed within the magnetic hole, which led to a strong energy dissipation. Thus, the electron vortex magnetic hole probably provided an additional energy dissipation channel besides the electron diffusion region adjacent to the hole. We suggest that magnetic reconnection provided favorable conditions for the formation of this kinetic‐scale magnetic hole and is an important source of magnetic holes in space plasma.

Diffuser performance of centrifugal compressor in supercritical CO2 power systems

The paper focuses on understanding the performance of a vaned diffuser in a supercritical CO2 compressor using real gas assumptions. The rapidly changing properties of CO2 in the non-ideal thermodynamic region can have a significant impact on the performance of the diffuser. To account for this, the relationship between the flow properties (i.e. fundamental derivative) and the local geometry (i.e. cross-sectional area of the nozzle) has been discussed theoretically. To examine it analytically, the study has considered the influence of real gas properties on the performance of a vaned diffuser using computational fluid dynamics (CFD) modelling. The selected compressor stage geometry is similar to the compressor impeller tested in the Sandia sCO2 compression loop facility. The effect of changes in the number of blades and the corresponding changes in the cross throat area on the flow properties such as density and speed of sound were investigated and discussed. The results illustrate that a diffuser with a higher number of blades (smaller throat area) compared to a diffuser with a wider throat area has a higher probability of creating flow instability in the passage stage.

Experimental evidence of non-ideal compressible effects in expanding flow of a high molecular complexity vapor

Supersonic expansions of a molecularly complex vapor occurring within the non-ideal thermodynamic region in the close proximity of liquid-vapor saturation curve were characterized experimentally for the first time. Results for two planar converging–diverging nozzles in the adapted regime and at different inlet conditions, from highly non-ideal to dilute gas state, are reported. Measurements of upstream total pressure and temperature are performed in the plenum ahead of the nozzle, while static pressure and supersonic Mach number measurements are carried out along the nozzle centerline. The investigated expansions are of interest for both fundamental research on non-ideal compressible flows and industrial applications, especially in the energy field. Siloxane MDM (octamethyltrisiloxane, text {C}_8text {H}_{24}text {O}_2text {Si}_3), a high molecular complexity organic compound, is used. Local pressure ratio P/P_mathrm{T} and Mach number M measurements display a dependence on the inlet total state, a typical non-ideal feature different from dilute gas conditions.

Rapid, deep dopant diffusion in crystalline silicon by laser-induced surface melting

As solar cell back contact schemes have improved in recent years, the non-ideal emitter region has become a dominant contributor to overall losses in solar cell efficiency. Our analysis shows that these losses can be greatly reduced by creating a lightly (< 1018 cm−3), uniformly doped emitter that is about 10 µm deep. However, the constraints imposed by current manufacturing techniques, namely using a tube-furnace for solid state dopant diffusion, limits the emitter to a much more highly doped (~ 1020 cm−3) and shallow (< 500 nm) region. A laser-based process by which dopants are diffused in a liquid silicon state can overcome these limitations. In this work, we provide semiconductor device simulations that compare the effects of these two types of emitters on device performance. Then, we used a heat transport model to demonstrate that a focused laser line beam can create a molten region at the surface of a silicon wafer that would allow dopants to diffuse deeply within a short amount of time. We then performed the laser processing with a scanned laser line beam on preheated silicon samples. The resulting junction depth (> 10 µm) is measured by cross-sectional etching and electron beam-induced current measurements. Electrochemical capacitance-voltage measurements are used to measure both the depth as well as the dopant profile resulting from the laser-driven process. We also analyse dislocation defects induced by the large thermal gradients inherent to the laser-based process which would greatly limit the device performance.

A hybrid deconvolution approach for estimation of in vivo non-displaceable binding for brain PET targets without a reference region.

Background and aimEstimation of a PET tracer’s non-displaceable distribution volume (VND) is required for quantification of specific binding to its target of interest. VND is generally assumed to be comparable brain-wide and is determined either from a reference region devoid of the target, often not available for many tracers and targets, or by imaging each subject before and after blocking the target with another molecule that has high affinity for the target, which is cumbersome and involves additional radiation exposure. Here we propose, and validate for the tracers [11C]DASB and [11C]CUMI-101, a new data-driven hybrid deconvolution approach (HYDECA) that determines VND at the individual level without requiring either a reference region or a blocking study.MethodsHYDECA requires the tracer metabolite-corrected concentration curve in blood plasma and uses a singular value decomposition to estimate the impulse response function across several brain regions from measured time activity curves. HYDECA decomposes each region’s impulse response function into the sum of a parametric non-displaceable component, which is a function of VND, assumed common across regions, and a nonparametric specific component. These two components differentially contribute to each impulse response function. Different regions show different contributions of the two components, and HYDECA examines data across regions to find a suitable common VND. HYDECA implementation requires determination of two tuning parameters, and we propose two strategies for objectively selecting these parameters for a given tracer: using data from blocking studies, and realistic simulations of the tracer. Using available test-retest data, we compare HYDECA estimates of VND and binding potentials to those obtained based on VND estimated using a purported reference region.ResultsFor [11C]DASB and [11C]CUMI-101, we find that regardless of the strategy used to optimize the tuning parameters, HYDECA provides considerably less biased estimates of VND than those obtained, as is commonly done, using a non-ideal reference region. HYDECA test-retest reproducibility is comparable to that obtained using a VND determined from a non-ideal reference region, when considering the binding potentials BPP and BPND.ConclusionsHYDECA can provide subject-specific estimates of VND without requiring a blocking study for tracers and targets for which a valid reference region does not exist.

Where is the electric current driven in the Blandford-Znajek process?

AbstractThe Blandford-Znajek process, the steady electromagnetic energy extraction from a rotating black hole, is widely believed to work for driving relativistic jets, although it is still under debate where the electric current is driven. We address this issue analytically by investigating the time-dependent state in the Boyer-Lindquist and Kerr-Schild coordinate systems. This analysis suggests that a non-ideal magnetohydrodynamic region is required in the time-dependent state, while not in the steady state.

Laboratory study of diffusion region with electron energization during high guide field reconnection

Floating potential profile was measured around the X-point during high guide field reconnection in UTST merging experiment where the ratio of guide field (Bg) to reconnecting magnetic field (Brec) is Bg/Brec&amp;gt;10. Floating potential measurement revealed that a quadrupole structure of electric potential is formed around the X-point during the fast reconnection phase due to the polarization by inductive electric field. Also, our floating potential measurement revealed the existence of parallel electric field in the vicinity of the X-point. While field-aligned components of inductive electric field (E∥ind) and electrostatic electric field (E∥es) cancel out with each other away from the X-point, E∥ind exceeds E∥es around the X-point, indicating the deviation from ideal MHD criterion within the region. The diffusion region extends in the outflow region and the scale length of region is an order of ion skin depth, which is quite different from the VTF experiment result. Based on the measured magnetic field and electric field profile, our particle trajectory analysis indicates that fast electrons with energies over 300 eV are produced within 1 μs around the X-point in the non-ideal MHD region. These results indicate that production of fast electrons or electron heating are expected to be observed in the vicinity of the X-point.

Quantifying three dimensional reconnection in fragmented current layers

There is growing evidence that when magnetic reconnection occurs in high Lundquist number plasmas such as in the Solar Corona or the Earth's Magnetosphere it does so within a fragmented, rather than a smooth current layer. Within the extent of these fragmented current regions, the associated magnetic flux transfer and energy release occur simultaneously in many different places. This investigation focusses on how best to quantify the rate at which reconnection occurs in such layers. An analytical theory is developed which describes the manner in which new connections form within fragmented current layers in the absence of magnetic nulls. It is shown that the collective rate at which new connections form can be characterized by two measures; a total rate which measures the true rate at which new connections are formed and a net rate which measures the net change of connection associated with the largest value of the integral of E|| through all of the non-ideal regions. Two simple analytical models are presented which demonstrate how each should be applied and what they quantify.

Theoretical and Numerical Analysis of Discharge Characteristics in Pulsed Electromagnetic Accelerators

Discharge is critical physical process in pulsed electromagnetic accelerators for arc plasma jet device, and its characteristics directly determines the accelerator performance. The mechanisms of discharge plasma and flow in the accelerator are analyzed by magnetohydrodynamics (MHD). The model is coupled with electric circuit model based on weakly nonideal plasma conductivity and ablation model. Calculation results show that there is some nonideal plasma region which has important effects on electrical conductivity; most ablated gases are ionized at the half cycle of the discharge time and are accelerated by Lorentz force to high exhaust velocity; electrical conductivity, plasma temperature and density are increasing with discharge energy unleashed, and gradually reduce in the post-discharge.

Proton acceleration in antiparallel collisionless magnetic reconnection: Kinetic mechanisms behind the fluid dynamics

[1] This paper investigates the proton kinetic mechanisms leading to the formation of plasma jets in antiparallel magnetic reconnection. In particular, the interaction of the protons with the Hall electric field in the proton non-ideal region is discussed. The study, based on a two-dimensional hybrid simulation, details the important role of the proton pressure force in the acceleration process and its role in maintaining open and steady the proton outflow channel. When no fluid closure is assumed, it is found that this force arises from a strong anisotropy in velocity space which comes from kinetic effect. By analyzing the distribution functions and the individual particle dynamics, it is shown that the mixing of protons bouncing in a divergent electrostatic potential well associated to the Hall effect statistically couples the two in-plane velocity components of the particles. This coupling results, from the macroscopic point of view, in off-diagonal components of the pressure tensor.

Torsional magnetic reconnection: The effects of localizing the non-ideal (ηJ) term

AbstractMagnetic reconnection in three dimensions (3D) is a natural extension from X-point reconnection in two dimensions. Of central importance in the 3D process is a localized non-ideal region within which the plasma and magnetic field decouple allowing for field line connectivity change. In practice, localized current structures provide this localization; however, mathematically a similar effect can be achieved with the localization of plasma resistivity instead. Physically though, such approaches are unrealistic, as anomalous resistivity requires very localized currents. Therefore, we wish to know how much information is lost in localizing η instead of current? In this work we develop kinematic models for torsional spine and fan reconnection using both localized η and localized current and compare the non-ideal flows predicted by each. We find that the flow characteristics are dictated almost exclusively by the form taken for the current profile with η acting only to scale the flow. We do, however, note that the reconnection mechanism is the same in each case. Therefore, from an understanding point of view, localized η models are still important first steps into exploring the role of non-ideal effects.

Medical Ultrasound Transducer Having Non-Ideal Focal Region

A mechanically formed transducer capable of producing a non-ideal focal region is described. The transducer has a plurality of piezoelectric elements suspended in an epoxy and heat molded into a desired shape. One or more shaped irregularities in the transducer provides for a mechanically induced non-ideal focal field without the need for electronic steering or lens focusing. Systems and methods of making the same are also described.

On the solutions of three-dimensional non-null magnetic reconnection

Here we present solutions of a stationary magnetohydrodynamic (MHD) model for three-dimensional (3D) magnetic reconnection in the absence of a null point. The solutions are found in the form of an expansion scheme with a localized nonideal region. A wide variety of both analytical and numerical solutions of the resistive MHD equations can be obtained via an integration scheme, which includes free functions to match boundary conditions. General analytical solutions are obtained for the first few orders, whereas higher order solutions require numerical integration. Thus, numerical techniques have been used to examine the contribution of some higher order terms. The obtained solutions show important differences between 3D solutions and the commonly used two-dimensional models. In particular, they show the existence of more complicated current and flow structures in the reconnection region.