Layer Model Research Articles

Model of non-equilibrium near-cathode plasma layers for simulation of ignition of high-pressure arcs on cold refractory cathodes

The introduction of secondary ion-electron emission into an approximate model of non-equilibrium plasma layers on hot (thermionic) cathodes of high-pressure arc discharges allows extending the model to low cathode surface temperatures. Analysis of evaluation results shows that the extended model describes glow-like discharges on cold cathodes and thermionic arc discharges on hot cathodes, as it should. In the course of glow-to-arc transitions on cold cathodes, a transient regime occurs where a hot arc spot has just formed and a significant fraction of the current still flows to the cold surface outside the spot, so that the near-cathode voltage continues to be high. The power input in the near-cathode layer is very high in this regime, and so is the electron temperature in the near-cathode region. The mean free path for collisions between the atoms and the ions in these conditions exceeds the thickness of the layer where the ion current to the cathode is generated. A new method for evaluation of the ion current under such conditions is implemented. The developed model is applicable for cathode surface temperatures below the boiling point of the cathode material and may be used for multidimensional simulations of ignition of high-current arcs on refractory cathodes.

Validity of LiPON Conductivity Determined by Impedance Spectroscopy

A hypothesis that the generally accepted value of the LiPON conductivity should be attributed to the absorption and displacement currents is substantiated. The reason is a small contribution of the drift current due to field screening by the electric double layer. The basis for this assumption is the measurement of the LiPON absorption capacitance, according to which its dielectric constant is about 106. An alternative equivalent circuit containing a non-ideal absorption element is proposed and its impedance is calculated. It is shown that the Bode diagrams of the alternative circuit approximate the experimental curves well. Parameters and the magnitude of electric field screening are calculated based on a proposed model of a double electric layer. Considering the screening effect, the drift conductivity of LiPON is obtained, which is in good agreement with the data on lithium concentration and ion mobility.

Atomistic Characterization of Healthy and Damaged Hair Surfaces: A Molecular Dynamics Simulation Study of Fatty Acids on Protein Layer.

Amid the bourgeoning demand for in-silico designed, environmentally sustainable, and highly effective hair care formulations, a growing interest is evident in the exploration of realistic computational model for the hair surface. In this work, we present an atomistic model for the outermost layer of the hair surface derived through molecular dynamics simulations, which comprises 18-Methyleicosanoic acid (18-MEA) fatty acid chains covalently bound onto the keratin-associated protein 10-4 (KAP10-4) at a spacing distance of ~1 nm. Remarkably, this hair surface model facilitates the inclusion of free fatty acids (free 18-MEA) into the gaps between chemically bound 18-MEA chains, up to a maximum number that results in a packing density of 0.22 nm2 per fatty acid molecule, consistent with the optimal spacing identified through free energy analysis. Atomistic insights are provided for the organization of fatty acid chains, structural features, and interaction energies on protein-inclusive hair surface models with varying amounts of free 18-MEA (FMEA) depletion, as well as varying degrees of anionic cysteic acid from damaged bound 18-MEA (BMEA), under both dry and wet conditions. In the presence of FMEA and water, the fatty acid chains in a pristine hair surface prefers to adopt a thermodynamically favored extended chain conformation, forming a thicker protective layer (~3 nm) on the protein surface. Our simulation results reveal that, while the depletion of FMEA can induce a pronounced impact on the thickness, tilt angle, and order parameters of fatty acid chains, the removal of BMEA has a marked effect on water penetration. There is a "sweet spot" spacing between the 18-MEA whereby damaged hair surface properties can be reinstated by replenishing FMEA. Through the incorporation of the protein layer and free fatty acids, the hair surface models presented in this study enables a realistic representation of the intricate details within the hair epicuticle, facilitating a molecular scale assessment of surface properties during the formulation design process.

Resistivity Model of Clayshale Layers in Dry Season and Early Rainy Season Conditions Case Study of the Jragung Dam Project

Resistivity Model of Clayshale Layers in Dry Season and Early Rainy Season Conditions Case Study of the Jragung Dam Project

Presenting a CBR Estimation Model and Compaction Characteristics of Base Layer of Pavement Using a Dynamic Cone Penetrometer (DCP) Test

Presenting a CBR Estimation Model and Compaction Characteristics of Base Layer of Pavement Using a Dynamic Cone Penetrometer (DCP) Test

Modeling of Pore-Scale Capillary-Dominated Flow and Bubble Detachment in PEM Water Electrolyzer Anodes Using the Volume of Fluid Method

Fluid dynamics models complement expensive experiments with limited measurement accuracy that investigate the mass transport in PEM water electrolysis. Here, a first-principle microscale model for oxygen transport is successfully validated that accounts for (1) uncertain transport processes in catalyst layers, (2) numerically challenging capillary-dominated two-phase flow and (3) bubble detachments in channels. We developed algorithms for the stochastic generation of geometries and for the coupling of flow and transport processes. The flow model is based on the volume of fluid method and reproduces experimentally measured pressure drops and bubble velocities within minichannels with a 30% and 20% accuracy, respectively, provided that the capillary number is above 2.1 × 10−7. At lower capillary numbers, excessive spurious currents occur. Correspondingly, two-phase flow simulations within the porous transport layers are stable at current densities above 0.5 A cm−2 and match operando gas saturation measurements within a 20% margin at relevant locations. The simulated bubble detachments occur at pore throats that agree with porosimetry and microfluidic experiments. The presented model allows explaining and optimizing mass transport processes in channels and porous transport layers. These were found to be negligibly sensitive to transport resistances within the catalyst layer, providing information on boundary conditions for future catalyst layer models.

Computational fluid dynamics model-based design of continuous forced convection freezing processes for human induced pluripotent stem cells considering supercooling of extracellular solutions

This work presents a computational fluid dynamics (CFD) model-based process design of forced convection continuous freezing for human induced pluripotent stem (hiPS) cells considering supercooling of extracellular solutions. The overall model consists of a CFD model for velocity field and heat transfer calculations including the effect of the supercooling, and a cell layer model for cell survival rate calculations. Experimental temperature profiles were obtained using a forced convection-based batch freezer, and the validation of the heat transfer and solidification models was performed. The experiments were carried out by applying a 1.0 K min–1 cooling rate with an inlet velocity of 2.0 m s–1. The model was applied to three different freezer sizes with shelves containing 10, 20 and 30 rows. The applied coolant inlet velocities ranged from 0.50 m s–1 to 4.0 m s–1. It was found that the application of an inlet velocity of 3.0 m s−1 yielded an average cell survival rate of 0.934 with low survival rate heterogeneity in the freezers. This way, the freezing process for hiPS cells could be scaled to up to 170-fold compared to currently used equipment for hiPS cell freezing.

Crack layer modeling of butt-fusion joints induced slow crack growth in high-density polyethylene pipes

The design and reliability of high-density polyethylene (HDPE) pipes can be dictated by the damage tolerance of their butt-fusion joints. A slow crack growth (SCG) model based on the crack layer theory for HDPE pipes internal and external circumferential and butt-fusion joints cracks is developed to investigate the discontinuous SCG behavior and lifetime tf variations. Using the developed model, the discontinuous SCG patterns, jump lengths and lifetime tf can be accurately simulated. In addition, the effects of pipes standard dimension ratio, internal pressure, and temperature on the SCG behavior and tf are investigated. Compared to pipe cracks, it was found that butt-fusion induced SCG can reduce the pipe tf > 60 %. Unlike longitudinal cracks, tf of external circumferential cracks, were found shorter than the internal ones, mandating an earlier evaluation. The new SCG model shows good accuracy with the experimental results. The same substitute geometry approach used can be followed for othercomplex designs, which aids in establishing a fundamental methodology for more realistic lifetime predictions.

Performance and modeling of freezing crystallization in desalination: Heat transfer and impurities flow

This work applies the freezing crystallization in the desalination and establishes the theoretical models with experiments, to correlate the technical parameters with product properties. We first establish the heat flow models to simulate the 3-dimensional spatiotemporal temperature distribution and deduce the two heat flows through the ice layer, in which the latent heat from the phase transition plays a dominant role in heat transfer. Next, mass transfer and boundary layer models are proposed to evaluate the desalination efficiency and demonstrate the roles of kinetic and thermodynamic factors on the impurity migration. Later, three process optimization strategies, including cooling rate regulation, air bubble-assisted, and crystal seed-induced techniques, are imported to enhance the separation efficiency. At last, sweating is incorporated to reach the secondary purification effect, in which the desalination ratio under the optimal trajectory exceeds 83 %. The established sweating models accurately predict the product properties with time and can trace the impurities flow from the ice layer and adherent inclusion. The inclusion occupies a major discharged melt at the initial sweating stage, but more ice layer begins to melt and enter into the sweating liquid, confirming that a slight increase in product purity accompanies the huge yield loss.

Modifications to the CLASS Boundary Layer Model for Improved Interaction Between the Mixed Layer and Clouds

AbstractThe impact of clouds on the mixed layer (ML) is critical for understanding the evolution of boundary layer humidity and temperature over the course of a day. We found that accounting for moistening of the cloud layer (CL) by humidity originating in the ML dramatically alters the interaction between the ML and the CL in a one‐dimensional cloud‐topped boundary layer model: Chemistry Land‐surface Atmosphere Soil Slab (CLASS) (Vilà‐Guerau de Arellano et al., 2015, https://doi.org/10.1017/CBO9781316117422). We demonstrate that enabling CLASS to moisten the lower CL improves the prediction of humidity (and the flux of humidity) both above and below the ML top (h). To account for this moistening, we propose a length scale, L, above h, over which mixing of mass fluxes into the environment occurs. The mass fluxes are assumed to decrease linearly from h to a height L meters above h, analogous to a convective plume detraining into the environment at a height‐independent rate. Accounting for this process is accomplished by modifying the differential equations representing the growth of the jumps (sharp changes in humidity and temperature) at h. From analysis of a large number of diurnal Large Eddy simulations (covering approximately 11,000 different early morning initial conditions), we provide a regression model for parameterizing L from early morning weather variables. With the regression‐based estimate of L, the modified model (CLASS‐L) accounts for moistening the lower CL, and as a result, yields improved humidity dynamics, humidity flux profiles, and cloud growth under a broad range of conditions.

Структура электрического поля в конвективно-турбулентном приземном слое атмосферы

Electrodynamic models of the surface layer of the atmosphere, taking into account turbulent and convective transport, are constructed and studied. The models are based on the so-called total current equation derived from the equations of the theory of the electrode effect in the atmosphere. From the point of view of mathematics, this is a partial differential equation of a parabolic type with variable coefficients. Since in this type of equations the differential operator is not necessarily the Sturm-Liouville operator, in appropriate cases it is necessary to use different approaches to integrating the total current equation. This, in turn, makes it necessary to consider various hypotheses about the ratio of the intensities of local factors that affect the structure of the equation. The paper considers several cases of the model corresponding to the convective turbulent and convective-turbulent electrode layer. Analytical solutions of the stationary equation of the total electric current are obtained. in various approximations. Electric field strength profiles in the surface layer of the atmosphere for various physical conditions are constructed and studied.

Numerical Study on Rotor–Building Coupled Flow Field and Its Influence on Rotor Aerodynamic Performance under an Atmospheric Boundary Layer

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural atmospheric conditions. A high-fidelity atmospheric boundary layer (ABL) model described by an exponential law is established herein. The solution of the coupled flow field is based on the Reynolds-averaged Navier–Stokes (RANS) equations, with the rotor’s rotation achieved through the overset grid method. Based on the dominant wind features, the building flow field is distributed into four regions, where the updraft along the headwind side impacts the rotor, bringing about a 76% increase in pitching moment. On the lateral side of the building, distorted rotor wake squeezed upward into the rotor disk, leading to severe blade–vortex interaction (BVI). During low-altitude hovering over rooftops, the mixing of building shed vortices with forward flow wakes causes the formation of a circulation region on the rotor’s windward side, resulting in a thrust loss of approximately 7.8%. Meanwhile, the flow environment on the leeward side of the buildings is more stable. Therefore, it is recommended that helicopters adopt a headwind approach during rooftop operations. However, an 11.4% loss in the average hover figure of merit is observed due to consistent thrust losses caused by the recirculation region.

Employing machine learning techniques for estimating the differential code biases of GPS satellites

ABSTRACT In this study, the capabilities of Machine Learning (ML) are exploited to predict the Differential Code Biases (DCBs) of Global Positioning System (GPS) satellites from the broadcast Total Group Delays (TGDs), satellite numbers, satellite block types, and Sunspot numbers. Firstly, a detailed analysis of the DCB and TGD values over five years is provided. Then, different ML models are trained and tested. The results showed that the bagged trees, the rational quadratic Gaussian Process Regression, and the Feed-Forward Neural Networks (2 hidden layers) models can be used efficiently to predict the DCB values of GPS satellites.

Molecular dynamics study of cross‐linking degrees effect on the aging resistance of epoxy asphalt: Insights from oxygen diffusion

AbstractTo interpret the diffusion behavior of oxygen in epoxy asphalt with different cross‐linking degrees, epoxy asphalt‐oxygen diffusion layer models were constructed. The effect of temperature on oxygen diffusion and the number of oxygen molecules penetrating the epoxy asphalt was quantitatively analyzed. Fick's second law was used to determine the oxygen diffusion coefficient. The Mean square displacement (MSD) was extracted to analyze the effect of cross‐linking degree on the molecular motion of the base asphalt. The results show that as the cross‐linking degree increases, the number of oxygen in the epoxy asphalt decreases, accompanied by a reduction in the oxygen diffusion coefficient. Temperature significantly affects the rate of oxygen diffusion, with higher temperatures leading to greater diffusion depths over the same simulation time. The oxygen diffusion coefficient of epoxy asphalt ranges from 4.60 × 10−11 to 2.20 × 10−10 m2/s at temperatures of 298–373 K. The epoxy system markedly restricts the movement of base asphalt molecules, with saturate being most affected by cross‐linking degree and asphaltene the least. A high cross‐linking network impedes the asphalt‐oxygen contact oxidation, enhancing epoxy asphalt's anti‐aging capacity. These findings provide support for optimizing epoxy asphalt formulations and guiding the development of anti‐oxidant epoxy asphalt.

A Rapid Modeling Method for Airborne FSS Radomes Based on Dynamic Customizable Primitives

The digital model of airborne frequency selective surface radomes (AFSSRs) is the basis of design, simulation analysis, manufacturing, and other related research on AFSSRs. This paper proposes a rapid modeling method for AFSSRs based on dynamic customizable primitives. Firstly, a layered digital model construction scheme for AFSSRs is presented based on the typical radome wall structure. Then, according to the characteristics of various surface configurations and the complex wireframe information of AFSSRs, the dynamic primitives are raised to express the boundary and contour information of all kinds of radomes. Focusing on the undevelopable characteristics of the aerodynamic shape surface of the AFSSR, the arrangement solution and mapping method for frequency-selective elements on undevelopable surfaces are proposed. Furthermore, the implementation logic of this method for the creation of each layer model and the assembly of the whole machine model is introduced. Finally, a rapid modeling system (RMS) is established based on this method, enabling the automated creation of digital models of AFSSRs. Utilizing this system resulted in modeling time savings ranging from 20% to 97.5% compared to traditional methods, which verifies the feasibility and effectiveness of this method.

An Improved Non‐Local Planetary Boundary Layer Parameterization Scheme in Weather Forecasting and Research Model Based on a 1.5‐Order Turbulence Closure Model

AbstractPlanetary boundary layer (PBL) modeling is a primary contributor to uncertainties in a numerical weather prediction (NWP) model due to difficulties in modeling the turbulent transport of surface fluxes. The Weather Research and Forecasting model (WRF) has provided many PBL schemes that may feature a non‐local transport component driven by large eddies or a one‐and‐half order turbulence closure model, but few of them possess the two features at once. In the present study, a turbulent kinetic energy (TKE)‐based eddy diffusivity/viscosity method is integrated into the non‐local Asymmetric Convective Model version 2 (ACM2) PBL scheme and implemented in WRF. The original first‐order eddy‐diffusivity term in ACM2 is discarded and an extra prognostic equation for TKE, which considers the tendency of TKE by buoyancy, wind shear, vertical transport, and dissipative processes, is supplied to calculate the diffusivity/viscosity. Non‐local transport is modeled the same as ACM2 using the transilient matrix method. Idealized tests using prescribed surface heat flux and roughness length are performed. TKE‐ACM2 displays advantages over the PBL scheme developed by Bougeault and Lacarrère (hereinafter referred to as Boulac) and ACM2 in the wind speeds (WS) profile because it better matches large‐eddy simulations results in the surface momentum flux. Real case simulations show that TKE‐ACM2 generally outperforms in the diurnal vertical profiles of WS under stable conditions. TKE‐ACM2 also produces a better alignment under moderately unstable conditions in the early nighttime at the urban LiDAR station. However, the model exhibits discrepancies more apparently under a more unstable condition during the winter daytime.

Application of Passive Technique to Cocoa Beans Batch Dryer and Assessment of Thin Layer Models

Application of Passive Technique to Cocoa Beans Batch Dryer and Assessment of Thin Layer Models

Investigation of refrigerant-dependency on the performance of conical double helix tube Joule-Thomson cryocooler

Miniature Joule-Thomson (J-T) cryocoolers are widely used in the cryogenic field due to their advantages of small size, and fast cooling. Selecting the appropriate refrigerant is a crucial task in designing a J-T cryocooler, as it significantly affects its cooling performance. To study the refrigerant-dependent influencing on the cryocooler's performance, an improved one-dimensional model for a conical double layer J-T cryocooler was developed. The model has been verified to have higher accuracy, faster computing speed, and applicability across a wider range of operating conditions. Nitrogen and argon, commonly used refrigerants with similar saturation temperatures, were investigated. Both simulation and experimental results indicate that argon exhibits a faster cooling rate, while nitrogen achieves a lower cooling temperature under the working conditions. The numerical studies suggest that argon's higher density and lower J-T coefficient contribute to its faster cooling characteristic, resulting in a higher heat transfer quantity in the double layer heat exchanger. However, increasing the vessel pressure can quickly reduce the difference in cooling rates between nitrogen and argon, and it may even make nitrogen more optimal. Moreover, it was observed that a significant portion of the cooling capacity is utilized to cool the cryocooler itself for both nitrogen and argon.

Mechanism and characterization of laser-assisted hybrid processing for chemical vapor deposited diamond micro milling cutters

The fabrication of superhard micro milling cutters with extreme sharpness is highly demanded to meet the strict requirements of micro structures in terms of machining accuracy, surface roughness and burr height. In this study, nanosecond laser induced graphitization assisted grinding was proposed by considering machining efficiency and machining quality simultaneously for chemical vapor deposited (CVD) diamond micro flat-end milling cutters. An optimal cut-section was obtained by adopting moderate laser cutting energy and avoiding unstable thermodynamic coupling effect. The following laser induced graphitization mechanism on the cut-section was studied by analysing the different graphitization behaviours. The extensive graphitization caused sintered and banded graphite while the weak graphitization could not eliminate the defects caused by laser cutting. The uniform and dense graphitization resulted from appropriate energy distribution contributed to the smooth transition layer which was the significant factor in subsequent grinding. Moreover, the subsequent grinding behaviours of different transition layers were investigated, the grooved defects on transition layer caused the unstable grinding and fracture removal model, leading to the cracked ground surface and blunt cutting edge. Nevertheless, the grinding model of smooth transition layer was scratching without transcrystalline cracks, resulting in the smooth ground surface and sharp cutting edge. Thus, the laser parameters were finally optimized based on the feedback. Furthermore, the even graphitization, undamaged transition layer, scratching, as well as less material stress resulted in the extreme sharpness. In this way, the CVD diamond micro flat-end milling cutter (CVDM) with a diameter of 200 μm, surface roughness Sa of 30 nm, aspect ratio of 3, and edge radius of around 0.12 μm was prepared, the extreme sharpness was indicated by comparing with the edge radius of 1–5 μm reported heretofore. Finally, the micro grooves with surface roughness Sa of 17.8 nm and tiny burrs were machined on Ti-6Al-4 V by the homemade CVDM, which thereby indicated the outstanding cutting performance of the CVDM in micro-milling.

Cooperative MAC Protocol based on Best Data Rate (CMAC-DR)

As wireless signals are broadcast in nature, which implies that, a broadcast communication purposive to a predetermined destination may be received by a non-intended intermediate station. Cooperative transference, which employ interposed stations to pass on the eavesdropped data to attain the contrast gains, has a substantial capability to revamp the channeling effectiveness in wireless systems. In this it is evident that having cooperation amid stations in a wireless system can accomplish higher throughput with enhanced network lifetime. Proffered work bestows a model for medium access layer called Cooperative MAC protocol based on optimal Data Rate (CMAC-DR). In the proffered work, stations with more data rate aid stations having lesser data rate in their communication by redirecting their congestion. In CMAC-DR model, utilizing the conveyance of eavesdropped information, potential helper stations with more data rate Send out Helper Ready to Send (HRTS), the stations with less data rate maintains a table, called Co-op table of potential helper stations, that can aid in its transmissions. During communication, the source station with low data rate chooses either transmitting by the way of a helper station, so that it lowers the end to end transference delay and increases the throughput or opt only direct transmission, if no potential helper is found or if CMAC-DR becomes an overhead. By analyzing varied simulated scenarios, CMAC-DR evaluates the elevation in the overall network lifetime, throughput and minimization of delay. The CMAC-DR protocol is unambiguous and in accordant with legacy 802.11 also when compared to this, we find improved performance in terms of delay throughput and network lifetime since data rate is considered as relay selection condition.