Terms Of Transport Research Articles

Enhanced osmosis model with bilateral total variation for effective shadow removal

This research paper presents an innovative technique for shadow images removal. The method involves redefining a contemporary osmosis model by incorporating bilateral total variation (TV) operators. This integration allows to take advantage of robust anisotropic diffusion, resulting in improved image restoration. The paper also outlines new mathematical derivation of the bilateral TV and a combination with nonlinear anisotropic transport term. The experimental results substantiate the effectiveness of the anisotropic osmosis model, showcasing its superior qualitative and quantitative performance when compared to current state-of-the-art techniques.

A novel direct interpolation boundary element method formulation for solving diffusive–advective problems

The capability of dealing with the advective transport term constitutes a challenging issue for the performance of the majority of the numerical techniques, which significantly lose their precision with the increasing in the relative magnitude of this term. Recently, a new boundary element technique called direct interpolation (DIBEM) has emerged, mainly characterized by the approximation of the entire kernel of the remaining domain integrals. The DIBEM model has been successfully applied to several scalar field problems and recently applied to certain diffusive–advective problems with superior accuracy compared to dual reciprocity formulation (DRBEM). Using DIBEM, a broader range of precise responses for flows with higher Peclet numbers can be reached beyond a lower computational cost due to the simplicity of its matrix operations. These advantages are due DIBEM concept that employs a simple interpolation procedure to approximate the kernel of the advective domain integral. However, it was noticed that in some physical scenarios with spatial variation in the velocity field, the accuracy of DIBEM did not have the same quality observed in other applications. Therefore, this work presents a new DIBEM model so that the integral equations include the explicit calculation of spatial derivatives and simultaneously solve the variation of the divergent velocity field if this is not zero. Conversely, reactive and source terms were also included to expand numerical comparisons. Thus, in the proposed examples, the results of two DIBEM models, the standard (DIBEM-S) and the new, so-called alternative model (DIBEM-A), are compared with DRBEM and also with available analytical solutions.

Existence, uniqueness and regularity of solutions to the stochastic Landau–Lifshitz–Slonczewski equation

In this paper we are concerned with the stochastic Landau–Lifshitz–Slonczewski (LLS) equation that describes magnetisation of an infinite nanowire evolving under current-driven spin torque. The current brings into the system a multiplicative gradient noise that appears as a transport term in the equation. We prove the existence, uniqueness and regularity of pathwise solutions to the equation.

Effect of hydrogen constraints on predicting thermal conductivity of hydrocarbons in molecular dynamics simulation

Large overestimation has been reported while predicting the thermal conductivity of hydrocarbons using an all-atom force field model in molecular dynamics (MD) simulations. Although it has been guessed as resulting from the high-frequency vibration of the hydrogen atoms and hydrogen constraints method is suggested to be employed to reduce the deviation, how hydrogen constraints affect the heat conduction and local structure of hydrocarbons in MD simulation is still not fully understood. In this work, the effect of hydrogen constraints on the prediction of thermal conductivity of n-decane in MD simulations with the all-atom force field is studied. The results show that the deviation of the thermal conductivity of n-decane can be narrowed down by 72.48 % in simulations if the hydrogen constraints with a SHAKE algorithm is employed. The analysis of heat flux decomposition indicates that employing hydrogen constraints can reduce the contribution of transport term and non-bonded interactions to the heat flux, which in turn can help improve the accuracy while predicting the thermal conductivity in MD simulations. Furthermore, results of the vibrational density of states show that hydrogen constraints can dismiss the high-frequency vibration mode of molecules, thus effectively reducing the overestimation of thermal conductivity of hydrocarbon systems in MD simulations. The findings of this work sheds light on the molecular mechanism of heat transfer in hydrocarbon systems.

The topology-conditioned turbulence kinetic energy budget

The paper reports on the conditionally averaged turbulence kinetic energy (TKE) budget, where the conditioning is based on the invariants of the velocity gradient tensor. Three different datasets are utilized for this analysis. The particular terms of the budget are presented in the (R, Q) plane, showcasing a striking similarity (both quantitative and qualitative) among the results from each dataset. The importance of conditional averages for the overall variance of the specific terms of the TKE budget is also evaluated. Subsequently, the budgets are presented along conditional mean trajectories (CMTs), revealing the dynamics of the TKE budget associated with the evolution of local flow topology. Results obtained for different CMTs approximately collapse when suitably normalized (at least for certain parts of the trajectories). The conditional budget is clearly dominated by inertial and pressure transport terms, indicative of a “sweeping” effect.

Особенности функционирования транспортной терминосистемы в современных англоязычных новостных интернет-ресурсах

This article is devoted to the problems of English transport terminology, as well as the peculiarities of its functioning. The purpose of the study is to determine the features of the functioning of English–language transport terminology based on the material of English-language news resources covering the state of transportation. The scientific novelty of this study lies in its exploration of the unique characteristics of the transport terminology system, as revealed for the first time through an analysis of English-language online news sources that focus on specific modes of transportation. In the article, 532 transport terms selected from media texts were divided into thematic groups, classified according to partial criteria, and the peculiarities of their functioning were revealed. As a result of the study, it was found that the terms identified in the analyzed material relate to general transport, but their meaning is specified due to attributive units, which causes their transition to a narrowly sectoral terminology. The extralinguistic processes aimed at the implementation of practices for the development of environmental friendliness in the transport industry are reflected in the functioning of terminological phrases formed by combining transport and environmental terms. It is revealed that the specifics of the considered transport terminology are diffusion processes, the reason for which is the transition of a significant part of it into the category of commonly used vocabulary.

Transcriptomic landscape of seedstick in Arabidopsis thaliana funiculus after fertilisation

BackgroundIn Angiosperms, the continuation of plant species is intricately dependent on the funiculus multifaceted role in nutrient transport, mechanical support, and dehiscence of seeds. SEEDSTICK (STK) is a MADS-box transcription factor involved in seed size and abscission, and one of the few genes identified as affecting funiculus growth. Given the importance of the funiculus to a correct seed development, allied with previous phenotypic observations of stk mutants, we performed a transcriptomic analysis of stk funiculi from floral stage 17, using RNA-sequencing, to infer on the deregulated networks of genes.ResultsThe generated dataset of differentially expressed genes was enriched with cell wall biogenesis, cell cycle, sugar metabolism and transport terms, all in accordance with stk phenotype observed in funiculi from floral stage 17. We selected eight differentially expressed genes for transcriptome validation using qPCR and/or promoter reporter lines. Those genes were involved with abscission, seed development or novel functions in stk funiculus, such as hormones/secondary metabolites transport.ConclusionOverall, the analysis performed in this study allowed delving into the STK-network established in Arabidopsis funiculus, fulfilling a literature gap. Simultaneously, our findings reinforced the reliability of the transcriptome, making it a valuable resource for candidate genes selection for functional genetic studies in the funiculus. This will enhance our understanding on the regulatory network controlled by STK, on the role of the funiculus and how seed development may be affected by them.

Biological invasions and epidemics with nonlocal diffusion along a line.

The goal of this work is to understand and quantify how a line with nonlocal diffusion given by an integral enhances a reaction-diffusion process occurring in the surrounding plane. This is part of a long term programme where we aim at modelling, in a mathematically rigorous way, the effect of transportation networks on the speed of biological invasions or propagation of epidemics. We prove the existence of a global propagation speed and characterise in terms of the parameters of the system the situations where such a speed is boosted by the presence of the line. In the course of the study we also uncover unexpected regularity properties of the model. On the quantitative side, the two main parameters are the intensity of the diffusion kernel and the characteristic size of its support. One outcome of this work is that the propagation speed will significantly be enhanced even if only one of the two is large, thus broadening the picture that we have already drawn in our previous works on the subject, with local diffusion modelled by a standard Laplacian. We further investigate the role of the other parameters, enlightening some subtle effects due to the interplay between the diffusion in the half plane and that on the line. Lastly, in the context of propagation of epidemics, we also discuss the model where, instead of a diffusion, displacement on the line comes from a pure transport term.

Complete quasilinear model for the acceleration-driven lower hybrid drift instability and a computational assessment of its validity.

A complete quasilinear model is derived for the electrostatic acceleration-driven lower hybrid drift instability in a uniform two-species low-beta plasma in which current is perpendicular to the background magnetic field. The model consists of coupled nonlinear velocity space diffusion equationsfor the volume-averaged ion and electron distribution functions. Each species' diffusion coefficient depends on a time-evolving spectral density of the electric-field energy per unit volume and a time-evolving dispersion relation. The dispersion relation is expressed analytically in integral form without the use of asymptotic limits and applies to arbitrary distribution functions, so long as they can be expressed as a function of one velocity coordinate, e.g., f(v_{y}) or f(v_{⊥}). The quasilinear model conserves energy and is complete in that it fully describes the evolution of the distribution functions, including resonant and nonresonant particle-wave interactions, while accounting for distribution-function-dependent mixed-complex frequencies. The quasilinear diffusion model is solved numerically and self-consistently using a Crank-Nicolson temporal discretization and a second-order finite-volume velocity-space discretization. Numerical solutions are compared to nonlinear fourth-order accurate continuum kinetic Vlasov-Poisson simulations. Evolution of electric-field energy, growth rates, distribution functions, and diffusion coefficients are shown to be in agreement with Vlasov simulations. The quasilinear model is shown to predict anomalous transport terms, like resistivity and heating, to within a factor of order unity. Discrepancies between the quasilinear model and Vlasov simulations are assessed and attributed primarily to lack of damping in the quasilinear description and to the use of unperturbed-orbit susceptibilities in the linear theory dispersion relation. The results illuminate the predictive accuracy of the quasilinear model, place approximate bounds on its validity, and provide much needed vetting of quasilinear theory's ability to predict the nonlinear state of a microturbulent plasma.

Robust discontinuous Galerkin-based scheme for the fully-coupled nonlinear thermo-hydro-mechanical problem

Abstract We present and analyze a discontinuous Galerkin method for the numerical modeling of the nonlinear fully-coupled thermo-hydro-mechanic problem. We propose an arbitrary-order weighted symmetric interior penalty scheme that supports general polytopal grids and is robust with respect to strong heterogeneities in the model coefficients. We focus on the treatment of the nonlinear convective transport term in the energy conservation equation and we propose suitable stabilization techniques that make the scheme robust for advection-dominated regimes. The stability analysis of the problem and the convergence of the fixed-point linearization strategy are addressed theoretically under mild requirements on the problem data. A complete set of numerical simulations is presented in order to assess the convergence and robustness properties of the proposed method.

Characteristics of Atmospheric Diabatic Heating of the Southwest China Vortex That Induces Extreme Rainstorms in Sichuan

In this study, we aimed to demonstrate the importance of diabatic heating in extreme rainstorm weather events induced by the Southwest China vortex (SWCV) in different precipitation regions with a similar circulation background. The results showed that atmospheric diabatic heating had indicative significance for the intensity evolution of the SWCV and the precipitation area. Changes in the diabatic heating intensity preceded the intensity evolution of the SWCV, and the diabatic heating region was consistent with the heavy precipitation region. The variation in diabatic heating was mainly due to the positive contribution of its vertical transport term. The two types of spatially non-uniform heating effects were similar; however, the western type was located southeast of the SWCV, with an asymmetric distribution on the southeastern and northwestern sides. The eastern type was located in the northeast of the SWCV, with an asymmetric distribution on the northeastern and southwestern sides. The vertically non-uniform heating effect played a decisive role in the distribution and evolution of the spatially non-uniform heating terms. The vertically non-uniform heating effect affected the intensity evolution of the SWCV. In contrast, the horizontally non-uniform heating effect, in opposition to the vertically non-uniform heating effect, had a slightly weaker intensity than the vertically non-uniform heating effect. For the SWCV system, which induces extreme rainstorms, the magnitude of the horizontally non-uniform heating effect could reach that of vertically non-uniform heating; thus, the possible impact of horizontally non-uniform heating should be considered.

Roles of synoptic characteristics and microphysics processes on the heavy rain event over Beijing region during 29 July to 2 August 2023

The “23.7” event, an extreme rainstorm that affected North China from July 29 to 2 August 2023, was simulated using the Weather Research and Forecasting (WRF) model, version 4.2. We focus on dynamically diagnosing and analyzing the mass and latent heat budgets of rainwater during the extreme precipitation event on July 31 in the Beijing area, where the hourly rainfall reached an extraordinary 111.8 mm. Generally, the model effectively simulated the rainstorm, enabling further assessment of the extreme precipitation. Results indicated that under the combined influence of three major weather systems—the residual circulation of Typhoon Doksuri (a low-pressure system after typhoon landfall), the embryonic stage of Typhoon Khanun, and the North China high-pressure dam—a continuous influx of moisture and energy was transported to the North China region, promoting heavy precipitation. Application of vorticity equation diagnostics indicates that the horizontal transport term is the primary source term. Mass balance analysis reveals that the primary source of rainwater is the accretion of cloud droplets by rain, and the condensation of water vapor into cloud droplets is the main contributor to the latent heat.

A chemistry load balancing model for OpenFOAM

Efficient simulation tools are crucial for studying complex systems such as reacting flows where computational costs of computing chemical reaction rates can vastly exceed the costs for the integration of the convective and diffusive transport terms. Load imbalance in parallel computing poses a significant challenge for massively parallel reacting flow simulations. In response, a novel load balancing library has been developed to enhance OpenFOAM's solver performance in parallel environments. This library seamlessly integrates with OpenFOAM, offering ease of use and applicability to any OpenFOAM reacting solver incorporating finite-rate chemistry. In addition, it supports the standard and the dynamic adaptive chemistry model (TDAC) of OpenFOAM.The newly developed load-balanced standard and TDAC models address significant load imbalances by exchanging information between processes via MPI calls and tracking ODE solution times on a cell level. The TDAC model introduces dual tables on each core and enables immediate addition of computed solutions, enhancing computational efficiency. Validation on various test cases, including simulations on the HLRS Hawk supercomputer with up to 8000 cores, confirms identical results compared to the original unbalanced models, with notable speed-up factors of up to 6 for the standard and 5 for the TDAC model. Despite non-linear scaling at lower cell count per processor, load-balanced models consistently outperform unbalanced counterparts, making them the preferred choice for reacting flow simulations in OpenFOAM.

LES of Premixed Turbulent Combustion Using Filtered Tabulated Chemistry

AbstractThe filtered tabulated chemistry (FTACLES) approach utilizes data from pre-tabulated explicitly filtered 1D flame profiles for closure of the LES-filtered transport terms. Different methodologies are discussed to obtain a suitable progress variable c from detailed chemistry calculations of a methane/air flame. In this context, special focus is placed on the analytical modeling of the reaction source term using series of parameterized Gaussians. For increasing effective filter sizes in LES (i.e. including the flame thickening) the precise shape of the reaction rate profile becomes less and less relevant. In particular, it is shown that for one-step chemistry, a single Gaussian is sufficient to derive an explicitly expressible 1D flame profile with a prescribed laminar flame speed and thermal flame thickness. The resulting artificial flame profile is shown to have similarities with profiles based on carbon chemistry and detailed reaction mechanisms. Next, the behavior of the filtered c-transport equation is analyzed and several possible closure methods are compared for a wide range of filter widths. It is shown that the unclosed contribution of the filtered diffusion term can be combined with the subgrid convection term, thus simplifying the FTACLES formulation. The model is implemented in OpenFOAM and validated in 1D for a variety of LES filter sizes in combination with artificial flame thickening. A power-law-based wrinkling model is modified for use with artificial flame thickening and combined with the FTACLES model to enable 3D simulations of a premixed turbulent Bunsen burner. The comparison of 3D Large Eddy Bunsen flame simulations at increasing levels of turbulence intensity shows a good match to experimental results for most investigated cases. In addition, the results are mostly insensitive to the variation of the mesh size.

A PINN-DeepONet framework for extracting turbulent combustion closure from multiscalar measurements

In this study, we develop a novel framework to extract turbulent combustion closure, including closure for species chemical source terms, from multiscalar and velocity measurements in turbulent flames. The technique is based on a physics-informed neural network (PINN) that combines models for velocity and scalar measurements and a deep operator network (DeepONet) to accommodate spatial measurements and experimental parameters as separate input streams. An additional key innovation is the estimate of the unconditional means of the species’ chemical source terms as additional “observations” to constrain the prediction of these rates. This estimate is based on a convolution of the means of species reaction rates conditioned on principal components of the multiscalar data and the joint probability density functions of these principal components. The PINN-DeepONet method is implemented on the so-called Sydney flames, where training is carried out on 3 flames and validated on 4 flames. The results show that, despite the limited samples of experimental parameters, including the inlet flow and the fuel jet recess length within the air flow, the PINN-DeepONet approach can construct velocity and scalar fields along with important closure terms for turbulent transport and reaction rates.

Quasilinear Theory Approximations

If the instability increases exponentially without any limitation, evidently, this does not reflect the reality and it is therefore necessary to identify a mechanism responsible for the saturation of this instability. The aim of this work is to add such a capability, the first step is to let vary slowly (compared to the wave period) over time. The quasilinear theory has been precisely introduced to describe such an evolution. It is clear that when collisions are neglected, we are in the presence of diffusion equation. In fact, in its Fokker-Planck form, the collision operator is splitting into a transport and diffusive terms. The resulting phenomenon is known as the quasilinear diffusion: under the conjugate effects of the wave on one hand and collisions on the other hand, the variation of the distribution function has a diffusive nature.

Multiscale interaction analysis of Landfall Typhoon Lekima (2019) based on vorticity equation diagnosis

To investigate the multiscale interaction characteristics of Landfall Typhoon Lekima (2019), this study analyzed the characteristics of the different scale vortex structure and interactions among different scales based on vorticity equation diagnosis. The analysis is based on the simulation results of the WRF model which has been thoroughly verified. The main results are as follows: the original vorticity dominated by the meso-α scale vorticity increases with height and then decreases, with maximum vorticity distributed at 900 hPa. The meso-β scale vorticity varies significantly with altitude, while the meso-γ scale vorticity field exhibits obvious positive vorticity below 850 hPa. The meso-α scale vorticity tendency primarily maintains negative, contributing significantly to the overall reduction in the original vorticity field over time. The increase in mid-to-upper-level (above 550 hPa) original vorticity is mainly related to the variations in the meso-β and meso-γ scale vorticity fields. The original vorticity dominated by the meso-α scale vorticity increases with height and then decreases, and the whole layer vorticity decreases over time. The meso-β scale vorticity varies significantly with altitude and time, while the meso-γ scale vorticity field consistently exhibits significant positive vorticity below 850 hPa. The vorticity equation diagnosis revealed that the primary source terms of the vorticity tendencies are the twisting and stretching terms, and the main sink terms being horizontal and vertical vorticity transport terms below 900 hPa. The source terms and sink terms exchange above 850 hPa. Scale separation results show that the primary contributions of all impact factors originate from the meso-α and meso-γ scale fields (accounting for over 80% of the total), with the contribution of the meso-α scale being less than that of the meso-γ scale and a notable contribution over 35.5% of the interactions between different scales.

Turbulent kinetic energy budget of sediment-laden open-channel flows: bedload-induced wall-roughness similarity

New experiments in highly turbulent, steady, subcritical and uniform water open-channel flows have been carried out to measure the mean turbulent kinetic energy (TKE) budget of sediment-laden boundary layer flows with two sizes (dp = 3 mm and 1 mm) of Plexiglas particles $({\rm relative\ density}\ = 1.192)$ . The experiments covered energetic sediment transport conditions (Shields number of $0.35 < \theta < 1.2$ ) ranging from non-capacity to full-capacity flows in bedload-to-suspension-dominated transport modes (suspension number of $0.5 < {w_s}/{u_\ast } < 1.3$ where ${w_s}$ is the settling velocity and $u_*$ is the friction velocity) and for weakly to highly inertial, finite size turbulence-particle conditions (Stokes number of 0.1 < St < 3.5 and dp/η > 10 where $\eta$ is the Kolmogorov length scale). It was shown that the effects of sediments on the TKE budget are very pronounced in all large particle experiments for which a bedload layer of several grain diameter thickness is developed above the channel bed. When compared with the corresponding reference clear-water flows, the TKE shear-production rate for the 3 mm particle flows is strongly reduced in the wall region corresponding to the bedload layer. This turbulence damping is seen to increase with sediment load until full capacity for flows with constant Shields value, as well as with Shields number value. Inside this damped TKE shear-production zone, a distinct peak of maximal turbulence production appears to coincide with the upper edge of the bedload layer delimited by a sharp gradient in mean sediment concentration. This vertically upshifted peak of TKE production is accompanied by an enhanced net downward oriented TKE flux when compared with the reference clear-water flows. The downward diffused TKE is found to act in the bedload layer as a local energy source in reasonable balance with the sediment transport term. The mechanism behind this downward TKE transport was further analysed on the basis of coherent flow structure dynamics controlled by ejection- and sweep-type events. The agreement between the height of downward directed mean TKE flux and the height below which sweep-type events dominate the Reynolds shear-stress contribution over ejections, revealed the leading role played by sweeps in mean TKE transport. This agreement holds for all reference clear-water flows supporting the well-known wall-roughness-induced dominance of the sweep contribution in turbulent, rough clear-water boundary layer flows. Furthermore, for all 3 mm particle flows, the two referred to transition levels were significantly and similarly upshifted to the upper edge of the bedload layer. Only for these sediment-laden flows, the bedload layer thickness is seen to exceed the wall-roughness sublayer of the reference clear-water flows. This supports a strong analogy between wall-roughness effects in clear-water flows and bedload layer effects in sediment-laden flows, on the mean TKE budget induced by a similarly modified coherent flow structure dynamics. The bedload layer-controlled wall roughness is finally confirmed by the good prediction of the wall-roughness parameter ks of the logarithmic velocity distribution. An empirical formulation fitting the presented measurements is presented, valid over the range of Shields number values covered herein.

The Role of Turbulence Transport in Mechanical Energy Budgets

Abstract In this article, we study the role of turbulence transport on loss prediction using high fidelity scale-resolving simulations. For this purpose, we use eight high-fidelity simulation datasets and compute flux of entropy and stagnation pressure transport equation budgets for all the cases. We find that under certain unsteady inflow conditions, the stagnation pressure coefficient is not a reliable loss metric even at low Mach number conditions. This is due to the turbulence transport terms. The impact of these terms, typically assumed to be negligible, made stagnation pressure loss coefficient underpredict loss from 0% to over 40% when compared to entropy loss coefficient for cases considered here. This effect was most pronounced for the cases with highly unsteady inflow conditions and at low Reynolds numbers.

River plastic transport and storage budget

Rivers are one of the main conduits that deliver plastic from land into the sea, and also act as reservoirs for plastic retention. Yet, our understanding of the extent of river exposure to plastic pollution remains limited. In particular, there has been no comprehensive quantification of the contributions from different river compartments, such as the water surface, water column, riverbank and floodplain to the overall river plastic transport and storage. This study aims to provide an initial quantification of these contributions. We first identified the main relevant transport processes for each river compartment considered. We then estimated the transport and storage terms, by harmonizing available observations on surface, suspended and floodplain plastic. We applied our approach to two river sections in The Netherlands, with a focus on macroplastics (≥2.5 cm). Our analysis revealed that for the studied river sections, suspended plastics account for over 96% of item transport within the river channel, while their relative contribution to mass transport is only 30%–37% (depending on the river section considered). Surface plastics predominantly consisted of heavier items (mean mass: 7.1 g/#), whereas suspended plastics were dominated by lighter fragments (mean mass: 0.1 g/#). Additionally, the majority (98%) of plastic mass was stored within the floodplains, with the river channel accounting for only 2% of the total storage. Our study developed a harmonized approach for quantifying plastic transport and storage across different river compartments, providing a replicable methodology applicable to different regions. Our findings emphasize the importance of systematic monitoring programs across river compartments for comprehensive insights into riverine plastic pollution.