LS Model Research Articles

Eulerian simulations of local liquid distribution in a Trickle Bed: Effects of flow rates and liquid properties

We performed Eulerian simulations of gas–liquid flow in a Trickle Bed Reactor (TBR) to understand contributions of gas–liquid, gas–solid and liquid–solid interaction forces (F→GL,F→GS,F→LS), capillary-pressure (F→C) and mechanical-dispersion (F→D) forces to local liquid spreading and how their contributions change with changes in flow rates and physical properties. Further, we simulated effects of these parameters on pressure drop (ΔP), overall liquid hold-up (〈εL〉) and importantly on local liquid spreading and validated the predictions using measurements. We have shown that F→LS significantly contributes to local liquid spreading, ΔP and 〈εL〉, whereas F→D contributes marginally. The modified F→LS model led to satisfactory predictions of local liquid spreading, ΔP and 〈εL〉 for a wide range of fluid flow rates and physical properties and predictions are in a satisfactory agreement with the measurements. The present work is an important step in extending the CFD model for simulating reactions and heat effects in TBRs.

Improving MODIS Precipitable water vapour in mainland China based on the LSF model

Precipitable Water Vapour (PWV) measurements derived from the Moderate-resolution Imaging Spectroradiometer (MODIS) exhibit considerable promise for global high-resolution PWV monitoring but with limited accuracy. This study proposes a correction model for MODIS PWV, leveraging the least squares method (LS) and fast Fourier transform (FFT). The study used Global Navigation Satellite System (GNSS) PWV products (the accuracy is equivalent to Radiosonde-derived PWV) from 230 stations provided by the Crustal Movement Observation Network of China (CMONOC) for 2016 to 2019, serving as the ground truth for correcting MODIS PWV. Subsequently, the model undergoes an external coincidence test utilising the data from 2020. Initially, a linear or quadratic expression (LS model) was established through the application of the least squares method, effectively capturing the trends between the two PWV datasets. Then the periodic characteristics of residuals from the LS model were analysed by FFT. The outcomes reveal that within regions and seasons abundant in PWV, the quadratic expression is more consistent with the trend. The primary variation period of residuals exhibits variability across regions, with the annual period emerging as the primary fluctuation pattern in the majority of regions. Following this, we constructed the correction model (LSF model) that considered the cycle characteristics of residuals with the model type adopted for the LS model as the main part. After correction by the LSF model, the root-mean-square error (RMSE) of MODIS PWV decreased by 33.1%, 55.8%, 33.0%, and 19.4% in four seasons, respectively. Compared to the LS model, the LSF model showcased relative enhancements of the coefficient of determinations (R2) by 119.8%, 99.6%, 165.9%, and 39.6% in the four seasons, respectively, with an overall further decrease of 35.7% in RMSE. The LSF model demonstrates a superior degree of fitting and yields improved correction effects, thus effectively enhancing the reliability of MODIS PWV.

Modeling probabilistic-based reliability assessment of gridded rainfall thresholds for shallow landslide occurrence due to the uncertainty of rainfall in time and space

Abstract This study aims to model a probabilistic-based reliability assessment of the gridded rainfall thresholds for shallow landslide occurrence (RA_GRTE_LS) to quantify the effect of the uncertainty of rainfall in time and space on the rainfall thresholds under consideration of local soil properties. The proposed RA_GRTE_LS model is developed by coupling the uncertainty analysis with the logistic regression equation using a significant number of the landslide-derived rainfall thresholds of the specific warning times. The 30 historical gridded hourly rainstorms at 10 study grids in the study area (Jhuokou River watershed) are used in 1,000 simulations of rainfall-induced shallow landslides under an assumption of the soil layer of 310 cm. The results reveal that the shallow landslide in the study area probably occurs at the time step of less than the 36th hour around the bottom of the soil layer (about 275 cm) during a rainstorm; also, using the proposed RA_GRTE_LS model, the resulting rainfall thresholds and quantified reliabilities, especially for the warning time of less than 18 h, exhibit a sizeable varying trend in space due to the variations in rainfall and soil properties; accordingly, the short-term rainfall thresholds for shallow landslide occurrence could be locally determined under acceptable reliability.

Wave propagation in thermo-poroelasticity: A finite-element approach

We have developed continuous and discrete-time finite-element (FE) methods to solve an initial boundary-value problem for the thermo-poroelasticity wave equation based on the combined Biot/Lord-Shulman (LS) theories to describe the porous and thermal effects, respectively. In particular, the LS model, which includes a Maxwell-Vernotte-Cattaneo relaxation term, leads to a hyperbolic heat equation, thus avoiding infinite signal velocities. The FE methods are formulated on a bounded domain with absorbing boundary conditions at the artificial boundaries. The dynamical equations predict four propagation modes, a fast P (P1) wave, a Biot slow (P2) wave, a thermal (T) wave, and a shear (S) wave. The spatial discretization uses globally continuous bilinear polynomials to represent solid displacements and temperature, whereas the vector part of the Raviart-Thomas-Nedelec of zero order is used to represent fluid displacements. First, a priori optimal error estimates are derived for the continuous-time FE method, and then an explicit conditionally stable discrete-time FE method is defined and analyzed. The explicit FE algorithm is implemented in one dimension to analyze the behavior of the P1, P2, and T waves. The algorithms can be useful for a better understanding of seismic waves in hydrocarbon reservoirs and crustal rocks, whose description is mainly based on the assumption of isothermal wave propagation.

Lesson Study Model Perception Scale: Validity and Reliability Study

This study aimed to develop the “Lesson Study Model Perception Scale” (LSMPS) and to determine the psychometric properties of the scale. The study was designed as a survey model. A survey model is a research approach that aims to describe a situation as it is. When all the findings obtained to determine the psychometric properties of the scale developed within the scope of the research are evaluated together, it is investigated that the measurements obtained from the scale and the inferences to be made based on these findings are reliable and valid. Existing literature revealed that there are limited number of studies that determine how the LS model is perceived by teachers. It is seen that none of these studies attempted to develop a scale to measure teachers’ perceptions of the LS model. The lack of a study in this context in the literature shows the originality of the study.

Assessment of RANS turbulence models on predicting supercritical heat transfer in highly buoyant horizontal flows

This paper rigorously validates the RANS models against the DNS on predicting turbulent flow and heat transfer of highly buoyant horizontal supercritical fluids. The low-Reynolds number turbulence models of RNG, AKN, V2F and ( k − ω ) SST that are recommended in literature are selected. Also, the LS model demonstrating good performance in some in-house CFD codes has been reimplemented via User-Defined Functions (UDFs) and examined for supercritical simulations, in particular with strong buoyancy effects. The results indicated that the AKN model works best among the tested models on the reproductions of some bulk parameters that are of interest (such as wall temperature, Nusselt number and skin friction coefficient) and the distortions of the turbulent velocity profile caused by the strong buoyancy, closely followed by the V2F model. The UDFs implemented LS model exhibits much better performances than the originally incorporated version in FLUENT, which is attributed to the more proper model implementation that leads to better treatments on the fluid flow and heat transfer, especially in the near-wall regions. Regarding the reproductions on the turbulence kinetic energy generations under the studied conditions, the RANS models are unable to give satisfactory results, the simulated suppression in the top half is more drastic. Similar to the vertical supercritical fluids, with quite high-strength buoyancy, the heat transfer recovers around the horizontal pipe top wall but the RANS models' response to the “recovery” is poor. The model performance on reproducing the turbulent statistics is closely related to the implementation of the vital structural parameters.

Magneto-Thermoelasticity with Thermal Shock Considering Two Temperatures and LS Model

The present investigation is intended to demonstrate the magnetic field, relaxation time, hydrostatic initial stress, and two temperature on the thermal shock problem. The governing equations are formulated in the context of Lord-Shulman theory with the presence of bodily force, two temperatures, thermal shock, and hydrostatic initial stress. We obtained the exact solution using the normal mode technique with appropriate boundary conditions. The field quantities are calculated analytically and displayed graphically under thermal shock problem with effect of external parameters respect to space coordinates. The results obtained are agreeing with the previous results obtained by others when the new parameters vanish. The results indicate that the effect of magnetic field and initial stress on the conductor temperature, thermodynamic temperature, displacement and stress are quite pronounced. In order to illustrate and verify the analytical development, the numerical results of temperature, displacement and stress are carried out and computer simulated results are presented graphically. This study helpful in the development of piezoelectric devices.

New Formulation of LS Model for Accurate Iron Loss Modeling at Extreme B and dB/dt: Experimental Analysis and Test on a High-Speed PMSM

New Formulation of LS Model for Accurate Iron Loss Modeling at Extreme B and dB/dt: Experimental Analysis and Test on a High-Speed PMSM

A new integrable model of long wave-short wave interaction and linear stability spectra.

We consider the propagation of short waves which generate waves of much longer (infinite) wavelength. Model equations of such long wave–short wave (LS) resonant interaction, including integrable ones, are well known and have received much attention because of their appearance in various physical contexts, particularly fluid dynamics and plasma physics. Here we introduce a new LS integrable model which generalizes those first proposed by Yajima and Oikawa and by Newell. By means of its associated Lax pair, we carry out the linear stability analysis of its continuous wave solutions by introducing the stability spectrum as an algebraic curve in the complex plane. This is done starting from the construction of the eigenfunctions of the linearized LS model equations. The geometrical features of this spectrum are related to the stability/instability properties of the solution under scrutiny. Stability spectra for the plane wave solutions are fully classified in the parameter space together with types of modulational instabilities.

On propagation of harmonic plane waves under the Moore–Gibson–Thompson thermoelasticity theory

ABSTRACT The present work is aimed at a detailed investigation of harmonic plane wave propagation through an isotropic, unbounded and homogeneous thermoelastic medium under the recently proposed Moore–Gibson–Thompson (MGT) thermoelasticity theory. The dispersion relation is derived and its solution for the longitudinal plane wave propagation is obtained analytically. Two different modes of longitudinal wave are identified as elastic and thermal mode waves. The asymptotic expressions of various important characteristics of the wave fields such as phase velocity, specific loss and penetration depth for both the waves are obtained for limiting cases of very high and low frequency values. The Whitham stability of harmonic plane waves is established. Further, the computational tool is used to achieve numerical results for these wave characteristics and to illustrate the analytical findings graphically. Some important observations about the prediction of the MGT model in comparison to the other existing models, i.e. classical coupled thermoelastic model, LS model and GN-III model, are highlighted. Effects of material parameters on the propagation of waves are analyzed in a detailed manner. From the theoretical as well as numerical results, it is investigated that the MGT model accounts for finite speed of elastic wave as well as thermal wave.

Improving the Accuracy of Fractional Evergreen Forest Cover Estimation at Subpixel Scale in Cloudy and Rainy Areas by Harmonizing Landsat-8 and Sentinel-2 Time-Series Data

Evergreen forest provides essential ecosystem services such as maintaining the balance in carbon and oxygen cycles and air purification. However, under cloudy and rainy weather conditions, it is difficult to obtain optical remote sensing images with high spatial resolution and complete time series. In addition, surfaces underlying the forest canopy can be complex and fragmented. To solve this problem, we developed a new approach (NDVI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CV</sub> -LS) for mapping urban evergreen forest at the subpixel scale. In order to capture more accurate growth characteristics of evergreen forest, we harmonized Landsat-8 and Sentinel-2 images with cloud cover less than 10% acquired within 1 year to denser the time-series dataset. In view of the time series fluctuation stability of evergreen forest, the coefficient of variation (CV) of the normalized difference vegetation index (NDVI) was used to distinguish evergreen forest from other vegetation. Meanwhile, the annual minimum NDVI (NDVI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ann-min</sub> ) was used as the parameter in a dimidiate pixel model for estimating fractional evergreen forest cover (FVC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ever</sub> ). Hefei, a cloudy and rainy subtropical city in China, was selected as a case study to evaluate the validity of the model. The verification results revealed that harmonizing Landsat-8 and Sentinel-2 time-series images to extract evergreen forest improved the overall accuracy by 8% compared with using Landsat-8 images alone, indicating that the NDVI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CV</sub> -LS model can improve the accuracy of FCV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ever</sub> estimation, especially for areas with complex underlying surfaces under cloudy and rainy conditions.

Propagation of surface waves in generalized thermoelastic media under influence of magnetic field and rotation and its applications in engineering and geophysics

This paper aims to study the propagation of surface waves in generalized magneto-thermoelastic media under influence of magnetic field and rotation and its applications in Engineering, Geophysics, and Petroleum extracting. The governing equations are considered for generalized thermoelastic problem under magnetic field and rotation and solved to obtain the general solution in x-z plane. The Lame's potential method considering harmonic functions for the physical quantities is used to obtain the secular equation and then the velocity and attenuation coefficient for the types of waves: Stoneley, Love, and Rayleigh. The appropriate boundary conditions at an interface between two dissimilar half-spaces are satisfied with appropriate particular solutions to obtain the frequency equation of the surface wave in the medium. Some special cases as: Stoneley waves, Rayleigh and Love waves also discussed and presented graphically to show the physical meaning of the external parameters effect on the petroleum extracting phenomena and its contributions in KSA vision 2030 in crystal, Iron and steel. A comparison is made with the previous results considering LS model and the absence of rotation that deduces to the previous results as a special case from the present study. Also, if the magnetic field and rotation vanish, the results obtained in the present work are discussed. Experimentally, the results obtained agree with the labs results obtained. The results obtained indicate to a significant impact of the magnetic field and rotation on the waves propagation phenomenon that contributes on the industries and related topics.

Radial vibrations of functionally graded spheres due to thermal load

A study on radial vibrations of functionally graded, isotropic, thermoelastic, thick-walled hollow sphere due to a thermal load has been carried out in the context of non-Fourier law of heat conduction (LS model). The material and thermal parameters have been assumed to vary according as simple power-law function of the radial coordinate. Closed-form solution to the problem has been derived with the aid of Laplace transform and elimination procedure. The inverse Laplace transforms of radial displacement and temperature have been obtained by employing the theory of residues. The solution in case of uncoupled and classical coupled thermoelasticity has been obtained directly by deducing the results of present analysis. The deduced results have been validated with the benchmark results available in the literature. Also the radial stress, hoop stress, temperature gradient for various grading parameters at different radial distances have been computed and presented graphically for validating and giving more emphasis on these field quantities. A significant effect of grading parameter on the stress and temperature gradient produced in the sphere has been noticed. A comparative analysis has been done for homogeneous and functionally graded spheres.

LANDSLIDES SUSCEPTIBILITY ZONATION OF THE TERRITORY OF NORTH MACEDONIA USING ANALYTICAL HIERARCHY PROCESS APPROACH

Landslides are natural disasters that have an impact in many areas around the world including the territory of the Republic of Macedonia. In this country, about 300 large landslides are registered, most of which cause serious damage to the infrastructure almost every year. In that sense, the mapping of sites that are susceptible to landslides is essential for the management of these areas. This is a crucial step to prevent landslides in places where this could be expected or to mini-mize its damages. Therefore, a heuristic approach of Analytical Hierarchy Process (AHP) combined with Geographic In-formation System (GIS) and Remote Sensing (RS) is used in this work for the assessment of potential landslide areas in the Republic of Macedonia. In the procedure, 6 triggering factors indicating a strong influence on the landslide activity are selected, including lithology, slope angle, land cover, terrain curvature, distance from rivers and distance from roads. Through the procedure, expert-based weight of these factors is made. The LS model is produced with the summing up of the factor layers in the form of harmonized raster grids. Finally, the values of the grid model are classified according to the quantiles and natural breaks scheme. The produced maps show acceptable results confirmed by validation methods and ROC analysis, indicating that about 40% of the country area is under high and very high landslide susceptibility. This ap-proach can be further improved if combined with statistical methods in the form of a hybrid model.

Paradoxical Bactericidal Effects of Hydrophobic Lung Surfactant Proteins and Their Peptide Mimics Using Liposome Molecular Trojan.

Lung surfactant, besides alveolar stability, also provides defence against pathogens by surfactant proteins (SP), SP-A and SP-D. The hydrophobic proteins SP-B and SP-C enhance surface activity. An unusual and paradoxical effect of bovine LS and synthetic model LS with SP-B/-C was bactericidal to Staphylococcus aureus and Escherichia coli. Bacterial proliferation were investigated with bovine lung surfactant extract (BLES), dipalmitoylphosphatdylcholine, palmitooleylglycerol, in combination with SP-B/-C using standard microbiological colony forming unit (CFU) counts and structural imaging. BLES and other surfactant-SP-B/-C mixtures inhibit bacterial growth in the concentration range of 0 -7.5 mg/mL, at > 10 mg/mL paradoxical growth of both the bacterial species suggest antibiotic resistance. The lipid only LS have no effect on bacterial proliferation. Smaller peptide mimics of SP-B or SP-B1-25, were less efficient than SP-Cff. Ultra structural studies of the bacterial CFU using electron and atomic force microscopy suggest some membrane damage of S. aereus at inhibitory concentration of BLES, and some structural alteration of E. coli at dividing zones, suggesting utilization and incorporation of surfactant lipid species by both bacteria. The results depicted from in vitro studies are also in agreement with protein-protein interactions obtained from PatchDock, FireDock and ClasPro algorithm. The MD-simulation decipher a small range fluctuation of gyration radius of the LS proteins and their peptide mimics. The studies have alarming implications in the use of high dosages (100 mg/mL/kg body weight) of exogenous surfactant for treatment of respiratory distress syndrome, genetic knock-out abnormalities associated with these proteins, and the novel roles played by SP-B/C as bactericidal agents.

A probabilistic model for evaluating the reliability of rainfall thresholds for shallow landslides based on uncertainties in rainfall characteristics and soil properties

This study aims to develop a probabilistic rainfall threshold estimation model for shallow landslides (PRTE_LS) in order to quantify its reliability while being affected by uncertainties in the rainfall characteristics and soil properties. The rainfall characteristics include the rainfall duration, depth and storm patterns in which their uncertainties result from temporal variation. The effective cohesion of soil, the unit weight of soil, the angle of internal friction, hydraulic conductivity and hydraulic diffusivity are the soil properties represented as the soil parameters in the TRIGRS model in which uncertainties are attributed to spatial variation. After analyzing the sensitivity of rainfall characteristics and TRIGRS parameters to the estimation of rainfall thresholds, the maximum rainfall intensity, storm pattern and soil parameters (soil cohesion, soil friction angle and total unit weight of soil) are retreated as uncertainty factors used in the model development. The proposed PRTE_LS model is used for the reliability assessment of the issued rainfall thresholds in the Jhoukou River watershed, southern Taiwan, to demonstrate its applicability. The results indicate that the corresponding exceedance probability (i.e., underestimated risk) approximates 0.1 on average. In other words, its reliability reaches 0.9. However, issued rainfall thresholds with high reliability might hardly achieve the goal of early warning because shallow landslides can possibly happen before the actual rainfall amount exceeds the threshold. Consequently, the proposed PRTE_LS model can modify issued rainfall thresholds with the specific occurrence probability under the critical safety factors and warning durations being considered. As a result, the proposed PRTE_LS can not only quantify the reliability of the issued rainfall thresholds, but its results can also be referred to in modifying the issued thresholds in order to enhance the early-warning performance.

Control of sulphur for spring steel killed by Si–Mn and with low basicity slag

Experiments are carried out in the case of low basicity slag for spring steel killed by Si and Mn, then the changes of the sulphur content, the sulphur distribution ratio LS and inclusions are investigated. Finally, the effect on desulphurisation of oxygen content in molten steel, the calculated and measured lgLS and the deep desulphurisation of the vacuum degassing station are discussed. It is found that the most sulphur in liquid steel is mainly removed during the early stage of LF refining. The average sulphur content in steel and the sulphur distribution ratio after the soft bottom-blown are 0.0047% and 115, respectively. It is very accurate and credible to use the LS model to predict LS. During the early stage of LF refining, to reduce the oxygen content in steel quickly is very crucial for the rapid desulphurisation of the Si and Mn killed spring steel with low basicity slag. The desulphurisation of molten steel can be further carried out during the VD refining station and it is beneficial to reduce the sulphur content for the control of sulphide in spring steel killed by Si–Mn and with low basicity slag.

Quasi steady state approximation of the small clusters in Becker–Döring equations leads to boundary conditions in the Lifshitz–Slyozov limit

This papers addresses the connection between two classical models of phase transition phenomena describing different stages of the growth of clusters. The Becker-D\"oring model (BD) describes discrete-sized clusters through an infinite set of ordinary differential equations. The Lifshitz-Slyozov equation (LS) is a transport partial differential equation on the continuous half-line $x\in (0,+\infty)$. We introduce a scaling parameter $\varepsilon>0$, which accounts for the grid size of the state space in the BD model, and recover the LS model in the limit $\varepsilon\to 0$. The connection has been already proven in the context of outgoing characteristic at the boundary $x=0$ for the LS model, when small clusters tend to shrink. The main novelty of this work resides in a new estimate on the growth of small clusters, which behave at a fast time scale. Through a rigorous quasi steady state approximation, we derive boundary conditions for the incoming characteristic case, when small clusters tend to grow.

Numerical optimization algorithms for wavefront phase retrieval from multiple measurements

Wavefront phase retrieval from a set of intensity measurements can be formulated as an optimization problem. Two nonconvex models (MLP and its variant LS) based on maximum likelihood estimation are investigated in this paper. We derive numerical optimization algorithms for real-valued function of complex variables and apply them to solve the wavefront phase retrieval problem efficiently. Numerical simulation is given with application to three test examples. The LS model shows better numerical performance than that of the MLP model. An explanation for this is that the distribution of the eigenvalues of Hessian matrix of the LS model is more clustered than that of the MLP model. We find that the LBFGS method shows more robust performance and takes fewer calculations than other line search methods for this problem.

Eigenvalue approach on a two-dimensional thermal shock problem with weak, normal and strong conductivity

The present paper is devoted to the study of a two-dimensional thermal shock problem with weak, normal and strong conductivity using the eigenvalue approach. The governing equations are taken in the context of the new consideration of heat conduction with fractional order generalized thermoelasticity with the Lord-Shulman model (LS model). The bounding surface of the half-space is taken to be traction free and subjected to a time-dependent thermal shock. The Laplace and the exponential Fourier transform techniques are used to obtain the analytical solutions in the transformed domain by the eigenvalue approach. Numerical computations have been done for copper-like material for weak, normal and strong conductivity and the results are presented graphically to estimate the effects of the fractional order parameter.