Mesh Scale Research Articles

A new method to improve precipitation estimates by blending multiple satellite/reanalysis-based precipitation products and considering observations and terrestrial water budget balance

Merging multiple satellite/reanalysis-based precipitation products (SPPs) is a critical way to improve the accuracy of spatial precipitation (P) estimation. In this paper, a new method was proposed to merge multiple SPPs by considering rain gauge-based observations and water budget closure. Based on the errors of SPPs at gauged regions, the proposed method first estimates the mesh-based errors of SPPs as the intermediate variable using the error in water budget closure and then calculates the respective merging weights of SPPs in data merging. The performance of this proposed method was verified by comparing its results with the input of original SPPs and the data merged by five existing merging methods in mainland China at mesh scale and in nine major basins. Two scenarios were designed for the period from 2003.02 to 2016.12 at a monthly temporal resolution − with and without water budget closure constraints. Seven popular SPPs were considered, including GPM IMERG, PERSIANN, GSMaP, CHIRPS, ERA5, CFSV2, and TerraClimate. The results showed that the proposed method improved the P estimates in terms of CC, RMSE, MAE, PBIAS and KGE in both scenarios, and that closing the terrestrial water budget would slightly reduce the accuracy of SPPs against observations. The reduction percentage is about 5% in term of CC and KGE, and 12% in term of RMSE. This study is the first attempt to merge SPPs and gauge-based rain observation with consideration of water budget closure. It provides not only an effective and robust tool for the merging of multiple SPPs, but also important insights into the further development of SPP merging methods by considering water budget closure.

Microgrid-Patterned Ni Foams as Current Collectors for Ultrafast Energy Storage Devices

Current research is focused on developing active materials through surface functionalization, porosity, composites, and doping for ultrafast electric double layer capacitors (EDLCs). In this study, deviating from existing strategies focused on active materials, we designed tunable 3D microgrid-patterned (MP) surface morphologies on Ni foams used as current collectors using SUS meshes as rigid stamps during roll pressing. The surface geometries of the MP-Ni foams were controlled to standard mesh scales of 24, 40, and 60 (denoted as 24MP-Ni, 40MP-Ni, and 60MP-Ni, respectively). The three MP-Ni samples with different microgrid sizes presented different surface geometries, such as root-mean-square roughness (Rrms), skewness roughness (Rsk), and width/depth scales of the microgrid patterns. Consequently, 40MP-Ni demonstrated an optimized surface geometry with high Rrms (35.4 μm) and Rsk (−0.19) values, which facilitated deep slurry infiltration and increased its contact area with the active material. Surface optimization of the MP-Ni enabled ultrafast and reversible charge transport kinetics owing to its relaxed electron transfer resistance and robust adhesion to the active material compared with bare Ni foam. EDLC electrodes with 40MP-Ni achieved an ultrafast-rate capability (96.0 F/g at 20 A/g) and ultrafast longevity (101.9% capacity retention after 5000 cycles at 5 A/g) without specific modification of active material.

Using Spatial Scan Statistics and Geographic Information Systems to Detect Monthly Human Mobility Clusters and Analyze Cluster Area Characteristics.

This study evaluated the detection of monthly human mobility clusters and characteristics of cluster areas before the coronavirus disease 2019 (COVID-19) outbreak using spatial epidemiological methods, namely, spatial scan statistics and geographic information systems (GIS). The research area covers approximately 10.3 km2, with a population of about 350,000 people. Analysis was conducted using open data, with the exception of one dataset. Human mobility and population data were used on a 1-km mesh scale, and business location data were used to examine the area characteristics. Data from January to December 2019 were utilized to detect human mobility clusters before the COVID-19 pandemic. Spatial scan statistics were performed using SaTScan to calculate relative risk (RR). The detected clusters and other data were visualized in QGIS to explore the features of the cluster areas. Spatial scan statistics identified 33 clusters. The detailed analysis focused on clusters with an RR exceeding 1.5. Meshes with an RR over 1.5 included one with clusters for 1 year which is identified in all months of the year, one with clusters for 9 months, three with clusters for 6 months, three with clusters for 3 months, and four with clusters for 1 month. September had the highest number of clusters (eight), followed by April and November (seven each). The remaining months had five or six clusters. Characteristically, the cluster areas included the vicinity of railway stations, densely populated business areas, ball game fields, and large-scale construction sites. Statistical analysis of human mobility clusters using open data and open-source tools is crucial for the advancement of evidence-based policymaking based on scientific facts, not only for novel infectious diseases but also for existing ones, such as influenza.

Spectral Descriptors for 3D Deformable Shape Matching: A Comparative Survey.

A large number of 3D spectral descriptors have been proposed in the literature, which act as an essential component for 3D deformable shape matching and related applications. An outstanding descriptor should have desirable natures including high-level descriptive capacity, cheap storage, and robustness to a set of nuisances. It is, however, unclear which descriptors are more suitable for a particular application. This paper fills the gap by comprehensively evaluating nine state-of-the-art spectral descriptors on ten popular deformable shape datasets as well as perturbations such as mesh discretization, geometric noise, scale transformation, non-isometric setting, partiality, and topological noise. Our evaluated terms for a spectral descriptor cover four major concerns, i.e., distinctiveness, robustness, compactness, and computational efficiency. In the end, we present a summary of the overall performance and several interesting findings that can serve as guidance for the following researchers to construct a new spectral descriptor and choose an appropriate spectral feature in a particular application.

Numerical Investigation of Oil–Air Flow Inside Tapered Roller Bearings with Oil Bath Lubrication

Oil–air flow within an oil bath lubrication tapered roller bearing is essential for the lubrication and cooling of the bearing. In this paper, we develop a simulation model to investigate the flow field of tapered roller bearings with oil bath lubrication. The multiple reference frame (MRF) approach is used to describe the physical motion of the bearing, and the volume of fluid (VOF) two–phase flow model is used to track the oil–air interface in the flow field. The effects of mesh scale, geometric gap, and oil reservoir size on calculation time and convergence accuracy are examined in detail, and the effects of inner ring rotational speed and lubricant viscosity on frictional torque are systematically studied. The results of the numerical simulation indicate that as the gap distance between the raceway and the rolling elements decreases, the frictional torque is mainly generated by churning losses at the inner raceway and the rolling elements. The frictional torque increases with increasing inner ring speed and lubricating oil viscosity, with the rolling element contributing the largest portion at approximately 50% of the total. We demonstrate the effectiveness of a method to reduce frictional torque by optimizing the internal structure of the bearing to control oil flow. By optimizing the cage structure and reducing the roller half-cone angle, frictional torque can be reduced by 29.1% and 26.2%, respectively.

Evaluating the quality of life for sustainable urban development

As urbanization is rapidly progressing worldwide, the cities need to assess their quality of life (QOL) not only to check their infrastructure but also to keep pace with the changing citizens' sense of values and lifestyles. We propose an integrated method to evaluate urban QOL from the detailed spatial aspects of a city with the subjective preferences of its citizens. In this study, we collected the spatial data of urban setting attributes at a 500-m mesh scale, and the subjective preferences that vary based on individual attributes, to evaluate the QOL across five metropolitan areas in Japan. Our results reveal a greater disparity in QOL within larger metropolitan areas. The optimal urban population density for the best QOL tends to be around 4000 people/km2. This level strikes a balance between the benefits and drawbacks associated with urban QOL, such as enhanced living and cultural opportunities versus high housing costs and limited space. Moreover, QOL within a city varied according to geographic location, and these differences were amplified by subjective preferences. These findings contribute to our understanding of the disparities in urban QOL, and provide a scientific basis for urban policies that achieve diversity and inclusiveness.

Using Multiscale Direct Simulation Approach to Understanding Transports Behavior Inside PEM Water Electrolyzer

In this work, numerical modeling techniques were developed to predict oxygen bubble evolution through complex pore geometries to provide information of gas transport pathways inside saturated porous transport layers (PTL). Each PTL undergoes an image processing technique that uses X-ray CT images to generate accurate 3D microstructures. An example of a generated PTL structure is shown in Figure 1.Historically, meshing of the complex geometry was tedious and non-automated. Due to the random particle size across the geometry, a constant base size for meshing resulted in an inadequate mesh for accurate predictions. The Lattice-Boltzmann method is therefore more commonly used because a lattice is easier than a finite volume mesh to generate. Although sufficiently fine lattices adhered to the topology of the physical structure, simulations required a timestep between 1e-8 and 1e-10 seconds, resulting in long computational time.Meshing techniques have improved and can now be applied to complex geometries. Using the finite volume method accompanied with an adaptive mesh and adaptive time scale, provides an accurate representation of the PTL structure and larger timesteps. A volume of fluid (VoF) method was used to model two phase flow, using liquid water and gaseous oxygen, through different PTL structures. Evolution, growth, size, velocity, and surface interaction of oxygen bubbles through microstructures were studied as also shown in Figure 2. Findings from the work will provide better understanding of oxygen evolution through saturated PTLs Figure 1

Improved radial basis functions mesh deformation based on parallel point selection strategy and incremental LDLT decomposition

Mesh deformation based on radial basis functions (RBF) is widely used in CFD simulations with moving boundaries due to its simplicity, generality, and robustness, among which selecting an optimum reduced set from all boundary nodes is a crucial data reduction step for fewer support points. However, there remains a great need to reduce the computation costs for large-scale mesh. To solve this issue, a parallel point selection strategy and incremental LDLT decomposition method are proposed. With all boundary nodes distributed to all processors on average, the displacements of boundary nodes are calculated at local ones, and the nodes with local maximum error in divergent processors are added to the support point set in parallel. Besides, the matrix decomposition and solution of weight coefficients are conducted with full uses of corresponding results in the last iteration in incremental LDLT decomposition method. The calculation costs of conventional methods and proposed approaches are theoretically analyzed and compared. Three typical test cases of different mesh scales and motion modes are carried out for validation, including the rigid motion of a NACA0012 airfoil, the bending of an ONERA M6 wing, and the pitch of a missile. The results demonstrate that the proposed approaches greatly improve the efficiency of the data reduction procedure compared with the conventional methods, with similar deformation effect represented by support point distribution and deformed mesh quality.

Design and Implementation of Evaluation Method for Spraying Coverage Region of Plant Protection UAV

Plant protection UAVs are becoming the preferred plant protection method for agricultural pest control. At present, the evaluation of droplet distribution in aerial spraying is collected and evaluated after the completion of prevention and control operations, and there is a lack of real-time evaluation methods. Based on the flight parameter during the UAV plant protection process, real-time estimation of droplet distribution is the key to solving this problem and further improving the effectiveness of aerial spraying. This study proposes a merging algorithm for arbitrary polygonal regions, meshing the boundaries of the region, divide the mesh segments based on the overlapping meshes between the two regions, and connect the valid mesh connection segments of the two regions according to certain rules to obtain the intersection, union, and residual operation results between the regions. Afterwards, software based on this algorithm was developed and applied to generate spraying coverage regions, leakage spray regions, and repeated spray regions. The experimental results on theoretical and irregular routes show that the algorithm can accurately generate droplet distribution regions. The error of the calculation results with a mesh scale of 0.05 m is within 7‰, and the operating speed is above 30 Hz, meeting the real-time requirements. The smaller the mesh scale is, the higher the accuracy of the calculation results is, but the slower the calculation speed. Therefore, in practical applications, it is necessary to choose an appropriate mesh scale based on hardware computing power and accuracy level requirements. This study solves the problem of cumulative calculation of droplet distribution during the operation of plant protection UAVs, providing a basis for objectively evaluating the operation quality of plant protection UAVs and optimizing the setting of operation parameters.

Verification of neutronics and thermal-hydraulic coupled system with pin-by-pin calculation for PWR core

As an important part of the digital reactor, the pin-by-pin wise fine coupling calculation is a research hotspot in the field of nuclear engineering in recent years. It provides more precise and realistic simulation results for reactor design, operation and safety evaluation. CORCA-K a nodal code is redeveloped as a robust pin-by-pin wise neutronics and thermal-hydraulic coupled calculation code for pressurized water reactor (PWR) core. The nodal green's function method (NGFM) is used to solve the three-dimensional space-time neutron dynamics equation, and the single-phase single channel model and one-dimensional heat conduction model are used to solve the fluid field and fuel temperature field. The mesh scale of reactor core simulation is raised from the nodal-wise to the pin-wise. It is verified by two benchmarks: NEACRP 3D PWR and PWR MOX/UO2. The results show that: 1) the pin-by-pin wise coupling calculation system has good accuracy and can accurately simulate the key parameters in steady-state and transient coupling conditions, which is in good agreement with the reference results; 2) Compared with the nodal-wise coupling calculation, the pin-by-pin wise coupling calculation improves the fuel peak temperature, the range of power distribution is expanded, and the lower limit is reduced more.

On dynamic response and damage evaluation of bridge piers under far-field explosion loads

This paper aims to investigate of the dynamic response and damage mechanism of typical bridge piers under far-field explosions numerically and develop a feasible scheme for rapid damage evaluation of bridge piers. An ANSYS-AUTODYN-based explicit finite element formulation is introduced in which the dynamic input method of blast waves is developed using subroutines. The tests of drop hammer impact and far-field explosion are referenced to verify the reliability of the formulation and the mesh scale applicable to beam-column members is determined. Based on the validated formulation, the refined fluid–solid coupling models of typical single-column and double-column piers are established to explore their far-field blast responses. The effects of input parameters (i.e., the strength and angle of the blast wave,) on the pier response are analyzed. It is demonstrated that bending damage occurs in bridge piers is similar to that of cantilever beam under different strength loads, while the damage of double-column pier members under the constant displacement increases with the increase of the blast wave angle. By incorporating the crack distribution, quantitative assessing criterion and P-I diagram, a damage evaluating scheme is proposed and the damage regularities of piers under far-field blast loads are acquired. The present work can serve as a valuable reference for blast-resistant design and damage assessment of bridge piers under far-field blast loads.

Trajectory of bearing movement during Oxford mobile-bearing unicompartmental knee arthroplasty using a kinematic alignment technique.

Trajectory of bearing movement during Oxford mobile-bearing unicompartmental knee arthroplasty using a kinematic alignment technique.

Persistence of dynamic consistency of nonstandard numerical schemes for the Fisher-KPP equation

Finite difference schemes for the Fisher-KPP equation are considered that are constructed using non-local discretization of non-linear terms and standard/nonstandard denominators. Their dynamic consistency with respect to positivity, boundedness, steady-states, and diffusion-front propagation are established. Diffusion-fronts are obtained that inflate, deflate, or remain constant at a geometric rate determined by the time-space step size functional relationship. The persistence of said dynamic consistency in terms of their boundedness, positivity, and determining-diffusion curves at small and large scales is rigorously analyzed and numerically supported. Comparisons are presented for three cases using the Euler, nonstandard finite difference, or exact spectral derivative discretization finite difference denominators. Finally, general measures of robustness in persistence are introduced that incorporate (mesh) scale sizes and are used to rank the robustness of the schemes investigated.

A PANS Method Based on Rotation-Corrected Energy Spectrum for Efficient Simulation of Rotating Flow

A partially averaged Navier–Stokes method with a new expression of fk based on the rotation-corrected energy spectrum is proposed. It is coupled with the shear-stress transport turbulence model to simulate two typical rotating flows: rotating channel flow and flow in a centrifugal pump impeller. The results of two traditional energy spectrum-based fk expressions (ES1 and ES2) and DNS/experimental results are used for comparison. The results show that the fk distribution predicted based on the rotation-corrected energy spectrum is more reasonable. In the region with enhanced turbulence, more turbulence scales exist, such as the pressure side in the rotating channel flow, where the fk value is low and more turbulence scales are resolved. While in the region with suppressed turbulence, fewer turbulence scales exist, such as the suction side, where the fk value is relatively high. The model with a new fk expression can produce better results since it can give a more reasonable fk distribution. At the same time, the new model is more efficient since it shows better calculation performance with the same mesh scale and low cost with comparable calculation performance.

ARIMA-FEM Method with Prediction Function to Solve the Stress–Strain of Perforated Elastic Metal Plates

Stress analysis and deformation prediction have always been the focuses of the field of mechanics. The accurate force prediction in plate deformation plays important role in the production, processing and performance analysis of materials. In this paper, we propose an ARIMA-FEM method, which can be used to solve some mechanical problems of 2D porous elastic plate. We have given a detailed theory and solving steps of ARIMA-FEM. In addition, three numerical examples are given to predict the stress–strain of thin porous elastic metal plates. This article uses CST, LST and Q4 elements to discrete the rectangular plates, square plates and circle plates with holes. As for variable force prediction, this paper compared with linear regression, nonlinear regression and neural network prediction, and the results show that the ARIMA method has a higher prediction accuracy. Furthermore, we calculate the numerical solution at four mesh scales, and the numerical convergence is consistent with the theoretical convergence, which also shows the effectiveness of our method. The image smoothing algorithm is applied to keep edge information with high resolution, which can more concisely describe the plate internal changes. Finally, the application scope of ARIMA-FEM, model expansion, superconvergence analysis and other issues have been given enlightening views in the discussion section. In fact, this algorithm combined statistics and mechanics. It also reflects the knowledge integration of interdisciplinary and uses it better to serve practical applications.

Investigation of сomputational meshes for modeling the air dynamics in a vortex tube channel by OpenFOAM software

A vortex tube is a simple device with no moving parts that separates a swirling gas stream into two vortexes that differ in temperature, usually above and below the temperature of the inlet gas. This paper presents a mathematical model of a vortex tube which is based on gas dynamics laws and is supplemented by a k-ω turbulence model. A description of the technique for constructing a finite volume mesh with definition of the near-wall region based on the blockMesh utility is given when the conditions for the uniformity of the mesh elements are met while maintaining their orthogonalization. The numerical solution is carried out on a computational cluster using the sonicFoam solver of the OpenFOAM free software. Three series of numerical simulation experiments were carried out to determine the temperature distribution in the channel of a cold air diaphragm depending on the diaphragm diameter. One of the three computational mesh scales considered in this work is used. It is shown that mesh size reduction leads to convergence of simulation results. It is also demonstrated the qualitatively correct results can be obtained by generating a mesh in which the average linear size of a finite volume does not exceed 0.4 mm (0.025 in dimensionless representation). To improve the accuracy of quantitative data, an even greater computational mesh size reduction is required; in particular, a fine mesh with an average linear size of the finite volume less than 0.02 is considered in this work. The results obtained on a fine mesh are in a qualitative agreement with the results determined using a coarser mesh. However, the numerical values can differ significantly, which is shown by the calculations for the cold air diaphragm of large diameter. Thus, the computational time increases with decreasing mesh size, which implies that the construction of a computational mesh for vortex tube modeling requires finding a balance between the quality of results and the simulation time.

Numerical simulation of the flow around a circular cylinder at Reynolds number Re = 3900 by means of the PANS model

The paper presents a study of various versions of PANS approach for turbulence simulation using a flow around a cylinder at Reynolds number Re = 3900 as an example. The considered models were implemented in the in-house CFD package. The influence of the method of determining the parameter f k on the flow behind the cylinder was studied. The first method assumed a constant value of f k. In the second method, the f k value depended on the local computational mesh scale and the shear scale.

Subgrid corrections in finite-element modeling of storm-driven coastal flooding

Coastal flooding models are used to predict the timing and magnitude of inundation during storms, both for real-time forecasting and long-term design. However, there is a need for faster flooding predictions that also represent flow pathways and barriers at the scales of critical infrastructure. This need can be addressed via subgrid corrections, which use information at smaller scales to ‘correct’ the flow variables (water levels, current velocities) averaged over the mesh scale. Recent studies have shown a decrease in run time by 1 to 2 orders of magnitude, with the ability to decrease further if the model time step is also increased.In this study, subgrid corrections are added to a widely used, finite-element-based, shallow water model to better understand how they can improve the accuracy and efficiency of inundation predictions. The performance of the model, with and without subgrid corrections, is evaluated on scenarios of tidal flooding in a synthetic domain and a small bay in Massachusetts, as well as a scenario with a real atmospheric forcing and storm surge in southwest Louisiana. In these tests we observed that the subgrid corrections can increase model speed by 10 to 50 times, while still representing flow through channels below the mesh scale to inland locations.

An improved peak-selection algorithm using block-based recurrence Cholesky decomposition for mesh deformation

An improved peak-selection algorithm is proposed for mesh deformation. With the use of the newly derived block-based recurrence Cholesky (BRC) decomposition scheme, the computational complexity for solving the linear algebraic system in the data reducing procedure is reduced from O(Nc4/Np) to O(Nc3), where Nc denotes the total number of support nodes and Np denotes the number of support nodes added at a time. Because the BRC decomposition scheme introduces block matrices, it involves more multiplications between matrices rather than between vectors. Due to the fact that the computation of matrix multiplication is more efficient with the use of the linear algebraic library, the efficiency for solving the linear algebraic system can be further increased. Two deformation problems are applied to validate the algorithm. The results show that it significantly increases the efficiency for solving the linear algebraic system, allowing the time consumption of this process to be reduced to only one sixth. Moreover, the efficiency will increase with the mesh scale. The results also show that it allows the efficiency of the data reducing procedure to improve by two times. Furthermore, it is found that only 1.094 s in total is required to solve the linear algebraic system with serial computing by constructing a set of as many as 2999 support nodes in a large-scale mesh deformation problem. It is indicated that the bottleneck of mesh deformation caused by inefficient parallel computing for solving the linear algebraic system can thus be removed. This makes the algorithm favorable for large-scale engineering applications.

3D Wavelet Finite-Element Modeling of Frequency-Domain Airborne EM Data Based on B-Spline Wavelet on the Interval Using Potentials

We present a wavelet finite-element method (WFEM) based on B-spline wavelets on the interval (BSWI) for three-dimensional (3D) frequency-domain airborne EM modeling using a secondary coupled-potential formulation. The BSWI, which is constructed on the interval (0, 1) by joining piecewise B-spline polynomials between nodes together, has proved to have excellent numerical properties of multiresolution and sparsity and thus is utilized as the basis function in our WFEM. Compared to conventional basis functions, the BSWI is able to provide higher interpolating accuracy and boundary stability. Furthermore, due to the sparsity of the wavelet, the coefficient matrix obtained by BSWI-based WFEM is sparser than that formed by general FEM, which can lead to shorter solution time for the linear equations system. To verify the accuracy and efficiency of our proposed method, we ran numerical experiments on a half-space model and a layered model and compared the results with one-dimensional (1D) semi-analytic solutions and those obtained from conventional FEM. We then studied a synthetic 3D model using different meshes and BSWI basis at different scales. The results show that our method depends less on the mesh, and the accuracy can be improved by both mesh refinement and scale enhancement.