Mesh Geometry Research Articles

Development of a hybrid parallelism Monte Carlo transport middleware on mesh geometry

Mesh-based Monte Carlo particle transport is suitable for complex geometry modeling and for multi-physics coupling calculations. Performing large-scale mesh-based Monte Carlo simulations requires a quite large amount of computation and memory space. Therefore, parallel Monte Carlo computing is crucial. In this study, a hybrid parallelism Monte Carlo transport middleware on mesh geometry was developed. The middleware can provide the following algorithms and functions: 1. hybrid parallelism of domain decomposition and particle parallelism; 2. particle data structure, which manages particle information and automatically performs asynchronous communication between decomposed domains; 3. subset data structure, which provides an efficient management strategy for materials and tally data; 4. particle tracking method on structured/unstructured mesh and k-dimensional tree (KD-Tree) acceleration algorithm; 5. condensed application programming interface for the rapid development of Monte Carlo code based on the middleware. We transplanted the fixed source module of the J Monte Carlo transport code (JMCT) which was based on constructive solid geometry (CSG) to the middleware for verification. The results indicated that the serial particle tracking efficiency of an unstructured mesh model was 6.56 times as high as that of MCNP6 and the serial simulation efficiency of the corresponding structured mesh model was basically equivalent to that of JMCT. The parallel efficiency of domain decomposition was higher than that of JMCT. We also calculated the shielding problem of the Qinshan No. 1 reactor through hybrid parallelism. The results were in good agreement with the experimental data, and the hybrid parallel efficiencies were higher than 65% on 4000 CPU cores.

Revalorization of sheep-wool keratin for the preparation of fully biobased printable inks

Sheep wool waste has become a problem affecting the environment, as today the wool of most species has no commercial application and is considered a waste product. Sheep’s wool is mainly composed of keratin which, due to its protein nature and multiple functional groups, has attracted great interest in applications such as support materials in tissue engineering, bioactive materials, and targeted drug delivery. Support materials can be fabricated by 3D printing by syringe extrusion. However, keratin is not suitable for this technique as it does not present proper rheological characteristics. Alginate, a biopolymer derived from brown seaweed, offers a wide range of viscosities at room temperature and offers good performance in 3D printing. Thus, keratin and alginate-based mixtures, due to their properties and ecoefficiency, are interesting candidates to prepare 3D-printed scaffolds. The aim of this work was to develop fully biobased printable inks containing keratin, alginate, salvia extracts, and cellulose nanofibers. In a first stage, keratose, an oxidized form of keratin, was obtained from sheep wool by a clean extraction methodology, and the miscibility and viscosity of keratose-alginate mixtures were assessed. In a second stage, biobased inks were prepared parting from miscible keratose-alginate mixtures. Flow analysis, spectromechanical analysis, and recovery tests were carried out to analyze the effect of the ink formulation over rheological parameters and printability. Mesh and cylinder geometries were 3D printed and their mechanical properties, as well as shape fidelity and self-standing ability, were assessed.

State of the Art on Two-Phase Non-Miscible Liquid/Gas Flow Transport Analysis in Radial Centrifugal Pumps Part C: CFD Approaches with Emphasis on Improved Models

Predicting pump performance and ensuring operational reliability under two-phase conditions is a major goal of three-dimensional (3D) computational fluid dynamics (CFD) analysis of liquid/gas radial centrifugal pump flows. Hence, 3D CFD methods are increasingly applied to such flows in academia and industry. The CFD analysis of liquid/gas pump flows demands careful selection of sub-models from several fields in CFD, such as two-phase and turbulence modeling, as well as high-quality meshing of complex geometries. This paper presents an overview of current CFD simulation strategies, and recent progress in two-phase modeling is outlined. Particular focus is given to different approaches for dispersed bubbly flow and coherent gas accumulations. For dispersed bubbly flow regions, Euler–Euler Two-Fluid models are discussed, including population balance and bubble interaction models. For coherent gas pocket flow, essentially interface-capturing Volume-of-Fluid methods are applied. A hybrid model is suggested, i.e., a combination of an Euler–Euler Two-Fluid model with interface-capturing properties, predicting bubbly flow regimes as well as regimes with coherent gas pockets. The importance of considering scale-resolving turbulence models for highly-unsteady two-phase flow regions is emphasized.

Numerical simulation of turbulent natural convection heat transfer in an MW-class offshore wind turbine nacelle based on a multi-feature acquisition meshing technique

In order to improve the computational accuracy of numerical simulations of complex thermal environments in MW-class offshore wind turbine nacelles, this paper improves the numerical simulation method for 10 MW offshore wind turbine nacelles. Firstly, the model of the wind turbine generator system (WTGS) inside the nacelle is designed and the model is simplified. Secondly, a multi-featured acquisition meshing is performed for the turbulent thermal behavior in the nacelle, using a combination of mesh geometry parameters, mesh accuracy parameters, mesh irrelevance parameters and detection verification parameters to construct a structural mesh topology. The modified SST k-ω turbulence model is used to solve the momentum and energy equations of the nacelle model. The complex physical phenomena of air recirculation, boundary layer separation and thermal stratification in the nacelle are verified based on the calculated results and compared with the experimental data, which are in good agreement with the experimental results. This paper has certain application value and guidance significance in the field of engineering such as the design of offshore wind turbine nacelle structure and cooling system design.

Computerized Simulation of Meshing of S-gears and Modification Geometry

S-gear is a new type of gear with the advantages of small sliding coefficient, high meshing efficiency and large load-bearing capacity due to the concave-convex contact in a vicinity of the meshing start and end. In view of the excellent characteristics and potential value of S-gears, this paper deeply studies the designation and meshing characteristics of the S-gears. First, based on the relationship of S-shaped rack-cutter and machining motion, the tooth surface of the S-gears is generated. Second, by superimposing the surface of modified volume with the standard tooth surface, the modified tooth surface of S-gears is constructed. On this basis, using MATLAB programming, the coordinates of 3D grid node of modified S-gears are calculated. Third, loaded tooth contact analysis (LTCA) is used to study the meshing characteristics of the S-gears with longitudinal modifications and misalignment angle errors. Ultimately, one example is presented and the result shows that after tooth surface modification, the load distribution of S-gears is effectively improved and error sensitivity is greatly reduced. S-gear is a new type of gear which is different from involute gears and has great potential application prospect in large load-bearing field, which will be further studied in the future.

HLPW-4/GMGW-3: High-Order Discretization Technology Focus Group Workshop Summary

This paper summarizes the High-Order Technical Focus Group (HO-TFG) submissions for the joint 4th AIAA High Lift Prediction (HLPW-4) and 3rd Geometry and Mesh Generation Workshop (GMGW-3). The goal of the workshop was to assess the state-of-the-art in mesh generation and computational fluid dynamics software. The Common Research Model High-Lift (CRM-HL) variant served as the primary focus of the workshop, and a two-dimensional airfoil section from the CRM-HL was used as a verification test case. The HO-TFG was tasked with generating high-order curved meshes for both geometries, and computing high-order solutions using both Reynolds-averaged Navier–Stokes and scale-resolving formulations. While limited by computational resources, the final results demonstrate the potential of higher-order methods to increase solution accuracy with a lower degree-of-freedom count relative to second-order discretizations.

General-purpose numerical deposition modeling methodology based on mesh geometry reconstruction strategy in cold spray additive manufacturing system

Cold spraying is an emerging additive manufacturing (AM) process that is receiving more and more attention, with very broad applications. At present, the focus of cold spray additive manufacturing (CSAM) is on the study of deposition mechanisms and coating performances. The deposit growth is influenced by many kinematic spraying parameters, such as the spraying angle, the stand-off distance, and the traverse speed. Achieving the desired deposition by trial and error is costly. More importantly, the manufacturing of complex components layer by layer implies the observation of the deposition process in real time to adjust the spraying strategy. This paper suggests a general-purpose MATLAB numerical deposition modeling based on a mesh geometry reconstruction strategy in CSAM to simulate the deposition process more accurately. Simulations and experiments were carried out to verify the effectiveness of the proposed methodology. The results showed that the methodology could accurately simulate the deposit growth during the CSAM process, which provides a practical guiding significance for CSAM system.

The capability of square-meshes and fixed-shape meshes to control codend size selection

Trawl codends are commonly made of diamond-mesh netting. However, diamond-mesh codends vary in mesh geometry along its length and during fishing due to catch build up. This introduces variability in the size selection process. This phenomenon compromises the rationality of regulating exploitation patterns in trawl fisheries through adjustments in codend mesh size. One technical solution often applied to achieve more well-defined size selection is turning the codend netting 45 degrees (square-mesh). However, there is a lack of evidence that square-mesh codends result in more constant size selectivity. Therefore, we aimed at quantifying the variability in size selection in square-mesh codends. We tested the size selectivity of three codends; a standard square-mesh codend, and two rigid codends where mesh geometries were fixed in diamond shape with an opening angle of 60° and square shape, respectively. The two rigid codends were used to establish baselines with limited variability in size selection. The size selectivity of these codends was compared to results - previously obtained for a standard diamond-mesh codend. Using Atlantic cod (Gadus morhua) as a case study, we demonstrated that the standard square-mesh codend had significantly larger variability in size selection compared to the fixed diamond-mesh codend. Moreover, we found no evidence that the standard square-mesh codend had lower variability in size selection than a standard diamond-mesh codend with same mesh size. These results demonstrate that the use of standard square-mesh codends is not sufficient to reduce variability in codend size selection. Additionally, we demonstrate that the sizes of fish retained is strongly dependent on mesh shape and openness. We conclude that a profound re-thinking over codend designs is required in order to achieve better control of size selection in trawl fisheries.

New Optimized Equal-Area Mesh Used in Axisymmetric Models for Laminar Transient Flows

The current paper aims at assessing the effect of the radial mesh on the description of the axial velocity in steady-state and transient conditions and at presenting the results of a new optimized equal-area mesh. For this purpose, a quasi-2D model is implemented and tested for different mesh configurations and sizes. A new two-region mesh geometry with 40 cylinders is proposed to optimize the description of the wall shear stress immediately after each pressure variation. This mesh is composed of two regions: one with a high-resolution near the pipe wall and the second with a coarser grid in the pipe core. Different configurations of this mesh are analysed for both steady and unsteady conditions. Results are compared with those obtained by a 1D model and with experimental data for laminar flows, discussed in terms of the computation effort and accuracy. The proposed two-region mesh has demonstrated: (i) a reduction in the simulation error by five times when compared with standard meshes for the same computational effort and for the instantaneous valve closure; (ii) an important improvement in accuracy for an experimental S-shape valve maneuver, particularly for meshes with few cylinders; and (iii) a correct description of the transient pressures collected in the experimental tests.

Visualizing Spatial Gaze Data in the Perception of 3D Objects

AbstractIn response to the rapid development of mobile eye tracking, this paper proposes methods for the visualization of gaze patterns in three dimensions. Methods are divided into two basic categories, beginning with translations from 2D graphic conventions to those that incorporate 3D mesh geometries. They are first discussed in principle and thereafter demonstrated on actual gaze data of sculptural reproductions. The tracing of eye movements of objects in the round required consideration of variables typically unaccounted for in conventional eye-tracking visualization, most importantly with regards to the moving position of the viewing eye. A major advantage of 3D visualizations is the capacity to present gaze information simultaneously on obverse, reverse, and oblique surfaces of perceptual attention. The included methods provided for effective communication of a subject’s perceptual distribution over potentially complex stimulus geometries.

A Rational Approach to Meshing Cerebral Venous Geometries for High-Fidelity Computational Fluid Dynamics.

Computational fluid dynamics (CFD) of cerebral venous flows has become popular owing to the possibility of using local hemodynamics and hemoacoustics to help diagnose and plan treatments for venous diseases of the brain. Lumen geometries in low-pressure cerebral veins are different from those in cerebral arteries, often exhibiting fenestrations and flattened or triangular cross section, in addition to constrictions and expansions. These can challenge conventional size-based volume meshing strategies, and the ability to resolve nonlaminar flows. Here we present a novel strategy leveraging estimation of length scales that could be present if flow were to become transitional or turbulent. Starting from the lumen geometry and flow rate boundary conditions, centerlines are used to determine local hydraulic diameters and cross-sectional mean velocities, from which flow length scales are approximated using conventional definitions of local Kolmogorov and Taylor microscales. By inspection of these scales, a user specifies minimum and maximum mesh edge lengths, which are then distributed along the model in proportion to the approximated local Taylor length scales. We demonstrate in three representative cases that this strategy avoids some of the pitfalls of conventional size-based strategies. An exemplary CFD mesh-refinement study shows convergence of high-frequency flow instabilities even starting from relatively coarse edge lengths near the lower bounds of the approximated Taylor length scales. Rational consideration of the length scales in a possibly nonlaminar flow may thus provide a useful and replicable baseline for denovo meshing of complicated or unfamiliar venous lumen geometries.

High Precision Mesh-Based Drone Image Stitching Based on Salient Structure Preservation and Regular Boundaries

Addressing problems such as obvious ghost, dislocation, and distortion resulting from the traditional stitching method, a novel drone image-stitching method is proposed using mesh-based local double-feature bundle adjustment and salient structure preservation which aims to obtain more natural panoramas.The proposed method is divided into the following steps. First, reducing parallax error is considered from both global and local aspects. Global bundle adjustment is introduced to minimize global transfer error, and then the local mesh-based feature-alignment model is incorporated into the optimization framework to achieve more accurate alignment. Considering the sensitivity of human eyes to linear structure, the global linear structure that runs through the images obtained by segment fusion is introduced to prevent distortions and align matching line segments better. Rectangular panoramas usually have better visual effects. Therefore, regular boundary constraint combined with mesh-based shape-preserving transform can make the results more natural while preserving mesh geometry. Two new evaluation metrics are also developed to quantify the performance of linear structure preservation and the alignment difference of matching line segments. Extensive experiments show that our proposed method can eliminate parallax and preserve global linear structures better than other state-of-the-art stitching methods and obtain more natural-looking stitching results.

Robust Topological Construction of All-hexahedral Boundary Layer Meshes

We present a robust technique to build a topologically optimal all-hexahedral layer on the boundary of a model with arbitrarily complex ridges and corners. The generated boundary layer mesh strictly respects the geometry of the input surface mesh, and it is optimal in the sense that the hexahedral valences of the boundary edges are as close as possible to their ideal values (local dihedral angle divided by 90°). Starting from a valid watertight surface mesh (all-quad in practice), we build a global optimization integer programming problem to minimize the mismatch between the hexahedral valences of the boundary edges and their ideal values. The formulation of the integer programming problem relies on the duality between boundary hexahedral configurations and triangulations of the disk, which we reframe in terms of integer constraints. The global problem is solved efficiently by performing combinatorial branch-and-bound searches on a series of sub-problems defined in the vicinity of complicated ridges/corners, where the local mesh topology is necessarily irregular because of the inherent constraints in hexahedral meshes. From the integer solution, we build the topology of the all-hexahedral layer, and the mesh geometry is computed by untangling/smoothing. Our approach is fully automated, topologically robust, and fast.

Curvature Weighted Decimation: A Novel, Curvature-Based Approach to Improved Lidar Point Decimation of Terrain Surfaces

Increased availability of QL1/QL2 Lidar terrain data has resulted in large datasets, often including large quantities of redundant points. Because of these large memory requirements, practitioners often use decimation to reduce the number of points used to create models. This paper introduces a novel approach to improve decimation, thereby reducing the total count of ground points in a Lidar dataset while retaining more accuracy than Random Decimation. This reduction improves efficiency of downstream processes while maintaining output quality nearer to the undecimated dataset. Points are selected for retention based on their discrete curvature values computed from the mesh geometry of the TIN model of the points. Points with higher curvature values are preferred for retention in the resulting point cloud. We call this technique Curvature Weighted Decimation (CWD). We implement CWD in a new free, open-source software tool, CogoDN, which is also introduced in this paper. We evaluate the effectiveness of CWD against Random Decimation by comparing the resulting introduced error values for the two kinds of decimation over multiple decimation percentages, multiple statistical types, and multiple terrain types. The results show that CWD reduces introduced error values over Random Decimation when 15 to 50% of the points are retained.

Perspectives of computational fluid dynamics methods in the study of membrane processes

In mathematical modeling of membrane processes, the study of structural features of used membranes and the significant limitation of information in the formal description of their separation properties led to the development of physical models that take into account not only the features of structures of real membranes, but also their peculiarities of functioning. When compiling physical models of membrane processes, it is impossible to objectively quantify most of the factors due to their great diversity and variability, which distances the mathematical model from the real process. That is why methods of computational fluid dynamics reliably and efficiently perform calculations for all physical models and types, including stationary or transient flow, incompressible or compressible flow (from small subsonic to hypersonic), simulation of laminar or turbulent flows, Newtonian or non-Newtonian fluids, ideal or real gas. An electronic geometric model of the plant was built, a choice of mesh geometry with different densities was made to optimize the calculation time and solution accuracy for a particular case, the kinetic dependence of cell growth was calculated, the flow rates of feeding medium into the intra- and inter-fiber spaces of the bioreactor were determined, and the hydrodynamic conditions were analyzed.

Mechanical properties and osteointegration of the mesh structure of a lumbar fusion cage made by 3D printing

The currently popular 3D printing makes it possible to produce spatial scaffolds, the main purpose of which is to obtain implants that have favourable mechanical properties to promote cell adhesion. This study aims to prove the influence of changes in selected geometrical parameters of scaffolds, used in intervertebral cages, on the mechanical properties obtained and thus on the osteointegration of the studied constructs with osteoblasts and fibroblasts. The stiffness values and maximum failure force of four modifications to geometric dimensions of the meshes were determined from the intendation test. Adhesion assays were conducted (including gentle pendulum motion) for Balb/3T3 fibroblasts and NHOst osteoblasts. The study revealed that an important geometrical parameter affecting the strength of the mesh is the height (h) of the connection point between arms of successive mesh cells. There was no significant effect of the mesh geometry on the abundance and survival of Balb/3T3 and NHOst cells. At the same time, fibroblasts were more likely to form colonies in the area where there is fusion of mesh cells, as opposed to osteoblasts that were more numerous at vertices of the mesh.

Automated geometry and hexahedral mesh generation for kilometer-scale atmospheric flow simulations

This article introduces a methodology for automatic generation of geometries and meshes for kilometer-scale Atmospheric Boundary Layer (ABL) flow simulations, with topography and elevation. The proposed programmatic (hence automatable) \emph{template morphing approach} facilitates interpolation of scattered point cloud terrain data on a template geometry domain, morphing a high-quality quadrilateral template mesh for the interpolated geometry, and setup as well as execution of Computational Fluid Dynamics (CFD) flow simulation. The proposed method specifically addresses the previously reported problems of sustaining an ABL structure across the simulation domain by imposing the velocity and turbulence properties on all vertical surfaces. We present a validation study for the proposed method on an artificial Gaussian hill terrain. A real-world localized wind forecast application from the Turku Archipelago, Finland, is also presented, using open terrain data from National Land Survey of Finland. Such localized wind forecasts aim to assist ships in autonomous navigation and maneuvering in complex port or fairway environments, which is the motivation for this study.

MOOSE Reactor Module: An Open-Source Capability for Meshing Nuclear Reactor Geometries

The U.S. Department of Energy (DOE) Nuclear Energy Advanced Modeling and Simulation (NEAMS) program has developed numerous physics solvers utilizing the open-source Multiphysics Object-Oriented Simulation Environment (MOOSE) framework for multiphysics reactor analysis. These solvers require input finite element meshes representing the discretized spatial domain. Typically, reactor analysts turn to licensed tools for the creation of reactor geometry meshes. Recently, open-source functionality has been added to the MOOSE framework to mesh common reactor geometries and improve MOOSE-based nuclear reactor application user workflows. The new functionality is primarily contained in the new Reactor module of MOOSE and includes support for hexagonal pins, assemblies, and cores, extended Cartesian geometry support, options for modeling static and rotating control drums within a hexagonal assembly, core periphery triangulation, and automatic tagging of pin, assembly, plane, and depletion regions for easier post processing of physics results. A set of reactor geometry mesh builder objects further streamlines the construction of hexagonal and Cartesian cores and allows mapping of materials to regions during mesh generation. The meshes produced with the MOOSE Reactor module may be used directly within MOOSE-based applications or exported as Exodus II files for use in other finite element solvers. The tools have been demonstrated and verified using a variety of NEAMS physics solvers on a range of reactor applications, including a sodium-cooled fast reactor core analysis using Griffin, a fast reactor assembly thermal deformation analysis using MOOSE Tensor Mechanics, and a heat pipe–cooled microreactor coupled analysis using Griffin, Bison, and Sockeye. MOOSE’s Reactor module provides significant advantages compared to the use of external meshing tools when analyzing Cartesian and hexagonal reactor lattices using MOOSE-based applications: immediate accessibility (open-source) to the end user, low barrier to entry for new users, speed of mesh generation, volume preservation of meshed fuel pins, and simplification of analysis workflow when used in conjunction with MOOSE-based applications.

Numerical Study on a Supersonic Flow around a Bullet

In this research paper, a numerical analysis in Computational Fluid Dynamics uses the Finite Volume Method to visualize the external flow characteristics over a bullet speeding at Mach 2.0. The simulation results evaluate the experimental drag coefficient of the supersonic bullet airflow in a wind tunnel. The numerical simulation assumes that the inviscid model remains non-rotating. The generation of the mesh geometry varies between Coarse, Medium, and Fine types, and proper selection of the grid density improves the accuracy of the numerical result. The Fine Quadrilaterals mesh of 150,000 elements achieved considerable punctuality along with the numerical method of the second-order linear differential equations. The drag coefficient value of 0.222 gives a 0.9 percent error relative to the attained experiment value. The Mach number, pressure ratio, and flow simulation velocity contours obtained with ANSYS FLUENT software represent the validation of the experimental data with numerical analysis method in a typical fluid mechanics problem.

Highly Conductive Omnidirectionally Stretchable 2D Transparent Copper Mesh Electrodes and Applications in Optoelectronic Devices

Abstract2D stretchable transparent electrodes (STE) are required to conform to non‐flat complex 3D surfaces for next‐generation stretchable optoelectronic devices. However, it is a great challenge to simultaneously maintain omnidirectional stretchability, high transmittance, and the least change in conductivity at large strain. In this work, omnidirectionally stretchable 2D transparent electrode is achieved by hybrid printed copper mesh embedded in an elastic material. The electrode displays exceedingly low sheet resistance down to 0.12 Ω sq−1 while still maintaining 80% of optical transparency. Two types of mesh geometries, the horseshoe‐like and sinusoid‐like shapes, are thoroughly investigated by simulations and experiments. By optimizing the key geometrical parameters of mesh structure, the copper mesh can endure stretching up to 130% with no fractures and no resistivity change. After 1000 stretch‐and‐release cycles at 10% strain, the copper mesh remains intact with negligible resistance variation. For 2D stretchability, the copper mesh is stretched in eight directions simultaneously and can maintain its initial conductivity up to 50% tensile deformation. As a demonstration of application, the copper mesh STE is employed in a stretchable electroluminescent device that maintained uniform lighting up to 120% stretching and 100 stretch‐release cycles at 30% strain, showing its potential in stretchable and wearable optoelectronic applications.