Mesh Alignment Research Articles

Numerical calculation of air permeability of warp-knitted jacquard spacer shoe-upper materials based on CFD

Abstract In order to realize the rapid design of warp-knitted jacquard spacer shoe-upper materials and to explore the influence of different fabric surface organization structures on their air permeability, it is proposed to numerically simulate the air permeability performance of jacquard shoe-upper materials using ANSYS fluid analysis. First, four kinds of shoe material specimens with different upper and lower layer mesh alignment relationships are designed and tested, then the corresponding geometric structure models of the fabric are established based on the samples and appropriately processed, and finally the air permeability of the shoe material is numerically simulated and calculated based on computational fluid dynamics. The results show that, under the same conditions, the air permeability of double-sided mesh structure is significantly better than that of single-sided mesh structure, and its air permeability can be optimized by adjusting the relationship between the upper and lower layers of the fabric mesh; the airflow mainly passes through the fabric pores and gaps between the yarns, and the closer the fabric structure is, the more the air flow is hindered, and the worse the air permeability is. The simulation results of the established numerical model are consistent with the measured results, and the error is less than 10%, so it can be used to simulate and predict the air permeability of the warp-knitted jacquard spacer footwear materials, and provide theoretical support for the design and performance research of footwear materials.

Efficient Registration for Human Surfaces Via Isometric Regularization on Embedded Deformation.

3D registration is a fundamental step to obtain the correspondences between surfaces. Traditional mesh alignment methods tackle this problem through non-rigid deformation, mostly accomplished by applying ICP-based (Iterative Closest Point) optimization. The embedded deformation method is proposed for the purpose of acceleration, which enables various real-time applications. However, it regularizes on an underlying simplified structure, which could be problematic for intricate cases when the simplified graph doesn't fully represent the surface attributes. Moreover, without elaborate parameter-tuning, deformation usually performs suboptimally, leading to slow convergence or a local minimum if all regions on the surface are assumed to share the same rigidity during the optimization. In this paper, we propose a novel solution that decouples regularization from the underlying deformation model by explicitly managing the rigidity of vertex clusters. We further design an efficient two-step solution that alternates between isometric deformation and embedded deformation with cluster-based regularization. Our method can easily support region-adaptive regularization with cluster refinement and execute efficiently. Extensive experiments demonstrate the effectiveness of our approach for mesh alignment tasks even under large-scale deformation and imperfect data. Our method outperforms state-of-the-art methods both numerically and visually.

Coupling finite elements of class C1 on composite curved meshes for second order elliptic problems

SummaryFinite elements of class are suitable for the computation of magnetohydrodynamics instabilities in tokamak plasmas. In addition, isoparametric approximations allow for a precise alignment of the mesh with the magnetic field line. Mesh alignment is crucial to achieve axisymmetric equilibria accurately. It is also helpful to deal with the anisotropy nature of magnetized plasma flows. In this numerical framework, several practical simulations are now available. They help to understand better the operation of existing devices and predict the optimal strategies for using the international ITER tokamak under construction. However, a mesh‐aligned isoparametric representation suffers from the presence of critical points of the magnetic field (magnetic axis, X‐point). We here explore a strategy that combines aligned mesh out of the critical points with non‐aligned unstructured mesh in a region containing these points. By this strategy, we can avoid highly stretched elements and the numerical difficulties that come with them. The mesh‐aligned interpolation uses bi‐cubic Hemite‐Bézier polynomials on a structured mesh of curved quadrangular elements. On the other hand, we assume reduced cubic Hsieh‐Clough‐Tocher finite elements on an unstructured triangular mesh. Both meshes overlap, and the resulting formulation is a coupled discrete problem solved iteratively by a suitable one‐level Schwarz algorithm. In this paper, we will focus on the Poisson problem on a two‐dimensional bounded regular domain. This elliptic equation is a simplified version of the axisymmetric tokamak equilibrium one at the asymptotic limit of infinite major radius (large aspect ratio).

PyMAF-X: Towards Well-Aligned Full-Body Model Regression From Monocular Images.

We present PyMAF-X, a regression-based approach to recovering a parametric full-body model from a single image. This task is very challenging since minor parametric deviation may lead to noticeable misalignment between the estimated mesh and the input image. Moreover, when integrating part-specific estimations into the full-body model, existing solutions tend to either degrade the alignment or produce unnatural wrist poses. To address these issues, we propose a Pyramidal Mesh Alignment Feedback (PyMAF) loop in our regression network for well-aligned human mesh recovery and extend it as PyMAF-X for the recovery of expressive full-body models. The core idea of PyMAF is to leverage a feature pyramid and rectify the predicted parameters explicitly based on the mesh-image alignment status. Specifically, given the currently predicted parameters, mesh-aligned evidence will be extracted from finer-resolution features accordingly and fed back for parameter rectification. To enhance the alignment perception, an auxiliary dense supervision is employed to provide mesh-image correspondence guidance while spatial alignment attention is introduced to enable the awareness of the global contexts for our network. When extending PyMAF for full-body mesh recovery, an adaptive integration strategy is proposed in PyMAF-X to produce natural wrist poses while maintaining the well-aligned performance of the part-specific estimations. The efficacy of our approach is validated on several benchmark datasets for body, hand, face, and full-body mesh recovery, where PyMAF and PyMAF-X effectively improve the mesh-image alignment and achieve new state-of-the-art results. The project page with code and video results can be found at https://www.liuyebin.com/pymaf-x.

Investigation of the shear band evolution in soil-rock mixture using the assumed enhanced strain method with the meshes of improved numerical manifold method

Falling into the framework of the Petrov-Galerkin finite element formulation with embedded discontinuity, the assumed enhanced strain (AES) method could simulate the structural localization phenomenon and the associated loss of bearing capacity in a way insensitive to mesh alignment and refinement. For another hand, the improved numerical manifold method (INMM) naturally excels at dealing with heterogeneous problems such as the soil-rock mixture (SRM) slope with embedded soft soil region. Therefore, to simulate the shear band evolution in heterogeneous slope more efficiently, precisely and also mesh independently, this paper proposes to invoke the AES method with the meshes of the INMM. Beside, this paper proposes a simple and efficient method to address the constitutive integration for multi-surface plasticity induced by cutting the tensile part of the Drucker Prager model. Finally, the efficiency and accuracy of the proposed approaches are tested on some typical examples including heterogeneous block and slope.

Global–local analysis with Element Free Galerkin Method

Meshfree methods have been used as alternatives to the Finite Element Method, due to their flexibility in building approximations without mesh alignment sensitivity. Another attractive feature is the capacity of obtaining approximate solutions of high regularity. On the other hand, the lack of the Kronecker-delta property, a more complex computation of the shape functions, and numerical integration issues represent drawbacks that can overburden the computational analysis. Aiming to conciliate the efficiency of the finite element analysis with the flexibility of meshfree methods, coupling techniques for both methods have been proposed. The coupling proposed here is based on the enrichment strategy of the Generalized Finite Element Method under the global–local approach. The global domain of the problem is represented by a coarse mesh of finite elements. A region of interest defines the local domain, discretized by a set of nodes of the Element Free Galerkin Method (EFG). This local discretization is responsible for providing a numerically obtained function used to enrich the approximate solution of the global problem. A two-dimensional numerical example is extensively evaluated to discuss the effectiveness of the approach and its behavior related to the quality of the boundary conditions of the local domain, penalty parameter, numerical integration and size of the EFG influence domain.

On the importance of finite element mesh alignment along the fibre direction for modelling damage in fibre-reinforced polymer composite laminates

A finite element mesh, aligned along the fibre direction, has often been purported to yield more accurate results in the modelling of damage in composite structures constructed from unidirectional fibre reinforced polymer laminates. However, there has been a lack of a systematic assessment of this approach. This issue is addressed through modelling a selection of test cases; (i) end notched tension (ENT) coupons, (ii) simple tensile/compressive specimens, (iii) open-hole tension (OHT), (iv) low velocity impact (LVI) and (v) compression-after-impact (CAI) of laminated plates. In each case, two models were constructed, one using a uniform mesh, aligned with the global coordinate system, and independent of the fibre direction, and the other where each ply mesh was aligned along the fibre direction. In both cases the local material axes in each ply were correctly represented. Results show that a finite element mesh aligned along the fibre direction plays an important role in the prediction of damage, particularly in the presence of a crack. However, when matrix crack paths are not established a priori, or may not be the dominant damage mode, fibre mesh alignment is unnecessary. Rather, long-established approaches of refined meshes, robust damage models and well-defined material data and boundary conditions, are shown to be sufficient requirements.

PASM: Parallel aligned surface meshing

AbstractComputer‐aided design (CAD) models of industrial design are often plagued with a series of defects, including minute features, gaps, self‐intersections, and misalignments. The development of schemes in automatic defeaturing, gaps repairing, and intersection removal usually requires a discrete representation of the geometry. However, existing surface meshing methods could not effectively handle sliver surfaces and assemblies with complex contact conditions, including multiple misaligned curves/surfaces and degenerated or free‐form‐shaped interface of contact. A surface meshing method based on a meshing‐and‐synchronizing strategy is proposed, which tackles the mesh generation of sliver surfaces and the cleanup of misaligned assemblies by means of mesh alignment. The mesh generation is performed in a hierarchical manner with curves and surfaces being meshed in sequence. By incorporating the synchronization strategy into the curve/surface meshing process, curve/surface mesh alignment is achieved automatically without compromising the mesh quality. Thanks to the alignment, the curve mesh generated by aligned curve meshing (ACM) is free of intersections, which enhances the meshing of sliver surfaces. By enforcing mesh alignment, aligned surface meshing (ASM) can handle misaligned assemblies with complex contact conditions. ASM is parallelized by using OpenMP. Various assemblies characterized with difficult misaligned features and touches are well processed by parallel ASM.

Multiresolution analysis relying on Beta wavelet transform and multi-mother wavelet network for a novel 3D mesh alignment and deformation technique

In this paper, we propose a new 3D high mesh deformation technique to extract intuitive and interpretable deformation and alignment components. Our framework is based on a fast Beta wavelet transform for a multi-resolution analysis relying on multi-library wavelet neural network architecture. The main drawback of 3D high mesh deformation is the large number of triangles necessary to characterize a smooth surface; the majority of these techniques impose a very high computational cost. Our approach is based on the idea of combining the decomposition technique of multi-resolution analysis by Beta wavelet transform for each level of deformation process and a multi-mother wavelet network structure to construct an effective 3D alignment algorithm. We use, in our experiment, only the approximation coefficients at a chosen decomposition level to reduce the complexity of the mesh and to facilitate the alignment until reaching the target mesh, for the purpose of improving various executions and obtaining an optimal solution while reducing the error between the original and the reconstructed object to create a well-formed object. Then, to enhance the performance of wavelet networks, a novel learning algorithm based on multi-mother wavelet neural network architecture using trust region spherical is employed as an approximation tool for feature alignment between the source and the target models. This network architecture ensures the use of several mother wavelets to solve the problem of high mesh deformation utilizing the best wavelet mother that well models the object. Extensive experimental results demonstrate that the progressive deformation processes aim at avoiding the weaknesses of traditional approaches such as the slowness and the difficulty of finding an exact reconstruction.

Discontinuity-driven mesh alignment for evolving discontinuities in elastic solids

A special mesh adaptation technique and a precise discontinuity tracking are presented for an accurate, efficient, and robust adaptive-mesh computational procedure for one-dimensional hyperbolic systems of conservation laws, with particular reference to problems with evolving discontinuities in solids. The main advantage of the adaptive technique is its ability to preserve the modified mesh as close to the original fixed mesh as possible. The constructed method is applied to the martensitic phase-transition front propagation in solids.

Variational Modelling of Strain Localization in Solids: A Computational Mechanics Point of View

Strain localization is one of the most challenging phenomena in solid mechanics. It occurs when strains concentrate in very narrow bands within a solid, typically referred to as localization bands. This behaviour is related to different types of failure mechanisms: fracture, shear bands and slip lines. Being a dissipative process, the modelling of strain localization could seem to preclude the use of variational methods. However, a sound framework to deal with this issue has been developed in the last few decades. In this contribution, we review the modelling of strain localization by means of variational methods systematically, presenting the main underlying theoretical concepts. The issue of irreversibility is approached by means of the theory of generalized standard materials, which constitutes the basis for the variational approach. Then, typical problems occurring in the modelling of strain localization are analyzed: the tendency to localize in a band of zero thickness with no dissipation, the determination of the geometry of the localization band, and the orientation bias of such band with respect to mesh alignment in finite element discretizations. We discuss solutions for these problems, focusing on the approach that tackles the description of the localization band using phase fields.

On modeling subgrid-scale macro-structures in narrow twisted channels

Porosity-based subgrid topography models often fail to capture the effects of subgrid-scale topographic features in the interior of coarse grid cells. Existing approaches that modify bottom roughness or a drag coefficient are inadequate for macro-structures (large emergent or submerged obstacles) in subgrid-scale narrow twisted channels. Such structures partially block the cross-sectional area and provide enhanced topographic dissipation – effects that are not well represented by a drag coefficient that scales on a coarse-grid cell-averaged velocity and the cell volume. The relative alignment between mesh and flow further complicates this problem as it makes the subgrid model sensitive to mesh design. In the present study, three new approaches for simulating subgrid-scale macro-structures in narrow channels are proposed. The interior partial-blocking effect of structures is modeled as reduction of grid face-area. The sheltering of flow volumes around obstacles, which leads to topographic dissipation, is modeled by reducing the cell volume in the momentum equation (only). A mesh-shift procedure is designed to optimize mesh alignment for identifiable subgrid features. Combining the three subgrid methods improves the approximation of surface elevation and in-channel flow rate with a coarse-grid model. Tests are conducted for channelized flow using both synthetic domains and real marsh topography. The new methods reduce the overall mesh dependency of the subgrid model and provides stronger physical connection between effects of macro-structures and their geometry at coarse grid scales.

Developing a coupled turbine thrust methodology for floating tidal stream concepts: Verification under prescribed motion

Floating systems offer an opportunity to expand tidal energy resource through an increase in viable sites and greater flow speeds near the free surface. However, the close proximity of the free surface provides uncertainty regarding power delivery and survivability due to the presence of waves, which could be addressed through a numerical model that is capable of considering all components of a floating tidal system simultaneously. This paper presents the first step in the development of such a tool: using the open-source CFD libraries of OpenFOAM as a basis, a computationally efficient HATT model has been developed for generalised incident flow conditions using actuator theory. A thorough evaluation of the model's sensitivity to key considerations in the simulation of entire floating tidal systems, such as flow speed and mesh alignment, showed that the model is robust, ensuring that it is suitable for future extension to wave-driven environments and integration into a framework for such systems.

Length scale and mesh bias sensitivity of phase-field models for brittle and cohesive fracture

Being able to seamlessly deal with complex crack patterns like branching, merging and even fragmentation, phase-field models (PFMs) are promising in the computational modeling of fracture of solids. There are, however, some unclear issues such as (i) are phase-field models mesh-bias objective? and (ii) what value should be selected for the length scale parameter? This manuscript provides answers to these practical questions. Three popular PFMs for brittle and cohesive fracture in the literature are selected, implemented within a single code and used to study the sensitivity to the length scale parameter and the mesh alignment of the solutions to various brittle and quasi-brittle fracture problems with/without singularities and notches. The findings are useful to researchers and engineers who need to perform fracture simulations using a phase-field model.

Anisotropic mesh adaptation for steady convection-dominated problems based on bubble-type local mesh generation

ABSTRACTFor convection–diffusion equations, it is difficult to obtain accurate solutions due to the presence of layers when convection dominates the diffusion. In this work, a new anisotropic adaptive meshing algorithm for convection-dominated problems is designed to optimize the mesh alignment, size and aspect ratio. Three main techniques are used. First, the streamline upwind Petrov–Galerkin (SUPG) method is used to stabilize the numerical scheme. Second, the a posteriori error estimator is computed and a new metric tensor is deduced. Third, optimal anisotropic meshes are generated by the anisotropic bubble-type local mesh generation (ABLMG) method. Compared with other mesh generation strategies, high-quality mesh can be obtained efficiently. Our algorithm is tested on several examples and the numerical results show that the algorithm is robust.

Numerical Investigation of Influence of Mesh Property in Nearfield Sonic Boom Prediction

To investigate the influence of mesh property in nearfield sonic boom prediction, the over-pressures of several typical configurations are commutated and analyzed with an in-house Reynolds Average Navier-Stokes solver. The property of mesh alignment, mesh type and mesh distribution are analyzed based on the double cone configuration and the 69-degree Delta Wing Body configuration. The experimental data from wind tunnel are used as comparisons. The results show that the Mach cone aligned method has significant improvement to the accuracy for the prediction of sonic boom in nearfield. Both structured and un-structed mesh with a cylinder zone near the model can help to capture the distribution of the over-pressure, however, it is more convenient to use unstructured mesh when deal with complex configurations. The aspect ratio and circumferential spacing affect the captured shock wave peak value and the shapes. The accuracy of the prediction can be satisfied by carefully selecting these two factors. In the last, the summarized strategies for mesh generation are applied in the sonic boom prediction of a complex supersonic transport configuration, the Lockheed Martin 1021 to verify its practicability.

Scalable non-rigid registration for multi-view stereo data

We propose a new non-rigid registration method for large 3D meshes from Multi-View Stereo (MVS) reconstruction characterized by low-frequency shape deformations induced by several factors, such as low sensor quality and irregular sampling object coverage. Starting from a reference model to which we want to align a new 3D mesh, our method starts by decomposing it in patches using a Lloyd clustering before running an ICP local registration for each patch. Then, we improve the alignment using few geometric constraints and finally, we build a global deformation function that blends the estimated per-patch transformations. This function is structured on top of a deformation graph derived from the dual graph of the clustering. Our algorithm is iterated until convergence, increasing progressively the number of patches in the clustering to capture smaller deformations. The method comes with a scalable multicore implementation that enables, for the first time, the alignment of meshes made of tens of millions of triangles in a few minutes. We report extensive experiments of our algorithm on several dense Multi-View Stereo models, using a 3D scan or another MVS reconstruction as reference. Beyond MVS data, we also applied our algorithm to different scenarios, exhibiting more complex and larger deformations, such as 3D motion capture dataset or 3D scans of dynamic objects. The good alignment results obtained for both datasets highlights the efficiency and the flexibility of our approach.

Elastic Alignment of Triangular Surface Meshes

A novel region-based approach is proposed to find a thin plate spline map between a pair of deformable 3D objects represented by triangular surface meshes. The proposed method works without landmark extraction and feature correspondences. The aligning transformation is simply found by solving a system of integral equations. Each equation is generated by integrating a non-linear function over the object domains. We derive recursive formulas for the efficient computation of these integrals for open and closed surface meshes. Based on a series of comparative tests on a large synthetic dataset, our triangular mesh-based algorithm outperforms state of the art methods both in terms of computing time and accuracy. The applicability of the proposed approach has been demonstrated on the registration of 3D lung CT volumes, brain surfaces and 3D human faces.

Factors Governing the Predicted Performance of Multilayered Metal-Mesh Screens

Summary Multilayered metal-mesh screens (MMSs) are widely used as standalone screens for sand control in unconsolidated formations. The nominal rating of such screens is usually determined on the basis of the specifications of the filter layer. It is often found that screens with the same filter-layer nominal rating perform differently. It is shown in this study that the primary reason for this is that the sand-retention performance of multilayered MMSs is a strong function of not only the filter layer but also the protection and the support layers. This paper presents a systematic study that shows how the overlap between different mesh layers, the alignment of the protection and support layers, and the relative pore-size ratio, defined as the ratio of pore size of the protection/support layer to that of the filter layer, have a large impact on the sand-retention performance of an MMS. The pore-size distribution (PoSD) of multilayered plain-square-mesh (PSM) and plain-Dutch-weave (PDW) screens is calculated with a novel numerical technique. Influences of screen sintering, coupon sampling, and screen designs on the PoSD of a screen are modeled by varying the layer overlap, shifting the layer alignment, and modifying the design of the protection and support layers. The PoSD data are used as an input into an analytical model for evaluating sand production of PSM screens in slurry-type sand-retention tests (SRTs) for screen-design optimization. For PSM screens, the results show that the PoSD of a multilayered screen can be very different from the PoSD of the filter layer. In general, a decrease in sand production with an increase in layer overlap is observed; the trend exists irrespective of how mesh layers are aligned. A change in mesh alignment is found to cause a variation in sand production even with the same filter-layer pore size and layer overlap. The nominal rating of the filter layer of a multilayered PSM screen should be used to estimate sand production only when the pore sizes of the protection and support layers are much larger than the pore size of the filter layer. For PDW screens, layer overlap is shown to dominate the screen performance by affecting the filter-layer pore size. The PoSD of a PDW screen is found to be less affected by variations in layer alignment and relative pore-size ratio. This study clearly shows that the layer overlap, layer alignment, and relative pore-size ratio between mesh layers can have a significant impact on the sand-retention performance of a multilayered MMS. As such, widely different screen performances can be expected for screens with the same nominal screen rating. Our results have a direct bearing on how MMSs are manufactured, selected, and specified. Increasing the relative pore-size ratio appears to be a promising screen-design approach for obtaining consistent screen performance for multilayered MMSs.

Fabrication of macromolecular gradients in aligned fiber scaffolds using a combination of in-line blending and air-gap electrospinning.

The native tendon-bone interface contains a gradient of properties that ensures stability of the joint. Without this transition, failure can occur due to stress concentration at the bone insertion site. Electrospinning is a method commonly used to produce fibrous grafts with gradient properties; however, no current method allows for gradients in the direction of fiber alignment. This work details a novel electrospinning method to produce gradients in the direction of fiber alignment in order to better mimic transitional zones and improve regeneration of the tendon-bone interface. In addition to the biomechanical gradients demonstrated here, this method may also be used to generate gradients of macromolecular, biochemical, and cellular cues with broad potential utility in tissue engineering.