共查询到20条相似文献，搜索用时 31 毫秒
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In this paper we present a simple and fast approach for MAT generation in discrete form. It is used for manufacturability analysis in the part modelling stage of injected parts. The method is a volume thinning method based on straight skeleton computation, modified and applied in 3D on B-rep models in STL. The volume thinning of the B-rep model is based on its boundary surfaces offset towards the model interior. The surfaces’ offset is done with an adequately proposed offset distance which makes some of the non adjacent offset model surfaces overlap (they ‘meet’ in mid-surface or MAT). Offset surfaces are used to reconstruct the topology of a new B-rep model (offset model). Overlapping surfaces in the offset model are detected, separated and aggregated to MAT. For adequate MAT precision and adequate MAT radius function, we propose to treat B-rep model concave edges (vertices) as cylinders (spheres) of zero-radius and offset them in an adequate way. On these bases, we present an iterative algorithm in which MAT is constructed in an incremental way by consecutive volume thinning of the obtained offset models. MAT construction is finished when an empty offset model is obtained. An algorithm has been created and implemented in Visual C++. Some of the obtained results are presented in this paper. 相似文献
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Hao Xia Paul G. Tucker 《International journal for numerical methods in engineering》2010,82(1):114-134
Accurate and efficient computation of the nearest wall distance d (or level set) is important for many areas of computational science/engineering. Differential equation‐based distance/level set algorithms, such as the hyperbolic‐natured Eikonal equation, have demonstrated valuable computational efficiency. Here, in the context, as an ‘auxiliary’ equation to the main flow equations, the Eikonal equation is solved efficiently with two different finite volume approaches (the cell‐vertex and cell‐centered). The application of the distance solution is studied for various geometries. Moreover, a procedure using the differential field to obtain the medial axis transform (MAT) for different geometries is presented. The latter provides a skeleton representation of geometric models that has many useful analysis properties. As an alternative to other methods, the current d‐MAT procedure bypasses difficulties that are usually encountered by pure geometric methods (e.g. the Voronoi approach), especially in three dimensions, and provides better accuracy than pure thinning methods. It is also shown that the d‐MAT approach provides the potential to sculpt/control the MAT form for specialized solution purposes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Abstract This paper describes a novel neural network, called MATNET, to perform the medial axis transformation which is often used to extract a stick‐figure‐like representation from a binary object for pattern analysis or recognition. The MATNET is derived from the structure of the retina, which consists of five neural layers, namely, receptors, horizontal cells, bipolar cells, ganglion cells, and response. In principle, the horizontal cell is implemented for distance computation; the bipolar cell (B‐net) and the ganglion cell (G‐net) are implemented for calculation of local minimum and local maximum, respectively. The B‐net and G‐net are concerned with the maximal neural network (Maxnet). The properties of Maxnet are also discussed. Experimental results show that the MATNET performs reasonably. 相似文献
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计算几何评定国度的方法研究 总被引：2，自引：0，他引：2
和传统方法相比，计算几何方法评定圆度误差几何直观性强、结果准确，而又能解决同时存在多个最小径向间距MRS(Minimum Radial Separation)圆心的问题。按照被测轮廓的表示，该方法可分为两类：一类是用被测工件表面上取的样本点来近似地表示该轮廓；另一类是用这些样本点产生一个简单多边形来表示该轮廓。这两种方法确定的内接圆是不同的。文章对比分析了它们的适用性、精度和计算效率以及存在的问题。 相似文献
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Elena Tamayo‐Mas Antonio Rodríguez‐Ferran 《International journal for numerical methods in engineering》2015,101(7):489-520
A new continuous‐discontinuous strategy for the simulation of failure is presented. The continuous bulk is regularised by means of a gradient‐enhanced damage model, where non‐locality is introduced at the level of displacements. As soon as the damage parameter is close or equal to 1, a traction‐free crack is introduced. To determine the direction of crack growth, a new criterion is proposed. In contrast to traditional techniques, where mechanical criteria are used to define the crack path, here, a geometrical approach is used. More specifically, given a regularised damage field D( x ), we propose to propagate the discontinuity following the direction dictated by the medial axis of the isoline (or isosurface in 3D) D( x ) = D*. The proposed approach is tested on different two‐dimensional and three‐dimensional examples that illustrate that this combined methodology is able to deal with damage growth and material separation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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A. Dimitrov 《International journal for numerical methods in engineering》2004,60(4):773-801
In this paper, a numerical procedure is presented for the computation of corner singularities in the solution of three‐dimensional Stokes flow and incompressible elasticity problems near corners of various shape. For obtaining the order and mode of singularity, a neighbourhood of the singular point is considered with only local boundary conditions. The weak formulation of this problem is approximated using a mixed u , p Galerkin–Petrov finite element method. Additionally, a separation of variables is used to reduce the dimension of the original problem. As a result, the quadratic eigenvalue problem ( P +λ Q +λ2 R ) d = 0 is obtained, where the saddle‐point‐type matrices P , Q , R are defined explicitly. For a numerical solution of the algebraic eigenvalue problem an iterative technique based on the Arnoldi method in combination with an Uzawa‐like scheme is used. This technique needs only one direct matrix factorization as well as few matrix–vector products for finding all eigenvalues in the interval ??(λ) ∈ (?0.5, 1.0), as well as the corresponding eigenvectors. Some benchmark tests show that this technique is robust and very accurate. Problems from practical importance are also analysed, for instance the surface‐breaking crack in an incompressible elastic material and the three‐dimensional viscous flow of a Newtonian fluid past a trihedral corner. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Elena Tamayo-Mas Jordi Feliu-Fabà Montserrat Casado-Antolin Antonio Rodríguez-Ferran 《International journal for numerical methods in engineering》2019,120(1):86-104
A new continuous-discontinuous model for fracture that accounts for crack branching in a natural manner is presented. It combines a gradient-enhanced damage model based on nonlocal displacements to describe diffuse cracks and the extended finite element method (X-FEM) for sharp cracks. Its most distinct feature is a global crack tracking strategy based on the geometrical notion of medial axis: the sharp crack propagates following the direction dictated by the medial axis of a damage isoline. This means that, if the damage field branches, the medial axis automatically detects this bifurcation, and a branching sharp crack is thus easily obtained. In contrast to other existing models, no special crack-tip criteria are required to trigger branching. Complex crack patterns may also be described with this approach, since the X-FEM enrichment of the displacement field can be recursively applied by adding one extra term at each branching event. The proposed approach is also equipped with a crack-fluid pressure, a relevant feature in applications such as hydraulic fracturing or leakage-related events. The capabilities of the model to handle propagation and branching of cracks are illustrated by means of different two-dimensional numerical examples. 相似文献
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M. A. PRICE C. G. ARMSTRONG 《International journal for numerical methods in engineering》1997,40(1):111-136
A method is presented for the subdivision of a large class of solids into simple subregions suitable for automatic finite element meshing with hexahedral elements. The medial surface subdivision technique described previously in the literature is used as the basis for this work and is extended here to cover solids which have flat and concave edges. Problems where the medial surface is degenerated are also addressed. © 1997 by John Wiley & Sons, Ltd. 相似文献
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Effects of Multi‐Scale Patterning on the Run‐In Behavior of Steel–Alumina Pairings under Lubricated Conditions 
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下载免费PDF全文 Philipp G. Grützmacher Andreas Rosenkranz Adam Szurdak Carsten Gachot Gerhard Hirt Frank Mücklich 《Advanced Engineering Materials》2018,20(1)
In nature, many examples of multi‐scale surfaces with outstanding tribological properties such as reduced friction and wear under dry friction and lubricated conditions can be found. To determine whether multi‐scale surfaces positively affect the frictional and wear performance, tests are performed on a ball‐on‐disk tribometer under lubricated conditions using an additive‐free poly‐alpha‐olefine oil under a contact pressure of around 1.29 GPa. For this purpose, stainless steel specimens (AISI 304) are modified by micro‐coining (hemispherical structures with a structural depth of either 50 or 95 μm) and subsequently by direct laser interference patterning (cross‐like pattern with 9 μm periodicity) to create a multi‐scale pattern. The comparison of different sample states (polished reference, laser‐patterned, micro‐coined, and multi‐scale) shows a clear influence of the fabrication technique. In terms of the multi‐scale structures, the structural depth of the coarser micro‐coining plays an important role. In case of lower coining depths (50 μm), the multi‐scale specimens show an increased coefficient of friction compared to the purely micro‐coined surfaces, whereas larger coining depths (95 μm) result in stable and lower friction values for the multi‐scale patterns. 相似文献
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Sichao Du Wei Lu Ayaz Ali Pei Zhao Khurram Shehzad Hongwei Guo Lingling Ma Xuemei Liu Xiaodong Pi Peng Wang Hehai Fang Zhen Xu Chao Gao Yaping Dan Pingheng Tan Hongtao Wang Cheng‐Te Lin Jianyi Yang Shurong Dong Zhiyuan Cheng Erping Li Wenyan Yin Jikui Luo Bin Yu Tawfique Hasan Yang Xu Weida Hu Xiangfeng Duan 《Advanced materials (Deerfield Beach, Fla.)》2017,29(22)
High‐performance photodetectors operating over a broad wavelength range from ultraviolet, visible, to infrared are of scientific and technological importance for a wide range of applications. Here, a photodetector based on van der Waals heterostructures of graphene and its fluorine‐functionalized derivative is presented. It consistently shows broadband photoresponse from the ultraviolet (255 nm) to the mid‐infrared (4.3 µm) wavelengths, with three orders of magnitude enhanced responsivity compared to pristine graphene photodetectors. The broadband photodetection is attributed to the synergistic effects of the spatial nonuniform collective quantum confinement of sp2 domains, and the trapping of photoexcited charge carriers in the localized states in sp3 domains. Tunable photoresponse is achieved by controlling the nature of sp3 sites and the size and fraction of sp3/sp2 domains. In addition, the photoresponse due to the different photoexcited‐charge‐carrier trapping times in sp2 and sp3 nanodomains is determined. The proposed scheme paves the way toward implementing high‐performance broadband graphene‐based photodetectors. 相似文献
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Kai Jia Jiahua Ye Guoxin Zhuang Zanyong Zhuang Yan Yu 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(17)
Fabrication of low‐dimensional nano‐MOFs as well as nanoparticles/metal‐organic frameworks (MOFs) hybrids has sparked new scientific interests but remains a challenging task. Taking Cu3(BTC)2 as a proof of concept, it is demonstrated thats NH3?H2O solution of a confined pH value can readily shape the bulk Cu3(BTC)2 into nanoscale Cu3(BTC)2, beyond the need to control the crystal growth kinetics of MOFs. Adjusting the pH of NH3?H2O within a much small range (10–11) allows fine tuning over the size and shape of nanoscale Cu3(BTC)2. Particularly at pH = 11, NH3?H2O exhibits weak reducibility that triggers a reduction of part of Cu3(BTC)2 into Cu2O, while shaping the other into Cu3(BTC)2 nanowires. Benefiting from the coincidence of reduction and etching effects, the newly generated Cu2O dots can in situ anchor onto adjacent Cu3(BTC)2 nanowires at highly dispersive state, forming a well‐defined sponge‐like architecture built of Cu2O dots and nano‐Cu3(BTC)2. The CuOx derived from annealing of the Cu2O dots/nano‐Cu3(BTC)2 hybrid preserves the sophisticated sponge architecture and high porosity, and exhibits promising applications in phenol scavenging, with efficiency outperforming its counterparts and many other Cu‐based catalysts reported in literature. It is anticipated that the findings here pave the way for the rational design of intricate nano‐MOFs in a more efficient way. 相似文献
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Sichao Du Wei Lu Ayaz Ali Pei Zhao Khurram Shehzad Hongwei Guo Lingling Ma Xuemei Liu Xiaodong Pi Peng Wang Hehai Fang Zhen Xu Chao Gao Yaping Dan Pingheng Tan Hongtao Wang Cheng‐Te Lin Jianyi Yang Shurong Dong Zhiyuan Cheng Erping Li Wenyan Yin Jikui Luo Bin Yu Tawfique Hasan Yang Xu Weida Hu Xiangfeng Duan 《Advanced materials (Deerfield Beach, Fla.)》2017,29(22)
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Biho Kim Yonghwa Choi Minho Lee Hyung‐Min Park 《International journal of imaging systems and technology》2013,23(2):133-139
This article describes an effective human face recognition algorithm. Even though the principle component analysis (PCA) is one of the most common feature extraction methods, it is not suitable to implement a real‐time embedded system for face recognition because large amount of computational load and memory capacity are necessary. To overcome this problem, we employ the incremental two‐directional two‐dimensional PCA (I(2D)2PCA) which is a combination of the (2D)2PCA to demand much less computational complexity than the conventional PCA and the incremental PCA (IPCA) to adapt the eigenspace only by using a new incoming sample datum without reusing of all the previous trained data. Furthermore, the modified census transform (MCT), a local normalization method useful for real‐world application and implementation in an embedded system, is adopted to address robustness to illumination variations. To achieve better recognition accuracy with less computational load, the processed features are classified by the compressive sensing approach using ?2–minimization. Experimental results on the Yale Face Database B show that the described system using the ?2–minimization‐based classification method for input data processed by the I(2D)2PCA and the MCT provided efficient and robust face recognition. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 133–139, 2013 相似文献
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Wentuan Bi Xiaogang Li Rui You Minglong Chen Ruilin Yuan Weixin Huang Xiaojun Wu Wangsheng Chu Changzheng Wu Yi Xie 《Advanced materials (Deerfield Beach, Fla.)》2018,30(18)
Electrochemical conversion of CO2 to value‐added chemicals using renewable electricity provides a promising way to mitigate both global warming and the energy crisis. Here, a facile ion‐adsorption strategy is reported to construct highly active graphene‐based catalysts for CO2 reduction to CO. The isolated transition metal cyclam‐like moieties formed upon ion adsorption are found to contribute to the observed improvements. Free from the conventional harsh pyrolysis and acid‐leaching procedures, this solution‐chemistry strategy is easy to scale up and of general applicability, thus paving a rational avenue for the design of high‐efficiency catalysts for CO2 reduction and beyond. 相似文献
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Kun Zhou Leon M. Keer Q. Jane Wang 《International journal for numerical methods in engineering》2011,87(7):617-638
This paper develops a semi‐analytic solution for multiple arbitrarily shaped three‐dimensional inhomogeneous inclusions embedded in an infinite isotropic matrix under external load. All interactions between the inhomogeneous inclusions are taken into account in this solution. The inhomogeneous inclusions are discretized into small cuboidal elements, each of which is treated as a cuboidal inclusion with initial eigenstrain plus unknown equivalent eigenstrain according to the Equivalent Inclusion Method. All the unknown equivalent eigenstrains are determined by solving a set of simultaneous constitutive equations established for each equivalent cuboidal inclusion. The final solution is obtained by summing up the closed‐form solutions for each individual equivalent cuboidal inclusion in an infinite space. The solution evaluation is performed by application of the fast Fourier transform algorithm, which greatly increases the computational efficiency. Finally, the solution is validated by taking Eshelby's analytic solution of an ellipsoidal inhomogeneous inclusion as a benchmark and by the finite element analysis. A few sample results are also given to demonstrate the generality of the solution. The solution may have potentially significant applications in solving a wide range of inhomogeneity‐related problems. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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M. A. Price C. G. Armstrong M. A. Sabin 《International journal for numerical methods in engineering》1995,38(19):3335-3359
A method is presented for subdividing a large class of solid objects into topologically simple subregions suitable for automatic finite element meshing with hexahedral elements. The technique uses a geometric property of a solid, its medial surface, to define the necessary subregions. The subregions are defined explicitly to be one of only 13 possible types. The subdividing cuts are between parts of the object in geometric proximity and produce good quality meshes of hexahedral elements. The method as introduced here is applicable to solids with convex edges and vertices, but the extension to complete generality is feasible. 相似文献
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