Grid-characteristic method using high-order interpolation on tetrahedral hierarchical meshes with a multiple time step

The purpose of the present paper is to develop a grid-characteristic method for high-performance computer systems using unstructured tetrahedral hierarchical meshes, a multiple time step and the high-order interpolation for simulating complex spatial dynamic processes in heterogeneous environments. This method has the precise formulation of contact conditions and is suitable for the physically correct solution of seismology and seismic prospecting problems in complex heterogeneous environments. The use of the hierarchical meshes allows us to take into account a large number of nonhomogeneous inclusions (cracks, cavities, etc.). The use of this grid-characteristic method makes it possible to use a multiple time step and thereby increase productivity and significantly reduce the computation time. The methods developed for high-order interpolation on unstructured tetrahedral meshes can solve the problems of seismology and seismic prospecting with approximation in space of up to the fifth degree (inclusive).     

TMAH溶液中的(110)硅各向异性湿法腐蚀及其在不同添加剂下的腐蚀特性研究

研究了TMAH溶液中(110)硅片在不同几何形状掩膜窗口下的各向异性湿法腐蚀行为,探讨了(110)硅在TMAH与不同添加剂(过硫酸铵、异丙醇等)构成的腐蚀系统下的腐蚀特性.利用场发射扫描电子显微镜(SEM)观测(110)硅的腐蚀坑腔结构,利用扫描探针显微镜(SPM)测量(110)硅腐蚀的表面粗糙度.结果表明:(110)...     

An additive micromolding approach for the development of micromachined ceramic substrates for RF applications

The selective removal of the substrate from under devices can help improve Q-factors, reduce losses and parasitics and can be applied to microwave components (transmission lines, spiral inductors, and capacitors) critical to high-frequency communications systems. A novel molding process has been developed to produce cavities in ceramic substrates over which gold transmission lines can be suspended. The "additive" method of fabricating cavities in ceramics was primarily based on the production of a substrate with preexisting cavities, as opposed to generation of cavities by the removal or the "subtraction" of material. The preexisting cavities were generated using a transfer mold technique based on photolithography, anisotropic silicon etching and nickel electroplating. The approach was demonstrated successfully using a commercial glass ceramic material (DuPont 951 Green Tape) to yield 100-/spl mu/m-deep cavities that showed shape retention and dimensional stability.     

An Inverse Procedure for Crack Detection in Anisotropic Laminated Plates Using Elastic Waves

. This paper presents a computational inverse technique to detect the location and length of cracks in anisotropic laminated plates. The scattered elastic harmonic wave fields in the laminated plates with horizontal or vertical crack are calculated using the strip element method, whereby the anisotropic laminated plate is discretized into strip elements in the thickness direction. By applying the principle of virtual work, the governing differential equations of the wave propagation are derived for the field variables. These differential equations are solved analytically together with the vertical boundary conditions. The crack length and its location are then identified by minimizing an error function, which is defined as the difference between the scattered wave fields in plates with actual and searched parameters. A uniform micro-genetic algorithm is employed to search for the correct parameters that minimize the error function. Numerical examples are given to demonstrate the efficiency of the procedure in the detection of the location and the length of both horizontal and vertical cracks in composite laminates.     

一种基于改进渗流模型的混凝土表面裂缝快速检测算法

由于混凝土表面不平整、光照不均、裂缝背景较为复杂等因素的干扰,传统的基于图像处理的裂缝检测方法对裂缝检测的效果不佳,尤其是不清晰和比较细小的裂缝。基于渗流模型的裂缝检测方法充分考虑了裂缝亮度低、形状较为细长的特点,对裂缝的检测效果很好,尤其是图像中的细小裂缝,但是该方法需要大量的处理时间。为了解决上述问题,提出了一种加速渗流处理的算法,该算法通过暗点预提取来减少渗流时需要处理的像素点个数,以此来减少渗流处理时间。实验结果表明,所提算法能明显加快渗流处理的速度,并且精确率基本保持不变。     

金锡共晶X光图像的空洞检测

在金锡共晶焊接以及X射线检测缺陷技术广泛使用的背景下,针对PCB板缺陷经X射线成像后不易人工检测的问题,基于形态学方法提出了一种自动检测并标记烧结空洞的处理思路.经实验发现Sobel算子无法有效提取烧结空洞,分析得出以下结论:提取烧结空洞需要克服水平、垂直方向上的干扰,即密集分布于PCB板上的导线.由此提出利用形态学方...     

A structural neural system for mechanical, biological, and environmental systems

A structural neural system (SNS) and continuous sensors that mimic the neurons of the human biological system are described for monitoring the health of large structures. An example of use of the SNS to monitor damage on a nine meter long wind turbine blade is also described. The blade is a complex anisotropic structure that was tested at the National Renewable Energy Laboratory, Golden, Colorado, USA under quasi static loading to determine the strength and ability of the blade to withstand wind loading. The SNS along with piezoelectric sensors was installed to monitor the composite blade material during this testing. Multiple cracks originated during this test and were detected by the SNS well before the final failure of the blade. This testing provides confidence that SNS has the capability to monitor crack growth in complex anisotropic structures using piezoelectric sensors. The SNS is currently being extended to sense signals from other types of sensors including continuous sensors based on accelerometers, pressure sensors, piezoresistive, chemical, and biosensors. This would extend application of the SNS into biological and environmental systems where different types of sensors are used to measure chemicals and biological materials. It is predicted that the SNS can provide high accuracy, low cost, and simplicity for monitoring the health of many types of systems.     

Generation of Tetrahedral Meshes with Multiple Elements through Thin Sections

Finite element simulations in domains with strong gradients across thin sections typically require meshes with multiple elements through these sections to accurately capture the solution. Most of the published techniques for isotropic mesh generation are not suited for the creation of such meshes in general, arbitrarily complex, non-manifold domains. In this paper, an automatic method is described for identification of thin sections of a domain and anisotropic refinement of an initial mesh to introduce a user-requested number of elements through the thin sections. The method uses local mesh modification operations to effect the refinement and subsequent realignment of edges along the thickness direction and perpendicular to it. Results are presented for a number of general models to illustrate the capability of the mesh generator.     

Nonet-Cartesian Grid Method for Shock Flow Computations

A nonet-Cartesian grid method, based on anisotropic/isotropic refinement, is presented for solving the Euler equations in gas dynamic problems. Grids are generated automatically, by the recursive subdivision of a single cell into nine subcells for isotropic nonet-Cartesian grids and into three subcells independently in each direction for anisotropic nonet-Cartesian grids, encompassing the entire flow domain. The grid generation method is applied here to steady inviscid shock flow computation. A finite difference formulation for the Euler equation using nonet-Cartesian grids is used to treat complex two-dimensional configuration. Results using this approach are shown to be competitive with other methods. Further, it is demonstrated that this method provides a simple and accurate procedure for solving flow problems involving multielement airfoils.     

Minimal Sampling for Effective Acquisition of Anisotropic BRDFs

BRDFs are commonly used for material appearance representation in applications ranging from gaming and the movie industry, to product design and specification. Most applications rely on isotropic BRDFs due to their better availability as a result of their easier acquisition process. On the other hand, anisotropic BRDF due to their structure‐dependent anisotropic highlights, are more challenging to measure and process. This paper thus leverages the measurement process of anisotropic BRDF by representing such BRDF by the collection of isotropic BRDFs. Our method relies on an anisotropic BRDF database decomposition into training isotropic slices forming a linear basis, where appropriate sparse samples are identified using numerical optimization. When an unknown anisotropic BRDF is measured, these samples are repeatably captured in a small set of azimuthal directions. All collected samples are then used for an entire measured BRDF reconstruction from a linear isotropic basis. Typically, below 100 samples are sufficient for the capturing of main visual features of complex anisotropic materials, and we provide a minimal directional samples to be regularly measured at each sample rotation. We conclude, that even simple setups relying on five bidirectional samples (maximum of five stationary sensors/lights) in combination with eight rotations (rotation stage for specimen) can yield a promising reconstruction of anisotropic behavior. Next, we outline extension of the proposed approach to adaptive sampling of anisotropic BRDF to gain even better performance. Finally, we show that our method allows using standard geometries, including industrial multi‐angle reflectometers, for the fast measurement of anisotropic BRDFs.     

形态学与区域延伸相结合的图像裂缝检测算法研究

在复杂背景下,由于光照不均、混凝土气泡、阴影等噪声干扰,导致路面裂缝误检并存在不同程度的断裂。为了解决此问题并实现路面裂缝的精确检测,提出一种结合数学形态学和区域延伸的裂缝检测算法。该算法首先用形态学对自然条件下采集的路面图像进行预处理,并结合Canny边缘检测和形态学来对裂缝进行粗略检测,然后用区域延伸算法对裂缝进行精确检测,最后对检测裂缝进行后处理。实验结果表明,提出的算法能够对图像裂缝进行高效、精确的检测。     

基于改进Faster-RCNN的沥青路面裂缝检测

针对目前沥青路面裂缝检测存在的识别率低和细微裂缝在复杂背景下难以检测的问题, 提出了基于改进Faster-RCNN的裂缝检测方法. 首先, 通过多功能路面检测车采集路面图像, 将13 000张图片按8:2的比例分为训练集和测试集来建成路面裂缝检测数据集; 然后分别采用VGG16、MobileNet-V2和ResNet50网络替换Faster-RCNN模型中的特征提取网络对裂缝进行识别, 结果表明, ResNet50与Faster-RCNN结合对裂缝的检测准确率达到0.805 8, 效果最好; 裂缝都分布在同一水平面上, 不存在层次信息, 因此将ResNet系列其它网络与Faster-RCNN模型结合, 以期得到更好的检测效果, 结果表明, 相比于ResNet18和ResNet101, 还是ResNet50检测性能最好; 由于还存在细微裂缝漏检的问题, 将CBAM模块引入ResNet50, 并且比较不同插入位置对检测准确率的影响. 实验表明, 改进的Faster-RCNN模型检测精准度达到85.64%, 能有效检测出复杂背景下的细微裂缝.     

Analysis of two-dimensional mixed-mode crack problems by finite element alternating method

A finite element alternating method is presented and applied to analyze two-dimensional linear elastic mixed-mode fracture problems with single or multiple cracks. The method involves the iterative superposition of the finite element solution of a bounded uncracked plate and the analytical solution of an infinite two-dimensional plate with a crack subjected to arbitrary normal and shear loadings. The normal and shear residual stresses evaluated at the location of fictitious cracks are fitted by appropriate polynomials through the least-squares method. Based on those coefficients of the determined polynomials, the mixed-mode stress intensity factors can be calculated accurately. The interaction effects among cracks are also considered. This method provides a highly efficient way to deal with two-dimensional fracture problems.     

Dynamic pre-processing software for the hyperviscoelastic modeling of complex anisotropic biological tissue materials

Soft biological tissues are complex structures with intricate microstructure, which is usually highly anisotropic. These tissues are typically composed of multiple fiber bundles, which may have a unique orientation, defined for each single element in a large finite element mesh for modeling complex structures such as the human heart. These complex orientations can be difficult to define in an ABAQUS input deck using existing methods. In general, each change in fiber orientation requires a “new material” to be defined. Using the conventional method of defining material properties in ABAQUS is time consuming and, as a result of the large number of input constants required, is prone to errors. It is therefore deemed desirable to create a new means of material property input. The ⁷CC Cards method presented partitions the material property data for a time-dependent, anisotropic, material response into discrete card images, and thus eliminates much of the redundant data input required by ABAQUS. This strategy is also more efficient, both computationally and from the viewpoint of user time required.     

Visual Abstractions of Solvent Pathlines near Protein Cavities

Water is known to play a crucial role in protein structure, flexibility and activity. The use of molecular dynamics simulations allows detailed studies of complex protein‐solvent interactions. Cluster analysis and density‐based approaches have been successfully used for the identification and analysis of conserved water molecules and hydration patterns of proteins. However, appropriate tools for analysing long‐time molecular dynamics simulations with respect to tracking and visualising the paths of solvent molecules are lacking. Our method focuses on visualising the solvent paths entering and leaving cavities of the protein and allows to study the route and dynamics of the exchange of tightly bound internal water molecules with the bulk solvent. The proposed visualisation also represents dynamic properties such as direction and velocity in the solvent. Especially, by clustering similar path‐lines with respect to designated properties the visualisation can be abstracted to represent the principal paths of solvent molecules through the cavities. Its application in the analysis of long‐time scale molecular dynamics simulations not only confirmed conjectures based on previous manual observations made by chance, but also led to novel insights into the dynamical and structural role of water molecules and its interplay with protein structure.     

Oscillating bubbles in teardrop cavities for microflow control

Microstreaming generated from oscillating microbubbles has great potential in microfluidic applications for localized flow control. In this study, we explore the use of teardrop-shaped cavities for trapping microbubbles. Upon acoustic actuation, these microbubbles confined in teardrop cavities can be utilized to generate a directional microstreaming flow. We further show that by altering the acoustic excitation frequency, a flow-switch for altering flow direction in microfluidic environments can be achieved using two oppositely arranged teardrop cavities with different sizes. In the end, we show that an array of such bubble-filled teardrop cavities can act as a fixated microfluidic transport system allowing for on-chip particle manipulation in complex flow patterns. This inexpensive method to create flows to switch and transport elements based on teardrop cavities can be widely employed for microfluidic applications such as drug delivery systems.     

Micro crack detection with Dijkstra’s shortest path algorithm

A package based on the free software R is presented which allows the automatic detection of micro cracks and corresponding statistical analysis of crack quantities. It uses a shortest path algorithm to detect micro cracks in situations where the cracks are surrounded by plastic deformations and where a discrimination between cracks and plastic deformations is difficult. In a first step, crack clusters are detected as connected components of pixels with values below a given threshold value. Then the crack paths are determined by Dijkstra’s algorithm as longest shortest paths through the darkest parts of the crack clusters. Linear parts of kinked paths can be identified with this. The new method was applied to over 2,000 images. Some statistical applications and a comparison with another free image tool are given.     

Rapid Anisotropic Diffusion Using Space-Variant Vision

Many computer and robot vision applications require multi-scale image analysis. Classically, this has been accomplished through the use of a linear scale-space, which is constructed by convolution of visual input with Gaussian kernels of varying size (scale). This has been shown to be equivalent to the solution of a linear diffusion equation on an infinite domain, as the Gaussian is the Green's function of such a system (Koenderink, 1984). Recently, much work has been focused on the use of a variable conductance function resulting in anisotropic diffusion described by a nonlinear partial differential equation (PDE). The use of anisotropic diffusion with a conductance coefficient which is a decreasing function of the gradient magnitude has been shown to enhance edges, while decreasing some types of noise (Perona and Malik, 1987). Unfortunately, the solution of the anisotropic diffusion equation requires the numerical integration of a nonlinear PDE which is a costly process when carried out on a uniform mesh such as a typical image. In this paper we show that the complex log transformation, variants of which are universally used in mammalian retino-cortical systems, allows the nonlinear diffusion equation to be integrated at exponentially enhanced rates due to the nonuniform mesh spacing inherent in the log domain. The enhanced integration rates, coupled with the intrinsic compression of the complex log transformation, yields a speed increase of between two and three orders of magnitude, providing a means of performing rapid image enhancement using anisotropic diffusion.     

各向异性多尺度自相似随机场与地形构建

在长期自然环境的作用下,实际的地形表面是一个各向异性、非线性的2维场,且地形的自相似特性在整个尺度空间上并非恒定的,而是与度量的尺度范围相关。由于传统的自相似随机场的构建方法并不能准确反映地形的实际特性,因此提出一种首先应用多尺度自相似随机场构建各向同性地形表面,然后引入表征各向异性的结构滤波器,再通过谱变换构建具有各向异性的多尺度自相似地形的方法。实验结果表明,该地形构建方法不仅能够反映实际地形的自相似性依尺度而变化的特点,而且能构建山脉的走向。