浅谈网格化法逐斗称重精准控制水下散抛石工法

为解决常规抛石施工计量不精确、定位不准、成本偏高、工期延缓等问题,对水下散抛石护岸、护底的精准控制开展了专项研究,提出了网格化法逐斗称重精准控制水下散抛石施工工法。该工法抛投精确、厚度均匀、风险较小,且能够实现均衡连续施工,具备良好的工程和社会效益,值得大力推广。

复杂流态下网格化法充砂土工枕袋施工方法分析

文章以长江马鞍山河段二期整治工程(七标段)为例,进行了充砂枕袋施工方法应用的分析,首先根据设计和现场深水复杂流水条件,进行枕袋二次深化设计,优化聚丙烯编织袋规格尺寸、加筋数量及孔隙率,其次应用多波束测量仪扫描水下地形,合理划分水下抛投网格,最后采用自主发明的六通吹灌装置,同时连通4台泥浆泵和2根输浆管道,通过分析表明,既提高了施工工效,又保证了成型率,有利于节约成本和提高效益。

曲网格克里金网格化方法及其在重力测量近区地形改正中的应用

文中将研究一种高精度、强稳定性与灵活性的近区地改值计算方法。首先将克里金网格化技术与曲网格方法相结合,研究曲网格克里金网格化方法(简写为CGKG-M)及其扩边技术,进而实现数据的圆域网格化;再将该方法应用于圆域近区地改值的计算中,实现任意方位、任意环数的圆域近区地改值计算;最后进行了模型与实际地形的测试和误差分析。研究结果表明,CGKG-M近区地改算法具有方法简单、计算精度高、灵活性与稳定性强、计算速度快等特点,是与GTCS-1型近区地改仪数据采集格式相匹配的一种高效、快捷的近区地改值计算方法。

网格化分析法下的历史街区旧城更新——以杨梅竹斜街为例

北京旧城更新问题由来已久,在城市更新的诸多案例中,杨梅竹斜街的更新与以往北京旧城的更新有所不同遥它利用对旧城文化的全新视角对整条街道进行了分析,从而使得街道呈现新的活力遥利用网格化的手法,对杨梅竹斜街的更新改造工作进行分析,总结出杨梅竹斜街在街道更新方面的思路、方法、对策,对其优势进行解读,探究杨梅竹斜街原有的历史文化与现有建筑的联系,分析杨梅竹斜街在旧城更新改造中的借鉴意义。

基于模式匹配的网格扫描法在高铁线下结构检测中的应用

高铁是连接地区交通的纽带,我国计划2030年将建成近4万km的高速铁路,形成八横八纵铁路网;但是高速铁路线下结构在长期的运营中会产生如混凝土裂缝、结构层脱空、砂浆层离隙等病害。高速铁路线下结构病害检测要求效率高、精度高、设备集成化程度高;针对高铁线下结构的典型病害CA砂浆层脱空及离隙,提出了基于模式匹配法的网格化扫描检测方法,该方法基于线下结构标准设计,考虑砂浆层离隙的空间分布特征,建立三维有限元模型;通过数值模拟,模拟不同病害下网格化扫描法接收的弹性波响应,完成病害特征匹配库;通过多轮匹配、权重值矩阵和阈值函数,设计了模式匹配算法,对匹配的结构损伤识别要素进行敏感性分析,通过合理设计网格尺寸实现病害平面分布20 cm内的精确评价。设计了网格化检波器阵列,成功应用到沪杭高铁虹桥站线下结构检测中,完成线下结构快速、实时、定量化的病害检测。

基于网格化的区域突发环境事件风险分区研究

为开展区域环境风险分区研究,文章基于环境统计和基础地理数据,引入地理空间分析法和人口空间离散化方法,充分考虑水系级别及水质的影响,以1 km×1 km网格为基础单元,对石化产业密集型区域的环境风险进行评估。结果表明:(1)研究区环境风险场呈现以石化区为高值中心,向外辐射递减态势,环境风险受体敏感区与环境风险受体分布保持一致。(2)研究区以低风险区为主,其次为中风险区和较高风险区,其中较高风险区面积为4.87 km^(2),占研究区总面积的1.7%;中风险区面积为42.64 km^(2),占研究区总面积的14.6%;低风险区面积为244.52 km^(2),占研究区总面积的83.7%,不同等级环境风险呈现以风险源和受体集中区为中心,向周围辐射递减趋势,且在下级行政单元的分布存在差异。(3)研究区环境风险管控的优先次序为Sr_(24)(石化区)、Sr_(19)、Sr_(20)、Sr_(16)、Sr_(17)和Sr_(10),其中,Sr_(24)和Sr_(19)为较高风险区,属重点优先管控区域。文章旨在优化网格化环境风险分析法,为区域环境风险评估的宏观决策和环境风险分区分级管理提供科学依据。

区域环境风险评估指数法与网格法对比分析

以北方某沿海城市为例,通过收集资料、划分子区域、识别环境风险源及环境风险受体和调查区域突发环境事件应急能力及防治措施等,采用区域环境风险指数计算法与网格化环境风险分析法计算案例区域环境风险等级,对比分析2种方法区域环境风险评估结果。结果表明,案例区域水环境风险、大气环境风险和综合环境风险2种方法计算结果差异较大。指数法适用区域综合环境风险等级判断,网格法适用小尺度区域水、大气环境风险等级精确计算。

Visualization of 3-D Field of Explosion

In order to visualize the 3-D field of explosion and describe the complex physical phenomena of explosion, the 3-D data resulting from numerical simulation by 3-D multi-material in cell (MMIC), and the application of volume visualization is explored, based on the characteristics of explosion and shock. Based on this, a visualization system for 3-D explosion--ViSC3D is designed. Approaches for the visualization of 3-D field of explosion are presented. The algorithm and the functions of ViSC3D are also presented. ViSC3D is thus a useful tool to observe and analyze either the full picture or the details of a 3-D field of explosion, that are difficult to observe and analyze directly. With ViSC3D, the field of explosion between the hill slopes is visualized. The cutaway views and 2-D slices are also given. The full picture and partial details of 3-D field of explosion can be observed clearly. Furthermore, ViSC3D can be used to visualize other similar 3-D data fields.

Gridding cropland data reconstruction over the agricultural region of China in 1820

Recent studies have demonstrated the importance of LUCC change with climate and ecosystem simulation, but the result could only be determined precisely if a high-resolution underlying land cover map is used. While the efforts based satellites have provided a good baseline for present land cover, what the next advancement in the research about LUCC change required is the development of reconstruction of historical LUCC change especially spatially-explicit historical dataset. Being different from other similar studies, this study is based on the analysis of historical land use patterns in the traditional cultivated region of China. Taking no account of the less important factors, altitude, slope and population patterns are selected as the major drivers of reclamation in ancient China, and used to design the HCGM （Historical Cropland Gridding Model, at a 60 km×60 km resolution）, which is an empirical model for allocating the historical cropland inventory data spatially to grid cells in each political unit. Then we use this model to reconstruct cropland distribution of the study area in 1820, and verify the result by prefectural cropland data of 1820, which is from the historical documents. The statistical analyzing result shows that the model can simulate the patterns of the cropland distribution in the historical period in the traditional cultivated region efficiently.

火力发电厂空预器堵塞原因及处理

空预器中包含蓄热元件,蓄热元件吸收烟气的热量,再将热量加热一次风、二次风,达到提升风温的目的。SCR脱销装置存在氨逃逸,在空预器冷端形成硫酸氢铵(NH4HSO4),其具有粘稠性,硫酸氢铵黏附于蓄热元件上,硫酸氢铵可沾黏大量灰尘。文中通过讲解空预器内部原理和硫酸氢铵反应机理,分析空预器堵灰的影响因素,针对硫酸氢铵黏附在蓄热元件表面的问题,提出网格化喷氨法、烟气余热利用和在线冲洗方法的建议。

A Parallel Algorithm for Adaptive Local Refinement of Tetrahedral Meshes Using Bisection

Local mesh refinement is one of the key steps in the implementations of adaptive finite element methods. This paper presents a parallel algorithm for distributed memory parallel computers for adaptive local refinement of tetrahedral meshes using bisection. This algorithm is used in PHG, Parallel Hierarchical Grid Chttp：//lsec. cc. ac. cn/phg/）, a toolbox under active development for parallel adaptive finite element solutions of partial differential equations. The algorithm proposed is characterized by allowing simukaneous refinement of submeshes to arbitrary levels before synchronization between submeshes and without the need of a central coordinator process for managing new vertices. Using the concept of canonical refinement, a simple proof of the independence of the resulting mesh on the mesh partitioning is given, which is useful in better understanding the behaviour of the biseetioning refinement procedure.

The Glacier Area Changes in the Qangtang Plateau Based on the Multi-temporal Grid Method and its Sensitivity to Climate Change

Glacier area changes in the Qangtang Plateau are analyzed during 1970-2000 using air photos,relevant photogrammetric maps and satellite images based on the multi-temporal grid method.The results indicate that the melting of glaciers accelerated,only a few of glaciers in an advancing state during 1970-2000 in the whole Qangtang Plateau.However,the glaciers seemed still more stable in the study area than in most areas of western China.We estimate that glacier retreat was likely due to air temperature warming during 1970-2000 in the Qangtang Plateau.Furthermore,the functional model of glacier system is applied to study climate sensitivity of glacier area changes,which indicates that glacier lifespan mainly depends on the heating rate,secondly the precipitation,and precipitation increasing can slow down glacier retreat and make glacier lifespan prolonged.

Wave field forward modeling and theoretical analysis of weakness in discrete media

The elasticity, viscosity, and the relationships derived from rheology weakness properties are taken into account in mechanics. Comparing with the corresponding relationships derived from damage mechanics, we find the weakness factor has the same significance as the damage factor. We simulate the wave field using a staggered-grid pseudospectral method to show the influence of the weakness factor qualitatively. Applying the analytical solution of plane waves, we give the velocity and attenuation coefficient of three body waves, which are affected by the wave frequency and the weakness factor of saturated discrete media. Our results show that velocity decreases with increasing weakness factor, the attenuation coefficient increases with an increase in the weakness factor, and that the influence of weakness depends on the mode of the body waves.

Unstructured Grid Immersed Boundary Method for Numerical Simulation of Fluid Structure Interaction

This paper presents an improved unstructured grid immersed boundary method.The advantages of both immersed boundary method and body fitted grids which are generated by unstructured grid technology are used to enhance the computation efficiency of fluid structure interaction in complex domain.The Navier-Stokes equation was discretized spacially with collocated finite volume method and Euler implicit method in time domain.The rigid body motion was simulated by immersed boundary method in which the fluid and rigid body interface interaction was dealt with VOS(volume of solid) method.A new VOS calculation method based on graph was presented in which both immersed boundary points and cross points were collected in arbitrary order to form a graph.The method is verified with flow past oscillating cylinder.

Three dimensional efficient meshfree simulation of large deformation failure evolution in soil medium

An efficient Galerkin meshfree formulation for three dimensional simulation of large deformation failure evolution in soils is presented. This formulation utilizes the stabilized conforming nodal integration, where for the purpose of stability and efficiency a Lagrangian smoothing strain at nodal point is constructed and thereafter the internal energy is evaluated nodally. This formulation ensures the linear exactness, efficiency and spatial stability in a unified manner and it makes the conventional Galerkin meshfree method affordable for three dimensional simulation. The three dimensional implementation of stabilized conforming nodal integration is discussed in details. To model the failure evolution in soil medium a coupled elasto-plastic damage model is used and an objective stress integration algorithm in combination of elasto-damage predictor and plastic corrector method is employed for stress update. Two typical numerical examples are shown to demonstrate the effectiveness of the present method for modeling large deformation soil failure.

Adaptive triangular mesh coarsening with centroidal Voronoi tessellations

We present a novel algorithm for adaptive triangular mesh coarsening. The algorithm has two stages. First, the input triangular mesh is refined by iteratively applying the adaptive subdivision operator that performs a so-called red-green split. Second, the refined mesh is simplified by a clustering algorithm based on centroidal Voronoi tessellations (CVTs). The accuracy and good quality of the output triangular mesh are achieved by combining adaptive subdivision and the CVTs technique. Test results showed the mesh coarsening scheme to be robust and effective. Examples are shown that validate the method.

ARAP++:an extension of the local/global approach to mesh parameterization

Mesh parameterization is one of the fundamental operations in computer graphics(CG) and computeraided design(CAD). In this paper, we propose a novel local/global parameterization approach, ARAP++, for singleand multi-boundary triangular meshes. It is an extension of the as-rigid-as-possible(ARAP) approach, which stitches together 1-ring patches instead of individual triangles. To optimize the spring energy, we introduce a linear iterative scheme which employs convex combination weights and a fitting Jacobian matrix corresponding to a prescribed family of transformations. Our algorithm is simple, efficient, and robust. The geometric properties(angle and area)of the original model can also be preserved by appropriately prescribing the singular values of the fitting matrix. To reduce the area and stretch distortions for high-curvature models, a stretch operator is introduced. Numerical results demonstrate that ARAP++ outperforms several state-of-the-art methods in terms of controlling the distortions of angle, area, and stretch. Furthermore, it achieves a better visualization performance for several applications, such as texture mapping and surface remeshing.

Surface remeshing with robust user-guided segmentation

Surface remeshing is widely required in modeling, animation, simulation, and many other computer graphics applications. Improving the elements' quality is a challenging task in surface remeshing. Existing methods often fail to efficiently remove poor-quality elements especially in regions with sharp features. In this paper, we propose and use a robust segmentation method followed by remeshing the segmented mesh. Mesh segmentation is initiated using an existing Live-wire interaction approach and is further refined using local mesh operations. The refined segmented mesh is finally sent to the remeshing pipeline, in which each mesh segment is remeshed independently. An experimental study compares our mesh segmentation method as well as remeshing results with representative existing methods. We demonstrate that the proposed segmentation method is robust and suitable for remeshing.

Simulation of hard–soft material interaction under impact loading employing the material point method

Understanding the mechanisms of hard–soft material interaction under impact loading is important not only in the defense industry but also in daily life.However,traditional mesh-based spatial discretization methods that are time consuming owing to the need for frequent re-meshing,such as the finite element method and finite difference method,can hardly handle large deformation involving failure evolution in a multi-phase interaction environment.The objective of this research is to develop a quasi-meshless particle method based on the material point method for the model-based simulation of the hard–soft material interaction response.To demonstrate the proposed procedure,scenarios of a hard–soft material impact test are considered,where a force is applied to layers of materials and a hard bar with an initial velocity impacts a target with layers of different materials.The stress wave propagation and resulting failure evolution are simulated and compared with available data.Future research tasks are then discussed on the basis of the preliminary results.

Triangular element partition method with consideration of crack tip

In fracture simulation,how to model the pre-existing cracks and simulate their propagation without remeshing is an important topic.The newly developed triangular element partition method(TEPM)provides an efficient approach to this problem.It firstly meshes the cracked body regardless of the geometry integrity of the interesting object with triangular elements.After the meshing procedure is completed,some elements are intersected by cracks.For the element intersected by a crack,the TEPM takes the element partition technique to incorporate the discontinuity into the numerical model without any interpolation enrichment.By this approach,the TEPM can simulate fracture without mesh modification.In the TEPM,all the cracked elements are treated as the usual partitioned elements in which the crack runs through.The virtual node pairs(the intersection points of crack faces and elements)at the opposite faces of the crack move independently.Their displacements are respectively determined by their neighbor real nodes(nodes formatted in the original mesh scheme)at the same side of the crack.However,among these cracked elements,the element containing a crack tip,referred to as the crack tip element thereafter,behaves differently from those cut through by the crack.Its influence on the singular field at the vicinity of the fracture tip becomes increasingly significant with the element size increasing.In the crack tip element,the virtual node pair at the crack tip move consistently before fracture occurs while the virtual node pair separate and each virtual node moves independently after the fracture propagates.Accordingly,the crack tip element is automatically transformed into the usual partitioned element.In the present paper,the crack tip element is introduced into the TEPM to account for the effect of the crack tip.Validation examples indicate that the present method is almost free from the element size effect.It can reach the same precision as the conventional finite element method under the same meshing scheme.But the TEPM is much more efficient and convenient than the conventional finite element method because the TEPM avoids the troubles that the conventional finite element method suffers,e.g.,the meshing problem of cracked body,modification of mesh scheme,etc.Though the extended finite element method can also avoid these troubles,it introduces extra degrees of freedom due to node interpolation enrichment.Due to the simplicity of the present TEPM,it is believed that its perspective should be highly inspiring.