一种实用的多投影仪显示墙色彩校正方法

针对多投影仪显示墙系统色彩不均匀性的问题,提出一种快速、实用的独立于几何校正结果的色彩校正方法。该方法利用细分网格变形技术将现有针对平面投影屏幕的色彩校正方法推广到适应任意光滑曲面投影屏幕,同时利用加权最小二乘曲线拟合思想降低色彩测量数据量。实际进行色彩校正时,采用可编程图形处理单元(GPU)的像素着色器对投影图像的每个像素进行实时校正计算,并在实际多投影仪显示墙系统中验证了方法的有效性。     

基于重要目标区的三维地形快速渲染方法

三维地形的显示需要绘制大量的三角形网格,为了提高地形显示速度目前广泛采取了三角形网格简化技术。针对弹道导弹作战区域地形的特殊性,提出了一种基于重要目标区的网格简化方法。从BMP位图读取地形高度信息,以四叉树保存网格数据,按照区域重要性静态确定地形网格疏密程度。并采用DirectX平台,实现了导弹战区三维地形显示,提高了渲染效率。     

细分曲面求交交线计算方法的研究

主要针对三角网格的细分曲面求交提出了一种有效的交线计算的方法,该方法适用于任意三角网格的细分曲面中.在利用AABB和二部图进行初始控制网格相交性检测后,利用该方法快速有效地求出细分曲面的交线.     

基于图像建模的多视图模型合并

通过基于单幅图像的建模方法或者基于立体像对的建模方法,可以重建图像序列中每一幅图像或者立体图像对对应的模型。但所得的是局部模型,并非物体的完整模型。针对这一问题,提出了一种基于序列图像建模的多视图模型合并方法。基于已重建出的同一物体不同角度的三角形网格模型,在统一坐标系下,对相邻角度下的三角形网格模型求取其重合区域,记录刚好包围重合区域的原始网格区域,对该区域重新进行网格划分,最后得到物体完整的三角网格模型。实验结果表明,该方法是可行的、有效的。     

基于神威·太湖之光的非结构网格计算加速算法

在国产异构众核平台神威·太湖之光上的非结构网格计算具有稀疏存储、离散访存、数据依赖等特点,严重制约了众核处理器的性能发挥。为解决稀疏存储和离散访存问题,提出一种N阶对角染色算法,以有效平衡主从核计算并利用从核将全局访存转化为LDM访问。针对数据依赖造成的计算竞争问题,采用自适应和无依赖的任务划分方法,避免并行计算时的数据冲突。为对处理器架构和非结构网格计算进行优化,采用主核与从核异步并行的方式,差异化使用主从核以充分利用硬件资源,同时,取消处理器提供的寄存器通信机制,降低从核阵列的同步开销同时便于扩展到新一代神威平台。此外,使用计算访存异步重叠技术来充分隐藏访存延迟。利用SpMV、Integration、calcLudsFcc算子进行实验,结果表明,相比主核实现,组合加速算法在不同算例规模下平均取得了10倍的加速效果,加速比最高可达24倍,N阶对角染色算法相比非染色分块算法取得了超过5.8倍的性能加速,有效提升了数据局部性和计算并行度。该算法对有依赖关系的计算冲突算子同样具有良好的加速性能,验证了自适应和无依赖任务划分方法的有效性。     

On mesh restrictions to satisfy comparison principles,maximum principles,and the non-negative constraint: Recent developments and new results

This article concerns mesh restrictions that are needed to satisfy several important mathematical properties—maximum principles, comparison principles, and the nonnegative constraint—for a general linear second-order elliptic partial differential equation. We critically review some recent developments in the field of discrete maximum principles, derive new results, and discuss some possible future research directions in this area. In particular, we derive restrictions for a three-node triangular (T3) element and a four-node quadrilateral (Q4) element to satisfy comparison principles, maximum principles, and the nonnegative constraint under the standard single-field Galerkin formulation. Analysis is restricted to uniformly elliptic linear differential operators in divergence form with Dirichlet boundary conditions specified on the entire boundary of the domain. Various versions of maximum principles and comparison principles are discussed in both continuous and discrete settings. In the literature, it is well-known that an acute-angled triangle is sufficient to satisfy the discrete weak maximum principle for pure isotropic diffusion. Herein, we show that this condition can be either too restrictive or not sufficient to satisfy various discrete principles when one considers anisotropic diffusivity, advection velocity field, or linear reaction coefficient. Subsequently, we derive appropriate restrictions on the mesh for simplicial (e.g., T3 element) and nonsimplicial (e.g., Q4 element) elements. Based on these conditions, an iterative algorithm is developed to construct simplicial meshes that preserve discrete maximum principles using existing open source mesh generators. Various numerical examples based on different types of triangulations are presented to show the pros and cons of placing restrictions on a computational mesh. We also quantify local and global mass conservation errors using representative numerical examples and illustrate the performance of metric.     

A distortion measure to validate and generate curved high‐order meshes on CAD surfaces with independence of parameterization

A framework to validate and generate curved nodal high‐order meshes on Computer‐Aided Design (CAD) surfaces is presented. The proposed framework is of major interest to generate meshes suitable for thin‐shell and 3D finite element analysis with unstructured high‐order methods. First, we define a distortion (quality) measure for high‐order meshes on parameterized surfaces that we prove to be independent of the surface parameterization. Second, we derive a smoothing and untangling procedure based on the minimization of a regularization of the proposed distortion measure. The minimization is performed in terms of the parametric coordinates of the nodes to enforce that the nodes slide on the surfaces. Moreover, the proposed algorithm repairs invalid curved meshes (untangling), deals with arbitrary polynomial degrees (high‐order), and handles with low‐quality CAD parameterizations (independence of parameterization). Third, we use the optimization procedure to generate curved nodal high‐order surface meshes by means of an a posteriori approach. Given a linear mesh, we increase the polynomial degree of the elements, curve them to match the geometry, and optimize the location of the nodes to ensure mesh validity. Finally, we present several examples to demonstrate the features of the optimization procedure, and to illustrate the surface mesh generation process. Copyright © 2015 John Wiley & Sons, Ltd.     

Powell–Sabin B‐splines and unstructured standard T‐splines for the solution of the Kirchhoff–Love plate theory exploiting Bézier extraction

The equations that govern Kirchhoff–Love plate theory are solved using quadratic Powell–Sabin B‐splines and unstructured standard T‐splines. Bézier extraction is exploited to make the formulation computationally efficient. Because quadratic Powell–Sabin B‐splines result in ‐continuous shape functions, they are of sufficiently high continuity to capture Kirchhoff–Love plate theory when cast in a weak form. Unlike non‐uniform rational B‐splines (NURBS), which are commonly used in isogeometric analysis, Powell–Sabin B‐splines do not necessarily capture the geometry exactly. However, the fact that they are defined on triangles instead of on quadrilaterals increases their flexibility in meshing and can make them competitive with respect to NURBS, as no bending strip method for joined NURBS patches is needed. This paper further illustrates how unstructured T‐splines can be modified such that they are ‐continuous around extraordinary points, and that the blending functions fulfil the partition of unity property. The performance of quadratic NURBS, unstructured T‐splines, Powell–Sabin B‐splines and NURBS‐to‐NURPS (non‐uniform rational Powell–Sabin B‐splines, which are obtained by a transformation from a NURBS patch) is compared in a study of a circular plate. Copyright © 2015 John Wiley & Sons, Ltd.     

丝网状镍钴硫金属化合物电化学性能研究

通过简单两步水热的方法在泡沫镍基底上成功制备出丝网状三维网络结构的Ni Co2S4,研究了材料的电化学性能,结果表明,Ni Co2S4@泡沫镍电极材料具有高的面积比电容,在电流密度为10 m A/cm~2时,面积比电容可达到2.87 F/cm~2;电流密度从10 m A/cm~2增大到50 m A/cm~2,电容保持率为60.9%;在负载量为6.21 mg/cm~2时,在30 m A/cm~2的高电流密度下充放电1 000次,电容保持率仍为67.3%。