城市地质中基于剖面的3维层状地质体动态建模

为解决城市地质中的基于剖面的浅层地质体建模过程中的地质剖面自动对比问题,实现3维地质体模型的动态重构与局部更新,将3维拓扑推理引入3维地质建模,通过剖面投影方法在3维空间曲面上实现拓扑关系的自动构建与推理,提升地质剖面对比维数,提高地质剖面自动对比自动化程度,实现城市地质中3维层状地质体动态建模。该方法已应用于南京城市地质3维建模中,结果表明该方法适应多种剖面数据,提高了地质空间3维建模效率。     

多点地质统计学在数字岩心重构中的算法研究

在一个多孔介质中流体物质的渗流依赖孔隙空间几何结构和拓扑结构特性。因此,描述介质特征及预测其流动特性最重要的第一步是对一个多孔介质的三维孔隙空间进行重构。有介于此,一种随机模拟技术被提了出来,应用二维切片训练图像重构一个三维的孔隙图像。这项技术基于从连续的二维多点统计模拟拟合多尺度二维调节数据提取的过程。单一标准方程模拟算法(SNESIM),最初作为一种模拟引擎,起到了对地质构造的曲线特征进行复制的作用。     

基于同态球的多孔材料三维模型快速重构方法

研究多孔材料的三维模型重构问题,提高重构效率。多孔材料真实孔隙空间的结构异常复杂,孔隙空间的构成面较大,需要计算的孔隙像素量繁多,传统的基于二元表示法的重构方法,将孔隙空间逐一映射成像素点实现几何形态描述无法有效处理大量的孔隙像素量,巨大的计算量造成重构效率不高的问题。为此,提出了一种基于同态球的多孔材料三维模型重构方法。通过确定孔隙空间的"同态球"并据此定义孔隙体,将多孔材料的孔隙空间几何形态用孔隙体和吼道来表示,利用孔隙体和吼道之间的联系重构三维模型,避免了对孔隙空间逐一分析而造成的重构效率不高的问题。仿真实验表明,这种方法形象描述几何形态,有效减少了重构计算量,能够快速完成多孔材料三维模型的重构。     

离散数据复杂曲面的粗加工

提出一种基于离散数据的复杂曲面数控粗加工方法，被加工曲面用多面体模型来描述，采用分层切削方法加工，基于二维等值平面图的拓扑结构，求出各层的有效加工区域，利用数控编程自动生成刀具轨迹。该方法成功地解决了层切法加工复杂曲面时不能处理岛中岛的难题，经实践检验，效果良好。     

管状组织的中轴-元球造型方法

传统的医学体数据造型方法往往局限于将体数据表达为镶嵌在轮廓线族中的三角片集合,或者是简单的三维体元阵列.实际上,生物体的结构相当复杂,采用这些简单的造型方法显然不能适应绘制的要求.文章探讨了适用于气管、血管等管状、多分枝结构的造型方法,采用离散的中轴点表达分枝的拓扑结构,结合基于元球（metaball）的隐式曲面造型方法构造管状组织的模型.这种造型方法不仅可以使管状组织复杂的拓扑结构得以保留,而且保证了分枝之间连接的光滑性.     

基于MPS和多重模板的多孔介质重构方法

在油汽探测的研究中,提高探测的准确性,结多孔介质三维重构在油气探测有着重要意义,用规方法对多孔介质中长的孔隙通道和复杂的孔隙空间形状重构效果较差.为了提高探测精度,提出一种基于多点地质统计(MPS)和多重模板的多孔介质三维重构方法.将微米精度的多孔介质体数据作为训练图像,把逐渐密集化的网格作为多重数据模板提取其空间结构...     

三维地质结构模型中闭合地质块体的构建

三维地质建模中现有地质闭合区块搜索算法基于网格单元间的拓扑进行拓扑搜索,面临着拓扑信息冗余、计算量大、计算复杂度高等缺点.针对这一问题,以搜索拓扑封闭三维地质区块作为研究目标,提出一种适合表达地质界面复杂拓扑关系的拓扑模型,并在该模型上实现快速地质闭合块体搜索.由于地质闭合区块的搜索本质上应该在拓扑空间进行,因此分别定义了拓扑分界点、拓扑分界线、拓扑分界面片、拓扑分界面、闭合区块来表达复杂的地质模型在拓扑空间中的结构,将几何空间与拓扑空间分开表达存储,并在构建过程利用地质曲面的边界信息,遵从点、线、面、体的顺序逐级进行构建:依据拓扑分界点定义在三维曲面边界信息中构建拓扑分界点;在2个拓扑分界点间构建拓扑分界线并填充其拓扑信息;在拓扑分界面上追踪由拓扑分界线组成的封闭拓扑分界面片;对全局拓扑分界面片进行拓扑分析得到闭合区块.实例测试表明,由于拓扑模型的构建过程只利用了地质曲面的边界信息,因此构建过程快速,大大简化了识别的复杂度,可以满足任意复杂曲面间的接触关系的处理,也就从理论上解决了任意复杂的三维地质闭合区块的快速识别问题.     

多孔介质孔隙结构的网络模型应用

本研究分别用毛细管束模型和网络模型对多孔介质的孔构型进行描述。为了克服毛细管束模型在反映真实结构存在的局限性 ,有必要发展更为精确的方法。在诸多的多孔介质模型中 ,网络模型经过多年的研究、发展 ,已经可以较好地实现对过程机理进行定量预测。进一步通过引入非线形分形理论 ,对复杂孔隙结构可望得到更为真实可靠的构型模型     

多孔介质孔隙结构的网络模型应用

本研究分别用毛细管束模型和网络模型对多孔介质的孔构型进行描述。为了克服毛细管束模型在反映真实结构存在的局限性,有必要发展更为精确的方法,在诸多的多孔介质模型中,网络模型经过多年的研究、发展,已经可以较好地实现对过程机理进行定量预测,进一步通过引入非线形分形理论,对复杂孔隙结构可望得到更为真实可靠的构型模型。     

基于四边形网格的可调细分曲面造型方法

提出了一种基于四边形网格的可调细分曲面造型方法。该方法不仅适合闭域拓扑结构，且对初始网格是开域的也能进行处理。细分算法中引入了可调参数，增加了曲面造型的灵活性。在给定初始数据的条件下，曲面造型时可以通过调节参数来控制极限曲面的形状。该方法可以生成C1连续的细分曲面。试验表明该方法生成光滑曲面是有效的。     

多孔介质孔隙模型及其应用——毛细管束模型

在多孔介质中许多物理化学行为均与其自身的孔隙结构构型密切相关 ,建立一种切实可行的孔隙模型将会对研究材料和化工过程多孔介质提供很大的帮助。毛细管模型是一种较为简单的实用孔隙模型 ,它可以通过使用毛细管压对多孔介质的浸渗和排空情况进行计算 ,也可以用于对多孔介质中的浸渗和排空过程进行定性的解释。针对在研项目 ,对毛细管束模型情况做一评述     

Study of a Jacobian-free approach in the simulation of compressible fluid flows in porous media using a derivative-free spectral method

The development of Jacobian-free software for solving problems formulated by nonlinear partial differential equations is of increasing interest to simulate practical engineering processes. For the first time, this work uses the so-called derivative-free spectral algorithm for nonlinear equations in the simulation of flows in porous media. The model considered here is the one employed to describe the displacement of miscible compressible fluid in porous media with point sources and sinks, where the density of the fluid mixture varies exponentially with the pressure. This spectral algorithm is a modern method for solving large-scale nonlinear systems, which does not use any explicit information associated with the Jacobin matrix of the considered system, being a Jacobian-free approach. Two dimensional problems are presented, along with numerical results comparing the spectral algorithm to a well-developed Jacobian-free inexact Newton method. The results of this paper show that this modern spectral algorithm is a reliable and efficient method for simulation of compressible flows in porous media.     

Visualization of connectivity in octree based models

An interesting problem in the oil and gas industry is the visualization of the movement of oil and gas in porous media. An example of such a medium is a rock sample with some distribution of holes (pores) connected by channels (pore throats), the solid parts of the rock are called grains. In our work we have simulated the porous medium using a pointer-based octree, representing these pores and grains. This data structure allows us to model the connectivity of the pores and thus visualize fluid penetration within the medium. Whereas earlier models represent a serious simplifications or two dimensional homogeneous layers, our model provides us with a statistically accurate distribution in three dimensions and a more accurate representation of the connectivity. In this paper we present our data structure and the techniques which were used to create models of porous media and their porous networks. Next, we present algorithms for connectivity in octrees and we show how to apply them to modelling and visualization of fluid penetration in porous media.     

A non-stiff boundary integral method for 3D porous media flow with surface tension

We present an efficient, non-stiff boundary integral method for 3D porous media flow with surface tension. Surface tension introduces high order (i.e., high derivative) terms into the evolution equations, and this leads to severe stability constraints for explicit time-integration methods. Furthermore, the high order terms appear in non-local operators, making the application of implicit methods difficult. Our method uses the fundamental coefficients of the surface as dynamical variables, and employs a special isothermal parameterization of the interface which enables efficient application of implicit or linear propagator time-integration methods via a small-scale decomposition. The method is tested by computing the relaxation of an interface to a flat surface under the action of surface tension. These calculations employ an approximate interface velocity to test the stiffness reduction of the method. The approximate velocity has the same mathematical form as the exact velocity, but avoids the numerically intensive computation of the full Birkhoff–Rott integral. The algorithm is found to be effective at eliminating the severe time-step constraint that plagues explicit time-integration methods.     

Reconstructing Animated Meshes from Time‐Varying Point Clouds

In this paper, we describe a novel approach for the reconstruction of animated meshes from a series of time‐deforming point clouds. Given a set of unordered point clouds that have been captured by a fast 3‐D scanner, our algorithm is able to compute coherent meshes which approximate the input data at arbitrary time instances. Our method is based on the computation of an implicit function in ?⁴ that approximates the time‐space surface of the time‐varying point cloud. We then use the four‐dimensional implicit function to reconstruct a polygonal model for the first time‐step. By sliding this template mesh along the time‐space surface in an as‐rigid‐as‐possible manner, we obtain reconstructions for further time‐steps which have the same connectivity as the previously extracted mesh while recovering rigid motion exactly. The resulting animated meshes allow accurate motion tracking of arbitrary points and are well suited for animation compression. We demonstrate the qualities of the proposed method by applying it to several data sets acquired by real‐time 3‐D scanners.     

Segment Tracing Using Local Lipschitz Bounds

We introduce Segment Tracing, a new algorithm that accelerates the classical Sphere Tracing method for computing the intersection between a ray and an implicit surface. Our approach consists in computing the Lipschitz bound locally over a segment to improve the marching step computation and accelerate the overall process. We describe the computation of the Lipschitz bound for different operators and primitives. We demonstrate that our algorithm significantly reduces the number of field function queries compared to previous methods, without the need for additional accelerating data-structures. Our method can be applied to a vast variety of implicit models ranging from hierarchical procedural objects built from complex primitives, to simulation-generated implicit surfaces created from many particles.     

Interaction mining and skill-dependent recommendations for multi-objective team composition

Web-based collaboration and virtual environments supported by various Web 2.0 concepts enable the application of numerous monitoring, mining and analysis tools to study human interactions and team formation processes. The composition of an effective team requires a balance between adequate skill fulfillment and sufficient team connectivity. The underlying interaction structure reflects social behavior and relations of individuals and determines to a large degree how well people can be expected to collaborate. In this paper we address an extended team formation problem that does not only require direct interactions to determine team connectivity but additionally uses implicit recommendations of collaboration partners to support even sparsely connected networks. We provide two heuristics based on Genetic Algorithms and Simulated Annealing for discovering efficient team configurations that yield the best trade-off between skill coverage and team connectivity. Our self-adjusting mechanism aims to discover the best combination of direct interactions and recommendations when deriving connectivity. We evaluate our approach based on multiple configurations of a simulated collaboration network that features close resemblance to real world expert networks. We demonstrate that our algorithm successfully identifies efficient team configurations even when removing up to 40% of experts from various social network configurations.     

ReduceM: Interactive and Memory Efficient Ray Tracing of Large Models

We present a novel representation and algorithm, ReduceM, for memory efficient ray tracing of large scenes. ReduceM exploits the connectivity between triangles in a mesh and decomposes the model into triangle strips. We also describe a new stripification algorithm, Strip‐RT, that can generate long strips with high spatial coherence. Our approach uses a two‐level traversal algorithm for ray‐primitive intersection. In practice, ReduceM can significantly reduce the storage overhead and ray trace massive models with hundreds of millions of triangles at interactive rates on desktop PCs with 4‐8GB of main memory.     

Symbolic Model Checking of Software

Model checking is a popular formal verification technique for both software and hardware. The verification of concurrent software predominantly employs explicit-state model checkers, such as SPIN, that use partial-order reduction as a main technique to deal with large state spaces efficiently. In the hardware domain, the introduction of symbolic model checking has been considered a breakthrough, allowing the verification of systems clearly out-of-reach of any explicit-state model checker.This paper introduces ImProviso, a new algorithm for model checking of software that efficiently combines the advantages of partial-order reduction with symbolic exploration. IMPROVISO uses implicit BDD representations for both the state space and the transition relation together with a new implicit in-stack proviso for efficient partial-order reduction. The new approach is inspired by the Twophase partial-order reduction algorithm for explicit-state model checking.Initial experimental results show that the proposed algorithm improves the existing symbolic model checking approach and can be used to tackle problems that are not tractable using explicit-state methods.