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。     

Haptics-based virtual reality periodontal training simulator

This paper focuses upon the research and development of a prototype dental simulator for training of periodontal procedures. By the use of virtual reality and haptics technology, the periodontal simulator allows trainees to learn performing diagnosis and treatment of periodontal diseases by visualizing a three-dimensional virtual human mouth and feeling real tactile sensations while touching the surface of teeth, gingiva, and calculi with virtual dental instruments. Since periodontics requires dentists to depend primarily on tactile sensations to perform diagnostic and surgical procedures, the use of haptics is unquestionably crucial for a realistic periodontal simulator. The haptics-based virtual reality periodontal training simulator has been validated by a experiment conducted by the College of Dentistry at University of Illinois at Chicago (UIC) with faculty members and dental students, which demonstrates the scientific contribution and usefulness of the simulator as a vital part of the curriculum of the Department of Periodontics at UIC.

Hierarchial implicit dynamic least-square solution algorithm

This paper develops an implicit type transient solution strategy which possesses hierarchial levels of application. In particular, due to the manner of formulation, stiffness updating, assembly inversion, solution constraint, as well as iteration are all performed at a localized level. The level of iterative calculations depends on the type of hierarchial partitioning employed, namely degree of freedom, nodal, elemental, material/nonlinear group, substructural, and so on. Since the iterative solution process and application of constraints are applied at a local level, the resulting so-called hierarchial implicit solution algorithm possesses very stable and efficient numerical properties and is highly storage efficient. To demonstrate the scheme, the results of several benchmark examples are presented. These enable comparisons with the Newton-Raphson solved implicit transient solution method. Overall the comparisons illustrate the superior stability and efficiency of the hierarchial scheme.     

交互式过程隐函数云建模方法

计算机生成云已成为虚拟环境中不可或缺的自然景观之一。提出了两层次结构的交互式云建模系统。利用隐式体函数定义的元球（blob）构建云的基本结构,同时采用过程噪声生成云细节部分。利用粒子系统创建元球的分裂和消亡规则,在基本结构的基础上自动生成层次更为丰富的云形状。方法适用于建模多种不同类型的云,并能交互式绘制建模结果。     

Free-form geometric modeling by integrating parametric and implicit PDEs

Parametric PDE techniques, which use partial differential equations (PDEs) defined over a 2D or 3D parametric domain to model graphical objects and processes, can unify geometric attributes and functional constraints of the models. PDEs can also model implicit shapes defined by level sets of scalar intensity fields. In this paper, we present an approach that integrates parametric and implicit trivariate PDEs to define geometric solid models containing both geometric information and intensity distribution subject to flexible boundary conditions. The integrated formulation of second-order or fourth-order elliptic PDEs permits designers to manipulate PDE objects of complex geometry and/or arbitrary topology through direct sculpting and free-form modeling. We developed a PDE-based geometric modeling system for shape design and manipulation of PDE objects. The integration of implicit PDEs with parametric geometry offers more general and arbitrary shape blending and free-form modeling for objects with intensity attributes than pure geometric models     

Free-form solid modeling using deformations

One of the most important problems of available solid modeling systems is that the range of shapes generated is limited. It is not easy to model objects with free-form surfaces in a conventional solid modeling system. Such objects can be defined arbitrarily, but then operations on them are not transparent and complications occur. A method for achieving free-form effect is to define regular objects or surfaces, then deform them. This keeps various properties of the model intact while achieving the required visual appearance. This paper discusses a number of geometric modeling techniques with deformations applied to them in attempts to combine various approaches developed so far.     

Database support for solid modeling

Geometric solid modeling plays one of the most important roles in CAE (Computer Aided Engineering) activities. In order that geometric solid modeling functions sufficiently in the CAE environment, an EDBMS (Engineering Database Management System) supporting solid modeling is highly desirable. In this paper we present a new approach to the design of a geometric solid database system. In the proposed approach an EDBMS with capability of object-oriented accessing and manipulation is developed, and a solid sharing model that is a scheme for representing and manipulating a collection of interrelated solids is proposed. The solid sharing model is used as a basis for designing and manipulating a solid database managed by the EDBMS. Also explored is a mechanism for supporting a long transaction which generates many intermediate designs.     

Combining CSG modeling with soft blending using Lipschitz-based implicit surfaces

In this paper a general method is given for combining CSG modeling with soft blending using implicit surfaces. A class of various blending functions sharing some desirable properties like differentiability and intuitive blend control are given. The functions defining the CSG objects satisfy the Lipschitz condition that gives the possibility of fast root finding but can also prove useful in the field of collision detection and adaptive triangulation.     

DigitalSculpture: a subdivision-based approach to interactive implicit surface modeling

This paper presents DigitalSculpture, an interactive sculpting framework founded upon iso-surfaces extracted from recursively subdivided, 3D irregular grids. Our unique implicit surface model arises from an interpolatory, volumetric subdivision scheme that is C¹ continuous across the domains defined by arbitrary 3D irregular grids. We assign scalar coefficients and color to each control vertex and allow these quantities to participate in the volumetric subdivision of irregular grids. In the subdivision limit, a virtual sculpture is obtained by extracting the zero-level from the volumetric, scalar field defined over the irregular grid. This novel shape geometry extends concepts from solid modeling, recursive subdivision, and implicit surfaces; facilitates many techniques for interactive sculpting; permits rapid, local evaluation of iso-surfaces; and affords level-of-detail control of the sculpted surfaces.     

服装动态效果的仿真技术

真实性和实时性一直是服装动态效果仿真所追求的目标.为了对服装的动态效果进行真实的仿真,就必须对织物的所有主要参数进行精确的模拟,如弹力和粘力.实时服装动画的一个难点就是对服装褶皱的模拟,以及相应的碰撞检测问题.对服装动态效果仿真技术的现状进行了介绍,并对未来的发展提出了一些看法.     

基于MAS的动态企业建模方法

动态企业建模技术是为适应企业多变的市场环境和经常的企业业务过程重构而发展起来的技术;而Agent技术和MAS系统具有自治性、社会性、理性等突出特点。对运用具有不同性质的Agent构成三层企业模型MAS的方法进行了深入的研究,它在不同层次上支持企业业务、组织结构的重组,增加了企业模型的柔性。     

Recent developments in analytic solid modeling

Solid modeling has improved communications among the three major elements of an engineering process: design, analysis and manufacture. Recent developments in analytic solid modeling are reviewed that extend these improvements to conceptual design and to the representation of materials with internal geometry. Vector fields, Boolean operations on sculpted solids and new data links to engineering tomography in the PATRAN system are representative of these developments. Applications are reviewed using new advanced materials that indicate extensions of the current IGES system are needed to define material geometry for solids that include one or more fibrous phases. Working with these materials is a challenge facing an increasing number of designers and analysts in almost all fields of engineering.     

A road map to solid modeling

The objective of solid modeling is to represent, manipulate and reason about the 3D shape of solid physical objects by computer. Such representations should be unambiguous. Solid modeling's major application areas include design, manufacturing, computer vision, graphics and virtual reality. The field draws on diverse sources, including numerical analysis, symbolic algebraic computation, approximation theory, applied mathematics, point set topology, algebraic geometry, computational geometry and databases. In this article, we begin with some mathematical foundations of the field. We next review the major representation schemata of solids. Then, major layers of abstraction in a typical solid modeling system are characterized. The lowest level of abstraction comprises a substratum of basic service algorithms. At an intermediate level of abstraction there are algorithms for larger, more conceptual operations. Finally, a yet higher level of abstraction presents to the user a functional view that is typically targeted towards solid design. We look at some applications and at user interaction concepts. The classical design paradigms of solid modeling concentrated on obtaining one specific final shape. Those paradigms are becoming supplanted by feature-based, constraint-based design paradigms that are oriented more toward the design process and define classes of shape instances. These new paradigms venture into territory that has yet to be explored systematically. Concurrent with this paradigm shift, there is also a shift in the system architecture towards modularized confederations of plug-compatible functional components     

Cyclides in surface and solid modeling

It is shown that Dupin cyclides (C.P. Dupin, 1822), as surfaces in computer-aided geometric design (CAGD), have attractive properties such as low algebraic degree, rational parametric forms, and an easily comprehensible geometric representation using simple and intuitive geometric parameters. Their alternative representations permit the transition between forms when one or the other is more convenient for a specific purpose. Cyclides provide is useful extension of geometric coverage in solid modeling, primarily as blending surfaces for many commonly occurring situations. The geometry, properties, and uses of the Dupin cyclide in free-form surface modeling and blending are discussed     

Variational solid modeling for tolerance analysis

A variational model is a computer representation of a variational class and stands for a collection of different instances of the part or assembly modeled in CAD. The different basic approaches to variational modeling are reviewed. A surface-based approach to variational modeling is discussed. The approach is applied to solving the problems of eliminating rigid-body motion, handling incidence and tangency constraints, and modeling form variations. The application of variational modeling to automated tolerance analysis is also discussed     

Accurate solid modeling using polyhedral approximations

Although curved-surface solid modeling systems achieve a higher level of accuracy than faceted systems, they also introduce a host of topological, geometric, and numerical complications. A method for calculating accurate boundary representations of solid models is introduced that reduces the impact of these complications. The method uses a pair of bounding polyhedral approximations to enclose the boundary of each object. A structural analysis automatically determines where to make adaptive refinements to the polyhedrons to assure the topological validity of the results. Potential singularities are localized. The implementation is an experimental extension to the Geometric Design Processor (GDP) solid modeling system     

Arbitrary crack representation using solid modeling

This paper describes the fundamental modeling approaches adopted for crack nucleation and propagation in a software system that is specifically designed to simulate problems with evolutionary geometry. Only the topological and geometrical aspects of crack modeling, and how these aspects affect the database representation in the system, are addressed in the present discussion. The following are the innovative features of the present crack modeling approach: (a) crack simulation is done with a true geometric representation of the structure, via solid modeling; (b) crack modeling relies on the sophisticated, topology-based data structure of this system to support linkage to the solid model, fast interaction and accurate representation of evolving flaw shapes; (c) the system provides the ability to specify flaws of arbitrary shape (including non-planar flaws), size and orientation at arbitrary locations in the geometric model; (d) the flaw is specified at the desired location in the actual structure geometry, rather than at a location in the mesh; (e) the system uses all its automatic and local remeshing capabilities for the simulation of flaw initiation and growth.     

A block LU-SGS implicit dual time-stepping algorithm for hybrid dynamic meshes

A block lower-upper symmetric Gauss-Seidel (BLU-SGS) implicit dual time-stepping method is developed for moving body problems with hybrid dynamic grids. To simulate flows over complex configurations, a hybrid grid method is adopted in this paper. Body-fitted quadrilateral (quad) grids are generated first near solid bodies. An adaptive Cartesian mesh is then generated to cover the entire computational domain. Cartesian cells which overlap the quad grids are removed from the computational domain, and a gap is produced between the quad grids and the adaptive Cartesian grid. Finally triangular grids are used to fill this gap. With the motion of moving bodies, the quad grids move with the bodies, while the adaptive Cartesian grid remains stationary. Meanwhile, the triangular grids are deformed according to the motion of solid bodies with a ‘spring’ analogy approach. If the triangular grids become too skewed, or the adaptive Cartesian grid crosses into the quad grids, the triangular grids are regenerated. Then the flow solution is interpolated from the old to the new grid. The fully implicit equation is solved using a dual time-stepping solver. A Godunov-type scheme with Roe’s flux splitting is used to compute the inviscid flux. Several sub-iteration schemes are investigated in this study. Both supersonic and transonic unsteady cases are tested to demonstrate the accuracy and efficiency of the method.