Automated modeling for structural analysis

The numerical computations required for structural analysis are well defined and easy to automate. If structural analysis is to be automated fully, however, the modeling process, as well as the numerical computations, must be automated. This paper outlines a procedure for the automation of the entire modeling and analysis sequence.Structural analysis is considered as one of several planning, design, and analysis applications to be included in a computerintegrated design system. An essential ingredient of such a system is a central data base that supports all applications. A data base using a hierarchicalcomponent-connection concept is first described. A procedure is then outlined by which a modeler program can extract analysis models from this data base. Whereas the central data base describes the structure in terms of its components and connections, the analysis model is in terms of nodes, elements, substructures, slaving constraints, and so on. The features required in a structural analysis program to analyze the resulting model are also described. This program follows well-established principles, but is substantially different in its arhitecture from conventional analysis programs.A simple frame building is used as an example. However, the procedure is believed to be applicable to structures of a variety of types.     

Computer graphics techniques for modeling cloth

In this survey, we present a contemporary overview of cloth modeling techniques. 19 modeling techniques are summarized and categorized by their main theoretical method: geometrical, physical, or hybrid. The techniques within each category do not follow well-defined patterns. We therefore generally report each work independently according to the chronology of publication. At the end of the discussion of all techniques, we summarize their features in a table. We conclude by speculating on future research directions that could optimize the agreement between the requirements of visual realism and physical accuracy. The recommendations for future work consider the different goals in textile engineering and computer graphics     

Computer modeling and critical theory

The explicit consideration of literary theory has become increasingly important both in the field of textual studies generally and in undergraduate literature courses. But theory can seem vague and inconsequential to undergraduates. Our students use hypertext to model intertextuality and the Linear Modeling Kit (a software program we have developed) to model structuralist ideas about narrative. In making computer models, students explore the implications of analytic ideas by attempting to represent them in formal (in the sense of programmable) terms. Our experience shows that such modeling stimulates student questioning and discussion of marked precision and sophistication.Peter Havholm and Larry Stewart, both Professors of English at The College of Wooster, have collaborated on the use of computers in the teaching of literature since 1987 and have published several papers on the subject. They won an EDUCOM/NCRIPTAL Award for Distinguished Curricular Innovation in 1989. Stewart is co-author of A Guide to Literary Criticism and Research (3rd ed., Harcourt Brace Jovanovich, 1996). Havholm recently returned to teaching after fifteen years in administration. He has published Kipling and Fantasy, anthologized in Harold Orel, ed., Critical Essays on Rudyard Kipling (Boston: G.K. Hall, 1989), 92–105.     

Computer modeling approach for microsphere-packed bone scaffold

A computer modeling approach for constructing a three-dimensional microsphere-packed bone graft structure is presented. The modeling approach consists of both geometric and CAD-based computer modeling. The geometric model uses two extreme microsphere packing models (minimum-density packing and maximum-density packing) and a statistical packing model to determine the number of microspheres packed in a synthesized bone graft. The pore size of the packed internal porous structure is predicted, and a parametric study of the effect of microsphere diameter on the number of microspheres and pore size is conducted. Based on the results obtained from the geometric model, a CAD modeling approach for designing randomly microsphere-packed three-dimensional bone grafts was developed. The hierarchy of the CAD model and the steps for constructing a bone graft model are described, and application of the CAD-based bone graft model in internal structural examination, visualization, prediction and comparison with in vitro bone ingrowth is presented.     

Computer graphics techniques for modeling page turning

Turning the page is a mechanical part of the cognitive act of reading that we do literally unthinkingly. Interest in realistic book models for digital libraries and other online documents is growing. Yet, actually producing a computer graphics implementation for modeling page turning is a challenging undertaking. There are many possible foundations: two-dimensional models that use reflection and rotation; geometrical models using cylinders or cones; mass-spring models that simulate the mechanical properties of paper at varying degrees of fidelity; and finite-element models that directly compute the actual forces within a piece of paper. Even the simplest methods are not trivial, and the more sophisticated ones involve detailed physical and mathematical models. The variety, intricacy, and complexity of possible ways of simulating this fundamental act of reading is virtually unknown. This article surveys computer graphics models for page turning. It combines a tutorial introduction that covers the range of possibilities and complexities with a mathematical synopsis of each model in sufficient detail to serve as a basis for implementation. Illustrations are included, which are generated through our implementations of each model. The techniques presented include geometric methods (both two- and three-dimensional), mass-spring models with varying degrees of accuracy and complexity, and finite-element models. We include a detailed comparison of experimentally determined computation time and subjective visual fidelity for all the methods discussed. The simpler techniques support convincing real-time implementations on ordinary workstations. We also address the question of whether such techniques are worthwhile in practice by describing results from a user study that compared the performance of a page-turning book model with HTML and PDF presentations of the same material—and with physical books. This demonstrates that the book model has many advantages over conventional document formats.     

Computer aided structural analysis

A tutorial survey directed to the practicing engineer who is interested in computerized techniques for static and dynamic structural analysis.The discussion is directed to the general questions which occur in the application of computer aided analysis. Consideration is given to structural modeling, input preparation procedures, solutions algorithms, numerical errors, and output interpretation. The emphasis is on large general purpose programs and on establishing a definition of the current state of the art.     

Computer program for regression model for discontinuous structural surfaces

A regression model for discontinuous structural surfaces requires nonlinear normal equations. A computer program FAULTS is presented which estimates parameters of the regression equations. The program algorithm, which simulates possible natural-fault movements, has been tested on various multifaulted structural surfaces. The prefault geometry of subsurface structures can be reconstructed using estimates of the fault displacements.A method based on the geographic distribution of large residuals is proposed for detecting unmapped subsurface faults; a mapped fault in the Portrero oilfield (California) has been predicted accurately by this method.     

Computer graphics for water modeling and rendering: a survey

A key topic in computer graphics is the realistic representation of natural phenomena. Among the natural objects, one of the most interesting (and most difficult to deal with) is water. Its inherent complexity, far beyond that of most artificial objects, represents an irresistible challenge for the computer graphics world. Thus, during the last two decades we have witnessed an increasing number of papers addressing this problem from several points of view. However, the computer graphics community still lacks a survey classifying the vast literature on this topic, which is certainly unorganized and dispersed and hence, difficult to follow. This paper aims to fill this gap by offering a historical survey on the most relevant computer graphics techniques developed during the 1980s and 1990s for realistic modeling, rendering and animation of water.     

Weakly and fully coupled methods for structural optimization of flexible mechanisms

The paper concerns a detailed comparison between two optimization methods that are used to perform the structural optimization of flexible components within a multibody system (MBS) simulation. The dynamic analysis of flexible MBS is based on a nonlinear finite element formulation. The first method is a weakly coupled method, which reformulates the dynamic response optimization problem in a two-level approach. First, a rigid or flexible MBS simulation is performed, and second, each component is optimized independently using a quasi-static approach in which a series of equivalent static load (ESL) cases obtained from the MBS simulation are applied to the respective components. The second method, the fully coupled method, performs the dynamic response optimization using the time response obtained directly from the flexible MBS simulation. Here, an original procedure is proposed to evaluate the ESL from a nonlinear finite element simulation, contrasting with the floating reference frame formulation exploited in the standard ESL method. Several numerical examples are provided to support our position. It is shown that the fully coupled method is more general and accommodates all types of constraints at the price of a more complex optimization process.     

Somel system: Computer aids for the fabrication of structural steel

Structural steel fabricators earn their living by manufacturing pieces of steel and erecting them on site. The design is often carried out by an outside organization who translate this into a form best suited to the operators who drive the cutting and drilling machines. For large quantities of the work this is in the form of numerical lists. The Somel system enables draughtsmen, who traditionally initiate the process, to directly produce these lists, together with supplementary drawings where additional explanation is required for assembly. The system consists of seven linked programs, which are described together with comments, the effect on drawing office organization and benefits to be gained.     

Computer simulation and modeling in railway applications

An electrified railway system includes complex interconnections and interactions of several sub-systems. Computer simulation is the only viable means for system evaluation and analysis. This paper discusses the difficulties and requirements of effective simulation models for this specialized industrial application; and the development of a general-purpose multi-train simulator.     

Computer modeling 3-D nucleation and growth

A mathematical model is proposed for 3-D nucleation and growth—an initial stage in the process of metal electrocrystallization. Expressions have been obtained which make it possible to calculate the current response for an arbitrary dependence of the applied potential on time, for any values of the charge-transfer and nucleation parameters. These calculations require solving convolution-type stiff integral equations. An algorithm, developed previously for solving those equations, has been adapted to solve the present problem, A FORTRAN program is given for computing the current transient with a correction for the overlap of the diffusion fields of growing nuclei.     

Computer graphics for computer assisted learning of structural analysis

There is currently a lack of specialized educational software for the teaching of matrix structural analysis. Presented are the development and application of an interactive computer graphics program, CAL/CGI, to complement an enhanced version of the CAL program which has been used extensively for teaching matrix structural analysis. The basic commands of the CAL/CGI program are summarized and its application to support the understanding of the theory of the direct stiffness method is illustrated using simple examples.     

Application of Lagrange multipliers for coupled problems in fluid and structural interactions

One challenging aspect of the computation of multidisciplinary phenomenas is the accurate prediction of physical effects in space and time domain. The present paper focuses on the data transmission over non-matching grids. To fulfil energy conservation, a weak formulation of the continuity conditions on the common interface is used by introducing Lagrange multipliers. The coupling approach of the full system utilizes Hamilton’s principle. Several transfer schemes based on Galerkin’s method, dual-Lagrange multipliers, or the Sobolev-norm are presented. Two strategies to improve the accuracy of the transmission method are shown; namely use of merged mesh and quadtree-based h-refinement of the integration mesh. Simulations of an oscillating three-dimensional wing structure are presented to show the applicability and performance of the concepts. Further, computations of thin-walled structures with nonlinear behavior in transonic fluid flows are given. The impact of the presented transfer methods on the accuracy of the results are discussed.     

Improved image interpreting and modeling technique for automated structural optimization system

The automated structural optimization system (ASOS) proposed in the previous work incorporates the image-preprocessing techniques, the image-interpreting technique, and the automated shape-optimization modeling techniques to successfully obtain an autonomously integrated topology and shape optimization. However, the characteristic value-based image-interpreting technique used in ASOS is unable to accurately interpret complicated hole shapes, necessitating the use of the hole shape-adjusting strategy in addition to the hole-expanding strategy and the interference analysis in the automated shape-optimization modeling techniques to obtain a viable initial design and side constraints of design variables. In order to solve the above-mentioned problem in ASOS, this paper proposes the improved automated structural optimization system (IASOS) and uses the polygonal image-interpreting technique to replace the characteristic value-based image-interpreting technique used in ASOS. This alteration significantly increases the accuracy of image interpretation. Moreover, it can simplify the process of automated shape-optimization modeling techniques, reduce the design duration, and produce better results.     

交流耦合蔡氏电路的计算机仿真研究

该文用计算机仿真的方法分析了采用电容交流耦合的非线性负阻对蔡氏电路混沌特性的影响,其结果验证了当耦合电容相对振荡频率足够大时,该电容的加入对蔡氏电路的混沌特性影响不大。采用交流耦合后,利用高频电路实现的各类等效负阻器件得以在蔡氏电路中应用,因而可以获得工作在更高频段的混沌振荡。作为应用实例,该文给出了一个采用标准偏置隧道二极管实现的、混沌带宽达到数百兆赫兹的混沌电路。该电路可以用于宽带载波通信电路中。