Institute for Systems Research
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Item XBUILD: Pre-processor for Finite Element Analysis of Steel Bridge Structures(1992) Austin, Mark; Creighton, Steven L.; Albrecht, Pedro; ISRHistorically, the lack of interactive pre-processors to describe tedious finite element models has hindered the use of the finite element method for bridge analysis. The work performed in the present study mitigates this problem by providing an interactive graphically based pre-processor for the finite element analysis of highway bridges with high-speed engineering workstations. The name of the pre-processor is XBUILD. Version 1 of XBUILD is written in the C programming language, uses Sun View graphics, and runs on SUN SPARCstations. The pre-processor gives engineers the choice of using both keyboard and mouse styles of interaction to describe and edit bridge geometries, set boundary conditions, define sub-structure and highway vehicle objects, and place trucks at desired positions on the bridge. The capabilities of XBUILD Version 1 are demonstrated by working through the step-by- step details of creating a finite element model for the FHWA-AISI test bridge.Item Structural Optimization in a Distributed Computing Environment(1991) Voon, B.K.; Austin, Mark; ISRThis report presents the formulation and testing of a Feasible Sequential Quadratic Programming (FSQP-DIS) optimization algorithm customized to a Distributed Numerical Computing environment (DNC). DNC utilizes networking technology and an ensemble of loosely coupled processors to compute structural analyses concurrently. Each iterate of the FSQP-DIS is partitioned for concurrent computations in the direction calculation, and the steplength calculation. The prototype environment is tested on three applications; a mathematical programming problem, the design of a two-story planar steel frame, and finally, the optimal design of a two-story three- dimensional steel frame.Item High Order Integration of Smooth Dynamical Systems: Theory and Numerical Experiments(1991) Austin, Mark; ISRThis paper describes a new class of algorithms for integrating linear second order equations, and those containing smooth nonlinearities. The algorithms are based on a combination of ideas from standard Newmark integration methods, and extrapolation techniques. For the algorithm to work, the underlying Newmark method must be stable, second order accurate, and produce asymptotic error expansions for response quantities containing only even ordered terms. It is proved that setting the Newmark parameter t to 1/2 gives a desirable asymptotic expansion, irrespective of the setting for ݮ Numerical experiments are conducted for two linear and two nonlinear applications.Item Solid Modeling of Reinforced Concrete Beams, Part I: Data Structures and Algorithms, Part II: Computational Environment(1991) Austin, Mark; Preston, J.L.; ISRThis 2-part paper describes a solid modeling methodology for the interactive design and analysis of reinforced concrete (RC) beam structures. Part I covers the data structure and algorithms for steel reinforcing bar trajectories, and a three dimensional boundary representation of the concrete beam solid. Algorithms are given for slicing the beam, extracting cross sections, and computing the ultimate strength. Part 2 of this series discuss the design and implementation of an interactive design environment called Beam Tool.Item Almost Poisson Integration of Rigid Body Systems(1991) Austin, Mark; Krishnaprasad, Perinkulam S.; Wang, L.S.; ISRIn this paper we discuss the numerical integration of Lie-Poisson Systems using the mid-point rule. Since such systems result from the reduction of hamiltonian systems with symmetry by Lie Group actions, we also present examples of reconstruction rules for the full dynamics. A primary motivation is to preserve in the integration process, various conserved quantities of the original dynamics. A main result of this paper is a third order error estimate for the Lie-Poisson structure where h is the integration step-size. We note that Lie-Poisson systems appear naturally in many areas of physical science and engineering, including theoretical mechanics of fluids and plasmas, satellite dynamics, and polarization dynamics. In the present paper we consider a series of progressively complicated examples related to rigid body systems. We also consider a dissipative example associated to a Lie-Poisson system. The behavior of the mid-point rule and an associated reconstruction rule is numerically explored.Item Pre-Processor for Finite Element Analysis of Highway Bridges(1990) Creighton, Steven L.; Austin, Mark; Albrecht, Pedro; ISRHistorically, the lack of interactive pre-processors to setup tedious finite element problem descriptions has hindered the use of the finite element method for bridge analysis. The work performed in the present study mitigates this problem via the use of highspeed engineering workstations. This report presents an interactive, graphically based pre-processor for the analysis of highway bridges with the finite element method. With the pre- processor, bridge design engineers can use both keyboard and mouse styles of interaction to describe bridge geometries. The UNIX tool YACC has been used to create a command language for describing and manipulating of structural geometries, material types, loads, and boundary conditions. The pre-processor was successfully used to create input files in a format acceptable to the finite element analysis program ANSYS. In fact, less than 20 minutes was needed to create a finite element model of the prototype bridge tested at the Turner-Fairbanks Laboratory in Langley, Virginia, in a joint FHWA-AISI project. This report describes the development of the pre-processor in words that can hopefully be understood by civil engineers and computer scientists alike.