Arturo Cifuentes

A performance study of tetrahedral and hexahedral elements in 3-D finite element structural analysis

Abstract This study compares the performance of linear and quadratic tetrahedral elements and hexahedral elements in various structural problems. The problems selected demonstrate different types of behavior, namely, bending, shear, torsional and axial deformations. It was observed that the results obtained with quadratic tetrahedral elements and hexahedral elements were equivalent in terms of both accuracy and CPU time.

Dynamic response of a beam excited by a moving mass

Abstract This paper presents a combined finite element/finite difference technique to determine the response of a beam excited by a moving mass. The technique introduced herein is based on a Lagrange Multiplier formulation that allows one to represent the compatibility condition at the beam/mass interface using a set of auxiliary functions. This approach can be easily adapted to a standard finite element code. In addition, its extension to treat more complex problems is straightforward. Two examples of application are discussed.

Modeling of multilevel structures: a general method for analyzing stress evolution during processing

This work presents a general modeling technique for following the evolution of the stress field during the manufacturing of multilevel structures. This technique combines the finite element method with a modeling strategy that uses artificial nodes to simulate material interfaces. It can be applied to both linear and nonlinear structures. The main advantage of this approach is that it allows one to account for all topological and geometric changes during the manufacturing process, as well as the residual stresses introduced at each stage. Its implementation is very straightforward since it is compatible with current finite element technology and most commercial codes. The usefulness of this technique is illustrated with an example concerning an encapsulated copper line. >

Nonlinear system identification based on modelling of restoring force behaviour

This paper introduces a system identification algorithm based upon modelling of the restoring force behaviour of the structure. This algorithm is more efficient than traditional algorithms based upon matching the time history of response of the structure, since error evaluation does not require the solution of any differential equations. The effectiveness of this system identification approach, in coordination with a model for deteriorating structures is demonstrated by an example using actual earthquake data from the Bank of California building which was damaged during the 1971 San Fernando earthquake.

A general method to determine the dynamic response of a plate to a moving mass

Abstract This paper presents a general technique to determine the dynamic response of a plate excited by an orbiting mass. The technique relies on a finite element discretization in which the mesh is consistent with the trajectory of the orbiting mass, combined with a Lagrange multiplier formulation. This allows one to represent the compatibility condition at the mass-plate interface using a set of auxiliary functions. This technique can be applied to plates of any shape, excited by masses describing any type of trajectory. An example is presented to illustrate the method.

Some Modeling Issues on the Finite Element Computation of Thermal Stresses in Metal Lines

Thermal stresses are a major concern in the reliability of metal lines. This paper addresses some modeling issues concerning the determination of thermal stresses in such structures. Specifically, a finite element technique that allows one to follow the evolution of the stress field as a function of the steps of the manufacturing process is discussed. In addition, comparisons between several modeling strategies, namely, plane stress versus plane strain, geometric nonlinearity versus geometric linearity, “frozen view” models versus “evolving” models, etc., are presented. A detailed example describing the manufacturing of a copper line is included to illustrate these points.

Estimating the dynamic behavior of printed circuit boards

The dynamic behavior of printed circuit (PC) boards plays an important role in the reliability of a package. This paper is concerned with four issues that are important in estimating the dynamic response of PC boards, namely, limitations of estimates based on the first vibration mode, the importance of geometric nonlinearities, the influence of a component location on the modal mass distribution and the relative importance of errors in the mass and stiffness estimates of a board component. >

A low-capacitance bipolar/BiCMOS isolation technology. II. Circuit performance and device self-heating

For pt. 1 see ibid., vol. 41, no. 8, p. 1379-87 (1994). Device and circuit results from transistors fabricated with a novel bipolar isolation technology are presented and discussed. The isolation structure, called sequentially planarized interlevel isolation technology (SPIRIT), is fabricated by using a combination of selective epitaxial growth of silicon and a preferential polishing technique as the key process elements. This structural concept aims for reduced collector-substrate and collector-base capacitances, as well as a lower extrinsic base contact resistance, in a partial-SOI structure without significantly increasing the device temperature during operation. The feasibility of the isolation structure is demonstrated through ECL ring oscillators with gate delays of 23.6 ps at 0.72 mA and 47 ps at 0.23 mA. The temperature contours for SPIRIT and other bipolar isolation structures are simulated by using a finite-element method. It is shown that the capacitance versus self-heating tradeoff of SPIRIT is significantly improved over that of conventional trench or SOI isolation structures. >

The One-Factor Gaussian Copula Applied To CDOs: Just Say NO (or, If You See a Correlation Smile, She Is Laughing at Your “Results”)

The one-factor Gaussian copula method has become the de facto standard to analyze most synthetic collateralized debt obligation structures. Unfortunately, this method produces a peculiar phenomenon known as a correlation smile (the implied correlation determined by the model depends on the CDO tranche one is considering instead of being tranche-independent). Market participants are divided regarding this issue. Many suspect that the correlation smile is caused by a flaw in the above-mentioned modeling strategy although they have been unable to articulate why. Others insist that the smile is actually correct and reveals important and relevant tranche-dependent characteristics, but have failed to produce convincing evidence to support this view. In this article the authors present evidence that the correlation smile is really a by-product (artifact) of an unfortunate modeling strategy and has no financial or market-driven interpretation whatsoever. Moreover, the authors argue that this modeling approach should be abandoned at once.

Valuation of Projects with Stochastic Cash Flows and Intertemporal Correlations: Practical Modeling Guidelines

AbstractThis paper explores the influence of cash-flow correlations on the behavior of the net present value (NPV) and internal rate of return (IRR) when performing valuations. In general, correlation has a negligible effect on the expected value of both the NPV and IRR. Even in cases of high correlation the IRR distribution departs very little from normality. In cases of moderate to low correlation, very good approximations of the SD of the NPV and IRR can be obtained, assuming that the cash flows are independent. These results, coupled with the simple two-parameter correlation structure investigated, provide a useful framework to perform valuation analysis of large-scale civil engineering projects.