Efficient non‐linear reanalysis of skeletal structures using combined approximations

Non‐linear reanalysis of large‐scale structures usually involves much computational effort, because the set of non‐linear equations must be solved repeatedly during the solution process. Various approximations that are often used for linear reanalysis are not sufficiently accurate for non‐linear problems. In this study, solution procedures based on the combined approximations approach are developed and compared in terms of efficiency and accuracy. Various path‐independent non‐linear analysis and reanalysis problems are considered, including material non‐linearity, geometric non‐linearity and buckling analysis. Numerical examples demonstrate the effectiveness of the procedures presented. It is shown that in various cases accurate results can be achieved efficiently. Copyright © 2007 John Wiley & Sons, Ltd.     

Interfuel substitution in the primary metals industries

This paper applies a translog price possibility frontier to a pooled sample in order to measure the extent of interfuel substitution effects in the primary metals industries. The results clearly indicate that relative changes in fuel prices across primary metals industries have significant effects on energy consumption. This, in turn, has important implications for public policy. In particular, the market system appears better able to deal with exogenous shifts in energy supplies than has frequently been assumed in the formulation of public policies toward the energy crisis.     

Synthesis of elastic structures with controlled forces

An analytical model is presented for synthesis of elastic structural systems under external loads and desired “controlled forces”. In the first stage, the optimal force distribution and the final cross sectional dimensions are chosen, solving an optimization problem with elastic compatibility temporarily excluded. In the second stage, the force due to the external loads is determined for the optimal structure by elastic analysis, and the desired controlled force needed for the optimal cross sections and force distribution is obtained by subtracting the above result from the optimal force of the first stage. The final design which has been determined in the first stage, satisfies both conditions of equilibrium and compatibility. It is a lower-bound solution for a similar incontrolled elastic system. In some cases the first-stage optimization problem may be cast in linear programming form. Numerical examples of continuous beam and indeterminate truss demonstrate application of the proposed method.     

Gesture, speech, and computational stages: A reply to McNeill.

McNeill (1985) claimed that speech and its accompanying gestures "share a common computational stage" that is located early in the speech production process. This position depends on two crucial arguments that we believe are unsound: first, that gestures "are synchronized with linguistic units in speech" and, second, that gestures "have semantic and pragmatic functions that parallel those of speech." Careful analysis of the relevant data indicated that although the processes underlying gestural production are globally autonomous, they are linked to speech production at more than just one computational stage. An account is offered that explicates these links. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decaking of bituminous coals by alkaline solutions

Experimental results are reported concerning the decaking effect of alkalies on two Western Kentucky coals. Decaking treatment with dilute sodium hydroxide solutions was the most effective of the various methods examined. Caking and agglomerating character were destroyed when about 1–2 wt % (dry basis) sodium hydroxide was retained by the coal following the solution treatment. The free-swelling index was considerably reduced for both seam coals. In contrast, 20 wt % of sodium hydroxide was required in a dry mixing method. The amount of decaking reagent required for effective solution treatment varied with seam of origin but the difference in particle size range and/or mineral content may have been significant. Independent effects of these variables were not determined. Experimental results indicate that the decaking reactions occur at temperatures above 300 °C, but the actual mechanisms are not known. The alkaline-solution decaking treatment was conceived as a possible step in coal preparation for a coal-gasification process. Various important questions remain for continued study.     

Synthesis of structural geometry using approximation concepts

Some approximation concepts for efficient synthesis of structural geometry are presented. Using the force method of analysis and neglecting temporarily the implicit compatibility conditions, an approximate explicit problem (AEP) is introduced. Solving the AEP, a lower bound of the optimum is efficiently obtained. To evaluate the true optimum of the implicit problem, the compatibility conditions are considered for the final geometry of the AEP.Choosing the geometric variables as the independent ones, multilevel solution procedures are proposed. To improve the solution efficiency, the number of independent variables is reduced by geometric variable linking. Also, the number of trial geometries is reduced by introducing a coarse grid in the independent variables space.Several approximation concepts are proposed for efficient solution of the explicit fixed geometry problem. Linear programming models and approximate treatment of the displacement constraints are presented. The proposed solution procedures do not involve multiple implicit analyses of the structure.Numerical examples show that in a variety of structures, where the optimal geometry is not appreciably affected by the compatibility conditions, a single exact analysis is sufficient to evaluate the final optimum. The efficiency of the solution process and the quality of the approximations used are demonstrated.     

Smooth approximation and forecasting of load duration curves

The purpose of this paper is to develop a methodology for forecasting a load duration curve. The approach adopted in the development is to estimate a load duration curve as a combined linear-exponential function and relate the coefficients of this function to a set of economic and weather related variables. This relationship allows one to forecast the coefficients which are in turn used to provide a forecast of the coefficients of interest.The model presented, for a specific set of data, forecasts well and presents a substantial improvement over existing approaches to obtaining future load duration curves.     

The demand for electrical energy by agriculture in the USA

This paper examines the responsiveness of US agriculture to changes in the price of electricity. Price and demand equations for electricity are estimated using data for 48 American states over the period 1975–1977. Price elasticity is then estimated and found to be of sufficient magnitude to dispel doubts about the market mechanism in curtailing demand.