Approximate techniques of strctural reanalysis

A study is made of two approximate techniques for structural reanalysis. These include Taylor series expansions for response variables in terms of design variables and the reduced basis method. In addition, modifications to these techniques are proposed to overcome some of their major drawbacks. The modifications include a rational approach for the selection of the reduced basis vectors and the use of Taylor series approximation in an iterative process. For the reduced basis a normalized set of vectors is chosen which consist of the original analyzed design and the first-order sensitivity analysis vectors.The use of the Taylor series approximation as a first (initial) estimate in an iterative process, can lead to significant improvements in accuracy, even with one iteration cycle. Therefore, the range of applicability of the reanalysis technique can be extended.Numerical examples are presented of space truss structures. These examples demonstrate the gain in accuracy obtained by using the proposed modification techniques, for a wide range of variations in the design variables.     

Reduction method for the non-linear analysis of symmetric anisotropic panels

Reduction method and computational procedures are presented for reducing the size of the analysis model and the number of degrees of freedom used in predicting the non-linear response of symmetric anisotropic panels. The two key elements of the method are (a) operator splitting, or decomposition of the characteristic arrays of the finite element model into sums of orthotropic and non-orthotropic contributions, (b) application of a reduction method through the successive use of the finite element method and the classical Rayleigh-Ritz technique. The finite element method is first used to generate a small number of global approximation vectors (or modes). Then the amplitudes of these modes are computed by using the classical Rayleigh-Ritz technique. The global approximation vectors are selected to be those commonly used in single (or multiple) parameter perturbation techniques, namely a non-linear solution corresponding to zero non-orthotropic arrays and a number of its derivatives with respect to an anisotropic tracing parameter (and possibly, to a load or arc-length parameter in the solution space). The size of the analysis model used in generating the global approximation vectors is identical to that of the corresponding orthotropic structure. The effectiveness of the proposed reduction method is demonstrated by means of a numerical example, and its potential for solving quasi-symmetric non-linear problems of anisotropic panels is discussed.     

Sensitivity analysis of frictional contact/ impact response on distributed-memory computers

Multilevel parallel computational strategies are presented for predicting the frictional contact/impact response and evaluating the sensitivity coefficients of axisymmetric composite structures. Both implicit and explicit temporal integration techniques are considered. For implicit techniques, parallelism is exploited in both the spatial and temporal domains. Spatial parallelism is achieved by using a parallel sparse equation solver based on a nested dissection node-ordering scheme. The explicit techniques exploit parallelism using both an element-based domain decomposition strategy, as well as concurrent evaluation of sensitivity coefficients. Implementations of the strategies on distributed-memory computers are described. The strategies are applied to the problem of an axisymmetric composite spherical cap impacting a rigid surface, and the performance characteristics are assessed on the IBM SP2 and the Cray T3D parallel computer systems.     

Nonlinear dynamic analysis of space trusses

A computational procedure is presented for predicting the dynamic response of space trusses with both geometric and material nonlinearities. A mixed formulation is used with the fundamental unknowns consisting of member forces, nodal velocities and nodal displacements. The governing equations consist of a mixed system of algebraic and differential equations. The temporal integration of the differential equations is performed by using an explicit half-station leap-frog method. The advantages of the proposed computational procedure over explicit methods used with the displacement formulation are discussed. The high accuracy of the procedure is demonstrated by means of numerical examples of plane and space trusses. The constitutive relations in these examples are assumed, for convenience, to be represented by the Ramberg-Osgood polynomials. Comparison is also made with solutions obtained by using implicit multistep temporal integration schemes.     

Analysis of spatial beamlike lattices with rigid joints

Micropolar beam models are developed for the static, free vibration and buckling analysis of repetitive spatial beamlike lattices with rigid joints. The micropolar beam models have independent microrotation and displacement fields and are characterized by their strain energy, potential energy due to initial stresses and kinetic energy from which the governing differential equations and boundary conditions can be derived. The procedure for developing the expression for the strain energy of the micropolar beam involves introducing basic assumptions regarding the variation of the displacement and microrotation components in the plane of the cross-section, and obtaining effective elastic coefficients of the continuum in terms of the material properties and geometry of the original lattice structure. The high accuracy of the solutions obtained by the micropolar beam models is demonstrated by means of numerical examples for vierendeel and double-laced lattice girders with triangular cross-sections.     

Surface and pore structure of deoiled acid-and heat-treated spent bleaching clays

Samples of spent bleaching clay were deoiled by hexane, methanol, hexane-methanol, and supercritical CO₂ extractions. The deoiled clays were regenerated by acid and heat treatments. Nitrogen adsorption isotherms for these samples are type IV with hysteresis loops corresponding to type H3, indicating slit-shaped pores. Used deoiled and dried samples have smaller surface areas and pore volumes than unused clay. The surface areas and pore volumes increased after heat treatment. Acidified heat-treated deoiled samples have smaller surface areas and greater pore volumes than unused clay, except for the methanol-deoiled sample. Thus, heat and acid treatments removed substances adsorbed in the pores that were not removed by solvents or CO₂ extraction. This was confirmed from the ratios of the cumulative surface area/BET surface area, as well as analysis of the pore size distributions, which indicated an increase in mesopores with radii of between 25 and 100 Å. The t-plots showed that smaller pores with sizes between 7 and 25 Å, present originally in the unused clays, were closed by heat treatment. These pores were absent in the deoiled and the heat-treated samples except for the heat-treated sample that was deoiled by hexane followed by methanol. Smaller pores, accompanied by an increase in surface area, were also observed for all deoiled samples after acid and heat treatments.     

An interrogative visualization environment for large-scale engineering simulations

An interrogative visualization environment is described for the interactive display and querying of large datasets. The environment combines a web-based intelligent agent facility with a visualization engine. The intelligent agent facility (IAF) incorporates a rule-based expert system for natural-language understanding, voice and text input facilities, a hierarchical clickable command list, an interface for multimodal devices such as menu-based wireless handheld devices and gesture recognition devices, and human-like avatars acting as virtual assistants. The IAF interacts with, and controls, the visualization engine through a TCP/IP network socket interface. The environment enables multiple users using a variety of interaction modes and devices to effectively browse through large amounts of data, focus on and query interesting features, and more easily comprehend and make use of the data. Application of the environment to the visualization of engineering simulations is described.     

Plasmodium falciparum: increased proportion of severe resistance (RII and RIII) to chloroquine and high rate of resistance to sulfadoxine-pyrimethamine in Peninsular Malaysia after two decades

Uncomplicated falciparum malaria patients were randomly assigned to receive either 25 mg/kg chloroquine (CHL) over 3 d or a statim dose of 25 mg/kg sulfadoxine (SDX) plus 1.25 mg/kg pyrimethamine (PYR). Patients were followed up for 28 d and the parasite response graded according to World Health Organization criteria. Overall resistance to CHL was 63.3% and 47.4% to SDX/PYR. RI, RII and RIII rates were 9.1%, 42.4% and 12.1% for CHL and 10.5%, 21.1% and 15.8% for SDX/PYR, respectively. Degree and rates of resistance to CHL were significantly correlated with pre-treatment parasite density, but not those to SDX/PYR. Plasma CHL and SDX/PYR levels were within the reported ranges and were not significantly different in patients with sensitive and resistant responses.     

Second-order effects in self-similar laminar compressible boundary-layer flows

Second-order effects associated with longitudinal curvature, transverse curvature, entropy gradients, stagnation enthalpy gradient, velocity slip, temperature jump and displacement speed in self-similar two-dimensional and axisymmetric flows of a compressible fluid are studied. The self-similar governing equations for second-order effects show that the four parameters, due to longitudinal curvature, transverse curvature, displacement and body shape are needed to describe the flow. Numerical solutions and several closed form solutions are obtained. The present study is found to contain all the previous studies in the self-similar domain as special cases.     

Recursive and iterative algorithms for computing eigenvalues ofHermitian Toeplitz matrices

The numerical solution of the complete eigenspectrum for Hermitian Toeplitz matrices is presented. Trench's algorithm (1989), which employs bisection on contiguous intervals, and the Pegasus method are used to achieve estimates of distinct eigenvalues. Several modifications of Trench's algorithm are examined; the goals are an increase in the rate of convergence, even at some reduction in estimate accuracy, and an accommodation of eigenvalue multiplicity or clustering. A promising approach that contains three key ingredients is found. They are: a modification of Trench's procedure to employ noncontiguous intervals, a procedure for multiplicity identification, and a replacement of the Pegasus method by the modified Rayleigh quotient iteration. The result is the basis for a novel eigenspectrum solver with a cubic convergence rate and good estimation accuracy. Simulation results for high-order Hermitian Toeplitz matrices are provided