Performance optimization of nonlinear electrical networks

A program suite for the optimization of nonlinear networks is described. This suite provides an interactive automated design aid within a small-machine environment.A unified approach for time-domain design is presented. A generalized form of performance function is used and is based on the development of the adjoint-network from Tellegen's theorem. A suitable set of the adjoint-network excitations is also obtained.The constrained optimization of the performance function is transformed by a change of variables into an unconstrained problem. Powell's algorithm for unconstrained minimization is used. The optimization algorithm requires the value of the performance function and its derivatives which are obtained from analyses of the network and its adjoint.The program is implemented on a small computer with 16k words of (16-bit) core store. The overall structure of the program suite is described and results of the optimization of some simple circuits are given.     

复杂系统可靠性设计中费用最小化的一个方法

本文用分解定理和分割树求出了复杂系统可靠性的函数表达式,给出了复杂系统可靠性 设计中费用最小化的一种方法.本方法简单,适合工程应用.     

Design objectives with non-zero prescribed support displacements

When non-zero prescribed support displacements are involved in addition to design independent loads for a continuum/structure, then the objectives of minimum compliance (total elastic energy) and of maximum strength lead to different designs. This is verified by the presented sensitivities. Designs from neither of the two objectives are characterized by uniformly distributed energy density. However, simple iterations with the goal of obtaining uniform energy density show that the strength is favored by this approach. These observations leads to a rejection of the objectives of compliance minimization as well as that of direct strength maximization; we choose the objective of obtaining uniform energy density and show by examples that the obtained solutions are close to fulfilling also strength maximization, with the price of increased compliance. Optimal design examples are presented and discussed in detail for different combinations of non-zero prescribed support displacements and design independent loads.     

A unified approach to shaft calculations using a microcomputer

This paper describes a program written for a microcomputer which allows shaft (or beam) calculations to be made for a wide range of geometrical, loading and support conditions. Expressions for generalized support conditions are developed including support flexibility and unloaded support misalignment. The program, occupying 6100 bytes of memory without problem data statements, is shown applied to a simple flexible support problem and to a complex paper-making machine shaft mounted on 21 supports.     

The finite element solution of a class of elastica problems

A finite element procedure for the analysis of an inextensional elastica bent through frictionless supports is presented. Element displacements are expressed in terms of cubic Hermite polynomials with nodal displacements and derivatives being determined to minimise the strain energy. It is shown that the axial force at any point is proportional to the square of the bending moment, which enables member incremental stiffness matrices to be expressed in a similar form to those used in stability analysis. The iterative procedure proposed for solving the nonlinear stiffness equations may readily be incorporated into any continuous beam program by the modification and addition of very few statements. An example is considered which indicates that accurate solutions may be obtained to a wide range of practical problems using the proposed technique.     

A posteriori error estimator and adaptive procedures for computation of shakedown and limit loads on pressure vessels

Adaptive finite element procedures are presented for the computation of upper bounds estimates of limit and shakedown loads for pressure vessels. The method consists of an h-type adaptive mesh refinement strategy based upon an a-posteriori error estimator measured by the energy norm. The problem is formulated in a kinematic approach using Koiter's shakedown theorem. A constitutive model, for elastic-perfectly plastic materials, relates the plastic strains increments and curvatures to plastic multipliers through the flow law associated with a shell piecewise-linear yield surface (hexagonal prism). A consistent relationship between nodal displacements and nodal plastic multipliers is enforced by minimizing the strain residual between the total strain and the plastic strain increments, which is measured with respect to the energy norm. Discretization of the shell into finite elements allows the reduction of the problem to a minimization problem which is solved by linear programming.     

Simultaneous topology optimization of structure and supports

The purpose of this paper is to demonstrate a method for and the benefits of simultaneously designing structure and support distribution using topology optimization. The support conditions are included in the topology optimization by introducing a new set of design variables that represents supported areas. The method is applied to compliance minimization and mechanism design. In the case of mechanism design, the large displacements of the mechanism are modelled using geometrically nonlinear FE-analysis. Examples with minimization of the compliance demonstrate the effects of using variable cost of supports in a design domain. Other examples show that more efficient mechanisms are obtained by introducing the support conditions in the topology optimization problem.     

A general computer program for the calculation of chemical equilibria and heat balances

A general purpose computer program for chemical process design has been developed on the basis of the Eriksson method for Gibbs energy minimization. A simple directive language and an on-line databank of thermodynamic data have been provided, as well as facilities for rapid exploration and optimization of chemical systems.     

Finite topology variations in optimal design of structures

The method of optimal design of structures by finite topology modification is presented in the paper. This approach is similar to growth models of biological structures, but in the present case, topology modification is described by the finite variation of a topological parameter. The conditions for introducing topology modification and the method for determining finite values of topological parameters characterizing the modified structure are specified. The present approach is applied to the optimal design of truss, beam, and frame structures. For trusses, the heuristic algorithm of bar exchange is proposed for minimizing the global compliance subject to a material volume constraint and it is extended to volume minimization with stress and buckling constraints. The optimal design problem for beam and frame structures with elastic or rigid supports, aimed at minimizing the structure cost for a specified global compliance, is also considered.     

Stability of beamlike lattice trusses

A simple procedure is presented for predicting the buckling loads associated with general instability of large repetitive beamlike trusses. The procedure is based on replacing the original lattice structure by an equivalent continuum beam model and obtaining analytic solutions for the beam model. The continuum beam model accounts for warping and shear deformation in the plane of the cross section and is characterized by its strain energy and potential energy due to initial stresses from which the governing differential equations are derived. The high accuracy of the buckling predictions of the proposed continuum beam is demonstrated by means of numerical examples.     

Java过程蓝图

1 引言计算机应用正进入网络时代,Java是一种广泛使用的网络编程语言,被称之为网络上的“世界语”。Java作为一种程序设计语言不仅具有简单、面向对象、分布式、解释执行、鲁棒、安全、平台无关、可移植、高性能、多线程以及动态性等特点,更重要的是它支持以网络为中心的新型计算模式——Java计算模式,从而使Ja-     

Conformational energy analysis of peptides using microcomputers: Description of PepCAD™ and analysis of N-formyl-N′-methylalanineamide

A computer program (called PepCAD™) was developed for performing conformational analysis of peptides on an Apple Macintosh personal computer. The program takes advantage of the mouse-based user interface and graphics of the Macintosh. PepCAD displays peptide molecules, calculates conformational energies, and performs energy minimization on peptides of up to 10 residues. Written in C, PepCAD supports an interactive mode and a batch processing mode, contains about 17,000 lines of code in 11 modules, and utilizes the ECEPP/2 and MINOP equations and parameters for energy calculation and minimization. Conformational energy minimization was done on N-formyl-N′-methylalanineamide. The number of minima and their relative energies were essentially the same as those of N-acetyl-N′-methylalanineamide.     

VB过程蓝图

ＶＢ过程蓝图是一种面向Ｖｉｓｕａｌ　Ｂａｓｉｃ语言的程序处理逻辑图表化表示法。这种工程化表示法支持 逻辑和实现两个层次的程序抽象表示,是一种简单实用、容易理解、结构良好的程序设计工具。文中 给出ＶＢ过程蓝图的形式化模型,抽象逻辑结构图的图形表示方法,以及程序设计的基本过程。     

PASCAL过程蓝图

提出一种面向标准PASCAL语言的程序处理逻辑图形化表示法－PASCAL过程蓝图,这种工程化表示法支持逻辑和实现两个层次的程序抽象表示,是一种简单实用、容易理解、结构良好的程序设计工具。文中给出PASCAL过程蓝图的形式化模型、抽象逻辑结构图的图形表示方法,以及程序设计的基本过程。     

Micropolar beam models for lattice grids with rigid joints

A simple, rational approach is presented for developing micropolar beam models for large repetitive beam-like planar lattices with rigid joints. The micropolar beam models have independent microrotation, and displacement fields and are characterized by their strain and kinetic energies, from which the equations of motion 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.     

Mathematical models for assessment of the safety of steel beams based on average strains from long gage optic sensors

Most fiber optic sensors are point sensors that can measure the strain only at a local point of a beam, although strain distribution is non-uniform along the length of a beam. Long gage fiber optic sensors that measure integrated strain over a relatively long length can consider strain variation. This type of sensor was found to be efficient and useful for monitoring large-scale structures. On the other hand, the maximum strain in a beam cannot be measured with long gage optic sensors; the safety of a steel beam is analyzed by a comparison between the maximum stress measured during monitoring and the allowable stress of the beam calculated by a design code. Therefore, in this paper, simple mathematical models are presented for the determination of the maximum values of strains or stresses in a beam based on the average strains measured by long gage optic sensors. The model was tested in an experiment by comparing the maximum strain directly obtained from electrical gages and the calculated maximum strain from long gage optic sensors.     

Strength optimized designs of thermoelastic structures

For thermoelastic structures the same optimal design does not simultaneously lead to minimum compliance and maximum strength. Compliance may be a questionable objective and focus for the present paper is on the important aspect of strength, quantified as minimization of the maximum von Mises stress. With compliance defined as the product of resulting displacements and their corresponding total loads, then for thermoelastic problems compliance is different from total elastic energy. An explicit formula for this difference is derived and numerically illustrated in the optimized examples. As an alternative to mathematical programming, which with a large number of both design variables and strength constraints, is found non-practical, we choose simple recursive iterations to obtain uniform energy density and find by examples that the obtained designs are close to fulfilling also strength maximization. In compliance minimization it may be advantageous to decrease the total volume, but for strength maximization it is argued that it is advantageous to keep the total permissible volume. With the thermoelastic analysis presented directly in a finite element formulation, simple explicit formulas for equivalent thermoelastic loads are appended.     

Identification and elimination of parasitic shear in a laminated composite beam finite element

A displacement-based finite element for the analysis of laminated composite beams is formulated using strain gradient notation. The definition of the beam’s longitudinal displacement possesses only the independent term (axial displacement) and a term which is linear in the thickness coordinate z. Thus, the finite element is first-order shear deformable. As strain gradient notation is physically interpretable, the contents of the coefficients of the polynomial expansions are identified a priori. Thus, the modeling capabilities as well as modeling deficiencies of the element are identified during the formulation procedure. A single parasitic shear term (spurious) is found to be present in the transverse shear strain expression of the element, which is responsible for locking. This parasitic shear term is also found to be the cause of a qualitative error existing in the representation of transverse shear strain along the length of a typical beam model. As the spurious term has been clearly identified, it can easily be removed to correct the element. The effectiveness of the procedure is shown through numerical analyses performed using the element containing the spurious term and then corrected for it. The beam model is validated by comparing numerical solutions with analytical solutions provided by the minimization of the total potential energy for a given laminated composite beam.     

Deformation analysis of thin elastic membranes in multiple contact

This article presents the deformation analysis of thin elastic membranes, supported at the boundaries, and lifted by multiple rigid indentors. This study is motivated by a problem that is encountered in the design of flexible elastomeric surface tooling for prototyping free-form shapes made of composite materials. The deformation analysis was carried out using a mathematical programming approach and assuming contacts between the membrane and indentors to be frictionless. The Mooney form of strain energy function is used for potential energy calculations. The conjugate gradient method in the presence of contact constraints is used for energy minimization. The results are presented for three numerical examples describing the realizability of ruled and doubly curved surface shapes.