System Identification of Partially Restrained Composite Plates Using Measured Natural Frequencies

A nondestructive evaluation technique established on the basis of a global minimization method is presented for the system identification of laminated composite plates partially restrained by elastic edge supports. Six natural frequencies extracted from the vibration data of the flexibly restrained plate are used to identify the system parameters of the plate. In the identification process, the trial system parameters are used in the Rayleigh–Ritz method to predict the theoretical natural frequencies of the plate, an error function is established to measure the sum of the differences between the experimental and theoretical predictions of the natural frequencies, and the global minimization method is used to search for the best estimates of the parameters by making the error function a global minimum. The accuracy and efficiency of the proposed technique in identifying the parameters of several flexibly supported plates made of different composite materials are studied via both theoretical and experimental approaches. The excellent results obtained in this study have validated the applicability of the proposed technique.     

Vibration and Stability of Thick Plates on Elastic Foundations

Natural frequencies and buckling stresses of a thick isotropic plate on two-parameter elastic foundations are analyzed by taking into account the effect of shear deformation, thickness change, and rotatory inertia. Using the method of power series expansion of the displacement components, a set of fundamental dynamic equations of a two-dimensional, higher-order theory for thick rectangular plates subjected to in-plane stresses is derived through Hamilton's principle. Several sets of truncated approximate theories are used to solve the eigenvalue problems of a simply supported thick elastic plate. To assure the accuracy of the present theory, convergence properties of the minimum natural frequency and the buckling stress are examined in detail. The distribution of modal transverse stresses are obtained by integrating the three-dimensional equations of motion in the thickness direction. The present approximate theories can accurately predict the natural frequencies and buckling stresses of thick plates on elastic foundations as compared with Mindlin plate theory and classical plate theory.     

Elastic Constants Identification of Shear Deformable Laminated Composite Plates

A constrained minimization method is presented for the identification of elastic constants of shear deformable laminated composite plates. Strains and∕or displacements obtained from static testing of laminated composite plates are used in the proposed method to identify the elastic constants of the plates. In the identification process, the trial elastic constants of a laminated composite plate are used in a finite-element analysis to predict the strains and displacements of the plate. An error function is established to measure the differences between the experimental and theoretical predictions of strains and∕or displacements. A constrained minimization technique is used to minimize the error function and update the trial elastic constants. The best estimates of the elastic constants of the plate are then determined by subsequently reducing the size of the feasible region of the elastic constants and making the error function a global minimum. The accuracy and applications of the proposed method are demonstrated by means of a number of examples. A sensitivity analysis is also performed to study the effects of variations of experimental data on the accuracy of the identified elastic constants.     

Simultaneous Design and Control of Stiffened Laminated Composite Structures

The problem investigated here concerns the simultaneous design and control of structures. The structure considered is a laminated stiffened composite plate for which an optimum control system is designed by the minimization of an appropriate performance index with respect to both the control forces and structural design variables consisting of stiffener areas and the number of plies of a given orientation. To ensure a physically realistic structure appropriate constraints on the stiffener sizes, total weight, and structural frequencies are imposed. Nonlinear mixed‐integer programming is used to force the number of plies to take on integral values. The entire problem is posed as a three‐level optimization problem. Using the well‐known independent modal space control method, effects of plate geometry, initial disturbance conditions, and control effort penalty parameters on the optimal design are considered. The minimization process requires derivatives of eigenvalues and eigenvectors with respect to the design variables. These derivatives can be computed by an involved analytical procedure or a relatively simple finite‐difference procedure. This paper also examines the computer cost‐effectiveness of these two procedures for the sensitivity‐derivative calculations.     

Applications of Genetic-Taguchi Algorithm in Flight Control Designs

A genetic algorithm (GA), a well-known numerical method, is widely applied in different areas of optimal studies. It is found that if the solution-search space is wide or if the selected fitness function is highly nonlinear, the GA’s solutions can strongly depend on the set parameters, which include population size, crossover rate, mutation rate, and the remaining size of the parent in the GA. This paper combines the Taguchi experimental method, which serves as a rough search tool, with the GA, which serves as a fine search tool, to find the best combination of the GA parameters for different flight-control problems. The purpose of such a combination is to make control more robust and closer to the optimal solution. To demonstrate this new idea, the writers consider its application to different flight-control problems for the F-16 fighter by using autostabilization, linear quadratic regulator (LQR) and H∞ design. The simulation results not only achieve the expected optimal design for flight-control problems but also justify the reliability and feasibility of the combination of the GA and the Taguchi method.     

Free-Vibration Analysis and Material Constants Identification of Laminated Composite Sandwich Plates

Free vibration of symmetrically laminated composite sandwich plates with elastic edge restraints is studied via the Rayleigh–Ritz approach. The proposed Rayleigh–Ritz method is constructed on the basis of the layer-wise linear displacement theory. The accuracy of the method in predicting natural frequencies of composite sandwich plates with different boundary conditions is verified by the results reported in the literature or the experimental data obtained in this study. The proposed method is then applied to the material constant identification of free composite sandwich plates using the first six theoretical natural frequencies of the plates. In the identification process, trial material constants are used in the present method to predict the theoretical natural frequencies, a frequency discrepancy function is established to measure the sum of the squared differences between the experimental and theoretical natural frequencies, and a stochastic global minimization algorithm is used to search for the best estimates of the material constants by making the frequency discrepancy function a global minimum. Applications of the material constant identification technique are demonstrated by means of several examples.     

Stability of Stiffened Plates with Initial Imperfections

An experimental study of the effect of plate slenderness ratio and column slenderness ratio on the collapse load of simply supported stiffened plates with initial imperfections, loaded in compression, is presented. A generalized computer program for the semiempirical solutions based on the strut approach and the orthotropic plate approach is developed. A finite element analysis program based on the orthotropic plate approach is developed and a new collapse criterion is introduced. The analytical calculations are compared with the experimental results and uncertainty parameters are calculated. The effect of initial geometric imperfections, plate slenderness ratios, and column slenderness ratios on the collapse load of stiffened plates is studied. A set of conclusions is drawn based on the experimental and analytical studies carried out.     

Moment-Inelastic Rotation Behavior of Longitudinally Stiffened Beams

The significance for inelastic design of moment-inelastic rotation behavior with respect to interior pier sections of steel girder bridges is experimentally investigated. Under center span loading conditions, 12 welded, built-up, simply supported beams with various slenderness ratios of the flange and web plates are tested. In this test, lengths and locations for partial longitudinal stiffeners on the web plates are varied, and the results are then compared with the inelastic deformation capacity of beams without longitudinally stiffened web plates. The results are also compared with the inelastic design code in AASHTO LRFD bridge design specifications. It is concluded that (1) the ultimate strength of stiffened beams is governed by the local buckling at the compression flange of the far end from the loading point due to the presence of a partial longitudinal stiffener; and (2) the inelastic rotation capacity and ultimate strength of a beam with a stiffened web plate are remarkably improved. The optimum length and location of stiffeners on the plates are given.     

Parametric Study on the Dynamic Instability Behavior of Laminated Composite Stiffened Plate

This paper deals with the study of dynamic or parametric instability behavior of laminated composite stiffened plates with step-uniform and concentrated in-plane harmonic edge loading. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the plate and the stiffeners, respectively. The method of Hill’s infinite determinant is applied to analyze the dynamic instability regions. Numerical results are presented through convergence and comparison with the published results from the literature. The effects of parameters like loading type, stiffening scheme, lamination scheme, dynamic load factor, and boundary conditions are considered in the dynamic instability analysis of laminated composite stiffened plate. It has been shown that the type of loading and the width of loading have remarkable effect on the dynamic instability characteristics of the stiffened plate.     

Analysis of Thick Circular Plates Undergoing Large Deflections

This investigation considers the effect of transverse shear deformation on bending of the axisymmetrically loaded isotropic and orthotropic circular and annular plates undergoing large deflection. The analysis treats the nonlinear terms of lateral displacement as fictitious loads acting on the plate. The solution of a von Kármán‐type plate is, therefore, reduced to a plane problem in elasticity and a linear plate‐bending problem. Results are presented for simply supported and clamped plates and are in good agreement with the available solutions. For plates considered in this study, the influence of shear deformation on lateral displacement becomes more significant as the orthotropic parameter increases. The linear and nonlinear solutions for orthotropic plates deviate at a low value of the maximum deflection‐to‐thickness ratio (w/h). Consequently, the extent of w/h within which the small‐deflection theory is applicable to orthotropic plates is much lower than the value of about 0.4 typically used for isotropic plates, and it depends, in general, on the degree of orthotropy. The technique employed in this study is well suited for the analysis of nonlinear plate problems.     

Stochastic Finite-Element Analysis for Elastic Buckling of Stiffened Panels

The variability of the random buckling loads of beams and plates with stochastically varying material and geometric properties is studied in this paper using the concept of the variability response function. The elastic modulus, moment of inertia, and thickness are assumed to be described by homogeneous stochastic fields. The variance of the buckling load is expressed as the integral of the auto- and cross-spectral density functions characterizing the stochastic fields multiplied by the deterministic variability response functions. Using this expression spectral-distribution-free upper bounds of the buckling load variability are established. Further, the buckling load variability for prescribed forms of the spectral density functions is calculated. Using a local average approach, the commercial finite-element package ABAQUS is incorporated into the analysis of these random buckling loads. The technique is applied to study variability of the critical buckling load of a stiffened steel plate used in experiments to model a barge deck.     

Effect of Longitudinal Stress Gradients on Elastic Buckling of Thin Plates

This paper analyzes the effect of longitudinal stress gradients on the elastic buckling of thin isotropic plates. Two types of thin plates are considered: (1) a plate simply supported on all four edges and rotationally restrained on two longitudinal edges; and (2) a plate simply supported on three edges with one longitudinal edge free and the opposite longitudinal edge rotationally restrained. These two cases illustrate the influence of longitudinal stress gradient on stiffened and unstiffened elements, respectively. A semianalytical method is derived and presented herein to calculate the elastic-buckling stress of both types of rectangular thin plates subjected to nonuniform applied longitudinal stresses. Finite-element analysis using ABAQUS is employed to validate the semianalytical model for plates with fixed and/or simple supports. Empirical formulas are produced to calculate the buckling coefficients of plates with fixed and/or simple supports under longitudinal stress gradients. The results help establish a better understanding of the effect of longitudinal stress gradients on the elastic buckling of thin plates and are intended to aid in the development of design provisions to include these effects in the strength prediction of thin-walled beams under moment gradients.     

Global Search Method for Locating General Slip Surface Using Monte Carlo Techniques

Searching for the critical slip surface and the lowest factor of safety in slope stability analysis can be achieved by means of optimization techniques. A new search procedure in generating kinematically admissible slip surfaces has been introduced in this paper. Such a procedure is based, mainly, on the Monte Carlo methods, where both the critical global slip surface as well as its associated factor of safety is determined. Several practical examples, of known minimum factor of safety and its associated slip surface, have been used to demonstrate the efficiency and capability of the proposed method. The method is intended to be robust and effective to solve problems that involve extremely complicated slope geometry. It is as powerful as any other powerful optimization methods.     

Robust Optimal Design of Activated Sludge Bioreactors

This paper proposes an algorithm for a robust optimal design of the biological reactor and secondary settling facilities in suspended growth nitrogen and phosphorus removal systems. Robust optimization includes uncertainty in the decision-making procedure and seeks a solution that remains “close” to optimal for all potential operation scenarios. It thus differs fundamentally from the deterministic and stochastic approaches, where uncertainty is ignored or a solution based on either the most likely scenario or the average performance over all potential scenarios is produced. The robust optimization of a suspended growth system is a multiobjective optimization problem concerned with minimization of the global costs and variability of the system’s performance around the optimal. The proposed robust optimization approach uses the ASM3 model, making use of its performance prediction capabilities to produce a powerful tool for designing activated sludge systems. The algorithm was applied to the design of the biological reactor and secondary settling facilities for the Vila Real municipal wastewater treatment plant (Portugal).     

抗弯刚度比对加劲板屈曲性能的影响

以一大型薄壁钢结构的加劲板为研究对象,采用有限元方法,考虑了13种不同的刚度比、多种不同的加劲肋布置方式以及边界条件等因素,分析了加劲板线性屈曲和非线性屈曲性能.抗弯刚度比对加劲板的屈曲性能影响显著,加劲板最佳抗弯刚度比将其线性屈曲模态划分为整体屈曲和局部屈曲,其值为10~20.加劲板非线性屈曲荷载随抗弯刚度比增大而提高.另外,在加载方向增加加劲肋布置可以提高加劲板局部屈曲荷载,在非加载方向增加加劲肋布置对加劲板的局部屈曲性能影响较小.      

Comparison of Using Mixed-Integer Programming and Genetic Algorithms for Construction Site Facility Layout Planning

The use of modular construction has gained wide acceptance in the industry. For a specific construction facility layout problem such as site precast standardized modular units, it requires the establishment of an on-site precast yard. Arranging the precast facilities within a construction site presents real challenge to site management. This complex task is further augmented with the involvement of several resources and different transport costs. A genetic algorithm (GA) model was developed for the search of a near-optimal layout solution. Another approach using mixed-integer programming (MIP) has been developed to generate optimal facility layout. These two approaches are applied to solve with an example in this paper to demonstrate that the solution quality of MIP outperforms that of GA. Further, another scenario with additional location constraints can also be solved readily by MIP, which, however, if modeled by GA, the solution process would be complicated. The study has highlighted that MIP can perform better than GA in site facility layout problems in which the site facilities and locations can be represented by a set of integer variables.     

Development of High Deformation X70 Pipeline Steel Plates in NISCO

A series of trial tests for high deformation (HD) X70 pipeline steel plates were performed in NISCO,and the technical routes as thermal mechanical controlled rolling process (TMCP),TMCP + Quenching (Q) and TMCP +Q & tempering (T) were studied systematically through the plate shape quality,properties and microstructure characters.The results show that problems as plate shape and inhomogeneous microstructures are for finish rolling at low temperature and high cooling rate after the rolling by the route of TMCP.By the route of TMCP+Q,the yield strength (YS) of the trial steels is not sufficient.By the route of TMCP+QT,the YS is enhanced,as well as good toughness and plasticity due to the martensite decomposition at low temperature tempering process,and 4 sheets of HD X70 pipeline steel plates by the route TMCP+QT with superior plate shape quality,microstructure and comprehensive properties were successfully developed in NISCO.     

Thermal Postbuckling Behavior of Composite Sandwich Plates

By considering the total transverse displacement of a sandwich plate as the sum of the displacement due to bending of the plate and that due to shear deformation of the core, a 72 degrees of freedom high precision high order triangular-plate element is developed for the thermal postbuckling analysis of rectangular composite sandwich plates. Due to an uneven thermal expansion coefficient in the two local material directions, the buckling mode of the plate can be changed from one mode to another as the fiber orientation or aspect ratio of the plate is varied. By examining the local minimum of total potential energy of each mode, a clear picture of buckle pattern change is presented. Numerical results show that for a sandwich plate with cross-ply laminated faces, buckle pattern change may occur when the plate has a long narrow shape. However, for sandwich plates with angle-ply laminated faces, the buckling mode is dependent on the fiber orientation and aspect ratio of the plate. The effect of temperature gradient on the postbuckling behavior of the sandwich plate is limited except for angle-ply laminated sandwich plates with fiber angle greater than 70° or less than 20°.     

Informational social influence and product quality judgments.

Eight groups of 15 college females each rated the quality of 1 paper plate while exposed to simulated quality evaluations of other raters. Others' evaluations were manipulated by presenting the modal evaluation as higher or lower than the control (no influence) mean rating and by varying the uniformity of others' ratings at 2 levels of dispersion. The availability of intrinsic (product composition) cues during prerating examination of the plate was manipulated by making available, or withholding, 2 comparison plates. Others' modal evaluations significantly affected the Ss' quality ratings of the plate. This effect was substantially stronger when others' evaluations were more uniform. The presence or absence of comparison plates had no effect on the influence conditions. Results are interpreted, in conjunction with those of J. B. Cohen and E. Golden (see record 1972-11926-001) as providing support for the effect of informational social influence on ratings of product quality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)