Strength Hypothesis Applied to Hard Foams

2011 ◽  
Vol 70 ◽  
pp. 99-104 ◽  
Author(s):  
Vladimir A. Kolupaev ◽  
Alexandre Bolchoun ◽  
Holm Altenbach
Keyword(s):  
Experimental Data ◽  
Closed Surface ◽  
Material Behavior ◽  
Optimal Solutions ◽  
Objective Functions ◽  
Stress Space ◽  
Hydrostatic Tension ◽  
Special Cases ◽  
Tension And Compression ◽  
Principal Stress Space

The analysis of well-known strength hypotheses leads to the derivation of a generalized model, which contains a number of known hypotheses as special cases and could be used for the description of the 3D-failure of hard foams. This model in the case of the strength hypothesis for hard foams is characterized by a closed surface in the principal stress space. In order to fit the model to the experimental data certain objective functions are formulated. The optimization results are shown in the Pareto-diagram (optimal solutions for several targets). The results of the fitting are plotted in the Burzyński-plane. It can be seen that reliable modeling requires the knowledge of the material behavior under hydrostatic tension and compression.

Extension of a Material Model for Pipeline Steels

2012 ◽  
Author(s):  
James D. Hart ◽  
Nasir Zulfiqar ◽  
Joe Zhou ◽  
Keith Adams
Keyword(s):  
Pipe Steel ◽  
Material Behavior ◽  
Matched Pair ◽  
Pipe Material ◽  
Stress Space ◽  
Stress Strain ◽  
Fitting Procedure ◽  
Yield Functions ◽  
Tension And Compression ◽  
Longitudinal Tension

Pipeline steel stress-strain curves obtained from tension and compression testing of longitudinally and circumferentially oriented specimens of the pipe wall can be significantly different e.g., the pipe material is anisotropic. The anisotropic behavior can result from the manufacturing process (e.g., due to cold expansion of UOE pipe) and can also be influenced by strain aging effects (e.g., due to heated application of pipe coating materials). As described in previous work, the Mroz multilinear kinematic hardening plasticity theory has the ability to accurately model different types of anisotropic pipe material behavior including relatively “sharp” uniaxial circumferential tension response and relatively well-rounded uniaxial longitudinal tension and compression response. The stress-strain curve fitting is accomplished by essentially selecting the sizes and initial positions of elliptical von Mises yield functions in stress-space. A previously developed and published 8-parameter model is well-suited for fitting a matched pair of longitudinal tension (LT) and hoop tension (HT) stress-strain curves as might typically be available from a strain-based pipeline design project. Fitting a pair of “target” LT-HT stress-strain curves is accomplished using a “2-root” fitting procedure where the roots correspond to locations where the yield functions intercept the stress axes in two-dimensional (longitudinal-hoop) stress space. In this paper, the previously described 8-parameter/2-root fitting procedure is extended to a 10-parameter/3-root fitting procedure for situations where a matched “triple” of pipe steel stress-strain curves are available (e.g., LT, HT and longitudinal compression or LC). This extension allows for analysis of strain-based design conditions using an analytical pipe steel, which provides an accurate representation of the uniaxial longitudinal and circumferential stress-strain response of the pipeline material. This paper reviews the 8-parameter/2-root fitting procedure and outlines the extension to the 10-parameter/3-root fitting approach including example application.

Study of Strength Criterion for Dynamic Compression of Concrete under Biaxial Equal Proportion Loading

2010 ◽  
Vol 163-167 ◽  
pp. 1819-1822
Author(s):  
Guan Ping ◽  
Peng Liu ◽  
Tao Xu
Keyword(s):  
Experimental Data ◽  
Stress Ratio ◽  
Dynamic Compression ◽  
Strength Criterion ◽  
Biaxial Stress ◽  
Strain Rates ◽  
Equal Proportion ◽  
Stress Space ◽  
Principal Stress Space ◽  
Stress Ratios

The dynamic compressive experiments of cubic concrete specimens under various biaxial equal proportion loading were preformed. The biaxial equal proportion stress in the tests were kept constant at 1:0, 1:0.5 and 1:1, respectively, and the tested strain rate ranged from 10−5/s to 10−2/s. Based on the experimental results, the influence of the strain rates on compressive characteristics of concrete under various biaxial stress ratios were researched. The unified strength criterion in terms of principal stress space considering the influence of strain rates and biaxial stress ratio is proposed. The fitting curves by the present strength criterion agree well with experimental data.

Multi Objective Design Optimization of Two Bar Truss Using NSGA II and TOPSIS

2014 ◽  
Vol 984-985 ◽  
pp. 419-424
Author(s):  
P. Sabarinath ◽  
M.R. Thansekhar ◽  
R. Saravanan
Keyword(s):  
Design Optimization ◽  
Optimization Problems ◽  
Optimization Methods ◽  
Optimal Solutions ◽  
Objective Functions ◽  
Nsga Ii ◽  
Multi Objective ◽  
Total Displacement ◽  
Design Variables ◽  
Conflicting Objectives

Arriving optimal solutions is one of the important tasks in engineering design. Many real-world design optimization problems involve multiple conflicting objectives. The design variables are of continuous or discrete in nature. In general, for solving Multi Objective Optimization methods weight method is preferred. In this method, all the objective functions are converted into a single objective function by assigning suitable weights to each objective functions. The main drawback lies in the selection of proper weights. Recently, evolutionary algorithms are used to find the nondominated optimal solutions called as Pareto optimal front in a single run. In recent years, Non-dominated Sorting Genetic Algorithm II (NSGA-II) finds increasing applications in solving multi objective problems comprising of conflicting objectives because of low computational requirements, elitism and parameter-less sharing approach. In this work, we propose a methodology which integrates NSGA-II and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) for solving a two bar truss problem. NSGA-II searches for the Pareto set where two bar truss is evaluated in terms of minimizing the weight of the truss and minimizing the total displacement of the joint under the given load. Subsequently, TOPSIS selects the best compromise solution.

Mathematical Modelling of Materials Behavior Under Creep Conditions

2001 ◽  
Vol 54 (2) ◽  
pp. 107-132 ◽  
Author(s):  
J. Betten
Keyword(s):  
Experimental Data ◽  
Mathematical Modelling ◽  
Mechanical Behavior ◽  
Review Article ◽  
Material Behavior ◽  
Experimental Investigations ◽  
Rational Basis ◽  
Complex Material ◽  
Interpolation Methods ◽  
Materials Behavior

This article will provide a short survey of some recent advances in the mathematical modelling of materials behavior under creep conditions. The mechanical behavior of anisotropic solids requires a suitable mathematical modelling. The properties of tensor functions with several argument tensors constitute a rational basis for a consistent mathematical modelling of complex material behavior. This article presents certain principles, methods, and recent successful applications of tensor functions in creep mechanics. The rules for specifying irreducible sets of tensor invariants and tensor generators for material tensors of rank two and four are also discussed. Furthermore, it is very important that the scalar coefficients in constitutive and evolutional equations are determined as functions of the integrity basis and experimental data. It is explained in detail that these coefficients can be determined by using tensorial interpolation methods. Some examples for practical use are discussed. Finally, we have carried out our own experiments to examine the validity of the mathematical modelling. Furthermore, an overview of some important experimental investigations in creep mechanics of other scientists has been provided. There are 243 references cited in this review article.

An enhanced surrogate-assisted differential evolution for constrained optimization problems

2021 ◽  
Author(s):  
Rafael de Paula Garcia ◽  
Beatriz Souza Leite Pires de Lima ◽  
Afonso Celso de Castro Lemonge ◽  
Breno Pinheiro Jacob
Keyword(s):  
Differential Evolution ◽  
Optimization Problems ◽  
Optimization Procedure ◽  
Nearest Neighbors ◽  
Engineering Optimization ◽  
Optimal Solutions ◽  
Objective Functions ◽  
Constrained Optimization Problems ◽  
Engineering Problems ◽  
Complex Engineering

Abstract The application of Evolutionary Algorithms (EAs) to complex engineering optimization problems may present difficulties as they require many evaluations of the objective functions by computationally expensive simulation procedures. To deal with this issue, surrogate models have been employed to replace those expensive simulations. In this work, a surrogate-assisted evolutionary optimization procedure is proposed. The procedure combines the Differential Evolution method with a Anchor -nearest neighbors ( –NN) similarity-based surrogate model. In this approach, the database that stores the solutions evaluated by the exact model, which are used to approximate new solutions, is managed according to a merit scheme. Constraints are handled by a rank-based technique that builds multiple separate queues based on the values of the objective function and the violation of each constraint. Also, to avoid premature convergence of the method, a strategy that triggers a random reinitialization of the population is considered. The performance of the proposed method is assessed by numerical experiments using 24 constrained benchmark functions and 5 mechanical engineering problems. The results show that the method achieves optimal solutions with a remarkably reduction in the number of function evaluations compared to the literature.

scholarly journals Evaluation Method of Multiobjective Functions’ Combination and Its Application in Hydrological Model Evaluation

2020 ◽  
Vol 2020 ◽  
pp. 1-23 ◽  
Author(s):  
Jiuyuan Huo ◽  
Liqun Liu
Keyword(s):  
Objective Function ◽  
Parameter Optimization ◽  
Optimization Problem ◽  
Hydrological Model ◽  
Pareto Optimal ◽  
Pareto Optimal Solutions ◽  
Optimal Solutions ◽  
Objective Functions ◽  
Hydrological Forecasting ◽  
Model Parameter Optimization

Parameter optimization of a hydrological model is intrinsically a high dimensional, nonlinear, multivariable, combinatorial optimization problem which involves a set of different objectives. Currently, the assessment of optimization results for the hydrological model is usually made through calculations and comparisons of objective function values of simulated and observed variables. Thus, the proper selection of objective functions’ combination for model parameter optimization has an important impact on the hydrological forecasting. There exist various objective functions, and how to analyze and evaluate the objective function combinations for selecting the optimal parameters has not been studied in depth. Therefore, to select the proper objective function combination which can balance the trade-off among various design objectives and achieve the overall best benefit, a simple and convenient framework for the comparison of the influence of different objective function combinations on the optimization results is urgently needed. In this paper, various objective functions related to parameters optimization of hydrological models were collected from the literature and constructed to nine combinations. Then, a selection and evaluation framework of objective functions is proposed for hydrological model parameter optimization, in which a multiobjective artificial bee colony algorithm named RMOABC is employed to optimize the hydrological model and obtain the Pareto optimal solutions. The parameter optimization problem of the Xinanjiang hydrological model was taken as the application case for long-term runoff prediction in the Heihe River basin. Finally, the technique for order preference by similarity to ideal solution (TOPSIS) based on the entropy theory is adapted to sort the Pareto optimal solutions to compare these combinations of objective functions and obtain the comprehensive optimal objective functions’ combination. The experiments results demonstrate that the combination 2 of objective functions can provide more comprehensive and reliable dominant options (i.e., parameter sets) for practical hydrological forecasting in the study area. The entropy-based method has been proved that it is effective to analyze and evaluate the performance of different combinations of objective functions and can provide more comprehensive and impersonal decision support for hydrological forecasting.

scholarly journals BOFdat: Generating biomass objective functions for genome-scale metabolic models from experimental data

2019 ◽  
Vol 15 (4) ◽  
pp. e1006971 ◽  
Author(s):  
Jean-Christophe Lachance ◽  
Colton J. Lloyd ◽  
Jonathan M. Monk ◽  
Laurence Yang ◽  
Anand V. Sastry ◽  
...  
Keyword(s):  
Experimental Data ◽  
Objective Functions ◽  
Metabolic Models ◽  
Genome Scale

scholarly journals Stochastic Search Technique with Variable Deterministic Constraints for the Estimation of Induction Motor Parameters

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 273
Author(s):  
Carmenza Moreno Roa ◽  
Adolfo Andrés Jaramillo Matta ◽  
Juan David Bastidas Rodríguez
Keyword(s):  
Experimental Data ◽  
Induction Motor ◽  
Stochastic Search ◽  
The Other ◽  
Objective Functions ◽  
Search Technique ◽  
Single Cage ◽  
New Strategy ◽  
A New Technique ◽  
Stochastic Search Technique

This paper deals with the implementation of a new technique of stochastic search to find the best set of parameters in a mathematical model, applied to the single cage (SC) model of the induction motor (IM). The technique includes a new strategy to generate variable constraints of the domain, seven error functions, weight for the operating zones of the IM, and multi-objective functions. The results are validated with experimental data of the torque and current in an IM, and show better fitting to the experimental curves compared with the results of two different techniques, one deterministic and the other one stochastic. The results obtained allow us to conclude that the best set of parameters for the model depends on the weights assigned to the objective functions and to the operating zones.

Implosion Analysis of Concrete Cylindrical Vessels

1979 ◽  
Vol 101 (1) ◽  
pp. 98-102
Author(s):  
H. Suzuki ◽  
W. F. Chen ◽  
T. Y. Chang
Keyword(s):  
Experimental Data ◽  
Finite Element Analysis ◽  
Fracture Behavior ◽  
Constitutive Relations ◽  
Analysis Procedure ◽  
Material Behavior ◽  
Ultimate State ◽  
Element Analysis ◽  
Proposed Model ◽  
Effect Of Hydrostatic Pressure

Concrete constitutive relations which can simulate the overall material behavior up to and including its ultimate state under general triaxial loading conditions have been developed. The proposed constitutive relations include: 1) plastic deformation considering the effect of hydrostatic pressure, 2) a dual criterion predicting the fracture of concrete in terms of either stresses or strains, and 3) post-fracture behavior of concrete. Corresponding to the constitutive model, a finite element analysis procedure has also been utilized. Based on the proposed model, implosion pressures and load-deformation responses of several concrete vessels were obtained. The numerical results correlate quite well with the experimental data when the dual criterion was used.

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