A parameter optimization heuristic for a temperature estimation model

We present a heuristic technique for solving a parameter estimation problem that arises in modeling the thermal behavior of electronic chip packages. Compact Thermal Models (CTMs) are network models of steady state thermal behavior, which show promise in augmenting the use of more detailed and computationally expensive models. The CTM parameter optimization problem that we examine is a nonconvex optimization problem in which we seek a set of CTM parameters that best predicts, under general conditions, the thermal response of a particular chip package geometry that has been tested under a small number of conditions. We begin by developing a nonlinear programming formulation for this parameter optimization problem, and then develop an algorithm that uses special characteristics of the optimization problem to quickly generate heuristic solutions. Our algorithm descends along a series of solutions to one-dimensional nonconvex optimization problems, obtaining a locally optimal set of model parameters at modest computational cost. Finally, we provide some experimental results and recommendations for extending this research. The authors are indebted to four anonymous referees for their help in improving the contribution and presentation of this paper.     

Aircraft parameter estimation — A tool for development of aerodynamic databases

With the evolution of high performance modern aircraft and spiraling developmental and experimental costs, the importance of flight validated databases for flight control design applications and for flight simulators has increased significantly in the recent past. Ground-based and in-flight simulators are increasingly used not only for pilot training but also for other applications such as flight planning, envelope expansion, design and analysis of control laws, and handling qualities investigations. Most of these demand a high-fidelity aerodynamic database representing the flight vehicle. System identification methodology, evolved over the past three decades, provides a powerful and sophisticated tool to identify from flight data aerodynamic characteristics valid over the entire operational flight envelope. This paper briefly presents aircraft parameter estimation methods for both stable and unstable aircraft, highlighting the developmental work at the DLR Institute of Flight Mechanics. Various aspects of database identification and its validation are presented. Practical aspects like the proper choice of integration and optimization methods as well as limitations of gradient approximation through finite-differences are brought out. Though the paper focuses on application of system identification methods to flight vehicles, its use in other applications, like the modelling of inelastic deformations of metallic materials, is also presented. It is shown that there are many similar problems and several challenges requiring additional concepts and algorithms.     

Creep and shrinkage prediction model for analysis and design of concrete structures— model B3

RILEM Draft Recommendation107-GCS Guidelines for the Formulation of Creep and Shrinkage Prediction Models

Creep and shrinkage prediction model for analysis and design of concrete structures— model B₃     

Anisotropic and tension–compression asymmetric model for composites consolidation

A constitutive model for anisotropic and tension–compression asymmetric response of a fibrous preform is developed and solved using a FE software. Applicability of the method to complex geometries is demonstrated by analysis the consolidation of an axisymmetric filament wound pressure vessel made from commingled yarns. Three different winding patterns are considered. In conclusions, the consolidation of the whole vessel, except at the opening, is prevented by the loading mode, where the pressure is applied on the interior. To succeed in manufacturing of this type of pressure vessel, use of an oversized preform that allows extension in the fibre direction is suggested.     

An analog of the Rayleigh–Sommerfeld integral for anisotropic and gyrotropic media

In this work, the integral representations of Maxwell’s equations solutions for anisotropic and gyrotropic media with separable longitudinal and transverse components are derived in a complete analytic form. In particular cases, the integral expressions are reduced to an analog of the Rayleigh–Sommerfeld integral.     

An elastic–plastic asperity contact model and its application for micro-contact analysis of gear tooth profiles

This paper presents a continuous elastic–plastic asperity contact model with or without the consideration of friction to investigate the micro-contact properties of gear tooth profiles. The model for normal or side contact analysis is established according to Hertz contact theory and the asperity morphology feature, which yields to similar results as obtained from the model proposed by Chang W.R., Etsion I., and Bogy D.B. (CEB model) and the model proposed by Kogut L. and Etsion I. (KE model). More importantly, this model avoids the constant average contact stress as predicted by the CEB model, and the noncontinuous contact stress and deformation within the ultimate strength as given by the KE model. As a application of the present theoretical model in micro-contact analysis of rough tooth profiles, a finite element model (FE model) for elastic–plastic asperity in normal or side contact is established according to the measured surface parameters of a spur gear pair. It is shown that the extreme point of Von Mise stress of the asperities along the normal vector is ascertained by FE model, and that the extreme point is relative to the initial occurrence of the asperities plastic deformation. Compared with the present theoretical model, the similar normal contact stress along the contact radius is attained by FE model. Though the contact stress isogram in the specific plane in normal or side contact of the asperities is a circle or ellipse respectively when the plastic deformation is expanded from the inside of the asperities to their surfaces, it is in line with the distribution of elastic and plastic region of the theoretical model. Compared with CEB model, KE model, and FE model, the consistent results are attained by the present theoretical model in elastic–plastic asperity contact analysis. The results indicate that the theoretical model is applicable to the elastic–plastic asperity contact analysis on the rough surface of a spur gear drive.     

An analytical model for predicting the freeze–thaw durability of wood–fiber composites

The development and validation of an analytical model that predicts the onset of frost-induced damage in wood–plastic composites (WPCs) is presented in this work. The mathematical model is based on the mechanics of a hollow cylinder subjected to an internal pressure caused by the expansion of freezing moisture bound in the wood–fiber reinforcement. The model is substantiated using experimental data from several published studies. Using a stochastic approach, the model is implemented to analyze the effect of wood fiber specie, fiber volume fraction, and matrix material properties on the frost resistance of fully and partially saturated WPCs. Results show that WPCs with high fiber contents, high moisture contents, and low polymer tensile strengths are most susceptible to frost-induced damage. Data also suggest that the use of softwood fibers (e.g., pine, spruce) and polymers with low moduli and high tensile strengths enhances the frost-resistance of WPCs.     

Multidimensional parallelepiped model—a new type of non-probabilistic convex model for structural uncertainty analysis

Non-probabilistic convex models need to be provided only the changing boundary of parameters rather than their exact probability distributions; thus, such models can be applied to uncertainty analysis of complex structures when experimental information is lacking. The interval and the ellipsoidal models are the two most commonly used modeling methods in the field of non-probabilistic convex modeling. However, the former can only deal with independent variables, while the latter can only deal with dependent variables. This paper presents a more general non-probabilistic convex model, the multidimensional parallelepiped model. This model can include the independent and dependent uncertain variables in a unified framework and can effectively deal with complex ‘multi-source uncertainty’ problems in which dependent variables and independent variables coexist. For any two parameters, the concepts of the correlation angle and the correlation coefficient are defined. Through the marginal intervals of all the parameters and also their correlation coefficients, a multidimensional parallelepiped can easily be built as the uncertainty domain for parameters. Through the introduction of affine coordinates, the parallelepiped model in the original parameter space is converted to an interval model in the affine space, thus greatly facilitating subsequent structural uncertainty analysis. The parallelepiped model is applied to structural uncertainty propagation analysis, and the response interval of the structure is obtained in the case of uncertain initial parameters. Finally, the method described in this paper was applied to several numerical examples. Copyright © 2015 John Wiley & Sons, Ltd.     

Iceberg stability — An error analysis

Towing icebergs to protect offshore drilling operations in iceberg rich waters is a constant problem for oil companies. Unstable icebergs are especially problematical, being notoriously difficult to tow. Evidently being able to detect potentially unstable icebergs would be beneficial. In this paper, the authors consider the possibility of using underwater sonar mapping techniques to determine the geometry of the iceberg and thence its stability characteristics. The question as to whether or not that might be performed sufficiently accurately to be able to detect the effect of a 100 t pull on an iceberg is considered. Using a simple ‘Monte Carlo’ error model it is shown that such a determination of an iceberg's stability is unlikely to be acheived except possibly for sufficiently small icebergs.     

Effects of pressure sensitivity on the η factor and the J integral estimation for compact tension specimens

In this paper, the effects of pressure-sensitive yielding on the factor and the J integral estimation for compact tension specimens are investigated. The analytical expressions for and J for pressure-insensitive von Mises materials are generalized to pressure-sensitive Drucker-Prager materials using a lower bound approach. The factor as a function of the pressure sensitivity and the normalized crack depth for compact tension specimens is derived under plane stress and plane strain conditions. The numerical results indicate that the factor decreases as the pressure sensitivity increases. The effects are more pronounced under plane strain conditions than under plane stress conditions. However, the effects of the pressure sensitivity on are found to be mild in general. For rigid perfectly-plastic materials, the J estimation for pressure-sensitive materials is also reduced to a simple expression of the tensile yield stress times the crack tip opening displacement as for the von Mises materials.     

Speckle interferometry for analysing anisotropic thermal expansion—application to specimens and components

This paper describes a non-destructive optical technique, digital speckle pattern interferometry (DSPI), that has been developed particularly for strain analysis and has proved well suited for thermal deformation measurement. Fibre-reinforced composites with both metal and polymer matrices have been analysed by DSPI to determine their thermal expansion behaviour as a function of direction and temperature. Complete series of measurements can be performed quickly and without any restriction on the specimen shape. Engineering components including composite structures have been the subject of investigation. Besides quantitative results, real-time observation provides basic information for materials understanding.     

Cramér-Rao analysis of orientation estimation: influence of target model uncertainties

We explore the use of Cramér-Rao bound calculations for predicting fundamental limits on the accuracy with which target characteristics can be determined by using imaging sensors. In particular, estimation of satellite orientation from high-resolution sensors is examined. The analysis role that such bounds provide for sensor/experiment design, operation, and upgrade is discussed. Emphasis is placed on the importance of including all relevant target/sensor uncertainties in the analysis. Computer simulations are performed that illustrate that uncertainties in target features (e.g., shape, reflectance, and relative orientation) have a significant impact on the bounds and provide considerable insight as to how details of the three-dimensional target structure may influence the estimation process. The simulations also address the impact that a priori information has on the bounds.     

A two‐parameter quasi‐linear model for gauged river basins

Abstract

Two rainfall intensity dependent parameters are incorporated into a quasi‐linear representation of the outflow to analyze the hydro‐logic response problems of a gauged river basin.

The model is employed to generate the unit hydrographs of a (non‐linear) small basin due to different rainfall inputs, to exhibit the storage‐discharge relation in a medium basin due to a single storm event, and to synthesize the rainfall‐runoff process in two large river basins due to storm events at different times. In all three cases, the analytical results from the model compare nicely with the experimental observations.     

Metamodel-based inverse method for parameter identification: elastic–plastic damage model

This article proposed a metamodel-based inverse method for material parameter identification and applies it to elastic–plastic damage model parameter identification. An elastic–plastic damage model is presented and implemented in numerical simulation. The metamodel-based inverse method is proposed in order to overcome the disadvantage in computational cost of the inverse method. In the metamodel-based inverse method, a Kriging metamodel is constructed based on the experimental design in order to model the relationship between material parameters and the objective function values in the inverse problem, and then the optimization procedure is executed by the use of a metamodel. The applications of the presented material model and proposed parameter identification method in the standard A 2017-T4 tensile test prove that the presented elastic–plastic damage model is adequate to describe the material's mechanical behaviour and that the proposed metamodel-based inverse method not only enhances the efficiency of parameter identification but also gives reliable results.     

A simple model for geo‐materials involving shear‐induced anisotropic degradation

Abstract

When geo‐materials, such as soil, gravelly soil and soft rocks, are loaded by shear stress, they frequently exhibit volumetric deformation, either dilation or compression, that cannot be modeled by conventional elasticity of isotropic material. This study aims, using as few parameters as possible, to develop a material model designed to simulate the main deformation of geo‐materials. A constitutive model based on the concept of shear‐induced anisotropic degradation is proposed. The proposed constitutive model is characterized by the following features: (1) significant shear‐induced volumetric deformation prior to failure, (2) modulus stiffening under hydrostatic loading and degradation under shearing; (3) stress‐induced anisotropy; and (4) being versatile in representing many geo‐materials and their behaviors under various stress paths.

In the proposed model, the deformational moduli, E, G, and G ^', vary according to stress state. The stiffening and degradation of these moduli render the deformational behavior of geo‐materials. The proposed model needs only six material parameters, all of which possess physical meaning and can be easily obtained. Finally, the versatility of the proposed model is demonstrated by simulating various geo‐materials such as sandstone, gravelly soil and shale loaded under different stress paths.     

Optical methods for complete stress determination — An experimental alternative to finite-element analysis

Experimental optics provides an interesting alternative to finite-element analysis (FEA) for estimating stress distribution in bodies subjected to load. Complete determination of the state of stress in a two-dimensional transparent model of the body was performed, using modern interferometry in combination with conventional photoelasticity. Stress concentrations and singularities may be evaluated in the same experimental set-up by means of the methods of caustics.The present approach eliminates the effect of limited optical quality of the model material, which is an advantage in engineering applications of the methods proposed. In contrast to most testing procedures using interferometry, this technique provides particularly simple handling of equipment and ease in evaluation. The paper describes an application to restorative dentistry of these methods of experimental stress analysis.