On the validation of solid mechanics models using optical measurements and data decomposition

Engineering simulation has a significant role in the process of design and analysis of most engineered products at all scales and is used to provide elegant, light-weight, optimized designs. A major step in achieving high confidence in computational models with good predictive capabilities is model validation. It is normal practice to validate simulation models by comparing their numerical results to experimental data. However, current validation practices tend to focus on identifying hot-spots in the data and checking that the experimental and modeling results have a satisfactory agreement in these critical zones. Often the comparison is restricted to a single or a few points where the maximum stress/strain is predicted by the model. The objective of the present paper is to demonstrate a step-bystep approach for performing model validation by combining full-field optical measurement methodologies with computational simulation techniques. Two important issues of the validation procedure are discussed, i.e. effective techniques to perform data compression using the principles of orthogonal decomposition, as well as methodologies to quantify the quality of simulations and make decisions about model validity. An I-beam with open holes under three-point bending loading is selected as an exemplar of the methodology. Orthogonal decomposition by Zernike shape descriptors is performed to compress large amounts of numerical and experimental data in selected regions of interest (ROI) by reducing its dimensionality while preserving information; and different comparison techniques including traditional error norms, a linear comparison methodology and a concordance coefficient correlation are used in order to make decisions about the validity of the simulation

Computational model validation of structural components by full-field optical measurements

The primary objective of the present work is to demonstrate the full field validation methodology proposed in [1], for the comparison of simulation and experimental displacement and strain results acquired by simulation and Digital Image Correlation (DIC). Three-point bending of an I-beam with open holes in the web has been selected for the investigation. Perforated I-beams are widely used in light-weight structures e.g. as aircraft wing spars, in civil engineering e.g. in metallic building frames, as well as in other civilian applications . The I-beam deformation was captured with by a three-dimensional DIC optical system, deployed for this purpose. A detailed Finite Element model was also developed in order to predict the stress / strain and displacement fields under three-point bending loading. In Figure 1 (left), the three-point bending experimental set-up of the aluminum I-beam is shown. A finite element model of the aluminum beam under three-point bending is generated using 23136 Ansys type 'shell181' elements (Figure 1-right). A finer mesh is generated around the open holes. An elastoplastic material model with kinematic hardening is used. The numerical post-processing includes the acquisition of beam full-field displacement and strain contour plots, such as comparisons to the respective experimental results on the selected regions of interests of the beam web is performed (Figure 2). Before a comparison between modelling and experimental data is performed. a radical reduction of the dimensionality of data fields from a matrix consisting of million values to a feature vector with, ideally between twenty and hundred elements is required. An efficient means for performing this task is the application of image decomposition techniques based on e.g. orthogonal polynomials. Zernike polynomials were used for data decomposition of displacement and strain data fields in the present case. Once DIC and FE displacement and strain images are decomposed, feature vectors are available from both experimental and numerical results, which are compared against one another, in the form of the plot shown in Figure 3. Concluding, a quantitative comparison between DIC displacement / strain maps and the respective FE data by exploiting the capabilities of Zernike moment decomposition was performed and the validity of simulation was assessed. A reliable validation methodology of computational solid mechanics models has been successfully demonstrated in the case of a common structural element of many engineering applications

The 1999 Center for Simulation of Dynamic Response in Materials Annual Technical Report

Introduction: This annual report describes research accomplishments for FY 99 of the Center for Simulation of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility in which the full three dimensional response of a variety of target materials can be computed for a wide range of compressive, ten- sional, and shear loadings, including those produced by detonation of energetic materials. The goals are to facilitate computation of a variety of experiments in which strong shock and detonation waves are made to impinge on targets consisting of various combinations of materials, compute the subsequent dy- namic response of the target materials, and validate these computations against experimental data

Bidirectional irradiance transposition based on the Perez model

The Perez irradiance model offers a practical representation of solar irradiance by considering the sky hemisphere as a three-part geometrical framework, namely, the circumsolar disc, the horizon band and the isotropic background. Furthermore, the simplified Perez diffuse irradiance model, commonly known as the Perez transposition model, is one of the most widely adopted models in tilted irradiance modeling. Although the set of model coefficients reported by Perez et al. (1990) is considered to be at an asymptotic level of optimization, later analyses have shown that coefficients which are adjusted to local conditions may perform better than the original set.<p></p> The model coefficients can be adjusted locally based on multiple datasets of diffuse and global irradiance on tilted and horizontal planes. In this paper, we present a different approach to adjust the coefficients, by using only measurements of global irradiance on tilted and horizontal planes from a tropical climate site, Singapore. A complete set of mathematical solutions to the inverse problem, i.e., irradiance transposition from tilt to horizontal, is also proposed. The data can then be used to generate irradiance maps from in-plane irradiance measurements at photovoltaics (PV) systems. Such maps provide relevant information for PV grid integration.<p></p&gt