Papers by Keyword: Inverse Problem

Abstract: This paper describes an interesting approach aimed at analysis of material properties. This work is based on simulated measurements of transmission coefficients of multi-layered materials. These measurements (in a waveguide) are taken as a product of a certain situation, therefore there is an inverse problem in which we try to estimate the original properties of the layers. This study employs analysis of closed-form solutions and numerical multi-parameter optimization.

Abstract: An efficient numerical approximation for two phase flow in 1D is presented. Mathematicalmodel is based on two Richard’s type equations using Van Genuchten-Mualem (vG-M) model for capillarypressure-saturation and hydraulic permeability versus saturation of wetting liquid. The wettingand non-wetting liquids are incompressible and immiscible. The method is suitable for determinationof soil parameters (as a tunning parameters in vG-M model) via solution of inverse problem. Wettingliquid (-water) is injected into the sample originally saturated with non-wetting liquid (-oil) by gravitation,or centrifuge driving forces. In a series of experiments we discuss noninvasive (easy-to-measure)measurement scenarios which are satisfactory in a solution of inverse problem.

Abstract: This paper studies on the eigenvalue^[1-5] of the a class of upper triangular matrix with linear relation. It discusses the feature of existence and uniqueness of matrix via two given two characteristic pairs(λ,χ),(μ,γ) . Solutions and expressions are provided under satisfied conditions. The possibilities are exanimated by numerical example.

Abstract: Based on a brief review of the developing history of vehicle handling inverse dynamics. Using radial basis function neural networks, completely considered the cornering force of tyres, the nonlinear mapping relation between lateral angular velocity and steering angle input is found. The identification results of step steering angle input show the feasibility of the approach and its advantage in accuracy, convergence and stability.

Abstract: This paper presents two of the most recent approaches for impact force reconstruction, applied to a curved composite panel. The first one is based on the development of an artificial neural network, while the other on the evaluation of transfer functions in the frequency domain. Both methods provide advantages and disadvantages so that a detailed study should be conducted in order to determine which one can be considered more suitable for impact identification purposes. The aim of this paper is to present a comparison between these two methods, in particular when impacts on different surfaces of the plate are present. The main contribution is the application of the two approaches on a curved composite panel. The radius of curvature plays an important role in the contact force due to impacts on the inner or outer surface of the panel, introducing one more parameter in the reconstruction problem.

Abstract: This study discusses the applicability of eddy current testing to the non-destructive evaluation of the depth of a flaw. Three-dimensional finite element simulations are carried out to calculate eddy current signals due to a flaw, and subsequent calculations correlate the difference between signals due to two flaws with the difference between the depths of the flaws. Standard deviation of the difference between the depths of the flaws is used to discuss the ill-posedness of the problem. A flaw is modeled as a sufficiently long rectangular region with a constant width and uniform electrical conductivity; an absolute pancake probe is considered. This study reveals that lift-off and coil diameter do not have a large effect on the ill-posedness, which supports that it is reasonable to decide parameters in actual inspections so that signal-to-noise ratio is maximized. The results obtained also indicate the difficulty in evaluating the depth of a flaw deeper than 1 mm using the signals obtained using an absolute pancake probe.

Abstract: The problem on radial oscillations of an elastic cylinder with inhomogeneous residual stress (RS) is considered. Two acoustic techniques of RS reconstructing are suggested. Within the framework of the first method, a set of radial displacement values is assumed to be known, while the frequency is fixed. Within the framework of the second method, the radial displacement value at the outer radius is assumed to be known for a set of frequencies. The examples of numerical identification experiments are presented.

Abstract: X-ray stress analysis suffers from homogeneity limitations of the stress field in the analyzed volume. When this homogeneity is not fulfilled, it is possible to reduce the irradiated volume down to stress homogeneity achievement. New limitation however occurs : the diffracting sites become too few for stress homogenization. We show that the diffractometry analysis corresponds to a spatially convoluted stress field. The inverse convolution problem is posed. An example of regularization method is given.

Abstract: A simple and robust methodology is presented to identify damages in a structure using changes in vibration data. A comparison is made among damage indicators such as natural frequencies, mode shape data, curvature damage factors and flexibility matrices to study their efficacy in damage assessment. Continuous ant colony optimization (ACO_R) technique is used to solve the inverse problem related to damage identification. The outcome of the simulated results demonstrates that the flexibility matrix as a damage indicator provides better damage identification.

Abstract: The achievement of reliable simulations, in the case of complex processes as is the investment casting, is not a trivial task. Their accuracy is significantly related with the knowledge of the material properties and boundary conditions involved, but the estimation of these values usually is highly complex. One helpful option to try to avoid these difficulties is the use of inverse modelling techniques, where experimental temperature measurements are used as base to correlate the simulation models. The research presented hereafter corresponds to the correlation of a finite element model of the investment casting process of two nickel base superalloys, Hastelloy X and Inconel 718. The simulation model has been developed in a commercial software focused specifically on metal casting simulation. The experimental measurements used as base for the adjustment, have been performed at industrial facilities. The methodology employed combines the use of an automatic tool for model correlation with the manual adjustment guided by the researchers. Results obtained present a good agreement between simulation and experimental measurements, according to the industrial necessities. The model obtained is valid for the two studied cases with the only difference of the alloy material properties. The values obtained for the adjusted parameters in both cases are reasonable compared with bibliographic values. These two circumstances suggest that the obtained correlation is appropriate and no overfitting problems exist on it.