Tadej Kosel, Igor Grabec and Franc Kosel
In Part I, an intelligent acoustic emission (AE) locator is described while the Part II discusses a blind source separation, time delay estimation and location of two continuous…
Abstract
In Part I, an intelligent acoustic emission (AE) locator is described while the Part II discusses a blind source separation, time delay estimation and location of two continuous AE sources. AE analysis is used for characterization and location of developing defects in materials. AE sources often generate a mixture of various statistically independent signals. A difficult problem of AE analysis is a separation and characterization of signal components when the signals from various sources and the mode of mixing are unknown. Recently, blind source separation (BSS) by independent component analysis (ICA) has been used to solve these problems. The purpose of this paper is to demonstrate the applicability of ICA to locate two independent simultaneously active AE sources on an aluminum band specimen. The method is promising for non‐destructive testing of aircraft frame structures by AE analysis.
Acoustic emission analysis (AE) is used for characterization and location of developing defects in materials. AE sources often generate a mixture of various statistically…
Abstract
Acoustic emission analysis (AE) is used for characterization and location of developing defects in materials. AE sources often generate a mixture of various statistically independent signals. One difficult problem of AE analysis is the separation and characterization of signal components when the signals from various sources and the way in which the signals were mixed are unknown. Recently, blind source separation (BSS) by independent component analysis (ICA) has been used to solve these problems. The main purpose of this paper is to demonstrate the applicability of ICA to time‐delay estimation of two independent continuous AE sources on an aluminum beam. It is shown that it is possible to estimate time delays by ICA, and thus to locate two independent simultaneously emitted sources.
Details
Keywords
Tadej Kosel, Igor Grabec and Franc Kosel
The intelligent acoustic emission (AE) locator is described in Part I while Part II discusses a blind source separation, time delay estimation and location of two simultaneously…
Abstract
The intelligent acoustic emission (AE) locator is described in Part I while Part II discusses a blind source separation, time delay estimation and location of two simultaneously active continuous AE sources. Location of AE on complicated aircraft frame structures is a difficult problem of non‐destructive testing. In this article an intelligent AE source locator is described. The intelligent locator is comprised of a sensor antenna and a general regression neural network, that solves the location problem based on learning from examples. The locator performance was tested on different test specimens. The tests have shown that accuracy of location depends on sound velocity and attenuation in the specimen, the dimensions of tested area, and properties of stored data. The location accuracy achieved by the intelligent locator is comparable to that obtained by the conventional triangulation method. This is a promising method for non‐destructive testing by AE method of aircraft frame structures.
Details
Keywords
Goran Visnjic, Dejan Nožak, Franc Kosel and Tadej Kosel
The purpose of this paper was to investigate and evaluate the influence of geometrical and structural design changes in order to reduce shear-lag and increase specific strength…
Abstract
Purpose
The purpose of this paper was to investigate and evaluate the influence of geometrical and structural design changes in order to reduce shear-lag and increase specific strength and stiffness of thin-walled composite I-beam wing spars.
Design/methodology/approach
A detailed FEM model of a cantilevered I-beam spar was used to investigate the influence of increased transition fillet radius and increased web sandwich core thickness on the shear-lag effect at different width to thickness ratios of flanges. Evaluation functions were used to assess specific strength and stiffness of different spar configurations.
Findings
Increased web core thickness has greater influence on normal stress distribution and the reduction of the shear-lag than fillet size. Additional weight of thicker core is not compensated enough through reduction of stress concentration. Increased transition fillet and web core thickness increase optimum flanges width to thickness ratio. Shear-lag reduces the strength of the spar more than the stiffness of the spar.
Practical implications
Findings in this study and detailed insight in the shear-lag effect are important for aircraft design when minimum weight of the airframe is of supreme importance.
Originality/value
This combined shear-lag and weight optimization study deals with composite I-beams and loads that are specific for aerospace engineering. This study does not only evaluate the shear-lag phenomena, but primarily analyses fine structural details in order to reduce it, and increases specific strength and stiffness of I-beam spars.
Details
Keywords
Viktor Šajn, Dejan Nožak, Tadej Kosel and Franc Kosel
This paper aims to present an algorithm for local mesh refinement of finite elements in a two‐dimensional compressible fluid flow.
Abstract
Purpose
This paper aims to present an algorithm for local mesh refinement of finite elements in a two‐dimensional compressible fluid flow.
Design/methodology/approach
The algorithm works on a principle of maximum gradient of fluid variables, e.g. pressure, velocity and density. The simulation of two‐dimensional, transient, viscous, compressible, adiabatic flow of turbulent fluid through a De Laval nozzle was performed by the finite element method. The pressure gradient was used as a condition for mesh refinement.
Findings
With the gradient method faster numerical calculations can be obtained. Boundary layer separation and locations of normal shock waves can be described on locally refined mesh.
Research limitations/implications
Further development of the algorithm is required, especially the determination of the gradient criterion.
Originality/value
The paper provides a new approach to mesh refinement. The mesh is refined automatically. Calculation time and required computer memory are decreased.