Neural Network-Based Inverse Analysis for Defect Identification with Laser Ultrasonics

Abstract

This paper describes an application of the neural network-based inverse analysis method to the identification of a surface defect hidden in a solid, using laser ultrasonics. The inverse analysis method consists of three subprocesses. First, sample data of identification parameters versus dynamic responses of displacements at several monitoring points on the surface are calculated using the dynamic finite-element method. Second, the back-propagation neural network is trained using the sample data. Finally, the well-trained network is utilized for defect identification. Fundamental performance of the method is examined quantitatively and in detail, through both numerical simulations and laser ultrasonics experiments. Locations and depths of vertical defects are successfully estimated within 12.5% and 4.1% errors relative to the specimen thickness, respectively.     

Neural Network-Based Inverse Analysis for Defect Identification with Laser Ultrasonics

This paper describes an application of the neural network-based inverse analysis method to the identification of a surface defect hidden in a solid, using laser ultrasonics. The inverse analysis method consists of three subprocesses. First, sample data of identification parameters versus dynamic responses of displacements at several monitoring points on the surface are calculated using the dynamic finite-element method. Second, the back-propagation neural network is trained using the sample data. Finally, the well-trained network is utilized for defect identification. Fundamental performance of the method is examined quantitatively and in detail, through both numerical simulations and laser ultrasonics experiments. Locations and depths of vertical defects are successfully estimated within 12.5% and 4.1% errors relative to the specimen thickness, respectively.     

A meshless method with conforming and nonconforming sub‐domains

An accurate and easy integration technique is desired for the meshless methods of weak form. As is well known, a sub‐domain method is often used in computational mechanics. The conforming sub‐domains, where the sub‐domains are not separated nor overlapped each other, are often used, while the nonconforming sub‐domains could be employed if needed. In the latter cases, the integrations of the sub‐domains may be performed easily by choosing a simple configuration. And then, the meshless method with nonconforming sub‐domains is considered one of the reasonable choices for computational mechanics without the troublesome integration. In this paper, we propose a new sub‐domain meshless method. It is noted that, because the method can employ both the conforming and the nonconforming sub‐domains, the integration for the weak form is necessarily accurate and easy by selecting the nonconforming sub‐domains with simple configuration. The boundary value problems including the Poisson's equation and the Helmholtz's equation are analyzed by using the proposed method. The numerical solutions are compared with the exact solutions and the solutions of the collocation method, showing that the relative errors by using the proposed method are smaller than those by using the collocation method and that the proposed method possesses a good convergence. Copyright © 2016 John Wiley & Sons, Ltd.     

Advanced 4‐node tetrahedrons

Tetrahedral elements are indispensable to complex finite element structural analysis. Two existing and two newly developed advanced 4‐node tetrahedrons are studied in this paper. The existing elements that use complicated displacement fields are significantly simplified. The spurious zero‐energy modes typical of all these elements are identified to be rigid‐body‐alike modes and are found to be naturally suppressible, making it possible to avoid any stabilization techniques and unknown parameters in formulation. Through the simplified form, we connect these four tetrahedrons and view them in a general framework of the partition‐of‐unity‐based approximation. This general view allows us to reveal many promising features of the newly developed tetrahedrons by comparing them with their existing counterparts: the newly developed tetrahedrons have straightforward formulation, no unsuppressed zero‐energy modes, no stabilization required, no unknown parameters contained, and a high consistency in implementation, in addition to good accuracy and extremely straightforward mesh generation. Copyright © 2006 John Wiley & Sons, Ltd.     

Task transmission control with dynamic lightpath setup for constant processing delay in an optical grid

This paper proposes a task transmission control with dynamic lightpath setup in an optical grid. In our proposed method, a job manager changes the number of tasks in a resource manager dynamically so as to maintain a constant processing delay. It leads to effective utilization of computing resource. I‐PD control is applied to maintain efficient network management. Furthermore, in order to avoid frequent lightpath setup process, multiple lightpaths are established simultaneously by our proposed algorithm. Numerical results show the effectiveness of the proposed task transmission method. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Porting an industrial sheet metal forming code to a distributed memory parallel computer

The parallel version of the sheet metal forming semi-implicit finite element code ITAS3D has been developed using the domain decomposition method and direct solution methods at both subdomain and interface levels. IBM Message Passing Library is used for data communication between tasks of the parallel code. Solutions of some sheet metal forming problems on IBM SP2 computer show that the adopted DDM algorithm with the direct solver provides acceptable parallel efficiency using a moderate number of processors. The speedup 6.7 is achieved for the problem with 20000 degrees-of-freedom on the 8-processor configuration.     

Improvement in output power of vibration generators based on piezoelectric elements by using internal capacitor cancel control rectifier

Recently, energy harvesting has attracted increasing attention. The present study focuses on vibration generators based on piezoelectric elements by proposing an internal capacitor cancel control (ICCC) rectifier to improve the output power. The proposed rectifier cancels the internal capacitor to improve the output power while retaining the maximum output power. Accordingly, this paper experimentally demonstrates the improvement in output power by using the ICCC rectifier compared to conventional circuits and the previous proposed circuit.     

Controlled Polarizability of One‐Nanometer‐Thick Oxide Nanosheets for Tailored,High‐κ Nanodielectrics

An important challenge in current microelectronics research is the development of techniques for making smaller, higher‐performance electronic components. In this context, the fabrication and integration of ultrathin high‐κ dielectrics with good insulating properties is an important issue. Here, we report on a rational approach to produce high‐performance nanodielectrics using one‐nanometer‐thick oxide nanosheets as a building block. In titano niobate nanosheets (TiNbO₅, Ti₂NbO₇, Ti₅NbO₁₄), the octahedral distortion inherent to site‐engineering by Nb incorporation results in a giant molecular polarizability, and their multilayer nanofilms exhibit a high dielectric constant (160–320), the largest value seen so far in high‐κ nanofilms with thickness down to 10 nm. Furthermore, these superior high‐κ properties are fairly temperature‐independent with low leakage‐current density (<10^?7 A cm^?2). This work may provide a new recipe for designing nanodielectrics desirable for practical high‐κ devices.     

Changes in organic constituents in river water during incubation

A water sample collected from Tama River in the Tokyo area was incubated 29 days in the dark conditions at 25 ± 3°C to determine the extent and rate of the degradation of organic constituents and changes in their composition. The majority (>95%) of n-alkanes, fatty acids and sterols were degraded, although total organic carbon (TOC) and extractable organic carbon with ethyl acetate (EOC) remained in considerable amounts (>23%). The degradation of organic constituents occurred apparently in two or three steps. The rate constants for the degradation of TOC, EOC, hydrocarbons, fatty acids and sterols for the first step were 0.090, 0.18, 0.082, 1.4 and 0.23 day⁻¹, respectively. The relative abundances of total fatty acids and sterols as carbon in TOC (EOC) decreased remarkably during incubation (0–11 days) from 7.18 to 0.28% and 0.46 to 0.07%, respectively (31.2-2.2% and 2.0-0.6%, respectively), whereas those of hydrocarbons were not significantly changed.     

Comparative study on organic constituents in polluted and unpolluted inland aquatic environments—V: Organic carbons and hydrocarbons in sediments

Organic carbons and hydrocarbons were analysed for polluted sediments from Tama River and sludges from night soil and sewage treatment plants in the Tokyo area and unpolluted sediments from river and reservoirs from Chichi-jima Island in the Ogasawara (Bonin) Islands to characterize their features for polluted and unpolluted aquatic environments. In addition the relationships of the features of organic constituents between waters and sediments were given. The contents of n-alkanes (C₁₄-C₃₆). squalane and unresolved complex mixture of hydrocarbons (UCMH) for the sediments from Tama River ranged from 16 to 94, 0.86–15 and 250–1100 μ g⁻¹ dry base, which are much higher than those of the sediments from Chichi-jima Island. The major constituents of hydrocarbons in the sediments and sludges from the Tokyo area were mainly odd-carbon numbered n-alkanes and squalane, whereas those of the island were only odd-carbon numbered n-alkanes. Hydrocarbons as carbon (total content × 0.851. as C₂₀H₄₂, HCC)/total organic carbon (TOC), HCC/extractable organic carbon with ethyl acetate (EOC), squalane as carbon (SqC)/TOC. SqC/EOC and UCMH/n-Alkane (C₁₅-C₃₃) values for the sediments from Tama River were much higher than those of the sediments from the island, while carbon preference index (CPI_H) values for the sediments of Tama River were considerably lower than those of the island. It was thus indicated that HCC/TOC, HCC/EOC, UCMH/n-Alkane and CPI^H values should be the important indicators of hydrocarbon pollution for aquatic environments. In addition SqC/TOC and SqC/EOC ratios are apparently useful measures of urban-industrial activities on aquatic environments.The similarity of the nature of hydrocarbons of sediments and sludges from the Tokyo area indicated that the sewage contributed considerably to urban river sediments. Further it was also indicated that hydrocarbons were concentrated in sedimentary environments, although the features of hydrocarbons in sediments are generally similar to those of waters.