Full-wave modeling of ultrasonic scattering for non-destructive evaluation

The physical modeling and simulation of nondestructive evaluation (NDE) measurements has a major role in the advancement of NDE and structural health monitoring (SHM). In ultrasonic NDE (UNDE) simulations, evaluating the scattering of ultrasound by defects is a computationally-intensive process. Many UNDE system models treat the scattering process using exact analytical methods or high-frequency approximations such as the Kirchhoff approximation (KA) to make the simulation effort tractable. These methods naturally have a limited scope. This thesis aims to supplement the existing scattering models with fast and memory-efficient full-wave models that are based on the boundary element method (BEM). For computational efficiency, such full-wave models should be applied only to those problems wherein the existing approximation methods are not suitable. Therefore, the adequacy of different scattering models for representing various test scenarios has to be studied. Although analyzing scattering models by themselves is helpful, their true adequacy is revealed only when they are combined with models of other elements of the NDE system, and the resulting predictions are evaluated against measurements. Very few comprehensive studies of this nature exist, particularly for full-wave scattering models. To fill this gap, two different scattering models-- the KA and a boundary-element method-- are integrated into a UNDE system model in this work, and their predictions for standard measurement outputs are compared with experimental data for various benchmark problems. This quantitative comparison serves as a guideline for selecting between the KA and full-wave scattering models for performing UNDE simulations. In accordance with theoretical expectations, the KA is shown to be inappropriate for modeling penetrable (inclusion-type) defects and non-specular scattering, such as diffraction from thin cracks above certain angles of incidence. A key challenge to the use of full-wave scattering methods in UNDE system models is the high computational cost incurred during simulations. Whereas the development of fast finite element methods (FEM) has inspired various applications of the FEM for ultrasound modeling in 3D heterogeneous and anisotropic media, very few applications of the BEM exist despite the progress in accelerated BEMs for elastodynamics. The BEM is highly efficient for modeling scattering from arbitrary shaped 3D defects in homogeneous isotropic media due to a reduction in the dimensionality of the scattering problem, and this potential has not been exploited for UNDE. Therefore, building on recent developments, this work proposes a fast and memory-efficient implementation of the BEM for elastic-wave scattering in UNDE applications. This method features three crucial elements that provide robustness and fast convergence. They include the use of (1) high-order discretization methods for fast convergence, (2) the combined-field integral equation (CFIE) formulation for overcoming the fictitious eigenfrequency problem, and (3) the multi-level fast-multipole algorithm (MLFMA) for reducing the computational time and memory resource complexity. Although numerical implementations based on a subset of these three elements are reported in the literature, the implementation presented in this thesis is the first to combine all three. Some numerical examples are presented to demonstrate the importance of these elements in making the BEM viable for practical applications in UNDE. This thesis contains the first implementation of the diagonal-form MLFMA for solving the CFIE formulation for elastic wave scattering without using any global regularization techniques that reduce hypersingular integrals into less singular ones

The Surabhi Theatre–An Oasis of Telugu Theatre

This document is a thesis submitted in partial fulfillment of the Master of Arts degree in Theatre Arts. It is a detailed account of author Pradeep Aswini Gurrala’s study of the Surabhi Theatre in Telangana, India. The thesis follows the journey of a 134-year-old theatre company in four chapters: puppet show to stage show; the evolution of the Surabhi Theatre; the decline of Surabhi Theatre; and Surabhi Theatre as a cultural heritage. Appendices and works cited are included

Efficient Power Allocation Schemes for Hybrid Decode-Amplify-Forward Relay Based Wireless Cooperative Network

Cooperative communication in various wireless domains, such as cellular networks, sensor networks and wireless ad hoc networks, has gained significant interest recently. In cooperative network, relays between the source and the destination, form a virtual MIMO that creates spatial diversity at the destination, which overcomes the fading effect of wireless channels. Such relay assisted schemes have potential to increase the channel capacity and network coverage. Most current research on cooperative communication are focused broadly on efficient protocol design and analysis, resource allocation, relay selection and cross layer optimization. The first part of this research aims at introducing hybrid decode-amplify-forward (HDAF) relaying in a distributed Alamouti coded cooperative network. Performance of such adaptive relaying scheme in terms of symbol error rate (SER), outage probability and average channel capacity is derived theoretically and verified through simulation based study. This work is further extended to a generalized multi HDAF relaying cooperative frame work. Various efficient power allocation schemes such as maximized channel capacity based, minimized SER based and total power minimization based are proposed and their superiority in performance over the existing equal power allocation scheme is demonstrated in the simulation results. Due to the broadcast nature of wireless transmission, information privacy in wireless networks becomes a critical issue. In the context of physical layer security, the role of multi HDAF relaying based cooperative model with control jamming and multiple eavesdroppers is explored in the second part of the research. Performance evaluation parameters such as secrecy rate, secrecy outage and intercept probability are derived theoretically. Further the importance of the proposed power allocation schemes in enhancing the secrecy performance of the network in the presence of multiple eavesdroppers is studied in detail through simulation based study and analysis. For all the proposed power allocation schemes in this research, the optimization problems are defined under total power constraint and are solved using Lagrange multiplier method and also evolutionary algorithms such as Differential evolution and Invasive Weed Optimization are employed. Monte Carlo simulation based study is adopted throughout the research. It is concluded that HDAF relaying based wireless cooperative network with optimal power allocation schemes offers improved and reliable performance compared to conventional amplify forward and decode forward relaying schemes. Above research contributions will be applicable for future generation wireless cooperative networks

Modelling and Analysis of Custom Power Device for Improve Power Quality

Abstract: This paper describes the model and analyzes custom power devices for compensating voltage sag and swell conditions in three phase systems. Faults occurring in power distribution systems or facilities in plants cause the voltage sag or swell. If a fault occurs, it can damage the power system or user’s facility. Sensitivity to voltage sags and swells varies within different applications. For sensitive loads (PLC’s, paper mills etc.), even voltage sags of short duration can cause serious problems in the entire system. Normally, a voltage interruption triggers a protection device, which causes shutdown of the entire system. In order to mitigate power interruptions, this paper proposes a scheme for voltage sag support based on a pulse width modulated autotransformer. The proposed scheme is able to quickly recognize the voltage sag or swell condition, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the voltage during swell events.DOI:http://dx.doi.org/10.11591/ijece.v1i1.4

Full Wave Modeling of Ultrasonic Scattering Using Nystrom Method for NDE Applications

Approximate methods for ultrasonic scattering like the Kirchhoff approximation and the geometrical theory of diffraction (GTD) can deliver fast solutions with relatively small computational resources compared to accurate numerical methods. However, these models are prone to inaccuracies in predicting scattered fields from defects that are not very large compared to wavelength. Furthermore, they do not take into account physical phenomena like multiple scattering and surface wave generation on defects. Numerical methods like the finite element method (FEM) and the boundary element method (BEM) can overcome these limitations of approximate models. Commercial softwares such as Abaqus FEA and PZFlex use FEM, while CIVA has a 2D FEM solver [1-3]. In this work, we study the performance of the Nyström method (NM) [4,5], an alternative boundary integral equation solver to the BEM, in modeling ultrasonic scattering from defects. To handle larger problems, the Nyström method is accelerated by the multilevel fast multipole algorithm (MLFMA). We apply the NM to benchmark problems and compare its predictions with those of exact and approximate analytical models as well as with experimental results from the World Federation of NDE Centers (WFNDEC). Several examples will be presented to demonstrate the prediction of creeping waves by the NM while also illustrating its improved accuracy over the Kirchhoff approximation. We will conclude with a discussion on the validity and limitations of the NM in modelling practical NDE problems

Online signature verification techniques

Signature is a behavioral biometric: it is not based on the physical properties, such as fingerprint or face, of the individual, but behavioral ones. Signature verification is split into two according to the available data in the input. Offline (static) signature verification takes as input the image of a signature and is useful in automatic verification of signatures found on bank checks and documents. Online (dynamic) signature verification uses signatures that are captured by pressure-sensitive tablets that extract dynamic properties of a signature in addition to its shape. The purpose of project is to develop an authentication system based on personal signatures. Signature verification is an important research topic in the area of biometric authentication. In this project the work is done in such a way that the signatures are captured using WEBCAM. A visual-based online signature verification system in which the signer’s pen tip is tracked. The data acquisition of the system consists of only low-cost cameras (webcams) and does not need special equipment such as an electronic tablet. Online signature data is obtained from the images captured by the webcams by tracking the pen tip. The pen tip tracking is implemented by the Sequential Monte Carlo method in real time. Then, the distance between the input signature data and reference signature data enrolled in advance is computed using Dynamic Time Warping (DTW). Finally, the input signature is classified as genuine or a forgery by comparing the distance with a threshold

Development of Dissolution Test Method for Drotaverine Hydrochloride/Mefenamic Acid Combination Using Derivative Spectrophotometry

Purpose: To develop and validate a dissolution test method for tablets containing 80 mg of drotaverine hydrochloride (DRT) and 250 mg of mefenamic acid (MEF).Methods: Sink conditions, drug stability and specificity in different dissolution media were tested to optimize a dissolution test method using a USP paddle type dissolution test apparatus set at a speed of50 rpm. The dissolution medium consisted of 900 ml of phosphate buffer (pH 6.8) containing 0.25% w/v cetrimide at 37 ± 0.5 oC and 45 min time-point. To determine both drugs simultaneously, a first derivative UV spectrophotometric method was developed and validated. Drug release was analyzed by first derivative UV method at 253.8 nm and 304 nm for DRT and MEF respectively. The dissolution method was validated as per ICH guidelines.Results: The two brands each showed 98% of drug release for both drugs when the developed dissolution method was used. The regression plot was linear in the concentration range 4 - 24 ìg/mL for each of the drugs and regression coefficient (r2) was greater than 0.999 for each drug. Relativestandard deviation (% RSD) for precision and accuracy of proposed method was < 2.Conclusion: The proposed dissolution method is simple, cost-effective, precise, accurate and specific. It can be successfully employed in routine quality control of DRT and MEF combination tablets.Keywords: Drotaverine hydrochloride, Mefenamic acid, First derivative spectrophotometry, Dissolution, Validatio

Fast Uncertainty Propagation of Ultrasonic Testing Simulations for MAPOD and Sensitivity Analysis

Model-assisted probability of detection (MAPOD) and sensitivity analysis (SA) are widelyused for measuring the reliability of nondestructive testing (NDT) systems., such as ultrasonictesting (UT), and understanding the effects of uncertainty parameters. In this work, a stochastic expansion-based metamodel is used in lieu of the physics-based NDT simulation model for efficient uncertainty propagation while keeping satisfactory accuracy. The proposed stochasticmetamodeling approach is demonstrated for MAPOD and SA on a benchmark case for UT simulations on a fused quartz block with a spherically-void defect. The proposed approach is compared with direct Monte Carlo sampling (MCS), and MCS with Kriging metamodels. The results indicate that around one order of magnitude reduction in the number of model evaluations required for MAPOD analysis can be obtained. Moreover, the results indicate around two orders of magnitude reduction of the number of model evaluations for the convergence of the statistical moments and obtaining the problem sensitivities