Application of Level-Set Type Topology Optimization Analysis for Cavity Shape Estimation Problem in Structures Based On Non-Destructive Hammering Test

In this study, we present application of the level-set type topology optimization analysis for the cavity shape estimation problem in structures based on the non-destructive hammering test. The cavity shape is identified so as to minimize a performance function. The performance function is defined as the square sum of the residual between computed and the observed displacements on structure surface. In this study, accuracy of identified cavity shape is investigated by changing numerical parameters in the topology optimization

Quantitative roughness characterization of non-gaussian random rough surfaces by ultrasonic method using pitch-catch and pulse-echo configurations

Fundamental study to quantitatively evaluate not only the root-mean-square (rms) roughness Rq but also skewness Rsk of non-Gaussian random rough surfaces by ultrasonic method is presented. In this work, Johnson distribution together with Kirchhoff theory have been employed to derive a newly proposed Johnson characteristic function, which provides a theoretical relationship among ultrasonic reflection coefficient, Rq and Rsk. Based on the characteristics of such relationship, an effective ultrasonic measurement method consisting of a pitch-catch and a pulse-echo configuration to quantitatively characterize Rq and Rsk has been proposed. A general guideline for such characterization method has also been suggested. The validation of the proposed method has then been conducted numerically in the case of an air-coupled ultrasound. Good agreements between the numerically estimated Rq and Rsk and the corresponding reference values thus confirm the validity of the proposed metho

Ultrasonic Lateral Displacement Sensor for Health Monitoring in Seismically Isolated Buildings

An ultrasonic lateral displacement sensor utilizing air-coupled ultrasound transducers is proposed. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for measuring lateral displacement. The measurement system is composed of several air-coupled ultrasound transducers as a receiver and several transmitters. The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side. In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced. The difference between the corrected lateral displacement and the reference displacement is estimated to be 0.2 mm at maximum for the two transmitters system. A good responsiveness is demonstrated by conducting a dynamic response experiment. When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm. In both cases, the fluctuations to the measurement ranges show less than 1%. These results indicate that the developed sensor system is useful for measuring relative lateral displacement of a seismically isolated building in the field of structural health monitoring

Measuring Liquid-Level Utilizing Wedge Wave

A new technique for measuring liquid-level utilizing wedge wave is presented and demonstrated through FEM simulation and a corresponding experiment. The velocities of wedge waves in the air and the water, and the sensitivities for the measurement, are compared with the simulation and the results obtained in the experiments. Combining the simulation and the measurement theory, it is verified that the foundation framework for the methods is available. The liquid-level sensing is carried out using the aluminum waveguide with a 30° wedge in the water. The liquid-level is proportional to the traveling time of the mode 1 wedge wave. The standard deviations and the uncertainties of the measurement are 0.65 mm and 0.21 mm using interface echo, and 0.39 mm and 0.12 mm utilized by end echo, which are smaller than the industry standard of 1.5 mm. The measurement resolutions are 7.68 μm using the interface echo, which is the smallest among all the guided acoustic wave-based liquid-level sensing