Ronald A. Roberts

Reflection from a boundary with periodic roughness: Theory and experiment

Reflection of elastic waves from a traction‐free solid–air boundary of periodic sawtooth profile is investigated experimentally and analytically. For an incident plane wave the surface displacements on the profile are computed as the solution of a singular integral equation. The reflected field is subsequently obtained by using an integral representation for the reflected field. Experimental results are presented for the relative amplitude spectrum for reflection from brass–air, perspex–air, and steel–air boundaries. Both the theoretical and the experimental results show that surface resonances of the profile significantly affect the frequency spectrum of the reflected waves. It is shown that the existence of sharp dips in the amplitude spectra of reflected waves can be attributed to destructive interference between direct reflections and reradiation from surface‐resonance motions. Good agreement is obtained between calculated results and experimental data.

Tissue characterization for beef grading using texture analysis of ultrasonic images

The primary factors in determining beef quality grades are the amount and distribution (or marbling) of intramuscular fat. Under the current USDA Grading system, the quality is subjectively graded by certified inspectors. There is a growing demand in the meat industry for an objective system of evaluating the quality of beef carcasses as well as live animals. A real-time ultrasound technique was used to characterize intramuscular fat in the longissimus dorsi (rib-eye) muscle of 126 live animals. Two approaches of B-mode image texture analysis, namely spacial gray-level dependence matrices and gray-level run-length matrices, were used. The significant texture parameters were used to develop models for predicting intramuscular %fat. With validation testing of these models, from more than 75 percent of the images, the %fat values were predicted to within 1.5 percentage and from about 68 percent of the images, the %fat was predicted to within one percent. The preliminary results showed a good potential of ultrasound and texture analysis for tissue characterization and objectively evaluating beef quality

Leak detection in spacecraft using structure-borne noise with distributed sensors

We have developed and tested in the laboratory a method for in-orbit detection and location of air leaks in manned spacecraft that uses only a small number of sensors distributed arbitrarily on the inner surface of the spacecraft skin. Then, structure-borne ultrasound in the range of 300–600 kHz is monitored from each of the sensors. When cross correlations between measured sensor waveforms indicate the presence of a leak, these correlations are compared with a large dynamically generated database of simulated correlations to locate the the leak on the pressure vessel. A series of experimental tests were performed and at worst the method identified some false locations, but the true location of the leak always appeared.

Two-sensor ultrasonic spacecraft leak detection using structure-borne noise

Micrometeorite hits can create air leaks in manned spacecraft. Leak-generated-guided ultrasonic waves can be monitored within the platelike spacecraft skin to detect and locate leaks. Cross-correlation techniques allow measurement of the deterministic behavior of the leak-generated noise. Measured leak-into-vacuum cross-correlations of noise signals from two adjacent transducers are recorded as the transducer pair is rotated to determine the relative phase delay as a function of rotation angle. The direction to the leak is found from the variation of phase with angle or from synthetic aperture analysis. The leak is then located through triangulation from two or more sensor-pair locations.

Locating air leaks in manned spacecraft using structure-borne noise.

All manned spacecraft are vulnerable to leaks generated by micrometeorite or debris impacts. Methods for locating such leaks using leak-generated, structure-borne ultrasonic noise are discussed and demonstrated. Cross-correlations of ultrasonic noise waveforms from a leak into vacuum are used to find the location of the leak. Four methods for sensing and processing leak noise have been developed and tested and each of these can be used to reveal the leak location. The methods, based on phased-array, distributed sensor, and dual sensor approaches, utilize the propagation patterns of guided ultrasonic Lamb waves in the spacecraft skin structure to find the source or direction of the leak noise. It is shown that each method can be used to successfully locate the leak to within a few millimeters on a 0.6-m2 aluminum plate. The relative merits of the four methods are discussed.

Elastodynamic response of contacting fluid and solid half-spaces to a three-dimensional point load

Abstract The dynamic response of contacting fluid and solid elastic half-spaces to a point load is addressed. The problem considered is the three-dimensional one in which the point load acts in the fluid or in the solid in an arbitrary direction. Integral expressions of displacements and stresses are obtained by using integral transform techniques, and techniques for numerical evaluation are discussed. Results are presented for time harmonic and impulsive loads acting in both the solid and the fluid. Surface and subsurface displacements are compared for fluid half-spaces of water and air. This comparison shows the effect of wavefield coupling at the interface.

Integrated Decision Algorithms for Auto-steered Electric Transmission System Asset Management

Electric power transmission systems are comprised of a large number of physical assets, including transmission lines, power transformers, and circuit breakers, that are capital-intensive, highly distributed, and may fail. Managing these assets under resource constraints requires equipment health monitoring integrated with system level decision-making to optimize a number of various operational, maintenance, and investment-related objectives. Industry processes to these ends have evolved ad-hoc over the years, and no systematic structures exist to coordinate the various decision problems. In this paper, we describe our progress in building a prototype structure for this purpose together with a software-hardware environment to deploy and test it. We particularly focus on the decision algorithms and the Benders approach we have taken to solve them in an integrated fashion.

Array‐Based Acoustic Leak Location in Spacecraft Structures

An array‐based leak location sensor is being developed for spacecraft application which uses spatial Fourier transformation of plate wave signals to robustly determine leak location, independent of the effects of dispersive multiple mode signal transport. The underlying principle of operation is outlined. The performance of a prototype array sensor on structural skin containing integrally machined stiffeners is demonstrated. A significant frequency dependence of transmission efficiency on stiffener geometry is observed, indicating the importance of pass‐band optimization.

The Role of Propagation Characteristics in Acoustic Emission Pipeline Leak Location

The highly dispersive nature of fluid-filled pipeline systems makes the use of traditional time-of-flight source location techniques generally ineffective. Because such methods rely on the assumption of a non-dispersive signal, they do not compensate for the multimodal characteristics of a real acoustic signal. This paper describes on-going work at ISU to understand the underlying principles of multi-mode propagation in fluid-filled pipes and to develop leak location signal processing which accounts for these propagation characteristics. Results which examine some of the practical problems to be encountered in the application of the previously-reported method, which uses both spatial and temporal transforms to isolate modes and determine source location, are reported. Data are presented that show the effect of transmission line interruptions. It is shown that the characteristics of a pipeline vary as a function of distance along the pipe, and that these characteristics can be determined empirically. Results indicating the effect of system background noise are also presented.

Ultrasound Tissue Characterization for Quality Grading of Beef Carcasses

In the Unites States, beef carcasses are subjectively graded by certified inspectors from the United States Department of Agriculture (USDA). The primary factors in determining beef quality grades are the amount and distribution (or marbling) of intramuscular fat. The intramuscular fat level is estimated by visual inspection of texture pattern in a cross-sectional area of the Longissimus dorsi (ribeye) muscle between 12th and 13th ribs. The four primary grades, from high to low marbling, are Prime, Choice, Select, and Standard. There is a growing demand in the meat industry for an objective system of evaluating the quality of beef carcasses as well as live animals. With some sort of instrument grading system, the beef industry could move towards a long desired goal of value-based marketing.