A Novel Equivalent Time Sampling-Based Method for Pulse Transit Time Estimation with Applications into the Cardiovascular Disease Diagnosis

The increasing incidence of cardiovascular diseases (CVDs) is reflected in additional costs for healthcare systems all over the world. To date, pulse transit time (PTT) is considered a key index of cardiovascular health status and for diagnosis of CVDs. In this context, the present study focuses on a novel image analysis-based method for PTT estimation through the application of equivalent time sampling. The method, which post-processes color Doppler videos, was tested on two different setups: a Doppler flow phantom set in pulsatile mode and an in-house arterial simulator. In the former, the Doppler shift was due to the echogenic properties of the blood mimicking fluid only, since the phantom vessels are non-compliant. In the latter, the Doppler signal relied on the wall movement of compliant vessels in which a fluid with low echogenic properties was pumped. Therefore, the two setups allowed the measurement of the flow average velocity (FAV) and the pulse wave velocity (PWV), respectively. Data were collected through an ultrasound diagnostic system equipped with a phased array probe. Experimental outcomes confirm that the proposed method can represent an alternative tool for the local measurement of both FAV in non-compliant vessels and PWV in compliant vessels filled with low echogenic fluids

The development of a road profile measuring device with reference to endurance testing of motor vehicles

Includes bibliography.This project describes the development of a device to measure the profile of a road. The data describing the roads characteristics are used to compare the qualities of the test tracks at present used by Volkswagen SA (Pty) Ltd for endurance testing of their products, and the Synthetic Road used on their new hydraulic road simulator

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations

Next-generation equipment and procedures for combined resonant column and torsional shear testing

In this dissertation, work aimed at developing next-generation equipment and procedures for combined resonant column and torsional shear (RCTS) testing are detailed. The work in this dissertation covers three key areas of RCTS testing that need improvement to reach the next level of RCTS testing. The first area involved improvement in measurement resolution with modern control and monitoring equipment. Concurrently, original software was written to enhance the efficiency, accuracy, and repeatability of the test. The second area involved advancing concepts for evaluating and modeling nonlinear behavior of soil, which was done in part by using raw RCTS test data collected and stored from 2013-2017. The third area involved evaluating and modifying the design of the existing RCTS device to accommodate higher levels of shearing strain and provide higher loading capacity. First, when testing at small shear strains (< 0.001%) within the linear-elastic range of soils, very small excitation voltages must be used and very small voltages are recorded from the RCTS sensors. Obtaining accurate measurements in the linear-elastic range is critically important when testing at low confining pressures (in the range of 0.1 to 1 atm). In traditional RCTS data acquisition systems, very small recorded voltages are lost due to limited resolution of the control and monitoring subsystems. Concurrently, the very small recorded voltages are generally heavily contaminated by environmental background noise that invalidates the automated process for reducing raw data into engineering results. Control and monitoring equipment and software were developed that can enhance the measurement and data reduction process when making low-strain measurements. Second, testing of soil in the nonlinear shear strain range (typically greater than 0.001%) is a complex process that departs from traditional dynamic models for single-degree-of-freedom (SDOF) systems. Traditionally, RCTS results from testing in the nonlinear shear strain range involve slight adaptation of traditional SDOF models to obtain nonlinear relationships. Nonlinear dynamics model concepts were taken from literature and adapted to better understand and model nonlinear behavior of soils in RCTS testing. Furthermore, development of nonlinear models at moderate strains help to bridge the spectrum of soil testing which tends to divide into evaluating soils at small to moderate strains (< 0.2%) or at large strains (≥ 0.2%). Third, when testing soils at large shearing strains (> 0.2%), traditional RCTS systems are physically or electronically limited. At higher confining pressures (> 2 atm) where soils become quite stiff, the traditional RCTS control equipment is electronically incapable of driving enough torque output to strain soils in shear above desired levels (> 0.1%). At low confining pressures ( 0.5%). An RCTS testing device was designed that has a torque-output capacity at least three times greater than a traditional RCTS device and an allowable degree of twist that can generate shearing strains above 1%.Civil, Architectural, and Environmental Engineerin

Análisis de métodos para estimar desplazamientos a partir de aceleraciones medidas, en estructuras sometidas a diferentes tipos de excitación

Este trabajo presenta un análisis comparativo de algunos métodos para estimar desplazamientos a partir de aceleraciones medidas, con el objetivo de valorar su bondad para estimar desplazamientos debidos a vibraciones ocasionados por diferentes tipos de excitación (armónica, vehicular, peatonal y sísmica). La importancia de este estudio radica en la falta de consenso entre investigadores respecto a la validez/precisión de los desplazamientos calculados a partir de aceleraciones. Para este trabajo se midieron desplazamientos y aceleraciones en el mismo punto y dirección. Dichas mediciones se realizaron utilizando transformadores diferenciales de variación lineal (LVDT) y acelerómetros de balance de fuerza (FBA). Los registros medidos fueron comparados con los estimados utilizando tres parámetros: el coeficiente de correlación cruzada, la amplitud del desplazamiento máximo y la raíz cuadrada del error cuadrático medio. Los resultados muestran que excepto para los casos con mucho ruido y pequeños desplazamientos, es posible estimar desplazamientos con un alto coeficiente de correlación cruzada y con errores pequeños, con respecto a los desplazamientos medidos. Los resultados obtenidos indican que la selección del método para calcular los desplazamientos depende de la amplitud de los desplazamientos, de la información de la señal que se requiere (el valor máximo o toda la historia de los desplazamientos), y de la magnitud del desplazamiento final esperado. Los resultados corroboran la hipótesis planteada al inicio de este estudio: es posible estimar desplazamientos a partir de aceleraciones medidas con un coeficiente de correlación cruzada mayor a 0.85 respecto a los medidos para los tipos de señales estudiadasSecretaria de Relaciones Exteriores de Méxic

Hilbert Transform applications in signal analysis and non-parametric identification of linear and nonlinear systems

Hilbert Huang Transform faces several challenges in dealing with closely-spaced frequency components, short-time and weak disturbances, and interrelationships between two time-varying modes of nonlinear vibration due to its mixed mode problem associated with empirical mode decomposition (EMD). To address these challenges, analytical mode decomposition (AMD) based on Hilbert Transform is proposed and developed for an adaptive data analysis of both stationary and non-stationary responses. With a suite of predetermined bisecting frequencies, AMD can analytically extract the individual components of a structural response between any two bisecting frequencies and function like an adaptive bandpass filter that can deal with frequency-modulated responses with significant frequency overlapping. It is simple in concept, rigorous in mathematics, and reliable in signal processing. In this dissertation, AMD is studied for various effects of bisecting frequency selection, response sampling rate, and noise. Its robustness, accuracy, efficiency, and adaptability in signal analysis and system identification of structures are compared with other time-frequency analysis techniques such as EMD and wavelet analysis. Numerical examples and experimental validations are extensively conducted for structures under impulsive, harmonic, and earthquake loads, respectively. They consistently demonstrate AMD\u27s superiority to other time-frequency analysis techniques. In addition, to identify time-varying structural properties with a narrow band excitation, a recursive Hilbert Huang Transform method is also developed. Its effectiveness and accuracy are illustrated by both numerical examples and shake table tests of a power station structure --Abstract, page iii

Cost-Effective Monitoring of Railroad Bridge Performance

The railroad network carries 40 % of the freight in the US. Railroad bridges are the most critical part of the network and they need to be properly maintained for safety of operations. Railroad managers need to inspect the bridges in order to assess their structural condition. Railroad managers are interested in measuring displacements under train crossing events to prioritize their bridge management and safety decisions. However, bridge displacements are difficult to collect in the field, because they require a fixed reference from where to measure. Accelerations can be used to estimate dynamic displacements but to this date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate the total displacements of a railroad bridge under live train loads using acceleration and tilt data without a need for fixed reference. Researchers used real bridge displacement data representing different bridge serviceability level under train traffic. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic. This experiment configuration includes the use of a shake table to input the recorded signal from the field into a railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. The different acceleration readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. The results show that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference. In addition, this paper studies the use of a low-cost data acquisition platform to measure reference-free dynamic displacements of railroad bridges by combining low-cost microcontrollers and accelerometers. Researchers used the new system to measure accelerations and reconstruct reference-free displacements from several railroad bridge crossing events. The results obtained from the proposed low-cost sensors were compared with those of commercial sensing equipment. The results show that low-cost sensors and commercial sensing systems can measure reference-free displacements with comparable accuracy. The results of this study show that the proposed platform estimates reference-free displacements with a peak error between 20 % and 30 % and a root mean square (RMS) error between 10 % and 20 %, which is similar to commercial SHM systems. The proposed low-cost system is approximately 300 times less expensive than the commercial sensing equipment. In conclusion, this study evaluates the accuracy of cost-effective systems to measure the reference-free displacement of railroad bridges. The conclusions of this study propose a cost-effective method to measure the reference-free displacement of railroad bridges that all railroad companies can afford. The ultimate goal of this research is to provide stakeholders with means to design, develop, own, and operate their own SHM systems

Design of a mechatronic measurement system for surface fatigue of dental composites

PhD ThesisThis thesis focuses on the design and development of a rolling-ball mechatronic system for on-line testing and measurement of surface contact fatigue of dental composites, and is based on a technique initially developed at the Newcastle Dental School. The mechatronic system synergistically combines the mechanical/electronic hardware with a low-cost embedded digital signal controller (DSC microcontroller) hardware and software to monitor and measure in real-time surface wear due to contact fatigue. ISO/TS 14569-2.2001 standard specification for testing of dental materials was used for selecting appropriate test variables. The mechatronic system attempts to simulate the human oral environment with temperature and moisture being controlled. A closed-loop PI control algorithm combining both optical encoder pulse timing and counting methods is used to drive a dc brushless motor at speeds of 240 and 2040 rpm. A small (2mm diameter) ruby ball is mounted in a V-grooved mandrel which over time creates a circular orbital wear path in the dental composite material. One algorithm has been designed to acquire and process the on-line measurement of wear using a linear voltage differential transformer (LVDT), with another monitoring the fatigue cycling process. A graphical user interface (GUI) has also been designed and implemented on a laptop which is connected to the rig embedded controller. A kinematic model of the rolling ball constrained in a V-groove has been developed along with a finite element analysis of the surface deformation. This has been augmented by a comprehensive test programme, in dry, moisturized and elevated temperature (i.e. 37°C), using Synergy D6 specimens. Using ANOVA test, 70% reproducibility of fatigue track measurements was attained. A comparison of LVDT transducer and profilometer measurements indicated 5% consistence with each other. The insight gained from the testing programme sets a basis for an extensive programme to qualify and validate the measurement system basing on ISO/TS 14569-2.2001 specifications.The Tanzania Government: The University of Dar es Salaam