SLDV technology for measurement of mistuned bladed disc vibration

Bladed discs are very sensitive structures and the amplitude vibration of each blade can vary significantly from blade to blade due to a series of factors such as geometrical inhomogeneity between blades or material properties. These factors lead to bladed disks mistuned thus the forced response amplitudes can be much higher than the level predicted for a tuned assembly. Designed models need to be “validate” to predict the response of a real bladed disc within the tolerances set by the manufactures and this process is very expensive as well as difficult. The validation process needs “reference data” as fundamental input against what all predictions can be compared and validated. Data that can be provided both under stationary conditions and under rotating conditions and the latter is the most difficult to achieve, especially for bladed disc assemblies which are very sensitive to any structural modification as it could be attaching a transducer to measure vibrations. There are contact-less measurement techniques available which, however, provide limited information because they can measure only limited areas of the vibrating structures. The aim of this study is to design measurement methods, using a standard Scanning Laser Doppler Vibrometer (SLDV) and to integrate it into a software platform which will be able to handle a series of measurement tasks both under stationary and rotating conditions. The main contribution of this thesis is to extend the use of Continuous Scanning LDV (CSLDV) to the rotating structures, such as bladed discs, thus to perform synchronous measurements. Hence, a bladed disc is needed to be designed to perform vibration predictions and measurements and a mathematical model of the measurement test to control, critically, all possible sources of errors involved in measurement under rotating conditions; all these to produce a robust measurement method. While the primary focus is the measurement method, the study also extends to evaluation of the sensitivity properties of the bladed disk test pieces that are the object of the measurement tool

Laser based tracking and spin measurement

The sports ball market is extremely competitive and in the US alone valued in excess of $1305 million (SGMA 2008). Original equipment manufacturers (OEMs) are continually trying to create a competitive edge over their rivals. In order to research and develop sports balls it is vital to quantitatively measure launch and flight characteristics of the ball, in an attempt to create a ball that has better flight and/or impact characteristics. A launch or flight monitor allows consistent measurement and benchmarking of the ball under test. Current top of the range soccer ball monitors are assessed for performance. Predominantly the sports engineering community uses high speed video (HSV) cameras in this benchmarking process. This technique however is extremely susceptible to errors in spin measurement. These errors are explored in detail and recommendations are given in order to improve the measurements. The properties of laser light make it an ideal tool for accurate, non-contact measurements. It has gained such widespread use, that living in the 21" century it is inconceivable to avoid laser technology. In this thesis, optical laser techniques are pursued for ball launch angle, velocity and spin measurement. In order to successfully utilise these techniques a system that is capable of accurately steering the laser beam to the desired target is developed. A novel laser tracking system (NLTS) has been designed, developed and proven to work successfully, allowing tracking capability of an arbitrarily moving soccer ball, that has no special fiducials. The system is demonstrated to be capable of measuring the position of the ball in space, therefore the NLTS is capable of acting as a launch monitor. The system is proven to track soccer balls in the laboratory and in a more realistic player testing environment. A valuable design feature is that the natural and ambient lighting conditions are inconsequential for the operation of the system. The tracking technique could be applied to any sports ball and could conceivably be transferred to other applications, e.g. military and automotive. Single point vibrometry work and the NLTS are combined to add spin measurement capability. Actual and measured spin rate values show high levels of similarity when tracking a ball with angular, but no translational velocity. A purpose built 'pendulum rig' is used to carry out measurements on a ball with both translational and angular velocity. The testing highlights how influential the radial measurement distance from the spin axis is, regarding the outputted spin rate value. The current set-up would require further development to allow accurate spin rate measurement using the 'pendulum rig'. The main sources of error and recommendations for future developments of this device are outlined and discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of a measurement procedure for the assessment of carotid blood pressure by means of Laser Doppler Vibrometry

L'ipertensione è uno dei principali fattori di rischio per numerose patologie, quali infarto del miocardio, insufficienza cardiaca e renale, ictus, e rappresenta la principale causa di morte al Mondo. Risulta, pertanto, fondamentale il monitoraggio della pressione arteriosa nell'ambito della prevenzione dell'insorgere di gravi patologie. Lo scopo del presente lavoro è di validare una procedura di misura per la determinazione della pressione arteriosa carotidea mediante la tecnica della vibrometria Laser Doppler (LDV). Essa è una tecnica di misura senza contatto ad elevata sensibilità, in grado di rilevare le vibrazioni della pelle legate all'attività cardiovascolare. Nel presente lavoro, il segnale LDV è stato acquisito su 28 soggetti sani ed è stato calibrato per mezzo di un opportuno modello matematico esponenziale per ottenere la forma d'onda di pressione carotidea a partire dallo spostamento del vaso sanguigno. I risultati ottenuti sono stati confrontati con due tecniche di riferimento, la sfigmomanometria e la tonometria arteriosa. La pressione sistolica ottenuta dal segnale LDV calibrato ha mostrato una deviazione percentuale inferiore del 4% e del 8 % rispetto a quella ottenuta tramite cuffia sfigmomanometrica e tonometria rispettivamente. L'integrazione del segnale e l'applicazione di un modello di calibrazione sono state considerate quali significative fonti di incertezza, e si è stimata un'incertezza complessiva di circa il 15 % nella misura della pressione sistolica. Dal segnale LDV sono stati determinati altri significativi parametri emodinamici quali il tempo di eiezione del ventricolo sinistro e la rigidità arteriosa. In conclusione, la tecnica di misura proposta mostra buona correlazione con i metodi di misura di riferimento, benchè vadano prese in considerazione alcune criticità quali l'individuazione del punto di misura, la presenza di artefatti da movimento e di fenomeni di riflessione non legati all'impulso pressorio oggetto di studio.High blood pressure is a great risk factor for several physiological diseases, i.e. myocardial infarction, heart failure, stroke, renal failure. Therefore, blood pressure measurement is a fundamental aspect of health monitoring. The aim of the present work is to validate a measurement procedure for the assessment of carotid blood pressure by means of Laser Doppler Vibrometry (LDV). LDV is a non-contact technique able to detect the skin vibrations due to the cardiovascular activity. In this study, LDV signal was acquired from 28 healthy participants and it was calibrated by means of an exponential mathematical model in order to obtain the carotid pressure waveform from the displacement of the vessel. The results have been compared with two standard techniques for the assessment of blood pressure, sphygmomanometric method and arterial applanation tonometry. The systolic peak of the calibrated waveform from LDV showed an average percentage deviation inferior to 10 % from the one assessed by means of reference techniques. The accuracy of the present measurement technique is discussed, considering the signal integration and the application of the calibration model as significant contributions to the total amount of uncertainty. An average percentage uncertainty of around 15 % has been obtained in the measure of carotid systolic pressure. Moreover, other hemodynamic significant parameters, such as arterial stiffness and Left Ventricular Ejection Time, have been derived from LDV data, showing good correlation with the measures of the reference methods. In conclusion, the proposed measurement technique, for the assessment of carotid blood pressure, shows good agreement with the reference techniques. Overall, some critical issues must be considered, such as the correct localization of the measurement point, the presence of movement artifacts and reflection phenomena not related to the pressure pulse in the investigated vessel

Rotating blade vibration analysis using photogrammetry and tracking laser Doppler vibrometry

Online structural dynamic analysis of turbomachinery blades is conventionally done using contact techniques such as strain gauges for the collection of data. To transfer the captured data from the sensor to the data logging system, installation of telemetry systems is required. This is usually complicated, time consuming and may introduce electrical noise into the data. In addition, contact techniques are intrusive by definition and can introduce significant local mass loading. This affects the integrity of the captured measurements. Advances in technology now allow for the use of optical non-contact methods to analyse the dynamics of rotating structures. These include photogrammetry and tracking laser Doppler vibrometry (TLDV). Various investigations to establish the integrity of photogrammetry measurements for rotating structures involved a comparison to data captured using accelerometers. Discrepancies that were noticed were attributed to the intrusive nature of the contact measurement technique. As an extended investigation, the presented work focuses on the validation of photogrammetry applied to online turbomachinery blade measurements, using TLDV measurements. Through a frequency based characterization approach of the dynamics of the two scanning mirrors inside the scanning head of a scanning laser Doppler vibrometer (SLDV), TLDV is employed in developing a system that can be used to achieve a perfect circular scan with a Polytec SLDV, (PSV 300). Photogrammetry out-of-plane displacements of a laser dot focused on a specific point on a rotating blade are compared to displacements captured by the laser scanning system. It is shown that there is good correlation between the two measurement techniques when applied to rotating structures, both in the time and frequency domains. The presence of slight discrepancies between the two techniques after elimination of accelerometer based errors illustrated that the optical system noise floor of photogrammetry does contribute to inconsistences between photogrammetry and other measurement techniques.http://www.elsevier.com/locate/jnlabr/ymssp2017-08-31hb2016Mechanical and Aeronautical Engineerin

Modal testing using high speed digital speckle pattern interferometry

This thesis introduces the application of a high-speed speckle pattern interferometer (SPI) to perform quantified impact modal testing. The interferometer acts as a non-contact multipoint vibrometer that removes the mass-loading effects of contact transducers to improve measurement accuracy and decreases measurement time by the use of multiple measurement points. A temporal phase-stepped CMOS high-speed SPI system was used to capture the transient vibration response of two overlapping plates, the system had a maximum surface velocity of 1.4 mm/s and the results were compared to accelerometer data and correlated against a finite element model. To extend the surface velocity to 2.7 mm/s a spatial phase-stepped CMOS SPI system was used and compared to the finite element model. Both the temporal phase-stepped system and the spatial phase-stepped system showed high performance for quantified modal testing: showing high correlation for the natural frequencies and the modal assurance criterion correlated over 60% for the first six modes of vibration. The interferometer was improved by the application of spatial phase-stepping but was still limited by the maximum measurable velocity. The thesis also applied the SPI to the novel measurement of traveling waves on a centre-clamped disc. Traveling waves can be caused by structural problems or damage and are difficult to measure without the ability to capture the relative phase across multiple points. This was achieved through the spatial phase-stepped CMOS SPI system and the traveling waves were excited on the disc through a frequency modulated signal that excited the degenerate modes that occurred within 1 Hz of the disc’s second resonant frequency. The multipoint system identified the waveshape, direction and was able to show the ratio of standing wave to traveling wave in the measurements

Virtual vibration measurement using KLT motion tracking algorithm

This paper presents a practical framework and its applications of motion tracking algorithms applied to structural dynamics. Tracking points (“features”) across multiple images is a fundamental operation in many computer vision applications. The aim of this work is to show the capability of computer vision (CV) for estimating the dynamic characteristics of two mechanical systems using a non contact, marker less and simultaneous Single Input Multiple Output (SIMO) analysis. KLT (Kanade-Lucas-Tomasi) trackers are used as virtual sensors on mechanical systems video from high speed camera. First we introduce the paradigm of virtual sensors in the field of modal analysis using video processing. To validate our method, a simple experiment is proposed: an Oberst beam test with harmonic excitation (mode 1). Then with the example of helicopter blade, Frequency Response Functions (FRFs) reconstruction is carried out by introducing several signal processing enhancements (filtering, smoothing). The CV experimental results (frequencies, mode shapes) are compared with classical modal approach and FEM model showing high correlation. The main interest of this method is that displacements are simply measured using only video at FPS (Frame Per Second) respecting the Nyquist frequency

Laser doppler vibrometry for cardiovascular monitoring and photoacoustic imaging

Nowadays, techniques for health monitoring mainly require physical contact with patients, which is not always ideal. Non-contact health monitoring has become an important research topic in the last decades. The non-contact detection of a patient's health condition represents a beneficial tool in different biomedical fields. Examples can be found in intensive care, home health care, the nursing of the elderly, the monitoring of physical efforts, and in human-machine interactions. Cardiovascular diseases (CV) are one of the most spread causes of death in developed countries. Their monitoring techniques involve physical contact with patients. A non-contact technique for cardiovascular monitoring could overcome problems related to the contact with the patient such as skin lesions. It could also expand the availability of monitoring to those cases where contact is not possible or should be avoided to reduce the exposure of medical personnel to biochemical hazard conditions.Several research groups have investigated different techniques for non-contact monitoring of health; among them, the laser Doppler Vibrometry (LDVy) has one of the highest accuracies and signal to noise ratios for cardiorespiratory signals detection. Moreover, the simplicity of data processing, the long-distance measurement range, and the high bandwidth make the laser Doppler vibrometer (LDV) suitable for daily measurements. LDVy is an interferometric technique employed for the measurements of displacement or velocity signals in various fields. In particular, it is deployed in the biomedical field for the extraction of several cardiovascular parameters, such as the PR-time. Generally, the extraction of these parameters requires ideal measuring conditions (measuring spot and laser direction), which are not realistic for daily monitoring in non-laboratory conditions, and especially in tracking applications. The first scientific hypothesis of this work is that the PR-time detected with LDV has an acceptable uncertainty for a realistic variety of measurement spot positions and angles of the incident laser beam. Therefore, I investigated the uncertainty contribution to the detection of the PR-time from LDV signals resulting from the laser beam direction and from the measurement point position; these investigations were carried out with a multipoint laser Doppler vibrometer. The uncertainties were evaluated according to the Guide to the Expression of Uncertainty in Measurement. Successively, the ranges of PR-time values where it is possible to state with 95% certainty that a diagnosis is correct are identified. Normal values of PR-time are included in the range 120 ms -200 ms. For single value measurements with precise alignment the reliable range for the detection of the healthy condition is 146.4 ms -173.6 ms. The detection of CV diseases is reliable for measured values lower than 93.6 ms and greater than 226.4 ms. For mean value measurements with precise alignment the reliable range for the detection of the healthy condition is 126.6 ms -193.4 ms. The detection of CV diseases is reliable for measured values lower than 113.4 ms and greater than 206.6 ms. Therefore, for measured values included in the mentioned ranges, the detection of the PR-time and relative diagnosis with the LDVy in non-laboratory conditions is reliable. The method for the estimation of the uncertainty contribution proposed in this work can be applied to other cardiovascular parameters extracted with the LDVy. Recently, the LDVy was employed for the detection of tumors in tissue-mimic phantoms as a noncontact alternative to the ultrasound sensors employed in photoacoustic imaging (PAI). A non-contact method has considerable advantages for photoacustic imaging, too. Several works present the possibility to perform PAI measurements with LDVy. However, a successful detection of the signals generated by a tumor depends on the metrological characteristics of the LDV, on the properties of the tumor and of the tissue. The conditions under which a tumor is detectable with the laser Doppler vibrometer has not been investigated yet. The second scientific hypothesis of this work is that, under certain conditions, photoacoustic imaging measurements with LDVy are feasible. Therefore, I identified those conditions to determine the detection limits of LDVy for PAI measurements. These limits were deduced by considering the metrological characteristics of a commercial LDV, the dimensions and the position of the tumor in the tissue. I derived a model for the generation and propagation of PA signals and its detection with an LDV. The model was validated by performing experiments on silicone tissue-micking phantoms. The validated model with breast-tissue parameters reveals the limits of tumor detection with LDVy-based PAI. The results show that commercial LDVs can detect tumors with a minimal radius of ≈350 μm reliably if they are located at a maximal depth in tissue of ≈2 cm. Depending on the position of the detection point, the maximal depth can diminish and depending on the absorption characteristics of the tumor, the detection range increases.Heutzutage erfordern Techniken zur Gesundheitsüberwachung hauptsächlich den physischen Kontakt mit dem Patienten, was nicht immer ideal ist. Die berührungslose Gesundheitsüberwachung hat sich in den letzten Jahrzehnten zu einem wichtigen Forschungsthema entwickelt. Die berührungslose Erkennung des Gesundheitszustands eines Patienten stellt ein nützliches Instrument in verschiedenen biomedizinischen Bereichen dar. Beispiele finden sich in der Intensivpflege, der häuslichen Krankenpflege, der Altenpflege, der Überwachung körperlicher Anstrengungen und in der MenschMaschine-Interaktion. Herz-Kreislauf-Erkrankungen sind eine der am weitesten verbreiteten Todesursachen in den Industrieländern. Ihre Überwachungstechniken erfordern einen physischen Kontakt mit den Patienten. Eine berührungslose Technik für die Überwachung von Herz-KreislaufErkrankungen könnte Probleme im Zusammenhang mit dem Kontakt mit dem Patienten, wie z. B. Hautverletzungen, überwinden. Verschiedene Messgeräte wurden für die berührungslose Überwachung der Gesundheit untersucht; unter ihnen hat das Laser-Doppler-Vibrometrer (LDV) eine der höchsten Genauigkeiten und Signal-Rausch-Verhältnisse für die Erkennung kardiorespiratorischer Signale. Darüber hinaus ist das Laser-Doppler-Vibrometer (LDV) aufgrund der einfachen Datenverarbeitung, des großen Messbereichs und der hohen Bandbreite für tägliche Messungen geeignet. LDV ist ein interferometrisches Verfahren, das zur Messung von Weg- oder Geschwindigkeitssignalen in verschiedenen Bereichen eingesetzt wird. Insbesondere wird es im biomedizinischen Bereich für die Extraktion verschiedener kardiovaskulärer Parameter, wie z. B. der PR-Zeit, eingesetzt. Im Allgemeinen erfordert die Extraktion dieser Parameter ideale Messbedingungen (Messfleck und Laserrichtung), die für die tägliche Überwachung unter Nicht-Laborbedingungen und insbesondere für TrackingAnwendungen nicht realistisch sind. Die erste wissenschaftliche Hypothese dieser Arbeit ist, dass die mit dem LDV ermittelte PR-Zeit eine akzeptable Unsicherheit für eine realistische Vielzahl von Messpunktpositionen und Winkeln des einfallenden Laserstrahls aufweist. Daher wurde der Unsicherheitsbeitrag zur Ermittlung der PR-Zeit aus LDV-Signalen untersucht, der sich aus der Laserstrahlrichtung und der Messpunktposition ergibt; diese Untersuchungen wurden mit einem Mehrpunkt-Laser-Doppler-Vibrometer durchgeführt. Die Unsicherheiten wurden gemäß der Technische Regel ISO/IEC Guide 98-3:2008-09 Messunsicherheit – Teil 3: Leitfaden zur Angabe der Unsicherheit beim Messen bewertet. Nacheinander werden die Bereiche der PR-Zeit-Werte ermittelt, in denen mit 95%iger Sicherheit eine korrekte Diagnose gestellt werden kann. Die in dieser Arbeit vorgeschlagene Methode zur Schätzung des Unsicherheitsbeitrags kann auch auf andere kardiovaskuläre Parameter angewendet werden, die mit dem LDV extrahiert werden. Kürzlich wurde das LDV zur Erkennung von Tumoren in gewebeähnlichen Phantomen als berührungslose Alternative zu den Ultraschallsensoren eingesetzt, die bei der photoakustischen Bildgebung (PAI) verwendet werden. Eine berührungslose Methode hat auch für die photoakustische Bildgebung erhebliche Vorteile. In mehreren Arbeiten wird die Möglichkeit vorgestellt, PAIMessungen mit LDV durchzuführen. Die erfolgreiche Erkennung der von einem Tumor erzeugten Signale hängt jedoch von den messtechnischen Eigenschaften des LDV sowie von den Eigenschaften des Tumors und des Gewebes ab. Die Bedingungen, unter denen ein Tumor mit dem LDV detektierbar ist, wurden bisher nicht untersucht. Die zweite wissenschaftliche Hypothese dieser Arbeit ist, dass unter bestimmten Bedingungen photoakustische Bildgebungsmessungen mit dem LDV möglich sind. Daher wurden diese Bedingungen ermittelt, um die Nachweisgrenzen von LDV für PAI-Messungen zu bestimmen. Diese Grenzen wurden unter Berücksichtigung der messtechnischen Eigenschaften eines handelsüblichen LDV, der Abmessungen und der Position des Tumors im Gewebe abgeleitet. In dieser Arbeit wurde ein Modell für die Erzeugung und Ausbreitung von PA-Signalen und deren Nachweis mit einem LDV abgeleitet. Das Modell wurde durch Experimente an Silikongewebe-Phantomen validiert. Das validierte Modell mit Parametern des Brustgewebes zeigt die Grenzen der Tumorerkennung mit LDV-basierter PAI auf. Die Ergebnisse zeigen, dass kommerzielle LDV Tumore mit einem minimalen Radius von ≈350 μm zuverlässig erkennen können