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Mechanical support design of analyzer for a diffraction enhanced x-ray imaging (DEI) systemAlagarsamy, Nagarajan 18 May 2007 (has links)
Diffraction Enhanced X-ray Imaging (DEI) uses synchrotron X-ray beams prepared and analyzed by perfect single crystals to achieve imaging contrast from a number of phenomena taking place in an object under investigation. The crystals used in DEI for imaging requires high precision positioning due to a narrow rocking curve. Typically, the angular precision required should be on the order of tens of nanoradians.<p>One of the problems associated with DEI is the inability to control, set, and fix the angle of the analyzer crystal in relation to the beam exiting the monochromator in the system. This angle is used to interpret the images acquired with an object present and the usual approach is to determine where the image was taken after the fact. If the angle is not correct, then the image is wasted and has to be retaken. If time or dose is not an issue, then retaking the image is not a serious problem. However, since the technique is to be developed for live animal or eventually human imaging, the lost images are no longer acceptable from either X-ray exposure or time perspectives.<p>Therefore, a mechanical positioning system for the DEI system should be developed that allows a precise setting and measurement of the analyzer crystal angles. In this thesis, the fundamental principles of the DEI method, the DEI system at the National Synchrotron Light Source (NSLS) and the sensitivity of the DEI system to vibration and temperature has been briefly studied to gain a better understanding of the problem. The DEI design at the NSLS was analyzed using finite element analysis software (ANSYS) to determine the defects in the current design which were making the system dimensionally unstable. Using the results of this analysis, the new analyzer support was designed aiming to eliminate the problems with the current design. The new design is much stiffer with the natural frequency spectrum raised about eight times. <p> This new design will improve the performance of the system at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory, New York, USA and should assist in the development of a new DEI system for the Bio-Medical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS), Saskatoon, CANADA.
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Numerische Umsetzung der Galbrun-Gleichung zur Modalanalyse strömender Medien in Außenraumproblemen unter Einsatz finiter und infiniter ElementeRetka, Stefanie 09 July 2012 (has links) (PDF)
In der vorliegenden Arbeit wird ein Programmcode zur numerischen Modalanalyse dreidimensionaler Fluide in komplexen akustischen Systemen, speziell in Resonatoren, entwickelt. Mit diesem Code ist es möglich, turbulente Strömungen im Rahmen der Modalanalyse zu berücksichtigen. Hierzu wird ein realistisches Strömungsprofil, ermittelt mithilfe eines 3D-Navier-Stokes-Lösers, verwendet.
Der Hauptteil der Arbeit befasst sich mit der Herleitung der für die Berechnung notwendigen Galbrun-Gleichung und deren Aufbereitung zur numerischen Analyse. Für die numerische Umsetzung kommt die Methode der finiten Elemente in Verbindung mit komplex konjugierten, infiniten Astley-Leis Elementen zur Anwendung. Die infiniten Elemente werden genutzt, um in den betrachteten Außenraumproblemen die Abstrahlung in das Fernfeld abzubilden.
Nach der Anwendung des entwickelten Programmcodes auf einfachere Modelle erfolgen Untersuchungen zur Intonation einer Blockflöte. Hierzu wird das Fluid innerhalb und im Nahfeld des Instruments unter Berücksichtigung des turbulenten Strömungsprofils, welches sich beim Spielen der Blockflöte ausbildet, betrachtet. Im Ergebnis stehen die Eigenwerte des Instruments in Abhängigkeit von der gewählten Griffkombination. Zur Evaluierung der Ergebnisse und zur Untersuchung des Einflusses der Strömung auf den Klang erfolgt der Vergleich mit den exakten Eigenfrequenzen.
Die Galbrun-Gleichung wurde bereits von anderen Autoren untersucht und auf akustische Problemstellungen angewendet. Im Rahmen dieser Arbeit erfolgt jedoch erstmalig die Anwendung der Galbrun-Gleichung auf Eigenwertprobleme. Darüber hinaus sind der Autorin keine Arbeiten bekannt, die sich mit dreidimensionalen Modellen befassen. In der vorliegenden Arbeit werden somit erstmals komplexe dreidimensionale Modelle unter Anwendung der Galbrun-Gleichung untersucht.
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THE MODAL DISTRIBUTION METHOD: A NEW STATISTICAL ALGORITHM FOR ANALYZING MEASURED RESPONSEChoi, Myoung 2009 May 1900 (has links)
A new statistical algorithm, the "modal distribution method", is proposed to
statistically quantify the significance of changes in mean frequencies of individual
modal vibrations of measured structural response data. In this new method, a power
spectrum of measured structural response is interpreted as being a series of independent modal responses, each of which is isolated over a frequency range and treated as
a statistical distribution. Pairs of corresponding individual modal distributions from
different segments are compared statistically.
The first version is the parametric MDM. This method is applicable to well-
separated modes having Gaussian shape. For application to situations in which the
signal is corrupted by noise, a new noise reduction methodology is developed and
implemented. Finally, a non-parametric version of the MDM based on the Central
Limit Theorem is proposed for application of MDM to general cases including closely
spaced peaks and high noise. Results from all three MDMs are compared through
application to simulated clean signals and the two extended MDMs are compared
through application to simulated noisy signals. As expected, the original parametric MDM is found to have the best performance if underlying requirements are met:
signals that are clean and have well-separated Gaussian mode shapes. In application
of nonparametric methods to Gaussian modes with high noise corruption, the noise reduction MDM is found to have lower probability of false alarms than the nonparametric MDM, though the nonparametric is more efficient at detecting changes.
In closely related work, the Hermite moment model is extended to highly skewed
data. The aim is to enable transformation from non-Gaussian modes to Gaussian
modes, which would provide the possibility of applying parametric MDM to well-
separated non-Gaussian modes. A new methodology to combine statistical moments
using a histogram is also developed for reliable continuous monitoring by means of
MDM.
The MDM is a general statistical method. Because of its general nature, it may
find a broad variety of applications, but it seems particularly well suited to structural
health monitoring applications because only very limited knowledge of the excitation
is required, and significant changes in computed power spectra may indicate changes,
such as structural damage.
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Human Tibial Bone Strength Prediction By Vibration Analysis For Diagnosing Progressing OsteoporosisBediz, Bekir 01 July 2009 (has links) (PDF)
Osteoporosis is a metabolic bone disease that needs to be properly diagnosed. The current diagnosing procedure of osteoporosis is based on the mineral density of bones measured by common methods such as dual energy X-ray absorptiometry (DXA). However, due to the deficiencies and limitations of these common methods, investigations on the utilization of other non-invasive diagnosing methods have been executed. For instance, using vibration measurements seems to be a promising technique in diagnosing metabolic bone diseases such as osteoporosis and also in monitoring fracture healing. Throughout this study, bone structural modal parameters obtained from vibrations experiments with decreasing mineral density are examined and therefore, it is aimed to find a new approach to detect osteoporosis or progressing osteoporosis by investigating a relation between structural dynamic properties and mineral density of bone. The main advantage of this study is that loss factor, which is an inherit property of bone, is investigated since in the previous studies mainly the changes in natural frequency of bones with the state of osteoporosis is examined.
In this thesis, both in vitro and in vivo experiments are carried out on human tibia specimens. The measured frequency response functions (FRFs) are analyzed using modal identification techniques to extract the modal parameters of the human tibia. The results obtained from in vitro experiments show that loss factor may be a powerful tool in diagnosing osteoporosis, however due to the difficulties encountered in the case of in vivo experiments makes the use of this parameter as a diagnosing tool difficult. It is also seen from in vivo experiments that there is a weak correlation between the natural frequencies of tibia and BMD measurements of patients. Therefore, in order to investigate the parameters affecting the natural frequencies of tibia, finite element (FE) model of human tibial bone is constructed. Using this FE model tibia, the effect of boundary conditions of experiments and geometry of the bone on natural frequencies of bone is examined. These analyses show that the effect of both boundary conditions and geometry of tibia is very high. Therefore, it is concluded that if the necessary conditions are satisfied, the using natural frequency information of tibia seems to be a possible and practical method that can be used to detect progressing osteoporosis. Also, using the FE model of tibia, the changes of natural frequencies of tibia with the variation in elastic modulus are investigated.
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Model Updating Of A Helicopter Structure Using A Newly Developed Correlation Improvement TechniqueAltunel, Fatih 01 December 2009 (has links) (PDF)
Numerical model usage has substantially increased in many industries. It is the aerospace industry that numerical models play possibly the most important role for development of optimum design. However, numerical models need experimental verification. This experimental verification is used not only for validation, but also updating numerical model parameters. Verified and updated models are used to analyze a vast amount of cases that structure is anticipated to face in real life.
In this thesis, structural finite element model updating of a utility helicopter fuselage was performed as a case study. Initially, experimental modal analyses were performed using modal shakers. Modal analysis of test results was carried out using LMS Test.lab software. At the same time, finite element analysis of the helicopter fuselage was performed by MSC.Patran & / Nastran software.
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Initial updating was processed first for the whole helicopter fuselage then, tail of the helicopter was tried to be updated.
Furthermore, a new method was proposed for the optimum node removal location for getting better Modal Assurance Criterion (MAC) matrix. This routine was tried on the helicopter case study and it showed better performance than the Coordinate Modal Assurance Criterion (coMAC) that is often used in such analyses.
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Solution to Shape Optimization Problem of Linear Elastic Continuum with Prescribed Vibrational Eigen-modeINZARULFAISHAM, Abd Rahim, AZEGAMI, Hideyuki 03 1900 (has links)
Proceedings of the 50th JSME Tokai Branch Meeting. n.013-1, 2001, p.97-98
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An evaluation of the FE-model adopted for modal analysis in the fan booster spool project, GEnx.Andersson, Johan January 2008 (has links)
<p>Avsikten med denna avhandling är att utvärdera den FE-modell som använts i modalanalyser av komponenten fan booster spool, framtagen och tillverkad av Volvo Aero Corporation, Trollhättan. Detaljen ingår i den civila flygplansmotorn GEnx som är utvecklad för flygplanet Boeing 787 Dreamliner.</p><p>Inledande tester av spolen påvisade en mycket god korrelation mellan analys och test men när spolen senare provkördes i en komplett monterad motor noterades en uppenbar skillnad i resultat. Den andra noddiameterns egenfrekvenser indikerade att spolen i test hade ett något styvare beteende än vad som beräknats i analys.</p><p>En teori utvecklades som byggde på att en initiell kontakt mellan rotor och ett slitskikt på statorn kunde framkalla en förstyvande effekt på spolen när rotorn på grund av rotationslaster expanderar radiellt. Detta examensarbete initierades då för att undersöka om denna kontakt kunde inkluderas i FE-modellen och för att utreda om kontakten har en möjlighet att förstyva spolen.</p><p>Avhandlingen utvärderar FE-modellen med avseende på randvillkor, laster och modelleringsteknik i FE-programmet Ansys 10.0. En grundlig kartläggning av spolens känslighet påvisar en robust komponent med hög motståndskraft mot yttre och inre störningar.</p><p>En förstyvande effekt relaterad till en initiell kontakt mellan slitskikt och spole bekräftas i denna avhandling. Kontakten har visat sig ha särskild inverkan på den andra noddiametern och dess egenfrekvenser. Ett förslag på modelleringsteknik där den förstyvande effekten inkluderas har däremot inte föreslagits i detta arbete då effekten enligt uppgift går förlorad efter en inkörningsperiod.</p><p>Det har i detta arbete visats att det kommando som i Ansys tidigare använts för att kompensera för så kallade spin softening-effekter, kspin, resulterar i konservativa värden för spolens egenfrekvenser. En rekommendation baserad på de resultat som framkommit är därför att utesluta funktionen kspin i modalanalyser för denna komponent. Valet av sektorstorlek och kopplingsmetod mellan masselement och spole har också visats ha en tydlig inverkan på de beräknade egenfrekvenserna.</p><p>Spolens radiella förskjutningar har analyserats som funktion av rotationshastigheten. Resultatet visar att den hastighet då kontakt mellan tätningständer och spole etableras är nästintill identisk med den hastighet då töjningar först börjar uppträda i spolen enligt testdata från töjningsgivarprov.</p>
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Screening procedure to identify power system events of the Texas Synchrophasor NetworkSant, Aprajita 09 July 2012 (has links)
This work presents a method for screening synchrophasor data to search for power system events of interest. The method employs prony algorithm to perform modal analysis and estimate mode amplitude, frequency, and damping ratio on the data obtained from the Texas Synchrophasor Network. The procedure uses seven different Linear Prediction Model (LPM) orders, plus a 10 second window width that slides in steps of 1 second, to minimize the possibility of overlooking events of interest. Further, the algorithm is extended to include user defined modal characteristics thresholds, window length and step size to capture specific power system events. / text
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Modal Analysis on a MIMO System : For an asphalt roller CC1200You, You, Chen, Daxin January 2015 (has links)
Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a few weaknesses for modal testing when using hammer, such as short response time, limited frequency resolution, poor quality of frequency response functions. Therefore, a more advanced excitation equipment is needed to improve the measurement quality. The object for this study is to compare two different measuring methods. The thesis will show a comparison between the hammer testing and the shaker MIMO testing compared with analytical model in a highly damped system. It will also give a reference for further highly damped modal analysis and budgetary assessment to decide the budget expenditure. Result from shaker testing shows a little better correlation than hammer testing compared with FEM model. While the correlation between FEM model and measurement is bad due to many reasons, such as many local modes that can not excited, lack of excitation points, unexpected noise and error from the measurement. While considering the compared results obtained from this machine for now, a simpler structure experiment is suggested to be carried on in the future. Shorter length of stinger can be used to enable higher amplitude of force to excite the property on this machine.
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An evaluation of the FE-model adopted for modal analysis in the fan booster spool project, GEnx.Andersson, Johan January 2008 (has links)
Avsikten med denna avhandling är att utvärdera den FE-modell som använts i modalanalyser av komponenten fan booster spool, framtagen och tillverkad av Volvo Aero Corporation, Trollhättan. Detaljen ingår i den civila flygplansmotorn GEnx som är utvecklad för flygplanet Boeing 787 Dreamliner. Inledande tester av spolen påvisade en mycket god korrelation mellan analys och test men när spolen senare provkördes i en komplett monterad motor noterades en uppenbar skillnad i resultat. Den andra noddiameterns egenfrekvenser indikerade att spolen i test hade ett något styvare beteende än vad som beräknats i analys. En teori utvecklades som byggde på att en initiell kontakt mellan rotor och ett slitskikt på statorn kunde framkalla en förstyvande effekt på spolen när rotorn på grund av rotationslaster expanderar radiellt. Detta examensarbete initierades då för att undersöka om denna kontakt kunde inkluderas i FE-modellen och för att utreda om kontakten har en möjlighet att förstyva spolen. Avhandlingen utvärderar FE-modellen med avseende på randvillkor, laster och modelleringsteknik i FE-programmet Ansys 10.0. En grundlig kartläggning av spolens känslighet påvisar en robust komponent med hög motståndskraft mot yttre och inre störningar. En förstyvande effekt relaterad till en initiell kontakt mellan slitskikt och spole bekräftas i denna avhandling. Kontakten har visat sig ha särskild inverkan på den andra noddiametern och dess egenfrekvenser. Ett förslag på modelleringsteknik där den förstyvande effekten inkluderas har däremot inte föreslagits i detta arbete då effekten enligt uppgift går förlorad efter en inkörningsperiod. Det har i detta arbete visats att det kommando som i Ansys tidigare använts för att kompensera för så kallade spin softening-effekter, kspin, resulterar i konservativa värden för spolens egenfrekvenser. En rekommendation baserad på de resultat som framkommit är därför att utesluta funktionen kspin i modalanalyser för denna komponent. Valet av sektorstorlek och kopplingsmetod mellan masselement och spole har också visats ha en tydlig inverkan på de beräknade egenfrekvenserna. Spolens radiella förskjutningar har analyserats som funktion av rotationshastigheten. Resultatet visar att den hastighet då kontakt mellan tätningständer och spole etableras är nästintill identisk med den hastighet då töjningar först börjar uppträda i spolen enligt testdata från töjningsgivarprov.
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