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Kannappan, Laxmikant Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Damage detection in structures using natural frequency measurements". Awarded by:University of New South Wales - Australian Defence Force Academy. Aerospace, Civil & Mechanical Engineering, 2009. http://handle.unsw.edu.au/1959.4/44852.
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In the last two decades, the emphasis in aircraft maintenance has been on developing online structural health monitoring systems to replace conventional non destructive inspection techniques which require considerable down-time, human effort and cost. Vibration based damage detection is one of the most promising techniques for implementation in Structural Health Monitoring (SHM). In vibration based methods, the presence of damage is detected by monitoring changes in one of the dynamic parameters of the structure, resonant frequencies, modeshapes or damping characteristics. Compared to modeshape based methods, frequency based methods have the advantage that measurements need to be taken only at a single location. Previous developments on frequency based techniques have relied on Finite Element Model updating; analytical techniques have hitherto been restricted to beams due to the complexity in developing equations for cracked two dimensional structures. In this thesis the analytical approach using an energy formulation is extended to plates with through-thickness cracks, where modeshapes from either numerical modelling or experimental measurements can be employed to determine the energy of vibration. It is demonstrated that by using a hybrid approach, incorporating experimentally measured modeshapes along with measured changes in frequencies, the damage parameters can be estimated without resorting to theoretical modelling or numerical analysis. The inverse problem of finding the crack location, size and orientation from measured changes in frequencies is addressed using minimisation techniques. The forward problem and the inverse algorithm is first validated using numerical simulation and experimental testing of beams with edge cracks and centre cracks. The application of the methodology to the two dimensional case is then validated by numerical simulation and experimental modal analysis of plates with through thickness cracks. A statistical procedure is developed for determination of the 90/95 probability of crack detection and the minimum detectable crack size in both cases. It is demonstrated that the measurement of frequency changes can be successfully employed to detect and assess the location and size of cracks in beams and plates, using modeshapes from theory, Finite Element Analysis.
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Shao, Fei. "Natural frequency analysis for osseointegration trans-femoral implant". Thesis, University of Surrey, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443397.
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Beavers, Timothy Allan. "Fundamental Natural Frequency of Steel Joist Supported Floors". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/35880.
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Three aspects in determining the first natural frequency of
steel joist supported floors were studied. The aspects are:
1) determining which finite element model best predict the behavior
of joist-slab tee-beams, 2) investigating the ability of
proposed equations to calculate the effective moment of
inertia of joist-slab tee-beams, and 3) developing a
finite element model to predict the first natural frequency
of steel joist supported floors.
Several finite element models were tested to determine which
one best predicted the experimental results of six
joist-slab setups. The model which best predicted the
experimental results was used.
Next, a study was done to determine the ability of a
proposed equation to predict the effective moment of
inertia of joist-slab tee-beams. The study modeled and
analyzed 130 joist-slab configurations and compared the
results to those calculated using the proposed equations.
Finally, a finite element modeling technique was developed
to predict the first natural frequency of steel joist
supported floors. Seven in-situ floors were experimentally
tested, and those results were compared to the predicted
values given by the models.Master of Science
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Labib, Amr. "Crack detection in frames using natural frequency degradations". Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/88543/.
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Crack detection at an early stage can prevent catastrophic structural failures. In this thesis, the inverse problem of crack detection in frames is studied. The direct problem of calculating the natural frequencies of beams and frames with multiple cracks is first tackled. A new method for natural frequency calculation is devised. The cracks are modelled as rotational springs. 4 × 4 dynamic stiffness matrices for beams are evaluated in a recursive manner, according to the number of cracks, by applying partial Gaussian eliminations. The resulting transcendental eigenvalue problem is solved using the Wittrick–Williams algorithm to extract the natural frequencies. Additional sign counts resulting from the partial Gaussian eliminations must be accounted for when applying the algorithm. The dynamic stiffness matrix of a frame with multiply cracked members is then assembled. The natural frequency calculation method forms a basis for detecting a single crack in a frame using only natural frequency measurements. Each frame member is discretised into a number of points. Selected natural frequencies are calculated accurately in the uncracked case and when the crack is placed individually at each discretisation point. The variation between the uncracked and cracked frequencies is normalised giving a number of curves corresponding to the selected frequencies. The normalisation is then applied on the measured frequencies. For noise free measurements, point crack locations are obtained. Applying the principles of interval arithmetic, noisy measurements give crack location ranges. Empirical probability distributions are used to graphically represent these ranges and their relative probabilities. Crack severity ranges are then obtained. The detection method is validated experimentally on a frame with scaled down dimensions. The fast Fourier transform is used to convert the time domain vibration signal into the frequency domain. Using higher order natural frequencies, two enhancement procedures for the detection method are devised and applied theoretically.
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Lane, Dewey Hobson III. "Identification of natural frequency components of articulated flexible structures". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15972.
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Lawrence, Emma Jane. "Identifying natural modifiers of meiotic crossover frequency in Arabidopsis thaliana". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289733.
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During meiosis, homologous chromosomes pair and undergo reciprocal genetic exchange, producing crossovers. This generates genetic diversity and is required for balanced homolog segregation. Despite the critical functions of crossovers, their frequency and distribution varies extensively within and between species. This crossover variation can be caused by trans-modifiers within populations, which encode diffusible molecules that influence crossover formation elsewhere in the genome. This project utilised natural accessions of Arabidopsis thaliana to identify trans-modifying loci underlying crossover variation within the species. I performed Quantitative Trait Loci (QTL) mapping using a fluorescence-based crossover reporter system to measure recombination frequency in a genomic interval on chromosome 3, termed 420. Mapping in a Col-420 × Bur-0 F2 population revealed four major recombination QTLs (rQTLs) that influence crossover frequency. A novel recessive rQTL on chromosome 1 that reduced crossovers within the interval was fine-mapped to a premature stop codon in TATA Binding Protein (TBP)-associated factor 4b (TAF4b) in Bur-0 (taf4b-1). TAF4b is a subunit of the TFIID complex, a multi-protein general transcription factor complex comprising TBP and numerous TAFs that forms a component of the pre-initiation complex that recruits RNA polymerase II to promoters. Transformation-based complementation experiments and the isolation of several independent taf4b alleles provided genetic proof that TAF4b is essential for wild-type levels of crossover within 420. Analysis of the prevalence of the taf4b-1 mutation in the global Arabidopsis accession collection demonstrated its specificity to three accessions in the British Isles. A combination of cytology, genetic analysis using additional fluorescent reporter lines, and sequencing in F2 recombinant populations demonstrated a genome-wide reduction in crossover frequency in taf4b-1. In addition, RNA sequencing identified numerous transcriptional changes in taf4b-1. Both up- and down-regulated gene sets displayed significant enrichment for genes that are predominantly expressed in meiocytes, and several gene ontology terms pertaining to protein modification and meiotic processes. These results further demonstrate the existence of genetic modifiers of crossover frequency in natural populations of A. thaliana, and the characterisation of a novel trans-modifier of recombination, TAF4b. This signifies a novel function for TAF4b in Arabidopsis, and further enhances our understanding of the molecular factors controlling the frequency and distribution of meiotic crossovers in plants.
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Zhao, Shengjie. "Natural frequency based damage identification of beams using piezoelectric materials". ASME 2015 International Mechanical Engineering Congress and Exposition, 2015. http://hdl.handle.net/1993/31652.
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Following the studies of natural frequency based damage detection methods, an advanced technique for damage detection and localization in beam-type structures using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage on the change of the natural frequencies of the damaged structure to realize the high detection sensitivity. Based on the vibration characteristic tuning procedure, a scan-tuning methodology for damage detection and localization is proposed. From analytical simulations, both crack and delamination damage in the beams are detected and located with over 20% change in the natural frequencies. Finite element method (FEM) simulations are conducted to verify the effectiveness of the proposed methodology.October 2016
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Hall, Julie Maria. "Nature, frequency and natural history of intracranial cavernous malformations in adults". Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/9532.
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Scottish Intracranial Vascular Malformation Study was the first prospective, population-based study of the major types of intracranial vascular malformations; arteriovenous, cavernous and venous malformations including dural fistulae and carotid-cavernous fistulae. It was based in Scotland and designed in 1998 by my supervisor Professor Charles Warlow and the first Research Fellow Dr Rustam Al-Shahi supported by the SIVMS steering committee (www.saivms.scot.nhs.uk). Recruitment and follow-up began in January 1999. Recruitment and follow-up of all vascular malformation types was done by Dr Al-Shahi until March 2002 and this role then transferred to me in April 2002 until I left in August 2004. The main duties of the Research Fellow were to collect and review all the clinical material of cases notified to SIVMS and arbitrate with the relevant expertise where there was doubt whether the case met the criteria for inclusion in SIVMS. Apart from my clinical responsibilities in recruitment and follow-up, the post also involved supervision of the part-time study administrator and also weekly meetings with the study programmer. I was also responsible for convening and presenting updates of the study progress weekly to my supervisor Professor Charles Warlow, biannually to the Study steering committee meetings, and annually to my funding body, the Stroke Association. This Research Fellowship also allowed me to gain an appreciation of the efforts needed to sustain collaborators’ interest in a long running study and I made presentations to improve the profile of the study on the national and international stage. For my duration as the SIVMS Research Fellow, I recruited and followed-up all types of newly diagnosed intracranial vascular malformations (IVMs). This thesis, however, is based solely on the incident intracranial cavernous malformations (ICMs) recruited to the study by both Dr Al-Shahi and myself between January 1999 and December 2003. The follow-up data in this thesis were that available to me on August 31st 2004. The data cleaning and the analysis for this thesis has been performed by me alone under the supervision of Professor Warlow. Although the core study design was well-established and tested prior to my involvement with SIVMS, I did divise new studies such as the Sensitivity and Specificity of MRI in the diagnosis of intracranial CMs. This cavernoma imaging study was a separate study designed, executed and analysed by myself, a medical student Sue Liong, the Cavernoma Imaging Study Group [appendix 1] with guidance from Professor Warlow, Dr Al-Shahi, Dr Andrew Farrall (consultant neuroradiologist) and Dr Steff Lewis (Medical Statistician). Computing support was provided by Aidan Hutchison (SIVMS programmer).
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Feng, Gaoyang. "Colour information in natural scenes : frequency of metamerism and colour gamut". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/colour-information-in-natural-scenesfrequency-of-metamerism-and-colour-gamut(0987f4cf-b0e3-49f9-b6c0-cc79a0b8d1a5).html.
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Colour is an important source of information in the natural world. It can be used for distinguishing and identifying surfaces and objects and separating one region from another. For instance, flowers and grasses in a garden can be distinguished by their colours despite a change in illuminant. Intuitively, the identifiability of surfaces in a scene can be described by their volumes of colour gamuts. But is this approximation of the identifiability accurate? On the other hand, the existence of metamerism in natural scenes shows that colour is sometimes unreliable for surfaces identification. Estimating frequency of metamerism normally requires many comparisons between surface colours to determine their distinguishability under different illuminants. Is there a simpler approach to predict the frequency of metamerism in natural scenes? The aim of this thesis was to address these two questions about the identifiability of surfaces in natural scenes. To answer the first question, the volumes of colour gamuts were estimated over 50 natural scenes under different illuminants. The logarithm of the gamut volume was regressed on the differential entropy of colours. It was found that gamut volume can be an accurate approximation, given a colour difference threshold representing the visual distinguishability within an approximately perceptually uniform colour space. To answer the second question, the frequency of metamerism was estimated over 50 natural scenes with changes in illuminant; and predictive models were constructed based on different combinations of Shannon differential entropies of colours. There was strong dependence of the frequency of metamerism on the combination of the differential entropy and the conditional differential entropy of colours. It means that the frequency of metamerism can be predicted by the informational quantities of the colours in a scene.
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Ng, G. H. T. "Finite element model updating by using natural frequency and mode shape sensitivities". Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638321.
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Three finite element model updating approaches are considered in this thesis. In the first updating approach, a line search method is used in conjunction with the existing two level Gauss-Newton approach. This two level updating approach was used to tackle the problem of shape function discretization and enabled a coarse finite element model to be updated without discretization bias. The purpose of the line search method is to place the updated estimates, which are obtained at each iteration step of the Newton method, in a superior position for the next Newton iteration. Accordingly, convergence can be achieved with the use of line searching in some non-convergent problems. The effectiveness of this updating technique is illustrated by both simulated and experimental case studies. The second approach is concerned with reduction methods for use in finite element model updating. Particular attention is paid to the performance of dynamic condensation and modal truncation schemes. In both cases, subspace iteration and the efficient computation approaches which incorporate the skyline storage method are used in conjunction with the updating method. Moreover, an efficient method is proposed for the computation of eigenvector sensitivities in principal co-ordinates. Two simulated updating problems containing over one thousand degrees of freedom are examined for a variety of cases using different forms of sensitivity data. Another area of interest in the present thesis is the modelling and updating of adhesive, welded and bolted joints. In the case of the adhesive joint, two modelling approaches, referred to as the simplified 'element strip' model and the complex 'full joint' model are examined. For the updating of the welded joint, careful parameterization is found to be critical. The use of nodal offset dimensions is shown to result in an updated joint with physical meaning. When applied to the non-linear adhesive and bolted joints, model updating will produce equivalent linearized representations. The methods and their effectiveness for mechanical joint model updating are demonstrated by experimental case studies.
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Zografos, Nikolaos. "The role of natural formant frequency change over time in speech segregation". Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398752.
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Sim, Zhi Wei. "Radio frequency energy harvesting for embedded sensor networks in the natural environment". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/radio-frequency-energy-harvesting-for-embedded-sensor-networks-in-the-natural-environment(b0f3db83-8a82-4376-841b-d79bcd0d16ae).html.
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The agricultural sector is an emerging application area for Wireless Sensor Networks (WSNs). This requires sensor nodes to be deployed in the outdoor environment so as to monitor pertinent natural features, such as soil condition or pest infestation. Limited energy supply and subsequent battery replacement are common issues for these agricultural sensor nodes. One possible solution is to use energy harvesting, where the ambient energy is extracted and converted into usable electrical form to energise the wireless sensors. The work presented in this thesis investigates the feasibility of using Radio Frequency (RF) energy harvesting for a specific application; that is powering a generic class of wireless ground-level, agricultural sensor networks operating in an outdoor environment. The investigation was primarily undertaken through a literature study of the subject. The first part of the thesis examines several energy harvesting/ wireless energy transfer techniques, which may be applicable to power the targeted agricultural WSN nodes. The key advantages and limitations of each technique are identified, and the rationale is being given for selecting far-field RF energy harvesting as the investigated technique. It is then followed by a theoretical-based system analysis, which seeks to identify all relevant design parameters, and to quantify their impact on the system performance. An RF link budget analysis was also included to examine the feasibility of using RF energy harvesting to power an exemplar WSN node - Zyrox2 Bait Station. The second part of the thesis focuses on the design of two energy harvesting antennas. The first design is an air-substrate-based folded shorted patch antenna (FSPA) with a solid ground plane, while the second design is a similar FSPA structure with four pairs of slot embedded into its ground plane. Both antennas were simulated, fabricated and tested inside an anechoic chamber, and in their actual operating environment - an outdoor field. In addition, a power harvester circuit, built using the commercially available off-the-shelf components, was tested in the laboratory using an RF signal generator source. The results from both the laboratory and field trial were analysed. The measurement techniques used were reviewed, along with some comments on how to improve them. Further work on the RF energy harvester, particularly on the improvement of the antenna design must be carried out before the feasibility and viable implementations for this application can be definitively ascertained.
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Griffin, Catherine Helen. "Investigation of natural genetic modifiers of meiotic crossover frequency in Arabidopsis thaliana". Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/277143.
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Meiotic recombination, known as crossover, is a vital mechanism for generating genetic diversity in sexually reproducing populations. Recombination events are non-uniform across the genome, due to a variety of influences including chromatin structure, DNA-sequence, epigenetic marks and interference from other recombination events. These known factors do not fully explain the distribution of recombination events, and additionally do not account for all the variability in recombination frequency observed both between and within species. Furthermore, of the mechanisms that have been identified, many are not yet fully understood. In Arabidopsis thaliana, considerable variation is observed in recombination frequency and distribution between natural accessions. By investigating recombination events in A.thaliana, this project aimed to identify trans-acting modifiers of recombination frequency that varied between natural accessions. Identification of meiotic recombination modifiers was performed through Quantitative Trait Loci (QTL) mapping in A.thaliana natural-accession cross populations. Populations were generated from crosses between two accessions which differed significantly for recombination frequency as measured across a defined region of the genome flanked by a fluorescent-reporter system. F1 plants were then self-fertilised to produce segregating mosaic F2 populations for mapping. Recombination frequency for specific genomic intervals was determined for each individual in the population through measurement of the segregation of flanking fluorescence-genes expressed in the products of meiosis - seeds or pollen. Individuals were also genotyped using accession-specific markers across the genome, at a marker density of one marker per 2-5Mb, depending on the chromosome. Association of variation in recombination frequency with specific sections of the genome differing between the parental accessions through QTL mapping revealed significant modifiers of meiotic recombination segregating within the populations. This resulted in the identification of three significant large-effect modifiers that differed between Col-0 and Cvi-0 accessions, on chromosomes 1 ,2 and 5, affecting recombination in an interval in the sub-telomere region of chromosome 3. An additional modifier on chromosome 4 affecting the same sub-telomeric interval was identified that differed between the Col-0 and Can-0 accessions. Further fine-mapping of modifiers to improve location resolution was performed by repeated backcrosses into the Col-0 genetic background to remove the influence of other large-effect QTL and possible unknown small-effect modifiers. Improving the resolution provided a number of potential candidates for genes underlying the recombination phenotype for each QTL. Candidate testing was then performed, either through transformation of different accession alleles into the fluorescent-reporter system, or through analysis of T-DNA insertion lines that interrupted candidate genes. Preliminary results from T-DNA insertion mutants crossed to the fluorescent-reporter system suggest a potential role for the AT2G31510 gene in modification of meiotic recombination frequency, though the mode of action remains unknown. These results demonstrate the presence of large-effect modifiers of meiotic recombination frequency that vary between the natural A.thaliana accessions Col-0, Cvi-0 and Can-0. Confirmation of underlying genes or sequence elements and characterisation of their mechanism of action are opportunities for exploration in future experiments.
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Baer-Henney, Dinah. "On natural and probabilisic effects during acquisition of morphophonemic alternations". Master's thesis, Universität Potsdam, 2009. http://opus.kobv.de/ubp/volltexte/2009/3681/.
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The acquisition of phonological alternations consists of many aspects as discussions in the relevant literature show. There are contrary findings about the role of naturalness. A natural process is grounded in phonetics; they are easy to learn, even in second language acquisition when adults have to learn certain processes that do not occur in their native language. There is also evidence that unnatural – arbitrary – rules can be learned.
Current work on the acquisition of morphophonemic alternations suggests that their probability of occurrence is a crucial factor in acquisition. I have conducted an experiment to investigate the effects of naturalness as well as of probability of occurrence with 80 adult native speakers of German. It uses the Artificial Grammar paradigm: Two artificial languages were constructed, each with a particular alternation. In one language the alternation is natural (vowel harmony); in the other language the alternation is arbitrary (a vowel alternation depends on the sonorancy of the first consonant of the stem).
The participants were divided in two groups, one group listened to the natural alternation and the other group listened to the unnatural alternation. Each group was divided into two subgroups. One subgroup then was presented with material in which the alternation occurred frequently and the other subgroup was presented with material in which the alternation occurred infrequently. After this exposure phase every participant was asked to produce new words during the test phase. Knowledge about the language-specific alternation pattern was needed to produce the forms correctly as the phonological contexts demanded certain alternants. The group performances have been compared with respect to the effects of naturalness and probability of occurrence.
The natural rule was learned more easily than the unnatural one. Frequently presented rules were not learned more easily than the ones that were presented less frequently. Moreover, participants did not learn the unnatural rule at all, whether this rule was presented frequently or infrequently did not matter. There was a tendency that the natural rule was learned more easily if presented frequently than if presented infrequently, but it was not significant due to variability across participants.Suffixe, die an Wortstämme angehängt werden, tragen grammatische Informationen. Bei Verben wird dabei die Person, Numerus, Tempus, Modus und Genus Verbi angezeigt, bei Nomen Kasus, Numerus und Genus. Durch phonologische Kontexte bedingt kann eine solche morphologische Markierung ihre Gestalt ändern und unterschiedliche Oberflächenformen annehmen. Die dabei entstandenen Allomorphe werden durch regelbasierte Prozesse von dem zugrunde liegenden Morphem abgeleitet. Es zeigt sich, dass der Erwerb morphophonemischer Alternationen ein aufwendiger und schwieriger Lernprozess ist. Die vorliegende Arbeit beschäftigt sich nun mit Faktoren, die den Erwerb der Alternationen positiv beeinflussen können. Zum einen wird der Faktor Natürlichkeit, zum anderen der Faktor Auftretenshäufigkeit diskutiert. Trotz einiger widersprüchlicher Evidenzen bezüglich des ersten Faktors hat sich in der neueren Forschung herausgestellt, dass ein natürlicher Prozess leichter zu lernen ist als ein unnatürlicher. Oft konnte ein Vorteil der natürlichen gegenüber den unnatürlichen Prozessen festgestellt werden. Allerdings zeigt sich dieser Umstand nicht immer – dann wiederum zeigt sich kein Vorteil gegenüber einem der beiden Prozesse. Die Ursachen dafür sind in der Methode oder der Herangehensweise zu suchen. Mache Methode scheint nicht sensitiv genug zu sein, den Vorteil aufzudecken, und manche Studien gehen unterschiedlich an die generelle Frage heran, was denn überhaupt ein natürlicher Prozess ist. Unter Berücksichtigung der einschlägigen Literatur habe ich Charakteristika eines typisch natürlichen Prozesses herausgearbeitet und damit die definitorische Grundlage für die empirische Untersuchung derselben bestimmt. Die Auftretenshäufigkeit eines Prozesses scheint auch ein entscheidender Faktor für den Erwerbsprozess zu sein. Dabei wird der Prozess leichter gelernt, der frequent im Input vorliegt, wohingegen ein Prozess schwieriger zu lernen ist, je weniger häufig er vorkommt. In verschiedenen Studien konnte gezeigt werden, dass die bloße Verteilung eines Musters in Wörtern bzw. im Lexikon schon ausreichen kann, zugrunde liegende Repräsentationen zu formen. Dabei ist immer das frequentere Muster das zuverlässigere. Anhand einer experimentellen Studie habe ich beide Faktoren direkt miteinander verglichen. Es wurde die Lernbarkeit einer natürlichen künstlichen Sprache mit der einer unnatürlichen künstlichen Sprache verglichen. Die Sprachen unterschieden sich lediglich in der Regel, nach der eines von zwei Pluralmorphemen ausgewählt werden musste, wobei die natürliche Sprache nach Vokalharmonie alternierte und die unnatürliche Sprache nach einer arbiträren Regel. In zwei Hauptgruppen wurde 80 erwachsenen Deutschen entweder die eine oder die andere Sprache präsentiert. In jeder Gruppe wurde die Hälfte der Probanden häufig (zu 50%) mit der Alternation konfrontiert, die andere Hälfte infrequent (zu 25%). Nach der Familiarisierungsphase ohne expliziten Lernauftrag war die Aufgabe aller Probanden, von neuen Wörtern der Sprache(n) den Plural zu bilden. Die Analyse der Reaktionen ergab einen Effekt der Natürlichkeit, aber keinen der Auftretenshäufigkeit: Die natürliche Sprache war deutlich besser zu lernen als die unnatürliche. Die Auftretenshäufigkeit in beiden Sprachen führte zu keinem signifikanten Unterschied. Kein einziger von den 40 Probanden, die die unnatürliche Regel präsentiert bekamen, hat die Regel für die entsprechende Alternation gelernt. Es zeigt sich jedoch eine Tendenz bei den Probanden, die die natürliche Sprache erlernen sollten: Diejenigen scheinen einen Vorteil zu haben, die häufiger die Alternation während der Familiarisierungsphase hören. Aber auch unter den Probanden, die mit der natürlichen Sprache konfrontiert wurden, zeigten einige gar keinen Lernerfolg, weshalb ich vermute, dass wegen der großen Varianz in den Daten die Auftretenshäufigkeit als einflussreicher Faktor empirisch nicht belegt werden konnte. Zusammenfassend konnte nachgewiesen werden, dass das Lernen der Alternationen sehr stark von einem bias für Natürlichkeit beeinflusst wird. Allein mit der distributionellen Analyse der verschiedenen Pluralendungen hätte der Vorteil für die Alternation der natürlichen Sprache nicht erklärt werden können.
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Kadhim, Ammar. "Natural frequency and transient dynamic analysis of vehicle integrated RBS 70 NG system". Thesis, Karlstads universitet, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-68935.
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Abstract This study is a master thesis in mechanical engineering at Karlstad’s University that treats operation disturbances that occur during the use of a vehicle integrated air-defense system called Robot-system 70 New Generation (RBS 70 NG) in cooperation with SAAB Dynamics AB. RBS 70 NG is a man-portable air-defense system (MANPADS) which is designed for anti-aircraft warfare and can be used in all climate zones. The system usually operates on a hard surface such as gravel or hard soil, but for this project the aim is to integrate the system to operate on a vehicle platform. There are two disturbing factors that could affect the system during operation; the first is that the system is displaced due to the external forces that act on the system during use. The second disturbance specification is that the natural frequency of the entire system should be within a range of 3.5-6 Hz for vehicles installed RBS 70 NG [1]. The system is studied by using a simple mathematical model and by the use of computer aided software programs including CATIA V5 R22 and ANSYS R18.1. The modified design of the complete system showed that by adding four external legs to the platform, a natural frequency in-between the given interval is reached. A Transient Response Analysis was done to analyze the MANPADS ground version in order to make have some sort of a reference when studying the vehicle version of the RBS 70 NG and to make both system as similar as possible. The displacement of the system sight was similar for both versions of the system, when operating on the ground and on a vehicle.Sammanfattning Den här studien är ett examensarbete inom maskinteknik på Karlstads Universitet, som behandlar driftstörningar för ett fordon integrerat ”Robotsystem 70 New Generation” i samarbete med SAAB Dynamics AB. Robotsystem 70 (RBS 70 NG) är ett luftvärnsrobotsystem som tillverkas i Sverige av SAAB Dynamics AB. Systemet används vanligtvis på hårda underlag som till exempel mark och grus, men i den här rapporten studeras integrationen av systemet på ett fordons plattform. Två störningsspecifikationer uppkommer vid användning av RBS 70 NG som tas hänsyn till, den första är att systemets förskjutning som exciteras via de krafter som uppkommer vid utskjutning inte stör systemet under drift. Den andra störningsspecifikationen är att den naturliga frekvensen för hela systemet bör ligga på ett intervall mellan 3,5–6 Hz för fordon installerat RBS 70 NG [1]. Analyserna har gjorts dels genom en förenklad teoretisk modell av systemet och genom användning av datorbaserade program såsom CATIA V5 R22 och ANSYS R18.1. Konstruktions ändringar på plattformen gjordes för att uppnå den minimala gränsen på egenfrekvensen på ca 3,5 Hz. Montering av fyra externa stödben på plattformen gav godkända värden på egenfrekvensen. En så kallad ”Transient Response Analysis” utfördes med hjälp av ANSYS R18.1 som visade att systemet utan konstruktions ändringar förskjuts med mindre än det minimala tillåtna värdet som tidigare beskrivet och att de pålagda krafterna inte var tillräckligt stora för att störa systemets drift.
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Dong, Jessica. "Identification of novel NK cell-mediated immunosurveillance function: immunogenicity regulation by monitoring antigen frequency". PLoS One, 2012. http://hdl.handle.net/1993/22039.
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Computational analysis of total amino acid sequences indicate that select combinations that occur less frequently are correlated to increased immunogenicity in humans. Much evidence has been gathered in silico, but little is known about in vivo experimental validation. This concept can be applied to adjuvant research where increased immunogenicity is desirable and can aid in the potency and efficacy of vaccines. A rare peptide called 5mer4 was found to adjuvant influenza vaccines by increasing survival, humoral and cellular immune responses with a speculated NK cell mediated mechanism. Therefore we hypothesize that rare peptides are able to stimulate an increased immune response in comparison to common peptides through a NK-mediated fashion. The first aim of this study is to determine whether rare sequences are able to stimulate an increased immune response collectively in comparison to commonly occurring peptides. Mice vaccinated with rare, semi-common and common peptides indicate a trend of heightened cellular immune response from rare peptides. However, select rare peptide sequences based on high IFNγ responses do not always correlate directly to increased vaccine efficacy against H5N1-H05 influenza virus, indicating that additional immune parameters need to be taken into consideration. When compared against other adjuvants, 5mer4 performed better in both humoral and survival studies. Previous findings suggest NK cell involvement warranted the second aim of this thesis which is to further delineate the role of NK cells as rare peptide immune modulators. Macrophages were evaluated to determine the effect of peptide, but no increase in stimulation could be observed. NK cells incubated with rare peptides show increased levels of early activation marker CD69 in comparison to common peptides. Microscopy data indicates that rare, but not common peptides are able to bind to NK cells. Depletion of NK abrogated adjuvant activity of 5mer4 peptide, suggesting the necessary role of NK cells for adjuvant effect. Taken together, rare peptides have shown the ability to modulate the immune response through NK cell activation verifying our hypothesis. These findings can be extrapolated towards multiple fields such as anti-tumor therapies and can lead to the development of immunomodulators with high efficacy at a lower cost.
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Alder, Tyson Scott. "Determining Natural Frequencies Using Embedded and Placed Sensors under Ambient and Shaker Excitation". DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/5857.
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Dynamic monitoring of structures is a method of detecting changes and damage to the structure. Vibration based monitoring has been used to detect damage in rotating machinery and is gaining popularity in the field of Structural Health Monitoring (SHM). Monitoring involves detecting changes in natural frequencies and changes in mode shapes. These changes reflect changes to properties of the bridge which can indicate damage.
The Nibley Bridge is a single span bridge comprised of ten deck bulb girders. The bridge spans 25.91m (85 ft.) and includes two lanes, sidewalks on both sides, and a small median. The Nibley Bridge was constructed with monitoring in mind. A dynamic monitoring system was planned to detect frequencies for long term monitoring. Initial monitoring of the embedded accelerometers was ineffective, so additional testing was required. An impact test was done with additional sensors to calibrate the embedded sensors. To further define the natural frequencies and mode shapes of the bridge, two shaker tests were also performed.
The embedded sensors were noted as having a large noise range. Also, they required a specific data logger to detect meaningful data. Recommendations for the use of the embedded accelerometers were determined and defined. The additional tests were able to assist in calibrating the accelerometers, as well as defining the natural frequencies and mode shapes of the structure. Natural frequencies were defined for each test and the changing condition of the bridge between those tests. The addition of asphalt occurred between two tests and a change of approximately 20° C between the other two tests. Though there is not much information to form a correlation, the detected changes define the dynamic aspects of the bridge.
Lastly, mode shapes were determined and a Modal Assurance Criterion (MAC)analysis was done to correlate the measured and analytical mode shapes. This model helped to indicate which parameters effect the mode shapes of the structure. Comparison between these parameters and changes between them help to indicate the predicted behavior of the structure under different circumstances. Though these tests do not define all of the dynamic properties of the bridge, they do provide a general baseline of values that can be expected for future tests of the structure.
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Sullivan, Daniel Edward. "Evaluation of Word and Paragraph Embeddings and Analogical Reasoning as an Alternative to Term Frequency-Inverse Document Frequency-based Classification in Support of Biocuration". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/80572.
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This research addresses the problem, can unsupervised learning generate a representation that improves on the commonly used term frequency-inverse document frequency (TF-IDF ) representation by capturing semantic relations? The analysis measures the quality of sentence classification using term TF-IDF representations, and finds a practical upper limit to precision and recall in a biomedical text classification task (F1-score of 0.85). Arguably, one could use ontologies to supplement TF-IDF, but ontologies are sparse in coverage and costly to create. This prompts a correlated question: can unsupervised learning capture semantic relations at least as well as existing ontologies, and thus supplement existing sparse ontologies? A shallow neural network implementing the Skip-Gram algorithm is used to generate semantic vectors using a corpus of approximately 2.4 billion words. The ability to capture meaning is assessed by comparing semantic vectors generated with MESH. Results indicate that semantic vectors trained by unsupervised methods capture comparable levels of semantic features in some cases, such as amino acid (92% of similarity represented in MESH), but perform substantially poorer in more expansive topics, such as pathogenic bacteria (37.8% similarity represented in MESH). Possible explanations for this difference in performance are proposed along with a method to combine manually curated ontologies with semantic vector spaces to produce a more comprehensive representation than either alone. Semantic vectors are also used as representations for paragraphs, which, when used for classification, achieve an F1-score of 0.92. The results of classification and analogical reasoning tasks are promising but a formal model of semantic vectors, subject to the constraints of known linguistic phenomenon, is needed. This research includes initial steps for developing a formal model of semantic vectors based on a combination of linear algebra and fuzzy set theory subject to the semantic molecularism linguistic model. This research is novel in its analysis of semantic vectors applied to the biomedical domain, analysis of different performance characteristics in biomedical analogical reasoning tasks, comparison semantic relations captured by between vectors and MESH, and the initial development of a formal model of semantic vectors.Ph. D.
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Boice, Michael DeLancey. "Study To Improve The Predicted Response Of Floor Systems Due To Walking". Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/31213.
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The scope of this study is divided into three topics. To begin, more accurate methods for estimating the fundamental natural frequencies of floors were explored. Improvements for predicting the behavior of floor systems using several criteria were also investigated. The final topic compared the AISC and SCI methods for analyzing vibrations acceptability.
Natural frequency prediction was studied by examining 103 case studies involving floor systems of various framing occupied or being constructed in the United States and Europe. Based on the results from these comparisons, it was reasonably concluded that the predicted bay frequency using Dunkerly's estimate (fn2) is not the most accurate method for predicting the system frequency using the AISC Design Guide for all types of framing analyzed. The predicted beam frequency using AISC methods provided sound correlations with the measured bay frequencies. On the other hand, with the exception of floor systems with joist girders and joists, the results showed that the SCI methods provided more accurate predictions of bay frequency despite a fair amount of data scatter.
Evaluations based on the AISC Design Guide 11, the SCI criteria Murray Criterion, and Modified Reiher-Meister scale were compared with subjective field analyses for each case study in the second part of this study. The AISC Design Guide criterion is the most consistent method for predicting floor behavior. The SCI criterion is the next most consistent method for floor acceptability, followed by the Murray Criterion then the Modified Reiher-Meister scale.
In the final part of this study, predicted accelerations and floor behavior tolerability for 78 case studies were evaluated using the AISC and the SCI criteria. The two prediction methods are in agreement for 82 % (64 of 78) of the case studies, and strongly disagree for only 12 % (9 of 78) of the case studies.Master of Science
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Scott, Mikael. "Interactions of Divalent Cations with the Carboxylate Moiety : A Vibrational Sum Frequency Study". Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-243910.
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The interactions between the divalent salts CaCl2, MnCl2 and NiCl2 with the carboxylicacid groups in an arachidic acid Langmuir monolayer are studied using vibrational sumfrequency spectroscopy (VSFS). At low salt concentrations the charging of the monolayer is shown to behave in accordance with classical theories of the electrical doublelayer. However, deviations from classical theories are readily apparent at concentrations starting from 1 μM and shown to differ depending on the nature of the cation, indicating an ion specific effect. From the analysis of the carboxylate symmetric vibration at least two different types of ion pair interactions between the divalent cations and the carboxylicacid moiety are detected: a solvent-separated and two (or more) possible contact ion-pairs and/or complexes. By using different VSFS polarization schemes the molecular orientation of the vibration is elucidated and further insight into the state of the carboxylic acidis gained. The ordering of water molecules in the diffuse layer as a result of the surfacepotential of the charged monolayer is also probed and found, at low ionic strengths, to bein agreement with the behaviour predicted by the Gouy-Chapman model. At high concentrations the hydration within the Stern layer can be detected and found to differ with the nature of the electrolyte. Additionally, the importance of the purity grade of the salts used for correctly interpreting the results is shown theoretically and verified experimentally,where trivalent ions affect the surface at concentrations several orders of magnitude below those from mono and divalent ions. Finally, diffusion is shown to play a major rolein the kinetics of deprotonation of the monolayer at submicromolar concentrations, while higher valency cations are also shown to deprotonate the surface at a quicker rate through electroflux.
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Björklind, Malin. "Soil profile analysis by vibration theory and the natural frequency : Applied on a case project". Thesis, Luleå tekniska universitet, Geoteknologi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67151.
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To explore soil conditions at sites of infrastructure projects a number of geotechnical soundings are performed at appropriate intervals. Results are, in the nature of their set up, limited to the specific points at which the sounding is performed. To safely assume the area between bore holes a new method is applied and tried at the case railroad project Stenkumla – Dunsjö. By applying vibration theory in conjunction with the studied soils’ geodynamic properties the natural frequency for the soil can be calculated. The properties of the natural frequency also makes it possible to detect in vibration measurements. The method studied in this master thesis is that of utilizing the natural frequency of the soil to try and establish a soil profile from vibration measurements. An important step in the method is to transform the vibration with the Fast Fourier Transform algorithm. This allows the comparison and analysis of natural frequencies. The measurements were performed by using and attaching an accelerometer to a train. Results are partly transformed measurement data in frequency graphs and partly natural frequency calculations according to the site investigations. These are compared in the analysis section to try to confirm the methods’ reliability and to see if the method can be used to refine geotechnical investigations. The reliability of the method is tested by watching for the expected frequencies from the calculations in the measurement data. The method show more consistency closer to the ground surface rather at greater depths. It is also more reliable for stark contrast layers, i.e. if the soil layers have much of the same properties then it is difficult to spot the differing natural frequencies, as they are too similar. In trying to establish the soil profile between bore holes the method is inconclusive, partly due to the fact that the investigated area consists of relatively alike soil layers that make the result graphs difficult to get information from. However, the suggested soil profiles from the analysis of this part of the master thesis bear resemblances to bore holes close by, so the method can be usable in some regard. Quality of measurement results would probably be better by running the train faster than was done in this master thesis. The quality of the analysis would also benefit from performing specific soundings to establish the soils’ geodynamic properties rather than using recommended empirical formulas as were used here. The primary possible application for this method is to use it as a prioritizing tool at an early stage in infrastructure projects. Running the vibration measurement and getting a preliminary picture of the soil conditions could act as a way of steering investigations resources to where greater shifts in the data occur.I det förberedande skedet inför infrastrukturprojekt genomförs geotekniska undersökningar för att kartlägga jordförhållanden. Detta genomförs bland annat med ett antal olika borrhålsmetoder. Genom sin utförandeform levererar dessa resultat som, strikt uttryckt, är knutna till de specifika punkter där de utförs. I detta examensarbete provas en ny metod där jordprofilen mellan- och vid punkten för borrhål ska kartläggas. Metoden provas ut på järnvägsprojektet Stenkumla – Dunsjö. Vibrationsteori och geodynamiska egenskaper hos jorden utnyttjas för att fastställa olika jordlagers egenfrekvens. Egenfrekvensens definition gör det möjligt att detektera denna i vibrationsmätningar. Metoden som provas i examensarbetet är att genom vibrationsmätningar fastställa jordprofilen baserat på jordlagrens egenfrekvens. Ett viktigt steg i metodens process är att transformera resultatet från vibrationsmätningen med Fast Fourier Transformation, en algoritm för databehandling. Genom att applicera Fast Fourier Transformation kan en jämförelse mellan egenfrekvenser från olika källmaterial göras. De primära vibrationsmätningarna genomfördes genom att fästa en accelerometer på ett tåg. Resultat består i transformerade grafer från vibrationsmätningar samt egenfrekvensberäkningar baserade på de geotekniska undersökningarna vid projekt Stenkumla – Dunsjö. På detta följer en jämförande analys där metodens tillförlitlighet och applicerbarhet runt geotekniska undersökningar diskuteras. Tillförlitligheten testas genom att identifiera beräknade förväntade värden på egenfrekvensen i mätdatat från tåget. Metoden visar högre tillförlitlighet närmare markytan än djupare ner i jordprofilen. Metodens precision är mer utvecklad för jordprofiler där jordlagren är differentierade från varandra i dess egenskaper. Detta uppstår som en följd av att mer lika drag hos jordlagren får liknande egenfrekvens, vilket gör dem svårare att identifiera och särskilja i frekvensspektrat. Metoden visade sig vara ofullständig i att fastställa en jordprofil mellan geotekniska borrprover. En anledning till detta är att det område som användes för vibrationsmätningar består av en jordprofil utan allt för varierande egenskaper, vilket gör att en tillräckligt tillförlitlig analys är omöjlig med den mängd data som fanns att tillgå. Den jordprofil som itererades fram i analysavsnittet har dock liknande uppbyggnad som de jordprofiler som fastställts av geotekniker i den geotekniska undersökningsrapporten, vilket ändå tyder på viss användningspotential. Kvalitén på vibrationsmätningen skulle förbättras av att öka farten, och så vibrationen, på tåget som mätaren var fäst på. En annan förbättringsmöjlighet är att få tillgång till uppmätta geodynamiska egenskaper hos jorden istället för de empiriska formler som användes i detta arbete. Det primära användningsområdet för metoden är att använda den som ett prioriteringsverktyg i ett tidigt skede vid infrastrukturprojekt. Genom att genomföra en vibrationsmätning kan en preliminär bild av jordförhållandena erhållas. Detta kan sedan användas som ett sätt att styra geotekniska undersökningsresurser mer effektivt mot områden där stora avvikelser i vibrationsdatat identifierats.
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Trotter, Meridith V. y n/a. "Frequency-dependent selection and the maintenance of genetic variation". University of Otago. Department of Zoology, 2008. http://adt.otago.ac.nz./public/adt-NZDU20081114.120926.
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Frequency-dependent selection has long been a popular heuristic explanation for the maintenance of genetic diversity in natural populations. Indeed, a large body of theoretical and empirical work has already gone into elucidating the causes and consequences of frequency-dependent selection. Most theoretical work, to date, has focused either on the diallelic case, or dealt with only very specific forms of frequency-dependence. A general model of the maintenance of multiallelic genetic diversity has been lacking. Here we extend a flexible general model of frequency-dependent selection, the pairwise interaction model, to the case of multiple alleles.
First, we investigate the potential for genetic variation under the pairwise interaction model using a parameter-space approach. This approach involves taking a large random sample of all possible fitness sets and initial allele-frequency vectors of the model, iterating each to equilibrium from each set of random initial conditions, and measuring how often variation is maintained, and by which parameter combinations. We find that frequency- dependent selection maintains full polymorphism more often than classic constant-selection models and produces more skewed equilibrium allele frequencies. Fitness sets with some degree of rare advantage maintained full polymorphism most often, but a variety of non-obvious fitness patterns were also found to have positive potential for polymorphism.
Second, we further investigate some unusual dynamics uncovered by the parameter-space approach above. Long-period allele-frequency cycles and a small number of aperiodic trajectories were detected. We measured the number, length and domains of attraction of the various attractors produced by the model. The genetic cycles produced by the model did not have periods short enough to be observable on an ecological time scale. In a real world system, allele-frequency cycling is likely to be indistinguishable from stable equilibrium when observed over short time scales.
Third, we use a construction approach to model frequency-dependent selection with mutation under the pairwise interaction model. This approach involves the construction of an allelic polymorphism by bombarding an initial monomorphism with mutant alleles over many generations. We find that frequency-dependent selection is able to generate large numbers of alleles at a single locus. The construction process generates a wide range of allele- frequency distributions and genotypic fitness relationships. We find that constructed polymorphisms remain permanently invasible to new mutants. Analysis of constructed fitness sets may even reveal a signature of positive frequency dependence.
Finally, we examine the numbers and distributions of fitnesses and alleles produced by construction under the pairwise interaction model with mutation from existing alleles, using several different methods of generating mutant fitnesses. We find that, relative to more general construction models, generating mutants from existing alleles lowers the average number of alleles maintained by frequency-dependent selection. Nevertheless, while the overall numbers of alleles are lower, the polymorphisms produced are more stable, with more natural allele-frequency distributions.
Overall, frequency-dependent selection remains a powerful mechanism for the maintenance of genetic variation, although it does not always work in intuitively obvious ways.
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Duncan, Fiona Helen. "Fatigue after stroke : its frequency, natural history and associations with mood, physical activity and physical fitness". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25407.
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Background: Fatigue is common and distressing after stroke. Many stroke survivors say it is their worst or one of their worst symptoms. The frequency of clinically significant fatigue, whether fatigue is likely to be more or less problematic over time, and its aetiology are unknown. There are currently no known treatments. One hypothesis is that fatigue after stroke is triggered by physical deconditioning which sets up a self-perpetuating cycle of fatigue, avoidance of physical activity, further deconditioning and more fatigue. Another theory is that low mood may contribute to fatigue. Aims: This thesis therefore aims to investigate the frequency and natural history of fatigue after stroke and to explore its associations with mood, physical activity and/or fitness. Method: These aims were addressed by carrying out: 1) a systematic review of all longitudinal observational studies which have assessed fatigue on at least two separate time points and reported its frequency, 2) a systematic review of all observational studies which have measured both fatigue poststroke and one or more measures of physical activity and/or fitness at the same time point and 3) a longitudinal cohort study which assessed clinically significant fatigue, mood and physical activity and fitness at one, six and 12 months after stroke. Results: Frequency of fatigue ranged from 30% to 92% at first time point and frequency of fatigue decreased over time in seven of the ten studies identified in the systematic review of longitudinal studies. The second systematic review found that only two of the eight studies identified found a significant direct relationship between fatigue and physical activity and/or fitness poststroke. In the longtidudinal cohort study, clinically significant fatigue was identified in 32.6% of 132 participants at one month and was still present in a fifth of 91 participants at 12 months, two-thirds of participants who had clinically significant fatigue at one month did not have it by six months and that most (60.4%) individuals either reported fatigue at all three time points or that they did not have fatigue at any time point. There were significant associations between daily step count and fatigue at each time point (p= < 0.0001, 0.011, 0.006). Physical activity (p=0.002, 0.006) and anxiety (p= < 0.0001, 0.001) at one month were independent significant predictors of fatigue severity at six and 12 months after stroke. Age, gender, fatigue before stroke, step count and anxiety at one month accounted for 22% and 27% of the variance in fatigue severity at six and 12 months respectively. No significant associations were found between fatigue and measures of physical fitness. Discussion and conclusion: The findings suggest that although fatigue is common and persistent after stroke, it is more likely to become less problematic over time. They also suggest that the de-conditioning hypothesis of the aetiology of fatigue may be too simplistic and that other factors are involved in the development and perpetuation of fatigue after stroke. Implications are that patients should be assessed for fatigue early after stroke and that the development of an intervention which increases activity and/or reduces anxiety may be beneficial.
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Markgraaff, Renier Francois. "Relationship between the natural frequencies and fatigue life of NGB–18 graphite / Renier Markgraaff". Thesis, North-West University, 2010. http://hdl.handle.net/10394/4813.
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NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor
Company (PBMR), and is used as the preferred material for the internal graphite core
structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18
graphite is manufactured using pitch coke, and is vibrationally molded.
To assess the structural behaviour of graphite many destructive techniques have been
performed in the past. Though the destructive techniques are easy and in some cases
relative inexpensive to perform, these methods lead to waste material and require
cumbersome time consuming sample preparations.
To overcome this problem numerous non–destructive testing techniques are available
such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency
Eddy current analysis, acoustic emission and impulse excitation techniques.
The Hammer Impulse Excitation technique was used as a method in predicting the
fatigue life of NBG–18 graphite by focussing on the application of modal frequency
analysis of determined natural frequencies. Moreover, the typical fatigue
characteristics of NBG–18 graphite were determined across a comprehensive set of
load ranges.
In order to be able to correlate modal frequency parameters with fatigue life, suitable
uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue
test specimens were manufactured from two NBG–18 graphite sample blocks. The
relationship between natural frequencies of uniaxial test specimens, fatigue life,
sample positioning and sample orientation was investigated for different principle
stress ratios.
Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the
Pearson correlation coefficients investigated. However, there was no significant trend
found between the natural frequency and the fatigue life.Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.
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Keeli, Anupama. "Low frequency transmission for remote power generating systems". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41190.
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The goal of this Masters Thesis research is to evaluate alternative transmission systems from remote wind farms to the main grid using low-frequency AC technology. Low frequency means a frequency lower than nominal frequency (60/50Hz). The low-frequency AC network can be connected to the power grid at major substations via cyclo-converters that provide a low-cost interconnection and synchronization with the main grid. Cyclo-converter technology is utilized to minimize costs which result in systems of 20/16.66 Hz (for 60/50Hz systems respectively). Low frequency transmission has the potential to provide an attractive solution in terms of economics and technical merits.
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Herrmann, Manuel. "Torsional Stiffness and Natural Frequency Analysis of a Formula SAE Vehicle Carbon Fiber Reinforced Polymer Chassis using Finite Element Analysis". DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1692.
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Finite element is used to predict the torsional stiffness and natural frequency response of a FSAE vehicle hybrid chassis, utilizing a carbon fiber reinforced polymer sandwich structure monocoque and a tubular steel spaceframe. To accurately model the stiffness response of the sandwich structure, a series of material tests for different fiber types has been performed and the material properties have been validated by modeling a simple three-point-bend test panel and comparing the results with a physical test. The torsional stiffness model of the chassis was validated with a physical test, too. The stiffness prediction matches the test results within 6%. The model was then used to model the natural frequency response by adding and adjusting the materials’ densities in order to match physical mass properties. A hypothesis is made to explain the failure of the engine mounts under the dynamic response of the frame.
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Lu, Haohui. "Vibration Properties and High Speed Stability of a Rotating Piezoelectric Energy Harvesting Device That Experiences Gyroscopic Effects". OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2050.
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This study investigates the vibration of a rotating piezoelectric device that consists of a proof mass that is supported by elastic structures with piezoelectric layers. Vibration of the proof mass causes deformation in the piezoelectric structures and voltages to power electrical loads. The coupled electromechanical equations of motion are derived using Newtonian mechanics and Krichhoff's circuit laws. The free vibration behavior is investigated for devices with identical (tuned) and nonidentical (mistuned) piezoelectric support structures and electrical loads. These devices complex-valued have speed-dependent eigenvalues and eigenvectors as a result of their constant rotation. The imaginary parts of the eigenvalues physically represent the oscillation frequencies of the device. The real parts represent the decay or growth rates of the oscillations, depending on their sign. The complex-valued components of the eigenvectors physically represent the amplitudes and phases of the vibration. The eigenvalue behaviors differ for tuned and mistuned devices. Due to gyroscopic effects, the proof mass in the tuned device only vibrates in either forward or backward decaying circular orbits in single-mode free response. This is proven analytically for all tuned devices. For mistuned devices, the proof mass has decaying elliptical forward and backward orbits. The eigenvalues are shown to be sensitive to changes in the electric load resistances. Closed-form solutions for the eigenvalues are derived for open and close circuits. At high rotation speeds these devices experience critical speeds and instability. Closed-form solutions for the critical speeds are derived. Tuned devices have one degenerate critical speed that separates stable speeds from unstable speeds, where flutter instability occurs. Mistuned devices have two critical speeds. The first critical speed separates stable speeds from speeds where divergence instability occurs. Divergence instability continues for small speeds above the second critical speed. At higher supercritical speeds flutter instability occurs. Transitions between stable and unstable eigenvalues are investigated using root locus diagram. This device has atypical eigenvalue behavior near the critical speeds and stability transitions compared to conventional gyroscopic systems.
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Bhatt, Samir. "Statistical analysis of natural selection in RNA virus populations". Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:64341c38-f09e-48ed-84e8-7ab9f171a753.
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A key goal of modern evolutionary biology is the identification of genes or genome regions that have been targeted by natural selection. Methods for detecting natural selection utilise the information sampled in contemporary gene sequences and test for deviation from the null hypothesis of neutrality. One such method is the McDonald Kreitman test (MK test), which detects the the molecular 'footprint' left by natural selection by considering the frequency of observed mutations within the sampled population. In this thesis I investigate the applicability of the MK test to viral populations and develop several new methods based on the original MK test. In chapter 2, I use a combination of simulation and methodological improvements to show that the MK test can have low error when applied to analysis of RNA virus populations. Then, in chapter 3, I develop an extension of the MK test with the purpose of estimating rates of adaptive fixation for all genes of the human influenza A virus subtypes H1N1 and H3N2. My results are consistent with previous studies on selection in influenza virus populations, and provide a new perspective on the evolutionary dynamics of human influenza virus. In chapter 4 I develop a formal statistical framework based, on the MK test, for calculating the number of non neutral sites at any frequency range in the site frequency spectrum. In this framework, I introduce a new method for reconstructing the site frequency spectrum that incorporates sampling error and allows for the inclusion of prior knowledge. Using this new framework I show that the majority of nucleotide sites in hepatitis C virus sequences sampled during chronic infection represent deleterious mutations. Finally, in chapter 5 I use the generalised framework introduced in chapter 4 to develop a statistic for evaluating the deleterious mutation load of a population. I apply this test sequences that represent 96 RNA virus genes and show that my approach has comparable power to equivalent phylogenetic methods. In this thesis I have developed computationally efficient methods for analysis of genetic data from virus populations. It is my hope that these methods will become useful given the explosion in sequence data that has accompanied recent improvements in sequencing technology.
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Eriksson, Jennifer. "Horizontal natural frequency in a 10 story building : A comparison between CLT and concrete using estimate calculations". Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-152131.
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Tall slender buildings are easily set in motion by wind and earthquakes but by estimating the buildings horizontal natural frequencies in the design phase, these motions can be kept within acceptable boundaries. There are many parameters that decides the natural frequency of a building and it can therefore be difficult to calculate it. There are a few ways though to estimate horizontal natural frequencies of tall buildings and two methods have been tested in this report. Both methods give the frequency of a clamped-free cantilever but one of them requires a single degree of freedom system whilst the other handles a multi degree of freedom system. The methods are called SDOF method and MDOF method in this report. A fictional building was created for this project to be the reference object in the comparison between the two methods SDOF and MDOF. The walls and floors of the building was designed with the support of both an acoustic engineer and a structural engineer to create a realistic building. A building’s natural frequency is dependent of the self-weight, stiffness and height of the building and it was therefore important to design these components with care. The fictional building is called House 1 and is a 10 story, almost square building about 20 m wide and broad and 30 m high. This report does not only compare the natural frequencies obtained from the two different calculation methods, but it also shows the difference in frequency in timber and concrete structures. Shear walls constitutes the horizontal stabilization system of the fictional building and both a CLT core and a concrete core is designed and compared. It is only the walls that comes in two different versions, the floorings consist of CLT boards for both structures tested. The horizontal natural frequencies of House 1 were about 2 Hz and 3 Hz for the CLT version and concrete version respectively. It was expected to get frequencies within that range considering the height of House 1. The CLT core having a lower frequency than the concrete core was also expected since concrete is a stiffer material than wood. To be able to make a fair comparison between the SDOF method and the MDOF method, House 1 was designed with the same dimensions and stiffness on all floors because the SDOF method requires that. The results from the two methods are almost identical with only 0.3 Hz and 0.4 Hz difference for the concrete and CLT respectively. For a shear wall structure with a consistent stiffness, weight and dimension, any of the two methods can be used to estimate the horizontal natural frequency. However, it is not realistic for a building of 30 m or higher, to have the same dimensions on the load bearing structure on all floors which makes the MDOF method more accurate in more cases than the SDOF method.Höga slanka byggnader kan sättas i svajande rörelser av vind och jordbävningar, men genom att uppskatta byggnadernas horisontella egenfrekvenser i den tidiga konstruktionsfasen kan dessa rörelser hållas inom acceptabla gränser. Det är många parametrar som bestämmer byggnadens egenfrekvens och det kan därför vara svårt att beräkna den. Det finns dock några sätt att uppskatta horisontella egenfrekvenser hos höga byggnader och två metoder har testats i denna rapport. Båda metoderna ger frekvensen av en fast inspänd konsolbalk men en av dem kräver ett enfrihetsgradsystem medan den andra kan hantera ett system med flera frihetsgrader. Metoderna kallas SDOF-metoden och MDOF-metoden i denna rapport. En fiktiv byggnad skapades i detta projekt för att vara referensobjekt i jämförelsen mellan de två metoderna SDOF och MDOF. Byggnadens väggar och golv konstruerades med stöd av både en akustiker och en konstruktör för att skapa en realistisk byggnad. Byggnadens egenfrekvens är beroende av byggnadens egenvikt, styvhet och höjd och det var därför viktigt att utforma dessa komponenter med omsorg. Den fiktiva byggnaden kallas House 1 och är en 10 vånings-, nästan fyrkantig byggnad ca 20 m lång och bred och 30 m hög. Denna rapport jämför inte bara egenfrekvenserna erhållna från de två olika beräkningsmetoderna, den visar även skillnaden i frekvens i trä- och betongkonstruktioner. Skjuvväggar utgör det horisontella stabiliseringssystemet för den fiktiva byggnaden och både en KL-kärna och en betongkärna har utformats och jämförts. Det är bara väggarna som skiljer de två olika versionerna åt, bjälklagen består av KL-skivor i båda fallen. De horisontella egenfrekvenserna hos House 1 var ca 2 Hz och 3 Hz för KL-version respektive betongversion. Frekvenser inom detta område var väntade med tanke på höjden av House 1. Att KL-kärnan skulle ha en lägre frekvens än betongkärnan förväntades också eftersom betong är ett styvare material än trä. För att kunna göra en rättvis jämförelse mellan SDOF-metoden och MDOF-metoden, var House 1 utformad med samma dimension och styvhet på alla våningsplan eftersom SDOF-metoden kräver det. Resultaten från de två metoderna är nästan identiska med endast 0,3 Hz och 0,4 Hz skillnad för betong respektive KL. För en skjuvväggskonstruktion med en kontinuerlig styvhet, vikt och dimension kan båda de två metoderna användas för att uppskatta den horisontella egenfrekvensen. Det är dock inte realistiskt för en byggnad på 30 m eller högre att ha samma dimensioner på den lastbärande konstruktionen på alla våningar vilket gör MDOF-metoden mer korrekt i fler fall än SDOF-metoden.
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Nichols, Gilbert. "Statistical Models of I-15 Bridge C-846: Changes in Natural Frequencies due to Temperature". DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/5260.
Texto completoResumen
Structural Health monitoring is to determine the condition of a bridge based on instrument measurements. The C-846 Bridge in Salt Lake City has such instrumentation. The bridge is located in Salt Lake City at about 2100 South and Interstate 15. This bridge has two kinds of instruments on it: accelerometers and thermocouples. The accelerometers measure the vibrations of the bridge. The accelerometers have been recording data on the bridge since 2001. The thermocouples, which measure temperature, were added as part of this thesis in April 2016.
In light of recent research, damage may be detected from measuring the change in the natural frequency of a bridge, which can be obtained by manipulating the accelerometer data. However, the natural frequencies of a bridge change due to environmental effects, especially temperature. Temperature effects must be accounted for in order to better understand the damage.
The purpose of this research is not to detect damage. The bridge that is being monitored does not have any damage. The purpose of this study is to show how the dynamic properties of the C-846 Bridge in South Salt Lake City correlate with temperature. Additionally, several frequencies including the fundamental frequency of the bridge are identified.
It was found that the natural frequencies of the bridge increase with a decrease in temperature, and that the fundamental frequency of the bridge is 1.15 Hz.
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Xu, Weiwei. "Effect of Bolted Joint Preload on Structural Damping". Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4794.
Texto completoResumen
Bolted joints are integral parts of mechanical systems, and bolt preload loss is one of the major failure modes for bolted joint structures. Understanding the damping and frequency response to a varying preload in a single-bolted lap-joint structure can be very helpful in predicting and analyzing more complicated structures connected by these joints.
In this thesis, the relationship between the bolt preload and the natural frequency, and the relationship between the bolt preload and the structural damping, have both been investigated through impact hammer testing on a single-bolted lap-joint structure. The test data revealed that the bolt preload has nonlinear effects on the structural damping and on the natural frequency of the structure. The damping ratios of the test structure were determined to increase with decreasing preload. An increase in structural damping is beneficial in most engineering circumstances, for it will reduce the vibrational response and noise subjected to external excitations. It was also observed that the modal frequency increased with increasing preload, but remained approximately constant for preload larger than 30% in the bolt yield strength. One application for studying the preload effect is the detection for loose bolts in structures. The possibility of using impact testing for estimating preload loss has been confirmed, and the modal damping was determined to be a more sensitive indicator than the natural frequency in a single-bolted lap-joint structure.
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DIAS, JOSE LUIZ. "A METHODOLOGY FOR METROLOGICAL EVALUATION AND DETERMINATION THE FREQUENCY OF CALIBRATION IN FISCAL AND ALLOCATION NATURAL GAS MEASUREMENT SYSTEMS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11027@1.
Texto completoResumen
PETRÓLEO BRASILEIRO S. A.No presente trabalho, de interesse da indústria de petróleo, é desenvolvida uma metodologia para avaliação metrológica e determinação da periodicidade de calibração em sistemas de medição de vazão de gás natural com placas de orifício, usando históricos de dados bimestrais de medidores instalados em pontos fiscais da bacia de Campos. O estudo analisa dados de calibração de medidores de temperatura, pressão e pressão diferencial de um transmissor eletrônico de vazão multivariável, contribuindo para o entendimento do impacto das incertezas destas variáveis na incerteza total do sistema de medição como um todo. Como resultados das avaliações metrológicas, foram determinados intervalos entre calibrações sucessivas, de modo que as exigências de incerteza de medição da portaria conjunta no 1 ANP/INMETRO de 19/6/2000 possam ainda ser atendidas nos pontos de medição fiscal e de apropriação . Inicialmente, foi mostrado que os valores de incertezas calculadas de vazão pela norma ISO 5167-2 (2003) atendem os requisitos da portaria. Finalmente, foi mostrado que o intervalo entre calibrações sucessivas dos medidores poderia ser aumentado do valor atualmente requerido pela portaria (2 meses) para pelo menos 6 meses para pressão diferencial e pressão, e 14 meses para temperatura. Este resultado tem um impacto econômico e operacional nas empresas de gás natural.
In the present work, of interest of the oil industry, a methodology was developed for metrological evaluating and determination the frequency of calibration of natural gas flow rate measurement systems with orifice plates, using calibration data obtained every two months from measurement instruments installed in fiscal points of the Campos Basin. The study evaluates the calibration data of temperature, pressure and differential pressure measurement from a multivariable transmitter, contributing to a better understanding of the influence of those variables in the uncertainty of flow rate as a result of the methodological evaluating, the intervals between two successive calibrations was determined, so that the requirements of the Portaria Conjunta n° 1 ANP/INMETRO, 19/06/2000, could be met in the fiscal and allocation points. First of all, it was shown that the flow rate uncertainty values, as calculated by ISO 5167-2 standard was fully covered by the requirements. Finally, it was shown the interval between successive calibrations could be increased of the value nowadays required by portaria (2 months) to 6 months for pressure and differential pressure, and to 14 months for temperature. This results has an economic and operational impact in the natural gas industry.
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Menon, K. Rajalakshmi. "Application Of High Frequency Natural Resonances Extracted From Electromagnetic Scattering Response For Discrimination Of Radar Targets With Minor Variations". Thesis, Indian Institute of Science, 2001. https://etd.iisc.ac.in/handle/2005/159.
Texto completoResumen
Radars, as the name suggests, were traditionally used for Radio Detection and Ranging. Nevertheless, advances in high resolution electromagnetic simulations, Ultra Wide-Band sources, signal processing and computer technologies have resulted in a possible perception of radars as sensors for target discrimination. In this thesis, the feasibility of discrimination between targets even with minor variations in structure and material composition on the basis of radar echoes is effectively demonstrated.
It is well-known that the echoes from any target are affected by its natural frequencies which are dependent only on the shape and material composition of the target, and independent of the aspect angle or the incident waveform. The E-pulse technique is based on the fact that incident waveforms can be designed that uniquely annihilate the echoes from chosen regions of a target, and forms the basis of the method of discrimination proposed in this thesis.
Earlier methods reported in the literature, effectively discriminated only between different classes of targets with substantial variations in the overall dimensions of the body. Discrimination of targets of the same class with a minor structural modification or with a material coating on specific areas was rather difficult. This thesis attempts and successfully validates a method which comprehensively addresses this problem. The key idea of this method is to use the higher frequency resonances (which characterise the finer details of a target) in the E-pulse technique.
An obviously important aspect of target discrimination is therefore that of precisely estimating the natural frequencies for each target and understanding the changes in these frequencies, and their associations with the changes in structure and material composition. Current approaches to determine these frequencies are either based In the time or frequency
domains. While the latter approach comprises the computation of the roots of a related determinantal equation, in the time domain, the natural frequencies are extracted from the
response of a target to an impulse. Such a response can either be generated from actual experiments or by simulating the scattering response using Computational Electromagnetic (CEM) techniques. In this work, the impulse response is obtained from the frequency response of the scatterers in the frequency range of interest. Since no single CEM technique can effectively cover the entire range of frequencies needed for the E-Pulse synthesis. The Method of Moments and Physical Optics have been used for low and high frequency scattering respectively. The results obtained using the latter technique are validated by comparing with those obtained using Method of Moments at the transition frequencies and Geometrical Theory of Diffraction (GTD).
The natural frequencies (i.e., poles of a corresponding transfer function) are extracted from the impulse response using Prony's algorithm. One of the parameters in this method is the number of such poles (i.e.. the order of the transfer function) present in the response, and the accuracy of the computed pole values depends on this assumed order. Here, the Hankel singular values of a transfer function is used to estimate the number of poles. This in turn implies that a specific norm of the error between a transfer function corresponding to the frequency response generated earlier, and a transfer function with an assumed order obtained using Prony's method is minimised.
In the thesis, a wide range of target shapes are considered for purposes of illustration: wires, cylinders, spheres, plates and complex bodies such as aircraft, and the discrimination capability is demonstrated by introducing minor perturbations in their shape and/or material composition. .The following cases are considered here: (a) Wires: Conducting wires with a protrusion in one segment; conducting wire from another coated with a dielectric in a segment, (b) Cylinders: Conducting cylinders with one perturbed; conducting cylinders with a portion scrapped off in the middle, (c) Plates: Conducting plates with a elongation on one comer; conducting plate with another one with a hole in the centre, (d) Spheres: Conducting spheres with different radii; conducting spheres with Radar Absorbing Material coated spheres with different coating thickness; conducting spheres with chiral coated spheres with varying coating thickness, (e) Aircraft: Canonical model of MiG-29 aircraft from a similar one with stores placed under the wing.
34
Menon, K. Rajalakshmi. "Application Of High Frequency Natural Resonances Extracted From Electromagnetic Scattering Response For Discrimination Of Radar Targets With Minor Variations". Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/159.
Texto completoResumen
Radars, as the name suggests, were traditionally used for Radio Detection and Ranging. Nevertheless, advances in high resolution electromagnetic simulations, Ultra Wide-Band sources, signal processing and computer technologies have resulted in a possible perception of radars as sensors for target discrimination. In this thesis, the feasibility of discrimination between targets even with minor variations in structure and material composition on the basis of radar echoes is effectively demonstrated.
It is well-known that the echoes from any target are affected by its natural frequencies which are dependent only on the shape and material composition of the target, and independent of the aspect angle or the incident waveform. The E-pulse technique is based on the fact that incident waveforms can be designed that uniquely annihilate the echoes from chosen regions of a target, and forms the basis of the method of discrimination proposed in this thesis.
Earlier methods reported in the literature, effectively discriminated only between different classes of targets with substantial variations in the overall dimensions of the body. Discrimination of targets of the same class with a minor structural modification or with a material coating on specific areas was rather difficult. This thesis attempts and successfully validates a method which comprehensively addresses this problem. The key idea of this method is to use the higher frequency resonances (which characterise the finer details of a target) in the E-pulse technique.
An obviously important aspect of target discrimination is therefore that of precisely estimating the natural frequencies for each target and understanding the changes in these frequencies, and their associations with the changes in structure and material composition. Current approaches to determine these frequencies are either based In the time or frequency
domains. While the latter approach comprises the computation of the roots of a related determinantal equation, in the time domain, the natural frequencies are extracted from the
response of a target to an impulse. Such a response can either be generated from actual experiments or by simulating the scattering response using Computational Electromagnetic (CEM) techniques. In this work, the impulse response is obtained from the frequency response of the scatterers in the frequency range of interest. Since no single CEM technique can effectively cover the entire range of frequencies needed for the E-Pulse synthesis. The Method of Moments and Physical Optics have been used for low and high frequency scattering respectively. The results obtained using the latter technique are validated by comparing with those obtained using Method of Moments at the transition frequencies and Geometrical Theory of Diffraction (GTD).
The natural frequencies (i.e., poles of a corresponding transfer function) are extracted from the impulse response using Prony's algorithm. One of the parameters in this method is the number of such poles (i.e.. the order of the transfer function) present in the response, and the accuracy of the computed pole values depends on this assumed order. Here, the Hankel singular values of a transfer function is used to estimate the number of poles. This in turn implies that a specific norm of the error between a transfer function corresponding to the frequency response generated earlier, and a transfer function with an assumed order obtained using Prony's method is minimised.
In the thesis, a wide range of target shapes are considered for purposes of illustration: wires, cylinders, spheres, plates and complex bodies such as aircraft, and the discrimination capability is demonstrated by introducing minor perturbations in their shape and/or material composition. .The following cases are considered here: (a) Wires: Conducting wires with a protrusion in one segment; conducting wire from another coated with a dielectric in a segment, (b) Cylinders: Conducting cylinders with one perturbed; conducting cylinders with a portion scrapped off in the middle, (c) Plates: Conducting plates with a elongation on one comer; conducting plate with another one with a hole in the centre, (d) Spheres: Conducting spheres with different radii; conducting spheres with Radar Absorbing Material coated spheres with different coating thickness; conducting spheres with chiral coated spheres with varying coating thickness, (e) Aircraft: Canonical model of MiG-29 aircraft from a similar one with stores placed under the wing.
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Hrivňák, Ján. "Analýza dynamických vlastností pneumatického aktuátoru". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230570.
Texto completoResumen
This thesis deas with dynamic analysis of pneumatic actuator which is used as regulation mechanis of turbochargers with Variable Nozzle Turbine (VNT) technology. The first part of work is focused on experimental modeling which goal is obtaining Frequency Response Function on specify frequency range by Frequency Response Function Analysis – FRFA. Dominant vibrations of pneumatic actuator active parts is expected on this specify frequency range. Results of experimental modeling will be used for gaining input parameters for numerical computation as well. The second part deal with Pre-Stressed Modal Analysis and subsequently Harmonic analysis. Obtained results with numerical and experimental analysis will be compared. This part of diploma thesis is solved in programmatic environment ANSYS Workbench.
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Isbring, Evelina. "A longitudinal study of the frequency of knee pain and the effect on countermovement jump at a sports secondary school". Thesis, Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-33937.
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Background: Studies have shown that participation in sports during adolescence has several positive aspects, both physical and mentally. Today there is more focus on competition than before and more adolescents choose to specialize in one sport. High sport specialization can cause a higher risk of injuries. Knees are one of the most common sites for adolescence to experience pain in and girls are more often exposed to this problem, compared to boys. Aim: The aim of the study was to longitudinally investigate the frequency of reported knee pain in 7th grade and 9th grade in a secondary school with a sports profile stratified for sex, difference in frequency of knee pain between 7th and 9th grade and whether knee pain affected performance in countermovement jump with arm swing. Methods: To compare frequency of knee pain between 7th and 9th grade, the test subjects (n=42, 17 girls and 25 boys) that answered the questionnaire about knee pain both years were included. The questionnaire had six options for frequency, where those who reported “never” or “rarely” were grouped as “no knee pain”. Those who reported “monthly”, “weekly”, “more than once a week” or “almost daily” were grouped as “knee pain”. Jump height was measured by countermovement jump with arm swing. The tests were performed twice, in May 2014 when the test subjects were in 7th grade (age: mean (SD) 14±0.2) and in May 2016 in 9th grade (age: 16±0.2). Results: In 7th grade, 74% reported knee pain (girls 82 %, boys 68%). In 9th grade, 36% reported knee pain (girls 36%, boys 35%). The difference between the frequency of knee pain in 7th and 9th grade was significant, with a lower frequency in 9th grade. In 7th grade the jump height for those with knee pain was 32.9±7.5 cm, and for those with no knee pain 33.8±5.6 cm. In 9th grade the jump height for those with knee pain was 33.5±7.2 cm, and for those with no knee pain 36.5±10.1 cm. Conclusion: The frequency of knee pain decreased significant from 7th to 9th grade. There was no significant difference regarding jump height in countermovement jump with arm swing between the group that reported monthly to almost daily knee pain, and the group that reported that they experienced knee pain rarely or never. The result of this study therefore indicates that self-reported knee pain does not affect jumping performance.
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Banadaki, Davood Dehgan, Sunay Sami Durmush y Sharif Zahiri. "Statistical Assessment of Uncertainties Pertaining to Uniaxial Vibration Testing and Required Test Margin for Fatigue Life Verification". Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-2147.
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In the automotive industry uniaxial vibration testing is a common method used to predict the lifetime of components. In reality truck components work under multiaxial loads meaning that the excitation is multiaxial. A common method to account for the multiaxial effect is to apply a safety margin to the uniaxial test results. The aim of this work is to find a safety margin between the uniaxial and multiaxial testing by means of virtual vibration testing and statistical methods. Additionally to the safety margin the effect of the fixture’s stiffness on the resulting stress in components has been also investigated.
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Sanchez, Telmo Andres. "Experimental and Analytical Study of Vibrations in Long Span Deck Floor Systems". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/42733.
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Experimental and analytical research was conducted to address the vibration properties of Long Span Deck Floor Systems (LSDFS). The research comprised three stages. In the first part, experimental in-situ tests were conducted on thirteen bays of buildings under construction. The natural frequencies and acceleration responses were captured to observe the vibration behavior of the tested floors.
In the second part, a laboratory footbridge was constructed to determine the fixity level attained at the supports when a LSDFS is supported by CMU walls. For this purpose, the footbridge was tested with three support conditions, and a number of experiments were carried out to determine the dynamic properties of the structure. Static tests using both point and distributed loadings were conducted to measure the deflections at the footbridge midspan. The static test results were compared to the theoretical deflections for a pinned-end beam and a fixed-end beam. Dynamic tests using experimental modal analysis techniques were conducted to determine the natural frequencies and mode shapes of the structure. The measured fundamental natural frequency of the footbridge was compared to the frequencies calculated for a simply supported beam and a beam with fixed ends, to determine the degree of fixity attained in the connection between the LSDFS and the supporting walls.
In the last part of the research, three analytical procedures to predict modal characteristics of long span deck floor systems are studied. Floor frequencies are calculated using finite element analyses. Two design guides for floor vibration analysis were used to calculate natural frequencies and response accelerations. The predicted results obtained from the analytical methods are compared to the experimental results to determine their accuracy. Recommendations for the use of the analytical methods are provided.Master of Science
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Anson, Simon Richard. "An investigation into the molecular role of qrf, a natural antisense transcript of the Neurospora crassa circadian clock gene frequency". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702310.
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Huang, wei-Juyn y 黃威軍. "Natural Frequency and Histological Analysis". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/69040339014554444654.
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碩士台北醫學院
口腔復健醫學研究所
90
Abstract Title of hesis：Natural Frequency and Histological Analysis of Dental Implant Author：Wei-Juyn Huang Thesis directed by： Sheng-Yang Lee DDS,MS,PhD Bay-Rong Guo DDS,MS The goal of this study is to use the natural frequency analytic test, measuring the natural frequency within the bone healing process after the implantation, than comparing the histological sections, so that we could analyze the correlations between the natural frequency signal changes and bone healing around the boundary condition for the dental implant, current study will also established a data base. In the end to develop a simple interment which is capable of providing a objective and noninvasive quantitative assessment for the evaluation of the condition right after the implantation and in the following healing stages. This study uses 8 adult beagle dogs ( weight from 9 to 12 kgs), bone healing observation stages divided in to 8 stags: 1, 2, 3, 4, 9, 12, 16, and 26 wks. Each stage has one dog. Every dog was implanted with 6 pure titanium implants: fixture ( 10 mm x 4.0 mm), .healing cap ( 2.0 mm x 4.0 mm) We performed natural frequency model testing over each stage after operation. After that we made histological sections. The histological assessment indicates that the peri-implant bony structure becomes amateur and complete osseointegration in 9 weeks, and the bone structure appears stable without changes until 26 weeks. The trend of statistical analysis over natural frequency shows identical results. The natural frequency of a successful dental implant is 7.0 kHz ~ 9.0 kHz. Natural frequency test is a useful non-invasive detective method that is capable of providing a noninvasive quantitative assessment for the evaluation of the condition right after the implantation and in the following healing stages for dental implants. Key Words: dental implant, natural frequency, osseointegration
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WEI, JEN-CHI y 任紀為. "Natural Frequency Analysis of Portal Frames". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/26409554540440554464.
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Mortier, Annelies. "Statistical Studies of Planet Frequency: understanding Planet Formation". Tese, 2013. https://repositorio-aberto.up.pt/handle/10216/70190.
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Wahaia, Faustino. "Spectroscopic and Imaging Techniques using Terahertz frequency Band Biomedical Applications". Tese, 2011. https://repositorio-aberto.up.pt/handle/10216/65131.
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Mortier, Annelies. "Statistical Studies of Planet Frequency: understanding Planet Formation". Doctoral thesis, 2013. https://repositorio-aberto.up.pt/handle/10216/70190.
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LIU, CHE CHIA y 劉哲嘉. "NATURAL FREQUENCY OF CURVED SKEW BOX GIRDER BRIDGE". Thesis, 1998. http://ndltd.ncl.edu.tw/handle/92613060586093925004.
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Wahaia, Faustino. "Spectroscopic and Imaging Techniques using Terahertz frequency Band Biomedical Applications". Doctoral thesis, 2011. https://repositorio-aberto.up.pt/handle/10216/65131.
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Li, Yuan-You y 李元祐. "Natural frequency calculation of thin wall structure during machining". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/56179213671911708463.
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碩士國立中興大學
機械工程學系所
105
To avoid thin-walled workpieces arising chatter, it can be based on the chatter stability lobes. The chatter stability lobes can be got by the natural frequencies of the thin-walled workpieces. This study applies the Rayleigh-Ritz method (RRM) to calculate natural frequencies of vise-clamped thin-walled workpieces in the vise-clamped. The Rayleigh-Ritz method is suitable for multi-degree-of-freedom systems and the calculation time is shorter. Compared Rayleigh-Ritz method with other commercial software is also quite accurate. The study has two goals 1. To discuss accuracy between different theories and choose a suitable theory to calculate natural frequencies. 2. Applying the Rayleigh-Ritz method to calculate the natural frequencies of the rectangular plates and the stepped thickness plates in the vise-clamped, and validate the accuracy of the theory with experiment.
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Fang, Chien-Lan y 方建嵐. "Study of Natural Frequency of Rectangular Plate with Crack". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/96075214793682463080.
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碩士中原大學
機械工程研究所
89
ABSTRACT The natural frequency of the rectangular plate with a straight crack analysis is investigated in this study. Using ANSYS5.5 software to build two dimensional finite element mesh of the rectangular plate, and selection the geometry of element mesh around crack tip, the natural frequency of the rectangular plate with the straight crack is determined. In the crack of geometry range, the ratio of crack length to the plate length is considered between 0.0 and 0.5. And the aspect ratio of the plate is considered between 0.5 and 2.5. The natural frequencies under the different boundary conditions (C-F-F-F and S-S-S-S) and the different positions of the crack length in the plate are considered. By comparing the natural frequency for different crack length with appropriated published results, the variations of natural frequency on center and edge location have been discussed. Based on ANSYS results of natural frequency of rectangular plate with straight crack, the dimensionless frequency parameters are determined by curve fitting technique. The dimensionless frequency parameter of the rectangular plate decreases with increasing of the crack length. The dimensionless frequency parameter of simply supported plate increases with the increasing the aspect ratio in this study.
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(6620237), Sokheang Thea. "Identification of Stiffness Reductions Using Partial Natural Frequency Data". Thesis, 2019.
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In vibration-based damage detection in structures, often changes in the
dynamic properties such as natural frequencies, modeshapes, and derivatives of
modeshapes are used to identify the damaged elements. If only a partial list of
natural frequencies is known, optimization methods may need to be used to
identify the damage. In this research, the algorithm proposed by Podlevskyi & Yaroshko (2013) is used to determine
the stiffness distribution in shear building models. The lateral load resisting
elements are presented as a single equivalent spring, and masses are lumped at
floor levels. The proposed method calculates stiffness values directly, i.e., without optimization, from the known partial list of natural frequency data and mass
distribution. It is shown that if the number of stories with reduced
stiffness is smaller than the number of known natural frequencies, the stories
with reduced stiffnesses can be identified. Numerical studies on building
models with two stories and four stories are used to illustrate the solution
method. Effect of error or noise in given natural frequencies on stiffness
estimates and, conversely, sensitivity of natural frequencies to changes in
stiffness are studied using 7-, 15-, 30-, and 50-story numerical models. From
the studies, it is learnt that as the number of stories increases, the natural
frequencies become less sensitive to stiffness changes. Additionally, eight
laboratory experiments were conducted on a five-story aluminum structural
model. Ten slender columns were used in each story of the specimen. Damage was
simulated by removing columns in one, two, or three stories. The method can
locate and quantify the damage in cases presented in the experimental studies. It
is also applied to a 1/3 scaled 18-story steel moment frame building tested on
an earthquake simulator (Suita et al., 2015) to identify the reduction in the
stiffness due to fractures of beam flanges. Only the first two natural
frequencies are used to determine the reductions in the stiffness since the
third mode of the tower is torsional and no reasonable planar spring-mass model
can be developed to present all of the translational modes. The method produced possible cases of the
softening when the damage was assumed to occur at a single story.
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Amaral, Miguel Santana de Freitas. "Time-memory trade-off in graphlet counting & Orbit vertex frequency vs. degree in the expected degree model". Dissertação, 2019. https://hdl.handle.net/10216/124896.
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