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No description available.

Vibrations in machines increase friction on moving parts which cause chafing that will tear down the fabric of the machine components when given time, thus monitoring and analysis of machine vibrations are important for preventive maintenance. Vibration analysis utilizes time domain as well as frequency domain analysis for which there have been analog solutions for quite some time. This work has been about moving a predominantly analog mixed signal system onto an FPGA and making it mostly digital. Vibration analysis on an FPGA have its own challenges and benefits compared to other methods. The inherent parallelism of the FPGA makes it suitable for high performance signal analysis. This report shows through two proof-of-concept solutions that the translation of a predominantly analog system is viable, economic and can deliver improved performance. The two solutions have utilized two different units from Xilinx, the Spartan-6 FPGA and the Zynq-7000 system on chip FPGA. The solution implemented on Spartan-6 produces a result in 9.32 ms and the other implementation based on Zynq-7000 produces a result in 9.39 ms, which is more than a 10-fold increase in performance of the current system. The results obtained show that both solutions can perform the calculations for the proof of concept within 20% of the allotted time. Costs of both solutions as well as other qualities of each solution are presented in this paper.

Rapporten består utav en teoretisk undersökning kring hur vibrationer i en svarvbom vid resonans kan dämpas på ett enkelt sätt. CS Produktion, för vilka undersökningen gjorts, har velat öka sin invändiga bearbetning från 1,5 m till 2,5 m. Med så långa överhäng på en bom är det risk för resonansvibrationer som ger dålig ytfinhet och kan i värsta fall skada maskin och personal. Bom och infästning har arbetats fram i ett tidigare arbete, efter arbetet kvarstod utvecklandet av en lösning för dämpningen av bommen. Problemet har undersökts teoretiskt avseende två möjligheter, utifrån om störfrekvensen träffar en eller flera egenfrekvenser för bommen. Störfrekvensen uppstår från den skärande bearbetningen och måste mätas upp för att senare kunna avgöra vilket av de två fallen som är lämpligt att utgå ifrån. Den första modellen för en träff av egenfrekvensen är en inre stång med en vikt i den fria änden av stången, med den andra änden inskruvad i bommens ändplatta. Anordningen beräknas så att egenfrekvensen sammanfaller med bommens egenfrekvens som är i riskområdet för resonans. Den inre anordningen fungerar som massdämpare. Den andra modellen för flera träffar av egenfrekvenserna har två lösningar som beror på hur bommen beter sig vid ingrepp. Grunden är ett inre rör som kan liknas vid en mindre version av bommen för att den ska få liknande egenskaper. Röret beräknas så att det får likvärdiga egenfrekvenser som bommen och kommer då följa modellen för ett system med två frihetsgrader vid resonans. För varje egenfrekvens på bommen ger röret en vibrationsdämpande effekt vid resonansområdena. Projektet visar att empiriska mätningar behöver göras för att med säkerhet kunna avgöra hur problemet ska avhjälpas. Med mätningar kan också koncepten vidareutvecklas, alternativt ligga till grund för att ta fram mer avancerade lösningar. / The report consists of a theoretical study of how vibrations in a boring bar at resonance can be minimized in a simple way. CS Produktion, the commissioning company, wanted to increase their capacity for internal turning from 1.5 m to 2.5 m. With a long overhang there is a risk of dangerous resonant vibrations that can give a bad surface, or may even damage the equipment and injury employees. The bar and the attachment has been developed in another project, but the project lacked a solution for the resonant vibrations. The problem has been studied from two theoretical possible scenarios, based on whether the interference frequency matches one or more natural frequencies of the bar. Interference frequency arises from the cutting work and must be measured in order determine which of the two cases that is appropriate to start from. The first model for one hit of the natural frequency is a single rod with a weight at the free end of the rod, with the other end screwed into the end plate of the bar. The device is calculated so that the natural frequency coincides with the natural frequency of the bar that is in the danger zone for resonance and function as mass damper. The second model for multiple hits of the natural frequencies have two solutions that depend on how the bar behaves when machining. The design is an inner pipe that resembles a smaller version of the bar for it to have similar properties. The pipe has been calculated to have equal natural frequencies as the bar, and will then follow the system of two degrees of freedom at resonance. The pipe provides a vibration dampening effect on the resonance regions. To be able to reliably determine how the problem should be solved, this project shows that empirical measurements are needed. These measurements could serve as a basis for further concept development or more advanced concepts.

This thesis is concerned with the free vibration analysis of stiffened circular cylindrical and conical shells. The study was carried out with a view to improving the accuracy and efficieny of various modelling techniques for the prediction of the stiffened shells natural frequencies and mode shapes. A review of the existing literature covering various aspects of the shell vibrations problem and modelling techniques has been given at the beginning of each chapter with a critical appraisal of the assumptions made and results obtained. Initially the continuum energy approach was used for the analysis. The developed method allows for discrete consideration of stiffeners having arbitrary location and properties. Energy of bending in two planes and rotary inertia have been included in the analysis. Various types of stiffened shells with shear diaphragm ends condition were analysed using this method for the prediction of their natural frequencies. The predicted results have been compared with published experimental results. The finite element technique was also used for the prediction of natural frequencies and mode shapes of stiffened shells. Axisymmetric shell of revolution element, Facet shell element, semi-100f element and various types of beam elements, which are available within the PAFEC 75 suite of programs, were used for these studies. An efficient modelling technique has been introduced for ring stiffened cylindrical and conical shells by the use of the shell of revolution element. For improved accuracy of the predicted frequencies and a more economical model, shell symmetry was utilized for the free vibration analysis of unstiffened and stiffened shells. Half, quarter and one eighth models were studied by developing the appropriate boundary conditions and are discussed here. The free vibration characteristics of orthogonally stiffened cylindrical shells and an orthogonally stiffened cylindrical panel have been studied. An eight noded stiffened super shell element was developed for this study. This element was used for modelling various other types of stiffened shells and the predicted natural frequencies have been compared with known published experimental and theoretical results. Experimental verification of theoretical predictions of natural frequencies and mode shapes of an orthogonally stiffened cylindrical panel was carried out and is reported here.

Civil engineering construction frequently requires the use of piles to carry structural loads to stronger ground strata or to control lateral ground movements. A variety of techniques are available to install piles into the ground. Of central interest to this research is the vibratory hammer, or vibrodriver, which is the preferred method used to drive piles into granular soils. .The installation of sheet and bearing piles by vibrodriver causes periodic vibration in the adjacent ground which is severe very close to the piles, but attenuates with distance. A potential consequential effect of the vibrations that are caused by vibrodriving is ground compaction, which may be observed as differential surface settlement. It is desirable that vibration induced ground compaction settlement should be estimated for contracts where loose to medium-dense granular soils occur, especially when buildings on shallow foundations or poorly bedded service pipes are adjacent. It is unlikely that a simple in-situ soils test will allow accurate, specific estimates, but rather that a range of vibratory tests should be performed which can then be used as a knowledge base. Settlement trends and associated parameters can then be identified which will allow the prediction of settlement with reference to the in-situ soil and the ground vibration data. This argument forms the basis of the laboratory test programme. A range of granular soils were studied using an adapted 150mm Rowe cell (a hydraulic oedometer). Use of the Rowe cell enabled samples to experience compaction under effective stress conditions that are appropriate for equivalent soils in the field. The complete cell was mounted on an electromagnetic shaker and after static consolidation, the samples were vibrated under maintained hydraulic load, at frequencies and accelerations that are appropriate for soils adjacent to vibrodrivers. Change in sample height was recorded for controlled vertical (and horizontal) vibrations, typically in the range of 0.lg to 5.0g at 25Hz and 40Hz. Soils were tested under a range of effective stresses and moisture content. The results of the laboratory programme and subsequent data analysis are presented in tables and diagrams. Expressions that describe a good relationship between acceleration, soil type, relative density and static load allow upperbound estimates of vibratory settlements to be made for accelerations of up to 6.0g. An additional expression is presented that accounts for the influence of moisture content, ground vibration frequency and vibration duration. Summary tables are presented that define categories of vibration induced ground compaction settlement based on settlement potential, risk and severity. The use of the settlement equations and the influence of various parameters are demonstrated for a range of example applications, hi addition, data is abstracted from case studies found in the literature and sites that were visited during the research. The abstracted data are then used to perform settlement estimates which are compared to the reported examples. Good correlation between observed and calculated settlement is demonstrated in many cases. However, in some instances, it appears that ground settlements were exacerbated by at least one additional mechanism, such as cumulative pore water pressure increase, or lateral movement of sheet piles, in addition, extraction of piles by vibrodriver appears to contribute significantly to the reported cases of ground settlement.

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Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 92-95). / ix, 95 leaves, bound ill. (some col.) 29 cm

Leaf of corrections inserted before back end-paper. / Bibliography: p. 204-219. / xiv, 219 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigates the non-adiabatic behaviour of diatomic molecular systems having overlapping potential curves, especially the predissociation of NaI by the ionic-covalent crossing. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1996