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1
Fletcher, Patrick Alan. "High pressure vibrational and EXAFS spectroscopy." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/33673.
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Deni, Mohd Salleh Mohd. "Vibrational anharmonicity and the elastic behaviour of some antiferromagnetic materials." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380942.
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Pollet, Didier Michel. "A study of low force fabric characteristics and vibrational behaviour for automated garment handling." Thesis, University of Hull, 1998. http://hydra.hull.ac.uk/resources/hull:11092.
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One of the fundamental concepts in automated garment assembly is that the orientation of a fabric panel should never be lost. However, if a panel does become distorted, several techniques, such as vision, air flotation tables, and vibratory conveyors are available to restore the orientation. This thesis has investigated the behaviour of a fabric panel on a vibratory table. Several table parameters such as amplitude of vibration, frequency and angle of inclination, together with some important fabric properties as friction and compressibility are required to understand the behaviour. However, most work on friction in textiles considers fibre-fibre or fabric-fabric friction, which is not appropriate to this and so low force frictional properties between unloaded fabric and engineering surfaces (i.e., aluminium, Formica and rubber) have been studied. The influence of several experimental variables on friction is demonstrated, in particular, the effect of humidity and velocity. Further, an in depth study is made on the stick-slip of fabric panels wherein a novel measuring technique is introduced. An estimate of the damping, which is required to model the fabric, has been obtained from an in-plane vibration test. The second significant fabric property to be studied is the compression both static and impact. Again, only low-force compression tests are carried out since these are the typical forces experienced by fabrics on a vibrating table. The static compressibility of knitted and woven materials is verified with van Wvk's equation. which gives a near indistinguishable fit with the experimental data.
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Lydiatt, Francis Peter. "Vibrational sum-frequency spectroscopy : towards understanding adsorbate behaviour on substrates relevant to the nuclear fuel cycle." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/vibrational-sumfrequency-spectroscopy-towards-understanding-adsorbate-behaviour-on-substrates-relevant-to-the-nuclear-fuel-cycle(3a81bdcc-75d9-4fed-a949-ad43198625be).html.
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The primary goal of this thesis was to commission an instrument for vibrational sum frequency spectroscopy (VSFS), and exploit it for the study of solid/gas interfaces; of ultimate interest is characterisation of substrate surfaces in humid environments. Such effort is motivated by interest in understanding the potential for atmospheric corrosion in dry storage facilities of spent nuclear fuels or other nuclear-related wastes. VSFS is a non-linear, interface specific, vibrational spectroscopy, in which two photons of different energies (infrared (IR) and visible (VIS)) impinge upon a surface at the same point at the same time, leading to the generation of a third (sum-frequency generation (SFG)) photon. Features in VSFS spectra can be assigned to vibrational modes of interfacial species, and so enable details of interfacial structure and chemistry to be elucidated. An instrument for such measurements has been developed using laser facilitates located in the Photon Science Institute (PSI) of The University of Manchester. More specifically, an ultra-fast (femtosecond) laser has been employed as a light source, enabling acquisition of spectra (~250 cm-1 in width at a resolution of ~11 cm-1) without the need for scanning the energy of either IR or VIS beams, i.e. so called broad-band VSFS. To test performance, data have been acquired from self-assembled monolayers of alkanethiols (octadecanethiol) on gold substrates, which demonstrate the utility of the instrument. Subsequent to commissioning, the VSFS instrument was initially exploited to study the interaction of two organic molecules, acetonitrile and acetic acid, with a single crystal TiO2(110) substrate; measurements were performed with the sample exposed to the vapour of each organic species under ambient conditions. Surface adsorption was identified through the appearance of the CH3 symmetric stretch. Furthermore, spectra as a function of light (IR/VIS/SFG) polarization combinations have been recorded to explore adsorbate angular geometry. Finally, VSFS measurements have been undertaken from a number of substrates (GaAs, Au, Zn, Fe, Cr, stainless steel), as a function of relative humidity; D2O was employed to overcome the issue of loss of IR beam intensity due to interaction with atmospheric H2O. Signal quality varies significantly with substrate, with the most insight being gained for the interaction of D2O with polycrystalline Zn. Clear vibrational resonances due to both hydroxyls (OD) and molecular water (D2O) are observed, which vary with relative humidity, indicating that there are significant changes in interface structure with relative humidity.
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Rafferty, M. P. "Studies on the tonal qualities of violins : vibrational behaviour of the treble from the new violin family." Thesis, Bucks New University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376440.
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Avosani, Sabina. "Behaviour, ecology, and vibrational manipulation of insect vectors: the case of the meadow spittlebug Philaenus spumarius, with notes on a psyllid pest." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/319182.
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Insects can cause economic and environmental damages by transmitting bacterial pathogens to plants, making the use of control and prevention measures imperative. On the other hand, methods aimed at preventing crop pests’ outbreaks, such as tilling and insecticide applications, pose a threat to human and ecosystems health. Innovative and more sustainable control methods are therefore urgently needed to address farmers’ needs and preserve ecosystem services provided by biodiversity. Biotremology is an emerging science that studies the substrate-borne vibrational signals emitted by insects to communicate and interact with their others in the environment. As many insect pests rely on these signals to communicate, their behaviour can be manipulated by transmitting vibrations to the substrate where they thrive. Vibrational signals can, for instance, interfere with target’s behaviours such as mating, feeding, and residence time on the plant, and can therefore support integrated pest management strategies alternative to insecticides.
In this work, I investigated the mating behaviour and vibrational communication of two insect vectors having an important economic impact: Philaenus spumarius (Hemiptera: Aphrophoridae) and Bactericera cockerelli (Hemiptera: Triozidae). I also provided novel insights regarding the vibrational manipulation of their behaviour.
I characterised the sexual behaviour and associated vibrational signals of the meadow spittlebug P. spumarius, and I described other intraspecific interactions. I evaluated the correlation between the female signalling activity and development of the reproductive organs, suggesting that a vibrational mating disruption could be effective only if applied from the onset of egg maturation, which triggers the female proceptivity (from August onwards). Besides gathering behavioural data, I used occupancy models to estimate P. spumarius presence and detection probability in Trentino (Northern Italy), a rarely deployed approach to study insect distribution. Site covariates impacted P. spumarius detectability, suggesting that spittlebug presence can be overlooked if detection is not considered. As plant composition influences the presence and abundance of the spittlebug, I studied the association between P. spumarius and its host plants. Such information can support monitoring programs and control strategies aimed at reducing P. spumarius population in crops of interest by shaping the plant composition of the ground cover. After investigating the behaviours and the ecology of the spittlebug, I attempted to disrupt its feeding activity using vibrations, opening the gates for future research. In this regard, I combined for the first time biotremology with the Electrical Penetration Graph (EPG) technique.
The tomato potato psyllid B. cockerelli is an important threat to New Zealand crops. Besides the characterisation of the pair formation process and associated vibrational signals, I used vibrations to disrupt mate finding by transmitting vibrations to the host plant. Given that the stimulus attracted male psyllids at small scale, this strategy is a feasible approach that could be implemented for use in fields and greenhouses. In this way, an innovative trapping and mating disruption device could join the farmers’ toolbox for monitoring and controlling B. cockerelli.
In conclusion, I provided new information regarding the ethology of two insect vectors and suggested that there is room for applied biotremology to support sustainable management strategies.
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Fumis, Cristiana. "Mechanical Wave Propagation in Civil Engineering Materials." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Mechanical wave propagation in civil engineering materials is important for different application fields, such as thermal conductivity, damage detection and sound transmission (including filters and sound barriers). A current open challenge is to understand how the chemistry and microstructures of cementitious materials impact the propagation of mechanical waves in them.
The challenge is heightened by the fact that cementitious materials are very heterogeneous at the microscale. In this project, molecular and nanoparticle based simulations will be used in order to construct microstructures of cement hydrates with a range of chemistries and morphologies. I will simulate the dynamic behaviour of these model structures and quantify it in terms of vibrational band structure and density of states. This will open
the way to a new and fundamental understanding of how the chemistry and microstructure of cementitious materials can be tailored in order to engineer their vibrational behaviour, for controlled thermal conductivity, soundroof applications, and more efficient damage detection.
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Al-Share, Mohammad A. (Mohammad Abdel). "Anomalous Behavior in the Rotational Spectra of the v₈=2 and the v₈=3 Vibrations for the ¹³C and ¹⁵N Tagged Isotopes of the CH₃CN Molecule in the Frequency Range 17-95 GHz." Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc330976/.
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The rotational microwave spectra of the three isotopes (^13CH_3^12C^15N, ^12CH_3^13C^15N, and ^13CH_3^13C^15N) of the methyl cyanide molecule in the v_8=3, v_8=2, v_7=1 and v_4=1 vibrational energy levels for the rotational components 1£J£5 (for a range of frequency 17-95 GHz.) were experimentally and theoretically examined. Rotational components in each vibration were measured to determine the mutual interactions in each vibration between any of the vibrational levels investigated.
The method of isotopic substitution was employed for internal tuning of each vibrational level by single and double substitution of ^13C in the two sites of the molecule. It was found that relative frequencies within each vibration with respect to another vibration were shifted in a systematic way. The results given in this work were interpreted on the basis of these energy shifts. Large departure between experimentally measured and theoretically predicted frequency for the quantum sets (J, K=±l, ϑ=±1), Kϑ-l in the v_8=3 vibrational states for the ^13c and ^15N tagged isotopes of CH_3CN showed anomalous behavior which was explained as being due to Fermi resonance. Accidently strong resonances (ASR) were introduced to account for some departures which were not explained by Fermi resonance.
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Wang, Zhongsheng. "VIbration behaviour of prestressed concrete beams." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420369.
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Jubb, Aaron Michael. "Vibrational Spectroscopic Investigations of Sulfate Behavior at Environmental Interfaces." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337782832.
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Che, Kar Suriani Binti. "Oscillatory behaviour and strategy to reduce drilling vibration." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15831.
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Drill String dynamic behaviour during the oil drilling operation, was a major source for the failure of the Bottom Hole Assembly (BHA). The behaviour produced torsional vibration, which underpins the stick slip phenomena. Besides threatening the safety of the oil drilling process, such failure cause interruptions in the drilling operations and incurred high maintenance cost to the oil drilling company. This issue can be resolved with the implementation of the optimum control mechanism while operating the drill string. In this research, an optimum control mechanism was proposed to suppress the torsional vibration as well as mitigate the risk of stick slip phenomenon from occurring. The mechanism was proposed through a series of rigorous research strategies i.e. updated-mathematical equation modelling, experimentation and simulation. As the first step, a mathematical equation model describing system dynamics was derived to set the parameter of investigation. Representing the freedom torsional of the two degrees - conventional vertical drill string, the model was used to predict the frictional Torque On Bit (TOB) through non-linear friction force, denoting the ground-formation behaviour during drilling activity. Using a velocity feedback system, the drill-string oscillation was reduced while gradually increasing its velocity via gain scheduling method - allowing fast response to load disturbance. To avoid the motor torque from exceeding the maximum threshold, a Weight On Bit (WOB) was introduced. This approach remarks the novel contribution of this research. Next, an experiment on the preliminary test rig within a controlled laboratory set up was conducted. The rotary drill rig was assembled to identify the dynamics (i.e. parameters) of an individual part of the drill string. The results obtained were then applied in the drill string operation experiment, to identify the optimum control mechanism that can avoid the torsional vibration. To enable triangulation of results, a simulation was conducted by applying the same parameters obtained from the test rig experiment in the model- which is the optimum control mechanism that was proposed in this research to minimise torsional vibration, as well as reducing the chance of drill-string failure due to stick-slip phenomenon.
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Isreb, Abdullah. "The use of solubility parameters to predict the behaviour of a co-crystalline drug dispersed in a polymeric vehicle : approaches to the prediction of the interactions of co-crystals and their components with hypromellose acetate succinate and the characterization of that interaction using crystallographic, microscopic, thermal, and vibrational analysis." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5525.
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Dispersing co-crystals in a polymeric carrier may improve their physicochemical properties such as dissolution rate and solubility. Additionally co-crystal stability may be enhanced. However, such dispersions have been little investigated to date. This study focuses on the feasibility of dispersing co-crystals in a polymeric carrier and theoretical calculations to predict their stability. Acetone/chloroform, ethanol/water, and acetonitrile were used to load and grow co-crystals in a HPMCAS film. Caffeine-malonic acid and ibuprofennicotinamide co-crystals were prepared using solvent evaporation method. The interactions between each of the co-crystals components and their mixtures with the polymer were studied. A solvent evaporation approach was used to incorporate each compound, a mixture, and co-crystals into HPMCAS films. Differential scanning calorimetry data revealed a higher affinity of the polymer to acidic compounds than their basic counterparts as noticed by the depression of the glass transition temperature (Tg). Moreover, the same drug loading produced films with different Tgs when different solvents were used. Solubility parameter values (SP) of the solvents were employed to predict that effect on the depression of polymer Tg with relative success. SP values were more successful in predicting the preferential affinity of two acidic compounds to interact with the polymer. This was confirmed using binary mixtures of naproxen, flurbiprofen, malonic acid, and ibuprofen. On the other hand, dispersing basic compounds such as caffeine or nicotinamide with malonic acid in HPMCAS film revealed the growth of co-crystals. A dissolution study showed that the average release of caffeine from films containing caffeine-malonic acid was not significantly different to that of films containing similar caffeine concentration. The stability of the caffeine-malonic acid co-crystals in HPMC-AS was prolonged to 8 weeks at 95% relative humidity and 45°C. The theory developed in this project, that an acidic drug with a SP value closer to the polymer will dominate the interaction process and prevent the majority of the other material from interacting with the polymer, may have utility in designing co-crystal systems in polymeric vehicles
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Ferreira, Janito Vaqueiro. "Dynamic response analysis of structures with nonlinear components." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299871.
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Ebadi, Mohammad Mehdi. "Vibration Behaviour of Glulam Beam-and-Deck Floors." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36443.
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Low-amplitude floor vibrations have become a governing serviceability performance design consideration for floors constructed with low mass-to-stiffness ratio materials such as wood. Studies reported here were conducted at the University of Ottawa to assess vibration serviceability performance of glued-laminated-timber (glulam) beam-and-deck floor systems. Such floors are applicable in non-residential buildings having spans up to about 10 m. The primary goal was to use test and numerical analysis methods to investigate how construction variables (e.g. beam span, beam spacing, addition of nonstructural overlays) affect the vibration responses of such floors. A secondary goal was to assess applicability of vibration serviceability design criteria proposed for other types of floors to glulam beam-and-deck floors. Apart from tests aimed at characterizing responses of laboratory built rectangular plan floors, focus groups were asked to subjective rate acceptability of the performances of those floors. Focus group ratings determined ability of humans to discern alterations in floor motions resulting from construction modifications, based on an opinion survey technique developed by other researchers. This determined that humans can detect and rate performance of floors having different engineering design characteristic, but cast doubts on the consistency of the employed opinion survey technique.
Laboratory tests revealed that mid-span displacements of floors are functions of two-way deflected shapes of floors and are reduced by adding nonstructural overlays and extra beams. Adding non-structural overlays reduces fundamental natural frequency demonstrating gain in modal mass was greater than for modal stiffness. There was inconsistency between the result of focus group evaluations and predictions of acceptability of floors made using available suggested vibration serviceability design criteria.
Finite Element (FE) models of glulam beam-and-deck floor systems were created and verified using laboratory test data. Based on those models it was concluded that fundamental natural frequencies and mid-span displacements of floors are relatively insensitive to variations in floor width-to-span ratios. However, higher order natural frequencies are strongly affected by floor width-to-span ratios. Increasing thickness of deck elements can decrease natural frequencies and cause them to cluster in ways that amplify surface motions caused by dynamic forces like human footfall impacts.
Field vibration tests were conducted to investigate the dynamic behaviour of a large glulam beam-and-deck office floor having a complex plan shape and support conditions. That floor has long beam spans and partial continuity between bays defined by a mixture of column and wall supports. It was tested before non-structural floor toppings were added and after building completion and occupation. FE modeling of the floor was created and predicted modal characteristics (i.e. mode shapes, natural frequencies) compared with experimentally derived ones. Controlled walking tests were conducted to assess the dynamic response under office occupation conditions. It was concluded the vibration serviceability response of the floor was satisfactory based on peak acceleration measurements and lack of office worker dissatisfaction. Importance of this is the floor has low order natural frequencies less than 8Hz, which means existing proposed design practices created for lightweight timber floor would incorrectly classify its performance. The discrepancy is indicative that such design practices fail to capture effects of construction variables and damping characteristics of large floors.
In general, vibration characteristics of lightweight floors are highly related to effects of construction details such as plan aspect ratio, boundary conditions and presence of nonstructural elements. Apart from clarifying specifics of how glulam beam-and-deck floors vibrate, this thesis is intended to contribute to Canadian and international efforts to create engineers design methods that robustly predict whether or not specific floors will have adequate vibration serviceability performance under defined floor occupancy conditions.
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Bean, Ralph. "Vibrational control of chaos in artificial neural networks /." Online version of thesis, 2009. http://hdl.handle.net/1850/10645.
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Smith, Jonathan Hurndall. "Stick-slip vibration and is constitutive laws." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304168.
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Cao, Da. "Modelling of the vibrational behavior of housing plates filled with fibrous material." Thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276478.
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Silencers are used in vehicles to reduce the noise in the engine system. How-ever, silencers themselves may produce break-out noise due to the interaction with the exhaust gas flow and structure. In this Master thesis project, the numerical simulation of vibrational behavior of housing plates of silencers is developed.The housing plate is composed of two steel plates and a fibrous material layer. Measurement results show that the fibrous material has good damping effect to decrease the vibration and radiated sound of steel plates. Steel plates are connected by spot welding. Modeling of spot welds can improve the modal assurance criterion between simulation and measurements. Interface damping is introduced into the simulation models to simulate the contact effect between two steel plates so that the simulated amplitude can have a good agreement with measurement result.Several numerical models of fibrous material are investigated. The Miki model is not chosen for the final result due to the limit of range of frequencies. The rigid frame model can simulate the sound absorption but is unfeasible for the simulation of vibration. The limp frame model can simulate the vibration of light glass wool but cannot simulate the vibration of heavy glass wool. Finally, the Biot-Allard model which is a poro-elastic model is investigated for the final result. The simulation results show good agreement with the measurement result.Ljuddämpare används i fordon för att används för att minska buller i motorsystemet. Ljuddämpare kan emellertid själva producera utbrottsbuller på grund av samspelet mellan avgassflödet och ljuddämpare. I detta examensarbete utvecklas den numeriska simuleringen av vibrationsbeteende hos husplåter för ljuddämpare. Husplåten består av två Plåtar av stål och ett fibröst materiallager. Resultaten av mätningen visar att det fibrösa materialet har god dämpningseffekt för att minska det utstrålade ljudet och vibrationen hos plåterna. Plåterna ansluts med punktsvetsning. Modellering av punktsvetsar kan förbättra kriteriet för modal försäkring mellan simulering och mätning. Dämpning av gränssnitt införs i simuleringsmodellerna för att simulera kontakteffekten mellan två plåtar så att simuleringsamplituden kan ha ett bra överensstämmelse med mätresultatet. Flera numeriska modeller av fibröst material undersöks i detta projekt. Miki-modellen används inte för slutresultatet på grund av gränsen för frekvensområden. Stiv modell kan simulera ljudabsorptionen men är omöjlig för simulering av vibrationer. Limpmodell kan simulera vibrationer av lätt glasull men kan inte simulera vibrationer av tung glasull. Slutligen undersöks Biot-Allard-modellen som är en poroelastisk modell för slutresultatet. Simuleringsresultaten visar bra överensstämmelse med mätresultatet.
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Lam, Frank C. F. "Analytical and experimental studies of the behaviour of equipment vibration isolators under seismic conditions." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25110.
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Analytical and experimental studies of the behaviour of equipment vibration isolators under seismic conditions are presented. A preliminary parametric study of the effect of equipment-structure interaction on the ultimate equipment response of general equipment-structure systems is considered first. The results of this study indicate the conditions under which a non-interactive approach can yield adequate ultimate equipment response estimates.
A model of a prototype air handling unit mounted on vibration isolators was constructed for use in the experimental studies. Two types of vibration isolators -elastomeric isolators and open spring isolators with uni-directional restraint - were tested under static and dynamic conditions. The frequency and seismic response characteristics of these vibration isolated systems were obtained. The experimental results indicate that the vibration isolators have nonlinear stiffness characteristics and high damping values. The results also show that the elastomeric isolators can survive a substantially higher level of base excitation than the open spring isolators with uni-directional restraint
Analytical models of the vibration isolated systems, based on the model identification test results, have been formulated. A numerical procedure, utilizing time series analysis, was used to solve the equations of motion of the systems. Good agreement between the experimental results and the analytical results was observed. This study indicates that the analytical procedure can be used to accurately predict the response characteristics of vibration isolated equipment systems subjected to known base excitation inputs.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Li, Z. "Non-smooth dynamic behaviour of friction-induced self-excited vibration." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3015902/.
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Friction is everywhere and important in our daily life as well as in industry. In general, dry friction acts as a resistance to the relative motion and dissipates energy of a system; however, under certain conditions, it can cause self-excited vibration of a system, which is known as friction-induced vibration. Friction-induced vibration can potentially cause problems like wear, fatigue failure, and noise, among which brake squeal is a typical engineering problem. As a comprehensive understanding of friction-induced vibration has not been achieved, friction-induced vibration is still a challenging research topic. The aim of this research is to carry out a theoretical study of the dynamic behaviour of nonlinear/non-smooth friction-induced vibration of phenomenological mechanical models. Discrete and continuous mechanical models with dry friction that involve nonlinear contact stiffness, stick-slip motion, or separation and reattachment at the contact interface are proposed, and numerical simulations of the transient dynamic behaviour of the non-smooth frictional systems are implemented. Their complex dynamic behaviour and the influences by various system parameters are predicted. In addition, a reduction strategy for the complicated frictional systems is presented and validated via theoretical and experimental results, which is a preliminary step in analysing complicated systems (real structures) with nonlinear/non-smooth friction behaviour in future research. The main objectives of the research work reported in this thesis are: 1. To carry out the transient dynamic analysis of non-smooth friction-induced vibration. A varying time-step numerical algorithm, which combines Runge-Kutta method that is specifically for the second-order differential equation of motion and the bisection method, is proposed (Chapter 3). This algorithm ensures the accuracy of the results of the non-smooth vibration in which the motion states keep switching among distinct motion states of separation and reattachment, or stick and slip, which is testified by providing the same results of a classic non-smooth stick-slip vibration of a single-degree-of-freedom model. 2. In consideration of improving previous research on theoretical mechanical models with the assumptions that the contact stiffness is linear or separation is ignored, a nonlinear 2-degree-of-freedom slider-on-moving-belt model developed from Hoffmann’s model and the theoretical formulations are proposed (Chapter 4), in which a cubic contact spring is included; loss of contact (separation) at the slider-belt interface is allowed and importantly reattachment of the slider to the belt after separation is also considered. The stability and dynamic behaviour of the system are investigated. Complex eigenvalue analysis (CEA) indicates that the roles of the preload and the nonlinear stiffness on the stability of the nonlinear system are not monotonous. Transient dynamic analysis (TDA) shows that separation and reattachment could happen. Ignoring separation between bodies in sliding frictional contact in vibration is unsafe as this may underestimate the vibration amplitude, and predicts incorrect effects of the key parameters on the vibration, thus considering separation is very important. Moreover, frequency domain results show the necessity of implementing both CEA and TDA in the study of nonlinear friction-induced vibration and the importance of considering separation from the frequency domain point of view. Finally, non-smooth Coulomb’s law of friction is introduced in the nonlinear 2-degree-of-freedom (2-DoF) slider-belt model. Numerical results show that diverse dynamic behaviour of this 2-DoF system with nonlinearity/non-smoothness can be generated when both of the stick-slip and mode-coupling instability are involved. 3. Separation, reattachment and impact are considered in the study of friction-induced vibration of a system having an elastic disc, excited by the in-plane stick–slip vibration of a moving mass-damper-spring slider attached to a rigid wall that is dragged around on the disc surface at a constant rotating speed (Chapter 5). Theoretical formulations and the numerical procedure for the current non-smooth system are developed. Numerical results show that separation and reattachment could occur in a low speed range well below the critical disc speed in the context of a constant rotating load. Poincare maps of the system of the two distinct cases (considering separation and ignoring separation) are plotted which exhibit the diversity of nonlinear dynamic behaviour of the system and the importance of considering separation. Furthermore, the roles of the key system parameters on the vibration are investigated. Time-frequency analysis reveals the time-varying properties of this system and the contributions of separation and in-plane stick-slip vibration to the system frequencies. One major finding is that ignoring separation, as is usually done, often leads to very different dynamic behaviour and possibly misleading results. 4. Based on the idea of mode synthesis method, a reduction strategy for complicated frictional systems is put forward, in which the natural contact interfaces and the tangential friction force are involved, and its applications and experimental validation are presented (Chapter 6). Firstly, its application to a theoretical multi-degree-of-freedom model with linear contact verifies the accuracy and feasibility of the strategy. The influence of the system parameter, and the mode number that is used in the reduced model on the stability of the reduced model are investigated. The reduced model is capable of preserving the key features (bifurcation of the eigenvalue and unstable frequencies) of the original model. Furthermore, a specific reduction strategy, for a real pad-on-disc test rig and its corresponding finite element model which involve direct contact of the interface, is proposed. The results of the reduced model with a small number of modes of the substructures correlate fairly well with theoretical results of the full model and the test results in terms of predicting mode-coupling instability and unstable frequencies, which validates this promising method for future work on friction-induced vibration of complicated frictional systems or real structures.
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Reynolds, Thomas Peter Shillito. "Dynamic behaviour of dowel-type connections under in-service vibration." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608327.
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This study investigated the vibration serviceability of timber structures with dowel-type connections. It addressed the use of such connections in cutting-edge timber structures such as multi-storey buildings and long-span bridges, in which the light weight and flexibility of the structure make it possible that vibration induced by dynamic forces such as wind or footfall may cause discomfort to occupants or users of the structure, or otherwise impair its intended use. The nature of the oscillating force imposed on connections by this form of vibration was defined based on literature review and the use of established mathematical models. This allowed the appropriate cyclic load to be applied in experimental work on the most basic component of a dowel-type connection: a steel dowel embedding into a block of timber. A model for the stiffness of the timber in embedment under this cyclic load was developed based on an elastic stress function, which could then be used as the basis of a model for a complete connector. Nonlinear and time-dependent behaviour was also observed in embedment, and a simple rheological model incorporating elastic, viscoelastic and plastic elements was fitted to the measured response to cyclic load. Observations of the embedment response of the timber were then used to explain features of the behaviour of complete single- and multiple-dowel connections under cyclic load representative of in-service vibration. Complete portal frames and cantilever beams were tested under cyclic load, and a design method was derived for predicting the stiffness of such structures, using analytical equations based on the model for embedment behaviour. In each cyclic load test the energy dissipation in the specimen, which contributes to the damping in a complete structure, was measured. The analytical model was used to predict frictional energy dissipation in embedment, which was shown to make a significant contribution to damping in single-dowel connections. Based on the experimental results and analysis, several defining aspects of the dynamic response of the complete structures, such as a reduction of natural frequency with increased amplitude of applied load, were related to the observed and modelled embedment behaviour of the connections.
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de, Luna Richard M. "EFFECT OF LOW VELOCITY IMPACT ON THE VIBRATIONAL BEHAVIOR OF A COMPOSITE WING." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1551.
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Impact strength is one of the most important structural properties for a designer to consider, but it is often the most difficult to quantify or measure. A major concern for composite structures in the field is the effect of foreign objects striking composites because the damage is often undetectable by visual inspection. The objective for this study was to determine the effectiveness of using dynamic testing to identify the existence of damage in a small scale composite wing design. Four different impact locations were tested with three specimens per location for a total of 12 wings manufactured. The different impact locations were over the skin, directly over the rib/spar intersection at the mid-span of the wing, directly over the middle rib, and directly over the leading edge spar. The results will be compared to a control group of wings that sustain no damage. The wing design was based on an existing model located in the Cal Poly Aerospace Composites/Structures lab. The airfoil selected was a NACA 2412 airfoil profile with a chord length of 3 inches and a wingspan of just over 8 inches. All parts cured for 7 hours at 148°F and 70 psi. The wings were each tested on a shaker-table in a cantilever position undergoing 1g (ft/s2) acceleration sinusoidal frequency sweep from 10-2000 Hz. The 1st bending mode was excited at 190 Hz and the 2nd bending mode was excited at 900 Hz. After the pre-impact vibrational testing each wing was impacted, excluding the control group. To verify the experimental results, a finite element model of the wing was created in ABAQUS. The frequency and impact numerical results and the experimental results were in good agreement with a percent error for both the 1st and 2nd mode at around 10%.
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Zhang, Xingnan. "The effect of vibrations on the behaviour of lubricated elastohydrodynamic contacts." Thesis, University of Sussex, 2017. http://sro.sussex.ac.uk/id/eprint/71822/.
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It is known that rolling element bearings are the second most extensively used machine components in various mechanisms and machines. Consequently, the demand of pursuing higher bearing performance, increased load carrying capacity and prolonged operation life is crucial. The lubrication regime in which rolling element bearings operate is called Elastohydrodynamic Lubrication (EHD). The EHD lubrication regime in steady-state conditions, where working parameters such as load, geometry or speed of the surfaces are constant, is nowadays well understood. Nevertheless, in practice EHD contacts never work in completely steady-state regimes. For example, the contacts of rolling element bearings operating in a machine, which runs at constant speed, has no shock loading from the end effector still experience variable loading when the rolling elements enter and exit the loaded zone and variable speed at the start up and shut down of the machine. Factors related to the working cycle of the machine or mechanism cannot be avoided or simply the start or stop of those will always introduce unsteadiness into the EHD contacts. Vibrations in EHD contacts cause variation of load, and implicitly pressure and contact size, fluctuations of film thickness, which in their turn cause localized fluctuations of the pressure. The vibrational behavior is directly related to noise generation, which significantly influences bearing performance. The current research is focused on the effect of forced harmonic vibrations on oil and grease lubricated EHD contacts. Experiments were carried out using a test rig that simulates real – life EHD contacts by a steel ball on glass disc contact. The method used for measuring the lubricant film thickness was optical interferometry, adapted for the specifics of this research. Lubricant film thickness was measured in systematically – designed tests where a wide range of lubricants and working parameters was employed. The trends of EHD film behaviour under variable loading were evaluated and maps of the likelihood of film thickness perturbation occurrence were drawn for the first time. An analytical model of the lubricant film thickness variation during rapid variation of load was also devised and successfully compared to the experimental findings. The systematic study of the effect of vibrations upon EHD film recovery in limited lubricant supply conditions was also carried out and published. An experimental study on the effect of vibrations was successfully extended into grease-lubricated contacts. The scientific information gained will be a useful tool in the hands of both, lubricants and machine elements producers, with the aim of extending the life expectancy of those elements.
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Jrad, Wassim. "Dynamic behavior of thin-walled beams : Analytical, numerical and experimental approaches." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0271.
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Les poutres à parois minces à sections ouvertes sont des éléments de base des ouvrages courants en génie civil, de l'automobile et de l'aéronautique. En raison de leur élancement et la forme des sections, elles sont très sensibles à la torsion et aux instabilités aussi bien en statique qu’en dynamique. En dynamique, les modes de vibration en torsion sont plus dominants par rapport au modes de flexion classiques. Pour ces raisons, les défaillances planaires de telles structures sont connues pour être une exception plutôt qu'une règle. Dans ce travail de thèse, on s’intéresse au comportement dynamique de poutres à parois minces et à section ouvertes arbitraires. En se basant sur le modèle de Vlasov qui prend en compte de la torsion et du gauchissement, les équations de mouvement 3D sont dérivées à partir du principe d’Hamilton. Des solutions analytiques originales pour différentes conditions aux limites sont dérivées pour des modes supérieurs en vibrations libres. Dans ces solutions, les effets des termes de rotation inertiels en flexion et torsion sont pris en compte. Pour des cas généraux, un modèle élément fini de poutre 3D est décrit et implémenté. Dans le modèle, un degré de liberté (ddl) est affecté au gauchissement. Toutes les matrices de rigidité masse de base sont calculées par intégration numérique (intégration de Gauss). Dans le modèle, les calculs en vibrations libres et forcées sont possibles. Le modèle est validé par comparaison aux solutions numériques et expérimentaux de la littérature. Une comparaison aux simulations des codes commerciaux est aussi suivie. Afin de valider le modèle théorique et numérique utilisé, une campagne d’essais a été suivie au LEM3 à Metz. Des essais de vibration libre et forcée sont effectués sur des poutres à parois minces avec différentes conditions aux limites. Les solutions analytiques, numériques et les mesures expérimentales sont comparées et validées. Un bon accord entre les différentes solutions est constaté. Le modèle est étendu aux poutres 3D retenues latéralement par des entretoises. Des ressorts élastiques et visqueux 3D sont ajoutés dans le modèle numérique. L'effet des entretoises est étudié dans le but d’améliorer le comportement des poutres à parois minces vis-à-vis des modes indésirables de type flexion latérale et torsionThin-walled beams with open section constitute main elements in engineering applications fields as in civil engineering, automotive and aerospace construction. Due to slenderness and cross section shapes, these elements are very sensitive to torsion and instabilities in both statics and dynamics. In dynamics, the torsional and flexural-torsional modes of vibration are often lower frequencies compared to the classical plane pure bending modes. Thus, planar failures of such structures are known to be an exception rather than a rule. In torsion, warping is important and governs the behavior. In this thesis work, we are interested with the dynamic behavior of thin-walled beams with arbitrary open cross sections. Based on the Vlasov’s model accounting for warping, the 3D motion equations are derived from the Hamilton’s principle. Original analytical solutions for different boundary conditions are derived for higher free vibration modes. In these solutions, the effects of the inertial rotation terms in bending and torsion are taken into consideration. For more general cases, a 3D beam finite element model is described and implemented. Compared to conventional 3D beams, warping is considered as an additional Degree Of Freedom (DOF). The mass and stiffness matrices are obtained by numerical integration (Gauss method). In the model, free and forced vibration analyses are possible. The model is validated by comparison with benchmark solutions available in the literature and other numerical results obtained from simulation on commercial codes. In order to validate the present model, laboratory test campaign is undertaken at the LEM3 laboratory in Metz. Tests are carried out on thin-walled beams with different boundary conditions. Free and forced vibration tests are performed using impact hammer and shaker machine. In the presence of arbitrary sections, flexural-torsional vibration modes are observed. The analytical, the numerical and the experimental solutions are compared and validated. Moreover, the numerical and experimental dynamic response spectra are compared. A good agreement between the various solutions is remarked. The model is extended to 3D beams in presence of lateral braces. 3D elastic and viscous springs are added in the finite element model. The effect of the springs is studied in order to improve the behavior of thin-walled beams against undesirable lateral bending and torsion modes
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Abhyankar, N. S. "Studies in nonlinear structural dynamics: chaotic behavior and poynting effect." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/12523.
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Ustundag, Burak. "On the free vibration behavior of cylindrical shell structures." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67717.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 105-106).
Shell structures, especially cylindrical shells, are widely used in aerospace and naval architectural industries. Submarine hulls and aircraft bodies can be idealized as cylindrical shell structures. The study of vibrations of cylindrical shells is an important aspect in the successful applications of the cylindrical shells. The free vibration characteristics of a submarine hull have an important influence on the noise signature of the submarine. That makes the free vibration problem of the submarine hull a particular interest for the submarine community. The natural frequencies of cylindrical shells are clustered in a very narrow band and they are thus more prone to becoming involved in resonant vibrations. The determination and control of these frequencies is significant to manage the acoustic signature of the submarine. This thesis focuses on the free vibration characteristics of stiffened and unstiffened cylindrical shells. The analysis is carried out mainly in two parts. First, the unstiffened cylindrical shell is modeled and the free vibration problem is analyzed as the shell thickness decreases. Then the cylindrical shell is stiffened with ring stiffeners and the free vibration problem of the stiffened cylindrical shell is studied. The vibration modes of the unstiffened cylindrical shell are studied for four shells with different thicknesses. Initial tensile and compressive membrane stresses are applied separately to the shells to study the effect of the initial stresses on the free vibration modes. The vibration modes of the stiffened cylindrical shell are studied in two steps. First, the influence of the positions of two ring stiffeners on the fundamental frequencies is studied; second, the free vibration modes of the stiffened cylindrical shell are studied. Two cylindrical shells with different thicknesses are used and they are stiffened with different numbers of ring stiffeners, which are uniformly distributed along the longitudinal axis of the shell. The results are compared with available analytical results and finite element solutions of similar problems from the literature.
by Burak Ustundag.
S.M.
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Smith, Andrew. "Dynamical behaviour of water-immersed fine grains subjected to vertical vibration." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438426.
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Currey, Mary Noelle. "On the behavior of exterior acoustic modes of structures." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17670.
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Najm, Désirée. "Quels capteurs de vibrations pour la surveillance de santé des structures mécaniques ?" Thesis, Paris Est, 2015. http://www.theses.fr/2015PEST1072/document.
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La thèse a pour objectif de définir les principes et les approches d’une mise en œuvre pratique des capteurs de vibrations pour l’évaluation dynamique des structures, notamment la détection d’endommagements. L’idée générale est d’étudier les combinaisons instrumentation/méthode de détection. Ainsi, une étude numérique de sensibilité de différentes méthodes de détection et de localisation d’endommagement utilisant les paramètres modaux (essentiellement fréquences propres et déformées modales) a été réalisée en fonction du type de capteur utilisé, du nombre de capteurs, de la sévérité du défaut et de la dispersion des paramètres modaux. Le cas d’application choisi est celui d’une poutre en aluminium bi-encastrée. Un panorama des capacités de chacune des méthodes pour l’évaluation dynamique des ouvrages a ainsi pu être dressé. Dans l’ensemble, l’application des méthodes de détection d’endommagement a fourni de meilleurs résultats à partir de jauges de longue base de mesure. Une méthode développée au sein de l’équipe Dynamique, appliquée numériquement et expérimentalement, a également permis de localiser un défaut de masse et/ou de rigidité ainsi que de quantifier ces changementsThe aim of the thesis is to define principles and approaches of a practical implementation of vibration sensors for dynamic monitoring of structures, specially damage detection. The general idea is to study the combinations instrumentation /detection method. Thus, a numerical sensitivity study of different damage detection and localization methods using modal parameters (mainly natural frequencies and mode shapes) was performed according to the type of sensor used, to the number of sensors, to the severity of the damage, and to dispersion of modal parameters. The case-study is conducted on an aluminium clamped-clamped beam. A panorama of the capacity of each method for dynamic assessment of structures has been presented. Overall, long base strain gauges provide better results for damage detection methods. A method developed in the Dynamic group applied to numerical and experimental data, is able to locate mass and/or flexural rigidity modifications and to quantify these perturbations
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Thornhill, Lindsey Dorough. "Fatigue behavior of flexhoses and bellows due to flow-induced vibrations." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/17624.
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Tassini, Nicola. "Modelling the vibration damping behaviour of APS and EB-PVD ceramic coatings." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444241.
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De, Togni Robert S. "The role of system dynamics on the behavior of elastomeric friction." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-10102009-020240/.
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Chen, Wangshu. "Microscopic study of the behavior of water in a single pore under vibration to intensify drying." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC054/document.
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Une meilleure performance économique du séchage industriel consiste à la fois en l'amélioration de la qualité des produits et de l’optimisation énergétique. Plusieurs technologies peuvent être appliquées pour intensifier le processus de séchage. Ce travail s’intéresse à l'effet des vibrations, qui peuvent accélérer le séchage via un échauffement par dissipation visqueuse, une amélioration de la migration de l’eau liquide et de la vapeur à l'intérieur du milieu poreux et une augmentation des coefficients de transferts externes de chaleur de masse. Toutefois, malgré les études numériques et expérimentales antérieures, l'évaluation de l'importance relative de ces mécanismes d'intensification doit encore être améliorée.Ce travail porte sur l'échelle du pore, simulée par un tube capillaire, partiellement rempli d'eau soumis à des vibrations sinusoïdales. Un dispositif expérimental complet a été conçu, développé et utilisé. Grâce à une procédure de traitement d'images pertinente, le comportement de l'eau à l'intérieur du tube (déplacement et le rayon du ménisque) ont été étudiés pour différentes configurations de vibrations (fréquence, amplitude, taille du tube). Les expériences avec des géométries symétriques et asymétriques sont destinées à imiter le transfert d'humidité pendant le séchage d'un milieu poreux. Quelle que soit la configuration étudiée, l'intensification du séchage a été clairement confirmée.Pour la configuration symétrique, une nouvelle cartographie 2D basée sur des nombres adimensionnels est définie pour résumer les effets capillaires et visqueux, et ainsi expliquer le comportement de l'eau en fonction des conditions vibratoires (rayon du tube, fréquence et amplitude). Pour la configuration asymétrique, les résultats expérimentaux sont discutés et comparés aux simulations obtenues avec deux modèles numériques (un modèle 0-D et un modèle 1-D). Le potentiel de la modélisation a été mis en évidence, mais il est encore limité par les hypothèses physiques aux interfaces. D'autres développements sont proposés afin d'augmenter la plage de validité et d'approfondir l'étude de ce système physiqueA better economic performance of industrial drying consists both in product quality improvement and energy efficiency enhancement. Several technologies can be applied to intensify the drying process. This work is focused on the effect of vibration that can assist the drying through heating-up due to viscous dissipation, enhancement of liquid and vapor migration inside the porous medium and the increase of the external heat and mass transfer. However, despite previous numerical and experimental studies, the assessment of the relative importance of these intensification mechanisms has still to be improved.This work is focused on the pore scale, simulated by a capillary tube, partially filled with water subjected to sinusoidal vibrations. A full experimental device was conceived, developed and used. Thanks to a relevant image processing chain, the behavior of water inside the tube (displacement and meniscus radius), was investigated for various vibration configurations (frequency, amplitude, tube size). Experiments with both symmetrical and asymmetrical geometries are intended to mimic the moisture transfer during drying of a porous medium. Whatever the configuration, the drying intensification was clearly confirmed.For the symmetrical configuration, a new 2D dimensionless number map is set to summarize the capillary and viscous effects and thus to explain the water behavior depending on vibration conditions (tube radius, frequency and amplitude). For the asymmetrical configuration, the experimental results are discussed and compared to the simulations obtained with two computational models (a 0-D model and 1-D model). The potential of modeling was evidenced but still limited by the surrounding physical assumptions. Further developments are proposed to increase the validity range and further investigate this physical system
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Oz̈bek, M. Akif. "Short- and long-term dynamical behavior of beam type structures with computer graphics." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19017.
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Zhang, Yong Liang. "A theoretical and experimental study of the dynamic behaviour of initially-stretched cylindrical tubes conveying fluid." Thesis, University of Aberdeen, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323142.
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Hameiri, Avikam. "Soil/geotextile filtration behavior under dynamic conditions of cyclic flow and vibration." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/NQ48642.pdf.
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Friesen, Timothy. "A numerical investigation of large bubble translation behaviour due to forced vibration under microgravity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0024/MQ50339.pdf.
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Kalapala, Phani Krishna. "VIBRATORY BEHAVIOR OF ROLLING ELEMENT BEARINGS, A LAGRANGIAN APPROACH." Cleveland State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=csu1307044116.
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Samarbakhsh, Sina. "Investigation of the Lock-in behavior of an eccentrically rotating cylinder in regard to turbomachinery application." Thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154358.
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Interaction of fluctuating vortex shedding with blade vibration can lead to a new class of aeromechanical instability referred as Non-synchronous vibrations. Investigating a well-known case that shows similar NSV features such as a circular cylinder can develop the understanding of physics behind NSV. A common approach to further investigating the vortex induced vibration is to control the motion of the cylinder and allowing the response of the wake to the motion to be studied in isolation. It has been found very important to carefully match the experimental conditions between free and controlled vibration. Many of research in the field of vortex induced vibration apply a rigid cylinder mounted horizontally and moving transversely to the flow stream as a paradigm for understanding the physics behind this phenomenon. Regarding the difficulties of implementation of vertically moving cylinder in experimental study, vortex dynamic and lock-in behavior of eccentrically rotating cylinder is studied in this M.Sc. Thesis. The main focus of this research is to understand to what extend a general feature of free vortex-induced vibration can be observed in the case of eccentrically rotating cylinder. If the present case captures the essential characteristics of freely oscillating cylinder the results of the forced motion via eccentrically rotating cylinder can be applied to predict the motion of an elastically mounted body. To do so a CFD model is established to predict the response, vorticity structure in near wake, timing of vortex shedding and the range of lock-in region over specific parameter space of the introduced alternative case. A commercial CFD code, Ansys/CFX, was implemented to perform this numerical study. Existences of synchronization region, striking similarity in lift force coefficient and wake mode have been observed in the current study.
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AMORIM, MAYARA LOBO. "ANALYSIS OF THE DYNAMIC BEHAVIOR OF HISTORICAL BUILDINGS SUBJECTED TO TRAFFIC-INDUCED VIBRATIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36975@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
No Brasil as primeiras cidades surgiram no início do século XVI e, com a descoberta de novos territórios, foram surgindo novas cidades cujas construções remanescentes devem ser preservadas não somente pelo seu valor histórico, como também por suas técnicas construtivas. Estas construções são de uma época onde não havia fluxo intenso de tráfego, os veículos não eram pesados e não possuíam capacidade de atingir altas velocidades. Após a revolução industrial, com o aumento do transporte rodoviário e ferroviário, a preocupação com vibrações advindas do fluxo do tráfego em construções históricas ganhou importância, isso porque as cidades modernas se desenvolveram em torno dos seus núcleos históricas e o fluxo, peso e velocidade dos veículos nestas áreas são cada vez mais intensos. A excitação induzida por tráfego, dependendo da sua intensidade e frequência, pode gerar ou intensificar danos já existentes, além de causar desconforto aos usuários. Ela depende prioritariamente da qualidade dos pavimentos que é bastante irregular nas cidades históricas brasileiras. Para garantir a segurança de nossas construções históricas, geralmente de materiais frágeis, é fundamental o monitoramento das vibrações em ambientes urbanos. Nesta dissertação são apresentados os materiais mais relevantes utilizados em construções e pavimentos das cidades históricas no Brasil e uma revisão bibliográfica e análise das normas e critérios de projeto relativos ao efeito das vibrações induzidas por tráfego nessas construções. Com a finalidade de se entender como as vibrações se propagam nestas estruturas, foram construídas duas paredes de alvenaria apresentando variação da espessura da argamassa e diferentes tipos de fundação, sendo estas submetidas a cargas móveis e de impacto. Uma análise experimental detalhada mostra como em cada caso variam as acelerações, velocidades e deslocamentos ao longo das paredes, permitindo avaliar a influência do tipo de carregamento e da fundação nestas grandezas. Adotou-se para a avaliação de sensibilidade, a norma alemã DIN 4150.
The first cities in Brazil emerged in the early sixteenth century and, with the discovery of new territories; new cities emerged whose remaining buildings must be preserved not only for their historical value, but also for their constructive techniques. These constructions are of a time where there was no intense traffic flow, the vehicles were not heavy and did not have the capacity to reach high speeds. After the industrial revolution, with the increase in road and rail transport, the concern with vibrations arising from the flow of traffic in historical buildings gained prominence, because modern cities developed around their historical centers and the flow, weight and speed of the vehicles in these areas are becoming more intense. Traffic- induced excitation, depending on its intensity and frequency, can generate or intensify existing damages, and usually cause discomfort to users. It depends primarily on the quality of the pavements, which is quite irregular in Brazilian historical cities. To ensure the safety of our historic constructions, usually of fragile materials, the monitoring of vibrations in urban environments is fundamental. This dissertation presents the most relevant construction materials used in constructions and pavements of historic cities in Brazil and a bibliographica l review and analysis of the codes and design criteria related to the effect of traffic - induced vibrations in these constructions. In order to understand how the vibratio ns propagate in these structures, two masonry walls were built in the laboratory with different mortar thickness and different types of foundation, being these subjected to mobile and impact loads. A detailed experimental analysis shows how in each case the accelerations, speeds and displacements vary along the walls, allowing evaluating the influence of the type of load and foundation characteristics in these quantities. The German standard DIN 4150 was adopted for the sensitivit y assessment.
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Koivurova, H. (Hannu). "Dynamic behaviour of an axially moving membrane interacting with the surrounding air and making contact with supporting structures." Doctoral thesis, University of Oulu, 1998. http://urn.fi/urn:isbn:9514249496.
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Abstract
Axially moving material problems are concerned with the dynamic response, vibration and stability of slender members which are in a state of translation. In Finland these are particularly important in the functioning of paper machines, in which out of plane vibration in the paper web, known as flutter, which from the point of view of mechanics is a phenomenon typical of an axially moving material, limits operation speeds and therefore the productivity of the machines. This subject links together a number of physical phenomena associated with aerodynamics, web movement, material behaviour and the geometry of the system. The aim of this research is to present a theoretical and numerical formulation of the nonlinear dynamic analysis of an axially moving web.
The theoretical model is based on a mixed description of the continuum problem in the context of the dynamics of initially stressed solids. Membrane elasticity is included via a finite strain model, and the membrane transport speed through a kinematical study. Hamilton's principle provides nonlinear equations which describe the three-dimensional motion of the membrane.
The incremental equations of Hamilton's principle are discretized by the finite element method. The formulation includes geometrically nonlinear effects: large displacements, variations in membrane tension and variations in transport velocity due to deformation. This novel numerical model was implemented by adding an axially moving membrane element to a FEM program which contains acoustic fluid elements and contact algorithms. This allowed analysis of problems including interaction with the surrounding air field and contact between supporting structures.
The model was tested by comparing previous experiments and present nonlinear description of the dynamic behaviour of an axially moving web. The effects of contact between finite rolls and the membrane and interaction between the surrounding air and the membrane were included in the model. The results show that nonlinearities and coupling phenomena have a considerable effect on the dynamic behaviour of the system. The nonlinearities cause a noticeable stiffening of the membrane, and the vibration frequency of nonlinear system increases as the amplitude grows. At high values of transport velocity the first mode frequency passes over the second linear harmonic, and even the third. The results also show that the cylindrical supports have a distinct influence on the behaviour of an axially moving sheet. The boundary of the contact region clearly moves and weakens the nonlinear hardening phenomena that otherwise increase the fundamental frequency. This influence strengthens as the radius of the cylinders increases.
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Hall, Eric K. "A study of slender beams: finite deformations, chaotic vibrations, and active control." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/12919.
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Wu, Hailong. "Modelization and control of synchronous reluctance machines for the torque ripple minimization - study of vibrational and acoustic behavior." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCA003.
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Cette thèse porte sur l’optimisation du contrôle des Machines Synchrones à Réluctance Variable (MSRV) et en particulier sur la compensation des phénomènes vibratoires. Elle comprend trois points forts : le développement d’une méthode de minimisation des pulsations de couple et sa validation expérimentale, l’études des facteurs qui peuvent influencer la méthode et l’influence de cette méthode sur les autres performances de la MSRV.Tout d’abord, une méthode de contrôle permettant de compenser les ondulations de couple d’une MSRV existante a été développée. Premièrement, une équation analytique du couple est proposée et analysée afin d’exprimer la relation analytique harmonique entre le couple et les courants d’alimentation. La notion de « fonction de couple » est ensuite introduite. Une stratégie basée sur l’utilisation de cette fonction pour minimiser les ondulations du couple est présentée. Deux méthodes de réduction des ondulations de couple utilisant les différents harmoniques de la fonction de couple sont mises en évidence en. Elles ont été analysées et comparées pour répondre aux différents objectifs. Par la suite, la méthode a été validée par les résultats des simulations pour trois technologies de rotor de MSRV parmi les plus répandues. La méthode est aussi validée par la modélisation analytique et la simulation dynamique à l’aide du logiciel Matlab/Simulink ainsi que par les résultats d’expérimentation avec l’aide du banc d’essai.Ensuite, les facteurs qui peuvent influencer la méthode proposée pour réduire les ondulations de couple et les performances dynamiques ont analysés. Dans un premier temps, une amélioration sensible de l’aptitude au démarrage de la MSRV lorsque la compensation des ondulations de couple est mise en œuvre est mise en évidence. D’autre part la sensibilité de la méthode aux erreurs de mesure de position est évaluée afin de quantifier sa fiabilité dans le cas de l’utilisation d’estimateurs lors du contrôle sans capteur. Enfin, l’influence de la saturation sur la méthode proposée est aussi étudiée à l’aide d’une analyse par éléments finis du comportement magnétique de la MSRV.Finalement, l’influence de la méthode de compensation des ondulations de couple sur d’autres performances de la MSRV est analysée. Les courants optimaux ont plus harmoniques que les courants originaux. Par conséquent, les pertes dans le cuivre, dans le fer et dans les semi-conducteurs de l’onduleur sont modélisées analytiquement, calculées et comparées. Les conclusions montrent que les pertes dans le cuivre sont les plus sensibles à la compensation des harmoniques de couple tandis que les pertes dans le fer et dans l’onduleur sont faiblement affectées. D’autre part, la réduction des ondulations de couple peut changer le comportement vibro-acoustique de la MSRV. La dernière partie est consacrée à l’étude de la relation entre les ondulations de couple et le bruit. Une équation est proposée pour évaluer la variation du bruit produit par la compensation des ondulations de couple. Dans cette partie, les simulations dans Flux 2D sont effectuées pour calculer la variation du bruit. En outre, le logiciel professionnel Manatee réalisant l’analyse des vibrations et de l’acoustique est utilisé dans le but de conforter les résultats obtenus par la modélisation analytiqueThis thesis aims to study the control and optimization of a synchronous reluctance machine for the purpose of improving the vibrational performance. The main works of the thesis can be classified into three parts: the proposed torque ripple reduction method, the factors which can influence the proposed method and the influence of the proposed method.At first, the torque ripple of synchronous reluctance machine is reduced by a control method. Firstly, a torque equation is proposed in order to present the relationship between torque ripple and the optimal currents. Then a new parameter, torque function, is put forward. Based on the torque function, the torque ripple reduction strategy is presented. Two different torque ripple minimizations are proposed by applying different torque function harmonics. They are analyzed and compared in order to define the optimal method. In order to test the proposed method further, the selected torque ripple minimization approach is applied to three SynRMs. The results of finite element simulations imply that the proposed method is effective to decrease the torque ripples of these three SynRMs. The proposed torque ripple reduction method is verified according to the models built in MATLAB/Simulink and the experiment results respectively.Then the factors which could influence the proposed torque ripple reduction method are analyzed. Firstly, torque function is a function of rotor position, current angle and saturation. Based on the model in Simulink, the influence of different starting position on the performance of the studied SynSR is analyzed. Besides, the estimated position errors produced by senserless control could also affect the toque ripple minimization by changing torque function. At last, the influence of saturation on the proposed torque ripple reduction method is introduced because the amplitudes of the optimal currents are increased.In addition, the influence of torque ripple reduction on the other perfomances of SynRM is analyzed. The optimal currents have more harmonics than the original sinusoidal currents. So three losses (copper losses, iron losses and inverter losses) are modeled, calculated, analyzed and compared. According to the results, the copper losses are the most sensible losses. The iron losses and the inverter losses are a little increased and the increased parts can be neglected. Besides, reducing torque ripple by adding stator currents could influence the vibro-acoustic of the studied SynRM. Thus this section aims to explain the relationship between torque ripple reduction and acoustic noise. An analytical equation is proposed in order to evaluate the variation of noise produced by torque ripple reduction. Simulations in Flux 2D have been performed in order to calculate the variation of noise resulted by torque ripple reduction. At last, the software Manatee which is professional in studying the vibration and noise is applied for the purpose of comparing the results with those of the finite element analysis
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Sweger, Alexander L. "Courtship Signaling, Sexual Selection, and the Potential for Acoustic Communication in the “Purring” Wolf Spider Gladicosa Gulosa." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1504781228686818.
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Roettgen, Andrew M. "Vibrational Energy Distribution, Electron Density and Electron Temperature Behavior in Nanosecond Pulse Discharge Plasmas by Raman and Thomson Scattering." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1428940661.
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Cowans, John Q. "The effects of viscoelastic behavior on the operation of a delayed resonator vibration absorber." Connect to this title online, 2006. http://etd.lib.clemson.edu/documents/1171901509/.
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Reiman, Stephen E. "Exploitation of Nonlinear Behavior to Improve the Performance of a Magnetic Sensor." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5244.
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While nonlinear behavior in mechanical systems typically degrades the behavior and performance the devices, the presence of system nonlinearities can sometimes improve the quality of the system. A reason for avoiding nonlinearities within a device is the difficulty in controlling the device due to the effects of the nonlinearities on system behavior. However, careful analysis of nonlinear systems can allow for one to take advantage of the nonlinear behavior to improve system performance.
The objective of this thesis is to exploit the use of nonlinearities to enhance system performance, specifically the sensitivity of a micromachined magnetic sensor. A device design will be presented that is similar to a prototype that has been fabricated by a student within the Electrical and Computer Engineering Department at Georgia Tech. The operating principle of the device is that changes in the orientation and the strength of an external magnetic field will result in changes in the dynamic behavior of the sensor. While previous device provided a proof of the design concept, it was unable to achieve a sensitivity that would allow for its use as a compass. Improvements in the sensitivity of the sensor are achieved through the modeling and optimization of the magnetic sensor. The optimization and redesign of the magnetic sensor will improve the quality of the device and provide another step towards sensor commercialization. A new design that incorporates the use of variable force comb drives will be proposed that will further improve the sensitivity of the device by modifying the dynamic behavior of the sensor.
Another approach that is presented to exploit the nonlinear behavior of the magnetic sensor involves a frequency detection scheme that uses nonlinear vibrations to characterize sensor behavior. Some benefits of this detection technique are that it is insensitive to noise in the vibration of the sensor and is also independent of the damping present within the system. In addition, the implementation of this sensing technique can be readily applied to variety of sensors types without the redesign of a system or the addition of complex components such as vacuum packaging or signal processing electronics.
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Courtois, Loïc. "Monofilament entangled materials : relationship between microstructural properties and macroscopic behaviour." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0138.
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Les matériaux architecturés attirent de plus en plus d’attentions de par leur capacité à combiner différentes propriétés ciblées. Dans ce contexte, les matériaux enchevêtrés, et plus particulièrement les matériaux monofilamentaires enchevêtrés, présentent des propriétés intéressantes en terme de légèreté, de ductilité, et de facteur de perte. En raison de l’architecture interne complexe de ces matériaux, leur caractérisation et la compréhension des mécanismes de déformation nécessitent une méthodologie adaptée. Dans cette étude, l’enchevêtrement est réalisé manuellement pour différents fils d’acier et soumis à une compression oedométrique. De manière à étudier le comportement sous charge de ce type de matériaux, un dispositif de compression uniaxiale guidée a été mis en place dans le tomographe. Il est ainsi possible de suivre, à l’aide de mesures quantitatives, la déformation de l’échantillon et l’évolution du nombre de contacts pour différentes fraction volumiques. L’utilisation de ces données microstructurales a permis un meilleure compréhension du comportement mécanique de tels enchevêtrements. Une rigidité pouvant varier de 20 à 200 MPa en fonction des paramètres de mise en forme (diamètre et forme du fil, fraction volumique, matériau constitutif) a été déterminé. Un matériau homogène de rigidité plus faible a pu être obtenu en pré-déformant le fil sous forme de ressort avant enchevêtrement. Le facteur de perte du matériau a ensuite été mesuré à la fois sous chargement statique et dynamique. L’analyse mécanique dynamique a mis en évidence la capacité de ce matériau à absorber de l’énergie avec une valeur de facteur de perte d’environ 0.25. Les propriétés mécaniques du matériau ont tout d’abord été modélisées analytiquement par un modèle de poutres et un bon accord avec les résultats expérimentaux a pu être obtenu en définissant un paramètre d’orientation equivalent, spécifique à la compression oedométrique de matériaux enchevêtrés. En parallèle, un modéle éléments discrets a été developé afin de simuler le comportement en compression de matériaux monofilamentaires enchevêtrés. Ce modèle s’appuie sur une discrétisation du fil en éléments sphériques, acquise à partir de données de tomographie. Bien que seul le comportement élastique du fil constitutif ait été pris en compte, une bonne adéquation entre résultats numériques et expérimentaux a été obtenu en ajustant les coefficients de frottement du modèlePlaying with the architecture of a material is a clever way of tailoring its properties for multi-functional applications. A lot of research have been made, in the past few years, on what is now referred to as “architectured materials” (metal foams, entangled materials, steel wool, etc), mostly for their capacity to be engineered in order to present specific properties, inherent to their architecture. In this context, some studies have been carried out concerning entangled materials but only a few on monofilament entangled materials. Such a material, with no filament ends, could exhibit interesting properties for shock absorption, vibration damping and ductility. In this study, entanglements were manually produced, using different types of wire, and submitted to constrained (inside a PTFE die) in-situ compressive tests within the laboratory tomograph. This technique enabled a 3D, non destructive, microstructural characterization of the complex architecture of these materials, along with the analysis of their macroscopic mechanical properties. The stiffness of this material was found to be in a 20-200 MPa range and homogeneous samples could be obtained, while lowering their stiffness, by pre-deforming the initial wire as a spring. Damping measurements were performed using different types of entanglements (constitutive materials, volume fraction, wire diameter, wire shape) under both monotonic and dynamic loadings and directly linked to the measurements of the number of contacts. The Dynamic Mechanical Analysis underlined the great capacity of this material to absorb energy with a loss factor of about 0.25 and damping was found to decrease with the stiffness of the entanglement. The mechanical properties of this material were first modeled using an analytical “beam” model based on the experimental evolution of the mean distance between contacts and a good agreement was found with the experimental results. In parallel, a Discrete Element Method was used in order to model the compressive behaviour of Monofilament Entangled Materials. Although purely elastic properties were taken into account in the model, a very good agreement with the experimental results was obtained by adjusting the friction coefficients of the model. This tends to prove that the plasticity of these entangled materials is rather due to the structure (friction) than to the constitutive material itself
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Donohue, Brian. "The transient behavior of the co-axial non-synchronous rotating assembly of a decanting centrifuge." Thesis, University of Canterbury. Mechanical Engineering, 2014. http://hdl.handle.net/10092/8920.
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This study identifies the cause of unstable vibrations that sporadically occur in decanting centrifuges as being caused by a combination of internal bearing clearance, conveyor unbalance and low bearing loads. These centrifuges are different from other rotating equipment common in industry (pumps, fans, compressors, electric motors) in that they are dual rotor systems – one rotor inside the other. Unbalance in either rotor can produce severe vibration of the whole machine when the running speed is close to a mode of vibration – that is, running at or near a critical speed. The external rotor, called the bowl, is subjected to an internal pressure generated by the centrifugal force of the product being separated. The internal rotor is supported from the bowl and is in the form of an auger screw. The main supporting bearings are subjected to forces from both the bowl and the auger - the liquid end bearing also supports the gearbox. Being able to predict critical speeds through numerical or computational analysis is a necessary step in the design process or for troubleshooting vibration problems. As part of the study, the main rolling element bearings were replaced by oil-film journal bearings to assess the viability of their use. Journal bearings are simpler, of lower cost and generate less noise than their rolling element counterparts. However, instability in running above the first critical speed can result due to oil film forces and internal hysteresis of the rotor assembly. The auger is asymmetric so instability in running is possible at around half the first critical speed.
This study was undertaken to understand the dynamics of decanting type centrifuges and develop a methodology for identifying their critical speeds and cause of unstable vibration. In the longer term this will assist in the generation of new designs that are quieter, use less energy and have better separation efficiencies.
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Pierson, Kristopher C. "Multiphysics Cavitation Model with Application to the Dynamic Behavior of Journal Bearings." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555440702757939.
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Ghezzi, Ilaria. "Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon : The case of the spring-brake system." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI116.
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Les travaux de thèse proposent une approche complémentaire, combinant analyses dynamiques et tribologiques, au problème de stick-slip d’un contact graissé, dans un frein mécanique à ressort. L’instabilité de stick-slip est le résultat du couplage entre la réponse dynamique du système mécanique (frein) et la réponse locale du contact lubrifié à l’interface de freinage. La réponse locale du contact graissé a d’abord été caractérisée par des tests expérimentaux effectués sur tribomètre. Ensuite, les conditions qui conduisent à l'instabilité ont pu être investiguées en détail, à l’aide d’un modèle numérique a paramètres concentres du système complet. Ce modèle simule le comportement dynamique global du système de freinage mécanique. En entrées, il prend les paramètres propres au fonctionnement et à la conception du frein, ainsi que les courbes de frottement locales. En sortie, le poids de chacun des paramètres sur la génération du stick-slip a donc pu être analysé. Enfin, une étude expérimentale de l’influence des différents composants de la lubrification (DLC et graisse) sur le comportement du contact frottant lubrifié a été réalisée. Dépendante de l’épaississant, de l’huile et des additifs, la rhéologie complexe de la graisse est un point clé pour comprendre l'apparition du stick-slip. En effet si la lubrification est traditionnellement censée réduire les pertes par frottement, elle peut malgré tout participer à l’apparition d’instabilités. La compréhension des conditions pour lesquelles un système est prédisposé au phénomène de stick-slip peut permettre de prévenir l'apparition de telles instabilités et des nuisances qu’elles engendrent. Néanmoins, en présence de contacts lubrifiés, la littérature n’y consacre que peu de travaux. C’est dans ce contexte que l’analyse multi-approches présentée dans cette thèse permet de contribuer à la compréhension de l’apparition des instabilités de frottement dans les contacts lubrifiés avec graisse, en apportant également des éléments de solution dans le cas d’une application spécifiqueThe thesis works propose a complementary approach, combining dynamic and tribological analyzes, to the stick-slip problem of a greased contact, in a mechanical spring brake. Stick-slip instability is the result of the coupling between the dynamic response of the mechanical system (brake) and the local response of the lubricated contact at the brake interface. The local response of the greased contact was first characterized by experimental tests performed on a tribometer. Then, the conditions which lead to instability have been investigated in detail, using a numerical lumped model of the complete system. This model simulates the overall dynamic behavior of the mechanical braking system. As inputs, it takes the parameters specific to the operation and design of the brake, as well as the local frictional behavior obtained experimentally. At the output, the influence of each of the parameters on the generation of the stick-slip has been therefore analyzed. Finally, an experimental study of the influence of the different lubricant components (DLC and grease) on the behavior of the lubricated frictional contact has been carried out. Dependent on thickener, oil and additives, the complex rheology of grease is a key point for the understanding of the stick-slip appearance. Indeed, if lubrication is traditionally supposed to reduce friction losses, it can also participate in the appearance of instabilities. Understanding the conditions for which a system is predisposed to the stick-slip phenomenon can help prevent the appearance of such instabilities and the nuisance they cause. However, in the presence of lubricated contacts, the literature shows a lack of informations. It is in this context that the multi-approach analysis presented in this thesis makes it possible to contribute to the understanding of the appearance of friction instabilities in contacts lubricated with grease, by also providing elements of solution in the case of a specific application