<p> Flexural vibrations of a shaft mounted at each end on a non - linear spring have been studied. Theoretical analysis is carried out for the cubic non-linear spring. </p> <p> The effect of mountirig of a heavy rotor on the shaft has been considered. The stability analysis of the system is also given in the theoretical analysis.</p> / Thesis / Master of Engineering (ME)

The production of faulty parts poses significant challenges for production facilities, as it leads to increased inventory levels, operating costs, and impedes overall productivity. Despite its fundamental nature, this issue remains prevalent in manufacturing operations. To effectively reduce the rate of faulty parts, it is crucial to have a thorough understanding of the manufacturing process and exercise control by monitoring various parameters.  The aim of this study is to investigate the right prerequisites which enable quality assurance through in-line failure detection by vibration analysis. The research questions formulated for this thesis are as follows:  RQ1: What are the essential prerequisites for quality assurance through in-line failure detection by vibration analysis in the machining of splines? RQ2: How suitable is the use of vibration measurements in identifying and sorting out poor quality in the specific machining process of splines? The study was conducted through a literature review and a single case study of a gear hobbing process in an industrial manufacturing company.  The collection of data was acquired via interviews, observations, and vibration measurements during the spline manufacturing process. To analyse the collected data several tools got used. Python was used as the tool for performing several operations on the dataset, such as FFT of the vibration signals. To later visualize the results which facilitated the analysis of the entire dataset.  The results of the study indicate several similarities between the documented fault progression in gear systems and the manufacturing of splines. However, further research is needed to identify the core differences between these two fault progressions.  Furthermore, the study identified the essential prerequisites for implementing vibration analysis as an in-line failure detection method in spline manufacturing operations. Additionally, it concluded on the suitability of vibration analysis for identifying faults in this context.

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[pt] Este trabalho se propõe a estudar o comportamento de máquina operatriz sob condições reais de operação, tendo em vista sua estabilidade de funcionamento. É analisado o efeito da variação da força de corte sobre a estrutura elástica de uma Furadeira Radial de Bancada, através da interpretação da Curva de Ressonânica, do Lugar Geométrico de Resposta Harmônica e do Diagrana de Estabilidade. E este último indica as faixas de velocidade de operação onde não há risco de instabilidade, em função do diâmetro e do avanço da broca. No final, é apresentada uma proposta de Teste de Aceitação para Máquinas Operatrizes, englobando aspectos dinâmicos e construtivos. / [en] The behavior of a machine tool, under real cutting conditions, here is studied, mainly considering its dynamic stability. The effect of the cutting force variation on the elastic structure of Radial Drilling Machine is analyzed by the Ressonance Curve, the Harmonic Response Locus and Stability Chart. This chart indicates the chatter-free rotational speed range, according to the tool diameter and infeed per revolution. An acceptance test for Machine Tools is proposed at the end, considering dynamic and constructive aspects.

Today's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided or minimized if a quiet building site is selected in the first place. Accelerometers and gauss meters combined with a computer for acquisition and analysis provide a low cost method of evaluating noise levels at proposed building sites. This work examines low frequency vibration and electromagnetic fields at two proposed sites for the planned Physical Science Building at the University of Central Florida.

Data acquisition systems for rotordynamic analysis and machine vibration were explored for the purpose of replacing the obsolete Bently Nevada ADRE 208 and ADRE for Windows system. These included the development of Matlab based custom data acquisition systems and a user interface. A model of an anisotropic rotor response undergoing transient speed was developed for the rapid prototyping and testing of data acquisition systems. Several methods for the measurement of amplitudes and phase in both the time domain and frequency domain were developed and compared. An alternate data acquisition method which is more inline with industry practices was created for the purpose of spectral analysis. Additionally, an optimized data acquisition strategy was developed for implementation within the Matlab app which included batch processing, state-based acquisition, and differentiated vector and waveform acquisition rates. A Bently Nevada 2300/20 vibration monitor was configured for use in the lab but found unsuitable for replacing the ADRE 208. Ultimately a Bently Nevada ADAPT 3701/44 Vibration Monitor was configured and found to be an adequate replacement for the ADRE 208 system for use in the Cal Poly Vibrations Lab.

The objective of this work is to study the local and global nonlinear vibrations of isotropic single-layered and multi-layered cross-ply doubly curved shallow shells with simply supported boundary conditions. The study is based-on the full nonlinear partial-differential equations of motion for shells. These equations of motion are based-on the von K\'rm\'{a}n-type geometric nonlinear theory and the first-order shear-deformation theory, they are developed by using a variational approach. Many approximate shell theories are presented. We used two approaches to study the responses of shells to a primary resonance: a $direct$ approach and a $discretization$ approach. In the discretization approach, the nonlinear partial-differential equations are discretized using the Galerkin procedure to reduce them to an infinite system of nonlinearly coupled second-order ordinary-differential equations. An approximate solution of this set is then obtained by using the method of multiple scales for the case of primary resonance. The resulting equations describing the modulations of the amplitude and phase of the excited mode are used to generate frequency- and force-response curves. The effect of the number of modes retained in the approximation on the predicted responses is discussed and the shortcomings of using low-order discretization models are demonstrated. In the direct approach, the method of multiple scales is applied directly to the nonlinear partial-differential equations of motion and associated boundary conditions for the same cases treated using the discretization approach. The results obtained from these two approaches are compared. For the global analysis, a finite number of equations are integrated numerically to calculate the limit cycles and their stability, and hence their bifurcations, using Floquet theory. The use of this theory requires integrating $2n+(2n)^2$ nonlinear first-order ordinary-differential equations simultaneously, where $n$ is the number of modes retained in the discretization. A convergence study is conducted to determine the number of modes needed to obtain robust results. The discretized system of equation are used to study the nonlinear vibrations of shells to subharmonic resonances of order one-half. The effect of the number of modes retained in the approximation is presented. Also, the effect of the number of layers on the shell parameters is shown. Modal interaction between the first and second modes in the case of a two-to-one internal resonance is investigated. We use the method of multiple scales to determine the modulation equations that govern the slow dynamics of the response. A pseudo-arclength scheme is used to determine the fixed points of the modulation equations and the stability of these fixed points is investigated. In some cases, the fixed points undergo Hopf bifurcations, which result in dynamic solutions. A combination of a long-time integration and Floquet theory is used to determine the detailed solution branches and chaotic solutions and their stability. The limit cycles may undergo symmetry-breaking, saddle node, and period-doubling bifurcations. / Ph. D.

Icing on aircraft wings is one of the leading causes of aircraft crashes. It is mainly caused due to accumulation of ice or snow on the wing surface due to impact with supercooled droplets when passing through clouds at high altitudes, causing loss of lift obtained by the wings. It was found that droplet impact characteristics are dependent on droplet size, surface roughness, surface material hydrophobicity, and droplet impact velocity. As a continuation of the study of droplet impact contact characteristics by varying surface roughness and impact velocity, this study focuses on droplets impacting the vibrating surface at frequencies between 2-7 kHz. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. The first set of data is collected by keeping roughness constant and increasing the amplitude of the vibration to observe the critical amplitude at which atomization is initiated. The surface roughness is varied for the second set of experiments. The data is quantified using image processing of the high-speed videos to obtain the rate of ejection for each case. / Master of Science / Icing on aircraft wings is among the leading causes of crashes, which involves small freezing water drops sticking to the wing surface thus reducing the lift. This study is an investigation to experimentally observe how small water droplets interact with surfaces vibrating at high frequencies when impacted. Surface roughness, materials, droplet velocities, and frequency of vibration have been varied and the droplet was captured using high-speed photography to study their effect on the aforementioned interaction. Glass, PET-G. and aluminum having specific roughness were fabricated using laser and chemical etching. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. A relation between the amplitude of the vibration and the rate of atomization was found. The effect of varying frequencies and surface roughness has also been documented.

This thesis investigates the implementation of a passive isolator with a pressurized air cushion for spacecraft payloads in mission architectures implementing in-space assembly technologies. A pressurized air bed capable of briefly surviving the space environment for cargo delivery was prototyped and experimentally evaluated for launch vehicle vibration dynamics resulting in a 72%, 93%, and 88% reduction in experienced GRMS loads for the X-Axis, Y-Axis, and Z-Axis, respectively. A preliminary Total Mass Loss evaluation of the Low-Density Polyethylene Film utilized for the air bed resulted in a mass loss of 0.7%, indicating that commercial off-the-shelf films might require minimal modification for flight readiness. An analytical model of a planar rectangular payload experiencing free vibrations with a Winkler foundation is generated and compared to the experimental results, showing a potential way for characterizing and designing such a foundation to reduce experienced vibrations. These preliminary results show a potential path for a non-cost-prohibitive method for space payloads to reduce loads experienced during launch as inspired by the successful hosted payloads program aboard the International Space Station.