A flex-fan has flexible blades which undergo large deformation under centrifugal forces to give the desired air-flow and power-consumption characteristics with speed. The finite element technique has been used to obtain the deflected shape of the blade of such a fan used for automobile radiator cooling. The natural frequencies of vibration are also evaluated at different speeds, up to 5,000 rpm. A partially conforming deflection function has been used in the analysis. The blade has been treated as a thin shell, idealized as an assembly of thin flat triangular elements. / Thesis / Master of Engineering (ME)

<p> The optimization study of space frames has been considered in two aspects in this project work. The first was to develop a suitable optimization technique for a nonlinear programming problem including equality constraints, without any particular reference to structural optimization. The necessacity for the above requirement was due to the fact that almost all existing methods on optimization have some limitation. The second object of this study was to set up the necessary equations for the constraints on stress and on frequency for the structural model used, and then to use the developed technique to optimize the structural model for minimum weight. </p> <p> A simple and effective strategy, which is a combination of direct search and linear approximate programming is believed to have been developed for optimization of simple nonlinear type equations. </p> <p> The analysis of the space structure and the study of structural optimization revealed several difficulties inherent in the evaluation of constraining equations for the stresses and frequencies, which makes the optimization very difficult. </p> / Thesis / Master of Engineering (ME)

<p> The present investigation deals with Gas Turbine Blade Vibrations. Literature on the techniques employed for experimental investigation of gas turbine blade vibration characteristics has been summarised. Various steps have been explained by reviewing the different techniques. Several causes for possible excitation of blades as well as damping methods to suppress the resulting vibrations are also included. Attempts were made to determine experimentally the natural frequencies of cantilever plates of thin uniform rectangular cross section, with and without pretwist. First natural frequency_ -of the plate without twist was in good agreement with the one calculated from the plate formula. Free vibration analysis of cantilever plates of thin uniform rectangular cross section is made. Finite Element Technique is used to determine the elastic and inertial properties of a fully compatible triangular element. Computed values of natural freqencies and mode shapes are compared with other analytical results. </p> / Thesis / Master of Engineering (ME)

No description available.

No description available.

Presently, auto manufacturers do not have do not have efficient or accurate methods to determine the amount of refrigerant (R-134a) in an air conditioning system of an automobile. In the research presented, vibration analysis is examined as a possible method to determine this R-134a amount. Initial laboratory tests were completed and experimental modal analysis methods were investigated. This approach is based on the hypothesis that the natural frequency of the accumulator bottle is a function of the mass of refrigerant in the system. Applying this theory to a working automotive air conditioning bench test rig involved using the roving hammer method—forcing the structure with an impact hammer at many different points and measuring the resulting acceleration at one point on the structure. The measurements focused on finding the natural frequency at the accumulator bottle of the air condition system with running and non-running compressor scenarios. The experimental frequency response function (FRF) results indicate distinct trends in the change of measured cylindrical natural frequencies as a function of refrigerant level. Using the proposed modal analysis method, the R-134a measurement accuracy is estimated at ±3 oz of refrigerant in the running laboratory system and an accuracy of ±1 oz in the non-running laboratory system. / Master of Science

[pt] Estruturas de cascas delgadas descritas por superfícies regradas têm sido frequentemente utilizadas em engenharia civil, devido ao fato de que elas são uma das soluções estruturais mais econômicos para cobrir grandes vãos. Superfícies regradas são obtidas pelo movimento de uma ou mais linhas ao longo de uma ou mais curvas. Sendo assim, elas são fáceis de construir, o que justifica a sua escolha em muitos casos. Por razões estéticas e estruturais, estas estruturas são geralmente superfícies abatidas, o que leva, como no caso de arcos abatidos, a uma forte não linearidade geométrica. Entre as cascas descritas por superfícies regradas, as cascas conoidais são frequentemente favorecidas para coberturas de grandes áreas livres de colunas, pela facilidade de construção, elegância estética e pelo bom fornecimento de luz natural. Uma casca conoidal é um caso especial de cilindróide, pertencente às superfícies de Catalan, e é gerada por uma linha reta em movimento paralelo a um plano, conhecido como o plano diretor, com uma de suas extremidades em uma curva plana e a outra em uma linha reta. Por vezes, uma parte da superfície conoidal no extremo reto é suprimida dando origem a uma configuração truncada. O objetivo deste trabalho é analisar, utilizando uma formulação de elementos finitos, as características de flambagem e vibração desta forma estrutural. Uma análise paramétrica detalhada é realizada para compreender a influência das condições de contorno e dimensões físicas da casca no seu comportamento estático e dinâmico. São apresentadas conclusões específicas no final do trabalho, para resumir os resultados do presente estudo, que pretende servir como importante subsídio para os engenheiros envolvidos na construção de estruturas similares. / [en] Slender shell structures described by ruled surfaces have been frequently used in civil engineering due to the fact that they are one of the most economical structural solutions to cover large spans. Ruled surfaces are obtained by the movement of one or more lines along one or more curves. So they are easy to cast, which justifies their choice in many cases. For aesthetic and structural reasons these structures are usually shallow surfaces, which leads, as in the case of shallow arches, to a strong geometric nonlinearity. Among the shells described by ruled surfaces, conoidal shells are frequently favored as roofing units to cover large column-free areas due to the ease of fabrication, aesthetic elegance and good provision of natural light. A conoidal shell is a special case of cylindroids belonging to Catalan’s surfaces and is generated by a variable straight line moving parallel to a plane, known as the director plane, with one of its ends on a plane curve and the other on a straight line. Sometimes a part of the conoidal surface at the straight end is cut off giving a truncated configuration. The objective of this work is to analyze, using a finite element formulation, the buckling and vibration characteristics of this structural form. A detailed parametric analysis is conducted to understand the influence of boundary conditions, different spans, widths, and other physical dimensions on the static and dynamic characteristics of the structure. Specific conclusions are drawn at the end, to summarize the contributions of the present investigation, which are expected to serve as important design aids to engineers engaged in shell construction.

It is widely acknowledged that bearing failures are the primary reason for breakdowns in rotating machinery. These failures are extremely costly, particularly in terms of lost production. Roller bearings are widely used in industrial machinery and need to be maintained in good condition to ensure the continuing efficiency, effectiveness, and profitability of the production process. The research presented here is an investigation of the use of acoustic emission (AE) to monitor bearing conditions at low speeds. Many machines, particularly large, expensive machines operate at speeds below 100 rpm, and such machines are important to the industry. However, the overwhelming proportion of studies have investigated the use of AE techniques for condition monitoring of higher-speed machines (typically several hundred rpm, or even higher). Few researchers have investigated the application of these techniques to low-speed machines ( < 100 rpm), This PhD addressed this omission and has established which, of the available, AE techniques are suitable for the detection of incipient faults and measurement of fault growth in low-speed bearings. The first objective of this research program was to assess the applicability of AE techniques to monitor low-speed bearings. It was found that the measured statistical parameters successfully monitored bearing conditions at low speeds (10-100 rpm). The second objective was to identify which commonly used statistical parameters derived from the AE signal (RMS, kurtosis, amplitude and counts) could identify the onset of a fault in either race. It was found that the change in AE amplitude and AE RMS could identify the presence of a small fault seeded into either the inner or the outer races. However, the severe attenuation of the signal from the inner race meant that, while AE amplitude and RMS could readily identify the incipient fault, kurtosis and the AE counts could not. Thus, more attention needs to be given to analysing the signal from the inner race. The third objective was to identify a measure that would assess the degree of severity of the fault. However, once the defect was established, it was found that of the parameters used only AE RMS was sensitive to defect size. The fourth objective was to assess whether the AE signal is able to detect defects located at either the centre or edge of the outer race of a bearing rotating at low speeds. It is found that all the measured AE parameters had higher values when the defect was seeded in the middle of the outer race, possibly due to the shorter path traversed by the signal between source and sensor which gave a lower attenuation than when the defect was on the edge of the outer race. Moreover, AE can detect the defect at both locations, which confirmed the applicability of the AE to monitor the defects at any location on the outer race.

Condition based maintenance is becoming increasingly popular in many industrial contexts, offering substantial savings and minimising accidental damage. When applied to rotating machinery, its most common tool is vibration analysis, which relies on well-established mathematical models rooted in the theory of cyclo-non-stationary processes. However, the extraction of diagnostic information from the real world vibration signals is a delicate task requiring the application of sophisticated signal processing techniques, tailored for specific machines operating under restricted conditions. Such difficulty in the current state of the art of vibration analysis forces the industry to apply methods with reduced diagnostic capabilities but higher adaptability. However in doing so most of the potential of vibration analysis is lost and advanced techniques become of use only for academic endeavours. The aim of this document is to reduce the gap between industrial and academic applications of condition monitoring, offering ductile and automated tools which still show high detection capabilities. Three main lines of research are presented in this document. Firstly, the implementation of stochastic resonance in an electrical circuit to enhance directly the analog signal from an accelerometer, in order to lower the computational requirements in the next digital signal processing step. Secondly, the extension of already well-established digital signal processing techniques, cepstral prewhitening and spectral kurtosis, to a wider range of operating conditions, proving their effectiveness in the case of non-stationary speeds. Thirdly, the main contribution of the thesis: the introduction of two novel techniques capable of separating the vibrations of a defective component from the overall vibrations of the machine, by means of a threshold in the amplitude spectrum. After the separation, the cyclic content of the vibration signal is extracted and the thresholded signals provide an enhanced detection. The two proposed methods, phase editing and amplitude cyclic frequency decomposition, are both intuitive and of low computational complexity, but show the same capabilities as more sophisticated state of the art techniques. Furthermore, all these tools have been successfully tested on numerically simulated signals as well as on real vibration data from different machinery, lasting from laboratory test rigs to wind turbines drive-trains and aircraft engines. So in conclusion, the proposed techniques are a promising step toward the full exploitation of condition based maintenance in industrial contexts.

<p>This master’s thesis work was performed at Volvo Powertrain in Köping, Sweden, which manufactures gearboxes and integrated transmission systems for heavy vehicles. The thesis is a continuation of a previous master’s thesis performed at the Köping factory in 2009. After manufacturing and assembly, each gearbox is manually validated to ensure the gearbox quality and functionality. When validating the gearbox gears, the operator shifts the gearbox in a predefined manner and listens for irregularities. If an error sound is heard the operator must then locate the source of error. With numerous of cog wheels rotating at the same time this task requires extensive knowledge and experience of the operator. The main objective is to develop an automatic diagnostic system for detection of cog errors and assist the operator in the process of locating the faulty component.</p><p>The work consists of two parts. In the first part the automatic diagnostic system is developed and a database of gearbox recordings is stored. The amounts of logged non-faulty gearboxes are significantly much larger (50) than the logged faulty gearboxes (1). Therefore, when determining thresholds needed for the diagnosis, the data obtained from the non-faulty gearboxes are used. Two statistical methods are presented to extract the thresholds. The first method uses an extremevalue distribution and the other method a Gaussian distribution. When validated, both methods did successfully detect on cog faults. In the second part an investigation is made of how shaft imbalance can be detected and implemented in the developed system.</p><p>Volvo Powertrain continually follows-up all faults found at the validation station to ensure the quality of their work and eliminate the sources of error. During system testing one logged gearbox was found faulty. The automatic diagnostic system did successfully detect and locate the faulty component which later also was confirmed when the gearbox was dismounted. With only one detected error it is difficult to conclude the system performance and further testing is required. However, during the testing no false detections were made.</p>