Rotating blades are considered to be the one of the most common cause of failures in rotating machinery. Blade failure modes normally occur as a result of cracks due to unexpected operating conditions, which are normally caused by accidents of foreign objects damage, high cycle fatigue, blade rubbing, blade root looseness, and degradation from erosion and corrosion. Thus, detection of blade faults has an important role in reducing blade related failures and allowing repairs to be scheduled for the machinery. This in turn will lead to reduction in maintenance costs and thus raise productivity and safety aspects of operation. To maintain vital components of rotating machines, such as blades, shafts, bearings and gear boxes, at optimal levels, detection of failures in such components is important, because this will prevent any serious damage that could affect performance. This research study involves laboratory tests on a small rig with a bladed disc rotor that applied vibration measurements and analysis for blade fault detection. Three measurements: shaft torsional vibration, on-bearing vibration (OBV) and on-casing vibration (OCV), are used. A small test rig of a single stage bladed disc holding 8-blades was designed and manufactured, to carry out this research study to assess the usefulness and capability of each vibration technique in detection of incipient defects within machine blades. A series of tests was conducted on a test rig for three different cases of blade health conditions: (a) healthy blade(s) with mistuned effects, (b) blade root looseness and (c) cracks in a blade on two different blade sizes (long and short blades) in order to discover changes in blades' dynamic behaviour during the machine running-up operation. The data were collected using the three measurements during machine run-up and then recorded. The measured vibration data were analysed by computing the blades' resonance at different engine orders (EOs) related to the blade(s) resonance frequencies and their higher harmonics, to understand the blade(s) dynamics behaviour for the cases of healthy and faulty blade(s). Data have been further processed using a polar plot presentation method which provides clear results that can be used for monitoring blade integrity. To validate the obtained experimental results, a simplified mathematical model was also developed. Finally, a comparative study between three methods was undertaken to understand the relative advantages and limitations in the blade heath monitoring.

[pt] Uma prospecção bem sucedida de petróleo e gás requer muitos esforços para se sobrepor os desafios encontrados, tais como vibrações axiais, laterais e torcionais. Estes fenômenos podem causar a falha prematura de componentes do sistema de perfuração, disfunção nos equipamentos de medição e aumento no tempo e custo no processo de perfuração. Em particular, vibrações torcionais estão presentes em grande parte dos processos de perfuração e podem alcançar um estado crítico: stick-slip. Um melhor entendimento sobre este fenômeno proporciona ferramentas para evitar o aumento do tempo e do custo da prospecção, assegurando o investimento e sucesso do processo de perfuração. Neste trabalho, é descrito um procedimento experimental com um atrito não linear objetivando induzir stick-slip e é feito uma modelagem analítica simples do problema. O modelo de atrito é baseado em um atrito seco imposto por um dispositivo de freio desenvolvido. O comportamento não linear da bancada experimental é analisada e o modelo numérico é validado comparando diagramas de bifurcações numérica e experimentais. / [en] A successful oil and gas prospecting requires many efforts to overcome the encountered challenges, some of these challenges include drill string axial, lateral and torsional vibrations. These phenomena may cause premature component failures of the drilling system, dysfunction of measurement equipments, and increase time and costs of the prospecting process. Torsional vibrations are present in most drilling processes and may reach a severe state: stick-slip. An improved understanding about the stick-slip phenomenon provides tools to avoid the increase of prospecting time and costs, assuring the investment and success of the drilling process. Firstly, a numerical analysis of the drill string is performed with different friction models. These models are proposed in order to get familiar with the drill string dynamics. Also, it is described the experimental procedure with a nonlinear friction aiming to induce stick-slip and is performed a simple analytical modeling of the problem. The friction model is based on dry friction imposed by a break device. The nonlinear behavior of the experimental apparatus is analyzed and the numerical model is validated comparing experimental and numerical bifurcation diagrams.

[pt] Este trabalho apresenta um estudo do comportamento dinâmico de uma bancada de testes representativa do sistema real de perfuração, composta por um motor CC acoplado a um sistema físico torcional, sujeita a fontes de atrito que induzem um regime de stick-slip no sistema em duas regiões distintas. O estudo incluiu a identificação de parâmetros da bancada de testes por meio de uma série de ensaios experimentais; e a caracterização do atrito, por meio do levantamento experimental da curva do coeficiente de atrito, em função da velocidade angular dos rotores principais. O intuito inicial foi a obtenção de um modelo numérico que fosse o mais simples possível e que representasse bem a bancada de testes. Uma vez obtido o modelo numérico, prosseguiu-se com uma série de simulações que permitissem uma caracterização indireta do regime de atrito ao qual estivessem submetidos os rotores principais, partindo-se apenas de medições de parâmetros no motor. Esse estudo é de grande relevância para a compreensão qualitativa da dinâmica do sistema real de perfuração, uma vez que ainda hoje não há técnicas totalmente confiáveis para caracterização do comportamento da coluna no fundo do poço a partir de dados da superfície somente. / [en] This paper presents a study of the dynamic behavior of a representative test bench of a real rotary drilling system, comprising a DC motor coupled to a very exible torsional system subjected to sources of friction which can induce self-excitation into two distinct regions of the system. The study includes the identification of parameter settings from the test bench by means of a series of experimental tests and characterization of friction, by obtaining the experimental curve of the friction coefficient as a function of the angular speed of the main rotor. The initial aim was to obtain a numerical model as simple as possible, capable of representing the test bench. Once obtained the numerical model, a series of numerical simulations were done, which allow an indirect characterization of the friction condition to which main rotors were subjected, starting only with the parameters measured at the drive. This study is of great importance for a qualitative understanding of the dynamics of the real drilling system, since today there is no fully reliable techniques to characterize the behavior of the column in the deep from surface data only.

[pt] Parte do processo de exploração e desenvolvimento de um campo de petróleo consiste nas operações de perfuração de poços de petróleo e gás. Particularmente para poços de águas profundas e ultra-profundas, a operação requer o controle de uma estrutura muito flexível que é sujeita a condições de contorno complexas, tais como as interações não-lineares entre broca e formação rochosa ou entre a broca e a parede de poço. Quanto a esta complexidade, o fenômeno stick-slip é um componente primordial relacionado à vibração torsional. Este pode excitar vibrações tanto axiais quanto laterais. Isso pode causar falha prematura de componentes de corda de perfuração. Assim, a redução e eliminação de oscilações do tipo stick-phase são itens muito valiosos em termos de economia financeira e de tempo de exploração. Com este propósito, este estudo tem como principal objetivo confrontar o problema de vibração torsional simulando uma estratégia de controle robusto em tempo real. A abordagem é obtida seguindo alguns passos, tais como: análise em malha aberta do sistema de perfuração considerando um atuador top drive e o sistema de coluna de perfuração; concepção de um novo controlador que utiliza diferentes velocidades angulares de referência num sistema de controle de malha fechada; controle da vibração torsional considerando a não-linearidade devida à interação de atrito na parede do poço e no fundo do poço; avaliar por meio de simulações sistemas de controle ininterruptos durante a perfuração; validação dos modelos por meio de simulações numéricas. Esta dissertação apresenta a base teórica por trás do sistema de perfuração, bem como exemplos de resultados numéricos que proporcionam uma operação de perfuração controlada estável e satisfatória. / [en] Part of the process of exploration and development of an oil field consists of the drilling operations for oil and gas wells. Particularly for deep water and ultra deep water wells, the operation requires the control of a very exible structure which is subjected to complex boundary conditions such as the nonlinear interactions between drill bit and rock formation and between the drill-string and borehole wall. Concerning this complexity the stick-slip phenomenon is a major component, related to the torsional vibration and it can excite both axial and lateral vibrations. That may cause premature failure of drill-string components. So, the reduction and avoidance of stickslip oscillations are very valuable items in terms of savings and exploration time. With these intentions, this study has the main goal of confronting the torsional vibration problem using a real-time robust control strategy. The approach is obtained following some steps such as: Open-loop analysis of the drilling system considering a top-drive actuator and the drill-string system; Design of a novel controller using different angular velocity setpoints in a closed-loop system; Control of the torsional vibration considering the nonlinearity due to friction interaction in the wall and in the donwhole system; valuate a non-stop control system while drilling; Verification by numerical simulations. In this presentation the theoretical basis behind the drilling system will be given, as well examples of numerical results providing a stable and satisfactory controlled drilling operation.

[pt] Uma linha de pesquisa de grande interesse no estudo de colunas de perfuração de poços de petróleo aponta para a necessidade de se aumentar a taxa de penetração (ROP) na perfuração em rochas duras. Procurando suprir tal necessidade, este trabalho tem como objetivo estudar mecanismos e propor um novo dispositivo, utilizando as próprias vibrações geradas na coluna durante a perfuração. As várias formas de vibrar da coluna são, geralmente, indesejadas durante a perfuração. Porém, é possível utilizar algumas destas formas de vibrar para melhorar a eficiência do processo de perfuração. Inicialmente, avalia-se a influência das vibrações torcional e axial na ROP. Posteriormente, estuda-se a perfuração na ressonância e alguns aspectos e cuidados no uso desta nova técnica de perfuração, que vem sendo desenvolvida por empresas do setor. Por fim, é desenvolvido um novo dispositivo de perfuração, chamado de perfuração com martelo em ressonância ou perfuração percussiva- rotativa auto-excitada. Este dispositivo tem como premissa usar a vibração axial gerada no processo de corte, para criar uma carga harmônica na broca e excitar uma massa de aço (martelo). Desenvolve-se um modelo com vibro-impacto e atrito seco, representando o martelo e a resistência da rocha, respectivamente. Faz-se aqui, um estudo numérico e uma validação experimental do movimento percussivo de um modelo que representa a broca com este novo dispositivo. Os resultados mostram que a melhor forma do dispositivo operar é impactando a cabeça da broca, em condição de período-1, com um impacto por ciclo de forçamento. Adicionalmente, os parâmetros do experimento são identificados e os resultados numérico-experimental são comparados, mostrando que são similares. / [en] An area of interest in the study of drillstrings is due to the device of increasing the rate of penetration (ROP) in hard rocks. Trying to supply such necessity, this work aims to study mechanisms and to propose a new device, using vibrations generated in the drillstring itself. The various forms of drillstring vibrations are generally regarded as detrimental in the question. However, it is possible to use some of these vibrations forms in such a way as to enhance drilling performance. Initially, the influence of the torsional and axial vibrations in ROP is analyzed. Next, the resonance drilling, that is being developed by companies in this area, and some aspects and cares in the use of this new drilling technique are studied. At the end, a new drilling device, called resonance hammer drilling or self excited percussive rotary drilling, is developed. This device has as premise to use the axial vibration due to the cutting process, to generate a harmonic load at the bit and to excite a steel mass (hammer). A model with vibro-impact and dry friction is developed, representing the hammer and the resistance of the medium, respectively. It is presented a numeric study and an experimental validation of the percussive motion of the model, that represent the bit. The results show that the best way of the hammer to operate is impacting the bit head, in period-1 condition, ie, with one impact per cycle. Moreover, the experimental parameters are identified and since the numerical-experimental results are similar, the model used is validated.

The aim of this thesis is design crankshaft for four-cylinder diesel engine with cylinder deactivation. Further, to perform stress analysis of designed crankshaft with considering torsional vibration.

The aim of this diploma thesis is design of configuration and balancing of crankshaft which is determined for four-cylinder gasoline engine. The thesis investigates kinematics, dynamics and possible ways of balancing the inertial forces and moments of the rotating and sliding parts of the central crank mechanism. Subsequently, the 3D CAD model is designed according to the presented drawing. It is transformed into a spare torsion system, from which the calculations of its own and forced torsional vibrations are based. The proposed 3D CAD model is then spatially transmitted in the FEA software Ansys Workbench and modified (boundary conditions, etc.) in the FEA software Ansys Mechanical APDL so that it can be calculated according to the selected LSA method. From the selected results of the LSA method, the crankshaft safety factor against fatigue damage is calculated.

This thesis deals with comparison of straight four-cylinder petrol engine with a displacement of 1,5 litres and its three-cylinder alternative, which is based on a four-cylinder. The thesis starts with a research, where are examples of some currently manufactured engines. The research is followed by design of both engines, where the design of the crank mechanisms is made more in detail. After that, both crank mechanisms are subjected to dynamic analysis using FEM and MBS methods. The thesis ends with comparison of both engines in terms of crankshaft load, mass and dimensions.

The thesis deals with the structural design of a steel connecting rod for the aircraft engine Walter Mikron III, which is currently still manufactured and developed by company PARMA-TECHNIK, s.r.o. The proposed connecting rod would replace the current duralumin connecting rod. The work also contains a strength analysis of the designed component, in which it was aimed to verify the stress on the connecting rod, based on which the fatigue safety factor was performed. This is crucial for dynamically stressed parts of internal combustion engines. Furthermore, was investigated the effect of the change of the connecting rod on the torsional vibration of the crank mechanism. For this purpose, was built a discrete torsion model. The output of the whole work is the drawing documentation of the new connecting rod, meeting the requirements for application in an aircraft engine.

This diploma thesis contains a summary of the general information about the torsion vibration of the crankshaft. The main task is to prepare a flexible model of the crankshaft in the FEM program ANSYS and the subsequent export into the MBS ADAMS / Engine. According to parameters the model of four-cylinder line tractor engine with flexible crankshaft is built. Crank mechanism is analyzed to determine the natural frequencies and natural modes. Finally the results are evaluated and compared with analytical calculations.