The increased depth of castellated beams presents stability problems, specifically during erection. During erection the castellated beam must support the weight of an erector and self-weight until the continuous bracing of the floor deck is in place. The stability of the unbraced member is based on its resistance to lateral-torsional buckling. The cross-sectional properties that are related to lateral-torsional buckling, such as out-of-plane bending, warping constant, and torsional constant were calculated using three different approaches to model the unique geometry of castellated beams. These properties were used in various lateral-torsional buckling solutions to determine which procedure should be used to check for this mode of failure. Two specimens were tested to evaluate the results of the analytical unbraced length determination process. The tests results were used to better model the contribution of the web-to-column flange double angle connection on the stability of the castellated beam. / Master of Science

This thesis introduces lamina emergent mechanisms (LEMs) and presents components that can be used as building blocks to create LEMs capable of more complex motion. As the name suggests, lamina emergent mechanisms are fabricated out of planar materials (the lamina) but their motion is out of that plane (emergent). Lamina emergent mechanisms can provide benefits that include reduced manufacturing costs and minimal volume when in the planar state. The compact initial state of LEMs is beneficial in reducing shipping costs, especially in volume critical applications. LEMs also exhibit the potential benefits of compliant mechanisms, namely increased precision, reduced weight, reduced wear, and part count reduction. The LEM components presented in this thesis include flexible segments, fundamental mechanisms, and a new complaint joint, the lamina emergent torsional (LET) Joint. The flexible segments are developed through changes in geometry, boundary/loading conditions, and material. The fundamental mechanisms presented have motion similar to planar change-point four-bar and six-bar mechanisms, and spherical change-point mechanisms. The LET Joint is presented as a compliant joint suited for applications where large angular rotation is desired, but high off-axis stiffness is not as critical. The joint is introduced and the equations necessary for determining the force-deflection characteristics and stress are presented. Since the LET Joint can be fabricated from a single planar layer, it is well suited for macro and micro applications. Illustrative examples of the LET Joint are provided with devices fabricated from materials as diverse as steel, polypropylene, and polycrystalline silicon.

Horisontella laster som uppstår från till exempel vindlast, snedställning och initialkrokighet kan ge upphov till vippning och måste därför hanteras. En vanlig metod som tillämpas för att hantera vippning är stagning, men för att kunna staga ett konstruktionselement är det viktigt att ha kännedom om hur elementet beter sig under vippning. Denna studie har behandlat stagningens betydelse för fackverk som utsatts för initialkrokighet. Med hjälp av ett FEM-program har krokiga modeller ritats upp och analyserats i syfte att ge en djupare förståelse för hur stagning av fackverk är betydande. För modellerna har flera olika typer av tvärsnittshöjder, upplagsförhållanden (fritt respektive kontinuerligt upplag) och randvillkor för diagonalerna prövats. Fackverk är ett konstruktionselement som i många avseenden verkar likt en balk, men hur det beter sig under vippning är ett hittills inte fullt utrett område. Vid en jämförelse mellan fackverksmodell och en anpassad balkmodell med samma förutsättningar påvisades att skillnaden mellan konstruktionselementen låg i underramens upplag. Studien har visat hur fackverkets överram kan stagas av ett takfackverk i horisontalplanet, men för att fackverket ska kunna uppnå global stabilitet är det kritiskt att underramen stagas via överramen från ovanliggande åsar. Detta realiseras först då diagonalerna kan tillgodogöra sig vridinspänningen från åsarna, vilket innebär att en fast inspänning mellan diagonaler och överram måste utformas på ett tekniskt korrekt sätt. Resultaten har påvisat att ett allmänt förhållande mellan stagkraft och axialkraft existerar, och att detta har kunnat jämföras mot rekommendationen från Eurokoderna EC3. Resultaten har också visat att en rekommendation för förhållande mellan lokala moment i knutpunkter och axialkraft kan ges, vilket är av betydelse vid knutpunktsutformning. / Horizontal loads caused by, for example, wind loads, initial sway imperfections and initial bow imperfections, can result in lateral torsional buckling and must therefore be managed. A common method used to handle lateral torsional buckling is lateral and torsional restraints, but in order to restrain a constructional element it’s important to have knowledge of how the element behaves during lateral torsional buckling. In this study the importance of the restrain for truss elements affected by initial bow imperfections has been considered. The truss element is a constructional element that in many ways acts like a beam, but how it behaves during lateral torsional buckling is a non-fully investigated area. With the help of a FEM-software initial bow imperfect models have therefore been drawn up and analysed to provide deeper understanding for how and when lateral and torsional restraints are of importance. The models have been trialled with different section heights, support conditions (simply and continuously supported) and boundary conditions for the diagonals. When comparing a truss model to a beam model with the same conditions, it was demonstrated how the difference between the elements were due to the support conditions of the lower chord. The study has demonstrated how the upper chord of the truss element can be restrained by a horizontal truss construction, but for the truss element to reach global stability it’s critical that the lower chord is restrained via the upper chord by overlying ridges. This cannot be realised until the diagonals can utilize the torsional connection from the ridges, which means that a fixed connection between diagonals and upper chord of truss element must be executed in a technically correct manner. The results have shown that a general relationship between restraint force and axial force exists, and that it can be compared with the recommendation from the Eurocode EC3. The results have also shown that a recommendation for the relationship between local moment appearing in the truss connections and axial force can be provided, which is helpful to the design process of the connections.

[pt] A vibração excessiva da coluna de perfuração leva à perda da eficácia do processo de perfuração de poços de petróleo e causa danos prematuros ao equipamento. Portanto, entender a dinâmica do sistema é essencial. O comportamento complexo das colunas de perfuração estimulou um grande número de publicações sobre a dinâmica de perfuração. A vibração torsional está presente na maioria dos processos de perfuração, eventualmente atingindo o fenômeno de stick-slip. Essa vibração torsional resulta da interação não linear entre brocas e rochas. Apesar da complexidade da interação broca-rocha, a relação entre torque e velocidade de broca é, frequentemente, tratada como uma força de atrito seco em um sistema delgado. Um grande número de modelos de atrito é usado para descrever a interação entre brocas e rochas, embora um modelo adequado seja necessário para uma interpretação precisa de sistemas com atrito. Esta contribuição utiliza dados experimentais de uma bancada de testes, capaz de reproduzir o comportamento torsional de um sistema real, equipada com dispositivos de freio simples para introduzir atrito ao sistema, perturbando o movimento de rotação. A bancada é matematicamente modelada como um pêndulo de torção atuado. Esta dissertação propõe um modelo de atrito baseado em dados experimentais e analisa vários fenômenos observados em relação ao atrito, incluindo a histerese. Os resultados experimentais são usados para identificação dos parâmetros do modelo proposto. Por fim, simulações numéricas e resultados experimentais são comparados para validação do modelo de atrito proposto. / [en] Excessive drill string vibration leads to loss of the drilling process effectiveness and premature damage to the equipment. Therefore, understanding the system dynamics is essential. The complex behavior of drill strings attracted considerable attention in specialized literature. Due to the drill string slenderness, torsional vibration is present in most drilling routines, eventually reaching the stick-slip phenomenon. This torsional vibration results from the nonlinear interaction between drill-bits and rocks. Despite the complexity of the bit-rock interaction, researchers often treat the relationship between torque and bit velocity as a dry friction force in a slender system. A large number of dry friction models is used to describe the interaction between drill bits and rocks although a proper model is required for a precise interpretation of systems with friction. This contribution utilizes data from a test rig that is capable of reproducing full-scale system torsional behavior with simple brake devices to introduce friction into the system, disturbing the rotating motion. This test rig is modeled as an actuated torsional pendulum for the numerical investigations of the experimental friction. This dissertation proposes a friction model based on experimental data and analyzes various frictional phenomena observed, including hysteresis. The experimental results are used to identify the proposed model parameters. Lastly, it compares numerical simulations with the experimental results and validates the proposed friction model.

<p dir="ltr">Post-tensioned concrete is a popular structural system in modern bridge design, allowing for longer bridge spans and the construction of curved, spliced, and segmental girders. When designed and constructed properly, post-tensioned concrete can offer improved durability over reinforced concrete as it is more resistant to cracking. However, corrosion of prestressing strands can compromise the integrity of post-tensioned construction. Grouting has been the primary method of providing corrosion protection to the prestressing strands. However, grouting of tendons presents numerous limitations and results in multiple problems in practice. As a result, there has been increased interest in the use of unbonded tendons. Corrosion protection can still be achieved in unbonded tendons through the use of flexible fillers such as grease and microcrystalline wax. Limited research has been conducted on unbonded tendons, and no known research exists regarding the behavior of unbonded tendons subject to torsion. The objective of this research was to investigate the torsional behavior and strength of unbonded post-tensioned bridge girders. The scope of work included testing six specimens to investigate the difference in behavior between bonded and unbonded tendons as well as the influence of internal versus external ducts. The influence of transverse reinforcement was also considered.</p>

The aim of this diploma thesis is the design of the configuration and the method of balancing the crank mechanism with the specified parameters. For a particular configuration, a crankshaft drawing is processed and a strength analysis, considering the crankshaft torsional vibrations is performed in Ansys FEM software. At the end of the thesis, an ideological design of the torsional vibration damper and its effect on the crankshaft stress in the Ansys FEM software is performed.

The diploma thesis focuses on the design of the crankshaft for a four-cylinder diesel engine for commercial vehicles, the main task of this work are the design configuration of the crankshaft balance inertia forces and torques at the crank mechanism, drawing documentation crankshaft design strength check considering torsional vibration.

The diploma thesis ‚Rubber Torsional Vibration Damper Of a Four-Cylinder Diesel Engine‘ covers all the development phases related to a design of a rubber damper for a specified engine. The individual phases of it are discussed in details throughout the thesis. At first, the construction plan of a crankshaft is given. The computational checks for torsional vibrations and forced torsional vibration are performed then. With regards to it there might be derived the basic parameters and dimensions of a rubber torsional vibration damper. The knowledge of them enables to prepare the constructional plan of a rubber torsional vibration damper. By using this damper construction plan the torsional displacements (deviations) and forced vibrations are calculated. Finally, a mechanical and thermal stress test of this damper is performed and a crankshaft production drawing is produced.

Varactors form an important part of many communication circuits. They are utilized in oscillators, tunable matching networks, tunable filters and phase-shifters. This thesis deals with the design, analysis, characterization and applications of a novel MEMS varactor. Lower actuation voltage and higher dynamic range are the two important issues widely addressed in the study of MEMS varactors. The pull-in instability, due to which only 33% of the gap between plates could be covered smoothly, greatly reduces useful dynamic range of MEMS varactors. We propose a torsional MEMS varactor that exploits “displacement amplification” whereby pull-in is overcome and wide dynamic range is achieved. The torsion beam in the device undergoes torsion as well as bending. Behavior of the device has been analyzed through torque and force balance. Based on the torque balance and the force balance expressions, theoretical limits of torsion angle and bending for stable operation have been derived. Torsional MEMS varactors and its variants are fabricated through a commercial fabrication process (polyMUMPS) and extensive characterization has been carried out. Capacitance-voltage characteristics show a maximum dynamic range of 1:16 with parasitic capacitance subtracted out from the capacitance values. A bidirectional torsional varactor, in which the top AC plate moves not only towards bottom plate but also away from bottom plate, is also tested. The bottom AC plate is isolated from low resistivity substrate with a thin nitride layer. This gives rise to large parasitic capacitances at higher frequencies. So to avoid this, a varactor with both AC plates suspended in air is designed and fabricated. A dynamic range of 1:8 including parasitic capacitances has been achieved. Self-actuation is studied on fabricated structures and a torsional varactor that overcomes self-actuation has been proposed. Hysteresis behavior of the torsional varactor is analyzed for different AC signals across the varactor plates. Effects of residual stress on C-V characteristics are studied and advantages and disadvantages of residual stress on device performance are discussed. The torsional varactors have been cycled between Cmax and Cmin for 36 hours continuously without any failure. High-frequency characteristics of torsional varactors are analyzed through measurements on one-port and two port configurations. Measurements are done on polyMUMPS devices to study the capacitance variation with voltage, quality factor (Q) and capacitance variation with frequency. Effects of substrate are de-embedded from the device and characteristics of device are studied. An analog phase shifter based on torsional varactor proposed and analyzed through HFSS simulations. Very high tuning range can be achieved with a LC-VCO based on torsional varactors. A LC VCO with the torsional varactor as a capacitor in LC tank is designed. The torsional varactor and IC are fabricated separately and are integrated through wire bonding. Bond-wires are used as inductors.

[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.