264 research outputs found

    Piezoelectric digital vibration absorbers for vibration mitigation of bladed structures

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    Climate change and resource scarcity pose increasingly difficult challenges for the aviation industry requiring a reduction in fossil fuel consumption. To address these problems and increase the efficiency of aircraft engines, some of their parts are now manufactured in one piece. For example, a rotor of the compressor stage of an airplane engine consist of a drum with a large number of blades and is called BluM. These structures are lightweight and feature low structural damping and high modal density. Their particular dynamic characteristics require sophisticated solutions for vibration mitigation of these structures. This is precisely the starting point of this thesis. Based on a digital realization of piezoelectric shunt circuits, we provide a damping concept that is able to tackle the complex dynamics of bladed structures and to mitigate their vibrations. To this end, multiple digital vibration absorbers (DVAs) are used simultaneously. Two new strategies to tune these DVAs are proposed in the thesis, namely the isolated mode and mean shunt strategies. These strategies not only take advantage of the fact that multiple absorbers act simultaneously on the structure, but they also address the problem of closely-spaced modes. In order to target multiple families of BluM modes, these strategies are incorporated in a multi-stage shunt circuit. The concepts are demonstrated experimentally using two bladed structures with increasing complexity, namely a bladed rail and a BluM. Both methods exhibit excellent damping performances on multiple groups of modes. In addition, they prove robust to changes in the host structure which could, e.g., be due to mistuning. Thanks to their digital realization, DVAs are also easily adjustable. Finally, this thesis reveals the parallel that exists between resonant piezoelectric shunts with a negative capacitance and active positive position feedback (PPF) controllers. Based on this comparison, a new H∞ norm-based tuning rule is found for a PPF controller. It is demonstrated using both numerical and experimental cantilever beams. To this end, a method that accounts for the influence of modes higher in frequency than the targeted one is developed.Le changement climatique et la raréfaction des ressources posent des défis de plus en plus complexes à relever pour l'industrie aéronautique. Un de ces défis est la réduction de la consommation en énergies fossiles. Pour accroître l'efficacité des moteurs d'avion, certains de leurs composants sont désormais fabriqués en une seule pièce. Dans le cas des compresseurs, ces pièces monoblocs sont appelées BluMs et sont constituées d’un tambour avec un grand nombre d'aubes. Ce type de structures bénéficie d'un allègement significatif, ce qui conduit à un faible amortissement structurel. De plus, ces pièces monoblocs présentent une densité modale élevée en raison du nombre important de diamètres nodaux. Ces caractéristiques dynamiques particulières nécessitent des solutions d'amortissement sophistiquées. Cette thèse de doctorat aborde cette problématique. En exploitant le concept d'absorbeur de vibration digital (DVA), nous proposons une nouvelle technique d'amortissement des structures aubagées. Deux nouvelles stratégies d'accordage de ces DVA sont développées dans cette thèse, à savoir la stratégie du mode isolé et la stratégie du shunt moyen. Ces méthodes tirent non seulement parti du fait que plusieurs absorbeurs agissent simultanément sur la structure, mais elles s'attaquent aussi au problème des modes proches en fréquence. Afin de cibler plusieurs familles de modes, ces stratégies ont été incorporées dans un circuit de shunt à plusieurs étages. Les concepts sont testés expérimentalement sur deux structures aubagées de complexité croissante, à savoir un rail à aubes et un BluM comme application finale. Ces méthodes permettent d'obtenir d'excellentes performances d'amortissement sur plusieurs groupes de modes. Elles s'avèrent également robustes face à des variations de la structure, dues par exemple à un désaccordage de celle-ci. Il est à noter que, grâce à leur caractère digital, ces méthodes sont facilement adaptables. Finalement, nous révélons le parallèle qui existe entre les shunts piézoélectriques résonants avec une capacitance négative et le contrôleur actif à rétroaction positive de position (PPF). Sur base de cette comparaison, de nouvelles règles d'accordage basées sur la norme H∞ sont développées pour le contrôleur PPF. Leur efficacité est démontrée à la fois numériquement et expérimentalement sur une poutre encastrée-libre. Dans ce but, une méthode prenant en compte l'influence des modes dont la fréquence est supérieure au mode ciblé a été mise sur pied au moyen de facteurs de correction

    Applied Mathematics to Mechanisms and Machines

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    This book brings together all 16 articles published in the Special Issue "Applied Mathematics to Mechanisms and Machines" of the MDPI Mathematics journal, in the section “Engineering Mathematics”. The subject matter covered by these works is varied, but they all have mechanisms as the object of study and mathematics as the basis of the methodology used. In fact, the synthesis, design and optimization of mechanisms, robotics, automotives, maintenance 4.0, machine vibrations, control, biomechanics and medical devices are among the topics covered in this book. This volume may be of interest to all who work in the field of mechanism and machine science and we hope that it will contribute to the development of both mechanical engineering and applied mathematics

    Intelligent Road-Adaptive Semi-Active Suspension and Integrated Cruise Control †

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    The availability of road and vehicle data enables the control of road vehicles to adapt for different road irregularities. Vision-based or stored road data inform the vehicle regarding the road ahead and surface conditions. Due to these abilities, the vehicle can be controlled efficiently to deal with different road irregularities in order to improve driving comfort and stability performances. The present paper proposes an integration method for an intelligent, road-adaptive, semi-active suspension control and cruise control system. The road-adaptive, semi-active suspension controller is designed through the linear parameter-varying (LPV) method, and road adaptation is performed with a road adaptivity algorithm that considers road irregularities and vehicle velocity. The road adaptivity algorithm calculates a dedicated scheduling variable that modifies the operating mode of the LPV controller. This modification of operation mode provides a trade-off between driving comfort and vehicle stability performances. Regarding the cruise control, the velocity design of the vehicle is based on the ISO 2631-1 standard, the created database, and the look-ahead road information. For each road irregularity, the velocity of the vehicle is designed according to previous measurements and the table of ISO 2631-1 standard. The comfort level must be selected in order to calculate dedicated velocity for road irregularity. The designed velocity is tracked by the velocity-tracking controller evaluated with the LPV control framework. The designed controllers are integrated, and the operation of the integrated method is validated in a TruckSim simulation environment

    Modelagem e controle de um atuador eletromagnético linear tubular para aplicação em suspensão ativa

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    Este trabalho apresenta o desenvolvimento de procedimentos para modelagem dinâ- mica e controle de um atuador eletromagnético linear tubular para aplicação em sistemas de suspensão ativa. A suspensão ativa é um conceito de suspensão que utiliza um elemento ativo para inserir força no sistema e atenuar as vibrações indesejadas entre duas partes móveis. A modelagem dinâmica do atuador é desenvolvida, os parâmetros da má- quina necessários neste modelo são obtidos, e a descrição é feita no espaço de estados com realimentação linearizante. Um ambiente de cossimulação entre modelo de elementos finitos, parte mecânica e acionamento, é criado para auxiliar na validação do modelo dinâmico. Este modelo também é validado em malha aberta através de ensaios experimentais que permitem avaliar o comportamento dinâmico do atuador quando submetido a diferentes referências de tensão elétrica. Partindo deste modelo, o controle de posição do atuador é desenvolvido para seguimento ou rejeição de sinais periódicos considerando variações harmônicas e componente CC, operando com e sem carga. Para alcançar este objetivo uma estratégia multi-loop é desenvolvida com controladores Proporcional-Integral e Proporcional-Integral-Ressonante, baseada na estratégia de controle por orientação de campo. Os parâmetros de sintonia do controlador são projetados a partir da solução de um problema de otimização com restrições na forma de desigualdades matriciais lineares. Após isso, um aparato experimental que caracteriza uma plataforma de suspensão para representar vibrações e um sistema com massa-mola-amortecedor é modelado e caracterizado em função da sua resposta em frequência para representar perfis normatizados de rodovias e outros sinais periódicos. O atuador eletromagnético linear, inserido neste aparato, forma um sistema de suspensão ativa. O controle do atuador no sistema de suspensão é realizado baseado na estratégia skyhook, alocação de polos e minimização da norma H∞. Os resultados mostram que o atuador linear é capaz de atuar num sistema de suspensão ativa, garantindo seguimento da pista ou melhorando significativamente o conforto dos passageiros através da redução de aceleração na massa suspensa.This work presents the development of procedures for dynamic modeling and control of a linear tubular electromagnetic actuator for application in active suspension systems. Active suspension is a concept of suspension that uses an active element to insert force into the system and reduces undesirable vibrations between two moving parts. The dynamic modeling of the actuator is developed, the machine parameters necessary for this model are obtained, and the state-space description is made using feedback linearization. A co-simulation environment between the finite element model, mechanical part, and drive is created to improve the validation process of the dynamic model. This model is also validated in open-loop through experimental tests that allow the evaluation of the dynamic behavior of the actuator when subjected to different excitation voltages. Based on this model, the actuator position control is developed for tracking or rejecting periodic signals considering harmonic content and DC component, operating with load and no load. To achieve this goal, a multi-loop strategy is developed with Proportional-Integral and Proportional-Integral-Resonant controllers, based on the field-oriented control strategy. The controller tuning parameters are designed from the solution of an optimization problem with constraints in the form of linear matrix inequalities. After that, an experimental apparatus featuring a suspension platform to represent vibrations and a massspring-damper system is modeled and characterized in terms of its frequency response to represent normalized road profiles and other periodic signals. The linear electromagnetic actuator, placed into this apparatus, creates an active suspension system. The actuator control in the suspension system is performed based on the skyhook strategy, pole allocation, and minimization of the H∞ norm. The results show that the linear actuator can operate to ensure tracking of references, or significantly improve passenger comfort by isolating the sprung mass of vibrations

    Exploring the Boundaries of Patent Commercialization Models via Litigation

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    This thesis explores direct patent commercialization via patent assertion, particularly patent infringement litigation, a complex nonmarket activity whose successful undertaking requires knowledge, creativity, and financial resources, as well as a colorable infringement case. Despite these complexities, firms have increasingly employed patents as competitive tools via patent assertions, particularly in the United States. This thesis explores the business models that have been created to facilitate the direct monetization of patents. Since secrecy underpins the patent assertion strategies studied, the thesis is based on rich and enhanced secondary data. In particular, a data chaining technique has been developed to assemble relevant but disparate data into a larger coherent data set that is amenable to combination and pairing with other forms of relevant public data. This research has discovered that one particularly successful business model that employs a leveraging strategy, known as the non-practicing entity (“NPE”), has itself spawned at least two other business models, the highly capitalized “patent mass aggregator” and the “patent privateer.” The patent privateer, newly discovered in this research, is particularly interesting because it provides a way for firms to employ patents to attack competitors by forming specialized NPEs in a manner that essentially expands the boundaries of the firm. This research has also examined plaintiff firm management processes during litigations brought under leveraging and proprietary strategies, the two patent litigation strategies in which firms affirmatively initiate infringement litigations. In particular, this research investigates the commercial contexts that drive patent assertion strategies to explore the effective limits of the patent right in a litigation context. The investigation concludes that a variety of robust business models and management processes may be quite successful in extracting value from patents in the US

    Design, Modelling and Control of an Adaptive Vibration Isolator Featuring Magnetorheological Elastomer

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    Magnetorheological elastomers (MREs) are smart materials whose viscoelastic properties can be varied upon the application of an external magnetic field. They are solid analogue of well-known MR fluids (MRFs) in which magnetic particles are embedded in a non-magnetic elastomer matrix instead of carrier fluids. Compared with their fluid counterparts, MREs do not have problems associated with particles' sedimentation, stability and leakage often encountered in MRFs. Besides in contrast to MRF-based adaptive devices, MRE-based systems can provide field dependent variable stiffness and damping simultaneously due to viscoelastic properties of MREs. This unique behaviour of MREs enable them to be effectively utilized in the development of adaptive isolators or absorbers to supress vibrations in wide range of frequencies. The present research study aims to provide a comprehensive investigation of the material characterization and phenomenological modelling of MREs under varying dynamic loading conditions, design and development of a novel vibration and shock isolator featuring magnetorheological elastomers, design optimization of the proposed isolator to enhance its dynamic range and finally design and implementation of semi-active control strategies to mitigate vibration and shock under different external disturbances. MREs with a 25% volume fraction of soft magnetic particles (carbonyl iron) were used to investigate variation of storage and loss moduli of MRE under varied frequencies, strain amplitudes, and magnetic field densities. Considering operation of MREs in the linear range, field dependent linear viscoelastic models based on the Kelvin–Voigt, Maxwell, Standard Linear Solid, and Generalized Maxwell models, were formulated to predict the variation of storage and loss moduli under varying driving frequency and applied magnetic flux densities. The performance of these models to capture the response behaviour of MREs under different applied frequencies and magnetic field were subsequently compared. A semi-active MRE-based vibration isolator operating under shear mode with embedded electromagnet was then proposed. Analytical magneto-static model of the magnetic circuit of the proposed adaptive isolator was first formulated using Ampere’s law to estimate the induced magnetic flux density in the MRE region gaps versus applied current to the electromagnet. The validity of the analytical results was verified using the finite element magneto-static analysis. A multidisciplinary design optimization problem was subsequently formulated to optimize the isolator geometrical parameters as design variables to maximize its frequency bandwidth under weight, material magnetic saturation, and total volume constraints. A hybrid approach based on combination of Genetic Algorithm (GA) and gradient based Sequential Quadratic Programming (SQP) was used to accurately capture the global optimal solution for the optimization problem. Finally, closed-loop control strategies, based on on-off sky-hook and PID, were implemented and compared to assess the capability of the proposed adaptive isolator to mitigate vibration and shock under different disturbances

    On semi-active inerters for improving machining productivity

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    The inerter is a mechanical element, synthesised in 2002 as an analogue to the electrical capacitor. Originally used in Formula 1 racing as the `J-damper', its potential has since been explored in other vehicles, as well as for vibration control of civil structures. In very recent years, some study has been given to the design and control of semi-active inerters. Such devices would be capable of varying their inertance in response to a control signal. To date, no study has been made of the semi-active inerter in the context of machining chatter. This undesirable form of vibration, leading to poor surface finish on machined parts, is a major issue in machining. The growing requirements of high speed machining of lightweight, flexible parts mean that the need to develop new strategies to tackle chatter will only increase. This thesis seeks to fill this gap in the literature. As a feasibility study, two chatter suppression strategies are developed using a simplified single degree of freedom chatter model. Both strategies assume the existence of an ideal semi-active inerter placed between the vibrating element and ground, allowing the natural frequency to be adjusted on-line. The first of these strategies, discrete inertance variation, is analogous to an existing lobe seeking strategy conducted by changing the spindle speed. It is shown that, with relatively modest ranges of inertance, this is an achievable strategy for high speed machining. The second strategy relies on cyclically adjusting the natural frequency to disrupt self-excited vibration. It is found that the amplitude of this variation is the important characteristic, rather than the ratio of the frequency of inertance variation to the tooth passing frequency. In both cases, the need to be able to rapidly control inertance is noted. The design needs of a semi-active helical inerter are considered, with magnetorheological fluid providing the semi-active control. Three different layouts are studied using quasi-static models. The bypass valve type layout is selected as the most promising for future study. The design of the valve is considered and a new optimisation scheme is developed which better suits the need of the bypass valve than previous schemes. The inerter model is extended into a quasi-dynamic model, which allows the varying inertance to be considered. This model would be key for developing any practical control scheme. Prototype inerters were designed and tested. Initially an oil-based designed is built, followed by a design using magnetorheological fluid. The prototype was tested using a servo-hydraulic actuator, with the goal of validating the models developed in the previous chapter. Unfortunately, trapped air in both systems led to these results being inconclusive in both cases. The use of magnetorheological fluid for flow directional control in this way is unusual at this scale and this work is important for any future researchers who wish to work with the fluid in this way. With this in mind, the issues encountered with the experimental rig are further analysed. Improvements to the design and filling method are proposed. Some more substantial design changes are also presented. Finally, some focus is given to the practical issues of implementing semi-active inerters in machining. The need to miniaturise the design to fit into modern machine tools is highlighted. Two areas in which this would be less of an issue -- fixturing and robotic machining -- are discussed. Notably, key challenges for robotic machining include the number and placement of the inerters, and whether new strategies would be needed to tackle mode-coupling chatter

    Inverse Dynamics Problems

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    The inverse dynamics problem was developed in order to provide researchers with the state of the art in inverse problems for dynamic and vibrational systems. Contrasted with a forward problem, which solves for the system output in a straightforward manner, an inverse problem searches for the system input through a procedure contaminated with errors and uncertainties. An inverse problem, with a focus on structural dynamics, determines the changes made to the system and estimates the inputs, including forces and moments, to the system, utilizing measurements of structural vibration responses only. With its complex mathematical structure and need for more reliable input estimations, the inverse problem is still a fundamental subject of research among mathematicians and engineering scientists. This book contains 11 articles that touch upon various aspects of inverse dynamic problems

    Compendium in Vehicle Motion Engineering

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    This compendium is written for the course “MMF062 Vehicle Motion Engineering” at Chalmers University of Technology. The compendium covers more than included in that course; both in terms of subsystem designs and in terms of some teasers for more advanced studies of vehicle dynamics. Therefore, it is also useful for the more advanced courses, such as “TME102 Vehicle Modelling and Control”.The overall objective of the compendium is to educate engineers that understand and can contribute to development of good motion and energy functionality of vehicles. The compendium focuses on road vehicles, primarily passenger cars and commercial vehicles. Smaller road vehicles, such as bicycles and single-person cars, are only very briefly addressed. It can be mentioned that there exist a lot of ground-vehicle types not covered at all, such as: off-road/construction vehicles, tracked vehicles, horse wagons, hovercrafts, and railway vehicles.Functions are needed for requirement setting, design and verification. The overall order within the compendium is that models/methods/tools needed to understand each function are placed before the functions. Chapters 3-5 describes (complete vehicle) “functions”, organised after vehicle motion directions:\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 3:\ua0Longitudinal\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 4:\ua0Lateral\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 5:\ua0Vertical\ua0dynamicsChapter 1 introduces automotive industry and the overall way of working there and defines required pre-knowledge from “product-generic” engineering, e.g. modelling of dynamic systems.Chapter 2 also describes the subsystems relevant for vehicle dynamics:• Wheels and Tyre\ua0• Suspension\ua0• Propulsion\ua0• Braking System\ua0• Steering System\ua0• Environment Sensing SystemThe compendium is released in a new version each year, around October, which is the version your read now. A "latest draft" is more frequently updated and often includes some more, sometimes unfinished, material: https://chalmersuniversity.box.com/s/6igaen1ugcjzuhjziuon08axxiy817f
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