20 research outputs found
Semi-Active Magneto-Rheological Damper and Applications in Tension Leg Platform / Semi-Submersible
A reliable and cost-effective way to protect the hydrocarbon production modules in harsher environments has been crucial to the success of offshore oil and gas projects. Nevertheless, the excessive tension variations in the top-tensioned risers (TTRs) can lead to catastrophic structural integrity issues. Magneto-rheological (MR) damper is a controllable device which can reduce the tension variations. However, the integration and behaviors of MR damper are remained as significant challenge for floating platforms. The main purpose of this research is to develop numerical analysis tool to analyze the specific characteristics of MR damper in offshore structural dynamics and interactively changing the structural behaviors correspond to various external loadings.
The research methodologies were initiated by modeling the hydro-pneumatic tensioner (HPT) of TTR in component-level, which included hydro-pneumatic components and viscous fluid frictional effect. The HPT model was numerically incorporated with MR damper. This numerical tool combined with CHARM3D, a fully-coupled time-domain dynamic analysis program for floating bodies, mooring lines, and risers. The responses of combined numerical model were simulated by coupling with tension leg platform (TLP) and dry-tree semi-submersibles (DTS), respectively, under 100-year extreme condition and 1000-year survival condition of central Gulf of Mexico (GOM). The MR damper was controlled by using semi-active controllers that were developed in fuzzy-logic and skyhook schemes. Mathieu’s stability analysis was utilized to predict TTR’s parametric stability.
The results manifested that total required stroke length in DTS can be reduced by as much as 0.963 meter in the studied case after MR damper was incorporated with semi-active fuzzy logic controller. By providing damped and deformed contact surface, MR damper was able to redistribute the excessive tension in the tensioner cylinders during extreme bottom-out motion. Moreover, the dynamic tension variations of TTR can be suppressed by 94 percent in the case of TLP. In conclusion, these results are beneficial to assure service life span of TTR’s tensioner and moderate the relevant operational expenditure (OPEX). In addition, the reductions of the total required stroke length and tension variations in DTS have enabled the platform designer to be more flexible in the sizing of the DTS and TTR tensioners
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A new operability and predictability enhanced riser control system for deepwater marine operation: an integrated riser hybrid tensioning system
This dissertation presents a novel riser hybrid tensioning system by integrating an electrically powered riser tensioning system into existing hydro-pneumatic tensioners. Compared to current passive hydro-pneumatic tensioners, this new riser hybrid tensioning system provides the capability of dynamically controlling the tension in the riser string. This feature opens a wide horizon of different active riser control strategies to achieve the systematic riser control solution. The objective of this study is to increase the predictability and safety of the whole riser system, and to extend the operability of the riser tensioning system into other operations. An overall structure framework of this novel hybrid riser tensioning system is proposed, comprising a direct driven electrical tensioners, hydro-pneumatic tensioners, a super-capacitor based energy storage system, power dissipaters, an overall tension controller and a power management controller. Hardware configurations are suggested. A riser data logging system is introduced, providing more comprehensive riser status data. A power management control strategy and overall coordination architecture to integrate the whole system are proposed. As the main functionality of the riser tensioning system, a new active heave compensation control strategy is analyzed in detail, by using this new riser hybrid tensioning system. A LQG controller and a H [subscript infinity symbol] controller are designed. The position chasing technique produces predictive and accurate tension commands for the electrical tensioners. Both Matlab simulation and hardware implementation confirm the feasibility of this concept, and further verifies that a more accurate control performance could be achieved by the electrical tensioners 180° compensating the tension fluctuation caused by the hydro-pneumatic tensioners. A novel testability and predictability enhanced anti-recoil control algorithm is implemented in the electrical tensioners. A position control strategy is proposed with the objective of moving the riser body to a desired elevation height in a predictive manner. A system model and a Kalman estimator are built, and a LQG controller is designed. The simulation demonstrates that the riser lifting height can adjust to any reasonable value for different test environment. This anti-recoil control concept reduces the risk of catastrophic damage, and allows us to perform maintenance tests much more frequently to bring back operator’s confidence. During harsh sea state, the VIV can be suppressed by using the dynamic control of the hybrid tensioning system, at frequencies and magnitudes made available by the electrical tensioning system. The objective is to achieve the VIV suppression by avoiding the excitation of the oscillation locking into the resonance conditions, and by reducing oscillation energy to be built in riser. A modal analysis of a tensioned Euler-Bernoulli beam is studied. Two control methods are proposed. Simulations results demonstrate that the oscillation is effectively reduced at the dominant lock-in frequency. Finally, this riser hybrid tensioning system opens the possibility to extend the tensioning system operability into other drilling operations. A motion stabilizer supporting the heave compensation of the drill pipes and the DST tools can be eliminated by connecting the drill pipes onto the telescopic joint. Another application would be that the electrical tensioners can run under position control mode after the riser is recoiled and soft hang-off on tensioners. The riser string position with respect to the seabed can still be controlled, during the vessel moving among different well heads.Electrical and Computer Engineerin
Impact of Ear Occlusion on In-Ear Sounds Generated by Intra-oral Behaviors
We conducted a case study with one volunteer and a recording setup to detect sounds induced by the actions: jaw clenching, tooth grinding, reading, eating, and drinking. The setup consisted of two in-ear microphones, where the left ear was semi-occluded with a commercially available earpiece and the right ear was occluded with a mouldable silicon ear piece. Investigations in the time and frequency domains demonstrated that for behaviors such as eating, tooth grinding, and reading, sounds could be recorded with both sensors. For jaw clenching, however, occluding the ear with a mouldable piece was necessary to enable its detection. This can be attributed to the fact that the mouldable ear piece sealed the ear canal and isolated it from the environment, resulting in a detectable change in pressure. In conclusion, our work suggests that detecting behaviors such as eating, grinding, reading with a semi-occluded ear is possible, whereas, behaviors such as clenching require the complete occlusion of the ear if the activity should be easily detectable. Nevertheless, the latter approach may limit real-world applicability because it hinders the hearing capabilities.</p
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Remote-controlled ambidextrous robot hand actuated by pneumatic muscles: from feasibility study to design and control algorithms
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonThis thesis relates to the development of the Ambidextrous Robot Hand engineered in Brunel University.
Assigned to a robotic hand, the ambidextrous feature means that two different behaviours are accessible from a single robot hand, because of its fingers architecture which permits them to bend in both ways. On one hand, the robotic device can therefore behave as a right hand whereas, on another hand, it can behave as a left hand. The main contribution of this project is its ambidextrous feature, totally unique in robotics area. Moreover, the Ambidextrous Robot Hand is actuated by pneumatic artificial muscles (PAMs), which are not commonly used to drive robot hands. The type of the actuators consequently adds more originality to the project. The primary challenge is to reach an ambidextrous behaviour using PAMs designed to actuate non-ambidextrous robot hands. Thus, a feasibility study is carried out for this purpose. Investigating a number of mechanical possibilities, an ambidextrous design is reached with features almost identical for its right and left sides. A testbench is thereafter designed to investigate this possibility even further to design ambidextrous fingers using 3D printing and an asymmetrical tendons routing engineered to reduce the number of actuators. The Ambidextrous Robot Hand is connected to a remote control interface accessible from its website, which provides video streaming as feedback, to be eventually used as an online rehabilitation device. The secondary main challenge is to implement control algorithms on a robot hand with a range twice larger than others, with an asymmetrical tendons routing and actuated by nonlinear actuators. A number of control algorithms are therefore investigated to interact with the angular displacement of the fingers and the grasping abilities of the hand. Several solutions are found out, notably the implementations of a phasing plane switch control and a sliding-mode control, both specific to the architecture of the Ambidextrous Robot Hand. The implementation of these two algorithms on a robotic hand actuated by PAMs is almost as innovative as the ambidextrous design of the mechanical structure itself
Condition monitoring of belt based motion transmission systems
A key asset of Royal Mail Group consists of a nationwide network of sorting offices
that forms a constituent component of the means through which the organisation
provides an efficient nationwide postal service within the United Kingdom. It may be
argued that the efficiency currently possessed by modem sorting offices is due to the
utilisation of machines that automate the process of sorting items of mail. The modem
letter-sorting machine possessed by Royal Mail can sort up to 30,000 letters per hour;
such machines serve as an example of an achievement of the application of
Mechatronics. The maintenance of letter sorting machines constitutes a large overhead for the
organisation. In the face of competition from pervasive electronic media within the
personal communications market and the prospect of deregulation, Royal Mail seeks
to streamline its operation in part by the reduction of the overheads incurred through
maintenance of letter sorting machinery. The adoption of condition based
maintenance techniques and predictive maintenance, for letter sorting machine
components such as belts and bearings, forms part of the strategy through which
Royal Mail seeks to reduce this overhead. Utilisation of flat belts and timing belts for
the implementation of key functions in letter sorting machinery, such as the transportation of items of mail within the mail sorting process, results in the use of
many such components within letter sorting machinery. A direct link exists between
the maintenance of peak performance of a sorting machine and the maintenance of belt drives; as such the maintenance of belt drives forms a substantial component of
the maintenance overhead.
The focus of this thesis consists of the condition monitoring of belt based motion
transmission systems and in particular, flat belts. The research that forms the basis of
this thesis consists of three elements. Firstly, consideration of current knowledge of
belt based power transmission such as knowledge of the mechanics of the belt based
power transmission process within the context of condition monitoring... [cont'd
Robotics 2010
Without a doubt, robotics has made an incredible progress over the last decades. The vision of developing, designing and creating technical systems that help humans to achieve hard and complex tasks, has intelligently led to an incredible variety of solutions. There are barely technical fields that could exhibit more interdisciplinary interconnections like robotics. This fact is generated by highly complex challenges imposed by robotic systems, especially the requirement on intelligent and autonomous operation. This book tries to give an insight into the evolutionary process that takes place in robotics. It provides articles covering a wide range of this exciting area. The progress of technical challenges and concepts may illuminate the relationship between developments that seem to be completely different at first sight. The robotics remains an exciting scientific and engineering field. The community looks optimistically ahead and also looks forward for the future challenges and new development
Development and optimization of a low-cost myoelectric upper limb prosthesis
Tese de Mestrado Integrado, Engenharia Biomédica e BiofÃsica (Engenharia ClÃnica e Instrumentação Médica), 2022, Universidade de Lisboa, Faculdade de CiênciasIn recent years, the increase in the number of accidents, chronic diseases, such as diabetes, and
the impoverishment of certain developing countries have contributed to a significant increase in
prostheses users. The loss of a particular limb entails numerous changes in the daily life of each user,
which are amplified when the user loses their hand. Therefore, replacing the hand is an urgent necessity.
Developing upper limb prostheses will allow the re-establishment of the physical and motor functions
of the upper limb as well as reduction of the rates of depression. Therefore, the prosthetic industry has
been reinventing itself and evolving. It is already possible to control a prosthesis through the user's
myoelectric signals, control known as pattern recognition control. In addition, additive manufacturing
technologies such as 3D printing have gained strength in prosthetics. The use of this type of technology
allows the product to reach the user much faster and reduces the weight of the devices, making them
lighter. Despite these advances, the rejection rate of this type of device is still high since most prostheses
available on the market are slow, expensive and heavy. Because of that, academia and institutions have
been investigating ways to overcome these limitations. Nevertheless, the dependence on the number of
acquisition channels is still limiting since most users do not have a large available forearm surface area
to acquire the user’s myoelectric signals.
This work intends to solve some of these problems and answer the questions imposed by the
industry and researchers. The main objective is to test if developing a subject independent, fast and
simple microcontroller is possible. Subsequently, we recorded data from forty volunteers through the
BIOPAC acquisition system. After that, the signals were filtered through two different processes. The
first was digital filtering and the application of wavelet threshold noise reduction. Later, the signal was
divided into smaller windows (100 and 250 milliseconds) and thirteen features were extracted in the
temporal domain. During all these steps, the MatLab® software was used. After extraction, three feature
selection methods were used to optimize the classification process, where machine learning algorithms
are implemented. The classification was divided into different parts. First, the classifier had to
distinguish whether the volunteer was making some movement or was at rest. In the case of detected
movement, the classifier would have to, on a second level, try to understand if they were moving only
one finger or performing a movement that involved the flexion of more than one finger (grip). If the
volunteer was performing a grip on the third level, the classifier would have to identify whether the
volunteer was performing a spherical or triad grip. Finally, to understand the influence of the database
on the classification, two methods were used: cross-validation and split validation.
After analysing the results, the e-NABLE Unlimbited arm was printed on The Original Prusa i3
MK3, where polylactic acid (PLA) was used.
This dissertation showed that the results obtained in the 250-millisecond window were better than
the obtained ones in a 100-millisecond window. In general, the best classifier was the K-Nearest
Neighbours (KNN) with k=2, except for the first level that was LDA. The best results were obtained for
the first classification level, with an accuracy greater than 90%. Although the results obtained for the
second and third levels were close to 80%, it was concluded that it was impossible to develop a
microcontroller dependent only on one acquisition channel. These results agree with the anatomical
characteristics since they are originated from the same muscle group. The cross-validation results were
lower than those obtained in the training-test methodology, which allowed us to conclude that the inter variability that exists between the subjects significantly affects the classification performance.
Furthermore, both the dominant and non-dominant arms were used in this work, which also increased
the discrepancy between signals. Indeed, the results showed that it is impossible to develop a
microcontroller adaptable to all users. Therefore, in the future, the best path will be to opt for the
customization of the prototype. In order to test the implementation of a microcontroller in the printed model, it was necessary to design a support structure in Solidworks that would support the motors used
to flex the fingers and Arduino to control the motors. Consequently, the e-NABLE model was re adapted, making it possible to develop a clinical training prototype. Even though it is a training
prototype, it is lighter than those on the market and cheaper.
The objectives of this work have been fulfilled and many answers have been given. However,
there is always space for improvement. Although, this dissertation has some limitations, it certainly
contributed to clarify many of the doubts that still exist in the scientific community. Hopefully, it will
help to further develop the prosthetic industry.Nos últimos anos, o aumento do número de acidentes por doenças crónicas, como, por exemplo,
a diabetes, e o empobrecimento de determinados paÃses em desenvolvimento têm contribuÃdo para um
aumento significativo no número de utilizadores de próteses. A perda de um determinado membro
acarreta inúmeras mudanças no dia-a-dia de cada utilizador. Estas são amplificadas quando a perda é
referente à mão ou parte do antebraço. A mão é uma ferramenta essencial no dia-a-dia de cada ser
humano, uma vez que é através dela que são realizadas as atividades básicas, como, por exemplo, tomar
banho, lavar os dentes, comer, preparar refeições, etc. A substituição desta ferramenta é, portanto, uma
necessidade, não só porque permitirá restabelecer as funções fÃsicas e motoras do membro superior,
como, também, reduzirá o nÃvel de dependência destes utilizadores de outrem e, consequentemente, das
taxas de depressão. Para colmatar as necessidades dos utilizadores, a indústria prostética tem-se
reinventado e evoluÃdo, desenvolvendo próteses para o membro superior cada vez mais sofisticadas.
Com efeito, já é possÃvel controlar uma prótese através da leitura e análise dos sinais mioelétricos do
próprio utilizador, o que é denominado por muitos investigadores de controlo por reconhecimento de
padrões. Este tipo de controlo é personalizável e permite adaptar a prótese a cada utilizador. Para além
do uso de sinais elétricos provenientes do musculo do utilizador, a impressão 3D, uma técnica de
manufatura aditiva, têm ganho força no campo da prostética. Por conseguinte, nos últimos anos os
investigadores têm impresso inúmeros modelos com diferentes materiais que vão desde o uso de
termoplásticos, ao uso de materiais flexÃveis. A utilização deste tipo de tecnologia permite, para além
de uma rápida entrega do produto ao utilizador, uma diminuição no tempo de construção de uma prótese
tornando-a mais leve e barata. Além do mais, a impressão 3D permite criar protótipos mais sustentáveis,
uma vez que existe uma redução na quantidade de material desperdiçado. Embora já existam inúmeras
soluções, a taxa de rejeição deste tipo de dispositivos é ainda bastante elevada, uma vez que a maioria
das próteses disponÃveis no mercado, nomeadamente as mioelétricas, são lentas, caras e pesadas. Ainda
que existam alguns estudos que se debrucem neste tipo de tecnologias, bem como na sua evolução
cientÃfica, o número de elétrodos utilizados é ainda significativo. Desta forma, e, tendo em conta que a
maioria dos utilizadores não possuà uma área de superfÃcie do antebraço suficiente para ser feita a
aquisição dos sinais mioelétricos, o trabalho feito pela academia não se revelou tão contributivo para a
indústria prostética como este prometia inicialmente.
Este trabalho pretende resolver alguns desses problemas e responder às questões mais impostas
pela indústria e investigadores, para que, no futuro, o número de utilizadores possa aumentar, assim
como o seu Ãndice de satisfação relativamente ao produto. Para tal, recolheram-se os sinais mioelétricos
de quarenta voluntários, através do sistema de aquisição BIOPAC. Após a recolha, filtraram-se os sinais
de seis voluntários através de dois processos diferentes. No primeiro, utilizaram-se filtros digitais e no
segundo aplicou-se a transformada de onda para a redução do ruÃdo. De seguida, o sinal foi segmentado
em janelas mais pequenas de 100 e 250 milissegundos e extraÃram-se treze features no domÃnio temporal.
Para que o processo de classificação fosse otimizado, foram aplicados três métodos de seleção de
features. A classificação foi dividida em três nÃveis diferentes nos quais dois algoritmos de
aprendizagem automática foram implementados, individualmente. No primeiro nÃvel, o objetivo foi a
distinção entre os momentos em que o voluntário fazia movimento ou que estava em repouso. Caso o
output do classificador fosse a classe movimento, este teria de, num segundo nÃvel, tentar perceber se o
voluntário estaria a mexer apenas um dedo ou a realizar um movimento que envolvesse a flexão de mais
de que um dedo (preensão). No caso de uma preensão, passava-se ao terceiro nÃvel onde o classificador
teria de identificar se o voluntário estaria a realizar a preensão esférica ou em trÃade. Para todos os nÃveis
de classificação, obtiveram-se resultados para o método de validação cruzada e o método de teste e
treino, sendo que neste, 70% dos dados foram utilizados como conjunto de treino e 30% como teste.
Efetuada a análise dos resultados, escolheu-se um dos modelos da comunidade e-NABLE. O modelo foi
impresso na impressora The Original Prusa i3 MK3S e o material escolhido foi o ácido poliláctico
(PLA). Para que fosse possÃvel testar a implementação de um microcontrolador num modelo que
originalmente depende da flexão do cotovelo realizada pelo utilizador, foi necessário desenhar uma
estrutura de suporte que suportasse, não só os motores utilizados para flexionar os dedos, como, também,
o ArduÃno. O suporte desenhado foi impresso com o mesmo material e com a mesma impressora.
Os resultados obtidos mostraram que a janela de 250 milissegundo foi a melhor e que, regra geral,
o melhor classificador é o K-Nearest Neighbors (KNN) com k=2, com exceção do primeiro nÃvel, em
que o melhor classificador foi o Linear Discriminant Analysis (LDA). Os melhores resultados
obtiveram-se no primeiro nÃvel de classificação onde a accuracy foi superior a 90%. Embora os
resultados obtidos para o segundo e terceiro nÃvel tenham sido próximos de 80%, concluiu-se que não
era possÃvel desenvolver um microcontrolador dependente apenas de um canal de aquisição. Tal era
expectável, uma vez que os movimentos estudados são originados pelo mesmo grupo muscular e a
intervariabilidade dos sujeitos um fator significativo. Os resultados da validação cruzada foram menos
precisos do que os obtidos para a metodologia de treino-teste, o que permitiu concluir que a
intervariabilidade existente entre os voluntários afeta significativamente o processo de classificação.
Para além disso, os voluntários utilizaram o braço dominante e o braço não dominante, o que acabou
por aumentar a discrepância entre os sinais recolhidos. Com efeito, os resultados mostraram que não é
possÃvel desenvolver um microcontrolador que seja adaptável a todos os utilizadores e, portanto, no
futuro, o melhor caminho será optar pela personalização do protótipo. Tendo o conhecimento prévio
desta evidência, o protótipo desenvolvido neste trabalho apenas servirá como protótipo de treino para o
utilizador. Ainda assim, este é bem mais leve que os existentes no mercado e muito mais barato. Nele é
ainda possÃvel testar e controlar alguns dos componentes que no futuro irão fazer parte da prótese
completa, prevenindo acidentes.
Não obstante o cumprimento dos objetivos deste trabalho e das muitas respostas que por ele foram
dadas, existe sempre espaço para melhorias. Dado à limitação de tempo, não foi possÃvel testar o
microcontrolador em tempo-real nem efetuar testes mecânicos de flexibilidade e resistência dos
materiais da prótese. Deste modo, seria interessante no futuro fazer testes de performance em tempo real
e submeter a prótese a condições extremas, para que a tensão elástica e a tensão dos pins sejam testadas.
Para além disso, testar os mecanismos de segurança da prótese quando o utilizador tem de fazer muita
força é fundamental. O teste destes parâmetros evitará a ocorrência de falhas que poderão magoar o
utilizador, bem como estragar os objetos com os quais a prótese poderá interagir. Por fim, é necessário
melhorar o aspeto cosmético das próteses. Para que isso aconteça, poderão ser utilizados polÃmeros com
uma coloração próxima do tom da pele do utilizador. Uma outra forma de melhorar este aspeto, seria
fazer o scanning do braço saudável do utilizador e usar materiais flexÃveis para as articulações e dedos
que, juntamente com uma palma de termoplásticos resistentes e um microcontrolador, permitissem um
movimento bastante natural próximo do biológico.
Em suma, apesar de algumas limitações, este trabalho contribuiu para o esclarecimento de muitas
das dúvidas que ainda existiam na comunidade cientÃfica e ajudará a desenvolver a indústria prostética
Time Localization of Abrupt Changes in Cutting Process using Hilbert Huang Transform
Cutting process is extremely dynamical process influenced by different phenomena such as chip formation, dynamical responses and condition of machining system elements. Different phenomena in cutting zone have signatures in different frequency bands in signal acquired during process monitoring. The time localization of signal’s frequency content is very important.
An emerging technique for simultaneous analysis of the signal in time and frequency domain that can be used for time localization of frequency is Hilbert Huang Transform (HHT). It is based on empirical mode decomposition (EMD) of the signal into intrinsic mode functions (IMFs) as simple oscillatory modes. IMFs obtained using EMD can be processed using Hilbert Transform and instantaneous frequency of the signal can be computed.
This paper gives a methodology for time localization of cutting process stop during intermittent turning. Cutting process stop leads to abrupt changes in acquired signal correlated to certain frequency band. The frequency band related to abrupt changes is localized in time using HHT. The potentials and limitations of HHT application in machining process monitoring are shown
Dynamic safety analysis of managed pressure drilling operations
The exploration and development of oil and gas reserves located in harsh offshore environments are characterized with high risk. Some of these reserves would be uneconomical if produced using conventional drilling technology due to increased drilling problems and prolonged non-productive time. Seeking new ways to reduce drilling cost and minimize risks has led to the development of Managed Pressure Drilling techniques. Managed pressure drilling methods address the drawbacks of conventional overbalanced and underbalanced drilling techniques. As managed pressure drilling techniques are evolving, there are many unanswered questions related to safety and operating pressure regimes. Quantitative risk assessment techniques are often used to answer these questions. Quantitative risk assessment is conducted for the various stages of drilling operations – drilling ahead, tripping operation, casing and cementing. A diagnostic model for analyzing the rotating control device, the main component of managed pressure drilling techniques, is also studied. The logic concept of Noisy-OR is explored to capture the unique relationship between casing and cementing operations in leading to well integrity failure as well as its usage to model the critical components of constant bottom-hole pressure drilling technique of managed pressure drilling during tripping operation. Relevant safety functions and inherent safety principles are utilized to improve well integrity operations. Loss function modelling approach to enable dynamic consequence analysis is adopted to study blowout risk for real-time decision making. The aggregation of the blowout loss categories, comprising: production, asset, human health, environmental response and reputation losses leads to risk estimation using dynamically determined probability of occurrence. Lastly, various sub-models developed for the stages/sub-operations of drilling operations and the consequence modelling approach are integrated for a holistic risk analysis of drilling operations