To see the other types of publications on this topic, follow the link: Chattels.
Dissertations / Theses on the topic 'Chattels'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Chattels.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Bools, Michael D. "The ocean bill of lading as a document of title to goods in Anglo-American law." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307475.
Full text
2
Douglas, Simon. "The protection of property in chattels through the law of torts." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543689.
Full text
3
Cintra, Adjair de Andrade. "Aplicabilidade do princípio da insignificância aos crimes que tutelam bens jurídicos difusos." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/2/2136/tde-13062012-165850/.
Full textAbstract:
O trabalho foi desenvolvido para analisar a aplicabilidade do princípio da insignificância aos crimes que tutelam bens jurídicos difusos. O conceito de bem jurídico é o único elemento prévio à legislação com capacidade de limitar materialmente o poder punitivo estatal, sendo inaceitável o seu abandono, relativização ou flexibilização. O bem jurídico difuso é tutelado tendo em vista a proteção e o pleno desenvolvimento do ser humano, e suas características favorecem a tipificação de crimes de perigo abstrato e de crimes cumulativos, sendo inaceitáveis crimes de mera desobediência. O princípio da insignificância é uma ferramenta interpretativa do tipo penal e deve ser dividido em insignificância absoluta, hipótese em que a conduta sequer afeta o bem jurídico abstratamente considerado, apresentando uma ofensividade reduzidíssima e carecendo de tipicidade material; e insignificância relativa, hipótese em que se exclui a culpabilidade do agente no caso de ser diminuta a lesão ao bem jurídico individualizado e reduzidíssima a reprovabilidade do agente, devendo o fato ser considerado axiologicamente irrelevante, não havendo necessidade ou merecimento de pena. As lesões ao bem jurídico difuso atingem apenas indiretamente o indivíduo, ainda que socialmente tomado, e quando o reflexo da lesão ao bem jurídico difuso atingir o indivíduo (de hoje ou do futuro) de forma reduzida, deve ser ela considerada insignificante, sendo a insignificância relativa o instrumento mais compatível com a análise das condutas que se subsumem a crimes de perigo abstrato e a crimes cumulativos.This work was developed to analyze the applicability of the insignificance principle to the crimes that protect the diffuse juridical chattels. The juridical chattel is the only element previews to the legislation capable of limiting the punishing power of the State, and it is unacceptable to abandon it, to relativize it or to loosen it. The diffuse juridical chattel is protected to preserve the human being and its full development, and its characteristics facilitate the creation of abstract danger crimes and cumulating crimes, but it is unacceptable crimes of mere disobedience. The insignificance principle is a interpretative tool for the criminal type and must be divided into absolute insignificance, which occurs when the action do not affect the juridical chattel abstractly considered, having a very reduced offensiveness, lacking of material typicality, and relative insignificance, which excludes the culpability when it entail a small damage to the juridical chattel individually taken, what makes this action axiologically irrelevant, and the punishment unnecessary and undeserved. The damages to the juridical chattel strike only indirectly the individual, even when socially taken, and when the reflex of the damage to the juridical chattel strikes the individual (of the present or of the future) in a reduced way, it must be considered insignificant, and the relative insignificance is the most compatible tool to analyze the insignificance of the action that may be considered an abstract danger crime or a cumulating crime.
4
Nascimento, Stefanie Giulyane Vilela do. "A gestão patrimonial de bens móveis de caráter permanente na UFPB e na UFRN." Universidade Federal da Paraíba, 2013. http://tede.biblioteca.ufpb.br:8080/handle/tede/5897.
Full textAbstract:
Made available in DSpace on 2015-05-14T12:20:05Z (GMT). No. of bitstreams: 1
ArquivoTotalStefanie.pdf: 2224943 bytes, checksum: d5c4b4a09f9af9e33cde8af708a5cb67 (MD5)
Previous issue date: 2013-11-13Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
This paper aims to analyze the process of patrimony management of permanent movables in two public universities: UFPB and UFRN. The specific objectives are to carry out a diagnosis about the patrimony management of permanent movables on UFPB and to investigate the possible improvements that could be achieved by using the SIPAC, from experience of UFRN. For that, it describes the current public management, rescuing ideas that guide the behavior of these institutions in the management of public resources and identify legal, doctrinal and regulatory requirements to patrimony management in public agencies and on the institutions studied. Advocates the importance of information technology in the provision of public services and addresses the use of information systems as an important tool to support the performance of various organizational activities. Provides information about the SIPAC and others SIG developed by UFRN, characterizing it as potentially effective tool in helping management activities of chattels. This research is qualitative and quantitative and utilizes as a method of data analysis The Content Analysis. The data were collected from interviews and questionnaires answered by officers of UFPB as well as from interviews with UFRN servers. As auxiliary work tool was used the application NVivo 10 from QSR International. It concludes that both the general goal and the specific objectives were achieved. It is possible to have a vision of how has been worked the process of patrimony management of movables permanent in UFPB just like it is possible the understanding of how the patrimony management of chattels has been worked in UFRN from the use of SIPAC. This allows the perception of what this tool, if successfully implemented, would offer to the services of patrimony management on UFPB. At the end of this paper have some proposals to improvement in the management activities of chattels on UFPB.
Esse trabalho tem por objetivo analisar o processo de gestão patrimonial de bens móveis de caráter permanente em duas universidades públicas, UFPB e UFRN. Entre os objetivos específicos estão a realização de um diagnóstico da gestão patrimonial de bens móveis permanentes na UFPB e a investigação das possíveis melhorias que poderiam ser alcançadas na gestão dos bens móveis dessa Instituição com a utilização do SIPAC, a partir da experiência da UFRN. Para isso, contextualiza a gestão pública atual, resgatando as ideias balizadoras do comportamento dessas instituições na gestão de recursos públicos e identificando as exigências normativas, legais e doutrinárias referentes à gestão patrimonial em órgãos e entidades públicas e nas instituições estudadas. Advoga a importância das tecnologias da informação na prestação de serviços públicos e aborda a utilização dos sistemas de informações como importante ferramenta de suporte no desempenho de diversas atividades organizacionais. Traz informações sobre o SIPAC e demais SIG desenvolvidos pela UFRN, caracterizando-o como ferramenta potencialmente eficaz no auxílio das atividades de gestão de bens móveis. Essa pesquisa tem caráter qualitativo e quantitativo e utiliza como método de análise dos dados a Análise de Conteúdo. Os dados foram coletados a partir de entrevistas e questionários respondidos por funcionários dos setores de patrimônio da UFPB, bem como a partir de entrevistas com servidores da UFRN. Como ferramenta auxiliar de trabalho foi utilizado o aplicativo NVivo 10 da QSR International. Conclui-se que tanto o objetivo geral, quanto os objetivos específicos foram alcançados. É possível ter uma visão de como tem funcionado a gestão patrimonial de bens móveis na UFPB e quais são suas maiores deficiências. Também é possível perceber como tem funcionado a gestão de bens móveis na UFRN a partir da utilização do SIPAC, o que permite a percepção do que essa ferramenta, se implementada com sucesso, ofereceria de ganho potencial para os serviços de Patrimônio da UFPB. No final do trabalho, algumas propostas são discutidas com fins de alcançar uma melhoria considerável na gestão dos bens móveis permanentes da UFPB.
5
Orthmann, Claudia. "Strukturen der Chat-Kommunikation konversationsanalytische Untersuchung eines Kinder- und Jugendchats /." [S.l. : s.n.], 2004. http://www.diss.fu-berlin.de/2004/78/index.html.
Full text
6
Breay, Claire. "The cartulary of Chatteris Abbey /." Woodbridge ; Rochester (N.Y.) : the Boydell press, 1999. http://catalogue.bnf.fr/ark:/12148/cb371916050.
Full text
7
Johansson, Martina. "Lögner på Internets chatter." Thesis, University of Skövde, Department of Computer Science, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-761.
Full textAbstract:
Chattande har på kort tid blivit en mycket vanlig sysselsättning bland framförallt ungdomar. Denna studie syftar till att öka förståelsen för chattkulturen, genom att åskådliggöra hur chattare ser på, och själva använder, lögner. 101 gymnasieelever har besvarat en enkät, utifrån vilken resultatet har analyserats. I undersökningen framkom att hur fel en osanning är påverkar om den betraktas som en lögn eller inte. Ju mer fel, desto troligare är det att den anses vara lögn. Ungefär hälften av osanningarna som används anses av den egna personen vara lögner, men bland sådana osanningar som inte används är andelen lögner större, enligt vad chattarna själva menar är lögner. Deltagarna använder alltså osanningar som de själva ser som lögner, även om de ofta låter bli att använda rena lögner. Det är också så att det aktiva självet ändras när man chattar. Detta är inte konstigt, då aktiva självet är kontextberoende. De flesta av deltagarna i undersökningen kunde själva känna att de ändras på chatten, vilket tyder på att den verkliga skillnaden är stor.
8
Chan, Philip K. F. "Chatter avoidance in milling." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29467.
Full textAbstract:
One of the major limitations on productivity in metal cutting is chatter. Chatter is a form of unstable self-excited vibration which causes poor surface finish, as well as cutter and machine tool damage. The investigation of chatter suppression in milling using continuously variable spindle speed is presented in this thesis.
The fundamental mechanism in regenerative chatter is due to favorable phasing between
the inner and outer modulations on the chip thickness. In this thesis, the spindle speed is sinusoidally varied to prevent the dynamic cutting process from locking on to a constant phase shift and causing unstable cutting, or chatter. Because of the nonlin-earities and complexities of the process, time domain simulation of the dynamic cutting process has been modelled. The influence of various parameters, such as axial depth of cut, process damping from flank interference, and amplitude and frequency of speed variation have been investigated using the simulation model. The trends predicted by simulation results have been experimentally verified using cutting tests on a milling machine.
It has been concluded from simulation and milling tests that a variable spindle speed can partially increase the chatter limit, but can never totally prevent chatter. The variable
spindle speed strategy is incorporated into a proposed in-process chatter detection and avoidance algorithm. The milling process is monitored using the sound pressure signal measured by a microphone. When the amplitude of the sound spectrum near the natural frequency exceeds a threshold value, chatter has been detected and the spindle speed is oscillated until stability is regained. The proposed algorithm is implemented on line and experimental results are presented.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
9
Johnson, Alana Ingrid Nicole. "The abolition of chattel slavery in Barbados, 1833-1876." Thesis, University of Cambridge, 1994. https://www.repository.cam.ac.uk/handle/1810/251935.
Full text
10
Ly, Eric Thich Vi. "Chatter--a conversational telephone agent." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/29067.
Full text
11
PENG, WU, and Sebastian Levin. "Chatter Vibration Damping in Parting Tools." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-16798.
Full text
12
Ganguli, ABHIJIT. "Chatter reduction through active vibration damping." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210980.
Full textAbstract:
The aim of the thesis is to propose active damping as a potential control strategy for chatter instability in machine tools.The regenerative process theory explains chatter as a closed loop interaction between the structural dynamics and the cutting process. This is considered to be the most dominant reason behind machine tool chatter although other instability causing mechanisms exist.
The stability lobe diagram provides a quantitative idea of the limits of stable machining in terms of two physical parameters: the width of contact between tool and the workpiece, called the width of cut and the speed of rotation of the spindle. It is found that the minimum value of the stability limit is proportional to the structural damping ratio for turning operations. This important finding provides the motivation of influencing the structural dynamics by active damping to enhance stability limits of a machining operation.
A direct implementation of active damping in an industrial environment may be difficult. So an intermediate step of testing the strategy in a laboratory setup, without conducting real cutting is proposed. Two mechatronic "Hardware in the Loop" simulators for chatter in turning and milling are presented, which simulate regenerative chatter experimentally without conducting real cutting tests. A simple cantilever beam, representing the MDOF dynamics of
the machine tool structure constitutes the basic hardware part and the cutting process is simulated in real time on a DSP board. The values of the cutting parameters such as spindle speed and the axial width of cut can be changed on the DSP board and the closed loop interaction between the structure and the cutting process can be led to instability.
The demonstrators are then used as test beds to investigate the efficiency of active damping, as a potential chatter stabilization strategy. Active damping is easy to implement, robust and does not require a very detailed model of the structure for proper functioning, provided a collocated sensor and actuator configuration is followed. The idea of active damping is currently being implemented in the industry in various metal cutting machines as part of the European Union funded SMARTOOL project (www.smartool.org), intended to propose smart chatter control technologies in machining operations.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
13
Walden, Thomas. "Online vermittelte Beziehungen : Beziehungskonstruktionen von Internetchatterinnen und -chattern /." Hamburg : Kovač, 2008. http://www.verlagdrkovac.de/978-3-8300-3286-1.htm.
Full text
14
Walden, Thomas. "Online vermittelte Beziehungen Beziehungskonstruktionen von Internetchatterinnen und -chattern." Hamburg Kovač, 2006. http://d-nb.info/986036099/04.
Full text
15
Iannini, Craig, and Craig Iannini. "Contracted chattel : indentured and apprenticed labor in Cape Town, c.1808-1840." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/23252.
Full textAbstract:
This thesis examines indentured and apprenticed labor in Cape Town between the years 1808 and 1840. Through analysis of primary material such as the South African Commercial Advertiser, the Colonist, and the Mediator, as well as contemporary travel accounts, contracts of indenture and apprenticeship, and an examination of the records of the Cape Town Magistrates, this study explores the attitudes and perceptions towards indentured and apprenticed labor by both employers and indentured and apprenticed servants.This study hopes to add to the existing literature pertaining to nineteenth-century Cape Colony labor. This thesis commences with an examination of the different indenture and apprenticeship systems which existed in Cape Town between the years 1808 and 1840. It explores the issue of how employers and the government sought to maintain a constant supply of labor in the city as the prominence of urban slavery declined. It also discusses the important issue of how employers defined the terms apprentice and indenture. Chapter two explores the topic of child apprenticeship in Cape Town between the years 1812 to 1840, and illustrates that the notion of child apprenticeship was understood in different ways between employers and parents of apprenticed children. Chapter three investigates the stereotypes Cape Town's English speaking employers held towards the city's indentured and apprenticed laborers. The final chapter explores the question of status and incorporation into Cape Town society for the city's indentured and apprenticed laborers, and demonstrates that laborers did not enjoy equal status to the city's slaves.
16
Venter, Giuliana Sardi. "Reduzindo chatter em processos de torneamento através do uso de material piezoelétrico considerando aspectos não-lineares." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-06042015-173654/.
Full textAbstract:
Chatter é uma vibração auto-excitada que ocorre durante usinagens e limita a produtividade do processo. Esta instabilidade causa qualidade superficial inaceitável, diminuição da vida da ferramenta e ruído. Estratégias para definição de modelos e controle desta vibração são importantes, devendo ser avaliadas e implementadas. Neste trabalho foram realizados experimentos e características como frequências naturais, respostas em frequência e respostas temporais foram obtidas. Analisando tais resultados é possível a visualização do acoplamento existente nas duas direções de vibração. Uma estratégia de redução de chatter foi implementada, através do uso de shunts passivos conectados ao sistema mecânico por meio de material piezoelétrico, e sua viabilidade foi verificada. A estratégia foi adaptada para ser utilizada nas duas direções de vibração e o resultado da redução da vibração se provou mais eficiente após esta adaptação. Diagramas de fase, respostas temporais e espectros foram obtidos durante a usinagem e um comportamento não-linear se mostrou presente. Após a validação do uso de material piezoelétrico para o controle de chatter, existe a necessidade de modelos numéricos para a descrição do fenômeno, para que controles ativos e mais efetivos possam ser desenvolvidos. Devido ao acoplamento entre as duas direções de vibração e ao comportamento não linear do fenômeno, modelos que contenham tais características foram estudados, modificados e adaptados. Os resultados numéricos obtidos pelos modelos estudados foram então comparados aos resultados experimentais e conclusões sobre similaridades foram apresentadas. Considerando os resultados obtidos, acredita-se que o modelo que melhor representa o sistema real pode ser utilizado para o desenvolvimento de controles ativos, que garantam uma redução mais efetiva do chatter.Chatter is a self-excited vibration that leads to instability during ongoing machining, which affects productivity. Chatter instability causes poor surface quality, diminishes the tool\'s life and may cause clatter. Therefore, strategies to control chatter and chatter models are highly necessary, and must be evaluated and implemented. In an experimental campaign done during this work, characteristics such as natural frequencies, frequency responses and temporal responses were obtained. Trough these analysis, it was observed that the system presents a coupling in its two normal directions of vibration. One strategy for chatter reduction was then implemented, in which a passive shunt using piezoelectric material was used. The feasibility of this chatter reduction strategy for one direction could be verified. In addition, the strategy was adapted in order to be utilized in both main vibration directions and the results confirmed that this approach grants better results for the reduction of chatter. Phase-planes, temporal responses and spectras could also be derived from the turning experiments and a nonlinear behavior could be seen present. Being verified the possibility of using a piezoelectric material in chatter control, numerical models that describe the phenomena should be pursued, so that more effective active control could be developed. Because the experiments show the mode coupling between two directions and a nonlinear behavior, models that represent such characteristics were studied, modified and adapted. The numerical results from this models were then compared to the experiments and conclusions were drawn. Considering the obtained results, it is believed that the most similar model should be used in the development of active control that could guarantee a better chatter reduction.
17
Pranz, Sebastian. "Theatralität digitaler Medien : eine wissenssoziologische Betrachtung medialisierten Alltagshandelns /." Wiesbaden : VS Verlag für Sozialwissenschaften, 2009. http://d-nb.info/989381781/04.
Full text
18
Stocker, Yvonne-Olivia. "OnE - Ist Online=Einsam eine Online-Fragebogenstudie mit Chattern." Saarbrücken VDM Verlag Dr. Müller, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3001490&prov=M&dok_var=1&dok_ext=htm.
Full text
19
Kilic, Murat Zekai. "Nonlinear Dynamic Modeling And Analysis Of Spindle-tool Assemblies In Machining Centers." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610861/index.pdf.
Full textAbstract:
Chatter is unwanted since it causes deteriorating effects on the milling process. Stability lobe diagrams are developed in order to determine the stable cutting conditions at which chatter-free machining can be made. The need of cutting away more chips to make milling operations quicker has brought the concept of high-speed milling. This increased the importance of estimating stability lobe diagrams of the milling process more accurately. The state-of-art chatter and spindle-toolholder-tool models predict the stability lobe diagram for milling process quite effectively. However, sometimes chatter might occur even at
cutting conditions selected using theoretically obtained stability lobe diagrams. One of the reasons for that may be nonlinearities in the system. This being the motivation, in this work, nonlinearities at the bearings of spindle-toolholder-tool system are investigated. In this thesis, cubic nonlinearity is assumed to represent stiffness of a bearing in a spindle-toolholder-tool system. Effects of nonlinearity on stability lobe diagram of a milling process are studied by using the mathematical model developed for such a system. Frequency response function of spindle-toolholder-tool system without bearings is obtained using Timoshenko beam model. Then, bearings are modeled by using describing function theory and coupled to the dynamics of spindle-toolholder-tool modeled. Solution of the equations of motion of the system in frequency domain is obtained via Newton's method with ALC. It is an effective frequency domain method in which turning points on frequency response function are traced. This is important for the system studied, as bearing nonlinearity may introduce turn backs in the response of the system. Case studies are carried out to study the effects of bearing nonlinearity on stability lobe diagram. The effects of the following factors are studied: Magnitude of cutting force, degree of nonlinearity and number of teeth on cutter. Displacement amplitude dependent stiffness of bearings affects the dynamic response due to rigid body modes of the system. It is observed that an increase in cutting force magnitude or in coefficient of bearing nonlinearity results in increase of natural frequencies, thus showing hardening behavior. Shifting of frequencies in the response curve shifts stability lobes related to the affected modes, to the right. For increased number of flutes on cutter, effect of nonlinearity at bearings on stability of the milling process becomes lower. Experimental studies to determine the changes in dynamics of a system during cutting are also carried out in this thesis. Inverse chatter analysis is conducted to obtain modal parameters of a single-degree-of-freedom system using the experiment data. Decrease in natural frequency is observed at high cutting speeds for the particular spindle used. This shift may be due to speed-dependent bearing dynamics and real time adjustment of preload on bearings.
20
Park, Jong-Suh. "The Prediction of Chatter Stability in Hard Turning." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5235.
Full textAbstract:
Despite a large demand from industry, a realistic chatter modeling for hard turning has not been available due to the complexity of the problem, which is mainly caused by flank wear and nonlinearity in hard turning. This thesis attempts to develop chatter models for predicting chatter stability conditions in hard turning with the considerations of the effects of flank wear and nonlinearity. First, a linear model is developed by introducing non-uniform load distribution on a tool tip to account for the flank wear effect. Second, a nonlinear model is developed by further incorporating nonlinearity in the structure and cutting force. Third, stability analysis based on the root locus method and the describing function approach is conducted to determine a critical stability parameter. Fourth, to validate the models, a series of experiment is carried out to determine the stability limits as well as certain characteristic parameters for facing and straight turning. From these, it is shown that the nonlinear model provides more accurate predictions than the linear model, especially in the high-speed range. Furthermore, the stabilizing effect due to flank wear is confirmed through a series of experiments. Fifth, to fully account for the validity of linear and nonlinear models, an empirical model is proposed to fit in with the experimental stability limits in the full range of cutting speed. The proposed linear and nonlinear chatter models will help to improve the productivity in many manufacturing processes. In addition, chatter experimental data will be useful to develop other chatter models in hard turning.
21
Dorta, Gabriel. "Soziale Welten in der Chat-Kommunikation Untersuchungen zur Identitäts- und Beziehungsdimension in Web-Chats." Bremen Hempen, 2005. http://deposit.ddb.de/cgi-bin/dokserv?id=2623571&prov=M&dok_var=1&dok_ext=htm.
Full text
22
Fix, Tina. "Generation @ im Chat : Hintergrund und explorative Motivstudie zur jugendlichen Netzkommunikation /." München : KoPäd-Verl, 2001. http://www.gbv.de/dms/ilmenau/toc/338486623.PDF.
Full text
23
Eynian, Mahdi. "Chatter stability of turning and milling with process damping." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/19234.
Full textAbstract:
The prediction of chatter instability in machining steel and thermal-resistant alloys at low cutting speeds has been difficult due to unknown process damping contributed by the contact mechanism between tool flank and wavy surface finish. This thesis presents modeling and measurement of process damping coefficients, and the prediction of chatter stability limits for turning and milling operations at low cutting speeds.
The dynamic cutting forces are separated into regenerative and process damping components. The process damping force is expressed as a product of dynamic cutting force coefficient and the ratio of vibration and cutting velocities. It is demonstrated that the dynamic cutting coefficient itself is strongly affected by flank wear land. In measurement of dynamic cutting forces, the regenerative force is eliminated by keeping the inner and outer waves parallel to each other while the tool is oscillated using a piezo actuator during cutting.
Classical chatter stability laws cannot be used in stability prediction for general turning with tools cutting along non-straight cutting edges; where the direction and magnitude of the dynamic forces become dependent on the depth of cut and feed-rate. A new dynamic cutting force model of regeneration of chip area and process damping, which considers tool nose radius, feed–rate, depth of cut, cutting speed and flank wear is presented. The chatter stability is predicted in the frequency domain using Nyquist stability criterion.
The process damping is considered in a new dynamic milling model for tools having rotating but asymmetric dynamics. The flexibility of the workpiece is studied in a fixed coordinate system but the flexibility of the tool is studied in a rotating coordinate system. The periodic directional coefficients are averaged, and the stability of the dynamic milling system is determined in the frequency domain using Nyquist stability criterion.
The experimentally proven, proposed stability models are able to predict the critical depth of cut at both low and high cutting speeds.
24
Wang, Zhanchen. "Chatter analysis of machine tool systems in turning processes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63715.pdf.
Full text
25
Ash, Jesse. "The figure of speech : the politics of contemporary chatter." Thesis, Goldsmiths College (University of London), 2010. http://research.gold.ac.uk/3143/.
Full textAbstract:
This thesis focuses on informal linguistic transactions that operate in relation to, and as part of spectacle in contemporary society. In contrast to presenting such transactions as a subordinated public, exchanging meaningless chatter, these communicative acts are seen to be a formalization of language revealing processes, networks, and territories that have positive possibilities for the public engaged in these communications. Using examples such as the act of communication evident in the recent exponential growth of web 2.0 (on-line social networking), the sound of language represented in the murmur of political demonstrations, and the audibility of voices on the underground network, this thesis builds upon and extends discussions that have asserted the political resistance inherent in rumour, gossip, idle talk, and hearsay. This specific analysis focuses upon both our physical, corporeal, and virtual relations to chatter within the developing systems of new technology that transfer the majority of today’s informal exchanges—investigating the sounds, repetitions, occupation of networks, and gestures of communication rather than the exchange of specific content. Using a methodology that acknowledges the ephemeral, transgressive and fluid nature of its subject, this project uses regular first person narrated sections supporting theoretical discussion, refuses the ‘permanence’ of visual illustration, and is directly informed by concerns within my art practice. Responding to the ideas inherent to my art practice—concerning the form and presentation of information presented (by the media and political authorities) to the public from which a political cognition is constructed, both text and practice elements of this project focus on an abstract, formal reading of contemporary communication. These abstract experiences of communication and collective action are acknowledged as an integral reading of contemporary politics, and that this sphere should be activated, extended and expanded upon in order to discover the positive possibilities inherent within it.
26
Zhang, Yuanming. "Piezoelectric damping for chatter suppression in high-speed milling." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434511.
Full text
27
Gibbons, Tom. "Structural modification for chatter avoidance in high speed milling." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19468/.
Full textAbstract:
High speed machining operations, such as milling, are widely used in many industries including the aerospace sector. Elevated manufacturing costs coupled with ever more complex geometry components have led to the need to cut deeper and faster than ever; the dynamics of the structures involved, however, greatly restrict these boundaries. As speed and depth of cut are increased, self-excited vibrations, known as chatter, can occur due to the dynamic interaction between the tool tip and the workpiece. This has undesirable consequences such as poor surface finish, rapid tool and machine wear, and high noise levels, all of which lead to a reduction in production rates and an increase in production costs. Efforts to reduce and control chatter are therefore of great importance to industrial engineers. Selection and design of appropriate cutting tools, in an attempt to minimize the occurrence of chatter, are well established methods in the manufacturing industry; however, the choice of tool (type, diameter, length) is often restricted by the required operation, and since the spindle is set by the machine itself, the only other variable component in the machining structure is the tool holder. Little research has been carried out on the dynamics of the tool holder, despite it being a much simpler structure. This thesis shows that the geometry of the tool holder has a significant effect on the dynamics at the tool tip (source of chatter). Therefore the overall focus of this work is to show how the geometry of the tool holder may be utilised to control the speed and depth at which chatter occurs. Structural modification theory allows for models of smaller, simpler structures to be combined to predict the dynamics of larger, more complex structures. One of its main advantages is that experimental models may be combined with numerical models, allowing for experimental structures to be optimised numerically. Structural modification theory is applied to the problem of tool holder dynamics and chatter control. Inverse structural modification is used to optimise the tool holder geometry in terms of tool tip dynamics and, in-turn, the onset of chatter. A prototype tuneable tool holder prototype is designed and tested for use with this structural modification model. In addition to the focus on machining, it will be shown that spatial incompleteness is, perhaps, the largest draw-back with structural modification methods. For structural modification to give accurate results, a full spatial model, including rotational degrees of freedom is needed. Since direct measurement of such information requires specialist equipment, often not available to industry, numerical methods such as the finite difference technique have been developed to synthesise rotational data from translational measurements. As with any numerical method the accuracy of the finite difference technique relies on the correct spacing, however, there is currently no method to select an optimum spacing. An error analysis of the finite difference technique with non-exact data is carried out for application to rotational degree of freedom synthesis.
28
Saleh, Khaled. "Modelling and analysis of chatter mitigation strategies in milling." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4482/.
Full textAbstract:
Machining stability plays a major role in improving machine tool performance and product quality. Uncontrolled chatter phenomenon causes too many defects and problems in manufacturing industry such as increased surface roughness, tool wear and even machine breakdown. In this subject area, great effort has been focused on developing different mechanisms and techniques in an attempt to reduce and control the machining vibrations. Spindle speed variation is one of the common approaches that has received attention recently. Non-uniform tool geometry is an alternative method that could be used for regenerative chatter suppression. Basically these two methods focus on breaking up the regeneration of surface waves. A phenomenon known a process damping also has a vital effect on the stability improvement, particularly at low cutting speeds. Process damping is believed to be influenced by the interference of the relief face of the cutting tool with the waveform traced on the arc surface. An alternative explanation for process damping is known with the short regenerative effect. This concept is based on the distribution of forces along the tool flank face. In the present research, a new approach based upon energy analysis is developed for more detailed interpretation of the stability of these different chatter mitigation mechanisms. Moreover, a comprehensive time domain model is developed to allow multiple effects such as variable spindle speed, process damping, loss of contact, variable helix tool and energy to be considered. Meanwhile performance of this milling model has been further benchmarked along with these effects to enable the numerical prediction to be computed more quickly with an acceptable numerical accuracy.
29
Huyanan, Satienpong. "An active vibration absorber for chatter reduction in machining." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486712.
Full textAbstract:
In the early days of the manufacturing industry, the limiting factor in obtaining higher material removal rates was 'Chatter', an unstable cutting condition with excessive vibrations. Maximum productivity can only be obtained using the knowledge of the theory of regenerative chatter. In the era of modem manufacturing industry, where the greater quality and productivity are increasingly demanded, especially the requirement to understand and avoid chatter is even greater. The key answering to this challenge is to increase the rate of material removal while maintaining stable cutting conditions through reducing chatter during machining operations. In this regard, an active vibration absorber can be used to effectively reduce the undesired vibrations of the structure, thereby increasing the border line of chatter stability. However, to date there has been little attention in applying this technique in the application ofmilling chatter suppression, especially for a flexible workpiece. In this thesis, the stability of milling process dynamics is theoretically investigated using the method of semi-discretization. An alternative means of improving stability in milling is also presented by developing the extended method of semi-discretization for the milling systems with variable time delay. This can be used to predict not only the stability but also the chatter frequencies for milling with irregular pitch cutters. Motivated by an interest in practically improving the stability margin in the milling process, a practical and straightforward active vibration control system with acceleration feedback is implemented using a proof-mass actuator. Based on the general framework of virtual passive control, three controller strategies are first demonstrated and evaluated through a laboratory based vibration study, consisting of virtual sky-hook damper, virtual passive absorber and virtual passive-active absorber. The· results indicate that virtual passive absorber control could be a simple and robust solution to the application ofmachining chatter reduction. Through the initial study of the theory of regenerative chatter, analytical optimizations of dynamic vibration absorbers are developed for application to chatter suppression. The performance of a virtual passive absorber to suppress workpiece chatter during high speed machining is then experimentally investigated for each tuning scheme, including the virtual sky-hook damper scheme. The results demonstrate that although the performance of the active milling chatter suppression system is limited by the actuator saturation, the chosen control strategy can provide at least a 6-fold improvement in the workpiece stability using a small actuator.
30
Blasingame, Dionne. "The Trauma of Chattel Slavery: A Womanist Perspective Women on Georgia in Early American Times." Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/english_theses/138.
Full textAbstract:
This thesis explores the psycho-socio-cultural dynamics that surrounded black womanhood in antebellumGeorgia. The goal is twofold: first, to examine how slave narratives, testimonies, and interviews depicted the plight of enslaved black women through a womanist lens and second, to discover what political and socio-cultural constructions enabled the severe slave institution that was endemic toGeorgia. Womanist theory, psychoanalytic theory, and trauma theory are addressed in this study to focus on antebellum or pre-Civil WarGeorgia.
31
Atlar, Sibel. "Modelling Part Dynamicsin Machining Processes Considering Material Removal." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12609154/index.pdf.
Full textAbstract:
Self-excited chatter vibration in machining is one of the most important limitations on utilizing the increasing productivity of modern machine tools. In order to predict stable depth of cuts at high cutting speeds, the stability lobe diagram for a spindle-tool holder-tool combination must be developed. The frequency response function (FRF) of the system must be known for analytical prediction of the stability lobe diagrams. When the flexibility of the workpiece is important, the workpiece itself should be included in the system model by considering the variation of its dynamics at different stages of the machining process.
In this thesis, an exact structural modification method is used to find the frequency response functions of the workpiece to be machined at every stage of the machining process. In order to obtain the system matrices and the modal parameters of the original structure, a commercial finite element program MSC. Marc©is used. The frequency response functions of workpiece are calculated by using the computer program developed in this thesis, and are compared with the ones found by MSC. Marc©
. The stability lobe diagram of the system is obtained by combining the FRFs of the tool with those of the workpiece. The effects of the dynamic of the workpiece on the stability lobe diagrams are studied extensively by using the results of case studies presented in this thesis. In order to increase productivity, minimum chatter-free machining times are also calculated for different cases. For this purpose the effects of the different radial depth of cuts and different cutting strategies on the stability and the machining time are examined with various case studies.
32
Chiou, Yunshun. "Acoustic emission dynamics in turning with tool wear and chatter." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/17990.
Full text
33
Goldie, Anna Darling. "CHATTER : a spoken language dialogue system for language learning applications." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66420.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 110).
The goal of this thesis is to build a Computer Aided Language Learning game that simulates a casual conversation in Mandarin Chinese. In the envisioned system, users will chat with a computer on topics ranging from relationship status to favorite Chinese dish. I hope to provide learners with more opportunities to practice speaking and reading foreign languages. The system was designed with generality in mind. The framework allows developers to easily implement dialogue systems to allow students to practice communications in a variety of situations, such as in a street market, at a restaurant, or in a hospital. A user simulator was also implemented, which was useful for the code development, as a tutor for the student, and as an evaluation tool. All of the 18 topics were covered within the 20 sample dialogues, no two dialogues took the same path, questions and remarks were worded differently, and no two users had the same profile, resulting in high variety, coherence, and natural language quality.
by Anna Darling Goldie.
M.Eng.
34
Pratt, Jon Robert Jr. "Vibration Control for Chatter Suppression with Application to Boring Bars." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29344.
Full textAbstract:
A mechatronic system of actuators, sensors, and analog circuits is demonstrated to control the self-excited oscillations known as chatter that occur when single-point turning a rigid workpiece with a flexible tool. The nature of this manufacturing process, its complex geometry, harsh operating environment, and poorly understood physics, present considerable challenges to the control system designer. The actuators and sensors must be rugged and of exceptionally high bandwidth and the control must be robust in the presence of unmodeled dynamics. In this regard, the qualitative characterization of the chatter instability itself becomes important. Chatter vibrations are finite and recognized as limit cycles, yet modeling and control efforts have routinely focused only on the linearized problem. The question naturally arises as to whether the nonlinear stability is characterized by a jump phenomenon. If so, what does this imply for the "robustness" of linear control solutions?
To answer our question, we present an advanced hardware and control system design for a boring bar application. Initially, we treat the cutting forces merely as an unknown disturbance to the structure which is essentially a cantilevered beam. We then approximate the structure as a linear single-degree-of-freedom damped oscillator in each of the two principal modal coordinates and seek a control strategy that reduces the system response to general disturbances. Modal-based control strategies originally developed for the control of large flexible space structures are employed; they use second-order compensators to enhance selectively the damping of the modes identified for control.
To attack the problem of the nonlinear stability, we seek a model that captures some of the behavior observed in experiments. We design this model based on observations and intuition because theoretical expressions for the complex dynamic forces generated during cutting are lacking. We begin by assuming a regenerative chatter mechanism, as is common practice, and presume that it has a nonlinear form, which is approximated using a cubic polynomial. Experiments demonstrate that the cutting forces couple the two principal modal coordinates. To obtain the jump phenomena observed experimentally, we find it necessary to account for structural nonlinearies. Gradually, using experimental observation as a guide, we arrive at a two-degree-of-freedom chatter model for the boring process. We analyze the stability of this model using the modern methods of nonlinear dynamics.
We apply the method of multiple scales to determine the local nonlinear normal form of the bifurcation from static to dynamic cutting. We then find the subsequent periodic motions by employing the method of harmonic balance. The stability of these periodic motions is analysed using Floquet theory.
Working from a model that captures the essential nonlinear behavior, we develop a new post-bifurcation control strategy based on quench control. We observe that nonlinear state feedback can be used to control the amplitude of post-bifurcation limit cycles. Judicious selection of this nonlinear state feedback makes a supplementary open-loop control strategy possible. By injecting a harmonic force with a frequency incommensurate with the chatter frequency, we find that the self-excited chatter can be exchanged for a forced vibratory response, thereby reducing tool motions.Ph. D.
35
Cho, Wonsang. "Towards Additively Manufactured Tool Holder with Cavity to Mitigate Chatter." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1449820259.
Full text
36
Pranz, Sebastian. "Theatralität digitaler Medien eine wissenssoziologische Betrachtung medialisierten Alltagshandelns." Wiesbaden VS, Verl. für Sozialwiss, 2008. http://d-nb.info/989381781/04.
Full text
37
Anwar, Sohel. "Modeling and predictive control of chatter instabilities in single point turning." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187130.
Full textAbstract:
Based on the concept of long range prediction in the context of self-tuning control theory, a generalized predictive kinetic energy controller (GPKEC) suitable for applications to high speed machining processes is developed. A three dimensional lumped mass model capable of representing both tool and workpiece dynamics in a single point turning operation on a lathe machine is first developed to accurately reflect their interactions in a machining process. Based on the linearized uncoupled one dimensional model for the machining dynamics and noting that feed can effectively be used to control the unstable machine-tool dynamics, a single-input single-output (SISO) discrete time predictive control law (GPKEC) is derived by minimizing the predicted incremental kinetic energy of the cutting process. The instantaneous feed is used as the control variable of this controller which is calculated using the feedback of instantaneous displacement of the tool tip in the feed direction. It is observed from the simulation results that the proposed GPKEC controller is capable of suppressing the unstable and marginally stable system dynamics in their incipient stages, even in the presence of uncertain disturbances. The GPKEC strategy is also found to be robust against modeling or estimation errors. In order to verify the simulation results, a number of experimental runs are carried out. An estimate of acceleration signal, instead of displacement, in the feed direction is used as feedback signal due to practical reasons. A servomotor, which is connected to the main feed drive shaft through a high performance timing (HPT) belt, has been used to control the instantaneous feed of a cutting process. It is observed that there has been a good agreement between the experimental and simulation results. The experimental results show that the GPKEC strategy can effectively suppress the chatter vibration in a machining process. It is also observed from experimental results that the proposed controller is robust against overparametrization, estimation errors, uncertain inputs, system noise, and even against changes in the system dynamics.
38
Rohatgi, Gaurav. "Approaches for chatter reduction in deep cavity and intricate surface milling." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50532.
Full text
39
Pesch, Alexander Hans. "Development of Chatter Attenuation Robust Control for an AMB Machining Spindle." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1401198790.
Full text
40
Elmkvist, Gillis. "Vill dagens elever kommunicera matematik med varandra via sociala medier? : En undersökning om chattens potential för matematisk kommunikation." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-11855.
Full textAbstract:
Bakgrund: Allt fler eleverna har tillgång till egna bärbara dator i gymnasieskolan. I skolan där undersökningen genomfördes fick eleverna inte ta med sig sin dator på matematiklektionerna. Här använde eleverna endast boken och miniräknare. Eleverna som deltar går andra året på gymnasiets Teknikprogram och läser MaD. Eleverna är uppväxta med datorspel och internet. Syfte: Undersökningen handlar om möjligheter och svårigheter med att införa ett chattprogram på matematiklektionerna. Hur vida chatten kan stödja kommunikation i termer av dess potential att stimulera eleverna till att kommunicera matematik och reflektera över sina egna, men även över andras strategier och lösningar. Det ingick även att undersöka hur eleverna upplever själva chattprogrammet ”TodaysMeet”, som verktyg. Resultatet: Studien visar att chattens främsta egenskap var att skapa tystnad och fokus på en enskild fråga, när en gemensam dator används. Därmed skapade chatten en förutsättning för en pedagogisk diskussion i klassrummet. Elevernas upplevelse av att använda ”TodaysMeet” var att det var krångligt, onödigt och opersonligt. I samband med införandet av chatten, framkom fem kritiska aspekter: användarvänlighet, behovet, digital identitet, gruppdynamik och chattens mervärde. Det finns även en antydan till ett samband mellan elever som känner eller inte känner sig övervakade, vad det gäller att hålla på med annat på datorn. Detta kan även tolkas som att eleverna behöver lära sig att samarbeta via sociala medier.Magisteruppsatsen har inriktingen matematikdidaktik.
41
Alan, Salih. "Development Of A Fast Analytical Method For Prediction Of Part Dynamics In Machining Stability Analysis." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611096/index.pdf.
Full textAbstract:
The objective of this study is to develop and implement practical and accurate methods for prediction of the workpiece dynamics during a complete machining cycle of the workpiece, so that FRFs of the workpiece can be used in chatter stability analysis. For this purpose, a structural modification method is used since it is an efficient tool for updating FRFs due to structural modifications. The removed mass is considered as a structural modification to the finished workpiece in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on representative parts such as turbine blades. The predictions are compared and verified with the data obtained using FEA. The FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied.
42
Shirai, Hiromi. "Eine kontrastive Untersuchung zur deutschen und japanischen Chat-Kommunikation." Frankfurt, M. Berlin Bern Bruxelles New York, NY Oxford Wien Lang, 2008. http://d-nb.info/996598758/04.
Full text
43
Tuschling, Anna. "Klatsch im Chat Freuds Theorie des Dritten im Zeitalter elektronischer Kommunikation." Bielefeld Transcript, 2006. http://d-nb.info/988747774/04.
Full text
44
Caulfield, F. Donald. "Electromechanical Actuator Development for Integrated Chatter Prediction on High Speed Machining Centers." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-04222002-234733/.
Full textAbstract:
Machine tool chatter imposes limitations on the productivity and quality of modern high speed machining (HSM) operations. It has been shown that chatter prediction and avoidance strategies can lead to increased machining productivity if certain modal characteristics of the machine are known. The objectives of this research are to design and demonstrate an electromechanical actuator (EMA) to easily and accurately identify these characteristics. Design specifications for this actuator reflect a wide range of machine tools and operating conditions. A simulation-based design strategy is employed, based on traditional electromechanical analysis, finite element analysis (FEA), and computer simulations to ensure performance meets the design specifications. A prototype EMA system is built to validate the analytical results and demonstrate its capabilities as part of an automated chatter prediction and avoidance system. The EMA is shown to generate the required modal characteristics, namely frequency response functions (FRFs) and stability lobe diagrams (SLDs) quickly, accurately, and with fewer technical skill requirements than other vibration testing methods. Experimental machining tests demonstrate that the EMA can be an effective component of an integrated chatter prediction and avoidance system.
45
Bickraj, Kimberly L. "Monitoring Tool Wear and Chatter by Using an Index Based Reasoning Approach." FIU Digital Commons, 2007. http://digitalcommons.fiu.edu/etd/2431.
Full textAbstract:
This work addressed the ongoing attempt for establishing a reliable yet simple system for the detection of tool wear and chatter in vertical milling machines. For this reason, a simple closed-loop system that utilizes wireless sensors, a dynamometer replacement and an artificial intelligence system for signal processing were designed. Various signal analysis techniques were applied to real force signal information containing chatter and wear to determine if they were suitable instruments for detection of such unwanted disturbances. An Index Based Reasoner (IBR) was proposed as a solution for overall signal processing. Furthermore, a novel Torque Analysis Device (TAD) that utilizes piezoelectric sensors was developed to replace the inconvenient and expensive dynamometer that is typically used to obtain force and torque information from vertical mills. When all aspects of this research were tested, the results were found to be successful and thus combined to form the closed-loop monitoring system.
46
Xu, Diancheng. "A fuzzy logic approach for chatter detection and suppression in end milling." Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26351.
Full textAbstract:
In metal cutting processes, excessive vibration or chatter has an adverse effect on productivity and product surface quality. Various studies have been reported in the literature over the past few decades. However, the real application of the outcome of these studies has been very limited. A new system has been developed in this study for chatter detection and chatter suppression. The coherence function values of the frequency spectra from two accelerometers in orthogonal directions were used as a chatter indicator. The vibration energy was used to offset the over-vigilance behaviour of the coherence function. A fuzzy logic control approach was used for chatter suppression based on both the coherence function value and vibration energy level. To improve the adaptability of the fuzzy controller, a self-learning algorithm has also been developed for on-line updating the fuzzy rule base. A direct output tuning method was also proposed to improve the responsiveness of the system.
The proposed system has been tested using both steel and aluminium workpieces with and without thin-walls. The experimental results show that the proposed system worked reasonably well for on-line chatter detection and suppression.
The thesis also explored the possibility of using the coherence function for chatter prediction. The verification of its feasibility may be carried out in the future.
47
Dassanayake, Achala Viomy. "Machining dynamics and stability analysis in longitudinal turning involving workpiece whirling." Thesis, [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1817.
Full text
48
Cervelin, José Eduardo. "Redução de vibrações mecânicas em processos de torneamento usando material piezelétrico." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18156/tde-16062014-135146/.
Full textAbstract:
Vibrações mecânicas oferecem grande limitação para a produtividade, qualidade ou mesmo viabilidade das operações de usinagem, especialmente quando se trata das autoexcitadas (chatter). Neste trabalho, foram desenvolvidas estratégias que tem como objetivo diminuir a intensidade de vibrações em processos de torneamento por meio do acoplamento de material piezelétrico ao suporte de ferramenta em conjunto com uso de shunts resistivo, indutivo e resistivo-indutivo em série ou em paralelo, criando assim estruturas eletromecânicas passivamente amortecidas. Para tanto, foram construídos modelos eletromecânicos de parâmetros distribuídos para mostrar a capacidade que tais estruturas eletromecânicas possuem em oferecer um maior amortecimento quando comparadas com estruturas mecânicas convencionais. Com os modelos construídos, foi possível verificar a influência causada pela espessura da camada de material piezelétrico bem como a influência dos shunts no comportamento da estrutura, sendo constatado que camadas mais espessas aumentam a capacidade de amortecimento da estrutura e que os shunts resistivo-indutivo, tanto em série quanto em paralelo, funcionam como um amortecedor dinâmico de vibrações amortecido e oferecem o melhor desempenho. A seguir, construiu-se o diagrama de lóbulos de estabilidade para comparar as estruturas com e sem shunts e observou-se que as estruturas com shunts resistivo-indutivo possuem um melhor desempenho. Também foram executados testes de impacto (tap tests) para a verificação experimental do comportamento da estrutura quando conectadas aos shunts e os resultados mostraram que há um maior amortecimento. Considerando os resultados obtidos, acredita-se que seja possível melhorar o desempenho de processos de torneamento usando material piezelétrico.Mechanical vibrations offer great limitation for the productivity, quality or even feasibility of the machining operations when chatter is present. In this work it was developed strategies aiming to diminish the intensity of the vibration in turning processes. By coupling a piezoelectric material with a turning tool and by using different associations of resistive and inductive shunt (series or parallel) it was created electromechanical structures passively damped. Electromechanical models of distributed parameters were developed in order to show the capacity that these structures has to offer a greater dumping when compared with conventional mechanical structures. By using these constructed models it was possible to verify the influence of the thickness of the piezoelectric material as well as the influence of shunts in the behavior of structure. It was observed that thicker layers increase the damping capacity of the structure that resistive-inductive shunt (series or parallel) works as a damped dynamic vibration absorber which offer better performance. Latter was developed a stability lobes diagram in order to compare the structures with and without shunts and it was observed that structures connected to resistiveinductive shunt has a better performance. Tap tests were performed for the purpose of study the experimental behavior of the structure connected to shunt and results showed that there is a better damping in this situation. Considering the results obtained, is fair to believe that is possible to improve turning process by using piezoelectric materials.
49
Crosson, Amélie. "Adaptation théâtrale de "La Chatte" de Colette: Fidélité et trahison." Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27573.
Full textAbstract:
Dans l'élaboration de cette thèse, mon objectif était d'entreprendre une adaptation théâtrale et, ce faisant, de mieux comprendre les enjeux du processus de création d'une oeuvre à partir d'une oeuvre existante, en l'occurrence, La Chatte, un roman que Colette a écrit en 1933. Les théories sur l'adaptation théâtrale étant rares, j'ai entrepris une étude de deux des adaptations que Colette a écrites en collaboration avec Leopold Marchand, les pièces La Vagabonde et Chéri qui m'ont servi d'exemples et aussi de contre-modèles pour résoudre les questions de concentration du récit et de transposition scénique. En outre la mise en scène du roman devait relever un défi de taille, l'omniprésence de la chatte, personnage éponyme du roman où elle est traitée de l'extérieur par un narrateur omniscient. De plus l'oeuvre de Colette s'inscrit dans une époque et un milieu social qui trouve peu d'échos dans le public contemporain. Le processus d'adaptation se devait de prendre en compte la réception et d'inclure des éléments, tant scéniques que thématiques, pour rapprocher l'oeuvre originale du spectateur potentiel. L'adaptation a ainsi tirer parti de techniques audio-visuelles et de la familiarité du public avec des traitements modernes sur les plans de la structure, du temps et de l'espace pour créer une pièce qui soit contemporaine tout en rendant justice au roman et à son auteure.
50
Arellano, Diego Patricio Calero. "Avaliação numérica e experimental de soluções passiva e ativa para redução de chatter em processos de torneamento usando material piezelétrico." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-30112017-143459/.
Full textAbstract:
O chatter é o principal problema de instabilidade nos processos de usinagem, e é causado pelas ondulações deixadas na superfície durante cortes sucessivos, ou chamado processo de regeneração, e é caracterizado pelo ruído e qualidade superficial ruim nas superfícies usinadas. Portanto, a comunidade científica tem se preocupado em desenvolver ações, tanto para a predição do fenômeno, como para desenvolver estratégias para sua redução. Neste trabalho avalia-se numérica e experimentalmente, a utilização de pastilhas piezelétricas acopladas no suporte da ferramenta, e aplicando estratégias de controle passivo e ativo, procurando a redução do chatter em processos de torneamento. A solução passiva consiste em conectar os terminais das pastilhas piezelétricas a um circuito elétrico dissipador de energia. A solução ativa propõe usar uma das pastilhas como sensor e a outra como atuador para aplicar leis de controle de realimentação. Na avaliação numérica foi considerado um modelo eletromecânico de parâmetros distribuídos usando a teoria de viga engastada de Euler-Bernoulli, e as equações constitutivas elétricas e mecânicas do material piezelétrico. A comparação das funções de resposta em frequência (FRFs) do sistema, obtidas numericamente, mostra uma adição de amortecimento ao sistema quando é usado um circuito de dissipação com uma resistência e uma indutância como solução passiva. A avaliação numérica da solução ativa indica que o controle de realimentação de velocidade adiciona amortecimento do sistema. A melhora da estabilidade no processo de torneamento destas duas estratégias é comprovada num diagrama de lóbulos de estabilidade. Na parte experimental foram obtidas as funções de resposta em frequência do sistema suporte da ferramenta, usando um sistema de aquisição de dados, com o fim de comparar as magnitudes da resposta, e foram feitos testes de torneamento com o fim de comparar qualitativamente as qualidades superficiais obtidas nas peças usinadas. A medição das FRFs com circuitos de dissipação indicou uma atenuação da resposta para um sistema com circuito em série, estratégia que foi avaliada em testes de torneamento, e mostrando uma melhora no acabamento superficial.Chatter is the main problem of instability in machining processes, caused by the modulations left on the surface during the successive cuts, called regeneration process, and is characterized by violent vibrations, noise and poor surface quality on machined surfaces. Thus, the scientific community has been concerned with developing actions for both the phenomenom prediction, and developing strategies to reduce them. This work evaluates numerically and experimentally the use of piezoelectric layers embedded to the tool-holder, and applying active and passive strategies trying to reduce the chatter in turning processes. For the passive case, the conductive electrode pairs of the piezoelectric layers are connected to a shunt circuit which modifies the system dynamics. The active solution proposes to use one of the piezoelectric layers as sensor an the other one as actuator, in order to apply feedback control laws. A numerical evaluation considers an electromechanical distributed parameter model based on Euler- Bernoulli cantilever beam theory, and the electrical and mechanical constitutive equations of the piezoelectric material. A comparison of the system frequency response functions (FRFs), numerically obtained, shows an increase of system damping when a resistive-inductive shunt circuit is used as a passive solution. The numerical evaluation of the active solution shows that the velocity feedback control increases the system damping. The turning process stability improvement using both strategies, is shown in a stability lobe diagram. Frequency response functions of the tool-holder system were obtained experimentally using a data acquisition system, in order to compare the response amplitudes. Turning tests were performed in order to compare surface qualities obtained of machined parts. Measurement of FRFs using series resistive-inductive shunt circuits shows a system response attenuation, later this strategy was evaluated in turning tests, showing an improvement in surface finish.