Thèses sur le sujet « Modelli ARCH »
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1
Putzulu, Matteo. « Modelli ARIMA implementati in ambiente Python applicati a serie temporali GNSS ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25884/.
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Nella presente tesi, si è discusso sul corretto trattamento dei dati di posizione, provenienti da una stazione permanente GPS in PPP, per studiarne l’andamento e successivamente elaborarne le previsioni per il futuro. E' stato utlizzato un approccio con la classe del Modelli ARIMA implementati su linguaggio Python.
2
Dalton, Matthew W. « Experimental modelling of vascular haemodynamics ». Thesis, Nottingham Trent University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273762.
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Miri, Mahmoud. « Modelling of repair techniques for masonry arch bridges ». Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/55998/.
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Small scale centrifuge models were used to study the behaviour of arches repaired using different techniques. The models under test were 1/12th scale replicas of a 6 metre single span three ring arch. Two types of arch geometry, with span/rise of 4 and 2, were studied as a shallow and deep arch geometry. The models were tested in a centrifuge under a steady equivalent gravity of 12g. Two types of 2-D and 3-D arch models were studied which had the same geometry but different in the addition of spandrel walls. The 3-D models were built with spandrel walls but without any wing walls or parapet. Both 2-D and 3-D arch models were tested under rolling and failure loads. The models were usually tested with fourteen passes of a rolling load and then up to the observation of first signs of failure to enable them to be suitable for applying a repair method. The repaired models were tested using the same procedure but up to the full failure load. To understand the behaviour of the arch models under unsymmetrical loads different roller weights were applied at different positions. The arch deflection and the soil/masonry interaction in arch extrados were measured in all the tests and compared with each other. Plastic mesh reinforcement, stitching, and concrete slab on top of the soil backfill were applied as repair methods to the 2-D arch models. A review of the results has shown an increase in arch stiffness, decrease in deflections and a significant improvement in the ultimate load carrying capacity. A significant effect on the pressure distribution on the arch barrel was observed due to the application of the concrete slab on top of the backfill. Stitching of arch barrel and the barrel to the spandrels, applying partial saddle concrete and strengthening of spandrel wall using reinforced concrete were tested in the 3-D arch models. The results showed improvements in the stiffness and ultimate arch load carrying capacity due to these repair techniques. The results provide a valuable data base for validation of numerical models and an initial attempt to use them with a commercial finite element program is included.
4
Gong, Nai-Guang. « Finite element analysis of masonry arch bridges ». Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335791.
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5
Pytlos, Michal. « New tools for modelling soil-filled masonry arch bridges ». Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/13674/.
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This study is concerned with the development of new numerical and physical tools suitable for modelling soil-filled masonry arch bridges. Firstly, a novel modelling approach is presented which makes use of the Box2D rigid body physics engine, widely used in the computer games industry. A description of the simulation method implemented in Box2D is provided and it is shown that this tool is capable of accurately simulating disc and block interaction dynamics, and can successfully capture the critical state response of granular media. Four Box2D based computer programs, constituting a ‘virtual laboratory’, are presented and are shown to be capable of accurately simulating load tests to failure on both bare and soil-filled masonry arches. It is also demonstrated that the macro-scale properties of a virtual soil material, modelled as an assembly of randomly shaped polygons, are independent of the simulated scenario. Practical issues associated with the use of Box2D as a modelling tool are considered and advantages compared with the traditional distinct element method are discussed. Secondly, an innovative experimental facility developed by the author and suitable for testing medium-scale sand-filled masonry arch bridges is described. The test facility features a novel sand conveyance and pouring system which provides very good control over backfill properties and significantly speeds up the deposition process. Initial test results from the test facility are described and recommendations for future work are made.
6
Nzuza, Mbongeni Hopewell Sabelo. « Thermo-mechamical modelling of arch dams for performance assessment ». Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/5017.
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Includes abstract.Includes bibliographical references.
This document underscores various temperature related components and procedures for undertaking a successful performance analysis of concrete arch dams. Arch dams experience high temperature variations, which are generally assessed using finite element models. Deterioration of arch dams is caused principally by thermal effects, with 19% cases attributed to freezing and thawing, and 9% to temperature variations (Daoudu et al., 1997). The temperature loading conditions cause a high expanse of stresses at the various interface locations due to change in environmental conditions. Past research has shown that stresses caused by temperature change can be larger than those from reservoir loading (Bureau of Reclamation, 1977). The proposed finite element model for this study focuses on the performance assessment of arch dams in operation due to thermal loading.
7
Vezi, Mfundo. « Dynamic modelling of arch dams in the ambient state ». Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9083.
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Includes bibliographical references.To date, dam failures have resulted in significant losses in the commercial economy and in human life. Raising awareness in the field of structural health monitoring is neccesary to develop contemporary structural analysis and monitoring methods to ensure the integrity of these structures. Hence, the research aims at developing an analytical formulation that can be used in the dynamic modelling of arch dams, for structural health monitoring purposes. A hypothetical arch dam model was created to investigate the influence of a reservoir’s orientation and geometry on the dam’s dynamic properties, and the discrepancies between the Westergaard and Fluid Structure Interaction (FSI) analysis methods. The two analysis methods were then utilized to develop an updatable finite element model, in a case study pertaining to the 72m high Roode Elsberg concrete-arch dam. Thereafter, ambient vibration tests were conducted on the Roode Elsberg dam to measure its dynamic properties and validate the finite element models. The excitation on the dam was provided by the wind and the reservoir flowing over the spillway. Vibrations of the dam were measured and recorded by accelerometers placed on the cantilevered arch blocks. Finally, the Frequency Domain Decomposition (FDD) algorithm was used to analyse the acquired data and identify the natural frequencies of the dam.
8
Taunton, Paul R. « Centrifuge modelling of soil/masonry structure interaction ». Thesis, Cardiff University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244112.
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9
Javidi, Shirvan Alireza. « Modelling of Electric Arc Welding : arc-electrode coupling ». Licentiate thesis, Högskolan Väst, Avd för maskinteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-5826.
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Arc welding still requires deeper process understanding and more accurateprediction of the heat transferred to the base metal. This can be provided by CFD modelling.Most works done to model arc discharge using CFD consider the arc corealone. Arc core simulation requires applying extrapolated experimental data asboundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arcmodel. The most critical part is then the interface layer between the electrodesand the arc core. This interface is complex and non-uniform, with specific physicalphenomena.The present work reviews the concepts of plasma and arc discharges that areuseful for this problem. The main sub-regions of the model are described, andtheir dominant physical roles are discussed.The coupled arc-electrode model is developed in different steps. First couplingsolid and fluid regions for a simpler problem without complex couplinginterface. This is applied to a laser welding problem using the CFD softwareOpenFOAM. The second step is the modelling of the interface layer betweencathode and arc, or cathode layer. Different modelling approaches available inthe literature are studied to determine their advantages and drawbacks. One ofthem developed by Cayla is used and further improved so as to satisfy the basicprinciples of charge and energy conservation in the different regions of thecathode layer. A numerical procedure is presented. The model, implementedin MATLAB, is tested for different arc core and cathode conditions. The maincharacteristics calculated with the interface layer model are in good agreementwith the reference literature. The future step will be the implementation of theinterface layer model in OpenFOAM.
10
Zhang, Quan. « Modelling of turbulent SF6 switching arcs ». Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2013339/.
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There is an overwhelming experimental and theoretical evidence indicating SF6 arc burning in a supersonic nozzle (known as the switching arc) is turbulent and in local thermodynamic equilibrium (LTE). Such an arcing arrangement is commonly used as the interrupter in gas blast circuit breakers. In order to reduce the development cost of gas blast circuit breakers, it is highly desirable to predict the arc behaviour under the operational conditions encountered in a power system. The major difficulty in achieving full computer aided predictive design of gas blast circuit breakers is the satisfactory prediction of the thermal interruption capability of an arc under turbulent conditions. Mathematical modelling of turbulent SF6 switching arcs, thus, forms the subject matter of this thesis. The approach for the modelling of turbulent switching arcs is similar to that for turbulent shear flows due to a direct resemblance between a nozzle arc and a round free jet both of which are dominated by shear flow. The conservation equations for switching arcs are, therefore, derived using Reynolds’s approach. The closure of these equations is based on the adoption of Boussinesq assumption to relate Reynolds stress to the time averaged velocity gradients through eddy viscosity. The turbulent heat flux is assumed to be related to Reynolds stress through a constant turbulent Prandtl number. Additional equations are introduced to determine the turbulence length scale and velocity scale required by eddy viscosity, which are provided by turbulence models. There are numerous turbulence models but none of them are specifically devised for switching arcs. The objective of the present investigation is, therefore, to choose relevant turbulence models to model turbulent SF6 switching arcs. Our choice of turbulence models is restricted to those which have been applied with success to similar flow conditions as those of a switching arc as well as their suitability for engineering application. We therefore choose the standard k-epsilon model and its two variants (the Chen-Kim model and the RNG model) for the modelling of SF6 turbulent switching arc. Since the application of the Prandtl mixing length model to SF6 switching arcs has met considerable success, this turbulence model is included in our investigation for comparison. In order to demonstrate the effects of turbulence, results based on laminar flow model are presented. Therefore, altogether five flow models have been used to study the nozzle arcs. Computational results are obtained by the five flow models under a wide range of discharge conditions in terms of different nozzle geometries, the rate of change of current (di/dt) before current zero and the stagnation pressure (P0). A detailed analysis of the physical mechanisms encompassed in each flow model is given to show the adequacy of a particular model in describing the rapidly varying arc during current zero period. The computed values of the critical rate of rise of recovery voltage (RRRV) are compared with corresponding measurements. It is found that RRRV predicted by laminar flow model is a few orders of magnitude lower than that measured, which indicates that turbulence plays a decisive role in the determination of thermal interruption capability of a nozzle arc. Of the four turbulence models, the Prandtl mixing length model gives the best prediction of RRRV when compared with experimental results. The drawback is that the value of the turbulence parameter of the Prandtl mixing length model needs to be derived from one test result for a given geometry. With our current understanding of the physics of turbulent arcs, the Prandtl mixing length model is the only turbulence model which can be used to predict the thermal interruption capability of a nozzle arc arrangement.
11
Wang, Junzhe. « Numerical modelling of masonry arch bridges : investigation of spandrel wall failure ». Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629673.
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Masonry arch bridges still play an important role in the transportation infrastructure today in the United Kingdom. Previous research has mainly focused on the load carrying capacity in the span direction. The three dimensional behaviour is often investigated by simplifying into two dimensions with modified arch parameters but these simplified analyses cannot represent all aspects of behaviour. Spandrel wall failure in some railway masonry arch bridges has raised concerns recently, and this is one aspect which cannot be modelled in two dimensions. This thesis presents a research which attempts to model the interaction behaviour between arch, backfill and spandrel wall with the aim of representing the three dimensional nature of real bridges. It mainly focuses on the spandrel wall defects under increasing load, including crack development across the wall and longitudinal cracks in the arch barrel underneath spandrel wall. Experimental results from the laboratory tests on engineering blue brick and a hydraulic premixed mortar as well as brickwork masonry specimens are presented. Numerical analysis was initially performed on these brickwork masonry specimens for validation. Three dimensional FE models were proposed for both small and large scale bridges. The general behaviour of the small scale bridge under rolling load and large scale bridge under increasing load were studied. Reasonable agreement between the FE analyses and experimental results from previous literature was obtained, indicating the model validated for small masonry specimens could be scaled up to full-scale bridges. A series of computer models were constructed to investigate the relationship between a range of geometric and material parameters and the lateral behaviour of arch bridges. The backfill depth and spandrel wall thickness have greatest impact on both bridge strength and lateral behaviour. The fill properties also have an importance influence on the load carrying capacity. This provides an indication of which bridge should be more closely monitored for spandrel wall defects. Separate FE models was constructed to simulate existing longitudinal cracks found in the arch barrel for old bridges and the influence of strengthening of spandrel wall with tie bars. The general behaviour under a concentrated load is studied and discussed. It has been demonstrated that it is possible to effectively model the three dimension behaviour of masonry arch bridges and in particular, spandrel wall failures.
12
Gadient, Yves. « ARCH-/GARCH-Modelle und deterministisches Chaos : eine empirische Analyse von Renditezeitreihen des Swiss Market Index (SMI) / ». [S.l.] : [s.n.], 2006. http://www.gbv.de/dms/zbw/520528271.pdf.
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Lima, Tatyanna Nadabia de Souza. « Flexibilização do regime de metas inflacionárias por regras de política monetária ». Universidade Federal da Paraíba, 2011. http://tede.biblioteca.ufpb.br:8080/handle/tede/4975.
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The objective is to achieve and suggest the inclusion of a financial indicator in the monetary policy rule that captures oscillations in capital markets, thereby promoting the flexibility of the inflation targeting system in order to preserve its effectiveness and transparency. It is argued that in periods of high volatility, the performance should be broader monitoring of financial assets in an attempt to avoid a process of asset deflation which led the economy into recession. The theoretical basis of this work is guided studies of Bernanke and Gertler (1999, 2000) that argue pro-introduction of a financial variable in the Taylor rule; the monetary policy should take into account the fluctuations in the stock market when they alter the forecast of future inflation. The models Vector autoregression (VAR) and extensions of the ARCH model will be addressed in order to justify the inclusion of the financial indicator in the system of inflation targets. It was observed that the volatility models presented persistence in the crisis period (2007-2009) for the financial variable while for the SELIC, the persistence of shocks has been lower intensity which implies that monetary policy may not be reacting properly variations in the financial market. For the VAR model, there was confirmation of the central hypothesis of the work since, in time of crisis, the effect on the financial indicator of the SELIC rate is higher compared to pre-crisis period. Therefore, the results support the hypothesis of Bernanke and Gertler (1999) that the Central Bank should consider the financial market only in times of high volatility, and clearly present their strategies and reports of communication with the market.
O objetivo é obter e sugerir a inclusão de um indicador financeiro na regra de política monetária que capte as oscilações no mercado de capitais, promovendo, assim, a flexibilização do regime de metas inflacionárias de forma a preservar a sua eficácia e transparência. Argumenta-se que em períodos de grande volatilidade, seja conveniente a atuação mais ampla no monitoramento dos ativos financeiros buscando evitar um processo de deflação de ativos que conduzisse a economia à recessão. A base teórica deste trabalho pauta-se nos estudos de Bernanke e Gertler (1999, 2000) que argumentam pró-introdução de uma variável financeira na Regra de Taylor; a política monetária deve levar em consideração as oscilações no mercado de capitais quando estas alteram a previsão de inflação futura. Os modelos de Vetores Auto-Regressivos (VAR) e extensões do modelo ARCH serão utilizados como forma de justificar a inclusão do indicador financeiro no sistema de metas inflacionárias. Observou-se que os modelos de volatilidade apresentaram persistência no período de crise (2007-2009) para a variável financeira enquanto que para a SELIC, a persistência dos choques tem sido em menor intensidade o que implica que a política monetária pode não estar reagindo adequadamente às variações no mercado financeiro. Para o modelo VAR, houve confirmação da hipótese central do trabalho visto que, no período de crise, o efeito do indicador financeiro sobre a SELIC é maior comparado ao período pré-crise. Portanto, os resultados apóiam a hipótese de Bernanke e Gertler (1999) de que o Banco Central deve levar em consideração o mercado financeiro apenas em momentos de grande volatilidade, e apresentar claramente suas estratégias e seus relatórios de comunicação com o mercado.
14
Markgren, Jakob. « CFD Modelling of Pressure-control Devices in Substations ». Thesis, Umeå universitet, Institutionen för fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96455.
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Alliwa, Maher. « Modelling inflation, output growth and their uncertainties ». Thesis, Brunel University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707765.
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This thesis consists of three studies that cover topics in inflation and output growth, and their uncertainties in G7 and developing countries. We utilise the Consumer Price Index (CPI) and Industrial Price Index (IPI) as proxies for the inflation rate (price level) and the growth rate (output), respectively. Chapter 2 considers the case of three developing countries Turkey, Egypt and Syria. We analyse the inflation and growth using asymmetric PGARCH model. In accordance with this, we estimate all the models using two alternative distributions the normal and Student’s t. Moreover, dummy variables are chosen in the inflation data according to some economic events in Turkey, Egypt and Syria. Even more, the mean equation is adjusted to include these dummy variables on the intercept. To summarize, the results show an evidence of the Cukierman–Meltzer (1986) hypothesis, which is labelled as the ‘opportunistic Fed’ by Grier and Perry (1998), in Egypt and Syria. On the other hand, an evidence of the Holland (1995) hypothesis is obtained in Turkey, this result suggests that the ‘stabilizing Fed’ notion is plausible. Moreover, an evidence for the first leg of Friedman (1977) hypothesis is obtained in Egypt and Turkey. Chapter 3 examines the causal relationship between inflation and output growth, and their variabilities for G7 countries by applying the bivariate constant conditional correlation CCC – GARCH (1,1)-ML models. Moreover, we employ the models including dummy variables in the mean equations to investigate the impact of economic events on inflation and output. Briefly, there are evidences of the second leg of Friedman (1977) hypothesis in the US, UK, Germany, Italy, France and Canada while there is an evidence of Dotsey and Sarte (2000) in Japan. In addition, there are evidences for positive effect of inflation uncertainty on inflation in the US, Germany, Japan and France in line of Cukierman and Meltzer (1986) hypothesis. Moreover, the results of estimation CCC-GARCH (1,1) in mean models including dummy variables highlight a strong support for the two legs of Friedman (1977) hypothesis and Cukierman and Meltzer (1986). Lastly, Chapter 4 is based on examining the inflation rates for three developing countries Turkey, Syria and Egypt by applying the Bai and Perron (2003) breakpoint specification technique in the monthly inflation data of our sample. As a result, three possible break points for each of the inflation rates in the conditional variance have been determined. In addition, we employ GARCH model to control the breaks in the conditional mean and variance equations. To conclude, the autoregressive coefficients seem to cause a statistically significant impact on the breaks only in the case of Turkey, also, the parameters of the mean equation show time varying characteristics across three breaks. As far as the conditional variance is concerned the ARCH parameter (?) shows no time varying behaviour while for the GARCH parameter only one significant break seems to impact the inflation rate in Syria.
16
Arfelli, Francesco. « Bowstring bridges : static behaviour, critical issues and FEM modelling ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25735/.
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The present Master’s Thesis paper is aimed at analysing the fundamental characteristics of the static behaviour of structural arch schemes focusing the attention on two critical issues and their respective practical solutions as applied to a real study case.
After providing a theoretical and historic overview of arches, two crucial aspects of the design phase of an arch bridge have been chosen and discussed. Thus, the construction project of a real structure is taken into consideration with the purpose of discussing a possible solution to the issues highlighted previously.
The study case is identified in the new bowstring bridge crossing the River Enza, in the suburbs of Parma. The static analysis of the structure is carried out comparing the FEM results to the analytical findings.
17
Valderhaug, Aasgeir Mikael. « Modelling and control of submerged-arc ferrosilicon furnaces ». Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for teknisk kybernetikk, 1992. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19565.
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Absi, Alfaro Sadek Crisostomo. « Mathematical modelling of narrow gap submerged arc welding ». Thesis, Cranfield University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232955.
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Cronje, M. « Finite element modelling of shielded metal arc welding ». Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/2649.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005.This study involved the modelling and verification of the Shielded Metal Arc Welding of mild steel with the focus on displacement and temperature distribution prediction of welded plates. The project was divided into three phases namely; the literature survey into finite element modelling of welding processes, the modelling of a welding process and verification of the modelling with experimental results. A working welding model was created using a commercial finite element software package with the capabilities to model welding processes. The welding model was systematically developed from a two-dimensional model into a threedimensional full physics process model. Experimental measured welding heat input parameters were applied in the model, temperature dependent material properties were applied and actual structural restraints from the experiments were modelled. Displacement and temperature distributions were measured on mild steel plates welded with the Shielded Metal Arc Welding process. The plate temperature was measured at various locations with K-type thermocouples spot welded onto the plates. Plate deformation was measured at various stages of the manufacturing process. Tendencies in plate displacement were investigated with a change in certain welding parameters. The finite element model was verified and good correlations were found, especially for the temperature distribution in the welded plates.
20
Caballero, Jorge Tomasio. « Comparação da estabilidade dos arcos dentários em pacientes com e sem fissura labiopalatina após tratamento ortodôntico/reabilitador ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/25/25146/tde-31082018-174817/.
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O propósito do presente estudo foi comparar as variações das dimensões lineares dos arcos dentários de pacientes com fissura labiopalatina após o tratamento ortodôntico e protético com prótese parcial fixa e pacientes sem fissura labiopalatina imediatamente após a ortodontia e pelo menos um ano após a remoção do aparelho ortodôntico. Este estudo longitudinal retrospectivo, foi composto por uma amostra de 70 modelos digitais, dos quais 30 modelos eram de pacientes com fissura labiopalatina unilateral completa, que receberam uma prótese parcial fixa na região da fissura (n=15), grupo fissura (GF); e 40 modelos de pacientes sem fissura labiopalatina (n=20), grupo controle (GC); com idade entre 18 e 30 anos. Os modelos foram obtidos em dois tempos: (T1) término do tratamento ortodôntico, e (T2) pelo menos 1 ano após a reabilitação protética (GF); e (T1) término do tratamento ortodôntico e (T2) pelo menos um ano após remoção do aparelho ortodôntico (GC). As medidas das dimensões dos arcos dentários foram realizadas diretamente nas imagens escaneadas, por meio do Scanner 3Shapes R700TM e mensuradas pelo Software Appliance Designer. As dimensões avaliadas foram: distância inter-caninos, distância inter-1os. pré-molares, distância inter-molares, e comprimento incisivo-molar. Um examinador previamente calibrado e treinado realizou as avaliações. Foram realizadas comparações entre os grupos, em tempos distintos (T1 e T2); e na diferença entre T2 e T1 nos grupos (GF e GC); utilizando o teste T ou de Mann- Whitney, com um nível de significância de 5% (p<0.05). Houve diferença estatística (p=0,005) no valor da variação de T2-T1 na distância inter-caninos com aumento da distância no GF e diminuição no GC. Na variação da distância inter-prémolar o GF apresentou diminuição do valor e o GC mostrou aumento, com diferença estatisticamente significativa (p=0,008). Nos demais parâmetros (inter-molar e incisivo molar) não houve diferença estatística. Não houve estabilidade no GC na distância inter-caninos e observou-se estabilidade no GF, não houve estabilidade no GF na distância inter-pré molar e houve estabilidade no GC. A Prótese Parcial Fixa estabiliza os resultados obtidos com a ortodontia.The aim of the present study was to compare the linear dimensions of dental arches of patients with cleft lip and palate following orthodontic and prosthetic treatment with fixed partial denture and patients without cleft lip and palate immediately after orthodontics and at least one year after removal of the orthodontic appliance. This retrospective longitudinal study consisted of a sample of 70 digital models, of which 30 models were from patients with complete unilateral cleft lip and palate, who received a fixed partial prosthesis in the cleft region (n = 15), cleft lip and palate group (CLPG); and 40 patient models without cleft lip and palate (n = 20), control group (CG); aged between 18 and 30 years. The models were obtained in two stages: (T1) end of orthodontic treatment, and (T2) at least 1 year after prosthetic rehabilitation (CLPG); and (T1) end of orthodontic treatment and (T2) at least one year after removal of the orthodontic appliance (CG). Measurements of the dimensions of the dental arches were performed directly on the scanned images, using the 3Shape\'s R700TM Scanner and measured by the Appliance Designer Software. The dimensions evaluated were: inter-canine distance, inter-1st premolars distance, intermolar distance, and incisormolar length. A pre-calibrated and trained examiner performed the assessments. Comparisons were made between the groups at different times (T1 and T2); and in the difference between T2 and T1 in the groups (CLPG and CG); using the T or Mann- Whitney test, with a significance level of 5% (p <0.05). There was a statistical difference (p = 0.005) in the value of the T2-T1 variation in the intercanine distance with increase in the ClG distance and decrease in the CG. In the interprémolar distance variation the ClG presented a decrease in value and the CG showed an increase, with a statistically significant difference (p = 0.008). In the other parameters (intermolar and molar incisors) there was no statistical difference. There was not stability in the CG in the intercanine distance and there was stability in the CLPG, there was stability in the CG in the inter-pre-molar distance and there was no stability in the CLPG. Partial Fixed Prosthesis stabilizes the results obtained with orthodontics.
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Wendelstorf, Jens. « Ab initio modelling of thermal plasma gas discharges (electric arcs) ». [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961148527.
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Goodarzi, Massoud. « Mathematical modelling of gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) processes ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27936.pdf.
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Tibulo, Cleiton. « MODELOS DE SÉRIES TEMPORAIS APLICADOS A DADOS DE UMIDADE RELATIVA DO AR ». Universidade Federal de Santa Maria, 2014. http://repositorio.ufsm.br/handle/1/8334.
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Time series model have been used in many areas of knowledge and have become a current necessity for companies to survive in a globalized and competitive market, as well as climatic factors that have always been a concern because of the different ways they interfere in human life. In this context, this work aims to present a comparison among the performances by the following models of time series: ARIMA, ARMAX and Exponential Smoothing, adjusted to air relative humidity (UR) and also to verify the volatility present in the series through non-linear models ARCH/GARCH, adjusted to residues of the ARIMA and ARMAX models. The data were collected from INMET from October, 1st to January, 22nd, 2014. In the comparison of the results and the selection of the best model, the criteria MAPE, EQM, MAD and SSE were used. The results showed that the model ARMAX(3,0), with the inclusion of exogenous variables produced better forecast results, compared to the other models SARMA(3,0)(1,1)12 and the Holt-Winters multiplicative. In the volatility study of the series via non-linear ARCH(1), adjusted to the quadrants of SARMA(3,0)(1,1)12 and ARMAX(3,0) residues, it was observed that the volatility does not tend to influence the future long-term observations. It was then concluded that the classes of models used and compared in this study, for data of a climatologic variable, showed a good performance and adjustment. We highlight the broad usage possibility in the techniques of temporal series when it is necessary to make forecasts and also to describe a temporal process, being able to be used as an efficient support tool in decision making.Modelos de séries temporais vêm sendo empregados em diversas áreas do conhecimento e têm surgido como necessidade atual para empresas sobreviverem em um mercado globalizado e competitivo, bem como fatores climáticos sempre foram motivo de preocupação pelas diferentes formas que interferem na vida humana. Nesse contexto, o presente trabalho tem por objetivo apresentar uma comparação do desempenho das classes de modelos de séries temporais ARIMA, ARMAX e Alisamento Exponencial, ajustados a dados de umidade relativa do ar (UR) e verificar a volatilidade presente na série por meio de modelos não-lineares ARCH/GARCH ajustados aos resíduos dos modelos ARIMA e ARMAX. Os dados foram coletados junto ao INMET no período de 01 de outubro de 2001 a 22 de janeiro de 2014. Na comparação dos resultados e na seleção do melhor modelo foram utilizados os critérios MAPE, EQM, MAD e SSE. Os resultados mostraram que o modelo ARMAX(3,0) com a inclusão de variáveis exógenas produziu melhores resultados de previsão em relação aos seus concorrentes SARMA(3,0)(1,1)12 e o Holt-Winters multiplicativo. No estudo da volatilidade da série via modelo não-linear ARCH(1), ajustado aos quadrados dos resíduos dos modelos SARMA(3,0)(1,1)12 e ARMAX(3,0), observou-se que a volatilidade não tende a influenciar as observações futuras em longo prazo. Conclui-se que as classes de modelos utilizadas e comparadas neste estudo, para dados de uma variável climatológica, demonstraram bom desempenho e ajuste. Destaca-se a ampla possibilidade de utilização das técnicas de séries temporais quando se deseja fazer previsões e descrever um processo temporal, podendo ser utilizadas como ferramenta eficiente de apoio nas tomadas de decisão.
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Westermoen, Andreas. « Modelling of Dynamic Arc Behaviour in a Plasma Reactor ». Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1709.
Texte intégral
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MacRosty, Richard Swartz Christopher L. E. « Modelling, optimization and control of an electric arc furnace ». *McMaster only, 2005.
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Ridings, Gareth E. « Neural network modelling of submerged arc weld metal properties ». Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/34693.
Texte intégralRésumé :
There are many problems in welding metallurgy for which it is difficult to develop a first principles scientific model due to their complexity. A significant problem faced by today's welding engineers, is the need to relate welding parameters to the quality of the finished weld. This is usually done by experience, and the need for many experimental trials, eventually leading to optimal welding parameters. Important characteristics in the evaluation of line-pipe seam weld quality are the weld bead shape and size, which can have a significant effect on the microstructure and mechanical properties of the weldment through heat flow effects. Properties of the final weld may therefore be difficult to predict, especially quantities such as weld metal toughness, which are known to be dependent on many factors. One approach to such complex problems is to use neural networks. A neural network is an artificial simulation of the brain which models data through a learning process and stores the information as a set of rules akin to knowledge. This research is concerned with the application of neural network techniques to the prediction of the mechanical and physical properties, including the shape of the weld bead, of submerged arc line-pipe steel welds. A limited experimental investigation has been carried out using optical and transmission electron microscopy to establish an understanding of the complex microstructures that result from the welding processes used in the production of line-pipe.
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Crisp, Jennifer J. « Measurement and modelling of Arc faults in flameproof enclosures ». Thesis, Queensland University of Technology, 1993.
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High-power
enclosures
arcing experiments are described
of differing styles and volumes.
for seven flameproof
The tests involve
introducing into the enclosures, single and three phase arcs faults,
with currents up to 14000A, supplied at 1.lkV, 3.3kV and 6.6kV. The
experiments use two styles of electrode, one designed to contain the
arc, the other permitting arc bowing. Electrode spacings range from
69mm to 150mm.
Pressure rise and flame containment capability are examined for the
cases of arcing in the enclosures, and combined methane and arcing
tests, compared with methane spark ignition tests. The effect on
pressure rise and flame containment, of exposing common organic
insulating materials to the presence of arcing is also examined.
Simple models are derived to describe the pressure-time development
in enclosures containing high-power arc faults, and those with
methane also present. Implications for the design of flameproof
enclosures are then considered in the light of these results.
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La, Torre Flores Carlos Alberto. « “Modelos ARCH Y GARCH aplicados a series financieras peruanas, para la variable tipo de cambio” ». Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2018. https://hdl.handle.net/20.500.12672/8170.
Texte intégralRésumé :
El documento digital no refiere un asesorPublicación a texto completo no autorizada por el autor
Realiza un estudio sobre la variable tipo de cambio para el caso peruano, para ello se formulan modelos de volatilidad como los ARCH desarrollados por Robert Engle (1982) y los GARCH desarrollados por Bollerslev (1986). Se trata básicamente de comparar ambos modelos ARCH y GARCH y determinar cuál de ellos realiza mejores estimaciones y pronósticos para la variable en estudio, nuestros datos comprende desde el 1 de enero de 2013 hasta el 31 de marzo del 2017 contando con un total de 1105 observaciones tomadas en los cinco días laborales del mercado intercambiario.
Trabajo de suficiencia profesional
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Scotti, A. « Process modelling to establish control algorithms for automated GMAW ». Thesis, Cranfield University, 1991. http://dspace.lib.cranfield.ac.uk/handle/1826/10518.
Texte intégralRésumé :
The feasibility of fully automatic GMAW processes may rely on the
development of sophisticated equipment to emulate the manual welding
torch oscillation pattern or on the development of high level methods of
control to prevent the appearance of defects, especially the lack of sidewall
fusion. An intermediate solution is to optimise the weaving
parameters of a conventional pattern oscillator in such a way as to
minimise the level of rejection.
A prototype of a computerised system to work with Pulsed-GMAW
equipment, in the vertical-up position, was proposed to produce a minimal
level of rejection for welds in plates up to 25 mm thick. The system
basically consists of optimised mode control algorithms, based on
theoretical and experimental models of weld pool behaviour. Three tasks
are performed by the system; the selection of parameters for an optimum
working point, an off-line simulation of the operation and real-time error
monitoring of the process.
Statistical experimental modelling was applied in order to build
most of the optimised models, because of the large number of variables
to be treated and their complex inter-correlation. The welding variables
were correlated with single responses. Partial and Correlation Analysis
techniques were used to discover the relationship between the variables
and the responses. Regression Analysis was then applied as a means of
obtaining the 'weight' of the most significant variables. Finally, since
some variables were found to be collinear, a corrective technique for
biased variables was employed.
Acceptance criteria for bead shapes were proposed and assessed.
The effect of the oscillation parameters and other welding variables on
the bead formation was analyzed and an operational 'envelope' for the
parameters determined. A theoretical approach to predict the occurrence
of poorly shaped beads, due to the lack of metal bridge between the joint
walls, was successfully developed and applied in parallel with the
statistical experimental methods. Equations for optimising the bead shape
and for determining the operational envelope contours were subsequently
generated and evaluated.
An extension of the system to an actual adaptive control scheme
was discussed and sensors and signals to be used were evaluated. Finally,
a process instability phenomenon in long test plates was identified and
investigated. This instability may prevent the use of GMA W in some
conditions in the vertical-up position.
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Reis, Daniel Leal de Paula Esteves dos. « Análise de desempenho de indicadores de volatilidade ». Universidade Federal de Juiz de Fora, 2011. https://repositorio.ufjf.br/jspui/handle/ufjf/2124.
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FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais
Medidas de volatilidade se constituem numa preocupação por parte de estudiosos e profissionais do mercado financeiro. Modelos da família ARCH/GARCH a partir dos retornos diários produzem um indicador de volatilidade, mas, não conferem ao pesquisador uma medida observável do grau de variabilidade dos retornos em torno de seu valor esperado. A recente disponibilidade de dados de frequência inferior a um dia de negociação permitiu a elaboração de indicadores de volatilidade observáveis por meio de uma medida conhecida como volatilidade realizada. A partir de então, é possível elaborar um indicador observável de volatilidade diária com base em dados de natureza intradiária, de modo a representar uma medida mais apropriada do grau de risco de um ativo ou carteira de ativos, e, a partir de então, estimar a volatilidade por meio de processo da família ARIMA. De posse dos dados de alta-frequência de um papel preferencial da Petrobrás S.A., o presente trabalho se propõe, portanto, em construir a medida de volatilidade realizada por meio da soma dos quadrados dos retornos obtidos em intervalos regulares (5, 15 e 30 minutos) durante cada dia de negociação do papel PETR4 durante o período de 02/01/2007 à 29/10/2010. Posteriormente à criação do indicador de volatilidade realizada que se supõe como mais apropriado para se mensurar o grau de risco, pretende-se comparar a qualidade do ajustamento e a capacidade preditiva de cada um dos métodos de modelagem da volatilidade. A comparação dos modelos baseados em dados diários e intradiários dar-se-á por meio do cômputo do erro quadrático médio (EQM) e dos testes de Diebold e Mariano e de Harvey para avaliação da acurácia preditiva dos modelos. Os resultados mostraram que, em geral, os modelos da família ARIMA são mais apropriados para a avaliação do grau de ajustamento, e produz previsões mais satisfatórias que os modelos da família ARCH/GARCH.
Volatility measures constitute a concern among scholars and professionals of the financial market. Models of the ARCH/GARCH class from the daily returns produce an indicator of volatility, but do not give the researcher an observable measure of the degree of variability of returns around their expected value. The recent availability of data at frequencies below a trading day allowed the development of indicators of volatility observable through a measurement known as realized volatility. Since then, they can build an observable indicator of daily volatility based on intraday data, so as to represent a more appropriate measure of the riskiness of an asset, and from then estimate volatility through a process of ARIMA family. Provided with the data of a high frequency preferential role of Petrobrás S. A., the present paper therefore proposes to construct a measure of realized volatility by the sum of the squares of the returns obtained at regular intervals (5, 15 and 30 minutes ) during each trading day for the paper PETR4 during 02/01/2007 to 29/10/2010. After the creation of the realized volatility indicator that is supposed to be more appropriate to measure the degree of risk, the intent is to compare the goodness of fit and predictive ability of each of the methods of volatility’s models. The comparison of models based on daily data and intraday give will be through the calculation of the mean square error (MSE) and tests of Diebold and Mariano and Harvey to evaluate the predictive accuracy of models. The results in general showed that the models of the ARIMA class are more suitable for assessing the degree of adjustment and produces predictions more satisfactory than the models of the ARCH/GARCH class.
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Gaio, Luiz Eduardo. « Gestão de riscos no mercado financeiro internacional : uma análise comparativa entre modelos de volatilidade para estimação do Value-at-Risk ». Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/96/96132/tde-03052010-173001/.
Texte intégralRésumé :
Durante os últimos anos, tem havido muitas mudanças na maneira como as instituições financeiras avaliam o risco. As regulações têm tido um papel muito importante no desenvolvimento das técnicas de medição do risco. Diante das diversidades de técnicas de estimação e análise de risco utilizadas pelas bolsas de valores e de futuros, nacionais e internacionais, bem como as Clearings de controle de risco, este estudo propôs uma análise comparativo de modelos de volatilidade para o cálculo do Value-at-Risk (VaR) aplicados aos principais índices de ações do mercado financeiro internacional. Utilizouse os modelos de volatilidade condicional da família ARCH levando em consideração a presença de longa dependência em seus retornos (memória longa) e assimetria na volatilidade. Em específico, utilizaram-se os modelos GARCH, EGARCH, APARCH, FIGARCH, FIEGARCH, FIAPARCH e HYGARCH estimados a parir de quatro diferentes distribuições, Normal, t-Student, G.E.D. e t-Student Assimétrica. Analisaramse os índices dos principais mercados de ações do mundo, sendo: Dow Jones, S&P 500, Nasdaq, Ibovespa, FTSE e Nikkei 225. Testou-se também a capacidade preditiva do modelo Riskmetrics desenvolvido pelo J.P. Morgan para o calculo do VaR, comparado com os modelos de volatilidade. Os resultados obtidos sugerem que o pacote desenvolvido pelo J.P.Morgan não se aplica adequadamente à realidade do mercado acionário mundial, como ferramenta de gestão e controle do risco das oscilações dos preços das ações de empresas negociadas nas bolsas de Nova Iorque, Nasdaq, BM&FBOVESPA, bolsa de Londres e bolsa de Tóquio. Os modelos que consideram o efeito de memória longa na volatilidade condicional dos retornos dos índices, em especial o modelo FIAPARCH (1,d,1), foram os que obtiveram melhor ajuste e desempenho preditivo do risco de mercado (Value-at-Risk), conforme valores apresentados pelo teste de razão de falha proposto por Kupiec (1995).In recent years, there have been many changes in how financial institutions assess risk. The regulations have had a very important role in the development of techniques for measuring risk. Considering the diversity of estimation techniques and risk analysis used by stock exchanges and futures, national and international, as well as clearing houses of risk control, this study proposed a comparative analysis of volatility models for calculating Value-at-Risk (VaR) to the major stock indexes of international finance. It used models of conditional volatility of the ARCH family taking into account the presence of long dependence on their returns (long memory) and asymmetry in volatility. Specifically, it used the models GARCH, EGARCH, APARCH, FIGARCH, FIEGARCH, FIAPARCH and HYGARCH estimated the birth of four different distributions, Normal, t-Student, GED and t-Student Asymmetric. It analyzed the contents of the major stock markets of the world, being: Dow Jones, S & P 500, NASDAQ, Bovespa index, FTSE and Nikkei 225. Was also tested the predictive ability of the RiskMetrics model developed by JP Morgan for the calculation of VaR, compared with the models of volatility. The results suggest that the package developed by JPMorgan does not apply adequately to the reality of global stock market as a tool to manage and control the risk of fluctuations in stock prices of companies traded on the New York Stock Exchange, Nasdaq, BM&FBOVESPA, London Stock Exchange and Tokyo Stock Exchange. Models that consider the effect of long memory in conditional volatility of returns of the indices, especially the model FIAPARCH (1, d, 1), were the ones showing better fit and predictive performance of market risk (Value-at-Risk) , according to figures provided by the ratio test proposed by Kupiec (1995).
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Rossetti, Nara. « Análise da volatilidade dos mercados de renda fixa e renda variável de países emergentes e desenvolvidos no período de 2000 a 2011 ». Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18157/tde-10092015-094310/.
Texte intégralRésumé :
O presente trabalho analisou as volatilidades dos mercados de renda fixa e variável de onze países, sendo eles: Brasil, Rússia, Índia, China, África do Sul (neste país apenas renda fixa), Argentina, Chile, México, Estados Unidos, Alemanha e Japão no período de janeiro de 2000 a dezembro de 2011. Os indicadores utilizados para representar cada mercado foram os índices dos mercados de ações e as taxas de juros interbancárias. Para tanto, o estudo se utilizou de modelos de heterocedasticidade condicional auto-regressiva: ARCH, GARCH, EGARCH, TGARCH e PGARCH, verificando quais destes processos eram mais eficientes para modelagem da volatilidade dos mercados dos países da amostra. Esta pesquisa também verificou qual dos modelos (ARIMA ou modelos GARCH e suas extensões) conseguiria prever melhor as séries de tempo analisadas. Além disso, por meio dos índices de correlação, covariância e causalidade Granger, foram comparados os retornos e a volatilidade do mercado de ações entre os países BRIC, entre os países latinos americanos e entre os países desenvolvidos e o Brasil. Os resultados sugerem que a volatilidade, tanto do mercado de renda fixa quanto do mercado de renda variável, é mais bem modelada por processos GARCH assimétricos (EGARCH e TGARCH), demonstrando efeitos de alavancagem nas séries estudadas. Quanto aos modelos de previsão, os modelos ARIMA, também para os dois mercados, mostrou-se mais eficiente que os modelos GARCH e suas extensões. Além disso, as volatilidades dos mercados de ações entre os países analisados parecem ser mais correlacionadas e possuir maior causalidade Granger do que os retornos destes países. Entre os dois mercados, renda fixa e variável dentro de cada país, as correlações dos retornos e da volatilidade são muito baixas, em algumas vezes negativa, e há pouca relação de causalidade Granger.This study analyzed the volatility of fixed income and stocks markets for eleven countries, namely: Brazil, Russia, India, China, South Africa (just fixed income), Argentina, Chile, Mexico, United States, Germany and Japan from January 2000 to December 2011, using interbank interest rate as a fixed income market indicator and stock index to each country, as a stock market indicator. Therefore, the study used models of autoregressive conditional heteroscedasticity: ARCH, GARCH, EGARCH, TGARCH e PGARCH to verify which of these processes were more effective for in volatility modeling in each country. This research also found that the models (ARIMA or GARCH models and their extensions) could be used as the best forecast models. Moreover, by means of correlation coefficients, covariance and Granger causality, were used to compare the returns and volatility of the stock market among the BRIC countries, among the Latin American countries and between developed countries and Brazil. The results suggest that the volatility of both the fixed income market as the stock market is best modeled by processes asymmetric GARCH (EGARCH and TGARCH) demonstrating leverage effects in the time series. Regarding prediction ARIMA models was more efficient for both markets than GARCH models and extensions. In addition, the volatility of stock markets across countries analyzed seem to be more correlated and have higher Granger causality than returns these countries. Between the two markets, for each country, the correlations of returns and volatility are very low, if not positive, and there is low Granger causality.
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Eid, Júnior William. « Avaliação de opções : o caso brasileiro : utilização de modelos Arch na estimação dos parâmetros ». reponame:Repositório Institucional do FGV, 1995. http://hdl.handle.net/10438/4431.
Texte intégralRésumé :
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Previous issue date: 1995-09-21T00:00:00ZO trabalho se refere à avaliação de opções através do modelo conhecido pelo nome de seus autores, Black-Scholes. É descrito o desenvolvimento da teoria de opções, desde os primórdios da existência de mercados organizados deste derivativo, no século XVII, até os mais importantes trabalhos dos primeiros anos da década de 1990. É destacado o papel fundamental da estimação correta dos parâmetros a serem inseridos no modelo de avaliação. Após esta revisão, um teste do modelo Black-Scholes é realizado no mercado de opções sobre ouro da BM&F, utilizando-se mecanismos tradicionais de estimação dos parâmetros e apurando-se a diferença existente entre o valor dado pelo modelo de avaliação e o observado no mercado. Novos mecanismos de apuração dos parâmetros fundamentais, volatilidade e taxa de juros, são propostos, baseados no comportamento das séries históricas a eles referentes. A análise deste comportamento mostra a adequação destas séries à uma classe de modelos econométricos conhecidos como ARCH - Autorregressive Conditional Heterocedasticity Model . Três novos testes do modelo Black-Scholes no mercado de opções são realizados: o primeiro usando a volatilidade estimada através de um modelo ARCH(1) e a taxa de juros estimada de forma tradicional, o segundo usando a taxa de juros estimada através de um modelo ARCH-M(1) e a volatilidade estimada de forma tradicional e, finalmente, o terceiro, usando a volatilidade estimada através de um modelo ARCH(1) e a taxa de juros estimada através de um modelo ARCH-M(1). As diferenças, nos três casos, entre os valores dados pelo modelo Black-Scholes e os observados no mercado, foram computadas. Os resultados indicaram que o uso da volatilidade estimada através do modelo ARCH(1) melhora a performance do modelo Black-Scholes, perfomance esta medida pelo erro quadrático médio entre os valores dados pelo modelo e os observados no mercado. O mesmo não ocorreu com a utilização da taxa de juros estimada pelo modelo ARCH-M(1), apesar da compatibilidade teórica apresentada entre a série temporal destas taxas e o modelo. O autor acredita que este resultado seja devido à problemas encontrados na estimação dos parâmetros deste modelo ARCH-M(1). Também a inserção conjunta dos dois parâmetros estimados através dos modelos da classe ARCH não foi frutífera, ainda em função dos problemas de estimação dos modelos referentes à taxa de juros. As conclusões básicas do trabalho indicam que as série temporais em estudo são modeláveis e que os modelos da classe ARCH se apresentam como promissores para este fim, ao menos no que tange à volatilidade.
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Herrmann, Frank. « Integration und Volatilität bei Emerging Markets / ». Wiesbaden : Dt. Univ.-Verl, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016088203&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Oscar, Ericsson. « Modelling of breaking arcs when they are extinguished by current zero-crossings ». Thesis, Uppsala universitet, Elektricitetslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-226204.
Texte intégralRésumé :
When breaking large currents in switching devices, arcs are created, which continue to carry the current. It is desirable to extinguish these in order to break the current. In this master thesis a model of the arcs behavior during current zero-crossings was made and put into a module, which is to be used when simulating electrical AC arcs. The module will be used when designing switches, e.g. contactors. When the current falls to 0 A there is a race between the transient recovery voltage and the dielectric strength, which determines if the arc will extinguish or restrike. The arc is extinguished if the dielectric strength is greater than the transient recovery voltage through the whole cycle. The transient recovery voltage is only dependent on the circuit used. The dielectric strength was found to mainly depend on the arc current, gap length and contact material. A model of the dielectric strength was made to determine if the arc will restrike or not.
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Khalaf, Gholam Hossein. « Neuro-fuzzy control modelling for gas metal arc welding process ». Thesis, Loughborough University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263585.
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Breznik, Alexander, et Truls Malmberg. « Volatilitetsprognoser för OMXS30 : Utvärdering av ARCH/GARCH-modeller till prognostisering av volatilitet för OMXS30 med realiserad volatilitet som referenspunkt ». Thesis, Örebro universitet, Handelshögskolan vid Örebro Universitet, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-67985.
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Modenesi, P. J. « Statistical modelling of the narrow gap gas metal arc welding process ». Thesis, Cranfield University, 1990. http://dspace.lib.cranfield.ac.uk/handle/1826/831.
Texte intégralRésumé :
The J-laying technique for the construction of offshore pipelines requires a fast welding process that can produce sound welds in the horizontal-vertical position. The suitability of narrow gap gas metal arc welding (NG-GMA W) process for this application was previously demonstrated. The present programme studied the influence of process parameters on the fusion characteristics of NG-GMA welding in a range of different shielding gas compositions and welding positions. Statistical techniques were employed for both designing the experimental programme and to process the data generated. A partial factorial design scheme was used to investigate the influence of input variables and their interaction in determining weld bead shape. Modelling equations were developed by multiple linear regression to represent different characteristics of the weld bead. Transformation of the response variable based on the Cox-Box method was commonly used to simplify the model format. Modelling results were analysed by graphical techniques including surface plots and a multiplot approach was developed in order to graphically assess the influence of up to four input variables on the bead shape. Conditions for acceptable bead formation were determined and the process sensitivity to minor changes in input parameters assessed. Asymmetrical base metal fusion in horizontalvertical welding is discussed and techniques to improve fusion presented. At the same time, the interaction between the power supply output characteristic and the bead geometry was studied for narrow gap joints and the effect of shielding gas composition on both process stability and fusion of the base metal was assessed. An arc instability mode that is strongly influenced by arc length, power supply characteristic and shielding gas composition was demonstrated and its properties investigated. An optimized shielding gas composition for narrow gap process was suggested.
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Davies, Mark H. « Numerical modelling of weld pool convection in gas metal arc welding / ». Title page, contents and abstract only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phd2563.pdf.
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Smailes, Allan J. « Thermal modelling of gas metal arc welding using finite element analysis / ». Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09ENS/09enss635.pdf.
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Ortega-Calderon, Jose Enrique. « Modelling and analysis of electric arc loads using harmonic domain techniques ». Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/445/.
Texte intégralRésumé :
Abstract It has been reported that as much as 12% of global electricity production goes into producing artificial light using arc discharge lamps and that global annual production of these lamps may be as much as 1.2 billion units. In the liquid steel production industry, one metric tone of steel demands, on average, 400 kW-hr and in the year 2007, the crude steel output reached 1,343.5 million metric tons. In both instances, engineered electric arcs are present and represent major loads in electrical power systems which require the utmost attention. They observe a highly non-linear behaviour with the capacity to export harmonic distortion and flicker into the power system. Electric arc furnace installations, in particular, are well-known to be sources of dynamic disturbances affecting neighbouring loads. Arc discharge lamps, on aggregate, may exhibit the same perturbing effect. Over the years, the non-linear nature of these loads and their ubiquitous nature have caught the interest of researchers in all corners of the world and from different backgrounds, including this author. The research work reported in this thesis advances current knowledge in the modelling and simulation of electric arcs with particular reference to arc discharge lamps with electromagnetic ballasts and electric arc furnaces with particular reference to operational unbalances and the impact in the installation of ancillary power electronics equipment. In these two quite distinct applications, linked by the presence of engineered electric arcs, the fundamental modelling item is a non-linear differential equation which encapsulates the physic of the electric arc by applying power balance principles. The non-linear differential equation uses the arc conductance as state variable and adapts well to model a wide range of characteristics for which a set of experimental coefficients are available. A fact of perhaps equal relevance is that the non-linear differential equation is amenable to algebraic representations using operational matrices and suitable for carrying out periodic steady-state solutions of electric circuits and systems. The modelling and numerical solution takes place in the harmonic space where all harmonics and cross-couplings between harmonics are explicitly represented. Good application examples are the harmonic domain solution of arc discharge lamps with electromagnetic ballasts and the harmonic domain solution of electric arc furnaces with ancillary power electronics equipment. Building on the experience gained with the representation of the arc discharge lamps with electromagnetic ballasts, the research turns to the representation of the electric arc furnace installation with provisions for reactive power compensation using power electronic control and harmonic filters. This is a three-phase application which comprises several nodes, giving rise a large-scale model of a non-linear system which is solved in the direct frequency domain using a blend of the Newton-Raphson method and the Gauss-Seidel method, achieving robust iterative solution to a very tight tolerance. Both algorithms are implemented in MATLAB code and the raw simulation results which are the harmonic complex conjugated vectors of nodal voltages are used to assess in a rather comprehensive manner the harmonic interactions involved in both kinds of applications.
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Davis, I. C. « Arc furnace and shunt reactive compensation modelling for voltage flicker reduction ». Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372680.
Texte intégral
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Barborak, Darren Matthew. « Modelling and real-time control of gas metal arc weld profile / ». The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488203158827754.
Texte intégral
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Yusoff, Hamdan bin Mohamed. « Continuous Production of Carbon Nanotubes Using Carbon Arc Reactor : Anode Surface Temperature Study and CFD Modelling ». Thesis, University of Canterbury. Chemical and Process Engineering, 2008. http://hdl.handle.net/10092/4386.
Texte intégralRésumé :
The mass production of carbon nanotubes (CNTs) by a cost effective process is still a challenge for further research and application of CNTs. This research focussed on the deposition of CNTs on a continuously-fed carbon substrate via arc discharge at atmospheric pressure. In this work, modifications, control and optimization of the available arc-discharge reactor were conducted. New reactor support and new tape feeding mechanisms were added to the reactor for better temperature assessment, longer operating period and better control of the speed of the tape.
The influence of inter-electrode gap, substrate velocity and arc current on the surface temperature were investigated. Multiwalled carbon nanotubes (MWNTs) were produced at lower currents (< 20 A) and at larger inter-electrode gaps. Further investigation shows that inter-electrode gap influenced both the arc characteristic and the anode surface temperature (Ts). Here, Ts was measured by an optical pyrometer.
The inter-electrode gap was found to indirectly affect the formation of NTs. Anode surface temperature (Ts) varied with gap, reaching a minimum at an intermediate gap. Higher CNTs yield was found at this lowest Ts. This minimum Ts is consistent with the presence of a cloud of nanoparticles ejected by the heated graphite/carbon surfaces. These graphene fragments are thought to later fold and form nanotube “seeds” and then develop into multiwall nanotubes. This cloud of nanoparticles also may affect the electrical conductivity at the front of the anode. Simulation of the arc behaviour, i.e. temperature distributions and flow properties of the plasma, using a computer package Comsol Multiphysics 3.2, was stable only when the electrical conductivity of a dusty plasma near to the electrodes was included.
Our experiments show that carbon nanotubes grew better at a Ts range of ~ 3650 K - 3700 K and at the tape speed of 3 mm/s. The results from our work also strongly suggested that tiny carbon crystallites are the main intermediates for CNT growth in an electric arc. The limiting factor for a solid state growth mechanism, therefore, is high temperature annealing of carbon or graphene fragments. Further work should aim to understand the growth mechanism of CNTs, produce comprehensive analysis on the arc plasma composition and also explore the possibility of producing CNTs at higher rates.
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Katsiampa, Paraskevi. « Nonlinear exponential autoregressive time series models with conditional heteroskedastic errors with applications to economics and finance ». Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18432.
Texte intégralRésumé :
The analysis of time series has long been the subject of interest in different fields. For decades time series were analysed with linear models, which have many advantages. Nevertheless, an issue which has been raised is whether there exist other models that can explain and forecast real data better than linear ones. In this thesis, new nonlinear time series models are suggested, which consist of a nonlinear conditional mean model, such as an ExpAR or an Extended ExpAR, and a nonlinear conditional variance model, such as an ARCH or a GARCH. Since new models are introduced, simulated series of the new models are presented, as it is important in order to see what characteristics real data which could be explained by them should have. In addition, the models are applied to various stationary and nonstationary economic and financial time series and are compared to the classic AR-ARCH and AR-GARCH models, in terms of fitting and forecasting. It is shown that, although it is difficult to beat the AR-ARCH and AR-GARCH models, the ExpAR and Extended ExpAR models and their special cases, combined with conditional heteroscedastic errors, can be useful tools in fitting, describing and forecasting nonlinear behaviour in financial and economic time series, and can provide some improvement in terms of both fitting and forecasting compared to the AR-ARCH and AR-GARCH models.
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Liu, J. « Modelling and simulation of air and SF6 switching arcs in high voltage circuit breakers ». Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3003675/.
Texte intégralRésumé :
This thesis is concerned with the modelling of switching arcs in air in high voltage circuit breakers and with a comparative study of interruption capability of air and SF6 switching arcs. Emphasis is given to the identification of dominant energy transport processes for arc interruption and the material properties associated these processes. There have been renewed interests in air arcs because of its possible use in a mixture with other gases as a replacement for SF6 in circuit breakers for environment protection. Computer simulation of the switching air arc has been carried out using arc models based on laminar flow and on turbulent flow for the experimental set up of Fang et al [41] under DC current and that of Frind and Rich [66] for the current zero period. DC arc voltages predicted by arc model assuming laminar flow (LAM) are much lower than those measured. Thus, turbulence is introduced to account for additional power loss mechanism not included in the laminar flow model. Two turbulence models have been used to take into account of turbulence enhanced momentum and energy transport: the Prandtl mixing length model (PML) and the standard k-epsilon model or its modified version. For the DC air nozzle arc of Fang et al [41] the value of the turbulence parameter, c= 0.06, in PML has been chosen to match the predicted arc voltage with that measured at 1 kA DC and a stagnation pressure of 10 bar. PML can give satisfactory agreement with experiments over a DC current range from 250 A to 3 kA. When the standard k-epsilon model is used, the predict arc voltage is much higher than that measured indicating that turbulence cooling is too strong. One of the turbulence parameters of the standard k-epsilon model which controls the dissipation rate of turbulent kinetic energy is adjusted to match the predicted arc voltage with the experimentally measured arc voltage under the same discharge conditions as those for finding the value of c in PML. With this chosen value of 1 = 1.62, the modified k-epsilon model (MKE) gives similar results to those of PML. Three arc models (LAM, PML and MKE) are used to compute the critical rate of rise of recovery voltage (RRRV) for the air nozzle arc of Frind and Rich [66]. The presence of the shock inside the nozzle in the presence of the arc prevents the optimisation of the value of turbulence parameter for PML due to numerical convergence problems. RRRV predicted by PML and LAM are much lower than the experimental value. MKE with 1 = 1.65 is successful in predicting satisfactorily the RRRV at di/dt= 13.5 A/μs for several stagnation pressures. However, it has been found that a single value of 1 chosen for one value of di/dt cannot give satisfactory prediction of RRRV for other values of di/dt. A comparative computational study of SF6 and air switching arcs based on MKE has been carried out for the experimental conditions of Frind and Rich [66] for di/dt= 13.5A/μs at several stagnation pressures. Under the same discharge conditions RRRV of SF6 switching arc is one order of magnitude higher than that of air switching arc. Such large difference in the interruption capabilities of SF6 and air is due to the different dominant energy transport processes responsible for the arc cooling during current zero period. Two material properties of the arc plasma, the product of density and specific heat at constant pressure (ρCP) and that of density and enthalpy (ρh) are responsible for the distinctive arc features for SF6 and air. SF6 switching arc has a distinctive arc core surrounded by a thin region with steep temperature gradient. Under the same discharge conditions as those of SF6 air switching arc has no distinctive core structure. Its radial temperature profile is very broad and arc radius is much bigger than that of SF6. Such broad radial temperature profile of air arc is due to the peaks of turbulent thermal conductivity at 4,000 K and 7,000 K produced by the corresponding peaks of the material property of ρCP of air. For SF6 ρCP has a peak just below 4,000 K, which ensures rapid temperature decay above 4,000 K and a gentle temperature tail below 4,000 K. In comparison with SF6 under the same pressure difference across the nozzle the velocity inside air arc is much higher than that of SF6. With ρh of air being greater than that of SF6 for temperature higher than 7,000 K together with higher velocity enthalpy transport capability of air arc is much higher than that of SF6. Energy balance calculation for the current carrying core indicates that after the breakdown of quasi-steady state turbulent thermal conduction is the dominant energy transport process for SF6 while for air arc axial convection is dominant. As a consequence the rates of decay of arc temperature and arc radius for air arc a few microseconds before current zero are much slower than those of SF6, thus resulting in a large difference between RRRVs for the two gases under the same discharge conditions. To find an alternative arc quenching gas with similar interruption capability to that of SF6 one should aim at ρCP and ρh of the alternative gas with similar features to those of SF6.
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Posinasetti, Praveen. « Process modelling and control of pulse gas metal arc welding of aluminum ». Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16530/1/Praveen_Posinasetti_Thesis.pdf.
Texte intégralRésumé :
Recent developments in materials and material joining [specifically Aluminum and Pulse Gas Metal Arc Welding (GMAW-P) technology] have increased the scope and extent of their areas of application. However, stern market demand for the improved weld quality necessitates the need for automation of the welding processes. As a result, improvements in the process parameter feedback, sensing and control, are necessary to successfully develop the automated control technology for the welding processes. Hence, several aspects of the GMAW-P process have been investigated in this study in order to improve its control techniques.
Welding was conducted on 6XXX aluminium, using 1.2 mm diameter 4047 aluminum electrode and argon shielding gas. An extensive collection of high speed camera pictures were taken over a wide range of pulse parameters and wire feed rates using a xenon shadowgraph setup to improve understanding of the physics of GMAW-P process. Current and voltage signals were recorded concurrently too.
This investigation explores the effects of different process parameters namely pulsing parameters (Peak current (IP), Base Current (IB), Peak time (TP), Base Time (TB)) and wire feed rate on metal transfer phenomena in GMAW-P. Number of drops per pulse, arc length and droplet diameter were measured for aluminium electrodes by high speed videography. The pulsing parameters and wire feed rate were varied to investigate their effect on the metal transfer behaviour. Analysis showed that transition between the different metal transfer modes is strongly influenced by the electrode extension. Lower electrode extension reduced the number of droplets detached per pulse, while at higher electrode extension, spray mode is observed due to increased influence of the resistance heating.
Analysis of the current and voltage signals were correlated with the high speed films. A simple derivative filter was used to detect the sudden changes in voltage difference associated with metal transfer during GMAW-P. The chosen feature for detection is the mean value of the weld current and voltage. A new algorithm for the real time monitoring and classification of different metal transfer modes in GMAW-P has been developed using voltage and current signals. The performance of the algorithm is assessed using experimental data. The results obtained from the algorithm show that it is possible to detect changes in metal transfer modes automatically and on-line.
Arc stability in the GMAW-P has a close relationship with the regularity of metal transfer, which depends on several physical quantities (like voltage, current, materials, etc.) related to the growth and transfer of the metal droplet. Arc state in GMAW-P can be assessed quantitatively in terms of number of drops per pulse, droplet diameter and arc length. In order to assess the arc state in GMAW-P quantitatively, statistical and neural network models for number of drops/pulse, droplet diameter and arc length were developed using different waveform factors extracted from the current waveform of GMAW-P. To validate the models, estimated results were compared to the actual values of the number of drops per pulse, droplet diameter and arc length, observed during several welding conditions.
Determination of stable one drop per pulse (ODPP) parametric zone containing all the combinations of peak current (IP), base current (IB), peak time (TP), and base time (TB) that results in stable operation of GMAW-P, is one of the biggest challenges in GMAW-P. A new parametric model to identify the stable ODPP condition in aluminium which also considers the influence of the background conditions and wire feed has been proposed.
Finally, a synergic control algorithm for GMAW-P process has been proposed. Synergic algorithm proposed in this work uses the sensing and prediction techniques to analyse state of the arc and correct the pulsing parameters for achieving the stable ODPP. First arc state is estimated using the signal processing techniques and statistical methods to detect the occurrence of short circuit, unstable ODPP or multiple drops per pulse (MDPP) in GMAW-P system. If the arc state is not stable ODPP, then parametric model and genetic algorithm (GA) is used to assess the deviation of the existing pulsing parameters from the stable operation of GMAW-P process and automatically adjust pulsing parameters to achieve stable ODPP.
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Posinasetti, Praveen. « Process modelling and control of pulse gas metal arc welding of aluminum ». Queensland University of Technology, 2007. http://eprints.qut.edu.au/16530/.
Texte intégralRésumé :
Recent developments in materials and material joining [specifically Aluminum and Pulse Gas Metal Arc Welding (GMAW-P) technology] have increased the scope and extent of their areas of application. However, stern market demand for the improved weld quality necessitates the need for automation of the welding processes. As a result, improvements in the process parameter feedback, sensing and control, are necessary to successfully develop the automated control technology for the welding processes. Hence, several aspects of the GMAW-P process have been investigated in this study in order to improve its control techniques.
Welding was conducted on 6XXX aluminium, using 1.2 mm diameter 4047 aluminum electrode and argon shielding gas. An extensive collection of high speed camera pictures were taken over a wide range of pulse parameters and wire feed rates using a xenon shadowgraph setup to improve understanding of the physics of GMAW-P process. Current and voltage signals were recorded concurrently too.
This investigation explores the effects of different process parameters namely pulsing parameters (Peak current (IP), Base Current (IB), Peak time (TP), Base Time (TB)) and wire feed rate on metal transfer phenomena in GMAW-P. Number of drops per pulse, arc length and droplet diameter were measured for aluminium electrodes by high speed videography. The pulsing parameters and wire feed rate were varied to investigate their effect on the metal transfer behaviour. Analysis showed that transition between the different metal transfer modes is strongly influenced by the electrode extension. Lower electrode extension reduced the number of droplets detached per pulse, while at higher electrode extension, spray mode is observed due to increased influence of the resistance heating.
Analysis of the current and voltage signals were correlated with the high speed films. A simple derivative filter was used to detect the sudden changes in voltage difference associated with metal transfer during GMAW-P. The chosen feature for detection is the mean value of the weld current and voltage. A new algorithm for the real time monitoring and classification of different metal transfer modes in GMAW-P has been developed using voltage and current signals. The performance of the algorithm is assessed using experimental data. The results obtained from the algorithm show that it is possible to detect changes in metal transfer modes automatically and on-line.
Arc stability in the GMAW-P has a close relationship with the regularity of metal transfer, which depends on several physical quantities (like voltage, current, materials, etc.) related to the growth and transfer of the metal droplet. Arc state in GMAW-P can be assessed quantitatively in terms of number of drops per pulse, droplet diameter and arc length. In order to assess the arc state in GMAW-P quantitatively, statistical and neural network models for number of drops/pulse, droplet diameter and arc length were developed using different waveform factors extracted from the current waveform of GMAW-P. To validate the models, estimated results were compared to the actual values of the number of drops per pulse, droplet diameter and arc length, observed during several welding conditions.
Determination of stable one drop per pulse (ODPP) parametric zone containing all the combinations of peak current (IP), base current (IB), peak time (TP), and base time (TB) that results in stable operation of GMAW-P, is one of the biggest challenges in GMAW-P. A new parametric model to identify the stable ODPP condition in aluminium which also considers the influence of the background conditions and wire feed has been proposed.
Finally, a synergic control algorithm for GMAW-P process has been proposed. Synergic algorithm proposed in this work uses the sensing and prediction techniques to analyse state of the arc and correct the pulsing parameters for achieving the stable ODPP. First arc state is estimated using the signal processing techniques and statistical methods to detect the occurrence of short circuit, unstable ODPP or multiple drops per pulse (MDPP) in GMAW-P system. If the arc state is not stable ODPP, then parametric model and genetic algorithm (GA) is used to assess the deviation of the existing pulsing parameters from the stable operation of GMAW-P process and automatically adjust pulsing parameters to achieve stable ODPP.
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Chang, Tsangyao. « An Application of Autoregressive Conditional Heteroskedasticity (Arch) and Generalized Autoregressive Conditional Heteroskedasticity (GARCH) Modelling on Taiwan's Time-Series Data : Three Essays ». DigitalCommons@USU, 1995. http://digitalcommons.usu.edu/etd/4040.
Texte intégralRésumé :
In this dissertation, three essays are presented that apply recent advances in time-series methods to the analysis of inflation and stock market index data for Taiwan. Specifically, ARCH and GARCH methodologies are used to investigate claims of increased volatility in economic time-series data since 1980.
In the first essay, analysis that accounts for structural change reveals that the fundamental relationship between inflation and its variability was severed by policies implemented during economic liberalization in Taiwan in the early 1980s. Furthermore, if residuals are corrected for serial correlation, evidence in favor of ARCH effects is weakened. In the second essay, dynamic linkages between daily stock returns and daily trading volume are explored. Both linear and nonlinear dependence are evaluated using Granger causality tests and GARCH modelling. Results suggest significant unidirectional Granger causality from stock returns to trading volume. In the third essay, comparative analysis of the frequency structure of the Taiwan stock index data is conducted using daily, weekly, and monthly data. Results demonstrate that the relationship between mean return and its conditional standard deviation is positive and significant only for high-frequency daily data.
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Jorge, Paula Karine. « Evaluation of the dental arch in children with cleft lip and palate by means of 3D digital models ». Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/61/61132/tde-14012015-103434/.
Texte intégralRésumé :
The aim of this study was to evaluate the dimensional alterations of dental arches of cleft lip and palate children after cheiloplasty at two rehabilitation centers. The sample was composed of 94 digital models and divided in two groups: Group I 23 children, assisted at University of Zurich with presurgical orthopedic intervention (Hotz plate); Group II 24 children, assisted at Hospital for Rehabilitation of Craniofacial Anomalies of the University of São Paulo without presurgical orthopedic intervention. The three dimensional images were used to evaluate before lip repair (stage 1) and approximately 1 year old (stage 2). The obtained measures were: intercanine distance, intertuberosity distance, anterior-posterior arch distance, anterior-posterior cleft length, anterior and posterior cleft width. The comparison between stages 1 and 2 was evaluated in group I, group II and between group I and II. The alterations between groups were verified by Independent t test. If the sample did not present a normal distribution, Wilcoxon and Mann-Whitney tests were used. In Group I, the comparisons between stages 1 and 2 showed that the intertuberosity and anterior-posterior arch distance increased and the intercanine, anterior and posterior cleft distances decreased. In Group II, the comparisons between stages 1 and 2 showed that intertuberosity distance increased and intercanine, anteriorposterior cleft length distances, anterior and posterior cleft widths decreased. The comparison of the dimensional alterations of dental arches between the two rehabilitation centers exhibited differences: in the stage 1, the intercanine distance decreased in Group II; in the stage 2, the anterior cleft width, the intercanine distance and the anterior-posterior cleft length decreased in Group II, suggesting the superposition of maxillary segments; in Group II, there was a greater narrowing of the anterior and posterior cleft widths, suggesting that Hotz plate induced a more evenly and equidistant approximation of maxillary segments in Group I. It is worth emphasizing that more studies should be conduct to reduce the variability in treatment protocols for cleft lip and palate patients, thus assuring the best evidencebased treatment.O propósito deste estudo foi avaliar as alterações dimensionais dos arcos dentários de crianças com fissura de lábio e palato após a queiloplastia em dois centros de reabilitação. A amostra foi composta por 94 imagens digitais de modelos de gesso, e dividida em dois grupos: Grupo I - 23 crianças, tratas na Universidade de Zurique, com intervenção ortopédica pré-cirúrigica (placa de Holtz); Grupo II - 24 crianças tratadas no Hospital de Reabilitação de Anomalias Craniofaciais da Universidade de São Paulo, sem intervenção ortopédica pré-cirúrgica. As imagens tridimensionais dos modelos de gesso foram avaliados antes da queiloplastia (estágio 1) e com aproximadamente 1 ano de idade (estágio 2). As seguintes dimensões foram obtidas: comprimento anteroposterior da fissura, amplitude anterior da fissura, amplitude posterior da fissura, comprimento anteroposterior do arco, distância intercaninos e distância intertuberosidades. As comparações foram realizadas entre os estágios 1 e 2 e entre os grupos I e II. As diferenças entre os grupos foram verificadas pelo teste t independente, os testes de Wilcoxon e Mann-Whitney foram usados. No Grupo I, entre os estágios 1 e 2, as distâncias intertuberosidade aumentou e as distâncias intercaninos, distância anteroposterior da fissura, amplitude anterior e posterior da fissura diminuíram. A comparação entre as alterações dimensionais dos arcos dentários entre os dois centros de reabilitação apresentaram diferenças: no estágio 1, a distância intercaninos foi menor no Grupo II que no Grupo I; e no estágio 2, a amplitude anterior da fissura, a distância intercaninos e o comprimento anteroposterior da fissura foram menos no Grupo II que no Grupo I, sugerindo sobreposição dos segmentos maxilares. No Grupo II, houve maior estreitamento nas amplitudes anterior e posterior da fissura, sugerindo que a placa de Holtz no Grupo I induziu a aproximação dos segmentos maxilares de forma mais uniforme e equidistante. É importante salientar que mais estudos longitudinais precisam ser conduzidos a fim de reduzir a variabilidade de protocolos de tratamento em pacientes com fissura de lábio e palato, garantindo o melhor tratamento baseado em evidências científicas.