No description available.

<p>The MUSCL-Hancock finite volume method with different slope limiters has been analyzed in the context of a fast transient flow problem. A derivation and analysis of the axial forces inside a pipe system due to a flow transient is also performed. </p><p>The following slope limiters were implemented and compared: MC, van Leer, van Albada, Minmod and Superbee. The comparison was based on the method's ability to calculate the forces due to a flow transient inside a pipe system.</p><p>The tests and comparisons in this thesis show that the MC, van Leer, van Albada and Minmod limiters behave very much the same for the flow transient problem. If one would rank these four limiters with respect to the numerical error, the order would be the one presented above, the MC limiter being the most accurate. The error the four limiters produce is mainly of diffusive nature and it is just the magnitude of the diffusion that seems to differ between the methods. One should also note that the workload rank of the four limiters is the same as the order presented above. The MC limiter being the least efficient of the four and the Minmod limiter the most efficient.</p><p>In most of the tests performed the Superbee limiter display a rather negative unpredictable behavior. For some relatively simple cases this particular approach shows big difficulties maintaining the dynamical properties of the force. However, the upside of the Superbee limiter is its remarkable ability to maintain the maximum value of the forces present in the pipe system, preventing underestimation of the maximum magnitude of the force.</p>

The MUSCL-Hancock finite volume method with different slope limiters has been analyzed in the context of a fast transient flow problem. A derivation and analysis of the axial forces inside a pipe system due to a flow transient is also performed.  The following slope limiters were implemented and compared: MC, van Leer, van Albada, Minmod and Superbee. The comparison was based on the method's ability to calculate the forces due to a flow transient inside a pipe system. The tests and comparisons in this thesis show that the MC, van Leer, van Albada and Minmod limiters behave very much the same for the flow transient problem. If one would rank these four limiters with respect to the numerical error, the order would be the one presented above, the MC limiter being the most accurate. The error the four limiters produce is mainly of diffusive nature and it is just the magnitude of the diffusion that seems to differ between the methods. One should also note that the workload rank of the four limiters is the same as the order presented above. The MC limiter being the least efficient of the four and the Minmod limiter the most efficient. In most of the tests performed the Superbee limiter display a rather negative unpredictable behavior. For some relatively simple cases this particular approach shows big difficulties maintaining the dynamical properties of the force. However, the upside of the Superbee limiter is its remarkable ability to maintain the maximum value of the forces present in the pipe system, preventing underestimation of the maximum magnitude of the force.

[pt] Os procedimentos de calibração de transdutores piezoelétricos, abordados pela base normativa de ensaios de munições leves, carecem de detalhes cruciais para assegurar a confiabilidade metrológica nas medições de pressão transiente dessas munições leves. Diante deste fato, cabe aos laboratórios, como requisito para a acreditação segundo a norma ISO/IEC 17025:2017, comprovarem a eficácia dos métodos empregados, sobretudo nas calibrações, o que motivou a realização do estudo. A abordagem metodológica baseou-se em pesquisas bibliográficas, documentais, experimentais e de laboratório, visando a coleta de dados conforme as etapas de avaliação dos métodos de calibração. Inicialmente realizou-se a avaliação de certificados de calibração de transdutores piezoelétricos, estudando, sobretudo, as características da regressão linear adotada pela base normativa nos procedimentos de calibração. Nesta etapa, a pesquisa propôs a adoção da incerteza do ajuste como parâmetro principal de avaliação de transdutores piezoelétricos, mostrando sua viabilidade em relação ao erro de linearidade. Em seguida, foi realizada a caracterização e modelagem da cadeia de medição de pressão transiente, composta por transdutor piezoelétrico e amplificador de carga. A modelagem permitiu a simulação de diferentes metodologias de calibração, resultando na previsão de erros, e proporcionando a avaliação da influência do amplificador de carga nas medições de pressão transiente. Por último, foram comparadas duas metodologias distintas de calibração, destacando a importância de sistemas automatizados de calibração para maior confiabilidade metrológica. / [en] The calibration procedures of piezoelectric transducers, addressed by the normative basis of small arms ammunition testing, lack crucial details to ensure metrological reliability in the transient pressure measurements of these small arms munitions. In view of this fact, it is up to the laboratories, as a requirement for accreditation according to ISO/IEC 17025:2017 standard, to prove the effectiveness of the methods used, especially in calibrations, which motivated the study. The methodological approach was based on bibliographic, documentary, experimental and laboratory research, aiming at data collection according to the stages of evaluation of calibration methods. Initially, the evaluation of calibration certificates of piezoelectric transducers was carried out, studying, above all, the characteristics of the linear regression adopted by the normative basis in the calibration procedures. At this stage, the research proposed the adoption of fit uncertainty as the main parameter for the evaluation of piezoelectric transducers, showing their feasibility in relation to linearity error. Then, the characterization and modeling of the transient pressure measurement chain, composed of a piezoelectric transducer and a charge amplifier, was performed. The modeling allowed the simulation of different calibration methodologies, resulting in the prediction of errors, and providing the evaluation of the influence of the charge amplifier on transient pressure measurements. Finally, two different calibration methodologies were compared, highlighting the importance of automated calibration systems for greater metrological reliability.

Reservoir testing and analysis are fundamental tools in understanding reservoir hydraulics and hence forecasting reservoir responses. The quality of the analysis is very dependent on the conceptual model used in investigating the responses under different flowing conditions. The use of reservoir testing in the characterization and derivation of reservoir parameters is widely established, especially in conventional oil and gas reservoirs. However, with depleting conventional reserves, the quest for unconventional reservoirs to secure the increasing demand for energy is increasing; which has triggered intensive research in the fields of reservoir characterization. Gas hydrate reservoirs, being one of the unconventional gas reservoirs with huge energy potential, is still in the juvenile stage with reservoir testing as compared to the other unconventional reservoirs. The endothermic dissociation hydrates to gas and water requires addressing multiphase flow and heat energy balance, which has made efforts to develop reservoir testing models in this field difficult. As of now, analytically quantifying the effect on hydrate dissociation on rate and pressure transient responses are till date a huge challenge. During depressurization, the heat energy stored in the reservoir is used up and due to the endothermic nature of the dissociation; heat flux begins from the confining layers. For Class 3 gas hydrates, just heat conduction would be responsible for the heat influx and further hydrate dissociation; however, the moving boundary problem could also be an issue to address in this reservoir, depending on the equilibrium pressure. To address heat flux problem, a proper definition of the inner boundary condition for temperature propagation using a Clausius-Clapeyron type hydrate equilibrium model is required. In Class 1 and 2, crossflow problems would occur and depending on the layer of production, convective heat influx from the free fluid layer and heat conduction from the cap rock of the hydrate layer would be further issues to address. All these phenomena make the derivation of a suitable reservoir testing model very complex. However, with a strong combination of heat energy and mass balance techniques, a representative diffusivity equation can be derived. Reservoir testing models have been developed and responses investigated for different boundary conditions in normally pressured Class 3 gas hydrates, over-pressured Class 3 gas hydrates (moving boundary problem) and Class 1 and 2 gas hydrates (crossflow problem). The effects of heat flux on the reservoir responses have been addressed in detail.