Alexandre Kepler Soares

Transient vaporous cavitation in viscoelastic pipes

The research focuses on the analysis of transient cavitating flow in polyethylene pipes, which are characterized by a viscoelastic–rheological behaviour. A hydraulic transient solver incorporating the description of the rheological–mechanical behaviour of these pipes and the cavitating pipe flow has been developed. Both the discrete vapour cavity model and the discrete gas cavity model have been used to describe transient cavitating flow. These assume that discrete air cavities are formed at fixed pipe sections and consider a constant wave speed in the pipe reaches between the cavities. An experimental programme was conducted in a pipe-rig composed of a high-density polyethylene (HDPE) pipeline. Numerical results have been compared with collected data resulting in a good agreement. Effects related to the viscoelasticity of HDPE pipes and to the occurrence of vapour pressures during the transient events are also discussed.

Unsteady Flow with Cavitation in Viscoelastic Pipes

The current paper focuses on the analysis of transient cavitating flow in pressurised polyethylene pipes, which are characterized by viscoelastic rheological behaviour. A hydraulic transient solver that describes fluid transients in plastic pipes has been developed. This solver incorporates the description of dynamic effects related to the energy dissipation (unsteady friction), the rheological mechanical behaviour of the viscoelastic pipe and the cavitating pipe flow. The Discrete Vapour Cavity Model (DVCM) and the Discrete Gas Cavity Model (DGCM) have been used to describe transient cavitating flow. Such models assume that discrete air cavities are formed in fixed sections of the pipeline and consider a constant wave speed in pipe reaches between these cavities. The cavity dimension (and pressure) is allowed to grow and collapse according to the mass conservation principle. An extensive experimental programme has been carried out in an experimental set-up composed of high-density polyethylene (HDPE) pipes, assembled at Instituto Superior Tecnico of Lisbon, Portugal. The experimental facility is composed of a single pipeline with a total length of 203 m and inner diameter of 44 mm. The creep function of HDPE pipes was determined by using an inverse model based on transient pressure data collected during experimental runs without cavitating flow. Transient tests were carried out by the fast closure of the ball valves located at downstream end of the pipeline for the non-cavitating flow and at upstream for the cavitating flow. Once the rheological behaviour of HDPE pipes were known, computational simulations have been run in order to describe the hydraulic behaviour of the system for the cavitating pipe flow. The calibrated transient solver is capable of accurately describing the attenuation, dispersion and shape of observed transient pressures. The effects related to the viscoelasticity of HDPE pipes and to the occurrence of vapour pressures during the transient event are discussed.

Damping Analysis of Hydraulic Transients in Pump-Rising Main Systems

AbstractThis paper focuses on the analysis of unsteady pipe flows caused by a pump trip in a water pipeline system. Field experiments have been carried out to collect transient pressure and steady-state flow rate data in the Prado–Instituto Politecnico da Guarda (IPG) pumping system located in Guarda, Portugal. Observed transient pressures were compared with numerical results. Results obtained were excellent both in terms of damping and phase shift of the transient pressure signal, provided that unsteady friction effects were taken into account and an appropriate downstream end boundary condition was considered. The downstream end boundary condition was described by small tanks with variable level and with free discharge into the storage tank; the variation of water level in these small tanks results in the relief of extreme transient pressures (conversely to what is observed in the line-packing effect) and changes the shape of transient pressure waves. This analysis has shown that classical water hammer ...

Transient vaporous cavitation in a horizontal copper pipe

ABSTRACT This research focuses on the analysis of transient cavitating flow in a horizontal copper pipe. Experiments have been conducted in a reservoir-pipe-valve copper pipe-rig to collect transient pressure data with and without cavitation. A hydraulic transient solver incorporating unsteady friction losses and distributed cavitation flow (discrete gas cavity model) has been developed. The system behaviour and the obtained transient pressure signal have been compared with the experimental results for sloping pipes reported in previous studies and a good agreement has been observed. Numerical results are compared with collected data and effects related to the unsteady friction losses and to the occurrence of transient vapour pressures are discussed.

Calibração de um modelo hidrodinâmico em um canal urbano utilizando algoritmos genéticos multiobjetivos

Este trabalho tem por objetivo efetuar a calibracao de um modelo hidrodinâmico para canais abertos utilizando algoritmos evolucionarios multiobjetivos a partir de medicoes de nivel da agua. O metodo foi aplicado em um canal urbano com revestimento lateral de Gabiao e com macrorrugosidades de fundo. Por ser um modelo hidraulico com poucos parâmetros, empregou-se apenas um evento para calibracao dos parâmetros do coeficiente de rugosidade de Manning, referentes aos trechos apenas com revestimentos com Gabiao e com macrorrugosidade de concreto. Outros tres eventos foram usados para validacao. Para tanto, foram empregadas duas funcoes objetivo na calibracao pelo uso do algoritmo de otimizacao NSGA-II, o coeficiente de eficiencia de Nash-Sutcliffe e o erro da cota de pico. O NSGA-II apresentou excelentes resultados, obtendo-se coeficientes de Nash-Sutcliffe superiores a 0,96, e erros da cota maxima inferiores a 0,40 cm, tanto para calibracao quanto para validacao, em todos os eventos. Os valores medios encontrados para os coeficientes de rugosidade de Manning foram de 0,0905 para o trecho com macrorrugosidade de fundo de concreto e de 0,0277 para o trecho com Gabiao. Palavras-chave: Otimizacao multiobjetivo; Equacoes de Saint-Venant; Escoamento nao permanente; NSGA-II; curva-chave. HYDRODYNAMIC MODEL CALIBRATION IN AN URBAN CHANNEL USING MULTIOBJECTIVE GENETIC ALGORITHMS ABSTRACT This paper aims to perform calibration of a hydrodynamic model for open channels using evolutionary algorithms multi-objectives from water level measurements. The method was applied in an urban channel with gabion coating with bottom macro-roughness. An event was used to calibrate parameters and three events for validation. Two objective functions were used in the optimization, the Nash-Sutcliffe efficiency coefficient and the error of the peak quota. The NSGA-II optimization algorithm presented excellent results, obtaining Nash-Sutcliffe coefficients higher than 0.96, and errors of maximum dimension less than 0.40 cm for both calibration and validation of every event. The value of the roughness was found to be 0.0905 for the path with obstacles and 0.0277 for the part with gabion. Keywords: Multi-objective optimization; Saint-Venant equations; Unsteady flow; NSGA-II; Rating curve.