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A hierarchy of models exists in the literature for the simulation of pipe transients. One-dimensional water hammer models are readily available and provide a cost-effective tool for the analysis of such transients. The main shortcoming of 1D models is the quasi-steady approximation of the frictional term, which results in poor modelling of the attenuation of the transient. To overcome this drawback, quasi-2D water hammer models were introduced, which allow the computation of the unsteady velocity profile and hence provide improved modelling of the attenuation phenomenon. Recently, interest has developed in the use of CFD models based on the Navier-Stokes equations in the simulation of fluid transients. Both axisymmetric CFD models and full 3D CFD models are used in this regard. The aim of the current paper is to carry out a comparative study between the performance of quasi-2D water hammer models, axisymmetric CFD models and full 3D CFD models. Numerical computations using the three models are performed for both laminar and turbulent flow cases. Present results show that the quasi-2D water hammer model and the axisymmetric CFD model provide near identical results in terms of computing the magnitude, phase and attenuation of the transient. Reported results also demonstrate the computational efficiency of the quasi-2D model, which provides results that agree reasonably well with the full 3D CFD model results while using a grid density which is an order of magnitude lower than the grid requirements for the full 3D CFD model.
Nuno M. C. Martins; Essam M. Wahba. On the Hierarchy of Models for Pipe Transients: From Quasi-2D Water Hammer Models to Full 3D CFD Models. Journal of Pressure Vessel Technology 2021, 1 .
AMA StyleNuno M. C. Martins, Essam M. Wahba. On the Hierarchy of Models for Pipe Transients: From Quasi-2D Water Hammer Models to Full 3D CFD Models. Journal of Pressure Vessel Technology. 2021; ():1.
Chicago/Turabian StyleNuno M. C. Martins; Essam M. Wahba. 2021. "On the Hierarchy of Models for Pipe Transients: From Quasi-2D Water Hammer Models to Full 3D CFD Models." Journal of Pressure Vessel Technology , no. : 1.
The current paper aims to develop and to apply a methodology for assessing the hydroenergy harvesting potential in water systems taking into account both technical and economic aspects. The methodology is a five-step procedure: (i) data collection and analysis; (ii) technology identification; (iii) energy harvesting assessment; (iv) economic analysis; and (v) final recommendation of the technological solution. The case study is located in the water source of the Alviela River, in Portugal. The energy harvesting potential is assessed for three turbine types, adequate for the 2.5 m available head: two propeller turbines, with and without adjustable blades, and the Archimedes screw turbine. Results show that the most feasible solution is the Archimedes screw turbine, with 3 m
Pedro Oliveira; Nuno Martins; Pedro Fontes; Dídia Covas. Hydroenergy Harvesting Assessment: The Case Study of Alviela River. Water 2021, 13, 1764 .
AMA StylePedro Oliveira, Nuno Martins, Pedro Fontes, Dídia Covas. Hydroenergy Harvesting Assessment: The Case Study of Alviela River. Water. 2021; 13 (13):1764.
Chicago/Turabian StylePedro Oliveira; Nuno Martins; Pedro Fontes; Dídia Covas. 2021. "Hydroenergy Harvesting Assessment: The Case Study of Alviela River." Water 13, no. 13: 1764.
Pressurised pipe systems transport fluids daily over long distances and sediment deposits are responsible for narrowing the cross-sectional area of the pipe. This reduces the carrying capacity in gravity pipes and increases the energy consumption in rising mains. As partial blockages do not give rise to any external evidence, they are considered the most insidious fault occurring in pipe systems. Thus, the refinement of reliable techniques for detecting partial blockages at an early stage is of great interest to water utilities. This paper presents a computational fluid dynamics (CFD)-based analysis of the steady-state flow through a sharp-edged orifice which corresponds to the most straightforward partial blockage feature in a pipe. The main motivation is the fact that the interaction between pressure waves and a partial blockage – on which Transient Test-Based Techniques for fault detection are based – is strongly influenced by the pre-transient conditions at the partial blockage. The refined CFD model has been validated by considering experimental data selected from the literature. The comparison of obtained results demonstrates good performance of the numerical model. This authorised exploring in detail the features of the flow through the orifice as a necessary premise to its use within the successive transient analysis.
Nuno M. C. Martins; Dídia I. C. Covas; Silvia Meniconi; Caterina Capponi; Bruno Brunone. Characterisation of low-Reynolds number flow through an orifice: CFD results vs. laboratory data. Journal of Hydroinformatics 2021, 1 .
AMA StyleNuno M. C. Martins, Dídia I. C. Covas, Silvia Meniconi, Caterina Capponi, Bruno Brunone. Characterisation of low-Reynolds number flow through an orifice: CFD results vs. laboratory data. Journal of Hydroinformatics. 2021; ():1.
Chicago/Turabian StyleNuno M. C. Martins; Dídia I. C. Covas; Silvia Meniconi; Caterina Capponi; Bruno Brunone. 2021. "Characterisation of low-Reynolds number flow through an orifice: CFD results vs. laboratory data." Journal of Hydroinformatics , no. : 1.
Myringotomy with tympanostomy tube is the most common otologic surgery and some patients are still advised to avoid water. However, there is no evidence supporting this, with published papers questioning the need for this advice. A Multiphase Computational Fluid Dynamics (CFD) model was created using computerized tomography images of a child's healthy ear. It was then used to study the flow of fluids through the external ear, tympanic cavity, and auditory tube, with and without submersion. The model accurately described the behavior of the air retained in the patient's nasopharynx and tympanic cavity. A simulated elevation of pressure in the external auditory canal without submersion, without increase of pressure in the nasopharynx, demonstrated that fluids promptly crossed the tympanostomy tube into the middle ear. However, simulated elevation of pressure in the external auditory canal with concurrent elevation of air pressure in the nasopharynx during submersion did not lead to passive tube opening nor to any detectable flow through the tympanostomy tube. In the model, submersion increases pressure in the nasopharynx which offsets the pressure in the external auditory canal. So, in the absence of a pressure gradient, no passive tubal opening took place, and no air or fluid flow was detected through the transtympanic tube. This model now includes the exhaust function of the auditory tube in the model and shows its relevance.
Joao Subtil; Nuno Martins; Teresa Nunes; Dídia Covas; Paulo Vera-Cruz; Richard Voegels; Joao Paco. Including auditory tube function on models is relevant to assess water exposure after tympanostomy tubes–Multiphase computerized fluid dynamics model. International Journal of Pediatric Otorhinolaryngology 2018, 111, 187 -191.
AMA StyleJoao Subtil, Nuno Martins, Teresa Nunes, Dídia Covas, Paulo Vera-Cruz, Richard Voegels, Joao Paco. Including auditory tube function on models is relevant to assess water exposure after tympanostomy tubes–Multiphase computerized fluid dynamics model. International Journal of Pediatric Otorhinolaryngology. 2018; 111 ():187-191.
Chicago/Turabian StyleJoao Subtil; Nuno Martins; Teresa Nunes; Dídia Covas; Paulo Vera-Cruz; Richard Voegels; Joao Paco. 2018. "Including auditory tube function on models is relevant to assess water exposure after tympanostomy tubes–Multiphase computerized fluid dynamics model." International Journal of Pediatric Otorhinolaryngology 111, no. : 187-191.
The aim of this paper is the experimental characterization of a ball valve under steady and unsteady conditions, based on experimental tests carried out in a pressurized pipe system assembled at Instituto Superior Técnico. Data analysis showed that the response of the valve under steady-state conditions depends not only on the valve geometry and closure percentage, but also on the flow regime (i.e., Reynolds number); the comparison with values published in literature confirmed that typical valve head loss curves presented in manuals and textbooks refer to turbulent flows. The behavior under unsteady conditions was also analyzed based on transient pressure head measurements showing that the valve effective closure time varies between 4 and 10% of the total time of the maneuver. Two mathematical functions (hyperbolic and sigmoidal) are proposed to describe the discharge variation as a function of the total time of the maneuver and of the initial steady-state discharge; the most appropriate function depends on the simplifications imposed on the hydraulic transient simulator. A computational fluid dynamics (CFD) model was used to support the observed experimental behavior and to highlight the effect of the pipe length on the discharge variation.
João Paulo B. C. C. Ferreira; Nuno M. C. Martins; Dídia I. C. Covas. Ball Valve Behavior under Steady and Unsteady Conditions. Journal of Hydraulic Engineering 2018, 144, 04018005 .
AMA StyleJoão Paulo B. C. C. Ferreira, Nuno M. C. Martins, Dídia I. C. Covas. Ball Valve Behavior under Steady and Unsteady Conditions. Journal of Hydraulic Engineering. 2018; 144 (4):04018005.
Chicago/Turabian StyleJoão Paulo B. C. C. Ferreira; Nuno M. C. Martins; Dídia I. C. Covas. 2018. "Ball Valve Behavior under Steady and Unsteady Conditions." Journal of Hydraulic Engineering 144, no. 4: 04018005.
The aim of this paper is to investigate the complex nature of the transient energy dissipation by using a computational fluid dynamics (CFD) model with a high spatial and temporal resolution together with one-dimensional (1D) models incorporating different unsteady friction (UF) formulations. The analysis focuses on a transient event in a single pipe system with a smooth-wall turbulent flow (with an initial Reynolds number equal to 7,638) generated by an instantaneous valve closure. For the considered flow condition, the numerical experiments point out the importance of the used UF model with regard to the wall shear stress simulation. In such a context, it is shown that the convolution-based UF models better describe the pressure signal than the instantaneous acceleration–based ones because they take into account a set of previous time steps. This is due to the fact that, similarly to the laminar regime, to simulate the characteristics of low turbulent transients the flow time history plays a crucial role.
N. M. C. Martins; B. Brunone; S. Meniconi; H. M. Ramos; D. I. C. Covas. CFD and 1D Approaches for the Unsteady Friction Analysis of Low Reynolds Number Turbulent Flows. Journal of Hydraulic Engineering 2017, 143, 04017050 .
AMA StyleN. M. C. Martins, B. Brunone, S. Meniconi, H. M. Ramos, D. I. C. Covas. CFD and 1D Approaches for the Unsteady Friction Analysis of Low Reynolds Number Turbulent Flows. Journal of Hydraulic Engineering. 2017; 143 (12):04017050.
Chicago/Turabian StyleN. M. C. Martins; B. Brunone; S. Meniconi; H. M. Ramos; D. I. C. Covas. 2017. "CFD and 1D Approaches for the Unsteady Friction Analysis of Low Reynolds Number Turbulent Flows." Journal of Hydraulic Engineering 143, no. 12: 04017050.
In this paper, the analysis of fast laminar transients in pressurized pipes is developed using a computational fluid dynamics (CFD) model, combined with the Zielke model and laboratory data. The systematic verification of the performance of the CFD model executed in the first part of the paper allows defining the most efficient set of the discretization parameters capable of capturing the main features of the examined transient. In this framework, the crucial role of radial discretization is pointed out. In the second part of the paper, the refined and efficient CFD model is used to examine some aspects of interest for understanding the dynamics of transients. Specifically, the uniformity of the instantaneous pressure distributions along the pipe radius, which validates the results of the most popular quasi-two-dimensional (2D) models, has been revealed. Moreover, it has been shown that the strongest link between the wall shear stress and the axial component of the velocity occurs in the region close to the pipe wall as well as that the time-shift between the wall shear stress and the local instantaneous flow acceleration increases significantly as time elapses.
Nuno M. C. Martins; Bruno Brunone; Silvia Meniconi; Helena M. Ramos; Dídia I. C. Covas. Efficient Computational Fluid Dynamics Model for Transient Laminar Flow Modeling: Pressure Wave Propagation and Velocity Profile Changes. Journal of Fluids Engineering 2017, 140, 011102 .
AMA StyleNuno M. C. Martins, Bruno Brunone, Silvia Meniconi, Helena M. Ramos, Dídia I. C. Covas. Efficient Computational Fluid Dynamics Model for Transient Laminar Flow Modeling: Pressure Wave Propagation and Velocity Profile Changes. Journal of Fluids Engineering. 2017; 140 (1):011102.
Chicago/Turabian StyleNuno M. C. Martins; Bruno Brunone; Silvia Meniconi; Helena M. Ramos; Dídia I. C. Covas. 2017. "Efficient Computational Fluid Dynamics Model for Transient Laminar Flow Modeling: Pressure Wave Propagation and Velocity Profile Changes." Journal of Fluids Engineering 140, no. 1: 011102.
Pierfabrizio Puntorieri; Giuseppe Barbaro; Nuno M. C. Martins; Dídia Covas; Vincenzo Fiamma; C. A. Brebbia; P. Vorobieff. HYDRAULIC TRANSIENT EXPERIMENTAL STUDY IN A COPPER PIPE. Computational and Experimental Methods in Multiphase and Complex Flow IX 2017, 1, 27 -33.
AMA StylePierfabrizio Puntorieri, Giuseppe Barbaro, Nuno M. C. Martins, Dídia Covas, Vincenzo Fiamma, C. A. Brebbia, P. Vorobieff. HYDRAULIC TRANSIENT EXPERIMENTAL STUDY IN A COPPER PIPE. Computational and Experimental Methods in Multiphase and Complex Flow IX. 2017; 1 ():27-33.
Chicago/Turabian StylePierfabrizio Puntorieri; Giuseppe Barbaro; Nuno M. C. Martins; Dídia Covas; Vincenzo Fiamma; C. A. Brebbia; P. Vorobieff. 2017. "HYDRAULIC TRANSIENT EXPERIMENTAL STUDY IN A COPPER PIPE." Computational and Experimental Methods in Multiphase and Complex Flow IX 1, no. : 27-33.
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.
Alexandre K. Soares; Nuno M. C. Martins; Dídia I. C. Covas. Transient vaporous cavitation in a horizontal copper pipe. Journal of Hydraulic Research 2017, 55, 731 -736.
AMA StyleAlexandre K. Soares, Nuno M. C. Martins, Dídia I. C. Covas. Transient vaporous cavitation in a horizontal copper pipe. Journal of Hydraulic Research. 2017; 55 (5):731-736.
Chicago/Turabian StyleAlexandre K. Soares; Nuno M. C. Martins; Dídia I. C. Covas. 2017. "Transient vaporous cavitation in a horizontal copper pipe." Journal of Hydraulic Research 55, no. 5: 731-736.
Nuno Martins; Joao N. Delgado; Helena M. Ramos; Dídia I. C. Covas. Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model. Journal of Hydraulic Research 2017, 55, 506 -519.
AMA StyleNuno Martins, Joao N. Delgado, Helena M. Ramos, Dídia I. C. Covas. Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model. Journal of Hydraulic Research. 2017; 55 (4):506-519.
Chicago/Turabian StyleNuno Martins; Joao N. Delgado; Helena M. Ramos; Dídia I. C. Covas. 2017. "Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model." Journal of Hydraulic Research 55, no. 4: 506-519.
Nuno M.C. Martins; Alexandre Kepler Soares; Helena M. Ramos; Dídia Isabel Cameira Covas. CFD modeling of transient flow in pressurized pipes. Computers & Fluids 2016, 126, 129 -140.
AMA StyleNuno M.C. Martins, Alexandre Kepler Soares, Helena M. Ramos, Dídia Isabel Cameira Covas. CFD modeling of transient flow in pressurized pipes. Computers & Fluids. 2016; 126 ():129-140.
Chicago/Turabian StyleNuno M.C. Martins; Alexandre Kepler Soares; Helena M. Ramos; Dídia Isabel Cameira Covas. 2016. "CFD modeling of transient flow in pressurized pipes." Computers & Fluids 126, no. : 129-140.
The current paper aims at the experimental and numerical analysis of the cavitating pipe flow during the occurrence of hydraulic transients in a quasi-horizontal straight copper pipe rig. Transient events were simulated by the quasi-instantaneous closure of a pneumatically actuated ball valve located at the downstream end of the pipe. A hydraulic transient model has been developed for describing cavitating pipe flow by means of two approaches – the discrete vapour cavity model (DVCM) and the discrete gas cavity model (DGCM). Firstly, the model has been calibrated by using transient data without cavitation. Numerical results have been compared with collected data and a good agreement has been observed as long as the unsteady friction losses are considered. Secondly, DVCM and DGCM have been used to describe cavitating flows. Results of both models have been compared, and the DGCM model has shown to better describe transient events with cavitation.
Alexandre K. Soares; Nuno Martins; Dídia Isabel Cameira Covas. Investigation of Transient Vaporous Cavitation: Experimental and Numerical Analyses. Procedia Engineering 2015, 119, 235 -242.
AMA StyleAlexandre K. Soares, Nuno Martins, Dídia Isabel Cameira Covas. Investigation of Transient Vaporous Cavitation: Experimental and Numerical Analyses. Procedia Engineering. 2015; 119 ():235-242.
Chicago/Turabian StyleAlexandre K. Soares; Nuno Martins; Dídia Isabel Cameira Covas. 2015. "Investigation of Transient Vaporous Cavitation: Experimental and Numerical Analyses." Procedia Engineering 119, no. : 235-242.
The aim of the current paper is the development and application of a systematic and comprehensive approach for obtaining the most efficient meshes, described in terms of dimensionless parameters, for modelling pressurized water flows in pipes using Computational Fluid Dynamics (CFD). This analysis is carried out for the combination of three dimensionless mesh parameters: λa, the dimensionless mesh size in the axial direction expressed in terms of number of diameters; λc, the dimensionless mesh size in the circumferential direction expressed in terms of the pipe perimeter; and λr, the ratio between the first layer thickness (FLT) and the thickness of the viscous sublayer for a specific turbulent flow. A four-step systematic approach has been used to obtained the most efficient meshes: (i) the mesh is generated in a meshing software using the 3-D fluid domain which is defined in a computer-aided design software; (ii) steady state fluid flow is simulated by using the CFD until the convergence criteria is met; (iii) the accuracy of the numerical results is evaluated by comparing the computed velocity profiles with exact or semi-empirical solutions; and (iv) the previous three steps are repeated for different combinations of mesh parameters and for two flows (laminar and turbulent) and the most efficient meshes are obtained by the compromise between the maximum accuracy and the minimum computational effort. The use of the most efficient meshes in other pipe flows is discussed.
Nuno M.C. Martins; Nelson J.G. Carriço; Helena M. Ramos; Dídia I.C. Covas. Velocity-distribution in pressurized pipe flow using CFD: Accuracy and mesh analysis. Computers & Fluids 2014, 105, 218 -230.
AMA StyleNuno M.C. Martins, Nelson J.G. Carriço, Helena M. Ramos, Dídia I.C. Covas. Velocity-distribution in pressurized pipe flow using CFD: Accuracy and mesh analysis. Computers & Fluids. 2014; 105 ():218-230.
Chicago/Turabian StyleNuno M.C. Martins; Nelson J.G. Carriço; Helena M. Ramos; Dídia I.C. Covas. 2014. "Velocity-distribution in pressurized pipe flow using CFD: Accuracy and mesh analysis." Computers & Fluids 105, no. : 218-230.
The current paper aims to discuss the main uncertainties associated with the hydraulic transient modelling of raising pipe systems with and without surge protection. A one-dimensional hydraulic transient solver was developed based on the classic water hammer theory and solved by the Method of Characteristics (MOC). The solver incorporates the pump-element described by Suter parameters, a pressurised surge tank (hydropneumatic vessel, HPV) and Vitkovsky's (2000) formula for unsteady friction description. The model was tested using transient pressure data and steady-state flow data from two hydraulic circuits installed at the Hydraulics Laboratory of the Civil Engineering Department, in Instituto Superior Técnico (Lisbon, Portugal). Pressure data were obtained at two/three locations (at the upstream end, at a middle section and at the downstream end). Transient tests with and without the HPV connected to the system were carried out for different flow rates. Transients were generated by the sudden stoppage of the pump. Collected data were compared with the results of the numerical modelling and used to calibrate model parameters. Good agreement between data and numerical results was obtained. Some tests with the HPV connected lead to higher pressure surges than when there was no protection in the system. These analyses are important to develop more solid and reliable numerical models as well to create awareness of the main uncertainties of developed models.
J.N. Delgado; N.M.C. Martins; D.I.C. Covas. Uncertainties in Hydraulic Transient Modelling in Raising Pipe Systems: Laboratory Case Studies. Procedia Engineering 2014, 70, 487 -496.
AMA StyleJ.N. Delgado, N.M.C. Martins, D.I.C. Covas. Uncertainties in Hydraulic Transient Modelling in Raising Pipe Systems: Laboratory Case Studies. Procedia Engineering. 2014; 70 ():487-496.
Chicago/Turabian StyleJ.N. Delgado; N.M.C. Martins; D.I.C. Covas. 2014. "Uncertainties in Hydraulic Transient Modelling in Raising Pipe Systems: Laboratory Case Studies." Procedia Engineering 70, no. : 487-496.