Rita F. Carvalho

Numerical computation of the flow in hydraulic jump stilling basins

The formation of a hydraulic jump in a stilling basin downstream of a spillway with Froude number Fr = 6 and developed upstream flow was investigated using a physical and a numerical model. The numerical model is based on the 2D Reynolds-averaged Navier–Stokes equations, where the free surface is represented using a refined Volume-Of-Fluid (VOF) algorithm, the internal obstacles are described by means of the Fractional Area–Volume Obstacle Representation (FAVOR) method and the turbulence dynamics are represented using a specially developed RNG k–e closure model. Additional features of the code that are vital for its practical application include an automatic time step control, high–order schemes for advection and a variety of boundary conditions for the dependent variables on the free surface and adjacent to the internal obstacles.With this model, the hydraulic jump characteristics were analysed in two stages. First the turbulence model was not used, to describe the initial stages of jump formation and obtain suitable initial and boundary conditions. Then the full model was used to compute the time history of the dependent variables at selected locations and sections. The computed velocity, pressure values were compared with laboratory measurements and formulae available in the literature. The agreement between the numerical results and laboratory measurements was satisfactory.

Numerical and experimental investigation of a gully under surcharge conditions

This paper deals with numerical and experimental investigation of a gully under exceptional situations after the sewer system becomes pressurized. These results are useful for the calibration and validation of the linking elements found in Dual Drainage (DD) models. The experimental results were obtained in the MLE (Multiple-Linking-Element) experimental installation that allows the simulation of full surcharge flow through a gully. The installation consists of an 8 m long and 0.5 m wide channel, fitted with a 0.6 × 0.3 × 0.3 m gully with a 80 mm diameter pipe inlet at the bottom. The numerical results were obtained using a three-dimensional structured mesh simulated in the OpenFOAMTM Toolbox. The results characterization focuses mainly on the jet area, whereby pressure-flow relations were derived for this specific gully. The good agreement found between numerical and experimental results, allowed the extrapolation to larger flow rates.

Characterization of the hydraulic performance of a gully under drainage conditions

During rainfall events with low return periods (1-20 years) the drainage system can provide some degree of protection to urban areas. The system design is based not only on good hydraulic performance of the surface and the sewer network but also on their linking elements. Although the linking elements are of utmost importance as they allow the exchange of flow between the surface and the sewer network, there is a lack of studies that thoroughly characterize them. One crucial structural part of those elements is the gully. State-of-the-art dual-drainage models often use simplified formulae to replicate the gully hydraulic behaviour that lacks proper validation. This work focuses on simulating, both numerically and experimentally, the hydraulic performance of a 0.6 × 0.3 × 0.3 [m] (L × W × D) gully located inside an 8 × 0.5 × 0.5 [m] rectangular channel. The numerical simulations are conducted with the OpenFOAM toolbox and validated with water level measurements in the Multiple-Linking-Element experimental installation located at the Laboratory of Hydraulics of the University of Coimbra. The results provide a complete three-dimensional insight of the hydraulic behaviour of the flow inside the gully, and discharge coefficient formulae are disclosed that can be directly applied in dual-drainage models as internal boundary conditions.

Virtual chromoendoscopy can be a useful software tool in capsule endoscopy

BACKGROUND capsule endoscopy (CE) has revolutionized the study of small bowel. One major drawback of this technique is that we cannot interfere with image acquisition process. Therefore, the development of new software tools that could modify the images and increase both detection and diagnosis of small-bowel lesions would be very useful. The Flexible Spectral Imaging Color Enhancement (FICE) that allows for virtual chromoendoscopy is one of these software tools. AIMS to evaluate the reproducibility and diagnostic accuracy of the FICE system in CE. METHODS this prospective study involved 20 patients. First, four physicians interpreted 150 static FICE images and the overall agreement between them was determined using the Fleiss Kappa Test. Second, two experienced gastroenterologists, blinded to each other results, analyzed the complete 20 video streams. One interpreted conventional capsule videos and the other, the CE-FICE videos at setting 2. All findings were reported, regardless of their clinical value. Non-concordant findings between both interpretations were analyzed by a consensus panel of four gastroenterologists who reached a final result (positive or negative finding). RESULTS in the first arm of the study the overall concordance between the four gastroenterologists was substantial (0.650). In the second arm, the conventional mode identified 75 findings and the CE-FICE mode 95. The CE-FICE mode did not miss any lesions identified by the conventional mode and allowed the identification of a higher number of angiodysplasias (35 vs 32), and erosions (41 vs. 24). CONCLUSIONS there is reproducibility for the interpretation of CE-FICE images between different observers experienced in conventional CE. The use of virtual chromoendoscopy in CE seems to increase its diagnostic accuracy by highlighting small bowel erosions and angiodysplasias that weren´t identified by the conventional mode.

Stepped Spillway with Hydraulic Jumps: Application of a Numerical Model to a Scale Model of a Conceptual Prototype

Hydraulic jumps on the steps of a stepped spillway were investigated analytically, physically, and numerically. Using classic hydraulic formulae, a conceptual prototype was designed. A large scale model was adapted and an experimental study was conducted to examine similarity of hydraulic jumps on each step, minimizing hydraulic jump length and maximizing discharge per unit width. A numerical model based on the 2D Reynolds averaged equations, where the free-surface is represented using a refined volume-of-fluid algorithm, the internal obstacles are described by means of the fractional area-volume obstacle representation method, and the turbulence is represented by a specially developed RNG (Renormalization Group) k-e closure model was used for evaluating velocities and pressures, and for characterizing hydrodynamic forces on the baffles and sills. Preliminary design criteria are proposed for stepped spillways with hydraulic jump formation of simple shapes and adequate relations of critical depth/step heig...

Physical And Numerical Investigation of the Skimming Flow Over a Stepped Spillway

In the last two decades experimental research on stepped chute hydraulics has been very active. In this paper, the developing flow region over the stepped spillway was investigated using a physical and a numerical model. The numerical model is based on the 2D Navier-Stokes equations, where the free surface is represented using a refined Volume-Of-Fluid (VOF) algorithm, the internal obstacles are described by means of the Fractional Area-Volume Obstacle Representation (FAVOR) method. The numerical results were compared with experimental data obtained in a large scale model using the particle image velocimetry technique. The stepped channel is 0.50 m wide and 2.0 m high, with step height of 0.05 m and bottom inclination of 51.3o corresponding to a slope (V:H) of 1:0.8. At the upstream region of the chute the free surface is smooth and glassy and no air entrainment occurs, the numerical model is suitable for obtaining the characteristics and the influence of the presence of the steps. Typical flow phenomena in the cavity of the steps, in the shear layer and in the main flow are described. Velocity and turbulence intensities profiles are presented. The agreement between the numerical results and laboratory measurements was satisfactory.

Diagnostic accuracy of lugol chromoendoscopy in the oesophagus in patients with head and neck cancer

BACKGROUND AND AIM patients with head and neck squamous cell malignancies have a higher risk of oesophageal squamous cell carcinomas. Lugol chromoendoscopy in oesophagus is a simple technique with a high diagnostic yield in premalignant lesions. The objective was to analyze its diagnostic accuracy in dysplasia and carcinoma of the oesophagus in high-risk patients. METHODS prospective study from April/2008 to January/2012 using lugol chromoendoscopy with biopsies of suspicious lugol voiding areas > or = 5 mm. Patients with head and neck malignancies were included, except the ones with iodine allergy, oesophageal varices and contra-indications to standard endoscopy. The reference method was histopathology. RESULTS 89 patients were enrolled (mean age 62.8 + or - 13.3 years, 87 % men). Primary tumour was located in oropharynx in 37 (41.6 %), in oral cavity in 29 (32.6 %) and in the larynx in 23 (25.8 %) cases. 40.4 % patients had previous treatments and 87 % reported alcohol or tobacco addition. All exams performed without anaesthesia or complications. Nine suspicious lugol voiding areas were observed and biopsied. Histopathological analysis revealed high-grade dysplasia in 2 (2.2 %) and inflammation or normal findings in the others. The sensitivity and specificity for detecting high-grade dysplasia were 100 % and 92 % (95 % CI: 87-97), respectively. Diagnostic accuracy of the test was 92 % (95 % CI: 86-98). CONCLUSION lugol staining of the oesophagus during endoscopy seems to be a feasible, safe and justified procedure in high-risk populationas it enhances the detection of premalignant lesions.

Assessment of the Ability of a Volume of Fluid Model to Reproduce the Efficiency of a Continuous Transverse Gully with Grate

This paper deals with the numerical investigation of the drainage efficiency of a continuous transverse gully with the grate’s slots aligned in the flow direction and compared with experimental data sets. The gully efficiency attained with a three-dimensional (3D) numerical model is compared and validated against experimental data. The numerical simulations are performed using a computational fluid dynamics volume of fluid solver. Different slopes, from 0 to 10%, and a wide range of drainage flows, from 6.67 to 66.67??L/s/m66.67??L/s/m, are simulated. The linear relation between Froude number and efficiency of the gully is in agreement to the one experimentally obtained.

Turbulence Characterization in a Gully with Reverse Flow

AbstractThis work presents an experimental investigation on turbulent flow characteristics in a typical gully with reverse flow. Four different flow rates (the inlet Reynolds number ranged between 2.8e+04 and 7.4e+04) were characterized in a laboratory facility using an acoustic Doppler velocimeter. A complete signal analysis was carried out to identify and remove the influence of errors in acoustic Doppler measurements on the computation of the mean velocity, turbulent kinetic energy, and Reynolds stresses. The flow showed a similar pattern between the different analyzed experimental conditions in terms of mean velocity and turbulent kinetic energy. A macroanticlockwise spanwise axis vortex was identified based on the mean velocity field in the region encompassed between the upstream wall and the inlet centerline. Maximum mean velocity magnitudes were approximately 25% of the inlet velocity and characterized the outer flow of the vortex. Higher turbulent kinetic energies were observed at the inlet center...

Roughened Channels with Cross Beams Flow Features

AbstractThe implementation of roughened channels with cross beams (RCCB) in drainage systems reduces the negative effects of high kinetic energy on flood flows, such as the increased erosion of infrastructures or of the ground. This paper aims to highlight the importance of using RCCB in drainage systems and to contribute to a better knowledge of flow characteristics in RCCB. The performance of RCCB was studied under diverse conditions through the use of a physical model in which several cross beams were installed with different thickness, longitudinal spacing between them, and at different heights. Results of free-surface profile, pressure head, and velocity measurements for different arrangements of slopes, cross-beam dimensions, and spacing were compared with the scarce data available in literature and put together to form empirical relations to predict flow characteristics in the engineering practice dealing with RCCB design, such as discharge limit, maximum flow, water depth, and friction factor. In ...