Inês Meireles

Skimming Flow in the Nonaerated Region of Stepped Spillways over Embankment Dams

Traditionally, research on stepped spillway hydraulics has been focused on the air-water flow region but for the hydraulic design of small embankment dams experiencing relatively large overtopping flows, the nonaerated region can be very important. Empirical formulas are presented for predicting skimming flow properties upstream of the point of inception of air entrainment for 1V:2H sloping stepped spillways, and the location and flow depth at the point of inception. Particular emphasis is placed on the clear-water depth, velocity distribution, and the energy dissipation characteristics in the developing nonaerated flow region. The velocity distribution is well described by a power law. The normalized clear-water depth and the normalized specific energy varied with the relative distance along the spillway and the effect of the normalized critical depth was negligible. Finally, the rate of energy dissipation was small, which has direct implications for the design of the downstream energy dissipator.

Air entrainment onset in skimming flows on steep stepped spillways: an analysis

ABSTRACT We discuss, apply and validate several physics-based criteria for air entrainment into flows on steep stepped spillways, using laboratory observations and numerical results published elsewhere. To the best of our knowledge, this is the first time a validation of these criteria is undertaken for any chute flow in general, and for the skimming flow in steep stepped spillways in particular. To undertake the validation, we employed experimental and numerical data covering a considerable range of volume flow rates and step heights. We observed an overall good performance of most of the criteria, especially taking into account the intrinsic difficulties in defining the time-averaged location and depth of the inception point of air entrainment experimentally. Finally, we present two novel non-dimensional numbers designed to facilitate the physical interpretation of the location of the inception point of air entrainment.

Anomalies in Wall Renders: Overview of the Main Causes of Degradation

The assessment of historical buildings is usually focused on: 1) structural features related to brick or stone walls, wooden floors and other structural elements, or 2) highly valued decorative features, such as frescoes, stuccos, and facade details. During the last quarter of the 20th century, some “secondary” elements also started to receive their share of attention from researchers and practitioners. Wall renders are one of the most important of such elements because of their role as a sacrificial protective layer and the numerous problems that were encountered in the past as a result of incompatibility issues in rehabilitation works. This article discusses the main causes of the deterioration of wall renders, with emphasis on lime-based renders; these renders thoroughly reviewed and their relative weight in the overall degradation is addressed.

Comparison of the inspector and rating protocol uncertainty influence in the condition rating of sewers

Wastewater drainage systems asset management decisions, in particular regarding rehabilitation interventions, are largely dependent on close-circuit television (CCTV) inspection results. However, the results of CCTV inspections are affected by several sources of uncertainty. Within the present communication, the inspectors uncertainty is quantified by comparing periodic inspection reports from three trunk sewers of a Portuguese sewer system. The inspections were carried out by the same experienced inspector using the same equipment. Therefore, the uncertainties from the lack of experience and the difference of the inspector and equipment were ruled out. The protocol uncertainty is also quantified comparing the results obtained with the Water Research Center (WRc) and the National Research Council of Canada (NRC) protocols condition ratings. Both operational and structural condition rating were analysed, but emphasis was given to the later since it dictates the repair and replacement interventions.

Characterization of turbulence statistics on the non-aerated skimming flow over stepped spillways: a numerical study

In this work we address the mean flow and turbulence statistics in the non-aerated region of a stepped spillway by using two different numerical strategies in two dimensions. First, we present results regarding the flow in a large portion of the spillway, simulated with a volume of fluid (VoF) method to capture the position of the free surface (case A). Numerically-obtained data are in very good agreement with particle image velocimetry (PIV) data; further, results suggest that profiles of mean velocity, turbulent kinetic energy (TKE) and dissipation rate of TKE at the step edges are approximately self-similar. It was also found that values of TKE and dissipation rate of TKE in the boundary layer development region follow universal similarity laws which are valid for open-channel flows. In addition, the field of simulated dimensionless pressure and pressure distributions at the step edges are qualitatively similar to those reported in a recent experimental work. Second, additional simulations were developed as a pressure-driven flow for only a portion of the spillway (case B). This was possible due to prior knowledge of the water depths. We show that, despite the fact that the pressure field can not be interpreted as in case A, the numerical simulations closely reproduce the experimental data regarding averaged velocity, vorticity, and the turbulence statistics. It was also found that turbulence intensity profiles in the intermediate region are consistent with published experimental results for open-channel flows. These numerical results offer new avenues for the simulation of portions of stepped spillways to assess the physics at the inception point of air entrainment with more sophisticated turbulence closures.

The Influence of the Construction Technology in Time-Cost Relationships of Sewerage Projects

Time-cost models have been developed in various contexts to assist in forecasting the duration of different types of projects. The present research explores the influence of the construction technology on the time-cost relationship. For that purpose, the data from 21 sewerage projects using trenchless technology and from 49 sewerage projects using the traditional open-cut method was analyzed. The 70 sewerage projects analyzed were completed in Chicago, U.S., between 1994 and 2002. The influence of the construction technology in the time-cost relationship was found to be statistically significant and time-relationships were determined for sewerage projects using trenchless technology and the traditional open-cut method. Furthermore, along with the Bromilow type models an alternative approach was tested using the time normalized by the project cost as dependent variable, allowing additional insight into the time performance of the open-cut and lining technology used (cured in place).

Modeling the Degradation Rate of the Wood Frame Doors and Windows of the National Palace of Sintra, Portugal

AbstractModeling the service life of building components is a key requirement for several purposes, including the implementation of an effective and efficient asset-management system, life-cycle assessments, or life-cycle cost calculations. Because the phenomena underlying the degradation of building components is highly complex, it is common to use statistical approaches for modeling purposes. This paper is focused on the statistical modeling of the service life of the wood frame doors and windows of the National Palace of Sintra. A review of the main factors of degradation of traditional linseed-based painted wood frame doors and windows and of the approaches that have been used to model the service life of building materials and components is presented. The influence of the exposure to weather agents on the degradation rate of external wood frame doors and windows is investigated and a model to estimate the average condition level is proposed. The proposed model takes into account radiation and wind-dr...