João Pedro Pêgo

Clear-water scour at comparatively large cylindrical piers

AbstractNew long-duration clear-water scour data were collected at single cylindrical piers with the objective of investigating the effect of sediment coarseness, Dp/D50 (Dp = pier diameter; D50 = median grain size) on the equilibrium scour depth and improving the scour depth time evolution modeling by making use of the exponential function suggested in the literature. Experiments were carried out for the flow intensity close to the threshold condition of initiation of sediment motion, imposing wide changes of sediment coarseness and flow shallowness, d/Dp (d = approach flow depth). The effect of sediment coarseness on the equilibrium scour depth was identified; existing predictors were modified to incorporate this effect for U/Uc≈1.0; Dp/D50>≈60 and d/Dp≥0.5; the complete characterization of a known scour depth time evolution model was achieved for U/Uc≈1.0, 60

Clear-water scour at pile groups

AbstractGroups of piles are frequently used as bridge foundations. Different group configurations, characterized by different pile spacing, skew-angle, number, and arrangement of pile group columns interact differently with the flow field and lead to different scour patterns and equilibrium scour depth. There have been a number of past studies on the characterization of scouring at pile groups, but most of them report short duration scour experiments. A priori, such short durations may be postulated to inherently carry important uncertainties into existing scour predictors. In this study, 75 long-duration laboratory tests were run under steady, clear-water flow close to the threshold for initiation of sediment motion, to address the effect of time, pile spacing, skew-angle and number of pile group columns on the equilibrium scour depth. Pile groups consisted of matrical arrangements of one, two, or three columns of four rows, with spacings of 1, 2, 3, 4.5, and 6 pile diameters; the tested skew-angles were...

Characterization of the scour cavity evolution around a complex bridge pier

A study on the time development of local scour around a complex pier was developed using a small-scale model embedded in a sediment bed. A total of 15 laboratorial tests were performed at the Hydraulics Laboratory of the Faculty of Engineering of the University of Porto. The duration of each experiment was previously established to progressively characterize the scour cavity. After each experiment, the flume was gradually emptied to facilitate the application of close-range photogrammetry. The scour depth values resulting from the application of photogrammetry at the pile cap front agree well with the values obtained experimentally. The temporal development of the scour cavity is presented and discussed. Empirical formulas for the scour cavity time development and for the relation of scour depths to scour cavity volumes were obtained. The obtained three-dimensional models can also be used for calibration and validation of numerical models.

Photogrammetric characterization of the scour cavity time evolution around a complex bridge pier

The temporal development of local scour around a complex bridge pier was experimentally studied using a small-scale model embedded in a uniform diameter sand. A set of 15 experiments were conducted at the Hydraulics Laboratory of the Faculty of Engineering of the University of Porto under steady clear-water conditions. Experiments lasted between five minutes and eleven days for a progressive characterization of the scour cavity until the equilibrium stage. Good agreement was achieved by comparing the scour depths directly read in the laboratory with the obtained from application of close-range photogrammetry. The time evolution of the scour cavity is studied. Important empirical relations for the temporal development of the scour cavity and for correlating scour depths with scour cavity volumes were derived. The resultant three-dimensional models can also be usefully used for the calibration and validation phases of a numerical model.

Forces and Velocity Measurements in Ship Propulsion Systems

Pod drives are modern outboard ship propulsion systems with a motor encapsulated in a watertight pod. The motor’s shaft is connected directly to one or two propellers. The whole unit hangs from the stern of the ship and rotates azimuthally, thus providing thrust and steering. In the past decade pod drive propulsion has developed to be a reliable and serious alternative to conventional ship propulsion, especially for cruiser liners [1,2]. The overall efficiency of the system is determinant for the economical success of the vessel and for this reason it is necessary to improve the efficiency of the propulsor recurring to non-conventional solutions.