Peter Lloyd

TL;DR: In this article, the impact of a rigid horizontal plate onto a wave crest and, in the limit, onto a flat water surface was investigated using a two-phase incompressible-compressible smoothed particle hydrodynamics (SPH) method.

TL;DR: In this paper, experiments have been conducted to study the unsteady wakes of submerged conical islands using wind tunnel visualization studies, which used a rigid top plate to produce the effect of fluid depth, support the results from the water channel.

Abstract: A series of experiments has been conducted to investigate recirculating shallow-water flow in the wakes of conical model islands with gently sloping sides. Four islands have been used with side slopes ranging from 33.1 to 8.0°. For all tests reported here the water depth was less than the island height; the islands are said to be surface piercing. Measurements of flow velocity have been made in the laboratory using a digital particle tracking velocimetry (PTV) system. This produces instantaneous, whole-field velocity vector maps of the wake flows. A “wake stability parameter” \iS, has been used to classify the island wakes into “vortex shedding” or “unsteady bubble” types. The stability parameter is a measure of the stabilizing effect of bed friction relative to the destabilizing influence of transverse shear. For small values of \iS (<0.2) vortex shedding was well organized and vigorous in the island wakes. Vortex shedding was found to cease for larger values of \iS (0.35–0.40). These values are similar to those found by other researchers for the shallow wakes of vertically sided circular cylinders. The influence of the island side slope angle on the wakes is discussed. Depth-averaged and three-dimensional (3D) numerical shallow-water flow models with the usual hydrostatic pressure assumption have been used to simulate the experimental flows. The models are based on a fully coupled semi-implicit Lagrangian numerical method. For cases where vortex shedding occurred, the 3D model was found to predict a more 3D far wake than was observed. The two-dimensional (2D) model produced good overall agreement with experimental results. For very shallow depths with the wake stabilized by bed friction, the 3D model demonstrated closer agreement to the measured results than the 2D model.

TL;DR: In this paper, a particle tracking velocimetry (PTV) based method was developed for obtaining surface-velocity fields in unsteady flows which is useful for hydraulic model studies.

TL;DR: In this article, a balanced sample, with respect to age, sex and socio-economic status (SES), of 578 children (5-11 years) was given a 35-item test of speaker and listener skills using a variety of pictorial material.