A Shear Plate for Use in Oscillatory Flow

Abstract

In this paper a flexurally supported shear plate is described. It was designed for use under oscillatory flow where the periods of motion range from 0.5 to 15 seconds. The range of possible shear measurements is +100 N/m 2 with sensitivities as low as 0.015 N/m 2 . Special emphasis is placed on the calculation of corrections for secondary forces which may contribute a large proportion of the recorded apparent shear. Comparison of the corrected shear with laminar theory gives very good agreement. An example is given to illustrate the results obtained using this shear plate in an oscillating water tunnel for laminar and turbulent flow over both smooth and rough beds. RésuméOn décrit une plaque sensible dont Ie léger mouvement parallèle au fond permet de determiner la contrainte de cisaillement parié-tale. La plaque est concue pour l'étude des régimes oscillants ayant une période comprise entre 0,5 et 15 s. Des contraintes allant jusqu'a + 100 N/m 2 peuvent être mesurées avec une précision de l'ordre de 0,015 N/m 2 . On attache une importance particuliere au calcul des termes correctifs correspondant aux écoule-ments secondaires, ceux-ci pouvant représen-ter une part considerable des valeurs apparentes. Les contraintes corrigées sont en tres bon accord avec Ie calcul en régime laminaire. L'emploi de la plaque sensible est illustré par des experiences en tunnel a eau en régime d'écoulement oscillatoire. Ces experiences portent sur des lits lisses et rugueux en régimes laminaire et turbulent.

Recent advances in modeling swash zone dynamics: Influence of surf‐swash interaction on nearshore hydrodynamics and morphodynamics

“…Direct measurement of bed shear stress using a shear plate displaced in the direction of the applied stress has been widely used under steady flows and wave motion [ Riedel and Kamphuis , 1973; Grass et al , 1995; Myrhaug et al , 2001]. In the swash, application of this technique is complicated by the intermittent nature of the flow, which can lead to hydrostatic loading on the plate and pressure gradients on the plate boundaries that vary very rapidly with time.…”

Direct bed shear measurements under loose bed swash flows

“…Further, even at field scale or in large scale experiments, obtaining reliable velocity profile measurements at the leading edge of the swash flow is beyond the state of the art, even with PIV or ADVP instrumentation. A comprehensive review of recent measurements is presented by Allis et al, 2014. Previous laboratory measurements have focused predominantly on smooth beds or fixed beds Pujara and Liu, 2014;Riedel and Kamphuis, 1973;Seelam et al, 2011;You and Yin, 2007). The most recent work for these bed conditions was reported by Torres-Freyermuth et al (2013) and reaches similar conclusions to Barnes et al (2009).…”

Onset of sediment motion under waves and currents

“…It was concluded that, given adequate precautions and care, shear plates can be used successfully for steady currents, where the pressure gradient term is low, but in accelerating flow, especially under waves, the pressure gradient and inertia terms cannot be estimated with sufficient accuracy, so that there are very large errors in the residual estimates of shear stress. Riedel and Kamphuis (1973) have used a shear plate in an oscillating water tunnel, but had to make extensive corrections.…”