A rigorous framework involving flow decomposition and averaging is presented, within which the mechanics of rough-(e.g., rippled-) bed oscillatory flows can be better interpreted and understood. Spatiallyaveraged equations for conservation of fluid mass and momentum are developed for analyses of rapidly-changing bed conditions, e.g., for growing ripples. Where repeated observations of the changing bed conditions are available, the ensemble and spatially-averaged versions of these equations can be used for more detailed analyses of the flow dynamics.The double-averaged (in space and phase or time) equations of mass and momentum conservation are shown to be appropriate for analyses of flows over fixed rough beds and equilibrium ripples. The value of the present framework is highlighted herein by its application to PIV-measured oscillatory-flow velocities, stresses and vorticities over growing and equilibrium wave-induced intermediate-depth orbital-vortex ripples. In particular, discussions are provided regarding the mechanisms by which gravity-induced and pressure-gradient-induced momentum is transferred to the bed, with the analysis framework naturally and explicitly including the combination of the full range of fluid stresses and boundary form and skin friction drag that is important in defining the flow mechanics.

Laser Doppler anemometry (LDA) is conventionally used for flow velocity measurements of particles in liquids and gases. The application of LDA to acoustic fields provides the potential for non-intrusive and direct measurement of acoustic velocity. This paper describes a dual-beam LDA system developed for the measurement of acoustic particle velocity in minimal photon scatter/seeding environments using a photon-correlation method and low optical power. The system has been used to measure the acoustic pressure in a standing-wave-tube with a 0.2dB agreement with that of a standard 12-in microphone at low frequencies. The optical method offers the potential for the direct calibration of microphones against acoustic pressure, rather than an indirect method such as reciprocity that is the current internationally accepted method.

A cost-effective Particle Image Velocimetry (PIV) system has been developed that is capable of resolving flow fields at frequencies of up to 200 Hz (covering the typical scales of interest for hydraulic researchers), with recording durations of over 8 min. The system uses a highspeed camera to image flow fields illuminated by a scanning-beam lightsheet, where the lightsheet is generated by a galvanometer-driven mirror (computer controlled) together with a parabolic mirror. The system has several advantages over rotating-polygon type scanning systems, including: that the mirror is always positioned at the focal point of the parabola, and that the lightsheet generation is extremely versatile, with the lightsheet width (for a single parabolic mirror) and beam scan velocities easily and independently adjustable. Additionally, the beam scan velocity, which is typically nonlinear in rotating-polygon systems due to inherent properties of parabolic reflectors, can be constant in a galvanometer-based system (giving a uniform intensity lightsheet) by driving the galvanometer at an unsteady angular velocity. Integrated synchronisation options for the system permit frame-straddling techniques to be used in order to reduce interframe times to below I /(camera frame rate). The system also offers additional benefits over equivalent double-pulsed or twin-laser setups that rely on beam expansion by lens systems, and that typically only allow measurement at frequencies up to 50 Hz. Manipulation of the beam diameter using lens systems is outlined. The system has been implemented and used to obtain PIV measurements in flows of water and oil. (c) 2007 Elsevier Ltd. All rights reserved.

Experiments utilizing two-dimensional fixed dune profiles and varying flow depth (dune regime flows) highlight the equilibrium (self-similar) nature of the near-bed boundary layer over developing dunes with flow separation in the dune lee. The negligible variation in roughness layer (comprising the interfacial and form-induced layers) flow structure for developing dunes was confirmed in terms of spatial fields of time-averaged velocities and stresses; and vertical distributions of: (a) double-averaged (in time and space) longitudinal velocity, (b) double-averaged normal stresses, and (c) the components of the momentum balance for the flow. The finding of an equilibrium nature for the near-bed flow over developing dunes is significant in its centrality to understanding the feedback loop between flow, bed morphology, and sediment transport that controls erodible-bed development. Further research is required into the form of the distribution of double-averaged velocity in the form-induced layer above roughness tops, and also to complete generalization for varying dune steepness of the universal expression for double-averaged longitudinal velocity (varying linearly with elevation) determined herein for the interfacial layer (below roughness tops). Work is presently focusing on the additional effects on flow structure due to sediment transport and three-dimensional flow and bed morphology, although it is expected that the equilibrium boundary layer flow structure patterns identified herein will still be evident for these more complex systems.

This report documents the results of a literature survey into optical methods for the measurement of acoustic parameters ion air and water. The report reviews existing methods for the measurement of sound in air and in water in order to establish the requirements for metrology-based optical methods in sound measurement. The favoured approach for developing fundamental standards for acoustics based on optical methods are laser Doppler anemometry (LDA) using photon correlation for air, and laser Doppler vibrometry (LDV) using a reflecting membrane in the acoustic field for water. A review of current progress on the project is also presented with recommendations made for the direction of work to be undertaken in the second phase of the project. This report is the Deliverable for the Phase One Work Package for Project 3.6 of the NMS Quantum Metrology Programme of the UK Department of Trade and Industry. The project is being undertaken by a consortium of the National Physical Laboratory, Loughborough University and Edinburgh University, with Laser Optical Engineering Ltd and QinetiQ as sub-contractors.