111,966 research outputs found
Implications of hyposaline stress for seaweed morphology and biomechanics
No full textSeaweeds are primary producers that form a key component of coastal ecosystems. In estuaries and the intertidal zone they are frequently exposed to temporary hyposaline conditions. Previous research has shown that seaweed health status and photosynthetic activity are reduced due to hyposaline stress, but its effects on seaweed physical properties are unknown. This knowledge gap has important implications for the prediction of seaweed hydrodynamics and mechanical failure due to hydrodynamic stress, particularly in extreme conditions (e.g. storm events). In this study, we begin to address this knowledge gap by investigating the effects of hyposaline stress on the morphological and mechanical properties of the kelp Saccharina latissima (order Laminariales). We analysed the morphology of 23 seaweed blades and performed tension and bending tests on more than 90 samples prepared from them. The obtained data provide evidence that both morphology and mechanics of S. latissima are affected by hyposaline stress, i.e.: (i) blades bleach, develop blisters underneath the cortex, and change dimensions (increased volume and thickness, decreased width); and (ii) blade material becomes more flexible and more difficult to break (i.e. tougher). The results indicated a significant correlation between the time of exposure and changes in biomechanics of S. latissima with potential implications for seaweed hydrodynamics and survival strategies
Intermittency and interrelationships between turbulence scaling exponents: phase-randomisation tests
No full textOn the definition of solid discharge in hydro-environment research and applications
No full textVarious forms of mass balance equations are commonly used in sediment transport studies and applications. However, the quantities involved in such equations are not always clearly defined, with sediment flux (or solid discharge) as a typical example. Starting with the fundamental definitions, this paper provides a general and consistent framework for integral (Eulerian) mass balances and gives scale-consistent definitions for instantaneous and time-averaged variables. In particular, alternative expressions for the instantaneous and averaged solid discharge are proposed and compared with the existing formulations. Conceptual developments of this study are illustrated using sediment transport data from laboratory experiments
Statistics and characteristic scales for bed load in a channel flow with sidewall effects
No full textOn statistical properties of bed load sediment concentration
No full textData from a long-duration laboratory experiment involving optical measurements of moving particles in a bed load layer are presented. The data analysis is focused on identification of (1) the effects of the spatial measuring scale on concentration estimates, (2) statistical and scaling properties of sediment concentration, and (3) relationships between near-bed turbulent flow and sediment motion. The obtained results are integrated into a conceptual model that can be instrumental in studying statistical properties of solid transport rate, which, in most cases, can be linearly associated with the particle concentration
Active interactions between turbulence and bed load: Conceptual picture and experimental evidence
No full textThis paper reports results from experiments with simultaneous measurement of areal bed-load sediment concentration and water velocity (horizontal and vertical components) made at 1.5 particle diameters above the mean bed. The same spatial and temporal scales were employed to measure the kinematic properties of flowing water and sediments. The obtained data, covering a range of low sediment discharges, were analyzed in terms of bulk statistics, autocorrelation and cross-correlation functions, and quadrant decomposition of fluctuations. At the lowest transport rates, the motion of sediment particles was found to be mostly associated with sweep events. However, with increasing flow rate and bed-load discharge, the process mechanics changed, and the transport of sediments was also found to be significantly correlated with ejections. The obtained results are integrated into a conceptual picture attempting to bridge previous depictions of the bed-load transport mechanics
Flow-seaweed interactions of Saccharina latissima at a blade scale : turbulence, drag force, and blade dynamics
No full textAcknowledgements The work described in this publication was undertaken during the Ph.D. study of Davide Vettori at the University of Aberdeen funded by a scholarship from the Northern Research Partnership, Scotland. The authors gratefully acknowledge: Peter Davies and Paul Mitchell for their support and guidance; David Attwood for his assistance during seaweed collection; Hamish Biggs for his assistance during seaweed collection and transport to the University of Aberdeen, and in setting up LED used to synchronise instruments; and Roy Gillanders and Benjamin Stratton for meticulous technical support. Many insightful comments provided by the Associate Editor Professor J. D. Ackerman and anonymous reviewer helped to improve the quality of the fnal manuscript.Peer reviewe
Application of UVP within porous beds
No full textStandard measurement devices do not normally provide detailed information about flows in porous media because either they are too intrusive (e.g., hot/film wire anemometers) or because the solid phase impedes their physical access to the flow as in the case of laser Doppler anemometers or particle image velocimetry (PIV). In this study, a Metflow ultrasonic velocity profiler (UVP) is used to measure instantaneous velocity fields within porous media composed of plastic balls packed in a cubic pattern. Simple considerations of the ultrasound beam properties and propagation, plus a comparison with measurements performed by a PIV system, demonstrate that UVP devices are suitable for such a purpos
- …
