Measurement of local bed shear stress in streams using a Preston‐static tube

Ackerman, Josef Daniel; Hoover, Trent M.

doi:10.4319/lo.2001.46.8.2080

Cited by 44 publications

(29 citation statements)

References 24 publications

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“…1). In this case, u* was taken as the von Karman's constant ( ϭ 0.4) multiplied by the slope obtained from a graph of velocity (u) versus height (ln z) in the logarithmic region of the boundary layer (Ackerman and Hoover 2001). The velocity profiles were obtained using sil- ver-coated hollow glass spheres (mean diameter 16 m, density 2.0 g cm Ϫ3 , Potters Industries), which were tracked in a particle image velocimetry (PIV) system (Lasiris Magnum SP diode laser, StockerYale; Model 500 Pulse Generator, Berkeley Nucleonics; TM-9701 Progressive Scan Camera, PULNiX America; Video Savant Version 3.0, IO Industries; PIVView 2.1, PivTec GmbH), and measured velocities, based on 150 image pairs, were obtained in 1-mm vertical resolution.…”

Section: Methodsmentioning

confidence: 99%

A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins

Nishizaki

Ackerman

2005

Limnol. Oceanogr.

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Responses to predator odors or chemical alarm cues or both from conspecifics in aquatic systems generally involve a single chemical cue. We report a secondary chemical cue, released by adult red sea urchins after they detect primary chemical cues from a predatory sea star. This secondary cue, which is detected by juvenile urchins, leads to the aggregation of juveniles underneath adults for protection. In choice experiments, juvenile Strongylocentrotus franciscanus moved toward adults in response to a chemical cue produced by adults held downstream of a predatory sea star (Pycnopodia helianthoides), but showed no such response to predators presented in the absence of adults or when adults were held upstream of predators. Furthermore, this response was size dependent and not symmetrical, since larger urchins did not respond to the secondary cue. This secondary chemical cue system may confer a selective advantage for juveniles, allowing them to balance risk of predation versus competition with adults. This result underscores the significance of postsettlement processes in the recruitment of mobile benthic invertebrates, which in the case of red sea urchins involves a unique behavioral strategy.

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Section: Methodsmentioning

confidence: 99%

A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins

Nishizaki

Ackerman

2005

Limnol. Oceanogr.

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“…Vertical profiles of the momentum boundary layer at the upstream and downstream locations were obtained for V. spiralis and V. americana in the flat and twisted configurations using PIV. Shear velocities, which were determined by multiplying the von Karman constant (=0.41) by the slope of the velocity vs ln(z) in the logarithmic portion of the boundary layer (Ackerman and Hoover, 2001), were used to estimate k c and the ␦ DSL (Dade, 1993) where:…”

Section: Scmentioning

confidence: 99%

The interaction of CO2 concentration and spatial location on O2 flux and mass transport in the freshwater macrophytes Vallisneria spiralis and V. americana

Nishihara

Ackerman

2007

Journal of Experimental Biology

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SUMMARY The biology of aquatic organisms determines the maximum rates of physiological processes, but the mass transport of nutrients determines the nominal rates at which these processes occur. Maximum O2 flux(Pmax) at 17.1 mmol m–3 CO2was higher for the leaves of the freshwater macrophyte Vallisneria spiralis [Pmax=0.013±0.001 mmol m–2 s–1 (gchla+bm–2)–1 (mean ± s.e.m.)] than for the closely related species, Vallisneria americana[Pmax=0.008±0.001 mmol m–2s–1 (gchla+bm–2)–1]. The O2 flux saturated at freestream velocities >4.5±1.2 cm s–1 and was spatially invariant for both species. However, a tenfold decrease in CO concentration to 1.71 mmol m–3 changed the nature of the relationship between O2 flux and spatial location along the leaf surface, and reduced the O2 flux of V. spiralis to values similar to V. americana. The O2 flux[Pmax=0.007±0.001 mmol m–2s–1 (gchla+bm–2)–1] saturated at the upstream location(i.e. 1 cm from the leading edge of the leaf) but was found to increase linearly with freestream velocity [slope=0.057±0.011 mmol m–2 s–1 (gchla+bm–2)–1 (m s–1)–1] at the downstream location (i.e. 7 cm from the leading edge) at freestream velocities >1.8±0.9 cm s–1. Conversely, mass transfer rates did not vary with CO2 concentration, and were characteristic of a laminar concentration boundary layer at the upstream location and a turbulent concentration boundary layer at the downstream location. Rates of mass transfer measured directly from O2 profiles were not predicted by theoretical values based on hydrodynamic measurements. Moreover, the concentration boundary layer thickness (δCBL) values measured directly from O2 profiles were 48±2% and 21±1% of the predicted theoretical δCBL values at the upstream and downstream locations, respectively. It is evident that physiological processes involving mass transport are coupled and vary in space. Mass transport investigations of biological systems based solely on hydrodynamic measurements need to be interpreted with caution.

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“…Both the Pitot tube and ADV measurements contained uncertainties because of the effects of the angle of attack. Ackerman and Hoover (2001) showed that for a Pitot-static tube oriented at angles up to ±20°, relative to the direction of the approaching flow, the velocity measurements were reasonably consistent. In the Pitot tube tested, the probe support ensured that the angles of attack were below this limit.…”

Section: An Alternative Methods For Measuring Velocities In Open-channmentioning

confidence: 81%

An alternative method for measuring velocities in open-channel flows: perfomance evaluation of a Pitot tube compared to an acoustic meter

Almeida

Souza

2017

RBRH

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Hydrometric measurements undertaken in channels with high velocities are conditioned to the particularities of the flow, which is often characterized by instantaneous fluctuations and disturbances on the free surface. In such cases, the uncertainties associated with velocity fluctuations exceed the precision offered by the instruments that are employed in conventional techniques. A reasonable accuracy of the results is therefore sufficient to accomplish the objective of the measurements. The use of devices based on Pitot's principle in fast open-channel flows could be an effective alternative to conventional velocity meters. This study aimed to develop a Pitot tube in its simplest configuration and evaluate its performance in a laboratory channel at velocities ranging from 0.2 to 2.0 m/s. The uncertainties in the static and total head readings were propagated to the output velocities, showing that the device built has the potential for measurements over 1.2 m/s, but it is not recommended for low velocities (<0.6 m/s). The results were compared to those taken using an Acoustic Doppler Velocimeter (ADV). The instantaneous velocity readings indicated uncertainties of the same order of magnitude in both instruments. The differences between the mean velocities measured by the Pitot tube and the ADV were restricted to an agreement range of 15%, which is expected to be gradually reduced with further increase in flow velocity. The results showed the similar performances of both devices regarding the higher velocity estimates. Therefore, velocity meters should be developed to employ Pitot devices as an alternative method in high-velocity open-channel flows.Keywords: Hydrometry; Open channel flow; Differential head meters; Pitot tube. RESUMOAplicações de hidrometria em canais com altas velocidades estão sujeitas às condições do fluxo, que geralmente é caracterizado por flutuações instantâneas e perturbações na superfície livre. Nesses casos, as incertezas associadas às flutuações de velocidade superam a precisão oferecida pelos instrumentos empregados nas técnicas convencionais. Uma exatidão razoável dos resultados é, portanto, suficiente para atender ao objetivo das medições. O uso de dispositivos baseados no princípio de Pitot em escoamentos rápidos pode ser uma alternativa eficaz ao uso dos medidores de velocidade convencionais. Este estudo teve por objetivo confeccionar um tubo de Pitot em sua configuração mais simples e avaliar seu desempenho em um canal experimental para velocidades variando no intervalo de 0,2 a 2,0 m/s. As incertezas nas leituras de carga estática e de carga total foram propagadas para as velocidades estimadas, mostrando que o dispositivo construído tem potencial para medições acima de 1,2 m/s, mas não é recomendado para baixas velocidades (<0,6 m/s). Os resultados foram comparados com um Velocímetro Acústico de Efeito Doppler (ADV). As leituras de velocidade instantânea indicaram incertezas de mesma magnitude em ambos os instrumentos. As diferenças entre as velocidades médias estimadas co...

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Measurement of local bed shear stress in streams using a Preston‐static tube

Cited by 44 publications

References 24 publications

A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins

A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins

The interaction of CO2 concentration and spatial location on O2 flux and mass transport in the freshwater macrophytes Vallisneria spiralis and V. americana

An alternative method for measuring velocities in open-channel flows: perfomance evaluation of a Pitot tube compared to an acoustic meter

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