Search results for "buoy"

Detecting the chaotic nature of advection in complex river flows

2012

In order to detect signatures of chaotic advection in river surface motion, surface buoys equipped with GPS were deployed in a field experiment in River Danube, Hungary. The buoys were released in the vicinity of groynes where complex mixing processes occur. A detailed analysis of the trajectories was carried out, focusing on the time evolution of the distance between buoy pairs. The analysis included the determination and comparison of local Lyapunov exponents and prediction times of finite-time hyperbolic behaviour, which is related to strong mixing. Despite of the small number of applied buoys we found evidence on Lagrangian chaos in the wake of a groyne field. In order to supplement the…

Bench-scale investigation of inclined dense jets

2005

In this work experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented. The surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl. Four parameters were changed in the experiments, namely nozzle diameter and inclination, and jet density and flow rate. Jet trajectories were revealed by a colored tracer. Images of the jet were recorded by a digital camera and then further digitally processed, eventually resulting in a time-averaged tracer intensity field. All the jet geometrical parameters, once normalized, were found to be very well correlated to the densimetric Froude number. Mod…

Modeling Atmospheric Turbulence via Rapid Distortion Theory: Spectral Tensor of Velocity and Buoyancy

2017

Abstract A spectral tensor model is presented for turbulent fluctuations of wind velocity components and temperature, assuming uniform vertical gradients in mean temperature and mean wind speed. The model is built upon rapid distortion theory (RDT) following studies by Mann and by Hanazaki and Hunt, using the eddy lifetime parameterization of Mann to make the model stationary. The buoyant spectral tensor model is driven via five parameters: the viscous dissipation rate ε, length scale of energy-containing eddies L, a turbulence anisotropy parameter , gradient Richardson number (Ri) representing the local atmospheric stability, and the rate of destruction of temperature variance . Model outp…

Validation of buoyancy driven spectral tensor model using HATS data

2016

We present a homogeneous spectral tensor model for wind velocity and temperature fluctuations, driven by mean vertical shear and mean temperature gradient. Results from the model, including one-dimensional velocity and temperature spectra and the associated co-spectra, are shown in this paper. The model also reproduces two-point statistics, such as coherence and phases, via cross-spectra between two points separated in space. Model results are compared with observations from the Horizontal Array Turbulence Study (HATS) field program (Horst et al. 2004). The spectral velocity tensor in the model is described via five parameters: the dissipation rate (), length scale of energy-containing eddi…

Reducing Stress and Enhancing Academic Buoyancy among Adolescents Using a Brief Web-based Program Based on Acceptance and Commitment Therapy : A Rand…

2018

Acceptance and commitment therapy programs have rarely been used as preventive tools for alleviating stress and enhancing coping skills among adolescents. This randomized controlled trial examined the efficacy of a novel Finnish web- and mobile-delivered five-week intervention program called Youth COMPASS among a general sample of ninth-grade adolescents (n= 249, 49% females). The intervention group showed a small but significant decrease in overall stress (between-group Cohen’s d = 0.22) and an increase in academic buoyancy (d= 0.27). Academic skills did not influence the intervention gains, but the intervention gains were largest among high-stressed participants. The results suggest that …

The role of academic buoyancy and emotions in students' learning-related expectations and behaviours in primary school.

2019

Background. Academic buoyancy refers to students’ ability to come through ordinary challenges they face in the academic context, and it can positively contribute to students’ beliefs and behaviours in learning situations. Although buoyancy has been found to be related to positive academic outcomes, previous studies have not examined how buoyancy influences academic emotions in learning situations and how these emotions further affect students’ learning-related expectations and behaviours. \ud Aims. This study investigated to what extent academic buoyancy predicts students’ failure expectations, avoidance behaviour, and task-oriented planning in learning situations, and to what extent academ…

Analytical Study of the Thermal Induced Oscillations Known as Heartbeats

1998

Abstract A laser beam traveling horizontally at a short distance below the free surface of an absorbing solution exhibits various oscillatory states (periodic, quasiperiodic, and chaotic) which depend on both the buoyancy (Archimedes force) and the thermal coefficient of the surface tension (Marangoni effect). The beam oscillations have been called “heartbeats.” In this work, the heartbeats were produced by pumping 1-(2-pyridylazo)-2-naphthol (PAN) solutions in silicone oil with an Ar+continuous-wave laser beam. The relationships between PAN concentration and the other parameters that control the oscillatory behavior were studied. The frequency of the oscillations sensitively varied with sm…

Effect of pseudo-gravitational acceleration on the dissolution rate of miscible drops

2017

The effect of pseudo-gravitational acceleration on the dissolution process of two phase miscible systems has been investigated at high acceleration values using a spinning drop tensiometer with three systems: 1-butanol/water, isobutyric acid/water, and triethylamine/water. We concluded that the dissolution process involves at least three different transport phenomena: diffusion, barodiffusion, and gravitational (buoyancy-driven) convection. The last two phenomena are significantly affected by the centrifugal acceleration acting at the interface between the two fluids, and the coupling with the geometry of the dissolving drop leads to a change of the mass flux during the course of the dissol…

Separation of Ferrocolloids in Thermodiffusion Columns: the Effect of Solute Buoyancy

2002

Birth of the Biscane

2017

This paper describes the unprecedented storm Stephanie, which exhibited tropical characteristics over the Bay of Biscay on 15 September 2016. Remote sensing observations reveal a cloud-free area surrounded by a circular precipitation pattern and an axisymmetric wind field, while buoy observations show an abrupt drop in wind speed during the passage of the storm centre. Model analysis further corroborates an ongoing tropical transition from a frontal cold-core to a symmetric warm-core system. By analogy with ‘Medicanes’ (Mediterranean hurricanes), we name this storm a ‘Biscane’ (Biscay hurricane). Weather systems of this kind may become more frequent in a warmer climate.