Stereo Thermal Marking Velocimetry

Savelyev, Ivan; Fuchs, J.

doi:10.3389/fmech.2018.00001

Cited by 28 publications

(4 citation statements)

References 25 publications

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“…The image processing algorithm used to identify, locate, and track thermal marks is described in detail by Savelyev et al () and Savelyev and Fuchs (). In short, it relies on two major principles: first, 2D fast Fourier transform (FFT2) is used to compute function

F = italiciFFT 2 ((), italicFFT 2 ((), frameA) \cdot italicFFT 2 {(italicframeB)}^{*}),

which peak corresponds to the global shift between two consecutive frames.…”

Section: Methodsmentioning

confidence: 99%

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The Impact of Nonbreaking Waves on Wind‐Driven Ocean Surface Turbulence

2020

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A comprehensive study on the properties of upper ocean turbulence and its response to a variety of wind and wave forcing conditions was conducted at the Surge Structure Atmosphere INteraction (SUSTAIN) facility, University of Miami, RSMAS. The dimensions of SUSTAIN wind-wave-current tunnel are 18 m long, 6 m wide, and 2 m high, uniquely allowing for freely forming turbulence unconstrained by side walls. The grid of input parameters covered a range of wave steepness (ak: 0-0.27) within each investigated wind speed (U 10 : 2-20 m/s), allowing for the isolation of wave effects on the turbulence driven by both wind and waves. The response of turbulence to each pair of wind-wave parameters was measured in steady-state conditions (after 20+ min of settling time) by a suite of nonintrusive turbulence visualization techniques, located at 10 m fetch. These included 3-D visualization of water tracing dye entrainment by turbulence, underwater particle image velocimetry, and passive and active thermal imagery resolving surface skin temperature and velocity fluctuations. The resulting data set includes both qualitative 3-D view of subsurface turbulent structures and precise quantitative turbulent kinetic energy (TKE) measurements mapped out in response to the grid of input parameters. In lower winds, TKE was found to grow substantially in response to increasing wave steepness, in line with the expected effect of increasing wave forcing. However, in higher winds the effect of increasing wave steepness on TKE was found to be negative. It is hypothesized to be due to the rise of airflow separation, effectively sheltering much of the water surface from turbulence production by wind friction.Plain Language Summary This laboratory study aims to visualize and quantify small-scale turbulence taking place below the ocean surface. Of a particular interest here is the effect of surface wave motion, outside of wave breaking, and how it influences ocean turbulence, which is otherwise forced by wind. Unlike in the field, the laboratory setup allows independent control of wind and wave parameters, thus allowing decomposition of wind-and wave-driven aspects of the turbulent flow. A mixture of well-known and novel nonintrusive turbulence visualization techniques employed in this study gave unprecedented clear view of turbulent response under varying forcing conditions. Two major counteracting wave-dependent processes were found to impact surface turbulence. One is additional turbulence production due to the action of wave induced drift current, another is turbulence dampening due wave induced airflow separation, causing a reduction in wind friction.

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F = italiciFFT 2 ((), italicFFT 2 ((), frameA) \cdot italicFFT 2 {(italicframeB)}^{*}),

which peak corresponds to the global shift between two consecutive frames.…”

Section: Methodsmentioning

confidence: 99%

“…The image processing algorithm used to identify, locate, and track thermal marks is described in detail by Savelyev et al (2012) and Savelyev and Fuchs (2018). In short, it relies on two major principles: first, 2D fast Fourier transform (FFT2) is used to compute function…”

Section: Thermal Marking Velocimetrymentioning

confidence: 99%

The Impact of Nonbreaking Waves on Wind‐Driven Ocean Surface Turbulence

2020

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“…Onto this patch of sea, Savelyev projects beams of infrared laser light-light just below the visible spectrum-that he has arranged into grids, points, and lines. He images those lines through two cameras (to compose a stereo image) whose feeds he can translate into visibility on his laptop in FLIP's science lab (see figure 11 for an image from one screen-we look down here onto the sea surface, striped with infrared-and see Savelyev and Fuchs 2018).…”

Section: Beholding the Wavesmentioning

confidence: 99%

Flipping the Ship: Ocean Waves, Media Orientations, and Objectivity at Sea

Helmreich¹

2021

Media+Environment

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The FLoating Instrument Platform (FLIP), a seagoing vessel managed by the Scripps Institution of Oceanography, in La Jolla, California, offers an unorthodox vantage point on the sea. In its horizontal conformation, FLIP travels like an ordinary oceangoing craft. But by “flipping” 90 degrees into a vertical position once it arrives at its destination—with all the furniture and instrumentation inside swiveling correspondingly—it becomes an enormous spar buoy, more or less stationary in the wave field. With most of the platform’s 108-meter length below the surface, scientists can work in a stable environment, which helps them study sea surface phenomena such as waves against a largely unwavering baseline. This article offers an anthropologically informed media studies account of work on FLIP, as the author reports on working ethnographically alongside wave scientists in this Escheresque environment, a setting that often sees scientists shifting between aspirations to steady objectivism and moments of fleeting but motivating wonder. Placing FLIP in a longer history of physical oceanography, the author also argues that what wave scientists take ocean waves to be has been strongly imprinted by the techniques and technologies—mathematics, photography, spectral analysis, wave tanks—through which waves have been studied and come to be known. Wave science also inherits knowledge from mid-twentieth-century ocean observation projects in the Pacific Ocean that were conditioned by Cold War American maritime expansion. The paper suggests that the technological mediations, orientations, and re-orientations offered to scientists at sea on FLIP may serve as allegories for apprehending American oceanography’s oscillating visions of the relationship of science to society, of present research to future implications, and of objectivity to politics — visions that come into focus as scientists (and their anthropological interlocutors) switch, alternate, and flip their paradigm scripts, their frames of epistemic reference.

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“…Aubourg et al [6] used a stereo-PIV set-up with 3 cameras making it possible to measure the wave field and the velocity field at the free surface. A stereo-refraction approach was used by Gomit et al [7] to measure the wave field while a stereo-thermal PIV approach was used by Savelyev & Fuchs [8] to measure the free-surface elevation and the velocity field at the free surface. The stereo-PIV method requires seeding in the fluid with floating particles which may be missing in certain areas (e.g.…”

Section: Introductionmentioning

confidence: 99%

Towards accurate stereo-video based free-surface reconstruction for wave tank experiments

Page

Tassin

Caverne

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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Measuring accurately the shape of the free surface in medium-scale hydrodynamic testing facilities is challenging with conventional wave gauges. To overcome this problem, it is necessary to go towards higher resolution measurement systems. For this purpose, we investigate the ability of stereo-video acquisition systems to reconstruct free surface waves in laboratory conditions. This technique has been proven to give satisfactory results in open sea conditions, although it is dependent on the environmental conditions (weather, solar incidence angle). At sea, the stereo-video reconstruction algorithm makes profit of the short waves generated by the wind in order to correlate the points from the left and right images. The main challenge of adapting this technique to laboratory conditions, i.e. in absence of sun and wind, is to overcome the absence of texture on the free surface. This paper presents recent work aiming at developing a stereo-vision measurement system for laboratory conditions. Our efforts have been devoted to finding an adapted lighting system and generating a texture suitable for the reconstruction algorithm. Different lighting configurations have been tested in order to understand its impact on the reconstructions. For the texture generation, we have investigated different means of generating short surface waves (water droplets, air blowing, circulation current, underwater acoustic emissions) in different experimental facilities. Our conclusions show that it is possible to reconstruct the shape of surface gravity waves in the presence of short surface waves and that the effects of lighting and texture on the quality of the reconstruction are strongly coupled.

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Stereo Thermal Marking Velocimetry

Cited by 28 publications

References 25 publications

The Impact of Nonbreaking Waves on Wind‐Driven Ocean Surface Turbulence

The Impact of Nonbreaking Waves on Wind‐Driven Ocean Surface Turbulence

Flipping the Ship: Ocean Waves, Media Orientations, and Objectivity at Sea

Towards accurate stereo-video based free-surface reconstruction for wave tank experiments

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