|Webster, Donald||Georgia Institute of Technology (GA Tech)||Principal Investigator, Contact|
|Soenen, Karen||Woods Hole Oceanographic Institution (WHOI BCO-DMO)||BCO-DMO Data Manager|
The data files contain the fluid velocity measurements in the Burgers vortex flow field. Vortex orientations are horizontal and vertical, each with 4 levels of intensity, as indicated via the file name. Data were measured using tomographic particle image velocimetry.
The tomographic particle image velocimetry (tomographic PIV) technique was used to measure the three-dimensional flow field (Elsinga et al., 2006) and to quantitatively confirm that it matches the target parameters of small-scale eddies in copepod habitats. The tomographic PIV technique reconstructed the volumetric position of small particles suspended in the fluid, the position of which was imaged by collecting scattered laser light via four cameras simultaneously. Particle displacements were calculated via cross-correlation of particle locations in consecutive volumetric reconstructions in order to measure the local three-dimensional velocity vector. Three-dimensional flow measurements were required for this flow since the local velocity vector included three components of motion and the flow field varied in three coordinate directions.
The tomographic PIV system (Murphy et al., 2012) used four high-resolution (Phantom v210, 1280 × 800 pixels), cameras to measure flow fields at the scale of the copepod. Images were captured digitally at a rate of 24 frames per second. To resolve the small length scales in this study, a 105 mm focal length lens (Nikon) was used for each camera. Scheimpflug mounts were used to change the orientation of the lens to correct the plane of focus on the cameras (Murphy et al., 2012). Orgasol polyamide powder (20 micron diameter; specific weight of 1.03 g cm-3; Arkema group) tracked the fluid motion within the tank. An infrared laser (808 nm wavelength) was used to illuminate the tracer particles. Experiments were performed in a dark room to eliminate any light outside the control volume that could increase the level of error in the flow measurements.
The vortex volume was reconstructed in the DaVis software ( LaVision DaVis 8.4 - LaVision Inc.) using MART algorithms. A three-dimensional cross-correlation technique calculated the velocity field in the vortex by measuring particle displacements in consecutive reconstructed volumes (Elsinga et al., 2006).
|X||horizontal coordinate||millimeters (mm)|
|Y||horizontal coordinate||millimeters (mm)|
|Z||vertical coordinate||millimeters (mm)|
|V_x||horizontal velocity field||meters per seconds (m/s)|
|V_y||horizontal velocity field||meters per seconds (m/s)|
|V_z||vertical velocity field||meters per seconds (m/s)|
|Flow_field||orientation of the vortex axis: horizontal or vertical||unitless|
|Level||level of intensity: 1, 2, 3, 4||unitless|
|Dataset-specific Instrument Name|| |
Tomographic particle image velocimetry
|Generic Instrument Name|| |
Particle Image Velocimetry (PIV) system
|Dataset-specific Description|| |
Data were measured using tomographic particle image velocimetry
|Generic Instrument Description|| |
Measures 2D velocity flow fields, usually by scanning particles with a laser beam and capturing images of the illuminated particles.
Copepods are ubiquitous animals in marine environments and play a critically-important function in the food web of the world's oceans. The ability of a copepod to sense fluid motion provides an advantage for critical survival tactics such as finding food, finding mates, and avoiding predators. This project will examine the capability of copepods to detect turbulent flow. A turbulent-like flow will be mimicked in a laboratory aquarium as a small vortex (i.e., swirling motion like a tornado), and copepod swimming behavior will be observed in and around the vortex. The goal is to understand the variations in the sensory ecology of three species of copepods with three representative sensor arrays to better explain their temporal and spatial distribution in the ocean in response to turbulence conditions. The project also has a strong education and outreach plan. It will provide interdisciplinary training for graduate and undergraduate students in fields such as engineering, biology, and computational sciences. Further, research results will provide context for planned outreach efforts to educate the general public at local high schools and aquariums.
The project will deconstruct the turbulence-copepod interaction by performing detailed kinematics analysis of swimming in three species of copepods in and around a laboratory realization of a Burgers' vortex that mimics in situ turbulent vortices in the dissipation range of scales. The goal is to test the hypothesis that the copepods Acartia tonsa, Temora longicornis, and Calanus finmarchicus detect hydrodynamic cues related to vortices in turbulent flows and actively respond via changes in swimming kinematics. Using a custom designed and calibrated apparatus, a turbulent-like vortex will be created in the laboratory. By holding the turbulent vortex stable in space, cameras will be focused on a small region of the feature to record the animal behavior relative to well-quantified flow characteristics. The approach has the advantage of eliminating the time-varying and stochastic nature of turbulent flows that make such mechanistic understanding so challenging to achieve. Hypotheses will address questions about the influence of swimming style, setal array architecture, and the interaction of chemical and hydrodynamical cues on the turbulence-copepod interaction. Specifically, the investigators will examine how copepod species with different sensory structures and swimming orientation respond to a stable well-defined laboratory stimulus to determine how copepods exploit the shape and orientation of turbulent features. The species of copepods chosen for this work provide a range of sensory architectures, swimming orientations, sizes, and mate tracking abilities.