scholarly journals A Self-Contained Identification Scheme for Eddies in Drifter and Float Trajectories

2006 ◽  
Vol 23 (11) ◽  
pp. 1583-1592 ◽  
Author(s):  
Matthias Lankhorst
Keyword(s):  
Field Experiments ◽  
Simple Calculation ◽  
Simple Type ◽  
Physical Oceanography ◽  
Autoregressive Processes ◽  
Trajectory Data ◽  
Identification Scheme ◽  
Lagrangian Coordinate ◽  
Surface Drifters ◽  
Lagrangian Coordinate System

Abstract It is becoming increasingly recognized that the eddy field plays an important—possibly dominating—role for oceanic motions in many aspects (e.g., transport of properties and risk assessment in the case of extreme events). This motivates the study of individual eddy events. In the Lagrangian coordinate system, vorticity possibly associated with eddies appears in two forms: as shear vorticity between neighboring particles, and as curvature of the trajectory of a single particle. Typical field experiments in physical oceanography using surface drifters or subsurface floats do not reach data densities high enough to produce enough encounters of drifters to calculate shear vorticity between them. However, curvature in individual tracks is easily observed. This study presents a methodology that extracts segments from within a trajectory that are “looping,” which will be interpreted as a drifter being caught in an eddy. The method makes use of autoregressive processes, a simple type of stochastic processes, which easily enables a fit to the nonperfectly shaped trajectory data usually expected from field experiments. These processes also deliver frequency and persistence of the detected eddies by a very simple calculation, which makes the methodology highly suited for automatized scanning of larger datasets.

scholarly journals A quasi-Lagrangian coordinate system based on high resolution tracer observations: implementation for the Antarctic polar vortex

2008 ◽  
Vol 8 (4) ◽  
pp. 16123-16173 ◽  
Author(s):  
E. V. Ivanova ◽  
C. M. Volk ◽  
O. Riediger ◽  
H. Klein ◽  
N. M. Sitnikov ◽  
...  
Keyword(s):  
High Resolution ◽  
Coordinate System ◽  
Vortex Core ◽  
Polar Vortex ◽  
Mixing Ratio ◽  
Lagrangian Coordinate ◽  
Antarctic Polar Vortex ◽  
The Antarctic ◽  
Lagrangian Coordinate System

Abstract. In order to quantitatively analyse the chemical and dynamical evolution of the polar vortex it has proven extremely useful to work with coordinate systems that follow the vortex flow. We propose here a two-dimensional quasi-Lagrangian coordinate system {χi, Δχi}, based on the mixing ratio of a long-lived stratospheric trace gas i, and its systematic use with i = N2O, in order to describe the structure of a well-developed Antarctic polar vortex. In the coordinate system {χi, Δχi} the mixing ratio χi is the vertical coordinate and Δχi = χi(Θ)−χivort(Θ) is the meridional coordinate (χivort(Θ) being a vertical reference profile in the vortex core). The quasi-Lagrangian coordinates {χi, Δχi} persist for much longer time than standard isentropic coordinates, potential temperature Θ and equivalent latitude φe, do not require explicit reference to geographic space, and can be derived directly from high-resolution in situ measurements. They are therefore well-suited for studying the evolution of the Antarctic polar vortex throughout the polar winter with respect to the relevant chemical and microphysical processes. By using the introduced coordinate system {χN2O, ΔχN2O} we analyze the well-developed Antarctic vortex investigated during the APE-GAIA (Airborne Polar Experiment – Geophysica Aircraft in Antarctica – 1999) campaign (Carli et al., 2000). A criterion, which uses the local in-situ measurements of χi=χi(Θ) and attributes the inner vortex edge to a rapid change (δ-step) in the meridional profile of the mixing ratio χi, is developed to determine the (Antarctic) inner vortex edge. In turn, we suggest that the outer vortex edge of a well-developed Antarctic vortex can be attributed to the position of a local minimum of the χH2O gradient in the polar vortex area. For a well-developed Antarctic vortex, the ΔχN2O-parametrization of tracer-tracer relationships allows to distinguish the tracer inter-relationships in the vortex core, vortex boundary region and surf zone and to examine their meridional variation throughout these regions. This is illustrated by analyzing the tracer-tracer relationships χi : χN2O obtained from the in-situ data of the APE-GAIA campaign for i = CFC-11, CFC-12, H-1211 and SF6. A number of solitary anomalous points in the CFC-11 : N2O correlation, observed in the Antarctic vortex core, are interpreted in terms of small-scale cross-isentropic dispersion.

Drift velocity of spatially decaying waves in a two-layer viscous system

1995 ◽  
Vol 299 ◽  
pp. 217-239 ◽  
Author(s):  
Ismael Piedra-Cueva
Keyword(s):  
Mass Transport ◽  
Lower Layer ◽  
Mass Conservation ◽  
Layer System ◽  
Transport Velocity ◽  
Mass Transport Velocity ◽  
Lagrangian Coordinate ◽  
Progressive Waves ◽  
Lagrangian Coordinate System ◽  
Good Agreement

This paper analyses the mass transport velocity in a two-layer system induced by the action of progressive waves. First the movement inside the two layers is obtained. Next the mass transport of spatially decaying waves is calculated by solving the momentum and mass conservation equations in the Lagrangian coordinate system. Two different physical situations are analysed: the first is waves in a closed channel and the second is waves in an unbounded domain, where the steady-state mass flux may be non-zero. The influence of the viscous properties of the lower layer on the mass transport in both layers is studied. Comparison with the experiments of Sakakiyama & Bijker (1989) in a water-mud system shows good agreement. The results show that the mass transport velocity can be quite different from the velocity given by the rigid bed theory, depending on the physical properties of the lower layer.

scholarly journals Submesoscale dispersion of surface drifters in a coastal sea near offshore wind farms

2018 ◽  
Author(s):  
Ulrich Callies ◽  
Ruben Carrasco ◽  
Jens Floeter ◽  
Jochen Horstmann ◽  
Markus Quante
Keyword(s):  
Wind Farm ◽  
Field Experiments ◽  
Velocity Structure ◽  
Power Spectra ◽  
Wind Farms ◽  
Spatial Separation ◽  
Offshore Wind ◽  
Turbulence Theory ◽  
Relative Dispersion ◽  
Surface Drifters

Abstract. We analyse relative dispersion of surface drifters released as pairs (6 instances) or triplets (2 instances) during three field experiments in the German Bight in close proximity to wind farms. Drifter pairs can be classified in a remarkably clear way into those with spatial separation growing either exponentially or non-monotonously. There is some tentative evidence that exponential relative dispersion growth rates preferably occur for drifter pairs that are most exposed to the possible influence of a wind farm. Kinetic energy spectra and velocity structure functions suggest that turbulent energy could be injected by tides, possibly also via an interaction between tidal currents and wind turbine towers. Applicability of inertial range turbulence theory, however, can be doubted given distinct peaks of overtides observed in velocity power spectra. More comprehensive studies would be needed to better separate submesoscale effects of wind farms, tides and possibly baroclinic instabilities on observed drifter behaviour in a complex coastal environment.

scholarly journals A Theory of Elastic/Plastic Plane Strain Pure Bending of FGM Sheets at Large Strain

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 456 ◽  
Author(s):  
Sergey Alexandrov ◽  
Yun-Che Wang ◽  
Lihui Lang
Keyword(s):  
Residual Stresses ◽  
Plane Strain ◽  
Material Properties ◽  
Large Strain ◽  
Thickness Distribution ◽  
Functionally Graded ◽  
Pure Bending ◽  
Lagrangian Coordinate ◽  
Lagrangian Coordinate System ◽  
General Method

An efficient analytical/numerical method has been developed and programmed to predict the distribution of residual stresses and springback in plane strain pure bending of functionally graded sheets at large strain, followed by unloading. The solution is facilitated by using a Lagrangian coordinate system. The study is concentrated on a power law through thickness distribution of material properties. However, the general method can be used in conjunction with any other through thickness distributions assuming that plastic yielding initiates at one of the surfaces of the sheet. Effects of material properties on the distribution of residual stresses are investigated.

scholarly journals The Lagrangian coordinate system and what it means for two-dimensional crowd flow models

2016 ◽  
Vol 443 ◽  
pp. 272-285 ◽  
Author(s):  
Femke van Wageningen-Kessels ◽  
Ludovic Leclercq ◽  
Winnie Daamen ◽  
Serge P. Hoogendoorn
Keyword(s):  
Coordinate System ◽  
Two Dimensional ◽  
Flow Models ◽  
Lagrangian Coordinate ◽  
Lagrangian Coordinate System

scholarly journals Detecting flow features in scarce trajectory data using networks derived from symbolic itineraries: an application to surface drifters in the North Atlantic

2020 ◽  
Vol 27 (4) ◽  
pp. 501-518 ◽  
Author(s):  
David Wichmann ◽  
Christian Kehl ◽  
Henk A. Dijkstra ◽  
Erik van Sebille
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Boundary ◽  
Boundary Current ◽  
Trajectory Data ◽  
Surface Transport ◽  
The North ◽  
The North Atlantic ◽  
Surface Drifters ◽  
Double Gyre

Abstract. The basin-wide surface transport of tracers such as heat, nutrients and plastic in the North Atlantic Ocean is organized into large-scale flow structures such as the Western Boundary Current and the Subtropical and Subpolar gyres. Being able to identify these features from drifter data is important for studying tracer dispersal but also for detecting changes in the large-scale surface flow due to climate change. We propose a new and conceptually simple method to detect groups of trajectories with similar dynamical behaviour from drifter data using network theory and normalized cut spectral clustering. Our network is constructed from conditional bin-drifter probability distributions and naturally handles drifter trajectories with data gaps and different lifetimes. The eigenvalue problem of the respective Laplacian can be replaced by a singular value decomposition of a related sparse data matrix. The construction of this matrix scales with O(NM+Nτ), where N is the number of particles, M the number of bins and τ the number of time steps. The concept behind our network construction is rooted in a particle's symbolic itinerary derived from its trajectory and a state space partition, which we incorporate in its most basic form by replacing a particle's itinerary by a probability distribution over symbols. We represent these distributions as the links of a bipartite graph, connecting particles and symbols. We apply our method to the periodically driven double-gyre flow and successfully identify well-known features. Exploiting the duality between particles and symbols defined by the bipartite graph, we demonstrate how a direct low-dimensional coarse definition of the clustering problem can still lead to relatively accurate results for the most dominant structures and resolve features down to scales much below the coarse graining scale. Our method also performs well in detecting structures with incomplete trajectory data, which we demonstrate for the double-gyre flow by randomly removing data points. We finally apply our method to a set of ocean drifter trajectories and present the first network-based clustering of the North Atlantic surface transport based on surface drifters, successfully detecting well-known regions such as the Subpolar and Subtropical gyres, the Western Boundary Current region and the Caribbean Sea.

The Stretching of a Viscoplastic Thread of Liquid

2003 ◽  
Vol 125 (6) ◽  
pp. 946-951 ◽  
Author(s):  
M. A. M. Al Khatib
Keyword(s):  
Coordinate System ◽  
Yield Stress ◽  
Special Interest ◽  
Inertial Effects ◽  
Viscoplastic Fluids ◽  
Lagrangian Coordinate ◽  
Lagrangian Coordinate System

The problem of stretching a viscoplastic (yield-stress) thread of a liquid hanging vertically is considered. The length of the thread at later times and the time at which it ruptures is determined. A Lagrangian coordinate system is used to analyze the extension of the thread as it sags under its own weight, with negligible inertial effects. The biviscosity model has been used to characterize viscoplastic fluids; the Newtonian and Bingham models can be recovered as limiting cases. The Bingham limit is of special interest.

scholarly journals Detecting flow features in scarce trajectory data using networks derived from symbolic itineraries: an application to surface drifters in the North Atlantic

2020 ◽  
Author(s):  
David Wichmann ◽  
Christian Kehl ◽  
Henk A. Dijkstra ◽  
Erik van Sebille
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Boundary ◽  
Boundary Current ◽  
Trajectory Data ◽  
Surface Transport ◽  
The North ◽  
The North Atlantic ◽  
Surface Drifters ◽  
Double Gyre

Abstract. The basinwide surface transport of tracers such as heat, nutrients and plastic in the North Atlantic Ocean is organized into large scale flow structures such as the Western Boundary Current and the Subtropical and Subpolar Gyres. Being able to identify these features from drifter data is important for studying tracer dispersal, but also to detect changes in the large scale surface flow due to climate change. We propose a new and conceptually simple method to detect groups of trajectories with similar dynamical behaviour from drifter data using network theory and normalized cut spectral clustering. Our network is constructed from conditional bin-drifter probability distributions and naturally handles drifter trajectories with data gaps and different lifetimes. The eigenvalue problem of the respective Laplacian can be replaced by a singular value decomposition of a related sparse data matrix. The construction of this matrix scales with O(NM + Nτ), where N is the number of particles, M the number of bins and τ the number of time steps. The concept behind our network construction is rooted in a particle's symbolic itinerary derived from its trajectory and a state space partition, which we incorporate in its most basic form by replacing a particle's itinerary by a probability distribution over symbols. We represent these distributions as the links of a bipartite graph, connecting particles and symbols. We apply our method to the periodically driven double-gyre flow and successfully identify well-known features. Exploiting the duality between particles and symbols defined by the bipartite graph, we demonstrate how a direct low-dimensional coarse definition of the clustering problem can still lead to relatively accurate results for the most dominant structures, and resolve features down to scales much below the coarse graining scale. Our method also performs well in detecting structures with incomplete trajectory data, which we demonstrate for the double-gyre flow by randomly removing data points. We finally apply our method to a set of ocean drifter trajectories and present the first network-based clustering of the North Atlantic surface transport based on surface drifters, successfully detecting well-known regions such as the Subpolar and Subtropical Gyres, the Western Boundary Current region and the Carribean Sea.

scholarly journals Submesoscale dispersion of surface drifters in a coastal sea near offshore wind farms

Ocean Science ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 865-889 ◽  
Author(s):  
Ulrich Callies ◽  
Ruben Carrasco ◽  
Jens Floeter ◽  
Jochen Horstmann ◽  
Markus Quante
Keyword(s):  
Wind Farm ◽  
Field Experiments ◽  
Velocity Structure ◽  
Power Spectra ◽  
Wind Farms ◽  
Turbulent Energy ◽  
Offshore Wind ◽  
Turbulence Theory ◽  
Relative Dispersion ◽  
Surface Drifters

Abstract. We analysed relative dispersion of surface drifters released as pairs (six instances) or triplets (two instances) during three field experiments conducted in the German Bight in close proximity to wind farms. There is some tentative evidence that nearly exponential growth of relative dispersion (non-local dispersion) preferably occurs for drifter pairs that are most exposed to the influence of a wind farm. Kinetic energy spectra and velocity structure functions are analysed with regard to the assumption that turbulent energy could be injected by tides, possibly also via an interaction between tidal currents and wind turbine towers. Applicability of inertial range turbulence theory, however, can be doubted given distinct peaks of overtides observed in velocity power spectra. More comprehensive studies would be needed to better separate submesoscale effects of wind farms, tides and possibly baroclinic instabilities on observed drifter behaviour in a complex coastal environment.

Slow Dripping of Yield-Stress Fluids

2005 ◽  
Vol 127 (4) ◽  
pp. 687-690 ◽  
Author(s):  
M. A. M. Al Khatib ◽  
S. D. R. Wilson
Keyword(s):  
Coordinate System ◽  
Yield Stress ◽  
Special Interest ◽  
Vertical Tube ◽  
Viscoplastic Fluids ◽  
Yield Stress Fluids ◽  
Lagrangian Coordinate ◽  
Lagrangian Coordinate System

The dripping problem of a viscoplastic (yield-stress) liquid running slowly out of a narrow vertical tube is considered. The volume of the drops which break away is determined. A Lagrangian coordinate system is used to analyze the extension of the thread as it sags under its own weight, neglecting inertia and capillarity. The biviscosity model has been used to characterize viscoplastic fluids; the Newtonian and Bingham models can be recovered as limiting cases. The Bingham limit is of special interest.

Sign in / Sign up

Export Citation Format

Share Document