n Active Current Selection for Lagrangian Profilers

Jouffroy, Jérôme; Zhou, Qiuyang

doi:10.4173/mic.2013.1.1

Cited by 12 publications

(16 citation statements)

References 16 publications

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“…where ∆f s is bias compensation, such that the point-wise fitness is 0 when all three vectors are collinear, a a is a special instance of the parameter tuple a of the logistic function f s presented earlier in (11). Fig.…”

Section: B Roms Parametersmentioning

confidence: 99%

“…Since there is a cost associated with estimating currents at each depth, in practice we want the controller to work with as few depths as possible. An active drifter is controllable if the currents in the area span the plane positively [11]. This criterion can be reformulated as follows max…”

Section: B Roms Parametersmentioning

confidence: 99%

“…In contrast, we assume no explicit knowledge about the dynamics of the ocean, except the vertical component of the flow, which we assume to be zero. In [11] the target application is to control the absolute position of a drifter in a coastal scenario, where the drifter can anchor itself at the sea bottom if necessary. As an extension, the deep ocean scenario for a single drifter is examined under idealized conditions (the drifter is assumed to have instant estimates of currents at the present location, the ocean currents are assumed to be stationary and to span the plane positively).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Active drifters: Towards a practical multi-robot system for ocean monitoring

Molchanov

Breitenmoser

Sukhatme

2015

2015 IEEE International Conference on Robotics and Automation (ICRA)

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We propose a method for controlling multiple active drifters in the presence of external forcing induced by the ocean. Our active drifters have one actuator: they can lower and raise their drogues in depth. By exploiting the vertically stratified nature of ocean currents, we show how classical multi-robot tasks (spreading out and aggregation) can be accomplished by the multi-drifter system. Tests with a realistic simulation based on an ocean model suggest that a practical implementation of active drifters which aggregate and disperse in the coastal ocean could be realized through our control method with relatively inexpensive components. Specifically, we are able to show that over a 90 day deployment a significant fraction of drifters can be made to aggregate in few clusters suitable for recovery.

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Section: B Roms Parametersmentioning

confidence: 99%

Section: B Roms Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Active drifters: Towards a practical multi-robot system for ocean monitoring

Molchanov

Breitenmoser

Sukhatme

2015

2015 IEEE International Conference on Robotics and Automation (ICRA)

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“…Furthermore, it is tied to works related to motion planning in oceanic flows. Recent work (Jouffroy et al, 2013) explores the possibility of actively utilizing tidal currents so that drifters can autonomously reach a desired destination. The flowfield considered there is a time-varying model with no horizontal spatial dependency and a piecewiseconstant dependency on depth.…”

Section: Introductionmentioning

confidence: 99%

Robust coordinated rendezvous of depth-actuated drifters in ocean internal waves

Ouimet

Cortés

2016

Automatica

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This paper considers a team of spatially distributed drifters that move underwater under the influence of an ocean internal wave. The overall objective is for the drifters to use the known depth-dependent ocean flowfield to rendezvous underwater and then return to the surface as a cluster for easy retrieval. From the structure of the internal wave, the ocean flowfield is time-varying and spatially dependent on depth and position along the wave propagation direction. The drifters can control their depth by changing their buoyancy and are otherwise subject to the horizontal flowfield at their given depth. We consider two different drifter dynamical models: a first-order Lagrangian model, useful when the drifter's mass is sufficiently small, and a second-order linear model, where the drag force caused by the water accelerates the drifter. We design provably correct distributed algorithms that rely on the drifters opportunistically changing their depth so that the ocean flowfield takes them in a desirable direction to perform coordinated motion. Under the proposed algorithms, the drifters converge asymptotically to the same depth and position along the wave propagation direction. We also investigate the algorithms' robustness against errors in actuation, estimation of the wave parameters, or state measurements. Various simulations illustrate our results.

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“…Being an order of magnitude cheaper to fabricate, float networks have the potential to achieve similar coverage performance as much more expensive AUV networks, by also being able to move back to their initial deployment locations fully covering the RoI. Previous works have considered the problem of path planning for single [93,180,182] and widely spaced 2D arrays of floats [42,130], making this thesis the first to examine exploiting the mobility of UWSNs consisting of profiling floats for 3D coverage.…”

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confidence: 99%

Drifting 3D Underwater Wireless Sensor Networks for Pollution Monitoring

Ren¹

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<p>Increasing demands by a growing population for food and oil have resulted in synchronous rises in the past 40 years of aquaculture and offshore oil drilling. Growth in these industries has highlighted the potential crippling impacts of coastal pollution, with marine farms likely to be susceptible to damage from harmful algal blooms and oil platforms to cause oil spills, as headlined by the 2010 Deepwater Horizon incident in the Gulf of Mexico. Drifting underwater wireless sensor networks (UWSNs) represent a technology that can greatly enhance our understanding of such processes. Consisting of a swarm of untethered sensor nodes, an UWSN can be deployed over a large segment of the feature. The feature is carried through to different positions by underwater currents, the nodes, also drifting with the currents, are able to follow it and track it. To enable UWSNs, work is proceeding at multiple laboratories throughout the world on the design of localization, medium access control and routing protocols that can adapt to the problem that a drifting network topology has over short time intervals: frequent neighbour changes. However, the long-term impact that current drift has on 3D drifting UWSNs is poorly understood. Current mobility models used to generate the motion of drifting nodes in simulation do not reflect how devices in real-life will disperse in water. At present, UWSN protocol schemes are evaluated in simulations where the current mobility of nodes is generated by unrealistic land-based random waypoint and other stochastic mobility models, or coarsely resolved numerical ocean models. Recently, a physically-inspired current mobility model known as MCM has been proposed. This is only defined along the water's surface, in 2D, however, and 3D extensions of this model have been simplistic and arbitrary. The lack of realistic 3D current mobility models motivates this thesis to develop one so that the simulated evolution of UWSNs can more accurately reflect real-life. A consideration of the oceanographic data on which MCM is based is used to derive a 3D extension of the model that reflects observed features of the Gulf Stream current. The speed of the current declines with depth. This model is utilized to advect a drifting UWSN in an oil plume monitoring scenario and study the performance of two pressure routing protocols, Depth Based Routing (DBR) and HydroCast, over time. Previously, these schemes had only been validated in unrealistic stochastic and depth-invariant mobility models and their time-averaged performances were only reported. Our findings show that 3D UWSNs cannot expect to stay connected and functioning if nodes only passively drift with the currents, with results demonstrating that a fully connected network can be so dispersed after three hours that no paths to sinks exist at all. Nodes must be equipped with some form of mobility to prevent their being separated and carried out of the monitoring region. Autonomous underwater vehicles (AUVs) capable of omnidirectional motion are expensive however, and instead UWSNs consisting of pro ling floats are considered in this thesis. Floats can move up and down by adjusting their buoyancy, which also allow them to move in 3D by exploiting water layers that are flowing in different directions to proceed along a desired heading. Recently, promising results in 2D path planning and formation control of floats have been presented. However, these works consider the floats to have infinite vertical velocity whereas in reality this is around 0:3 metres per second. In this thesis, a practical node movement scheme is proposed for extending the coverage lifetime of a 3D UWSN consisting of floats. By accounting for the finite profiling velocity of floats, the scheme is able to position nodes at coverage holes with greater precision than existing 2D strategies. The scheme's performance is analysed by simulations. The results support the use of floats for achieving partial coverage, which can achieve similar levels of coverage as an AUV strategy while requiring less cost to deploy. In determining the lifetime of the network, we find that both energy and dispersion limit the lifetime of the network. Without propulsion, the nodes are carried out of and cease to cover the monitoring region. Using mobility to remain with the region, at the end of a 5 day mission duration floats have had to use up some or almost all of their battery capacity in profiling.</p>

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n Active Current Selection for Lagrangian Profilers

Cited by 12 publications

References 16 publications

Active drifters: Towards a practical multi-robot system for ocean monitoring

Active drifters: Towards a practical multi-robot system for ocean monitoring

Robust coordinated rendezvous of depth-actuated drifters in ocean internal waves

Drifting 3D Underwater Wireless Sensor Networks for Pollution Monitoring

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