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Modeling and Control of Trawl Systems
Karl-Johan Reite, SINTEF Fisheries and Aquaculture
Supervisor: Professor A. J. Sørensen * Advisor: Professor H. Ellingsen * * Norwegian University of Science and Technology
Outline Motivation and objective of thesis Main parts: Mathematical modeling Control concept Control architecture
Summary and concluding remarks
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Background The world capture fisheries
95 million tons of fish 80 billion dollars
Negative impacts of trawling Damage to the seafloor Pollution (poor energy efficiency) Poor selectivity
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Goals of trawl control Bottom contact Energy consumption Selection properties
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Trawl system Trawling vessel
Warp
Trawl door
Bridles Trawl net Cod end
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Trawl door
To the vessel
To the trawl net
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Control of trawl system Today Manual control
Vessel speed Vessel heading Warp length
Measurements
Future Automatic control Local actuators Observer
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Main control objectives
Robustness Integration against existing control systems Integration against existing sensors Complex objectives Industrial constraints
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Objective of thesis Trawl system model Trawl door control concept Trawl system observer Trawl control system architecture
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Mathematical modeling Levels of complexity, efficiency and accuracy:
Fast control plant model (MPC optimization) Accurate control plant model (Control concept
optimization, trawl system observer) Process plant model (Evaluate trawl control
system)
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Angle of attack
Angle of slip
Definition of hydrodynamic angles
αd v
v
βd
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Trawl door steady-state forces and moments
Wind tunnel experiments Experiment setup 6 force components 90 combinations of
orientation angles
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Parameterization Parameterization gives:
Smooth model Filtering of measured values
Resulting parameterization:
Extrapolation by interpolating towards simple damping coefficients.
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Example: Parameterization of lift force
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Parameterization results
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Transient effects What forces act on the trawl door during transient
motions? May reduce computational effort Would have a small bearing on trawl system behavior Are estimated using a numerical method
Illustration of 2D unsteady foil from “Marine Hydrodynamics” (1977) by J. N. Newman.
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Vortex lattice method (VLM)
Ring vortices placed on the mean surface of the foil Strength of vortices calculated to give zero fluid flow through the foil Vortices shed from the trailing edge forms the wake Forces and moments calculated from the strength of the vortices
Γ (i,j)F
Γ (i,1)W
Γ (i,j+1)F
Γ (i,2)W
kvΔt
Foil
Trailing vortices
Bound vortices
Ring vortex
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Parameterization of the transient results Circulation build-up Step responses of
linear systems Acceleration No cross coupling
Angular velocity No cross coupling
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Forces and moments from circulation
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Forces from relative accelerations and angular velocities. (“Added mass” and “angular damping”)
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Resulting hydrodynamic model
Steady-state hydrodynamic forces and moments Circulation build-up Forces and moments from accelerations (“Added mass“ ) Forces and moments from angular velocities (“Damping“ )
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Trawl door control concept How can the hydrodynamic forces on the trawl doors be
controlled? Method:
Evaluate former proposed concepts Analyze new possibilities Towing tank experiments Numerical optimization
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Control concept choice
Towing tank experiments Criteria
Energy efficiency Control performance
Warp control is chosen.
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Control concept optimization
Optimization routine
Objective function Design
parameters
Objective value
Estimated optimum
Simulations
Simulation results
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Control concept results
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Trawl system control architecture How can the trawl system be automatically controlled? Requirements:
Integration against existing controllers and actuators Use of trawl door control concept Ability to include complex objectives Industrial constraints
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Model predictive control (MPC) Optimization
routine
Objective function
•Dynamic trawl system model
•Constraints
•Performance requirements
•Objective evaluation
Control signal
Objective value
Optimum control signal
Trawl system
Initial states
Measurements
Operator requests
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Observer
Model corrector
Trawl system
Independent model
Estimated states
Model parameters
What is happening in the trawl system? Position, depth, shape,
bottom contact Catch Velocities
Available measurements Few Low update rate Inaccurate Expensive
Estimated states
Control input
Measure-ments
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Control system main components
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Case studies: Model comparison
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Case studies: Trajectory controller
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Case studies: MPC, 3000 iterations
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Conclusions
A mathematical model of the hydrodynamic forces on a trawl door has been developed
A trawl door control concept has been developed A trawl system control structure has been proposed
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References
Reite, Karl J: Modeling and control of trawl systems. Tapir Akademisk Forlag 2006 (ISBN 82-471-8024-3) 238 s.
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