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 2
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 3
4 Goals of trawl control Bottom contact Energy consumption Selection properties
5 Trawl system Trawling vessel Warp Trawl door Bridles Trawl net Cod end
6 Trawl door To the vessel To the trawl net
7 Control of trawl system Today Manual control Vessel speed Vessel heading Warp length Measurements Future Automatic control Local actuators Observer
Main control objectives Robustness Integration against existing control systems Integration against existing sensors Complex objectives Industrial constraints 8
Objective of thesis Trawl system model Trawl door control concept Trawl system observer Trawl control system architecture 9
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) 10
11 Definition of hydrodynamic angles Angle of attack v α d Angle of slip β d v
Trawl door steady-state forces and moments Wind tunnel experiments Experiment setup 6 force components 90 combinations of orientation angles 12
Parameterization Parameterization gives: Smooth model Filtering of measured values Resulting parameterization: Extrapolation by interpolating towards simple damping coefficients. 13
Example: Parameterization of lift force 14
Parameterization results 15
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. 16
Vortex lattice method (VLM) Ring vortex Trailing vortices Γ (i,j) F Bound vortic es Foil Γ (i,j+1) F Γ (i,1) W Γ (i,2) W kvδt 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 17
Parameterization of the transient results Circulation build-up Step responses of linear systems Acceleration No cross coupling Angular velocity No cross coupling 18
Forces and moments from circulation 19
Forces from relative accelerations and angular velocities. ( Added mass and angular damping ) 20
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 ) 21
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 22
Control concept choice Towing tank experiments Criteria Energy efficiency Control performance Warp control is chosen. 23
24 Control concept optimization Optimization routine Design parameters Objective value Estimated optimum Objective function Simulation results Simulations
Control concept results 25
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 26
27 Model predictive control (MPC) Objective value Optimization routine Control signal Optimum control signal Trawl system Objective function Dynamic trawl system model Initial states Constraints Measurements Performance requirements Objective evaluation Operator requests
Observer What is happening in the trawl system? Position, depth, shape, bottom contact Catch Velocities Available measurements Few Low update rate Inaccurate Expensive Measurements Model parameters Trawl system Model corrector Estimated states Independent model Estimated states Control input 28
Control system main components 29
Case studies: Model comparison 30
Case studies: Trajectory controller 31
Case studies: MPC, 3000 iterations 32
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 33
34 References Reite, Karl J: Modeling and control of trawl systems. Tapir Akademisk Forlag 2006 (ISBN 82-471-8024-3) 238 s.