Method and system for dynamic positioning of instrumented cable towed in water

1. A method for dynamic positioning of an instrumented cable ( 100 ) towed in water or an array thereof (streamer-array), to which control devices ( 20 ) are arranged for controlling the shape and positioning of the individual instrumented cables ( 100 ) in relation to other instrumented cables ( 100 ) and counteracting crosscurrents or other dynamic forces affecting a cable-array towed behind a seismic survey vessel ( 110 ) with a control central ( 111 ) for controlling the instrumented cable ( 100 ) or cable array, the control central ( 111 ) communicating with the instrumented cables ( 100 ) and control devices ( 20 ), comprising the steps of:

(a) using a nominal controller ( 51 ) for each control device ( 20 ) for controlling the instrumented cable ( 100 ) based on previous knowledge about the properties of the total system consisting of the vessel ( 110 ) with instrumented cables ( 100 ) and control devices ( 20 ); and

(b) using a model predictive adaptive controller ( 70 ) for each control device ( 20 ), the model predictive adaptive controller ( 70 ) including a cable group motion predictor ( 71 ) for collecting the sum of all model insecurities in a single variable, and an adaption rule ( 72 ) providing an adaptive estimate ( 73 ) driven by a prediction error ( 74 ) given by deviation between predicted motion estimate from the cable group motion predictor ( 71 ) and motion measurements from a measuring system ( 63 ),

wherein the adaptive estimate ( 73 ) is used for compensating power control output for the control devices ( 20 ) along the instrumented cables ( 100 ) from the nominal controller ( 51 ) for counteracting the effects of un-modelled dynamics, insecurities in model parameters, and external forces affecting the force balance of the instrumented cable ( 100 ).

2. The method of claim 1 , comprising the step of using the cable group motion predictor ( 71 ) for simulating in real-time and predicting behavior of the total system for calculating a predicted motion estimate by using a dynamic prediction model of the total system.

3. The method of claim 2 , comprising using information about external forces from the nature or operational equipment affecting the force balance of the instrumented cables ( 100 ) for calculating the predicted motion estimate.

4. The method of claim 1 , comprising the step of performing measurement selected from one or more of the group consisting of:

(i) measuring relative position between nodes based on acoustics, and

(ii) measuring absolute position/velocity of nodes based on Global Navigation Satellite System, and

(iii) measuring angular velocities and orientation based on inertial sensors and magnetometer for nodes.

5. The method of claim 1 , comprising the step of stabilizing the prediction error ( 74 ) by feedback in the cable group motion predictor ( 71 ).

6. The method of claim 1 , comprising the step of using the prediction error ( 74 ) for updating the cable group motion predictor ( 71 ).

7. The method of claim 1 , comprising the step of driving the nominal controller ( 51 ) by a position reference ( 41 ) for each control device ( 20 ), generated from a survey plan ( 44 ) or manual settings for depth or roll references ( 45 ).

8. A system for dynamic positioning of an instrumented cable ( 100 ) towed in water, or an array thereof (streamer-array), to which control devices ( 20 ) are arranged for controlling the shape and positioning of the individual instrumented cables ( 100 ) in relation to other instrumented cables ( 100 ) and counteracting crosscurrents or other dynamic forces affecting a cable-array towed behind a seismic survey vessel ( 110 ) with a control central ( 111 ) for controlling the instrumented cable ( 100 ) or cable array, the control central ( 111 ) communicating with the instrumented cables ( 100 ) and control devices ( 20 ), comprising:

a nominal controller ( 51 ) for each control device ( 20 ) for controlling the instrumented cable ( 100 ) based on previous knowledge about the properties of the total system consisting of the vessel ( 110 ) with instrumented cables ( 100 ) and control devices ( 20 );

a model predictive adaptive controller ( 70 ) for each control device ( 20 ), which model predictive adaptive controller ( 70 ) includes a cable group motion predictor ( 71 ) which collects the sum of all model insecurities in a single variable, and an adaption rule ( 72 ) which provides an adaptive estimate ( 73 ) driven by a prediction error ( 74 ) given by deviation between predicted motion estimate from the cable group motion predictor ( 71 ) and motion measurements from a measuring system ( 63 ),

wherein the adaptive estimate ( 73 ) is used for compensating power control output for the control devices ( 20 ) along the instrumented cables ( 100 ) from the nominal controller ( 51 ) for counteracting the effects of un-modelled dynamics, insecurities in model parameters, and external forces affecting the force balance of the instrumented cable ( 100 ).

9. The system of claim 8 , wherein the cable group motion predictor ( 71 ) includes a dynamic prediction model of the total system arranged for receiving information about external forces from the nature or operational equipment affecting the force balance of the instrumented cables ( 100 ), for real-time simulation and prediction of behavior of the total system.

10. The system of claim 8 , comprising a measuring system ( 63 ) including one or more system or sensor from the group consisting of:

(i) acoustics for relative position measurement between nodes,

(ii) Global Navigation Satellite System for absolute position or velocity measurement of nodes, and

(iii) inertial sensors and magnetometer for measurement of angular velocities and orientation of nodes.

11. The system of claim 8 , comprising a guidance or reference system ( 40 ) for receiving a survey plan ( 44 ) or manual settings for depth or roll references ( 45 ), the reference system ( 40 ) arranged for generating position reference ( 42 ) for cable group, position reference ( 43 ) for each instrumented cable ( 100 ) and position reference ( 41 ) for each control device ( 20 ).

12. The system of claim 9 , comprising a guidance or reference system ( 40 ) for receiving a survey plan ( 44 ) or manual settings for depth or roll references ( 45 ), the reference system ( 40 ) arranged for generating position reference ( 42 ) for cable group, position reference ( 43 ) for each instrumented cable ( 100 ) and position reference ( 41 ) for each control device ( 20 ).

13. The system of claim 10 , comprising a guidance or reference system ( 40 ) for receiving a survey plan ( 44 ) or manual settings for depth or roll references ( 45 ), the reference system ( 40 ) arranged for generating position reference ( 42 ) for cable group, position reference ( 43 ) for each instrumented cable ( 100 ) and position reference ( 41 ) for each control device ( 20 ).

14. The system of claim 8 , wherein the nominal controller ( 51 ) is driven by the position reference ( 41 ) for each control device ( 20 ).

15. The system of claim 9 , wherein the nominal controller ( 51 ) is driven by the position reference ( 41 ) for each control device ( 20 ).

16. The system of claim 10 , wherein the nominal controller ( 51 ) is driven by the position reference ( 41 ) for each control device ( 20 ).

17. The method of claim 2 , comprising using information about external forces from the nature or operational equipment affecting the force balance of the instrumented cables ( 100 ).