Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented.acceptedVersio

Dynamic Bias for RF Class A Power Amplifiers

This thesis focuses on class A radio frequency power amplifiers in dynamic supply modulation architectures (dynamic bias). These are promising efficiency enhancement techniques where the device is driven harder by varying its bias signals. Non linearities that arise are considered as digitally compensated through, for example, digital predistortion (DPD). Bias signals are meant as functions of the PA?s output power level (P out). Therefore, the input power level (P in) as well as the feeding signals are thought as quantities the amplifier need to give a certain P out. The selected set of bias points the device sweeps through is called bias trajectory or bias path. A tool to find a suitable bias trajectory is developed considering the requirements a class A power amplifier should satisfy: high power added efficiency, acceptable gain and output phase variations as P out changes (allowing a DPD algorithm to be effective), low harmonic distortion and not too complicated bias signals patterns. The tool consists of two softwares: ADS and Matlab. ADS simulates the device under test while Matlab allows the user to analyze the data and find a suitable bias path. Once a trajectory is identified, ADS can sweep along it and give more information on linearity and efficiency through, for instance, 2-tone harmonic balance simulations. Note that only static characteristics are evaluated and memory effects disregarded. The path searching algorithm is then applied to a HBT transistor, at a frequency of 1.9GHz and to a complete pHEMT class A PA (frequency of 6Ghz). In both cases a suitable trajectory is identified and analyzed back in ADS. The Matlab plots are qualitatively similar to each other when switching form one device to another. The HBT transistor has then been tested in the laboratory and static measurements have been performed showing good agreement with simulations. Keywords: Bias trajectory, dynamic bias, efficiency, HBT, linearity, pHEMT, power amplifie

Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented

Path Following Control of Underactuated Surface Vessels in the Presence of Multiple Disturbances

An integral version of the line-of-sight guidance method is shown to compensate for both kinematic and dynamic disturbances generated by wind, waves and sea currents. The guidance law is designed for path following tasks of underactuated marine vessels moving in the horizontal plane. Specifically, the control system consists of an integral line-of-sight heading reference generator in a cascaded configuration with an adaptive surge-yaw controller. The total drifting effect of the environmental disturbances is modeled as a combination of a constant and unknown kinematic drift, and a constant, unknown and heading-dependent dynamic pressure acting on the vessel. The closed loop stability analysis shows that path following is achieved with global k-exponential stability properties. The theoretical results are supported by simulations.acceptedVersio

Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented

Path following of underactuated marine surface vessels in the presence of unknown ocean currents

This paper considers path following control of snake robots and has two contributions. The first contribution is a description of how a straight line path following controller previously proposed by the authors can be extended to path following of general curved paths. The second contribution of this paper is a waypoint guidance strategy for steering a snake robot along a path defined by waypoints interconnected by straight lines. The waypoint guidance strategy builds on the straight line path following controller previously proposed by the authors. The paper presents simulation results that illustrate the performance of the proposed guidance strategy

Semiglobal exponential stability of a counter-current and co-current guidance scheme

A control technique for counter-current and co-current guidance of underactuated marine vehicles is revisited and stronger stability properties are shown. In particular, the stronger property of uniform semiglobal exponential stability is shown for the complete multiple-equilibria closed loop system, that has previously been shown to be uniformly semiglobally asymptotically stable and uniformly locally exponentially stable. Compared to the original proof, the analysis presented in this paper does not invoke the theory developed for cascaded systems; it follows instead a direct approach where a Lyapunov function for the full system is identified. This shows that analysing stability of a complex non-linear system by means of proper Lyapunov function candidates can yield significant results, leaving however the designer with the challenging task of identifying the right candidate. The theory is supported by simulations.publishedVersion© 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd

Robust adaptive backstepping DP control of ROVs

Dynamic positioning is an important control feature for an underwater remotely operated vehicle. This paper presents a nonlinear dynamic positioning controller suited for application to vehicles with model uncertainties, operating in environments with unpredictable disturbances, such as an aquaculture net cage. The proposed controller combines the backstepping approach with an adaptation term to ensure robustness. Using Lyapunov theory and Matrosov’s theorem the origin of the closed-loop system is proven to be: (i) globally asymptotically stable when assuming persistency of excitation, and (ii) stable and bounded, with the true position converging to the desired position if there is no persistency of excitation. This paper also presents results from simulations where the proposed controller is contextualized and compared to similar controllers, showing promising results. Finally, as the main result of the manuscript that demonstrates the effectiveness of the proposed control law, an extensive field trial campaign is conducted at a full-scale aquaculture site using an industrial ROV where the proposed controller is successfully tested under realistic operational conditions.publishedVersio

Integral Line-of-Sight Guidance of Underwater Vehicles Without Neutral Buoyancy

This paper analyzes an integral line-of-sight guidance law applied to an underac-tuated underwater vehicle. The vehicle is rigorously modeled in 5 degrees of freedom usingphysical principles, and it is taken into account that the vehicle is not necessarily neutrallybuoyant. The closed-loop dynamics of the cross-track error are analyzed using nonlinear cascadedsystems theory, and are shown to achieve uniform semiglobal exponential stability. Hence, theintegral line-of-sight guidance law compensates for the lack of neutral buoyancy, and it is nolonger necessary to assume that the vehicle is perfectly ballasted. The exponential convergenceproperties of the guidance law are demonstrated in simulations of an autonomous underwatervehicle