Stefan Wirtensohn

• HTWG Konstanz - University of Applied Sciences

Autonomous surface vessels are a promising building block of the future's transport sector and are investigated by research groups worldwide. This paper presents a comprehensive and systematic overview of the autonomous research vessel Solgenia including the latest investigations and recently presented methods that contributed to the fields of auto...

In this brief, trajectory tracking for a fully actuated surface vessel while performing automated docking is addressed. Environmental disturbances, integral action, as well as physical actuator quantities are directly integrated into the approach, avoiding the need for additional control allocation. By employing a backstepping design, uniform local...

This paper presents a systematic comparison of different advanced approaches for motion prediction of vessels for docking scenarios. Therefore, a conventional nonlinear gray-box-model, its extension to a hybrid model using an additional regression neural network (RNN) and a black-box-model only based on an RNN are compared. The optimal hyperparamet...

In this paper, a novel feature-based sampling strategy for nonlinear Model Predictive Path Integral (MPPI) control is presented. Using the MPPI approach, the optimal feedback control is calculated by solving a stochastic optimal control (OCP) problem online by evaluating the weighted inference of sampled stochastic trajectories. While the MPPI algo...

The Unscented Kalman Filter (UKF) is widely used for the state, disturbance, and parameter estimation of nonlinear dynamic systems, for which both process and measurement uncertainties are represented in a probabilistic form. Although the UKF can often be shown to be more reliable for nonlinear processes than the linearization-based Extended Kalman...

A reliable quantification of the worst-case influence of model uncertainty and external disturbances is crucial for the localization of vessels in marine applications. This is especially true if uncertain GPS-based position measurements are used to update predicted vessel locations that are obtained from the evaluation of a ship’s state equation. T...

Random matrices are widely used to estimate the extent of an elliptically contoured object. Usually, it is assumed that the measurements follow a normal distribution, with its standard deviation being proportional to the objects extent. However, the random matrix approach can filter the center of gravity and the covariance matrix of measurements in...

In this paper, a systematic comparison of three different advanced control strategies for automated docking of a vessel is presented. The controllers are automatically tuned offline by applying an optimization process using simulations of the whole system including trajectory planner and state and disturbance observer. Then investigations are condu...

The trajectory tracking problem for a fully-actuated real-scaled surface vessel is addressed in this paper. The unknown hydrodynamic and propulsion parameters of the vessel’s dynamic model were identified using an experimental maneuver-based identification process. Then, a nonlinear model predictive control (NMPC) scheme is designed and the control...

In this paper, the mechanical subsystem of a proportional solenoid excited by a dither signal is considered. The objective is to find a suitable friction model that reflects the characteristic mechanical properties of the dynamic system. Several different friction models from the literature are compared. The friction models are evaluated with respe...

In this paper, a gain-scheduled nonlinear control structure is proposed for a surface vessel, which takes advantage of extended linearisation techniques. Thereby, an accurate tracking of desired trajectories can be guaranteed that contributes to a safe and reliable water transport. The PI state feedback control is extended by a feedforward control...

In this paper, utilisation of an Unscented Kalman Filter for concurrently performing disturbance estimation and wave filtering is investigated. Experimental results are provided that demonstrate very good performance subject to both tasks. For the filter, a dynamic model has been used which was optimised via correlation analysis in order to obtain...

In this work an approach to generate collisions-free trajectories for vessels is presented. The approach consist of a global path planner and a local evasive trajectory planner. The global path planner uses chart information from ENCs to estimate waypoints for a global path avoiding obstacles defined in a chart. The local evasive trajectory planner...

This paper addresses the problem of navigation algorithms in the context of high accuracy motion control for a unmanned surface crafts. The effectiveness of an unscented Kalman filter algorithm in combination with a detailed nonlinear 3DOF dynamical model for motion estimation is shown. Water currents are regarded as slowly varying parameters estim...

This paper presents a method to efficiently solve the control allocation problem of vessels propelled by two azimuth thrusters with limited panning range. The use of rotatable thrusters results in a configuration matrix that, in the context of control allocation, typically leads to a constrained nonlinear optimization problem. It is shown, how this...

This paper provides an overview of the development of a catamaran-like autonomous surface vessel. The vessel is intended to serve as an experimental platform to study algorithms for control, sensor data fusion as well as path planning and collision avoidance. The mechanical design, the electronics and software architecture is described together wit...

In this paper, the process and results of a parameter identification task for a maritime unmanned surface vehicle are presented. The system has been modeled using state of the art methodology, and the parameters have been estimated via a weighted least square optimization approach. The required measurement data have been taken from various maneuvre...