Line-of-sight iceberg edge-following using an AUV equipped with multibeam sonar

Obtaining 3D information about ice features, like icebergs, are of interest to researchers and offshore operators moving into the Arctic. Icebergs are affected by wind, and ocean currents, and can have unpredictable drift patterns, causing challenges when it comes to mapping objectives. Autonomous underwater vehicles (AUVs) equipped with multibeam echosounders are suitable for obtaining measurements of the underwater geometry of icebergs, but advances in autonomy are needed to map drifting icebergs reliably. This paper details a guidance algorithm for detecting and circumnavigating an iceberg - following the iceberg edge. The guidance scheme is implemented as a state machine, starting in an iceberg detection-mode. Once an iceberg is detected, the AUV will enter a mapping-mode. An edge detection algorithm will determine the position of the edge, and a line-of-sight approach will be used for edge-following. A six degree-of-freedom AUV simulator is used to perform a simulation study, to show how AUV dynamics affect the results. The simulation study presented shows the algorithm's effectiveness, both when the iceberg is assumed stationary, and when the iceberg is drifting and rotating with constant velocity

Supervisory Control of Line Breakage for Thruster-Assisted Position Mooring System

Thruster-assisted position mooring (TAPM) is an energy-efficient and reliable stationkeeping method for deep water structures. Mooring line breakage can significantly influence the control system, and ultimately reduce the reliability and safety during operation and production. Therefore, line break detection is a crucial issue for TAPM systems. Tension measurement units are useful tools to detect line failures. However, these units increase the building cost of the system, and in a large portion of existing units in operation line tension sensors are not installed. This paper presents a fault-tolerant control scheme based on estimator-based supervisory control methodology to detect and isolate a line failure with only position measurements. After detecting a line break, a supervisor switches automatically a new controller into the feedback loop to keep the vessel within the safety region. Numerical simulations are conducted to verify the performance of the proposed technique, for a turret-based mooring system.© 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. This is the authors’ accepted and refereed manuscript to the articl

Particle Filter for Fault Diagnosis and Robust Navigation of Underwater Robot

This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. © IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.A particle filter (PF)-based robust navigation with fault diagnosis (FD) is designed for an underwater robot, where 10 failure modes of sensors and thrusters are considered. The nominal underwater robot and its anomaly are described by a switching-mode hidden Markov model. By extensively running a PF on the model, the FD and robust navigation are achieved. Closed-loop full-scale experimental results show that the proposed method is robust, can diagnose faults effectively, and can provide good state estimation even in cases where multiple faults occur. Comparing with other methods, the proposed method can diagnose all faults within a single structure, it can diagnose simultaneous faults, and it is easily implemented

Optimal Force Allocation for Overconstrained Cable-Driven Parallel Robots: Continuously Differentiable Solutions With Assessment of Computational Efficiency

In this article, we present a novel method for force allocation for overconstrained cable-driven parallel robot setups that guarantees continuously differentiable cable forces and allows for small penalized errors in the resulting wrench. For the latter, we also provide a bound on the error under some assumptions. We study real-time feasibility by performing numerical simulations on a large set of configurations.acceptedVersio

Comparison of ultrasound vector flow imaging and CFD simulations with PIV measurements of flow in a left ventricular outflow trackt phantom - Implications for clinical use and in silico studies

In this study we have compared two modalities for flow quantification from measurement data; ultrasound (US) and shadow particle image velocimetry (PIV), and a flow simulation model using computational fluid dynamics (CFD). For the comparison we have used an idealized Quasi-2D phantom of the human left ventricular outflow tract (LVOT). The PIV data will serve as a reference for the true flow field in our setup. Furthermore, the US vector flow imaging (VFI) data has been post processed with model-based regularization developed to both smooth noise and sharpen physical flow features. The US VFI flow reconstruction results in an underestimation of the flow velocity magnitude compared to PIV and CFD. The CFD results coincide very well with the PIV flow field maximum velocities and curl intensity, as well as with the detailed vortex structure, however, this correspondence is subject to exact boundary conditions.publishedVersio