Line-of-Sight Path Following for Dubins Paths with Adaptive Sideslip Compensation of Drift Forces

This is the author’s final, accepted and refereed manuscript to the article.We present a nonlinear adaptive path-following controller that compensates for drift forces through vehicle sideslip. Vehicle sideslip arises during path following when the vehicle is subject to drift forces caused by ocean currents, wind and waves. The proposed algorithm is motivated by a lineof-sight (LOS) guidance principle used by ancient navigators, which is here extended to path following of Dubins paths. The unknown sideslip angle is treated as a constant parameter, which is estimated using an adaptation law. The equilibrium points of the cross-track and parameter estimation errors are proven to be uniformly semiglobally exponentially stable (USGES). This guarantees that the estimated sideslip angle converges to its true value exponentially. The adaptive control law is in fact an integral LOS controller for path following since the parameter adaptation law provides integral action. The proposed guidance law is intended for maneuvering in the horizontal-plane at given speeds and typical applications are marine craft, autonomous underwater vehicles (AUVs), unmanned aerial vehicles (UAVs) as well as other vehicles and craft where the goal is to follow a predefined parametrized curve without time constraints. Two vehicle cases studies are included to verify the theoretical results.http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6868251 "(c) 2014 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.

Late Jurassic to Late Cretaceous canyons on the Måløy Slope: Source to sink fingerprints on the northernmost North Sea rift margin, Norway

The Måløy Slope is a key area for studying the connection between onshore and offshore geology of South Norway. It has functioned as an area of bypass, erosion and deposition between the Norwegian mainland source area and the offshore northern North Sea sink area since the Permian. The slope was faulted into N–S-trending rift fault-blocks through flexural down-bending during the large-scale extension and rapid rift basin subsidence in the Late Jurassic and Early Cretaceous. Mapping of 3D seismic data has revealed a profound network of E–W-oriented erosional submarine canyons. These canyons cut up to 500 m into the crystalline bedrock on the rift-related fault-block crests. We suggest that the canyons were first established prior to the faulting associated with late Jurassic rifting. The canyons may have been important feeders in the Oxfordian, Kimmeridgian and Tithonian like canyons in the Uer Terrace to the south, although we lack direct evidence for this. Further erosion and deepening of the canyons into the basement occurred during Cretaceous in a post-rift setting. The position of the main canyons sustained during recurring periods of erosion from the Late Jurassic until burial within the slope in the Late Cretaceous. By the aid of detailed bathymetric maps, the main canyons can be correlated with onshore faults and drainage systems (fjords and valleys). The evolution of the slope canyon system over time is controlled by both tectonic and isostatic movements and, as discussed in the text, can help understand when and where the pre-fjord drainage was established. Multiple incision events have been detected, and each of these express some correlation to regional tectonic events in (1) Late Jurassic–Earliest Cretaceous, (2) Late Aptian–Albian and (3) Turonian– Coniacian.publishedVersio

From Caledonian collapse to North Sea Rift: The extended history of a metamorphic core complex

Extensional systems evolve through different stages due to changes in the rheological state of the lithosphere. It is crucial to distinguish ductile structures formed before and during rifting, as both cases have important but contrasting bearings on the structural evolution. To address this issue, we present the illustrative ductile‐to‐brittle structural history of a metamorphic core complex (MCC) onshore and offshore western Norway. Combining geological field mapping with newly acquired 3‐D seismic reflection data, we correlate two distinct onshore basement units (BU1 and BU2) to corresponding offshore basement seismic facies (SF1 and SF2). Our interpretation reveals two 40 km wide domes (one onshore and one offshore), which both show characteristic kilometer‐scale, westward plunging upright folds. The gneiss domes fill antiformal culminations in the footwall of a >100 km long, shallowly west dipping, extensional detachment. Overlying Caledonian nappes and Devonian supradetachment basins occupy saddles of the hyperbolic detachment surface. Devonian collapse of the Caledonian orogen formed dome and detachment geometries. During North Sea rifting, brittle reactivation of the MCC resulted in complex fault patterns deviating from N‐S strike dominant at the eastern margin of the rift. Around 61°N, only minor N‐S faults (<100 m throw) cut through the core of the MCC. Major rift faults (≤5 km throw), on the other hand, reactivated the detachment and follow the steep flanks of the MCC. This highlights that inherited ductile structures can locally alter the orientation of brittle faults formed during rifting.publishedVersio

Effectiveness of 'motivational interviewing' on sick leave: a randomized controlled trial in a social insurance setting

Objective This study aimed to evaluate the effectiveness of motivational interviewing (MI) – a counselling approach offered by caseworkers at the Norwegian Labor and Welfare Administration (NAV) – on return to work (RTW) for individuals sick-listed for ≥8 weeks due to any diagnoses. MI was compared to usual case management and an active control during 12 months of follow-up. Methods In a randomized clinical trial with three parallel arms, participants were randomized to MI (N=257), usual case management (N=266), or an active control group (N=252). MI consisted of two MI sessions while the active control involved two sessions without MI, both were offered in addition to usual case management. The primary outcome was number of sickness absence days based on registry data. Secondary outcomes included time to sustainable RTW, defined as four consecutive weeks without medical benefits. Results The median number of sickness absence days for the MI group was 73 days [interquartile range (IQR) 31–147], 76 days (35–134) for usual care, and 75 days (34–155) for active control. In total 89%, 88% and 86% of the participants, respectively, achieved sustainable RTW. The adjusted hazard ratio (HR) for time to sustainable RTW was 1.12 (95% CI 0.90–1.40) for MI compared to usual case management and HR 1.16 (95% CI 0.93–1.44) compared to the active control. Conclusions This study did not provide evidence that MI offered by NAV caseworkers to sick-listed individuals was more effective on RTW than usual case management or an active control. Providing MI in this context could be challenging as only half of the MI group received the intervention.publishedVersio

Biology and distribution patterns of some deepwater demersal fishes in the North Atlantic, with special reference to Antimora rostrata A study related to the project “Patterns and Processes of the ecosystems of the northern Mid-Atlantic”, MAR-ECO, 2001-2008

The study seeks to increase our knowledge on deepwater demersal fish assemblages and the biological adaptations of Antimora rostrata. This widespread deep-living demersal teleost is essentially used as an example species. Managing deepwater resources and communities is especially difficult since our knowledge of the community structure, ecology and biology of individual species is limited, and fishery independent information is scarce. In this account focus is directed towards the use of longlines in describing deepwater assemblages. New information on the biology of A. rostrata is presented, and experimental and alternative ageing methods are explored. The study was an element of MAR-ECO, a field project of the Census of Marine Life (www.coml.org), studying the diversity and biology of biota along the mid-Atlantic Ridge (MAR). As part of the 2004 MAR-ECO expedition to the mid-Atlantic Ridge, the chartered Norwegian fishing vessel M/S Loran deployed longline sets across the ridge axis, sampling a depth range of about 4000 m. Overall, chondrichthyans dominated the catches on the MAR and contributed nearly 60% in terms of weight and numbers. Multivariate analysis (MDS) using species-by-station data indicated an assemblage distribution that related primarily to factors varying by depth and latitude. Grouping patterns of stations were not very pronounced, suggesting a gradual rather than abrupt change in species composition by depth or latitude. Catch rates peaked at the shallower stations in the Charlie-Gibbs Fracture Zone (CGFZ), and generally decreased with depth. Relatively large individuals dominated, and the overall mean weight was 2.4 kg. Average fish weight was higher in the sub-area sampled just north of the Azores archipelago than in the CGFZ sub-area. No depth-related pattern of individual fish size was found. The findings suggest that the use of longline is a valuable and possibly necessary tool for describing the larger scavenging fish assemblages on rough bottom at greater depths. Among the many different species caught frequently on longlines A. rostrata was analysed in more detail. Additional data from MAR, off Greenland and the British Isles were included, and used to exemplify adaptations of a deepwater species with respect to distribution and life history traits. Data on A. rostrata are presented from 42°N on the MAR to 65°N on the slope off West and East Greenland, along a northsouth range of approximately 1400 nm (~2600 km). The species occurred in the depth interval 670-3060 m in trawl and longline experiments sampling the depth range 400-4300 m. Length frequencies indicated both latitudinal and depth-related variation. Along the ridge abundance peaked between 1200 and 2700 m with generally low or no catches outside this range. Examination of growth patterns in transverse sections of otoliths suggested a strong cyclic zonation pattern in A. rostrata. Similarly, frequency distributions of fish length and otolith weight showed a number of modes, suggesting groups of specimens of similar size and age. Distances between modes were consistent and corresponded to what was expected based on the interpretation of the zonation pattern in otoliths. Assuming that the otolith growth zones counted represent annuli and that unbiased age readings was achieved, the growth of A. rostrata seemed linear with age for both otolith weight and fish length within the length range investigated. This corresponded to approximately 25 mg/y and 4 cm/y respectively. The oldest fish recorded was about 25 years old and sexual growth dimorphism, where females grow larger, older, and possibly faster, was suggested. The results indicate that more attention should be directed towards using frequency distributions, especially of otolith weight, for deriving information on age structure and population growth data for certain fish stocks. For A. rostrata, and many other deepwater species, greater efforts should be made to validate age determination methods

Nonlinear Passive Control and Observer Design for Ships

Starting with passivity of the ambient water-ship system this article proceeds with nonlinear observer design, design of dynamic ship positioning systems and weather optimal positioning control systems exploiting the passivity properties of the vessel and the surrounding water. The article gives an overview of methods for passive ship control and observer design

Nonlinear modelling and control of underwater vehicles

oai:DiVA.org:ntnu-151