1,720,970 research outputs found
AZIMUTH-DRIVE ESCORT TUG MANOEUVRABILITY MODEL, SIMULATION AND CONTROL
No full textThe ability to predict Escort tug's handling, effectiveness, and safety at early design stage is paramount in view of an optimal design process. In this framework, the availability of a reliable manoeuvrability prediction model is beneficial. A deep insight into the manoeuvring characterisation of a wider class of Azimuthal Stern Drive Escort tugs is undertaken, giving rise to a dedicated novel four Degrees-of-Freedom (4-DOF) parametric manoeuvrability model. An extensive captive model testing campaign is exploited to develop suitable mathematical models, conceived following an `MMG-inspired' modelling concept, i.e. a non-linear manoeuvring prediction method developed by the Japanese Manoeuvring Modelling Group (Ogawa et al., 1977) and later standardised by the Japan Society of Naval Architects and Marine Engineers JSNAOE (2013). The mathematical formulation pursues a physics-based approach aimed at characterising the complete manoeuvring hydrodynamics of a category of vessels, based onto a reference tug geometry. The hull+skeg and azimuthals force contributions are analysed separately and are then coupled to include their reciprocal interaction. Collaterally, computational fluid dynamics techniques (RANSE) are cross-validated and further explored to extend the parent hull modelling in function of a series of skeg geometries. The aim of the investigation is to physically characterize and quantify by suitable models the influence of the different extit{skeg} designs and sizes onto manoeuvring, with the scope of covering the largest class of Azimuthal Stern Drive Escort tugs. To prove the adequacy of the mathematical formulations, two independent validation processes have been pursued. The first -- model-scale -- reproduces the Escort-towing tests performed at towing tank basin onto the parent hull. The second -- full-scale -- is devised to check the simulator capability of describing the model free-sailing performance of a different but compatible hull, having dimensions, propulsion, skeg characteristics significantly different with respect to the `parent design' used to principally develop the code. In conclusion, a wider `Simulation-for-Design' strategy discloses, enriched by the combination of an original parametric architecture of the Azimuthal Stern Drive Escort tug, with a fully controllable and scalable tanker, and a tunable tow-line. Full real-time Escort-towing dynamics of convoy are envisaged, enabling the study and investigation of several real-case emergency scenarios and paving the way for future design strategies. The ability of addressing real-world operative profiles, in fact widens even more the advantages of a `parametric model', promising to become a very useful tool for tug designers, tug masters/pilots, port authorities, or flag administrations. Among them are the direct assessment of the impact of design choices on operational effectiveness and safety; towing-service risk assessment-to-mitigation techniques; real-scenario simulation with focus on technical failures, human factor and underlying delay chain; and, last bot not least, `model-based' benchmarking environment for control design techniques
Numerical analysis of escort tug manoeuvrability characteristics
No full textThe adoption of RANS techniques is widely spread in terms of resistance and self-propulsion prognosis for merchant and military vessels; however, on the other hand, the captive evaluation of hydrodynamic manoeuvring forces across numerical procedures still concerns great computational effort and challenge. When it comes to deal with Escort or tractor tugs, characterised by rather full hull forms, typical of harbour tugs, with the addition of extensive foiled shaped fore-skegs solutions, the ability of predicting manoeuvring and handling of such vessels becomes a great added value at an early design stage, as an alternative to physical model scale testing, since very scarce data are present in open literature. Escort vessels in particular, both operate at low and high speed, in addition to the typical harbour tasks entailed, making the manoeuvring modelling even more complicated. In present work, a low-speed and high-speed numerical methodology based on the OpenFOAM finite volume method on polyhedral unstructured mesh is investigated and validated against purposely designed model tests carried out in towing tank: Pure yaw, pure drift, drift and yaw, and drift and heel simulation results are compared with experimental data in terms of forces first, and impact on manoeuvring lastly, showing satisfactory agreement with experiments. Finally, Escort capability tests run at tank are compared with a purposely calibrated manoeuvring model on the RANS results
Z-Drive Escort Tug manoeuvrability model and simulation
No full textThe ability to predict the tug’s handling, effectiveness, and safety at early design stage is paramount in view of an optimal design process. In this framework, the availability of a reliable manoeuvrability prediction model is beneficial. This paper presents a novel 4-DOF parametric manoeuvrability model dedicated to the manoeuvrability analysis of Azimuthal Stern Drive Escort Tugs. An extensive captive model testing campaign is exploited to develop the mathematical model, conceived following the MMG model concept. The modelling pursues a physics-based approach aimed at characterising the complete manoeuvring hydrodynamics of the vessel. The hull+skeg and azimuthals force contributions are analysed separately and are then coupled to analyse their interaction. A complete, real-time simulator is presented, which is capable of simulating the dynamics of a towing convoy in several real case scenarios. This capability is envisaged to become a very useful tool for the tug designer, allowing to address realistic operational conditions with a focus on manoeuvring capabilities, risk assessment, risk mitigation, operational safety and effectiveness
A New Escort Tug Family Designed to Anticipate New Safety Requirements and Operational Needs
No full textThe aim of the paper is to describe an industry-academic collaboration to conduct a research project whose main goal is the design of a new escort tug family characterized by high intact/damage stability margins, good maneuvering capability and stable behavior during escort indirect assistance. The project is focused on three main research areas: hydrodynamic design and internal subdivision of the hull, simulation of the escort capabilities in different operational scenario, development of control logics that will allow autonomous or unmanned operations. The paper describes the methodological approach adopted for the design and will show some preliminary results. The tug has been designed to be in compliance with new amendments of the 2008 Intact Stability Code (Res. MSC.415(97)) which will enter into force on 1st January 2020) both for towing and for escort operations. Furthermore, a significant step towards enhancement of ship's safety is granted by tug's capability to withstand a damage in accordance with criteria applicable to OSVs. This paper describes the prototype hull and its stability characteristics. CFD calculations and towing tank tests have been performed in order to assess the hull design and to infer simulation models able to describe the behavior of a family of vessels. In particular, the propulsion and maneuverability aspects in escort operations are deeply investigated. Results of the project will form the bases for the conceptual application to a remotely controlled or autonomous escort tug
Numerical analysis of escort tug manoeuvrability characteristics – Part II: The skeg effect
No full textan Azimuth Stern Drive Escort Tug. This study is devoted to identifying a proper mathematical model to be included in a dynamic manoeuvring simulator. The hydrodynamic problem is therefore decomposed in the hull and skeg components. The hydrodynamic characteristics of the skeg were so explored by varying its span and chord systematically, allowing deep insight into the physics of both components and their mutual interaction. The distribution of the forces acting on hull and skeg were studied in detail in their dependence from the skeg geometrical characteristics. Suitable mathematical formulations for the skeg forces were implemented in an MMG-like manoeuvring model-based onto the CFD captive simulations. Lastly, the impact on the tug’s manoeuvrability
of the previously mentioned variations was then investigated. Turning, Zig-Zag, Escort Capability, Escort Mirror ability and Escort Stability manoeuvres were simulated. The results of these manoeuvres are presented, showing the great potential of this manoeuvring model in representing a wider class of Escort tugs
Development and assessment of CFD methods to calculate propeller and hull impact on the rudder inflow for a twin-screw ship
No full textThe purpose of this study is to investigate the feasibility of a simple but robust approach for the identification of the main interaction effect of hull and propeller on the rudder inflow in a conventional manoeuvring simulator. The manoeuvring simulator adopts a modular/MMG based approach in which the hull, the rudders and the propellers are described by separate mathematical models which take into account the interaction phenomena. The propeller–rudder interaction factor is examined by means of a numerical model developed in OpenFOAM for the prediction of the performance of a rudder in behind propeller condition. Differently the hull–rudder interaction factor is numerically obtained by means of two different approaches. The proposed kinematic method shows the minimum additional computational cost without loss of accuracy. It is based on the analysis of rudder inflow fields (in a PIV fashioned), therefore It can be carried out in a post-processing phase of CFD simulations adopted to extract the hydrodynamic coefficients. This study validates the method by comparing it with the classical approach also used in the experimental campaign, based on the analysis of rudder forces from virtual captive tests. The approaches demonstrate to improve the overall accuracy of the main manoeuvring parameters with respect to the ones obtained by means of a calibrated semi-empirical model
Manoeuvring model and simulation of the non-linear dynamic interaction between tethered ship and tug during escort
No full textWhen dealing with towing and Escort operations – indissolubly – a wider and complete modelling of the involved dynamics becomes fundamental, on both ship and tug side, even more so making unavoidable the need of correctly ponder the cables constraining coupling. With the aim to better understand the
peculiarities of tug-ship interaction, a 6-DOF time domain simulator comprehensive of the propulsion dynamics has been developed, across the inter-connection imposed by the towing-line. Particular attention is focused on discovering the operational capabilities of the tug in exerting a force on the assisted ship during Escort, and the subsequent great influence that the reaction makes on the tug handling and effectiveness. A conceptual and critical discussion stands out, preparing the ground to future design strategies and hinting different solutions to be investigated, directly facing the operative profile of the vessel
Follow-the-Leader Guidance, Navigation, and Control of Surface Vessels: Design and Experiments
No full textA novel follow-the-leader approach for azimuth-driven vessels is devised and experimentally tested in a model-scale outdoor scenario. The vessels are equipped with global navigation satellite and inertial navigation systems. A line-of-sight algorithm ensures the yaw-check ability of the follower vessel along the leader's path, while a speed-regulation allows to track its velocity. Track generation, guidance, navigation, and control modules are designed and assembled to be executed on-board in real time. The results of an outdoor experimental campaign are illustrated to show the effectiveness of the proposed approach.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport Engineering and Logistic
Z-drive escort tug manoeuvrability modelling: From model-scale to full-scale validation
No full textA deep insight into the manoeuvring characterisation of a wider class of Azimuthal Stern Drive Escort tugs (ASD) is undertaken with the scope of defining a real-time parametric manoeuvring simulation code for the free-sailing and towing operations. To this end, given a simple set of tug design parameters (main dimensions, skeg size, azimuthal size, propeller pitch, choice of main engines, etc.), a physics-based 4-DOF mathematical prediction tool for the dynamic behaviour of the ASD tug has been developed in calm seas. To prove the suitability of the modelling, two independent validation processes have been provided in the present paper. The first successfully demonstrates the ability of the mathematical formulations to reproduce model-scale
Escort-towing operations carried out on the same parent hull which was tested in towing tank (RM2812). The second validation test envisages simulator’s capability of describing the full scale free-sailing performance of a different but compatible hull, having dimensions, propulsion, skeg characteristics significantly different with respect to the ”parent design” used to principally develop the code. The verification involved the measurements purposely performed during sea trials onto two sister-ship ASD new-buildings (RM3213)
Twin-screw vessel manoeuvrability: The traditional twin-rudder configuration vs pod-drives
No full text- …
