Azimuthing Thruster

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J. L. Cozijn - One of the best experts on this subject based on the ideXlab platform.

  • The Wake Flow Behind Azimuthing Thrusters: Measurements in Open Water, Under a Plate and Under a Barge
    Volume 1: Offshore Technology, 2012
    Co-Authors: J. L. Cozijn, R. Hallmann
    Abstract:

    The wake flow behind a ducted Azimuthing Thruster was investigated. The Thruster wake is an important factor in Thruster interaction effects. Model tests were carried out for 3 different configurations; a Thruster in open water conditions, a Thruster under a flat plate and a Thruster built into a barge. Two different Thrusters were considered, a ‘normal’ Thruster with a horizontal propeller axis and a ‘tilted’ Thruster with a propeller axis and nozzle oriented 7 deg down-wards. In the tests the propeller thrust and torque were recorded, as well as the nozzle thrust and unit thrust. The velocities in the wake of the Thruster were measured using a PIV (particle image velocimetry) system, for down-stream locations up to x/D = 19. The influence of the Thruster tilt, the plate above the Thruster and bilge radius on the Thruster wake flow were investigated.Detailed PIV measurements were carried out on the wake flow behind the Thruster in open water conditions. The PIV system used can measure 3D velocities in large set of points in a 2D plane, which is illuminated by a laser light beam. The flow velocities were measured in a large number of cross sections at different distances from the Thruster. The PIV measurements provide a detailed image of the flow velocities in the Thruster wake, showing the axial velocities, as well as the rotation and divergence of the wake.Subsequently, PIV measurements were carried out for the Thruster under a flat plate and the Thruster under a barge. The measurement results show a Thruster wake that is deformed by the presence of the plate and the barge. The plate and the bottom of the barge form a flat plane above the Thruster, clearly flattening the cross section of the Thruster wake. Furthermore, the wake flow at the side of the barge, near the bilge radius, results in a low pressure region, causing the wake flow to diverge up as it flows from under the barge into the open water. This phenomenon is known as the Coanda effect and is strongly dependent on the bilge radius and the distance between the Thruster and the side of the barge. The effect of both these parameters was confirmed in the model test results presented. The typical flow patterns observed as a result of the Coanda effect are illustrated in Figure 1 below.The results of the present model test research are used to further improve the understanding of the physics of Thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations.Copyright © 2012 by ASME

  • Hydrodynamic Research Topics for DP Semi Submersibles
    All Days, 1999
    Co-Authors: J. L. Cozijn, Bas Buchner, R. R. T. Van Dijk
    Abstract:

    Abstract The study of the behavior of dynamically positioned semisubmersibles in the time domain can deliver important information on the positioning accuracy and Thruster loading of the structure. It is not sufficient to only consider a static equilibrium of environmental and Thruster forces. Dynamic effects in the stationkeeping performance of the semi submersible may play an important role. The environmental loads contain both mean and low frequency varying components. Results from calculations and regular wave tests show that the use of diffraction analysis to calculate the wave drift forces on a semi submersible will lead to an underestimation of the loads. The total thrust force delivered by the Azimuthing Thrusters on a semi submersible is influenced by a large number of variables. Interaction effects, such as Thruster-hull, Thruster-current and Thruster-Thruster interactions, are the result of complex physical phenomena. Results of model tests show, that the thrust loss due to Thruster-hull interaction effects can be up to 40% of the open water thrust. Other examples of dynamic effects in the stationkeeping behavior of a DP semi submersible include filtering of measured position signals, the application of wind feed forward, the Thruster response times and the use of forbidden sectors for the Azimuthing Thrusters. It is possible to include these effects in DP model tests. Introduction Dynamically positioned semi submersibles are being used for deep water drilling in areas such as the Gulf of Mexico, Campos Basin and West of Africa. There are a number of hydrodynamic aspects, which can be of importance in the design of the DP system. These aspects include environmental loads as well as the response of the DP system and Thrusters. The design of a DP system often involves a static footprint approach, which can be very useful, especially in the early design stage. However, this approach only considers the mean environmental loads and Thruster forces, while in practice dynamic aspects may also play an important role, e.g. vessel drift off in severe environmental conditions will typically occur after passing of a large wave group. In the present paper the dynamic behavior of dynamically positioned semi submersibles is discussed. For the dynamic behavior of a semi submersible three different aspects can be distinguished.The environmental loads on a semi submersible may vary in time. The total environmental loads show mean and low frequency varying contributions, as well as wave frequency contributions. The mean and low frequency varying environmental loads will lead to a mean position error and low frequency structure motions to which the DP system will respond. The wave frequency variations only lead to first order (oscillatory) structure motions to which the DP system must not respond.The delivered thrust force of an Azimuthing Thruster may differ considerably from its open water thrust in bollard pull condition. Thruster-hull, Thruster-current and Thruster-Thruster interaction effects are caused by complex physical phenomena.Filtering of the measured position causes phase lag in the determination of the low frequency position of the structure, which serves as input for the closed loop DP controller. Furthermore, the performance of the hardware of the DP system may lag behind the required total thrust forces. The resulting phase lag changes the effect of the adjusted P(I)D control coefficients and thus the behavior of the system. Time domain computer simulations and DP model tests offer the possibility for assessing the dynamic behavior of the system. Results of this approach include positioning accuracy and Thruster loading in

Youngjun You - One of the best experts on this subject based on the ideXlab platform.

  • Thruster-Wave Interaction During DP Stationkeeping: Model Tests in Open Water and Under a Ship Hull
    Volume 1: Offshore Technology, 2017
    Co-Authors: Hans Cozijn, Jin Woo Choi, Youngjun You
    Abstract:

    Wave orbital motions may cause variations in the inflow conditions of Thrusters, resulting in variations in thrust and torque. Physical scale model tests were carried out to investigate these Thruster-wave interaction effects, with an Azimuthing Thruster running at constant RPMs. The observed effects include a change in mean thrust and torque values, as well as wave frequency variations. The test conditions were systematically varied to investigate the effects of the incoming waves, the presence of the hull and the vessel motions. First, measurements were carried out on an Azimuthing Thruster in open water conditions. The thrust and torque in regular waves were compared with bollard pull conditions. Second, measurements were carried out on the Azimuthing Thruster under the hull of a vessel, which was rigidly connected to the basin carriage. Again, regular wave tests were performed, showing the effect of the presence of the hull. Third, measurements were carried out on the same Azimuthing Thruster under the hull of the vessel in a soft-mooring system. This kept the vessel in position and at the required heading, while allowing unrestricted wave frequency motions. Again, regular wave tests were performed, now showing the combined effects of the passing waves, the presence of the vessel hull and the vessel motions.

S. Pavlioglou - One of the best experts on this subject based on the ideXlab platform.

  • Modernizing Thruster Design: A Numerical Investigation of a Ducted Azimuthing Thruster in Oblique Flow
    2015
    Co-Authors: S. Pavlioglou
    Abstract:

    The rudder-propeller, as the Azimuthing Thruster was originally called, can be rotated 360 degrees and is capable of delivering full propulsive power in any direction. The Azimuthing Thruster makes use of a mechanical transmission in order to deliver the power from the prime mover to the propeller. The good maneuverability and the absence of a need for a rudder of such a propulsion unit are counteracted by lack of detailed knowledge for this unconventional propulsion device. The field of uncertainty lies primarily in the very nature of the Thruster, namely the fact that it is capable of rotating while operating. The oblique angle of the inflow to the Thruster can be the source of a series of complex phenomena, not all of which have been systematically monitored and analyzed. The goal of the present study is: to investigate in depth the hydrodynamic characteristics of a ducted Azimuthing Thruster and to showcase the potential impact of findings on the current detailed design approach. By means of CFD numerical software StarCCM+, the Thruster was modelled in a way which would allow the simulation of oblique inflow cases. A realization of a series of operating conditions for various advance velocities, RPM and steering positions of the Thruster was followed by a thorough explanation of the observed physical phenomena. The information acquired by the numerical simulations was then compared with characteristic rules of thumb that represent the prevailing method of design nowadays. Finally, a few selected cases were used as the basis for the realization of a force propagation analysis with the purpose of comparing the bearing reaction forces of the propeller shaft to the respective values that arise based on simplistic rule of thumb calculations. Through the course of this project, valuable information was acquired for the behavior of the Thruster unit in oblique inflow. The majority of the cases have been found to be in accordance with the imposed rules of thumb. However, a few cases demonstrated divergence from the predicted values in very large inflow angles.

Doroski, Adam D - One of the best experts on this subject based on the ideXlab platform.

  • Precision stationkeeping with Azimuthing Thrusters
    Massachusetts Institute of Technology, 2011
    Co-Authors: Doroski, Adam D
    Abstract:

    Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references.Precision positioning of an unmanned surface vehicle (USV) in a nautical environment is a difficult task. With a dual Azimuthing Thruster scheme, the optimization of Thruster outputs uses an online method to minimize the amount of error. It simplifies necessary calculations by the assumption that the rotating Thrusters are always parallel thus making the system holonomic. The scheme accommodates for limitations in actuator outputs, including rotation limits and time-lagged thrusts and was implemented in a MATLAB simulation that tested its response to step errors and disturbance forces, similar to what it would encounter in actual implementation. It successfully achieved commanded outputs in all three degrees of freedom, typically within 25 seconds. It also rejects constant and sinusoidal disturbance forces. However, specific configurations arise where the USV, at times, is uncontrollable and the system only recovers after being further perturbed into a controllable configuration.by Adam D. Doroski.S.B

William C. Webster - One of the best experts on this subject based on the ideXlab platform.

  • Design and characterization of a small-scale Azimuthing Thruster for a mobile offshore base module
    Marine Structures, 2001
    Co-Authors: Stephen C. Spry, Daniel M. Empey, William C. Webster
    Abstract:

    The mobile offshore base (MOB) will consist of a number of large semi-submersible modules connected together to form a runway approximately 2 km long. In order to conduct model-based testing of such a system with reasonably sized models, it is necessary to use models with a very small scale. In this paper, we outline the design and characterization of a 5 cm diameter Azimuthing Thruster unit designed for use on a 1:150 scale model of a MOB module. Experimental results are presented regarding thrust performance, thrust response dynamics, thrust level stability and repeatability, effects of pontoon proximity and azimuth angle relative to pontoon, and effects of advance velocity. The results indicate that the Thruster performs well and is suitable for use in model-testing applications.