Azimuth Thrusters Research Articles

A numerical model calibrated by in-situ measurement for predicting the underwater radiated noise of an azimuth thruster structure of a passenger ship

In a global context of limiting the impact of noise pollution on the behavior of marine fauna, the understanding of acoustic radiation phenomena from underwater sound sources of a passenger ship is of primary importance. Although diesel engines and propellers are considered to be ones of the main sources of ship noise, our observations have shown that immersed motors contribute significantly to the noise radiated into the water by passenger ships at low speeds. This contribution summarizes a semi-empirical method for estimating the noise radiated into the water from an azimuth thruster-type structure. An analysis of the vibroacoustic behavior in water of the structure excited by an internal acoustic source is detailed. Beyond the complexity of performing full-scale measurements in a noisy environment, the analysis of the measurements allows to estimate the vibration modes of the immersed structure. A numerical model of the dedicated structure, calibrated on the basis of an experimental modal analysis, is used to estimate the pressure field radiated by the structure into the water. As a result of these analyses, a simplified model of radiated noise in the water is developed for use in nominal thruster operation.

Synthesis of a dynamic positioning algorithm for wheeled boats

The work analyzes the controllability indicators of a vessel with a wheeled propulsion-steering complex and an azimuth thruster in order to identify the possibility of developing high-precision control algorithms, such as the dynamic positioning task. The influence of the parameters of the wheel-propulsion steering complex and the azimuth thruster on the dynamics of the vessel is considered, and the areas of controllability of the vessel are identified for various propulsion parameters. The influence on the dynamics of the vessel of external wind influence, which has a great influence on the dynamics of the vessel due to its design features (shallow draft, flat bottom, large windage), has been studied. The areas of controllability of the vessel under conditions of external influence when changing wind parameters (force and direction) and parameters of propulsors with separate and joint use of propulsors are determined. An algorithm has been synthesized for dynamically holding a vessel at a given point under wind influence while maintaining a given hull position. The dynamic positioning algorithm consists of two parallel processes. The first is the return of the center of mass of the vessel, which has shifted under the influence of external influences, to a given point due to the wheeled propulsion and steering complex. The second is maintaining a given orientation of the ship's hull using an azimuth thruster. Computer simulation confirmed the high quality indicators of the proposed control algorithm.

Effects of ventilation on open water characteristics of azimuth propellers under shallow water conditions

Inland waterway vessels can accommodate relatively large propellers due to the specially shaped sterns of these ships. Specifically, they can accommodate up to 20 percent larger diameter propellers, thereby enabling operation without ventilation. However, for an azimuth thruster with a freely positioned propeller, ventilation can occur due to the small distance between the water surface and the propeller. This can lead to dangerous operational situations, such as an inability to maneuver. Systematic investigations comprising model testing and numerical URANS simulations were performed to analyze open water characteristics of a typical azimuth thruster fitted with the newly invented shallow water duct. This so-called shallow water duct was developed to prevent air drawing of the thruster's propeller, i.e., to avoid the inception of propeller free surface ventilation inception (aeration). A typical thruster fitted with this duct was investigated at an immersion depth smaller than the minimum immersion depth recommended by the ITTC for open water tests. Compared to a thruster fitted with a conventional standard duct, the performance of the thruster fitted with this shallow water duct was improved significantly. At lower propeller advance coefficients, especially during bollard pull conditions, it generated more continuous thrust and torque with the propeller operating at the same operating point although, at higher propeller advance coefficients, this duct caused the thruster to act like a break. Especially when fitted with the shallow water duct, thrusters accommodated on inland waterway vessels represent a constructive solution to improve the maneuverability and operational safety of ships navigating in confined waters of limited depth. Fitting the shallow water duct is expected to improve the ability of the thruster to initially accelerate the ship.

Study of control allocation algorithm for over-actuated underwater robot motion control using azimuth thrusters

The paper considers a problem of a mobile over-actuated underwater reconfigurable robot motion control using azimuth thrusters. To solve the control allocation problem, a configurator has been introduced into the control sys-tem. This makes it possible to synthesize the control law regardless of the number, position and type of the propul-sion-steering complex components. A control allocation algorithm is studied to determine both the control and the orientations of the azimuth thrusters.

Lake Environmental Data Harvester (LED) for Alpine Lake Monitoring with Autonomous Surface Vehicles (ASVs)

This article introduces the Lake Environmental Data Harvester (LED) System, a robotic platform designed for the development of an innovative solution for monitoring remote alpine lakes. LED is intended as the first step in creating portable robotic tools that are lightweight, cost-effective, and highly reliable for monitoring remote water bodies. The LED system is based on the Shallow-Water Autonomous Multipurpose Platform (SWAMP), a groundbreaking Autonomous Surface Vehicle (ASV) originally designed for monitoring wetlands. The objective of LED is to achieve the comprehensive monitoring of remote lakes by outfitting the SWAMP with a suite of sensors, integrating an IoT infrastructure, and adhering to FAIR principles for structured data management. SWAMP’s modular design and open architecture facilitate the easy integration of payloads, while its compact size and construction with a reduced weight ensure portability. Equipped with four azimuth thrusters and a flexible hull structure, SWAMP offers a high degree of maneuverability and position-keeping ability for precise surveys in the shallow waters that are typical of remote lakes. In this project, SWAMP was equipped with a suite of sensors, including a single-beam dual-frequency echosounder, water-quality sensors, a winch for sensor deployment, and AirQino, a low-cost air quality analysis system, along with an RTK-GNSS (Global Navigation Satellite System) receiver for precise positioning. Utilizing commercial off-the-shelf (COTS) components, a Multipurpose Data-Acquisition System forms the basis for an Internet of Things (IoT) infrastructure, enabling data acquisition, storage, and long-range communication. This data-centric system design ensures that acquired variables from both sensors and the robotic platform are structured and managed according to the FAIR principles.

Research on the effect of shallow draft on the performance of azimuth thruster under bollard conditions

For the azimuth thruster installed on shallow draft ships, the shallow water effect leads to a decrease in propulsive performance, especially under the bollard condition. In order to accurately predict the bollard propulsion performance of the azimuth thruster under shallow draft conditions, this paper firstly obtains the bollard thrust performance in several waters through the shallow water test, and then analyzes the effect of hull wake and cavitation on the bollard thrust performance of the azimuth thruster by using the CFD method. The results are consistent with the test results under the open water. When the water depth is less than 1.0D, the thrust coefficient increases with the increase of water depth, when the water depth is greater than 1.0D, the thrust coefficient basically does not change; Considering the influence of hull wake, the axial inlet velocity of the azimuth thruster is 7.27% higher than that of the open water condition; meanwhile considering the influence of the hull wake and cavitation, the leading edge of the bottom of the azimuth thruster conduit and the back of the paddle blade are susceptible to cavitation, which leads to average decrease of the thrust coefficient and torque coefficient by 7.03% and 6.12%, respectively.

Experimental Study on Adaptive Backstepping Synchronous following Control and Thrust Allocation for a Dynamic Positioning Vessel

Cargo transfer vessels (CTVs) are designed to transfer cargo from a floating production storage and offloading (FPSO) unit into conventional tankers. The dynamic positioning system allows the CTV to maintain a safe position relative to the FPSO unit using a flexible cargo transmission pipe, and the CTV tows the tanker during operating conditions. The operation mode can be considered a synchronization tracking control problem. In this paper, a synchronization control strategy is presented based on the virtual leader–follower configuration and an adaptive backstepping control method. The position and heading of the following vessel are proven to be able to globally exponentially converge to the virtual ship by the contraction theorem. Then, the optimization problem of the desired thrust command from the controller is solved through an improved firefly algorithm, which fully considers the physical characteristics of the azimuth thruster and the thrust forbidden zone caused by hydrodynamic interference. To validate the effectiveness of the presented synchronous following strategy and thrust allocation algorithm, a scale model experiment is carried out under a sea state of 4 in a seakeeping basin. The experimental results show that the CTV can effectively maintain a safe distance of 100 m with a maximum deviation of 3.78 m and an average deviation of only 0.99 m in the wave heading 180°, which effectively verifies that the control strategy proposed in this paper can achieve safe and cooperative operation between the CTV and the FPSO unit. To verify the advantages of the SAF algorithm in the thrust allocation, the SQP algorithm and PSO algorithm are used to compare the experimental results. The SAF algorithm outperforms the SQP and PSO algorithms in longitudinal and lateral forces, with the R-squared (R2) values of 0.9996 (yaw moment), 0.9878 (sway force), and 0.9596 (surge force) for the actual thrusts and control commands in the wave heading 180°. The experimental results can provide technical support to improve the safe operation of CTVs.

Torque Reconstruction for Maritime Powertrains Using Trend Filtering

This paper presents a convex optimization approach for the simultaneous reconstruction of unknown input torque and torsional response in the driveline of an azimuth thruster. Accurate estimates of the shaft torque responses are necessary for condition monitoring purposes. Estimating torque responses also enables flexibility in the choice of sensor location, with subsequent potential savings in installation and maintenance costs. It is shown that the unknown inputs and states can be reconstructed using batch torque measurements from a single location in the propulsion line. The estimation problem is formulated as a trend-filtering problem, enforcing the smoothness of input estimates. The performance of the proposed method is evaluated by means of simulations and experiments on a small-scale testbench of a maritime azimuthing thruster. The results show that the torsional response of the propeller shaft can be accurately reconstructed using torque measurements from sensors installed near the driving motor at the opposite end of the driveline.

Experimental Identification of Decoupled Ship Dynamic Models for an Autonomous Catamaran Urban Cargo Vessel

KU Leuven developed and launched the Maverick catamaran in 2023, designed specifically for autonomous cargo transportation in narrow urban waterways. This vessel features a distinct actuation system utilizing two 360-degrees-steerable azimuth thrusters, positioned at the bow and stern. This study proposes and experimentally identifies decoupled ship dynamic models for the Maverick that concentrate on surge and yaw. The models aim to predict the vessel's speed and heading, particularly when steered by a bow thruster, sailing stably around service speed along the waterway. To do so, two sets of experiments were designed, each dedicated to collecting data for the individual identification of the decoupled models. These experiments deviate from the conventional use of standard maneuvers such as zigzag or turning, which are intended for maneuverability assessment of sea-going rudder-propeller vessels. Instead, sinusoidal excitation maneuvers were employed to better suit the dynamic system of the Maverick with its unique actuation system and operational strategy. Finally, a comparison is made between model predictions and a manually executed waterway-following maneuver recorded for reference. The results underline the suitability of the identified models for accurate trajectory prediction during the stable sailing scenario with small external disturbance and minor course curvature.

A Numerical Study on Modeling Ship Maneuvering Performance Using Twin Azimuth Thrusters

A methodology of mathematical testing is proposed for a ship with twin azimuth thrusters based on numerical calculations. An unmanned surface vessel (USV) powered by two azimuth thrusters is considered, which is a model-scale configuration. The Ship Maneuvering Mathematical Model Group (MMG) model is introduced to describe forces on the hull and propellers. A set of captive tests (planar motion mechanism (PMM) and open-water tests) were simulated using STAR-CCM+ (16.06.008-R8) software to obtain hull hydrodynamic derivatives and azimuth thruster hydrodynamic coefficients. A maneuvering test of the model-scale ship with two azimuth thrusters is built based on numerical results, and numerical results are compared with the model-scale experimental data to validate the feasibility of numerical methods. The findings show that the usability of the developed mathematical test in predicting the maneuvering ability of ships with two azimuth thrusters is confirmed through numerical calculations.

Design and Build of an Autonomous Catamaran Urban Cargo Vessel

This study introduces a novel test bed, named the Maverick, which aims to advance the field of autonomous inland waterborne freight transportation and facilitate its eventual implementation. More specifically, the Maverick focuses on operating in small waterways within urban areas, aligning its application scenario with the European project AVATAR. The hull form of the Maverick was selected to be a catamaran, as it offers several advantages, including a large open deck area, high transverse stability, and excellent maneuverability at low speeds. The Maverick is equipped with two 360-degrees-steerable azimuth thrusters, one at the bow and one at the stern. This configuration makes the Maverick over-actuated, and offers more advanced motion control possibilities compared to conventional rudder-propeller actuated vessels. The Maverick is composed out of modular building blocks combined with a flexible interface, which enables it to accommodate diverse control terminals for future developments. Furthermore, to illustrate the feasibility of the Maverick within an urban context, this study also includes results of several trail tests. The interactive communication framework that was successfully employed in the autonomous sailing experiment is introduced. The Maverick offers a versatile platform for testing and developing a wide range of technologies in situation awareness, autonomous sailing, smart waterway logistics, and other interconnected domains. Therefore, this innovative research vessel can pave the way for the development of a new freight transport mode within European urban areas, contributing valuable experiences to the field.

On the continuity of control allocation for surface vessels with two azimuth thrusters

This paper presents two novel results concerning the control allocation problem (CAP) for marine crafts with 2 azimuth thrusters. The first result is a novel closed form solution for the CAP which ensures Lipschitz continuity of the azimuth angle. The second result is a convex optimization reformulation of the CAP for the case of limited rate of changes for the actuators orientation which includes a novel regularization term that avoids anomalous behaviors due to underactuation. The effectiveness of the two methods are showcased through numerical simulations.

Faults prevention for the gear coupling of the azimuth thruster L-drive through a study of shaft alignment measurements

The propulsion system is one of the most important systems in a vessel. It is considered critical, since if it fails, directly compromises the operation and safety. A common fault on the azimuth propulsion L-drive system is the gear coupling failure, where on the last stage of damage the shaft can broke causing propulsion loss. The two main reasons of this problem are the shaft misalignment and lack of gear coupling teeth lubrication. Through a specific alignment measurement procedure, performed on three different vessels and 17 azimuth thruster L-drive, this study will prove that the shaft alignment between motor and thruster is affected by the steering rotation of the azimuth system. The alignment changes due to steering position sometimes can be greater than alignment tolerance values, generating gear coupling damages. Then a specific procedure is proposed to measure, evaluate, and correct the alignment to prevent gear coupling failures and improve the system reliability.

A thrust allocation method for DP vessels equipped with rudders

The thrust allocation unit is an important part of dynamic positioning system. Many dynamic positioning vessels are equipped with propellers and rudders, but the complex hydrodynamic characteristics of the propeller-rudder combination make thrust allocation a challenging task. However, research on thrust allocation methods has primarily focused on azimuth thrusters, and only limited attention has been given to the propeller-rudder combination. In this study, we propose a model-based thrust allocation method that incorporates an interaction model between the rudder and propeller, while also considering other factors such as the energy consumption and actuator mechanics. The proposed thrust allocation method is tested by using the dynamic positioning model test in a basin and the experimental results show that our method effectively maintains vessel position even in adverse sea conditions, with the thrust allocation results following the control commands well. The experimental results validate the effectiveness of the proposed thrust allocation method, indicating its potential application in real ship dynamic positioning systems.

Dynamic Positioning Capability Assessment Based on Optimal Thrust Allocation

Abstract The article presents an efficient method of optimal thrust allocation over the actuators in a dynamically positioned ship, according to the DNV-ST-0111 standard, Level 1. The optimisation task is approximated to a convex problem with linear constraints and mathematically formulated as quadratic programming. The case study is being used to illustrate the use of the proposed approach in assessing the DP capability of a rescue ship. The quadratic programming-based approach applied for dynamic positioning capability assessment allows for fast calculations to qualitatively compare different ship designs. In comparison with the DNV tool, it gives 100% successful validation for a ship with azimuth thrusters and a pessimistic solution for a ship equipped with propellers with rudders. Therefore, it can be safely applied at an early design stage.

Powering Design of Portable Dynamic Positioning Thruster for 150 FT Cable Laying Barge: A Case Study of Untung Jawa-Tanjung Pasir Submarine Power Cable Laying

Indonesia, an archipelagic nation with most of its electrical power produced by steam power plant. The distribution of electrical power is done through the main island to the smaller island, by means of according to Ministry of Energy and Mineral Resource is done through a submarine cable. In the study case area, Untung Jawa-Tanjung Pasir sea, the most appropriate cable laying platform is a barge. A barge is not equipped with the propulsion system and considering the cable laying operation requirement, barge given condition, environmental disturbances, the barge must be equipped with portable dynamic positioning thruster. An azimuth thruster is the proposed way to overcome this problem. The research done shall determine the barge’s necessary engine and propeller to fulfil its need. Using ship manoeuvring equation, the required thrust of the barge for surge, sway, and yaw are 274.36 kN, 289.21 kN, 3292.67 kNm respectively. To produce the required forces and moment, the researcher utilizes Cummins KTA38 (634 kW) diesel engine, Masson Marine gearbox (5.542:1), and Ka4-70 Nozzle 24 with the diameter of 1.6 m and P/D value of 1.06. In the free running condition, the barge will run with the speed of 3.52 m/s or 6.85 knots.

Dynamic Response Characteristics of the Hydraulic Rotary System of an Azimuth Thruster for a Dynamic Positioning Vessel

The composition characteristics and working principle of the hydraulic rotary system of the azimuth thruster were analyzed. The mathematical model of the rotary dynamic system of the pump-controlled hydraulic motor driving the gear reduction mechanism was established. Additionally, a fast tracking method for the azimuth angle of the azimuth thruster was proposed to analyze the rotary azimuth angle, angular velocity and dynamic response characteristics of the hydraulic system for different desired azimuth angles. The simulation results show that the established dynamic model can simulate the rotary motion response process of the real thruster, and can realize the rapid and accurate tracking of the azimuth angle. At the same time, the physical constraints of the rotary dynamic response were established. It provides an important reference for research on the motion control methods of dynamic positioning vessels.

Designation of the Boundary Conditions for Estimating the Thrust Loss due to Thruster-Hull Interactions

The azimuth thruster is mainly installed on a vessel that requires a dynamic positioning (DP) function for special purposes. When the azimuth thruster on a vessel operates for DP, the thrust loss is induced by the thruster-hull interaction. This study examined the influence of boundary conditions in numerical simulations for predicting thrust loss. Wind turbine installation vessels (WTIV) and floating production storage and offloading (FPSO) were chosen as a target vessels. In this study, two types of boundaries were defined. The first consideration is that the boundary condition was assigned with consideration of the azimuth angle of the thruster, whereas it is fixed regardless azimuth angle of the thruster. The predicted thrust loss according to these boundary conditions showed a difference. This observation originated from the current load of the vessel. Therefore, the boundary conditions for which the current load is not induced need to be designated to obtain a realistic thrust loss in a numerical simulation.

Nonlinear fault-accommodation thrust allocation for over-activated vessels using artificial neural network and multivariate analysis

This study seeks to develop a better understanding of the thrust allocation process of over-actuated marine vessels. A two-stage analysis framework is proposed for thrust allocation when thrusters experience faults. In Stage-I, sequential quadratic programming with a multi-start mechanism (SQP-MultiStart) is used to find the optimal solution to the nonlinear fault-accommodation thrust allocation problem. According to the solution feasibility, another two different optimization models are considered in Stage-II. A newly developed meta-heuristic optimization approach, neural network algorithm (NNA), and SQP-MultiStart method are employed to find optimal solutions. Histories of decision variables and thrust allocation status are obtained. Self-organization mapping (SOM) and principal component analysis (PCA) are utilized to mine the hidden information in the thrust allocation. A deepwater pipe-laying crane vessel with 7 azimuth thrusters is selected to illustrate the analysis procedure. The features of thrust allocation are investigated and the effectiveness of the proposed framework is verified. Simulation results extend the understanding of the thrust allocation process and assist in choosing the thrust allocation model in different cases. The framework is suitable for fault-free and faulty cases. Neural network technique and multivariate analysis help to mine the knowledge about the thrust allocation performances.

The Effect of Azimuth Thruster on the Manoeuvring Ability of a Stern Trawler in Rough Weather Conditions

The results of computational analyses on the manoeuvring performance of a stern trawler with an azimuth thruster located in the forward part of the vessel are presented. The initial design of the vessel with a single shaft, propeller and rudder is considered to have insufficient manoeuvring performance with a trawl pull load of 40 tons in moderate environmental conditions with a forward speed of 3 knots. The modified design is equipped with an azimuth thruster located in the forward part of the vessel that can rotate 360 degrees to produce additional thrust. In order to assess and simulate the manoeuvring performance of the vessel, the surge, sway and yaw equations are set and solved in the time domain. The hydrodynamic forces due to surge and sway motions and the yaw moment are represented by a nonlinear modular mathematical model. The manoeuvring coefficients of the mathematical model employed are estimated by two distinct approaches; the first one is based on semi-empirical methods and the other is based on computational fluid dynamics (CFD). The external forces due to wind, current and waves are mathematically represented by proven semi-empirical methods based on the results of scaled model tests and full-scale measurements. A comprehensive computational test matrix is established and extensive computational analyses and manoeuvring simulations were carried out to indicate that an azimuth thruster with sufficient thrust located in the forward part of a stern trawler could significantly improve the manoeuvring performance of the vessel despite adverse environmental conditions.