Tunnel Thrusters Research Articles

Roboat III: An autonomous surface vessel for urban transportation

AbstractIn this paper, we present our novel autonomous surface vessel platform, a full‐scale Roboat for urban transportation. This 4‐m‐long Roboat is designed with six seats and can carry a payload of up to 1000 kg. Roboat has two main thrusters for cruising and two tunnel thrusters to accommodate docking and interconnectivity between Roboats. We build an adaptive nonlinear model predictive controller for trajectory tracking to account for payload changes while transporting passengers. We use a sparse directed graph to represent the canal topological map and then find the most time‐efficient global path in a city‐scale environment using the algorithm. We then employ a multiobjective algorithm's lexicographic search to generate an obstacle‐free path using a point‐cloud projected two‐dimensional occupancy grid map. We also develop a docking mechanism to allow Roboat to “grasp” the docking station. Extensive experiments in Amsterdam waterways demonstrate that Roboat can (1) successfully track the optimal trajectories generated by the planner with varying numbers of passengers on board; (2) autonomously dock to the station without human intervention; (3) execute an autonomous water taxi task where it docks to pick up passengers, drive passengers to the destination while planning its path to avoid obstacles, and finally dock to drop off passengers.

Trajectory Optimization for Autonomous Berthing of a Twin-Propeller Twin-Rudder Ship

Autonomous berthing is a crucial technology for autonomous ships, requiring optimal trajectory planning to prevent collisions and minimize time and control efforts. This paper presents a two-phase, two-point boundary value problem (TPBVP) strategy for creating an optimal berthing trajectory for a twin-propeller, twin-rudder ship with autonomous berthing capabilities. The process is divided into two phases: the approach and the terminal. Tunnel thruster use is limited during the approach but fully employed during the terminal phase. This strategy permits concurrent optimization of the total trajectory duration, individual phase trajectories, and phase transition time. The efficacy of the proposed method is validated through two simulations. The first explores a scenario with phase transition, and the second generates a trajectory relying solely on the approach phase. The results affirm our algorithm's effectiveness in deciding transition necessity, identifying optimal transition timing, and optimizing the trajectory accordingly. The proposed two-phase TPBVP approach holds significant implications for advancements in autonomous ship navigation, enhancing safety and efficiency in berthing operations.

Estimation of water momentum and propeller velocity in bow thruster model of autonomous surface vehicle using modified Kalman filter

<span lang="EN-US">Autonomous surface vehicle (ASV) is a vehicle in the form of an unmanned on-water surface vessel that can move automatically. As such, an automatic control system is essentially required. The bow thruster system functions as a propulsion control device in its operations. In this research, the water momentum and propeller velocity were estimated based on the dynamic bow thruster model. The estimation methods used is the Kalman filter (KF) and ensemble Kalman filter (EnKF). There are two scenarios: tunnel thruster condition and open-bladed thruster condition. The estimation results in the tunnel thruster condition showed that the root mean square error (RMSE) by the EnKF method was relatively smaller, that is, 0.7920 and 0.1352, while the estimation results in the open-bladed thruster condition showed that the RMSE by the KF method was relatively smaller, that is, 1.9957 and 2.0609.</span>

Trajectory Envelope of a Subsea Shuttle Tanker Hovering in Stochastic Ocean Current—Model Development and Tuning

Abstract A subsea shuttle tanker (SST) concept for liquid carbon dioxide transportation was recently proposed to support studies evaluating the ultra-efficient underwater cargo submarine concept. One important topic is the position keeping ability of SST during the offloading process. In this process, the SST hovers above the well and connects with the wellhead using a flowline. This process takes around 4 h. Ocean currents can cause tremendous drag forces on the subsea shuttle tanker during this period. The flow velocities over hydroplanes are low throughout this process, and the generated lift forces are generally insufficient to maintain the SST’s depth. The ballast tanks cannot provide such fast actuation to cope with the fluctuation of the current. It is envisioned that tunnel thrusters that can provide higher frequency actuation are required. This paper develops a maneuvering model and designs a linear quadratic regulator that facilitates the SST station-keeping problem in stochastic current. As case studies, the SST footprints at 0.5 m/s, 1.0 m/s, and 1.5 m/s mean current speeds are presented. Numerical results show that the designed hovering control system can ensure the SST’s stationary during offloading. The required thrust from thrusters and the propeller are presented. The presented model can serve as a basis for obtaining a more efficient design of the SST and provide recommendations for the SST operation.

Using Lean to Transform the Product Development Process in a Marine Company: A Case Study

The motivation of this research is to investigate if the Lean concept can be used to improve a company’s product development (PD) process and thereby providing cost-effective methods for development, engineering and manufacturing of products to sustain competitiveness. This longitudinal study builds upon an initial assessment of Lean practices in a company in the Nordics Marine sector starting in 2017. An improvement opportunity identified was defining measures to ensure improved integration of functional areas, especially manufacturing, from the beginning of the PD process. As a follow-up of the assessment, we studied the application of a set of new PD practices outlined for the development stage of a new, optimized tunnel thruster. The purpose of this paper is to share our findings related to the application of these practices and their effect on a Lean transformation in PD. Data collection was done through a participatory approach for observing team activities, including two workshops with key people in the thruster project. The results indicate that early integration of manufacturing competence in PD is important to improve production (integration), reduce time and cost. In addition, the use of design demonstrators and physical testing enable improved cost control and leverage learning throughout the PD process. A re-assessment of company practices relative to Lean, made during the autumn of 2020, identifies that six out of thirteen capabilities are improved in terms of the gap between current and desired future states. However, increased capability gap is identified in utilizing rigorous standardization to reduce variations, since existing company standards are challenged by new project innovations. It is concluded that the effect of introducing new PD practices to reduce capability gaps in Lean Product Development (LPD) is promising, especially for principles that are managed within the project control.

DRY-DOCKING TIME AND LABOUR

The duration of stay of a ship in a drydock depends on the scope of routine underwater (submerged portion of the ship’s hull) repairing works (dry-docking works only) to be carried out. More specifically, the repairing works that are affected by outside water. These are, mainly, hull cleaning, coating (blasting and painting), rudder, propeller, stern tube aft seal, hull anodes, ICCP, sea valves, sea chests, tunnel thruster(s), bottom plugs, underwater structural steel (bottom and shipside) and so on. These dry-docking works dictate ships’ dry-docking time (days) and labour (man-days). Then what about the deadweight, age and type? Do these have any impact on dry-docking time and labour? An attempt has been made in this article to examine if there exist any possible relationship between a ships’ dry-docking time and its labour, and deadweight, age and type. Dry-docking time and related information for 586 cargo ships and dry-docking labour and related information for 50 cargo ships of various deadweights, ages and types were collected from a single shipyard. These were analyzed and presented in both tabular and graphical forms to demonstrate the possible relationship between dry-docking time and labour, and deadweight, age and type of ships. Ships’ dry-docking time and labour are very vital for both the ship owner and the shipyard because various charges in drydock are many folds higher than that at quay- side. As such, the reduction in ships’ dry-docking time and labour contributes in saving for the ship owner and increases the earning for the shipyard. A proper estimation of ships’ dry-docking time and labour can achieve this. In order to do so, the past information/data about ships’ dry-docking time and labour may serve a practical guide to prepare an achievable time and labour planning for dry-docking works. In this article, the authors have attempted to identify the independent variables that influence ships’ dry-docking time and labour (dependent variables) and suggested their possible inter-relationships. The inter-relationships between the independent variables (deadweight, age and type) and dependent variables (time and labour) appear to be linear.

Real-Time Control Allocation for Autonomous Surface Vehicle Using Constrained Quadratic Programming

Control system is very important for each autonomous surface vehicle (ASV), which involves the problem of maintaining the vehicle’s position and heading using feedback controller and achieving the desired forces through thrust allocation. In this paper, we present a practical thrust allocator for under-actuated and fully-actuated vehicles, which can be represented as a quadratic programming (QP) problem with linear constraints. Such an optimization method allows us to consider common propulsion system, including tunnel thruster, azimuth thruster, and fixed propeller with rudder. These linear constraints enable us to explicitly account for the rate, amplitude and azimuth constraints of each propeller on the vessel. The proposed methods have been illustrated by simulated and experimental maneuvers for different thruster layout of a vehicle.

Computational hydrodynamic optimization of galvanic anode shapes for tunnel thrusters

We introduce a computational method for designing minimum-drag galvanic anodes for tunnel thrusters, assuming a given maximum anode mold diameter and a given anode weight. The method is illustrated for a tunnel of 1000 mm radius, and the results are evaluated by using Computational Fluid Dynamics (CFD). For a representative 45° tunnel flow, the pressure drop caused by a single anode can be reduced by 92% and the risk of cavitation mitigated relative to a rectangular block anode shape

Application of Measurement Sensors and Navigation Devices in Experimental Research of the Computer System for the Control of an Unmanned Ship Model.

Unmanned autonomous transport vessels (MASS) are the future of maritime transport. The most important task in the design and construction of unmanned ships is to develop algorithms and a computer program for autonomous control. In order for such a computer program to properly control the ship (realizing various functions), the ship must be equipped with a computer system as well as measurement sensors and navigation devices, from which the recorded parameters are processed and used for autonomous control of the ship. Within the framework of conducted research on autonomous ships, an experimental model of an unmanned ship was built. This model was equipped with a propulsion system not commonly used on transport vessels (two azimuth stern thrusters and two bow tunnel thrusters), but providing excellent propulsion and steering characteristics. A complete computer system with the necessary measuring sensors and navigation devices has also been installed in the model of the ship, which enables it to perform all functions during autonomous control. The objective of the current research was to design and build a prototype computer system with the necessary measurement sensors and navigation devices with which to autonomously control the unmanned ship model. The designed computer system is expected to be optimal for planned tasks during control software tests. Tests carried out on open waters confirmed the correctness of the operation of the computer system and the entire measurement and navigation equipment of the built model of the unmanned transport vessel.

Experimental study on the selected aspects of bow thruster generated flow field at ship zero-speed conditions

The paper presents the results of experimental study on the interaction between the bow thrusters understood as the flow field changes generated by bow tunnel thruster in deep water conditions operated as a single and twin units. The research was limited to zero-speed case for the ship dead in the water. The influence of the hull form and jet spread between the neighbouring thrusters for several combinations of the applied bow thruster propeller revolutions has been discussed. The results of the flow field measurements - velocity field, volume of fluid rate, mean velocity and thrust have been compared with the measurements of hydrodynamic forces generated by the bow thrusters on the hull. Both experiments were conducted at zero-speed using the same large physical man-manned model of a car–passenger ferry in 1:16 scale.

Maneuverability Analysis of a Novel Portable Modular AUV

ZFAUV is a novel portable modular AUV. There are four fixed thrusters at tail, and two tunnel thrusters are set at front. The maneuverability of ZFAUV is relatively high. It can turn around in situ, move lateral or move up/down vertical. The yaw and pitch can be controlled by tunnel thrusters or differential control of tail thrusters, but differential control will reduce the forward force. Different from propeller-rudder AUVs, the turning radius is related to speed forward: the smaller the speed forward, the smaller the turning radius. The minimum turning radius tends to be zero. The mathematical model is built first; then CFD is used to predict the thrust and torque of tail thrusters and tunnel thrusters. Through numerical simulation, zigzag maneuver analysis in horizontal plane, and trapezoidal steering maneuver analysis in vertical plane, the maneuverability of ZFAUV is obtained. The maneuverability of ZFAUV becomes worse with the increase of speed. The maneuverability of differential control is better than that of tunnel control. In the case of specific thrust distribution of tail thrusters and tunnel thrusters, ZFAUV can turn around in situ (the maximum angular velocity is about 24.1°/s), move lateral or move up/down vertical (the maximum velocity is about 0.4m/s). Finally, an example, PID parameters tuning, is given to illustrate the application of maneuverability analysis. The dynamic performance of ZFAUV can be quickly and accurately analyzed by mathematical method, which has important guiding significance for the choice of control strategy and experiments and also has reference value for the later development of AUVs.

Alternative approach for dynamic-positioning thrust allocation using linear pseudo-inverse model

Application of ship Dynamic-Positioning systems strongly depends on physical ability of actuators (Thrusters) in providing commanded loads. This will consequently introduce some constraints and limitations to Thrust Allocation problem in design and control of such systems. However, there is a special case in which a simple explicit solution could be found by fixing orientation of azimuth thruster relative to vessel regarded as linear model. In this paper, three new alternative approaches based on linear model are introduced. Case study is a time domain simulation of Station-Keeping (instant Point-Tracking) operation for a supply vessel called Northern Clipper in North Sea with Beaufort number 6. As is evident by results, these approaches improve maneuvering performance and power consumption efficiency compared to the conventional linear model. Results show improved robustness of yaw control in Point-Tracking operation and decreased overall consumption of power compared to linear model. Furthermore, it is apparent from the results that these approaches are particularly efficient in tunnel thrusters compared to linear counterpart.

Effects of Blade Loading Distribution on the Cavitation and Excitation Forces of a Tunnel Thruster

Compared with open propellers, the impeller of a tunnel thruster is more vulnerable to cavitation and structural vibration problems because the impeller is typically subject to severe non-uniformity of inflow produced by the blunt gearbox. Model tests and numerical simulations are carried out in the cavitation tunnel of Shanghai Jiao Tong University for a tunnel thruster using a “flat plate” impeller and a tip-unloaded one. The characteristics of fluctuating pressures on the tunnel wall and the resultant excitation forces are investigated. It is found that although unloading the blade tips of an impeller is effective in reducing the fluctuating pressures in a local tunnel wall area near the tips, the same trend does not apply to the case of the excitation forces. The results show that care should be taken when the experimentally measured fluctuating pressures are utilized as the input to the analysis of structural vibrations.

Dry-Docking Time and Labour

The duration of stay of a ship in a drydock depends on the scope of routine underwater (submerged portion of the ship’s hull) repairing works (dry-docking works only) to be carried out. More specifically, the repairing works that are affected by outside water. These are, mainly, hull cleaning, coating (blasting and painting), rudder, propeller, stern tube aft seal, hull anodes, ICCP, sea valves, sea chests, tunnel thruster(s), bottom plugs, underwater structural steel (bottom and shipside) and so on. These dry-docking works dictate ships’ dry-docking time (days) and labour (man-days). Then what about the deadweight, age and type? Do these have any impact on dry-docking time and labour? An attempt has been made in this article to examine if there exist any possible relationship between a ships’ dry-docking time and its labour, and deadweight, age and type. Dry-docking time and related information for 586 cargo ships and dry-docking labour and related information for 50 cargo ships of various deadweights, ages and types were collected from a single shipyard. These were analyzed and presented in both tabular and graphical forms to demonstrate the possible relationship between dry-docking time and labour, and deadweight, age and type of ships. Ships’ dry-docking time and labour are very vital for both the ship owner and the shipyard because various charges in drydock are many folds higher than that at quay-side. As such, the reduction in ships’ dry-docking time and labour contributes in saving for the ship owner and increases the earning for the shipyard. A proper estimation of ships’ dry-docking time and labour can achieve this. In order to do so, the past information/data about ships’ dry-docking time and labour may serve a practical guide to prepare an achievable time and labour planning for dry-docking works. In this article, the authors have attempted to identify the independent variables that influence ships’ dry-docking time and labour (dependent variables) and suggested their possible inter-relationships. The inter-relationships between the independent variables (deadweight, age and type) and dependent variables (time and labour) appear to be linear.

Experimental investigation of the effects of blade geometry on pressure fluctuation and noise of tunnel thrusters

ABSTRACTTunnel thrusters are more vulnerable to cavitation due to the tip clearance flow, blockage effect of the gearbox, and heavy blade loads as compared with open propellers, which makes the problems of structure vibration and radiated noise more serious. Unfortunately, there are few public sources of relevant experimental study. In this context, model experiments have been carried out in the cavitation tunnel of the Shanghai Jiao Tong University to investigate the effects of blade geometry on pressure fluctuation and noise. The experimental results indicate that the traditional ‘flat plate’ blade is unfavourable for vibration excitation, while unloading towards the tip can effectively reduce both the fluctuating pressure and the noise levels.

Longitudinal Motion Due to Action of Tunnel Thrusters

Abstract Tunnel thrusters are propulsion and active control devises that provide a side force, or transverse thrust, to support mooring operations or position keeping. They shorten the time of manoeuvring, reduce the cost of towage and since inception, manoeuvrability specifically in ports has become a lot easier. Tunnel thrusters can either be operated manually or with the help of Dynamic Positioning systems which makes it even more efficient. Theoretically, the transverse force due to tunnel thruster action should generate only lateral and rotational motion. Therefore, it is typical and a common practice during manoeuvring simulations that the longitudinal motion due to the action of tunnel thrusters is neglected. Nevertheless, the experience of masters and pilots shows that some longitudinal motion due to the action of tunnel thrusters appears. This paper shows some examples of turning manoeuvres carried out with bow thrusters only, i.e. no additional control devices or tug assistance have been used. The manoeuvres have been carried with minimal possible initial longitudinal nor lateral speed. Model tests have been done with the use of large manned models of VLCS, PCTC and LNG carrier, which differ in hull shape, dimensions and shape coefficients. Results obtained from the tests confirm that the motion caused by bow thruster besides rotational and lateral motion consists additionally of longitudinal motion. Analysis of the combination of motions due to the action of tunnel thrusters have been done and some rationale for this phenomenon has been presented. Additionally a short analysis of position of pivot point during tunnel thruster test has been carried out.

Cross-coupling effect and motion control of an autonomous underwater vehicle with internal actuators

Hybrid autonomous underwater vehicles (AUVs) use internal actuators, e.g., tunnel thruster, moving mass, and ballast chamber, for yaw and pitch steering. Unlike control surfaces, internal actuators perform independently of relative flows around AUVs, thus suitable for missions which require excellent low-speed maneuverability. This research focuses on an investigation into the control design of an REMUS AUV using internal actuators to steer its heading direction. It has been shown that an internal moving mass together with a tunnel thruster is capable of providing actuations to serve the purpose. However, our analysis indicates that a coupling between roll and pitch motion causes the internal actuators to oscillate if depth-plane motion is neglected when deriving control laws for the internal actuators. We present a novel control strategy by taking advantage of the cross-coupling effect when designing the heading autopilot system with internal actuators. The effectiveness and robustness of the proposed design are validated by simulation results.

AUV Thrust Allocation with Variable Constraints

Modern multipurpose Autonomous Underwater Vehicles (AUVs) represent the nextgeneration of robotic systems with new technological tasks faced by researchers. One methodof extending the functionality of the vehicle is installing tunnel thrusters in addition to the sternpropulsion system. Thereby the vehicle becomes able to undertake both survey-style missionsand low speed interactions with the environment. But the efficiency of the tunnel thruster dependsstrongly on the vehicle’s velocity, due to hydrodynamic aspects. The usual solution to this problemuses different control models and thrust allocation methods for these types of mission. A unifiedapproach to thrust allocation is presented in this paper. The approach is based on solving theallocation problem by quadratic programming with variable constraints, depending on the velocityof the AUV and the thrusters’ angle of attack. The well-known implementation of active setmethod was used to model the proposed allocation method.

Study of tunnel thruster performance and flow by quasi-steady Reynolds-averaged Navier-Stokes simulation

A numerical approach based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations using the shear-stress transport (SST) turbulence model has been employed to investigate the hydrodynamic performance and flow of tunnel thrusters. The flow passages between adjacent blades are discretized with prismatic cells so that the boundary layer flow is resolved down to the viscous sub-layer. The hydrodynamic performances predicted by the quasi-steady approach agree well with the experimental data for three impellers covering a range of blade area and pitch. Through analysis of the flow field, the reason why the hub of impeller also contributes to thrust which can amount to 40%—60% of the impeller thrust, and the mechanism of the impeller inducing an axial force on the hull are elucidated.

Nonlinear heading control of an autonomous underwater vehicle with internal actuators

Designs of hybrid autonomous underwater vehicles (AUVs), which use internal actuators instead of control surfaces to steer, have emerged recently in the ocean engineering community. This paper focuses on the heading autopilot design for a REMUS AUV by using an internal moving mass. A nonlinear dynamical system is first derived which describes the horizontal-plane motion of the vehicle coupled with an internal moving mass. It is shown that a displacement of the internal mass in the sway direction can affect the flow of the dynamical system in phase space. Using displacement as the system input, a LQR controller is designed to stabilize the heading angle of the vehicle by taking advantage of the position and inertia of the internal moving mass. The linear controller cannot deal with large perturbations due to the constraints on the maximum displacement and movement speed of the internal moving mass. Consequently, a tunnel thruster is added to the design in order to address the problem. A nonlinear full-state feedback law is derived based on backstepping and Lyapunov redesign technique to control the displacement of the internal mass and the force exerted by the tunnel thruster. Simulation results demonstrate the effectiveness of the proposed design.