Marine Thruster Research Articles

Behavior of marine thruster lip seals under typical operating conditions

Marine thruster lip seals pose a condition monitoring challenge, yet they are seldom studied tribologically. The present work studies the behavior of a 300 mm diameter NBR marine thruster lip seal (n = 3) under typical operating conditions. Frictional torque and subsurface temperature were measured under 27 combinations of oil temperature, oil pressure, and rotational speed. The frictional torque increased with increasing oil pressure and decreased with increasing oil temperature. The subsurface temperature increased with increasing oil temperature, oil pressure, and rotational speed. There was no clear relation between the frictional torque and subsurface temperature. The frictional torque ranged 9.6–14.4 Nm, and subsurface temperature 57–94 °C. Preliminary wear measurements showed a wear track width of 0.2–0.3 mm and a wear rate of 0.031 ± 0.001 mm3/hour.

Performance characterization of marine lip seals: Contact temperature and frictional torque

This paper investigates the performance of marine thruster lip seals. Marine lip seals have received much less attention in the published literature than lip seals used in other fields. The main differences between marine and non-marine lip seals are the harder material compound, the higher oil pressure, and the larger diameters. The lip seals that are studied in this paper have a nominal diameter of 300 mm. The counterface is a tungsten-carbide-coated stainless steel shaft liner. The studied lip seals and their counterfaces are commonly used in marine applications. A full-scale test device is built to study the effects of marine-specific parameters on the behavior of the lip seal, using a parameter sweep of the oil temperature, oil pressure, and rotational speed. Air bearings are used to allow for a more accurate measurement of the frictional torque. The subsurface temperature at the contact is measured using a wireless temperature probe inside the rotating shaft liner. In future work, the subsurface temperature is used in a thermal finite element model to estimate the average contact temperature.

A marine thruster’s model identification based on experimental-simulation approach

In recent years, underwater vehicles play a very important role in the marine field, and tasks cannot be accomplished quickly and accurately without the use of such devices. Despite the progress achieved, these vehicles still have prob- lems with their controls in order to have a very good dynamic positioning or a path tracking accurately, and these problems have a direct link to their thrusters, either by negligence or by ignorance of its mathematical model. Several works were carried out to have an accurate model of them, but its behavior is still diffi- cult to be described and it strongly influences the behavior of a vehicle in which it is integrated. In this work we try to deal this problem in the aim to iden- tify a marine thruster designed by us using a low-cost test bench and a hybrid identification approach, which combines the both experimental and simulation parts. The thruster will be integrated on a remotely operated vehicle under devel- opment by AVCIS-Lab to make simulation using UUV (unmanned underwater vehicle) Simulator and ROS (Robot Operating System) toolbox under Matlab. The outcomes will be presented at the end of this paper.

Performance of an Advanced Intelligent Control Strategy in a Dynamic Positioning (DP) System Applied to a Semisubmersible Drilling Platform

Oil drilling and extraction platforms are currently being used in many offshore areas around the world. Whilst those operating in shallow seas are secured to the seabed, for deeper water operations, Dynamic Positioning (DP) is essential for the platforms to maintain their position within a safe zone. Operating DP requires intelligent and reliable control systems. Nearly all DP accidents have been caused by a combination of technical and human failures; however, according to the International Marine Contractors Association (IMCA) DP Incidents Analysis, DP control and thruster system failures have been the leading causes of incidents over the last ten years. This paper will investigate potential operational improvements for DP system accuracy by adding a Predictive Neural Network (PNN) control algorithm in the thruster allocation along with a nonlinear Proportional Integral derivative (PID) motion control system. A DP system’s performance on a drilling platform in oil and gas deep-water fields and subject to real weather conditions is simulated with these advanced control methods. The techniques are developed for enhancing the safety and reliability of DP operations to improve the positioning accuracy, which may allow faster response to a critical situation during DP drilling operations. The semisubmersible drilling platform’s simulation results using the PNN strategy show improved control of the platform’s positioning.

Two novel marine thruster concepts based on the Coanda effect

Two novel marine thruster concepts based on the Coanda effect

Modeling working processes of the marine thruster of the PMM-2M ferry-bridge machine

Objective. The article deals with aspects of modeling the working processes occurring in marine thrusters of amphibious vehicles, taking into account the specifics of their operation. Methods. The methods of 3D modeling of propellers in CAD and CAE packages are applied, which can determine and optimize the parameters of ongoing work processes with reliable accuracy. Results. A mathematical construct is proposed that allows calculating the characteristics of marine thrusters of amphibious vehicles. The propeller is designed to provide more thrust compared to the original design, making it possible to increase the speed of movement on the water and reduce the radius of circulation when moving through the water. The calculated version of the propeller provides an increase in thrust by 36%, allows developing a high speed on the water, and significantly reduces the radius of circulation of the ferry-bridge machine when maneuvering on the water. Conclusion. The proposed option for increasing the speed and maneuverability of ferry vehicles on the water is the most effective and least expensive; a promising direction for further research to achieve maximum efficiency is the creation and verification of software, hardware, and methodological complexes for modeling the joint operation of the "marine thruster - hull - power plant" system.

Towards online adaptation of digital twins

Abstract Digital twins have gained a lot of attention in modern day industry, but practical challenges arise from the requirement of continuous and real-time data integration. The actual physical systems are also exposed to disturbances unknown to the real-time simulation. Therefore, adaptation is required to ensure reliable performance and to improve the usability of digital twins in monitoring and diagnostics. This study proposes a general approach to the real-time adaptation of digital twins based on a mechanism guided by evolutionary optimization. The mechanism evaluates the deviation between the measured state of the real system and the estimated state provided by the model under adaptation. The deviation is minimized by adapting the model input based on the differential evolution algorithm. To test the mechanism, the measured data were generated via simulations based on a physical model of the real system. The estimated data were generated by a surrogate model, namely a simplified version of the physical model. A case study is presented where the adaptation mechanism is applied on the digital twin of a marine thruster. Satisfactory accuracy was achieved in the optimization during continuous adaptation. However, further research is required on the algorithms and hardware to reach the real-time computation requirement.

Investigation on the Performance of a Ducted Propeller in Oblique Flow

In this study, the ducted propeller has been numerically investigated under oblique flow, which is crucial and challenging for the design and safe operation of the thruster driven vessel and dynamic positioning (DP) system. A Reynolds-averaged Navier–Stokes (RANS) model has been first evaluated in the quasi-steady investigation on a single ducted propeller operating in open water condition, and then a hybrid RANS/LES model is adapted for the transient sliding mesh computations. A representative test geometry considered here is a marine model thruster, which is discretized with structured hexahedral cells, and the gap between the blade tip and nozzle is carefully meshed to capture the flow dynamics. The computational results are assessed by a systematic grid convergence study and compared with the available experimental data. As a part of the novel contribution, multiple incidence angles from 15 deg to 60 deg have been analyzed with different advance coefficients. The main emphasis has been placed on the hydrodynamic loads that act on the propeller blades and nozzle as well as their variation with different configurations. The results reveal that while the nozzle absorbs much effort from the oblique flow, the imbalance between blades at different positions is still noticeable. Such unbalance flow dynamics on the blades, and the nozzle has a direct implication on the variation of thrust and torque of a marine thruster.

Failure analysis of a gear wheel of a marine azimuth thruster

A failure analysis of two helical gear wheels of a ducted azimuth thruster is presented. The research work consisted of a fracture examination of the material in order to determine the damage root causes. The samples for the failure analysis were obtained from two broken teeth of two helical gear wheels. An analysis through the scanning electron microscope (SEM) was carried out close to the crack initiation. It was found that the damage in the bevel gears were by the fatigue fracture mode. The SEM analysis showed that the gear teeth were under severe contact stress during the operation aggravated by an inappropriate lubricating. A possible misalignment between the pinions and the gear wheels teeth could also contribute for the premature failure.

ON MODELING OF MARINE THRUSTERS FOR UNDERWATER VEHICLES

This paper deals with the problem of modeling of marine thrusters especially for underwater vehicules. It examines several models for ducted propeller type marine thrusters. First, reported main thrusters dynamics are reviewed. Second, a study of the validity of basic hydrodynamic relation is carried on simulation. Experimental testing validates the steady-state of marine thruster models presented, and raises questions and especially on the transient model and then the thrust control problem.

Development, comparison, and preliminary experimental validation of nonlinear dynamic thruster models

This paper examines dynamical models for bladed-propeller-type marine thrusters. Previously reported thruster dynamics models are reviewed, and a simplified model is proposed. Experimental testing of both the transient and steady-state performance of a marine thruster corroborates previously reported data, validates the simplified thruster model, and raises new questions. A companion paper reports preliminary experiments in the design and testing of thrust controllers which incorporate the dynamical thruster models described in the present paper.