Rim-driven Thruster Research Articles

Global Magnetic Field Distribution and Open Water Hydrodynamic Performance of a Flux-Modulated Rim-Driven Thruster

Global Magnetic Field Distribution and Open Water Hydrodynamic Performance of a Flux-Modulated Rim-Driven Thruster

Numerical Investigation of Hydrodynamic Characteristics of a Rim-Driven Thruster Coupled with an Underwater Vehicle

In this paper, the hydrodynamic characteristics of a rim-driven thruster (RDT) behind the hull of an underwater vehicle are investigated. The studied underwater vehicle is the benchmark DARPA (Defense Advanced Research Projects Agency) suboff model, with and without full appendages. In order to verify and validate the numerical model, a grid sensitivity analysis is made for the AFF-1, AFF-8 and the ducted propeller cases, respectively. Then, the resistance and pressure distribution over the surface of the suboff with and without appendages are compared with available experimental measurements and good correlations were observed. As for the propeller, a well-studied ducted propeller, the 19A duct in combination with Ka-47 blades, is employed, and the numerical results exhibit a close relationship with the available experimental data under a wide range of advance coefficients. Afterwards, the self-propulsion characteristics of the suboff models propelled by RDTs using different duct configurations are studied, more specifically, the unsteady effects of the flow field induced by the interactions between propeller and hull under various working conditions. The results indicate that due to the influence of the hull, the RDTs operate in different working conditions compared to open water and exhibit distinct hydrodynamic characteristics. Moreover, the duct profile can have a significant effect on the unsteady pressure fluctuations in the flow field, especially in the vicinity of the propeller.

Rim Driven Thruster as Innovative Propulsion Element for Dual Phase Flows in Plug Flow Reactors

The purpose of this work was to test a new setup to pump water with entrained air for application in gas fermentation. A mixed flow, where gas is contained in a liquid to be pumped, rapidly reduces the efficiency of a conventional pump, due to the compressibility of the gas. It is not always possible to degas the fluid, for instance in gas fermentation, which is preferably carried out in tubular reactors (loop fermenters) to achieve a high conversion rate of the gaseous feedstocks. Method: In this work, a rim-driven thruster (RDT) was tested in a lab-scale, cold flow model of a loop reactor with 5–30% (by volume) of gas fraction (air) in the liquid (water) as alternative propulsion element (6 m total pipe length, ambient temperature and pressure). As a result, it was found that the RDT, in connection with a guiding vane providing swirling motion to the two-phase fluid, could pump a mixed flow with up to 25.7% of gas content (by volume) at atmospheric pressure and 25 °C and 0.5 to 2 m/s flow speed. In conclusion, an RDT is advantageous over a classic propulsion element like a centrifugal pump or axial flow pump for transporting liquids with entrained gases. This article describes the potential of rim-driven thrusters, as known from marine propulsion, in biotechnology, the chemical industry, and beyond, to handle multiphase flows.

Numerical analysis of the effect of the duct geometry on the hydrodynamic performance of rim-driven thruster

This paper studies the effect of the duct geometry on the hydrodynamic performance of rim-driven thruster (RDT) based on Computational Fluid Dynamics (CFD) method. The effect of the thickness of the duct, the radius of the leading edge of the duct and the geometry of the trailing edge of the duct on the thrust coefficient, torque coefficient and efficiency are investigated and analyzed. The conclusion shows the thrust coefficient increases with the thickness of the duct decreasing, however the torque coefficient increases with the increase of the thickness of the duct, so the efficiency increasing with the decrease of the thickness of the duct. On the other hand, the radius of the leading edge of the duct has no significant effect on the thrust coefficient of the RDT. However, the torque coefficient of RDT decreases with the increase of the radius of the leading edge of the duct, so the efficiency of RDT increases with the increase of the radius of the leading edge of the duct. A comprehensive comparison shows that the RDT 15-0.5 (the duct thickness is 15 mm, the ratio of the radius of the leading edge of the duct and the duct thickness is 0.5) has the best hydrodynamic performance among the investigated RDT models in this work.

Performance analysis of hubless rim-driven thruster based on the number of blades: a CFD approach

Performance analysis of hubless rim-driven thruster based on the number of blades: a CFD approach

Multi-Parameter Fuzzy-Based Neural Network Sensorless PMSM Iterative Learning Control Algorithm for Vibration Suppression of Ship Rim-Driven Thruster

Aiming to reduce motor speed estimation and torque vibration present in the permanent magnet synchronous motors (PMSMs) of rim-driven thrusters (RDTs), a position-sensorless control algorithm using an adaptive second-order sliding mode observer (SMO) based on the super-twisting algorithm (STA) is proposed. In which the sliding mode coefficients can be adaptively tuned. Similarly, an iterative learning control (ILC) algorithm is presented to enhance the robustness of the velocity adjustment loop. By continuously learning and adjusting the difference between the actual speed and given speed of RDT motor through ILC algorithm, online compensation for the q-axis given current of RDT motor is achieved, thereby suppressing periodic speed fluctuations during motor running. Fuzzy neural network (FNN) training can be used to optimize the STA-SMO and ILC parameters of RDT control system, while improving speed tracking accuracy. Finally, simulation and experimental verifications have been conducted on the vector control system based on the conventional PI-STA and modified ILC-STA. The results show that the modified algorithm can effectively suppress the estimated speed and torque ripple of RDT motor, which greatly improves the speed tracking accuracy.

Comparison Study of the k − kL − ω and γ − Reθ Transition Model in the Open-Water Performance Prediction of a Rim-Driven Thruster

The present work examines the capabilities of two transition models implemented in ANSYS Fluent in the open-water performance prediction of a rim-driven thruster (RDT). The adopted models are the three-equation k−kL−ω and the four-equation γ−Reθ models. Both of them are firstly tested on a ducted propeller. The numerical results are compared with available experimental data, and a good correlation is found for both models. The simulations employing two transition models are then carried out on a four-bladed rim-driven thruster model and the results are compared with the SST k−ω turbulence model. It is observed that the streamline patterns on the blade surface are significantly different between the transition and fully turbulent models. The transition models can reveal the laminar region on the blade while the fully turbulent model assumes the boundary layer is entirely turbulent, resulting in a considerable difference in torque prediction. It is noted that unlike the fully turbulent model, the transition models are quite sensitive to the free-stream turbulence quantities such as turbulent intensity and turbulent viscosity ratio, as these quantities determine the onset of the transition process. The open-water performance of the studied RDT and resolved flow field are also presented and discussed.

Improvement of the efficiency for rim-driven thrusters through acceleration of gap flow

Efficiency optimization of the rim-driven thruster (RDT) has emerged as a prominent research topic in recent years. In this work, the Reynolds-averaged Navier-Stokes (RANS) solver is employed for simulating open water performance of RDTs, aiming at improving the efficiency of RDTs. Specifically, a series of RDTs are obtained by modifying the Ka4-70 propeller with a 19A duct, and their thrust and torque components, as well as efficiency and gap flow, are thoroughly examined. The investigation commences by exploring the impact of different rim sizes on RDT efficiency. A comparison is conducted between the open water performance of RDTs and the ducted propeller. Subsequently, a case with relatively high efficiency is identified, serving as a basis for the development of a series of modified RDTs equipped with acceleration devices. These devices facilitate accelerated axial flow in the gap, thereby enhancing the thrust generated by the duct, while simultaneously reducing the torque exerted on the rim through accelerated circumferential gap flow. Comparative analysis reveals that the improved RDTs can achieve an open water efficiency increase of up to 10.9% when the advance coefficient is set to 0.6, resulting in an efficiency value of 0.519. The findings presented in this paper introduce a novel direction for optimizing the efficiency of RDTs, contributing to the advancement of this field of study.

Numerical investigation on hydrodynamic performance of shaftless rim-driven thruster

As a new type of propulsion method, the shaftless rim-driven thruster (RDT) has become a research hotspot for ship propulsion due to the absence of the propeller propulsion shaft system setting and the advantages of small cabin occupancy, low noise and low vibration. Numerical investigations were performed to study the effect of blade inclination angle on the hydrodynamic performance of shaftless Rim-driven Thruster. To verify the feasibility of the simulation method, the No.19A + Ka4-70 duct propeller was analysed first and the geometric model of the RDT for the hydrodynamic properties was established in reverse engineering. The hydrodynamic performance of the shaftless rim thruster was studied based on the RANS method, and the performance data of this shaftless rim thruster at each inlet speed coefficient were obtained. Additionally, the characteristics of the change in the inclination angle of the blade relative to its centre axis were examined and the effect of the change in inclination angle on the hydrodynamic performance of the shaftless rim thruster was investigated. Additionally, the numerical calculation results show that a five degree increase in the Z-axis circumferential inclination results in the increase of all the hydrodynamic coefficients of the RDT. Among them, the total thrust is increased by about 14%, the total torque is increased by about 15% and the total efficiency is also comparable to the original thruster efficiency.

Improved efficiency with concave cavities on S3 surface of a rim-driven thruster

Rim-driven thrusters (RDT) are of great interest for the development of integrated electric motors for underwater vehicles. Gap flow is one of the most prominent flow characteristics and plays an important role in the hydrodynamic performance of RDT. In this study, the rim in a carefully designed RDT was modified with several concave cavities defined by four parameters, and their influence on hydrodynamics was carefully calculated and analyzed. The simulations were performed using the k-ω shear stress transport turbulence model by solving the unsteady Reynolds-averaged Navier–Stokes equations. The numerical method was verified using a popular combination. The numerical results showed that the concave cavities on the rim improve the propulsive efficiency of RDT by a maximum of 3.52%. The increase in the propulsive efficiency is directly associated with the parameters of the concave cavities. Nevertheless, the flow in the gap has a negligible effect on the main flow field through the RDT. According to the numerical analysis, the different pressure integrals at the front and back surfaces of the concave cavities are the main reason for the improvement of the propulsive efficiency. The modification of the rim is helpful and practical for the hydrodynamic optimization of the RDT.

Load Carrying Capacity Enhancing Design and Lubrication Investigation of the Magnetic-Water Double Suspension Elastic Support Thrust Bearing

Aiming at the problem that the traditional water-lubricated bearing cannot carry the heavy load and adapt to the constantly changing operating conditions for the high-power Rim Driven Thruster (RDT), the principle structure of the Magnetic Water-double-suspension Elastic-support Thrust Bearing (MWETB) is designed and the optimal structure parameters of the bearing are selected using simulation. To demonstrate the reliability of the MWETB under the RDTs’ actual working conditions, performance tests, which include the magnetic flux density, magnetic force, and lubrication performance, are carried out. The simulation and experimental results indicate that the optimal offset ratios are in two intervals, and the magnetic alignment and sheath materials have a great effect on the load reduction. The load-carrying force has obvious zoning characteristics with the change in bearing clearance. Besides, compared with the water-lubricated thrust bearings, the MWETB has advantages in terms of minimum film thickness and friction coefficient.

The effects of domain division types on the performance prediction of a rim-driven thruster

The rim-driven thruster (RDT) is an innovative propulsion thruster. The rotating subdomain can contain different assemblies with different domain division types (DDT). This paper tried to figure out the effects of DDT on the performance of RDT. This paper uses the Delayed Detached Eddy Simulation (DDES) turbulence model to conduct the simulations. Three DDTs are carefully analyzed to understand their effects on predictive performance. The convergence analysis is performed by taking a typical method: Grid Convergence Index (GCI). Some theoretical results and the experimental hydrodynamics of a popular combination of Ka 4–70 and MARIN 19 A are used to validate the numerical method. The numerical results demonstrate that the computational efficiency is influenced by the cell number on the interfaces between two subdomains and an inherent characteristic of DDT. Moreover, the torques acting on rim surfaces are closely accounting for the gap flow. Moreover, regarding the morphology and variables of the vortex system, the third type of DDT enhances vortices presenting in the hub region and vortex-instability region. Although the present analysis is performed for an RDT, the findings should be generally applicable for other RDT designs with similar structures and operational conditions.

Influence of bearings on the open water performance of a rim-driven thruster

The rim-driven thruster (RDT) represents an important advance in the marine propulsion system. Its innovative structure introduces several outstanding advantages but also rises some major challenges. This paper aims to investigate the influence of bearings on the rim-driven thruster in terms of hydrodynamic performance with computational fluid dynamics. Bearing parameters including the shape of the contact surface and the number of grooves are considered. The simulation results indicate that the presence of the bearings in the gap has an influence on the overall performance of the thruster by changing the flow regime in the gap and the interactions between different components in the RDT. The shape of the bearings also exhibits significant impacts: the conical bearings, even though with simpler structure, shows the worst performance among all three bearing configurations, while the ordinary bearings always have a higher hydrodynamic efficiency than the other two bearing configurations under all considered advance coefficients. The difference in efficiency at the design point can reach up to 3% between the ordinary and conical bearing configurations.

Numerical study of scale effects on the open water performance of a rim-driven thruster

This paper presents the study of scale effects on the open water performance of a rim-driven thruster (RDT) based on Computational Fluid Dynamics (CFD) simulations. For marine propellers, the effects of viscosity are often significant when there is a dramatic change in Reynolds number, which occurs when the results from model scale tests are extrapolated to propellers at full scale. Reynolds-Averaged Navier–Stokes (RANS) simulations with the Moving Reference Frame (MRF) approach are carried out in ANSYS Fluent for the RDTs under different working conditions. Considering the potential transitional flow on the propeller at model scale, the γ−Reθ transition model is adopted which can better resolve the boundary layer and yield more accurate results for transitional flows. From the simulations, it is observed that the duct and rim are more affected by the scale effects than the propeller. When the Reynolds number increases, there is a small amount of increment in the total thrust coefficient but a significant decrease in the total torque coefficient, resulting in a substantial improvement in hydrodynamic efficiency of the full scale RDT compared to the model scale.

The effect of tip rake distribution on the hydrodynamic performance of shaftless rim-driven contra-rotating thruster

Shaftless rim-driven contra-rotating thruster (RDCRT) has recently become the research focus for marine propulsion, primarily due to low vibration, low overall torque, and energy saving as its advantage. This study applied 4-order B-spline theory to vary the rake distribution of the blade tip for a shaftless rim-driven thruster (RDT) originated from duct propeller Ka4-70+No.19A, and constructed four shaftless RDTs with different blade tip rakes. Through CFD simulation, the impact of blade tip rake on the open water performance, wake distribution, and sheet cavitation performance of the shaftless RDTs with single propeller were evaluated. On the basis of the above, we further compared the effect of tip rake on the open water performance, wake distribution, pressure distribution, and sheet cavitation performance of three shaftless RDCRTs. It was found that the tip rake inclined to the pressure side of shaftless RDCRT is in favor of both propulsion efficiency and anti-cavitation performance, while the tip rake inclined to the suction side adversely exerts opposite effects. With the aid of the tip rake inclined to the pressure side for the front and rear propellers, the maximum propulsion efficiency of shaftless RDCRT tends to rise by 2.6%, together with the wake stretching more uniformly. For shaftless RDCRT, the optimization design from the aspect of tip rake would be capable of validating its performance and advantages.

Multi-objective optimization design of shaftless rim-driven thruster

This paper proposes a multi-objective optimization design method for shaftless rim-driven thruster (RDT) based on the ISIGHT platform. The pitch ratio, the blade area ratio and the advance coefficient of RDT were considered as the design optimization variables, the thrust and efficiency of the RDT were the optimization objectives. The multi-objective optimization design method was based on the surrogate module and the optimization module in the ISIGHT platform. Two analytical methods (response surface methodology (RSM) and radial basis function Model (RBF)) were used to build the surrogate model. The Muti-Island GA optimization algorithm was adopted in the optimization module. The paper indicates that both RSM model and RBF model are feasible to build the surrogate model, the RBF model has better accuracy and reliability than RSM model. The blade obtained by RBF method has larger thrust and smaller torque than that of the blade obtained by RSM method. For the large advance coefficient ( J > 0.6), the efficiency of the blade obtained by RBF method is slightly higher than that of the blade obtained by RSM method.

Discrete non-elliptical probability imaging based on UGWs for anisotropic anti-corrosive structure damage detection of rim-driven thruster

Aiming at health monitoring for anisotropic anti-corrosion structure of rim-driven thruster (RDT), a discrete non-elliptical probability imaging (DNEPI) based on ultrasonic guided waves is proposed. The elliptical location without analytical solution for anisotropic structures is analyzed theoretically. Through reverse thinking, it’s avoided by discretization and introducing reference point. Combined with Hausdorff damage sensitivity index (DSI), the damage probability is estimated. All paths’ probability is fused and displayed by images. The proposed DNEPI is verified by experiments. The results show that the damage probability energy ratios (Er) of DNEPI (Hausdorff DSI and scattering DSI) and elliptical probability imaging (EPI) are 0.29%, 0.22%, and 0.26% respectively, and improved to 4.55%, 1.89%, and 1.10% with 95% threshold. Compared with EPI, the Er of DNEPI imaging is improved by 3.45%. The robustness of Hausdorff DSI is better than scattering DSI. The proposed DNEPI not only visually presents the damage but also provides higher accuracy.

Optimization design of the duct of a rim-driven thruster using the adjoint approach

In this study, the adjoint method is employed for the duct optimization of a rim-driven thruster (RDT). The work is mainly focused on the efficiency improvement of the thruster by adopting a more effective duct profile. As baseline design, a duct with symmetrically round-shaped ends and a flat middle part with a Ka4-70 propeller inside is considered. For applicability considerations, steady-state numerical simulations are carried out to solve the Reynolds-averaged Navier–Stokes equations (RANS) with the moving reference frame (MRF) method. The adjoint method modifies the geometry of the symmetric duct into a more streamlined shape while keeping the aspect ratio (the ratio of duct length and thickness) constant. The original and final profiles of the duct and their influence on the overall performance of the RDT are presented and analyzed. The results indicate that after optimization, the efficiency of the thruster is increased by an absolute value of 3 to 10%, depending on the advance coefficient. The thrust torque ratios of the propeller and rim have also increased, meaning the RDT can provide a higher thrust for an equivalent absorbed torque. Moreover, a preliminary examination of the cavitation number based on the lowest pressure on the blade surface indicates that the RDT with optimized duct has a better cavitation performance as well.

Research on Position Sensorless Control of RDT Motor Based on Improved SMO with Continuous Hyperbolic Tangent Function and Improved Feedforward PLL

With the increasing use of electric propulsion ships, the emergence of the shaftless rim-driven thruster (RDT) as a revolutionary integrated motor thruster is gradually becoming an important development direction for green ships. The shaftless structure of RDTs leads to their dependence on position sensorless control techniques. In this study, a novel control algorithm using a composite sliding mode observer (SMO) with a modified feed-forward phase-locked loop (PLL) is presented for achieving high accuracy position and speed control of shaftless RDT motors. The deviation between the observed and actual currents is exploited to develop a current SMO to extract back electromotive force (back-EMF) errors. On this basis, a back-EMF observer is established to achieve accurate estimation of the back-EMF. The basic structure of the PLL was modified and incorporates a speed feedforward mechanism, which enhances the performance of rotor position estimation and facilitates bidirectional rotation. The stability of the algorithm has been verified in Matlab/Simulink for a range of steady-state, dynamic, and ship propeller loading conditions. Remarkably, the control algorithm boasts an impressive adjustment time of approximately 0.006 s and its position estimation error may be as low as 0.03 rad. Simulation results highlight the performance of the algorithm to achieve bidirectional rotation, while exhibiting fast convergence, minimal vibration, exceptional control accuracy, and robustness.

Hydrodynamic performance of a rim-driven thruster improved with gap geometry adjustment

The hubless rim-driven thruster (RDT) has become increasingly interesting for ship propulsion. Gap flow has been proven as the main feature of RDT that cannot be simply neglected. In this study, based on a classical hubless RDT, the effects of the gap geometry are studied by adjusting its axial passage length, and inlet and outlet oblique angles. The hydrodynamic characteristics of the RDT were simulated with OpenFOAM based on the k – ω shear stress transport turbulence model. Due to the pressure increase after the main flow passes through the rotating blades, the flow inside gap is driven upstream, which is opposite to the main flow direction. It is found that the hydrodynamic efficiency is increased as the gap axial passage length is shortened, which is realized by increasing the oblique angle with the fixed inlet and outlet positions. Moving the inlet and outlet to further downstream and upstream positions has negligible effects on the hydrodynamic efficiency and leads to recirculating flow within the gap near its inlet. These findings shed light on the design of the gap geometry to improve the RDT hydrodynamic performance.