Hydrodynamic State of Art Review: Rotor – Stator Marine Propulsor Systems Design

The paper covers the important topic of rotor–stator propulsor system design and operation. For the stand-alone marine screw propeller, both the design criteria for loading distribution and the theoretical efficiency limits are well described in the basic literature. This is in contrast to the combined propulsor system like a propeller cooperating with a pre-swirl device. The paper describes the current state of the art, summarising results obtained by various researchers by installing energy-saving devices on particular vessels. The design methods utilised are briefly outlined, with the main characteristics underlined. Rough analysis of the gathered data confirms the expected trend that a higher efficiency gain due to ESD installation is possible for a higher propeller loading.

Activated Flooded Jets and Immiscible Layer Technology Help to Remove and Prevent the Formation of Bottom Sediments in the Oil Storage Tanks

Two flooded jet methods of tank bottom sediments caving based on either screw propeller generation or nozzle jets generated with entering crude head oppose each other. The comparison is not advantageous for the first one. Exceptionally if crude oil contains some concentration of high molecular weight polymer which can perform Drag Reduction. In this case, the jet range increases by many times, thus, upgrading the capability of caving system. Preventing the sedimentation of crude oil heavy components may be put into practice with Immiscible Layer Technology. Before filling the tank with crude oil, some quantity of heavy liquid, that is immiscible with all the components of crude oil, is poured into the tank. The most suitable/fit for purpose and available liquid is glycerin. Neither paraffin and resins, nor asphaltenes can penetrate through the glycerin layer to settle down at the tank bottom because of its density, which is equal to 1.26 g/cm3. Instead, sediments are concentrated at/on the glycerin surface and when it is heated in external heat exchanger all the sediments ought to move upwards with the convection streams. Thus, no deteriorate sediment is formed in the tank bottom.

Augmenting Maneuverability of UUVs with Cycloidal Propellers

This paper investigates a novel concept of using cycloidal propellers to augment the maneuverability of unmanned underwater vehicles. Cycloidal propellers are cross-flow propellers that utilize 360$^{\circ}$ thrust vectoring to provide agile maneuvering to surface vessels like yachts, tug boats, buoy tenders and double ended ferries, but have yet to be utilized on present-day unmanned and autonomous marine vehicles. Through 360$^{\circ}$ thrust vectoring, cycloidal propellers enable surface vessels to execute spot turns, and surge in forward and backward directions with equal ease. Such compact maneuvers are difficult to execute with the conventional screw propeller-rudder setup found on marine vehicles today. On unmanned and autonomous marine vehicles, cycloidal propellers can potentially enable controlled and decoupled maneuvering in all six degrees-of-freedom while overcoming disturbances like waves and currents, and extreme flow conditions like cavitation and ventilation. This is critical for marine vehicles operating at low speeds and in restricted waters. Therefore, the objective of this paper is to study the maneuvering characteristics of a UUV driven by a screw propeller and control fins only, and compare it to that of the UUV augmented with retractable cycloidal propellers. The cases considered are a turning circle maneuver, a low-speed 180$^{\circ}$ turn and a low-speed heave maneuver. A six degrees-of-freedom motion prediction model that accounts for the non-linear and coupled loads on an underwater vehicle is developed and validated. Simulation results showed that compared to conventional propulsion systems, cycloidal propellers could potentially enable more swift, compact and decoupled maneuvers in unmanned marine vehicles. Integrated with robust control systems, cycloidal propellers can be explored for use in dynamic positioning, ocean exploration, station-keeping, seakeeping and teaming of unmanned and autonomous marine vehicles.

Augmenting Maneuverability of UUVs with Cycloidal Propellers

This paper investigates the novel concept of augmenting the maneuverability of underwater vehicles with cycloidal propellers. Cycloidal propellers have the potential of providing agile manoeuvring capabilities to an underwater vehicle such as enabling pure heave motion and spot turns. They will also enable the vehicle to surge in forward and backward directions with equal ease. Such manoeuvres are not possible with the more conventional screw propeller and control fin combinations. Moreover, cycloidal propellers can enable precise dynamic positioning in low speed applications like station-keeping, underwater surveying and maintenance, minesweeping and teaming activities. In this paper, manoeuvring capabilities of an underwater vehicle with conventional screw propeller and control fins only are compared with one augmented with cycloidal propellers. The cases considered include a turning circle manoeuvre, a low speed 180o turn and a low speed heave manoeuvre. A six degrees-of-freedom non-linear hydrodynamic motion prediction model was developed and validated. Simulation results demonstrated that compared to conventional propulsion systems, cycloidal propeller augmented underwater vehicles can be more swift and compact in low speed manoeuvres, making a case for further investigation into this concept.

Blade Section Profile Array Lifting Surface Design Method for Marine Screw Propeller Blade

The lifting surface model is widely used in screw propeller design and analysis applications. It serves as a reliable tool for determination of the propeller blade mean line and pitch distribution. The main idea of this application was to determine the blade shape that would satisfy the kinematic boundary condition on its surface with the prescribed bound circulation distribution over it. In this paper a simplified lifting surface method is presented – in which the 3D task for the entire blade is replaced by a set of 2D tasks for subsequent blade section profiles.

Analysis of Loading Change Effect to Boat Velocity on a 2.5GT Fishing FRP Boat with a Field Test

In order to determine the effect of load change to ship velocity on a 2.5 GT fishing boat, a field test is conducted in the present study. The boat model used in the field test is an actual size boat made from fiber reinforced plastic (FRP) material. The boat is powered by 2 (two) 15 HP direct drive engines each equipped with 3-bladed single screw propeller. Two loading cases are investigated and analyzed which are no load case and with load case. For each case, 4 (four) engine power variations are performed which are 25%, 50%, 75% and 100%. The main parameters measured are boat draught, engine power percentage, shaft revolution speed and boat velocity. From the field test, it is found that even though the propulsion performance increases larger loading and displacement, the increased boat resistance due to larger wetted surface make the boat velocity reduces.

OpenModelica Modelling of the Thruster in a Compact Subsea Work-Class Remotely Operated Vehicle

Thrusters are vital for the functionalities of remotely operated vehicles (ROVs). The development of thruster design is a trade-off between cost, thrust force, physical weight and size. A six degree of freedom model is created in OpenModelica to investigate the vibrations and bearing responses in thruster systems. The model consists of a marine propeller, a shaft, and two bearings. The propeller used is based on the Wageningen B-screw propeller series. The hydrodynamic added mass and damping forces are calculated from empirical equations based on open water tests and are functions of the propeller geometry, rotational speed and fluid density. Meanwhile, the mean thrust and torque are obtained from open water test data of the relevant propeller and are used to calculate the dynamic forces and moments from the marine propeller. Displacements in the axial, horizontal, and vertical directions are calculated and used to investigate vibration amplitudes and bearing life. Initial steady-state simulations show that the bearing life of the bearings in the thruster is found to be highly dependent on the axial load acting on the bearing, i.e., the thrust force. Moreover, if the propeller is not balanced then high centrifugal forces can occur and result in severe forces in the radial direction which can be of concern regarding the bearing life.