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Market Overview and Related Research on RDP
For the past few years new actors on the electrical maritime market have been emerging and the public interest in electrical transportation has never been higher. In Sweden there are two big actors, Candela (Candela, 2020) and XShore (XShore, 2020). Their products are both completely electric but at-tempts to solve the issues with electrical driven water crafts in diﬀerent ways. Candela has chosen to implement foils in their design to overcome the drag from water on the hull, whilst XShore has chosen a bigger battery to counter the resistance from the water. Currently both of these companies use a regular propeller for propulsion, this is also the case for other companies on the market such as Strana (Starna, 2020) and HWILA25 (Hwila25, 2020).
Another type of water propulsion is the rim driven propeller, most com-monly used on bigger container ships as prow and stern thrusters to move the ship sideways. One of the leading manufacturers for smaller water crafts are the German company Torque-Jet (Torque-Jet, 2020). They have adapted the regular bow thruster to be used as a propulsion motor by reshaping the blades and adapting other properties to be more eﬀective in one rotational direction. Furthermore, a French company named FinX have developed a membrane mo-tor that removes any rotating parts and instead uses a wave-like motion to move the water through the engine (FinX, 2020). The motor is said to be safer and more robust than conventional propellers. The current models are still in de-velopment but pre-orders can be made.
Research on the subject of rim driven propulsion as a valid substitute for propellers as propulsion is relatively scarse, although companies that are cur-rently developing and manufacturing this type of machine most certainly have their own confidential research on the subject. There have been research done by the School of Marine Science and Technology in China where they, much like Andersen, compared hub-type and hub less rim driven thrusters to anal-yse eﬃciency and other aspects of the configuration(Song et al., 2015). Their research concluded that a hub-less design would be have an increased thrust, a higher torque and a smaller thrust ratio compared to using a hub in the middle of the rotor. The same finding was also concluded in the work by Lan et al. in their work « Study on Hydrodynamic Performance of Hubless Rim-Driven Propulsors with Variable Parameters »(Lan et al., 2017). However, both of the studies was preformed on a standard rim-driven thruster at relatively low ro-tational speeds (approximately 1000 rpm) and not with a jet-configuration. Another research project from University of Southampton investigated the rotor–stator interaction in rim driven thrusters to better understand the fluid dynamics related to this design solution (Dubas et al., 2015). Dubas et al. conclude that the methods used in the study lack in accuracy and that further studies on the subject should be conducted to better understand and predict the eﬀects of rotor–stator interaction.
In 2017, engineers S. Fletcher and R. Hayes at Frazer-Nash Consultancy presented a pros and cons discussion on the future of electrical propulsion. They state that the shipping industry has seen a shift during the recent years in the use of technology and that integration of electrical propulsion is emerging (Fletcher and Hayes, 2017). They also discuss the potential of Rim-Driven Propulsors (RDP) and the benefits that this technology could have for the fu-ture of ship architecture. One key area Fletcher and Hayes present is the eﬃ-ciency potential of a RDP. More specifically, the lack of a centre hub or shaft that would reduce the potential energy loss from turbulence, while at the same time increasing the control over rapid changes in the rotational speed. In a paper from The Hong Kong Polytechnic University Cheng et al. discuss zero emission electric vessel development. It is concluded that the emerging trend of electrical water vessels will result in the replacement of short range vessels within the next ten years (K.W.E. et al., 2015).
In a paper review written by Yan et al. from 2017 it is concluded that « Rim-driven thruster (RDT) propulsion device has several notable advantages compared to the traditional shafting propulsion plant and POD propulsion plant (e.g., better working principles, eas-ier product maintenance, and occupying less engine room space), but also that high-power RDT propulsion devices are considerably more complex. High-power driven motors and high-load carry-ing, wear-resistant, water-lubricated bearings have yet to be fully developed. » (Yan et al., 2017).
As stated above, rim driven propulsion has potential to be the future of water propulsion if the specified technical obstacles can be overcome. In their review, a number of cases are listed that research the use of rim driven, as well as shaft less rim driven thrusters. In their list, only the work done by Andersen investigates the use of rim thrusters in a water jet configuration.
In a world where climate change is aﬀecting everyone, new leaps for a more sustainable future is made every day. Electrical cars are now something most have grown accustom to, although this was not the case 10 years ago. As mentioned earlier, Cheng et. al predicts in their paper from 2015 that in ten years electric solutions will be replacing small short range vessels. Moreover, Dubas et al. concludes in their paper that further research in the area of rotor stator interaction regarding rim driven propulsion would be of considerable value to a number of applications (Dubas et al., 2015).
This project builds on previous work on the Rim Jet solution first started by Thor Andersen six years ago with the aim to theoretically validate if a Rim Jet solution for SSRS could be suﬃcient. Andersens thesis concluded that a Rim Jet design could work in practice with some minor eﬃciency set back because of the loss of a centre hub (Andersen, 2014). Following Andersen was Pablo Sánchez Santiago and most recently Magnus Munoz. Munoz suggested that future research should focus on a prototype validation and investigate the integration of the Rim Jet with the Rescue Boat. Before production can begin the design of the Rim Jet must be finalised, as-suring that all parts can be both manufactured individually and assembled as a unit. The production methods chosen must be reasonable in cost and accuracy as the budget for SSRS is limited. Moreover, the assembly and disassembly of the product must be valid and optimised for changes and future improvements. The method of DFMA is most commonly used for products in large quantities, however in this research core principles will be used to investigate and evalu-ate the potential of DFMA on a single prototype, in this case the Rim Jet with hopes that the philosophy of DFMA will improve the overall design.
Hence, the purpose of this project is to further develop and advance the concept of a rim less water jet using DFMA. Both for the potential use within SSRS as a tool for rescue operations, but also to further investigate rim driven propulsion regarding RDT as a valid option for smaller maritime vessels which operate at higher speed. Through adoption of DFMA to this case study, eval-uation of the principles will be conducted to investigate the pros and cons of DFMA on singular product and fill the research gap within this area. The project will also include a proposal for system integration and preparations for upcoming testing, with the aim to provide recommendations for up coming work on the Rim Jet and Rescue Vessel project as a whole.
The limitations for this thesis are:
No major changes will be made to the current design. However, reducing and simplifying the current drawings for manufacturing will be done.
The methods used for manufacturing are chosen in regards to their time eﬃciency and cost for one unit. It might therefore be important to change manufacturing methods for future products to reduce production costs.
No Computational Fluid Dynamics (CFD) simulation will be made within this project as the time for this project is limited.
The current engine provided by SSRS for the project has a smaller hub diameter than previous calculations done by students have accounted for. However, no changes to the engine can or will be made at this stage and the goal is therefore in this thesis to design a working prototype with the current engine.
Water Jet Propulsion
Water jet propulsion as a concept dates back to 1661, but it is only in later years that its potential use on larger water vessels have been considered Carl-ton (2012). A water jet utilises Newtons second law of motion “Every action has an equal and opposite reaction”. Water is drawn in from underneath the craft, into the pump house and then forced out through the exit nozzle. This flow of water generated by the rotor is what pushes the craft forward. See Fig-ure 3.1
Water enters the inlet tube from underneath the craft, it is then lead into the rotor blades and accelerated towards the rear. The rotating impeller blades are formed like screws to transfer the energy from the engine to the water, whilst the stator blades have a more axial angle to straighten the flow of the water for higher eﬃciency. Water then exits the jet from the steering nozzle which usually is used to control the direction of water and hence steer the vessel. To reverse the flow on a water jet a reversing bucket is used. Through a mechanic or hydraulic actuator it is possible to go from full forward thrust to full reverse within seconds. For some designs of the reverse bucket, it is also possible to use the full capacity of the water jet when manoeuvring the craft by spilling some of the water backward and forward at the same time. This makes it possible to rotate the vessel without moving it backward or forward.
Rim Driven Propulsion
Rim Driven Thruster (RDT) or Rim Driven Propulsion (RDP) is an alter-native solution to the traditional shaft transmission solution. The rudimen-tary principal of a RDT is, compared to classical propulsion techniques, to move the origin of rotational force from a centre axle to the outer rim of the tube. This means a compleate re-moval of the drive shaft as depicted in Figure 3.1. RDP as a concept has been around since the early 20th cen-tury, with diﬀerent design solutions and patents. Shown in Figure 3.2 is a German patent from 1940 that was meant to be powered by electricity. It should be noted that the design de-picted still utilises a center hub for blade stabilisation in contrast to the rim jet design in this project. Other transmission solutions tried to utilise gear-boxes to transfer the energy but proved to generate to much friction and energy losses. (Satterthwaite and Macy.Jr, 1970).
RDTs of today primarily use magnets to set the rotor in motion. The hous-ing, illustrated as b) in Figure 3.2 drawing Abb.1 is static and mounted to the craft and consists of several electromagnets. The rotating ring a) has multiple small permanent magnets mounted around the blades on a tube. By altering the current through the electromagnets the rotor is set in motion, in the same was as any electrical motor.
The Rescue Vessel
Figure 3.3: The original Rescuerunner developed by Fredrik Falkman. Swedish sea rescue society (2020)
Currently in use by the SSRS is the Rescuerunner(SafeAtSea, 2020), a small water craft designed by Fredrik Falkman at SSRS for their operations. The boats hull is designed to be stable and durable in harsh sea while providing the driver with easy manoeuvrability and power. The Rescuerunner is built to access places larger crafts can not and the relatively small size also makes it easy for one person to operate.
Figure 3.4: The new Rescue Vessel designed by Fredrik Falkman
Since then, the ownership and production of the Rescuerunner has been acquired by Safe At Sea, however Fredrik Falkman has been developing a new type of rescue craft. This water craft is slightly bigger than the original Res-cuerunner but is still as reliable and durable as its predecessor. Currently there has only been one prototype produced with the intention to work as a testing unit for the potential Rim Jet.
Table of contents :
2.3 Market Overview and Related Research on RDP
3 Frame of reference
3.1 Water Jet Propulsion
3.2 Rim Driven Propulsion
3.3 The Rescue Vessel
3.3.1 Technical Requirements
4.1 Thor Peter Andersen
4.2 Kiran Ashok Naganalli
4.3 Pablo Sánchez Santiago
4.4 Magnus Munoz
5 Redesign of the Rim Jet
5.1 Tools chosen for the Rim Jet project
5.1.1 Selection of Materials and Processes
5.1.2 Design for Assembly
5.1.3 Design for Manufacture
5.2 Design Overview of the Rim Jet
5.2.1 Problematic Areas
5.2.2 Analysis and evaluation of the initial Rim Jet design
5.3 Design Modifications of the Rim Jet
5.3.1 Rotor Tube
5.3.2 Bearing Housing RS
5.3.3 Cover Plate RS
5.3.4 Sealing Positioner RS
5.3.5 Bearing Positioner RS
5.3.6 Rotor Blades
5.3.7 Bearing Positioner SS
5.3.9 Bearing Housing SS
5.3.10 Cover Plate SS
5.3.11 Stator Blade Housning
5.3.12 Stator Blade
5.3.13 Pass Through Bolts
5.3.14 Standard parts
5.5 Service and Maintenance
5.6 Final Prototype Design
5.6.1 Comparison of Initial Design to New Design Using DFMA evaluation
6.0.1 CNC Machining
6.0.2 Additive Manufacturing
6.0.3 External suppliers
7 Calculations On the New Design
7.1 Calculations with Current Specifications and Comparisons
7.1.1 Thrust Prediction
7.1.2 Energy Model
8 Battery and Power Solution
8.1 Power Requirements
9 System Integration
9.1 Sections and Integration
9.1.1 Rescue Boat
9.1.2 Rim jet
9.1.3 Control box
9.1.4 Battery solution
10.1 Test on Rescue Boat
10.1.1 Bollard Pull
10.1.2 Engine maximum rotational speed
10.1.3 Maximum torque
10.1.4 Delivered power at maximum rotation per minute
10.1.5 Vessel Speed
10.1.6 Issues with proposed methods
11 Discussion and Conclusions
11.1 Discussion DFMA
11.2 Discussion Rim Jet
11.4 Future work