TRA Visions 2016

Idea Number: L1-109

PILLAR / TRANSPORT MODE

ROAD RAIL MARINE CROSS MODAL

Project Related

to:

RA1: Environment – Decarb., Sustainability & Energy Efficiency RA2: Vehicle & Vessels Technology, Design & Production RA3: Urban and Long-Distance People Mobility – Systems and Services RA4: Freight Transport & Logistics RA5: Safe, Secure and Resilient Transport Systems RA6: Transport Infrastructures RA7: Human Factors, Socio-Economics and Foresights RA8: Automation and Connectivity RA9: Enabling Environment for Innovation Implementation

Project Title:

Racing Human Powered Submarine

TRA VISIONS 2016 is funded by

the European Union

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1. Introduction Underwater technology is often called a “low cost space technology substitute”. Especially in case of sport related competition it leads to highly optimized solutions requiring an application of the most advanced technologies, engineering skills and thinking out of the box. These requirements attracted a group of scuba diving enthusiasts, studying Ocean Engineering. We started a development of human powered underwater vehicle for European Sub Race competition (http://www.subrace.eu). The aim is a development of device presenting the minimal drag, maximal propulsion efficiency and manoeuvring properties, familiarization with the most advanced design approaches, technologies, software tools, teamwork and

HAVING A GOOD TIME!

2. Selection of research area Presented project fits pretty well to 2 research areas: RA1 (Drag reduction, Optimisation of energy use) and RA2 (Bicycles, Lightweight design, innovative design). Due to competition requirements we concentrates on energy use efficiency, which is critical for success in Sub Race competition, as well as has the highest potential impact on industry applications.

3. Literature Survey The most important sources of knowledge in selected area are reports published by organizers of SubRace as well as other Human Powered Vehicle competitions: 1. http://www.subrace.eu/ 2. European International Submarine Races, Conetstant’s Rule Book with post

eISR2014 Recommendations. 3. http://www.isrsubrace.org/ 4. https://www.facebook.com/internationalwaterbikeregatta/ 5. http://www.ihpva.org/home/ 6. https://www.asme.org/events/competitions/human-powered-vehicle-challenge-

(hpvc) 7. http://www.recumbents.com/home/ 8. http://solarsplash.com/

It covers also standard engineering knowledge (machine development, hydrodynamics) as well as our own experiences, gathered during cooperation with students participating in International Wateribke Regatta and Dong Solar Challenge.

4. Proposed Solution-Description of Idea Winning the Sub Race competition requires solving of 3 main design problems: a) Reduction of vehicle drug. b) Improvement of efficiency of energy use. c) Finding a reasonable compromise between speed and maneuverability properties

(which are contradictory each other). After analysis of existing solutions, we propose new approach based on: a) Vector propulsion and removal of steering fins. The control fins (usually 2

horizontal and 2 vertical ones) can generate even 20% of the vehicle total drag. We replaced them by the propeller able to be rotated about vertical and horizontal-transverse axes. This solution minimizes drag, increases maneuverability as well as allows also for maneuvering on low speed.

b) Design of unique human/propeller power transmission system. As a general rule we have to design a “wet sub” (the hull is filled by water, the pilot/propulsor is breathing with scuba equipment). It means a large part of pilot’s energy is wasted on “mixing water inside the vehicle”. We propose unique pedaling mechanism replacing typical synchronic-circular mode with asynchronic-linear one.

http://www.subrace.eu/http://www.isrsubrace.org/https://www.facebook.com/internationalwaterbikeregatta/http://www.ihpva.org/home/https://www.asme.org/events/competitions/human-powered-vehicle-challenge-(hpvc)https://www.asme.org/events/competitions/human-powered-vehicle-challenge-(hpvc)http://www.recumbents.com/home/http://solarsplash.com/

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5. Address potential technology gaps The concept is based on holistic approach and synergic joining of known solutions as well as modular construction and easy replacing of each important component for its new/better version. The only technological gap seems to be a proposed flexible propeller, which will be a subject of our research next few years. The first version of the vehicle will be equipped with metal, non-deformable propeller. Due to commercial potential we take under consideration also an “electric gear” solution (electric generator/motor assembly), which would be easily adjusted to non-competition requirements – simple replacing of generator with set of batteries converts our vehicle into recreational diving device.

6. Detailed design description The factors having a greatest impact on vehicle design are detailed technical requirements defined in Sub Race rules, which can be shortly summarized as:

The vehicle is “wet”.

There are 2 classes allowed: 1 and 2 persons.

No energy storage devices are allowed.

There is only one, composite trial, merging requirements of speed, manoeuvrability and control.

After detailed analysis of competition rules, existing vehicles and their results in Sub Race 2014, we have defined our problems for solving as:

Reduction of vehicle drug.

Improvement of efficiency of energy use.

Finding a reasonable compromise between speed and maneuverability properties (which are contradictory each other).

The last mentioned problem seems to be a key to success and its solving by joining functions of propulsion and control into single component, is a foundation idea of entire project. Although azipodal propulsion is nothing new, our idea is unique due to adding second degree of freedom (rotating around Z and Y axis). We consider 4 alternative solutions: homokinetic joint, flexible shaft, cascade of right angle gears as well as “electric gear”. At current stage 2 first solutions are preferred.

Fig.1 Homomkinetic joint and flexible shaft

(source: http://www.pattakon.com; http://machinedesign.com) The problem of drag reduction was decomposed into few, low-level technical, detailed problems related to: a) hull size, b) hull shape, c) hull surface, d) appendances.

http://www.pattakon.com/PatDan/PatCVJ10.exehttp://www.google.pl/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiU7sve3KvKAhWJ1ywKHarVDb0QjRwIBw&url=http://machinedesign.com/mechanical-drives/flexible-rotary-shaft-operation-uses-and-advances&psig=AFQjCNEBoTpD__ny3dH-YZDJXLg_nu8JvQ&ust=1452944109926836

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The problem of energy use efficiency was also decomposed into simpler problems related to: e) “human engine”, f) transmission, g) propeller efficiency. Ad a) Hull/pilot size – unlike land cycling competitions, in case of wet sub the pilot must accelerate much higher mass, including ca. 500 kg of water inside the vehicle. Basic modeling theory suggests the “scale effect” will promote large size of pilot and vehicle. Also simple comparison of extreme cases (typical pilots parameters: 160cm/60kg/250W and 200cm/100kg/500W), shows better power/mass coefficient for a “large person”. We have decided to set the size adjusted to “largest” team member. Parametric model of human body was defined and used later for adjustment of hull shape.

Fig.2 Definition of human body parametrs.

Fig.3 Axisymmetric hull based on NACA 67-021 profile, adjusted to pilot dimensions Ad b) Optimization of hull shape is based on assumption the hull is axial-symmetric (easier/better manufacturing due to lathe machining applicable, easier/better propeller design due to symmetric wake). In this case we compare 3D shapes by comparison of drag coefficients of CL section profiles (done using Profili2 program).

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Fig.4 Comparison of the most promising profiles.

Due to different width distribution along the profile length, final shape, adjusted to pilot dimensions can have a different maximal breadth for each profile, so simple Cx comparison is not enough – CFD simulation had to be applied. Finally profile NACA 67-021 was selected.

Fig.5 Final dimensions of NACA 67-021 profile based hull

In case on 2-persons vehicle, the hull will be produces using the same form and lengthened by adding cylindrical part after transverse cutting in the wider cross-section. Ad c) Surface treatment is additional way of drag reduction. Due to competition rules, using of polymer soft coatings is limited (possible contamination of water in research towing tank hosting the competition). We take under consideration alternative, bionic-inspired solution - riblets, which can be added by laser surface texturing.

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Fig.6 Riblets idea (source: http://www.bionicsurface.com/en).

Ad d) Appendances drag can also be a significant part of entire hydrodynamic resistance. CFD analyses performed using STAR-CCM+ program, showed it can reach 20% of total drag, especially during slalom trial. This problem is mostly avoided by replacement of steering fins by Z,Y rotating propeller.

Fig.7 Results of CFD analysis

Similar problem is generated also by edges of entry hatch. Very precise matching of hull opening and hatch is difficult. The simplest way of avoiding this problem is shaping the edges as parallel to streamlines. Subdivision by horizontal plane, crossing X axis seems to be the best. It is suited for manufacturing process (the hull will be produced as glass reinforced composite in half-hull form), makes maintenance and assembly operations extremely easy (it allows for easy access to all internal component of the vehicle after removal of the hatch) as well as makes easy access to the pilot in case of loss of consciousness (basic safety requirement).

Fig.8 Hull/hatch subdivision.

Ad e) The pilot is also a “human body engine”, and his properties are critical for efficiency of propulsion system. There are important characteristics which must be taken under consideration: maximum power and its changes in the time and pedalling

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cadence. High efficiency propeller reaches design parameters only in relatively narrow range of input, so available input power and rotational velocity should be stable during entire trial (c.a. 1 minute) Fig. 9 presents measured output power for selected team member, and we can observe significant decrease of available power. Conclusion: propulsion system should be designed for available power lower than maximum value (maximum, stable 1 minute value),what requires detailed research for each pilot.

Fig.9 Measured athlete’s power changes in the time

Available power depends also on pedalling cadence. In case of typical cycling, optimal value is usually between 90 and 100 strokes per minute (Fig.10 – blue plot). Unfortunately under water significant part of energy is wasted on “mixing water” inside wet hull (red plot). In effect available power is lower and reaches its maximum for lower cadence (green plot). Again detailed values must be measured for each pilot, but general design conclusion is: “we have less power, we must work on lower cadence than in case of surface cycling”.

Fig.10 Estimated usable propulsion power

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The last important human factor is cycling synchronicity. In typical cycling mode the time of work of each leg is equal, and during work of one leg the second one is resting. Different approach can be observed during top-level sport swimming, when arms work asynchronously. The time arm spends under water is longer than returning time over surface – in effect both arms work together in part of stroking period. From design viewpoint it is very important, because such approach can limit power fluctuations in the time and make propeller work more smooth and efficient. It can be achieved by special crank mechanism (with varying rotational speed during cycle) or by proper athlete training in case of independent crank for each leg. Problem is important for single person configuration. In case of 2 persons vehicle, we can achieve this result by constant phase offset for both athletes. We can also increase available power by including 2nd athlete arms into powering system (the first on must have free hands for vehicle control)

Fig.11 Comparison of synchronously and asynchronously generated output power for single athlete (series 1,2 for each leg, series 3 – sum with offset for better visibility).

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Ad f) Type of pedalling. In general we can observe 2 different types of pedalling sequences in all human powered vehicle: circular (the most popular and natural) and linear. In case of underwater work simple analysis shows advantages of linear approach. Lower translation of each leg (Fig. 12, left), as well as lower translation velocity for each leg (Fig.12, right) - which both result in lower energy waste. Additionally, implementation of asynchronous pedalling sequence is very easy in this case (each lever assembled independently on directional clutch).

Fig.12 Comparison of circular and linear pedaling.

Fig.13 Linear pedaling device.

Ad g) Propeller efficiency optimization is a routine design task, although in our case done partly in non-standard way. The most important ideas cover:

Use a single propeller. Due to propulsion simplicity we refused counter rotating twin propeller. In case of lack of control fins this approach can result in rolling (rotating about X axis) of the vehicle. We decided about compensation of rolling moment by using movable iron ballast, travelling on internal ring (Fig.14). First estimation shows 4 kg brick should be sufficient.

Use of heavy propeller. Due to rules limitations no flywheels are allowed. On the other hand we have a large reserve of buoyancy. Propeller made of heavy metal (e.g steel) doesn’t consume this reserve and works like flywheel, making its rotation more smooth and efficient.

Avoiding of very slim propellers – they have very high efficiency at design speed, but at low velocity they produce low thrust. Achieving of design speed takes a lot of time. First version will be equipped with typical B-Wageningen B-2-30 propeller (ca. 350 mm diameter).

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Fig.14 Internal structure rings, used also for ballast movement.

Future research will cover application of riblets on the propeller surface, as well as usage of flexible propeller with relatively low torsional blade stiffness, which automatically decreases a pitch, when overloaded at low speed.

7. Conclusions

Our project presents synergic, holistic approach to design process and the most important skills covering: a) Ability to practical implementation of theoretical knowledge by redefinition of high-

level functional requirements as low-level technical problems. b) Ability to design a “future ready” solution, which can be easily modified and

improved due to its modular structure. c) Innovative approach to standard problems. d) Efficient CAD/CAE software usage, especially integrated modelling tools

(Siemens NX) and CFD programs (STAR-CCM+ from CD-adapco). e) Efficient teamwork involving students from different classes and specialties. The concept will be also developed next years, especially in context of its commercial application. First stage will cover implementation of electrical propulsion system, containing generator/motor based power transmission system, with easy replacement of generator by high-capacity batteries. The second stage will cover 2-persons vehicle version. The third one – preparation of fund-rising crowd sourced project (Kickstarter) for starting vehicle production.

The project is currently at the stage of preparation of the form for hull production (GRP laminates) and final design work related to propulsion system.