University of Plymouth

Design Development Report

MECH232

Group M

5/20/2016

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Anthony McNamaraKate MartinimoTarig M A Halim

Annabella ConmeeTemi DansoAbdul Eleson

Parit Halai

Contents1. Introduction...........................................................................................................2

2. Initial Ideas and Discussion..................................................................................2

3. Development of Final Idea....................................................................................3

1.1 Speed Calculations........................................................................................3

1.2 Shape of Hull.................................................................................................4

1.3 Nose Cone/Hatch...........................................................................................4

1.4 Feasibility Calculations...................................................................................5

2 Components.........................................................................................................6

2.1 Propeller.........................................................................................................6

2.2 Fins................................................................................................................6

2.3 Steering..........................................................................................................8

4. Manufacturing Methods......................................................................................10

5. Final Design........................................................................................................10

6. Conclusion..........................................................................................................10

7. References.........................................................................................................10

1 IntroductionThis report gives insight into the design development process from concept to final design of Mazu, the two person human powered submarine. The design challenge is to package two riders into as small and streamlined submarine shell as possible while ensuring the submarine is safe and controllable.

Project meetings occurred once a week to constantly ensure all group members were on task. The progress of these can be seen in the Gantt Chart and Meeting Minutes that were made each week. The idea was constantly developed through an iterative process. Throughout this process, weekly meetings were done to enhance communication with the clients. Critical components analysis was done with the use of CES Edupack.

Section 2 includes initial design sketches and CAD models. Information on the selection of materials and manufacturing methods is found in Section 5. By careful evaluation and research, alterations were made to create a fully functional final design. All calculations that were made are shown in their respective sections.

2 Initial Ideas and DiscussionA specification was created and a brainstorm was made to generate innovative ideas. Initial research was done on the steering, prop design, geometrics and propulsion methods. Following that, 8 initial designs were drawn and labelled with various rider positions and component ideas. A feasibility matrix and FMECA was made with 5 failure modes for each design.

An evaluation matrix was used on the 8 designs mentioned above. The following 3 concepts were chosen and combined to create the final design. Another feasibility matrix was made comparing the time taken, cost, stability, ease of manufacture and safety for the 3 chosen concepts. Table 2-1 shows the key differences between the 3 concepts.

Table 2-1: Features of Concept Designs Concept

Shape of Hull

Rider Position

Sitting Position

Driver System

Driver System Position

Fins Fin Position

A Long, narrow

Inline Upright Variable pitch propeller

Rear of submarine

4 Rear

B Wide Side by Side

Laying forward

Single propeller

Rear of submarine

2 Centre

C Long, narrow, compact

Inline Front facing

Contra rotating

Rear of submarine

2 Centre

3 Development of Final Idea3.1 Speed CalculationsTable 3-2 below shows the calculations that were carried out for the speed predictions of concepts A, B, C and the final design.

Table 3-2: Speed predictions for concept and final designs

Concept Length

(m)

Width

(m)

Height

(m)

Total Final Resistance at

Gate 4(N)

Time from Gate 1 to

Gate 4(s)

Average Speed (Gate 1 to Gate 4)

(m/s)A 6.09 0.87 0.87 75.15 37.732 1.916B 2.40 1.18 0.93 78.377 37.559 2.081C 3.85 1.00 1.00 75.137 37.026 1.918Final Design

3.18 0.68 0.95 92.827 27.780 3.6

The length, width and height were obtained from the CAD models. Equation 1 was used to calculate the total resistance at Gate 4 and the values that were used to perform this calculation are shown in Error: Reference source not found.

RTOTAL=12× ρ×v2×cdATOTAL

Equation 1

Table 3-3: Values used in Equation 1

Symbol Meaning Units Formulae Value Sourceρ Water

Densitykg/m3 1000 Water

tablesv2 Final

velocitym/s

cdATOTAL Torpedo drag coefficient x area

m2 Typeequationhere . calculated

RTOTAL RTOTAL=12× ρ×v2×cdATOTAL

calculated

The time from gate 1 to gate 4 was calculated using Equation 2 and the average speed was calculated using Equation 4Equation 3.

t g (1¿4)=t g4−t g1

Equation 2

vavg=s4−s1t g(1¿4 )

Equation 3

where:

s1 – distance at Gate 1

s4 – distance at Gate 4

3.2 Shape of Hull

3.3 Nose Cone/HatchInitially a combined nose cone hatch was considered shown in Figure 1. The hatch would be manufactured using a transparent material, with a hinge placed at the bottom of the hatch in order for it to be opened/closed. Although this

Concept AOriginally concept A was chosen for the shape of

the hull and rider position, yet this design led to an excess of wasted space due to the great length. This excess space meant the submarine had a

larger surface area than necessary, therefore not as optimised, resulting in lower speed predictions

shown in .

Concept B

In order to minimise this wasted space, reduce resistive forces and make the

submarine rider positions as compact as possible Design D was carried forward, thus

resulting in faster speeds.

Concept C

The large width (shown in table 1) needed to cater for two riders side by side led to an increase in drag. Although the final speed

was less than that of concept A the resistive forces meant that speeds were not optimal.

Final Design

The final design utilises all space, therefore decreasing drag forces and resulting in the

fastest speeds.

Figure 1: Original combined nose cone/hatch (Idea A)

design provided ease of access, especially ease of access when manufacturing and maintaining components within the submarine, ISR guidelines (ref 1) state that ‘crew’s face and head areas shall be visible to the support and safety divers at all times’.

The agreed upon separate nose cone and hatch enables divers to easily see the riders from above at all times. Additionally rigidity of the hull will be increased with a separate nose cone/hatch arrangement. The visibility of the riders has not been impaired as the new rider position encompasses a

step up position. The emergency hatch will be placed on the top of the submarine, with equal ease of access to both riders, yet only one rider will be able to exit at a time.

4 Components4.1 PropellerThe two propeller types that were considered are the variable pitch propeller and the contra-rotating propeller. Concept B utilised a variable pitch propeller while Concept C used a contra-rotating propeller. The advantages and disadvantages of each are listed in Table 4-4 below.

Table 4-4: Advantages and disadvantages of two different types of propellers

Variable Pitch Propeller Contra-Rotating PropellerAdvantages Disadvantages Advantages Disadvantages

Forward and astern operation

High initial cost 15-20% more efficient

Noisy

Sources (Piksrys, et al., 2015)

(CPP - Controllable Pitch PropellersExplained, 2009)

(Contra Rotating Propeller Drive System User Guide, 2012)

(Purpose of contra-rotating props, 2015)

Can change speed of ship without a change of main engine

Requires regular inspection

Torque cancels out

Heavy

Sources (Piksrys, et al., 2015)

(CPP - Controllable Pitch PropellersExplained, 2009)

(Contra Rotating Propeller Drive System User Guide, 2012)

(Purpose of contra-rotating props, 2015)

A contra-rotating propeller was chosen as the desired propeller to use. The ISR race is a straight line race with the purpose of producing maximum speed for the duration of the race. Torpedoes such as Bliss-Leavitt torpedo commonly use contra-rotating propellers to give the maximum speed possible within a limited diameter as well as the ability to counteract torque. The torpedo has a maximum speed of 26 knots over an 800 yard range (Detailed description of torpedoes, 1956).

Although, the contra-rotating propeller is noisy, this does not apply to Mazu as it is a human powered submarine. Another disadvantage is the weight because performance is sacrificed in order to carry it. However, an advantage is that the torque cancels out. This is because there are now two contra-rotating propellers cancelling out the opposite’s torque.

4.2 FinsInitially using only 3 fins was considered to limit manufacturing costs, two on the side and one on the top. This proved unfeasible as the submarine would roll and lose stability; hence using 4 fins was agreed upon with two planes of control:

Two rudder planes will act together controlling the yaw and two dive planes will be able to act together and in opposition, controlling both the roll and pitch. The contra-rotating propeller will also minimise the unwanted roll.

Max Chord: 0.15m Mean Span: 0.3m Pivot Axis Position: 0.03m +/-30° Rotation on all planes

Using the NACA 0012 foil profile:

Max thickness at 12.2%: 0.0366mDistance from front of fin (x): At 22.5% of chord length: 0.0338

(NACA 0012 AIRFOILS (n0012-il), 2016)

Figure 3: Side view of the fin

Side View

Pivot Axis Position

Max Chord

Mean Span

Figure 2: Top view of the fin

Top View

Distance from x

Max Thickness

4.3 SteeringThe steering mechanism for the chosen design was a system initially designed for aircraft when hydraulic systems were not implemented. Since both aircraft and submarines require similar control method it can be used for either machine. The three control mechanisms required are yaw control, pitch control and roll control. The basis of the system is to use cables and pulleys to create

a system in tension where adjusting the yoke results in one side creating slack in the line while the opposite creating tension and so changing the direction around a fixed axis. All control mechanisms for this design can be implemented on a single yoke. The controls required are shown in Figure 4.

Figure 4: Control mechanism for an aircraft (A.I.B. Hasri, 2012)

For the submarine vehicle, there are four fins, the control mechanism shown above needs to be adjusted accordingly. The elevator control turns along the dotted axis to allow the elevator to turn up or down and this controls the pitch. The rudder control turns along the dotted axis to give the left and right controls and this controls the yaw. The aileron control turns along the axis to allow the ailerons to act in opposing directions, meaning that when the right

aileron acts downwards the left would move upwards and this is to control the roll. So to implement this in to a single system, the diagrams below in Figure 5, , Error: Reference source not found show the controls

for a single rider.

Figure 5: Layout for pitch and roll control SIDEVIEW

The layout shown on the left and above demonstrates the basic layout within the hull of the vessel. The cables can be pulled further to the side and conform to the shape of the hull. This opens up more space for the riders. The yoke has two movement ranges in the image to the left these are longitudinal (forward/backward) and lateral (left/right). For the longitudinal movement as both cables are pulled forward or backward, the cable attaches to the appropriate pulley and is guided so it does not slip off the transitional pulley. As seen in the diagram below, the layout has a lower pulley and upper pulley and these are the control mechanisms for the roll control. This system allows the top to pull to the left while the bottom pulls right and vice versa.

The overall design also needs to take both riders requiring controls as a problem which needs a solution and one way to do that is shown in the

design below.

One of the major components in the system is the cable, and the selection of this component was critical due to the requirements for the performance of the cable. The system will put tension on the cable as it requires the system to pull the hinges on the fins. The overall material comparison list is limited by factors such as cost, mass, tensile strength and elastic modulus.

Figure 6: Layout for pitch and roll control TOPVIEW

Figure 7: Layout of the yaw

The cable must have an acceptable plastic limit so that the safety of the riders is maintained. The overall chosen material for the steering cables is NYLON Braided Cord rope 5mm in Figure 8, which has a very good tensile strength to weight ratio. The pulley types are 52 mm round groove- nylon pulley wheel rollers with 5mm rope allowance. The total amount required based on the layout is 12 pulleys.

Figure 8: Nylon pulleys (ddopacc, 2016)

4.4 BearingsIn addition to the gears, the bearing is another essential component used to aid the functionality of the submarine and its system of propulsion. It is a piece of machinery used to supplement and assist the rotating shaft by reducing friction between each of the moving parts. So the basic concept of the component is simple: things roll better when they are able to slide.

Ordinarily, bearings undergo two types of loading as shown in Figure 9Error: Reference source notfound, which are radial loading and axial loading. In the case of the submarine and the type of

gears that have been selected to be used (bevel gears) the loading will be a combination of both as the bearings will not only be used for the shaft but also the pedals and the drivetrain.

When first looking at bearings, it must be established which type is most ideal and conventionally there are 2 primary types of bearings which are ball bearings and roller bearings. Each of these can be split into sub-groups with different specialities.

The bearings used are for a variety of functions. One application is for the transition of pedal movement. This can use a basic ball bearing system.

Figure 10: Sketch of Drivetrain

The other load points are the point between the hollow shaft and the solid shaft at the inner propeller as shown in Figure 10. This requires the most attention and is used to support the radial and axial load between the two components this requires a rolling type component so that the two shafts can turn independently to each other as this is the whole purpose of the contra-rotating propeller shaft design.

For the transition of pedal movement mentioned above, a pre-fabricated bottom bracket can be used Figure 11. The Shimano UN55 Bottom Bracket is the most viable choice for the system.

For the Bearings we require a bearing between the holder bracket and the outer shaft. The second bearing is between the inner shaft and the outer shaft. To calculate the appropriate bearings, a set of mathematical formulae are used in conjunction with loads and manufacturer data regarding different bearing types.

Figure 9: Above we can see the direction of the axial load on the shaft (parallel) as well

as the radial load (perpendicular). The bearing

seen in the middle is the medium between the rotating inner shaft and the counter-

rotating outer shaft

Figure 11: Shimano UN55 bottom bracket with crank bearings Invalid source specified.

Initially the shaft radial and axial loads are needed to calculate the dynamic load on the system. The radial load is calculated using Equation 4 whereas the radial load is the predetermined force (thrust) found in the load calculations spreadsheet. The Lf mentioned in the equation relates to the load connecting factor. For this particular setup the load connecting factor Lf is 1.25.

Fr=T ×LfR

Fr=12.43309649×1.250.02

Equation 4: Radial load calculation

P= (X× Fr )+ (Y ×Fa ) P=(0.56×777.0685306 )+(1.67∗221.5458489)

Equation 5: Dynamic load calculation

The value for P= 805.139948313N.

It is assumed the submarine will be tested multiple times before the competition and that the total number of revolutions will amount to exactly 1000000 revolutions. Also assuming that the reliability of the bearing is 90% then the safety factor would in turn be 1 Invalid source specified.. The life exponent value for a roller type bearing would be 10/3 and so by rearranging the basic life rating Equation 6 we can find the load rating value Cr.

Cr=( p√L10 )×PCr=( 103√1)×805.139948313Equation 6: Basic life rating equation

Symbol Meaning Units Value Sourced bore diameter m 0.02 Calculations spreadsheetD Total shaft diameter m 0.05 Calculations spreadsheetW width space between

shaftsm 0.01 Invalid source specified.

Fr Radial load N 777.0685306 calculatedFa Axial load N 221.5458489 Calculations spreadsheetT Torque Nm 12.43309649 Calculations spreadsheetLf load connecting factor - 1.25 Invalid source specified.R Radius m 0.02 Calculations spreadsheetP Equivalent dynamic load N 805.1399448 calculatedX Radial factor - 0.56 Invalid source specified.Y Axial factor - 1.67 Invalid source specified.S.F Safety factor (90%) - 1 Invalid source specified.RPM revolutions per minute r/min 440 Calculations spreadsheetr revolutions - 1000000 assumedL10 Basic life rating 106

revolutions

1 calculated

Cr Basic dynamic load rating N 805.1399448 calculatedp Life exponent - 3.333333333 Invalid source specified.

Value of Cr = 805.139948313N.

When looking through a data base of bearings for the most appropriate selection is the SKF NX 20 bearing shown in Figure 12 which is a roller type needle bearing that has a ball bearing component added to support the axial load Invalid source specified.. The bearing conforms to the Criticla load factor and the width limitations of the prop shaft.

The various values calculated are assumed to be exactly the same for both shafts as they are equal and opposite in the contra-rotating design of the shaft. This also means that for a housing bearing,

which is used to support the shaft the same values hold true. As a result for the housing bearing a SY20TR SKF 20mm bore can be used.

4.5 GearsThe gearing system required for the drivers is based on a tandem Bicycle and follows the da Vinci tandem design as in Error: Reference source not found to allow individual rotation.

For the basic system a premade gearing system works more efficiently in the scope of the project timeline. For this reason, a variety of gearing systems are compared and the shimano FC-M171 Triple chainset is an option considered. The diagram in Figure 14 shows the chainset implements a 170mm crank arm and is made from a combination of aluminium and stainless steel components to provide a lightweight and

strong component.

This system is paired with the Shimano Acera FD-M360 front derailleur system to complete a three- speed gearing system for riders to be able to accelerate from zero to max velocity and then maintain the power output.

For the timing on the da Vinci design, a simple timing crank is also required and a standard 24t crank can be attached to the secondary pedal crack arrangement.

The rear freewheel is a component that attaches the front chainset to the drivetrain. Since the

speed gearing is only selected for the front chainset, the rear freewheel is a simple sprocket with 18 teeth that is connected to a chain tensioner. The shimano onespeed freewheel in Error: Reference source not found is a very good option for this component and is shown below.

Front rider chain

Figure 12: NX20 series bearing

Figure 13: SY20TR SKF

Figure 14: Shimano FC-M171 triple chainset Invalid source specified.

Figure onespeed freewheel

source specified.

4.5.1 Gear arrangement Initially, the choice for which gear system was most suitable in terms of functionality for the submarine was between Worm and Bevel gears. 

Although both gears are able to change the direction of motion by 90° we agreed on using bevel gears.  The worm screw typically drives the worm gear and the worm screw is usually powered by a shaft. Our design requires the reverse of this gear design, as the shaft will need to be powered by the gear.  

In comparison, the bevel gear is comprised of two gears set at perpendicular positions to each other. The system works in rolling motion where the teeth push against each other. The bevel gear will work well with the calculated 4:1 ratio, and easily change the direction needed to power the shaft. 

 

Figure 2: Initial Sketch of Gear Drive 

 

4.5.2 Gear Material When selecting the material for the gears, yield and tensile strength, price and durability in fresh water were all considered.  

Material Price £/kg Corrosion in fresh water σUTS σYield

Medium Carbon Steel 0.326-0.364 Acceptable 410-1200 305-900

Low Alloy Steel 0.351-0.389 Acceptable 550-1760 400-1500

Stainless Steel 3.69-4.07 Excellent 480-2240 170-1000

Aluminium Alloy 1.37-1.51 Excellent 65-386 50-130

Table 4: Material selection factors (ref CESEdupack) 

We decided upon using low alloy steel, due to its high tensile and yield strength, cheap price and as the submarine is not in constant use, we agreed that its acceptable durability in fresh water was satisfactory for our design. 

  

3. Gear Sizing  

A gear ratio of 4:1 for the propeller shaft was calculated using the submarine speed prediction spreadsheet in order to give the highest average speed when the riders input is 50rpm at a maximum 700W. Gears will be α = 20o made from low alloy steel with σUTS = 550 Mpa and σYield = 400 Mpa. 

Assumptions: 

18 teeth on the pinion therefore 72 teeth on the gear.  Lewis Form Factor= 0.27  Factor of safety =4 gives σmax = 400/4 = 100 MPa  Module= 2mm 

 

D pinion=m×N pinion

¿0.002m×20¿0.04m

K v 6/ (6+V )

¿ 66+0.419m /s

¿0.935

V π×D×n60

¿π ×D×n60

¿(π ×0.04m×200 rpm)/60¿0.419m /s

P=π× D pinion

N pinion

¿ π ×0.0418

¿0.0062m

F=(

W t

K v×m×Y×σmax)

105

¿( 16170.935×0.002m×0.32×100

)/105

¿0.279m

F Allow−min=3×P¿3×0.0062m¿0.0188m

F Allow−max=5×P¿5×0.0062m¿0.0314m

W t P /V

¿ 700W0.419m /s¿1671N

Symbol Meaning Units Value Source

Npinion Pinion Teeth 20 Assumed

Ngear Gear Teeth 80 Gear ratio xNpinion

Y Lewis Form Factor 0.32 (BudynasandNisbett, 2011)

m Module m 0.002 Assumed

Dpinion Pitch diameter pinion m 0.04 Calculated

Dgear Pitch diameter gear m 0.16 Calculated

V Velocity (pitch line) m/s 0.419 Calculated

Wt Force N 1671 Calculated

Kv Velocity Factor 0.935 Calculated

F Face Width m 0.028 Calculated

Sd Shaft centres distance apart m 0.1 Calculated

P Pitch m 0.0062 Calculated

Fallow-min Allowable face width minimum m 0.0188 Calculated

Fallow-max Allowable face width maximum m 0.0314 Calculated

 

The gears will be outsourced, an example was found from HPC gears (HPC, no date) which matches the module, and gear ratio. The necessary gears will cost £283.94 and will weigh 1.52kg.

4.6 HarnessTo keep the riders in place and give them an anchor point a simple harness is devised which attaches with a clip to a hook on the beam. This gives the rider an opposing pull force to the pushing force on the pedals. This is easily achieved with a Panoply Standard Body Harness shown in Figure 16. This will be attached to a Harness Clip with a "D" Ring as seen in Figure 17Figure 16. The harness clip attaches to a hooking point on the frame.

: Harness clip

Figure 16: Panoply Harness

5 Manufacturing Methods5.1. Material of HullThe material used for the hull of the submarine was decided based on the most important mechanical properties that were required for the design. These included fibre to volume ratio, fibre orientation and void % (percentage of air bubbles). Also, things such as the tolerances, dimensions of the hull and its geometric complexity was also analysed. All in all, with these facets of the design considered, it was concluded that fibreglass would be used as the base material of the hull. It is a material that enables considerable flexibility in terms of the design as it can be fabricated using simple tools; not requiring any welding or torches (Gerard, 2015).

It is extremely lightweight (acFibreglass, 2004) and only 2/3 the weight of aluminium and 25% the weight of steel (Gerard, 2015).

It possesses high mechanical strength. It is incredibly strong and stiff for its weight and can out-perform other materials such as steel & aluminium (acFibreglass, 2004).

It has high impact strength so the submarine wouldn’t change shape if it was to rupture or undergo any plastic deformation from any impact. (Smith, 1991).

It has very good formability:1. Easier to mould into the desired shape than most other materials (acFibreglass, 2004). 2. Good formability means it’s also cheaper to manufacture than other materials which helps

reduce the overall cost of the submarine design.

It has low maintenance. (acFibreglass, 2004).

It has good stiffness with a modulus of elasticity of 2.8 x 10^6 psi (Gerard, 2015).5.1 Material for Nosecone & Hatch

For the nose cone and hatch of the

submarine, it was decided that the material used would be perspex glass which is a form of acrylic Error: Reference source not found.

It is a material that possesses high strength & durability, good formability as well as being cheap (Hargrove, 2015).

Good formability means that it can be moulded into the concave shape for the sub more efficiently (PLASKOLITE, 2016).

It is lightweight and much easier to carry when compared to ordinary glass (PLASKOLITE, 2016).

It has transparent properties that enable good and clear view through the front of the sub by passengers (Hargrove, 2015).

Figure 18: An image displaying a boat hull made from fibre glass (ec21, 2009)

5.2 Hinges

It was decided that a rubber (silicone) seal would be used for the hatch and nose cone of the submarine. Evidently, this will act as a seal around the edges to eliminate any spaces where water may seep in. The silicone elastomer used to create the sealant is useful for this as it has properties such as being: non-reactive, stable and resistant to extreme conditions which is very useful for a submerged vessel.

For the selection of the hinges used for the hatch, it was important to consider that the door that comprised the hatch would need to be able to be pushed all the way to the top so the hatch used needed to have this degree of flexibility. It was also important that the hatch had a locking mechanism so that when the door was opened it wouldn’t come crashing back down again. The hatch that was selected was able to encompass all of these desires and this was a stainless steel, self-closing hinge. Stainless steel was used to prevent the rusting of the component from exposure to water.

Figure 19: Image of stainless steel locking hinge (Alibaba, 2014)

To ensure the hatch is kept in place during operation, a simple bar lock can be used on the opposite side of the hinges. The image below shows this mechanism

Figure 20: (McNaughtuns, 2016) image of lock preventing the hatch from opening during operation.

5.3 Foam MaterialIt was essential that our submarine design possessed some sort of component that would help maximise its buoyancy and stability in water.

This component would be foam with the material being syntactic foam which is a composite material has glass microspheres within an epoxy resin matrix (Synfoam, 2016).

It has high strength, low density with very low moisture absorption with the latter two properties being most required (Luong, 2011). The low density is what enables it to supplement the sub’s buoyancy and increases efficiency whilst it’s low moisture absorption implies that it does not react and is unaffected by water when the submarine is submerged.

Figure 21: Image displaying the microspheres within the epoxy resin matrix of (ec21, 2009) the foam (PHYS ORG, 2015)

6 Final Design

Figure 22 shows an image of our final design with a representation of all the components, the rider positions, fins, propellers and overall shape of the submarine.

Figure 22: Solidworks drawing of Final Submarine

7 ConclusionIn conclusion or final project met all the requirements and design specifications. The FEA analysis was successful resulting in high probability of success of the vessel for the race. The final velocity and time taken for the vessel was very fast resulting in a good race performance. The manufacturing process and material that will be used for the design are environmentally friendly as well cheap. The vessel is fairly easy to design due to the simplicity of components used. The overall design was made so that the vessel is as small as possible resulting in a good performance.

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