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OMER 7 Final Design Report

10th ISR

Final design report – OMER 7

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Table of contents

Introduction ............................................................................................................................................ 6 1. Presentation of the submarine ........................................................................................................ 7

1.1. General characteristics of the submarine .................................................................................. 7 1.2. Propulsion system .................................................................................................................... 8 1.3. Explanation of the movement of the wings ............................................................................... 8 1.4. Explanation of the Bernoulli phenomenon ................................................................................ 8 1.5. Vectorial explanation of the system .......................................................................................... 9 1.6. Power to hand over ................................................................................................................ 10

2. Hull ................................................................................................................................................ 11 2.1. Methodology .......................................................................................................................... 11 2.2. Constraints ............................................................................................................................. 11 2.3. The software .......................................................................................................................... 12

2.3.1. LIBRAIRY module ............................................................................................................. 13 2.3.2. MODELING module ......................................................................................................... 14 2.3.3. Hull construction (modelisation sub-module) ................................................................... 15 2.3.4. ANALYSE module ............................................................................................................. 19 2.3.5. EXPORTATION module .................................................................................................... 19

2.4. Hydrodynamic analysis ........................................................................................................... 19 2.5. Numerical simulation .............................................................................................................. 20 2.6. Final hull ................................................................................................................................. 21

3. Propulsion system ......................................................................................................................... 22 3.1. Parameters to optimize .......................................................................................................... 22

3.1.1. Wings cart’s stroke ......................................................................................................... 22 3.1.2. Synchronized system ....................................................................................................... 22 3.1.3. Axis-to-axis distance ....................................................................................................... 22

3.2. Preliminary design .................................................................................................................. 22 3.3. Propulsion system modeling ................................................................................................... 23

3.3.1. Stroke and synchronism .................................................................................................. 23 3.3.2. Standard sprockets ......................................................................................................... 23 3.3.3. Optimization ................................................................................................................... 24 3.3.4. Final solution .................................................................................................................. 24

3.4. Propulsion system description ................................................................................................ 25 3.5. Technical specifications .......................................................................................................... 26 3.6. Variable pitch ......................................................................................................................... 26 3.7. Mechanical conception ........................................................................................................... 27 3.8. Electrical system ..................................................................................................................... 28

4. Wings and fins ............................................................................................................................... 29 4.1. Important parameters ............................................................................................................ 29 4.2. Calculation methods ............................................................................................................... 29 4.3. Parameters influence.............................................................................................................. 30 4.4. Acquired Results ..................................................................................................................... 31

4.4.1. Profiles selection ............................................................................................................. 31 4.4.2. Results of the final iteration ............................................................................................ 32


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4.5. Construction of the wing ........................................................................................................ 33 4.5.1. Strength calculation and reactions to supports ................................................................ 34 4.5.2. FEA ................................................................................................................................. 35

5. Fins ................................................................................................................................................ 37 5.1. Determination of hydrodynamic coefficients of the hull ......................................................... 37 5.2. Pressure center’s position....................................................................................................... 37 5.3. Determination of the fins’ and stabilizers’ hydrodynamic coefficients ..................................... 38 5.4. Results .................................................................................................................................... 39

6. Security system ............................................................................................................................. 40 6.1. System operation ................................................................................................................... 40 6.2. Presentation of the pneumatic diagram .................................................................................. 41 6.3. Design of the doors opening system ....................................................................................... 41 6.4. Placement of the elements in the submarine .......................................................................... 42

7. Electrical system ............................................................................................................................ 44 7.1. Electrical system’s conception ................................................................................................ 44 7.2. Modules ................................................................................................................................. 45

7.2.1. Onboard monitor ............................................................................................................ 45 7.2.2. RPM, pressure and speed modules .................................................................................. 45 7.2.3. Joystick ........................................................................................................................... 46 7.2.4. Master: ........................................................................................................................... 47 7.2.5. Direction: ........................................................................................................................ 47 7.2.6. Variable pitch.................................................................................................................. 48 7.2.7. OMERLINK and OMERSIM ............................................................................................... 50

Conclusion ............................................................................................................................................. 53 Appendix I ............................................................................................................................................. 54 Appendix II ............................................................................................................................................ 55 Appendix III ........................................................................................................................................... 57


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Table of illustrations

Figure 1 - OMER 7 hull, seen from the front ........................................................................................ 7 Figure 2 - OMER 7 hull, seen from the side (see appendix I) ................................................................ 7 Figure 3 - Wing's movement ............................................................................................................... 8 Figure 4 - Lift phenomenon ................................................................................................................. 8 Figure 5 - Position of pilots .................................................................................................................11 Figure 6 - Constraints modeling..........................................................................................................12 Figure 7 - Software's main structure...................................................................................................13 Figure 8 - LIBRAIRY module's detail ....................................................................................................13 Figure 9 - Standard wing foil ..............................................................................................................13 Figure 10 - MODELING module detail .................................................................................................14 Figure 11 - Creation of a points cloud .................................................................................................15 Figure 12 - Effect of the K factor on a quarter of ellipse ......................................................................16 Figure 13 - nuage.m algorithm ...........................................................................................................17 Figure 14 - Graph of the K factor ........................................................................................................18 Figure 15 - Hydrodynamic reaction ....................................................................................................19 Figure 16 - Example of a CFD result ....................................................................................................20 Figure 17 - Boundary conditions .........................................................................................................20 Figure 18 - Final meshing example .....................................................................................................20 Figure 19 - Final hull (see appendix II for more pictures) ....................................................................21 Figure 20 - Propulsion system schematic ............................................................................................23 Figure 21 - Sprocket positioning .........................................................................................................24 Figure 22 - Propulsion system positioning ..........................................................................................25 Figure 23 - Propulsion system components ........................................................................................25 Figure 24 - Technical specifications ....................................................................................................26 Figure 25 - Explanation of the angle of attack.....................................................................................27 Figure 26 - Variable pitch components ...............................................................................................27 Figure 27 - Variable pitch amplitude...................................................................................................28 Figure 28 - 2D airfoil characteristics ...................................................................................................30 Figure 29 - Light cutting wing section in 3 dimensions. .......................................................................30 Figure 30 - Induced angle formation ..................................................................................................30 Figure 31 - Wing tip vortex .................................................................................................................30 Figure 32 - Lengthening explications ..................................................................................................31 Figure 33 - Aspect ratio formula .........................................................................................................31 Figure 34 - Elliptical wing’s parameters (wing overview) ....................................................................31 Figure 35 - Airfoil J5012 et GEO460 ....................................................................................................32 Figure 36 - Optimal tridimensional model of the wing ........................................................................33 Figure 37 - Representation of the final assembling of the wing and a picture of the parts inside the final

assembly. .........................................................................................................33 Figure 38 - Calculation of strengths and moments..............................................................................34 Figure 39 - Carbon fiber model from CATIA software .........................................................................34 Figure 40 - FEA of the insert from the CATIA software ........................................................................35 Figure 41 - FEA for the ANSYS software ..............................................................................................35 Figure 42 - FEA of the whole from the CATIA software .......................................................................35 Figure 43 - Result of the shaft realized with the « Wet Lay-Up » method ............................................36 Figure 44 - Result of the shaft realized with « Prepreg » carbon .........................................................36


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Figure 45 - Analysis environment of the hull ......................................................................................37 Figure 46 - Equation of center of pressure where p(x) is the pressure function of the position profile 38 Figure 47 - Positions of the pressures obtained for the calculation of center of pressure....................38 Figure 48 - Fins in its boundary box ....................................................................................................39 Figure 49 - CFD analysis in COSMOSFLOWORKS .................................................................................39 Figure 50 - Requirements and operation of security system ...............................................................40 Figure 51 - Pneumatic system’s diagram ............................................................................................41 Figure 52 - Modeling of closing mechanism ........................................................................................42 Figure 53 - Components seen from the front of the sub .....................................................................43 Figure 54 - Components seen from the front of the sub .....................................................................43 Figure 55 - LCD screen........................................................................................................................45 Figure 56 - Computer routing of the RPM PCB ....................................................................................46 Figure 57 - Speed sensor in its casing .................................................................................................46 Figure 58 - Direction components ......................................................................................................48 Figure 59 - Direction casing (first in front) ..........................................................................................48 Figure 60 - Variable pitch inner part ...................................................................................................49 Figure 61 - Variable pitch test ............................................................................................................50 Figure 62 - OMERSIM software ..........................................................................................................51 Figure 63 - OMERLINK sofware ...........................................................................................................52 Figure 64 - Drawing of the whole sub .................................................................................................54 Figure 65 - Drawing of the hull ...........................................................................................................55 Figure 66 - Half of hull (laminated with resin infusion system) ............................................................56 Figure 67 – Foam core preparation for sandwich laminate process ....................................................56 Figure 68 - Propulsion system ............................................................................................................57

Table of tables

Table 1 - Last speed world records by OMER submarines .................................................................... 6 Table 2 - Vectorial explanation of the system ...................................................................................... 9 Table 3 - Constraints’ positioning .......................................................................................................12 Table 4 - Standard teeth configuration ...............................................................................................24 Table 5 - Final solution (propulsion system configuration) ..................................................................24 Table 6 - Variable pitch mechanical parameters .................................................................................28 Table 7 - Best profiles results .............................................................................................................32 Table 8 - Optimal parameters of the wing ..........................................................................................32 Table 9 - Generated strength by the final wing ...................................................................................33 Table 10 - Safety system detail ...........................................................................................................44 Table 11 - Variable pitch detail ...........................................................................................................49


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Introduction

Since the beginning of the 1990s, the OMER Submarine Club members display much effort to raise the standards of the International Submarine Race (ISR). Up to now, the OMER Club holds the speed record in three categories out of four.

Table 1 - Last speed world records by OMER submarines

SUBMARINES CATEGORY YEAR SPEED (Knots)

OMER 4 One person, propeller 2001 7.192

OMER 5 Two person, propeller 2007 8.035

OMER 6 One person, non-propeller 2007 4.642

In a continuity objective, it has been decided to conceive and build OMER 7. In order to get the only missing record, this new submarine will evolve in the two person non-propeller category. Moreover, the construction of OMER 6 enabled to develop an expertise of the non-propeller submarines that the ISR 9 of 2007 has enabled to recognize. This competition has enable to understand and to analyze every variant around the non-propeller, and thus to define the spots to improve in the former propulsion system.

Many novelties are present on the OMER 7 submarine. In addition to present a propulsion system able to welcome two cyclists, the whole security system has been remade to be activated both manually and in a pneumatic way. As for them, the wings are longer than before and have an elliptic shape. The hull has been optimized to produce as less drag as possible, and finally a complete electrical system has been installed.

This report exposes the fruits of the labor for a year of approximately fifteen students. It aims to explain the working of the OMER 7 submarine in a technical and detailed way. Each component of the sub will be covered, but let’s begin by an overall view of the OMER team’s latest creation.


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1. Presentation of the submarine

1.1. General characteristics of the submarine

The basic principle of the OMER 7 submarine will be similar to the one of OMER 6, which means a system of wings that oscillate on each side of the fuselage. During the conception of OMER 6, some phenomenons were unknown to us. For example, on OMER 6 the propulsion system is located behind the centroid of the hull. The effect of this is to make the back of the submarine oscillate up and down, making it unstable and difficult to pilot. To counter this phenomenon, a new hull has been calculated to enable to fit the propulsion at its center. During its conception, it has been discovered that the smallest hull possible would allow to fit two people. That is why OMER 7 will be a two person non-propeller.

Figure 1 - OMER 7 hull, seen from the front

Figure 2 - OMER 7 hull, seen from the side (see appendix I)

The general dimensions of the submarines are a length of 4.9m, a width of 0.59m and a height of 0.74m. Once the wings are put in place on the propulsion system, it reaches a total width of 2.3m. Finally, the total volume is of 1.065m3.

An important characteristic of the submarine is that it is filled with water. To control it with a fin system, it is important to be sure that it will be neutral at a depth of 7.5 meters, that is to say that it will not sink or will not float. The principle of Archimedes says that for a solid completely immerged, with the same weight and the same volume as the liquid in which it is, this solid will be neutral. By applying this principle, we find that the volume of the submarine under water will be equal to the water volume that it moves. Thus, with a density of 1000 kg/m3 for water, we find that its volume is of 1065 kg.


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1.2. Propulsion system

As mentioned above, OMER 7 is a submarine made to participate to the competitions in the category two person non-propeller. Thus, the goal of the propulsion system is to hand over, in an efficient way, the power from the two cyclists to an oscillating wing system. These wings must be located on each side of the fuselage and at the centroid of the submarine.

1.3. Explanation of the movement of the wings

The wings are located on both sides of the submarine. (See Figure 1) It is a continuous up and down oscillating movement that enables the submarine to move forward. A complete cycle of the oscillating system is shown on the following picture.

Figure 3 - Wing's movement

1.4. Explanation of the Bernoulli phenomenon

The principle of the propulsion system is based on the same one as from the wing of an airplane. The matter is to make an airfoil move forward at a certain speed in a given fluid to then create a lift force. The lift phenomenon is produced when we have a pressure difference between the upper and lower surfaces. The Bernoulli principle tells that the more the speed of a fluid raises, the more the pressure it makes around it lowers. Thus, the side of the wing where the flow is the longest will be in depression.

Figure 4 - Lift phenomenon


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In the figure above, an example of flow is shown. The decrease of pressure under the wing will create a force to the front and to the bottom. It is on this principle that OMER 7 will move.

1.5. Vectorial explanation of the system

To visualize better the forces that are involved as well as the different generated speeds, it is simpler to represent the oscillating movement with a vectorial system. In the nautical field, the speed is counted in knots. The conversion of a knot is of 1.85 Km/h.

In the next table, we represent the speed of the airfoil by the vector V and the generated force, which is the lift of the wing, by the vector P.

Table 2 - Vectorial explanation of the system

At zero speed, the fluid arrival direction is only

vertical. The lift being perpendicular to this

direction, it is all used to push the submarine

forward. Tests had proven that a wing angle

between 80 and 85° is optimal.

As the submarine gain speed, fluid begins to

arrive not only vertically but also horizontally.

This creates a combined fluid direction that

changes the lift’s effect. In addition to its useful

component oriented forward, a vertical force

appears. It can be upward or downward

depending of the cycle.


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This effect accentuates as the sub gains speed.

Consequently, the vertical component of the lift

forces the sub to oscillate following the up-down

cycle of the wings. Only the rear of the sub is

affected because of the gravity center’s position,

which is further left on the image.

Around 5 knots, the sub speed is too high

compare to the wings’ speed given by the pilot.

This situation leads to a fluid’s arrival direction

that is near the horizontal; the optimal angle of

the wing is too thin to be applied. At this

moment, the sub maximal speed is reached.

1.6. Power to hand over

During the conception of OMER 6, a power of 1.2 HP, generated by the cyclist, has been used to proportion the components of the submarine. Now, for OMER 7, a power of 1.75 HP will be used for two cyclists. It is not possible to multiply directly 1.2 HP by two because the cyclists weaken each other when they are coupled on a same system.


2. Hull

The hull of a submarine being one of the elements having the most influence on its performances, the idea of building a modeling parametric tool has appeared. Such a tool aims to enable the team to make an optimal hull in terms of dimensions according to the basic constraints and criteria, for instance the size of the pilots. Moreover, a hydrodynamic analysis enables to test the aptitude of the different sizing scenarios to efficiently move in water.

2.1. Methodology

The goal of this tool is then very simple: to make and design a hull of a two person non-propeller submarine (of the same type as OMER 6). Many tools are successively used to do so. As a first stage, a parametric stage in MATLAB code will do the modeling of the hull (sizing) with the help of iteration. As a second stage, sub-functions of the principal program do the necessary calculations to approximate the aerodynamic performances of the chosen hull models. As a third stage, a standard calculation model (a template) is realized to do digital analyses by finished elements with the help of the software FLUENT. These analyses confirm the approximate analysis of the parametric modeling tool. As a last stage, the final modeling of the hull is made with the software CATIA; a points cloud is exported in this CAO software.

2.2. Constraints

An important parameter of the software is the internal space constraint, which needs to be respected. This constraint corresponds to the volume that the two pilots occupy inside the submarine. The following figure represents the position of both pilots inside the hull.

Figure 5 - Position of pilots

The configuration of the pilots’ position doesn’t differ from the one seen in the previous submarines. More especially, the configuration proposed is the same as for the OMER 5 submarine, the latest two person submarine from the team. The pilots are in lying position and their feet are gathered in the center of the submarine towards the propulsion system.

That way, the constraints studied in the software correspond to the amount of space occupied by both pilots in the lying position. With the aim to reduce the number of constraints to study, the focus

HULL - The main lines

1. Sizing of the hull (MATLAB);

2. Approximate hydrodynamic

analysis (MATLAB);

3. Hydrodynamic analysis by

finished elements (FLUENT);

4. Modeling (CATIA);


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is put only on the point located at the top of a certain occupied spaces. The following table indentifies the constraints studied as well as their positions. Only the pilot at the front is considered, the second pilot’s position being the same, except for the x values that are the exact opposite.

Table 3 - Constraints’ positioning

Name of the restraint Position (inch)

x y z

Head 78 4 3

Shoulders 73 7 3

Knees 35 8 10.5

Feet 13 8 10.5

The constraints’ position is based on the past experience. In fact, these dimensions were the ones used for OMER 6 shell. Moreover, in order to eliminate the vertical force’s effect created by the propulsion of the OMER 6 submarine, the wings axis position is imposed towards the centre of gravity. Since the movement of the pilots is linked to the position of the propulsion system, the position of the constraints is dynamic. These positions are fixed according to the centre of gravity the shell. Finally, the location needed for the breathing apparatus as well as all mechanical systems are not studied.

Figure 6 - Constraints modeling

2.3. The software

The software is built following an assembly of various modules. A module receives the entering data, treats them and records the results. To function, each depends on the results of the previous one. Each of them will be briefly described in the following paragraphs. The following figure shows the link between the modules of the software.


Figure 7 - Software's main structure

Figure 8 - LIBRAIRY module's detail

2.3.1. LIBRAIRY module

The role of this module is to assemble the different files describing airfoils in order to create a library of guide curves. Five under-functions fill this mandate.

First, the library module contains the complete inventory of standard wing foil. These can be NACA airfoil for example. They are store in .dat files that contains the points describing a unitary wing profile, which means X values varying from 0 to 1.

Figure 9 - Standard wing foil

LIBRARY

ANALYZE

EXPORT


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Secondly, the module examen_librairie examines all the airfoils in the library in order to select only the «aeronautic» airfoils. These are characterized by two elements; the symmetry on a horizontal axis and their predisposition to reduce drag. Also, the shape of these profiles is similar to a sub-marine’s hull.

Thirdly, the ajustement_profil function applies a scaling factor on the airfoil coordinates. The factor corresponds to the total distance between constrains. This operation enables the obtaining of all the profiles that can contain that the constraints

Fourthly, since a hull is defined by two guide curves, (see figure 11) the function formation_paire returns pairs of curves for their modeling. This is done by creating a matrix that expresses all the possible matches between two curves. These curves come from the airfoil library.

Finally, the module Enregistrer_resultats records the files containing the library of airfoil and the work groups in the folder /Penobscot.

2.3.2. MODELING module

The function of this module is to model the hulls and to obtain their characteristics. The hulls are created from two guide curves that come from the librairie.mat files (see figure 11). The pairs were created previously. A hull is created for each curves pair. The creation of a hull is over when, after successive scaling, all the constraints are held into the cloud the hull. After, a file containing the points forming the hull is saved again the folder /Penobscot, the name of each file being the number of the pair in the matrix. The following figure represents the scheme of the module.

Figure 10 - MODELING module detail


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2.3.3. Hull construction (modelisation sub-module)

Here is how the software constructs a hull. Most of those steps take place in the modelisation sub-module contained in the MODELING module.

A hull is defines by two guide curves, the dorsal ad the flank. These curves come from the airfoil library. Then, with a multitude of plans perpendicular to the x axis, an ellipse is traced. The half-height and the half-width of the ellipse correspond to the interpolation of the height of the guide curves at this position. Thus, on each plans, an ellipse that intersects the two guide curves is traced. A function then comes to take the coordinates of a defined number of points. This process is repeated for the entire length of the axis and all the points obtained define a hull. The following figure illustrates the process.

Figure 11 - Creation of a points cloud

The software uses the ellipse to define the curve on each plan for the following reasons. First, the equation used is the one of an ellipse centered at the origin. This insures that the surface of the hull will be continued and perpendicular to the plans on which are the guide curves. Also, the equation of the ellipse can be modified by varying only one parameter in order to even the curve. The following figure shows the phenomenon.


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Figure 12 - Effect of the K factor on a quarter of ellipse

In this graphic, three curves are represented. Each curve has the same a and b parameters, only the exponent is different.

The modelisation.m function rules the structure that contains the attributes of a hull. The following section will study in details the nuage.m algorithm. It’s the function that does the iterative process leading to the points cloud that defines a hull. The following illustration represents the function’s algorithm.

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 1 2 3 4 5

Dis

tan

ce (1

un

it)

Distance (1 unit)

Ellipse shape depending on the K-factor

K factor = 2

K factor = 3

K factor = 4


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Figure 13 - nuage.m algorithm

The function establishes a loop that creates that points cloud by studying the constraints one by one.

First, the role of the Iteration_nuage function is to create, by an iterative process, a points cloud that describes a hull. The method to create the cloud is the one describes previously. However, the modelisation strategy requires an iterative process. Indeed, the constraints are positioned in the hull depending on the centroid position, the centroid is function of the geometry of the hull and the position of the bumps on the surface depends on the constraints position. Therefore, these three inter-dependant factors must be known to create a points cloud.

The strategy adopted to resolve this problem is to guess the centroid position. With this hypothesis, it is possible to trace the vector that describes the K factor depending on the position on the hull. The following figure is an example of such factor.


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Figure 14 - Graph of the K factor

Since the position of the centroid is defined, it is possible to position the constraints. The graph shows a flat section on the curve. This flat zone corresponds to the amplitude of the bumps that is situated between the two knees. The two slopes on each sides of the flat zone represent the transition between the regular ellipses and the deformed ones that define the bumps.

After, a points cloud is realized. The software then comes measuring the position of the centroid of the cloud and compares it with the hypothetic position. In the case where the difference is greater than a certain tolerance, the hypothesis is adjusted according to the measured value and the process starts over. This process is repeated until the difference respects a certain convergence criteria.

At this point, the points cloud is said stable and the point matrix is returned to the nuage.m function.

Secondly, the decalage_centroide function operates a translation on the matrix that defines the internal constraints. The constraints are moved so that their position is relative to the hull’s centroid.

Thirdly, interpolation function verifies the studied constraint’s position compared to the hull surface. By interpolation, the function traces the cut plan that is defined by the studied constraint position in x. On that plan, the ellipse is traced and the function verifies the position of the constraint point compared to the curve. The function returns true if point is outside the ellipse.

Then, a condition verifies the state of the studied constraint point compared to the surface of the hull. If the constraint is outside the cloud, the condition increases the flat zone of the K factor. This has for an effect to increase the amplitude of the bumps on the hull. If the K factor reaches the imposed limit, it is reset to its initial value and the condition applies a scaling factor to the entire cloud. This has for an effect to increase the surface of the hull equally in every direction. In the case where the constraint is inside the points cloud, the loop in incremented and the function studies the next constraint. The hull is done when all the constraints are inside the points cloud.


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2.3.4. ANALYSE module

The analysis module is, without a doubt one of the most important module of the MATHLAB program because it decides which hull is the best between the entire pool. Since there is thousands of hulls, to manually analyze them would be almost impossible, this is why the module was created. Although its importance, the algorithms of the module are rather simple. To resume, the module receives the hulls and orders them by performance (top 10, 20, 25, 100, etc.).

2.3.5. EXPORTATION module

The function of the exportation module is to transform the data format so that other software can interpret it. The goal of the software is to model a great quantity of hull and to determine which ones present the best advantages. The IGES format was chosen because of its great versatility at its compatibility with the GAMBIT and CATIA software.

2.4. Hydrodynamic analysis

Since the beginning of the OMER submarine, the conception of the hull has always been a hard step, especially when it was time to calculate the hydrodynamic performance yet, the hull is one of the most maybe even the most important part to obtain the finale performances.

It is possible to affirm that the factor that has the most influence on the submarine’s performances, excluding the power brought by the pilot and the propulsion system, is the resistance of the fluid on the surface of the hull when the submarine is moving, also called the drag force. In reality, la the drag force is the horizontal component of the relative fluid displacement at the surface of the hull. The following figure shows the drag phenomenon.

Figure 15 - Hydrodynamic reaction

It is then required to reduce the drag force in order to increase the submarine speed. However, to reduce this resistance force, it is necessary to determine its point of action on the submarine surface.


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2.5. Numerical simulation

The CFD or « computational fluid dynamics » consists into analyzing the movement of a fluid around a solid by resolving, with an iterative method, a number of mathematical equations ruling fluid behavior. It consists into separating the fluid in small zones (meshing) and to calculate the fluid effect in every single zone. GAMBIT software is used to achieve the meshing. After, the equations are resolved using software called FLUENT. It is then possible to obtain the pressure variation around a wing profile as shown on figure 16. It is also possible to find the advancement resistance of a body is a fluid, which particularly is interesting in the case of a hull. Figures 17 and 18 display respectively the meshing around a profile used during the conception of the hull for OMER 7 and the boundary conditions used for the tests that are used by the equations.

Figure 16 - Example of a CFD result

Figure 17 - Boundary conditions

Figure 18 - Final meshing example


2.6. Final hull

The final hull is a combination of naca16015 airfoil on the dorsal and naca16012 on the flanks. A “K-factor” (see section 3.2.2) of 2.2 was applied, with as a result a drag force 133 N. The hull on its own, however, does not allow the determination of the drag coefficient of the entire submarine. Other elements to be added on the submarine (such as the fins) will allow a more precise analysis.

Figure 19 - Final hull (see appendix II for more pictures)


3. Propulsion system

It’s trough the last competition and during tests in pool that several problems have been revealed in the propulsion system. As an example, the pilot felt that the reaction force in the pedals was not continuous, this resulting in a loss of power. A solution has been found to this obstacle and many others. That was a part of this year’s objectives along with the modifications to receive two people instead of just one and the addition of an electronic variable pitch system that controls the angle of the wings.

3.1. Parameters to optimize

Thanks to the knowledge acquired with OMER 6, some parameters have been aimed to be the ones to optimize on the new propulsion system.

3.1.1. Wings cart stroke

The first parameter to optimize is the total length of the wings cart stroke (a stroke represent an up-down-up cycle). In a complete cycle, two moments are particularly critical: the end of the stroke, or more precisely when the wings operate a complete change of direction. This represent a dead time were the power given by the pilot cannot be canalized. By increasing the cart stroke, there is more effective length for the same amount of direction change.

3.1.2. Synchronized system

Pool tests have shown that moments when the pilot was giving his greater push were timed with stroke’s dead moments. This was resulting in a great loss of energy and in a risk of injury for the pilot. This is why it is important to time the pilot pushing frequency with the stroke. A ratio of one revolution of the chain gear for a half cycle of the wings would be perfect. This would give a travel of one length (from the top to the bottom of the sub) for one legs revolution by the pilot.

3.1.3. Axis-to-axis distance

The axis-to-axis distance between the two pedal boards was an important factor in the conception of the new hull. It was established that the smallest possible value must be used to minimize the total length of the sub. Thus, the maximal axis-to-axis value was 24 inches.

3.2. Preliminary design

After numerous sketches, it was decided that the operation principle would be as seen on OMER 6, but with to pedal boards. A single cart will be cycling all the way from the top of the propulsion to the bottom transmitting the power to the wings. They will slide on two linear bearings on both sides of it. The following figure shows this concept.

PROPULSION – The main lines

1. Identify the parameters to

optimize;

2. Construction of the

propulsion system,

(numerical analysis on

SIMULINK);

3. Mechanical conception;

4. Variable pitch conception.


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Figure 20 - Propulsion system schematic

3.3. Propulsion system modeling

The first step to achieve the propulsion system’s modeling was to create a numerical model on the MATLAB SIMULINK software. The created algorithm includes every variable of the propulsion, namely available power, each sprocket teeth count, etc. Most precisely, this analyze will serve to determine the pilot leg ideal timing.

The results had shown that an angle of 90 degrees between the pedal boards revolution cycle is optimal. The following paragraphs list other decision that has been taken regarding the propulsion system.

3.3.1. Stroke and synchronism

The maximal stroke length, the synchronism and the cart speed are directly related to the chosen sprocket’s ratio. A maximal stroke of 23.5 in is imposed, as it is the maximum allowable length in the already conceived hull. A 1 m/s speed is aimed for the cart.

3.3.2. Standard sprockets

The first sprocket to consider is the one that will be mounted on the pedal board. The second links the pedal board to the bottom shaft of the second chain. The third, finally, is mounted on both the bottom and the top shaft of the propulsion system and carry the wings cart. All of them have to be chosen within a restricted amount of standard teeth configurations. All of those are listed below.


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Figure 21 - Sprocket positioning

Table 4 - Standard teeth configuration

Sprocket Chain pitch Available teeth configuration

N1 1/2 22, 24, 26, 28, 30, 32, 34, 36, 38, 39, 40, 42, 44, 46, 48, 52, 53 N2 1/2 13 à 21 N3 3/8 21 à 26, 28, 30, 32, 35

3.3.3. Optimization

A MATLAB algorithm finds possible sprocket configurations by choosing in table 4. The first sprocket is however limited to three choices. Indeed, a Shimano Alivio pedal board has been chosen to equip the new propulsion as it includes a 22, a 32 and a 42 teeth sprocket. By limiting the first sprocket to these choices, many possibilities are eliminated and therefore the calculation time shortened.

3.3.4. Final solution

Many possibilities that were given by the algorithm were plausible, but since some materials was already available at school without further investment (two 30 teeth stainless steel sprockets that left from previous OMER versions) it’s on the following solution that will be base the new propulsion system.

Table 5 - Final solution (propulsion system configuration)

Winning solution

Pedal board’s speed 100 RPM

Cart’s speed: 1.02 m/s

Total stroke: 21.96 in Center to center distance

(pedal boards): 18.375 in


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N1 32 teeth

N2 15 teeth

N3 30 teeth

This solution respect all pre-requisite, to be a rotational speed of approximately 100 RPM, a cart speed of 1 m/s and a stroke less than 23.5 inches long.

3.4. Propulsion system description

A big concern of the new propulsion system’s conception was to be able to position at the exact center of the submarine. The following figure shows that the propulsion is situated at 2.4 meters from the nose of the sub. Figure 23 shows the different parts of the system.

Figure 22 - Propulsion system positioning

Figure 23 - Propulsion system components


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3.5. Technical specifications

The following picture shows the speeds of the different moving parts. Appendix III shows the final CAD of the propulsion system.

Figure 24 - Technical specifications

3.6. Variable pitch

The variable pitch’s role is to adjust the wing’s angle of attack to conserve the optimal hydrodynamic properties at every moment (fig 25). Only an electro-mechanical system is able to achieve such task at a sufficient level. This is a problem since the amount of space needed by this system is restrained to the inside of the cart’s shaft. In concrete terms, this means a 2 inches diameter cylinder about 1 foot long.


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Figure 25 - Explanation of the angle of attack

3.7. Mechanical conception

In order to enables the variation of the pitch, a stop mechanism and a slide works together. This creates a kind of cam shown in figure below the denomination Female cam. This cam moves along with the wings and can be moved laterally with the help of the ball screw it’s connected to. When the wings are neutral in the water, meaning that they are totally horizontal, the male cam stays in the middle of the female cam’s triangular groves as shown on figure 27. As the angle of attack grows up, the side of the grove gets closer to the male cam until it reaches it and limits the angle of attack. To change the movement’s amplitude, a motor drives the ball screw that’s moves the female cam. This position is function of the RPM of the pedal boards and the speed of the submarine. Figure 28 shows multiple positions of the female cam at the maximum angle of attack.

Figure 26 - Variable pitch components


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Figure 27 - Variable pitch amplitude

The table bellow shows the mechanical parameters of the variable pitch.

Table 6 - Variable pitch mechanical parameters

Variable pitch mechanical properties

Smallest possible angle 8 degrees Larger possible angle 66 degrees

Total travel length 49 mm Travel length for a 1 degree variation of the

attack angle 0.8448 mm

Reducer ratio 111:1 Thread pitch 2 mm/rev

3.8. Electrical system

One of the predicted problems of the variable pitch system is the speed sensor’s lack of precision. If it’s effectively the case, its sudden data variation would have a too big influence on the angle of attack variation. A strategy to counter this would be to set the variable pitch’s chip to gradually lower the angle from the beginning to the end of the race. Another would be to derivate the optimal angle from the RPM of the pilot and the time since the beginning of the race. All of this will depend on the precision of the speed sensor.


4. Wings and fins

Two tasks were needed to get the OMER 7 wings knowing that knew wings have been made for OMER 6 last year. The first task was to modify the MATLAB program used to calculate the wings properties in order to, as an example, change the wings shape. The second task was to design the submarine wings according to the first task results.

4.1. Important parameters

To determine the wings dimensions to get a maximum speed, it is required to know all the parameters that affect the wings. The most important parameters for the wings are:

• The wingspan. This is a very important parameter in our search for the best solution. In fact, we will get more efficiency as the wing length increase.

• The aerodynamic wing foil. There is no absolute best wing foil. Each of them has its own properties and advantages. That’s why it is important to define the usage context in order to choose the wing foil that will fit the needs. The only parameter to respect in a first time is the « aeronautic » condition (see section 2.3.2).

• The pilot power. The main factor to reach our targeted speed is power. Of course it is important to maximize it but also to minimize the mechanical lost power.

• The wing’s surface. For a square wing, the length multiplied by the chord determines the surface. Thus, two wings can have the same lengths but different surfaces. For an elliptical wing, an integral equation is used to find the exact surface. There is no straight correlation between surface and the maximum speed. Each solution has to be evaluated separately.

• The submarine drag. The submarine drag due to the shell is important to consider. The faster the sub goes, greater the drag is. If the estimate drag is accurate, it is possible to find the right wing’s oscillations speed.

• The wing’s shape. The wing’s shape influence the induce angle by the lift. In three dimensions, a rectangular shaped wing’s end will cause more drag than an ellipse.

4.2. Calculation methods

Listing the maximum speed parameters is simple, but finding the best wing considering all the parameters is not. Fluid mechanics formulas are the first tools to use. Under is the lift coefficient formula.

Many today’s specialized softwares are to be used for the calculation of wing profile properties. The following figure shows the example of a graph about the lift coefficient that is function of the angle of attack.

WINGS – The main lines :

1. Optimal dimensions

(MATLAB);

2. Optimal profile (MATLAB);

3. Mechanical design

(CATIA) ;

4. Variable pitch design

(CATIA).


Figure 28 - 2D airfoil characteristics

Figure 29 - Light cutting wing section in 3 dimensions.

The knowledge of 2D properties not necessarily means that predictions can be done about real reactions. The lift line theory has been useful to develop a MATLAB algorithm to be able to calculate the lift force on several cross sections of the 3D wing.

Briefly, this theory gives basis to calculate the effect of wing tip vortex over an entire wing, according to its whole geometry. Those wing tip vortexes are created by the pressure difference between the air flowing above and under the wing. Following figures illustrate this phenomenon.

Figure 30 - Induced angle formation

Figure 31 - Wing tip vortex

4.3. Parameters influence

Once the important parameters are determined, it is possible verify the influence of each of them on the wing’s performances. Here are the main conclusions.


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• An increase of the wing lengthening increases the performances. In fact, a higher aspect ratio (square length divided by the width) leads to better performances in terms of speed. A thin wing however tends to be too fragile. This limits the application of this phenomenon.

Figure 32 - Lengthening explications

Figure 33 - Aspect ratio formula

• An elliptical wing shape leads to better performances. For the same surface and the same length, an elliptical shaped wing needs to oscillate at a lower frequency than a rectangular shaped wing. This means a greater wing’s efficiency under water.

Figure 34 - Elliptical wing’s parameters (wing overview)

• The power produce by the pilot have a direct effect on the submarine’s speed. It is not a linear phenomena due to the increasing drag force. Tests reveal that an average man could produce 750 watts for an approximate duration of 15 seconds.

4.4. Acquired Results

4.4.1. Profiles selection

The 5 best symmetrical airfoils were found during the study carried out for the wings of OMER 6. Here are the last results.


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Table 7 - Best profiles results

Airfoil J5012 fxl142k n63012a m3 lwk79100

Submarine speed (m/s) 2.5417 2.5410 2.5407 2.5404 2.5404

Oscillation speed of wings (m/s)

1.0467 1.0130 1.1372 1.1173 1.1402

Angle of attack (deg.) 5.0000 7.0000 5.0000 4.0000 6.0000

The J5012 airfoil has been selected for the conception of the new wing of OMER 7. However, this profile is not thick enough to contain the aluminum shaft used to tie the wing to the propulsion system. This is why a combination of this profile and of the GEO460 is used which allows more space to the internal structural elements.

Figure 35 - Airfoil J5012 et GEO460

4.4.2. Results of the final iteration

The caracteristics of the wings obtained in the iteration MATLAB are presented in the following table. A tridemensional model follows.

Table 8 - Optimal parameters of the wing

Parameters Values

Wing length (m) 0.85

Root chord (m) 0.17145

Area of the wing (m2) 0.098

Elongation 7.37

Angle of attack (deg) 6

Used power (watt) 1119

Submarine speed (knot) 7.577

Oscillation speed of wing (m/s) 1.187


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Figure 36 - Optimal tridimensional model of the wing

4.5. Construction of the wing

Table 9 - Generated strength by the final wing

Lift strength (N) 563

Drag strength (N) 50

Strength in the axis of the submarine (N) 236

The strengths of maximal reactions obtained during the movement of the chosen wing are exposed in table 9. It is from these strengths that the internal mechanical structure must be conceived. A preliminary conception realized with CATIA has allowed generating the model of the figure below.

Figure 37 - Representation of the final assembling of the wing and a picture of the parts inside the final assembly.

The wing covering is composed of fine layers of carbon fiber that offer an excellent surface finish as well as being highly resistant. The interior of the wing is filled with aeronautical foam in which an aluminum rod is inserted that links the wing to the propulsion system. To give even more rigidity to the wing, a carbon cone extends the aluminum rod inside the wing.


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4.5.1. Strength calculation and reactions to supports

The calculation of the reactions to supports was made from a little MATLAB scrip. We use the theory of the sum of moments to find the strengths corresponding to the places wanted. Figure 39 represents the strengths and moments involved on each component.

Figure 38 - Calculation of strengths and moments

For the different strengths found in the table 9 we find a total moment (MT) of 288 Nm. As a result, the strength at the end of the carbon shaft (FA) is 810.06 N and 1890.2 N for the aluminum cone (FI). From these data, finished elements analyses (FEA) were made with the aim to know the main constraints. It is from CATIA and from its composite materials and structure analysis modules that the tests were made. CATIA offers the possibility to conceive the layout of each fold of carbon and to create a material. It is then possible to visualize each of the folds, to know their thickness and orientation and most of all to know the constraints exerted inside each of them.

Figure 39 - Carbon fiber model from CATIA software


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4.5.2. FEA

For the aluminum rod, the FEA has allowed to target a weak zone (figure 39). This zone is located at the second section change and supports a load of 101 MPa. The assembly of the rod and the cone supports a restraint of 105 MPa while presenting a weakness at the joint level, between the carbon and the aluminum. According to these analyses, we find a security factor of 2.42 before plastic distortion.

Figure 40 - FEA of the insert from the CATIA software

Figure 41 - FEA for the ANSYS software

Figure 42 - FEA of the whole from the CATIA software

It is also important to verify the fatigue constraint. During a 100-meter run, the pilot gives a maximum of 75 spin of the pedal. After, it is necessary to make 4 spins on the pedal so that the restraint on the shaft switches from compression to tension to finally come back to compression. We calculate a maximum of 20 races during the competition.


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The piece cannot brake in fatigue considering the really small number of cycle it receives. Moreover, the forces used in the analysis occur only at the maximum speed of the submarine. We can then say that the constraint that has been calculated is not going to be repeated 375 times, but more around 50 times.

To validate the resistance and the methods of fabrication of the composite shaft, a destructive essay on two shafts has been realized. Only the application methods of the carbon fiber differed from one essay to another. In the first test, the “Wet Lay-Up” method has been used, while for the second, pre impregnated carbon was used as raw material. The results were beyond expectations for the two processes. The following figures show the rupture of each test that was carried out.

Figure 43 - Result of the shaft realized with the « Wet Lay-Up » method

The rupture of the shaft fabricated with the “Wet Lay-Up” method has resisted to a force of 2403.45 N. This force gives a security factor of 2.97. This security factor greatly fulfills the level of resistance required.

Figure 44 - Result of the shaft realized with « Prepreg » carbon

The rupture of the shaft fabricated with the « Prepreg» carbon method has resisted to a force of 3776.85 N. This test fulfills even more the requirements needed since it is not the carbon shaft that gave way but the complete assembly. We obtain for this test a security factor of 4.66. It is this method that is used for the construction of the wings of OMER 7.


5. Fins

The fins and the stabilizers of the last three submarines, including OMER 6, have been positioned more or less randomly. In fact, they were positioned at some place that looked adequate, but no calculations or analyses have been done for this. This method generated a lot of stability problems at the last competition. Four stabilizers have been added during the 2007 competition on OMER 6 to complete the races. To avoid this situation, OMER 7 has been analyzed. It will help to obtain better results in race and avoid errors.

5.1. Determination of hydrodynamic coefficients of the hull

The hydrodynamics coefficients of the various components of the submarine have been used to determine the lift and drag generated by the fluid on the components. These coefficients have been inserted in the model to evaluate the submarine’s behavior. The hull’s hydrodynamics coefficients have been calculated with the application FLOWORKS of the software SOLIDWORKS 2008.

Figure 45 - Analysis environment of the hull

The equations of the lift and drag coefficient in function of the angle of attack for both the XY and XZ plane have been determined. An example of the equation of the lift coefficient on the XZ plane is displayed below (where x is in degrees).

5.2. Pressure center’s position

The pressure centre’s position is the spot where the lift and drag forces are applied. This position is the average location of pressure’s gradient on the hull. It can be calculated by the equation below.


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Figure 46 - Equation of center of pressure where p(x) is the pressure function of the position profile

To determine the equation of the pressure in function of the position, many pressures have been collected at different location on the hull. Each equation is based on 20 points; 10 on the inner surface of the hull and 10 on the outer surface of the wing. The pressures of the points with the same location compared with the line chord have been added together.

Figure 47 - Positions of the pressures obtained for the calculation of center of pressure.

Thereafter, the center of pressure has been calculated. This position varies in function of the angle of attack. The calculation of the pressure center has been done at many attack angles. Its position has been fixed at 2169 mm compared to the nose of the hull. Having the pressure at a fixed spot simplifies the model. Its variation is thus negligible.

5.3. Determination of the fins’ and stabilizers’ hydrodynamic coefficients

The fins used on OMER 7 are the same than those used on OMER6. The evaluation of the hydrodynamics coefficients allows knowing the influence of the fins and stabilizers on the submarine’s handling.

The fins have been made from a NACA0012 airfoil swept on elliptical form. The fins are also used like stabilizers. The hydrodynamics coefficients of these profiles have been analyzed in the software


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COSMOSFLOWORKS. The fluid parameters are the same than those used for the analysis of the hull. This means that the fluid is water and the speed 1m/s.

Figure 48 - Fins in its boundary box

Figure 49 - CFD analysis in COSMOSFLOWORKS

The analysis environment of the fins is dimensioned to ensure that the surface of fixation between the hull and the fins is the limit of the environment. In this way the effect of the hull of the submarine on the hydrodynamics of the fin is approximate.

5.4. Results

All the previous information has been incorporate in a SIMMECHANICS model. This model allows simulating the comportment of the submarine in a dynamic way.

The optimal position of the fins is near to the submarine’s tail to obtain force acting with a long enough lever. It is this moment that generates the change of direction of the submarine.

The determinations of the stabilizers’ optimal position have been done by three tests. First, the submarine has been simulated without fins with different positions of stabilizers. The submarine had an initial attack angle of ten degrees and the analyzed parameters were the time of stabilization and the change of depth in 60 seconds.

A second test has been done with the PID controller. The submarine had to go up until 0.5 meter. The analyzed parameters were the stabilization time and the movement of the fins. The third test was the same as the second. But, the difference was that the submarine had to go up until 2 meters instead of 0.5 meter.

In summary, the tests demonstrated than the dorsal stabilizers must be positioned as far as possible of the gravity center. Unfortunately, the doors prevent to position the stabilizers in an optimal way.


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They will be positioned as close as possible from the optimal spot. The laterals stabilizers must be positioned at equal distance from the wings and the fins to reduce their influence. This position represents a good compromise between the stabilization time and the fins’ movement.

6. Security system

The security system of OMER 7 is a new concept; it will be pneumatic and mechanic at the same time. Of course, some the competition specifications have to be respected and it’s having that in mind that it has to be designed.

First, a door opening system from the inside of the submarine is required. Secondly, a “dead-man switch” security system will be installed on the submarine. This competition’s minimum requirement forces the teams to place a buoy that will be automatically launch by the pilot in case of distress. In OMER 5, this buoy was a door situated at the back. This idea will be reused in OMER 7. Finally, it will be really important to design systems that protect the two pilots. Thus the system should be redundant and designed to avoid failures. In addition, the triggering mechanism of the buoy will be combined with the door opening system. This will open the doors in case of distress in addition to facilitating the rescue of the pilots by the divers. It will also ensure that the pilot won’t get stuck in the event of a system failure.

6.1. System operation

Here is a brief summary of operating requirements:

Figure 50 - Requirements and operation of security system

Systems Operations Requirements

Doors opening system

Order the doors open when the pilot inside the submarine wishes

• A driver opens the doors by pressing a

button in order to coordinate efforts at the end of the race and for the security.

• The lock system is operated by a system of pneumatic cylinders.

• Each driver has in his possession a button to order the opening.

The triggering mechanism of the buoy

Order the doors open and the triggering of the buoy if the pilot loses consciousness or is in distress.

• Pilots must maintain in position at all times a button pressed. When this valve is released, the buoy and the doors of the two drivers are released.

• In case of system failure, it must be

impossible to be trapped inside.


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6.2. Presentation of the pneumatic diagram

Figure 51 - Pneumatic system’s diagram

The schematic of the system in figure 50 shows the different components used and the connections needed in order to do the actions wanted. The two manuals valves at the right are the valves for the triggering of the safety buoy while the two valves at the left will be used for the doors opening. It can be easily seen that if one of the two security valves is released, the two doors are released and the safety buoy is launched. It is important to clarify that the ejection of the doors is done by the withdrawal of the cylinder. Moreover, if one of the air ducts is disconnected at any point in the system, the cylinders automatically release the doors of the pilots.

6.3. Design of the doors opening system

The mechanism used for opening doors is composed primarily of a pneumatic actuator, a linear rail and a spring. The cylinder is supplied with air by the circuit shown in figure 50 and is shown in figure 51. The linear rail serves here as a slide to facilitate the opening of the door and must be dimensioned correctly to take the moment imposed by the clasp. The spring is used to prevent a pilot to be trapped in the submarine. Thus, if a lack of air, opening of the door will be done automatically. Moreover, the mechanism must be removable to allow the installation of the propulsion in the submarine.


Figure 52 - Modeling of closing mechanism

6.4. Placement of the elements in the submarine

Figures 52 and 53 below show the location of major components in the submarine. Feeding tubes and valves of logic were not modeled because the size of these components is negligible.


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Figure 53 - Components seen from the front of the sub

Figure 54 - Components seen from the front of the sub


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Table 10 - Safety system detail

NO. QTE. NOM DESCRIPTION

1 2 Door opening valve NVM230-N02-08

2 1 Pop-up buoy switch Manufactured (OMER) 3 4 Air container 13 PI

3 Already in stock

4 1 Dead-man switch Manufactured (OMER) 5 2 Door releasing system Manufactured (OMER) 6 3 SOUTHCO Latch SOUTHCO 7 1 5/2 pneumatic valve SYA5120-01T

7. Electrical system

One of the key aspects of OMER 7 is its electrical system. Although this sub is conceived to be able to work completely mechanically, a network of independent electro-mechanical systems and communication software have been set up to enhance its performances. Next sections will cover the whole concept behind it the electrical components of the new sub, present each component individually and show OMERLINK, the software developed to store races’ data and to monitor sub’s performances.

7.1. Electrical system’s conception

The electronic system of OMER 7 is built according to the CAN system, the same for the cars. This allows every module to be totally independent from one another. If need be to modify the system in the future, the modules could be added or removed without affecting the global efficiency of the system. Here are all the modules onboard will be described in the next section.

Thanks to the CAN protocol, the communication between the modules is made at high speed and with an excellent management of the sources of mistakes. It operates by a really simple process; modules are just releasing information they want to share with other modules on a common line when their turn comes. This line is carrying all the information relevant to every module in addition to the electrical power coming from the batteries located at the rear of the sub. If a module wants information, it has to wait to its turn and to catch data travelling through the line. Those “turn” are commonly called “token” and they ensure certain cohesion between modules, meaning that they can just speak or listen following a certain order that is repeated again and again. In concrete terms, if the RPM modules wants to send information the LCD screen, it will release the value on the line and the next time the LCD will own the token it will receive it an display it. If the LCD is removed, the RPM module will not be affected and will continue to send the value turn after turn.

Every electronic system will evolve in the worst environment for the electronics: water. That is why the power team and the mechanics team have worked jointly on the conception of waterproof and independent modules. This way, every electronic circuit is confined in a custom-made aluminum box and cleverly designed to reduce as much as possible the water infiltration hazards and allowing the circuits to support pressure variations when they will be immerged.


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7.2. Modules

Many aspects of a submarine can be driven electrically. The rudders are a good example of something that can be electrified in order to ease a race and to ensure fast response. Many feature can however be obtained only by the addition of some electronics, like a post-race data analysis. Here is a description of each of the modules that will be in OMER 7.

7.2.1. Onboard monitor

With the aim of creating a tool to help the pilot to manage efficiently his energy, a LCD screen will be mounted in OMER 7. This 160 by 128 pixels monochrome LCD screen will display information about the sub status. The RPM, the sub speed, the time and the depth will be displayed as big green digits that will evolve in real time. In addition, the pilot can reach two magnetic switches at any time. The first one is to start and to stop the data recording. At the beginning of a race, the pilot toggle it on to start the internal clock that is displayed on the screen and to start sending information to the master. He only needs to toggle it back off to stop this process. The second switch…

This is without a doubt one of the key feature of OMER 7. By the past, one of our pilots’ most frequent comment was that they weren’t able to gage well enough the race distance to be at their optimal force all race long and in the maximum speed trap. This is particularly important due to the air quality that is really not the best. This module, obliviously with the help of all sensors in the sub, will solve this problem.

Figure 55 - LCD screen

7.2.2. RPM, pressure and speed modules

The RPM is a key element of the propulsion and of the variable pitch. Being the frequency of the pedal board rotation per minute, it indicates how many cycles the wings are doing. This information,


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along with the speed module’s one, enables the developed power calculation. This is particularly when comes the time to evaluate a pilot’s performances and the sub efficiency after a race. More importantly, the speed and the RPM together give the real speed of the wings in the water and the direction of the flow. This data is needed to gives the angle to the wings in real time with the variable pitch system.

The speed itself is also important for the pilot as it gives him a motivation and an indication on when to give a boost. The pressure is for its part helpful to keep the same depth in water for the entire race.

Figure 56 - Computer routing of the RPM PCB

Figure 57 - Speed sensor in its casing

7.2.3. Joystick

It’s with the help of a joystick that the four rudders can be controlled. By the simple movement of his thumb, the pilot can precisely direct the sub. All he has to do to get the rudders back in the neutral position is to let the joystick free or to put it in its central position. This was not the case in OMER 6 where the mechanical system was made of wires and of a big metal lever for the depth control and of a twisting rubber handle for the left-right control. This was forcing the pilot to gage each rudder’s neutral position at the beginning of each race to be able to keep it during the race.


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The OMER 7’s handle is composed by to printed computer boards (PCB), one supporting the Game Cube’s joystick and the other the chips and other components. The ergonomic handle is made of aluminum and of a rubber cover that protects that joystick at the same time as it lets it moves.

7.2.4. Master

With the need to see all race data at the end of it comes the need to store the mat least for the race duration and the need to transfer them to a nearby computer. The master fulfills all those demands. With is internal memory, its USB key and its ability to send information through the air using Bluetooth technology, it is the ultimate communication tool. The RPM, the speed, the depth and the wing’s angle of attack are all stocked in function of the time since the pilot turn the switch in the LCD screen. When the sub is carried at the surface of the water at the end of a race, software receives the info and analyzes them. The USB key stays there as a backup system and an extra storage system.

7.2.5. Direction

The direction system is composed of three sealed cases that each contains a servomotor, a mechanical system linking it to the rudder’s axe and the electrical hardware to drive all of this. The rudders have a travel of 30 degrees on each side, which gives 60 degrees total amplitude. Limit switches ensure the respect of those boundary values. At the startup of the electric system, an algorithm finds the neutral position of each rudder by moving it against the limit switches. That way, neither the pilot nor the mechanical team has to wonder about the direction of the sub during the race!


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Figure 58 - Direction components

Figure 59 - Direction casing (first in front)

7.2.6. Variable pitch

The variable pitch is an electromechanical system that automatically adjusts the angle of attack of the wings to maximize the performance of the propulsion system. Everything is done according to the race data given by the RPM and speed modules. Once each second, the angle of attack of the wings is adjusted according to a hydrodynamic calculus. However, mechanical specifications of the screw that is driving the system are imposing variation limits. In other words, the angle of attack cannot change radically. Even if this seems to be inconvenient, it isn’t so. In fact, this prevents sudden change caused by the irregular power that the pilot is bringing.

On the hardware side, the variable pitch system has demand an effort of miniaturization and optimization. As shown on figure 59, many electrical components, like a motor, and encoder and a PCB had to be fitted in a watertight space along with mechanical elements. For this reason, many casing parts are non-standard and have to be machined. Figure 60 shows a test that has been done prior to the final conception of the variable pitch.


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Figure 60 - Variable pitch inner part

Table 11 - Variable pitch detail

Item Description Material Qte Source

1 Motor plug Aluminum 1 Manufactured 2 A-max 26 Maxon motor Misc 1 Bought 3 6-32 x ½ flat head screw Stainless steel 9 Bought 4 Motor support Aluminum 1 Manufactured 5 Coupling Aluminum 1 Bought 6 M3 x 10 SHCS Stainless steel 8 Bought 7 M2.5 x 8 mechanical screw Stainless steel 4 Bought 8 Limit switch Plastic 2 Bought 9 Bearing support Aluminum 1 Manufactured

10 WBK06R-11 support unity Stainless steel 1 Bought 11 RMA08-01C7S-180 ball screw Steel 1 Bought 12 Female cam Aluminum 1 Manufactured 13 Bearing support Aluminum 1 Manufactured 14 698 bearing Stainless steel 1 Bought 15 ¼ x 7 in tube Stainless steel 1 Bought 16 Slide Stainless steel 1 Manufactured 17 Plug Aluminum 1 Manufactured 18 PCB Misc 1 Manufactured 19 Variable pitch’s principal shaft Aluminum 1 Manufactured 20 Wire support Aluminum 1 Manufactured


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Figure 61 - Variable pitch test

7.2.7. OMERLINK and OMERSIM

OMER 7 will be equipped with systems that can be readjusted, calibrated and/or improved from a distance. This semi-intelligent system is accessible by simply connecting a computer to the Bluetooth wireless communication protocol attached to the system. In order to do this, some software had to be developed. These softwares will ensure three tasks:

• Configure electrical components;

• Analyze submarine’s performances after a race;

• Analyze pilot’s performances in an indoor simulator

The two softwares conceived by OMER’s members are OMERLINK and OMERSIM. While the first communicate with the sub wirelessly and can display race’s data and send command to the sub, the other can be connected directly to a National Instrument card that translate information coming from a RPM sensor and a load cell. Those two instruments are used in a basin big enough for OMER 6 to fitted in. This way, pilots can get real training before the competition.

OMERLINK is really a tool that will help the entire team. Having it, the whole adjustments can be carried out by a person who does not know electronics, but who is comfortable with the fundamental notions necessary to the mechanism of a submarine with the help of the graphics


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interface and the automatic data transmission. In addition, an entire race can be simulated, meaning that all the software sends information on the line in order to verify the module’s reaction. Everything is display on screen, even the movement of the joystick! When the sub is out of the water, every single action of the electrical system is displayed on the computer.

Figure 62 - OMERSIM software


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Figure 63 - OMERLINK sofware


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Conclusion

Many efforts have been put throughout the year to get the best submarine out of the shop. The past

years have brought to the surface many defects of OMER 6 that have been corrected for the present

version of OMER.

The new wings, which are longer and narrower, the new hull, of which the hydrodynamic has been

studied, the new security system and the new electrical system will for sure help the OMER team to

push further the speed limit for a two person submarine. All of those innovations, along with the

ability to record races’ data and to analyze them, are great additions to this sub.

The fabrication methods are also not to be forgotten. A better way to mold carbon fiber has been

applied for the hull and the wings, and new machines have been used by OMER members to achieve

certain complicated parts. The result is a good-looking submarine that shears the water and that can

resist long enough. Pushing it to its limits will be possible.

Tests in pool will have to be done before the competition to ensure a good team work at the

competition. The real test will perhaps stay the 10th ISR!


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Appendix I

Figure 64 - Drawing of the whole sub


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Appendix II

Figure 65 - Drawing of the hull


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Figure 66 - Half of hull (laminated with resin infusion system)

Figure 67 – Foam core preparation for sandwich laminate process


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Appendix III

Figure 68 - Propulsion system

omer 7 - final design reportv2chemori/temp/jyothsna/fish-modelling/fins_propuls… · final design...

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