senior design project optimization of the oscillating ...optimization of the oscillating hydrofoil...

HPS – Optimization of Oscillating Hydrofoils ___________________________________________________ 1

Senior Design Project

Optimization of the Oscillating Hydrofoil Propulsion System for the Human Powered Submarine [1]

Sarah Blake Scott Eaton Mary Girard

Hassan Mazi University of Maine

Mechanical Engineering

May 7, 2004

ABSTRACT The mechanical engineering department’s Human Powered Submarine is powered by two sets of oscillating hydrofoils. Coupling the two sets of hydrofoils requires a connecting link with a rotating arm. Mounting the propulsion system to the hull requires a composite internal frame and housings. Testing showed that the new coupling method allows for smooth motion through the full hydrofoil cycle.

I. INTRODUCTION The Human Powered Submarine Contest is an annually held student competition. It is alternately hosted by the American Society of Mechanical Engineers (ASME) and International Submarine Races (ISR). The University of Maine’s mechanical engineering department has been working since the fall of 2001 on a submarine for this competition. Past senior design projects have dealt with design and fabrication of the hull, controls system, and the ballast and buoyancy controls [2, 3, 4]. The senior design projects dealing with the HPS for 2003-2004 include this project on the optimization of the oscillating hydrofoils and another project dealing with the ergonomics and safety. The department hopes to enter their submarine in the competition for the first time in the summer of 2005.

Design groups from previous years have purchased two MirageDrives from Hobie Kayak, a kayaking outfitter [5]. See Appendix A for patent information. Each drive, as shown in Figure 1, consists of two oscillating hydrofoils designed to be operated with a stepping motion. The propulsion mechanism of the submarine consists of coupling the two MirageDrives.

Figure 1: Labeled Diagram of Hobie MirageDrive

II. PROBLEM DEFINITION The first design problem with the submarine was to attach the two sets of oscillating hydrofoils together. Each MirageDrive has two input links, which move in opposite directions. The original connecting method connected the input links on each side of the MirageDrives with a single connecting link. This formed a four-bar linkage, as illustrated in Figure 2. The problem with this method is that it prevented smooth motion through the hydrofoil cycle, resulting in a rocking motion of the foil set. Another problem with the original connecting link design was that the bolts used to attach the connecting links to the input links rubbed against each other during a foil cycle.

Input Links

Pin

End Mounts

Input LinksPin

Support


Figure 2: Original Connecting Link Design

The second design problem was mounting the hydrofoil sets to the submarine hull while keeping the support completely fixed. The submarine hull has a foam core which is weak in compression, so a large surface area is needed for mounting. Past senior design groups were unsuccessful in achieving an adequate bond area [2].

III. PROJECT OBJECTIVES Our task was to optimize the oscillating hydrofoil propulsion system for the human-powered submarine. Specific results of this project were desired to solve the two problems described. These results are:

• Design of connecting links between two hydrofoil sets

• Fabrication of connecting links • Design of mounting and boundary conditions for

hydrofoil system • Fabrication of mounting system • Test and installation of propulsion system

IV. DESIGN APPROACH There were two design concerns for this project. First, how to effectively connect two hydrofoil sets and, second, how to attach the hydrofoil sets to the hull.

A. Comprehension of Hobie MirageDrive Mechanics 1. 3-D Modeling. Given the complex function and geometry of the Hobie MirageDrive, it wasn’t easy to analyze the mechanism without modeling. It was worthwhile to invest the time in creating a 3-D model to approach the problem. There were two objectives for modeling: 1) to visualize and understand the previous design problems and 2) to analyze and critique the proposed design solutions.

The starting point was to understand the Hobie MirageDrive mechanism. After determining the important parts that would affect the design, the Faro Arm Platinum Coordinate Mapping Machine (CMM) at the Advanced Manufacturing Center (AMC) was used to get dimensions. These parts were modeled and the MirageDrive was assembled using Pro/ENGINEER. Refer to Appendix B for nomenclature and filename description. The assembly of the final model of the MirageDrive is shown in Figure 1.

2. Mechanism Analysis. The chains and cables were not modeled since it would be time-consuming and the Student Edition of Pro/ENGINEER doesn’t support cables or flexible parts. Professor Senthil Vel suggested splitting the MirageDrive into two sections as shown in Figure 3. The top section consists of the fins and the fin axes – the bar the fins rotate about. This section is used to determine the force that the chains would exert on the wheel given an applied force on the fins. The bottom section consists of the support, the wheel, and the input links. The applied forces on the fins were roughly estimated as illustrated in the Appendix C.

Figure 3: Top and Bottom Sections of Hobie MirageDrive Model

Thus, in order to mimic a full MirageDrive cycle, the fins were assumed to move from 0 to ± 87.5° and the input links were assumed to move from 0 to ± 40°. A total of four position drivers – per MirageDrive – were setup to


provide the required range of motion. Refer to Appendix D for step-by-step instructions for running the analysis.

3. The Pin Separation. The most important design parameter is the pin separation – which is the vertical distance between two MirageDrive pins. This parameter is critical since it has an effect on the submarine’s drag, design of connecting link, and the operator’s leg room. The first-pass design had a pin separation of 26 inches. In order to test this configuration, a boundary that represents the inside of hull was created to observe the behavior of the MirageDrives. This way, the design could be checked, for example, to see if the operator has enough leg room. A range of pin separations was tested and the design was qualitatively assessed. The final design has a pin separation of 24 inches which allows for full motion through a hydrofoil cycle, provides adequate leg room for the operator, and minimizes the drag. The choice of a pin separation of 24 inches also depended on the analysis described in the next section.

B. New Connecting Link Design Process 1. Solving the Problem. Using the techniques of Design I (MEE 380), the first length of a connecting link was graphically determined [6]. A part called the Connector was created as a channeled bar (Figure 4). The animation of the mechanism was then started. An error showed up saying that there is not enough tolerance in the mechanism. Hence, the tolerance (i.e. the maximum allowed movement from the joints) was increased from 0.001 to 0.1 in. The animation ran, however, it was not smooth as the forces at the joints were high. With that being said, the cause of the unsmooth or “rocking” motion was detected; a constant length connecting link doesn’t work.

Figure 4: Model of Channeled Bars

This issue was investigated in detail to determine the required link length. In Pro/ENGINEER, a parameter called “Link Length” was set to measure the distance between the two pedal positions through the cycle. It was found that the required link length changes as a function of the pin separation through a cycle as shown in Figure 5. Hence, a new design with better understanding of the problem was proposed.

Figure 5: Required Link Length as a Function of Pin Separation

2. The New Design. The basic design of the new connecting link is similar to the old one; aluminum bars with channels to hold the MirageDrive input link. The new one, however, is wider to contain a rotating arm – that accounts for the required change in length – and has a nominal length obtained from the previous plot. This new mechanism creates a five-bar linkage as shown in Figure 6. Refer to Appendix E for the connecting link CAD drawing and Appendix F for notes on this new design.

Figure 6: The 5-Bar New Connecting Link Design

Link Length as a Function of Time and Pin Separation

11.0

11.2

11.4

11.6

11.8

12.0

12.2

12.4

12.6

0.0 1.0 2 . 0 3 . 0 4.0 5.0Time (sec)

Con

nect

ing

Link

Len

gth

(in)

X=24 X = 25 X = 26 X=27


Final sizing of the new connecting links was dependent on hand calculations as well as Pro/Engineer modeling. These calculations can be seen in Appendix G.

3. Model Analysis. A 3-D model of the connecting link was built to test the design and determine if there are any toggle positions. It was also used to select the length of the channels, and the width of the links. Different types of standard bolts were tested to ensure that the links have enough clearance space to move.

C. Design of Mounting Solution As mentioned earlier, it was important to attach the hydrofoils to the hull over the largest surface area possible. It was determined the best way to accomplish this was to build a frame inside the hull that would extend outside to hold the hydrofoils. The frame consists of two hoops, one at the front of the foil sets and one at the rear. Each hoop has a tab extending through the hull at the top and the bottom.

A housing, which attaches to the tabs, surrounds each MirageDrive and supports it at the pins and end mounts. There are a total of eight housing pieces. Four housing pieces are rectangular in shape and have the function of holding the pins. The other four housing pieces are half-moon in shape and restrict the end mounts of the hydrofoils.

Once a rough estimate of the inner profile of the hull was obtained, it was used to create a model of the hoops. The MirageDrives and the connecting links were positioned at the center of the hull. From there, drawings were created to determine the required length of the tabs.

D. Material Selection 1. Finite Element Analysis. As a part of design analysis, the 3-D model was used for finite element analysis (FEA) with Pro/MECHANICA. The selected material for the connecting links is aluminum and no further analysis was performed. On the other hand, the material selection for the hoops needed more careful investigation. Our current analytical background was not sufficient to determine stresses and consequently material selection. Hence, FEA models of the hoops were used to help in the process. With the resources available, there were two options for hoop manufacture, either chopped glass fiber or woven glass fiber fabric.

2. Effective Engineering Properties. Since there is not enough research on stress analysis of chopped fiber, Professor Vel was consulted. He suggested that an under-estimate of the engineering properties of chopped fiber would be to use the properties of the epoxy (Appendix H). The ultimate tensile strength of Fibre Glast Epoxy Resin 2000 with Hardener 2060 is

45,170 psi, which is not enough to withstand the estimated stresses on the hoop. Therefore, the chopped fiber hoop did not satisfy the design criteria.

The other alternative was to over-design and use glass fiber with wood core. A first-pass analysis was performed by assuming the properties of white pine wood. The hoops seemed to withstand the applied load with much less deformation. The second pass involved using a very specific stacking sequence as in Appendix I. Using a Mathcad program, Appendix J, the effective engineering properties of the fiber glass composite were estimated. These values were input into Pro/MECHANICA and further supported the design choice of glass fiber with a plywood core.

V. FABRICATION Parts were required to solve both problems for the oscillating hydrofoil propulsion system. This section describes the fabrication process of each part produced.

A. New Connecting Link Design Each new connecting link design consists of two parts: a channeled bar and a rotating arm. There are two new connecting links for the hydrofoil propulsion system.

1. Channeled Bars. Each channeled bar was machined from aluminum. The through holes have 3/8” diameter for standard machine screws. Holes for the pedals were made adjustable at two positions. The pedal pin thread is 9/16”-20 which is the standard English bike pedal. Left- and right-hand thread taps were provided from Rose Bike Shop.

2. Rotating Arms. The small rotating arms that complete the linkage were originally made from purchased brass parts which were modified, as shown in Figure 7. After these parts disappeared with time running out, the rotating arms were made from steel mending plates. This was adequate for testing, but machining parts from brass or stainless steel will be necessary for greater strength and corrosion resistance.

Figure 7: Brass Rotating Arms

3. Assembly. For dry testing purposes, emphasis was paid to ensure that the connecting link design solves the problem. Hence, the issue of selecting machine screws was put on hold. Aluminum posts and screws (also called Chicago Bolts) which provide the smallest head


height in the market were used. This way, side link clearance was insured.

Since the tapped holes were too wide for the aluminum posts, aluminum spacers (or sleeves) for #10 screws and different outer diameters were used. The inner diameters of the spacers were then bored using a 13/64” reamer to fit the aluminum posts. Figure 8 shows the final assembly of the new connecting linkage.

Figure 8: Final Connecting Link Assembly

B. Hoops The basic composition of the hoops is glass fiber with a plywood core. Layers of coarse woven boat glass fiber with a 0°/90° weave were chosen for the majority of the part because of its high strength. A medium 0°/90° weave, less coarse than the boat glass fiber, was used on the outside of the tabs for a smoother appearance. Unidirectional carbon fiber was added to reinforce areas with stress concentrations. Two pieces of plywood ¾” thick were used as two main core pieces in the composite. The plywood was cut a little smaller than the mold with a jigsaw. Small pieces of foam core were used as supplementary core pieces and were placed between the two pieces of plywood.

See Appendix K for photographs of the hoop making process. Also, see Appendix L for additional information on materials used for part fabrication.

1. Test run of mold creation and lay up. Before the time and materials were invested into making the molds and final hoops, a small test piece was made. The purpose of the test piece was to establish good procedures and techniques for the hoop composite making. The test piece was made in essentially the same way as described below. It led to using a disposable mold for the hoops, vacuum bagging, closer sizing of the core, and addition of foam core pieces. See the final test piece in Figure 9.

Figure 9: Composite Test Piece

2. Mold creation. The hoops were each made in two pieces, so that they could be inserted into the hull and bonded together. Each hoop was divided in the middle of the curve on both sides of the hoop to form top and bottom halves. In order to make the hoops fit the inside of the submarine, it was first necessary to obtain the profile of the hull. Since no drawings were available, cardboard was cut to fit inside. For each hoop, a mold was made from three layers of 1” thick insulation foam, which were glued together with a hot glue gun. The bottom layer was left whole, while a hole was cut through the top two layers to fit the profile of the hull, with the larger, front profile on top. The desired shape of the tabs was cut from the top layer.

Body filler was used to smooth the mold and create a non-porous surface on which to lay up the composite. The mold was first coated in epoxy to prevent the body filler from reacting with the foam. Then, body filler was applied and sanded using assorted 3M sandpaper. Two coats of sandable, non-glossy primer were sprayed on the smoothly sanded bodyfiller, with light, wet sanding between coats using 3M 400-grit sandpaper. Three coats of Krylon enamel spray paint were applied. Several coats of Turtle Wax carnuba wax were applied to help release the part from the mold. A final picture of the hoop mold can be seen in Figure 10.

Figure 10: Final hoop mold, before lay up

Rotating Arms


Note: After the part cured, the paint and primer did not pull off from the part and had to be sanded off. A good technique to allow for molds to release off parts completely was not found and this problem was also encountered by other senior project design groups working with composites. Aluminum flashing was used to separate the two halves of the hoop. It was cut to fit inside the mold, covered with body filler, sanded, primed, and painted, then attached to the mold with modeling clay/poster adhesive. 3. Lay up. See Appendix I for the lay up of the hoops. Figure 11 shows some of the materials used for lay up.

Figure 11: Selected Lay Up Materials

The epoxy chosen for the hand lay up of the hoops was Fibre Glast Epoxy Resin 2000 with Hardener 2060. The Fibre Glast Hardener 2060 has a pot life of 60 minutes and is a more favorable working resin for this complicated lay up. This epoxy mix has a cured tensile strength of 45,170 psi. See Appendix H for data on Fibre Glast products. It was mixed by weight using a 5-lb capacity scale. For each layer of fiberglass, some epoxy was dribbled onto the strip, and the strip was wiped with a plastic scraper, then it was pressed into the mold.

A layer of Fibre Glast peel ply was laid on top of the laid up part. Two layers of Fibre Glast bleeder fabric were placed on top of the peel ply. Additional bleeder was added to lead to the female end of the vacuum port used. The hoop was vacuum bagged directly onto the foam mold to apply a constant pressure over the part to eliminate epoxy rich areas in the finished part. A large rectangle of dum dum adhesive tape was applied around the curing part. A piece of Fibre Glast vacuum bagging material, 4’ x 6’, was attached to the mold. Small pieces of dum dum were used to make creases in the vacuum bag to allow close draping over the three dimensional part. The vacuum was pulled for 24 hours

using a Precision Direct Drive Vacuum Pump. Figure 12 shows the vacuum being pulled on one of the hoops.

Figure 12: Pulling Vacuum on Hoop Mold

4. Finish work. Once the part was broken from the mold, it had to be sanded to remove any extra body filler, primer, and paint. Extra composite material was removed using a Dremel tool borrowed from Professor Peterson.

There were ridges present in the inside of the finished hoops. A mix of Fibre Glast Epoxy Resin 2000/2060, Fibre Glast talc filler, and milled glass fiber was used to smooth out the ridge. This mixture was spread into any grooves found in the hoop.

C. Housing There are a total of eight housing pieces. Four housing pieces are rectangular in shape and have the function of holding the pins. The other four housing pieces are half-moon in shape and restrict the end mounts of the hydrofoils.

1. Housing Parts for Pins. The rectangular parts on the sides of the housing were made from fiber glass/epoxy composite with plywood cores. A flat Plexi glass surface was used to lay up the parts. This surface was waxed and a layer of peel ply was laid down before the lay up of the fabric began. Three layers of medium 0°/90° weave glass fiber fabric were hand laid down. The core was laid on top, and then three more layers were molded over the top and sides of the core. A layer of peel ply was placed on top of the part and then two layers of bleeder fabric cut exactly to size were laid down. Additional bleeder was added to lead to the female end of the vacuum port used. Each part was individually vacuum bagged using plastic bagging material and dum dum.

After the parts had cured, the excess fabric was trimmed off using a Craftsman Router borrowed from Daniel Fiore. Holes were cut to fit bearings for the pins, with a milling machine and a starter bit. The holes were

Bleeder

Peel Ply

Foam Core

Medium Fabric

Coarse Fabric


coated in epoxy to seal out water, and 0.5” hole diameter brass bearings were inserted. It was determined after initial fittings with the Hobie MirageDrives that additional padding material was needed at the end of each rectangle to form a perfect box around the foilset. The padding was made using Fibre Glast Epoxy Resin 2000/2060, milled fiber, and Fibre Glast chopped fiber to get a viscous consistency. The padding was applied using small rectangular molds made out of plastic covered aluminum flashing taped together. These molds worked surprising well once the right consistency was achieved. Figure 13 shows the finished housing parts.

Figure 13: Parts for One Housing

2. Housing Parts for End Mounts. The half moon shaped parts that fit on the ends of the tabs were made using the same method as the rectangular parts. Holes were cut in the bottom of each part so that they fit over the end mounts. The holes were cut using a milling machine and then, coated with epoxy for waterproofing.

Strips of coarse 0°/90° weave boat glass fiber were laid up on each part as shown in Figure 13, in order to bolt these end mount pieces to the tabs. Holes were cut in the strips to line up with the holes in the tabs.

3. Corner Braces. It was decided that the rectangular parts of housing should be attached using corner braces. Due to the high cost and waiting time involved in ordering stainless steel corner braces, the braces were instead made from angle fiber-reinforced plastic (FRP). The FRP was cut to 2” lengths, and holes were drilled for two bolts on each side.

D. Assembly Before the hoops were bonded into the hull, holes were cut in the tabs and epoxy-coated brass wood inserts were screwed in to allow the attachment of the corner braces. The brass wood inserts take a ¼”-20 bolt.

The hoops were bonded into the hull using a toughened epoxy adhesive purchased from Prairie Technology Group, Inc. See Appendix M for more part information. The top of both hoops were clamped at the tabs held outside the hull with layered wood and shimming.

After the adhesive had cured, the rectangular housing parts were lined up with the tabs and holes were marked on the rectangular housing pieces using the corner braces. Holes were drilled in the rectangular housing pieces and filled with epoxy coated brass wood inserts for ¼”-20 bolts.

For each housing box, there are four ¾” long ¼”-20 stainless steel hex bolts, four 1.5” long ¼”-20 zinc plated hex bolts (that go through the tabs), four ¼”-20 threaded zinc nuts, and numerous stainless steel washers. The 1.5” long zinc plated hex bolts and zinc plated nuts were used due to time constraints and should be replaced with stainless steel 1.5” long ¼”-20 hex bolts and stainless steel nuts. The stainless steel hardware was purchased from McMaster-Carr. It also might be recommended that the hex bolts be replaced with Allen screws so as to make assembly easier. It was found difficult to fit a socket wrench inside the housing setup to tighten bolts.

Figure 14 shows the housing assembled with the Hobie MirageDrives on the submarine.

Figure 14: Assembled Housing on Submarine

Padding

Attached Strips

Corner Braces

Brass Bearing


VI. TESTING FOR MECHANICAL LABORATORY III See Appendix N for additional information on materials and equipment used for testing.

A. Objective The primary objective of the testing was to show that the new connecting link, with the small rotating arm, allows for smooth motion through the hydrofoil cycle. A comparison of the old and new connecting link designs was also desired.

B. Fabrication There was some fabrication involved in the test setup. Galvanized angle steel was purchased and assembled in order to hold the two foil sets 24” apart. This frame design and material was chosen so that it could be modified for future experiments. Also, eight aluminum pieces were machined to form a test housing. Four pieces were machined to hold the end mounts and four to hold the pins. The housing pieces were held together by purchased angle braces. The test stand includes a bench for the operator to sit or lay on. See Figure 15 for the completed test stand.

Figure 15: Test Stand

C. Method Displacement testing was chosen to quantify the smooth motion and to show that the new design solved the rocking motion. Linear variable displacement transducers (LVDTs) were chosen as the measuring tool. An LVDT consists of a primary coil and two secondary coils, seen in Figure 16. The primary coil is excited with an AC signal. As the magnetic core is moved between the primary and two secondary coils, a voltage is induced in the secondary coils. The induced voltage is linearly related to the displacement seen by the magnetic core.

Figure 16: Internal Diagram of LVDT

The location of the two LVDTs was selected based on preliminary observations of the rocking motion in the original stand and in our fabricated steel test stand. The sizes of the LVDTs were selected based on estimated displacement seen with the old links. A 0.5” stroke range LVDT was chosen to measure the displacement of the test stand in the x-direction, seen in Figure 17. A 0.125” stroke range LVDT was chosen to measure the displacement in the vertical z-direction. A close up picture of the location of the 0.5” LVDT can be seen in Figure 18. A close up view of the location of the 0.125” LVDT can be seen in Figure 19.

Figure 17: Setup of LVDTs on Test Stand

Primary Coil

Secondary Coil Secondary Coil

Magnetic Core Threaded Rod

0.5” LVDT

0.125” LVDT

X

Z


Figure 18: Location of 0.5” Stroke Range LVDT

Figure 19: Location of 0.125” Stroke Range LVDT

There were three distinct steps to the testing performed: calibration, zeroing of LVDTs, and the actual displacement testing.

1. Calibration. Figure 20 shows the LVDT calibration setup used before the LVDTs were used for testing.

Figure 20: Block Diagram of Calibration Setup for each

LVDT

a. Instrumentation of LVDT Calibration:

1. 0.5” Stroke Range LVDT 2. 0.125” Stroke Range LVDT 3. Power Supply (built by Dr. Vincent Caccese) 4. Meterman 5XL Voltmeter (z-displacement) 5. Calibration Transducer (built by Dr. Vincent

Caccese) b. Calibration Technique: Using a calibration transducer borrowed from Dr. Vincent Caccese, known displacements were applied to each LVDT in turn. A voltage readout was then recorded at each applied displacement. Data points were taken over the operating range of each LVDT. Appendix O contains the recorded data as well as the Microsoft Excel Spreadsheet used to find the calibration curve for each LVDT. The calibration equation for the 0.5” stroke range LVDT is:

)(01861.0050698.0)( inVDCVininx +⋅⎟⎠⎞

⎜⎝⎛−=∆

The calibration equation found for the 0.125” stroke range LVDT is:

)(00085.001253.0)( inVDCVininz +⋅⎟⎠⎞

⎜⎝⎛−=∆

These calibration equations were used to convert the voltage output range recorded during testing to displacement in inches. Figure 21 shows the calibration transducer that was used.

Digital Output of Displacement

Voltmeter

Power Supply & Output

Calibration Transducer

LVDT

HPS – Optimization of Oscillating Hydrofoils __________________________________________________ 10

Figure 21: LVDT Calibration Transducer

2. Finding Location of Zero Displacement Output of LVDTs. Figure 22 shows the setup used to find the location of zero displacement output of the LVDTs.

Figure 22: Block Diagram of Setup for Finding Location of

Zero Displacement Output of LVDTs

a. Instrumentation of LVDT zeroing:

1. 0.5” Stroke Range LVDT 2. 0.125” Stroke Range LVDT 3. Power Supply (built by Dr. Vincent Caccese) 4. Meterman 5XL Voltmeter (z-displacement) 5. Micronta Auto-Range Digital Multimeter (x-

displacement)

b. Technique Used to Zero LVDTs: Once the LVDTs were attached to the test stand and the foilset, it was important to make sure the primary coil of the LVDT was operating in the same location as that used for calibration. This was done by observing the voltmeters to check that the LVDT was in a location that fell within the range of the LVDT. The LVDTs were moved so that at the zero or original position of the stand, the voltage output from the LVDT would be about 0.0 V DC.

3. Displacement Testing. Figure 23 shows the setup used to test the old and new linkages.

Figure 23: Block Diagram of Displacement Testing Setup

a. Instrumentation of Displacement Testing:

1. 0.5” Stroke Range LVDT 2. 0.125” Stroke Range LVDT 3. Power Supply (built by Dr. Vincent Caccese) 4. Hewlett Packard Oscilloscope

Figure 24 shows the instruments that were used for testing.

Oscilloscope

Power Supply & Output Relay

0.125” LVDT

0.5” LVDT

Voltmeter Voltmeter

Power Supply & Output

0.125” LVDT

0.5” LVDT


Figure 24: Testing Equipment

b. Technique Used for Testing: Displacement measurements were taken by two LVDTs in two different directions. Maximum displacement values were the result because the operation of the hydrofoils is cyclic producing a periodic output in voltage. The range in voltage output of each LVDT was taken in turn on the HP oscilloscope. Hassan Mazi was the operator of the connected propulsion drive. Measurements were taken using the old connecting links and the new connecting links.

D. Results The old connecting links could only be connected if the foils were in a certain position. It was difficult to move the linkage through the complete cycle. More force was required by the operator than with the new links. With the new links, it was very easy to move the linkage through the complete cycle. The stand moved visibly less in the x-direction with the new links than with the old ones. Table 1 contains the numerical results obtained.

Old Links New Links Maximum Displacement of Stand in the x-direction 0.091 in 0.017 in

Maximum Displacement of Foil Set in z-direction 0.031 in 0.019 in

Table 1: Block Diagram of Setup for Finding Location of Zero Displacement Output of LVDTs

The maximum displacement of the stand in the x-direction was decreased by 81% with the new connecting link design. The maximum displacement of the foilset in the z-direction was decreased by 39 % with the new connecting link design.

E. Conclusions Testing showed that the new connecting link design allows for smooth motion through the hydrofoil cycle. It shows that the design solves the initial rocking motion observed. Testing allowed us to better understand why the old connecting link design is unsatisfactory and to compare the old and new connecting link design, both qualitatively and quantitatively.

VII. CONCLUSIONS The two problems in this project were successfully solved and all the objectives were completed. The two MirageDrives were connected together and to the sub effectively. Final results include:

• Pin separation of 24 inches • Connecting links with small rotating arms allow for

smooth motion • Extremely durable fiberglass composite with

plywood core mounting system With this work completed, the department should be able to compete in the human powered submarine competition in the summer of 2005.

VIII. FUTURE WORK It is highly recommended that students working on the submarine in the future have new rotating arms machined for the connecting links. It is suggested that the parts be machined at the AMC from stainless steel because of their delicate and precise nature. Drawings of the suggested design can be found in Appendix E and notes in Appendix F. Also, it is recommended that future students:

• Test the submarine in water to determine the drag force

• Test using load cells to determine the forces exerted by the foil sets on the housings

• Manufacture farings to decrease the drag on the housing

• Replace any zinc-plated hardware with stainless steel for longer part life

IX. AUTONOMOUS UNDERWATER VEHICLE Part of the senior design project was to take what was learned about the human powered submarine propulsion system and apply it to a new department project, the autonomous underwater vehicle.

A. Background The Autonomous Underwater Vehicle (AUV) project began at the University of Maine Mechanical


Engineering Department in the Fall of 2003. The Autonomous Underwater Vehicle competition is an annually held student competition held by the Association for Unmanned Vehicle Systems International (AUVSI) and the Office of Naval Research (ONR). In 2003 and 2004, it was held at the Space and Warfare Systems Center in San Diego, California. A vehicle qualifies as an AUV if it can operate without control or communication from any off-board computer or person. Some important constraints for the AUV design include [7]:

• The mass of the vehicle must be less than 140 lb. • The vehicle must fit inside a box that is 6 feet

long, 3 feet wide, and 3 feet deep. • The vehicle must be battery operated.

A senior design group for 2003-2004 has designed and built a modular hull of the AUV, as well as a motor-driven propeller propulsion system. This modular hull should allow for the option of using an oscillating hydrofoil propulsion system.

B. Objectives Our task was to produce a preliminary paper design for an oscillating hydrofoil propulsion system for the AUV. Goals of this project were to:

• Research hydrofoils and AUVs • Determine the number and shape of hydrofoils

needed • Determine the desired motion of the hydrofoils • Design a linkage to produce the desired motion

C. Hydrofoil Motion Design Research began with two journal papers supplied by Professor Peterson [8, 9] on biomimetic and biologically inspired designs for foils. Other research resources were found from references listed in the first two papers [10-16]. The purpose of the research was to find exactly what motion was needed to be achieved with the hydrofoils. The research was difficult due to inexperience with biomimetics, fish biology, and advanced fluids.

It was determined, based on similar AUV hydrofoil driven designs, that several hydrofoils would be needed to control the movement of the proposed AUV. At least four hydrofoils with large surface areas are needed for the main propulsion of the vehicle, similar to those on the Hobie MirageDrive. Additional smaller, more flexible foils would be needed for maneuvering and for reverse motion.

D. Linkage Design It was thought that a simple linkage design could produce the necessary foil motion from a rotating motor shaft. Some basic designs were brainstormed and are included in Appendix P. Professor Peterson indicated that the Geneva linkage might be a possible solution, but no successful design was found using this linkage.

E. Conclusions Due to the extensive design and fabrication required for the full optimization of the oscillating hydrofoil propulsion system for the human-powered submarine, there was insufficient time to design a preliminary linkage for the AUV. Included in the references section are all the resources that were found to be helpful.

F. Future Work Future students working on a hydrofoil propulsion system design for the AUV should first study the existing AUV hull and power supply. It is recommended that they review the references listed. Various motors, with speed reducers and other options, need to be investigated. The addition of team members with controls, biomechanical, and advanced fluid mechanics backgrounds would facilitate the hydrofoil design process for this application.

ACKNOWLEDGEMENTS Special thanks to our advisor, Professor Michael Peterson, to Professor Senthil Vel for help with modeling, to Professor Vincent Caccese for the use of LVDT testing equipment, and to Art Pete for help with tools. Also, special thanks to Brian Barker at the AMC for help using the Faro-Arm Platinum CMM, Ryan Beaumont for help with testing, and Keith Berube and Michael Robinson for help with composite fabrication.

REFERENCES 1. Project Website:

http://www.umeme.maine.edu/mick/Classes/Design2003_04/OE%20Propulsion/index.htm

2. Alley, B., B. Baillargeon, M. Jolin, P. Melrose, B. Meserve & Dekin Scroggins. Human Powered Submarine. 2002.

3. Foss, R. & E. Goodine. Human Powered Submarine Ballast and Buoyancy Controls. 2003.

4. Miyakozawa, T. & E. Lowe. HPS Controls. 2003.

5. www.hobiecat.com

6. Norton, Robert L. Design of Machinery: An Introduction to the Synthesis and Analysis of Mechanisms and Machines. 2nd ed. New York: McGraw-Hill, 2001.

7. www.auvsi.org

8. Fish, F.E., G.V. Lauder, R. Mittal, A.H. Techet, M.S. Triantafyllou, J.A. Walker & P.W. Webb. Conceptual


Design for the Construction of a Biorobotic AUV Based on Biological Hydrodynamics. 2003.

9. Triantafyllou, M.S., A.H. Techet & F.S. Hover. Review of Experimental Work in Biomimetric Foils. 2003.

10. Reisenthel, P.H., W. Xie, I. Gursul & M.T. Bettencourt. An Analysis of Fin Motion Induced Vortex Breakdown. 1999.

11. Median/Paired Fin Propulsion. www.ece.eps.hw.ac.uk/ research/oceans/projects/flaps/mpfmodes.htm

12. Walker, J.A. & M.W. Westneat. “Performance limits of labriform propulsion and correlates with fin shape and motion”. Journal of Experimental Biology, 205, 177-187 (2002).

13. Drucker, E.G. & J.S. Jensen. “Kinematic and Electromyographic Analysis of Steady Pectoral Fin Swimming in the Surfperches”. Journal of Experimental Biology, 200, 1709-1723 (1997).

14. Tu, Xiaoyuan. “Visualization of the Pectoral Motions”.

15. Sfakiotakis, M., D.M. Lane & J.B.C. Davies. “Review of Fish Swimming Modes for Aquatic Locomotion”. IEEE Journal of Oceanic Engineering, Vol. 24, No. 2, April 1999.

16. Kato, Naomi. “Hydrodynamic Characteristics of a Mechanical Pectoral Fin”. Journal of Fluids Engineering, September 1999, Vol. 121, p. 605-613.

17. http://www.isrsubrace.org

18. http://www.asme.org/sections/sd/hps2004.htm

APPENDIX A. Hobie MirageDrive Patent Information

B. ProENGINEER Parts and Filename Description

C. Estimation of Applied Force on Fins

D. Instructions for ProE Mechanism Analysis

E. CAD Drawings

F. Notes on New Rotating Arm Design

G. Estimation of Required Connecting Link Size

H. Fibre Glast Product Information

I. Hoop Lay Up Design

J. Effective Engineering Properties of Composites

K. Hoop Fabrication Process

L. Table of Materials Used for Fabrication

M. Prairie Technology Inc. Product Information

N. Table of Materials Used for Testing

O. LVDT Calibration Spreadsheet

P. AUV Sketches

Q. Design Project Poster

senior design project optimization of the oscillating ...optimization of the oscillating hydrofoil...

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