Sea Dragon Velocity Float Sponsored by:

Mr. Mark Gillcrist

Written by: Alan Duong, Harry Miller, Tung Nguyen, Aaron Spanner, and Kendra Toy

MAE 156B - Fundamental Principles of Mechanical Design II Department of Mechanical and Aerospace Engineering Jacobs School of Engineering University of California, San Diego

Under the Instruction of ​Dr. Tustaniwskyj

Chapter 1: Project Description Background Spawar is an industry leader that provides hardware and software to the United States Navy. Specializing in command, control, communications, computers, Intelligence, surveillance and reconnaissance(C4ISR), Spawar provides products and research to the Navy to help them operate with the best tools available. Product design requires extensive research and testing before the final product is fabricated and given to the Navy.

The Sea Dragon Velocity Float is a segment of an experiment that will be performed by Spawar engineers. A series of experiments will be conducted on the seabed to move a cart along a track. The primary method of cart motion will be the drive float. The buoyancy of the drive float will be adjusted between trials in order to achieve varying test speeds. Upon initiating the experiment, the drive float is released via an undetermined mechanism. As the drive float rises to the sea surface the cart travels horizontally along the track and the velocity float is towed down due to the pulley configuration of the experiment. The velocity float will not be starting at surface of the ocean. The buoyancy of the float will ensure the cable connecting the velocity float and cart is in tension.

The velocity float will house waterproof-self-logging-pressure sensors. Once the experiment is completed, the pressure sensors will be removed from the velocity float via a diver. The data from the sensors will be downloaded to a computer on a boat that will be used by Spawar engineers to conduct the experiment. The pressure data will be converted to depth and allow Spawar engineers to measure the dynamics of the cart (velocity, acceleration, and deceleration).

Review of Existing Solutions The pitot tube is used to measure velocity of a fluid. Applications of pitot tubes can be found on aircraft, boats, ships, submarines, and in the UCSD MAE 171A Water Channel experiment. The design is rather simple with a very straight forward theory. As an immersed object travels through a fluid (fluid flow over the body) the pressure felt by the moving fluid particle is the same as the pressure around the particle. This is known as static pressure, ​p. The pitot tube has two holes: one aligned with fluid flow and one aligned perpendicular to fluid flow. As the fluid enters the hole aligned with flow, it is accelerated from some velocity to zero by a frictionless process. The momentum of the fluid will apply an additional amount of pressure known as dynamic pressure. The total pressure felt by the static pressure and the dynamic pressure is known as the stagnation pressure, ​p0. The perpendicular hole only experiences the static pressure affects. For incompressible flow, the Bernoulli equation relates the changes in pressure and speed along a streamline.

According to the Bernoulli equation, p ρ

2

+ V2 = constant

Therefore, p0 ρ

+

V 20 2

2

= pρ + V2 ; ​where V​0,​ stagnation velocity, is zero.

So,

p0 = p + 12 ρV 2

Solving for V, V =

√

2(p0−p) ρ

This is a very good method for measuring velocity, because no differentiation of position is necessary, which increases noise and error into the analysis. Differential pressure sensors are available as well and pitot tubes are affordable. Pitot tubes were not chosen for our application because the addition of extra holes for routing tubing and pitot tubes into our design was not desired. Also, the expenses of self-logging differential pressure sensors to create a digital manometer was excessively high when compared to the Star Oddi sensors already in possession of the sponsor which added no cost towards the budget. Another method to measure the velocity of an object is to record high speed video footage of the object traveling in front of a backdrop of known length increments. This way one can use the known frames per second of the recording to obtain the time it takes the object to travel a known distance increment from the backdrop. These can be used to compute velocity over time. See image from Mythbusters below, where a ball was ejected from a truck, and it’s velocity could be determined from the time it took to travel past the grid-pattern of the backdrop:

This is highly useful for measuring velocity over a few meters, but as the distance of concern increases in length, it becomes much more difficult to get the whole length into the frame without distorting the image and thereby leaving the measurements worthless. Since the distance we were concerned with was about 50 feet of travel, this method did not suit our needs. In addition, the complications from trying to set up a camera and backdrop below 80 feet of water would have made this solution near impossible.

Statement of Requirements After current methods are discussed and alternate ideas are brainstormed with Mr. Gillcrist, it is decided that the prototype of velocity float is designed, built, tested, and documented for the static condition. During the test, the pressure sensor as well as the prototype are checked carefully for their accuracy and precision.

Deliverables At the end of the project, the Spawar will be provided with: Table 1. Hardware Deliverables

Item

Function

Velocity Float

To transport the sensor as it is pulled by the cart

Star-Oddi Sensor

To record temperature and pressure data

Detachable mount

To mount the sensor and to allow diver(s) to retrieve sensor

Cable

To connect the velocity float to the cart

Algorithm

To convert pressure signal to velocity

Manual

To explain how to set up the system with the velocity float

Table 2. Software Deliverables

Item

Function

Webpage

To demonstrate progress and achievements of the project, to provide contact information for team and sponsor information, and to present details of the project process

CAD files

To allow for the reproduction of the velocity float by containing all drawing files, part files, and assembly files involved

Powerpoint Presentations

To keep the sponsor and other interested parties updated and to present higher-level information

Final Report

To detail the design process, prototype, and final conclusions in a comprehensive and presentable report

Poster

To compactly present the main points covered in the final report, especially for presentation purposes

Acknowledgements The Sea Dragon Velocity Float team would like to thank the following people for their guidance and expertise on this project: UCSD Department of Mechanical and Aerospace Engineering Dr. Jerry Tustaniwskyj Ian Richardson Tom Chalfant Spawar Mr. Mark Gillcrist

References Table of Appendices Appendix 1: Executive Summary Appendix 2-1: Project Management and Responsibilities Responsibilities Project Milestones Appendix 2-2 Budget Appendix 3-1​: ​Cable Component Analysis Functional Requirement The primary function of the cable is to connect the velocity float to the cart on the seabed. Due to the configuration of the experiment bed, this will be achieved through a series of pulleys. The cable will need to withstand the force exerted on it from the cart and drive float. Prior to the initialization of the experiment, the water current (maximum of 1kt) will be the only horizontal

force acting on the float and cable. In order to minimize the line tilt the cable, and the float, it is necessary for both items to have low lateral drag. Component Options Monofilament Fishing Line Monofilament fishing line is the most popular fishing line for fishermen. It is a single strand of material that is typically extruded from nylon and other copolymers to create a fishing line that is strong and abrasion resistant. Spectra-Braided Fishing Line Spectra braided fishing line, is typically constructed from Dyneema with multiple strands in order to create a fishing line. Upon construction, the strands are bonded together to increase strength and prevent strands from fraying apart. Spectra fishing line is popular due to its strength and thickness. The line is thinner and stronger than monofilament fishing line; allowing fishermen to have more line in their reels. Steel Strand Wire Rope Wire rope is a rope comprised of smaller steel strands to form a rope. Wire rope was developed after iron chains due to the mechanical failure of chains. The multiple strands in the rope help compensate other strands for any flaws created in the manufacturing process. Wire rope is widely used where heavy duty cables are needed (i.e.: tow boats, elevators, aircraft controls, suspension bridges, etc.) Monofilament Fishing Line Pro Abrasion resistance

Near-neutral buoyancy In the water, the weight of the line will have less of an effect on the dynamics of the system Inexpensive Monofilament is widely available and is a popular option for fisherman because it is cheap. 100yards of 500lb test

Con Designed to stretch This is beneficial to fishermen in order to keep the line taught when fighting fish, but in this experiment the stretch will lead to an error in recording the motion of the cart from the velocity float. This is the largest issue with monofilament line for this experiment

monofilament costs approximately $17 (tackledirect.com)

Spectra-Braided Fishing Line Pro

Con

Does not stretch Braided fishing line was designed to be very sensitive and to help fishermen with sensing action on the other end of their line.

Knots Spectra is thin and has a smooth coating on it to help prevent drag. These characteristics make it difficult to tie and hold certain knots. Several fishing knots are specially designed to help secure the line without sacrificing much line strength.

Thin Diameter Braided fishing line has one of the best tensile strength to diameter ratios. The thinner line helps to reduce drag in the water as well. Light Weight The thin line also allows for the line to be lighter Buoyant Spectra is designed to float in water Inexpensive Although it costs more than monofilament, spectra is still affordable. 150 yards of 500lb test spectra costs about $52 (tackledirect.com)

Steel Strand Wire Rope Pro

Con

Very Strong Wire rope is used in heavy duty industrial applications because it is known for its strength. Most wire ropes sold use units of

Heavy Wire rope is typically used in heavy duty industrial applications. For this experiment, wire rope may prove to be too heavy to

“tons” for breaking strength

use with the velocity float Expensive Wire rope is typically sold per foot in most civilian stores. The price is typically around $2 a foot.

Conclusion From the research performed, it appears that for this application Spectra-Braided fishing line is the best option for the cable. Due to the thin diameter and coating on the Spectra fishing line will have less drag in the water. This means that the current in the water will create less line tilt than if we were to use monofilament or wire rope. Spectra- braided fishing line is offered up to 500lb test or ~2224 N. This strength rating also complies with the dynamics of our system and factor of safety. The analysis to determine the force of tension on the line was performed using static equations. Certain numbers cannot be displayed due to confidentiality. The lightweight line will not add any factors to the experiment that will skew the pressure readings or the experiment itself. References Berkley-Fishing, West Marine, Tackle Direct, Spectra by Honeywell D. FARIVAR. "Turbulent uniform flow around cylinders of finite length", AIAA Journal, Vol. 19, No. 3 (1981)

Appendix 3-2: Float Construction Material Component Analysis

Functional Requirement The velocity float requires use of pipe material in the design for the structural, static and dynamic characteristics desired. The float must withstand pressures as high as 80 feet of seawater during operation. The float must be as buoyant as possible with as low of a drag as possible to minimize the line tilt. The diameter of the float is directly related to both buoyancy and drag, so a compromise will be necessary in the design. Component Options Schedule 40 Polyvinyl Chloride (PVC) pipe This pipe is often used in building construction for delivery of water. It is easy to cut and fasten which makes it a great choice for pipe- fitters and plumbers to use. The material can be offered with an ultra-violet (uv) protective coating and generally offers great corrosion resistance. Schedule 80 PVC pipe This pipe is often used where higher water pressures are found when high flowrates are desired. The increase in the strength of this pipe allows for underground application

where a compressive load may be applied such as under roadways. There are uv coating options available as well. Schedule 40 Acrylonitrile-Butadiene-Styrene (ABS) pipe This pipe is used in construction applications where gravity-flow systems are needed such as drains and vents. It is used more frequently in new construction and where old PVC systems are being replaced. Schedule 40 PVC Pro

Con

Low density The effective specific gravity of one meter section of pipe filled with air showed this material had the lowest density.

Lowest collapse pressure rating 8-inch pipe size gave only a factor of safety of only 1.4 over the expected sea water pressure.

Highest buoyancy The low effective specific gravity results in the highest buoyancy of these materials. Least expensive The average percent difference in price for various size pipe at ten foot lengths was 52 percent lower for this material

Schedule 80 PVC Pro

Con

Highest collapse pressure rating 8-inch pipe size gave a factor of safety of 4.9 over expected max pressures. The factory of safety for 2-inch pipe size was 18.3

Most expensive option The average percent difference in price for various size pipe at ten foot lengths was 52 percent higher for this material. 4-inch size was as high as 59 percent

higher. Larger pipe sizes have competitive buoyancy 8-inch pipe size was within 14 percent difference when compared to other same sized pipes.

Heavy The material has thicker walls and comes with a higher weight than other options.

Greatest wall thickness The material is thick which might allow for better fastening of components such as fins for stability and rails for a bail and ballast system.

Schedule 40 ABS Pro

Con Expensive Not the most expensive, but still more expensive than schedule 40 PVC. Inconsistent pressure ratings Any pressure ratings found were inconsistent or not listed by suppliers

Conclusion After carefully considering the available options, schedule 40 PVC may be the favorable option for pipe sizes below 8 inches. The factor of safety is too marginal for the 8-inch schedule 40 pipe size at depths of 80 feet in sea water. The price is substantially cheaper than schedule 80 PVC. The buoyancy is higher than the other options which suggest less line tilt in static equilibrium and subsequently less error in velocity determination. The outside dimensions are the same as the heavier grade pipe, so dynamic loads due to drag will be the same across the board for each given pipe size. ABS piping does not have consistent rating that were found and the supplier fails to mention the ratings although all PVC pipe ratings were listed. The lack of consistent pressure ratings is sufficient to eliminate this material as an option altogether. References

www.mcmaster.com www.pvc.org Fox and McDonald’s Introduction to Fluid Mechanics 8​th​ ed. Appendix 3-3: Pressure Sensor Component Analysis Functional Requirements: It is crucial that the calculated velocity profile be within +/- 0.5 ft/s, as per SPAWARS’s request, and thus it is important that the sensors used have a low enough error and high enough sampling rate to achieve this when the measurement errors are propagated to the final velocity curve. The equation that governs this relationship is as follows:

In addition to these critical sensor specifications, the sensor should also be: ·​ ​

Small and lightweight

·​ ​

·​ ​

Water-proof Self-logging and self-powered

Component Options: With these considerations in mind, SPAWAR suggested the use of the Star Oddi DST centi-TD sensor. These sensors were already purchased by SPAWAR, and so cost and lead times are zero. After looking through the other options Star Oddi has available, the DST tilt sensor was also selected as a potential option, because it could measure tilt as well as pressure. Finally, a third option was found using the web to find other oceanographic pressure sensors. Valeport is a well known sensor manufacturer, and their ultraP sensor was the best product for our use. Technical Specifications: Star Oddi DST centi-TD:

Star Oddi DST tilt:

Valeport ultraP

Resolution: +/- 0.5 inches

Resolution: +/- 0.5 inches

Resolution: +/- 0.04 inches

Max sample rate: 10 Hz

Max sample rate: 5 Hz

Max sample rate: 16 Hz

Size: 46 x 15mm

Size: 46 x 15mm

Size: 110 x 38mm

Mass: 0.02 kg

Mass: 0.02 kg

Mass: 0.3 kg

9-year battery life

9-year battery life

No internal batteries

300,000 bytes memory

300,000 bytes memory

No internal memory

Cost: None (purchased)

Cost: $700 per sensor

Cost: $2000 per sensor

Pros and Cons: Pressure Sensor

Pros

Cons

Star Oddi:

Can obtain velocity profile within +/- 0.5

Not the most accurate or fastest

DST centi-TD

ft/s, very small and lightweight, internal

sampling rate, cannot measure

battery and memory storage, zero cost

tilt.

because already purchased.

Star Oddi:

Can measure tilt, which would help in

Lower sampling rate means

DST tilt

getting more accurate velocity profile.

much higher velocity profile error,

Very small and lightweight, internal

more expensive than DST centi

battery and memory storage.

because would need to purchase.

Valeport:

Extremely accurate and high sampling

Larger and heavier than other

ultraP

rate.

options, no internal batteries or memory storage (wired), cannot measure tilt, much more expensive.

Conclusion: We decided to go with the Star Oddi DST centi-TD because it does obtain a velocity profile to within the necessary +/- 0.5 ft/s, it has a very small profile and is very lightweight, is self-powered and stores its own data, and has zero cost to us because it has already been purchased by SPAWAR. The tilt option was ruled out because the sampling rate was too low to provide an accurate velocity profile, and the Valeport option was ruled out due to the fact that it had to be plugged into an external power and data storage system. References: Keywords: Ocean, piezo, sensor, pressure Contact: Baldur Sigurgeirsson at Star Oddi Email: [email protected]

Phone: (354) 533-6060 Appendix 3-4: Fin Component Analysis

Functional Requirements: Most of moving objects under water require fins which are used for balance, stability, and steering. Moreover, the size and shape of the fin (height, base length, and rake) determine the characteristics of the movement of the objects such as speed, ease of maneuver, and friction. Component Options: FIN DESIGN

RAKE The rake, or sweep, is how far the front edge of a fin arcs backwards. Fins with a small rake (large offset) help propel the board, are very stable and predictable.

BASE/LENGTH The base length of the fin is the widest part of the fin, and sits flush with the object once installed. This length can affect how the object will respond to turns. Longer fin bases create trajectories for water to go past--so the object will move faster.

HEIGHT/DEPTH The height (depth) is measured from the base of the fin to the tallest point of the fin. A taller fin will be more forgiving and handle turns in a relaxing manner so that the object is easy to control.

Thoroughly Understanding these characteristics helps choose the appropriate fin for the project. Three options: 1/ Creatures of Leisure Fin Mitch Coleborn Arc Series is designed for extra drive and more drawn out turns. These are ideal for carving maneuvers, rail to rail transitions, and down the line surfing. 2/ Creatures of Leisure Fin Icon Vert Series is lightweight with a fluid flex pattern that provides maximum speed and responsiveness

3/ Prosea FGH18 Surfboard fins FCS Base Surfing thrusters made of Fiberglass and Honeycomb. Lightweight fins with remarkable flex, a smooth feel and an impressive aesthetic

Pros/Cons of Various Options Pros

cons

Creatures of Leisure Fin Mitch Coleborn Arc Series

·​ ​

·​ ​

Light weight Maximum

speed ·​ ​

Creatures of Leisure Fin Icon Vert Series

·​ ​

Prosea FGH18 Surfboard fins FCS Base Surfing thrusters

·​ ​

·​ ​

responsiveness Lightweight

·​ ​Vertical maneuvers Lightweight Remarkably

flex

References: 1. A guide to fcs fins: http://www.surffcs.com/community-story/community-blog/2013/03/01/a-guide-to-fcs-fins

2. How to choose surf fin: http://www.evo.com/how-to-choose-surf-fis 3.​ ​Surf fin options http://www.hansensurf.com/collections/surf-fi n 4.​ T ​ he definitive surfboard fin guide

http://www.boardcave.com/the-surfers-corner/the-surfboard-fin-guide/#fin_size

Appendix 3-5: Sensor Housing and Locking Mechanism Component Analysis