UnderSea Solutions, Inc.

Arctic AUV Proposal

OCE 4542

12/8/00

Team Members:

Ryan Roberts Nicky Samuelson

Chris Duer Adam Kay

Instructor:

Dr. Stephen Wood

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Introduction

This project entails the conceptual design and analysis of an AUV, Autonomous

Underwater Vehicle, for Arctic under-ice water sampling. As such, the primary goals of the

project are twofold: to apply engineering principles to real world design, and to work

cooperatively in a team that approximates the organization by which design is carried out in real

world situations.

In order to properly organize the design project, a company was created called UnderSea

Solutions, Inc. A complete company hierarchy was created to differentiate different systems in

the project and thus maintain clarity throughout the project. The company hierarchy is shown

below.

Chief Executive Officer

Ryan Roberts

Mechanical Engineer Electrical Engineer Computer Engineer

Nicky Samuelson Chris Duer Adam Kay

The three main company divisions are each tasked with several components of the overall

AUV design. These are as follows:

Mechanical Design:

? Hull Design

? Materials Standards & Testing

? Maneuverability/Control

? Layout & Arrangement

? Deployment & Retrieval Mechanisms

Electrical Design:

? Power Consumption

? Battery Requirements & Selection

? Thrust Motor Requirements & Selection

? Control Plane Motor Selection

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Computer Design and Instrumentation:

? Command & Control Systems

? Navigation Sonar & Collision Avoidance

? Instrumentation & Sensing

? Data Acquisition, Storage & Retrieval

Design Parameters & Requirements

The basic design criteria are imposed by the environment in which the AUV will be used,

the requirements of the operators and the overall ease with which the AUV may be operated.

Mission Statement:

The Arctic AUV will be used for under-ice water sampling in Alaska’s coastal waters.

Turbidity measurements will be made at known relative and absolute points along the

AUV’s survey track. The AUV must be functional in a harsh marine environment, user

friendly with respect to data collection and retrieval and easily stowed, deployed and

retrieved.

Environmental Characteristics

? 0o to –40o C Air Temperature

? 5o to –5o C Water Temperature

? Low to Moderate Currents (0.5 knot maximum)

? 40 ft. maximum water depth

? 6 ft. ice cap

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AUV Requirements

? Light Weight

? Deployable through a 15 inch diameter hole

? Variable Speed Capability

? Capable of navigating under ice field and returning to deployment point

? Collect water quality data with corresponding locations

? Distinguish sonar signals (Collision Avoidance)

? Cruising Speed: 2 kts.

? Maximum Speed: 20 kts.

? 5 hours endurance at cruise speed

Required Instrumentation

? Nephelometer

? CTD

? Camera

? Turbidity instrument

Main Design Points

? Design for Assembly and Disassembly

? Design for serviceability and multiple reuse

? Design for Interchangeability and modularity

? Commonality between computer components

Mechanical Design

We are focused on producing an innovative product, which is simple, reliable and

manufactured to the highest standards.

The Artic water sampler is a small, compact, extremely capable, high performance

professional AUV system, which can be used for a variety of underwater tasks such as water

sampling, survey and observation, etc.

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Performance/Dimension

Depth Rating: 33 meters standard 100 feet

Dimensions:

Length 1.12 m 7 feet

Outer radius 15.5 mm 6"

Thickness 6.3 mm 0.25"

Maximum Velocity/Operational Current:

Maximum velocity 20 Kt

Standard cruise 2 Kt

Housing

The Artic water sampler housing is constructed of Aluminum incorporating the following

features:

Aluminum housing with low temperature resistant O-ring seals

Acrylic dome for nose cone

Lift points

Hull Form

The hydrodynamic form of the AUV determines the propulsion energy required, as well

as the stability and maneuverability at various operating speeds. A hull form may also impose

limitations on vehicle access, launch and recovery, and maintenance.

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The speed for the AUV is between ½ and 20 knots. In most applications, the vehicle will

maintain a steady cruising speed of 2 knots throughout the mission. The following considerations

drive the selection of the hull form:

? Minimization of overall vehicle drag

? Minimization of flow separation, especially for efficient propulsion near the tail

? Stability as a sensor platform at 2 knots

? Stability and maneuverability at speeds as low as ½ knots

Longer, more slender shapes tend to be better. We have chosen the torpedo hull form

because of its many advantages

? Streamline shape for low resistance and high ability to store lots of equipment

? Maneuverability

? Small diameter (needed to launch and recover the vehicle through the ice)

Equipment layout and arrangement

Front Bulb Collision Avoidance Sonar Array

Industry Standard Camera with RCA video output

2 Lights (20 Watt halogens)

Mid-compartment 1 Data Storage

Command and Controls

Mid-compartment 2 Batteries

Aft compartment Watertight Fin Servos

Aft External Thrust Motor

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Figure 1: Equipment layout and arrangement

Maneuverability and Control:

The Artic water sampler has six fins for stability maneuverability:

? Two forward fixed fins for stability

? Four controllable fixed fins for maneuverability:

o Two rudder

o Two driving planes

The aft fins are controlled by watertight heavy duty professional Series Tone Servos

SSPS-105.

PVC Flexural Tests

The flexural test on PVC, Polyvinyl Chloride, measures the deflection of a 6” inside

diameter Schedule 40 pipe length. An idea of the elasticity of this material and its applicability

as a pressure vessel may partially be obtained from this test. The maximum loading before

rupture may also be determined.

The apparatus for testing the PVC pipe is as follows:

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? Digital Extensiometer

? End supports

? Duct tape

? Loads: batteries and dive weights

? Scale

PVC Pipe

Pipe Support

Figure 2: PVC End Support

Load

Dial GageSupport

PVC Pipe

Figure 3: PVC Flexural Test Apparatus

Procedure

The following steps outline the procedure for the flexural testing of PVC pipe.

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1. Place two tables approximately 5 feet apart.

2. Fix supports on each inside edge of table.

3. Place PVC pipe on supports ensuring that both ends have the same contact surface area.

4. Using bookshelves and books as sheaves, place extensiometer at mid-span, with plunger

depressed approximately halfway.

5. Reset the readout to zero and ensure that the reading will give a positive answer as the

plunger is allowed to come out.

6. Weigh and record the masses of the batteries and dive weights.

7. Place each load as close to the center as possible, one at a time.

8. Record the deflection of the pipe.

9. Repeat procedure until failure occurs or until all weights have been used.

Results

Weight

(lb)

4 8 12 16 20 26 32 40.9 49.9 58.8 67.7 76.7

Deflecti

on (in)

0.002

4

0.008

7

0.01

5

0.022

2

0.028

5

0.03

8

0.048

7

0.066

2

0.08

2

0.095

7

0.106

2

0.115

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Table 1: 1st Trial Results

Weight

(lb)

9 17.9 26.8 35.7 44.7 58.7 72.7

Deflection

(in)

0.015 0.0306 0.0441 0.0589 0.073 0.087 0.1055

Table 2: 2nd Trial Results

Battery # 1 2 3 4 5

Weight (lb) 8.9 9.0 8.9 8.9 9.0

Table 3: Battery Weights

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Deflection Vs. Load

0102030405060708090

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Deflection (in)

Load

(lb)

1st Trial2nd Trial

Figure 4: Results Plot

PVC Destructive Impact Tests

For the impact test on PVC we will be performing a destructive impact test (or simple

beam test). This test will be performed on a 1 foot long, 6” inside diameter Schedule 40 pipe at

room temperature and at -70?C.

Results:

PVC Failure

Room temperature Never

-70?C 110 ft/lb

-50?C Never

-70?C 75 ft/lb

-60?C 110 ft/lb

Table 4. Impact Test Results

The variation in the results from the five tests were a function of the time that the PVC

was allowed to cool. The PVC that failed with the lowest applied force was the specimen that

was allowed to cool the shortest amount of time. In the third trial, the specimen did not fail.

This was because the specimen cooled for too long, almost to room temperature.

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We ultimately decided not to use the PVC because of the possibility of brittle fracture

and because of the great deflection when the specimen did not fracture. The PVC specimens

deformed enough that the seals of the AUV would leak.

Electrical Design

The electrical design for the AUV is composed of 5 individual systems. These systems

are the thrust motor, control plane motors control systems, navigation system and

instrumentation.

Thrust Motor

The thrust motor is manufactured by Minn Kota. The Riptide Saltwater Bow-Mount

Motor RT65/AP was chosen for its thrust to amp draw to voltage ratio of 65 lb:38 Amp/hr:12 V,

which was the best of all motors surveyed.

Control Plane Motor

The control plane motor used is a CK Design Technology Heavy Duty Professional

Series Tone Servo SSPS-105. This motor requires an average of 1 amp/hr.

Control system, Navigation System and Instrumentation

The computer systems, described in the Computer Design section require only a minimal

amount of amp draw. The total draw is 5280 mA, or approximately 5 Amp/hr. The following

table is a breakdown of the draw for each individual computer component.

Computer Component Controls

Amp Draw

(mA)

2 PC/104 Boards brain/navigation/instrumentation/collision 1400

Relay Board on/off 250

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ADC & DCA 480

Video Capture camera 350

Motor Controller x3 thrusters & fin servos 1050

Signal Processor transducers (navigation & collision) 150

Matrix Keypad & LCD command entry & display 100

Hard Drive video & data storage 1500

Total 5280

~5Amp/hr

Total Amp Draw

The total Amp/hour draw of the AUV is laid out in the following table.

Item Amp Draw

Computer Equipment 5 Amp/hr

Thruster Motor 38 Amp/hr

Control Plane Motor x2 1 Amp/hr

Total 45 Amp/hr

Battery Requirement

The AUV will house four 12V batteries and have four more on reserve to be changed out

between each run. This decreases turnaround time between each run. The batteries are each 12

volt 30 Amp batteries.

Computer Design and Instrumentation

System Requirements

In order for the Arctic AUV to perform its mission of transporting scientific

instrumentation from one point to another under the ice, it must be able to control its thrust motor

and fins, find its way from the start to finish and back, and avoid obstacles along the way. All of

these, along with storage of the scientific data are handled by the computer systems on board the

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vehicle. The Arctic AUV contains two separate computer systems. The first is the main control

system, which is responsible for getting the payload from start to finish and back. The second

system is the data logger for the scientific instrumentation, including the storage of pictures

taken with the onboard camera.

Main Control System

The main control system handles the navigation (getting the vehicle from start to finish

and back), collision avoidance (avoiding obstacles along the way), and motor control (changing

and storing thruster speed and fin position). This system is centered around a high-power

PC/104 form-factor single board computer that will simultaneously run 4 mission programs in a

real-time OS. These programs are:

? Central Command

? Navigation

? Collision Avoidance

? Thruster and Fin Control

Central Command

The central command program ties together input and output from the other three

programs. If the navigation system determines that the AUV is off the desired course, the central

command program will check with the collision avoidance program to insure that the path is

clear, before telling the thruster and fin control system to make any adjustments.

Navigation

The navigation program is only a part of the complete navigation system, which begins

with hydrophones recessed in the front fixed fins of the AUV. These hydrophones are tuned to

hear the frequency that the navigation buoys will continuously transmit. The signal from these

hydrophones is amplified and then sent to a PC/104 signal processor board which “listens” for a

certain shift in the pings received form the navigation buoys. When this part of the ping is

detected, the board will immediately notify the navigation program on the single board computer

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via the PC/104 main bus of the occurrence and on which hydrophone the shift was heard. The

navigation program will wait until the signal processor has reported for both hydrophones and

will determine what course change (if any) is necessary based on the time difference between the

receptions of the ping shift. If the ping shift is heard by one hydrophone before the other than at

turn needs to be made towards the first reporting hydrophone to get back on course. The

navigation program will report to the central command program towards which direction, if any

the course needs to be adjusted.

Collision Avoidance

In order to avoid obstacles encountered along the way, the Arctic AUV will have a 5-

transducer sonar array mounted in the front dome in order to actively ping in many different

direction to detect objects that the AUV may be approaching. The collision avoidance program

will send a signal to begin an active ping of all the transducers through a PC/104 digital IO board

and store the exact time of this order in memory. After sending the ping, the transducers will

then be used for listening for the reflected signal. The transducers in this array will have their

reception signals amplified in much the same way as the navigation hydrophones. These

amplified signals will be sent to the same PC/104 signal processor, which will report to the

collision avoidance program reception of the reflected signal from each transducer. By recording

the time of each reception into memory and comparing with the send time, the collision

avoidance program can determine the distance to the nearest obstacle in every direction and then

use a logic program to determine if any of the obstacles warrant a course change and, if so,

which direction to take to avoid the obstacle. The basics of this logic program are shown in

Figure 5 in flow-chart format. In the flowchart the directions (front, bottom, top, left, and right,

are the time differences between send and reception of the signal and their corresponding

variables (F, B, T, L, & R) are a pre-determined distance at which the obstacle is a threat to the

vehicle and is based on the speed of the vehicle and the rate at which it can turn at that speed.

All action blocks are outputs to the central command program. Action blocks with bold boarders

cause the program to return to the top left decision block with a double line border.

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Slow Front > F

Bottom > B & Top > T

Left > L & Right > R

Up

No

Speed >

½ kn

Speed =

½ kn Bottom > B

Yes Down

Yes

Yes

No

Top > T Yes

Up Only Bottom < B

Yes

Down

No

Only Top < T

Yes

No

No

Slow Speed =

½ kn Left > Right

Speed >

½ kn

Left

Right

Yes

No

Right Only Left < L

Yes

Left

No

Only Right < R

Yes

No

No

Slow Ui = 2kn

Top > T Ui > 2kn

Up

Down

Yes

No

Bottom > B

Yes No

Reverse Figure 5: Collision Avoidance Flow Chart

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Thruster and Fin Control

The thruster and fin control program simply stores the speed of the thruster and the

position of the fins and makes necessary adjustments as directed by the central command

program. The control of the fin servos and thrust motors is done by PC/104 motor controller

boards with communication via the PC/104 main bus.

Miscellaneous

The main control system will also include a keypad and LCD interface board (also

PC/104) that will allow the user to input mission data via a small keypad with the options

displayed on a small LCD display. The LCD display will be viewable though an acrylic window

in the pressure housing and the keypad will be accessible by opening as small hatch in the

housing.

Data Logging System

The data logging system stores data from the scientific instruments and camera to a

laptop hard drive. The system is composed of a low power, Ethernet capable PC/104 single

board computer, PC/104 video capture board, laptop hard drive, RS232 compatible scientific

instruments, and video camera with an RCA output. The single board computer will capture data

from the scientific instruments via RS232 COM ports and record this data to a file on the hard

drive. The video capture board will periodically capture frames from the video camera, which

the single board computer will store as picture files on the hard drive. These time intervals for

data capture can be set by placing a mission data file on the hard drive via an Ethernet link

between the single board computer and a laptop computer. Also, data will be able to be retrieved

through the same link after mission completion. The Ethernet plug will be accessible through the

same hatch used to access the keypad.

The following pages contain pictures and basic information about the computer boards

mentioned in this section. They are all manufactured by Arcom Control System and are taken

from their PC/104 Product Guide.

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The SBC-386 provides the performance and reliability of previous generation boards, with the addition of on-board Ethernet at a reduced cost. The SBC features the low power, high performance 25MHz 386EX CPU from Intel surrounded by a host of functionality including: (3) serial ports, debug port, 10baseT Ethernet, 2MB DRAM, 1MB Flash, up to 512K battery backed SRAM, and an on-board 8-18VDC (or 10-16VAC) power supply.

The SBC-386 is rated at an operating temperature of –20 to +70C, and has been designed to meet European CE standards. The board is supplied as standard with Treck’s Real-Time TCP/IP stack and Supertask Multitasking Operating System pre-installed, and has the backing of a full suite of software development tools offered by Arcom.

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Conclusion

UndeSea Solutions, Inc. has created an under-ice sampling AUV that will function

effortlessly in less than desirable conditions in North Alaska. This AUV is the culmination of an

entire semester worth of research, design, and testing in the areas of mechanical, electrical, and

computer engineering. This AUV was engineered to the highest degree to be both structurally

sound as well as operate to the fullest efficiency.