Control configured design for smooth, highly-maneuverable, underwater vehicles

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Control Configured Design for Smooth,

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Highly-Maneuverable, Underwater Vehicles

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by

Anirban Mazumdar

B.S., Mechanical Engineering, Massachusetts Institute of Technology, 2007

M.S. Mechanical Engineering, Massachusetts Institute of Technology, 2009

Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of

Doctor of Philosophy at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

June 2013

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Author

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Department of Mechalical Engineering May 22, 2013

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H. Harry Asada Ford Professor of Mechanical Engineering Thesis Supervisor

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A ccepted by ... .,,...

David E. Hardt Chairman, Department Committee on Graduate Students Department of Mechanical Engineering

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Control Configured Design for Smooth,

Highly-Maneuverable, Underwater Vehicles

by

Anirban Mazumdar

Submitted to the Department of Mechanical Engineering on May 22, 2013, in partial fulfillment of the

requirements for the degree of Doctor of Philosophy

Abstract

We describe the development of a new type of robotic underwater vehicle designed specifically for the inspection of critical infrastructures such as boiling water reactor nuclear power plants. These applications require vehicles that can access confined areas, maneuver precisely, and move easily in several directions. In addition, external appendages such as fins or propellers should be avoided in order to reduce the risk of damage through collisions.

We propose a smooth, spheroid shaped vehicle that uses an internal propulsion system to generate and direct water-jets for propulsion and maneuvering. Draw-ing inspiration from aeronautics and ocean engineerDraw-ing, we treat this system as a control-configured vehicle (CCV) and design the system specifically for superior con-trol performance. Like many modern CCV aircraft, our robot is designed to be open loop unstable in order to avoid bulky external stabilizers. We refer to this new type vehicle as a Control Configured Spheroidal Vehicle (CCSV).

An integrated pump-valve maneuvering system is developed by combining pow-erful centrifugal pumps with compact Coanda-effect valves. This system is used to design and construct a compact, multi-degree-of-freedom (DOF) prototype vehicle. To achieve precision orientation control, high speed valve switching is exploited using a unique Pulse Width Modulation (PWM) control scheme. Dead zones and other complex nonlinear dynamics of traditional propeller thrusters and water jet pumps are avoided with use of integrated pump-valve control. Three simple control al-gorithms for coordinating valve switching and pump output are presented and are verified through experiments.

Planar control is complicated by the presence of hydrodynamic instability. A dy-namic control system that augments stability and achieves high maneuverability is outlined and implemented. A nonlinear hydrodynamic model is formulated, and its linearized dynamics are analyzed to attain insights into how physical design parame-ters, such as jet direction and body shape, influence controllability and stability. The integrated design method is implemented and shown to achieve high maneuverability and stability.

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ap-proaches. The vehicle open loop dynamics are studied and a plant zero is shown to significantly influence closed loop performance. Jet angle and vehicle shape are explored through the lens of optimizing this plant zero location, and design recom-mendations are presented for both ideal and practical situations. These lessons can be used to design new CCSV systems for a variety of scales and applications.

Thesis Supervisor: H. Harry Asada

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Acknowledgments

I would like to start by thanking my adviser, Professor Harry Asada, for all his guidance over the past six years. I still remember how excited I was to join this lab as a fresh graduate student, and I look back on those days and marvel at how much

I have learned and grown as a researcher and as a person. Professor Asada pushed

me to take on new and exciting challenges, and in doing so allowed me to learn both creativity and confidence. To have an adviser who helps you learn and develop every day is truly a privilege.

I also must thank my thesis committee members. Professor Triantafyllou's classes introduced me to Ocean Engineering and underwater vehicle design, and I have been hooked ever since. His immense knowledge on vehicle design and hydrodynamics was an invaluable resource for me throughout this process, and his feedback was critical to several key achievements on this project. Professor Youcef-Toumi also deserves special thanks for introducing me to control system design. He gave me my first research opportunity at MIT, and my work on robotic fish for my Senior Thesis helped me learn many valuable skills that I used for this project. Professor Youcef-Toumi was never too busy to help me with my work, and his knowledge of design and controls was very helpful to both this project and to my growth as an engineer.

I gratefully acknowledge the Electric Power Research Institute (EPRI) as well

as the National Science Foundation Graduate Research Program for their generous support of this work. John Lindberg and Greg Selby at EPRI were valuable and knowledgeable partners, and I appreciate their practical insights and expertise on nuclear power plant inspection in particular.

Similarly, this project as a whole was a collaborative effort. Meagan Roth was my first senior thesis student, and her work on initial prototypes, circuit design and software set the framework for much of this project. Martin Lozano was my star 2.12 student who I managed to convince to join our laboratory. His work on the electronics and "brain board" as he calls it was pivotal to miniaturizing the robot and achieving wireless control. We still use the circuit boards he designed and I

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always enjoy showing them to envious graduate students. Wyatt Ubellacker recently joined our group, but has already made real contributions to communications, and robust design. Finally, I must thank my good friend Aaron Fittery for his immense contributions over the past 2 years. Aaron, on his own initiative, learned CFD and used it to miniaturize and design new valves. It has been a pleasure to work alongside Aaron and watch him develop into a confident researcher.

I owe thanks to my my fellow lab members both past, and present. Ian Rust

was my collaborator on this project and deserves special thanks. Similarly, I must specifically thank lab alumni Levi Wood, Manas Menon, Tom Secord, Geoff Karasic, Patrick Barragan, and Shinichiro Tsukahara for their advice and assistance over the past years.

One of the best things about MIT is the people. My basketball friends Kimi Shirasaki, Daniel Kraemer, Yasu Shirasaki, Victor Wang, Kevin Sung, Cody Fleming, Conrad Miller, and Miguel Saez helped keep me humble and provided something to look forward to at the end of the day. Dyan Melvin was perhaps my closest friend during graduate school. While I appreciated his visits to lab and encouragement during quals, I am most grateful for him letting me beat him at one on one every once in awhile on the Rockwell Courts. Lastly I must thank Ellen Chen for her kind support and encouragement for the past couple years. She is my confidante and my number one supporter, and I truly cherish the time we have spent together.

I should also like to thank my "extended family" back in Irvine. Michelle and Irv Walot have always been there for me, and Dan and Jeanne Stokols are a constant source of encouragement. Christine King has been my ally since my days at University High School. Without her tough love I would not have made it to MIT.

Finally I will attempt to convey my deep gratitude to my parents. I cannot thank them enough for all their love and for teaching me to truly value learning and higher education. Going to school thousands of miles away from my parents has been one of the hardest things I have ever done. But whether through late night phone calls or impromptu cooking lessons, I feel like they have been part of this journey for every step of the way. I certainly know none of this would have been possible without them.

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7 CCSV-RAD Prototype Performance 117 7.1 Vehicle Performance ... ... 117 7.1.1 Surge Performance ... 118 7.1.2 Sway Performance ... 118 7.1.3 Stationary Turning . . . . 120 7.1.4 Turning at Speed . . . . 122 7.1.5 Heave Translations . . . . 123 7.1.6 Pitching Motions . . . . 125

7.2 Switching Between Motion Families . . . . 125

7.3 Exploring Passive Yaw Stability . . . . 125

7.3.1 Hydrofoil Modeling . . . . 126

7.3.2 Sample Tail Fin . . . . 127

7.3.3 Experimental Evaluation . . . . 129

7.4 Sum m ary . . . . 132

8 General Design Approaches 133 8.1 General Properties of the CCSV Design . . . . 133

8.2 Controllability of the CCSV Design . . . . 134

8.3 Designing for Control Performance . . . . 136

8.3.1 Determinant of Controllability Matrix . . . . 136

8.3.2 Vehicle Zero . . . . 137

8.4 Using Zero Location to Inform Vehicle Design . . . . 138

8.4.1 Jet Angle . . . 138

8.4.2 Vehicle Shape . . . 139

8.5 Examining Vehicle Performance . . . . 141

8.6 Additional Performance Considerations . . . . 142

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8.6.2 Practical Considerations . . . .1

8.7 Summ ary . . . . 9 Fundamental Control Performance Limitations 9.1 Bode's Integrals 9.2 9.3 9.4 Sensitivity Analysis . . CCSV Performance . . A General Tool . . . . 10 Additional Vehicle Prototypes 10.1 4-Pump CCSV . . . . 10.1.1 Jet Design . . . . 10.1.2 Vehicle Prototype ... 10.2 Propeller Based Design . . . . 10.2.1 Vehicle Design . . . . 10.2.2 Vehicle Performance . . . 10.3 Summary . . . . 11 Conclusions 11.1 Summary of Thesis Contributions 11.2 Future Work . . . . 11.2.1 Practical Considerations . . . . . 147 149 149 150 151 153 155 155 155 157 159 159 159 161 163 . . . . 163 . . . . 165 . . . . 165

11.2.2 Potential Research Directions . . . . 166

144

. . . .

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List of Figures

1-1 A diagram illustrating a GE Boiling Water Reactor system . . . . 25

1-2 A simple diagram for illustrating desired vehicle motions. . . . . 26

1-3 A rendering of the CCSV concept. . . . . 28

2-1 An illustration of the coordinate frame convention. . . . . 34

2-2 An illustration of the bistable fluidic amplifier concept. . . . . 36

2-3 A CFD illustration of the bistable fluid amplifier fluid dynamics. . . . 37

2-4 An illustration showing the full pump-valve concept. . . . . 38

2-5 A figure outlining the relevant geometric parameters for pump-valve m odeling. . . . . 39

2-6 A simulation plot illustrating the dependence of output force on the exit area for the combined pump-valve system. . . . . 41

2-7 CFD simulations showing a "good" valve design that avoids spillover (a) and a poor design that suffers from spillover (b). . . . . 42

2-8 A plot comparing the analytical model predictions of L, with CFD. . 43 2-9 A plot illustrating how the switching length, L, does not vary with a range of values for the input flow rate,

Q

. . . . . 44

2-10 A visual illustration of pump voltage control. The voltage control model is shown (a) as well as the use of voltage level to modulate output force (b). . . . . 45

2-11 A visual illustration of pump speed control. Using speed control to modulate force is shown in (a) as well as the speed-force input output relationship (b). . . . . 45

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2-12 CFD simulation illustrating valve switching dynamics for various force levels. . . . . 47

3-1 A photograph of the TCS M400 micropump that we will use

through-out this thesis. . . . . 50 3-2 A figure illustrating how to use the exit nozzle area to optimize the

output force . . . . . 51 3-3 Diagrams showing the dimensions of the final valve design. . . . . 52

3-4 Photograph of a full valve prototype with the switching mechanism (a) and a plot showing the high-low switching scheme. . . . . 53 3-5 Photograph of a fully assembled pump-valve system. . . . . 54

3-6 Pump voltage control over pump-valve system. Both directions of the

valve are shown. . . . . 55 3-7 Experimental data illustrating the switching dynamics of the valve.

The pump is running at full voltage. . . . . 55 3-8 Experimental data illustrating the switching dynamics of the valve for

several pump voltages. . . . . 56

4-1 A diagram illustrating the jet arrangement for the CCSV design. . . . 58

4-2 A diagram from The Encyclopedia Britannica illustrating a common type of centrifugal pump design. . . . . 59

4-3 A close up photograph showing the symmetric impeller. . . . . 60

4-4 A CFD simulation illustrating an in-line dual-output pump design. . 61

4-5 A CFD simulation illustrating the 90 degree pump. Note how when the impeller direction is reversed, the jet switches exits completely without any back-flow. . . . . 61

4-6 Experimental data comparing 3 pump design methodologies. . . . . . 62

4-7 Photograph of a BAU prototype. Two fluidic valves are combined with an orthogonal dual output port pump to generate forces in 4 directions. 62 4-8 A rendering showing the pump-valve system for the CCSV-RAD

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4-9 Photographs of the CCSV-RAD prototype. A fully assembled proto-type is shown (a) along with a closer view of the maneuvering system

is shown (b) . . . . 66

4-10 Photographs of the outside of the CCSV-RAD prototype. . . . . 66

4-11 An overview of the electrical components for the CCSV system. . . 67

4-12 Eagle software schematic layout for the robot brain board PCB. . . 68

4-13 Images showing the brain board layout and its fully assembled form. 69

4-14 A photograph showing the inner components of the robot. Note the metal cap, this is used for sealing the watertight electronics chamber. 70

4-15 A photograph showing the CCSV-RAD prototype performing a diving m aneuver. . . . . 71 5-1 A diagram illustrating the principal of combined pump-valve control

with a single input from the controller and and a single force output. 74

5-2 A diagram illustrating the components of a PWM Signal. . . . . 75 5-3 Dual pump-valve control algorithms: (a) pump speed control, (b) valve

PWM control, and (c) hybrid control. Each sub-figure includes i) PWM Duty Cycle, ii) pump output, and iii) resultant force, all in relation to the controller output, u. . . . . 75

5-4 Illustration of vehicle heading angle (a) and a diagram showing the capability of the vehicle to turn in place using dual jets (b). . . . . . 78 5-5 A plot of simulated yaw oscillations. The 4 solution cases are each

labeled. . . . . 82

5-6 A comparison of the full nonlinear solution with the closed form

non-linear approximation. . . . . 84

5-7 A block diagram of the heading controller. . . . . 85 5-8 A plot illustrating how a design curve can be used to tune the PWM

frequency. . . . . 86 5-9 Illustration of the simplified pump-valve static model. . . . . 87 5-10 Simulated response with and without a dead zone. . . . . 88

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5-11 Simulated response with PID pump speed control with deadzone. The

integral action slowly eliminates steady state error (a). Note the pres-ence of chattering in the valve signal (b). . . . . 89 5-12 Simulated response with PD valve PWM control. The improvement in

the overshoot and settling time is shown in the angle trajectory (a) as well as the force output of the pump-valve system(b). . . . . 90 5-13 Valve PWM using 2 different PWM frequencies. Note how the

oscilla-tions for fPWM = 1.5 are significantly higher than those for fPwM =

2.5H z. . . . . 91

5-14 Simulated response comparing valve PWM with hybrid control. Note the improvement in the rise time (a) as well as the amplitude adjust-ment in the force output (b) . . . . . 92 5-15 A set of frames from the hybrid control experiment. The dashed black

lines are a reference to illustrate the angle tracking. The dot is used to indicate the front of the robot, and the arrows indicate the direction of the vehicle angular velocity. . . . . 93 5-16 Experimental data from the CCSV-RAD prototype showing the

per-formance improvements from using valve PWM control. . . . . 93 5-17 Zoomed in view of the valve PWM control experimental results. . . . 94

5-18 Experimental data from the CCSV-RAD prototype showing how

hy-brid control can be used to improve the transient response. . . . . 95

6-1 An illustration of the body fixed coordinate frame. . . . . 98 6-2 An illustration of the Munk moment and how the stagnation points

create a turning motion on streamlined shapes. . . . . 100 6-3 A diagram illustrating how fins can provide both passive stabilization

or destabilization based on the direction of the vehicle. . . . . 101

6-4 An illustration of the key parameters for the planar vehicle model. . . 104

6-5 A pole-zero plot (a) and root locus plot (b) for the SISO vehicle

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6-6 A schematic diagram showing the role of jet angle in vehicle control

perform ance. . . . . 109

6-7 A pole zero plot for the closed loop SISO system. The closed loop

poles (pcL,1, PcL,2, PcL,3) are shown as are the zeros (zc, zi) and the open loop poles (pi, P2, P3). Note how the system is stabilized using PD control. . . . . 112

6-8 Simulated response for the open loop performance of the robot vehicle. The trajectory in fixed global coordinates,(XI, Y1), is provided in (a) and the yaw angle is provided in (b). . . . . 113 6-9 Simulated results illustrating the poor control performance when the

jet angle, -y, is set to zero. . . . . 113 6-10 Simulations of the closed loop system response. The angle (a) and

velocity (b) results of both the linearized model and the full nonlinear model are shown. . . . . 114

6-11 Experimental video data showing the vehicle trajectories for both open

loop control (a) and PD closed loop stabilization (b). . . . . 115 6-12 Experimental data showing the vehicle angle trajectory for both a

straight test (a) and a disturbance rejection test (b). . . . . 116 7-1 Video (a) and numerical (b) data illustrating the forward and back

performance of the CCSV-RAD prototype. . . . . 119 7-2 Video (a) and numerical (b) data illustrating the sway translation

ca-pability of the CCSV-RAD prototype. . . . . 120

7-3 Angle trajectory data for pure sway translation (a) as well as angle adjustments while moving sideways (b). . . . . 121 7-4 Video (a) and numerical (b) data illustrating the turn-in-place

capa-bility of the CCSV-RAD prototype. . . . . 121

7-5 Video (a) and angle tracking (b) data illustrating the turn-at-speed capability of the CCSV-RAD prototype. . . . . 122

7-6 Video (a) and velocity (b) data illustrating the turn-at-speed capability of the CCSV-RAD prototype. . . . . 123

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7-7 Video (a) and velocity (b) data illustrating the diving capability of the

CCSV-RAD prototype. . . . . 124

7-8 Pump reversal dynamics. . . . . 126 7-9 A simple diagram illustrating the hydrodynamic forces on a hydrofoil. 127 7-10 Lift and drag coefficients for a NACA 0015 airfoil. . . . . 128 7-11 Photographs comparing the OL stable prototype (a) and the OL

un-stable prototype (b). . . . . 129 7-12 Video data illustrating the stabilizing effect of the tail fin. The vehicle

moves relatively straight without any feedback control. . . . . 130 7-13 Video (a) and yaw rate data (b) data comparing the stationary turning

performance of the two vehicle designs. . . . . 131

7-14 Video (a) and angle tracking (b) data comparing the turning at speed performance of the two vehicle designs. . . . . 132

8-1 A diagram illustrating the jet arrangement for the CCSV design. . . . 134

8-2 Simulations illustrating the poor control performance of a spherical shape. ... ... 136 8-3 A diagram illustrating the key design parameters, a, b, and yj. . . . . 138

8-4 A plot illustrating the dependence of z, on the aspect ratio for m =

0.9kg. Note that for these aspect ratios, z1 is actually negative. . 140

8-5 Simulation data illustrating the control performance for various aspect ratios vary from 1.01 to 4. . . . . 142

8-6 Drag coefficients and forces for various aspect ratios. . . . . 143

8-7 A figure showing all 3 performance metrics and the role of aspect ratio. 144 8-8 A figure showing all 3 performance metrics. In this case a minimum

radius, b, is im posed. . . . . 145

8-9 A figure showing all 3 performance metrics. In this case a minimum

radius, b, is imposed, and aspect rations above 1.3 are penalized. . . . 146

8-10 Simulated data showing the XY trajectory (a) and the sway response (b) for various aspect ratios when a minimum radius is imposed. . . . 147

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9-1 A block diagram of the SISO yaw control system. . . . . 150 9-2 A prototype sensitivity function that should provide good control

per-form ance. . . . . 151 9-3 A plot showing how the Bode Integral analysis can be used to find the

vehicle speed limit. . . . . 152

9-4 A plot showing the values for P for various aspect ratios. . . . . 154

10-1 A rendering illustrating the maneuvering system for the 4-Pump CCSV. 156

10-2 A photograph of the maneuvering system for the 4-Pump CCSV pro-totype. . . . . 157 10-3 A photograph of the outside of the 4-Pump CCSV prototype. The

lights on the camera are clearly visible. . . . . 158

10-4 An image taken from the onboard recording camera during a vertical weld inspection. . . . . 158 10-5 A rendering illustrating the maneuvering and propulsion system for

the propeller based design. . . . . 160 10-6 Photographs illustrating the maneuvering system as well as the outer

shape of the propeller based robot prototype. . . . . 160 10-7 Heading angle data for both the straight test (a) and the disturbance

rejection test (b). . . . . 161 10-8 Heading angle data for both turning at speed (a) and stationary turning

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List of Tables

3.1 Summary of the M400 Pump. . . . . 50

4.1 Summary of Maneuvering Primitives. ... 58

4.2 Summary of Pump and Valve Combinations for Vehicle Motions. . . . 64

5.1 Summary of Solution Cases . . . . 80 5.2 Summary of Region Boundary Conditions . . . . 81 5.3 Summary of CCSV-RAD prototype yaw dynamics properties. .... 85 6.1 Summary of Physical Properties for CCSV-RAD Prototype. . . . . . 111

7.1 Summary of Vehicle Performance. . . . . 118 7.2 Summary of Physical for Sample Tail Fin. . . . . 129

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Chapter 1 Introduction

1.1 Underwater Robots for Cluttered Environments

Modern societies have become increasingly dependent on water based infrastruc-tures whether they are power systems, ports, piping systems or water treatment plants. As these systems age, they require repairs and inspections with increasing frequency. Since many of these systems are essential to public safety, there exist strict protocols for inspection. For example, for Boiling Water Reactor (BWR) nu-clear powerplants, there exist very strict and specific visual inspection protocols. For many of these applications, it is difficult, costly, dangerous, and sometimes even im-possible to send humans to inspect and assess. In addition, for many systems, inspec-tions cannot be performed with the system running and must instead be performed during a shutdown. These shutdowns are not only inconvenient and disruptive, they can be extremely costly economically. As a result, the inspection of cluttered aquatic environments is a rapidly growing area of research and technical innovation.

Already underwater robots are being developed and deployed for the inspection of ports [1], [2], dams [3], water piping systems [4], shipwrecks [5], and nuclear power plants [6], [7]. Some key challenges for these types of robots relate to accessing and inspecting complex environments where small size and high maneuverability are required. In addition, robustness is an important characteristic for vehicles operating in constrained environments where collisions are inevitable. For example, nuclear power plants are subject to foreign material exclusion (FME) rules that stipulate that

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no outside materials can be left within the plant after an inspection. This means that the robot must be able to survive collisions without breaking and without external components falling off.

1.2 Nuclear Power Case Study

The challenging nature of underwater infrastructure inspection is perhaps best illustrated with boiling water nuclear plants. Boiling water reactors serve as a good case study example because they are complex water-filled systems, highly regulated, and must satisfy strict inspection protocols. In addition, nuclear power plants are clearly areas where direct inspection using human workers is something that must be avoided.

There exist 35 boiling water reactors in the USA [8], and 84 world wide [9]. Nuclear power is an extremely highly regulated industry, and the plants must satisfy regu-lations developed by the Nuclear Regulatory Commission (NRC), ASME (American Society of Mechanical Engineers) and EPRI (Electric Power Research Institute). Vi-sual inspections using cameras are the most common inspection methodology. Some-times this will be combined with techniques such as ultrasound in order to provide more detailed measurements.

As Fig. 1-1 illustrates, the inspection of the reactor environment is a very chal-lenging problem. The system can be treated roughly as a 15m diameter, 40m deep pool of water filled with nozzles, guides, pipes and tubes that must all be navigated and inspected. An illustration of the inside components of a BWR plant can be found in Fig. 1-1, which provides a popular diagram of a General Electric (GE) re-actor assembly [10]. As Fig. 1-1 shows, the environment is very complex with small areas such as the top guide (item 12 in the figure) placing restrictions on size and ac-cess. Deploying and then finely maneuvering tools within this environment is clearly challenging and requires robots that are relatively small and nimble as well as robust. As mentioned previously, nuclear powerplants are shut down during inspection (usually during the refuel cycle). This means that there is a clear economic incentive for rapid inspections. Inspections that are slowed by sluggish or unreliable equipment can cost power companies and inconvenience thousands of people and businesses.

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BWR

/6

REACTOR ASSEMBLY

1. VENT AND HEAD SPRAY

2. STEAM DRYER IIFTING .UO

3, STEAM DRYER ASSEMBLY

4. STEAM OUTLET

G. CORE SPRAV INLET

6. STEAM SEPARATOR ASSEMBLY

?, F.FDWATER INLET

8. FEMDWATER SPAROER

9. LOW PRES"IRE COOLANT

INJECTION INLET

10. CORE SPRAY INE 11, CORE SPRAY SPARGER

- 12. TOP GUIDE

13. JET PUMP ASSEMBLY 14. CORE SHROUD

15. FUELt ASSEMBLIES

16. CONTROL 1LADE

17. CORE PLATE

11. JET PUMPI RECIRCULATION WATER INLET

I9. RECIRCULATION WATER OUTLET 2D. VESSEL SUPPORT SKIRT 21. SHIELD WALL 22. CONTROL ROD DRIVES 23. CONTROL ROD DRLVE

HYDRAULIC LIKES 24. IN-CORE FLUX MONITOR

DENEIALO ELECTRIC

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Therefore, it is not surprising that developing robotic systems which can enter the re-actor environment, maneuver precisely, and obtain visual data are an area of growing innovation and research.

1.3 Functional Requirements

We can use the nuclear powerplant inspection case study to help us generate functional requirements for inspection robots. These functional requirements will be used to examine prior work, generate design concepts, and evaluate our designs. As illustrated below, these functional requirements are very general and therefore also summarize the needs for a wide class of underwater inspection robots. Therefore, robots systems that meet these requirements will likely be generally applicable to a

wide class of emerging inspection applications.

1.3.1 Motions in Multiple Directions

In order to traverse a complex environment and aim a camera or other sensors, inspection robots should have the ability to move in 5 directions. To illustrate these motions we will use the coordinate frame fixed to the center of mass of the vehicle in Fig. 6-1 The motions that we require are include surge (translation alog x), sway (translation along y), and heave (translation along z), as well as yaw (rotations about

z) and pitch (rotations about y). will also be required. The only degree of freedom that we will not need is roll (rotation about the x axis). Roll is generally not useful for visual inspection tasks, as turning sideways or upside down serves no obvious purpose. This is especially true for symmetric vehicles where rolling would not help fit into confined areas.

rx

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1.3.2 Bidirectional Motions

Precise motions within a constrained space require the ability to move forwards and backwards with equal ease. While this may seem like an obvious requirement, many underwater vehicles due to their design and propulsion system cannot simply

reverse direction. The inspection robots we aim to develop must be able to move in both the positive and negative direction for each degree of freedom. This means that they will able to move quickly, stop, reverse, and carefully adjust their position and orientation in order to navigate obstacles and aim their sensors precisely and quickly. Bidirectional capability will greatly simplify vehicle control and path planning.

1.3.3 Maneuverability at a Range of Speeds

The ability to maneuver well at many operating speeds is essential for efficient inspections. A robot that can only maneuver at higher speeds makes precision inspec-tion very challenging. This is especially true for tasks such as visual inspecinspec-tion where the sensors sample slowly and are susceptible to blurring. Similarly, a robot that can only maneuver at slow speeds will not be able to move quickly between inspec-tion locainspec-tions and will not be able to react dynamically to changing condiinspec-tions. The inability to maneuver at higher speeds therefore reduces efficiency, prolongs mission times, and leaves the robot vulnerable in uncertain environments.

1.3.4 Robust to Collisions

As discussed previously, nuclear power plant inspection requires extremely robust robot systems. In fact, the fear of robot damage and violation of FME rules has meant that the industry has been cautious in their adaptation of robotic technologies. Robot systems must be extremely robust to collisions by virtue of their design. This means that components that can potentially break and fall off during a collision must be avoided. Conventional underwater systems have many such systems such as spinning propellers, fins, and rudders. These types of systems that protrude from the vehicle

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1.4 Design Concept: Control Configured Spheroidal

Vehicle

Based on these functional requirements we developed a conceptual design which is a novel and innovative to approach the challenge of infrastructure inspection. Specif-ically, we propose a vehicle that is completely smooth and spheroidal in shape. The vehicle propels itself and maneuvers using water jets that can be modulated and switched between various exit ports. The symmetric and smooth nature of the shape allow for bi-directional motions, high maneuverability, and robustness to collisions. The use of jets for propulsion rather than propellers means that the risk of a spinning propeller breaking during a collision or becoming tangled is removed. In addition, the absence of stabilizers such as fins means that there are no components that can snag on obstacles. We describe this approach as the "Control Configured Spheroidal Vehicle (CCSV)" We use this title because we emulate the Control Configured Vehicle ideas from aeronautical engineering [11]. Specifically, the vehicle is designed specif-ically to achieve multi-degree-of-freedom (DOF) motions and high fidelity feedback control performance. We are faithful to the CCV concept by thoroughly analyzing projected control performance and using it to educate vehicle design. Finally, just like many modern CCV type vehicles, our design is open loop unstable and uses feedback control instead of passive stabilizers to achieve superior performance.

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While this type of approach appears simple and intuitive, examples of such smooth, multi-DOF and bidirectional robots are extremely rare in the literature. The Eyeball ROV proposed by Rust and Asada [12], uses a creative internal moving mass and gimbal system to achieve rotational motions, but still relies on external propellers to generate its forward thrust. Similarly, the University of Hawaii's ODIN robot is spherical in shape but uses several external propeller thruster to propel and maneuver

[13]. Work by Lin describes a smooth sphere propelled by jets, but only achieves 3

DOF by using modified bow thrusters [14]. The vehicle design that comes closest to matching the performance and overall shape we desire is the BFFAUV design de-veloped by Licht and Triantafyllou. This design is capable of bidirectional motions, multiple DOF, and high maneuverability through the use of biologically inspired flap-ping foils [15]. However the large external flapflap-ping foils means that the vehicle does not have a completely smooth external shape.

In our view there are two main technical challenges that make designs like this

CCSV concept difficult to realize. The first is the design of a propulsion and

ma-neuvering system that can fit within a small, streamlined shell. The most popular approach for underwater vehicles is to use propeller thrusters, but these have to sit in the ambient fluid to operate properly. In addition, combining several external pro-pellers to achieve multi-DOF propulsion results in several propro-pellers on the outside of the vehicle, making it less hydrodynamically efficient and more difficult to posi-tion precisely. The second major technical challenge is associated with the presence of hydrodynamic stability. This instability is generally dealt with by adding fins at the tail of the vehicle. However, these are not only large appendages, but they will destabilize the vehicle if the vehicle direct is reversed, making bidirectional motions

challenging.

1.5 Thesis Overview

This work will focus on the analysis, design and evaluation of this new CCSV concept. We discuss the development of a novel pump plus fluidic valve propulsion system that can be built into a smooth shell and used to achieve very precise control. We will also discuss how this system can be used as an enabling technology to design

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small and smooth robots. We will also analyze in depth the nature of the hydrody-namic instability and propose a unique and realizable stabilizing controller. Finally we will perform general analysis on how to design specific vehicle components and how to determine the best vehicle shape. Lastly, a full robot prototype is constructed and used as a test-bed for these new concepts and ideas.

Chapter 2 of this thesis focuses on the development of the unique pump plus

fluidic valve system that serves as the building block for this work. We describe the current state of the art in jet propulsion and examine the role our system plays in advancing the field. We then illustrate the functionality of the device with both analytical models and computational fluid dynamics (CFD) simulations.

Chapter 3 describes the construction of a functional pump-valve system.

Experi-ments are used to evaluate the pump and valve performance and the results are shown to correspond well to the models in Chapter 2.

Chapter

4

illustrates how the pump-valve systems can be used to design a robot that is completely smooth and capable of motions in 5 directions. A unique

or-thogonal, dual-output port pump is outlined and used to generate reduced actuation designs. The Control Configured Underwater Vehicle (CCSV) concept is introduced, and a fully functional prototype which uses reduced actuation design is presented. This prototype is referred to as CCSV-RAD. Each critical component is described in detail.

Chapter 5 discusses the use of combined pump-valve control to achieve precision

orientation control. The pump-valve nonlinearities are addressed through the use of two novel pump-valve control algorithms that exploit Pulse Width Modulation (PWM) of the fluidic valves. Rigorous mathematical analysis is performed to pre-dict vehicle oscillations, and design methods are provided. The pump-valve control systems are evaluated using both simulations and experiments.

Chapter 6 focuses on planar vehicle control in the face of hydrodynamic

instabil-ity. The hydrodynamics of the smooth vehicle are examined, and the Munk moment is shown to result in instability. The coupled nonlinear equations are linearized about a trim state and used to design a stabilizing control system. This linear analysis

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pro-vides several unique insights into vehicle control and performance. Finally, a unique stabilizing controller which uses only angle and angle rate measurements is outlined and used to achieve impressive planar performance. The controller is implemented on the CCSV-RAD prototype robot and is shown to stabilize the vehicle even in the face of substantial disturbances.

Chapter 7 uses the stabilizing control system from Chapter 6 to illustrate the

unique performance capability of the CCSV prototype. Multi-DOF motions are shown including forward and backwards translations, sideways motions, diving, and high speed turning. This vehicle performance is also compared with a prototype that uses a fixed tail fin to achieve stability. The actively stabilized CCSV-RAD prototype is shown to provide substantially improved performance, especially with regard to low and high speed turning.

Chapter 8 explores CCSV design from a more general perspective by examining

the role of jet angle and vehicle shape. Linear analysis is used to explore uncontrollable shapes and behaviors, and control system analysis is used to explore optimal aspect ratios. Simulations are used to validate these concepts, and ideal ranges for both jet angle and vehicle aspect ratio are provided.

Chapter 9 analyzes the fundamental limitations of using closed loop control to

stabilize unstable underwater vehicles. Bode's Integrals and results from a seminal paper in the field are used to explore "speed limits" for our control configured design. These concepts are then used to examine the broader ramifications of closed loop stabilization.

Chapter 10 develops some additional designs that combine the pump-valve

sys-tems with additional pumps or propellers in order to improve control and efficiency. Photographs of two prototypes along with preliminary experimental results are

pro-vided.

The thesis concludes with Chapter 11 which provides final conclusions and a summary of the key contributions.

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Chapter 2 Appendage Pree Propulsion and

Maneuvering

In this chapter we describe our unique pump-valve propulsion and maneuvering sys-tem for smooth underwater vehicles. We first introduce basic terminology and nomen-clature, then we provide an overview of existing technologies. We then propose a novel system based on powerful centrifugal pumps and fluidic valves. Models for predicting force output are outlined and a design procedure for maximizing force output while ensuring proper valve performance is described. Finally, this chapter discusses pump models and pump-valve dynamic modeling.

2.1 Nomenclature

Throughout this thesis we will be using terminology and nomenclature derived from the field of Ocean Engineering. Specifically we will use kinematics and and dynamics based on a body centered coordinate system shown in Fig. 6-1. This system was developed by the Society of Naval Architects and Marine Engineers in

1952 and is prevalent in the underwater vehicle literature [16], [17].

As the figure illustrates, u, v, w represent translational velocities about the x, y, and z axes respectively. These motions are also described as "surge," "sway," and "heave," respectively. Similarly, rotational velocities about the x, y, z axes are referred to as p, q, r respectively. These motions are also known as "roll," "pitch," and "yaw."

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p

Y

X

z

Figure 2-1: An illustration of the coordinate frame convention.

2.2 Current Approaches

Traditionally, propeller thrusters and lifting surfaces (fins or rudders) have been the most common forms of propulsion and steering. Lifting surfaces in particular function extremely well for vehicles moving at high speeds because they provide forces that are proportional to the square of the fluid velocity. However, at low speeds, these forces become very small and many lifting surfaces such as rudders lose their ability to provide turning forces and moments (this does not necessarily apply to flapping or heaving foils). As a result, a common approach is to use a number of propeller

thrusters to achieve multi-DOF motions.

In order to function properly, propellers must have access to a relatively unob-structed flow. This means that many systems must be placed so that they protrude off the vehicle body. As a result, having many thrusters make the vehicle body bulkier and less maneuverable. One emerging solution to this issue is the use of tun-nel thrusters [181. These systems use a concentric stator with the propeller and rotor sitting in the middle. As a result, these types of thrusters can be placed in an opening in the vehicle hull. These devices hold promise because they can be incorporated into a streamlined vehicle shape. However, since the fluid must flow through the hull, tunnel thrusters still take up substantial space. In addition, the prototypes presented in [18] are quite large (70mm diameter).

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For precision maneuvering propeller thrusters present additional challenges. Pro-peller thrusters tend to have substantial nonlinearities such as varying time response, dead zones, and asymmetric performance [19], [20], [21]. Precision maneuvering tasks frequently involve switching the thrust direction back and forth rapidly. Reversing the propeller direction causes large current spikes when the motor is at zero veloc-ity. In addition, many screw type propellers are designed to turn in one direction. Reversing the direction changes the flow profile substantially. Similarly, propeller-thruster nonlinearities become more pronounced at lower operating speeds [18], [19]. The presence of dead zones can further degrade control performance. Dead zones are common in propeller thrusters and are present in examples from the literature such

as [20] and [21].

As a result of these issues with propeller thrusters, developing alternatives is a growing research field. Much of this work has focused on the development of biologi-cally inspired robots with flexible bodies such as [22, 23, 24]. A field that has recently emerged is using alternative actuation technologies to propel flexible, biologically in-spired fish. The authors in [25] and [26] use Ionic Polymer-Metal Composite (IPMC) to develop very small fish-like robots. Another novel approach is to use jet action and fluttering fluid to create oscillatory tail motions [27]. These vehicles emulate fishlike swimming to achieve unique efficiency and robustness. However, in this case, fish-like behavior is not necessarily appropriate for our applications of multi-DOF motions in confined spaces. Caudal fin propulsion meas that turning and longitudinal motions are coupled and turning in place is challenging. In addition, these types of fishlike robots cannot achieve pure sway rotations.

Another area of particular relevance is the development of biologically inspired synthetic jet thrusters. These systems can be incorporated into streamlined shapes and used to achieve impressive multi-DOF performance. Examples from the literature include [28], [29], and [30]. Thus far these systems have been paired in order to achieve bidirectional performance. This adds to the size requirements for multi-DOF, bidirectional robot systems.

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2.3 Pump-Valve Concept

In this thesis, we propose a different approach. We construct a propulsion system with powerful DC motor based centrifugal pumps. The pumps are used to generate high velocity water jets that can be used to propel the robot. We choose centrifugal pumps due to their mechanical and electrical simplicity, small size, and commercial availability. One issue with centrifugal pumps is that they often have a preferred di-rection. This means that achieving equal bidirectional forces is challenging. The most obvious approach would be to combine two centrifugal pumps in a back back config-uration in order to achieve forces 1800 apart. However, such an approach increases the size and weight of the robot substantially.

In order to achieve bidirectional forces we draw inspiration from the field of fluidics. Fluidic technology emerged in the 1960s and 1970s as a way of making fluid logic circuits and computers. One such component that is particularly relevant is the "bistable fluidic amplifier". This device which emerged as early as the 1960's was used to switch the direction of a powerful input jet by modulating two small control ports [31]. The system exploits the Coanda Effect (discovered by Henri Coanda in

1932), or the tendency of fluid jets to attach themselves to curved surfaces [32, 33, 341.

Exit E, Exit E2

rEntrained: _Entrained

_D

fluid flud

Control Control Control Control

PortC₁ PortP_or tort C1 Port C2

closed to open to open to closed to

ambient ambient ambient ambient

Input flow Q Input flow Q

Figure 2-2: An illustration of the bistable fluidic amplifier concept.

As Fig. 2-2 illustrates, the device can be used to switch a high velocity fluid jet between two output ports. The device sits in the ambient fluid, and an input flow

Q

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is injected at the input. The control ports, C1 and C2 are used to switch the direction of the jet. If control port C1 is closed while control port C2 is open to the ambient fluid, a small amount of fluid will be entrained through port C2 and the jet will bend and exit through exit E1. If the control port C1 is closed and control port C2 is closed the jet will then switch and exit through exit E2. Depending on the dimensions and

jet parameters, very high switching speeds can be achieved using this type of system

[35]. If the dimensions of the valve are designed improperly, the the jet will not bend

completely (or not at all) and flow will exit through both exit ports. This is problem is called "spillover" and will be discussed further in this chapter.

Figure 2-3: A CFD illustration of the bistable fluid amplifier fluid dynamics.

A CFD plot in Fig. 2-3 provides a visual illustration of the fluid dynamics of

bistable switching amplifiers. The figure shows clearly how if the system is designed properly it can be used to achieve bidirectional jet switching. The switching mech-anism itself is quite simple, all that is required is to open and close the two small control ports. Since the control ports are never open or shut simultaneously, a simple switching system can be developed using a small solenoid or DC motor. Since we will use the fluidic amplifiers to switch a jet direction, we will refer to our fluid amplifier systems as fluidic valves for the remainder of this thesis.

We develop a pump-plus-fluidic-valve system by attaching one of these fluidic valves to the output of a centrifugal pump. A visual illustration of this system is provided in Fig. 2-4. The pump draws fluid inward radially (blue arrows) and then

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Fluid Force Fon Control Volume

Output Jet

ILX

C, Open 1NC2 Closed

Inlet Flow

lnlet ~ _- _- _Inlet_Flow

Inlet Flow

Reaction Moment MR Exerted On Control Volume

Figure 2-4: An illustration showing the full pump-valve concept.

injects the jet into the fluidic valve. If C1 is open and C2 is closed, the output water

jet will exit in the positive X direction (jet labeled in red). Analyzing the output force, F, will be discussed later in this chapter.

This mechanical simplicity as well as the high switching speed has meant that such devices have become popular for a variety of diverse applications. A few examples from the literature include amplifier architectures have been used for mechanical and biomedical system identification [35], [36]. Similar systems have also been explored for aerospace applications [37], [38] and fuel injection systems [39]. There exist numerous other examples for aeronautical and gas-jet flow control, but very few cases exist for use in underwater vehicles. One such example is [40], where the author explored using a jet diverter to explore hovering control. A patent describes using fluidic amplifier architectures to maneuver ships but experimental validation and published works are not provided [41]. In addition, no previous work describes the design for a multi-DOF underwater robot system using pumps and fluidic valves.

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2.4 Modeling Pump-Valve Static Performance

2.4.1 Static Force Performance

To analyze and properly design the pump-valve system, we need simple models that can be used to predict performance. In Fig. 2-5, we illustrate the relevant physical dimensions. An input volumetric flow rate,

Q,

is injected through a nozzle of area A, and then exits through either exit of area Ae. We assume a fixed ratio between A, and Ae (in practice A, = 2A,). We assume the exits are square shapes.

Throughout this thesis we treat the fluid as an incompressible and inviscid fluid with density p. We assume that the pump has a no load flow of

Qm

and a no flow pressure of Pma.

Exit

El

-- -

Exit

E

₂ Ae C1 LsC2

A

Inlet I

Figure 2-5: A figure outlining the relevant geometric parameters for pump-valve modeling.

We use a simple relationship to determine the flow,

Q,

as a function of the pressure. The equation is provided in eq.2.1.

Q(P)

= x P +Qmax (2.1)

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0=-P(

)

'+ '

Q-Pmax

(2.2)

2 An

Qina

We can use Bernoulli's equation to model the flow exiting the pump. Note that we neglect minor pipe losses due to elbows and the contraction at the nozzle. The result from eq. 2.1 can be substituted resulting in the following relationship for the

flow rate based on the nozzle area.

Finally, we can use conversation of linear momentum to determine the output force, F. Since the pump and valve are fixed to a floating vehicle, all the resulting reaction forces and moments will affect vehicle motion. To analyze the reaction forces and moments we create a control volume that encloses both the pump and valve. This control volume is illustrated in Fig. 2-4. Note that the fluid enters the pump radially and therefore creates no planar force. The output jet bends 900 before exiting. We assume that the jet exits through one port completely (no spillover). This is treated as an internal force based on our choice of control volume. This modeling convention is consistent with the literature [35]. The reaction force on the control volume, F is in the -x direction. The rotation of the pump impeller generates a pure reaction moment, MR on the control volume. If this moment is large enough it can cause

the robot to spin. In practice, for the systems analyzed in this thesis, the reaction

moment, MR, is negligible.

Using this control volume we can determine the reaction force, F. The expression for F as a function of the flow rate,

Q,

is provided in eq. 2.3.

F = p- Q(2.3) Ae

We assume that Ae = 2An and then perform a simulation using parameters and

dimensions from real devices. The output force, F, is plotted in Fig. 2-6 as a function of the exit area, Ae. The figure corresponds with intuition for the extreme cases. For example, a very small exit leads to nearly zero flow rate due to large pressure buildup.

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Similarly, very large exit area leads to small force due to very small exit velocities. Most importantly, there exists an optimal exit area at which F is maximized. This result can be used to size the fluidic valve in order to match the pump properties. Making the ratio between Ae and An smaller can improve the output force but will greatly affect the switching performance. Most analysis assumes that An acts as a nozzle with respect to the other dimensions. In fact, for other systems in the literature, such as [35] and [36] use much larger ratios. From our experience through

CFD and experiments, reducing the ratio of Ae/An below 2 leads to poor switching

performance. 0.25 0.2 Z 0.15- 0.1-20 40 60 80 100

A

An,pmp [M

[min]

Figure 2-6: A simulation plot illustrating the dependence of output force on the exit area for the combined pump-valve system.

2.4.2 Switching Length

As noted in the previous section, the static force analysis assumes that the jet bends completely and exits through only one exit port. If this does not occur and flow instead exits through both exit ports, we refer to this as "spillover." An illustration of an improperly designed valve is provided in Fig. 2-7. The control ports are configured so that the flow exits through the right hand exit, but some flow does not switch and instead exits through the left hand exit. This substantially degrades the output force

Control configured design for smooth, highly-maneuverable, underwater vehicles

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Control Configured Design for Smooth,

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Highly-Maneuverable, Underwater Vehicles

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Control Configured Design for Smooth,

Highly-Maneuverable, Underwater Vehicles

by

Anirban Mazumdar

Abstract

Acknowledgments

Contents

. . . .

. . . .

. . . .

. . . .

List of Figures

Q

List of Tables

Chapter 1

Introduction

1.1

Underwater Robots for Cluttered Environments

1.2

Nuclear Power Case Study

BWR

/6

1.3

Functional Requirements

1.3.1

Motions in Multiple Directions

1.3.2

Bidirectional Motions

1.3.3

Maneuverability at a Range of Speeds

1.3.4

Robust to Collisions

1.4

Design Concept: Control Configured Spheroidal

Vehicle

1.5

Thesis Overview

4

Chapter 2

Appendage Pree Propulsion and

Maneuvering

2.1

Nomenclature

Y

X

2.2

Current Approaches

2.3

Pump-Valve Concept

D

Q

2.4

Modeling Pump-Valve Static Performance

2.4.1

_D