90% of global commerce is conducted by sea
Inland waterways link coastal cities to the open
ocean
Heavy commercial and military traffic
The mission of the Navy is to maintain, train and
equip combat-ready naval forces capable of
winning wars, deterring aggression and
maintaining freedom of the seas.
Underwater mines severely hinder the progress
of naval fleet
Importance of Maritime Travel
2
(Wired)
Underwater Mines
Types
• Sea floor/Bottom
• Floating/Surface
• Moored, etc.
Sensing Techniques
• Contact
• Acoustic
• Pressure
• Magnetic, etc.
Damage
• Warheads can weigh between
100 and 700+ kg
• 1991: USS Tripoli struck a
contact mine 3
(21st Century U.S. Navy Mine Warfare)
(NOAA)
Current Detection Process
4
Current System
• Manned Helicopter
• Towing sonar
Sonar Operation Procedure
• Sends out sound waves
• Receives sound wave echoes
• Towed through the water
Active Sonar Equation
5
𝑳𝒔 : Source level radiated by and measured at sonar
𝑵𝒘 : Propagation loss en route to receiver
𝑻𝑺 : Target strength (measure of sound reflected by target)
𝑳𝑵 : Sonar self-noise
𝑨𝑮 : Array gain (how much noise the array cuts out)
𝑫𝑻 : Detection threshold (Signal to Noise Ratio (SNR) required for detection)
𝑺𝑬 : Signal excess (Processed SNR)
All terms in dB
Detection if SE ≥ 0
Stakeholder Interactions
6
SYSTEM
Environmental
Groups
Taxpayers
Servicemen
Minelayers
Beneficiaries System Customers
Designers &
Manufacturers System Operators
3. Need for system 1. Mine laying
2. Need for action
4. Create system 5. Countermeasure
Cost
New procedures Environmental impact
Concern over value of investment
Concern over new procedures Concern over environmental impact
Primary
Tertiary
Secondary Intended interaction
Indirect impact
Response to impact
Problem / Need
7
Need: There is a need for the U.S. Navy to improve the effectiveness of mine
clearance systems.
•Reduce operational cost
•Increase the rate of detection and neutralization of underwater mines
•Remove safety risk of personnel
Problem: Mines are a very effective method of blocking shipping lanes, restricting Naval
operations.
The placing of mines in waterways can have severe negative economic and
environmental impact.
Time required to clear a mine field can be up to 200 times the time required to
place the minefield.
Cost to lay a minefield can be as low as 0.5% of the cost required to clear a
minefield.
Mission Requirements
8
• Fuel cost to search 1 square
mile shall be less than $62.15
• System shall require fewer
than 5 people to operate
• Vehicle acquisition cost shall
be minimized
• Sonar acquisition cost shall be
minimized
• Sonar shall be able to search a
width of 300 meters
• System shall have endurance
greater than 2 hours
• Vehicle shall accelerate to a
velocity of 12 knots
• System shall be transportable
on current Navy ships
• Probability of false detection
shall be less than 0.5%
• System operators shall be
protected from mine
explosions
• Environmental impact shall
be minimized
System Requirements
Cost Requirements Performance Requirements Safety Requirements
Design Alternatives: Sonar
9
Small Example: Klein/L-3 5900
Large Example: Raytheon AN/AQS-20A
Speed: up to 12 knots
Weight: 360 lbs.
Length: 7.75 ft.
Diameter: 8 in
~$1M
Speed: 10 to 12 knots
Weight: 975 lbs.
Length: 10.5 ft.
Diameter: 15.5 in
~$11.83M
Design Alternatives: Vehicle
10
Air Surface Submersible
Small
Ex: K-Max
Large
Ex: Fire Scout
Small
Ex: Hammerhead
Large
Ex: Fleet Class
CUSV
Ex: RMMV
Weight: 5,145 lbs.
Lift capacity: 6,000
lbs.
Flight endurance: 2-
3 hours
~$5.1M
Weight: 6,000 lbs.
Lift capacity: 2,650
lbs.
Flight endurance: 5-8
hours
~$18.4M
Weight: 1,984 lbs.
Length: 17 ft.
Beam: 4.7 ft.
Endurance: 8 hours at
20 knots
~$100K
Weight: 22,000 lbs.
Length: 39 ft.
Beam: 10.25 ft.
Draft: 2 ft., 2 in.
Range: 1,200 NM
Length: 23 ft.
Diameter: 4ft.
Weight: 14,500 lbs.
Speed: >16 knots
Operating Depth: 10-
200 ft.
~$12M
(Northrop Grumman) (Lockheed Martin)
(Meggitt Training
Systems) (AAI/Textron) (Lockheed Martin)
Simulation Objectives/Assumptions
11
Objectives
Predict cost of mine detection
operations
Predict system performance
Assumptions
Pre-determined area
Moored mines only
Overt operation
Detection only (no
neutralization)
Urgent clearance
Sea state 0
Airborne Alternative
15
(drag due to air resistance)
𝜃
lift
drag
tow
mg
F Propulsion
*Principles of Helicopter Aerodynamics, J. Leishman
*
Drag Equation Data
Component Alternative Drag Coefficient (C) Area (m2)
Sonar Large 0.295 [37] 4.08[20] wetted
Small 0.295 [37] 1.52[32] wetted
Underwater Vehicle 0.04 [36] 58.37 [28] wetted
Surface Vehicle
Small (Air portion) 0.7 [37] 1.68 [33] frontal
Small (Water portion) 0.12 [37] 14.04 [33] wetted
Large (Air portion) 0.7 [37] 5.71 [26] frontal
Large (Water portion) 0.12 [37] 34.25 [26] wetted
Air Vehicle Small 1.35[31] 15.58 [35] frontal
Large 1.35[31] 4.77 [30] frontal
16 Density of water: 1027 kg/m3
Density of air: 1.225 kg/m3
Energy to Cost Calculation
17
Energy Density Cost per Volume
.
Energy Density : Fuel Price:
• Diesel = 128,450 BTU/gal.[38] $3.873/gal.[15]
• Gasoline = 116,090 BTU/gal.[38] $3.296/gal.[15]
• Jet Fuel = 125,217 BTU/gal.[8] $2.966/gal.[16]
Processed SNR
18
Parameter Description Large sonar (dB) Small sonar (dB)
Source Level 212 197
Propagation Loss Normal(70,12) Normal(70,12)
Target Strength 15 15
Noise Level Normal(58,12) Normal(58,12)
Array Gain 15 13.6
Detection Threshold 14 14
𝑳𝒔 − 𝟐𝑵𝒘 + 𝑻𝑺 − 𝑳𝑵 − 𝑨𝑮 − 𝑫𝑻 = 𝑺𝑬
Naval Operations Analysis (Wagner et al)
Gaussian distribution
Case Study: Inland Waterway Mouth of the Chesapeake Bay
3rd and 4th largest ports on
East Coast
• Hampton Roads
• Baltimore
Homeports to 69 Navy ships
19
(NOAA Nautical Chart 12222)
(Google Maps)
• 2 spans of tunnel
• Each 1 mile wide
Design of Experiment
20
Inputs Output
Sonar Vehicle Energy Time P(Detection)
Alt
ern
ativ
es
1
Large
Airborne Small
2 Large
3 Surface
Small
4 Large
5 Submersible
6
Small
Airborne Small
7 Large
8 Surface
Small
9 Large
10 Submersible
11 Baseline: Seahawk helicopter with Raytheon
sonar
Fuel Burn Results
Sonar Vehicle Vehicle Type Avg Gallons
of Fuel
Avg Fuel Cost Rank
Large
Small Air
4.457 $13.22 4
Large 6.168 $18.30 8
Small
Surface
5.021 $16.55 7
Large 9.210 $30.36 10
Underwater 3.617 $14.01 5
Small
Small Air
3.242 $9.62 2
Large 4.958 $14.71 6
Small
Surface
3.672 $12.10 3
Large 7.887 $26.00 9
Underwater 2.458 $9.52 1
Baseline: Seahawk helicopter with Raytheon sonar 21.032 $62.38 11
21
Small sonar dominant using all vehicles
Underwater option consumes least amount of fuel
Small sonar/Underwater vehicle has the best fuel economy
1 square mile travel
0
100
200
300
400
500
600
700
800
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10 0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
Nu
mb
er o
f O
ccu
ran
ces
Signal Excess (dB)
Processed SNR
22
10,000 replications • 95% Confidence Interval
• 1% half width
Large Sonar
87% SE≥ 𝟎
𝝁𝑺𝑬 = 30
Small Sonar
69% SE≥ 𝟎
𝝁𝑺𝑬 = 𝟏𝟑
𝒛𝜶/𝟐𝒑 (𝟏 − 𝒑 )
𝒏 − 𝟏
𝒛.𝟎𝟐𝟓.𝟖𝟕𝟏 (.𝟏𝟐𝟗)
𝟏𝟎𝟎𝟎𝟎−𝟏 = .66% < 1%
𝒛.𝟎𝟐𝟓.𝟔𝟖𝟗 (.𝟑𝟏𝟏)
𝟏𝟎𝟎𝟎𝟎−𝟏 = .91% < 1%
P(Detection) Results
23
(Principles of Underwater Sound, R.J. Urick)
Pro
bab
ilit
y o
f D
etec
tion,
per
cent
Pro
bab
ilit
y o
f D
etec
tion,
per
cent
Probability of False Alarm, percent Probability of False Alarm, percent
P(False Alarm) = 0.5%
𝜇𝑆𝐸 (Small) = 13, 𝜇𝑆𝐸 (Large) = 30
Small sonar: P(Detection) = 0.82 Large sonar: P(Detection) = 0.998
Life Cycle Cost
25
Life Cycle Cost
• Acquisition
• Operational cost
• Staffing requirements
Assumptions
• 1 Mine detection operation every 2 weeks for 20 years
• 5 square mile operation
Staffing requirements
• SH-60S Seahawk – 2 pilots, 2 air crew
• Unmanned vehicles – 1 person
• Sonar – 1 person
The Small sonar offers a cheaper alternative but the utility of the
Large sonar is higher.
• Small sonar, Small boat: Utility = .158, Cost = $3.5M
• Large sonar, Small boat: Utility = .433, Cost = $14.4M
• Marginal cost of utility: $3,942,389 / .1 units of utility
Utility vs. Cost Analysis
26
Uti
lity
Cost ($ million)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.00 10.00 20.00 30.00 40.00 50.00
Small Sonar, Small Boat
Small Sonar, Small Helicopter
Small Sonar, Large Helicopter
Small Sonar, Underwater Vehicle
Large Sonar, Small Boat
Large Sonar, Small Helicopter
Large Sonar, Large Helicopter
Large Sonar, Underwater Vehicle
Current System
Additional Alternatives
27
•Improved P(D)
•Same Process Time
•2x Fuel Burn
•Same P(D)
•½ Process Time
•Same Fuel Burn
•Improved P(D)
•½ Process Time
•2x Fuel Burn
Improved P(D):
New P(D) = P(D) + [(1-P(D))*P(D)] = 0.82 + [(1-0.82)*0.82] = 0.968
Utility vs. Cost Analysis (2)
28
Uti
lity
Cost ($ million)
2x Small sonar, Small boat (Time emphasis):
• Utility = .718, Cost = $7.03M
2x Small sonar, Small boat (Detection emphasis):
• Utility = .378, Cost = $7.06M
4x Small sonar, Small boat:
• Utility = .938, Cost = $14.06
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.00 10.00 20.00 30.00 40.00 50.00
Small Sonar, Small Boat
Large Sonar, Small Boat
Current System
2x (Time Emphasis)
2x (Detection Emphasis)
4x
Recommendations
30
Alternative Utility
Improvement
over current
system
Cost
Savings over
current
system
2x
Small sonar,
Small boat
(time
emphasis)
.718 156% $7.03M $39.76M
4x
Small sonar,
Small boat
.938 235% $14.06M $32.73M
References
32
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30. N/A, “MQ-8C Fire Scout” [Online] Available: http://www.northropgrumman.com/Capabilities/FireScout/Documents/pageDocuments/MQ-8C_Fire_Scout_Data_Sheet.pdf [Accessed: 10/22/2013].
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