Stealthy
Ships
Technology, of AWCT
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SUMMARY
Proposed is a technology (AWCT) for adding Stealth properties
to existing U.S. Fleet surface ships by the use of sprayed sea water.
The Adaptive Water Curtain Technology (AWCT) is intended to deflect
and scatter enemy radar waves thus reducing the ship’s radar cross section
(RCS). It consists of (highly conductive) sea water sprayed in a fashion
that effectively creates an angled radar reflective curtain around the
ship.
To reduce the ship’s remaining RCS, the water curtain can be
"modulated" such that the returns appear as "Sea Clutter." This could be
done by determining the surrounding Sea State--either locally, or from
satellite Sea State data, i.e., deriving the Sea Clutter Spectrum; and
applying the appropriate coefficients to the modulating process for optimum
mimicry.
This approach is suggested as an "Add-On" to existing surface
ships, an interim measure until the next generation DD(X)
of stealthy surface ships has replaced this class. The Arleigh Burke class
Destroyer--which has rudimentary stealth technology, is used as an example
of a recipient ship for this technology. Although this class of ship has
a reduced RCS over its predecessor, it can still benefit significantly
from the proposed technology.
This is a Work in Progress.
There are fundimental questions yet to be answered. See
List
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-Sea
Clutter-
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| Insufficient Threshold -----------------------------Raised
Threshold |
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Optimum Threshold -----------------------------Excessive
Threshold
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-Illustration
of Sea Clutter overlaid by Detection Threshold-
Targets Detected above the Clutter-
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-Sea
Clutter Noise relative to Target Signal-
Sll-
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-Sea
State
Sea State = Sea Clutter
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Sea State Defined:
Sea State refers to the condition of the sea's surface, quantified
in terms of wave height, period, and character. The large number of variables
involved in describing Sea State such as wedges, cusps, waves, foam, turbulence,
and spray, as well as breaking events of all sizes and masses of falling
water. Any or all of these might contribute to the scattering of electromagnetic
waves responsible for sea clutter. The basic oceanographic descriptor of
the sea surface, however, is the wave spectrum, which, while saying little
about these features, contains a great deal of information about the sea
surface in general and is central to the application of the Bragg scattering
hypothesis.
There is the need to understand the sea surface in order to understand
sea clutter and the prominence of the Bragg hypothesis in existing clutter
models.
There are basically two types of surface waves, capillary and gravity,
depending on whether surface tension or gravity is the dominant restoring
force. The transition between one and the other takes place at a wavelength
of about 2 cm; so the smaller capillary waves supply the surface fine structure
while gravity waves make up the larger and most visible surface structures.
Waves have their origin ultimately in the wind, but this does not mean
that the "local" wind is a particularly good indicator of what the wave
structure beneath it will be. In order to arouse the surface to its fully
developed or equilibrium state, the wind must blow for a sufficient time
(duration) over a sufficient distance (fetch). That part of the wave structure
directly produced by these winds is called sea. But waves propagate, so
even in the absence of local wind, there can be significant local wave
motion due to waves arriving from far away, perhaps from a distant storm.
Waves of this type are called swell, and since the surface over which the
waves travel acts as a low-pass filter, swell components often take the
form of long-crested low-frequency sinusoids.
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State of the Sea
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Scale
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Description
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Height of wave
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| 0 |
Calm sea |
0 or less than 1 foot |
| 1 |
Smooth sea |
1 to 2 feet |
| 2 |
Slight sea |
2 to 3 feet |
| 3 |
Moderate sea |
3 to 5 feet |
| 4 |
Rough sea |
5 to 8 feet |
| 5 |
Very rough sea |
8 to 12 feet |
| 6 |
High sea |
12 to 20 feet |
| 7 |
Very high sea |
20 to 40 feet |
| 8 |
Precipitous sea |
40 feet and over |
| 9 |
Confused sea |
Record chief direction |
The 1938 edition of the US Navy Hydrographic
Office publication No. 9
The most recent Sea State Descriptors: The
Beaufort Scale |
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One more of the many Sea State Descriptors
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-Gradations
of Wave Action-
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Smooth -------------------------------------------------Slight
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Moderate -------------------------------------------------Rough
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High -------------------------------------------------Very
High
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Smooth Bore Nozzle for Solid Stream
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Typical input diameter to output opening is 2:1
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Remote Controllable Monitors with Nozzles
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Monitor using Hydraulics
for Fast Response
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Monitor with "Dither Modulation
Mechanism"
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-Linear
Nozzle Array-
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-Omnidirectional
Nozzle Array-
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Linear Nozzle Array
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Array shown with one section in up, or operational, position.
The external "central feeder pipe" is an indication of the "add on"
nature of the AWCT.
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End View Diagram
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-10,000
GPM Diesel Pump-
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-Distance
Chart Combination Nozzle 100 PSI
Approximate Effective Stream Trajectory at 30° Elevation in
No Wind Conditions. Distance to Last Water Drop Approximately 10% Farther
| Curve |
A |
B |
C |
D |
E |
F |
G |
| US GPM |
300 |
500 |
600 |
750 |
1000 |
1500 |
2000 |
| Nozzle
Reaction (LBS) |
152 |
250 |
303 |
380 |
505 |
758 |
1010 |
| Horozontal |
178
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200
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210
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221
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238
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262
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280
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| Vertical |
37
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40
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44
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47
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50
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55
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59
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Based on nozzle pressure of 100
psi.-
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Angle
/ Distance Table: Straight Solid Stream
Using Smooth Bore Nozzle Minitors
Nozzle
Angle of Elevation |
1½"(38mm)
Orifice
668 US GPM Flow |
1¾"(45mm)
Orifice
918 US GPM Flow |
2"(51mm) Orifice
1188 US GPM Flow |
| PSI |
Distance
in Feet
V--------H |
PSI |
Distance
in Feet
V--------H |
PSI |
Distance
in Feet
V--------H |
| 32º |
100 |
57 |
172 |
100 |
75 |
185 |
100 |
84 |
195 |
| 150 |
70 |
185 |
150 |
88 |
212 |
150 |
93 |
224 |
| 200 |
86 |
200 |
200 |
95 |
225 |
200 |
98 |
233 |
| 250 |
93 |
215 |
300 |
98 |
242 |
250 |
105 |
265 |
| 45º |
100 |
85 |
147 |
100 |
105 |
159 |
100 |
112 |
176 |
| 150 |
102 |
157 |
150 |
115 |
174 |
150 |
128 |
191 |
| 200 |
113 |
163 |
200 |
127 |
195 |
200 |
136 |
205 |
| 250 |
123 |
179 |
250 |
134 |
210 |
250 |
144 |
216 |
| 75º |
100 |
134 |
55 |
100 |
149 |
56 |
100 |
153 |
57 |
| 150 |
160 |
57 |
150 |
173 |
60 |
150 |
178 |
63 |
| 200 |
171 |
62 |
200 |
192 |
67 |
200 |
201 |
70 |
| 250 |
187 |
65 |
250 |
203 |
69 |
250 |
214 |
75 |
| Fire (Water) Streams cease to be effective where they lose body, direction
or force. Beyond this point the water is in the form of heavy rain and
is easily carried away by air currents. The point of effective reach of
the fire streams tabulated above was established as the point where the
slugs of water which broke away from the main body of the stream were still
closely enough grouped to be effective in extinguishing a fire. As these
slugs became further separated from the stream and broke into spray the
stream was considered ineffective. Tests were conducted under good conditions
(5 mph winds). Adverse winds will considerably reduce the effective range
of monitor nozzle streams. |
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Water Stream Velocity verses PSI
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Velocity is measured at Nozzle Orifice
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DDG-51 Destroyer with Rear-Directed Water Curtain-
Note that the rear-directed water streams augment the ship's propulsion.-
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Propulsion Augmentation
Water Stream is Angled Back at 45° and Out at 45°
(only one stream is shown for simplicity)-
Each Stream Contributes to the Ship's Thrust by
virtue of the Water Jet Reaction of each Nozzle.
Note that each nozzle's net contribution to the ship's
forward motion is ~50% of the nozzle's reaction (thrust).-
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GE LM6000 Gas Turbine |
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| Horse Power |
57,300 |
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| Thrust, Lbs. |
255,300 |
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| GPM |
1,079,508 |
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| MW |
>40 |
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Water Stream Reaction verses Flow Rate (GPM)
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-Wind
Effects on Water Streams-
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Bow Stream, Straight into
the Wind
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Ideal Water Stream, @ <5knts
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Wind Affected Water Stream, @ >>5knts
(Note the Nozzle/Monitor is tilted for compensation)
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Near Orthogonal Stream,
Ship Straight into the Wind
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Ideal Water Stream, @ <5knts
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Wind Affected Water Stream, @ >>5knts
(Note the Nozzle/Monitor is rotated for compensation)
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-Determining
Required Water Volume in GPM-
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Ship Circumference = 1,076'
Splash Circumference = 1,316' |
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Stream Geometry
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GPF
Tspl
Nsp
Wst
Wmin
Wavg
Wsp
TL
Cshp
Cspl
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Solve for GPM
Gallons per Foot (velocity)
Time to Splash-
Nozzle Spacing-
Width Start-
Width Minimum-
Width Average-
Width at Splash-
Throw Length-
Ship Circumference-
Splash Circumference- |
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Possible Number of Nozzles Needed
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| Nsp |
1.0'
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1.5'
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2.0'
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2.5'
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3.0
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| Nozzles- |
1076
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807
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538
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430
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360
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| GPM- |
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Illustration of 45° Stream Trajectories (Throw Length)
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Throw Lengths (TL) are in Red
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