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Overview (10.1) SUBMARINES 200+ Years Old (Turtle (1775) and Hunley (1864)) Navy mostly uses submarines (indefinite underwater endurance) Commercial industry uses submersibles (limited endurance) Expensive but stealthy!

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submarines

Overview (10.1)

SUBMARINES
  • 200+ Years Old (Turtle (1775) and Hunley (1864))
  • Navy mostly uses submarines (indefinite underwater endurance)
  • Commercial industry uses submersibles (limited endurance)
  • Expensive but stealthy!
  • Share characteristics of both surface ships and aircraft

CSS Hunley

submarines2

Submarine Structural Design (10.2)

SUBMARINES
  • Longitudinal Bending - Hogging & sagging causes large compressive and tensile stresses away from neutral axis. A cylinder is a poor bending element.
  • Hydrostatic Pressure = Major load for subs. Water pressure attempts to implode ship. Transverse frames required to combat loading. A cylinder is a good pressure vessel!
  • Recall:
submarines3

Submarine Inner Hull (10.2)

SUBMARINES
  • Holds the pressure sensitive equipment (including the crew!)
  • Must withstand hydrostatic pressure at ops depth.
  • Transversely framed with thick plating.
  • Strength  = $ ,  , space  , but depth  .
  • Advanced materials needed due to high .
submarines4

Submarine Outer Hull (10.2)

SUBMARINES
  • Smooth fairing over non-pressure sensitive equipment such as ballast and trim tanks and anchors to improve vessel hydrodynamics.
  • High strength not required so made of mild steels and fiberglass.
  • Anechoic (“free from echoes and reverberation”) material on outer hull to decrease sonar signature.
submarines5

Submarine General Arrangements (10.2)

SUBMARINES
  • Main Ballast Tanks
  • Variable Ballast Tanks

PRESSURE HULL

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Main Ballast Tanks (MBT) (10.2)

SUBMARINES
  • Largest tanks.
  • Alter  from positive buoyancy on surface (empty) to near neutral buoyancy when submerged (full).
  • Main Ballast Tanks are “soft tanks” because they do not need to withstand submerged hydrostatic pressure. (Located between inner & outer hulls.)
submarines7

Variable Ballast Tanks (10.2)

SUBMARINES
  • Depth Control Tank (DCT)
    • Alter buoyancy once submerged.
    • Compensates for environmental factors (water density changes).
    • ‘Hard tank’ because it can be pressurized (has access to outside of pressure hull).
  • Trim Tanks (FTT/ATT)
    • ‘Soft tanks’ shift water to control trim (internal)
submarines8

U.S. Submarine Types (10.3)

SUBMARINES
  • Ohio Class
    • Sub Launched Ballistic Missiles (SLBMs) aft of sail
    •  greater than many surface ships (i.e. BIG)
submarines9

U.S. Submarine Types (10.3)

SUBMARINES
  • Los Angeles Class (SSN688)
submarines12

U.S. Submarine Types (10.3)

SUBMARINES

Virginia Class

Displacement: 7,800 tons

Length: 377 feet

Draft: 32 feet

Beam: 34 feet

Depth: 800+ feet

submarines13

U.S. Submarine Types (10.3)

SUBMARINES

USS Dolphin

AGSS-555

NR1

L = 165 feet

Diesel/Electric

3000 feet depth!

L = 145 feet

Nuclear

2400 feet depth

submarines15

Submarine Hydrostatics (10.4)

SUBMARINES
  • Static equilibrium and Archimedes Principle apply to subs as well.
  • Unlike surface ships, subs must actively pursue equilibrium when submerged due to changes in density () and volume ().
  • Depth Control Tanks & trim tanks are used.
submarines16

Hydrostatic Challenges (10.4)

SUBMARINES
  • MAINTAIN NEUTRAL BUOYANCY
    • Salinity Effects
    • Water Temperature Effects
    • Depth Effects
  • MAINTAIN NEUTRAL TRIM AND LIST
    • Transverse Weight Shifts
    • Longitudinal Weight Shifts
submarines17

Hydrostatics (Salinity Effects) (10.4)

SUBMARINES

Water density ()  as salinity level .

  • Decreased  = less FB
  •  sub weight > FB.
  • Must pump water out of DCT
  • Changes in salinity common near river estuaries or polar ice.
  • Mediterranean salinity is higher from evaporation.
submarines18

Hydrostatics (Temperature Effects) (10.4)

SUBMARINES

Water density ()  as temperature .

  • Decreased  = less FB
  •  sub weight > FB.
  • Must pump water out of DCT to compensate.
  • Changes in temperature near river estuaries or ocean currents (Gulf Stream, Kuroshio, etc.)
submarines19

Hydrostatics (Depth Effects) (10.4)

SUBMARINES
  • As depth increases, sub is “squeezed” and volume () decreases.
  • Decreased  = less FB
  •  sub weight > FB.
  • Must pump water out of DCT
  • Anechoic tiles cause additional volume loss as they compress more.
submarines20

Neutral Trim - General (10.4)

SUBMARINES
  • When surfaced, geometric relationships similar except that “G” is below “B” for sub.
  • Neutral trim on sub becomes extremely critical when submerged.
  • Note the positions of “G”, “B”, “MT”, and “ML” in the following figures!
submarines21

Neutral Trim - General (10.4)

SUBMARINES
  • Recall: these relationships can be used in transverse or longitudinal directions to find KMT or KML for a surface ship.
submarines22

Neutral Trim - General (10.4)

SUBMARINES
  • Surfaced submarine similar to surface ship except G is below B.
    • For clarity, MT is shown above B although distance is very small in reality.
submarines23

Neutral Trim - General (10.4)

SUBMARINES
  • When submerging, waterplane disappears, so no second moment of area (I), and therefore no metacentric radius (BML or BMT).
  • “B”, “MT” and “ML” are coincident and located at the centroid of the underwater volume -the half diameter point (if a cylinder).
  • Very sensitive to trim since longitudinal and transverse initial stability are the same.
submarines24

Neutral Trim - General (10.4)

SUBMARINES
  • When completely submerged, the positions of B, MT and ML are in the same place.
submarines25

Trim & Transverse Weight Shifts (10.4)

SUBMARINES
  • Recall In Surface Ship Analysis:
    • GMT is found by equation (& Incline Experiment) to calculate the vertical center of gravity, KG.
    • Equation was only good for small angles () since the metacenter is not stationary at larger angles.
    • Large  only available from analysis of Curve of Statical Intact Stability.
submarines27

Trim & Transverse Weight Shifts (10.4)

SUBMARINES

For a Submarine:

(GM is replaced by BG!)

submarines28

Trim & Transverse Weight Shifts (10.4)

SUBMARINES
  • In Submarine Analysis:
    • Calculation of heeling angle simplified by identical location of Center of Buoyancy (B) and Metacenter (M).
    • Analysis involves the triangle G0GTB and a knowledge of the weight shift.
    • This equation is good for all angles:
submarines29

Trim & Transverse Weight Shifts (10.4)

SUBMARINES
  • Surface Ship analysis complicated because vessel trims about the center of floatation (F) (which is seldom at amidships).
  • Sub longitudinal analysis is exactly the same as transverse case. For all angles of trim:
  • Moment arm l  t, so trim tanks to compensate.
submarines32

Submarine Intact Stability (10.5)

SUBMARINES
  • Initial stability simplified for subs.
  • The distance BG is constant (=GM) Righting Arm (GZ) is purely a function of heel angle.
  • EQUATION IS TRUE FOR ALL SUBMERGED SUBS IN ALL CONDITIONS!
submarines33

Submarine Intact Stability (10.5)

SUBMARINES
  • Since righting arm equation good for all , curve of intact statical stability always a sine curve with a peak value equal to BG.
submarines34

Submerged Stability Characteristics (10.5)

SUBMARINES
  • Range of Stability: 0-180°
  • Angle of Max Righting Arm: 90°
  • Max Righting Arm: Distance BG
  • Dynamic Stability: 2SBG
  • STABILITY CURVE HAS THE SAME CHARACTERISTICS FOR ALL SUBS!
submarines35

Submarine Resistance (10.6)

SUBMARINES
  • Recall Coefficient of Total Hull Resistance
    • CV = viscous component, depends on Rn.
    • CW = wave making resistance, depends on Fn.
    • CA = correlation allowance, surface roughness and “fudge factor”.
submarines36

Submarine Resistance (10.6)

SUBMARINES
  • On surface (acts like a surface ship):
    • CV dominates at low speed, CW as speed increases (due to bigger bow and stern waves and wake turbulence).
  • Submerged (acts like an aircraft):
    • Skin friction (CF CV) dominates. (Rn is more important when no fluid (air/water) interface).
    • CW tends toward zero at depth.
    • Since CT is smaller when submerged, higher speeds are possible.
submarines38

Skewed Propellers (10.6)

SUBMARINES
  • Advantages:
    • Reduced Vibration (eases into flow).
    • Reduced Cavitation.
  • Disadvantages:
    • Inefficient backing.
    • Expensive & difficult to make.
    • Reduced strength.
  • Operational need outweighs disadvantages!
submarines39

Submarine Seakeeping (10.7)

SUBMARINES
  • Subjected to same as surface ships
    • 3 translation (surge, sway, heave) and 3 rotational (roll, pitch, yaw).
    • Recall heave, pitch, and roll are simple harmonic motions because of linear restoring force.
  • If e = resonant freq, amplitudes maximized (particularly roll which is sharply tuned).
  • Roll motion accentuated by round shape. Why?
submarines40

Submarine Seakeeping - Suction Force (10.7)

SUBMARINES
  • Water Surface Effect
    • Submarine near surface (e.g. periscope depth) has low pressure on top surface of hull causing net upward force.
    • Magnitude depends on speed, depth, and hull shape.
    • Minimize by reducing speed and having bow down trim.
  • Wave Action
    • Top of sub has faster velocity due to similar lower pressure effect as above.
    • Minimize by going deeper or beam on to waves.
submarines41

Submarine Maneuvering and Control (10.8)

SUBMARINES
  • Lateral motion controlled with rudder, engines, and props, but also has to control depth.
  • Depth control accomplished by:
    • Making the buoyant force equal the submarine displacement as in previous section.
    • Finer and more positive control achieved by plane (control) surfaces.
submarines42

Fair-Water Planes (10.8)

SUBMARINES
  • Primarily to maintain an ordered depth.
    • Positioning the planes to the "up" position causes an upward lift force to be generated.
    • Since forward of the center of gravity, a moment (M) is also produced which causes some slight pitch.
  • The dominant effect is the lift generated by the control surface.
submarines43

Fair-Water Planes (10.8)

SUBMARINES
  • Primarily DEPTH CONTROL
submarines44

Stern and Bow Planes (10.8)

SUBMARINES
  • Primarily to maintain pitch because of the distance from the center of gravity.
    • Positioning the planes to creates a lift force in the downward direction creates a moment (M) which causes the submarine to pitch up.
    • Once the submarine has an up angle, the hull produces an upward lift force.
  • The net effect is that the submarine rises at an upward angle.
submarines45

Stern and Bow Planes (10.8)

SUBMARINES
  • Maintain Pitch
  • (better control than with fairwater planes)
submarines46

FINAL THOUGHT...

SUBMARINES

There are times when accurate control is nice!

naval engineering i
NAVAL ENGINEERING I

Good Luck and Good “Boating”!