stability and control of deeply submerged submarine.pptxnew
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STABILITY AND CONTROL OF DEEPLY
SUBMERGED SUBMARINE
PRESENTED BY
NAVIN KUMAR
SEM-VIII
ROLL NO.-21
INTRODUCTION
Normal ships are designed to move on the surface of the water. Submarines are designed to be able to submerge and travel under the
water's surface, as well as on the surface. When normal ships go down, they stay down. Submarines are able to
come back up after they go down.All American submarines are nuclear powered. With the exception of
Aircraft carriers, surface ships are powered conventially.
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has
only limited underwater capability The term submarine most commonly refers to large crewed
autonomous vessels; however, historically or colloquially, submarine can also refer to medium sized or smaller vessels (midget submarines
, wet subs), remotely operated vehicles or robots The word submarine was originally an adjective meaning "under the
sea"; consequently other uses such as "submarine engineering" or "submarine cable" may not actually refer at all to the vessel.
INTRODUCTION CONTINU
Submarine was in fact shortened from the proper term, "submarine boat", and is often further shortened to "sub" when the word is employed informally. Submarines should
always be referred to as "boats" rather than as "ships", regardless of their size.
The English term U-boat for a German submarine comes from the German word for submarine, U-
Boot, itself an abbreviation for Unterseeboot ("undersea boat")
Most large submarines comprise a cylindrical body with hemispherical (and/or conical) ends and a vertical structure, usually located amidships, which houses communications and sensing devices as well as periscopes. In modern submarines this structure is the "sail" in American usage, and "fin" in European usage
APPLICATION
Military uses Before and during World War II, the primary role of the submarine was
anti-surface ship warfare. Submarines would attack either on the surface or submerged, using
torpedoes or (on the surface) deck guns They were particularly effective in sinking Allied transatlantic shipping
in both World Wars, and in disrupting Japanese supply routes and naval operations in the Pacific in World War II.
Mine-laying submarines were developed in the early part of the 20th century. The facility was used in both World Wars.
Submarines were also used for inserting and removing covert agents and military forces, for intelligence gathering, and to rescue aircrew during air attacks on islands, where the airmen would be told of safe places to crash-land so the submarines could rescue them. Submarines could carry cargo through hostile waters or act as supply vessels for other submarines.
The development of submarine-launched ballistic missile and submarine-launched cruise missiles gave submarines a substantial and long-ranged ability to attack both land and sea targets with a variety of weapons ranging from cluster bombs to nuclear weapons
APPLICATION CONTINU
The primary defense of a submarine lies in its ability to remain concealed in the depths of the ocean.
The primary defense of a submarine lies in its ability to remain concealed in the depths of the ocean
Civil uses Although the majority of the world's submarines are
military ones, there are some civil submarines. They have a variety of uses, including tourism,
exploration, oil and gas platform inspections and pipeline surveysT.he first tourist submarine was
launched in 1985, and by 1997 there were 45 of them operating around the world
A semi-civilian use was the adaptation of U-boats for cargo transport during World War I and World War II.
Submersion and trimming
All surface ships, as well as surfaced submarines, are in a positively buoyant condition, weighing less than the volume of water they would displace if fully submerged
To submerge hydrostatically, a ship must have negative buoyancy, either by increasing its own weight or decreasing its displacement of water. To control their weight, submarines have ballast tanks, which can be filled with outside water or pressurized air.
For general submersion or surfacing, submarines use the forward and aft tanks, called Main Ballast Tanks or MBTs, which are filled with water to submerge, or filled with air to surface. Under submerged conditions, MBTs generally remain flooded, which simplifies their design, and on many submarines these tanks are a section of interhull space
For more precise and quick control of depth, submarines use smaller Depth Control Tanks or DCTs, also called hard tanks due to their ability to withstand higher pressure. The amount of water in depth control tanks can be controlled either to reflect changes in outside conditions or change depth. Depth control tanks can be located either near the submarine's center of gravity, or separated along the submarine body to prevent affecting trim.
Submersion and trimming CONTINU
When submerged, the water pressure on submarine's hull can reach 4 MPa (580 psi) for steel submarines and up to 10 MPa (1,500 psi) for titanium submarines like Komsomolets, while interior pressure remains relatively unchanged. This difference results in hull compression, which decreases displacement.
Water density also increases with depth, as the salinity and pressure are higher, but this incompletely compensates for hull compression, so buoyancy decreases as depth increases.
A submerged submarine is in an unstable equilibrium, having a tendency to either fall or float to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surface
Submarines in a neutral buoyancy condition are not intrinsically trim-stable. To maintain desired trim, submarines use forward and aft trim tanks. Pumps can move water between these, changing weight distribution, creating a moment pointing the sub up or down. A similar system is sometimes used to maintain stability
The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several surfaces, which can be moved to create hydrodynamic forces when a submarine moves at sufficient speed
Submersion and trimming CONTINU
When submerged, the water pressure on submarine's hull can reach 4 MPa (580 psi) for steel submarines and up to 10 MPa (1,500 psi) for titanium submarines like Komsomolets, while interior pressure remains relatively unchanged. This difference results in hull compression, which decreases displacement.
Water density also increases with depth, as the salinity and pressure are higher, but this incompletely compensates for hull compression, so buoyancy decreases as depth increases.
A submerged submarine is in an unstable equilibrium, having a tendency to either fall or float to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surface
Submarines in a neutral buoyancy condition are not intrinsically trim-stable. To maintain desired trim, submarines use forward and aft trim tanks. Pumps can move water between these, changing weight distribution, creating a moment pointing the sub up or down. A similar system is sometimes used to maintain stability
The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several surfaces, which can be moved to create hydrodynamic forces when a submarine moves at sufficient speed
Submarine hull
Modern submarines are cigar-shaped. This design, visible in early submarines is sometimes called a "teardrop hull". It reduces the hydrodynamic drag when submerged, but decreases the sea-keeping capabilities and increases drag while surfaced. Since the limitations of the propulsion systems of early submarines forced them to operate surfaced most of the time, their hull designs were a compromise
Single/double hullModern submarines and submersibles, as well as the oldest ones, usually have a single hull. Large submarines generally have an additional hull or hull sections
outside. This external hull, which actually forms the shape of submarine, is called the outer hull (casing in the Royal Navy) or light hull, as it does not have to
withstand a pressure difference. Inside the outer hull there is a strong hull, or pressure hull, which withstands sea pressure and has normal atmospheric pressure
inside
Pressure hullThe pressure hull is generally constructed of thick high strength steel with a complex
structure and high strength reserve, and is separated with watertight bulkheads into several compartments. There are also examples of more than two hulls in a submarine, like the Typhoon class, which has two main pressure hulls and three
smaller ones for control room, torpedoes and steering gear, with the missile launch system between the main hulls
Submarine hull CONTINU
The building a pressure hull is difficult, as it must withstand pressures at its required diving depth. When the hull is perfectly round in cross-section, the pressure is evenly distributed, and causes only hull compression.
If the shape is not perfect, the hull is bent, with several points heavily strained. Inevitable minor deviations are resisted by stiffener rings, but even a one inch (25 mm) deviation from roundness results in over 30 percent decrease of maximal hydrostatic load and consequently dive depth.[
The hull must therefore be constructed with high precision. All hull parts must be welded without defects, and all joints are checked multiple times with different methods, contributing to the high cost of modern submarines. (For example, each Virginia-class attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement
Buoyancy and Stability
Buoyancy force FB is equal only to the displaced volume rfgVdisplaced.
Three scenarios possible1. rbody<rfluid: Floating
body2. rbody=rfluid: Neutrally
buoyant3. rbody>rfluid: Sinking
body
stability of deeply submerged submarine
The stability criteria are based on examination of the values of BGv, metacentric height, GMv, and righting lever, GZ, achieved in submerged, surfaced and damaged conditions. The aims of the criteria are: a. To provide sufficient stability to prevent capsize induced by environmental hazards which the submarine might encounter during its life. b. To limit submarine motions to reasonable levels during normal operational evolutions. c. To provide sufficient reserves of stability to enable the submarine to recover safely from flooding accidents and collision damage.
The MRS defines the weight margins to be provided in the initial design to provide for future upgrades and capability enhancements over the life of the submarine.
Alternative criteria may be proposed for use on any new vessel. Any such proposal shall be accompanied by a full risk assessment and a justification for the acceptability of the proposal. Acceptance of an alternative set of criteria shall be at the Commonwealth's discretion
Consequences of Poor Performance or Hazard
Failure to achieve required stability levels represents a hazard to crews due to the impact of ship motions under a seaway while surfaced. Poor stability alongside can also lead to excessive heeling of the submarine during maintenance or related activities.
Failure to achieve required freeboards presents a flooding hazard when submarines are required to operate on the surface with a hatch open, or while moored alongside.
Failure to achieve the design weight margins for future growth will adversely impact on the ability to introduce new capabilities into the submarine through its
FUNCTIONAL AND PERFORMANCE REQUIREMENTS
Intact Surfaced StabilityIntact Submerged Stability Stability during Normal Surfacing or Diving Evolutions
Stability during Emergency Surfacing
Reserve of Buoyancy freeboad
Weight & Compensation Margins Damaged Conditions
Stability While Docking
Intact Surfaced Stability
Conditions to be assessed. Surfaced stability is to be assessed for
the submarine in the standard surfaced condition. The free surface of all partially filled tanks is to be included in calculations of BG and GM. VV
Where the submarine can operate in several alternative configurations the stability assessment is to be conducted against each of these conditions.
Requirements to be met. The criteria for intact surfaced stability are based on
consideration of the shape of the GZ curve, and on the ability of the submarine to withstand beam winds without adopting large angles of heel.
The shape of the GZ curve for a cylindrical submarine on the surface differs from those of most surface vessels in that GZ increases approximately in proportion to sin Φ. This results in a healthy reserve of stability at large heel angles and ensures that the GZ curve is not depressed at small angles. The criteria are as follows:
1.GMv is to be not less than 0.30 metres. 2.GZ at 30° heel is to be not less than 0.15 metres. 3.The area under the GZ curve up to 30° heel is to be not less
than 2.4 metre degrees. 4.The area under the GZ curve up to 40° heel is to be not less
than 4.0 metre degrees. 5.The angle of maximum GZ is to be not less than 50 degrees. Very high values of GMv may result in high roll accelerations
when surfaced and this aspect is to be investigated further if GMv is predicted to be in excess of 0.6 metres.
Figure 1 Wind Heeling Lever and GZ Curve Definitions
Low surfaced freeboard and lack of superstructure make submarines less susceptible to heeling due to beam winds than surface warships. Therefore for all seagoing surfaced conditions the submarine’s stability is to be assessed against a 100 knot wind, the maximum expected to be encountered by ocean going vessels. The method of producing the curve of wind heeling lever is given in DEF(AUST) 5000 Vol 3 Part 2 – Stability of Surface Ships and boats. The wind heeling criteria are based on a comparison of the intact righting lever GZ and wind heeling lever as shown in Figure 1. The criteria are:
1.The angle of heel due to a 100 knot wind is not to exceed 15°. 2, The GZ at the steady heel angle (GZc) is not to exceed 60% of
the GZ at 50°. 3.The area ratio A1/A2 is to be not less than 1.4. The limit of range
is to be taken as 60°.
During the design the impact on surfaced stability of changes due to fuel or payload usage and subsequent changes to compensating water levels is to be considered. The following GMv criterion is to be met:
-GMv is not to be less than 0.27 metres in the worst standard combination of fuel & payload usage and compensating water GM may be adversely impacted by unusual or non-standard loading
states. To address this situation, an in-service Limiting GMv of not less than 0.25 metres shall apply, regardless of loading or operating condition
During maintenance periods alongside the impact of adding or removing equipment can have a major impact on the submarine’s stability. It is necessary for the submarine to have sufficient stability alongside in harbour to avoid excessive heel due to wind or loading/unloading of fuel or stores. If necessary an ad-hoc inclining is to be undertaken to determine the submarine’s GM. After taking into account any equipment added or removed from the submarine, the following criteria are to be met:
1. GMv is to be not less than 0.15 metres. 2. Heel under a 30 knot wind is not to exceed 7°. All configuration changes to the submarine through its life
are to be controlled to ensure that the stability is not compromised through the uncontrolled addition of equipment.
Intact Submerged Stability
Conditions to be assessed Submerged stability is to be assessed for the submarine in the standard
submerged condition. The free surface of all partially filled tanks is to be included in calculations of BG and GM.
Where the submarine can operate in several alternative configurations the stability assessment is to be conducted against each of these conditions
Requirements to be met. The measure of intact submarine stability when submerged is BGv. The
tendency of the submarine to roll or heel due to underwater manoeuvres, operations under waves or transverse static imbalance will reduce with increased BGv. The criterion to be met is:
BGv is to be not less than 0.30 metres
Stability during Normal Surfacing or Diving Evolutions
Conditions to be assessed. During normal surfacing (non emergency) and diving the value of
GMv.is to be assessed using the following quasi-static assumptions
Buoyancy equals weight at all times The submarine is at level trim. The water in the casing and bridge fin has drained down to the surface
waterline The main ballast tanks are emptied such that at any instant each
contains the same percentage of its total capacity The free surface effect of main ballast tanks is taken into account
Note: The above assumptions achieve equilibrium of static forces but not necessarily equilibrium of trimming moments.
At any instant during transition GMv is to be not less than 0.05 metres
Stability during Emergency Surfacing
Conditions to be assessed
Emergency surfacing from deep having blown the main ballast tanks with HP air will produce a less stable condition than normal surfacing since free flood water in the bridge fin and casing will drain down slower than the rate of submarine emergence. Stability during emergency surfacing is an important consideration in sizing free flood space drainage holes. Calculation of surfacing stability is to be performed based on the following simplifying assumptions
That the submarine surfaces at a level trim That all of the MBTs have been fully blown. A rise rate of 4 metres/second, or when it is known, the
maximum rise rate of the centre of gravity obtained from emergency recovery simulations
Stability during Emergency Surfacing CONTINU
The effects of water draining down from the bridge fin and casing are to be taken into account as follows
Water above the surface waterline is to be treated as an added mass, allowing for permeability
Free surface effects of water in the casing and bridge fin are to be included, allowing for the effect of longitudinal subdivision but ignoring the presence of internal equipment
Free surface effects of the residue in the main ballast tanks are to be taken into account
Ideally, the above assessment is to utilise a dynamic model of casing/bridge fin draining performance, should such a validated model be available. Alternatively, the stability of the submarine on the surface with the casing and bridge fin fully flooded can be calculated, together with a number of cases of partial drainage, eg bridge fin empty, casing full
Stability during Emergency Surfacing CONTINU
Requirements to be met.
Preferably the drainage arrangements are to be sized such that GMv remains positive throughout emergency surfacing. However, other design requirements and constraints may prevent achievement of this criterion. In such cases GMv is only to remain negative for a short period and it will be necessary to examine the dynamic rolling performance of the submarine under such conditions. Under these circumstances the submarine is not to roll to an angle greater than 20°.
Reserve of Buoyancy
Conditions to be assessed The reserve of buoyancy is to be calculated for the
submarine in its standard surfaced condition Where the submarine can operate in several alternative
standard configurations the reserve of buoyancy assessment is to be conducted against the least favourable of these conditions
Requirements to be met The main factor affecting reserve of buoyancy is the capacity of the main
ballast tanks, which is directly related to the reserve of buoyancy when operating on the surface as follows:
Reserve of buoyancy = (∇subm - ∇surf)/∇surf
The reserve of buoyancy is based on the surface displacement related to the blowable (external) main ballast tank volume
Reserve of Buoyancy CONTINU
The reserve of buoyancy and its distribution affect many parameters in the surface condition, such as draught, freeboard, trim, propulsor/rudder immersion, vulnerability to damage and internal flooding, stability and seakeeping. However, these design parameters are not solely dependent on the reserve of buoyancy
Also in the submerged condition the reserve of buoyancy influences the overall size and form of the submarine and hence its power/speed characteristics and detectabilty
The required volumes of ballast tanks derived from the reserve of buoyancy are the net usable volume, ie the volume of water which can be expelled from the tanks. In order to determine the required gross capacity of the tanks (to the outside of plating it is necessary to make allowance for
growth of equipment within the tank unblowable/pumpable residue tank structure; stowed solid ballast air, bottles
Freeboard Conditions to be assessed The freeboard to the casing and each hatch is to be calculated for the
submarine in its standard surfaced condition Where the submarine can operate in several alternative standard
configurations the freeboard assessment is to be conducted against the least favourable of these conditions
Requirements to be met. The ability of the crew to operate on the casing depends on the
freeboard, submarine length, hull lines, speed, heading and sea state. The freeboard requirements will be affected by the operational requirements for access to the casing. The design criteria is that the casing freeboard amidships is not to be less than 2.25 m.
A further requirement is that the freeboard to the upper hatch of the conning tower is not to be less than 4 metres
For other hatches which may be opened at sea the freeboard is to be not less than 1 metre in any surface trim condition. Hatches with less freeboard are not to be opened at sea without a full operational risk assessment being conducted
Weight & Compensation Margins
Conditions to be assessed. The submarine is to be assessed to ensure it can maintain neutral buoyancy
and level trim across the full range of operating conditions. This is to
include: Changes in seawater density as required by the OCD Changes in displacement due to compression of the hull and anechoics etc
over the full diving range to DDD Consumption of consumables such as fuel, lube oil, stores, potable water,
compressed air etc Discharge of payload eg weapons, decoys, bathythermographs etc Flooding or draining of diver lockouts, dry deck shelters etc Flooding or draining of exhaust or induction masts Accumulation or discharge of waste eg bilge water, sewage, slop drain tanks
etc
Raising or lowering of masts and periscopes Variations in diesel fuel oil density between 0.82 t/m3 and 0.86 t/m3. Variations in crew numbers and movement of crew Allowances as defined in the OCD for fitting/removal of mission specific
equipment Allowances for change in battery weight
Damaged Conditions
Conditions to be assessed The surfaced damaged stability of the submarine and freeboard to each
hatch is to be assessed by producing a GZ curve for the standard surfaced condition with each combination of two adjacent Main Ballast Tanks damaged. The damaged ballast tanks are to be assumed as free flooding for the damaged stability assessment. The curve is to be assessed together with a 60 knot beam wind
The change in KGv of the submarine is to be assessed for the standard surfaced condition plus water in bilges following the worst case flooding scenario defined in DEF(AUST)5000-Vol 09 Pt 11 Submarine Watertight Integrity with all main ballast tanks assumed to be half blown.
The surfaced damaged stability of the submarine is to be assessed by producing a GZ curve for the standard surfaced condition plus water in bilges following the worst case flooding scenario defined in DEF(AUST)5000-Vol 09 Pt 11 Submarine Watertight Integrity.. The curve is to be assessed together with a 60 knot beam wind.
Damaged Conditions CONTINU
Reserve of buoyancy is to be calculated for the submarine in the standard surfaced condition following the loss of the largest main ballast tank
Reserve of buoyancy is to be calculated for the submarine in the standard submerged condition following the worst case flooding scenario . The reserve of buoyancy is to assume recovery to the surface has been conducted only by propulsion and blowing of main ballast tanks, ie full pumping of ballast tanks has not taken place.
Requirements to be met. With any two adjacent ballast tanks damaged, the following criteria are to be
met (see Figure 2 ) The steady heel angle is to be less than 20°. The ratio A1/A2 is to be greater than 1.4. Freeboard to any hatch is to be not less than 0.25m
The rise in KGv following flooding of bilges and half blowing of all main ballast tanks should be no more than 0.05m
Stability While Docking
Conditions to be assessed The stability while docking is to be assessed.
The standard surfaced condition less weapons is to be used as the initial basis for the calculations
Requirements to be met. GMv must remain positive during docking until
external support is provided. If it is necessary to impose any restrictions or variations to the submarine’s condition for docking to achieve this criterion, these restrictions must be clearly identified
Forces acting on a vessel during a manoeuvre
Hydrodynamic forces acting on the hull and appendages due to ship velocity and acceleration.
Inertial reaction forces caused by ship acceleration. Environmental forces due to wind, waves and currents. External forces such as tugs and thrusters.
The concept of path keeping is strongly related to the concept of course stability or stability of direction.
For optimum path keeping, it would be desirable for the ship to resume its original path after passage of the disturbance with no intervention by the helmsman.
The various motion stabilities possessed by ships are :
Straight line stability If a ship possesses this stability, the final path after release
from a disturbance retains the straight line characteristic of the initial state, but the direction is not retained.
Directional stability If a ship possesses this stability, the final path after release
from a disturbance retains not only the straight line attribute of the initial path, but also its direction.
Position motion stability If a ship possesses this stability, the final path has not only
the same direction, but also the same transverse position relative to the surface of earth.
Achieving straight line stability is the designer’s usual goal.
A surface ship sailing in calm sea possesses position motion stability in the vertical plane with controls fixed.
The only kind of motion stability possible with self propelled ships with controls fixed is straight line stability.
An idea of the linear theory would be useful in understanding the concepts of sea keeping
The path keeping and path changing ability of a ship depends on:
a. The magnitude and frequency of any yawing moments and sway forces acting to disturb the ship from the desired path.
b. The response of the ship with controls fixed to these disturbances.
Thank you
for your attention!!! Questions???