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TECHNICALITIES OF AN UNDERWATER HABITATRajat K5620 B. Arch Xth
SemCONTENTS
IntroductionArchimedes PrincipleHydrostatic PressureMoon
PoolAirlock mechanismForm follows pressureMATERIAL
SELECTIONFOUNDATIONS
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TECHNICALITIES OF AN UNDERWATER HABITATRajat K5620 B. Arch Xth
Sem The underwater world, which has been largely captivating to
humans since generations, follows a simple language of physics
based forces to keep itself different from rest of the world. The
forces are responsible for the evolution of marine life in the
forms we see today. These forces are born out of the characteristic
features of water .
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Sea water contains about 3.5% salt on average, plus smaller
amounts of other substances. The physical properties of sea water
differ from fresh water in some important respects. It freezes at a
lower temperature (about 1.9 C) and its density increases with
decreasing temperature to the freezing point, instead of reaching
maximum density at a temperature above freezing. The salinity of
water in major seas varies from about 0.7% in the Baltic Sea to
4.0% in the Red Sea.PROPERTIES OF SEA WATER
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The factors considered while designing an underwater habitat
are:- Archimedes Principle of buoyancy.
Hydrostatic Equilibrium Governing the form
Material for construction
Foundations
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Archimedes Principle of buoyancy When a body is immersed in a
liquid, it experiences an upward thrust (loses weight) equal to the
weight of the liquid displaced by it.
The apparatus shown here illustrates the law.The density of
stone in normal conditions is 0.67N.The density after immersion is
0.4 N.The loss in density id due to the upward thrust exerted by
water.The weight of water displaced is equal to the magnitude of
the upward thrust exerted by the liquid.
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Archimedes Principle of buoyancy The fate of body after
immersion is determined by the density. The 3 cases can be observed
upon immersion of the body in water -
CASE 1
If the density of the body is more than the density of liquid,
it sinks.
In this case, weight of the body is more than upward thrust.
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Archimedes Principle of buoyancy
CASE 2
If the density of the body is equal to the density of liquid, it
stays in equilibrium anywhere in the liquid.
In this case, weight of the body is equal to the upward
thrust.
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Archimedes Principle of buoyancy
CASE 3
If the density of the body is less than the density of liquid,
it floats.
In this case, weight of the body is less than the upward
thrust.
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Role in project
The use of this phenomenon is observed in submarines, which were
the primitive underwater habitats meant for combat.
The working of submarine can be observed in the following
illustration
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Role in project
The use of this phenomenon is observed in submarines, which were
the primitive underwater habitats meant for combat.
The working of submarine can be observed in the following
illustrationThe density of the sub is reduced below the density of
liquid because water in the ballast tank is least or just enough
for the object to stay afloat.
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Role in project
The use of this phenomenon is observed in submarines, which were
the primitive underwater habitats meant for combat.
The working of submarine can be observed in the following
illustrationThe density of the sub is equalized to the density of
liquid because water in the ballast tank increases the density of
the object to keep it in equilibrium position
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Role in project
The use of this phenomenon is observed in submarines, which were
the primitive underwater habitats meant for combat.
The working of submarine can be observed in the following
illustrationThe density of the sub is more than the density of
liquid because water in the ballast tank increases the density of
the object to be more than the liquid.
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Role in project
The illustrations above depict the intermediary phase of the
project viz. assembling it on the shop-floor and then immersing it
in the sea.
The entire structure can be fabricated on the land station and
then immersed in water and fixed to the foundations casted
earlier.
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Role in project
The structure shown here is Ithaa underwater restaurant on
Rangali island, Maldives.
The structure built in Singapore weighed 175 tons after
construction. Later 85 tons of sand was placed inside the structure
to sink it.
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Role in project
Further the structure was secured to concrete piles each
measuring 750 mm in diameter.
The structure is an ambient pressure habitat with a rectangular
floor measuring 9m x 5m, the height being 2.7m, in the centre of
section shown below. The restaurant offers a 270 degree view of the
sea.
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HYDROSTATIC PRESSURE
It is the pressure exerted by a fluid at equilibrium due to the
force of gravity . A fluid in this condition is known as
hydrostatic fluid.
As per the thumb rule used by the divers, pressure of sea water
increases by 1 atm (1kg force per centimeter square) with every 10m
increase in depth.
Pressure consideration is very important from the design point
of view, as the material to be selected, form of the structure and
its thickness are solely governed by the pressure it has to
withstand. Apart from that the pressure was the foremost evil in
creating underwater habitats, as divers faced a lot of trouble
dealing with it.High pressure was responsible for many illnesses
like decompression sickness, eardrum damage, barotrauma, paranormal
sinuses etc. The earlier habitats depict the architectural feature
of dealing with pressure through compressed air, the installation
known as MOON POOL or wet WET PORCH.
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MOON POOL IN UNDERWATER HABITATS
Very deep moon pools are used in underwater habitatssubmerged
chambers used by divers engaged in underwater research,
exploration, marine salvage, and recreation. As seen in the
diagram, there is no dry access between the chamber and the sea
surface, and the moon pool is the only entry and exit to the
chamber.
The air pressure inside the chamber with opening in the bottom
is equal to the air pressure of the water at depth d.
If the depth d = 30mts = 10 x 3m, then Pressure (P) = 3 x 1 atm
= 3 atm
Therefore the pressure of compressed air inside has to be
maintained at 3atm to prevent the water from flooding inside the
chamber.
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MOON POOL IN UNDERWATER HABITATS
Moon Pools used in earlier underwater habitats for access these
structures . Divers needed a certain amount of time to adjust to
the pressure inside the moon pool after entering the structure and
the same type of problem upon descending back the surface. Entrance
to Jules Undersea Lodge shows a small opening in the bottom of the
floor.
This chamber serves as the main access to the habitat and the
other rooms are directly connected to it.
The whole structure relies on this mechanism to prevent the
water from flooding inside.
Therefore, a continuous power back-up, to keep the air
compressed is provided within the lodge.
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AIRLOCK OR DECOMPRESSION CHAMBER
The airlock or lock-out chamber was a relief for the divers to
adjust to the different pressure zones, after entering the habitat
and before leaving it. The diver had to stay in the decompression
chamber after reaching the surface, to combat decompression
sickness.
The installation of airlock within the habitat helped in
reducing the need for a decompression chamber upon reaching the
surface.
Airlock consists of 2 doors fixed opposite to each other, which
do not open simultaneously.
The pressure in the habitat is forced to fill the enclosure when
one door opens.
The diver adjusts to this pressure zone and steps into the
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AIRLOCK OR DECOMPRESSION CHAMBER
The pressure is adjusted to normal atmospheric pressure by
closing both the doors and then opening one of the doors.
The diver adjusts to this pressure and then returns to the
surface.
Airlock mechanism in Aquarius Reef Base, Key Largo Florida
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FORM FOLLOWS PRESSURE The forces acting upon terrestrial
structure, which help in developing the form can be known from the
following diagram. This help in further understanding the design of
an underwater structures.
Compression surfaces need to be more rigid in order to withstand
buckling.
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FORM FOLLOWS PRESSURE
Lesser rigid tension members
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FORM FOLLOWS PRESSURE
As seen in the figure, the form of arched frame is developed out
of a trussed frame
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FORM FOLLOWS PRESSURE
The form and the material to be used for underwater structures
is governed by the hydrostatic pressure.
The geometry of arch explains the internal resolution of
forces.
Surface structures are the structures consisting of thin wide
surfaces which function structurally by resolving only the internal
forces within their surfaces.
Compression surfaces need to be more rigid in order to withstand
buckling. Compression resistive surface structures with curvature
are called shells.
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FORM FOLLOWS PRESSURE
Shell structures with curvature with curvature can be termed as
domes, spheres, cones, cylinders; which are derived out of a series
of arches in three dimensions.
The series of arches in linear geometry shown in the drawing is
termed as barrel vault; is a primitive shell structure that
resolves forces in all directions.
This type of geometry can be observed in Ithaa Underwater
Restaurant.
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FORM FOLLOWS PRESSURE
The Arch if revolved by rotating it on its axis, develops from a
barrel vault to a dome. The dome which happens to be a derivative
of sphere resolves forces in all directions(on all axes) through
its geometry .
The reliance on members is reduced to a large extent. Further,
the floor plan may not necessarily be circular it can also be
square.
Dome A structurally stable and a long lasting form.
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FORM FOLLOWS PRESSURE The dome can be further evolved into a
sphere which encloses the maximum volume within least required
surface area of the material.
Sphere The form can resist the forces in all directions, hence
most appropriate for seismic structures as well
Conceptual view of a spherical enclosure
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FORM FOLLOWS PRESSURE The form of vaulted arch and dome is used
as a combination in the suites in hotel poseidon.
View of the suite
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FORM FOLLOWS PRESSURE The other forms derived out of curvature
that are used in underwater structures are-
Tubular
Jules Undersea Lodge
Aquarius Reef Base
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FORM FOLLOWS PRESSURE The other forms derived out of curvature
that are used in underwater structures are-
Jellyfish
Crescent Hydropolis Hotel
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FORM FOLLOWS PRESSURE Other curved forms that can be observed in
Hydropolis for large and small span structures -
Crescent Hydropolis Hotel
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FORM FOLLOWS PRESSURE Other curved forms that can be observed in
Hydropolis for large and small span structures -
Crescent Hydropolis Hotel
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FORM FOLLOWS PRESSURE Analysis of different shapes - SPHERE
ADVANTAGE
The most structurally efficient i.e. less wall thickness is
required to withstand a given pressure.
DISADVANTAGES
Offers the minimum amount of space for a given diameter, unlike
(say) a circular cylindrical vessel, which can be made long.Not
suitable for storageNot suitable for transport High manufacturing
costLoss of space, as shown in the figure
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FORM FOLLOWS PRESSURE Analysis of different shapes - CYLINDRICAL
BLOCKED BY 2 HEMIDPHERICAL DOMES PLACED HORIZONTALLY
ADVANTAGES Can offer a greater amount of space than a spherical
shell with the same diameter.Less manufacturing costs than the
spherical shell.Simply making the cylinder longer can increase the
space.The two hemispherical shell domes can still be used and not
affect the submerged depth.In the case where more space is required
in the future, this can be simply achieved by making the
cylindrical part longer; this is considered to be a premium
advantage.
DISADVANTAGESA greater thickness is required than a spherical
shell in order to withstand the same pressure.Loss of space, as
shown in the figure. If the circular cylinder is very long, the
buckling resistance could be small.
Aquarius Reef Base
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FORM FOLLOWS PRESSURE Analysis of different shapes - CYLINDER
BLOCKED BY 2 HEMISPHERICAL DOMES PLACED VERTICALLY
ADVANTAGES No loss of headspace.
DISADVANTAGESIn order to reach the space requirements, the
internal radius is made larger than in shape 2, which in turn
requires a greater submerged depth.Simply making the cylinder
longer cannot increase useful space, as there is no room for
horizontal expansion.
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MATERIAL SELECTION The material should possess the following
properties
Clear, where appropriate, to allow for a clear view of the
surrounding marine life. Low creep.A good impact resistance. A good
insulator of noise i.e. Minimise noise transition.Lightweight i.e.
high strength to weight ratio, to ensure where appropriate a
reserve in buoyancy. High mechanical strengthLow moisture
absorptionNeither food retardant nor toxic, especially in places
where it is likely that direct contact is made with individuals or
the surrounding marine life. Fully recyclable, this is important
when dealing with the decommissioning part of the hotel. Easy to
clean and maintain.Easy to shape into creative designs i.e.
manufacturing is made easier and cheaper. Excellent resistance to
chemical attack and high corrosion resistance, prolonging the parts
life. Low cost.Available on request.
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MATERIAL SELECTION As per the specifications given above, the
material to be selected for areas with visibility is Glass Fibre
Reinforced Plastic(GFRP)
Very high strength to weight ratio. Low cost as compared to
other composites. Good sound absorption.Does not corrode in
seawater.
The role of the above material in constructing the underwater
hotel is to reinforce the structure and used in places where
visibility is not a desired property.Since cost, weight, heat and
electrical loss and maintenance are significant factors in
designing the underwater hotel, it can be seen that the advantages
of using composites favour the requirements, and therefore
composites are considered the ideal materials used for
construction.
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MATERIAL SELECTION As per the specifications given above, the
material to be selected for areas with visibility is Acrylic
Acrylic is less dense than glass; acrylic being.Acrylic has
higher impact strength than glass and does not shatter.Acrylic has
similar refracting index as water, therefore the natural size and
color of the surrounding marine life is maintained. Acrylic is a
good transmitter of light; 92% of light is transmitted.Acrylic is a
good electrical insulator (for low frequency work), this is
important when considering the health and safety of both
individuals and the surrounding marine life. A good resistance to
chemical attack. Chemicals such as alkalis, water and most aqueous
salt solutions. Acrylic has better insulation properties than
glass. Acrylic sheets are said to be easier to handle than
glass.
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ACRYLIC VIEWPORTSITHAA UNDEWATER RESTAURANTHOTEL POSEIDON
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MATERIAL SELECTION As per the specifications given above, the
material to be selected for areas with visibility is Acrylic
Acrylic is less dense than glass; acrylic being.Acrylic has
higher impact strength than glass and does not shatter.Acrylic has
similar refracting index as water, therefore the natural size and
color of the surrounding marine life is maintained. Acrylic is a
good transmitter of light; 92% of light is transmitted.Acrylic is a
good electrical insulator (for low frequency work), this is
important when considering the health and safety of both
individuals and the surrounding marine life. A good resistance to
chemical attack. Chemicals such as alkalis, water and most aqueous
salt solutions. Acrylic has better insulation properties than
glass. Acrylic sheets are said to be easier to handle than
glass.
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MATERIAL SELECTION As per the specifications given above, the
material to be selected for areas with visibility is Acrylic
Acrylic is less dense than glass; acrylic being.Acrylic has
higher impact strength than glass and does not shatter.Acrylic has
similar refracting index as water, therefore the natural size and
color of the surrounding marine life is maintained. Acrylic is a
good transmitter of light; 92% of light is transmitted.Acrylic is a
good electrical insulator (for low frequency work), this is
important when considering the health and safety of both
individuals and the surrounding marine life. A good resistance to
chemical attack. Chemicals such as alkalis, water and most aqueous
salt solutions. Acrylic has better insulation properties than
glass. Acrylic sheets are said to be easier to handle than
glass.
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FOUNDATIONS
Deep foundations or PILE Foundations are distinguished from
shallowfoundations by the depth they are embedded into the ground.
The common reasons for using these type of foundations are :1. very
large design loads,2. a poor soil at shallow depth,3. or site
constraints (like property lines).4. Good seismic resistance There
are different terms used to describe different types of deep
foundationsincluding piles, drilled shafts, caissons, and piers.
The naming conventionsvary between engineers. Deep foundations can
be made out of timber, steel,R.C.C, and pre-stressed concrete. Deep
foundations can be installed by eitherdriving them into the ground
or drilling a shaft and filling it with concrete,mass or
reinforced.
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FOUNDATIONS
The extensions of island is very weak in terms of its load
bearing capacity and hence piles are driven into the bedrock to be
able to provide a solid base to the superstructure. The piles in
this situation need to have an exceptionally good chemical
resistance. Hence piles encased in FRP are used.
BedrockSECTION THROUGH THE SITE
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FOUNDATIONS
The extensions of island is very weak in terms of its load
bearing capacity and hence piles are driven into the bedrock to be
able to provide a solid base to the superstructure. The piles in
this situation need to have an exceptionally good chemical
resistance. Hence piles encased in Fibre Reinforced Plastic(FRP)
are used. The construction of FRP encased pile can be understood
from the upcoming slide.
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FOUNDATIONS
(1) FRP tubes received at the precast plant(2) Concrete poured
into the bucket(3) Installation of foil gauges inside the FRP
tube(4) Concrete pouring controlled by the operators in the
adjacent lift
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FOUNDATIONS
(5) Insertion of instrumented rebar cage in the FRP tube (6) Top
of the pile after construction
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FOUNDATIONS
Driving of FRP shelled concrete piles
FRP tube with steel cage placed verticallyTo prepare for
concrete filling(2) Bracing system used to secure FRP and steel
cage in a vertical position
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FOUNDATIONS
Driving of FRP shelled concrete piles
(3) Driving of FRP pile
(4) Bolting of pile to the concrete slab
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FOUNDATIONS
Driving of FRP shelled concrete piles
(3) Driving of FRP pile
(4) End of driving FRP pile
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CAISSONS
Caisson is a retaining, watertight structure used, to work on
the foundations of a bridge pier, for the construction of a
concrete dam, or for the repair of ships.
These are constructed so that the water can be pumped out so the
working environment is dry. When piers are to be built using the
open caisson and it is not practical to reach suitable soil,
friction pilings may be driven to form a suitable sub-foundation.
These piles are connected by a foundation pad upon which the column
pier is erected
Shallow caissons may beopen to the air, while deepcaissons to
penetrate softmud may be sealed at thetop and filled withcompressed
air to keepwater and mud out at depth.
Schematic Section through the caisson
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REFERENCES
www.google.com
www.Wikipedia.org
Space Grid Structures - John Chilton
Structure and Architecture - Angus J McDonald
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