TRIM, STABILITY, AND STRESS (PRELIM) Flashcards
K
KEEL
M
Meta Center
KM
HEIGHT OF META CENTER
G
CENTER OF GRAVITY
KG
HT OF CENTER OF GRAVITY
GM
METACENTRIC HT
B
CENTER OF BUOYANCY
KB
HT OF CENTER BUOYANCY
G = B
V/L FLOATS
G > B
V/L SINKS
That point at which all the vertically downward forces of weight are considered to be concentrated the center of the mass of the vessel
Center of Gravity.
That point at which all the vertically upward forces of buoyancy are considered to be concentrated; the center of volume of the immersed portion of the vessel
Center of Buoyancy.
Metacentric height distance from the center of gravity to the transverse metacenter
GM
Linear distance from the keel to the center of buoyancy when vessel is upright.)
KB
Height of center of gravity above keel
KG
Height of metacenter above keel
KM
The highest point to which G may rise and still permit the vessel to have positive stability. Found at the intersection of the line of action of B when the ship is erect with the line of action of B when the ship is given a small inclination
Metacenter.
Distance between B and M
Metacentric Radius.
Vessel with low center of gravity and large metacentric height
Stiff Ship
A vessel with small metacentric height; top-heavy
Crank Ship or Tender Ship
is the vessel’s ability to return to an upright position after being heeled by an external forces
stability
A ship is lying at an _ when the weights onboard are unevenly distributed and the static condition of the vessel is at an angle of inclination away from the vertical
angle of List
A ship is lying at an _ when external forces, such as waves or wind, shift the vessel over to an angle of inclination away from the static condition, perhaps only for a short time
angle of Heel
this results in a moment that brings the ship back to its original upright position
stable equilibrium
for a ship to be in stable equilibrium
the center of gravity (G) must be below the metacenter (M)
Exists when G coincides with
M. The vessel does not tend to return to an upright
position if inclined, nor to continue its inclination if
the inclining force is removed
Negative Stability
this causes the ship to heel over to one side and will at that angle of heel
neutral buoyancy
for a ship to be in a neutral buoyancy
the center of gravity (G) and the metacenter (M) coincide or nearly coincide
this is a dangerous state and too much heel would capsize the ship
unstable equilibrium
unstable equilibrium state
the centre of gravity is above the metacenter
- Archimede’s
Principle
Principle of Flotation
states that when a
body is wholly or partially immersed in a
fluid it appears to suffer a loss in mass
equal to the mass of the fluid it displaces
“Archimede’s” Principle
“A ship displaces
a weight of water
that is equal to its
own weight.”
“Archimede’s” Principle
, states that when a body floats in a fluid, the
weight of the body is exactly equal to the weight of
the fluid it displaces
Archimedes Principle, when applied to a floating
body
“Archimede’s” Principle vessel will
experience
an
upthrust that is
equal to the weight
of the displaced
water.
the vessel will float when
When Buoyancy (B)
is equal to Gravity (G)
THE WEIGHT OF ANY SHAPE IS ACTING ONLY
AT A CERTAIN POINT WHICH IS CALLED
CENTRE OF GRAVITY
IS DEFINED AS A POINT WHERE THE SHIPS WEIGHT
IS CONCENTRATED
CENTRE OF GRAVITY
is the point at which
all the mass of the body may be assumed to be
concentrated and is the point through which the
force of gravity is considered to act vertically
downwards, with a force equal to the weight of the
body. It is also the point about which the body
would balance
center of gravity of a body
The center of gravity of the body will always move
_ of any weight
moved within the body
parallel to the shift of the center of gravity
is the point
through which the force of gravity may be
considered to act vertically downwards
center of gravity of a body
When a _ is center of gravity is
considered to be at the point of suspension.
weight is suspended
The center of gravity of a body will _
from the center of gravity of any weight removed.
move directly away
he center of gravity of a body will _ the center of gravity of any weight added
move directly
towards
is the mutual actual between the parts
of a material to preserve their relative positions
when external loads are applied to the material
stress
- is defined as the load put on a piece of
material or a structure.
stress
is defined as the permanent deformity or
weakness caused by excessive stress
STRAIN-
3 MAIN TYPES OF STRESS
- Tensile/ Tensioning
- Compressive/ Compression
- Shear
When an external load is applied to a material in
such a way as to cause an extension of the
material it is called a
‘tensile’ load
an
external load tending to cause compression of
the material is a
‘compressive’ load
tendency to pull the material apart
tensioning
tendency to crush the material or to buckle
compression
is the effect of two forces acting in opposite directions and along parallel lines
shear
is a stress within a material
which tends to break or shear the material
across
shearing stress
If the wave crest is considered at mid-ships then
the buoyancy in this region will be increased. With
the wave trough positioned at the ends of the ship,
the buoyancy here will be reduced. This loading
condition will result in a significantly increased
bending moment, which will cause the ship to
hog
This will be an extreme condition giving the
maximum bending moment that can occur in the
ship‟s structure
Hogging due to waves
Consider a ship loaded with the weights concentrated at
the bow and the stern, which tends to droop. This leads
to
hogging of the ship hull
In a heavy seaway, a ship may be supported at the ends
by the crests of waves while the middle remains
unsupported. If the wave trough is now considered at
midships then the buoyancy in this region will be
reduced. With the wave crest positioned at the ends of
the ship, the buoyancy here will be increased. This
loading condition will result in a bending moment which
will cause the ship to
sag.
Consider heavy weights concentrated at the midships of
a ship. The middle hull part tends to droop more than the
ends. This causes
sagging of ship hull
The forces acting on a ship may be
static or
dynamic.
the ship at sea or lying in still water is constantly being subjected to a wide variety of stresses and strains, which results from the actions of forces from outside and within the ship. these forces may initially be classified into
static or
dynamic. forces
are due to the
difference in the weight and buoyancy,
which occur through out the ship
static forces
are cause by the
motion of the ship at sea and the action of
the wind and wave
dynamic forces
They result from
* The ship’s motion at sea.
* The action of wind and waves.
* The effects of operating machinery.
dynamic forces
These are due to
* Internal forces resulting from structural weight, cargo and machinery weight.
* External static forces including the hydrostatic pressure of the water on the hull.
STATIC FORCES
ship movement of dynamic forces
six degrees of freedom ( three linear and three rotational)
is the motion of the ship when the ship have being up by a wave or sea.
Heave