DESIGN AND ANALYSIS OF AN UNDER
WATER WEAPON
Vinodh. Peram1
PG scholar, Department of Mechanical
Nirma College of Engineering & Technology
Vijayawada, India
peramvinodhchowdary@gmail.com
Abstract—Under
water vehicles viz. torpedoes,
submarines etc are used in defense applications. These
are designed for moderate to extreme depths of
operation with minimum structural weight for
increasing performance, speed and endurance. In
general Homing head shell is the front part of the
torpedo and its main purpose is target detection and
tracking. The present thesis deals with the design and
structural analysis of homing head shell of a torpedo.
Keywords— Torpedo Sections, Homing Torpedoes,
Acquisition Areas, Shell93 Element Description, Various
Aray Configurations, Static Analysis, BucklingAnalysis
Basic analytical design for static loads was carried
out using theory of shells methodology and British
Standard BS: 5500. The finalized configuration was
analyzed. The FEA stress and displacement results
were compared with analytical solution. Due to the
complex features of the design, stress concentrations
were observed at certain places. A number of design
iterations were made at these locations to bring the
design to be within the acceptable stress limits. As the
torpedo is carried either on a ship or submarine, the
vibration loads due to these platforms has to be
considered. Modal analysis was carried out to see
whether the natural frequency is within the operating
range of these platforms. While launching of these
torpedoes, the torpedo experiences the water entry
shock. The shell was analyzed for the shock load. The
stresses developed due to the above shock load were
found to be within the acceptable limit.
I. INTRODUCTION
The Torpedo is one of the oldest weapons in the
Naval Inventory, having been invented over 130 years
ago, But at the same time it remains one of the
deadliest anti-ship and anti-submarine weapon, it is
far more lethal to submarines and surface ship than
any other conventional weapon.
A torpedo is a self propelled underwater weapon that
carries a high explosive charge to its target. A torpedo
can do more damage than a projectile from the biggest
Sri. G. Adi Narayana M.Tech (Ph.D)2
Associate Professor
Nirma College of Engineering & Technology
Vijayawada, India
adi.gudepu@gmail.com
guns on a battleship. There is more explosive in a
torpedo warhead than there is in any projectile.
Torpedo warhead explodes under water, and that
increases its destructive effect. When projectile
explodes, the surrounding air absorbs a part of its
force. But when the torpedo warhead explodes the
water transfers almost full force of the explosion to
the hull of the target ship. Thus, even if a projectile
could carry the same amount of explosive, the torpedo
would do more damage.
Torpedoes make it possible for small ships to carry
heavy armament. But of course it cannot make ship
the equal of a large one in a combat. A torpedo moves
slowly compared to a projectile and its effective range
is much shorter.
Heavy weight torpedoes are mainly confined to
submarines (with a few notable exceptions) and Light
weight torpedoes are used both as offensive weapons
in anti- submarine warfare and as defensive antisubmarine weapons by surface warship.
Although a number of elderly weapons still rely on
gyroscopic guidance. The majority of modern
torpedoes rely on Active or Passive acoustic homing
or Wake homing. Passive homing is used to detect
submarine’s noise signatures. But this fails 2 when the
submarine switches to silence mode. Thus it is very
hard for passive seekers to detect them, and today
active seekers offers the best way of attacking
submerged submarines.
Homing torpedoes are a relatively recent
development they have been perfected since the end
of World War II. With homing torpedoes, a destroyer
can attack a submerged submarine, even when its
exact position and depth are unknown. The homing
torpedo is becoming increasingly important as a
weapon with which one submerged submarine may
attack another.
II. DIFFERENT TYPES OF TORPEDOES
A. TorpedoesMark14 type and Mark 23 type:
These torpedoes are only 20 1/2 feet long, to fit in
submarine tubes. The Mark 14 has two speeds. The
low-power setting will give a range of 9,000 yards at
approximately 32 knots, and the high-power setting, a
range of 4,500 yards at 46 knots. Its war head contains
about 700 pounds of high explosive.
There are no side-gear assemblies in the main engine
of this torpedo. The two speed settings are obtained
by changing the number of nozzle jets in use (two for
low speed, five for high) and by altering the size of
the restrictions in the air, fuel, and water delivery
lines.
The Mark 14 torpedo has a governor whose
function is to stop the torpedo, if the starting lever is
tripped accidentally, before the engine develops
excessive speed, and thereby to safeguard personnel
and to prevent serious damage to the torpedo.
B. Torpedo Mark 18 type:
The Mark 18 is an electrically propelled torpedo
designed for use in submarines. It is single-speed,
designed to run for 4,000 yards at an average speed of
about 29 knots. The primary advantage of the Mark
18 is that it is wakeless.
In place of an air-flask section this torpedo has a
battery compartment, which contains a lead-acid
storage battery, a hydrogen eliminator, and a
ventilating system. The battery runs a 90-horsepower
series electric motor (located in the afterbody) whose
armature is connected by the main drive shaft and
gearing to two counter-rotating propellers.
Compressed air-required to close the starting switch,
spin the gyro, and operate the depth and steering
engines-is stored at 3,000 psi in three small flasks in
the afterbody. The gyro is of “run-down” type. After
the initial spin the air is shut off and the gyro is
unlocked; the gyro wheel continues to spin of its own
momentum. The war head contains about 600 pounds
of high explosive.
C. Homing torpedoes:
The torpedoes described above are designed to take
up the course set on their gyro mechanisms, and then
run in a straight line. Homing torpedoes can also
follow a gyro course. In addition, a homing torpedo
can search for a target, and, when it finds one, chase it
until it secures a hit. Some types can switch back and
forth between gyro control, search pattern, and
homing control, as appropriate. Several types of
homing torpedoes are now in the Fleet, and others are
in various stages of development. For security
reasons, only a short and very general discussion can
be given here. At present, homing torpedoes are
acoustic (operated by sound). In general, they are of
two types-active and passive. The active type sends
out short pulses of sound, and “listens” for echoes
from the target. When an echo is detected, the torpedo
steers itself toward the source of the echo. The passive
type merely listens for target sounds (such as
propeller and machinery noises), then steers itself
toward the source of the sounds.
III. EXISTING SYSTEM
A. Acquisition Areas :
The primary task of torpedo sonar is to detect
acoustically the target and thus compensate for the
position errors of the torpedo relative to the target,
which are inevitable and become greater with an
increasing distance. If the acquisition area is too
small, then the risk of passing the target without any
target contact becomes high and the probability of
success goes down. The various errors to be
considered will become very large, due to the
navigational errors of the firing submarines and due to
flow in homogeneities.
The homing head of the torpedo is required to be
designed with the following requirements in view.
 Provision for maximum possible Transducer
Elements
 Placement of Transmitting and Receiving
SOBID elements
 Housing the Echo sounder at the bottom of the
homing head
 Peripheral positioning of 4 Numbers
proximity Fuse 17
 Mounting arrangements for
front-end
electronics and Signal processing Unit.
IV. PROPOSED METHOD
VARIOUS CONFIGURATIONS
Taking into consideration of all the requirements of
the homing head, various configurations were tried
out, without compromising on the functional aspects.
Four configurations were worked out and they are as
follows.
Planar Array
Conformal array
Circular array
A. Planar Array :
This is the simplest configuration tried out. In this
configuration the homing transducer elements are
placed in a planner array. The planar array consists of
6 x 6 or 8 x 8 array. The transducer mounting plate in
this configuration is a flat plate with 36 or 64 circular
holes, through which the stress rod of the transducer
elements will project into the interior. The SOBID
elements are placed at the periphery of the array for
object identification and transmission .Two SOBID
elements for object receiving and the other two for
transmission. The main disadvantage of this model is
as the number of transducer elements are less the
viewing area is less so an optimum search of the
target is not possible. In order to overcome this look
up area and the number of transducer elements are to
be increased so that the torpedo can view through
better area.
V. RESULTS AND ANALYSIS OF AN UNDER
WATER WEAPON
A. Static Analysis :
The following plot shows the vonmises stress values
on the model. The maximum stress is 458.408Mpa,
but this has no meaning as this is seen on a support
region. Except the value at singularity the maximum
stress is observed near the circumference of the
homing transducer pocket opening and is equal to
152.803Mpa. The stress value is in the range of
160Mpa, which is in agreement with the theoretical
value calculated.
Element SHELL 93
Poison’s ratio 0.32
Young’s Modulus 71000 MPa
Planar array
Loads:
An external pressure of 72 bar is applied on the outer
shell
Boundary conditions
Ux=Uy=Uz=0 at Y=0
Axis of the shell - Y axis
B. Conformal Array :
In order to increase the viewing area the planner
arrangement of the transducer elements in the above
configuration have been modified to conformal
arrangement. The conformal array consists of two
arrays. The mounting plate for the transducer
elements in this configuration is a box cut which has
96 circular holes. SOBID elements are placed.
Acoustic proximity fuse are placed which determines
the proximity of the torpedo with the target. The look
up area compared to planar array has been increased
but the hydrodynamic shape has been violated.
static analysis of maximum vonmises stress is
458.408Mpa
Conformal array
C. Circular Array :
Due to the arrangement of the transducers adapted
to the head shape(conformal array ),the simultaneous
reception of acoustic signals over the entire angular
range of +/-90 degree and more with reference to the
torpedo axis is assured with out any negative impact
on the acquisition range, this offering a considerable
advantage over a flat head (Planar Array)design..
160.02N/mm²
Theoretical stress
152.803N/mm²
FEM Result stress
B. Buckling Analysis :
As the shell is subjected to external pressure and the
length to diameter ratio is more the shell is prone to
buckling failure. In the above analysis the model is
checked for yield failure. In this section we will
model the shell for buckling analysis with FEM. The
stress variations at the singularities are found to be
having boundless values.
The shell model is used to reduce the computational
expenses. The solution for working analysis requires
solving the eigen value problem with the size of
matrix equal to the number of degrees of freedom of
the model. By simplifying the model the size is
brought down by many times compared to the model
with solid elements.
The buckling analysis result is presented in the
following figures. The shell with 72 bar external
pressure is found to have a buckling factor of
0.69186. Different views of first mode shape of the
buckling failure are shown in the following figures.
Element - SHELL 93
Density Poison’s ratio - 0.32
Young’s Modulus - 71000 Mpa
Loads: An External pressure of 72 bar is applied on
the outer shell
Boundary Conditions:
Ux=Uy=Uz=0
Axis of the shell - Y axis
SET BUCKLING FACTOR :
1. 0.69186---------Critical Buckling Factor
2. 0.71185
3. 0.71324
4. 0.72510
5. 0.78632
6. 0.81938
Buckling mode shapes (A)
(B)
COMPARISION BETWEEN STATIC &
DYNAMIC & BUCKLING ANALYSIS
STATIC
DISPLACEMENT
DYNAMIC
DISPLACEMENT
BUCKLING
2.14mm
0.227598mm@18.117
Hz
0.00219
VI. ACKNOWLEDGEMENT
The authors would like to thank Department of
Mechanical Engineering of K.L. Song Huanhuan, Navy
Univ. of Eng., Wuhan, China.
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