ISSN 2319-8885 Vol.03,Issue.39 November-2014,

Pages:7896-7899

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Design and Analysis of an Under Water VINODH PERAM1, SRI. G. ADI NARAYANA2 1PG scholar, Dept of Mechanical Engineering, Nirma College of Engineering & Technology, Vijayawada, AP, India, E-mail: [email protected]. 2Associate Professor, Dept of Mechanical Engineering, Nirma College of Engineering & Technology, Vijayawada, AP, India, E-mail: [email protected].

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 is the front part of the 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. 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.

Keywords: Torpedo Sections, Homing Torpedoes, Acquisition Areas, Shell93 Element Description, Various Array Configurations, Static Analysis, Buckling Analysis.

I. INTRODUCTION defensive anti-submarine by surface warship. The Torpedo is one of the oldest weapons in the Naval Although a number of elderly weapons still rely on Inventory, having been invented over 130 years ago, But at gyroscopic guidance. The majority of modern torpedoes rely the same time it remains one of the deadliest anti-ship and on Active or Passive acoustic homing or Wake homing. anti-submarine weapon, it is far more lethal to submarines Passive homing is used to detect submarine’s noise and surface ship than any other conventional weapon. A signatures. But this fails 2 when the submarine switches to torpedo is a self propelled underwater weapon that carries a silence mode. Thus it is very hard for passive seekers to high charge to its target. A torpedo can do more detect them, and today active seekers offers the best way of damage than a projectile from the biggest guns on a attacking submerged submarines. Homing torpedoes are a battleship. There is more explosive in a torpedo than relatively recent development they have been perfected since there is in any projectile. Torpedo warhead explodes under the end of World II. With homing torpedoes, a destroyer water, and that increases its destructive effect. When can attack a submerged submarine, even when its exact projectile explodes, the surrounding air absorbs a part of its position and depth are unknown. The homing torpedo is force. But when the torpedo warhead explodes the water becoming increasingly important as a weapon with which transfers almost full force of the explosion to the hull of the one submerged submarine may attack another. target ship. Thus, even if a projectile could carry the same amount of explosive, the torpedo would do more damage. II. DIFFERENT TYPES OF TORPEDOES Torpedoes make it possible for small ships to carry heavy A. Torpedoes Mark14 Type and Mark 23 Type armament. But of course it cannot make ship the equal of a These torpedoes are only 20 1/2 feet long, to fit in large one in a combat. submarine tubes. The Mark 14 has two speeds. The low- power setting will give a range of 9,000 yards at A torpedo moves slowly compared to a projectile and its approximately 32 knots, and the high-power setting, a range effective range is much shorter. Heavy weight torpedoes are of 4,500 yards at 46 knots. Its war head contains about 700 mainly confined to submarines (with a few notable pounds of high explosive. There are no side-gear assemblies exceptions) and Light weight torpedoes are used both as in the main engine of this torpedo. The two speed settings are offensive weapons in anti- submarine warfare and as obtained by changing the number of nozzle jets in use (two

Copyright @ 2014 IJSETR. All rights reserved. VINODH.PERAM, SRI.G.ADI NARAYANA for low speed, five for high) and by altering the size of the  Provision for maximum possible Transducer restrictions in the air, fuel, and water delivery lines. The Elements Mark 14 torpedo has a governor whose function is to stop the  Placement of Transmitting and Receiving SOBID torpedo, if the starting lever is tripped accidentally, before the elements engine develops excessive speed, and thereby to safeguard  Housing the Echo sounder at the bottom of the personnel and to prevent serious damage to the torpedo. homing head  Peripheral positioning of 4 Numbers proximity Fuse B. Torpedo Mark 18 Type 17 The Mark 18 is an electrically propelled torpedo designed  Mounting arrangements for front-end electronics for use in submarines. It is single-speed, designed to run for and Signal processing Unit. 4,000 yards at an average speed of about 29 knots. The primary advantage of the Mark 18 is that it is wakeless. In IV. PROPOSED METHOD VARIOUS place of an air-flask section this torpedo has a battery CONFIGURATIONS compartment, which contains a lead-acid storage battery, a Taking into consideration of all the requirements of the hydrogen eliminator, and a ventilating system. The battery homing head, various configurations were tried out, without runs a 90-horsepower series electric motor (located in the compromising on the functional aspects. Four configurations afterbody) whose armature is connected by the main drive were worked out and they are as follows. shaft and gearing to two counter-rotating propellers.  Planar Array Compressed air-required to close the starting switch, spin the  Conformal array gyro, and operate the depth and steering engines-is stored at  Circular array 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 A. Planar Array the gyro is unlocked; the gyro wheel continues to spin of its This is the simplest configuration tried out. In this own momentum. The war head contains about 600 pounds of configuration the homing transducer elements are placed in a high explosive. planner array as shown in Fig.1. The planar array consists of 6 x 6 or 8 x 8 array. The transducer mounting plate in this C. Homing Torpedoes configuration is a flat plate with 36 or 64 circular holes, The torpedoes described above are designed to take up through which the stress rod of the transducer elements will the course set on their gyro mechanisms, and then run in a project into the interior. The SOBID elements are placed at straight line. Homing torpedoes can also follow a gyro the periphery of the array for object identification and course. In addition, a homing torpedo can search for a target, transmission .Two SOBID elements for object receiving and and, when it finds one, chase it until it secures a hit. Some the other two for transmission. The main disadvantage of this types can switch back and forth between gyro control, search model is as the number of transducer elements are less the pattern, and homing control, as appropriate. Several types of viewing area is less so an optimum search of the target is not homing torpedoes are now in the Fleet, and others are in possible. In order to overcome this look up area and the various stages of development. For security reasons, only a number of transducer elements are to be increased so that the short and very general discussion can be given here. At torpedo can view through better area. 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. Fig.1. Planar array.

International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.39, November-2014, Pages: 7896-7899 Design and Analysis of an Under Water Weapon B. Conformal Array Young’s Modulus 71000 MPa In order to increase the viewing area the planner Loads: An external pressure of 72 bar is applied on the outer arrangement of the transducer elements in the above shell configuration have been modified to conformal arrangement. The conformal array consists of two arrays as shown in Fig.2. B. Boundary Conditions The mounting plate for the transducer elements in this Ux=Uy=Uz=0 at Y=0 configuration is a box cut which has 96 circular holes. Axis of the shell - Y axis 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.

Fig.3. Static analysis of maximum vonmises stress is 458.408Mpa Theoretical stress 160.02N/mm² FEM Result stress 152.803N/mm² Fig.2. Conformal array. C. Circular Array C. Buckling Analysis Due to the arrangement of the transducers adapted to the As the shell is subjected to external pressure and the length head shape(conformal array ),the simultaneous reception of to diameter ratio is more the shell is prone to buckling acoustic signals over the entire angular range of +/-90 degree failure. In the above analysis the model is checked for yield and more with reference to the torpedo axis is assured with failure. In this section we will model the shell for buckling out any negative impact on the acquisition range, this analysis with FEM. The stress variations at the singularities offering a considerable advantage over a flat head (Planar are found to be having boundless values. The shell model is Array)design. used to reduce the computational expenses. The solution for working analysis requires solving the eigen value problem V. RESULTS AND ANALYSIS OF AN UNDER WATER with the size of matrix equal to the number of degrees of WEAPON freedom of the model. By simplifying the model the size is A. Static Analysis brought down by many times compared to the model with The following plot shows the vonmises stress values on solid elements. The buckling analysis result is presented in the model. The maximum stress is 458.408Mpa, but this has the following figures. The shell with 72 bar external pressure no meaning as this is seen on a support region. Except the is found to have a buckling factor of 0.69186. Different value at singularity the maximum stress is observed near the views of first mode shape of the buckling failure are shown circumference of the homing transducer pocket opening and in the following figs.4 and 5. is equal to 152.803Mpa. The stress value is in the range of 160Mpa, which is in agreement with the theoretical value Element - SHELL 93 calculated. Density - N/mm² 9 10 7.2 Element SHELL 93 Poison’s ratio - 0.32 Density 9 10 7.2 Young’s Modulus - 71000 Mpa Poison’s ratio 0.32

International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.39, November-2014, Pages: 7896-7899 VINODH.PERAM, SRI.G.ADI NARAYANA Loads: An External pressure of 72 bar is applied on the outer TABLE I: Comparison between Static & Dynamic & shell Buckling Analysis

Boundary Conditions:

Ux=Uy=Uz=0 VI. ACKNOWLEDGEMENT Axis of the shell - Y axis The authors would like to thank Department of Mechanical Engineering of K.L. Song Huanhuan, Navy Set Buckling Factor: Univ. of Eng., Wuhan, China. 1. 0.69186------Critical Buckling Factor VII. REFERENCES 2. 0.71185 [1]Modern torpedoes and counter measures, BHARAT 3. 0.71324 RAKSHAK MONITOR. 4. 0.72510 [2] Ross C.T.F -Pressure vessels under external pressure, 5. 0.78632 statics and dynamics; Elasivier applied science publishers, 6. 0.81938 1990. [3] British standards 1490 Aluminum Ingots. [4] Report on Structural static Analysis of Nose cone of an under water weapon. [5] Report on Planar array versus conformal array. [6] Theory of thin shells by Harvey, CBS publishers. [7] Cylindrical shell buckling: A characterization of localization and periodicity discrete and continuous - G.W.Hunt, G.J.Lord Discrete and continuous dynamical systems-series Vol3 Nov4, Nov2003. [8] Submersible meeting paper pressure hull design parameters: SNAME transactions, annual. [9] Dynamic Plastic buckling of copper cylindrical shells International journal of solids and structures, vol 27, No1, pp.89-103, 1991. [10] The effect of initial imperfections of dynamic buckling of shells(Journal of engineering mechanics,Vol15,no,5,pp1075-1093,May 1989. [11] British Standards 5500 specifications for o unfired fusion welded pressure vessels British standards institutions, April1985. [12] Theory of shells-edited by W.T.Koiter and Fig.4. Buckling mode shapes (A). G.K.Mikhailov. [13] Vibrations of shells and plates (second edition, revised and expanded) Werner soedel. [14] Theory of shells and plates, Timoshenko.

Fig.5.

International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.39, November-2014, Pages: 7896-7899