How do submarines float or sink as desired

Experimental Analysis on Sinking Time of Littoral Submarine in Various Trim Angle

Luhut Tumpal Parulian SINAGA1,a* 1Senior Researcher at PTRIM, BPPT Laboratorium Hydrodinamika Indonesia, Surabaya

aluhuttps@yahoo.com.sg

*corresponding author

Keyword: Littoral submarine, dive, sink, experiment.

Abstract. A submarine must conform to Archimedes’ Principle, which states that a body immersed in a fluid has an upward force on it (buoyancy) equal to the weight of the displaced fluid, (displacement). Submarines are ships capable of being submerged. The history of submarines and their operation have largely revolved around being able to alter the density of the vessel so that it may dive below the surface, maintain a depth, and return to the surface as needed. The way modern submarines accomplish this task is to bring in and remove water from tanks in the submarine called ballast tanks. Ballast tanks fit into two categories: those used for major adjustment of mass (main ballast tanks); and those used for minor adjustments (trim tanks). The effect of each tank is plotted and this is compared with the changes in mass and trimming moment possible during operations using a trim polygon to determine whether the ballast tanks are adequate. On the water surface, metacentric height (GM) is important, whereas below the surface it is the distance between the centre of buoyancy and the centre of gravity (BG) which governs the transverse stability of a submarine.

Introduction A submarine or a ship can float because the weight of water that it displaces is equal to the

weight of the ship. This displacement of water creates an upward force called the buoyant force and acts opposite to gravity, which would pull the ship down. Unlike a ship, a submarine can control its buoyancy, thus allowing it to sink and surface at will [1].

As with any object in a fluid, a submarine must conform to Archimedes’ Principle, which states that a body immersed in a fluid has an upward force on it (buoyancy) equal to the weight of the displaced fluid, (displacement). This applies whether the submarine is floating on the water surface, or deeply submerged [2, 3].

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air (see Fig. 1). When the submarine is on the surface, the ballast tanks are filled with air and the submarine's overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy) [4, 5].

A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks. In addition, the submarine has movable sets of short "wings" called hydroplanes on the stern (back) that help to control the angle of the dive. The hydroplanes are angled so that water moves over the stern, which forces the stern upward; therefore, the submarine is angled downward [2].

Figure 2 shows the location of the MBT's in a submarine. The bulk of the MBT's are located at the bow and aft sections of the boat and a small MBT surrounds the pressure hull in the center of the boat. A large portion of the space between the pressure hull. It is important to note that the MBT is only used to change the buoyancy of the boat from very positive to slightly positive.

Applied Mechanics and Materials Submitted: 2017-02-06 ISSN: 1662-7482, Vol. 874, pp 128-133 Revised: 2017-08-22 doi:10.4028/www.scientific.net/AMM.874.128 Accepted: 2017-08-29 © 2018 Trans Tech Publications, Switzerland Online: 2018-01-10

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.scientific.net. (#113698139, ProQuest, USA-29/03/19,15:02:51)

https://doi.org/10.4028/www.scientific.net/AMM.874.128
(a) Surface (b) Dive

Figure 1. Submarine diving process.

Figure 2. Location ballast tank of submarine.

As the righting moment at an angle of heel must be the same for these two definitions of displacement, the relationship between the centres can be obtained from Eq. 1.

BFGF x ΔF = BH x GH x ΔH (1)

Therefore,

𝐵𝐵𝐹𝐹𝐺𝐺𝐹𝐹 𝐵𝐵𝐻𝐻𝐺𝐺𝐻𝐻

= 𝛥𝛥𝐻𝐻 ∆𝐹𝐹

(2)

where 𝛥𝛥𝐻𝐻 = Total mass Hydrostatic displacement, other than free flood water ∆𝐹𝐹 = Total mass Form displacement, including free flood water 𝐵𝐵𝐻𝐻 = Centre of gravity Hydrostatic displacement 𝐺𝐺𝐻𝐻 = Centre of gravity Hydrostatic displacement 𝐵𝐵𝐹𝐹 = Centre of buoyancy Form displacement 𝐺𝐺𝐹𝐹 = Centre of buoyancy Form displacement The Main Ballast Tanks (MBTs), are usually ballast tanks external to the pres- sure hull, which

are free flooding when the submarine is submerged, as shown in Fig. 3. The purpose of the MBTs is to allow major adjustment of the submarine mass to enable it to

operate submerged as well as on the water surface. Water and air enter and leave the MBTs through flooding holes at the bottom and vents at the top of the tanks.

Applied Mechanics and Materials Vol. 874 129

Figure 3. Schematic of typical main ballast tank system.

During operations the mass and longitudinal centre of gravity of a submarine will change due to use of consumables including fuel, and weapons discharge. In addi- tion, changes in seawater density, hull compressibility and surface suction when operating close to the surface will all result in the need to be able to make small changes to the submarine mass and longitudinal centre of gravity.

The trim and compensation ballast tanks are used to make these small adjust- ments. A schematic of such a typical system is shown in Fig. 4.

Figure 4. Schematic of typical trim and compensation ballast tanks.

At the design stage it is necessary to determine whether the trim and compensation ballast tanks are adequate to cope with all possible changes in submarine mass and longitudinal centre of gravity. To do this, the effect of each tank is plotted as a function of mass and trimming moment as shown in Fig. 5 [6].

In this figure, the point with zero mass and zero trimming moment is where all the tanks are empty. The forward trim tank (FTT) is then filled. In this case, the tank is a soft tank, not open to the sea, so there is no change in mass, just a move- ment of the centre of gravity forward from the aft trim tank (ATT) to the forward trim tank. Thus, the effect is a forward trimming moment with no change in mass. This is shown by a horizontal line.

To perform a quick dive, the front ballast is filled with water and then forms the angle required to perform the dive, so the submarine has an effective range, see Fig. 6. Once the boat is trimmed to more or less neutral buoyancy, the depth of the boat is controlled with the hydroplanes. To use the hydroplanes the boat requires speed to create a force on the tilted planes. At slow speeds, the fore hydroplanes are exclusively used to keep the boat at the required depth

The dive technology was shown that the bulk buoyancy of the boat is changed with the MBT followed by fine tuning with the MBT and finally the correct depth is maintained using the hydroplanes. Due to the application of the real submarine technology is not always possible. In the following, some of the available model diving technologies will be treated [7].

This research focuses on the study of the influence of sloshing against the coupling movement heave the ship while the ship conducted a quick dive using Physical Tests in Indonesia Hydrodynamics Laboratory.

130 Marine Systems and Technologies

Figure 5. Polygon showing the effect of trim and compensation ballast tanks.

Figure 6. Quick dive submarine.

Methodology The investigation was carried out experimentally. The experimental work was conducted using

towing tank and tested at various angle of trim. Physical models of the submarine are shown in Fig.7. The model is made from FRP (fibreglass reinforced plastics) in order to obtain appropriate displacement as scaled from full ship mode in accordance with Froude law of similarity. Principal particulars of the submarine given in Table 1.

Table 1. Main dimension submarines model.

Dimension SHIP (m) MODEL (mm) LOA 22.00 700.00 B Total 4.29 136.30 D Total 5.13 163.30 T 2.60 82.70 dim. Press Hull 3.00 95.50 JR. FS 1.10 35.00 JR. WL 1.00 31.80 JR. BL 0.30 9.50 Scala 31.43

Applied Mechanics and Materials Vol. 874 131

Figure 7. Design of submarine.

Results and Discussion To get a angle dive effective when quick dive at model of litoral submarine, has obtained the

water depth in Cavitation Tunnel = 0.6 m a summary of the test results that can be seen from the Table 2 below:

Table 2. Angle of Attack Pitch Ballast Water Depth.

Volume of ballast in Fwd. Tank (gr.)

Angle of Trim Sinking time (sec.) Sinking velocity (V m / sec)

150 5⁰ 3.2 0.188 300 7.5⁰ 3.0 0.200 400 10⁰ 2.8 0.214 500 12.5⁰ 2.7 0.220 550 15⁰ 2.5 0.240

In Table 2 was obtained dives fastest ship that is for 2.5 seconds at an angle of 150 trim. This is due to the angle trim large enough so that the size of the area aboard the front facing the water flow becomes tighter. It is also their ballasts volume large enough to add to the weight of the model submarine. As shown in Fig. 8, the addition of ballast resulted in a bigger angular change also. However, the time it takes to sink even less.

Furthermore by addtion 150 gr ballast at forward ballast tank, submarine can be have trim 50. But, Litorral submarin have 3.2 sec in singking time. This is due to wide cross section and blocking into the water, causing longer sinking time.

The conditions of trim described apply of submarine operations by flooding the forward ballast tank. However, these buoyancy conditions always be considered with respect to the law of the lever on each side of the center of gravity of the boat. The trimming of the submarine is accomplished by varying, or adjusting, the amount of water in the variable ballast tanks. The trim system is the means by which this adjustment is made. However, the trim has been so carefully adjusted that by flooding the main ballast tanks and adding the required amount of water to the special ballast tanks, the submarine can be made to submerge at the desired rate [8].

132 Marine Systems and Technologies

Figure 8. Sinking time for submarine.

Conclusions Ship model testing was conducted to determine the model to the required time to dive to the

bottom. From the tests of models with angle of attack 150 has the fastest time in the amount of 2.5 seconds or has a speed of 0.24 m/sec to reach the bottom of the pool of test.

In general the vessel can sink due to a sharp angle so that the area of the bow that is exposed to water is smaller so that the resistance becomes small and the weight gain due to the addition of the front ballast. As the next stage should be calculated comprehensively on navigation vessels arising from the movement of the ship.

References [1] Dmitri Kuzmin, Introduction to Computational Fluid Dynamics, Institute of Applied Mathematics University of Dortmund, http://www.mathematik.uni-dortmund.de /_kuzmin/ cfdintro/ cfd.html (2000). [2] M. Mackay, The Standard Submarine Model: a Survey of Static Hydrodynamic Experiments and Semi empirical Predictions, Defence R&D, TR 2003-079, 2003. [3] Erwandi, T.S. Arief, C.S.J. Mintarso, The study on hydrodynamic performances of ihl-mini- submarine, In: Proc. The Second International Conference on Port, Coastal, and Offshore Engineering (2nd ICPCO), Bandung, 12-13 November 2012. [4] S.W. Lee, H.S. Hwang, C.M. Ryu, H. I. Kim, S.M. Sin, A Development of 3000-ton class submarine and the study on its hydrodynamic performances, In: Proc. the Thirteenth (2003) International Offshore and Polar Engineering Con-Prosiding InSINas 2012 HK-6 0026: Erwandi dkk. ference Honolulu Hawaii, USA May 2003. [5] L.T.P. Sinaga, Theoretical Analysis Of Sloshing Effect On Pitch Angel To Optimize Quick Dive On Litoral Submarine 22 M. In: The 8th International Conference on Physics and Its Applications (ICOPIA 2016), August 23, 2016, Denpasar, Indonesia, 2016. [6] A. F. Molland, S.R. Tunock, D.A. Hudson, 2011, Ship Resistance and Propulsion, Cambridge University Press, New York, 2001. [7] A. Prisdianto, A. Sulisetyono, Perancangan ROV dengan Hydrodinamic Performance yang Baik untuk Misi Monitoring Bawah Laut, ITS, Surabaya, 2012. [8] A. Sulisetyono, D. Purnomo, The Mini-Submarine Design for Monitoring of the Pollutant and Sewage Discharge in Coastal Area, In: Proc. 5th International Conference on Asian and Pacific Coasts, NTU, Singapore, 2009.

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