Experimental Analysis of Pitching Motion in Various Angle of Attack for Mini Submarine On Surface Condition

Transcription

1 Experimental Analysis of Pitching Motion in Various Angle of Attack for Mini Submarine On Surface Condition Luhut Tumpal Parulian Sinaga Senior Researcher at Balai Pengkajian dan Penerapan Teknologi (BPPT) Indonesian Hydrodynamic Laboratory, Surabaya, Indonesia Abstract For the operational mini submarine necessary to analyze pitching motion when it probably to adaptation from snorkeling to dive condition. Further more, function of angle of attack is urgently needed. However, slope adaptation reach optimal as information urgently needed for navigator guidance. Furthermore, need to be realized for feasibility study more detail with various angle of attack to find maximum angel of attack on the mini submarine. This feasibility study was conducted in MOB Hydrodynamic Laboratory amplitude resonance. Sloshing has been studied for many years by analytical and numerical methods[5,6]. Index Terms mini submarine, slope, physical model test, MOB I. INTRODUCTION Figure 2. Submersion proccess Submarine is designed with the main ballast tanks fulls, the weight of water displaced will be as close as possible to the weight of the boat, see Fig. 1. That is, there should be a balance between displacement and buoyancy, referred to as neutral buoyancy [1], [2]. If true neutral buoyancy is achieved the boat will float at whatever depth it presently is, unless something acts on it to make it rise or sink, see Fig.2. In practice, submariners prefer to maintain very slight positive buoyancy, so that if power if lost the boat may be expected to slowly rise to the surface. In a quick dive, the negative tank is important. By flooding this tank the boat is made negatively buoyant, which gets the boat under water quicker. Once submerged, though, the negative tank is blown to the mark. the submarine to be heavier than the water it displaced while diving, because you want to get under as quickly as possible. The equations of motion for a submarine are similar to those for a surface ship, however they include all six degrees of freedom[7]. For a submarine it is normal to take the origin as the longitudinal center of gravity (LCG), rather than mid- ships, as this simplifies the equations, and for a submarine this position is fixed (unlike for a surface ship)[8]. The axis system used is shown in the notation. Note that the origin is on the centerline, which is where the transverse center of gravity is assumed to be. Positive directions are along the positive axes, and positive rotations are clockwise as seen from the origin looking along the positive direction of the axes. The first approach in the modeling of sloshing liquids involves using numerical schemes based on linear and/or non-linear potential flow theory. These type of models represent extensions of the classical theories by Airy and Boussinesq for shallow water tanks. Faltinsen [9] introduced a fictitious term to artificially include the effect of viscous dissipation. Considering the importance of nonlinear effects in the sloshing response, Faltinsen [9] analyzed nonlinear sloshing by perturbation theory. Figure 1. Ballast tank submarine The problem of water sloshing in closed forepeak ballast. This phenomenon can be described as a free surface movement of the contained fluid due to sudden loads [3]. Sloshing is a liquid vibration phenomenon caused by the movement of the ballast. When the ballast is in transit, the sloshing would affect stability of the system severely caused by pitch of angle when submarine in quick dive cause couple motion [4]. So it is necessary to minimize the impact of sloshing and avoid large Manuscript received September 12, 2017; revised January 2, doi: /ijmerr

2 Numerical simulation of sloshing waves in a 3-D tank has been conducted by [10,11]. Two experimentally derived empirical constants were included to account for the increase in liquid damping due to breaking waves and the changes in sloshing frequency, respectively. The attenuation of the waves in the mathematical model due to the presence of dissipation devices is also possible through acombination of experimentally derived drag coefficients of screens to be used in a numerical model [12]. II. METHODOLOGY Figure 4. Littoral submarine model The design model is based on a plan lines obtained from the owner. From the lines of this plan will be made for the scale model of the ship. The next stage is to use the offset table for plotting the results of the previous scale. After the scale has been determined then in print and create models. The dimension of submarine as shown Table I and was designed by computer in Fig. 3. In this case the force, the left-hand side of the equation, is the hydrodynamic force acting on the submarine, and the right-hand side is the rigid body dynamics. This equation is transformed into body fixed axes, and the right hand side of the equation is given as follows: TABLE I. MAIN DIMENSION SUBMARINES MODEL Dimension SHIP (m) MODEL (mm) LOA B Total D Total T dim. Press Hull JR. FS JR. WL JR. BL Scala (1) If the origin of the axes is taken at the position of the longitudinal, and transverse centre of gravity, then both xg and yg will be equal to zero, simplifying these equations. M is the total hydrodynamic pitch moments respectively. If these hydrodynamic forces and moments can be determined as functions of time for a motion submarine. In addition, if the effects of geometry on these forces and moments are understood then this can be used to assist in the design of the submarine. the equation of moment couple motion is given as follows (2) (3) Figure 3. Design littoral submarine When surfacing. water is retained in the casing, and other free flood spaces, for a period before it can escape[13,14]. This will raise the centre of gravity above that assumed forthe steady state calculations used to generate Fig. 5. The length of time that this Eater talies to escape will depend on the size of the free flooding holes. The large holes may affect the hydro-acoustic noise generated when submerged[15]. Testing submarine models at even keel condition. It could be at the time of testing, the condition of the submarine model trim by bow and trim by stern. The physical state at the time of testing the other is the lack of waves. In addition, the volume dispalsemen, the model and the station to be checked again. Model of submarines appropriate scale and created a system to regulate ballast trim of the submarine models. In Fig. 4 shows a model submarine that has been created. 47

3 moment that results in a drastic decrease in the water plane area. Since the longitudinal metacentric height will be proportional to the on the waterplane area, any trimming moment rapidly reduces the metacentric height. III. RESULT AND DISCUSSION In order to exercise the method developed above, submarine considered. A sketch of the submarine is shown in Fig. 8 to 10. The Submarine has the following geometric and mass properties: length = 700 mm, reference diameter = 163 mm, mass = 4,8 kg Pitch curves as in Fig. 11. The test results indicate that the pitch behaviour of the submarine-like body is highly nonlinear and derivation of a single correlation factor for all experimental configurations would not be practical. The closed casing configuration which provides additional buoyancy and hence a greater restoring moment. This creates a stiffer system and therefore a smaller pitch period. The submarine had a pitch period of about 4, 3 seconds for 5 degrees, 1.4 seconds for 10 degrees and 4.8 seconds for 15 degress. The primary effect from the smaller period appears to be a pitch coupling interaction during the first two or three cycles causing the hump in the decrement curve and reducing much of the initial roll motion As part of a validation of the coupled motion and sixdegree-of-freedom method were performed to predict the flow field, hydrodynamic coefficients, and the motion paths of submarine at an initial speed = 0 knots. It clearly shows the orientation of the body at that instant in time and the resulting flow field due to the body at angle of attack. Figure 5. Curve of stability when passing through free surface A submarine in surfaced condition has to satisfy the same stability principles as that of a surfaced ship, see Fig. 6. The primary requirement in surfaced condition is that, it should remain afloat even after any kind of damage. Which means, there should be a significant volume of the hull above the waterline. This is called the Reserve of Buoyancy (ROB). The figure below represents the volume of the hull that contributes to reserve of buoyancy. Figure 6. Submarine in submerged and surfaced conditions. The ROB of a submarine is basically the ratio of the effective volume of all the MBTs to the volumetric displacement of the submarine in surfaced condition. The effective volume is the total blowable volume of the tanks (i.e. volume of the tank required to be filled to submerge the submarine). And just like surfaced ships, the surface displacement of the submarine is the weight of the submarine minus the free flood water. Now note in Fig. 7, that in submerged condition, the only structure providing buoyancy is the pressure hull. Hence, the weight of the submerged submarine minus the free flood water is equal to the buoyancy on the fully pressure hull. hull that contributes to reserve of buoyancy. Figure 8. Angle of attack 5 degree Figure 7. Volume of Hull contributing to ROB of a submarine. Submarines are very weight sensitive, as in, during the entire operation of a submarine, all operations are to be carried out in such a way so that there is minimum shift in the longitudinal position of the centre of gravity. As shown in the figure below, the slightest change in longitudinal centre of gravity will cause a trimming Figure 9. Angle of attack 10 degree 48

4 REFERENCE [1] [2] [3] [4] Figure 10. Angle of attack 15 degree [5] [6] [7] [8] [9] Figure 11. Pitch motion [10] IV. CONCLUSION A series physical model experiments were carried out to determine the effects of a free flooding casing on pitch motions of a submarine operating at the surface. The goals were to determine whether a free flooding casing was necessary for a seakeeping model of the submarine, which would add complexity and expense to the experiments and if so, how to construct it to best duplicate the full scale dynamics. The physical experiments showing little to no change in pitch damping for the different blockage configurations, but an increase in pitch damping when going from a large to a small casing opening size. The change in position of the centre of gravity that used in the physical experiments led to an analysis of the vessel s pitch period as a function of KG. At the experimental condition, the pitch period became very sensitive to any changes in the GM caused either by a change in the vertical centre of gravity, or the centre of buoyancy resulting from an open or closed casing[12]. The natural pitchperiod of a vessel is a critical parameter for seakeeping experiments, as it affects where resonance occurs in various sea states. The study concluded that a free flooding casing physical experiments showed any flow over the top of the pressure vessel. Extra consideration will also be given to the model GM and pitch radius of gyration to ensure roll period is reflective of the full scale vessel. [11] [12] [13] [14] [15] [16] Luhut Tumpal Parulian Sinaga, was born in Mulberry on April 19, He currently works as an employee Agency for the Assessment & Application of Technology (BPPT) with the rank of associate researcher at UPT.BPPH, BPPT, Jl. The complex hydrodynamics Sukolilo ITS Surabaya. Expertise: Sloshing and Motion of Ship. ACKNOWLEDGMENTS Further thanks to all co-bppt Indonesian Hydrodynamics Laboratories who have been involved in the testing of submarine Litoral. R. K. Burcher and L. J. Rydill, Concepts in Submarine Design, Cambridge University Press, 1995 G. Conte and A. Serrani, Modelling and simulation of underwater vehicles, in Proc. the 1996 IEEE International Symposium on Computer-Aided Control System Design, Dearborn, Michigan, September, 1996, pp O. F. Rognebakke and O. M. Faltinsen, Coupling of sloshing and ship motions, Jour Ship Research, vol. 47, pp , J. M. J. Journée, Liquid cargo and its effect on ship motion, in Proc. STAB 97 (Six Internationall Conference on Stability of Ships and Ocean Structures), Varna-Bulgaria, September 2227, 1997, pp X. W. Xiong, Z. B. Wei, C. G. Xiang, Practical stability of submarine motion under sloshing impacts, Journal of Chongqing Jiaotong University(Natural Science), vol. 31, no. 3, pp , O. M. Faltinsen, O. F. Rognebakke, A. N. Timokha, Resonant three dimensional nonlinear sloshing in a square-base basin. Part 2: Effect of higher modes, Journal of Fluid Mechanics, vol. 23, no. 5, pp , E. V. Lewis, (ed.), Principles of naval architecture, Second Revision. Society of Naval Architects and Marine Engineers (SNAME), Jersey City, 1988 J. P. Feldman, State-of-the-art for predicting the hydrodynamic characteristics of submarines, in Proc. the Symposium on Control Theory and Naval Applications, pp , O. M. Faltinsen and O. F. Rognebakke, Sloshing, Int. Conf. on Ship and Shipping Research, NAV, Venice, Italy, N. E. Mikelis, Sloshing in partially filled liquid tanks and its effect on ship motions: Numerical simulations and experimental verification, RINA Spring meeting, London, G. X. Wu, Q. W. Ma, and R. Eatock-Taylor, Numerical simulation of sloshing waves in a 3D tank based on a finite element method, Applied Ocean Research, vol. 20, pp , P. A. Hsieh, J. D. Bredehoeft, and J. M. Farr, Determination of aquifer transmissivity from Earth tide analysis, Water Resources Research, vol. 23, no. 10, pp , E. D. Hoyt and F. H. Imlay, The influence of metacentric stability on the dynamic longitudinal stability of a submarine, David W. Taylor Model Basin Report C-158, October A. B. Phillips, S. R. Turnock, and M. Furlong, Influence of turbulence closure models on the vortical flow field around a submarine body undergoing steady drift, Journal of Marine Science and Technology, vol. 15, no. 3, 2010, pp G. Hermanski, Victoria class submarine: 2D investigation of free flow phenomenon, National Research Council of Canada Institute of Ocean Technology Report TR , April S. L. Toxopeus, P. Atsavapranee, E. Wolf, S. Daum, R. Pattenden, R. Widjaja, J. T. Zhang, and A. G. Gerber, Collaborative CFD exercise for a submarine in a steady turn, In Proc. ASME 31st International Conference on Ocean, Offshore and Artic Engineering, number OMAE , Rio de Janeiro, Brazil, July

5 He has extensive experience in the field of hydrodynamics research mainly related to the field of sloshing. and often involved preformance government projects in the field of liquid cargo ship to transport eg FLNG. In addition, the field which he understood was the building structure coast and has been involved in port development projects in Indonesia. Dr. Ir. Luhut Tumpal Parulian Sinaga MT, is an active member The Royal Institution of Naval Architects (RINA) headquartered in the UK and is still active in research in the field of hydrodynamics and publishing in various countries 50