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Hydrodynamic Design of Integrated Bulbous Bowlsonar Dome for Naval Ships

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Hydrodynamic Design of Integrated Bulbous Bowlsonar Dome for Naval Ships CORE Metadata, citation and similar papers at core.ac.uk Provided by Defence Science Journal Defence Science Journal, Vol. 55, No. I, January 2005, pp. 21-36 O 2005, DESIDOC Hydrodynamic Design of Integrated Bulbous Bowlsonar Dome for Naval Ships R. Sharma and O.P. Sha Indian Institute of Technology Khnragpur, Khnragpur-721 302 ABSTRACT Recently, the idea of bulbous bow has been extended from the commercial ships to the design of an integrated bow that houses a sonar dome for naval ships. In the present study, a design method for a particular set of requirements consisting of a narrow range of input parameters is presented. The method uses an approximate linear theory with sheltering effect for resistance estimation and pressure distribution, and correlation with statistical analysis from the existing literature and the tank-test results available in the public domain. Though the optimisation of design parameters has been done for the design speed, but the resistance performance over the entire speed range has been incorporated in the design. The bulb behaviour has been discussed using the principle of minimisation of resistance and analysis of flow pattern over the bulb and near the sonar dome. It also explores the possible benefits arising out of new design from the production, acoustic, and hydrodynamic point of view. The results of this study are presented in the form of design parameters (for the bulbous bow) related to the main hull parameters for a set of input data in a narrow range. Finally, the method has been used to design the bulbous bow for a surface combatant vessel. Keywords: Bulbous bow, hydrodynamic design, integrated bow, sonar dome, sheltering effect, wave resistance, naval ship, bulb behaviour NOMENCLATURE C~ Prismatic coefficient Am Area of ram bow in longitudinal direction C,, Prismatic coefficient at the entrance Am Cross-sectional area at forward (fwd) CWL Waterline coefficient perpendicular (FP) C~ Frictional coefficient *MS Mid-ship sectional area C~ Residual coefficient B~ Maximum breadth of bulb area A, C,,, Residual power displacement coefficient B,, Breadth of ship at mid-ship AC,,, Residual power displacement reduction C~ Block coefficient coefficient C~ Mid-ship coefficient c~~~ Lateral parameter Revised 25 Feburary 2004 2 1 DEF SCI J, VOL. 55, NO. I, JANUARY 2005 Cross-sectional parameter Ss Ship's wetted surface Breadth parameter S~ Ship's free surface Length parameter - ss Projection of Ss on the y = 0 plane Volumetric parameter in percentage distributed Projection of SF on the z = 0 plane fwd of FF' Tr CFD Computational fluid dynamics Re Vs. L,, / v = Reynolds number cm Depth parameter vs Design speed of the ship cc, Volumetric longitudinal distributional parameter V,,, Total bulb volume Volumetric parameter distributed aft and fwd cvm, V Protruding volume of bulb, fwd of FP of FP V, Displacement volume of ship V, I = Froude number w Tank width nondimensionalised by LL, Mean draft of ship Submergence of point doulilet Breadth of ship z I H 1 LL, z, Height of the foremost point above keel line Height of A, on the bulb at FP ~.LLWL/vS? '1, Propulsive efficiency Length of entrance v Kinematic viscosity of water Length on load waterline P Density of water Protruding length of bulb g Accclcration duc to gravity Superscript Doublet strength in + x or - x direction as per sign, and source distr~bution Nondimensionalised by LLwLdenoted as i, 1 when m = 0, 2 when m = 1 1. INTRODUCTION Delivered R.E. Froude, who perhaps conceived a bulbous Frictional bow for the first time, had interpreted the lower resistance of a torpedo boat after fitting a torpedo Residual tube as a wave reduction effect of the thickening Effective frictional of the bow. The protruding bulb form hydrodynamically affects the velocity field in the vicinity of the bow; Effective residual power in the region of rising bow wave. Primarily, the bulb attenuates the bow wave system, which results Residual power reduction factor in a reduction of wave resistance with a properly Ship's wave resistance designed bulb. Since the flow around the forebody SHARMA & SHA: HYDRODYNAMIC DESIGN OF INTEGRATED BULBOUS BOWISONAR DOME FOR NAVAL SHIPS is smoothened, it may lead to reduction in the manoeuvring characteristics. Because of limited viscous resistance also. For fast ships, the use of resources, a complete integrated design approach a bulb allows a departure from the hitherto accepted is beyond the scope of the present study. Hence design principles for the benefit of a better underwater in this study, mainly the design forresistanceperfomance, form. Since, a suitably shaped and carefully designed and some other effects have been investigated bulb affects nearly all the hydrodynamic properties using standardised tests and their interpretations. of a ship, it is important for the protruding bulb that the main parameters, ie, size ; volume distributed Since the quantitative parameters are essential propcrly forward and aft of forward perpendicular; for the design of a bulb form, in theoretical accordance position and shape design for optimal performance with the previous work3, three linear and four nonlinear subject to the constraint of the design. A properly parameters have been used to describe and design designed bulbous bow reduces the resistance, but the bulb form. These seven parameters are also enhances propeller cavitation characteristics, nondimensionalised with the ship particulars and reduces fuel consumption, improves maximum speed are presented in decreasing order of importance. and range, and may offer better housing for auxiliary These are: sonar system. CLpR: It is the length parameter and defined The sonar domes &re in use for a variety of as CLPR = LPR LL,. naval ships, principally to house sonar transducers. These are located below the keel line of the ship, CAE, : It is the cross section parameter and and in general, do not affect the wave-making defined as CAB, = A,, / A,,. resistance significantly. The design of a sonar dome is done mainly for size, volume, and location. Again, C,, : It is the volumetric parameter and defined in percentage as C,, = V, lV, *loo. modern bulbous bows are appendages- - that are mainly designed for the improvement in ship's resistance, The volume V,, is distributed forward of and are, in general, placed above the keel line and FP. protrude longitudinally from forward (fwd) The total volume V,,, is defined as the sum of perpendicular (FP). The bulbous bow's nabla V, and fairing volume required aft of FP to fair shape, location near the free surface, and the reduced the bulb in the ship. In the same manner, another size, volume, and breadth-to-height ratio are in volumetric coefficient is defined as C,,, = V,, / V, . direct contradiction to the geometry of the sonar C, C, : It is volumetric distributional parameter dome located below the keel line. that is LCG, of the bulb volume as distributed Because of these reasons, recently the idea of (+ ve if located forward of FP and - ve if bulbous bow has been extended from the commercial located aft of FP) divided by (L,. Fn2) of the ships to the design of an integrated bow with a ship C, = LCG, l (L,. FnZ). sonar dome for the naval shipsIz. In the present C,,: It is the breadth parameter and defined study, the detalled hydrodynamic design of the same ideahas been investigated and a design method as C,, = B, /B,, . for an integrated bulbous bow that houses a sonar C,, : It is the depth parameter and defined as dome for the naval ships, has been presented. c,, = z, /H. Though the main objective of the bulbous bow design is for the reduction in resistance, and hence CAB, : It is the lateral parameter and defined less power, but there are other constraints that as CAB, = A,, /AMs. govern the final design of the integrated bulbous bow. Some of these constraints are: Effect on In the area of ship design in naval science, any sonar dome performance, effect on hull structural design methodology is subjected to the following elements, effect on anchor handling and other three stages. DEF SCI J, VOL. 55, NO. I, JANUARY 2005 Stage 1. Preliminary hydrodynamic analysis Hence, the present study follows the previous one4,but with the model-tested results. The present This is CFD-based analysis. It deals with method uses an approximate linear theory with flow and performance characteristics (eg, resistance sheltering effect for resistance estimation and pressure estimation, pressure distribution, flow pattern study distribution, and correlation with statistical analysis witli flow-field streamlines, velocity and wave from the existing literature and tank-test results profiles, etc). If the results are encouraging then available in the public domain. The bulb behaviour the design proceeds to the next stage. If the over and near the sonar dome has been discussed results are not satisfactory, then based upon the using model-tested calm water resistance results, CFD analysis, the design of the body is modified and other standardised tests; with one example of and the analysis is repeated till the results are the integrated bulbous bow design for a surface satisfactory. combatant vessel. Stage 2. Detailed hydrodynamic analysis 2. LITERATURE REVIEW This is typically done by model testing (eg, also referred to as tank testing). A model (ie, pre- Early studies to know the effect of bulbs on selected one on a scale) is manufactured using the hulls were camed out using experimental techniques some material and towed in a carriage tank to on methodical series with Taylor bulbsS-''. Later, study and measure the flow and performance theoretically, the design ofbulbous bow was studied characteristics (eg, calm water resistance estimation, using linearised theory of wave resistancei1.Though flow pattern study with paint flow test, image analysis the linearised theory gives abetter understanding of the photographs at various velocities, etc).
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