RESTRICTED CHAPTER 1 INTRODUCTION 1. The ability to perform numerical potential flow calculations using codes has made it possible for naval architects to look into hull modifications prior to tank testing. The actual flow fields and viscous effects are not accurately predicted by the potential flow calculations, but they are sufficiently accurate in a relative sense to optimise the hull form prior to model testing, even though tank testing is still necessary at the end. Several scientists have successfully employed this hull design optimisation method in recent years. 2. The first point of contact of the ship with the fluid is its bow, thus, making changes to the bow geometry of the ship may lead to significant changes in ship total resistance. The second chapter of this report talks about the literature survey for this area of study. 3. This study was carried out with the objective to investigate the effect of adding a bulbous bow to a fast-moving vessel with a finer hull form on the resistance of the ship. The hull form selected was DTMB 5415 from David Taylor Model Basin design. The bulbous bow was designed and faired to the hull form as per Alfred M. Kratch’s “Design of Bulbous Bow” [1]. The design parameters for the bulb have been discussed in the third chapter. 4. The fourth chapter consists of the modelling of bulbous bow using SolidWorks and the consecutive chapter discusses the conditions for conducting CFD over the model. 5. Chapter 5 talks about the results obtained from the simulations for focussing on the variation of resistance for varying Froude number. The consecutive chapter consists of conclusions drawn from the simulations and the potential use of a bulbous bow in a final hull design of DTMB 5415. RESTRICTED RESTRICTED CHAPTER 2 LITERATURE REVIEW 1. Approximately ninety years ago, R. E. Froude explained that a torpedo boat's reduced resistance following the installation of a torpedo tube was caused by the thickening of the bow as a result of the torpedo tube. The bulbous bow was first identified by D.W. Taylor as a simple tool for lowering the resistance that creates waves. He added a bulbous bow to the battleship Delaware in 1907 so that it could travel faster while maintaining consistent power. Despite significant efforts in the experimental domain to investigate its possibilities, it took seventy years for the bulb to emerge as a fundamental tool in actual shipbuilding. Almost every aspect of a ship is impacted by a bulb that is appropriately rated and designed. 2. The inclusion of a bulb permits a deviation from previously accepted design rules for the purpose of a superior underwater form, particularly for rapid ships. The only drawback is the greater building costs. The hydrodynamic fluctuation of the velocity field near the bow, or in the vicinity of the rising ship waves, is influenced by the projecting bulb form. The bow wave system is primarily attenuated by the bulb, which typically results in a decrease in wave resistance. 3. The inclusion of a bulb permits a deviation from previously accepted design rules for the purpose of a superior underwater form, particularly for rapid ships. The only drawback is the greater building costs. 4. The hydrodynamic fluctuation of the velocity field near the bow, or in the vicinity of the rising ship waves, is influenced by the projecting bulb form. The bow wave system is primarily attenuated by the bulb, which typically results in a decrease in wave resistance. RT= RV + RWF + RWB = RF + RVR + RWF + RWB where, RT = Total Resistance RV = Viscous Resistance RWF = Wavemaking Resistance RWB = Wavebreaking Resistance RF = Frictional Resistance RVR = Viscous Residual Resistance RESTRICTED RESTRICTED RWF and RWB are the components of wavemaking resistance. They vary from ship to ship according to the respective block coefficients and speeds. 5. The frictional resistance (RF), which makes up the majority of the viscous component (Rv), is always increased by the greater bulb surface. Since the velocity field varies in the near bow region, it is still unclear if the bulb has an impact on the viscous residual resistance (RV). Regarding the impact of the bulbous bow on wavemaking resistance RW, there is no question. The main contribution to the understanding of this issue has come from the linearized theory of wave resistance. This idea states that the bulb problem is just an interference between the ship's and the bulb's free wave systems. There may be a complete mutual cancellation of the two interfering wave systems, depending on the phase difference and amplitudes. The phase difference is caused by the bulb's longitudinal position, whereas the amplitude is related to its volume. Through examination of the free wave patterns obtained in model experiments, the wave resistance is determined. 6. The wave-breaking resistance RWB is a function of the usual spray phenomena and is directly influenced by the emergence and growth of local and free waves in the area of the forebody. Comprehending the breaking phenomenon of ship waves is crucial for designing bulbs for complete ships. The entire energy loss resulting from the breaking of very steep bow waves is included in the wave-breaking resistance. Wake measurements are useful for detecting the majority of this energy. 7. The primary source of this resistance component is the local wave system. The two back waves of the bow and stern, which are produced by the momentum's deflection, make up the majority of this wave system. The reduction of the wave-breaking resistance is limited to the extent that bow wave breaking can be avoided. This can only be achieved, given the rationale behind its design, by altering the momentum deflection or the bow's proximity to the velocity field, respectively. This can generally be accomplished with both a bulbous bow and the right hydrofoils. 8. The shape, speed, and loading conditions of the ship all affect how bulbous bows affect the aforementioned components of resistance. It is crucial to understand that a certain ship-bulb combination that performs well under certain conditions may react badly under off-design conditions. 9. Given the significance of bulb form in lowering a ship's resistance, bulbs must be categorised using a few geometrical factors. Kracht [1] classified bulbs into three primary groups based on the cross-sectional form of the bulb measured at the forward perpendicular. RESTRICTED RESTRICTED Δ – Type Delta Drop-Shaped Sectional Area Center of Area in the lower half part Concentration of bulb volume near the base O - Type Oval Oval-Shaped Sectional Area Center of Area in the middle Central Volumetric Concentration Table1: Types of Bulb RESTRICTED ∇ - Type Nabla Inverse Drop-Shaped Sectional Area Center of Area in the upper half part Volume concentration near the free surface
