Bulbous Bow Research Articles

Surrogate-Based Optimization Using an Open-Source Framework: The Bulbous Bow Shape Optimization Case

Shape optimization is a very time-consuming and expensive task, especially if experimental tests need to be performed. To overcome the challenges of geometry optimization, the industry is increasingly relying on numerical simulations. These kinds of problems typically involve the interaction of three main applications: a solid modeler, a multi-physics solver, and an optimizer. In this manuscript, we present a shape optimization work-flow entirely based on open-source tools; it is fault tolerant and software agnostic, allows for asynchronous simulations, and has a high degree of automation. To demonstrate the usability and flexibility of the proposed methodology, we tested it in a practical case related to the naval industry, where we aimed at optimizing the shape of a bulbous bow in order to minimize the hydrodynamic resistance. As design variables, we considered the protrusion and immersion of the bulbous bow, and we used surrogate-based optimization. From the results presented, a non-negligible resistance reduction is obtainable using the proposed work-flow and optimization strategy.

An underwater spoiler on a warship: why, when and how?

Abstract There are a lot of energy saving devices for ships on the market, but few have seen wide adoption on naval ships, with one exception: the bulbous bow. The bulbous bow was developed for naval ships in the early 20th century and is now widespread on a variety of ship designs. Many have wondered if the effect of the bulbous bow — reducing the resistance of a ship by reducing the bow wave — could be replicated somehow at the stern — by reducing the stern wave. This is exactly what is done by a novel and patented energy saving device called Hull Vane®. Invented by Dutch hydrodynamicist Dr Peter van Oossanen for an America’s Cup sailing yacht in the early 21st century, research over the years has shown that this wing-shaped appendage works best on ships that combine a relatively high displacement with a relatively high top speed requirement — even if most sailing hours are done at half speed. Examples are certain offshore vessels, superyachts, patrol vessels and naval ships. On offshore patrol vessels, the resistance reduction from the Hull Vane® ranges typically from 10 to 20% over the entire useful speed range. In this paper, the working principles of the Hull Vane® will be described to give a better under-standing of the device. An overview will be given of the work carried out on naval ships and coastguard ships (25 to 142 m), based on Computational Fluid Dynamics studies, model tests and full-scale applications. The question ‘Why?’ will be answered by translating the hydrodynamic effects to concrete capability improvements for naval ships: a lower fuel consumption, a longer range, reduced signature, a higher top speed and improved seakeeping. The question ‘When?’ will zoom in on whether a Hull Vane® is something to be included in a newbuild or if it is something to be retrofitted to an existing ship. Finally the answer to the question ‘How?’ will explain the process of either integrating a Hull Vane® in a newbuild project or retrofitting it during a midlife upgrade of an existing ship.

Experimental analysis of the seakeeping performance of catamaran forms with bulbous bows

This paper explores the effects of adding different forms of bulbous bows onto catamaran hulls and assesses the implications on the seakeeping performance. There has been a large body of work that assess’ the effect of wave wake wash and recently studies have been undertaken to determine the effects of bulbous bows on reducing wave wake wash. However, not much research has been published on the effects of bulbous bows on the seakeeping performance of catamarans fitted with bulbous bows. This paper presents experimental results that will allow a ship designer to understand the effects of bulbous bows on heave, pitch and added resistance in waves. In conclusion it ranks the importance of different bulbous bows on the seakeeping performance.

Heave and sway hydrodynamic coefficients of ship hull sections in deep and shallow water using Navier-Stokes equations

A methodology is presented to numerically determine the hydrodynamic coefficients of ship hull sections using a time domain Navier-Stokes model. Results are presented for three topologically distinct sections of a ship hull (skeg, midship and bulbous bow) subjected to heave and sway motions in shallow and deep water. The simulations have been performed with the open source Computational Fluid Dynamics OpenFOAM software. A preliminary assessment of the necessity of viscosity consideration on the determination of the hydrodynamic coefficients, which should depend on the section topology and depth, is carried out. Results demonstrate an overall good agreement of the added mass and damping coefficients between the calculated values and the ones obtained with a boundary equation method potential flow formulation. An exception is the skeg section in shallow waters.

Hydrodynamic study of the influence of bulbous bow design for an Offshore Patrol Vessel using Computational Fluid Dynamics

The resistance of a ship is of vital importance in giving greater viability to the development of a design project, since at lower ship resistance, the power demand to achieve a desired design speed will be lower which will reduce the amount of power to be installed in the ship resulting in lower fuel consumption. The use of computational fluid dynamics to analyze and optimize hull form and its appendages permits the hydrodynamic performance of the ship to be improved from the early design stages, allowing improvements to the hull shape and appendages. This paper shows a qualitative analysis which was performed to reduce the resistance of the OPVMKII (Second Generation Offshore Patrol Vessel) in its preliminary design stage by means of designing and integrating three types of bulbous bow with the ship´s hull and analyzing the resistance curves obtained using computational fluid dynamics.

The sensitivity of ship resistance to wall-adjacent grids and near-wall treatments

Numerical simulations of turbulent flows around KCS have been performed to study the sensitivity of ship resistance to wall-adjacent grids and disclose the influence of near-wall treatment on the sensitivity of ship resistance. The resistance coefficients of viscous and pressure forces were compared when using realizable k-ε and SST k-ω turbulence models in structured and unstructured grids, respectively. The calculation of friction velocity was found to be mainly responsible for the reduction of viscous and total resistances when the height of wall-adjacent cells increased. Since the assumption of equilibrium state between turbulent production and dissipation was not met in a bulbous bow, it was more reasonable to iteratively calculate the friction velocity from empirical laws of the wall for near-wall treatment rather than explicitly estimate it from the turbulent kinetic energy.

Analysis of Effect of Bulbous Bow Shape to Ship Resistance in Catamaran Boat

Ship resistance is one of the main factors affecting the design of a ship. Catamaran boat is a ship with small wet surface area that able to reduce drag and improve ship power. Generally, a bulbous bow is implemented to reduce wave resistance because the bulbous shape is believed to attenuate the bow wave system. Additionally, the bulbous bow also tends to reduce viscous resistance. When the flow around the body is smooth, the total ship resistance can be reduced significantly if the optimum bulbous bow is obtained. In this study, the main purpose is to get the bulbous bow shape in catamaran boat which produces the smallest ship resistance by using computational fluid dynamic (CFD). Generating the variation of the bulbous bow shapes apply the one-to-one correspondence of the cross section parameter (ABT) and lateral parameter (ABL). The result of investigation shows that application of bulbous bow on catamaran boat can reduce about 11-13% of total resistance of ship.

Bulbous bow applications on a catamaran fishing vessel for improving performance

This study aims to prove the usefulness of a bulbous bow traditional catamaran fishing vessel. Bulbous bow applications are widely used to reduce wave resistance. The fishing vessel resistance was calculated using CFD (Computational Fluid Dynamic) approach and combined with classical slender body theory. In this research, the application of bulbous bow was being adopted on traditional catamaran fishing vessel to reduce the total resistance. The bulbous bow has adopted based on Kracht method. Modeling procedure was developed by using linear form coefficients. The ship resistance was simulated using Tdyn software which basically Finite Element Method. The results show that adding bulbous bow can decrease or increase the ship’s total resistance.

Self-blending method for hull form modification and optimization

A self-blending method has been developed and applied to the modification of a bulbous bow. The method is capable of transforming ship hulls automatically. In this method, few representative number of cross sections (the key points of the cross sections) of the baseline geometry are selected. New cross sections are generated through merging the two cross sections next to each other, using a prescribed weight factor. Different weight factors are assigned to the x, y and z coordinates of the key points of the cross section. The method thus can be one, two or three parameters self-blending method. The surface of the ship hull generated through the method is smooth so that it can be readily used for meshing and CFD (computational fluid dynamics) applications. Combined with CFD and DOE (design of experiment) techniques the shape of bulbous bow of a fishing vessel is optimized and the resistance is reduced by 2%.

Research on bulbous bow optimization based on the improved PSO algorithm

In order to reduce the total resistance of a hull, an optimization framework for the bulbous bow optimization was presented. The total resistance in calm water was selected as the objective function, and the overset mesh technique was used for mesh generation. RANS method was used to calculate the total resistance of the hull. In order to improve the efficiency and smoothness of the geometric reconstruction, the arbitrary shape deformation (ASD) technique was introduced to change the shape of the bulbous bow. To improve the global search ability of the particle swarm optimization (PSO) algorithm, an improved particle swarm optimization (IPSO) algorithm was proposed to set up the optimization model. After a series of optimization analyses, the optimal hull form was found. It can be concluded that the simulation based design framework built in this paper is a promising method for bulbous bow optimization.

Analytical method to assess double-hull ship structures subjected to bulbous bow collision

The paper presents simplified analytical methods to assess the plastic deformation and failure of double-hull ship structures subjected to bulbous bow collision. To validate the methods, numerical simulations are conducted on double-hull tanker side structures including three frame spacings along the longitudinal direction and two stringer spacings along the vertical direction. The paper estimates the extent of damage within double-hull ship structures during minor ship-to-ship collision, where the inner hull does not participate in dissipating incident energy. In the analytical methods, the nose shape of striking bulbous bow is simplified as a hemisphere or a cylinder with hemispherical ends. This equivalence is validated against the similar numerical force-displacement responses using the actual bulbous bow and the simplified strikers. The analytical methods derive expressions to estimate the relation between the plastic deformation and the crushing force of the double-hull structures. The onset of fracture in the outer hull is evaluated by a simple formula based on experimental and theoretical analyses. Finally, the probabilistic structural absorbed energy until the rupture of specific struck ship with respect to the displacement of striking ship is assessed according to the statistical data of ship dimensions and the design principles of bulbous bow.

단파장 영역에서 운항 자세가 KCS의 선체 저항에 미치는 영향

Numerical simulations of turbulent two phase flows around KCS have been performed to investigate effects of trim conditions on ship resistance of KCS in short waves by utilizing waves2foam. The wave lengths of LPP/2 and LPP/4 with 1m and 2m wave heights were imposed at inlet boundary. The resistance reduction at 2m trim by head and the increase of resistance at trims by stern were observed regardless of wave lengths and wave heights. The hull pressure on fore-and-aft rather than wave patterns around bulbous bows was mainly responsible for the total resistance coefficients of KCS in short waves. A phase diagram of contribution of hull pressure to the total resistance coefficients disclosed that the phase of representing the maximum resistance in time history played an important role in the effect of trim conditions on ship resistance of KCS in short waves.

Geometric Modelling and Deformation for Shape Optimization of Ship Hulls and Appendages

The precise control of geometric models plays an important role in many domains such as computer-aided geometric design and numerical simulation. For shape optimization in computational fluid dynamics (CFD), the choice of control parameters and the way to deform a shape are critical. In this article, we describe a skeleton-based representation of shapes adapted for CFD simulation and automatic shape optimization. Instead of using the control points of a classic B-spline representation, we control the geometry in terms of architectural parameters. We assure valid shapes with a strong shape consistency control. Deformations of the geometry are performed by solving optimization problems on the skeleton. Finally, a surface reconstruction method is proposed to evaluate the shape's performances with CFD solvers. We illustrate the approach on two problems: the foil of an AC45 racing sail boat and the bulbous bow of a fishing trawler. For each case, we obtained a set of shape deformations and then we evaluated and analyzed the performances of the different shapes with CFD computations.

Dynamics Finite Element for Ship Damage Collision Analysis

¾ Along with the growing fleet of vessels, ship collision accident cases are becoming more frequent. It is unavoidable that the rapid shipping due to the number of vessels that operate relatively large and the ship is waiting for the loading and unloading at the port. This study will examine the design of the solid bulk cargo ship safe for shipping operations congested areas. The finite element method is used to determine the amount of internal energy in the structure of damaged vessel. The striking ship is assumed a tanker that have a bulbous bow. Bulk carrier is designed with space of double skin 1.8 m and the structure of wing tank is determined previously. The results obtained from this research is the design of the cargo hold of bulk carrier that has a double skin to protect the leaking compartment when the ship was crashed. Penetration in depth 1.8 m will be occurred at ship if ship crashed is with speed 12 knots and weight 1400 tons.

Experimental assessment of buoyant cylinder impacts through high-speed image acquisition

In this paper, we experimentally study the water entry of a set of buoyant bodies with a circular cylindrical shape, which is relevant for several engineering applications, being related to aircraft fuselages in sea landing, solid rocket boosters, and bulbous bows of large ships. Free fall experiments are conducted for three different specimen weights and four different falling heights. The hydrodynamics of the interaction of the buoyant cylinders with the water free surface upon impact is analyzed through an accelerometer, a high-frequency potentiometer and a high-speed camera. Results are presented in terms of impact velocity, kinematics of the cylinder penetration and free surface dynamics, comprising the pile-up and water jet dynamics. Further, the air cavity development is analyzed after the cylinder is completely immersed below the undisturbed free surface.

NURBS-based parametric optimization and design of bulbous bow

NURBS-based parametric optimization and design of bulbous bow

정렬 및 비정렬 격자를 이용한 선박 저항 계산에서 Courant 수의 공간 분포 및 LTS 기법의 효율성에 관한 연구

Numerical simulations of ship resistance have been performed to compare spatial characteristics of Courant number when using structured and unstructured meshes. When Euler scheme was used for time integration, the structured mesh provided a more efficient calculation because the calculation time interval was larger than that of unstructured mesh. The automatic generation of very small meshes in the unstructured mesh was mainly responsible for the limitation of calculation time interval. When local time stepping Euler scheme was applied, however, the ship resistance of unstructured mesh showed a rapid convergence while a slow convergence of ship resistance in structured mesh was caused by the small time interval in bulbous bow.

Homotopy method for inverse design of the bulbous bow of a container ship

The homotopy method is utilized in the present inverse hull design problem to minimize the wave-making coefficient of a 1300 TEU container ship with a bulbous bow. Moreover, in order to improve the computational efficiency of the algorithm, a properly smooth function is employed to update the homotopy parameter during iteration. Numerical results show that the homotopy method has been successfully applied in the inverse design of the ship hull. This method has an advantage of high performance on convergence and it is credible and valuable for engineering practice.

Design Optimization of the Lines of the Bulbous Bow of a Hull Based on Parametric Modeling and Computational Fluid Dynamics Calculation

To reduce the ship wave-making resistance, the lines of the bulbous bow of a hull are optimized by an automatic optimization platform at the ship design stage. Parametric modeling was applied to the hull by using non-uniform rational basis spline (NURBS). The Rankine-source panel method was used to calculate the wave-making resistance. A hybrid optimization strategy was applied to achieve the optimization goal. A Ro-Ro ship was taken as an example to illustrate the optimization method adopted, with the objective to minimize the wave-making resistance. The optimization results show that wave-making resistance obviously reduces and the wave-shape of the near bow becomes gentle after the lines of the bulbous bow of the hull are optimized, which demonstrates the validity of the proposed optimization design strategy.

Investigation and modelling of the turbulent wall pressure fluctuations on the bulbous bow of a ship

For the effective operation of sonar systems mounted inside the bulb of fast ships, it is important to reduce all the possible noise and vibration sources that radiate noise and interfere with sonar sensor response. In particular, pressure fluctuations induced by turbulent boundary layers on the sonar dome surface represent the major source of self-noise for on-board sensors. Reliable calculations of structural vibrations and noise radiated inside the dome require valid statistical descriptions of wall pressure fluctuations beneath the turbulent boundary layer. Previous research about wall pressure fluctuations deals with equilibrium turbulent boundary layers on flat plates in zero pressure gradient flow, for which scaling laws for power spectral densities and empirical models for the cross spectral densities are well established. On the contrary, turbulent boundary layers on bulbous bow exhibit the combined effects of three-dimensionality, streamline and spanwise curvatures and pressure gradients. In order to collect information about realistic configurations, wall pressure fluctuations were measured in an experimental campaign performed in a towing tank; data were collected at two different locations along a large scale model of a ship bulb and their spectral characteristics were investigated in terms of auto and cross spectral densities. Mean flow parameters of the boundary layer, required in the analysis, were obtained by a finite volume code that solves the Reynolds Averaged Navier Stokes Equations. The applicability of classical scaling laws for pressure spectra on zero pressure gradient flat plate was investigated, together with the spatial characterization of the wall pressure fluctuations in the space-frequency domain; parameters of some semi-empirical models available in the scientific literature were tuned to fit the measured pressure field.