International Journal of Maritime Technology
Volume:5 Issue: 7, Autumn-Winter 2017

Moonpool is an opening in the floor or base of a hull ship which can be used to lower tools and vehicles into the sea in a protected area. In this paper, the effect of a rectangular cross section moonpool on the resistance force of a supply vessel was investigated both by experimental and numerical methods. For both methods a 1:37.2 scale of a surface vessel was used. Experiments were carried out at various Froude numbers in the range of 0.185-0.370 in the towing tank for cases with moonpool, i.e, when the entrance at the bottom of the ship was open and without moonpool, i.e, when the entrance was closed. A two phase flow CFD simulation based on volume of fluid (VOF) method was used to calculate the resistance coefficients of the vessel and to investigate fluid flow around the ship and inside the moonpool. The acquired numerical results showed fair agreement with the experimental results. The results showed that the resistance coefficient of the ship with moonpool was about 21 percent larger than that of the ship without moonpool.

Planing vessels usually have low ratios of resistance to weight, so they can move fast on sea surface than the displacement or semi-displacement ships. Access to higher speeds is one of the attractions for designers and users. To achieve higher speeds, reducing the hydrodynamic resistance is a necessity for this class of vessels. In this study, a 3D finite volume approach is used to analyze the hydrodynamics of the Cougar high-speed vessel, a hard chine planing hull. In addition to use of the URANS equations for momentum, SIMPLE algorithm for coupling of the pressure and velocity field and the k-e for turbulence modeling, the fluid phases of air/water and the free surface are modeled using the volume of fraction (VOF) scheme. Moreover, in the simulations, instead fixing the freedom of the model regards to the computational domain, the vessel motions are also considered to have two degrees of freedom, 2-DOF, using the newly developed moving mesh technique of Overset. The grid independency study shows a good consistency between the numerical results and experiments for the vessel resistance, trim angles and the heave. Main emphasis of this paper is on study of the effects of different loading conditions, the vessel weight and the longitudinal center of gravity, on the hydrodynamic characteristics such as resistance, trim angle and the vessel sinkage. All of the numerical simulations are done using the commercial software of Star CCM.

In this paper a computational method is presented for predicting the unsteady hydrodynamic forces acting on partial immersed propeller (SPP). In order to simulate the unsteady viscous flow around a SPP, a Reynolds-Averaged Navier–Stokes (RANS) solver is used. The time-accurate calculations are made by applying the sliding mesh method. Structured and unstructured mesh techniques are used. The method is applied in the case of the straight condition. Hydrodynamic coefficients are compared with experimental data and show good agreement between them. Also, ventilation pattern, pressure distribution and unsteady forces/moments on key blade of SPP is presented and discussed.

Cross-shore sediment transport is one of the effective factors in erosion and sedimentation, and affects dynamics of the beach profile in coastal areas. Furthermore, sandbar migration due to cross-shore sediment transport mostly effects beach nourishment, displacement of pollutions trapped in sediments, and organism and plants’ lives. In this manuscript, sandbar migration due to cross-shore sediment transport is studied and results have been compared to field data. Field data used here have been measured at the southern Caspian Sea, Noshahr coasts, Iran. During the measurement period, two high-energy events with significant wave height of approximately 1.4 m have been measured. All simulations have been done based on a one dimensional cross-shore transect. Wave transformation during propagation toward the coast has been modeled using the third generation model SWAN, and long-shore wave-induced current has been simulated by solving alongshore momentum equilibrium equation. To include the morphological change, the cross-shore sediment transport rate has been estimated using Bagnold [1966], Bowen [1980], and Bailard’s [1981] (BBB) energetic sediment transport model, and results has been compared to the model developed by Plant et al. [2001], which itself is an energetic model based on Bagnold [1966]. Finally, bathymetric changes has been forecasted by solving cross-shore mass conservation equation which indicated slight outperform of BBB rather than Plant et al. model in this study area.

Second generation intact stability criteria for few past years had been under development by International Maritime Organization (IMO). Since the draft proposed amendments shall be amended to International code on Intact Stability (IS code 2008), new regulations shall enter into force for ships of length more than 24 meter. Generally second generation intact stability criteria (SGISC) refers to vulnerability ship stability modes which occurs when the ship navigating in rough seas. As waves passes the ship, dynamic phenomenon will affects ship stability that may lead to capsizing. Unlike IS code 2008, which study ship stability in calm water with a single level criteria, SGISC check the stability in different levels. In this method, if a ship passes only one level of criteria, means it is safe according to respective dynamic phenomena. In this article in order to understand the functionality of the proposed criteria in last draft amendment provided by IMO, numerical tools have been used to assess the effect of three phenomenon, pure loss of stability, parametric rolling, and surf-riding/broaching. Wide range of ships including fishing, passenger, cargo, Fiber glass and container ships, navigating in Persian gulf and Oman sea are considered to assess a comprehensive effects of proposed criteria. The results shows that all ships pass pure loss of stability and parametric rolling criteria but all passenger ships, 2 tugs, 1 fiberglass and 1 fishing vessel failed the surf riding/broaching criteria. It should be concluded that to pass the vulnerability criteria of surf riding, existing ships (specially passenger ships) should decrease their speed and new building vessels should be designed so that their Froude number do not encounter critical Froude number range as defined by the regulations.

This work addresses an autonomous underwater vehicle (AUV) for applying nonlinear control which is capable of disturbance rejection via intelligent estimation of uncertainties. Adaptive radial basis function neural network (RBF NN) controller is proposed to approximate unknown nonlinear dynamics. The problem of designing an adaptive RBF NN controller was augmented with sliding mode robust term to improve trajectory tracking and regulation in presence of uncertainties. Moreover, stability proof of proposed control scheme was shown with Lyapunov theory. Furthermore, the control, design and simulation results are provided without any simplification of the entire system. Although the design approach of this paper is implemented on REMUS this point of view can be applied on any AUV using the same technique.