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Maritime transportation is becoming increasingly complex owing to the fluctuation of oil prices, the introduction of environmental guidelines, and the onset of climate change. Although optimal routing has been researched for decades, few studies have investigated speed loss in rough waves for ships with blunt shape and low speed. Onboard measurement of a 28,000DWT bulk carrier has been conducted for six years in rough sea voyages in the Southern Hemisphere. It is necessary to validate the wave and wind conditions in order to discuss speed loss in these situations. Here, numerical simulation of speed loss is developed and conducted for each estimated wave condition. The speed losses under different numerical models of added resistance are quantitatively compared in two rough sea voyages. The simulated results of speed loss are in good agreement with the measured results if the estimated wave is accurate and the wave direction is properly defined. The speed loss accuracy is significantly influenced by the wave estimation accuracy or wave direction setting compared to that in the numerical models of added resistance in actual seas. Simulated results provide important information to evaluate the performance of a ship with blunt shape in rough waves. [ABSTRACT FROM AUTHOR]

In addition to wind tunnel tests and regression formulae, numerical simulation has begun to be used at the design stage of ships as a method for estimating the wind force and moments of superstructures. However, no specific approach has been proposed to verify the grid dependence around superstructures, and the degree to which differences in computational conditions affect the results has not yet been systematically clarified. Therefore, a new approach to grid sensitivity analysis is carried out. The effect of some computational conditions on the computed result is investigated using an in-house solver with an overset grid technique with a Japan Bulk Carrier(JBC) model. The method that verifies the grid sensitivity of the hull and the superstructures separately can obtain equivalent results to the method of simultaneously verifying both of them. The grid sensitivity analysis of the superstructures can be performed separately from the hull. The comprehensive comparative study reveals five findings: the blockage effect of the tank size is slight, the steady-state computation is capable of estimating as well as unsteady computation, wall function can be applied to object surfaces, a difference of wind profiles of incident flow can be recovered by the normalization based on the momentum integration in a shear flow, and the Reynolds number effect does not need to be considered if it is greater then 1. 0 × 1 0 6 . The computations for other ship types are also performed. The computed results show good agreement with the measured data, while the regression formula shows differences from the measured data in some cases. The above study has shown that steady-state CFD analysis is capable and viable in estimating the wind forces and moments of superstructures of a ship model in a wind tunnel for various ship types. • A comprehensive comparative study of the wind loads of superstructures is conducted. • Two different approaches are examined for the grid sensitivity analysis. • The computations with various computational conditions are carried out with JBC. • The computations for a chemical tanker, a container ship, and a PCC are also performed. • CFD analysis is capable and viable in estimating wind loads of various ship types. [ABSTRACT FROM AUTHOR]

The present global society has made the development of a safe and efficient maritime transportation system more imperative than ever before. Of particular impetus is the steep rise in the price of crude oil, which has required shipping companies to minimize the fuel consumption of their ships. Moreover, the emission of carbon dioxide has been restricted by the EEDI (Energy Efficiency Design Index) issued by the IMO (International Maritime Organization). Weather routing services have become more important to shipping companies. However, there are accuracy deficiencies in the numerical models employed by such services for purposes such as weather forecast and the ship speed loss phenomenon. Moreover, the development of weather routing models has been hampered by insufficient accumulation of continuous data on ship motions, and the navigation, engine, and weather parameters. The data used for this study was collected over one year from a 20,000 DWT class bulk carrier on worldwide voyages. Some new relationships regarding ship motions, speed loss, and wave conditions were developed, which were verified by experimental data and numerical simulations of the frequency response of the ship motion and of the weather and ocean. [ABSTRACT FROM AUTHOR]

A comprehensive parametric study concerning added resistance and ship motion in head waves is conducted with an overset approach based on a structured grid system using an in-house Navier-Stokes solver and recommended configurations are proposed as a guideline. The overset approach enables studying wave propagation separately from viscous flow around a hull by omitting the grid for the hull. The parametric study on computing wave propagation of different configurations without a hull in different wavelengths provides recommended domain size, grid resolution and computational conditions such as the time interval. Computations with a hull of Japan bulk carrier (JBC) are conducted to investigate interactions between incident waves and ship motions by using the overset approach. Surge motion can be fixed, and wall function can be applied to the near-wall region. The obtained configuration is applied to a different hull form, the Duisburg Test Case (DTC) and computed results show good agreement with measured data. The achieved configurations are validated and provide a common practice for computing the added resistance and ship motion in head waves by using the flow solver with the described numerical framework. [ABSTRACT FROM AUTHOR]