Experimental investigation on the effects of froude number on manoeuvring characteristic of a research vessel
Oceanographic research vessels (ORVs) are used to collect ocean data and analyse them to understand the physical, chemical and biological characteristics of seawater, seabed and other ocean-related factors affecting climate changes. These task require vessel to track a predefined trajectory at different speeds. It is crucial to understand the effect of different speed on manoeuvring characteristics of the ship so as to assign appropriate control parameter and techniques to make its position/track keeping ability to an acceptable level. This paper attempts to estimate hydrodynamic derivatives of ORV by performing planar motion mechanism experiments at different speeds to understand the effect of Froude number on the hydrodynamic forces and subsequently on the different coefficient appearing in equations of motion and then on its turning performance. Sensitivity analysis is carried out as part of current work to understand the effect of different hydrodynamic derivative value variation on different turning parameter of vessel.
Numerical study on the influence of head wave on the hydrodynamic derivatives of a container ship
Traditionally, ship maneuvering performances are predicted in calm water condition to evaluate the directional stability and turning ability of the ship in the early design stages. Evaluation of maneuvering performance of a ship including wave effect is more realistic and important for the safety of ships at sea. Determination of hydrodynamic derivatives is the basic step in solving maneuvering equations of motion. Accurate estimation of hydrodynamic derivatives is necessary for the prediction of vessel trajectories. As the ship maneuvers through seaway, the effect of wave load will alter the maneuvering derivatives, consequently the vessel trajectory will be affected significantly. Hence, the influence of wave on hydrodynamic derivatives needs to be determined. For the present study, horizontal planar motion mechanism tests are numerically simulated for a container ship in head sea condition using RANS-based CFD solver. Obtained force/moment time series include both wave excitation forces/moment and hydrodynamic forces on the hull due to PMM motions. Fast Fourier transform (FFT) algorithm is used to filter the hydrodynamic forces/moment from the estimated total force/moment time series. The Fourier series expansion method is used to derive the hydrodynamic derivatives from the estimated force/moment time series. A comparison study is done with the wave-effected hydrodynamic derivatives and derivatives in still water condition.
Manoeuvring prediction of a container ship in shallow water using numerical planar motion mechanism
Manoeuvring behaviour of a vessel changes drastically when it enters from deep water region to a shallow water region. Flow characteristics, around the hull changes and the vessel, respond poorly to the use of control surfaces. Aim of this paper is to study the manoeuvring behavioural changes in a container ship for different water depth conditions. Computational fluid dynamic (CFD) methods are used for simulating static and dynamic captive model tests. Variation in hydrodynamic reaction forces and moments caused by the reduction in water depth and the subsequent effect in hydrodynamic derivatives appearing in the equation of motion are explained in detail. Standard turning circle and zigzag manoeuvring tests are simulated using the CFD generated hydrodynamic derivatives to assess the manoeuvring characteristics of the vessel.