SHIP MANOEUVRING PREDICTION BASED ON NUMERICAL TOWING TANK TECHNIQUE

A practical procedure is proposed in this paper to predict ship manoeuvrability. A three degrees of freedom MMG (Japanese Manoeuvring Mathematical Modelling Group)-type model is established to simulate rudder manoeuver. Propeller thrust and rudder loads are calculated by empirical formulas, whereas the hull forces as well as moment are determined with hydrodynamic derivatives which are derived from CFD (Computational Fluid Dynamics) computations. An own developed RANS (Reynolds-Averaged Naiver-Stokes) solver on the base of OpenFOAM is applied to simulate a range of PMM (Planar Motion Mechanism) tests and Fourier analyses of the computed results are carried out to obtain the required derivatives. In order to demonstrate the effectivity of the whole procedure and the RANS computations, the US (United States) combatant DTMB 5415 is taken as a sample for an application. Forced motions of surge, sway, yaw and yaw with drift for the bare hull with bilge keels are simulated. Thereafter, simulations of standard rudder manoeuvers, i.e. turning and zigzag, are performed by applying the computed derivatives. The results are compared with available measured data. It has been shown that the present procedure together with the RANS method can be used to evaluate the manoeuvrability of a ship since general good agreements between the simulated results and measured data are achieved.

Hydrodynamic study of the flow developed around a bare hull ship in static drift motion

The present study gives a Computational Fluid Dynamics (CFD) based insight into the three-dimensional incident flow developed around a very large crude carrier ship during static drift motion. The research proposes a set of virtual Planar Motion Mechanism (PMM) tests of “static drift” type conducted for a number of seven drift angles in the range of -9o to +9o . The emergence and development of vortical structures along the 1:58 KRISO Very Large Crude Carrier 2 (KVLCC2) tanker model are examined and explained, the influence of the considered drift angles being highlighted.

Benchmark Study and Uncertainty Assessment of Planar Motion Mechanism Tests on KVLCC2 in a Circulating Water Channel

The benchmark experiment research for the maneuverability of a small-scaled ship model is critical for investigating the scaled effect on the maneuvering hydrodynamic derivatives, and validating the CFD technology. Till now, there is little research on the benchmark study and uncertainty analysis for the small-scaled ship which is frequently used in the Circulating Water Channel (CWC). Therefore, an experimental study of the planar motion mechanism (PMM) tests is performed in the CWC of the SJTU. The PMM tests performed in the CWC can avoid some disadvantages of those in the towing tank, such as the limitations on the acquisition time and frequency due to the size of the towing tank, interference of the carriage on the signal acquisition. In addition, the flow field visualization for the tests in the CWC is easier to achieve compared with the experiments in the towing tank, which helps the scholars to understand the characteristic of the wake field during maneuvers. The benchmark ship is the KVLCC2 with a scaled ratio of 1/128.77. The hull forces are recorded and processed to obtain the maneuvering hydrodynamic derivatives. To assess the quality of the acquired data, randomness analysis, stationarity analysis, normality analysis, and statistical convergence are performed for the PMM tests in the CWC for the first time. Finally, the uncertainty analysis (UA) method for the PMM tests performed in the CWC is also developed.

A Linear Model Analysis of the Unsteady Force Response of a Planing Hull Through Forced Vertical Plane Motion Simulations

The prediction of planing hull motions and accelerations in a seaway is of paramount importance to the design of high-speed craft to ensure comfort and, in extreme cases, the survivability of passengers and crew. The traditional approaches to predicting the motions and accelerations of a displacement vessel generally are not applicable, because the non-linear effects are more significant on planing hulls than displacement ships. No standard practice for predicting motions or accelerations of planing hulls currently exists, nor does a nonlinear model of the hydrodynamic forces that can be derived by simulation. In this study, captive and virtual planar motion mechanism (VPMM) simulations, using an Unsteady RANSE finite volume solver with volume of fluid approach, are performed on the Generic Prismatic Planing Hull (GPPH) to calculate the linearized added mass, damping, and restoring coefficients in heave and pitch. The linearized added mass and damping coefficients are compared to a simplified theory developed by Faltinsen [6], which combines the method of Savitsky [12] and 2D+t strip theory. The non-linearities in all coefficients will be investigated with respect to both motion amplitude and frequency. Nonlinear contributions to the force response are discussed through comparison of the force response predicted by the linear model and force response measured during simulation. Components of the planing hull dynamics that contribute to nonlinearities in the force response are isolated and discussed.

Investigation of the Flow Field of a Ship in Planar Motion Mechanism Tests by the Vortex Identification Method

Planar motion mechanism (PMM) tests provide a means of obtaining the hydrodynamic derivatives needed to assess ship maneuverability properties. In this paper, the self-developed computational fluid dynamic (CFD) solver based on the open source code platform OpenFOAM, naoe-FOAM-SJTU, associated with the overset grid method is used to simulate the complex viscous flow field of PMM tests for a benchmark model Yupeng Ship. This paper discusses the effect of several parameters such as the drift angle and period on the hydrodynamic performance of the ship and compares the time histories of the predicted forces and moments with experimental data. To investigate the complex viscous flows with a large separation, four vortex identification methods are used to capture the vortex structures. The results show that the forces and moments are in good agreement in static drift and dynamic tests. By comparing the vortex structures, it is found that the third generation vortex identification methods, OmegaR and Liutex, are able to more accurately capture the vortex structures. The paper concludes that the present numerical scheme is reliable and the third generation vortex identification methods are more suitable for displaying the vortex structures in a complex viscous flow field.