Vladimir Shigunov

Duisburg Test Case: Post-Panamax Container Ship for Benchmarking

Abstract Duisburg Test Case (DTC) is a hull design of a typical 14000 TEU container ship, developed at the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) for benchmarking and validation of numerical methods. Hull geometry and model test results of resistance, propulsion and roll damping are publicly available. The paper presents existing data from model tests and computations.

A Rankine Panel Method for Added Resistance of Ships in Waves

A new Rankine panel method and an extended Reynolds-Averaged Navier–Stokes (RANS) solver were employed to predict added resistance in head waves at different Froude numbers of a Wigley hull, a large tanker, and a modern containership. The frequency domain panel method, using Rankine sources as basic flow potentials, accounts for the interaction of the linear periodic wave-induced flow with the nonlinear steady flow caused by the ships forward speed in calm water, including nonlinear free surface conditions and dynamic squat. Added resistance in waves is obtained by the pressure integration method. The time domain RANS solver, based on a finite volume method, is extended to solve the nonlinear equations of the rigid body six-degrees-of-freedom ship motions. The favorable comparison of the panel and RANS predictions demonstrated that the Rankine method is suitable to efficiently obtain reliable predictions of added resistance of ships in waves. Comparable model test predictions correlated less favorably, although the overall agreement was felt to be acceptable, considering the difficulties associated with the procedures to obtain accurate measurements.

RANKINE SOURCE METHOD FOR SEAKEEPING PREDICTIONS

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations.Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.Copyright

Operational Guidance for Prevention of Cargo Loss and Damage on Container Ships

Abstract Ship-specific operational guidance onboard container carriers can assist the ship master to avoid excessive motions and accelerations and thus prevent loss and damage of cargo. The paper outlines considerations regarding such operational guidance, particularly relevant factors for cargo loss and damage, conditions of excessive roll motions in waves, probabilistic criteria and standards, numerical methods and methodology of numerical simulations. Examples are shown for a modern container ship.

Application of CFD in Long-Term Extreme Value Analyses of Wave Loads

Abstract This paper discusses ways to embed time-domain field methods in extreme value predictions. Approaches are suggested that appear to give most reliable results. They rely on Monte-Carlo simulations, a reduction of parameter variations and extrapolation of exceedance rates over significant wave height. The computational effort is large, yet it can be handled with modern cluster computers.

Added resistance of ships in waves

Abstract Added resistance of ships in waves is determined by a newly developed potential flow method, a Rankine source method, a strip method, and by RANS (Reynolds-averaged Navier-Stokes) equations solvers. For 10 ships, results of all these methods are compared with each other, with published computed and experimental results, and with approximation formulae submitted to IMO (International Maritime Organisation). The focus is on waves that are short relative to ship length. In spite of the large scatter of results, existing prediction methods appear useful for practical application.

Manoeuvrability in Adverse Conditions

Slow steaming and regulatory drive towards more energy efficient ships have raised a problem of ensuring sufficient manoeuvrability of ships under adverse weather conditions when installed power is reduced. This paper discusses possible criteria for sufficient manoeuvrability in adverse conditions and proposes practical assessment procedure and examples of its application. Further, the paper outlines necessary developments.Copyright

Towards Safer Container Shipping

Abstract Casualty statistics show that container loss in heavy weather is an important issue for innovative container ship designs. The paper describes research activities at Germanischer Lloyd aiming at the reduction of cargo losses. One example is ship-specific operational guidance, assisting the ship master to avoid excessive motions and accelerations in heavy weather. Another example is the definition of design accelerations, underlying the operational guidance. The study includes the effects of container flexibility, not addressed explicitly in the present classification rules.

Green Water Loads on a Cruise Ship

A linear boundary-element method and a Reynolds-averaged Navier-Stokes (RANS) equations solver were combined to predict maximum green water loads on a typical cruise ship of medium size. For structural analysis, a one-way coupling mapped the hydrodynamic pressure from the finite-volume grid onto the computational structural dynamics finite element mesh. First, linear long-term maximum ship responses were determined by a boundary element method combined with long-term statistics based on spectral methods; transfer functions of these responses were used to define response-conditioned wave trains inducing the linear long-term maximum ship response. The investigated wave sequences were correlated to a dedicated probability level for a lifecycle time of 20 years in the North Atlantic environmental wave conditions and for a ship speed of six knots.Critical impact locations were found to include the weather deck in the foreship, the front wall of the superstructure and the overhanging bridge deck. Predicted loads were compared to experimental data obtained in conditioned wave trains and in extreme irregular sea states. Numerical and experimental results revealed significantly higher loads than design loads specified by classification society rules. Pressure peaks on the weather deck and the superstructure front wall were comparable to rule-based design pressures for breakwaters on containerships and exceeded pressure peaks on the bridge deck.Copyright

Prediction of non-linear ship responses in waves considering forward speed effects

This article describes the development of a non-linear time-domain boundary element method to determine non-linear ship responses (motions and loads) in waves. The general approach by Cummins was used to express the equation of motion in the time domain. Hydrodynamic forces were split into inertia, radiation, diffraction, Froude–Krylov and restoring components. Radiation forces were determined in time domain by convolution of the impulse response of the ship with the motion velocity. The Froude–Krylov and restoring forces were computed over the instantaneous wetted surface, taking into account ship motions, the undisturbed wave and stationary wave system. Diffraction forces were computed from the complex force amplitude resulting from the linear problem of the incident wave diffraction. The impulse response of the ship can be determined using the linear hydrodynamic damping coefficients or added masses. In this work, these two approaches were compared. Ship motions calculated with the developed method were compared with model test and RANSE-based simulations as well as with linear frequency domain results for three different ship types at various forward speeds. It was shown that the convolution integral represents the radiation forces satisfactorily. The convolution integral based on damping coefficients showed distinct advantages at zero speed. With increasing forward speed, the added mass-based convolution integral leaded in some cases to better results.