Jerzy Matusiak

Probability modelling of vessel collisions

Among engineers, risk is defined as a product of probability of the occurrence of an undesired event and the expected consequences in terms of human, economic, and environmental loss. These two components are equally important; therefore, the appropriate estimation of these values is a matter of great significance. This paper deals with one of these two components—the assessment of the probability of vessels colliding, presenting a new approach for the geometrical probability of collision estimation on the basis of maritime and aviation experience. The geometrical model that is being introduced in this paper takes into account registered vessel traffic data and generalised vessel dynamics and uses advanced statistical and optimisation methods (Monte Carlo and genetic algorithms). The results obtained from the model are compared with registered data for maritime traffic in the Gulf of Finland and a good agreement is found.

Sloshing Forces on a Tank With Two Compartments, Application of the Pendulum Model and CFD

Two different methods, pendulum model and computational fluid dynamics (CFD), to predict the forces on the ship caused by the flooded water are compared against the model test results. Calculations were performed for a tank in forced motions at different frequencies, for which experimental results were available. The tank had a dividing wall with an opening. The overall behaviour of the force time history was well captured with the pendulum model. In particular at lower frequency the agreement of the force range is very good. Some small force peaks due to the sloshing were predicted in a good correspondence with the CFD simulations. At a higher frequency slight discrepancy is shown also in the CFD calculations. The free surface behaviour is captured in detailed level by the CFD calculations, but the overall motion of the water is captured also with the pendulum model with plane surface model. Comparison to the model tests shows the applicability of the pendulum model in simulating sloshing case with the exchange of water between the compartments. These comparisons show that the pendulum model is a sufficiently accurate and calculation time wise efficient method. It provides a tool to perform a great amount of simulations in order to study the impact of different parameters and the statistical probabilities of ship survival under different accident scenarios.© 2014 ASME

Influence of Sloshing on the Transfer of Water Between Neighbouring Compartments Considering Three Different Opening Configurations

Model tests to generate validation data for the codes predicting the sloshing and progression of water through an opening in case of a damaged ship were planned and performed. Behaviour of the flooding water after the damage is greatly dependent on the internal compartment geometries and vessel motions. Vessels angular position and motions in turn are affected by the flooding water. Thus accurate prediction of this strongly coupled flooding phenomenon requires simultaneous solving of the ship motions and behaviour of the internal water. In order to produce validation data for calculation methods for internal flood water behaviour, tests for water motion between two connected neighbouring compartments were designed. Model tests concentrated purely on the internal sloshing motion under forced compartment motions, thus uncoupling the vessel response.Copyright

Hydrodynamic Added Mass and Damping of the Kaplan Turbine

Kaplan turbine runner rotates in water flow inside an enclosed discharge ring. The vibratory runner motion in the fluid flow induces pressure forces onto the wet runner surfaces with inertia effects conveniently described by the so-called hydrodynamic added mass and damping. These inertia effects influence the wet natural frequencies and the amplitudes. The role of the hydrodynamic added mass and damping in the Kaplan turbine shaft rotor dynamics has not been sufficiently well understood. This paper focuses on comprehensive understanding of these phenomena across the Kaplan design range. The results are based on a method derived from Theodorsen’s unsteady thin airfoil theory and on the Finite Element Method (FEM). The former method includes the water flow, the runner rotation and the circulatory effects, which makes it possible to calculate the added damping and evaluate the accuracy of FEM. The most critical vibration modes and shaft line configurations have been identified with inherent weaknesses in typical shaft line models. The added damping has been quantified. The numerical results have been compared to the experimental results.Copyright