Investigation Of Ship Parametric Roll Resonance In Irregular Waves

Shipping is the main form of transportation for bulk cargo in the modern world.It is of great significance to keep the safety of ship sailing.Parametric roll resonance will lead to large amplitude roll motion,which will lead to container falling into the sea and destroy,structural damage and main engine failure,even ship capsizing,which will threaten the safety of ship crew,cargo and ship sailing.Thus,study on ship parametric roll resonance can help improve the safety of ship sailing.Parametric resonance is caused by the time varying parameter in the system.For a sailing ship in waves,the time varying metacentric height in the system will lead to the parametric roll resonance.Ship parametric roll resonance is a main form of ship instability,the mechanism and motion of which is obviously nonlinear and random.Parametric roll resonance in real sea is one kind of randomly excited parametric resonance.Therefore,study according to irregular wave theory is helpful to have a better understanding of its mechanism.Towing tank experiments have verifed the existence of ship parametric roll resonance.Though some researchers have studied ship parametric roll resonance in irregular waves,the corresponding theories are not sufficient enough to have a good explanation of its mechanism.Study of parametric rolling in irregular waves still needs further exploration.Study of ship parametric roll resonance is conducted according to irregular wave theory in this paper,the main work is as follows:1.Analytical study for parametric roll resonance in irregular waves and the obtain of Ince-Strutt stability chartDerive the equation for parametric roll resonance in irregular waves and obtain the corresponding Ince-Strutt stability chart.Achieve the aim of analytical prediction of parametric roll resonance in irregular waves.The differences of stability charts in regular and irregular waves are compared to notify the significance of irregular wave study.Study the influence of damping,wave phases and wave peak period on stability charts.Study ship design variables according to stability chart.2.Propose probabilistic method for parametric roll resonance in irregular wavesTwo probabilistic indexes are utilized in this passage: ‘severity probability index'(SPI)considering the amplitude of roll motion;‘Conditional Severity Probability Index'(CSPI)considering both the amplitude of roll motion and its duration.SPI can deduce the typical case for the probability design against parametric roll resonance.Such typical case has the largest probability for the occurrence of parametric roll resonance.By combining roll amplitude and its duration,CSPI aims to have a more comprehensive assessment of parametric roll resonance.3.Sensitivity analysis of ship parametric roll resonanceSensitivity analysis of ship parametric roll resonance is conducted from two different mothods:(1)according to the emperimental design;(2)according to the nonlinear equation.Without the need of specific ship parameters,sensitivity analysis according to experimental design is conducted by hydrodynamic estimation formulas.Basic ship variables like ship length,breadth,drought,block coefficient and forward velocity are taken into consideration.Nonlinear equation considers the nonlinear effect of ship motion.Compare the differences of sensivity in regular and irregular waves.Study the influence of initial motion condition on probabilistic study.4.Control of parametric roll resonance in regular wavesAnalyze the influence of control variables(metacentric height,initial rolling condition,forward velocity and forward acceleration)on parametric roll resonance by two dimentional bifurcation map and Poincare map.According to these analysis,control method in regular waves is analyzed,which is aimed to provide operation advice for a sailing ship.