Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran

Abstract

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.

Vibration Characteristic Research of 100 m New Polar Exploration Cruise Based on Finite Element Modeling

“…In terms of foreign research, Jadee et al [15] investigated the free vibration attributes of isotropic plates utilizing the FEM and experimental techniques. McVicar et al [16] investigated the impact of slam force duration on the vibration response of a high-speed catamaran. Ogawa et al [17], showing that hull girder vibration and ship operations substantially influence wave load statistics, caution against omitting them, as this could lead to overestimation errors.…”

Hydrodynamic Lubrication of Elastic Foil Gas Bearing Using Over Relaxation Iteration Method and Non-Dimensional Equation

“…The elastic characteristics of foil lead to the high impact resistance of foil bearing and the high tolerance to rotor thermal expansion and centrifugal expansion [5]. At the same time, the friction effect between the flat foil and the support foil, and between the support foil and the bearing pedestal can eliminate a lot of useless energy, thus improving the damping characteristics of the foil bearing and improving the stability of the rotor system [6]. Since the 1970s, the research on gas foil bearing has gradually increased and deepened, and foil bearing has been gradually successfully applied to high-speed light load rotating machinery such as air circulator and oilfree turbo expander [7].…”