Modeling of Ship Roll Dynamics and Its Coupling with Heave and Pitch
In order to study the dynamic behavior of ships navigating in severe environmental conditions it is imperative to develop their governing equations of motion taking into account the inherent nonlinearity of large-amplitude ship motion. The purpose of this paper is to present the coupled nonlinear equations of motion in heave, roll, and pitch based on physical grounds. The ingredients of the formulation are comprised of three main components. These are the inertia forces and moments, restoring forces and moments, and damping forces and moments with an emphasis to the roll damping moment. In the formulation of the restoring forces and moments, the influence of large-amplitude ship motions will be considered together with ocean wave loads. The special cases of coupled roll-pitch and purely roll equations of motion are obtained from the general formulation. The paper includes an assessment of roll stochastic stability and probabilistic approaches used to estimate the probability of capsizing and parameter identification.
FIVE YEARS OF NUMERICAL NAVAL SHIP HYDRODYNAMICS AT DTNSRDC
Abstract : In 1974 the Numerical Naval Ship Hydrodynamics Program was established at the David W. Taylor Naval Ship Research and Development Center. The objective of the program is to develop new numerical methods which can be used to evaluate those hydrodynamic performance characteristics which cannot be satisfactorily predicted by traditional methods. In this report, the accomplishments during the first five-year period (1974-1979) are discussed. During this initial period, the effort was devoted entirely to naval ship free-surface problems. Several successful methods have been developed for solving fully three-dimensional ship-motions, ship-wave-resistance and local-flow problems using linearized free-surface boundary conditions. Numerical methods have also been developed for unsteady and steady two-dimensional problems where the exact free-surface conditions are satisfied. These new numerical methods are more accurate than the conventional computational methods and they can be used to analyze several naval free-surface problems which previously could only be investigated experimentally. It is concluded that the Numerical Naval Ship Hydrodynamics Program should include consideration of all areas in naval ship hydrodynamics where it is believed that the application of advanced numerical techniques and computers can result in better solution techniques. (Author)
The Determination of Physicochemical Characteristics of Biodiesel and Its Blending Oils
The viscosity,combustion heat,sulfur content,carbon residue,ash,flash point,moisture and cetane value of biodiesel and its blending oils with diesel were determined.The influence of temperature on the viscosity was studied,and the physicochemical characteristics of biodiesel and its blending oils were compared with diesel.The results indicated that biodiesel and its blending oils had some superior performances and good application prospect.