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.
An evaluation of the use of low-cost accelerometers in assessing fishing vessel stability through period of heave motion
This paper assesses the use of low-cost accelerometers for fishing vessel stability. These sensors provide vessel operators with a novel, autonomous, low-cost method of implementing vessel stability theory. This research evaluates the ability of low-cost, easy-to-use platforms to accurately measure the period of vessels heave motions. This was done using a Derritron Shaker in combination with a signal generator to simulate heave motion at frequencies between 0.2 Hz and 1.0 Hz. The Fast Fourier Transform (FFT) was used to convert the measured time signal into the frequency domain. FFT analysis not only enables the detection of the peak period and frequency of heave motion, but also provides the heave response spectra. Results indicate that low-cost, readily available devices with inertial measurement units such as mobile phones and Raspberry Pis can be used to determine the period of heave motions. Their low-cost makes them suitable solutions for improving safety of fishing vessels.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.