PLANING HULL SEAKEEPING IN IRREGULAR HEAD SEAS
UDC 629.5.017/018.71 Summary The paper presents the results of planing hull seakeeping tests in irregular seas. The tested model belongs to a small systematic series developed at the University of Naples; it is a prismatic hull very similar to the well-known Fridsma’s models. The 16.7 degrees deadrise angle, length-to-breadth and load coefficient are representative of modern hull forms of pleasure boats. Tests in irregular waves have been performed at three speeds for one displacement in three sea states. The measured heave, pitch, acceleration at the centre of gravity and at bow have been analysed in the time domain and the results are presented in terms of significant values (the mean of 1/3 rd highest values). They are given in tabular and graphical form. Furthermore, the obtained results are commented with respect to the state of the art in planing hull seakeeping, and compared with the available experimental data from literature. The conclusions highlight the applicability of these data in design practice, commenting on trends and the range of significant parameters.
A decision-making process for the selection of better ship main dimensions by a Pareto frontier solution
Abstract Initial ship design necessitates the evaluation of main ship parameters to obtain a feasible design solution satisfying the objectives. Traditionally, relationship between main dimensions and design parameters of proven designs provides a safe solution. This approach restrains the designer from improving the design with respect to conflicting design criteria. Pareto frontier technique has widely been utilized in the design of ships, mainly at advanced design stages for optimization problems. As the principal dimensions of a ship are also vital on the performance of the vessel, major improvements in performance may be achieved by selecting better principal dimensions. This paper proposes to integrate the Pareto technique to the design cycle at an early stage as a decision-making process for selection of better main dimensions with respect to multiple conflicting criteria A Pareto Front has been observed for two case studies (a destroyer and a planing craft) indicating a technological barrier for performance with respect to main dimensions. As the design process begins with main dimensions along the technological barrier, performance is improved with respect to conflicting design criteria at the beginning of the design process which serves as a better basis for further optimization studies to be conducted at advanced stages.
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.