Threshold Energy for Transient Cavitation Free-bubbles

Assuming the model of a sigle free cavity in an incompressible, inviscid liquid, a threshold energy for the transient cavitation is obtained as a function of the rest radius of the cavity. The comparison with available experimental data from laser induced cavitation bubbles was carried out, and it gave satisfactory agreement with experiment. Moreover, considering the energy per unit mass of the cavity content at collapse, a simple explanation of the absence of cavitation effects above about 2.5 MHz of the driving field is found

Risonanze ultrarmonica e subarmonica nel moto di rollio di una nave soggetta a mare regolare al traverso

In questo lavoro si \ue8 estesa l'analisi della risposta in rollio della nave al di fuori della zona di sincronismo. Il moto \ue8 rappresentato da un'equazione differenziale del secondo ordine con momento raddrizzante lineare+cubico e smorzamento sia lineare che non lineare. Per entrambe le equazioni si sono trovate, con metodo perturbativo, le soluzioni approssimate per frequenze della forzante multiple e sottomultiple della frequenza naturale di rollio. Si sono successivamente trovate le equazioni che descrivo l'ampiezza stazionaria in zona ultra- e sub-armonica e la soglia per l'innesco di quest'ultima

Effects of the Angle-dependent Damping on the Rolling Motion of Ships in Regular Beam Seas

An examination of the influence of the damping effects on the ship rolling motion in regular beam seas has been made. The assumed damping includes both the linear and quadratic contributions, where, in particular, for the linear term a given dependence on heeling angle is assumed. An approximate analytical solution in the resonance region was determined by a perturbation method and compared with a numerical solution. The results showed that the maximum rolling amplitude attainable for a given excitation is markedly affected by the angle-dependent part which was introduced in the linear damping

Steady Wave Field Influence on Seakeeping Performance of a Fishing Vessel

The seakeeping performance of a typical Mediterranean fishing vessel is investigated by means of a 3D Rankine panel method, which takes into account the influence of the fully nonlinear steady wave field on the unsteady wave field. The method provides in-depth information for the steady flow characteristics, so that the influence on the unsteady wave field is numerically controlled in a simple and efficient manner. Moreover, information related to hydrodynamic forces, ship motions and unsteady wave field (diffraction wave) is obtained. The radiation condition is satisfied by the shifting technique for both inter-connected flows, i.e., steady and unsteady. The effectiveness of the numerical method in predicting the unsteady wave field with good accuracy is underlined by comparison with experimental data

Stabilit\ue0 della nave e movimento di rollio: caso di momento sbandante non variabile

Il moto di rollio della nave \ue8 stato descritto mediante un'equazione differenziale non lineare del secondo ordine includente gli ffetti di uno smorzamento quadratico e di una causa sbandante non variabile. Il momento raddrizzante inoltre \ue8 stato rappresentato mediante un polinomio di quinto grado che costituisce un'ottima approssimazione della curva reale di stabilit\ue0 statica. La stabilit\ue0 della posizione di equilibrio \ue8 stata discussa con il criterio di Routh Hurwitz. Si \ue8 trovato quindi il dominio di stabilit\ue0 asintotica applicando il metodo diretto di Liapunov. Sono stati ottenuti, come casi particolari, i ben noti criteri di stabilit\ue0 statica e dinamica della nave. Per esemplificare l'applicazione del metodo teorico si \ue8 considerata una motonave da carico di piccole dimensioni

Ultraharmonics and Subharmonics in the Rolling Motion of a Ship: Steady-state Solution

In this paper the roll motion of a ship with particular regard to the nonlinearity phenomena is examined. The behaviour in a regular beam sea is studied in cases where the encounter frequency is an integer multiple or sub-multiple of the natural roll frequency of the ship. The approximate analysis of the equation of motion, carried out with the Bogoliubov-Krylov-Mitropolsky asymptotic method, shows that, apart from the synchronism, other resonance regions typical of nonlinear systems also exist. It deals with resonances of higher order, ultra- and sub-harmonics respectively. In these nonlinear resonance regions the ship has a steady state rolling amplitude which could be much greater than that predictable by linear theory. The analytical predictions are compared with the numerical results obtained by solving the equation of motion with the Runge-Kutta method. The agreement of the frequency response curves appears to be optimum in the whole interval of frequency, up to considerable rolling amplitudes

Reflecting, Iterating, and Tolerating Ambiguity: Highlighting the Creative Process of Scientific and Scholarly Research for Doctoral Education

Producing quality original research requires advanced analytic skills, but also the creative intelligence to design a project as well as the ability to handle the inevitably ambiguous research process. This study unveils important aspects of how successful interdisciplinary scholars understand their research process and how they mentor students through research. Using interviews with nine faculty members and qualitative analysis of classroom sessions, the study investigates the mindsets and behaviors that experienced scholars bring to their work. Results suggest that innovative faculty see creativity as central to their research and actively seek to balance the creative and analytical aspects of their work, use an iterative “learning by doing” approach to refining questions and methods, and view setbacks as opportunities for further learning. However, faculty varied in the extent to which they made this messiness and comfort with ambiguity explicit for their students. By uncovering the mindsets that scholars bring to their research, we hope to better support doctoral students in building not just their analytical but also their creative capacity

Research as design: Developing creative confidence in doctoral students through design thinking

This paper explores the benefits of design thinking training to enhance doctoral student problemsolving ability, creative confidence, and emotional well-being. Our team adapted the design thinking curriculum taught by Stanford University's Hasso Plattner Institute of Design to the challenges of developing and carrying out original research, and has taught thirteen workshops to over 240 graduate students, research staff, and faculty over two years. Using a design-based research framework, we reflect on our observation of the workshops, student debriefs, and a prepost survey of participants to assess the value of design thinking for doctoral education. We find that participants felt the workshops enhanced creativity, productivity, and confidence, participants appreciated applying the mindsets of a bias toward action and embracing experimentation to their research, participants learned to be mindful of their research process, and participants valued the emotionally supportive, nonjudgmental atmosphere cultivated in the workshops. The research suggests (1) that creative problem solving methods can be adopted by doctoral students and (2) that there is a demand for graduate training to more explicitly treat students' intellectual needs in tandem with their emotional needs to create happy, productive researchers

Impact of Thruster Interaction Effects on Optimal Thrust Allocation in Dynamic Positioning Systems

Existing strategies and proposed methods for optimal thrust allocation in dynamic positioning systems of floating objects are primarily focused on minimization of power consumption with treating of numerous limitations and conditions that should be satisfied at the same time. On the other hand, one can notice that thruster interaction effects such as axial and transverse current, thruster-hull interaction, thruster-thruster interaction and ventilation are rarely taken into account. These effects, whether they occur separately or in combinations, can cause significant thrust losses which can consequently degrade reliability of dynamic positioning systems, decrease accuracy, increase response time and power/fuel consumption, etc. The main goal of this paper is quantification of selected aforementioned effects as well as the proposal of their implementation in optimal thrust allocation strategies based on Moore-Penrose pseudoinverse matrix. Moreover, the thrust allocation procedure here considered has been performed with and without thrust loss effects together with comparative analysis of these two approaches