The course concerns the behavior at sea of standard ships (seakeeping) and offshore structures (stationkeeping) and the assessment of relevant design and operational criteria for a successful activity of the examined marine unit. A driving question is: How can we ensure safe, effective and efficient marine activities? This leads to complementary questions such as: What is the relevant sea environment for an examined marine unit? How can we classify the sea loads and motions induced on the marine structure in terms of nonlinearities and physical phenomena involved? Which prediction methods can be used? What are their applicability regions and reliability limits?
The main steps of the course are the following. First, the sea environment is characterized in terms of waves, wind and currents. The loads and/or motions induced on the marine structures are examined as linear, second and higher-order wave effects, within potential-flow theory. Then, viscous effects connected with steady current and wind and/or with waves are studied. Occurrence, features and consequences of vortex induced oscillations and of galloping are discussed. Emphasis is given to the mean and slowly-varying motions in waves, wind and currents. They are important for the stationkeeping of marine structures. In this context design and challenges of dynamic positioning are discussed. Finally, fully nonlinear phenomena connected to the wave-body interactions are analyzed in terms of slamming, water-entry and water-exit.
In the aim to increase the vessels operability, the course will examine how to minimize wave induced motions by passive and active tools. This includes anti-roll devices for ships and dynamic positioning for offshore platforms. In the aim to propose relevant prediction methods for the seakeeping, the course provides information both on simplified methods and on experimental techniques.
Main objectives of the course are:
- To provide insights on critical problems at sea for a given marine structure, the relevant response variables and the related safety/operational criteria.
- To build up knowledge on orders of magnitude for design environment conditions, structure natural periods and resonant and unstable motions.
- To generate physical understanding of the phenomena connected with the fluid-structure interaction problems of practical interest and to make use of simple methods for an early design stage, for marine operation planning or for checking practical computer results or model experiments.
Among the learning outcomes for the students, with respect to knowledge and skills, one can list:
- To be able to identify critical environmental and operational conditions for standard ships and offshore structures.
- To be able to estimate relevant response variables (motions, relative motions, accelerations, etc.) within linear theory and assess safety and operational limit criteria for the specific marine unit.
- To understand how to estimate second-order effects in the loads, i.e. mean, difference-frequency and sum-frequency effects caused by wave-body interactions and to know the limit of applicability of the approximated approaches. To learn how to estimate added-resistance in short waves and to know the major sources of slow-drift damping.
- To be able to estimate the slowly-varying loads connected with wind gust, the mean and oscillatory loads connected with current (and wind), the effect of wake interactions using a simplified wake solution.
- To be able to check possible occurrence of VIV and to know the related consequences in terms of vortex-shedding frequency, natural frequency of the structure and oscillation amplitude. To know the difference between VIV and galloping and occurrence of the latter.
- To know the features and consequences of stationkeeping, the factors reducing performances of thrusters and the challenges in building up a proper dynamic positioning.
- To be able to roughly assess occurrence of water on deck and slamming and to know the physical phenomena and factors connected with slamming, its relevance and consequences. To learn the general features of the major methods used to predict slamming loads on vessels and to check slamming operational criteria.
Recommended previous knowledge
TMR4247 Marine Technology - Hydrodynamics.