Fluid - Structure Interaction in Maritime Structures

Maritime structures are constantly subjected to hydrodynamic loading, due to interaction with the free surface of the water. In order to define the topology and scantlings of structural members, a fluid and structural dynamic analysis is required. The fluid loads need to be transferred to the structure, to calculate the structural response in terms of deflections, stress, strain, energy, etc.

For many problems, the fluid dynamics analysis can be performed independently of the structural analysis, producing rigid body motions and distributed loading. This, in turn, can be used as input to calculate the structural response. The simplest version of this process is a quasi-static application of the loading - however, for abrupt loading conditions, or frequencies of excitation close to resonance, dynamic response is excited. This course covers the dynamic responses of maritime structures, which are excited by loading from the free surface.

The coupling between fluid and structure can have various levels of complexity, depending on the problem at hand. If the flexible deflections of the structure are small in comparison to its rigid body displacements, a one-way coupling (a hydro-structural analysis) might be sufficient. In this case, we are assuming that the magnitude of the fluid loading is not affected by the structure's vibration. However, for larger flexible responses this assumption might be no longer applicable, in which case a two-way coupling (a hydro-elastic analysis) is required.

The flexible response can significantly affect operational aspects and influence limit state considerations (e.g. buckling, fatigue, and fracture).

This course will introduce use of fluid-structure interaction techniques to determine the dynamic response of maritime structures, the consequences of said responses and the appropriate selection of modelling assumptions based on the problem at hand. This will be performed through two separate applications:

Application 1: Transient hydrodynamic loading

1. Focus on local and regional response

2. Semi-analytical methods based on Von Karman and Wagner slamming models, including inertia and free vibration stage characteristics and analytical beam dynamics

3. Time-domain solutions using implicit/explicit numerical integration, for instance Newmark and/or 4th-order Runge-Kutta formulations

Application 2: Continuous wave loading

1. Focus on global response (springing)

2. Numerical solutions based on potential flow simulations and beam finite element models

3. Frequency-domain solutions through modal decomposition and superposition

For both applications, the following topics will be covered:

1. Hydrodynamic boundary value problem formulation and resulting load distributions

2. Structural dynamic problem formulation through Euler-Bernoulli/Timoshenko beam modelling

3. Modal superposition for both dry and wet problems

4. Effects of hydro-structural and hydroelastic assumptions depending on problem parameters, and associated criteria

5. Applicability of one-way or two-way coupling, depending on problem parameters

6. Effects of fluid-structure interaction on limit state characteristics

7. Sizing of structural members based on calculated dynamic response