Lecture Notes for OE3035 - Motion of Ships and Floating Systems
Course Overview
Welcome to OE3035: Motions of Ships and Floating Systems course. This set of course notes will act as the single document that the students need to refer to while taking this course.
Learning Outcomes
By the end of this course, students will be able to:
- Explain the importance of undamped and damped natural frequency, damping ratio, homogeneous and particular response to sinusuidal forcing of a single degree of freedom system
- Explain how Fourier transform can be used to reduce the seakeeping in irregular waves into multiple regular wave problems
- Explain the governing equations of motion of a marine vehicle
- Explain the difference between incident, scattering and radiation forces and how to calculate them
- Interpret response amplitude operator (RAOs) for ships and offshore structures
- Explain the statistical nature of the ocean and its characterization by sea states
- Explain the importance of spectrum and autocorrelation function
- Calculate the response of a ship to an irregular sea state
- Explain the importance of roll motion of ships and the different ways to control it
- Conduct a hydrodynamic analysis of a ship or an offshore platform
Course Content
- Single degree of freedom system
- Free vibration
- Forced vibration
- Fourier series and Fourier Transforms
- Principle of superposition
- Ship motions in regular waves
- Coordinate systems
- Six degreee of freedom coupled equations of motion
- Inertia forces
- Hydrodynamic froces
- Froude Krylov forces and moments
- Scattering/diffraction forces and moments
- Radiation forces and moments
- Encounter frequency
- Setup of boundary value problem
- Linear superposition
- Response amplitudes operator
- Ship motions in irregular waves
- Random processes and their statistical properties
- Wave spectra - JONSWAP, Pierson Moskowitz, Bretschneider spectra
- Directional spectra
- Response spectra
- Response of a ship in irregular sea
- Ship dynamic phenomena
- Local and relative motions
- Green water effects, Slamming
- Parametric rolling, Broaching
- Added resistance, Powering in waves
- Motion sickness index
- Ship and floating system motion control
- Control of roll
- Bilge keel, free surface tanks, U-tanks, moving weight, fin stabilisers, gyro, active-tanks and rudder stabilization
- Control of pitch
- Control of roll
- Ship design considerations
- Wave induced motions on floating structures
- Responses in regular and irregular seas
- Wave induced motions and loads on a tension leg platform
- Wave induced motions and loads on a spar
- Heave and pitch motion of a semi-submersible
- Discussion of natural period, damping and excitation
Project/Practical
- Estimation of hydrodynamic coefficients and RAOs using strip theory / 3D panel methods
- Calculate the loads for a ship / platform for a specified design life
Experiments
- Roll and heave damping coefficient estimation using free oscillation tests
- Ship and floating body motion response in regular/irregular waves