OE3035
Motion of Ships and Floating Systems
From single-degree-of-freedom vibration to ship motions in regular and irregular waves, RAOs, and motion control.
Seakeeping of ships and floating systems — from the response of a single-degree-of-freedom oscillator through motions in regular and irregular waves to roll control and hydrodynamic analysis of offshore platforms.
Course content
Single degree of freedom systems
- Free and forced vibration
- Fourier series and Fourier transforms
- Principle of superposition
Ship motions in regular waves
- Coordinate systems; six-degree-of-freedom coupled equations of motion
- Inertia forces and hydrodynamic forces (Froude–Krylov, scattering/diffraction, and radiation)
- Encounter frequency; boundary-value problem setup
- Linear superposition and response amplitude operators (RAOs)
Ship motions in irregular waves
- Random processes and their statistical properties
- Wave spectra (JONSWAP, Pierson–Moskowitz, Bretschneider) and directional spectra
- Response spectra and ship response in an irregular sea
Ship dynamic phenomena
- Local and relative motions; green water and slamming
- Parametric rolling and broaching
- Added resistance and powering in waves
- Motion sickness index
Motion control and design
- Roll control: bilge keels, free-surface and U-tanks, moving weight, fin stabilisers, gyros, active tanks, and rudder stabilisation
- Pitch control and ship design considerations
Floating structures
- Wave-induced motions and loads on TLPs, spars, and semi-submersibles
- Natural period, damping, and excitation
Practical and experiments
- Hydrodynamic coefficients and RAOs via strip theory / 3D panel methods
- Design-life load calculation for a ship or platform
- Roll and heave damping from free-oscillation tests
- Motion response in regular and irregular waves
Learning objectives
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 sinusoidal 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
Lecture notes for the course are at oe3035.mavlab.in.