The University of Southampton
Courses

# SESS2015 Hydrodynamics and Seakeeping

## Module Overview

This module provides the fundamental aspects of fluid dynamics, dynamics and statistics associated with random processes and integrates them so that the students have a good understanding of hydrodynamics and seakeeping for a range of marine structures operating on or below the free water surface. There are two laboratories and one assignment (on seakeeping), which support understanding and application of the concepts taught.

### Aims and Objectives

#### Learning Outcomes

##### Knowledge and Understanding

Having successfully completed this module, you will be able to demonstrate knowledge and understanding of:

• A classical fluid mechanics knowledge base established on fundamental principles.
• The determination of loads acting on, and the fluid flow around, simple marine/ship-like structures.
• Classical dynamics and their application to modelling the rigid body motions of floating structures.
• The basic unit of seaways (ie. the regular wave) and its definition with respect to a moving ship.
• To review statistics and understand/apply probabilistic methods to waves and ship motions.
• Understand and apply the principles of dynamic response for basic systems.
• Model the seaway using deterministic and probabilistic approximations.
• Model the dynamic behaviour of rigid floating structures in waves.
• Construct suitable mathematical models to describe physical fluid-structure interactions and to calculate the fluid interaction characteristics

### Syllabus

Description - Part A; Basic elements of hydrodynamics: • Linearization technique • Flow velocity and acceleration • Definition of inviscid flow and irrotational flow. • Equation of continuity • Definition of velocity potential. • Definition of stream function for two-dimensional and special three-dimensional flows. • Equation of motion, total derivative. • Laplace Equation; Cauchy-Riemann conditions. • Derivation of Bernoulli Equation for steady and unsteady flows. • Mathematical operations of grad, div, curl, etc. Surface waves: • Formulation of wave equation for finite depth with travelling waves. • Hydrodynamic theory applied to towing tank and circulating water experiments • Investigation of phase speed relationship. • Standing waves - application in tanks. • Dynamic pressure in waves. • Mean rate of propagation of energy in waves. • Group velocity. • Shallow water wave theory. Flow patterns: • Velocity potential and stream function for source, sink, vortex and uniform stream. • Combination flows - Rankine Oval, cylinders, etc. • Multipoles - dipoles, quadropoles, images, etc. • Added mass, virtual mass, added moment of inertia of simple ship shaped hulls. • Lewis forms defining two-dimensional hull shapes. Laboratory: Wave Experiment, where the wavemaker in the towing tank is employed to produce regular wave for the physical understanding of basic wave elements such as encounter frequency, dispersion relation, wave group and potential flow assumptions. Part B; Systems with One and Two Degrees of Freedom : • Summary of systems with one degree of freedom • Two degrees of freedom systems in translation and/or rotation. Free motion and natural • frequencies. Forced (sinusoidal) motion, resonance and motion amplitudes. • Response of one degree of freedom systems to non-sinusoidal excitation. • Response Amplitude Operator (RAO), Fourier series representation, discrete frequency spectra. Wave Properties and Statistics • Encounter frequency: relationship between ship speed, heading and wave frequency (or number) in head and following waves. • Review of statistical methods; Probability density and distribution functions; Rayleigh and Gaussian distributions; Probability of exceedance; Mean, Mean Square and Significant values. • Introduction to random processes. Irregular seaway; Fourier transform; Wave energy spectra; Definition of standard wave spectra (Pierson-Moskowitz, ITTC, ISSC); Directionality and • spreading. System with One and Multiple Degrees of Freedom in Waves: • Equations of motion for heave, pitch and coupled heave and pitch in regular waves. Added mass, hydrodynamic damping and their evaluation. Generalisation to six degrees of freedom. • Relationships between excitation and response. RAOs; Response spectra, RMS values. Absolute and relative motions. • Equation of roll motion in regular waves. Roll control devices and active control. Laboratory: Roll Stabilisation experiment, a ship model in the towing tank is used to understand and record the fundamental aspects of free and forced roll motion and the influence of hydrodynamic roll damping and compare measurements to analytical predictions. Seakeeping Assignment, where the students perform a seakeeping analysis to select the best of two proposed designs based on performance with reference to severe responses (slamming, deck wetness and bow acceleration) in realistic waves – an application of what is learnt in lectures.

### Learning and Teaching

#### Teaching and learning methods

Description Teaching methods include • Lectures tutorials laboratory experiments • Learning activities include • Directed reading/independent learning • Example sheets for problem solving exercises • Experimentation • Report-writing (laboratory experiments; seakeeping assignment) • Application of hydrodynamics and seakeeping knowledge through the seakeeping assignment • Use of Ship Motions software for the seakeeping assignment • Intermediate quizzes with feedback

TypeHours
Revision26
Tutorial6
Supervised time in studio/workshop2
Follow-up work35
Lecture27
Preparation for scheduled sessions10
Total study time150

Resources and reading list. Available on blackboard

### Assessment

Quiz

#### Summative

MethodPercentage contribution
Assignment 15%
Examination  (120 minutes) 75%
Laboratory Report 10%

#### Repeat

MethodPercentage contribution
Examination  (120 minutes) 100%

#### Referral

MethodPercentage contribution
Examination  (120 minutes) 100%

#### Repeat Information

Repeat type: Internal & External