Sea ice floes dissipate the energy of steep ocean waves

A laboratory experimental model of an incident ocean wave interacting with an ice floe is used to validate the canonical, solitary floe version of contemporary theoretical models of wave attenuation in the ice-covered ocean. Amplitudes of waves transmitted by the floe are presented as functions of incident wave steepness for different incident wavelengths. The model is shown to predict the transmitted amplitudes accurately for low incident steepness but to overpredict the amplitudes by an increasing amount, as the incident wave becomes steeper. The proportion of incident wave energy dissipated by the floe in the experiments is shown to correlate with the agreement between the theoretical model and the experimental data, thus implying that wave-floe interactions increasingly dissipate wave energy as the incident wave becomes steeper. 

Sea ice floes dissipate the energy of steep ocean waves

Toffoli, A., Bennetts, L.G., Meylan, M.H., Cavaliere, C., Alberello, A., Elsnab, J., Monty,

J.P., 2015. Sea ice dissipate the energy of steep ocean waves. Geophys. Res. Lett., 42, doi: 10.1002/2015GL065937

An idealised experimental model of ocean surface wave transmission by an ice floe

Bennetts, L.G., Alberello, A., Meylan M.H., Cavaliere, C., Babanin A.V., Toffoli, A.,

2015. An idealised experimental model of ocean surface wave transmission by an ice  Ocean Modelling, In Press, doi: 10.1016/j.ocemod.2015.03.001

Rogue waves in opposing currents

When a perfectly stable wave or wave packet enters into a region of strong adverse current gradient (an accelerating opposing current or a decelerating following current), its dynamical behaviour is expected to change. As such, waves become higher and shorter. This increases wave steepness, which in turn enhances nonlinear properties. As a result, the interaction with the current amplifies wave modulation and accelerates nonlinear wave focusing. If enough space is allowed for wave evolution, rogue waves will appear eventually, even if the initial wave conditions are less prone

to extremes. An example of wave evolution on an adverse current in a laboratory facility is shown in Fig. 1.

FIGURE 1: Spatial evolution of an initially stable wave packet over an opposing current: no current U/cg = 0, with U the background current and cg the group velocity, (left panel); with current U/cg = 0.1 (right panel).

To verify the effect of an opposing current on wave dynamics, a theoretical study (Onorato et al. 2011) and laboratory experiments in three independent facilities (Toffoli et al. 2015) were carried out. Results demonstrate in a consistent and robust manner that opposing currents induce a modification of nonlinear dynamics (see Fig. 2). For random sea state, this means that a sharp and rapid transition from weakly to strongly non-Gaussian properties occurs. This is associated with a substantial increase in the probability of occurrence of rogue waves for both unidirectional and directional sea states (Toffoli et al. 2015), for which the occurrence of extreme and rogue waves is normally the least expected (see Figs. 2 and 3).

Figure 2: Effect on an opposing current on regular and irregular wave fields (unidirectional case)

FIGURE 3: Exceedance probability of wave crests for a directional sea state with spreading coefficient N = 50 (a narrow swell).

Coastal and Maritime Engineering

MRE80001

2015

Swinburne University of Technology

Faculty of Science, Engineering and Technology

Swinburne University of Technology in collaboration with Nortek will offer a unit on Coastal and Maritime Engineering (MRE80001) in Semester 2, 2015. This unit is presented by industry and academic experts and provides an in-depth overview of oceanic and coastal waves, hydrodynamics, ocean and coastal engineering applications and numerical modelling (a draft unit outline is presented below).

This subject is one of the five subjects in the Graduate Certificate in Port and Harbour Engineering offered by the Swinburne University. The subject can be taken as a single unit of study or as a part of the Graduate Certificate, the first formal Port Engineering qualification in Australia.

Other core subjects of the Graduate Certificate are Port and Harbour Engineering, Dredging Engineering, Port Access and Navigation, and Port Structural Design; the former two are offered in Semester 1, while the latter two are Semester 2 subjects. None of these five subjects is a pre-requisite to another, and the subjects can be taken separately:

http://www.swinburne.edu.au/study/courses/Graduate-Certificate-in-Engineering-(Port-and-Harbour)-GC-EPH/local

Students can formally enrol in the MRE80001 unit or in the Graduate Certificate in Engineering/Port and Harbour and complete the assignment for credits, or can choose to register and attend the seminars only. The assessment involves three short assignments, due throughout the second half of the semester.

Full flyer at: 

https://www.cubbyusercontent.com/pli/Coastal_and_Maritime_Eng_flyer_2015_SWIN_LOGO.pdf/_0e35eeaa9b73496997bc16c3011c3fa4

When:

A week of intensive seminars will be held on 14 – 18 September 2015 (36 hours).

Where:

The classes will be held at the Swinburne University of Technology, Hawthorn campus.

Cost:

Information on tuition fees for the Graduate Certificate can be found at the following link:

http://www.swinburne.edu.au/study/courses/Graduate-Certificate-in-Engineering-(Port-and-Harbour)-GC-EPH/local

For a single unit of study, fees can be found at the following link:

http://www.swinburne.edu.au/student-administration/fees/schedules.html

How to apply:

All applications are due by 24 August 2015

Application to enrol in Coastal and Maritime Engineering as a single unit of study:

This will provide you with recognition of enrolment in this unit. You would receive a Swinburne transcript with the respective grade for your assessment in this single unit of study. Successful completion of this unit gains 12.5 points credit towards the Swinburne’s Graduate Certificate of Engineering/Port and Harbour Engineering (50 credit points).

For admission, applicants should have completed a bachelor degree or diploma in engineering, or have relevant industry experience.

To enrol in Coastal and Maritime Engineering as a single unit of study or to enrol in the Graduate Certificate, follow the instructions here:

http://courses.swinburne.edu.au/courses/Graduate-Certificate-in-Engineering-%28Port-and-Harbour%29-C110/local

Seminar registration:

To attend the seminars without submitting any assessment (i.e. seminar only), complete and return the attached registration form with payment to the Finance Officer, Faculty of Engineering and Industrial Sciences (contact details are provided on the form).

Further Information

Enrolment / registration:

Faculty Office, Faculty of Science, Engineering and Technology

Telephone:   +61 3 9214 8372

Email:           engineering@swin.edu.au

For information about the content of the unit:

Dr Alessandro Toffoli, Faculty of Science, Engineering and Technology

Telephone:   +61 3 9214 5262

Email:          atoffoli@swin.edu.au

Or

Professor Alex Babanin, Faculty of Engineering and Industrial Sciences

Telephone:   +61 3 9214 8033

Email:           ababanin@swin.edu.au

Tentative detailed outline of MRE80001 (further changes can be expected)

Coastal and Maritime Engineering

MRE80001

Day 1

Introduction (1 hours)

·      Purpose and scope of Coastal and Maritime Engineering

·      Coastal diversity

·      Wave types

Linear Wave Theory (4 hours)

·               Mathematical problem

·               Boundary conditions

·               Linearization

·               Dispersion relation

·               Properties of surface elevation

·               Regular and Irregular waves

·               Wave kinematics

·                Orbital motion

·                Phase velocity

·                Group velocity

Nearshore wave transformation (2 hours)

·               Refraction and long-shore current

·               Diffraction

·               Reflection

·               Shoaling

·               Breaking

Nonlinear waves (1) (1 hours) 

·               Nonlinear terms

·               Second-order theory

·               Effects on surface elevation

Day 2

Nonlinear waves (2) (1 hours) 

·               Effects on wave orbital motion

·               Shallow water waves

Long waves (2 hour)

·               Infragravity waves

·               Storm Surges

·               Seiches

·               Tides

Wave spectrum (1 hours)

·               Definition of wave spectrum

·               Spectral parameters

·               Model spectra

·                1D

·                2D

Wave measurements (2 hours)

·               Buoys

·               Tidal gauges

·               Downlooking lasers

·               Pressure sensors

·               Acoustic Doppler Current Profiler (ADCP)

·               Anemometers

·               Remote sensing

Analysis of wave records (1 hours)

·               Time series analysis

·               Spectral analysis

Day 3

Analysis of wave records (2 hours)

·               Wave statistics

·                Short term stats

·                Long term stats

Wave impacts on coastal and ocean engineering structures (2 hours)

·               Design sea state

·               Wave forces

·               Run-ups

·               Marine Renewable Energy

Hydrodynamics and wave modelling (1) (2 hours)

·               Introduction to MIKE21

·               Theoretical concept

·               Numerical schemes

Laboratory demonstration (2 hours)

·               Wave flume

·               Wave properties

·               Wave breaking

Day 4

Hydrodynamics and wave modelling (2)   (8 hours)

·               Set up of the hydrodynamics and wave modules for Port Phillip Bay

·               Simulations of wave characteristics:

o   Water level

o   Surface waves

o   Currents

Day 5

Hydrodynamics and wave modelling (3)   (3 hours)

·               Exercises

Data Analysis (2 hours)

·               Computer aided analysis

·                Time domain analysis

·                Spectral domain analysis

         

Seminar Registration Form

Please do not use this form if you wish to enrol in the subject for credit.

Seminar Details

Subject:                   MRE80001 Coastal and Maritime Engineering Dates:                       14-18 September 2015 Registration fee:      $2,900 GST Excl.

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Caroline Ditchburn, Research Centre Co-Ordinator (COEST)

Swinburne University of Technology

Faculty of Science, Engineering and Technology (COEST)

PO Box 218 Hawthorn, Victoria 3122, Australia

H39, Room 713c, Ph +61 3 9214 5722, cditchburn@swin.edu.au

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