PUBLIC LECTURE : Simulating Long Waves in a Harbour 3D Physical Model Using Short Wave Spectra

• Report rights infringement
• published: 23 Jan 2016
• views: 184

PUBLIC LECTURE : Simulating Long Waves in a Harbour 3D Physical Model Using Short Wave Spectra & Saving $20 Million on a Breakwater Repair Design Using Physical & Numerical Modelling Eng. Indra Jayewardene (Senior Engineer at Manly Hydraulics Laboratory, Public Works New South Wales (NSW) Presenter: He completed his undergraduate engineering degree in Sri Lanka (Peradeniya) and obtained his master’s degree in systems and coastal engineering from the University of Florida Gainesville. He has been with Manly Hydraulics Lab for 25 years. He is a senior engineer at Manly Hydraulics Laboratory, Public Works New South Wales (NSW) with 35 years of experience in Sri Lanka, Denmark, Maldives and Australia in coastal and ocean engineering data collection and analysis, numerical and physical modelling of coastal processes. His interest is in wave and structure interactions. He has authored over 35 publications in international journals and proceedings. He is a past chairperson of the Coastal, Ocean and Port Engineering Panel (COPEP) of NSW, Engineers Australia. He has an advanced diver license and has spent over four decades diving on the coastlines of Sri Lanka, Maldives and Australia. Abstracts:  Simulating Long Waves in a Harbour 3D Physical Model Using Short Wave Spectra This paper presents examples of field data of extreme seiche waves measured at Coffs Harbour by MHL and describes the generation and measuring methodology to detect and reduce seiche (long wave) agitation in the Coffs Harbour boat ramp using a 3D physical model. The paper also discusses the techniques in investigating a short wave problem of stability in the same model where a long wave is simulated. Waves offshore of Coffs Harbour at 80m depth have been recorded by MHL for a period of over 30 years. Long waves have been simultaneously measured in the harbour over a period of a decade. These data enabled the model to be verified on two dates (4/6/12, 5/9/14) when high long waves were recorded at the boat ramp harbour under storm and non-storm conditions. Long waves are generated in harbours due to group bounded long wave and surf beat or edge waves. The paper presents methodologies of generating long waves both numerically and by using physical models and discusses the advantages and disadvantages of these generation techniques. Numerical modelling carried out using long period regular waves in a previous investigation predicted reductions up to 50% due to change of planform of the boat ramp harbour where an area next to the boat ramp was excavated and roughness elements introduced to dampen long periods. The 3D physical model simulated a 25% decrease in the long wave energy in the boat ramp when a suitable change in the planform was made. A 3D undistorted model of scale 1:58 was used in the investigation. The presentation also provides a theoretical basis for long wave generation at a harbor entrance. Keywords: Seiche, Group Bounded Long Waves, Surf Beat, Planform.  Saving $20 Million on a Breakwater Repair Design Using Physical and Numerical Modelling The Coffs Harbour East Breakwater is arguably the most exposed breakwater in NSW. Manly Hydraulics Laboratory (MHL) has been involved in the condition assessment of the 68 breakwaters in NSW for over two decades. When private consultants provided designs for the repair of this breakwater MHL was requested to assess the design. MHL’s repair strategy resulted in a $20 million saving to government which was acknowledged in the hansard. The presentation will provides details of the modelling leading to the redesign of the breakwater repair strategy and provides data on storms and damage recorded after repair. Keywords: 100 year return period, Wave groups, Primary Armour Stability, Historical Storms Involvements of Local projects in Sri Lanka A few projects whilst working for the Coast Conservation Department and LHI (1) Deployment of the first Wave data Buoy in SL and the first directional wave data Buoy, including many others in Colombo, Galle, Tangalle, and Trincomalee. Also in the Maldives. - 1981-1990-Involved in the deployment ,diving ,data collection and analysis (2) Fieldwork relating to sediment transport analysis from the Kelani river using isotope tracers. (3) Data collection,diving and analysis for the proposed coal terminal in Trincomalee for Alex Macknight Australia (4) Projects such as the physical modeling of World Bank funded development of the Galle harbour (5) Physical modeling of the proposed developments for Colombo harbour (6) Physical modeling of proposed offshore breakwaters at Negombo (7) Modeling ship movement for the Beruwala fishery harbour development. * * * *