Andrew Cornett

EXPERIMENTAL INVESTIGATION OF TSUNAMI IMPACT ON FREE STANDING STRUCTURES

As tsunami waves propagate towards the shoreline, they break where the water depth is approximately equal to the incident wave height. Following breaking, waves run up the shore in form of a hydraulic bore. Video footage of the 26 December 2004 Indian Ocean Tsunami shows that, upon reaching the shoreline, tsunami waves broke and transformed into a hydraulic bore that propagated onshore with considerably high velocity. However, mechanisms of hydraulic bore impact on structures are not yet well understood. Analogies between a tsunami-induced hydraulic bore and a dam-break induced wave have been previously demonstrated and published by various researchers. In order to advance the existing understanding of the complex interaction between hydraulic forces and the impacted structures, an experimental approach was taken where a dam-break induced flow, generated by the fast opening of a gate, impacted various free standing structures of different shapes located downstream of the gate. The pressures exerted on the upstream and lateral sides of a cylindrical structure, together with the bore height and the flow velocities in the flume were measured. In addition, the time history of the total force exerted on the cylindrical structure was also recorded. For the square structure, local forces on the upstream side were recorded. The effects of upstream obstacles and flow constrictions on flow velocities and on local forces exerted on a square structure were also investigated. In addition, to further understand the impact of debris during tsunami-induced flooding, wooden logs were added to the bore in order to act as water-borne missiles, while the structures reaction was measured.

Experimental Modeling of Extreme Hydrodynamic Forces on Structural Models

This paper presents the results of a comprehensive experimental program focused on the impact of extreme hydrodynamic forces on structural models generated by a turbulent hydraulic bore. The parameters investigated include: (1) bore depth-time history; (2) initial flume-bed conditions (dry bed versus wet); and (3) damping effect of mitigation walls on the hydrodynamic forces. At impact, the maximum inundation (bore) depths varied between 250 mm and 450 mm and the bore front velocity ranged from 2.6 m/s to 5.0 m/s. High-speed video recordings of the bore-structural model interaction were captured simultaneously with the base shear force-, pressure-, base overturning moment-, and top lateral displacement-time histories experienced by the structural models. Three force components were identified in the bore-induced force-time histories: impulsive, run-up (transient hydrodynamic force), and quasi-steady hydrodynamic. The impulsive or run-up force was the maximum force component experienced by the structural models under initial dry-bed flume conditions; while for the initial wet-bed flume condition, the run-up force component was the maximum force. The effect of 100 mm and 150 mm low-height mitigation walls inclined at angles of 45° or 90°, which were installed at distances of 305 mm or 915 mm upstream from the structural model, was also investigated. The angle of inclination of the mitigation walls, its location relative to the structural model, and its cross-sectional shape all influence the base shear force- and base overturning moment-time histories. The base shear forces in the direction of the flow measured during experimental testing were greater than those estimated using the Federal Emergency Management Agency (FEMA) document P646, while the Structural Design Method of Buildings for Tsunami Resistance (SMBTR) overestimated the base shear forces.

WAVE STRESSES ON RUBBLE MOUND ARMOUR

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

DAMAGE ANALYSIS FOR RUBBLE-MOUND BREAKWATERS

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Inventory of Canada’s Offshore Wave Energy Resources

Global warming, the depletion of conventional energy reserves and the rising cost of electricity generation have sparked renewed interest in renewable wave energy within Canada and internationally. Significant advances in wave energy converters have been made in recent years, and there is a growing realization in many countries, particularly those in Europe, that these technologies will be ready for large scale deployments within the next five to ten years (ABP, 2004). Despite these recent developments, very little effort has been directed to quantifying and mapping wave energy resources in Canada in the past. This paper presents results from a recent study in which the wave energy resource in Canada’s Pacific and Atlantic waters is quantified by analysing a large quantity of data obtained from four sources: direct wave measurements; two wind-wave hindcasts of the North Atlantic; and a single hindcast of the Northeast Pacific. Each data source is described and the methods used to analyse the data sets are explained in detail. The derived wave power estimates, including their seasonal and spatial variability, are presented and discussed. Results obtained from the direct measurements and the wind-wave hindcasts are also compared. The paper also includes a review of the theoretical background required to estimate wave energy. The waters off Canada’s Pacific and Atlantic coasts are endowed with rich wave energy resources. The results presented here define the scale of these resources, as well as their significant spatial and seasonal variations.Copyright

Appraisal of the IEC Technical Specification for Assessment of Wave Energy Resources

This article describes and presents results from research focused on appraising the new technical specification (TS) for the assessment of wave energy resources developed by technical committee 114 of the International Electro-technical Commission (IEC-TC-114). The new IEC TS is appraised through an extensive pilot application to the waters off the west coast of Vancouver Island, British Columbia, Canada. A series of wave models are developed and used to simulate the wave conditions and estimate the wave energy resource over the study area. The accuracy of the various resource estimates derived from the model outputs is assessed through comparison with measurements from a directional wave buoy. Furthermore, sensitivity analyses are conducted to determine the main sources of error and uncertainty impacting the precision of resource assessments obtained following the IEC methodology. Preliminary results indicate that the IEC TS can be applied to the estimation of wave energy resources with a reasonable level of effort and accuracy.Copyright

WAVE-IN-DECK LOADS FOR AN INTRICATE PILE-SUPPORTED PIER AND VARIATION WITH DECK CLEARANCE

Many deck structures are located at elevations low enough to be impacted by large waves. However, due to the highly complex and impulsive nature of the interactions between wave crests and intricate deck structures, establishing reliable estimates of extreme pressures and forces for use in design remains challenging. In this paper, results from an extensive set of three-dimensional scale model tests conducted to support the design of a large pile-supported pier (or jetty) are presented and discussed. Relationships between maximum wave-in-deck loads and the deck clearance (air gap) are presented and discussed. Results from numerical simulations of the wave-structure interaction process obtained using the three-dimensional CFD software FLOW-3D® are also presented and discussed. Finally, some initial comparisons between the numerical and physical modelling are also included. This paper provides new insights concerning the character and magnitude of the hydrodynamic pressures and loads exerted on intricate pile-supported deck structures due to impact by non-linear shallow-water waves, and the relationships between the hydrodynamic forcing and the deck clearance or air gap.Copyright

Field and numerical investigations of the morpho-hydrodynamic processes of the tidal inlet at Shippagan Gully, New Brunswick, Canada

ABSTRACT This paper presents the result of a multiyear study consisting of field measurements and numerical modeling of a highly dynamic tidal inlet located on the west side of the Gulf of Saint Lawrence near Le Goulet, New Brunswick, Canada. Due to a lack of human intervention in the past few decades, natural processes have taken hold of this tidal inlet and large volumes of sediment have been deposited within the inlet. The Shippagan Gully inlet transects the Acadian Peninsula and is therefore subject to tidal forcing from both ends. An appreciable phase lag present in the two open ocean boundaries results in ebb flows through Shippagan Gully, which regularly exceed 2 m/s, to be twice as strong as the flood flows. This flow imbalance along with a long history of human intervention has created a complex and highly dynamic tidal inlet. The purpose of the study was to develop a numerical model of the hydrodynamic and morphological processes that occur at Shippagan Gully and to use the model to assess alternative engineering measures that could be implemented to promote a safe and navigable channel through the inlet.

Optimization of Rock Berms for Pipeline Stabilization Subject to Intense Hydrodynamic Forcing

This article describes a comprehensive study in which 2D and 3D physical modelling at 1:40 scale was used to optimize the design and validate the performance of dynamically stable rock berms to be used for stabilizing several large pipelines traversing water depths from 5m to 65m and potentially exposed to large waves and strong currents generated by intense tropical cyclones. For added realism, all of the model rock berms were constructed using a scaled simulation of rock installation by fall pipe vessel to be used in the field. Special attention was also given to simulating the self-stability of the model pipeline segments, including special end constraints designed to mimic the behaviour of a continuous pipeline. A large data set concerning the behaviour of dynamically reshaping rock berms in a range of water depths under intense hydrodynamic forcing due to three-dimensional waves and currents was produced and used to develop efficient and cost-effective rock berm designs for all depth zones.Copyright

EXPERIMENTAL STUDY OF STRUCTURES IMPACTED BY SIMULATED TSUNAMI BORE

acceptance number: p0091 PAPER TITLE: Experimental Study of Structures Impacted by Simulated Tsunami Bore 1 Author: Al-Faesly, Taofiq 2 Author: Nistor, Ioan 3 Author: Palermo, Dan 4 Author: Cornett, Andrew Physical modeling Tsunami forces Tsunami Bore Large scale tests Tsunami mitigation walls Tsunami resistant buildings Coastal structures