V. Sriram

Improved MLPG_R method for simulating 2D interaction between violent waves and elastic structures

Interaction between violent water waves and structures is of a major concern and one of the important issues that has not been well understood in marine engineering. This paper will present first attempt to extend the Meshless Local Petrov Galerkin method with Rankine source solution (MLPG_R) for studying such interaction, which solves the Navier-Stokes equations for water waves and the elastic vibration equations for structures under wave impact. The MLPG_R method has been applied successfully to modeling various violent water waves and their interaction with rigid structures in our previous publications. To make the method robust for modeling wave elastic-structure interaction (hydroelasticity) problems concerned here, a near-strongly coupled and partitioned procedure is proposed to deal with coupling between violent waves and dynamics of structures. In addition, a novel approach is adopted to estimate pressure gradient when updating velocities and positions of fluid particles, leading to a relatively smoother pressure time history that is crucial for success in simulating problems about wave-structure interaction. The developed method is used to model several cases, covering a range from small wave to violent waves. Numerical results for them are compared with those obtained from other methods and from experiments in literature. Reasonable good agreement between them is achieved.

NWF; propagation of tsunami and its interaction with continental shelf and vertical wall

In this article, tsunamis represented as solitary waves was simulated using the fully nonlinear free surface waves based on Finite Element method developed by Sriram et al. (2006). The split up of solitary wave while it propagates over the uneven bottom topography is successfully established. Wave transmission and reflection over a vertical step introduced in the bottom topography is in good agreement with the experimental results from Seabra-Santos et al. (1987). The wave transformation over a continental shelf with different smooth slopes reveals that the solitary wave reflection increases while the continental slope varies from flat to steep. The interaction of the solitary wave with a vertical wall for different wave steepness has been analysed. The reflected shape of the profile is in good agreement with the observation made by Fenton and Rienecker (1982) and an increase in wave celerity is observed.

A hybrid method for modelling two dimensional non-breaking and breaking waves

This is the first paper to present a hybrid method coupling a Improved Meshless Local Petrov Galerkin method with Rankine source solution (IMLPG_R) based on the Navier Stokes (NS) equations, with a finite element method (FEM) based on the fully nonlinear potential flow theory (FNPT) in order to efficiently simulate the violent waves and their interaction with marine structures. The two models are strongly coupled in space and time domains using a moving overlapping zone, wherein the information from both the solvers is exchanged. In the time domain, the Runge-Kutta 2nd order method is nested with a predictor-corrector scheme. In the space domain, numerical techniques including ‘Feeding Particles’ and two-layer particle interpolation with relaxation coefficients are introduced to achieve the robust coupling of the two models. The properties and behaviours of the new hybrid model are tested by modelling a regular wave, solitary wave and Cnoidal wave including breaking and overtopping. It is validated by comparing the results of the method with analytical solutions, results from other methods and experimental data. The paper demonstrates that the method can produce satisfactory results but uses much less computational time compared with a method based on the full NS model.

Characterization of breaking wave impact on vertical wall with recurve

Abstract Large-scale experiments were conducted at the Coastal Research Centre (FZK), Germany to characterize the mechanics and characteristics of impact pressures due to breaking waves on a vertical sea wall with a recurve. The characteristics and distribution of impact pressure are found to be greatly depending on the breaking case, so the breaking wave impact is classified into different case like the slow breaking wave, breaking with small air trap and breaking wave with large air trap. When a small air is entrained between the breaking waves and the structure, there is a significant increase in impact pressures. However, if the entrapped air volume increases, impact pressure reduces because of the breaking of waves into smaller water droplets. The impact pressure variation at the vertical wall and recurve along the vertical direction are reported in different breaking cases from the experimental results and the relation between maximum impact pressures with respect to rise time is described by a power equation.

EXPERIMENTAL AND NUMERICAL STUDIES ON THE TSUNAMI WAVE CHARACTERISTICS

ABSTRACT The devastating effects of the great Indian ocean tsunami has forced researchers in focusing their attention more vigorously on understanding the behaviour during its propagation and its effects on structures. This can obviously be accomplished through numerical and physical model studies or combination of both. The characteristics of a tsunami wave can approximately be same as that of a solitary wave which is basically a shallow water wave. Hence, the studies on the characteristics of shallow water waves have become an emerging topic of interest. An important aspect of a mitigation effort is to predict the tsunami wave kinematics. A combination of experimental and numerical simulation of tsunami represented by the solitary wave was studied and their comparison is discussed in this paper. The details of the numerical approach, methodology, instrumentation and measurement adopted for the present study are reported. The disagreement of the experimental simulation of solitary wave elevations with that of numerical simulation has been addressed and the possible discrepancies are overcome, the procedure of which are briefly discussed. The dynamics of the tsunami wave propagation over an uneven topography is studied using the developed numerical model.

Propagation and breaking characteristics of solitons and N-wave in fresh water and brine

ABSTRACT In this paper, the results of the study on the wave propagation and breaking of solitons and N-waves in fresh water and brine are reported. The experiments were performed in the twin flume facility at the Franzius Institute, Leibniz University of Hannover. Brine from Dead Sea was used for the study. The objective of the experimental study was to determine the flood safety levels along the banks of the Dead Sea and to arrive at the empirical equations for run-up. A weakly coupled numerical model based on the fully nonlinear potential flow and Navier–Stokes equation was used to validate the experimental results. The proposed numerical model is in good agreement with the present experimental results and the available analytical solutions for run-up estimation. The breaking N-waves were found to have a reduced run-up when compared to breaking solitons. The paper shows that the long wave propagation and run-up in both brine and water has similar characteristics.