Sriram Venkatachalam

In this paper, a new set of experiments on the focused wave (using the 2nd order wavemaker theory) and current interactions with cylinder is being carried out. In order to represent a uniform current in laboratory, cylinder is towed with a velocity opposite to the wave propagation directions. This paper discusses about the experimental setup and test cases that was released for the comparative study in the ISOPE 2020. In order to obtain good correlation with different runs, the repeatability of the experiments is confirmed by comparing the surface elevation measurements at the fixed wave gauge location near the wave paddle and uncertainty analysis was carried out. Different test cases with varying frequency bandwidth of the focusing waves, speed of the cylinder and the locations of focusing are investigated and will be reported in this paper. Further, a comparison for the dynamic pressure on cylinder is reported between experiments with wave and wave with uniform current.

The paper presents coupling between a mesh-based finite-element model for Boussinesq equations (FEBOUSS Agarwal et al., 2022) with a meshless local Petrov–Galerkin model for the Navier–Stokes equations (MLPG_R Agarwal et al., 2021) in 3D. Boussinesq equation models are widely used for simulating wave-propagation over large domains with uneven topography using a 2D surface mesh. Mesh-less models inherently capture large free-surface deformations and have shown promise in simulating wave-structure interaction, run-up and breaking phenomenon. The hybrid approach in this paper assumes a 3D MLPG_R sub-domain surrounded by the 2D mesh of FEBOUSS. The coupling interface in MLPG_R consists of relaxation zones that can be placed along multiple boundaries of the sub-domain for exchanging particle velocity from FEBOUSS. This hybrid model is therefore capable of simulating directional waves, that has not been reported previously. The paper first presents the procedure for calculating the depth-resolved velocities in 3D from the Boussinesq model. The resultant velocities are compared against theory, experiments and other models. The following sections present the coupling algorithm along a single and multiple coupling interfaces in MLPG_R. Validation results for this hybrid model are provided using surface elevation and velocity measurements for regular waves, including directional cases. In general, the results from the hybrid model are reported to have marginal over-prediction of peaks compared to purely MLPG_R simulation. Finally, the interaction of a vertical cylinder with direction regular wave is simulated using the 3D hybrid model.

This is the first paper to present a hybrid method coupling an 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. © 2014 Elsevier Inc.

The present study aims at generating the fully nonlinear waves based on Finite Element method (FEM) used by SRIRAM et al. (2006). The author simulated the nonlinear waves based on structured mesh by regenerating the mesh at each and every time step using the Mixed Eulerian and Lagrangian (MEL) scheme. In this paper, it has been extended to unstructured mesh. The mesh is adapted at each and every time step by using the spring analogy method instead of regenerating at every time step which makes the above method called as Semi- Arbitary Lagrangian and Eulerian (Semi-ALE/SALE). The simulation has been carried out in a numerical wave tank (NWT) with a surface piercing rectangular object. For such a situation, the diffraction by a surface piercing object becomes relevant in connection to breakwater studies where the primary interest is wave reflection and wave transmission. Regular waves and solitary waves are generated from one end of the tank. The nonlinear wave reflection and transmission characteristics reveals that the transmission is less for regular waves, while in the case of solitary waves the reflected energy is very small and the transmission is more.

The estimation of the sediment flux due to individual ship movement is necessary to identify adverse effects on the river banks in tidally-driven waterways. The separation of each wake event due to ship propagation from the tides is cumbersome. The present study focuses on the study of the ship waves on the sediment resuspension in intertidal waterways through a field survey. The time–frequency analysis proved to be an effective tool for separating the high-frequency ship waves from the tides. The ship-generated SSC was estimated by using the backscattering intensity from the acoustic sensors after proper calibration. The individual effect of each ship wake event on the sediment resuspension was estimated by filtering the ship-generated SSC from the total SSC by using a moving average filter. The overall contribution of the ship waves during the survey tenure was 24.66% with respect to the ambient SSC. The approximate amount of sediment flux by ship waves in a calendar year could be 1.46∗106g/m2. Finally, a new empirical equation to predict the sediment flux from the depth Froude number is proposed, which could be used in long-term analysis of SSC after proper calibration and validation.

The following sections are included: Introduction Tsunami Warning Detection of Tsunamis with Sea-Level Sensors Indian Tsunami Early Warning System (ITEWS) Experimental Studies Summary References.

Hydroelasticity is an important problem in the field of ocean engineering. It can be noted from most of the works published as well as theories proposed earlier that this particular problem was addressed based on the time independent/ frequency domain approach. In this paper, we propose a novel numerical method to address the fluid-structure interaction problem in time domain simulations. The hybrid numerical model proposed earlier for hydro-elasticity (Sriram and Ma, 2012) as well as for breaking waves (Sriram et al 2014) has been extended to study the problem of breaking wave-elastic structure interaction. The method involves strong coupling of Fully Nonlinear Potential Flow Theory (FNPT) and Navier Stokes (NS) equation using a moving overlapping zone in space and Runge kutta 2nd order with a predictor corrector scheme in time. The fluid structure interaction is achieved by a near strongly coupled partitioned procedure. The simulation was performed using Finite Element method (FEM) in the FNPT domain, Particle based method (Improved Meshless Local Petrov Galerkin based on Rankine source, IMPLG-R) in the NS domain and FEM for the structural dynamics part. The advantage of using this approach is due to high computational efficiency. The method has been applied to study the interaction between breaking waves and elastic wall.

Destruction of the structures in coastal areas due to an extreme coastal event like a tsunami necessitates the deeper understanding of flow behaviour to improve the design guidelines. The characteristics of inland propagating tsunami surge or bore consist of an initial aerated surge or bore tip followed by the gradual increase in water depth (quasi-steady flow phase). During the bore interaction, the structure initially experiences an impulsive pressure, bore pressure followed by quasi-static pressure (quasi-steady flow phase) depending on the ratio of the structure obstruction width to flow channel width (b/W), incoming bore Froude number (Fr), the shape of the structure, and the orientation of structure to the direction of flow. From field surveys and video observations during the 2004 Indian Ocean Tsunami and the 2011 Tohoku tsunami, the structure failure during the quasi-steady state of tsunami flow is found to be predominant. Also, most of the literature in the past focused on the interaction of bore on a single structure in which the flow channelling effect (b/W) is not considered. Thus, the present experimental study gives a detailed insight into the b/W and Fr effect in the force acting on the rectangular structure during the quasi-steady flow of tsunami-like events. To estimate the hydrodynamic force in the quasi-steady flow phase, we have adopted the hydrostatic force equation by incorporating bore height at the structure front (hf) and bore height at the structure back (hr). A simplified semi-analytical method is proposed based on conservation of mass and momentum to estimate the force on the rectangular structures. This approach of force estimation is showed to reasonably predict experimental force-time history. Since design guidelines use the hydrodynamic drag force equation for force estimation, the present study also provides the drag force coefficient (Cd) for b/W > 0.2 and Fr between 0.6 and 2. Along with the consideration of Fr and b/W, the study attempted to provide a closed-form set of equations to the quasi-static force, which helps designers with a convenient force determination method.

Tsunamis pose a substantial threat to coastal communities around the globe. To counter their effects, several hard and soft mitigation measures are applied, the choice of which essentially depends on regional expectations, historical experiences and economic capabilities. These countermeasures encompass hard measures to physically prevent tsunami impacts such as different types of seawalls or offshore breakwaters, as well as soft measures such as long-term tsunami hazard assessment, tsunami education, evacuation plans, early-warning systems or coastal afforestation. Whist hard countermeasures generally aim at reducing the inundation level and distance, soft countermeasures focus mainly on enhanced resilience and decreased vulnerability or nature-based wave impact mitigation. In this paper, the efficacy of hard countermeasures is evaluated through a comprehensive literature review. The recent large-scale tsunami events facilitate the assessment of performance characteristics of countermeasures and related damaging processes by in-situ observations. An overview and comparison of such damages and dependencies are given and new approaches for mitigating tsunami impacts are presented.

In the present paper, the hybrid numerical model (Sriram et al. (2014)) is used for the estimation of long wave run-up. The model is based on the strong coupling between the fully nonlinear potential flow theory (FNPT) at the far-field and Navier-Stokes (NS) equations in the nearshore. The simulations are carried out for the propagation and evolution of the tsunami-like waves, i.e., elongated single pulses having a realistic timescale. The model is validated from large scale experiments for the wave propagation as well as for run-up (Sriram et al., 2016). The numerical simulations are found to agree well with experiments. The model capability is shown for two different scenarios over a slope: (a) a rapidly rising tide including surging and spilling breaking and (b) undular bore formation and its plunging breaking on a beach. For the first case, the numerical model is also compared with the analytical estimates. The second case, undular bore breaking over a slope, shows the capability of the meshfree method and the requirements of the hybrid model. In many of the existing particle-based methods, dense distribution of particles is required to simulate the rapidly rising tide, which is not needed in the present model.