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.

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.

This paper discusses the possibility to study propagation, shoaling and run-up of these waves over a slope in a 300-meter long large wave flume (GWK), Hannover. For this purpose long bell-shaped solitary waves (elongated solitons) of different amplitude and the same period of 30 s are generated. Experimental data of long wave propagation in the flume are compared with numerical simulations performed within the fully nonlinear potential flow theory and KdV equations. Shoaling and run-up of waves on different mild slopes is studied hypothetically using nonlinear shallow water theory. Conclusions about the feasibility of using large scale experimental facility (GWK) to study tsunami wave propagation and run-up are made.

The nonlinear viscous flow generated from forced heaving oscillation of 2D floating body in calm water is carried out numerically using Improved Meshless Local Petrov-Galerkin (IMLPGR) method based on Rankine Source function. In the present particle-based method, the gradient calculation has been improved using ghost particle method. However, for estimating pressure, only single layer of the boundary particles are used. This is the first paper to extend the application of the IMLPGR for heave oscillations of the floating body. Simulations are carried out for vertical oscillation of rectangular shaped mono hull and twin hull. Hydrodynamics of these hulls for various amplitude and frequency of oscillations are performed and the numerical results agree well with existing literature results.

Failure of structures during extreme coastal flood events like a tsunami is common due to inadequate structural design, resulting in substantial material loss. Nevertheless, improvements in the design could reduce the global structural failure. Although many studies developed force equations for non-overtopping structures, many critical and non-critical structures still exist along coastlines with low heights. In this study, we investigate the effect of flow overtopping in the case of low-rise structures, typically representing a residential building, using our in-house CFD solver IITM-RANS3D. The numerical performance of IITM-RANS3D for violent impact and over-topping scenarios is first benchmarked against the experiments of Kleefsman et al. [1], wherein a comparison with OpenFOAM is also presented. After validation, structures of different heights are tested with the dam-break bore to replicate the tsunami bore. The flow and force characteristics are compared with the non-overtopping condition to understand the flow overtopping effect. The results presented herein indicate that the horizontal force on the structure and the bore height at the structure front decreases with a decrease in structure height.

Jackets are structures used in the offshore industry as a bottom supported platform for oil and gas production. The jackets have to be built in order to withstand the harsh sea environment. Such designs demand in depth analysis to predict the loads acting on the structure and its response. Depending on the sea states in which the structure needs to be installed, breaking load can be important. Estimation of breaking load for single cylinder exists in literature, since the breaking load on the jacket structure needs a lot more clarity. The aim of this paper is to estimate the impact force on a model jacket using Duhamel integral, which was not explored before. The impact load so far analyzed was compared with theoretical explanations given by Goda, et al. (1966), Wienke and Oumeraci (2005). The scope of the study is limited to plunging type of breakers. Five loading cases include wave breaking at far-front of a structure, in front of structure, on the front leg, on the rear leg and a non-breaking case was considered.

The simulation of interaction of nonlinear waves with structures has been investigated by several investigators adopting Boundary element Method (BEM) and Finite Element Method (FEM). In handling complex geometries using FEM, simulation with unstructured mesh is required. The two options that are available in handling unstructured mesh are: regenerating the mesh for each time step, requiring a higher computational cost and the mesh moving procedure widely used in solid mechanics. In this paper, the application of two different spring analogies (Vertex and Segment methods) on the simulation of nonlinear free surface waves and its interaction with a submerged structure is reported. The numerical method has been extended to generate solitary waves, the results of which have been compared with laboratory tests that include the wave kinematics using PIV measurements. Copyright © 2009 by The International Society of Offshore and Polar Engineers (ISOPE).

This paper presents a 2D/3D hybrid numerical model for studying the interaction of non-breaking waves with cylindrical structure. The work combines the strengths of mesh-based and particle-based methods, where the wave propagation is solved using 2D mesh-based potential theory model and the interaction with the structure is solved using 3D particle-based Navier-Stokes model. The paper presents the formulation of the two models and the weak-coupling methodology, along with recent improvements in the 3D MLPG R (Mesh-less Petrov-Galerkin based on Rankine source solution) particle based method. The numerical results from interaction of fixed cylinder with solitary and focussed waves are compared with experimental data. The work demonstrates a significant reduction in simulation time for wave-structure interaction problems achieved using this hybrid approach without compromising on accuracy.

Debris generated during extreme events like the tsunami can impose substantial impact loading on structures closer in the coastal zone. Majority of design codes do not quantify the impact forces close to reality owing to uncertainties in defining the wave characteristics and a lack of knowledge in understanding the underlying physical processes. The present study focuses on the measurement of forces which a coastal structure would encounter due to the impact of debris in motion during such an extreme event. The study herein focuses the motion of the debris due to undular bores. 1:20 scaled model of structure and the debris were used. Experiments were conducted in a wave flume 72.5 m long and 2 m wide. A beach slope of 1:30 is laid to replicate the coastal zone. By varying the wave heights and time periods, different types of waves such as elongated single pulse waves, symmetrical N waves and unsymmetrical N waves were generated replicating the characteristics of a tsunami as close as possible. The impact tests were conducted using box shaped smart devices as debris of weight 4.62 kg, 5.82 kg and 7.02 kg. The debris is attached with an accelerometer for measuring the impact acceleration. In order to have a better understanding of the behavior of debris during the impact, a camera at a speed of 120 fps is operated. The force acting on the structure is measured with a load cell. The forces due to the velocity of the debris and the mass is compared with the force measured using load cell. The details of the testing facility, model parameters, test set-up, test procedure, analysis of results and discussion are presented in the paper.

This paper presents very long, i.e. real tsunami-like wave generation in a large scale wave flume using a piston type wave maker. Waves of periods between 30 s and more than 100 s were generated at 1 m water depth using two different approaches: (i) deriving the wave board motion directly by integration of the water surface elevation, composed of a different number of solitons (sech2 waves) and (ii) using an iterative self correcting method (SCM). The importance of very long wave generation instead of solitary waves and the necessity for long testing facilities is discussed and results from GWK experiments are presented for single pulses (elongated solitons), N-waves and real tsunami records, either approximated as a combination of solitons or applying the SCM to the time series directly.