Showing papers by "Vallam Sundar published in 2009"

Wave-induced sloshing pressure in a liquid tank under irregular waves

Abstract: The sloshing pressures on the side wall and on the top cover plate of a tank partially filled with liquid and rigidly mounted on a barge in irregular waves are investigated through physical model tests. The barge was allowed to oscillate freely in the combined degrees of excitation, i.e. sway, heave, and roll. Four liquid fill levels with aspect ratios hs/l (where hs is the static liquid depth and l is the tank length) of 0.163, 0.325, 0.488, and 0.585 are considered for the present study. The effect of peak wave excitation frequencies on the pressure variation is studied in detail, the results of which are herein reported. It is observed that the impact pressure on the top panel of the tank is about 1.6 times the pressure observed on the side wall.

Quantification of phase shift in the simulation of shallow water waves

Abstract: Numerical simulation of nonlinear waves to reproduce the laboratory measurements has been a topic of great interest in the recent past. The results reported in the literature are mainly focused on qualitative comparison or on the relative errors between the numerical simulation and measurements in laboratory and hence lack in revealing the existence of phase shift in nonlinear wave simulation. In this paper, the simulation of nonlinear waves in mixed Eulerian and Lagrangian framework using finite element method (FEM) is investigated by applying two different velocity calculation methods viz, cubic spline and least squares (LS). The simulated wave surface elevation has been compared with the experimental measurements. The coherence analysis has been carried out using the wavelet transformation, which gives a better understanding between the numerical and the experimental results with respect to the time–frequency space, compared with the conventional Fourier transformation. It is observed that the application of cubic spline approach leads to a higher phase difference for steeper waves. The present study has shown that the phase difference exists at the higher modes rather than at the primary period. For waves with steepness (wave height/wave length) higher than 0.04, LS approach is found to be effective in capturing the higher-order frequency components in the event of nonlinearity. In addition, the comparison of numerical simulations with that from PIV measurements for the tests with solitary waves is also reported. Copyright © 2009 John Wiley & Sons, Ltd.

Wave-Induced Pressures and Forces on Deck Slabs near the Free Surface

Abstract: The hydrodynamic interaction of regular and random waves with a model offshore deck has been investigated in a wave flume. The hydrodynamic pressures and forces on the model as well as its reflection and transmission characteristics are investigated in a dimensionless form. The experiments were carried out for three different clearances (e) between the still water level and the subface of the model. In order to investigate the effects of relative clearance of the deck ( e/H in case of regular waves and e/ Hs in case of random waves), different wave steepnesses ( H/L in case of regular waves and Hs / Lp in case of random waves) were employed by varying wave height (H) and wavelength (L) . The effects of the wave steepness, relative clearance of the deck, relative length of the model ( B/L in case of regular waves and B/ Lp in case of random waves) on the pressures and forces on the deck slab are investigated with a well controlled experimental program. The variation of the pressures along the length of the...

Attenuation of Wave Energy by Double Chambered Breakwaters

Abstract: The hydrodynamic performance of a double chambered breakwater system formed by two wave screens placed on the seaward side of an impermeable vertical wall is investigated in detail through an experimental program The wave screens are made up of a series of horizontally placed circular elements at constant spacing so as to form horizontal slots of required porosity The experimental model consists of an impermeable vertical wall on the leeside of screen 1 and screen 2 with porosities of 231% and 91%, respectively The model was subjected to regular waves with normal wave incidence The change in reflection characteristics of the vertical wall as well as the dynamic pressures on it due to the presence and absence of wave screens are studied The chamber oscillations are also measured and reported In addition, efforts have been made to investigate the effect of the depth of submergence of the seaward side wave screen on the reflection characteristics of the wall For this purpose three different relative depth of submergence (d s /d=025, 050, 075) were adopted The details of the experimental set-up, procedure, results and discussion are presented in this paper

Role of vegetation on the attenuation of forces on structures due to Cnoidal waves

Abstract: The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, • The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. • The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%.