K. Vijayalakshmi

Bio: K. Vijayalakshmi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Caisson & Cylinder. The author has an hindex of 3, co-authored 6 publications receiving 70 citations.

Wave runup on a concentric twin perforated circular cylinder

Abstract: The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements.

Hydrodynamics of a Concentric Twin Perforated Circular Cylinder System

Abstract: An experimental investigations was carried out on a perforated circular cylinder ( 0.50 m diameter) encircling an impermeable cylinder ( 0.05 m diameter) at a constant water depth of 0.7 m for both regular and random waves in the wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras, India. The porosity of the outer cylinder was varied from 4.54 to 19.15% to study the influence of porosity on wave forces on and water surface fluctuations in and around the twin cylinder system. A numerical method is developed based on the boundary integral equation method along with a porous body boundary condition, where the porosity is modeled using the resistance coefficient f and added mass coefficient Ca for regular waves. The resistance coefficient increases with the increase in porosity and wave heights except for a porosity of 4.54%, whereas the added mass coefficient is almost zero. Porosity in the range of 10–15% can be recommended for the perforated cylinder based on the exper...

Wave forces on a seawater intake caisson

Abstract: The wave force on a seawater intake structure consisting of a perforated square caisson of 400 mm×400 mm size encircling a vertical suction pipe of 160-mm diameter is investigated using physical model studies. The porosity of caisson was varied from 1.6 to 16.9%. Regular and random waves of wide range of heights and periods were used. It is found that the force ratio (ratio of the force on perforated caisson to the force on caisson with zero percent porosity) reduces to an extent of up to 60% with increase in porosity of the caisson from 1.6 to 16.9%. The force ratio was found to increase with increase in relative wave height and reduces with increase in relative width. Multiple regression analysis of the measured data points was carried out and predictive equations for wave force ratios are obtained both for regular and random waves. The results of this investigation can be used in the hydrodynamic design of perforated caissons, which are widely used as seawater intake structures.

Short-crested wave interaction with a concentric porous cylindrical structure

Abstract: In this paper, theoretical study is carried out to investigate the general 3D short-crested wave interaction with a concentric two-cylinder system. The interior cylinder is impermeable and the exterior cylinder is thin in thickness and porous to protect the interior cylinder. Both cylinders are surface-piercing and bottom mounted. Analytical solution is derived based on the linear potential theory. The effects of the wide range wave parameters and structure configuration including porosity of the exterior cylinder and the annular spacing on the wave forces, surface elevations and the diffracted wave contours are examined.

Short-crested waves interaction with a concentric cylindrical structure with double-layered perforated walls

Abstract: This paper aims at extending the semi-analytical scaled boundary finite element method (SBFEM) to deal with the short-crested waves interaction with a surface-piercing concentric cylindrical structure, which consists of a solid inner cylinder and a coaxial double-layered perforated wall. The whole fluid domain is divided into three sub-domains including two bounded and one unbounded domains, and a variational principle formulation is used to derive the SBFEM equation in each sub-domain. Hankel functions and Bessel functions are chosen as the basis function for the solution of the unbounded and bounded domains, respectively. Although the structure adds a porous cylinder compared to that of Tao's work (2009) , the SBFEM also needs to discretize only the outermost porous cylinder with curved surface finite-elements and keeps the radial differential equation solved completely analytically. However, the unknown coefficient vectors for solving the SBFEM equations increase compared with that of Tao's work. Thus we re-derive the solving process for the SBFEM equations. The results of numerical verification show that the present method yields excellent results with only a few nodes and quick convergence. The major factors including wave parameters and structure configuration that affect the wave forces, surface elevations and the diffracted wave contours are examined.

Dynamic Analysis and Design of Offshore Structures

Abstract: This chapter deals with the evolution of platform and various types of offshore platforms and their structural action under different environmental loads. The newly evolved structural forms and their discrete characteristics are discussed in this chapter. This chapter also gives the reader a good understanding about the structural action of different forms in the offshore. An overview of the construction stages of offshore plants and their foundation systems is presented.

Uplift capacity prediction of suction caisson in clay using a hybrid intelligence method (GMDH-HS)

Abstract: Suction caissons are widely used for offshore facilities foundation or anchor system. They should be very stable and also to provide stability of main massive structures those are upon them. Suction caisson uplift capacity is the main issue to determine their stability. During recent years, many artificial intelligence (AI) methods such as artificial neural network (ANN), genetic programming (GP) and multivariate adaptive regression spline (MARS) have been used for suction caisson uplift capacity prediction. In this study, a novel hybrid intelligent method based on combination of group method of data handling (GMDH) and harmony search (HS) optimization method which is called GMDH-HS has been developed for suction caisson uplift capacity prediction. At first, the Mackey-Glass time series data were used for validation of developed method. The results of Mackey-Glass modeling were compared to conventional GMDH with two kinds of transfer function called GMDH1 and GMDH2. Five statistical indices such as coefficient of efficiency (CE), root mean square Error (RMSE), mean square relative error (MSRE), mean absolute percentage error (MAPE) and relative bias (RB) were used to evaluate performance of applied method. Then the GMDH-HS method has been used for suction caisson uplift capacity prediction. The 62 data set of laboratory measurements were collected from published literature that 51 sets used to train new developed method and the remaining data set used for testing. Not only the results of suction caisson uplift capacity prediction using GMDH-HS were evaluated with statistical indices, but also the results were compared to some artificial methods by previously works. The results indicated that performance of GMDH-HS was found more efficient when compared to other applied method in predicting the suction caisson uplift capacity.

Hydroelastic analysis of surface wave interaction with concentric porous and flexible cylinder systems

Abstract: The present study deals with the hydroelastic analysis of gravity wave interaction with concentric porous and flexible cylinder systems, in which the inner cylinder is rigid and the outer cylinder is porous and flexible. The problems are analyzed in finite water depth under the assumption of small amplitude water wave theory and structural response. The cylinder configurations in the present study are namely (a) surface-piercing truncated cylinders, (b) bottom-touching truncated cylinders and (c) complete submerged cylinders extended from free surface to bottom. As special cases of the concentric cylinder system, wave diffraction by (i) porous flexible cylinder and (ii) flexible floating cage with rigid bottom are analyzed. The scattering potentials are evaluated using Fourier–Bessel series expansion method and the least square approximation method. The convergence of the double series is tested numerically to determine the number of terms in the Fourier–Bessel series expansion. The effects of porosity and flexibility of the outer cylinder, in attenuating the hydrodynamic forces and dynamic overturning moments, are analyzed for various cylinder configurations and wave characteristics. A parametric study with respect to wave frequency, ratios of inner-to-outer cylinder radii, annular spacing between the two cylinders and porosities is done. In order to understand the flow distribution around the cylinders, contour plots are provided. The findings of the present study are likely to be of immense help in the design of various types of marine structures which can withstand the wave loads of varied nature in the marine environment. The theory can be easily extended to deal with a large class of problems associated with acoustic wave interaction with flexible porous structures.