Presence of perforated members in ocean structures reduces the wavestructure interaction significantly; breakwaters with perforated members are classicalexamples of such kind. Detailed analyses to quantify the force reduction ocean structures encompassed with perforated covers are scarce in the literature. Present study is focused on the hydrodynamic response of perforated members under regular waves using numerical simulation; results are also validated with the experimental studies. Hydrodynamic responses of cylinders with and without perforated cover are estimated for different sea states. Force reduction, in the presence of perforated outer cover is quantified and validated with the existing experimental results. Based on the studies carried out, it is shown that the maximum reduction is about 14 %. Results of the numerical simulations compare well with that of the existing experimental results with the maximum error of about 6 %. © Springer India 2015. All rights reserved.

Srinivasan Chandrasekaran

Department of Ocean Engineering

N. Madhavi

Saravanakumar Sampath

FLUID DYNAMICS

Hydrodynamics

Numerical models

Ocean currents

Oceanography

CATIA

DIFFERENT SEA STATE

FORCE REDUCTIONS

Hydrodynamic response

Maximum error

PERFORATED MEMBERS

Regular waves

Wave-structure interaction

OCEAN STRUCTURES

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Force Reduction on Ocean Structures with Perforated Members

Advances in Structural Engineering: Mechanics, Volume One

Perforated piles are used in near-shore breakwaters for coastal protection and deep water platforms for oil exploration. Emerged and submerged perforated cylindrical structures reduce wave-structure interactions and scouring problems considerably, but their use on a floating structure is limited. Mathematical model is developed to introduce perforated walls in floating structures and method of solution is discussed. Eigenfunction expansion approach is used to derive velocity potentials based on which hydrodynamic forces on perforated cylinders are obtained. An example tension leg platform having perforated caissons is chosen; length of the perforated region and its location on tension leg platform are varied to determine their influence on its motion. For increase in perforation length, fluid-structure interaction reduces, causing decrease in surge and pitch responses. However, increase in perforated length in the lower part of column does not significantly increase these responses; heave remains relatively unaffected regardless of the length of perforation in the columns. © 2010 Taylor &amp; Francis.

Ships and Offshore Structures

Potential-flow-based numerical study for the response of floating offshore structures with perforated columns

An experimental investigations was carried out on a perforated circular cylinder (0.50m diameter) encircling an impermeable cylinder (0.05m diameter) at a constant water depth of 0.7m 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 experimental results of wave forces and the water surface fluctuations inside the perforated cylinder. © 2008 ASCE.

Journal of Waterway, Port, Coastal and Ocean Engineering

Hydrodynamics of a concentric twin perforated circular cylinder system

Diffraction of linear waves around a group of dual porous cylinders consisting of a thin and porous outer cylinder with an impermeable inner cylinder is investigated analytically based on the eigenfunction expansion method proposed by Spring and Monkmeyer [Spring BH, Monkmeyer PL. Interaction of plane waves with vertical cylinders. In: Proceedings 14th international coastal engineering conference. 1974. p. 1828-47] and further modified by Linton and Evans [Linton CM, Evans DV. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 1990;215:549-69]. The present formulation is an extension of the work of Wang and Ren [Wang KH, Ren X. Wave interaction with a concentric porous cylinder system. Ocean Engineering 1994;21(4):343-60], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. This paper aims at investigating the influence of multiple interactions between the cylinders in the group on the hydrodynamic wave forces, wave run-up and free-surface elevation in their vicinity. Further, the study focuses on the variation of the forces and run-up on the individual cylinders within the group compared to that on isolated cylinders. © 2008 Elsevier Ltd. All rights reserved.

Applied Ocean Research

Interaction of regular waves with a group of dual porous circular cylinders

The wave force on a seawater intake structure consisting of a perforated square caisson of 400 mmx400 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. © 2002 Elsevier Science Ltd. All rights reserved.

Journal	Data powered by TypesetAdvances in Structural Engineering: Mechanics, Volume One
Publisher	Data powered by TypesetSpringer India
Open Access	No