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

Fully nonlinear axisymmetric viscous flow due to heave oscillation of a surface-piercing vertical cylinder is analyzed using a finite-difference method based on curvilinear coordinates. Of significance to numerical modeling is the present finding that the free-slip condition used to model the movement of the contact line affects neither the overall flow nor the hydrodynamic pressure force acting on vertical cylinder. The viscous-flow results are compared with fully nonlinear inviscid-flow results, which are obtained using a mixed Eulerian-Lagrangian formulation, to contrast the effects of viscosity on the flow field, hydrodynamic force, and radiating surface waves. New results are presented for a range of parameters to illustrate physical mechanisms of the inception and evolution of vertical structures due to body motion in a free surface and their effects on the hydrodynamic force.Fully nonlinear axisymmetric viscous flow due to heave oscillation of a surface-piercing vertical cylinder is analyzed using a finite-difference method based on curvilinear coordinates. Of significance to numerical modeling is the present finding that the free-slip condition used to model the movement of the contact line affects neither the overall flow nor the hydrodynamic pressure force acting on vertical cylinder. The viscous-flow results are compared with fully nonlinear inviscid-flow results, which are obtained using a mixed Eulerian-Lagrangian formulation, to contrast the effects of viscosity on the flow field, hydrodynamic force, and radiating surface waves. New results are presented for a range of parameters to illustrate physical mechanisms of the inception and evolution of vertical structures due to body motion in a free surface and their effects on the hydrodynamic force.

Department of Ocean Engineering

Journal of Engineering Mechanics

Radiation hydrodynamics of floating vertical cylinder in viscous fluid

Design of a propeller for Florida Atlantic University's Ocean Explorer (OEX) series autonomous underwater vehicle (AUV) is presented. The primary requirement of the design is that the vehicle achieve a steady forward speed of 5 [knots] using a direct-drive motor limited by a torque of 4 [N-m] at 1000 rpm. The thrust required to propel the vehicle at steady 5 [knots] was estimated to be ≈100 [N]. The estimation takes into account, empirically, the effects of hull-propeller interactions on flow into the propeller and vehicle drag. While an elaborate hydrodynamics analysis is envisaged for the design of AUV propellers in the future, a blade element method is used in the present design. Assuming a functional form of loading curve and radial variation of chord together with the blade-element method, a three-bladed propeller of diameter 34 [cm] and based on NACA 66-221 sections is designed. Sea trials are planned to evaluate the performance of the propeller.

World University root node

Oceans Conference Record (IEEE)

Design of AUV propeller based on a blade element method

Effects of sea floor and surface waves on the dynamics of autonomous underwater vehicle (AUV) are examined. A three-dimensional boundary integral method is developed for analyzing the hydrodynamic interaction between the underwater vehicle and sea floor, while a two-dimensional finite-difference method for the interaction between surface waves and the underwater vehicle. Results presented in this paper show that the suction force of the sea floor on the AUV is important when the body is within a height of one body length above the floor. Presence of surface waves on the other hand could exert large forces on the vehicle, thus demonstrating the need for efficient control surfaces and controller algorithms to enhance the performance of AUVs in shallow waters.

AUV motion in a wave field

Nonlinear axisymmetric viscous and inviscid solutions corresponding to the heave oscillation of a submerged vertical cylinder are presented. The fully nonlinear free-surface flow problem is solved using the finite-difference method based on curvilinear coordinates. A primitive-variables based fractional-step formulation is used for the analysis of viscous flow, and a mixed Eulerian-Lagrangian formulation for that of inviscid flow. New results obtained for a range of amplitudes and frequencies of body oscillation and mean depths of body submergence demonstrate the effects of a free surface on the dynamics of body-generated vortices and on the vortical component of hydrodynamic force acting on the body. The results indicate the occurrence of negative added mass at intermediate frequency when the submergence of the cylinder is small. Force calculations reaffirm that the effect of viscosity on hydrodynamic forces is of significance at low and intermediate frequencies.

International Journal of Offshore and Polar Engineering

Heave Oscillations of a Submerged Vertical Cylinder in a Viscous Fluid

Nonlinear interaction between surface waves and a submerged slender body is investigated. In the simulation, the incident waves are generated by a paddle type wavemaker. The fully-nonlinear, viscous, wave-body interaction problem is solved using a boundary-fitted coordinates based finite-difference method. Results are obtained for a range of parameters, with particular emphasis on that of small body-submergence and large-amplitude incident waves. In such highly-nonlinear cases, generation of breaking waves and strong free-surface vorticity layers are observed. Time-averaged hydrodynamic force reveal a negative drift force when the body is close to the free surface. Effect of wave motion on the transport of vortical structures is found to be significant in the presence of long incident waves.

Proceedings of the International Offshore and Polar Engineering Conference

Nonlinear diffraction of waves over a submerged body in a real fluid

Nonlinear axisymmetric viscous and inviscid solutions corresponding to the heave oscillations of a submerged vertical cylinder are presented. The fully nonlinear free-surface flow problem is solved using finite difference method based on curvilinear coordinates. A primitive-variables based fractional-step formulation is used for the analysis of viscous flow, while a mixed Eulerian-Lagrangian formulation is used for the analysis of inviscid flow. New results obtained for a range of amplitudes and frequencies of body oscillation and mean depth of body submergence demonstrate the effects of free surface on the dynamics of body-generated vortices and on the vortical component of the hydrodynamic force acting on the body.

Three-dimensional wave-body interactions in a viscous fluid: Heave oscillation of a submerged vertical cylinder

Nonlinear wave-body interactions corresponding to forced oscillation of a floating vertical cylinder in a viscous fluid is investigated. This radiation hydro-dynamics problem is of significance in naval architecture, in particular, for the prediction of ship motions in high seas. A robust finite difference method based on curvilinear coordinates is developed for the analysis. The governing equations are solved in primitive variables using a projection fractional-step method. Higher-order accurate schemes are developed for the discretization of the Navier-Stokes equations. The grids are generated using the concept of reference space and variational formulation. An approximate free-slip condition is used to model the movement of the contact line. Results are obtained for a range of frequency and amplitude of body oscillation and mean draft. Nonlinear effects, which are significant at large amplitude of oscillation and at shallow draft, manifest in the form of higher-order wave and force components. These new results also demonstrate effect of the coupling of wave and body motions on the generation of vortices and on their ensuing space-time evolution.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

Hydrodynamics of waves and vortices generated by an oscillating body

Various theoretical and experimental studies have been carried out to examine the generation of waves ahead of a translating body. Not all issues pertaining to this wave-motion problem are, however, fully resolved. In particular, mechanisms pertaining to generation of white-water instability and inception of vortices in the bow region are not fully understood. In this paper, the two-dimensional, unsteady, nonlinear, viscous-flow problem associated with a translating surface-piercing body is solved by means of finite-difference algorithm based on boundary-fitted coordinates. Effects of surface tension and surfactants are examined. Results of this work resolve certain classic issues pertaining to bow flows. A continuous generation of short and steepening bow waves is observed at low (draft) Froude number, a nonlinear phenomenon uncovered recently in the case of inviscid fluid also. This indicates that, steady-state nonlinear bow-flow solution may not exist, even at low speed. It is postulated that these short bow waves are responsible for the white-water instability commonly observed ahead of a full-scale ship. The amplitudes of these short bow waves are suppressed by surface tension, which is, possibly, the reason why white-water instability is not distinctly observed in laboratory-scale experiments. The presence of surfactants on the free surface is found to intensify the generation of free-surface vorticity, thus resulting in the formation of bow vortices. The accumulation of surface-active contaminants at the bow is hence responsible for the generation of bow vortices observed in laboratory experiments at low Froude number. At high Froude number, an impulsive starting motion of the body results in the generation of a jet-like splash at the bow and a gentle start an overturning bow wave, as previously observed in the case of inviscid bow flow.

Journal of Engineering Mathematics

Viscosity and Surface-Tension Effects on Wave Generation by a Translating Body

This work considers two-dimensional, nonlinear free-surface flow due to forced oscillation of a submerged body in a viscous fluid. The wave radiation problem is solved in primitive variables using a fractional-step finite-difference method and implemented using boundary-fitted coordinates. Representative results corresponding to heave and sway modes of oscillation are presented.

Proceedings of Engineering Mechanics

Radiation hydrodynamics of a slightly-submerged body

The Intelligent Distributed Control System (IDCS) is a control strategy that allows automated and semi-automated control of ocean-going vehicles. This concept combines intelligent and distributed control technologies to automate complex tasks in hazardous and unpredictable ocean environment. It is already being implemented in undergraduate courses in some engineering schools.

ASEE Annual Conference Proceedings

Intelligent system design in ocean engineering

In this paper, we present a numerical method developed for the analysis of unsteady, nonlinear interactions between air and water. The problem is modeled as a flow of two layers of viscous fluids separated by a material interface. The incompressible Navier-Stokes equations together with exact interface boundary conditions are solved in primitive variables using a finite difference method based on boundary-fitted coordinates. Using this solution method, the time evolution of periodic waves at the interface of air and water is studied. Results obtained for a range of initial wave amplitudes shed some light to better understanding of the behavior of interface vorticity and mechanisms involved in the growth of wind waves. The results also demonstrate the efficacy of the present numerical model for the analysis of nonlinear interface flows.

Analysis on nonlinear air-sea interactions

Two-dimensional unsteady viscous-flow problem associated with the normal incidence of a counter-rotating vortex pair on a free surface is analyzed. Effects of surface tension and insoluble surfactants on the generation of free-surface vorticity and surface waves are investigated. A recently developed finite-difference method based on boundary-fitted coordinates is used to solve the fully-nonlinear problem. Results show that in the absence of surfactants and at low Froude number (based on circulation strength and initial separation distance of the vortex pair), waves of short lengths are generated. However, secondary vorticity generated in this case is not strong enough to affect the outward translation of the primary vortices. At intermediate Froude number, a transient wave developing outboard of the primary vortex becomes steep, and eventually breaks because of local instability. Consequently, free-surface vorticity inhibits the outward translation of the primary vortices. Surface tension in a clean free surface dampens the steep short waves, hence also the generation of free-surface vorticity. However, variation in surface tension induced by surfactants intensifies the generation of surface vorticity, thereby causing the primary vortices to rebound. The increase in the rotational part of wave motion results in the dampening of overall free-surface deformations. However, it is found that the shear stress associated with a large gradient of surfactant concentration could cause local steepening of the short wave generated outboard of the primary vortex. © 1994.

Wave Motion

Nonlinear interaction of a vortex pair with clean and surfactant-covered free surfaces

The nonlinear viscous-flow problem associated with the heaving motion of a two-dimensional floating cylinder is considered. It is formulated as an initial-boundary-value problem in primitive variables and solved using a finite-difference method based on boundary-fitted coordinates. A fractional-step procedure is used to advance the solution in time. As a case study, results are obtained for a rectangular cylinder oscillating at a Reynolds number of 103. The nonlinear viscous forces are compared with those of linear potential theory. An assessment on the importance of viscous and nonlinear effects is made. The solution technique is sufficiently robust that extensions to consider other single and coupled modes of motion are possible. © 1992 Kluwer Academic Publishers.

Oscillation of a floating body in a viscous fluid

The problem of hydrodynamics interactions caused by a ship passing another moored vessel in a channel, restricted in width and depth, is analyzed by a numerical surface singularity method called panel method. In this case, the free surface is assumed to be rigid for a ship moving at slow speed or very small Froude Number (smaller than one). Then, the boundary of the channel and the body surface of the ship is divided into a fine mesh of plane elements. Upon imposing boundary conditions for the problem under consideration, a system of algebraic equations can be formulated for the source strengths. The source strength of each panel is, therefore, solved by computer, and the velocity potential, pressure, forces, and moments generated by the hydrodynamic interactions between the moving and moored vessels are calculated. The numerical interaction load co-efficients are presented. The numerical results are consistent with the argument of dimensional analysis which states that the interaction coefficient, with the assumption of a rigid free surface, is independent of a Froude number.