scispace - formally typeset
Search or ask a question
Author

Manhar R. Dhanak

Bio: Manhar R. Dhanak is an academic researcher from Florida Atlantic University. The author has contributed to research in topics: Boundary layer & Turbulence. The author has an hindex of 20, co-authored 82 publications receiving 1227 citations. Previous affiliations of Manhar R. Dhanak include Embry–Riddle Aeronautical University.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, a model for turbulent skin friction, proposed by Orlandi & Jimenez, involving consideration of quasi-streamwise vortices in the cross-stream plane, is used to study the effect on the skin friction of oscillating the surface beneath the boundary layer in the spanwise direction.
Abstract: A model for turbulent skin friction, proposed by Orlandi & Jimenez, involving consideration of quasi-streamwise vortices in the cross-stream plane, is used to study the effect on the skin friction of oscillating the surface beneath the boundary layer in the spanwise direction. Using an exact solution of the Navier–Stokes equations, it is shown that the interaction between evolving, axially stretched, streamwise vortices and a modified Stokes layer on the oscillating surface beneath, leads to reduction in the skin friction, the Reynolds stress and the rate of production of kinetic energy, consistent with predictions based on experiments and direct numerical simulations.

94 citations

Journal ArticleDOI
TL;DR: In this article, the authors consider the case of a turbulent flow generated near the ocean surface by a steady wind stress in the presence of Earth's rotation and propose a Bessel function solution that corresponds to the approximate effective viscosity profile and matches with the LES results.
Abstract: At urbulent Ekman layer created by a steady wind near the water surface is investigated using the numerical method of large-eddy simulations. The classical case of a flow unaffected by density stratification and surface waves is revisited to understand the internal structure of the flow and implications of the traditional assumptions of constant effective viscosity and the ‘f -plane’ approximation. A series of numerical experiments reveals that the Ekman solution needs correcting even in this case. The examination of the effective viscosity hypothesis confirms its validity but shows that the viscosity varies strongly with depth. It increases in the subsurface layer of thickness about 1/4 the turbulent length scale and decreases below this level. A Bessel function solution is proposed that corresponds to the approximate effective viscosity profile and matches with the LES results. Strong flow dependence on the latitude and wind direction is detected and explained by the effects of redistribution of turbulent kinetic energy between the velocity components and modification of the vertical transfer of turbulent momentum. In this paper, we consider the classical problem of a turbulent flow generated near the ocean surface by a steady wind stress in the presence of Earth’s rotation. Interest in this flow goes back to Ekman’s landmark work published in 1905. (An interesting historical review of Fridtjof Nansen’s polar expedition and other events preceding Ekman’s paper is given by Walker (1991).) Ekman assumed a balance between the Coriolis force, viscous friction and the pressure gradient, adopted the approximation of constant vertical eddy viscosity Az ,a ndderived a solution now known as the ‘Ekman spiral’. In the case of a steady wind in the x-direction, the steady-state Ekman velocity profile in the open ocean is (for the northern hemisphere) u = V0 cos π + π D z

76 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of two low-level controllers when displacement and drag properties are time varying and uncertain is evaluated for an unmanned surface vehicle (USV) using open-loop maneuvering tests.
Abstract: Experimental testing of an unmanned surface vehicle (USV) has been performed to evaluate the performance of two low-level controllers when displacement and drag properties are time varying and uncertain. The USV is a 4.3-m-long, 150-kg wave adaptive modular vessel (WAM-V) with an inflatable twin-hull configuration and waterjet propulsion. Open-loop maneuvering tests were conducted to characterize the dynamics of the vehicle. The hydrodynamic coefficients of the vehicle were determined through system identification of the maneuvering data and were used for simulations during control system development. The resulting controllers were experimentally field tested on-water. Variable mass and drag tests show that the vehicle is best controlled by a model reference adaptive backstepping speed and heading controller. The backstepping controller developed by Liao et al. (2010) is modified to account for an overprediction of necessary control action and motor saturation. It is shown that when an adaptive algorithm is implemented for the surge control subsystem of the modified backstepping controller, the effects of variable mass and drag are mitigated.

74 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: An overview of both historical and recent USVs development is provided, along with some fundamental definitions, and existing USVs GNC approaches are outlined and classified according to various criteria, such as their applications, methodologies, and challenges.

709 citations

01 Jan 2016
TL;DR: In this paper, the authors describe how to download and install guidance and control of ocean vehicles in the house, workplace, or perhaps in your method can be all best place within net connections.
Abstract: By searching the title, publisher, or authors of guide you in reality want, you can discover them rapidly. In the house, workplace, or perhaps in your method can be all best place within net connections. If you objective to download and install the guidance and control of ocean vehicles, it is utterly easy then, past currently we extend the colleague to buy and make bargains to download and install guidance and control of ocean vehicles therefore simple!

611 citations

Journal ArticleDOI
TL;DR: A summary of physical insights gained into three-dimensional linear instability through solution of the two-dimensional partial-differential-equation-based nonsymmetric real or complex generalised eigenvalue problem is presented in this article.

485 citations

Journal ArticleDOI
TL;DR: The One Atmosphere Uniform Glow Discharge Plasma (OMUGLDP) as mentioned in this paper was developed to cover the wings and fuselage of aircraft with a thin layer of glow discharge plasma at low energy cost.
Abstract: The development of the One Atmosphere Uniform Glow Discharge Plasma has made it possible to cover the wings and fuselage of aircraft with a thin layer of glow discharge plasma at low energy cost. This plasma layer provides, through Lorentzian collisions, a purely electrohydrodynamic coupling between an electric field and the neutral gas in the boundary layer. This coupling is strong enough to cause aerodynamically significant acceleration and manipulation of the boundary layer and free stream flow, including re-attachment of flow to an airfoil at high angles of attack, and the peristaltic induction of neutral gas flow by a traveling electrostatic wave on the surface of a flat plate.

425 citations

Book
S. A. Thorpe1
01 Jan 2005
TL;DR: The Turbulent Ocean as discussed by the authors describes the principal dynamic processes that control the distribution of turbulence, its dissipation of kinetic energy and its effects on the dispersion of properties such as heat, salinity, and dissolved or suspended matter in the deep ocean, the shallow coastal and the continental shelf seas.
Abstract: The subject of ocean turbulence is in a state of discovery and development with many intellectual challenges. This book describes the principal dynamic processes that control the distribution of turbulence, its dissipation of kinetic energy and its effects on the dispersion of properties such as heat, salinity, and dissolved or suspended matter in the deep ocean, the shallow coastal and the continental shelf seas. It focuses on the measurement of turbulence, and the consequences of turbulent motion in the oceanic boundary layers at the sea surface and near the seabed. Processes are illustrated by examples of laboratory experiments and field observations. The Turbulent Ocean provides an excellent resource for senior undergraduate and graduate courses, as well as an introduction and general overview for researchers. It will be of interest to all those involved in the study of fluid motion, in particular geophysical fluid mechanics, meteorology and the dynamics of lakes.

380 citations