Manhar Dhanak

Florida Atlantic University | FAU · Ocean and Mechanical

Performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA≤30° at a Reynolds number of 10⁵. The results of the numerica...

US ports and container/intermodal terminals are critical links in the marine transportation system. Disruption at a port can have a crippling economic effect in the coastal zone as well as the rest of the nation. Port stakeholders have a vested interest in the long-term function and viability of ports, but no standardized measures for performance o...

Aerosolized droplets play a central role in the transmission of various infectious diseases, including Legionnaire's disease, gastroenteritis-causing norovirus, and most recently COVID-19. Respiratory droplets are known to be the most prominent source of transmission for COVID-19; however, alternative routes may exist given the discovery of small n...

Aerosolized droplets play a central role in the transmission of various infectious diseases, including Legionnaire's disease, gastroenteritis-causing norovirus, and most recently COVID-19. Respiratory droplets are known to be the most prominent source of transmission for COVID-19, however, alternative routes may exist given the discovery of small n...

Several places across the world are experiencing a steep surge in COVID-19 infections. Face masks have become increasingly accepted as one of the most effective means for combating the spread of the disease when used in combination with social-distancing and frequent hand-washing. However, there is an increasing trend of people substituting regular...

This study is part of ongoing work on situational awareness and autonomy of a 16’ WAM-V USV. The objective of this work is to determine the potential and merits of application of two different station-keeping controllers for a fixed-pose motion control of the USV. The assessment includes performance and power consumption metrics tested under harsh...

Several places across the world are experiencing a steep surge in COVID-19 infections. Face masks have become increasingly accepted as one of the most effective means for combating the spread of the disease, when used in combination with social-distancing and frequent hand-washing. However, there is an increasing trend of people substituting regula...

The use of face masks in public settings has been widely recommended by public health officials during the current COVID-19 pandemic. The masks help mitigate the risk of cross-infection via respiratory droplets, however, there are no specific guidelines on mask materials and designs that are most effective in minimizing droplet dispersal. While the...

In this paper, results of a study of a submerged hydrofoil with a custom-designed internal slot are provided. The performance characteristics of the slotted hydrofoil in the presence of the free surface are investigated both numerically and experimentally, with angles of attack ranging from 0°≤AoA≤30° at a Reynolds number of 10⁵. Lift and drag coef...

Direct numerical simulation (DNS), based on solution of the Navier Stokes equations, is used to study the characteristics of the transformation of monochromatic waves over a simplified fringing reef, including wave shoaling, and wave breaking that occurs under certain circumstances. The reef geometry involves a sloped plane beach extended with a si...

In-water tests of automated launch and recovery (L&R) of a Hydroid REMUS 100 autonomous underwater vehicle (AUV) from a station-keeping 16-ft wave adaptive modular vehicle unmanned surface vehicle (USV) have been conducted to determine the feasibility of developed concepts of operation. The USV is a catamaran with a custom-configured propulsion sys...

Experimental data for untwisted airfoils are utilized to propose a model for predicting the lift coefficients of twisted airfoils with leading-edge tubercles. The effectiveness of the empirical model is verified through comparison with results of a corresponding computational fluid-dynamic (CFD) study. The CFD study is carried out for both twisted...

The characteristics of wave breaking in shallow waters that are of interest include whether a wave will break, the type of breaking that will occur, the breaking wave height, breaking depth, the position of breaking, the wave setup, and the transformation of the broken wave for given offshore wave characteristics and given bottom profile. Various m...

The objective of this study was to determine if electromagnetic field (EMF) emissions from undersea power cables impacted local marine life, with an emphasis on coral reef fish. The work was done at the South Florida Ocean Measurement Facility of Naval Surface Warfare Center in Broward County, Florida, which has a range of active undersea detection...

Numerical simulation of a downstream hydrokinetic turbine operating in the wake of an upstream turbine for feedback control design is presented. Wake effects from an upstream turbine are quantified in terms of wake velocity and amplified turbulence levels. These effects are integrated in an in-stream hydrokinetic turbine numerical simulation that u...

The characteristics of wave breaking over a fringing reef are considered using a set of laboratory experiments and the results are used to develop associated predictive models. Various methods are typically used to estimate the characteristics of nearshore wave breaking, mostly based on empirical, analytical and numerical techniques. Deo et al. (20...

This paper forms, optimizes, and evaluates three numerical approaches for characterizing mean velocities in far wake region behind ocean current turbines. These approaches are derived from wake models originally developed for wind turbines and are referred here as the Larsen/Larsen, Larsen/Ainslie, and Jensen/Ainslie approaches based on the researc...

A stereovision based methodology to estimate the position, speed and heading of a moving marine vehicle from a pursuing unmanned surface vehicle (USV) is considered, in support of enabling a USV to follow a target vehicle in motion. The methodology involves stereovision ranging, object detection and tracking, and minimization of tracking error due...

An approach for numerically representing turbulence effects in the simulation of Ocean Current Turbines (OCT)s is described. Ambient turbulence intensity and mean flow velocity are utilized to develop analytic expressions for flow velocities at a grid of nodes that are a function of time. This approach is integrated into the numerical simulation of...

The growing variety and complexity of marine research and application oriented tasks requires unmanned surface vehicles (USVs) to operate fully autonomously over long time horizons even in environments with significant civilian traffic. In order to address this challenge, we have developed a lattice-based 5D trajectory planner for USVs. The planner...

In this paper, a concept design for automated launch and recovery (L&R) of a small autonomous underwater vehicle (AUV) from an unmanned surface vehicle (USV) is described and its feasibility is assessed through modeling and simulation. The design is being implemented on a selected catamaran USV for deployment of a REMUS 100 AUV. The concept for lau...

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 meter long, 150 kilogram wave adaptive modular vessel (WAM-V) with an inflatable twin hull configuration and waterjet propulsion....

Marine hydrokinetic energy includes that due to waves, tides, and ocean currents. The characteristics of these forms of energy and the assessment of their potential for extraction are discussed briefly herein. Detailed consideration is given to the assessment of ocean current energy, including a case study of the resource assessment of the Florida...

Ocean engineering is a systems engineering field and requires a relatively broad background in several aspects of engineering. The role of hydrodynamics is central to all ocean engineering activities and despite an ocean engineer’s specialist designation, sooner or later some aspects of hydrodynamics will encroach upon the problem he or she is tryi...

The purpose of this chapter is to present the basic concepts of ocean wave energy conversion as an extension to the supporting subjects presented earlier in this handbook so that they can be useful to scientists, engineers and inventors. Although new research regarding all wave energy conversion aspects has been unveiling continuously over the past...

The performance of four automatically-generated path planning behaviors is evaluated through field-testing. Experiments were conducted using a model-referenced trajectory planner, which was implemented on unmanned surface vehicles (USVs) of different size, thrust, and maneuverability characteristics. The planner combines a local search based on the...

AUV-based field measurement and characterization of the electromagnetic field in coastal waters associated with live submerged cables is described. The effort is in support of a program to characterize the EMF emissions associated with submerged power transmission cables from offshore energy harvesting devices to shore and identifying their environ...

A general formulation for a morphing AUV operating in complex current environment was developed. Two sets of morphing X-canard rudders at the stern and aft of the vehicle were used. Morphing is introduced with Shape Memory Alloy (SMA) to deflect the rudders' trailing edge and therefore enhance lift and reduce drag. A numerical simulation using Simu...

We introduce a model-predictive trajectory planning algorithm for unmanned surface vehicles (USVs) operating in congested civilian traffic. The planner reasons about the availability of contingency maneuvers needed in case of any of the civilian vessels breaches the International Regulations for the Prevention of Collisions at Sea (COLREGs). Our ex...

There have been much technological advances and research in Unmanned Surface Vehicles (USV) as a support and delivery platform for Autonomous/Unmanned Underwater Vehicles (AUV/UUV) or Remotely Operated Vehicles (ROV). Advantages include extending underwater search and survey operations time and reach, improving underwater positioning and mission aw...

A robust computer vision system for an unmanned surface vehicle (USV) is being developed, in support of tracking a moving marine vehicle from the USV. A methodology to minimize the tracking errors regarding the raw 2-D measurements of the position of a target boat using a commercial stereo camera will be presented. This errors are mainly due to ima...

We describe the use of a spectral collocation method to compute the characteristics of incompressible, viscous flow in a lid driven right triangular cavity with wall motion away from the right angle. First, the 2-D Gauss–Lobatto grid on the square [-1,1]×[-1,1][-1,1]×[-1,1] is mapped to a triangular domain by means of a singular mapping. A singular...

We present a model-predictive trajectory planning algorithm for following a target boat by an autonomous unmanned surface vehicle (USV) in an environment with static obstacle regions and civilian boats. The planner developed in this work is capable of making a balanced trade-off among the following, possibly conflicting criteria: the risk of losing...

This article presents an experimental assessment of an Unmanned Surface Vehicle (USV) executing an approach behavior to several stationary targets in an obstacle field. A lattice-based trajectory planner is implemented with a priori knowledge of the vehicle characteristics. In parallel, a low-level controller is developed for the vehicle using a pr...

Sea-keeping characteristics of a wave-adaptive modular catamaran, developed by Marine Advanced Research Inc., is studied using at-sea experiments and dynamic modeling. The vehicle is based on the Proteus design and is supported by two inflatable pontoons with each pontoon attached to a center payload tray using an independent suspension system conn...

AUV-based measurement of the magnetic field offshore of South Florida is described. The effort is part of a measurement program involving observations from fixed and mobile sensor systems in the region in support of characterizing the local background magnetic field in coastal waters. A SeaSpy magnetometer is towed at some distance from a Bluefin 2...

Scale-model laboratory tests of a surface effect ship (SES) conducted in a near-shore transforming wave field are discussed. Waves approaching a beach in a wave tank were used to simulate transforming sea conditions and a series of experiments were conducted with a 1:30 scale model SES traversing in heads seas. Pitch and heave motion of the vehicle...

The goal of our research is to characterize the performance of an off-the-shelf Overhauser Sentinel magnetometer when towed by an autonomous underwater vehicle (AUV). It is well known that the hydrodynamic motion of conductive seawater in the oceans through the earth's field leads to electrodynamic phenomena based on the dynamo effect. Oceanographi...

Traditionally, renewable energy resources have been assessed through collection and analysis of extensive in situ observations; however, in situ data collection can be cost and time prohibitive, especially for initial site selection and feasibility studies. Ocean models, such as the HYbrid Coordinate Ocean Model (HYCOM), provide corresponding data...

The Florida Current has been noted as a potential resource for ocean hydrokinetic energy. The area encompassed by the geographical extent of Florida Current is substantial compared to the required footprint of an array of hydrokinetic turbines that may be implemented to harness the hydrokinetic energy of the current. A method has been developed to...

Pitching and heaving motions of an air-cushion vehicle, such as a surface effect ship (SES), in response to wave encounters as it transitions through a transforming wave-field such as in the near-shore zone are considered. The vehicle maintains a pressurized air cushion between its two side hulls and the deck hull. In head seas, the passage of wave...

Available ocean model and physically measured data from the Florida Current are analyzed to provide a detailed assessment of the hydrokinetic energy resource of the Florida Current, in support of harnessing a portion of it using ocean energy conversion devices. It has been estimated that approximately 25 GW of hydrokinetic power is available in the...

Ocean thermal energy conversion (OTEC) uses the energy stored in the thermocline to evaporate and condense a fluid in a Rankine power cycle. A thermal energy resource assessment is conducted for waters surrounding Florida to help qualitatively assess the best locations for electrical power production by an OTEC plant in that state, using data model...

The Florida Current has a large hydrokinetic power resource that could be extracted by ocean energy conversion devices. Historical estimates have predicted that approximately 25 GW of hydrokinetic power is available in the Florida Current. This estimate is based on the entire flow through a given cross-section. Using HYCOM velocity data, the hydrok...

The characteristics of the surface pressure fluctuations associated with a supersonic underexpanded jet impinging perpendicularly on a flat plate are numerically investigated using WIND-US 2.0. The time-dependent, inviscid, compressible axisymmetric Euler equations for perfect gas without body forces and external heat addition are employed for the...

Heave motion of an air-cushion vehicle in response to wave encounters as it transitions through the surf zone is presented. Wave transformation from deep waters to the beach is described using the model of Dally et al. (1985) and the shallow-water SWAN model. The vehicle considered is a surface effect ship (SES) that maintains an air cushion betwee...

National Naval Responsibility for Naval Engineers (NNRNE) program was established by the Office of Naval Research in 2001 to help ensure the future US capability to develop creative and innovative ship designers and designs to effectively meet defense needs and commercial market opportunities. It was also recognized that the universities need to su...

Technical design considerations for an offshore outfall at Myrtle Beach for discharge of stormwater carrying undesirable bacteria are described, together with dispersion characteristics of the discharge. Hydrodynamic forces associated with a 50yr design wave are considered to determine the required burial depths for the pipes and for providing rubb...

A turbulent 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 ef...

The subsurface current velocity in a littoral water column was examined during the passage of a low pressure atmospheric cold front and averaged over a period of approximately 6 hours, when the wind was constant in direction from the northwest with a magnitude of 10.9 ms-1. The subsurface current vectors follow the expected clockwise deflection and...

To succeed at developing a nationwide Integrated Ocean Observing System (IOOS), stakeholders in academia, government, and industry must forge and maintain strategic partnerships. The South Florida Ocean Measurement Center (SFOMC) is such a partnership model and mutually beneficial collaboration that is conducting year-in and year-out major at-sea o...

We investigate the role of density stratification on a turbulent Ekman layer induced by a wind on the ocean surface, using Large Eddy Simulations (LES). Analyses of the flow structure and statistics are presented, highlighting the effect of the stratification on modifying the depth of the Ekman layer. Strong initial stable stratification is effecti...

We present the results of large-eddy simulations (LES) of turbulent thermal convection generated by surface cooling in a finite-depth stably stratified horizontal layer with an isothermal bottom surface. The flow is a simplified model of turbulent convection occurring in the warm shallow ocean during adverse weather events. Simulations are perf...

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The cross-shelf shear layer at the western edge of the Florida Current is modeled as a uniform vortex layer and its linear instability to long waves is examined. The strength and thickness of the vortex layer is estimated from observations of the shear layer from an ocean surface current radar (OSCR) during July 1999. It is found from the idealized...

Subsurface observations of distribution of currents, temperature, salinity and water density over a 1km by 0.5km spatial region in littoral waters ( 20m deep) off the east coast of Florida during a passage of a low-pressure atmospheric front will be described. Meteorological and ocean surface current radar (OSCR) observations clearly show the passa...

A survey of small-scale subsurface variability within the synoptic observational field of an ocean surface current radar (OSCR) using an autonomous underwater vehicle (AUV) is described. The survey involved observation of a developing upper mixed layer in a littoral zone off southeast Florida, on the edge of a strong Florida current during the summ...

Bathymetry, current, temperature, and depth (CTD) measurements using a small, mobile, autonomous un- derwater vehicle (AUV) platform are described. Autonomous surveys of a shallow water column off the east coast of Florida during December 1997 were carried out using a 2.13-m long, 0.53-m maximum diameter Ocean Explorer series AUV, equipped with a 1...

We consider the laminar boundary–layer flow past a semi–infinite plate with a streamwise ridge. We seek similarity solution to the problem, when the freestream velocity takes the form x*n, where x* denotes the distance from the leading edge of the plate; such solutions may exist if the transverse and lateral scales o the ridge develop in the stream...

We consider the laminar boundary-layer flow past a semi-infinite plate with a streamwise ridge. We seek similarity solutions to the problem, when the freestream velocity takes the form x*n, where x* denotes the distance from the leading edge of the plate; such solutions may exist if the transverse and lateral scales of the ridge develop in the stre...

Small scale turbulence measurements over a warm continental shelf during the passage of a cold front over the Eastern Florida coast are described. Over a 22 hour period microstructure velocity shear, conductivity, and temperature, together with background current profiles and CTD were measured using an autonomous underwater vehicle. The aim was to...

Ambient turbulence in the ocean is responsible for dissipating the kinetic energy in the ocean at very small scales. Small autonomous underwater vehicles (AUVs) provide versatile mobile platforms for surveying a shallow water coastal environment at low operational costs. The platforms are uncoupled from the low frequency vibrations associated with...

The incompressible boundary layer in the corner formed by two intersecting, semi-infinite planes is investigated, when the free-stream flow, aligned with the corner, is taken to be of the form U[infty infinity]F(x), x representing the non-dimensional streamwise distance from the leading edge. In Dhanak & Duck (1997) similarity solutions for F(x...

The use of a small autonomous underwater vehicle (AUV) as a platform for making in situ flow measurements in the ocean environment is described. Two high-wavenumber shear probes and a dynamic Pitot tube, housed in a pressure vessel mounted on the nose of the AUV, allow measurements, in the dissipation range, of all three components of velocity. Mic...

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...

The use of Florida Atlantic University's the Ocean Explorer, a small autonomous underwater vehicle, as a mobile platform for oceanographic measurements is described. The OEX is a 2.4 m long versatile, Gertler body which can perform pre-programmed underwater missions to a depth of 300 m. At a speed of 1-2 m/s, it can perform missions over a period o...

Statistical description of the activity in the near-wall region of a turbulent boundary layer, including the skin friction at the wall surface, Reynolds stress distribution and the spectra for kinetic energy and surface pressure fluctuations are considered in terms of the individual dynamics of an ensemble of independent coherent streamwise vortice...

We consider similarity-type boundary-layer flows over corrugated surfaces with transverse and lateral dimensions comparable to the boundary layer thickness. The governing equations are similar to those studied in the context of corner boundary-layer flows by Dhanak & Duck (1997). As in this previous work, a thorough understanding of the far-field c...

The long-term goals of this proposal are to seek a better understanding about modeling and predicting littoral ocean processes and to further enhance the autonomous underwater vehicle sampling technology through a collaborative effort with the AUV team at Southampton Oceanography Center, UK. OBJECTIVES The scientific objectives are to both study La...

Small scale oceanic turbulence measurements, made during winter in 18m deep waters off the east coast of Florida using two shear probes mounted on board an autonomous underwater vehicle (AUV), are described. The measurements were made over a substantial region as the AUV dived to a depth of 9m while moving forward at 1m/s. The velocity spectra from...

Exact solutions of the Navier–Stokes equations describing the interaction of streamwise vortices with a rigid surface are utilized to develop a conceptual model for the surface pressure spectrum associated with the wall region of a turbulent boundary layer. The evolution of single as well as pairs of coherent streamwise vortices, which principally...

The incompressible boundary layer in the corner formed by two intersecting, perpendicular, semi-infinite planes is investigated; the freestream flow, aligned with the corner, is of the form x^*n, x representing the streamwise distance from the leading edge. Similarity-type solutions are derived, and it is found that non-uniqueness appears to be com...

Turbulence measurements in a shallow-water ocean environment using Florida Atlantic University's 2.2m long autonomous underwater vehicle (AUV) are described. Two high-wavenumber shear probes and a pitot tube, housed in a pressure-vessel mounted on the nose of the AUV, allow measurements, in the dissipation range, of all three components of velocity...

In this paper, we discuss making flow measurements in a shallow-water ocean environment using Florida Atlantic University's 2.2 m long autonomous underwater vehicle (AUV). An AUV has the advantage over tethered vehicles in that its self motion is not coupled to the motion of the sea surface and that of a mother ship, and it can potentially operate...