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1.
Proc Natl Acad Sci U S A ; 117(42): 26091-26098, 2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-33020279

RESUMO

We have demonstrated the effectiveness of reinforcement learning (RL) in bluff body flow control problems both in experiments and simulations by automatically discovering active control strategies for drag reduction in turbulent flow. Specifically, we aimed to maximize the power gain efficiency by properly selecting the rotational speed of two small cylinders, located parallel to and downstream of the main cylinder. By properly defining rewards and designing noise reduction techniques, and after an automatic sequence of tens of towing experiments, the RL agent was shown to discover a control strategy that is comparable to the optimal strategy found through lengthy systematically planned control experiments. Subsequently, these results were verified by simulations that enabled us to gain insight into the physical mechanisms of the drag reduction process. While RL has been used effectively previously in idealized computer flow simulation studies, this study demonstrates its effectiveness in experimental fluid mechanics and verifies it by simulations, potentially paving the way for efficient exploration of additional active flow control strategies in other complex fluid mechanics applications.

2.
Bioinspir Biomim ; 15(3): 035003, 2020 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-31896095

RESUMO

We demonstrate that shape-changing or morphing fins provide a new paradigm for improving the ability of vehicles to maneuver and move rapidly underwater. An ingenuous solution is employed by fish to accommodate both the need for stability of locomotion and the ability to perform tight maneuvers: Retractable fins can alter the stability properties of a vehicle to suit their particular goals. Tunas, for example, are large fish that are fast swimmers and yet they need rapid turning agility to track the smaller fish they pursue; they have perfected the use of their dorsal and ventral fins to ensure stability when retracted and rapid turning when erected. Although fish employ unsteady propulsors rather than propellers, we show that engineering rigid-hull underwater vehicles can also exploit similar solutions. We explore the basic flow mechanisms and design considerations of employing morphing fins to alter the stability and maneuvering qualities of vehicles and apply unsteady forces and moments under active control. We also show results from maneuvering simulations and experiments on a model of an underwater vehicle.

3.
Polymers (Basel) ; 10(7)2018 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-30960619

RESUMO

This paper presents the development of a chemical sensor which was microfabricated on top of liquid crystal polymer (LCP) substrate. As a result of the unique material properties of LCP, the sensor showed favorable flexibility as well as operational reliability. These features demonstrate potential for integration of the sensor into automated sensing vehicles to achieve real-time detection. The sensor consists of a gold working electrode, a silver/silver chloride reference electrode, and a gold counter electrode. The working electrode of the sensor was further modified with bismuth nanoparticles and Nafion. The modified sensor exhibited a significantly enhanced sensing capability toward cadmium metal ion (Cd(II)) in comparison to the unmodified one. The effects of deposition potential and deposition time on the sensing performance of the sensor were extensively investigated through electrochemical experiments. With optimized parameters, the sensor was capable of quantifying Cd(II) in the concentration range of 0.3 to 25 µg/L. The minimum Cd(II) concentration detected by the sensor was 0.06 µg/L under quiescent deposition. The obtained results suggest that the proposed sensor has a great potential to be deployed for in-situ Cd(II) determination.

4.
Bioinspir Biomim ; 13(2): 025002, 2018 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-29239859

RESUMO

Flow sensing, maneuverability, energy efficiency and vigilance of surroundings are the key factors that dictate the performance of marine animals. Be it swimming at high speeds, attack or escape maneuvers, sensing and survival hydrodynamics are a constant feature of life in the ocean. Fishes are capable of performing energy efficient maneuvers, including capturing energy from vortical structures in water. These impressive capabilities are made possible by the uncanny ability of fish to sense minute pressure and flow variations on their body. This is achieved by arrays of biological neuromast sensors on their bodies that 'feel' the surroundings through 'touch at a distance' sensing. The main focus of this paper is to review the various biomimetic material approaches in developing superficial neuromast inspired ultrasensitive MEMS sensors. Principals and methods that translate biomechanical filtering properties of canal neuromasts to benefit artificial MEMS sensors have also been discussed. MEMS sensors with ultrahigh flow sensitivity and accuracy have been developed mainly through inspiration from the hair cell and cupula structures in the neuromast. Canal-inspired packages have proven beneficial in hydrodynamic flow filtering in artificial sensors enabling signal amplification and noise attenuation. A special emphasis has been placed on the recent innovations that closely mimic the structural and material designs of stereocilia of neuromasts by exploring soft polymers.


Assuntos
Biomimética/instrumentação , Biomimética/métodos , Peixes/fisiologia , Nadadeiras de Animais , Animais , Organismos Aquáticos , Desenho de Equipamento , Peixes/anatomia & histologia , Hidrodinâmica , Ruído , Phoca/anatomia & histologia , Phoca/fisiologia
5.
J R Soc Interface ; 14(135)2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28978747

RESUMO

Albatrosses can travel a thousand kilometres daily over the oceans. They extract their propulsive energy from horizontal wind shears with a flight strategy called dynamic soaring. While thermal soaring, exploited by birds of prey and sports gliders, consists of simply remaining in updrafts, extracting energy from horizontal winds necessitates redistributing momentum across the wind shear layer, by means of an intricate and dynamic flight manoeuvre. Dynamic soaring has been described as a sequence of half-turns connecting upwind climbs and downwind dives through the surface shear layer. Here, we investigate the optimal (minimum-wind) flight trajectory, with a combined numerical and analytic methodology. We show that contrary to current thinking, but consistent with GPS recordings of albatrosses, when the shear layer is thin the optimal trajectory is composed of small-angle, large-radius arcs. Essentially, the albatross is a flying sailboat, sequentially acting as sail and keel, and is most efficient when remaining crosswind at all times. Our analysis constitutes a general framework for dynamic soaring and more broadly energy extraction in complex winds. It is geared to improve the characterization of pelagic birds flight dynamics and habitat, and could enable the development of a robotic albatross that could travel with a virtually infinite range.


Assuntos
Aves/fisiologia , Voo Animal/fisiologia , Modelos Biológicos , Animais
6.
Sensors (Basel) ; 17(8)2017 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-28788059

RESUMO

Blind cavefishes are known to detect objects through hydrodynamic vision enabled by arrays of biological flow sensors called neuromasts. This work demonstrates the development of a MEMS artificial neuromast sensor that features a 3D polymer hair cell that extends into the ambient flow. The hair cell is monolithically fabricated at the center of a 2 µm thick silicon membrane that is photo-patterned with a full-bridge bias circuit. Ambient flow variations exert a drag force on the hair cell, which causes a displacement of the sensing membrane. This in turn leads to the resistance imbalance in the bridge circuit generating a voltage output. Inspired by the biological neuromast, a biomimetic synthetic hydrogel cupula is incorporated on the hair cell. The morphology, swelling behavior, porosity and mechanical properties of the hyaluronic acid hydrogel are characterized through rheology and nanoindentation techniques. The sensitivity enhancement in the sensor output due to the material and mechanical contributions of the micro-porous hydrogel cupula is investigated through experiments.


Assuntos
Biomimética , Ácido Hialurônico , Hidrogel de Polietilenoglicol-Dimetacrilato , Mecanorreceptores , Sistemas Microeletromecânicos
7.
Science ; 357(6348): 251-252, 2017 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-28729498

Assuntos
Robótica , Atum , Animais , Peixes
8.
J R Soc Interface ; 12(111): 20150322, 2015 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-26423435

RESUMO

Using biological sensors, aquatic animals like fishes are capable of performing impressive behaviours such as super-manoeuvrability, hydrodynamic flow 'vision' and object localization with a success unmatched by human-engineered technologies. Inspired by the multiple functionalities of the ubiquitous lateral-line sensors of fishes, we developed flexible and surface-mountable arrays of micro-electromechanical systems (MEMS) artificial hair cell flow sensors. This paper reports the development of the MEMS artificial versions of superficial and canal neuromasts and experimental characterization of their unique flow-sensing roles. Our MEMS flow sensors feature a stereolithographically fabricated polymer hair cell mounted on Pb(Zr(0.52)Ti(0.48))O3 micro-diaphragm with floating bottom electrode. Canal-inspired versions are developed by mounting a polymer canal with pores that guide external flows to the hair cells embedded in the canal. Experimental results conducted employing our MEMS artificial superficial neuromasts (SNs) demonstrated a high sensitivity and very low threshold detection limit of 22 mV/(mm s(-1)) and 8.2 µm s(-1), respectively, for an oscillating dipole stimulus vibrating at 35 Hz. Flexible arrays of such superficial sensors were demonstrated to localize an underwater dipole stimulus. Comparative experimental studies revealed a high-pass filtering nature of the canal encapsulated sensors with a cut-off frequency of 10 Hz and a flat frequency response of artificial SNs. Flexible arrays of self-powered, miniaturized, light-weight, low-cost and robust artificial lateral-line systems could enhance the capabilities of underwater vehicles.


Assuntos
Células Ciliadas Auditivas/fisiologia , Mecanorreceptores/química , Sistemas Microeletromecânicos , Pele Artificial , Ar , Animais , Biomimética , Eletrodos , Peixes , Sistema da Linha Lateral/fisiologia , Neurônios/patologia , Distribuição Normal , Oscilometria , Polímeros/química , Engenharia Tecidual/métodos , Transdutores , Água
9.
Philos Trans A Math Phys Eng Sci ; 373(2033)2015 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-25512586

RESUMO

The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow-body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.

10.
Opt Lett ; 37(16): 3357-9, 2012 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-23381256

RESUMO

We propose quantitative localization measurement of a known object with subpixel accuracy using compressive holography. We analyze the theoretical optimal solution in the compressive sampling framework and experimentally demonstrate localization accuracy of 1/45 pixel, in good agreement with the analysis.

11.
Phys Rev Lett ; 107(13): 134502, 2011 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-22026858

RESUMO

We identify a dominant mechanism in the interaction between a slender flexible structure undergoing free vibrations in sheared cross-flow and the vortices forming in its wake: energy is transferred from the fluid to the body under a resonance condition, defined as wake-body frequency synchronization close to a natural frequency of the structure; this condition occurs within a well-defined region of the span, which is dominated by counterclockwise, figure-eight orbits. Clockwise orbits are associated with damping fluid forces.

12.
Phys Rev Lett ; 96(1): 014501, 2006 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-16486460

RESUMO

The wake of two oscillating cylinders in a tandem arrangement is a nonlinear system that displays Arnold tongues. We show by numerical simulations that their geometry depends on the phase difference theta between the two oscillating cylinders. At theta = 0 there may be holes inside these intraresonance regions unlike the solid Arnold tongues encountered in single-cylinder oscillations. This implies that, surprisingly, self-excitation of the system may be suppressed inside these holes, at conditions close to its natural frequency.

13.
Tissue Eng ; 10(1-2): 7-21, 2004.
Artigo em Inglês | MEDLINE | ID: mdl-15009926

RESUMO

This study presents the development of a biosynthetic fish skin to be used on aquatic robots that can emulate fish. Smoothness of the external surface is desired in improving high propulsive efficiency and maneuvering agility of autonomous underwater vehicles such as the RoboTuna (Triantafyllou, M., and Triantafyllou, G. Sci. Am. 272, 64, 1995). An initial step was to determine the seeding density and select a polymer for the scaffolds. The attachment and proliferation of chinook salmon embryo (CHSE-214) and brown bullhead (BB) cells were studied on different compositions of a poly(ethylene glycol terephthalate) (PEGT) and poly(butylene terephthalate) (PBT) copolymer (Polyactive). Polymer films were used, cast of three different compositions of PEGT/PBT (weight ratios of 55/45, 60/40, and 70/30) and two different molecular masses of PEGT (300 and 1000 Da). When a 55 wt% and a 300-Da molecular mass form of PEGT was used, maximum attachment and proliferation of CHSE-214 and BB cells were achieved. Histological studies and immunostaining indicate the presence of collagen and cytokeratins in the extracellular matrix formed after 14 days of culture. Porous scaffolds of PEGT/PBT copolymers were also used for three-dimensional tissue engineering of fish skin, using BB cells. Overall, our results indicate that fish cells can attach, proliferate, and express fish skin components on dense and porous Polyactive scaffolds.


Assuntos
Poliésteres , Polietilenotereftalatos , Robótica , Pele Artificial , Animais , Adesão Celular , Técnicas de Cultura , Peixes , Faloidina , Poliestirenos , Pele/citologia , Coloração e Rotulagem
14.
Science ; 302(5650): 1566-9, 2003 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-14645849

RESUMO

Fishes moving through turbulent flows or in formation are regularly exposed to vortices. Although animals living in fluid environments commonly capture energy from vortices, experimental data on the hydrodynamics and neural control of interactions between fish and vortices are lacking. We used quantitative flow visualization and electromyography to show that trout will adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments.


Assuntos
Metabolismo Energético , Contração Muscular , Músculo Esquelético/fisiologia , Oncorhynchus mykiss/fisiologia , Natação/fisiologia , Movimentos da Água , Animais , Fenômenos Biomecânicos , Eletromiografia , Peixes/anatomia & histologia , Peixes/fisiologia , Oncorhynchus mykiss/anatomia & histologia
15.
J Exp Biol ; 206(Pt 6): 1059-73, 2003 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-12582148

RESUMO

Most fishes commonly experience unsteady flows and hydrodynamic perturbations during their lifetime. In this study, we provide evidence that rainbow trout Oncorhynchus mykiss voluntarily alter their body kinematics when interacting with vortices present in the environment that are not self-generated. To demonstrate this, we measured axial swimming kinematics in response to changes in known hydrodynamic wake characteristics. We compared trout swimming in the Kármán street behind different diameter cylinders (2.5 and 5 cm) at two flow speeds (2.5 and 4.5 L s(-1), where L is total body length) to trout swimming in the free stream and in the cylinder bow wake. Trout swimming behind cylinders adopt a distinctive, previously undescribed pattern of movement in order to hold station, which we term the Kármán gait. During this gait, body amplitudes and curvatures are much larger than those of trout swimming at an equivalent flow velocity in the absence of a cylinder. Tail-beat frequency is not only lower than might be expected for a trout swimming in the reduced flow behind a cylinder, but also matches the vortex shedding frequency of the cylinder. Therefore, in addition to choosing to be in the slower flow velocity offered behind a cylinder (drafting), trout are also altering their body kinematics to synchronize with the shed vortices (tuning), using a mechanism that may not involve propulsive locomotion. This behavior is most distinctive when cylinder diameter is large relative to fish length. While tuning, trout have a longer body wavelength than the prescribed wake wavelength, indicating that only certain regions of the body may need to be oriented in a consistent manner to the oncoming vortices. Our results suggest that fish can capture energy from vortices generated by the environment to maintain station in downstream flow. Interestingly, trout swimming in front of a cylinder display lower tail-beat amplitudes and body wave speeds than trout subjected to any of the other treatments, implying that the bow wake may be the most energetically favorable region for a fish to hold station near a cylinder.


Assuntos
Oncorhynchus mykiss/fisiologia , Natação/fisiologia , Animais , Fenômenos Biomecânicos , Modelos Biológicos , Análise de Componente Principal , Gravação em Vídeo
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