Daniel P. Thivierge

Synchronization of Animal-Inspired Multiple High-Lift Fins in an Underwater Vehicle Using Olivo–Cerebellar Dynamics

The development of neuroscience-based control methodologies and their integration with the high-lift unsteady hydrodynamics of control surfaces inspired by swimming and flying animals are the subjects of this paper. A biology-inspired rigid autonomous undersea vehicle called the biorobotic autonomous undersea vehicle (BAUV) has been developed at the Naval Undersea Warfare Center (NUWC), Newport, RI. The BAUV is equipped with six simultaneously rolling and pitching fins for generating large unsteady control forces for performing agile maneuvers. First, as an exploratory example, we introduce the van der Pol oscillator as an oscillatory controller for the BAUV and we describe experiments performed to examine the fin forces (thrust and lift) and electric power requirement, and to demonstrate the effectiveness of the oscillators limit cycle property for disturbance rejection effectiveness. We then describe a BAUV control system that includes six inferior-olive (IO) neuron models for control of the pitch and roll motion of the six foils. These IO neurons exhibit limit cycle oscillation (LCO). For control of the BAUV, these IO neurons must oscillate in synchronism with specific relative phases. We present here four feedback linearizing control systems of varying complexity for control of the relative phases of the IO neurons. It is shown that each of the IO control systems accomplishes asymptotic regulation of the phases and thus enables the foils to produce the required control forces. The first controller has a global synchronization property, but the remaining controllers accomplish local synchronization. We present simulation results for tracking piecewise, time-varying phase angle commands as well as experimental results for control of the BAUV by IO neurons. The results show that with appropriate phasing of the fins, an optimal graceful gait of the BAUV is achieved where no untoward force or moment is present. An analog hardware version of the local controller with a cluster of six IO neurons has also been built, which allows five of the signals to rapidly synchronize to the reference, with or without prescribed phase shift, much like in the simulations. The designed controllers can be used in any platform or multivariate BAUV-like system requiring fast, accurate phase control. Laboratory test results for the phase synchronization of two servomotors (roll and pitch) using the designed analog hardware controller are also shown.

An Electronic Circuit for Trickle Charge Harvesting From Littoral Microbial Fuel Cells

In this paper, the design of an electronic circuit for harvesting energy trickling from benthic sources and the long-term performance in powering sensors and devices in a littoral tidal basin are considered. The process has to contend with the randomness, diurnal variations, and low levels and voltages in available energy compared to what is required by oceanographic sensors. The system has two components: a circuit for conditioning the power and a large area electrode array in a littoral basin. The circuit has two stages and is able to overcome the leaks in capacitors used to store the power; the energy is stored first in a small capacitor and then in a large one so that voltages compatible with sensors are produced. The footprint of the anode is 10 m2 and is inserted into the sediment and the cathode resides in the salt water above the sediment. Several different sensors and actuators have been autonomously powered by the stored energy (4.2 kJ at 12 V). A beacon and an underwater acoustic sensor (5 h of activation of combined hydrophone and three-axis accelerometer sensors, every 40 h; duty cycle has been doubled with recent improvements) have been powered over one to two months. Also, in-water propulsion (for 165 s at a time) of a 25-W biorobotic flapping fin propulsor has been achieved. The system is suitable primarily for powering sensors. It has been operated for more than three years at useful duty cycles, indicating sustainability for autonomous usage.

APPLICATION OF SENSORLESS ELECTRIC DRIVE TO UNMANNED UNDERSEA VEHICLE PROPULSION

Abstract Sensorless electric drive is an enabling technology in the realization of submersible propulsion systems such as the integrated motor/propulsor (IMP). The IMP concept features an electric motor embedded within the shroud of an undersea vehicles propulsor. This arrangement provides many advantages over conventional propulsion systems but prevents the use of conventional rotor position sensors because of reliability issues in the harsh submerged environment. In this paper, a position sensorless drive is applied to the IMP and experimental results are presented to demonstrate the effectiveness of the proposed technique.

Experiments on three-dimensional wall-layer scale Lorentz actuators in high-Reynolds-number axisymmetric turbulent boundary layers

Drag reduction of high-Reynolds-number axisymmetric bodies in saltwater flow using numerous small Lorentz actuators is considered. The actuators are three-dimensional and each of them encompasses the footprint of approximately one turbulence production domain at a Reynolds number Reτ of 103, based on friction velocity and boundary layer thickness. The actuators seed the turbulent boundary layer locally with pulsing toroids of vorticity that straddle the periphery of the actuators. The central downward jet of the toroid counters the upward flow between naturally occurring near-wall vortex pairs. Owing to the presence of the wall, the downward central jet is deflected into wall-jets that lie underneath the toroid. The agglomerated effects of the pulsing of the power applied to the three-dimensional actuators are modeled as Stokes oscillators. An axisymmetric body containing 210 numbers of subcentimeter-scale electromagnetic surface actuators was built. Measurements over this body show that drag reduction ef...

Wall-Layer Scale Electromagnetic Turbulence Control in an Axisymmetric Body

The progress made with the control of turbulence in a boundary layer developing over a small axisymmetric body in saltwater at moderate Reynolds numbers is briefly described. A resonance-interference mechanism of control by means of a small periodic Lorenz force confined to the near-wall region, designed to overcome the issue of low efficiency of electromagnetic turbulence control in general, is attempted to alter surface normal turbulence near-wall. At a low momentum thickness Reynolds number of 2300, drag is reduced by 15–25% at a freestream speed of 5.12 m/s with an efficiency of 2–3.4%. Bi-polar pulsing succeeds in lowering surface-normal turbulence intensity near wall. It also makes wall pressure fluctuations less spiky. Positive uni-polar pulsing is found to weaken the sources of wall-pressure fluctuations residing in the logarithmic region of the boundary layer. Further confirmatory work is needed with robust electrodes and drag measurements on a large diameter axisymmetric body.Copyright