Othon K. Rediniotis

Development of a shape memory alloy actuated biomimetic vehicle

The development of a biomimetic active hydrofoil that utilizes shape memory alloy (SMA) actuator technology is presented. This work is the first stage prototype of a vehicle that will consist of many actuated body segments. The current work describes the design, modeling and testing of a single-segment demonstration SMA actuated hydrofoil. The SMA actuation elements are two sets of thin wires on either side of an elastomeric component that joins together the leading and trailing edges of the hydrofoil. Controlled heating and cooling of the two wire sets generates bi-directional bending of the elastomer, which in turn deflects the trailing edge of the hydrofoil. In this paper the design of the hydrofoil and the experimental tests preformed thereon are explained. A detailed account of SMA actuator preparation (training) and material characterization is given. Finite-element method (FEM) modeling of hydrofoil response to electrical heating of the SMA actuators is carried out using a thermomechanical constitutive model for the SMA with input from the material characterization. The modeling predictions are finally compared with experimental measurements of the trailing edge deflection and the SMA actuator temperature.

A New Class of Synthetic Jet Actuators—Part II: Application to Flow Separation Control

We present the application of the new synthetic jet actuator (SJA) to flow separation control over a NACA 0015 wing. The actuator is compact enough to fit in the interior of the wing that has a chord of 0.375 m. The wing was tested in the Texas A&M University Aerospace Engineering 3 ftX4 ft wind tunnel. An experimental investigation into the effects of the synthetic jet actuator on the performance of the wing is described. Emphasis is placed on the capabilities of the actuator to control the separation of the flow over the wing at high angles of attack. The results include force balance measurements, on surface and off surface flow visualization, surface pressure measurements, and wake surveys. All of the reported tests were performed at a free-stream velocity of 35 m/s, corresponding to a Reynolds number of 8.96×10 5 . The angle of attack was varied from -2.0 deg to 29.0 deg.

Development of a Shape-Memory-Alloy Actuated Biomimetic Hydrofoil

The development and testing of a biomimetic active hydrofoil that utilizes Shape-Memory-Alloy (SMA) actuator technology is presented. This work is the second stage in the development of a vehicle that has a skeletal structure similar to that of aquatic animals and SMA actuators for muscles. The current work describes the development and testing of a six-segment demonstration vehicle and the control schemes used. Each SMA actuation element consists of a thin wire that joins together two adjacent vertebrae segments of the hydrofoil skeleton and induces relative movement of one with respect to the other. Controlled heating and cooling of the wire sets generates bi-directional rotation of the vertebrae, which in turn causes a change in the shape of the hydrofoil. Each SMA wire is embedded in an elastic water channel that facilitatesfast active SMA cooling via forced water circulation. This hydrofoil was able to deform to several shapes mimicking aquatic animal swimming, with controlled oscillation frequencies of up to 1 Hz, with 1/2 Hz oscillation producing the largest body motion amplitudes.

Microstructured Hydrophobic Skin for Hydrodynamic Drag Reduction

6Wood, D. H., “A Three-Dimensional Analysis of Stall-Delay on Horizontal-Axis Wind Turbine,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 37, 1991, pp. 1–14. 7Cebecci, T., An Engineering Approach to the Calculation of Aerodynamic Flows, Springer, Berlin, 1999, pp. 51–62. 8Banks, W. H. H., and Gaad, G. E., “Delaying Effect of Rotation on Laminar Separation,” AIAA Journal, Vol. 1, No. 4, 1963, pp. 941, 942.

Adaptive Control of Shape Memory Alloy Actuators for Underwater Biomimetic Applications

In actuator technology active or smart materials have opened up new horizons in terms of actuation simplicity, compactness, and miniaturization potential. One such material is the nickel-titanium shape memory alloy (NiTi SMA), which is gaining widespread use in a variety of applications. The numerous advantages of SMA over traditional actuators are of particular interest in the area of underwater vehicle design, particularly the development of highly maneuverable vehicles of a design based on the swimming techniques and anatomic structure of e sh. An SMA actuation cycle consists of heating/cooling half-cycles, currently imposing a limit on the frequency of actuation to well below 1 Hz in air because of slow cooling. The aquatic environment of underwater vehicles lends itself to cooling schemes that use the excellent heat-transfer properties of water, thus enabling much higher actuation frequencies. A controller for SMA actuators must account not only for large hysteretic nonlinearities betweenactuatoroutput (strainordisplacement )andinput(temperature ),butalso thethermalcontrolforresistive heating via an applied current. The control of SMA in water presents a problem not encountered when actuating in air: accurate temperature feedback for the SMA is very dife cult in water. We overcome this problem by using a simplie ed thermal model to estimate the temperatureof the wire in conjunction with an adaptivehysteresismodel, which relates the actuator output to the estimated temperature. Experimental results are provided, showing that this method for control of an SMA wire works equally well both in air and in water, with only rough estimates (easily obtained )ofthethermal parameters.Successful tracking of referencedisplacementsignals with frequencies up to 2 Hz and relatively large amplitudes have been demonstrated experimentally. I. Introduction I N aerodynamicsand hydrodynamics birds and e sh have inspired and guided the development of aircraft and underwater vehicles. These manmademachinesseemsoprimitive compared to their natural counterparts in terms of intelligence, efe ciency, agility, adaptability, and functionalcomplexity. These and other similar observationsandissuesthathavebeenaddressedbythescientie ccommunity havetriggered theformulation of thescience ofbiomimetics and have inspired new approaches to old problems. In the area of underwater vehicle design, the development of highly maneuverable vehicles is presently of interest, with their design being based on the swimming techniques and anatomic structure of e sh; primarily the undulatory body motions, the highly controllable e ns, and the large aspect ratio lunate tail. The tailoring and implementation of the accumulated knowledge into biomimetic vehicles is a task of multidisciplinary nature with two of the dominant e elds being

The Compressible Calibration of Miniature Multi-Hole Probes

We present the development of a data reduction algorithm for non-nulling, multihole pressure probes in compressible, subsonic flowfields. The algorithm is able to reduce data from any 5- or 7-hole probe and generate very accurate predictions of the velocity magnitude and direction, total and static pressures, Mach and Reynolds number and fluid properties like the density and viscosity. The algorithm utilizes a database of calibration data and a local least-squares interpolation technique. It has been tested on four novel miniature 7-hole probes that have been calibrated at NASA Langley Flow Modeling and Control Branch for the entire subsonic regime. Each of the probes had a conical lip with diameter of 1.65 mm

Periodic vortex shedding over delta wings

again the edges were nearly parallel, and except for the formation of cells, the wakes organized themselves in a nearly twodimensional fashion. In the problem under discussion here, the edges form an angle of 30 deg, and moreover they are inclined with respect to the flow. Preliminary findings on this problem were published by the present authors in a short Note.18 The variation of the Strouhal number vs the angle of attack and the Reynolds number was partially investigated. The main thrust in the present effort is to explore the flowfield for organized natural oscillations and to identify their character. The existence of two different shedding modes (simultaneous and alternate) is now documented in terms of pairs of hot-wire signals. The angle-of-attack ranges in which each models present are investigated for the entire domain of shedding angles of attack (35 < a < 90 deg). The orientation of the shed vortices with respect to the wing and their evolution in time are studied. Finally, flow visualization techniques are used to support the earlier findings.

Miniature Multihole Pressure Probes and Their Neural-Network-Based Calibration

We present the development of miniature multihole pressure probes and a novel neural-network-based calibration algorithm for them. Seven-hole probes of tip diameters as low as 0.035 in. (0.9 mm) were successfully fabricated with high tip surface quality. Any of the typical probe tip geometries, i.e., hemispherical, conical, or faceted, could be fabricated. The miniature probes were calibrated and tested in a wind tunnel. A backpropagation-based neural-network calibration algorithm was developed for these probes, with flexibility in network architecture design and network self-optimization capabilities. In the feedforward mode the algorithm yields computational speeds an order of magnitude higher than those typically achieved by similar accuracy interpolation algorithms. The new algorithm has prediction accuracies of 0.28 deg in the flow angles and 0.35% in the velocity magnitude

A New Class of Synthetic Jet Actuators—Part I: Design, Fabrication and Bench Top Characterization

Although the potential of synthetic jets as flow separation control actuators has been demonstrated in the existing literature, there is a large gap between the synthetic jet actuators (SJA) used in laboratory demonstrations and the SJAs needed in realistic, full-scale applications, in terms of compactness, weight, efficiency, control authority and power density. In most cases, the SJAs used in demonstrations are either too large or too weak for realistic applications. In this work, we present the development of a new class of high-power synthetic jet actuators for realistic flow control applications. The operating principle of the actuator is the same as that of crankshaft driven piston engines, which makes a significant part of the technology necessary for the actuator development available off-the-shelf. The design of the actuator is modular and scalable. Several building block units can be stacked in series to create the actuator of the desired size. Moreover, active exit slot reconfiguration, in the form of variable exit slot width, decouples the actuator frequency from the actuator jet momentum coefficient and allows the user to set the two independently (within limits). We present the design, fabrication and bench top characterization of the actuator. Several versions of the actuator were designed, built and tested, leading up to the development of a six-piston compact actuator that has a maximum power consumption of 1200 W (1.6 hp) and can produce (for the tested conditions) peak exit velocities as high as 124 m/s.

Reduced Order Nonlinear Navier-Stokes Models for Synthetic Jets

While the potential for the use of synthetic jet actuators to achieve flow control has been noted for some time, most of such flow control studies have been empirical or experimental in nature. Several technical issues must be resolved to achieve rigorous, model-based, closed-loop control methodologies for this class of actuators. First, we seek to derive and evaluate model order reduction methods based on proper orthogonal decomposition that are suitable for synthetic jet actuators. Second, we seek to derive rigorously stable feedback control laws for the derived reduced order models