Conventionally cast GTD-111EA first stage buckets from GE Frame 5001P-NT engine after 42,000 hours of service, directionally solidified GTD-111DS Frame 5002C buckets after 49,000 hours of service, and conventionally cast IN-738 Frame 5002B buckets after 81,000 hours of service were evaluated before and after refurbishment. These buckets were coated with GT-29, GT-29 plus and RT-22 coatings respectively. Coating condition, microstructural degradation, tensile properties, and creep properties were evaluated in the service aged condition. Microstructure was assessed after the hot isostatic pressing (HIP) and solution heat treatment and again after the full refurbishment and recoating of the buckets. It was found that the GT-29 coating was breached 100% by oxidation in the 5001P engine after service. The GT-29 plus coating on the 5002C engine was breached very slightly and the majority of the coating was still in good condition. The RT-22 coating on the IN-738 bucket was stripped before it was received for evaluation at SwRI. Gamma prime growth, coalescence and agglomeration were found in all of the buckets. Continuous carbide network near the airfoil leading edge was found in the GTD-111EA bucket. Significant improvement in the microstructural condition was observed after the refurbishment for the GTD-111 buckets. However, the gamma prime morphology was not normal for the IN-738 bucket. Both tensile and creep properties of the GTD-111 buckets showed significant improvement after refurbishment. However, for the IN-738 bucket little improvement on the mechanical properties was observed. The reasons for this and the correlation between the microstructure and properties are discussed in this paper.

Pneumatic artificial muscles (PAMs) are used in robotics applications for their light-weight design and superior static performance. Additional PAM benefits are high specific work, high force density, simple design, and long fatigue life. Previous use of PAMs in robotics research has focused on using “large,” full-scale PAMs as actuators. Large PAMs work well for applications with large working volumes that require high force and torque outputs, such as robotic arms. However, in the case of a compact robotic hand, a large number of degrees of freedom are required. A human hand has 35 muscles, so for similar functionality, a robot hand needs a similar number of actuators that must fit in a small volume. Therefore, using full scale PAMs to actuate a robot hand requires a large volume which for robotics and prosthetics applications is not feasible, and smaller actuators, such as miniature PAMs, must be used. In order to develop a miniature PAM capable of producing the forces and contractions needed in a robotic hand, different braid and bladder material combinations were characterized to determine the load stroke profiles. Through this characterization, miniature PAMs were shown to have comparably high force density with the benefit of reduced actuator volume when compared to full scale PAMs. Testing also showed that braid-bladder interactions have an important effect at this scale, which cannot be modeled sufficiently using existing methods without resorting to a higher-order constitutive relationship. Due to the model inaccuracies and the limited selection of commercially available materials at this scale, custom molded bladders were created. PAMs created with these thin, soft bladders exhibited greatly improved performance.

Pneumatic artificial muscles (PAMs) are lightweight, flexible actuators capable of higher specific work than comparably-sized hydraulic actuators at the same pressure and electric motors. PAMs are composed of an elastomeric bladder surrounded by a helically braided sleeve. Lightweight, compliant actuators are particularly desirable in portable, heavy-lift robotic systems intended for interaction with humans, such as those envisioned for patient assistance in hospitals and battlefield casualty extraction. However, smooth and precise control remains difficult because of nonlinearities in the dynamic response. The objective of this paper is to develop a control algorithm that satisfies accuracy and smooth motion requirements for a two degree-of-freedom manipulator actuated by pneumatic artificial muscles and intended for interaction with humans, such as lifting a human. This control strategy must be capable of responding to large, abrupt variations in payload weight over a high range of motion. In previous work, the authors detailed the design and construction of a proof-of-concept PAM-based manipulator. The present work investigates the feasibility of combining output feedback using proportional-integral-derivative control or fuzzy logic control with model-based feedforward compensation to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the geometric parameters of the pneumatic actuators, and the arm dynamics. Simulations were performed in order to validate the control algorithm, guide controller design, and predict optimal gains. Using real-time interface software and hardware, the controller was implemented and experimentally tested on the manipulator. Performance was evaluated for several trajectories, and different payload weights. The effect of varying the feedforward gain was also analyzed. Model refinement further improved performance.

Copper alloy netting is increasingly used for offshore aquaculture, harbor protection and other marine applications. Its advantageous characteristics include high resistance to biofouling and increased strength compared to polymer nets. However, the hydrodynamic properties of copper nets are not well studied. In this paper, the results of experimental studies of drag forces on copper alloy net panels are reported. Based on these studies, empirical values for drag coefficients are proposed for various types of copper nets, and compared to the corresponding data for polymer netting. It is shown that copper nets exhibit significantly lower resistance to the current flow which corresponds to lower values of drag coefficient. Coefficients obtained from the experiments are incorporated into the finite element program Aqua-FE, developed at the University of New Hampshire for analysis of flexible structures subjected to waves and currents in marine environment. The results of the numerical simulations for a small volume fish cage, subjected to two different sets of environmental conditions, are analyzed to compare how introduction of copper netting instead of traditional nylon nets affects the dynamic response of the system.

Recent advances in actuator technology suggest that the implementation of reliable, high power-to-weight ratio pneumatic actuation systems is now possible for robotic platforms. Current robotic manipulator arms for casualty extraction and patient placement use hydraulic actuation, whereas related robotic prosthetic devices use large, heavy actuator motors. We have developed an alternative solution to robotic manipulation that employs pneumatic artificial muscles (PAMs) to generate desired joint torque and range of motion. The goal of this study is to determine the size and configuration of a robotic manipulator for battlefield casualty extraction. Following characterization and comparison of different-sized PAM actuators, a prototype of a PAM robotic manipulator arm was constructed. A quasi-static model for the PAM actuators is applied to system modeling. This model includes the Gaylord force from pressure effects on the braid, as well as a nonlinear Mooney-Rivlin term that considers the elastic energy of the bladder. Experiments are performed to measure joint torque over the manipulator range of motion. The model developed here is experimentally validated.

As wind turbines continue to grow larger, problems associated with adverse aerodynamic loads will grow more critical. Thus, the wind energy technical community has begun to seriously consider the potential of aerodynamic control methodologies for mitigating adverse aerodynamic loading. Spatial and temporal attributes of the structures and processes present in these flow fields hold important implications for active aerodynamic control methodologies currently being contemplated for wind turbine applications. The current work uses complementary experimental and computational methodologies, to isolate and characterize key attributes of blade flow fields associated with axisymmetric and yawed turbine operation. During axisymmetric operation, a highly three-dimensional, shear layer dominated flow field yields rotational augmentation of both mean and standard deviation levels of aerodynamic forces. Under yawed operating conditions, pseudo-sinusoidal inflow angle oscillations elicit dynamic stall, which significantly intensifies aerodynamic load production. Both rotationally augmented and dynamically stalled flows possess attributes likely to pose central challenges for turbine flow control. Whether active control of turbine aerodynamics can help alleviate adverse aerodynamic loads will depend on comprehension and command of the issues documented herein.

Surface pressure data were acquired using the NREL Unsteady Aerodynamics Experiment, a full-scale horizontal axis wind turbine, which was erected in the NASA Ames 80 ft × 120 ft wind tunnel. Data were collected first for a stationary blade, and then for a rotating blade with the turbine disk at zero yaw. Analyses compared aerodynamic forces and surface pressure distributions under rotating conditions against analogous baseline data acquired from the stationary blade. This comparison allowed rotational modifications to blade aerodynamics to be characterized in detail. Rotating conditions were seen to dramatically amplify aerodynamic forces, and radically alter surface pressure distributions. These and subsequent findings will more fully reveal the structures and interactions responsible for these flow field enhancements, and help establish the basis for formalizing comprehension in physics based models.

As the aquaculture industry considers moving into the open ocean, understanding the dynamic response of fish containment structures becomes critical. Identification of possible resonant conditions and motion characteristics is necessary for system structural integrity and maximizing fish survivability. In this study, heave (vertical motion) free release tests of a central spar fish cage were conducted using a combination of physical and finite element models and field observations. These tests were performed to investigate the added mass, damping ratio and natural period of the system in the vertical direction. The test results were analyzed considering both linear and nonlinear damping. The comparison of these tests show that (1) the damped natural period of this fish cage is longer than 20 seconds, (2) the numerical model underestimates the damping and the cage oscillates longer and at a higher frequency than observed with the field tests and (3) the physical model is nearly critically damped near equilibrium due to Reynolds number effects at the model scale.

Blade rotation routinely and significantly augments aerodynamic forces during zero yaw HAWT operation. To better understand the flow physics underlying this phenomenon, time dependent blade surface pressure data were acquired from the NREL Unsteady Aerodynamics Experiment, a full-scale HAWT tested in the NASA Ames 80 ft × 120 Ft wind tunnel. Time records of surface pressures and normal force were processed to obtain means and standard deviations. Surface pressure means and standard deviations were analyzed to identify boundary layer separation and reattachment locations. Separation and reattachment kinematics were then correlated with normal force behavior. Results showed that rotational augmentation was linked to specific separation and reattachment behaviors, and to associated three-dimensionality in surface pressure distributions.

To further reduce the cost of wind energy, future turbine designs will continue to migrate toward lighter and more flexible structures. Thus, the accuracy and reliability of aerodynamic load prediction has become a primary consideration in turbine design codes. Dynamically stalled flows routinely generated during yawed operation are powerful and potentially destructive, as well as complex and difficult to model. As a prerequisite to aerodynamics model improvements, wind turbine dynamic stall must be characterized in detail and thoroughly understood. In the current study, turbine blade surface pressure data and local inflow data acquired by the NREL Unsteady Aerodynamics Experiment during the NASA Ames wind tunnel experiment were analyzed. The dynamically stalled, vortex dominated flow field responded in systematic fashion to variations in wind speed, turbine yaw angle, and radial location, forming the basis for more thorough comprehension of wind turbine dynamic stall and improved modeling.

Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of micro engineering, most notably in the development of diamond coated micromilling tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp 3 character have a profound effect on the tribological properties of the films deposited. In this paper we present experimental results on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of micromilling tools. The sp 3 character optimises at 200 ppm of nitrogen and above this value the surface becomes much smoother and crystal sizes decrease considerably. Fracture induced wear of the diamond grain is the most important mechanism of material removal from a micromilling tool during the grinding process. Fracture occurs as a consequence of tensile stresses induced into diamond grains by grinding forces to which they are subjected. The relationship between the wear of diamond coated milling tools, component machining forces, and induced stresses in the model diamond grains is described in detail. A significant correlation is found between the maximum value of tensile stress induced in the diamond grain and the appropriate wear parameter, in this case the grinding ratio. It is concluded that the magnitude of tensile stresses induced in the diamond grain by machining forces at the rake face is the best indicator of tool wear during the micromachining process.

The advent of nanotechnology has created a demand for precision-machined substrates so that ‘bottom-up’ nanomanufacturing processes can be used to produce functional products at the nanoscale. However, machining processes must be scaled down by an order of magnitude that requires very stable desktop machine tools to produce precision-machined substrates using cutting tools that are rotated at speeds in excess of one million revolutions per minute. Therefore, the mechanics of chip formation at this scale are critical when one considers the effect of chip formation on the generation of surface roughness on the substrate. The tight curl of a machined chip in orthogonal machining appears to be part of the primary shear process. It is also known that transient tight curl occurs before a secondary shear zone develops ahead of the removal of the chip from the cutting zone. However, continuum models predict that curled chips incorporate stresses due to the establishment of a secondary shear zone. A model is presented in terms of the heterogeneous aspects of continuous chip formation, which shows very good agreement with experimental data.