Numerical and experimentl evaluation of drag force on coupled fish

The aim of the work was to investigate the presence of a hydrodynamic benefit arising from the proximity among fish. In order to do this, both numerical simulations and laboratory experiments were done. Numerical simulations results shows no evidences of the supposed benefit. However, experimental results were not reliable enough to validate simulations. The pattern showed by fish might comes from other benefit which does not comes from fish hydrodynami

Aerodynamics and Aeroacoustic Sources of a Coaxial Rotor

Vehicles with coaxial, contra-rotating rotor systems (CACR) are being considered for a range of applications. Design parameters are identified that effect the fundamental aerodynamics and fluid dynamic features of a CACR in hover, vertical, and edgewise flight. Understanding the fluid dynamic features is a precursor to studying the aeroacoustics of a coaxial rotor. Rotor performance was computed initially using Navier-Stokes solver with prescribed blade section aerodynamic properties, the results validated against generic experimental test cases. Using a A 2D potential flow code and 2D OVERFLOW compressible-flow Navier-Stokes solver, the fluid dynamics of blade interactions was simplified and broken into a 2D blade crossing problem, with crossing locations and velocity fields from the rotor results to understand circulation, thickness, compressibility, shed vorticity, downwash, and viscosity effects. A calculation tool has been developed to identify time and location of blade overlap and BVI time location for CACR. Specific aerodynamic phenomena that occur for each noise source relevant to CACR are presented, along with computational tools to predict these occurrences

Autonomous Vehicles

This edited volume, Autonomous Vehicles, is a collection of reviewed and relevant research chapters, offering a comprehensive overview of recent developments in the field of vehicle autonomy. The book comprises nine chapters authored by various researchers and edited by an expert active in the field of study. All chapters are complete in itself but united under a common research study topic. This publication aims to provide a thorough overview of the latest research efforts by international authors, open new possible research paths for further novel developments, and to inspire the younger generations into pursuing relevant academic studies and professional careers within the autonomous vehicle field

Numerical Simulation of Wind Turbines

The book contains the research contributions belonging to the Special Issue "Numerical Simulation of Wind Turbines", published in 2020-2021. They consist of 15 original research papers and 1 editorial. Different topics are discussed, from innovative design solutions for large and small wind turbine to control, from advanced simulation techniques to noise prediction. The variety of methods used in the research contributions testifies the need for a holistic approach to the design and simulation of modern wind turbines and will be able to stimulate the interest of the wind energy community

Pneumatic Artificial Muscle Driven Trailing Edge Flaps For Active Rotors

This research focuses on the development of an active rotor system capable of primary control and vibration reduction for rotorcraft. The objective is to investigate the feasibility of a novel Trailing Edge Flap (TEF) actuation system driven by Pneumatic Artificial Muscles (PAMs). A significant design effort led to a series of experimental apparatuses which tested various aspects of the performance of the actuators themselves and of TEF systems driven by them. Analytical models were developed in parallel to predict the quasistatic and dynamic behavior of these systems. Initial testing of a prototype blade section with an integrated PAM driven TEF proved the viability of the concept through successful benchtop testing under simulated M = 0.3 loading and open jet wind tunnel tests under airspeeds up to M = 0.13. This prototype showed the ability of PAM actuators to generate significant flap deflections over the bandwidth of interest for primary control and vibration reduction on a rotorcraft. It also identified the importance of high pneumatic system mass flow rate for maintaining performance at higher operating frequencies. Research into the development and improvement of PAM actuators centered around a new manufacturing technique which was invented to directly address the weaknesses of previous designs. Detailed finite element model (FEM) analysis of the design allowed for the mitigation of stress concentrations, leading to increased strength. Tensile testing of the swaged actuators showed a factor of safety over 5, and burst pressure testing showed a factor of safety of 3. Over 120,000,000 load cycles were applied to the actuators without failure. Characterization testing before, during, and after the fatigue tests showed no reduction in PAM performance. Wind tunnel testing of a full scale Bell 407 blade retrofitted with a PAM TEF system showed excellent control authority. At the maximum wind tunnel test speed of M = 0.3 and a derated PAM operating pressure of 28 psi, 18.8° half-peak-to-peak flap deflections were achieved at 1/rev (7 Hz), and 17.1° of half-peak-to-peak flap deflection was still available at 5/rev (35 Hz). A quasistatic system model was developed which combined PAM forces, kinematics and flap aerodynamics to predict flap deflection amplitudes. This model agreed well with experimental data. Whirl testing of a sub-span whirl rig under full scale loading conditions showed the ability of PAM TEF systems to operate under full scale levels of centrifugal (CF), aerodynamic, and inertia loading. A commercial pneumatic rotary union was used to provide air in the rotating frame. Extrapolation of the results to 100% of CF acceleration predicts 15.4° of half-peak-to-peak flap deflection at 1/rev (7 Hz), and 7.7° of half-peak-to-peak flap deflection at 5/rev (35 Hz). A dynamic model was developed which successfully predicted the time domain behavior of the PAM actuators and PAM TEF system. This model includes control valve dynamics, frictional tubing losses, pressure dynamics, PAM forces, mechanism kinematics, aerodynamic hinge moments, system stiffness, damping, and inertia to solve for the rotational dynamics of the flap. Control system development led to a closed loop control system for PAM TEF systems capable of tracking complex, multi-sinusoid flap deflections representative of a combined primary control and vibration reduction flap actuation scheme. This research shows the promise that PAM actuators have as drivers for trailing edge flaps on active helicopter rotors. The robustness, ease of integration, control authority and tracking accuracy of these actuators have been established, thereby motivating further research

Maine Tidal Power Initiative: Environmental Impact Protocols for Tidal Power

As a result of ongoing climate change, the pressure for the development of new sources of renewable energy has increased. It is extremely likely that climate change is caused by anthropogenic activities. Thus even if dramatic gains are made in energy efficiency; the addition of novel renewable energy sources is critical to reducing fossil fuel emissions. Even current goals for a reduction in the growth of greenhouse gas emissions mean that all possible low-carbon or non-carbon emitting energy sources be considered. In the marine environment, energy in tidal currents, waves, and thermal structure may be extracted to produce electricity. These energy sources are a critical element in the overall renewable portfolio since, unlike wind and solar energy, both marine thermal and tidal energy are reliable additions to the overall electrical grid. In the case of tidal energy, the contribution of periodic but reliable sources of renewable energy becomes increasingly critical as wind and solar penetration in the grid increase. In a high renewable energy penetration grid, a resource like tidal energy does not provide the same base load capacity as, for example, a nuclear power plant. However, tidal energy can have the effect of reducing the size of either storage or peaking capacity that is required for grid stability by providing power for recovery of dispatchable loads. However, as an immature technology, significant questions remain regarding basic questions like the scale of the potential resource, the impact on sediment transport, the effects on fish populations and communities, and the ability to design a system which is acceptable by the people in the associated communities. The objectives of the funded project were to examine tidal power development in Maine from all perspectives: engineering, resource assessment, biological effects, and social dimensions. Resource and environmental research focused on data collection for the Cobscook Bay/Western Passage, possibly the most viable commercial tidal energy site in the US, tidal power sites along with initial evaluation of the suitability of the approach for at least two other tidal development sites in Maine. Concomitantly, alternative energy research is used as a basis of education for a number of graduate and undergraduate students at the University of Maine and Maine Maritime Academy. The Maine Tidal Power Initiative has developed resource and environmental assessment protocols in conjunction with the deployment of a specific marine hydrokinetic device. The protocols are transferrable throughout Maine and the US to evaluate tidal energy resources and better understand the potential impact of this development on the environment. Again, site-specific social science and environmental research focused on the Cobscook Bay/Western Passage area near Eastport Maine. The protocols and methods developed at these sites have also been used to perform initial scoping reviews of locations in Castine Harbor and Wiscasset, Maine that represent a more modest and more typical small scale energy resource. Specific barrier issues which have been addressed for the industry are technologies and protocols for measuring and modeling tidal flows, responses of fishes to those flows, and people interacting in these environments. Measuring tidal flows is critical to the key economic driver for this industry, the size of the potential resource. The second barrier issue is the need for methods for measuring the impact of marine hydrokinetic (MHK) devices on fish. Acoustic methods have been used with ground truth validation from trawls. The protocols developed in this project have already had a significant impact on the approach that has been taken at other sites. Finally the assessment of the human community response to these technologies and impact on community cohesion and participation is perhaps the largest single barrier to the acceptance of the projects. This work also has the potential to be replicated at other sites, although in both the case of the environmental effects and the social response to these projects, details of the species impacted and the economic and social environment are the ultimate determinants of impact and acceptance. The technology focus for most of this work has been the cross-flow turbine developed by Ocean Renewable Power Company. Testing in the University of Maine tow tank has allowed a large design space to be explored for the optimization of the commercial turbine design. The design code developed for the project was validated using this data set. Both the design code and the data will be placed in a public repository. The most important outcome of the turbine design portion of the work is some general design parameters that can be used to assist in the site assessment and for benchmarking of proprietary designs. The design as well as the data is available for resource assessment and design comparisons. The appeal of this turbine design is that the potential exists for a low solidity turbine with lower tip speed ratios, which will have good performance. The low solidity and tip speed ratio is likely to reduce the risk of fish impacts and thus reduce environmental impact and community resistance to these technologies. The need for low carbon energy sources is undeniable. Resistance to large-scale renewable energy development also continues to increase. The overall approach to this project, where the design of the system considers environmental impacts and social acceptance from the initial engineering design stages and continues with an adaptive management scheme, is the only option for addressing energy needs at the scale required

Physics-based Machine Learning Methods for Control and Sensing in Fish-like Robots

Underwater robots are important for the construction and maintenance of underwater infrastructure, underwater resource extraction, and defense. However, they currently fall far behind biological swimmers such as fish in agility, efficiency, and sensing capabilities. As a result, mimicking the capabilities of biological swimmers has become an area of significant research interest. In this work, we focus specifically on improving the control and sensing capabilities of fish-like robots. Our control work focuses on using the Chaplygin sleigh, a two-dimensional nonholonomic system which has been used to model fish-like swimming, as part of a curriculum to train a reinforcement learning agent to control a fish-like robot to track a prescribed path. The agent is first trained on the Chaplygin sleigh model, which is not an accurate model of the swimming robot but crucially has similar physics; having learned these physics, the agent is then trained on a simulated swimming robot, resulting in faster convergence compared to only training on the simulated swimming robot. Our sensing work separately considers using kinematic data (proprioceptive sensing) and using surface pressure sensors. The effect of a swimming body\u27s internal dynamics on proprioceptive sensing is investigated by collecting time series of kinematic data of both a flexible and rigid body in a water tunnel behind a moving obstacle performing different motions, and using machine learning to classify the motion of the upstream obstacle. This revealed that the flexible body could more effectively classify the motion of the obstacle, even if only one if its internal states is used. We also consider the problem of using time series data from a `lateral line\u27 of pressure sensors on a fish-like body to estimate the position of an upstream obstacle. Feature extraction from the pressure data is attempted with a state-of-the-art convolutional neural network (CNN), and this is compared with using the dominant modes of a Koopman operator constructed on the data as features. It is found that both sets of features achieve similar estimation performance using a dense neural network to perform the estimation. This highlights the potential of the Koopman modes as an interpretable alternative to CNNs for high-dimensional time series. This problem is also extended to inferring the time evolution of the flow field surrounding the body using the same surface measurements, which is performed by first estimating the dominant Koopman modes of the surrounding flow, and using those modes to perform a flow reconstruction. This strategy of mapping from surface to field modes is more interpretable than directly constructing a mapping of unsteady fluid states, and is found to be effective at reconstructing the flow. The sensing frameworks developed as a result of this work allow better awareness of obstacles and flow patterns, knowledge which can inform the generation of paths through the fluid that the developed controller can track, contributing to the autonomy of swimming robots in challenging environments

Contributions to the Understanding of Wind Turbine Aerodynamics Using a RANS Solver with Transition Modeling

Wind turbine sizes have been steadily increasing to reduce the cost of generating electricity using wind energy. The increased wind turbine blade size has led to increased interest in the accurate prediction of the aerodynamics of large wind turbine blades. In this work, two-dimensional simulations of wind turbine airfoils and three-dimensional simulations of the Sandia 100 m wind turbine blade were conducted. The focus of the simulations was to evaluate improvements in turbulence modeling for wind turbine applications. The flow field was modeled using a Reynolds-Averaged Navier-Stokes flow solver. The turbulence model included transition modeling to capture the significant regions of laminar flow found on wind turbine airfoils and wind turbine blades. The turbulence model was also modified to increase sensitivity to adverse pressure gradients. The effects of modifying the turbulence modeling were quantified using lift and drag for two-dimensional simulations while wind turbine thrust and power were used as metrics for three-dimensional simulations. The two-dimensional studies showed that the adverse pressure gradient correction lowered lift predictions post-stall by about 13%, significantly reducing lift over-prediction and bringing simulations closer to experimental results. Transition modeling lowered drag predictions by 30% to 50% at low angles of attack bringing the predicted values into good agreement with experimental results. The addition of transition modeling in the three-dimensional simulations increased the predicted thrust by 1% to 3% and predicted power by 3% to 6%. The extent of laminar flow was visualized using intermittency. Laminar flow was observed on large portions of the Sandia 100 m blade at normal operating conditions. A preliminary study on the effects of leading edge tubercles on the Sandia 100 m blade was performed, no significant changes in wind turbine performance were observed at nominal operating conditions

Aeronautical engineering: A continuing bibliography with indexes (supplement 267)

This bibliography lists 661 reports, articles, and other documents introduced into the NASA scientific and technical information system in June, 1991. Subject coverage includes design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; theoretical and applied aspects of aerodynamics and general fluid dynamics; electrical engineering; aircraft control; remote sensing; computer sciences; nuclear physics; and social sciences