Improving Swimming Performance and Flow Sensing by Incorporating Passive Mechanisms

As water makes up approximately 70% of the Earth\u27s surface, humans have expanded operations into aquatic environments out of both necessity and a desire to gain potential innate benefits. This expansion into aquatic environments has consequently developed a need for cost-effective and safe underwater monitoring, surveillance, and inspection, which are missions that autonomous underwater vehicles are particularly well suited for. Current autonomous underwater vehicles vastly underperform when compared to biological swimmers, which has prompted researchers to develop robots inspired by natural swimmers. One such robot is designed, built, tested, and numerically simulated in this thesis to gain insight into the benefits of passive mechanisms and the development of reduced-order models. Using a bio-inspired robot with multiple passive tails I demonstrate herein the relationship between maneuverability and passive appendages. I found that the allowable rotation angle, relative to the main body, of the passive tails corresponds to an increase in maneuverability. Using panel method simulations I determined that the increase in maneuverability was directly related to the change in hydrodynamic moment caused by modulating the circulation sign and location of the shed vortex wake. The identification of this hydrodynamic benefit generalizes the results and applies to a wide range of robots that utilize vortex shedding through tail flapping or body undulations to produce locomotion. Passive appendages are a form of embodied control, which manipulates the fluid-robot interaction and analogously such interaction can be sensed from the dynamics of the body. Body manipulation is a direct result of pressure fluctuations inherent in the surrounding fluid flow. These pressure fluctuations are unique to specific flow conditions, which may produce distinguishable time series kinematics of the appendage. Using a bio-inspired foil tethered in a water tunnel I classified different vortex wakes with the foil\u27s kinematic data. This form of embodied feedback could be used for the development of control algorithms dedicated to obstacle avoidance, tracking, and station holding. Mathematical models of autonomous vehicles are necessary to implement advanced control algorithms such as path planning. Models that accurately and efficiently simulate the coupled fluid-body interaction in freely swimming aquatic robots are difficult to determine due, in part, to the complex nature of fluids. My colleagues and I approach this problem by relating the swimming robot to a terrestrial vehicle known as the Chaplygin sleigh. Using our novel technique we determined an analogous Chaplygin sleigh model that accurately represents the steady-state dynamics of our swimming robot. We additionally used the subsequent model for heading and velocity control in panel method simulations. This work was inspired by the similarities in constraints and velocity space limit cycles of the swimmer and the Chaplygin sleigh, which makes this technique universal enough to be extended to other bio-inspired robots

Computational Fluid Dynamics Simulations of Oscillating Wings and Comparison to Lifting-Line Theory

Computational fluid dynamics (CFD) analysis was performed in order to compare the solutions of oscillating wings with Prandtl’s lifting-line theory. Quasi-steady and steady-periodic simulations were completed using the CFD software Star-CCM+. The simulations were performed for a number of frequencies in a pure plunging setup. Additional simulations were then completed using a setup of combined pitching and plunging at multiple frequencies. Results from the CFD simulations were compared to the quasi-steady lifting-line solution in the form of the axial-force, normal-force, power, and thrust coefficients, as well as the efficiency obtained for each simulation. The mean values were evaluated for each simulation and compared to the quasi-steady lifting-line solution. It was found that as the frequency of oscillation increased, the quasi-steady lifting-line solution was decreasingly accurate in predicting solutions

CFD Analysis of Plunging Flat Plates at Low-Reynolds Number

Unsteady aerodynamics include the study of flows that pass an object subjected to oscillations, and therefore, has a strong link with bioinspired flows and flapping airfoils. The central objective of the dissertation is to study the propulsive characteristics of two flat plates at a Reynolds number, Re, of 3.1 × 103 with straight and sharp trailing edges. The reduced frequency, k, is kept between 1.0 and 5.0 with a nondimensional amplitude, k, ranging between 0.125 and 0.500. The problem is solved numerically using Computational Fluid Dynamics (CFD), and results show that different from what is typically observed in airfoils, the mean thrust coefficient, Ct, does not increase monotonically with the reduced frequency, for h = 0.250, having a dip around k = 3.0. The same is not verified for the mean power coefficient, CP , which increases continuously with the reduced frequency for the entire dimensionless amplitude domain studied. Through analysis of pressure contours around the flat plates, a low-pressure zone was detected near the trailing edge, creating a suction effect in that zone. By analyzing the CP and Ct over one period, the recirculation influence was evidenced, displaying a strong effect on the thrust coefficient parameter. However, results also show the influence of another phenomenon. The LEV’s evolution with k was analyzed, via the normalized distance between its center and the surface of the plate, evidencing a behavior similar to the Ct one previously observed. An attempt to relate the phenomena with the Strouhal number, St, was made, identifying a predictable feature of the performance parameters for St ranging between 0 and 1. The trailing-edge shape revealed to influence the propulsive coefficients, being the overall CP values higher and the Ct lower for the flat plate with a straight trailing edge, when compared to the plate with a sharp one.A análise aerodinâmica em regime transiente passa pelo estudo de objetos sujeitos a oscilações e rotações e, portanto, possui uma forte associação com escoamentos bioinspirados. O principal objetivo desta dissertação é o estudo das características propulsivas de duas placas planas com bordo de fuga reto e afiado para um número de Reynolds, Re de 3, 1 × 103 . A frequência reduzida, k, é mantida entre 1, 0 e 5, 0 com uma amplitude adimensional, h, variando entre 0, 125 e 0, 500. O problema é resolvido numericamente usando Dinâmica de Fluidos Computacional (DFC), e os resultados mostram que, contrariamente ao descrito na literatura para perfis alares, o coeficiente de tração médio, Ct, não aumenta monotonamente com a frequência reduzida, reduzindo em torno de k = 3, 0 para h = 0, 250. O mesmo não se verifica para o coeficiente de potência médio, CP , aumentando continuamente com a frequência reduzida para todo o domínio de amplitude adimensional estudado. Analisando os contornos de pressão em torno das placas planas, uma zona de baixa pressão foi detetada perto do bordo de fuga, criando um efeito de sucção naquela zona. Ao analisar os parâmetros CP e Ct ao longo de um período foi evidenciada a influência da recirculação, apresentando um forte impacto no coeficiente de tração. Contudo, os resultados evidenciam a influência de outro fenómeno. A evolução do vórtice de bordo de ataque com k foi analizada, recorrendo a uma distancia normalizada entre o centro do vórtice e a superfície da placa plana, resultando num comportamento similar ao de Ct previamente observado. É realizada uma tentativa de relacionar os fenómenos observados com o número de Strouhal, St, identificando-se um carácter previsível dos parâmetros de desempenho no intevalo 0 = St = 1. A geometria do bordo de fuga aparenta ter influência nos coeficientes propulsivos obtidos, sendo, na sua generalidade, os valores de CP mais altos e os de Ct mais baixos para a placa de bordo de fuga reto, relativamente à placa de bordo de fuga afiado

Aeronautical Engineering: A special bibliography with indexes, supplement 74

This special bibliography lists 295 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1976

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Propulsion through wake synchronization using a flapping foil

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 145-150).The design issues associated with underwater vehicles operating in the surf zone or other high-energy environments are likely to have viable biomimetic solutions. The flapping fin is capable of producing high instantaneous forces, giving fish the ability to turn and accelerate rapidly, and fish are capable of sensing the flow characteristics in their environment using the lateral line, aiding obstacle entrainment, schooling, rheotaxis, and prey detection. A highly maneuverable vehicle that is capable of sensing the changing flows in its environment would have a considerably higher survival rate in dangerous currents. As an initial foray into the sensory and control methods that could be used by a biomimetic vehicle, we studied energy extraction through synchronization with an incoming Karman wake for both fish and mechanical flapping foils. Rainbow trout (Oncorhynchus mykiss) swimming within a flow channel voluntarily positioned themselves 4D downstream from a 2" D-section cylinder, and synchronized with the cylinder wake in both frequency and phase. The phase of the trout's lateral position relative to the wake, described through a Wake Function W(x, t) defined as the lateral-sum of vorticity at a point downstream from the cylinder, was 100Ê» for the head, 160Ê» for the center-of-mass, and 240Ê» for the tail, implying that the trout's mass was moving laterally with the flow in a low-power swimming mode, but that its head and tail had flow across them. A euthanized trout passively synchronized with the wake and accelerated forward towards the cylinder, through fluid-excited motion only, proving that trout benefit not only from drafting in the velocity deficit behind the cylinder, but also through interaction with the vortices in the wake.(cont.) The thrust and efficiency of a heaving and pitching foil depends on how the foil interacts with the wake of an upstream cylinder. A systematic set of tests varying foil motion within the wake revealed that thrust was considerably more sensitive to wake interaction then efficiency, with the coefficient of thrust varying by 0.4, and the efficiency by 0.1, depending on the phase between foil and cylinder heave motions. Thrust and power input was always highest when the foil leading-edge motion opposed the lateral velocities in the wake, likely due to an increase in the angle-of-attack across the foil. When thrust production was high (CT 1), the foil was most efficient when it led the wake by 30Ê» for the leading-edge and 120Ê» for the trailing-edge, but when thrust was low (CT 0.3), efficiency was highest for interactions similar to that of the trout, leading the wake by 125Ê» for the leading-edge and 215Ê» for the trailing-edge. Since the trout's coefficient of thrust was also low, these results were in agreement despite the many differences between the fluid-mechanical systems. I designed and tested an algorithm that could synchronize the foil with an unknown wake using simple sensors and calculations. Additionally, I studied the foil moving passively in the wake using force-feedback to model the foil supports as a spring-mass-damper. The foil produced 0.27 N of thrust at a negative mean power input of 90 mW (energy extraction), a feat impossible for a passive device within a uniform stream.by David Nelson Beal.Ph.D

Wind Turbine Blades Made of Functional Materials

Blades are designed to have good rigidity to be able to minimise the destruction that could be caused by rapid wind load and gust. The increase in length of the wind turbine contributes to the susceptibility of the wind turbine blade to the unpredictable destruction caused by random gusts. One of the ways to effectively increase the blade flexibility as well as increase its unloading effect led to the focus of this research on adaptive wind turbine blades. The project aims to investigate the potential benefits of flapping blades in the extraction of wind energy and proposing an analytical model for the prediction of the normalised induced twist with the sole purpose of having a robust tool for optimal design of adaptive wind turbine blades. In order to achieve these goals, the project is carried out in two aspects. Firstly, a proof of concept of a flapping blade; this report presents the preliminary results of the numerical simulation of a flapping-pitching rectangular flat plate in a uniform air flow. Various combinations of flapping amplitude, flapping frequency and pitching amplitude are analysed and their effect on the instantaneous and maximum lift coefficient is presented. The change in the flapping frequency and amplitude were shown to have considerable effect on the lift coefficient. It can be deduced from the results that the lift coefficient is influenced by the flapping frequency and flapping amplitude combination. The lift coefficient is most affected by the flapping amplitude when compared to the flapping frequency. The results indicate that the pitching amplitude initially enhances the lift coefficient. However, excessive pitching amplitude results in low lift coefficient. The second aspect is to develop a robust analytical model for the prediction of the normalised induced twist of an adaptive blade. Wind turbine adaptive blade design is a coupled aero-structure (CAS) design process, in which, the aerodynamic performance evaluation requires structural deformation analysis of the adaptive blade. However, employing finite element analysis (FEA) based commercial packages for the structural deformation analysis as part of the aerodynamic objective evaluation process has been proven to be time consuming. In order to develop the robust tool for the prediction of the normalised induced twist, the effect of shell thickness distributions, fibre angle distributions and materials are investigated using arbitrary lay-ups configurations. The structural/material configurations and the analyses of the adaptive blades are performed using an auxiliary software tool developed via MATLAB codes for implementing structural deformation analysis. The results are generated in ANSYS Parametric Design Language (APDL), which are read using ANSYS for the extraction of the results. Static and dynamic analyses are carried out for several cases, and the results are used to develop the analytical model for the prediction of the normalised induced twist. The proposed analytical model performance is validated by comparing the normalised induced twist predicted using the proposed model with those obtained using the ANSYS and the results suggest that the proposed model is efficient in predicting the normalised induced twist of an adaptive blade

Aeronautical engineering. A continuing bibliography with indexes, supplement 114

This bibliography lists 394 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1979

Aeronautical Engineering: A Continuing Bibliography with indexes

This bibliography lists 426 reports, articles and other documents introduced into the NASA scientific and technical information system in August 1984. Reports are cited in the area of Aeronautical Engineering. The coverage includes documents on the engineering and theoretical aspects of design, construction, evaluation, testing operation and performance of aircraft (including aircraft engines) and associated components, equipment and systems