A Multi-Body Dynamics based numerical modelling tool for solving aquatic biomimetic problems

In this paper, a versatile Multi-Body Dynamic (MBD) algorithm is developed to integrate an incompressible fluid flow with a bio-inspired multibody dynamic system. Of particular interest to the biomimetic application, the algorithm is developed via four properly selected benchmark verifications. The present tool has shown its powerful capability for solving a variety of biomechanics fish swimming problems, including self-propelled multiple degrees of freedom with a rigid undulatory body, multiple deformable fins and an integrated system with both undulatory fish body and flexible fins. The established tool has paved the way for future investigation on more complex bio-inspired robots and live fish, for either propulsion or manoeuvring purposes

Numerical simulation of a multi-body system mimicking coupled active and passive movements of fish swimming

A multi-body system model is proposed for the mimicking of swimming fish with coupled active and passive movements. The relevant algorithms of the kinematics and dynamics of the multi-body system and coupled fluid solver are developed and fully validated. A simplified three-body model is applied for the investigation of the hydrodynamic performance of both an active pitch motion and passive movement. In general, there is an optimal stiffness, under which the model swims with the fastest velocity. The effect of the damper can be drawn only when the stiffness is small. Comparing with the rigid tail, the flexible tail leads to a faster speed when the stiffness and damping coefficients are in a suitable range

Quantitative analysis of take-off forces in birds

The increasing interest on Unmanned Air Vehicles (UAV’s) and their several utilities blended with the need of easy carrying and also the stealth, lead to the need to create the concept of Micro Air Vehicles (MAV’s) and the Nano Air Vehicles (NAV’s). Due to the current interest and the present lack of knowledge on the insect’s and bird’s flight, this study was intended to interpret the forces involved on the moment of the take-off of a bird, recurring to an experiment involving a fast data acquisition force sensor and high speed camera, in addition known facts from earlier studies. In order to do that a bibliographic revision was done, to know what was already studied and to find what could yet be studied. That way could be formed a link on the factors involved on the propulsion of a bird at the moment of take-off. The main conclusions obtained by this work is that the bird can produce movements that will enhance the total moment when the bird stretches its neck forward and moving head down followed by stretching even more its neck and moving head up impelling himself into the air, resulting in a main role on the mechanical forces (against perch) for the bird first moments momentum. Columba livia can generate about 4 times its weight worth mechanic force (against perch) and above 8 times its weight during the 2nd downstroke.O interesse crescente nos Veículos Aéreos não Tripulados “Unmanned Air Vehicles (UAV’s)” e suas diversas utilidades em conjunto com a necessidade de seu fácil transporte e furtividade, levaram à necessidade de criar o conceito dos Micro Veículos Aéreos “Micro Air Vehicles (MAV’s)” e os Nano Veículos Aéreos “Nano Air Vehicles (NAV’s)”. Este tipo de veículos tem como fonte inspiradora os insetos e aves devido à necessária produção simultânea de sustentação e propulsão. Tal como no voo convencional, também no voo animal podem ser identificadas as fases de levantamento (descolagem) e aterragem como diferenciadas do voo longe de uma superfície de apoio. Este trabalho é dedicado ao estudo da fase de levantamento de voo de uma ave columba livia. Foram realizadas experiências para medir a força inicial produzida pela ave para iniciar o voo e a respetiva trajetória na zona próxima do ponto de apoio inicial. Estas medidas foram efetuadas com um sensor de força dotado de elevada velocidade de aquisição de dados e uma camara de alta velocidade. As principais conclusões obtidas com a realização deste trabalho é o facto de que a ave consegue produzir movimentos, que aumentar o momento total quando a ave estica o pescoço para a frente e movendo a cabeça para baixo seguido por continuação de esticamento do pescoço e movimento da cabeça para cima impelindo-se para o ar, resultando num papel principal relativamente às forças mecânicas (contra o poleiro) para o momento linear actuante nos primeiros momentos. Columba livia consegue gerar cerca de 4 vezes o seu peso em força mecânica e acima de 8 vezes o seu peso durante o 2º downstroke

3D locomotion biomimetic robot fish with haptic feedback

This thesis developed a biomimetic robot fish and built a novel haptic robot fish system based on the kinematic modelling and three-dimentional computational fluid dynamic (CFD) hydrodynamic analysis. The most important contribution is the successful CFD simulation of the robot fish, supporting users in understanding the hydrodynamic properties around it

Bioinspired fluid-structure interaction problems: gusts, load mitigation and resonance

Mención Internacional en el título de doctorNature often serves as a reference for the design and development of sustainable solutions in numerous different fields. The recent development of small-scale robotic vehicles, asMicro-Air Vehicles (MAVs), is not an exception, and has had an increasingly important impact on society, proposing new alternatives in areas as surveillance or planetary exploration. Trying to mimic the flight of insects and small birds, these devices try to offer more efficient designs and with higher manoeuvrability abilities than the already existing designs. It happens similar with robotic swimmers, with many different existing prototypes. Indeed, it is even possible to find designs of bioinspired small-scale wind turbines based on auto-rotating seeds looking for a more efficient energy harvesting. Besides, in order to develop sustainable designs, increasing their lifetime and reducing the maintenance costs are crucial factors. Depending on the device to design, different methodologies may be followed in order to achieve these two goals while meeting the design requirements. One clear example can be found in the development of wind turbines. Their blades must be designed to withstand not only maximum loads and stresses but also the fatigue caused by the fluctuations around the load required to operate correctly. Reducing fatigue issues by limiting the amplitude of those fluctuations using passive or active control is a viable option to improve their lifetime. The aimof this dissertation is to contribute to the understanding of the underlying physics in biolocomotion. To this end, direct numerical simulations of different examples and problems at low Reynolds number, Re, have been performed using an existing fluid-structure interaction (FSI) solver. This FSI solver relies on the coupling of an incompressible-flow solver with robotic algorithms for the computation of the dynamics of a system of connected rigid bodies. The particularities of this solver are detailed in the thesis. The second part of the thesis includes the analysis of these examples and problems mentioned above.More in detail, the aerodynamic and aeroelastic behaviour of airfoils and wings at Re Æ 1000 in various conditions and environments has been analysed. Natural flyers and swimmers are immersed in turbulent and gusty environments which affect their aerodynamic behaviour. The first problem that has been studied is that of the unsteady response of airfoils impacted by vortical gusts. This first example focuses on how the impact of viscous vortices of different size and intensity on two-dimensional airfoils modify their response. Although in a simplified framework, this analysis allows to gather relevant information about the aerodynamic performance of the airfoils. This aerodynamic response is seen to be self-similar, and the work proposes a semi-empirical model to determine the temporal evolution of the lifting forces based on an integral definition of the vertical velocity induced by the gust, which can be known a priori. The target of the second problem is to analyse the load that can be mitigated in airfoils undergoing oscillations in the angle of attack using passive-pitching trailing edge flaps. This corresponds, for example, to a simplification of the problem of load mitigation in small-scale wind turbines. The use of passive-pitching trailing edge flaps is a strategy that has recently been recently proposed for large-scale wind turbines. Here, we investigate the validity of this strategy on a completely different scenario. Contrary to what happens in experiments at higher Reynolds numbers, whose results match the predictions of a quasi-steady linear model when the kinematics are within the range of applicability of this model, the load mitigation obtained in this work differs from the values of this theory. The load mitigated is larger or smaller than the predicted values depending on the amplitude of the oscillations in the angle of attack. However, the results of this work show that an increase in the length of the flap while the chord of the airfoil is kept constant leads to an equal change in the reduction of load, in line with the predictions of the quasi-steady model. The development of vortical structures is clearly affected by the flap when it is sufficiently large, which also involves changes in the dynamics of the flap and the forces seen by the airfoil. The repercussion that several of the variables defining the parametric space have on the aerodynamic behaviour of the foil and the dynamics of the flap are analysed. This allows to gather more information for an appropriate selection of those variables. Finally, the third and fourth problems involve the study of the effects of spanwise flexibility on both isolated wings and pairs of wings arranged in horizontal tandem undergoing flapping motions. The wings are considered to be rectangular flat plates, and the spanwise flexibility is modelled discretizing these flat plates in a finite number of rigid sub-bodies that are connected using torsional springs. The wings are considered to be rigid in the chordwise direction. Isolated spanwise-flexible wings find an optimal propulsive performance when a fluid-structural resonance occurs. At this flexibility, the time-averaged thrust is maximum and twice the value yielded by the rigid case, and the increment in efficiency is around a 15%. Flexibility and the generation of forces are coupled, such that the structural response modifies the development of the vortical structures generated by the motion of the wing, and vice versa. The optimal performance comes from a combination of larger effective angles of attack, properly timed with the pitching motion such that the projection of the forces is maximum, with a delayed development of the vortical structures. Besides, while aspect ratio effects are important for rigid wings, this effect becomes small when compared to flexibility effects when the wings become flexible enough. In fact, while the increase in thrust coefficient for rigid wings with aspect ratio 4 is 1.2 times larger than that provided by rigid wings with aspect ratio equal to 2, the value of this coefficient for resonant wings is twice the value yielded by rigid wings of aspect ratio 4. While forewings of the tandem systems are found to behave similarly to isolated wings, the aeroelastic response of the hindwings is substantially affected by the interaction with the vortices developed and shed by the forewings. This wake capture effect modifies the flexibility at which an optimal propulsive behaviour is obtained. This wake capture effect is analysed through an estimation of the effective angle of attack seen by both forewings and hindwings, linking the optimal behaviour with the maximisation of the effective angle of attack at the right instants. Based on the obtained results, a proof-of-concept study has been carried out analysing the aerodynamic performance of tandem systems made of wings with different flexibility, which suggests that the latter could outperformsystems of equally flexible wings.This thesis has been carried out in the Aerospace Engineering Department at Universidad Carlos III de Madrid. The financial support has been provided by the Universidad Carlos III de Madrid through a PIPF scholarship awarded on a competitive basis, and by the Spanish Ministry of Economy and Competitiveness through grant DPI2016-76151-C2-2-R (AEI/FEDER, UE).Programa de Doctorado en Mecánica de Fluidos por la Universidad Carlos III de Madrid; la Universidad de Jaén; la Universidad de Zaragoza; la Universidad Nacional de Educación a Distancia; la Universidad Politécnica de Madrid y la Universidad Rovira i VirgiliPresidente: José Ignacio Jiménez González.- Secretaria: Andrea Ianiro.- Vocal: Manuel Moriche Guerrer

Oscillating Foil Propulsion

In this thesis, an investigation on the use of oscillating foil propulsion for marine vehicle as an alternate effective propulsion system is presented. Three different oscillating foil propellers, namely: two-dimensional oscillating foil propeller; flexible fin propeller, and rotary foil propeller, have been studied. The thesis is made up of four parts: one related to each type of propeller and one on the application of oscillating foil propellers along with general conclusions. Two-Dimensional Oscillating Foil Propeller A review on the hydrodynamic forces and moments acting on a two-dimensional oscillating foil is presented. The equations for estimating the force system have been extended to cover different phase lags between heave and pitch and to calculate the force system at a particular instant of time within an oscillating cycle. The sensitivity of the propulsive thrust coefficient and the hydromechanical efficiency has been investigated for a range of different parameters. The operating condition for optimum performance is identified. Flexible Fin Propeller The theoretical model of the flexible fin propeller, which has been set up by combining linearised unsteady foil theory and large deflection beam theory, is described. Non-dimensional parameters are established to study the performance of this type of propeller. A flexible fin propeller model and its test rig was designed and built. The model was tested in the Hydrodynamics Laboratory at the Department of Naval Architecture and Ocean Engineering, the University of Glasgow. The performance of the propeller was examined at both forward and zero speeds. Results have been compared with theoretical predictions. Conclusions on the performance of the flexible fin propeller are drawn based on the theoretical predictions and experimental results. The stress acting on the flexible bar has been computed and discussed. The selection of material has been discussed and promising materials identified. The feasibility of using flexible fin propellers for wave propulsion to absorb wave energy and convert it into propulsive thrust has been studied. A one-fifth scale model of a three quarter ton racing yacht with a flexible fin propeller model mounted at the stem was tested. At a low Froude number, there is a significant reduction in the motion response and in the required thrust around the resonance zone, where the encounter wave length is equal to the ship length. Rotary Foil Propeller A three bladed propeller model with high-aspect ratio blades was tested in forward and reverse directions and zero speed conditions. The experimental results on the performance of the model at forward speed have been compared to that predicted by Bose [1987] using multiple stream tube theory and discussed. Application of Oscillating Foil Propeller and General Conclusions The practical application of three oscillating foil propellers and economic studies of their operation have been studied and discussed. Three ship examples with the same Froude number but different in sizes and a high speed craft have been used in these studies. Three types of oscillating foil propeller are designed for each ship example. The required stem hull form and the driving mechanism have been discussed. The application of the flexible fin propeller in wave propulsion has been demonstrated. The natural frequency of a full scale flexible fin propeller was calculated and found to be much higher than the optimum driving frequencies in the operating condition. The net present value method has been applied in the economic studies where breakeven conditions, different interest rates, fluctuation of oil price, and different additional maintenance costs have been considered. The main conclusions of this research have been drawn up and are presented. Recommendation on the design of these propeller are also made

Consultants Second Report, Volume 2: Technical Appraisal Of The Devices - Part 1

This report is the second general assessment prepared by the Consultants for the Wave Energy Steering Committee, the first having been submitted in August 1977. The primary objective of this report is to present to those responsible for directing the U.K. wave energy programme a full assessment of the devices now under development from the point of view of their potential for large scale implementation. The Consultants have attempted to assemble as firm a basis of factual information as is possible at this stage, to guide future decision making. The report is presented in three volumes, Volume 1 is an Executive Summary and includes the conclusions for the whole report. Volume 2 is the main body of the report and deals with the technical assessment, Volume 3 contains the costing information. The report assesses devices and not Device Teams. The Consultants have tried to present as fair a picture as possible of the devices as conceived by the Teams, and the Teams are of course the principal source of information. However, the text also refers to work from other sources. Every effort has been made to identify the inherent strengths and weaknesses of the devices independently of the work of the development Teams. It is recognised that at some stage certain devices will be dropped from the programme to allow concentration of effort on the more promising schemes. The Consultants have therefore given special prominence to those topics which are likely to have most influence on such decisions. An important limitation imposed on this report is its timing. It finds many Device Teams halfway through planned programmes of work, and in many areas detailed information necessary for a complete assessment is missing. In these areas attention is drawn to those factors which may later modify the stated conclusions on particular aspects of devices. However, the Consultants feel that it is now possible to reach reliable conclusions on many of the broader aspects of device development. Seven devices are included in the assessment. Some are much further advanced than others, and some are much more complex. The depths of the assessments carried out reflect these factors. Chapters 4 to 10 of this Volume present for each device a Reference Design which has been used as the basis of assessment. Table 1.1 sets out the key parameters of the Reference Designs. These designs have either been produced in their entirety by the Device Teams, or have been in part worked up by the Consultants in consultation with the Device Teams. The devices are described and assessed technically in terms of their material and workmanship content, and in terms of their annual average power output (termed 'productivity' in this report). For each device a brief summary of the fundamental mechanism of wave power extraction is given as general information, and for comparison between devices. There is a strong link between these fundamentals and the most important engineering problems, including costs. Except where it is directly applicable to the assessment, this report does not deal in any detail with the extensive programme of support work which has been initiated in areas of interest to all devices. This work is undertaken by Technical Advisory Groups (TAGS) and their work is documented in numerous separate reports

Modulating yaw with an unstable rigid body and a course-stabilizing or steering caudal fin in the yellow boxfish (Ostracion cubicus)

Despite that boxfishes have a rigid carapace that restricts body undulation, they are highly manoeuvrable and manage to swim with remarkably dynamic stability. Recent research has indicated that the rigid body shape of boxfishes shows an inherently unstable response in its rotations caused by course-disturbing flows. Hence, any net stabilizing effect should come from the fishes' fins. The aim of the current study was to determine the effect of the surface area and orientation of the caudal fin on the yaw torque exerted on the yellow boxfish, Ostracion cubicus, a square cross-sectional shaped species of boxfish. Yaw torques quantified in a flow tank using a physical model with an attachable closed or open caudal fin at different body and tail angles and at different water flow speeds showed that the caudal fin is crucial for controlling yaw. These flow tank results were confirmed by computational fluid dynamics simulations. The caudal fin acts as both a course-stabilizer and rudder for the naturally unstable rigid body with regard to yaw. Boxfishes seem to use the interaction of the unstable body and active changes in the shape and orientation of the caudal fin to modulate manoeuvrability and stability

BIO-INSPIRED PUMPING MECHANISMS IN AN INTERMEDIATE REYNOLDS NUMBER

Pumps are important to applications across a wide range of scales. Most of traditional applications occur within a range where inertia is the dominating factor influencing the pump performance, and hence many practical designs are based on mechanisms that rely on this assumption. As one moves towards smaller devices, however, the increasing effect of viscosity renders these traditional mechanisms ineffective. The current work looks towards a bio-inspired system consisting of an array of oscillating plates to contend with this challenge. The plates are placed within a channel, and the pumping performance generated is examined for a small range of Reynolds numbers intermediate between inertial and viscous regimes (0.1 < Re < 10). The goal of this work is to observe the effect of how different plate kinematics can be utilized to break the symmetry the system to produce a net pumped flow. Rigid and flexible plates are studied, using both sinusoidal and triangle wave actuation kinematics. The tests are first conducted with a single appendage, and then repeated with an array of 5 closely spaced plates to observe the effect of their interaction on the overall performance. The results of the single plate tests indicate that increased asymmetry introduced in the triangle wave actuation results in increased pumping performance as well as energy consumption. Tests were conducted at two Reynolds number conditions, Re = 0.6 and 6. The pumping performance was found to be an order of magnitude higher for the Re = 6 case. In the case of flexible plates, the results show that a mass specific pumping efficiency was higher for the flexible case with a higher frequency at the same Reynolds numbers. For the plate array, the results indicate five flexible plates with 〖∆θ〗_i=-90 will generate more than 4 times the flow rate in comparison to the single flexible plate. Asymmetric triangle actuation in conjunction with symplectic metachronal motion (〖∆θ〗_i=30) exhibits pumping performance more than 10 times of using a single rigid plate. Total work is noticeably higher for multiple plate system and will result in a reduced overall pumping efficiency in comparison to the single appendage

The development of a biologically inspired propulsor for unmanned underwater vehicles

IEEE Journal of Oceanic Engineering, 32(3): pp. 533-550Fish are remarkable in their ability to maneuver and to control their body position. This ability is the result of the coordinated movement of fins which extend from the body and form control surfaces that can create and vector forces in 3-D. We have embarked on a research program designed to develop a maneuvering propulsor for unmanned undersea vehicles (UUVs) that is based on the pectoral fin of the bluegill sunfish. For this, the anatomy, kinematics, and hydrodynamics of the sunfish pectoral fin were investigated experimentally and through the use of computational fluid dynamics (CFD) simulations. These studies identified that the kinematics of the sunfish pectoral fin are very complex and are not easily described by traditional “rowing”- and “flapping”-type kinematics. A consequence of the complex motion is that the pectoral fin can produce forward thrust during both its outstroke (abduction) and instroke (adduction), and while doing so generates only small lateral and lift forces. The results of the biological studies were used to guide the design of robotic pectoral fins which were built as experimental devices and used to investigate the mechanisms of thrust production and control. Because of a design that was based heavily on the anatomy of the sunfish fin, the robotic pectoral fins had the level of control and degrees of freedom necessary to reproduce many of the complex fin motions used by the sunfish during steady swimming. These robotic fins are excellent experimental tools, and are an important first step towards developing propulsive devices that will give the next generation of UUVs the ability to produce and control thrust like highly maneuverable fish