Hydrodynamics of Biomimetic Marine Propulsion and Trends in Computational Simulations

[Abstract] The aim of the present paper is to provide the state of the works in the field of hydrodynamics and computational simulations to analyze biomimetic marine propulsors. Over the last years, many researchers postulated that some fish movements are more efficient and maneuverable than traditional rotary propellers, and the most relevant marine propulsors which mimic fishes are shown in the present work. Taking into account the complexity and cost of some experimental setups, numerical models offer an efficient, cheap, and fast alternative tool to analyze biomimetic marine propulsors. Besides, numerical models provide information that cannot be obtained using experimental techniques. Since the literature about trends in computational simulations is still scarce, this paper also recalls the hydrodynamics of the swimming modes occurring in fish and summarizes the more relevant lines of investigation of computational models

Developing High Performance Linear Carangiform Swimming

This thesis examines the linear swimming motion of Carangiform fish, and investigates how to improve the swimming performance of robotic fish within the fields of kinematic modeling and mechanical engineering, in a successful attempt to replicate the high performance of real fish. Intensive research was conducted in order to study the Carangiform swimming motion, where observational studies of the common carp were undertaken. Firstly, a full-body length Carangiform swimming motion is proposed to coordinate the anterior, mid-body and posterior displacements in an attempt to reduce the large kinematic errors in the existing free swimming robotic fish. It optimizes the forces around the centre of mass and initiates the starting moment of added mass upstream therefore increasing performance, in terms of swimming speed. The introduced pattern is experimentally tested against the traditional approach (of posterior confined body motion). A first generation robotic fish is devised with a novel mechanical drive system operating in the two swimming patterns. It is shown conclusively that by coordinating the full-body length of the Carangiform swimming motion a significant increase in linear swimming speed is gained over the traditional posterior confined wave form and reduces the large kinematic errors seen in existing free swimming robotic fish (Achieving the cruising speeds of real fish). Based on the experimental results of the first generation, a further three robotic fish are developed: (A) iSplash-OPTIMIZE: it becomes clear that further tuning of the kinematic parameters may provide a greater performance increase in the distance travelled per tail beat. (B) iSplash-II: it shows that combining the critical aspects of the mechanical drive system of iSplash-I with higher frequencies and higher productive forces can significantly increase maximum velocity. This prototype is able to outperform real Carangiform fish in terms of average maximum velocity (measured in body lengths/ second) and endurance, the duration that top speed is maintained. (C) iSplash-MICRO: it verifies that the mechanical drive system could be reduced in scale to improve navigational exploration, whilst retaining high-speed swimming performance. A small robotic fish is detailed with an equivalent maximum velocity (BL/s) to real fish

A numerical study of fin and jet propulsions involving fluid-structure interactions

Fish swimming is elegant and efficient, which inspires humans to learn from them to design high-performance artificial underwater vehicles. Research on aquatic locomotion has made extensive progress towards a better understanding of how aquatic animals control their flexible body and fin for propulsion. Although the structural flexibility and deformation of the body and fin are believed to be important features to achieve optimal swimming performance, studies on high-fidelity deformable body and fin with complex material behavior, such as non-uniform stiffness distributions, are rare. In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI) solver is developed to investigate the flow field evolution and propulsion performance of caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver, the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the finite volume method with a multi-block grid system. The solid dynamics are solved by a nonlinear finite element method. The coupling between the two solvers is achieved in a partitioned approach in which convergence check and sub-iteration are implemented to ensure numerical stability and accuracy. Validations are conducted by comparing the simulation results of classical benchmarks with previous data in the literature, and good agreements between them are obtained. The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion involving body deformation. Specifically, the effect of non-uniform stiffness distributions of fish body and/or fin, key features of fish swimming which have been excluded in most previous studies, on the propulsive performance is first investigated. Simulation results of a sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g., increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable fish body stiffness does not yield fish-like midline kinematics observed in real fish, suggesting that fish movement involves significant active control that cannot be replicated purely by passive deformations. Subsequent studies focus on the jet propulsion inspired by squid locomotion using the developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet propulsion system, whose inflation is actuated by an added external force that mimics the muscle constriction of the mantle and deflation is caused by the release of elastic energy of the structure, suggest larger mean thrust production and higher efficiency in high Reynolds number scenarios compared with the cases in laminar flow. A unique symmetry-breaking instability in turbulent flow is found to stem from irregular internal body vortices, which cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion system in the presence of background flow is studied by prescribing the body deformation and jet velocity profiles. The effect of the background flow on the leading vortex ring formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet are revealed as well. Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from an initial position to a target location and then hold the station there. Despite the same swimming distance, a swimmer whose departure location is closer to the cylinder requires less energy consumption to reach the target and hold the position there.Fish swimming is elegant and efficient, which inspires humans to learn from them to design high-performance artificial underwater vehicles. Research on aquatic locomotion has made extensive progress towards a better understanding of how aquatic animals control their flexible body and fin for propulsion. Although the structural flexibility and deformation of the body and fin are believed to be important features to achieve optimal swimming performance, studies on high-fidelity deformable body and fin with complex material behavior, such as non-uniform stiffness distributions, are rare. In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI) solver is developed to investigate the flow field evolution and propulsion performance of caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver, the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the finite volume method with a multi-block grid system. The solid dynamics are solved by a nonlinear finite element method. The coupling between the two solvers is achieved in a partitioned approach in which convergence check and sub-iteration are implemented to ensure numerical stability and accuracy. Validations are conducted by comparing the simulation results of classical benchmarks with previous data in the literature, and good agreements between them are obtained. The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion involving body deformation. Specifically, the effect of non-uniform stiffness distributions of fish body and/or fin, key features of fish swimming which have been excluded in most previous studies, on the propulsive performance is first investigated. Simulation results of a sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g., increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable fish body stiffness does not yield fish-like midline kinematics observed in real fish, suggesting that fish movement involves significant active control that cannot be replicated purely by passive deformations. Subsequent studies focus on the jet propulsion inspired by squid locomotion using the developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet propulsion system, whose inflation is actuated by an added external force that mimics the muscle constriction of the mantle and deflation is caused by the release of elastic energy of the structure, suggest larger mean thrust production and higher efficiency in high Reynolds number scenarios compared with the cases in laminar flow. A unique symmetry-breaking instability in turbulent flow is found to stem from irregular internal body vortices, which cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion system in the presence of background flow is studied by prescribing the body deformation and jet velocity profiles. The effect of the background flow on the leading vortex ring formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet are revealed as well. Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from an initial position to a target location and then hold the station there. Despite the same swimming distance, a swimmer whose departure location is closer to the cylinder requires less energy consumption to reach the target and hold the position there

Intersection between natural and artificial swimmers: a scaling approach to underwater vehicle design.

Approximately 72% of the Earth’s surface is covered by water, yet only 20% has been mapped [1]. Autonomous Underwater Vehicles (AUVs) are one of the main tools for ocean exploration. The demand for AUVs is expected to increase rapidly in the coming years [2], so there is a need for faster and more energy efficient AUVs. A drawback to using this type of vehicle is the finite amount of energy that is stored onboard in the form of batteries. Science and roboticists have been studying nature for ways to move more efficiently. Phillips et al. [3] presents data that contradicts the idea that fish are better swimmers than conventional AUVs when comparing the energetic cost of swimming in the form of the Cost of Transport (COT). The data presented by Phillips et al. only applies to AUVs at higher length and naval displacement (mass) scales, so the question arises of whether an AUV built at different displacements and length scales is more efficient than biological animals and if current bio-inspired platforms are better than conventional AUVs. Besides power requirements, it is also useful to compare the kinematic parameters of natural and artificial swimmers. In this case, kinematic parameters indicate how fast the swimmer travels through the water. Also, they describe how fast the propulsion mechanism must act to reach a certain swimming speed. This research adopts the approach of Gazzola et al. [4] where the Reynolds number is associated with a dimensionless number, Swim number (Sw) in this case, that has all the kinematic information. A newly developed number that extends the swim number to conventional AUVs is the Propulsion number (Jw), which demonstrates excellent agreement with the kinematics of conventional AUVs. Despite being functionally similar, Sw and Jw do not have a one-to-one relationship. Sw, Jw, COT represent key performance metrics for an AUV, herein called performance criteria, which can be used to compare existing platforms with each other and estimate the performance of non-existent designs. The scaling laws are derived by evaluating the performance of 229 biological animals, 163 bioinspire platforms, and 109 conventional AUVs. AUVs and bio-inspired platforms have scarce data compared with biological swimmers. Only 5% of conventional and 38% of bio-inspired AUVs have kinematic data while 30% of conventional and 18% of bio-inspired AUVs have energetic data. The low amount of performance criteria data is due to the nature of most conventional AUVs as commercial products. Only recently has the COT metric been included in the performance criteria for bio-inspired AUVs. For this reason, the research here formulates everything in terms of allometric scaling laws. This type of formulation is used extensively when referring to biological systems and is defined by an exponential relationship f (x) = axb, where x is a physical parameter of the fish or vehicle, like length or displacement. Scaling laws have the added benefit of allowing comparisons with limited data, as is the case for AUVs. The length and displacement scale (physical scale) must be established before estimating the performance criteria. Scale is primarily determined by the payload needed for a particular application. For instance, surveying the water column in deep water will require different scientific tools than taking images of an oyster bed in an estuary. There is no way to identify the size of an AUV until it is designed for that application, since these scientific instruments each have their own volume, length, and weight. A methodology for estimating physical parameters using computer vision is presented to help determine the scale for the vehicle. It allows accurate scaling of physical parameters of biological and bio-inspired swimmers with only a side and top view of the platform. A physical scale can also be determined based on the vehicle’s overall volume, which is useful when determining how much payload is needed for a particular application. Further, this can be used in conjunction with 3D modeling software to scale nonexistent platforms. Following the establishment of a physical scale, which locomotion mode would be most appropriate? Unlike conventional AUVs that use propeller or glider locomotion, bio-inspired platforms use a variety of modes. Kinematics and energy expenditures are different for each of these modes. For bio-inspired vehicles, the focus will be on the body-caudal fin (BCF) locomotion, of which four types exist: anguilliform, carangiform, thunniform, and ostraciiform. There is ample research on anguilliform and carangiform locomotion modes, but little research on thunniform and ostraciiform modes. In order to determine which locomotion mode scales best for a bio-inspired AUV, this research examines the power output and kinematic parameters for all four BCF modes. In order to achieve this, computational fluid dynamics simulations are performed on a 2D swimmer for all four modes. Overset meshes are used in lieu of body-fitted meshes to increase stability and decrease computational time. These simulations were used to scale output power over several decades of Reynolds numbers for each locomotion mode. Carangiform locomotion was found to be the most energy efficient, followed by anguilliform, thunniform, and ostraciiform. In order to utilize the above scaling laws in designing a novel platform, or comparing an existing one, there must be a unifying framework. The framework for choosing a suitable platform is presented with a case study of two bio-inspired vehicles and a conventional one. The framework begins by determining how the platform can be physically scaled depending on the payload. Based on the physical scale and derived scaling laws, it then determines performance criteria. It also describes a method for relative cost scaling for each vehicle, which is not covered in the literature. The cost scaling is based on the assumption that all payloads and materials are the same. The case study shows that a conventional AUV performs better on all performance criteria and would cost less to build

Underwater Vehicles

For the latest twenty to thirty years, a significant number of AUVs has been created for the solving of wide spectrum of scientific and applied tasks of ocean development and research. For the short time period the AUVs have shown the efficiency at performance of complex search and inspection works and opened a number of new important applications. Initially the information about AUVs had mainly review-advertising character but now more attention is paid to practical achievements, problems and systems technologies. AUVs are losing their prototype status and have become a fully operational, reliable and effective tool and modern multi-purpose AUVs represent the new class of underwater robotic objects with inherent tasks and practical applications, particular features of technology, systems structure and functional properties

Modeling and Control of a Spherical Underwater Robot Vehicle by Using a Variable Ballast Mechanism

A mechanism of variable ballast system which manipulates volume of water in the ballast tank is designed and modeled in this thesis. The mechanism is designed to make water always fulfill space in the variable ballast tank with varying volume. Therefore the internal dynamic that is caused by the movement of water in the tank can be avoided. The variable ballast is utilized for vertical motion actuator of a spherical URV by controlling the difference between buoyant force and gravitational force. In this thesis, the VBS can change the weight of URV body, ΔW, in range ± 9.96N in order to make URV in positive buoyancy, neutral buoyancy or negative buoyancy. The buoyancy of URV is considered as a constant value. By using this mechanism, then the URV can move in vertical plane in the range of velocity ±1.019ms−1 . Two approaches, i.e. linearized approximation and nonlinear approach, are presented to design the controller of the dynamic model which behaves as nonlinear system. In linearized approximation, the nonlinear model is linearized about the equilibrium point by using Taylor series. Since the linearized model is controllable then a linear control strategy is applied. In order to analyze the stability of the system, Lyapunov’s linearization method is used. Since the eigenvalues of the linearized model is zero, λ = 0, then the Lyapunov’s linearization method cannot determine whether the nonlinear system is stable or unstable. The second method of Lyapunov stability analysis, i.e. Lyapunov direct method, is also applied. By using this method, it can be known that the equilibrium point of this depth positioning system is unstable, furthermore, nonlinear approach, i.e. state-space feedback linearization and inputoutput feedback linearization, are also used to stabilize this system. These control strategies are then simulated in MATLAB/Simulink. All control strategies designed in this thesis can asymptotically stabilize the equilibrium point, for t →∞ , e→0 . The linearized approximation approach is the fastest to reach steady state compare to the others, but it consumes more power. For tracking a trajectory, input-output linearization gives better performance compare to the others by resulting smallest error. If the change of trajectory is constant, then error of input-output feedback linearization converges to zero. For linearized approach and state-space feedback linearization, if change of input is 0.1ms−1 then absolute error converge to 2.408m and 6.082m respectively, and if change input is 0.2ms−1 then absolute error converge to 6.361m and 12.163m respectively

An analysis of the locomotory behaviour and functional morphology of errant polychaetes

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modeling and Control of a Spherical Underwater Robot Vehicle by Using a Variable Ballast Mechanism

A mechanism of variable ballast system which manipulates volume of water in the ballast tank is designed and modeled in this thesis. The mechanism is designed to make water always fulfill space in the variable ballast tank with varying volume. Therefore the internal dynamic that is caused by the movement of water in the tank can be avoided. The variable ballast is utilized for vertical motion actuator of a spherical URV by controlling the difference between buoyant force and gravitational force. In this thesis, the VBS can change the weight of URV body, ΔW, in range ± 9.96N in order to make URV in positive buoyancy, neutral buoyancy or negative buoyancy. The buoyancy of URV is considered as a constant value. By using this mechanism, then the URV can move in vertical plane in the range of velocity ±1.019ms−1 . Two approaches, i.e. linearized approximation and nonlinear approach, are presented to design the controller of the dynamic model which behaves as nonlinear system. In linearized approximation, the nonlinear model is linearized about the equilibrium point by using Taylor series. Since the linearized model is controllable then a linear control strategy is applied. In order to analyze the stability of the system, Lyapunov’s linearization method is used. Since the eigenvalues of the linearized model is zero, λ = 0, then the Lyapunov’s linearization method cannot determine whether the nonlinear system is stable or unstable. The second method of Lyapunov stability analysis, i.e. Lyapunov direct method, is also applied. By using this method, it can be known that the equilibrium point of this depth positioning system is unstable, furthermore, nonlinear approach, i.e. state-space feedback linearization and inputoutput feedback linearization, are also used to stabilize this system. These control strategies are then simulated in MATLAB/Simulink. All control strategies designed in this thesis can asymptotically stabilize the equilibrium point, for t →∞ , e→0 . The linearized approximation approach is the fastest to reach steady state compare to the others, but it consumes more power. For tracking a trajectory, input-output linearization gives better performance compare to the others by resulting smallest error. If the change of trajectory is constant, then error of input-output feedback linearization converges to zero. For linearized approach and state-space feedback linearization, if change of input is 0.1ms−1 then absolute error converge to 2.408m and 6.082m respectively, and if change input is 0.2ms−1 then absolute error converge to 6.361m and 12.163m respectively

The Effects of Asymmetry on Oscillatory Propulsion

Owing to the problems caused by propellers, research has turned to the biological world for inspiration for non-propeller propulsion. Rays were chosen for further study and it was found that a key feature of their swimming is the asymmetric-in-time movements of their pectoral fins. The main goal was to determine whether asymmetric-in-time oscillations produced a larger resultant force. Two flexible fins were used (NACA and biomimetic stiffness profile "BIO"). Asymmetry was defined by the proportion of the time period taken to effect one half-stroke. The experiments showed that at low frequencies, asymmetric oscillation produced greater resultant force and that this force was at an angle to the chord of the fin at rest. At high frequencies, the BIO fin produced lower resultant force when oscillating asymmetrically and the angle of the resultant force was the same as for the symmetric oscillations. There was no difference between the resultant force magnitude or direction produced by the NACA fin at high frequencies. More power was used when oscillating asymmetrically but the force efficiency, the resultant force per watt, was often the same for symmetric and asymmetric oscillations. The trailing edge kinematics of the fins were analysed. Some of the kinematics variables correlated with the resultant force magnitude independently of fin type. The wake structures behind the fins oscillating at two different frequencies were examined. The wakes were geometrically asymmetric behind both fins oscillating asymmetrically at low frequency. At the higher frequency, the wakes behind the asymmetrically oscillating fins were no different to their symmetric counterpartsEThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Design and Development of a Mobile Colonoscopy Robot

The conventional colonoscopy is a common procedure used to access the colon. Despite it being considered the Gold Standard procedure for colorectal cancer diagnosis and treatment, it has a number of major drawbacks, including high patient discomfort, infrequent but serious complications and high skill required to perform the procedure. There are a number of potential alternatives to the conventional colonoscopy, from augmenting the colonoscope to using Computed Tomography Colonography (CTC) - a completely non-invasive method. However, a truly effective, all-round alternative has yet to be found. This thesis explores the design and development of a novel solution: a fully mobile colonoscopy robot called “RollerBall”. Unlike current passive diagnostic capsules, such as PillCam, this device uses wheels at the end of adjustable arms to provide locomotion through the colon, while providing a stable platform for the use of diagnostic and therapeutic tools. The work begins by reviewing relevant literature to better understand the problem and potential solutions. RollerBall is then introduced and its design described in detail. A robust prototype was then successfully fabricated using a 3D printing technique and its performance assessed in a series of benchtop experiments. These showed that the mechanisms functioned as intended and encouraged the further development of the concept. Next, the fundamental requirement of gaining traction on the colon was shown to be possible using hexagonal shaped, macro-scale tread patterns. A friction coefficient ranging between 0.29 and 0.55 was achieved with little trauma to the tissue substrate. The electronics hardware and control were then developed and evaluated in a series of tests in silicone tubes. An open-loop strategy was first used to establish the control algorithm to map the user inputs to motor outputs (wheel speeds). These tests showed the efficacy of the locomotion technique and the control algorithm used, but they highlighted the need for autonomy. To address this, feedback was included to automate the adjusting of the arm angle and amount of force applied by the device; a forward facing camera was also used to automate the orientation control by tracking a user-defined target. Force and orientation control were then combined to show that semi-autonomous control was possible and as a result, it was concluded that clinical use may be feasible in future developments