Review of Computational Fluid Dynamics Analysis in Biomimetic Applications for Underwater Vehicles

Biomimetics, which draws inspiration from nature, has emerged as a key approach in the development of underwater vehicles. The integration of this approach with computational fluid dynamics (CFD) has further propelled research in this field. CFD, as an effective tool for dynamic analysis, contributes significantly to understanding and resolving complex fluid dynamic problems in underwater vehicles. Biomimetics seeks to harness innovative inspiration from the biological world. Through the imitation of the structure, behavior, and functions of organisms, biomimetics enables the creation of efficient and unique designs. These designs are aimed at enhancing the speed, reliability, and maneuverability of underwater vehicles, as well as reducing drag and noise. CFD technology, which is capable of precisely predicting and simulating fluid flow behaviors, plays a crucial role in optimizing the structural design of underwater vehicles, thereby significantly enhancing their hydrodynamic and kinematic performances. Combining biomimetics and CFD technology introduces a novel approach to underwater vehicle design and unveils broad prospects for research in natural science and engineering applications. Consequently, this paper aims to review the application of CFD technology in the biomimicry of underwater vehicles, with a primary focus on biomimetic propulsion, biomimetic drag reduction, and biomimetic noise reduction. Additionally, it explores the challenges faced in this field and anticipates future advancements

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

Animal-Robot Interactions: Electrocommunication, Sensory Ecology, and Group Dynamics in a Mormyrid Weakly Electric Fish

Mormyrid weakly electric fish possess a specialized electrosensory system. During the process of active electrolocation, these animals perceive self-generated electric organ dis-charges (EOD) and are thereby able to detect objects in their nearby environment. The EOD is a short, biphasic pulse, which is simultaneously used to communicate with conspe-cifics. There are two principles according to which information exchange occurs during electrocommunication. The waveform of the EOD constitutes a relatively stable identity marker that signals species, gender, and status of an individual. In contrast, the temporal sequence of inter-discharge intervals (IDI) is highly variable and encodes context-specific information. Modifications of IDI-duration not only alter the instantaneous discharge fre-quency but also enable the generation of specific signaling patterns and interactive dis-charge sequences. One such interactive discharge behavior is the so-called echo response, during which a fish responds with a constant latency of only a few milliseconds to the EOD of a conspecific. Animals can synchronize their signaling sequences by mutually generating echoes to each other's signals over a coherent period. Although active electrolocation and electrocommunication are mediated by different types of electroreceptor organs and neural pathways, an unambiguous assignment of electromotor behavior to only one of the two functions is often problematic. In this thesis, the significance of IDI-based signaling sequences during motor and electro-motor interactions of the mormyrid fish Mormyrus rume proboscirostris were investigated. To this end, different electrical playback sequences of species-specific EODs were generated via mobile fish dummies, and the motor and electromotor responses of live fish were analyzed. In Part One of this thesis, electrocommunication strategies of the fish were analyzed, and particularly the functions of double pulses, discharge regularizations, and echo responses were examined in an adaptive context. Double pulses were classified as an aggressive mo-tivation signal, whereas regularizations may have a communicative function during the early stages of the sequential assessment of a potential opponent. In this context, discharge synchronization by means of echo responses may enable a mutual assessment for the net benefit of both contestants. Because echo responses occur in various behavioral contexts, and artificial echoes of the dummy evoked increased echoing by the fish, it was hypothesized that the echo response serves a more general purpose by enabling mutual allocation of social attention between two fish. In Part Two of this thesis, a biomimetic robotic fish was designed to investigate the senso-ry basis on which fish followed the dummy. It was shown that electrical playback signals induced following-behavior in live fish, whereas biomimetic motility patterns had no ef-fect. By subsequently reducing the mobile dummy to only the electric signaling sequence from the perspective of the fish, it could be shown that passive perception of electrical communication signals is also involved in mediating the spatial coordination of social in-teractions. This passive perception is likely mediated by the same electroreceptor organs that are used during electrocommunication. The EOD can therefore be considered to be an essential social stimulus that makes it possible to integrate a dummy into a group of weak-ly electric fish as an artificial conspecific. The influence of an interactively signaling mobile dummy fish on small groups of up to four individuals was investigated in Part Three of this thesis. Typical schooling behavior was a rare occurrence in this context. However, EOD-synchronizations through mutual echo responses between two fish, or between a fish and the interactive dummy, were fre-quently observed during social interactions in small groups. Motor interactions during synchronization episodes supported the hypothesis that mormyrids may use discharge synchronizations between individuals to allocate social attention, and the echo response may thus adopt a particularly useful function during communication in groups.Schwach elektrische Fisch aus der Familie der Mormyriden verfügen über ein spezialisier-tes elektrosensorisches Sinnessystem. In einem Prozess, der als aktive Elektroortung be-zeichnet wird, sind diese Tiere in der Lage, selbstgenerierte elektrische Organentladungen (EOD) wahrzunehmen, und dadurch Objekte in ihrer unmittelbaren Nähe zu detektieren. Das EOD ist ein kurzer bipolarer Puls, der gleichzeitig auch zur Kommunikation mit Artge-nossen dient. Informationsaustausch während der Elektrokommunikation basiert auf zwei verschiedenen Prinzipien: Die Wellenform des EOD stellt einen relativ konstanten Identi-tätsmarker dar, der beispielsweise Art, Geschlecht und Status eines Individuums signali-siert. Die zeitliche Abfolge der Intervalle zwischen den EODs ist hingegen höchst variabel und kodiert kontextspezifische Information. Durch Modifikation der Intervalldauer ändert sich nicht nur die Entladungsfrequenz, sondern es können auch spezifische Signalmuster und interaktive Entladungssequenzen generiert werden. Ein interaktives Entladungsver-halten stellt beispielsweise die Echoantwort dar, bei der ein Fisch mit einer konstanten Latenz von wenigen Millisekunden auf das EOD eines Artgenossen reagiert. Zwei Tiere können ihre Entladungssequenzen synchronisieren, indem sie ihre Signale über einen kohärenten Zeitraum gegenseitig mit Echos beantworten. Obwohl aktive Elektroortung und Elektrokommunikation über unterschiedliche Rezeptororgansysteme und neuronale Pfade vermittelt werden, ist eine eindeutige Zuordnung der elektromotorischen Verhal-tensäußerungen der Fische zu nur einer der beiden Funktionen oft problematisch. In der vorliegenden Arbeit wurde die Bedeutung intervallbasierter EOD-Sequenzen für motorische und elektromotorische Interaktionen des Mormyriden Mormyrus rume proboscirostris erforscht. Hierzu wurden verschiedene elektrische Playbacksequenzen artspezifischer EODs generiert und durch mobile Fischattrappen wiedergegeben. Die mo-torischen und elektromotorischen Verhaltensreaktionen der Fische wurden analysiert. Im ersten Teil der Arbeit wurden Elektrokommunikationsstrategien der Fische analysiert und die adaptive Funktion insbesondere von Doppelpulsen, Entladungsregularisierungen und Echoantworten untersucht. Doppelpulse wurden als aggressives Motivationssignal kategorisiert, wohingegen die Kommunikationsfunktion von Regularisierungen im gegen-seitigen Einschätzen zu Beginn einer kompetitiven Begegnung zu liegen scheint. Entla-dungssynchronisation durch gegenseitige Echoantworten kann dabei eine Einschätzung des Gegenübers zum Vorteil beider Parteien erleichtern. Da Echoantworten in verschiede-nen Verhaltenssituationen auftreten und artifizielle Echoantworten der Attrappe vermehrt zu Echos vonseiten der Fische führten, wurde postuliert, dass die Echoantwort eine generellere Funktion bei der Fokussierung gegenseitiger sozialer Aufmerksamkeit über-nehmen kann. Im zweiten Teil der Arbeit wurde ein biomimetischer Fischroboter konstruiert, um zu untersuchen, auf welcher sensorischen Grundlage die Fische der Attrappe folgen. Es konnte gezeigt werden, dass elektrische Playbacksignale, nicht aber biomimetische Bewe-gungsmuster, Folgeverhalten der Fische induzieren. In einem weiteren Schritt konnte durch die Reduktion der Attrappe auf die elektrischen Signalsequenzen aus der Perspektive der Versuchsfische gezeigt werden, dass passive Wahrnehmung elektrischer Kommu-nikationssignale auch bei der räumlichen Koordination sozialer Interaktionen von Bedeu-tung ist. Dies wird mutmaßlich über die gleichen Rezeptororgane vermittelt, die auch für die Elektrokommunikation verantwortlich sind. Das EOD kann daher als ein soziales Signal betrachtet werden, das es ermöglicht, eine Attrappe als künstlichen Artgenossen in eine Gruppe schwach elektrischer Fische zu integrieren. Der Einfluss einer elektrisch interaktiven mobilen Fischattrappe auf kleine Gruppen von bis zu vier Individuen wurde im dritten Teil der Arbeit getestet. Typisches Schwarmver-halten konnte in diesem Zusammenhang nur selten beobachtet werden. In kleinen Gruppen kam es während sozialer Interaktionen jedoch häufig zu EOD-Synchronisationen durch Echoantworten zwischen zwei Fischen, oder zwischen einem Fisch und der interaktiven Attrappe. Motorische Verhaltensinteraktionen im Zeitraum dieser Synchronisationen stützen die Hypothese, dass Mormyriden durch elektrische Entladungssynchronisation soziale Aufmerksamkeit zwischen Individuen herstellen können, und die Echoantwort somit besonders in Gruppen eine nützliche Kommunikationsfunktion übernehmen kann

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

Design, fabrication and stiffening of soft pneumatic robots

Although compliance allows the soft robot to be under-actuated and generalise its control, it also impacts the ability of the robot to exert forces on the environment. There is a trade-off between robots being compliant or precise and strong. Many mechanisms that change robots' stiffness on demand have been proposed, but none are perfect, usually compromising the device's compliance and restricting its motion capabilities. Keeping the above issues in mind, this thesis focuses on creating robust and reliable pneumatic actuators, that are designed to be easily manufactured with simple tools. They are optimised towards linear behaviour, which simplifies modelling and improve control strategies. The principle idea in relation to linearisation is a reinforcement strategy designed to amplify the desired, and limit the unwanted, deformation of the device. Such reinforcement can be achieved using fibres or 3D printed structures. I have shown that the linearity of the actuation is, among others, a function of the reinforcement density and shape, in that the response of dense fibre-reinforced actuators with a circular cross-section is significantly more linear than that of non-reinforced or non-circular actuators. I have explored moulding manufacturing techniques and a mixture of 3D printing and moulding. Many aspects of these techniques have been optimised for reliability, repeatability, and process simplification. I have proposed and implemented a novel moulding technique that uses disposable moulds and can easily be used by an inexperienced operator. I also tried to address the compliance-stiffness trade-off issue. As a result, I have proposed an intelligent structure that behaves differently depending on the conditions. Thanks to its properties, such a structure could be used in applications that require flexibility, but also the ability to resist external disturbances when necessary. Due to its nature, individual cells of the proposed system could be used to implement physical logic elements, resulting in embodied intelligent behaviours. As a proof-of-concept, I have demonstrated use of my actuators in several applications including prosthetic hands, octopus, and fish robots. Each of those devices benefits from a slightly different actuation system but each is based on the same core idea - fibre reinforced actuators. I have shown that the proposed design and manufacturing techniques have several advantages over the methods used so far. The manufacturing methods I developed are more reliable, repeatable, and require less manual work than the various other methods described in the literature. I have also shown that the proposed actuators can be successfully used in real-life applications. Finally, one of the most important outcomes of my research is a contribution to an orthotic device based on soft pneumatic actuators. The device has been successfully deployed, and, at the time of submission of this thesis, has been used for several months, with good results reported, by a patient

Between Species: Choreographing Human and Nonhuman Bodies

BETWEEN SPECIES: CHOREOGRAPHING HUMAN AND NONHUMAN BODIES is a dissertation project informed by practice-led and practice-based modes of engagement, which approaches the space of the zoo as a multi-species, choreographic, affective assemblage. Drawing from critical scholarship in dance literature, zoo studies, human-animal studies, posthuman philosophy, and experiential/somatic field studies, this work utilizes choreographic engagement, with the topography and inhabitants of the Toronto Zoo and the Berlin Zoologischer Garten, to investigate the potential for kinaesthetic exchanges between human and nonhuman subjects. In tracing these exchanges, BETWEEN SPECIES documents the creation of the zoomorphic choreographic works ARK and ARCHE and creatively mediates on: more-than-human choreography; the curatorial paradigms, embodied practices, and forms of zoological gardens; the staging of human and nonhuman bodies and bodies of knowledge; the resonances and dissonances between ethological research and dance ethnography; and, the anthropocentric constitution of the field of dance studies