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

SMA-Based Muscle-Like Actuation in Biologically Inspired Robots: A State of the Art Review

New actuation technology in functional or "smart" materials has opened new horizons in robotics actuation systems. Materials such as piezo-electric fiber composites, electro-active polymers and shape memory alloys (SMA) are being investigated as promising alternatives to standard servomotor technology [52]. This paper focuses on the use of SMAs for building muscle-like actuators. SMAs are extremely cheap, easily available commercially and have the advantage of working at low voltages. The use of SMA provides a very interesting alternative to the mechanisms used by conventional actuators. SMAs allow to drastically reduce the size, weight and complexity of robotic systems. In fact, their large force-weight ratio, large life cycles, negligible volume, sensing capability and noise-free operation make possible the use of this technology for building a new class of actuation devices. Nonetheless, high power consumption and low bandwidth limit this technology for certain kind of applications. This presents a challenge that must be addressed from both materials and control perspectives in order to overcome these drawbacks. Here, the latter is tackled. It has been demonstrated that suitable control strategies and proper mechanical arrangements can dramatically improve on SMA performance, mostly in terms of actuation speed and limit cycles

Multi-fin kinematics and hydrodynamics in pufferfish steady swimming

Pufferfish swim and maneuver with a multi-fin system including dorsal, anal, caudal, and pectoral fins, which presents sophisticated ventures in biomimetic designs of underwater vehicles. Distinguished from those ‘typical’ fish with streamlined body shape and body-caudal fin (BCF) undulations, pufferfish adopt non-streamlined plump body shape and rely on the oscillations and interplay of fins to achieve high performance maneuvering. Aiming at unveiling novel mechanisms associated with multi-fin kinematics and hydrodynamic performance in pufferfish swimming, we carried out an integrated study by combining measurement and digitizing of multi-fin kinematics and three-dimensional deformations and computational fluid dynamic (CFD) modeling of steady swimming. We constructed a realistic multi-fin kinematic model to mimic motions and deformations of the dorsal, anal, and caudal fins. We further built up a CFD model of the pufferfish with a realistic body and multi-fin geometry to evaluate the hydrodynamic performance of its multi-fin system. Our results demonstrate that in pufferfish steady swimming, caudal, dorsal and anal fin rays oscillate while performing significantly passive bending and twist deformations but show a noticeable out-of-phase feature, leading to neutralizing rotational forces and hence suppressing yaw motion, particularly at fast swimming. Numerical simulation suggests that the caudal median fin plays a key role in thrust generation while the dorsal and anal fins also provide a considerable contribution

Magnetic Field-Driven Dynamic Undulatory Composites for Flow-Induced Antifouling

Department of Mechanical EngineeringFouling, which is the surface contamination or failure by the accumulation of unwanted materials, has been unsolved problems in many different fields such as medical devices, human body, water pipes, marine structures, and ship surfaces. To solve these problems, diverse bioinspired antifouling strategies have demonstrated effective fouling-resistant properties with good biocompatibility, sustainability, and long-term activity. However, previous studies on bioinspired antifouling materials have mainly focused on material aspects or static architectures of nature without deep consideration of kinetic topographies or dynamic motion. To this end, we propose a magnetically responsive multilayered composite that can generate coordinated, undulatory topographical waves with controlled length and time scales as a new class of dynamic antifouling materials. The first aspect of the magnetically responsive multilayered composite dealt in the dissertation is the interaction between the magnetic field and structural deformation. The composition of the multilayered structure and mechanical properties were analyzed for optimization of deformation. As the proposed dynamic surface contains ferromagnetic particle in a form of composite, local deformation was induced by the external magnetic field. In this phenomenon, variables including magnetic field density, Maxwell electromagnetic stress, mechanical stress, and strain govern the deformation. Numerical analysis using the finite element method (FEM) was carried out to analyze and model the magnetic field-induced structural deformation using theoretical governing equations. Comparisons of the numerical calculation with experimental results were also conducted for validation. Based on the analyses, depth and frequency of deformation were also modulated. The secondly dealt aspect is structural deformation-induced fluidic behavior, which is also called fluid-structure interaction (FSI). In this case, two-way FSI was used to explain the system. The surface undulation of the dynamic composite induced substantial velocity changes of the fluid right above the deformed region. This phenomenon is observed and analyzed using particle image velocimetry (PIV) method under controlled periodic undulatory surface motion. To validate the experimental observation, numerical analysis was conducted through the dynamic and kinematic coupling of stress tensors in the solid and fluid domain. Among diverse types of fluidic behavior, especially vortices and shear stresses near the dynamic surface were observed. As it was found that quantities of vorticity and shear stress play a crucial role to prohibit fouling, these antifouling-relevant physical quantities were modulated and optimized by controlling deformation depth and frequency. The third aspect dealt in the dissertation is the antifouling properties originated by dynamic fluidic behavior. Local and global vortices and shear stresses acted as barriers fundamentally inhibiting initial attachment of foulants, by sweeping those away from the surface. To observe and analyze bacterial movement with and without magnetic field-induced deformation, fluorescence zooms microscopy and moment scaling spectrum (MSS) analysis were used. The results showed that bacterial behavior in the culture medium fluid above the dynamic composite is strongly affected by the magnetic field-induced surface deformation. The antifouling properties of the dynamic undulatory composite were quantified by colony-forming unit (CFU) and areal coverage. The antifouling performance was increased as deformation frequency and depth increase, and this was proven to be statistically significant. Further enhancement of antifouling properties was also conducted by the addition of nanostructure and chemical moieties on the top surface of the composite. Based on these results, the application of the research to the medical tube having an undulatory inner wall was suggested.clos

Energy Based Control System Designs for Underactuated Robot Fish Propulsion

In nature through millions of years of evolution fish and cetaceans have developed fast efficient and highly manoeuvrable methods of marine propulsion. A recent explosion in demand for sub sea robotics, for conducting tasks such as sub sea exploration and survey has left developers desiring to capture some of the novel mechanisms evolved by fish and cetaceans to increase the efficiency of speed and manoeuvrability of sub sea robots. Research has revealed that interactions with vortices and other unsteady fluid effects play a significant role in the efficiency of fish and cetaceans. However attempts to duplicate this with robotic fish have been limited by the difficulty of predicting or sensing such uncertain fluid effects. This study aims to develop a gait generation method for a robotic fish with a degree of passivity which could allow the body to dynamically interact with and potentially synchronise with vortices within the flow without the need to actually sense them. In this study this is achieved through the development of a novel energy based gait generation tactic, where the gait of the robotic fish is determined through regulation of the state energy rather than absolute state position. Rather than treating fluid interactions as undesirable disturbances and `fighting' them to maintain a rigid geometric defined gait, energy based control allows the disturbances to the system generated by vortices in the surrounding flow to contribute to the energy of the system and hence the dynamic motion. Three different energy controllers are presented within this thesis, a deadbeat energy controller equivalent to an analytically optimised model predictive controller, a $H_\infty$ disturbance rejecting controller with a novel gradient decent optimisation and finally a error feedback controller with a novel alternative error metric. The controllers were tested on a robotic fish simulation platform developed within this project. The simulation platform consisted of the solution of a series of ordinary differential equations for solid body dynamics coupled with a finite element incompressible fluid dynamic simulation of the surrounding flow. results demonstrated the effectiveness of the energy based control approach and illustrate the importance of choice of controller in performance

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

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