Numerical modelling and experimental testing of the hydrodynamic characteristics for an open-frame remotely operated vehicle

The remotely operated vehicles (ROVs) are important to provide the technology support for both the traditional offshore structures and rapidly-growing renewable energy facilities during their full-lifecycles, such as site survey, installation, inspection, maintenance and repair. Regarding the motion and performance of a ROV, the understanding of its hydrodynamic properties is essential when exposing to the disturbances of wave and current. In this study, a numerical model is proposed within the frame of an open-source platform OpenFOAM. The hydrodynamics of the adopted ROV (BlueRov2) in its four principal degrees of freedoms (DOFs) is numerically simulated by a Reynolds-Averaged Navier-Stokes (RANS) solver. Meanwhile, an experimental test is carried out by using a novel technique on measuring the hydrodynamic forces and moments. To validate the numerical prediction methodologies, a set of systematic simulations of the ROV subjected to the disturbances caused by various flow conditions are performed. Comparing to the model test measurement, the numerical model proved to be reliable in offering a good estimation of the hydrodynamic parameters. This also indicates that the presented numerical methodologies and experimental techniques can be applied to other types of open-frame ROVs in quantifying the hydrodynamic parameters, capturing the physics of the fluid-structure interaction (FSI) and feature of the turbulent vorticity which are all essential for the effective control of the ROVs under the nonlinear flow disturbances

Preliminary Analysis of ROV AF-150114 Movement Using CFD Method (Comutional Fluid Dynamics)

This research was carried out with the aim of measuring the effect of the body on the fluid flow that occurs around it and measuring the stress that occurs in the ROV AF-150114 design. The research method uses software with a CFD model approach to analyze the stress that occurs in the designs made. In general, there are three stages that must be passed in a CFD simulation: Pre-processing. Solving and post-processing. What is calculated is the velocity, viscosity and pressure of the water flow around the ROV body. The results obtained show that the balance of the ROV body greatly affects the ability to dive and maneuver during maneuvers. The highest pressure/pressure for fluid flow occurs at the ROV AF-150114 speed of 2.5 m/s with a value 39,825 Pa and the value of viscosity is 10,860 Nm/s2. ROV AF-150114 movement test results found that the experiment has a faster movement time speed than the calculation.

Hydrodynamic Optimization of a torpedo-shaped hull

Nowadays, it is not fully clear how the Ocean seabed can contribute to Earth ecosystems. However, several steps are being taken to completely understand Ocean’s seabed. Lately, many methods are being developed to explore the Oceans, although there is one method which fulfill the desired trade-off (between low operational costs and high quality data collection). This efficient method developed to explore the Ocean’s depth is known as submarine vehicles, and the most efficient of them, to explore and mapping, is certainly the Autonomous Underwater Vehicle (AUV). The increasing use of AUV’s is leading to a point in which its design parameters are crucial. Characteristics as high endurance, long operation time, high maneuverability and range are demanded at an early design stage; thus, it is essential to find an optimum hull shape design to improve these characteristics. This thesis presents the effect of hydrodynamic forces of axisymmetric underwater vehicles through the variation of the shape of a torpedo-shaped hull body. Furthermore, this thesis is intended to analyze, experimentally, the length-to-Diameter (D) ratios of nose (N) and tail (T), as well as its shapes, in order to find the optimum ratios and shape combinations for the minimization of Drag. The experimental tests were conducted in the towing tank of the University of Beira Interior (UBI). However, due to the Towing Tank dimensions, the development of a scaled model had to be made. A similarity between the scaled model and the full-scale prototype must be done to assume similar flow conditions. Several torpedo-shaped combinations were tested experimentally and further validated the numerical simulations. Moreover, parameters such as the pitch angles (or Angle of Attack (AoA)) [0 - 20°] and velocities [0.50 – 1 m/s] were investigated to understand their influence on the hydrodynamic Drag. The experimental setup is hereby fully described, showing the various procedures adopted until the data collection phase. A strain gauge system (load cell) was used to measure the Drag induced by the hull body. Experimental results demonstrate an optimum configuration for N/D = 0.8 (Elliptical shape) and T/D = 1.6 (Conical shape). From the experimental and numerical data, it could be seen that the Drag increases with the increase of velocity. Same occurrence happens for AoA, where Drag increases with higher AoA’s. Therefore, it can be concluded that the influence of AoA on Drag is higher for greater velocities. The experimental measurements have been used to validate results obtained from a Computational Fluid Dynamics (CFD) software that uses Reynolds Average Navier-Stokes (RANS) equations (ANSYSTM FLUENT). A mesh-independency study was made to investigate two turbulence models: Standard ?-e and ?-? SST models. Standard ?-e showed to be the most appropriate model to this study with a lower computational cost. Results between Experimental and Numerical methods showed a good agreement, considering the conditions mentioned.Hoje em dia, não é ainda completamente claro de que maneira o fundo dos oceanos podem contribuir para os Ecossistemas da Terra. Contudo, vários esforços estão a ser feito para compreender em profundidade os fundos marinhos dos Oceanos. Atualmente, o método mais eficiente, já desenvolvido, para explorar a profundeza dos oceanos é conhecido como veículos submarinos, e especificamente, o mais eficiente para pesquisa e exploração destes é conhecido como Veículo Autónomo Subaquático (AUV). O aumento do uso de AUV’s tem levado a um ponto em que os parâmetros de projeto são cruciais. Características como a resistência ao avanço, o alto tempo de operação, a grande manobrabilidade e o grande alcance são exigidos numa fase primária de projeto; desta forma, é fundamental encontrar uma forma ótima do corpo hidrodinâmico, ainda durante a fase de projeto, ambicionando melhorar as suas características. Esta dissertação apresenta o efeito das forças hidrodinâmicas de veículos subaquáticos axi- simétricos através da variação da forma de um corpo em forma de torpedo. Além disso, nesta dissertação pretende-se ainda analisar, experimentalmente, os rácios comprimento/diâmetro do nariz e da cauda do corpo, assim como as suas formas, para que seja possível os rácios e combinação ótimos do ponto de vista da minimização da resistência ao avanço. Os testes experimentais foram feitos num tanque de água da Universidade da Beira Interior (UBI). No entanto, devido às dimensões do tanque de água, o desenvolvimento de um modelo à escala foi a opção mais viável. Uma similaridade entre o modelo à escala e o protótipo foi feita para garantir as mesmas condições de escoamento entre ambos. Várias combinações foram testadas experimentalmente e seguidamente validadas por simulações numéricas. Adicionalmente, parâmetros como o ângulo de ataque (de 0 - 20°) e a velocidade (entre 0.50 – 1 m/s) foram alterados para perceber a sua influência na resistência hidrodinâmica. A preparação experimental é totalmente descrita, mostrando vários procedimentos adotados até à fase de recolha de dados. Um sistema de tensão/compressão (célula de carga) foi utilizado para medir a resistência induzido pelo corpo. Os resultados experimentais demonstraram uma configuração ótima que se situa nas proximidades de N/D = 0.8 (Forma Elítica) e T/D = 1.6 (Forma Cónica). Pode ser visto que a resistência aumenta com o aumento da velocidade. Da mesma forma para os ângulos de ataque, a resistência aumenta para ângulos de ataque maiores. Os dados experimentais foram usados para validar os resultados obtidos de um software CFD que usa as equações RANS. Um estudo de independência da malha foi feito para investigar dois modelos turbulentos: Modelos Standard ?-e e ?-? SST. O modelo turbulento Standard ?-e mostrou ser o mais apropriado para este estudo com um menor custo computacional. Os resultados entre os métodos experimentais e numéricos mostraram uma boa concordância, considerando as condições mencionadas

Wave Excited Mass-Spring-Damper System for a Self-recharging Autonomous Underwater Vehicle

Autonomous underwater vehicles\u27 (AUVs) endurance is constrained by the lifetime of their batteries and the distance that tether wires can traverse. Solving the endurance problem of AUV using the enormous potential of ocean wave energy is the motivation behind this thesis. The objective of this research is to model a mass-spring-damper system to emulate the permanent magnet linear generator (PMLG) of a self-recharging AUV and identify its energy absorption capability through numerical simulation and experimental testing. The research activities started with modeling and fabricating a 1:5 scale model. The scaling was done by comparing the most common AUV size of 1.5m. The preliminary dry testing result confirmed the inadequate damping of the devised prototype. After detailed wave tank testing with a fixed PTO, the vertical orientation of the converter was chosen for the second stage research. A modified 1:3 large-scale prototype was developed in the next phase. The model showed strong oscillating mass motion in the dry test rig. Comparison with numerical simulation showed that for lower wave frequency, the damping coefficient of the model matches well with the experimental result. But the prototype damping behavior is much more complex for a higher wave frequency. The tank testing confirmed that the prototype pitch amplitude in the wave needs to be enhanced for higher energy absorption

A comparison study of biologically inspired propulsion systems for an autonomous underwater vehicle

The field of Autonomous Underwater Vehicles (AUVs) has increased dramatically in size and scope over the past two decades. Application areas for AUVs are numerous and varied; from deep sea exploration, to pipeline surveillance to mine clearing. However, one limiting factor with the current technology is the duration of missions that can be undertaken and one contributing factor to this is the efficiency of the propulsion system, which is usually based on marine propellers. As fish are highly efficient swimmers greater propulsive efficiency may be possible by mimicking their fish tail propulsion system. The main concept behind this work was therefore to investigate whether a biomimetic fish-like propulsion system is a viable propulsion system for an underwater vehicle and to determine experimentally the efficiency benefits of using such a system. There have been numerous studies into biomimetic fish like propulsion systems and robotic fish in the past with many claims being made as to the benefits of a fish like propulsion system over conventional marine propulsion systems. These claims include increased efficiency and greater manoeuvrability. However, there is little published experimental data to characterise the propulsive efficiency of a fish like propulsive system. Also, very few direct experimental comparisons have been made between biomimetic and conventional propulsion systems. This work attempts to address these issues by directly comparing experimentally a biomimetic underwater propulsion system to a conventional propulsion system to allow for a better understanding of the potential benefits of the biomimetic system. This work is split into three parts. Firstly, the design and development of a novel prototype vehicle called the RoboSalmon is covered. This vehicle has a biomimetic tendon drive propulsion system which utilizes one servo motor for actuation and has a suite of onboard sensors and a data logger. The second part of this work focuses on the development of a mathematical model of the RoboSalmon vehicle to allow for a better understanding of the dynamics of the system. Simulation results from this model are compared to the experimental results and show good correlation. The final part of the work presents the experimental results obtained comparing the RoboSalmon prototype with the biomimetic tail system to the propeller and rudder system. These experiments include a study into the straight swimming performance, recoil motion, start up transients and power consumption. For forward swimming the maximum surge velocity of the RoboSalmon was 0.18ms-1 and at this velocity the biomimetic system was found to be more efficient than the propeller system. When manoeuvring the biomimetic system was found to have a significantly reduced turning radius. The thesis concludes with a discussion of the main findings from each aspect of the work, covering the benefits obtained from using the tendon drive system in terms of efficiencies and manoeuvring performance. The limitations of the system are also discussed and suggestions for further work are included

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

A Novel Propeller Design for Micro-Swimming robot

The applications of a micro-swimming robot such as minimally invasive surgery, liquid pipeline robot etc. are widespread in recent years. The potential application fields are so inspiring, and it is becoming more and more achievable with the development of microbiology and Micro-Electro-Mechanical Systems (MEMS). The aim of this study is to improve the performance of micro-swimming robot through redesign the structure. To achieve the aim, this study reviewed all of the modelling methods of low Reynolds number flow including Resistive-force Theory (RFT), Slender Body Theory (SBT), and Immersed Boundary Method (IBM) etc. The swimming model with these methods has been analysed. Various aspects e.g. hydrodynamic interaction, design, development, optimisation and numerical methods from the previous researches have been studied. Based on the previous design of helix propeller for micro-swimmer, this study has proposed a novel propeller design for a micro-swimming robot which can improve the velocity with simplified propulsion structure. This design has adapted the coaxial symmetric double helix to improve the performance of propulsion and to increase stability. The central lines of two helical tails overlap completely to form a double helix structure, and its tail radial force is balanced with the same direction and can produce a stable axial motion. The verification of this design is conducted using two case studies. The first one is a pipe inspection robot which is in mm scale and swims in high viscosity flow that satisfies the low Reynolds number flow condition. Both simulation and experiment analysis are conducted for this case study. A cross-development method is adopted for the simulation analysis and prototype development. The experiment conditions are set up based on the simulation conditions. The conclusion from the analysis of simulation results gives suggestions to improve design and fabrication for the prototype. Some five revisions of simulation and four revisions of the prototype have been completed. The second case study is the human blood vessel robot. For the limitations of fabrication technology, only simulation is conducted, and the result is compared with previous researches. The results show that the proposed propeller design can improve velocity performance significantly. The main outcomes of this study are the design of a micro-swimming robot with higher velocity performance and the validation from both simulation and experiment

Manta Ray Robot

The goal of this project was to improve UAV efficiency through use of biomimetic design. This was achieved through the application of a hydraulically actuated soft robotic fin. Drawing inspiration from the manta ray, a custom actuator was developed to achieve a feasible, lifelike locomotion method. The actuator was incorporated into a prototype robot to assess the performance and ease of integration