A COLLISION AVOIDANCE SYSTEM FOR AUTONOMOUS UNDERWATER VEHICLES

The work in this thesis is concerned with the development of a novel and practical collision avoidance system for autonomous underwater vehicles (AUVs). Synergistically, advanced stochastic motion planning methods, dynamics quantisation approaches, multivariable tracking controller designs, sonar data processing and workspace representation, are combined to enhance significantly the survivability of modern AUVs. The recent proliferation of autonomous AUV deployments for various missions such as seafloor surveying, scientific data gathering and mine hunting has demanded a substantial increase in vehicle autonomy. One matching requirement of such missions is to allow all the AUV to navigate safely in a dynamic and unstructured environment. Therefore, it is vital that a robust and effective collision avoidance system should be forthcoming in order to preserve the structural integrity of the vehicle whilst simultaneously increasing its autonomy. This thesis not only provides a holistic framework but also an arsenal of computational techniques in the design of a collision avoidance system for AUVs. The design of an obstacle avoidance system is first addressed. The core paradigm is the application of the Rapidly-exploring Random Tree (RRT) algorithm and the newly developed version for use as a motion planning tool. Later, this technique is merged with the Manoeuvre Automaton (MA) representation to address the inherent disadvantages of the RRT. A novel multi-node version which can also address time varying final state is suggested. Clearly, the reference trajectory generated by the aforementioned embedded planner must be tracked. Hence, the feasibility of employing the linear quadratic regulator (LQG) and the nonlinear kinematic based state-dependent Ricatti equation (SDRE) controller as trajectory trackers are explored. The obstacle detection module, which comprises of sonar processing and workspace representation submodules, is developed and tested on actual sonar data acquired in a sea-trial via a prototype forward looking sonar (AT500). The sonar processing techniques applied are fundamentally derived from the image processing perspective. Likewise, a novel occupancy grid using nonlinear function is proposed for the workspace representation of the AUV. Results are presented that demonstrate the ability of an AUV to navigate a complex environment. To the author's knowledge, it is the first time the above newly developed methodologies have been applied to an A UV collision avoidance system, and, therefore, it is considered that the work constitutes a contribution of knowledge in this area of work.J&S MARINE LT

Aquatic Robot Recovery Craft

In situations where someone is trapped underwater, rescue personnel must attempt a search for the body. However, this task is extremely dangerous for the divers that attempt to locate it. Drowning, hypothermia, and decompression sickness are some dangers that could happen to a diver while trying to locate a missing person. This project proposes the Aquatic Robotic Recovery Craft (ARRC), which can take the place of a diver during the search for the missing person. This system is capable of powering its thrusters to drive through the water, using a camera to look at the surrounding area, and using visual tracking to map the bottom of a body of water. Ideally, the prototype for the robot could be used by any rescue team to search for a body underwater in a safe and effective way

Teleprogramming: Remote Site Research Issues: (Dissertation Proposal)

This document proposes the development of the remote site workcell for teleoperation with significant communication delays (on the order of one to 20 seconds). In these situations, direct teleoperation becomes difficult to impossible due to the delays in visual and force feedback. Teleprogramming has been developed in order to overcome this problem. In teleprogramming, the human operator interacts in real time with a graphical model of the remote site, which provides for real time visual and force feedback. The master arm and the manipulator/model interactions, given predefined criteria of what types of motions are to be expected. These commands are then sent via a communication link, which may delay the signals, to the remote site. Based upon a remote world model, predefined and possibly refined as more information is obtained, the slave carries out commanded operations in the remote world and decides whether each step has been executed correctly. The remote site receives commands sent via the delayed communication link. These commands must be parsed and translated into the local robot control language, which includes insertion of dynamic parameters that are not generated by the master system. The commands are then executed by the hybrid position/force controller, and the resulting motions monitored for errors. This proposal addresses the following remote site issues: low level manipulator control using an instrumented compliant wrist for sensory feedback, higher level command execution implementing dynamic parameters, and remote manipulator tool usage and control

Technical-economic analysis, modeling and optimization of floating offshore wind farms

The offshore wind sector has grown significantly during the last decades driven by the increasing demand for clean energy and to reach defined energy targets based on renewable energies. As the wind speeds tend to be faster and steadier offshore, wind farms at sea can reach higher capacity factors compared to their onshore counterparts. Furthermore, fewer restrictions regarding land use, visual impact, and noise favors the application of this technology. However, most of today's offshore wind farms use bottom-fixed foundations that limit their feasible application to shallow water depths. Floating substructures for offshore wind turbines are a suitable solution to harness the full potential of offshore wind as they have less constraints to water depths and soil conditions and can be applied from shallow to deep waters. As several floating offshore wind turbine (FOWT) concepts have been successfully tested in wave tanks and prototypes have been proven in open seas, floating offshore wind is now moving towards the commercial phase with the first floating offshore wind farm (FOWF) commissioned in 2017 and several more are projected to be constructed in 2020. This transition increases the need for comprehensive tools that allow to model the complete system and to predict its behavior as well as to assess the performance for different locations. The aim of this thesis is to analyze from a technical and economic perspective commercial scale FOWFs. This includes the modeling of FOWTs and the study of their dynamic behavior as well as the economic assessment of different FOWT concepts. The optimization of the electrical layout is also addressed in this thesis. The first model developed is applied to analyze the performance of a Spar type FOWT. The model is tested with different load cases and compared to a reference model. The results of both models show an overall good agreement. Afterwards, the developed model is applied to study the behavior of the FOWT with respect to three different offshore sites. Even at the site with the harshest conditions and largest motions, no significant loss in energy generation is measured, which demonstrates the good performance of this concept. The second model is used to perform a technical-economic assessment of commercial scale FOWFs. It includes a comprehensive LCOE methodology based on a life cycle cost estimation as well as the computation of the energy yield. The model is applied to three FOWT concepts located at three different sites and considering a 500MW wind farm configuration. The findings indicate that FOWTs are a high competitive solution and energy can be produced at an equal or lower LCOE compared to bottom-fixed offshore wind or ocean energy technologies. Furthermore, a sensitivity analysis is performed to identify the key parameters that have a significant influence on the LCOE and which can be essential for further cost reductions. The last model is aimed to optimize the electrical layout of FOWFs based on the particle swarm optimization theory. The model is validated against a reference model at first and is then used to optimize the inter-array cable routing of a 500MW FOWF. The obtained electrical layout results in a reduction of the power cable costs and a decrease of the energy losses. Finally, the use of different power cable configurations is studied and it is shown that the use of solely dynamic power cables in comparison to combined dynamic and static cables results in decreased acquisition and installation costs due to the avoidance of cost-intensive submarine joints and additional installation activities.El sector eólico marino ha crecido significativamente durante las últimas décadas impulsado por la creciente demanda de energía limpia. Los parques eólicos en el mar pueden alcanzar factores de capacidad más altos en comparación a los parques eólicos en la tierra debido a que las velocidades del viento tienden a ser más altas y constantes en el mar. Ademas, existen menos restricciones con respecto al uso de la tierra, el impacto visual y el ruido. Sin embargo, la mayoría de los parques eólicos actuales utilizan subestructuras fijas que limitan su aplicación factible a aguas poco profundas. Las subestructuras flotantes para turbinas eólicas marinas (FOWTs en inglés) son una solución adecuada para aprovechar todo el potencial de la energía eólica, ya que tienen menos restricciones para las profundidades del agua y el fondo marino. Dado que varios prototipos de FOWTs se han probado con éxito en el mar, la industria ahora esta entrando a la fase comercial con el primer parque eólico flotante (FOWF en inglés) operativo y se proyecta que se pondrán en marcha más en los próximos anos. Esta transición aumenta la necesidad de herramientas integrales que permitan modelar el sistema completo y predecir su comportamiento, así como evaluar el rendimiento para diferentes lugares. El objetivo de esta tesis es analizar desde una perspectiva técnica y económica los FOWFs a escala comercial. Esto incluye el modelado de FOWTs, el estudio de su comportamiento dinámico, y la evaluación económica de diferentes conceptos. La optimización del diseño eléctrico también se aborda en esta tesis. El primer modelo desarrollado se aplica para analizar el rendimiento de un FOWT tipo Spar. El modelo se prueba con diferentes tipos de carga y se compara con un modelo de referencia. Los resultados de ambos modelos muestran una buena concordancia. Posteriormente, el modelo se aplica para estudiar el comportamiento con respecto a tres lugares diferentes. Los resultados muestran que incluso en el sitio con las condiciones más severas, no se mide ninguna pérdida significativa en la generación de energía, lo que demuestra el buen rendimiento de este concepto. El segundo modelo se utiliza para realizar una evaluación técnico-económica de los FOWF a escala comercial. Esto incluye una metodología integral del costo nivelado de energía (LCOE en ingles). El modelo se aplica a tres conceptos de FOWTs ubicados en tres lugares diferentes y considerando un parque eólico de 500MW. Los resultados indican que los FOWTs son una solución altamente competitiva y que la energía se puede producir con un LCOE igual o inferior en comparación con los parques eólicos con subestructuras fijas o las tecnologías de energía oceánica. Asimismo, se realiza un análisis de sensibilidad para identificar los parámetros claves que tienen una influencia significativa en el LCOE y que pueden ser esenciales para reducciones de costos. El último modelo se aplica para optimizar el diseño eléctrico en función de la teoría de optimización por enjambre de partículas. Inicialmente el modelo se valida contra un modelo de referencia y luego se utiliza para optimizar la conexión de los cables entre los FOWTs. El diseño eléctrico obtenido da como resultado una reducción de los costos de cables y una disminución de las pérdidas de energía. Finalmente, se estudia el uso de diferentes configuraciones de cables y se demuestra que el uso de cables únicamente dinámicos en comparación con los cables dinámicos y estáticos combinados da como resultado una disminución de los costos de adquisición e instalación debido a que evitan la necesidad de juntas submarinas costosas y costos adicionales de instalación.Postprint (published version

Model Based Teleoperation to Eliminate Feedback Delay NSF Grant BCS89-01352 First Report

We are conducting research in the area of teleoperation with feedback delay. Delay occurs with earth-based teleoperation in space and with surface-based teleoperation with untethered submersibles when acoustic communication links are involved. the delay in obtaining position and force feedback from remote slave arms makes teleoperation extremely difficult. We are proposing a novel combination of graphics and manipulator programming to solve the problem by interfacing a teleoperator master arm to a graphics based simulator of the remote environment coupled with a robot manipulator at the remote, delayed site. the operator\u27s actions will be monitored to provide both kinesthetic and visual feedback and to generate symbolic motion commands to the remote slave. the slave robot will then execute these symbolic commands delayed in time. While much of a task will proceed error free, when an error does occur the slave system will transmit data back to the master and the master environment will be reset to the error state

Search methods for an autonomous underwater vehicle using scalar measurements

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution July 1996The continuing development of the autonomous underwater vehicle as an oceanographic research tool has opened up the realm of scientific possibility in the field of deep ocean research. The ability of a vehicle to travel to the ocean floor untethered, collect data for an extended period of time and return to the surface for recovery can make precise oceanographic surveying more economically practical and more efficient. This thesis investigates several scalar parameter searching techniques which have their basis in mathematical optimization algorithms and their applicability for use specifically within the context of autonomous underwater vehicle dynamics. In particular, a modified version of the circular gradient evaluation in the simulated environment of a hydrothermal plume is examined as a test case. Using a priori knowledge of the expected structure of the scalar parameter contour is shown to be advantageous in optimizing the search

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

Closed-loop well construction optimization (CLWCO) using stochastic approach under time uncertainty

There is a digital step change taking place in well construction today. More and better data will become available for a vast number of analyses. The well construction process is complicated and includes several hundred parameters. There are many inhouse drilling analytics tools used by service and consulting companies. The objective of this paper is to aim at a complete time optimization and to improve health, safety and the environment (HSE) in a time-effective way. In this paper we establish and apply a full approach methodology for closed Loop well construction optimization (CLWCO) under time uncertainty. CLWCO involves six major steps: data gathering,a work-breakdown structure (WBS) in drilling scenarios, time estimation (budget time &technical time),time simulation (MCS&PERT), scenario analysis & optimization and finally updating time model. CLWCO involves three major concepts: optimizing the time plan based on current time knowledge, drilling new wells and collecting time data, finally updating multiple time models based on all of the available data. In the CLWCO step, work breakdown structure (W.B.S), time and controls for new wells are optimized by Monte-Carlo Simulation and program evaluation review technique (PERT). This paper goals are to identify and in best case quantify “the value of Monte Carlo simulation and Program Evaluation Review Technique (PERT) in batch & conventional time drilling optimization” in offshore wells for clients or operating company. Batch drilling does not combine professionally with modern techniques yet.we fill this gap by using modern techniques to optimize and enhance drilling work. We evaluate and analysis above-mentioned approach for batch drilling which has become increasingly prevalent in the petroleum industry as large and small investors alike seek to increase their profit margin. The insight of many of these oil and gas companies was to drill and complete wells using new techniques with the desire of considerable reduction in drilling time and cost for the field. when similar hole sections such as 32″,24″,16″,12 ¼″ and 8 ½″ of different wells were drilled one after the other efficiency and profits would be greatly increased. According to obtained results in closed loop well construction optimization (CLWCO), these methods are successful as it needs less time and cost to drill a lot of wells using the same platform. we simulated a drilling program for the case study of SP field by Monte-Carlo Simulation and program evaluation review technique (PERT),at the end we propose the optimum probable time to do future drilling program in SP field. The time versus depth graph of drilling project show that the improved drilling efficiency for drilling project designed as 11 wells would reduce the total drilling time around 15% in compare of previous drilling projects in phase SP6,SP7 and SP8,totally average drilling time have been improved between 2.5 and 8 days in MCS and PERT simulation technique for each well by using CLWCO.We presented the optimal plan coupling with batch drilling could be implemented in the future phases of SP field, which has resulted in decreasing drilling time to 30 days by using casing-drilling and liner-drilling technology.acceptedVersio

Model Based Teleoperation to Eliminate Feedback Delay NSF Grant BCS89-01352 Second Report

We are conducting research in the area of teleoperation with feedback delay. Delay occurs with earth-based teleoperation in space and with surface-based teleoperation with untethered submersibles when acoustic communication links are involved. The delay in obtaining position and force feedback from remote slave arms makes teleoperation extremely difficult leading to very low productivity. We have combined computer graphics with manipulator programming to provide a solution to the problem. A teleoperator master arm is interfaced to a graphics based simulator of the remote environment. The system is then coupled with a robot manipulator at the remote, delayed site. The operator\u27s actions are monitored to provide both kinesthetic and visual feedback and to generate symbolic motion commands to the remote slave. The slave robot then executes these symbolic commands delayed in time. While much of a task proceeds error free, when an error does occur, the slave system transmits data back to the master environment which is then reset to the error state from which the operator continues the task