Faheem Rehman | University College London (original) (raw)
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Papers by Faheem Rehman
International Conference of Control, Dynamic Systems, and Robotics, 2019
This paper considers two HAUVs undertaking underwater transportation of a spherical payload via c... more This paper considers two HAUVs undertaking underwater transportation of a spherical payload via cylindrical manipulators. The rigid body connection method of transportation is explored. In this analysis, the nonlinear coupled dynamic model is developed to get an accurate representation of the actual system. Hydrodynamic parameters for all the part bodies are calculated about the centre of the combined system. The hydrostatic terms of the HAUVs and manipulators are selected such that their weight is slightly less than the buoyancy, in order to bring the entire system to surface in case of an emergency. The weight of the payload is selected such that the difference between weight and buoyancy is within the thrust limit of the vertical thrusters on the two HAUVs. The propulsion model is developed taking the effect of all the thrusters on the two HAUVs about the combined centre of body. The simulation platform is developed to observe the response of the entire system and of the individual HAUVs in the system at different revolutions of the thrusters. The stability of the entire system is ensured by maintaining the connection between the vehicles and payload. The simulation results show that stability and motion accuracy are compromised in the axial direction due to the opposite revolutions of the axial thrusters on the two HAUVs.
Journal of Robotics and Control (JRC), 2021
Transportation using multiple autonomous vehicles with detection avoidance capability is useful f... more Transportation using multiple autonomous vehicles with detection avoidance capability is useful for military applications. It is important for such systems to avoid collisions with underwater obstacles in an effective way, while keeping track of the target location. In this paper, sensor-based and path-planning methods of external collision avoidance were investigated for an underwater transportation system. In particular, sensor-based wall-following and hard-switching collision avoidance strategies and an offline RRT* pathplanning method was implemented on the simulation model of the transportation system of four Hovering Autonomous Underwater Vehicles (HAUVs). Time-domain motion simulations were performed with each method and their ability to avoid obstacles was compared. The hard-switching method resulted in high yaw moments which caused the vehicle to travel towards the goal by a longer distance. Conversely, in the wallfollowing method, the yaw moment was kept to zero. Moreover, the wall-following method was found to be better than the hardswitching method in terms of time and power efficiency. The comparison between the offline RRT* path-planning and wallfollowing methods showed that the fuel efficiency of the former is higher whilst its time efficiency is poorer. The major drawback of RRT* is that it can only avoid the previously known obstacles. In future, offline RRT* and wall following can be blended for a better solution. The outcome of this paper provides guidance for the selection of the most appropriate method for collision avoidance for an underwater transportation system.
Journal of Marine Science and Engineering, 2021
Underwater transportation is an essential approach for scientific exploration, maritime construct... more Underwater transportation is an essential approach for scientific exploration, maritime construction and military operations. Determining the hydrodynamic coefficients for a complex underwater transportation system comprising multiple vehicles is challenging. Here, the suitability of a quick and less costly semi-empirical approach to obtain the hydrodynamic coefficients for a complex transportation system comprising two Unmanned Underwater Vehicles (UUVs) is investigated, where the interaction effects between UUVs are assumed to be negligible. The drag results were verified by Computational Fluid Dynamics (CFD) analysis at the steady state. The semi-empirical results agree with CFD in heave and sway; however, they were overpredicted in surge due to ignoring the wake effects. Furthermore, experiments were performed for the validation of the time-domain motion simulations with semi-empirical and CFD results. The simulations which were performed with the CFD drags were close to the exp...
International Conference of Control, Dynamic Systems, and Robotics, 2019
This paper considers two HAUVs undertaking underwater transportation of a spherical payload via c... more This paper considers two HAUVs undertaking underwater transportation of a spherical payload via cylindrical manipulators. The rigid body connection method of transportation is explored. In this analysis, the nonlinear coupled dynamic model is developed to get an accurate representation of the actual system. Hydrodynamic parameters for all the part bodies are calculated about the centre of the combined system. The hydrostatic terms of the HAUVs and manipulators are selected such that their weight is slightly less than the buoyancy, in order to bring the entire system to surface in case of an emergency. The weight of the payload is selected such that the difference between weight and buoyancy is within the thrust limit of the vertical thrusters on the two HAUVs. The propulsion model is developed taking the effect of all the thrusters on the two HAUVs about the combined centre of body. The simulation platform is developed to observe the response of the entire system and of the individual HAUVs in the system at different revolutions of the thrusters. The stability of the entire system is ensured by maintaining the connection between the vehicles and payload. The simulation results show that stability and motion accuracy are compromised in the axial direction due to the opposite revolutions of the axial thrusters on the two HAUVs.
Journal of Robotics and Control (JRC), 2021
Transportation using multiple autonomous vehicles with detection avoidance capability is useful f... more Transportation using multiple autonomous vehicles with detection avoidance capability is useful for military applications. It is important for such systems to avoid collisions with underwater obstacles in an effective way, while keeping track of the target location. In this paper, sensor-based and path-planning methods of external collision avoidance were investigated for an underwater transportation system. In particular, sensor-based wall-following and hard-switching collision avoidance strategies and an offline RRT* pathplanning method was implemented on the simulation model of the transportation system of four Hovering Autonomous Underwater Vehicles (HAUVs). Time-domain motion simulations were performed with each method and their ability to avoid obstacles was compared. The hard-switching method resulted in high yaw moments which caused the vehicle to travel towards the goal by a longer distance. Conversely, in the wallfollowing method, the yaw moment was kept to zero. Moreover, the wall-following method was found to be better than the hardswitching method in terms of time and power efficiency. The comparison between the offline RRT* path-planning and wallfollowing methods showed that the fuel efficiency of the former is higher whilst its time efficiency is poorer. The major drawback of RRT* is that it can only avoid the previously known obstacles. In future, offline RRT* and wall following can be blended for a better solution. The outcome of this paper provides guidance for the selection of the most appropriate method for collision avoidance for an underwater transportation system.
Journal of Marine Science and Engineering, 2021
Underwater transportation is an essential approach for scientific exploration, maritime construct... more Underwater transportation is an essential approach for scientific exploration, maritime construction and military operations. Determining the hydrodynamic coefficients for a complex underwater transportation system comprising multiple vehicles is challenging. Here, the suitability of a quick and less costly semi-empirical approach to obtain the hydrodynamic coefficients for a complex transportation system comprising two Unmanned Underwater Vehicles (UUVs) is investigated, where the interaction effects between UUVs are assumed to be negligible. The drag results were verified by Computational Fluid Dynamics (CFD) analysis at the steady state. The semi-empirical results agree with CFD in heave and sway; however, they were overpredicted in surge due to ignoring the wake effects. Furthermore, experiments were performed for the validation of the time-domain motion simulations with semi-empirical and CFD results. The simulations which were performed with the CFD drags were close to the exp...