摘要 :
Through the Air Force's Propulsion Outreach Program, Ohio University mechanical engineering students were challenged to complete theoretical and technical work to solve an aerospace problem. The project incorporates multi-discipli...
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Through the Air Force's Propulsion Outreach Program, Ohio University mechanical engineering students were challenged to complete theoretical and technical work to solve an aerospace problem. The project incorporates multi-disciplinary design techniques to research and modify a small gas turbine engine to produce thrust vectoring and prevent windmilling for a specified drop-launch scenario. The team developed a conceptual design that incorporates the project requirements while also balancing the system for size, weight, and simplicity. The design implements advanced mechanical systems with electrical components by using one actuator to operate an extended nozzle to +/-10 degrees of thrust vectored and a fairing that blocks air from entering the engine. The design was analyzed and tested evaluating thermal, material, and mechanical properties to ensure it would operate under the extreme conditions of the engine. After completing multiple iterations and design reviews, a prototype was created utilizing 3D printing and then assembled to demonstrate that the design accomplishes the project goals.
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摘要 :
Through the Air Force's Propulsion Outreach Program, Ohio University mechanical engineering students were challenged to complete theoretical and technical work to solve an aerospace problem. The project incorporates multi-discipli...
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Through the Air Force's Propulsion Outreach Program, Ohio University mechanical engineering students were challenged to complete theoretical and technical work to solve an aerospace problem. The project incorporates multi-disciplinary design techniques to research and modify a small gas turbine engine to produce thrust vectoring and prevent windmilling for a specified drop-launch scenario. The team developed a conceptual design that incorporates the project requirements while also balancing the system for size, weight, and simplicity. The design implements advanced mechanical systems with electrical components by using one actuator to operate an extended nozzle to +/-10 degrees of thrust vectored and a fairing that blocks air from entering the engine. The design was analyzed and tested evaluating thermal, material, and mechanical properties to ensure it would operate under the extreme conditions of the engine. After completing multiple iterations and design reviews, a prototype was created utilizing 3D printing and then assembled to demonstrate that the design accomplishes the project goals.
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摘要 :
Through the Air Force's Propulsion Outreach Program, undergraduate mechanical engineering students from Ohio University were tasked to complete the theoretical and technical work to solve an aerospace problem. The project incorpor...
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Through the Air Force's Propulsion Outreach Program, undergraduate mechanical engineering students from Ohio University were tasked to complete the theoretical and technical work to solve an aerospace problem. The project incorporated multi-disciplinary design techniques to research and modify a small, gas turbine engine to allow operation where the airframe blocks the engine face requiring a duct to reach six inches from center. A conceptual design was developed from optimized parameters from literature, and analysis of functional prototypes was used to further optimize the S-duct's performance. The final design utilized modular 3D printed sections to create the S-duct geometry. The final design was tested using the Ohio University engine test stand, and at a static, ground level test, the design achieved a total pressure recovery of 99.39%, a maximum thrust decrement of 0.49%, and an improved thrust specific fuel consumption while satisfying the six-inch offset requirement from the engine's centerline.
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Automated collision avoidance for small unmanned vehicles operating at low altitude can be challenging as a system may need to autonomously make decisions about safe path deviation to avoid aerial obstacles. Historical avoidance a...
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Automated collision avoidance for small unmanned vehicles operating at low altitude can be challenging as a system may need to autonomously make decisions about safe path deviation to avoid aerial obstacles. Historical avoidance alert systems, such as TCAS and ACAS, specific to manned aircraft were designed with human operation in mind and have proven reliability. These collision avoidance methods may not be appropriate for autonomous systems with control and decision delays since human intervention can be immediately required. Additionally, a single operator may be monitoring and controlling several unmanned aerial systems at the same time and may not have the same level of situational awareness as a manned aircraft's pilot. This effort examined a commonly used path planning algorithm to generate collision avoidance paths along with a method for path recovery. Since the autonomous vehicle may be performing aerial data collection at specific pre-defined locations or may need to operate in known locations, returning to the original mission path in a direct and efficient manner becomes essential. Clothoids that consider vehicle turn rate were used to identify a return trajectory after avoiding a collision to provide less mission path deviation when compared to picking a single waypoint and following a straight line segment in two dimensional simulations. Collisions were detected using forward facing cones projected on two separate fixed-wing aircraft representing possible future flight paths. Cross track error with and without clothoid recovery paths was computed to evaluate the collision avoidance process with recovery and identify improvements. Results indicate that the addition of a recovery planning phase in a collision avoidance system provides less cross track error resulting in less time spent off the original planned path and tighter coverage of mission areas requiring continuous monitoring.
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摘要 :
Uncrewed vehicles require recovery routes to return autonomously to a mission after collision avoidance. The leading techniques for crewed aircraft such as ACAS do not directly translate to the explicit path definitions required f...
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Uncrewed vehicles require recovery routes to return autonomously to a mission after collision avoidance. The leading techniques for crewed aircraft such as ACAS do not directly translate to the explicit path definitions required for autonomous systems. Processes for automated route recovery such as the Path Recovery Automated Collision Avoidance System (PRACAS) are capable of returning a vehicle to an original mission, but has only been investigated for straight paths and the effects of interception point placement on recovery time has not been identified. Minimal deviation and recovery time is desired for maximum time and coverage in continuous monitoring tasks while ensuring safe operation in known airspace. The present work investigated the effects of intercept point placement on return time to mission routes in three simulation environments including a straight path, holding pattern, and a path generated from an exponential function to explore performance in common and curved paths and identified the first viable interception point. Clothoid return using the first viable interception point generated more cross track error and time to recover compared to non-linear guidance and pure pursuit, but had control on vehicle heading at path acquisition for smoother path following after interception. The general trend was that interception points for clothoid return farther along a path generated more cross track error and recover time, but had tighter control on acquisition heading. Impact of this work is an investigation of curved path interception within the PRACAS process to identify the first viable point meeting fixed wing turn rate limits to minimize path deviation so time spent in the desired operating region can be maximized where only straight paths had been previously considered.
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Obstacle avoidance may be incorporated into vector field guidance using repulsive vector fields. The influence of these repulsive vector fields is limited to a certain region by scaling the field strength with a decay function. Th...
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Obstacle avoidance may be incorporated into vector field guidance using repulsive vector fields. The influence of these repulsive vector fields is limited to a certain region by scaling the field strength with a decay function. The present work examines the effects of five different obstacle vector field decay functions on vehicle performance using gradient vector field guidance. Three scenarios were simulated: single object avoidance with different vehicle velocities, single object avoidance with different vehicle approach angles, and multiple object avoidance. For the examined conditions, the best performance was achieved using a hyperbolic tangent decay function when the vehicle velocity to obstacle radius ratio is less than 10. It appears that effective avoidance is achieved when the obstacle field strength rapidly drops to zero once outside of the obstacle radius.
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摘要 :
Obstacle avoidance may be incorporated into vector field guidance using repulsive vector fields. The influence of these repulsive vector fields is limited to a certain region by scaling the field strength with a decay function. Th...
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Obstacle avoidance may be incorporated into vector field guidance using repulsive vector fields. The influence of these repulsive vector fields is limited to a certain region by scaling the field strength with a decay function. The present work examines the effects of five different obstacle vector field decay functions on vehicle performance using gradient vector field guidance. Three scenarios were simulated: single object avoidance with different vehicle velocities, single object avoidance with different vehicle approach angles, and multiple object avoidance. For the examined conditions, the best performance was achieved using a hyperbolic tangent decay function when the vehicle velocity to obstacle radius ratio is less than 10. It appears that effective avoidance is achieved when the obstacle field strength rapidly drops to zero once outside of the obstacle radius.
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Autonomous aerial vehicle path following requires robust guidance commands for successful mission completion. Discrete waypoints are typically used, but only allow for straight line path following. Following smooth trajectories is...
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Autonomous aerial vehicle path following requires robust guidance commands for successful mission completion. Discrete waypoints are typically used, but only allow for straight line path following. Following smooth trajectories is desired so ground features or tight turns can be highly controlled which can not be achieved while using waypoint guidance. Vector field guidance providing heading commands representing the desired path can instead be used to provide smooth path following for fixed wing aircraft, but requires the use of carrot chasing for multi-rotor vehicles using position control where a point is placed in front of the vehicle along the commanded heading. The carrot chasing method can create lagged areas causing velocity oscillation and drift from the planned path on curved trajectories resulting in poor path following performance without explicit velocity control. Components from vector field guidance field can be used to generate velocity control commands instead of position commands which rely on carrot chasing for multi-rotor aircraft. The present work investigates velocity control for vector field guidance enabling smooth path following for multi-rotor autonomous vehicles so carrot chasing with position control can be replaced. Comparisons between vector field velocity control and carrot chasing position control path following performance using cross track error are made to identify improvements and deteriorations. Results may be used to obtain smoother path following using vector field guidance and velocity control with multi-rotor autonomous systems resulting in shorter flight times and less energy consumption compared to carrot chasing methods.
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摘要 :
Autonomous aerial vehicle path following requires robust guidance commands for successful mission completion. Discrete waypoints are typically used, but only allow for straight line path following. Following smooth trajectories is...
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Autonomous aerial vehicle path following requires robust guidance commands for successful mission completion. Discrete waypoints are typically used, but only allow for straight line path following. Following smooth trajectories is desired so ground features or tight turns can be highly controlled which can not be achieved while using waypoint guidance. Vector field guidance providing heading commands representing the desired path can instead be used to provide smooth path following for fixed wing aircraft, but requires the use of carrot chasing for multi-rotor vehicles using position control where a point is placed in front of the vehicle along the commanded heading. The carrot chasing method can create lagged areas causing velocity oscillation and drift from the planned path on curved trajectories resulting in poor path following performance without explicit velocity control. Components from vector field guidance field can be used to generate velocity control commands instead of position commands which rely on carrot chasing for multi-rotor aircraft. The present work investigates velocity control for vector field guidance enabling smooth path following for multi-rotor autonomous vehicles so carrot chasing with position control can be replaced. Comparisons between vector field velocity control and carrot chasing position control path following performance using cross track error are made to identify improvements and deteriorations. Results may be used to obtain smoother path following using vector field guidance and velocity control with multi-rotor autonomous systems resulting in shorter flight times and less energy consumption compared to carrot chasing methods.
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Accurate localization estimation in a global or local frame is needed for a navigation solution which results in safe and efficient vehicle guidance. SLAM is a common approach to vehicle localization in GPS denied environments, bu...
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Accurate localization estimation in a global or local frame is needed for a navigation solution which results in safe and efficient vehicle guidance. SLAM is a common approach to vehicle localization in GPS denied environments, but solutions often require odometry that may not be available to UAVs. ICP and Hector SLAM are common approaches for vehicle localization that rely on scan matching without the need for odometry, however both suffer when operating in long corridors with limited features for 2D single laser LiDAR scan matching. The present work injected localization solutions for the ICP method with known pose while the vehicle injection rate to velocity ratio was varied to explore their effects on average cross track error, accumulated position error, and to compare to Hector SLAM, another common method for scan matching based SLAM. The impact of the present work is that there has been an investigation on how vehicle velocity and known pose injection rate effect cumulative localization accuracy using scan matching ICP based SLAM techniques. Performance was measured using the cross track error and accumulative position error of ICP and Hector SLAM when compared to known vehicle position in simulation. Results may be used to identify system constraints such as maximum vehicle velocity for a successful mission completion given a known position injection rate and acceptable localization error.
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