Axial Compressor Design with Counter-Rotation and Variable RPM for Stall Mitigation

Compressor Stall, an aerodynamic instability due to abnormal air flow in the compressor resulting in loss of total pressure and compressor performance. One of the reasons of compressor stall is due to rise in static back pressure at compressor exit which may result from an imbalance of incidence angle at the rotor and stator and rotational speed. The paper presents the results of a new axial compressor design with counter rotation and variable RPM. Counter-Rotation is used to push compressor performance during stall by moving the operating point away from surge line with a higher pressure ratio rise. Initially an axial compressor is designed with counter-rotation at design point. The flow is modelled by means of Navier-Stokes computation using the upstream rotor conditions and exit static pressure condition with k-epsilon as the turbulence model. Compressor exit conditions are then changed to stall the compressor. After the compressor stalls the RPM of the counter-rotating stage is varied until the compressor recovers from the stall. This novel idea unlike the conventional stall control systems mitigates the stall without compromising compressor performance, in fact it helps to increase the performance and pressure ratio of the compressor with the means of counter-rotation and variable RPM

Adaptive-Optimal Control of Spacecraft near Asteroids

Spacecraft dynamics and control in the vicinity of an asteroid is a challenging and exciting problem. Currently, trajectory tracking near asteroid requires extensive knowledge about the asteroid and constant human intervention to successfully plan and execute proximity operation. This work aims to reduce human dependency of these missions from a guidance and controls perspective. In this work, adaptive control and model predictive control are implemented to generating and tracking obstacle avoidance trajectories in asteroid’s vicinity. Specifically, direct adaptive control derived from simple adaptive control is designed with e modification to track user-generated trajectories in the presence of unknown system and sensor noise. This adaptive control methodology assumes no information on the system dynamics, and it is shown to track trajectories successfully in the vicinity of the asteroid. Then a nonlinear model predictive control methodology is implemented to generate obstacle avoidance trajectories with minimal system information namely mass and angular velocity of the asteroid. Ultimately, the adaptive control system is modified to include feed-forward control input from the nonlinear model predictive control. It is shown through simulations that the new control methodology names direct adaptive model predictive control (DAMPC), is able to generate sub-optimal trajectories. A comparative study is done with Asteroid Bennu, Kleopatra and Eros to show the benefits of DAMPC over adaptive control and MPC. A study on effect of noisy measurements and model is also conducted on adaptive control and direct adaptive model predictive control

Computationally Efficient Data-Driven Discovery and Linear Representation of Nonlinear Systems For Control

This work focuses on developing a data-driven framework using Koopman operator theory for system identification and linearization of nonlinear systems for control. Our proposed method presents a deep learning framework with recursive learning. The resulting linear system is controlled using a linear quadratic control. An illustrative example using a pendulum system is presented with simulations on noisy data. We show that our proposed method is trained more efficiently and is more accurate than an autoencoder baseline

Adaptive Modified RISE-based Quadrotor Trajectory Tracking with Actuator Uncertainty Compensation

This paper presents an adaptive robust nonlinear control method, which achieves reliable trajectory tracking control for a quadrotor unmanned aerial vehicle in the presence of gyroscopic effects, rotor dynamics, and external disturbances. Through novel mathematical manipulation in the error system development, the quadrotor dynamics are expressed in a control-oriented form, which explicitly incorporates the uncertainty in the gyroscopic term and control actuation term. An adaptive robust nonlinear control law is then designed to stabilize both the position and attitude loops of the quadrotor system. A rigorous Lyapunov-based analysis is utilized to prove asymptotic trajectory tracking, where the region of convergence can be made arbitrarily large through judicious control gain selection. Moreover, the stability analysis formally addresses gyroscopic effects and actuator uncertainty. To illustrate the performance of the control law, comparative numerical simulation results are provided, which demonstrate the improved closed-loop performance achieved under varying levels of parametric uncertainty and disturbance magnitudes

Direct-Adaptive Nonlinear MPC for Spacecraft Near Asteroids

In this work, we propose a novel controller based on a simple adaptive controller methodology and model predictive control (MPC) to generate and track trajectories of a spacecraft in the vicinity of asteroids. The control formulation is based on using adaptive control as a feedback controller and MPC as a feed-forward controller. The spacecraft system model, asteroid shape and inertia are assumed to be unknown, with the exception of the estimated total mass and angular velocity of the asteroid. The MPC is used to generate feed-forward trajectories and control input using only the mass and angular velocity of the asteroid combined with obstacle avoidance constraints. However, since the control input from MPC is calculated using only an approximated model of the asteroid, it fails to control the spacecraft in the presence of disturbances due to the asteroid’s irregular gravitational field. Hence, we propose an adaptive controller in conjunction with MPC to handle unknown disturbances. The numerical results presented in this work show that the novel control system is able to handle unknown disturbances while generating and tracking sub-optimal trajectories better than adaptive control or MPC solely

Direct-Adaptive Nonlinear MPC for Spacecraft Near Asteroids

In this work, we propose a novel controller based on a simple adaptive controller methodology and model predictive control (MPC) to generate and track trajectories of a spacecraft in the vicinity of asteroids. The control formulation is based on using adaptive control as a feedback controller and MPC as a feed-forward controller. The spacecraft system model, asteroid shape and inertia are assumed to be unknown, with the exception of the estimated total mass and angular velocity of the asteroid. The MPC is used to generate feed-forward trajectories and control input using only the mass and angular velocity of the asteroid combined with obstacle avoidance constraints. However, since the control input from MPC is calculated using only an approximated model of the asteroid, it fails to control the spacecraft in the presence of disturbances due to the asteroid’s irregular gravitational field. Hence, we propose an adaptive controller in conjunction with MPC to handle unknown disturbances. The numerical results presented in this work show that the novel control system is able to handle unknown disturbances while generating and tracking sub-optimal trajectories better than adaptive control or MPC solely

Adaptive Modified RISE-based Quadrotor Trajectory Tracking with Actuator Uncertainty Compensation

This paper presents an adaptive robust nonlinear control method, which achieves reliable trajectory tracking control for a quadrotor unmanned aerial vehicle in the presence of gyroscopic effects, rotor dynamics, and external disturbances. Through novel mathematical manipulation in the error system development, the quadrotor dynamics are expressed in a control-oriented form, which explicitly incorporates the uncertainty in the gyroscopic term and control actuation term. An adaptive robust nonlinear control law is then designed to stabilize both the position and attitude loops of the quadrotor system. A rigorous Lyapunov-based analysis is utilized to prove asymptotic trajectory tracking, where the region of convergence can be made arbitrarily large through judicious control gain selection. Moreover, the stability analysis formally addresses gyroscopic effects and actuator uncertainty. To illustrate the performance of the control law, comparative numerical simulation results are provided, which demonstrate the improved closed-loop performance achieved under varying levels of parametric uncertainty and disturbance magnitudes

Anaesthetic significance and management of a child with neonatal purpura fulminans

Protein C deficiency is a rare autosomal-dominant disorder of varying severity. Patients with homozygous and compound heterozygous protein C deficiency present with neonatal purpura fulminans (NPF). Other presentations usually include disseminated intravascular coagulation and venous thromboembolism. This disorder usually poses a unique anaesthetic challenge to the anaesthesiologist, requiring special precautions to prevent various intra- and post-operative complications. We hereby report the successful anaesthetic management of a 1-month-old infant who presented with NPF

Anesthetic management of peripartum cardiomyopathy using "epidural volume extension" technique: A case series

Peripartum cardiomyopathy is a rare cause of dilated cardiomyopathy in parturients, occurring in approximately one in 1000 deliveries, manifesting during the last few months or the first 5 months of the postpartum period. It can result in severe ventricular dysfunction during late puerperium. The major concern while managing these patients is to optimize fluid administration and avoid myocardial depression, while maintaining stable intraoperative hemodynamics. We present a case series of five parturients that were posted for elective cesarean section and managed successfully by the epidural volume extension technique

Transition to active learning in rural Nepal: an adaptable and scalable curriculum development model

International audienceBackgroundTraditional medical education in much of the world has historically relied on passive learning. Although active learning has been in the medical education literature for decades, its incorporation into practice has been inconsistent. We describe and analyze the implementation of a multidisciplinary continuing medical education curriculum in a rural Nepali district hospital, for which a core objective was an organizational shift towards active learning.MethodsThe intervention occurred in a district hospital in remote Nepal, staffed primarily by mid-level providers. Before the intervention, education sessions included traditional didactics. We conducted a mixed-methods needs assessment to determine the content and educational strategies for a revised curriculum. Our goal was to develop an effective, relevant, and acceptable curriculum, which could facilitate active learning. As part of the intervention, physicians acted as both learners and teachers by creating and delivering lectures. Presenters used lecture templates to prioritize clarity, relevance, and audience engagement, including discussion questions and clinical cases. Two 6-month curricular cycles were completed during the study period. Daily lecture evaluations assessed ease of understanding, relevance, clinical practice change, and participation. Periodic lecture audits recorded learner talk-time, the proportion of lecture time during which learners were talking, as a surrogate for active learning. Feedback from evaluation and audit results was provided to presenters, and pre- and post-curriculum knowledge assessment exams were conducted.ResultsLecture audits showed a significant increase in learner talk-time, from 14% at baseline to 30% between months 3–6, maintained at 31% through months 6–12. Lecture evaluations demonstrated satisfaction with the curriculum. Pre- and post-curriculum knowledge assessment scores improved from 50 to 64% (difference 13.3% ± 4.5%, p = 0.006). As an outcome for the measure of organizational change, the curriculum was replicated at an additional clinical site.ConclusionWe demonstrate that active learning can be facilitated by implementing a new educational strategy. Lecture audits proved useful for internal program improvement. The components of the intervention which are transferable to other rural settings include the use of learners as teachers, lecture templates, and provision of immediate feedback. This curricular model could be adapted to similar settings in Nepal, and globally