Piecewise Polynomial Model Identification using Constrained Least Squares for UAS Stall

Before the construction of the bridge bored pile in the karst area, geological conditions of the excavation area should be investigated. In order to avoid the karst caves in underground space making adverse impacts on the construction, bearing capacity, and stability of pile foundation, in this paper, we use the transient electromagnetic method to detect the karst development in the bearing layer of the pile foundation, which is different from the traditional karst survey method. To improve the interpretation accuracy of transient electromagnetic detection for karst caves, the quantum particle swarm optimization (QPSO) algorithm was combined with the smooth constrained least squares (CLS) algorithm, and the transient electromagnetic inversion based on the QPSO‐CLS joint algorithm was generated. Better inversion results were achieved by the proposed method in this study. Based on the inversion calculation results of simulation data and field test data, it is further demonstrated that the QPSO‐CLS joint algorithm has high optimization efficiency without manually setting the initial model. The interpretation results are consistent with the theoretical model and drilling logging results, which proves the adaptability of the proposed algorithm.

This paper addresses the challenge of embedded computing resources required by future autonomous Unmanned Aircraft Systems (UAS). Based on an analysis of the required onboard functions that will lead to higher levels of autonomy, we look at most common UAS tasks to first propose a classification of UAS tasks considering categories such as flight, navigation, safety, mission and executing entities such as human, offline machine, embedded system. We then analyse how a given combination of tasks can lead to higher levels of autonomy by defining an autonomy level. We link UAS applications, the tasks required by those applications, the autonomy level and the implications on computing resources to achieve that autonomy level. We provide insights on how to define a given autonomy level for a given application based on a number of tasks. Our study relies on the state-of-the-art hardware and software implementations of the most common tasks currently used by UAS, also expected tasks according to the nature of their future missions. We conclude that current computing architectures are unlikely to meet the autonomy requirements of future UAS. Our proposed approach is based on dynamically reconfigurable hardware that offers benefits in computational performance and energy usage. We believe that UAS designers must now consider the embedded system as a masterpiece of the system.

The integration of Unmanned Aircraft Systems (UAS) in the National Airspace represents new operational concepts required in civil aviation. These new concepts are evolving as the nation moves toward the Next Generation Air Transportation System (NextGen) under the leadership of the Joint Planning and Development Office (JPDO), and through ongoing work by the Federal Aviation Administration (FAA). The desire and ability to fly UAS in the National Air Space (NAS) in the near term has increased dramatically, and this multi-agency effort to develop and implement a national plan to successfully address the challenges of UAS access to the NAS in a safe and timely manner is well underway. As part of the effort to integrate UAS in the National Airspace, NASA Glenn Research Center is currently involved with providing research into Communications systems and Communication system operations in order to assist with developing requirements for this implementation. In order to provide data and information regarding communication systems performance that will be necessary, NASA GRC is tasked with developing and executing plans for simulations of candidate future UAS command and control communications, in line with architectures and communications technologies being developed and or proposed by NASA and relevant aviation organizations (in particular, RTCA SC-203). The simulations and related analyses will provide insight into the ability of proposed communications technologies and system architectures to enable safe operation of UAS, meeting UAS in the NAS project goals (including performance requirements, scalability, and interoperability), and ultimately leading to a determination of the ability of NextGen communication systems to accommodate UAS. This presentation, compiled by the NASA GRC Modeling and Simulation team, will provide an update to this ongoing effort at NASA GRC as follow-up to the overview of the planned simulation effort presented at ICNS in 2013. The objective of presentation will be to describe the progress made in developing both a NAS-Wide simulation architecture application and the detailed radiocomm system models for this research, and will present interim data and information compiled in the process of developing these simulation capabilities to date.

High-altitude, long-endurance unmanned aircraft systems (HALE UAS) are capable of extended flights for atmospheric sampling. A case study was conducted to evaluate the potential impact of dropwindsonde observations from HALE UAS on tropical cyclone track prediction; tropical cyclone intensity was not addressed. This study employs a global observing system simulation experiment (OSSE) developed at the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) that is based on the NOAA/National Centers for Environmental Prediction gridpoint statistical interpolation (GSI) data assimilation system and Global Forecast System (GFS) model. Different strategies for dropwindsonde deployment and UAS flight paths were compared. The introduction of UAS-deployed dropwindsondes was found to consistently improve the track forecast skill during the early forecast up to 96 h, with the caveat that the experiments omitted both vortex relocation and dropwindsondes from manned flights in the tropical cyclone region. The more effective UAS dropwindsonde deployment patterns sampled both the environment and the body of the tropical cyclone.

Eaves are rooftop augmentations that can shield indoor climate from direct sun-oriented radiation. These facades not provide ventilation but also prevent wetting by wind-driven rain. This article assesses the influence of eaves angle on wind effect ventilation of long span industrial roof structures. Eaves pitch angle varying from 35 ° to 65 ° with the interval of 10° is investigated. 3D steady Reynolds-Averaged Naiver–Stokes (RANS) approach is used to perform Computational Fluid Dynamics (CFD) simulations. Following best practice guidelines, the CFD simulation is done, and the wind profiles are validated with wind-tunnel measurements from the literature. The wind effect ventilation assessments are based on the indoor velocities and flow rate volume. Eave length is chosen 1/6 of the building height, and the eaves pitch angle is varied on all sides of the structure. The result showed that evaes with a pitch angle of 65 ° marks the highest flow rate volume (55%) compared to the conventional roof structures (without eaves). Also, the aerodynamic force coefficient is less (Cd = 0.73) compared to others. The wind pressure coefficient decreases with increasing eaves angle. The flow through the eaves amplifies the wind and enhances the indoor climate. The use of eaves on roof structures increases the volume flow rate by an average of 28.4%.

Simple mechanical linkages are often unable to cope with the many control problems associated with high performance aircraft maneuvering over a wide flight envelope. One procedure for retaining uniform handling qualities over such an envelope is to implement a digital adaptive controller. Towards such an implementation an explicit adaptive controller, which makes direct use of online parameter identification, has been developed and applied to the linearized equations of motion for a typical fighter aircraft. The system is composed of an online weighted least squares identifier, a Kalman state filter, and a single stage real model following control law. The corresponding control gains are readily adjustable in accordance with parameter changes to ensure asymptotic stability if the conditions for perfect model following are satisfied and stability in the sense of boundedness otherwise.

Rotor and ducted-fan structured unmanned helicopters have shown energy efficiency in low flight speed and hovering, due to the novel ducted-fan structure. However, its aerodynamic characteristics may change dramatically when flight at higher speed, resulting in a wide flight envelope when compared with conventional structured helicopters. Hence, the flight controller is required to schedule itself based on the flight states and guarantees the overall performances of the helicopter on the entire flight envelop. This paper presents a switching system theory based approach to design the optimal controllers over a wide region of flight envelop. In the proposed method, a family of robust controller are designed based on typical operational conditions and the controller is adjusted to guarantee the stability when the switching event is trigged. A hysteresis switching logic is utilized to ensure smooth transient between specific operational subspaces. The stability of the proposed control method was analyzed through Lyapunov theory. Nonlinear simulations based flight dynamics of the prototype helicopter have demonstrated the flexibility and efficiency of the proposed work.

The H∞ loop-shaping design procedure (referred to hereafter as LSDP) was used to design fixed gain controllers for the HIRM. It was found that a single fixed gain controller designed for the linearisation ini3005, performed adequately over the whole flight envelope of the HIRM. As scheduling would most probably be required for a real fighter aircraft with a much wider flight envelope, the control law has been developed with a structure suitable for scheduling. As the longitudinal and lateral dynamics are essentially decoupled, two separate controllers were designed. The lateral controller has an inner loop for stabilisation and an outer loop for tracking. The longitudinal controller has one single loop that provides both functions. A second fixed gain controller was designed for the HIRM using the multi-model approach described on pp. 67–72 in [247]. This method enables the designer to find a fixed gain controller that makes the normalised coprime factor cost function flat over the whole flight envelope. Details about how to apply this method can be found in [191]. The design team found it relatively easy, even with the limited time available, to satisfy the specifications set out in Chapter 27.

Abstract. A climate model represents a multitude of processes on a variety of timescales and space scales: a canonical example of multi-physics multi-scale modeling. The underlying climate system is physically characterized by sensitive dependence on initial conditions, and natural stochastic variability, so very long integrations are needed to extract signals of climate change. Algorithms generally possess weak scaling and can be I/O and/or memory-bound. Such weak-scaling, I/O, and memory-bound multi-physics codes present particular challenges to computational performance. Traditional metrics of computational efficiency such as performance counters and scaling curves do not tell us enough about real sustained performance from climate models on different machines. They also do not provide a satisfactory basis for comparative information across models. codes present particular challenges to computational performance. We introduce a set of metrics that can be used for the study of computational performance of climate (and Earth system) models. These measures do not require specialized software or specific hardware counters, and should be accessible to anyone. They are independent of platform and underlying parallel programming models. We show how these metrics can be used to measure actually attained performance of Earth system models on different machines, and identify the most fruitful areas of research and development for performance engineering. codes present particular challenges to computational performance. We present results for these measures for a diverse suite of models from several modeling centers, and propose to use these measures as a basis for a CPMIP, a computational performance model intercomparison project (MIP).

Electric vehicle (EV) drivetrains have witnessed remarkable progress, prompting intensified research into advanced transmission systems. Magnetorheological fluids (MRF) clutches offer precise modulation of input currents, enabling swift and seamless torque delivery for EV transmission systems, owing to their exceptional performance. The transmission of an EV requires MRF-based clutches to deliver a precise and rapid torque transfer during gear shifting. In these scenarios, the inherent current rate-dependent hysteresis of the MRF-based clutches between the output torque and input current poses a significant challenge in accurately regulating output torque. Therefore, an accurate clutch model of the MRF-based clutches that can describe the rate-dependent hysteresis is crucial to achieve precise control of the output torque. This study investigates the nonlinear hysteresis phenomena using a prototyped MRF dual-clutch (MRFDC) for the transmission system of EVs, followed by a comprehensive analysis of three widely used hysteresis models: two parametric models, including the Bouc-Wen (BW) model and algebraic model (AM), and a non-parametric model, the NARX model. Accuracy, fitting time, and stack size are selected as the main indicators to evaluate the three models comprehensively. Results indicate that the NARX model has exceptional accuracy compared to the others, while it has a much higher memory requirement. The algebraic model shows a great advantage in computational efficiency because it has a straightforward expression. The BW model is in the middle position for all three indicators. To optimize the classic BW model (CBW), a fractional-order modified BW model (FOMBW) is proposed based on the polynomial input function and fractional-order derivatives. The proposed FOMBW model demonstrates superior capability in capturing asymmetric and rate-dependent characteristics compared to the CBW model. These findings provide the basis for choosing an appropriate model to effectively capture nonlinear current hysteresis phenomena within MRFDC with the requirement for precise torque control during gear shifting.

Hysteresis phenomena in transverse galloping of triangular cross-section bodies

Some aspects about the influence on the current collection of the aerodynamic action on a pantograph, due to the incoming flow generated by train speed are investigated considering pantograph–catenary dynamic interaction. Starting from the quasi-steady theory formulation of the drag and lift forces on the collectors, and considering the turbulence of the incoming flow, the dynamic variation of the contact force between pantograph and catenary is taken into account, within an already developed simulation model. Aerodynamic coefficients of the collectors are obtained from wind tunnel measurements, and the aerodynamic forces are applied to the collectors of the pantograph. The interrelation among the geometry of the collector suspension, the collector shape, and the level of the incoming wind turbulence, and their effect on the contact force, are all considered in this article by means of numerical simulation. Results concerning the advantage of modifying the shape of the collector are outlined.

Breakable charge density waves

Prediction of aerodynamic force is a crucial issue for parafoil canopy as the strong nonlinear fluid–structure interaction (FSI) between the flexible canopy material and flow field. Flight tests and wind tunnel experiments are difficult to analyze the aerodynamics of parafoil because of the limitation and difficulty of data measurement in an unknown environment. The objective of this study was to computationally derive the aerodynamic characteristics of parafoil, as an alternative to expensive and unrepeatable test regimes. Different from previous works that assume canopy structure as a rigid body and serve for the design of parafoil, this study focused on the precise dynamic modeling of parafoil based on FSI simulations. To investigate the aerodynamic performance of the full-scale canopy with stabilizers for better control, the strong coupling FSI simulations were performed using the incompressible computational fluid dynamics techniques. The highlight of this paper is to explore the effects of canopy inflation and trailing edge deflections on aerodynamic performance. Then the aerodynamic coefficients are identified by a linear regression method using the obtained database of high fidelity lift and drag forces. Furthermore, an accurate six-degree-of-freedom dynamic model of the parafoil system is implemented based on the estimated coefficients. Simulations are conducted to prove the dynamic stability of the model and the feasibility of trajectory tracking. At last, simulation results of basic motions are compared with airdrop testing data, which demonstrates that the established model is capable of accurately predicting the flight behaviors of the parafoil system.

This paper focused on the development of a model to represent longitudinal aerodynamics of a wing and/or flight vehicle in ground effect when height is a function of time including high angles of attack. A general aerodynamic model of a wing and/or airplane in ground effect which includes high angles of attack was created. The aerodynamic coefficients of wings studied herein were obtained by the unsteady vortex lattice method with Kirchhoff-based correction (UVLM-K). Wind tunnel measurements presented in the literature were used to validate the UVLM-K. Then, a rectangular wing was simulated at high angles of attack in takeoff and flare, and the aerodynamic characteristics at different heights aboveground were obtained along with the h derivatives during these maneuvers. The mathematical model presented herein is capable to model unsteady aerodynamic phenomena in ground effect at high angles of attack. When this model was used in static ground effect, values of R2 equal to and greater than 0.999, 0.981, 0.993 were obtained for lift, induced drag, and pitching moment coefficient, respectively. In dynamic ground effect, the model can adjust the aerodynamic coefficient during the maneuvers.