Journal of Aerospace Engineering

This paper addresses the attitude tracking control problem for a quadrotor considering model uncertainty and internal and external disturbances. A high-order sliding mode control scheme and a control gain adaptation law are proposed for a class of nonlinear multiinput multioutput (MIMO) systems to design an attitude controller for a quadrotor. The proposed control method has four advantages: (1) Boundary information of the uncertainties is not necessary; (2) The control signal is continuous, and hence, chattering effects can be attenuated; (3) The measurements of the system state are only the output variable and its first time derivative, which makes this approach very useful in practical applications; and (4) The complexity of the control structure is reduced via the proposed control scheme. Finite time convergence of the tracking errors is achieved, robustness against uncertainty is ensured, and control precision is significantly improved over conventional sliding mode control (SMC). The effectiveness of the presented method was verified through a case study comparison and six-degree-of-freedom (6-DOF) simulations.

This paper proposes a novel approach for determining the three-dimensional (3D) attitude of on-orbit satellites in a spin condition using radar cross-section (RCS) measurements. The core idea of the approach lies in the matching process between the RCS real measurement sequences and the simulated sequences implemented using the mean square error (MSE) optimization rule. In this manner, the attitude determination problem is transformed into the optimization problem solved by minimizing the matching function. A hybrid particle swarm optimization (HPSO) algorithm is developed to precisely solve the optimization problem. The simulation and real measurements are used to verify the algorithm in the experiments. The numerical results prove the correctness of the proposal and demonstrate the better performance of HPSO than conventional particle swarm optimization (PSO) in terms of accuracy. The accuracy and antinoise ability of the proposed method to determinate spinning satellites’ attitude are verified by processing the RCS real measurement data of the PS-1A satellite.

The main aim of this work is to investigate some design uncertainties on the static response of powerline cables. A cable diameter is treated in this study as the design input random parameter distributed according to a Gaussian distribution, and its impact is analyzed for various thicknesses of ice covers and different outdoor temperatures. The static response of the single bay cable is found in an analytical way for this purpose and then is used in the least-squares method approximations of polynomial responses connecting cable sag, normal force, and, separately, fundamental eigenfrequency with its diameter. A further randomization procedure has been completed using the iterative generalized stochastic perturbation technique of the tenth order utilized for the Gaussian distribution to determine the basic probabilistic characteristics of the cable responses, such as expectations, coefficients of variation, and skewness and kurtosis. These computations have been compared with the Monte-Carlo simulation and semiprobabilistic analysis to validate the proposed strategy. The entire numerical procedure has been programmed in the computer algebra system MAPLE 2019 and can be further linked with any finite-element method system for the reliability-based optimal design of cable structures. It can be extended next toward the correlated and/or uncorrelated randomization of characteristics wind speed, ice covers, external temperatures, some geometric parameters of the existing and designed powerlines, and some stochastic dynamic response of the cable.

The identification of distributed dynamic loads is an important but challenging task because a distributed dynamic load is composed of both time and space functions. This paper proposes a novel method for the identification of distributed dynamic loading in one spatial dimension using only partial structural responses. The method is based on combing wavelet decomposition of space functions and the identification of time function by the improved Kalman filter with unknown input (KF-UI) developed by the authors. First, the unknown load space function of a distributed dynamic loading is approximated by wavelet decomposition with unknown scale coefficients. Under the given values of wavelet scale coefficients, the spatial information and the equivalent nodal loads of a beam-type structure can be estimated by finite-element modeling. Structural nodal responses in time-domain and the unknown load time function can be identified based on the improved KF-UI using data fusion of partial measurements of structural acceleration and strain responses. Finally, the objective function is established utilizing the error between the calculated and measured responses, and the optimal wavelet coefficients are estimated by minimizing the objective function. Therefore, the unknown distributed dynamic loading can be estimated by combing the reconstructed load space function from the optimal wavelet coefficients and the identified load time function. Numerical simulations of a simply supported beam under different unknown distributed loading verified the effectiveness of the proposed method.

A magnetic transport system for regolith particles on the Moon and Mars was developed, taking advantage of the fact that lunar and Martian regolith particles are magnetic. A multistage coil gun mechanism was used to realize long-range regolith transport. The system has a simple configuration, consisting of a tube in which regolith is transported, solenoid coils attached to the tube, and a power supply that consists of a direct current (DC) power supply, capacitor, and switching circuit. A series of pulse currents was applied by discharging the charged capacitor to the coils, which were arranged in series along the longitudinal direction of the tube. It was demonstrated that a substantial number of particles can be transported in the tube for a long distance by adjusting the pulse time and interval between pulses. A multistage terraced path was preferable to transport particles for a long distance than a straight path. Because the magnetic permeability of the lunar and Martian regolith is low and environmental conditions on the Moon and Mars are different from those on Earth, the performance in those environments was estimated by numerical calculation using the modified discrete-element method. The numerical calculation suggested that regolith particles could be successfully transported in the low-gravity environment of the Moon, but improvement is needed to apply the system on Mars. The system does not require mechanical moving and sticking parts, consumables such as gases or liquids, and its control is simple; thus, it is potentially reliable for use in space. The system can be implemented as reliable particle transportation for in situ resource utilization, which supports future long-term crewed missions on the Moon and Mars.

This paper presents a semiclosed-form physics-based rotordynamic analysis which determines the transient bird-strike load at the blade root and at the support bearings of a rotating fan shaft. This research considered a turbofan aeroengine application of a continuous fan shaft supported at multiple bearing locations and subjected to an impact loading caused by bird ingestion during normal flight operation of the aircraft. The mathematical formulation of the governing equation considers inertial effects as well as all circulatory terms involving gyroscopic and Coriolis forces. In the numerical simulation, the incoming bird was a cylindrical projectile and the blade was the target. The large impulsive load generated by the bird-strike incident traveled through the airfoil, fan disk, rotor shaft, rolling element bearings, and finally to the entire engine support structure. The structural details of the fan disk and shaft were treated as an overhung spinning beam supported on three bearings system. The highly nonlinear transient dynamic numerical results for all the relevant dynamical design parameters have been presented for a typical large commercial jet engine. It has been shown that the dynamic magnification factor for the transient vibratory response of the fan rotor impacted by a bird strike can be as much as 3 times that of the normal steady-state response of the similar unbalance.

This paper presents a composite control approach that facilitates both stable attitude tracking and vibration suppression of a space flexible slewing truss. An improved proportional-differential (PD) master controller was developed to track the desired slewing trajectory by adopting state feedback methods, which is more stabile than the traditional PD controller; an auxiliary controller based on linear modal observing is proposed to dissipate the vibration energy of the flexible truss. With the improved composite control scheme, the performance of the attitude tracking greatly improved in both response time and convergence character. An adaptive back-stepping controller was designed to guarantee the precision of synchronization precession of dual driving gyro. Simulation results demonstrated the validity of the composite control strategy.

Despite the many advantages of the design optimization technique, this method is costly for real engineering problems. This cost will increase sharply for issues with a multidisciplinary and uncertain nature and more than one objective function. In this paper, the metamodel concept has been used to overcome this problem. Because of the ability of neural networks to approximate the behavior of complex engineering systems, this tool has been used to create a surrogate model. Because multidisciplinary design optimization and robust design optimization methods have been used in this study and according to the high cost of the multidisciplinary analysis module, a surrogate model of this module has been made to reduce the imposed costs. To show the capability of the considered approach, robust multidisciplinary design optimization of an unmanned aerial vehicle (UAV) has been done. Take-off weight and cruise drag are the considered objective functions in this study, and the nondominated sorting genetic algorithm (NSGA-I) has been used for minimization of them. The optimization results show that the use of the metamodeling concept has reduced computational costs by 94.1%.

A retention compartment is an isotropic cylindrical shell with load-bearing structures. When a rocket is launched, this structure is streamed by supersonic high-temperature exhaust gas flow. This generates the transient temperature field in the retention compartment. The transient stress-strain state of the retention compartment is generated by this temperature field. These stress states and the temperature fields of a retention compartment are analyzed. The objective of this research is the development of the general semiempirical approach for thermostress-state calculations of a retention compartment. It consists of several steps. At first, computations of fluid dynamics (CFD)-simulation of the exhaust gas is performed by using the commercial software Solid Works Flow Simulation. The local transient thermal boundary conditions for the retention compartment surface are obtained on the basis of the velocity, temperature, and pressure fields using the empirical criterion equations. Convective and radiant heat fluxes are accounted for in these boundary conditions. These boundary conditions permit one to calculate the transient temperature field. Then the stress-strain state with an account of elastoplastic deformations is analyzed. The finite-element method, which is implemented in the commercial software NASTRAN version 2014, is used to calculate the stress-strain state. The conclusions about the strength of the retention compartment are made.

A two-dimensional (2D) meshless model based on the vortex method is developed to predict the aerodynamic noise of a noncompact open cavity, which calculates the flow and sound field results simultaneously. The evolution of the shear layer over the cavity mouth is described through discrete vortices, and key parameters including strength, position, and velocity of the vortices are obtained. Meanwhile, the vortices are employed as the sound source to simulate the sound generation by using vortex sound theory, together with the time-domain boundary element method (TDBEM) to account for the sound scattering effect of the rigid wall. The predicted results coincide reasonably well with the previous experimental data, and the computational cost is remarkably reduced compared with pure numerical methods. Moreover, the influence of the vortex convection velocity in the streamwise direction on the oscillation frequency and the mode jump characteristics are discussed in detail, which helps to improve the basic understanding of cavity noise.

Casing treatment design and application typically focus on improving stall margin while minimizing efficiency penalty for tip-loaded rotors. When successful casing treatment configurations are found, it often is assumed that their beneficial effects will occur across the whole operating line. Our investigation revealed the effects of casing treatment on the compressor stability in circumstances such as an off-design situation in which the rotor tip becomes unloaded; that is, in which stall originates elsewhere than at the rotor tip. A widely used circumferential groove casing treatment configuration was installed in a non-tip-loaded rotor, and computational fluid dynamics was employed to simulate the internal flow. The numerical results showed that the stall was induced by a detached vortex located at 90% span near the trailing edge, and the grooves near the blade leading edge significantly negatively affected the stall margin. Based on a computational fluid dynamics analysis, it was found that a special flow structure consisting of a spanwise tornadolike separation vortex and a stream of radial underflow establishes a connection between the grooves and the stall-critical detached vortex away from the tip. Our research explained the stall mechanism and showed that the casing treatment does not always have a beneficial or neutral effect on compressor stall margin. On the contrary, it significantly can decrease the stability for non-tip-loaded rotors. Thus for conditions in which the rotor tip becomes unloaded, potential harmful effects of casing treatment on the stability margin need to be considered.

In the current research, an active-flow control scheme characterized by leeward slot jet over a circular cylinder was experimentally investigated to manipulate the vortex shedding from the cylindrical test model and stabilize the unsteady cylinder wake. A slot installed on the leeward stagnation point of the circular cylinder was used to implement steady jet. The experimental research was conducted in a wind tunnel at a subcritical Reynolds number (Re) of $2.17\times {10}^4$. The high-speed particle image velocimetry (PIV) system was utilized to visualize and analyze the vortical structures in the wakes of the baseline and controlled cylinders to evaluate the effectiveness and mechanism of the active slot jet control technique with various equivalent blowing momentum coefficient $C_{\mu }$. Experimental results reveal that the slot generates a pair of symmetric jet vortices that interact with the sheared layer from the cylinder wall, which thus modifies effectively the flow features in the cylinder wake. With such dynamic interactions, the unsteady separation flows rolled up from the upper and lower surfaces of the test model are elongated and push the alternating vortex shedding downstream. Owing to the convection between the jet vortices and the cylindrical wake vortical structures, a modal transition from asymmetric to symmetric of the cylinder wake was realized. It is also shown that the flow characteristics such as Reynolds shear stress and turbulent kinetic energy are controlled to be quite low. Furthermore, a linear stability analysis is carried out to imply that the stability characteristics in the flow field behind the cylindrical model can be manipulated by the blowing slot jet.

Jet screech is an intense pure tone which has attracted decades of research interest due to its possible detrimental effect on engineering structures. Its modes and closure mechanisms have been investigated analytically, experimentally, and numerically; however, there are still outstanding questions regarding the generation and propagation of instabilities in the near-field region. Recent studies have identified that these instabilities travel inside the jet potential during the screech process to form the complete feedback loop. Using dynamic mode decomposition on a three-dimensional pressure near field from large-eddy simulation results, the present study examines the viability of modal decomposition to provide further insights into the screech mode and its associated characteristics, and investigates the effect of temperature mixing in jet screech. The results show that modal decomposition identifies the helical structure of screech mode. Furthermore, a method is proposed to reveal the temporal evolution of dynamic screech mode. It was found that the bulk behavior of the pressure field at screech frequency propagates backward toward the nozzle exit.

This paper discusses the safe landing process of a reentry capsule in detail with respect to landing attitude and rebound response. First, the discrete-element method (DEM) of the land soil and the finite-element method (FEM) of the reentry capsule structure are established. The dynamic response of the reentry capsule landing are analyzed using the DEM-FEM coupling algorithm and then compared with the results obtained from experiment and LS-DYNA. Second, the effects of the landing velocity and attitude on the landing process are discussed. Finally, the effects of mass and friction coefficient between particles on the rebound response of the reentry capsule are analyzed. The study shows that soil particles contribute to the absorption of the impact energy of the reentry capsule. The inclined landing is more conducive to the safe landing of the reentry capsule. The rebound velocity of the reentry capsule is relatively smaller when the friction coefficient between the particles is smaller and the mass of the reentry capsule is larger.

Improving aerodynamic performance with limited dimensions is becoming more important in the design of multirotor aircraft. Complex coupling interactions exist between the structural parameters and aerodynamic performance of the double-layer staggered rotor octocopter. This paper develops an integrated aerostructural design optimization approach based on a surrogate model to reduce the high computation cost of computational fluid dynamics (CFD) simulation experiments, where the surrogate model is constructed by using the Latin Hypercube design, and different approximation methods are compared. Aiming to improve the global accuracy of the surrogate model, computer-aided design (CAD) modeling and CFD simulation experiments were carried out according to the sample points designed by the Latin Hypercube method. A radial basis function surrogate model was constructed based on 63 sample points obtained with CFD simulations after comparison with other approximation methods. The optimization for aerodynamic/structural design was formulated and solved by the multiisland genetic algorithm. The results show that the surrogate model has an accurate predictive ability, and the optimal solution obtained from the optimization has a better aerodynamic performance than the samplings. Compared with the initial optimum data, the optimum solution proposed in our study could generate 102.7% more thrust, and the objective function $y$ is improved by 105.1% according to the CFD simulation results. The approximation and optimization approach effectively reduces the cost of many CFD calculations in aircraft design and provides a global prediction for the performance of the octocopter.

The interaction noise that radiates from ducted contra-rotating (CR) fans are theoretically characterized using Green’s analytical functions for lined and unlined circular ducts containing uniform mean flow. The derived models can be used to analyze the spectral characteristics and directivity patterns of noise in various modes. The axial wavenumbers determining modal propagation are treated numerically with the specified boundary conditions. The solved results show that for each cut-on mode, an imaginary part is added to the axial wavenumber, while for the cutoff mode, the already-existing imaginary part is increased. Therefore, it is indicated that both types of modes will attenuate as they propagate along the lined casing, whereas the modes at higher frequencies experience more noise attenuations than those at lower frequencies, which is experimentally verified. Meanwhile, the discrepancy between predicted and experimental results in terms of noise reduction can also be found and is probably due to near-field source modification resulting from the recasting of the tip-clearance flow. Furthermore, the modal directivity patterns of the interaction tone at 2,332 Hz have been investigated. In theory, the lined casing makes the directivity pattern thinner and lean more to the rotation axis than the one with the unlined casing. For both types of casings, the variation trends in experiments are accurately captured by theoretical predictions. The current study is anticipated to improve the understanding of the underlying mechanisms of interaction noise as well as provide an essential reference for devising noise control methods for ducted CR fans.

In recent years, the use of drones has becomes more common in commercial applications as well as among hobbyists. However, the characteristic loud buzz emanating from their use has been an issue, causing a nuisance to the user and those in the vicinity of the drone. Thus, in this study, the effects of various prepregs and their combinations on the aeroacoustic performance of the propeller were investigated experimentally for the objective of designing a low-noise propeller for drones. It was found that a propeller that made from pure carbon prepreg generated the highest noise level and produced the highest thrust force, whereas a propeller made from pure flax prepreg generated the lowest noise level and produced the lowest thrust force. The noise levels generated by propellers made from hybridization of carbon and flax prepregs are lower than those of the pure carbon prepreg propeller but higher than those of a pure flax prepreg propeller. A similar phenomenon was observed for the result of thrust force. It can be concluded that in addition to its low-noise characteristic, the propeller made from flax prepreg has a short prepreg curing time and is light weight, and it is also the cheapest propeller among the four propellers that were investigated in the present study.

Cycloidal rotors have revealed a noticeable potential to be further enhanced when running at different operating conditions. The present work demonstrates the active control methodology in order to achieve improved performances in cycloidal rotors operating in forward-flight and lift-up phases. The proposed optimization analysis comprises computational fluid dynamics (CFD) simulations for the numerical database and an artificial neural network (ANN) to propose optimum operating states in each of the mentioned flying phases instead of the hover state under ground effects. CFD predictions were conducted for various operating conditions of pitching oscillations and rotating speeds at each forward or lift-up speed. By training the ANN algorithm using the database attained from CFD simulations, the optimization process was further surveyed for each corresponding flying mode. The targeting concept is to operate with an active mode of employing pitching angles rather than using constant oscillations at all rotation speeds. The ANN approach effectively proposed an optimized pitching schedule for both forward and lift-up phases after analyzing a wide range of parameters in order to reach an optimum aerodynamic efficiency. Because the blade and flow properties are all considered at each specific point on the continuous azimuth of the circular (360°) trajectory, the mutual collaboration of CFD and ANN analysis showed to be advantageous for enhanced operations.

The seismic safety evaluation of tall building structures is necessary, but the multidegree-of-freedom feature of tall buildings increases the difficulty of joint identification of structural states, structural parameters, and unknown seismic excitations. Therefore, the state-input-system identification of tall buildings under unknown seismic excitations is the focus of this paper. To avoid the complex work of establishing a structural motion equation in absolute coordinate system, the simple structural motion equation in relative coordinates is directly adopted, but the measured absolute accelerations are used to establish the observation equation. In this way, the establishment of approximate assumptions is avoided, and direct feedback is not reflected in the observation equation. Also, the modal expansion technique is adopted to reduce the dimension of the motion equations and the size of the structural state to be identified. Different from the previous methods based on modal Kalman filtering, the unknown seismic excitation is treated as an unknown input instead of unknown modal forces in this paper, so the dimension of unknown forces in the identification process is not increased. When structural parameters of tall buildings are known, the generalized modal Kalman filtering with unknown input (GMKF-UI) proposed by the authors can simultaneously identify structural states and unknown seismic excitations by observing partial absolute acceleration responses. When extended to the case of unknown structural parameters, a generalized modal extended Kalman filtering with unknown input (GMEKF-UI) is proposed in this paper to simultaneously identify structural states, the unknown seismic inputs, and tall building systems using only partial absolute acceleration responses. Two numerical examples are used to verify the effectiveness of the proposed method.

As the basis of protection control, supersonic inlet plays an important role in a supersonic air-breathing propulsion system. To reduce the negative effects of buzz flow on the supersonic inlet and ensure safe and stable operation, it is of great significance to develop methods for monitoring the flow patterns. Traditionally, several manually engineered features are extracted as indicators to evaluate the operation status, but this process can be heavily dependent on professional experience and is time-consuming. This paper proposes a novel network called DTW-RBF-KF which integrates dynamic time warping (DTW) and the Kalman filter (KF) into a radial basis function (RBF) network architecture to directly determine flow patterns from the dynamic sensor signals. The proposed network replaces the Euclidean distance in the static RBF kernels with DTW distance, and exploits the flexible alignment ability of DTW to deal with the temporal distortions. The second-order Levenberg–Marquardt optimization algorithm then is employed to allow the efficient training of the proposed network. To improve the classification performance when the network structure is fixed, the KF is applied as a postprocessing technique to linearly convert the predicted output of RBF into a value closer to the true output. Experimental results demonstrated that the proposed DTW-RBF-KF network has the highest average monitoring accuracy, 94.10%, and requires less calculation compared with all competitive methods. The average time required to test a sample of DTW-RBF-KF network is $1.19\mathrm{ms}$, which is shorter than the sample duration, and can be exploited for real-time applications. The addition of a linear KF module further increases the monitoring accuracy to a higher level with negligible computation. The proposed method has better comprehensive performance for monitoring the flow patterns of supersonic inlet in terms of monitoring accuracy and real-time performance.

The existence of water (ice) has been discovered in the polar regions of the Moon, and it is expected to be used to support life for astronauts and to provide the raw material of hydrogen and oxygen. Because the exact location of ice, including the depth from the lunar surface, chemical and physical forms, and the amount of water, is unclear, the Japan Aerospace Exploration Agency (JAXA) is planning to search for ice directly by operating an uncrewed rover on the Moon. A long drill, approximately 1.5 m long, will be screwed in the regolith layer, and regolith mixed with ice will be captured and transported from the lower deep portion of the regolith layer to chemical and physical analyzers mounted on the rover. A long-range technology for vertical ice transport is indispensable for ice exploration. To this end an electrodynamic sampling system that can transport crushed ice particles vertically up to the 1.5-m height is developed. Parallel ring electrodes were attached to a collection tube, and four-phase rectangular wave high voltage was applied to the electrodes to form an electrodynamic traveling wave. Ice particles were transported upward synchronized to the traveling wave. It was demonstrated that this system could be used to capture and transport crushed ice particles, as well as regolith particles. Performance in the lunar environment (1/6-G and absence of air drag) was evaluated by the numerical calculation based on the modified discrete-element method.

A study was conducted to determine the mass and power of an in situ propellant production plant producing 10.5 t of liquid oxygen per year from the regolith at the lunar south pole. The carbothermal reduction process was selected for oxygen extraction from the regolith, using direct solar energy from a concentrator for the thermal heating in the carbothermal reactor, and solar arrays for the remaining electrical power needs. The baseline lander design selected for delivery of the production plant is capable of landing a payload mass of 3,600 kg and has significant cargo area available below the propulsion deck close to the ground for the in situ resource utilization (ISRU) hardware. Total mass for the 10.5-t oxygen plant, including all power systems, structure, command and control, communication, thermal management, and 30% margin, was 4,145 kg, exceeding the lander’s payload capability. A second design of a smaller plant producing 7 t of oxygen per year resulted in a mass of 3,459 kg, which is within the lander’s capability. Mass payback ratio for the 10.5- and 7-t oxygen plants is 0.4 and $0.5(\mathrm{kg}\mathrm{hardware})/(\mathrm{kg}\mathrm{oxygen}/\mathrm{yr})$, respectively, and indicates that a net gain of mass on the lunar surface can be realized in three to four months.

The removal of lunar dust adhered to spacesuits is indispensable for crewed lunar exploration. A handheld cleaning tool was developed using magnetic and electrodynamic forces. The tool comprises a stationary multipole magnetic roller made of a rare-earth permanent magnet, rotating aluminum sleeve that covers the magnetic roller, screen electrode placed adjacent to the sleeve, and collection bag with a plate magnet. The sleeve is pressed on the dust adhered to the fabric of a spacesuit and pulled in the lateral direction. Magnetic lunar dust is attracted to the magnetic roller and transported via the rotating sleeve owing to magnetic and adhesion forces. The multipole magnetic roller is designed in a manner such that a strong attractive force acts on the adhered dust particles at the portion of contact with the fabric and a repulsive force acts on the trapped particles at an opposite position to the contact portion. When the trapped particles are transported to this opposite position, particles are released from the sleeve. To aid the magnetic release, a high AC voltage is applied between the screen electrode and the sleeve. The dust adhered to the sleeve is captured at the screen electrode and passed through the opening of the screen electrode using electrodynamic force. The captured dust is subsequently collected in the collecting bag; therefore, by sweeping the fabric surface, the tool can continuously capture, release, and collect lunar dust adhered to spacesuits. The demonstrated cleaning rate was approximately 64% by weight for a lunar regolith simulant. However, this rate will be higher for real lunar dust, whose magnetic permeability is higher than that of the simulant.

Trailing edge noise is a common noise source in aerodynamic applications. Many prior experiments have shown that trailing edge serrations can reduce this noise, but the mechanism by which serrations reduce noise and their aerodynamic impact near the edge is not fully understood. Previous theoretical models have assumed that the turbulence convecting past a serrated trailing edge is unchanged by the presence of the serrations, but experiments have shown that this is not accurate. This work attempts to further the understanding of unsteady surface pressure fluctuations on sawtooth serrations. Experiments were performed in an anechoic wall-jet wind tunnel on an undercut trailing edge with a straight and serrated edge configuration. The magnitude of unsteady surface pressure fluctuations was found to increase near the tips of the serrations for Strouhal numbers near 0.5 based on edge thickness. Spanwise coherence was increased on a single serration, while coherence across the root of adjacent serrations was similar to results across a straight trailing edge at similar spanwise separation distance.

An adaptive sliding mode fault-tolerant control method is proposed for vertical tail damage. Firstly, the damaged aircraft model is introduced, and a novel nonlinear integral sliding surface is designed. Then, a sufficient condition is proposed to guarantee a damaged aircraft kinematic model with damage degree stability by using the linear matrix inequality (LMI) technique. Next, the damage-tolerant controller is designed based on an adaptive sliding mode control for analyzing damaged aircraft systems. Furthermore, the hyperbolic tangent function is utilized to replace the symbolic function in the controller; it is worth mentioning that it has been proven theoretically. Finally, an example for a Boeing-747 100/200 model is given to demonstrate the efficiency of the theoretical results by recognizing the structural fault of the aircraft. The numerical results show that the control law has a positive impact on the performance of the closed-loop system, but compared with the traditional damage aircraft stability control method, the control law has better fault tolerance and robustness to external disturbances.

Miura-ori is a form of origami and is widely used in aerospace. The aerodynamic characteristics of Miura-ori composite structure are greatly influenced by its configuration. In this paper, the aerodynamic performance of Mirua-ori sheet in different deployable configurations is studied. Through the analysis of a three-dimensional model of Miura-ori sheet, it is found that the largest pressure is on the foremost crease of Miura-ori sheet, which is prone to failure. A two-dimensional model can be used to refine the analysis of the special orientation of this crease. Next, the aerodynamic characteristics of the sheet with and without grooves are studied, with results showing the former can significantly reduce drag. Then, the aerodynamic characteristics of the grooves with holes are studied, and it is found that holes in the front wall increase the drag and holes in the rear wall reduce the drag. Finally, the arrangement and combination of grooves with different apex angles are studied. It is found that the model with the shape of a check sign has the best drag reduction, which is due to a large separation vortex formed in the upper part. During the negative pressure landing of the airship, the internal pressure is relatively low, and when the wind speed is high, it is prone to local snap-through instability and global collapse (contact and squeeze) instability. The adjustment of drag force through reconfiguration of origami is of great significance to the study of shape retention and stability of stratospheric airship envelopes.