Journal of Aerospace Engineering

How to conveniently tune the flexibility of the composite anisotropic flapping wing to an optimum level to improve flight efficiency is still an open question. Two simple methods have been put forward to realize the quick adjustment of flexibility to improve flight efficiency: one is to change the diameters of two outer ribs of the baseline flapping wing, and the other is to add a minor mass lump at the end of two outer ribs of the baseline flapping wing. The ground experimental results show that adding a minor mass lump at the end of the outer ribs can simultaneously improve the static thrust and the static propulsive efficiency, whereas increasing diameter can only improve the static thrust. A flight test was performed to verify that adding a proper mass lump can effectively improve the flight efficiency by 9% compared with that of the baseline flapping wing. Adding a mass lump can simultaneously improve the static thrust and propulsive efficiency. However, the trade-off between the loss of lift and the increase of thrust that arises from the nonlinear wing deformation and the increase of power consumption contributed by the added mass should be carefully weighed. Furthermore, a new parameter can be used to determine whether the flight performance can be effectively improved simply by tuning the mass distribution.

The aerodynamic performance of aircraft can be improved via shape morphing of wings actuated by piezoelectric material. An integrated design approach of piezo-actuated wings was developed while simultaneously considering aeroelastic tailoring of the base wing and actuator optimization. The main purpose was to investigate how the anisotropic composite substrate and the anisotropic piezocomposite actuators affect each other in both passive and active aspects. To this end, an aeroelastic model was established using the finite element method combined with unsteady aerodynamic loads. A structural/actuator integrated design scheme was developed by taking the incremental lift change and the wing thickness as objective functions. The general genetic algorithm (GA) and improved nondominated sorting genetic algorithm II (NSGA-II) were used to solve the single-objective and multiobjective problems, respectively. The results indicate that, with a fixed thickness, control ability on lift change can be improved with lower flutter speed constraint, increased number of layers, smaller incremental angle, and increased number of actuators. The Pareto frontier for the multiobjective case, presenting better control ability, will be available with relatively larger wing thickness. The distribution of the $\pm 45°$ layers plays a key role in balancing the tradeoff between shape control ability and flutter stability. The designs of the substrate and actuators interact in both passive (mass and stiffness properties) and active (shape morphing and lift enhancement) aspects. The best solution must be obtained by considering the aeroelastic tailoring and actuator optimization in an integrated way.

Large-scale plate-like structural components have been widely used in various aerospace structures. Subject to complex loading conditions and environmental factors, the integrity of plate-like structures is threatened by the occurrence and accumulation of structural damages, calling for the development of structural health monitoring (SHM) methods and techniques. Guided wave-based SHM methods have been demonstrated with a high sensitivity to small-scale damage. In particular, the probability-based diagnostic imaging (PDI) algorithm is able to achieve enhanced accuracy and efficiency of damage localization. Typically, the PDI defines damage index (DI) in terms of the deviation between the baseline and real-time guided wave signals. However, as the baseline signals are highly sensitive to environmental factors, such as temperature, the DI may exhibit large instability subject to varied environmental factors and lead to inaccurate damage detection results. In this study, a novel damage diagnostic imaging approach free of a baseline signal is presented for nonpenetrating damages. The approach is established based on the modification of conventional baseline-dependent PDI, into which the converted mode extraction (CME) strategy is integrated to give rise to the DI in terms of the energy of the converted modes. As the essential part of the CME-PDI approach, the converted modes caused by nonpenetrating damages as structural thickness variation are extracted from the primitive multimode wave signals according to a recently proposed CME method featured by intrinsic basis mode reconstruction. The effectiveness of the approach is first examined numerically, and then an experiment is carried out by taking into account the temperature effect. Compared with conventional PDI, the CME-PDI approach shows apparently enhanced accuracy and stability in damage localization.

Carbon nanotubes (CNTs) have attracted many researchers during the last three decades due to their versatile nature and exceptional mechanical properties. In this study, a functionally graded CNT-reinforced laminated composite (FG-CNTRLC) plate subjected to different types of localized in-plane loadings was analyzed semianalytically to determine its dynamic instability and nonlinear vibration characteristics. The effective mechanical properties of the FG-CNTRLC plate were estimated using the extended rule-of-mixture technique. The FG-CNTRLC plate was modeled based on higher-order shear deformation theory (HSDT) in conjunction with von Kármán nonlinearity. The distribution of prebuckling stresses within the plate due to localized in-plane loading was estimated by solving the in-plane elasticity problem using Airy’s stress approach. The nonlinear governing partial differential equations (PDEs) of the FG-CNTRLC plate were derived using Hamilton’s principle. The Galerkin method was used to convert these nonlinear PDEs to the nonlinear ordinary differential equations (ODEs). The nonlinear ODEs were solved using the incremental harmonic balance (IHB) method to obtain the nonlinear vibration response of the FG-CNTRLC plate. After dropping the nonlinear terms, the linear ODEs were solved by the Bolotin method to trace the dynamic instability regions. The effect of different parameters such as volume fraction of CNTs, different types of localized in-plane loadings, types of CNTs distribution, the static and dynamic load factor on the dynamic instability regions, and the nonlinear vibration characteristics of the FG-CNTRLC plate, were examined.

Hover performance for tiltrotor-like vehicles lacks experimental data and computationally efficient models for single-rotor-wing interactions at low disk loadings and low Reynolds numbers. As such, this paper discusses a rotor-wing interaction experiment near the micro-air-vehicle (MAV) regime (Reynolds number $<\mathrm{100,000}$ and disk loading $<100\mathrm{N}/{\mathrm{m}}^2$). The experiment and corresponding analysis examine the effect of rotor height and rotor disk coverage in terms of hover performance and download force on the wing. Also, the paper details the development of a potential flow solution for single-rotor-wing interactions based on actuator disk theory, image vortices, and momentum theory. The analytical model only requires the rotor radius, which assists in preliminary design studies on tiltrotor-like vehicles. The analytical results compare well with the experimental data in terms of magnitude and trend.

Porous materials have been widely investigated as a mean for noise reduction. Numerical simulations can be used to investigate the physical mechanisms responsible for noise reduction; however, a correct modeling of the porous medium through an equivalent fluid model is essential to minimize the computational costs. This paper reports a detailed review of a few applications of the equivalent fluid model based on a three-layer approach, a method that is particularly useful to account for the variation of porous material thickness in aerospace applications. The multilayer approach has been applied in three relevant aerodynamic noise issues: leading-edge impingement noise, turbulent boundary-layer trailing-edge noise, and jet installation noise. Comparison with experiments is used to validate the simulation approach.

Porous material–inspired noise reduction has been proved to be an effective method to reduce airfoil self-noise during the last few decades. However, the used porous materials in previous studies generally have homogenous physical properties. In order to obtain higher airfoil self-noise reduction, in this paper, nonhomogenous porous trailing edges are proposed, which feature a piecewise gradient distributed property in pores per inch (ppi). Detailed acoustic measurements performed in the $0.55\times 0.4\text{-}\mathrm{m}$ aeroacoustic wind tunnel showed that the proposed gradient distributed porous trailing edges can achieve a peak noise reduction of up to 43.68 dB and a maximum decrease in overall sound pressure level of up to 19.72 dB, mainly due to the mitigation of vortex-shedding noise of the laminar flow. For turbulent flow, the noise-reduction ability is weakened but can still reduce up to 5.25 dB of turbulent broadband noise. A parameter study of gradient distributed properties on noise reduction revealed several design principles for the proposed modifications, i.e., the porous treatments with larger porous coverage and located at the last 5% chord length of the airfoil gain better noise reduction. Moreover, airfoil self-noise reduction is enhanced when the porous treatments provide a gradual transition from the solid main body to that of the downstream free flow.

This work presents a novel global reduced-order modeling and parameter estimation of a maneuvering aircraft up to poststall angles of attack using radial basis functions. A computational fluid dynamics approach is adopted to accurately predict the flow field around the maneuvering standard dynamic model. High-amplitude chirp motions are used to excite the aerodynamic system in both longitudinal and lateral-directional axes up to poststall conditions. Subsequently, a radial basis function neural network is employed to construct a nonlinear aerodynamic model from 20% of the numerical simulation data. Next, a continuous wavelet transform is applied to gain insight into the frequency-time behavior of the aerodynamic moments. Based on the results, the network can predict the great unsteady aerodynamic characteristics of the aircraft under deep dynamic stall and coupled yaw-pitch motion over the unseen test data, compared with the entire numerical simulations. Moreover, instantaneous stability derivatives are computed, which are required for design of a maneuvering aircraft flight control system. A great dependency of the stability derivatives on reduced frequency and angle of attack is perceived in the results. In addition, high coupling is seen in lateral-directional derivatives, expressing the strong influence of the angle of attack on the associated moment coefficients.

To study the noise reduction effect of a variable-bend slat, both experimental and numerical investigations are carried out on a two-dimensional high-lift configuration with a stowed flap at varying angle of attack. With respect to the base configuration, the different geometrical settings of the variable-bend slat at varying bending angles of the trailing edge are described, and the gap between the slat and the main wing is completely sealed with a bending angle of 18°. At smaller bending angles, the slat noise is reduced, especially for tones generated from the self-excited oscillation within the leading-edge slat cove. With the increase of the bending angle, the tonal frequency in the same mode gradually decreases, which agrees well with the predicted formula proposed by Terrocal. Moreover, the noise reduction effect of the bending slats decreases with the increase of the angle of attack. To provide further understanding of the noise reduction effect on tones at varying bending angles, flow parameters related to the self-excited oscillation are extracted using numerical calculation results. It is found that change in self-excited oscillation is mainly a consequence of change of shear layer length $L_v$ and average vortex convection velocity along the shear layer $U_v$. As the bending angle increases, the main mode of self-excited oscillation gradually switches to a higher mode, which agrees well with the relationship between the flow parameters and the main mode of traditional nondeformable slat.

Structural health monitoring can be performed through long-term monitoring of key structural parts to obtain the structural response information of civil engineering structures in real service environments. This enables the provision of on-site measurement data for in-depth understanding of the structural performance and verifying design parameters. To address the issue of limited information from sensors, this paper proposes a structural response estimation method based on Kalman filtering and multitype measurements for beam-type structures. Starting from the structural motion equation, an internal structural model equation by extracting the modal external excitation frequency component and the structure’s inherent characteristics are used for structural response estimation. The frequency component of external excitation should be known in the proposed method. Then, based on the multitype measurements, the system and observation noises are considered, and a structural response estimation equation based on Kalman filtering is formulated. Finally, particle swarm optimization is applied to optimize the Kalman error parameter values and achieve multilocation and multitype structural response estimation based on the multitype measurements. The effectiveness and feasibility of the proposed method are verified via experimental analysis of the Binzhou Yellow River Bridge mode, where only pedestrian loading is used.

This paper presents an experimental investigation of tip vortex formation noise produced by wall-mounted finite airfoils. Acoustic measurements were taken in the open jet anechoic wind tunnel at Brandenburg University of Technology with a planar 47-microphone array. A parameter space of eight airfoil models with variations in airfoil profile shape (thickness and camber) and tip geometry were tested at a range of angles of attack and Reynolds numbers. The acoustic survey shows that tip noise is a strong contributor to the overall airfoil noise signature at mid-to-high frequencies above 2–3 kHz. A critical frequency was defined to distinguish the effect of the thickness of the airfoil on the noise spectra, which increases with Reynolds number and appears constant with angle of attack. Above the critical frequency, a thicker airfoil is shown to produce a lower amplitude tip noise peak, especially at mid-to-high frequencies above 5 kHz. An increase in camber does not affect the frequency of the tip noise peak but increases the noise level, especially for $f\ge 3\mathrm{kHz}$ and high angles of attack. Further, the presence of a rounded tip is found to be effective in decreasing the noise levels by up to 5.6 dB over the frequency range of 5–15 kHz. To explore the tip flowfield, velocity data were also obtained using planar particle image velocimetry in the anechoic wind tunnel at the University of New South Wales for a few targeted cases. The results show that the size of the vortex and its turbulence intensity are influenced by the tip geometry. Specifically, the vortex size for the cambered airfoils decreases along the streamwise direction, while for symmetric airfoils it increases from $x/c=1.2$ to 1.8. Collectively, these databases can be used to aid tip noise prediction models and validate computational fluid dynamic and computational aeroacoustic simulations.

The present study reports an experimental investigation of the near-field aeroacoustic characteristics of a cambered NACA 65-410 airfoil. The experiments were performed in an aeroacoustic wind tunnel facility at a moderate chord-based Reynolds number of $4.2\times {10}^5$. Detailed static and dynamic surface pressure information was recorded to reveal the pre- and post-stall dynamics. By varying the angle of attack from 7° to 15°, a stall behavior similar to thin airfoil stall is observed from the evolution of the static and dynamic surface pressure spectra at different chordwise locations. Moreover, while the surface pressure spectra show a monotonic decrease with constant gradients after entering full stall, the pre-stall behavior shows a different trend and partly resembles the attached and stalled flows. Furthermore, the unsteady surface pressure spectra are compared to those obtained from a NACA 0012 airfoil, showing notable differences in the near-field stall dynamics. A scaling formula proposed by a previous study is applied to the present pressure spectra and found to scale well except for measurements close to the leading edge. The present near-field measurements and the streamwise and spanwise length scales can be useful input to the modeling of airfoil separation and stall noise for cambered airfoils.

The flexural behavior of functionally graded composite panels with single and multiple rectangular perforations is examined subjected to complex loading conditions, including uniform/sinusoidal pressure and uniform/linear/nonlinear thermal field. The constituent materials are assumed to be temperature-dependent, whereas the instantaneous material properties are evaluated using the power-law function via Voigt’s homogenization scheme. Here, the displacement field is based on the equivalent single-layer higher-order kinematics with nine degrees of freedom. The equations of motion are obtained using minimum total potential energy principle and isoperimetric finite-element approximations via Lagrange elements. The mesh convergence test is carried out to show the stable and appropriate mesh density; however, to check the correctness, the present solution is compared with the benchmark solutions. In addition, new numerical examples are presented to demonstrate the effect of different parameters, such as the number of perforations, power-law coefficients, aspect ratios, loading, and edge conditions on the deflection responses of perforated functionally graded composite panels.

In fluid flow, the frictional effects from interior surfaces of flow components create pressure loss across the surface. Understanding this inherent pressure loss due to friction and other phenomena is important when designing a flow system. For conventional manufacturing, friction loss has been empirically studied and is well known in the engineering community. However, newer manufacturing techniques, such as laser powder bed fusion (LPBF), an additive manufacturing technique, need to be understood. The inherent flow conditions resulting from the additive processes were studied. Test samples were printed with the flow path oriented in the vertical direction with different channel diameters to characterize the inherent fundamental flow properties of the process. Moody diagrams were replicated for a greater understanding of possibilities and shortfalls when implementing LPBF into design applications. Experimental flow testing revealed that greater effective sand grain roughness resulted from this process when compared to conventional machining methods. This roughness did not correlate well to the average roughness measured with a laser scanning microscope but was consistent with the average particle size of the powder metal feedstock.

The zigzag theories are a class of the shear deformation theories that combine the accuracy of the layerwise theories and the efficiency of the equivalent single-layer theories. A nine variable zigzag theory is presented in this work for the laminated piezoelectric plates. Unlike any existing zigzag theory, the transverse shear boundary conditions on the lateral surfaces are not imposed. The theory satisfies interlaminar continuity of displacements and transverse shears stresses. A variational principle is used in deriving governing equations. Bending responses have been obtained under sinusoidal and uniformly applied mechanical and electromechanical loads. Three-dimensional (3D) exact elasticity and piezoelasticity solutions have been used to assess the accuracy of the present theory for a number of simply supported rectangular laminated composite and piezoelectric plates. The transverse shear stress relaxation condition at the boundary surfaces has led to improved predictions in the displacements, stresses, and electric field entities. Present theory is also compared with a number of shear deformation theories to illustrate how significantly the responses get improved due to the transverse shear relaxation.

Coaxial compound helicopters feature high-speed characteristics that are not possessed by conventional helicopters. The aim of this paper is to develop a flight dynamics model of coaxial compound helicopters and investigate the trim, stability, and controllability. A flight dynamics model including a coaxial rotor model and a propeller model is introduced. Based on the flight dynamics model, the trim of hover and level flights of a coaxial compound helicopter is performed. Considering the influence of flapping motions, stability and control derivatives are assessed under the small disturbance hypothesis by using a numerical differentiation method. Then, stability and response of the coaxial compound helicopter are presented. The results of trim show good agreement with those of the reference, which verifies the flight dynamics model. The speed static stability derivative is stable in whole trim range, while the angle of attack static stability derivative is unstable. The yawing control with collective differential of the coaxial compound helicopter will induce serious roll effect in high-speed flights.

The focus of this investigation is on the development and validation of nonintrusive structural dynamic reduced-order models (ROMs) for the geometrically nonlinear response of flat cantilevered structures, e.g., beams and plates. The specificities of these structures, compared to those supported all around, are first highlighted. These findings are then used to develop, for these structures, a modification of the identification of reduced-order modeling strategies that provide a complete representation of the structural response, i.e., including both transverse and in-plane displacement fields. This variation of the ROM methodology is successfully applied to several flat beam and plate models under both static and dynamic loads spanning large and very large deflections.

A numerical study on the performance parameters of supersonic mixed compression air intake has been carried out at a design Mach number of 2.2 with and without air jets at various back-pressure ratios using a commercially available software, Ansys 2019. The k-omega turbulence model was selected to capture the viscous effects. The injection pressure and the gap between the air jets were also varied to see the effect on flow field inside the air intake. The location of the air jets was kept fixed in the longitudinal direction and the position of the normal shock was varied by changing the back pressure. Mass flow ratio, flow distortion, total pressure recovery, and skin friction coefficient were chosen to measure the performance of air intake. The results suggest that a proper combination of the number of air jets and their injection pressure can improve the performance and flow field of the supersonic air intake. Deployment of four air jets with an injection pressure ratio of 4 has shown the best performance for all back-pressure cases studied.

The increasing number of defunct and fragmented spacecraft poses a growing hazard to existing onorbit assets. The redundant continuum manipulator with high flexibility provides dual-arm robotic systems with apparent advantages in active debris removal missions in space. Existing autonomously-coordinated control approaches for dual-arm continuum manipulators require a real-time inverse kinematic solution and a security assurance mechanism for possible collisions, which are difficult to upscale for space debris capture systems with high-speed maneuverability. In this paper, we consider collision avoidance and input saturation control in proposing a multiagent reinforcement learning approach, named the multiagent twin delayed deep deterministic policy gradient (MATD3), to generate a real-time inverse kinematic solution for coordinated manipulators. During the training process, the MATD3 algorithm performs lower overestimation than the multiagent deep deterministic policy gradient (MADDPG) algorithm. Then, a feedback dynamics controller is designed for the continuum manipulators. Under the guidance of the policy networks, each agent can schedule the joint trajectory design online according to the collaborator and target debris information. During the capture operation, a competitive mechanism for the anticollision function is developed through reasonable reward functions to maintain dual arms at a safe distance. Simulation results show that the average accuracy of the proposed approach is 42% higher than that of MADDPG in inverse kinematic trajectory planning. The designed integrated tracking controller can effectively perform capture missions in the simulation environment. Multiagent reinforcement learning shows promise for future onorbit servicing missions.

Poor calculation efficiency is a major issue in the investigation of time-domain aerodynamics of turbomachinery bladings by fluid–structure coupling. In this work, a numerical methodology for 3D time-domain fluid–structure coupling analysis was carried out to investigate aerodynamic stability of blades. Based on an assumptive gross elastic structure, the computational fluid dynamics (CFD) mesh-deformation is generated effectively, while the structural response is calculated using a modal approach. Accuracy of the method is validated by the traditional two-way fluid–structure interaction (FSI) approach on ANSYS Workbench and the literature, while computational efficiency is improved notably. The flutter boundary of the compressor at rotating speeds ranging from 100% to 80% was performed. When the flow rate is low enough, the second-order modal response is more likely to run into surge than the first-order modal response. The aerodynamic characteristics of the blades on two interblade phase angles (IBPAs) were also studied. The results indicate a much more significant increase in aerodynamic stability at 180° IBPA than that at 0° IBPA.

Cycloidal rotors have shown to be susceptible to achieving larger efficiency enhancements when being subjected to various designs and operating conditions. In this work, an improvement on the performance of a unmanned aerial vehicle (UAV)-scale cycloidal rotor is demonstrated at hovering mode and for various operating conditions with three end wall designs. The novel concept of actively controlling the pitching oscillations at different rotational speeds is obtained from a coupled methodology of computational fluid dynamics (CFD) and artificial neural network (ANN). In this approach, rather than a free-sided rotor, the effects of employing single and double end walls are targeted for optimizing the operation at hover state. A detailed database from numerous combinations of operating conditions is obtained from CFD predictions. Over 18 principal parameters are processed and computed along the continuous 360° circular trace, which is showing novel results. Subsequent to performing a precise database from the rotating-oscillating blades under various operating conditions for all three designs, the ANN approach is trained from the CFD data for optimization analysis and to propose the optimum pitching schedules by using a parametric study on the cyclorotor performance at each operating condition. Because each design can be used in its specific application, the optimum operating state for each of the end wall designs is further illustrated and reported as baseline data. The coupled analysis from CFD and ANN methodologies reports the efficiency achieved with free sides, doubled end walls, and a single side end wall, respectively. Moreover, employing a single side end wall results in 18.8% efficiency, and the double-sided model in 13.6% efficiency reduction compared with the free-sided cyclorotor. The computations on horizontal and vertical force productions are revealing an 8% and 11% higher horizontal force for the free-sides design than those of double end wall and single end wall models, and an average of 7% and 16% higher values in vertical force generation in double end wall model compared with free-sided and single end wall designs.

This paper presents modeling and control law design for a bi-tiltrotor unmanned aerial vehicle for autonomous payload delivery. An ultralight bi-tiltrotor aerial vehicle was developed for a payload delivery contest using only two motors attached to a carbon fiber tube with an additional cube basket to carry the payload. To achieve desirable three-dimensional (3D) trajectory tracking performance with unknown payload, an adaptive control system has been developed, which consists of two components: (1) a baseline control law, including a lateral speed controller, forward speed controller, yaw angle controller, and altitude controller; and (2) an adaptive augmentation to all these four channels to compensate for modeling uncertainties and disturbances caused by the payload, which has large influence on system dynamics due to the light weight of the vehicle. A mathematical model of the vehicle has been built using the Newton-Euler method and simplified based on reasonable assumptions to facilitate control design. The baseline control law employs conventional proportional-derivative control structure. Subsequently, ${\mathcal{L}}_1$ adaptive control theory is adopted in the adaptive augmentation design. Simulation examples verify the efficacy of the proposed adaptive control solution.

Solar Doppler velocimetry navigation, which utilizes the Doppler frequency shift between the standard solar and measured solar spectra to invert the velocity of the spacecraft, is an emerging and promising celestial autonomous navigation method. However, its accuracy of estimation does not fulfill the requirement of solar Doppler velocimetry navigation. To solve this problem, we developed nonuniform discrete Fourier transform compressive sensing (NDFT-CS) and applied it to solar spectrum velocimetry navigation. Mirror NDFT-CS consists of the mirror Fourier low-frequency measurement matrix, the Doppler frequency-shift dictionary, and the Taylor matching process. Namely, the mirror Fourier low frequencies of the NDFT matrix are used as the measurement matrix. The solar spectra with different Doppler frequency shifts merge to form a Doppler frequency-shift dictionary. Taking the Taylor formula as the objective function, we matched the measured solar spectrum with the dictionary to estimate a Doppler frequency shift. According to the estimated Doppler frequency shift, the velocity of the spacecraft is inverted. Due to the sparsity of solar spectrum signals, the measurement matrix is small, which means a small computational load and high accuracy. Simulation results demonstrate that the solar spectrum velocimetry method using mirror NDFT-CS has high accuracy in real time.

The problem of controlling coupled six-degrees-of-freedom (6-DOF) relative motion of an integrated-actuation spacecraft in the presence of actuator faults, and especially failures, is investigated in this paper. Considering the complications and limitations of the common control paradigm (which requires a mathematical model of a plant), a novel data-driven control framework is proposed. Specifically, the subspace predictive control (SPC) approach (which is an elegant data-driven framework based on a special combination of the model predictive control method and the subspace system identification technique) is developed and extended to control nonlinear plants and to tolerate abrupt and severe faults. Accordingly, a model-free fault-tolerant control method for coupled nonlinear time-variant plants is provided, such that its only fault diagnostic requirement is detection of the occurrence time of faults. Furthermore, a fully decentralized multispacecraft strategy is proposed and formulated that is quite suitable for a data-driven cooperative control approach. The effectiveness of the developed framework is demonstrated via simulation.

RocketPy is a new open-source Python library specialized in trajectory simulations of sounding rockets and high-powered rockets. Having a modular structure and being built on top of a six degree-of-freedom flight dynamics model that includes detailed mass variation effects, RocketPy allows for accurate trajectory prediction of different rocket configurations. Additionally, weather data from several meteorological agencies, such as reanalysis, forecasts, and ensembles, are an innovative feature directly integrated into the library, providing precise information about atmospheric conditions for each simulation. The software was successfully validated for three rockets developed by different universities, with apogee predictions showing deviations of the order of 1% when compared to actual flight data. Furthermore, due to its modular nature, RocketPy can be easily employed in optimization studies and Monte Carlo analyses. The latter was a key aspect of this work, enabling the calculation of landing dispersion ellipses based on input uncertainties. Since running several Monte Carlo analyses is computationally expensive, a new algorithm was proposed to significantly speed up results based on rejection sampling. The code described here and made available online enhances the state of the art represented by several widely used software and can serve as a framework for future research on rocket dynamics, control, flight optimization, and dispersion analysis.

Numerical investigations for passive and active controls on aerodynamic interactions of the rotor/wing of a tiltrotor aircraft are conducted in hovering flight. The moving embedded grid method and the helicopter code CLORNS are adopted to simulate the unsteady flowfield of the tiltrotor/wing, and the droop leading edge (DLE), trailing edge flap (TEF), and blowing jet are combined to investigate the control effects on the download of a wing in a three-dimensional (3D) rotor/wing interaction environment. The numerical results indicate that both the passive and active controls have the possibility to decrease the download of a wing, and the download coefficient could be reduced by approximately 72.4% using the combination of DLE and TEF. Moreover, the jet with a combination of DLE and TEF could effectively suppress the flow separation at the trailing edge region, thus improving the aerodynamic characteristics of the tiltrotor and wing, and the loss of rotor thrust and download of the wing could be reduced to 10.3% and 60.6%, respectively.

The growing applications involving unmanned aerial vehicles (UAVs) are requiring more advanced control algorithms to improve rotary-wing UAVs’ performance. To preliminarily tune such advanced controllers, an experimental approach could take a long time and also be dangerous for the vehicle and the onboard hardware components. In this paper, a simulation model of a quadcopter is developed and validated by the comparison of simulation results and experimental data collected during flight tests. For this purpose, an open-source flight controller for quadcopter UAVs is developed and a linear quadratic regulator (LQR) controller is implemented as the control strategy. The input physical quantities are experimentally measured; hence, the LQR controller parameters are tuned on the simulation model. The same tuning is proposed on the developed flight controller with satisfactory results. Finally, flight data and simulation results are compared showing a reliable approximation of the experimental data by the model. Because numerous state-of-the-art simulation models are available, but accurately validated ones are not easy to find, the main purpose of this work is to provide a reliable tool to evaluate the performance for this UAV configuration.

In this study, we propose a positive adaptive control approach for spacecraft in proximity. The new control law aims to track a predefined path under various uncertainties, such as physical parameters of the vehicle and others persisting in the external environment. Besides, the proposed method also considers the divergent performance and the nature of monodirectionality of the thrusters to ensure each control command is strictly nonnegative. In other words, the proposed method is capable of not only compensating for various uncertainties but also automatically allocating active thrusters with strictly positive manners. The numerical simulation results demonstrate the potential of the proposed algorithm by comparing the magnitude of fluctuation of the states concerning the activation of the adaptive scheme. Considering the findings, we attempt to perform a hardware experiment by utilizing the recently developed air-bearing-based hardware-in-the-loop spacecraft test facility. The results of the experiment clearly suggest the practical effectiveness of the proposed controller by showing that individual thrust magnitudes are manipulated based on the estimation of scale factor errors and other external uncertainties under their boundaries.

The Japan Aerospace Exploration Agency is planning to operate an uncrewed rover on the Moon to search for water ice, which exists at the polar regions of the Moon. The rover’s 1.5-m-long drill will penetrate the regolith layer of the lunar surface and capture ice particles mixed with the regolith. A transportation system for crushed ice particles mixed with the lunar regolith has been developed utilizing a vibration transportation mechanism that realizes the lifting of particles to physical and chemical analyzers installed on the rover. In this mechanism, the friction force between the inner wall of the tube and particles mainly plays the role of conveying particles upward while the tube inserted vertically into the bulk of the regolith is oscillating up and down. A parametric experiment was conducted to deduce the optimal configuration and operational conditions, and it was achieved that simulant particles and crushed ice particles mixed with lunar regolith are transported through the long tube. In addition, it was predicted by numerical calculations based on the discrete element method that the transportation performance in the lunar environment is better than that on Earth owing to low gravitational acceleration on the Moon.

This paper presents an approach to accurately characterize three-dimensional (3D) wire screen geometries as simplified two-dimensional (2D) screens for low Reynolds numbers. This is achieved by identifying 2D screen geometric features that provide appropriate approximations to a 3D realistic wire screen geometry. The simplified 2D screen geometries are obtained by varying geometric characteristics such as the streamwise pitch to diameter ratio within the range of $0\le C/D\le 1$ for side-by-side cylinders. Both in-line and staggered cylinders with spanwise pitch to diameter ratios ranging from $2.94\le P/D\le 5.56$ are examined here. A parametric study is performed for equivalent wire screen open area ratios varying within the range of $43.56\%\le \beta \le 67.26\%$. Numerical flow field comparisons between a 3D wire screen and its approximate 2D simplification are performed, with results further validated against documented experiments. The equivalent 2D flow loss coefficients agree very closely with the full 3D results, where for some Reynolds numbers, they are found to be within 6% of the experimental results. Both 2D and 3D results are found to underpredict the experimental values. The 2D results are also found to be much more accurate than the well-known flow correlations that are commonly used. 2D turbulence intensities measured at 570 diameters downstream of the screen were found to have the same values as the experimental results for some Reynolds numbers and were within 10% at worst. This demonstrates a real advantage over a 3D model, where such a long numerical domain would be very computationally expensive. Out-of-phase vortex shedding patterns exist for both in-line and staggered screen configurations in the range of $0\le C/D\le 1$. The contribution of this work will enable design studies to perform preliminary fast analysis of the effect of wire screens when applied as flow or noise control technologies.

Nonlinear progressive failure analysis (PFA) of piezolaminated composite shell panel under mechanical out-of-plane loading in the hygro-thermal environment is performed. The higher-order shear deformation theory (HSDT) with von-Karman nonlinear kinematics are used for basic formulation. Using variational principle governing equation for panel structure obtained by Newton’s Raphson approach through finite element method is employed to compute the necessary PFA. The second-order perturbation technique (SOPT) is utilized to obtain statistics in terms of mean and corresponding coefficient of variance (COV) of first ply and last ply failure load (FPFL and LPFL) through ply-by-ply failure counting by assuming random input system parameters. Convergence and validation analysis is performed to check the exactness of MATLAB version 2013a code. Shell panels are subjected to environmental conditions with uniform temperature and moisture distribution over entire shell panels. Initially, the paper presents the response of the composite plate and shell with the application of uniformly distributed flexural loading in the form of transverse central deflection (TCD) and mean FPFL and LPFL using a deterministic approach. Then, statistics in terms of mean and corresponding COV of FPFL and LPFL are obtained using a probabilistic approach through PFA. The effect of thickness and aspect ratio, types of loading, lamination sequences, curvatures, temperature increment, moisture content, the position of piezoelectric layers, and voltage variation on statistics of PFA has been examined.

A perspective on CFD/CSD-based time accurate computational aeroelasticity (CCA) is presented by a researcher who has been actively pursuing this research area since its beginning in late 70s. Discusses the use of terminology focusing on differences between the time accurate coupling and loose coupling methods in CCA. Highlights the misplaced interpretation of tight coupling. Need for time accurate CCA is illustrated with an example that compares CCA results with wind tunnel data that could not be computed using the linear aerodynamic theory. The paper provides a guideline for newcomers to the ever growing CCA research field.

Microwave sintering is regarded as a high-efficiency, energy-saving, and rapid-heating technique for the preparation of structural materials on the Moon. However, the influencing factors (i.e., ilmenite content and sintering temperature) on microwave sintering processes are not well-understood. Herein, five lunar regolith simulants with different contents of ilmenite (i.e., 4.6%, 28.5%, 43.9%, 65.8%, and 80.9% by weight) were used for microwave sintering experiments at 1,050°C, 1,150°C, and 1,300°C. The characterization of the microstructure, mineralogy, thermal conductivity, and mechanical properties of the products shows that the ilmenite content and sintering temperature significantly affected the properties of the microwave-sintered products. The sintering product containing 4.6% by weight ilmenite at 1,300°C showed a dense texture, good thermal insulation properties (thermal conductivity of $0.15\pm 0.005\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$), and optimal compressive strength ($74.0\pm 7.1\mathrm{MPa}$). This suggests that adding ilmenite to lunar regolith does not improve the properties of microwave-sintered products. The results in this paper provide reference for the preparation of structural materials on the Moon in the future.