Journal of Aerospace Engineering

This study discusses simultaneous adaptation of the process and measurement noise covariance matrixes for a nontraditional attitude filtering algorithm. The nontraditional attitude filtering algorithm integrates the singular value decomposition (SVD) method with the unscented Kalman filter (UKF) to estimate the attitude of a nanosatellite. The SVD method uses magnetometer and Sun sensor measurements as the first stage of the algorithm and estimates the attitude of the nanosatellite, giving one estimate at a single frame. Then these estimated attitude terms are used as input to an adaptive UKF. The conventional UKF and the proposed adaptive UKF were compared with demonstrations of the attitude and attitude rate estimation of the satellite. Specifically, the Q (process noise covariance)-adaptation method is proposed. In the case of process noise increment, which may be caused by the changes in the environment or satellite dynamics, the performance of the Q-adaptive UKF was investigated.

Posthazard traffic networks are often disrupted, not only because of direct impacts on transportation infrastructure but also because of indirect impacts originating from the interdependent nature of infrastructure systems and environments. These indirect impacts include roads blocked by debris from adjacent buildings, traffic accidents, or fallen trees or light poles. For all these scenarios with partially blocked roads and bridges following extreme events, traffic capacity and travel time are very different what they are with intact road infrastructures and, therefore, become hard to predict. A new simulation methodology of the traffic performance of partially blocked roadway and bridge links due to hazardous events is proposed in this paper. The methodology was based on improved microscopic-scale traffic flow simulation techniques that can be applied to degraded road/bridge links with various types of obstacles (different sizes, numbers, and distributions). Following validation with the published results of traffic congestion induced by a work zone, two typical partially blocked scenarios resulting from infrastructure damage and accidents were numerically analyzed to demonstrate the feasibility of the application of the methodology to the traffic performance prediction of disrupted roadways due to extreme events. Parametric studies, such as the impact of truck proportion, blockage configuration, and traffic control measures, were also conducted. It was found that the proposed framework can predict the traffic performance of degraded transportation systems due to various causes, which could contribute to a wide array of future studies, such as community resilience modeling, emergency response and evacuation planning, and so forth.

Smart piezoelectric fiber composite materials have the potential to improve the aerodynamic properties and aeroelastic responses of flexible wings. Aeroelastic control performance significantly depends on the configurations of such anisotropic actuators. In this paper, configuration optimization of piezocomposite actuators, including locations and lead zirconate titanate (PZT) fiber orientations, is investigated to enhance the aeroelastic control authority of flexible wings within a flight envelop. The effect of fiber orientation on the anisotropic actuation characteristics of the piezocomposite actuator is analyzed. A mathematical model of the piezocomposite-actuated flexible wings is established with the integration of the finite element model, actuation forces, and Theodorsen unsteady aerodynamic loads. An optimization approach is developed based on a controllability Gramian matrix and solved using a genetic algorithm (GA). The effects of fluid-structure interaction and flight speed on the optimal configurations of piezocomposite actuators are investigated and discussed. The results imply that both the best location and the PZT fiber orientation of the piezocomposite actuator are affected by fluid-structure interaction. The torsional modes receive greater controllability in aeroelastic control than the pure structural vibration control of flexible wings, and the optimal fiber orientations increase with flight speed.

Tartaric sulfuric anodizing (TSA) and $\gamma$-glycidoxypropyltrimethoxysilane silanization ($\gamma$-GPS) were tested as treatments of Al-2024 and Al-2198 aluminum (Al) alloys for promoting adherence and corrosion protection of the Al–carbon fiber-reinforced plastics (Al–CFRPs) interface in Al–CFRP cocured hybrid materials, and compared with chromic acid anodizing (CAA). The corrosion resistance and the durability of the Al–CFRP interface were investigated and discussed. Polarization curves and Evans diagrams were achieved in NaCl solution, and the adhesion and durability of the interface were evaluated by mechanical tensile test on single-lap joint specimens before and after salt-spray exposure. The results are discussed and compared with CAA to evaluate the proposed treatments as CAA substitution candidate in the REACH European regulation (Registration, Evaluation, Authorization and Restriction of Chemicals). It was found that TSA and $\gamma$-GPS can provide as good adhesion as CAA before salt-spray exposure, but a higher mechanical strength depletion of the interface is obtained after long-term salt-spray exposure compared with CAA. This depletion was attributed to an insufficient long-term corrosion resistance of TSA or $\gamma$-GPS compared with CAA.

In this paper, a longitudinal dynamic model of a variable-sweep-wing morphing aircraft is proposed based on the Firebee unmanned aerial vehicle (UAV), accounting for changes in aerodynamic and inertial properties. Wing geometries and aerodynamic performance are also analyzed in six morphing configurations. The eigenvalues, damping, and frequency are investigated within short-period and phugoid modes. In addition, a classic proportional–integral–derivative (PID) controller is designed with different gains according to six morphing configurations. In three degrees of freedom (DOF) nonlinear simulations, the morphing aircraft maintains a straight and level flight in dash configuration at first and then changes to a loiter configuration at a fast and slow morphing rate. Except for the morphing moment caused by wing gravity, other morphing forces and moments can be ignored. Simulation results show that the designed controller works well with good trajectory-tracking performance, and a larger morphing rate leads to greater magnitudes in attitude, velocity, and altitude variations.

Mach number prediction plays a crucial role in wind tunnel systems. Due to the complicated system behavior, many existing predictors cannot obtain the desired level of accuracy. In addition, the presence of outliers in databases further negatively influences predictive accuracy. In this paper, we address these two problems in one scheme. In contrast to robust regression models, in this paper the problems of prediction and outlier detection are considered separately but are solved by one paradigm. We propose an ensemble model as a predictor, in which a Gaussian process model is used as the base learner. The motivation for using the Gaussian process is its superiority in solving complex nonlinear regression problems. The objective of the ensemble model is to further improve the predictive accuracy of the Gaussian process model. Our outlier detection model is also based on a Gaussian process. It is composed of two complementary components; one is based on Gaussian process regression, and the other is based on Gaussian process classification. We verify our predictor and outlier detection model with three data sets from a real-world wind tunnel system. The results not only verify the model’s predictive performance but also underline the superiority of the detection model.

Recent Unmanned Aerial Vehicle (UAV) design procedures rely on full aircraft steady-state Reynolds-Averaged-Navier-Stokes (RANS) analyses in early design stages. Small sensor turrets are included in such simulations, even though their aerodynamic properties show highly unsteady behavior. Very little is known about the effects of this approach on the simulation outcomes of small turrets. Therefore, the flow around a model turret at a Reynolds number of 47,400 is simulated with a steady-state RANS approach and compared to experimental data. Lift, drag, and surface pressure show good agreement with the experiment. The RANS model predicts the separation location too far downstream and shows a larger recirculation region aft of the body. Both characteristic arch and horseshoe vortex structures are visualized and qualitatively match the ones found by the experiment. The Reynolds number dependence of the drag coefficient follows the trend of a sphere within a distinct range. The outcomes indicate that a steady-state RANS model of a small sensor turret is able to give results that are useful for UAV engineering purposes but might not be suited for detailed insight into flow properties.

In this paper, the dynamic response of a functionally graded carbon nanotube–reinforced (FG-CNTRC) composite plate is obtained based on higher-order quasi-three-dimensional (3D) shear deformation theory (i.e., assuming a linear variation of transverse displacement through the thickness). The governing equations of motion are developed using the energy principle and solved using finite-element methods. Newmark’s time integration techniques are employed to obtain the forced response of FG-CNTRC plates. The accuracy of the present formulation is validated by tackling a few numerical cases and comparing finite-element solutions with accessible outcomes. Also, several new results are obtained for covering various features like thickness ratio, aspect ratio, and fiber volume fraction, among others, which can be considered as the benchmark study for future researchers. The outcomes demonstrate that the impact of Winkler foundation stiffness is not as great as the shear foundation stiffness on the natural frequency of the FG-CNTRC plates. The results also show that the free-vibration regime of the plate is highly influenced by duration of dynamic load on the plate. The present formulation gives excellent concurrence with the accessible literature.

Self-starting ability defines the operational envelope of a hypersonic inlet. To demonstrate the feasibility of enlarging the self-starting operational envelope using a splitter, numerical analyses were conducted on the self-starting process of a generic two-dimensional hypersonic inlet with and without a splitter. The studied generic two-dimensional hypersonic inlet has a large internal contraction ratio and a strong cowl-surface compression intensity. The results show that the baseline inlet does not start until ${\mathsf{M}}_0=6.843$, whereas the inlet implemented with a splitter successfully starts at ${\mathsf{M}}_0=4.227$. The underlying mechanisms for the improved self-starting owing to the introduction of a splitter are discussed.

A novel adaptive fault-tolerant control strategy is proposed for a spacecraft rendezvous maneuver. The six-degree-of-freedom (6-DOF) nonlinear model is expressed in the pursuer’s body frame, which consists of relative attitude and orbit dynamics in the presence of unknown time-varying inertia parameters, bounded disturbances, and actuator faults. A continuous adaptive control strategy is developed for the pursuer where a modification term and projection algorithm are employed in the adaptation laws to ensure the estimates of the unknown parameters remain positive and bounded. It is proven that the proposed strategy ensures the ultimate boundedness of all the signals in the closed-loop system and the asymptotic stability of the relative dynamics. Numerical simulations verify the effectiveness of the proposed control strategy.

The effect of wavelength and amplitude of a sinusoidal wavy ground on the aerodynamics and flowfield of a NACA 0012 airfoil at low Reynolds numbers was investigated experimentally. The results show that, regardless of wave length and amplitude, the periodic variation in the sectional lift and pitching moment persisted, and that the smaller wavy ground distance the larger lift and pitching moment became. The pitching moment also had an opposite trend to the lift. The maximum and minimum lift always occurred at wave peak and valley, respectively. The maximum and minimum lift and pitching moment increased drastically with increasing wave amplitude while depended weakly on the wave length. However, the change in the drag force over the wavy ground was found to be nonmonotonic.

A fairly large amount of existing bridges in the United States are in an urgent need of repairing and upgrading. With the increasing application of fiber-reinforced polymers (FRPs), the FRP-based structural system is a new exploration for bridge rehabilitation. In the present study, a new FRP-wrapped balsa wood bridge deck is adopted to replace the damaged steel deck of a bridge in Louisiana. Comprehensive experimental tests and live load field tests are developed to evaluate and continuously monitor the new composite system throughout its service life. Two innovative monitoring systems, i.e., fiber Bragg grating (FBG)-based moisture monitoring system and optical time-domain reflectometer (OTDR)-based interface slip/debonding monitoring system, are proposed and verified in the laboratory. The field test is then conducted with the objective of assessing the global structural performance, evaluating the adhesively bonded deck-girder interface, and calibrating a numerical model to further study the composite behavior between the deck and girder. The field evaluation reveals the overall structural performance and helps establish the baseline for future condition evaluation.

This research computationally evaluates the performance variations of two common types of supersonic air intakes, external and mixed compression, due to changes in the geometries of the intakes as well as some flow conditions. A computational fluid dynamics (CFD) solver was developed by the authors and used to simulate the compressible, two-dimensional (2D), and turbulent flow inside and around the supersonic air intakes. The main objective of this paper is to evaluate the role of geometric parameters, including spike angle, exit area, overall intake length, and flow parameters, such as the flight Mach number and back pressure ratio (BPR), on the performance of the intakes. Total pressure recovery (TPR), mass flow ratio (MFR), flow distortion (FD), and drag coefficient (${\mathrm{C}}_{\mathrm{D}}$) were considered as the performance factors of the supersonic intakes. The results indicated that increments of BPR had desirable effects on the performance of the intakes at supercritical conditions, and increments of the free-stream Mach number deteriorated the performance of both intakes. FD was the most sensitive parameter to the geometric variations, while TPR and MFR were almost unchanged. In addition, the superiority of the mixed compression intake was shown in terms of lower drag coefficient and FD in comparison with the external compression intake.

This paper presents a study of Lamb wave scattering and mode conversion at a delamination in quasi-isotropic (QI) composite laminates. The study employs the fundamental antisymmetric mode (${\mathrm{A}}_0$) Lamb wave as the incident wave and investigates the ${\mathrm{A}}_0$ scattered Lamb wave and mode converted fundamental symmetric mode (${\mathrm{S}}_0$) Lamb wave (${\mathrm{A}}_0\text{-}{\mathrm{S}}_0$) at the delamination. A three-dimensional (3D) explicit finite-element (FE) model is proposed to predict the Lamb wave propagation in the QI composite laminates, and ${\mathrm{A}}_0$ scattered wave and ${\mathrm{A}}_0\text{-}{\mathrm{S}}_0$ mode converted wave at the delamination. An experimental study is also carried out to demonstrate that the 3D FE model is able to provide a reasonable prediction of the ${\mathrm{A}}_0$ and ${\mathrm{S}}_0$ Lamb wave propagation in the QI composite laminates. The results show that the amplitudes of the ${\mathrm{A}}_0$ scattered and ${\mathrm{A}}_0\text{-}{\mathrm{S}}_0$ mode converted Lamb waves depend on the fiber orientation of the outer laminae, and the size and through-thickness location of the delamination. In summary, the results of this study can further advance the delamination detection techniques using Lamb wave and gain physical insights into the scattering and mode conversion of Lamb wave at the delamination.

The umbrella cable-net structure is one of the most popular forms for deployable space reflectors and has been successfully applied to many in-orbit deployable antennas. The umbrella ribs only provide open support for the cable net, so designing the geometric shape and the internal tension of the umbrella cable-net structure is complex. This paper suggests several double-layer cable-net structures for a deployable umbrella reflector. First, a typical composition of the umbrella reflector was introduced and the design basis of its geometric topology was further discussed. Then, two methods for the static equilibrium analysis of the cable-net structure were introduced for the mechanical calculation of the cable-net structure. Next, three types of the cable-net structure—wedge-shaped/wedge-shaped (W/W), triangular/triangular (T/T), and triangular/wedge-shaped (T/W)—were put forward. The three cable-net types were applied to a reflector and their performances were analyzed and compared with each other to demonstrate their feasibility and applicability.

Ice shedding represents a threat to aircraft safety because ice blocks can strike rear components or be ingested by engines. The accuracy of current numerical methods for predicting ice block paths in the design phase of an aircraft still needs improvement. For the verification and validation of new trajectory calculation methods, shed blocks can be modeled for simplification as sphere or six-degree-of-freedom (6-DOF) plates. The objective of this paper is to propose a mathematical model for the dynamic moments of the plates and use it to numerically simulate ice block paths. The results will be useful for verifying high-fidelity methods. Equations of motion in a Lagrangian frame are presented together with the correlations to be used for the aerodynamic coefficients of the ice blocks. The plate model involves the quaternions and a dynamic moment coefficient function of the angular velocity. After the model is validated with test cases obtained from the literature, the trajectories around the blended wing body are plotted. The sensitivity of the trajectories and footprints to the chosen dynamic moment model is highlighted.

In this study, a new model for analyzing delaminated plates was developed using three-dimensional (3D) degenerated elements. The elements were developed using the degenerated solid approach based on Reissner-Mindlin assumptions. Thus, the shear deformation and rotary inertia effect were considered, and the 3D field was reduced to a two-dimensional (2D) field in terms of midsurface nodal variables. The delamination was incorporated using Heaviside step functions. The proposed model was found to be very accurate and also faster in comparison with layerwise/higher-order theories. Results for natural frequencies of plates and beams with and without delamination were compared with theoretical and experimental results available in the literature and were in excellent agreement. New results were generated using the proposed method for different boundary conditions, ply orientations, size of delamination, and location of delamination; these will serve as benchmarks for future research.

This paper provides two new solutions to the energy-optimal impulsive correction for argument of perigee using Gauss’s variational equations (GVEs). A linear analytical approximation was derived by solving a cubic polynomial based on the classical linear GVEs. Compared with the existing analytical methods (e.g., special-point-based maneuver, circumferential impulse), the proposed linear analytical method can save energy cost and it is also valid for the large-eccentricity case. Moreover, a second-order numerical method was proposed based on the second-order GVEs and optimization technique. The proposed second-order method requires solving a three-dimensional equation, whereas the classical Lawden’s method solves a six-dimensional equation. Numerical examples with different eccentricities and different changes of argument of perigee were provided to verify the proposed linear analytical method and the second-order numerical method. The results showed that the proposed second-order method needs less computational time while ensuring enough accuracy.

In this study, based on the high energy-dissipating capacity of viscoelastic dampers with shearing deformation, damped stay cable crossties were proposed to mitigate the vortex-induced vibration (VIV) of stay cables in long-span bridges. Viscoelastic dampers were installed at the connection points of cable crossties to dissipate the kinetic energy of stay cable vibration. Three stay cable models incorporating different numbers of damped crossties were set up in a wind tunnel. Experimental investigations on the control efficacy of the proposed damped stay cable crossties and their parametric influence on the mitigation of the VIV of stay cables were conducted. Numbers of the damped crossties connected with a target main stay cable at different locations were experimentally studied, when the first three modal VIV of three stay cable models were excited respectively. On the basis of the test results, the oscillation behavior of the VIV of the three stay cable models with and without control was ascertained. The experimental results indicated that the proposed damped stay cable crossties can significantly reduce the VIV of stay cables by increasing the stiffness and damping of the cables, and can enhance the modal frequency and the onset wind velocity of the VIV of stay cables due to the increased stiffness.

The cable-net structure is an important part of the deployable mesh antenna, which determines the accuracy of the reflector surface and also has a nonnegligible influence on the deployment of the antenna. In this study, the AstroMesh antenna (Astro Aerospace, Northrop Grumman, Oxnard, California) is investigated. First, this influence is studied from the perspective of work. Then, the driving force for the deployment of the antenna is deduced considering the nonlinear factors, such as the cable-net and friction, according to the conservation of energy. Moreover, the effects of the cable force and the height of the rear net on the driving force are studied. According to the aforementioned research, an optimization model of the cable-net structure is proposed. By designing the cable net reasonably, the performance of work and the deployment for the antenna are coordinated well. Finally, according to the prototype of a 2-m-aperture deployable AstroMesh antenna, different cable-net structures are designed. The corresponding peak value of the driving force and the fundamental frequency of the deployed antenna are measured. The experimental results verify the validity of the optimization method.

In the present investigation, flow structures over a slender delta wing with a 70° sweep angle, $\mathrm{\Lambda }$ at an angle of attack, $\alpha$ of 30°, and under the variation of yaw angles within the range of $0°\le \beta \le 20°$ were investigated experimentally. To analyze the flow structure qualitatively and quantitatively, dye visualizations, surface oil visualizations, surface pressure measurements, and velocity measurements using the stereo particle image velocimetry (PIV) were conducted at Reynolds numbers of $\mathrm{Re}=2\times {10}^4$ and $\mathrm{Re}=1\times {10}^5$. Instantaneous and time-averaged flow data were analyzed to demonstrate the effect of yaw angle ($\beta$) on the alterations of leading-edge vortex formation, vortex breakdown, and also vortical flow structures over the wing surface. Time-averaged distributions of streamwise velocity component, $\overline{u}/U$, transverse velocity component $\overline{v}/U$, patterns of streamline, $\mathrm{\Psi }$, and distributions of turbulent kinetic energy $\mathrm{TKE}/U^2$ were presented to reveal the physics of flow structures under yaw angle ($\beta$) variations. Distribution of pressure coefficients, ($-C_p$) at various $x/c$ and $y/c$ locations were also presented. The experimental results demonstrated that the variation of yaw angles ($\beta$) has a strong effect on the alterations of the flow structure, the leading-edge vortex formation, and its breakdown. An increase of yaw angle ($\beta$) causes asymmetrical flow structures and hence expands this asymmetrical flow domain further.

X-ray pulsar navigation has been considered a great potential navigation method for high-attitude missions and deep-space explorations. One of the main problems of X-ray pulsar navigation is that its accuracy is low. In this paper, a pulsar/star tracker/inertial navigation system (INS)–integrated navigation method was studied. Unlike the traditional pulsar-based integrated navigation method, the novel system was decomposed into two parts according to the speed of the filtering rate, the attitude filter and the velocity and position filter, which could improve the navigation efficiency and reduce the amount of calculation. The simulation results showed that the accuracy of the proposed integrated navigation method was improved by more than 50% compared to pulsar navigation, proving the effectiveness of the integrated navigation scheme proposed in this paper in improving navigation accuracy.

Energy addition has been considered a means to improve the performance of supersonic inlets. The energy addition to supersonic inlets can be considered as a virtual cowl, which can be implemented during off-design conditions to essentially emulate the shock-on-lip (SOL) condition obtained at the design point. The primary purpose of this work is to increase the mass capture and the pressure recovery and reduce flow distortion at the exit of the isolator section by finding the optimum location and energy required to enhance the performance of the intake section. Parameters like magnitude and location of energy addition were examined. The performance was assessed using mass capture, total pressure recovery, static-pressure rise, and flow distortion. The effects of shock reflections at the exit and the shifting of separation zones due to energy addition have also been understood and discussed. An energy addition of $0.2\mathrm{MW}/\mathrm{m}$ was found to be most suitable at a region that is near the cowl leading edge. Moving below or far above the cowl line was found to decrease the performance. The improvement in mass capture with suitable parameters can be up to 15%.

This paper discusses the coupling dynamics behavior of spacecraft equipped with flexible appendages and liquid propellant tanks. The moving pulsating ball model (MPBM) is used to imitate large-scale liquid propellant motion in a tank. The flexible appendage is modeled as a three-dimensional Bernoulli–Euler beam with a free end and an end fixed to the rigid part of the spacecraft. Governing equations for the beam’s elastic motion, a set of nonlinear partial differential equations, are discretized into an infinite system of nonlinear ordinary differential equations by two different methods: assumed mode method (AMM) and rigid-flexible coupling mode method (RFM). For AMM, the beam mentioned previously is assumed to be a cantilever beam. For RFM, the modal shapes and frequencies of the beam are determined by mutual interaction between spacecraft motion and an appendage’s elastic motion, which is neglected in AMM. The spacecraft’s attitude transition is carried out using a momentum transfer technique, and a feedback controller is designed accordingly. Numerical simulations demonstrate the beam elastic vibration, spacecraft angular rates, liquid propellant motion, liquid-flexible coupling behaviors, and a comparison between AMM and RFM results. The work presented here may provide new insights into the coupling dynamics of liquid-filled flexible spacecraft systems.

In this study, the performance of large-diameter circular diaphragm walls in a deep excavation in Shanghai soft clay is investigated, which has a diameter of 121 m and a maximum excavation depth of 31.1 m. Through a comprehensive field monitoring program, the distribution and development of total lateral pressure, including earth pressure and water pressure, are discussed in association with the dewatering process in the confined aquifer. The lateral deflections of the circular diaphragm walls are analyzed and compared to similar cases in the literature. Moreover, comparisons of hoop force and hoop stiffness between the diaphragm walls and ring beams are presented. Results indicated that (1) because of the symmetrical excavation scheme in this case, the circular diaphragm walls maintained in a small eccentric compression state throughout the excavation; (2) the computed lateral pressures using lateral pressure coefficient at rest agree well with the measured lateral pressure at both initial as final excavation stages if the effect of groundwater drawdown on the lateral pressure was considered; (3) due to the decrease of the lateral pressure outside of the excavation and increase of the internal supporting system stiffness, the maximum deformation occurred at a depth of about 10–15 m above the final excavation surface; (4) based on the investigation of 14 circular diaphragm wall cases in soft soil area, a reciprocal relationship between normalized wall deformation and hoop stiffness is proposed; and (5) the ring beams behaved more stiffly than the diaphragm wall panels because they were casted integrally.

A new quasi-three-dimensional (quasi-3D) displacement model considering the effects of fifth-order shear deformation and fourth-order normal deformation is developed for the accurate prediction of displacements, in-plane stresses, and transverse shear stresses in laminated composite and sandwich plates. The present theory involves nine unknowns in the displacement field and satisfies traction-free boundary conditions at top and bottom surfaces of the plate. The governing differential equations and associated boundary conditions are obtained using the principle of virtual work. Analytical solutions are obtained using Navier’s solution technique. All the displacements and stresses are obtained for simply supported boundary conditions. Transverse shear stresses of laminated composite and sandwich plates are obtained using equilibrium equations of the theory of elasticity by direct integration method. The numerical results are found in excellent agreement with exact elasticity solutions compared with other higher-order theories available in the literature. Hence, it is concluded that the present theory yields accurate predictions of displacements and stresses in laminated composite and sandwich plates.

Wall heat flux distributions under different configurations for a kerosene-fueled supersonic combustor were experimentally studied. The influences of combustion, global fuel equivalence ratio, mass flow rate, total temperature, and inlet Mach number on the wall heat flux of the kerosene-fueled supersonic combustor were systematically presented and analyzed for the first time. Methods to calibrate and validate the in-house-developed heat flux sensors are also presented. The revealed trends would be useful to guide the design of thermal management systems for kerosene-fueled scramjets.

The flame dynamics of ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) composite propellant subject to the acoustic oscillations in solid rocket motors (SRMs) is numerically investigated in this article. A multilayer sandwich model is established to provide the flame with a combustion environment that can interact with the flame. The effect of the HTPB segment size is analyzed as well. The results indicate the mass transfer processes could occur between the flame and combustion environment and increase the reactant concentrations of the final flame. Thus, the average temperature of the final flame is higher. The temperature fluctuation of the final flame is greatly reduced as well. The HTPB segment size has a different effect on the near-burning surface flame and final flame. The wider HTPB segment thickness can result in a higher temperature of the near-burning surface flame because more gaseous pyrolysis products of HTPB are provided. However, larger HTPB segment size can reduce the final flame temperature because the impact of the environment has been weakened.

The wind environment and aerodynamic characteristics of vehicles are easily affected by the structural form of the railway. To investigate the aerodynamic effects of viaduct-cutting connection sections on vehicles, models of standard cutting, viaduct, and China Railway Highspeed (CRH2) trains at a scale of 1:20 were tested in wind tunnel tests. The wind speed profiles and vehicle aerodynamic coefficients were developed using a Cobra probe and balance, respectively. Additionally, the effects of wind barriers were applied. The test results indicate that the wind speed profile at the railway juncture is almost independent of the lateral positions at the same position. The aerodynamic influence of vehicles on different tracks (windward and leeward railway tracks) is different. Moreover, wind barriers can change both wind speed profiles and aerodynamic coefficients and significantly reduces wind speed and changes the aerodynamic coefficients to improve vehicle wind-resistant performance.

External disturbance and measurement noise during flight tests inevitably degrade the identification of the aircraft aerodynamic models. Traditional approaches, however, need to differentiate the measured signals to build the identification models, which results in a dedicated preprocessing to avoid noise amplification. The aim of this paper is to assess the influence of four derivative estimation techniques on the parameter estimation of an aircraft aerodynamic model. Among the four studied techniques, two come from the field of robot identification. The other two techniques are the standard one in aircraft identification based on the Savitzky-Golay algorithm and a suggested one based on wavelet denoising coupled with finite differences. The two techniques coming from robot identification are the usual one relying on a low-pass filter applied in both forward and backward directions and a recently suggested method based on a Kalman filter with a first-order random walk model. The comparison simulation results illustrate that the first robot differentiation strategy not only performs well in providing accurate stability and control derivatives even in the presence of colored disturbance but also is competitive with respect to the standard method in aircraft identification.

To solve the problems of a hypersonic unpowered gliding reentry vehicle controlled by only one actuator, a combination bank-to-turn control mode with a moving mass and nonredundant reaction control system (RCS), which can not only optimize the internal space of flight vehicle, but also avoid ablation of the aerodynamic control surfaces and improve control efficiency, is proposed in this paper. Firstly, a seven-degree-of-freedom dynamical model of the gliding vehicle in the period of reentry was established. The layout and control sequence of nonredundant RCS are described in detail. Taking into account coupling phenomena caused by displacement of a moving mass, a new configuration that can weaken the coupling effect is presented based on dynamics analysis. The inertial coupling and the Dutch roll coupling for the new control mode are described. On the basis of the analysis of dynamics and coupling, the attitude control system was designed by sliding mode theory. The adaptive compensation that makes the control system have high robustness to aerodynamic parameter uncertainties was designed. Finally, the simulation results are presented to demonstrate the validity of the proposed composite control mode.

In this paper, the aeroelastic response of a hingeless rotor blade in hover is investigated. The hingeless rotor blade was modeled by using the geometrically exact fully intrinsic beam equations combined with the quasi-steady aerodynamic loads and uniform inflow. The partial differential equations were discretized by using the time-space scheme. A particular blade with precone angles was considered, and the stability boundaries of this blade were determined. Then the aeroelastic response of the blade for stable and unstable regions was determined. It was found that the blade experiences different types of responses depending on the system parameters. A more comprehensive study is required to characterize the effective parameters and what type of response a blade may experience in the postaeroelastic instability region.

Since 1960, when the first probes landed on the Moon, multiple specimens of lunar soil have been available for research. The very limited volume of lunar soil samples means that they can be utilized only for the most important research programs. Therefore, multiple artificial lunar soil materials, called lunar soil simulants (LSSs), have been developed over the last 55 years. Lunar soil simulants are used to enable large-scale lunar research programs. They are supposed to be precise copycats of lunar soil in chemical composition, mineralogy, grading, and mechanical characteristics. Nevertheless, the vast majority of artificial and commercially available simulants have not met scientific expectations and proved unsuitable for specific lunar engineering purposes. There is a pressing need for a complex but at the same time efficient, reliable, and fast method for the assessment of lunar soil simulants. In the authors’ opinion, an analytical approach based on multivariate statistics involving multiple parameters of a given simulant would be the most feasible solution to this problem. Principal component analysis, which is a special case of factor analysis, was chosen as the most suitable for the task. Moreover, based on chemical composition data from real lunar samples and the results of multivariate calculations, we proposed to use the ilmenite sand as the base for LSSs that could be easily obtained, separated, and standardized in both terrestrial and extraterrestrial locations.