Journal of Aerospace Engineering

Uncertainties can be introduced into the structural performance of cable-network antennas by inevitable manufacturing errors, which may result in failure in service. In this paper, robust optimization is first adopted to address the design of cable-network antenna structures with imperfect cable lengths. First, an analytical sensitivity analysis method is proposed to evaluate the effects of the uncertainties on the shape precision and cable tensions. Second, based on the sensitivities, the mathematical model of the robust design is established. At last, the proposed method is applied to a 3-m-diameter cable-network antenna structure. The analytical sensitivities are validated by comparing with the sensitivities computed by finite-difference method, and the feasibility of the presented robust design model is demonstrated by Monte Carlo simulations. The numerical experiments show that the robustness is greatly increased by the application of the robust design method. The results recommend that higher tension level, more elastic cables, thicker tension ties, and slenderer net cables can benefit the robust ability of cable network antenna structures.

This study investigates the steady three-dimensional flow of viscous nanofluid past a permeable shrinking surface with velocity slip and temperature jump. An incompressible fluid fills the porous space. The fluid is electrically conducting in the presence of an applied magnetic field. The governing nonlinear partial differential equations are reduced to ordinary differential equations by similarity transformations. The analytic solutions are presented in series form by the homotopy analysis method. Convergence of the obtained series solutions is explicitly discussed. The velocity and temperature profiles are shown and analyzed for different emerging parameters of interest. It is observed that by increasing the volume of copper nanoparticles, the thermal conductivity increases and the boundary layer thickness decreases. The velocity profile increases and temperature profile decreases for the larger velocity slip parameter. The temperature is a decreasing function of the thermal slip parameter. Hence, less heat is transferred to the fluid from the sheet.

The low-moon gravity has a significant influence on the mechanical properties of lunar soils at low-stress levels. To better understand the shear strength and deformation behavior of lunar soils at low confining stress and to facilitate the modeling and simulation of lunar activities, a series of consolidated drained triaxial compression tests were performed on numerous samples of lunar-soil simulant developed by Tsinghua University, China (named as QH-E). Great care was taken to conduct the experimental studies at low confining stresses such that reliable results can be obtained. The measured data suggest that QH-E samples exhibited strain-softening behavior with typical residual shear strength behavior characteristics. It was also found the residual internal friction angle ${\phi }_{cs}$ approximately 40°, regardless of confining stress, ${\sigma }_3$ and relative density, $D_r$, whereas the peak apparent cohesion intercept $c_{a-p}$ is not equal to zero owing to the nonlinear behavior of shear strength of QH-E. However, the residual value of apparent cohesion intercept $c_{a-cs}$ is equal to zero. The rate of change of dilatancy angle at low confining stress values is greater than those at the conventional confining stress values. Further, based on the measured data from this study, two empirical models were suggested to predict the tangent modulus $E$ and shear modulus $G$ of QH-E at low confining stress, and according to the prediction models for internal friction angle and dilatancy angle in the literature, the model parameters of QH-E at low confining stress were determined.

The present study examines the effect of slip and convective boundary condition on magnetohydrodynamic (MHD) stagnation point flow and heat transfer due to Casson nanofluid past a stretching sheet. Similarity transformation is used to convert the nonlinear governing equations and their associated boundary conditions into dimensionless form. The resulting system of ordinary differential equations is then solved numerically using the Runge-Kutta-Fehlberg method along with shooting technique. Numerical results are obtained for velocity, temperature, and concentration distribution as well as for the skin friction coefficient, the local Nusselt number, and Sherwood number. It is found that the local Nusselt number and Sherwood number decrease with an increase in Casson parameter $\gamma$. However, the skin friction coefficient -$f^{″}(0)$ increases with an increase in Casson parameter $\gamma$ and decreases with an increase in velocity ratio parameter $A$. The results are displayed both in graphical and tabular form to illustrate the effect of the governing parameters on the dimensionless velocity, temperature, and concentration. Then, comparison has been made and found to be in good agreement with a previous published result on special cases of the problem.

This paper deals with the investigations of supersonic flutter characteristics of laminated composite plates. The composite plates are modelled using a recently developed nonpolynomial shear deformation theory, which considers the required shear deformation effects in terms of an inverse hyperbolic function of thickness coordinate. The aerodynamic load is calculated by implementing linear piston theory including the influence of yaw angle. An isoparametric generalized finite-element formulation is developed for the aeroelastic analysis taking into account of required structural equations such as constitutive relations, kinematics relations, displacement field, and the principle of minimum potential energy together with the supersonic aerodynamics based on linear piston theory. The results are obtained by solving the developed system of governing equations for the flutter boundary, and the obtained results are validated against the existing analytical and numerical solutions. It is concluded that the developed formulation is accurate and efficient for the investigation of flutter behavior of laminated composite plates. Moreover, the strength and stiffness properties of composite plates are greatly influenced by fiber orientation, stacking sequence and material orthotropic ratio, flow characteristics are dependent on the flow angle, and geometric conditions mainly depend upon the boundary conditions. The influences of these stiffness characteristics (fiber orientation, stacking sequence, and material orthotropic ratio), geometric characteristics, and flow characteristics on the flutter boundary are examined and various benchmark conclusions are made. It is concluded that stiffness, flow, and geometric parameters must be considered as essential design parameters for enhanced flutter speed of supersonic vehicles fabricated of composite materials.

Stable control of large flexible structures has long been a challenge. Even though other research showed that direct velocity control and then position-and-velocity control are feasible, they require perfect or almost perfect collocation of velocity sensors and actuators. A very simple parallel feedforward device, which uses basic stabilizability properties of systems in order to allow implementation of strict positive real configurations, is tested here and is shown to eliminate the need for velocity feedback and collocation.

A detailed analysis of a finite-span synthetic jet in a quiescent fluid is presented, with the goal of achieving a high speed and momentum synthetic jet, with a peak velocity exceeding $200\mathrm{m}/\mathrm{s}$. A total of two scales of actuator apparatuses having either 40- or 80-mm-diameter piezoelectric discs were used. A temperature-compensated hot wire, laser displacement sensor, and dynamic pressure transducers were used to quantify the performance of a given actuator. The synthetic jet generation process was divided into its main components, diaphragm displacement, cavity pressure, and orifice velocity, which were analyzed in detail in both their peak values and time responses. The phase shift between the disc displacement and velocity signals were found to be mainly attributed to compressibility effects. Doubling the diameter and thickness of the piezoelectric disc was found to double the output jet velocity and shift the operation frequency range of the system. In addition, a dual disc configuration was used, which yielded an approximately 40% higher jet velocity than its single disc configuration. Using the knowledge acquired from these experiments resulted in a synthetic jet having a peak velocity of $211\mathrm{m}/\mathrm{s}$ out of a $12\times 1\text{-}\mathrm{mm}$ rectangular orifice at 700 Hz, which is significantly stronger than any similar actuator reported in the literature.

This paper studies the problem of finding the optimum time-dependent trajectory for an unmanned aerial vehicle (UAV) or any aerial robot flying on a low-altitude terrain following/threat avoidance (TF/TA) mission. Using a grid-based discrete scheme, a modified minimum cost network flow (MCNF) algorithm over a large-scale network is proposed. Using the Digital Terrain Elevation Data (DTED) and discrete dynamic equations of motion, the four-dimensional (4D) trajectory (three spatial and one time dimensions) from a source to a destination is obtained exactly through minimization of a cost functional subject to the nonlinear dynamics and mission constraints of the UAV. Several objectives (including the arc length, fuel consumption, flight time, and risk of threat regions) may be assigned to each arc in the network. The algorithm uses scalarization, by which a multiobjective problem can be tackled by repeatedly solving a single-objective subproblem. An attempt is made to reduce the time order of the algorithm using innovative techniques to construct a polynomial-time algorithm. Moreover, owing to the increasing deviation of the inertial navigation system (INS) in terms of time, flying safely and avoding a collision with terrain at low altitudes is a significant problem in the trajectory design of this type of vehicle. An attempt is made to add this constraint to the algorithm to produce a practical and safe trajectory with no evident increase in the complexity and execution time. Numerical results are presented to verify the capability of the proposed approach to generate an admissible trajectory in the minimum possible time compared to previous approaches.

A new scheme of robust fault-tolerant control allocation is designed for a discrete-time aerodynamic model in a research environment (ADMIRE) aircraft model in this paper. The control strategy has two steps. In the first step, a discrete-time robust virtual controller is designed to produce three axis moments. In the second step, the fault information will be used to reconfigure the robust fault-tolerant control allocation once an actuator fault is detected. A fault-detection scheme is assumed to exist for estimating the actuator fault. The robust virtual controller and the proposed robust fault-tolerant control allocation are applied to a discrete-time ADMIRE aircraft model. Simulation results demonstrate that the reference signals can be well tracked when the control surface is damaged. Thus the proposed robust fault-tolerant control allocation scheme is valid for input-redundant systems to recover from control surface failure, and simultaneously guarantee robustness to the uncertain control effectiveness matrix and disturbance.

During maneuvering flight, a spacecraft is subject to the engine thrust besides the gravitational force fields of celestial bodies. Moreover, the engine thrust model can hardly be built accurately due to its imbalance. Accordingly, the traditional orbit dynamic mode cannot predict the state accurately, which results in a great decline of navigation filter performance. In order to solve this problem, a state prediction model based on starlight Doppler is proposed for orbital maneuver. In this model, the velocity of the spacecraft is obtained from the starlight Doppler measurement instead of the orbit dynamic model. According to the measured velocities and the constant acceleration model, the state in the navigation filter can be predicted precisely. By this means, the state prediction is not influenced by engine thrust. The proposed state prediction model is applied in the XNAV (X-ray pulsar navigation) system for orbital maneuver. In this navigation system, the starlight Doppler velocity and the pulse time-of-arrival from the X-ray pulsar are utilized to predict and update the state, respectively. The simulation results demonstrate that the state provided by the starlight Doppler-based state prediction model is immune to the engine thrust. The starlight Doppler prediction-based XNAV can provide highly-accurate navigation information for spacecraft orbital maneuvers.

With the increasing complexity of modern aircraft technology and tight coupling among subsystems, the design of aircraft requires collaborative work of experts in various fields to make the right decisions, and therefore achieve the expected performance with less cost and risk. In this paper, an agile decision support system (ADSS) for aircraft design was proposed by comprehensively integrating and applying modeling and simulation (M&S), artificial intelligence, data mining, and group decision-making technology. The ADSS provides a rich set of simulation, assessment, and optimization tools for decision makers, which can offer an important objective reference to effectively improve the decision accuracy. A simulation and test environment was implemented for rapid assessment of different designs based on the developed multidisciplinary and multiphysical coupling virtual prototyping models and three kinds of virtual test methods. In the process of group decision making, valuable application modes can be discovered through data mining to reduce decision-making difficulty and improve the efficiency. Furthermore, a sensitivity analysis–based multilevel optimization strategy was developed for high-dimensional optimization design problems to meet the fast response requirement of the ADSS. Different cases were given for the data mining application, virtual test, and optimization design, respectively, to validate the proposed agile decision-making process.

An analytical study is presented for the effects of chemical reaction and mass transfer on the free convective flow of a viscous and incompressible fluid past a vertical isothermal cone surface. The derived fundamental equations on the assumption of small magnetic Reynolds number are solved. A comparison between the analytical and numerical solution has been included in the analysis. The effects of buoyancy parameter, chemical reaction parameter, and Schmidt number on the flow field are discussed through graphs.

The stagnation-point flow of viscous fluid induced by an exponentially stretching sheet is investigated in the presence of viscous dissipation and thermal radiation. Appropriate transformations reduced the partial differential equation into the ordinary differential equations. The resulting nonlinear problems are computed. Nusselt number values are tabulated. Comparative study between present and previous attempts made in a limiting sense. The flow quantities through pertinent parameters are examined.

A mathematical model for free convective boundary-layer flow of a nanofluid with second-order velocity slip over a permeable vertical flat plate has been presented. The system of governing equations is first nondimensionalized, and then similarity transformations are used to convert the governing partial differential equations into a set of coupled ordinary differential equations. A numerical algorithm is applied to this boundary value problem (BVP) of coupled ordinary differential equations. Collocation method is used for the solution of the nonlinear ordinary BVP. The dimensionless analysis revealed that the dimensionless field variables (velocity, temperature, and nanoparticle volume fraction), and the flow characteristics (skin friction factor, heat transfer, and nanoparticle volume fraction transfer) in the respective boundary layers depend on the Prandtl number ($\mathsf{Pr}$), the Lewis numbers (Le), the thermophoresis parameter (Nt), the Brownian motion parameter (Nb), the buoyancy ratio parameter (Nr), the convective parameter ($\gamma$), the reaction parameter ($K$), first-order velocity slip parameter ($a$), and second-order velocity slip parameter ($b$). Flow field and physical quantities strongly depend on the governing parameters. The present problem has applications in nanofluid synthesis for medicine. A tabular validation of the present numerical approach with the existing results in the literature is provided as a limiting case.

Inertial/astronomic integration is an effective way to improve the accuracy of attitude determination of hypersonic cruise vehicles (HCVs). Compared with common low-dynamic aircraft, the environmental affection during hypersonic flight leads to the non-Gaussian noise character of astronomic observation. Meanwhile, rapid star geometry changing during HCVs’ rapid movement causes redistribution of errors in astronomic measurements and significant variation of its main Gaussian characteristic. A kind of robust inertial/astronomic attitude determination algorithm with adaptive star geometrical error model is proposed. The adaptive star geometrical error distribution model is established for obtaining the main Gaussian model of astronomic measurement misalignment errors in flight. After that, inertial/astronomic integration model–based on misalignment errors is proposed, which avoids Euler angle transformation. On these bases, the improved robust filter algorithm is designed, which utilizes real-time astronomic error distribution as the weighting standard of Huber-based optimal estimation. Simulation results indicate that by taking the changing of main Gaussian distribution into consideration, the accuracy of inertial/astronomic integration is improved approximately 30% more than traditional algorithms adopting constant main Gaussian model in non-Gaussian HCV navigation environments.

A novel cubature predictive filter (CPF) is presented for relative position and attitude estimation of satellite formation taking into account the ${\mathit{J}}_2$ perturbation. A coupled relative translational dynamics is derived to represent orbital motion of arbitrary feature points on deputy, and the relative attitude motion is formulated by the rotational dynamics for the satellite. Based on the proposed coupled dynamics, the CPF is developed based on the third-degree spherical-radial cubature rule, extending the study of a traditional predictive filter (PF). The algorithm flow of the CPF is proposed first. Then, it is demonstrated that the estimated accuracy of the model error and system state for CPF is higher than that of traditional PF. In addition, a cubature Kalman filter (CKF) is also employed in order to evaluate the performance of the proposed CPF. Several different scenarios are simulated to validate the effectiveness of the coupled dynamics model and the performance of the proposed CPF. Through comparisons, the proposed CPF is shown to yield to obtain more accurate relative position and attitude estimation for satellite formation.

This article describes the effect of heat transfer on the magnetohydrodynamic peristaltic flow of Walters B fluid in a vertical symmetric channel. The flow is investigated in a wave frame of reference moving with the velocity of the wave. A perturbation method is used to obtain the approximate analytical solution for the stream function, temperature, and pressure gradient. The pressure difference and frictional force are obtained numerically. The variation of velocity, pressure gradient, temperature, stream function, pressure difference, and frictional force are sketched for various embedded parameters. The behavior of the Nusselt number and skin friction is presented in tables for the different parameters involved. Graphical results are also presented for four different wave shapes.

Stellar refraction-based celestial navigation is an attractive method with high accuracy and low cost. Most existing research works only focus on orbit determination problems for orbital vehicles in outer space while its working domain is limited. In order to expand its applicable area and improve information utilization, a new fault-tolerant stellar refraction-based inertial/celestial integrated navigation system is designed in this work, which is supposed to provide accurate position, velocity, and attitude information for aerospace vehicles that either make a maneuvering flight in near space or move in a predetermined Earth orbit in outer space. First, a new nonlinear navigation system dynamic model is established by error-prorogation equations of the strapdown inertial navigation system (SINS) in the Earth-centered inertial (ECI) frame, in which additive quaternion with less model error is used for attitude computation. Secondly, celestial navigation subsystem (CNS) is used to indirectly sense the horizon by utilizing the starlight atmospheric refraction model and determine the vehicle attitude by means of a multistar vector observation method. Thirdly, a fault-tolerant federated unscented Kalman filtering (FFUKF) algorithm is employed to perform information fusion, aiming at improving the navigation accuracy and reliability. Numerical simulations are conducted for an aerospace vehicle either in a near space maneuvering flight or in an orbital flight along a low Earth orbit. The results show that the proposed strategy achieves higher accuracy than traditional methods, and all the navigation parameters can be estimated. Moreover, different measurement faults are introduced in the simulations, and the FFUKF algorithm manages to detect and isolate them and keep the navigation system working in normal operation.

A general probabilistic fatigue-crack growth prediction methodology for accurate and efficient damage prognosis is proposed in this paper. The methodology is based on an equivalent stress transformation and the inverse first-order reliability method (IFORM). The equivalent stress transformation aims to transform the random variable amplitude loading to an equivalent constant amplitude loading spectrum. The proposed transformation avoids the cycle-by-cycle calculation under general random variable amplitude loadings. An IFORM is used to evaluate the probabilistic fatigue-crack growth behavior and to further enhance the computational efficiency. The computational cost of the proposed study is significantly reduced compared with the direct Monte Carlo simulation. Thus, the proposed method is very suitable for real-time damage prognosis because of its high computational efficiency. Numerical examples are used to demonstrate the proposed method. Various experimental data under variable amplitude loadings are collected for model validation.

This paper describes the conceptual design of a vertical takeoff and landing unmanned aerial vehicle (VTOL-UAV), mountable on an unmanned ground vehicle (UGV) for their combined operation as a team. The design aims to compensate for the weak points of each platform by providing carrying, launching, recovery, and recharging capabilities for the mounted VTOL-UAV through the host UGV. A sphere-shaped mechanical docking interface between the UAV–UGV is proposed to allow flexible and accurate positioning, and its operational concept with a coaxial rotorcraft UAV is suggested as one particular instance. A vision-based, target-tracking method to enhance the precision landing performance also was investigated and tested with a ground-based experimental setup.

The three-dimensional (3D) boundary layer flow of Jeffrey nanofluid subject to the convective boundary condition is analyzed. The flow is induced by a bidirectional stretching surface. Effects of thermophoresis and Brownian motion are considered. Newly developed boundary condition with the zero nanoparticles mass flux is employed. Mathematical modeling is made under boundary layer approach. Similarity variables are used to convert the governing partial differential equations into the nonlinear ordinary differential equations. The resulting nonlinear ordinary differential equations have been solved for the velocities, temperature, and nanoparticles concentration. Graphs are plotted to examine the influence of various physical parameters on the dimensionless temperature and nanoparticles concentration distributions. Numerical values of local Nusselt number are tabulated and discussed. It is found that the effects of the Biot number on the temperature and nanoparticles concentration are quite similar. Both the temperature and nanoparticles concentration are enhanced for the larger values of Biot number.

An analytical quasi-three-dimensional crack tip element model is developed to provide a quick assessment of the delamination behavior for composite laminates. A closed-form solution for the average total strain energy release rate is obtained by taking into consideration of all the displacement components defined in the classical laminated plate theory. By means of numerical experiments, it is shown that the presented method can predict the average total strain energy release rates with satisfactory accuracy for a relatively large variety of composite layups under opening and in-plane-shearing loading conditions. It indicates that the influence of out-of-plane transverse displacements on the total energy release rate can be significant for certain type of layups even under in-plane loading conditions. Furthermore, an orthotropic parameter is introduced to represent the influence of out-of-plane transverse effects.

A single-gimbal control moment gyro (CMG) is considered to be an ideal torque-generating actuator for rapid attitude maneuvering due to its relatively large output torque. A new attitude control method that is based on the modified Rodrigues parameter (MRP) sliding mode control law for a pyramidal configuration using four CMGs is proposed. Robust inverse steering logic is used to avoid issues of the singularity of the CMGs. The proposed approach is expected to provide rapid and stable attitude maneuvering while avoiding the singularity of the CMGs. In addition, this method is demonstrated on a small satellite, named TSUBAME, designed by the Laboratory of Space Systems at the Tokyo Institute of Technology. The proposed control algorithm is verified through a Monte Carlo simulation and a software-in-the-loop attitude simulator for TSUBAME. The Monte Carlo simulation demonstrated that the new sliding mode control approach successfully tracks a time varying attitude for a nanosatellite model with a range of system uncertainties and unmodeled dynamics. The software-in-the-loop simulation results successfully demonstrated the efficacy and feasibility of the proposed control law.

The yaw control problem of a prototype unmanned helicopter (UH) with novel configuration is addressed in this paper. The yaw control method based on adaptive model feedback and error compensation is proposed, which can achieve desired flight performance and guarantee the convergence of adjustable parameters in the presence of parametric uncertainties and measurement noises. Moreover, the adaptive error compensator with automatic fade-in and fade-out function can contribute greatly to reducing the tracking error in the initial stage of the adaptive learning process, and eliminate the adverse effect of measurement noises on the output of the adjustable system in the later stage. The effectiveness of the proposed controller is proved by a series of near-ground flight tests. The new methodologies proposed in this study are very effective control tools that help bridge the gaps between adaptive control theory and practical applications in high-performance UHs.