Journal of Aerospace Engineering

In this paper, a reduced-order modeling approach based on computational fluid dynamics is presented for an elastic wing with control surfaces in the transonic regime. To treat the computational fluid dynamics grid around the geometrical discontinuities, due to the deflection of control surfaces, the constant volume tetrahedron method and the transpiration method are combined together without deforming the grid. Based on the input–output data from the computational fluid dynamics solver, one multiple-input/multiple-output discrete-time state-space model for the wing is identified via a robust subspace algorithm. For each control surface, one one-input/multiple-output discrete-time state-space model is identified using the same algorithm. With the precomputed state-space models for a few flight parameters, the generalized aerodynamic forces over a range of flight parameters can be computed by interpolating the output data. The methodology is applied to an elastic wing model with two control surfaces and the generalized aerodynamic forces are compared with the results from the computational fluid dynamics solver to validate the reduced-order modeling approach in transonic regime.

Numerical studies on the applications of the microblowing technique (MBT) on a supercritical airfoil are performed based on a microporous wall model (MPWM) to represent the macroscaled collective characteristics of the huge number of microjets. The influences on the aerodynamic characteristics by microblowing with a MBT zone on different locations are analyzed. It is found that a MBT zone near the leading edge of the airfoil could achieve more reduction of skin-friction drag than a zone near the trailing edge. While for pressure drag, microblowing does not always result in a pressure drag penalty but could even reduce the pressure drag if the MBT porous zone is arranged on the region near the trailing edge. For the flow field without a shock wave, the MBT zone should be arranged on the lower wall and near the trailing edge. The typical configuration followed this guideline could simultaneously decrease the pressure drag and skin-friction drag while also increasing the lift. Numerical results indicate that a 12.8–16.8% reduction of total drag and 14.7–17.8% increase of lift could be achieved by this typical configuration with a blowing fraction 0.05. However, for the flow field with a shock wave on the upper wall, the performance of the microblowing is obviously suppressed by the existence of the shock wave.

Force measurements and wake surveys have been conducted on two swept NACA 0021 wings. One wing had a smooth leading edge, while the other wing had a tubercled leading edge. The force measurements and the wake survey results were in good agreement. Between 0 and 8° angles of attack, tubercles reduced the lift coefficient by 4–6%. For the same range of angles of attack, tubercles reduced the drag coefficient by 7–9.5%. Tubercles increased the lift-to-drag ratio of this wing by 2–6%, and increased the maximum lift-to-drag ratio by 3%. At angles of attack higher than 8°, tubercles typically decreased the lift coefficient and the lift-to-drag ratio, while substantially increasing the drag coefficient. The wake surveys revealed that tubercles reduced the drag coefficient near the wingtip and that they also spatially modulated the drag coefficient into local maxima and minima in the spanwise direction. Typically, tubercles reduced the drag coefficient over the peaks where the tubercle vortices produced downwash. Conversely, tubercles increased the drag coefficient over the troughs, where upwash occurred. The majority of the drag coefficient reduction occurred over the tubercled wingspan.

In this paper, effects of the surface-catalysis efficiency on aeroheating characteristics are studied. The Navier–Stokes solver with a cell-centered finite-volume scheme, including the finite-rate chemistry and two-temperature thermal nonequilibrium models, is implemented in this work. The ELECTRE flight trajectory at 53 km is used for validating the developed solver. Several cases with different catalytic recombination coefficients are studied to investigate the effects of catalysis efficiency under the condition of radiative equilibrium for the C series of Radio Attenuation Measurement project II flight trajectory at 71 km. It is revealed that distributions of heat flux and wall temperature have the similar tendency for all cases except for the Stewart model. Heat flux and wall temperature do not grow endlessly as the catalytic recombination coefficients are increased. It is the gradient of species density rather than gradient of temperature that leads to the significant differences of heat flux and wall temperature for different cases. The results indicate that the zone influenced by catalysis efficiency for atomic oxygen is larger than the one for atomic nitrogen and that the recombination reactions of atomic oxygen are more active.

The present paper reports a numerical study of the aerodynamic properties for a novel disc-shaped airship. Different configurations are considered, some of which present a circular opening connecting the bottom and top surface of the airship. The aim of the study is to understand the flow dynamics, in order to define the aerodynamic efficiency and the stability properties of the flying vehicle. Such information is crucial for the design of the propulsion system and of the mission profile of these innovative airships. Results show that, in general, disc-shaped airships are characterized by large values of drag and small levels of lift. Interestingly, it appears that lift keeps increasing up to very high angles of attack. This feature is found to be related with strong tip effects, which induce a significant flow of air from the high-pressure region at the bottom surface to the low-pressure region at the top surface. This air flow energizes the upper boundary layer, thus contrasting the flow separation on the top surface. This phenomenon is found to be useful for the stability properties of the airship: in fact, it shifts the center of pressure closer to the geometrical center of the airship, hence implying a reduction of the aerodynamic moment. The role of openings is also addressed and found to positively contribute to the stability properties of the airship, by further reducing the levels of aerodynamic moment.

The platform for resource observation and in situ prospecting for exploration, commercial exploitation, and transportation (PROSPECT) instrument package is under development by the European Space Agency for the upcoming Luna-27 mission to the lunar south pole. The purpose of the instrument is to detect and quantify volatiles on the lunar surface with the processing and analysis unit ProSPA. This paper describes the feasibility study and early breadboarding activities on ProSPA sample ovens during the Phase A study. The review of similar sample oven concepts led to the conclusion that none of these concepts satisfies new requirements of ProSPA regarding sample size and target temperatures. The trade studies presented in this paper include the estimation of power demands for scaled-up ovens, the influence of oven insulation, the compatibility of the utilized materials, and an experimental validation of the design. Experimental tests showed that the new oven design allows reaching the target temperatures and following most of the specified heating profiles with an imposed maximum power of 70 W. During the heating tests with the lunar regolith simulant NU-LHT-2M, sintering of the sample, reduction of the FeO content, and the creation of gas cavities were observed.

Efficient global optimization of aerodynamic shapes with the high-fidelity method is of great importance in the design process of modern aircrafts. In this study, modifications are made to the particle swarm optimization (PSO) algorithm and the radial basis function (RBF) model for further improvements of efficiency and accuracy of optimization. Specifically, a PSO algorithm with randomly distributed cognitive and social parameters, exponential decrease of maximum velocity and inertia weight, and periodic mutation of particle position is proposed. Furthermore, a nonuniform shape parameters strategy is introduced for the RBF surrogate model. Validations on test functions show that the new PSO has remarkable speed of convergence, and the new RBF model has superior approximation accuracy. The PSO algorithm and RBF model are then combined to construct the computational fluid dynamics (CFD)–based optimization framework. Finally, optimizations of transonic airfoil and supersonic launch vehicle are performed and results show that the drag coefficients in the two cases are significantly reduced (14 and 15%, respectively). The successful applications also indicate that the proposed PSO and RBF as a whole have apparent advantages over their original versions, and the optimization framework is effective and practical for design of aerodynamic shapes.

In this paper, a spacecraft radiator formed in a honeycomb structure is designed to enhance the thermal performance while reducing its mass. Examples of design guidelines for radiator configurations, such as the distance between heat pipes, facesheet thickness, and honeycomb core density, are suggested. To derive the analytic solution of the governing equation, a linear approximation is used and the accuracies of the solutions are verified with a fourth-order finite-difference method. There exist optimal combinations of design parameters that minimize the radiator mass while maintaining its heat rejection capacity. The heat rejection rate that minimizes the mass per unit heat rejection and the pertinent radiator shape also is presented. The combinations of optimal design are different among the three surface treatments and their characteristics are investigated.

Textbooks state that the lift, drag, and thrust coefficients $C_L$, $C_D$, and $C_T$, are numbers that must be dimensionally proper (i.e., dimensionless) for their use in comparing different data sets. This paper posits that for the meaningful comparison of different data sets, numbers must be dimensionally and physically proper. The physical propriety is satisfied by expressing the number as a ratio of work and the energy available at an aerodynamic system during the generation of lift, drag, or thrust. The aerodynamic systems addressed in this paper are aircraft, propellers and lift rotors, cylinders in Magnus effect, and flapping wings. This paper introduces the normalized lift, ${\eta }_L$, normalized drag ${\eta }_D$, and normalized thrust, ${\eta }_T$, numbers that are dimensionally and physically proper and can evaluate the ability of generating lift, drag, and thrust of these aforementioned systems and compare this ability between different systems. These numbers are shown to act like the thermal efficiency $\eta$ in thermodynamics as they represent the ratio of work exerted onto the surrounding flowfield and the kinetic energy available at the system, are associated with a maximum value ${\eta }_{\max }$ (that may exceed 1) and can be read on a stand-alone basis. Their common mathematical format facilitates crosspollination between engineering, biomechanics, and biology. A numerical calculation of the normalized lift ${\eta }_L$ of the blades of the record-breaking quadcopter AeroVelo Atlas is presented and compared with its lift coefficient $C_L$ as calculated by the AeroVelo group.

To improve the overall performance of mission planning for the unmanned aerial vehicles (UAVs), a multistage path prediction (MPP) for trajectory generation with rendezvous is addressed in this paper. The proposed real-time algorithm consists of four stages: path estimation, path planning, flyable trajectory generation, and trajectory modification for rendezvous. In every planning horizon, each UAV utilizes the local $A^{*}$ algorithm to estimate all probable paths and then the results serve as input for the task assignment system. A simple assignment algorithm is briefly introduced to validate the effectiveness of MPP. Based on the assignment, the polygonal paths are further obtained by using the global $A^{*}$ algorithm. Then these paths are smoothed to be flyable by using the cubic $b$-spline curve. In the last stage, the trajectories are modified for rendezvous of the UAVs to execute specific many-to-one tasks. Results of different stages are continuously revised and delivered to the task assignment system as feedback in the whole mission process. Numerical results demonstrate the performance of the proposed approach for stochastic scenarios.

The lightweight design of the sandwich mirror, as a commonly used space primary mirror structure, is one of the key topics for the design of space-based optomechanical systems. Owing to the limitation of traditional manufacturing capabilities, the induced holes on the mirror back are usually of the open or half-open form, which compresses the optimization design space. With rapid development of additive manufacturing (AM) technologies, it is possible to fabricate a closed-back sandwich mirror with a complex internal structure to achieve outstanding performance. In this paper, a novel topology optimization model for a closed-back primary mirror of a large-aperture space telescope is proposed. First, extrusion constraints are considered in the optimization model to obtain the layout design of stiffening webs inside the mirror core. Then, a simply connected constraint, as one type of constraint in AM, is considered to avoid enclosed voids in the structures. Through solving the proposed model, a new closed-back sandwich mirror configuration with nonclosed treelike vertical stiffening webs, is achieved. In addition, the thicknesses of the internal stiffening webs are optimized for minimizing the weight with the constraint of the surface shape error of the mirror face. Compared with the classical and existing sandwich mirror configurations, the optimized mirror has significant superiorities on optical performance and the lightweight ratio, which illustrates the effectiveness of the presented method. The method is a prospective study in the design of a space mirror fabricated using AM.

This paper presents a robust impact angle guidance law for maneuvering target interception with autopilot dynamics compensation based on a systematic backstepping control technique. Since the future course of action of the target, an independent entity, cannot be predicted beforehand, an adaptive-control approach is introduced in guidance law derivation. In order to address the problem of explosion of terms caused by analytic differentiation of the virtual control laws in the standard backstepping method, a tracking differentiator is adopted as an alternative way to obtain the derivatives of the virtual control laws. Stability analysis shows that both the line-of-sight angular rate and impact angle error can be stabilized in a small region around zero asymptotically. Simulation results explicitly show that accurate interception is achieved with a wide range of impact angles.

In this paper, an adaptive backstepping controller, which can attenuate external disturbance, is proposed for flight vehicle attitude control subject to amplitude and rate saturations of the elevator. First, the elevator rate saturation is incorporated into the amplitude saturation, which results in realistic amplitude-saturation bounds. Then, an attitude-control law is proposed based on the adaptive-backstepping scheme in which the comprehensive elevator amplitude saturation is explicitly considered. In this design approach, two adaptive gains, which are related to the external disturbance and realistic saturation bounds, respectively, are tuned in the control law. The resulting closed-loop system is proved to be uniformly ultimately bounded by the Lyapunov stability analysis approach. Simulation results show the effectiveness of the proposed method.

This paper proposes a scale-dependent model to investigate the dynamic-pull-in characteristics of a functionally graded carbon nanotubes (FGCNTs) reinforced nanodevice with a piezoelectric layer. Based on nonlocal beam theory, the nonlinear thermoelectromechanical coupling dynamic governing equation of an electrostatically actuated nanodevice is derived. The material properties of the functionally graded layer depend on temperature environment, thickness, volume ratio, and distribution of carbon nanotubes (CNTs) reinforcement. The van der Waals interaction and Casimir force are considered in the dynamic-pull-in analysis. The homotopy perturbation method is used to obtain a second-order approximated analytical function of nature frequency with respect to initial amplitude. The influences of piezoelectric effect, temperature change, nonlocal parameters, distribution, and volume ratio of CNTs and initial amplitude on dynamic-pull-in behaviors and natural frequencies of the nanodevice are discussed. The results show that the system has one stable focus point at the domain of small initial amplitude and appears in a particular homoclinic orbit originating point and ends at an unstable saddle point.

In this paper, a new guidance law, which is called virtual sliding target (VST) guidance law, is designed based on the concept of the virtual target (VT). The presented law is applicable for short- and medium-range missiles. It is shown that by using proportional navigation (PN) and considering the aerodynamic characteristics of the missiles, this law leads to a better performance than the PN law. In this approach, motion of the VT is started from a position higher than the real target. By controlling the speed of VT, which slides toward a predicted intercept point (PIP), speed, position, and trajectory of the missile can be controlled. Since arrival times of the missile to the VT and the VT to the real target are equal, the collision will happen. Furthermore, a new optimal guidance law is presented for long-range missiles based on the concept of the waypoint (WP) and VT. In the mentioned law, there are two important points. The first one is a constant point that is called a waypoint and the second one is called a virtual target, which slides toward the PIP. Then a teaching-learning–based optimization (TLBO) algorithm is used to find the optimal initial position of the WP and the VT to maximize the intercept speed. Simulation results illustrate better performance of the VST law over the PN law in terms of the intercept speed.

The authors have developed an electrostatic sampler for the reliable and autonomous collection of regolith particles on asteroids. The sampler, which employs Coulomb and dielectrophoresis forces to capture regolith particles and transport them to a collection capsule, can collect a lunar regolith simulant containing particles of various sizes less than approximately 1.0 mm in diameter in a low-gravity environment. However, there might be large particles with diameters of 1.0 mm or larger on asteroid surfaces. The authors conducted a numerical calculation and a model experiment to confirm whether the sampler can collect particles larger than 1.0 mm in diameter in a low-gravity environment. The numerical calculation, performed using the distinct element method, predicted the effect of the particle diameter on the sampler performance, indicating that particles 1.0 mm in diameter or larger could be successfully sampled in a low-gravity environment. Glass particles 2 mm in diameter were experimentally sampled in a $0.01g$ environment reproduced by a parabolic aircraft flight, and rocks 4 mm in diameter were agitated under $0.01g$ and successfully sampled under microgravity.

Targeted at one kind of on-orbit servicing spacecraft that contains flue containers, momentum actuators, space manipulators, and captured unknown objects, a specific attitude control problem during orbital maneuvers is under investigation in this paper. To overcome strong uncertainties during the onboard service, a parameter-identification algorithm is developed to estimate all inertial parameters of each part of the spacecraft system, and the identification results are obtained based solely on the measurement of the inertial navigation system. Therefore, the disturbance from the torque coupling of the orbital engine can be thus effectively compensated. Based on the identified parameters, the attitude stabilization problem is taken into practical consideration to tackle the strong influence from the orbital engine disturbance of concern. In order to specifically suppress the disturbance, a hybrid control strategy based on the momentum actuators and thrusters is proposed, which not only provides better precision than the conventional thruster-based method but also guarantees the momentum actuators against the momentum saturation issues. Numerical simulations are conducted to verify the effectiveness of the proposed algorithms.

The nonlinear static deflections of a functionally graded carbon nanotube (FG-CNT) reinforced flat composite panel are examined under a uniform thermal environment for different end conditions. The temperature-dependent material properties of the matrix and the fiber (carbon nanotubes) are considered in conjunction with the different gradients of carbon nanotube concentrations through the thickness direction. The mathematical model of the carbon nanotube reinforced flat composite panel is formulated for different types of gradients using the Green-Lagrange geometrical strain in the framework of the shear deformable higher-order kinematic theory. Further, the equilibrium equation of the panel is obtained using the variational method and discretized through the finite-element concept. The nonlinear deflections are worked out numerically using the direct iterative method via a suitable computer code. The validation and the convergence performance of the present numerical results were checked. Finally, the significance and inevitability of such a higher-order nonlinear model for the analysis of gradient carbon nanotube structure are established by solving different numerical examples for various parameters (types of grading, aspect ratios, thickness ratios, volume fractions, thermal field, and end conditions) and discussed in detail.

In this paper, an alternative approach was developed for the form-finding of cable-membrane structures. The prestress of a triangular finite element was firstly equivalent to the axial force densities and uniform vertical loads on the three edges. The static equations and tangent stiffness matrices of the cable-membrane were then formulated with the aid of the nonlinear force density method. In order to obtain a high accurate surface of cable-membrane structures, an iterative strategy was presented to solve the nonlinear force density equations and optimize the initial geometrical shape based on the Newton-Raphson method. Eventually, the proposed method was applied to the form-finding of the cable-membrane structure, a hoop truss antenna, and a numerical example was conducted to confirm the efficiency of the method.

This paper investigates two robust finite-time controllers for the attitude control of spacecraft based on rotation matrix. The first controller can compensate external disturbances with known bounds, whereas the second one can deal with both external disturbances and input saturation by using the hyperbolic tangent function and auxiliary system. Both controllers can avoid the singularity and converge to zero in finite time by using novel fast nonsingular terminal sliding mode control. Because the controllers are designed based on a rotation matrix that represents the set of attitudes both globally and uniquely, the system can overcome the drawbacks of unwinding. Numerical simulations are presented to demonstrate the effectiveness of the proposed control schemes.

Orbital maneuvering of microsatellite and nanosatellite requirements can be efficiently addressed by planar nozzles, in which real-time thrust control is gained actuating on the nozzle throat area. In the present work, the method of characteristics is used to design a hypersonic contour; then, the resulting profile is laser cut, assembled, and built into a propulsion system to finally perform tests in a vacuum chamber under several working conditions. Results are used to validate the profile and modeling assumptions and investigate overall behavior. Tests showed that thrust-inlet pressure ratio is a linear function of separation between nozzle contours and that no additional losses are introduced in the system. The corresponding design/manufacture/assembly tools can be used to a provide low-cost/low-weight controllable propulsion systems to the small-satellite industry with no efficiency loss.