Journal of Aerospace Engineering

Over the past decades, substantial research has been undertaken in the design of intelligent architecture for the rotorcraft-based unmanned aerial vehicles (RUAV). Designing intelligent architecture is a challenging problem because future RUAVs are utterly autonomous and their performance is comparable with that of manned vehicles. This paper deals with the design and development of a layered architectural framework that addresses the issue arising in autonomous intelligent control systems. The architecture consists of two layers. The high-level layer is occupied by planning routines. In this level, the waypoints and mission tasks from the command center are executed. The function of the low-level layer is to stabilize the flight and follow the commanded trajectory from the upper layer. These layers integrate the following functionalities: (1) waypoint navigation and control, which includes auto-landing; (2) obstacle detection and avoidance; (3) fault detection and identification; and (4) system reconfiguration in two levels (high-level and low-level controllers). The resulting layered architecture is discussed in detail. Moreover, the novel fault detection and identification method is developed to address multiplicative and additive faults. A testing environment for RUAV is developed to validate this architecture. Complete setup is carried out using an embedded board run under a real-time operating system. The algorithms are tested and evaluated using hardware-in-the-loop simulation (HILS). The simulation result proves that the proposed architecture demonstrates the desired efficiency and reliability.

Exploration of the Moon and Mars calls for robots that are increasingly capable in regolith, or granular soil. Beyond traversing and avoiding entrapment, future robots will excavate and process regolith as a resource. This work distinguishes concerns governing the performance of regolith operations, based on load-haul-dump tasks motivated by in situ resource utilization and lunar outpost site work. Payload ratio (mass of regolith payload capacity normalized by robot mass) and driving speed are identified as key parameters governing the productivity of small site work robots. Other parameters, such as number of wheels, are not as important. Experiments with a small robotic excavator and task-level simulations (for which a modeling framework is described) determine the relative sensitivity of productivity to changes in these variables. These findings provide direction for the development of future lightweight robotic excavators.

A thermomechanical electronic multifunctional structure prototype has been modeled and optimized. The model focuses on the description of thermal and electrical phenomena, but leaves aside structural issues. It couples a three-dimensional thermal network with representations of different possible thermal control laws, namely on/off control, proportional logic, proportional-integral-derivative strategy, and the usage of positive temperature coefficient heaters. The parametric model was first validated and correlated through a comparison with simple physical solutions, and then with the actual results of a thermal vacuum test. Multiobjective optimization (based on genetic algorithms) has been used to define the best heater layout options, to identify the best control strategy in terms both of panel isothermia and energy consumption, and to fine-tune the parameters of the selected control strategy. The research reported in this paper has led to the definition of an optimal thermal control solution. An examination of the optimization results has shown that the simultaneous adjustment of the geometrical layout as well as the control strategy and its parameters can lead to energy savings of about 52%.

This paper considers the attitude tracking problem of a rigid spacecraft involving inertia matrix uncertainty and external disturbance. First, an adaptive integral sliding mode control (ISMC) is proposed for when the upper bound on the lumped uncertainty is unknown in advance. It is shown that such a combination can produce a much smaller switching gain than the current adaptive sliding mode control (ASMC); hence, the overadaptation problem in existing ASMC design is effectively solved. Additionally, the system performance is improved by virtue of the global sliding mode feature of ISMC. A similar, but more flexible, ASMC design is introduced to further enhance the results; this design is developed on the basis of the reference trajectory scheme. The validity of the proposed strategies is verified by both theoretical analysis and simulation results.

The jitter control technique by using dual-stage vibration isolation system for optical payload on satellites is discussed, and it is applied on a satellite to improve the imaging performance. The dual-stage vibration isolation system includes two vibration isolation platforms. The first vibration isolation platform is at the actuator disturbance source, like control moment gyroscopes (CMGs). The second one is installed between the top of the satellite bus and the optical payload. In this paper, the first step constructs a general satellite dynamic model including a dual-stage vibration isolation system, a cluster of CMGs and solar arrays by Newton-Euler method and Kane equations, while the validity of this dynamic model is verified by a computer software program. The transmissibility matrices from CMGs motion to satellite motion and that to optical payload motion are then obtained according to the simplified satellite dynamic model. The parameters constraint conditions of the vibration isolation platform for the CMGs are described, with its influence on the attitude control system analyzed. The third part selects the reasonable parameters of the dual-stage vibration isolation system and those of the flexible solar arrays. Then the frequency domain characteristics of the dual-stage vibration isolation system are presented. Finally, using these reasonable parameters, the performance of this vibration isolation system on the satellite is testified by numerical simulations.

This paper focuses on the magnetohydrodynamic (MHD) boundary layer flow and heat transfer of a non-Newtonian nanofluid over a stretching sheet. The presence of Brownian motion and thermophoresis effects lead to a coupled nonlinear boundary value problem. Convective boundary conditions have been handled for the thermal boundary layer problem. Similarity transformations have been invoked to reduce the arising partial differential equations into ordinary ones. Series expressions of velocity, temperature, and nanoparticles concentration are obtained by homotopy analysis method (HAM). The homotopy solutions are validated with the obtained numerical solutions. It is noticed that velocity and the boundary layer thickness are increasing functions of the non-Newtonian (elastic) parameter for second grade fluid. However, the thermal and nanoparticles concentration boundary layers thin when the viscoelastic effects strengthen. Moreover, there is an appreciable increase in the temperature and the thermal boundary thickness when the strength of Brownian motion and thermophoresis effects are increased.

In this article, three-dimensional flow of an incompressible Jeffrey fluid over a bidirectional stretching surface is investigated. Two cases of heat transfer, the prescribed surface temperature and prescribed surface heat flux, are examined. The concept of heat source/sink is employed. A homotopy analysis method is adopted for the development of series solutions. Limiting solutions available in the literature are deduced as special cases of the present results. Plots are prepared and discussed for the pertinent parameters.

The waverider configuration is a type of aerodynamic shape providing a high lift-to-drag ratio and reasonable flight capacity for hypersonic vehicles. However, hypersonic waveriders are marred by serious design problems wherein the flight performance continually deteriorates if there are deviations in the expected flight conditions. As a result, a combination of hypersonic vehicle design with intelligent morphing technologies may be advantageous in addressing flight stability issues experienced during large flight envelopes. This paper discusses the concepts of nonlinear dynamics and integrated design methods with regard to morphing waveriders. First, a parameterized longitudinal model of a hypersonic vehicle is established in terms of the resulting lift, drag, moment, and thrust obtained from oblique shock theory, the Prandtl–Meyer equation, and the quasi-one-dimensional Rayleigh flow principle. Then the influence of active deformation on waverider control quality is considered by adjusting the configuration parameters in relation to the control action. Finally, the control system of a morphing waverider is designed using the model reference adaptive control methods, and a simulation example for morphing waveriders is demonstrated with regard to integrated action among aerodynamics, propulsion, and control.

The ignition transient phase in a model supersonic combustor with transverse fuel injection upstream of a cavity flame holder was experimentally investigated. Three types of ignition processes for scramjet startup were covered and compared: gaseous ethylene ignition, direct kerosene ignition by high-energy spark, and indirect ignition piloted by a preestablished ethylene flame. The flame propagation process and precombustion shock wave train dynamics were captured by using a high-speed camera and schlieren photography system. Three kinds of flame propagation failures were observed before a successful ignition result, after increasing the injection pressure to an ignitable pressure. The ignition limits of ethylene covered a much broader injection pressure range than ethylene when sparked directly in the cavity. The evolvement of the precombustion shock wave train for ethylene ignition indicated that the initiation of the ethylene flame was characterized by a subsonic flame expanding within the cavity. The enhanced mixing and evaporation process by the precombustion shock wave train provided another mechanism for piloted ignition, in addition to high-temperature heating of the ethylene flame.

For structures deployed in space using cables in which vibration damping is critical for structural stability, the understanding of cable damping is particularly significant to the structural performance. This paper describes an experimental setup for the measurement of cable vibration damping under varying cable tensile force, length, and configuration. The damping is determined by the half-power bandwidth method and the logarithmic decrement method. The testing results showed that the cable damping is related to cable tension, length, and configuration. A finite-element model is presented to simulate cable vibration and cable damping. The natural frequencies of the tested cables are determined by spectral analysis and agree well with those of finite-element simulation and theoretical analysis. The time history responses recorded by the accelerometers agree well with those from the finite-element simulation, which demonstrates that selected elements are capable of modeling the dynamic response of cables, and that the Rayleigh damping is adequate for modeling the damping of carbon fiber cables.

Magnetohydrodynamic (MHD) three-dimensional flow of an incompressible fluid induced by an exponentially stretching surface is investigated. Analysis is carried out when the surface exhibits convective condition. Mathematical formulation is completed by employing continuity, momentum, and energy equations. The governing nonlinear partial differential equations are reduced into the ordinary differential equations. Series solutions are constructed for the velocity components and temperature. Results are discussed by plotting graphs. A comparative study between the present solutions is made with the previous available results.

Curvic couplings are extensively used in aerospace machinery, such as helicopters, aeroengines, or other aircraft. In this paper, the behavior of bolted joints with curvic couplings is investigated to determine a method to describe the relationship between the stiffness parameters and the geometry of the parts of curvic coupling and external loads. The validity of the method is proven through experiments and finite-element simulation. Additionally, the study investigates the effects of the curvic height, curvic width, curvic thickness, pressure angle of curvic surface, and friction coefficient of curvic surfaces on the stiffness of disc parts. The analytical results show that the compression stiffness of both the curvic and ring parts of the disc has a relationship with the curvic rotation. Although the curvic compression stiffness tends to be constant in the bolt-tightening process for different curvic geometrical dimensions, the compression stiffness of the other disc parts has obvious differences owing to the various curvic geometrical parameters. By choosing appropriate pressure angles of the curvic surface or number, the stiffness of the curvic coupling can be kept stable in the bolt tightening course. The stiffness parameters of curvic couplings can be determined by the analytical model, regardless of how the geometry of the parts of curvic couplings or the external loads are changed.

This paper proposes a method to identify sources of variation in the assembly of a horizontal stabilizer using finite-element analysis (FEA) and the full factorial design (FFD) method. The horizontal stabilizer is mainly assembled with edges and ribs. The ribs are the typical thin-walled deformable aluminum components used in a horizontal stabilizer. Residual stress, machining distortion, and other stochastic variables result in the distortion of the ribs. Part-to-part assembly of these compliant components regularly causes difficulties associated with dimensional variations. The FEA and FFD methods are used to analyze the deviation induced by the ribs. The FEA variation analysis is utilized in a case study of the assembly of a horizontal stabilizer system and good performance is obtained. The results show that the precision of the rib bears directly upon the whole geometrical precision of the trailing edge and provide a quantitative evaluation of the rib’s distortion affecting the trailing edge. This study will enhance the understanding of the deformation of compliant components during assembly and help systematically improve the efficiency of precision control in the assembly of civil aircraft.

Experiments are carried out to study the self-excitation of axisymmetric underexpanded sonic impinging jets on flat plates with and without coaxial hole. Feedback studies indicate that the self-excitation of secondary small plate impingement tones ($S_2$) involves an acoustic feedback to the nozzle. The role of an acoustic feedback to the nozzle in the self-excitation of primary small plate impingement tone ($S_1$) depends on the impinging plate diameter. The frequency of small plate tones (both $S_1$ and $S_2$) from plate with coaxial hole of diameter $0.5D_e$ is less than the plate without hole for the same nozzle pressure ratio (NPR) and nozzle-plate spacing. Small plate impingement tones ($S_1$ and $S_2$) are suppressed in the case of plate with coaxial hole of diameter $1.0D_e$.

Influence of thermal radiation on the laminar two-dimensional incompressible flow of upper-convected Maxwell (UCM) fluid is investigated. An entirely different aspect of Rosseland approximation for thermal radiation is captured. The relevant equations are first modeled and then solved numerically by the shooting method using a fourth-order Runge-Kutta integration technique. The solutions are validated with the built-in solver bvp4c of the software MATLAB. Graphs are sketched to examine the behaviors of interesting parameters entering into the problem.

This paper outlines the use of a three-dimensional topology optimization scheme for the conceptual design of compliant flapping micro air vehicle mechanisms. Each trilinear finite element within the design domain is assigned to a density variable that smoothly interpolates between 0 (void) and 1 (solid), using a well-known methodology. A mechanism topology is found that converts a series of sinusoidal actuation point loads along the lower surface into a dynamic structural deformation, which in turn provides the desired flapping kinematics. Specifically, a mechanism is desired that can independently control more than one flapping rotation (i.e., flapping and feathering) at the same time.

In this paper, an ${\mathcal{L}}_1$ adaptive control system is designed for the control of a projectile fin. The rotational motion of the fin on the projectile is controlled by a flexible cantilever beam with a piezoelectric active layer, mounted inside the fin. The model includes time-varying disturbance input. In the closed-loop system, the applied voltage accomplishes regulation of the fin angle using the feedback of the fin angle and its derivative. Interestingly, the structure of the controller is independent of the dimension of the model. Simulation results show precise control of the fin angle, despite large parameter uncertainties and disturbance input.