Journal of Aerospace Engineering

The gravitationally coupled orbit–attitude dynamics of a rigid body in a $J_2$ gravity field is a generalization of the traditional point-mass $J_2$ problem to take into account the gravitational orbit–attitude coupling of the considered body. Linear and nonlinear stability of nonclassical relative equilibria in the coupled orbit–attitude dynamics are studied with geometric mechanics in the present paper. Conditions of stability are obtained through the linear system matrix and projected Hessian matrix by using the energy–Casimir method. Linear and nonlinear stability regions are plotted in a wide range of system parameters. It is found that the stability regions are similar to those of classical relative equilibria while, at the same time, some differences do exist. For example, in some cases, the linear stability region contains not only the two regions that are analogues of the Lagrange region and DeBra–Delp region, but also a small irregular region in the third quadrant. Same as the case of classical relative equilibria, the nonlinear stability region is the subset of the linear stability region in the first quadrant, which is the analogue of the Lagrange region.

The objective of this paper is to minimize fuel consumption needed for geostationary Earth orbit station keeping by Xenon Ion Propulsion System (XIPS) thrusters in failure mode under eclipse constraints. Two diagonal XIPS thruster pairs, each pair consisting of one north thruster and one south thruster, are mounted on the antinadir face of the satellite. In failure mode, only one diagonal thruster pair fires. The original failure-mode station-keeping strategy without consideration of the eclipse constraints fires the remaining diagonal thrusters a second time with equal duration in the vicinity of $\sim 0°$ or 180° right ascensions (RA), in addition to a first time in the vicinity of $\sim 90$ and 270°RA, which also results in the problem of excessive fuel consumption. The eclipse constraints are considered in this paper and the feasible firing location for station keeping during eclipse time is established. A optimal failure-mode station-keeping strategy under eclipse constraints is presented with the firing locations and durations of one diagonal thruster pair as design variables. The optimal station-keeping model is built and applied for maintaining a geostationary satellite within a predefined space box. Precise orbital simulation results show that the proposed optimal failure-mode station-keeping strategy can both save fuel and satisfy eclipse constraints.

This paper focuses on the dynamics and control of spacecraft with multiple liquid propellant tanks. The liquid slosh dynamics are included by using an improved moving pulsating ball model. The moving pulsating ball model is an equivalent mechanical model that is capable of imitating the liquid reorientation process, especially for large-amplitude slosh. This model is improved by incorporating a static capillary force and an effective mass factor. The improvements are validated with previously published experiment results. The spacecraft attitude maneuver is implemented by the momentum transfer technique. The designed feedback control strategy is demonstrated to be efficient and robust for the coupled liquid-filled spacecraft system. For the two-tank system, two eccentric cases of concern are an asymmetric tank arrangement and an unbalanced propellant mass distribution in the two tanks. The effects of the two eccentric cases on sloshing torque and control torque are investigated. Some conclusions obtained are useful in the overall design of liquid-filled spacecraft.

Teleoperation rendezvous and docking (RVD) in the lunar orbit may not reach the required RVD accuracy because of the inherent time delay in the communication link and the measurement error. To solve this problem, the shared control strategy for teleoperation RVD based on the potential field function was studied in this work. On the basis of the relative dynamic equations, a predictive display model to depict the predictive ability of the operator was established to overcome the time delay effect. The automatic mode was designed based on the potential field function, which regarded the relative distance and speed with respect to the safe corridor as reference quantities. In addition, this article outlines the concept of shared control weighting coefficient and its derivation on the basis of the influencing factors. Finally, a validation experiment was conducted on a nine-degree teleoperation RVD simulator. Results showed that the shared control method can overcome the influence of time delay in the communication loop and effectively improve the RVD accuracy compared with manual and automatic control modes. The control performance and success probability of RVD tasks were also enhanced.

The railgun system is an electromechanical coupled system. In this paper, electromechanical coupled dynamics equations of the electrical system in the railgun are proposed. The free oscillation of the electrical system in the railgun is investigated, changes in the natural frequency and the damping coefficients of the electrical system, along with the time and related parameters, are analyzed, the forced responses of the current to the voltage fluctuation are discussed, and the dynamic electromagnetic forces in the railgun are determined. The results show that a small voltage fluctuation of the electrical system in the railgun can cause a large dynamic magnetic force on the rails under some conditions.

In this study, the effects of acoustic excitation frequency on flow over an NACA 2415 airfoil were determined, and all of the experiments were done both with and without the presence of the acoustic excitation. The acoustic excitation was applied for a range of angles of attack (0°–25°) and Reynolds numbers of 50,000, 75,000, 100,000, 150,000, and 200,000. To examine the effects of acoustic excitation on the flow, force measurements, pressure measurements, hot-wire anemometry, smoke-wire flow-visualization, and particle image velocimetry techniques were employed. The results indicated that for stall and some limited poststall angles of attack of the acoustic excitation having a frequency in a certain range forced the separated shear layer to reattach to the surface of the airfoil. As the Reynolds number increased, the effective excitation frequency increased, but the range of Zaman number [$\mathsf{St}/({\mathsf{R}}^{1/2})$] was the same. With the acoustic excitation, the stall angle was delayed from 12° to 16° at $\mathsf{R}=\mathrm{50,000}$, and there was a 30% and 50% increase on the maximum value of the lift coefficient and the ratio of the lift and drag forces, respectively. Moreover, the stall angle was delayed from 13° to 17° at $\mathsf{R}=\mathrm{75,000}$, from 15° to 18° at $\mathsf{R}=\mathrm{100,000}$, from 15° to 17° at $\mathsf{R}=\mathrm{150,000}$. Furthermore, it was concluded that acoustic excitation shrunk laminar separation bubble, and an effect of the acoustic control on the separation bubble decreased as the Reynolds number increased.

Magnetic sensors are reliable, lightweight, and low power consumption sensors that are utilized in almost all nanosatellites and microsatellites for a magnetic attitude control system using magnetic torquers (MTQs). In some nanosatellites and microsatellites, magnetic sensors are utilized for magnetic moment estimation to compensate for torques owing to magnetic dipole disturbances, which are the dominant disturbances in these small satellites. To estimate the magnetic moment accurately, the errors of the magnetic sensors caused by the magnetic anomaly and bias noise from electrical devices should be estimated and compensated precisely. Although several previous studies have focused on the estimation and compensation of the errors of the magnetic sensors, the magnetic anomaly of the geomagnetic field has not been considered, even though the anomaly introduces large estimation errors. This research proposes a method to estimate the time-variable errors arising from both magnetometer bias and the magnetic anomaly of the geomagnetic field using an extended Kalman filter (EKF) and unscented Kalman filter (UKF). Based on numerical simulation results, this study concludes that the effects of both magnetic sensor bias and magnetic anomalies can be compensated for by the proposed method.

In this study, multifunctional panels with structural and self-healing capabilities were experimentally investigated under high velocity impact conditions. The panels were composed of two layers, one made of fiber-reinforced plastics (FRP) and the other of a self-healing ionomer, assembled in four different configurations with surface density ranging from 6.85 to $7.49\mathrm{kg}/{\mathrm{m}}^2$. A total number of 16 impact experiments are reported, where spherical aluminium projectiles with diameters from 2.3 to 4.5 mm were shot at impact velocity, which varied from 2.0 to $2.5\mathrm{km}/\mathrm{s}$. The panel response was analysed in terms of (1) impact damage; and (2) capability to protect equipment located behind the panel from the cloud of fragments ejected downrange after panel perforation. Successful hole sealing was observed in panels consisting of a carbon FRP laminate and ionomer plate hit by projectiles up to 3.5 mm in diameter. The damage of the target was somewhat smaller when the ionomer was on the panel’s rear side. Such panels presented smaller debris cloud spread angle but lower momentum transfer to witness plates, suggesting that this panel configuration is preferable from the point of view of nearby equipment shielding effectiveness.

The optimal satellite-formation collision-avoidance maneuver problem is investigated in terms of relative eccentricity and inclination vectors (E/I vectors) in relative E/I vectors plane. Using the relative E/I vectors theory and under the relative inclination vector unchanged assumption, first, the fuel-optimal collision-avoidance maneuver problem to maneuver the final target configuration with predefined passive safety parameters using minimal fuel is transferred to the geometrical problem to find the shortest distance from the initial point determined by the current relative eccentricity vector to the hyperbolic curve, which is determined by a predefined passive safety parameter in the relative E/I vectors plane. This case is solved using the Newton interaction method. Second, the optimal collision-avoidance maneuver problem to maneuver the final target configuration having maximum passive safety parameter under limiting fuel constraint is interpreted as the geometrical problem to find the optimal curve that has maximum passive safety parameter and is tangent to the maneuverable circle, whose center and radius are the initial point determined by the current relative eccentricity vector and the limited fuel, respectively. The equivalent geometrical problem is solved by applying a simple heuristic search method. The validities of the proposed optimal collision-avoidance methods in terms of relative E/I vectors are confirmed by numerical simulations.

The time-dependent flow past an impulsively started vertical infinite isothermal plate in a viscous electrically conducting natural convective incompressible nanofluid is considered in this paper by taking into account the effects of heat absorption, heat generation, and radiation. An analytical study is performed to obtain exact solutions for different water-based nanofluids containing Cu, Ag, CuO, ${\mathrm{Al}}_2{\mathrm{O}}_3$, and ${\mathrm{TiO}}_2$. The presented closed-form formulas are beneficial for investigating and understanding the detailed features of the momentum and thermal fields together with the skin friction coefficient and the Nusselt number.

Unsteady compressible flow analyses of helicopter rotor–fuselage interaction in hover and forward flight conditions are carried out using commercially available computational fluid dynamics (CFD) solver FLUENT. The individual effects of each component on the flow are investigated by simulating the isolated fuselage and the isolated rotor configurations. Then, the rotor-fuselage interaction problem is analyzed. Azimuthal variations of the flap and pitch motions of the blades are prescribed a priori as a first-order Fourier series through a user-defined function feature of the code. The prescribed blade motion may result in meshes with undesirable grid qualities, which may lead to unphysical solutions. A non-overset dynamic mesh motion method that applies volume mesh deformation and cell remeshing within a priori organized block mesh structure is used to accommodate the rigid blade motion. The remeshing is performed when the grid deformation is more than a predefined skewness value of 0.95. The near wall flow region is discretized using triangular base prismatic layers. The remaining part of the computational domain is modeled by tetrahedral volume elements. The results of the present study have been compared with the experiments and other available numerical results found in literature. The present single grid methodology has given similar successful results with much lower number of grid elements, thus resulting in much shorter computing times, using modest computational power.

This paper presents a novel method for the modal system identification of a large mechanical structure by combining results from simulations and physical measurements. Specifically, reconstruction of mode shapes was accomplished by comparing simulated and measured amplitude ratios generated using a Nyquist analysis. The methodology developed in this paper improves upon traditional techniques by allowing for statistically cross-referencing relatively few sensor measurements and a relatively simple simulation model. This methodology was used to identify three major modal frequencies and mode shapes of the main aluminum honeycomb sandwich panel gondola structure of the balloon-borne imaging testbed (BIT). BIT was a stratospheric ballooning project for astronomy that was launched on September 18, 2015, from Timmins, Ontario, Canada. Ensuring that structural vibrations do not adversely affect the pointing accuracy of the on-board telescope is crucial to the success of the project. This paper also highlights some of the advantages and drawbacks of the presented methodology and suggests improvements for future applications in balloon-borne experiments.

Carbon dioxide removal assembly (CDRA) is an essential subsystem in an air revitalization system (ARS) to control ${\mathrm{CO}}_2$ concentration in a long-term manned spacecraft cabin. At the same time, it is a main power consumption subsystem. ${\mathrm{CO}}_2$ concentration control performance and power consumption are both key factors that need to be considered. To design this subsystem reasonably, some basic processes are analyzed carefully in this paper, such as mass and heat transfer processes in ${\mathrm{CO}}_2$ adsorption beds, power consumption for fan and electric heater, and entropy generation in heat transfer process. The relationship between CDRA and other subsystems are also analyzed carefully. Based on these analyses, a multiobjective optimal method is developed in this paper. Its objective functions are specified as cabin ${\mathrm{CO}}_2$ concentration level, power consumption, and entropy generation. The optimal parameters are air velocity, absorption bed length, adsorption time (half cycle time), and molecular sieve mass loaded in the absorption bed. An improved genetic algorithm, Nondominated Sorting Genetic Algorithm-II (NSGA-II), is adopted to obtain the final optimal solution set. Furthermore, a CDRA for a space station with three astronauts is taken as an example to show the implementation of the proposed method. Optimal results show that the presented optimal method can obtain the design solution set for the CDRA. The optimal parameter combination is recommended as the final optimal design solution by analyzing the global pareto optimal front of the solution set. This multiobjective optimal method can realize an optimization process for a complex system design by taking a comprehensive consideration of various factors and running performances.

In this paper, a method is introduced for determination of satellite attitude using heat fluxes absorbed by the satellite. Heat fluxes are measured using heat-flux measurement sensors. The heat flux equation then is solved inversely to determine satellite attitude. Advantages of this method in comparison to the other attitude determination methods are its employment of only one measurement system rather than a combination of different attitude sensors, ease of implementation, negligible power consumption, low mass budget, and no need for calibration by other devices. This method is evaluated by simulating three test cases of satellites in orbit. Results show that the present method works very well in all cases. Satellite attitude can be determined accurately during the sunlight part of the orbit and with error in the shadowed part of the orbit. It was also observed that the accuracy of the present method strongly depends on the resolution of the temperature sensors.

In this article, a practical temperature control issue of gas for a high-speed heat-airflow wind tunnel (HSHAWT) is solved. Based on the principal analysis and the system configuration description, the mathematical models to describe the dynamic characteristics of the fuel delivery system and the fuel combustion system are established. Two control frameworks of gas temperature for HSHAWT are proposed. One is to realize the gas temperature control by using the method that regulates the fuel flow rate on the basis of the air flow rate being a constant; the other is the two-loop cascade control framework that takes gas temperature as a controlled objective, fuel flow rate as a controlled object in the secondary control loop, and gas temperature as the controlled object in the main control loop. Furthermore, experimental comparative studies on the flow rate of fuel and temperature of gas are carried out by using a variety of control algorithms, and a satisfactory control effect on the gas temperature is achieved.

There are many course correction fuze concepts for improving the precision of a spin-stabilized projectile. Some of them consist in a despun fuze equipped with canards. Canards provide continuous and, possibly, modulable maneuvering capabilities in crossrange and downrange. This paper analyzes the efficiency of this type of course correction fuze and determines the best configuration for the canards. To do so, four concepts of canards-based course correction fuze are proposed and tested. To properly operate the fuzes, a guidance algorithm, based on point-of-impact prediction, and two autopilots, a poles/zeros cancellation controller and a proportional integrator controller, are developed. The fuzes efficiency is studied with their control authority footprint and achieved performances during Monte-Carlo simulations. All the tests are done with a pseudo-seven-degrees-of-freedom simulator including the developed algorithms. Those tests demonstrate that the four concepts significantly improve the precision of a spin-stabilized projectile and that, with the proposed algorithms, the best precision is obtained when the canards directly handle the projectile longitudinal acceleration.

Aeroelastic tailoring of a composite forward-swept wing model is investigated to achieve a minimum structure weight with increasing divergence speed and flutter speed. A novel hybrid pattern search method is proposed to perform the aeroelastic tailoring of the wing structure subject to multiple constraints including static deformation, strength, buckling, and aeroelastic characteristics. In the new hybrid pattern search method, the sensitivity analysis method and the genetic algorithm are combined to enhance the global convergence rate and obtain a global optimal solution, respectively. A global search is performed by using the genetic algorithm to obtain elite individuals as the initial values for further optimizations, and the sensitivity analysis method is applied to improve the optimization efficiency. The comparative study of the optimized results obtained by other existing modern heuristic optimization methods shows that the present method can achieve the lightest structure weight and cost the least CPU computing time. After optimization of the present method, the structure weight of the initial design can be reduced by 14.21%, whereas the divergence speed and the flutter speed are increased by 40.6 and 14.38%, respectively. This study demonstrates that the proposed hybrid pattern search method is quite suitable for the global optimization of the aeroelastic tailoring of composite forward-swept wings.

The aerothermal analysis of a hypersonic vehicle is of fundamental interest for designing its configuration. The convection coefficients and wall temperatures due to aerodynamic heating to critical surfaces of a hypersonic vehicle are obtained computationally. Convective heat flux to the swept-back leading edge (SBLE) surface is obtained by splitting the velocity vector along and perpendicular to the surface, and thereby appropriately using the two-dimensional (2D) stagnation region and flat plate heat fluxes together. The main purpose of this work is to propose aerothermal concepts for configuration design of a swept leading edge hypersonic vehicle. Results obtained from these computational analyses reveal the existence of temperature and drag-minimized sweepback, temperature and heat flux-variations-minimized sweepback, and most importantly, the thermally benign sharp SBLE effect. There exists an optimum sweepback angle that is different from drag and temperature-minimized sweepback. These aerothermal concepts are also potential candidates for consideration in the configuration design of hypersonic vehicles.

When a service spacecraft docks successfully with its target spacecraft and forms a docked spacecraft, it will cause a large shift in the dynamics of the docked spacecraft. Not only do the mass properties change, but so do the reaction wheels’ configuration. Meanwhile, the attitude of the docked spacecraft will inevitably change, under the influence of contact and impact, and it may lead to instability of the entire system. Due to the limited control torque and saturation, the control system of the reaction wheel may not guarantee the system stability, and the thruster can generate large control torque, but it consumes valuable jet fuel. Since the space manipulator may generate a greater coupling torque by movement, this paper proposes an attitude coordinated control method for docked spacecraft based on the estimated coupling torque. The method adopts the chaotic particle swarm optimization (CPSO) algorithm to plan the coordinated motion trajectory of space manipulator, and then designs a coordinated control law based on the estimated coupling torque of space manipulator to achieve the attitude control of docked spacecraft in order to guarantee the system stability. Numerical simulations validate the feasibility of the proposed method. In comparison with the traditional attitude control method, the attitude coordinated control method makes use of the coupling torque of the space manipulator, and overcomes the shortcomings of the limited control torque and saturation of reaction wheel, without consuming expensive jet fuel.

During the development of ventilation and air conditioning systems, it is important to verify the functionality of the devised system, especially the method by which air fills the space. In this case, an optical visualization method of introducing helium bubbles into the airflow can be used for this function. A special generator produces small bubbles filled with helium. These bubbles are visible particles of airflow, making it possible to determine the shape of such a flow. This article describes the evaluation of flow images visualized by helium bubbles. Bubbles are detected by comparing intensities and subsequently cleaning faulty bubbles. For a convex airflow shape, exact geometric methods are used, and for a more precisely nonconvex shape of airflow, a genetic algorithm is used, in which a sophisticated algorithm of arranging a boundary line from selected points is applied. The algorithm also includes a specific approach of representing individuals in population inclusive of determining their fitness values.

This attempt addresses the effects of nonlinear thermal radiation and magnetohydrodynamics (MHD) in mixed convection flow of Burgers’ fluid over a stretching sheet embedded in a thermally stratified medium. A transformation method has been employed to reduce the nonlinear partial differential equation (PDE) into the nonlinear ordinary differential equation (ODE). The resulting nonlinear coupled ordinary differential equations are solved for the series solutions. Convergence of derived series solutions is explicitly explored. Physical interpretation of different parameters through graphs and numerical values of local Nusselt number is discussed.

A numerical static aeroelastic analysis procedure, applying a modal approach in coupling the fluid dynamic and structural solutions, is presented. The method is based on a preliminary structural modal analysis from which a number of natural modes is selected to be used in the creation of a fluid dynamic domain morphing criterion. The mesh is made parametric on modal coordinates and updated using a mesh morphing tool based on radial basis functions (RBF) within the progress of the fluid dynamic computation. An intrinsically elastic numerical model is then created, and no further iteration with the structural solver is required. The modal forces are extracted by integrating the pressure on the wall boundaries and used to define the weights of the morphing action of each modal shape. This is a simplifying alternative to the traditional fluid dynamic-structural analysis coupling approach that makes it possible to bypass several complexities related to the implementation of 2-way fluid-structure interaction procedures. Furthermore, the modal approach is not affected by the error introduced by the interpolation required in the load-mapping procedure between the nonconformal fluid dynamic and structural meshes. Piaggio property static experimental measurements of a complete aircraft model in transonic conditions were used to validate the accuracy of the method. The modal solution was also compared to the one obtained by applying a traditional 2-way coupling procedure. The modal analysis was found to provide a solution extremely similar to the 2-way one also if adopting just a few modes.

Structural health monitoring (SHM) has been adopted in the aircraft and civil industries over the last two decades. The ultrasonic guided wave propagation technique is a promising damage detection approach in airplane thin wall structures because of their long distance traveling ability and low attenuation. In fact, by efficiently designing the pattern of sensors one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This detection approach could be effectively assisted by numerical simulation techniques like finite-element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, the finite-element technique is employed for simulation of wave propagation in thin wall structures. Also, the influence of artificial crack (cut-damage) on propagated Lamb waves is investigated. An instantaneous baseline damage detection based on cross-correlation (CC) analysis is carried out to detect the damage, and the results show good agreement with the experimental test results available in the literature. In addition, another proposed instantaneous baseline damage detection technique based on wavelet analysis is examined here. The fast Fourier transform (FFT) and time of flight (TOF) techniques are also used to estimate the size and location of the detected damage instantaneously without the need for prior baseline signals. Conclusively, the numerical simulation can assist in designing an effective a process for damage identification using piezoelectric wafer active sensors. Furthermore, due to the nature of elastic wave velocity in metallic structures, the reported techniques shows that the localization of damage is more accurate than using damage size identification.