Journal of Aerospace Engineering

To understand the response of polymeric materials used in fiber-reinforced composite structures, it is necessary to examine their brittle failure mechanisms under various loading scenarios. As such, this study presents the quasi-static and dynamic fracture response of aerospace resins 3502 and PR-520. Quasi-static fracture investigations were performed on precracked samples using single edge notch tension (SENT) configuration in a standard load frame. Dynamic fracture investigations were conducted using a unique long bar device where a projectile impacts the sample to generate wave-driven Mode-I (opening) fracture. Digital image correlation (DIC) is used in conjunction with ultrahigh-speed imaging to extract the stress intensity factor (SIF) at crack initiation using the stationary crack solution. Both material systems exhibited rate-dependent fracture behavior. For 3502, the average quasi-static fracture toughness was $0.60\mathrm{MPa}\sqrt{\mathrm{m}}$, 56% lower than the average dynamic fracture toughness of $1.07\mathrm{MPa}\sqrt{\mathrm{m}}$. However the PR-520 samples exhibited the opposite behavior, demonstrating greater quasi-static fracture toughness averaging $1.60\mathrm{MPa}\sqrt{\mathrm{m}}$ with dynamic values of $0.71\mathrm{MPa}\sqrt{\mathrm{m}}$. The difference in behavior between the resins may be attributed to polymer chain crosslinking, where the lower degree of crosslinking in PR-520 enables increased elastic deformation and resistance to fracture under quasi-static loading, and the higher degree of crosslinking in 3502 gives rise to an increased resistance to fracture under dynamic loading.

Lighthill’s aeroacoustic analogy connects acoustic source terms with vortical and turbulent structures. For resolving vortical and turbulent structures in computational fluid dynamics (CFD) simulations, mesh refinements in certain regions of the computational domain are crucial. Regarding complex geometric structures, the location of turbulence and, therefore, aeroacoustic source terms cannot be predicted in advance. Iterative approaches, performing multiple transient simulations for establishing sufficient mesh refinements, are computationally demanding. Consequently, we investigate the source location prediction capabilities of coarse Reynolds averaged Navier-Stokes (RANS) simulations in combination with moving reference frames (MRF) to predict the spatial distribution of aeroacoustic source terms for performing mesh refinements. For validating the computed source terms, a detached Eddy simulation (DES) with advanced mesh refinements and a rigid body rotation (RBR) was used. By performing two different grid studies, it could be shown that RANS simulations are capable of predicting quantitative information of the actual aeroacoustic source terms location for any mesh. Furthermore, RANS simulations were capable of resolving global quantities, such as the isentropic efficiency, the pressure ratio, and the mass flow adequately. Connecting those to findings, it is shown that computing source terms are more sensitive regarding mesh coarsening than computing global quantities. Consequently, global measurements cannot be used as an indicator of whether the computed locations of the source terms are still sufficient. However, computing a coarse RANS simulation for obtaining source term locations is about 996 times faster than computing a DES simulation. Furthermore, the main advantage in this study is that for most operating points of a DES simulation, a RANS is necessary to obtain initial conditions.

The optimization of piezoelectric actuator placement has been widely investigated in connection with active vibration control. In this paper, a modified optimization criterion considering the control spillover effect is proposed based on modal controllability. A coupled model of a stiffened plate and piezoelectric stack actuators (PSAs) is designed. By the combination of a genetic algorithm and pattern search algorithm, a hybrid optimization method is developed to obtain the optimal installation locations of PSAs. Furthermore, an active control system is designed by multichannel filtered-x least-mean-square (FxLMS) algorithm to suppress the vibration responses of the stiffened plate subjected to broadband random excitation. Using the optimized placements of PSAs, active vibration control experiments are performed to validate the effectiveness of the proposed optimization criterion. The experimental results show that the vibration responses of the first three modes of the system can be suppressed effectively. Furthermore, compared with the traditional optimization criterion, the use of the proposed optimization criterion can limit the undesirable effects of active control on residual modes. This study demonstrates that the proposed methodology could achieve improvement in active control performance, which can be applied to the vibration control of engineering structures under broadband random loads.

An active attitude control system using a novel six-layer electromagnetic embedded printed magnetorquer for a 3-U nanosatellite is presented in this paper. The proposed design was optimized in terms of size, dissipated power, torque produced, and generated magnetic dipole moment. The designed printed magnetorquer is the optimum choice for a 3-U small-satellite attitude stabilization in terms of reconfigurability, modularity, lower space occupation, low mass, and lower cost. The printed magnetorquer was designed and analyzed for a 3-U nanosatellite with CubeSat standard dimensions of $10\times 10\times 30{\mathrm{cm}}^3$. The design was implemented with commercial off-the-shelf (COTS) high-performance microdevices that are reliable and easily accessible for reducing procurement cost. The printed magnetorquer was embedded in internal layers of a printed circuit board (PCB) that does not require additional space on the satellite. Time-varying rotational analyses were performed for various coil arrangements to test the rotation times for spin-stabilized 3-U nanosatellites. Thermal analysis of the 3-U nanosatellite was done to sustain thermal operation and satisfy the feasibility requirements of the system. Essential performance parameters like magnetic moment generated, resultant torque, and power dissipation were examined for comparison with the existing commercial state of the art. The proposed printed magnetorquer with more configurability ($2\times 3$, $3\times 2$, $1\times 18$, $18\times 1$, $9\times 2$, $6\times 3$ hybrid) features provides versatility to the design aspects by changing the configuration through the onboard computer according to mission needs.

In this paper, the problem of spacecraft formation attitude control in the presence of state constraints has been investigated. Multiple constraints such as a spacecraft’s forbidden-attitude avoidance and also the maximum allowable spacecraft actuation limit have been considered during their reconfiguration maneuvers. Unlike previous papers, spacecraft formation keeping is also considered along with the station-keeping goal during the mission. This is critical when their relative attitudes with respect to each other become important due to implementation issues such as relative forbidden-attitude avoidance. Virtual structure approach with decentralized coordinated control scheme is utilized to perform both station-keeping and formation keeping for each spacecraft. The aforementioned goals achieved by the proposed proportianal-derivative (PD)-like global formation controller are incorporated with a local optimal controller in a close loop manner. Also, convergence and stability analysis based on continuous-time interior point method is presented to guaranty the proposed architecture performance.

The purpose of this study was to investigate the energy-harvesting performance of a piezoelectric free-flying aircraft model under discrete gust. A fluid-structure-electric coupled simulation framework was established by loose coupling the computational fluid dynamics (CFD) solver and the electromechanical finite-element model. The field velocity method was used to introduce vertical gust velocities to the CFD computation. The pitch and plunge rigid degrees of freedom (DOF) were considered, together with elastic DOF in the electromechanical finite-element model by means of multibody dynamics. The output energy density and mean power were used to evaluate the harvesting performance. The effects of external load resistance, free-flow velocity, and gust frequency, especially the rigid DOFs were studied, respectively. A prototype of the piezoelectric free-flying aircraft model was fabricated. The output voltage was tested at different flow velocities and different sinusoidal gust frequencies with a given external load resistance of $10.3\mathrm{M\Omega }$ in the wind tunnel test. The macrofiber composite (MFC) received an optimal voltage of 107 V and an optimal mean power of 0.188 mW at the flow velocity of $22\mathrm{m}/\mathrm{s}$ and a gust frequency of 3.5 Hz, around the first bending mode. Moreover, the electromechanical finite-element model and the coupled simulation framework were verified by the ground vibration test and the wind tunnel test, respectively. Results indicated that the rigid pitch and plunge DOF may decrease the harvested energy to only one-third of the energy of a wall-mounted structure. The present work provides an effective theoretical and experimental basis for further studying the energy harvesting and vibration control of free-flying aircraft.

The complexity of the kinematics and aerodynamics of rotors is a challenging problem for achieving accurate modeling for prediction of rotor loads. The present paper describes an unsteady aerodynamic model based on strip theory for the prediction of local aerodynamic loads on helicopter blades in translational flights. The proposed model accounts aerodynamically for unsteady behavior, poststall, leading-edge suction, and, structurally, local elastic torsion. Also, the local pitching moment coefficient is calculated according to the local parameters of both aerodynamic characteristics and unsteady angle of attack. A case study with published experimental data is selected to validate the model for the same operating conditions. The case is the 7A rotor high-speed test (point 312) performed in the French Space Lab’s (ONERA) S1MA wind tunnel in Modane-Avrieux, France. The proposed model is capable of predicting, qualitatively, the variation in both local normal force and pitching moment coefficients. Computational solver results are compared with experimental results to qualitatively clarify the physical differences between them. The main conclusion is that the proposed model calculations generally reflect the same trends as the test data, providing confidence in the ability to increase the model’s fidelity in calculating the aerodynamic behavior of rotors.

This paper addresses the maintenance of a halo orbit around the $L_1$ point of the Sun-Earth system in a circular restricted three-body problem. To this effect, a trajectory tracking problem is formulated and solved by designing various controllers using the linear quadratic method and Lyapunov stability theory. The linear quadratic formulations are performed using two approaches: the first one linearizes the equations of motion at several operating points, while the second approach uses a state-dependent coefficient system matrix that requires solving the state-dependent Riccati equation (SDRE). To handle the nonlinearity and to reduce the computational complexity as compared to the linear quadratic method, the controller is also derived using Lyapunov stability theory. The proposed controllers are tested for their effectiveness in reducing the orbit insertion errors as well as for disturbance rejection. The disturbances being considered are primarily due to the eccentricity of Earth’s orbit around the Sun, solar radiation pressure, and the gravitational pull of the Moon. The simulation results are presented to delineate the performances of the proposed controllers. The superiority of a Lyapunov theory-based controller over the LQR-based controllers is demonstrated.

Large deformation analyses of structures are of great importance to the evaluation of structural performance under extreme environmental loads, but currently available methods are time-consuming because of the requirement of factorizing large-scale matrices. The inelasticity-separated finite-element method (IS FEM), which can keep the global stiffness matrix unchanged and uses the Woodbury formula as the solver, was presented recently to provide a highly efficient tool for local material nonlinear analysis. To extend the high efficiency advantage of the IS FEM to large deformation analyses, in which the material nonlinearity may be nonlocal and the geometric nonlinearity should be considered, this paper proposes a novel numerical solution scheme by incorporating the updated Lagrangian (UL) formulation into the IS FEM framework. Within this scheme, a Woodbury approximation method (WAM) is introduced as an efficient solver, in which the changing global stiffness matrix is approximated as a constant matrix within a short time period, and a linear equation related to the Schur complement matrix is solved by the combined approximations (CA) method. To eliminate the additional error induced by the approximation, an adaptive iteration strategy (AIS) is presented, in which the approximation error involved in WAM solution is evaluated based on energy norm concept, and the global stiffness matrix is required to be updated adaptively according to the calculated error. The high efficiency and accuracy of the proposed method are finally demonstrated by the time complexity analysis and numerical examples.

It is seemingly inevitable that one day humans will land on the surface of Mars. Between the Apollo lunar missions, International Space Station, and Martian rovers and landers, much of the technology required to transport astronauts to Mars already exists; however, how those humans will live and sustain themselves on the Martian surface is yet to be clearly defined. Since at least the 1980s, researchers have envisioned what a Martian habitat may look like and what its inhabitants will require. Spanning from domed cities to lava tube shelters, the bases of conceived designs are vast. Through NASA’s 3D-Printed Habitat Challenge, the American space agency has put large-scale 3D-printing technology at the forefront of this endeavor. This paper presents the rationale for the Martian habitat designed by Northwestern University, in partnership with Skidmore, Owings and Merrill, for submission in NASA’s 3D-Printing Habitat Challenge Virtual Design Levels. The habitat includes housing for four astronauts, room for one year of supplies, $93{\mathrm{m}}^2$ living space, and various prescribed volumes of equipment, to name a few. Defined by a unique outer-parabolic and inner-hemispherical shell, the proposed habitat takes a 3D-printing-centered approach for its architecture and fabrication.

Reducing rotor blade–vortex interaction (BVI) noise is a major challenge in rotorcraft research. This paper presents a high-resolution numerical study of the effects of blade surface blowing on BVI noise reduction. Using the improved fifth-order weighted essentially non-oscillatory (WENO-Z) scheme and high-resolution grid system, BVI noise is accurately predicted in the nonblowing baseline case. Four slot locations are examined to study the effects of jet slot location on the control of BVI noise. Additionally, the parametric effects of jet velocity and jet slot area are analyzed. Blowing near the trailing edge on the upper surface is effective for weakening BVI. The optimal jet velocity for reducing BVI noise is 20% of the rotor tip speed, which is $45.2\mathrm{m}/\mathrm{s}$ in the case study. Compared with the baseline case, the sound pressure level is reduced by 3.6 dB. By adjusting the jet slot area, surface blowing can effectively reduce the rotor BVI noise by over 3 dB with minimal thrust penalties.

Blade-vortex interaction (BVI) noise is a significant source of rotor noise. In recent years, active flap control (AFC) has been used successfully to control BVI by adding a trailing edge flap to the blade. However, due to the rotor’s complex shape and motion in AFC, the accurate simulation of the motion and unsteady flow field is challenging. Therefore, studies of noise control by AFC have mostly focused on experimental methods. Few numerical simulations were conducted on the noise reduction mechanism. In order to understand the noise reduction mechanism of the AFC clearly, this paper establishes a computational fluid dynamics (CFD) method based on an overset grid and tries to simulate the AFC airfoil flow field with the artificial vortex interaction. The noise characteristics are obtained from an acoustic analogy method based on the Farassat 1A (F1A) equation. By parameter analysis study and by testing the airfoil load and vertical interference distance, the results show that the proposed active control method exactly reduces the airfoil-vortex interaction noise. A maximum noise reduction of 1.56 dB is observed, and the most critical control parameter is the deflection phase of the trailing edge. When the vortex core passes over the airfoil, the load fluctuation and the interaction noise can be reduced by an upward deflection of the trailing edge. The flapping of the trailing edge significantly changes the vortex core’s path, which can further control the downstream airfoil-vortex interaction and achieve noise reduction.

Honeycomb-core sandwich structures are commonly utilized as orbital debris shielding in unmanned satellites. This study investigated the effects of projectile shape on the ballistic performance of aluminum honeycomb-core sandwich panels subjected to $7\mathrm{km}/\mathrm{s}$ (hypervelocity) impacts at normal incidence. The shape of the reference projectile was a sphere, and other projectiles had a disk topology, including simple disks and disks with a central hole (ring projectiles), with different aspect ratios. To facilitate the investigation, a numerical simulation model was developed and verified against experimental data and predictions from an empirical ballistic limit equation. The verified model was then used to investigate hypervelocity impact scenarios involving different projectile shapes, honeycomb grades with different cell sizes, and different projectile/honeycomb cell alignments. It was found that of the shapes considered here, ring projectiles were of the highest concern: the volume of a $7\mathrm{km}/\mathrm{s}$ ring projectile that could be resisted by a honeycomb-core sandwich panel without perforation of the rear facesheet was 1.65 times lower than that of a spherical projectile. In contrast, simulations with simple disks (without a central hole) did not show any significant change in the ballistic performance of the panel compared to impacts with a spherical projectile. Additional simulations conducted with ring projectiles demonstrated the strong influence of honeycomb cell size and projectile/honeycomb cell alignment on damage to the rear facesheet of the panel.

In this paper, a passive fault tolerant attitude control is investigated for a nano-satellite with three magnetorquers and one reaction wheel in the presence of actuator constraints, external disturbances, and partial loss of actuator effectiveness as unknown actuator faults. For this purpose, a variable structure control approach is employed due to its ability to deal with the partial loss of actuator effectiveness and adjusting the maximum amplitude of the control signal by a control gain. A modified sliding variable is designed based on angular velocity and attitude errors with an adaptive parameter coefficient. The dynamics equation of the adaptive parameter is extracted during the stability proof of the closed-loop system. Changing the value of this parameter changes the effect intensity of the quaternion errors on the sliding variable and causes the attitude errors to maintain within a limited range. Applying this parameter to the modified sliding variable makes the controller perform well even if the adaptive parameter is significantly reduced. Furthermore, directly using the adaptive parameter in the structure of control law makes the controller generate a chattering-free torque. Comparing the simulation results with the results of two variable structure control methods designed in previous articles shows that its performance in attitude tracking commands has improved. In addition, Monte Carlo simulations with random actuator faults are performed to show the robustness of the proposed controller in the presence of actuator constraints and external disturbances.

In this study, overlapped biaxial and seamless twill carbon fiber pipes and vessels were manufactured. Steel pressure vessels were repaired with flexible twill and biaxial fabric. The pipes and vessels were subjected to hydrostatic pressure, internal cyclic pressure, postfatigue functional failure (FF) and burst pressure. Overlapped tubes with composite and metallic end caps experience premature FF at less than 50% of the theoretical pressure due to delamination. However, seamless tubes almost reached the theoretical pressure. Fatigue tests were applied to the tubes at stress levels of 45% and 75% FF pressure up to 9,000 cycles. Thin seamless tubes sustained the cyclic hydrostatic pressure at 45% of FF up to 9,000 cycles, while at 75% of FF some slight damage occurred. The overlapped tubes showed little damage at 45% FF after 9,000 cycles, but severe damage at 75% FF with an explosion. The fatigued seamless and overlapped composite tubes showed a maximum of 30% and 50% reduction of FF pressures. The reorientation of the flexible fiber tows in seamless vessels is the primary energy dissipation mechanism and avoids failure. The repaired pressure vessels experienced FF at 40% of the theoretical FF. The ASME boiler and pressure vessel equations safely predict the load-carrying capacity of the seamless tubes.

In situ resource utilization (ISRU) of lunar regolith is indispensable for the success of large-scale and long-term human lunar explosions at lower costs. Many new technologies must be developed to realize efficient ISRU. Because particle sorting is one of the essential processes of ISRU, a unique technology has been developed using the balance between electrodynamic and gravitational forces. First, a sorting system using an electrodynamic standing wave was developed. The particles on the parallel-line electrodes were agitated by the electrodynamic force created by the application of a standing wave, and floated small particles at a high altitude were collected in a box located above the electrodes. The experiment and numerical calculation indicated that although a high collecting position was preferable for sorting small particles, a large number of small particles hardly reached a high position and a high yield was not attained. Next, an improved sorting system that uses a traveling wave instead of a standing wave was developed to mitigate the incompatibility. When a four-phase high voltage is applied to the vertically supported parallel-line electrodes, an electrodynamic traveling wave is formed above the electrodes, forcing small regolith particles to move upward at a high position, while large particles are apt to fall. Additionally, particles were fed through a vibrating sieve to break off the aggregated particles. Finally, an averaged particle size of $12\mu \mathrm{m}$ and 30% in a yield of particles less than $10\mu \mathrm{m}$ particles was attained. The system would be suitable for space applications because it is simple, lightweight, has low power consumption, and does not require any mechanical drive or consumables.

In this paper, computational fluid dynamics (CFD) numerical simulation and wind tunnel tests are used to study the wind environment of typical buildings in coastal cities. Firstly, the geometric three-dimensional model is established, and the overall wind environment characteristics of the building complex are determined by wind tunnel testing. Secondly, the experimental data are used to fit the inflow wind profile and turbulence profile, and the secondary development is used as the entrance boundary condition of large eddy simulation (LES). In order to ensure the accuracy of the numerical simulation, the grid of the numerical simulation model is analyzed. Finally, the flow field characteristics and distribution patterns of staggered buildings are obtained by numerical simulation. The results show that when the wind tunnel test is used as the boundary condition of the numerical simulation entrance, the velocity of the numerical wind field in the atmospheric boundary layer environment decreases gradually due to the occlusion effect of the front buildings. Only considering the velocity wind profile as the inflow condition, the results are quite different from the wind tunnel test results. If considering the effect of turbulence profile and velocity wind profile simultaneously, the deviation is smaller. The flow field is different in different wind directions. The wind environment of the buildings in the back row at the 0° wind direction angle is deeply affected by the buildings in the front row. The reduction degree of wind speed is high at the 30° and 60° wind direction angles. The wind speed of the ventilation corridor along the 90° wind direction angle is faster, but the area of the static wind area at the leeward side of the buildings is larger, which is not conducive to the air circulation.

The closed-loop performance of an inertial stable platform (ISP) affects the operation of navigation in moving objects. In this paper, the issue of high-performance control of ISP is discussed. By proposing a novel backstepping controller, the ISP plant with external stochastic disturbance, unknown dynamics, and actuator saturation is stabilized and regulated to the desired reference. Since unfamiliar terms appear in the practical ISP plant, a novel adaptive neural network model is suggested. To deal with the stochastic disturbance and modeling error, the stochastic bounded stability scheme is considered. Moreover, the practical problem of actuator saturation is involved in the design procedure. The suggested robust controller needs only one scalar adaptation law for all of the neural network gains. The virtual command inputs are propagated into a first-order filter to eliminate the conventional procedure of calculating the time-derivative terms. Eventually, a novel control technique is suggested for a nonlinear three Degrees of Freedom (3-DOF) ISP plant case study. Results illustrate the high performance of the robust controller in the presence of stochastic disturbance and input saturation.

This paper investigates the dynamical behaviors of Earth frozen orbits including the critical inclination orbit in the zonal problem with terms of perturbations up to $J_{15}$. From the mean element theory, an analytical expansion of the dynamics model is derived to obtain the frozen conditions. The global existence of Earth frozen orbits is numerically illustrated by exploration of equilibria in the equations of motion based on Lagrangian formulations. Frozen orbits are widely located at the inclination between 0° and 90°, which may be grouped into families: one for the elliptic orbit case, another for the quasicircular orbit case and the other for the critical inclination orbit case. For the elliptic and quasicircular orbit cases, orbits evolve periodically around the frozen ones, and elliptic orbits tend to be more sensitive than quasicircular ones with respect to variation of initial orbital elements. Frozen orbit bifurcations near the critical inclination are shown to illustrate the origins, evolutions, and stability of frozen orbits. For the last critical inclination case, it is observed that eccentricities keep evolving periodically instead of being frozen at the specified ones compared with that in the $J_2$ problem, and then a relationship between the evolution period and terms of zonal perturbations is illustrated.

A new design method of scramjet nozzles within predetermined geometrical space is proposed to optimize the nozzle aerodynamic performance. The main characteristic of the proposed method is that the design factors and flow angle are employed to control the nozzle configuration and customize the performance. Firstly, the proposed method and the method of characteristics are introduced. Secondly, the grid resolution is studied, and the proposed method is validated using the computational fluid dynamics (CFD) approach. Then, impact studies are carried out on the design factors and the flow angle in the nozzle design process. The results show that the asymmetry factor has little effect on thrust coefficient, and the lift and pitching moment firstly increase and then decrease with the increase of the asymmetry factor. The thrust coefficient increases firstly and then decreases with the increase of the flow angle, whereas both the lift and the pitching moment present approximately linear increasing trends. After that, the superiority of the proposed method is demonstrated by comparing with the traditional method. The proposed method can improve the thrust coefficient, lift, and pitching moment by 33.94%, 326.42%, and 32.24% at identical design conditions. Finally, a cold flow experiment and the three-dimensional CFD are conducted out to evaluate the effectiveness and accuracy of the proposed method. The experimental results show good agreement with that of numerical simulation. In conclusion, the proposed method not only fully utilizes the geometrical space to increase the aerodynamic performance but also provide further customizability and flexibility in the nozzle design.

The paper considers practical aspects of mathematical modeling in predictions of the level of near-field pressure pulsations of a near-future prototype supersonic business aircraft. A numerical modeling technique based on the numerical solution of the Navier-Stokes equations is proposed. The method is verified by near-field simulations of the NASA C608 supersonic low-boom demonstrator. We consider a supersonic flight with $M=1.4$ at a flight altitude of 16,215 m. Good convergence of our predictions with experimental data and results of other researchers is shown. Near-field sonic-boom simulations of the prototype supersonic business aircraft are used to illustrate how the method can be applied in practice for building a second-generation supersonic passenger aircraft. Two aerodynamic configurations of the aircraft are considered: no-tail and canard no-tail. The canard no-tail configuration in the as-is aircraft dimension and design was found to have no advantages over the no-tail configuration in the level of its near-field pressure pulsations because of its nonoptimality. Further recommendations for solving the near-field sonic-boom minimization problem are related to the construction of a comprehensive mathematical model enabling coupled simulations due to smooth integration of a parametrized aircraft geometry, an aerodynamic solver, and an optimizer.

With the development of hypersonic vehicles, considerable attention has been paid to thermal protection systems (TPSs). Among the different types of TPS, integrated TPS (ITPS) has attracted extensive interest because of its light weight, cost effectiveness, bearing capacity, and easy maintenance. However, ITPS, with its complex structure and reusable requirement, is facing challenges and it is worth devoting much effort to this. In an effort to overcome these challenges, we develop a novel approximate analytical method based on separation of variables and orthogonal expansion technique, which is presented for the prediction of heat transfer. The approximate analytical method has the ability to consider the effects of temperature-dependent thermal material properties, convection and radiation. Moreover, a ${\mathrm{C}}^0$ higher-order layer-wise finite-element model combined with homogenization techniques and a simplified three-dimensional (3D) finite-element model based on the periodic structure characteristic are proposed to estimate the thermal–mechanical response and stability of ITPS effectively. In addition, an optimization procedure based on the proposed methods for ITPS is developed. Implementation of the optimization is demonstrated by applying it to design the ITPS of space shuttles and hypersonic vehicles. By comparing with conventional thermal protection systems (CTPSs), ITPS exhibits an outstanding advantage in weight and an acceptable disadvantage in size. The objective of this paper is to establish an accurate and efficient design method aiming at determination of the optimal performance of ITPS, and puts forward the foundation for the development of a hypersonic vehicle.

This paper investigates the robust continuous fractional-order nonlinear sliding mode (RCFONSM) control scheme for controlling a disturbed uncertain quadrotor (DUQ). First, the fractional-order nonsingular terminal sliding mode (FONTSM) manifolds are designed for the altitude and attitude, and a finite-time convergence is realized in the sliding mode phases of the DUQ system. Then, based on fast terminal sliding, reaching laws are proposed to enhance the tracking performance against disturbances and ensure finite-time convergence in the reaching phases of the DUQ system. The proposed robust continuous fractional-order nonsingular terminal sliding mode (RCFONTSM) switch element may effectively improve the dynamical performance of the fractional-order nonlinear sliding mode (FONSM) surface by substituting the integral and derivative operators with fractional-order operators for the error dynamics. The Lyapunov theory is used to prove the stability of the tracking errors and the stabilization of the DUQ simultaneously. The proposed sliding manifolds and fast reaching laws ensured good robustness against disturbances/uncertainties, fast convergence, and high precision. Numerical simulation of the proposed controller compared with fractional-order (FO) backstepping sliding mode control (SMC) is given to demonstrate the superiority of the RCFONSM.

The compliance of the mixed-mode bending (MMB) test fixtures can influence the interlaminar fracture toughness measurements for different mixed-mode ratios in an unpredictable way. The purpose of this article is to introduce the improved mixed-mode bending (IMMB) apparatus with slight modifications to the current MMB apparatus and universally recognized by current standards. The MMB apparatus is used to measure any Mode I to Mode II strain energy release rate (SERR) ratio from 0 to approximately 5. The original MMB components were investigated using a finite-element optimization algorithm and an analytical model for exploring the relationship between the component’s stiffnesses and MMB compliance. Two IMMB designs are presented. The first design addresses MMB’s compliance by modifying the dimensions of the most impactful components. The second design introduces new components in addition to dimensional changes to maximally increase MMB stiffness. The new designs enhance the MMB apparatus’s stiffness by 27% and 87%, respectively.

Flat-ended projectiles were used to impact three distinct thicknesses of 2024-T351 plate. Ballistic limit velocities were determined, and optical microscopic examination revealed evidence of adiabatic shear bands within the impacted plates, which can result in a low-energy failure mechanism and reduced ballistic performance. A two-dimensional axisymmetric numerical model was developed in LS-DYNA to model the impacts using the generalized incremental stress state model (GISSMO). This provided an improved understanding of the formation of adiabatic shear bands in the aluminum and how adiabatic shear failure can be predicted using an instability criterion.

Computational fluid dynamics is applied to reproduce the characteristics of the liquid methanol burner presented by the National Institute of Standards and Technology (NIST). Reynolds average Navier-Stokes (RANS) and large-eddy simulations (LES) are employed, along with the steady nonadiabatic flamelets combustion model (using an extended reaction mechanism). The spray is not directly simulated, but instead, the linearized instability sheet atomization (LISA) model is implemented. The results obtained with RANS are used to estimate the scales of turbulence and design a mesh suitable for LES. The velocity field, spray characteristics, temperature, and combustion products are compared against the experimental data reported in the literature. Both simulations show similar results, differing mainly in the spray characteristics (size of the injected droplets). This seems to be related to the parameters of the Rosin-Rammler distribution used by the LISA model. Although a fraction of the spray evaporates downstream of the reaction zone, the fraction of unburned fuel is underestimated, which is expected considering the assumption of infinitely fast reaction. There is no formation of a vortex breakdown nor strong recirculation zone in the flow (due to the relatively low swirl number); nevertheless, some coherent structures are reproduced, showing the capacity of LES to capture the bigger scales of turbulence.

This paper proposes a robust adaptive predefined-time control scheme for spacecraft rendezvous maneuvers with the consideration of input saturation and external disturbances. To ensure the rendezvous maneuver completing within a predefined time, a constructive performance function is utilized to impose time-varying constraints on system errors. Subsequently, a nonlinear mapping method is employed to transform the constrained problem into an unconstrained one, thus simplifying the design process significantly. Then, two compensation signals are introduced by the feat of an auxiliary system to optimize the steady-state performance of the system. With the combination of backstepping design and compensating signals, the input saturation constraint will be dealt with properly. All of the closed-loop signals are proved to be bounded under the proposed controller. Finally, simulation results demonstrate the validity of the proposed control scheme.

Oxygen-consuming fuel tank inerting technology is a novel technology with a simple structure and a high efficiency for tank explosion suppression based on flameless catalytic combustion. To verify the feasibility of the oxygen-consuming inerting system for RP-3 aviation fuel tanks, a test bench was constructed based on a self-developed catalyst, and the system performance was studied on the ground. The results showed that both the oxygen volume fraction in the fuel tank and the mixed inert gas decreased gradually with time, and the oxygen volume fraction in the tank dropped to 12% and 9% after 11.3 and 15.3 min, respectively, which demonstrated that the oxygen-consuming inerting system for RP-3 fuel tanks was successful. In addition, the influence of key parameters on the system performance was also analyzed. The results indicated that the higher the fan flow, inlet gas temperature, and fuel temperature, the faster the oxygen volume fraction decreased. In addition, the formation of CO, NO, and ${\mathrm{SO}}_2$ was also observed during the experiment. The research results can be used as references for the application of oxygen-consuming inerting systems for RP-3 aviation fuel tanks.