Journal of Aerospace Engineering

This paper reports on a method developed for predicting the fretting wear-fatigue of an aero-engine’s involute spline couplings, including finite-element analysis, method development, and model prediction. The contact stress and sliding distance of the engine’s spline couplings have been investigated using the finite-element method. The fretting wear was calculated based on modified Archard’s equations and application of the in-built Arbitrary-Lagrangian-Eulerian (ALE) adaptive mesh-smoothing algorithm in Abaqus software. Ignoring the direction and position of the fretting fatigue cracks and taking into consideration the influence of fretting wear on fretting fatigue, a method for estimating the fretting wear-fatigue life of an aero-engine’s involute spline couplings has been proposed in this paper. The results have shown that the contact stress was proportional to the torque, which first decreased before increasing when the contact region moved from the top of the tooth to its root. Following this increase, the sliding distance started to decrease along the axial direction of the spline tooth. In order to improve the fretting wear-fatigue life of the spline coupling, further measures should be taken to reduce the dynamic load factor of the spline coupling as far as possible, as well as to increase the contact length of the spline coupling and reduce the friction coefficient of the spline coupling’s materials. A reliable numerical basis for the design and maintenance of aero-engine’s involute spline couplings has been provided in this paper.

The aerodynamic performance of long-span bridges under extreme environmental conditions, such as under strong winds and heavy traffic, is critical for bridge design. Either free vibrational or forced vibrational tests are usually carried out to obtain the flutter derivatives, either traditional eight flutter derivatives from two-degree-of-freedom (2-DOF) model tests or 18 flutter derivatives from 3-DOF model tests, to evaluate structural dynamic performance. In the present study, an experimental facility is developed based upon a digitally controlled 3-DOF forced vibration system to enable the extraction of 18 flutter derivatives of bridge decks through wind-tunnel tests. After validating the proposed forced vibration test facility using typical section types, i.e., a thin-plate section and a truss-girder section, the 18 flutter derivatives for the truss-girder section are extracted and used for bridge dynamic performance assessment considering combined loads from traffic and wind. The case study of a truss bridge shows that ignorance of the additional 10 flutter derivatives can result in a significant overestimation of the bridge lateral responses, especially under high wind speeds. However, ignorance of the additional 10 flutter derivatives on the bridge vertical and torsional responses, as well as on the dynamic responses of the running vehicles, are not significant. Similar observation were also applied to the stress responses at the critical location of the bridge deck.

Wind tunnel experimental tests were performed to investigate the influence of the damage to the Tu-154M aircraft wing on its aerodynamic performance. The wing damage concerned the detachment of one-third of the aircraft left wing and the loss of the left slat and flap and the loss of the left outer wing. The presented research referred to the Polish government aircraft Tu-154M disaster near the Smolensk airdrome on October 4, 2010, and one of the hypotheses about its causes. The experimental investigation was carried out in the Institute of Aviation low speed wind tunnel T-1 with a 1.5 m diameter test section at the ${\mathrm{V}}_{\infty }=40\mathrm{m}/\mathrm{s}$. The Tu-154M aircraft model at the $1:40$ scale was used. Aircraft aerodynamic characteristics were obtained by balance measurements. Wind tunnel tests showed that the damage of the aircraft left wing results in the appearance of the aircraft rolling moment of a significant value. The investigation proved that in the case of one-third wingtip loss there were opportunities to balance the aircraft flight by simultaneous aileron (at 20°) and spoiler deflection (at 45°) on the right wing or by putting the aircraft into a sideslip.

The utilization of composite carbon–epoxy tubes for space structures, such as antennas and solar arrays, has attracted considerable attention in recent decades due to their high strength-to-weight ratio and multifunctional applications. Among complex space environmental factors, thermal effects induced by uneven solar irradiance could generate temperature stress, cause thermal behavior and affect the guidance and control of spacecraft structures. In this paper, a series of temperature experiments for the identification of material properties and ground vacuum radiant experiments for the determination of the structural behavior of a composite carbon–epoxy tube are carried out with respect to space environments. Moreover, numerical models on the basis of experimental observations are developed to investigate corresponding thermal and structural behavior. It is found that the specific heat and thermal conductivity of two typical specimens increase linearly with temperature rise and are dependent on carbon directions. For thermal and structural experiments, a significant temperature difference of 30°C exists between top and bottom surfaces resulting from different radiation and heat conduction. A temperature difference of 8.7°C is found in the thick direction on the bottom surface, which could result in noticeable shear deformation during the service period. Average strains on top and bottom surfaces are $-\mathrm{1,526}$ and $-\mathrm{1,310}\mathrm{\mu \epsilon }$, respectively. Furthermore, numerical temperatures on the top surface are in good agreement with experimental results, while those on the bottom surface are higher than experimental temperatures due to the radiant effects of the chamber and complex interactions between the tube and tracks. A further numerical analysis on the thermal and structural behavior of the supporting frame could provide guidance for designing future corresponding structures.

This paper presents a probabilistic analysis methodology for a nonablative thermal protection system (TPS) of spacecraft at the conceptual design stage. The probabilistic analysis focuses on uncertainty characterization and uncertainty in failure prediction. TPS selection and sizing using sequential quadratic programming design optimization are first performed to provide the nominal values of the distribution parameters for uncertainty parameters such as the allowable temperature limits and thickness of TPS materials. Multi-input and multi-output support vector machines are utilized to approximate the thermal responses when failure modes are constructed, which dramatically reduces computational effort. Generalized subset simulation is used to estimate the failure probabilities at all nodes with a single simulation run, which further reduces the computational burden. The proposed methodology is applied to a lifting body vehicle model and a spacecraft model for conceptual design. Difficulties encountered and the performance of the method are investigated.

This study attempts to provide and analyze the performance parameters and transient features of a long-time working hybrid rocket motor (HRM) for its potential applications. To conduct the long-time working HRM firing tests, an experimental system was designed. Two long-time firing tests of HRMs, using hydroxyl-terminated polybutadiene as the base fuel and 98% hydrogen peroxide as the oxidizer, were carried out. The working time of the two tests was 192 and 202 s, respectively. A data-processing program was developed to estimate and deal with the test data, and the transient parameters and motor performances were then determined and analyzed. The results show that chamber pressure and motor thrust decrease with working time, due to the nozzle erosion and regression rate reduction, in which the former has a significant effect. The growth of grain port diameter is the main cause of the decrease of regression rate with time. As the time goes on to 200 s, the regression rate decreases from about 0.5 to $0.1\mathrm{mm}/\mathrm{s}$. The oxidizer-to-fuel ratio has a large variation during the firing test, which makes it deviate from an optimum condition and therefore reduces the motor working efficiency. The long-time working tests of the two HRMs have a lower specific impulse, which is mainly caused by serious nozzle erosion.

Computational costs of robust-based design optimization methods may be very high. Evaluation of new procedures for the management of uncertainty with applications to hybrid rocket engines is here carried out. Two newly developed procedures are presented (hybrid algorithm and iterated local search), and their performances are compared with those of two previously developed procedures (genetic algorithm and particle swarm optimization). A liquid oxygen/paraffin-based fuel hybrid rocket engine that powers the third stage of a Vega-like launcher is considered. The conditions at third-stage ignition are assigned, and a proper set of parameters are used to define the engine design and compute the payload mass. Uncertainties in the regression rate are taken into account. An indirect trajectory optimization approach is used to determine a mission-specific objective function, which takes into account both the payload mass and ability of the rocket to reach the required final orbit despite uncertainties. Results show that for this kind of problem, particle swarm optimization and iterated local search outperform the genetic algorithm, but the use of a local search operator may slightly improve its performance.

Civil aircraft with electric taxi systems use traction motors to rotate their wheels to move on the ground. When these aircrafts land on a runway, they are able to prerotate main wheels to reduce longitudinal forces applied on the wheels by the runway. To analyze the longitudinal forces, a new rigid-flex coupling prototype model was established. The new model consists of an aircraft body with six degree-of-freedom flexible landing struts and powered main wheels. Based on the new model, landing simulations were performed to analyze the dynamic responses of the powered main wheels. The dynamic responses included spin-up and spring back of the wheels, which were caused by extreme spin-up and spring back drag loads. The extreme loads applied on tires under three landing conditions were obtained and compared. After landing simulations, ground taxiing simulations were performed to analyze the dynamic responses of the powered main wheels. In the ground taxiing simulations, the aircraft movement was driven by the powered main wheels instead of by the main engines. Through the simulations of the powered main wheels, three conclusions were obtained: the prerotation of the powered main wheel decreases the spin-up and spring back drag loads; the rigid-flex coupling prototype model caused more vibration of the longitudinal forces; and adopting the powered main wheels for turning results in a smaller turning radius than using the main engines.

The present investigations are centered on understanding the discrepancies in shock wave boundary-layer interaction (SWBLI) for perfect and real gas laminar flows. In view of this, the in-house-developed computational fluid dynamics (CFD) solvers are integrated with a gradient-based optimization algorithm to predict the critical radii of SWBLI in the case of perfect and real gas flows. The developed high-fidelity approach has been observed to be useful in the precise estimation of critical radii of bluntness. Further, studies for SWBLI revealed that real gas effects reduce the extent of separation in comparison with the perfect gas flow and also necessitate lower magnitudes of critical radii. It has been noted that a reduced requirement of a high entropy layer thickness and upstream overpressure region demonstrate a need for a lower value of inversion and equivalent radii for real gas flow conditions. Therefore, a larger estimate of the equivalent radius of SWBLI, obtained for perfect gas flow conditions, or any radius larger than that would definitely provide the necessary separation control for real gas flows.

This paper provides a new, relatively fast procedure of high-aspect-ratio wing design for endurance maximization. It is based on genetic algorithm and allows optimizing a set of airfoils along the wingspan without time-expensive computations. In this method, the airfoils are optimized in a segregated manner using lift coefficient distribution along the wingspan. The trim drag is taken into account by means of a special algorithm. The design method is implemented in the computer program NeoOptimizer, specially developed for aerodynamic optimization tasks. The program uses XFOIL code to evaluate aerodynamic characteristics of the airfoils. It is especially applicable to low-Reynolds-number regimes. A test case of the high-aspect-ratio wing was considered. Two airfoils for this wing were designed to minimize drag at the maximum flight duration regime.

Experimental and computational investigations were performed on a 76-40° sweep double-delta wing (DDW) at different angles of attack corresponding to a Reynolds number of 220,000 based on chord length. Experiments consisted of the measurements of forces and moments and surface flow visualization using oil flow technique. Effect of the anhedral and dihedral angles over a DDW was obtained. Results indicated that the use of small anhedral angle compels the vortices to move inward and helps in the augmentation of the lift at higher angles of attack in comparison with the case of nonplanar and dihedral angles. Reasonable agreement of experiments and computation was observed.

In this research, free vibration analysis of composite-faced soft-core sandwich plates is conducted using a higher-order theory. Third-order shear theory is used to model face sheets and third- and second-order functions are used to model the in-plane and transverse displacements of the core. Therefore, the in-plane and transverse flexibility of the core is considered in this theory. The theory is also capable of satisfying the continuity of transverse shear stresses and zero shear stress conditions on both upper and lower surfaces of a plate. The equations of motion are derived using Hamilton’s principle, and an analytical solution of these equations is presented for simply supported sandwich plates. To evaluate the accuracy and efficiency of the present theory, the obtained results are compared with those obtained by the elasticity method and other valid theories. Studies show that the results of the present theory fit quite well with accurate answers.

Local roof failure is the most typical form of wind-induced failure of large-span terminals, especially in southeast coastal regions with frequent occurrence of strong typhoons. Since existing theoretical systems of typhoon model in civil engineering are too simplified, the mesoscale weather research and forecasting (WRF) mode based on the non-static-equilibrium Eulerian equation model was introduced into for high temporal-spatial resolution simulation of the Typhoon Megi. Wind field characteristics in the landing process of Megi, including wind intensity, pressure intensity, rainfall intensity and temperature stratification, were analyzed by the multigrid nesting technology in mesoscale mode. Key attentions were paid to wind direction angles and wind intensity before, during, and after the landing of Megi. Results verified the validity of the mesoscale simulation of Megi. Later, the wind velocity profile in the boundary layer of the typhoon field was gained by combining the nonlinear least-squares method. The three-dimensional (3D) flow field information and the time history of surface fluctuating wind pressure of the roof system of the terminals in Xiamen International Airport were acquired from three-dimensional wind field simulation under typhoon and Type A monsoon (hereinafter referred to as monsoon) conditions. The three-dimensional wind field simulation was accomplished by the microscale computational fluid dynamics (CFD) large-eddy simulation technique. On this basis, the mechanisms of flow field action and spatial characteristics of mean wind pressures, fluctuating wind pressure and extreme wind pressure on roof surface under monsoon and typhoon conditions were compared. Moreover, correlation, coherence, power spectral characteristics, and non-Gaussian characteristics of fluctuating wind pressure were analyzed. Results demonstrate that the WRF/CFD coupling mode can simulate a typhoon field in terminals effectively. A mesoscale typhoon can increase the mean wind pressures, fluctuating wind pressure, and extreme wind pressure on roofs significantly, which all occur on the upper-eave areas. The non-Gaussian characteristics of wind pressures on a terminal roof under typhoon conditions are influenced greatly by wind direction angle, but the correlation of time-frequency domain of wind pressures is weak. Major research conclusions not only provide some references for prediction of wind loads on similar large-span spatial structures under typhoon conditions, but also deepen understanding on the nesting mechanism of mesoscale/microscale wind fields.

The wind records in a basic interval are usually regarded as a stationary random process in analysis of wind characteristics. However, field measurements have also captured nonstationary features of the boundary layer wind during extreme wind events. To reasonably characterize the wind records, the nonstationarity of the signals should be evaluated properly before signal processing. In this study, the local recurrence rate loss (LRRL) is proposed as a novel recurrence measure for nonstationarity evaluation of wind records. Specifically, the LRRL is defined as the quality loss function (QLF) of the local recurrence rate (LRR) that is conducted from the recurrence plot (RP) using the recurrence quantification analysis (RQA). To demonstrate the feasibility of the proposed LRRL, five typical signals are utilized first to evaluate its performance. Subsequently, the extreme wind records collected from the structural health monitoring system (SHMS) installed on the Sutong Bridge is employed to further assess the performance of the proposed LRRL. For both the synthetic signals and real-time wind records, the commonly used measure recurrence trend (RT) is presented for comparison purpose. The results show that the proposed LRRL performs better than the RT in nonstationarity evaluation of both the synthetic signals and real-time wind records.

Owing to the complexity of aircraft structural damage, directly measuring the pattern and severity of damage using onboard sensors is difficult. This paper proposes a linear parameter-varying (LPV) model–based online estimation and indirect adaptive control scheme for aircraft with severe structural damage. Specifically, the unmeasurable damage parameters are designed as the gain scheduling coefficients (GSCs) of the LPV model. By employing the proposed LPV model, the online computational load is significantly reduced compared with that of typical existing methods. Furthermore, an online identification algorithm with a Lyapunov stability guarantee is presented to estimate the GSCs, and an online-designed model reference controller that combines a state-feedback decoupling controller and a disturbance rejection term is adopted to implement attitude control. The closed-loop system is simulated with the National Aeronautics and Space Administration (NASA) generic transport model under a left wing tip damage scenario. The simulation results demonstrate that the proposed method can estimate GSCs and the uncertainty of the aircraft rapidly and accurately, and the closed-loop system precisely achieves the desired attitude responses.

As fluid sloshing usually brings some serious issues on the safe storage and transportation of cryogenic fuels, some in-depth investigations should be conducted to improve its negative effects. In the present study, the fluid sloshing hydrodynamic performance in a cryogenic storage tank is numerically investigated under different types of sloshing excitation. Both the external heat penetration and the internal heat exchange are accounted for in the numerical model. With the external sloshing excitation realized by user-defined functions, the free interface fluctuation is predicted with the volume-of-fluid method. Meanwhile, the treatment of mesh motion is adopted as well. The model validation is made against the related experimental results, and the maximum relative errors are limited in 5.0%. On the basis of the developed model, the sloshing force and moment suffered by the tank are calculated. The pressure variations of vapor and liquid monitors are predicted. Moreover, the interface dynamic response is specially investigated in different sloshing excitations. It shows that the intermittent sloshing excitation has some influence on the hydrodynamic characteristics in the liquid oxygen tank. With some valuable conclusions obtained, the present study is significant to the proper design of tank pressure adjustments by adopting the unconventional sloshing excitation.

The efficiency of a solar energy collection (SEC) is of great significance to the power generation and overall efficiency of a space solar power satellite (SSPS). The Orb-Shape Membrane Energy Gathering Array (OMEGA) SSPS concept, inspired by the Arbitrarily Large Phased Array (ALPHA) SSPS, is designed for modular assembly, and the spherical condenser is subdivided into many polygons. Deployable beams, surrounding these polygons and acting as a support system, affect not only the SEC efficiency but also the sphere’s RMS structural displacement, mass, eigenfrequency, and shielding fraction for incoming sunlight. This paper subdivided the spherical condenser into hexagons and pentagons organized in modules and carried out a theoretical analysis of the geometric deviations from a sphere. A dynamic analysis in orbit determined the internal force distribution for calculating the RMS value. An integrated optimization model was used that considers RMS, mass, oscillation frequency, and solar shielding fraction. The optimal dimensions of the structural beams for the condenser system were obtained, providing a fundamental structural size for input for further research.

Unconventional aircraft configurations, such as biplane, joined-wing, tandem-wing, and box-wing configurations, have considerable application potential due to aerodynamic interference between the front wing and rear wing airfoils. Here, the aerodynamic interference of a two-dimensional front wing and rear wing airfoil system with different relative positions was simulated using a computational fluid dynamics (CFD) method, and the significance of the correlations between the aerodynamic coefficients and stagger or gap variations was investigated by ANOVA. The results indicate that the front wing and rear wing aerodynamic coefficients are distributed unilaterally with stagger and gap variations at a small angle of attack, although regional differentiation behavior was observed for an angle of attack exceeding 4°. The fake stall phenomenon, which is caused mainly by a decrease in the front wing upper surface suction force, is proposed and discussed. The significance level analysis results highlight that (1) the rear wing lift coefficient is the most sensitive to stagger and gap variations among the four lift and drag coefficients, and (2) the front wing lift coefficient is hardly affected by the stagger variation.

This study considers the attitude disturbance torque caused by the magnetic shape anisotropy of onboard magnetic substances in low Earth orbit (LEO) satellites. The gravity gradient, solar radiation pressure, aero drag, and residual magnetic disturbance torques are normally considered in attitude control in LEO satellites. In general, attitude disturbance, magnetic disturbance to be specific, strongly affects these small-sized satellites. The residual magnetic torque in nano- and microsatellites is based on a simple steady magnetic moment; however, in most satellite cases, an unsteady magnetic moment is not considered. This study aims to understand attitude dynamics in small satellites more accurately on the basis of an unsteady magnetic moment, with a focus on magnetic disturbance due to the magnetic shape anisotropy or, in similar terms, to study the magnetic torque caused by a magnetic substance with an asymmetrical shape in a uniform magnetic field. Asymmetrical magnetic substances, such as the iron cores of magnetic torquers and magnetic hysteresis dampers of passive attitude control systems, are installed in a variety of small satellites. In LEO, these substances can cause disturbance torques to the satellites of approximately the same magnitude with the residual magnetic disturbance, which are typically stronger than the aero drag and solar radiation attitude disturbances. In the case of Cubesat XI-IV, the torque strength of the magnetic substance is on the order of $1\times {10}^{-6}\mathrm{Nm}$ in the worst case, which is the same order of the residual magnetic disturbance torque. In this paper, first, the magnetic substance torque is analyzed with a simple ellipsoid model with an analytical approach to clarify the characteristics of the magnetic disturbance. Then the magnetic disturbance is investigated using a finite-element method (FEM) to obtain more accurate findings. The results of the simple ellipsoid model and the numerical FEM simulations conclude that the magnetic torque due to the magnetic shape anisotropy is one of the strong attitude disturbance torques in LEO in small satellites, although this magnetic disturbance torque has not been considered clearly in previous satellites.

A numerical investigation of Knudsen layer effects in high-speed flows in a rarefied flow regime has been carried out. The conventional compressible flow computational fluid dynamics (CFD) solver is reformed based on the effective mean free path model to augment the validity of the Navier-Stokes-Fourier equations in the slip-transition flow regime. The mean free path is expressed as a function of the distance from the surface and local flow gradients, and has been used to modify linear constitutive relations, as well as slip and jump boundary conditions, to incorporate Knudsen layer correction. The improved solver has been validated against direct simulation Monte Carlo (DSMC) data of benchmark test cases of hypersonic flow ($\mathrm{Mach}\mathrm{number}=6.1$ and 12.7) over a flat plate in the slip-flow regime ($\mathrm{Knudsen}\mathrm{number}=0.004$), and Mach 10 flow over a circular cylinder in the transition flow regime ($\mathrm{Knudsen}\mathrm{number}=0.25$). The results show that the accuracy of the conventional CFD solver has been significantly improved due to the implementation of the Knudsen layer approach in the near-wall region and the bulk-flow region. Crucial nonlinear trends are captured in the nonequilibrium regions of high-speed flows, such as shock waves and the Knudsen layer. The location of an oblique shock around the flat plate is accurately captured and overall, the Knudsen layer incorporation has exhibited good agreement with the DSMC with deviations within 4% in the upstream region of the cylinder.

Additive manufacturing (AM) is one of the most promising techniques for on-site manufacturing on extraterrestrial bodies. In this investigation, layerwise solar sintering under ambient and vacuum conditions targeting lunar exploration and a moon base was studied. A solar simulator was used in order to enable AM of interlockable building elements out of JSC-2A lunar regolith simulant. Solar additively manufactured samples were characterized mechanically regarding their compressive and bending properties. Moreover, samples were analyzed morphologically using X-ray tomography and scanning electron microscopy (SEM) followed by density measurements. AM for identical process parameters led to final products with different physical and chemical characteristics when performed under ambient and vacuum conditions. Hence, process parameters were optimized under each individual working atmosphere. The experimental data were further integrated into finite-element (FE) calculations. This led to the refinement of the design of interlocking building elements for lunar applications. These blocks have the potential to form structures for shielding a pressurized inflatable habitat from radiation and micrometeorite impacts or creating nonpressurized shelters for robotic machinery.

This numerical study focuses on the extreme response of a sea-crossing bridge tower under correlated wind and waves in order to predict structural response with sufficient accuracy. The wind and wave data were obtained by field measurements, and different copula models were compared by Akaike information criterion (AIC), under which the optimal model was selected to simulate the correlation of wind and wave parameters. The fluctuating wind considering multipoint correlation was then simulated by a spectral representation model (SRM), and the random wave considering pile group was generated by a linear superposition method. After verifying the reliability of the numerical method by comparison with an experiment case, dynamic responses of the bridge tower in the freestanding status under directional extreme wind and wave loads are carefully discussed. Furthermore, the response surface method (RSM) is proposed to improve computational efficiency and systematically evaluate the dynamic behavior of the bridge tower. The results show that the response of the bridge tower is highly sensitive to the load direction of wind and waves. The response contours indicate that the tower top displacement is mainly dominated by wind loads, but the base shear is dominated by wave loads.

The problem of vibration and stability of coaxial circular cylindrical shells of finite length is considered when the region between the shells is partially filled with an incompressible liquid. The frequencies of vibration of the hydroelastic system are found depending on the filling depth and the gap thickness. A loss of static stability of the inner shell under the influence of hydrostatic pressure is identified. The equations to investigate the stability and natural oscillations of the studied hydroelastic system are presented. The value of the critical depth of liquid at which the shell loses stability is analytically computed. It is shown that, with fixed physical and geometric parameters of the examined system, there exists a critical number of waves around the circumference that leads to instability. The characteristic equation to compute the frequencies of oscillations of the hydroelastic system is also determined, and both nonphase and common-mode cases of oscillations are documented.