Journal of Aerospace Engineering

To reduce ground displacements induced by dewatering and excavation in foundation engineering, it is crucial to predict the ground displacements before construction. Two types of analyses, i.e., transient analysis (TA) and steady state analysis (SSA), are often used to predict ground displacements. To facilitate appropriate use of the two analyses in this study, both TA and SSA are carried out for a large-scale excavation in Shanghai, China. The calculations include groundwater table, ground settlement, and horizontal displacement. Comparisons between the calculated results and the measured results are made. Both the calculated and the measured results suggest that the deep mixing soil walls and diaphragm walls play an important part in preventing groundwater seepage and constraining soil movement. The calculated results show similar tendencies to the measured results, although the magnitudes were different. The comparisons indicate that TA is more accurate, and it is appropriate for detailed analysis of construction processes. SSA requires less calculation and is suitable for preliminary evaluation.

As an important add-on to Shanghai Hongqiao International Airport, the Shanghai Hongqiao International Airport transport hub is the biggest transport center in China. The transport hub consists of interchange stations for five different metro lines, two traffic squares, a high-speed railway station, and a station for the maglev train connecting the Hongqiao and Pudong international airports. The excavation area of the project reached up to $\mathrm{350,000}{\mathrm{m}}^2$ and the excavation depth ranged from 9 to 29 m. A combined retaining system, which consisted of slope excavation, a gravity retaining wall, and a diaphragm wall, was adopted. Sloped excavation and a gravity wall were used for the shallow excavation area, while a diaphragm wall braced by two levels of concrete struts was adopted for the deep excavation area. An extensive instrumentation program was carried out to monitor the performance of the large deep excavation and hence verify the design work. The deformations of the combined retaining system during and after the construction were recorded and analyzed. Based on the field monitoring results, the combined retaining system adopted in this project proved to be feasible for such large and deep excavations in the soft Shanghai soils.

Security of metro tunnels is extremely important, but the influence of new underground construction on existing tunnels has become more and more important. To control the existing tunnel deformation induced by an adjacent excavation, a novel construction method for excavations crossing above underlying tunnels, referred to as the divided alternate excavation method (DAEM), is presented in this paper. In this method, several dividing walls are constructed to divide the overlying excavation into small independent pits. During construction, several small pits are excavated at intervals simultaneously, and the remaining soil in other pits can resist the tunnel heave. After the underground structures of these pits are constructed, soil is backfilled onto their roof to decrease the rebound of the existing tunnels, and the remaining small pits can then be constructed. The proposed construction method is applied in the case of tunnel excavation above running metro tunnels. Field data reveal that the novel method has advantages in controlling deformation of the underlying metro tunnels.

In this paper, a super-large diameter earth pressure balance (EPB) shield tunnel crossing below an operating airport in a soft soil region is introduced to investigate the environmental effect of EPB shield tunneling. The new tunnel with a length of 1,862.7 m was constructed using the EPB shield machine with a diameter of 14.27 m. Field tests of 100 tunnel segments tunneling were conducted prior to the construction of the airport area. The distribution of pore water pressure and soil pressure on the excavation surface of the super-large diameter EPB shield and its relationship with the construction parameters are studied. In addition, the influence of the shield construction parameters on the ground movements is investigated by monitoring the surface settlement. The construction control criteria of EPB shield tunneling under the airport is then recommended, including the chamber earth pressure setting, synchronous grouting, advance speed, and stopping excavation. Application and practice show that the large EPB shield tunnel was excavated through the airport smoothly, which means that the proposed control methods contributed to a successful construction.

Dewatering-induced ground settlement is an important issue, and there a cumulative effect in stratified soil settlement. Detailed research of the stratified soil settlement devotes to a better evaluation of ground settlement. To better investigate the dewatering-induced stratified settlement characteristics of the soil strata in Shanghai, an intensive field-monitoring program was carried out for the excavation of an underground metro station, which involved the dewatering of confined aquifers in urban areas. Analyses of monitoring results suggest that the groundwater tables dropped steadily. The ground settlement decreased with an increasing distance from the excavation, and the maximum ground settlement was less than the allowable value. The results for stratified settlement monitoring showed that the ground settlement was less than the settlement at the bottom of the soft soil clay layer, which indicates that the clay layer swelled during dewatering in the underlying soil layer. This special phenomenon, referred to as dewater-caused soil expansion, has not been reported in the existing literature. This project acts as a special case study and provides a basic insight into this phenomenon.

Underground pipelines for transportation and commercial usage are in high demand for meeting both sustainable population and economic growth in well-established metropolitan areas. This study presents the postbuckling analysis of buried geodesically stiffened pipelines of finite length subjected to combined loading of external pressure and axial compression. The pipeline, treated as a shell structure, is embedded in soil, and the pipe–soil interactions are modeled as a Pasternak elastic foundation. The governing equations are based on Reddy’s higher order shear deformation shell theory with the von Kármán-Donnell type of kinematic nonlinearity. Nonlinear prebuckling deformation and initial geometric imperfection of the liner are both taken into account to investigate the buckling and postbuckling behavior of geodesically stiffened cylindrical pipes under combined loading cases. The effect of stiffeners (e.g., geodesic, axial, and ring stiffeners) is evaluated by a smeared approach, and a singular perturbation technique is employed to determine the interactive buckling loads and postbuckling equilibrium paths. Numerical postbuckling analysis is performed of perfect or imperfect, stiffened or unstiffened pipes with different liner parameters under different load-proportional values. The present study can facilitate design analysis and optimization of stiffened pipes, and it can be used to develop remedial schemes (e.g., design of thickening pipe walls and stiffening ribs) for underground pipes against instability during service and during the pipe-jacking process.

In this paper, a back-analysis method of deep excavation based on the Pareto multiobjective optimization is proposed and a multiobjective optimization algorithm multialgorithm genetically adaptive multiobjective method (AMALGAM) is implemented in a commercial FEM software to identify soil parameters based on multiple types of field observations. The proposed method is applied to a well-instrumented deep excavation, i.e., the Taipei National Enterprise Center (TNEC) project. The observed wall deflection and ground surface settlement at Stage 3 of the excavation are simultaneously used to estimate the nine soil parameters of the modified Cam-clay (MCC) model for three clay layers. The Pareto front in the biobjective space exhibits a rectangular shape, which implies that the simultaneous minimization of both objectives can be achieved. The back-analyzed soil parameters of the compromise solution from the biobjective back-analysis can reasonably simulate both the wall deflection and ground surface settlement for Stage 3. The differences of the predictions and the actual observations for Stages 4 to 7 using the back-analyzed soil parameters from Stage 3 are mainly because the inadequacy of the MCC model to simulate the small strain soil behaviors of excavation.

In this paper, the displacement performance of deep excavations supported by contiguous bored pile walls (CPWs) in soft clay is studied by analyzing the excavation case for a new main building for the Shanghai Civil Aviation Hospital. The relationships between the maximum displacements of CPWs, the maximum ground settlements, and excavation depth are analyzed, and compared with the statistical values presented in the literature. Empirical expressions are presented to predict the lateral deflection profile of CPWs, distribution curve of ground settlements, horizontal displacement in subsoil, and settlements of adjacent buildings. The parameters in these empirical expressions are obtained based on field measurements. A simple method is developed to predict the displacement performance of the deep excavations with CPWs, proving an approach to assess the deep excavations and leading to an optimized design and construction.

A pretension design method based on the projection principle is proposed for space deployable mesh reflector antennas. First, the equilibrium tension of the plane cable net structure is obtained by a force equilibrium method. Then, the obtained cable tensions of the plane cable net structure are projected to the spatial cable net reflector to obtain the spatial cable tensions. Finally, the implication relationship between the plane cable tensions and the tension distributions of front and back cable nets is revealed. A general analytical expression is deduced for the axisymmetric reflector, and an optimization model is established for the offset reflector. Some hoop truss deployable mesh antennas are examined as examples of pretension design. The uniform cable tensions and high surface accuracy of reflectors are obtained to verify the effectiveness of the proposed method.

A design method employed for preliminary integration of a hypersonic vehicle airframe configuration with its propulsion flow path is described. This method is primarily based on the integration of the variable cross section inward-turning inlet and the airframe. Three typical configurations include lifting body, sim-waverider, and semi-axisymmetric cone. Rectangular-to-circular, erose-to-circular, and sector-to-circular shape transition Busemann inlets are designed to integrate these three vehicle bodies, respectively. The results of numerical simulations show that the aerodynamic performance of these configurations, coupled with the propulsion flow path, inherits the characteristics of their original airframe shapes, such as the high lift/drag ratio of sim-waverider and the low-drag performance of semi-axisymmetric cone configuration. The computed results also demonstrate that the inward-turning inlets integrate smoothly with their respective vehicle airframes and that the design method is viable.

One key issue in the simulation of bare electrodynamic tethers (EDTs) is the accurate and fast computation of the collected current, an ambient dependent operation necessary to determine the Lorentz force for each time step. This paper introduces a novel semianalytical solution that allows researchers to compute the current distribution along the tether efficient and effectively under orbital-motion-limited (OML) and beyond OML conditions, i.e., if tether radius is greater than a certain ambient dependent threshold. The method reduces the original boundary value problem to a couple of nonlinear equations. If certain dimensionless variables are used, the beyond OML effect just makes the tether characteristic length $L^{*}$ larger and it is decoupled from the current determination problem. A validation of the results and a comparison of the performance in terms of the time consumed is provided, with respect to a previous ad hoc solution and a conventional shooting method.

This paper considers the application of compound control method to high-performance autopilot design for aerodynamically controlled agile missiles. The control objective in this paper is to track a reference angle of attack command signal in the presence of external disturbance and aerodynamic coefficient uncertainty with desired performance. The external disturbances and the aerodynamic uncertain terms are first lumped together as the lumped uncertainties, which can be estimated accurately by the introduced extended state observer (ESO). Combining the sliding mode control (SMC) and backstepping techniques, a robust nonsmooth (but continuous) compound control law is developed for angle of attack tracking. With the aid of Lyapunov stability criteria, it is proven that the angle of attack tracking error will converge into a small neighborhood around the origin in finite time. Theoretical analysis and simulation results demonstrate the robustness and effectiveness of the proposed composite method.

This paper presents the variable cross section spar (VCSpar) concept that facilitates varying the shear center position relative to the aerodynamic center, allowing the external aerodynamic loads to twist the structure and maintain its deformed shape. The VCSpar is considered in this paper as integrated within the wing of a representative unmanned aerial vehicle (UAV) to enhance its flight performance and control authority. A preliminary design study was conducted to assess the potential benefits of the concept using a low-fidelity design tool. Then, aeroelastic modeling of the concept was performed where the VCSpar was modeled as a two-dimensional equivalent aerofoil using bending and torsion shape functions to express the equations of motion in terms of the twist angle and plunge displacement at the wingtip. The aerodynamic lift and moment acting on the equivalent aerofoil were modeled using Theodorsen’s unsteady aerodynamic theory. A low-dimensional state-space representation of an empirical Theodorsen’s transfer function was adopted to allow time-domain analyses.

An offset-free output feedback robust model predictive control for a generic hypersonic vehicle (HV) under disturbances is investigated. The disturbances are appended to the states of the HV to constitute an extended state, and a full-order nonlinear Luenberger-like observer is designed to estimate the disturbances and states of the HV. The influences of the disturbances on the velocity and altitude are attenuated by the target generator and the model predictive controller based on the estimated disturbances and states. Simulation results show that the velocity and altitude can track the given references accurately under external disturbances and parameter uncertainties.

The current work is a contribution to the potential effect of the aft fuselage stiffness modifications on the flutter characteristics of a T-tail. The rear fuselage is simulated by beam elements, based on a fixed T-tail structure. Their stiffness ranges from $1\times {10}^5\mathrm{N}\text{-}{\mathrm{m}}^2$ to infinite. The present analyses and discussion predict that a combination of out-of-plane or in-plane bending and torsion of the fuselage, fin, and stabilizer affects modes, and critical flutter and divergence speeds and flutter mechanisms, when the fuselage stiffness continuously varies. With the distinct segmental stiffness of the simulated fuselage, the different flutter results are compared and investigated. This paper also points out that the increasing joint stiffness of the stabilizer and fin can benefit the flutter characteristics. The calculated and analyzed database should be available to use for the structural design of the empennage in engineering

Vibration isolation is an important method of spacecraft vibration control, and the study of vibration isolation performance is the theoretical basis to design isolators and analyze transmissibility characteristics. This paper mainly studies a type of fluid microvibration isolators and a new nonlinear three-parameter model is first constructed in which a $p$th power damping and a $q$th power stiffness are placed in series. With the application of the harmonic balance method (HBM), the force and absolute displacement transmissibility curves under different parameters are obtained. Then based on self-defined evaluation indexes of vibration isolation performance, the corresponding transmissibility characteristics are estimated and the effects of key factors, e.g., excitation amplitude and ratio of stiffness, are also analyzed. Moreover, the analytical results are numerically validated by the Runge-Kutta method, and a stability analysis is further carried out to show the practicability of these solutions. Finally, an optimization method called the generalized pattern search (GPS) algorithm is proposed and applied to identify the nonlinear model parameters. The presented theory and method can be used to analyze the multiparameter nonlinear models, and they can also provide a reference and a theoretical basis for the design and engineering application of this type of fluid microvibration isolators.

The effects of material variability on the mechanical response and failure of composites under high strain rate and impact loading are investigated in this paper. A previously developed strain rate–dependent, sectional micromechanics model is extended to account for the variability in microstructure and constituent material properties. The model presented in this paper also includes a three-dimensional damage law based on a work potential theory and a microscale failure criterion. Microstructural characterization of the composite is performed to obtain the statistical distributions needed for the stochastic methodologies. A Latin hypercube sampling technique is used to model the uncertainties in fiber volume fraction and viscoplastic material constants. A comparison of general Monte Carlo simulation and Latin hypercube–based Monte Carlo shows that the Latin hypercube technique converges using fewer simulations. The modulus and failure strain obtained using the developed methodology show good correlation with the experimental data. This novel stochastic sectional model is shown to correlate better with the available experimental data compared with the deterministic sectional model. A laminate level, parametric study is also conducted to investigate the effect of uncertainty on the residual energy of a composite laminate during impact.

To guarantee the reliability of hydraulic systems, it is of vital importance to do impulse testing for hydraulic components. A hydraulic impulse-testing system with pressure difference feedback from a second-stage valve is studied. A mathematical model of the system is built, and it shows that the inner closed-loop damping ratio of the system is influenced by the pressure difference feedback of the control chambers of the second-stage valve. And by changing the pressure difference feedback gain, various damping ratios can be achieved, which is a key factor affecting the system overshoot. The results of both the simulation and experiment show that with the same square wave input the system overshoot can be freely controlled between 0 and 50% by adjusting the pressure difference feedback gain, which is a new method to obtain both peak wave impulse pressure cycle and square wave impulse pressure cycle utilizing the same system and the same input.

An $n$-harmonic traveling-wave excitation (nTWE) system that was developed for the U.S. air force research laboratory turbine engine fatigue facility (TEFF) is described. This traveling-wave system is designed to simulate engine order excitations on stationary integrally bladed rotors (IBRs) and dual flow-path IBRs (DFIBRs) for the purpose of measuring forced response amplification due to mistuning. This new system extends beyond traditional traveling-wave systems by its capability to generate a combination of $n$ engine order (EO) harmonics for IBRs as well as different EO harmonics simultaneously to both inner- and outer-blade sets of DFIBRs. This system can excite both IBRs and DFIBRs of differing sizes and number of blades with electromagnetic excitation. Scanning vibrometry mounted above the test specimen is used to measure any localization due to mistuning. Sources of error in the nTWE system are discussed and experimental forced response levels are shown for a 22-blade IBR.

This paper presents a numerical method to simulate the dynamic interaction between the structural deformation and the aerodynamic characteristics of flexible flapping wing for micro air vehicle (MAV). A fluid-structure coupling solver is developed based on the Navier-Stokes equations and the structural dynamic equations. In addition, the interface data exchange method based on the radial basis function and the moving mesh generation method based on the infinite interpolation are applied, which play an important role in the coupling research. The preceding method is validated by comparison with the wind tunnel experimental results. For the research scope of this article ($\mathsf{R}=5\times {10}^4$), the flexible deformation impacts of flapping wing on aerodynamic performance are presented. The simulation results proved that the structural deformation has a significant effect on the aerodynamic forces, especially on the thrust, and the structural deformation is determined by aerodynamic and inertial forces together, but with different impact ratio as the change of flapping frequency. Moreover, the flow details are further investigated to discuss the influence of flexible deformation on the aerodynamics.

Drilling is a material removal process that introduces the plastic deformation and stresses around the hole. When large amounts of drilling stresses are added up, there will be deformation in the aerostructural assembly. This paper presents an aerostructural assembly deformation predicting method considering drilling-induced stresses around the riveting hole. Drilling-induced stresses are simulated with additional temperature fields. The assembly of the two riveted plates are considered to illustrate effects of drilling-induced stresses coupling and validate the proposed model. The simulation and experimental results show that one hole’s drilling-induced stresses have negligible impact on the riveting deformation, while a lot of holes’ drilling-induced stresses must be considered in assembling. When a lot of drilling-induced stresses are added up, there will be significant deformation in the aircraft’s structure. The deformation predicting method outlined in this paper will enhance the understanding of the compliant components deformation resulting from the drilling stresses and help systematically improve the precision control efficiency in the civil aircraft industry.

This paper describes a prototype and analytical studies of a three-degree of freedom (3-DOF) spherical momentum exchange actuator for three-axis attitude control. Its moving part, without any gimbal structures cascaded, can be directly driven by a stator electromagnetic field instead of servomotors, which sets it apart from conventional control moment gyros. First, the motion of equation and torque exchange model are developed. Analysis shows that the proposed actuator possesses a considerable torque amplification effect. Then a two-level torque-sharing strategy tailored for this device is presented to decouple the command torque into reaction flywheel/gimbal torque and further assign them to each of the stator coils. The physical limit of the rotor’s tilt range is investigated and an $n$-step incremental Euler eigenaxis rotation is resorted to as the solution. Numerical simulation results present a desirable dynamic response, revealing that the single device has the potential to provide limited three-axis control for spacecraft. Finally, the pros and cons of this device are analyzed. This study may serve as a reference on the design and research of new future momentum exchange devices for spacecraft attitude maneuvers.