Journal of Aerospace Engineering

In this study, an equivalent structural modeling and structural analysis are proposed for the engine nozzle of a launch vehicle. A specific shell element that combines an optimal triangle (OPT) membrane element and a discrete Kirchhoff triangle (DKT) plate–bending element is developed. Equivalent structural modeling is performed for a complex three-dimensional component and especially for the launch vehicle engine nozzle by considering the outer/inner surfaces and cooling channel of an engine nozzle. Shell element and an optimization approach are used for the relevant orthotropic material properties. Laminated composite material and curved geometry are considered in the shell analysis to consider a realistic engine nozzle component. The accuracy and efficiency of the present structural analysis are validated by performing a relevant modal analysis. The results indicate that the equivalent structural modeling procedure is correlated with the prediction that accounts for the original solid element assemblage. The efficiency of the equivalent structural modeling is ascertained by the reduction in the number of degrees of freedom and computational cost. The application of the present equivalent structural modeling for a more complex component, i.e., multiple-clustered engine nozzles facilitates large-size fluid–structure interaction analysis.

The objective of this study was to present a new approach for determining the truck weight limit of simply supported steel girder bridges. This approach is based on the fatigue reliability of bridge girders under the action of random traffic flows considering the presence of multiple trucks. A simply supported steel girder bridge designed according to the current codes was used as the bridge model to illustrate the presented approach. Based on the collected traffic data from Wisconsin, random traffic flows were generated using the Monte Carlo method and were used as the traffic loading. Numerical simulations were carried out to investigate the effects of three important parameters, including the fraction of traffic in the fast lane ($FTFL$), violation rate ($VR$), and truck weight limit ($TWL$), on the average fatigue damage accumulation ($AFDA$) induced by each truck in the random traffic flow. Based on the Miner’s cumulative damage model and the S-N curve, the effects of these parameters on the fatigue reliability index of bridge girders were also analyzed. The truck weight limit that can ensure the target fatigue reliability of the bridge girders after 75 years of service was determined based on the fatigue reliability analysis of the bridge girder.

Metro lines buried in soft soil in coastal regions will inevitably suffer long-term uneven deformation during operation. In this study, the long-term deformation characteristics of metro lines in Shanghai soft deposits are analyzed based on extensive field data of four metro lines, i.e., Shanghai metro lines (SMLs) 1–4. Settlement processes of complete lines and typical sections including both the tunnel and the station are illustrated. The cumulative longitudinal settlements of the four lines in 2008 and 2015 are presented and comparatively analyzed. The bending deformation process is analyzed and severe bending deformation is examined using the curvature radius and the relative deflection. All the extensive field data indicate that (1) SML 1 had the largest cumulative settlement and SML 4 showed the smallest cumulative settlement. The cumulative settlement is closely related to the time when the metro line was built. SMLs 1–4 settled before 2008 and uplifted entirely and slightly since then. (2) The deformation of the metro tunnel was gentle, whereas the deformation of the elevated metro line showed periodic fluctuations. (3) The bending deformation was more severe in the elevated metro line than those in the metro tunnel, although SML 3 was built later than SML 1. (4) Severe bending deformation appeared at the connections among the station and tunnel, tunnel entrance or exit, and side passageway. (5) The curvature radius was more suitable for examining the severe bending deformation of the elevated metro and the relative deflection was more suitable for examining that of the metro tunnel.

A damage identification method named the pseudoexcitation (PE) approach was established previously, the principle of which resides on local examination of perturbation of structural dynamic equilibrium conditions. While showing significant sensitivity to structural damage with small sizes, the approach exhibited high vulnerability to measurement noise owing to the involvement of high-order derivatives of the vibration displacements in the expression of the damage index. On the other hand, several baseline parameters (e.g., Young’s modulus and density) are necessary to implement the approach and limits the practical application of the approach. A weak formulation of the PE approach was established to circumvent the interference from measurement noise. However, the weak formulation of two-dimensional (2D) structural component has not been developed, and the reliance of the weak formulation on baseline parameters remains an unsolved issue. In this paper, the 2D weak formulation of the PE approach was proposed by introducing a weighting function in terms of the 2D Gauss function. Through an integration operation, the selected weighting function was able to significantly highlight the feature of structural damage and largely suppress noise influence. Furthermore, a statistical strategy was developed to inversely estimate the values of baseline parameters, which signifies the elimination of the dependence of the PE approach on preobtained baseline parameters. As a proof-of-concept investigation, multidamage in a plane structure consisting of both beam and plate components were identified by using the modified damage identification method. A hybrid data fusion algorithm was then used to enhance the accuracy of damage detection, revealing not only the locations, but also the sizes of damaged zones.

The safety of operational tunnels impacted by nearby deep excavations has led to growing interest in the field of practical civil engineering. Many researchers have studied the performance of shield tunnels during adjacent excavation processes, but few discussed the behavior of a cut-and-cover tunnel bounded by a new excavation. Based on the field-monitoring results of a case in Shanghai, this paper investigates the performance of an existing cut-and-cover tunnel between two large-scale deep excavations. In this case, the diaphragm walls of the cut-and-cover tunnel are also used as retaining walls of the new deep excavations. Vertical displacements of the tunnel and different diaphragm walls, variation of underground water level, and the stratified settlement of subsoil close to the tunnel are monitored and analyzed. The results show that the cut-and-cover tunnel uplifted due to the nearby deep excavations while the shield tunnels settled. The vertical displacement distribution curves for the cut-and-cover tunnel were bell-shaped. By installing the partition walls, the direct influence of the large pits was avoided so that the impact of the large-scale excavation on the tunnel was reduced. Because all diaphragm walls (partition walls, cross walls, and retaining walls) and the cut-and-cover tunnel were connected, responses of the tunnel were mainly affected by the diaphragm wall system. The effect of the soil heave inside the excavation on the partition walls can be transferred to the tunnel by cross walls. To control the displacement of the cut-and-cover tunnel, the cross walls should be constructed after the excavation of large pits, and dewatering in the confined aquifer also has an active effect to reduce the heave.

The use of high-permeability porous material to control supersonic flow around a bluff body is a new concept. To obtain an insight into the role of porous spike with regard to its aerodynamic controlling effect, two-dimensional numerical results for supersonic flow around a blunt solid configuration with foam porous spike are presented in this paper. The compressible, axisymmetric governing equations for both the porous and nonporous regions were integrated based on the single-domain approach at the continuum scale. Transient fluid-thermal coupled analysis was conducted for both porous and solid spiked configurations with optimized spike shape at Mach 5.0 flight condition. Results show that there exists a recirculation zone within the porous spike, whereas the size and vortex rotating intensity of the recirculation zone is attenuated compared with the solid one. During the coupling period, the blunt body with porous spike yielded a better aerodynamic thermal performance in terms of slower thermal response. Moreover, it shows that thermal evolution within the porous spike exerts considerable influence on the temperature field of a frontal flow field, which further affects the aerodynamic drag force acted on the forebody surface. A maximum drop of approximately 15% of peak pressure coefficient was achieved for the porous spiked body compared with the solid one in the range of simulation time. These results reveal the combined role of porous spike in redistributing and aerodynamically heating the incoming airflow, which results in both lower drag and aerodynamic heating level.

The steel stiffened segment in a steel–concrete connection joint is critical to the load capability of the cable-stayed bridge with hybrid girders. The research focused on the improvement of steel stiffened segments by investigating their failure reasons, mechanical behavior, and transmission efficiency. In order to achieve that, both the experiments and finite-element (FE) analysis of three classical types of stiffened segments subjected to axial compression were conducted, and FE results were consistent with test data. Effects of element sizes, geometric imperfections, and residual stresses were considered in FE models, and proper values for the imperfections were suggested. With refined models, transmission efficiency and stress concentration of three types of steel stiffened segments have been investigated. Segments with a U-shaped stiffener inserted T-stiffener and U-shaped stiffener circumscribed double T-stiffener are suggested for better force transmission and less local stress concentration. Furthermore, parameter studies on two suggested types above are carried out. Results show that the vertical plate could be thinning when the condition of stability is satisfied. Proper thickness of the vertical plate in a single T-stiffener and proper spacing between vertical plates in a double T-stiffener are given.

Fiber-reinforced plastics (FRPs), with their unique material and structural properties, offer many advantages over conventional structural materials such as concrete and steel. However, their brittle failure mechanisms at the ultimate stage make them difficult for use in important structural applications. When it comes to glass FRP (GFRP) bridge deck systems, due to the existence of various configurations of structural elements and the nonavailability of acoustic emission (AE) monitoring standards, the need for further exploration of damage identification for the unique configurations adopted in field bridges has become a necessity. The GFRP laminate coupon samples originating from a new FRP-balsa wood composite bridge built in Louisiana were investigated to obtain insight into their structural performance and possibly assess damage mechanisms. In order to assess the critical failure modes in the GFRP laminate samples, three separate sets of specimens were prepared to initiate certain damage mechanisms, and several tests were carried out under varied load conditions to study the critical failure modes such as fiber breakage, matrix cracking, and delamination. Those tested specimens were then examined using the scanning electron microscopy (SEM) technique to identify the failure modes through material changes at the microlevel. Acoustic emission sensors were also installed to collect AE data for further study.

Time-dependent elevated temperature behavior of a two-dimensional (2D) woven melt-infiltrated Sylramic (SiC) ceramic matrix composite (CMC) is investigated. A micromechanics-based model that includes consideration of matrix and interfacial damage and of creep/relaxation of the matrix is used. The model also accounts for composite fabrication process induced residual stress in the constituents and load transfer between the constituents due to damage and creep. Test data from undirectionally loaded specimens are used to obtain values of all relevant material properties and damage parameters. Next, the model is used with the finite-element method to predict time-dependent behavior under multiaxial stresses and stress concentrations. Predictions are compared with measurements including postcreep stress-strain response in specimens with and without holes.

Nanosatellite 2 (NS-2) is a science and technology experimental nanosatellite developed by Tsinghua University. Since it was launched, NS-2 has operated properly and has been used as a low-cost, rapid-response satellite platform for on-orbit experiments with microelectromechanical system devices. The design, mathematical model, numerical simulation, and on-orbit telemetry data analysis of the NS-2 attitude determination and control system (ADCS) are presented in this paper. A bias momentum wheel and three-axis magnetic torquers were used and an actuator fault-tolerance control algorithm was proposed. Flight data confirmed that NS-2 ADCS achieved a three-axis stabilized control with an accuracy of 2.5° and an angular rate within $0.05°/\mathrm{s}$ in each axis, which met the mission requirements. In addition, single event effects were detected during the NS-2 flight, which led to attitude control failures. A simple and practical fault processing method was uploaded to NS-2 ADCS by the ground station to solve this problem. On-orbit operation validated the efficacy of this method. This paper provided reference for the study and design of nanosatellites.

Phononic crystals and metamaterials have been widely investigated over the last decade. In recent years, by integration with piezoelectric transducers, phononic/metamaterial-based piezoelectric energy harvesters (PEHs) have gained increasing research interest for achieving multifunctionalities. This paper proposes a general framework for modelling phononic/metamaterial beams bonded with piezoelectric transducers based on a one-dimensional piezoelectric composite finite element derived using the generalized Hamilton’s principle. A method for calculating band structures of infinitely long models of phononic/metamaterial beams that can carry piezoelectric transducers is then developed. This method is demonstrated via two case studies. The first case study investigates a metamaterial beam without piezoelectric coverage, and the proposed method is verified by the transfer matrix method (TMM). Compared with the TMM, the proposed method provides a dispersion relationship in a simpler form and thus demonstrates higher computational efficiency. The second case study investigates a metamaterial beam with periodic piezoelectric coverage. The proposed method takes into consideration the piezoelectric effect. Band structures of such a piezoelectric metamaterial beam under short-circuit and open-circuit conditions are evaluated. Subsequently, corresponding finitely long models of the two case studies are analyzed. The transmittances and open-circuit voltage responses of the piezoelectric transducers are then calculated. The predicted band gaps from transmittances match well with those from band structures. In addition, the transmittances and open-circuit voltage responses of piezoelectric transducers predicted based on the proposed model are verified against the finite-element solution produced by the ANSYS FE program.

For the broken-line path following problem of unmanned aerial vehicles (UAVs), to enhance the ability to reject wind disturbance and reduce position error overshoot when a UAV turns in the switching position of a broken-line path, this paper proposes a novel UAV three-dimensional broken-line path following control system. The control system is divided into four linear active disturbance rejection control (LADRC) loops based on a novel proportional-integral extended state observer (PI-ESO), a guidance law based on inverse dynamic resolving method and the broken-line path switching methodology. For the LADRC loops, inspired by proportional-integral observer, integral terms are introduced to a linear ESO (LESO) and a novel PI-ESO is proposed. A parameter tuning method for the PI-ESO is proposed for engineering application according to the idea of bandwidth parameterization. The broken-line path switching methodology adjusts the ground speed of a UAV at the proper time and speed magnitude according to the direction of the UAV and the relative position between the UAV and waypoints. The process contains three stages: speed reduction at uniform acceleration, turning at a lower speed, and speed recovery based on a fuzzy logic controller. The simulations demonstrate the effectiveness of the proposed path following control system.

In recent years, much attention has been paid to the research and development of a new kind of passive control device named a particle damper, which has a very similar configuration and application method to the tuned mass damper; however, the damping mechanisms are different. Hence, systematic comparative studies on these dampers are very important for future applications. In this paper, three cases including single-degree-of-freedom structure, 5-story linear-elastic steel frame and 20-story nonlinear benchmark building, are used as primary structures to compare the structural performance with optimal tuned mass damper and optimal particle damper. The optimal parameters of the particle damper are designed by a differential evolution algorithm and the optimal parameters of the tuned mass damper are designed by the classical Den Hartog theory, providing the same additional mass. The numerical simulation shows that the properly designed particle damper certainly has better vibration control effect than that of the optimal tuned mass damper, not only for elastic performance indexes, but also for nonlinear performance indexes, such as the number and maximum rotation of plastic hinges, and energy dissipation of components. Moreover, the more obvious advantages are that, compared with the optimal tuned mass damper system, the optimal particle damper can significantly reduce the relative displacement between primary structure and the damper itself, as well as its better robustness.

This paper investigates a fault tolerant problem for the rigid spacecraft in the presence of additive faults and nonlinear disturbances. An adaptive observer and an adaptive terminal sliding mode observer (ATSMO) are presented respectively to distinguish the faults and external disturbances in finite time. Then, we develop a novel finite-time continuous terminal sliding mode controller (CTSMC) to compensate the detected faults. Unlike most of the existing online fault estimation, the proposed approach could achieve finite-time reconstruction of unknown faults and disturbances simultaneously, while the upper bound knowledge is unnecessary. Moreover, the proposed finite-time fault-tolerant controller (FTC) is only based on the information of available output and its first derivative. The effectiveness of the proposed methodology is demonstrated by simulation results.

A new method of structural stress monitoring based on piezoelectric (PZT) impedance frequency shift is proposed in this paper. Since the sensitive frequency of the imaginary part of admittance signature discussed in this paper reaches several megahertz and no specified signature frequency in such a high range is given, several groups of experiments and a theoretical analysis are conducted. In the experiments, the PZT patches are bonded on the aluminum plate and the aluminum rod for the tensile and compressive experiments, respectively. The experimental results show that in such a high-sweep frequency band (MHz), when the host structure is subjected to a tensile stress, the resonances in the admittance spectrum of PZT increases linearly, and the tensile force also increases. While the host structure is subjected to a compressive load, the resonances decrease linearly as the compressive force increases. Theoretical analysis shows that while the tensile force increases the stiffness of both the host structure and the PZT material, and the compressive force decreases it, the stiffness changes cause the resonance shift in the PZT admittance spectrum. The method based on the PZT impedance frequency shift can monitor the health of the stressed structure, and it has a promising application in engineering fields.

Two innovative composite tip structures that combine a honeycomb with a prismoid or spherical bottom have been proposed to actively control the tip leakage flow in a turbine cascade. The mechanisms of inhibiting leakage flow are mainly analyzed from the aspects of detailed flow field, vortex structures, and turbulent kinetic energy dissipation. The influence of geometric parameters like depth and dihedral angle of the prismoid and depth of spherical bottom are discussed. The results show that both composite structures can enhance the vortices generated in cavities and intensify the mixing between honeycomb jets and upper clearance flow, thus achieving better control effect. For a honeycomb-prismoid tip, a 45° dihedral angle performs best, and the control effect is obviously weakened when the depth is greater than 1.5 times that of the honeycomb. A honeycomb-spherical bottom tip reduces the vortex development resistance, which benefited from the smooth transition of the spherical bottom. Its control effect is parabolic with the depth of spherical bottom, and the optimum depth is one-third of the diameter of its corresponding inscribed ball. Compared with a flat tip, a honeycomb tip, honeycomb-prismoid tip, and honeycomb-spherical bottom tip reduce the tip leakage flow by 11.11%, 13.77%, and 15% as well as the loss by 8.17%, 9.4%, and 10.42%.

The signal detected by a force-measurement system (FMS) is transient in an impulse combustion wind tunnel, and the transient property of the FMS will affect the measurement result significantly. This study presents a method to improve the measurement accuracy of aerodynamic loads and achieve the goal of transient measurement. First, the dynamics equation of the FMS is established. Second, the virtual static calibration and modal analysis are conducted to acquire its coefficient matrix, lower-order natural frequencies, and modes. Third, transient analysis is conducted to obtain its output responses. Results show that the mean value of the test signal can be treated as the output of the aerodynamic loads to a certain degree, and that the measurement accuracy can be improved by an order of magnitude after the inertia compensation. The measurement error rates of the drag, lift load, and pitching moment are lower than 8%, 10%, and 7%, respectively, when the frequency of the input load or moment is far from the natural frequency. However, not only can the balance easily be damaged, but the measurement errors also increase sharply when the frequency of the sine load is equal or close to the natural frequency. The results of a force measurement test show that the inertia compensation method can suppress the disturbance of the inertial loads to the output.

Structural control plays an important role in suppressing structural vibration under different loads. During a severe earthquake, a structure will exhibit nonlinear behaviors. In this case, the control method for structural nonlinear vibration is important for further study. In this paper, a semiactive control method considering the nonlinear magnetorheological (MR) damper model is proposed for structural vibration control. Due to the complexity of the structural and damper models, fuzzy systems are used to approximate these models. Based on these fuzzy systems, a sliding mode control method is developed, and the chattering phenomenon is mitigated by a fuzzy controller. Numerical simulations are conducted on the third-generation nonlinear benchmark model with the proposed structural control. The results verify the effectiveness of the proposed method.

This paper proposes a new type of energy dissipation brace system that is composed of superelastic Nitinol shape memory alloy (SMA) helical springs to reduce seismic responses of a frame structure. To investigate the earthquake-resistant effectiveness of the proposed brace system, a 2-story steel frame structural model was fabricated, and four SMA springs were trained in the laboratory. To describe the nonlinear force-displacement relationship of the SMA helical springs under general dynamic load, a mathematical model was developed based on a stress-strain relationship of SMA material, and the model agreed well with the test results. A numerical simulation model of the 2-story frame with the new energy dissipation brace system was then established to obtain the responses of the frame subjected to an earthquake. To verify the effectiveness of the numerical model, a series of vibration table experiments were carried out. The experimental results have very good agreement with the numerical simulation results, and the proposed brace system can effectively suppress structural vibrations. Compared with the steel spring brace and the viscous damper brace, the new energy dissipation brace can provide better vibration reduction effects, simultaneously reducing the displacement and acceleration responses of the frame. Considering its abilities of energy dissipation as well as fully recentering, the Nitinol SMA spring brace system has a great potential for frame structural vibration reduction.

Attention has been devoted to the construction of off-earth base construction and mineral mining in recent years. This paper studies the influence of extraterrestrial gravities on the arching effect surrounding deeply buried structures in planetary regolith using trapdoor experiments. Off-earth regoliths are physically simulated using a magnetically sensitive planetary regolith simulant, whereas the gravities are simulated by applying a uniform magnetic body force. The results show that the gravity has a significant influence on both the unloading rate for soil pressure on the trapdoor and the reduction in soil pressure. Both soil pressure and normalized soil pressure unload rapidly when moving the trapdoor down at a lower gravity. The unloading rate for soil pressure increases when gravity increases. However, that of the normalized soil pressure decreases. With further increases in gravity, the normalized soil pressure appears to reach a stable state. A theoretical solution for the soil pressure on the trapdoor is proposed which includes the effect of gravity-induced stress level and stress gradient on interparticle friction resistance. The predicted soil pressure demonstrates good agreement with the experimental results. This study provides an approach to estimate the downward loading on trapdoor-like underground structures in off-earth engineering applications.

Recently, the occurrence frequency of extra-heavy trucks (EHTs, gross weight $\ge 80\mathrm{t}$) in China has significantly arisen due to the increasing demand of heavy freight transportation. Load characteristics, such as traveling speed, axle weight, and axle distance, of EHTs are different from those of normal traffic loads and vary by region. In the present study, the site-specific load characteristics of EHTs are analyzed based on weigh-in-motion (WIM) data measured from two typical routes of China. Then, the EHT load cases are extracted and a bridge–vehicle simulation is conducted. Finally, the bending capacities of small- to medium-span bridges are assessed. It is found that more attention should be paid to the site-specific load characteristics of EHTs because they are significantly different among different routes. The focused small- to medium-span bridges under EHT load can satisfy the safety requirements and the safety reserves of the bending capacity of such bridges on Chinese highway, which are higher than those of Chinese expressways under EHT load.

In this study, a novel reduced-order scheme is proposed to model the airspeed and the air density uncertainties of an aeroelastic system. Based on the present reduced-order scheme, the dimensions of uncertainties could be significantly reduced through separating the quadratic term of airspeed into the linear terms. Based on the proposed scheme, two robust controllers, i.e., a single-input/single-output controller and a multi-input/multioutput controller, were designed to suppress the flutter instability of the aeroelastic system. To illustrate the performance of the designed robust controllers, a three-dimensional multiple-actuated wing was chosen as the test case. The numerical results show that the flutter instability can be effectively suppressed. Besides the numerical investigations, the wind-tunnel tests for active flutter suppression were also implemented to further verify the performance of the robust controllers. The experimental results showed that the present robust controllers could effectively suppress the flutter instability and expand the flutter boundary of the multiple-actuated wing.

This paper proposes a novel self-centering negative stiffness damper (SCNSD), which combines superelastic shape memory alloy (SMA) and prepressed springs in parallel for damping enhancement. A mechanical model of the damping force is established and experimental tests are conducted for verification. The influence of the negative stiffness provided by the prepressed springs is investigated by parametric analysis. A single-degree-of-freedom (SDOF) structure is used as a case to study the damping effectiveness of the proposed damper. The low limit of the negative stiffness is established, and the additional equivalent damping ratio is deduced theoretically. Frequency response under harmonic excitation is evaluated by using the average method. Numerical simulation is carried out to explore the damping effectiveness of the SCNSD for suppressing the seismic response of the SDOF structure. These numerical simulation results show that the SCNSD can achieve a larger damping ratio due to the effect of the negative stiffness, and the acceleration and displacement response of the SDOF system can be reduced remarkably.

An experimental investigation on asymmetric vortex breakdown flow over three delta wings with sweep angle of 85°, 80°, and 70° was carried out in a wind tunnel at high angles of attack and Reynolds number of $1.215\times {10}^6$ using particle image velocimetry and pressure measurement techniques. First, vortex breakdown flow over delta wings with different sweep angles was measured to confirm the asymmetric flow phenomenon and its formation conditions. Time-averaged vortex breakdown flow over the 70° swept wing was found to be symmetric, whereas flow is asymmetric over the 80° and 85° swept wings. Instability due to crowding together of both leading-edge vortices is the cause of asymmetric vortex breakdown flow. Second, a special test that two nose sections with the same size and shape, named NT1 and NT2, was used to explore the effect of manufacturing imperfection of nose on the asymmetry of vortex breakdown flow was designed. Unpredictable manufacturing imperfection at the nose tip was found to be key natural perturbation of the instability, which led uncertain asymmetric vortex breakdown flow. Finally, the effects of an artificial spherical microperturbation with diameter of 0.2 mm fixed at the nose tip were examined to confirm the nondeterminacy of natural perturbations. With artificial microperturbations, rolling moment induced by asymmetric vortex breakdown flow can be controlled in a skillfully deflected manner.

The coupled responses of partially liquid-filled containers equipped with multielastic baffles subjected to lateral excitations have been investigated. The liquid domain has been divided into some subdomains. The analytical solutions of the velocity potential of the subdomains are obtained using the separation variable method. The wet modes of the multi baffles are then presented based on the dry-modal functions. Finally, the coupled modes are obtained by expressing the free surface equations, the continuity conditions, and the coupled vibration equations in the form of Fourier–Bessel series. The orthogonality among the natural modes of the coupled system has been proved. The dynamic response equations of the coupled system are established. The formulae of the coupled responses are derived. The effect of the baffle parameters on the coupled responses are discussed in detail. With the help of the MATLAB optimization toolbox, the present method can be used for the optimization of the baffled container subjected to seismic excitations.

As focal length significantly affects the performance of a telescope, the performance of spatial telescopes in astrophysical missions is mainly limited by the launchers’ capabilities. An appealing solution is a deployable structure that expands after launch and thus acquires increased focal lengths. Many published articles have focused on the design and analysis of novel deployable mechanisms with a high packing ratio. However, few studies have focused on enhancing the performances of existing designs that have been flight proven. This paper highlights the idea of a unidimensional deployable structure by sequentially assembling reconfigurable extended joints, to strengthen the able deployable articulated mast (ADAM). This design inherits advantages of the ADAM mast, changes the ADAM mast from a trusslike structure (tensegrity structure) to a rigid frame once deployed, and meanwhile retains the diagonal cables. The reconfigurable extended joint is proved to be a reconfigurable parallel mechanism with many motion types, which is a special variant of the Wren platform. The stowed and deployed states can be converted with Bricard motion. Once fully deployed, the moving platform can be self-locked, utilizing the limbs’ self-motions. Several advantages emerge by adopting the sequential assembling of the reconfigurable extended joints: Firstly, the whole structure can easily be deployed synchronously, because it transforms from a stowed state to a deployed state (and vice versa) with only one degree of freedom. Secondly, in the deployed state, the whole structure can be firmly self-locked by folding an arbitrary unit; thus, complicated latch mechanisms are avoided. Moreover, the tip of the structure does not rotate during the deployment due to the reciprocating deployment of adjacent units. Analysis results show that stiffness of the ADAM mast can be greatly enhanced, and the corresponding influence factors (such as the material property, element size, etc.) can be obtained analytically. Several prototypes have been developed and verified.

This paper proposes two strategies that generate the entry trajectories using pigeon inspired optimization (PIO) for a lifting type reentry vehicle. The obtained entry trajectory should be within the entry corridor formed by the specified upper bounds on heat rate, dynamic pressure, and load factor. In both the approaches, bank angle which is parametrized to be a linear function of energy and angle of attack are considered as the control variables. This paper presents a methodology that converts the path constraints to allowable bounds on the angle of attack. The angle of attack at any instant is obtained by using the load factor constraint in the first approach and in the second approach, the angle of attack is obtained using the heat rate and load factor constraints. Hence, the path constraints are satisfied by modulating the angle of attack alone. In both cases, bank angle is suitably modulated to achieve the desired terminal range-to-go and also to maintain the equilibrium glide condition. The terminal heading angle offset is minimized using traditional bank reversal logic. These two scrategies are simulated for common aero vehicle (CAV-H) with a high lift to drag ($\mathrm{L}/\mathrm{D}$) ratio. Simulation results show that the entry trajectories obtained using the PIO algorithm have satisfied the path constraints and achieved the terminal range-to-go accurately.

This paper proposes a nonlinear aerodynamic reduced-order model robust to different Mach numbers based on a recursive neural network. To model the nonlinear features with varying flow parameters, the Mach number is adopted as an additional input variable. The training case is a weighted filtered Gaussian white noise with wide ranges of frequency and amplitude. For a better generalization capability, proper orthogonal decomposition and partial particle swarm optimization algorithm are introduced to the training process. The approach is tested by predicting the unsteady aerodynamic forces and nonlinear aeroelastic behaviors of a NACA 64A010 airfoil in transonic flow across multiple flow conditions. Comparisons of harmonic aerodynamic responses in the time domain and the frequency domain demonstrate that the model accurately captures the main flow characteristics in a range of transonic flows. After coupling the structural equations of motion and the nonlinear reduced-order model, the proposed method precisely predicts the limit-cycle oscillation trends changing with Mach numbers or structural parameters. The computational time of the present approach is only about 4% of the total time cost of full-order simulations based on a computational fluid dynamics solver. Moreover, as the Mach number range is extended, the resulting model can still account for the parameter-varying linear dynamics, providing a good flutter behavior approximation.

Condition assessment of existing bridge structures is a valuable tool for bridge owners to make reasonable and optimal maintenance and management decisions. Structural condition assessment based on monitoring data is well-recognized within the civil engineering community as an efficient method to understand structural behavior and performance. One of the significant issues related to structural health monitoring is how to accurately interpret monitoring data in order to provide reliable condition assessment results. In this study, monitoring data obtained from a structural health monitoring system installed on an existing three-span prestressed concrete bridge are analyzed for condition assessment. The central span of the bridge contains eight precast post-tensioned girders with half joints, which are located at the ends of cantilevered lengths of the side girders. The half joints also contain external strengthening. The objective of this study is to conduct purely data-based investigations to explore the feasibility of using several condition indicators to identify any changes occurring to the bridge condition. These indicators include the maximum strain responses in the girders and vertical strengthening rods of half joints, transverse moment-distribution factors, and neutral-axis locations. Measured strain data from a number of events recorded from the structural health monitoring (SHM) system are analyzed, and the distribution as well as statistical characteristics of the afore-mentioned indicators are considered for bridge condition assessment.

Wind tunnel tests were conducted to investigate the wind pressure characteristics of sawtooth roofs in a simulated open country wind field with relatively low turbulence intensity. Models of monosloped and sawtooth roof (two to four spans) buildings that were $1:200$ scale were constructed with intense pressure taps installed on the 15° sloped roofs. Both local and area-average pressure coefficients were determined under different wind directions. Preliminary results indicated that the local peak negative pressure coefficients were slightly lower than the literature results. The increase of roof slope led to higher peak design pressure coefficients for sawtooth roofs, especially in the interior and edge regions of roofs. The peak values of negative pressure captured in high corner regions of monosloped roofs were similar to the corresponding data measured on the windward span of sawtooth roofs, which indicated that the American standard provisions for wind pressure design of monosloped roof structures and the Chinese local wind pressure provisions for sawtooth roofs may underestimate the critical wind suction on high corner regions of monosloped roofs. Generally, the area-average pressures heavily depend on the size of tributary area and the region concerned, and higher roof slope led to faster reduction.

In the last few years, a new type of passive damper, the pounding tuned mass damper (PTMD), has been proposed and studied for passive structural vibration control. Experiments and numerical simulations verify the effectiveness of PTMDs. Studies have shown that PTMDs have a larger vibration dissipation capability and better robustness than traditional tuned mass dampers (TMDs). The design of a PTMD involves several parameters, and a numerical parametric study has been performed, but no experimental parametric study of a PTMD has been carried out. This paper experimentally studies the parameter sensitivity of the pounding tuned mass damper for a traffic signal structure. The control of free vibration and forced vibration at different harmonic frequencies are obtained to assess the sensitivity of the PTMD. This study considers four parameters: the viscoelastic (VE) material thickness, the gap between the delimiter and vibrating rod, the mass ratio, and the natural frequency of the PTMD. The parametric studies yield interesting findings that can guide future design of PTMDs.

Deep excavations conducted close to tunnels will cause an adverse impact on tunnels, and countermeasures must be taken during the excavation to ensure the safety of the tunnels. However, the effectiveness of measures to control the vertical displacement of tunnels is still unclear, especially when a cut-and-cover tunnel is tied to a deep excavation. In this study, a three-dimensional (3D) numerical method is used to evaluate the effectiveness of control measures for excavation-induced tunnel deformations. Based on a recent case of a deep excavation in Shanghai, a quasi-three-dimensional numerical model considering the soil–structure interaction and fluid–solid coupling was built by the use of finite difference software, i.e., FLAC3D v5.0. Four countermeasures, i.e., zoned excavation with partition walls and cross walls, piles tied to the walls, soil reinforcement, and dewatering in the confined aquifer, were implemented in this model. The numerical model was validated by field data and the effectiveness of these measures was evaluated comprehensively. Results indicate that the zoned excavation can reduce the vertical displacement of the tunnel, while the cross wall will cause an adverse impact on restraining the tunnel heave. Installation of tie piles can decrease the uplift of tunnels, and the maximum tunnel heave decreases with the increase of the length of the tie piles. Soil improvement is the most effective countermeasure that can reduce the tunnel heave significantly. Dewatering in a confined aquifer can be adopted as a countermeasure to restrain the tunnel heave during excavation.

The classical hose-drogue system has been modified by adding an automated control surface (ACS) at the point where the hose is connected to the drogue. This control surface stabilizes the static position as well as improves the dynamic characteristics of the hose-drogue system. The hose is assumed to behave as a tensed cable with no bending forces. Under the assumption that the dynamic response is small compared with the static deformation, linearized expressions for both the perturbed motion of the hose in the vertical plane and the hose tension are obtained. The resulting dynamic linear equations have variable coefficients that depend on both the initial steady-state static equilibrium position and the static tension of the hose. Owing to the control surface motion, unsteady aerodynamic forces are generated. These forces depend on the drogue local vertical velocity and on the hose slope at the drogue position, and are approached by means of Theodorsen’s theory. The natural frequencies and normal modes of the complete system are calculated. In addition, the responses to the tanker oscillation/pulse excitation to gust and turbulence are obtained. Finally, the influence of the different parameters on the dynamic response of the hose-drogue–control surface system is presented.

Global geometrical relationships are proposed between the design parameters and configuration parameters of the osculating-cone method. A kind of double swept waverider is discussed primarily as an attempt to remedy some of the deficiencies of a traditional waverider. Using nonuniform rational B-spline (NURBS) to represent design curves, the flexibility of the method improves and the smooth surface of the waverider is ensured. Computational fluid dynamics (CFD) analysis is employed to validate the design method and evaluate the advantageous performances of the double swept waverider, such as subsonic characteristics and longitudinal stability. The work provides a novel approach to the aerodynamic shape design for wide-velocity-range hypersonic vehicles.