Journal of Aerospace Engineering

Spacecraft are subjected to various dynamic loads due to shock from stage and fairing separations, resonant burn of the rocket motor, pressure oscillation in liquid engines, wind and gust, etc. These dynamic loads are very detrimental to spacecraft components, electronics, and instruments. Hence, for the successful launching of a spacecraft, a whole-spacecraft vibration isolator (WSVI) is often applied to the launching process. In this paper, a novel active whole-spacecraft isolation system based on voice coil motors (VCMs) is designed, fabricated, and tested. The proposed WSVI system is composed of VCMs, supporting leaf springs, and actuator supports. It is nonintrusive to existing hardware, lightweight, and small, and it satisfies the design requirement of vibration isolation without changing the payload adaptor fitting structure. The characteristics of the spacecraft with and without the isolation system were tested. A controller design method based on the system identification and $H_{\infty }$ control law is proposed. A prototype was designed and tested to validate the isolation performance of the proposed system. Experimental results show that the novel WSVI system is valid for significant reduction of the amplitude of the spacecraft’s vibration response.

Recently, magnetorheological elastomer–based vibration control devices have attracted increasing attention due to their field dependence of stiffness characteristics. It is crucial to develop a comprehensive model for precisely predicting mechanical behaviors of magnetorheological elastomers (MREs). In this work, silicon rubber–based MRE samples were prepared and investigated through dynamic and quasistatic stretch tests. Experimental results suggest that the samples possess an obvious magnetorheological effect, as well as frequency- and amplitude-dependent mechanical behavior. In order to depict these properties in a unified scheme, an extended fractional-order derivative model was developed to consider the Payne effect using the framework of the Kraus model. A comparison with experimental data indicates that this new model is accurate in predicting the mechanical behavior of MREs.

Degradation of interfacial adhesive strength is the main reason for failure of the hidden frame–supported glass curtain wall that is now widely used in the construction field. In this paper, a nonlinear ultrasonic Lamb wave detection method was developed for hidden frame–supported glass curtain walls. Both theoretical and experimental studies were carried out to verify the feasibility of the method. First, an excitation signal modulated by the Hanning window was generated through piezoceramic transducers. The artificial intervention of thermal aging was applied to accelerate the degradation of the interfacial adhesion strength, and the reflection signal of different aging periods was obtained. Then, two methods of discrete Fourier transform (DFT) and wavelet packet decomposition were used to feature extraction, and normalization and regression analysis were adopted to compare two methods more reasonably. The experiment results show that the amplitude integral method using the second-order relative nonlinear coefficient can reflect the interfacial adhesion strength sensitively, whereas the variation curve of the third-order relative nonlinear coefficient was not obvious. The result of the wavelet packet energy method was close to the amplitude integral method and consistent with reality. The second-order relative nonlinear coefficient fluctuated over a small range at first; then there was a decline, and it finally increased with the thermal aging time. However, the mean squared error (MSE) of the wavelet energy method was smaller. The wavelet packet energy method is more accurate and has a higher allowable error ability in characterizing the trends.

Fiber-reinforced polymer (FRP) is commonly used to strengthen or retrofit reinforced concrete (RC) structures. FRP debonding may initially occur around tiny cracks and then propagate to other parts of the structure, ultimately leading to the brittle failure of the strengthened structure. Therefore, the secure bonding of FRP onto the strengthened structure should be closely monitored using a reliable approach. In this study, an electromechanical impedance (EMI) technique is applied to monitor early FRP debonding in FRP shear-strengthened RC beams through experimental and numerical studies. Lead zirconate titanate (PZT) patches and strain gauges were bonded onto the surface of the FRP. The admittance and strain data were then collected and used to assess the FRP bonding condition. As the loads were increased, the beams began cracking, leading to FRP debonding and subsequent brittle failure of the beams. A root-mean square deviation index was adopted to quantify the debonding severity. The admittance data of the PZT patches were found more advantageous than the strain data and visual inspection to detect the debonding initiation. The EMI technique was then simulated through finite-element analysis. The FRP-concrete interface was modeled using a bond-slip model. Infinite elements were used to eliminate wave reflections at boundaries. The experimental and numerical results validate the effectiveness of the EMI technique in monitoring FRP debonding.

In this article, vibration characteristics and active vibration control (AVC) of an axially moving cantilever structure are investigated. First, the vibration equation of an axially moving cantilever beam with variable length and tip mass is derived from the Lagrange equation of the second kind. The natural frequencies and modes of vibration are calculated by solving a differential equation. Then, in order to suppress the transverse vibration of the axially moving cantilever structure, piezoelectric (PZT) ceramics are used as actuator in combination with proportional plus derivative (PD) or fuzzy algorithm to build a closed-loop feedback system. The simulation of AVC with two controllers is implemented using a commercially available software platform. The numerical examples illustrate that velocity and tip mass significantly affect vibration characteristics. The simulation results suggest that the PZT actuator is effective to suppress vibration.

Pipelines provide a convenient mode of transportation of fluids, and their safe usage is one of the foremost concerns. In our previous work, a hoop strain–based negative pressure wave (NPW) approach was proposed to detect and localize pipeline leakages by employing a series of bare fiber Bragg grating (FBG) sensors. To enhance the leakage detection capability especially for small leakage rate cases, a FBG hoop strain sensor with adjustable sensitivity has been developed to measure the pressure drop induced by pipeline leakage. This paper analyzes the performance of the developed FBG hoop strain sensors with consideration of NPW energy attenuation. The detectable range $[x_R]$ of each hoop strain sensor is investigated, and thus the sensor quantity can be determined. A case study is conducted on a 32-km pressurized pipeline to demonstrate the analysis procedure, with further discussion of different pipeline parameters’ influences on $[x_R]$. The results show that the smallest detectable leakage rate can be enhanced at least 30% by setting mounts of sensors. The most effective way to enhance the overall performance of the leakage detection system is to develop higher-sensitivity FBG hoop strain sensors.

This paper extends a previous modified axisymmetric analog method to predict heating rates on hypersonic vehicles in conjunction with inviscid computational fluid dynamic (CFD) codes which can provide more accurate inviscid solutions and are suited for complex configurations. The major problem is the heating anomalies encountered in the stagnation region, as the quality of the heating solution is very sensitive to the quality of the inviscid solution in the high-gradient stagnation region. To overcome this problem, a hybrid approach is developed to eliminate noise in the inviscid solution in the near-stagnation region by recalculating a noise-free inviscid solution in that region using an engineering method. As a result, there is no need to spend much effort to compute a high-quality inviscid solution in the near-stagnation region when solving the inviscid solution using an inviscid CFD code, thus significantly reducing run times. The proposed method is applied to several typical hypersonic vehicles and compared with existing approaches to validate its effectiveness. The results show that the proposed method can predict surface heating rates on complex configurations with reasonable accuracy but requires much shorter computational times.

To improve the prediction of the response of braided composite structures, a subcell approach is under development. This method has shown successes in predicting the moduli of braided composites. To examine its capability in strength prediction, a combined experimental and analytical study has been conducted for a ${[0/60/-60]}_6$ braided composite. This includes experimental investigations of the tensile stress-strain behavior of the composite at five off-axis angles of 0, 30, 45, 60, and 90°, and numerical simulations of the experiments using the subcell approach. It was observed that the measured tensile strength, damage, and failure modes varied significantly with the off-axis angle. The subcell modeling approach was successful in predicting both the strength and failure mode for the 0, 30, and 60° coupons but overpredicted the strength for the 90° coupons, where a strong free edge effect on damage initiation and failure was seen in the experiment. The results show that, in the absence of local free edge effects, the subcell approach is promising as a viable and computationally efficient method for the modeling of triaxially braided composite structures.

The transonic buffet over large aircraft wings seriously affects flight safety and ride comfort; hence, improving transonic buffet characteristics by active or passive control methods has been the focus issue of international researchers. Current research shows that shock control bump (SCB) can decrease shock strength effectively at design conditions and improve buffet characteristics by eliminating shock-foot separation. However, SCB will enhance shock strength or produce a secondary shock at off-design conditions. This paper reveals that when the bump was mounted behind the shock position on the upper wing, it can delay the shock-foot separation merged with trailing edge separation in a wide range of free-stream Mach numbers and improve buffet characteristics. Based on the discovery, three-dimensional studies on Wing1, which was released during the Third Drag Prediction Workshop, were presented in this paper. A full-span bump was added on Wing1 at the rearward position behind the shock, and then buffet characteristics of the basic wing and the wing with bump were analyzed using Reynolds-averaged Navier–Stokes and unsteady Reynolds-averaged Navier–Stokes methods. The results show that the bump can improve the buffet performance of Wing1 over a wide range of free-stream conditions; however, it may deteriorate the aerodynamic performance at prebuffet conditions and improve the aerodynamic performance near the buffet-onset conditions.

In order to estimate mean droplet size of spray, a theoretical model using the energy conservation law was derived. In this approach, the loss of kinetic energy leads to the occurrence of atomization phenomenon. The derived formulation shows that the mean droplet size is inversely proportional to atomization efficiency and liquid Weber number. This model needs inputs that are provided using a computational fluid dynamics (CFD) submodel independent of the experimental data. To obtain a prediction of the mean droplet size, an estimation of the atomization efficiency and Weber number is mandatory. Thus, to estimate the atomization efficiency and Weber number, the CFD analysis was conducted for the fluid flow inside the injector considering environmental domain. Prediction of the proposed model has close agreement with available experimental data. Parametric investigation was also done to study the effects of some parameters on the mean droplet size. Consequently, the combined model can be applied as a time-saving and simple model to achieve a good prediction for the mean droplet size of spray.

The terminal state error under impulse orbit maneuver uncertainty is minimized using the linear covariance method. A new actuation-error model is proposed for practical engineering application, which requires that the thrust direction be aligned with the impulse vector. The polar angle in the error model can be adjusted to reduce the terminal error. This paper studies two impulse-maneuver problems, including short-range orbit rendezvous and translunar midcourse correction. First the state transition matrices for the two problems are provided. Then the control error matrix is derived under impulse-magnitude and impulse-direction errors. The terminal linear covariance matrix is obtained by considering both navigation and actuation errors. Finally, the optimal polar angle is numerically solved by the golden-section search. Numerical examples are provided to verify the proposed method for the analytical linear covariance matrix and the optimal polar angle.

The aviation environmental design tool (AEDT) is simulation software for estimating the environmental ramifications of aircraft. Because the AEDT would be repeatedly used for applications such as airport noise assessment, a computational cost may arise as a concern for aviation environmental research. To expedite noise evaluation using the AEDT, this research devised a rapid approximation of the AEDT via reduced-order modeling (ROM) because the technique is effective in approximating large-dimensional data. In particular, proper orthogonal decomposition (POD) and ordinary Kriging were leveraged for orthonormal basis extraction and basis coefficient prediction, respectively. For demonstration, a reduced-order AEDT model was developed by associating two AEDT outputs—departure and approach noise—with five atmospheric parameters—elevation, temperature, pressure, relative humidity, and headwind—for single departure and arrival flights using straight tracks. With the help of POD, the reduced-order AEDT noise model was formed based on the first three leading basis vectors, and the three corresponding basis coefficients were estimated by separate Kriging models according to atmospheric variation. After the model construction, the reduced-order AEDT noise model was verified using the training and testing data sets and exhibited reliable approximation capability. Overall, the employed POD-based ROM with Kriging was able to tremendously accelerate the AEDT noise simulation, thus encouraging the use of the AEDT for aviation environmental impact studies, particularly those involving many airports operating a multitude of flights.

Random decrement technique (RDT) is a popular time-domain approach to extract modal properties of structures from ambient vibration data; however, it may result in poor estimation results when structural modes are closely spaced. In this study, a method of combining analytical mode decomposition (AMD) and RDT is presented to determine the modal properties of structures with closely spaced modes from ambient vibration data. The measurement acceleration data are first decomposed into a series of subsignals by way of the AMD. Then, the RDT is applied to each subsignal to extract the random decrement signature from which the modal properties of the structure are identified. The proposed AMD-based RDT method is compared with the multimode random decrement technique (MRDT) and stochastic subspace identification (SSI) through numerical simulation data from a four-degrees-of-freedom system with close modes. It is shown that the present method performs better than the MRDT and SSI. When significant modal interaction occurs, decomposing into the multimode subsignals successfully separates responses of close modes from those of other modes, which permits accurate identification of the modal properties for the relevant modes. The modal parameters of a curved cable-stayed footbridge are estimated by the proposed method, demonstrating that the method is viable in practical applications.

Unmanned aerial vehicle (UAV) technologies combined with digital image processing have been applied to the crack inspection of bridge structures to overcome the drawbacks of manual visual inspection. However, because of environmental interference such as uneven natural light, noises produced by the UAV hardware, spots on the road surface, and UAV jitter, the collected images by UAVs are usually fuzzy and have relatively low contrast. In the processing of such collected images the traditional edge detection algorithms such as Canny algorithm, Prewitt algorithm, and Sobel algorithm have low detection accuracy because of their poor antinoise ability. K-means clustering method is one of the unsupervised learning methods. Nevertheless, in the case of a small amount of images, it cannot achieve the accurate identification of the cracks from the collected image. In this paper, a new crack detection method based on the crack central point, namely crack central point method (CCPM), is proposed to address these essential issues. With a small amount of images, the new method can quickly and accurately identify the cracks in the collected images. Compared with the traditional edge detection methods and K-means clustering method, the CCPM method has better adaptability and robustness.

The present paper is the first study of free vibration analysis of laminated composite rhombic (skew) elliptic paraboloids with mass variation via multiple cutouts and concentrated mass. To solve the vibration problem of a laminated composite skew elliptic paraboloid with multiple cutouts and concentrated mass, cubic variation in the displacement field and cross-curvature effects of the shell are considered. The parabolic variation of transverse shear strain is considered; hence, no shear correction factor is required. The zero transverse shear stress conditions at the top and bottom of the shell are imposed in the mathematical model. The finite-element implementation of the present realistic mathematical model is done using a nine-noded curved isoparametric element with seven unknowns at each node. The ${\mathrm{C}}^0$ finite-element (FE) implementation of the present mathematical model has been done and coded in FORTRAN. The present model results are compared and found in good agreement with experimental, analytical, and other solutions published in the literature. A free vibration study has been done for skew elliptic paraboloids with multiple cutouts and concentrated mass having different curvatures, ply orientations, and thickness ratios.

Railway track is one of the most important parts of the railway system, and monitoring its condition is essential to ensure the safety of trains and reduce maintenance cost. An adaptive regularization approach is adopted in this paper to identify the parameters of a railway ballasted track system (substructure) from dynamic measurements on in-service vehicles. The vehicle-track interaction system is modeled as a discrete spring-mass model on a Winkler elastic foundation. Damage is defined as the stiffness reduction of the track due to foundation settlement, loosening in the rail fastener, and lack of compaction of the ballast. Accelerometers are installed on the underframe of the train to capture the dynamic responses from which the interaction forces between the vehicle and the railway track are determined. The damage of the railway track can be detected via changes in the interaction force. Numerical results show that the proposed approach can identify all stiffness parameters successfully at a low moving speed and at a high sampling rate when measurement noise is involved.

This paper proposes a structural damage identification approach based on model updating with electromechanical impedance sensitivity and the sparse regularization technique to identify the location and severity of minor damage in structures. The sensitivities of the resonance frequency shifts in the impedance responses with respect to the stiffness parameters of the host structure are calculated and used to identify the damage with a small number of resonance frequency shifts. Numerical verifications on a single lead zirconate titanate (PZT) transducer patch and a PZT on a narrow aluminum plate structure are conducted to validate the finite-element modeling technique to calculate the impedance. The effectiveness and performance of the proposed structural damage identification approach are demonstrated with numerical simulations on an aluminum plate model attached to a PZT transducer patch. The initial finite-element model and a limited number of resonance frequency shifts in the impedance responses are used for the identification. Sparse regularization, namely, the $l_1$ regularization technique, is used for solving the inverse problem. Single and multiple damage scenarios are considered. The effects of noise in the measured impedance signals and the number of available frequency shifts on the performance of the proposed damage identification approach are investigated. The results demonstrate the performance and robustness of the proposed approach.

In this paper, a novel adaptive model-free attitude tracking control method is investigated for rigid spacecraft with consideration of the external disturbance, unknown inertia matrix, and input saturation. First, the considered attitude tracking system with input saturation is transformed into a Lagrangian model, and a dead zone–based model is used to describe the saturation nonlinearity. Second, using the prescribed performance control theory, a static prescribed performance attitude control scheme is presented, by which the transient and steady-state performance (including the convergence rate, overshoot, and boundedness) of the attitude tracking system is proved to be guaranteed. Third, in order to improve the performance of the static prescribed performance control scheme, a novel learning-based supplementary control scheme is presented based on the approximate dynamic programming. Finally, two groups of numerical simulations are used to illustrate the effectiveness of the proposed learning-based prescribed performance attitude control method.

Eddy current damping has been widely applied in mechanical engineering; however, its adaptation for civil engineering applications remains rather limited due to its low density of energy dissipation. This study presents the development of a new type of eddy current damper and theoretical and experimental characterization of its damping properties. In addition to rectangular permanent magnets and conductive plate, both primary back iron and secondary back iron are considered in the proposed eddy current damper, which represents an improved design over previous configurations. The analytical method based on the charge model of permanent magnets is extended to simulate the extra damping effect of the primary back iron and secondary back iron, and the magnet field and damping properties of the dampers are evaluated analytically. The use of a back iron in the proposed damper is shown to increase the damping coefficients by a factor of up to 5. The analytical results are compared with those obtained with the finite-element analysis in terms of accuracy in magnetic field distributions, eddy current distributions, and damping coefficients. The linear assumption, which implies the damping force is linearly proportional to velocity in the analytical model, is also examined for different motional velocities and relative permeability of the permanent magnet. It is shown that the linear damping assumption in the analytical model is only valid for a limited range of low velocity, and this velocity range can be increased by reducing the thickness or conductivity of the conductive plate. In addition, a modification is needed for the analytical model if the relative permeability of the permanent magnet significantly deviates from the assumed value of 1.0. Finally, the accuracy of the analytical model and the finite-element model is verified by experiment of a prototype damper mounted in a laboratory steel frame.

Concrete recycling is an important element of sustainable development. Demolished concrete lumps (DCLs) can be blended with fresh concrete as a filler, but achieving good compactness of the compound concrete can be a problem. An effective compactness-monitoring method for DCL compound concrete is needed urgently. In this study, a simple and rugged lead zirconate titanate (PZT)-based smart aggregate (SA) for monitoring compactness using transient excitation was tested in the laboratory. The same type of sensor was used as both the excitation and the receiver transducer. The level of compactness was measured by directly propagating longitudinal stress waves in a specimen of concrete $600\times 600\times \mathrm{1,000}\mathrm{mm}$. Twenty-four transducers were deployed at four heights to create 12 parallel monitoring paths. The excitation signal is a smoothed tone burst with an amplitude of 90 V and frequency of 70 kHz. Reliabilities of velocity, amplitude, and central frequency of the received stress waves as the compactness-monitoring index were evaluated by comparing with core sample tests. The technique demonstrated great potential in monitoring the compactness of DCL compound concrete.

A low-frequency continuous torsional motion technique (CTMT) is presented to efficiently extract the aerostatic force coefficients (AFCs) of bridge decks. In contrast to the conventional numerical simulations at a series of discrete angles of attack, the CTMT can conveniently obtain the continuous angle-varying AFCs. Thus, the numerical modeling labor efforts and computation time are significantly reduced. The CTMT accuracy is validated by calculating the AFCs of one flat plate and comparing it to the theoretical solutions. The AFCs of two representative deck cross sections (both streamlined and bluff) are numerically calculated and compared to those of testing results, by which the applicability and limitation of this newly developed method are examined. Due to its convenience in obtaining more ample information without losing accuracy compared to the traditional discrete technique, the CTMT is strongly recommended for future numerical simulations of AFCs of bridge decks.

This paper proposes a novel index, the extreme value of the largest principal component scores of the generalized likelihood ratio based on the statistical process control chart, to develop a structural stiffness identification method for assessing traditional Chinese mortise-tenon joints. The proposed method involves four stages. First, a generalized likelihood ratio test is conducted by transforming the collected acceleration signals into the generalized likelihood ratio matrix. Second, principal component analysis (PCA) is used to reduce data dimensionality and extract the extreme values of the first principle component scores as a novel control index. Subsequently, a statistical process control chart is drawn via the proposed control index. Finally, the ratio of the structural stiffness reduction can be evaluated by establishing the relationship between the stiffness and number of control indices outside the upper and lower control limits in the statistical process control chart. The proposed method is validated by vibration test data acquired from a traditional timber frame under reversed cyclic loads and vibration in a laboratory. The results show that (1) the proposed index performed in the statistical process control chart is able to monitor the novelty of the mortise-tenon timber joint; and (2) the proposed method can be used to assess the states of the timber structure and even predict further structural stiffness.

This article presents the aerodynamic mixing efficiency of triangular and inverted triangular tabs, placed in a Mach 2 supersonic jet at $0D$, $0.25D$, $0.5D$, and $0.75D$ downstream of the nozzle exit, in the presence of different levels of nozzle expansion in the range from 0.383 to 1.022. Both tabs offer the same blockage of 5% of the nozzle exit area. The results show that the mixing caused by the triangular tab with its vertex down is better than an inverted triangular tab for all the tab positions tested in this study. Among the shifted locations, $0.5D$ proves to be the best location, resulting in a core length reduction of 68% for the triangular tab, in the presence of a marginal favorable pressure gradient of 2.2%, corresponding to nozzle pressure ratio 8. However, this mixing promotion is considerably lower than that by the same tab at the nozzle exit ($0D$) at the same nozzle pressure ratio, which promotes mixing, leading to a core length reduction up to 92%. But even at the $0D$ position, the core length reduction caused by an inverted triangular tab, at nozzle pressure ratio (NPR) 8, is only 35.6%.

Accurate and rapid condition assessment of in-service structural components is critical to ensure safety and serviceability. One major assessment consideration is the detection and quantification of structural section loss due to deterioration, for instance, from corrosion. Modern three-dimensional (3D) imaging techniques, which generate high-resolution 3D point clouds, are capable of detecting and measuring these deteriorations. However, despite advancements in the fields of automated point cloud analysis for as-built modeling and structural inspection, the potential use of spatial 3D data for updating numerical finite-element (FE) models of structures is still an emergent topic. This paper presents a localized methodology for the automatic and systematic detection and quantification of damages in structural components using high-fidelity 3D point cloud data, followed by a corresponding local update to an FE model. In this study, 3D point cloud data of a targeted structure were first obtained by using dense structure from motion (DSfM) algorithms. Section loss damage was then identified and located through computer vision and 3D data processing techniques. In order to preserve data integrity and resolve localized high-fidelity details, direct 3D point cloud comparisons were performed. An experimental study validating the developed approach is presented as well. The results indicate that the presented methodology will enable engineers to use the updated structural model to determine the reserved capacity and remaining service life of structural elements, though further studies on methods to improve mesh generation and defect quantification are warranted.

Thermal vacuum and swivel table tests of a control moment gyroscope (CMG) are designed and the start-up hesitation and rotation break of the CMG are analyzed. In order to study the fault mechanism, a thermo-structural coupling simulation was performed on the CMG under the temperature conditions of 60°C and approximately 20°C, as well as the static and dynamic working conditions of the swivel table and gimbal. The simulation results show that the main reason for the start-up hesitation and rotation break of the gimbal is an elliptical deformation in different circumferential positions of the gimbal shell and the gimbal bearing. Under certain combinations of temperature and dynamic conditions, the shrinkage of the radial and axial clearances of the gimbal bearing causes the faults, which is consistent with the test results. The test and simulation results are also helpful in determining the temperature limits of the CMG under different conditions and can help improve their thermal design.

Energy harvesting from ambient vibrations using piezoelectric materials has garnered much research focus over the years due to its immense potential to replace/recharge batteries in wireless sensor nodes and low-power-consuming autonomous electronic devices. Practical implementation of conventional linear piezoelectric energy harvesters is not an effective solution because they suffer from narrow operational bandwidth due to their single resonant peak response in frequency spectrum. Several techniques, such as oscillator arrays, passive/active resonant tuning, and nonlinear methods, have been proposed to broaden the bandwidth of harvesters. This paper proposes a novel trident (three-pronged spear) shaped multimodal (three degrees of freedom) piezoelectric energy harvester to harness electrical energy from wideband, low-frequency, and low-amplitude ambient vibrations. A single patch of piezoelectric material is used for power generation from multiple modes of the structure. The harvester structure consists of a primary cantilever beam with a patch of macrofiber composite bonded on it and three branched beams with tip masses attached to the free end of the primary beam. The first three bending modes of the harvester are used for power generation. The proposed harvester can be designed to operate in the frequency range of the target vibration source. A parametric study varying the geometric parameters of the harvester is conducted using ANSYS finite-element analysis software to obtain the three resonant peaks in the 15–20 Hz bandwidth. The prototype of multimodal harvester is fabricated in accordance with the parametric study and tested under harmonic and random excitations. When tested at $0.2g_{\mathrm{rms}}$ harmonic excitation, the harvester generates 3738, 47, and 123 μW at the three resonant peaks. When tested under random excitation, the harvester accumulates sufficient energy in a capacitor to support a low-power standalone wireless sensing unit.

Future human or robotic missions to the Moon will require efficient ascent path and accurate orbit injection maneuvers, because the dynamical conditions at injection affect the subsequent phases of spaceflight. This research focuses on the original combination of two techniques applied to lunar ascent modules, i.e., (1) the recently introduced variable-time-domain neighboring optimal guidance (VTD-NOG), and (2) a constrained proportional-derivative (CPD) attitude control algorithm. VTD-NOG belongs to the class of feedback implicit guidance approaches aimed at finding the corrective control actions capable of maintaining the spacecraft sufficiently close to the reference trajectory. CPD pursues the desired attitude using thrust vector control while constraining the rate of the thrust deflection angle. The numerical results unequivocally demonstrate that the joint use of VTD-NOG and CPD represents an accurate and effective methodology for guidance and control of lunar ascent path and orbit injection in the presence of nonnominal flight conditions.

Physical pressure sensors installed on a vehicle’s surface are the general way to find air data, such as true airspeed, attack angle, and sideslip angle. Under extreme flight conditions, failure of pressure measurements are a possibility. Estimating air data based only on navigation information and flight control parameters is a potential method for providing a backup virtual air data system (VADS). Ordinarily, wind velocity is assumed to be known in VADS. To solve the air data estimation problem without initial wind velocity, we propose air data estimation algorithms with and without wind models. We used kinematics equations and aerodynamic models to establish the relationship between navigation information and wind velocity. We estimated wind speed using nonlinear filtering algorithms, then obtained air data parameters. We ran simulation experiments with the proposed estimation algorithms, and the results show that the proposed method achieves higher convergence speed and estimation accuracy.

This study investigated structural safety evaluation of in-service tunnels. Considering the factors that affect the safety of in-service tunnels, the indices and grading standards for structural safety evaluations of concrete tunnels were first introduced. Subsequently, a safety evaluation system was established based on an adaptive neuro-fuzzy inference system (ANFIS). Taking a concrete tunnel as an example, according to structural characteristics of the tunnel and a Chinese specification, the indices and grading standards for the structural safety evaluation of the tunnel were determined, and a safety evaluation system for the tunnel was established. In the safety evaluation system, the effect of data size on the training results of the system was analyzed based on the theory of statistics and the Delphi method that are used for data inspection. The results show that the evaluation system has good learning and application ability. By using the field measured data of an in-service tunnel, after learning, the system can effectively imitate experts to do nonlinear fuzzy inference.

Although giant magnetostrictive actuators (GMAs) have been widely studied in the field of active vibration control, the effectiveness of GMAs to control the vibration of cable structures has not been reported yet. This paper proposes an active control method of stay cable vibration using a GMA. A bilinear motion equation of a small-sag stay cable equipped with a GMA is established and the optimal active control algorithm of this control system is designed based on Lyapunov theory. A GMA is developed for the active control of a stay cable model and dynamic properties of the GMA are tested to determine the relationship between the input voltage and the output force. Numerical simulations and experimental tests for the active control of a stay cable model using the designed GMA are performed under free and forced vibration. The results indicate that the designed GMA can effectively reduce the cable vibration based on the proposed optimal active control algorithm.

An algorithm to detect damage size and shape using a lead zirconate titanate (PZT) transducer array for a plate structure is developed in this paper. During the process of detection, the predetermined PZT transducers are chosen as actuators to generate Lamb waves, and others are chosen as sensors to detect the Lamb waves. When there is damage, the Lamb wave reflects at the boundary of the damage. The reflection point is on an ellipse with two foci at the actuator and sensor, and this ellipse is tangent to the boundary curve of the damage at the reflection point. The reflection point can be obtained by finding a special point on the ellipse, and this point has the shortest distance to the center of the curvature of the damage boundary curve. As a result, the damage boundary curve can be determined by finding various reflection points, and the envelope of the identified reflection points is employed to represent the shape of the damage. Experiments are conducted on an aluminum plate with 12 piezoceramic transducers to identify the sizes and shapes of bonded masses, which are considered as simulated damages. The experimental results indicate that the proposed method can obtain the size and shape of bonded masses with a relatively small error.

Axial-flow compressors work against varying inlet boundary layers in real working conditions and are therefore required to perform well and robustly. This paper presents a surrogate-based optimization procedure applied to a transonic compressor to improve its efficiency and reduce the sensitivity of efficiency variation to uncertain inlet boundary layer thicknesses while maintaining the total pressure ratio. The aerodynamic optimization of compressors involves high-fidelity computational models that would cost high amounts of computational time. To implement the optimization, a region-segmentation combining surrogate model is used that is based on combinational use of the region-segmentation idea and combining surrogate modeling method to further improve prediction accuracy and reduce computational cost. Based on the region-segmentation combining surrogate model, an optimization procedure is constructed and applied to a transonic compressor. The computational results of the benchmark function and compressor optimization indicate the validity of the region-segmentation combining surrogate model in improving the prediction accuracy and computational efficiency. The optimization procedure also presents the ability to improve the compressor efficiency and make the compressor perform well and robustly at uncertain inlet boundary layer thicknesses while maintaining the total pressure ratio. The achieved aerodynamic benefits of the compressor have demonstrated the feasibility and effectiveness of the optimization strategy.

In this study, experiments were conducted in a Mach 2.92 supersonic flow to investigate the combustion process in an ethylene-fueled model scramjet combustor with a rear-wall-expansion geometry. It is concluded that at low equivalence ratios, successful ignitions would become rather hard in the cavity with a low rear wall height. Increasing the equivalence ratio could improve the ignition environment within such cavity geometry. During a stable combustion process, the rear-wall-expansion cavity with a higher rear wall height would always achieve an improvement in combustion performance in the combustor. At a relatively high equivalence ratio, when increasing the cavity rear wall height, the flame stabilization mode would vary from cavity shear layer-stabilized mode to cavity-assisted jet wake–stabilized mode, and finally to the thermal choking state. Besides, reaction zones flashback phenomenon is obviously observed during the flame propagation process at such equivalence ratio. It has been demonstrated that the cavity with a lower rear wall height is more able to prevent thermal choking in the combustor.

Uncertainty and external disturbance during the Mars entry process inevitably degrade the performance of Mars entry guidance and control algorithms. Traditional approaches focus on suppressing disturbances and compensating uncertainties, which usually results in larger control responses beyond the limited control capability of a Mars entry vehicle. This paper further takes the limited actuator ability into consideration and proposes the Mars entry robust attitude control strategy using the terminal sliding mode control (TSMC) with antiwindup (AW) and a supertwisting sliding mode disturbance observer (SMDO). First, terminal sliding mode control with antiwindup is developed to robustly track the nominal attitude command under uncertainty and limited control capability. Then, the supertwisting sliding mode disturbance observer is introduced to online estimate the disturbances and further enhance the attitude control accuracy and robustness. Finally, the comparison simulation results illustrate that the proposed control strategy not only performs well in tracking the reference commands even in the presence of uncertain disturbance, but also avoids the control saturation issue.

The purpose of this study is to present a design for a removable tray containing measuring instruments for flight tests dedicated to the PW-6U glider. The design was made at the Rzeszow University of Technology (RUT) within the Advanced In-flight Measurement Techniques 2 (AIM²) project, which was carried out to develop optical methods and tools for in-flight measurements. Because of the specific light weight construction and the restricted space in the glider’s cabin, a special tray was required to hold infrared thermography (IRT) and image pattern correlation technique (IPCT) cameras. The tray was made of carbon epoxy composite as a pylon with a nacelle mounted on its top to hold the cameras inside.