Journal of Aerospace Engineering

This research was devoted to the development of a structural health monitoring (SHM) system for helicopter structures using the acoustic emission (AE) method. Experiments were carried out on a test bench to test helicopter fuselage and tail boom joints under dynamic loads. During the experiments, several bolted joints fractured. The process of crack development in the bolt material was controlled by the AE method. The results presented in the paper link AE parameters to the process of crack development. Fractographic analysis was used to validate the experimental results. The dependence of fatigue crack growth in a bolt material taking into account bolt retightening in the joint between the tail boom and fuselage was revealed.

Because the Martian atmosphere is composed mainly of ${\mathrm{CO}}_2$, electrochemical conversion of ${\mathrm{CO}}_2$ to ${\mathrm{O}}_2$ is one of the most efficient methods of extracting oxygen, which is indispensable for astronauts to breathe and can be used as an oxidant for rocket engines. In order to realize a reliable oxygen production system, a large amount of ${\mathrm{CO}}_2$ gas must be accumulated and compressed in an electrolytic conversion system. However, dust present in the Martian atmosphere because of dust storms could damage the oxygen conversion system or cause it to malfunction. Thus, a dust removal system is necessary before ${\mathrm{CO}}_2$ gas can be introduced into the system. To this end, an electrostatic precipitator suitable for use in the low-pressure Martian atmosphere has been developed. First, a precipitator consisting of a wire and parallel-plate electrodes was constructed. In a preliminary study, the efficiency of dust removal was 75%–80% without corona discharge, and almost no dust was collected at the corona discharge region in the low-pressure (700 Pa) ${\mathrm{CO}}_2$ atmosphere that simulated the Martian atmosphere. In this case, dust was collected on the surface of the wire electrode, contrary to the case for a pressure of ${10}^5\mathrm{Pa}$ (1 atm). The mechanism of these phenomena was investigated by direct observation and numerical calculation of particle motion in the precipitator. It was clarified that the low charge density of particles in the low-pressure atmosphere caused a relatively large dielectrophoresis force in comparison with the Coulomb force, and the particles were attracted to the wire electrode, i.e., the dielectrophoresis forces dominate in the low-pressure regime, whereas Coulomb forces dominate in the high-pressure regime. Poor performance in the low-pressure atmosphere was caused by the low charge density and low electrostatic field owing to the low limited voltage. Although the performance deteriorated rapidly in the low-pressure atmosphere because of the deposition of dust on the fine wire electrode, it was easy to vibrate the wire electrode and remove dust on the wire.

In this paper, a new, simple, and robust method is presented to calculate the shape factor and stress intensity factor (SIF) of cracked stiffened panels in a mode-I condition repaired with a single-side composite patch. For this purpose, huge finite element (FE) analyses are carried out to achieve a simple equation using normalized parameters and a fitting technique for a vast range of repaired stiffened panels. The parametric study was performed using five effective parameters, including crack length, stiffeners and panel moment of inertia, material, and thickness of the composite patch. Using the proposed formulation in this paper, performing the complex and time-consuming FE analyses to calculate the stress intensity factors for such repaired complex components is not necessary. The obtained results are verified using several FE models. The maximum differences between the predicted shape factors using the proposed equation with those obtained from FE analyses are indicated to be approximately 7%, which is acceptable for engineering purposes.

Overturning failures of curved concrete box-girder bridges with single-column piers have occurred frequently in China in recent years. Lack of an appropriate design to resist the forces caused by unevenly distributed temperatures may be one of the main reasons for these failures. In design practice, only vertical temperature differences are accounted for in the design, and transverse temperature difference effects on curved bridges have been ignored. In order to achieve deeper understanding of temperature effects on curved concrete bridges with single-column piers, the authors studied solar radiation effects on a curved bridge, investigating the transverse and vertical temperature differences in the box girder using three-dimensional finite-element analysis. Then, the stresses and displacements of a curved bridge with different support arrangements were calculated and compared. The results show that the displacements and stresses caused by transverse temperature differences are comparable with those from vertical temperature differences in the curved box girder, which indicates that displacements and stresses are significantly underestimated by only considering vertical temperature differences for curved bridges. After comparing the stresses and displacements for different support layouts, it is concluded that the use of two pinned connected supports in the middle piers significantly reduces the vertical displacement by 46.2% under transverse temperature differences and by 55.6% under vertical temperature differences, whereas the thermal stresses do not vary with a change of support layouts.

With the advantage of satisfying zero shear stress conditions on surfaces, the sinusoidal theory has been widely used for static and dynamic analysis of composite laminated structures. Nevertheless, sinusoidal theories accounting for zig-zag effects have hitherto rarely been reported in the literature because zero shear stress conditions on the surfaces will be violated once the existing zig-zag function is taken into account. Thus, a new zig-zag function that can satisfy traction-free boundary conditions has been developed in this paper. Introducing the developed zig-zag function into the sinusoidal model, a new sinusoidal shear deformation beam theory including the zig-zag function has been proposed, which can accurately describe the zig-zag effect. Other higher-order theories and the first-order theory proposed by other investigators are also considered for the evaluation. By investigating the typical bending problems of multilayer beams, comparison of the present results with three-dimensional elasticity solutions and the results obtained independently using other models shows that the proposed model can more precisely produce the displacements and stresses of laminated composite and sandwich beams in comparison with other models considered in this article.

The response of a thermally and mechanically loaded metal-ceramic spatially graded composite structural panel is considered. The load profiles that are representative of in-flight high-speed loading conditions have been evaluated. Thermal loads due to aerodynamic heating include laminar, turbulent, and transitional (laminar to turbulent) heat fluxes applied on the outer surface of the panel. One- and two-directional graded panels are studied using finite element analysis. The effect of grading on temperature gradients and stress concentrations are investigated. The benefits of the spatial grading for the panels subjected to uniform and nonuniform surface heat fluxes are examined, and the results are compared with those of a Ti-6Al-4V panel with an Exelis Acusil II syntactic foam thermal protection system (TPS). The results show that through-thickness temperature gradients are effectively eliminated in the panel graded in the through-thickness direction as compared with the traditional panel with the attached TPS. Additional grading in the direction parallel to the flow significantly reduces in-plane surface temperature gradients when the panel is subjected to nonuniform transitional heat flux.

High-fidelity computational fluid dynamics (CFD) simulation is now of growing importance to predict the aerodynamic forces of turbine engine blades involving stator-rotor interaction. However, CFD simulation is time-consuming. An efficient Volterra reduced-order modeling (ROM) method is presented to reduce the CFD simulation costs for accurately predicting the aerodynamic forces caused by upstream wake and downstream blocking in stator-rotor interaction problems. The ROM method calculates the aerodynamic forces by first-order multi-input–multioutput (MIMO) Volterra series. The upstream wake (or downstream blocking) is represented by the total pressure waves (or backpressure waves) of a point at the inlet (or outlet) using the traveling wave method. The ROM kernels corresponding to inlet and outlet perturbations are identified by the step method. The accuracy of the proposed method is discussed by two-dimensional (2D) blade examples. The results show that the proposed method is feasible.

Corrosion-induced metal loss in critical structures is a widespread and urgent problem across multiple industries. In this paper, a novel corrosion sensor was proposed based on the theory of electromechanical impedance (EMI). The sensor was fabricated by bonding a lead-zirconate-titanate (PZT) patch onto the metal plate of the same cross-sectional area. The principle of the corrosion sensor is that corrosion-induced thickness loss of the metal plate leads to the change in the EMI of the sensor. Therefore, the corrosion amount can be determined from the impedance response of the PZT. EMI simulation of the sensor, together with modal analysis, was performed through finite-element analysis (FEA). Experimental verification studies were also conducted to validate the simulation results. Results showed that the peak frequency of the first transverse bending mode decreases with the loss of thickness, which can be used to determine the corrosion amount quantitatively. The proposed corrosion sensor has the advantages of low cost, quantitative determination of corrosion amount, and on-line and remote monitoring capability, which shows promising application potential.

Prefabricated RC shear walls are widely used in practical engineering due to their convenient construction. For ease of transport, they are commonly divided into smaller limbs and assembled on site. Steel panel shear keys are therefore adopted to connect the wall limbs and ensure assembly strength and ductility. However, the relative displacement between precast wall limbs can lead to severe damage of floors and, conversely, the wall limbs may be damaged due to the uncoordinated deformation of floor slabs. To this end, the present paper proposes a slotted floor slab with polystyrene-infilled slots set near the wall limbs for increasing the independence of the deformation of limbs. The study focused on the interaction of shear wall limbs and slotted floors. Three specimens of reinforced concrete prefabricated shear walls with shear keys were designed: (1) one specimen without floor slabs; (2) one specimen equipped with a conventional floor slab; and (3) one specimen with a slotted floor slab. Quasi-static tests were conducted, which revealed that conventional floor slabs can increase the lateral resistance and stiffness of the specimen while sacrificing ductility. The slotted floor slabs, in comparison, guarantee deformation ability without weakening the dry-connected shear walls. Above all, floor slabs are better protected if slots are set to release concentrated deformation.

Data-enabled approaches using statistical machine learning are emerging to help engineers identify damage among sensory data, which could be extremely helpful for decision making and data management in structural health monitoring. Although time-series data analysis using different feature extraction methods has been developed to improve data classification in machine learning, one of the remaining challenges is the spatial effects of sensory data. Methods that are suitable for individual sensor data are often limited due to their inability to account for system-level multivariate analysis of a group of sensory data. In this study, we attempted to develop a singular value decomposition (SVD)-based feature extraction method by designing a Hankel matrix to enhance multivariate analysis. We also presented a conventional autoregressive model (AR) and multivariate vector autoregressive model (VAR) for comparison to demonstrate the effectiveness of the SVD method for feature extraction. Further discussion was presented to qualitatively quantify the effects of uncertainty due to noise interference on the features and quantitatively evaluate the robustness of the feature extraction methods under different noise levels. The case study of a laboratory-based frame structure revealed that three feature extractions exhibited high capability in capturing designed damage scenarios, when sensory data was collected near the damage resources. However, the AR and VAR methods were both insensitive in detecting change when data were not near the event, which could be the case in real-world applications. By contrast, the SVD-based feature extraction method exhibited promising results for all cases.

In this study, a piezoelectric-based active sensing system was used to conduct the structural health monitoring (SHM) of a one-bay, two-story reinforced concrete (RC) space frame structure subjected to earthquake loadings. The RC frame in which were installed piezoelectric-based actuators and sensors was tested on a shaking table with ground excitation of various intensities. The embedded sensors in the RC frame were used to diagnose the health status of the tested RC frame during the tests, and an energy-base damage index was adopted to quantify the severity of the damage. The test results indicate that the piezoelectric-based active sensing method for SHM revealed the severity of damage of the tested RC frame after earthquake excitations. A simplified and accurate method for simulating the dynamic responses of the tested RC space frame is presented; it was based on the moment-curvature method and identified fundamental frequencies. The calculated displacement time histories and maximum ductility demands of the structural members were compared with those measured in the shake table test, and excellent agreement was achieved.

Structural responses and response sensitivities are frequently required in structural health monitoring, whereas the computation of structural responses and response sensitivities of a large-size model is time consuming. This paper proposes a substructuring method for the fast computation of structural responses and response sensitivities. Structural responses are projected onto the range space of a few master substructural eigenvectors to construct a simplified vibration equation. The contribution of slave eigenvectors is compensated by a residue space to achieve high accuracy. Due to this compensation of the residue, a few master eigenvectors are needed to ensure the fast computation of structural responses and response sensitivities with high accuracy, avoiding the inclusion of numerous substructural eigenvectors. In addition, response sensitivities with respect to a parameter are calculated from master eigenvector derivatives of one substructure only, whereas derivatives of other substructures are zeroes. As simplified vibration equations are quite small, the proposed substructuring method can very quickly calculate structural responses and response sensitivities. The proposed method is verified by a frame structure and a bridge structure.

The paper presents the pulse-powered turbine engine concept with implemented rotating valve timing system. The engine stands out a big energy efficiency and simple construction. A characteristic feature, and at the same time the main assumption, of the presented engine concept is the isochoric combustion process, which takes place in a stationary combustion chambers. The engine works according to Humphrey’s thermodynamic cycle, which has a larger energy efficiency than the Brayton-Joule cycle that serves as the basis for classical turbine engines. The operation of investigated engine concept requires consecutive stages of preparation of high-pressure gases and supplying the turbine with these gases. The engine is powered by pulses, completely different than classical turbine engines, which are continuously powered. A realization of pulse powering requires the use of a valve timing system. It is crucial element of the presented engine concept, and has a decisive impact on its effective operation. The effectiveness of different valve timing systems was investigated by means of computational fluid dynamic (CFD) analysis. The analysed various intermediate valve timing concepts have led to the development of innovative rotating valve timing system, which seems to resolve many problems addressed in the beginning of the article.

Air-data measurements are one of the essential observations for system identification of flapping-wing unmanned aerial vehicles (UAVs). The effects of intensive high-amplitude oscillations of ornithopters on air-data measurements were studied in detail. The movements of an average-sized ornithopter were simulated through a two-degree-of-freedom (2-DOF) mechanism in a wind tunnel, and measurements of an air-data system (pitot and air vane) attached to the mechanism were studied. pitot tests were conducted at different airspeeds and angles of attack (AoAs) using three pitot tubes. The same experimental conditions were created for air-vane measurements. Results revealed that within certain limits, the average measured airspeed was close to the true airspeed values. Two filters were proposed and used for real-time airspeed estimation. Based on the measurements, the oscillation amplitude of the air vane was almost twice that of the real AoA oscillations. However, the mean values of air-vane measurements and real AoAs coincided over one flapping period. For real-time estimation of AoA, which varies very fast with flapping, an estimator based on the least-squares method was implemented.

Fast adaptation is commonly required in model reference adaptive control (MRAC) to handle uncertainties and achieve precise command tracking. High adaptive gain achieves fast adaption, and introduces high-frequency oscillation into the control signal. In this paper, we propose a robust compensator–based MRAC (R-MRAC) for an aircraft to tackle the problem of control signal high-frequency oscillation. First, the architecture of a standard MRAC with state augmentation is presented. Second, the control architecture is modified by introducing a robust compensator to guarantee transient performance of the closed-loop system. Finally, the proposed R-MRAC is applied to control the altitude of the aircraft with significant uncertainty in control effectiveness and aerodynamic coefficients. Numerical simulations results show that the proposed R-MRAC can effectively eliminate high-frequency oscillation.

The early stages of the design process of wind-excited tall buildings involve several decisions on structural typology, shape, orientation, optional control system, and type and distribution of nonstructural elements. Focusing on this last aspect, the main issue addressed in this paper is a systematic comparative cost-based analysis accounting for the damage at the nonstructural system level induced by extreme wind loads. This design task is accomplished in this study by making use of a cost-based decision framework developed by the authors, designated life cycle cost wind design (LCCWD), specifically tailored for wind-excited tall buildings. Various design configurations are investigated by comparing the lifetime cost induced by wind-load damage as evaluated by adaptation of the Pacific Earthquake Engineering Research Center (PEER) equation, which was originally conceived for seismic engineering. This choice emphasizes the role of a multihazard-inspired design process. The following items are jointly considered: (1) uncertainties in wind-load characterization, structural response, and damage models; (2) wind directionality; (3) dynamic response model accounting for non-shear-type vibration modes and torsional effects; and (4) monetary loss accumulation by partitioning nonstructural damage effects among various building components. Furthermore, the LCCWD is expanded to include internalization of external costs, whereby acceleration-based perception effects on occupants’ comfort lead to business interruptions and consequent downtime losses; these items at are included as indirect costs. Application of the procedure to a case study enables automated, systematic, and cost-effective comparison of various design alternatives.

With the rapid development of optical-fiber sensing technology recent years, it has been widely used for various purposes in engineering fields. However, the strain concentration generated by different types of pavement damage may exceed the ultimate tensile strain of many types of optical-fiber sensors, resulting in a low survival rate. To solve this problem, in this paper, a macrobend optical-fiber sensor with a helical-bending structure is developed and tested. Theoretical calculations and laboratory experiments have been conducted to verify the applicability of this novel optical-fiber strain sensor for pavement strain monitoring. Results show that it has a greater strain measurement range with satisfactory accuracy and is a promising approach to monitor the mechanical response of pavement under actual loads.

This paper presents an analytical study of the transverse vibration of sandwich beams considering the thermal-induced nonuniform cross-sectional properties. Free vibration frequency formulas of sandwich beams, under linearly varied nonuniform temperature distribution scenarios, with and without considering the effect of transverse shear deformation, were derived. The effects of transverse shear deformation of the middle part of the sandwich beam and of the reduction of Young’s modulus in the bottom layer and of the shear modulus in the middle part near the bottom layer on the transverse vibration of the sandwich beam were discussed. The results highlight the importance of considering nonuniform cross-sectional properties and associated shear effects in the dynamic analysis of sandwich beams.