Abstract:The structures of hypersonic vehicle surfaces, engine baldes, internal ducts and exhaust ducts are pronse to thermal-acoustic fatigue damage when exposed to high temperature and high-intensity nosie environments. Thus, it is of more significance for improving the durability and reliability of such structures to study the thermal-acoustic fatigue problems. On the basis of literature review and summarization, this paper comprehensively ealborated on the new progress in the research of thermal-acoustic fatigue problems of aerocraft structures both domestically and internationally. Firstly, the research status of structural thermal-acoustic fatigue in foreign countries was reviewed from the 1970s to the present from a time perspective. Then, the work carried out by domestic research institutes and higher education institutions in this field was introduced according to the classification of research units. It showed that significant progress had been made in the theoretical research, simulation analysis and experimental technology of thermal-acoustic fatigue both domestically and internationally after half a century of development. The technical difficulties faced by the research on thermal-acoustic fatigue of aerocraft structures and the issues that need further research were also discussed at last.

Abstract:Experimental modal analysis is a method of measuring the natural vibration characteristics of a structure through experiments. The analysis results are mainly used to modify the structural dynamic models and provide data support for structural dynamics, aeroelastic analysis and vibration control design. This article systematically reviews the research progress of experimental modal analysis methods at home and abroad, starting from two aspects: classic experimental modal analysis methods and modern modal analysis methods, and summarizes the basic principles of the two mainstream methods, the classic phase resonance method and the phase separation method, briefly introduced the experimental modal analysis methods developed in recent years, and summarized the characteristics of different modal analysis methods. Finally, the current problems and possible future development trends of experimental modal analysis methods are given.

Abstract:Flexible materials to achieve deformable wing technology requires high mechanical properties of flexible materials, the existing research on chiral structures as flexible materials to drive deformable wings is based on the case of linear small deformations. In order to investigate the mechanical properties of chiral structures under large deformation conditions, this paper takes five common chiral system negative Poisson"s ratio structures, such as tri-chiral, anti-tri-chiral, tetra-chiral, anti-tetra-chiral, and hex-chiral structures, as the object of study, and based on the theory of cellular structural mechanics, compares and analyses the effect of topological structure and cellular element geometrical parameter on the in-plane compression and energy absorption characteristics of chiral system negative Poisson"s ratio structures of the intrinsic model of ideal plastic materials. properties of the chiral structure. It is found that the elastic modulus, plateau stress and energy absorption capacity of the chiral structure are inversely proportional to the cell element parameter ?? and positively proportional to the cell element parameter ??. The comprehensive comparison concludes that the topology affects the energy-absorbing properties of chiral structures significantly, i.e., the energy-absorbing capacity of chiral structures with the same single-cell geometrical parameter is significantly enhanced with the increase in the number of ligaments.

Abstract:Addressing the challenge of low identification accuracy in traditional load identification methods based on the truncated singular value decomposition (TSVD) method, especially when the external load frequency approaches or reaches the natural frequency of the structure, we propose the LSTM-CNN load identification model. This model combines the feature extraction capabilities of the convolutional neural network (CNN) with the long-term memory function of the long short-term memory network (LSTM). The load identification method based on the LSTM-CNN model is then applied to research load time domain waveform identification on the GARTEUR aircraft model. For model training and load identification, we collect response data and excitation data from the structure. The identification results are compared with the TSVD method, LSTM method, and DCNN method. The findings demonstrate that the load identification method based on the LSTM-CNN model proves effective for sinusoidal load identification problems, especially under the natural frequency excitation of the structure. The method exhibits high identification accuracy and robust noise resistance capabilities.

Abstract:Open-cell foam material is an advanced functional and structural integration material that can meet the practical needs of aerospace and other high-tech fields, and has a good prospect in practical engineering production applications. In this paper, a method of constructing a 3D open-cell foam model using Voronoi diagram is proposed to simulate the geometrical characteristics of the open-cell foam microstructure, and the disturbance factor K is defined to measure the degree of irregularity of the microstructure. The smaller the disturbance factor, the more regular the microstructure. The generated porous foam solid model with cross-section properties can be imported into a variety of finite element software to complete the finite element calculation such as mechanics and acoustics, and the corresponding physical model can be generated by photosensitive resin printing technology. The accuracy of the generated model is further verified by mechanical and acoustic experiments and simulations. This paper provides an idea and method for the construction of three-dimensional Voronoi open-cell foam model, and has certain reference significance for the further study of properties and production of porous materials.

Abstract:At present, the most widely used control algorithm in the field of Active Noise Control (ANC) is the classic FxLMS algorithm and its improved methods. This type of algorithm has the characteristics of simple structure, low computational complexity, easy implementation, and good stability. However, when applied to large space and large range noise control such as the cockpit of turboprop aircraft, as the number of channels in the ANC system increases, the computational complexity of the algorithm will rapidly expand, The real-time performance of the algorithm is difficult to meet, and the noise reduction effect of the system is greatly compromised or even ineffective. The Sequential Partial Update FxLMS (SPU-FxLMS) algorithm effectively solves this problem, but its convergence performance is weaker than the FxLMS algorithm. This article makes improvements to the problem of slow convergence of the SPU-FxLMS algorithm, allowing it to converge at a faster speed in the initial stage and continue to run with low computational complexity after converging to a stable state. Theoretical derivation and simulation analysis were conducted on the algorithm, and the simulation results showed that the method not only significantly reduces computational complexity, but also has good noise reduction performance and robustness.

Abstract:In traditional methods, the absorption of flexural waves in beams and plates is often achieved by incorporating complex and heavy structures with additional damping materials. In addition, new vibration reduction methods for beams and plates have emerged in recent years, such as phononic crystals and acoustic black holes. Among them, the research on absorbers based on continuous bound states, which can achieve near-100% absorption without the need for additional damping materials, has garnered extensive attention. However, this research is based on the time-domain coupled mode theory, which is not applicable to all models and results in a complex design process, making it difficult for widespread application in industrial engineering. Therefore, this paper proposes a research method for elastic absorbers based on the acoustic impedance matching theory. Theoretical calculations, numerical simulations, and experimental validations have demonstrated that this theory can accurately predict the absorption curve of the proposed absorbers and can quickly and easily realize the structural design of elastic absorbers, bringing new possibilities for the research on flexural waves absorption and vibration reduction design. The theoretical method and absorption structure proposed in this paper do not need additional damping materials, which is more conducive to meet the requirements of lightweight structures in aeronautical engineering. At the same time, it brings new possibilities for the field of vibration wave absorption, especially the design of efficient absorption and vibration reduction of curved waves.

Abstract:The damage effect of the explosion shock wave generated by the explosion of the air to air missile warhead on the aircraft skin structure is influenced by various factors, and the function mechanism is relatively complex, so that a large number of experimental and computational samples are required to evaluate the damage of shock waves to aircraft skin structures accurately. Thus, static explosion experiments of aluminum alloy reinforced plates with fixed supports were performed, and their dynamic response and deformation patterns under shock wave loading were analyzed. The finite element analysis software LS-DYNA was employed to simulate the structural response under explosive impact, and the simulation model were validated by comparing them with the experimental results. The effects of adding prefabricated holes to the target plate and changing the incident angle of explosion on the target damage resistance were studied using the validated simulation model. The results indicate that: the target plate is prone to tensile failure with tearing at the fixed boundary when the hole area ratio of the reinforced plate exceeds 1‰, and increasing the hole diameter or the number of holes enhances the risk of perforation damage between holes; the target deformation increases with the incident angle of explosion, and the target deflection can increase by more than 30% when the angle increases from 30° to 60° at a constant explosion distance.

Abstract:Aviation aircraft will be subjected to a large number of complex random vibration loads during service, and its structure is prone to vibration fatigue, which leads to damage or even failure, causing serious losses. The vibration fatigue test and theoretical analysis are carried out on a typical cantilever beam as an object ,the SIF solution method for cracked beams under random vibration loading is investigated, and a time-domain method based on Hudson"s theory is proposed to estimate the vibration fatigue crack growth life by combining with the Paris formula. It is found that the time-domain method proposed based on the Hudson method compares well with the experimental estimation results, which verifies that the model can effectively describe the random vibration crack growth behavior.

Abstract:A predictive study is conducted on the vibration response of aircraft wall panels with Macro Fiber Composite (MFC) patches under basic harmonic excitation. Based on classical laminate plate theory, electromechanical coupling constitutive equations, and the energy method, an analytical model of the MFC-panel system under basic harmonic excitation is established. By employing velocity feedback control and modal superposition principles, the vibration response of the structure system before and after active control under such an excitation load is successfully solved. The analytical model and its prediction results are extensively validated through the literature data and experimental data obtained from a vibration testing system that is assembled. The research results indicate that, compared to the literature results, the maximum deviation in the calculation of natural frequencies by the proposed model does not exceed 2 %. Additionally, the maximum error in predicting the first two order resonance responses by the model is less than 8.6 %, with both of them being within an acceptable range. The analytical model and response prediction method presented in this study provide a new approach and analytical tool for analyzing and evaluating the dynamic mechanics and vibration control performance of MFC-panel structures.

Abstract:In aircraft ground vibration test, an appropriate excitation scheme can significantly shorten the test’s period and improve the accuracy of mode identification. In this paper, QR decomposition based on the finite element model is used for global planning of exciter placement, and mode participation is introduced to evaluate the plan’s exciting efficiency. The multivariate mode indicator function is used to modify the exciting force vector for closely spaced modes.Finally, these methods are verfied in a small general aircraft’s ground vibration test, which significantly improves the test’s efficiency and reduces the difficulty of closely spaced modes identification.

Abstract:The turbine blades of aero-engines are subjected to cyclic high-low cycle loads in actual service environments, which is a typical high-low cycle micro motion fatigue condition. The frequent occurrence of fatigue fracture in turbine blades due to fretting fatigue seriously affects the safe operation of aero-engines. In order to study the high-low cycle fretting fatigue problems of hot end component materials, this paper designs an Inconel718 tenon connection simulation component and conducts high-low cycle composite fretting fatigue tests on it. Five different load/frequency experiment conditions were designed to compare the life distribution of the simulated parts under different conditions. The results show that high/low cycle load has significant influence on fretting fatigue life. With the increase of high/low cycle load or frequency, the fretting fatigue life of joints decreases.

Abstract:The rubbing of the labyrinth sealing structure is a common problem during the operation of aeroengine air system. Due to the difficulty in observing the process of crack initiation and propagation on the sealing ring during actual rubbing, using finite element method for numerical simulation can provide a deeper understanding of the process and mechanism of crack initiation and propagation. This study established a sealing ring model with wear grooves after rubbing. The surface convective heat transfer coefficient, rubbing force and rubbing temperature of the sealing ring were considered. XFEM was used to numerically study the temperature field, stress field, and crack initiation and propagation of the sealing ring. The crack numerical simulation result was compared with the result of rubbing experiment. The results showed that the crack initiation and propagation direction obtained from numerical simulation were basically consistent with those obtained from rubbing experiment. The mechanism of crack initiation has been revealed, and it has been proven that this method can effectively simulate the process of crack initiation and propagation caused by rubbing.

Abstract:As an advanced composite sandwich structure, folded core sandwich panels are expected to be applied as sound insulation structures in transportation vehicles such as aircraft and high-speed trains. However, the configuration of folded core is diverse, and previous research has mostly focused on the V-shaped folded core, while there is still relatively little research on the sound insulation performance of other configurations. Therefore, this article establishes a numerical model of a four sided simply supported M-shaped folded core sandwich panel under vertical incident sound pressure excitation, and conducts numerical simulation of its sound insulation performance based on finite element software. The theoretical predicted sound transmission loss curve of the honeycomb sandwich panel is compared with the simulation results to verify the effectiveness of the numerical method proposed in this article. Based on simulation models, the sound insulation performance of M-type folded core sandwich panel structure was systematically studied, and the qualitative influence of geometric parameters of folded core cell on sound insulation performance was discussed. Subsequently, the influence of relative misalignment and laying angle of the upper and lower layers of M-type folded core sandwich panel with double-layer core on sound insulation performance was proposed and studied, the results show that the sound insulation performance is improved when the upper and lower layers of core are staggered and stacked in the Z-shaped line step direction of the cell, and it is better than single-layer folded core sandwich panel with the same surface density; when the relative laying angle of the upper and lower layers of core changes, the maximum weighted sound insulation is achieved when the axis of the upper and lower layers of core is vertically laid, and the trend prediction curve of the mean transmission loss with the change of the laying angle of the core is obtained, providing a reference for the optimization design of sound insulation in sandwich panels with folded core sandwich structures.

Abstract:Aiming at the problems of difficult time coordination and high cost of the aerodynamic noise test of counter-rotating propellers in wind tunnels, the aerodynamic noise test system of counter-rotating propellers, which is capable of simulating the driving state of counter-rotating propellers on the ground, has been developed by relying on the acoustic environment of the ground. The aerodynamic noise test was carried out on a perforated counter-rotating propeller and a reference propeller to validate the test system and evaluate the noise reduction effect of the perforated counter-rotating propeller, and the results show that the perforated counter-rotating propeller can effectively reduce the noise under the prerequisite of guaranteeing the aerodynamic performance in the range of the tested working conditions. In the 90° pointing angle, which has the most significant effect on the aircraft cabin, the noise reduction at the second-order passing frequency reaches 5dB.The designed aerodynamic noise test system can provide assistance for the evaluation of aerodynamic noise of the rotary propeller and the design of noise reduction.

Abstract:The pipeline space configuration of fuel pump accessory is complex, and it is difficult to simulate directly in vibration environment test. In this paper, the system equivalent reduction expansion process(SEREP) is used for the dynamic equivalent design of the pipelines to meet the test requirements. Select the specific nodes on the pipeline as the main DOFs, and reduce the original pipeline model to the main DOFs model, then the reduced mass and stiffness matrix is obtained. The sub-mode matrix is decomposed by SVD to further simplify the reduced mass and stiffness matrix, then the new reduced mass and stiffness matrixes of low-order pipeline model are obtained. The "mass ball-beam spring" structure model is proposed, , which maps the reduced mass and stiffness matrices using "mass ball" and "beam spring" respectively, thereby determining equivalent design and processing parameters. Finally, the implementation of the equivalent design method was verified through examples, and the first frequency error between the equivalent pipeline and the original pipeline was mostly within 10%, meeting the requirements of engineering applications.

Abstract:The mechanism of contra-rotating propeller’s aerodynamic noise is very complicated, and propeller-driven aircrafts are not equipped passive noise reduction components such as nacelle liner to absorb noise during sound transmission, the noise generated by propeller will straightforward radiated to the fuselage and surrounding. Therefore, reducing the intensity of propeller noise is the key to the development of low-noise propeller aircraft. In this paper, a "soft blade" module is formed by placing a "small hole and through channel" structure on the suction front edge of spiral blade tip to balance the peak pressure at the leading edge of blade and reduce the load noise. According to the optimal parameters, the conventional propeller and the soft-blade propeller are manufactured, and the radiation noise measurement is carried out on the basis of the counter-rotating propeller aerodynamic noise test system. The results show that the counter-rotating propeller with perforated structure can effectively reduce the noise as well as ensuring the aerodynamic performance. At the 90° pointing Angle, which has the most significant effect on the aircraft cabin, the noise reduction at the second-order passing frequency reaches 5dB.

Abstract:Aviation Fuel pump faces the flow-induced noise problem which affects the unit operation stability and staff’s working security. To solve these problems, the noise reduction technique for fuel pump is introduced in this case. Firstly, noise data of fuel pump are acquired during the on-land system test of air plane. The amplitude and frequency are analyzed. Then, numerical simulation is conducted to understand the flow regime in the fuel pump. Results show that the main reason of flow-induced noise is the pressure fluctuation caused by rotor-stator interaction between impeller and guide vane. Finally, optimizations are done for impeller and guide vane of fuel pump. Numerical and experimental results find that the pressure fluctuation can be reduced by increasing the impeller and vane blade number and applying the alternate loading technique. After optimization, the noise of pump decreases by 6.5 dB. The results and conclusions can be a good reference for similar fuel pump’s optimization cases.

Abstract:The suppression of vibration and noise has always been an important issue in engineering, and metamaterials have shown significant application value in vibration and noise reduction. This paper designs a novel hollow star-shaped chiral metamaterial by incorporating chiral structural characteristics into traditional hollow star-shaped metamaterials and further evolves it into a solid star-shaped chiral metamaterial. The bandgap formation mechanism was analyzed through vibration mode analysis, and the effects of different structural parameters on the bandgap were studied. The propagation characteristics of elastic waves in the structure were investigated through dispersion surfaces, wave propagation direction, group velocity, and phase velocity. Finally, the transmission characteristics of finite periodic structures were studied. The results show that the solid star-shaped chiral metamaterial can generate an ultra-wide bandgap with a width of 5116 Hz. The bandgap formation is mainly due to the rotational vibrations of the concave stars and ligaments dissipating the energy of elastic waves. Additionally, a decrease in the inner concave angle α and an increase in the angle θ between the ligaments and the horizontal direction result in a wider largest bandgap. The finite periodic structure can generate significant displacement amplitude attenuation within the bandgap range. This novel metamaterial has excellent vibration isolation performance and potential applications in complex vibration control.

Abstract:To analyze the heat source of the bearing-support system, the heat source mainly includes the heat transfer between the main flow path and the support structure, the heat generated by the high-speed roller bearing, the heat generated by the seals inside the bearing-support system, the heat transfer between the high-temperature environment outside the bearing chamber and the wall surface of the support structure, the heat transfer of the shaft, as well as the heat generated by the gears and splines. 1D thermal-fluid coupling calculations of the bearing-support system are carried out to obtain the wall temperature and convective heat transfer coefficient (HTC) of the compressor/turbine intermediate bearing support frame, respectively. The wall temperature of the right frame of the compressor intermediate support system increases radially upward by 1.73%, and HTC increases radially upward by 20 times due to the presence of interstage sealing between the main flow path and the disk cavity. The intermediate bearing support frames of the aero-engine compressor and turbine are analyzed for heat generation separately to evaluate the effects of different heat sources on the heat generation of the bearing-support system under cruise operating conditions. Among them, the heat sources with the highest percentage of heat generation are through the support walls, bearings, and seals, and heat generation by the seals in the bearing-support system accounts for 29% in the intermediate bearing support frame of the compressor and 35% in the intermediate bearing support frame of the turbine. Therefore, by optimizing the number and location of seals in the bearing-support system, the heat generation in the bearing-support system can be significantly reduced, and the bearing chamber oil feeding rate can be further reduced.