The dominant flow modes contributing to far-field noise and time-dependent location of the acoustic source are identified to analyse the generation mechanism of rod-airfoil interaction noise. First, the flow and acoustic characteristics of the rod-airfoil configuration are numerically simulated and validated against experimental results. Then, based on the numerical dataset, proper orthogonal decomposition (POD), principal correlation decomposition (PCD) and wavelet-based functional beamforming are applied to investigate underlying noise generation mechanism. POD analysis reveals that the major flow modes, associated with large-scale vortex shedding structure, account for 41 % of the total flow energy. The far-field radiated noise primarily originates from these large-scale vortex modes. PCD results show that the correlation energy between the first two dominant flow modes and the far-field noise reaches 97 %. Additionally, wavelet-based functional beamforming results indicate that the noise source location fluctuates near the airfoil leading edge at the vortex-shedding frequency. Vorticity analysis further confirms that the noise source movement within a single vortex-shedding cycle aligns with the motion of large-scale vortices. Thus, the impingement of large-scale shedding vortices on the airfoil leading edge is the predominant generation mechanism of rod-airfoil interaction noise.

With the rapid advancement of industry, the demand for effective noise control in complex operational environments has grown significantly, prompting increasing attention to multifunctional acoustic metamaterials. In this work, a composite neck-embedded Helmholtz resonator with a porous material liner integrated into the cavity is proposed, achieving excellent low-frequency sound absorption and enhanced thermal insulation. Theoretical and simulation results demonstrate that the incorporation of the porous material liner effectively broadens the sound absorption bandwidth, thereby enabling broadband absorption with a reduced number of absorptive units. Meanwhile, analysis indicates that a rise in temperature leads to an upward shift in the structure’s peak absorption frequency and a broadening of the bandwidth. Furthermore, a broadband absorber comprising nine such units arranged in parallel was designed and fabricated. Experimental results show an average absorption coefficient above 0.9 from 300 to 700 Hz with a deep sub-wavelength thickness of 52 mm. Additionally, measurements reveal that the incorporation of melamine foam as a porous material liner results in a 17% reduction in thermal conductivity. The proposed design thus offers dual advantages of enhanced sound absorption and thermal insulation, showing potential for engineering applications.

The vibration-based identification method has long been used as an alternative to mechanical tests for material characterization. Its non-destructive nature, high efficiency in parameter identification of anisotropic materials and its ability to achieve structure-level homogenization make it very attractive for both academic community and industry. Due to the absence of explicit mapping from the result of vibration test to elastic constants, conventional vibration-based identification approaches generally rely on the minimization of a cost function built on modal properties or Frequency Response Function (FRF) curve. In this paper, a direct relation from FRFs to mechanical properties is established by deep neural network, which offers a new perspective to solve the inverse identification problem. Specifically, this mapping is approximately built with Multilayer Perceptrons (MLPs) and the network’s weights are learned from massive training data. The training data-i.e., the FRF curves, is generated by a finite element model whose input parameters are selected by Latin Hypercube Sampling (LHS). After training, the obtained model is validated by dataset unseen during training process and will be further used to predict mechanical properties of materials from FRFs obtained by vibration test. The effectiveness and efficiency of the developed method are demonstrated on the case study of an aluminum plate. Both the Young’s modulus and Poisson’s ratio are retrieved with high accuracy.

Abstract The present study investigates the impact of sound transmission loss of vertical noise barriers for high-speed railways on insertion loss at various speed grades and heights. The findings reveal an initial increase in insertion loss followed by a plateau as sound transmission loss improves. A threshold value exists for weighted sound transmission loss, beyond which the insertion loss remains relatively constant. This threshold referred to as the minimum weighted sound transmission loss decreases with increasing train speeds and increases with higher noise barrier heights. The variation in insertion loss was calculated for noise barriers at heights of 2m and 3m under different sound transmission loss conditions, using measured sound source data corresponding to train speeds of 150km/h, 200km/h, 250km/h, 300km/h, and 350km/h. By polynomial fitting, at a train speed of 400 km/h, the minimum weighted sound transmission loss for 2m and 3m high noise barriers are determined to be 20dB and 21dB respectively.

The report of the 19th National Congress of the Communist Party of China proposes accelerating the construction of an ecological civilization, "returning nature to serenity, harmony, and beauty". The key to attaining serenity is noise prevention. The recent passing and implementation of the Noise Pollution Prevention and Control Law indicate that China's work on noise control for more than 60 years has moved into the fast lane of legalization and standardization. However, noise pollution in the present day has many new characteristics, and further development of noise prevention technology in China still lacks the guidance of top-level planning and deployment. Currently, the promotion of scientific and technological development by various agencies to treat noise prevention in China is generally provisional and passive, responding to noise problems only where required. As a result, it suffers from problems such as overlapping investment, incomplete basic theory studies (e.g., noise mechanisms), weak technical applications, a lack of core technology and intellectual property rights, and insufficient international competitiveness in industrial products. To solve these issues, based on China's experience in noise pollution prevention, this paper examines knowledge and technical systems from many disciplines related to noise control and, considering the novel aspects of noise pollution in the present day, proposes a science and technology action plan for a "Quiet China". This plan aims to cope with the challenges presented by the main sources of noise pollution, noise transmission, and varying citizen response and meet the strategic needs of noise control for related products and equipment. The plan proposes the theoretical basis and technical system of noise control, the promotion of basic research and key technologies, and the expansion of typical application scenarios. The plan sets the goals of mastering the core technologies of noise control, reducing the noise emitted by primary sources by more than 10 dB, and promoting relevant scientific and technological fields in 10-15 years. This paper discusses some of the major issues in constructing a Quiet China and the key technologies of noise control. It addresses the opportunities and challenges of basic research on noise control in China, the role that creating a Quiet China may play in leading the technology and driving the industry and the difficulties it may cause. The paper also explains the connotations, objectives, technical directions, key technologies, and expected effects of the science and technology action plan for a Quiet China. Finally, it puts forward a number of policy suggestions to promote the plan. This paper holds that the scientific and technological action plan for a Quiet China adheres to the unique characteristics of the times in terms of goal orientation, source governance, data empowerment, and intelligent control. In addition, it suggests that relevant research will strongly support the implementation of the new noise law and contribute to establishing "serenity, harmony, and beauty" in China.

The vibration-based identification method has long been used as an alternative to mechanical tests for material characterization. Its non-destructive nature, high efficiency in parameter identification of anisotropic materials and its ability to achieve structure-level homogenization make it very attractive for characterization of composite materials. Due to the absence of explicit mapping from the result of vibration test to elastic constants, conventional vibration-based identification approaches generally rely on the minimization of a cost function built on modal properties or Frequency Response Function (FRF) curve through massive iterations. In this paper, a direct relation from FRFs to mechanical properties is established by deep neural network, which offers a new perspective to solve the identification problem. Specifically, this mapping is approximately built with Multilayer Perceptrons (MLPs) and the network's weights are learned from massive training data. The training data-i.e., the FRF curves, is generated by a finite element model whose input parameters are selected by Latin Hypercube Sampling (LHS). After training, the obtained model is validated by datasets unseen during training process. The identification of mechanical properties of an orthotropic plate from synthetic data is presented and both training loss and validation loss are acceptable.

This work reveals that the addition of periodically distributed stitches to sandwich structure enables a significant reduction of vibration in stop-band and this new functionality is systematically investigated. Firstly, a finite element model which is capable of taking into consideration the three layers of the sandwich as well as the stitches is developed. The diagram of dispersion is calculated by applying Floquet-Bloch theorem to the boundaries of unit cell. With properly chosen properties of stitches, a stop-band for flexural wave is observed. This stop-band is further confirmed by the forced response of a large stitched sandwich panel under point excitation. The level of vibration in the stop-band is significantly reduced. The influence of the stitch rigidity and density on upper and lower limits of stop-band is also examined, which confirms that stitched sandwich can be tuned to mitigate vibration in a certain frequency band with appropriate stitch properties. These investigations have demonstrated the potential application of stitched sandwich in the area of vibration reduction.

Open acoustic barriers exhibit excellent sound transmission reduction property at a certain frequency/frequencies which highly depends on the configuration of its unit cell. Design of unit cell configuration for minimum sound transmission at predefined objective frequency remains an open question. This paper aims at providing an automatic design method for open acoustic barriers with multi-material unit cell. Firstly, a wave finite element method is developed to calculate the sound transmission through an infinite array of periodic scatterers. As the unit cell contains infinite fluid domain, the application of Floquet-Bloch theorem to the boundaries of perfectly match layers (PML) is necessary and has been resolved in this paper. This wave finite element method with the implementation of PML is validated by comparing to analytical solution of sound transmission through an array of steel cylinders. Then a genetic algorithm is employed to optimize the sound transmission loss with respect to material distribution of a bi-material unit cell. Finally, the effectiveness of this inverse design is demonstrated by examples with different predefined frequencies. Corresponding unit cell typologies are obtained and the dips of sound power transmission coefficient curve are successfully tuned to objective frequencies.

In order to improve the low frequency sound absorption of the perforated panel resonator, the perforated panel resonator with flexible tube bundles (PPR-FTB), was presented in 2000. The incorporation of the tube bundles into the resonant absorber is helpful to improve its low frequency sound absorption. Due to the artificial prolongation of air column length inside the aperture neck may increase acoustic mass, so that the resonance frequency can be shifted to a lower frequency correspondingly. Therefore, the PPR-FTB can be used as a low frequency sound absorber. Later on, some derivative sound absorption structures of the PPR-FTB were also developed individually in order to broaden sound absorption frequency bandwidth or further enhance sound absorption coefficients, such as micro-slotted resonator with flexible tube bundles, sound absorption structure with compact capillary tube bundles, the perforated panel resonator with flexible tube bundles based on bypass circuits. The acoustical impedance tube measurements show that there is a wider frequency range of sound absorption which is similar to that of traditional porous materials. It avoids the inherently excessive fluctuation of sound absorption for traditionally acoustical resonators. Furthermore, by utilizing sound path difference principle, low frequency sound wave destructive interference may be achieved. For practical noise control engineering applications without an intention to use fibrous materials, the conceptual design of quasi-full-bandwidth sound absorber in the frequency range of 100Hz-10kHz may be fulfilled by utilization of the PPR-FTB and its derivative sound absorption structures. Not only middle and high frequency noise can be reduced, but also low frequency noise may be suppressed considerably. By reasonably utilizing the tube and cavity coupling resonances, a quasi-fullbandwidth absorber may be presented.

在水热体系中研究了以阳离子表面活性剂为主,阴离子表面活性剂、非离子表面活性剂、中性伯胺等为辅的混合表面活性剂对合成锆掺杂介孔分子筛的影响,考察了水/SiO2摩尔比、晶化温度、晶化时间及混合表面活性剂/SiO2摩尔比对所制分子筛结构的影响,对优化条件下合成的样品进行了表征.结果表明,锆掺杂介孔分子筛的最佳合成体系为阴阳离子表面活性剂混合体系,最佳合成配方为水/SiO2摩尔比58,混合表面活性剂/SiO2摩尔比0.15,100℃下晶化48 h.最佳条件下合成的样品在小角区域有一个明显的衍射峰,表明其具有一定的长程有序性,晶面间距d=9.71 nm,平均孔径为5.55 nm,壁厚4.16 nm,具有三维蠕虫状孔道结构,吸附亚甲基蓝、罗丹明B与甲基橙的混合溶液时,对亚甲基蓝的吸附选择性较好,吸附率达90.24％.

A simulation analysis method based on frequency division is proposed. Simulation analysis of the sound insulation for complex panels is done by using this method. The accurate simulation results of sound simulation for the complex panels are obtained. In the intermediate frequency region, considering the boundary condition and loss factor, the FEM method is used for the simulation analysis. While in the low frequency region below the first-order natural frequency, which is the stiffness control region, the equivalent method is adopted for the simulation. To raise the computational efficiency in the high frequency region, the SEA method is applied. The simulation results of the overall sound insulation in the whole frequency range are all in good agreement with the experimental results, which verifies the validity of the frequency division method.

The dispersion characteristics of axisymmetric (n=0) waves offer a way to gain physical insight into the low-frequency vibrational behaviour of underground pipe systems. Whilst these can be found in the literature, they are generally calculated numerically. Coupled equations of motion for the n=0 waves that propagate in a buried fluid-filled pipe are presented in this paper and, from this, an analytical solution is developed for the fluid-dominated (s=1) wavenumber. The effect of the frictional stress at the pipe–soil interface on the dispersion behaviour of the s=1 wave is characterised by adopting a soil loading matrix. Overall, the fluid loading has a greater effect on the propagation wavespeed compared with the soil loading: for metal pipes, the effect of soil loading is negligible; for plastic pipes, however, simply neglecting the effect of soil loading can lead to a considerable underestimation in the calculation of the wavespeed. The wave attenuation increases significantly at higher frequencies regardless of pipe material resulting from the added damping due to radiation into the soil. Theoretical predictions of the s=1 wavenumber are compared with experimental data measured on an MDPE water pipe. The degree of agreement between prediction and experiment makes clear that, although the wavespeed is only slightly affected by the presence of the frictional stress, the frictional stress at the pipe–soil interface needs to be appropriately taken into account for attenuation predictions.

In order to get a further reduction on pressure loss of a reactive muffler, the interior flow field of the muffler and the generation mechanism of pressure loss are investigated by the CFD method. Then, the influences of the insert tube length on the acoustic and aerodynamic performance of the expansion chamfer muffle are discussed. Results show that the spatial location of expansion or compression vents are so extremely important for the acoustic modes that one can adjust their locations to promote the acoustic and aerodynamic performance of the reactive muffler.

To study large coupled structures,such as,high speed train bodies,their energy transfer coefficients should be solved firstly when using energy methods,such as,the energy flow finite element method (EFFEM).By using two semi-infinite plates to substitute a L-shaped coupled plate and considering flexural wave,longitudinal wave and share wave in plane simultaneously,the characteristics of wave transforming were investigated and transfer coefficients were solved at the coupled boundary by using the traveling wave method.Furthermore,the effects of incident wave's incident angle,plate thickness and incident wave excitation frequency (20rad /s 2e6rad /s)on the wave transforming and energy transfer coefficients were analyzed.The results showed that the plate thickness and the incident wave excitation frequency have important influences on the wave transforming and energy transfer coefficients;the actions of longitudinal wave and shear wave in plane become larger with increase in plate thickness and incident wave excitation frequency,they can not be neglected.

It is effective to solve the high speed railway noise problem by mounting the noise barrier at the side of the track. The performance of noise barriers largely depends on their profiles. This paper studied acoustic performance of noise barriers with quadratic residue diffusers for high speed railway. The properties of noise barriers are optimized based on acoustic diffuser theory. The insertion loss is simulated by establishing a numerical model to evaluate the acoustic performance of noise barriers. The introduced noise barrier is compared with the traditional rectangular and T-shaped noise barrier of the same height.

Based on acoustical designing demand of backing material for ultrasound transducer, multiple scattering(MS) theory has been carried out by studying the methods of impedance matching for different layered materials. Typical acoustic properties of the periodic structure in ultrasonic frequency band have been given as well. In order to increase acoustic impedance to match the active materials and improve the absorption performance at the same time, it’s a good way to fill metallic particles in the viscoelastic materials. Preliminary test results show that these composites behave good acoustical and mechanical performance. It makes a solid foundation and good prospect for the application of backing material in broadband ultrasonic transducer.

Traditional OPAX method for vibration transfer path analysis has two drawbacks: (1) errors are caused by isolation simplification; (2) much job is needed to be done in measuring the excitation to the target transfer function. Although Operational transfer path analysis method (OTPA) will give wrong results when there is obviously signal crosstalk in reference channels, its measurement procedure is very easy for there is no need in measuring force to velocity transfer function. A perfect OPAX method was put forwards in this paper, which combines OPAX method with OPTA method. It uses the four-terminal parameters of the isolator to set up a more reasonable reference signal, the reference signal is combine by the top and lower vibration velocity of the isolator and induces no crosstalk error. Simulations were done and its validation was proved.

The train carriage body in white (BIW),with the length of 7 meters,was divided into 6 subsystems. Based on the energy balance equation,the interrelation among total loss factor,internal loss factor and coupling loss factor of subsystems was determined.Internal loss factor and coupling loss factor can be calculated by using experimental results of total loss factor and the energy ratio.In order to improve the accuracy of experimental results of total loss factor,a method of Hilbert transform,without need of measuring input power,was introduced to calculate the logarithmic decrement of transient response.The results of loss factors can be used for building up the statistical energy analysis (SEA)model of high speed railway carriage.

Experimental modal analysis of high-speed railway carriage Body in White (BIW) with 7 meters long is presented in this paper. The validity of modal testing is verified by comparing mode shapes of the entire carriage with that of beam structures assembled at the bottom floor. Results show that, the demarcation frequency between low frequency vibration and high frequency vibration is 100 Hz. As below 100 Hz, all 6 global modes are included; while above 100 Hz, the mode count within a 1/3 octave frequency bandwidth is higher than 5, which means it could be regarded as high frequency range in statistic energy analysis. Results of modal testing can be provided to modify the finite element model of the carriage structure.