Li Suobin, Xi Yanhui, Chen Tianning, Wang Xiaopeng «Modulating Lamb wave band gaps using an elastic metamaterial plate» Акустический журнал, 63, № 5, с. pp. 508-516 (2017)

Modulating band gaps (extending the bandwidths or shifting into a lower frequency range) is a challenging task in phononic crystals. In this paper, elastic metamaterial plates composed of a square array of “hard” stubs or “soft” stubs on both sides of a 2D binary locally resonant plate are proposed, and their band structures are studied. The dispersion relationships and the displacement fields of the eigenmodes are calculated using finite element methods. Numerical results show that the band gaps are shifted to lower frequencies and the bandwidths are enlarged compared to classic elastic metamaterial plates. A conceptual “analogousrigid mode” that includes an “out-of-plane analogous-rigid mode” and an “in-plane analogous-rigid mode” is developed to explain these phenomena. The “out-of-plane analogous-rigid mode” mainly adjusts the band gaps into the lower frequency range, and the “in-plane analogous-rigid mode” mainly enlarges the bandwidth. Furthermore, the band gap effects of composite “hard” stubs and “soft” stubs are investigated. The results show that the location of the band gaps can be modulated into a relatively lower frequency and the bandwidth can be extended by the use of different composite stubs. These elastic wave properties in the proposed structure can be used to optimize band gaps and possibly produce low-frequency filters and waveguides.

Yang Liu, Huang Jun, Yi Mingxu, Zhang Chaopu, Xiao Qian «A numerical study of the effects of design parameters on the acoustics noise of a high efficiency propeller» Акустический журнал, 63, № 6, с. pp. 699-710 (2017)

A numerical study of a high efficiency propeller in the aerodynamic noise generation is carried out. Based on RANS, three-dimensional numerical simulation is performed to obtain the aerodynamic performance of the propeller. The result of the aerodynamic analysis is given as input of the acoustic calculation. The sound is calculated using the Farassat 1A, which is derived from Ffowcs Williams–Hawkings equation, and compared with the data of wind tunnel. The propeller is modified for noise reduction by changing its geometrical parameters such as diameter, chord width and pitch angle. The trend of variation between aerodynamic analysis data and acoustic calculation result are compared and discussed for different modification tasks. Meaningful conclusions are drawn on the noise reduction of propeller.

Ma Huayuan, Long Yuan, Zhong Mingshou, Li Xinghua, Xie Quanmin «Study on Ground Vibration Mode of Physical Explosion of High Pressure Natural Gas Pipeline» Акустический журнал, 65, № 5, с. pp. 583-592 (2019)

In this paper, an explosion experiment was carried out on the OD1219mm-X90-12Mpa natural gas pipeline to study the vibration hazard. Based on a series of experiments, the spatial distribution of the vibration energy was studied. The vibration distribution field was drawn by interpolation method based on re-harmonic equation and it was found that the field was non-circular symmetry. Through in-depth research, it was preliminarily proved that the vibration field had interference characteristics, which was caused by the special vibration source of the pipeline explosion. There was a significant difference in the frequency components between the interference strengthened region and the weakened region. The results shown that the strengthening effect of the interference in the 90° and 30° direction should be taken into account when evaluating the damage scope of the explosion accident. Research provided reference for safety design of parallel pipelines and buildings.

Xu Shi-da, Li Yuan-hui, Liu Jian-po «Detection of cracking and damage mechanisms in brittle granites by moment tensor analysis of acoustic emission signals» Акустический журнал, 63, № 3, с. 359-367 (2017)

An acoustic emission (AE) testing of rock cracking was performed under uniaxial loading conditions by precut varisized circular holes in selected brittle granites. Based on AE-source location technique and AE-theory for moment tensor analysis, rules of the temporal–spatial evolution of micro-cracks in different failure mechanisms were explored and types of micro-cracks were analyzed as well. The results revealed that the micro-cracks are uniquely easy to generate in the positions where stress are concentrated. Tensile fractures are easy to form on the roof and floor of a circular hole, while shear fractures are easy to be found on both sides. The locations of initial cracks generated around the holes in the loading process are the direction or vertical direction of maximum principle stress. Macroscopic crack orientation agrees with the direction of maximum principle stress approximately. As the size of circular opening increases and the relative size of pillar decreases, shear cracks are dominant with the percentage more than 45%, tension cracks are fewer, accounted for less than 40% of the total events, and mixed-mode cracks represent a minimum proportion, despite the decrease of percentage of shear cracks. The findings of this work can serve for supporting design of tunnel or roadway to avoid collapse.