Design Intent of Future Tunnels

The sound barrier for bullet trains remains a challenge due to the piston effect causing compression waves at the entry and exit of the tunnel. The air ahead of the train nose is compressed, and the wave propagates through the tunnel at the speed of sound and exits with the generation of micro pressure waves. It gives rise to a complex wave pattern comprising compression at the train nose & expansion at the train tail leading to the positive pressure around the nose and suction around the tail. This is intended to provide exhaustive input for the proper design of a futuristic tunnel. The cross-sectional shapes of the tunnel, whether square, rectangular, circular, or semi-circular, will experience pressure compression wave generated by high-speed train but will influence the flow pattern and hence the compression wave. This paper presents the pressure load on the walls of long and short tunnels for subsonic compressible and transonic flows. The experimental investigation is carried out only for length parameters to study short and long tunnels. Further, flow visualization is also provided after the formation of the sonic boom. The results of this investigation can be an essential data source for optimum design of high-speed tunnels so as to suppress or break the sound barriers, thus, resulting in a safer high-speed train network.

Structural Optimization of Road Fully Enclosed Sound Barrier Based on Three-Dimensional Finite Element Analysis

With the help of the finite element analysis software ANSYS, this paper establishes a finite element model of a fully enclosed sound barrier of elevated road, calculating and analyzing the stress of supporting structure under different working conditions, checking the strength, stiffness and stability of the structure under the most unfavorable working condition. Finally we optimize the structure according to its characteristics.

Detection, Integration, and Optimization of Acoustic Field Simulation in the Closed Space

Noise pollution in the closed space such as railway carriage is an important problem because the noise pollution seriously affects comfort and health of people in the closed space. We propose the method to detection, integration, and optimization of acoustic field simulation in the closed space. First, we analyze the acoustic field distribution in the virtual 3D close space. We use harmonic sound wave propagation in the closed space and present the distribution according to geometric analysis. Second, we introduce Delaunay triangulation and k-means clustering into visualization to form the quiet zone and show it in 3D perspective. Our method used acoustic simulation to develop the sound barrier system. The simulation results show that our method can improve the analysis of the noise problem in the closed space.

Comparative noise reduction effect of sound barrier based on statistical energy analysis

In this paper, based on statistical energy analysis (SEA), the noise attenuation effect of highway sound absorbing barrier is predicted. The theoretical formula value is compared with the calculated value of statistical energy analysis (SEA) to verify its effectiveness in the prediction of sound barrier. And the insertion loss of sound barrier of mineral wool with diverse material thicknesses and coverage are calculated. The results showed that the noise attenuation of the sound barrier increased by 1.5 dB when the sound absorbing materials are attached to the sound barrier near the acoustic source. The noise attenuation effect of mineral wool is improved in the frequency band below 600 Hz when the thickness is increased. The coverage of mineral cotton increased by 25%, and the noise attenuation increased by 0.4 dB. Meanwhile, it also reflects the advantages of fast and convenient statistical energy analysis (SEA) – only one time modelling and changing its parameters can obtain the corresponding statistical results, which has some excellent reference function.

Manufacturing of Ecofriendly Bricks Using Microdust Cotton Waste

Large amounts of cotton microwastes are accumulated in textile industries. The cotton microdust is less to ignite and causes serious environmental problems and health hazards. This paper presents an experimental study, which investigates the potential use of cotton microdust to produce new and lightweight brick for construction industries. The physical and mechanical properties of brick mixes having different levels of cotton microdust ratio were investigated. The test results recorded for compressive strength, unit weight, and water absorption values satisfy the relevant required standards for normal construction bricks. The results show that the replacement of clay soil and cement by cotton microdust does not exhibit a sudden brittle fracture even beyond the failure loads, indicates high energy absorption capacity, reduces the unit weight dramatically, and introduces smother surface compared to the current concrete bricks in the market. The results also show that usage of cotton microdust with different mixing ratios for bricks will give light-weight composite, and brick could be an economical alternative to be used for partition of board concrete blocks and sound barrier panels.

Biobased insulating panels from mulberry stems

In this work, Mulberry Stems (MS) obtained as a by-product of sericulture have been used as reinforcement for Polypropylene (PP) composites intended for green building, furniture and automotive applications. Mulberry stems are lignocellulosic and are renewable and sustainable sources but remain unutilized and are usually discarded as waste by burning or burying. An attempt has been made to utilize mulberry stems as substitutes for commonly used non-biodegradable composites using a simple and clean fabrication technique. The effects of reinforcement percentage (80% to 95% w/w) of MS and density (0.5 g cm−3 to 1.25 g cm−3) of composites on the properties have been studied. Results revealed that, 90/10 (MS/PP w/w %) was the optimum ratio that provides highest mechanical strength. Increasing the density enhanced the strength, thermal insulation, sound transmission loss, water stability and flame retardancy. The 1.25 g cm−3, 90/10 ratio composite had a high sound transmission loss of 46.6 dB and thermal conductivity of 0.130 W/mK which is 70% lower than neat gypsum board used in false ceiling applications. The high insulation and sound barrier properties of mulberry stem based composites are due to the unique hollow morphology of MS which aids in efficient absorbtion and dissipation of the thermal energy and sound waves. Weight loss of MS/PP composite after soil burial test for 120 days varied between 8.9% and 31.4%. MS/PP composites could be potentially used as a green replacement for ply, particleboards, false ceiling, automotive parts and other applications.

Vibration Characteristics of Fully Enclosed Sound Barriers on Railway Bridges under the Movement of Trains

A field test was conducted to investigate the vibration of the fully enclosed sound barrier (FESB) of a railway bridge, and a numerical method was proposed and validated for evaluating the vibration of the bridge-FESB system by combining the train-track coupled theory and the motion equation. Additionally, a numerical analysis of the vibration distribution of the FESB was performed. The results indicated that the vibrations of the FESB were mainly caused by the vertical vibration of the bridge under the dynamic wheel-rail interaction with the greatest vibration level from 1/4 to 1/2 part of the steel arch and were not affected by the train position but increased with an increase in the speed of the train.

Bilayer ventilated labyrinthine metasurfaces with high sound absorption and tunable bandwidth

The recent advent of acoustic metamaterials offers unprecedented opportunities for sound controlling in various occasions, whereas it remains a challenge to attain broadband high sound absorption and free air flow simultaneously. Here, we demonstrated, both theoretically and experimentally, that this problem can be overcome by using a bilayer ventilated labyrinthine metasurface. By altering the spacing between two constituent single-layer metasurfaces and adopting asymmetric losses in them, near-perfect (98.6%) absorption is achieved at resonant frequency for sound waves incident from the front. The relative bandwidth of absorption peak can be tuned in a wide range (from 12% to 80%) by adjusting the open area ratio of the structure. For sound waves from the back, the bilayer metasurface still serves as a sound barrier with low transmission. Our results present a strategy to realize high sound absorption and free air flow simultaneously, and could find applications in building acoustics and noise remediation.