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.

Noise Reduction Using Concrete Barriers: A Case Study

Noise pollution is becoming more and more acute, and hence many researchers are studying the noise attenuation effect and prevention of noise. In this study an attempt has been made to find the reduction in noise levels at National Highway 45 near peerkankaranai in Chennai. Two sensitive places were selected along NH 45 by examining attenuation of noise by providing noise barriers in the form of concrete structures. The primary goal of this project was to identify innovative design of noise barrier that has the potential to be implemented in NH 45, Chennai. Based on the research and evaluation conducted for this study, it was recommended that two innovative barrier designs be implemented in Chennai. First, a noise prediction is made at the specified location on the highway under certain traffic conditions in order to determine the noise level by measurement and decide on the barrier requirement. The installation of sound barriers is feasible enough to cause a significant decrease in noise pollution at the roads. Considerable noise attenuation is achieved by providing concrete noise barrier. The paper provides Leq at the time of traffic data recorded was 105.1 dBA at NH45 and 91.108 dBA at NH5 during the time of observation at installation of barrier the values are 70.09 dBA 79.11 dBA, respectively. Noise reduction is possible and noise reduction is predominantly reduced by providing barrier.

Acoustic Performance Evaluation of Sugarcane Bagasse Using Ambient Sound Meter and Scanning Electron Microscopy

Non-stop research is afoot to replace synthetic materials with green-materials for sound absorption purposes. Employing of agricultural waste as building materials has been a successful trend throughout the years. This research targets to utilize sugarcane bagasse (SB) fibers as sound barriers with sodium silicate as an adhesive. The SB fibers were treated in an alkaline solution for delignification and to improve the surface morphology. The SB fibers were casted into sheet and further tested for sound transmission loss. Experimentation revealed that the fabricated sheets can be viable option as a sound absorbing medium. A tubular porous structure was observed through Field Emission Scanning Microscope (FESEM). It has the capability to be used as a low-cost, biodegradable, and eco-friendly acoustic material as compared to glass wool and other synthetic acoustic materials. Keywords: Acoustic material, Alkali-treatment, Ambience, FESEM microscopy, Low-cost, Natural fiber, Performance, Sugarcane Bagasse, Sustainability

Acoustical Materials: Solving the Challenge of Vehicle Noise

For a limited time only, SAE is offering a 20% discount off the list price of $70. Purchase today for $56. What is acoustics? What is noise? How is sound measured? How can the vehicle noise be reduced using sound package treatments? Pranab Saha answers these and more in Acoustical Materials. Acoustics is the science of sound, including its generation, propagation, and effect. Although the propulsion sources of internal combustion engine (ICE) vehicles and electric motor-powered vehicles (EV) are different and therefore their propulsion noises are different, both types of vehicles have shared noise concerns: Tire and road noise Wind noise Vehicle noise and vibration issues have been there almost from the inception of vehicle manufacturing. The noise problem in a vehicle is very severe and is difficult to solve only by modifying the sources of noise and vibration. Sound package treatments address the noise and vibration issues along the path to reduce in-cabin noise. In Acoustical Materials, readers will grasp the science of reducing sound and vibration using sound absorbers, sound barriers, and vibration dampers. Sound provides information on the proper operation of the vehicle, but if unchecked, can detract from the consumer experience within the vehicle and create noise pollution outside the vehicle. Acoustical Materials provides essential information on the basics of sound, vehicle noise source, how these are measured, how vehicle owners perceive sound, and ultimately, how to solve noise problems in vehicles using sound package materials.

Insertion loss (IL) of finite sound barriers of different contours - An introduction to geometrical solutions in 3-D space

The design of finite sound barriers noise sources and control points requires calculations beyond those that are used when the Maekawa formula is applied, since the problem involves polygon sd barriers located in various possible orientations in 3D space. We present here some means that are linked to basic mathematical geometrical tools. Those means are relatively simple, as compared to the physical formulation of the relevant diffraction solutions for sound barriers (e.g. Rosenhouse, 2019, 2020). Such calculations can apply algebraic, trigonometric or vector analysis and their combinations to define the geometries of barrier IL. This approach includes the location of the sources and control points, which are essential as data for finding IL and other issues of environmental acoustics. We will show solutions including results of IL for a common rectangular barrier, as compared to IL of a barrier with a sloped top and side, among other possibilities.

Confusion in the evaluation of sound barriers under harmonized standard

After the obligatory introduction of the declaration of uncertainty in EN 1793-2:2018, the B categories shall not be used to prevent further confusion. Contrary to the updated standard, B categories remain a ubiquitous contractual criterion in the Czech Republic. Contractors continue to request insulation category B3 products determined according to the cancelled EN 1793-2:1997. The current standard only specifies a test method for determining the intrinsic airborne sound insulation performance of noise barriers designed for tunnel roads, deep trenches or covered spaces. EN 1793-6:2018 shall be used for barriers designed for non-reverberant conditions. Notified bodies involved in barriers testing should exercise care and analyze whether supporting test standards in the cancelled but still harmonized EN 14388:2005 can be used or whether the latest testing procedures will be considered. A guidance document is vital because the situation is becoming increasingly confusing. Common rules should be established across the EU to prevent invalid contractual requirements concerning B3 category barriers designed for non-reverberant conditions. The paper analyzes the current unsatisfactory situation, discusses the application of single number rating involving uncertainties, and proposes decision rules for logical and illogical contractual requirements.

Noise Pollution in Urban Residential Environments: Evidence from Students’ Hostels in Awka, Nigeria

Noise pollution and its concomitant effects on humans and environment has reached dangerous levels in many urban areas across the world. However, very little is known about the sources and effects of noise pollution within students’ hostels in a developing country like Nigeria. This study investigated urban noise pollution in residential neighbourhoods, using the Nnamdi Azikiwe University students’ off-campus accommodation in Awka, southeast Nigeria as the study area. Data were obtained through measurements of noise levels using sound level meter and by conducting a survey to gather feedback from 260 students in the study area. Descriptive statistics and Chi-Square tests were used to analyse the data; the results revealed mean noise levels of 89.8 dB(A) and 46.9 dB(A) during noisy and quiet periods, respectively. The main sources of noise were portable electricity generators, vehicular traffic and loudspeakers used by students and business operators; they were found to have deleterious effects such as low tolerance, headache, anger, lack of concentration and low productivity on the students. The study concludes by noting that to effectively minimize the effects of noise pollution within urban residential neighbourhoods in the study area and beyond, architects and urban planners should engage in proper land use zoning and the application of sound absorbing materials on walls and locating balconies of residential buildings away from noise sources. In addition, vegetation belts and sound barriers of earth mounds or wood, metal or concrete could also be constructed between the sources of noise and residential buildings, especially in the case of roadside communities.

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.

A Fano-based acoustic metamaterial for ultra-broadband sound barriers

Ultra-broadband sound reduction schemes covering living and working noise spectra are of high scientific and industrial significance. Here, we report, both theoretically and experimentally, on an ultra-broadband acoustic barrier assembled from space-coiling metamaterials (SCMs) supporting two Fano resonances. Moreover, acoustic hyper-damping is introduced by integrating additional thin viscous foam layers in the SCMs for optimizing the sound reduction performance. A simplified model is developed to study sound transmission behaviour of the SCMs under a normal incidence, which sets forth the basis to understand the working mechanism. An acoustic barrier with 220 mm thickness is then manufactured and tested to exhibit ultra-broadband transmission loss overall above 10 dB across the range 0.44–3.85 kHz, covering completely nine third-octave bands. In addition, unconventional broadband absorption in the dampened barrier (65%) is experimentally observed as well. We believe this work paves the way for realizing effective broadband sound insulation, absorption and sound wave controlling devices with efficient ventilation.

Outdoor environmental investigation of old communities during summer in hot summer and cold winter regions

The outdoor physical environments of many old communities are unable to meet modern living requirements and require improvement urgently. This is especially true for communities in regions with extremely hot summers and cold winters, which may cause additional difficulties. This study used measurements and questionnaire data to investigate outdoor environment (the thermal, sound, light environments and air quality) and resident sensations in four such communities. Results revealed some key factors affecting outdoor environmental comfort, including summer shading, winter sunlight, air temperature, air quality, the sound environment and odour. The results also revealed that the main problems were noise, insufficient illumination and high air temperatures in summer, all of which had seriously affected comfort during outdoor activities. Specifically, noise values during the most unfavourable periods were between 57.4 and 80.6 dB(A), while average air temperatures were between 32.3°C and 35.8°C, and average illuminances were below 2.9 lx. As such, this paper proposes improvement measures such as sound barriers and greening. Further, we propose a method for prioritizing these factors for such improvements based on a combination of subjective and objective factors. This study provides data and technical references for the reconstruction of old communities in regions with hot summers and cold winters.