The major use and need of the multi-rotor UAV in various fields has increased the importance to study the aerodynamics of multi-rotor Unmanned Aerial Vehicles such as the secondary flow over the ...blade, reduction of noise due to the propeller of the UAV, and the optimization of the design on the propeller with more blades to increase efficiency of the UAV. This paper mainly deals with the reduction of noise which is induced by the propeller. Since there is a demand for compact multi-rotor quite UAV as it has a low probability of detection using radar and infrared but as it generates high drive-line noise caused by propeller it cannot be implemented for some critical applications. As a result, an idea is launched to design a propeller with low drive-line noise levels. A methodology is developed to design a low noise as well as efficient propellers for multi-rotor UAVs. The important parameters like blade thickness, tip loss and blade loading are considered in this research. Also, the effects of propeller important parameters such as activity factor, advance ratio are considered. After the finalization of design consideration of UAV’s propeller and the furthermore noise reduction methodologies also studied such as leading-edge comb, trailing edge tuft, and upper surface porosity in order to generate a perfect UAV for military applications. In order to minimize the noise produced by the propeller the idea of modifying the leading-edges is finalized. Computer-AidedDesign of base propeller and propeller with leading-edge modifications has been generated with the help of CATIA V5 and the acoustic analysis for the static base and propellers with leading-edge modifications with different velocities has been simulated using ANSYS Workbench Fluent 16.2. Finally, a propeller with the leading-edge modification has been found to induce low noise. Keywords: Noise, CFD, Decibel, Propeller, Quite UAV.
Background: Noise pollution is a risk factor for human health which is continuously increasing in Sylhet City corporation, located in the Sylhet division in Bangladesh. Methods: In this study, we ...assessed the noise pollution level in Sylhet City by comparing it with the standard noise level. Also, the outcomes of this study were compared to other studies from different countries. In order to measure the noise level in decibel, BSWA 308 device was used in this study. A total of 38 samples were taken from different geographical locations in Sylhet City Corporation. The 38 samples provided 96 to 99% accuracy with a 95% confidence level of >36. Results: The decibel values ranged from 72 to 86 dB. From the observed data we calculated the values as follows: L10, L50 and L90 and Noise Climate (NC)=12.7 dB, equivalent continuous noise level Leq=77.18 dB and noise pollution level Lnp=89.88 dB. A contour map of the area was made using Arc GIS software version 10.5. Every line in the contour map defined a specific decibel value. The map was made by 2 dB intervals between the corresponding contour lines. More than 30% of the study area was vulnerable to a high level of noise (>82 dBA), and about 30% had the lower level of noise (<77 dBA). Only 40% of the area had moderate noise levels (i.e., between 77 to 82 dBA). Conclusion: After comparing the outcomes of noise level in this study with previous studies, we observed that the noise level of this area was more than acceptable limit for all parameters.
After a walk-through survey of existing units in Anzali Steel Ingot factory and the factory work schedule, 21 sampling points were selected in process, office and service units of the factory. Noise ...map of the factory revealed that in almost 68% of job groups in the factory, daily-averaged noise level is greater than the occupational exposure limit (OEL). Workers in furnace installation, electricity and facility units experienced the highest exposure with a daily exposure of more than 100 dB(A). The NIHL in process units increases between 1.25 and 7.5 dB, annually. The maximum increase has been observed at units whose workers' noise exposure is within 5 dB of the exposure limits, which is due to the lack of use of personal protective equipment (PPE). The daily exposure of the workers, who spend at least 25 % of daily working time in the furnace installation area, is above 100 dB(A), despite regular wearing of earplugs. Due to the ineffectiveness of the exposure time reduction, the best solution for these workers is to increase the noise reduction coefficient of the chamber's walls in the furnace installation unit, installing barriers in the furnace installation open area and increasing the number of chambers. In other process units, full inspection of the regular wearing of the PPE over a period of time is recommended. Thereafter the hearing loss of workers will be checked again and in case of inefficiency, changing the workplace of workers in different process units is recommended to reduce the exposure.
The issue of sound insulation in enclosing structures continues to be extremely prevalent in both newly constructed and exploited buildings. Standard fencing solutions frequently employ contemporary ...wall materials without the additional sound insulation that is required. This study investigates the materials applied to soundproofing in various residential buildings and evaluates the extent to which they assist in reducing noise levels indoors. The research suggests measurement techniques to assess how effectively certain building materials and architectural layouts perform in terms of acoustics when used during the construction. The results of the study expand knowledge of noise absorption materials used in the context of urban development and provide recommendations for construction regulations and architectural designs to improve living environments while minimizing noise-related complaints.
Several emerging economies, including India, use diesel widely to produce electric power. This is accomplished through millions of small or medium sized generators driven by diesel engines. These ...engine-alternator combinations, or gensets, are extremely noisy, generate vibrations, and pollute air. There is a pressing need to find alternatives to diesel for such applications. Diesel-alcohol blends (diesohols) could be such alternatives. However, not much effort has been made till so far to evaluate their noise, vibration, emissions, performance, and combustion characteristics. This work fills such a gap by comprehensively investigating the efficacy of four different diesel/n-butanol blends. For this, a single-cylinder 4-stroke naturally aspirated direct injection diesel genset engine was operated at a fixed rpm and at six different load conditions. Detailed measurements of combustion noise, exhaust noise, total noise from the engine, engine vibrations, emissions (NOx, HC, CO, and smoke), engine pressure, and fuel consumption were made. Data from these measurements were used to establish inter-relationships between engine’s noise, vibration, emission, combustion and performance parameters. Linkages between these parameters, and key physical and chemical properties of test fuels were explored. Results show that noise and vibration characteristics of test diesohols are somewhat better especially at lesser loads. However, this trend reverses at higher loads. Analyses of results show strong correlation between combustion noise, rate of pressure rise, and vibration characteristics of test fuels. This work provides a detailed phenomenological explanation for such correlations in terms of fuel properties. Diesohols were also found to perform better for CO, NOx, and smoke emissions. However, the same may not be said for hydrocarbon emissions and engine efficiency particularly for diesohols with high n-butanol content. Finally, this work establishes that blends of n-butanol and diesel are viable alternatives for diesel for genset applications.
El ruido generado durante el proceso constructivo de las infraestructuras viales urbanas es uno de los problemas ambientales que inciden negativamente en la calidad de vida de los trabajadores y de ...la población aledaña. Este estudio tiene el propósito de analizar los diferentes niveles de presión sonora generados por la maquinaria de construcción en vías urbanas con pavimento rígido. Los niveles de ruido monitoreados han sido realizados al equipo mecánico pesado y liviano en proceso de operación. Los resultados globales indican rangos de niveles de presión sonora que van desde 69.6 dBA a 98.4 dBA, siendo los equipos mecánicos livianos los más influyentes con dosis que exceden el 100%. La etapa más ruidosa es la del corte de concreto en pavimento que presenta un nivel de presión sonora de 89.12 dBA en la tarea con dosis que excede en más del 100%, en las demás tareas no hay excedencia de los valores críticos estipulados para una jornada laboral de 8 horas de trabajo; sin embargo, influyen en la población adyacente debido a que exceden los 60 dBA para zona residencial en horario diurno. En conclusión, el equipo mecánico utilizado en la construcción de vías de concreto emite niveles de presión sonora superiores a los límites permisibles incidiendo en la población y trabajadores, recomendándose el uso de protectores auditivos de un nivel mínimo NRR 19 dB para operadores de equipo mecánico pesado y NRR 35 dB para equipos livianos.
•Current noise level measurements in piglet rearing during various management measures indicate that the sound level was on average below the 85 dB(A) limit specified in the legislation of the ...European Union for sustained noise in piggeries.•There were also brief sound level peaks that exceeded the human pain threshold of 120 dB(A).•The rehousing of piglets at the end of the nursery period resulted in the highest sound levels followed by anaesthesia before castration of male piglets.•For the farm staff the wearing of hearing protection is recommended due to high noise levels from piglet screams or using pig paddles.
In the present study, sound level measurements were taken during management measures with expected high noise exposure on three German pig farms in order to quantify the noise level for pigs and farm staff. The sound level was measured during different activities, such as teeth grinding and tail docking of piglets, vaccination, castration with anaesthesia, stabling and rehousing the pigs. The equivalent continuous sound level (LAeq) was measured as well as the actual sound level (LAF) and the peak sound pressure level (LCPKmax). The latter two were assigned to specific sound events during the individual measures, such as piglet screams or using the pig paddle. Rehousing the pigs at the end of the nursery period resulted in the highest continuous sound levels (LAeq= 83.3 ± 4.9 dB(A)), followed by anaesthesia before castration (LAeq = 78.1 ± 7.4 dB(A)) and teeth grinding and tail docking of piglets (LAeq = 77.5 ± 3.6 dB(A)). The peak sound pressure level LCPKmax was more than 100 dB(A) for all measures with an absolute maximum of 129.7 dB(A) when pigs were being moved out of the nursery compartment. Furthermore, the human pain threshold of 120 dB(A) was exceeded in isolated cases when nursery pigs were being moved to the stable (LCPKmax = 121 dB(A)) and during anaesthesia before castration (LCPKmax = 125.2 dB(A)). During the individual measures, particularly high sound levels were generated when using a pig paddle (LAF = 92.1 ± 7.8 dBA)), when pigs ran over a loading ramp of a transporter (LAF = 93.8 ± 1.4 dB(A)) or when piglets screamed (LAF = 87.9 ± 7.5 dB(A)). The piglets’ screams were particularly loud during anaesthesia before castration (LAF = 90.0 ± 9.2 dB(A)), during vaccination (LAF = 89.6 ± 6.5 dB(A)) and during teeth grinding and tail docking (LAF = 89.5 ± 5.9 dB(A)).
Even if the LAeq was always below 85 dB(A), i. e. the limit specified in European legislation (EU Directive 2008/120/EC) for continuous noise in piggeries, there were brief sound peaks that exceeded the pain threshold of 120 dB(A). In the interest of animal welfare and human health, noise should be reduced by a gentle handling of pigs. The use of the pig paddle should be restricted whenever possible. Additionally, farm staff should wear hearing protection when carrying out those measures that were identified as particularly noise-intensive in this study.
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