共查询到19条相似文献,搜索用时 281 毫秒
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《Planning》2017,(10)
提高消声器的声学性能,通常会导致空气动力性能的增大,因此要对消声器的综合性能进行评价。利用COMSOL Multiphysics和FLUENT商业软件,对某汽车排气抗性消声器的综合性能进行研究,分别对其在具有4种不同内插管长度组合情况下的声场和流场进行数值模拟,获得消声器的声压分布特性、传递损失及压力损失,并分析和研究了内插管长度对消声器声学性能和空气动力学性能的影响。模拟结果表明,随着内插管长度的增加,消声器的传递损失在低频段明显提高,且消声器的压力损失有所下降,从而汽车排气抗性消声器的综合性能得到了提高。 相似文献
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《Planning》2016,(23)
针对1种基于气体分流对冲降低排气速度的新型结构排气消声器,使用计算流体力学的方法对其空气动力学性能进行分析。首先建立了消声器的仿真模型,并利用计算流体力学CFD技术对分流对冲排气消声器设定入口流速下的流场进行了仿真,分析了分流对冲排气消声器内部气体的流动特性和压力分布特性,并对新型消声器在不同入口气体速度下的压力损失进行模拟分析以及试验验证,并以CG25型单缸柴油机为样机,对新型消声器的声学性能进行了现场测试。结果表明:分流对冲排气消声器具有很好的空气动力性能,在柴油机标定转速下(2 200rad/min),新型消声器的插入损失为8.7dB,在柴油机不同工况下,新型消声器的插入损失高于原装消声器,证明了新型消声器具有良好的消声性能。 相似文献
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汽车发动机进排气噪声是汽车主要噪声源之一,汽车尾气的排放会导致PM2.5浓度的升高,造成环境污染问题.在进排气系统上使用净化消声器可以有效地降低汽车进排气噪声和尾气浓度.传统的净化消声器设计都是将催化转化载体与消声器作为2个独立的部分进行设计,加大了生产成本,增加了安装空间.由于催化转化载体的蜂窝结构可以视为多孔介质,具有一定的消声作用,因此,设计出一种改进之后的新型净化消声器,通过将载体放入消声器内部,形成一个统一的结构,在假定消声器的净化作用的情况下,运用声学及流场的数值仿真分析消声器的传递损失和压力损失,结果证明新型净化消声器既节省了空间,又达到了消除噪声的目的. 相似文献
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《Planning》2021,(1)
To reduce low-frequency noise of the water-filled pipeline system,a compact flexible micro-perforated muffler with a flexible back cavity(FMPMFBC) is proposed.The flexible pipe wall is made of a rubber-cord composite material.A numerical solution for the transmission loss is derived.Firstly,the flexible micro-perforated panel(FMPP) is equivalent to a flexible porous material based on Biot-Allard porous-elastic theory.Then,a periodic structural unit of the aramid fabric cloth is established with the two-scale method,and the equivalent stiffness matrix is obtained.Besides,a multi-layer composite model for the flexible pipe wall is constructed according to the lamination theory.Coupling with the internal sound field,the transmission loss of the FMPMFBC is calculated.On a water-filled impedance tube,the transmission loss curves of the FMPMFBC prototypes are measured with the two source-location method,and compared with those of a flexible micro-perforated muffler with a rigid back cavity(FMPMRBC)and an expansion muffler.Theoretical results are experimentally verified.The FMPMFBC is a hybrid muffler combining reflection with dissipation,capable of attenuating broadband lowfrequency noise.The transmission loss of prototype B2 in the frequency bands of [40 300] Hz and [40 1200] Hz is 36 dB and 30 dB,respectively,while the transmission loss of the same-sized expansion muffler in the corresponding frequency bands is 7 dB and 11 dB,respectively. 相似文献
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An experimental study of the effect of local contact loss on the earth pressure distribution on existing tunnel linings 总被引:2,自引:0,他引:2
C. LeungM.A. Meguid 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2011,26(1):139-145
This study presents the results of the experimental investigation that has been conducted to examine the effect of local contact loss between a tunnel lining and the surrounding ground on the earth pressure distribution acting on the tunnel liner. An experimental setup has been designed using a mechanically adjustable tunnel model to simulate the initial lining pressure that results from shield tunnelling. A local separation between the lining and the surrounding soil was introduced at different locations around the tunnel and the changes in contact pressure were measured. Results indicated significant changes in earth pressure in the close vicinity of the area that has experienced the contact loss. The changes in earth pressure differed greatly depending on the location of the induced separation. When located at the invert and haunches results showed an increase in pressure by about 28%, whereas a pressure decrease of about 75% was measured immediately above the separated section when located at the springline. The above results suggest that the presence of a small lining area that is not in direct contact with the surrounding ground can have a significant impact on the performance of the tunnel lining. 相似文献
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针对当前石材矿山开采气动凿岩机噪声污染严重问题,分析了气动凿岩机工作原理以及噪声机理。介绍了气动凿岩机噪声污染的特点和性质。提出了控制噪声的基本原理和方法,并对现有的消声器进行了改进,实际应用显示了良好的效果。 相似文献
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Investigations on noise nuisance of patients and nursing staff. The aim of this study was to assess the exposure to noise in intensive care units. Therefore, sound pressure level measurements have been carried out in both the sickroom and the ward corridor. A high noise exposure in the sickroom was found. In addition the measurement results proves that sleep disturbing noise is occurring at all hours. This high noise density has a dramatic impact on the patients' convalescence and recovery process. One for healthy patients “certain wake‐up threshold” was defined, which is exceeded 5 times per hour also in the night. There is no regulation by the German law regarding the patients' exposure to noise in hospitals. While in the ward corridor the intellectual work of the nursing staff according to VDI 2058 is disturbed significantly in every shift investigated, the permissible guideline limit for mechanical works in this specific working environment is almost achieved. But the guidelines of the current labour law are always complied with, because there is only one limit for protection against noise induced hearing loss. The magnitude of noise and stress caused thereby, for both the patients and the nursing staff, show the urgent need of specific regulations by German law. 相似文献
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任世漫 《土木建筑与环境工程》1999,21(1):10-13
预拌混凝土泵送性能是一个综合性能,目前尚无确切表示方法,本文通过对不同泵送剂配制的泵送混凝土的坍落度及坍落度损失,压力泌水率等项指标的试验结果分析,提出了综合评定预拌混凝土泵送性能的可能性。 相似文献
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介绍了噪声的概念及其危害 ,分析了空调系统产生的噪声源 ,从空调系统机械设备的选型和设备布置等方面 ,提出了空调系统消声设计的具体措施 相似文献
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《Soils and Foundations》2009,49(5):807-811
Matric suction is an important stress state parameter in unsaturated soil mechanics. Many studies have been carried out in the past to determine the matric suction through direct and indirect methods. Direct measurement of matric suction has been proven possible with high-suction tensiometer; however high-suction tensiometers are still susceptible to cavitation. The axis translation technique developed by Hilf (1956) has been employed in many laboratory tests for unsaturated soils to avoid problem of cavitation in the water pressure measurement system. However in laboratory testing of unsaturated soils, air and water pressures are usually independently controlled and there is no need for a feedback control. The matric suction of soil can be measured using a modified pressure plate apparatus by actively changing the air pressure to maintain the water pressure to be close to zero thus imposing negligible water content change in the soil. A major setback of the existing practice is the need to manually adjust the air pressure of the modified pressure plate in response to the changes in the water pressure. This paper presents an active control system for the modified pressure plate apparatus for matric suction measurement. The experimental results obtained from modified pressure plate apparatus with active control system show good performance as compared to the high suction tensiometer. 相似文献