JB23—60型冲床噪声机理及降噪方法的研究

It is difficult to control the noise of punch press. In this paper, using experiment way, the mechanism of noise generation on JB2360 type punch press which is widely used in works is investigated. According to experiment results,a method for reducing pun     

施工噪声对特种养殖动物造成伤害的司法鉴定

以司法鉴定为切入点,通过案例分析,阐述了特种养殖动物和珍禽在繁育期间特别容易受到噪声污染的伤害;告诫侵权方在从事生产经营活动中要严格遵守《中华人民共和国环境噪声污染防治法》及《中华人民共和国环境影响评价法》;提醒受害方要树立维权意识并做好证据保全.     

Analysis of Elevated Structure Radiated Noise with BEM-FEM Method

Urban rail transit is becoming an important means of transportation and elevated structure is one important part of urban rail transit. So the radiation noise induced by elevated structure attracts more and more attention. Based on the theory of Helmholtz integral equation of BEM and fluid-structure coupling system of FEM, the sound pressure transmission vector reflecting the relation between structural vibration acceleration and radiation of sound pressure is derived and solved by the element radiation superposition method. The calculated results are in good agreement with the experimental data from a viaduct section of the Beijing airport rapid rail transit.     

Test Method of Indoor Noise for Micro-surfacing Mix

Micro-surfacing mix has been wildly used in the pavement maintenance for its water proofing, anti-skidding and wear resistance. However, micro-surfacing pavement has higher noise than the common asphalt pavement and its noise can not be measured effectively and accurately. Therefore, the indoor noise test method of micro-surfacing mix based on wet track abrasion test was explored. The micro-surfacing mix specimens were used to imitate the micro-surfacing pavement. The wet track abrasion tester was used to provide the vehicle loads. The sound level meter was used to measure the noise between tire and pavement. Furthermore, the indoor noise of nine kinds of micro-surfacing mixes with different gradation was examined. The results show that the equivalent sound level in the second time period has good relationship with the surface texture depth by sad patch method. Then the test method and test procedure for the indoor noise of micro-surfacing mix based on wet track abrasion test were given. Finally, two micro-surfacing mixtures with different gradations were made to validate the test method. The results show that the evaluation method can effectively distinguish the difference of micro-surfacing mixes with different gradation and can supplement the mix design method of micro-surfacing mixes.     

带有可乘白噪音的广义G i n z b u r g - L a n d a u方程的随机吸引子

主要证明随机的广义Ginzburg-Landau方程的解生成一个随机动力系统,该动力系统在L2中存在紧的随机吸引子.     

减压阀噪声研究进展

为了全面深刻理解减压阀噪声的具体生成过程及现有研究基础,分析了减压阀内噪声产生的机理,总结了目前国内外减压阀噪声的研究方法,并从来源降噪和传播降噪两方面回顾了国内外降噪技术的研究现状.经过分析总结,探讨了目前研究存在的主要问题：减压阀内流动复杂、旋涡流动发生位置不明确和高速射流相互作用的影响不确定等;指出未来方向应在综合理论分析、试验研究和数值模拟的基础上,确定减压阀内噪声源位置并分析噪声指向性,明确降噪机理,进而研究降噪技术,实现根源降噪.未来对减压阀噪声的控制应从流动机理和结构创新同时着手,进而推出一套普适性低噪声阀门设计理论.研究减压阀内噪声可以为有效并针对性地降低噪声提供可靠依据.     

Bats adjust temporal parameters of echolocation pulses but not those of communication calls in response to traffic noise

Many studies based on acute short‐term noise exposure have demonstrated that animals can adjust their vocalizations in response to ambient noise. However, the effects of chronic noise over a relatively long time scale of multiple days remain largely unclear. Bats rely mainly on acoustic signals for perception of environmental and social communication. Nearly all previous studies on noise‐induced vocal adjustments have focused on echolocation pulse sounds. Relatively little is known regarding the effects of noise on social communication calls. Here, we examined the dynamic changes in the temporal parameters of echolocation and communication vocalizations of Vespertilio sinensis when exposed to traffic noise over multiple days. We found that the bats started to modify their echolocation vocalizations on the fourth day of noise exposure, with an increase of 42–91% in the total number of pulse sequences per day. Under noisy conditions, the number of pulses within a pulse sequence decreased by an average of 17.2%, resulting in a significantly slower number of pulses/sequence (P < 0.001). However, there was little change in the duration of a pulse sequence. These parameters were not significantly adjusted in most communication vocalizations under the noise condition (all P > 0.05), except that the duration decreased and the number of syllables/sequences increased in 1 type of communicative vocalization (P < 0.05). This study suggests that bats routinely adjust temporal parameters of echolocation but rarely of communication vocalizations in response to noise condition.     

Aerodynamic sound and self-excited vibration of circular saw with step thickness I: Comparison of dynamic characteristics between the common circular saw and the circular saw with step thickness

The natural frequencies, aerodynamic noise, whistling noise, and self-excited vibration between the common circular saw with uniform thickness and the circular saw with step thickness (thin on its outer part and thick on its inner part) were researched during idling. The natural frequencies of the circular saw with step thickness increased with an increase in the thickness and in the radius of the thick part. The frequencies of the circular saws with step thickness (thick at the inner part) were higher than that of the thin circular saw with a uniform thickness of 0.5mm. The aerodynamic sound pressure level induced from circular saw teeth increased with an increase in the tooth thickness. The whistling noise and self-excited vibration easily occurred in the thick circular saws (1.5, 2.0, and 2.5mm). The whistling sound pressure level and the vibration amplitude increased with an increase in the thickness of the saw. None of the designed circular saws with step thickness generated whistling noises or self-excited vibration during idling.Part of this report was presented at the 45th annual meeting of the Japan Wood Research Society at Tokyo, April 1995 and the 12th International Wood Machining Seminar at Kyoto, October 1995     

自寻优调整机床主轴转速消除切削振动

提出根据机床切削稳定性的变化规律自寻优调整机床主轴转速的抑振新方法。理论分析和试验结果表明,机床主轴前后两转（次）切削振动的相位差ψ反映了切削振动的本质和特征,ψ＝２７０°是切削过程最稳定的状态。同时,机床主轴转速的变化会直接使相位差发生改变,只要调整主轴转速使相位差为２７０°,切削过程便可以在稳定区进行。作者提出的抑振方法控制振动效果可靠,可在生产中推广应用。