蜗壳形状对离心泵流动诱导噪声的影响

由于蜗壳对离心泵流动诱导噪声的产生及传播具有重要影响,在原马蹄形断面蜗壳的基础上重新设计了一种矩形断面蜗壳,并将两种断面的蜗壳与同一叶轮组合进行流场数值模拟和声学求解.流动诱导噪声的求解基于Lighthill声类比理论,采用大涡模拟和声学有限元法相结合的混合算法.在原型泵的基础上还分析了采用矩形隔舌和圆角隔舌的扬程、效率和声学性能差异,并对模拟结果进行了试验验证.计算结果表明:矩形断面蜗壳模型泵和马蹄形断面蜗壳模型泵的水力性能近似;2种断面模型泵内流动诱导噪声的主频均为叶片通过频率290 Hz;从内部流场的压力云图、速度矢量分布及方向分析可发现矩形断面蜗壳内的流动状态更佳;相对于马蹄形断面蜗壳,采用矩形断面蜗壳模型泵的声压级平均小5 dB,声学性能更优;相对于矩形隔舌模型,采用圆角隔舌模型泵的水力性能更优,声学性能也较好,声压级平均小4 dB.     

基于经验模态分解和形态学的风电并网电压故障检测

针对风电场并网点电压故障引起的风机大规模脱网问题,提出了基于柔性形态算子和经验模态分解(empirical mode decomposition,EMD)去噪技术的电网电压故障检测方法。首先,利用EMD对采样信号进行时频自适应预处理,从而确定噪声主导模态;然后,通过柔性形态学变换加阈值输出,有效放大信号奇异点,避免了因电网电压信号周期性变化和噪声引起的背景梯度对检测结果的影响,实现故障定位检测。通过对不同噪声强度的电压暂降故障信号进行检测对比分析发现,随着信号信噪比下降,标准形态学方法的检测误差进一步增大,当信噪比达到25db时,甚至出现了误检现象,而柔性形态EMD检测方法仍然可以有效检测故障扰动的起止时间,表明该方法与标准形态学和小波阈值方法相比,在简化运算过程的同时可以获得更高的检测精度。最后,对某风电场并网点故障电压的分析结果与实测数据的一致性,验证了该方法可以有效检测电网电压的瞬态故障信息,从而为风电场无功补偿装置的投切控制提供了依据。     

基于FFT的电机实时噪声信号频谱分析

对电机进行噪声测量项目时通过对噪声进行采集分析,采用比对信号特征的方法可以早期发现产品可能存在的某些潜在缺陷,为分析研究提供依据。文章在测量方法与实现方面给出了针对几种电机的研究结果。     

哈尔滨市道路交通噪声污染分析及防护研究

随着哈尔滨城市建设的迅猛发展,通畅的道路为经济发展提供便利的同时,交通主干道两侧的交通噪声污染问题也日益突出,严重影响了人们的健康生活。本文通过对哈尔滨市道路交通噪声进行全新的监测,并对测量数据进行详细的分析研究,有针对性地提出一些交通噪声的防护与控制措施。     

Synthetic aperture radar raw signal generation and image simulation of typical targets

Synthetic aperture radar (SAR) raw signal generation and SAR image simulation of typical targets are very significant for the validation of SAR imaging algorithms, the interpretation of SAR images, and automatic target recognition of SAR images. Based on analysis of the existing SAR raw signal generation and SAR image simulation methods, a new method for SAR raw signal generation and SAR image simulation is proposed. This method combined the curved surface pixel method (CSPM) and the two dimensional FFT (2DFFT) based SAR raw signal generation model. CSPM is used to calculate the target reflectivity, while the 2DFFT method is employed to obtain the raw signal. The simulations are carried out, and the effectiveness of this method is validated by the results of simulating some typical targets.     

A novel approach for palatal cyst ablation in a horse

An 18-month-old Welsh Cob was referred to a university teaching hospital for investigation of abnormal respiratory noise at rest. Video-endoscopy revealed persistent displacement of the soft palate with bilateral 2–3 cm diameter raised areas on either side of the midline. Neither trans-nasal nor oral approaches allowed sufficient visualisation of the caudal soft palate for diagnosis or treatment. Latero-lateral radiographs showed a blunted, thickened caudal edge of the soft palate consistent with a palatal cyst. Two palatal cysts were thermally ablated with a transendoscopic diode laser via temporary tracheotomy. The horse recovered uneventfully and resolution of the displacement was evident on follow-up endoscopy 11 months later. This report documents a novel surgical approach to the caudal aspect of the soft palate.     

柴油发电机组噪声分析和降噪方案设计

通过对柴油发电机组噪声源的分析,采取隔音、吸音、消音、减振等措施对云内YN25型柴油发电机组进行优化设计;根据发电机组噪声源分布特点设计了静音箱、进风罩、消音器、进气管、减振器等结构并进行试验验证,试验结果表明:发电机组噪声从90dB降低到30dB,验证了计算和设计的合理性;在有限的空间内实现了较大的降噪量,取得良好的效果。为柴油发电机组降噪减振研究提供了理论参考。     

Income and labour productivity of collection and use of indigenous fruit tree products in Zimbabwe

Rural people in Africa periodically rely on wild fruits to supplement their diet and to generate cash income. However, scientific evidence on the economics of using indigenous fruit tree (IFT) products is scarce. The objective of the study was to fill in some of the gaps for which farm-household surveys were conducted in Zimbabwe during 1999–2000. Gross margins and returns to labour in collection, use and sale of products of Uapaca kirkiana (Muell. Arg., Wild Loquat), Strychnos sp. (S. cocculoides (Baker) and S. spinosa (Lam.), Monkey Orange) and Parinari curatellifolia (Planch. ex. Benth., Fever Tree) were compared with other farming activities. A random sample of over three hundred households in the Murehwa Communal and the Takawira Resettlement Areas was interviewed to gather income and expenditure data. Additionally, income, expenditure and labour allocation of 39 households were closely monitored for one year. Results indicated that the majority of rural households benefited from consumption and sale of indigenous (IF), although the extent varied among households. Within the households, children were the main consumers of fruits. Marketing of IF are carried out by women who used the receipts to purchase household goods. While U. kirkiana fruits were more important in generating cash income than others, fruits of P. curatellifoliawere important for home consumption during periods of food shortages. The gross margins for collection of IFT products were lower than for livestock and crop production. However, returns to labour from collection and use of IFT products were considerably greater than from other activities including gardening and livestock rearing. The study indicates that collection of IFT products is an efficient labour allocation strategy in Zimbabwe. This revised version was published online in June 2006 with corrections to the Cover Date.     

Removing White Noises from Fault Signals of Motors with Dyadic Wavelets

The properties of fault signals of motors are studied using dyadic wavelets transform in this paper,which can be treated as signals with sigularities.The method of removing white noises is presented by using the difference between the wavelets transforms of white noises and those of fault signals of motors in this paper."Denoised" signals can be reconstructed by using this practical algorithm.     

Hearing in catfishes: 200 years of research

Ernst Weber stated in 1819, based on dissections, that the swimbladder in the European wels (Silurus glanis, Siluridae) and related cyprinids serves as an eardrum and that the ossicles connecting it to the inner ear function as hearing ossicles similar to mammals. In the early 20th century, K. von Frisch showed experimentally that catfishes and cyprinids (otophysines) indeed hear excellently compared to fish taxa lacking auxiliary hearing structures (ossicles, eardrums). Knowledge on hearing in catfishes progressed in particular in the 21st century. Currently, hearing abilities (audiograms) are known in 28 species out of 13 families. Recent ontogenetic and comparative studies revealed that the ability to detect sounds of low-level and high frequencies (4–6 kHz) depends on the development of Weberian ossicles. Species with a higher number of ossicles and larger bladders hear better at higher frequencies (>1 kHz). Hearing sensitivities are furthermore affected by ecological factors. Rising temperatures increase, whereas various noise regimes decrease hearing. Exposure to high-noise levels (>150 dB) for hours result in temporary thresholds shifts (TTS) and recovery of hearing after several days. Low-noise levels reduce hearing abilities due to masking without a TTS. Furthermore, auditory evoked potential (AEP) experiments reveal that the temporal patterns of fish-produced pulsed stridulation and drumming sounds are represented in their auditory pathways, indicating that catfishes are able to extract important information for acoustic communication. Further research should concentrate on inner ears to determine whether the diversity in swimbladders and ossicles is paralleled in the inner ear fine structure.