室内箱式变压器结构声污染及对策

通过对置于住宅楼底层室内箱式变压器引起的结构声污染进行调查实测，在对箱式变压器结构声传播进行声学分析基础上，提出了切实可行的防治对策，经实际工程应用验证，效果较好。对机房正上方住房主卧内降噪量为5.0dB，室内夜间噪声降为30.2dB，各层住户夜间烦恼度普遍从非常烦恼或烦恼降为有点烦恼和不大烦恼。这从噪声污染控制的角度证明了变配电房置于住宅楼等噪声敏感建筑物室内底层甚至更高楼层在技术上是可行性的。同时也为杭州市正在试点推广的箱式变压器置于噪声敏感建筑物底层提供了实践依据。     

用空气弹簧降低变压器结构噪声的工程实践

绿岛华庭变压器安装于居民住宅楼一层,其运行噪声长期对楼上居民产生干扰。文中详细分析了变压器产生结构噪声的机理,介绍了一种自适应装置的空气弹簧减振器,用该减振器对变压器结构噪声进行了卓有成效的治理。     

关于《工业企业厂界环境噪声排放标准》倍频带声压级结构传播固定设备室内噪声排放限值使用的探讨

根据现行国家噪声排放标准排放限值,文中从噪声危害角度根据噪声评价曲线,论证了结构传播固定设备室内噪声等效声级排放限值与结构传播固定设备室内倍频带声压级的等效关系。     

道路交通噪声预测模式预测结果的比较

为了分析实际环境影响评价中常用的各种公路交通噪声预测模型预测结果之间存在的差异,并验证各预测方式与实测值之间的相符性,通过对选取的高速公路和市政快速公路采用各种预测模型计算比较,并用实际监测值对各模型预测结果进行验证,结果发现,不同的预测方式会造成预测结果之间昼间4～9 dB、夜间5～10 dB的差异,采用2006版规范计算车速和单车噪声源强,距离衰减考虑车流量大小的预测方式得到的预测结果与实测值最为接近。     

城市配电室噪声与振动控制分析

环境污染与治理一直是社会关注的热点问题,随着城市化进程快速发展,因城市规划与用地的限制,作为重要电力分配场所的配电室越来越多地安置于城市办公区或居民楼区内。配电室内变压器、风机等设备运行时会产生环境噪声污染。同时设备振动会通过地面以及建筑结构向外传播,不仅激发环境振动污染,而且还可能诱发二次结构噪声。面对日益增多的投诉与矛盾,对城市配电室所致噪声振动的产生机理、传播规律以及合理的降噪减振措施进行研究具有十分重要的意义。通过现场测试对配电室噪声振动及其传播特性进行分析,以一10 k V典型配电室为例,设计降噪减振的方案和措施,以期达到噪声振动达标排放,改善居民生活和居住环境的目的。     

试油测试燃烧器噪声场的计算

在试油测试期间,燃烧器喷射和燃烧产生的噪声会对人员和坏境造成较大的危害,故有必要对燃烧过程中噪声预测展开研究,其结果对于评估平台燃烧噪声危害、优化作业设计及进一步采取降噪措施有重要意义。结合测试燃烧器实际情况提出相应声学计算模式。基于经典燃烧噪声理论及流体动力学噪声的Lighthill理论,通过相似准则的量纲分析方法推导出喷射及燃烧噪声计算公式,并通过声波叠加原理得到声源噪声。同时考虑指向性、扩散衰减、空气吸收、水喷淋消音等减噪因素建立测试燃烧器的噪声计算模型。结合测试燃烧器高压喷射的湍流及多相流特点开展CFD数值模拟计算,数值模拟计算噪声声压级结果与噪音模型计算结果吻合较好。通过该噪声模型计算结果与现场实测数据及某西方公司软件计算结果比较,表明该计算模型可以较好的应用于测试燃烧器噪声预测。     

广州市内环路交通噪声模拟与降噪措施评估研究

基于单车辆噪声排放模型,考虑距离衰减及声屏障的遮挡作用,建立了高架道路交通噪声模拟模型,计算了广州市内环路的交通噪声分布,并基于地理信息系统(GIS)绘制了内环路的交通噪声地图。同时,以环市东路路段为例,评估了限速、限行及加装声屏障等降噪措施的降噪效果。结果表明:(1)内环路昼间的噪声污染较严重,靠近道路的第1排建筑物大部分处于65～70dB的噪声环境之下,面对路面的建筑物的开窗位置,噪声达到70～75dB。噪声较严重的地区为环市东路路段、火车站路段、中山一路路段、南岸路路段、环市西路路段等,这些地区都可能成为内环路噪声投诉事件的高发地区。相同地区的噪声在夜间下降了一个级别,能够达到《城市区域环境噪声标准》(GB 3096—93)的限值要求(55dB)。(2)加装声屏障的措施,能够在不影响现有路面行车状态的情况下达到降噪要求,是比较推崇的方法。     

高架道路渐变空腔微穿孔声屏障的设计和降噪

针对道路交通噪声的频谱特性,提出了一种采用渐变空腔的微穿孔声屏障,根据微穿孔吸声理论推导了渐变空腔微穿孔声屏障吸声性能的计算方法,并对其吸声性能进行预测计算和实验室测量.采用RLS 90预测模型计算渐变空腔微穿孔声屏障的降噪效果,并对高架道路试验工程段进行了声屏障降噪效果的现场测量.结果表明,渐变空腔微穿孔声屏障在道路噪声的主要频谱范围内具有良好的吸声性能,吸声频带为2个倍频程,峰值可达0.7;高架道路声屏障降噪效果的计算值和实测值吻合良好,声屏障和防撞墙总高度为4 m,对6层以下高度的建筑物有良好的降噪效果,最大降噪效果达10.3 dB.     

道路交通噪声影响人体心电指标的规律研究

借助多功能动态生理检测仪、现场道路交通噪声信号采集系统及室内道路交通噪声信号回放系统等精密仪器设备,研究了道路交通噪声对人体心电的短时影响,并运用统计学、时间序列理论对噪声影响心电指标的规律进行了分析,提出了一种解释道路交通噪声影响人体心电指标规律及确定噪声安全阈值的理论方法。结果表明,不同噪声声压级对心电低频(LF)、高频(HF)之比(LF/HF)时间序列的自相关系数衰减速率影响不同,声压级越高,LF/HF时间序列的自相关系数衰减到0.500时的速率越慢,经历的延迟期越长;当道路交通噪声超过43dB时,有可能对人体心电状态造成潜在的影响。     

高架道路声屏障的降噪效果

详细介绍了德国RLS 90道路交通噪声预测模型,运用RLS 90模型对具有典型道路参数的高架道路试验段在不同距离、不同高度下进行了辐射噪声和声屏障降噪效果特性的预测计算,并进行了实际测量.结果表明,高架道路对低于其路面高度的近距离区域有显著的噪声遮蔽作用,对于高架道路,声屏障对路面高度附近的区域降噪效果最佳,4 m高声屏障的最大降噪效果达10 dB.结果还表明,采用RLS 90模型得到的高架道路噪声级和声屏障降噪效果计算值和实测数据吻合良好.     

Model estimation and measurement of ammonia emission from naturally ventilated dairy cattle buildings with slatted floor designs

Laboratory experiments were carried out in a wind tunnel with a model of a slurry pit to investigate the characteristics of ammonia emission from dairy cattle buildings with slatted floor designs. Ammonia emission at different temperatures and air velocities over the floor surface above the slurry pit was measured with uniform feces spreading and urine sprinkling on the surface daily. The data were used to improve a model for estimation of ammonia emission from dairy cattle buildings. Estimates from the updated emission model were compared with measured data from five naturally ventilated dairy cattle buildings. The overall measured ammonia emission rates were in the range of 11-88 g per cow per day at air temperatures of 2.3-22.4 degrees C. Ammonia emission rates estimated by the model were in the range of 19-107 g per cow per day for the surveyed buildings. The average ammonia emission estimated by the model was 11% higher than the mean measured value. The results show that predicted emission patterns generally agree with the measured one, but the prediction has less variation. The model performance may be improved if the influence of animal activity and management strategy on ammonia emission could be estimated and more reliable data of air velocities of the buildings could be obtained.     

Soil temperature effect in calculating attenuation and retardation factors

The effect of annual variation of daily average soil temperature, at different depths, in calculating pesticides ranking indexes retardation factor and attenuation factor is presented. The retardation factor and attenuation factor are two site-specific pesticide numbers, frequently used as screening indicator indexes for pesticide groundwater contamination potential. Generally, in the calculation of these two factors are not included the soil temperature effect on the parameters involved in its calculation. It is well known that the soil temperature affects the pesticide degradation rate, water-air partition coefficient and water-soil partition coefficient. These three parameters are components of the retardation factor and attenuation factor and contribute to determine the pesticide behavior in the environment. The Arrhenius equation, van't Hoff equation and Clausius-Clapeyron equation are used in this work for estimating the soil temperature effect on the pesticide degradation rate, water-air partition coefficient and soil-water partition coefficient, respectively. These dependence relationships, between results of calculating attenuation and retardation factors and the soil temperature at different depths, can aid to understand the potential pesticide groundwater contamination on different weather conditions. Numerical results will be presented with pesticides atrazine and lindane in a soil profile with 20 degrees C constant temperature, minimum and maximum surface temperatures varying and spreading in the soil profile between -5 and 30 degrees C and between 15 and 45 degrees C.     

A field study of the ecotoxicology of copper to bryophytes

The impact of particulate copper, emitted from a copper rod-rolling plant, on the distribution of common grassland bryophytes has been investigated. Several areas of managed grassland, differing in total and water-extractable soil copper content, surrounding the factory were surveyed to establish species composition and distribution of the bryophyte flora. Clear differences emerged in the distribution patterns of the main acrocarpous (upright/tufted growth form) and pleurocarpous (horizontal/spreading growth form) species present, with some species being more or less confined to soils with elevated copper (Pohlia nutans), whilst others were absent from such sites. The distribution of acrocarpous species was not related to increasing soil copper concentrations, whereas pleurocarpous species showed considerable sensitivity. This may not be a simple reflection of sensitivity to copper; ecological factors such as differences in patterns of water and soluble copper uptake between the different growth forms may be significant factors, as may be changes in the vascular plant flora giving rise to differences in population densities of potential competitors between sites. Pleurocarpous species are absent from grassland where total soil copper >550 microg g(-1) dry weight, whilst the less sensitive acrocarpous species occur at total soil copper levels in excess of 2000 microg g(-1) dry weight.     

Parameter sets for upper and lower bounds on soil-to-indoor-air contaminant attenuation predicted by the Johnson and Ettinger vapor intrusion model

Migration of volatile chemicals from the subsurface into overlying buildings is known as vapor intrusion (VI). Under certain circumstances, people living in homes above contaminated soil or ground water may be exposed to harmful levels of these vapors. A popular VI screening-level algorithm widely used in the United States, Canada and the UK to assess this potential risk is the “Johnson and Ettinger” (J&E) model. Concern exists over using the J&E model for deciding whether or not further action is necessary at sites, as many parameters are not routinely measured (or are un-measurable). Using EPA-recommended ranges of parameter values for nine soil-type/source depth combinations, input parameter sets were identified that correspond to bounding results of the J&E model. The results established the existence of generic upper and lower bound parameter sets for maximum and minimum exposure for all soil types and depths investigated. Using the generic upper and lower bound parameter sets, an analysis can be performed that, given the limitations of the input ranges and the model, bounds the attenuation factor in a VI investigation.     

The application of ground penetrating radar attenuation tomography in a vadose zone infiltration experiment

Cross-borehole ground penetrating radar (XBGPR) is used in monitoring a long-term vadose zone infiltration experiment at a test site in Socorro, NM in order to examine contaminant transport in the vadose zone. XBGPR attenuation tomography is conducted in order to test the ability of using images of electromagnetic attenuation for hydrogeologic investigations. The results of four pre-infiltration attenuation inversions shows standard deviations below 0.1 Np/m, and demonstrate the consistency of the XBGPR tomography technique for making time-lapse observations. Correlation to the core records indicates that XBGPR attenuation tomograms provide high-resolution images of clay distribution in the vadose zone. Water infiltration at the ground surface was initiated in February 1999 at a constant rate of 2.7 cm/day, and continued at this rate throughout the data collection experiment. Time-lapse attenuation tomograms show that attenuation increases by approximately 0.3 Np/m during the water infiltration, and indicate a snowplow effect may be occurring where salts are dissolved by the water and concentrated at the front of the plume. Seasonal temperature changes may also cause changes in electromagnetic attenuation images, and masking the evidence of water infiltration. Thus caution must be taken when using time-lapse attenuation images to interpret the movement of a water plume during a long-term experiment as temperature changes.     

Non-aqueous phase liquid spreading during soil vapor extraction

Many non-aqueous phase liquids (NAPLs) are expected to spread at the air-water interface, particularly under non-equilibrium conditions. In the vadose zone, this spreading should increase the surface area for mass transfer and the efficiency of volatile NAPL recovery by soil vapor extraction (SVE). Observations of spreading on water wet surfaces led to a conceptual model of oil spreading vertically above a NAPL pool in the vadose zone. Analysis of this model predicts that spreading can enhance the SVE contaminant recovery compared to conditions where the liquid does not spread. Experiments were conducted with spreading volatile oils hexane and heptane in wet porous media and capillary tubes, where spreading was observed at the scale of centimeters. Within porous medium columns up to a meter in height containing stagnant gas, spreading was less than ten centimeters and did not contribute significantly to hexane volatilization. Water film thinning and oil film pinning may have prevented significant oil film spreading, and thus did not enhance SVE at the scale of a meter. The experiments performed indicate that volatile oil spreading at the field scale is unlikely to contribute significantly to the efficiency of SVE.     

Modelling of physical and reactive processes during biodegradation of a hydrocarbon plume under transient groundwater flow conditions

Numerical experiments of non-reactive and reactive transport were carried out to quantify the influence of a seasonally varying, transient flow field on transport and natural attenuation at a hydrocarbon-contaminated field site. Different numerical schemes for solving advective transport were compared to assess their capability to model low transversal dispersivities in transient flow fields. For the field site, it is shown that vertical plume spreading is largely inhibited, particularly if sorption is taken into account. For the reactive simulations, a biodegradation reaction module for the geochemical transport model PHT3D was developed. Results of the reactive transport simulations show that under the site-specific conditions the temporal variations in groundwater flow do, to a modest extent, affect average biodegradation rates and average total (dissolved) contaminant mass in the aquifer. The model simulations demonstrate that the seasonal variability in groundwater flow only results in significantly enhanced biodegradation rates when a differential sorption of electron donor (toluene) and electron acceptor (sulfate) is assumed.     

Effect of Plantings on Radiation of Highway Noise

The body of information presented in this paper is directed to those individuals concerned with the location of highways relative to either existing or planned residential communities. The paper treats in depth the expected attenuation of automobile and particularly diesel tractor-trailer generated hoise by the interposition of extensive and dense planting of trees and shrubs between the highway and the community. The results of research, by the author and others cited in the paper, gives clear indication that a belt of dense man-made growth of tall trees and underbrush can give as much as 5 to 8 dB truck/car noise reduction per 100 ft of planting depth. Natural growth of deep forests were measured to give from 3 to 5 dB attenuation per 100 ft of planting depth. Planting depth of at least 100 ft is required to give reliable results, with tree heights of 40-50 ft desirable and densities of 50-70 ft visibility needed for good effect.

The paper provides considerable experimental verification by an analysis of the current literature. The types of noise sources in cars and trucks are briefly treated as are community reactions to noise from such sources. The dBA is used as the accepted measure for characterizing truck and automobile noise. Both spherical and cylindrical radiation of sound are discussed for low density and high density traffic, respectively.

The paper concludes with an example of attenuation of a typical truck noise by spherical and cylindrical radiation for low- and high-density traffic and a 200-ft deep planting of dense, mature forest. It is concluded that a mature belt of either coniferous or deciduous forest with underbrush can produce barely acceptable noise levels in the community which is separated by such a noise barrier from a heavily traveled highway.     

Estimating the potential for ammonia emissions from livestock excreta and manures

This paper reports a desk study to quantify the total-nitrogen (N) and ammoniacal-N contents of livestock excreta, and to compare them with estimates of N losses to the environment from that excreta. Inventories of ammonia (NH3), nitrous oxide (N2O), dinitrogen (N2), and nitric oxide emissions (NO), together with estimates of nitrate (NO3-) leaching and crop N uptake were collated. A balance sheet was constructed to determine whether our estimates of N in livestock excreta were consistent with current estimates of N losses and crop N uptake from that N, or whether emissions of N compounds from livestock excreta may have been underestimated. Total N excretion by livestock in England and Wales (E&W) was estimated as 767-816 x 10(3) t of which 487-518 x 10(3) t was estimated to be total ammoniacal-N (TAN). Estimates of NH3 and N2O losses during housing and storage were derived from the difference between the total amount of TAN in excreta deposited in and around buildings, and the total amount of TAN in manure (i.e. the excreta deposited in and around buildings after collection and storage) prior to spreading and were ca. 64-88 x 10(3) t. The NH3-N emission from livestock buildings and manure storage in E&W quoted in the UK Emission Inventory (Pain et al., 1999. Inventory of Ammonia Emission from UK Agriculture, 1977. Report of MAFF contract WAO630, IGER, North Wyke) is ca. 80 x 10(3) t. Losses from NO3- leaching in the season after manure application and grazing were estimated as 73 and 32 x 10(3) t, respectively. Other gaseous losses of N were estimated as ca. 54 x 10(3) t. Crop uptake of manure N was estimated to be between 7 and 24 x 10(3) t. For manures, estimated N losses, immobilization and crop uptake total 326 x 10(3) t compared with estimates of 293-319 x 10(3) t TAN in excreta. Total N losses and crop uptake from TAN deposited at grazing were estimated to be 179-199 x 10(3) t compared with ca. 224 x 10(3) t TAN excreted. Thus all the TAN in manures appears to be accounted for, but ca. 25-45 x 10(3) t of TAN in urine deposited at grazing were not, and could be an underestimated source of gaseous emission or nitrate leaching.     

Wind tunnel investigation on the retention of air pollutants in three-dimensional recirculation zones in urban areas

The article discusses an experimental investigation of turbulent dispersion processes in a typical three-dimensional urban geometry, in reduced scale, in neutrally stable conditions. Wind tunnel experiments were carried out for characterizing the flow and the dispersion of a pollutant around a scaled model (1:400) of a group of eight 10-floor buildings surrounding a square. The situation corresponded to the dispersion of fine inertialess particles released from a line source positioned upstream of the urban geometry. After the sudden interruption of the source generation, the particles persisted in the recirculation cavity between the buildings, with the concentration decaying exponentially with time. This is in accordance with previous works on the dispersion process around bluff bodies of different shapes [e.g., Humphries and Vincent, 1976. An experimental investigation of the detention of airborne smoke in the wake bubble behind a disk. Journal of Fluid Mechanics 73, 453–464; Vincent, 1977. Model experiments on the nature of air pollution transport near buildings. Atmospheric Environment 11, 765–774; Fackrell, 1984. Parameters characterizing dispersion in the near wake of buildings. Journal of Wind Engineering and Industrial Aerodynamics 16, 97–118]. The main parameter in the investigation was the characteristic time constant for the concentration decay. The measurements of the variation in the concentration of the fine particles were performed by means of a photo-detection technique based on the attenuation of light. The velocity fields were evaluated with the particle image velocimetry (PIV) technique. The dimensionless residence time H for the particles (H=τU/L, where τ is the time constant for the concentration decay, U the free-stream velocity, and L is a characteristic dimension for the urban geometry, as defined by Humphries and Vincent [1976. An experimental investigation of the detention of airborne smoke in the wake bubble behind a disk. Journal of Fluid Mechanics 73, 453–464] was determined for various locations in the scaled model, in the range of Reynolds numbers (Re) between 8000 and 64,000. H was found to be 6.5±1.0.