关于一起汽轮发电机定子接地保护动作的分析与处理

某电厂一台210 MW汽轮发电机的三次谐波定子接地保护动作后,通过对该保护A、B屏有关数据的分析比较,排除了该发电机在中性点附近发生定子单相接地故障的可能。经检查,发现了该保护回路中的接线错误,重新接线后,使保护恢复了正常。并对该保护动作方程中的变比平衡系数进行了分析,给出了计算方法,结合实测数据,在不同的变比平衡系数下,对该保护的动作量和制动量进行了理论计算。通过对比分析,并考虑到发电机中性点接地方式的特点,指出了该保护在应用上和定值整定上存在的问题。     

Finite-Volume-Particle Methods for Models of Transport of Pollutant in Shallow Water

We present a new hybrid numerical method for computing the transport of a passive pollutant by a flow. The flow is modeled by the Saint-Venant system of shallow water equations and the pollutant propagation is described by a transport equation. The idea behind the new finite-volume-particle (FVP) method is to use different schemes for the flow and the pollution computations: the shallow water equations are numerically integrated using a finite-volume scheme, while the transport equation is solved by a particle method. This way the specific advantages of each scheme are utilized at the right place. This results in a significantly enhanced resolution of the computed solution     

Soil moisture retrieval using thermal inertia, determined with visible and thermal spaceborne data, validated for European forests

Variations in soil moisture strongly affect surface energy balances, regional runoff, land erosion and vegetation productivity (potential crop yield). Hence, the detection of soil moisture content (SMC) is very valuable in the social, economic, humanitarian (food security) and environmental segments of society. A method to estimate SMC from optical and thermal spectral information of METEOSAT imagery based on thermal inertia (TI) is presented. Minimum and maximum TI values from time series are combined in the Soil Moisture Saturation Index (SMSI). To convert surface to soil profile values, a Markov type filter is used, based on a simple two layer water balance equation (the surface layer and the reservoir below) and an autocorrelation function. Ten-daily SMC values are compared with up-scaled (using AVHRR/NDVI) observations on 10 EUROFLUX sites in Europe for the 1997 growing season (March-October). Moreover, the thermal inertia approach is compared for 1997, with ERS Scatterometer data for eight EUROFLUX sites. METEOSAT pixels are up-scaled to accommodate the ERS Scatterometer spatial resolution. The regression coefficients (slope, intercept and R²) of the thermal inertia approach versus the up-scaled soil moisture observations from EUROFLUX sites vary between 0.811-1.148, − 0.0029-0.66 and 0.544-0.877, respectively, with a RRMSE range of 3.9% to 35.7%. The regression coefficients of the comparison of ERS Scatterometer derived Soil Water Index (SWI) versus the up-scaled Soil Moisture Saturation Index for the pooled case (binning the eight EUROFLUX sites) are 0.587, 0.105 and 0.441, respectively, with a RRMSE of 38%. A simple error propagation model applied for the thermal inertia approach reveals that the absolute and relative errors of the obtained soil moisture content is at least 0.010 m³ m^− 3 or 2.0% with a SMC of 0.203 m³ m^− 3. Recommendations are made to test and implement the TI methodology using NOAA/AVHRR imagery.     

Comparing the utility of microwave and thermal remote-sensing constraints in two-source energy balance modeling over an agricultural landscape

A two-source (soil + vegetation) energy balance model using microwave-derived near-surface soil moisture as a key boundary condition (TSM_SM) and another scheme using thermal-infrared (radiometric) surface temperature (TSM_TH) were applied to remote sensing data collected over a corn and soybean production region in central Iowa during the Soil Moisture Atmosphere Coupling Experiment (SMACEX)/Soil Moisture Experiment of 2002 (SMEX02). The TSM_SM was run using fields of near-surface soil moisture from microwave imagery collected by aircraft on six days during the experiment, yielding a root mean square difference (RMSD) between model estimates and tower measurements of net radiation (Rn) and soil heat flux (G) of approximately 20 W m^− 2, and 45 W m^− 2 for sensible (H) and latent heating (LE). Similar results for H and LE were obtained at landscape/regional scales when comparing model output with transect-average aircraft flux measurements. Flux predictions from the TSM_SM and TSM_TH models were compared for two days when both airborne microwave-derived soil moisture and radiometric surface temperature (T_R) data from Landsat were available. These two days represented contrasting conditions of moderate crop cover/dry soil surface and dense crop cover/moist soil surface. Surface temperature diagnosed by the TSM_SM was also compared directly to the remotely sensed T_R fields as an additional means of model validation. The TSM_SM performed well under moderate crop cover/dry soil surface conditions, but yielded larger discrepancies with observed heat fluxes and T_R under the high crop cover/moist soil surface conditions. Flux predictions from the thermal-based two-source model typically showed biases of opposite sign, suggesting that an average of the flux output from both modeling schemes may improve overall accuracy in flux predictions, in effect incorporating multiple remote-sensing constraints on canopy and soil fluxes.     

A downscaling method for distributing surface soil moisture within a microwave pixel: Application to the Monsoon '90 data

A downscaling method for the near-surface soil moisture retrieved from passive microwave sensors is applied to the PBMR data collected during the Monsoon '90 experiment. The downscaling method requires (1) the coarse resolution microwave observations, (2) the fine-scale distribution of soil temperature and (3) the fine-scale distribution of surface conditions composed of atmospheric forcing and the parameters involved in the modeling of land surface-atmosphere interactions. During the Monsoon '90 experiment, eight ground-based meteorological and flux stations were operating over the 150 km² study area simultaneously with the acquisition of the aircraft-based L-band PBMR data. The heterogeneous scene is hence composed of eight subpixels and the microwave pixel is generated by aggregating the microwave emission of all sites. The results indicate a good agreement between the downscaled and ground-based soil moisture as long as the intensity of solar radiation is sufficiently high to use the soil temperature as a tracer of the spatial variability of near-surface soil moisture.     

非线性振动系统的主共振的增量谐波平衡法

利用增量谐波平衡法来研究单自由度非线性振动系统的主共振 .用傅里叶级数展开与时间有关的量 ,然后应用增量谐波平衡法 ,得到一个非线性的代数方程组 ,并建立了适合于计算机运算的数值模型 ,算例表明此方法是有效的     

利用Linux虚拟服务器实现大容量邮件系统的负载均衡

电子邮件是网络服务中的最主要的内容之一。随着Internet应用的普及和用户不断的增加 ,传统的集中式邮件系统已经不能满足大容量的需求。本文阐述了基于第四层交换的原理 ,应用Linux虚拟服务器来实现分布式邮件服务器集群的负载均衡。本文分析和比较应用多种请求分配算法进行实验分析的结果     

气缸功率平衡试验在现代汽车发动机诊断中的运用

本文作者介绍了气缸功率平衡试验在现代汽车发动机诊断中的作用,试验注意事项,试验步骤,以及如何通过试验结果对发动机状况进行判断.     

六缸柴油机曲轴动平衡量分解方法研究

介绍了六缸曲轴动平衡量的分解方法，对六缸曲轴确定了六个去重平面，在完成两面不平衡量测量后，依据力学原理将其分解到六个去重平面，该方法提高了曲轴动平衡的工作效率。     

纸张含水量对印刷效果的影响及其控制

本对纸张含水量影响因素，张纸含水量对印刷效果的影响进行了分析，并提出了控制纸张含水量的措施。