奇点法在叶轮机械任意回转面亚音速可压缩流动计算中的应用

本文在[3]的基础上,进一步将传统奇点法的应用范围从计算不可压缩流动推广到叶轮机械任意回转面亚音速可压缩流动的计算,并在数值处理方面做了有益的改进.算例和设计实例表明本方法计算可靠并具有实用性,为叶轮机械准三元流动计算中S_1和S_2两类流面间的反复迭代提供了一个有力的计算工具.     

柳杨沟泥石流特征及其工程影响分析

2001年7月11日晚11点至12日凌晨,位于小天都水电站下闸址以下约600 m的柳杨沟爆发泥石流,造成数十万元的经济损失,对小天都电站下闸址造成了一定影响。通过现场调查和室内计算,研究了柳杨沟泥石流的发育特征和运动特征,并分析在各种设计概率下发生泥石流对水电工程可能造成的影响。     

氮气火花开关击穿机制的理论和数值研究

三电极气体火花开关带有触发极,相比两电极开关,其开关导通的可控性较高,工作电压较低且抖动小,所以气体火花开关中三电极开关的应用较为广泛.本文针对大气压氮气环境下的两电极开关和三电极开关的击穿机制进行了理论与数值模拟研究.通过理论和数值计算发现,对于平板-平板的两电极开关来说,低电压下(小于6.3 kV)无法产生流注击穿,高电压下(大于6.3 kV)会先形成由阴极到阳极的负流注,然后再形成由阳极向阴极的正流注.而在三电极开关的击穿过程中,首先会在触发极和绝缘体之间发生击穿,然后这个通道不断向阴阳极扩展,最终形成阴阳极之间的电弧通道.在本文的计算工况下,如果需要阴极-触发极、阳极-触发极同时击穿的话,其阴极-触发极之间的外加电压需要大于1.18 kV,而阳极-触发极之间的外加电压需要大于3 kV.当考虑触发极的场致发射后,该击穿阈值可以显著降低.     

A second order solution for the distortion of large scale turbulence around a 2-D obstacle

The problem of large scale (d/L « 1, where d is the dimension of the dimension of the body and L is the integral length scale of turbulence) three dimensional turbulence approaching an arbitrary two dimensional body is analysed following Hunt's (1973) theory. The analysis, based on Rapid Distortion Theory, incorporates both blocking and weak distortion of the velocity field caused by the obstacle. Besides obvious engineering applications, the solution illustrates the application of RDT for inhomogeneous turbulence problems.     

Experimental Study of the Linear Stability of a Falling Liquid Film in the Presence of a Turbulent Gas Stream

Using the local electrical conductivity method, the parameters of the linear waves generated on the surface of a falling liquid film in the presence of a co- or counter-current gas stream are measured. The Reynolds numbers of the fluid and the gas were varied from 24 to 125 and from 0 to 8000, respectively. The results are presented in the form of dispersion relations. In the case of the absence of a gas stream, the results are compared with calculations based on a linear integral theory. It is shown that a gas stream increases the instability of the film and a counter-current gas flow has a greater effect on the wave phase velocity than a co-current flow.     

Study of a Model for the Interaction Between Heavy Metals and Sediments of the Pisuerga River

Abstract

We have applied a competitive model, first proposed by Mouvet and Bourg, to explain the interaction between the heavy metals zinc, cadmium, lead, nickel and cobalt and bottom sediments from the Pisuerga River. Two sampling sites were chosen, the first located on an urban sewer and the second downstream from the polluting zone. The calculated constants for the first sediment were always lower than those found for the second one. The validity of the model is demonstrated by the existence of a correlation between the calculated constants and the first hydrolysis constants of the metals examined. All metal determinations were made by means of voltammetric techniques.     

Effects of ultrasonic irradiation and direct heating on extraction of priority pesticides from marine sediments

Priority pesticides (alachlor, aldrin, γ-chlordane, chlorfenvinphos, chlorpyrifos, dieldrin, 4,4′-DDT, 4,4′-DDD, 4,4′-DDE, α-endosulfan, β-endosulfan, endosulfan sulphate, endrin, α-HCH, β-HCH, γ-HCH, δ-HCH, HCB, HCBD, heptachlor, heptachlor epoxide, isodrin, methoxychlor, mirex, quintozene, terbuthylazine and trifluralin) are a group of toxic substances that are known by their persistency in the aquatic environment. Their screening in marine sediments may provide information on the sources and distribution in the water mass of fresh-transitional and coastal waters. This work proposes a rapid and reliable method to extract multi-residues of priority pesticides by ultrasounds irradiation from marine sediments. Multiple variables have been optimised: ultrasound frequency, sonication intensity, signal operation mode, time of extraction and water bath temperature. After sample clean-up and pre-concentration of the pesticides by stir bar sorptive extraction, the compounds were analysed by gas chromatography-mass spectrometry (GC-MS) using the selective ion monitoring acquisition mode (SIM). Better performance was found for ultrasonic-assisted extractions (UAE) at frequency of 35 kHz and an output intensity of 60% in a sweep mode of operation. An increase of water bath temperature to 80°C had a significant effect on the extraction of pesticides with high octanol-water partitioning coefficients (K_ow). Under optimal conditions, method detection limits (MDLs) and method quantification limits (MQLs) ranged from 0.3 to 4.4 ng g^?1 and from 0.8 to 14 ng g^?1, respectively. Recoveries between 70 and 111%, at high precision levels, were found at different types of marine sediments with a single extraction cycle. Method performance was in good agreement with quality control guidelines.     

Decommissioning of a Nuclear Power Plant: Determination of Site-Specific Sorption Coefficients for Co-60 and Cs-137

Abstract

Assessment of radiological risks in strategies for decommissioning of nuclear installations have to consider not only technical concepts such as cutting and decontamination techniques but, even more important, requirements for input of reliable information on the hydrological situation and retardation capabilities of relevant radionuclides specific to the respective decommissioning operation.

In this paper we describe appropriate methods for obtaining site-specific sorption data and present results achieved from a case study performed as a commercial contractual work preliminary to the planned decommissioning of a nuclear power plant. A detailed mineralogical study of the sediment used in our sorption experiment highlights the necessity of a thorough sample homogenization and characterization. Batch experiments using radiotracer techniques for the determination of site-specific sorption coefficients show significant retardation for Co-60 and Cs-137 after only 2h of equilibration between the preconditioned groundwater and sediment. Sorption is more effective in the groundwater of a deeper aquifer containing a higher amount of colloidal clay (illite) particles < 0.63 μn. The Co-60 radiotracer is more completely sorbed than the Cs-137 radiotracer. Equilibration of radionuclide distribution is slow, particularly for Co-60. Presence of EDTA reduces sorption of Co-60 efficiently while Cs-137 sorption remains unaffected.     

Modified Galerkin Method for Unsteady Two-Dimensional Viscous Fluid Flow Analysis

The Modified Galerkin Method (MGM) has been proposed as one of the most efficient methods for two-dimensional convection-diffusion equations. In the MGM, the non-symmetric matrices, which are derived from the convection term in the Galerkin formulation, are not used, and an artificial diffusion is introduced through an error analysis approach to improve its discretization accuracy in both time and space directions. In this study, the MGM is applied for two-dimensional viscous fluid flow analysis, and the driven cavity flow problems are solved up to Reynolds number of 10,000 using the vorticity-stream function formulation and non-uniform meshes. The results show the effectiveness of MGM.     

Lumineszenzdatierung quartärer Sedimente

The purpose of this paper is to discuss briefly the basis, technique and efficiency of luminescence dating. Thermoluminescence and optically-stimulated luminescence are useful for dating of quaternary sediments. Contents: Sediment Dating, Thermoluminescence Dating, Thermoluminescence (TL), Dating Method, Sources of Error, Dosimetry, Dating Techniques, Optical Dating (OSL), Sediments, References.