Stability of large-scale coal-fired MHD channels

Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analysis, and (2) time-dependent 1-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current. Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u - a and u waves are unstable.     

A quantitative evaluation of time-independent and time-dependent deformations of lead-free and lead-containing solder alloys

A method to separate plasticity and creep is discussed for a quantitative evaluation of the plastic, transient creep, and steady-state creep deformations of solder alloys. The method of separation employs an elasto-plastic-creep constitutive model comprised of the sum of the plastic, transient creep, and steady-state creep deformations. The plastic deformation is expressed by the Ramberg-Osgood law, the steady-state creep deformation by Garofalo’s creep law, and the transient creep deformation by a model proposed here. A method to estimate the material constants in the elasto-plastic-creep constitutive model is also proposed. The method of separation of the various deformations is applied to the deformation of the lead-free solder alloy Sn/3Ag/0.5Cu and the lead-containing solder alloy Sn/37Pb to compare the differences in the plastic, transient creep, and steady-state creep deformations. The method of separation provides a powerful tool to select the optimum lead-free solder alloys for solder joints of electronic devices.     

Influence of bias-temperature stressing on the electrical characteristics of SiOC:H film with Cu/TaN/Ta-gated capacitor

Experiments on bias-temperature stressing, capacitance-voltage measurements, current-voltage characteristics, and time-dependent dielectric breakdown were performed to evaluate the reliability of Cu and low-k SiOC:H integration. A high leakage current of ∼8 × 10⁻¹⁰ to 2 × 10⁻⁸ A/cm² at 1 MV/cm in SiOC:H dielectrics in a Cu-gated capacitor, and a lower 2 × 10⁻¹⁰ to 5 × 10⁻¹⁰ A/cm² at 1 MV/cm in a Cu/TaN/Ta-gated capacitor, were observed at evaluated temperatures. The drift mobility of the Cu⁺ ions in the Cu/TaN/Ta-gated capacitor was lower than that in a Cu-gated capacitor. A physical model was developed to explain the observed kinetics of Cu⁺ ions that drift in Cu-gated and Cu/TaN/Ta-gated capacitors. The electric field in the Cu-gated MIS capacitor in the cathode region is believed to be increased by the accumulation of positive Cu⁺ ions, which determines the breakdown acceleration. Good Cu⁺ ions drift barrier layers are required as reliable interconnects using thin TaN and Ta layers. Additionally, Schottky emission dominates at low electric fields, E<1.25 MV/cm, and Poole-Frenkel emission dominates at high fields, E>1.5 MV/cm.     

在役结构随机时变可靠性分析

根据在役结构的特点,考虑结构抗力退化及相关化,给出了在役结构随机时变可靠度的两种近似计算方法和算例。     

Quasielastic scattering from dilute polymer solutions

The initial slope $\text{Ω(q)}$ of the time-dependent scattering function and the static structure factor S(q) of macromolecules in good solvents are calculated without using the Gaussian assumption. For S(q), the scaling relation S(q)～q^?1.7 is confirmed in the intermediate q range, whereas no q dependent cross-over behaviour can be observed. The calculation of $\text{Ω(q)}$ reveals a q³ dependence in this range and no evidence is seen for an exponent apart from 3. The time-dependent scattering function S(q,t) is treated within the framework of the Gaussian assumption. Hydrodynamic as well as excluded volume interactions are incorporated. It has been found that excluded volume effects decrease the decay of the scattering function in comparison with the Gaussian chain.     

缓坡方程的有限分析数值模式

基于时间关联的双曲型缓坡方程,采用九点有限分析法,建立近岸波浪传播变形的数值模式,在对时间关联的双曲型缓坡方程数值离散时,空间导数采用九点有限分析法,时间导数仍采用有限差分法,再采用质量集中方法得到本文的数值模式。为了验证本模式的数值精度和有效性,分别对Berkhoff(1972)实验和突堤地形进行数值模拟,结果表明本模式的模拟值与物理模型试验值、解析解及有限差分模式的模拟值吻合良好,表明本模式可以对近岸波浪传播过程中折射、绕射、反射、浅水变形、波浪破碎和弱非线性等因素的影响进行较好的预测。     

格林函数时间卷积法在输运求解中的应用

利用瞬时源的格林函数卷积,可求解具有一定时间分布源粒子的输运问题。首先从输运方程的一般形式推导得到了格林函数时间卷积法的公式,并结合蒙特卡罗数值模拟算例,验证了格林函数时间卷积法在定态含时输运问题中的适用性,为相关问题的求解提供了新的思路。进一步数值分析表明,对于某些实际模型的蒙特卡罗求解,在同样计算样本条件下,格林函数卷积法还能实现较高的计算精度。     

Time-dependent movements of the hangingwall at the Kiirunavaara mine

The hangingwall deformation behaviour at the Kiirunavaara mine has been characterised after several years of collecting surveying data from the ground surface. The monitoring system was implemented to track surface subsidence because the city of Kiruna and the railway are situated on the hangingwall. Data time–displacement and time–velocity curves were used and different stages of deformation behaviour were identified – regressive, progressive and steady state. The movement starts with a regressive behaviour for which subsidence is characterised by continuous deformations. At the end of this stage the movement accelerates, marking the beginning of the progressive behaviour where subsidence becomes more discontinuous. A steady state stage is reached when the strength of the failure surface decreases to the residual value. To predict displacement in the vicinity of the railway, accumulated displacements per year were analysed for several stations for which data for the full regressive stage were available. Displacement tendencies were fitted with quadratic polynomial functions. Therefore, the rate of movement follows a linear trend with a constant acceleration. Finally, a critical horizontal strain limit was determined based on the estimated displacement.     

大位移水平井两层不稳定岩屑传输模型研究

本文在Martins提出的两层模型基础上．考虑了悬浮层岩屑颗粒的扩散，建立了与时间相关的两层不稳定岩屑传输数学模型。用有限容积法求解了此偏微分方程组。研究结果表明：在一定条件下，环空岩屑传输流动达到稳定状态需要很长的时间，这表明用稳定流动模型来模拟环空中岩屑传输问题有其局限性；粘度的增加、环空返速的提高和机械钻速的降低有助于水平环空中岩屑的传输。