Non-smooth multisurface plasticity and viscoplasticity. Loading/unloading conditions and numerical algorithms

Rate-independent plasticity and viscoplasticity in which the boundary of the elastic domain is defined by an arbitrary number of yield surfaces intersecting in a non-smooth fashion are considered in detail. It is shown that the standard Kuhn-Tucker optimality conditions lead to the only computationally useful characterization of plastic loading. On the computational side, an unconditionally convergent return mapping algorithm is developed which places no restrictions (aside from convexity) on the functional forms of the yield condition, flow rule and hardening law. The proposed general purpose procedure is amenable to exact linearization leading to a closed-form expression of the so-called consistent (algorithmic) tangent moduli. For viscoplasticity, a closed-form algorithm is developed based on the rate-independent solution. The methodology is applied to structural elements in which the elastic domain possesses a non-smooth boundary. Numerical simulations are presented that illustrate the excellent performance of the algorithm.     

考虑异方差效应的风电不确定性建模及其在调度中的应用

随着风电在电力系统中渗透率的不断提升,其不确定性为电网的安全经济运行带来了重大挑战。为获得精准的风电不确定性模型,帮助运行人员实现系统的安全经济运行,文中提出了考虑异方差效应的风电预测误差条件概率分布建模方法。首先,分析了风电预测误差与各类因素的相依性水平,并基于分析结果与动态Copula理论,建立了风电波动性与风电预测误差的动态相依性模型;之后,针对边缘分布所显示出的时域特征,结合差分整合移动平均自回归(ARIMA)模型与广义自回归条件异方差(GARCH)模型,考虑异方差效应,建立了时变边缘分布模型;最后,将两模型相结合,给出了不同波动水平下的风电条件预测误差分布情况,并在不确定性机组组合模型中进行验证,证明了模型的有效性。     

Portable TL dosemeter--ESD phantom combination for chest and lumbar spine radiography

A thermoluminescence dosemeter (TLD)—entrance surfacedose (ESD) phantom combination was calibrated in terms of air-kermain IEC RQR X-ray radiation qualities between 50 and 150 kV.The ESD phantom was designed and constructed as a part of thework. With the combination, air-kermas were measured for fourradiological examinations (two chest and two lumbar spine examinationsin two hospitals), and converted to ESD_a using Monte–Carlocalculated BSF data tabulated for different tube voltages, filtrationsand beam diameters at 1 m distance. The results agreed withthe ionisation-chamber measurements within the reported overalluncertainty of the TLD method. In the calibration, the ESD phantomcan be replaced by the ISO water slab phantom unaffecting thereported overall uncertainty. Backscatter-related parametersfor the ISO water slab phantom and the newly designed ESD phantomwere determined for the IEC RQR qualities used in the secondarystandard dosimetry laboratory of STUK at 1 m distance, includingan approximate H_p(10)/H_p(0.07) ratio.     

Simulation of pressure swing adsorption in fuel ethanol production process

Fermentation derived ethanol is gaining wide popularity as a car fuel additive. A major challenge in the production of ethanol is the high energy cost associated with the separation of ethanol from the large excess of water. Distillation is usually the method of choice; however, water cannot be completely removed due to the presence of the azeotrope. The pressure swing adsorption (PSA) process is attractive for the final separation since it requires little energy input and is capable of producing a very pure product. The goal of this work was to perform a thorough analysis of the PSA process and find process improvements with the aid of mathematical modeling.

A general purpose package for the simulation of a cyclic PSA process was developed. The system of partial differential equations was solved via method of lines using a stiff equation integration package. Parameters for the model are based on the data from an operating plant as well as data from the literature. For the ethanol production technology our model provides a fundamental understanding of the dynamics of the cyclic process and effects of some operating parameters.