FRP拉挤复合材料本构关系模型研究

为了更加精确的描述厚型拉挤复合材料的力学性能和力学响应特征,文中以厚型E玻璃纤维/环氧树脂拉挤型复合材料系统为例,运用三维细观力学模型描述材料的非线性本构关系。模型从纤维和基质成分的角度对由粗纱层和玻纤双轴布构成的层合材料进行材料响应描述,最终建立了相应的有限元模型并通过试验进行校准。试验和数值分析结果表明:三维细观力学模型能够准确的描述E玻璃纤维/环氧拉挤型复合材料的力学响应,其精确度可以通过横向试样拉伸试验结果进行校准提高。

水文干旱与气象干旱临界转变条件的判定及响应关系

水文干旱与气象干旱的响应关系对于建立健全干旱监测预报系统具有重要意义。基于区域水文干旱指数(SHI)与标准化降水指数(SPI),结合游程理论和非线性关系模型分析喀什河流域水文干旱与气象干旱的特征、响应关系及驱动因素。结果表明:水文干旱的年平均干旱历时和干旱烈度大于气象干旱,且随着SPI和SHI时间尺度的增加,识别出的干旱历时和干旱烈度也有所增加。基于三参数(log 3 P1)对数函数(Logarithm)模型可以更好地表征两者的响应关系。在3个月尺度下,气象干旱历时至少为1.10个月且干旱的烈度至少为0.83时,将诱发水文干旱;在6个月尺度下,气象干旱历时至少为1.60个月且干旱的烈度至少为0.91时,易发生水文干旱。

Relationship between coal size reduction and energy input in Hardgrove mill

Hardgrove grindability index （HGI） is an important indicator of coal grindability, and is one of the most important parameters to determine the capacity of coal pulverizer in power station. However, HGI is an empirical grindability index without linkages to any known physical parameters. To investigate the effect of energy input on the grinding in Hardgrove mill. a T20WN torque meter was installed on the shaft of a modified Hardgrove mill to record the torque driving the mill. Samples from four kinds of coals with HGI ranging from 36 to 72 were prepared according to the procedure of standard HGI test and ground in a modified Hardgrove mill at different revolutions. The relation of sample size reduction degree to specific comminution energy （Ecs） was studied with Shi-Kojovic model, The results show that Shi-Kojovic model predicted well the coal size reduction degree with Ecs in Hardgrove mill. The griadability index given by Shi-Kojovic model has a similar trend with HGI. The relation of sample size reduction degree to Ecs reveals that HGI has a non-linear relationship with effective specific energy in Hardgrove mill, which explains the non-linear relation of HG1 to industrial pulverizer capacity.

Nonlinear correlation between RMB internationalization and nonferrous metal prices

The correlation between Renminbi(RMB) internationalization and nonferrous metal prices was studied using the nonlinear Granger causality test and the dynamic conditional correlation-generalized autoregressive conditional heteroskedastic(DCC-GARCH) model. The results indicate that the relationship between RMB internationalization and nonferrous metal prices reflects a complex nonlinear mechanism. There was no mutual influence between RMB internationalization and nonferrous metal prices prior to the trials of the RMB settlement in the cross-border trade in July 2009. Since then, however, a bidirectional causal relationship between RMB internationalization and the price of copper and a unidirectional causal relationship from the price of aluminum to RMB internationalization were examined. In addition, due to the impact of extreme events, such as economic and financial crises, RMB internationalization and nonferrous metal prices are not always positively correlated but are rather occasionally negatively correlated.

Modelling of Eruptive Fire Occurrence and Behaviour

Eruptive fires are one of the main causes of human losses in forest fire fighting. The sudden change in fire behaviour due to a fire eruption is extremely dangerous for fire-fighters because it is unpredictable. Very little literature is available to support either modelling or occurrence prediction for this phenomenon. In this study, an unsteady physical model of fire spread is detailed, which describes the initiation and development of eruptive fires with an induced wind sub-model. The latter phenomenon is proposed as the mainspring of fire eruptions. Induced wind is proportional to the rate of spread and the rate of spread is in a non-linear relationship with induced wind. This feedback can converge or diverge depending on the conditions. The model allows both explaining why an eruption can occur and predicting explicitly its occurrence according to meteorological conditions, topographic parameters, fuel bed properties and fire front width. The model is tested by comparing its results to a set of experiments carried out at laboratory scale and during an outdoor wildfire, the Kornati accident.

Seismic Performance of Dry-Friction Devices in Shear-Frame Buildings

In recent years the application of friction-based passive energy dissipation devices have been proven very effective in reducing structural response to earthquake excitations and also implemented for a large number of buildings. Their design heavily relies on numerical simulations to model the influence of the energy dissipation devices. The modeling of friction forces must be accurate for realistic simulation of the influence of these devices. In state-of-the-practice, the hysteretic behavior of friction devices has been typically modeled with Coulomb friction having a constant coefficient of friction. However, the basic laws for typical sliding materials and experimental investigations show non-linear relationship between friction and sliding velocity, which includes stiction and Stribeck effect. The influence of stiction and Stribeck effect may be significant and can not be ignored in simulating the dynamic responses of structures with friction-based energy dissipation devices. In this paper the optimal performance of dry friction device in shear-frame buildings when subjected to earthquake ground motions has been investigated. The focus of this paper is on the optimal minimization of response of the shear-frame building. Since buildings with friction devices behave in a highly nonlinear manner, nonlinear response-history analysis considering comprehensive sliding friction models has been carried out. The performance has also been evaluated using the various response measures： the maximum absolute acceleration, the maximum base shear, and the maximum inter-story drift. Different performance indices have been used to quantify the influence of the device properties.

Non-Linear Dependence in Oil Price Behavior

In this paper, the authors analyze the adequacy of GARCH-type models to analyze oil price behavior by applying two types of non-parametric tests, the Hinich portmanteau test for non-linear dependence and a frequency-dominant test of time reversibility, the reverse test based on the bispectrum, to explore the high-order spectrum properties of the Mexican oil price series. The results suggest strong evidence of a non-linear structure and time irreversibility. Therefore, it does not comply with the i.i.d （independent and identically distributed） property. The non-linear dependence, however, is not consistent throughout the sample period, as indicated by a windowed test, suggesting episodic nonlinear dependence. The results imply that GARCH models cannot capture the series structure.

文化产业组织冗余与企业创新绩效实证研究

组织冗余对于企业内部决策有着重要的意义。本文针对于文化产业,提出了一个组织冗余与企业绩效、企业创新绩效的两阶段非线性关系模型,并对中国文化产业159个上市公司2008-2011年的数据进行了实证分析,结果表明：组织冗余与企业绩效之间存在两阶段非线性关系,组织冗余在第一阶段对企业绩效的影响是负向的,在第二阶段对企业绩效的影响是正向的;然而在这段期间内,组织冗余与企业创新绩效之间没有显著的相关关系。