Damage Constitutive and Failure Prediction of Artificial Single-Joint Sandstone Based on Acoustic Emission

The effect law of deformation and failure of a jointed rock mass is essential for underground engineering safety and stability evaluation. In order to study the evolution mechanism and precursory characteristics of instability and failure of jointed rock masses, uniaxial compression and acoustic emission (AE) tests are conducted on sandstones with different joint dip angles. To simulate the mechanical behavior of the rock, a jointed rock mass damage constitutive model with AE characteristic parameters is created based on damage mechanics theory and taking into account the effect of rock mass structure and load coupling. To quantify the mechanism of rock instability, a cusp catastrophe model with AE characteristic parameters is created based on catastrophe theory. The results indicate that when the joint dip angle increases from 0° to 90°, the failure mechanism of sandstone shifts from tensile to shear, with 45° being the critical failure mode. Sandstone's compressive strength reduces initially and subsequently increases, resulting in a U-shaped distribution. The developed damage constitutive model's theoretical curve closely matches the test curve, indicating that the model can reasonably describe the damage evolution of sandstone. The cusp catastrophe model has a high forecast accuracy, and when combined with the damage constitutive model, the prediction accuracy can be increased further. The research results can provide theoretical guidance for the safety and stability evaluation of underground engineering.

     

立交桥曲线箱梁动力分析模型

提出了1种双脊骨空间有限元模型,用来模拟和分析立交桥曲线箱梁的固有振动特性和动力反应。将曲线箱梁分别看作是由空间梁或壳组成的空间结构,并分别采用分段空间直梁模型、壳元模型和实体元模型进行模拟,分析相同曲线箱梁的振动特性和地震时程反应,通过与双脊骨模型的计算结果的比较验证双脊骨模型的可靠性。初步研究了在相同曲率半径下不同跨度的曲线箱梁的固有振动特性,分析了双脊骨模型的脊骨间距、横向连接间距等参数对模型计算结果的影响。研究结果可为曲线梁桥抗震性能和地震反应分析提供参考。     

Stochastic Response Analysis of Piled Offshore Platform Excited by Stationary Filtered White Noise

In this paper,the analysis method of stochastic response of piled offshore platform excited bystationary filtered white noise is presented.With this method,the strong ground motion is considered asthree direction stationary filtered white noise process,the theoretic solutions of three special integrationequations are derived with the residue theorem,and the expression of response nodal displacements andmember forces of offshore platform excited by the stationary filtered white noise is put forward.Thestochastic response of a piled offshore platform excited by the stationary filtered white noise,which is lo-cated 114.3m in water depth,is computed.The results are compared with those obtained with the re-sponse spectrum analysis method and the stationary white noise model analysis method,and the corre-sponding conclusion is drawn.     

Geothermal potential evaluation and development prioritization based on geochemistry of geothermal waters from Kangding area,western Sichuan,China

Kangding geothermal area is located in the western Sichuan, belonging to southeastern margin of Tibetan Plateau. Similar to world-renowned south Tibetan and western Yunnan geothermal belt, western Sichuan has intensive surface thermal manifestations including boiling and hot springs. The emerging temperature of thermal waters ranges from 47 to 79 °C with total dissolved solids lying between 899 and 2550 mg/L. δ²H–δ¹⁸O isotopes indicate a meteoric source for the thermal waters and a significant positive oxygen-18 shift in the southern region. It is suggested that southern thermal waters experienced stronger water–rock interaction and are closer to thermodynamic equilibrium, which is also proved by the water type classification. The reservoir temperature calculated by empirical and theoretical chemical thermometry is 180–225 °C for the north and 225–310 °C for the south. Evidences of hydrogeochemistry, stable isotopes, geothermometry and radiocarbon dating indicate that southern region of Kangding area shows greater geothermal potential than the northern region. In addition, based on the hydrogeochemical modeling of mineral saturation, underlying problem of scaling is likely to occur in the study area. According to the results of reservoir temperature, south Kangding sub-district has greater potential in geothermal power generation and development than northern Kangding. Therefore, further exploration and drilling work should give priority to the south Kangding area.     

The effect of expansion ratio on the critical Reynolds number in single fracture flow with sudden expansion

Flow in a single fracture (SF) is an important research subject in groundwater hydrology, hydraulic engineering, radioactive nuclear waste repository and geotechnical engineering. An abruptly changing aperture is a unique type of SF. This study discusses the relation between the values of the critical Reynolds number (Re_c) for the onset of symmetry breaking of flow and the expansion ratio (E) of SF, which is defined as the ratio between the outlet (D) and inlet (d) apertures. This study also investigates the effect of inlet aperture d on Re_c for flow in an SF with abruptly changing apertures (SF‐ACA) using the finite volume method. Earlier numerical and experimental results showed that flow is symmetric in respect to the central plane of the SF‐ACA at small Reynolds number (Re) but becomes asymmetric when Re is sufficiently large. Our simulations show that the value of Re_c decreases with the increasing E, and the relationship between the logarithm of Re_c and E can be described accurately using either a quadratic polynomial function or a logarithmic function. However, the relationship of Re_c and d for a given E value is vague, and Re_c becomes even less sensitive to d when E increases. This study also reveals that the hydraulic gradient (J) and flow velocity (v) follow a super‐linear relationship that can be fitted almost perfectly by the Forchheimer equation. The inertial component (J_i) of J increases monotonically with Re, whereas the viscous component (J_v) of J decreases monotonically with Re. The Re value corresponding to equal inertial and viscous components of J (named as the transitional point Re) decreases when E increases, and such a transitional point Re should be closely related to the critical Reynolds number Re_c, although a rigorous theoretical proof is not yet available. Copyright © 2015 John Wiley & Sons, Ltd.     

静力平衡近似下大气中非线性对称运动的稳定性、分岔和突变

本文在考虑基本气流具有非线性切变情况下,导出了对称运动所满足的非线性常微分方程,并用非线性系统的稳定、分岔、突变理论,严格地讨论了非线性对称运动的稳定性、分岔和突变问题,获得了一个推广的对称不稳定判据,找到了突变产生的条件。     

电涌保护器的简易检测方法

根据电涌保护器特点,对电涌保护器的二种简易的检测方法(外观检查和参数测试)进行分析,提出了易于操作的检测方法,供广大防雷检测人员借鉴.     

FIRST TRANSITION OF THE CIRCULATIONS IN ASIA AROUND MID－MAY FROM 7－YEAR MEAN ECMWF DATA

The time evolution of the general circulation over the South China Sea and surrounding areas during the period from April to June is studied using ECMWF data of 1980-1986. The first transition from the second (6-10 May ) to the third (11-15 May ) pentads is characterized by the distinct change of low-level (850 hpa ) winds from southeasterlies to southwesterlies along 15°N over the South China Sea, and by the sudden movement of the center of South Asian high in the upper troposphere (200 hpa ) from 10-15°N to 15-20°N over Southeast Asia. Corresponding to the abrupt change in circulations, the gradients of the temperature and humidity intensity along latitudes center on 30°N over East Asia at 850 hpa. The time sequence of the 850- 200 hpa layer thickness shows that the layer-mean temperature over the southeastern Tibetan Plateau-East China Plain region increases abruptly at the same time. The corresponding sudden increase of the vertically integrated heat source over the warming areas reveals that the heat source plays an evident role in the drastic changes. The time series of over the northern part of the South China Sea shows that the drastic increase of the areamean is also found but it is 5-10 days late than the change of corresponding wind fields. The time series of Xisha SST shows a continuous increase to about 29. 5°until May 10 when the abrupt changes in circulation occur.     

The Geochemical Significance of Deep-water Coral and Their Food Source

Deep-sea corals live in the dark cold-water environments, the food of which that provides them with energy and nutrition is a key ecological and biogeochemical problem. Currently, the most common understanding is that their food mainly comes from organic matter produced by and deposited from surface seawater. However, more and more studies have found that they can also obtain food supply through symbiosis with a variety of chemosynthetic autotrophs and heterotrophs. Carbon and nitrogen isotopes have been used to trace and reveal the food sources of deep-sea corals. They also have been successfully used to reconstruct the phytoplankton community structure and the changes of nitrate isotopes in surface seawater in the past, thus providing valuable biogeochemical data for paleoceanographic study. However, due to the widespread existence of symbiosis with chemosynthetic autotrophs, further studies are needed to assess the reliability of organic carbon and nitrogen isotopes of deep-sea corals to reflect changes in the surface seawater. The deep-sea gorgonian coral, like those gorgonian forests recently found in the South China Sea, is relatively new and insufficiently studied in the field of deep-sea corals. Thus, basic biochemical and paleoceanographic researches on the South China Sea deep-water gorgonians will provide profound and novel insights to understanding the cold-water coral system.