锦屏大理岩动态劈裂拉伸破坏及能量演化特征分析

劈裂拉伸破坏是隧洞围岩失稳破坏的主要形式之一。现阶段,在动态劈裂条件下岩石裂纹扩展及对应阶段的能量演化机制鲜有涉及。基于此,采用分离式霍普金森压杆对锦屏大理岩试样进行了不同弹速下的劈裂试验,并借助ANSYS/LS-DYNA有限元软件,模拟试样动态劈裂破坏过程。从试验测试和数值计算角度,重点分析大理岩劈裂过程中的裂纹扩展机制以及能量演化特征。结果表明：在应变率为5～35 s−1时,大理岩的动态拉伸强度与应变率呈线性正相关,同其他地区大理岩相比较,锦屏大理岩的应变率敏感性相对较低;随着弹速的增加,系统内能和动能均增大,在试样破坏的瞬间系统内能降至最低;采用标定的Cowper-Symonds本构模型参数进行数值模拟,所得的试样最终破坏形态与试验观察到的现象基本一致。研究结果可为具体工程应用提供指导和参考。     

地磁场能量在地球内部的分布及其长期变化

用国际参考地磁场模型(IGRF)分析了地磁场能量在地球内部的分布及其长期变化.结果表明,从1900年到2005年,地核以外地磁场总能量由6.818×1018J减少到6.594×1018J,减小了3.3%,地表以外地磁场总能量由8.658×101J减小到.63×101J,减小了11.4%.分析地球内部不同圈层地磁场能量的变化表明,地壳(A层)、上地幔(B层)、转换带(C层)、下地幔D′层的地磁场总能量在减小,但是下地幔"层的地磁场总能量却在快速增加.磁能密度随时间的变化更清楚地显示出磁能增加和减小的分界面在r=3840km处.上述结果表明,地核和地表以外地磁场总能量在趋势性减小的同时,也在进行重新分配.进一步分析表明,下地幔D"层磁能快速增长,主要是由高阶磁多极子的增强引起的.在地磁场倒转前,偶极矩减小而多极性相对增强在能量分布上的表现就是磁能向下地幔底部(特别是D"层)集中.     

A consistent derivation of the wave-energy equation from basic hydrodynamic principles

Based on a decomposition of the velocity into mean flow, turbulent and wave components, momentum and hereafter a wave-energy equation is derived. It contains a turbulent energy dissipation term which is closed by applying a wave-related mixing length model and linear wave theory solutions. This closure produces a non-linear turbulent wave-energy dissipation including the wave energy in a 5/2 power law. The theory is able to predict correctly the shape of deep-water wave spectra according to Phillips' similarity law.Responsible Editor: Hans Burchard     

绝对和相对输入能量谱对比及延性系数的影响研究

利用266条强震记录,在研究绝对输入能量谱和相对输入能量谱衰减规律的基础上,对由衰减关系所确立的两种输入能量谱进行对比分析,讨论了延性系数对这两种输入能量谱的影响. 研究发现,在弹性情况下,两种输入能量谱在周期0.5~1.0 s范围内相差不大; 在非弹性情况下 两种输入能量谱在周期0.5 s处相差不大. 周期较小时,绝对输入能量谱要大于相对输入能量谱;周期较大时,绝对输入能量谱小于相对输入能量谱. 延性系数对这两种输入能量谱影响均比较大, 对绝对输入能量谱而言,周期小于0.3 s时,随着延性系数的增大, 能量谱升高;周期大于0.3 s时,随着延性系数的增大能量谱降低. 不同延性系数的绝对输入能量谱在分界点0.3 s左右相等. 相对输入能量谱受延性系数影响与绝对输入能量谱相似, 但分界点在0.5 s左右. 与绝对输入能量谱相比, 相对输入能量谱在短周期段受延性系数的影响较大, 特别是当场地较软时更为明显.      

The Linkage between Midwinter Suppression of the North Pacific Storm Track and Atmospheric Circulation Features in the Northern Hemisphere

The midwinter suppression(MWS) of the North Pacific storm track(NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980 s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling.From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.     

风电场风资源测量与计算的精度控制

根据多个复杂地形风电场观测操作实践和大量观测数据的计算分析,提出了对观测数据和计算质量精度控制的主要措施,包括:复杂地形测风站布设的5个原则,仪器的合理选型和设置;对由于测风仪固有的系统误差和缺测数据的插补订正可能引起的计算误差进行了定量估算,通过对大量实测数据的对比计算显示:①目前普遍采用的进口风速计的相对偏差在1.6%～5.25%之间,由此可导致轮毂高度附近的年平均风功率密度误差在5%以上,最大达13.8%;②在季风气候区、复杂地形和风的年变率较大的地区,进行缺测数据插补订正时,应选取同季或同一主导风向的数据作为插补订正的基础数据,否则可能导致其平均风功率密度相对误差达20%～50%.     

基于能量原理的Park & Ang损伤模型简化计算方法

Park＆Ang损伤模型综合考虑了结构最大变形和累积滞回耗能的耦合作用,具有一定的先进性,被国内外研究者广泛采用;但由于该模型中参数的计算困难,尤其涉及结构滞回耗能的计算问题时,该模型的应用受到了一定的限制;文中从能量的关系入手,寻找出结构滞回耗能与结构最大位移的关系,利用该关系可方便求解出结构的滞回耗能,从而为该模型的计算提供了一种简便方法;最后,例题分析证明本文的方法简便可行,计算效率高。     

Energy distributions of the large-scale horizontal currents caused by wind in the baroclinic ocean

Wind is the main energy source for the generation of the internal waves and the ocean mixing. Wunsch[1] estimated that about 1 TW (1 TW = 1012 W) energy was transported into the ocean from the winds by us-ing the altimeter data. Watanabe et al.[2] numerically calculated that the mixing processes obtained 0.7 TW energy from the global wind, which afforded most of the energy needed by the maintenance of the Merid-ional Overturning Circulation (MOC). During the past 50 years, in the Norther…     

Cuttability assessment of hard coal seams

Summary A number of field and laboratory tests have been carried out on more than 15 coal seams of compressive strengths ranging from 19 MPa to 44 MPa to evolve methods which would help in the selection of suitable coaling machines for hard coal seams. The effect of physico-mechanical properties on cuttability were studied in the laboratory for all these coal seams to identify the relevant parameters affecting the specific energy of coal cuttability. These data were subjected to regression analysis to find the best fit for estimation of laboratory specific energy of coal samples on the basis of simple laboratory and field tests for the strength parameters. Field studies were also conducted over a large number of active mechanized coal faces to study in situ cuttability along with the geo-mining conditions of the site. The field and the laboratory data so generated were correlated and an attempt is made to establish a relationship for estimating the field specific energy for a particular capacity of coaling machines by considering the geo-mining domain of the field in totality.     

CFD modelling of a small–scale fixed multi–chamber OWC device

Wave Energy Converters (WECs) have excellent potential as a source of renewable energy that is yet to be commercially realised. Recent attention has focused on the installation of Oscillating Water Column (OWC) devices as a part of harbor walls to provide advantages of cost–sharing structures and proximity of power generation facilities to existing infrastructure. In this paper, an incompressible three–dimensional CFD model is constructed to simulate a fixed Multi–Chamber OWC (MC–OWC) device. The CFD model is validated; the simulation results are found to be in good agreement with experimental results obtained from a scale physical model tested in a wave tank. The validated CFD model is then used for a benchmark study of 96 numerical tests. These investigate the effects of the PTO damping caused by the power take–off (PTO) system on device performance. The performance is assessed for a range of regular wave heights and periods. The results demonstrate that a PTO system with an intermediate damping can be used for all chambers in the MC–OWC device for most wave period ranges, except for the long wave periods. These require a higher PTO damping. An increased incident wave height reduces the device capture width ratio, but there is a noticeable improvement for long wave periods.