Estimation of critical convergence and rock load in coal mine roadways — an approach based on rock mass rating     

C. N. Ghosh  A. K. Ghose 《Geotechnical and Geological Engineering》1992,10(3):185-202

Summary Based on field instrumentation in eight different coal mines representing varying depths and strata conditions, a relation for obtaining the critical convergence value has been established. In development heading for bord and pillar workings this relation can be used successfully to control the premature collapse of the roof. An empirical relation for rock load has been established. This can be utilized for optimum design of support system. The roofs have been categorized as stable, short-term stable and unstable. Proper attention should be provided for an unstable roof and the support design is to be changed before the convergence reaches the critical value.  相似文献   

NUMERICAL SIMULATION OF TROPICAL CYCLONE MOVEMENT WITH THE RELATED CRITICAL POINT PHENOMENON^*          下载免费PDF全文

Luo Zhexian 《Acta Meteorologica Sinica》1994,8(2):161-167

A study is made of the paths of tropical cyclones under the joint action of environmental flow and heating fields in terms of a quasi-geostrophic barotropic model with the thermal forcing and dissipation terms involved,in which 16 experiments are designed and integrated for more than 7 model days.Results show that for different parameter values of the environmental flow and heating field,and the cyclone scale,such paths as counterclockwise looping,zigzag form and westward march with an abrupt turning towards the north are reproduced clearly in the model atmosphere,exhibiting their critical points of nonlinear character.  相似文献   

岩石断裂过程的声发射试验研究   总被引：3，自引：0，他引：3  

秦四清 《地质灾害与环境保护》1994,5(3):48-55

根据N-t,φ-t,E-t,A(t)-t曲线,并结合读数显微镜实测观察,可较准确地判定开裂点。在计算大理岩临界应力强度因子时,考虑了裂纹扩展长度的影响.导出了低脆性岩石N-K_1关系的一般表达式,并与Harris公式进行了比较.研究了声发射事件数与裂纹扩展长度增量的关系。  相似文献   

水电站进水口快速闸门水力学分析   总被引：2，自引：0，他引：2       下载免费PDF全文

刘维平 《水科学进展》1994,5(4):309-318

主要分析水电站进水口快速闸门在动水关闭过程中流量、临界开度和闸门受水流作用力(闸顶水压力、闸底水压力和闸门水平压力)等问题。根据模型试验所观测的水力现象和非恒定流计算理沦,提出了计算电站闸门、引水管道的水力参数(流量、水头和通气孔水位等)的数学模型。实例计算结果和模型试验结果基本吻合。  相似文献   

Critical State Sedimentation Line of Soft Marine Clays   总被引：1，自引：4，他引：1  

HONG  Zhen-shun 《中国海洋工程》2003,17(4):631-640

The compression behavior responsible for unity sensitivity is very valuable in quantitative assessment of the effects of soil structure on the compression behavior of soft marine sediments. However, the quantitative assessment of such effects is not possible because of unavailability of the formula for the compression curve of marine sediments responsible for unit sensitivity. In this study, the relationship between the remolded state and the conventional critical state line is presented in the deviator stress versus mean effective stress plot. The analysis indicates that the remolded state is on the conventional critical state line obtained at a relatively small strain. Thus, a unique critical state sedimentation line for marine sediments of unit sensitivity is proposed. The comparison between the critical state sedimentation line proposed in this study and the existing normalized consolidation curves obtained from conventional oedometer tests on remolded soils or reconstituted soils explains well the  相似文献   

地震折射波的虚拟速度——临界角谱的原理与制作方法     

焦湘恒  王修田 《中国海洋大学学报(自然科学版)》1987,(4)

虚拟速度—临界角谱是地震折射波虚拟射线理论的应用之一。根据共始点或共折射点记录的相似性,利用第一虚拟时距曲线方程,对时距曲线进行扫描计算,可以制作共始点谱和共折射点谱。 文中,通过实际介质模型的计算机试算结果,对该方法作了验证。  相似文献   

南麂列岛土壤环境调查研究     

应时理  熊健 《海洋学研究》1994,12(2):92-100

本文简述了南麂列岛土壤的理化特性，并探讨了土壤中重金属浓度的临界值及其客量。该土属红壤亚类，土壤质地以中壤土和重壤土为主，氮、磷及有机质含量中等偏下。重金属元素Ｃｕ，Ｐｂ，Ｚｎ，Ｃｄ，Ｃｒ的临界值分别为５０×１０－６，１００×１０－５，２００×１００－６，１０－６和１００×１０－６。南麂列岛土壤中重金属含量目前处于自然分布状态。土壤的现存容量与静容量相等，暗示了该土壤具有较大的纳污能量。  相似文献   

参数化浅海流体动力学模型中的耗散与频散     

孙文心 《中国海洋大学学报(自然科学版)》1992,(4)

对几个参数化浅海流体动力学模型的耗散性和频散关系进行了理论分析,提出三点结论:1.深度平均(或积分)的浅海流体动力学模式不能充分表达湍耗散;2.浅海中的强耗散将对长波振荡具有本质的影响;3.几种不同的湍参数化动力模型将对长波产生不同的频散效应。  相似文献   

Biological Impact of Elevated Ocean CO<Subscript>2</Subscript> Concentrations: Lessons from Animal Physiology and Earth History     

Hans O. Pörtner  Martina Langenbuch  Anke Reipschläger 《Journal of Oceanography》2004,60(4):705-718

CO₂ currently accumulating in the atmosphere permeates into ocean surface layers, where it may impact on marine animals in addition to effects caused by global warming. At the same time, several countries are developing scenarios for the disposal of anthropogenic CO₂ in the worlds' oceans, especially the deep sea. Elevated CO₂ partial pressures (hypercapnia) will affect the physiology of water breathing animals, a phenomenon also considered in recent discussions of a role for CO₂ in mass extinction events in earth history. Our current knowledge of CO₂ effects ranges from effects of hypercapnia on acid-base regulation, calcification and growth to influences on respiration, energy turnover and mode of metabolism. The present paper attempts to evaluate critical processes and the thresholds beyond which these effects may become detrimental. CO₂ elicits acidosis not only in the water, but also in tissues and body fluids. Despite compensatory accumulation of bicarbonate, acid-base parameters (pH, bicarbonate and CO₂ levels) and ion levels reach new steady-state values, with specific, long-term effects on metabolic functions. Even though such processes may not be detrimental, they are expected to affect long-term growth and reproduction and may thus be harmful at population and species levels. Sensitivity is maximal in ommastrephid squid, which are characterized by a high metabolic rate and extremely pH-sensitive blood oxygen transport. Acute sensitivity is interpreted to be less in fish with intracellular blood pigments and higher capacities to compensate for CO₂ induced acid-base disturbances than invertebrates. Virtually nothing is known about the degree to which deep-sea fishes are affected by short or long term hypercapnia. Sensitivity to CO₂ is hypothesized to be related to the organizational level of an animal, its energy requirements and mode of life. Long-term effects expected at population and species levels are in line with recent considerations of a detrimental role of CO₂ during mass extinctions in the earth's history. Future research is needed in this area to evaluate critical effects of the various CO₂ disposal scenarios. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

吞吐流量对湖泊流场结构影响的数值试验     

韩红娟  胡维平  晋义泉 《海洋湖沼通报》2007,(Z1)

本文利用EcoTaihu三维生态模型中的三维水动力学模型,开展了典型背景风场、多个吞吐流量条件下的湖流数值试验,分析比较流场达到稳定状态时。沿垂直方向平均流场随吞吐流量大小的变化特征。结果表明:随着吞吐流量的增加,湖泊垂向平均流场逐渐由受风生流控制转变成受吞吐流场控制,在此转变过程中存在临界吞吐流量值。当吞吐流量大小超过该值时,流场结构发生明显的改变,湖泊内小尺度的环流先消失,规模最大的环流最后消失;环流中流向和吞吐流流向一致的区域流速得到加强.而与吞吐流流向相反或差异较大的区域.流速先减小,后增加。风向和风速是影响临界吞吐流量值大小的主要因素。本文的研究结果对认识湖泊流场特征和了解物质在湖泊内的输移扩散具有重要意义,为合理规划引调水、准确预测水质、重建健康生态湖泊提供基础科学依据。  相似文献