Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

Multiple longshore sand bars in the upper Chesapeake Bay     

Thomas J. Dolan  Robert G. Dean 《Estuarine, Coastal and Shelf Science》1985,21(5):727-743

In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism.  相似文献   

Particulate organic matter in the coastal and estuarine waters of Goa and its relationship with phytoplankton production     

X.N. Verlencar  S.Z. Qasim 《Estuarine, Coastal and Shelf Science》1985,21(2):235-243

In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l^?1 and from 0.28 to 5.24 mg l^?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l^?1 and from 0.78 to 20.34 μg l^?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m^?3 and 938.1 mg C m^?2 day^?1 in the coastal waters and 4.3 mg m^?3 and 636.5 mg C m^?1 day^?1 in the estuarine waters, respectively.$\text{POC}\text{chl}$ ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).  相似文献   

论中国盐溶角砾岩的特征和分类     

魏东岩 《岩石学报》1991,7(3):73-80,T001

中国的蒸发岩矿床非常丰富,与蒸发岩在成因上密切相关的盐溶角砾岩极其发育。本文简述了中国盐溶角砾岩的分布,总结了盐溶角砾岩的一般特征,划分出盐溶角砾岩的主要类型,探讨了盐溶角砾岩与盐泉的关系。  相似文献   

Petrography and textural development of inorganic and biogenic lithotypes in a relict barite tufa deposit at Flybye Springs, NT, Canada     

SANDY M. BONNY  BRIAN JONES 《Sedimentology》2008,55(2):275-303

A relict mound of Holocene barite (BaSO₄) tufa underlies the Flybye Springs, a small, barium‐rich, cold sulphur spring system in the Northwest Territories of Canada. The tufa is composed of relatively pure barite with ≤0·34 wt% Ca²⁺ and ≤0·77 wt% Sr²⁺. The mound is made up of coated bubble, raft, undulatory sheet, stromatolitic, coated grain and detrital conglomerate barite tufa. Although previously unreported in barite, these lithotypes are akin to facies found in many carbonate spring deposits. Raft and ooid‐coated grain tufa was formed via ‘inorganic’ barite precipitation in spring water ponds and tributaries where rapid oxidation of sulphide to sulphate established barite supersaturation. Undulatory sheet tufa may have formed by the reaction of dissolved barium with sulphate derived from the oxidation of extracellular polysaccharide‐rich colloidal sulphur films floating in oxygenated, barite‐saturated spring water ponds. Coated bubble, oncoid‐coated grain and stromatolitic tufa with filamentous microfossils was formed in close association with sulphur‐tolerant microbes inhabiting dysoxic and oxygenated spring water tributaries and ponds. Adsorption of dissolved barium to microbial extracellular polysaccharide probably facilitated the development of these ‘biogenic’ lithotypes. Detrital conglomerate tufa was formed by barite cementation of microdetrital tufa, allochthonous lithoclasts and organic detritus, including caribou hair. Biogenic textures, organic artefacts and microfossils in the Flybye barite tufa have survived diagenetic aggradational recrystallization and precipitation of secondary cements, indicating the potential for palaeoecological information to be preserved in barite in the geological record. Similarities between the Flybye barite tufa and carbonate spring deposits demonstrate that analogous textures can develop in chemical sedimentary systems with distinct mineralogy, biology and physiochemistry.  相似文献   

Occurrence and evolution of the Xiaotangshan hot spring in Beijing, China   总被引：1，自引：0，他引：1  

Zhou Haiyan  Zhou Xun  Chai Rui  Yu Lan  Liu Chunhui  Li Liangping 《Environmental Geology》2008,53(7):1483-1489

Thermal groundwater occurs in bedrock aquifers consisting of the dolomite of the Wumishan Group of the Jixianin System and the Cambrian carbonate in the Xiaotangshan geothermal field near the northern margin of the North China Plain, China. The hot water in the geothermal field of basin-type discharges partly in the form of the Xiaotangshan hot spring under natural conditions. The hot water has TDS of less than 600 mg/L and is of Na·Ca-HCO₃ type. The geothermal water receives recharge from precipitation in the mountain area with elevation of about 500 m above sea level to the north of the spring. Thermal groundwater flows slowly south and southeast through a deep circulation with a residence time of 224 years estimated with the Ra–Rn method. The Xiaotangshan hot spring dried up in the middle of the 1980s owing to the increasing withdrawal of the hot water in the geothermal field in the past decades. The water level of the geothermal system still falls continually at an annual average rate of about 2 m, although water temperature changes very little, indicating that the recharge of such a geothermal system of basin-type is limited. Over-exploitation has a dramatic impact on the geothermal system, and reduction in exploitation and reinjection are required for the sustainable usage of the hot water.  相似文献   

辽宁省海洋环境保护与海岸带可持续开发利用     

刘现明 《海岸工程》1995,14(4):33-36

在分析综合辽宁省海岸带调查和沿海经济贝类污染监测资料基础上，根据辽宁海岸带水质，沉积物和生物污染现状及发展趋势。针对所存在的问题，讨论了辽宁省海洋污染特别是赤潮对海洋资源的破坏，并在组织机构，地方立法，海岸带环境保护规划，污染源控制与整体环境改进，监测方案等方面提出了建设海上辽宁、加强辽宁省海洋环境保护与海岸可持续开发利用的建议。  相似文献   

浙江省海岛沿岸水域微生物生态分布   总被引：2，自引：0，他引：2  

史君贤  陈忠元 《海洋学研究》1996,14(2):35-43

文章报道了浙江海岛沿岸水域中异养细菌、氨化细菌和反硝化细菌的数量分布及异养细菌的种群组成。结果表明：本调查海区异养细菌的数量较多，其数量分布范围在２．０４×１０４～８．３６×１０６个／ｄｍ３之间；氨化细菌数量分布范围在３．０×１０３～１．１×１０６个／ｄｍ３之间；反硝化细菌的数量分布范围在３．０×１０２～１．１－１０６个／ｄｍ３之间。细菌的数量与环境中营养盐的浓度之间存在密切关系。在不同的海区异养细菌的种群组成存在一定的差异，在浙北海区，革兰氏阴性菌所占比例为４１．６％，在浙中海区为４６．９％，在浙南海区为６４．９％。  相似文献   

亚热带沿海景观的旅游保护性开发及建设探讨--以福建沿海为例     

翁毅  周永章  张伟强  储德平 《台湾海峡》2006,25(2):285-294

依据地貌学和风景学的角度,福建沿海景观以闽江口和九龙江口为界可分为3个景观亚区,并具有多样性与复杂性、动态性与脆弱性和关联性与分异性等特征.本文运用景观生态的原理研究沿海景观的构成与格局,在沿海景观的分类和特征概括的基础上,探讨福建沿海景观旅游开发与建设的模式.通过维护沿海景观系统的稳定,优化沿海各景观亚区的分布格局,提高沿海景观的整体舒适性和挖掘文化景观的内涵等应对措施以实现福建沿海旅游的科学发展.  相似文献   

深圳发展东部滨海旅游度假区的前景探析   总被引：3，自引：0，他引：3  

杨群  盛红 《海岸工程》2003,22(3):70-75

深圳具备优良的海滨旅游资源，但其滨海旅游特色一直体现得不够充分，滨海度假旅游品牌在全国以至海外的影响力还很有限。深圳最近对东部滨海地区的发展进行了总体规划，根据深圳东部滨海地区发展现状和发展规划，就开发深圳东部滨海旅游度假胜地、将东部滨海旅游度假区打造成为具有国际水准的、以滨海休闲度假为特色的黄金海岸旅游胜地提出了的几点建议。  相似文献