Determination of wave energy dissipation factor and numerical simulation of wave height in the surf zone     

Y. H. Zheng  Y. M. Shen  X. G. Wu  Y. G. You 《Ocean Engineering》2004,31(8-9):1083-1092

Based on the time-dependent mild slope equation including the effect of wave energy dissipation, an expression for the energy dissipation factor is derived in conjunction with the wave energy balance equation. The wave height of regular and irregular waves is numerically simulated by use of the parabolic mild slope equation considering the energy dissipation due to wave breaking. Comparison of numerical results with experimental data shows that the expression for the energy dissipation factor is reasonable. The effects of the wave breaking coefficient on the breaking point and the distribution of wave height after breaking are discussed through the study of a specific experimental topography.  相似文献   

霄云煤矿1313工作面隐伏陷落柱突水机理分析          下载免费PDF全文

赵元强  李肖兰 《山东国土资源》2020,36(10)

水害已成为威胁煤矿安全生产的重要灾害之一,不仅会对井下工作人员的安全造成极大的威胁,还会给煤矿的经济造成重要的损失。煤矿的水文地质条件受地层、构造、岩浆岩等影响因素较大,使得水害的类型繁多,特别是对隐伏型导水构造的精细探查预测能力不足,使其成为了矿井水害的重要导水通道。霄云煤矿1313工作面发生突水灾害,虽然该区域位于三维地震范围内,但受地震技术手段的限制,3煤层之下岩煤层分辨率很低,三维地震精细报告及井下瞬变电磁成果均未解释此区域内有陷落柱发育。通过对矿井内的地质地层、构造、岩浆岩及水文地质概况等资料的研究以及对突水后的水质、邻近奥灰长观孔水文观测、水温的分析,认为突水水源为奥陶纪灰岩含水层,通过后期的注浆钻孔漏失深度及注浆情况,能够确定该处存在一个半径约为9.00m的陷落柱,发育高度约为116m。据此综合判断该次矿井突水的通道为隐伏在3煤层底板之下的陷落柱构造。  相似文献   

Precipitable water conversion rates over the Qinghai‐Xizang (Tibet) Plateau: changing characteristics with global warming     

Chenghai Wang  Yipeng Guo 《水文研究》2012,26(10):1509-1516

In this article, the trends and variability of precipitation and precipitable water (PW) over the Qinghai‐Xizang (Tibet) Plateau (QXP) (1970–2009) were analysed by using ERA‐40 (The European Center for Medium‐Range Weather Forecasts (ECMWF) 40 years Re‐analysis) and NCEP (The National Centers for Environmental Prediction)/NCAR reanalyses data and the ground observed precipitation data from 60 sites. The results showed that the precipitation over the QXP had an overall increasing trend; however, a slight decreasing trend was observed over the southeast. This decreasing precipitation trend might be related to the South Asia monsoon degradation. Since 1970, a decreasing PW trend has occurred over the QXP in which the southeast is the most significant region. Because of the rising temperatures in the QXP, a remarkable PW conversion rate (PWCR) increase of 0.87% per decade has occurred over the past 40 years. Because of its steep terrain, the PWCR in the middle eastern region of the QXP increased faster than that of the other regions. The mean PWCR in the wet southern region of the QXP was higher than that of the dry northern region, which was higher in the winter than that in the summer. Although much precipitation occurred in the summer, in the wet regions, the PWCR was higher in the winter than in the summer. The PWCR peak in the wet and dry regions occurred during the precipitation‐short and precipitation‐sufficient seasons, respectively. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Efficiency of rainwater harvesting of microcatchments and the role of their design     

《Journal of Arid Environments》2013

Microcatchment is a technique for collecting, storing and conserving local surface runoff in order to grow trees/shrubs. In this system, runoff water is generated on a plot and stored in the soil during runoff events, and trees/shrubs may utilize this water during the next dry season.Microcatchments have relatively small runoff generation areas (from dozens to hundreds sq. m) and are cheap and simple to implement Their collection area is usually a small depression located nearby the runoff generating area in which one or a few trees/shrubs may be planted Due to the short overland flow path runoff generation is efficient and even short low intensity storms may generate runoff. The drawback is however that due to the small size of the generating area small volumes of water are conveyed to the storage plots. Another drawback is susceptibility of the augmented water to evaporation. The main objective of present research presented hereafter was to estimate the effect the depth of the depression has on the efficiency of the water conservation in the soil profile. In the present study the storage plots were circular pits and the effect their depth had on evaporative losses and water distribution were studied.The results clearly show that the depth of the pit significantly affects evaporative water losses. The losses were separately computed for the soil cylinder whose upper surface is the bottom of the pit and for the surrounding shell. No differences between treatments were evident for losses from the inner cylinder. Significant differences in water losses were however observed for the surrounding shell where the shallow pits losing as much as six times more than the deeper pits.  相似文献   

Gypsum treatment as a restoration method for sediments of eutrophied lakes – experiments from southern Finland     

V.-P. Salonen  E. Varjo 《Environmental Geology》2000,39(3-4):353-359

The internal load of phosphorus can be treated with chemicals improving a sediment's phosphorus binding capacity. Gypsum (CaSO₄?2H₂O) is a novel material to be applied for this purpose. In the hypereutrophic Lake Enäjärvi, southern Finland, sediments were treated with gypsum in test basins. The basins were isolated from open water to create artificial anoxia, which allowed the effects of the treatment on the internal load to be measured. The results indicate that gypsum treatment decreases the sediment's release of nutrients under anoxic conditions. This was demonstrated as less increased total-P and total-N concentrations and decreased chlorophyll-a concentrations in the water column of treated basins as compared with the control basins. Because the gypsum treatment prevents internal load, it has potential in lake restoration in cases where the internal load of phosphorus is accelerated by anoxic conditions at the sediment/water interface.  相似文献   

富铁橄榄石的水溶性实验研究SCIEI北大核心CSCD     

杨家英  张琼  赵永红  李杨  KOHLSTEDTDavidL 《岩石学报》2022,38(4):1280-1284

地幔的力学性质主要受橄榄石流变性的控制,含水对橄榄石流变性质的影响很大,而橄榄石的水溶性受到温度和铁含量的影响,因此,本文进行了不同铁含量橄榄石在不同温度下的水溶性实验研究。实验使用的样品为天然橄榄石单晶Fa_(17)和Fa_(24.7)(Fe_(No.)=100×molar Fe/(Mg+Fe))以及人工合成的橄榄石单晶Fa_(22);橄榄石单晶的水溶性实验在300MPa围压和1273~1473K的温度条件下进行,每隔50K进行一组实验,氧逸度被控制在Ni NiO水平上。实验结束后,对橄榄石单晶沿b面进行双面研磨抛光,用电子探针分析确定橄榄石单晶成分,采用EBSD精确测量橄榄石的单晶方向,使用红外光谱仪(FTIR)的非偏振光路测试橄榄石单晶在b轴上的吸收光谱。对FTIR吸收光谱进行积分得到富铁橄榄石的水溶性实验结果:当温度由1273K升至1473K时,橄榄石单晶Fa_(17)的水溶性变化为600~1200H/10^(6) Si,橄榄石单晶Fa_(24.7)的水溶性变化为1000~1300H/10^(6) Si,人工合成的橄榄石单晶Fa_(22)的水溶性变化为500~900 H/10^(6) Si。因此,相同铁含量橄榄石单晶的水溶性随温度的增加而增加,相同温度条件下,天然形成的橄榄石的水溶性随着铁含量的增加而增加,百分之一的铁含量的增加,可以导致约百分之十的水溶性的增加。本文所研究的不同铁含量的橄榄石可以为更好地估算上地幔水溶性提供依据。  相似文献   

基于核磁共振的不同含水率黄土古土壤冻融循环试验研究     

叶万军  强艳红  景宏君  邹愈 《工程地质学报》2022,30(1):144-153

为明确不同含水率古土壤在冻融循环作用下其微观结构特性及古土壤损伤机制,采用核磁共振扫描仪对不同含水率冻融循环后的古土壤试样进行测试,研究冻融循环和含水率共同作用对古土壤微观结构的影响及土体内部损伤变化。结果表明:冻融循环下不同含水率使土体内部产生不同程度的损伤,损伤程度为含水率大的土体大于含水率小的土体。随着冻融循环次数增加,T₂谱曲线信号幅度增加,孔隙结构改变,大孔隙、最大孔隙含量增加,中孔隙含量减小; 同时含水率较大的土体孔隙体积增大幅度大于含水率较小的土体,说明在季节冻土区建设工程中含水率越大土体越易发生破坏,因此在工程中应注意防排水问题。依据损伤力学原理,得出土体颗粒连续性与孔隙率关系,进而得出有效应力与孔隙率关系; 根据核磁扫描结果,建立孔隙率与冻融循环次数关系,最终推导出古土壤有效应力与冻融循环次数关系表达式。研究成果为季节冻土区古土壤地层建设工程提供理论指导。  相似文献   

1980～2013年华东小雨减少及其主要影响因子分析   总被引：1，自引：0，他引：1  

张丽亚  周伟东  吴涧 《大气科学》2019,43(5):1005-1018

本文通过对1980～2013年华东区域447站各等级降水的时空分布特征进行分析,从低空气温、水汽、相对湿度入手,采用经验正交函数分析（Empirical Orthogonal Function,简称EOF）、合成分析等诊断方法揭示小雨与低空气温、水汽、相对湿度之间的关系;根据克劳修斯-克拉珀龙（Clausius-Clapeyron）方程,从物理角度对温度和水汽含量变化对小雨减少的相对贡献进行分析,并选取长三角区域利用能见度资料分析小雨减少的特征。研究主要得出以下结论:（1）华东区域1980～2013年总降水日和总降水量分布呈现南多北少随纬度增加递减趋势,总降水日主要以小雨日为主,小雨日占总降水日的71.84%。除暴雨外,其它各等级降水均呈现出减少趋势,以小雨的减少最为显著,小雨日和小雨量区域平均减少趋势为－3.37 d (10 a)-1、－6.52 mm (10 a)-1。小雨日EOF分解的第一模态呈现了华东区域小雨日一致减少的分布特征;第二模态则体现了小雨日变化的不均匀性,具有明显的区域差异。（2）小雨日的减少是伴随着低空增温发生的,低空温度上升了0.32 K (10 a)-1,同时可降水量呈现微弱的减少趋势。小雨日的变化与低空相对湿度有很好的正相关关系,EOF分解结果也揭示了低空相对湿度具有与小雨一致的空间分布特征。合成分析表明低空气温偏高（低）年,小雨日偏少（多）,可降水量偏多（少）年,小雨日偏多（少）,相对湿度偏高（低）年,小雨日偏多（少）。（3）根据Clausius-Clapeyron方程和相对湿度公式,低空增暖使饱和水汽压增加6% K-1～7% K-1,饱和水汽压增加在水汽微弱减少的前提下,导致了低空相对湿度的显著减少,从而导致了小雨的减少。对低空温度,比湿变化对小雨的影响进行分析,发现单纯由温度变化引起的相对湿度减少为－4.83%,而单纯由于比湿变化引起的相对湿度变化为－1.91%,分析表明了低空增暖是引起小雨日减少的主要原因。（4）能见度较差的区域,年均小雨日和小雨量偏少,但是小雨的长期减少趋势主要还是由低空增暖引起的相对湿度的减少导致的。  相似文献   

Quantifying urban water supply security under global change     

《Global Environmental Change》2019

Urban water supply security is commonly measured in terms of per capita water availability at the city level. However, the actual services that citizens receive are influenced by several components, including (1) a city's access to water, (2) infrastructure for its treatment, storage and distribution, (3) financial capital for building and maintaining infrastructure, and (4) management efficacy for regulating and operating the water system. These four types of "capital" are required for the provision of public water supply services. A fifth capital “community adaptation” is needed when public services are insufficient. Here, we develop and test an integrated framework for the quantification of urban water supply security based on these five capitals. “Security” involves three dimensions: 1) the level of system function (i.e., supply services); 2) risks to these services; and 3) robustness of system functioning. We apply this Capital Portfolio Approach (CPA) to seven urban case studies selected from a wide range of hydro-climatic and socio-economic regions on four continents. Detailed data on urban water infrastructure and services were collected in two cities, and key stakeholder interviews and household surveys were conducted in one city. Additional cities were assessed based on publicly available utility and globally available datasets. We find that in cities with high levels of public services, adaptive capacity remains inactive, while cities with high levels of water insecurity rely on community adaptation for self-provision of services. Inequality in the capacity to adapt leads to variable levels of urban water security and the vulnerability of the urban poor. Results demonstrate the applicability of the presented framework for the assessment of individual urban water systems, as well as for cross-city comparison of any type of cities. We discuss implications for policy and decision-making.  相似文献   

黄海冷水团的化学水文学特征   总被引：2，自引：1，他引：1  

辛明  马德毅  王保栋 《海洋学报(英文版)》2015,34(6):5-11

Based on the field data obtained during summer cruises in 2006, the overall perspective of chemical and hydrographic characteristics of the Yellow Sea Cold Water Mass(YSCWM) are discussed through the crossYSCWM transect profiles and horizontal distributions of hydrological and chemical variables, with emphasis on the differences between the northern Yellow Sea Cold Water Mass(NYSCWM) and the southern Yellow Sea Cold Water Mass(SYSCWM). The results show that YSCWM is characterized by low temperature(10°C) and dissolved oxygen(DO) concentration, high salinity(32.0) and nutrient concentrations. Compared to the SYSCWM, the NYSCWM possesses lower values of temperature, salinity and nutrient concentrations but higher values of DO.Also its smaller variation ranges of variables(except for temperature) demonstrate that NYSCWM is more uniform than that of SYSCWM. In addition, thermocline is more intensive in the SYSCWM than that of NYSCWM.Furthermore, DO and Chl a maxima appear at the depth of 30 m in the SYSCWM, while these phenomena are not obvious in the NYSCWM.  相似文献