共查询到20条相似文献，搜索用时 140 毫秒
1.
高压水射流技术具有工作介质来源广泛与环保等优点,能够用于海底天然气水合物储层破碎。本文运用LS-DYNA有限元程序对淹没状态下高压水射流对海洋天然气水合物沉积物破碎过程进行数值模拟,研究了射流速度、喷嘴直径、靶距、入射角度四项关键参数对含水合物沉积物冲蚀体积的影响,得出以下主要结论：含水合物沉积物产生破碎需要满足射流速度大于临界流速;随着射流速度的增加冲蚀体积逐渐增大;喷嘴直径的增加会导致沉积物径向冲蚀体积的增大,从而使总体冲蚀体积增大;靶距的增加会使水射流在水域运动过程中能量损失增大,导致冲蚀体积的减小;在喷嘴入射角度增大过程中冲蚀体积将会先增大后减小最后趋于稳定,当入射角度为10°时冲蚀体积能够达到最大值。 相似文献
2.
3.
风沙电研究的现状及展望 总被引：6，自引：1，他引：6
扼要回顾了风沙电研究现状，主要内容包括研究动态：主要是从风沙电的野外实地观测和室内实验模拟测试，来揭示风沙电这一自然现象的规律；风沙电对电波传播影响研究：主要从折射效应、吸收、散射和带电沙粒的散射影响进行探讨。并提出了研究中存在的问题和发展趋势。 相似文献
4.
5.
近年的探测研究表明，由引力和范德华粘附力聚合成碎石堆结构可能是小行星的一种重要形成方式。为探究这类小行星的演化机制，文章基于离散元软件MatDEM进行二次开发，实现了单元的万有引力计算。建立直径为1.2 km“碎石堆”小行星数值模型，通过数值模拟分析了不同粘附强度和体积密度下，球形聚集体的旋转重塑和破坏过程。结果表明：球形聚集体受到其角速度初始增量的影响，以启动聚集体的重塑过程，导致其发生变形或者破坏；粘附强度越小，模型越容易被破坏，破坏前小行星会通过向扁圆状椭球体变形来保持自身构型的稳定性；对于粘附强度一定的小行星模型，体积密度的增大会有效增加其结构的稳定性，可以延后小行星破坏行为发生的时间，且颗粒脱落的数量随着密度的增大而减少；采用离散元分析可以较好地模拟小行星自旋演化过程。进一步与真实小行星数据相结合，有利于深入、全面地探索小行星自旋演化破坏机理。 相似文献
6.
为了研究和改善油气资源钻井工程中高压管汇系统受到流固体冲蚀的影响,本文根据近井口常规管汇布置情况,建立了0°、45°、90°三种角度弯管模型,并根据计算流体力学基本理论,结合实际工况,对压裂弯管内部流场进行数值模拟,最后设计了0°与45°压裂安装角度管汇布置结构,并根据此3种弯管安装角度及弯管材料选用,进行了室内冲蚀试验研究,得出了如下结论：（1）在不同的安装角度下,随着冲次增大,流体出口速度越大,在任何安装角度下,弯管部位会发生较大的速度波动,因此速度波动太大弯管部位会受到严重冲蚀;（2）高速流体冲蚀区域主要分布在近井口压裂头部位的管道入口位置,在两种错位情况下,管汇整体流体速度由出口到入口逐渐变小;（3）压裂头部位5个出口部位存在较大的冲蚀速度,速度和压力呈现阶梯状的变化,中间有压力和速度稳定时期,速度大的位置压力小。当安装角度为0°和45°时,流体的冲击速度会较小;（4）42CrMo防冲蚀能力较强,管道材料选用42CrMo有助于延长管道使用寿命。 相似文献
7.
YSC178A型液动锤射流元件底盖板外壁冲蚀机理 总被引：4，自引：0，他引：4
应用CFD动态分析技术,对具有内分流结构的YSC178A型液动锤的速度场进行了研究,分析了不同形状不同尺寸的分流孔对速度场的影响.研究发现:在一定直径的圆柱形分流孔出口处附近存在分流流束附壁现象,且附壁的分流流束特征与冲蚀坑的形状和大小之间有较好的对应关系,表明YSC178A型液动锤射流元件底盖板外壁出现冲蚀坑是由从一定直径的圆柱形分流孔喷出的分流流束附壁冲蚀造成的;分析结果还显示,喇叭形分流孔大大优于圆柱形分流孔,足够长且出口直径较大的喇叭形分流孔,其出口处附近流束附壁现象大幅度减轻以致消失,可以大幅度降低高速射流能量并减弱分流流束对底盖板外壁的冲蚀,避免出现显著冲蚀坑. 相似文献
8.
基于CFD的高能射流式液动冲击器活塞与缸体密封特性研究 总被引：1，自引：0，他引：1
通过计算流体动力学分析与实验室测试,对SC-86H型高能射流式液动冲击器活塞与缸体密封特性进行研究,分析了活塞密封段长度、环状间隙尺寸、活塞往复运动速度、角速度以及活塞外表面螺旋槽螺距与半径等参数对射流式冲击器前后腔之间泄漏量的影响。结果表明:活塞密封段长度、环状间隙尺寸、角速度以及活塞表面螺旋槽螺距均对射流式液动冲击器性能影响较小;活塞运动速度与泄漏量近似成正比例关系;随着活塞螺旋槽半径的增大,泄漏量会明显增大。活塞回程与冲程初期阶段,活塞运动速度较小,活塞处瞬时泄漏量占进入缸体前后腔流体流量的比例较大,使活塞无法快速加速运动,尤其是当活塞杆直径较大时,回程阶段泄漏量对活塞运动的影响更显著,导致冲击器工作性能大幅下降,甚至无法工作。 相似文献
9.
风沙活动对陆地生态系统影响研究进展 总被引：1，自引：0，他引：1
风沙活动及其物质输移运动是关键的陆地地表过程,对全球生态环境有显著的影响。归纳了风沙运动中养分的释放、搬运和沉降机制;总结了目前风沙运动中的物质及养分组成,养分流失与沉降对植物生长的影响、养分在植被群落中的分配和利用机理等方面的研究进展;揭示了大区域尺度上风沙运动与地表养分的释放和输移的关系及植被群落对风沙活动的响应;指出了风沙活动在陆地生态系统演化中扮演的角色。在已有研究的基础上,提出揭示风尘物质在远源陆地区域的沉降机制、风尘物质中有效养分的组成和含量、风尘物质养分的主要传输路径,建立风尘物质养分的源—汇模式,构建植被对风沙活动的响应过程,综合集成风沙活动与植被演化之间的动态关系等是未来主要研究方向的建议。 相似文献
10.
风沙物理学的发展与展望 总被引：9，自引：0，他引：9
介绍了风沙物理学研究在土壤风蚀、沙粒跃移和风沙流结构等方面取得的一些进展。展望了风沙物理学在地表风蚀、沙物质的风力搬运和沉积、风成地貌理论和相似理论、风沙工程理论与应用等研究领域的发展前景。针对我国的实际情况,提出了加强风沙物理学研究的建议。 相似文献
11.
Jin Liu Bin Shi Yi Lu Hongtao Jiang He Huang Gonghui Wang Toshitaka Kamai 《Environmental Earth Sciences》2012,65(3):589-595
Sand erosion due to wind is a serious problem in the relatively arid and semiarid areas. A new organic polymer sand-fixing
agent (PVIN), polymerized by the monomer of vinyl acetate, initiator and cross-linking agent, is introduced in this study.
To understand the effect of PVIN on sand fixation, the strength test, water-retaining test and wind erosion test were performed.
The results indicated that the presence of PVIN could improve the structural strength, water retaining and anti-wind erosion
ability. When the sand-fixing agent was applied on the sand surface, the crust in surface layer was produced. The structural
strength variations determined by micropenetrometer indicated that the specimens treated with concentrations of 1, 3, 5, 10,
and 20% PVIN have produced the crusts with thickness being approximately 1, 2, 4–5, 5, and 5–6 mm and the strength being around
1, 4.5, 18, 26 and 41, respectively. This crust has a good water-absorption, water-retaining and anti-evaporation properties.
It can also improve the anti-wind erosion ability, and also prevent the loose sand surface from forming a sand dune in the
wind erosion conditions. Additionally, this sand-fixing agent has a low cost, it is easier to produce and apply and also produces
no additional pollution. Therefore, this can be considered as an ideal soil-fixing agents to control sand erosion in the relatively
arid and semiarid areas. 相似文献
12.
On the effect of moisture bonding forces in air-dry soils on threshold friction velocity of wind erosion 总被引：5，自引：0，他引：5
SUJITH RAVI TED M. ZOBECK† THOMAS M. OVER‡ GREGORY S. OKIN PAOLO D'ODORICO 《Sedimentology》2006,53(3):597-609
Wind erosion is a dominant geomorphological process in arid and semi-arid regions with major impacts on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. The understanding and modelling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions. In arid regions during the dry season, the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity. By a series of wind tunnel tests and theoretical analyses, this dependence of threshold velocity on near surface air humidity is shown for three soils of different textures: sand, sandy loam, and clay loam. The results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40% and 65%, while above and below this range the threshold shear velocity increases with air humidity. A theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the humidity of the overlying atmosphere. The conditions under which soil-atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions. 相似文献
13.
Xunming Wang Caixia Zhang Hongtao Wang Guangqiang Qian Wanyin Luo Junfeng Lu Li Wang 《Environmental Earth Sciences》2011,64(4):1039-1050
A series of experiments to determine the direct emission of dust-sized particles from Gobi surfaces by clean wind (wind without
sand), and the potential for aeolian abrasion of Gobi surfaces and beds of gravel and mobile sand to produce fine (<100 μm)
and dust-sized (<10 μm, PM10) particles under sand-laden winds were conducted. Parent material was obtained from Gobi areas of the Ala Shan Plateau, the
region with high dust emissions in arid China. The fine particles produced by aeolian processes were collected using sand
traps and sieved the captured materials to exclude particles >100 μm in diameter and then PM10 by sedimentation was acquired. The Gobi surface provided most of the emitted fine particles during the initial dust emission
processes, but subsequently, release of the clay coatings of particles by abrasion becomes the dominant source of fine materials.
Under sand-laden winds, PM10 production rates produced by aeolian abrasion of Gobi surfaces ranged between 0.002 and 0.244% of blown materials. After
removal of sand, silt, or clay with low resistance to erosion from the Gobi surfaces by the wind, the PM10 production rates caused by aeolian abrasion were similar to those from gravel and sand beds. The results also indicated that
after the dust-sized particles with low resistance to erosion were removed, the production of dust-sized particles was unrelated
to wind velocity. Under aeolian processes, Gobi deserts in this region therefore play a major role in dust emissions from
arid and semiarid China. 相似文献
14.
Blown sand has caused considerable damage to the Dunhuang Mogao Grottoes of China. Controlling the blown sand requires a clear understanding of the processes that govern its production and movement. Experiments were conducted in a wind tunnel and in the field to define the relationships between sand production and gravel coverage in the gobi above the Mogao Grottoes. The gravel that covers the gobi’s surface controls wind erosion, irrespective of its shape and size. The equilibrium coverage by gravel over which no further sand is emitted due to wind erosion increases and the equilibration time that is taken to form the equilibrium gravel coverage decreases with increasing wind velocity. Gravel coverage has reached an equilibrium state in the portion of the gobi directly above the grottoes, but decreases towards the Mingsha Mountains. Drifting sand from these mountains is the main source of sand damage at the Mogao Grottoes. If no additional sand from the mountains were supplied to the gobi, gravel pavements would reach an equilibrium level of coverage and prevent further production of blowing sand. Sand blown from the gobi represents secondary reactivation of sediments originally produced in the Mingsha Mountains. Therefore, to control the blowing sand above the Mogao Grottoes, emphasis should be placed on controlling erosion from the Mingsha Mountains rather than local erosion of sand in the gobi. 相似文献
15.
黄河中游岩土侵蚀问题及防治对策探讨 总被引：1，自引：0，他引：1
黄河中游出露地层岩性主要有古生界奥陶系碳酸盐岩、石炭系和二叠系碎屑岩;中生界三叠系砂泥岩、侏罗系砂泥岩和白垩系砂泥岩;新生界古近系砂泥岩、新近系(原为第三系)红土及第四系风积黄土和现代风积沙。第四系黄土厚度大,结构松散,遇水易解体,具湿陷性,是黄河中游粗泥砂的主要物源;第四系风积沙分布于黄河中游北部,亦是黄河中游粗泥砂的主要物源。岩土侵蚀类型有五:一是风力侵蚀—风沙侵蚀;二是降雨对谷坡面的面状冲刷—坡面侵蚀;三是地表径流对谷底的侧蚀—沟谷侵蚀;四是滑塌对谷坡坡体的破坏—重力侵蚀;五是潜蚀。并对不同侵蚀类型提出了不同的防治对策。 相似文献
16.
选择青海共和盆地多石在沟河道中6道新月形沙丘链作为研究对象,采用Trimble4700DGPS与常规测量手段,结合野外风沙观测与自动气象站数据,初步观测分析了2006年多石在沟河道沙丘在不同季节的形态变化过程,计算出2006年风季前比雨季后多石在沟河道沙丘体积减小了548.3m3,风积量为2351m3,流水的蚀平量为2899m3,2006年风水两相营力对河道沙丘的侵蚀贡献率约为45%∶55%,流水的搬运作用强于风力的堆积作用。但从较长的时间尺度来看,研究区的风力侵蚀作用强于流水侵蚀作用,河道沙丘不断增大。多石在沟河道沙丘是一个典型的风水交互作用系统,河道成为风力与流水交互作用的"中转站",在风水的交替作用下,沉积物由风积环境进入流水环境中。 相似文献
17.
Over the past 100 years, the Isles Dernieres, a low lying barrier island chain along the coast of central Louisiana, Usa , has undergone more than 1 km of northward beach face retreat with the loss of 70% of its surface area. The erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition. At a site in the central Isles Dernieres, 8 days of wind and beach profile measurements during the passage of one winter cold front documented aeolian erosion and deposition patterns under both onshore and offshore winds. For offshore winds, the theoretical erosion rate, based on wind shear velocity, closely matched the measured erosion rate; for onshore winds, the theoretical rate matched the measured rate only after being corrected by a factor that accounted for beach face morphology. In late February 1989, a strong cold front moved into coastal Louisiana. That cold front stalled over the Gulf of Mexico, resulting in 4 days of strong northerly winds at a study site on the Isles Dernieres. During those 4 days, the wind moved sand from the backshore to the upper beach face. When the cold front finally moved out of the area, the wind shifted to the south and decreased in strength. The onshore wind then restored some of the upper beach face sand to the backshore while increased wave activity moved the rest into the nearshore. The theoretical estimate of 1·28 m3 m?1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1·26 m3 m?1, which was determined by comparing beach profiles from the start and end of the period of northerly winds. The theoretical estimate of 0·04 m3 m?1 for the rate of sand transport by the southerly wind, however, is notably less than the measured rate of 0·45 m3 m?1. The large discrepancy between the two rates can be explained by a difference in the shear velocity of the wind between the beach face, where the erosion occurred, and the backshore, where the wind stress was measured. Using an empirical relationship for the wind shear drag coefficient as a function of coastal environment, the theoretical estimate for the rate of sand transport by the southerly wind becomes 0·44 m3 m?1 相似文献
18.
19.
Air density effects on aeolian sand movement: Implications for sediment transport and sand control in regions with extreme altitudes or temperatures 总被引：3，自引：0，他引：3 
下载免费PDF全文
下载免费PDF全文 Aeolian sand transport results from interactions between the ground surface and airflow. Previous research has focused on the effects on sand entrainment and mass transport of surface features and wind velocity, but the influence of air density, which strongly constrains airflow characteristics and the resulting sand flow, has not been widely considered. In the present study, entrainment, saltation characteristics and transport rates were examined at nine experimental sites ranging in elevation from ?154 m below sea‐level (Aiding Lake) to 5076 m above sea‐level (Tanggula Mountain pass on the Qinghai–Tibetan plateau). At each site, a portable wind tunnel and high‐speed camera system were set up, and the friction wind velocity, threshold friction velocity and sand flow structure were observed systematically. For a given volumetric airflow, lower air density increases the wind velocity. Low air density also creates a high threshold friction velocity. The Bagnold wind erosion threshold model remains valid, but the value of empirical parameter A decreased with decreasing air density and ranged from 0·10 to 0·07, the smallest values reported in the literature. For a given wind velocity, increased altitude reduced total sand transport and creeping, but the saltation rate and saltation height increased. The present results provide insights into the fundamental mechanisms of the initiation and transport of sand by wind in regions with an extreme temperature or altitude (for example, alpine deserts and low‐lying lake basins) or on other planets, including Mars. These results also provide theoretical support for improved sand‐control engineering measures. The data and empirical equations provided in this paper improve the ability to estimate threshold and transport conditions for wind‐blown sand. 相似文献
20.
The region of Ain Sefra is an arid region suffering from sand encroachment. In this study, we are calculating the shifted sand quantity and efficient wind directions during a period of 30 years (1985 to 2015) in order to classify the danger. The study shows that efficient winds in the region are characterized by their potential drift estimated at 220 till 329. This classifies the region as medium. Besides, the resultant drift potential is 76 to 99 with a migration coefficient of 0.3 which gives a medium classification to the zone and proves the Aeolian erosion complex system and its interrelation with other factors. Efficient winds generally blow from South-west to North-east with an angle of 234°. Furthermore, there are other directions causing sand drifting. Sand movement quantity is estimated between 23.03 and 15,224 m3/m/year according to effective wind threshold speed, which is 5 to 6 m/s. Autumn is the period when sand mobility is higher, but it decreases in winter. On the other hand, sand potential movement was well shown through satellite imagery between 1985 and 2015. Indeed, it closely corresponded to the previous study. It showed sand movement direction from South-west to North-east, and sand surface increase reached 16.44% of the global zone surface. Whereas, it decreased ??2.5% between 1985 and 2015. There is an important concentration of sand accumulation under the western mountain foothills along which sand moves. This shows that the ground particularities play a crucial role in this phenomenon. 相似文献