【作者】 黄青青；

【导师】 刘晋浩；

【作者基本信息】 北京林业大学 ， 森林工程， 2014， 博士

【摘要】 我国沙害严重,在治理沙漠化的技术装备手段中,草沙障是应用最广的一种机械固沙工程方法。但当前对草沙障的作用机理研究不足,阻碍了治沙装备的研发和推广本文的以栽植草沙障的工程实践应用研究为目标,从广泛使用的防风固沙草方格沙障入手,利用激光扫描仪和图象等多传感器融合技术对沙面和沙障进行结构测绘,采集沙障地貌形态特征数据。在沙障3D点云模型基础上,进行沙障气动外形研究。利用风沙动力学、流体力学等的研究手段,对草沙障的基本结构和格网结构在流场中的作用机理进行了研究。基于流体力学数值计算方法及湍流理论,提出了沙障内流场存在稳定的沙障后方形成诱导涡流的现象的数值模拟方法,验证并分析了沙障后方稳定的诱导涡流结构对防风固沙效果有着重要影响；研究确立了涡流结构的稳定位置、尺寸与沙障尺寸参数的关系模型,利用CFD数值模拟,获得了系列不同尺寸规格的沙障后方诱导涡流的形态、作用机理和尺寸等特征规律。利用风沙作用模拟方法研究并构建了驻涡成型的沙面曲面函数,该外形曲线函数充分考虑了沙堆休止角作为背风边缘的设计参考因素,使阻滞沙流容量能力的最大化。同时能够根据不同的间隔尺寸进行调节,可确定出了草沙障的两个相关控制参数：基于侵蚀量的沙障间隔控制系数和基于侵蚀强度的凹坑深度控制系数。利用计算流体力学方法深入探讨了非平面条件下沙丘在气流场中附面层内压力梯度和速度矢量场变化的规律,利用k-ε湍流模型对凹坑形态条件下的结构化旋涡进行了模拟。结合具有一定孔隙度的沙障与沙垄模型,可选定于地形风力相适应的多边形沙障形态,通过沙坑平衡侵蚀积分条件给出了沙障填充的尺寸控制参数选择范围。针对草方格沙障减弱沙丘移动的本质性问题,以非光滑表面减阻的理论为切入点,根据沙凹坑曲线模型,设计了六边形的沙障和凹坑形貌,达到用料少、涡流大的目标.利用CFD软件行改进的方法和参数。并在沙障结构形态的要求基础上,探讨了作业装置的作业方式和轨迹控制的基本要求。本文针对治沙的技术装备要求,提出了涡流与沙障关系模型,创建了控制沙面和沙障的若干参数和工艺力法。这种关系模型和作用方法的创新性是利用流体的粘性特性,将惯性剪切方向的动能转换为涡流的环量动能,最终依靠这种稳定的凹坑型面和多边形结构减弱了主导风向的惯性剪切作用,减少了沙粒朝着主导风向迁移的速度,从而达到防风固沙的效果。本文的研究结论能够在荒漠化治理,特别是固定沙丘的固沙工程实践研究发挥理论指导作用。更多还原

【Abstract】 Desertification damage to the environment is serious all over northern and western China. Intechnical equipment means of desertification control, the checkerboard grass sand barrier is one of themost successful and widely used methods of sand fixation engineering. However, the current researchesof grass sand barrier mechanism still has defect in elaboration of its function. While successfullydeveloped a grass barrier automation laying equipment, the lack of the basic role of sand barrierproduced hamper effect on the application and popularization. In this paper, practical engineering research and application of the planting of grass sand barrierwas the research goal. The study was started from straw checkerboard barriers that widely used withsand-fixing function; then the sand barrier surface morphology aerodynamic shape research wasconducted by collecting sand barrier, sand beds, sand dunes and desert topography characteristics data;on the other hand, the mechanism of the flow field and blocking sand forming method affected by thebasic and grid structure of grass sand barrier was studied, by sand dynamics, fluid dynamics andcomputational geometry, such as research tools. For grass sand barrier mechanism and application of research methods, based on turbulence theory,this paper put forward that the phenomenon of sand flow field locally stable was caused of inducedvortex formation behind the sand barrier, and a numerical simulation algorithm was proposed to verifyand analyze the effect of wind prevention and sand fixation by the stable induced eddy current structurebehind sand barrier. This study established a relationship model between the stable positions, size andstructure of the vortex and sand barrier dimensional parameters, and through numerical simulation CFD,certain sizes form of induced eddy behind sand barrier, mechanism of action and the size and othercharacteristics rule were obtained. Research on the use of two-phase flow simulation was introduced and the role of vortex sandsurface intraction was interpated for its function as a windbreak, the shape of the curve function uses theangle of repose of the sand the edges as a design reference factors played a sand block to maximize flowcapacity capabilities. At the same time intervals can be based on different size adjustment, given thegrass sand barrier two design parameters:Size erosion intensity factor and volume erosion intensityfactor. Through rumerical simulation compared to traditional sand barrier structure and morphology,structure design has a positive role in the sand hexagonai shapc and the shape of sand pits in the surfaceof the vortex, quadrilateral sand-binding straw checkerboard barriers model results with the current useof construction, compared with more good production characteristics and coverage eddy size, process characteristics. Research based on the overall morphology of the terrain and sandy grass sand barrier,combined with sand barrier effect of the structured form of space, established its role model, gives theoptimized shape of the sand pit in the vortex of the grass and sand barrier model can design practices toimprove operations and equipment play a role. The conditions under non-planar flow field of sand dunes in the pressure drag and friction dragreduction measures fluid mechanics methods. Using the k-ε model for structured turbulent vortices formdimples under simulated conditions, the principle described inhibit separation of the boundary layer,the parameter calculation based on the experimental model of the structure size of the vortex. Througha combination of sand dune barrier model, selected and terrain contours adapt to changes in wind sandbarrier polygon shape, given the size of the sand barrier filling bunkers equilibrium parameters erosionintegral condition. For dune grass checkerboard barriers weaken the role of the nature, the main theory discovery is anon-smooth surface drag reduction, according to a newly designed sand barrier between the pit curvemodel, re-verify the condition of the structure of the vortex generator. Combined with the results ofnumerical simulation and geometric methods to achieve with less material, eddy big goals, and design asand barrier morphology hexagonal pits and using CFD software to simulate and study the results of theplanning results improved methods and parameters. By analyzing the role of the boundary layer nearthe surface of the flow field pits on the surface of the results of different structures. With a simpleone-size straw checkerboard barriers formed contours and topography pressure to adapt to multi-sizecheckerboard barriers polygonal pits, boundary layer flow field characteristics of a more stable, betterable to weaken the role of the sand dunes global. This study was inspired by when straw checkerboard barriers in the wind and sand successfulapplication process, first through field visits, found the grass in the sand box form a stable state, theinternal morphology showing pits. Through the above principles, this paper equipment of large-scalesand technical equipment requirements, proposed the relational model eddy and sand barrier, as well asa number of parameters to control the sand and the sand barrier and process methods. This inhibitingeffect by a simple method is not the force of inertia of the surface of the sand flow, but through the useof viscous properties of the fluid, the inertia of the kinetic energy is converted into shear directionvortex circulation kinetic energy created in favor of the existence of a stable vortex is generated andspatial dimensions conditions, and ultimately rely on this type of surface and stable pits polygonalstructure weakened the dominant wind shear inertia, reducing the migration of sand towards thedominant wind speed, so as to achieve the effect of wind and sand to stabilize the sand bed, furtherguidance can play a role in theoretical and applied research in the application process fixed dunes anddesertified land in.更多还原