【作者】 李昊；

【导师】 闫增峰；

【作者基本信息】 西安建筑科技大学 ， 建筑学， 2023， 博士

【摘要】 我国西北地区大风、沙暴天气频发,当地石窟类遗址受到强风的侵蚀作用,风蚀是半开敞式石窟石刻文物的典型病害。西北地区石窟通常位于山崖、台地、河谷等复杂山地,窟区风环境受复杂山地地形的影响。但是目前的研究中对复杂山地窟区风环境的形成机理不明确,无法准确描述窟区风环境与石刻文物保护的关系。针对上述问题,本文选择须弥山石窟作为复杂山地条件下半开敞式石窟的典型代表,开展复杂山地窟区风环境研究。首先对须弥山石窟窟区风环境进行现场测试,揭示了窟区风环境特征,优化了测试风剖面指数的方法;其次,建立了高效便捷的复杂山地地形建模方法;提出了适用于复杂山地风环境数值模拟的插值多尺度方法,并通过现场实测验证了方法准确性;分析了石刻文物风蚀病害的主要影响因素;研究多种地形参数对山地风环境特征影响规律,提出适用于山地地形的加速比修正计算公式;最后尝试通过合理设置窟区绿化景观等被动式技术调节窟区风环境,并提出重点针对代表性洞窟的防风林带设计方案。主要内容和结论如下:首先,为明确须弥山窟区及当地气候环境特征,对窟区及当地全年气象数据进行整理与分析,明确了复杂山地条件下气流的湍流脉动强度大、风速变化幅度大、风向稳定的特点;此外,针对须弥山窟区风环境展开实地调研,发现须弥山窟区风环境受到遮挡效应、越山风效应和峡谷风效应的影响,与平坦地形风环境有显著不同;针对传统风环境实测方法在空间分辨率和时间上存在的局限性,通过多旋翼气象无人机对垂直风剖面进行观测,确定了地表类型和为数值模拟提供了准确的入口边界条件。第二,为解决复杂山地风环境模拟中高精度几何模型难以获取的问题,建立了高效便捷的复杂山地建模方法。该方法首先利用无人机倾斜摄影、空中三角测量计算、多视影像密集匹配生成点云等关键技术,通过Terra Solid软件平台进行影像匹配点云的滤波和点云分类,得到研究区域数字高程模型(DEM)。然后结合地图绘制工具和逆向工程软件,实现了DEM文件与CFD(FLUENT)几何模型之间的方便快捷转化。第三,基于边界层和计算流体动力学基本理论,提出了适用于复杂山地风环境数值模拟的插值多尺度方法;从保护石刻文物免受风蚀病害入手,开展窟区风环境与石刻文物保护之间的关系研究。结果表明:插值多尺度数值模拟方法可以提供更加符合复杂地形真实流场特性的入口边界条件,相较于传统的经验拟合剖面法提高了数值模拟的精度;当入流风向为东向时,地形的漏斗效应会导致窟前风速增加,不利于石刻文物的保护;石刻文物风蚀机理为在大风的冲击作用下,岩体受到携砂风的撞击和旋磨作用,须弥山窟区石刻文物风蚀病害的主要影响因素为平均风速、表面压力和表面摩擦力。第四,为研究多种地形参数对山地地形风环境特征影响规律,构建了孤立山体和峡谷山体两种山体地形,建立山体长度、山体坡度和山体间距三种地形参数为变量的三维山体模型,提出适用于山地地形的加速比修正计算公式。结果表明:对于孤立和峡谷山体模型,山体长度为零是加速现象最为明显的地形条件。迎风面位置山顶处的风速最大,山腰处风速仅次于山顶位置风速。与只考虑二维和三维轴对称山体模型相比,同时考虑山体长度、山体坡度和山体间距地形参数而得到的加速比修正计算公式具有较高的计算精度。第五,尝试通过合理设置窟区绿化景观等被动式技术调节窟区风环境,针对复杂山地条件下防风林带周围流场展开数值模拟分析研究。结果表明:数值模拟引入多孔介质代表植物冠层参数化树木的空气动力学效应具有较好的效果。渗透气流与冠层上方的扰动压力和位移气流的相互作用使得在植物冠层背风面风环境得到明显改善。由于防风林带渗透气流和扰动压力之间的补偿效应使得在5号窟周围位置湍流强度并未显著增大,5号窟周围风环境具有低平均风速和低湍流强度特性。本研究通过探索石刻文物的预防性保护技术,可以缓解当前复杂山地条件下石窟内石刻文物的风蚀病害,对于石窟类遗址的保护技术具有十分重要的科学意义和工程价值。随着我国西北地区石窟类遗址的进一步开发保护,本研究成果具有广阔的应用前景。更多还原

【Abstract】 Strong winds and sandstorms occur frequently in northwest China,and the local Grottoes are eroded by strong winds.Wind erosion is a typical disease of stone carvings in caves.Grottoes in northwest China are usually located in complex mountain areas such as cliffs,platforms and valleys,and the wind environment in caves is affected by complex mountain terrain.However,the formation mechanism of the complex mountain wind environment is not clear in the current research,and the relationship between the cave wind environment and the protection of stone carvings cannot be accurately described.In view of the above problems,this paper takes Xumishan Grottoes as the representative of complex mountain grottoes to study the wind environment in complex mountain caves.Firstly,the field test of the wind environment in the cave area of Xumishan Grottoes was carried out to reveal the characteristics of the wind environment in the cave area,and the method of measuring the wind profile index was optimized.Secondly,a new and efficient modeling method for complex mountain terrain is established.A numerical simulation method of interpolating multi-scale wind environment is proposed for complex mountains,and its accuracy is verified by field measurement.The main influencing factors of wind erosion of stone carvings are analyzed.The influence law of various topographic parameters on the characteristics of mountain wind environment is studied,and the formula of acceleration ratio correction suitable for mountain terrain is proposed.Finally,the author tries to adjust the wind environment in the Grottoes through passive techniques such as reasonable setting of green landscape in the Grottoes,analyzing the changes of the wind environment in the Grottoes,and optimizes and adjusts the wind environment in the Grottoes.The main contents and conclusions are as follows:Firstly,in order to clarify the characteristics of the Xumishan Grottoes and the local climate environment,the local meteorological data of the cave area were compiled and analyzed throughout the year,and the characteristics of the turbulent in complex mountain conditions,the large variation of wind speed and the stability of wind direction were clarified;in addition,field research was conducted for the wind environment in the Xumishan Grottoes,and it was found that the wind environment in the Xumishan Grottoes is affected by the shading effect,the cross-mountain wind effect and the canyon wind effect,which is significantly different from the flat terrain.The wind environment in the Xumishan Grottoes is significantly different from flat terrain;to address the limitations of traditional meteorological sounding in terms of spatial resolution and time,the vertical wind profile was observed by a multi-rotor meteorological drone to determine the surface type and provide accurate entrance boundary conditions for numerical simulations.Second,a new and efficient complex mountain terrain modeling method is established to solve the problem of difficult to obtain high-precision geometric models in complex mountain wind environment simulation.The method firstly utilizes key technologies such as UAV tilt photography,aerial triangulation calculation,and multi-view image dense matching to generate point clouds,and then performs image matching point cloud filtering and point cloud classification through Terra Solid software platform to obtain high-precision DEM data of the study area.Then combined with mapping tools and reverse engineering software,the convenient and fast transformation between DEM files and CFD(FLUENT)solid models was realized.Third,based on the basic theory of atmospheric boundary layer and computational fluid dynamics,a numerical simulation method for wind environment in complex mountainous terrain is proposed;the relationship between wind environment and protection of stone carvings in the cave area is studied from the perspective of protecting stone carvings from wind erosion diseases.The results show that the interpolated multiscale numerical simulation method can provide inlet boundary conditions that are more consistent with the real flow field characteristics of complex terrain and improve the accuracy of numerical simulation compared with the traditional empirical fitting profile method;when the inlet wind direction is 90°,the funnel effect of the terrain will lead to an increase in the wind speed in front of the cave,which is not conducive to the protection of stone carvings;the main influencing factors of wind erosion damage of stone carvings in Xumishan Grottoes are the average wind speed,the surface pressure coefficient and the surface friction coefficient.The main influencing factors of wind erosion of rock carvings are the average wind speed,the surface pressure coefficient of the mountain and the surface friction stress.The mechanism of wind erosion of stone carvings is the impact of sand-carrying wind and spin abrasion on the rock body under the impact of high wind.By exploring the preventive protection technology of stone carving cultural relics,this study can effectively solve the problem of wind erosion of semi-open stone carving cultural relics in the current complex mountain conditions,which has very important scientific significance and engineering value for the protection technology of grottoes.With the further development and protection of grottoes in northwest China,the results of this study will have broad application prospects.Fourth,in order to study the influence law of various topographic parameters on the wind environment characteristics of mountain terrain,two typical mountain terrains,isolated mountain and canyon type mountain,were constructed,and a three-dimensional mountain model with three topographic parameters of mountain length,mountain slope and mountain spacing as variables was established,and the acceleration ratio correction calculation formula applicable to complex mountain terrain was proposed.The results show that for the isolated and canyon mountain models,zero mountain length is the most obvious terrain condition for acceleration phenomenon.Compared with the two-dimensional mountain and three-dimensional axisymmetric mountain models only,the acceleration ratio correction formula obtained by considering terrain parameters such as mountain length,mountain slope and mountain spacing at the same time has a higher calculation accuracy.Fifthly,the author tries to adjust the wind environment in the Grottoes through passive techniques such as reasonable setting of green landscape in the Grottoes,and carries out numerical simulation analysis and research on the flow field around the windbreak forest belt under complex mountain conditions.The results show that the numerical simulation of the aerodynamic effects of the parameterized trees represented by the canopy with porous media has a good effect.The interaction of permeable air flow with disturbance pressure and displacement air flow above the canopy significantly improved the wind environment on the lee side of the canopy.Due to the compensation effect between the permeable airflow and the disturbance pressure in the windbreak forest belt,there is no eddy current in the lee side of the forest belt,and the wind environment around Cave 5 has the characteristics of low average wind speed and low turbulence intensity.By exploring the preventive conservation technology of stone carving relics,this study can effectively solve the wind erosion disease problem of semi-open cave stone carving relics under the current complex mountain conditions,which has very important scientific significance and engineering value for the conservation technology of cave-like sites.With the further development and protection of cave-like sites in northwest China,the research results have broad application prospects.更多还原