沙丘演化人工干预因子的量化分析及单体沙丘稳态迁移的微观运动特性研究

Aeolian sand dune evolution accounts for the dynamic process of sand accumulation disaster, and guarantees the incessant feature of near-surface desertification. As the basic form of dune evolution, the balanced migration of individual sand dune becomes no doubt the center of dune research field. Unfortunately, the huge temporal and spatial scales of dune evolution under natural circumstances had brought invincible barriers for both direct wind tunnel simulation and complete field observation of the balanced dune migration. Under the request of observation in full dimensions and multiple scales, this project develops a synchronized measuring system for both granular motion and the dune shape variation, and introduces several types of active artificial interventions that could modulate the dune migration process. A comparison is then held between aeolian and subaqueous dune evolution to reveal the characteristics of granular motion in maintaining the balanced migration and the semi-balanced dune shape. This job has a potential to construct the model of balanced migration of individual dune, thus providing references for the control of sand accumulation disaster..Based on the three-dimensional and double-scale measurement, this project adopts the subaqueous and aeolian experiments separately as the main and supporting platforms, and introduces several types of normalized artificial interventions into them with the same condition parameters. A horizontal comparison would be able to reveal the external conditions and the granular activity that correspond to the existence of balanced dune evolution. The result could help constructing effective dune model as well as developing the simulation theory of fluid driven sand transport.

自然界风成沙丘的演化迁移是积沙危害的动力过程和地表沙漠化的根源所在，其发展空间广大，过程时间漫长。单体沙丘稳态迁移作为沙丘演化的基准形式，是沙丘研究领域的核心问题。受限于沙丘演化巨大的时空尺度，野外观测很难贯彻始终并同时兼顾宏观演化和微观颗粒运动，风洞实验则无法实现沙丘稳态迁移过程的缩尺模拟。本项目立足于“主动”逼近稳态迁移的单体沙丘演化系统，探讨沙丘演化的合理人工干预方案；以沙丘演化过程的微/宏观全维度动态测量为前提，搭建颗粒运动和沙丘形变的同步光学测量系统，开发沙丘表面复杂颗粒运动和沙丘三维形体的图像重构算法；通过对人工干预因子的量化，进行“干预力度相同”的风沙/水沙环境单体沙丘稳态迁移的横向比对实验，解析沙丘演化过程中宏观结构变化和微观颗粒运动特性的作用关系，建立单体沙丘稳态迁移模型。研究有助于完善现有沙丘演化数值模型，并为有效防治积沙和沙埋等风沙灾害提供理论依据。

项目结合大气边界层风洞实验、非接触式光学测量技术、颗粒数字图像处理算法及连续化数值模拟模型，围绕新月沙丘演化系统中的气相湍流运动、沙粒离散运动以及沙丘形态演化三方面开展研究，进一步完善了多尺度框架下的沙丘演化动力模型，有助于揭示迁移型风沙自组织结构演化规律。主要成果如下：.一、沙丘宏观形态演化实验方面，证实了人工干预手段获得逼近饱和态新月沙丘演化的可行性，揭示了沙丘演化流向特征尺度更为积极的响应特性及收敛模式。通过将实验结果与基于质量守恒的解析模型结果比较，明确了沙丘非饱和态演化的衰减特性。二、沙丘表面风沙两相流测量方面，基于变频自动控制系统+抽吸同步式大气边界层风洞复现时变阵风来流，明确了垂向及水平气流分量间的负相关关系；从粒子系散射理论出发，推导得到阵风来流条件下风沙流瞬时输沙率与图像灰度的本构关系，为沙丘表面风沙流量化分析提供新途径。三、沙丘表面颗粒离散运动测量方面，提出一种完全独立于传统连续性假设的离散粒子追踪测速VD-PTV算法；基于新算法对床面沙粒运动进行重构，得到了床面颗粒蠕移运动介观参数的统计特性和蠕移运动亚类模式的识别方法，为近床风沙面颗粒动力学模型提供了实验佐证。四、沙丘演化及相干行为的数值模拟方面，建立了“气相大涡模拟-沙丘形态动力学”耦合数值模型，对单沙丘演化和多沙丘相干行为进行了模拟。与所得实验结果进行对比，证明了人工干预手段逼近饱和态新月沙丘演化的有效性，从数值角度丰富了针对多沙丘融合及衍生等模式的理解。