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基于风洞试验的树木风致响应特征数值模拟研究
Numerical simulation study on wind-induced response characteristics of trees based on wind tunnel test
【目的】研究不同来流风下树木的风致响应特性,分析树叶数量和湍流度剖面对树枝和树干加速度概率分布特征和树干加速度极值的影响,为防护林的维护和管理提供参考。【方法】基于满足主要相似要求的树木缩尺气弹模型,设计8种不同树叶数量的树冠形态,参照工程科学数据集ESDU 85020中的全尺寸理论风场,在风洞中构建能够覆盖平坦、开阔和城郊地貌的4类风场,通过测量风速、树枝和树干加速度,开展树木风致加速度概率分布特征及极值研究。【结果】以基于对应80%累积概率的偏度和峰度值作为关键点,确定树干加速度高斯分布的判别准则。树干加速度概率分布多数符合高斯分布特征,树枝加速度概率分布不符合高斯分布特征。树枝加速度对应80%累积概率的偏度和峰度值随湍流度的增加而显著增加。通过对比广义极值理论Gumbel法、广义Pareto法、峰值因子法3种计算方法,广义Pareto法对树干顺风向加速度极值的拟合效果最好。二次多项式可以较好地拟合树干顺风向极限加速度与平均风速的关系,树干顺风向极限加速度随平均风速的增加而增加,随湍流度的增加而增加。【结论】基于树木气弹模型风洞试验研究,得到了能够反映全尺寸下树枝和树干加速度的概率分布特征和极值特征。
【Objective】This study aims to investigate the wind-induced response characteristics of trees across different terrains. It specifically examines to analyze how leaf quantity and turbulence profiles affect the acceleration probability distribution and extremes of the branches and trunks. By analyzing these factors, the study aims to provide valuable references for maintaining and managing protective forests. Understanding how environmental variables impact the aerodynamic behavior of trees can aid in designing better protective measures against wind damage.【Method】An aeroelastic model tree, designed to meet primary similarity requirements, served as the research foundation. Eight distinct crown shapes, varying in leaf quantity, were meticulously crafted to replicate realistic tree structures. These models were tested in wind tunnel terrains, constructed based on the Engineering Sciences Data Unit (ESDU) 85020 framework. Four terrain were replicated in the wind tunnel to measure wind-induced responses. Wind speed, along with branch and trunk accelerations, were recorded to explore the probability distribution and extremes of these accelerations. This comprehensive setup ensured a thorough investigation of how different wind conditions and tree structures affect wind-induced responses.【Result】Skewness and kurtosis values at the 80% cumulative probability were used to establish criteria for determining the Gaussian distribution of trunk acceleration. The number of leaves had a limited effect on the skewness and kurtosis values for trunk acceleration in the along wind and cross wind directions but had a strong effect on branch acceleration. The trunk accelerations in both wind directions generally followed a Gaussian distribution, while branch accelerations did not. Skewness and kurtosis values for branch acceleration significantly increased with turbulence intensity. Trunk acceleration samples in the along-wind direction approximately exhibited a bell shape, with a high peak and heavy tails. The Generalized Pareto distribution fited the central part of the sample data best, followed by the Gaussian distribution, while the Gumbel distribution fited the worst. Similarly, the Generalized Pareto distribution best fitted the tail data, followed by the Gaussian and Gumbel distributions. This indicated that the Generalized Pareto distribution was more effective for fitting the probability distribution of sample data than the Gaussian and Gumbel distributions. Among the three calculation methods, Generalized Extreme Value (Gumbel) method, Generalized Pareto method, and Peak Factor method, the Generalized Pareto method best fited extreme values of trunk accelerations in the along-wind direction. A quadratic polynomial effectively modeled the relationship between extreme trunk accelerations in the along wind direction and average wind speed. Trunk acceleration increaseed with both average wind speed and turbulence levels.【Conclusion】Based on wind tunnel tests with an aeroelastic model tree, this study provides insights into the probability distribution characteristics and extreme characteristics of branch and trunk accelerations at full scale.
树木气弹模型 / 风洞试验 / 风致响应 / 概率分布 / 极值
tree aeroelastic model / wind tunnel test / wind-induced response / probability distribution / extreme value
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王仁德, 邹学勇, 赵婧妍. 半湿润地区农田土壤粉尘释放的风洞模拟研究[J]. 地理科学, 2012, 32(11):1364-1369.
采用风洞模拟手段对地处半湿润区的北京市农田土壤风蚀中的粉尘释放规律进行研究。结果表明,研究区农田粉尘释放强度随风速增大呈指数规律增大,粉尘在风蚀物的含量随风速增大呈指数规律降低。近地表粉尘质量流量随高度增加呈幂函数规律降低,在风蚀物中的含量随高度增加呈线性增大。粉尘粒径随风速增大而变粗,之后达到稳定状态。近地表粉尘粒度组成沿垂直方向的变化可以划分为两段,0~20 cm高度层的双峰态分布和20~60 cm高度层的三峰态分布。随着高度增加,释尘粒度组成变细。
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土壤风蚀是包括风、植被、土壤特性、土地利用方式、降水、微地形等多要素交互作用, 发生在特定地理空间, 具有独特的气流—土壤界面相互作用机制的连续动力学过程。基于统计学理论的土壤风蚀经验模型, 不仅难以避免子模型之间有多个风蚀影响要素的交叉出现, 使子模型之间不能严格地相互独立, 导致建模理论基础存在不足, 而且不能客观反映土壤风蚀的动力学过程。在厘清土壤风蚀基本概念, 分析国际土壤风蚀影响因子和土壤风蚀模型研究历史与存在不足的基础上, 提出一个新的基于风蚀动力学理论的土壤风蚀模型理论框架, 以及在此模型框架下土壤风蚀影响因子的分类与表达。阐述了该模型框架和影响因子分类与表达的合理性, 并对土壤风蚀影响因子分类与表达的研究途径进行了探讨。
Soil erosion is an interaction of multi factors including wind, vegetation, soil characteristics, land use, precipitation, micro-geomorphology and so on. It is a continuous dynamic process occurring on airflow-soil interface in the specific geographical locations. Soil erosion empirical model, based on statistic theory, is difficult to avoid overlap of some factors affecting soil wind erosion between sub-models and not enable sub-models to be strictly independent from each other, thereby leading to lack of theoretical basis for modeling. Such empirical model is also not able to objectively reflect dynamic process of soil erosion. On the basis of clarifying basic concepts of soil erosion and analyzing the global research background and inadequacy, we proposed a new theoretical framework for soil erosion models based on wind erosion dynamics theory and the classification as well as representation of factors affecting soil wind erosion under the framework. We also elaborated the rationality of both the framework and the classification as well as the representation of factors affecting soil wind erosion, and further explored the research approaches on the latter. |
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【目的】对山东沿海7地市防护林树种分布适宜性进行分析,可综合反映不同立地因子对各防护林树种的影响,为更加科学地进行防护林树种规划提供理论依据。【方法】利用LandUSEM模型,以山东省森林资源管理“一张图”调查数据为基础,以1∶100万数字化土壤图和DEM数据为辅助数据,对山东沿海7地市防护林树种分布适宜性进行分析。【结果】受地貌因子影响较大的树种有26种,土壤类型对各优势树种的影响相对敏感,不同林种条件下各优势树种的适宜性差异较大。7种因素对49种优势树种影响的平均相对权重分别为地貌(0.19)>土壤类型(0.15)=坡度(0.15)=土层厚度(0.15)>林种(0.14)>坡位(0.13)>坡向(0.09)。目前在以黑松、赤松和刺槐为优势树种的防护林中,黑松、赤松分布的相对适宜度较高,90.48%的刺槐林分布不适宜或临界适宜。建议在刺槐林分布适宜性较差的低山丘陵区种植黑松、油松、麻栎、山楂、杜仲、蒙古栎、栎类、樱桃、酸枣等树种与其混交,提升刺槐林的生态效益。【结论】山东沿海7地市防护林树种分布适宜性整体较好,利用LandUSEM模型进行树种分布适宜性分析结果可靠。
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空气动力学粗糙度（Z<sub>0</sub>）和摩阻速度（u<sup>*</sup> ）是反映下垫面与大气相互作用的空气动力学参数，植被对Z<sub>0</sub>和u<sup>*</sup> 的调节起着重要作用。通过在野外种植沙打旺植被，设置4种植被盖度和3种植被布局，利用移动风洞进行原位测试。结果表明：（1）随着风速增大，Z<sub>0</sub>和u<sup>*</sup> 存在负相关，即随着u<sup>*</sup> 增大Z<sub>0</sub>呈线性减小趋势；相同输入风速下，随着植被盖度的增加，Z<sub>0</sub>和u<sup>*</sup> 存在正相关，两者增加趋势符合对数函数形式。（2）Z<sub>0</sub>与植被盖度符合对数函数变化规律，随着植被盖度增大Z<sub>0</sub>出现阈值现象。（3）不同植被布局的Z<sub>0</sub>为两行一带>交叉布局>一行一带。（4）从空气动力学角度提出沙打旺植被盖度为30%，布局为两行一带布局时，防风蚀效能较强。
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土壤风蚀是中国北方严重的环境问题，植被能够有效控制土壤风蚀。为给土壤风蚀防治方案设计提供依据，在毛乌素沙地南缘以中科1号羊草（Leymus chinensis）为对象，通过野外风洞试验，研究植被盖度（10%、20%、30%和40%）和配置方式（一行一带式、两行一带式、交叉分布式）对风沙流结构和输沙率的影响。结果表明：（1）各层输沙强度随风速增加而递增，随盖度增加而递减；输沙率与盖度符合指数函数关系。风沙流结构出现“象鼻效应”，风速和盖度的增加均使输沙强度峰值的高度层上移。（2）3种配置方式下输沙强度沿垂直高度的变化均呈指数函数分布，两行一带和交叉分布的阻沙效果大于一行一带。（3）从固沙效能最佳和经济效益角度考虑，中科1号羊草应种植盖度约为30%，风速较大的区域使用交叉分布的配置方式。
Soil wind erosion is a serious environmental problem in northern China， and vegetation can effectively control soil wind erosion. In order to provide a basis for the design of soil wind erosion control program， this experiment was carried out in the southern margin of Mu Us Sandy Land with Leymus chinensis “Zhongke No.1” as the object. The effects of vegetation coverage （10%， 20%， 30% and 40%） and configuration mode （one-row-and-one-belt， two-row-and-one-belt， and cross-distributed） on the structure of wind-drift sand and the amount of wind erosion were studied. The results showed that： （1） The sediment transport intensity of each layer increases with the increase of wind speed and decreases with increasing coverage. The rate of sand transport conforms to an exponential function with coverage. The “elephant's trunk effect” appears in the structure of wind-blown sand flow. The increase of wind speed and coverage makes the height level of the peak intensity of sand transport move upward. （2） The variation of sediment transport intensity along vertical height is an exponential function distribution， and the sediment inhibition effect of two-row-and-one-line and cross-distribution is greater than that of one-row-and-one-belt. （3） From the perspective of optimal sand fixation efficiency and economic benefits， Leymus chinensis “Zhongke No.1” should be planted with a coverage of about 30%， and areas with higher wind speeds use a cross-distribution configuration. |
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The response of four Scots pine trees to wind excitation was measured and analyzed. We investigated whether wind-induced tree sway in the fundamental mode is affected and enhanced by resonance effects between cyclic wind loading and oscillatory tree response. By combining results from wavelet analysis and analysis of phase amplitude coupling, we demonstrate that the response in the fundamental mode is an indirect reaction of the trees to displacement from their rest position mainly caused by large organized turbulent structures in the canopy airflow, such as sweeps and ejections. In particular, sweeps caused large tree displacement. It is suggested that sway in the fundamental mode mainly results indirectly from the trees' elastic energy that is stored in the stem and roots because of wind-induced compression and tension, and the damping that returns them to their rest position. Since no direct excitation of sway in the fundamental mode was found, it is concluded that there is no resonant response of the studied Scots pine trees to wind excitation.
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张泽宇, 惠记庄, 张浩博, 等. 发动机与液力变矩器的主次工况功率匹配方法研究[J]. 机械工程学报, 2023, 59(16):300-314.
为避免装载机传动系统因功率过剩导致能源浪费，或因功率不足影响作业性能，提出发动机与液力变矩器的主次工况功率匹配方法。以装载机V型工况为基础，以油门信号、档位信号和制动信号为6段式循环工况的划分依据，将其细分为11个工况片段，再进一步归类为铲掘、举升、起步和匀速4个牵引阶段，结合装载机不同循环阶段的主次工况，进行发动机和液力变矩器的功率匹配研究。利用主次工况法对不同牵引阶段下装载机液压系统的功率与发动机的油门开度进行分析，并结合发动机与液力变矩器的共同工作特性得出，在铲掘与举升阶段，发动机几乎工作在额定功率点，应尽量避免超载；而在起步与匀速阶段，发动机的输出扭矩点相对较低，具有承受部分负载波动的能力，且应尽可能地工作在经济燃油区间。进一步，构建装载机机电液系统联合模型，对发动机变功率控制下的主次工况进行对比与验证。基于箱线图的工程机械主次工况分析法和装载机的牵引工况构建方法为发动机与液力变矩器的分工况功率匹配奠定基础，也为车辆传动系统的效能优化提供参考。
In order to avoid energy waste due to excess power of the loader transmission system, or insufficient power to affect the performance, a power matching method for the primary and secondary working conditions of the engine and the hydraulic torque converter is proposed. Based on the V-type working condition of the loader, the throttle signal, gear signal and brake signal are used as the basis for dividing the 6-segment cycle working condition, and it is subdivided into 11 working condition segments, which are further divided. It is classified into four traction stages: shoveling, lifting, starting, and constant speed. Combining the primary and secondary working conditions of the loader at different cycle stages, the power matching study of the engine and the torque converter is carried out. Using the method of primary and secondary conditions to analyze the power of the hydraulic system and the throttle opening of the engine in different traction stages, and combined with the common working characteristics of the engine and hydraulic torque converter, it is concluded that the engine almost works at the rated power point in the digging and lifting stage. Overloading shall be avoided as far as possible; during the starting and constant speed phases, the output torque point of the engine is relatively low,has the ability to withstand partial load fluctuations, and works as far as possible in the economic fuel range. Furthermore, the model of loader is constructed to compare and verify the primary and secondary working conditions with the variable power control of engine. The analysis method of primary and secondary working conditions of construction machinery based on box diagrams and the classification method of traction working conditions of loaders lay the foundation for the power matching of engine and hydraulic torque converter under different working conditions, and also for the vehicle transmission system. Performance optimization provides a reference.
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Existing studies about wind pressure on agricultural greenhouse buildings concentrate on the mean wind pressure while ignoring the systematic research on fluctuating wind pressure characteristics and the influence of roof shape on the wind pressure characteristics, which are closely associated with the wind-induced damage mechanism. In this study, two typical agricultural greenhouse buildings on tropical islands are selected as prototypes to conduct pressure measurement experiments in the wind tunnel. Based on the wind pressure time series for the two greenhouses, the mean and fluctuating wind pressure distribution pattern and the localized high-pressure generation mechanism are analyzed. Then, the shape coefficient of the two greenhouses is compared in depth to the standards from four countries. Besides, wind pressure non-Gaussian determination criteria for agricultural greenhouse buildings considering the roof shape and wind directions are proposed. Lastly, the differences in wind pressure spectra on the roofs and walls of the two greenhouses are summarized. The results indicate the roof shape has a significant influence on the wind pressure characteristics. Compared with the pitched roof, the vaulted roof will increase the suction effect on the windward front zone and the middle area, mitigate the suction impact on the leeward roof, and weaken the wind pressure non-Gaussian characteristics. The experimental shape coefficient of the pitched-roof greenhouse is basically consistent with the standard from the U.S., while that of the vaulted-roof greenhouse has some deviation from the existing standards. The results provide a theoretical basis for the wind-resistant design of agricultural greenhouse buildings on tropical islands.
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