【作者】 高永毅；

【导师】 焦群英；

【作者基本信息】 中国农业大学 ， 车辆工程， 2003， 博士

【摘要】 植物生长在自然界中，必然会受到各种外界环境包括机械应力的刺激，因此生长和应力的关系一直是生物学家、物理学家和力学家所关心的课题，生物力学的开拓者之一冯元桢先生说过，“应力—生长关系是生物力学的活的灵魂”，对植物生物力学的研究也是如此。很早以前，人们就认识到机械力的作用对植物生长能产生明显的影响，诸多学者对机械应力刺激的研究结果表明，机械力的刺激在生物内部会产生一系列的复杂生理和化学响应；并且这些响应的强弱与外界机械刺激力的大小和类型有密切的关系。机械应力刺激对植物的生长发育和形态发生产生明显的影响，但其作用机理到现在为止并不清楚。要弄清“应力—生长关系”机理，首先要了解宏观的外力如何传递到细胞中去的和外力的刺激是如何在细胞间分布和传递，即要研究宏观的组织受力与细胞层次受力的关系。只有知道了宏观受力在细胞间的传递和分布特点，才能揭示机械应力刺激对植物的生长发育和形态发生影响的机理。同样要真正弄清水果蔬菜机械损伤的机理，也必须了解宏观的外力和水果蔬菜细胞力学性质的关系，以及外力在细胞间分布和传递，从而更深入认识细胞在外载作用下破裂的可能性。但目前关于外力在植物组织细胞内的传递和分布的研究几乎还是空白，而对水果损伤的研究主要集中在宏观损伤机理和实验的研究上，没有见到从细胞层次研究的报导。 本文主要研究宏观的外力如何传递到细胞中去的和外力的刺激是如何在细胞间分布和传递，即外力与细胞层次受力的关系，尝试从细胞受力的角度分析水果机械损伤的机理等问题。 本文根据植物细胞结构的力学特点和力学原理、利用有限元方法，以二维问题为研究对象，建立了能够描述植物细胞单体受力变形、细胞壁应力和内压变化和便于建立宏观植物组织力学模型的单细胞力学模型。在建立的单细胞力学模型的基础上，建立了细胞形状为多面体的植物组织的细胞力学模型。利用ANSYS有限元计算软件和MATLAB计算软件对植物单细胞和宏观组织力学模型进行了分析和计算。在细胞层次对压缩和剪切外力如何传递到细胞中去的和外力是如何在细胞间分布和传递，即宏观的组织受力与细胞层次受力的关系进行了分析。在对植物单细胞和植物组织宏观力学模型的分析计算中，推导出了细胞内压改变量的计算公式。获得了反映植物细胞变形时，面积保持不变的条件方程。给出了一个保证计算结果同时满足力的平衡与面积不变条件的新的计算方法。 在建立的植物组织的细胞力学模型的基础上，对细胞形状为多面体的植物(苹果等植物)的机械损伤进行了细胞层次的分析和模拟。利用实验直接和间接的证明了模型的正确性。 而且，还根据植物细胞膜上电荷分布的特点，利用电学和力学原理首次推出了植物细胞膜上电荷产生的细胞内压力的计算公式。分析了植物膜上的电荷所引起的细胞内压力的改变。 并且，根据葡萄、西红柿类水果的特点，提出了一个模拟模型。并利用该模型对葡萄受到压缩外力作用时，外力、变形、内压改变量和葡萄皮应力之间的关系进行了计算和分析，得到了体积改变量的变化值是一个常数，使得各力学量与葡萄总体变形量的关系是非线性关系的结论。更多还原

【Abstract】 It is well known that growth of plants is stimulated by environment, such as windows and stress. The stress induced growth is a concern problem all along by biologist, physicist and mechanical scientist. Professor Feng Yuanzhen who is an exploiter about biomechanics said the relationship between stress and growth is a live atman of biomechanics. The study of plant biomechanics is also alike. People has known that the mechanical stress influence botanic growth long before. The previous works shown that a series of complex physiological and chemical responses are brought in inside of organism by external forces. The complex physiological and chemical responses depend on the type and the strength of the applied forces. The mechanical stress excitement has considerable influence on the botanic growth and configuration. But the reason of the stress induced growth is not clear. To understand the stress induced growth, the study of the transference and distribution of the external force in the cells level inside of the tissue is a key problem. The knowledge about the transference and distribution of the applied force inside the fruit tissue in the cell level is very important for the study of the fruit damage. But few references could be found in this area. Although, a lot of works have been done on the fruit damage by means of experiment methods.The primary goal of the dissertation is to study how the applied forces transfer and distribute inside plant tissues in the cell level, and the relationship between the external force and turgor, as well as the stress of the cell wall. Furthermore, the fruits damage will be studied from a new point of view-梩he force applied on the cells.According the structural characteristic of the plant call, a hexagon mechanical model for plant cell was proposed. Then, using the mechanical theories and finite element method, the deformation, wall stress and turgor for plant cells, under compression and shear, was analyzed. The advantage of the proposed cell model is that it’s much convenient to integrate to form a tissue by cells. ANASYS software was used to compute the deformation, wall stress and turgor for single cell and tissue. While the cell deformation or distortion, the volume of the plant cell keeps un-changed. This is a very important constrain for the deformation or distortion of plant cells. A method that could make the results satisfy the equilibrium equations as well as the constrain equations was developed.The proposed method was used to analyze the damage of apple tissue. The simulated results were in good agreement with experimental data.Moreover, according to the electric charges distributing characteristic of the plant cell membrane, a formula about cellular pressure produced by the charges was deduced. The effect of the charges distributed on the cell membrane on the cell pressure was discussed.Finally, a mechanical model for grape or tomato kind of fruits was discussed. The mechanical parameters were evaluated by cure fitting of the experimental data. From this model, the deformation, stress of the grape skin and the change of the inner-pressure was obtained. It was found that the change of the volume for unit of force is a constant.更多还原