【摘要】：玉米籽粒形狀復雜,尺寸也不盡相同,如何建立其離散元法分析模型成為當今研究的一個熱點。特別是,如何建立一個合理的、近似于實際玉米籽粒的籽粒群體模型仍然需要深入研究。本文以兩個品種玉米籽粒為研究對象,測試了其物理力學性質(zhì),提出了基于多球充填的單個籽粒和玉米籽粒群體的建模方法。通過玉米籽粒的堆積、跌落、篩分等過程的仿真分析和試驗結(jié)果的對比,驗證本文所提出的玉米籽粒建模方法的可行性和有效性。本文的主要工作和結(jié)論如下。(1)以先玉335和白單678玉米籽粒為例,對其物理性質(zhì)和力學性質(zhì)(包括籽粒的幾何形狀、特征尺寸、密度、含水率、靜摩擦系數(shù)和碰撞恢復系數(shù)等)進行測試與分析,并分析了含水率對玉米籽粒尺寸、密度的影響。研究表明,玉米籽粒的形狀可以分為寬楔形、窄楔形、橢球錐和不規(guī)則形狀4種類型。其中,寬楔形和窄楔形玉米籽粒占90%以上。因此,在對同一品種玉米籽粒群體建模時,可選擇楔形玉米籽粒建立其幾何模型;定義楔形籽粒的上底尺寸為主尺寸,其他尺寸根據(jù)與主尺寸間的關(guān)系式計算得到。(2)通過三維掃描儀對玉米籽粒進行掃描,獲得玉米籽粒的三維點云數(shù)據(jù),通過手動充填組成球的方法建立籽粒的模型。此外,本文提出一種基于多球充填的單個籽粒建模方法,通過定義并控制球心距的不同,對兩個品種的寬楔形、窄楔形和楔形玉米籽粒分別建立了4種不同充填球數(shù)目的籽粒模型。(3)通過高速攝像技術(shù)記錄玉米籽粒的下落堆積過程,并通過離散元法分析軟件EDEM對4種籽粒模型的下落堆積過程進行仿真,通過仿真結(jié)果與試驗結(jié)果的對比,驗證本文提出的玉米籽粒建模方法的可行性和有效性。此外,通過對比容積密度的仿真與試驗結(jié)果,并考察4種籽粒模型仿真計算的CPU時間,分析出較為合理的充填球數(shù)目的籽粒模型。研究表明,當充填球數(shù)目達到14-16時,所建立的玉米籽粒模型效果較好。此外,還通過對籽粒模型的跌落過程、篩分過程的研究和參數(shù)靈敏度的分析,進一步驗證本文提出的籽粒建模方法的可行性。
[Abstract]:The shape and size of maize kernels are complex and different. How to establish the discrete element analysis model of maize seeds has become a hot topic in today's research. In particular, how to establish a reasonable, similar to the actual corn grain population model still needs to be studied in depth. In this paper, the physical and mechanical properties of two maize varieties were tested, and the modeling method of single grain and maize kernel population based on multi-ball filling was proposed. The feasibility and effectiveness of the corn kernel modeling method proposed in this paper are verified by the simulation analysis of the process of accumulation, dropping and screening of corn seeds and the comparison of the test results. The main work and conclusions of this paper are as follows. (1) taking Xianyu 335 and Baidan 678 maize seeds as an example, the physical and mechanical properties (including the geometric shape, characteristic size, density, moisture content of the seeds) were studied. The static friction coefficient and collision recovery coefficient were tested and analyzed, and the effects of moisture content on grain size and density of maize were analyzed. The results showed that corn grains could be divided into four types: wide wedge, narrow wedge, ellipsoid cone and irregular shape. Among them, wide wedge and narrow wedge corn grains accounted for more than 90%. Therefore, when modeling the grain population of the same variety of maize, we can select the wedge corn kernel to establish its geometric model. The upper and bottom dimensions of wedge-shaped grains are defined, and other dimensions are calculated according to the relationship between the main dimensions. (2) three-dimensional point cloud data of corn seeds are obtained by scanning corn seeds with a three-dimensional scanner. The model of grain was established by filling the forming ball manually. In addition, a single grain modeling method based on multi-ball filling is proposed in this paper. By defining and controlling the difference of spherical center distance, the wide wedge of two varieties is defined and controlled. Four seed models with different filling number were established for narrow wedge and wedge corn seeds respectively. (3) the falling accumulation process of corn seeds was recorded by high-speed camera technology. The falling accumulation process of four grain models was simulated by discrete element analysis software EDEM. By comparing the simulation results with the experimental results, the feasibility and effectiveness of the corn kernel modeling method proposed in this paper were verified. In addition, by comparing the simulation and test results of volume density, and investigating the CPU time calculated by four kinds of grain models, a more reasonable grain model with the number of filling balls was analyzed. The results showed that the corn kernel model was effective when the number of filling balls reached 14-16:00. In addition, through the drop process of grain model, screening process and parameter sensitivity analysis, the feasibility of the grain modeling method proposed in this paper is further verified.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：S513

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