The Research On Modeling Method Of Wheat Plants And Implementation Of Threshing Simulation Software

With the continuous development of computer graphics and the substantialimprovement of computer performance, the computer simulation has been widelyused in the national defense, aviation, electronics and other fields. In order to realizethe simulation of the real world, people make it through by abstracting, modeling ofthe real world, and converting it into a computer executable program. Plants are verycommon in nature and closely related to human production and living, therefore, inrecent years, simulation of plants has become an important research direction ofcomputer simulation. Because the plant has the characteristics of variety andstructural complexity, establishing the model of the plant becomes a significant anddifficult issue in computer simulation. After many years of researching, people putforward some general plants modeling methods, such as L-system model, particlesystem model, and the geometric design model, etc. Through these methods, peoplehave built a variety of complex plants models, and have made great progress in thestudy of virtual plants. But the above methods are more focused on the simulation ofthe morphology of the plant, and less consider the physical characteristics of plants,such as the plant’s movement when getting external forces, the shape changes, theinternal force changing, the fragmentation and so on. Therefore, when building a plantmodel, if we take the physical characteristics of the plant into consideration at thesame time, and use a computer to simulate the movement, harvest, threshing of plantsthat are in mechanical part, then the simulation results will have great significance andpractical value in agricultural machinery design.Wheat is one of the most important crops in the world and is also the secondlargest food crops in China, it is our important source of food, and is widely planted inmany provinces and cities of our country. In the process of threshing, what are peoplemost concerned about is the loss rate of grain and the threshing rate of wheat, andresearches have shown that in the process of threshing, the grain’s loss rate is veryhuge. So it is very significant to study the threshing effect and the threshing loss. Ifwe can computationally simulate the whole process of wheat harvest and threshing, we can make it easy and efficient to optimize the design of wheat thresher accordingto the simulation results, thus it can overcome the drawbacks of traditionalmechanical design process which is time consuming and causes low efficiency by justrepeating the experiments, what’s more we can save the cost of mechanical design.Our research group has been engaged in researching discrete element methodand developing application software for many years, and has raised a modeling of theear of wheat which is based on discrete element method; our group has also developedthe software for simulation. This paper presents a complete modeling of wheat plants,and improves the wheat plant’s neighbor search method; also the multi-core parallelprogram for the calculation part is completed in order to increase the speed of thesimulation program.Through the observation of the wheat plants, and by searching the relatedinformation, modeling the wheat plants can be divided into three main parts which arethe ear of wheat, wheat stalks and leaves. Preliminary work on modeling of the ear ofwheat has already been discussed by research group, this paper mainly studies themodeling approach of wheat plants especially the stalks and wheat leaves. Wheatstalks are composed of multiple nodes, and each node’s length and thickness aredifferent. While modeling, the wheat node is composed of some spherical particleswhich are arranged from top to bottom, the particle diameter is also the diameter ofthe node. By connecting all nodes together, the whole wheat stalk is formed. Becausethe wheat leaf is soft and transformable, when establishing the model we use thespring-mass model, spring-mass model has been widely used for the fabricsimulation. During the establishment of the wheat leaf model, mass is represented bya sphere particle, between each sphere some virtual springs are connected. Wheat leafis in strip-type shape, there are countless veins through the leaf. The shape of thewheat leaf is determined by the vein skeleton, the wheat leaf consists of many parallelveins and be described by cubic Bezier curves.On the basis of the work mentioned above, this paper studies the method foranalyzing and calculating the process of wheat plants threshing, which includes thecontact detection method and motion calculation method. Two contact detectionmethods were used. One is to detect contact without using grid, and the other is todetect contact by using grid. There is a great performance improvement by using gridcontact detection method when the number of wheat plants is huge. Linearviscoelastic model is used to calculate the contact forces when there is contact between wheat plant and wheat plants or between wheat plant and machinery parts,according to the resultant force and moment that act on wheat plants, Newton’ssecond law and kinetics of euler equation are adopted to calculate its movement.Linear viscoelastic connection mechanics model is used to calculate the interiorconnective force of the wheat plants (including grain and cob, cob and cob, cob andnode, node and node, etc.), also a fracture criterion of wheat plant and the treatmentafter fracture are presented.Based on the above modeling method and the threshing process analysis andcalculation method, the wheat plant threshing simulation program is finished. Thesimulation program is developed in Windows platform using the object-orienteddevelopment method, which realizes the process of wheat plants threshing simulationcalculation, the front-end display and performance analysis. And in order to improvethe computing speed of the program, the original serial program is changed tomulti-core parallel program; also in order to make better use of computer hardwareperformance, the original32-bit program is changed to64-bit. At the same time wheatplants preview program is developed to realize the function of previewing the shapeof wheat plants before simulation calculation, and it is integrated into the wheat plantsthreshing program.Finally, this paper tests the wheat plants threshing simulation program, whichincludes comparing the generated wheat plants model with the real wheat plants,testing wheat plants movement, leaf deformation effect, threshing effect and fractureeffect, etc. Through the test, the feasibility of wheat plants modeling method whichput forward in this paper, the established threshing process analysis and calculationmethod, and the feasibility and effectiveness of the developed software ispreliminarily proved; also a foundation for the further study of the wheat plantthreshing has been laid.