Studies On Greenhouse Structural Bionic Design Based On Dragonfly Wings

Agriculture in greenhouse is an important planting method. It controls environmentalfactors through artificial facilities, helps crops obtain suitable growing conditions, thusextends their growing season and achieves best output. The development of greenhouse cannot only reduce the use of arable land, but also reduce the use of water resource andchemical fertilizer. So it can be an environmentally-friendly planting method. The Quality ofgreenhouse structure has direct effect on the performance of greenhouse. So the quality ofgreenhouse structure is of great importance in improving the productivity and energyutilization, reducing the cost, guaranteeing the safety and stabilizing the production. Becauseof this, the structure design and technology utilization have become an top topic in domesticand foreign greenhouse research and development.Now, all scholars focus on the research of luminous environment, covering material andventilation system. There is little research on the safety and reliability of the greenhousestructure. On the one hand, most imported greenhouse in China has deficient draught, poorsnow load stress, and poor light transmission; on the other hand, our research on greenhousepays close attention to the environmental factors, rather than the structure safety, whichleaves much potential safety hazard. During recent years, many engineering accidentshappened due to strong wind and heavy snow, which took a heavy toll. It urgently needs thetheory and technology research of greenhouse structure.From the utilization of bionics in architecture, according to the thought of technologypropeller, combined with modern greenhouse technology, mechanization of farming, ITtechnology, bionics and maths, this essay will study the mechanics of dragonfly's wings,establish new space structure system of the greenhouse, thus offer theoretical foundation andreference for the bionics research and structure design of greenhouse. The main researchwork and results are as follows:(1) Mechanical research on the structural rigidity of the dragonfly's wings. We willbuild finite element modeling, analyze the deformation regularity of the model, the effect ofmain vein and secondary vein on the structural rigidity, and the deformation compatibilityperformance of the model of dragonfly's wings under different load pressure. Our result is:the main vein is the main load-bearing structure of the dragonfly wings, secondary veinshave little effect on the structural stiffness. Primary and secondary veins combining canimprove the overall strength of the structure and carrying capacity. Under the uniform loadand concentrated force, the dragonfly wing structure occurs only to the overall deformation,but the grid shape does not change.(2) Combined with characteristics of the spatial structure of dragonfly wings, we candivide into the four basic cantilever grid structure: quadrilateral mesh, staggeredquadrilateral mesh, hexagonal mesh and three, five, hexagonal combination of networkgrid as to the dragonfly wing structure. Respectively, we establish the spatial structure of thefinite element model to simulate dragonfly wings. Bearing the smallest lift, when combinedwith dragonfly wings' flying model, we separately applied to the same load F=10000bN×(1,2,3,4,5,6,7,8,9,10) for the stiffness analysis, and study the effect of their wrinkle structureand bagging structure on the structural stiffness:①The mechanical analysis of the dragonfly wings fold structure. According to the structuralcharacteristics of the main vein wrinkling, we take the quadrilateral and staggeredquadrilateral mesh to create different z fold (wrinkle height of0,1,3,5,7,9,10,12dmm)mechanical model separately applied to the same load F for large displacement staticanalysis. The observation z to the structural deformation maps and extract the maximum zdisplacement, structural analysis model in different folds. Coming to the same uniform load,the greater wrinkling of the height, the smaller the structural deformation; if corrugationheight is the same, with the increase of the load, deformation also increases, but the greaterthe wrinkle height, the smaller the amount of deformation load. At the same time, thestiffness of quadrilateral mesh structure is slightly larger than the cross-quadrilateral meshstructure; under the same load, the deformation of the membrane mesh structure is alwaysless than the membrane grid structure.②The mechanical analysis of dragonfly wings bagging structure. According to thestructural characteristics of dragonfly wings bi-directional camber, we take a hexagonal gridand three, five, hexagonal combination of grid to establish different mechanical model ofvarious arch heights (vector span ratio of0,1/8,1/71/6,1/5,1/4,1/3), separately appliedthe same load F to the models for the stiffness analysis. We obtain that, under the same loadconditions, the structural rigidity of the two mesh increase with bagging height; when loadand arch height is the same, the deformation of the membrane grid is less than themembrane-free mesh, the stiffness is significantly enhanced; Whether with membrane orwithout membrane, under the same load conditions, the hexagonal network deformation isalways greater than the combination of mesh, we can see from that, the larger the meshdensity, the greater the stiffness.(3) Research on the design of the greenhouse bionic structure. Based on the stiffnesscharacteristics of dragonfly wing structure and the basic principles of the mechanics of thewing structure, combined with the existing greenhouse structure and size characteristics, theestablishment of three new bionic spatial structure of the greenhouse, the overall shape of thegreenhouse structure is a bagging structure of a hexagonal grid, on the basis of bagging, weutilize quadrilateral grid wrinkling to form the main frame. By comparative analysis ofvarious working conditions under the three bionic structures, we can see model two in itsspatial structure is more reasonable compared with model1and model3, which shows goodmechanical properties, and therefore is chosen for the greenhouse skeletal structure, andfurther analyzed mechanically:①The design of material and size. We use different composite materials to simulatethe model, combining with the load combination of the greenhouse structure on model two,make static analysis of it and compare its own weight, deflection, stress and weight plus external loads. It shows that the structure of the skeleton and shell use of composite materials,the deflection was significantly reduced rod stress drop, the improvement of the elasticmodulus can increase the bending stiffness of the structure. Grouping to define the beam sizeand thickness of the shell model imposed1000N/m2uniformly distributed load for staticanalysis. It shows that, with the beam diameter and wall thickness increase, the deflectionand stress of the structure decreased, but the unit area of supplies also increased; the increaseof the thickness of the shell can improve the bending stiffness of the structure, but not much.Through the above analysis, considering the stiffness of the assurance and raw materialssavings, we determine the appropriate material and geometry of the greenhouse structure.②The effect of stress stiffening on structural rigidity. If1000N/m2of uniformlydistributed load applied to model two, compared with the three kinds of mechanicalproperties through static analysis, we know that, considering the stress stiffening effects ofthe small displacement, the maximum deflection of the structure reduces0.027m, only89.5%of the deflection value without considering the stress stiffening effect, the shelltension dramatically increased the bending stiffness of the structure. We make largedisplacement static analysis, taking into account higher order terms, the deflection value isslightly larger than without considering the small displacement static analysis of the stressstiffening effect. F=200N/m2×(1,2,3,4,5,6,7,8,9,10) uniform load imposed on thestructure, respectively, to make the deflection with the load curve analysis of the curveindicated with of with load increase, the stress stiffening effect is more pronounced, thegreater the decrease of the structural deflection. The stiffness in the structural design shouldnot be too great. In a certain degree of deformation, the beam and shell together will improvethe stiffness, thus achieve the better performance.③The effect of constraint conditions on the structural stiffness. If adding two pillarsof the vertical displacement constraints to model2, the maximum deflection and stressvalues change in different operating conditions, we can see the deflection of the structure toincrease constraint is only about10%of the maximum tensile of the original, andcompressive stress also decreased substantially in accordance with the approximateproportion of the greenhouse structure with the pillar of the vertical displacement constraints.It can significantly reduce the deflection of the entire structure, and plays an important rolein improving the stiffness. The design, based on the structure size is unchanged by addingstructural constraints to reduce the deformation, to meet the requirements of security, andmeanwhile, makes the most of the advantage of the stress stiffening effect and saves rawmaterials.(4) The design of multi-span greenhouse of biomimetic structure. along the lengthand cross-direction of model two, we build its mirror symmetry. By mechanical comparison,we can see in the same condition, regardless of the pillars of constraints added to thestructure, the maximum deflection of model1is less than model2, two partially symmetricstructure can contain each other's coordination, increasing the overall stiffness of thestructure. If we comprehensively utilize the symmetry of its structural advantages and dragonfly wings, and design two new large-span and multi-span greenhouse biomimeticstructure to meet the stiffness requirement, which should be based on land conditions, actualneeds, actual number of multi-span and the pillars of constraints.The innovation of this essay is: for domestic and international greenhouse structuraldesign theory and technology research, it puts forward the ideas of biomimetic design ofgreenhouse structure, and studies the overall stiffness of dragonfly wings and spatialstructure performance; designs several new types of bionic spatial structure of thegreenhouse and carries out further exploration and research on the mechanical properties;expands the biomimetic structure of the greenhouse, builds symmetrical large-span bionicstructure, and study the biomimetic design of multi-span greenhouse structure.The research on greenhouse structural design based on biomimetics offers new researchideas and reference for the development of industrialized agriculture.