Bionic Research For Dome Greenhouse Structure Based On Euryale (Euryale Ferox Salisb.) Leaf Vein

According to the reasonable and uniform force pattern of reticulated shell structure,based on bionics,the bird’s nest structure,triangular stability characteristics and the span size,dome greenhouse can be designed into a single-layer reticulated shell and double-layer space truss nest structure.The dome greenhouse has a large internal space,and the use of three-dimensional cultivation mode improves the land utilization rate,and it is suitable for any terrain.The completely transparent and translucent covering method can adapt to the lighting and insulation requirements of different regions,with higher strength and anti-snowstorm ability,which greatly promotes the development of sightseeing agriculture and planting industry.However,the existing domed greenhouse has dense lattice shell arrangement and complex geometric algorithm.The double-layer bird’s nest structure not only realizes large space and large span,but also increases the consumption of materials and construction difficulty,resulting in high cost and difficulty in large-scale promotion,and the related mechanical research literature is few.The leaf vein as a support structures,its distribution rule has a strong adaptability to the environment.Euryale ferox and Victoria Warren belong to nymphaeaceae,the leaf diameter can reach more than 1.5 m² m,the back mesh and grading veins make its excellent mechanical properties,internal air holes reduced leaf weight leaf and increased the buoyancy.Therefore,the reasonable leaf vein distribution provides a new way of high strength and lightweight design on the construction and mechanical components.Based on the Euryale leaf vein,several kinds of hemispherical dome greenhouse structures with the same 6m radius and height had been bionic designed in this paper.The finite element method was used to simulate the static,modal and nonlinear buckling analysis,and refer to the better structure,the scale model had been made and strain tests were carried out on it.And the accuracy of simulation parameters and loading method were verified,then by reducing the consumables as the goal,the structure was optimized and the optimal design scheme was obtained,which was used to design lager suitable dome greenhouse with radius of 12 m,18 mand 24 m.The main research contents and conclusions are as follows:（1）The entire leaf venation characteristics had been extracted through hand-held 3d scanner and the scanning point cloud data of Euryale vein was processed and repaired in Geomagic studio software,then the three-dimensional structure was restored.Regardless of leaves action,static simulation analysis on typical veins（the crosslaced primary-secondary vein and gradual branching vein from leaf base to leaf margin）and a single vein were carried out at the interface of ANSYS workbench.The results show the linear buckling critical load of primary-secondary vein is 1.193N,which is 10.31times of its weight,and it can reduces the deformation and stress of the whole veins in coordination when resisting the longitudinal and transverse loads,thus ensuring the leaf integrity.The primary vein plays a leading role in resisting transverse load,while it has little difference with the secondary vein in resisting longitudinal load.The linear buckling load of the gradual branching is 7.781 N at leaf base and is 0.874 N at leaf margin,which are 51.22 and5.75times of its own weight.The deformation and stress decrease gradually with the increase of the branching number,as which is 4,they reach the minimum value.Therefore,the highest branching number is 4,which is the most appropriate.The interior of the Euryale veins is spongy and contains many air chambers,so the solid and hollow two limit modes were taken from the single vein and then the pull and pressure simulation analysis were carried out on them,which obtained the tension and compression ratio of solid and hollow veins was 11.8 and 125.1.Thus,it can be concluded the Euryale vein is a kind of material with tensile resistance is better than pressure,and its mechanical properties and appearance is to adapt to its mechanical characteristics and form,so make it has strong ability to attack the bearing capacity and resistance to the outside destruction.（2）Based on the primary-secondary and gradual branching structure of Euryale leaf veins,the initial model of bionic dome greenhouse with radius of 6 m（the gradual branching structure is according to 2^x exponential form,the grid element structure is triangle or quadrilateral）was established,which has a total of 4 layers from top to bottom.The leaf areas between primary and secondary veins in the first branch were statistically analyzed and the results were normally distributed.The leaf area averages were calculated and compared with each floor area averages in the initial model,and in combination with the elastic modulus of the Euryale leaf,the mean elastic modulus of the covering material in the initial model was calculated,it can be showed excepting EVA film,the others all can be used as the initial model covering materials.The beam frame of the greenhouse is made of hollow steel tubes,by referring to the aspect ratio of vein section,wall thickness,leaf vein length and the longest and shortest beam length of the bionic greenhouse,the rectangular,circular and t-shaped steel tubes with the similar cross-sectional area were selected for the simulation analysis of length-thin ratio and nonlinear buckling,and the double-layer hollow PC board with 10mm thick was selected as the maximum density condition of the covering material,then all load combination values were calculated,the strength,stiffness and stability of different static simulation results were verified respectively.The results show the square steel tube with outer wall width of 75 mm and wall thickness of 2.5 mm meets the design requirements,and the maximum displacement and equivalent stress are mainly in the first and second layer,where stiffness is the main influencing factor,and the combination for dead load and wind load with the direction of perpendicular to ridge（load combination 2,horizontal direction）is most unfavorable for the initial model of bionic dome greenhouse.（3）The triangle was combined with the gradual branching structure of Euryale leaf veins,other three bionic dome greenhouses were designed with a radius of 6m:non-braching（not use branching structure）,one divided two-all triangle（the gradual branching structure is according to2^x exponential form,the grid element structures are all triangle）and one divided three（the gradual branching structure is according to 3^x exponential form,the grid element structures are all triangle）structure,which compared with the initial structure.The modal and static simulation and verification of the four greenhouses were carried out at the ANSYS Mechanical APDL interface.The results show the natural frequencies of the four greenhouses increase linearly with the increase of the order,and are similar to the initial frequencies.The frequency of one divided two-all triangle is the slowest,and the natural frequencies of one divided two-original（the initial model of the dome greenhouse）and one divided three are the highest.Four greenhouses were loaded with combination 1 load（combination of dead load and snow load,vertical direction）and combination 2（horizontal direction）respectively,the results show non-braching structure does not meet the stiffness requirements,and the other three greenhouses all meet the strength,stiffness and stability requirements.All variables in one divided two-all triangle and one divided three structure are the smallest,and the large deformation area are all the least.Combined with the results of modal and static simulation,the one divided two-all triangle and one divided three structure are better.Based on the similarity three theorem,the similarity constants are obtained by the dimensional analysis method,and the scale model was designed and made with one divided two-all triangle as the prototype（scale ratio is 25:1）.The concentrated force strain tests and simulation were carried out on the scale model.And the single sample t test and the relative error analysis method were used to compare the test and simulation value.It can be known the relative error was all less than 1%,and there was no significant difference between the two methods.（4）Based on the weight loading method,The uniform strain test of snow load simulation on the scale model was carried out,according to the the area proportion of bearing surface,the simulation load values of each beam in the scale model were calculated,and then conducted the static simulation analysis on it.Compared with the results of the uniform force strain test,the results show the test and simulation micro-strain are linearly positively correlated with the loading quality,and the correlation coefficients are all above 0.99.Moreover,when the length of the mesh size is 16 mm,the relative error between simulation and test is the smallest,and it is all less than10%.Therefore,the mesh size is 16 mm is suitable for the scale models with the radius of 240 mm,and this simulation load value calculation method is highly accurate,can well reflects the real load situation.（5）Taking the layer number A,number of vertical beams on the first floor B and branching mode C as factors,all design schemes of 6 m bionic dome greenhouse were analyzed by structural primary selection,linear buckling and mechanical verification respectively.Combined with the steel consumption,it can be obtained the optimal scheme is A₂B₂C₁（4 layers,the number of vertical beams on the first floor is 8 and mixed branching mode）,and compared with the dome greenhouse with four different branching modes before optimization,the steel consumption can be reduced by 76.2⁸1.7%.According to the optimal scheme A₂B₂C₁,12 m,18 mand 24 m dome greenhouses were designed in turn,according to the the area proportion of bearing surface,the simulation load values were calculated,and static simulation and verification were conducted on them respectively.The results all meet the design requirements,and the influence of combination2 on the structure gradually enhanced with the radius increasing,the stiffness is still the primary influencing factor.After calculation,compared with large multi span greenhouse,the steel consumption per unit volume of bionic dome greenhouse can be reduced by 38.3%⁷3.4%,therefore,the dome structure based on the mixed branching pattern is conducive to the lightweight design of greenhouse,its height advantage is more suitable for three-dimensional cultivation,and the large internal space is convenient for mechanized operation.