Research On The Envelope Structure And The System Of Ventilation And Cooling For The Horticultural Plastic Greenhouse

The plastic greenhouse area on china is the largest in the world, covering 2.3 million hectares. The plastic greenhouse is the important facility to realize the good quality and high output for the crops. The main attribute of greenhouse has protection the cultivation from natural disaster, and the intensive to using resources in the production process. The suitable microclimate environment for the plant culture will be provided. The potential of high production will be created and so on. Simultaneously also for improve the crops quality, carries on standardized the cultivation management. The paper research content comes from in the Zhejiang Province science and technology key project "The research on practical and intelligent horticultural greenhouse" (NO.02111102542).The greenhouse envelope facility and the inner equipment realizes the environment adjustment function. The greenhouse structure and facilitis occupy the majority of costs. Therefore, the greenhouse envelope structure optimization, the internal regulation system are discussed in the paper. The main research content and the result include:(1) The calculation parameter and a constitutive model for greenhouse film were obtained by a uniaxial tensile test. And a calculation model of the load effect for the greenhouse film was developed by the nonlinear finite element method and the method with artificial stiffness applied. According to the relative criterion, the safety coefficient of bearing capacity for the greenhouse film was discussed. Based on the models and methods mentioned above, the example for the bearing capacity of the film was calculated on the working conditions of snow and wind load, and the first principal stress and deformation of the film were obtained. In addition, the influence of different pre-tension on the bearing capacity of the film, and the concrete distributing of first principal stress were discussed. This paper presented the calculation model and theoretical method for the proper application of the film in the greenhouse design.(2) The method of ultimate bearing capacity calculation for the arch structure of plastic greenhouse was presented in the research. The nonlinear finite element analysis theory was applied in the method development. Based on the consistent mode imperfection method, the initial imperfection model was determined by the least order mode of eigenvalue buckling, and the maximum displacement value. Double nonlinear factor was considered in the structure analysis. To calculate the ultimate bearing capacity, the equilibrium path of the loading and displacement using arc-length method was traced. The ultimate bearing capacity of the multi-span plastic greenhouse under snow loading in the eastern-china was calculated by the method. The calculated result was close to the real bearing capacity, which showed that the method was suitable. (3) In order to study the load-bearing characteristics of the plastic greenhouse structure in the different stage.The structure test of the tunnel greenhouse was carried on. The stress and stain value in each measuring points was obtained in the experiment. The analysis of the experimental data showed basically the bearing load processes of plastic greenhouse structure. The processes include line elasticity, the large displacement, the material elastoplasticity, the buckle destroy. According to these structure characteristic of the different stage, using the geometry non-linearity and the material non-linear factor in the computation, and the initial imperfection model. The predicted values and the experimental data which obtains on each stages of load bearing have the very good uniformity.(4) The application of CFD numerical tunnel method on the determination of distribution of wind pressure on the plastic greenhouse surface was discussed. The CFD turbulent model uses realizeκ-εmodel. All-scale model of three multi-span plastic greenhouse was applied to multiple work condition analysis in the numerical wind tunnel. And then, the wind pressure was converted to shape coefficient to make comparison with the result of the design code. Under sealed work condition, the distribution characteristic of the wind pressure on greenhouse surface, as well as the value of wind pressure in the windward side and front eave had referential value. Under the unsealed greenhouse work condition with different opening size of side windows, the change value of wind pressure caused by the wind-induced internal pressure was very close to the value suggested in the code. The results indicated that numerical tunnel simulation for greenhouse based on CFD method could provide referential data of distribution characteristic and wind pressure, and offer basis for determining wind pressure within the proposed range of the design code.(5) The technology integration and development of the practical and intelligent horticultural greenhouse, which is suitable for subtropical monsoonal climate zone, were discussed. The optimized method for greenhouse structure, the hybrid ventilation and combination cooling system using multi-state control, the distributed control system and management software based on fieldbus control-CAN bus, and the cultivate management and information system based on web technology were covered in the paper. Based on multi-state principle for the cooling and ventilation system, the ability of suitable for climate and the saving for operation cost were improved. The change of the measured temperature inside the greenhouse and the ventilation simulation on the work condition of wind pressure, showed the hybrid ventilation system can improve natural ventilation function effectively.