Modeling Dissolved Oxygen In Aquaculture Water Of Crab

The production and consumption process of dissolved oxygen in aquaculture waters is of great value for the layout of aquatic plants and artificial aeration,so it is very important to study the mechanism model of dissolved oxygen.Photosynthesis is very important for the production of dissolved oxygen in aquaculture waters,but there are few literature on the mechanism model of dissolved oxygen in aquaculture waters based on photosynthesis.This paper considered various environmental factors of crab culture waters and photosynthetic activities,and studied the mechanism modeling of dissolved oxygen and the oxygenation control scheme to solve these problems.The specific work is as follows:1.A dynamic model for the DO in the aquaculture waters of crab with aquatic grass as the primary producer was built.Photosynthesis and respiration of macrophyte,water interface oxygen exchange,mechanical aeration,mineralization,and respiration of crab were considered.The dynamics model of dissolved oxygen system was established in the form of ordinary differential equation and the variation of dissolved oxygen in crab pond was simulated.The DO production capacity of aerator and macrophyte was evaluated,and sensitivity analysis was used to measure the effect of model parameters changes on DO level.The results show that the average absolute percentage error between the simulated and experimental values is 7.8%.Simulation results show that the main process that produces DO in the pond is photosynthesis of macrophyte,which accounts for 88.2% of the DO source.Mechanical aeration adds 9.2% of DO while reaeration adds 2.6% of DO.The decomposition of organic in water consumes 86.9%of the DO,which is the main consumption item.The respiration of aquatic plants consumes about 13.0% of the DO,while the respiration of crab accounts for a relatively small proportion of the DO consumption.The established DO model serves as a launching point for further research on artificial aeration control to improving aquaculture water environment.2.The vertical distribution model of DO in the aquaculture waters of crab was established based on the diffusion theory.The movement of oxygen molecules in water and the attenuation of solar radiation was considered,and the distribution and variation of DO at different depths of the pond was simulated.After the multilayer data of DO and water temperature being repaired,polynomial regression was used to expand the dissolved oxygen data,and CrankNicolson finite difference method was used to solve the diffusion equation.The DO in the bottom water of pond depends on the supplement of the upper water,and the bottom water more prone to hypoxia than the upper water.When the extinction coefficient of water increases,the diffusion coefficient decreases or the sediment concentration increases,the concentration of DO at the bottom of the pond will obviously decrease.The results show that the vertical model can accurately reflect the stratification and variation trend of DO and this model is of great significance for studying the vertical distribution of DO in crab culture pond.3.The automatic control of the PIDNN controller on the dissolved oxygen in the pond was studied.The control scheme used the error back propagation of the fully connected neural network to update the weight matrix automatically,so as to realize the automatic update of the three parameters of the traditional PID controller.The parameters are updated by using gradient descent method with momentum term.At the same time,the parameters of the mechanical aeration term in the dynamic mode of dissolved oxygen were optimized,and the relationship between the aeration rate of the aerator and the power of the motor was established.The simulation results show that the RMSE error between the simulated value and the set value of dissolved oxygen concentration can be controlled within 0.15 under low solar radiation conditions.Compared with the traditional artificial aeration control scheme,the real-time and effective control of dissolved oxygen can be realized by using PIDNN.The dissolved oxygen system dynamics model established in this paper provides a mathematical basis for farmers’ daily oxygenation management and aquatic grass planting.The dissolved oxygen vertical model is conducive to farmers’ understanding of the spatial distribution of dissolved oxygen concentration.The PIDNN-based dissolved oxygen control scheme reduces the risk of hypoxia in water.