Odor Source Declaration In Three-dimensional Environments Using Multiple Sensor Nodes

The leakage of poisonous and harmful gas is a serious threat to people's life and property,so it is of great significance to carry out the research of leakage source location.Odor(or gas)source location research mainly includes three parts: plume finding,plume tracking and odor source identification.In previous work,there are few studies about the declaration of odor sources,and most of the studies are based on the ground robots or sensor nets which make use of odor information in the two-dimension space.For the actual environment of the odor source(such as the damage of overhead gas pipeline),it is necessary to study the declaration of the odor source in the three-dimensional environment.This thesis introduces the concept of mass divergence and mass flux in the problems of odor source declaration.The key point is how to use the three-dimensional sensor network to collect the odor concentration and wind speed information in order to determine whether a suspicious location is the odor source.The main work is as follows:Firstly,an odor source declaration algorithm based on mass divergence is proposed.The algorithm derives from the law of mass conservation.When the divergence is greater than zero,it indicates the position is a source,while on the opposite the negative one represents a sink.And when the divergence is equal to zero,it means the position is only a point in the process of flow.Taylor series expansion method is used to solve the approximation of divergence,and several numerical simulations are designed to verify the feasibility of the method.The relationship between the number of sensor nodes and the calculation error has been discussed.Finally,the distributions of divergence are given in the whole three-dimensional space,with which the method proposed before can also be proved.Then,a mass flux algorithm is designed for odor source declaration.The method uses four sensor nodes to form a regular tetrahedron,and calculates the mass flux of the tetrahedron.It illustrates that the mass flux of a regular tetrahedron is equal to the sum of the mass fluxes of the surfaces forming the regular tetrahedron.The mass flux of each surface is solved by interpolation,mesh partition and so on.In the simulation of the mass flux algorithm,multiple kinds of wind speed conditions are set.Considering whether the enclosed curve surface includes an odor source or not,different results are derived given different scales.Finally,compared with another algorithm,the divergence method can locate the position of the odor source more accurately.However,if the center point of multiple sensor nodes does not exactly traverse the point where the odor source is located,it may cause a false alarm.The shortcoming can be further improved by the flux method,in which the position of the odor source is determined in a small range,and the algorithm is of great practicability.