| With the rapid development of social economy and urban construction,urban buildings show the characteristics of high size and density gradually.The increasing number of fire accidents and diversified forms increase the difficulty of fire control,which will easily cause huge casualties and property losses.In order to extinguish the fire and protect people’s lives and property effectively,it is important to locate the fire point precisely.However,in the actual jet process,the jet trajectory of fire water monitor will be affected by a variety of uncertain parameters,which will affect the prediction accuracy of jet target and reduce the fire-fighting efficiency.Therefore,it is of great practical significance and significant market value to study the uncertainty of jet trajectory and target of fire water monitor.This paper carries out the research from the following aspects mainly:(1)Particle kinematics and ballistic mechanics were used to analyze the jet microbody,and the jet breakup form and process were described based on liquid jet crushing theory.Considering the air resistance caused by the breakup time and the constant change of jet cross-sectional area,the state of droplet crushing and atomization was determined by the dimensionless parameter Je,and then the theoretical model of jet trajectory of fire water monitor was established.By combining theory with simulation,the simulation analysis is used to verify the accuracy of the jet trajectory.(2)Because of the fast velocity of fire water monitor jet at the exit,the jet is a turbulent jet which is not affected by internal and external forces.After the water jet enters the air,there will be a certain length of the area will not break,the core of the water jet is much faster than the surrounding droplets.Based on the breakup theory,the core area of actual jet trajectory was further considered,and the changing trend of water jet under different working conditions was analyzed.Taking WeberWe_g(28)22as atomization and height of jet H(28)0 as landing boundary conditions,the theoretical model of jet trajectory is established.The feasibility of the model is verified by comparing the simulation with the experimental value,which is of great significance to the design of fire water monitor and the improvement of its performance.(3)In actual firefighting,a variety of uncertainty factors will occur,and the uncertainty of these parameters will have an impact on the jet trajectory,resulting in a certain error between the actual target and the theoretical target.The uncertainty of the established jet trajectory model of fire water monitor was studied,and the interval algorithm,the gray algorithm and the combination algorithm were used to set certain error degrees respectively for the main factors affecting the jet trajectory,such as initial velocity of jet,pitch angle and wind speed.The influence of uncertain parameters on jet targets was determined,and the three algorithms were compared.The range of target range value obtained by the interval jet trajectory model was the largest,while the combination algorithm was relatively small.Exploring the uncertainty of actual parameters to control the range of target variation has a great influence on predicting the range of jet target in actual firefighting and improving efficiency of firefighting.The research results of this paper are helpful to deepen the research on the jet trajectory of fire water monitor,which can provide some references for the structural design and performance optimization of fire water monitor. |
