Simulation Study On Fire Spread Of Coniferous Bed Of Dahurian Larch(Larix Gmelinii)

Taking Larix gmelinii needles litter as the research object,and using surface pine needle combustibles in Larix gmelinii forests in Maoershan area as indoor ignition materials,the field environment was simulated,and the moisture content,load,and wind speed and slope conditions of different combustibles were simulated.The indoor fire spread simulation of a point burn test was conducted to study the effects of different combustible characteristics and environmental conditions on the fire behavior of larch needles litter.Through the pre-experiment,variables such as the characteristics of combustible materials,wind speed,and slope were set.A total of 4(flammable material load)× 4(combustible material moisture content)× 3(wind speed)× 3(slope)=144 burn tests were passed.The regression analysis was performed first to screen the variables,and the multivariate analysis of variance was used to calculate the percentage of the explanation of the spread variation of the factors,and a fire spread model suitable for Larix gmelinii coniferous forest was established.Based on the Logistic model,the probability of Larix gmelinii conifer spread was established.Predict the model and analyze the model.It is helpful for accurately predicting the occurrence of forest fires and assessing the level of forest fire danger,and provides a certain theoretical basis for fire prevention and suppression.The study found:(1)Within the test setting range,80%of the combustible bed is smoldering during the spreading process,and the spreading speed does not exceed 6 m·h-1 in the 75%interval,and the maximum value is 93.02 m·h-1,The minimum value is 0.41 m·h-1.(2)The influence of three significant variables of the combustible water content,wind speed,and slope on the spreading speed are:wind speed>combustible water content>slope.(3)The relative contribution of the four factors of the combustible material moisture content,combustible material load,wind speed,and gradient to the spreading speed is:moisture content × slope × wind speed(27.73%)>wind speed(17.22%)>moisture content ×slope × Wind speed × load capacity(13.01%)>water content × wind speed(11.01%)>slope ×wind speed(9.21%).(4)Through stepwise regression analysis,a prediction model R=-6.448+5.520W-0.719M+0.478S is established.The coefficient of determination after model adjustment is 0.41.M(5%?M?220%),W(2m·s-1?W<4m·s-1),S(0°?S ?20°).The standard estimated error of the model is 8.56,and the validation error is 12.93.(5)The probability model of the Larix gmelinii bed being ignited is:P=c(-9.442+0.765L+0.116S+2.027W)/1+c(-9.442+0.765L+0.116S+2.027W)(L is the load(t·hm-2),S is the slope(°),and W is the wind speed(m·s-1)).By comparison,when the threshold is 0.8,the accuracy rate of forecasting unspread is 81.8%,the accuracy rate of forecasting spread is 83.6%,and the total accuracy rate is 83.3%.