基于三维物质点法的咳嗽飞沫传播轨迹及防护分析

Trajectory simulation and protection analysis of droplet transmission based on three-dimensional material point method

目的了解咳嗽产生飞沫的传播轨迹及不同口罩对于飞沫的动力学影响。方法基于三维物质点法(MPM3D),建立咳嗽飞沫和口罩防护效果的动力学模型。结果取咳嗽时呼气速度为50 m/s,咳嗽时间为0.75 s,当t=0.05 s时,飞沫会形成体积约为2.75倍口腔体积的雾云;t=0.5 s时,飞沫扩散至周围1.17 m的环境;t=5 s时,飞沫浓度集中于距离地面0.6 m以下的地方;t=10 s时,空气中的飞沫浓度已经较低。N95口罩在1 m之内的穿透率0.06~0.20,在1.5 m以外衰减到≤0.03;一般口罩在1.5 m之内的穿透率0.08~0.40,在2 m以外衰减到≤0.03。结论呼吸系统疾病患者因咳嗽喷出的飞沫在0.5 s内可对周围1.17 m的环境形成强烈影响,在5 s之后对大部分成年人的影响较小。距离患者1 m以内,口罩防护效果不佳,在2 m内,N95防护效果较好,在2 m以外,一般口罩和N95口罩均可起到防护作用。

Objective To understand transmission trajectory of droplets and dynamics of droplets for different masks.Methods It was considered that the expiratory speed was 50 m/s when coughing and the total time was 0.75 s.The dynamics models for droplets and masks were developed based on three-dimensional material point method(MPM3D).Results After coughing t=0.05 s,droplets formed a cloud about 2.75 times size of the mouth volume.When t=0.5 s,droplets spread within 1.17 m around.When t=5 s,most of droplets were at less then 0.6 m above the ground.When t=10 s,the concentration of droplets was already low in the air.Penetration rates of N95 masks were 0.06-0.20 and≤0.03 when the distances from coughing people were 1 m and 1.5 m,respectively.However,penetration rates of ordinary masks were 0.08-0.40 and≤0.03 when the distances from coughing people were 1.5 m and 2 m,respectively.Conclusions The droplets expelled by coughing in patients with respiratory system diseases can have a strong impact on the surrounding of 1.17 m within 0.5 s,and have little impact on most adults after 5 s.Within 1 m from the patient,the mask can hardly have the protective effect.Within 2 m,the protective effect of N95 mask is good.Beyond 2 m,both general mask and N95 mask have protective effect.