The oxygen transportation from surrounding air to coating cracks is an important factor in the oxidation and ignition of titanium alloy. In this work, the oxygen transport and surface oxidation of titanium in inclined...The oxygen transportation from surrounding air to coating cracks is an important factor in the oxidation and ignition of titanium alloy. In this work, the oxygen transport and surface oxidation of titanium in inclined cracks of coating under parallel airflow are studied with the lattice Boltzmann method(LBM).A boundary scheme of LBM about surface reaction is developed. The conversion factors are utilized to build the relationship between the physical scale and the lattice scale. The reliability of the LBM model is validated by the finite element method(FEM). The results show that the convective mass transport driven by the surrounding airflow and the vortex structure formed inside the crack are the two significant factors that influence the oxygen transport in cracks. The convective mass transfer plays a major role in oxygen transport when the inclination angle of the crack is small. For the cases with a large inclination angle, the oxygen transfer from the top to the bottom of the crack is mainly controlled by mass diffusion mechanism. The oxygen concentration in inclined cracks is generally less than that in vertical cracks, and oxidation and ignition of the substrate titanium might be more likely to occur in relatively vertical cracks.展开更多
The COVID-19 was firstly reported in Wuhan,Hubei province,and it was brought to all over China by people travelling for Chinese New Year.The pandemic coronavirus with its catastrophic effects is now a global concern.F...The COVID-19 was firstly reported in Wuhan,Hubei province,and it was brought to all over China by people travelling for Chinese New Year.The pandemic coronavirus with its catastrophic effects is now a global concern.Forecasting of COVID-19 spread has attracted a great attention for public health emergency.However,few re-searchers look into the relationship between dynamic transmission rate and preventable measures by authorities.In this paper,the SEIR(Susceptible Exposed Infectious Recovered)model is employed to investigate the spread of COVID-19.The epidemic spread is divided into two stages:before and after intervention.Before intervention,the transmission rate is assumed to be a constant since individual,community and government response has not taken into place.After intervention,the transmission rate is reduced dramatically due to the societal actions or measures to reduce and prevent the spread of disease.The transmission rate is assumed to follow an exponential function,and the removal rate is assumed to follow a power exponent function.The removal rate is increased with the evolution of the time.Using the real data,the model and parameters are optimized.The transmission rate without measure is calculated to be 0.033 and 0.030 for Hubei and outside Hubei province,respectively.After the model is established,the spread of COVID-19 in Hubei province,France and USA is predicted.From results,USA performs the worst according to the dynamic ratio.The model has provided a mathematical method to evaluate the effectiveness of the government response and can be used to forecast the spread of COVID-19 with better performance.展开更多
基金supported by National Science and Technology Major Project (2017-VII-0012-0108)National Key Research and Development Program of China (2016YFB1102302)+2 种基金China Postdoctoral Science Foundation (2019M660664)National Natural Science Foundation of China (72004141)Basic and Applied Basic Research Foundation of Guangdong Province (2019A1515111074)。
文摘The oxygen transportation from surrounding air to coating cracks is an important factor in the oxidation and ignition of titanium alloy. In this work, the oxygen transport and surface oxidation of titanium in inclined cracks of coating under parallel airflow are studied with the lattice Boltzmann method(LBM).A boundary scheme of LBM about surface reaction is developed. The conversion factors are utilized to build the relationship between the physical scale and the lattice scale. The reliability of the LBM model is validated by the finite element method(FEM). The results show that the convective mass transport driven by the surrounding airflow and the vortex structure formed inside the crack are the two significant factors that influence the oxygen transport in cracks. The convective mass transfer plays a major role in oxygen transport when the inclination angle of the crack is small. For the cases with a large inclination angle, the oxygen transfer from the top to the bottom of the crack is mainly controlled by mass diffusion mechanism. The oxygen concentration in inclined cracks is generally less than that in vertical cracks, and oxidation and ignition of the substrate titanium might be more likely to occur in relatively vertical cracks.
基金This work is supported by National Key R and D Program of China(No.2017YFC0803300)National Science Foundation of China(Grant Nos.7204100828,91646201,U1633203)High-tech Discipline Con-struction Funding for Universities in Beijing(Safety Science and Engi-neering)and Beijing Key Laboratory of City Integrated Emergency Re-sponse Science.
文摘The COVID-19 was firstly reported in Wuhan,Hubei province,and it was brought to all over China by people travelling for Chinese New Year.The pandemic coronavirus with its catastrophic effects is now a global concern.Forecasting of COVID-19 spread has attracted a great attention for public health emergency.However,few re-searchers look into the relationship between dynamic transmission rate and preventable measures by authorities.In this paper,the SEIR(Susceptible Exposed Infectious Recovered)model is employed to investigate the spread of COVID-19.The epidemic spread is divided into two stages:before and after intervention.Before intervention,the transmission rate is assumed to be a constant since individual,community and government response has not taken into place.After intervention,the transmission rate is reduced dramatically due to the societal actions or measures to reduce and prevent the spread of disease.The transmission rate is assumed to follow an exponential function,and the removal rate is assumed to follow a power exponent function.The removal rate is increased with the evolution of the time.Using the real data,the model and parameters are optimized.The transmission rate without measure is calculated to be 0.033 and 0.030 for Hubei and outside Hubei province,respectively.After the model is established,the spread of COVID-19 in Hubei province,France and USA is predicted.From results,USA performs the worst according to the dynamic ratio.The model has provided a mathematical method to evaluate the effectiveness of the government response and can be used to forecast the spread of COVID-19 with better performance.
