Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress miti...Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.展开更多
This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading.The calibration of four typical failure parameters for 40CrMnSiB ...This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading.The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations.The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests.This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads.Building upon this foundation,the damage parameter D_(c),linked to the cumulative crack density,was defined based on the evolution characteristics of a substantial number of cracks.The relationship between the damage parameter and crack velocity over time was established,and the influence of the internal central pressure on the damage parameter and crack velocity was investigated.Variations in the fracture modes were found under different failure criteria,with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode.Through statistical analysis of the shell penetration fracture radius data,it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant.The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s,surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time.The increase in shell damage exhibited an initial rapid phase,followed by deceleration,demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave.This study provides an effective approach for investigating crack propagation and damage evolution.The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.展开更多
针对现有易感染者-已感染者-已恢复者(susceptible-infected-recovered,SIR)模型未考虑机场网络的拓扑结构对航班延误传播影响的问题,基于复杂网络理论计算机场网络的拓扑特征指标,利用熵权优劣解距离(technique for order preference b...针对现有易感染者-已感染者-已恢复者(susceptible-infected-recovered,SIR)模型未考虑机场网络的拓扑结构对航班延误传播影响的问题,基于复杂网络理论计算机场网络的拓扑特征指标,利用熵权优劣解距离(technique for order preference by similarity to ideal solution,TOPSIS)方法评估各个机场的综合重要度,将全部机场分为若干个类,据此建立不同类别机场航班延误传播的改进SIR模型,并求解模型的传播阈值;以2023年中国机场网络为例,将全部机场划分为5类,并用改进的SIR模型仿真不同初始条件下机场的航班延误传播。结果表明:改进的SIR模型在仿真延误传播时更具适用性;机场的综合重要度越高,延误传播范围越广、速度越快、恢复周期越长;当多个机场的航班发生延误时,E类机场的延误传播能力明显提升;机场网络拓扑结构对延误传播具有抑制性,延误难以波及全部机场。改进的SIR模型展现了机场重要度对延误传播的差异化影响,为航班延误管理策略的制定提供了参考。展开更多
基金supported by the National Natural Science Foundation of China (Grant No.52178515)。
文摘Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.
基金supported by the National Natural Science Foundation of China (Grant No.12302437)Natural Science Foundation of Jiangsu Province (BK20230939)China Postdoctoral Science Foundation (2021M701710)。
文摘This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading.The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations.The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests.This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads.Building upon this foundation,the damage parameter D_(c),linked to the cumulative crack density,was defined based on the evolution characteristics of a substantial number of cracks.The relationship between the damage parameter and crack velocity over time was established,and the influence of the internal central pressure on the damage parameter and crack velocity was investigated.Variations in the fracture modes were found under different failure criteria,with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode.Through statistical analysis of the shell penetration fracture radius data,it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant.The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s,surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time.The increase in shell damage exhibited an initial rapid phase,followed by deceleration,demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave.This study provides an effective approach for investigating crack propagation and damage evolution.The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.
文摘针对现有易感染者-已感染者-已恢复者(susceptible-infected-recovered,SIR)模型未考虑机场网络的拓扑结构对航班延误传播影响的问题,基于复杂网络理论计算机场网络的拓扑特征指标,利用熵权优劣解距离(technique for order preference by similarity to ideal solution,TOPSIS)方法评估各个机场的综合重要度,将全部机场分为若干个类,据此建立不同类别机场航班延误传播的改进SIR模型,并求解模型的传播阈值;以2023年中国机场网络为例,将全部机场划分为5类,并用改进的SIR模型仿真不同初始条件下机场的航班延误传播。结果表明:改进的SIR模型在仿真延误传播时更具适用性;机场的综合重要度越高,延误传播范围越广、速度越快、恢复周期越长;当多个机场的航班发生延误时,E类机场的延误传播能力明显提升;机场网络拓扑结构对延误传播具有抑制性,延误难以波及全部机场。改进的SIR模型展现了机场重要度对延误传播的差异化影响,为航班延误管理策略的制定提供了参考。
