When considering the bomb explosion damage effect,the air shock wave and high-speed fragments of the bomb case are two major threats.In experiments,the air shock wave was studied by the bare explosives superseding the...When considering the bomb explosion damage effect,the air shock wave and high-speed fragments of the bomb case are two major threats.In experiments,the air shock wave was studied by the bare explosives superseding the real cased bomb;in contrast,the bomb case influence was ignored to reduce risk.The air explosion simulations of the MK84 warhead with and without the case were conducted.The numerical simulation results showed that the bomb case significantly influenced the shock wave generated by the bomb:the spatial distribution of shock wave in the near field changed,and the peak value of shock wave was reduced.Breakage of the case and kinetic energy of the fragmentation consumed 3 and 38% of the explosion energy,respectively.The increasing factors of the peak overpressure induced by the bare explosive on the ground and in the air were 1.43-3.04 and 1.37-1.57,respectively.Four typical stages of case breakage were defined.The mass distribution of the fragments follows the Mott distribution.The initial velocity distribution of the fragments agreed well with the Gurney equation.展开更多
In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is pr...In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is proposed in this paper. A localized pressure pulse with a very high amplitude can be imposed on specified regions in a combustion chamber, the numerical procedure of which is described. Pressure oscillations actuated by the released constant-volume bomb can then be analyzed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are evaluated by the half-power bandwidth method. The predicted acoustic characteristics and their damping for a special engine combustor agree well with the experimental data, validating the mathematical model and its numerical procedures. A small-thrust liquid rocket engine chamber is then analyzed by the present model. The First Longitudinal（1L） acoustic mode can be excited easily and is hard to be damped. The axial position of the central constantvolume bomb has little influence on the amplitude and damping capacity of the First Radial（1R） and 1L acoustic modes. Tangential acoustic modes can only be triggered by an off-centered constant-volume bomb, among which the First Tangential（1T） mode is the strongest and regarded as the most harmful one. The amplitude of the 1L acoustic mode is smaller, but its damping factor is larger, as a constant-volume bomb is imposed approaching the injector face. These results are contributed to evaluate the acoustic characteristics and their damping of the combustion chamber.展开更多
It has been said that,once a bomb casing has fractured, "detonation gases will then stream around the fragments or bypass them,and the acceleration process stops there." However,while apparently copious gas ...It has been said that,once a bomb casing has fractured, "detonation gases will then stream around the fragments or bypass them,and the acceleration process stops there." However,while apparently copious gas flow through casing fractures indicates some pressure release,it is also an indication of significant gas drive pressure,post casing fracture.This paper shows two approaches to the problem of calculating the actual loss of drive.One presents first-order analytical calculations,in cylindrical geometry,of pressure loss to the inside surface of a fractured casing.The second shows the modelling of a selected example in the CTH code.Both approaches reveal that gas escape,while occurring at its own soundspeed relative to the adjacent casing fragments,has to compete with rapid radial expansion of the casing.Together with some historic experiments now publicly available,our calculations indicate that post-fracture casing fragment acceleration is,for most systems,unlikely to be reduced significantly.展开更多
Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The exp...Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The explosion test data are few.Most exsiting studies focus on the propagation of shock wave and the influence of blast wall on the propagation of shock wave.Discussion on the main parameters of blast wall design is meagre,such as the design of safety distance,the distance from the blast wall to the protective building,height and width of the blast wall.This paper uses the finite element programme LS-DYNA to design the blast wall.To analyze the convergence of the finite element model and to determine the mesh size of the model,this paper establishes several finite element models with different sizes of meshes to verify the model.Then,the overpressure distribution of the shock wave on the protective building is simulated to implement the blast wall design.The geometric parameters of the blast wall are preliminarily determined.And the influence of the safety distance on the overpressure of the building surface is mainly discussed,so as to determine the final design parameters.When the overpressure is less than 2 kPa,it is considered that there will be no damage to people caused by flying fragments.Eventually,the blast wall height is 3 m,the thickness is 1 m,and the safety distance is 35 m.The proposed method is used to demonstrate the design method,and the final design parameters of the blast wall can thus be used for reference.展开更多
文摘When considering the bomb explosion damage effect,the air shock wave and high-speed fragments of the bomb case are two major threats.In experiments,the air shock wave was studied by the bare explosives superseding the real cased bomb;in contrast,the bomb case influence was ignored to reduce risk.The air explosion simulations of the MK84 warhead with and without the case were conducted.The numerical simulation results showed that the bomb case significantly influenced the shock wave generated by the bomb:the spatial distribution of shock wave in the near field changed,and the peak value of shock wave was reduced.Breakage of the case and kinetic energy of the fragmentation consumed 3 and 38% of the explosion energy,respectively.The increasing factors of the peak overpressure induced by the bare explosive on the ground and in the air were 1.43-3.04 and 1.37-1.57,respectively.Four typical stages of case breakage were defined.The mass distribution of the fragments follows the Mott distribution.The initial velocity distribution of the fragments agreed well with the Gurney equation.
基金Financial support from the National Natural Science Foundation of China (Nos.51676111 and 11628206)
文摘In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is proposed in this paper. A localized pressure pulse with a very high amplitude can be imposed on specified regions in a combustion chamber, the numerical procedure of which is described. Pressure oscillations actuated by the released constant-volume bomb can then be analyzed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are evaluated by the half-power bandwidth method. The predicted acoustic characteristics and their damping for a special engine combustor agree well with the experimental data, validating the mathematical model and its numerical procedures. A small-thrust liquid rocket engine chamber is then analyzed by the present model. The First Longitudinal（1L） acoustic mode can be excited easily and is hard to be damped. The axial position of the central constantvolume bomb has little influence on the amplitude and damping capacity of the First Radial（1R） and 1L acoustic modes. Tangential acoustic modes can only be triggered by an off-centered constant-volume bomb, among which the First Tangential（1T） mode is the strongest and regarded as the most harmful one. The amplitude of the 1L acoustic mode is smaller, but its damping factor is larger, as a constant-volume bomb is imposed approaching the injector face. These results are contributed to evaluate the acoustic characteristics and their damping of the combustion chamber.
基金sponsored by the NWIPT Department of the U.K.Ministry of Defence
文摘It has been said that,once a bomb casing has fractured, "detonation gases will then stream around the fragments or bypass them,and the acceleration process stops there." However,while apparently copious gas flow through casing fractures indicates some pressure release,it is also an indication of significant gas drive pressure,post casing fracture.This paper shows two approaches to the problem of calculating the actual loss of drive.One presents first-order analytical calculations,in cylindrical geometry,of pressure loss to the inside surface of a fractured casing.The second shows the modelling of a selected example in the CTH code.Both approaches reveal that gas escape,while occurring at its own soundspeed relative to the adjacent casing fragments,has to compete with rapid radial expansion of the casing.Together with some historic experiments now publicly available,our calculations indicate that post-fracture casing fragment acceleration is,for most systems,unlikely to be reduced significantly.
基金This work was supported by the National Natural Science Foundation of China(No.51878507).
文摘Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The explosion test data are few.Most exsiting studies focus on the propagation of shock wave and the influence of blast wall on the propagation of shock wave.Discussion on the main parameters of blast wall design is meagre,such as the design of safety distance,the distance from the blast wall to the protective building,height and width of the blast wall.This paper uses the finite element programme LS-DYNA to design the blast wall.To analyze the convergence of the finite element model and to determine the mesh size of the model,this paper establishes several finite element models with different sizes of meshes to verify the model.Then,the overpressure distribution of the shock wave on the protective building is simulated to implement the blast wall design.The geometric parameters of the blast wall are preliminarily determined.And the influence of the safety distance on the overpressure of the building surface is mainly discussed,so as to determine the final design parameters.When the overpressure is less than 2 kPa,it is considered that there will be no damage to people caused by flying fragments.Eventually,the blast wall height is 3 m,the thickness is 1 m,and the safety distance is 35 m.The proposed method is used to demonstrate the design method,and the final design parameters of the blast wall can thus be used for reference.
