Numerical Simulation Of Interaction Between High Energy Laser And Flying Target

This thesis regards the warhead of the air vehicle as the irradiating object of HEL (High Energy Laser) weapon, regards the operational efficiency of HEL weapon as study object, and studys the factors concerned with the dynamic course of air-defence of HEL weapon. So long as the operational efficiency of HEL weapon is made clear, the designing of the range of HEL defence experiment can be optimized, and reference can be provided to the best usage of HEL weapon in real operation.In the project, multiple disciplines are concerned with and the whole course of air-defence of a HEL Weapon is dynamic, so according to the characteristics and complexity of the problem., this thesis adopts an overall point of view, and simplifys the problem when necessary. The research in this thesis is mainly based on analystic and numerical analysis.Firstly, by geometrical analysis of the course of dynamic heating the flying targe, overall knowledge about the whole course is achieved. The relative location between the laser and the flying target, the relative location between the laser and the projectile trajectory affect laser heating the flying target. In the respect of geometrical optics, those effects are studied. The concept of angle factor is advanced. It is decided by the normal unit vector of the surface of the flying target and the pointing direction unit vector of the laser. The temporal variation of the maximum angle factor is defined heating configuration. Space above the ground is devided into two kinds. For effectively heating flying target, the laser needs to be set in the kind of space in which there is always a moment when the laser beam can irradiate the side surface of the flying cylinder perpendicularly. The dissymmetry of the projectile trajectory caused by the air drag force is studied with the concept of temporal width of the heating configuration. By integrating the heating configuration balanced by decay coefficient of laser in the temporal width, the best place for the laser is found. At the same time, it implies the estimation of the operational efficiency of HEL at other locations on the ground. So in real operation, according to the relative location between the laser and the projectile trajectory, it can be decided from the estimation whether attacking the flying target or not. When the location is just so-so, the operational efficiency here is not enough to surpass the energy threshold for destroying the target, the attack command needs to be given up. Otherwise, attack.Secondly, the effect of the shock wave on the propagation of the laser beam is studied by computational fluid dynamics (CFD) and simulation technology of optical propagation. Numerical simulation gives the flow field around the target flying at supersonic speed. By comparison, it is suggested that, when discussing the effect of the interaction between shock wave and laser beam, the effect of thermal bloom on the flow field can be ommitted, and the effect of the flow field on the optical field is need to be discussed only.Thirdly, the critical problem of thermal explosion with high heat flux on the boundary is studied by the finite element method (FEM), deepening the knowledge of the nonlinearity of the thermal explosion. FEM and bisection method are combined to solve critical parameters and critical status. The term of super-runaway temperature is put forward. It is only decided by the property of the energetic material, can be regarded as a critical parameter of the thermal explosion. At the same power level, the laser irradiates a steel shell full of explosive and inducts the explosive to thermal explosion.. The lower limit of the irradiating time of the laser beam is discussed.Finally, three dimensional joint simulation of the whole course of HEL defence experiment is carried out by four dimensional optical propagation simulation, CFD, FEM and Object Oriented simulation. To be concrete, the six degree of freedom projectile trajectory simulation is used to get close-to-fact trajectory . Here, the flying status of the target keeps changing, and the axial direction is seldom along the tangent direction of the trajectory, so it cannot be avoided that the angle factor is affected by the trajectory. Two concepts related to the thermal bloom are put forward, one is the line of the maximum peak irradiance at a definite distance, the other is the line of the maximum peak irradiance with a definite focus length. In joint simulation, the former line is adopted, for it making the peak irradiance on the side surface of the projectile be the maximum which it can be. Based on all the research done ahead, Joint simulation is carried out. The best location for the laser is selected, and the threshold of the laser output power is determined. When the laser output power is lower than the threshold, the projectile cannot be destroyed out of the defence distance by the laser beam.By the study above, factors concerned with the dynamic course of HEL air-defence operation are dwelt on. The study deepens knowledge of the operational efficiency of HEL weapon. Optimized range design of HEL defence experiment is fulfilled. The result provides important reference for optimizing usage of HEL in incoming real air-defence operation.