Remarks on non-singular black holes

We briefly discuss non-singular black hole models, with the main focus on the properties of non-singular evaporating black holes. Such black holes possess an apparent horizon, however the event horizon may be absent. In such a case, the information from the black hole interior may reach the external observer after the complete evaporation of the black hole. This model might be used for the resolution of the information loss puzzle. However, as we demonstrate, in a general case the quantum radiation emitted from the black hole interior, calculated in the given black hole background, is very large. This outburst of the radiation is exponentially large for models with the redshift function α = 1. We show that it can be suppressed by including a non-trivial redshift function. However, even this suppression is not enough to guarantee self-consistency of the model. This problem is a manifestation of a general problem, known as the "mass inflation". We briefly comment on possible ways to overcome this problem in the models of non-singular evaporating black holes.

Fluid–structure interaction and flight dynamics analysis of parachute–payload system during uncontrolled airdrop process

The coupling behaviors of a special parachute’s inflation incorporating fluid–structure interaction and flight dynamics are investigated based on the multibody dynamic model and LS-DYNA nonlinear analysis code. A new coupling model is developed to predict both the opening phase of parachute and the trajectory of payload during airdrop mission in low attitude. The moving mesh technology is introduced to realize the finite mass inflation simulation. A simplified integration platform is built by coupling the fluid–structure interaction and flight dynamics model, and solved based on two-way data transfer to efficiently replicate the dynamic characteristics of parachute finite mass inflation. Finally, the opening performances of the parachute at different airdropping velocities are analyzed and compared with the experimental results. The unsteady flow dynamics is simulated and the wake re-contacts phenomenon occurred. Taking consideration of the periodical disturb of wind gust, the trajectory of parachute–payload system is simulated and compared with the real airdrop test results. In conclusion, the results show that this coupling model is efficient to simulate and predict the dynamics behaviors of parachute–payload system in a finite mass inflation scenario, which will be beneficial for airdrop missions.