Danger-aware Adaptive Composition of DRL Agents for Self-navigation

Self-navigation, referred as the capability of automatically reaching the goal while avoiding collisions with obstacles, is a fundamental skill required for mobile robots. Recently, deep reinforcement learning (DRL) has shown great potential in the development of robot navigation algorithms. However, it is still difficult to train the robot to learn goal-reaching and obstacle-avoidance skills simultaneously. On the other hand, although many DRL-based obstacle-avoidance algorithms are proposed, few of them are reused for more complex navigation tasks. In this paper, a novel danger-aware adaptive composition (DAAC) framework is proposed to combine two individually DRL-trained agents, obstacle-avoidance and goal-reaching, to construct a navigation agent without any redesigning and retraining. The key to this adaptive composition approach is that the value function outputted by the obstacle-avoidance agent serves as an indicator for evaluating the risk level of the current situation, which in turn determines the contribution of these two agents for the next move. Simulation and real-world testing results show that the composed Navigation network can control the robot to accomplish difficult navigation tasks, e.g., reaching a series of successive goals in an unknown and complex environment safely and quickly.Comment: 7 pages, 9 figure

Numerical study on mechanism of C-J deflagration

The mechanism of detonation instability and deflagration-to-detonation transition is studied by one-dimensional numerical simulation with overall one-step chemical reaction kinetics in this paper. The detonation is ignited at the left closed end of the one-dimensional detonation tube and propagates downstream. The activation energy is increased to trigger the instability of detonation. The numerical results show that the C-J detonation is stable at lower activation energy. The stable detonation does not have the von Neumann spike and the gas Mach number at detonation front is subsonic. The von Neumann spike appears and the gas Mach number becomes supersonic as the activation energy is increased. The detonation instability appears with the von Neumann spike synchronously. At very higher activation energy, the detonation quenches abruptly and degenerates into a C-J deflagration. The detonation is extinguished abruptly by the rarefaction wave induced by the higher von Neumann spike. Then the rarefaction wave moves in front of the heat release region and weakens the leading shock wave gradually. The C-J deflagration is composed of a precursor shock wave and a flame front, and the flame front is completely decoupled from the shock wave. The gas static temperature behind the leading shock wave is too low to ignite the mixture. The rarefaction wave from the wall ceases the mixture behind the leading shock, increases its static temperature and decrease its pressure. As a result, the combustion takes place at the interface. The pressure rise caused by the combustion at the interface offsets the influence of rarefaction wave, and this mechanism makes the C-J deflagration propagate downstream with a relatively constant velocity for a long time

Numerical Simulation of Three-Phase Flows in the Inverse Fluidized bed

The inverse three-phase fluidized bed has excellent potentials to be used in chemical, biochemical, petrochemical and food industries because of its high contact efficiency among each phase which leads to a good mass and heat transfer. The understanding of the hydrodynamics and flow structures in inverse three-phase fluidized beds is important for the design and scale up purposes. A CFD model based on the Eulerian-Eulerian (E-E) approach coupled with the kinetic theory of the granular flow is successfully developed to simulate an inverse three-phase fluidization system. The proposed CFD model for the inverse three-phase fluidization system is validated by comparing the numerical results with the experimental data. Investigations on the hydrodynamics and flow structures in the inverse three-phase fluidized bed under a batch liquid mode are conducted by numerical studies. The development of the fluidization processes and the general gas-liquid-solids flow structures under different operating conditions are further studied by the proposed three-phase E-E CFD model. Parametric studies including different inlet superficial gas velocities, particle densities, and solids loadings are investigated numerically. The numerical results show a general non-uniform radial flow structure in the inverse three-phase fluidized bed. It is also found that the particle distribution profiles in the axial direction relate to the solids loading, particle density and inlet superficial gas velocity. The existences of the liquid and solids recirculation inside the inverse three-phase fluidized bed are also noticed under the batch liquid mode. Moreover, the proposed CFD model for the inverse three-phase fluidized bed is further modified by adjusting the bubble size. The modified CFD model takes the bubble size effects into account and performs better on estimating the average gas holdup. In addition, a correlation between the bubble size and the superficial gas velocity, gas holdup and physical properties of the liquid and solid phases is proposed based on the numerical results. The predicted bubble size and the gas holdup in the inverse three-phase fluidized beds under a batch mode using the proposed correlation agree well with the experimental data. Therefore, the proposed three-phase E-E CFD model incorporated with the bubble size adjustment can be used to predict the performance of the inverse three-phase fluidization system more accurately

DYNAMIC ANALYSIS ON HUMAN OVERHAND THROWING

The purpose of this study was to establish a kinetic model to examine the kinetical interactions between segments of upper limb during overhand throwing. A model of threesegment kinetic chain consisting of upper arm, forearm and distal segment was established for kinetic calculation. Using Kane method to get resultant muscular moment. The conclusions can be drawn that the Kane method is effective in describing the upper himb movement and calculating the joint torque. Upper limb movement in Baseball pitching was study by this model and find out some relationships between motion technique and kinetic data