Simulation Research on the Effect of Spreading Process Parameters on the Quality of Lunar Regolith Powder Bed in Additive Manufacturing

Lunar surface additive manufacturing with lunar regolith is a key step in in-situ resource utilization.The powder spreading process is the key process,which has a major impact on the quality of the powder bed and the precision of molded parts.In this study,the discrete element method(DEM)was adopted to simulate the powder spreading process with a roller.The three powder bed quality indicators,including the molding layer offset,voidage fraction,and surface roughness,were established.Besides,the influence of the three process parameters,which are roller’s translational speed,rotational speed,and powder spreading layer thickness on the powder bed quality indicators was also analyzed.The results show that with the reduction of the powder spreading layer thickness and the increase of the rotational speed,the offset increased significantly;when the translational speed increased,the offset first increased and then decreased,which resulted in an extreme value;with the increase of the layer thickness and the decrease of the translational speed,the values for voidage fraction and surface roughness significantly reduced.The powder bed quality indicators were adopted as the optimization objective,and the multi-objective parameter optimization was carried out.The predicted optimal powder spreading parameters and powder bed quality indicators were then obtained.Moreover,the optimal values were then verified.This study can provide informative guidance for in-situ manufacturing at the moon in future deep space exploration missions.

Stress Testing of Liquidity Maturity Transformation Risk in Banks

One of the main causes of the past crisis was the inability of financial institutions to acquire funding at appropriate costs.The importance of applying a good liquidity risk measurement system becomes apparent.The present paper provides an approach to the measurement of liquidity maturity transformation risk within a stress testing framework,for middle-sized banks.The costs of liquidity arising due to a downturn in refinancing conditions are calculated by using modern risk measures.The forward-looking way is based on a liquidity gap report,where the consideration of the counterbalancing capacity enables to gain an insight into the real liquidity needs.The measurement of both,the portfolio-value in the respective time bucket and liquidity costs,is possible.Applying the expected shortfall can easily be included into the calculation.The results show that by using historical simulation,if no sufficient data are available,expected shortfall delivers an approximate value.Still,it can serve as an indicator of insurance against extreme events.The present approach combines a scenario-based view to a possible distress with a quantitative risk measurement.Therewith,it contributes to the bank’s wide stress testing as required by the regulatory authorities.

Study of Robinson instabilities with a higher-harmonic cavity for the HLS phase Ⅱ project

In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider the Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.