To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employe...To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employed to handle the interactions between the box and the fluids. In this study, both air and water were treated as compressible fluids and their properties were modeled through the equation of states. Calculated results show that the air cushion plays a very important role buffering the impinging. Under the deformed concave bottom an air cushion layer will be easier to form up. For high impact speed, the pressure for the elastic box is much lower than that for the rigid box. Excited by the impact, the impinging box oscillates with about its natural frequency.展开更多
该文利用软件组件间信息流的传递过程,提出了基于风险分析的回归测试用例优先级排序算法(Risk Analysis-based Test Case Prioritization,RA-TCP).该算法针对现有的优先级排序技术未能有效利用测试用例所覆盖信息的问题,在类粒度下将软...该文利用软件组件间信息流的传递过程,提出了基于风险分析的回归测试用例优先级排序算法(Risk Analysis-based Test Case Prioritization,RA-TCP).该算法针对现有的优先级排序技术未能有效利用测试用例所覆盖信息的问题,在类粒度下将软件抽象为基于信息流的类级有向网络模型,然后将每个测试用例所覆盖的类间信息传递关系用一组杠铃模型表示,结合概率风险评估方法和故障树理论计算杠铃模型的风险值,最后以测试用例所覆盖的杠铃风险总和作为其排序依据.实验结果表明,风险越高的测试用例覆盖错误的可能性越大,RA-TCP算法提高了具有严重风险的错误发现速率,与7种排序算法对比,RA-TCP算法具有较高的错误检出率及较好的稳定性.展开更多
The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train...The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train have been taken and the dynamics of upstream propagation of the oblique shock train have been analyzed from the synchronized schlieren imaging with the dynamic pressure measurements.The formation and propagation of the oblique shock train are initiated by the throttling device at the downstream end of the duct model.Multiple reflected shocks,expansion fans and separated flow bubbles exist in the unthrottled flow,causing three adversepressure-gradient phases and three favorable-pressure-gradient phases upstream the oblique shock train.The leading edge of the oblique shock train propagates upstream,and translates to be asymmetric with the increase of backpressure.The upstream propagation rate of the oblique shock train increases rapidly when the leading edge of the oblique shock train encounters the separation bubble near the shock reflection point and the adverse-pressure-gradient phase,while the oblique shock train slow movement when the leading edge of the oblique shock train is in the favorablepressure-gradient phase for unthrottled flow.The asymmetric flow pattern and oscillatory nature of the oblique shock train are observed throughout the whole upstream propagation process.展开更多
文摘To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employed to handle the interactions between the box and the fluids. In this study, both air and water were treated as compressible fluids and their properties were modeled through the equation of states. Calculated results show that the air cushion plays a very important role buffering the impinging. Under the deformed concave bottom an air cushion layer will be easier to form up. For high impact speed, the pressure for the elastic box is much lower than that for the rigid box. Excited by the impact, the impinging box oscillates with about its natural frequency.
文摘该文利用软件组件间信息流的传递过程,提出了基于风险分析的回归测试用例优先级排序算法(Risk Analysis-based Test Case Prioritization,RA-TCP).该算法针对现有的优先级排序技术未能有效利用测试用例所覆盖信息的问题,在类粒度下将软件抽象为基于信息流的类级有向网络模型,然后将每个测试用例所覆盖的类间信息传递关系用一组杠铃模型表示,结合概率风险评估方法和故障树理论计算杠铃模型的风险值,最后以测试用例所覆盖的杠铃风险总和作为其排序依据.实验结果表明,风险越高的测试用例覆盖错误的可能性越大,RA-TCP算法提高了具有严重风险的错误发现速率,与7种排序算法对比,RA-TCP算法具有较高的错误检出率及较好的稳定性.
基金supported by the National Natural Science Foundation of China(Nos.51476076 and 10702029)
文摘The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train have been taken and the dynamics of upstream propagation of the oblique shock train have been analyzed from the synchronized schlieren imaging with the dynamic pressure measurements.The formation and propagation of the oblique shock train are initiated by the throttling device at the downstream end of the duct model.Multiple reflected shocks,expansion fans and separated flow bubbles exist in the unthrottled flow,causing three adversepressure-gradient phases and three favorable-pressure-gradient phases upstream the oblique shock train.The leading edge of the oblique shock train propagates upstream,and translates to be asymmetric with the increase of backpressure.The upstream propagation rate of the oblique shock train increases rapidly when the leading edge of the oblique shock train encounters the separation bubble near the shock reflection point and the adverse-pressure-gradient phase,while the oblique shock train slow movement when the leading edge of the oblique shock train is in the favorablepressure-gradient phase for unthrottled flow.The asymmetric flow pattern and oscillatory nature of the oblique shock train are observed throughout the whole upstream propagation process.
