By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result o...By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result on the global existence and the blow-up phenomena of classical solutions of these systems. These results show that the dissipation is strong enough to preserve the smoothness of ‘small ’ solution.展开更多
In order to study the influence of gas-liquid two-phase flow on the performance and internal flow field of a centrifugal pump,the steady three-dimensional flow with different gas volume fractions was simulated by appl...In order to study the influence of gas-liquid two-phase flow on the performance and internal flow field of a centrifugal pump,the steady three-dimensional flow with different gas volume fractions was simulated by applying the Reynolds-average N-S equation and mixture gas-liquid two-phase flow model,and the compressibility of gas was taken into consideration in the simulation. Then the centrifugal pump characteristic and the gas distribution law in different gas volume fractions were analyzed. The computational results show that gas volume fraction has a certain influence on the performance of the centrifugal pump,and the efficiency and head of the pump are on the decline with the increase of it.Static pressure in the impeller increases in the radial direction,but the pressure gradient in the flow direction is different under the different gas volume fractions. The gas volume is distributed mainly in the ipsilateral direction of impeller back shroud in the flow channel of the volute. On the suction side of the blade inlet there is an obvious low-pressure area,which causes bubbles agglutination and higher gas volume fraction. With the gas entering passage flow,gas volume fraction in the suction decreases and the pressure surface rises gradually. Higher gas volume fraction causes air blocking phenomenon in the flow passage and the discharge capacity reduces. The increase of gas volume makes the turbulent motion within the impeller more and more intense,which leads to more and more energy loss.展开更多
Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both t...Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.展开更多
The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were prefor...The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.展开更多
为了探究石英岩力学性能劣化规律和热损伤机制,使用基于颗粒流程序的颗粒簇模型(grain-based model in particle flow code,简称PFC-GBM)开展了实时高温及自然冷却条件下石英岩单轴压缩模拟,分析了石英岩在两种温度条件下的应力-应变曲...为了探究石英岩力学性能劣化规律和热损伤机制,使用基于颗粒流程序的颗粒簇模型(grain-based model in particle flow code,简称PFC-GBM)开展了实时高温及自然冷却条件下石英岩单轴压缩模拟,分析了石英岩在两种温度条件下的应力-应变曲线、峰值应力、弹性模量及破坏模式随温度的演化,并基于裂纹和位移变化探讨了其热损伤机制。主要得到如下结论:自然冷却过程中石英岩内部温度整体上遵循由中心向表面逐渐降低的规律,700℃石英岩在冷却过程中的裂纹扩展导致非稳定热传导过程,进而产生等温线错位现象。实时高温条件下石英岩脆性−延性转变临界温度在25~300℃之间,相较于自然冷却条件下石英岩300~500℃的临界温度更低。实时高温条件下石英岩的峰值强度和弹性模量相较于自然冷却后石英岩试样分别降低了约20 MPa及10 GPa,且二者差值不随温度发生显著变化;在25~300℃范围内,弹性模量相较于峰值强度对热损伤更加敏感。随着温度升高,单轴压缩下石英岩破碎程度明显增加,表现出更多的劈裂破坏特征,热致微裂纹对石英岩破坏模式的控制作用不断增强,两种温度条件下的宏观破裂面均倾向于沿已有热致微裂纹通道扩展,自然冷却条件下宏观贯穿破裂面更加明显。展开更多
针对多视觉任务中传输成本高、解码端计算压力大的问题,提出一种自适应可伸缩视频编码(adaptive scalable video coding,ASVC)传输框架,将视频分为语义层和背景层,分别传输语义和背景信息。此外,提出一种自适应压缩算法,构建了C4.5决策...针对多视觉任务中传输成本高、解码端计算压力大的问题,提出一种自适应可伸缩视频编码(adaptive scalable video coding,ASVC)传输框架,将视频分为语义层和背景层,分别传输语义和背景信息。此外,提出一种自适应压缩算法,构建了C4.5决策树模型分析网络环境对视频进行压缩的决策判定,并对帧序列进行光流分析,在保留变化显著的帧基础上引入插值机制保持图像的平滑性。仿真结果表明,ASVC方法在不同码率环境下表现更高的识别精准率,视频质量和传输效率的显著提升。展开更多
文摘By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result on the global existence and the blow-up phenomena of classical solutions of these systems. These results show that the dissipation is strong enough to preserve the smoothness of ‘small ’ solution.
基金The National Natural Science Foundation of China(51679196,51879216,51339005)
文摘In order to study the influence of gas-liquid two-phase flow on the performance and internal flow field of a centrifugal pump,the steady three-dimensional flow with different gas volume fractions was simulated by applying the Reynolds-average N-S equation and mixture gas-liquid two-phase flow model,and the compressibility of gas was taken into consideration in the simulation. Then the centrifugal pump characteristic and the gas distribution law in different gas volume fractions were analyzed. The computational results show that gas volume fraction has a certain influence on the performance of the centrifugal pump,and the efficiency and head of the pump are on the decline with the increase of it.Static pressure in the impeller increases in the radial direction,but the pressure gradient in the flow direction is different under the different gas volume fractions. The gas volume is distributed mainly in the ipsilateral direction of impeller back shroud in the flow channel of the volute. On the suction side of the blade inlet there is an obvious low-pressure area,which causes bubbles agglutination and higher gas volume fraction. With the gas entering passage flow,gas volume fraction in the suction decreases and the pressure surface rises gradually. Higher gas volume fraction causes air blocking phenomenon in the flow passage and the discharge capacity reduces. The increase of gas volume makes the turbulent motion within the impeller more and more intense,which leads to more and more energy loss.
基金Projects(51109092,11272137)supported by the National Natural Science Foundation of ChinaProjects(2013M530237,2014T70479)supported by China Postdoctoral Science FoundationProject(SJLX15-0498)supported by Jiangsu Provincial Graduate Students Research and Innovation Program,China
文摘Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.
基金Project(2002AA305104) supported by the National High-Tech Research and Development Program of China
文摘The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.
文摘为了探究石英岩力学性能劣化规律和热损伤机制,使用基于颗粒流程序的颗粒簇模型(grain-based model in particle flow code,简称PFC-GBM)开展了实时高温及自然冷却条件下石英岩单轴压缩模拟,分析了石英岩在两种温度条件下的应力-应变曲线、峰值应力、弹性模量及破坏模式随温度的演化,并基于裂纹和位移变化探讨了其热损伤机制。主要得到如下结论:自然冷却过程中石英岩内部温度整体上遵循由中心向表面逐渐降低的规律,700℃石英岩在冷却过程中的裂纹扩展导致非稳定热传导过程,进而产生等温线错位现象。实时高温条件下石英岩脆性−延性转变临界温度在25~300℃之间,相较于自然冷却条件下石英岩300~500℃的临界温度更低。实时高温条件下石英岩的峰值强度和弹性模量相较于自然冷却后石英岩试样分别降低了约20 MPa及10 GPa,且二者差值不随温度发生显著变化;在25~300℃范围内,弹性模量相较于峰值强度对热损伤更加敏感。随着温度升高,单轴压缩下石英岩破碎程度明显增加,表现出更多的劈裂破坏特征,热致微裂纹对石英岩破坏模式的控制作用不断增强,两种温度条件下的宏观破裂面均倾向于沿已有热致微裂纹通道扩展,自然冷却条件下宏观贯穿破裂面更加明显。
文摘目的探讨二维相位对比(2D phase contrast,2D PC)磁共振成像(magnetic resonance imaging,MRI)序列在定量分析髂静脉压迫综合征(iliac vein compression syndrome,IVCS)患者静脉管腔内血液平均流速(mean blood flow velocity,MV)的应用价值。材料与方法前瞻性招募2023年12月到2024年7月在本院经数字减影血管造影(digital subtraction angiography,DSA)诊断明确为IVCS且需要血管腔内介入治疗的患者30例(试验组)及10名健康志愿者(对照组),收集患者临床资料并行1.5 T飞利浦超导MRI检查,在自由稳态进动(balance fast field echo,B-FFE)序列图像基础上分别在下腔静脉、双侧髂外静脉的冠状位、矢状位及轴位图上垂直扫描2D PC MRI序列,使用定量流量(quantitative flow,Q_FLOW)后处理软件得到血管垂直横切面感兴趣区(region of interest,ROI)内MV值。所有2D PC MRI检查进行两次,通过分析两次扫描结果的一致性(Bland-Altman图)来验证序列稳定性;分别比较IVCS试验组与对照组双侧髂外静脉MV值,评估IVCS患者髂总静脉受压对远端血流的影响;比较IVCS试验组(健侧髂外MV-患侧髂外MV)与对照组(右侧髂外MV-左侧髂外MV)髂外静脉MV差值,分析流速差诊断IVCS的效能;术中通过中心静脉导管(central venous catheter,CVC)测量IVCS患者组髂-下腔静脉压力梯度,并与患侧髂外静脉MV值进行相关性分析。结果两次2D PC MRI扫描结果一致性良好(P均<0.001);试验组患侧髂外静脉血液流速低于健侧(P<0.001),对照组双侧髂外静脉MV值差异没有统计学意义(P=0.518);使用双侧髂外静脉MV差值诊断IVCS效能高,AUC为0.939(95%CI:0.887~0.991),敏感度为81.7%,特异度为100.0%;术中CVC测量压力梯度结果与狭窄静脉远心端MV呈负相关(r=-0.951,P<0.001)。结论2D PC MRI定量分析IVCS患者静脉血液流速结果稳定、可靠,双侧髂外静脉MV差值诊断IVCS特异性高,IVCS患者髂外静脉MV值与髂-下腔静脉压力梯度符合伯努利原理,2D PC MRI可作为一种无创诊断IVCS及间接评估静脉血流压力的工具,为IVCS患者血管腔内介入治疗的手术指征提供重要参考。
文摘针对多视觉任务中传输成本高、解码端计算压力大的问题,提出一种自适应可伸缩视频编码(adaptive scalable video coding,ASVC)传输框架,将视频分为语义层和背景层,分别传输语义和背景信息。此外,提出一种自适应压缩算法,构建了C4.5决策树模型分析网络环境对视频进行压缩的决策判定,并对帧序列进行光流分析,在保留变化显著的帧基础上引入插值机制保持图像的平滑性。仿真结果表明,ASVC方法在不同码率环境下表现更高的识别精准率,视频质量和传输效率的显著提升。
