In lost foam casting (LFC), the distribution of polymer beads during the bead filling process is not uniform, and the collision between polymer beads determines the distribution of two-phase flow of gas and solid. The...In lost foam casting (LFC), the distribution of polymer beads during the bead filling process is not uniform, and the collision between polymer beads determines the distribution of two-phase flow of gas and solid. The interaction between the gas and solid phases reveals as coupling effect of the force that gas exerts on particles or vice versa, or that among particles. The gas-solid flow in filling process is nonlinearity, which makes the coupling effect an essential point to carry out a simulation properly. Therefore, information of each particle's motion is important for acquiring the law of filling process. In bead filling process, compressed air is pressed into mold cavity, and discharged from gas vent, creating a pressure difference between outer and inner space near the gas vent. This pressure difference directly changes the spatial distribution and motion trace of gas and solid phases. In this paper, Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) are employed to simulate the fluid dynamic character based on Newton's Third Law of Motion. The simulation results of some casting products such as pressure plate and valve handle are compared with the result obtained from practical experiment in order to test the feasibility of DEM. The comparison shows that this DEM method can be a very promising tool in the mould filling simulation of beads' movement.展开更多
Thermal stress simulation can provide a scientific reference to eliminate defects such as crack,residual stress centralization and deformation etc.,caused by thermal stress during casting solidification.To study the t...Thermal stress simulation can provide a scientific reference to eliminate defects such as crack,residual stress centralization and deformation etc.,caused by thermal stress during casting solidification.To study the thermal stress distribution during casting process,a unilateral thermal-stress coupling model was employed to simulate 3D casting stress using Finite Difference Method(FDM),namely all the traditional thermal-elastic-plastic equations are numerically and differentially discrete.A FDM/FDM numerical simulation system was developed to analyze temperature and stress fields during casting solidification process.Two practical verifications were carried out,and the results from simulation basically coincided with practical cases.The results indicated that the FDM/FDM stress simulation system can be used to simulate the formation of residual stress,and to predict the occurrence of hot tearing.Because heat transfer and stress analysis are all based on FDM,they can use the same FD model,which can avoid the matching process between different models,and hence reduce temperature-load transferring errors.This approach makes the simulation of fluid flow,heat transfer and stress analysis unify into one single model.展开更多
Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and ...Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.展开更多
In lost foam casting(LFC)the foam pattern is the key criterion,and the filling process is crucialto ensure the high quality of the foam pattern.Filling which lacks uniformity and denseness will cause variousdefects an...In lost foam casting(LFC)the foam pattern is the key criterion,and the filling process is crucialto ensure the high quality of the foam pattern.Filling which lacks uniformity and denseness will cause variousdefects and affect the surface quality of the casting.The influential factors of the filling process are realized in thisresearch.Optimization of the filling process,enhancement of efficiency,decrease of waste,etc.,are obtained bythe numerical simulation of the filling process using a computer.The equations governing the dense gas-solid two-phase flow are established,and the physical significanceof each equation is discussed.The Euler/Lagrange numerical model is used to simulate the fluid dynamiccharacteristics of the dense two-phase flow during the mould filling process in lost foam casting.The experimentsand numerical results showed that this method can be a very promising tool in the mould filling simulation of beads’movement.展开更多
目的探讨重组人脑利钠肽治疗老年心力衰竭的临床效果。方法选取2018年1月—2019年12月安庆市立医院收治的117例老年慢性心力衰竭患者作为研究对象,采用随机数字表法将患者分为对照组(59例)和观察组(58例)。两组患者接受吸氧、卧床休息...目的探讨重组人脑利钠肽治疗老年心力衰竭的临床效果。方法选取2018年1月—2019年12月安庆市立医院收治的117例老年慢性心力衰竭患者作为研究对象,采用随机数字表法将患者分为对照组(59例)和观察组(58例)。两组患者接受吸氧、卧床休息和常规抗心力衰竭治疗。观察组在对照组治疗的基础上给予注射用重组人脑利钠肽,以1.5μg/kg的负荷剂量静脉推注,用1.5 mL 5%葡萄糖注射液稀释,然后以0.0075μg/(kg·min)连续输注72 h后,将速率控制为0.01μg/(kg·min)。两组疗程均为2周。观察两组患者的临床疗效,同时比较两组患者治疗前后的心功能和血清学指标水平。结果治疗后,观察组的临床疗效分布优于对照组(P<0.05)。治疗后,两组左室射血分数(LVEF)、每搏输出量(SV)值显著升高,左室舒张末期内径(LVEDd)、左室收缩末期内径(LVESd)显著降低(P<0.05);且观察组治疗后的LVEF、SV值均高于对照组,LVEDd、LVESd值显著低于对照组(P<0.05)。治疗后,两组患者的血清超敏C反应蛋白(hs-CRP)、脑钠肽(BNP)和同型半胱氨酸(Hcy)水平均显著降低(P<0.05),且观察组hs-CRP、BNP和Hcy水平均显著低于对照组(P<0.05)。结论重组人脑利钠肽治疗老年心力衰竭患者具有更好的临床效果,可有效改善患者的心脏功能,降低hs-CRP、BNP的水平,值得在临床上推广使用。展开更多
基金supported by The Second Doctor Innovative Projects of Shenzhen Institute of Information Technology (BC2009013)
文摘In lost foam casting (LFC), the distribution of polymer beads during the bead filling process is not uniform, and the collision between polymer beads determines the distribution of two-phase flow of gas and solid. The interaction between the gas and solid phases reveals as coupling effect of the force that gas exerts on particles or vice versa, or that among particles. The gas-solid flow in filling process is nonlinearity, which makes the coupling effect an essential point to carry out a simulation properly. Therefore, information of each particle's motion is important for acquiring the law of filling process. In bead filling process, compressed air is pressed into mold cavity, and discharged from gas vent, creating a pressure difference between outer and inner space near the gas vent. This pressure difference directly changes the spatial distribution and motion trace of gas and solid phases. In this paper, Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) are employed to simulate the fluid dynamic character based on Newton's Third Law of Motion. The simulation results of some casting products such as pressure plate and valve handle are compared with the result obtained from practical experiment in order to test the feasibility of DEM. The comparison shows that this DEM method can be a very promising tool in the mould filling simulation of beads' movement.
基金supported by the National Natural Science Foundation of China (No.50805056)New Century Excellent Talents in University (No.NCET-09-0396)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education (2009)
文摘Thermal stress simulation can provide a scientific reference to eliminate defects such as crack,residual stress centralization and deformation etc.,caused by thermal stress during casting solidification.To study the thermal stress distribution during casting process,a unilateral thermal-stress coupling model was employed to simulate 3D casting stress using Finite Difference Method(FDM),namely all the traditional thermal-elastic-plastic equations are numerically and differentially discrete.A FDM/FDM numerical simulation system was developed to analyze temperature and stress fields during casting solidification process.Two practical verifications were carried out,and the results from simulation basically coincided with practical cases.The results indicated that the FDM/FDM stress simulation system can be used to simulate the formation of residual stress,and to predict the occurrence of hot tearing.Because heat transfer and stress analysis are all based on FDM,they can use the same FD model,which can avoid the matching process between different models,and hence reduce temperature-load transferring errors.This approach makes the simulation of fluid flow,heat transfer and stress analysis unify into one single model.
文摘Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.
基金The National High Technology Research and Development Program of China(863Program)(2006AA04Z140)The National Natural Science Foundation of China(NSFC)(50605024)
文摘In lost foam casting(LFC)the foam pattern is the key criterion,and the filling process is crucialto ensure the high quality of the foam pattern.Filling which lacks uniformity and denseness will cause variousdefects and affect the surface quality of the casting.The influential factors of the filling process are realized in thisresearch.Optimization of the filling process,enhancement of efficiency,decrease of waste,etc.,are obtained bythe numerical simulation of the filling process using a computer.The equations governing the dense gas-solid two-phase flow are established,and the physical significanceof each equation is discussed.The Euler/Lagrange numerical model is used to simulate the fluid dynamiccharacteristics of the dense two-phase flow during the mould filling process in lost foam casting.The experimentsand numerical results showed that this method can be a very promising tool in the mould filling simulation of beads’movement.
文摘目的探讨重组人脑利钠肽治疗老年心力衰竭的临床效果。方法选取2018年1月—2019年12月安庆市立医院收治的117例老年慢性心力衰竭患者作为研究对象,采用随机数字表法将患者分为对照组(59例)和观察组(58例)。两组患者接受吸氧、卧床休息和常规抗心力衰竭治疗。观察组在对照组治疗的基础上给予注射用重组人脑利钠肽,以1.5μg/kg的负荷剂量静脉推注,用1.5 mL 5%葡萄糖注射液稀释,然后以0.0075μg/(kg·min)连续输注72 h后,将速率控制为0.01μg/(kg·min)。两组疗程均为2周。观察两组患者的临床疗效,同时比较两组患者治疗前后的心功能和血清学指标水平。结果治疗后,观察组的临床疗效分布优于对照组(P<0.05)。治疗后,两组左室射血分数(LVEF)、每搏输出量(SV)值显著升高,左室舒张末期内径(LVEDd)、左室收缩末期内径(LVESd)显著降低(P<0.05);且观察组治疗后的LVEF、SV值均高于对照组,LVEDd、LVESd值显著低于对照组(P<0.05)。治疗后,两组患者的血清超敏C反应蛋白(hs-CRP)、脑钠肽(BNP)和同型半胱氨酸(Hcy)水平均显著降低(P<0.05),且观察组hs-CRP、BNP和Hcy水平均显著低于对照组(P<0.05)。结论重组人脑利钠肽治疗老年心力衰竭患者具有更好的临床效果,可有效改善患者的心脏功能,降低hs-CRP、BNP的水平,值得在临床上推广使用。
