Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable...Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.展开更多
The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle...The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension(2D)large rotational angles.In order to construct 2D rotational degrees of freedom(DOFs),a platform with 2D revolute joints is proposed first.Based on the constraint screw theory,the feasible limbs that can be connected in the platform are synthesized.In order to provide constant rotational axis for the platform,a class of redundant limbs are designed.A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion.The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform.The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed.The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.展开更多
为满足大管径、大容量连续油管承载及运输要求,根据国内外油田用户的实际作业需求及特殊地域和环境特点,研发了SLG450/73大管径拖挂式连续油管作业设备。重点介绍了该装备的大吨位注入头、高效换装油管滚筒、动力装置与牵引车集成、注...为满足大管径、大容量连续油管承载及运输要求,根据国内外油田用户的实际作业需求及特殊地域和环境特点,研发了SLG450/73大管径拖挂式连续油管作业设备。重点介绍了该装备的大吨位注入头、高效换装油管滚筒、动力装置与牵引车集成、注入头及鹅颈管整体举升以及液压控制系统的技术特点。该作业机注入头额定提升能力450 k N,适应连续油管直径50.8-73.0 mm,整体装备成本低,移运性能良好,操作维护简便,即将进行产品试制和油田现场工业试验。展开更多
Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the e...Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the elderly patients展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52209108 and 52079034)Sichuan Science and Technology Program(Grant No.2023YFQ0021)+1 种基金the Natural Science Foundation of Heilongjiang Province,China(Grant No.LH2023E058)China Postdoctoral Science Foundation(Grant No.2022M720948)。
文摘Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.
基金The authors gratefully acknowledge the financial support of the National Nature Science Foundation of China(Grant Nos.51975039 and 51675037)the Fundamental Research Funds for the Central Universities(Grant No.2018JBZ007).
文摘The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers.This paper focuses on designing a class of 2R1T(R:Rotation;T:Translation)parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension(2D)large rotational angles.In order to construct 2D rotational degrees of freedom(DOFs),a platform with 2D revolute joints is proposed first.Based on the constraint screw theory,the feasible limbs that can be connected in the platform are synthesized.In order to provide constant rotational axis for the platform,a class of redundant limbs are designed.A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion.The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform.The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed.The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.
文摘为满足大管径、大容量连续油管承载及运输要求,根据国内外油田用户的实际作业需求及特殊地域和环境特点,研发了SLG450/73大管径拖挂式连续油管作业设备。重点介绍了该装备的大吨位注入头、高效换装油管滚筒、动力装置与牵引车集成、注入头及鹅颈管整体举升以及液压控制系统的技术特点。该作业机注入头额定提升能力450 k N,适应连续油管直径50.8-73.0 mm,整体装备成本低,移运性能良好,操作维护简便,即将进行产品试制和油田现场工业试验。
文摘Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the elderly patients
