The paper studies the anti-eccentric load margin of a novel structure bearing lubricated by low viscosity medium. The lubrication dynamic model considering journal inclination angle is established. The effects of diff...The paper studies the anti-eccentric load margin of a novel structure bearing lubricated by low viscosity medium. The lubrication dynamic model considering journal inclination angle is established. The effects of different speeds, loads, and tilted angles on the interface attributes of the bearing under typical working conditions are studied. The results show that the special structure bearing has self-stability margin of anti-tilted and anti-eccentric load. Particularly under different speed conditions, analyses show that the eccentric load has little influence on the static/dynamic characteristics of the bearing. Under the same conditions, the stability margin of the bearing is higher than that of traditional bearings. The research provides a theoretical basis for the application of such kinds of special structure bearings.展开更多
By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques,the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significan...By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques,the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved.Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels：Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications.Both methods are obtained from conventional design rules based on the linear elastic theory,and only consider the hardening effect from materials.Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns.This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation,based on the elastic-plastic theory.Firstly,to understand the effect of strain hardening on material behavior,the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments.Secondly,to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations.Further,the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests,finite element analyses,and standards.The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered.Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard.The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels,the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening,but a 5%strain should be employed as a design limit.The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely.展开更多
随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调...随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调频控制策略。其次,充分考虑风电场内各机组的运行差异,提出一种基于裕度因子的功率分配策略,有效挖掘各机组的调频能力并确保其安全运行。同时,提出一种针对风电场内风机分组运行的持久备用功率再分配策略。该策略预先安排少数风电机组以低减载率的超速模式运行,当调频风机退出频率支撑后,减载风机将根据调频风机的转速,采用一种基于转速反比例因子的差异化能量分配策略,以有效弥补调频风机退出后的能量缺额,缓解频率二次跌落(secondary frequency drop,SFD)。仿真结果表明,所提策略能够实现风火联合参与一次调频,在保证经济性和可靠性的前提下,充分发掘风电调频性能,有效改善电力系统频率响应特性。展开更多
针对含柔性直流输电(voltage source converter-high voltage direct current,VSC-HVDC)的交直流系统电压稳定性问题,开发出一种适用于含VSC-HVDC的交直流系统连续潮流程序,以负荷裕度指标分析VSC-HVDC系统有功功率传输方向、有功功率...针对含柔性直流输电(voltage source converter-high voltage direct current,VSC-HVDC)的交直流系统电压稳定性问题,开发出一种适用于含VSC-HVDC的交直流系统连续潮流程序,以负荷裕度指标分析VSC-HVDC系统有功功率传输方向、有功功率传输容量及换流站与交流系统无功功率交换量的变化对系统电压稳定性的影响。进而利用系统电压崩溃点处雅可比矩阵,推导出系统负荷裕度对VSC-HVDC有功功率控制参数和无功功率控制参数的灵敏度,并基于该灵敏度提出一种适用于改善系统电压稳定性的VSC-HVDC调控策略。最后,将所提方法应用于修改的68节点和IEEE118节点交直流系统,仿真结果验证了所提方法的正确性和有效性。展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 52105205)Natural Science Basic Research Program of Shaanxi (Grant No. 2022JM-003)+2 种基金Guangdong Basic and Applied Basic Research Foundation (Grant No. 2022A1515010864)the 2021 Joint Projects between Chinese and CEECs’ Universities (Grant No. 2021101)the Fundamental Research Funds for the Central Universities (Grant No.D5000220095)。
文摘The paper studies the anti-eccentric load margin of a novel structure bearing lubricated by low viscosity medium. The lubrication dynamic model considering journal inclination angle is established. The effects of different speeds, loads, and tilted angles on the interface attributes of the bearing under typical working conditions are studied. The results show that the special structure bearing has self-stability margin of anti-tilted and anti-eccentric load. Particularly under different speed conditions, analyses show that the eccentric load has little influence on the static/dynamic characteristics of the bearing. Under the same conditions, the stability margin of the bearing is higher than that of traditional bearings. The research provides a theoretical basis for the application of such kinds of special structure bearings.
基金supported by National Key Technology R&D Program of China under the 11th Five-year(Grant No.2006BAK02B02),and China Special Equipment Science & Technology Cooperation Platform
文摘By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques,the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved.Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels：Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications.Both methods are obtained from conventional design rules based on the linear elastic theory,and only consider the hardening effect from materials.Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns.This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation,based on the elastic-plastic theory.Firstly,to understand the effect of strain hardening on material behavior,the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments.Secondly,to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations.Further,the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests,finite element analyses,and standards.The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered.Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard.The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels,the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening,but a 5%strain should be employed as a design limit.The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely.
文摘随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调频控制策略。其次,充分考虑风电场内各机组的运行差异,提出一种基于裕度因子的功率分配策略,有效挖掘各机组的调频能力并确保其安全运行。同时,提出一种针对风电场内风机分组运行的持久备用功率再分配策略。该策略预先安排少数风电机组以低减载率的超速模式运行,当调频风机退出频率支撑后,减载风机将根据调频风机的转速,采用一种基于转速反比例因子的差异化能量分配策略,以有效弥补调频风机退出后的能量缺额,缓解频率二次跌落(secondary frequency drop,SFD)。仿真结果表明,所提策略能够实现风火联合参与一次调频,在保证经济性和可靠性的前提下,充分发掘风电调频性能,有效改善电力系统频率响应特性。
文摘针对含柔性直流输电(voltage source converter-high voltage direct current,VSC-HVDC)的交直流系统电压稳定性问题,开发出一种适用于含VSC-HVDC的交直流系统连续潮流程序,以负荷裕度指标分析VSC-HVDC系统有功功率传输方向、有功功率传输容量及换流站与交流系统无功功率交换量的变化对系统电压稳定性的影响。进而利用系统电压崩溃点处雅可比矩阵,推导出系统负荷裕度对VSC-HVDC有功功率控制参数和无功功率控制参数的灵敏度,并基于该灵敏度提出一种适用于改善系统电压稳定性的VSC-HVDC调控策略。最后,将所提方法应用于修改的68节点和IEEE118节点交直流系统,仿真结果验证了所提方法的正确性和有效性。
