Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems res...Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve.It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.展开更多
On February 12,the Anhui ProvincialPeople’s Government made a decisionon the speeding up of the use of foreigncapital.The decision involved the followingseven aspects: 1.To seize the opportunity to reviseideology and...On February 12,the Anhui ProvincialPeople’s Government made a decisionon the speeding up of the use of foreigncapital.The decision involved the followingseven aspects: 1.To seize the opportunity to reviseideology and to open up a new situation formaking use of foreign capital.The decisionurges the various localities to seize the righttime to shift their focus to making good useof their own advantages,and improving thelocal investment climate and the quality ofservice in the light of their actual conditionsso as to absorb more foreign funds.Meanwhile,enterprises must be led to face the marketand to join equal competition so as to pushforward the use of foreign funds to a展开更多
电网受扰后频率最低点预测对新型电力系统的频率安全评估非常重要,而目前已有频率动态分析模型较难快速、准确、灵活地预测电网受扰后频率最低点,其中同步发电机调速系统的低阶通用建模以及新能源接入的影响建模是主要挑战。首先提出了...电网受扰后频率最低点预测对新型电力系统的频率安全评估非常重要,而目前已有频率动态分析模型较难快速、准确、灵活地预测电网受扰后频率最低点,其中同步发电机调速系统的低阶通用建模以及新能源接入的影响建模是主要挑战。首先提出了充分考虑频率响应特性的发电机调速系统低阶通用模型,结合新能源场站的通用频率响应模型,建立了新能源接入电网的通用平均系统频率(generic average system frequency,G-ASF)模型,在保证准确度的同时有效降低了模型阶数。然后,基于G-ASF模型直接预测电网在给定功率损失下的频率最低点。最后,在IEEE 3机9节点系统以及含新能源的IEEE 10机39节点系统中进行了仿真,结果表明提出的模型和方法在不同扰动或不同系统结构下均能准确预测频率最低点,且能够用于快速计算频率安全约束下的新能源渗透率极限值,验证了模型的准确性和通用性。展开更多
文摘Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve.It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.
文摘On February 12,the Anhui ProvincialPeople’s Government made a decisionon the speeding up of the use of foreigncapital.The decision involved the followingseven aspects: 1.To seize the opportunity to reviseideology and to open up a new situation formaking use of foreign capital.The decisionurges the various localities to seize the righttime to shift their focus to making good useof their own advantages,and improving thelocal investment climate and the quality ofservice in the light of their actual conditionsso as to absorb more foreign funds.Meanwhile,enterprises must be led to face the marketand to join equal competition so as to pushforward the use of foreign funds to a
文摘电网受扰后频率最低点预测对新型电力系统的频率安全评估非常重要,而目前已有频率动态分析模型较难快速、准确、灵活地预测电网受扰后频率最低点,其中同步发电机调速系统的低阶通用建模以及新能源接入的影响建模是主要挑战。首先提出了充分考虑频率响应特性的发电机调速系统低阶通用模型,结合新能源场站的通用频率响应模型,建立了新能源接入电网的通用平均系统频率(generic average system frequency,G-ASF)模型,在保证准确度的同时有效降低了模型阶数。然后,基于G-ASF模型直接预测电网在给定功率损失下的频率最低点。最后,在IEEE 3机9节点系统以及含新能源的IEEE 10机39节点系统中进行了仿真,结果表明提出的模型和方法在不同扰动或不同系统结构下均能准确预测频率最低点,且能够用于快速计算频率安全约束下的新能源渗透率极限值,验证了模型的准确性和通用性。
