Nozzle effects on thrust and inlet pressure of a multi-cycle air-breathing pulse detonation engine （APDE） are investigated experimentally. An APDE with 68 mm in diameter and 2 050 mm in length is operated using gaso...Nozzle effects on thrust and inlet pressure of a multi-cycle air-breathing pulse detonation engine （APDE） are investigated experimentally. An APDE with 68 mm in diameter and 2 050 mm in length is operated using gasoline/air mixture. Straight nozzle, converging nozzle, converging-diverging nozzle and diverging nozzle are tested. The results show that thrust augmentation of converging-diverging nozzle, diverging nozzle or straight nozzle is better than that of converging nozzle on the whole. Thrust augmentation of straight nozzle is worse than those of converging-diverging nozzle and diverging nozzle. Thrust augmentations of diverging nozzle with larger expansion ratio and converging-diverging nozzle with larger throat area range from 20% to 40% on tested frequencies and are better than those of congeneric other nozzles respectively. Nozzle effects on inlet pressure are also researched. At each frequency it is indicated that filling pressures and average peak pressures of inlet with diverging nozzle and converging-diverging nozzle with large throat cross section area are higher than those with straight nozzle and converging nozzle Pressures near thrust wall increase in an increase order from without nozzle, with diverging nozzle, straight nozzle and converging-diverging nozzle to converging nozzle.展开更多
The thrust generation by electro-hydrodynamic （EHD） effect has been studied for a wire-cylinder arrangement under high DC voltage. Series of measurements have been conducted in order to determine the relationship be...The thrust generation by electro-hydrodynamic （EHD） effect has been studied for a wire-cylinder arrangement under high DC voltage. Series of measurements have been conducted in order to determine the relationship between generated thrust and corona discharge current, as well as its dependence on geometrical characteristics of the electrodes, e.g. electrode gap, wire and cylinder radii. The experimental investigation has shown a linear relationship between the generated thrust and the discharge current, while parametric analysis showed that increased electrode gap and emitter radius reduces the thrust. On the other hand, large gaps favor the thrust per unit power ratio.展开更多
Because the mover and stator of a doubly-fed linear motor are both equipped with three-phase windings, the motor enables contactless energy to be transferred from the stator to the mover. Thus, when a doubly-fed linea...Because the mover and stator of a doubly-fed linear motor are both equipped with three-phase windings, the motor enables contactless energy to be transferred from the stator to the mover. Thus, when a doubly-fed linear motor is used in the linear driving system of trains, neither an overhead line nor a third rail is needed. However, the doubly- fed motor will lead to more severe thrust fluctuation than the unilateral motors. In order to overcome this shortcoming, the thrust fluctuation of the doubly-fed motor should be analyzed. In this paper, an expression for motor thrust is derived. It points out that the slot effect caused by the slotted structure is the main reason for the increase of thrust fluctuation. The method of adopting unequal pole pitch and unequal slot numbers per pole per phase of stator and mover, is proposed to weaken the slot effect when designing the motor slot parameters. Three different motor models are simulated by ANSOFT. The proposed method results in a motor thrust fluctuation coefficient of 8.4%, compared to 49.4% for the conventional method. Therefore, the motor＇s thrust fluctuation is effectively suppressed by the proposed method.展开更多
A new method to compensate the end effect of a linear induction motor （LIM） in low-speed maglev vehicles is proposed. With this method, the motors are close to each other so that the front motor＇s exit-end magnetic...A new method to compensate the end effect of a linear induction motor （LIM） in low-speed maglev vehicles is proposed. With this method, the motors are close to each other so that the front motor＇s exit-end magnetic field extends into the next motor＇s entry zone. As a result, the motor＇s magnetic field traveling wave become continuous and the end effect of short primary LIMs is greatly weakened. In the analysis of the air-gap magnetic field distribution, the LIM is assumedly divided into two identical motors vcith the distances of 20, 40, 60, and gO ram. The results show that the air-gap magnetic field is still continuous within these distances due to LIM＇s end effect. As the distance between two motors increases, the distortion of the air-gap magnetic field becomes more severe. Then, we investigate the relationship between the secondary speed and the thrust in three cases, i.e., a single LIM, two motors divided with 72 mm with pole pitch corrected, and two motors divided with 60 mm without the pole pitch being corrected. We find that the thrust has a small decrease when the speed increases, which means that the magnetic field is already continuous and its amplitude is approximately a constant. Furthermore, the thrust loss of case 3 is more than that of case 2, which indicates that the pole pitch correction is effective.展开更多
山区交通工程建设会产生大量由于开挖形成的路堑边坡,此类卸荷作用强烈的人工边坡的防护工程设计不能等同于一般自然斜坡。为了弄清路堑边坡设计安全下的失稳力学机制并提出考虑补偿效应的路堑边坡加固设计方法,在调研和追踪多个失稳路...山区交通工程建设会产生大量由于开挖形成的路堑边坡,此类卸荷作用强烈的人工边坡的防护工程设计不能等同于一般自然斜坡。为了弄清路堑边坡设计安全下的失稳力学机制并提出考虑补偿效应的路堑边坡加固设计方法,在调研和追踪多个失稳路堑边坡的基础上,复核路堑边坡设计措施的安全性,检查当前计算方法存在的问题,分析设计安全下路堑边坡加固失效的原因。结果表明:路堑边坡的失稳在于开挖卸荷造成的侧向约束解除使得边坡的变形发展超出了岩土体的变形允许值,且应力损失值没有得到及时充足的补偿。设计措施提供的水平加固力4277 k N/m,小于理正计算得到的剩余水平下滑力5278 k N/m,小于考虑力的补偿效应的水平加固力5878 k N/m,加固力不足和空间布局不合理是造成路堑边坡失稳的根本原因。利用考虑力的补偿效应的极限平衡法估算路堑边坡水平加固力,所得结果大于剩余推力法,方法简单易操作,既达到安全标准也小于静止土压力且不浪费。展开更多
基金National Natural Science Foundation of China(50976094, 51176158)Reseach Fund for the Doctoral Program of Higher Education of China(20096102110022)Doctorate Foundation of Northwestern Polytechnical University (CX200909)
文摘Nozzle effects on thrust and inlet pressure of a multi-cycle air-breathing pulse detonation engine （APDE） are investigated experimentally. An APDE with 68 mm in diameter and 2 050 mm in length is operated using gasoline/air mixture. Straight nozzle, converging nozzle, converging-diverging nozzle and diverging nozzle are tested. The results show that thrust augmentation of converging-diverging nozzle, diverging nozzle or straight nozzle is better than that of converging nozzle on the whole. Thrust augmentation of straight nozzle is worse than those of converging-diverging nozzle and diverging nozzle. Thrust augmentations of diverging nozzle with larger expansion ratio and converging-diverging nozzle with larger throat area range from 20% to 40% on tested frequencies and are better than those of congeneric other nozzles respectively. Nozzle effects on inlet pressure are also researched. At each frequency it is indicated that filling pressures and average peak pressures of inlet with diverging nozzle and converging-diverging nozzle with large throat cross section area are higher than those with straight nozzle and converging nozzle Pressures near thrust wall increase in an increase order from without nozzle, with diverging nozzle, straight nozzle and converging-diverging nozzle to converging nozzle.
文摘The thrust generation by electro-hydrodynamic （EHD） effect has been studied for a wire-cylinder arrangement under high DC voltage. Series of measurements have been conducted in order to determine the relationship between generated thrust and corona discharge current, as well as its dependence on geometrical characteristics of the electrodes, e.g. electrode gap, wire and cylinder radii. The experimental investigation has shown a linear relationship between the generated thrust and the discharge current, while parametric analysis showed that increased electrode gap and emitter radius reduces the thrust. On the other hand, large gaps favor the thrust per unit power ratio.
文摘Because the mover and stator of a doubly-fed linear motor are both equipped with three-phase windings, the motor enables contactless energy to be transferred from the stator to the mover. Thus, when a doubly-fed linear motor is used in the linear driving system of trains, neither an overhead line nor a third rail is needed. However, the doubly- fed motor will lead to more severe thrust fluctuation than the unilateral motors. In order to overcome this shortcoming, the thrust fluctuation of the doubly-fed motor should be analyzed. In this paper, an expression for motor thrust is derived. It points out that the slot effect caused by the slotted structure is the main reason for the increase of thrust fluctuation. The method of adopting unequal pole pitch and unequal slot numbers per pole per phase of stator and mover, is proposed to weaken the slot effect when designing the motor slot parameters. Three different motor models are simulated by ANSOFT. The proposed method results in a motor thrust fluctuation coefficient of 8.4%, compared to 49.4% for the conventional method. Therefore, the motor＇s thrust fluctuation is effectively suppressed by the proposed method.
文摘A new method to compensate the end effect of a linear induction motor （LIM） in low-speed maglev vehicles is proposed. With this method, the motors are close to each other so that the front motor＇s exit-end magnetic field extends into the next motor＇s entry zone. As a result, the motor＇s magnetic field traveling wave become continuous and the end effect of short primary LIMs is greatly weakened. In the analysis of the air-gap magnetic field distribution, the LIM is assumedly divided into two identical motors vcith the distances of 20, 40, 60, and gO ram. The results show that the air-gap magnetic field is still continuous within these distances due to LIM＇s end effect. As the distance between two motors increases, the distortion of the air-gap magnetic field becomes more severe. Then, we investigate the relationship between the secondary speed and the thrust in three cases, i.e., a single LIM, two motors divided with 72 mm with pole pitch corrected, and two motors divided with 60 mm without the pole pitch being corrected. We find that the thrust has a small decrease when the speed increases, which means that the magnetic field is already continuous and its amplitude is approximately a constant. Furthermore, the thrust loss of case 3 is more than that of case 2, which indicates that the pole pitch correction is effective.
文摘山区交通工程建设会产生大量由于开挖形成的路堑边坡,此类卸荷作用强烈的人工边坡的防护工程设计不能等同于一般自然斜坡。为了弄清路堑边坡设计安全下的失稳力学机制并提出考虑补偿效应的路堑边坡加固设计方法,在调研和追踪多个失稳路堑边坡的基础上,复核路堑边坡设计措施的安全性,检查当前计算方法存在的问题,分析设计安全下路堑边坡加固失效的原因。结果表明:路堑边坡的失稳在于开挖卸荷造成的侧向约束解除使得边坡的变形发展超出了岩土体的变形允许值,且应力损失值没有得到及时充足的补偿。设计措施提供的水平加固力4277 k N/m,小于理正计算得到的剩余水平下滑力5278 k N/m,小于考虑力的补偿效应的水平加固力5878 k N/m,加固力不足和空间布局不合理是造成路堑边坡失稳的根本原因。利用考虑力的补偿效应的极限平衡法估算路堑边坡水平加固力,所得结果大于剩余推力法,方法简单易操作,既达到安全标准也小于静止土压力且不浪费。
