Up to present, there have been no studies concerning the application of fluid-structure interaction（FSI） analysis to the lifetime estimation of multi-stage centrifugal compressors under dangerous unsteady aerodynami...Up to present, there have been no studies concerning the application of fluid-structure interaction（FSI） analysis to the lifetime estimation of multi-stage centrifugal compressors under dangerous unsteady aerodynamic excitations. In this paper, computational fluid dynamics（CFD） simulations of a three-stage natural gas pipeline centrifugal compressor are performed under near-choke and near-surge conditions, and the unsteady aerodynamic pressure acting on impeller blades are obtained. Then computational structural dynamics（CSD） analysis is conducted through a one-way coupling FSI model to predict alternating stresses in impeller blades. Finally, the compressor lifetime is estimated using the nominal stress approach. The FSI results show that the impellers of latter stages suffer larger fluctuation stresses but smaller mean stresses than those at preceding stages under near-choke and near-surge conditions. The most dangerous position in the compressor is found to be located near the leading edge of the last-stage impeller blade. Compressor lifetime estimation shows that the investigated compressor can run up to 102.7 h under the near-choke condition and 200.2 h under the near-surge condition. This study is expected to provide a scientific guidance for the operation safety of natural gas pipeline centrifugal compressors.展开更多
As the scaling of applications increases, the demand of main memory capacity increases in order to serve large working set. It is difficult for DRAM （dynamic random access memory） based memory system to satisfy the ...As the scaling of applications increases, the demand of main memory capacity increases in order to serve large working set. It is difficult for DRAM （dynamic random access memory） based memory system to satisfy the memory capacity requirement due to its limited scalability and high energy consumption. Compared to DRAM, PCM （phase change memory） has better scalability, lower energy leakage, and non-volatility. PCM memory systems have become a hot topic of academic and industrial research. However, PCM technology has the following three drawbacks： long write latency, limited write endurance, and high write energy, which raises challenges to its adoption in practice. This paper surveys architectural research work to optimize PCM memory systems. First, this paper introduces the background of PCM. Then, it surveys research efforts on PCM memory systems in performance optimization, lifetime improving, and energy saving in detail, respectively. This paper also compares and summarizes these techniques from multiple dimensions. Finally, it concludes these optimization techniques and discusses possible research directions of PCM memory systems in future.展开更多
针对大多数研究只分析了平面无线传感器网络第一个节点死亡(First Node Died Time,FNDT)网络寿命与延迟的情况,本文分析了网络全部节点死亡(All Node Died Time,ANDT)时网络寿命与延迟的情况.本文得到的相关工作如下:(1)分析得到了平面...针对大多数研究只分析了平面无线传感器网络第一个节点死亡(First Node Died Time,FNDT)网络寿命与延迟的情况,本文分析了网络全部节点死亡(All Node Died Time,ANDT)时网络寿命与延迟的情况.本文得到的相关工作如下:(1)分析得到了平面无线传感器网络全部节点死亡(All Node Died Time,ANDT)时网络寿命的计算方法;(2)给出了了网络从FNDT到ANDT过程网络延迟的变化规律与发展情况,以及计算方法;(3)提出了网络最大ANDT与延迟间的折中优化方法,从而得到网络性能优化时的节点发射半径以及节点调制级数的选取.本文分析结果较好的揭示了平面无线传感器网络ANDT与延迟的发展规律,并给出了提高网络性能的优化参数选取方法,可为传感器网络的设计、部署与优化提供较好的指导作用.展开更多
This paper aims at formulization and overview of the cost performance evolutions of proton exchange membrane (PEM) fuel cell power generation along with load and time. For this purpose, electricity-cost ratio (ECR) is...This paper aims at formulization and overview of the cost performance evolutions of proton exchange membrane (PEM) fuel cell power generation along with load and time. For this purpose, electricity-cost ratio (ECR) is proposed as the measuring parameter for the cost performance and a two-constant cost model is proposed to concisely describe the cost characteristic of the power generation as the opposite of a multi-constant cost model. Combination of the two-constant cost model and the ideal cell model developed recently produces an inclusive ECR equation that has three analytical expressions and thus allows of straight overviews of the cost performance evolutions in the working zones of the cells. The applications to real cells confirm the validity of the equation for operation optimization and technique evaluation of PEM fuel cells. And more insights into the cost performance evolutions are inferred by means of the equation to help promote the commercialization of PEM fuel cells.展开更多
基金Supported by National Natural Science Foundation of China(Grant No51406148)National Science Technology Support Program of China(Grant No.2012BAA08B06)Postdoctoral Science Foundation o China(Grant No.2014M552444)
文摘Up to present, there have been no studies concerning the application of fluid-structure interaction（FSI） analysis to the lifetime estimation of multi-stage centrifugal compressors under dangerous unsteady aerodynamic excitations. In this paper, computational fluid dynamics（CFD） simulations of a three-stage natural gas pipeline centrifugal compressor are performed under near-choke and near-surge conditions, and the unsteady aerodynamic pressure acting on impeller blades are obtained. Then computational structural dynamics（CSD） analysis is conducted through a one-way coupling FSI model to predict alternating stresses in impeller blades. Finally, the compressor lifetime is estimated using the nominal stress approach. The FSI results show that the impellers of latter stages suffer larger fluctuation stresses but smaller mean stresses than those at preceding stages under near-choke and near-surge conditions. The most dangerous position in the compressor is found to be located near the leading edge of the last-stage impeller blade. Compressor lifetime estimation shows that the investigated compressor can run up to 102.7 h under the near-choke condition and 200.2 h under the near-surge condition. This study is expected to provide a scientific guidance for the operation safety of natural gas pipeline centrifugal compressors.
基金This work was supported by the National Basic Research 973 Program of China under Grant No. 2011CB302502, the National Natural Science Foundation of China under Grant No. 61379042, Huawei Research Program under Grant No. YB2013090048, and the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No. XDA06010401.
文摘As the scaling of applications increases, the demand of main memory capacity increases in order to serve large working set. It is difficult for DRAM （dynamic random access memory） based memory system to satisfy the memory capacity requirement due to its limited scalability and high energy consumption. Compared to DRAM, PCM （phase change memory） has better scalability, lower energy leakage, and non-volatility. PCM memory systems have become a hot topic of academic and industrial research. However, PCM technology has the following three drawbacks： long write latency, limited write endurance, and high write energy, which raises challenges to its adoption in practice. This paper surveys architectural research work to optimize PCM memory systems. First, this paper introduces the background of PCM. Then, it surveys research efforts on PCM memory systems in performance optimization, lifetime improving, and energy saving in detail, respectively. This paper also compares and summarizes these techniques from multiple dimensions. Finally, it concludes these optimization techniques and discusses possible research directions of PCM memory systems in future.
文摘针对大多数研究只分析了平面无线传感器网络第一个节点死亡(First Node Died Time,FNDT)网络寿命与延迟的情况,本文分析了网络全部节点死亡(All Node Died Time,ANDT)时网络寿命与延迟的情况.本文得到的相关工作如下:(1)分析得到了平面无线传感器网络全部节点死亡(All Node Died Time,ANDT)时网络寿命的计算方法;(2)给出了了网络从FNDT到ANDT过程网络延迟的变化规律与发展情况,以及计算方法;(3)提出了网络最大ANDT与延迟间的折中优化方法,从而得到网络性能优化时的节点发射半径以及节点调制级数的选取.本文分析结果较好的揭示了平面无线传感器网络ANDT与延迟的发展规律,并给出了提高网络性能的优化参数选取方法,可为传感器网络的设计、部署与优化提供较好的指导作用.
文摘This paper aims at formulization and overview of the cost performance evolutions of proton exchange membrane (PEM) fuel cell power generation along with load and time. For this purpose, electricity-cost ratio (ECR) is proposed as the measuring parameter for the cost performance and a two-constant cost model is proposed to concisely describe the cost characteristic of the power generation as the opposite of a multi-constant cost model. Combination of the two-constant cost model and the ideal cell model developed recently produces an inclusive ECR equation that has three analytical expressions and thus allows of straight overviews of the cost performance evolutions in the working zones of the cells. The applications to real cells confirm the validity of the equation for operation optimization and technique evaluation of PEM fuel cells. And more insights into the cost performance evolutions are inferred by means of the equation to help promote the commercialization of PEM fuel cells.
