The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and verti...The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.展开更多
This article concerns a coupled LMIs approach to delay-dependent observer-based output feedback stabilizing controller design for linear continuous-time systems with multiple state delays. The advantage of our propose...This article concerns a coupled LMIs approach to delay-dependent observer-based output feedback stabilizing controller design for linear continuous-time systems with multiple state delays. The advantage of our proposed delay-dependent coupled LMIs criterion lies in that: ( 1 ) it can optimize one of multiple time delays with others selected properly, and at the same time, the feedback-gain and observer-gain can be obtained, respectively. (2) it is less conservative than the existing delay-independent ones in the literature. Algorithm to solve the coupled LMIs is also given. Numerical examples illustrate the effectiveness of our method. Keywords Delay-dependent criterion - Time-delay system - Multiple time-delay - Observer-based controller - Linear matrixinequality (LMI)展开更多
The complexity and various intentions or functions of literary translation cause different literary works.The general criteria tohelp evaluate and guide translators to strive for a good translation could be the tradit...The complexity and various intentions or functions of literary translation cause different literary works.The general criteria tohelp evaluate and guide translators to strive for a good translation could be the traditional three principles,these are faithfulness,fluencyand elegance,but it is also feasible to apply some other subordinate criteria to translate or analyze different literary works.The paper fo-cuses on the analysis of multiplicity and complementary of translation criterion on the poem translation,makes comparison and evalua-tion of Gu Zhengkun's Ode to the West Wind(stanza 4&5) with Zha Liangzheng's version,and proves that flexible application of thistranslation criterion makes the translated version truly different.展开更多
多直流送端系统内某一直流线路发生闭锁故障后,可以通过对其他非故障直流进行紧急功率支援(emergency DC power support,EDCPS)控制来提升系统受扰后的稳定性。如何有效量化EDCPS对系统稳定性的改善效果,从而提高安稳控制的效率,目前缺...多直流送端系统内某一直流线路发生闭锁故障后,可以通过对其他非故障直流进行紧急功率支援(emergency DC power support,EDCPS)控制来提升系统受扰后的稳定性。如何有效量化EDCPS对系统稳定性的改善效果,从而提高安稳控制的效率,目前缺少相应的指标;现有研究也尚未解决如何利用EDCPS最大程度提升多直流综合送出能力的问题。应用扩展等面积法(extended equal area criterion,EEAC)定量分析了EDCPS提升多直流送端系统暂态稳定性的机理;以两送出直流系统为例,推导了基于EEAC的暂态稳定裕度η对EDCPS的灵敏度公式;在此基础上,提出一种在不增加相关设备投入的前提下利用系统中现有稳控措施并结合暂态稳定裕度灵敏度的多直流送出能力提升控制方法,通过计算备选直流的暂态稳定裕度灵敏度,可以完整反映系统在遭受大扰动后的动态特性以及定量评估EDCPS对系统受扰后稳定性的改善效果,避免过去仅凭运行人员经验选取支援直流的问题,提高计算效率;最后,选取西北电网实际算例对所提出的多直流送出能力提升控制方法有效性进行仿真验证,以期为从事交直流混联电力系统稳定性分析与控制的学者和工程师们提供有益的参考。展开更多
Distributed radio access network (DRAN) is a novel wireless access architecture and can solve the problem of the available spectrum scarcity in wireless communications. In this paper, we investigate resource allocatio...Distributed radio access network (DRAN) is a novel wireless access architecture and can solve the problem of the available spectrum scarcity in wireless communications. In this paper, we investigate resource allocation for the downlink of OFDMA DRAN. Unlike previous exclusive criterion based algorithms that allocate each subcarrier to only one user in the system, the proposed algorithms are based on shared criterion that allow each subcarrier to be allocated to multiple users through different antennas and to only one user through same antenna. First, an adaptive resource allocation algorithm based on shared criterion is proposed to maximize total system rate under each user's minimal rate and each antenna's maximal power constraints. Then we improve the above algorithm by considering the influence of the resource allocation scheme on single user. The simulation results show that the shared criterion based algorithm provide much higher total system rate than that of the exclusive criterion based algorithm at the expense of the outage performance and the fairness, while the improved algorithm based on shared criterion can achieve a good tradeoff performance.展开更多
直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得...直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得现有的暂态电压评估方法难以准确评估直流系统的暂态电压问题。为此,基于现有的多二元表判据和直流系统暂态恢复特性,提出了两阶段暂态电压评估方法。首先,分析了直流系统的暂态电压恢复特性和现有多二元表在直流系统中的应用局限。其次,基于不同稳定性水平赋予不同权重的思想,提出两阶段暂态电压评估方法,结合直流控制参数和故障严重程度等信息,实现对暂态电压稳定性的评估。最后,基于双直流馈入系统和修改后含直流的IEEE 3机9节点系统验证两阶段暂态电压评估方法对直流系统的适用性,结果表明所提方法可以实现对直流受端系统暂态电压稳定的准确评估。展开更多
In this paper, we obtain the exact computation formulae to determine the stability of a multiple limit cycle with the third or fourth order degenerations. We employ the method of computing the expansion of the Poincar...In this paper, we obtain the exact computation formulae to determine the stability of a multiple limit cycle with the third or fourth order degenerations. We employ the method of computing the expansion of the Poincar′e map around the closed orbit using 'normal bundle' coordinates parameterized by time variable in a neighborhood of the closed orbit. An example is given to show the feasibility of our results.展开更多
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51874351,51474251)Hunan Provincial Innovation Foundation For Postgraduate,China(CX2018B047)the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University,China(CSUZC201923).
文摘The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.
文摘This article concerns a coupled LMIs approach to delay-dependent observer-based output feedback stabilizing controller design for linear continuous-time systems with multiple state delays. The advantage of our proposed delay-dependent coupled LMIs criterion lies in that: ( 1 ) it can optimize one of multiple time delays with others selected properly, and at the same time, the feedback-gain and observer-gain can be obtained, respectively. (2) it is less conservative than the existing delay-independent ones in the literature. Algorithm to solve the coupled LMIs is also given. Numerical examples illustrate the effectiveness of our method. Keywords Delay-dependent criterion - Time-delay system - Multiple time-delay - Observer-based controller - Linear matrixinequality (LMI)
文摘The complexity and various intentions or functions of literary translation cause different literary works.The general criteria tohelp evaluate and guide translators to strive for a good translation could be the traditional three principles,these are faithfulness,fluencyand elegance,but it is also feasible to apply some other subordinate criteria to translate or analyze different literary works.The paper fo-cuses on the analysis of multiplicity and complementary of translation criterion on the poem translation,makes comparison and evalua-tion of Gu Zhengkun's Ode to the West Wind(stanza 4&5) with Zha Liangzheng's version,and proves that flexible application of thistranslation criterion makes the translated version truly different.
文摘多直流送端系统内某一直流线路发生闭锁故障后,可以通过对其他非故障直流进行紧急功率支援(emergency DC power support,EDCPS)控制来提升系统受扰后的稳定性。如何有效量化EDCPS对系统稳定性的改善效果,从而提高安稳控制的效率,目前缺少相应的指标;现有研究也尚未解决如何利用EDCPS最大程度提升多直流综合送出能力的问题。应用扩展等面积法(extended equal area criterion,EEAC)定量分析了EDCPS提升多直流送端系统暂态稳定性的机理;以两送出直流系统为例,推导了基于EEAC的暂态稳定裕度η对EDCPS的灵敏度公式;在此基础上,提出一种在不增加相关设备投入的前提下利用系统中现有稳控措施并结合暂态稳定裕度灵敏度的多直流送出能力提升控制方法,通过计算备选直流的暂态稳定裕度灵敏度,可以完整反映系统在遭受大扰动后的动态特性以及定量评估EDCPS对系统受扰后稳定性的改善效果,避免过去仅凭运行人员经验选取支援直流的问题,提高计算效率;最后,选取西北电网实际算例对所提出的多直流送出能力提升控制方法有效性进行仿真验证,以期为从事交直流混联电力系统稳定性分析与控制的学者和工程师们提供有益的参考。
文摘Distributed radio access network (DRAN) is a novel wireless access architecture and can solve the problem of the available spectrum scarcity in wireless communications. In this paper, we investigate resource allocation for the downlink of OFDMA DRAN. Unlike previous exclusive criterion based algorithms that allocate each subcarrier to only one user in the system, the proposed algorithms are based on shared criterion that allow each subcarrier to be allocated to multiple users through different antennas and to only one user through same antenna. First, an adaptive resource allocation algorithm based on shared criterion is proposed to maximize total system rate under each user's minimal rate and each antenna's maximal power constraints. Then we improve the above algorithm by considering the influence of the resource allocation scheme on single user. The simulation results show that the shared criterion based algorithm provide much higher total system rate than that of the exclusive criterion based algorithm at the expense of the outage performance and the fairness, while the improved algorithm based on shared criterion can achieve a good tradeoff performance.
文摘直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得现有的暂态电压评估方法难以准确评估直流系统的暂态电压问题。为此,基于现有的多二元表判据和直流系统暂态恢复特性,提出了两阶段暂态电压评估方法。首先,分析了直流系统的暂态电压恢复特性和现有多二元表在直流系统中的应用局限。其次,基于不同稳定性水平赋予不同权重的思想,提出两阶段暂态电压评估方法,结合直流控制参数和故障严重程度等信息,实现对暂态电压稳定性的评估。最后,基于双直流馈入系统和修改后含直流的IEEE 3机9节点系统验证两阶段暂态电压评估方法对直流系统的适用性,结果表明所提方法可以实现对直流受端系统暂态电压稳定的准确评估。
基金Supported by the Fundamental Research Funds for the Central Universities
文摘In this paper, we obtain the exact computation formulae to determine the stability of a multiple limit cycle with the third or fourth order degenerations. We employ the method of computing the expansion of the Poincar′e map around the closed orbit using 'normal bundle' coordinates parameterized by time variable in a neighborhood of the closed orbit. An example is given to show the feasibility of our results.
