A novel yield criterion based on CPB06 considering anisotropic and tension-compression asymmetric behaviors of magnesium alloys was derived and proposed(called M_CPB06).This yield criterion can simultaneously predict ...A novel yield criterion based on CPB06 considering anisotropic and tension-compression asymmetric behaviors of magnesium alloys was derived and proposed(called M_CPB06).This yield criterion can simultaneously predict the yield stresses and the Lankford ratios at different angles(if any)under uniaxial tension,compression,equal-biaxial and equal-compression conditions.Then,in order to further describe the anisotropic strain-hardening characteristics of magnesium alloy,the proposed M_CPB06 criterion was further evolved to the M_CPB06ev model by expressing the parameters of the M_CPB06 model as functions of the plastic strain.As the model was developed,the stresses and Lankford ratios of AZ31B and ZK61M magnesium alloys at different angles under tensile,compressive and through-thickness compressive conditions were used to calibrate the M_CPB06/M_CPB06ev and the existing CPB06ex2 model.Calibration results reveal that compared with the CPB06ex2 yield criterion with equal quantity of coefficients,the M_CPB06 criterion exhibits certain advancement,and meanwhile the M_CPB06ev model can relatively accurately predict the change of the yield locus with increase of the plastic strain.Finally,the M_CPB06ev model was developed through UMAT in LS-DYNA.Finite element simulations using the subroutine were conducted on the specimens of different angles to the rolling direction under tension and compression.Simulation results were highly consistent with the experimental results,demonstrating a good reliability and accuracy of the developed subroutine.展开更多
In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well kn...In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well known <em>factorization method</em>, in which a computationally effective numerical scheme for the reconstruction of the shape of the scatterer is presented. This is possible, due to a <em>mixed reciprocity principle</em>, which renders the computation of the Green function at the background medium unnecessary. Moreover, to further refine our inversion algorithm, an efficient Tikhonov parameter choice technique, called <em>Improved Maximum Product Criterion</em> (IMPC) is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no <em>a priori</em> knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples.展开更多
针对弱连接条件下锁相环同步电压源变流器WG-VSC(weak grid connected voltage source converter)系统的暂态同步稳定问题,首先建立了适用于分析WG-VSC系统在严重电网故障期间的锁相环同步暂态稳定问题的等效转子摇摆方程模型。然后利...针对弱连接条件下锁相环同步电压源变流器WG-VSC(weak grid connected voltage source converter)系统的暂态同步稳定问题,首先建立了适用于分析WG-VSC系统在严重电网故障期间的锁相环同步暂态稳定问题的等效转子摇摆方程模型。然后利用改进的等面积定则I-EAC(improved equal area criterion)揭示了弱连接条件下VSC并网系统在严重电网故障下的暂态同步失稳机理;在此基础上,给出了系统在严重电网故障等大扰动下的保证系统暂态稳定的注入电流暂态稳定域的解析边界,为故障期间注入电流策略的制定提供了理论依据。最后,在PSCAD/EMTDC搭建了WG-VSC系统的详细开关模型,仿真结果验证了等效转子摇摆方程模型以及注入电流稳定域的有效性。展开更多
针对测量数据中粗差干扰及高程异常拟合方法选择较为困难的问题,结合格拉布斯(Grubbs)法判别粗差的原理,提出一种改进格拉布斯(Improved Grubbs,IGrubbs)结合局部加权线性回归(Local Weighted Linear Regression,LWLR)的拟合模型构建法...针对测量数据中粗差干扰及高程异常拟合方法选择较为困难的问题,结合格拉布斯(Grubbs)法判别粗差的原理,提出一种改进格拉布斯(Improved Grubbs,IGrubbs)结合局部加权线性回归(Local Weighted Linear Regression,LWLR)的拟合模型构建法。在原Grubbs法则的基础上,引入自适应迭代,在训练数据中,对粗差进行识别,并设定粗差剔除完成的指标参数,从而降低原方法中发生误判或漏判的概率,并利用局部加权线性回归法通过预处理后的训练样本数据来建立区域高程异常拟合模型。实验结果表明,相较于传统Grubbs法则,改进后的Grubbs法对于高程异常数据中的粗差剔除更为快速有效,且利用局部加权线性回归法所构建的区域高程异常拟合模型的预测精度及稳定性也得到一定程度的提高,对今后工程中的测高工作具备一定的参考意义。展开更多
基金Beijing Natural Science Foundation(No.L201010)the United Fund of Ministry of Education for Equipment Pre-Research(Grant No.6141A02033121)National Natural Science Foundation of China(Grant No.51975041).
文摘A novel yield criterion based on CPB06 considering anisotropic and tension-compression asymmetric behaviors of magnesium alloys was derived and proposed(called M_CPB06).This yield criterion can simultaneously predict the yield stresses and the Lankford ratios at different angles(if any)under uniaxial tension,compression,equal-biaxial and equal-compression conditions.Then,in order to further describe the anisotropic strain-hardening characteristics of magnesium alloy,the proposed M_CPB06 criterion was further evolved to the M_CPB06ev model by expressing the parameters of the M_CPB06 model as functions of the plastic strain.As the model was developed,the stresses and Lankford ratios of AZ31B and ZK61M magnesium alloys at different angles under tensile,compressive and through-thickness compressive conditions were used to calibrate the M_CPB06/M_CPB06ev and the existing CPB06ex2 model.Calibration results reveal that compared with the CPB06ex2 yield criterion with equal quantity of coefficients,the M_CPB06 criterion exhibits certain advancement,and meanwhile the M_CPB06ev model can relatively accurately predict the change of the yield locus with increase of the plastic strain.Finally,the M_CPB06ev model was developed through UMAT in LS-DYNA.Finite element simulations using the subroutine were conducted on the specimens of different angles to the rolling direction under tension and compression.Simulation results were highly consistent with the experimental results,demonstrating a good reliability and accuracy of the developed subroutine.
文摘In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well known <em>factorization method</em>, in which a computationally effective numerical scheme for the reconstruction of the shape of the scatterer is presented. This is possible, due to a <em>mixed reciprocity principle</em>, which renders the computation of the Green function at the background medium unnecessary. Moreover, to further refine our inversion algorithm, an efficient Tikhonov parameter choice technique, called <em>Improved Maximum Product Criterion</em> (IMPC) is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no <em>a priori</em> knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples.
文摘针对弱连接条件下锁相环同步电压源变流器WG-VSC(weak grid connected voltage source converter)系统的暂态同步稳定问题,首先建立了适用于分析WG-VSC系统在严重电网故障期间的锁相环同步暂态稳定问题的等效转子摇摆方程模型。然后利用改进的等面积定则I-EAC(improved equal area criterion)揭示了弱连接条件下VSC并网系统在严重电网故障下的暂态同步失稳机理;在此基础上,给出了系统在严重电网故障等大扰动下的保证系统暂态稳定的注入电流暂态稳定域的解析边界,为故障期间注入电流策略的制定提供了理论依据。最后,在PSCAD/EMTDC搭建了WG-VSC系统的详细开关模型,仿真结果验证了等效转子摇摆方程模型以及注入电流稳定域的有效性。
文摘针对测量数据中粗差干扰及高程异常拟合方法选择较为困难的问题,结合格拉布斯(Grubbs)法判别粗差的原理,提出一种改进格拉布斯(Improved Grubbs,IGrubbs)结合局部加权线性回归(Local Weighted Linear Regression,LWLR)的拟合模型构建法。在原Grubbs法则的基础上,引入自适应迭代,在训练数据中,对粗差进行识别,并设定粗差剔除完成的指标参数,从而降低原方法中发生误判或漏判的概率,并利用局部加权线性回归法通过预处理后的训练样本数据来建立区域高程异常拟合模型。实验结果表明,相较于传统Grubbs法则,改进后的Grubbs法对于高程异常数据中的粗差剔除更为快速有效,且利用局部加权线性回归法所构建的区域高程异常拟合模型的预测精度及稳定性也得到一定程度的提高,对今后工程中的测高工作具备一定的参考意义。
基金Projects(52222806, 52278216) supported by the National Natural Science Foundation of ChinaProject(2019JQ-481) supported by the Natural Science Foundation of Shaanxi Province, China。
