The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands ins...The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands instead of uniform distribution chosen by Zeng is used. By comparing the results of the improved method with those of the original method of Zeng, it turns out that the improved method of Zeng given in this paper is more efficient.展开更多
To analyze the influence of time synchronization error,phase synchronization error,frequency synchronization error,internal delay of the transceiver system,and range error and angle error between the unit radars on th...To analyze the influence of time synchronization error,phase synchronization error,frequency synchronization error,internal delay of the transceiver system,and range error and angle error between the unit radars on the target detection performance,firstly,a spatial detection model of distributed high-frequency surface wave radar(distributed-HFSWR)is established in this paper.In this model,a method for accurate extraction of direct wave spectrum based on curve fitting is proposed to obtain accurate system internal delay and frequency synchronization error under complex electromagnetic environment background and low signal to noise ratio(SNR),and to compensate for the shift of range and Doppler frequency caused by time-frequency synchronization error.The direct wave component is extracted from the spectrum,the range estimation error and Doppler estimation error are reduced by the method of curve fitting,and the fitting accuracy of the parameters is improved.Then,the influence of frequency synchronization error on target range and radial Doppler velocity is quantitatively analyzed.The relationship between frequency synchronization error and radial Doppler velocity shift and range shift is given.Finally,the system synchronization parameters of the trial distributed-HFSWR are obtained by the proposed spectrum extraction method based on curve fitting,the experimental data is compensated to correct the shift of the target,and finally the correct target parameter information is obtained.Simulations and experimental results demonstrate the superiority and correctness of the proposed method,theoretical derivation and detection model proposed in this paper.展开更多
文中采用主曲线方法对X80高强管线钢环焊缝在韧脆转变区的断裂韧性分布规律进行了系统研究.根据美国材料试验协会(American Society for Testing and Materials,ASTM)标准ASTM E1921-97《过渡区铁素体钢参考温度T_(0)测定的标准试验方法...文中采用主曲线方法对X80高强管线钢环焊缝在韧脆转变区的断裂韧性分布规律进行了系统研究.根据美国材料试验协会(American Society for Testing and Materials,ASTM)标准ASTM E1921-97《过渡区铁素体钢参考温度T_(0)测定的标准试验方法》,开展不同温度条件下的断裂韧性测试,并通过多温度法计算了参考温度T_(0)及不同失效概率下的断裂韧性预测曲线.此外,结合经验公式将夏比冲击能量转化为对应温度下的断裂韧性,与直接通过断裂韧性试验获得的结果进行了对比分析.为验证方法的有效性,收集了实际管道建设中的198组断裂韧性试验数据,通过单温度法确定了T_(0).结果表明,单温度法确定的T_(0)值与试验结果具有良好的一致性.充分证明了主曲线方法在描述X80管道环焊缝韧脆转变行为中的有效性和适用性,为高强管线钢断裂韧性评估提供了理论依据,同时为工程实践中管道完整性评价提供了可靠的方法支持.展开更多
基金This paper was supported by the National Natural Science Foundation of China
文摘The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands instead of uniform distribution chosen by Zeng is used. By comparing the results of the improved method with those of the original method of Zeng, it turns out that the improved method of Zeng given in this paper is more efficient.
基金supported by the National Natural Science Foundation of China(61701140).
文摘To analyze the influence of time synchronization error,phase synchronization error,frequency synchronization error,internal delay of the transceiver system,and range error and angle error between the unit radars on the target detection performance,firstly,a spatial detection model of distributed high-frequency surface wave radar(distributed-HFSWR)is established in this paper.In this model,a method for accurate extraction of direct wave spectrum based on curve fitting is proposed to obtain accurate system internal delay and frequency synchronization error under complex electromagnetic environment background and low signal to noise ratio(SNR),and to compensate for the shift of range and Doppler frequency caused by time-frequency synchronization error.The direct wave component is extracted from the spectrum,the range estimation error and Doppler estimation error are reduced by the method of curve fitting,and the fitting accuracy of the parameters is improved.Then,the influence of frequency synchronization error on target range and radial Doppler velocity is quantitatively analyzed.The relationship between frequency synchronization error and radial Doppler velocity shift and range shift is given.Finally,the system synchronization parameters of the trial distributed-HFSWR are obtained by the proposed spectrum extraction method based on curve fitting,the experimental data is compensated to correct the shift of the target,and finally the correct target parameter information is obtained.Simulations and experimental results demonstrate the superiority and correctness of the proposed method,theoretical derivation and detection model proposed in this paper.
文摘文中采用主曲线方法对X80高强管线钢环焊缝在韧脆转变区的断裂韧性分布规律进行了系统研究.根据美国材料试验协会(American Society for Testing and Materials,ASTM)标准ASTM E1921-97《过渡区铁素体钢参考温度T_(0)测定的标准试验方法》,开展不同温度条件下的断裂韧性测试,并通过多温度法计算了参考温度T_(0)及不同失效概率下的断裂韧性预测曲线.此外,结合经验公式将夏比冲击能量转化为对应温度下的断裂韧性,与直接通过断裂韧性试验获得的结果进行了对比分析.为验证方法的有效性,收集了实际管道建设中的198组断裂韧性试验数据,通过单温度法确定了T_(0).结果表明,单温度法确定的T_(0)值与试验结果具有良好的一致性.充分证明了主曲线方法在描述X80管道环焊缝韧脆转变行为中的有效性和适用性,为高强管线钢断裂韧性评估提供了理论依据,同时为工程实践中管道完整性评价提供了可靠的方法支持.
