基础频率响应的离散时间有理近似是构建基础振动分析的时域递归算法的起点,离散时间有理近似的稳定性和精度决定时域递归算法的稳定性和精度。该文采用双线性变换法从基础频响的连续时间有理近似获得离散时间有理近似,避免离散和连续时间频率相等情况下由于离散时间有理近似的周期性而产生的高频尾部丢失和混叠现象,保证离散和连续时间有理近似的稳定性和精度一致。基于部分分式展开,获得的离散时间有理近似分别实现为直接型和并联型时域递归公式。通过分析几个典型基础振动问题并与Wu-Lee集中参数模型结果进行对比验证了双线性变换的有效性。
Discrete-time rational approximation (DRA) of foundation frequency response is the first step for constructing various time-domain recursive evaluations (TDREs) in foundation vibration analysis. The stability and accuracy of DRA determine those of its TDREs. In this paper, the stability and identification of DRA are studied. The DRA can be obtained from a continuous-time rational approximation (CRA) of foundation frequency response. If the discrete-time frequency is set to equal the continuous-time one, the high-frequency loss and the aliasing may occur due to the periodic nature of DRA. To prevent this occuring, the bilinear transform is used in this paper, so that the stability and accuracy of the resulting DRA are identical with those of CRA. The resulting DRA is realized as the direct-form and parallel-form TDREs by partial-fraction expansion. The effectiveness of bilinear transform is verified by analyzing several typical foundation vibration problems using the resulting TDREs and comparing with the results of lumped-parameter models (LPMs).