As a reliable alternative option for traditional steel catenary risers (SCRs), steep wave risers (SWRs) have been widely applied to deepwater oil and gas production. However, the nonlinear dynamic analysis of SWRs is more complicated than that of traditional SCRs due to their special configuration and significant geometric nonlinearity. Moreover, SWRs are highly susceptible to fatigue failure under the combined excitation of irregular waves and top floater motions (TFMs). In this study, considering irregular waves and TFMs, a numerical SWR model with an internal flow is constructed based on the slender rod model and finite element method. The Newmark-β method is adopted to solve the dynamic behavior of SWR. Moreover, the Palmgren-Miner rule, a specified S-N curve, and rainflow counting method are applied to estimate the fatigue damage. An efficient numerical computation procedure, i.e., DRSWR, is programmed with MATLAB in this study. Calculation results are compared with those of OrcaFlex to verify the accuracy of the DRSWR. The nonlinear dynamic response and fatigue damage of an SWR under the combined excitation of irregular waves and TFMs are obtained, and a comprehensive parametric analysis is then conducted. The analysis results show that the buoyancy section undergoes the highest level of stress and fatigue damage under the combined excitation of irregular waves and TFMs. An internal flow with high velocity and high density produces a high level of fatigue damage. The buoyancy factor and length of the buoyancy section should be set moderately to reconcile the reduction of the top tension with increased fatigue life. These results are expected to provide some reference significance for the engineering design of SWR.

作为传统钢悬链线立管（SCR）的可靠替代方案，陡波立管（SWR）已广泛应用于深水油气生产。然而，由于 SWR 的特殊配置和显着的几何非线性，其非线性动态分析比传统 SCR 更为复杂。此外，在不规则波浪和顶部漂浮物运动 (TFM) 的联合激励下，SWR 极易发生疲劳失效。在这项研究中，考虑不规则波浪和TFM，基于细杆模型和有限元方法构建了具有内部流动的数值SWR模型。采用Newmark-β方法求解SWR的动态行为。此外，还应用了 Palmgren-Miner 规则、指定的 SN 曲线和雨流计数方法来估计疲劳损伤。IE, DRSWR, 在本研究中用 MATLAB 编程。将计算结果与 OrcaFlex 的结果进行比较，以验证 DRSWR 的准确性。获得了SWR在不规则波和TFMs联合激励下的非线性动力响应和疲劳损伤，并进行了综合参数分析。分析结果表明，在不规则波和TFMs联合激励下，浮力截面承受的应力和疲劳损伤程度最高。具有高速和高密度的内部流动会产生高水平的疲劳损伤。浮力段的浮力系数和长度应适当设置，以平衡顶部张力的降低和疲劳寿命的增加。这些结果有望为SWR的工程设计提供一定的参考意义。