Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the fl...Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the floating body＇s inner domain, an auxiliary equation is obtained by applying a Green function which satisfies the solid surface condition. Then, the auxiliary equation and the velocity potential equation are combined in the fluid domain to remove the solid angle coefficient and the singularity of the double layer potentials in the integral equation. Thus, a new velocity potential integral equation is obtained. The new equation is extended to the inner domain to reheve the irregular frequency effects; on the basis of the order analysis, the comparison is made about the contribution of all integral terms with the result in the second-order tow-frequency problem; the higher-order boundary element method based on NURBS is apphed to calculate the geometric position and velocity potentials; the slow drift motions are calculated by the spectrum analysis method. Removing the solid angle coefficient can apply NURBS technology to the hydrodynamic calculation of floating bodies with complex surfaces, and the extended boundary integral method can reduce the irregular frequency effects. Order analysis shows that free surface integral can be neglected, and the numerical results can also prove the correctness of order analysis. The results of second-order low-frequency forces and slow drift motions and the comparison with the results from references show that the application of the NURBS technology to the second-order low-frequency problem is of high efficiency and credible results.展开更多
为应对复杂多变的未知环境对海洋航行器运动预测所造成的挑战,提出了一种融合级联滤波与误差触发支持向量回归(error-triggered support vector regression,ETSVR)的智能预测系统。首先,该系统基于移动平均滤波对原始数据进行预处理,以...为应对复杂多变的未知环境对海洋航行器运动预测所造成的挑战,提出了一种融合级联滤波与误差触发支持向量回归(error-triggered support vector regression,ETSVR)的智能预测系统。首先,该系统基于移动平均滤波对原始数据进行预处理,以剔除异常值并抑制高频噪声,为后续预测提供高质量的数据集;其次,引入二阶扩展卡尔曼滤波对系统状态进行精确估计,进一步增强数据的平稳度和可靠性;最后,设计ETSVR算法对处理后的高质量数据集进行学习,以构建海洋航行器的运动预测模型,实现精准运动预测,并借助误差触发机制提升系统的实时性与计算效率。基于湖试数据的实验结果表明,所提出的智能运动预测系统在多项误差指标上均显著优于传统的线性回归算法。例如,在侧向速度预测中,均方误差较线性回归算法降低约53.2%;在转艏角速度预测中,最大误差减少了约58.2%。这些结果表明,提出的级联滤波与ETSVR算法相结合的智能预测系统,能够显著提升海洋航行器在复杂未知环境中的运动预测精度,具有较好的应用前景和重要的研究意义。展开更多
Based on the loading conditions of engine, applying difference method to solve the hydrodynamic lubrication equation of piston skirt movement, the force acting on piston skirt and the moment on wrist pin were obtained...Based on the loading conditions of engine, applying difference method to solve the hydrodynamic lubrication equation of piston skirt movement, the force acting on piston skirt and the moment on wrist pin were obtained. A computer program for simulating the piston second order motion was conducted to calculate the lateral motion of the upper part and the bottom part of piston skirts of the engine of automotive model CA1091. From the simulated result, the maximal impacting phase and the maximal impacting region of the piston were obtained. The result can be used for designing engine, diagnosing the noise of piston knocking cylinder wall and explaining many practical fault phenomena in theory.展开更多
文摘Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the floating body＇s inner domain, an auxiliary equation is obtained by applying a Green function which satisfies the solid surface condition. Then, the auxiliary equation and the velocity potential equation are combined in the fluid domain to remove the solid angle coefficient and the singularity of the double layer potentials in the integral equation. Thus, a new velocity potential integral equation is obtained. The new equation is extended to the inner domain to reheve the irregular frequency effects; on the basis of the order analysis, the comparison is made about the contribution of all integral terms with the result in the second-order tow-frequency problem; the higher-order boundary element method based on NURBS is apphed to calculate the geometric position and velocity potentials; the slow drift motions are calculated by the spectrum analysis method. Removing the solid angle coefficient can apply NURBS technology to the hydrodynamic calculation of floating bodies with complex surfaces, and the extended boundary integral method can reduce the irregular frequency effects. Order analysis shows that free surface integral can be neglected, and the numerical results can also prove the correctness of order analysis. The results of second-order low-frequency forces and slow drift motions and the comparison with the results from references show that the application of the NURBS technology to the second-order low-frequency problem is of high efficiency and credible results.
文摘为应对复杂多变的未知环境对海洋航行器运动预测所造成的挑战,提出了一种融合级联滤波与误差触发支持向量回归(error-triggered support vector regression,ETSVR)的智能预测系统。首先,该系统基于移动平均滤波对原始数据进行预处理,以剔除异常值并抑制高频噪声,为后续预测提供高质量的数据集;其次,引入二阶扩展卡尔曼滤波对系统状态进行精确估计,进一步增强数据的平稳度和可靠性;最后,设计ETSVR算法对处理后的高质量数据集进行学习,以构建海洋航行器的运动预测模型,实现精准运动预测,并借助误差触发机制提升系统的实时性与计算效率。基于湖试数据的实验结果表明,所提出的智能运动预测系统在多项误差指标上均显著优于传统的线性回归算法。例如,在侧向速度预测中,均方误差较线性回归算法降低约53.2%;在转艏角速度预测中,最大误差减少了约58.2%。这些结果表明,提出的级联滤波与ETSVR算法相结合的智能预测系统,能够显著提升海洋航行器在复杂未知环境中的运动预测精度,具有较好的应用前景和重要的研究意义。
文摘Based on the loading conditions of engine, applying difference method to solve the hydrodynamic lubrication equation of piston skirt movement, the force acting on piston skirt and the moment on wrist pin were obtained. A computer program for simulating the piston second order motion was conducted to calculate the lateral motion of the upper part and the bottom part of piston skirts of the engine of automotive model CA1091. From the simulated result, the maximal impacting phase and the maximal impacting region of the piston were obtained. The result can be used for designing engine, diagnosing the noise of piston knocking cylinder wall and explaining many practical fault phenomena in theory.
