共查询到19条相似文献，搜索用时 125 毫秒
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针对半参数回归模型求解过程可能出现的法方程病态问题，提出了用岭估计原则改进半参数模型的求解。通过模拟算例将岭估计解法和其他方法进行了比较，结果表明，岭估计解法能较好地解决半参数回归模型求解过程中的病态问题。 相似文献
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不规则重磁测线网误差模型的约束最小二乘平差 总被引：5，自引：1，他引：5
传统实用的海洋重力、磁力测线网平差方法主要为规则测线网设计,并只就线偏差进行调整,用于处理航次数据之间的拼接时效果不理想。为了解决重磁测线数据拼接和建库工作中碰到的误差难以调平的问题,设计、建立了不规则海洋重磁测线网的任意复杂误差模型的最小二乘平差方法,将线偏差纳入到任意复杂(如非线性和周期性)的误差模型中,归纳出最小二乘条件方程系数矩阵的直接构制法。针对可能出现的解不稳定,放弃不易实用的权矩阵,引入两种解决方法:先验确定部分测线误差分布的固定测线法和视误差大小实施系数矩阵对角线微扰动的泛约束法。 相似文献
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以单位四元数描述遥感影像共线条件方程,建立基于单位四元数的光束法平差模型。针对共线条件方程的非线性问题,基于LM(Levenberg-Marquardt)方法解算单位四元数光束法平差模型,并引入丹麦法实现无人机影像外方位元素的抗差估计。基于仿真数据和无人机影像对该方法进行了验证,结果表明:与基于单位四元数的无初值依赖算法进行比较,LM方法具有与单位四元数法相当的可靠性;引入丹麦法方法后可消除粗差观测值对参数估计的不利影响,得到较高精度的外方位元素估值。 相似文献
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《Coastal Engineering》1999,37(2):123-148
The Navier–Stokes equations and the exact free surface boundary conditions are solved to simulate wave deformation and vortex generation in water waves propagating over a submerged dike. Incident waves are generated by a piston-type wavemaker set up in the computational domain. Numerical results are compared with experimental data in order to confirm the validity of the numerical model. The fast Fourier transform and a wave resolution technique are applied to decompose the transformed waves and the higher harmonics. Effects of different parameters on wave transformation and vortex generation are studied systematically. These parameters include the Ursell number, the Keulegan–Carpenter number, the water depth ratio, the Reynolds number, the length aspect ratio of the dike, and the type of dike. 相似文献
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本文从大气的运动方程出发,利用实测的台风气压场资料和变分调整的方法,计算了进入渤海的台风风场,模拟了台风的不对称结构。经实测资料捡验吻合程度较好。 相似文献
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The incompressible viscous shear flow past a circular cylinder is analyzed by solving two-dimensional Navier-Stokes equations and pressure Poisson equation using a finite difference method. The shear flow is calculated for Reynolds numbers from 80 to 1000, and shear parameters up to 0.25. The numerical results indicate that the vortex shedding persists at the shear parameters up to 0.25 for the present Reynolds number range. The Strouhal number and the drag coefficient decrease as the shear parameter increases. There is a transverse force acting from the high velocity side toward the low velocity side in the shear flow. 相似文献
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Enhancements for the Bragg reflection are introduced for three sets of 2D higher order Boussinesq equations to improve the prediction of the Bragg reflection. The extension of the approach to other sets of Boussinesq equations is discussed. The analytical solutions for the Bragg reflection over an infinite number of sinusoidal bars are derived for these Boussinesq models and compared to the exact theoretical solution in order to determine the optimized values of the parameters in the new enhancement terms. Numerical simulations are also carried out for the Bragg reflection over a finite number of sand bars and compared with corresponding measurements to validate the enhancements. Comparisons with other forms of Boussinesq models are made to discuss the applicability of different forms of Boussinesq models to rapidly varying topography with sand bars. The effects of the mild slope assumption on the prediction of Bragg reflection and of wave reflection on a plane self are also discussed. 相似文献
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Bragg Reflection of Waves by Different Shapes of Artificial Bars 总被引：3，自引：1，他引：3
Experiments are performed in a wave flume to demonstrate the Bragg reflection of linear gravity waves by artificial bars. Three different artificial bars with rectangular, triangular and rectified cosinoidal shapes are placed discretely on the seabed for measurement of the Bragg reflection. A series of experimental conditions including the number of bars, the pe-riodic bar spacing, the water depth and various wave conditions are tested. Key parameters influencing the Bragg resonances are investigated. The experimental data are compared with the values from both theoretical and numerical models. Some key parameters have proved to be effective in describing the primary resonances. Predictive equations of the charac-teristics for the Bragg reflection are proposed in this paper. 相似文献
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Uplift capacity of circular piles in sands is one important design parameter for many pile foundations supporting important structures subjected to tensile forces. Even though a number of formulas based on the limit equilibrium or semi-empirical methods are proposed to predict the uplift capacity of piles in sands, there is a major limitation of the methods in obtaining the accurate predictions. In this paper, the computational limit analysis is employed to investigate the uplift capacity of circular piles in sands. The effects of the important variables including pile length and diameter, soil friction angle and unit weight, and roughness factor at soil-pile interface are examined extensively using the dimensionless parameters while the predicted failure mechanisms associated with the parameters are discussed and compared. Approximate statistical design equations of the uplift capacity of circular piles in sands are developed based on the numerically derived solutions and the existing experimental data. It is found that the proposed design equations provide the most accurate prediction of the uplift capacity of circular piles in sands as compared to the existing formulas. 相似文献
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In the paper two types of numerical models – a lumped-parameter model and a high-resolution two-dimensional hydrodynamic model – are used to analyse the response of a system of partially-connected tidal basins to inhomogeneous open sea forcing. The equations of the lumped-parameter model, suitable for an arbitrary number of basins with sloping walls, are formulated based on one-dimensional continuity and momentum equations. Numerical solutions to the equations are thoroughly examined, showing the influence of inhomogeneous open sea forcing and of geometrical parameters of the basins on the tidal range and the water transport through the system, with particular emphasis given to inter-basin water exchange and cumulative water transport through basins boundaries. The results of the lumped-parameter model simulations for the tidal basins of the German Wadden Sea are successfully compared with the results of calculations with the two-dimensional hydrodynamic model, which is used to investigate in more detail circulation patterns and the influence of specific local features of inlet bathymetry on the hydrodynamic processes in the study area. The influence of wind on the basins response is discussed as well. 相似文献
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Based on the second-order random wave solutions of water wave equations in tinite water depth, statistical distributions of the depth-integrated local horizontal momentum components are derived by use of the characteristic function expansion method. The parameters involved in the distributions can be all detemained by the water depth and the wavenumber spectrum of ocean waves. As an illustrative example, a fully developed wind-generated sea is considered and the parameters are calculated for typical wind speeds and water depths by means of the Donelan and Pierson spectrum. The effects of nonlinearity and water depth on the distributions are also investigated. 相似文献