利用车载LiDAR点云数据提取城市道路规则多边形

随着自动驾驶高精地图的发展,准确高效地提取道路规则多边形成为必要。本文以苏州市某城市快速路为研究对象,通过使用徕卡车载激光移动测量系统获得城市道路点云数据,观察了解车载点云数据各类属性信息,根据观察结果组合利用点云数据高差、点云灰度差值、点云强度差值,在此基础上再利用网格密度法实现道路规则多边形的提取,然后通过对目标的矢量化得到三维矢量规则多边形。最后对提取的矢量化结果进行精度评定。试验结果表明：该方法在提取道路规则多边形方面能得到较好的结果且能满足高精地图需求。     

拖网选择性对鱼类表型性状的选择作用研究

参照渔业生物学、渔业资源解析学、数量遗传学等有关理论模型,并应用数值模拟方法,对长期选择性捕捞（重点为渔具选择性）是否参与造成了渔业资源的生物学变化（体长、性成熟等）进行某些基础性探索。设计了一个具有一定体长遗传特征的模拟鱼类种群,并利用一种具有固定选择性参数的拖网对其进行长期捕捞。结果表明,多年的持续的捕捞压力使得模拟种群中鱼类体长逐渐减小,减小的幅度随开发率的增大而增大,而终止捕捞后种群的体长并没有发生恢复的迹象,说明这种变化很可能伴随种群遗传的变化,具有自然不可逆性。     

Two-dimensional scour simulations based on coupled model of shallow water equations and sediment transport on unstructured meshes

A two-dimensional scour model based on coupled system of shallow water equations (SWEs) and sediment transport on unstructured mesh is developed. The coupled system of hydrodynamic and morphodynamic equations is solved by finite volume method using Godunov scheme. Roe's approximate Riemann solver is used to calculate the inviscid fluxes. The use of unstructured mesh makes the model applicable to complex domains. However, it is difficult to evaluate the eigenvalues and eigenvectors of the Jacobian matrix in the global coordinate. The method proposed herein to deal with this difficulty is to transform the system into the local coordinate with one of the axes in the same direction as the interface outward normal vector. In the local coordinate system, the Jacobian matrix is simplified and the eigenvalues are analyzed using asymptotic method. Regular expansion breaks down when the flow is near critical. Uniformity of the expansion is achieved by changing the scales. Rotational invariance theorem is used to relate the interfacial fluxes in the global and local coordinate systems. Special treatment of the source term on unstructured grid makes the scheme stable and physically balanced (both mass and momentum). The method proposed in this paper for the eigen-system is very efficient comparing to iterative numerical methods. Results from the test cases show good agreement with the experiments.     

The effects of resolving the Canadian Arctic Archipelago in a finite element sea ice model

Though narrow straits may have a strong influence on the large-scale sea ice mass balance, they are often crudely represented in coarse resolution sea ice models. Unstructured meshes, with their natural ability to fit boundaries and locally increase the mesh resolution, propose an alternative framework to capture the complex oceanic areas formed by coasts and islands. In this paper, we develop a finite element sea ice model to investigate the sensitivity of the Arctic sea ice cover features to the resolution of the narrow straits constituting the Canadian Arctic Archipelago. The model is a two-level dynamic-thermodynamic sea ice model, including a viscous-plastic rheology. It is run over 1979–2005, forced by daily NCEP/NCAR reanalysis data. Confronting qualitatively numerical experiments with observations shows a good agreement with satellite and buoys measurements. Due to its simple representation of the oceanic interactions, the model overestimates the sea ice extent during winter in the southernmost parts of the Arctic, while the Baffin Bay and Kara Sea remain ice-covered during summer. In order to isolate the benefits from resolving the Canadian Arctic Archipelago, a numerical experiment is performed where we artificially close the archipelago. Focusing on the large-scale sea ice thickness pattern, no significant change is found in our model, except in the close surroundings of the archipelago. However, the local and short-term influences of the ice exchanges are nonnegligible. In particular, we show that the ice volume associated to the Canadian Arctic Archipelago represents 10% of the Northern Hemisphere sea ice volume and that the annual mean ice export towards Baffin Bay amounts to 125 km³ yr⁻¹, which may play an important role on the convective overturning in the Labrador Sea.     

Arbitrary Lagrangian–Eulerian method for large‐strain consolidation problems

In this paper, an arbitrary Lagrangian–Eulerian (ALE) method is generalized to solve consolidation problems involving large deformation. Special issues such as pore‐water pressure convection, permeability and void ratio updates due to rotation and convection, mesh refinement and equilibrium checks are discussed. A simple and effective mesh refinement scheme is presented for the ALE method. The ALE method as well as an updated‐Lagrangian method is then used to solve some classical consolidation problems involving large deformations with different constitutive laws. The results clearly show the advantage and efficiency of the ALE method for these examples. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulating the hydraulic characteristics of the lower Yellow River by the finite‐volume technique

The finite‐volume technique is used to solve the two‐dimensional shallow‐water equations on unstructured mesh consisting of quadrilateral elements. In this paper the algorithm of the finite‐volume method is discussed in detail and particular attention is paid to accurately representing the complex irregular computational domain. The lower Yellow River reach from Huayuankou to Jiahetan is a typical meandering river. The generation of the computational mesh, which is used to simulate the flood, is affected by the distribution of water works in the river channel. The spatial information about the two Yellow River levee, the protecting dykes, and those roads that are obviously higher than the ground, need to be used to generate the computational mesh. As a result these dykes and roads locate the element interfaces of the computational mesh. In the model the finite‐volume method is used to solve the shallow‐wave equations, and the Osher scheme of the empirical function is used to calculate the flux through the interface between the neighbouring elements. The finite‐volume method has the advantage of using computational domain with complex geometry, and the Osher scheme is a method based on characteristic theory and is a monotone upwind numerical scheme with high resolution. The flood event with peak discharge of 15 300 m³/s, occurring in the period from 30 July to 10 August 1982, is simulated. The estimated result indicates that the simulation method is good for routing the flood in a region with complex geometry. Copyright © 2002 John Wiley & Sons, Ltd.     

内陆单斜构造内咸水入侵淡水含水层三维数值模拟：——以山西柳林？…

本文建立了内陆单斜构造内咸水入侵淡水含水层的三维可混溶溶质运移模型。同时,为了尽可能提高模拟精度,还建立了区域二维水流模型和水质模型,为三维模型提供边界条件。模型应用于描述柳林电厂水源地咸－淡水界面运移特征,模拟效果良好,还据此预报了咸水入侵的可能性并探讨了淡水流的强弱对咸－淡水界面运移的影响。     

多边形有限单元形函数的几何构造方法

根据非均质材料的细观结构,划分多边形的计算网格。采用多边形单元进行有限元分析,实现了基于材料真实结构的数值模拟。给出了多边形有限单元形函数的几何构造方法,构造了一个辅助多边形,采用散度定理推导出多边形单元形函数的表达式。分析总结了多边形Wachspress插值、Laplace插值和平均值插值的构造方法和性质。     

Numerical Prediction of Hydrodynamic Forces on A Ship Passing Through A Lock

While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the ship may be remarkable, which may have an adverse effect on navigation safety. However, the complicated hydrodynamics is not yet fully understood. This paper focuses on the hydrodynamic forces acting on a ship passing through a lock. The unsteady viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k?ε turbulence model. User-defined function (UDF) is compiled to define the ship motion. Meanwhile, the grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Numerical study is carried out for a bulk carrier ship passing through the Pierre Vandamme Lock in Zeebrugge at the model scale. The proposed method is validated by comparing the numerical results with the data of captive model tests. By analyzing the numerical results obtained at different speeds, water depths and eccentricities, the influences of speed, water depth and eccentricity on the hydrodynamic forces are illustrated. The numerical method proposed in this paper can qualitatively predict the ship-lock hydrodynamic interaction. It can provide certain guidance on the manoeuvring and control of ships passing through a lock.     

Numerical prediction of hydrodynamic forces on a ship passing through a lock

While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the ship may be remarkable, which may have an adverse effect on navigation safety. However, the complicated hydrodynamics is not yet fully understood. This paper focuses on the hydrodynamic forces acting on a ship passing through a lock. The unsteady viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k-ε turbulence model. User-defined function(UDF) is compiled to define the ship motion. Meanwhile, the grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Numerical study is carried out for a bulk carrier ship passing through the Pierre Vandamme Lock in Zeebrugge at the model scale. The proposed method is validated by comparing the numerical results with the data of captive model tests. By analyzing the numerical results obtained at different speeds, water depths and eccentricities, the influences of speed, water depth and eccentricity on the hydrodynamic forces are illustrated. The numerical method proposed in this paper can qualitatively predict the ship-lock hydrodynamic interaction. It can provide certain guidance on the manoeuvring and control of ships passing through a lock.