SARS与COVID-19时空传播差异性及影响因素分析     

崔明洁  姚霞  方昊然  张杨成思  杨德刚  裴韬 《地球信息科学学报》2021,23(11):1910-1923

SARS和COVID-19的暴发对我国公众健康、社会经济等造成了严重影响,为揭示呼吸道烈性传染病的时空传播的共性规律和差异特征及背后原因,运用时空统计方法,系统分析并对比了SARS与COVID-19的时空传播差异性特征,并结合病毒本身传播特性及交通、温度等因子进行原因分析。研究表明：① 时间序列上,SARS从发病初始到结束经历了2个阶段,即上升期-平缓期,COVID-19经历了3个阶段,即上升期-急剧上升期-缓升期。② 空间传播模式上,COVID-19传播强度及传播范围大于SARS,且COVID-19的整体连通性较大,各省份与病毒暴发地的联系更为紧密;SARS和COVID-19的传播都存在明显的空间聚集性特征;二者均以邻近传播、远距离飞跃式为主,且SARS存在中次级传播中心,COVID-19扩散中心未发生转移。③ 空间传播方向上,SARS以北京市、香港特别行政区、广东省为中心,空间传播方向性更强,COVID-19仅以湖北省为中心向外扩散。④ 空间传播速度上,SARS各省份首例病例传播时间跨度较大,COVID-19各个省份首例病例传播时间大致以胡焕庸线为分界线,呈现出“东快西慢”的现象,传播时间跨度较短。⑤ R0是造成SARS和COVID-19空间传播范围与空间传播速度差异的主要原因;SARS和COVID-19病毒温度适宜性有所差异,但在温度接近的区域均发生了空间聚集性传播和邻近区域传播;除病毒本身传播能力、温度影响外,交通是影响SARS和COVID-19空间远距离飞跃式传播的主要原因,二者空间传播速度均与路网密度呈负相关关系。  相似文献   

Numerical and experimental analysis of the static behavior of highly deformed risers     

S.T. Santillan 《Ocean Engineering》2011,38(13):1397-1402

This paper models a slender, flexible structure used as a drill string or riser in the offshore oil and gas industry that connects the well-head with a floating control vessel. These systems are used in deep-water drilling applications and present considerable design challenges due to their extreme flexibility and susceptibility to buckling and vibration. Two typical configurations are used (Bai and Bai, 2005), with a common feature involving the attachment of a buoy designed to relieve some of the axial forces acting on the riser, especially at the attachment points. Previous work by the authors studied numerical results of small-amplitude vibrations and two other equilibrium configurations using parameter values that closely resemble the full-scale application (Santillan et al., 2008). Here, two new configurations are considered, and experiments are designed and conducted to verify these equilibrium results.  相似文献   

A variational formulation for three-dimensional analysis of extensible marine riser transporting fluid   总被引：1，自引：0，他引：1  

Chainarong Athisakul 《Ocean Engineering》2011,38(4):609-620

This paper presents a model formulation for static and dynamic analysis of three-dimensional extensible marine riser transporting fluid. A variational model formulation is developed based on the principle of virtual work-energy and the extensible elastica theory. The virtual work-energy functional is composed of the virtual strain energy due to axial stretching, bending, and torsion and the virtual work done by the external and internal fluid. The governing dynamic equilibrium equations are derived in the Cartesian coordinate. The finite element method is used to obtain the numerical solutions. The numerical examples are provided to demonstrate interesting effects of fluid transportation and axial deformation on large displacements and dynamic properties of the three-dimensional extensible marine riser.  相似文献   

Buckling of cross-ply cylinders under hydrostatic pressure considering pressure stiffness     

Izzet U. Cagdas  Sarp Adali 《Ocean Engineering》2011,38(4):559-569

Buckling behavior of cross-ply cylinders under hydrostatic pressure is investigated using a semi-analytical finite element based on a consistent first order shear deformable shell theory. Potential loss due to external pressure, also called pressure stiffness (PS) is taken into account by making use of Koiter's related energy expression. A number of verification problems are solved and the numerical results are compared with the analytical results available in the literature and excellent agreement is observed. New numerical results are presented to assess the effect of PS on buckling due to hydrostatic pressure. It is shown that PS causes a decrease in the buckling load and this decrease depends on the size of the cylinder and the material. Also, issues related to thickness optimization are examined and optimal lamina thicknesses are determined for a number of cases with and without PS taken into account.  相似文献   

A two dimensional hydrodynamic and sediment transport model for dam break based on finite volume method with quadtree grid     

Mingliang Zhang  W.M. Wu 《Applied Ocean Research》2011,33(4):297-308

This study aims to develop a robust, accurate and computationally efficient hydrodynamic and sediment transport model for dam break flows. The two dimensional shallow water equations are resolved based on the finite volume method with an unstructured quadtree mesh. The sediment transport and bed evolution modules are coupled with hydrodynamic module to predict simultaneously the hydrodynamics, sediment concentrations and morphological changes. The interface flux is computed by the HLL approximate Riemann solver with second order accuracy. The effects of pressure and gravity are included in source term in this model, which can simplify the computation and eliminate numerical imbalance between source and flux terms. For dam break flows occurring in complicated geometries, the quadtree rectangular mesh is used to refine the interesting area and important part. The model is first verified against results from laboratory experiments, existing numerical models and real life case. It is then used to simulate dam break flows over a mobile bed to investigate the bed evolution. The results are compared with experimental data and field data with good agreement. The method is simple, efficient, and conservative. It shows promise for handling hydrodynamic simulation and sediment transport for a wide range of dam break flows.  相似文献   

基于竞争力评价的区域旅游产业发展差异——以中国东部沿海三大旅游圈为例   总被引：2，自引：1，他引：1  

汪德根  陈田 《地理科学进展》2011,30(2):249-256

通过建构区域旅游竞争力评价三级指标体系,运用层次分析法和聚类分析法,测度和分析东部沿海三大旅游圈的旅游竞争力,并采用锡尔I(O)系数方法对旅游竞争力水平的差异进行分解,通过市场、效益、贡献、资源、设施、人才、经济、交通和环境等9个细分指标揭示东部沿海三大旅游圈旅游产业发展水平的差异,旨在从不同侧面进一步认识东部沿海旅游...  相似文献   

An FEM/VOF hybrid formulation for fracture grouting modelling     

《Computers and Geotechnics》2014

A numerical model using a hybrid formulation of a finite element method (FEM) coupled with the volume of fluid (VOF) technique to simulate the fracture grouting processes in soils is described. The numerical model considered the couplings of the stress distribution, with two-phase fluid flows, and the mesh element damage. The hardening of grout in soil is described by a time-dependent Young’s modulus and viscosity. Crack initiation, branching, propagation, and grout vein growth in homogeneous and heterogeneous soils can be numerically reproduced. Although the method is developed particularly for simulating fracture grouting, the processes of compaction grouting and permeation grouting can also be numerically simulated. Some grouting cases have been simulated with results similar to the experimental results. This further confirms the adequacy and the power of the numerical approach.  相似文献   

Prediction of pile settlement in an elastic soil     

《Computers and Geotechnics》2014

This paper presents a simple regression to predict settlement of a single floating pile supported by a homogeneous elastic soil and subjected to a vertical load. The regression, which is calibrated by a finite element model, allows the direct computation of the pile length required for serviceability limit state design of deep foundations.  相似文献   

Inverse calculation of in situ stress in rock mass using the Surrogate-Model Accelerated Random Search algorithm     

《Computers and Geotechnics》2014

A new approach is presented that incorporates the Surrogate Model Accelerated Random Search (SMARS) Algorithm to inversely determine the overall stress state in a rock mass based on sparse stress measurements. The SMARS algorithm relies on a random search component to maintain global search capabilities, while using the surrogate-model method to accelerate convergence to a solution estimate. Two examples sets are carried out in this presentation to display the utility of the proposed SMARS-based inverse characterization process. The first example set compares the SMARS algorithm with two other popular methods, namely a multiple linear regression analysis method and a neural network method, to estimate the in situ stress field for a simple numerically simulated test case. The results of the numerical testing verify that SMARS provides a relatively stable approach and gives rise to a relatively high accuracy and efficiency (i.e., with less computational expense) compared to the other contemporary approaches considered. Finally, an example is shown for utilizing the SMARS approach for in situ stress estimation based on an actual underground mine located in Pennsylvania. The SMARS results are shown to produce a realistic estimate of the distribution of stress within the area investigated, and overall, the approach has potential for practical use in realistic scenarios to efficiently and accurately estimate in situ stresses in rock mass.  相似文献   

Exact solution for the 1D transient response of saturated single-layer poroviscoelastic media     

《Computers and Geotechnics》2014

The basic equations for fluid-saturated porous media proposed by Biot are modified by replacing the classical linear elastic model of the solid skeleton with the Kelvin–Voigt model. Thus, the new theory can take into account the viscoelastic effect of the solid skeleton. After the establishment of appropriate boundary and initial conditions, a time-domain series solution for the transient response of a fluid-saturated single-layer poroviscoelastic medium is obtained by using the finite Fourier transform and the corresponding analytical inverse transform. Several numerical examples are provided to illustrate the validity of the exact solution and to investigate the influence of the viscosity coefficient, permeability coefficient, and load frequency on the transient response of a fluid-saturated single-layer poroviscoelastic medium.  相似文献