Open Boundary and Frictional Influences in 3D Tidal Models

Both 2D and 3D hydrodynamic models of the Irish Sea are used to examine the influence of the open boundary condition (OBC), bottom friction, and vertical eddy viscosity upon tidal currents in this region. Three eddy viscosity formulations, namely, a two-equation turbulence model, a simple flow-dependent eddy viscosity model, and a constant eddy viscosity of 1,000 cm2∕s, are considered. In an initial series of 2D calculations the influence of OBC and bottom friction coefficient (BFC) upon tidal elevations is examined with a view to determining an optimal value related to different OBCs, in the sense that the model can reproduce the extensive data set of elevations in the region. In subsequent 3D calculations in which bottom friction is related to the depth-mean current, the influence of vertical eddy viscosity upon computed currents is examined using identical BFCs to those used in the 2D model. These calculations clearly show the performance of different vertical eddy viscosity formulations in a 3D model. Calculations are also carried out using a single point model in the vertical. Results from the calculations and comparisons with data show that the optimal BFC can vary depending upon the vertical eddy viscosity formulation used in the calculation. Computed elevations and currents from a 3D model (in which bottom friction is computed from bottom current) are compared with observations and show a similar agreement for each viscosity parameterization provided the optimal BFC for this parameterization is used. These calculations suggest that to rigorously test a range of turbulence models in 3D calculations, in addition to accurate current measurements in the bottom boundary layer, it is also necessary to determine the bed types and forms and also to derive accurate tidal input to the model along its open boundaries.     

3D Numerical Model for Pearl River Estuary

A 3D numerical model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed. This model is based on POM (Princeton Ocean Model). In this model a second moment turbulence closure submodel is embedded and the stratification caused by salinity and temperature is considered. Furthermore, to adapt to estuary locations where the flow pattern is complex, the horizontal time differencing is implicit with the use of a time-splitting method instead of the explicit method in POM. This model is applied to the Pearl River estuary, which is the largest river system in South China, with Hong Kong at the eastern side of its entrance. The computation is verified and calibrated with field measurement data. The computed results mimic the field data well.     

Comparative Study of 3D Numerical and Puff Models for Dense Air Pollutants

To prepare for a chemical emergency response program in those industrial cities that might involve a release of chemical contaminants to the atmosphere, we have adopted a series of source emission models and a three-dimensional atmospheric model along with its companion diffusion module for predicting the dispersion and concentrations of these hazardous chemicals with various types of release scenarios. The three-dimensional atmospheric model predicts the wind, temperature, and turbulence fields in which the physical processes associated with terrain, clouds, radiation, and surface vegetation are included. The analytical framework is designed by the fact that the diffusion module uses the estimated release rate from a source emission model and the predicted winds and turbulence conditions from the atmospheric model to compute particle trajectories, concentrations, and dosages in the area of a release. In addition, the model results have been coupled with the geographical information system, which may be used for risk assessment at the urban industrial area of south Taiwan by emergency planners.     

Dispersion Model for Tidal Wetlands

Tidal wetlands in California are mostly estuarine salt marshes characterized by tidal channels and mudflats that are flooded and drained on a semidiurnal basis. Depths are rarely greater than 2 or 3 m, except where dredging occurs for harbor operations, and lengths from head to mouth are usually in the range of 1–10 km. This paper presents a coupled set of models for prediction of flow, solute transport, and particle transport in these systems. The flow and solute transport models are based upon depth-integrated conservation equations while the particle transport model is quasi-three-dimensional. Common to these models is an assumption that a turbulent boundary layer extends vertically from the bed and can be described by the law of the wall. This feature of the model accounts for: (1) momentum transfer to the bed, (2) longitudinal dispersion of dissolved material based on the work of Elder (1959), and (3) advection and turbulent diffusion of particles in three dimensions. A total variation diminishing finite volume scheme is used to solve the depth-integrated equations. Using this model, we show that dispersion can be accurately modeled using physically meaningful mixing coefficients. Calibration is therefore directed at modifying bed roughness, which scales both the rate of advection and dispersion.     

Multigrid Preconditioner for Unstructured Nonlinear 3D FE Models

Multigrid and multigrid-preconditioned conjugate-gradient solution techniques applicable for unstructured 3D finite-element models that may involve sharp discontinuities in material properties, multiple element types, and contact nonlinearities are developed. Their development is driven by the desire to efficiently solve models of rigid pavement systems that require explicit modeling of spatially varying and discontinuous material properties, bending elements meshed with solid elements, and separation between the slab and subgrade. General definitions for restriction and interpolation operators applicable to models composed of multiple, displacement-based isoparametric finite-element types are proposed. Related operations are used to generate coarse mesh element properties at integration points, allowing coarse-level coefficient matrices to be computed by a simple assembly of element stiffness matrices. The proposed strategy is shown to be effective on problems involving spatially varying material properties, even in the presence of large variations within coarse mesh elements. Techniques for solving problems with nodal contact nonlinearities using the proposed multigrid methods are also described. The performance of the multigrid methods is assessed for model problems incorporating irregular meshes and spatially varying material properties, and for a model of two rigid pavement slabs subjected to thermal and axle loading that incorporates nodal contact conditions and both solid and bending elements.     

Areas of Application for 3D and 4D Models on Construction Projects

In recent years more and more construction projects used three-dimensional/four-dimensional (3D/4D) models to support management tasks. However, project managers still struggle with evaluating how the 3D/4D model technology can be most efficiently applied on their specific project. One main reason for this struggle is that an account about how 3D/4D models have been used in the past is missing. This paper offers practitioners and researchers such an account of the application areas of 3D/4D model technologies including the purposes for which these technologies have been applied. The paper qualitatively aggregates the results of 26 case studies of 3D/4D model applications on construction projects to show researchers and practitioners how 3D/4D models have been applied to address project challenges. Using a “project challenge—3D/4D model application” matrix the paper explains each application area and describes why the application has been beneficial to the case study projects. The paper then analyzes the challenges that practitioners have faced with 3D/4D models on the test case projects. The main findings of this analysis are that practitioners on most of the test case projects have used the models for only one application area. The paper suggests that further research on the integration of 3D/4D model technologies into work and business processes of project teams is needed to address this opportunity for a more widespread use of 3D/4D models throughout the lifecycle of a project.     

Stage–Discharge Relations for Low-Gradient Tidal Streams Using Data-Driven Models

Development of stage–discharge relationships for coastal low-gradient streams is a challenging task. Such relationships are highly nonlinear, nonunique, and often exhibit multiple loops. Conventional parametric regression methods usually fail to model these relationships. Therefore, this study examines the utility of two data-driven computationally intensive modeling techniques namely, artificial neural networks and local nonparametric regression, to model such complex relationships. The results show an overall good performance of both modeling techniques. Both neural network and local regression models are able to predict and reproduce the stage–discharge multiple loops that are observed at the outlet of a 28.5?km2 low-gradient subcatchment in southwestern Louisiana. However, the neural network model is characterized with higher prediction ability for most of the tested runoff events. In agreement with the physical characteristics of low-gradient streams, the results indicate the importance of including information about downstream and upstream water levels, in addition to water level at the prediction site.     

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. I: Numerical Model

A general-purpose numerical method is developed for solving the full three-dimensional (3D), incompressible, unsteady Reynolds-averaged Navier-Stokes (URANS) equations in natural river reaches containing complex hydraulic structures at full-scale Reynolds numbers. The method adopts body-fitted, chimera overset grids in conjunction with a grid-embedding strategy to accurately and efficiently discretize arbitrarily complex, multiconnected flow domains. The URANS and turbulence closure equations are discretized using a second-order accurate finite-volume approach. The discrete equations are integrated in time via a dual-time-stepping, artificial compressibility method in conjunction with an efficient coupled, block-implicit, approximate factorization iterative solver. The computer code is parallelized to take full advantage of multiprocessor computer systems so that unsteady solutions on grids with 106 nodes can be obtained within reasonable computational time. The power of the method is demonstrated by applying it to simulate turbulent flow at R ? 107 in a stretch of the Chattahoochee River containing a portion of the actual bridge foundation located near Cornelia, Georgia. It is shown that the method can capture the onset of coherent vortex shedding in the vicinity of the foundation while accounting for the large-scale topographical features of the surrounding river reach.     

基于FLAC3D上向水平分层充填采矿法数值模拟

为了安全高效地回收宁南骑骡沟铅锌矿区残矿,采用FLAC3D有限元法对上向水平分层充填采矿法的结构参数和开采工艺过程进行了数值模拟,以便指导残矿的开采方案设计.数值模拟结果表明:上向水平分层充填采矿法的最大控顶高度为10m,最大空区暴露面积控制在150～250m2以内,采用3采1充或2采1充的回采工艺能保证安全产生.生产结果表明:应用数值模拟结果指导采矿方法和开采工艺设计是合理的.     

2D Numerical Model of Flooding in East Bangkok

We propose a new numerical flooding model oriented to water systems comprising large canal networks. Our approach is based on the diffusion wave equation related to a modified version of the so-called “calculations with apparent cross-sectional flow areas.” Our mathematical formulation is based on the analogy of a porous medium characterized by a permeability depending on parameters and directions of the canal network. Next, we combine the “continuous medium” approach with the nonnegative stable numerical algorithm (initially developed for the 1D diffusion wave equation). A numerical solution of our resulting finite-difference equations requires a tangible generalization of the nonnegative algorithm to the case of coupled 2D river-surface flows. Finally, we simulate the flood evolution in the lower Chao-Praya river basin (located in the eastern areas of Bangkok), and we demonstrate the computational efficiency of our proposed method.     

Experimental Study and 3D Numerical Simulations for a Free-Overflow Spillway

The main objectives of the present work were to investigate the flow field over a spillway and to simulate the flow by means of a three-dimensional (3D) numerical model. Depending on the wall curvature, the boundary layer parameters decreased or increased with increasing distance along the spillway. The growth of the boundary layer along the spillway is better described as a function of Reynolds number than the normalized streamwise length. A simplified form of the 3D momentum equation can be used to obtain a rough estimate of the skin friction. The velocity profile in the boundary layer along the spillway is described by a velocity–defect relationship. Numerical models provide a cost-effective means of simulating spillway flows. In this study, the water surface profiles and the discharge coefficients for a laboratory spillway were predicted within an accuracy range of 1.5–2.9%. The simulations were sensitive to the choice of the wall function, grid spacing, and Reynolds number. A nonequilibrium wall function with a grid spacing equal to a distance of 30 wall units gave good results.     

3D Finite Element Model for Asphalt Concrete Response Simulation

An extensive experimental, analytical, and numerical investigation on the response of asphalt concrete is currently in progress at Delft University of Technology. The objectives of this Asphalt Concrete Response (ACRe) project are: (a) the formulation and finite element implementation of a three‐dimensional, strain‐rate sensitive, temperature‐ and loading history‐dependent constitutive model, and (b) the development of the necessary experimental set‐ups, testing procedures, and data analysis methods for determination of the model parameters. These objectives are strongly interrelated: on the one hand, the model dictates what should be measured in a test, while on the other hand, the response observed in the tests sets the requirements for the model. As a result, model development/verification and experimental testing have been progressing in parallel throughout the project. In this contribution both the finite element and the experimental aspects of the project will be presented. The constitutive model has been implemented in the finite element system INSAP. The system has been used to simulate the initiation and propagation of damage in two flexible pavement structures due to repeated loading. The simulations illustrate the influence of geometry and material characteristics on the development of damage.     

1550连退数模分析软件开发

介绍了一个基于MATLAB的数模分析工具软件,为模型工程师提供对1550连退模型进行离线仿真、精度分析和参数优化的有效工具.凭借MATLAB强大的数学计算优势和灵活方便的图形界面制作,该工具软件的开发具有很大的推广价值.     

Simulation of a 3D Numerical Viscous Wave Tank

A numerical scheme was developed to solve the unsteady three-dimensional (3D) Navier–Stokes equations and the fully nonlinear free surface boundary conditions for simulating a 3D numerical viscous wave tank. The finite-analytic method was used to discretize the partial differential equations, and the marker-and-cell method was extended to treat the 3D free surfaces. A piston-type wave generator was incorporated in the computational domain to generate the desired incident waves. This wave tank model was applied to simulate the generation and propagation of a solitary wave in the wave tank and the diffraction of periodic waves by a semiinfinite breakwater. The computation was carried out by a PC cluster established by connecting several personal computers. The message passing interface (MPI) parallel language and MPICH software were used to write the computer code for parallel computing. High consistency between the numerical results and the theoretical solutions for the wave and velocity profiles confirms the accuracy of the proposed wave tank model.     

FLOW-3D V9.3铸造数值模拟技术之消失模铸造仿真

为了实现FLOW-3D V9.3消失模铸造模拟仿真,用基本消失模模型、重力用户模型及重力-排气能力用户模型对竖直板铸件分别进行了消失模数值模拟,并与该铸件充型实验结果进行了比较.研究结果,重力-排气能力用户模型金属液充型流动形态和时间与实验结果具有较高的吻合度.结果表明,FLOW-3D V9.3经二次开发能较好地模拟消失模铸造过程.     

1D Numerical Model of Muddy Subaqueous and Subaerial Debris Flows

A 1D numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented. The model incorporates the Herschel-Bulkley and bilinear rheologies of viscoplastic fluid. The more familiar Bingham model is integrated into the Herschel-Bulkley rheological model. The conservation equations of mass and momentum of single-phase laminar debris flow are layer-integrated using the slender flow approximation. They are then expressed in a Lagrangian framework and solved numerically using an explicit finite difference scheme. Starting from a given initial shape, a debris flow is allowed to collapse and propagate over a specified topography. Comparison between the model predictions and laboratory experiments shows reasonable agreement. The model is used to study the effect of the ambient fluid density, initial shape of the failed mass, and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows. It is found that initial failure shape influences the front velocity but has little bearing on the final deposit shape. In the Bingham model, the excess of shear stress above the yield strength is proportional to the strain rate to the first power. This exponent is free to vary in the Herschel-Bulkley model. When it is set at a value lower than unity, the resulting final deposits are thicker and shorter than in the case of the Bingham rheology. The final deposit resulting from the bilinear model is longer and thinner than that from the Bingham model due to the fact that the debris flow is allowed to act as a Newtonian fluid at low shear rate in the bilinear model.     

Finite Analytic Model for Flow and Transport in Unsaturated Zone

The finite analytic method is employed to solve the vertical, two-dimensional subsurface flow and transport equations in an unsaturated zone. The finite analytic method treats the nonlinear coefficient terms of the governing equations as constants in the element so that linearized partial differential equations can be obtained and solved in each element. The accuracy and limitations of the numerical method are systematically explored. The flow and transport simulations are examined using a one-dimensional laboratory infiltration test and an analytical solution of a two-dimensional subsurface transport problem, respectively. In the advection-dominant, vertical, one-dimensional infiltration problem, nine spatial weighting schemes are proposed to evaluate the averaged unsaturated hydraulic conductivity in a discretized element. Among them, the geometric mean weighting scheme provides the most accurate results as compared with the infiltration data. In verification of the two-dimensional solute transport problem, the nine-node elements are placed in the interior domain, and different layers of five-node elements are placed at the boundaries to investigate if the numerical experiment setup was proper and the algorithm was accurate. The developed numerical model is then applied to an irregular-domain landfill leaching problem to reveal the features of subsurface transport in unsaturated zone. Numerical aspects to be further explored are suggested.     

Numerical Modeling of a Servohydraulic Testing System for Structures

A realistic model of a dynamic testing laboratory for structures is presented, which includes the controller and the hydraulic loading equipment as well as the test specimen. The model provides a safe and easily controllable way of experimenting with a complex dynamic testing system, enabling the limits of the system to be explored prior to performing a physical test. The paper describes the representation of the proportional, integral, derivative, lag controller and the development of a detailed nonlinear model of the servovalve actuator system, together with their numerical implementation using the Matlab system-modeling package Simulink. Output from the model is compared with experimental results of both open-loop tests and real-time substructure tests, in which a physical test of part of a structure is coupled in real time to a numerical model of the remainder of the structure.     

昭通铅锌矿采空区稳定性的FLAC^3D数值模拟研究

昭通铅锌矿古采空区体积达60多万m3,且形态复杂.由于古采空区未得到处理和矿区民采泛滥,Ⅰ号矿带主矿体古采空区多次发生垮塌,并引发地表塌陷、山体开裂和井下采场垮塌等现象.本文采用FLAC3D快速拉格朗日差分分析方法,对采空区稳定性进行了数值模拟,以便对采空区处理方案提供理论依据.模拟结果表明,采空区顶板发生向下位移,围岩位移剧烈,引起地表变形大;采空区顶板处出现明显的竖直应力集中和水平应力集中,而采空区周围塑性区可延伸至地表.