Object Oriented Programming and Numerical Methods

Abstract: A generally applicable mathematical model, tailored for use on a Personal Computer, as the design tool to simulate unsteady flood flow in a network of interconnected rivers has been developed and applied to the Sham Chun River along the border between Hong Kong and the People's Republic of China. The effect on the improved Sham Chun River due to the proposed river training in the River Indus, one of its tributaries, is evaluated. The one-dimensional unsteady flow model itself is broadly applicable to a wide range of hydrologic conditions and varying field situations. It incorporates real hydraulic features including branched channels and 'tidal flats' flooding and drying. The time history of water stages and discharges are computed at any desired location throughout the connected essentially one-dimensional channel network subject to initial and boundary conditions. Details are given of techniques adapted in using the computational scheme to quantify the unsteady flow condition and the means to assure an efficient numerical solution as well as to verify the accuracy of the computed outputs by subjection to carefully selected schematic simplified test cases and real prototype cases with numerical solution method is a useful predictive engineering tool in river design.     

Validation of a 1D-2D dual drainage model under unsteady part-full and surcharged sewer conditions

This paper presents a 1D-2D dual drainage model to compute the rainfall-runoff transformation in urban environments. Overland flow in major drainage systems is modelled with the 2D shallow water equations, whereas the flow in a sewer network is computed with the 1D Saint-Venant equations using the two-component pressure approach to model pressure-flow conditions. The surface and sewer network models are linked through manholes, which allow water interchange in both directions. A new series of rainfall–runoff experiments in a real-scale physical model of a street section is used to validate the model under unsteady part-full and pressure flow conditions. The experimental measurements of water depth and discharge at several locations in a drainage network show a very satisfactory performance of the numerical model.     

海塘渗透破坏数值模拟及渗透特性

为研究海塘的洪水渗透规律和渗透破坏机制,提出了可考虑土体渗透性随渗透破坏而变化的饱和非饱和/非稳定渗流分析模型,编制了相应的程序.选取实际海塘进行了洪水渗透过程的数值模拟,并将计算结果与现场监测试验结果进行了对比,表明所建立的分析模型和计算程序是正确的.工程实例分析结果表明,海塘洪水渗透过程是一个涉及土体渗透性变化的饱和非饱和/非稳定渗流过程,塘身浸润线变化经历4个阶段,海塘渗透破坏是大渗流比降下洪水长时间渗透所导致的.因此海塘的洪水渗透破坏涉及破坏区土体渗透性的变化以及饱和-非饱和/非稳定渗流,按中国现行规范应用稳定渗流分析方法进行计算是存在问题的.     

The Use of Different Conveyance Calculations for Modelling Flows in a Compact Compound Channel

Flow measurements have been taken for steady and unsteady flows on a reach of a river having a compact compound channel. The 'single channel', 'divided channel' and 'lateral' distribution methods have been used to calculate conveyances for use in a one-dimensional unsteady flow model of the reach. Comparisons with measured flows show that the divided channel method and the lateral distribution method both underestimate floodplain flow depths. The lateral distribution method gives the closest accuracy in the relative depth range 0.15 ≤ Yr < 0.40. For large flow depths the single channel method becomes more accurate and slightly over-estimates flow depths.
The accuracy of unit width discharge distributions, calculated from the lateral distribution method are assessed by comparison with observed distributions for overbank flows.     

水力模型用于排水系统的设计优化

在传统的城市排水管网设计和管理中,一般采用恒定流水力学理论计算管网的汇流过程,无法反映真实水流的突涨突落的非恒定流特点,因此在上海市虹南排水系统的规划设计中,应用城市排水系统水力模型模拟技术详细分析了雨水排水系统的水力学特征,诊断了管网瓶颈,优化了其管网布局、调度方式和工程方案,为提高虹南雨水排水系统的规划、设计、管理、运行技术水平发挥了重要作用。     

Design of a monitoring network and assessment of the pollution on the Lerma river and its tributaries by wastewaters disposal

While the 2005 progress report of the United Nations Millennium Development Goals stresses out the need of a dramatic increase in investment to meet the sanitation target in the third world, it is important to anticipate about some parallel negative impacts that may have this optimistic programme (extension of sewer networks without sufficient treatment works). Research was initiated on Lerma River (Mexico), subjected to many rejects disposal, to design a monitoring network and evaluate the impact of wastewaters on its water quality. The discharges was inventorized, geo-positioned with a GPS and mapped, while the physico-chemical characteristics of the river water, its tributaries and main rejects were evaluated. Microtox system was used as an additional screening tool. Along the 60 km of the High Course of Lerma River (HCLR), 51 discharges, with a diameter or width larger than 0.3 m (including 7 small tributaries) were identified. Based on the inventory, a monitoring network of 21 sampling stations in the river and 13 in the important discharges (>2 m) was proposed. A great similitude was found between the average characteristics of the discharges and the river itself, in both the wet and dry seasons. Oxygen was found exhausted (<0.5 mg/L) almost all along the high course of the river, with COD and TDS average levels of 390 and 1980 mg/L in the dry season, against 150 and 400 mg/L in the wet season. In the dry season, almost all the sites along the river revealed some toxicity to the bacteria test species (2.9 to 150 TU, with an average of 27 TU). Same septic conditions and toxicity levels were observed in many of the discharges. Four of the six evaluated tributaries, as well as the lagoon (origin of the river), were relatively in better conditions (2 to 8 mg/L D.O., TU<1) than for the Lerma, acting as diluents and renewal of the HCLR flow rate. The river was shown to be quite a main sewer collector. The high surface water contamination by untreated wastewaters that is depicted in this research should be taken into account in the Millennium Goals strategies, by promoting treatment plan works simultaneously, when sewer networks in the third world would extend.     

A new approach to compute heat transfer of ground-coupled envelope in building thermal simulation software

This study presents a new approach to compute the heat transfer of ground-coupled envelope quickly and correctly which is suitable for implementation into building thermal simulation software. The heat transfer process is decomposed into three processes which are controlled by ground-coupled envelope surface temperature, outdoor ground surface temperature and the temperature difference of ground-coupled envelope surfaces. The three processes are computed by computing one-dimensional Equivalent Slab, simplifying outdoor temperature as harmonic and computing one-dimensional Extra Partition Wall. Validation indicates that the heat flux of ground-coupled envelope surface computed by the new approach is very close to that computed by Finite Difference Method (FDM) under unsteady boundary conditions. The computing time is much less than that with FDM.     

River Thames Flood Hydrology Design Curves

A quick method of defining design peak flows and hydrographs for any point on the River Thames between Days weir and Teddington is offered as a design tool for flood analysis. This paper presents the findings of a flood frequency and flood hydrograph analysis for the River Thames. The results were used in a hydraulic analysis of the river and its floodplain at Reading, but showed a wider application of the method on the river.     

赣江"S湾"活水岸公园: 自然驱动的河流景观生态修复实践

Possessing significant ecological and landscape values, river shorelines are regarded as a region’s most important interface to resist natural disasters while they are also extremely dynamic and sensitive. Therefore, it is critical to follow the laws of nature in design and planning of river shorelines to achieve the harmonious coexistence of human and nature free of flood catastrophes. This article takes the S River Park on the Living Shoreline of the Rule Lake New Town, Ganjiang New District, Jiangxi Province as an example of nature-based design approach: First, by examining remote sensing maps and water level data in different historical periods of the site, the design team learnt the evolving hydrological characteristics of the river; Second, the relations between the river’s evolution and major human interventions in history are clarified and sorted; Last but not the least, guided by the nature laws of water erosion and sedimentation, a naturebased design solution was approached—Bycatalyzing natural processes with appropriate human interventions, it aims at rehabilitating the damaged sandbar habitats through spontaneous remediation of the river, and creating fascinating riverfront experience out of a rational function zoning of the park based on various natural conditions, thus to make the new town more vibrant and resilient by connecting it with the seasonal waterfront landscape driven by the ebb and flow of the river.     

Which offers more scope to suppress river phytoplankton blooms: Reducing nutrient pollution or riparian shading?

River flow and quality data, including chlorophyll-a as a surrogate for river phytoplankton biomass, were collated for the River Ouse catchment in NE England, which according to established criteria is a largely unpolluted network. Against these data, a daily river quality model (QUESTOR) was setup and successfully tested. Following a review, a river quality classification scheme based on phytoplankton biomass was proposed. Based on climate change predictions the model indicated that a shift from present day oligotrophic/mesotrophic conditions to a mesotrophic/eutrophic system could occur by 2080. Management options were evaluated to mitigate against this predicted decline in quality. Reducing nutrient pollution was found to be less effective at suppressing phytoplankton growth than the less costly option of establishing riparian shading. In the Swale tributary, ongoing efforts to reduce phosphorus loads in sewage treatment works will only reduce peak (95th percentile) phytoplankton by 11%, whereas a reduction of 44% is possible if riparian tree cover is also implemented. Likewise, in the Ure, whilst reducing nitrate loads by curtailing agriculture in the headwaters may bring about a 10% reduction, riparian shading would instead reduce levels by 47%. Such modelling studies are somewhat limited by insufficient field data but offer a potentially very valuable tool to assess the most cost-effective methods of tackling effects of eutrophication.     

Comparison of Numerical and Experimental Results of Fire Induced Doorway Flows

The ability to calculate the changes to vent flows when a sprinkler activates can lead to improved predictions of fire environments outside of the room of origin in sprinklered occupancies, ultimately leading to an engineering design tool based on numerical simulations. Hence, for the current study, numerical calculations using NIST Fire Dynamics Simulator (FDS) are compared with real scale compartment experimental data for unsprinklered and sprinklered cases. Mass flow rate and temperature are typical parameters used to quantify the flow induced by a fire in a compartment. Hence, numerical results for doorway mass flow rate and temperature are compared with the experimental data for three fire sizes in order to validate the numerical model. Then, using current experimental data for sprinkler characteristics, numerical calculations for doorway mass flow rate and temperature are compared with the experimental data for the three fire sizes of the sprinklered case.     

基于泛函理论分析输气管道不稳定流动

在天然气输送管网中,枝状管网是的一种常见的形式。针对天然气枝状管道系统的组成特征,采用系统分析的观点,将管道系统划分成一系列基本组成单元,建立单元中不稳定流动方程,并根据单元之间的关系,综合考虑相关的连接条件、边界条件以及初始条件,从而提出了整个系统的联立模型。然后基于泛函分析理论和算子级数法求解联立模型,得到了问题的广义解。该方法具有解析解和数值解的特点,当所划分的基本单元较大时,可以得到直观的近似解析解;当所划分的基本单元较小时,可以得到更准确的数值解。由于管道单元和时间步长的取值可长可短,这就提高了求解的灵活性。以此为基础,编制了计算机程序,并应用于四川某气田管网的实际模拟。通过分析和应用表明,其模型和算法具有计算方便,精度高,省时和适用范围广等优点。     

Analysis of thermal impact in tidal rivers and estuaries

The paper presents a far field mathematical model for numerical simulation of transient one- or two-dimensional thermal distributions in regions with severe reversing flow conditions. The Eulerian formulation employs the integral form of the conservation principles for mass and thermal energy. The two-dimensional (2D) solution area is spanned by discrete elements of variable size and shape. The three-dimensional geometry of the flow region is accounted for by spatially integrating over the enclosure surfaces of the discrete element. The derivation of the two-dimensional depth-averaged temperature equations includes the contributions of the vertical variations of velocity and temperature. Surface heat transfer as well as turbulent effects are taken into account.Important mathematical and computational features of the model are summarized. There is a discussion of the four main algorithms, necessary to treat flow regions with complex shoreline geometries, viz. (i) specification of the boundary (ii) determination of all discrete element midpoints lying within the (possibly multiconnected) solution area (iii) construction of discrete elements of irregular geometry exactly matching the (curved) boundary, (iv) treatment of boundary conditions and numerical solution of the resulting mathematical system of weakly coupled, ordinary differential equations derived from the conservation principles.Preliminary results of a computer simulation are compared with the available data for a section of the Lower Elbe river. The calculation of the two-dimensional temperature distribution includes existing power plants and industrial sites. It is noted that the programs developed for this study are more widely applicable, potentially to solving the Poisson equation, in constructing the ion trajectories of an ion extraction system, or in calculating 1D and 2D flow fields.     

Assessing the Joint Probability of Fluvial and Tidal Floods in the River Roding

Water levels in the lower reaches of most rivers are controlled by the interaction of fluvial flows and tides. Assessment of the risk of over-bank inundation therefore requires an estimation of the probability of experiencing combinations of river floods and high tides and calculation of the water levels resulting from their interaction. This may be achieved by numerical integration of the marginal probability distributions of river floods and sea-levels, but this is complex mathematically and requires explicit knowledge of the correlation structure. In this paper a solution is developed for risk assessment in the lower River Roding, by reconstructing the historical water levels from river flow and tidal records using a hydraulic model. The resulting water-level series is then analysed statistically to estimate the probability that certain critical levels will be exceeded. The model allows for operation of the River Roding's flood-protection barrier and for the effects of a general rise in sea level.     

Calculation and design of tunnel ventilation systems using a two-scale modelling approach

This paper develops a novel modelling approach for ventilation flow in tunnels at ambient conditions (i.e. cold flow). The complexity of full CFD models of flow in tunnels or the inaccuracies of simplistic assumptions are avoided by efficiently combining a simple, mono-dimensional approach to model tunnel regions where the flow is fully developed, with detailed CFD solutions where flow conditions require 3D resolution. This multi-scale method has not previously been applied to tunnel flows. The low computational cost of this method is of great value when hundreds of possible ventilation scenarios need to be studied. The multi-scale approach is able to provide detailed local flow conditions, where required, with a significant reduction in the overall computational time. The coupling procedures and the numerical error induced by this new approach are studied and discussed. The paper describes a comparison between numerical results and experimental data recorded within a real tunnel underlining how the developed methodology can be used as a valid design tool for any tunnel ventilation system.This work sets the foundations for the coupling of fire-induced flows and ventilation systems where further complexities are introduced by the hot gas plume and smoke stratification.     

南京长江第四大桥航行条件数值模拟研究

结合二维水流数学模型和船舶运动数学模型,研究了拟建南京长江第四大桥对通航水流条件的影响,分析了桥墩周围的水流条件变化,模拟了船队在建桥前后通过桥区河段的航迹线,得到了航行过程中的航行参数,综合分析认为南京四桥修建对通航水流条件影响很小,对船舶航行也无明显影响。     

Parameter optimization of the QUAL2K model for a multiple-reach river using an influence coefficient algorithm

An influence coefficient algorithm and a genetic algorithm (GA) were introduced to develop an automatic calibration model for QUAL2K, the latest version of the QUAL2E river and stream water-quality model. The influence coefficient algorithm was used for the parameter optimization in unsteady state, open channel flow. The GA, used in solving the optimization problem, is very simple and comprehensible yet still applicable to any complicated mathematical problem, where it can find the global-optimum solution quickly and effectively. The previously established model QUAL2Kw was used for the automatic calibration of the QUAL2K. The parameter-optimization method using the influence coefficient and genetic algorithm (POMIG) developed in this study and QUAL2Kw were each applied to the Gangneung Namdaecheon River, which has multiple reaches, and the results of the two models were compared. In the modeling, the river reach was divided into two parts based on considerations of the water quality and hydraulic characteristics. The calibration results by POMIG showed a good correspondence between the calculated and observed values for most of water-quality variables. In the application of POMIG and QUAL2Kw, relatively large errors were generated between the observed and predicted values in the case of the dissolved oxygen (DO) and chlorophyll-a (Chl-a) in the lowest part of the river; therefore, two weighting factors (1 and 5) were applied for DO and Chl-a in the lower river. The sums of the errors for DO and Chl-a with a weighting factor of 5 were slightly lower compared with the application of a factor of 1. However, with a weighting factor of 5 the sums of errors for other water-quality variables were slightly increased in comparison to the case with a factor of 1. Generally, the results of the POMIG were slightly better than those of the QUAL2Kw.     

Modelling the advection equation under water hammer conditions

The quality of water delivered by a distribution network may degrade for many reasons. This research considers one of these, focusing attention on the connection between water quality and the hydraulic events in a pipe system. More specifically, pressure and velocity variations associated with hydraulic transients or water hammer conditions, particularly through leaks and rapid device adjustments, have the potential to degrade water quality. In most previous applications, numerical transport schemes have been coupled to quasi-steady hydraulic models. By contrast, the current contribution couples a finite difference solution of the advection-reaction equation to a fully unsteady, method of characteristics (MOC) based, hydraulic solution. Depending on system properties, the effects of advection, compressibility and reaction may be evident in the modelled response. The numerical properties of consistency, stability and convergence of the proposed model are investigated both analytically and numerically. Although some case studies have revealed important water quality implications associated with dynamic conditions, particularly in cases of contaminated water intrusion, it should be admitted that many transient simulations exhibit few differences compared with quasi-steady results.     

Flow measurement with multi‐instrumentation in a tidal‐affected river

Flow measurements in a tidal‐affected river provide important information of cyclic flow pattern characteristics in temporal and spatial variations. Reliability and accuracy of measured flow data can provide for numerical model calibration and verification. In the present study, we measured tidally affected river flow in the Danshui River of northern Taiwan during the 2008 summer and fall. The measured flow data, produced by both state of the art and conventional instruments including particle tracking velocimetry (PTV), acoustic Doppler profiler (ADP), horizontal acoustic Doppler current profiler (H‐ADCP) and Price‐type current metre (PCM) were compared and correlated during several tidal cycles. The mean flows by ADP were similar to that by PCM and highly correlated with those by PTV and H‐ADCP. Index velocity rating between ADP and H‐ADCP separately computed during the flood and ebb tides shows good correlation for the ebb tide and poor correlation for the flood tide due to subsurface maximum velocity in the middle‐ to near‐bottom layers.     

不稳定工况下燃气管网的模拟计算

本文采用偏微方程特征线的数值分析及拟牛顿法,对燃气管网不稳定流动问题从理论上进行了求解,并编出了用户负荷随时间变化时,管网各点压力分布的动态模拟程序。