Pipe Network Model Research Articles

Chemical accidents in freshwater: Development of forecasting system for drinking water resources

Chemical accidents have threatened drinking water safety and aquatic systems when hazardous chemicals flow into inland waterbodies through pipelines in industrial complexes. In this study, a forecasting system was developed for the prevention of drinking water resource pollution by considering chemical transport/fate through both pipelines and river channels. To this end, we coupled a pipe network model (Storm Water Management Model) with a calibrated hydrodynamic model (Environmental Fluid Dynamics Code). In addition, we investigated whether chemical transport through pipelines would make a difference in chemical concentration predictions. For both pipelines and river channels, the results showed lower peak concentrations than those without pipelines, whereas the time of peak concentration did not change significantly. When chemicals were transported with both pipelines and river channels, the peak concentrations were 25.81% and 41.91% lower than those of chemicals carried directly into the Han and Geum Rivers without the pipeline transport. Further, our system is automated from scenario generation to analysis and usage is straightforward, with a simple input of accident information. The results of this study can be utilized to establish a safe water supply system and preliminary countermeasures against accidental water pollution in the future.

Development and Verification of a Pipe Network Scale Model

The main function of a water supply and storm sewer pipe network is to properly maintain planned flow rates, water pressure, and water depth within pipes. This can be simulated with a numerical analysis model. In general, model experiments are required to verify and correct the accuracy of numerical analysis models, but due to the nature of complex facilities, scale model experiments and related studies are very limited. Therefore, this study aimed to develop a kit capable of general-purpose scale model experiments for water and sewage networks, and verified the applicability of the developed model through simple experiments. A set of model experimental parts, including manhole parts, pipe connections, and venturi meters for pipe network implementation and measurement, was manufactured with a three-dimensional printer (Stratasys F170). The angle, height difference, and slope of the pipe could be adjusted. A pipe connection cap was developed to implement all commercial circular pipes with a diameter of 300 mm to 1,200 mm based on 1/50 scale. A transparent acrylic pipe was used. EPANET analysis indicated that the scale model experiment of the water supply network, with 13 manholes, 18 pipelines, and 5 venturi meters had a flow error of about 13% in the total pipeline and about 8% in the venturi meter measurement value. In addition, a scale model of the storm sewer pipe network was developed to determine the change in water depth according to the connection angle of the pipe. Results of simulations in FLUENT showed a similar trend in water depth change.

Improvements to the Fracture Pipe Network Model for Complex 3D Discrete Fracture Networks

AbstractFractures widely present in the subsurface and play a critical role in the fluid flow processes in porous media. The Fracture Pipe Network Model (FPNM) is an efficient method to represent and calculate fluid flow properties as a particular part of Discrete Fracture Networks (DFNs) method compared to direct numerical simulations. However, the current FPNM formulation can result in large deviations in computed fluid flow properties when applied to complex interconnected DFNs, although it can produce good results for simple DFNs. To enhance the performance and versatility of current FPNMs, four modifications to the FPNM formulation are introduced from different perspectives to improve the accuracy of pipe conductance assignment and ensure the correct topology of the fracture network. Two benchmarking examples with complex interconnected fractures and two real fractured samples are presented and the results show the modifications significantly improve the accuracy of computed fluid flow properties in complex DFNs.

Intelligent Leakage Location of Urban Small Water Supply Network

In this paper, the leakage location model of pipe network is established based on EPANET software. Two intelligent swarm optimization algorithms, ant lion optimization algorithm and particle swarm optimization algorithm, are used to solve the model. Taking the industrial water supply network of a coastal city in North China as an example, the operation of the two algorithms is analyzed and compared. The results show that the ant lion optimization algorithm has stronger global optimization ability and higher search efficiency in the problem of leakage location; it also has high application value in practical engineering.

Water supply network modeling and pipe burst analysis based on WaterGEMS

In recent years, the water supply task of urban water supply pipe network is more and more heavy, and leakage accidents of pipe network often occur, among which the most serious leakage accident is pipe burst accident. To solve this problem, this study uses WaterGEMS software to establish the topological structure of water supply pipe network, adopts the water supply pipe network model and computer technology to carry out dynamic analysis on pipe burst accident of pipe network, and uses golden section method to predict the water leakage caused by pipe burst accident state.

Research and practice on optimal design method of the oilfield water injection system pipeline network

The efficiency of oilfield water injection system is generally low and energy consumption is high. With the deepening of oilfield exploitation, the water cut of the oilfield is increasing, the power consumption of the water injection system is increasing year by year, the oilfield exploitation cost is increasing, and energy conservation and consumption reduction are very important. In order to improve oilfield water injection efficiency and reduce water injection energy loss, this paper puts forward the pipe network optimization design method of partial pressure water injection, establishes the mathematical model of partial pressure water injection pipe network and throttling loss calculation model, compiles the calculation software of partial pressure water injection mathematical model, optimizes the partial pressure interval, calculates the partial pressure points, effectively reduces the energy loss of water injection system and improves the efficiency of water injection system.

Impact of fracture length distribution on seepage characteristics of fractured rock masses

This study presents a numerical investigation on the effect of fracture length distribution on the equivalent permeability of fractured rock masses. Three-dimension discrete fracture network (DFN) models with different fracture length distributions were generated using Monte Carlo method. The equivalent permeability was calculated by simplifying the 3D DFN models to equivalent pipe network (EPN) models. The results show that the equivalent permeability becomes less scattered with increasing side length of sub-models (L n), showing a clear tendency of reaching a representative element volume (REV) size. The root mean square (RMS) = 0.2 is utilized as the threshold to determine the REV size. The REV size of the DFN model is approximately 4.17×104 m3 in which the power exponent (a) of fracture length distribution is 4.5. The fracture density (P 32) decreases exponentially with the increment of a. This is because the number of short fractures in the DFN model with a larger a is larger. The P 32 of the DFN model is positively correlated to the equivalent permeability.

Optimization of Pipe Network Simulation Algorithm for Tree-Shaped Water Injection System in Large-Scale Oilfield

As intelligence technology develops, there is a higher requirement for computing speed and accuracy of water injection system simulation. In this paper, aiming at the tree-shaped water injection pipe network system of large-scale oilfields, based on the energy equation for calculating the pressure drop [Formula: see text] of pipe section, a mathematical model of the pipeline unit and the node unit is established, and finally, a mathematical model of pipe network for the entire water injection system is established; then, the improved iterative algorithm is used to solve the simulation model of water injection system. In this way, we determine the boundary calculation conditions, take the water injection station as reference node, and use the maximum pressure of water injection well as the initial value of the reference node for calculation, which reduces the number of iterations in model calculation; by comparing the simulation results of different iteration steps, 0.01 is selected as the iteration step size due to its higher calculation accuracy; and the calculation process has also been optimized. The process of solving the characteristic matrix [Formula: see text] is combined with the process of calculating the pressure drop [Formula: see text] of pipe section, and placed outside the algorithm loop, thereby shortening the calculation time of a single cycle and reducing the calculation amount of the algorithm. The application cases show that the proposed optimization algorithm for water injection system pipe network simulation can be used as an effective method to improve the solution speed and calculation accuracy of the simulation algorithm of tree-shaped water injection system in large-scale oilfields.

An equivalent pipe network model for free surface flow in porous media and its comparison with the continuum model

A simple and efficient equivalent pipe network method is developed for unconfined seepage problems in porous media. Instead of the continuum-based method, the porous media is represented by an orthogonal of pipe elements rather than triangular and quadrilateral elements in which water flow occurs. The equivalent expressions of the hydraulic conductivity parameters, the continuity equation, boundary conditions and finite element analysis are reduced to a one-dimensional problem of line elements. Two typical examples are applied to investigate the validity and advantages of the proposed equivalent pipe element method in comparison with the continuum-based method. From the steady-state free surface flow in the homogeneous, the equivalent pipe network method can well reproduce the free surface locations with the numerical solutions. However, the calculated results from the fractured porous media illustrate that the performance of the proposed method is better than the continuum-based method when considering a high- hydraulic conductivity horizontal fracture in the porous media.

Coupling of pipe network modelling and domain decomposition for flow in mineralised coal cores

Permeability of coal is highly dependent on the effective stress, which is found to decrease exponentially as effective stress increases. To study coal permeability at in-situ conditions, high pressure X-ray micro-CT imaging is performed. However, fractures are highly compressed at in-situ conditions, some of fracture apertures are below the resolution of images, which cannot be segmented properly for direct flow simulation. In this work, we utilise two sets of micro-CT images under ambient and high pressure conditions. The ambient micro-CT images are used to extract fracture pipe network model (FPNM), while the high-pressure greyscale images are used for measuring aperture sizes that are below image resolution. Minerals, which commonly occur in fractured coal samples, are additionally analysed and included in the FPNM. Domain decomposition is also applied during the construction of FPNM, to enhance the capability and efficiency of model extraction. It is found that domain decomposition can greatly reduce the computational cost while keeping the accuracy of permeability estimation. Permeability values with and without mineralisation are compared between improved FPNM and direct simulation, for verification purposes. Lastly, we use the modelling framework to estimate the permeability of a coal sample at in-situ condition. This improved FPNM modelling framework can improve the simulation efficiency of fluid transport processes within fractured media, which is central to many energy, geoscience and water resources applications.

Operation Characteristic Analysis and Parameter Optimization of District Heating Network with Double Heat Sources

The heating system is a practical engineering problem with multi-parameter coupling and multi-constraint restrictions. The use of optimization algorithms has guiding significance for its high efficiency and energy saving. This paper takes the district heating pipe network with dual heat sources as an example to analyze the operation characteristics of the heating pipe network and optimize its parameters. The thermodynamic model of the dual-heat source district heating pipe network is established, and the NSGA-II algorithm is applied to analyze the operating characteristics. By comparing the upper and lower limits of the interval and the interval when the pipe length and pipe diameter are the decision variables, it is believed that to reduce the loss during the operation phase of the system, quantity adjustment should be avoided as much as possible. The water supply temperature is greater than 95°C, the greater the system fluctuation. Through the NSGA-II algorithm, the Pareto front is obtained, and the TOPSIS optimization method is used to finally obtain the best operating parameters of the pipe network with the best closeness.

Impacts of climate change on groundwater flooding and ecohydrology in lowland karst

Abstract. Lowland karst aquifers can generate unique wetland ecosystems which are caused by groundwater fluctuations that result in extensive groundwater–surface water interactions (i.e. flooding). However, the complex hydrogeological attributes of these systems, linked to extremely fast aquifer recharge processes and flow through well-connected conduit networks, often present difficulty in predicting how they will respond to changing climatological conditions. This study investigates the predicted impacts of climate change on a lowland karst catchment by using a semi-distributed pipe network model of the karst aquifer populated with output from the high spatial resolution (4 km) Consortium for Small-scale Modelling Climate Lokalmodell (COSMO-CLM) regional climate model simulations for Ireland. An ensemble of projections for the future Irish climate were generated by downscaling from five different global climate models (GCMs), each based on four Representative Concentration Pathways (RCPs; RCP2.6, RCP4.5, RCP6.0 and RCP8.5) to account for the uncertainty in the estimation of future global emissions of greenhouse gases. The one-dimensional hydraulic/hydrologic karst model incorporates urban drainage software to simulate open channel and pressurised flow within the conduits, with flooding on the land surface represented by storage nodes with the same stage volume properties of the physical turlough basins. The lowland karst limestone catchment is located on the west coast of Ireland and is characterised by a well-developed conduit-dominated karst aquifer which discharges to the sea via intertidal and submarine springs. Annual above ground flooding associated with this complex karst system has led to the development of unique wetland ecosystems in the form of ephemeral lakes known as turloughs; however, extreme flooding of these features causes widespread damage and disruption in the catchment. This analysis has shown that mean, 95th and 99th percentile flood levels are expected to increase by significant proportions for all future emission scenarios. The frequency of events currently considered to be extreme is predicted to increase, indicating that more significant groundwater flooding events seem likely to become far more common. The depth and duration of flooding is of extreme importance, both from an ecological perspective in terms of wetland species distribution and for extreme flooding in terms of the disruption to homes, transport links and agricultural land inundated by flood waters. The seasonality of annual flooding is also predicted to shift later in the flooding season, which could have consequences in terms of ecology and land use in the catchment. The investigation of increasing mean sea levels, however, showed that anticipated rises would have very little impact on groundwater flooding due to the marginal impact on ebb tide outflow volumes. Overall, this study highlights the relative vulnerability of lowland karst systems to future changing climate conditions, mainly due to the extremely fast recharge which can occur in such systems. The study presents a novel and highly effective methodology for studying the impact of climate change in lowland karst systems by coupling karst hydrogeological models with the output from high-resolution climate simulations.

Mechanical Properties and Permeability Evolution of Red Sandstone Subjected to Hydro-mechanical Coupling: Experiment and Discrete Element Modelling

This paper presents the hydro-mechanical behaviors of a red sandstone from the Three Gorges reservoir area using laboratory testing and numerical modelling. A series of laboratory triaxial compression tests were performed on the red sandstone to understand the effect of confining stress and seepage pressure on the rock mechanical properties and permeability. The laboratory results show that the initial elastic modulus, Poisson’s ratio and peak strength of the red sandstone increase with confining stress, and decrease with the increase in seepage pressure. The change in the permeability of the red sandstone is slight during the initial and elastic deformation stages, but increases rapidly when approaching to the peak stress. Micromechanical insights on the sandstone’s hydro-mechanical behaviors were unveiled by implementing an improved pipe network flow model in the discrete element method. The improved pipe network model can well capture the stress–strain response and the permeability changes of the red sandstone that were consistent with the laboratory test results. The numerical results reveal that the distribution of flow rate, pore pressure, and force chains in rock is closely related to microcracking, and the permeability increases accordingly with the increase in the number of microcracks and their coalescence. The number of microcracks and the rock fracture angle with respect to the axial axis at peak stress increase with the effective confining stress. The damage process of the red sandstone during the hydro-mechanical loading is divided into three distinct stages based on the mechanical response and permeability evolution.

A series solution based formulation for discrete thermal element method of granular materials

This work performs further study on the discrete thermal element method (DTEM) (Feng et al., J. Comput. Phys. 227, 5072–5089 (2008)) of heat conduction in particle systems involving a large number of circular particles in 2D cases. Feng proposed the DTEM based on particular solution for the Laplace equation in a circular domain with Newmann boundary condition. In this paper, another version of DTEM is proposed based on the series solution for the same boundary value problem. The evaluation of the coefficients of the resistance matrix He is a main computational issue associated with the formulation of the DTEM. In this work, another accurate and less time consuming method for calculating He is presented. The resulting equation gives a better expression for hij while in Feng’s work, this was done numerically. An important mathematical property of He is also discovered and discussed. The More Diagonally-Dominant pipe-network model is proposed to make the pipe-network model (Feng et al., Powder Technol. 193, 248–256 (2009)) more accurate. Numerical experiments are conducted to establish the solution accuracy of the proposed method.

Hydraulic Calibration of Pipe Network Model Using An Improved Genetic Technique (Dept.C)

This research paper exhibits the development and calibration capability of a computer optimization code, called SO-OPTIM. This code copes with several problems concerning water distribution networks which include: new design, rehabilitation, calibration; optimal scheduling of pumps, optimal operation of pump stations in the presence of water elevated tanks, and optimal pressure regulation. These problems are treated using a powerful genetic algorithm optimization technique which consists of a nonlinear objective functions subjected to both linear and non linear constraints. Different modifications were carried out in the simple genetic algorithm. The mentioned code links the optimization model and a hydraulic solver which applies the principles of a new technique used for pipe network analysis in steady state conditions. The proposed code is applied in two different water distribution networks. The first one is a hypothetical network with synthetic calibration data and the SO OPTIM code is applied to perform extended period calibration. The second network is a real water distribution system of Damnhour city, Egypt, with actual data and field measurements and in this case the code performs steady state calibration.

Fast Equivalent Micro-Scale Pipe Network Representation of Rock Fractures Obtained by Computed Tomography for Fluid Flow Simulations

Fractures in rocks often provide preferential fluid migration pathways and their geometrical properties are the main factors influencing the permeability of the rock mass. By taking into account the complex geometries of rock fractures, including tortuous features, highly variable fracture apertures, rough fracture wall surfaces and complex fracture intersections, a highly effective approach is proposed in this work to investigate the behaviour of fluid flows in laboratory-scale fractured rocks. The computed tomography (CT) scanning was used to capture the micro-structures of non-planar fractures in a sandstone specimen. An image processing method was then developed to extract the three-dimensional fracture network. The fractures and fracture network were represented using an equivalent pipe network model, taking into consideration the complex geometries mentioned above. The nonlinear flow is incorporated into the model through the consideration of a friction factor in the pipe flow method (PFM). The absolute difference of the derived permeability between PFM and finite volume method (FVM) is 3.45%, but the FVM needs 15 times more CPU computation time. Therefore, the proposed approach is better than FVM in terms of computational efficiency. In addition, the use of the friction factor was demonstrated to be effective and efficient to model nonlinear flow within the fracture network, where the flow nonlinearity is caused by high flow velocity and the formation of eddies in certain parts of the fracture network, leading to a decrease in the overall apparent permeability and an increase in the flow tortuosity. The proposed method was further validated against flow test data covering a wide range of linear and nonlinear flow regimes.

Quantifying and Numerically Representing Recharge and Flow Components in a Karstified Carbonate Aquifer.

Karstified carbonate aquifers are highly heterogeneous systems characterized by multiple recharge, flow, and discharge components. The quantification of the relative contribution of these components, as well as their numerical representation, remains a challenge. This paper identifies three recharge components in the time and frequency domain. While the analysis in the time domain follows traditional approaches, the analysis of the power spectrum allows frequencies associated with specific spectral coefficients and noise types to be distinguished more objectively. The analysis follows the presented hypothesis that the different frequency‐noise components are the result of aquifer heterogeneity transforming the random rainfall input into a sequence of non‐Gaussian signals. The distinct signals are then numerically represented in the context of a semidistributed pipe network model in order to simulate recharge, flow, and discharge of an Irish karst catchment more realistically. By linking the power spectra of the modeled recharge components with the spectra of the spring discharge, the information usually gained by classical performance indicators is significantly widened. The modeled spring discharge is well matched in the time and frequency domain, yet the different recharge dynamics explain the signal of the aquifer outlet in different noise domains across the spectrum. This study demonstrates the conjunctive use of frequency analysis in conceptualization of a hydrological system together with modeling and evaluation.

Three-Dimensional (3D) Parametric Modeling and Organization for Web-Based Visualization of City-Scale Pipe Network

Underground pipe network is a critical city infrastructure, which plays an important role in smart city management. As the detailed three-dimensional (3D) scene of underground pipe networks is difficult to construct, and massive numbers of pipe points and segments are difficult to manage, a 3D pipe network modeling and organization method is explored in this study. First, the modeling parameters were parsed from the pipe network survey data. Then, the 3D pipe segment and point models were built based on parametric modeling algorithms. Finally, a heterogeneous data structure for the 3D pipe network was established through loose quadtree data organization. The proposed data structure was suitable for 3D Tiles, which was adopted by Cesium (a web-based 3D virtual globe); hence, a multitude of pipe networks can be viewed in the browser. The proposed method was validated by generating and organizing a large-scale 3D pipe network scene of Beijing. The experimental results indicate that the 3D pipe network models formed by this method can satisfy the visual effect and render the efficiency required for smart urban management.

An equivalent pipe network model for free surface flow in porous media

Free surface flow analysis in porous media is challenging in many practical applications with strong non-linearity. An equivalent pipe network model is proposed for the simulation and evaluation of free surface flow in porous media. On the basis of representative elementary volume with homogeneous pore-scale patterns, the pore space of the homogeneous isotropic porous media is conceptualized as a collection of capillary tubes. According to Hagen-Poiseulle's law and flux equivalence principle, equivalent hydraulic parameters and unified governing formulations for the pipe network model are deduced. The two-dimensional free surface flow problem is reduced to a one-dimensional problem of pipe networks and a one-dimensional procedure based on the finite element method is then developed by introducing a continuous penalized Heaviside function. The proposed equivalent pipe network model is verified with results from numerical solutions and laboratory-measured data available in the literature, and good agreements are obtained. The proposed equivalent pipe network model is shown to be effective in analyzing the free surface flow in porous media. The numerical results also indicate that the proposed equivalent pipe network model has weak sensitivity of the mesh size and penalty parameters.

A Study on the Effects of Model Structure and Demand Allocation on Water Network Modeling

Objectives:In order to reduce the uncertainty of the pipe network modeling, the model structure was basically included all distribution pipes and several models were proposed according to the location of the water meters.Methods:For models verification, first, a steady state simulation of each model was made by constructing a model including all water supply pipes (All-meters Model), which are the bases of 3 simplified models, and considering the location of all water meters. The network analysis was performed by dividing into the steady state and the extended period simulation.Results and Discussion:From the results of models comparison, ‘All-meters Model’ and ‘All-connections Model’ were found to obtain more accurate results for constructing a water network model for simulation of water quality events in distribution network. When constructing an ‘All-meters Model’ in all networks, the model becomes complicated and data management does difficult. Therefore this study suggests a hybrid model construction.Conclusions:It would be reasonable to construct a detailed model (All-meters or All-connections Model) in looped network in which the water flow path can be changed according to the difference of water head, and a skeletonized model (Street-meters aggregation or Reduced-meters Model) for a branch network that does not have a significant impact on demand allocations.