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Pipe Networks (pipe + network)
Selected AbstractsWater pipeline failure due to water hammer effectsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2006C. SCHMITT ABSTRACT A numerical model has been established in order to simulate the propagation of pressure waves in water networks. The present model formulation is based on a system of partial hyperbolic differential equations. This system has been solved via the characteristics method. The current model provides the necessary data and the necessary damping of water hammer waves, taking into account the structure of the pipe network and the pressure loss. The numerical algorithm estimates the maximum pressure values resulting from the water hammer when closing valves in the network and consequently, the maximum stresses in the pipes have been calculated. In the case of simultaneous closing of several valves, the over pressure can exceed the admissible pressure. In this case, the severity of a defect such as a corrosion crater (pit) has been estimated by computing a safety factor for the stress distribution at the defect tip. This allows the applied notch stress intensity factor to be obtained. To investigate the defect geometry effects, semi-spherical and semi-elliptical defects are deemed to exist in up to one-half of the thickness of the pipe wall. The outcomes have been introduced into the structural integrity assessment procedure (SINTAP) failure diagram assessment (FAD) in order to obtain the safety factor value. Conventionally, it is considered that a failure hazard exists if this safety factor is less than two. [source] Hydrological connectivity of soil pipes determined by ground-penetrating radar tracer detectionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2004Joseph Holden Abstract Soil pipes are common and important features of many catchments, particularly in semi-arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also signi,cantly in,uence catchment sediment and solute yield. However, there are often problems in ,nding and de,ning soil pipe networks which are located deep below the surface. Ground-penetrating radar (GPR) has been used for non-destructive identi,cation and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed signi,cant changes in re,ectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post-processing, when background levels were increased by more than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post-processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of ,owpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development. Copyright © 2004 John Wiley & Sons, Ltd. [source] Soil piping and catchment responseHYDROLOGICAL PROCESSES, Issue 12 2010J. A. A. Jones Abstract Over the 40 years, since soil piping was first considered to be a potential factor in the hydrological response of catchments, research has revealed a considerable amount about its hydrological role and its geographical, climatic and pedological distribution. Piping has been shown to be a major factor supporting the hypothesis that subsurface flow can be a significant contributor to quickflow by field experiments ranging from the United Kingdom to Canada, India and China. This research has demonstrated that, at least in some areas, soil pipes may contribute up to nearly 50% of stormwater discharge. Piping processes therefore merit inclusion within rainfall,runoff simulation models, but this has yet to be achieved. Some progress has been made in modelling pipeflow itself, but integration within a catchment model presents major problems, not least in quantifying or parameterizing the nature and distribution of pipe networks. The wider environmental implications of soil piping are also only just beginning to be recognized. These range from the effects of changing residence times on water chemistry, especially on the acidification of surface waters, to the effects of hillslope drainage patterns on soil development and vegetation diversity. Copyright © 2010 John Wiley & Sons, Ltd. [source] Soil pipe distribution and hydrological functioning within the humid tropics: a synthesisHYDROLOGICAL PROCESSES, Issue 12 2010Nick A. Chappell Abstract Some of the most responsive runoff systems in the world are found within the humid tropics. These runoff responses are likely to be affected by the presence of natural pipes within the soil. This study provides a synthesis of the hydrological aspects of these phenomena within the humid tropics. Of the studies reporting the presence of soil piping within the humid tropics, most are associated with Ultisol soils, and, locally, most pipe outlets are observed on the lower sections of hillslopes. While the drainage role of pipes has been observed (providing faster and slower components of stream hydrographs), the mechanism of their recharge remains less clear. In part, this is because their spatial extent is poorly mapped within the hillslopes of the humid tropics. Further studies quantifying the length and recharge of soil pipe networks within the humid tropics are needed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Performance of algebraic multi-grid solvers based on unsmoothed and smoothed aggregation schemesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2001R. WebsterArticle first published online: 31 JUL 200 Abstract A comparison is made of the performance of two algebraic multi-grid (AMG0 and AMG1) solvers for the solution of discrete, coupled, elliptic field problems. In AMG0, the basis functions for each coarse grid/level approximation (CGA) are obtained directly by unsmoothed aggregation, an appropriate scaling being applied to each CGA to improve consistency. In AMG1 they are assembled using a smoothed aggregation with a constrained energy optimization method providing the smoothing. Although more costly, smoothed basis functions provide a better (more consistent) CGA. Thus, AMG1 might be viewed as a benchmark for the assessment of the simpler AMG0. Selected test problems for D'Arcy flow in pipe networks, Fick diffusion, plane strain elasticity and Navier,Stokes flow (in a Stokes approximation) are used in making the comparison. They are discretized on the basis of both structured and unstructured finite element meshes. The range of discrete equation sets covers both symmetric positive definite systems and systems that may be non-symmetric and/or indefinite. Both global and local mesh refinements to at least one order of resolving power are examined. Some of these include anisotropic refinements involving elements of large aspect ratio; in some hydrodynamics cases, the anisotropy is extreme, with aspect ratios exceeding two orders. As expected, AMG1 delivers typical multi-grid convergence rates, which for all practical purposes are independent of mesh bandwidth. AMG0 rates are slower. They may also be more discernibly mesh-dependent. However, for the range of mesh bandwidths examined, the overall cost effectiveness of the two solvers is remarkably similar when a full convergence to machine accuracy is demanded. Thus, the shorter solution times for AMG1 do not necessarily compensate for the extra time required for its costly grid generation. This depends on the severity of the problem and the demanded level of convergence. For problems requiring few iterations, where grid generation costs represent a significant penalty, AMG0 has the advantage. For problems requiring a large investment in iterations, AMG1 has the edge. However, for the toughest problems addressed (vector and coupled vector,scalar fields discretized exclusively using finite elements of extreme aspect ratio) AMG1 is more robust: AMG0 has failed on some of these tests. However, but for this deficiency AMG0 would be the preferred linear approximation solver for Navier,Stokes solution algorithms in view of its much lower grid generation costs. Copyright © 2001 John Wiley & Sons, Ltd. [source] The Trickle-down Effect: Ideology and the Development of Premium Water Networks in China's CitiesINTERNATIONAL JOURNAL OF URBAN AND REGIONAL RESEARCH, Issue 1 2007ALANA BOLAND This article examines the relationship between networked infrastructure and uneven development in transitional cities through a study of premium water networks in China. Beginning in the mid-1990s, select buildings and housing enclaves began to bypass municipal tap water supply systems through the construction of small-scale secondary pipe networks for purified drinking water. I focus on the early development of these premium water networks to highlight the ideological interplay between a new more market-based approach to networked supply and the existing model characterized by relatively universal and uniform access within cities. I illustrate how this dual water supply model was well suited to the ideological conditions and contradictions associated with China's economic liberalization in the 1990s. While the emergence of premium water networks can be linked to ascendant forms of market reasoning in the environmental and social spheres, I also argue that they were enabled by unresolved ideological tensions associated with China's transitional program. Rather than providing a basis for resistance in the early development of premium water supply, the socialist legacy in urban water supply left its mark more in the noticeable absence of debate regarding the distributional outcomes. By examining premium water networks in relation to the politics of ideology in China's transitional period, my analysis highlights the complex and sometimes unexpected ways that ideologies can influence the development of new infrastructural spaces and processes of splintering urbanism. [source] A new model for gas flow in pipe networksMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 7 2010M. Herty Abstract We introduce a new model for gas dynamics in pipe networks by asymptotic analysis. The model is derived from the isothermal Euler equations. We present the derivation of the model as well as numerical results illustrating the validity and its properties. We compare the new model with existing models from the mathematical and engineering literature. We further give numerical results on a sample network. Copyright © 2009 John Wiley & Sons, Ltd. [source] Multiscale modeling for gas flow in pipe networksMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2008Mapundi K. Banda Abstract We consider a multiscale network of natural gas pipelines. Different arcs of the network are to be modeled by possibly different models depending on the requisite qualitative detail required: an isothermal Euler system of equations; linearized model derived from the isothermal Euler system or a steady-state model of gas flow also referred to as an algebraic model. At the vertices (or joints) of the network coupling conditions are defined. An analysis of the well posedness of the hierarchial coupling conditions is presented. The analytical results are tested numerically on different network configurations including a real-world network based on the Canadian mainline gas network. Copyright © 2007 John Wiley & Sons, Ltd. [source] Explicit Calculation of the Friction Factor for Non-Newtonian Fluids Using Artificial Neural NetworksASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2005W. H. Shayya An explicit procedure based on artificial neural networks (ANN) was developed for calculating the friction factor (f) for Herschel-Bulkley fluids under laminar and turbulent flow conditions in closed pipes. The Regula-Falsi method was used as an iterative procedure to estimate the f values for a range of flow behavior indexes (n), Reynolds numbers (Re), and Hedstrom numbers (He). In developing the ANN model, the input parameters Re and He and the output parameter f were transformed using a logarithmic scale to the base 10, while the input parameter n was taken on a linear scale. An ANN configuration with 16 neurons in each of two hidden layers was found to be optimal. However, a simpler ANN model with eight neurons in one hidden layer also produced reasonably good predictions. These values were in close agreement with those obtained using the numerical technique. The developed ANN model may offer significant advantages when dealing with flow problems that involve repetitive calculations of the friction factor such as those encountered in the hydraulic analysis of viscous non-Newtonian fluids in pipe networks. [source] | ||||||||||