The results of numerical simulations of inclined negatively buoyant jets are presented. These simulations address previously highlighted difficulties in capturing sufficient detail of critical flow processes to effectively predict the detailed flow behaviour. In particular, the new simulations are able to accurately capture the details of the buoyancy-induced instabilities, which are clearly evident in associated experimental investigations and that have significant impacts on the flow behaviour. This new information is captured for inclined negatively buoyant jets discharged at 45° above a horizontal reference plane. A Large Eddy Simulation (LES) approach is implemented that makes use of a Lagrangian Dynamic Sub-grid scale (SGS) model and a novel criterion for the adaptive meshing system. Comparisons with previously published simulation results and experimental data demonstrate that these new Adaptive LES simulations provide improved predictions of flow path, concentration and velocity fields, and associated mean and turbulent statistics. In addition, this study provides a set of methods for generating high-quality LES data sets for free shear flows, which are well beyond the level of detail that can be captured by current experimental systems.

This paper investigates the validity of using fluid transients as a rapid screening tool to augment existing methods for assessing the condition of buried water systems. In particular, the paper provides one of the first detailed investigations on the impact of pipe wall deterioration on the characteristic of transient waves in both laboratory and field experiments. Laboratory pipeline sections were deteriorated by an accelerated corrosion process using controlled electrolytic cell reactions, and three cases were considered: where corrosion is limited to the internal wall, limited to the external wall, and where both internal and external walls are corroded. Hydraulic transient tests were carried out to measure the transient wave speed in these corroded pipe sections, and the measurements are found to be consistent with the theoretical predictions using the observed wall thickness loss, confirming that wave speed can be used as an indicator of pipe wall deterioration. Field experiments were carried out in the water supply network in the Waimakariri District, New Zealand, to validate the performance of this pipe condition diagnostic methodology. Transient tests were conducted on selected 60-year-old sections of asbestos cement (AC) pipelines and sensors were connected to standard fire hydrants to measure the wave speeds and wave reflections. Compared with the theoretical calculated wave speed of intact pipelines, a 140–300 m/s wave speed decrease was observed in most of the tested sections which is in line with the expectation for pipelines of this age. The wave speeds were used to predict the in-situ thickness of the pipe wall and these predictions were found to match with computed tomography X-ray scan results of the excavated pipe with good accuracy. The same methodology was also used to correctly detect an unrecorded plastic pipe section in the AC pipe network.

The ambient noise in water pipelines are observed as spontaneous signal sources that can be used for pipe fault detection by correlation analysis. However, the limited bandwidth of these noise signal causes strong correlation sidelobes, which introduces significant ambiguities when extracting the system response from correlation results and this increases the risk of false alarms from fault detections. This paper proposes a compressive sensing based method that can extend the noise bandwidth and suppress the correlation sidelobes. Numerical and field experiment results have shown that with the recovered wider bandwidth, the correlation sidelobes can be significantly suppressed and the pipe faults can be identified with greater certainty. The impacts of fault size as well as noise bandwidth, strength and spectrum features on the proposed method are also assessed through numerical experiments.

Brine discharges from desalination facilities represent an important environmental consideration surrounding the use of desalination technologies. These discharges are typically released through a series of subsurface discharge ports, and the ability to quantify their flow behaviour is critical to mitigating adverse environmental effects. Previous experimental studies on desalination discharges or Inclined Negatively Buoyant Jets have highlighted discrepancies in the dilution measurements reported in the literature. These discrepancies are potentially due to the inconsistent treatment of the lower boundary in the experimental setup, which in practice represents the seabed. This issue is investigated through a series of experiments using the Laser Induced Fluorescence method. Three discharge angles (300, 450 and 600) are tested and the non-dimensional source height above the boundary (H/F0d) is varied between 0.06 and 1.84 (termed the bed proximity parameter). The results illustrate a relationship between dilutions measured at common reference points near the boundary and the bed proximity parameter. Dilutions are also shown to decrease by up to 30% compared to experiments without lower boundary influence. The outcomes from this study provide valuable insight into the previously reported discrepancies and enable the lower boundary to be incorporated into the design of desalination discharge systems.

A passive detection method has been proposed in a prior paper to extract key parameters and detect faults using the ambient noise present in water pipeline networks. This paper presents field experiments and data processing results to provide systematic experimental validation of this method. Field experiments were carried out in operational water pipeline networks at the University of Canterbury campus and the Waimakariri District, New Zealand, during which ambient noise was measured by pairs of pressure sensors installed at selected hydrants on pipelines of different materials, network topologies and simulated faults. Auto-correlation and cross-correlation analysis of noise at a single sensor and sensor pairs were carried out to estimate the wave speed and to locate faults in the networks. Data processing results indicate that water usage generating pressure transients are the dominant sources of ambient noise in operational water pipeline networks. This type of ambient noise can also be utilized by the passive detection method to achieve similar wave speed estimation accuracy and fault detection performance as the conventional active pressure wave detection methods.

Brine discharges from desalination facilities represent an important environmental consideration surrounding use of desalination technologies. These discharges are typically released through a through a series of subsurface discharge ports, and the ability to quantify their flow behavior is critical to mitigating adverse environmental effects. Previous experimental studies on desalination discharges or Inclined Negatively Buoyant Jets (INBJ) have highlighted discrepancies in the dilution measurements reported in the literature. These discrepancies are potentially due to the inconsistent treatment of the lower boundary in the experimental setup, which in practice represents the seabed. This issue is investigated through a series of experiments using the Laser Induced Fluorescence method. Three discharge angles (300, 450 and 600) are tested and the non-dimensional source height above the boundary (H/F0d) is varied between 0.06 and 1.84 (termed the boundary parameter). The results illustrate a relationship between dilutions measured at common reference points near the boundary and the boundary parameter. Dilutions are also shown to decrease by up to 30% compared to experiments without lower boundary influence. The outcomes from this study provide valuable insight into the previously reported discrepancies in the literature and enable the lower boundary to be incorporated into the design of desalination discharge systems.

Effective modeling of pipe network anomalies can supplement fluid transient diagnostic techniques. This study focuses on comparing modeling approaches for predicting the transient response due to air pockets entrapped outside the main flow path (offline), in particular testing the assumption that the flow inside the cavity can be predicted based on a lumped element. This assumption has been consistently made in previous modeling investigations in the time and frequency domains. The results are compared to a system frequency response model without the lumped inertia assumption by quantifying timing and signal frequency distribution errors. It is found that removing the lumped inertia assumption improved the prediction of the reflected and transmitted pulse frequency distributions by averages of 50% and 30%-35%, respectively. (c) 2021 American Society of Civil Engineers.

The results of experimental studies into the behavior of nonbuoyant discharges impacting a solid boundary are presented. The discharges were released perpendicular to the boundary at nondimensional heights (H/d) ranging from to 36 to 173, where H/d is the ratio of the jet discharge height above the boundary to the jet diameter. Although the primary focus was on concentration field measurements using a laser-induced fluorescence system, additional velocity field data are presented from a recent study that used a similar discharge configuration and a particle tracking velocimetry system. Integral models provided a relatively simplistic framework for quantifying and interpreting the flow behavior in the vicinity of the boundary. The new data sets enabled defining the scale of the impact region based on the ability of integral techniques to model the flow entering and leaving this region. These data sets also offered insights into the flow behavior in the impact region and provided the basis for determining the influence of the impact region on the flow behavior. (c) 2021 American Society of Civil Engineers.

AbstractAir pockets entrapped in pipeline systems are required to be non-intrusively diagnosed by fluid transients. In this study, experimental investigations are used to compare the transient tran...

Entrapped air in pipeline systems can compromise the operation of the system by blocking flow and raising pumping costs. Fluid transients are a potential tool for characterizing entrapped air pockets, and a numerical model which is able to accurately predict transient pressures for a given air volume represents an asset to the diagnostic process. This paper presents a detailed study on our current capability for modeling and predicting the dynamics of an inline air pocket, and is one of a series of articles within a broader context on air pocket dynamics. This paper presents an assessment of the accuracy of the variable wave speed and accumulator models for modeling air pockets. The variable wave speed model was found to be unstable for the given conditions, while the accumulator model is affected by amplitude and time-delay errors. The time-delay error could be partially overcome by combining the two models.

Monitoring pipeline thinning and material degeneration is becoming important for water-filled pipeline condition assessment. In this paper, an inverse method is proposed for estimating a pipeline's dimensional and material parameters using the dispersion characteristics of its modal wavenumbers. The inverse method is established by matching observed wavenumber dispersion characteristics of the water-filled pipeline with forward model predictions, where pipeline inner radius, thickness and density, and longitudinal and transverse wave speeds of the pipeline wall material are taken as unknown parameters. To account for the strong nonlinearity of the inverse problem and improve inversion efficiency, a Bayesian inversion scheme is formulated using a parallel-tempering Markov chain Monte Carlo approach. The characteristics and the performance of the proposed inverse method are investigated by systematic simulations which cover the impact of the number of modes utilized, dispersion frequency interval and observation errors. Laboratory experiments are utilized to validate the inversion method using wavenumber dispersion observations (below 50 kHz) from three metallic pipelines all with the same outer radius but different wall thicknesses and materials. The uncertainties of the estimated dimensional parameters are found to be lower than 0.2 mm and different materials are successfully distinguished and identified for the three pipelines. (C) 2019 Elsevier Ltd. All rights reserved.

Entrapped air blocking the flow in pipeline systems is a common cause of increased pumping costs. At present, air is generally removed via valves or pipeline excavation and drilling. This becomes inefficient in large networks where the precise location of the air is unknown. Fluid transients are a potential tool for detecting and locating air in pipelines. The effect of a stationary air pocket part of the way along the pipe, which occupies the main flow path and acts as a blockage without causing a hydraulic jump or column separation, has not previously been studied experimentally. This paper presents experimental results for a transient pulse interacting with an in-line air pocket for a range of pocket sizes and system pressures. In accordance with the impedance theory, the reflective power of the air increases with pocket size. Other notable characteristics of the interaction include frequency-dependent transmissivity, an out-of-phase reflection, and a substantial reflection under zero base flow. These effects set air pockets apart from solid blockages, allowing a transient detection methodology to differentiate between the two cases, although they have similar effects at steady-state.

This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into ‘trapped’ offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier–Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed.

The condition assessment of pipelines is central to the management of water systems but is only conducted sporadically due to the limited range and practical constraints of current technologies. This paper describes the successful international field trial of a new condition assessment approach that was tested in live water pipeline networks of large cities during peak water demand and traffic conditions. The system, referred to as PIPE SONAR (PCT/EP2015/059540), uses a piezoelectric actuator capable of generating customized, small amplitude (<0.4m) pressure signals. The field trial involved 1600 individual field tests covering 31 sites of water networks in New Zealand and China, across nine different pipe materials and pipe diameters ranging from 100mm to 600mm. The results of the condition assessment were independently confirmed using hydrant tests, low frequency transient tests, and direct inspection through excavation.

Experiments were performed with a particle tracking velocimetry system to investigate the behaviour of inclined negatively buoyant jets with source angles of 15°, 30°, 45°, 60°, 65°, 70°, and 75° in stationary ambient conditions. Velocities were measured in a plane aligned with the central axis of the flow and the experiments were designed such that the flow did not interact with boundaries in the region were the flow behaviour was measured. The results of this study complement previous research, which has largely focused on the mean geometric characteristics and the mean dilution of the discharged fluid. Geometric characteristics, spreading rates, and time-averaged (mean) centreline velocity results are compared with relevant experimental results from previous studies and integral model predictions. Axial and transverse mean velocity profiles at maximum height and the return point provide additional insights into the detrainment of discharged fluid due to the unstable density gradient on the inner side of the flow.

Large-scale desalination facilities are increasingly employed to supplement potable water supplies for many cities, where the demand for water is having a negative impact on the sustainability of natural water resources. A primary environmental concern with the establishment of these large-scale facilities is the effective disposal of the hyper-saline effluent brine, so that harmful effects on the marine environment are minimised. In countries with effective effluent discharge regulations, the negatively buoyant brine is typically released through submerged diffusers, where the ports are inclined towards the ocean surface to aid dispersion processes. Predictive models provide an inexpensive method of considering different sources and ambient design parameters. It has been demonstrated that predictive models developed primarily for positively buoyant discharges significantly underestimate dilution measured by physical studies, when applied to negatively buoyant desalination discharges. It has been shown recently that predicted dilution and geometric parameters can be improved if a reduction in the buoyancy flux of the main flow is incorporated into these models. Here, the reduced buoyancy flux (RBF) approach is modified through the use of a physically based buoyancy loss mechanism. Improvements in the predictive capabilities of the new model are demonstrated through comparisons with predictions from existing models and an extensive range of results from physical studies for geometric, dilution, and velocity parameters.

The waves generated by a submarine landslide, of great concern to coastal communities, exhibit strong dependence on the landslide motion along the sea floor. A series of two-dimensional physical experiments investigate the waves generated by a solid block landslide moving along a horizontal boundary, allowing measurement of both onshore- and offshore-propagating waves using the laser-induced fluorescence technique. This technique provides high-quality free surface measurements over the entire length of the experimental flume, and hence a data set that can be used to validate numerical models for this idealised scenario. The landslide motion is provided by a mechanical system, allowing testing of a range of landslide accelerations and terminal velocities. The landslide Froude number governs the overall behaviour of the wave field. At lower Froude numbers, the waves are almost entirely generated by the landslide acceleration and deceleration, and the offshore- and onshore-propagating wave groups contain approximately equal energy. Interactions between the landslide and the offshore-propagating waves become more important as the Froude number increases. Two inviscid-irrotational models demonstrate the importance of dispersive effects for tsunamis generated by a submarine landslide, and correctly predict the behaviour of the entire wave field at low Froude numbers. The predictions in the vicinity of the landslide worsen with increasing Froude number, due to the linear free surface conditions used by the models. Lower Froude numbers appear to be more representative of previous sloping-boundary experimental geometries, although rigid block landslides still represent an idealisation of a field scenario.

This paper investigates the effect that an extended blockage has on a transient signal by examining numerical and experimental results in the time and frequency domains. Extended blockages can develop in pipelines via the processes of tuberculation, scaling, bio film growth, sediment deposition or through designed reductions in pipe diameter. It is identified that consideration of the gradual formation of these faults is important in pipeline design as they can significantly change the fundamental period of a pipelines transient response, maximum and minimum transient pressure heads and the evolution of the transient signal, thus potentially increasing a systems susceptibility to failure. Analysis of transient signals affected by a blockage provides information on the property and location of the extended blockage. In this paper, comparisons between discrete and extended blockage models are made and the effects of changes in blockage diameter, length and wave speed on the transient response are investigated. Furthermore, the ability of existing models to represent extended pipeline faults under transient conditions is evaluated through comparisons of numerical transient responses with new experimental results from the laboratory. Results show that the transient behaviour is modelled with a good level of accuracy over the first few periods of oscillation and that the level of accuracy decays with time. A periodic Fourier analysis of the data demonstrates that the damping rates of the experimental response are higher than the numerical predictions. Applying this new method of signal analysis has shown that the transient signal exhibits larger damping rates in the higher frequency components of the response.

Trajectory and centerline mean dilution data obtained from negatively buoyant jets, using a laser-induced fluorescence system, are presented at locations beyond the point at which the discharged fluid returns to its release height. Although this return point has been a focus of recent studies, site specific variations in source height and boundary angle can result in the flow impacting the boundary at locations that are distinct from this reference point. The new data are presented for source inclinations of 30, 45, and 60 degrees above the horizontal. Previously developed semianalytical solutions are extended to include the aforementioned site-specific geometric parameters. The ability of these extended solutions and those of the CorJet model to predict the location and mean centerline dilution at various impact points are assessed for nominal boundary angles that range from 0-20 degrees below the horizontal for trajectory and 0-15 degrees for dilution. Comparisons with the experimental data indicate that the extended semianalytical solutions provide superior predictions under the prescribed conditions. (C) 2013 American Society of Civil Engineers.

A modified integral model is developed to predict the near-field behaviour of negatively buoyant discharges, which are typical of those created when releasing brine from desalination plants into a marine environment via a submerged outfall system. These predictions are compared with available laboratory data and the predictions from other integral formulations, both analytical and numerical. Based on these comparisons, it is evident that the modified model is capable of predicting the effects of the additional mixing noted in previous studies, for the range of initial conditions relevant to a submerged discharge from a desalination facility. The modified model is therefore superior to existing numerical integral formulations in this respect and is reasonably consistent with the predictions from previously published analytical solutions. A critical feature of the modified integral model is the reduction in buoyancy flux of the main flow, which provides a mechanism to account for the influences of additional mixing created by buoyancy induced instabilities on the inner side of the flow.