Multifactor analysis of specific storage estimates and implications for transient groundwater modelling

Specific storage (S$_S$) has considerable predictive importance in the modelling of groundwater systems, yet little is known about its statistical distribution and dependency on other hydrogeological characteristics. This study provides a comprehensive overview and compiles 430 values of S$_S$ from 183 individual studies, along with complementary hydrogeological information such as estimation methods, lithology, porosity, and formation compressibility. Further evaluation of different approaches to determine and utilize S$_S$ values for numerical groundwater modelling, along with the scale and source of uncertainty of different measurement methods, was carried out. Overall, S$_S$ values range across six orders of magnitude (from 3.2 × 10$^{–9}$ to 6 × 10$^{–3}$ m$^{–1}$) with a geometric mean of 1.1 × 10$^{–5}$ m$^{–1}$ and the majority (> 67%) of values are in the order of 10$^{–5}$ and 10$^{–6}$ m$^{–1}$. High S$_S$ values of ~10$^{–4}$ m$^{–1}$ were reported for glacial till and sandy lithologies, particularly for shallow and thin strata where leakage may obscure the estimation of S$_S$. A parallel assessment of 45 transient regional-scale groundwater models reveals a disconnect between findings of this study and the way S$_S$ is treated in practice, and that there is a lack of foundational S$_S$ data to conduct quantitative uncertainty analysis. This study provides the first probability density functions of S$_S$ for a variety of lithology types based on the field and laboratory tests collated from the literature. Log transformed S$_S$ values follow a Gaussian/normal distribution which can be applied to evaluate uncertainties of modelling results and therefore enhance confidence in the groundwater models that support decision making

Determination of the linear frequency response of single pipelines using persistent transient excitation: a numerical investigation

The linear frequency response of a fluid-filled pipeline extracted by fluid transient waves can be used to detect leaks in pipelines. This research conducts numerical analysis on how to accurately determine the linear frequency response diagram (FRD) of single pipelines using persistent transient pressure signals. Two types of persistent signals, the maximum-length binary sequence and the inverse-repeat sequence (IRS), are compared in terms of the accuracy in estimating the linear response of a pipeline at resonant frequencies. The IRS is found to be more appropriate for identifying the linear portion of the FRD of a pipeline, since its antisymmetric property can supress part of the nonlinear response. Numerical simulations are conducted to verify the findings. © 2013 © 2013 International Association for Hydro-Environment Engineering and Research.Jinzhe Gong, Angus R. Simpson, Martin F. Lambert & Aaron C. Zecchi

Single-event leak detection in pipeline using first three resonant responses

Hydraulic transients (water hammer waves) can be used to excite a pressurized pipeline, yielding the frequency response diagram (FRD) of the system. The FRD of a pipeline system is useful for condition assessment and fault detection, because it is closely related to the physical properties of the pipeline. Most previous FRD-based leak detection techniques use the sinusoidal leak-induced pattern recorded on the FRD, either shown on the resonant responses or the antiresonant responses. In contrast, the technique reported in the current paper only uses the responses at the first three resonant frequencies to determine the location and size of a leak. The bandwidth of the excitation only needs to be five times that of the fundamental frequency of the tested pipeline, which is much less than the requirement in conventional FRD-based techniques. Sensitivity analysis and numerical simulations are performed to assess the robustness and applicable range of the proposed leak location technique. The proposed leak location technique is verified by both numerical simulations and by using an experimental FRD obtained from a laboratory pipeline. © 2013 American Society of Civil Engineers.Jinzhe Gong, Martin F. Lambert, Angus R. Simpson, and Aaron C. Zecchi

Leak detection and condition assessment for water distribution pipelines using fluid transient waves

The focus of this PhD research is to develop non-invasive and cost-effective techniques for assessing the structural condition of pressurised pipelines using fluid transient pressure waves. The specific objectives include the detection of leaks and localised deterioration that is distributed along a pipeline, such as extended sections of corrosion or the spalling of cement lining. The latter is described by pipeline condition assessment in this thesis. The transient behaviour of a leak is studied in the frequency domain. Numerical studies conducted in this research demonstrate that two leak-induced patterns (on the resonant and the anti-resonant responses) can exist in a frequency response diagram (FRD). The amplitudes of the responses are related to the impedance of the valve in a reservoir-pipeline-valve (RPV) system. A new leak detection technique has been developed in this research based on the further understanding of the leak-induced patterns. This technique uses the relative sizes of the first three resonant responses to determine the location and size of a single leak in RPV systems. In reservoir-pipeline-dead end systems, the information required for single event leak detection is further reduced to the first two resonant responses. A new measurement strategy for the extraction of the FRD of single pipelines is proposed in this research. The boundary valve loss is used to adjust the amplitude of the leak-induced pattern on the resonant responses and also the sharpness of the resonant peaks. A specific type of pseudo-random binary sequence (PRBS) termed the inverse repeat sequence (IRS), is used as the excitation signal. The antisymmetric property of IRS enables part of the nonlinear responses of the system under excitation to be cancelled out, yielding a measured FRD close to the theoretical linear system response. A side-discharge valve based transient generator is designed and fabricated in this research to implement the new FRD measurement strategy. Laboratory experiments are conducted on an intact pipeline and a pipeline with a leak. This research also conducts analysis of the characteristics of distributed pipe wall deterioration and develops new detection techniques. In a measured pressure trace, the size of the reflection resulting from a section of pipeline with a change in wall thickness is indicative of the characteristic impedance of this section. Once the impedance of this section is determined, the wave speed and wall thickness can be estimated. A technique for the detection of a single deteriorated section in pipelines is developed based on the above analysis. Two other condition assessment techniques are developed to deal with the complexities induced by multiple deteriorated sections. The first technique is termed reconstructive MOC (method of characteristics) analysis, which uses the pressure trace measured at the upstream face of the valve in a RPV system to determine the distribution of the impedance along the pipeline. The algorithm reconstructs a MOC grid by calculating the MOC compatibility equations backwards in time, estimating the properties of the pipeline (impedance, wave speed) and the length of each pipe reach as discretised by the MOC grid from the valve towards the reservoir. Preliminary experimental verification is conducted to verify the applicability of the new technique. The second technique is reconstructive transient analysis (RTA), which can be conducted at any interior accessible points along a pipeline, and does not require a RPV boundary condition. The RTA uses two pressure transducers in close proximity to measure two transient pressure traces in one test. A signal processing algorithm is developed to extract the directional transient waves (traveling upstream and downstream). The use of the directional transient waves enables the step response function (SRF) of the section of pipe upstream or downstream of the paired pressure transducers to be obtained. The reconstructive MOC analysis is then adapted to interpret the SRF to yield the distribution of the impedance, from which the location and severity of distributed deterioration can be identified.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2014

A practical scheme for 3D geoelectrical forward modeling with finite-infinite element coupling method

In this study, fast and visualized pre and post processing for infinite element method was achieved by customized development based on the universal 3D modeling software named GiD, while infinite elements were introduced to form the finite-infinite element coupling method, which could substitute the conventional mixed boundary conditions and solve the problems cased by artificial boundary conditions. For the customized development on GiD, we only need to program the so-called problem types with simple script language, then models could be build in the graphic interface and output in the format fitting our calculation program. As to our finite-infinite element method, Astley mapped wave envelope infinite elements were employed to continue the electrical potential to infinity. Then, a new type of shape functions was created and it was proved to be the optimal one in both accuracy and time consumption by comparing with several other shape functions. Finally, the availability and superiority of this coupling algorithm were confirmed by several numerical tests with various electrode arrays

Study on the frequency response function of viscoelastic pipelines using a multi-element Kevin-Voigt model

AbstractThis research focuses on the study of the frequency response function (FRF) of viscoelastic pipelines. The transfer matrix of a uniform viscoelastic pipeline is derived using the generalized multi-element Kevin-Voigt (K-V) model. The analytical expressions of the characteristic impedance and propagation operator are presented. The frequency response diagrams (FRDs) of a viscoelastic pipeline, with or without unsteady friction, are obtained numerically and compared with the FRDs of an elastic pipeline, with or without unsteady friction. It is verified that the pipe wall viscoelasticity introduces not only frequency-dependent shifting of the resonant frequencies but also frequency-dependent damping of the resonant peaks

Experimental study of dynamic effects of iron cacteria-formed biofilms on pipeline head loss and roughness

Abstract not availableJinzhe Gong, Mason Erkelens, Martin F. Lambert and Peter Forwar