This study is an industrial project commissioned by British Gas plc. (UK) to investigate the state of in-service naturally aged polyethylene (PE) buried pipes and to define procedures or techniques available to facilitate the condition assessment programme of PE pipelines systems. The primary goal of this study was to establish a better understanding of the ageing process in commercial piping materials and to understand its effect on long term integrity of PE pipeline systems. Eltex, Rigidex and Aldyl A are trade names of the PE gas grade resins used in this study and they represent the range of pipe materials used in the transport of potable water and gas in the UK. Sections of pipes used in this project were supplied by British Gas plc. in the form of unaged pipes and pipes which were aged in-service. Laboratory based accelerated ageing of the pipe resin samples was also carried out. The ageing regimes considered were water ageing at 23°C, air-oven ageing at 80°C, water ageing at 80 C, vacuum ageing at 80°C and in-service aged samples. Compression moulded plaques were produced as reference material. By utilising specific instrumentation and designs, several reliable procedures were developed to produce specimens directly from pipes. The feasibility of using micro-samples instead of large samples was demonstrated. A methodology was developed to retrieve disk samples using electrofusion "tapping-tee" saddles. Appropriate test specimens were designed for chemical and physical evaluations. This sampling method negates the need for excavating large sections of pipe material for the purpose of condition assessment. Reliable micro and macro-sampling test methods were developed and established as techniques for the condition assessment programme. Characterisation techniques included: (i) differential scanning calorimetry (DSC) to measure (from the same specimen) both the degree of crystallinity and the oxidation induction time (OIT), (ii) HPLC analysis was used to quantify additives concentrations, (iii) Fourier transform infrared spectroscopy was used to monitor the carbonyl index and to identify a pipe resin type from site, (iv) micro- and macro-tensile and fatigue tests to assess the changes in the mechanical properties as function of ageing. The fatigue test procedure was developed to produce brittle fracture at laboratory scale within a shorter period of time as compared to existing procedures such as the hydrostatic test. A reference data-base was created using the above identified tools and the criteria and methodology for carrying out site condition assessment inspection was compiled. The fundamental mechanisms of chemical and physical ageing were studied along with the possibility of their effect on the mechanical properties of PE pipes.

Leakage and blockage of oil and gas pipeline systems, water pipelines, pipe-work of process plants and other pipe networks can cause serious environmental, health and economic problems. There are a number of non-destructive testing (NDT) methods for detecting these defects in pipeline systems such as radiographic, ultrasonic, magnetic particle inspection, pressure transient and acoustic wave methods. In this study, the acoustic wave method and a modal frequency technique, which based on a roving mass method, are used. The aim of the thesis is to employ acoustic wave propagation based methods in conjunction with stationary wavelet transform (SWT) to identify leakage and blockage in pipe systems. Moreover, the research is also aimed at using the difference of modal frequencies of fluid-filled pipes with and without defects and a roving mass, and consequently, to develop a roving mass-based defect detection method for pipelines. In the study, the acoustic finite-element analysis (AFEA) method is employed to simulate acoustic wave propagation in small and large air-filled water-filled straight pipe and pipe networks with leakage and blockage but without flow. Computational fluid dynamics (CFD) analysis was also employed to simulate acoustic wave propagation in air-and water-filled pipes with flow, leakage and blockage. In addition, AFEA was used to predict the modal frequencies of air- and water-filled pipes with leakage and blockage in the presence of a roving mass that was traversed along the axis of the pipes. Experimental testing was conducted to validate some of the numerical results. Two major experiments were performed. The first set of experiments consisted of the measurement of acoustic wave propagation in a straight air-filled pipe with leakage and blockage. The second set of experiments concerned the measurement of acoustic wave propagation in an air-filled pipe network comprising straight pipe, elbows and T-piece and flange. The AFEA and CFD analysis of fluid-filled pipe can be used to simulate the acoustic wave propagation and acoustic wave reflectometry of a fluid-filled pipe with leakage and blockage of different sizes down to a small leakage size of 1mm diameter and a blockage depth of 1.2mm in a pipe. Similarly, the AFEA method of a static fluid-filled pipe can be used to simulate acoustic wave modal frequency analysis of a fluid-filled pipe with leakage and blockage of different sizes down to a leakage of 1mm diameter and a blockage depth of 1.2mm. Moreover, the measured signal of acoustic wave propagation in an air-filled can be successfully decomposed and de-noised using the SWT method to identify and locate leakages of different sizes down to 5mm diameter, and small blockage depth of 1.2mm. Also, the SWT approximation coefficient, detail and de-noised detail coefficient curves of an air-filled pipe with leakage and blockage and a roving mass give leakage and blockage indications that can be used to identify, locate and estimate the size of leakage and blockage in a pipe.

Starting with tensor calculus and the variational form of the Hamiltonian functional, a generalized theory is formulated for doubly curved thin shells. The formulation avoids geometric approximations commonly adopted in other formulations. The theory is then specialized for cylindrical and toroidal shells as special cases, both of interest in the modeling of straight and elbow segments of pipeline systems. Since the treatment avoids geometric approximations, the cylindrical shell theory is believed to be more accurate than others reported in the literature. By adopting a set of consistent geometric approximations, the present theory is shown to revert to the well known Flugge shell theory. Another set of consistent geometric approximations is shown to lead to the Donnell-Mushtari-Vlasov (DMV) theory. A general closed form solution of the theory is developed for cylinders under general harmonic loads. The solution is then used to formulate a family of exact shape functions which are subsequently used to formulate a super-convergent finite element. The formulation efficiently and accurately captures ovalization, warping, radial expansion, and other shell behavioural modes under general static or harmonic forces either in-phase or out-of-phase. Comparisons with shell solutions available in Abaqus demonstrate the validity of the formulation and the accuracy of its predictions. The generalized thin shell theory is then specialized for toroidal shells. Consistent sets of approximations lead to three simplified theories for toroidal shells. The first set of approximations has lead to a theory comparable to that of Sanders while the second set of approximation has lead to a theory nearly identical to the DMV theory for toroidal shells. A closed form solution is then obtained for the governing equation. Exact shape functions are then developed and subsequently used to formulate a finite element. Comparisons with Abaqus solutions show the validity of the formulation for short elbow segments under a variety of loading conditions. Because of their efficiency, the finite elements developed are particularly suited for the analysis of long pipeline systems.

Starting with tensor calculus and the variational form of the Hamiltonian functional, a generalized theory is formulated for doubly curved thin shells. The formulation avoids geometric approximations commonly adopted in other formulations. The theory is then specialized for cylindrical and toroidal shells as special cases, both of interest in the modeling of straight and elbow segments of pipeline systems. Since the treatment avoids geometric approximations, the cylindrical shell theory is believed to be more accurate than others reported in the literature. By adopting a set of consistent geometric approximations, the present theory is shown to revert to the well known Flugge shell theory. Another set of consistent geometric approximations is shown to lead to the Donnell-Mushtari-Vlasov (DMV) theory. A general closed form solution of the theory is developed for cylinders under general harmonic loads. The solution is then used to formulate a family of exact shape functions which are subsequently used to formulate a super-convergent finite element. The formulation efficiently and accurately captures ovalization, warping, radial expansion, and other shell behavioural modes under general static or harmonic forces either in-phase or out-of-phase. Comparisons with shell solutions available in Abaqus demonstrate the validity of the formulation and the accuracy of its predictions. The generalized thin shell theory is then specialized for toroidal shells. Consistent sets of approximations lead to three simplified theories for toroidal shells. The first set of approximations has lead to a theory comparable to that of Sanders while the second set of approximation has lead to a theory nearly identical to the DMV theory for toroidal shells. A closed form solution is then obtained for the governing equation. Exact shape functions are then developed and subsequently used to formulate a finite element. Comparisons with Abaqus solutions show the validity of the formulation for short elbow segments under a variety of loading conditions. Because of their efficiency, the finite elements developed are particularly suited for the analysis of long pipeline systems.

Starting with tensor calculus and the variational form of the Hamiltonian functional, a generalized theory is formulated for doubly curved thin shells. The formulation avoids geometric approximations commonly adopted in other formulations. The theory is then specialized for cylindrical and toroidal shells as special cases, both of interest in the modeling of straight and elbow segments of pipeline systems. Since the treatment avoids geometric approximations, the cylindrical shell theory is believed to be more accurate than others reported in the literature. By adopting a set of consistent geometric approximations, the present theory is shown to revert to the well known Flugge shell theory. Another set of consistent geometric approximations is shown to lead to the Donnell-Mushtari-Vlasov (DMV) theory. A general closed form solution of the theory is developed for cylinders under general harmonic loads. The solution is then used to formulate a family of exact shape functions which are subsequently used to formulate a super-convergent finite element. The formulation efficiently and accurately captures ovalization, warping, radial expansion, and other shell behavioural modes under general static or harmonic forces either in-phase or out-of-phase. Comparisons with shell solutions available in Abaqus demonstrate the validity of the formulation and the accuracy of its predictions. The generalized thin shell theory is then specialized for toroidal shells. Consistent sets of approximations lead to three simplified theories for toroidal shells. The first set of approximations has lead to a theory comparable to that of Sanders while the second set of approximation has lead to a theory nearly identical to the DMV theory for toroidal shells. A closed form solution is then obtained for the governing equation. Exact shape functions are then developed and subsequently used to formulate a finite element. Comparisons with Abaqus solutions show the validity of the formulation for short elbow segments under a variety of loading conditions. Because of their efficiency, the finite elements developed are particularly suited for the analysis of long pipeline systems.

Starting with tensor calculus and the variational form of the Hamiltonian functional, a generalized theory is formulated for doubly curved thin shells. The formulation avoids geometric approximations commonly adopted in other formulations. The theory is then specialized for cylindrical and toroidal shells as special cases, both of interest in the modeling of straight and elbow segments of pipeline systems. Since the treatment avoids geometric approximations, the cylindrical shell theory is believed to be more accurate than others reported in the literature. By adopting a set of consistent geometric approximations, the present theory is shown to revert to the well known Flugge shell theory. Another set of consistent geometric approximations is shown to lead to the Donnell-Mushtari-Vlasov (DMV) theory. A general closed form solution of the theory is developed for cylinders under general harmonic loads. The solution is then used to formulate a family of exact shape functions which are subsequently used to formulate a super-convergent finite element. The formulation efficiently and accurately captures ovalization, warping, radial expansion, and other shell behavioural modes under general static or harmonic forces either in-phase or out-of-phase. Comparisons with shell solutions available in Abaqus demonstrate the validity of the formulation and the accuracy of its predictions. The generalized thin shell theory is then specialized for toroidal shells. Consistent sets of approximations lead to three simplified theories for toroidal shells. The first set of approximations has lead to a theory comparable to that of Sanders while the second set of approximation has lead to a theory nearly identical to the DMV theory for toroidal shells. A closed form solution is then obtained for the governing equation. Exact shape functions are then developed and subsequently used to formulate a finite element. Comparisons with Abaqus solutions show the validity of the formulation for short elbow segments under a variety of loading conditions. Because of their efficiency, the finite elements developed are particularly suited for the analysis of long pipeline systems.

Диссертация посвящена проблеме возникновения шума и вибрации от трубопроводных систем многоэтажных зданий. Предложен способ определения вероятности возникновения повышенных вибраций с помощью модального анализа в программном комплексеANSYS Workbench. Представлены результаты численного анализа влияния длины, диаметра и толщины стенки участка трубопровода на изменение значений частот его собственных колебаний с целью прогноза риска возможных резонансных режимов. Выполнены статистический и регрессионный анализы. / The dissertation discusses the occurrence of noise and vibration from the piping systems of multi-storey buildings. A method for determining the probability of excessive vibrations using modal analysis software complex ANSYS Workbench. The results of the digital analysis of influence of length, diameter and thickness of a wall of the pipeline’s section on change of values of frequencies of its natural oscillations are provided. Statistical and regression analyses are made.

The reported research provides a rough guide to the best practice of decision modeling concerning urban pipeline systems’ rehabilitation. The thesis aims to bring attention to the fact that a proper decision-making model is a cornerstone for efficient infrastructure management. More precisely, this thesis aims to increase the knowledge about applicable decision support methods by identifying relevant factors that should be considered in the decision-making process. This can, facilitate future rehabilitation attempts of existing urban infrastructure. A utility-based decision model was adopted for a water distribution network in Sweden to locate and rehabilitate leakages as an ultimate sign of failure. This was performed by implementing and evaluating a Bayesian decision model including the treatment of uncertainties in evaluating the best decision from a short-term perspective. Despite its simplicity, the result showed that the proposed model could facilitate problem-solving approaches when uncertainty is an issue. Considering the several interacting factors of services and the availability of information, the importance of problem structuring before applying a decision model was extensively acknowledged. As a result, a conceptual decision model was proposed to choose the most appropriate decision model applicable for a particular problem in the essence of deciding how to decide. The presented model illustrated the first steps of developing a theoretical framework for a rational yet practical decisionmaking. This approach, which is aimed to be further employed in rehabilitation strategies of urban pipelines, ensures that the chosen decision technique has explicitly considered different levels of uncertainty and would be the best-established solution for a particular type of problem, organization, and stakeholder. This effort may help the decision analysts define the problem and elicit objectives and values relatively early in the decision-making to ensure that decisions to be selected would support the desired outcomes, actions, and core values. Then, a critical evaluation of the decision strategy was presented by comparing the performed Bayesian approach with the proposed conceptual model. Then so, it was shown that the choice of the decision model is dissimilar if the presented specific basic components vary. This was performed by presenting two semi-fictitious case studies, exemplifying the framework’s importance in structuring the assessment of available means. / Forskningen som redovisas i denna uppsats utgör en översiktlig guide till en praktisktillämpning av beslutsmodellering gällande underhåll av urbana ledningssystem.Syftet med licentiatuppsatsen är att betona att en korrekt modell för beslutsfat-tande är nödvändig för en effektiv förvaltning av infrastruktur. Mer specifikt ärmålet att öka kunskapen om tillämpbara beslutsstödsmetoder genom att identifiera relevanta faktorer som bör beaktas i beslutsprocessen. Det förväntas underlätta framtida underhållsaktiveter för befintlig urban infrastruktur. En nyttobaserad beslutsmodell för åtgärdsplanering har applicerats på en del av ettsvenskt vattenledningssystem, där läckage är den kritiska händelse som hanteras.Modellen baserad på Bayesiansk beslutsteori har implementerats och utvärderatsmed avseende på hantering av osäkerheter och beslutsoptimering ur ett korttidsper-spektiv. Trots modellens enkelhet visar resultatet att den kan underlätta metodvalför problemlösning när det råder osäkerheter i förutsättningarna. Vikten av en tydlig och strukturerad problembeskrivning inför tillämpningen av enbeslutsmodell bekräftas, där beaktande av interaktioner mellan ibland flera faktoreri systemets funktion och den tillgängliga informationen är viktig. Som ett resultatföreslås en konceptuell metod för att välja den mest lämpliga beslutsmodellen förett specifikt problem med syftet att besluta hur man bör besluta. Den presenter-ade metoden utgör ett första steg i utvecklingen av ett teoretiskt ramverk för ettrationellt och samtidigt praktiskt beslutsfattande. Arbetet hjälper beslutsfattarenatt strukturera problemet och lyfta syftet och värden tidigt i beslutsfattandet föratt säkerställa att tagna beslut stödjer eftersökta utfall, åtgärder och kärnvärden. Vidare har en kritisk utvärdering av beslutsstrategier presenterats som en jämförelsemellan den Bayesianska beslutsmodellen och den konceptuella metoden. Den visaratt valet av beslutsmodell skiljer sig om de grundläggande förutsättningarna ärolika. Utvärderingen baseras på två semifiktiva fallstudier som visar på vikten avstrukturering i bedömningen av tillgänglig information och tillgängliga resurser. / <p>2022-10-24</p> / Mistra InfraMaint