Understanding static and dynamic nonlinear behavior of pipes and risers is crucial for the design aspects in offshore engineering fields. In this work, we examine two nonlinear problems in offshore engineering field: vortex Induced vibration of straight horizontal pipes, and boundary layer static solution of inclined risers. In the first study, we analyze the effect of the internal velocity of straight horizontal pipe and obtain the vortex induced vibration forces via coupling the pipe equation of motion with the recently modified Van Der Pol oscillator governing the lift coefficient. Our numerical results are obtained for two different pipe configurations: hinged-hinged, and clamped- clamped. The results show that the internal velocity reduces the vibration and the oscillation amplitudes. Also, it is shown that the clamped-clamped pipe configuration offers a wider range of internal velocities before buckling instability occurs. The results also demonstrate the effect of the end condition on the amplitudes of vibration. In the second study, we develop a boundary layer perturbation static solution to govern and simulate the static behavior of inclined risers. In the boundary layer analysis, we take in consideration the effects of the axial stretch, applied tension, and internal velocity. Our numerical simulation results show good agreement with the exact solutions for special cases. In addition, our developed method overcomes the mathematical and numerical limitations of the previous methods used before.

Bimodal polyethylene resins are frequently used for pipe applications. In this work, blending was used to produce polyethylenes with comparable properties, particularly with respect to processing, stress crack resistance and tensile properties. Suitable blend components were identified, and their performance screened used ECHIP experimental design software. Blends were characterized using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), tensile testing, stress crack resistance measurements, impact toughness testing, capillary rheometry and melt index measurements. GPC, DSC and melt index results reveal that the method of meltcompounding produced morphologically uniform blends, with different degrees of compatibility depending on the type and level of branching of blend components. Most of the blends produced showed higher crystallinity values compared to a reference bimodal resin. Binary high density polyethylene (HDPE) blends showed better stiffness and strength properties, whereas metallocene catalyzed linear low density polyethylene (mLLDPE) containing blends illustrated superior elongation and toughness properties compared to the reference polymer and other binary blends. The highest resistance to slow crack growth (SCG) was shown by low density polyethylene (LDPE) and mLLDPE containing blends due to their high branching content. The overall blend resistance to SCG or toughness can be enhanced with levels less than 20% by weight of LDPE or mLLDPE in the blend although the tensile properties are relatively unaffected at these low concentrations. The performance of blends was optimized by changing component polymers and their weight fractions, and a model to predict optimum blends was developed using the Maple code. Optimized blends showed higher branching content, comparable molecular weight, molecular weight distribution, tensile properties, viscosity and processing behaviour to the reference polymer. Optimized blend 3, in particular, encountered the same degree of shear thinning as the reference material. Better toughness and resistance to SCG were shown by the optimized blends when compared to the reference polymer.

The burdensome capital cost of urban water distribution systems demands the use of efficient optimization methods capable of finding a relatively inexpensive design that guarantees a minimum functionality under all conditions of operation. The combinatorial and nonlinear nature of the optimization problem involved accepts no definitive method of solution. Adaptive search methods are well fitted for this type of problem (to which more formal methods cannot be applied), but their computational requirements demand the development and implementation of additional heuristics to find a satisfactory solution. This work seeks to employ adaptive search methods to enhance the search process used to find the optimal design of any water distribution system. A first study presented here introduces post-optimization heuristics that analyze the best design obtained by a genetic algorithm--arguably the most popular adaptive search method--and perform an ordered local search to maximize further cost savings. When used to analyze the best design found by a genetic algorithm, the proposed post-optimization heuristics method successfully achieved additional cost savings that the genetic algorithm failed to detect after an exhaustive search. The second study herein explores various ways to improve artificial neural networks employed as fast estimators of computationally intensive constraints. The study presents a new methodology for generating any large set of water supply networks to be used for the training of artificial neural networks. This dataset incorporates several distribution networks in the vicinity of the search space in which the genetic algorithm is expected to focus its search. The incorporation of these networks improved the accuracy of artificial neural networks trained with such a dataset. These neural networks consistently showed a lower margin of error than their counterparts trained with conventional training datasets populated by randomly generated distribution networks.

No description available.

Inconel 738, which is a nickel base superalloy used for hot section components of aircraft and industrial turbines is difficult to fabricate and repair by fusion welding due to its susceptibility to heat affected zone (HAZ) intergranular cracking. Crack-free joining of the difficult-to-weld alloy is currently achieved by using linear friction welding (LFW). Nevertheless, oxidation along the joint during LFW is a major problem. Information about the effect of process parameters on the microstructural evolution of linear friction welded nickel base alloys is very limited. In this work, the effect of forging pressure on the microstructure of linear friction welded Inconel 738 was studied. The results as elucidated in this work showed that increased forging pressure caused strain-induced rapid solidification of metastable liquid, which resulted in complete elimination of deleterious liquid phase oxides in bonded material contrasting the generally accepted view that assumes extrusion of solid state oxides during LFW.

One of the primary concerns associated with timber harvesting is the production of sediments from stream crossings. While research has shown that using improved haul road crossings can mitigate sediment production in perennial streams compared to the use of unimproved crossings little research has been undertaken on temporary skidder crossings of headwater streams, a situation common to a significant percentage of ground skidding operations. This experiment consisted of a controlled replicated testing of the effectiveness of four types of temporary skidder stream crossings (unimproved ford, corrugated culvert, wood panel skidder bridge, and PVC pipe bundle) relative to bedload and suspended sediment production. Automated samplers were used to monitor sediment and bedload production during the construction, use, removal, and post-removal phases associated with the use of these temporary crossings. Results showed that elevated crossings mitigated total sediment production compared to unimproved fords. Further, wood panel bridges yielded lower amounts of sediment than culverts but PVC pipe bundles show no difference between bridges or culverts. Sediment production varied by crossing type and use phase. While no differences were found among crossings types during construction, there was a difference between improved crossings and fords during use. Further, bridges and PVC pipe bundle crossings produced significantly less sediments than culverts during both their removal and during post-removal sampling and fords produced the largest amount of sediments during these phases.

Modern construction practices require proper knowledge to predict concrete pumping pressure, especially in high-volume and high-rise applications. Despite the progress made over the last decades, the spread of concrete pumping to high-rise construction has been hampered by the lack of standardized operating procedures and performance criteria. By and large, the guidelines available today focus predominantly on pumping Conventional Vibrated Concrete (CVC), while ambiguity still surrounds pumping Self-Consolidating Concrete (SCC) and other types of Highly-Workable Concrete (HWC). This PhD dissertation focuses on the fundamental principles relevant to the flow of high-strength SCC in pumping pipes, and it aims to develop methods to predict and reduce the required pumping pressure. The flow pattern of SCC in pipes is analytically investigated, providing a numerical approach to predict the pumping pressure based on the properties of both concrete and the lubrication layer, the pipe diameter, and the flow rate. The analytical results are further validated through full-scale pumping tests executed at the laboratory of the Université de Sherbrooke. Through this phase 26 optimal concrete mixtures were pumped in a 30-m pumping circuit to investigate the interactions between the concrete properties and pressure loss. The same tests are also employed to empirically correlate pressure loss with rheological and tribological properties of concrete at different flow rates. The resulting correlations furnish instrumental models capable of computing pressure loss for a wide range of concrete properties. In another application, the experimental results are analyzed to identify the influence of pumping on concrete properties with time. Full-scale pumping results are statistically analyzed in order to establish a quantitative description of the most influential parameters governing the concrete flow in pipes. As a result, concrete pipe flow is statically modeled, allowing the computation of pressure loss at different flow rates based on the the rheological and tribological properties of the concrete and the pipe diameter. Another statistical model is derived to calculate the pressure loss as a function of the V-funnel flow time, granting the advantage of predicting the pressure loss on job sites without the need for complex rheological and tribological measurements. In light of the research findings of the previous phases, a new simple test method called the pipe flow test (PFT) is developed in the context of this research, specifically for predicting pipe flow pressure loss. With preceding research phases as insights, the final stage of this project is directed toward mix design optimization faced with the challenge of reducing the pumping pressure and meeting the strength requirements of high-strength SCC. Ultimately, the research findings emanating from this investigation provide practical guidelines and conclusive models to predict and reduce pumping pressure for a wide scope of concrete mixtures and pipe diameters.

A survey of relevant literature on the topic of wave propagation and scattering in pipes is given first. This review is followed by a theoretical framework which is pertinent to wave propagation in homogeneous, isotropic, pipes. Emphasis is placed on approximate solutions stemming from a computer based, Semi-Analytical Finite Element (SAFE) formulation. A modal analysis of the dynamic response of homogeneous, isotropic pipes, when subjected to a transient ultrasonic excitation, demonstrates that dominant features, i.e., singularities in an unblemished pipe’s displacement Frequency Response Function (FRF) coincide with its cutoff frequencies. This behaviour is confirmed experimentally. A novel technique is developed to deduce such a pipe’s wall thickness and elastic properties from three cutoff frequencies. The resulting procedure is simulated numerically and verified experimentally. Agreement between the new ultrasonic procedure and traditional destructive tests is within experimental uncertainty. Then a hybrid-SAFE technique is used to simulate waves scattered by various open rectangular notches. The simulations show, for the first time, that singularities distinct from the unblemished pipe’s cutoff frequencies arise in a displacement FRF when an axisymmetric notch is introduced. They also suggest that the new singularities depend on the properties of the parent pipe and the finite element region but effects are local to a notch. It is demonstrated further that the difference between the frequency at which a singularity introduced by a notch occurs and the nearest corresponding unblemished pipe’s cutoff frequency is a function of the notch’s dimensions. By plotting contours of constant frequency differences, it is shown that it is usually possible to characterize the notch’s dimensions by using two modes. However, the frequency difference for a third mode may be also needed occasionally. The more general case of nonaxisymmetric notches is shown to be a straightforward extension of the axisymmetric case.

The Swedish industry uses large volumes of compressed air. The compressed air process isenergy intensive and creates large amounts of excess heat. It is therefore important to utilizethe excess heat, optimize the operation of the compressors and to have a regular maintenanceon the system. This thesis is a pre-study to make a compressed air system energy efficient andis done in collaboration with Ljunghäll AB. Ljunghäll AB is one of Northern Europe's leadingdie casting companies and are located in Södra Vi, Sweden. The purpose is to describe andmap the compressed air system in the old part of the facility in Södra Vi. The thesis will alsogive an explanation of how Ljunghäll AB can improve the compressed air system. Providethem suggestions for energy savings and lower the environmental impact of production. Theobjective of the thesis is to create an understanding of how improvements in the compressedair system can be done by studying the operation, compressor, pipe system and leak detecting.The economic aspects of the solutions together with the effect of noise and engine operationof the compressors have not been taken into consideration. To reach improvement measures avisit to the facility in Södra Vi was made, where measuring and mapping was executed andthen compared with earlier studies and literature. The conclusions of the thesis show thatLjunghäll AB has a good operation and control of the compressors, through the variable speeddrive and steering system. It also showed that the choice of the existing compressors are goodfor their compressed air usage. The study also resulted in the following suggestions for theenergy efficiency and lowering of the environmental impact of production at Ljunghäll AB’scompressed air system: Water heat recovery, replacement of old pipes, cover the leakage,regular maintenance of compressors and fittings, training in compressed air for workers,centralized compressor central and sectioning of the pipe system.

Inconel 738, which is a nickel base superalloy used for hot section components of aircraft and industrial turbines is difficult to fabricate and repair by fusion welding due to its susceptibility to heat affected zone (HAZ) intergranular cracking. Crack-free joining of the difficult-to-weld alloy is currently achieved by using linear friction welding (LFW). Nevertheless, oxidation along the joint during LFW is a major problem. Information about the effect of process parameters on the microstructural evolution of linear friction welded nickel base alloys is very limited. In this work, the effect of forging pressure on the microstructure of linear friction welded Inconel 738 was studied. The results as elucidated in this work showed that increased forging pressure caused strain-induced rapid solidification of metastable liquid, which resulted in complete elimination of deleterious liquid phase oxides in bonded material contrasting the generally accepted view that assumes extrusion of solid state oxides during LFW.