The performance of a deep water composite production riser from a system perspective is presented, and its advantages are articulated through comparisons with a typical steel riser under identical service conditions. The composite riser joints in this study were considered to be a part of a single Tension Leg Platform (TLP) riser string to be installed at a depth of 6000 ft in Gulf of Mexico. A series of numerical analyses –burst, collapse, fatigue, global and local – have been performed, and the capacities of the composite riser have been determined utilizing long-term strength properties. The capacities associated with the hoop direction, i.e., burst and collapse, are limited by the presence of a steel internal liner whose function is to ensure pressure and fluid tightness. The collapse capacity of the riser can be drastically impaired by the presence of a debond between the liner and composite. Due to the high strength to weight ratio of the carbon/epoxy composite, its response under combined axial tension and bending moment showed great safety margins, favoring pursuits of greater water depths. The study also constructed damage envelopes associated with axial tension and bending moment, which facilitate feasibility checks for expanding the use of the composite joints to other locations or systems. The fatigue life of the composite body is expected to greatly exceed its design life, and the most critical element is the welds between the liner and metal end pieces. Since there is wide dispersion of S-N relationships for carbon/epoxy composites depending on the combinations of constituent materials, a parametric study was carried out in this study to suggest the range of acceptable S-N relationships. The composite riser is estimated to offer only moderate damping, due primarily to its specially orthotropic lay-up. The study also demonstrates that the use of Rayleigh stiffness proportional damping may not be suitable for deep water risers. A series of forced excitation analyses show that the system in sea water does not show notable resonance due to fluid drag. When compared with the steel riser, vibration amplitudes at low elevations are much lower.

The performance of a deep water composite production riser from a system perspective is presented, and its advantages are articulated through comparisons with a typical steel riser under identical service conditions. The composite riser joints in this study were considered to be a part of a single Tension Leg Platform (TLP) riser string to be installed at a depth of 6000 ft in Gulf of Mexico. A series of numerical analyses –burst, collapse, fatigue, global and local – have been performed, and the capacities of the composite riser have been determined utilizing long-term strength properties. The capacities associated with the hoop direction, i.e., burst and collapse, are limited by the presence of a steel internal liner whose function is to ensure pressure and fluid tightness. The collapse capacity of the riser can be drastically impaired by the presence of a debond between the liner and composite. Due to the high strength to weight ratio of the carbon/epoxy composite, its response under combined axial tension and bending moment showed great safety margins, favoring pursuits of greater water depths. The study also constructed damage envelopes associated with axial tension and bending moment, which facilitate feasibility checks for expanding the use of the composite joints to other locations or systems. The fatigue life of the composite body is expected to greatly exceed its design life, and the most critical element is the welds between the liner and metal end pieces. Since there is wide dispersion of S-N relationships for carbon/epoxy composites depending on the combinations of constituent materials, a parametric study was carried out in this study to suggest the range of acceptable S-N relationships. The composite riser is estimated to offer only moderate damping, due primarily to its specially orthotropic lay-up. The study also demonstrates that the use of Rayleigh stiffness proportional damping may not be suitable for deep water risers. A series of forced excitation analyses show that the system in sea water does not show notable resonance due to fluid drag. When compared with the steel riser, vibration amplitudes at low elevations are much lower.

The use of a slim, high-pressure drilling riser for surface blowout preventer operations in the deepwater Gulf of Mexico was assessed as an alternative to conventional drilling procedures from floating units. Comparison of the low- and high-pressure system was accomplished through a detailed qualitative (assigned frequency) and quantitative (reported incidents) risk analysis using generic fault tree models to statistically determine the reliability of the system based on metocean conditions from the Gulf of Mexico. It is hoped that this investigation will serve as a starting point for drilling companies and regulatory agencies to understand the risk of implementing a high-pressure riser for surface blowout preventer applications in the Gulf of Mexico, because specific failure events and conditions of the area were considered. Despite the generic description of the drilling riser and pressure control system, the models are flexible enough to be modified and adapted to a specific rig configuration and location. Results from the qualitative comparison suggest an acceptable risk and high reliability for high-pressure riser systems and surface preventers. The quantitative portion of the study is influenced by the data quality of the high-pressure system, however it provides a range of possible reliability values with an acceptable overall risk.

A research program was conducted to investigate the application of composite materials in repairing corroded offshore risers, leading to the development of an optimized repair using a hybrid carbon/E-glass system. The objective of this research program was to investigate the feasibility of extending onshore composite repair techniques to offshore risers by developing integrated analytical and experimental methods. The study considered loads typical for offshore risers including internal pressure, tension, and bending. To fulfill this objective efforts included a state of the art assessment of current composite repair technology, designing a carbon-based composite repair system optimized by numerical simulation with prototype testing, and providing guidelines for industry in repairing and reinforcing offshore risers using composite materials. Research efforts integrated numerical modeling, as well as full-scale testing that included four composite repair manufacturers to assess the current state of the art on pipe samples with simulated corrosion reinforced with composite materials. Analysis and testing were also performed on the optimized carbon/E-glass system. The results of this program demonstrated that composite materials are a viable means for repairing corroded offshore steel risers as adequate reinforcement ensures that the steel risers are not loaded beyond acceptable design limits. For corroded risers, the results demonstrated through analysis and full-scale testing efforts that properly designed composite repair systems can provide adequate structural reinforcement to ensure that excessive strains are not induced in the steel when subjected to internal pressure, axial tension, and bending design loads. This was verified experimentally using strain gages placed beneath the composite repair. This program is the first of its kind and is thought to contribute significantly to the future of offshore riser repairs. It is likely that the findings of this program will foster future investigations involving operators by integrating their insights regarding the need for composite repair based on emerging technology. One of the most significant contributions to the existing body of work is the use of limit analysis in developing design limits for the repair of steel pipes using composite materials.

The use of a slim, high-pressure drilling riser for surface blowout preventer operations in the deepwater Gulf of Mexico was assessed as an alternative to conventional drilling procedures from floating units. Comparison of the low- and high-pressure system was accomplished through a detailed qualitative (assigned frequency) and quantitative (reported incidents) risk analysis using generic fault tree models to statistically determine the reliability of the system based on metocean conditions from the Gulf of Mexico. It is hoped that this investigation will serve as a starting point for drilling companies and regulatory agencies to understand the risk of implementing a high-pressure riser for surface blowout preventer applications in the Gulf of Mexico, because specific failure events and conditions of the area were considered. Despite the generic description of the drilling riser and pressure control system, the models are flexible enough to be modified and adapted to a specific rig configuration and location. Results from the qualitative comparison suggest an acceptable risk and high reliability for high-pressure riser systems and surface preventers. The quantitative portion of the study is influenced by the data quality of the high-pressure system, however it provides a range of possible reliability values with an acceptable overall risk.

This master's thesis deals with the influence of the exothermic riser sleeves on the solidification time of aluminum alloys. The thesis is divided into five parts. The first chapter describes solidification of cast alloys. The second chapter deals with the designing of risers. The third chapter is focused on the types of risers. The fourth chapter describes ways of intensification of risers and chemical composition of exothermic and insulating mixtures for production of riser sleeves. The main fifth chapter focuses on experimental measurements of temperatures and solidification time of aluminum alloy in castings, risers and exothermic and insulating riser sleeves.

Riser sleeve thermophysical properties for simulation are developed using an inverse modeling technique. Casting experiments using riser sleeves are performed in order to measure temperatures in the liquid steel, the riser sleeve, and the sand mold. Simulations are created and designed to replicate the casting experiments. Riser sleeve material thermophysical properties are iteratively modified until agreement is achieved between the simulation and the measured data. Analyses of sleeve material performance are carried out using the developed thermophysical properties. The modulus extension factor (MEF) is used to quantify sleeve performance and is determined for all riser sleeve materials studied here. Values are found to range from 1.07 to 1.27. A sleeve material's effects on casting yield are shown to depend only on the MEF and therefore a sleeve's exothermic or insulating properties serve only to increase the overall quality of the sleeve, expressed by the MEF, and do not independently affect the casting yield at any casting size studied here. The use of riser sleeves is shown to increase the maximum yield up to 40% for chunky castings, however increases of only 8% are observed for very rangy castings. Riser sleeve thickness is shown to be extremely influential on casting yield. Scaling the sleeve thickness by the riser diameter shows that, for a typical sleeve, an optimum riser sleeve thickness is 0.2 times the riser diameter for chunky castings. A scaled sleeve thickness of 0.1 is found to be an optimum sleeve thickness for very rangy castings. Below a scaled sleeve thickness of 0.1 sleeve performance is found to be highly sub-optimal.

Casting as a manufacturing process to make complex shapes of metal materials in mass production may experience many different defects such as porosity and incomplete filling. How to improve the casting quality becomes important. Gating/riser system design is critical to improving casting quality. The objective of the research presented in this thesis is to optimize gating/riser systems based on CAD and simulation technology with the goal of improving casting quality such as reducing incomplete filling area, decreasing large porosity and increasing yield. Therefore in the thesis, an optimization framework is presented based on CAD and simulation technology. Given a CAD model of part design and after converted to a casting model, it is the first step to evaluate castability of the casting design. Then the runner and risers are represented parametrically, and CAD models generated by varying parameters can be used in the simulation. After analyzing simulation results, the gating/riser system design is optimized to improve casting quality. In the thesis, one engine block is used to verify the effectiveness of the optimization method. Compared with the initial design, it is found that the optimized casting design can decrease porosity around 18% while the yield increases 16%.

This work examines the ability of two dimensional CFD models to predict the unsteady flow downstream of a cylinder, with and without fairing, in uniform flow. PIV measurements of the flow-field downstream of the cylinder and fairing in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Velocity time histories are compared and hydrodynamic coefficients are discussed. In a general sense, two dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder or fairing. / text

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. Includes tables. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 104-108).