Papers by Keyword: Riser

Abstract: This work analyses a ‘Y’ wheel configuration for stair climbing and optimizes the mechanism for a dedicated staircase configuration. This stair climbing mechanism consists of a ‘Y’ shaped wheel with a gear system which changes its mode of operation from a simple gear train to an epicyclic gear train whenever it encounters step. The analysis consists of understanding the mechanics as the ‘Y’ wheel encounters a step, why the ‘Y’ wheel tends to climb the step and how it climbs the step and starts rolling. Each case is analysed by considering governing factors like the ‘Y’ wheel link length, end wheel radius, and weight and staircase configurations, and studied to show the variation in torque requirement and reaction forces. The stair climbing mechanism is optimized using graphical method and verified using linear programing in Matlab.

Abstract: The major challenge for producing and manufacturing risers for oil and gas production is to make them light weight so as to reduce the operational cost and improve the overall system requirements to make them an attractive option for marine and offshore industries. In the current research, the composite and metal-composite pipes (1) GFRP only (2) Al-GFRP and (3) PE-GFRP have been manufactured using filament winding machine operated using CADFIL and CADWIND CNC packages. The use of liners (Al and PE) has ensured the fluid tightness and collapse resistance of the pipe system. Small prototype pipes are manufactured based on optimized pipe design parameters for collapse under external pressure and burst under internal pressure using ANSYS 13 FEA analysis software. Experiments are conducted to verify the axial and hoop compressive strengths of the pipes with analytical results. The details of pipe manufacturing process using filament winding machine, simulation procedure to optimize the pipe parameters and validation of the simulation results with experimental results are the focal points of the current work.

Abstract: A 2D axi-symmetric, steady state and pressure-based model for the riser of an industrial RFCC unit was developed with ANSYS FLUENT in workbench 13.0. The EulerianEulerian approach was applied to simulate the flow behavior of the two phases and the catalytic cracking reactions. The k-ε gassolid turbulent flow per phase model was used, and the particle-level fluctuations are modeled in the framework of the kinetic theory of granular flow. Two different drag models were used separately to simulate the gas solid interaction in the riser fluidized bed. The 14-lump kinetic model was chosen to describe the complex catalytic cracking of the heavy residual feed stock. The particle volume fraction, velocity and temperature profiles, as well as product yields in the riser were analyzed and validated with results from open literature and the industrial RFCC plant data.

Abstract: The static and cyclic failure mechanisms of offshore pipe riser repaired with a designated laminate orientation of carbon/epoxy (C/E) system were studied. The finite element (FE) model takes into account failure mechanisms of the composite sleeve inter-layer delamination, debonding at the steel riser-composite surface interface, and the maximum permissible strain of the repaired riser. Design conditions of the combined static loads (coupled internal pressure, longitudinal tensile and transverse bending) were determined through a limit state analysis [1,2]. The limiting static bending load that causes catastrophic failure under a coupled internal pressure and tensile loadings was determined through Virtual Crack Closure Technique (VCCT). The effects of cyclic bending, mimicking the typical scenarios experienced in pipe riser exposed to dynamic subsea environment, were evaluated and compared against the static conditions. The low cycle fatigue of the composite repair system (CRS) is simulated using a direct cyclic analysis within a general purpose FE program, where the onset and fatigue delamination/disbonding growth are characterized through the Paris Law.

Abstract: For better understanding physical mechanism of radial disturbances, previously proposed to disturb the wake flow and vortex-induced vibration of risers, numerical simulations are carried out for the flow around the fixed cylinder with such disturbances at a Reynolds number of 100. After introducing disturbances, specific distributions of flow and vertical vorticity near cylinder surfaces are identified and related to different vortex patterns. The spanwise variation of free shear layers is discussed and physically explained. Different characteristics for the pressure on cylinder surfaces, frequency of vortex shedding and time history of lift are also analyzed and presented in detail.

Abstract: Solidification of metals continues to be a phenomenon of great interest to physicists, metallurgists, casting engineers and software developers. It is a non-linear transient phenomenon, posing a challenge in terms of modelling and analysis. This paper attempts to study heat flow within the casting, as well as from the casting to the mould, and finally obtains the temperature history of all points inside the casting. The most important instant of time is when the hottest region inside the casting is solidifying. ANSYS software has been used to obtain the last solidifying region in the casting process by performing transient thermal analysis. Location of the hot spot predicted by software simulation showed good agreement with the experimental trial. It was also observed that the simulation of casting helps in obtaining optimum design of riser.

Abstract: With the continuous development of the marine oil industry, risers have become necessary equipment in offshore drilling engineering. On the basis of mode-superposition response spectrum method which is used commonly in anti-seismic design, the seismic responses of the marine drilling riser is analyzed on the theoretical and the related anti-seismic calculation formulas of the discrete system are promoted to the continuous system. The earthquake force and the resultant internal forces when the earthquake happening are analyzed and calculated. The calculation formulas of shear force and bending moment for each cross section of a riser under the earthquake action are deduced, which can offers some theoretical reference for riser engineering design when considering earthquake action.

Abstract: As the offshore drilling expands to deep water, the influences of bottom ball joint corner and lateral force on drilling security become increasingly significant. During the force analysis, the environmental factors (e.g. wind, sea-flow force, sea ice, etc.) are usually taken into account. Besides, the engineering factors considered in research are top tension ratio and drilling vessel drift. In this paper, a finite element model is established by ANSYS to imitate the force condition of marine riser, so as to analyze the influence laws of top tension ratio and drilling vessel drift rate on marine riser stability (i.e. the corner and lateral force on bottom ball joint ) in Beaufort force scale 3 and 8 windy conditions. The results show that the lateral force increases with the drilling vessel drift rate and top tension ratio accordingly by linear mode. For the same tension increasing extent, the greater the drilling vessel drifts, the more increasing range the lateral force appears. The corner on bottom ball joint has a linear relation with the drilling vessel drift rate similarly. However, the corner on the bottom ball joint demonstrates a non-linear decreasing method as “fast followed by slow” due to the increasing top tension ratio. The research plays a role in the security assurance of sub-sea wellhead in deep-water drilling operation.

Abstract: Flow behavior of gas and particles is performed by means of gas–solid two-fluid model with the large eddy simulation for gas and the second order moment for particles in the riser. This study shows that the computed solids volume fractions of two cases are compared with the experimental data using a two-dimensional model. The gas and solid velocity is computed.

Abstract: The effects of coupled internal pressure and external tension on corroded offshore pipe riser repaired with a designated laminate orientation of carbon/epoxy (C/E) and E-glass/epoxy (EG/E) fibre reinforced composite (FRC) was evaluated. The steel riser (API 5L X60) was characterised through Ramberg-Osgood model while input data of the composites were extracted from those used as benchmark for analysis in the first world-wide failure exercise (WWFE) [1, 2]. It was found that the C/E composite provides superiority over the EG/E and laminates with a dedicated orientation is capable of enhancing the performance of risers subjected to the coupled loadings.