Kaliyaperumal G.,Intecsea |
Sengupta A.K.,Indian Institute of Technology Madras
Proceedings of the Institution of Civil Engineers: Structures and Buildings | Year: 2014
An existing reinforced concrete building with moment-resisting frames can be vulnerable during an earthquake owing to its deficient columns. The present paper reports a study on the enhancement of flexural strength and behaviour of columns, by concrete jacketing. First, the performance of the interface of additional concrete cast against the prepared surface of existing concrete was studied. Tests were then conducted on reference (without strengthening) and jacketed column specimens, to study the enhancement of strength of a retrofitted column section under the interaction of axial load and bending moment. Subsequently, interior beam–column–slab sub-assemblage specimens were tested under simultaneous vertical and lateral loading. It was observed that the selected jacketing scheme was effective in enhancing the flexural strength, as well as in retaining the ductility and energy dissipation in the behaviour. The moment–curvature behaviour of a retrofitted column section was predicted based on the layered analysis. The information was fed in the lateral load against drift analysis of a computational model of a retrofitted sub-assemblage specimen, using an incremental non-linear technique. The paper presents the method of analysis and guidelines for retrofitting of columns for seismic forces. © 2014, Thomas Telford Services Ltd. All rights reserved.
Proceedings of the Annual Offshore Technology Conference | Year: 2014
Oil and gas operators are developing subsea production systems at greater and greater distances from thenrespective hosts in deepwater basins worldwide. Many of these subsea systems have the potential to include subsea boosting systems (pumping and/or compression) in these installations, which presents the need for significant amounts of AC power to be delivered over these increasing distances. Recent experience and subsequent investigation has shown that the required AC power can be delivered efficiently and cost effectively to these installations via an innovative system approach involving a split of the major components of a typical Variable Frequency Drive (VFD) system, locating the AC/DC conversion equipment at the host facility where power is generated, locating the DC/AC conversion equipment on the seabed, in proximity to the subsea boosting equipment, and connecting the two via a DC transmission cable. Through utilization of DC power transmission, we expect to eliminate the reactive power issues and line harmonics issues associated with AC transmission. Innovational approaches such as this one will make these installations more practical and cost effective, and open the door to even further capability. Copyright 2014, Offshore Technology Conference. Copyright 2014, Offshore Technology Conference.
Marine Structures | Year: 2013
The objective of this paper is to examine non-linear bending of a flexible elastic bar near fixed termination and to develop analytical solutions that can be used in the design of bend stiffeners. The non-linear bending of prismatic bars of finite and se-infinite lengths is solved analytically, and results are employed to re-visit the problem of the " ideal" bend stiffener, which provides a constant curvature over its entire length. A complete solution is derived for all properties of the ideal bend stiffener, which is not limited by any assumptions on the system geometry and provides an improvement over known formulations. Other features of the non-linear bending of elastic bars are examined and examples are given to demonstrate application of the present theory to sizing bend stiffeners for flexible risers. © 2012 Elsevier Ltd.
Journal of Analytical Atomic Spectrometry | Year: 2013
Certified reference materials (CRM) for quantification of Radiofrequency Glow Discharge Optical Emission Spectrometry (Rf-GDOES) depth profiles of anodic oxide films are very limited. This paper demonstrates that CRM's for quantification of electrolyte-derived species can be more reliably obtained for inwardly mobile species (phosphorus) than for outwardly mobile species (vanadium) when anodising superpure aluminium in their respective solutions at several current densities. Superpure aluminium specimens were anodised to 150 V, in sodium metavanadate solution, at current densities 5, 10, 15, 20, 25 and 50 mA cm-2. Sufficiently different concentrations were obtained by RBS for the outwardly mobile vanadate species (0.68, 0.75, 0.13, 0.06, 0.09 and 0.13 at%) compared with 1.19, 1.42, 1.48, 1.49, 2.08 and 2.37 at% for the inwardly mobile phosphorus species. Evidently greater concentrations of phosphorus species are incorporated into the oxide film. Significant reduction in vanadium concentrations with current density correspond to a large destabilisation of the V2O7 - ion by the anodising electric field. Quantitative depth profiles are determined by means of calibration plots for vanadium and phosphorus. Excellent quantification accuracy of <±0.06 at% is obtained for inwardly mobile phosphorus species by comparing the concentration determined by Rutherford Backscattering Spectroscopy (RBS) with concentration obtained directly from the quantified Rf-GDOES depth profile whereas significantly less accurate quantification accuracies are obtained for the outwardly mobile vanadium species. Quantification accuracy for depth is excellent at ±1 nm as validated by Transmission Electron Microscopy (TEM). CRM's of inwardly mobile impurity species obtained by anodising at different current densities are therefore more reliable and accurate than those of outwardly mobile species. This journal is © 2013 The Royal Society of Chemistry.
Proceedings of the Annual Offshore Technology Conference | Year: 2014
The Lan Do gas field was developed to supplement the depleting production at existing Lan Tay field. It is a crucial development as more than 22% of the electricity capacity for Vietnam is dependent on gas supply from Lan Tay production facilities. Gas from Lan Do field contains 1.2% CO2 which required corrosion resistant alloy for the flowline. 13Cr was selected at an early stage to take advantage of preferential procurement agreement with the pipe manufacturer and to gain on-time delivery. 13Cr can be a cost effective solution for sweet CO2 service. However, 13Cr is known to be susceptible to hydrogen induced stress cracking resulting from the high potential generated by normal cathodic protection system. Specific industry guidance on the method to address this risk is still maturing. Current solution has been essentially limited to proprietary developed diode controlled anode system. For this project, a proprietary designed diode controlled aluminium alloy anode system was used. The presence of carbon steel fittings, equipment and structures where normal aluminium anodes were attached, imposed a strict requirement for electrical isolation from the 13Cr flowline. Electrical isolation techniques such as monolithic isolation joints were used for the flowline connections, whereas Teflon coating was introduced to isolate the structures. Specific welding details between 13Cr and CRA clad pipes were made to address differing thicknesses between these materials. Among the challenges in the installation phase was to land the in-line sled structure on a seabed characterized by mounts, valleys and hard rocky outcrops. To achieve a level seabed, remedial measure using grout bags dumping was used. The amount of grout bags dumped was large, requiring about 250 m3 of grout bags at a water depth of 185 m, which was rarely done. This paper describes the innovative approaches taken to address the challenges in engineering the 13Cr flowline and solutions developed to enable construction and installation of the flowline system on a very rugged seabed. The flowline was successfully installed and received first gas on 7 October 2012. Copyright 2014, Offshore Technology Conference.
Proceedings of the Annual Offshore Technology Conference | Year: 2014
Development of greenfield deep water oil and gas fields are generally known to be expensive, compared with conventional shallow water fields development. Having marginal fields in deep water only compounds the challenge to development. This paper discusses challenges associated with developing marginal gas fields in deep water. It however centers primarily on the subsea portion of the development. Marginal gas fields are typically less than 500 bcf, and are best developed when there is an opportunity to combine a number of such marginal fields for a clustered development. However, invariably, each field has different characteristics (volume, pressure, composition) and hence requires careful planning to ensure constant flow to production facilities. This paper elaborates on the use of software tools such as Maximus for phased field development planning to ensure base load gas production throughout the project lifetime. At FEED stage, the subsea facilities and topsides facilities are typically carried out by separate design contractors, involving an interface at the surface that needs to be managed well to ensure optimum overall system design for smooth economical operation. In the case of developments utilising FLNG the interface issues can become rather complicated when the subsea facilities design team at FEED stage has to interface with multiple FLNG FEED contractors participating in a design competition. The challenges centred round the subsea development itself include Field Layout planning, Floating Production Facility interfaces, subsea CAPEX, Flow Assurance, Hardware limitations (qualification), Technology (applications pertaining to hardware such as dual directional subsea wyes, subsea pigging launcher/receivers, and subsea processing equipment). This paper also elaborates on the use of other software tools such as ArcGIS for pipeline route layout planning and optimisation, and Star-CCM Plus for sand erosion CFD (Computational Fluid Dynamics) modeling. Copyright 2014, Offshore Technology Conference.
Journal of Offshore Mechanics and Arctic Engineering | Year: 2011
A new model for fluid structure interaction during vortex shedding process and associated vortex induced vibration (VIV) of a cylinder in transverse direction is proposed. The present work is based on restrained inline motion. Nevertheless, the model can be further extended to include inline interaction. This is not the scope of the present work. The model predicts the control of shedding frequency by reduced velocity and collapsing it to structure natural frequency. It captures the self-exciting and self-limiting nature of VIV excitations and adequately describes the transverse force and motions experienced by an oscillating cylinder in steady flow with lift, added mass, and damping. Thus, steady state responses obtained from the model represent the unique nature of VIV found in the laboratory over a range of reduced velocities of practical importance. The model will benefit future extension to include interaction due to inline motion such that a better VIV prediction could be obtained for free cylinder vibration. © 2011 American Society of Mechanical Engineers.
Proceedings of the Annual Offshore Technology Conference | Year: 2015
Most baby-boomers have some familiarity with the classical stigma surrounding aluminum conductors in residential and commercial applications: fire hazard. Mention aluminum wiring in a building or residence and, not surprisingly, a lot of folks will react as if the structure in question should be condemned. How did aluminum get this reputation? Was it deserved? Is it still a valid assumption with today's modern aluminum alloys? Many of the historical stigmas associated with aluminum can be attributed to technical design problems of the older alloys that have now been overcome by higher quality materials and/or addressed by aluminum specific design considerations. This paper addresses the aforementioned issues and investigates the current status of aluminum conductor technology as applied to subsea power cables with a specific emphasis on the following: The Element Aluminum; Early History of Aluminum; Historical Stigmas; Technical Advances; Aluminum (Al) versus Copper (Cu); Aluminum Subsea Cable Experience. Copyright © (2015) by the Offshore Technology Conference All rights reserved.
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 | Year: 2014
In the offshore industry small subsea structures are generally supported by mudmat foundations and these are often loaded with forces and moments acting in three directions. In deep water applications very soft clays are frequently encountered and, depending on the design, finite element analyses may be employed to verify that the capacity of the selected mudmat is sufficient to carry the expected load combinations safely. Most of these analyses are conducted based on available undrained shear strength data collected in-situ. The use of effective strength soil parameters and evaluation of stresses and deformations that may arise under longterm drained conditions has received less attention. The subsea structures supported by mudmats are generally connected to numerous pipelines and umbilical lines via elements called jumpers.Although there is some inherent flexibility in their design, foundation movements arising from settlement and operational loads can influence the integrity of the connectors at the joint locations. In this paper a mudmat resting on clay is analyzed for deflections and rotations. In particular, the influence of using effective soil strength parameters (instead of the typical undrained shear strength profile) and the influence of including a consolidation stage in the analysis is investigated. Different soil constitutive models, namely the Mohr Coulomb and the Hardening Soil models that are available in Plaxis 3D are used. Undrained and drained loading sequences are applied which reflect expected conditions that mudmats typically encounter over their service life. The results are evaluated with respect to the sensitivity of the calculated deformations to the modeling approach employed. © 2014 Taylor & Francis Group, London.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2013
Tie-in spools must be designed to resist a large number of onerous load combinations. These loads include gravitational, temperature, pressure and environmental loads along with various imposed displacements. Additionally, there are several design constraints that must be satisfied. Due to the three-dimensional geometric freedom of the spool there are many possible design scenarios that could be evaluated in the search for the optimum solution. It is the responsibility of the pipeline design engineer to use their own judgment and experience to find the best possible solution within the design period. Traditionally a trial and error design approach is used in an iterative manner. This method is typically slow and labor intensive and can be too focused on one design concept at the expense of others that are potentially superior. On similar engineering problems with many design parameters automated non-linear optimization routines have been shown to be very effective. Specifically, applying evolutionary algorithms is a robust, time-effective and adaptable approach. Such a tool assists the engineer in finding superior design solutions and assists in searching the entire design space. To test this design method, a multi-objective evolutionary algorithm has been applied to two semi-constrained spool design problems. The spool design has been modeled using finite element analysis. First, the algorithm was applied to the optimization of spool geometry for multiple design objectives. Within 24-hours of runtime the algorithm was able to find superior solutions to those found using a traditional iterative approach. Also, the trade-off between conflicting design objectives could be quantified and visualized to enable the designer to select the most appropriate candidate. The second problem evaluated was the placement of supports to mitigate the onset of vortex induced vibration (VIV). The algorithm was again able to quickly find a better solution and quantify the tradeoff between conflicting design objectives. The paper presents the results of this new design process as applied by subsea pipeline engineers to find optimum spool designs. Copyright © 2013 by ASME.