| 1. |
- Kumar, Saurabh, et al.
(författare)
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Inspection frequency optimization model for degrading flowlines on an offshore platform
- 2008
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Ingår i: International Journal of Reliability, Quality and Safety Engineering (IJRQSE). - 0218-5393. ; 15:2, s. 167-180
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Tidskriftsartikel (refereegranskat)abstract
- Many offshore oil and gas installations in the North Sea are approaching the end of their designed lifetimes. Technological improvements and higher oil prices have developed favorable conditions for more oil recovery from these existing installations. However, in most cases, an extended oil production period does not justify investment in new installations. Therefore cost-effective maintenance of the existing platform infrastructure is becoming very important. In this paper, an inspection frequency optimization model has been developed which can be used effectively by the inspection and maintenance personnel in the industry to estimate the number of inspections/optimum preventive maintenance time required for a degrading component at any age or interval in its lifecycle at a minimum total maintenance cost. The model can help in planning inspections and maintenance intervals for different components of the platform infrastructure. The model has been validated by a case study performed on flowlines installed on the top side of an offshore oil and gas platform in the North Sea. Reliability analysis has been carried out to arrive at the best inspection frequency for the flowline segments under study
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| 2. |
- Das, Supriyo Kumar, et al.
(författare)
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Phosphorus dynamics in shallow eutrophic lakes : an example from Zeekoevlei, South Africa
- 2009
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 619, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO4 (3-)), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.
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| 3. |
- Kumar, Rajesh, et al.
(författare)
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Implementation and execution of industrial service strategy : a case study from the oil and gas industry
- 2006
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Ingår i: Journal of Quality in Maintenance Engineering. - : Emerald. - 1355-2511 .- 1758-7832. ; 12:2, s. 105-117
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - The purpose of the paper is to discuss the complex issues, obstacles and factors that can have a significant role and influence on the implementation and execution of a performance-based industrial service strategy. Design/methodology/approach - A case study has been performed the oil and gas industry which maps the issues, challenges and opportunities in the process of implementing and executing a performance-based service strategy. Findings - The study identifies differences in practice with respect to conventional as compared to performance-based contracts. Furthermore, performance factors (i.e. cost drivers, performance killers and critical success factors) of the service strategy implementation and execution process are discussed in relation to the oil and gas industry in the North Sea. A performance-based service strategy needs to be upgraded, modified and customized based on performance measurements, as well as needs, wants and preferences of the involved parties during the contract period. Practical implications - The findings and discussions will help service strategy developers, implementers and executors to recognize the importance of a focused service strategy development process for industrial services. Moreover, the paper will guide developers, implementers and executors to decide about factors that need to be considered. Originality/value - The framework discussed can be used to develop a performance-based service strategy. The results of the research will ease the process of understanding and defining the implementation and execution process of a strategy by presenting the possible performance factors in advance.
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| 4. |
- Kumar, R. Rajesh, et al.
(författare)
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Parameterization of rain induced surface roughness and its validation study using a third generation wave model
- 2009
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Ingår i: Ocean Science Journal. - : Springer Science and Business Media LLC. - 1738-5261. ; 44:3, s. 125-143
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Tidskriftsartikel (refereegranskat)abstract
- The effect of raindrops striking water surface and their role in modifying the prevailing sea-surface roughness is investigated. The work presents a new theoretical formulation developed to study rain-induced stress on sea-surface based on dimensional analysis. Rain parameters include drop size, rain intensity and rain duration. The influences of these rain parameters on young and mature waves were studied separately under varying wind speeds, rain intensity and rain duration. Contrary to popular belief that rain only attenuates surface waves, this study also points out rain duration under certain condition can contribute to wave growth at high wind speeds. Strong winds in conjunction with high rain intensity enhance the horizontal stress component on the sea-surface, leading to wave growth. Previous studies based on laboratory experiments and dimensional analysis do not account for rain duration when attempting to parameterize sea-surface roughness. This study signifies the importance of rain duration as an important parameter modifying sea-surface roughness. Qualitative as well quantitative support for the developed formulation is established through critical validation with reports of several researchers and satellite measurements for an extreme cyclonic event in the Indian Ocean. Based on skill assessment, it is suggested that the present formulation is superior to prior studies. Numerical experiments and validation performed by incorporating in state-of-art WAM wave model show the importance of treating rain-induced surface roughness as an essential pre-requisite for ocean wave modeling studies.
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