| 1. |
- Ernens, Dennis, et al.
(författare)
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On the Sealability of Metal-to-Metal Seals With Application to Premium Casing and Tubing Connections
- 2019
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Ingår i: SPE Drilling & Completion. - : Society of Petroleum Engineers. - 1064-6671 .- 1930-0204. ; 34:4, s. 382-396
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Tidskriftsartikel (refereegranskat)abstract
- Metal-to-metal seals are used in connections of casing and tubing in oil and gas wells. This paper describes the mechanisms of sealing metal-to-metal seals as investigated using an experimental setup and a stochastic numerical sealing model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a stochastic numerical sealing model for sealability. The model couples a contact-mechanics model with a flow model and takes into account the influence of all the surface-topography features by introducing the concept of seal permeability. Once validated, the model was used together with the experimental results to better understand the sealing mechanisms of metal-to-metal seals.The sealing configuration is a face seal with an 80-mm roundoff radius on one face pressing against a flat on the other face. The face-seal specimens were manufactured from P110 tubing to ensure material properties that are representative for casing or tubing. The test setup used is designed for investigating only the metal-to-metal seal of the connection. The setup can perform rotary sliding under constant load to simulate surface changes during makeup and subsequently perform a leakage test. The sealing limit is determined by applying 700-bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data are subsequently used to validate the previously published stochastic numerical sealing model.The results indicate a strong dependence on the type of thread compound used for the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the stochastic numerical sealing model is capable of predicting the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. In particular, a surface manufactured by turning on a lathe that is in contact with, for instance, a smooth shot-blasted surface topography leads to highly localized contact areas, which in turn yield the best sealing performance.
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| 2. |
- Ernens, Dennis, et al.
(författare)
-
On the Sealability of Metal-to-Metal Seals with Application to Premium Casing Connections
- 2019
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Ingår i: SPE/IADC International Drilling Conference and Exhibition. - 9781613996423
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Metal-to-metal seals are used in connections of casing in oil and gas wells. This paper describes the mechanisms of sealing of metal-to-metal seals as investigated using an experimental set-up and a sealability model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a numerical model for sealability. The stochastic model couples a contact mechanics model with a flow model and takes the influence of all the surface topography features into account. Once validated, the model was used together with the experimental results to explain the sealing mechanisms of metal-to-metal seals. The sealing configuration is a face seal with an R=80 mm round-off radius pressing against a flat. The face seal specimens were manufactured from P110 tubing. The used test set-up is designed for investigating only the metal-to-metal seal of the connection. The set-up can carry out rotary sliding under constant load to simulate surface evolution during make-up and subsequently perform a leakage test. The sealing limit is determined by applying 700 bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data is subsequently used to validate a previously published model. The results indicate a strong dependence of the type of thread compound used on the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the sealability model is capable to predict the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. Namely, a turned against a flat surface topography leads to highly localized contact areas, which in turn yields the best sealing performance. The combination of experimental data with the validated model leads to much deeper insights for the sealing mechanisms than what could be obtained using either on their own.
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| 3. |
- Yaghootkar, Hanieh, et al.
(författare)
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Genetic Studies of Leptin Concentrations Implicate Leptin in the Regulation of Early Adiposity
- 2020
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 69:12, s. 2806-2818
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Tidskriftsartikel (refereegranskat)abstract
- Leptin influences food intake by informing the brain about the status of body fat stores. Rare LEP mutations associated with congenital leptin deficiency cause severe early-onset obesity that can be mitigated by administering leptin. However, the role of genetic regulation of leptin in polygenic obesity remains poorly understood. We performed an exome-based analysis in up to 57,232 individuals of diverse ancestries to identify genetic variants that influence adiposity-adjusted leptin concentrations. We identify five novel variants, including four missense variants, in LEP, ZNF800, KLHL31, and ACTL9, and one intergenic variant near KLF14. The missense variant Val94Met (rs17151919) in LEP was common in individuals of African ancestry only, and its association with lower leptin concentrations was specific to this ancestry (P = 2 × 10-16, n = 3,901). Using in vitro analyses, we show that the Met94 allele decreases leptin secretion. We also show that the Met94 allele is associated with higher BMI in young African-ancestry children but not in adults, suggesting that leptin regulates early adiposity.
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| 4. |
- Adjrad, M., et al.
(författare)
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Interference monitoring for GNSS bands in indoor and urban environments
- 2007
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Ingår i: Proceedings of the 20th International Technical Meeting of the Satellite Division of the Institute of Navigation. - : Institute of Navigation, The. ; , s. 1211-1220
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Konferensbidrag (refereegranskat)abstract
- A collaborative research project between the University of Leeds and Luleå University of Technology, Sweden, has taken place aiming to characterize the man-made noise in urban and indoor environments in the Galileo allocated frequency bands: E5 (1191.795 ± 25.575 MHz), E6 (1278.75 ± 20 MHz), and L1 (1575.42 ± 16 MHz), obviously, also covering the GPS L1 and L5 bands. This project has been co-funded by the European GNSS Supervisory Authority (EGSA), with funding from the 6th Framework Program of the European Community for research and technological development. The project includes the development of two receiver systems: the first instrument is based on the use of a spectrum analyzer (SA-based instrument), a wideband GNSS antenna, and a front-end capable of capturing each Galileo band separately using appropriate filtering and switches. The second instrument addresses the issues of cost and portability, providing interference detection and alarm triggering without the need for complex instrument. This is accomplished using low cost components in a small form factor where the instrument is based on a core GNSS front-end. This instrument will only cover the L1/E1 band. The interference measurement is obtained by combining the information from the automatic gain control (AGC) voltage that controls the AGC amplifier gain and the spectrum analysis of the analogue-to-digital converter (ADC) output raw data. The AGC information will be very important for detecting the presence of wideband interference signals where this will be difficult using spectrum analysis (in contrast to the case to narrowband interference signals). Control and data logging from both instruments are performed using a laptop computer where the spectrum analyzer traces and the FE-based instrument data are recorded for offline analysis via a suite of MATLAB® scripts. This paper describes the spectrum survey conducted at various indoor and urban locations, operationally significant to GNSS, in the North of the UK. The survey sites were selected to obtain geographically diverse measurement results and provide a general representation of the spectral environment. In addition, the temporal variation of man-made noise (MMN) is considered, this latter being correlated with the human activity at the measurement site, by performing the measurements day and night, weekdays and weekends.
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| 5. |
- Do, J., et al.
(författare)
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L and S bands spectrum survey in the San Francisco Bay area
- 2004
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Ingår i: PLANS 2004. - Piscataway, NJ : IEEE Communications Society. - 0780384164 ; , s. 566-572
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Konferensbidrag (refereegranskat)abstract
- The Global Positioning System (GPS) is a radio frequency (RF) communication system that consists of transmitters on the satellites and receivers on the ground. Because of substantial path loss, the received signal power from satellites is extremely weak and even below the thermal noise floor and as such is very sensitive to changes in the underlying noise floor. The goal of this work is to investigate the radio spectrum environment in the GPS band along with two additional bands, the Unified-S band and 2.4 GHz Industrial Scientific and Medical (ISM) band. The spectrum survey was conducted at various locations in the San Francisco Bay area including various urban, rural areas and airports and harbors which are operational significant to GPS. The measurement data collected in this study will provide a more accurate representation of the current status and the characteristics of the spectrum environment. Geographical variation within the sites will reveal correlation between the spectrum environment and the level of urbanization and also a comparative study on the frequency bands under different level of regulations can be used to investigate the effectiveness of the current spectrum policy
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| 6. |
- Kokkolaras, Michael, et al.
(författare)
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Mixed Variable Optimization of the Number and Composition of Heat Intercepts in a Thermal Insulation System
- 2001
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Ingår i: Optimization and Engineering. - 1389-4420 .- 1573-2924. ; 2:1, s. 42519-
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Tidskriftsartikel (refereegranskat)abstract
- In the literature, thermal insulation systems with a fixed number of heat intercepts have been optimized with respect to intercept locations and temperatures. The number of intercepts and the types of insulators that surround them were chosen by parametric studies. This was because the optimization methods used could not treat such categorical variables. Discrete optimization variables are categorical if the objective function or the constraints can not be evaluated unless the variables take one of a prescribed enumerable set of values. The key issue is that categorical variables can not be treated as ordinary discrete variables are treated by relaxing them to continuous variables with a side constraint that they be discrete at the solution. A new mixed variable programming (MVP) algorithm makes it possible to optimize directly with respect to mixtures of discrete, continuous, and categorical decision variables. The result of applying MVP is shown here to give a 65% reduction in the objective function over the previously published result for a thermal insulation model from the engineering literature. This reduction is largely because MVP optimizes simultaneously with respect to the number of heat intercepts and the choices from a list of insulator types as well as intercept locations and temperatures. The main purpose of this paper is to show that the mixed variable optimization algorithm can be applied effectively to a broad class of optimization problems in engineering that could not be easily solved with earlier methods
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| 7. |
- Marattukalam, Jithin J., et al.
(författare)
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Development of process parameters for selective laser melting of a Zr-based bulk metallic glass
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Parameters for selective laser melting of Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMZ4), allowing crack-free bulk metallic glass with low porosity, have been developed. The phase formation was found to be strongly influenced by the heating power of the laser. X-ray amorphous samples were obtained with laser power at and below 75 W. The as-processed bulk metallic glass was found to devitrify by a two-stage crystallization process within which the presence of oxygen was concluded to play an essential role. At laser powers above 75 W, the observed crystallites were found to be a cubic phase (Cu2Zr4O). The hardness and Young’s modulus in the as-processed samples was found to increase marginally with increased fraction of the crystalline phase.
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| 8. |
- Muthukumar, Kaliappan, et al.
(författare)
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Endohedral Fullerene Ce@C82 on Cu(111): Orientation, Electronic Structure, and Electron-Vibration Coupling
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:4, s. 1656-1662
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Tidskriftsartikel (refereegranskat)abstract
- Structural, electronic, and vibrational properties of the endohedral fullerene Ce@C82 on Cu(111) have been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). Ce@C82 forms islands on the substrate. Our STM measurements show relatively large differences in morphology and electron spectra of molecules within these islands indicating multiple molecular orientations on the substrate, while the vibrational spectra are more uniform. We have determined molecular orientations by comparing STM and DFT molecular morphology, and we have calculated Ce@C82 bound to Cu(111) and found that it is chemisorbed. We show that Ce@C82 adopts orientations on the surface that enables Ce to remain at its most favorable binding site inside C82. The effect of chemisorption on the structural and electronic properties of Ce@C82 is thus small, and the orientations are limited to configurations with Ce in the upper hemisphere of the molecular configurational space. We show that the variations in the dI/dV spectra between molecules of different orientations is due to Ce-cage orbitals that are localized in space and their involvement in tunneling depends on the molecular orientation on the substrate. The observed electron-vibration coupling modes in the STM-IETS (in-elastic tunneling spectroscopy) of Ce@C82 arise from cage modes only, and therefore, electron transport properties are expected to be different compared to Ce2@C80, which has active Ce-cage vibrations.
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| 9. |
- Powell, Sara J., et al.
(författare)
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Altimetry using gnss reflectrometry for L5
- 2012
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Ingår i: 2012 6th ESA Workshop on Satellite Navigation Technologies (Navitec 2012) & European Workshop on GNSS Signals and Signal Processing. - Piscaaway, NJ : IEEE Communications Society. - 9781467320108
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Konferensbidrag (refereegranskat)abstract
- GNSS reflectrometry offers a low cost alternative for Earth remote sensing and is used to measure, for example, ocean altimetry, wind speed, wind direction and modeling of the ocean surface state. A bistatic configuration, using one right-handed circular polarized and one left-handed circular polarized antenna, was built for this experiment in order to measure direct and reflected L1 and L5 signals. The direct and reflected signals were compared and the path difference between them calculated, leading to altitude measurements with both L1 and L5 signals. Compared to publicly available signals on L1, the higher code rate of L5 will provide higher measurement sensitivity
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| 10. |
- Vinande, E., et al.
(författare)
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Full-state software GNSS and reduced MEMS IMU measurement processing for urban navigation
- 2009
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Ingår i: Proceedings fo the 22nd international technical meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2009. - Manassas, Va : Institute of Navigation, The. ; , s. 2901-2909
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Konferensbidrag (refereegranskat)abstract
- This paper presents an integration of partial-IMU measurements into the codebase of an existing software GNSS receiver for land vehicle navigation. Full-state filtering was implemented in contrast to the traditional error-state filtering approach. The Kalman filter time update was performed with IMU acceleration and rotation measurements while the measurement update was performed with GNSS pseudorange and Doppler measurements. Inertial component biases were estimated while the vehicle velocity was below 1.2 m/s for at least 5 seconds. A truth reference system composed of a hardware GPS receiver and tactical-grade IMU provided a truth trajectory for experimental comparison. The results from a drive test in downtown Denver, CO showed a solution availability increase from 95% to 100% with the addition of partial-IMU to the software receiver. Horizontal positioning and heading angle 50th percentile errors also showed a corresponding decrease (8.4 m to 4.2 m and 5.3° to 1.7°, respectively).
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