The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
Lei Wang - One of the best experts on this subject based on the ideXlab platform.
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Secondary anchorage and residual prestressing force in locally corroded PT beams after strand fracture
Construction and Building Materials, 2021Co-Authors: Lizhao Dai, Yang Chen, Lei WangAbstract:Abstract An experimental test with six specimens is designed to investigate the secondary anchorage and residual prestressing force in locally corroded post-tensioned concrete (PT) beams after strand fracture. The secondary anchorage of fractured strand is investigated, and the correlation between prestressing force generated by secondary anchorage and strand fracture positions is established. The flexural behavior of locally corroded PT beams after strand fracture is discussed. An analytical method is proposed to determine the damage control section of locally corroded PT beams after strand fracture for the flexural capacity evaluation, and the accuracy of proposed method is validated by experimental results. Results show that corrosion-induced strand fracture leads to the formation mechanism of prestressing force changing from the end anchorage transfer to the cement mortar bonded transfer. The secondary anchorage of fractured strand can form a new prestressing force for resisting the applied load, and the residual prestressing force in locally corroded PT beams depends on the strand fracture positions. The prestressing force generated by the secondary anchorage will decrease gradually when the strand fracture position moves from the end anchorage Region to the mid-Span Region. The prestressing force loss is 16.7% when strand fractures in the end anchorage Region. Once it occurs in the mid-Span Region, the prestressing force loss reaches to 83.4%.
C E Taylor - One of the best experts on this subject based on the ideXlab platform.
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fluidelastic instability and work rate measurements of steam generator u tubes in air water cross flow
Journal of Pressure Vessel Technology-transactions of The Asme, 2005Co-Authors: Victor P Janzen, Erik Hagberg, M J Pettigrew, C E TaylorAbstract:The dynamic response of U-tubes to two-phase cross-flow has been studied in tests involving a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to air-water cross-flow over the mid-Span Region. Tube vibration and the interaction between tubes and supports were measured over a wide range of void fractions and flow rates, for three different tube-to-support clearances. The vibration properties and tube-to-support work-rates could be characterized in terms of the relative influence of fluidelastic instability and random-turbulence excitation. For the first time, in a U-bend tube bundle with liquid or two-phase flow, fluidelastic instability was observed both in the out-of-plane and in the in-plane direction. This raises the possibility of higher-than-expected tube-to-support work-rates for U-tubes restrained by flat bars, particularly if fluidelastic instability, random turbulence and loose supports combine adversely.
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vibration and work rate measurements of steam generator u tubes in air water cross flow
5th International Symposium on Fluid Structure Interaction Aeroelasticity and Flow Induced Vibration and Noise, 2002Co-Authors: Victor P Janzen, Erik Hagberg, M J Pettigrew, C E Taylor, James Patrick, Tim G WhanAbstract:In nuclear power plant steam generators, the vibration response of tubes in two-phase cross-flow is a general concern that in some cases has become a very real long-term wear problem. This paper summarizes the results of the most recent U-bend vibration-response tests in a program designed to address this issue. The tests involved a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to two-phase air-water cross-flow over the mid-Span Region of the U-bend. Tube vibration properties and tube-to-support interaction in the form of work-rates were measured over a wide range of flow velocities for homogeneous void fractions from zero to 90%, with three different tube-to-support clearances. The measured vibration properties and work-rates could be characterized by the relative influence of the two most important flow-induced excitation mechanisms at work, fluidelastic instability and random-turbulence excitation. As in previous similar tests, strong effects of fluidelastic instability were observed at zero and 25% void fraction for pitch velocities greater than approximately 0.5 m/s, whereas random turbulence dominated the tube vibration and work-rate response at higher void fractions. In both cases, a link between vibration properties and the effect of the flat-bar supports could be established by comparing the vibration crossing frequency, extracted from time-domain vibration signals, to the participation of the lowest few vibration modes and to the measured work-rate. This approach may be useful when fluidelastic instability, random turbulence and loose supports all combine to result in high work-rates. Such a combination of factors is thought to be responsible for excessive U-tube fretting-wear in certain types of operating steam generators.Copyright © 2002 by ASME
Yassine Souleimani - One of the best experts on this subject based on the ideXlab platform.
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Performance Desensitization for a High-Speed Axial Compressor
Volume 2A: Turbomachinery, 2018Co-Authors: Yassine SouleimaniAbstract:The increase in compressor tip clearance over the lifeSpan of an aero-engine leads to a long-term degradation in its fuel consumption and operating envelope. A highly promising recent numerical study on a theoretical high-speed axial compressor rotor proposed a novel casing treatment to decrease performance and stall margin sensitivity to tip clearance increase. This paper aims to apply and analyze, through CFD simulations, this casing treatment concept to a representative production axial compressor rotor with inherently lower sensitivity to tip clearance increase and complement the explanation on the mechanism behind the reduction in sensitivity. Simulations of the baseline rotor showed that the lower Span Region contribute as much to the pressure ratio sensitivity as the tip Region which is dominated by tip leakage flow. In contrast, the efficiency sensitivity is mainly driven by losses occurring in the tip Region. The novel casing treatment was successfully applied to the baseline rotor through a design refinement. Although the casing treatment causes some penalty in nominal performance, it completely reversed the pressure ratio sensitivity (i.e. pressure ratio increases with tip clearance) and reduced the efficiency sensitivity. The reversed pressure ratio sensitivity is explained by a rotation in the core flow in the lower Span Region indirectly induced by the flow injection from the casing treatment. The lower efficiency sensitivity comes from a reduction in the amount of fluid that crosses the tip clearance of two adjacent blades, known as double leakage. The casing treatment’s beneficial effect on stall margin sensitivity is less obvious because of the stall inception type of the baseline rotor and its change in the presence of the casing treatment.
Victor P Janzen - One of the best experts on this subject based on the ideXlab platform.
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fluidelastic instability and work rate measurements of steam generator u tubes in air water cross flow
Journal of Pressure Vessel Technology-transactions of The Asme, 2005Co-Authors: Victor P Janzen, Erik Hagberg, M J Pettigrew, C E TaylorAbstract:The dynamic response of U-tubes to two-phase cross-flow has been studied in tests involving a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to air-water cross-flow over the mid-Span Region. Tube vibration and the interaction between tubes and supports were measured over a wide range of void fractions and flow rates, for three different tube-to-support clearances. The vibration properties and tube-to-support work-rates could be characterized in terms of the relative influence of fluidelastic instability and random-turbulence excitation. For the first time, in a U-bend tube bundle with liquid or two-phase flow, fluidelastic instability was observed both in the out-of-plane and in the in-plane direction. This raises the possibility of higher-than-expected tube-to-support work-rates for U-tubes restrained by flat bars, particularly if fluidelastic instability, random turbulence and loose supports combine adversely.
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vibration and work rate measurements of steam generator u tubes in air water cross flow
5th International Symposium on Fluid Structure Interaction Aeroelasticity and Flow Induced Vibration and Noise, 2002Co-Authors: Victor P Janzen, Erik Hagberg, M J Pettigrew, C E Taylor, James Patrick, Tim G WhanAbstract:In nuclear power plant steam generators, the vibration response of tubes in two-phase cross-flow is a general concern that in some cases has become a very real long-term wear problem. This paper summarizes the results of the most recent U-bend vibration-response tests in a program designed to address this issue. The tests involved a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to two-phase air-water cross-flow over the mid-Span Region of the U-bend. Tube vibration properties and tube-to-support interaction in the form of work-rates were measured over a wide range of flow velocities for homogeneous void fractions from zero to 90%, with three different tube-to-support clearances. The measured vibration properties and work-rates could be characterized by the relative influence of the two most important flow-induced excitation mechanisms at work, fluidelastic instability and random-turbulence excitation. As in previous similar tests, strong effects of fluidelastic instability were observed at zero and 25% void fraction for pitch velocities greater than approximately 0.5 m/s, whereas random turbulence dominated the tube vibration and work-rate response at higher void fractions. In both cases, a link between vibration properties and the effect of the flat-bar supports could be established by comparing the vibration crossing frequency, extracted from time-domain vibration signals, to the participation of the lowest few vibration modes and to the measured work-rate. This approach may be useful when fluidelastic instability, random turbulence and loose supports all combine to result in high work-rates. Such a combination of factors is thought to be responsible for excessive U-tube fretting-wear in certain types of operating steam generators.Copyright © 2002 by ASME
N. Sitaram - One of the best experts on this subject based on the ideXlab platform.
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Investigations on low speed axial compressor with forward and backward sweep
Journal of Thermal Science, 2007Co-Authors: M. Govardhan, O. G. Krishna Kumar, N. SitaramAbstract:In the recent past, experimental studies have shown some advantages of blade lean and sweep in axial compressors. As most of the experimental results are combined with other features, it is difficult to determine the effect of individual parameters on the performance of the compressor. The present numerical studies are aimed at understanding the performance and three-dimensional flow pattern at the exit of swept and unswept rotors. Three rotors, namely; unswept, 20^0 forward swept and 20^0 backward swept rotors are analysed with a specific intention of understanding the pattern of the blade boundary layer flow. The analysis was done using a fully three-dimensional viscous CFD code CFX-5. Results indicated reduction in pressure rise with sweep. Backward sweep is detrimental as far as the performance near endwalls is considered. On the other hand total pressure loss in the wake in mid Span Region is less with backward sweep, which favours its application here. However, backward sweep adversely affects the stall margin. The ability of the forward sweep to deflect the streamlines towards hub gets diminished at low flow rates. Forward sweep changes the streamline pattern in such a way that the suction surface streamlines are deflected towards the hub and the pressure surface streamlines are deflected towards the casing. An opposite behaviour is observed in backward swept rotors.
