A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried...A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. The VOF (volume-of-fluid) multiphase flow method and a phase-change model for the mass transfer have been used. For an accurate modeling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT (fast Fourier transforms), in order to comprehend their behavior and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.展开更多
A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues.Prev...A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues.Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3 D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.展开更多
A numerical methodology for investigating compressor instabilities in a multistage environment is presented. The method is based on a stage-by-stage dynamic compression model and considers air compressibility explicit...A numerical methodology for investigating compressor instabilities in a multistage environment is presented. The method is based on a stage-by-stage dynamic compression model and considers air compressibility explicitly throughout the compressor. It involves discretizing the compression system into distinct elements and a use of the local elemental characteristic of mean performance. The models are presented in both nonlinear and linearized forms. The linearised form permits well surge condition prediction for multistage axial compressors, while the non-linear form is able to investigate the growth of local flow disturbances, and helps to develop practical control strategy. Validations were carried out using the data from several aircraft engine compressors. A good experiment-model consistency is achieved.展开更多
The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies.Several different technologies have been propos...The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies.Several different technologies have been proposed,but lots of problems remain to be solved before they can be applied in practice.A wide area measurement system(WAMS)based test platform is developed for transient stability detection and control.The design as well as main function modules of the platform are introduced.In addition,three generator power angle prediction methods and six response based transient instability detection technologies are given.Results of engineering application demonstrate that the developed test platform can provide a real-time operation environment,which can effectively compare and analyze the validity and practicability of these transient stability detection technologies.Based on the measured perturbed trajectories from actual power systems or the Real-Time Digital Simulators(RTDS),the platform can realize the assessment and visual result presentation of various responses from different transient instability detection technologies.The test platform can be applied to different power systems and it is convenient to embed new transient instability detection modules.Meanwhile some deficiencies and shortcomings in engineering application are pointed out and corresponding suggestions are given.In conclusion,the hardware and software structure,function modulus and engineering applications are presented.The application in actual power systems shows that it has a good application perspective.展开更多
文摘A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. The VOF (volume-of-fluid) multiphase flow method and a phase-change model for the mass transfer have been used. For an accurate modeling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT (fast Fourier transforms), in order to comprehend their behavior and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.
基金conducted as part of the research program of the Office of Mine Safety and Health Research of the National Institute for Occupational Safety and Health(NIOSH)
文摘A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues.Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3 D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.
基金This project is supported by National Natural Science Foundation of China (No.50146014) National Natural Science Foundation of Xi'an Jiaotong University, China (No.573023).
文摘A numerical methodology for investigating compressor instabilities in a multistage environment is presented. The method is based on a stage-by-stage dynamic compression model and considers air compressibility explicitly throughout the compressor. It involves discretizing the compression system into distinct elements and a use of the local elemental characteristic of mean performance. The models are presented in both nonlinear and linearized forms. The linearised form permits well surge condition prediction for multistage axial compressors, while the non-linear form is able to investigate the growth of local flow disturbances, and helps to develop practical control strategy. Validations were carried out using the data from several aircraft engine compressors. A good experiment-model consistency is achieved.
基金Supported by National Natural Science Foundation of China(51577049)Open Foundation of State Key Lab.of Alternate Electrical Power System with Renewable Energy Sources(Grant No.LAPS14005).
文摘The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies.Several different technologies have been proposed,but lots of problems remain to be solved before they can be applied in practice.A wide area measurement system(WAMS)based test platform is developed for transient stability detection and control.The design as well as main function modules of the platform are introduced.In addition,three generator power angle prediction methods and six response based transient instability detection technologies are given.Results of engineering application demonstrate that the developed test platform can provide a real-time operation environment,which can effectively compare and analyze the validity and practicability of these transient stability detection technologies.Based on the measured perturbed trajectories from actual power systems or the Real-Time Digital Simulators(RTDS),the platform can realize the assessment and visual result presentation of various responses from different transient instability detection technologies.The test platform can be applied to different power systems and it is convenient to embed new transient instability detection modules.Meanwhile some deficiencies and shortcomings in engineering application are pointed out and corresponding suggestions are given.In conclusion,the hardware and software structure,function modulus and engineering applications are presented.The application in actual power systems shows that it has a good application perspective.