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  • 1
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    Multi-scale modeling of the progressive damage in cross-ply laminates under thermal and mechanical loading (2012)
    Institute of Physics (IOP)
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    Publication Date: 2012-09-14
    Description: The progressive damage in cross-ply laminates was modeled by discrete element method (DEM). A particle radius expansion method was used to account for thermal loading applied to cross-ply laminates in which nominal fibers were introduced in the 0° plies so as to achieve the anisotropic thermal expansion behaviors. A series of convergence and validation tests of both mechanical and thermal properties of the 0° plies with nominal fibers have been carried out in order to validate the method. The DEM results of interfacial stress distribution of cross-ply laminates under pure thermal loading and under coupled thermal/mechanical loading were compared with other theoretical predictions. Microstructure of 90° plies was also studied by the DEM model. Transverse cracking which was formed by the coalescence of micro cracks in matrix and at fiber/matrix interface has been observed in the modeling results together with the ply-ply delaminations. It was found that the DEM model can predict n...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
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    Effects of pipe diameters on the pressures during delayed load rejection in high-head pumped storage power stations (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: High-head pumped storage power stations face serious problems related to the transient process, especially in the area of delayed load rejection in stations with annular piping layouts. The controlled pressures are adversely affected, which leads to many problems in the engineering design phase. In this study, we investigated this condition through theoretical analysis, numerical simulation, and actual engineering practice. We concluded that the root cause of the pressure issues is the flow switching resulted from the non-synchronous changes in pressure between each branch pipe. Moreover, we examined the impact of the diameters of the upstream main pipe and branch pipe on the controlled pressures and determined that the diameter of the branch pipe has a major influence on the pressures as it changes the flow switching rate. A similar investigation was conducted for downstream pipes. Our conclusions can be applied to actual engineering practice for high-head pumped storage power ...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 3
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    Study on the stability of waterpower-speed control system for hydropower station with upstream and downstream surge chambers based on regulation modes (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: In allusion to the hydropower station with upstream and downstream surge chambers, a complete mathematical model of waterpower-speed control system that includes pipeline system and turbine regulation system is established under the premise of the breakthrough of Thoma assumption in this paper. The comprehensive transfer functions and free movement equations that characterize the dynamic characteristics of system are derived when the mode of governor is respectively frequency regulation and power regulation. Then according to Routh- Hurwitz theorem, the stability domain that describes the good or bad of stability is drawn in the coordinate system with the relative areas of upstream and downstream surge chambers as abscissa and ordinate respectively. Finally, the effects of Thoma assumption, flow inertia, regulation modes, and governor parameters on the stability of waterpower-speed control system are analyzed by means of stability domain. The following conclusions have been come...
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  • 4
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    Numerical analysis of rotating stall instabilities of a pump- turbine in pump mode (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: Rotating stall may occur at part load flow of a pump-turbine in pump mode. Unstable flow structures developing under stall condition can lead to a sudden drop of efficiency, high dynamic load and even cavitation. CFD simulations on a pump-turbine model in pump mode were carried out to reveal the onset and developed mechanisms of these unstable flow phenomena at part load. The simulation results of energy-discharge and efficiency characteristics are in good agreement with those obtained by experiments. The more deviate from design conditions with decreasing flow rate, the more flow separations within the vanes. Under specific conditions, four stationary separation zones begin to progress on the circumference, rotating at a fraction of the impeller rotation rate. Rotating stalls lead to the flow in the vane diffuser channels alternating between outward jet flow and blockage. Strong jets impact the spiral casing wall causing high pressure pulsations. Severe separations of the stall...
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  • 5
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    Dynamic characteristics of a pump-turbine during hydraulic transients of a model pumped-storage system: 3D CFD simulation (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: The runaway process in a model pumped-storage system was simulated for analyzing the dynamic characteristics of a pump-turbine. The simulation was adopted by coupling 1D (One Dimensional) pipeline MOC (Method of Characteristics) equations with a 3D (Three Dimensional) pump-turbine CFD (Computational Fluid Dynamics) model, in which the water hammer wave in the 3D zone was defined by giving a pressure dependent density. We found from the results that the dynamic performances of the pump-turbine do not coincide with the static operating points, especially in the S-shaped characteristics region, where the dynamic trajectories follow ring-shaped curves. Specifically, the transient operating points with the same Q 11 and M 11 in different moving directions of the dynamic trajectories give different n 11 . The main reason of this phenomenon is that the transient flow patterns inside the pump-turbine are influenced by the ones in the pre...
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  • 6
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    Study on the stability of waterpower-speed control system for hydropower station with air cushion surge chamber (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: According to the fact that the effects of penstock, unit and governor on stability of water level fluctuation for hydropower station with air cushion surge chamber are neglected in previous researches, in this paper, Thoma assumption is broken through, the complete mathematical model of waterpower-speed control system for hydropower station with air cushion surge chamber is established, and the comprehensive transfer function and linear homogeneous differential equation that characterize the dynamic characteristics of system are derived. The stability domain that characterizes the good or bad of stability quantitatively is drawn by using the stability conditions. The effects of the fluid inertia in water diversion system, the air cushion surge chamber parameters, hydraulic turbine characteristics, generator characteristics, and regulation modes of governor on the stability of waterpower-speed control system are analyzed through stability domain. The main conclusions are as follo...
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  • 7
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    1-D MOC simulation software for hydraulic transients: TOPsys (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-07-31
    Description: The development of hydropower in China has entered the gold period nowadays. Numerous challenging hydropower projects have been presented to researchers and scholars. In order to adapt to this trend and the need of the nation, TOPsys, an one dimensional simulation software based on the method of characteristics (MOC) for hydraulic transients, has been developed in State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University recently. This software has been employed for transient flow simulations of more than thirty hydropower stations in China and overseas. The whole paper is organized as follows: first, basic mathematical theory of the software was introduced. Subsequently, several typical engineering applications, including conventional power stations and pumped storage power stations, were given for validation. Finally, the versatility as well as the expandability of this software was shown with several special engineering examples.
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  • 8
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    Numerical simulation on the characteristics of thermal buoyant jets with the different flow profiles in crossflow (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-11-06
    Description: In this paper, the numerical simulation on the characteristics of thermal buoyant jets of the cross-flow equal area of the round hole and square hole thermal jets is carried out, which based on the SIMPLE algorithm and Fluent’s RSM model. According to the calculation results, the variation characteristics of velocity and temperature of single-hole jets with the different flow profiles in crossflow are analyzed, and the decay laws of velocity and temperature in heat jet are obtained. The results show that the closer to the jet exit, the more rapidly the speed change, and there is a clear jet mainstream area, but the speed fluctuations gradually weaken with the flow to the downstream. The dimensionless temperature difference of the trajectory of thermal buoyant jets decreases gradually along the direction of incoming flow, and the trajectory centre of the thermal buoyant jets moves away from the outlet. Compared with the square hole, the round hole jet impactes on the incoming flo...
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  • 9
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    Effects of Excitation Current on Levitation Force of Electromagnetic Levitation of Silicon-Iron Droplets (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-11-08
    Description: In this paper, the relationship between the extraction current and the magnetic field had been discussed when the droplet was in the condition of vacuum electromagnetic levitation. The conclusion which the magnetic field was asymmetric could be simulated by finite element analysis in ANSYS software. Meanwhile, the shape of Silicon-Iron droplet was inferred as “up-wide and down-narrow” basing the magnetic field simulation results.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    Experimental Study on Phosphorus Removal from Ferrosilicon Alloys under Electromagnetic Levitation (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-11-08
    Description: Along with the growing demand of green energy, the study of solar energy continues to deepen and the production of solar cells is increasing ceaselessly. However, the cost of solar power has become an economic constraint to the large-scale production of solar power equipment. In order to meet the demand of solar power generation, metallurgical grade silicon may be used to replace solar grade silicon to generate electricity. The challenge is that metallurgical grade silicon contains phosphorus impurities. In this paper, electromagnetic levitation is recommended to remove the phosphorus in metallurgical grade silicon. The results show that when the mass of levitated droplets is 0.59-0.64g, the input current is 300-400A, the frequency is 280kHz, and the input power range is 3000-4500W, the removal rate of phosphorus in the ferrosilicon sample is as high as 41%. Therefore, it is feasible to use metallurgical grade silicon to replace solar grade silicon.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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