Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive da...Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive dam breaching mechanisms and we calculate the time-averaged headcut migration rate using an energy-based empirical formula. A numerical method is adopted to determine the initial scour position at the downstream slope in terms of the water head and dam height, and the broad-crested weir equation is utilized to simulate the breach flow. The limit equilibrium method is used to analyze the stability of breach slope during the breach process. An iterative method is developed to simulate the coupling process of soil and water at each time step. The calculated results of three dam breach cases testify the reasonability of the model, and the sensitivity studies of soil erodibility show that sensitivity is dependent on each test case's soil conditions. In addition, three typical dam breach models, NWS BREACH, WinDAM B, and HR BREACH, are also chosen to compare with the proposed model. It is found that NWS BREACH may have large errors for cohesive dams, since it uses a noncohesive sediment transport model and does notconsider headcut erosion, WinDAM B and HR BREACH consider headcut erosion as the breaching mechanism and handle well homogeneous cohesive dam overtopping failure, but overall, the proposed model has the best performance.展开更多
The machining accuracy of workpiece is influenced by its orientation deviation, which is caused by the fixture-workpiece error. Based on the spatial coordinate theory, the orientation deviation of workpiece is measure...The machining accuracy of workpiece is influenced by its orientation deviation, which is caused by the fixture-workpiece error. Based on the spatial coordinate theory, the orientation deviation of workpiece is measured by using an on-machine verification system, which can take into account the errors resulting from fixture manufacturing, installation and adjustment, location and clamping of workpiece. According to the least square method, the model of orientation deviation is built to determine the relationship between the theoretical and actual coordinate systems. The influence of orientation deviation on machining accuracy is quantified, and it is shown that the orientation deviation only affects the dimensional precision and position precision, rather than shape precision. In the experiment, the compensation processing of realtime errors was conducted, and the perpendicularity and inclination errors of the tetragonal part were reduced by 38.46% and 47.06%, respectively.展开更多
The servo system actuated by oscillating pneumatic cylinder for X-Y plate is a multi-variable nonlinear control system. Its mathematical model is established, and nonlinear factors are analyzed. Due to the existence o...The servo system actuated by oscillating pneumatic cylinder for X-Y plate is a multi-variable nonlinear control system. Its mathematical model is established, and nonlinear factors are analyzed. Due to the existence of deadlock zone and the small damp of the pneumatic oscillating cylinder, it is likely to result in overshoot, and there is also certain steady-state error, so online modifying of proportion-integration-differentiation （PID） parameters is needed so as to achieve better control performance. Meanwhile considering the stability demand for long-term run, a fuzzy adaptive PID controller is designed. The result of hardware-inloop （HIL） test and real-time control experiment shows that the adaptive PID controller has desirable serfadaptability and robustness to external disturbance and to change of system parameters, and its control per- fonnance is better than that of traditional PID controllers.展开更多
This paper summarizes the results of energy simulation analysis to determine the effectiveness of building characteristics in reducing electrical energy consumption in residential buildings （conditioned and unconditi...This paper summarizes the results of energy simulation analysis to determine the effectiveness of building characteristics in reducing electrical energy consumption in residential buildings （conditioned and unconditioned） and commercial buildings （office ＆ hotel） in Egypt. Specifically, the impact on building envelope performance is investigated for different strategies such as window size, glazing type and building construction for two geographical locations in Egypt. This paper also studies the energy savings in residential and nonresidential buildings for different lighting power densities （LPD）, energy input ratios （EIR）, set point temperatures （SPT） and heating, ventilation, and air conditioning （I-WAC） systems. The study shows certain findings of practical significance, e.g. that a window-to-wall ratio of 0.20 and reasonably shaded windows lower the total annual electricity use for nonresidential buildings by more than 20% in the two Egyptian locations.展开更多
In this paper,a rotational supercavitating evaporator(RSCE)was at first modeled by means of theoretical analysis approach.The geometrical characteristics of supercavity in the modeled RSCE were then studied through nu...In this paper,a rotational supercavitating evaporator(RSCE)was at first modeled by means of theoretical analysis approach.The geometrical characteristics of supercavity in the modeled RSCE were then studied through numerical simulations.The current research objectives consist in determination of shape of the supercavitator(which in the plane of rotation generates supercavity occupying the most volume between blades),and location of the area suitable for steam extraction by revealing the inner structure of supercavity.Analytical analysis was performed by solving empirical equations for the shape of RSCE,through which an evaluation of two-dimensional relative position of supercavity trailing edge for different shapes of the supercavitator has been realized.Numerical simulation was then carried out,by numerically solving the unsteady Navier-Stokes equations in their conservation form coupled with the Rayleigh-Plesset cavitation and Shear-Stress Transport turbulence models,for verification of the results obtained from empirical equations.Despite unreliable assumption of applicability of empirical equations we have confirmed similarity of the supercavity shapes obtained by both methods for the same RSCE.Therefore,the shape of supercavitator calculated by using empirical equations is acceptable,which provides a simple but reliable approach for design of RSCE.The inner structure of supercavity obtained by numerical simulation has indicated position and parameters for steam extraction openings for further numerical and experimental studies on the performance of RSCE.Practical application of steam or gas extraction is suggested for solving of some problems associated with cavitating pumping of cryogenic liquid.展开更多
基金Natural Science Foundation of China(Grant No.51379129,51539006,51509164)
文摘Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive dam breaching mechanisms and we calculate the time-averaged headcut migration rate using an energy-based empirical formula. A numerical method is adopted to determine the initial scour position at the downstream slope in terms of the water head and dam height, and the broad-crested weir equation is utilized to simulate the breach flow. The limit equilibrium method is used to analyze the stability of breach slope during the breach process. An iterative method is developed to simulate the coupling process of soil and water at each time step. The calculated results of three dam breach cases testify the reasonability of the model, and the sensitivity studies of soil erodibility show that sensitivity is dependent on each test case's soil conditions. In addition, three typical dam breach models, NWS BREACH, WinDAM B, and HR BREACH, are also chosen to compare with the proposed model. It is found that NWS BREACH may have large errors for cohesive dams, since it uses a noncohesive sediment transport model and does notconsider headcut erosion, WinDAM B and HR BREACH consider headcut erosion as the breaching mechanism and handle well homogeneous cohesive dam overtopping failure, but overall, the proposed model has the best performance.
基金Supported by National Natural Science Foundation of China (No.50975200)
文摘The machining accuracy of workpiece is influenced by its orientation deviation, which is caused by the fixture-workpiece error. Based on the spatial coordinate theory, the orientation deviation of workpiece is measured by using an on-machine verification system, which can take into account the errors resulting from fixture manufacturing, installation and adjustment, location and clamping of workpiece. According to the least square method, the model of orientation deviation is built to determine the relationship between the theoretical and actual coordinate systems. The influence of orientation deviation on machining accuracy is quantified, and it is shown that the orientation deviation only affects the dimensional precision and position precision, rather than shape precision. In the experiment, the compensation processing of realtime errors was conducted, and the perpendicularity and inclination errors of the tetragonal part were reduced by 38.46% and 47.06%, respectively.
基金Supported by Japanese SMC Corporation with contract (No. 05-07)
文摘The servo system actuated by oscillating pneumatic cylinder for X-Y plate is a multi-variable nonlinear control system. Its mathematical model is established, and nonlinear factors are analyzed. Due to the existence of deadlock zone and the small damp of the pneumatic oscillating cylinder, it is likely to result in overshoot, and there is also certain steady-state error, so online modifying of proportion-integration-differentiation （PID） parameters is needed so as to achieve better control performance. Meanwhile considering the stability demand for long-term run, a fuzzy adaptive PID controller is designed. The result of hardware-inloop （HIL） test and real-time control experiment shows that the adaptive PID controller has desirable serfadaptability and robustness to external disturbance and to change of system parameters, and its control per- fonnance is better than that of traditional PID controllers.
文摘This paper summarizes the results of energy simulation analysis to determine the effectiveness of building characteristics in reducing electrical energy consumption in residential buildings （conditioned and unconditioned） and commercial buildings （office ＆ hotel） in Egypt. Specifically, the impact on building envelope performance is investigated for different strategies such as window size, glazing type and building construction for two geographical locations in Egypt. This paper also studies the energy savings in residential and nonresidential buildings for different lighting power densities （LPD）, energy input ratios （EIR）, set point temperatures （SPT） and heating, ventilation, and air conditioning （I-WAC） systems. The study shows certain findings of practical significance, e.g. that a window-to-wall ratio of 0.20 and reasonably shaded windows lower the total annual electricity use for nonresidential buildings by more than 20% in the two Egyptian locations.
文摘In this paper,a rotational supercavitating evaporator(RSCE)was at first modeled by means of theoretical analysis approach.The geometrical characteristics of supercavity in the modeled RSCE were then studied through numerical simulations.The current research objectives consist in determination of shape of the supercavitator(which in the plane of rotation generates supercavity occupying the most volume between blades),and location of the area suitable for steam extraction by revealing the inner structure of supercavity.Analytical analysis was performed by solving empirical equations for the shape of RSCE,through which an evaluation of two-dimensional relative position of supercavity trailing edge for different shapes of the supercavitator has been realized.Numerical simulation was then carried out,by numerically solving the unsteady Navier-Stokes equations in their conservation form coupled with the Rayleigh-Plesset cavitation and Shear-Stress Transport turbulence models,for verification of the results obtained from empirical equations.Despite unreliable assumption of applicability of empirical equations we have confirmed similarity of the supercavity shapes obtained by both methods for the same RSCE.Therefore,the shape of supercavitator calculated by using empirical equations is acceptable,which provides a simple but reliable approach for design of RSCE.The inner structure of supercavity obtained by numerical simulation has indicated position and parameters for steam extraction openings for further numerical and experimental studies on the performance of RSCE.Practical application of steam or gas extraction is suggested for solving of some problems associated with cavitating pumping of cryogenic liquid.
