Water hammer occurs whenever the fluid velocity in vertical lifting pipe systems for deep-sea mining suddenly changes. In this work, the shock wave was proven to play an important role in changing pressures and period...Water hammer occurs whenever the fluid velocity in vertical lifting pipe systems for deep-sea mining suddenly changes. In this work, the shock wave was proven to play an important role in changing pressures and periods, and mathematical and numerical modeling technology was presented for simulated transient pressure in the abnormal pump operation. As volume concentrations were taken into account of shock wave speed, the experiment results about the pressure-time history, discharge-time history and period for the lifting pipe system showed that: as its concentrations rose up, the maximum transient pressure went down, so did its discharges; when its volume concentrations increased gradually, the period numbers of pressure decay were getting less and less, and the corresponding shock wave speed decreased. These results have highly coincided with simulation results. The conclusions are important to design lifting transporting system to prevent water hammer in order to avoid potentially devastating consequences, such as damage to components and equipment and risks to personnel.展开更多
To realize the accurate control of water hammer in pipes by valve stroking, based on basic differential equations of water hammer subjected to initial and boundary conditions, the traveling solution of wave equations ...To realize the accurate control of water hammer in pipes by valve stroking, based on basic differential equations of water hammer subjected to initial and boundary conditions, the traveling solution of wave equations in finite region was applied to the linear water hammer problem. With the given velocity function at the valve and the introduction of curve integration independent of integral path, the exact analytic solution of dimensionless water hammer pressure was obtained in the course of valve closing. Based on the definition of eigen wave height, optimal eigen wave height and observation time, the control goal of water hammer pressure and the judgment rule of the optimal eigen wave height were determined, then the optimal velocity function in the calculated example was derived, which can reduce the water hammer pressure maximally. According to this function, a valve closing program was set, and the optimal control of water hammer could be realized.展开更多
A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary...A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary conversion of the turbine.For the practical use,it is necessary to develop a design method which can consider the incident wave motion,the motion of the internal free surface affected in the structure such as a partly submerged wall,the fluctuation of air pressure in an air chamber,and the rotation of the air turbine.At here,the authors carried out the wave tank tests using the model OWC equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method.As the result,the efficiencies of the three cases with different speed ratio between generator and turbine,and the effects of the curtain wall depth and the wave length on the energy conversion performance were clarified.展开更多
Based on the derivation of the continuity equation of water hammer, the modification coefficient used in the wave speed formula is discussed thoroughly. Mistakes presented in current formulas are analyzed. Finally in ...Based on the derivation of the continuity equation of water hammer, the modification coefficient used in the wave speed formula is discussed thoroughly. Mistakes presented in current formulas are analyzed. Finally in this paper a summarizing comment is given on the problem that whether or not the slope term Vsina should be included in the characteristic equations.展开更多
Water hammers in pseudo-homogeneous flows and heterogeneous flows have been investigated, and equations for the wave propagation speed and the additional pressure due to water hammer in both flows have been developed....Water hammers in pseudo-homogeneous flows and heterogeneous flows have been investigated, and equations for the wave propagation speed and the additional pressure due to water hammer in both flows have been developed. These equations have been tested against available experimental data.展开更多
Impulse turbine, working as a typical self-rectifying turbine, is recently utilized for the oscillating water column(OWC) wave energy converters, which can rotate in the same direction under the bi-directional air f...Impulse turbine, working as a typical self-rectifying turbine, is recently utilized for the oscillating water column(OWC) wave energy converters, which can rotate in the same direction under the bi-directional air flows. A numerical model established in Fluent is validated by the corresponding experimental results. The flow fields, pressure distribution and dimensionless evaluating coefficients can be calculated and analyzed. Effects of the rotor solidity varying with the change of blade number are investigated and the suitable solidity value is recommended for different flow coefficients.展开更多
Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy convert...Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy converter(OWC-WEC). This study shows a numerical analysis of the diameter determination of two types of turbines, Wells and Impulse, installed in an onshore OWC device subjected to a hypothetical sea state. Commercial software FLUENT?,which is based on RANS-VoF(Reynolds-Averaged Navier-Stokes equations and Volume of Fluid technique), is employed. A methodology that imposes air pressure on the chamber, considering the air compressibility effect, is used. The mathematical domain consists of a 10 m deep flume with a 10 m long and 10 m wide OWC chamber at its end(geometry is similar to that of the Pico's plant installed in Azores islands, Portugal). On the top of the chamber, a turbine works with air exhalation and inhalation induced by the water free surface which oscillates due to the incident wave. The hypothetical sea state, represented by a group of regular waves with periods from 6 to 12 s and heights from 1.00 to 2.00 m(each wave with an occurrence frequency), is considered to show the potential of the presented methodology. Maximum efficiency(relation between the average output and incident wave powers) of46% was obtained by using a Wells turbine with the diameter of 2.25 m, whereas the efficiency was 44% by an Impulse turbine with the diameter of 1.70 m.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50875081)China Postdoctoral Science Foundation(Grant No.20080440992)+1 种基金the Planned Science and Technology Support Project of Hunan Province(Grant No.2009SK3159)Graduate Innovation Fund of Hunan University of Science and Technology(Grant No.S100109)
文摘Water hammer occurs whenever the fluid velocity in vertical lifting pipe systems for deep-sea mining suddenly changes. In this work, the shock wave was proven to play an important role in changing pressures and periods, and mathematical and numerical modeling technology was presented for simulated transient pressure in the abnormal pump operation. As volume concentrations were taken into account of shock wave speed, the experiment results about the pressure-time history, discharge-time history and period for the lifting pipe system showed that: as its concentrations rose up, the maximum transient pressure went down, so did its discharges; when its volume concentrations increased gradually, the period numbers of pressure decay were getting less and less, and the corresponding shock wave speed decreased. These results have highly coincided with simulation results. The conclusions are important to design lifting transporting system to prevent water hammer in order to avoid potentially devastating consequences, such as damage to components and equipment and risks to personnel.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50478025 and 50506009) the 46th China Postdoctoral Science Foundation(Grant No.20090460912)
文摘To realize the accurate control of water hammer in pipes by valve stroking, based on basic differential equations of water hammer subjected to initial and boundary conditions, the traveling solution of wave equations in finite region was applied to the linear water hammer problem. With the given velocity function at the valve and the introduction of curve integration independent of integral path, the exact analytic solution of dimensionless water hammer pressure was obtained in the course of valve closing. Based on the definition of eigen wave height, optimal eigen wave height and observation time, the control goal of water hammer pressure and the judgment rule of the optimal eigen wave height were determined, then the optimal velocity function in the calculated example was derived, which can reduce the water hammer pressure maximally. According to this function, a valve closing program was set, and the optimal control of water hammer could be realized.
基金This investigation was carried out as a continuation of the“Program for the Promotion of New Energy Infrastructure Development”,supported by the Mitsubishi Research Institute(MRI)/the Ministry of Economy,Trade and Industry(METI),Japan.
文摘A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary conversion of the turbine.For the practical use,it is necessary to develop a design method which can consider the incident wave motion,the motion of the internal free surface affected in the structure such as a partly submerged wall,the fluctuation of air pressure in an air chamber,and the rotation of the air turbine.At here,the authors carried out the wave tank tests using the model OWC equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method.As the result,the efficiencies of the three cases with different speed ratio between generator and turbine,and the effects of the curtain wall depth and the wave length on the energy conversion performance were clarified.
文摘Based on the derivation of the continuity equation of water hammer, the modification coefficient used in the wave speed formula is discussed thoroughly. Mistakes presented in current formulas are analyzed. Finally in this paper a summarizing comment is given on the problem that whether or not the slope term Vsina should be included in the characteristic equations.
文摘Water hammers in pseudo-homogeneous flows and heterogeneous flows have been investigated, and equations for the wave propagation speed and the additional pressure due to water hammer in both flows have been developed. These equations have been tested against available experimental data.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51279190 and 51311140259)the Shandong Province Natural Science Foundation for Distinguished Young Scholars(Grant No.JQ201314)
文摘Impulse turbine, working as a typical self-rectifying turbine, is recently utilized for the oscillating water column(OWC) wave energy converters, which can rotate in the same direction under the bi-directional air flows. A numerical model established in Fluent is validated by the corresponding experimental results. The flow fields, pressure distribution and dimensionless evaluating coefficients can be calculated and analyzed. Effects of the rotor solidity varying with the change of blade number are investigated and the suitable solidity value is recommended for different flow coefficients.
文摘Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy converter(OWC-WEC). This study shows a numerical analysis of the diameter determination of two types of turbines, Wells and Impulse, installed in an onshore OWC device subjected to a hypothetical sea state. Commercial software FLUENT?,which is based on RANS-VoF(Reynolds-Averaged Navier-Stokes equations and Volume of Fluid technique), is employed. A methodology that imposes air pressure on the chamber, considering the air compressibility effect, is used. The mathematical domain consists of a 10 m deep flume with a 10 m long and 10 m wide OWC chamber at its end(geometry is similar to that of the Pico's plant installed in Azores islands, Portugal). On the top of the chamber, a turbine works with air exhalation and inhalation induced by the water free surface which oscillates due to the incident wave. The hypothetical sea state, represented by a group of regular waves with periods from 6 to 12 s and heights from 1.00 to 2.00 m(each wave with an occurrence frequency), is considered to show the potential of the presented methodology. Maximum efficiency(relation between the average output and incident wave powers) of46% was obtained by using a Wells turbine with the diameter of 2.25 m, whereas the efficiency was 44% by an Impulse turbine with the diameter of 1.70 m.