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Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mixed-flow pumps are characterized by their wide operating range and high-efficiency region in the fields of agricultural irrigation, hydropower engineering, and urban water supply systems. The stability of the transient processes, such as start-up and shutdown, has drawn great attention to the increasing capacity and impeller diameter of mixed-flow pumps in the industrial field. Particularly, the start-up process of a mixed-flow pump is an extremely complex transient process. The mixed-flow pumps can experience shock loading, hydraulic vibrations, and cavitation damage during the start-up process, leading to a negative impact on the stable operation of the pump. The evolution of noise characteristics at the pump section is of great significance for stability monitoring during the start-up process of mixed-flow pumps. This study aims to investigate the variation and influencing factors of noise under different start-up modes. An acoustic vibration test system was selected to collect the noise, shaft vibration, and pressure fluctuation signal of mixed-flow pumps under linear and non-linear starting modes. Then, the collected noise signals were analyzed using acoustic signal processing, including the energy entropy ratio analysis, spectral chart analysis, and A-weighted sound pressure calculation. A systematic analysis was made to clarify the influence of start-up on the sound pressure level and spectral characteristics of noise. The energy intensity in the noise was also analyzed. A coherence analysis was then implemented to determine the correlation among the impeller outlet pressure fluctuation, shaft vibration, and pump noise during the start-up process. The results showed that there was a concentrated region in the high amplitude sound pressure of the noise starting at the end of the start-up process in the three start-up modes. The shortest time scale was achieved in the high amplitude noise region under the concave exponential function start-up mode, indicating the least persistent impact on the environment. There was a relatively minimal impact noise generated by the concave exponential function start-up mode, indicating that this start-up mode was beneficial to avoid the severe mechanical impact during start-up. In addition, the formant analysis of the noise spectrogram showed that there was the lowest probability of mixed-flow pump’s instability induced by the concave exponential function start-up mode among the three start-up modes. The highest A-weighted sound pressure level of the noise generated by the pump was located at the frequency band with the center frequency of 250 Hz. The maximum A-weighted sound pressure level and the total effective sound pressure level of the noise generated by the pump under the linear start-up mode were less than those of the other two start-up modes. Compared with the linear start-up mode, the concave exponential function start-up mode improved the sound pressure level of the medium- and low-frequency noise. The wavelet partial coherence analysis showed that the impeller outlet pressure fluctuation was the main factor affecting the dominant sound pressure level (center frequency was 250 Hz) of the noise during the start-up process. The radial vibration of the shaft only affected the noise at the very low-frequency band. [ABSTRACT FROM AUTHOR]

Biomass energy (such as biogas) has been one of the most important ways to reduce greenhouse gas emission during the economic transformation of China. It is necessary to carefully treat the transporting of biogas mixture, due to its high risk in rural areas, where there are extensive biogas projects. Particularly, a gas-liquid multiphase pump can be required higher stability during transportation. The condition of low discharge can be attributed to the unstable region of the pumps. In this case, the vibration of the pump can be aggravated to sharply deteriorate the stability of the pump. In severe cases, it may even cause damage to the components of the multiphase pumps. Therefore, it is highly urgent to clarify the influence of various factors on the vibration in the multiphase pumps under low discharge. Among them, a Gas Volume Fraction (GVF) is an important parameter in the operation of gas-liquid multiphase pumps. Taking a three-stage mixed-flow multiphase pump as the research object, this study aims to establish a multi-channel vibration test system, further to collect the vibration signals of the shaft and bearing, when transporting the liquid with different GVF at low discharge. The vibration signal processing was conducted to determine the influence of the GVF on the vibration of the shaft and bearing house. The results showed that the peak-to-peak value for the radial vibration of the shaft first increased and then decreased, with the increase of the GVF, indicating an outstanding nonlinear behavior. The radial vibration amplitude of the shaft caused by the increase of GVF reached 3.2 times that at pure water conditions. Besides, the increasing GVF mainly dominated the axial vibration of the bearing house, indicating a small effect on the radial vibration. The axial vibration amplitude of the bearing house was greater than the radial vibration at all working conditions. The amplitude frequency of the shaft radial vibration was attributed to the transition conversion of the gas-liquid two-phase flow pattern in the multiphase pump. Once the GVF increased from low to high, the two-phase flow pattern was changed from the bubble flow to the gas pocket flow in the multiphase pump. The local congestion in the pump inlet tee was induced the significant low-frequency components in the frequency spectrum for radial vibration of the shaft. The increasing GVF also presented a certain strengthening effect on the rotor-stator interaction between the impeller outlet and the guide vane inlet. In the range of (0-20%) GVF, the peak value of the Probability Density Function (PDF) for the radial vibration of the shaft decreased, with the increasing of the GVF. Once the GVF exceeded 20%, the peak value of the PDF increased in the radial vibration of the shaft, as the GVF increased, indicating two opposite trends. The finding can also provide a strong reference to evaluate the GVF in the mixed-flow pumps. [ABSTRACT FROM AUTHOR]

Hydropower energy is one of the most important clean energy sources in the world. Since the medium and high head hydropower energy presents a high economic index and exploitability, only a few resources are available at present in China. By contrast, low head hydropower resources become one of the key directions of hydropower development in the future. A Kaplan turbine has also been one of the main unit types for the low head hydropower resources. Nevertheless, cavitation has been only one factor to limit the application, although a wide range was achieved in the high efficiency region. Furthermore, the runner erosion and vibration induced by the cavitation can greatly shorten the normal operating cycle of the Kaplan turbine, even seriously detrimental to the economic benefits of water stations. The vibration and pressure fluctuation are the commonly-used indicators to report the stability of hydraulic turbines. As such, the effect of cavitation on the vibration and pressure fluctuation directly determines the stability and optimization of the Kaplan turbine. In this study, a synchronous test system was constructed to investigate the influence of cavitation on the pressure fluctuation of the draft tube and the runner vibration in a Kaplan turbine. The system included a high-speed camera, a Laser Doppler Vibrometer (LDV), and a high-frequency pressure fluctuation sensor. A Kaplan turbine model was also selected as the research object. The pressure fluctuation, radial vibration, and cavitation images of the runner were first captured under different cavitation coefficients in the synchronous test system. The Variational Mode Decomposition (VMD), the spectrum analysis, and the cross-correlation were then combined to explore the influence of cavitation on the radial vibration of the runner, and the pressure fluctuation on the draft tube. Finally, it was found that there was a significant increase in the amplitudes of pressure fluctuation on the draft cone tube, and the radial vibration velocity of the runner, with the decrease of cavitation coefficient. There was an obvious nonlinearity in the peak-to-peak value of pressure fluctuation on the draft cone tube and the radial vibration velocity of the runner, with the variation of cavitation coefficient. Specifically, the peak-to-peak values after complete cavitation reached 9.16 and 10.12 times that without cavitation, respectively. The increased severity of runner cavitation made the dominant frequency of pressure fluctuation on the draft cone tube change to blade passing frequency. But only a little influence was observed on the dominant frequency of runner radial vibration velocity. The dominant frequency of radial vibration velocity of the runner was basically the passing frequency of blades. The runner cavitation also induced the local migration of extreme value in the high-frequency energy, which increased the energy of low-frequency region of pressure fluctuation. The possibility of Kaplan turbine resonance was enhanced in this case. Moreover, the cavitation contributed to enhancing the energy in the high-frequency region of runner radial vibration in a Kaplan turbine. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydropower is a major source of renewable, noncarbon-based electrical energy. Although hydropower has many environmental advantages, hydropower dams alter the natural ecohydrological conditions of the rivers and cause significant ecological impact, especially for fish that live in or migrate through impounded river systems. Injury and mortality of fish that pass through hydraulic turbines and other downstream passage routes can result from several mechanisms, such as rapid and extreme pressure changes, shear stress, strike, cavitation, and grinding. For example, a large or fast pressure drop can lead to internal bleeding of fish, rupture of the swim bladder or vapor bubbles in eyes, which will result in direct mortality and reduces the ability to escape predators in the tailrace. Shear stress can causes fish scales flake, muscle tissue tearing, bruising, and even the fish body are cut off. So understanding the biological responses of fish to the conditions of hydraulic turbine is important for designing advanced fish-friendly turbines. Since the injury of fish may be caused by a combination of multiple damage mechanisms, it is necessary to identify primary and secondary damage mechanisms by research. In this paper, the computational fluid dynamic analyze method was adopted to simulate the three dimensional turbulent flow in an francis turbine. The simulation was conducted at different discharge conditions of maximum, rated and minimum head. The rated head of the turbine Hr is 106 m, the maximum head Hmax is 120 m and the minimum head Hmin is 73 m. The whole flow passage of the turbine was discretized by hexahedron structured mesh, and the SST k-ω turbulence model was used in the simulations. Then, the fish friendly threshold for pressure, pressure change rate and shear strain rate were used to analyze the volume size and distribution that may lead to the damage of fish. The ratio of the volume exceeding the fish friendly threshold to the total volume of the runner channel was defined as the fish damage probability. Finally, according to the calculation results, the main and secondary mechanisms of fish damage under different conditions were identified. Meanwhile, the law between the probability of fish injury caused by these mechanisms and the working conditions was further analyzed. From the results it can be seen that the volume which the pressure beyond the threshold in runner is mainly distributed at the outlet of the suction side of the runner blade, and the volume which the pressure change rate beyond the threshold is distributed at the leading and trailing edge of the runner blade. Besides, the volume which the shear strain rate beyond the threshold is distributed near the wall of the crown, band and runner blade. The fish damage probability caused by pressure, shear stress and pressure change rate were defined as P(A), P(B) and P(C) respectively in this paper. Based on the results of this paper, the probability P(A) reaches the maximum value at the condition L1. And the probability P(B) and P(C) reach the maximum value at the rated condition R1. The maximum value of P(A), P(B) and P(C) are 9.1%, 0.823% and 8.31% respectively. By comparing the fish damage probability of pressure, pressure change rate and shear stress under different discharge conditions at the same head, it can be concluded that the minimum pressure and the pressure change rate are the two important factors to prevent fish damage. The shear stress is less important than that of them. Therefore, in the process of designing fish friendly francis turbine runner, the pressure in the runner must be raised as much as possible. Meanwhile, the pressure change rate in runner must also be decreased. [ABSTRACT FROM AUTHOR]

As a form of ocean energy, tidal energy is extremely abundant in oceans, with the characteristics of being clean, reliable, predictable and renewable. In the development of tidal energy, a bi-directional tubular turbine has been widely adopted for power generation. The tubular turbine converts the energy extracted from tides into mechanical energy, and further into useful electricity. The tubular turbine has been well designed suitable for generating power from both flow directions, in order to take full use of the tidal energy not only in the flood tide state but also during the ebb tide state. However, the operation condition of the tubular turbine will be definitely affected by the movement of the wave caused by tide, especially for the reverse power generation direction in which the flow direction is from the ocean to the turbine installed in the hydraulic dam. In this case, under the influence of ocean wave current conditions, the change of hydrodynamic performance during the reverse operation of tidal energy units is an important issue to be considered during the development of tidal energy units. In this paper, the nonlinear second-order Stokes wave law was used to simulate the ocean tide flow, and the second-order Stokes wave formula ocean wave flow condition model has been established based on actual oceanic flow conditions. The chosen tubular turbine had 4 runner blades, with a hub ratio of 0.38 and a runner diameter of 2.5 m. The turbine consisted of an intake part with body, guide vanes, runner and straight draft tube. In addition, a 25 m×7.5 m×18 m size of ocean domain was attached to the turbine. In order to discrete the computational domains, the grid generation tool ICEM CFD was used to generate high quality structure grids. The number of grids chosen for simulations was approximately 6.5 million, after a grid-independent study with the hydraulic efficiency of the turbine being the examined criterion. The RNG k-e turbulence model was chosen to close the time-averaged N-S equations. Transient simulations with considering the effect of the ocean wave on the flow have been realized with the help of ANSYS CFX, with a VOF (volume of fluid) model being adopted in the ocean domain to simulate the free surface of the boundary between the liquid and air. Based on the numerical results, the internal flow characteristics of a tidal energy turbine tune turbine in reverse running under dynamic wave flow boundary conditions were studied. In addition, the influence mechanism of tidal wave on the stability of the tubular turbine operation was discussed in detail. The results showed that: 1) Considering the coupling of wave and flow, most of the kinetic energy was lost after the tidal wave collided with the dam, and the reflected wave flow was therefore formed, which covered the air before the next peak of the wave and produces bubbles entering into the interior of the ocean. 2) The interaction between the incoming tidal wave and the reflected tidal wave on the wall of the dam was the cause of the vortex at the water intake of the tidal tubular turbine. The formed vortex was rotated under the liquid surface and flows into the internal flow field. The upper side of the flow path compressed the flow area to form a low-pressure and low-speed vortex region, which changed the flow distribution of the internal flow field and the characteristics of the tubular turbine. 3) The action of the dynamic wave caused the force on the rotor blades of the tidal tubular turbine to fluctuate greatly, and the low-frequency amplitude of the blade force increases with the development of the air-entraining vortex. At the same time, the fluctuation of unit output under the influence of wave current reached 3.86%, which was much higher than that of less than 1% under no-wave condition, resulting in a decline in power quality. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydropower is one of the most reliable source of green energy and is widely used to meet real-time electricity demand. The ever escalating energy demand and iterative development in hydropower have pushed the generation of hydropower towards a low lost-cost and more flexible state which can work in a wider hydrodynamic region without compromising its performance. So the research on multidisciplinary optimization of hydro turbine needs to be carried out. Francis-type turbine is attractive because the efficiency of the unit at its design point exceeds the other types. As mentioned above, with the needs of robust operation in wide region without compromising its performance, the Francis turbine runner has to be optimized under multidisciplinary constraints. Multidisciplinary optimization technology of Francis runners has always been a key point in the field of turbine research. The coupling strength of each variable is the basis for establishing a concise and efficient multidisciplinary optimization strategy. So in the multidisciplinary optimization of Francis runner, it is necessary to analyze the coupling strength of design variables. In this paper, based on the global relative sensitivity of design variables, a coupling strength analysis method of runner design variables has been presented. First, combing three-dimensional (3D) inverse design theory with curve parametric method, a parametric 3D inverse-design method has been developed to control the Francis runner geometry. According to this parametric 3D inverse-design method, the meridional flow passage and geometry of runner blade can be controlled by a set of discrete parameters. These parameters are treated as runner design variables. The hydraulic efficiency of turbine, the minimal pressure coefficient on runner blade and the maximum static stress of blade are selected as objective functions. Then the global relative sensitivity of each objective function to design variables is calculated by an improved Morris OAT method. Compared with the traditional Morris OAT method, an optimal Latin hypercube design technique is adopted in the improved method. The optimal Latin hypercube design technique has a better space filling property than the traditional one. So the sampling only needs to be done once, which reduces the time of global relative sensitivity analysis without compromising its precision. On the basis of the improved Morris OAT method, the speed of global relative sensitivity calculation is improved obviously. Secondly, the set which contains global relative sensitivity of design variables is treated as universe, and the semi-trapezoidal function in fuzzy mathematics is imported to quantify the membership of each variable to objective functions. After obtaining the membership of each variable, a judgment principle of variable's coupling strength is presented in this paper. According to this judgment principle, the coupling strength property of each design variable can be defined as strong coupling, middle coupling and weak coupling. Finally, based on the coupling strength of each design variable, the multidisciplinary optimization strategy of Francis runner is established. And then the multidisciplinary optimization of Francis runner can be carried out. In order to validate the coupling strength analysis method, an application case is presented in the paper. In that case, the design variables of a Francis turbine runner with the head of 200 m are chosen as the analysis object. From the analysis result, it can be found that only the coupling strength property of maximum thickness is weak coupling, and the others are middle coupling. According to the result, a multidisciplinary optimization strategy is established and used in the optimization of Francis turbine runner. After optimization, both the hydraulic performance and strength property of the optimized runner are improved, demonstrating the effectiveness of the coupling strength analysis method. In conclusion, the method proposed in this paper can be adopted to analyze the coupling strength of design variables of Francis runner. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)