bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual Strength Prediction of Pipeline with Single Defect Based on SVM Algorithm
Authors: Liu Peisheng , Han Yunping , Tian Yi
Published: June 2021

With the continuous development of society, the increasing number and size of oil-gas pipelines, how to ensure the safe operation of the pipeline has become a major problem. At the same time, under the premise of defects, it is of great significance to predict the residual strength of pipeline for the safety of pipeline operation. At present, scholars at home and abroad have conducted in-depth studies on the evaluation of residual strength of pipelines, but there are mainly two problems in the research, namely, low evaluation accuracy and inconvenient application of evaluation method. Therefore, based on SVM algorithm, a residual strength prediction model for single-defect pipelines is established from four aspects, including model construction, parameter optimization, node number determination of hidden layers and kernel function optimization. The prediction results are highly feasible and advanced compared with various algorithms and standard methods.
Study on Simulation Method of Filtration for Oily Wastewater Treatment in Oilfield
Authors: Wang Y , Cao B H , Gao S , Ren Y L , Zhang R J , Peng Z G
Published: June 2021

Aiming at the filtration system in oily wastewater treatment, based on the simulation accuracy of wastewater treatment, the filtration process in wastewater treatment is numerically simulated, the corresponding mathematical model is established, and a hybrid modeling method combining trajectory tracking and network model method is proposed. Based on the analysis and calculation of the mechanical properties of suspended particles in the filter media, considering the coupling relationship between particles and channels, the dynamic displacement and the changes of channel diameter caused by the filtration process, the determination of channel diameter under different arrangement of filter media, the stress types of suspended particles in the channel, the establishment of mechanical model and the distribution of particles in the channel are studied in detail. Through the distance between the particle centre and the channel, it can be judged whether a particle can be adsorbed. From microcosmic to macroscopical, through the concentration calculated by mathematical model of particles and oil, the change rule and filtration effect of suspended particles and oil in the filtration process are obtained. This paper can increase the researchers’ understanding of the trajectory tracking method, improve the accuracy of the proportion of filter materials in the research process of oily wastewater treatment technology, so as to obtain reliable filtration parameters of the target suspended solids.
Research on Quantitative Analysis Method of Readers’ Demands in University Library
Authors: Xu Chuanjie
Published: June 2021

Readers’ demands analysis is an essential part of university library management. It is the key to improve reader satisfaction in daily service work. In order to adapt to the changes of The Times, improve readers’ satisfaction in an all-round way, and make university libraries provide better services for teaching and scientific research, in addition to vigorously building library books and materials, electronic resources, hardware facilities, library needs analysis is an essential part of university library management work. By using AHP method, this paper puts forward a method to quantify readers’ demands. Focusing on the mapping method, the paper presents the hierarchical model and the judgment matrix of readers’ demands. The values of the judgment matrix elements reflect the reader’s understanding of the relative importance of various factors, and generally adopt 1-9 reciprocal scale method. With the analysis of demands expression and level transformation, the ranking scheme of readers’ demands importance is present. Through this analysis and calculation, the weight index of readers’ different demands can be obtained, which can be used for further quantitative analysis. The proposed method can be used in the decision-making of University Library in the daily management of books and materials, and provides a new idea for improving the quality of library work.
Power Monitoring System of Laser Welding Equipment
Authors: Bo Wen , Yi Jiangang
Published: June 2021

In order to improve the operation stability of laser welding equipment, reduce the failure rate of equipment operation. This paper designs a power monitoring system of laser welding equipment based on computer technology and communication technology. The system is mainly controlled by STM32 series processor. The upper computer of the power monitoring system is designed by C# language and .NET framework. Each module between the system realizes communication through socket and serial communication. Through real-time monitoring and analysis of key data such as welding power of laser equipment in the process of laser welding production process, the system realizes the functions of digital monitoring, data query, data storage, segmented data acquisition, equipment control, equipment running state analysis and so on. On this basis, combined with the network technology, the system realizes the functions of remote data monitoring and remote device log export, so as to improve the extensibility of the equipment and improve the operation economy of the equipment.
Research on Handover Algorithm Based on Dynamic Beamforming in HSR Cutting Scene
Authors: Zhang Zepeng , Dang Jianwu , Li Cuiran , Xie Jianli
Published: June 2021

High-speed train passes through the cutting terrain, signal propagation is significantly affected by the steep sides, resulting in a high probability of handover interruption. To solve this problem, this paper proposes a location-assisted dynamic beamforming handoff algorithm. This solution uses the vehicle-mounted GPS and the arrival angle of the incoming wave to determine the location of the Mobile Relay Node (MRN) and ensure the stability of signal transmission during the operation of the train in the overlapping area. According to the path loss of the High-speed Railway (HSR) cutting scene, calculate the Handover Interruption Probability (HIP), the Handover Trigger Probability (HTP) and the Handover Success Probability (HSP). The simulation results have showed that the proposed algorithm has lower HIP and higher HSP, compared with the traditional handover solution. It ensures the stability of handover in complex scenes, and has better performance in improving the handover efficiency of HSR communication systems.
Multi-objective game theory optimization for balancing economic, social and ecological benefits in the Three Gorges Reservoir operation
Authors: Yu Yang , Zhao Rui , Zhang Jiahe , Yang Douqiang , Zhou Tianyu
Published: June 2021

Reservoir operation is an important and effective measure for realizing optimal allocation of water resources. It can effectively alleviate regional scarcity of water resources, flood disasters and other social problems, and plays an important role in supporting sustainable strategic development of water resources. Coordinating the stakeholders is key to the smooth operation of a multifunctional reservoir. This research examines the competition among stakeholders of a multi-objective ecological reservoir operation aiming to provide for economic, social and ecological demands. A multi-objective game theory model (MOGM) specified 10-day water discharge to meet the triple water demands (power generation, socio-economic consumption and environment) for multi-purpose reservoir operation. The optimal operation of the Three Gorges Reservoir (TGR), with the ecological objective of providing comprehensive ecological flow demanded for some key ecological problems that may occur in the middle and lower reaches of the Yangtze River, was chosen as a case study. Discharged water calculated by the MOGM and a conventional multi-objective evolutionary algorithm/decomposition with a differential evolution operator was then allocated to different demands. The results illustrate the applicability and efficiency of the MOGM in balancing transboundary water conflicts in multi-objective reservoir operation that can provide guidance for the operation of the TGR.
Research on the influence of new energy vehicle enterprise operation decision under the background of sharing economy
Authors: Li Y D , Liu F
Published: June 2021

At present, China’s energy structure is mainly based on fossil fuels, which has brought serious problems such as environmental pollution, low energy efficiency and poor development quality. In the automotive industry, in order to save energy and protect the environment, many countries are actively promoting the production of new energy vehicles, optimizing the use of resources and benefits, and achieving green development. Based on the idea of sharing economy, this paper constructs a two-stage model. Considering the different quality of new energy vehicles in the two stages, optimization theory, game theory and other methods are used to study the influence of sharing behavior on enterprise operation decisions, and the following conclusions are drawn. First, in the presence of product sharing, product quality is negatively correlated with the optimal profit of the enterprise. Second, there is a negative correlation between the charging rate of the third-party platform and the optimal profit of the enterprise, and with the increase of the charging rate of the platform, the decline of the optimal profit of the enterprise is less and less. Third, when product sharing exists, the ratio of product quality in the two stages is positively correlated with the optimal profit of the enterprise.
Equilibrium Analysis on the Main Energy and Ancillary Service Joint Market Considering Load Aggregators
Authors: Ye Qiang , Wang Xi , Ren Zhichao , Wang Haiyan
Published: June 2021

In-depth mining of the adjustment capacity and value of demand-side load resources under the background of marketization is an important support for realizing the safe operation of the power grid and efficient operation of the power market in the future. This paper takes the load aggregator as the object, exploring its market operation ability through the main energy and ancillary service joint market simulation analysis. Firstly, the transaction framework of main energy market and frequency modulation ancillary service joint market considering load aggregators is built, then the market participation mode and the cost of each entity are analyzed. Secondly, based on the game equilibrium theory of oligopoly competition, a load aggregators included multi-period equilibrium model of energy and frequency modulation ancillary service joint market is established. Finally, the nonlinear complementarity method is applied to solve the model, and the rationality and effectiveness of the proposed model are verified through typical case analysis. The results show that with the participation of load aggregators, the effect of “peak shaving and valley filling” on both load and active power price is obvious, up and down frequency regulation capacity prices of the system have decreased, and the downward adjustment is more prominent, the purchase cost is reduced, and the user profit and social welfare can increase. It provides reference for future market planning as well as EVA operation.
Analysis of Reverse Recovery Characteristics of Anti-parallel Diode
Authors: Wang Bo
Published: June 2021

Insulated gate bipolar transistor (IGBT) is widely used in various renewable green energy systems such as wind power generation and solar power generation at present. High-power IGBT modules usually include IGBT chips and anti-parallel diodes, and the transient characteristics of anti-parallel diodes will affect the external port characteristics of IGBT modules. Based on semiconductor physics and diode basic structure, this paper analyzes four stages of diode reverse recovery process, and describes the change process of turn-off time and stored charge by a step recovery process. Finally, the voltage and current waveforms of diode reverse recovery process are simulated and verified for a certain IGBT module.
How to use the atmospheric environmental self-cleaning capability effectively in China
Authors: Li Yating , Zhou Jingkun
Published: June 2021

Based on the analysis of the effectiveness and disadvantages of artificial intervention in the treatment of air pollution, this paper briefly describes the importance of the application of atmospheric environmental self-cleaning capability for the comprehensive prevention and control of environmental pollution. According to the concept and connotation of atmospheric environmental self-cleaning capability, and referring to the main methods of foreign atmospheric environmental self-cleaning capability, this paper puts forward some suggestions on how to effectively use atmospheric environmental self-cleaning capability in China, such as strengthening the research of atmospheric environmental self-cleaning capability in China, making full use of the dilution and purification effect of wind, using the purification effect of dry and wet deposition effectively, playing the purification effect of human-oriented design reasonably, speeding up the adjustment of industrial and energy structure in combination with the characteristics of regional self-cleaning ability level, and establishing a comprehensive and key self-purification ability system index. It hopes to provide a reference for China to achieve the goal of air pollution control.
Study on Spatial Distribution and Sustainable Development of Night Tourism Resources:Take the Central Guilin as an Example
Authors: Hu Hongmeng , Hou Yuxia
Published: June 2021

The concept of sustainable development organically unifies the long-term interests and short-term interests, overall interests and local interests, economic interests and social interests of a country or region, and finally achieves common, coordinated, fair, efficient and multi-dimensional development. Based on the theory of tourism sustainable development, the paper discusses the characteristics of tourism resources composition and spatial distribution in the central Guilin from the aspects of scale, per capita share and nearest neighbor index. It is found that there are various types of night tourism resources in the central Guilin, but the supply of resources is insufficient, and the spatial distribution type is condensed, which is characterized by “central agglomeration and zero stars around”. The imbalance in regional layout exacerbates the contradiction between the supply and demand of night tourism resources. The relevant departments should take the integration, uniqueness and economy as the planning principles, and promote the sustainable development of the night tourism market in the central Guilin by issuing the night tourism planning policy, optimizing the spatial layout, deepening the night tourism planning and development, and widening the marketing channels.
Review on application and research of trans-critical CO2 refrigeration system in food freezing and cold storage
Authors: Zhu Jie , Yang Dazhang , Xie Jing , Wang Jinfeng
Published: June 2021

As people pay more and more attention to environmental problems, the GWP and ODP of traditional halogenated hydrocarbon refrigerants are generally higher, and the natural refrigerants with low GWP are more mentioned. As a natural refrigerant, CO2 is excellent in safety and environmental protection. CO2 as a refrigerant also plays a role in various industries, especially in the food industry. In the actual use of CO2 trans-critical refrigeration system in food refrigeration, it is found that there are some defects in CO2 system. Therefore, in order to solve the problem of low efficiency in trans-critical CO2 cycle, this paper analyses the research of some technologies in trans-critical CO2 refrigeration system that can improve system performance, COP and refrigeration capacity, and summarizes the problems in recent years progress in energy efficiency. In this paper, the working principle, technical characteristics and the improvement of system performance of various improved technologies are discussed in detail, and the previous research is summarized.
Influencing Factors and Countermeasures to Promote the Large-scale Development of Rural Solar Houses in China
Authors: Li Xuesong , Dong Yaowu , Li Chenchen , Wang Zijie
Published: June 2021

The development and utilization of renewable energy, especially solar energy, is an important way to solve the problem that China’s rural conventional power grids cannot cover remote rural areas. It is also an inevitable requirement of China’s rural development strategy. This article explores the influencing factors of Chinese farmers’ vigorous promotion of the use of solar houses, studies relationships among perceived value, farmer’s attitude and willingness to convert traditional houses into solar houses. Using data collected by a questionnaire from 413 rural households in Chongqing, China, the results show that perceived value has a significant and positive effect on farmer’s attitude and willingness to convert traditional houses into solar houses. Most importantly, the results of this research show that farmers’ attitude partially mediates the effects of perceived value on willingness to convert. Finally, the study also proposes relevant suggestions for policy makers, marketing managers and further research.
On the Physical Mechanisms that Cause the Full Load Instability in Francis Turbines
Authors: Wack J , Riedelbauch S
Published: June 2021

Today, hydropower receives increased attention for the safe integration of volatile renewable energies as it is able to stabilize the electrical grid. For that reason, turbines are more often operated at off-design conditions with the drawback that undesirable flow phenomena like the full load instability can occur. To assess their hazard potential, it is of great importance to understand those phenomena. Even though the physical mechanisms behind the full load instability have been analyzed in the past, they are not yet fully understood. The goal of this study is to close this gap and to develop a complete understanding of the full load instability. Two-phase simulations of a Francis turbine at model scale are performed for a full load operating point that becomes unstable when the cavitation number falls below a certain threshold. The unsteady simulations are performed using the Zwart cavitation model and the SST turbulence model with applied curvature correction. For simulations at different cavitation numbers it is investigated how characteristic quantities like swirl number or cavitation volume differ between stable and unstable conditions. This allows getting a deeper insight into characteristic changes of the flow for the transition from stable to unstable conditions. It can be identified that the interaction between cavitation on the runner blades and the cavitating draft tube vortex plays a key role in the development process of the full load instability. All in all, a complete explanation for the development of the full load instability can be given. The new findings of this study allow proposing an adapted 1D model, which considers the occurrence of blade cavitation.
CAVITATION EROSION MECHANISM: NUMERICAL STUDY OF THE INTERACTION BETWEEN PRESSURE WAVES AND VAPOR BUBBLES
Authors: Leclercq C. , Fortes-Patella R. , Archer A.
Published: June 2021

Investigations on vapor bubble collapses dynamic were carried out by three-dimension simulations with the software Prototype Homogène Code_Saturne. The code solves, by applying a compressible homogeneous approach, the Euler’s equations coupled with transport equations (for the volume, mass and energy fractions) that model the phase changes and the thermodynamic effects. To close the system, the Stiffened Gas EOS (equation of state) was applied to link the pressure and the temperature to the internal energy and the density.

Different mesh types and computational domains were tested to study four configurations in water: a) the vapor bubble collapse in free-field case; b) the vapor bubble collapse near a solid wall; c) the collapse of a vapor bubble in free-field case and impacted by an external pressure wave; d) the collapse of a vapor bubble placed near a solid wall and impacted by an external pressure wave.

Pressure waves generated during these bubble implosions were studied and characteristic parameters (such as wave passage time and amplitude of the pressure peak applied at the solid wall) were calculated under different hydrodynamic conditions.

Simulations led to some expected phenomena such as: the bubble asymmetrical shape evolution when a rigid wall is present; observation of toroidal vapor cavities; generation of high amplitude pressure waves during bubble collapses and rebounds.

Original results obtained concern mainly the study of the interaction between external pressure waves and collapsing vapor bubbles. Analyses on the influence of the incoming external pressure wave amplitude on the bubble collapse time and on the pressure peak reached on the wall are also presented in the paper. The numerical study showed an amplification of the collapse pressure by the incoming pressure wave. This interaction mechanism between pressure waves and vapor structures leading to pressure amplitude amplification could be responsible for the material damages due to cavitation.
Experimental and Numerical Investigations of Erosion on Runner Seal of a Francis Turbine
Authors: Yonezawa K , Watamura T
Published: June 2021

To suppress sediment erosion in labyrinth seals is an important problem for hydro turbine design and operation. A numerical simulation was carried out to know the flow with solid particles and its influence on the erosion in the labyrinth seal. The result showed that the vortex took place in the intermediate space between the first and the second seal gaps and the solid particles impinged on the runner wall along the vortex. Experiments were also carried out to understand the characteristics of the flow with vortices in the labyrinth seal by changing the flow rate of the leakage through the seal. It was found that the vortex took place stably in the intermediate space regardless the flow rate of the leakage although the Taylor vortex pattern was significantly disturbed as the leakage flow rate increased.
Novel techniques for the analysis of dynamic pressure in penstocks
Authors: Chevillotte Fabien , Pavić Goran , Dubois Guillaume , Proulx Gilles , Gagnon Martin
Published: June 2021

This paper focuses on the analysis of dynamic pressure fluctuations in hydro-electric power plants. Pressure fluctuations are usually measured with remote sensors and the dynamic behaviour of the remote tubing line modifies the readings of dynamic pressure and thus introduces a bias. A method to characterize the remote tubing line and to correct the actual pressure is proposed. The corrected measurements are compared with those obtained using intrusive flush-mounted sensors as well as non-intrusive sensors (PVDF wires and strain gauges). Then, the technique to separate the forward and backward components of the obtained pressure pulsations is outlined. It is further shown how the pulsations and the hoop stresses can be reconstructed along the penstock. Finally, measurements carried out in a hydropower plant are presented to demonstrate the proposed techniques applicability for the analysis of dynamic pressure in a penstock. The results show that a pressure profile can be mapped along the penstock length which allows a comparison with the direct pressure sensor measurements.
Experimental investigation of sediment erosion in a double-suction centrifugal pump in sandy rivers
Authors: Qian Zhongdong , Su Jiahui , Guo Zhiwei , Yang Bing , Dong Jing
Published: June 2021

The characteristic of sediment erosion of the blade in a double-suction centrifugal pump is mainly studied because the blades of double-suction centrifugal pumps are widely observed to suffer severe erosion damage in water intake projects along the Yellow River. In order to clearly present the evolution of blade-erosion area for different sediment properties in real conditions, the experiment with multiple layers of paint method is designed. The obtained results show that the leading edge of the blade, suction side of the blade inlet, suction side of the blade outlet and pressure side of the blade outlet are easy to be observed with erosion. More important, relationships between the eroded area and operation time by using hyperbolic tangent function are firstly established, and this function can be used to predict the development of the eroded area of blades in long operation. The first section in your paper
Effect of the winglet on reduction of blade tip vortex from elliptical hydrofoil
Authors: Maeda S , Sano T , Iino M , Farhat M , Amini A
Published: June 2021

It is well known that the performance of the turbomachinery (losses, vibrations, noise, and erosion) is often affected by the trailing vortex from the blade tip (Tip Leakage Vortex; TLV) of the impeller or propeller, and sometimes cavitation occurs in the center of the vortex core (Tip Vortex Cavitation; TVC). Many researches on the vortex characteristics of isolated hydrofoil by numerical simulations or experiments have been done so far, however, the research on understanding the mechanism of the vortex control technique is not enough, and it is important to mitigate the effect of TLV or TVC, to enhance the performance of turbomachinery. In this study, numerical simulation and experimental investigation were carried out to clarify the effect of winglet, attached to the elliptical hydrofoil (NACA16020). Five different winglet patterns were tested, changing bending angle and direction. Experiments were carried out using the high-speed cavitation tunnel in Ecole Polytechnique Fédérale de Lausanne (EPFL). As for numerical simulation, it was carried out in the same condition of the experiment. As a result, it was clarified that TVC decreased as increasing the bending angle of winglet, and disappeared in the case of 90 degree bent toward pressure side. And it is clarified that the vortex strength, in other word, vortex core pressure is affected by the interaction of the leading edge vortex and the tip vortex, and in case of pressure side 90 degree bended winglet, both vortices were mutually affected and cancelled the strength of these vortices.
Developing a 1D-3D model to investigate the effect of entrapped air on pressure surge during the rapid filling of a pipe
Authors: Maddahian R , Shaygan F , Bucur D M
Published: June 2021

An uncontrolled rapid filling or discharging of a pipeline can create compressed air columns in an urban water supply or sewage system. The expulsion of entrapped air out of pipelines is considered as one of the most destructive phenomena. Generally, the air valves are mounted and used to release the air from the pipe. Any failure of the air venting system may lead to a pressure surge inside the pipeline and even damage to the water systems infrastructure. Most of the investigations of multiphase flow during a rapid filling are limited to small distribution systems due to high computational costs. The aim of the present research is to develop a 1D-3D coupled model with the capability to handle multiphase flows. The effects of air pocket length, orifice size and upstream pressure on the flow field and maximum pressure surge inside the pipe are investigated. The classical water hammer equations are solved for the 1D domain using the Godunov scheme while the rest of the system is simulated using the Volume of Fluid (VOF) method. The coupling between 1D and 3D domains are handled using the developed boundary conditions based on flow characteristics. The results of the numerical simulations are compared with available experimental data. The obtained results show that the model can predict the features of the two-phase flow inside the pipeline during a rapid filling. The required computational time decreases by a factor of 4 compared to 3D simulations. This gives the possibility to investigate large scale water distribution or drainage systems.
Numerical Prediction of Runaway Characteristics of Kaplan Turbines Applying Cavitation Model
Authors: Semenova A.V. , Chirkov D.V. , Ustimenko A.S.
Published: June 2021

In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. This value depends on the turbine type, the operating condition, the turbine flow passage and the runner geometry, and for Kaplan turbines might 2.5 times surpass the nominal rotational speed of the runner. The runaway speed is important for evaluation of mechanical resistance of the generator rotor. The value of runaway speed is determined based on the results of the model tests upon completion of the design works related to the runner. Therefore, accurate computation of the runaway speed will improve the design process for the runner and the whole turbine unit. Given in this paper is the numerical computation of the runaway speed for a Kaplan turbine of 40 m head. Calculations were carried out for a series of steady-state operating conditions with different runner speeds and the speed at which the torque on the runner shaft is equal to zero was determined. Two approaches for numerical simulation were compared. In the first one, the flow in the turbine was simulated using 3-D RANS equations of incompressible fluid using k-ε model of the turbulence. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. Steady-state computations were carried out in computational domain that included one guide vane channel, one runner channel, the whole draft tube, and the clearances between the runner blade and the hub as well as between the blade and the runner chamber. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.
Strain prediction in Francis runners by means of stationary sensors
Authors: Presas Alexandre , Valentin David , Zhao Weiqiang , Valero Carme , Egusquiza Monica , Egusquiza Eduard
Published: June 2021

The assessment of the remaining useful life due to fatigue in Francis turbine runners implies complex measurements with strain gauges that have to be installed in a submerged and rotating structure, which is excited with high pressure pulsations and strong turbulent flows. Furthermore, the conditioning, storage and transmission of these signals to the stationary frame involves complicated technical solutions. In order to avoid such complex and expensive measurements, in this paper we explore the feasibility of obtaining the strain on the runner with stationary sensors, which can be easily installed and used for a continuous monitoring of the machine. Based on the experimental strain tests performed in a Francis turbine unit, strain on the runner blade is correlated with relevant indicators obtained with stationary sensors. The correlation within indicators is obtained considering linear regression models and improved with artificial intelligence techniques.
Analysis of Transient Force Performances of Pump-Turbine during Stop Process in Pump Mode
Authors: Rao Yao , Huili Bi , Jun Wang , Tao Liu , Funan Chen , Honggang Fan , Zhengwei Wang , Jingshi Liu
Published: June 2021

The stop process occurs frequently for pump turbine due to the requirement of switching from pump mode to turbine mode. During stop process, the operating parameters such as the axial thrust, radial thrust and torque of the runner change rapidly, causing vibration of runner. In some cases, the rotating part can be lifted. In this paper, the unbalanced force acting on a pump-turbine during stop process in pump mode was studied using numerical simulation method. The CFD analysis was based on Reynolds averaged equation and the SST model was used to predict the transient flow characteristics. The clearance flow was also taken into consideration. Results show that the axial thrust was in opposite direction of gravity and changed with the variation of the head and torque. The axial thrust reached the maximum value in no-load condition.
Turbine Test Rig to Investigate Flow Instabilities in Draft Tube
Authors: Kumar S , Khullar S , Cervantes M J , Gandhi B K
Published: June 2021

Time-dependent phenomena in a reaction turbine such as rotor-stator interactions (RSI) and rotating vortex rope (RVR) contribute to pressure fluctuations, vibrations, and even failure of the machine. A small scale test rig is being developed to investigate RSI and RVR and to study RVR mitigation methods. The test rig is designed for a maximum available head and discharge of 8 meters and 0.05 m3/s, respectively. Provisions are made to operate the test rig in open and closed loops. The test rig is flexible to operate for the turbines of high specific speed (high head Kaplan turbine or very low head Francis) to low specific speed (high head Francis). The runner of the test rig is 200 mm in diameter at draft tube inlet. The turbine is connected with a variable speed generator to run up to 1000 rpm. This paper presents the design and arrangements of the test rig components according to the head and discharge conditions. Scale down design calculations for a model are performed using IEC 60193.
Model test with sensor equipped Francis runner for Part Load Operation
Authors: von Locquenghien Florian , Faigle Peter , Aschenbrenner Thomas
Published: June 2021

With the need for flexible operation Francis runners are exposed to various operating conditions outside the traditional operating range. These machines have to be designed for long time Part Load Operation to meet hydraulic and structural requirements. Deep Part Load Operation mainly consists of stochastic loads on the blades. Calculation methods for the dynamic stress at Full Load Operation are well established, whereas the calculation of the dynamics during low load operation are in the focus of the current research to increase the predication accuracy. Through a model test of a Francis runner with multiple sensors in the rotating frame, knowledge is gained about low load operating conditions. The sensors consist of both pressure transducers and strain gauges. On the basis of the results for multiple operating conditions a comparison between pressure sensors and strain gauges is made and connected to flow phenomena. Prototype strain gauge data is utilized to prove the feasibility of the data gained in model size.
Transient Analysis of Pelton Turbine Prototypes
Authors: Egusquiza M , Valentín D , Valero C , Presas A , Egusquiza E
Published: June 2021

One of the most critical operating conditions in hydraulic turbines is the start-up transient. This may be characterized by the presence of several resonances, which increase the vibration and stress levels on the runners. At present, its study is of interest due to the more frequent starts and stops of the turbines in the last years. The present study is focused on analysing the start-up transient of Pelton turbines. To do so, an experimental investigation was carried out in a horizontal shaft prototype unit. The procedure started by determining the natural frequencies and mode shapes of the turbine by means of impact testing. Several accelerometers were placed on the runner, on the shaft and on the bearings. With experimental modal analysis the main vibration modes of the rotor and the runner were found. Once the structural response of the turbine was determined, the start-up transient was studied. For the tests, different types of sensors were installed on the machine. Accelerometers, proximity probes and acoustic emission sensors were placed on the bearings and on the turbine casing. Moreover, an accelerometer and a strain gauge were installed on the shaft with an on-board system. Different situations are identified during the start-up. At the very beginning of the transient, the initial collision of the water jet on the still runner produces large vibration levels due to the excitation of many bucket modes. Once the turbine starts rotating, the vibration levels increase every time the jet excitation at the bucket passing frequency meets a natural frequency of the structure. The effect of the transient regarding the change in the vibration levels and runner deformations is presented in this paper. The sensitivity of the different sensors to measure the runner vibrations is analysed in order to optimize the detection of the transient effects. The best locations to install the sensors are also identified.
Special Pressure Fluctuation analyse of the pump turbine
Authors: Liu D M , Geng B , He H P , Zheng J S , Liu W C , Liang Q W , Zhao Y Z
Published: June 2021

In the 13th five-year planning, the pumped storage power stations have speeding up. A large number of pumped storage power stations will been installed. The current development of modern pump storage plants aims towards a higher flexibility and stability in operation, an extended operation range of the hydraulic machine. The stability of pump turbine has been paid more and more attention in the industry.

Hydraulic pressure pulsation is very important for the stability of pump turbine. For pump turbine, the pressure pulsation on vane-less area between guide vane and runner blade is very important. It is the fundamental source of unit stability and the direct embodiment of rotational and static interference.

This paper analyses the special pressure pulsation in the vane-less area of pump turbine, focusing on the pressure pulsation of one time rotating frequency and two times rotating frequency.

The amplitude and frequency of pressure pulsation and the source of pressure pulsation induced by this special frequency are analysed and detected from the perspective of numerical and model test. By optimizing the design of the runner, the pressure pulsation of that particular frequency is eliminated.
Nonlinear simulation of speed variation of variable-speed unit under large disturbance by Simulink
Authors: Huang Yifan , Yang Weijia , Zhao Zhigao , Yang Jiandong , Li Yulan , Ma Weichao , Yang Jiebin
Published: June 2021

The variable-speed pumped storage plant (VSPSP) has become an innovative technology and new orientation in recent years. Investigation of dynamic processes in operating and control of VSPSP is of great importance for safety, stability and efficiency. In this paper, a nonlinear integrated model for dynamic processes of VSPSP with doubly fed induction machines (DFIMs) is built based on Simulink. From the comparison between simulation results and on-site measurement data of a fixed-speed pumped storage plant (FSPSP), the model under load rejection is validated. Meanwhile, maximum rotational speed during transient processes is a key indicator for the safety of pumped storage units. Hence, the transient process and performance of VSPSP under load rejection are simulated and analyzed by using the model, and the speed variation of the variable-speed unit is specifically investigated. The speed rising value and relative speed rising value will decrease when the initial value increases because of the momentum conversion mechanism and the torque characteristic of pump-turbine. The result demonstrates that, if the initial speed increases in the operating range of variable-speed unit under load rejection, the maximum speed will not rise significantly, and there is a certain safety margin from the maximum allowable speed.
A coordination controller in variable speed pumped storage plant
Authors: Zhao Zhigao , Ma Weichao , Yang Jiandong , Yang Weijia , Huang Yifan , Wang Xuewu , Peng Yumin
Published: June 2021

With the integration of increased variable renewable energy generation, much attention has been devoted on the development of pumped storage. The variable speed pumped storage technology has become a research focus due to its wide operating range, high production efficiency and strong power regulation ability. Moreover, the coordination controller is the key component of variable speed pumped storage plant (VSPSP), it can coordinate the joint operation of governor and converter. The coordinated controller is studied in this work. Aiming at the coordinated control between governor and converter, the novel adaptive strategy of maximum efficiency point tracking is proposed. First, the optimal efficiency curves are described based on model experiment; and then the optimal operating curves of variable speed unit in the operation region is presented based on the BP neural networks; the convergence analysis of mean square error and regression analysis are applied to verify the reliability of results. Aiming at the application of adaptive strategy in the coordination controller, and ensuring the real-time performance, a new effective digital interpolation method is put forward, using programmable logic controller. The signal flows of the control system in variable speed unit are clarified. The proposed adaptive strategy could be easily applied in engineering, providing a technical means for the efficient and flexible operation of VSPSP.
Normalization by distributional resampling of high throughput single-cell RNA-sequencing data
Authors: Brown Jared , Ni Zijian , Mohanty Chitrasen , Bacher Rhonda , Kendziorski Christina
Published: June 2021

Motivation

Normalization to remove technical or experimental artifacts is critical in the analysis of single-cell RNA-sequencing experiments, even those for which unique molecular identifiers are available. The majority of methods for normalizing single-cell RNA-sequencing data adjust average expression for library size (LS), allowing the variance and other properties of the gene-specific expression distribution to be non-constant in LS. This often results in reduced power and increased false discoveries in downstream analyses, a problem which is exacerbated by the high proportion of zeros present in most datasets.

Results

To address this, we present Dino, a normalization method based on a flexible negative-binomial mixture model of gene expression. As demonstrated in both simulated and case study datasets, by normalizing the entire gene expression distribution, Dino is robust to shallow sequencing, sample heterogeneity and varying zero proportions, leading to improved performance in downstream analyses in a number of settings.

Availability and implementation

The R package, Dino, is available on GitHub at https://github.com/JBrownBiostat/Dino. The Dino package is further archived and freely available on Zenodo at https://doi.org/10.5281/zenodo.4897558.

Supplementary information

Supplementary data are available at Bioinformatics online.
Listening to Advice from Young People in Foster Care—From Participation to Belonging
Authors: Fylkesnes Marte , Larsen Marit , Havnen Karen , Christiansen Øivin , Lehmann Stine
Published: June 2021

Ensuring that young people in foster care receive the support they need at the right time, is a pressing issue across health- and social services. In this study, we aim to broaden the knowledge base on what constitutes appropriate help and support from the perspective of young people in long-term foster care in Norway. As part of a larger survey, young people in foster care (N = 178) aged eleven to eighteen years provided written accounts on the open-ended question: ‘What advice would you give adults who help young people living in foster care?’. We conducted a systematic content analysis to identify themes and categories across the data. Four main themes were identified: enable participation; build trusting relationships; ensure appropriate follow-up; and cultivate belonging. Participation served as a pivoting point across the themes, as a prerequisite for young people in care to receive the services they need and develop a positive self-relationship. Our findings indicate that services must be tailored to recognise how the strengths and needs of young people in foster care change over time and differ across individuals. Developing practice tools that enhance young people’s participation is therefore paramount, as social workers, foster parents and other adults are crucial to processes of well-being and belonging.
Pathological laughter and crying: insights from lesion network-symptom-mapping
Authors: Klingbeil Julian , Wawrzyniak Max , Stockert Anika , Brandt Max-Lennart , Schneider Hans-Ralf , Metelmann Moritz , Saur Dorothee
Published: June 2021

The study of pathological laughter and crying (PLC) allows insights into the neural basis of laughter and crying, two hallmarks of human nature. PLC is defined by brief, intense and frequent episodes of uncontrollable laughter or crying provoked by trivial stimuli. It occurs secondary to CNS disorders such as stroke, tumours or neurodegenerative diseases. Based on case studies reporting various lesions locations, PLC has been conceptualized as dysfunction in a cortico-limbic-subcortico-thalamo-ponto-cerebellar network.

To test whether the heterogeneous lesion locations are indeed linked in a common network, we applied ‘lesion network-symptom-mapping’ to 70 focal lesions identified in a systematic literature search for case reports of PLC. In lesion network-symptom-mapping normative connectome data (resting state functional MRI, n = 100) is used to identify the brain regions that are likely affected by diaschisis based on the lesion locations. With lesion network-symptom-mapping we were able to identify a common network specific for PLC when compared with a control cohort (n = 270). This bilateral network is characterized by positive connectivity to the cingulate and temporomesial cortices, striatum, hypothalamus, mesencephalon and pons, and negative connectivity to the primary motor and sensory cortices. In the most influential pathophysiological model of PLC, a centre for the control and coordination of facial expressions, respiration and vocalization in the periaqueductal grey is assumed, which is controlled via two pathways: an emotional system that exerts excitatory control of the periaqueductal grey descending from the temporal and frontal lobes, basal ganglia and hypothalamus; and a volitional system descending from the lateral premotor cortices that can suppress laughter or crying.

To test whether the positive and negative PLC subnetworks identified in our analyses can indeed be related to an emotional system and a volitional system, we identified lesions causing emotional (n = 15) or volitional facial paresis (n = 46) in a second literature search. Patients with emotional facial paresis show preserved volitional movements but cannot trigger emotional movements in the affected hemiface, while the reverse is true for volitional facial paresis. Importantly, these lesions map differentially onto the PLC subnetworks: the ‘positive PLC subnetwork’ is part of the emotional system and the ‘negative PLC subnetwork’ overlaps with the volitional system for the control of facial movements.

Based on this network analysis we propose a two-hit model of PLC: a combination of direct lesion and indirect diaschisis effects cause PLC through the loss of inhibitory cortical control of a dysfunctional emotional system.