bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

AbstractMotivationNormalization 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.ResultsTo 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 implementationThe 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 informationSupplementary 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

AbstractEnsuring 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

Abstract
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.
Neurons in the Dorso-Central Division of Zebrafish Pallium Respond to Change in Visual Numerosity
Authors: Messina Andrea , Potrich Davide , Schiona Ilaria , Sovrano Valeria Anna , Fraser Scott E , Brennan Caroline H , Vallortigara Giorgio 
Published: June 2021

Abstract
We found a region of the zebrafish pallium that shows selective activation upon change in the numerosity of visual stimuli. Zebrafish were habituated to sets of small dots that changed in individual size, position, and density, while maintaining their numerousness and overall surface. During dishabituation tests, zebrafish faced a change in number (with the same overall surface), in shape (with the same overall surface and number), or in size (with the same shape and number) of the dots, whereas, in a control group, zebrafish faced the same stimuli as during the habituation. Modulation of the expression of the immediate early genes c-fos and egr-1 and in situ hybridization revealed a selective activation of the caudal part of the dorso-central division of the zebrafish pallium upon change in numerosity. These findings support the existence of an evolutionarily conserved mechanism for approximate magnitude and provide an avenue for understanding its underlying molecular correlates.