bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Models of Fungi Interaction--based on Logistic models
Authors: Zhang Yunfei
Published: June 2021

As the key medium for decomposing wood fibers, fungi play a vital role in promoting the carbon cycle. The purpose of this paper is to establish mathematic models describing the process of fungi decomposing litter and wood fiber. The paper comprehensively consider the effects of temperature, moisture, location and other factors on fungal traits, and introduced the experimental data of the US Forest Service Center for Forest Mycology Research (CFMR).Based on the model of competition among populations and the modern coexistence theory, this paper establishes the competitive model between two fungi, then generalizes it to a variety of fungi and predicts the short-term and long-term effects.
Control of traveling localized spots
Authors: Martens S. , Ryll C. , Löber J. , Tröltzsch F. , Engel H.
Published: June 2021

Traveling localized spots represent an important class of self-organized two-dimensional patterns in reaction–diffusion systems. We study open-loop control intended to guide a stable spot along a desired trajectory with desired velocity. Simultaneously, the spot’s concentration profile does not change under control. For a given protocol of motion, we first express the control signal analytically in terms of the Goldstone modes and the propagation velocity of the uncontrolled spot. Thus, detailed information about the underlying nonlinear reaction kinetics is unnecessary. Then, we confirm the optimality of this solution by demonstrating numerically its equivalence to the solution of a regularized, optimal control problem. To solve the latter, the analytical expressions for the control are excellent initial guesses speeding-up substantially the otherwise time-consuming calculations.
Construction de l’identité professionnelle des étudiants en maïeutique : une étude exploratoire qualitative
Authors: David Laëtitia , Franck Eleonore , Paris Stephanie , Delacour Chloé
Published: June 2021

Contexte : Pour assurer la professionnalisation des étudiants, le périmètre de la formation initiale doit déterminer de manière explicite les compétences professionnelles à développer, la culture professionnelle à privilégier et l’identité professionnelle (IP) à soutenir. Définie comme une représentation subjective de soi en tant que professionnel, cette dernière permet une meilleure compréhension des rôles et développe le bien-être tant professionnel que personnel. Or, l’IP demeure mal définie au sein du référentiel de la formation initiale en maïeutique. But : Explorer et analyser la construction de l’IP lors de la formation initiale en maïeutique, afin d’en améliorer l’accompagnement lors de la formation. Méthodes : Étude qualitative à l’aide d’entretiens individuels semi-dirigés d’étudiants en deuxième année de formation en sciences maïeutiques. Résultats : Neuf entretiens ont été réalisés. L’IP des étudiants en maïeutique (EM) se construit dans le rapport à soi, à la profession, à la formation et aux autres, selon des processus de socialisation biographique et relationnelle. La construction de l’IP est ponctuée de périodes de « dissonance identitaire » permettant de concilier aspirations personnelles et projections professionnelles. Le développement des compétences professionnelles permet à l’EM de participer aux rôles et d’incorporer son IP en émergence. La construction est perturbée par l’incompréhension des attendus de la formation par les différents acteurs. Conclusion : Des perspectives s’envisagent pour soutenir les EM dans leur construction identitaire : reconnaître les périodes de rupture, engager précocement les étudiants dans la réflexivité et impliquer tous les acteurs de la formation pour une conception partagée.
Necrosis or Flap Loss After Deep Inferior Epigastric Perforator Reconstruction: Impact of Perforators and Recipient Vessels
Authors: Palve Johanna S. , Luukkaala Tiina H. , Kääriäinen Minna T.
Published: June 2021

Background The aim of this study is to analyze the impact of the number and location of perforators harvested and the recipient vessels used on deep inferior epigastric perforator (DIEP) flap survival and the occurrence of flap necrosis requiring re-operation.

Patients and Methods Four hundred and seventy-one DIEP flap reconstructions, performed between January 2008 and December 2019, were retrospectively analyzed.

Results Flap necrosis requiring re-operation was observed in 40 (9%) of flaps and total flap loss rate was 1% (n = 6). No significant differences were observed between internal mammary vessels (IMV, n = 287, 61%) and thoracodorsal vessels (TDV, n = 184, 39%) regarding postoperative re-anastomosis (p = 0.529) or flap survival (p = 0.646). Intraoperative conversion from IMV to TDV was performed on 64 (14%) patients. TDV were more commonly associated with problems in preparation of the vessels than IMV (p < 0.001). Second vein anastomosis was performed on 18 (4%) patients. In total, 81 flaps (17%) had one perforator, 165 (35%) had two, 218 (46%) had three to five, and 7 (2%) had more than five perforators. Flaps with three to five perforators were more commonly associated with flap necrosis (p < 0.001) than flaps with one or two perforators. Independent factors associated with necrosis were body mass index (BMI) > 30 (odds ratio [OR]: 2.28; 95% confidence interval: 1.06–4.91, p = 0.035) and perforator/s located on the lateral row (OR: 3.08, 95% CI 1.29–7.33, p = 0.011).

Conclusion We conclude that the occurrence of flap necrosis requiring re-operation may be higher in DIEP flaps with more than two perforators or perforator/s located on the lateral row and in obese patients. Neither the recipient vessels used nor the number of perforators harvested had any impact on the flap survival rate.
Are the First and Second Hip in Staged Bilateral Total Hip Arthroplasty Equal? A Hospital Adverse Event and Perioperative Risk Comparison
Authors: Villa Jesus M. , Pannu Tejbir S. , Higuera Carlos A. , Suarez Juan C. , Patel Preetesh D. , Barsoum Wael K.
Published: June 2021

Hospital adverse events remain a significant issue; even “minor events” may lead to increased costs. However, to the best of our knowledge, no previous investigation has compared perioperative events between the first and second hip in staged bilateral total hip arthroplasty (THA). In the current study, we perform such a comparison. A retrospective chart review was performed on a consecutive series of 172 patients (344 hips) who underwent staged bilateral THAs performed by two surgeons at a single institution (2010–2016). Based on chronological order of the staged arthroplasties, two groups were set apart: first-staged THA and second-staged THA. Baseline-demographics, length of stay (LOS), discharge disposition, hospital adverse events, and hospital transfusions were compared between groups. Statistical analyses were performed using independent t-tests, Fisher's exact test, and/or Pearson's chi-squared test. The mean time between staged surgeries was 465 days. There were no significant differences in baseline demographics between first-staged THA and second-staged THA groups (patients were their own controls). The mean LOS was significantly longer in the first-staged THA group than in the second (2.2 vs. 1.8 days; p < 0.001). Discharge (proportion) to a facility other than home was noticeably higher in the first-staged THA group, although not statistically significant (11.0 vs. 7.6%; p = 0.354). The rate of hospital adverse events in the first-staged THA group was almost twice that of the second (37.2 vs. 20.3%; p = 0.001). There were no significant differences in transfusion rates. However, these were consistently better in the second-staged THA group. When compared with the first THA, our findings suggest overall shorter LOS and fewer hospital adverse events following the second.

Level of Evidence Level III.
Testing the effects of Facebook usage in an ethnically polarized setting
Authors: Asimovic Nejla , Nagler Jonathan , Bonneau Richard , Tucker Joshua A.
Published: June 2021

Significance

Amid growing belief that social media exacerbates polarization, little is known about the causal effects of social media on ethnic outgroup attitudes. Through an experiment in Bosnia and Herzegovina where users refrained from Facebook usage during 1 wk of heightened identity salience, we find that—counter expectations—people who deactivated their accounts reported lower outgroup regard than the group that remained active, but this effect was likely conditional on the level of ethnic heterogeneity of respondents’ residence. Additionally, we replicate findings from a study on US users: Deactivation led to a decrease in news knowledge and suggestive improvements in subjective wellbeing. Our findings bring nuance to popular beliefs, frequently dichotomous and simplistic, of social media’s impact on societal dynamics.
Nonlinear Finite Element Analysis of RC Beam Exposed To Fire With and Without CFRP Strengthening
Authors: Obied Wissam , Stematiu Dan
Published: June 2021

The Nonlinear finite element (FE) model can accurately predict the behaviour of reinforced concrete (RC) with the RC beam’s safety with and without CFRP that is designed for resistance against high temperatures. Transient thermal finite element analysis is performed using the ANSYS software. The beam was subjected to a short-duration, high-intensity (SDHI) fire at the bottom and side surfaces, in the form of transient temperatures versus time, whereas maintaining constant transversal loading on the highest body. The validation of the finite element model without CFRP is confirmed by comparing the results with experimental testing results that are carried out at similar model conditions within the same geometry, reinforced, and boundary conditions. After that, added the carbon fiber reinforced polymer sheet (CFRP) at the bottom and side surfaces of the RC beam during fire exposure as a parametric study to investigate the effect of CFRP on the strength and stiffness of the RC beam at high temperatures. The results showed that CFRP strengthening would have a significant impact on RC beam stiffness.
The Status Quo of Renewable Energy Development and Utilization and the Prospects of Industrial Development
Authors: Liu Lei , Xiao Hanli , Shen Liang
Published: June 2021

Nowadays, the development and utilization of the renewable energy is more and more favored by countries all over the world for the purpose of solving the contradiction between the energy demand and the environmental protection. The application of renewable energy (including hydraulic energy, ocean energy, wind energy, solar energy, biomass energy and hydrogen energy) in our country develops rapidly and promotes the development of related industries at present. The optimization of energy structure will be realized, and the application prospect of the renewable energy industry will be broadened under the guidance of carbon peak and requirements of carbon neutral in the future.
Design of flexibility mechanism for electricity market to promote the consumption of new energy
Authors: Fang Yin , Xie Yi , Shi Yichuan
Published: June 2021

With the development of new energy, it is an irresistible trend for the demand side to consume new energy on a large scale and in a high proportion. At present, China’s installed capacity of new energy is growing rapidly, but the flexibility of the power system is insufficient, new energy consumption is difficult, and a large number of abandoned wind and light phenomena appear. In view of the high proportion of new energy consumption in the current environment, this paper designs the overall framework of the flexibility mechanism of the power market to promote new energy consumption, and puts forward the benefits of various market mechanisms in improving flexibility and promoting new energy consumption. Based on each market mechanism, the contribution index is put forward, the role of each market mechanism is analyzed quantitatively, and the considerable benefit of the market flexibility mechanism in promoting the consumption of new energy is proved by an example.
The Development of Integrated Centralized Control Platform for Electricity Meter Verification Device
Authors: Yan Liu , Jing-fen Zhang , Ying Yi , Jiang-ying Qin , Ji-ye Qin
Published: June 2021

The verification of power equipment in power grid is one of the basic guarantees to ensure the normal operation of power grid system. It is necessary to carry on the related verification to the electric power equipment of different specifications and models to ensure the functions, performance and stability of the equipment, so as to ensure the normal, safe and accurate operation of the power grid system. In this paper, a kind of electric energy meter verification device is designed. The verification platform can control the electric energy meter verification devices of different manufacturers and different models to carry out automatic verification of electric energy metering equipment. The verification platform is highly expandable, so long as the driver of the control device is implemented according to the interface method stipulated by the verification platform, the device can be seamlessly integrated into the verification platform.
Analysis of foundation bearing capacity and structural stability of suction bucket for offshore wind power
Authors: Xu Zhang
Published: June 2021

The large-scale wide and shallow bucket foundation of offshore wind power has a unique bucket top bearing mode, and the bucket foundation is provided with partition plates, which has greater bearing capacity as a whole. By numerical method, the solid and structural elements such as bucket body, rib plate connector and silo plate, as well as bucket-soil contact element are established, and the real three-dimensional complex model of bucket foundation and foundation soil is constructed in detail. The nonlinear contact calculation of bucket foundation under the combined loading modes such as horizontal load, wave force, vertical load and bending moment are simulated, and the deformation, bearing characteristics and safety of suction bucket are analyzed. The ultimate bearing capacity of foundation under horizontal load, vertical load and bending moment are calculated by Flac3d finite difference method, which provide reference for the foundation structure selection, bucket foundation design, implementation and safety evaluation of offshore wind farm projects.
Numerical simulation of fluid-solid coupling of stress failure characteristics of floor in coal mining face
Authors: Wu Weizheng , Wang ZHonghua
Published: June 2021

In order to explore the characteristics of floor stress failure in the mining face under the action of non-uniform water pressure, a fluid-solid coupling model of non-uniform water-bearing area was established. FLAC-3D simulation software was used to simulate and analyze the changes in the initial mining stage, the sudden stress increase stage, the stress slow increase stage, and the stable stress stage during the mining process of the working face, and the failure characteristics of the floor were analyzed. It reveals the reasons why water inrush accidents are likely to occur at the front of the working face, which has a certain significance for understanding the mechanism of water inrush from the floor.
Research on the Operation Measurement and Evaluation Method of Retail Packages under the Background of Electricity Market
Authors: Fei Wenjing , Tang Wei , Chen Ling , Ding Wenjiao , Yang Saite
Published: June 2021

With the liberalization of the electricity market, building a diversified and open competitive electricity retail market has become the focus of market reform and development. In the initial stage of the the retail market, the operating status of retail companies is an important evidence for the analysis of the current development of the retail market and the formulation of relevant rules. This paper designs a retail allocation method and proposes different business calculation and analysis methods based on 9 different types of retail packages in Yunnan electricity retail market. Based on a two-tier evaluation index system for retail packages and the electricity sales company, the FCE method combined with the AHP is used to evaluate the operating states of the electricity sales company and the retail packages.
Study on Extraction of Flavonoe Coated in Physalis alkekengi L
Authors: Li Ci Li , Huang Yu Yang , Yu Shi You
Published: June 2021

Flavones were extracted from Physalis alkekengi L. coating by ultrasonic method. Effects of material ratio, concentration of alcohol, ultrasonic time, temperature and power on the yield of flavones were studied. Optimal extracting conditions were determined through single factor and orthogonal experiments. The results showed that when ultrasonic power was 450 W, ratio of material to liquid was 1:50, the optimal extracting conditions were as follows: concentration of alcohol 50%, ultrasonic time 20 min, ultrasonic temperature 80°C, under above conditions, extraction yield of flavones was 1.93%. which approximated the predicted value of 2.05%.
CFD wind turbines wake effects by using UDF
Authors: Zhang Yi , Li Xuemin , Barasa Maulidi , Xu Weiming
Published: June 2021

The numerical simulation of wind turbine generators was carried out to investigate the relationship between wake expansion and distance of two wind turbine generators in a row. The commercial software ANSYS Fluent was used to perform the Computational Fluid Dynamics (CFD), and further, the standard k-ϵ turbulence modeling has been adopted to solve the steady-state, 3D Reynolds Averaged Navier-Stokes (RANS) equations. Results of near and far wake regions are analyzed. In fact, due to the squeezing effect of the wind turbine generators on the surrounding air, it is found that there is an acceleration area nearby the wind turbine rotors. The arrangement distance of wind turbine generators in a row is analyzed. The results show that as the arrangement distance of the wind turbine generators increases, the average wind speed and the wind power density in the acceleration area decrease. This conclusion has guiding significance for the arrangement of wind turbines in wind farms.
Explosion characteristic of stoichiometric syngas/air premixed gas in the flow state
Authors: Wang Baishi , Guo Pinkun , Wang Zhirong , Wang Xuxu , Liu Songjie , Xu Chuanqing , Chang Xinyue , Cao Xingyan , Wang Wei
Published: June 2021

With increasing attention to energy efficiency and environmental protection, syngas has attracted great interest as a clean fuel with broad development prospects. In order to further study the effect of the initial gas flow on the explosion of syngas, an explosion experiment of stoichiometric syngas/air premixed gas was carried out in a 3 × 3 × 100 cm square explosion pipe. The composition of the syngas used in the experiment is 50CO:50H2, the flow rate of the experiment gas is 0L/min-250L/min, and the Reynolds number (Re) is 0-9598.41. The experimental results show that the maximum explosion pressure Pmax and the maximum explosion pressure rise rate (dp/dt)max gradually increase with the increase of the initial flow rate and Re. The gas flow increases the flame area, and increase the combustion rate, thereby making the explosion more violent.
Prediction on Changes of Seabed due to Sluice Built on entrance of Haiyou Branch in Sanmen Bay
Authors: Shichang Huang , Xu Liu , Haiqian Han , Jinbin Mu , Haifeng Lou
Published: June 2021

Haiyou branch is the main branch of Sanmen Bay, it is an optional plan to construct sluice at the entrance of Haiyou branch to store fresh water for the utilization of freshwater resources in the Sanmen Bay basin. Basing on the verification of historical tidal currents and seabed erosion and deposition, numerical and physical models are established. Numerical calculations and physical model test show that the impact on hydrodynamic and seabed environment after the construction of sluice will be limited to the local sea area outside the sluice, where the downstream area of sluice, Shepan waterway and Maotou waterway are located, and the siltation strength decreases from the sluice towards Maotou waterway. After the construction of the sluice, the tidal inflow volume of Shepan section will decrease by 11.3% to 17.1%, the tidal volume of Maotou section decrease by 1.7% to 4.3%, and the tidal volume of Qinshan section and Qimen section remain basically unchanged. Within one year, the downstream area of sluice will be deposited with 0.5m∼0.7m, Maotou waterway with about 0.15m, and there is also little siltation at Qimen waterway and other waterway. Due to the impact of the sluice construction of Haiyou branch, after a long time, the deposition of deep pool in Maotou waterway is 2.0m∼2.5m. A once-in-50-year flood from the upper reaches will not cause significant seabed changes in the deep pool of Maotou waterway.
Research on evaluation index system of the operation efficiency in electricity market
Authors: Zhao Yuzhuo , Zhang Yanchi , Zhang Xinlin , Li He , Chen Dong , Xie Da
Published: June 2021

In order to ensure the efficient and stable operation of the electricity market, it is very important to set indexes to measure the market efficiency. In this paper, Herfindahl Hirschman Index (HHI) and social welfare index are used to measure the market efficiency. The article improves the traditional HHI. The HHI and social welfare index are standardized by min-max, and applied to a certain electricity market. The calculating results of each index and the result curve after standardization are given by example analysis.
Emergency Coordinated Frequency Control Strategy for Multi-DC Infeed Receiver Network
Authors: Li He , Zhang Yanchi , Chen Dong , Zhao Yuzhuo , Zhang Xinlin , Xie Da
Published: June 2021

For the receiver network with multiple DC feed-in, the DC locking fault seriously affects the safe and stable operation of the receiver network. This paper presents a frequency emergency coordinated control system which takes into account three measures: DC coordinated control, pumping and storage pump, and cutting off interruptible load. Two control strategies are developed, which are quick action from afar and frequency action on the spot. Both schemes have their own fault criteria. Finally, the two control strategies are analyzed and compared through the simulation of East China Power Grid.
Research on flow boiling in microchannel based on visualized flow patter
Authors: Wang Bingjun , Wang Jinfeng , Xie Jing , Yang Dazhang
Published: June 2021

Flow boiling in microchannel has become an effective solution for high-heat-flux cooling of electronic components and heat transfer equipment, research on flow boiling in microchannel benefits society. Visualization plays a key role in the research, flow patterns obtained by visualized tools contribute to the study of flow boiling in microchannels, it is embodied in the following two aspects: heat and mass transfer mechanism, flow pattern dynamics. Above two aspects are introduced and analysed so as to provide a reference for researchers who explore flow boiling in microchannels based on visualized flow patter.
Temporal and Spatial Changes of Land Use in Donghe District of Baotou City and Its Impact on Ecological Environment
Authors: Lv Jiankang , Sun Jianguo
Published: June 2021

Taking Donghe District, Baotou City, Inner Mongolia Autonomous Region as an example, research on land use change and its ecological environment response was carried out to provide theoretical support for the coordinated development of regional economy and ecological environment. Based on Landsat 4, 5 TM images from 1990 to 2010 and Landsat 8 OLI satellite remote sensing images from 2013 to 2018 to obtain land use maps, the land use transfer matrix explored the changes in land use and its ecological environment response in Donghe District from 1990 to 2018. The research results show that the urban development of Donghe District is gradually expanding to the northwest and southeast, and the area of residential and commercial service land has increased significantly in these two directions; the area of unused land has gradually decreased after soil improvement; the area of arable land has decreased in general; vegetation The area of the water body has gradually increased in recent years; the area of the water body has remained balanced as a whole. The quality of the ecological environment in Donghe District has improved.
Analysis on the causes of air pollution during the Spring Festival in Xi’an and the effectiveness of the government’s ban on fireworks
Authors: Jing Su , Yang Lin , Hongli Cao , Zhen Meng , Wei Li , Jiayi Hu
Published: June 2021

This paper analyzed the air pollution in view of the increasingly serious air pollution in Xi’an, this paper analyzes the air pollution in Xi’an, focused on the the effects of pollution source emission and meteorological conditions on ambient air quality. The results showed that the concentration of particulate matter decreased significantly during the Spring Festival with the increase of the ban on fireworks. In addition this paper combined with the public survey, discussed the necessity of banning fireworks and firecrackers, in order to provide ideas for the government to take feasible control measures in the work of pollution prevention and haze control.
Application and analysis of low temperature air source heat pump heating system in Cold Area
Authors: Wang Qiang , Zhu Xiaosheng , Liu Fengzhen , Zhang Wenke , Jiang Hongyang , Chen Shaojie
Published: June 2021

A low temperature air source heat pump (ASHP) heating system of residential building in cold area was designed and tested. The operating characteristics of the low temperature ASHP heating system in the typical day, typical month and the whole heating season were analyzed. The system energy saving performance in the whole heating season was also calculated. The results showed that the low temperature ASHP system operated stably in cold area and has energy-saving effect.
Analysis of Building Energy Saving Potential in High-speed Service Area Based on DeST Energy Consumption Simulation
Authors: Feng Ran , Gao Qingfei , Guan Xia , Du Peng , Jiang Hua , Zhang Lu , Wang Xu
Published: June 2021

High-speed service area buildings are located in specific areas and have special functions, so the research on energy consumption and energy-saving potential of high-speed service area buildings is different from that of conventional public buildings. In this paper, taking a high-speed service area building in Jinan as the research object, The dynamic benchmark model of hourly energy consumption of buildings in high-speed service area is established by using DeST energy consumption simulation software and the reference model is established. Comparing the annual energy consumption of the benchmark model with that of the reference model, this paper analyzes the energy-saving potential of the buildings in the high-speed service area.
Day-ahead sharing model of multi-integrated energy service providers based on source-load matching degree
Authors: Xu Weiting , Ma Ruiguang , Chen Chao , Wang Wei
Published: June 2021

The limited regulation capacity in the integrated energy community is a key factor restricting the development of the community-based integrated (distributed) energy system. Based on this, a model for optimal sharing of day-ahead energy in multi-communities considering the matching degree of source-load curves between communities is proposed. Firstly, the relationship between energy supply and multi-energy flow is analysed concretely in a single community. A mathematical model that includes electric vehicles and multiple energy conversion equipment is built, then, an objective function minimizing the cost of energy purchase, equipment operation and maintenance, and EV battery loss is established. Secondly, the comprehensive Spearman constant and Euclidean distance matching index based on photovoltaic and load data among the communities are considered to optimize the multi-community operation efficiency with the goal of minimizing the energy interaction cost. Finally, in a 3-community simulation system simulation, results show that the multi-energy sharing mode can effectively improve the overall economy of the system and the photovoltaic consumption capacity. The introduction of matching index also improves the energy transmission efficiency, verifying the rationality of the proposed model.
Research on Early Warning Model of Electric Vehicle Charging Safety
Authors: Jiang Linru , Zhang Yuanxing , Li Taoyong , Diao Xiaohong , Zhang Jing
Published: June 2021

At present, an effective evaluation system of the charging safety of electric vehicles has not been formed and lacks the corresponding safety early warning and protection control measures. It is of great significance to ensure the charging safety of electric vehicles and promote the rapid development of electric vehicles. Through the analysis of the establishment of the electric vehicle charging safety evaluation index system, the establishment method of the index system is studied. Finally, the demand analysis of the electric vehicle charging safety early warning and protection system is carried out. The function of establishing safety evaluation model in the system is clarified. For the comprehensive demonstration operation of electric vehicle, it is verified that the electric vehicle charging safety warning and protection system has real-time warning and protection function for battery, charging equipment and distribution network, which embodies the practical engineering value of the system.
Prediction of vortex precession in the draft tube of a model hydro turbine using mean field stability theory and stochastic modelling
Authors: Müller Jens S. , Sieber Moritz , Litvinov Ivan , Shtork Sergey , Alekseenko Sergey , Oberleithner Kilian
Published: June 2021

In this work we employ mean field stability theory (MFST) to predict the onset of the precessing vortex core (PVC) in the draft tube of Francis turbines. MFST is based on the linear stability analysis of the mean field of turbulent flows. Recent work shows that MFST very accurately predicts the formation of coherent structures in turbulent shear flows, such as the PVC. MFST may further reveal the flow regions that are most susceptible to flow actuation to suppress the PVC, which is of great practical relevance. In this work, MFST is accompanied by a data-driven approach to predict the linear growth rate of the PVC based on pointwise wall pressure measurements. The method is based on statistical evaluation of the probability density function of the PVC amplitude at limit cycle. It makes use of the intense noise induced by the background turbulence, which is expected to be a major driver of hydrodynamic instabilities. The empirical and analytic results are compared to phase-locked LDV measurements conducted inside the draft tube at various operating conditions, to assess the quantitative accuracy of the approach. The methodologies outlined in this work will be of relevance for future design of hydro turbines to run stable over a wide range of operating conditions.
CFD simulations of a Y-junction for the implementation of hydraulic short-circuit operating mode
Authors: Decaix J , Biner D , Drommi J-L. , Avellan F , Münch-alligné C
Published: June 2021

In the framework of the XFLEX HYDRO H2020 European Project, one of the demonstrators focuses on the implementation of the hydraulic short-circuit on the pump storage power plant of Grand-Maison owned by Electricité De France (EDF). The Grand-Maison power plant is a two-level plant production with one plant located above the downstream reservoir and equipped with four Pelton turbines; a second plant located downstream the reservoir and equipped with eight reversible pump-turbines. Hydraulic short circuit consists in running pumps and turbines in the meantime to balance the energy consumption of the pumps compared to the grid. Such an operating mode allows increasing the flexibility of the power plant and targeting the requirement of balancing the intermittent production due to the growing of new renewable energies such as wind and solar power plants. The hydraulic short-circuit operating mode leads to a change in the flow paths in the penstocks and junctions compared to the normal turbine or pump modes. Indeed, compared to the pump mode, this mode will lead to a flow derivation at the junction between the penstocks directed to the Pelton units and the penstocks directed to the upper reservoir. As this mode have not been scheduled at the beginning of the power plant construction, it is necessary to quantitatively assess the singular head losses generated at the junction to be able to simulate the complete behaviour of the power plant by means of a 1D model. CFD simulations are carried out with the Fluent software for several configurations of hydraulic short-circuit defined by the ratio of flow rate deviated to the Pelton turbines.
Assessment of advanced RANS turbulence models for the stability analysis of low specific speed pump-turbines
Authors: Del Rio A , Casartelli E , Mangani L , Roos D
Published: June 2021

Reversible pump-turbines, which can switch between pump and turbine operation, provide important support for the stabilization of the electrical grid. In order to fulfill their task, fast transition between the operation modes is required. This includes stable synchronization with the electrical grid during the process of turbine start at small guide vane openings (GVOs). However, the special geometry of pump-turbine impellers tends to produce unstable flow behavior, which can affect the synchronization process in a negative way.

The prediction of the stability behavior with the help of CFD during the design process is not yet fully developed. The simulation of small specific speed pump-turbines operating at small GVOs sets high requirements on the underlying numerical model. To capture all relevant flow structures accordingly, 3-dimensional unsteady computation of the entire pump-turbine domain is required. Further, it has been shown that turbulence modeling is a key factor in order to reproduce the 4-quadrant characteristic in the unstable S-shape region. Vortex structures in the vaneless space and runner channels are considered the root-cause for the occurring instabilities. Standard two-equation models are not able to predict the stability behavior under these difficult circumstances (highly separated flows, small specific speed, small GVO angle). Models, which consider the anisotropic behavior of Reynolds-stresses have shown to produce better results.

Considering the accurate prediction of mixing processes at off-design conditions, the focus was oriented to the anisotropy present in the turbulent structures. Standard models are often not sufficient to accurately predict vortices, which can have a huge impact on the performance, since based on the assumption of isotropic turbulence. Accordingly, they tend to dissipate and diffuse vortices too quickly. Improved models, which take the anisotropic nature of the Reynolds-stresses into account, can help in this context. The models can introduce the anisotropy via an explicit algebraic expression, or model directly the transport equations for the Reynolds-stresses. For this work the performance of a full Reynolds-stress model with improved coupling was investigated.

In order to obtain the predictions using advanced turbulence models a particularly robust framework based on a pressure-based fully coupled approach was used. The goal of this work is the development and testing of an improved full Reynolds-stress model for the application in the stability analysis of pump-turbines. The focus lies thereby on separation behavior and mixing/vortex dissipation.
MOC-CFD coupled model of load rejection in hydropower station
Authors: Mandair S , Morissette J F , Magnan R , Karney B
Published: June 2021

A modelling study investigates the consequences of transient flow conditions due to a turbine load rejection. The case study considers a large hydropower station with a long penstock. A three-dimensional (3D) Computational Fluid Dynamics (CFD) model is used to represent the spiral casing, guide vanes, runner, and draft tube. A one-dimensional (1D) Method of Characteristics (MOC) solver simulates water hammer in the penstock. The two models are coupled, to simulate a full load rejection. The results are compared with reference to field measurements and a pure 1D solver, combining the penstock and a turbine model based on machine and conveyance characteristics. A comparison of the high level data (head, flow, torque and rotational speed) reveals the two models reproduce the field data reasonably well. The exception being rotational speed toward the zero torque region, where both models underestimate speed. The model predicts high cycle pressure fluctuations on the turbine blade, which would produce serious mechanical loading. The source of the fluctuations is determined to be unstable vortices within the runner.
Assessment of turbulence models for the prediction of Bénard-Von Kármán vortex shedding behind a truncated hydrofoil in cavitation conditions
Authors: Chen Jian , Geng Linlin , De La Torre Oscar , Escaler Xavier
Published: June 2021

The transient cavitating flow in the wake of a hydrofoil at zero incidence angle has been simulated using a homogeneous mixture cavitation mass transfer model combined with both Reynolds Average Navier-Stokes (RANS) and Scale Resolving Simulation (SRS) turbulence models. The hydrofoil geometry corresponds to a 2D NACA 0009 with a truncated trailing edge which has already been extensively investigated in the High-Speed Cavitation Tunnel of the EPFL. The hydrodynamic conditions of interest correspond to a free stream velocity of 20 m/s (Re = 2 · 106) without cavitation and with two different degrees of cavitation. To improve the prediction of the vortex shedding behing the hydrofoil, the γ − Rθt
transitional boundary layer model has been coupled with the turbulence models. At cavitation-free regime, all the turbulence models with the exception of the SST and LES WALE ones have the ability to predict the experimentally measured vortex shedding frequency. Nevertheless, the results indicate that, neither the SST nor the DES-SST γ − Rθt
, can predict the vortex shedding frequency increase which has been experimentally observed when cavitation occurs. In contrast, the numerical results provided by the SST γ − Rθt
and the SSTCC γ − Rθt
show the capability to predict the expected shedding frequencies for both non cavitation and cavitation conditions. Beyond all expectation, the results provided by the LES WALE seem not only to overestimate the vortex shedding frequency at cavitation free conditions but also to underestimate the frequency when the cavitation number is significantly reduced.
Temporary shutdowns of the high-head run-of-river HPP Fieschertal to prevent excessive turbine erosion during floods
Authors: Felix D , Abgottspon A , Albayrak I , Boes R M
Published: June 2021

Hydro-abrasive erosion on hydraulic turbines is economically and energetically important. To better understand the causes and consequences of turbine erosion and to further develop mitigation measures, the suspended sediment concentration (SSC) and size distribution of mineral particles in the turbine water of the 64 MW high-head run-of-river hydropower plant (HPP) Fieschertal, Switzerland, have been continuously measured since 2012. An innovative combination of measuring techniques is used: turbidimeters, single-frequency acoustics, densimetry, laser diffraction and gravimetric analysis of water samples. Automatic warnings have been defined in the HPP’s control system to allow for systematic HPP shutdowns when the SSC in the valve chamber exceeds the threshold value of 10 g/l for at least 15 minutes. During the flood of July 29 and 30, 2017 with an SSC peak of 110 g/l, the intake was closed and the HPP was shut down for half a day. This prevented about 8000 tons of fine sediment from entering the HPP, which corresponds to 9 % of the turbines’ annual suspended sediment load (SSL) in 2017, or 12 % of the SSL in an average year without a significant flood. If the intake had been closed one hour earlier, the SSL could have been further reduced by about 3000 tons. For an earlier closing of the intake in case of floods, the turbidimeter at the intake shall be complemented by an additional instrument capable of measuring also medium to high SSC. Apart from the described flood event, SSC peaks in the range of 5 to 20 g/l occurring typically in late summer were attributed to re-suspension events in the storage tunnel due to HPP operation.
Research on State Evaluation and Prediction System of Hydraulic Turbine Based on Pressure Pulsation Parameters
Authors: Jiang Xiaoping , Gao Xiang , Hu Jiawei , Wang Ziting , Wang Lele
Published: June 2021

The pressure pulsation parameter of hydraulic turbine is one of the important indexes reflecting hydraulic stability of hydraulic turbine. Based on the pressure pulsation of the turbine, the health condition of the turbine unit is evaluated and predicted in this paper. Based on the measured data of pressure pulsation at four characteristic position of the hydraulic turbine, clustering was conducted by k-means method, and the health status of the hydraulic turbine unit was evaluated by finding the optimal k value for health status classification. The time series relationship of pressure pulsation was determined, and the evaluation result was taken as the prediction feature to establish the trend prediction model of pressure pulsation of hydraulic turbine set based on the time series change of long and short term memory network (LSTM). To realize real-time health assessment and prediction of unit running state and achieve quantitative assessment of equipment health state can provide technical basis for guiding unit maintenance.
Production flexibility of small run-of-river power plants: KWGO smart-storage case study
Authors: Münch-Alligné C , Decaix J , Gaspoz A , Hasmatuchi V , Dreyer M , Nicolet C , Alimirzazadeh S , Zordan J , Manso P , Crettenand S
Published: June 2021

In the framework of the new Swiss feed-in-tariff system for Small Hydropower Plants (SHP), the aim of the SmallFLEX project, led by HES-SO Valais and performed in collaboration with EPFL, WSL, EAWAG, PVE and FMV, is to show how SHP can provide winter peak energy and ancillary services, whilst remaining eco-compatible. The pilot and demonstrator site selected is the new SHP of Gletsch-Oberwald (KWGO) owned by FMV and commissioned end of 2017. This run-of-river power plant is equipped with two six-jets Pelton turbine units featuring a maximum power of 7.5 MW each while the average annual power is lower than 5 MW, with a maximum of production during the summer. The capacity of infrastructure, equipment, and other adaptation measures to produce in a flexible way is being assessed while measuring the impact of this new operation on the environment, production and revenues. The paper focuses on the two experimental campaigns and the numerical simulations carried out to assess the flexibility of the power plant by means of smart use of existing infrastructure as additional storage volumes: the settling basin, the forebay and the upper part of the headrace tunnel.
Effect of Inlet Section of Circular Section Spiral Case on Performance of Ultra-Low Specific Speed Diagonal Flow Turbine
Authors: Li Yanpin , Chen Xiaoyu
Published: June 2021

Variation of section area at volute inlet is a key factor affecting turbine performance. By changing the inlet section of the turbine volute, the inlet angle of the guide vane is changed, so the guide vane parameters will also be changed, which will affect the turbine performance. In order to study the influence of different volute inlet section areas on the overall hydraulic performance of ultra-low specific speed diagonal flow turbine, this paper redesigns the volute inlet section area of an ultra-low specific speed diagonal flow turbine. On the premise of applying the same runner, seven different volute inlet circular sections are designed. The numerical simulation of the full flow channel is carried out for each scheme, and the influence of inlet circular section area of different volutes on hydraulic performance of the ultra-low specific speed diagonal flow turbine is analyzed and compared. The results show that with the increase of flow rate, the calculated head and runner loss of the turbine increase, and the hydraulic efficiency of the turbine first increases and then decreases. When the turbine runs under small flow conditions (less than rated flow), the hydraulic efficiency of the turbine increases with the decrease of the diameter of the inlet circular section of the volute. When the turbine operates under high flow condition (greater than rated flow), the hydraulic efficiency of the turbine decreases with the decrease of the diameter of the inlet circular section of the volute. Through comparative analysis of seven schemes, the optimum radius of the inlet circular section of volute for the ultra-low specific speed diagonal flow turbine is 127mm and the corresponding inlet angle of guide vane is 32°. At this time, the efficiency of the turbine is 81.59% and the calculated head is 4.821m. The flow pattern inside the turbine is more uniform without whirlpools. It provides a reference for future design of similar type turbines and selection of suitable volute inlet circular section area.
Numerical investigation on a double suction twin-screw multiphase pump
Authors: Sun S H , Wu P B , Guo P C , Yi G Z , Kovacevic A , Zhang H, , Wu G K
Published: June 2021

Based on the dynamic mesh technology, the moving grids of the double-suction screw multiphase pump were generated by the software SCORG. Then the three-dimensional transient simulation model was established to investigate the two-phase flow mechanism inside the screw pump under different inlet gas volume fraction (IGVF). The results show that the pressure inside the working chamber increases step by step from inlet to outlet and is symmetrical. The pressure drops sharply at the inlet of circumferential clearance and then decrease linearly in the clearance. The curved flow in suction and discharge flow passage causes the gas separation and high gas volume fraction (GVF) area in suction and discharge chamber. Four vortices in cross section of discharge pipe cause four high GVF areas due to the centrifugal force produced by the vortices. The high GVF areas scatter in working chambers and change slightly with the rotation angle except the last chamber under the IGVF 10%. The two-phase leakage flow shows layered flow where the gas concentrates at the bottom of the gap. Thus, the high GVF areas on the surface of the rotors mainly exist at the position of gaps. The work will provide instructions for improving its performance under high IGVF.