bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental investigation of small axial hydro-kinetic turbines
Authors: Bucur D M , Dunca G , Bunea F , Chihaia R A , Grecu I S , Mitruţ R 
Published: October 2022

Abstract
In the present paper the prototypes of small axial hydro-kinetic turbines are designed, built and tested in laboratory conditions in order to demonstrate their operability. The hydrokinetic turbine prototypes have a 0.2 m tip diameter, three blades and are meant to be used in a free water stream flowing with 1 m/s velocity. Two geometries of the turbine runner are studied in order to determine the best correlation between the water flow velocity and the cross-sectional area of the turbine. The 3D designs of the turbine are used for the prototype printing in order to obtain a lightweight compact assembly of reduced dimensions. The experimental measurements are conducted in a closed-loop laboratory setup, specially designed for hydro-kinetic turbines prototypes testing. The flow velocity, runner speed and shaft torque are measured. The aim of the experimental testing is to determine the characteristic parameters for the tested turbines as power coefficient and mechanical power output.
Sensitivity analysis of a swirling flow to the GEKO model
Authors: Kranenbarg J , Jonsson P P , Mulu B G , Cervantes M J 
Published: October 2022

Abstract
Accurate numerical models for hydraulic turbine applications are highly coveted. They must be able to correctly capture the swirling flow found at off-design operating conditions in the turbine draft tube. The GEKO model is a relatively fast and flexible eddy viscosity turbulence model with adjustable coefficients to tune the model to different flow scenarios. In this study, the GEKO model is tested on a swirling flow inside a diffusor similar to the flow conditions found at part-load operation of a propeller turbine. The diffusor investigated corresponds to the Porjus U9 draft tube cone section, including the runner cone. Results showed that the near-wall coefficient, with a value of 2, increased the wall shear stress and moved the separation point from the runner cone further downstream. Moreover, with a value of 0.7, the separation coefficient increased the eddy viscosity, which also moved the separation point from the runner cone further downstream. Both coefficients gave velocity profiles closer to experimental values and increased the swirl number at the outlet of the diffusor by up to 36.9 % compared to the GEKO default model. Overall, the near-wall coefficient with a value of 2 gave the best results. The GEKO model provides an opportunity to tweak numerical models to swirling flow.
Repeatability and operational setting of Newly Developed Francis Turbine Test Rig
Authors: Kumar Sandeep , Khullar Subodh , Gandhi Bhupendra K 
Published: October 2022

Abstract
A small-scale test rig is developed to study the flow phenomena during off-design operations of a Francis turbine. The test rig can be operated in open and closed loops for a maximum head and discharge of 8 meters and 0.055 m3/s. The runner outlet diameter is 200 mm and rotates at 500 rpm. However, the test rig is not a model turbine test rig as per IEC 600193. Therefore, the repeatability of parameters is the key to establishing reliability in measurement and performance estimation. This paper presents the repeatability results of the turbine unit performed at a constant head. A control system is developed in the LABVIEW program with PID (Proportional, Integral, and Derivative) to run the turbine at the constant head with variable discharge and constant discharge at the variable head.
Numerical simulation of cavitating flows: comparison between two-fluid and homogeneous approaches
Authors: Ferhat J , Leclercq C , Fortes-Patella R , Archer A , Mimouni S , Aiouaz T. 
Published: October 2022

AbstractThe paper presents a new two-phase flow approach to simulate unsteady cavitating flows. The study applied the in-house codeneptune_cfd, which allows two-fluid modelling of liquid-vapor flows [1]. The code solves the ensemble-averaged equations of mass, momentum and energy conservation for each phase (liquid and vapour) for a total of six conservation equations. The equations system requires closure laws for the interfacial terms that represent the mass, momentum and energy transfers occurring between the liquid and vapor phases. An original approach is implemented by using an energy-source term based on the difference between the local enthalpy and its saturation value. 2D and 3D simulations are carried out for a NACA 65−012 hydrofoil with an angle of attack of 6°, a cavity length of 40% of the hydrofoil chord and different flow velocities. The methodology to obtain the cavity length and the main frequency of its periodic behavior is presented. Then the numerical results are compared with those previously obtained by a homogeneous approach [2] and with the available experimental data [3]. The quantitative predictions of the hydrodynamic characteristics (i.e. cavitation sigma number, cavity length, shedding frequency and cavity shape) obtained from two-phase flow modeling appear in better accordance with experimental data.
Flow-induced vibration analysis of a prototype pump-turbine runner during turbine start-stop transient process
Authors: Zhou Xijun , Yin Xilong , Wang Wenlong , Huang Xingxing , Zhang Shaozheng , Bi Huili , Wang Zhengwei 
Published: October 2022

Abstract
Recently more start-stops per day of the pump-turbine units are required by the power grid for load regulation. During the turbine start-up and shut-down transient processes, the flow and pressure of the prototype pump-turbine change dramatically at different guide vane opening angles. The extremely unsteady pressure fluctuation in the flow passages can induce large deformation, stress concentration, and strong vibration of the pump-turbine runner. Therefore, it is significantly important to study the unsteady flow characteristics and the corresponding flow-Induced vibration of the runner during turbine start-up and shut-down transient process. In this investigation, a 3D model of the pump-turbine unit including the flow passages of the spiral casing, stay vane, guide vane, runner, and draft tube, crown chamber, band chamber, labyrinth seals, and balance pipes are constructed. The flow characteristics of the unit during the turbine start-up and shut-down process were analysed by coupling the 1D pipeline calculation and 3D turbine flow domain calculation. By mapping the pressure distribution of the fluid domain to the runner structure domain, the flow-induced dynamic behavior of the pump-turbine runner is performed, and the large deformation and stress concentration of the runner are investigated in detail. The flow-induced vibration results achieved are able to provide meaningful suggestions for safe operation and for improving the pump-turbine runner design.
Numerical investigation of the pressure-time method
Authors: Kalantar M , Jonsson P , Dunca G , Cervantes M J 
Published: October 2022

Abstract
The flow rate is a challenging hydrodynamic parameter to measure in order to determine turbine efficiency. The pressure-time method is a cost-effective alternative to estimate the flow rate. Its principle is based on the transformation of momentum into pressure during the deceleration of the liquid mass. Numerical simulations give valuable information to develop the method. One of the challenges in the numerical study of the pressure-time method is modelling the valve movement. In previous numerical studies, the dynamic mesh has been used for valve closure modelling. The dynamic mesh may lead to divergence, and re-meshing makes this method more time-consuming.
In this paper, the valve closure is modelled considering immersed solid method. The results’ sensitivity is studied by different time-step, grid, and boundary conditions at the inlet. It is shown that the result is independent of the time-step size smaller than 0.1 ms. Furthermore, it is observed that only the opening boundary condition at the inlet can predict the oscillation of variables during water hammer phenomenon. Then, the numerical results are validated with experimental data. Finally, the pressure-time method is applied to the data, and the flow rate is estimated.
Numerical fatigue damage analysis of a variable speed Francis pump-turbine during start-up in generating mode
Authors: Biner Daniel , Alligné Sebastien , Nicolet Christophe , Dujic Drazen , Münch-Alligné Cécile 
Published: October 2022

Abstract
Variable speed hydropower units offer a large spectrum of grid regulation services and may therefore contribute to the stability of future power supply systems. Full Size Frequency Converters (FSFC) already found real world application in Pumped Storage Hydropower Plants up to a rated power of 100 MW and are even considered scalable up to a few hundred MW. Apart from the extension of the power range and grid regulation capacities, the FSFC technology also provides new control possibilities during transient operations such as start-up in generating mode. Thus, harsh conditions with damaging impact on the hydromechanical components may be avoided by tuning the operating point trajectory in the start-up phase. In this paper, runner fatigue damage during start-up in generating mode of a 5 MW variable speed Francis pump-turbine prototype equipped with a FSFC is numerically analyzed. The fixed speed solution is compared to a variable speed solution following a BEP tracking control strategy. 1D hydraulic transient simulations provide boundary conditions for detailed 3-D CFD/FEA simulations. Full and reduced numerical domains are used and compared. The overall outcome of the present numerical study indicates an important reduction of partial damages using variable speed drives for turbine start-up manoeuvres.
Towards accurate numerical fluid dynamics of pump-turbine runners in deep partial load operation
Authors: Zorn M , Khalfaoui K , Riedelbauch S 
Published: October 2022

Abstract
The operation of pumped storage power plants at off-design conditions requires an understanding of the flow field and the resulting damage to ensure a safe and economic operation. Within this study, CFD simulations are carried out for an existing pump-turbine at deep part load operation to enable calculating the damage in later structural analyses. Furthermore, this study includes the comparison between the SST and SBES turbulence model at different mesh sizes. The simulation results are compared with model test data regarding head, torque and pressure fluctuations at a bottom ring and draft tube cone sensor. Whereas all simulation setups are within a reasonable range to the available model test data, the pressure fluctuations on the runner blades as well as the resolved vortices within the runner blade channels show a qualitative difference between both models. The SBES turbulence model resolves more vortices and thus different pressure fluctuations. Subsequent structural analyses show higher accuracy of the SBES turbulence model compared with the SST model. A mesh refinement from 25 million nodes to 80 million nodes with the SBES model reveals a better resolution of vortices, but only local differences in pressure fluctuations.
Procedure to minimize rotor vibrations from flow-induced excitations in Kaplan turbines
Authors: Jonsson P P , Nässelqvist M L , Mulu B G , Högström C M 
Published: October 2022

Abstract
The flow pattern in the draft tube is commonly considered when investigating rotor vibration problems, especially for Francis turbines. However, phenomenon in the vaneless space for Kaplan turbines have been shown to induce rotor vibrations when operating in non-standard conditions such as speed no load (SNL). These flow disturbances develop in the vaneless space at small guide vane openings and high swirls. Depending on the number of flow disturbances and runner blades they can excite transversal, axial or torsional vibrations. In the case of transversal excitation they can in some cases cause resonance problems if the frequency is close to a natural frequency of the rotating structure. Recently it was observed that the excitation causes severe resonance in the rotating structure on a refurbished turbine when operated at SNL.
The present paper presents frequency analysis of the flow-induced excitations coupled to the shaft vibrations on an old and a refurbished Kaplan turbine. To investigate the causes of the resonance problem, measurements have been performed on both the model and prototype turbine and on a twin unit with the old runner design. The measurements on the prototypes consist of pressure, shaft bending moment, and vibrations. Pressure and radial forces were measured on the model.
The result shows the dependence of the runner blade opening on the transversal excitation and the frequency of the flow disturbances. The rotordynamic analysis showed the same phenomena with forward and backward precession. The results agree well between the model and prototype when measured data are normalized by the runner rotational frequency. It is proposed, when refurbishing a unit, to use measured pressures, shaft bending moment and vibrations on the prototype before the refurbishment and the new model turbine to identify critical excitation frequencies for the new prototype turbine, i.e., use the information from the tests to set rotordynamic requirements for the new prototype unit.
Hybridization in Kaplan turbines. Wear and tear assessment
Authors: Valentín David , Presas Alexandre , Egusquiza Mònica , Valero Carme 
Published: October 2022

Abstract
In the current energy market, hydraulic turbines are increasingly demanded to work in Frequency containment reserve (FCR) mode to compensate the constant frequency fluctuations in the electrical grid. To do so, hydraulic turbines change their generating power continuously which implies to regulate the flow rate. Kaplan turbines are double regulated machines that change the position of both guide vanes and runner blades to regulate the flow rate maximizing their efficiency. Therefore, guide vanes and runner blades are continuously moving when they provide FCR, leading to high wear and tear of the regulation system components.
Within the frame of the European project XFLEX Hydro, a new technology to reduce the wear and tear of the regulation system in FRC have been implemented. This technology consists in the hybridization of the unit with a battery system. In that way, the battery is the one in charge of providing part of the power fluctuations to the grid, reducing the movements of guide vanes and runner blades of the turbine. The battery system was successfully installed in August 2021 in one unit of the Vogelgrun powerplant, in France. Since that moment, the unit has been working in hybrid mode.
A monitoring system was installed in the power plant in two different units, the one hybridized and another without hybrid system. Several sensors were installed and different parameters were measured simultaneously to calculate the wear and tear of the different components. In this paper, a comparison between the hybrid mode and the standard mode (non-hybrid) is performed in terms of mileage and wear and tear of the guide vanes and runner blades servomotors.
Pushing the envelope of ancillary services with variable speed technology
Authors: Dreyer M , Nicolet C , Alligné S , Seydoux M , Jung A , Cordeiro D 
Published: October 2022

Abstract
Hydropower is the backbone of energy transition thanks to its operational flexibility and ability to provide ancillary services. These grid support capabilities are called upon to play a major role to maintain the grid vulnerability at acceptable levels in view of the increasing penetration of stochastic and intermittent renewable energies. In this context, variable speed reversible pump-turbine technology is a key asset as it can extend the head operating range of a powerplant, enable power network control in pump mode and further increase the flexibility services to the electrical grid. Furthermore, by taking advantage of the so-called flywheel effect, variable speed enables the fast active power injection/absorption in pumping and generating mode. The additional degree of freedom offered by the variable speed opens the door to different control strategies for the hydroelectric plant, as the converter can be used for speed or power control. This can be exploited to maximize either the efficiency or the power reserve dedicated to grid support. In this paper, the strategies to maximize the ancillary service of Frades 2 pumped storage power plant (PSPP) are investigated. The plant features two high-head single-stage reversible variable speed units, coupled with 420 MVA doubly-fed induction motor-generators (DFIM). Using a 1D numerical model to simulate the power plant behavior, it is explored to which extent Frades 2 can deliver frequency containment reserve (FCR) power, while complying with the ENTSO grid code, and speed deviation constrains inherent to DFIM. By choosing a strategy which fully exploits the flywheel effect, it is established that the FCR power band can be equal to the whole operating range of the power plant. Moreover, the fast frequency response capacity (FFR) is also evaluated. It is found that by maximizing the energy stored in the rotating masses, each unit of Frades 2 can deliver up to 110 MW of active power in 1.3 seconds.
Social Change, Gender Stratification and the Sex Gap of Homicide Victimization in 76 Countries, 1975–2017
Authors: Lu Yunmei , Santos Mateus R , Zhang Zhe 
Published: October 2022

Abstract
This study examines the longitudinal change in the sex gap of homicide victimization in 76 countries between 1975 and 2017. We compiled a cross-national dataset with homicide victimization data from WHO and structural measures from multiple databases. Our findings reveal that countries with low homicide rates and rapid homicide decline are more likely to have narrowing sex gaps, and that the narrowing gaps are mainly driven by male homicide decline. Different from the prior literature, we find null associations between most measures of gender stratification and the sex gap. Instead, results reveal that aging population is associated with a narrowing sex gap. Implications are discussed, including the specific effects of the study period and the shifting dynamics of homicide trends.
The politics of representation in Squid Game and the promise and peril of its transnational reception
Authors: Oh David C 
Published: October 2022

Abstract
This article introduces the special forum on representations and transnational reception of Squid Game. The purpose of the forum is to draw together two groups of scholars into dialogue. The first are Korea experts in communication and cognate fields, who consider the politics of representation in the show against the backdrop of neoliberal capitalist precarity, and the second are scholars of audience reception, who point to the ways Squid Game’s overseas reception is marked by power—hegemonic power that reifies dominant ideological meanings at the site of reception and resistive power for marginalized groups at the site of reception, who produce Squid Game-related paratexts to imagine inter-racial, affective connection.
The Elements of International Legal Positivism
Authors: Hovell Devika 
Published: October 2022

Abstract
This article contains a plea for continuing attention to the elements of international legal positivism. Using the language of ‘elements’ deliberately plays on the positivist tendency to describe the legal discipline as a legal science. Yet law’s elements differ in important ways from the usual objects of scientific inquiry. Law’s method does not seek to address the structure and behaviour of the physical world, but that of a particular society with its own political polarities, structure and functions. The fact that international law inherits its positivist method from the domestic legal context therefore presents complications. While the adoption of positivism as international law’s predominant legal method was animated in part by a desire to provide international law with the imprimatur it needs to claim credibility as a legal system, it has also served as an impediment to international law’s development in a distinctive fashion from domestic law. International law’s attachment to the positivist method has at times extended to an attachment to certain presuppositions more closely associated with the development of the modern European state. This article takes the position that it is important to engage with international legal positivism on its own terms. Part I traces the lineage of three important traditions of international legal positivism (‘social thesis’ positivism, ‘system-based’ positivism and ‘teleological’ positivism) highlighting their different emphases and in doing so identifying key elements. Part II interrogates certain presuppositions sometimes associated with these traditions and considers whether it is appropriate to rethink or re-engineer these aspects in their application to the international legal system. While positivism is sometimes associated with ‘purifying’ law as a discipline, the article takes the position that the positivist method can only endure if complemented by a rich legal, political and social discourse focused on understanding its relationship to the elements of the international legal system, in particular, international law’s community, authority and functions.
Mortality in Patients with Inflammatory Bowel Disease: Results from 30 Years of Follow-up in a Norwegian Inception Cohort (the IBSEN study)
Authors: Follin-Arbelet Benoit , Cvancarova Småstuen Milada , Hovde Øistein , Jelsness-Jørgensen Lars-Petter , Moum Bjørn 
Published: October 2022

Abstract

Background and Aims
Patients with longstanding inflammatory bowel disease [IBD] may be at an increased risk of death compared to the general population, especially elderly patients. The Inflammatory Bowel South-Eastern Norway [IBSEN] study has previously detected a small but not statistically significant increase in mortality 20 years after diagnosis. The aim of this study was to evaluate the overall and cause-specific mortality at 30 years of follow-up.

Methods
The IBSEN cohort included 519 incident patients with ulcerative colitis [UC] and 237 patients with Crohn’s disease [CD] between 1990 and 1993, each matched with five controls. Death certificate data were obtained from the Norwegian Cause of Death Registry. The underlying causes of death were categorized into five groups: all cancers, gastrointestinal cancers, cardiovascular diseases, infections and all other causes. Hazard ratios [HRs] were modelled using Cox regression.

Results
There was no statistically significant difference in the overall mortality rates. However, in patients with CD, male sex (HR = 1.65 [95% CI: 1.04–2.62]), onset after 40 years of age (HR = 1.72 [1.19–2.48]), colonic disease (HR = 1.57 [1.05–2.35]) and penetrating behaviour (HR = 3.3 [1.41–7.76]) were clinical factors associated with an increased mortality. IBD patients were at a higher risk of death due to cardiovascular disease: HR = 1.51 [1.10–2.08] for UC and 2.04 [1.11–3.77] for CD. When taking into account both the underlying and the immediate cause of death, infection was more frequent in patients with IBD.

Conclusions
Overall, all-cause mortality rates were similar between patients with IBD and controls. However, clinicians should remain alert to cardiovascular diseases and infections, particularly in specific subgroups of CD patients.