bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generalized Regge-Wheeler equation from Effective Field Theory of black hole perturbations with a timelike scalar profile
Authors: Mukohyama Shinji , Takahashi Kazufumi , Yingcharoenrat Vicharit 
Published: October 2022

Abstract
Recently, the Effective Field Theory (EFT) of perturbations on an arbitrary background metric with a timelike scalar profile was formulated in the context of scalar-tensor theories. Here, we generalize the dictionary between the coefficients in the EFT action and those in covariant theories to accommodate shift- and reflection-symmetric quadratic higher-order scalar-tensor theories, including DHOST as well as U-DHOST. We then use the EFT action to study the dynamics of odd-parity perturbations on a static and spherically symmetric black hole background with a timelike scalar profile. Finally, we obtain the generalized Regge-Wheeler equation that can be used, e.g., to determine the spectrum of quasinormal modes and tidal Love numbers.
Painlevé analysis, auto-Bäcklund transformations, bilinear forms and soliton solutions for a (2+1)-dimensional variable-coefficient modified dispersive water-wave system in fluid mechanics
Authors: Liu Fei-Yan , Gao Yi-Tian 
Published: October 2022

Abstract
In this paper, we investigate a (2+1)-dimensional variable-coefficient modified dispersive water-wave system in fluid mechanics. We prove the Painlevé integrability for that system via the Painlevé analysis. We find some auto-Bäcklund transformations for that system via the truncated Painlevé expansions. Bilinear forms and N-soliton solutions are constructed, where N is a positive integer. We discuss the inelastic interactions, elastic interactions and soliton resonances for the two solitons. We also graphically demonstrate that the velocities of the solitons are affected by the variable coefficient of that system.
Modelling the differential effects of age on transcranial magnetic stimulation induced electric fields
Authors: Alawi Mansour , Lee Poh Foong , Deng Zhi-De , Goh Yong Kheng , Croarkin Paul E 
Published: October 2022

Abstract

Objective. The therapeutic application of noninvasive brain stimulation modalities such as transcranial magnetic stimulation (TMS) has expanded in terms of indications and patient populations. Often neurodevelopmental and neurodegenerative changes are not considered in research studies and clinical applications. This study sought to examine TMS dosing across time points in the life cycle. Approach. TMS induced electric fields with a figure-of-eight coil was simulated at left dorsolateral prefrontal cortex regions and taken in vertex as a control region. Realistic magnetic resonance imaging-based head models (N = 48) were concurrently examined in a cross-sectional study of three different age groups (children, adults, and elderlies). Main results. Age had a negative correlation with electric field peaks in white matter, grey matter and cerebrospinal fluid (P < 0.001). Notably, the electric field map in children displayed the widest cortical surface spread of TMS induced electric fields. Significance. Age-related anatomical geometry beneath the coil stimulation site had a significant impact on the TMS induced electric fields for different age groups. Safety considerations for TMS applications and protocols in children are warranted based on the present electric field findings.
Vascular remodeling in sheep implanted with endovascular neural interface
Authors: John Sam E , Donegan Sam , Scordas Theodore C , Qi Weijie , Sharma Prayshita , Liyanage Kishan , Wilson Stefan , Birchall Ian , Ooi Andrew , Oxley Thomas J , May Clive N , Grayden David B , Opie Nicholas L 
Published: October 2022

Abstract

Objective. The aim of this work was to assess vascular remodeling after the placement of an endovascular neural interface (ENI) in the superior sagittal sinus (SSS) of sheep. We also assessed the efficacy of neural recording using an ENI. Approach. The study used histological analysis to assess the composition of the foreign body response. Micro-CT images were analyzed to assess the profiles of the foreign body response and create a model of a blood vessel. Computational fluid dynamic modeling was performed on a reconstructed blood vessel to evaluate the blood flow within the vessel. Recording of brain activity in sheep was used to evaluate efficacy of neural recordings. Main results. Histological analysis showed accumulated extracellular matrix material in and around the implanted ENI. The extracellular matrix contained numerous macrophages, foreign body giant cells, and new vascular channels lined by endothelium. Image analysis of CT slices demonstrated an uneven narrowing of the SSS lumen proportional to the stent material within the blood vessel. However, the foreign body response did not occlude blood flow. The ENI was able to record epileptiform spiking activity with distinct spike morphologies. Significance. This is the first study to show high-resolution tissue profiles, the histological response to an implanted ENI and blood flow dynamic modeling based on blood vessels implanted with an ENI. The results from this study can be used to guide surgical planning and future ENI designs; stent oversizing parameters to blood vessel diameter should be considered to minimize detrimental vascular remodeling.
Addressing transcranial electrical stimulation variability through prospective individualized dosing of electric field strength in 300 participants across two samples: the 2-SPED approach
Authors: Van Hoornweder Sybren , A Caulfield Kevin , Nitsche Michael , Thielscher Axel , L J Meesen Raf 
Published: October 2022

Abstract

Objective. Transcranial electrical stimulation (tES) is a promising method for modulating brain activity and excitability with variable results to date. To minimize electric (E-)field strength variability, we introduce the 2-sample prospective E-field dosing (2-SPED) approach, which uses E-field strengths induced by tES in a first population to individualize stimulation intensity in a second population. Approach. We performed E-field modeling of three common tES montages in 300 healthy younger adults. First, permutation analyses identified the sample size required to obtain a stable group average E-field in the primary motor cortex (M1), with stability being defined as the number of participants where all group-average E-field strengths ± standard deviation did not leave the population’s 5–95 percentile range. Second, this stable group average was used to individualize tES intensity in a second independent population (n = 100). The impact of individualized versus fixed intensity tES on E-field strength variability was analyzed. Main results. In the first population, stable group average E-field strengths (V/m) in M1 were achieved at 74–85 participants, depending on the tES montage. Individualizing the stimulation intensity (mA) in the second population resulted in uniform M1 E-field strength (all p < 0.001) and significantly diminished peak cortical E-field strength variability (all p < 0.01), across all montages. Significance. 2-SPED is a feasible way to prospectively induce more uniform E-field strengths in a region of interest. Future studies might apply 2-SPED to investigate whether decreased E-field strength variability also results in decreased physiological and behavioral variability in response to tES.
Comment on ‘The advanced tokamak path to a compact net electric fusion pilot plant’
Authors: Manheimer Wallace 
Published: October 2022

Abstract
This comment (letter) examines a recent GA concept which they hope will lead to a tokamak fusion pilot plant. As tokamaks are now the closest configuration to practical magnetic fusion, if they cannot do a pilot plant, almost certainly no other device can either. The conclusion is that constructing a tokamak fusion pilot plant at this time is enormously risky, and is almost certainly tremendous waste of scarce fusion resources, which could be better used on other efforts in the fusion effort.
Residual entropy of ice Ih by Wang–Landau Monte Carlo simulation of an effective Ising model
Authors: Li De-Zhang , Zhao Yu-Jun , Yang Xiao-Bao 
Published: October 2022

Abstract
Accurate evaluation of the residual entropy of three-dimensional ice systems remains a difficult task. In this work, we estimate the residual entropy of ice Ih (ordinary ice) by an improvement of the Wang–Landau Monte Carlo algorithm, which directly calculates the density of states of the system. We define an effective three-dimensional Ising model with nearest-neighbour interactions, and introduce the mapping of the spin configurations of this Ising model into the hydrogen configurations of ice Ih. The ground states of this Ising model are equivalent with the hydrogen configurations obeying the ice rules, therefore the ground state degeneracy directly determines the residual entropy. Our estimate is in good agreement with the famous theoretical approximation by Nagle in 1966, and other results evaluated from various methods. The advantage of making use of the equivalent Ising model is discussed. It is convenient to extend our approach to other lattice systems.
31st IAHR Symposium on Hydraulic Machinery and Systems
Authors: Trivedi Chirag 
Published: October 2022

Abstract
Hydropower is one of leading sources of energy used to meet the primary, secondary and territory ancillary services to balance the energy demand. Hydraulic turbine is essential component of a hydro power plant to generate electricity. The IAHR symposium on hydraulic machinery and systems provides unique opportunity to the academic and industrial research teams to exchange the stat-of-the-art knowledge and ideas on the development of the next-generation of hydropower technology. 31st Symposium on Hydraulic Machinery and Systems was organized by Norwegian University of Science and Technology, Trondheim, Norway, during 26 June – 01 July 2022. This preface describes the overall summary of the symposium, including the parallel sessions, scientific and cultural tours. For more specific detail, please visit the symposium website www.ntnu.edu/iahr2022. Scientific manuscripts reviewed by the experts, accepted and presented during the symposium are published in a proceeding at IOP Science EES conference series.
Experimental complex flow patterns in the pump intake with a low water level
Authors: Guo M , Tang X L , Li X Q 
Published: October 2022

Abstract
The present paper is an extension of the authors’ previous work [1], and the goal is to analyze and reveal the complex flow patterns in the pump intake with a low water level (lower than the critical water level) through PIV Technology (Particle Image Velocimetry). The results show that: the lower the water level (a) the geometric scale of the free-surface vortices increases, which potentially leads to pulling more air into the pipe system and the pump units of the pump station; (b) the sidewall-attached vortices have a larger geometric scale; (c) more backwall- and floor-attached vortices are captured, and their geometric scale is large. In brief, the experimental data of the paper indicate that the free-surface, backwall-, and floor-attached vortices are the main characters of the pump intake with a low water level. In engineering, the vortex suppression/eliminating devices in the vicinity of these locations should be emphasized.
Hydraulic geometric optimization on stagnating flow at the inlet of main pipe of underground pumping station
Authors: Guo M , Yao K W , Zhang S H 
Published: October 2022

Abstract
The underground pumping station is widely used in many important fields. However, the stagnating flow caused by the sharp geometric gradient at the interface between the primary pump intake and the main pipeline not only causes the performance deteriorations of the whole pump station but also leads to safety and operational stability challenges. In this paper, the numerical model of the related hydraulic phenomena is presented, moreover, the effectiveness and accuracy of the numerical model are verified by comparing it with the experimental results. The simulation results indicate that the hydraulic geometry optimization scheme at the inlet of the main pipe with 0.10 D (inner diameter of the main pipe) local rounding contributes the best effect on the hydraulic efficiency and operation stability of underground pump stations. The results may give a reference for the design of underground pump stations and the optimization of hydraulic geometry in related fields.
Experimental Investigation of a Free Runner Concept Downstream of Francis Turbines
Authors: Bosioc A I , Szakal R , Tanasa C , Susan-Resiga R.F. 
Published: October 2022

Abstract
The main purpose of the paper is to investigate experimentally a new concept by using a free runner downstream of the main hydraulic runner turbine to increase the flexibility in operation. The free runner concept supposes that rotates at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute between the shaft and the periphery the total pressure and the moment of momentum, such that the flux of total pressure and the moment of momentum are not altered. Moreover, the free runner does not modify the operating point of the main hydraulic turbine runner. The experimental investigation focuses on velocity profiles measurements with the LDV system and the unsteady pressure measurements downstream the free runner, in the draft tube cone.
Intermittent cavitating flow field in tandem cascades of Kaplan turbines
Authors: Susan-Resiga R F , Ciocan T , Stuparu A , Gherghe G G 
Published: October 2022

Abstract
Within the framework of the classical turbine design setup, we present a numerical investigation of unsteady cavitating flow in tandem cascades of guide vanes and rotor blades. The practical relevance of the present investigation is ensured by choosing real blade profiles and domain geometry for the large Kaplan turbines (9.5 m rotor diameter) from the Iron Gates I hydropower plant on the Danube River. The 2D tandem cascade setup is obtained with a conformal mapping of the circular guide vane cascade into a straight cascade, while the rotor blade cascade is by default a straight one for axial turbines. Both single-phase and two-phase cavitating flows results are presented and analysed. The single-phase liquid flow displays rather modest pressure and tangential force fluctuations, with the characteristic blade passing frequency, due to the interaction of the rotor blades with the wakes of guide vanes. The two-phase cavitating flow displays a completely different dynamics in comparison to the liquid flow, with periodic cavitation growth and collapse at a specific frequency lower than the blade-passing one. Moreover, the tangential force on the rotor blade displays severe intermittency and the force fluctuations are almost one order of magnitude larger than in the single-phase flow.
Numerical study on effect of operating condition and solid concentration on hydro-abrasive erosion of high head Francis turbine
Authors: Sharma S , Sharma S R , Gandhi B K 
Published: October 2022

Abstract
The powerplants in the Himalayan region are generally subjected to hydro-abrasive erosion. The deterioration of components due to erosion causes reduction in performance, changes the fluid flow pattern and even the breakdown of the turbine. In the present work, the Bhilangana-III powerplant Francis turbine is considered a reference turbine for numerical investigation using the computational fluid dynamics (CFD) tool. The study presented an evaluation of hydro-abrasive erosion of high head Francis turbine for the different operating conditions and sediment concentrations. The modified Grant and Tabakoff erosion model is used for the erosion rate calculation. To investigate the effect of various operating conditions, the study is conducted at part load, best efficiency point (BEP) and high load. Also, to examine the impact of suspended sediment on the erosion of turbine components, the solid concentration varies from 500, 1200, 2000, 3000 and 4000 ppm. The observed erosion pattern is similar at all operating conditions for the stay vane, guide vane and runner, but the density of erosion is different. The observed deterioration density due to erosion is higher for part and full load than in the BEP condition. The guide vanes and runner vanes are highly susceptible to erosion due to higher absolute velocity and relative velocity at guide vane and runner vane, respectively. The observed erosion rate variation is qualitatively in-line with the on-field turbine erosion condition. It is also found that the increase in erosion rate with the sediment concentration is almost linear but more than 90% and 79% higher for the runner than stay vane and guide vane, respectively.
Characterization of the hydrodynamic instabilities in a pump-turbine operating at part load in turbine mode
Authors: Cavazzini G , Zanetti G , Santolin A , Ardizzon G 
Published: October 2022

Abstract
Pump-turbines (RPT) nowadays represents the most common mechanical equipment adopted in the new generation of storage hydro plant. In order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources, RPT are forced to rapidly switch between the pumping and generating mode also extending their operation under off-design conditions in unstable operating areas. Because of the design criterion adopted for the development of a RPT, an unstable behavior represented by a typical S-shaped profile with a positive slope in the machine’s characteristic can occur near to the runaway condition.
With the purpose of evaluating the evolution of the fluid field near to the no-load condition, an in-depth CFD analysis of the RPT model test of the Norwegian Hydropower Center is performed by retracing the machine’s characteristic curve running through the flow-speed characteristic curve up to the turbine brake region for fixed guide vanes opening. To validate the numerical results, a comparison with the experimental results in terms of characteristic curves and pressure signals is performed.
The results allow to capture the 3D characteristics of the unsteady phenomena, progressively evolving in an organized rotating stall, highlighting also the influence of the flow rate change from partial loads to the turbine brake operation on their development. In order to characterize the pulsating nature of the instability phenomena developing in the runner and in the rotor-stator interaction, a time-frequency analysis is performed on the numeric pressure and torque signals. The combination between fluid-dynamic and time-frequency analysis makes it possible to identify and characterize three evolution phases: inception, growth and consolidation.
Experimental Investigation of Flow Inside the Back-Sidewall Gaps of Centrifugal Pump and its Impact on Axial Thrust
Authors: Zemanová L , Rudolf P , Zubík P 
Published: October 2022

Abstract
Despite the sidewall gaps of centrifugal pumps are tiny narrow spaces, the flow inside them can have a great impact on the flow field in the whole machine. Regardless of its influence, there is no full understanding of the flow in those regions. A theory exists for the simplified cylindrical cavity with a rotating disk, whose application to real hydraulic machines is questionable. To investigate the flow in the sidewall gaps of centrifugal pumps, a test rig including a real impeller has been built up. It enables observation of the flow in the back-sidewall gap by optical methods and evaluation of axial thrust and torque. The measurements were performed for a range of rotational speeds in order to map possible flow regimes and patterns. It was found out, that the basic theory and map of the flow regimes obtained for a simple rotating cavity is inapplicable for the back-sidewall gaps of real hydraulic machines. The flow field is significantly influenced by the impeller blades, and consequently, the map of the regimes is shifted compared to the one derived for the simple cylindrical cavity with a rotating disk. The discrepancies were described and a new map of flow regimes was introduced.
Investigation on hydrodynamic characteristics of a hydrofoil based on γ-Reθt
transition model
Authors: Ye Changliang , Wang Fujun , Zheng Yuan , Zhou Daqing , Van Esch B P M 
Published: October 2022

Abstract
The complex flow field caused by the dynamic stall can affect the operational stability of hydrodynamic machinery. In this paper, the NACA0009 blunt trailing edge hydrofoil is used as the object of study, and the dynamic stall characteristics of the hydrofoil are investigated by using the transition model and the dynamic mesh method. It is found that the hydrofoil deep stall calculated by the transition model is delayed compared to that calculated without the transition model. The hydrofoil dynamic stall can be divided into four stages, initial stage, development stage, stall inception stage and deep stall stage. In the initial stage and the development stage, the lift and drag characteristics are influenced by the shedding vortex. In the stall inception stage and the deep stall stage, the lift and drag characteristics are influenced by the leading edge separation vortex and the trailing edge vortex. The increase of angular velocity and Reynolds number of the dynamic hydrofoil delay the onset of the deep stall while accelerating the boundary layer transition. The research in this paper has a certain guiding effect for the safe and stable operation of hydrodynamic machinery.
Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments
Authors: Magnoli M.V. , Necker J. 
Published: October 2022

Abstract
The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode.
The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation.
The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results.
The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.