High Head Research Articles

Work-life balance, motivation, and satisfaction as determinants of job commitment

This study evaluated the work-life balance, motivation, job satisfaction, and commitment levels of high school teachers in a city in Laguna, Philippines during the academic year 2022-2023. It narrowed the gap by testing if work-life balance, motivation, and job satisfaction predict job commitment level and if demographic profiles have moderation effect to the relationship between the predictors and outcome variable. Utilizing descriptive-correlational design, 262 teachers were surveyed through multi-stage sampling. Adapted questionnaires were utilized, content validated by experts, and verified through reliability testing. Mean, Standard Deviation, Spearman Rho, Ordinal Regression, and Moderated Regression were employed for data analysis. Results revealed that the teachers’ level of work-life balance, job satisfaction, and job commitment were high, while motivation was very high. Work-life balance had negative very weak correlation with job commitment, while job satisfaction had positive moderately strong correlation with job commitment. Motivation did not show any significant association with job commitment. Only job satisfaction had a significant effect on job commitment, whereas work-life balance and drive did not have significant effect. Age, years of teaching, and position had moderation effect, while sex had no moderation effect, on the link between work-life balance and job commitment, and between job satisfaction and teachers’ job commitment. Further, years of teaching years and position had moderation effect, while sex and age had no moderation effect, on the relationship between motivation and their job commitment. Results of the study had strong implications to the high school teachers, school heads and school administrators.

A Phase II Trial of Xevinapant in Combination with Post-Operative Cisplatin and Radiotherapy for High Risk Head and Neck Cancer

A Phase II Trial of Xevinapant in Combination with Post-Operative Cisplatin and Radiotherapy for High Risk Head and Neck Cancer

Study on Impeller Optimization and Operation Method of Variable Speed Centrifugal Pump with Large Flow and Wide Head Variation

The benefits of variable speed centrifugal pumps include high stability, a broad operating range, and adjustable input power. In water distribution systems, the pump units are increasingly using variable speed technology. The energy-saving features and operational stability of the pump station are directly impacted by the hydraulic performance and the operation strategy. In this study, CFD numerical analysis and model tests were adopted to design and evaluate the hydraulic performance of the variable speed centrifugal pump with large flow and wide head variation in Liyuzhou Pump Station. Under the premise of ensuring the wide head variation, the optimized centrifugal pump met the requirements of hump margin and efficiency in the high head zone and the cavitation margin in the low head zone. The test results demonstrated that the operational range of the variable speed centrifugal pump was successfully widened by reasonable hydraulic parameters selection and impeller optimization. The safe and efficient operational range of the variable speed unit was determined by means of taking the performance requirements of the pump’s maximum input shaft power, cavitation characteristics and pressure fluctuation into consideration. The scientific and reasonable operational path to meet the various operation needs was also investigated and determined for the pump station’s actual operation needs. A high efficiency, safe operation, and a simplified control logic were achieved by using the operational path, which makes it a reasonable potential guide for hydraulic design and operational optimization of variable speed centrifugal pumps with large flow and wide head range.

Experimental and numerical study of the gated and ungated ogee spillway

This study was carried out by combining numerical modeling and experimental measurements to investigate the hydraulic characteristics of ungated and gated ogee spillways with high head ratios. The primary objective was to validate the use of a numerical model as a complementary approach to the experimental model for simulating the hydraulic behavior of these spillways, providing a more comprehensive understanding of their hydraulic properties under varying conditions of head ratios and relative gate openings. An Acoustic Doppler Velocimeter (ADV) was used to measure the vertical flow velocity distributions, and ultrasonic sensor wave gauges were used to obtain the time history of the water level. The results of the measurements were compared with the simulation results using a model fitted with three different turbulence models (realizable k-ε, RNG k-ε, k-ω SST). The numerical model was developed using OpenFOAM. With respect to the ungated spillway, three different head ratios ranging from 1.4 to 4.6, which correspond to high head ratios, were investigated. Similarly, three different relative gate openings ranging from 0.5 to 2 were investigated for the gated spillway. The results of water surface profiles and velocity profiles suggest that the numerical and experimental models achieve a good agreement for sections located further away from the spillway. For the ungated spillway, the simulation results for the near-spillway sections are enhanced when the head ratio increases. Considering the velocity profiles and error analysis, the realizable k–ε model was found to best predict the results of the experimental model. A discussion about the discharge equation, velocity fields, pressure fields, and the corner separation zone is also included in this study.

Rotor–stator interaction investigations in variable speed reversible pump-turbine at higher head

Efficiency and grid stability can be improved by variable speed operation using doubly fed induction machine technology for pumped storage plants experiencing significant head variations. With the higher penetration of intermittent and variable renewable energy sources, viz., solar and wind, the grid may be stabilized by operating the reversible pump-turbines (RPTs) in off-design conditions. In a turbine mode, the RPT is more susceptible to fatigue and vibrations when operating at a higher head as a result of hydraulic instability generated by rotor–stator interaction (RSI); therefore, its performance becomes even more critical. The powerhouse structural components, including floors and columns, could experience intense vibrations because of this instability. Therefore, it is essential to investigate the RSI in the variable speed RPTs at the higher head. These investigations present the results of a numerical analysis of RSI and its associated pressure fluctuations in the variable speed RPTs at the higher head. The high-head scaled model of variable speed RPT was used, and the numerical simulations were executed by utilizing the shear stress transport k-ω turbulence model. The numerical analysis was performed at the best efficiency point and high-head operating conditions having optimized rotational speed. The results show that the main source of pressure fluctuations in the variable speed RPT at all operating conditions is RSI, where the dominant frequencies are blade passing frequency (9fn) and its harmonics. It is also found that the variable speed operation lowers the pressure fluctuations in the RPT.

Water distribution system modelling of GIS-remote sensing and EPANET for the integrated efficient design

Abstract Urban settlement depends on water distribution networks for clean and safe drinking water. This research incorporates geographic information systems (GIS), remote sensing (RS), and hydraulic modelling software EPANET to analyse and construct water distribution systems in Bota town, India. Satellite images and hydrological data have been utilized for the management of the Bota town's water supply network, sources to cater the demand for urban centres. EPANET simulates hydraulic behaviour in the water distribution system under different operating situations. EPANET simulation shows network leaks, low pressure, and substantial head loss. These findings have advised for water distribution system improvements by analysing network shortcomings. Booster pumps, new pipelines, and repairing of existing leakages are examples of such improvements. GIS, RS, and EPANET provided a comprehensive water distribution system study and more accurate and efficient improvement identification. This study emphasizes the necessity of new technologies in water distribution system analysis and design. The study solves Bota town's water distribution system problems of low pressure, high head loss, and leaks utilizing GIS, RS, and EPANET. The findings of this research can help in enhancing the water delivery systems in other towns with comparable issues.

Analysis of upper and lower nappe profiles of large orifice for the design of bottom and roof profiles of high head orifice spillway

Abstract Large orifices are constructed for dams to release water and sediments from reservoirs. Such structures are called submerged spillways. Numerous studies have investigated discharge coefficient, velocity coefficient, and head loss coefficient of large orifices; however, the literature lacks data on the upper and lower nappes of the jets from these orifices. In the present experimental study, the upper and lower nappes are investigated up to 80 m head at different gate openings. The observed minor deviation between the lower nappe profile and trajectory profile equation suggests sensitivity to different factors. The significant role of the coefficient of velocity, averaging at 0.926, highlights its impact on minor deviation. Subsequently, the impact of the solid bottom profile on the discharge coefficient and upper nappe profile are also examined. The results show improvement in discharge coefficient of a sharp-edged large orifice, which increased from 0.69 to 0.74. The results also indicate that the upper nappe profiles and United States Bureau of Reclamation (USBR) profiles are similar. The improvement in the upper nappe profile indicates the significant role of the solid bottom profile, which consequently was found to be helpful in defining the roof profile of an orifice spillway. .

Numerical Calculation of Static Strength Performance of Planar Gate Structures

As an important part of the ecological environment, rivers provide an important guarantee for the production and life in China. At present, domestic and foreign for the construction of the gate has been gradually shaped, hydraulic steel gate gradually developed as a hydroelectric power station high head, flood discharge flow of large gate type, the smooth opening and closing of the gate is related to the entire water conservancy hub and downstream of the safety of the residents' lives. For the safety of plane gate, this paper adopts Ansys software to establish a finite element model of plane gate, and calculates the most dangerous point stress of plane gate by considering its most unfavourable loading condition. At the same time, the service life of the allowable stress reduction was considered. The analysis results show that the planar gate meets the strength safety. The main beam is simplified into slender beam and thin-walled deep beam, and the calculation formula of slender beam in the mechanics of materials and thin-walled deep beam in the literature is used to calculate the positive bending stress in the mid-span cross-section of the main beam of the gate, and a comparative analysis is carried out with the results of Ansys, which shows that the positive bending stress in the mid-span cross-section of the main beam obtained by simplifying the main beam into a thin-walled deep beam is more close to the results of Ansys calculation. The results of this paper provide an important reference for the structural strength analysis of planar gates.

Sexual dimorphism and allometry in the head and body size of two viperid snakes (genus Vipera)

Sexual dimorphism in the size and shape of the body and head is the result of manifold selective pressures acting on organisms. In snakes, sexual size dimorphism is common and has been well-studied. However, intersexual differences in relative head size and shape have attracted far less attention. Similarly, the allometric properties of head shape and size in snakes are poorly known. Here, we analyse sexual dimorphism in two viperid species: European adder Vipera berus (Linnaeus, 1758) and Steppe viper Vipera renardi (Christoph, 1861). We measured body length, tail length and several head characteristics: head length, head width, head height, pileus length, interorbital distance and internarial distance. Our findings were that males and females of both species did not differ in body length (SVL), but that males tended to have significantly longer tails; there were also significant differences in head characteristics – males tended to have higher heads, and larger internarial and interorbital distances. The head dimensions displayed negative allometry when compared against SVL but when scaled against head length, dimensions like head height and head width exhibited positive allometry. We argue that these differences may be related to sexual selection and that the wider heads may also serve as antipredatory signal.

A Comparative Study on the Cam Relationship for the Optimal Vibration and Efficiency of a Kaplan Turbine

Kaplan turbines are generally used in working conditions with a high flow and low head. These are a type of axial-flow hydro turbine that can adjust the opening of the guide vanes and blades simultaneously in order to achieve higher efficiency under a wider range of loads. Different combinations of the opening of the guide vanes and blades (cam relationship) will lead to changes in the efficiency of the turbine unit as well as its vibration characteristics. A bad cam relationship will cause the low efficiency or unstable operation of the turbine. In this study, the relative efficiency and vibration of a large-scale Kaplan turbine with 200 MW output were tested with different guide vane and blade openings. The selection of the cam relationship curve for both optimal efficiency and optimal vibration is discussed. Compared with the cam relationship given by the model test, the prototype cam relationship improves the efficiency and reduces the vibration level. Compared to the optimal efficiency cam relationship, the optimal vibration cam relationship reduces the efficiency of the machine by 1% to 2%, while with the optimal efficiency cam relationship, the vibration of the unit increases significantly. This research provides guidance for the optimization of the regulation of a large adjustable-blade Kaplan turbine unit and improves the overall economic benefits and safety performance of the Kaplan turbine power station.

DEVELOPMENT OF NEW DESIGNS OF HORIZONTAL BULB HYDROTURBINES

The key aspects and methods of increasing the energy and operational efficiency of hydraulic turbine equipment at hydroelectric power plants areconsidered. A detailed analysis of directions for improving the main indicators characterizing the advantages of horizontal-type bladed hydraulicturbines has been carried out. Particular attention is paid to direct-flow rotary-blade hydraulic turbines with a horizontal axis of rotation for thehydraulic unit. These hydraulic turbines offer significant advantages over those using a spiral casing for water supply, including high throughput and awide range of operating pressures and flow rates. The focus of the article is on the advantages of direct-flow bulb hydraulic turbines and their potentialuse at high pressures. However, existing direct-flow hydraulic units operate at low heads of up to 25 m. Therefore, there is a need to develop newdesigns for these turbines to operate efficiently at higher heads up to 280 m, expanding the reliable operation zone. The paper examines new designsolutions for which Ukrainian patents have been received, aiming at the effective use of horizontal bulb hydraulic units. The text highlights theproblems of increasing the energy and operational performance of hydraulic turbine equipment at hydroelectric power plants, presenting importanttasks for researchers to optimize structures and improve efficiency. Recommendations for carrying out numerical modeling in CFD (ComputationalFluid Dynamics) programs are proposed to provide a detailed understanding of hydrodynamic processes in the flow parts of hydraulic turbines. Thepurpose of numerical modeling is to evaluate the efficiency and productivity of new hydroturbines in different operating modes. This includesanalyzing the pressure distribution, flow rate and other characteristics inside the turbine. The obtained data will allow to identify potential "weak"points and optimize the blading and other structural elements for maximum efficiency. This integrated research approach, including both experimentaland multiple methods, will contribute to the development of efficient and reliable hydroturbines in line with modern requirements for sustainableenergy development.

Modelling and optimization of a forced convection heat exchanger for Mars waste heat rejection for power cycle and cryocooling applications

A forced convection heat exchanger for waste heat rejection to the Martian atmosphere is modelled for both a power generation and cryogenic refrigeration application. The modeling is based on existing as well as recent, experimentally validated heat transfer and pressure drop correlations for low-Reynolds-number, moderate-Knudsen number finned tube arrays and represents the first detailed examination of optimal heat exchanger design and performance in this regime. These correlations were developed from heat exchanger performance data taken in Mars-like conditions and are described in a separate, companion work [1]. A heat exchanger model based on the effectiveness-NTU method is developed using these correlations and the heat exchanger geometry is optimized using an open-source solver to minimize the overall system mass for a range of candidate heat exchanger materials and heat transfer rates. The optimal heat exchangers generally consisted of shallow, staggered banks of 1–2 mm diameter tubes and 2–4 mm fin spacing, although in some conditions bare tube arrays were optimal. These geometries tended to be preferred due to their low relative pressure drop, a necessity given the power requirement of producing high pressure head in the thin atmosphere. Curve fits that capture the heat exchanger performance are generated based on the input conditions in order to develop a reduced order model that can be used to integrate the heat exchanger model with an existing recuperated Brayton cycle high-temperature gas cooled reactor (HTGR) power cycle model. This power cycle model is used to determine the impact of using convective heat rejection on optimal system mass and compare this approach to radiative heat rejection. For a 40 kWe power output, the optimal overall cycle mass is found to decrease by 78 % when using convective heat rejection compared to a radiator; this is due to the decreased mass of the heat rejection system as well as the lower optimal rejection temperature which results in a lower recuperator mass. The heat exchanger itself has a mass of only 37 kg, a frontal area of 12.7 m2, and requires 2134 W of fan power to operate. The system is shown to perform well over a wide range of Mars ambient conditions. A high-power liquid Oxygen (LOx) reverse Brayton cryocooler cycle is also modeled to determine the benefit of using convective heat rejection for in-situ resource utilization (ISRU) applications. Across a range of power source options and ambient temperatures, using a convective heat rejection system reduced total system mass by up to 43 % and frontal area by up to 95 % compared to a radiator and also reduced the mass-optimal cycle power draw by increasing the optimal cycle efficiency. However, the magnitude of the mass reduction depends strongly on the specific power of the electrical source; the forced convection system provides only a 7 % improvement over a radiator when coupled with a photovoltaic power source due to the increased power demand of the fan. Overall, this technology offers significant performance advantages over radiative heat rejection systems for waste heat rejection applications on Mars and therefore may significantly benefit future crewed Mars missions.

Investigation of a new reverse drainage construction and the pressure-reducing effect of a tunnel in a water-rich karst location

It is quite simple to create cracking, leaking, and other disasters in the tunnel during operation because water-rich karst tunnels are subject to the action of the high head. If the drainage is not timely, this results in high-pressure water collection around the tunnel lining. The study was conducted depending on Tongzi Tunnel to resolve the issue of water pressure encountered by water-rich karst tunnel lining under high head action and to lessen the issue of operational tunnel illness under long-term water pressure. The mechanical reaction of the number of reverse drainage holes and the size of pipe diameter at the raised arch under various water heads on the tunnel construction was studied using model testing in combination with numerical simulation analysis. It was discovered that using the traditional drainage system would subject the supine arch to extremely high-water pressure, which is often hard to efficiently remove. The major issue causing the elevated arch bulging tragedy is that water pressure in the elevated arch increases as head height increases. High water pressure in the raised arch may be efficiently dealt with using the suggested reverse drainage approach. The pressure reduction rate compared to the traditional drainage method achieved 13.6 % for the investigation of the fractured Tongzi tunnel reverse drainage holes, which had a total of five holes with a diameter of roughly 100 mm. Reverse drainage structures have the potential to save project costs while also realizing “point to point” pressure reduction at the elevation arch of the tunnel and have positive effects on total tunnel pressure reduction. The study's findings can serve as a guide for designing and building comparable water-rich karst tunnel constructions as well as for maintaining drainage systems while they are in use.

Co-adjustable guide vane and diffuser vane to improve the energy generation potential of an axial-flow pump as turbine

Operating an axial-flow pump as turbine (APAT) with a high head can be a cost-effective solution for energy recovery applications. However, axial-flow pumps are characterized by a low head, which makes it difficult for an APAT to achieve high efficiency. In this study, computational fluid dynamics–based numerical simulations were performed using steady and unsteady Reynolds-averaged Navier-Stocks equations and a shear stress transport reattachment modification turbulence model to investigate how the energy performance and operating range of an APAT can be improved under low-head conditions. The experiment was conducted to evaluate the accuracy and reliability of the numerical results. Adjusting the diffuser vane (DV) and guide vane (GV) were identified as candidate solutions. The adjusting mechanism was designed and presented in both 2D drawings and 3D model. Further simulations were performed to evaluate the effect of the clearances at the hub and shroud of the GV and DV. While the clearances at the GV had no adverse effect on the energy performance, clearances at the DV greatly reduced the energy performance because of the formation and growth of leakage vortex flows. Adjusting the DV improved the energy performance more than adjusting the GV. A co-adjustable GV and DV is a comprehensive solution that was found to increase the efficiency of the APAT by 40.15 % under low-head conditions and weaken vibration and noise by suppressing the separation flow in the GV domain.

Modeling of temperature profile during heating of fuel oil with water steam in a single-pass tubular heat exchanger

Heat-exchange equipment of various types makes up a significant part of technological apparatuses in the gas and petrochemical industries. This is explained by the fact that almost all technological processes in the refining and petrochemical industries (heating, rectification, drying, evaporation, etc.) are associated, one way or another, with the need to supply or remove heat. The purpose of this work is to analyze the heat exchange apparatuses used in petrochemistry, to compile a methodology for calculating heat exchange apparatuses, to review existing mathematical models of heat exchange processes, and to formulate the corresponding boundary value problems, and to develop a mathematical model that allows us to calculate the temperature profiles when fuel oil is heated with water vapor in a single-pass tubular heat exchanger along the length of the heat exchange apparatus. Within the framework of the conducted research mathematical models of the thermal field at heating of fuel oil with water steam in a single-pass tubular heat exchanger depending on the design, geometric dimensions and operating conditions of the heat exchanger were created and realized. The proposed mathematical models can be used to select the optimal parameters of the heat exchanger and the optimal fuel oil pumping rate in the heat exchanger, which will provide a sufficiently high heat transfer coefficient and not too high head losses.

EXPLORING THE ROLE OF SCHOOL HEADS IN MAINTAINING SCHOOL DISCIPLINE IN PAKISTAN CONTEXT

The study was descriptive and quantitative in nature. The population of the study comprised of girls’ high school heads, teachers and students at both public and private levels in District Lakki Marwat but only teachers were selected as a sample of study (n = 200 respondents, 100 Government High School and 100 Private High School teachers by applying a simple random sampling technique. Main objective of the study was to know perception of teachers regarding role of school heads in maintaining school discipline in Pakistan. A questionnaire of 5-points Likert scale was used for the data collection. Data were statistically analyzed through SPPS by using Means and Standard Deviation, and independent samples t-tests during analysis. Results and conclusions were drawn by revealing that the private School head has a more effective role and interest in maintaining school discipline than Government School head. Some recommendations were suggested that the government, policy or the decision makers, scholars & education department may play a significant role to keep in touch with school heads from time to time by conducting meetings, training & seminars with them to ensure quality education at school level under supervision & leadership of school heads.

Development of a Novel High Head Impulse Hydro Turbine

The Pelton turbine has been widely regarded as the most efficient hydro turbine for high-head applications. However, the Pelton turbine buckets, especially the area commonly referred to as the ‘splitter’, are highly susceptible to erosion, drastically reducing efficiency over prolonged periods of time. This paper demonstrates a novel turbine idea that has been validated through both computational and experimental methods. This turbine addresses the issues associated with the erosion of the splitter through a redesign of the Pelton turbine to remove the need for a splitter and therefore potentially reducing downtime due to maintenance. The computational fluid dynamics (CFD) simulation results show that the turbine is capable of efficiencies greater than 82% with room for further improvement. The practical experimental results also show efficiencies within 6% of an optimized Pelton turbine. The results from this study indicate that through further optimization this turbine design could provide a means to produce power outputs similar to conventional Pelton turbines, with the added benefit of lower maintenance costs.

Quality Criteria for Studies Assessing the Acute Effects of Heading: Results from a UEFA Expert Panel.

There is increasing concern regarding the effects of heading in football on brain health including cognitive, behavioural and neuromotor function, with research suggesting an association between repeated ball-head impacts and neurodegenerative disease. While longitudinal studies to determine the long-term consequences of heading are challenging, there have been short-term 'acute' studies conducted, with some studies lacking appropriate methodology to ensure valid results. The Union of European Football Associations (UEFA)established a panel of experts to determine methodological recommendations for the conduct of studies that explore the acute effects of heading (defined as a single session of heading conducted either in a laboratory setting or following match play or a training session). The aim of this panel was to create quality criteria for acute heading studies that will form part of the eligibility assessment when applying for UEFAresearch funding (although the criteria can be applied to the conduct of acute heading research more widely). This process was deemed necessary to counter studies with poor methodological quality that used heading trials that did not accurately represent player exposure to ball-head impacts through football practice and match play (such as small sample sizes, unrealistically high heading exposure, and a lack of consideration of confounding variables). The panel identified core design decisions that authors should consider when designing and conducting acute heading research, with key methodological requirements for each domain pertaining to participants, heading trials, confounding variables, statistics and dependent/target variables and their measurement. After two rounds of reviews, the final list of quality criteria was agreed by the panel and will be applied to the next round of UEFAgrant applications.

Fatigue life prediction of steel spiral cases in pumped-storage power plants: Factors to be considered

Pumped-storage power plants are playing an increasingly critical role in electricity grids by providing them with great operational flexibility. The flexibility requires frequent operation-mode switches of pump turbines, which leads to frequent variations in internal water pressure (IWP) resisted by steel spiral cases (SSCs). Such IWP variations are usually of large amplitudes due to their high design heads. Consequently, SSCs in pumped-storage power plants should be confronted with relatively high fatigue failure risks in their service lives. The specific objective of this study is therefore to identify key factors that significantly affect fatigue life prediction of SSCs in pumped-storage power plants. The authors perform a numerical simulation of a spiral case structure of the Liyang pumped-storage power plant on the finite element analysis platform ABAQUS, with its temporary-pressurization construction process carefully modeled using the complete simulation procedure. Then the finite element analysis results are used as input for fatigue analysis of the SSC on the ANSYS nCode DesignLife platform. The case study suggests that the concrete damage should be considered in fatigue life prediction of a SSC as the damage (even local) weakens the restraining effect on the SSC. The second major factor identified is the cyclic loading input strategy. The key to the loading strategy is to capture the essential features of IWP variations, i.e. to repeat the IWP loading roughly between the upper- and lower-reservoir heads. The study has also shown that the effect of the mean stress correction is less important than expected. The factors identified therefore assist in our understanding of the role of adequate fatigue design and analysis of SSCs in pumped-storage power plants.

The antipassive in Kirundi

The Kirundi verbal suffix -an is notably polysemous with three possible meanings: reciprocal, associative, and antipassive. The contexts in which the antipassive is ambiguous or distinct raise questions for -an’s syntactic and semantic analysis. In this paper, I examine new data which demonstrate that -an’s primary function is to add a relation between the verb and an implicit argument. These data support an analysis where -an is a specialized high applicative head (ApplREL) which adds the semantics of such a relation. The distribution of the different meanings is then accounted for by differential semantic selection and binding. This analysis thereby simplifies -an to its relational role and accounts for the ambiguous and non-ambiguous contexts that characterize the suffix. Additionally, this paper addresses various questions about -an’s antipassive status and potential issues with the applicative approach.