Water Head Research Articles

Comparison of Procedures to Combine Operating Zones of Multiple Units into Plant-Based Operating Zones

The hydropower unit commitment (HUC) is often indirectly considered by combining individual units in a hydropower plant into a plant-based generator to alleviate the dimensional difficulty in short-term hydropower scheduling of cascaded reservoirs. This work presents three procedures to combine operating zones of units in a hydropower plant into the plant-based operating zones, including an exhaustive method (M01) that enumerates all the possible combinations, a discrete method (M03) that investigates discrete values to see if they are in an operating zone, and a bound oriented method (M04) that explores new operating zones with an optimization solver. The procedures are compared with a previous one (M02) that merges the operating zones of a unit one by one in order. The experiments of the methods in 11 case studies involving a variety of hydropower plants reveal that the second method (M02) should always be recommended due to its strength, which is even more prominent than any other methods in dealing with large-scale problems, and errors occur when using interpolation to estimate the plant-based operating zones at a water head between two sampling water heads.

Enhanced Organic Contaminant Retardation by CTMAB-Modified Bentonite Backfill in Cut-Off Walls: Laboratory Test and Numerical Investigation.

Adding organically modified bentonite into impervious wall materials may improve the adsorption of organic pollutants. In this study, cetyltrimethylammonium bromide organically modified bentonite (CTMAB bentonite) was mixed with sodium bentonite and kaolin to obtain two materials, which were then used as cut-off walls for typical pollutants. Soil column consolidation tests, diffusion tests, and breakdown tests were conducted to study migration of organic pollutants in soil columns. The parameter sensitivity of pollutant transport in the cut-off wall was analysed by numerical simulation. The sodium bentonite mixed with 10% CTMAB bentonite and kaolin-CTMAB bentonite showed the greatest impermeability: with a consolidation pressure of 200 kPa, the permeability coefficients were 1.03 × 10-8 m/s and 3.49 × 10-9 m/s, respectively. The quantity of phenol adsorbed on sodium bentonite-CTMAB bentonite increased with increasing water head height. The kaolin-CTMAB bentonite column showed the best rhodamine B adsorption performance, and the adsorption rate reached 98.9% on day 67. The numerical results showed that the permeability coefficient was positively correlated with the diffusion of pollutants in the soil column. The quantity adsorbed on the soil column was positively correlated with the retardation factor, and the extent of pollutant diffusion was negatively correlated with the retardation factor. This study provides a technical means for the optimal design of organic pollutant cut-off walls.

Prediction of the discharge coefficient for the rectangular notch with different hydraulic and geometric properties

Abstract This study aims to investigate experimentally the variation of the coefficient of discharge Cd with the rectangular notch hydraulic and geometric parameters such as water head h, notch height p, notch width B, and notch thickness t. The results show that the coefficient of discharge Cd increases with an increase of h and B while it decreases with t. There are no changes in the variation of actual discharge Qact and consequently the discharge coefficient Cd with h for notch height p more than 6 cm. An empirical formula was developed based on the dimensional analysis principle that can be used to predict the coefficient of discharge Cd value for the rectangular notch with known hydraulic and geometric data (h, B, p, and t).

The development of sand erosion induced by shield-tunnel joint leakage

Sand erosion induced by shield-tunnel joint leakage is one of the most frequent catastrophes, causing ground collapses and tunnel failures. In this paper, a self-designed test device that considers differences in water head, burial depth and leaky joint characteristics was used to investigate sand erosion and void development. The experimental results show that the development of sand erosion has obvious temporal and spatial evolution characteristics. In the temporal dimension, sand erosion development can be divided into four stages: vertical erosion, cavity formation, coarse-particle skeleton distribution (CPSR) and steady seepage. In the spatial dimension, it can be divided into three regions: the stable zone, slip surface and eroded zone shape. It is found that the erosion zone can be described by a rotating ellipsoid and the scope of the erosion zone increases with increasing water head, whereas the influence of the burial depth is not significant. The influence of the invert leakage on the volume flow rate is also determined to be larger than that of the vault leakage and the volume flow rate rapidly increases when the size of the leaky joint exceeds the critical outlet size. Finally, a theoretical model based on the test results is proposed to predict the volumetric flow rate of sand erosion.

Control mechanism of the migration of heavy metal ions from gangue backfill bodies in mined-out areas

In the process of solid backfill mining, the leaching of heavy metal ions from the gangue backfill body in the mined-out area can pose potential risk of polluting water resources in the mine. Accordingly, based on the environment of the gangue backfill body, the migration model of heavy metal ions from the gangue backfill body was established to reveal the pollution mechanism of water resources by the gangue backfill body in the mined-out area. The main factors that affect the migration of heavy metal ions were analyzed, and prevention and control techniques for the leaching and migration of heavy metal ions from gangue backfill bodies were proposed. Research showed that the heavy metal ions in gangue backfill bodies were subjected to the coupled action of seepage, concentration, and stress and then driven by water head pressure and gravitational potential energy to migrate downward along the pore channels in the floor, during which mine water served as the carrier. The migration distance of heavy metal ions increased with time. According to the migration rate, the migration process can be subdivided into three phases: the rapid migration phase (0–50 years), the slow migration phase (50–125 years), and the stable phase (125–200 years). It was concluded that the leaching concentration of heavy metal ions, the particle size of gangue, the permeability of floor strata, and the burial depth of coal seams were the main influencing factors of the migration of heavy metal ions. From the two perspectives of heavy metal ion leaching and migration, prevention and control techniques for the leaching and migration of heavy metal ions from gangue backfill bodies were proposed to protect water resources in mining area. The present study is of great significance to realizing utilization of solid waste in mines and protecting the ecological environment.

A numerical model for hydrothermal transport in unsaturated freezing soils considering thermodynamics equilibrium

AbstractThe analysis of frost heave in unsaturated subgrade soils should consider the coupled movement of liquid water, vapor, and heat, accompanied by phase transition of water, vapor, and ice. In this paper, the equilibrium relationship of the three phases of water in soils was comprehensively considered, and the water head and vapor density were determined under frozen and unfrozen conditions from the perspective of thermodynamics. Based on that, the governing equations of mass and energy conservation were then derived and a new transient finite element model was developed, considering the behavior of the phase change and coupled hydrothermal transport under frozen as well as unfrozen conditions. Since the discontinuities between the frozen and the unfrozen zones may bring difficulties to the numerical solution, two kinds of smoothing techniques were proposed to solve the discontinuities at the phase transition interface, which guaranteed robust convergence and enhanced computational efficiency. The model proposed was verified by comparing with some available test results and applied to analyze the frost heave process of unsaturated subgrade under impermeable road pavements, demonstrating the model's accuracy and applicative prospect. It is revealed that the movement of liquid water and vapor in the frozen zones may still exist, and its mechanism and performance are different from that in unfrozen zones. The significance of vapor migration on the subgrade frost heave is also emphasized.

Energy dissipation characteristics of an in-chamber longitudinal culvert system with three-layer side ports designed for a large-scale lock with 60m water head

With the rapid development of the water transportation industry in China, the scale of ships navigating in the inland waterway is increasing. However, the water head formed by dams is very high, especially for the hydroelectric projects constructed in the upper mountain river. Therefore, it is critically urgent to build several high-head and large-scale locks. Moreover, when the water head is increased to 60 m, huge water energy could be generated and then introduced into the corresponding lock chamber if the valve operating time is limited. This paper presented the in-chamber longitudinal culvert system with three-layer side ports to efficiently dissipate the water energy to ensure safe mooring conditions for ships during a lock operation. A three-dimensional CFD model for 1/4 local region of the corresponding chamber was developed to predict its hydraulic behavior. The numerical simulations were conducted to examine the effect of the vertical spacing between side ports on the energy dissipation result. Results showed that good energy dissipation performance was gained when the relative vertical spacing was set B/D=0.25 (B is the vertical spacing between side ports, D is the inner height of the culvert). Furthermore, the energy dissipation mechanism of this arrangement was presented based on the results of a three-dimensional hydraulic characteristic. In addition, the corresponding dissipation result of the present arrangement was compared with those of the single-layer and two-layer side ports. The dissipation performance of the present design was found to be the best if all the side ports’ cross-section area of each arrangement keeps the same.

Updated mortality estimation formulae for salmonids passing through Francis turbines at hydropower plants

Downstream migrating fish can be strongly affected by hydroelectric facilities. To set up adapted mitigation measures, it is important to identify these impacts (e.g. induced mortality rates). For Francis turbines, two mortality prediction formulas, developed in 1989 and updated in 2000, are currently used in France for salmonids according to turbine characteristics and fish size (Larinier and Dartiguelongue, 1989, updated by Bosc and Larinier, 2000). However, their use is limited when some parameters are unknown, such as turbine speed. Moreover, the updated version of can be criticized because of its unpublished development procedure and its unknown predictive power. The main purpose of this study is to update the existing formulae to meet the following objectives: (1) a transparent development procedure, (2) formulae simplification, (3) the use of simple (usually the best-known) turbine parameters, and (4) a maximization of the predictive power and an assessment of prediction errors. Based on data from 73 in situ mortality tests available in peer-reviewed and ‘grey’ literature, we developed two new formulae to estimate salmonid mortality rate in Francis turbines. The first one uses turbine peripheral speed, diameter and fish size (correlation between predicted and observed mortality rates r = 0.89, and root mean square error RMSE = 0.11). The second one is based on usually known parameters: turbine discharge, water head and fish size, to allow a broader applicability (r = 0.89, RMSE = 0.10). This study comforts the validity of previous formulae and provides two new ones allowing a satisfactory precision in the estimations.

The Attractive Ability Of Types Of Attractants Against Aedes sp. Mosquito Eggs Using Ovitrap

An attractant is a substance that attracts insects (mosquitoes) either chemically or visually. To prevent the spread of dengue, various methods have been employed, one of which is using ovitraps containing attractants. This study aimed to determine the number of Aedes sp. mosquito eggs based on different attractants. The research was experimental with a one-shot case study design, comparing various attractants and their effectiveness in attracting Aedes sp. mosquito eggs. The findings showed that the type of attractant significantly affected the presence of mosquito eggs, with a p-value of 0.000 (<0.05), allowing further analysis using a post hoc test. The post hoc test revealed significant differences between no attractant and shrimp paste water immersion, no attractant and shrimp head immersion, and no attractant and a brown sugar and yeast mixture. Significant differences were also found between shrimp paste soaked water and brown sugar and yeast mixtures and between shrimp head attractants and brown sugar and yeast mixtures. Shrimp head immersion attractant had a p-value of 0.199 (>0.05), indicating no significant difference compared to other attractants. Among the various attractants tested, shrimp paste soaking water and shrimp head soaking water were the most effective. It is recommended that communities use ovitraps with shrimp paste soaking solution to reduce the Aedes sp. mosquito population around homes, as these materials are relatively easy to obtain and ovitraps can be made using repurposed plastic cups.

ANALYSIS OF NON-FINANCIAL BUSINESS PERFORMANCE FACTORS IN DRINKING WATER COMPANIES IN ACEH, INDONESIA

This study aims to analyze factors of non-financial business performance in drinking water companies in Aceh province, Indonesia. The subjects of this study were the regional drinking water companies in Aceh, totaling 210 people, aimed at the directors of the regional drinking water companies and heads of sections. The technique used was convenience sampling, while the data were analyzed using Pearson's correlation and multiple regression, and bootstrapping. This study also aimed to determine the significant positive direct effect and the indirect influence of human capital factors, environmental uncertainty, wealth, and organizational innovation on the performance of the Regional Drinking Water Company in Aceh Province. The results of the analysis obtained Composite Reliability values for all constructs are excellent, namely > 0.70, meaning that all construct indicators are reliable or meet the reliability test: (1) human resources with Composite Reliability is 0.862; (2) Environmental Uncertainty with Composite Reliability is 0.801; (3) Ambidexterity with Composite Reliability is 0.803; (4) Coping House Indicated Wealth Resources with Composite Reliability is 0.864; (5) Organizational Innovation with Composite Reliability of 0.876; and (6) performance with Composite Reliability of 0.879. The implication is that there is a positive and significant direct effect among the following variables: Human Capital, Environmental Uncertainty, Ambidexterity, Resource–Induced Coping Heuristics (RICH), and Organizational Innovation on the Performance of Employees of the Regional Drinking Water Company in Aceh Province. Keywords: Human Capital, Environmental Uncertainty, Ambidexterity, Resource–Induced Coping Heuristics, Organizational Innovation DOI： https://doi.org/10.35741/issn.0258-2724.58.1.18

Study on Discharge Coefficients of Drain Orifices in Closed Cavities

The numerical method was used to simulate the discharge flow, and discharge coefficients were obtained. The main factors affecting the discharge coefficient of orifices were analyzed by dimensional analysis, and the empirical formulas for calculating discharge coefficient were fitted. The results show that when the water head height is less than 200mm, the discharge coefficient decreases with the increase of head height. When the water head height is more than 200mm, the discharge coefficient is stable around 0.61. The discharge coefficient with different thickness diameter ratio shows two different forms: the orifices with small thickness diameter ratio show thin orifice flow characteristics, and the discharge coefficient is about 0.6; the orifices with large thickness diameter ratio show thick orifice flow characteristics, and the discharge coefficient is about 0.8.

Experimental study of the surge- and bore-induced impact pressure on a vertical wall and its foundation

Both surge and bore impacts could lead to the failure of coastal structures. Nevertheless, differences between the surge- and bore-induced hydrodynamic impact processes on a vertical wall are still unclear. Meanwhile, investigation of the bed pressure features during the wall impact is also rare. In this study, a series of dam-break experiments were conducted to specify the hydrodynamic characteristics of the surge and bore impact pressure on a vertical wall and its foundation. In the experiment, same initial water head was applied with five different initial downstream water levels (IDWLs). Temporal variations of the surge/bore impact pressures at four elevations on the wall and four positions along the bed were recorded. The surge induced maximum water height on the wall is larger than the bore-induced one, which decreases with the increase in the IDWL. With the increase in the IDWL, the initial peak impact pressure gradually decays owing to the slowing down of flow velocity and the significant air entrainment at the bore front. Regarding the initial peak pressure and its rise time, it is confirmed that the initial surge impact pressure is sensitive to the wall elevation, whereas it is relatively uniform along the wall bottom region for the bore impact pressure. As for the measured bed pressure, the initial impact zone induced by the secondary flow near the wall and the falling impact zone caused by the falling down of water mass from the splash-ups away from the wall are identified, showing different hydrodynamic features.

A Study of Real-Time System of Water Distribution Networks: Case study of Hat Yai Waterwork Plant, Songkhla Province, Thailand

This study aims to optimize water distribution in a water supply network. One of the most important objectives for every waterwork plants is to minimize water loss in supplying system. The water supply network in Thailand is underground work and most of them have used for many years. Leakages are normally met especially when high pressure are required from demand side. This research will classify 13,580 households living around Hat Yai waterwork plant of Provincial Waterworks Authority in Hat Yai branch in Songkhla province as a demand side and put 5 water sources of Hat Yai district as a supplied side. EPANET program is used to simulate water distribution networks and SCADA application is selected to design controlling system. The result shows that water supply at the Hat Yai waterwork plant should be at least 48 meters to upper Hat Yai zone, however, booster pump may help reducing original water head to 40 meters into high-level areas. Hat Yai waterwork plant decreases energy consumption from pumping processes and also reduce water loss in water distribution system.

Experiments and Fluent–Engineering Discrete Element Method-Based Numerical Analysis of Block Motion in Underwater Rock-Plug Blasting

Underwater rock-plug blasting is a special blasting technique for excavating underwater inlets. In the process of rock-plug blasting excavation, the blasting-block movement from the difference in water pressure inside and outside the tunnel is one of the key factors for successful construction. Laboratory underwater rock-plug blasting experiments were conducted using small explosive charges, and a high-speed camera was adopted to observe and study block motion. Then, numerical simulations were conducted for the model experiment based on the Fluent and Engineering Discrete Element Method (EDEM) coupling program developed using the user-defined function (UDF) interface to reveal the mechanism underpinning the penetration of underwater rock-plug blasting. The results showed that the process of block motion in underwater rock-plug blasting can be divided into two stages. In the first stage, broken blocks move to two sides along the axis of the rock plug under the blast load. A blasting crater is formed on the downstream end face of the rock plug under the effects of the free face, while the upstream end face is loosened, or blocks are ejected under the influence of the water pressure. In the second stage, blocks flow to the broken-rock pit under the effects of water scouring and gravity, and, finally, the rock plug is penetrated. The larger the head of water and the opening angle of the rock plug are, the better the penetration effect for the rock plug is. The Fluent–EDEM coupling algorithm was in good agreement with the experimental results in terms of the rock-plug blasting effect and the velocity curve of the blocks, indicating that the coupling method had a favorable effect in simulating the interaction of blocks and water during underwater rock-plug blasting. The findings are expected to promote the application and popularization of the rock-plug blasting technique and can provide a reference for rock-plug blasting in water-intake and water-diversion projects.

Failure analysis and zoning control of water gushing in foundation pit

A water gushing failure of foundation pit in sand layers and deep confined aquifer in Nanjing, China, is presented in this study. During foundation pit excavation, the water gushing through the waste pile hole below the pit bottom caused local collapse failure and crown beam fracture in the southeast corner of the foundation pit. A series of urgent remedial measures were adopted to prevent the gushing from further developing, however, none of them worked until artificial recharge was proposed. The reasons for the water gushing and the effect of the urgent remedial measures are analyzed and discussed in this work. The gushing channel along the waste pile without effective plugging was established by the high level of confined water head from deep confined aquifer to pit bottom, which was the main reason for the gushing. Based on site reinvestigation and monitoring results, the soil around the foundation pit was divided into three disturbed areas: mild disturbance zone (MDZ), severe disturbance zone (SDZ), and collapse zone (CZ). The reinforcement and dewatering measures were proposed for different disturbance zones after rechecking the original design scheme with the disturbed soil parameters. Finally, the lessons learnt are summarized from the incident and provides practical experience and guidance for similar foundation pit projects.

A Coupled Darcy-Forchheimer Flow Model in Fractured Porous Media

Aiming at nonlinear flow in fractured porous media, based on the finite volume method, the discrete equations of Darcy flow in porous and Forchheimer flow in fracture were derived, and a solution method for coupling flow is proposed. The flow solution by the proposed method for single fracture and intersecting fracture is verified against Frih’s solution. Based on this method, nonlinear flow behavior for fractured rock deep-buried tunnels under high water heads was discussed. The results show that the hydraulic gradient of surrounding rock is characterized by “large at the bottom and small at the top”, with a maximum difference of 2.5 times. Therefore, the flow rate at the bottom of the tunnel is greater than that at the top. The fracture flow rate along the flow direction is also greater than that in the vertical flow direction, with a maximum difference of 60 times. The distribution homogeneity and density of fracture are the most important factors that affect the hydraulic behavior of fractured rock tunnels. The more fractures concentrated in the direction of water pressure and the greater the density, the greater the surrounding rock conductivity and the greater the flow rate of the tunnel. Under this condition, the water-inflow accident of the tunnel would be prone to occur. The research results provide a reference for the waterproof design and engineering practice of fractured rock tunnels.

Analisa kebocoran line warming up high pressure boiler feed pump menggunakan metode root cause and failure analysis di Pembangkit Listrik Tenaga Gas & Uap Grati

The reliability of the Grati Gas And Steam Power Plant equipment is highly maintained to support the operational readiness of the generation. The feed water system at the Grati Gas And Steam Power Plant is one of the most important factors, especially in the feed water pump equipment. One of the pumps that is highly reliable is the High Pressure Boiler Feed Water Pump which is used as a tool for supply feed water to the Heat Recovery Steam Generator. However, from the recap data of disturbances in the Grati Gas And Steam Power Plant, leaks often occur in the system, precisely in the line warming up which serves to provide flow to the standby High Pressure Boiler Feed Water Pump and comes from the backflow of the High Pressure Feed Water Header to the Discharge side of the pump. Analysis related to the leak is very necessary in order to minimize losses due to the occurrence of the disturbance using the Root Cause And Failure Analysis method to eliminate the main disturbance causing the leak. The research variables used include the independent variable: regulating the pump discharge opening, the dependent variable: flow rate and valve warming up opening and the controlled variable: standby pump temperature and pump operating temperature. By conducting a series of trials setting the discharge valve opening of the High Pressure Boiler Feed Water Pump starting from 80%, 85%, 90%, 95% and 100%. The results of these tests can be concluded that the greater the opening of the pump discharge valve, the higher the speed and flow rate, while the pump discharge pressure will decrease.

Effect of subgrade on leakage through a defective geomembrane seam below saturated tailings

Experiments are conducted to quantify leakage through saturated tailings (with 30% fines) underlain by a geomembrane with either a 100-mm-length knife cut slit defect or a 110-mm-length defective extrusion seam. Various subgrades, a poorly graded gravel (GP) with or without nonwoven geotextile (450 or 1420 g/m2) above, a well-graded gravel (GW), and a poorly graded sand (SP) are evaluated. Test results show that leakage through the slit defect and defective seam increase with the subgrade coarseness and subgrade unevenness. The inferred upper and lower bounds opening width of a slit based on the measured leakage increase with the overburden pressure and are categorized for each subgrade. Indentations in the overlapped defective extrusion seam area arise from both the entrapped materials inside the overlap and the materials underlying/overlying the geomembrane, incrementally inducing a greater interface transmissivity with the increasing stress. Overlain by tailings at total overburden pressure of 510 kPa and water head of 35m, leakage through the slit defect is 1.1L/day for SP, 2.2L/day for GW, 2.6–3.3L/day for both GP and uneven GW; leakage drops to 0.8L/day with a geotextile layer directly above the GP; leakage through the defective extrusion seam is 0.4L/day for SP and 0.8L/day for GW.

HYDRAULIC DESIGN AND SIMULATION OF DIFFERENT COMBINATIONS OF BLOCKS OPERATING IN TRICKLE IRRIGATION

There is little open-source software for trickle irrigation design and none of it is designed to simulate operating conditions on a specific hydraulic network already assembled in the field. Farmers employing trickle irrigation frequently need to change irrigation block operations over the years (parcel combinations), because of plant renovations in certain areas of the irrigated field or the adoption of precision irrigation. This work free software developed using Visual Basic® language that is able to simulate different block combinations of parcels, taking into consideration the pump parameters of flowrate, pressure, power requirements and efficiency and the main hydraulic network parameters of water speed, pressure and head loss. The software we developed was applied to a trickle irrigation system for citrus growing. The equations used to calculate head loss were Hazen-Williams and Darcy-Weisbach, and users could choose between these two equations depending on their application. The software worked efficiently for making the hydraulic calculations, providing simulations that graphically assisted users in choosing which combination of operation parcels (block combinations) and pump parameters (rotation speed and impeller diameter) for optimal operation of the irrigation system. The program ensured that the pressure along the irrigation network was compatible with the nominal operating pressure of the pipeline and safety valves.

A new draft tube shape optimisation methodology of introducing inclined conical diffuser in hydraulic turbine

A grid-connected integrated system incorporating cascade hydropower, solar/photovoltaic, and wind power requires a hydraulic turbine to operate frequently under off-design conditions, resulting in a series of instability issues, such as pressure fluctuations. In this study, a new draft tube shape optimisation methodology of introducing an inclined conical diffuser for a Francis turbine was proposed to eliminate vortex rope and mitigate the associated pressure fluctuations. Four different inclination angles in the range of 0°–16.8° were considered to investigate the effectiveness of the modified draft tube. The results demonstrated that the maximum pressure fluctuation amplitude within the draft tube was 1.64% times the equivalent pressure under the rated water head for the modified draft tube, showing an 18.4% reduction compared with that of the traditional case. In addition, an overall index of Pdegree was proposed to quantitatively measure the mitigating impact of this type of modified draft tube on the pressure fluctuations. When the inclination angle is 16.8°, the Pdegree on the downstream and upstream sides decreases by 34.1% and 23.1%, respectively, when compared to the traditional draft tube. Based on a comprehensive comparison of the vortex rope, instantaneous axial velocity, and pressure distribution, the mitigating mechanism of the modified draft tube was further explored. Finally, further optimisation direction was pointed out by means of entropy production theory.