Discharge Tunnel Research Articles

Effects of Air Vent Size and Location Design on Air Supply Efficiency in Flood Discharge Tunnel Operations

Effects of Air Vent Size and Location Design on Air Supply Efficiency in Flood Discharge Tunnel Operations

Effects and interactions of scouring abrasion and external sulfate attack on deterioration of lining concrete: Experiments and preliminary modeling

The conventional tests of dynamic water scouring abrasion (DWSA) on lining concrete for hydraulic discharge tunnel do not consider concomitant sulfate ions that may exist in aggressive aqueous environment and alter the mechanisms and deterioration kinetics of DWSA. In this study, an abrasion-erosion testing system based on natural conditions of the environment has been used to evaluate the influence of volumetric concentration of sediment and the velocity of the scouring flow on abrasion-erosion synergism of lining concrete. To this end, lining concretes were subjected ambient conditions similar to that in drainage tunnel, spillway and stilling basin geographic locations, while implementing abrasion and accelerated external sulfate attack (ESA) test alternately prior to various physical and microstructural analyses. A dynamically decrease of properties on a macroscopic scale was observed, as well as an increase of precipitated ettringite, leached calcium, harmful pore (>200 nm) and sheeted radial micro-cracks, in lining concretes exposed to sediment-laden flow simulated for discharge, which were involved in the co-occurrence of complex degradation mechanisms in specimens exposed to DWSA-ESA. Results indicate that a water body with a high-velocity flow and a high sediment concentration significantly accelerates the sulfate attack on concrete. In contrast, a water body with a low-velocity flow and a low concentration of sediment alleviates the traverse of sulfate ions in concrete due to the inside-out pressure potential. The implications of these synoptic findings may informatively improve the design of abrasion and erosion resistance for concrete when dual exposure to ESA and abrasion is occurred in hydraulic tunnel engineering.

Blominmäki wastewater treatment plant’s sewage tunnels: Challenging connection of a vertical shaft to the existing operating offshore tunnel.

The sewage tunnels of the Blominmäki Wastewater Treatment Plant (WWTP) consist of approximately 20 kilometers of inlet and discharge tunnels, access tunnels and shafts. The most challenging and technically critical part of this project was the connection of the operating offshore tunnel of the old treatment plant with the Blominmäki discharge route, through a vertical shaft. Lack of information regarding the exact location, the shape and the geological conditions of the existing tunnel called for an accurate excavation design to avoid a potential tunnel collapse and rock blocking or massive waterflow during breakthrough. An additional complexity related to the continuous operation of the tunnel in question, as both non-stop flow of treated wastewater and cooling water of the nearby heat and powerplant, had a huge impact to the ways that all work phases were carried out. All parts involved, including the clients, the contractor and a variety of consultants cooperated in order that one of the most demanding shaft excavations in Finland be carried out successfully. This paper aims to present an overview of the related challenges, along with the detailed design, risk assessment and respective mitigation measures, information about problem solving and lessons learned during the execution.

Initial Support Quality Inspection and Evaluation Standard for Diversion Water Discharge Tunnel of Sanhe Reservoir Project

Initial Support Quality Inspection and Evaluation Standard for Diversion Water Discharge Tunnel of Sanhe Reservoir Project

Deformation and simulation analysis of slope at outlet of flood discharge tunnel

The monitoring data of slope deformation are collected, the dynamic change and development trend of displacement are analyzed, and the deformation laws of different elevation parts are counted. Three-dimensional numerical model of the outlet slope of spillway tunnel is established by finite element method, and excavation simulation analysis is carried out. The results show that after the slope excavation is completed, the plastic zone gradually increases, mainly in compression-shear failure, and tensile-shear failure exists on faults, slope surfaces and local rock mass. The field measured deformation data show that the horizontal cumulative displacement and vertical cumulative displacement increase slowly, both exceeding 200 mm, and the horizontal displacement is larger than the vertical displacement. The monthly dynamic changes of horizontal displacement and vertical displacement are basically fluctuating within 5 mm. Through the combination of deformation measurement and simulation, the displacement variation law of slope and the distribution characteristics of plastic zone are analyzed, which can provide guidance for on-site slope stability prediction and safety construction.

Application of mathematical model on deposition study of pumped-storage power reservoir

Sediment deposition can cause a reduction in reservoir capacity and hydro-mechanical abrasion of pumped-storage power stations (PSPSs). To increase the operating efficiency and service life of PSPSs, sediment deposition in the process of reservoir water transfer needs to be addressed. Combined with hydrodynamics, reservoir sedimentation theory and a numerical model, a two-dimensional sediment model of the lower reservoir of Tianchi PSPS was established. Considering the characteristics of the upper and lower reservoirs of this PSPS, water and sediment exchange between the reservoirs was realised by setting source and sink terms. The process and distribution of sediment deposition were analysed over 50 years. Sediment deposition in the lower reservoir of the PSPS was found to be 0.5–1.8 km in front of the dam and triangular. The main stream of sediment-carrying flow could be moved from the right-hand channel to the sediment discharge tunnel and spillway by setting up a sediment discharge trench. The average sedimentation thickness of the reservoir during 10 years of operation was about 0.8 m with a sediment intercept weir (SIW) established, while it was more than 4.2 m in the main stream area outside the SIW. For operation of 50 years, these values were 3 m and 10 m, respectively. The SIW effectively reduced deposition near the inlet (outlet) of the PSPS, the amount of sediment passing the machine and deposition to the dam front. The results provide a reference for simulations and preventive measures of sediment deposition in PSPSs.

Study on the Shape of the Aerator of High-Head Discharge Tunnel with Mild Bottom Slope

Due to the high flow velocity and easy cavitation of high-head drainage tunnels, it is usually necessary to set up aeration facilities. In particular, when the bottom slope of the tunnel is mild, the aeration facilities often have problems such as difficulty with air intake, short cavity, and serious water accumulation, which aggravate the risk of cavitation damage. In this paper, based on the Rumei hydropower station and the Gushui hydropower station, a method combining theoretical analysis and model testing is used to solve the connection problem between the aeration facility and the 3% mild bottom slope of a tunnel body, and the aeration facility shape of “lifting ridge + flat (mild) slope + steep slope” is put forward. The research shows that the steep slope section can smoothly connect the water flow over the cantilever, reduce the jet impact angle, prevent the water from backtracking, and produce a long and stable cavity in the flat (mild) slope section. The aeration concentration along the bottom of the tunnel is higher than 3% at 140 m over the top of the dam. The aeration effect of this type is better, and it can provide effective long-distance protection for a drainage tunnel with high head and a mild bottom slope.

Effects of air bubble quantity on the reduction of cavitation erosion

Dam observations indicated that low-air concentration can avoid cavitation erosion. In the present study, a device with micron-scale orifice diameters was designed to introduce air bubbles in water, to study the effects of the reduction of cavitation erosion in an ultrasonic environment. The experimental results showed that low-air concentration imposes prominent effects on the development of cavitation erosion and can significantly reduce the effect of cavitation on the structural damage. If the air concentration and bubble quantity reach certain values, the erosion reduction effects do not change as the air conditions are altered. Based on the analysis of the average erosion reduction efficiency of a single-air bubble, aeration and erosion protection for the wall surface can be achieved. Moreover, a discharge tunnel with high-head and high-speed water flow is analyzed. With a high velocity and low-air concentration flow in the open channel, no cavitation erosion on the tunnel structure was observed. Combined with the present experimental results, this shows that the effect of the aeration erosion reduction can be evaluated and analyzed if the air bubble quantity meets the erosion reduction requirement. Consequently, the effect of aeration can be recognized effectively by number of air bubbles, and can promote the design and analysis of the aeration erosion reduction in hydraulic engineering.

Correction and laboratory investigation for energy loss coefficient of square-edged orifice plate.

A lot of studies have shown that the hydraulic characteristics of orifice plate are mainly controlled by its contraction ratio, but the thickness of square-edged orifice plate also has many impacts on energy loss characteristics. The primary objective of this study was to investigated the effects of square-edged orifice plate thickness on energy loss characteristics. In this paper, the effects of square-edged orifice plate thickness on energy loss characteristics are investigated by numerical simulation using CFD. Orifice plate discharge tunnel is axial symmetric, two dimensional numerical simulations of orifice plate discharge tunnel flow was used. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed. The results of the present research demonstrate that energy loss coefficient decreases with increase of the orifice plate thickness. The results of model experiment are consistence with the results calculated by using rectified equation in present paper. The CFD simulations and Model experiment for the flow through an orifice plate are carried out. For square-edged orifice plate energy dissipater, the relative orifice plate thickness T/D has remarkable impacts on its energy loss coefficient ξ. The Traditional equation (8) is corrected by numerical results. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed and this equation is available in the condition of d/D = 0.4-0.8, T/D = 0.05-0.25, and Re > 105(Re is Reynolds number). Comparing with the physical model experimental data, the relative errors of equation (9) is smaller than 15%.

Research on the Selection and Optimization of Horizontal Swirling Energy Dissipation Flood Discharge Tunnel

Through the study of the diameter control of the horizontal swirling efficiency shaft and the swirling tunnel and the cross-section of the aeration sill, a flood discharge tunnel with a scale of about 100 meters and a discharge volume of more than a thousand is obtained. The horizontal swirling energy dissipation type is combined with the diversion tunnel. At the time, the diameter of the shaft can be controlled and determined according to the average velocity of 15-20m/s; the diameter of the swirling hole can be calculated according to the empirical formula D=(Q2/g)0.2. In order to reduce the impact of water flow pulsation on the concrete lining and surrounding rock of the shaft, the flood discharge tunnel inlet should adopt a submerged flow pattern. Its discharge capacity will be controlled by the cross section (A) of the aeration sill in the shaft and the inlet section (σ) of the swirl chamber. When the slope of the aeration sill is 1:2.5 to 1:3.0, σ/A should be controlled at 1.05. The research results can provide a reliable basis for the design of horizontal swirling energy dissipation.

Study on Structure Design of Generator of Flood Discharge Tunnel with Level Swirling Flow

Through the design of the Generator of the spillway tunnel, the safe operation efficiency of flood discharge tunnel with the level swirling flow is further improved. This paper takes the horizontal swirl spillway tunnel of Gongboxia Hydropower Station on the Yellow River as an example. First, the project hub facilities of the Gongboxia Hydropower Station are introduced. Moreover, the design of the gradient section and the spinning chamber section in the Generator is also studied. Based on the calculation scheme of structural mechanics, the internal force of the structure under various load combinations such as external water pressure and internal water pressure is calculated. According to Design Codes For Hydraulic Concrete Structure, the structural reinforcement is computed. These provide the basis for the design of the flood discharge tunnel with level swirling flow of large hydropower engineering facilities in Northwest China.

Stability Monitoring and Analysis of High and Steep Slope of a Hydropower Station

Slope deformation and failure are major challenges for hydropower station engineering. Taking the left bank slope at the exit of the flood discharge tunnel of the Wudongde Hydropower Station in China as an example, the deformation mechanism of the high-steep rock slope was studied. The height of the slope is about 200 m, which is affected by slope excavation, rainfall, and atomized rain. The results of multipoint displacement meters, surface deformation monitoring, and anchoring stress meters showed that the deformation and deformation rate of the slope have increased dramatically. Through the comprehensive analysis of the slope, it is found that the overall lithology of the slope is poor, the excavation disturbance causes the redistribution of the stress in the slope, and the excavation surface is relatively steep, which provides space for the deformation of the slope rock mass. Unloading relaxation leads to a large number of new fissures in the slope rock mass. These new fissures and fault fracture zones provide convenient conditions for rainfall and atomized rain infiltration. The rainwater infiltrated along the slope surface, formed the seepage field in the slope body, and weakened the rock-soil mass parameters. Meanwhile, saturated runoff is formed on the slope, causing large deformation of the slope rock mass. However, the migration of water in the slope has a time effect, and its influence on the stability of the slope also has a time effect. It is difficult for traditional monitoring methods to monitor the resulting changes in internal sliding force of the slope. Therefore, a remote monitoring and early warning system for landslide anchor cable force was introduced to monitor the slope stability changes caused by the impact of water flow and rainfall infiltration, which provided a reasonable and scientific reference for subsequent slope construction.

Characterization of Microstructure and Composition of Plasma Electrolytic Oxide Film Formed on AZ31 Mg Alloy

Magnesium alloy has been widely investigated as a biodegradable implant material owing to its unique properties to degrade spontaneously in human body fluid without causing toxicity. However, the degradation rate needs to be controlled. An effective way to lower down the degradation rate of Mg alloy is by coating with plasma electrolytic oxidation (PEO) technique. In this research, the microstructure and mechanical hardness of the PEO film formed on AZ31 were investigated. The film was prepared under a constant current of 400 A/m2 in the Na3PO4 solution at 30°C. The voltage-time curve showed an immediate increase of current during the first 25 s before reaching a steady-state voltage of 150 V. The spark discharge revealed as white micro discharges. The film formed for 3 min exhibited a high surface roughness with a large variety of thickness in the range of 1-20 µm. The film contained pores and cracks. The big pores with diameter size 10-20 µm were formed as a result of gas entrapment, while the small pores with a radius of 1-3 µm were associated with the discharge tunnel during the PEO process. The X-ray diffraction pattern indicated that the film composed of crystalline Mg3(PO4)2.

Numerical investigation of air demand by the free surface tunnel flows

Air supply to free-surface water flows in tunnels is a key safety issue for high-head dams. The present study analyses the effects of approach water velocity and area residual of tunnel cross-section on air demand, using the volume of fluid (VOF) method in combination with the k–ε turbulence model. For a tunnel area residual less than 0.4, the attenuation of air velocity above the free-surface water flow decreases with an increase in water velocity. For larger area residuals, the air velocity distributions remain unchanged. The maximum ratio of mean air velocity to water velocity is obtained if the relative area residual is equal to 0.4. A relationship for the mean air velocity above the water flow is suggested. Without considering the flow aeration condition, the numerical simulations reproduce the air demand in the tunnel flow normally with an average error of ±25%. These results provide reference for air ventilation design of flood discharge tunnels.

Numerical Simulation and Risk Assessment of Cascade Reservoir Dam-Break

Despite the fact that cascade reservoirs are built in a large number of river basins nowadays, there is still an absence of studies on sequential embankment dam-break in cascade reservoirs. Therefore, numerical simulations and risk analyses of cascade reservoir dam-break are of practical engineering significance. In this study, by means of contacting the hydraulic features of upstream and downstream reservoirs with flood routing simulation (FRS) and flood-regulating calculation (FRC), a numerical model for the whole process of cascade reservoir breaching simulation (CRBS) is established based on a single-embankment dam-break model (Dam Breach Analysis—China Institute of Water Resources and Hydropower Research (DB-IWHR)). In a case study of a fundamental cascade reservoir system, in the upstream Tangjiashan barrier lake and the downstream reservoir II, the whole process of cascade reservoir dam-break is simulated and predicted under working schemes of different discharge capacities, and the risk of cascading breaching was also evaluated through CRBS. The results show that, in the dam-break of Tangjiashan barrier lake, the calculated values of the peak outflow rate are about 10% more than the recorded data, which are in an acceptable range. In the simulation of flood routing, the dam-break flood arrived at the downstream reservoir after 3 h. According to the predicted results of flood-regulating calculations and the dam-break simulation in the downstream reservoir, the risk of sequential dam-break can be effectively reduced by setting early warnings to decrease reservoir storage in advance and adding a second discharge tunnel to increase the discharge capacity. Alongside the simulation of flood routing and flood regulation, the whole process of cascade dam-break was completely simulated and the results of CRBS tend to be more reasonable; CRBS shows the great value of engineering application in the risk assessment and flood control of cascade reservoirs as an universal numerical prediction model.

The analogue experiment of small space debris impact inducing solar array discharge

High density and conductivity plasma will be induced when space debris impacts with spacecraft. The plasma can lead to a temporary discharge tunnel and triggering discharge. This has been reported as the mechanism of space debris impact inducing discharge and might be a big threat to spacecraft. The solar array is of vital importance to spacecraft and is regarded as vulnerable to space debris impact inducing discharge. Research of space debris larger than 1 mm impact solar array discharge has already carried out. Space debris smaller than 1 mm are predominant and will impact with spacecraft more frequently compared to space debris larger than 1 mm. If the impact of such debris with solar array can induce discharge, the threat will be more serious. However, the study of space debris smaller than 1 mm impacting solar array inducing discharge has not been reported. In this paper, the analogue experiment of smaller than 1 mm space debris impact solar array inducing discharge is carried out. Our results show that the space debris with 200 μm in diameter can trigger solar array discharge. If the voltage is high and the discharge current is large enough, secondary discharge can be triggered too. The discharge can make noticeable mechanical damage on the surface of solar cells.

Research on the Normal Use of a Plug Discharge Tunnel

This study analyzed the normal use of an unusual flood-releasing tunnel with a plug dissipator. Firstly, normal physical model tests based on the Froude criterion (1 : 50) were finished. Secondly, depression physical model tests based on the Froude criterion (1 : 50) and cavitation similarity criterion were finished. Thirdly, 3-dimensional numerical simulation of flow field was finished, and free surface profile was captured, which was based on RNGk-εtwo-equation turbulence model and VOF method. The focus of this study is on the relationship between normal use and cavitation characteristics (e.g., pressure, turbulence kinetic energy, and cavitation number). The results show that lowering the reservoir water level, reduced by 20.41 m at most, increases the risk of cavitation of a plug discharge tunnel, which means with the decrease of the flow cavitation number, the possibility of structural damage will increase dramatically, while reducing the outlet height can effectively raise the flow cavitation number, ensuring the safety of normal use. Under the conditions of free outflow, for theH1/evalues of 4.45, 4.00, and 3.55, the conditions in which the tunnel meets the requirements of anticavitation areh/D ≤ 0.42,h/D ≤ 0.39, andh/D ≤ 0.35, respectively. In addition, the discharge capacity of the tunnel is not significantly reduced with the lowering of outlet height, implying that operation under a low water head of the plug discharge tunnel, as low as 3.55 ofH1/ein the test, is feasible. The results obtained in this study can serve as reference information in engineering design of the plug discharge tunnel.

Quality Inspection and Evaluation of Lining of Flood Discharge Tunnel in Nam Lik 1-2 Power Station

In 2015, Laos Nam Lik 1-2 power station once dealt with the defect of the flood discharge tunnel. After the flood discharge hole was emptied in 2018, it was found that the concrete was peeled off and exposed. After on-site census, radar detection, rebound and core strength testing, it is judged that the tunnel has apparent defects but does not affect the flood season operation. In order to prevent the surface concrete from being washed by the water flow and continue to expand the shedding surface, it can be repaired and strengthened after the flood season, which provides a favorable scientific basis for the operator.

Influences of Fire Curtain on Smoke Exhaust Effect of Longitudinal Ventilation and Shaft Smoke Exhaust Combination Mode

The aim of this study is to investigate the Influence of fire curtain on smoke exhaust effect of Longitudinal ventilation and shaft smoke exhaust combination mode, combined with the actual project established a scale physical model of 1:3, and analyzed the smoke exhaust effect of longitudinal ventilation and vertical shaft smoke exhaust combination mode, measured the fire heat release rate, smoke spread, the temperature inside the tunnel. The results show that the tunnel fire, Longitudinal ventilation and shaft smoke exhaust combination mode has a certain effect to control of flue gas, open fire curtain, the flue gas is controlled to a certain range, there is conducive to better gas discharge tunnel, can provide protection for traffic safety.

Peces dentro de túneles de descarga de una central hidroeléctrica del río Porce

La corriente generada por el agua turbinada en las centrales hidroelectricas estimula el ingreso de peces potamodromos a los tuneles de descarga, ante el bloqueo que hace la presa a la migracion. El rescate de peces en el tunel de descarga es una medida de manejo para reducir la probabilidad de afectacion por atrapamiento que se produce dentro de los tuneles. En la central hidroelectrica Porce III, la presencia de los peces es detectada cuando el tunel de descarga de la central Porce III se desocupa para hacerle mantenimiento a las compuertas de descarga de las unidades de generacion. En los anos 2012, 2013 y 2015 se realizo el traslado de peces presentes en los tuneles de descarga hacia el cauce del rio Porce, aguas abajo de la presa. Se encontraron ocho especies de peces diferentes a las registradas en otras estructuras similares. En los traslados predominaron ejemplares de las especies migratorias que se desplazan dos veces al ano, desde las zonas bajas de la cuenca y que usan como ruta de migracion los diferentes rios tributarios. Esta estrategia de mitigacion ha sido favorable para evitar la mortalidad de peces por su atrapamiento dentro de estas estructuras durante los momentos de mantenimiento de las compuertas y frecuentemente se desarrolla como una actividad de manejo de las empresas de generacion de energia.