Downpull Force Research Articles

Prediction of Downpull Force Coefficient on the Underflow-Type Floating Gate

The experiment was conducted to compare the hydraulic openness by the buoyancy theory of the hydrostatic pressure and the hydraulic openness by the measurement, and the difference between the theory and the measured hydraulic openness was confirmed to be the effect by the downpull force. As a result of using the existing theoretical formulae to examine the downpull force of the buoyancy-type floating gate, it was found that the existing formulae were difficult to apply to the buoyancy-type floating gate. Therefore, this paper proposed the use of the multiple regression analysis and adaptive neuro-fuzzy inference system method for predicting downpull force coefficient of the buoyancy-type floating gate. The experimental results indicate that the downpull force coefficient decreased as the opening ratio increased. In addition, the downpull force increased as the opening ratio increased below the opening ratio of 0.300, however the downpull force decreased as the opening ratio increased from the opening ratio exceeding 0.300. Finally, prediction results by using the proposed relationship indicated that the errors are much smaller compared to the results of the existing theoretical formulae. In addition, the application of the adaptive neuro-fuzzy inference system method improved the prediction significantly, reducing the errors to the half of that by the existing theoretical formulae.

Application of CFD to predict the sluice gate jammed

The problem of sluice gate jamming in moving water occurs frequently in engineering practice. In this study, the reason for gate jamming is investigated by using computational fluid dynamics and verified by model tests with variable friction coefficients. The results show that the gate geometry is reasonable and the downpull force of the sluice gate can be fully utilized. Due to being submerged in water for many years, high friction coefficient is the main reason for the non-closure of a sluice gate. The permissible friction coefficient is related to the submerged weight, available areas of panel and beam, and water level difference. Decreasing the guide vane opening and lowering the water level difference to decrease the average pressure head are feasible ways to promote the gate closure in an emergency. Adding a convex bottom edge and dividing the whole gate into two sections to increase the permissible friction coefficient are effective ways to achieve complete closure in the modification stage.

Influence of Gate Lip Angle on Downpull Forces for Vertical Lift Gates

Underestimation of hydrodynamic downpull force is one of the most dangerous risks when operating a vertical lift gate. The downpull force acting on the gate is affected by gate geometry. The purpose of this study is to investigate the influence of gate lip angle on the downpull force of vertical lift gates using Flow-3D®, a commercial CFD software. Simultaneously, the performance of Flow-3D® in estimating downpull force is evaluated. The influence of gate lip angle on the downpull force is investigated by simulating flow under different gate lip angles at different gate openings. The setup of the numerical model is similar to the experiment setup used by Naudascher in 1964. Results show that the higher the gate lip angle, the higher the bottom downpull coefficient. Majority of the numerical results show good agreement with the experimental results. Case 2 at 30% gate opening and case 3 at 50% and 60% gate opening showed obvious deviation from the experimental results due to flow separation occurred at the gate lip. This could be due to the limitations of the Fractional Area-Volume Obstacle Representation (FAVOR) method employed by Flow-3D® in which gate lip part that is smaller than mesh cell could not be exactly reproduced.

Effects of Some Gate Lip Shapes on Downpull Force in Dam Tunnels

The gate which controls the flow through the dam tunnel is termed as lift gate. Such gates are subjected to the hydrostatic and hydrodynamics forces, since the flow passes over and beneath the gate and produces pressures at the top and bottom of the gate surfaces. The differences between these two pressure forces are termed as downpull force. The evaluation of this force is very important due to its effects on closure of the gate, its positive and / or negative values. 
 The estimation of downpull force requires the determination of top and bottom pressure coefficients for wide range of discharges, gate openings, velocity, and pressure distribution in many locations .For the present research these measurements have prepared for different types of gate lip shapes along with laboratory hydraulic tunnel model which have been used. Various flow conditions and gate openings have been examined .The results concluded from the measurements and analysis tend to confirm the effects of the gate lip shapes on the values of downpull force, which in case of its negative value will prevent the gate to close and make some failures and damages.

Emergency gates - model scale tests at turbine runaway condition

Emergency gates are the last link in the chain of safety of turbo-groups in case of distributor failure, safeguarding the power station from severe damage. These gates can be located at the turbine intake or at the outlet of the draft tube and can be controlled by gantry cranes or hoist hydraulic cylinders. Gates must descend with high flow for a short time to prevent the turbine from spinning at runaway velocity for periods longer than admissible, as that would entail the rise of uplift and downpull forces that may jeopardize their stability. Indeed, at the prototype scale, the closing maneuver entails a certain risk, because of which it is usually tested avoiding extreme conditions.In this work, the operation of emergency gates was tested against more severe conditions on a reduced-scale physical model. The case study involves three emergency gates controlled by gantry cranes and located at the intake of a large Kaplan turbine which underwent high levels of vibration when operated at prototype scale.Model tests were aimed at detecting and quantifying hydraulic phenomena that might emerge during operation with an eye on the proposal of alternative designs. Unlike most tests of this sort, the experimental setup includes the runner of the turbine assembled on a test rig, which allows for a more realistic flow distribution along the vanes during the gate closure under runaway conditions.Steady state tests were carried out under runaway conditions, while stems of servomotors enabled the regulation of the position of the gate. Downpull forces were found to start at 12 % of the gate opening. Flow asymmetry was observed, gate on the left of the semi-spiral casing being the most affected by higher flow velocities. The runner vortex rope frequency was measured also at gate lip for some particular conditions.

Variation of Pressure Coefficient Along Bottom of Dam Vertical Lift Gates

The vertical lift gates are exposed to hydrodynamic forces that arise as a result of pressurized flow established by the large-scale effect of the water levels in the dam reservoirs. The most influential forces are those that are applied on the gate vertically upward due to the intensity of the flow under the gate and downward as a result of passage flow above the gate. The difference between these two forces generates a downpull force that is the most important gate stability indicator. In this research, an arbitrary hydraulic model was constructed to investigate the effects of many gate lip shapes with and without extensions on the magnitudes and distribution of bottom pressure coefficient when the values of flow and shaft gap width ratio (b2/bl) are constant. The results indicate that the bottom pressure coefficient appears to vary uniformly with gate openings and seem to be influenced effectively by the gate lip geometry. So, for the given value of (b2/bl), the top pressure coefficient regarding the downward force will mostly be with uniform changes and hence the downpull coefficient depends on the magnitudes and distribution of bottom pressure coefficient. An attempt by using the correlation coefficient of Statistical Package of Social Sciences was made to determine whether the pressure fluctuation is significantly shown at the bottom pressure distribution curve, which in turn is considered as appropriate indicator for the vibration occurrence. Full range of maximum bottom pressure coefficients in a matrix form is made to assist in design purposes. The results are analyzed and many conclusions are obtained.

Simulation of Downpull Forces of Leaf Gate in High Dams

Simulation of Downpull Forces of Leaf Gate in High Dams

Numerical Investigations of Downpull Forces for leaf gate in high dams

Numerical Investigations of Downpull Forces for leaf gate in high dams

Effects of Dam Tunnel Longitudinal Slope, Flow Rates and Gate Lip Geometry on Top Pressure Coefficient

Hydrostatics and Hydrodynamics forces are generated and applied on the vertical lift tunnel gates due to the influence of wide range of heads and operation conditions. Many hydraulic and geometrical parameters control the initiation of these forces, especially, when the flow passing over and below the gate and consequently two forces are created along the top and bottom surfaces of the gate. The difference between these two forces generates the downpull force which in turn determines the stability of the gate and its sound performance and operation. In current study the focusing is applied on the top pressure coefficient and regarding factors those affect its values and distribution. A hydraulic model was build up and the effect of three flow rates, seven lip gate geometries and four tunnel longitudinal slopes on the behavior of top pressure coefficient are examined. The results show that the top pressure coefficient is effectively affected by change of discharge, gate lip angles, and slopes of tunnel and less effect are observed with change of gate openings ratios.

Application of computational fluid dynamics to predict hydrodynamic downpull on high head gates

PurposeHigh head gates are commonly used in hydropower plants for flow regulation and emergence closure. Hydrodynamic downpull can be a critical parameter in design of the lifting mechanism. The purpose of this paper is to show that a simplified two-dimensional (2D) computational fluid dynamics solution can be used in the prediction of the downpull force on the gate lip by comparison of computed results to experimentally measured data.Design/methodology/approachIn this study, ANSYS FLUENT CFD software was used to obtain 2D numerical solution for the flow field around a generic gate model located in a power intake structure which was previously used in an experimental study. Description of the flow domain, computational grid resolution, requirements on setting appropriate boundary conditions and methodology in describing downpull coefficient are discussed. Total number of 245 simulations for variable gate lip geometry and gate openings were run. The downpull coefficient evaluated from the computed pressure field as function of gate opening and lip angle are compared with the experimental results.FindingsThe computed downpull coefficient agrees well with the previous experimental results, except one gate with small lip angle where a separation bubble forms along the lip, which is responsible from this deviation. It is observed that three-dimensional (3D) effects are confined to the large gate openings where downpull is minimum or even reversed.Research limitations/implicationsIn large gate openings, three dimensionality of the flow around gate slots plays an important role and departure from 2D solutions become more pronounced. In that case, one might need to perform a 3D solution instead.Practical implicationsThis paper presents a very fast and accurate way to predict downpull force on high head gates in the absence of experimental data.Originality/valueAn extensive amount of simulations are run within the scope of this study. It is shown that knowing its limitations, 2D numerical models can be used to calculate downpull for a wide range of gate openings without the need of expensive experimental models.

Effects of Tunnel Dam Gate Lip Geometries on Downpull Force Coefficients

Effects of Tunnel Dam Gate Lip Geometries on Downpull Force Coefficients

Pressure Coefficients of Curved Lip of Vertical Lift Gate in Dam Tunnels

The vertical lift gate shaft is installed across the dam tunnel to regulate the flow rate passing toward the downstream side to satisfy the water demand in addition to the power generation requirements. The flow through the shaft is mostly divided into two parts, over and below the gate, and as a result, two forces will be created, vertically ,downward and upward on both top and bottom gate surfaces. The difference between these forces produces so-called hydrodynamic force or hydraulic downpull force which has a vital effect on gate operation, so that in the case of negative values, this force will prevent the closure of the gate. The downpull force influences by many parameters, however, the geometry of gate is considered as one of the most common effective factor that influence the values and behavior of downpull force. In present study, physical hydraulic model is used to assess the effects of different rounded gate lip shapes on downpull force with respect to different gate opening ratios. The variation of bottom pressure coefficient along the gate surface has also been studied and the results are discussed.

Prediction of downpull on closing high head gates

Downpull on tunnel gates installed in the intake structure of a hydroelectric power plant was studied experimentally using a hydraulic model. The pressure distribution on the gate lip surface was measured, and the lip downpull was evaluated by surface-area integration of the measured pressure distribution. An easy to use lip downpull coefficient was defined as a function of the lip angle and gate opening. The lip downpull coefficient function is linked to a one-dimensional mathematical model of unsteady flow in the intake-penstock system. The model is based on the integral energy and continuity equations. Overflow through the gate spacings is also included in the model to compute the water level in the gate shaft and to evaluate the downpull component on the top face of the gate. Time-dependent calculation of the total downpull force acting on a closing gate is exemplified. The total downpull is also measured by the direct weighing method for fixed and closing gates. Predictions of the mathematical model compare favorably with the downpull obtained from the direct weighing method.

Sault Ste. Marie Lock reconstruction: hydraulic model studies of the stop log emergency closure and lock filling and emptying systems

In July 1987, a section of the southwest wall of Sault Ste. Marie Lock failed during a locking operation when a portion of limestone facing, 60 m by 8 m, separated from the rubble backing wall. Engineering investigations resulted in the selection of the Recreational Lock Option, involving either downsizing the lock chamber within the existing lock or constructing a new lock as the most viable solutions. A Dry Dock Option, where the lock would be used to store craft during the winter months, was also considered. However, this option was abandoned during the course of testing. The engineering investigations also revealed that the emergency swing dam, constructed upstream of the existing lock to protect the system should the lock gates be damaged or carried away (as happened in 1909), was in poor condition and required rehabilitation in the order of over $0.5 million. A stop log emergency system was proposed as an alternative safety device designed to stop the flow of water through the canal in the event of gate failure. Physical hydraulic model studies were carried out to evaluate the feasibility of using an emergency stop log system. The tests showed that stop logs constructed with solid horizontal web plates top and bottom result in unacceptably high hydraulic downpull forces. Open truss stop logs can be deployed to stop the flow of water through the canal in the event of gate failure. The follower should also be constructed as an open truss such that the areas of steel exposed to the flow at the top and bottom of the follower are minimized. Hydraulic uplift forces that could prevent closure can be reduced by increasing the space between the stop log and the follower. Physical hydraulic model studies of the lock filling-emptying systems are described. The first and preferred option consists of downsizing the existing lock and retaining part of the existing wooden culverts and emptying system, if possible. A new filling port, filling valves, and supply culvert would be constructed upstream. In the event that the existing wooden culverts are found to be unserviceable, a second option was considered. This second option would be to fill in the wooden culverts and then construct a new filling port, filling valves, and supply culvert that would discharge into the lock through the upstream breast wall just above floor level. The existing emptying system would be retained or rebuilt. The third option, if both the filling and discharge culverts have to be condemned, would be to build a new lock. The results of the hydraulic model studies carried out to explore these three options are described.Key words: emergency closure, stop logs, follower, canal, lock, downpull, uplift, crane capacity, filling-emptying system, culverts.

Sault Ste. Marie Lock reconstruction: hydraulic model studies of the stop log emergency closure and lock filling and emptying systems

In July 1987, a section of the southwest wall of Sault Ste. Marie Lock failed during a locking operation when a portion of limestone facing, 60 m by 8 m, separated from the rubble backing wall. Engineering investigations resulted in the selection of the Recreational Lock Option, involving either downsizing the lock chamber within the existing lock or constructing a new lock as the most viable solutions. A Dry Dock Option, where the lock would be used to store craft during the winter months, was also considered. However, this option was abandoned during the course of testing. The engineering investigations also revealed that the emergency swing dam, constructed upstream of the existing lock to protect the system should the lock gates be damaged or carried away (as happened in 1909), was in poor condition and required rehabilitation in the order of over $0.5 million. A stop log emergency system was proposed as an alternative safety device designed to stop the flow of water through the canal in the event of gate failure. Physical hydraulic model studies were carried out to evaluate the feasibility of using an emergency stop log system. The tests showed that stop logs constructed with solid horizontal web plates top and bottom result in unacceptably high hydraulic downpull forces. Open truss stop logs can be deployed to stop the flow of water through the canal in the event of gate failure. The follower should also be constructed as an open truss such that the areas of steel exposed to the flow at the top and bottom of the follower are minimized. Hydraulic uplift forces that could prevent closure can be reduced by increasing the space between the stop log and the follower. Physical hydraulic model studies of the lock filling-emptying systems are described. The first and preferred option consists of downsizing the existing lock and retaining part of the existing wooden culverts and emptying system, if possible. A new filling port, filling valves, and supply culvert would be constructed upstream. In the event that the existing wooden culverts are found to be unserviceable, a second option was considered. This second option would be to fill in the wooden culverts and then construct a new filling port, filling valves, and supply culvert that would discharge into the lock through the upstream breast wall just above floor level. The existing emptying system would be retained or rebuilt. The third option, if both the filling and discharge culverts have to be condemned, would be to build a new lock. The results of the hydraulic model studies carried out to explore these three options are described.Key words: emergency closure, stop logs, follower, canal, lock, downpull, uplift, crane capacity, filling-emptying system, culverts.

EXPERIMENTAL STUDY ON EFFECT OF STONE ARCH BRIDGE ON FLOOD FLOW AND ITS STABILITY AGAINST FLOOD PRESSURE

The region of Nagasaki, Kyushu, Japan was inundated by heavy rainfall on the 23rd of July, 1982, and water flow of the River Nakajima and other rivers increased remarkably in this area. Many rivers in Kyushu are spanned by stone arch bridges.To study on the effect of flood flow on a stone arch bridge and to measure fluid pressure that may damage the bridge, a solid model of Fukuro bridge and a model stone masonry arch were prepared in the experimental water channel at Nagasaki University.The experiment was performed for two cases: in the first case the model stone arch was set in the water channel and in the second case no model arch was used. For each case, the hydraulic data and the resultant drag and down-pull forces working on the arch stones, were measured. Using the external forces obtained in the both tests, the stability of the stone arch bridge was calculated for the flood flow. The calculation confirmed that the arch stones of the Fukuro bridge could withstand the flood.

Discussion of “Hydraulic Downpull Forces on High Head Gates”

Discussion of “Hydraulic Downpull Forces on High Head Gates”

Hydraulic Downpull Forces on High Head Gates

The paper discusses model studies in the Bureau of Reclamation's Hydraulic Laboratory in which both the direct weighing method and the pressure area computation method were used to determine hydraulic downpull on two high head gates, and one model study in which the pressure area computation method alone was employed. Also described are the methods used and results obtained in the field measurements of the prototype installations.

Air Model Studies of Hydraulic Downpull on Large Gates

Studies to determine hydraulic downpull forces on large fixed wheel gate and on slide gate; applicability of air tests for this work; method of applying data which will be helpful in evaluating downpull forces on other similar gate structures.

Coaster Gate and Handling Equipment for River Outlet Conduits in Shasta Dam

Abstract At Shasta Dam, a coaster gate is used to close the intake of any one of the eighteen 102-in. conduits in the spillway section of the dam. Each conduit is provided with a control valve. The coaster gate is used to close the intake of each conduit whenever required for inspection and servicing of the control valve and conduit. It may also be used for emergency closure in the event of failure of a control valve. Since the gate design is predicated on emergency conditions of maximum head, when it is subjected to large unbalanced pressures, hydraulic model studies were conducted to determine the best shape of gate to minimize the downpull force to which it might be subjected in an emergency closing. The procedure followed in conducting the studies and the final installations are treated in this paper.