Hydraulic Scale Model Research Articles

Effect of residual cofferdam at the diversion tunnel inlet on the index of river closure and the dumped materials: A Case study

The cofferdam built at the inlet of the diversion tunnel may be left due to incomplete blasting demolition, which affects the river closure. Several indexes have been used to evaluate the difficulty of river closure, but all indexes suffer from their limitations in use. Thus, it is more useful to combination multiple indexes to analyze the impact of residual cofferdam. Taking the river closure project of a Hydropower Station in southwest China as an example, the influence of the residual cofferdam heights on the river closure was studied by experiments. The discharge of river closure is 590 m 3 /s and 758 m 3 /s. In this paper, the results of studies on a 1:50 scale hydraulic model based on the Froude similitude relationships are presented. The test results show that the discharge capacity of the diversion tunnel is reduced by 27.2% at most when this height is more than 2 m. The residual height mainly affects the maximum of stream energy with unit width, which increase by more than 50% at most compare to Non-existent residual cofferdam. However, the final drop, max-velocity along the gap axis, the local scour of riverbed and the flow pattern of the gap are basically not affected. In addition, with the height increase, the bank collapse is intensified, and the amount of dumped material with medium size increases, especially when it reaches 4 m, the large or Extra-large size stones begin to be dumped. Based on the comprehensive evaluation of multiple indexes and the type of dumped material, it is shown that the residual cofferdam height more than a certain value, the value is 2 m for the case study, will significantly increase the river closure difficult.

Concept and Practices Involved in Comprehensive River Control Based on the Synergy among Flood Control, Ecological Restoration, and Urban Development: A Case Study on a Valley Reach of Luanhe River in a Semiarid Region in North China

Many rivers in semiarid areas have ecological degradation and flood control problems that need to be addressed urgently. In order to maintain river health and to promote the sustainable development of cities near these rivers, a comprehensive river regulation project must be carried out. In this study, first, the factors influencing river health are discussed, and the principles and main restrictions involved in comprehensive regulations are studied. The scientific regulation mode is proposed, and new financing channels for water conservancy construction are also suggested. Second, a river reach adjacent to a city in the middle part of the Luanhe River in North China is used as a case study. The health status of the river is analyzed, and a comprehensive river regulation plan combined with urban development is put forward on this basis. The plan includes embankment construction, river regulations, multilevel rubber dam storage, ecological restoration, and artificial lake and riverside landscape construction. The influence of the engineering treatment on the river flood discharge capacity is examined, and the treatment effect is verified by a hydraulic scale model. After implementation of the comprehensive river regulations, the flood control safety of the city and river ecological environment are found to be significantly improved, with the hidden danger of dust storms eliminated. The treatment project incurs environmental, social, and economic benefits and preliminarily achieves the coordination and mutual promotion of river regulation and urban development.

Rationality in pier geometry of Kintaikyo Bridge from viewpoint of river engineering

The Kintaikyo Bridge, with its elegant wooden arches, has a unique pier shape and continues to be loved by residents and visitors alike. Although this bridge is an active footbridge and an important landscape element along with the Nishikigawa River and its river beach, the rationality or irrationality of the shape of its piers remains unknown. This paper is intended to clarify the river engineering characteristics of the piers for the first time by conducting 1/129 scale hydraulic model experiments. The shapes tested were a perfect spindle shape (which has been adopted as a common theory for many years) and a reconstructed current shape based on the spindle shape, and for comparison, an oval and a non-regular hexagon shape with the same width and area. The current shape, along with the spindle shape, suppressed the water level rise around the pier more than the others. As for the riverbed fluctuation, the current shape slightly increased the scour more than the others, but it also maximized the sedimentation around the scoured part. In other words, the current shape has the potential to facilitate the procurement of sediment for post-flood restoration. In addition, the current shape overwhelmingly reduced the statistical dispersion associated with the experiment, suggesting that it stabilizes the trend of riverbed fluctuation even during actual floods. Based on the results, the future conservation of the Kintaikyo Bridge was also discussed.

Technical Note: On the Production and Accuracy of CNC-Manufactured Hydraulic Scale Models

This Technical Note addresses the workflow for the production of hydraulic scale models using a Computer Numerically Controlled (CNC) production technique and investigates the possibilities to accurately reproduce topographical roughness features. Focusing on the construction of three scale models of unlined rock blasted tunnels, their accuracy is evaluated based on the comparison of differences between scaled prototype point clouds obtained by terrestrial laser scanning, spatially filtered meshes that served as input for the milling of the models, and digital twins of the constructed models that were created by Structure from Motion photogrammetry. The direct comparison between the point clouds and meshes as well as the comparison of derived statistical parameters show that the models could be reproduced with a high degree of accuracy. Observed deviations between the point clouds of the milled models and the milling meshes, as well as the scaled original point cloud, are identified and discussed in light of the production technique and the accuracy of the applied methods for the comparison.

Simulation in Reduced Scale Hydraulic Models of the Mooring System of Ships Docked Under the Effect of the Passage of Other Vessels (Passing Ship)

Simulation in Reduced Scale Hydraulic Models of the Mooring System of Ships Docked Under the Effect of the Passage of Other Vessels (Passing Ship)

Experimental investigation of hydraulic characteristics and energy dissipation in a baffle-drop shaft.

The baffle-drop shaft structure is usually applied in deep tunnel drainage systems to transfer shallow storm water to underground tunnels. At present, the definition of the maximum operational capacity of baffle-drop shafts is lack of scientific and reasonable analysis, and the researches on hydraulic and energy dissipation characteristics have been insufficient. In this paper, a 1:25 scale hydraulic model test was conducted to observe the flow phenomena during the discharge process, analyze the relationship between the maximum inflow discharge and the baffle parameters, and calculate the energy dissipation rate of the shaft under different flow conditions. The results demonstrated that three kinds of flow regimes were presented in the discharge process: wall-impact confined flow, critical flow, and free-drop flow. The impact wave majorly brought about the energy dissipation of water on the baffle. The impingement and breakup of the inflow at the bottom of the drop shaft, as well as the reverse flow, resulted in the final energy loss. The time-averaged pressure value of the upper baffle was 1.5-3 times that of the central and lower baffles. The baffle with a design angle could effectively reduce the time-averaged pressure of the water flow acting on the baffle. The energy dissipation rate of the drop shaft decreased with the increase in the inflow discharge, and the energy dissipation rate was found to range from about 63.14% to 96.40%. The optimal size of the baffle-drop shaft with the maximum energy dissipation rate was d/B = 0.485 and θ = 10° (d, B, and θ are the baffle spacing, width, and angle, respectively).

Enhancing stormwater sediment settling at detention pond inlets by a bottom grid structure (BGS).

Stormwater sediments of various sizes and densities are recognised as one of the most important stormwater quality parameters that can be conventionally controlled by settling in detention ponds. The bottom grid structure (BGS) is an innovative concept proposed in this study to enhance removal of stormwater sediments entering ponds and reduce sediment resuspension. This concept was studied in a hydraulic scale model with the objective of elucidating the effects of the BGS geometry on stormwater sediment trapping. Towards this end, the BGS cell size and depth, and the cell cross-wall angle were varied for a range of flow rates, and the sediment trapping efficiency was measured in the model. The main value of the observed sediment trapping efficiencies, in the range from 13 to 55%, was a comparative assessment of various BGS designs. In general, larger cells (footprint 10 × 10 cm) were more effective than the smaller cells (5 × 5 cm), the cell depth exerted small influence on sediment trapping, and the cells with inclined cross-walls proved more effective in sediment trapping than the vertical cross-walls. However, the BGS with inclined cross-walls would be harder to maintain. Future studies should address an optimal cell design and testing in an actual stormwater pond.

Hydraulic scale modelling of the rating curve for a gauging station with challenging geometry

Abstract Direct discharge measurements during flood events can be challenging from a technical as well as from a safety point of view. Therefore, flood discharges are often estimated by extrapolating a rating curve. Extrapolations far outside the range of the directly measured discharges are common, although the associated errors can be large. In this article, a novel method to determine suitable stage measurement locations and derive rating curves using a hydraulic scale model is presented. A hydraulic scale model for a natural gauging station site is produced with a computer numerical control technique, making a detailed representation of the prototype topography and bathymetry. The site is characterized by a complex geometry, and the results of the scale model study reveal that the current location of stage measurement is not suitable for determining the rating curve for high flows. The scale model is used to identify potential locations for future stage measurements, and a flood rating curve is constructed based on field measurements for low flows and scale model data for high flows. The study shows how hydraulic scale modelling can be used to provide more reliable rating curves for large discharges and evaluate new or existing gauging stations located at sites with challenging measurement conditions.

Use of impulses to determine the reaction force of a hydraulic structure with an overhang due to wave impact

This paper describes a method of determining the reaction forces of a vertical structure with an overhang to impulsive wave impacts. The aim is to develop a method to design a hydraulic structure exposed to the impulsive wave impact. At present, there is a lack of guidelines on the designing and verification with such a purpose. The impulse of the impact is taken as the primary design variable to estimate the impulsive reaction force instead of peak impact forces. By using extreme value analysis (EVA), the characteristic impulse (e.g., Iim,0.1%) can be determined. Then a simple structure model is used for obtaining reaction forces to the characteristic impact impulse. The sum of the impulsive reaction force and the quasi-steady wave force could represent the total reaction force, which can be used as a design load on the structure. The advantage of using the impact impulse could give an approach in which several aspects of the impulsive wave impact force can be incorporated better, like determining the exceedance probability of a certain load, incorporating the flexibility of the structure and correcting possible scale effects in small scale hydraulic models. The proposed method based on the characteristic value of the Iim,0.1% is applied to forces measured in a small scale model of the Afsluitdijk discharge sluice, and compared well to a full-time domain solution. The results indicate the initial assumption that using the impact impulse of the impact as the primary design variable, it is possible to estimate the dynamic response of the structure.

The effect of aeration through an internal gallery of a dam on the cavitation risk of Roberts splitters

Roberts splitters is an effective means of energy dissipation for dam spillways. Roberts' (1943) standard unaerated splitter design procedure is, however, limited to a spillway head (H) of 3.0 m (q ~ 12 m2/s). In order to avoid cavitation at higher design spillway heads, this study investigated the artificial aeration of the flow by local air vents positioned on the splitters. A 1:20 scale hydraulic model of an ogee spillway equipped with Roberts splitters was constructed. Two aerated models, with differently sized air vents, were compared to an unaerated control model in order to determine the effect that the proposed aeration system has on the cavitation risk of the splitters at prototype unit discharges (q) of up to 50 m2/s. At the maximum tested spillway head of 7.6 m (q = 50 m2/s) the minimum pressures and air concentration around the splitters of both aerated models increased considerably. It was further observed that the unaerated splitters were prone to drowning at high spillway heads, leading to unfavourable hydraulic conditions. Based on the results of this study, the addition of aeration through an internal aeration gallery can increase the unit discharge capacity of Roberts splitters to at least 50 m2/s, up by 43%, from the unaerated limit of 35 m2/s.

Through-water terrestrial laser scanning in hydraulic scale models: proof of concept

ABSTRACTRiver engineering research demands increasingly high-resolution topographic data of both exposed and submerged surfaces. Detecting the topography through water is challenging in real world applications and in hydraulic laboratories. For hydraulic scale models, non-intrusive and accurate methods are needed to detect the dynamics of the river bed and its morphology without model draining. The Leica ScanStation P15 terrestrial laser scanner was tested for dry surface and through-water laser scanning. An existing procedure was adapted to reduce the distortion caused by refraction at the air/water interface. A series of tests with flow depths smaller than 0.15 m indicated an accuracy of less than 1.4 mm, resulting in a method that can be applied in hydraulic scale models with a movable bed. A sensitivity analysis revealed that the angle of incidence is the most sensitive parameter whereas the refractive index is a robust parameter. A strong decay in accuracy was observed for angles of incidence larger than 60° due to uncertainties in the flow depth. The major limitations for an application in the laboratory are high turbidity and water surface deformations that lead to an inaccurate detection of the water surface.

Hydraulic scale modelling and thermodynamics of mass oscillations in closed surge tanks

ABSTRACTThe design and results from a hydraulic scale model of mass oscillations in a hydropower plant with a closed surge tank constructed as an underground rock cavern are presented. The results from the model test of an existing hydropower plant at scale 1:65 are compared with field measurements. The main contributions of this work include (1) an assessment of whether hydraulic models may be applied to evaluate hydropower tunnels with closed surge tanks, (2) a novel approach to scale atmospheric air pressure, and (3) an evaluation of the thermodynamic behaviour in the model and prototype. The hydraulic model is shown to provide an accurate representation of the maximum (first) amplitude, with a relative error of less than 4%. An estimate of the period of the oscillations has a relative error of less than 1%. The model has higher dampening compared with the prototype, resulting in the 20% relative error of the second amplitude. Both the model and prototype reveal approximately adiabatic behaviour of the closed surge tank.

EXPERIMENTAL STUDY ON THE PERFORMANCE OF COARSE GRAIN MATERIALS AS SCOUR PROTECTION

Large scale hydraulic model tests were carried out to investigate the erosive potentials, bed stability and the performance as scour protection of wide-graded quarry-stone material with fractions ranging from 0.063 – 200 mm. Within the two phase test program the material was exposed to several wave spectra during hydraulic model tests in the Large Wave Flume of the Forschungszentrum Kuste and additionally to an incrementally increased current in a closed-circuit flume at the Franzius-Institute. As result of the wave load, a maximum scour depth of S/D = 0.161 was observed after 9000 waves with a simulated storm duration of 20 h in model scale. Furthermore, fractional critical shear stresses were determined based on velocity measurements, which indicate highly selective incipient motion of individual fractions under steady current conditions. The selective mobility of this wide-graded material could not be expressed by the Shields approach.

流起式可動防波堤の小型模型による性能評価水理実験

This study aim to evaluate the fundamental performance of the Hydroplane Tsunami Barrier by using the 1/200 scale hydraulic model. The Hydroplane Tsunami Barrier is a kind of movable breakwater. The main body is fixed to the pedestal by the special rubber belt, and it rises by hydraulic force due to tsunami and storm surge. The effectiveness of this breakwater for tsunami countermeasures is indicated through experiments of response characteristics for hydraulic force, wave force acting on the main body and the damping effect for wave height. As a result, it is revealed that water pressure acting by the maximum wave height is larger than the impact force due to the rotation of the main body. It was confirmed that the damping effect increases with the height of the tsunami.

저수지 취수시설의 공기관을 통한 공기연행에 대한 실험적 연구

본 연구에서는 저수지 취수탑에 연결된 방류관의 게이트 직하류에서 발생하는 공기연행현상에 영향을 미치는 인자들을 수리모형실험을 통해서 파악하였다. 또한 측정자료의 <TEX>$\frac{Q_a}{Q_w}$</TEX>와 <TEX>$Fr_g-1$</TEX> 관계를 이용하여 공기관의 연행공기량 추정식을 개발하였다. 측정된 자료는 게이트 하류 흐름에 따라 구분되었으며, 개발된 실험식은 만관 흐름인 경우에 <TEX>$\frac{Q_a}{Q_w}=0.0304(Fr_g-1)^{1.0622}$</TEX>, 자유수면 흐름인 경우에 <TEX>$\frac{Q_a}{Q_w}=0.0271(Fr_g-1)^{1.8205}$</TEX>이었다. 측정 자료와 기존 연구결과들의 비교를 통해서 측정 자료가 기존 실험식의 추정 결과와 유사한 분포를 나타내고 측정 자료의 신뢰성이 확보된 것으로 파악되었다. 또한 공기관 부근에서 발생하는 공기연행현상은 게이트 하류에서 발생하는 사류 특성으로부터 영향을 받는 것으로 나타났다. 최종적으로 하류 만관 흐름 조건에 대한 실험식은 공기관 설계에 적용이 가능한 것으로 사료된다. In this study, factors that affect the air entrainment within a closed conduit by air drawn in through an air vent are investigated using a hydraulic scale model, which represents a gated circular conduit system connected to the intake tower of an irrigation reservoir. In addition, using data obtained during the hydraulic experiments, experimental equations are developed to estimate the amount of air drawn in through the air vent. In case of pressurized flow conditions downstream of hydraulic jumps, the relationships between <TEX>$\frac{Q_a}{Q_w}$</TEX> and <TEX>$Fr_g-1$</TEX> of the data form a experimental equation, <TEX>$\frac{Q_a}{Q_w}=0.0304(Fr_g-1)^{1.0622}$</TEX>; in case of free surface flow conditions, <TEX>$\frac{Q_a}{Q_w}=0.0271(Fr_g-1)^{1.8205}$</TEX>. Comparing two data sets observed under the two flow regimes with the results of previous researchers, patterns of the data sets are similar to the results estimated using the equations presented previously, and this indicates that the quality of the data obtained during the hydraulic experiments is ensured. In addition, it is revealed that air entrainment phenomena in the regions close to air vents are affected by the characteristics of supercritical flows downstream of gates. Finally, it is concluded that the equation developed for pressurized flow conditions can be applied to design of air vents.

Numerical simulations and laboratory experiments for evaluating the characteristics of pollutant transport

A wave hydraulic scale model was manufactured and used to investigate the characteristics of the transport of a pollutant in a coastal area. The experiments were performed using tracers having different properties. Experiments using variations of injection point and velocity were carried out by using NaCl and radioisotope (99mTc) tracers, respectively. The experimental data have been compared with the results of the numerical simulations. The conductivity meters and gamma ray detectors were installed at the bottom and middle area in the vertical direction, respectively. NaCl tracer moved into the bottom area due to the density effects, so the results showed some differences. But the experiments using the radioisotope showed better results for the comparison with the numerical simulations. It was shown that a radioisotope was one of the best tracers to investigate the pollutant transport in an aquatic environment.

野外大型水理模型実験における変動成分の計測と解析に関わる実際的技法の開発－分合流を例として－

野外大型水理模型実験における変動成分の計測と解析に関わる実際的技法の開発－分合流を例として－

Numerical analysis of a pollutant dispersion in subsurface soil

A hydraulic scale model was used in a laboratory experiment for the purpose of understanding the characteristics of a pollutant dispersion in subsurface soil. The experimental site was an area near a radioactive waste repository in the Republic of Korea. The hydraulic scale model was designed and manufactured in geometric similarity to the actual site. The tracer 99mTc which has a short half-life was injected instantaneously into the soil. Numerical simulations were performed to compare the measured radioisotope data and to investigate the overall dispersion patterns. The calculated concentrations are in good agreement with a time series of the measured concentrations at the midpoint of the detection lines.

Developing channel and floodplain dimensions with limited data: a case study in the Amazon Basin

ABSTRACTThis research builds on the concept of hydraulic geometry and presents a methodology for estimating bankfull discharge and the hydraulic geometry coefficients and exponents for a station using limited data; only stage‐discharge and Landsat imagery. The approach is implemented using 82 streamflow gauging locations in the Amazon Basin. Using the estimated values for the hydraulic geometry relations, bankfull discharge, discharge data above bankfull and upstream drainage area at each site, relationships for estimating channel and floodplain characteristics as a function of drainage area are developed. Specifically, this research provides relationships for estimating bankfull discharge, bankfull depth, bankfull width, and floodplain width as a function of upstream drainage area in the Amazon Basin intended for providing reasonable cross‐section estimates for large scale hydraulic routing models. The derived relationships are also combined with a high resolution drainage network to develop relationships for estimating cumulative upstream channel lengths and surface areas as a function of the specified minimum channel width ranging from 2 m to 1 km (i.e. threshold drainage areas ranging from 1 to 431,000 km2). At the finest resolution (i.e. all channels greater than 2 m or a threshold area of 1 km2), the Amazon Basin contains approximately 4.4 million kilometers of channels with a combined surface area of 59,700 km2. The intended use of these relationships is for partitioning total floodable area (channels versus lakes and floodplain lakes) obtained from remote sensing for biogeochemical applications (e.g. quantifying CO2 evasion in the Amazon Basin). Copyright © 2011 John Wiley &amp; Sons, Ltd.

HYBRID MATHEMATICAL MODEL FOR SURGE ANALYSIS: A CASE STUDY

ABSTRACT Over the past few decades mathematical modeling technique is in vogue. A large number of water hammer cases have been analyzed using this technique, not only for simple systems but also for those with rather complex situations. The present analysis for a water conductor system having intermediate boundary condition such as pump behavior needed a hybrid mathematical model. The results of analyzing such system and comparing them with those obtained from the hydraulic scale model give more confidence in adoption of the mathematical technique.