1,720,986 research outputs found
How far can you push a HEC-RAS model and other conundrums – a Nam Theun 2 case study
Full text linkDesigned by 2007, built by 2010, limits pushed by 2011; the occurrence of an extreme flood event at the Nam Theun 2 hydropower dam system in Laos sparked a reassessment of the hydrology resulting in a 30% increase in design flows and leaving the flood release infrastructure well short of the required capacity. This increase and subsequent attempts to re-analyse the release structures, ranging from simplified HEC-RAS modelling to sophisticated CFD and physical modelling, serve as examples of the uncertainty and risks that can be encountered in the design of hydraulic structures
Hydraulic structures and society - Engineering challenges and extremes in perspective
Full text linkA hydraulic structure is an artificial system which interacts with the flow of water. A number of engineering challenges are closely linked to the hydrodynamics and fluid flow motion. Two key issues during the design and operation of hydraulic structures are conveyance and energy dissipation. The energy dissipation at a hydraulic structure can be enormous and its estimate is far from trivial. The re-evaluation of spillway discharge capacity, including the spillway re-design, is a further challenge, especially in the regions with extreme hydrology and limited records. Our community needs to broaden the knowledge base in hydraulic structures, through the development of independent learning skills, further education in hydraulic engineering and innovative research and development (R&D). It is believed that the proceedings of the 5th IAHR International Symposium on Hydraulic Structures (ISHS2014) provide the engineering profession with real-world state-of-the-art expertise in hydraulic structure design
Rifle Creek Dam DIY physical modelling
Full text linkThe application of Computational Fluid Dynamic (CFD) models can be fraught with uncertainties for the inexperienced modeller. The simulation results can vary radically depending on assumptions made regarding; boundary conditions, model domain, turbulence parameters etc. The acquisition of valuable experience and engineering judgment comes with observation of relevant experimental data, which however is often difficult to source. For Rifle creek Dam near Mount Isa, Australia, the author took the unusual step of developing a DYI (Do it Yourself) physical model of the dam was in the backyard of the CFD modeller to do experimental comparison with VOF CFD (HELYX) results. While it was well outside of the project scope it was well within the required sleep-at-night factor. The purpose of the project was to investigate methods of increasing the spillway capacity of the 1920’s built dam as per ICOLD (International Committee on Large Dams) dam safely requirements for acceptable flood capacity. Many older dams are subject to similar investigations, due to revised estimated maximum flood sizes, which often also result in retrofit construction activities to increase spillway capacity. Comparison of the simulation and the physical model characteristic spillway flow of the spillway is demonstrated by numerous videos
Turbulent fluctuations in hydraulic jumps: a physical study
Full text linkIn an open channel, the transformation from a supercritical flow into a subcritical flow is a rapidly varied flow with large turbulent fluctuations, intense air entrainment and substantial energy dissipation: i.e., a hydraulic jump. New experiments were conducted for a wide range of Froude numbers (3.8 < Fr1 < 8.5) at relatively large Reynolds numbers (2.1×104 < Re < 1.6×105) to quantify the turbulent fluctuations. The time-averaged free-surface profile presented some self-similar profile. The longitudinal movements of the jump were observed and both fast and very slow fluctuations were documented for all Froude numbers. The air-water flow measurements quantified the intense aeration of the roller. Overall the present findings demonstrated the close interactions between the roller turbulence and free-surface fluctuations. Future investigations should be carried out over long durations to account for the very slow fluctuations in jump position
Analysis of nonuniform aerated skimming flows on stepped channels
Full text linkFor the hydraulic design of steep stepped channels, it is important to elucidate the aerated flow characteristics of skimming flows both in nonuniform and quasi-uniform flows. For the nonuniform aerated flow region, an analytical equation for calculation of the aerated flow depth is developed, and the surface profile and specific energy are calculated using this equation together with the continuity equation for the air phase. The results agree with the experimental data
Analysis of air concentration in a physical model of the bottom of a spillway chute with aerators
Full text linkGiven the inherent difficulties and constraints of taking measurements on a prototype and representing the behavior of air in a physical model, this paper presents comparative analysis results from air content measurements in a spillway bottom model with aerators. This was done using model measurements and an analytical model to define the accuracy and credibility of extrapolating results to the prototype. The numerical criterion used allows calculation of air concentration decay along the chute at the same point where the physical model measurements were made. Since air concentration can only be measured at the bottom of the prototype, it can be concluded that the analytical approach works well, and with some adjustments, the results can be extrapolated to measure other points on the prototype Air content at the bottom chute is the most important understanding for the protection spillway
Detailed two-dimensional modelling of a complex bridge arrangement – McKinlay River No. 2 Bridge, Alice Springs to Darwin railway
Full text linkThe Alice Springs – Darwin Railway Project involved the construction of 1420 km of new standard gauge track between Alice Springs and Darwin, including the McKinlay River No. 2 Bridge. During the 2006, 2007 and 2008 flood seasons, significant scour occurred around the McKinlay River No. 2 Bridge piers, raising concerns regarding the continuing stability of the structure. The site has complex geometry, with the river approaching the crossing at a significant angle and the remains of the original railway bridge just upstream of the new structure. Owing to the complex arrangement, a detailed 2-D hydrodynamic SOBEK model of the bridge crossing was developed to inform the design of scour protection works at the site. The model was used to analyse a number of options to reduce the potential for scour, and allowed for the scour protection works to be optimised for conditions at the site. The designed protection works were constructed in 2011, and have performed well in several subsequent flow events
Pressure fluctuations and air-water flow properties in hydraulic jumps
Full text linkA hydraulic jump is a rapidly-varied flow associated by large and rapid fluctuations of its two-phase properties. Herein a miniature total pressure probe was used simultaneously with a phase-detection probe and several acoustic displacement meters to characterise the instantaneous air-water turbulent properties and the free surface fluctuations. New laboratory experiments were performed for a range of Froude numbers (3.8 < Fr1 < 8.5). The total pressure was measured within the turbulent shear region showing maximum mean pressure and maximum pressure fluctuations slightly above the invert. The interactions between the instantaneous total pressure, void fraction and free-surface fluctuations were detailed based upon some correlation analyses. Altogether the experimental method provided a greater level of details into the instantaneous two-phase flow properties, highlighting the large and rapid fluctuations of the two-phase flow properties at the millimetric and sub-millimetric scales
Step cavity and gabion aeration on a gabion stepped spillway
Full text linkRecent advances in gabion construction techniques have increased the interest for gabion stepped spillways. The present study investigates the air entrainment process in the stepped cavity of a gabion stepped spillway through physical modelling. The microscopic air-water flow characteristics were investigated using a phase-detection probe, complemented by some video observations. The visual observations indicated a high level of interactions between stepped cavity flow and gabion seepage, including some bubbly flow motion in the gabions. The measurements showed relatively lower aeration, velocity and turbulence levels than that in the mainstream flow. The air-water measurements demonstrated some self-similarity of main flow properties above the pseudo-bottom formed by the step edges at all measured locations
Physical modelling of hydropower waterway with air cushion surge chamber
Full text linkThe interest for new large hydropower pumped storage plants in Norway is increasing. Such large plants have massive hydraulic transients, and the surge chamber design have crucial impact. The air cushion surge chamber design is the preferred design for large hydropower plants in Norway since the 1970’s, and new research is now initiated in order to further investigate the physical properties and optimum design of these constructions. A new physical model of a hydropower waterway with an air cushion surge chamber is currently under construction at the Norwegian University of Science and Technology. The model design is difficult due to huge impact of atmospheric air pressure. This paper will present the model design, dimensional analysis and a comparison of numerical simulations of the model and field measurements from the prototype in order to test the model design. The model design is found to be feasible, and the construction works are initiated
- …
