جستجوی مقالات مرتبط با کلیدواژه « استهلاک انرژی نسبی » در نشریات گروه « آب و خاک »

Spillways are used to transfer and discharge the excess water collected behind the dams downstream. There are different types of spillways in terms of geometry and place of use, which are used based on the topography of the region, hydraulic and hydrological conditions, etc. Based on this, in the current research, the effect of the frontal slope of a simple and blocky stepped spillway with a semi-circular crest on the hydraulic parameters of the spillway has been investigated using the Flow-3D® model and the RNG turbulence model. Three values were considered for the slope of the front area of the spillways step and the range of critical depth was between 11.9 and 14.5 cm. Numerical simulation showed that increasing the angle of the front of the step relative to the horizon, or in other words, reducing the slope of the front of the step, has increased the relative energy dissipation, so that the amount of energy dissipation increases in the spillway with a 90 degree step compared to a step with a 60 degree angle are 13.88% and 28.89% higher than the 45 degree angle stairs. On the other hand, the use of blocks has increased the consumption of energy in the overflow with a 90-degree step compared to a 60-degree angle step by 7% and compared to a 45-degree angle step by 32.24%. Also, the value of the downstream relative depth increases with the increase of the flow rate and with the increase of the downstream energy loss, the descent number of the downstream area of the stepped spillway decreases, and this decrease is about 60% more at the angle of 90 degrees than the angles were 45 and 60 degrees.

In the last decade, the use of gabion structures in hydraulic engineering for stabilizing the structure due to its high density and weight has become widespread. Also, the material's roughness and porosity cause it to be used in energy dissipation and drainage projects. This study evaluates the relative energy dissipation of gabion structures downstream of the ogee spillway in the conditions of a submerged hydraulic jump. The evaluated parameters in this study were Froude number, gabion height, gabion thickness, and material diameter. The experiments were performed with three average diameters of 1.5, 2.2, and 3 cm for rock material, three gabion heights of 10 and 20 cm, and Max. The end sill heights were 10, 20, and 30 cm. The operated discharges were regulated from 20 to 40 l/s. The results showed that by decreasing the average diameter of gabion aggregates, the amount of relative energy dissipation increases in all tested models, so that in gabion with a 1.5 cm average diameter of aggregates, the amount of energy dissipation increased by 3.6% in comparison with using the diameter of 3cm for the average diameter of the material. Increasing the height of the gabion to the extent that the flow is entirely inward can have up to 33% more relative energy dissipation than the gabion with a height of 10 cm. Also, by increasing the diameter of the gabion from 10 cm to 30 cm, relative energy dissipation increases up to 15%.

In the present study, the hydraulic characteristics of the flow and the phenomenon of flow hysteresis with the supercritical regime, which can appear in the vicinity of the additional structures in the flow path, such as contracting of the cross-section of the channel, were investigated experimentally. To achieve the objectives of the study, two average diameters of materials inside the gabion basket with sizes of 1.28 and 2.08 cm were used. The inlet flow rate increased in the primary flow and decreased in the secondary flow in the range of 300 to 650 liters per minute. The results of the present study show that by increasing the flow rate and then decreasing the flow, two different behaviors and regimes of flow are observed in the same experimentally conditions. So that with the formation of the phenomenon of hysteresis, the relative depths of the flow were increased by 69.39% and the Froude number of the gabion contraction section has increased significantly by 69.15% and the main cause of the hysteretic behavior of the flow is the current behavior of the flow following its previous behavior. On the other hand, the rate of flow energy dissipation in the use of gabion basket has increased by a relative amount of 71.35% compared to simple contracting. The results also showed that by increasing the size of the constriction and increasing the average diameter of materials in the gabion basket increases energy dissipation and relative downstream depth.

In this research, experimental evaluation of different hydraulic conditions on the performance of gabion sill in dissipating energy at downstream of Ogee spillway has been investigated. The parameters evaluated in this study included: Froude number, sill height, the amount of opening in the sill width and the diameter of the aggregates. The experiments were conducted by using flow discharges of 20 to 40 liters per second with two heights of 5 and 10 cm and openings of 10, 15, 20 and 30 cm in fixed sill widths with and without openings. The results showed by increasing the height of the sill, the relative length of the hydraulic jump increases and the amount of relative energy dissipation also increases. Also, by increasing the diameter of aggregates, the relative length of hydraulic jump and the amount of relative energy dissipation decreased. The highest amount of energy dissipation was related to aggregates with an average diameter of 1.5 cm in which the amount of energy dissipation and the length of hydraulic jump were 9 and 8.3 % more than the ones in 3 cm diameter of aggregates, respectively. The results also showed creating an opening and increasing it across the sill reduces the relative energy dissipation. So that the relative energy dissipation in the gabion with 30 cm opening was about 7% and its relative hydraulic jump length was about 9% less than the ones in sill without opening.