جستجوی مقالات مرتبط با کلیدواژه « مدل آزمایشگاهی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Groyns are some structures which are constructed in flow path to protect the river bank. One of the most significant challenges in groyns operation is production of scour hole at the nose. In this study; new arrangement is proposed for permeable groyns and effect of this arrangement on maximum depth of scour hole at the nose of the groyn is investigated experimentally. Amount of permeability for the groyn is selected to be 40%. 60% and 80% and the experiments were performed in clear water. The Froude number is considered to be constant in all experiments and the depth of scour hole was measured with laser meter with an accuracy of 1 mm. Impact of number of groyns in each permeability was investigated as well. Then, behavior of groyns because of change of permeability and also maximum depth of produced scour hole in the situation of nose of groyn with various numbers of bars was compared. Result of experiments shows that between performed experiments for groyn with radial deflecting arrangement, the scour hole depth is minimum on permeability of 80% and groyn with seven bars.

Login driftwoods into the river flow and their accumulation in the upstream of the bridge will decrease the flow carrying capacity of the bridge. Blockage may cause a strong reduction in the flow rate through the bridge and therefore a strong increase in upstream water level which may lead to flooding or nearby urbanized areas. Drift woods either accumulates at a single pier, or it spans between two or more piers or it gets blocked at the bridge deck. Since the evaluation of such a mechanism in nature and in flood time is very difficult and limited knowledge is currently available on the likelihood of bridge blocking by the driftwoods, therefore, it is necessary to evaluate experimentally the movement of the driftwoods through the river flow and the effect of bridge characteristics on driftwood accumulation and blockage. The main purpose of this experimental study is to analyze the driftwood blocking probability at bridge depending on drift dimensions, driftwood shape (single log and log with branches), flow characteristics, method of driftwood entry into the flow and bridge characteristics. Tests were carried out in an inclinable rectangular flume and a bridge with guard rails was installed into the flume. The tests were performed by different length of driftwood, smooth and with branches, the number of entering driftwood to the channel flow (individual or aggregate), in the presence and absence of bridge pier and with three levels of water flow in the upstream face of the bridge. Entering each case of driftwoods has been repeated 10 times and then bridge clogging probability has been determined. The results showed that in case of water level come to low cord of the bride's deck , the clogging probability a bridge with and without pier changed from 13% to 93% and 33% to 100 respectively. The results showed that lengthening and increasing the number of driftwood and trunk with branches, the presence of the pier, and finally the rising water flow will increases the clogging possibility.

Each year to control costs and prevent the destruction of heavily structure of scour in the downstream water is spent. This phenomenon can be extended endanger the stability of the structure، while the accumulation of eroded material by changing the digital output on the performance of coastal structures will be affected. Change the scour depth and length، height and the height of a pile of sand a pile of sand to the bottom section was fitted with a logarithmic relationship. According to the results over time، profiles of scour increased while increasing the size of the reduction profiles were discussed. In other words، most of the time scour the initial testing occurred، and then it is reduced significantly. Also studied the changes of the parameter profiles were then scour، scour profiles that are independent of time.

Scouring around the bridge piers is one of the most important issues in bridge piers hydraulic. This phenomenon has led to a discharge under the bridge piers and the results caused their reversal. The local scour mechanism around the piers is very complicated issue and many researchers were conducted to discuss the investigation of this important matter. Many bridges are destroyed due to their often piers scouring and causing human and financial losses. Generally, two fundamental factors of flow contact with the bridge pier and water flow separation from the pier, led to the formation of vortices around the pier at the bridge piers site and cause the local scour. The present research has investigated the effect of flow discharge and pier diameter in depth and scour volume around the bridge piers using a physical model. For analyzing the effect of flow discharge and also the size of the pier diameter on local scour around the bridge piers, three piers were used with 21, 30 and 40 mm diameter with five different discharges in each pier. Experiments were carried out in a sandy bed (with a median size of 0.88 mm) flume of 8.0, 0.255 and 0.3 m in length, width and height a, respectively. The results showed that by increasing the discharge and Froude number in each pier, the volume and scour depth were increased. In a constant Froude number, the volume and scour depth increased by increasing the pier diameter. In 21, 30 and 40 mm piers, the scour depth also increased by 128.5, 94.7 and 135.1 percent by increasing of 40, 68.7 and 23.9 percent of flow discharge.

Investigating local scour phenomena due to jet flow on downstream of hydraulic structure is an important and necessary issue. In this article, the results of a laboratory study about the impact of tail water depth on local scour below of jet flow are provided. Circular, square and rhombus sections with a water jet from a hole, and, with a discharge of 2.46 to 4.8 liters per second, on a medium material bed of d50 of three mm made of sand, with tail water depth ranged from 10 to 24.8 cm, for 60 minutes, was simulated. The dimensions of scour holes were measured and analyzed. Results demonstrated that the maximum scour depth, with increased tail water depth to a certain extent, increased, and then, tail water will be reduced with more depth. It also became clear that the dimensions of scour holes with the following parameters of, and their relation with power. Finally, the dimensional relationships for the estimation of scour depth of discharge and the tail water variety have been proposed.

Bridge abutments are among vulnerable structures during flooding events. Local scour around abutments seems to be the main cause for structural damage. It is well known that this type of scour occurs due to the contraction of flow and subsequent vortices and eddies formation. The complexity of flow behavior in channels as well as the large number of involved parameters has limited the use of numerical models. In contrary، many laboratory investigations have been conducted and numerous techniques have been developed to reduce the size and depth of scour hole around the abutments. In the present research، breakwater was employed for reducing the scour. To do this، three lengths and five distances were tested and for each case the scour hole was measured. The results are applicable to finding the position and the length of the protecting breakwater.

One of the common methods of river improvement and bank protection is using spur dikes. Building spur dikes makes the flow path to be modified. Concentrating the flow in the middle part of the river causes the river side not to be washed out. The new flow path makes the river bed next to the end of the spur dikes to be washed out. Usually the spur dikes are built in group because of extending the protected zone. The stability of these spur dikes against the river flow depends on stability of the first spur dike. The purpose of this laboratory research is to investigate different ways for reduction of erosion in the first spur dike. It is suggested to use a shorter (minor) spur dike at the upstream part perpendicular to the flow direction. Aim in this research، it is intended to find the optimum distance between shorter spur dike and first spur dike in order to have minimum erosion in the first spur dike. From the hydraulics point of view، L’/L (the length of shorter spur dike to the length of first spur dike)، X/L (the distance between first spur dike and shorter spur dike to the length of first spur dike) and Froude number has been studied and results has been presented in the form of equations.

Spur dikes are used widely to prevent outer bank river bends and path-modification river projects. Local scouring in spur dile nose is due to contraction and strong eddy is among the important problems occurring in designing Super dikes. Experimental study has been done on effect of length and alignment of minor spur dike to reduction of main spur dike scouring. In order to do this study a shorter spur dike was used in two stages، one perpendicular and one angled to flow channel direction. By non dimensional parameters، contraction ratio L/B=0. 3، 0. 35، 0. 4، 0. 45، (L=length of spur dike، B=width of channel)، Length ratio L’/L=0. 5، 0. 6، 0. 7، (L’= length of minor spur dike) and distance ratio x/L=0. 5، 1، 1. 5، 2، 2. 5 have been studied. Scour depths at nose of minor and main spur dike have been measured. Data collection were fitted by regression analysis and a relation for reducing scour depth at nose of first spur dike is provided، with and without minor spur dike.

River banks are exposed to destruction and bank erosion. Providing human requirements and reduce river's dangers is one of the river engineering's purposes. The extent and risk of this phenomenon must be recognized. Groin is suggested as one of the control methods to reduce erosion. Besides، it is helpful way to reclaim lands. Groin's length has effective influence on bank erosion control. Laboratory models were used to investigate river protection and reduce bank erosion. Tests were done in 3 groin's lengths and 5 discharges. Results show that increasing groin's length from 25 up to 35 cm، and discharges from 15 up to 25 lit/s can reduce bank erosion about 20-40 percent.