جستجوی مقالات مرتبط با کلیدواژه "تشدید" در نشریات گروه "عمران"

The passage of water through obstacles such as bridge piers in the river, dock piers in the sea, and piers of any other hydraulic structures located in an open channel causes the formation of a boundary layer upstream of the obstacles and the separation of flow lines in the downstream obstacles, leading to the formation of vortex flows. The overlap of the vortices created by each of the obstacles leads to the formation of surface waves whose propagation direction is perpendicular to the flow direction. Under special circumstances when the frequency caused by the vortex of the obstacles is equal to the natural frequency of the structure's oscillation, a resonance mode is created and transverse waves with maximum amplitude are formed along the flume width. The formation of transverse waves with maximum amplitude can affect the safety and stability of hydraulic structures including bridge piers. To this end, recognizing transverse waves can reveal the reasons for the occurrence of some phenomena. Most studies on transverse waves have been conducted in a flume with limited width and a few waves. Thus, by conducting experiments in a wide flume and creating more waves, this study aimed to investigate the effect of waves in different modes on the local scour around the cylindrical piers of bridge.

The experiments were carried out in the Physical and Hydraulic Modeling Laboratory of the Faculty of Water and Environmental Engineering, Shahid Chamran University, Ahvaz, using a rectangular flume with a length of 16 m, a width of 1.25 m, a height of 0.6 m, and a zero slope with glass walls. The flume bed was covered with sediments with an average size of d50 = 0.7 mm. The experiments were conducted with cylindrical pier groups in three stages. The experiments in the first stage were carried out without sediments and the cylindrical piers were placed on a fixed bed without sediments. The first stage experiments aimed to measure the wave parameters (wave amplitude, wave frequency, and flow depth) in the resonance. In the second stage, the sediment experiments were conducted with the formation of transverse waves. After adjusting the water level and forming the desired wave, 4 hours of equilibrium time was considered. Then, the pump was turned off and the end weir was slowly opened. After the complete discharge of the flow, the topography of the bed was measured using a laser meter with an accuracy of 1 mm as 1×1 cm2. The sediment experiments were in the third stage with the removal of transverse waves (control experiments) which were performed to compare with the results of the second stage experiments. A glass sheet was used for this purpose. The glass sheet prevented matching the natural frequency of the channel and the frequency caused by the tier vortex.

To investigate the effect of transverse waves caused by cylindrical piers on the maximum scour depth, each scour in the experiment with transverse waves was compared with the corresponding experiment conducted without transverse waves. The results showed that in wave modes 1, 2, and 3, the maximum scour depth was greater in the case with waves than in the case without waves. The maximum scour depth in wave mode 1 experiments at Froude numbers 0.059, 0.057, and 0.055 was 71, 55, and 54 percent higher than the scour depth in the experiments without waves, and for wave mode 2, the maximum scour depth in the experiments with waves at Froude numbers of 0.117, 0.110 and 0.106 was 90, 76 and 66 percent higher than the maximum scour depth in the experiments conducted without waves. The maximum scour depth in the wave mode 3 experiments with waves at Froude numbers of 0.156 and 0.151 was 70 and 68 percent was higher than the scour depth in the experiments without waves. This study also examined the effect of wave mode on the maximum scour depth. The results indicated that with an increase in the wave number, the maximum scour depth increased in each discharge. On average, the maximum scour depth in wave mode 3 increased by 130 percent compared to wave mode 1 and by 43 percent compared to wave mode 2, and the maximum scour depth in wave mode 2 increased by 60 percent compared to wave mode 1. Also, the maximum scour depth in each wave mode increased with an increase in the wave amplitude, indicating the existence of a direct relationship between the wave amplitude and the maximum scour depth. In addition to the maximum scour depth, transverse waves also affected the scour volume, which was greater in the experiments conducted with waves than in the experiments without waves. On average, the scour volume was 4.3 times in wave mode 1, 3.5 times in wave mode 2, and 9 times in wave mode 3 compared to the wave-free mode.

The present study examined the effect of transverse waves mode 1, 2, and 3 on the local scour around the cylindrical piers of the bridge. The formation of transverse waves affected the scouring of cylindrical piers, and the maximum scour depth in the experiments conducted with waves was greater than in the experiments without waves. On average, the maximum scour depth increased by 60 percent, 78 percent, and 69 percent in the wave modes 1, 2, and 3 compared to the wave-free mode respectively. Moreover, with an increase in the wave number, the maximum scour depth increased in each discharge, with the maximum and minimum scour depths being found in wave modes 3 and 1, respectively. Overall, the changes in the scour volume followed the same trend as the changes in the maximum scouring depth. On average, the scour volume was 4.3 times in wave mode 1, 3.5 times in wave mode 2, and 9 times in wave mode 3 compared to the wave-free mode.

In this paper, the effects of rail vibrations transferred from the ground to the building in the vicinity of the rail are studied. The additional forces mostly produced in the contact area of the wheel and structure’s rail influence on the building in the vicinity through the soil underneath. The building is a concrete chamber located between 2 high speed railroadand in 2 meters distance from them. The Ansys software was used which can model the train forces, soil, rail and building’s components. One of the ISO 14837-1 curves was used as a raw curve of train vibrations’ effect and was made ready to enter in the software by mathematical transformations. The results of the software model have been studied in case the vibration frequency received by the building is equal to one of the effective natural frequencies of the building, which leads to damage to the joinery of the building (if the building is old or historical, it will overturn). By using damping layers in the building, the effect of train vibrations on the building adjacent to the rails is greatly reduced, and with this solution, damage is not caused even in the joinery of the building. The damping layers are made of rubber and polyurethane, which is produced by the German company "BSW". Another way to reduce the resonant effect is to increase the damping of the structure in different ways.

Vortex is shed by flow collision with obstacles in its path. If the frequency of vortex shedding equals the frequency of natural oscillations of flow, resonance will be created and transverse oscillation perpendicular to flow with greatest wave amplitude will occur. In this study, in order to investigate the characteristics of the transverse wave caused by the vortex shedding of the obstacles, 135 cylinder barriers with a diameter of 20 mm in 5 different configurations were arranged in the laboratory flume. In total, 900 tests were carried out which variables were flow discharge, average flow depth, channel slope, longitudinal and transverse distance between obstacles. In each test, after the formation of transverse oscillations, their characteristics including amplitude and frequency of wave were recorded. Then, the effective variables on transverse wave characteristics and their effects on the involved dimensionless numbers were investigated. The results indicated whatever the flow discharge is increased, the maximum wave amplitude due to resonance occurs in larger average flow depth, which has more amount. Also by changing the longitudinal distance of obstacles, Roshko's changes relative to increasing of Ursell were ascending at the beginning and they were reversed after reaching a certain range of Ursell number; moreover, by increasing the flow discharge, the rate of Ursell changes relative to Roshko decreased. Finally, by using dimensional analysis and statistical software, the equations between Roshko with Ursell and Froude numbers were proposed for each of the modes I and II and the validation of equations were approved (R2= 0.92).

Bridge performance and health monitoring can be obtained from numerical models, site load test or combination of both. Load test approach illustrates bridge behavior with minimum inaccuracy without taking into account the assumptions and simplified approaches of structure analysis. In this research, the structure of Qale Morqi bridge was investigated in order to identify the bridge performance and defects that cause vibration to be induced into surrounding buildings. Numerical models of bridge were made and bridge model was loaded according to bridge Design codes. Bridge was instrumented with more than a hundred sensors, and then loading was implemented in static and dynamic steps. It was observed that the bridge vibrates intensively and instead of bending pattern, the first mode shape was torsional. Due to proximity of bridge first mode with peripheral building first mode, resonance is probable. In conclusion, some strategies for decreasing bridge vibration or preventing resonance in peripheral building arepresented.