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

By constructing a pipe containing fluids such as water and oil crosswise with the direction of the river, the pattern of river flow around the pipe changes. . These changes in the flow pattern around the pipe and an increase in shear stress on the substrate, which results in a scouring hole under the pipeline. Local scouring around pipelines across the river is one of the most important causes of their failure and destruction. Therefore, it is very important to study the mechanism of occurrence of this phenomenon around the pipelines and to evaluate the amount of scouring and the characteristics of the local scour hole around them. Wu and Chiew (2013) investigated the scour hole and the flow field around a pipeline under steady flow. The flow field in these experiments was measured by an acoustic Doppler velocimeter. The results of this study showed that the presence of vortices due to the pressure difference created upstream and downstream of the pipe causes the formation of a force for the movement and displacement of sediments. Also, the flow from under the pipe into the scour hole causes it to expand further. Zhao et al. (2015) performed laboratory and numerical study of scouring under two consecutive pipelines with different distances from each other. In moving bed conditions, it was observed that the depth of the scour hole under the upstream pipe is slightly greater than the scour hole under the single pipe, while the depth of the scour hole under the downstream pipe is much greater than the scour depth compared to the single pipe. Yan et al. (2020) numerically examined the local scour around the pipeline across the river under steady flow conditions. In their study, the CFD method and variable mesh technique were used to model the sediments transport and the results were compared with the results of the laboratory model. The results showed that the method used to model scour and sediment problems respond satisfactorily. The aim of this study was to investigate the effect of the installation depth of pipe across the river in steady flow on temporal changes in scour pattern and sedimentation around the pipeline were processed by recording video information during each experiment.

The present study was performed in the hydraulic laboratory of the Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz in a rectangular flume 10 m long, 0.74 m wide, and 0.6 m high. The walls of the flume were made of glass and the floor was made of steel. The flume had reservoirs at the beginning and end and a section to calm the flow. To investigate the scouring phenomenon around the pipe crossing the waterway, in the middle of the flume, in an area, 1.5 m long and 15 cm thick, uniform sediments with Medium size (d50) 0.7 mm, relative density (Sg) 2.65, and standard deviation (σg) 1.4 were poured. In this study, pipes with a diameter of 20, 40, and 60 mm at a quarter of the pipe diameter under the bed (e/D= -0.25), bed installation depth (e/D= 0), a quarter of the pipe diameter above the bed (e/D= 0.25), and half of the pipe diameter above the bed (e/D= 0.5) were used. The pipes were made of PVC and were installed perpendicular to the flow across the flume. The experiments were performed at a flow rate of 33 liters per second and a flow depth of 14 cm. The duration of all experiments was 120 minutes. The total number of experiments was 12. In these experiments, clear water conditions prevailed.

In most of the researches in this field, a comprehensive study has not been done on the temporal changes of the scour hole parameters and their focus has been mainly on the scour depth parameter when the pipe is placed on the bed. Comparing the present laboratory study with other studies related to the study of diameter and depth of installation, one of the most relevant studies is related to the laboratory estimation of scour under the pipeline by Ataieyan (2012). In which the scour under the pipeline is investigated with emphasis on the effect of installation depth. The maximum amount of scouring was observed at a depth of one-fourth of the pipe diameter at the top of the bed. The result of the experiments performed in the present study also confirms that at the depth of installation, e/D= 0.25, due to the narrowing of a certain distance between the sub-pipe and the surface of the sedimentary bed and The formation of vertical and horizontal vortices showed the highest maximum scour depth compared to other installation depths. The results related to the effect of installation depth for different modes are as follows, e/D= 0.25, e/D= 0, e/D= -0.25, e/D= 0.5 from maximum to minimum, respectively, they had the highest amount of scour depth. Another parameter studied for scouring is the distance between the maximum scouring depth and the center of the pipe. This parameter is indicated by Xds. the location of the maximum scouring depth at the beginning of the experiment was moving upstream of the pipe. At installation depth, e/D= 0.5, the highest rate of maximum scouring depth was observed downstream compared to all cases. In all experiments, about 80 to 90% of the height of the deposition ridge occurred in the first 10 to 20 minutes of each experiment.

The results of this study showed that at all installation depths, 80 to 90% of the scouring depth was performed in the first 40 minutes of each experiment. The depth of pipe installation was one of the most influential factors on the dimensions of the scour hole. In all experiments, sediment from erosion was deposited downstream of the pipe and formed a sediment ridge. The maximum and minimum deposition heights occurred at the installation depths of e/D= 0.5 and e/D= 0.25, respectively.

Natural gas transmission pipelines transport the natural gas at elevated temperature and high internal pressure. The pipelines will expand when they are put into operation under the influence of increased internal pressure and temperature. The movement due to such expansion is significant for large diameter pipelines which operate at high pressure and elevated temperature. The pipeline needs to be restrained near compressor stations in order to prevent the transmission of such movement to equipment and facilities within the station. Concrete anchor blocks are commonly used to restrain the movement of buried pipelines on both sides of compressor stations. Anchor blocks for transmission pipelines are usually massive because of the high axial stress in the pipe which results in large thrust force. Current design procedures are usually based on providing an adequate margin of safety against block sliding, block overturning and soil bearing pressure. This paper presents the results of an analytical study on the response of soil, pipeline and anchor block at different operating pressure and temperatures. Nonlinear finite element analyses which include modeling of soil-pipe and soil-block interactions are carried out to evaluate the design procedures. The results indicate that the concept used in current design procedures is fundamentally flawed because it is based on controlling forces rather displacements. Based on the results of these analyses a more rational design procedure which is based on controlling the displacements is introduced. The proposed design procedure results in a substantial reduction of the size of anchor blocks.

Water quality degrades due to the complex physical, chemical and biological processes passing through the transmission lines. One of these widely attracted processes is contaminant intrusion due to a transient event. When the negative pressure wave of water hammer reaches a structural deteriorations such as a leakage, it can suddenly sucks pollution from the surrounding area of leakage to the main pipeflow which can in turn endanger public health. The purpose of this study is to determine the effect of hydraulic parameters on the duration of negative pressure and the magnitude of negative pressure and subsequently the volume of contaminant intrusion in a reservoir-pipe-valve system with leakage. In this study, the Eulerian method of characteristics was used to model the transient flow. The total Volume of Contaminant Parcel (VCPt) from the leakage site taken from Lagrangian solution of the advection equation used as criterion to compare various transient senarios.The results are provided in a number of graphs which quantify the influence of each system parameter. The results indicate that the volume of contaminant intrusion is mostly dominated by the amount of negative pressure at leak. The amount of intrusion is investigated via several case studies..The reservoir pressure head, fluid velocity inside the pipe, the wave speed, the pipe diameter, the leak diameter and the leakage location are respectively the effective hydraulic parameters on contaminant intrusion. Investigation of the interaction of these factors in the volume of contaminant intrusion can be considered as a subject for future research.

Contaminant intrusion in pipelines is an important mechanism, which may lead to deterioration of the drinking water quality. One of these widely attracted processes is contaminant intrusion due to a transient event. When the negative pressure wave of water hammer reaches a structural deteriorations such as a leakage, it can suddenly sucks pollution from the surrounding area of leakage to the main pipeflow which can in turn endanger public health.In this research, numerical and mathematical modeling of a reservoir-pipe-valve system with leakage has been used to investigate the effect of the interaction of hydraulic parameters on the volume of contamination introduced into the pipelines during the waterhammer. In this study, the Eulerian method of characteristics was used to model the transient flow. The total Volume of Contaminant Parcel (VCPt) from the leakage site taken from Lagrangian solution of the advection equation used as criterion to compare various transient scenarios. In order to provide a better understanding of this phenomenon, in 72 different situations, contaminant intrusion has been investigated. The average rate of contaminant intrusion in the the long viscoelastic pipe line to elastic pipe is equal to 7.2%. This ratio is 49.6% in the case of a short viscoelastic pipeline.The results indicate that the volume of contamination sucked in the viscoelastic pipe in different conditions is less than that of elastic pipe. The results clearly outperform the viscoelastic pipe in preventing contaminant intrusion.

The global population is booming, and Iran is no exception. This additional capacity is placing considerable strain on many aspects of human life; in particular on transport. Fossil fuels will continue to play an important part of the transport fuel mix, and therefore the limited and dwindling reserves need to be optimized for economic, social and environmental reasons. The goal of this research is to determine the gasoline transport capacity from ports of the country and local refineries to different destinations throughout Iran. It is the aim of the study to determine an optimization alternative for the gasoline transport capacity from and to each specified destination by applying the trans-shipment model. The goal is to minimize transport expenses due to sending gasoline from two sources to seventy seven destinations, by using forty seven intermediate points and 6,076 decision variables (transport direction). By achieving this goal, industry is confronted with demand and supply restrictions, simplicity of use and non-negative portable gasoline capacity. Referring to the results obtained, the expense of 73% of gasoline transport by pipe-line was 70%, and for road transport of 23%, it came to 25% of the total gasoline transport expenses. Share of transfer by ship for 3.4% yields an expense equal to 5%, and in addition the results show a 17% cost saving of the gasoline distribution expense in 1387.Urban highways are one of the most important infrastructure facilities that play a vital role in daily transportation. There are several approaches for the management of urban highways; one of which is the Intelligent Transportation System (ITS), which integrates advanced information and control technologies to improve traffic flow in transportation networks. Different methods have been developed to improve the performance of highway networks, among which control strategies such as ramp metering (RM), variable speed limits (VSL), route recommendation and variable message signs (VMS) are recognized as the most effective for relieving traffic congestion. This research paper discusses the optimal coordination of variable speed limits and ramp metering in a highway traffic network. The control problem is to determine the optimal combination of control variables that result in the best network performance. Efficiency of this problem was evaluated based on the total time that a vehicle spent in the network (TTS). The applied co-ordination approach incorporates the macroscopic traffic flow model METANET as a prediction model, and a genetic algorithm as an optimization algorithm to co-ordinate the RM and VSL in a highway network. The proposed model was implemented on a highway network with two ramps and two VSLs upstream of each one. The results showed that in cases where ramp metering is insufficient to prevent congestion, variable speed limits can prevent a traffic system breakdown and maintain a higher outflow. In other words, optimal co-ordination of ramp metering and VSLs can significantly reduce congestion and result in a lower total time in the network for vehicles. The results have been compared with a previous study in this field and have been shown to be more beneficial, due to the use of the GA in comparison to the search methods used previously in the literature.