جستجوی مقالات مرتبط با کلیدواژه "numerical modeling" در نشریات گروه "عمران"

Due the limitations and lack of access to fresh water resources, groundwater is recognized as an important source. In this research, a novel method called Dual Discrete Finite Volume (DDFV) has been developed for modeling flow and contaminant transport in saturated and unsaturated porous media. In this method, structured and unstructured grids have been used to handle complex geometries. Flow and contaminant transport equations have been accurately modeled for each triangular element in the grid. This modeling process yields contaminant concentrations at the center and vertices of each element. First, the flow equation in an unsaturated medium has been solved. Parameters such as moisture content and hydraulic head have been calculated. Then, based on the obtained results, the water velocity in the soil was estimated. Finally, the contamination equation in an unsaturated medium was extracted, and the concentration values at the vertices of each element were calculated. This model has been validated for transient flow conditions with high accuracy. By comparing the two-dimensional case with the one-dimensional case, it was determined that there are no numerical oscillations in the two-dimensional case.

The majority of building and infrastructure projects are typically situated on soils that have a greater elevation than the underlying water table. As a consequence, these soils exist in an unsaturated state, resulting in the development of matric suction inside them. The manipulation of soil saturation levels significantly influences its mechanical and hydraulic characteristics. Swelling soils refer to a type of soil that undergoes volumetric expansion as a result of moisture absorption and a subsequent decrease in matric suction. Hence, this matter gives rise to irreversible harm in the realm of infrastructure, transportation networks, and facilities such as oil and gas. This study focuses on the numerical analysis and discussion of the swelling soil surrounding a gas well located within the Khangiran gas refinery. The findings from the numerical simulation demonstrated that, at the critical juncture of the steel pipe within the well structure, the tensile force induced by soil expansion infiltrates the surrounding area. To withstand this force, the design and permissible thickness of the well pipe can be evaluated using two approaches: load coefficients-resistance and allowable resistance. The action is permissible. The findings indicate that the thicknesses obtained are relatively small, thereby suggesting that there is no significant risk associated with soil swelling and the resultant tensile force exerted on the well casing. However, it is important to note that the durability of the well body's steel material over time is crucial in preventing breakage due to soil swelling-induced tension.

The widespread use of the cone penetration test in geotechnical engineering, due to its quick identification of soil layers and properties, has led to the development of various analytical methods for interpreting this test. Monitoring excess pore water pressure during the piezocone penetration test can be crucial for assessing the properties and engineering parameters of clayey soils. The initial stresses in the ground and the coefficient of lateral earth pressure at rest, K0, are important parameters needed for the design and analysis of various geotechnical problems such as piles, and slope stabilities. Due to the limited research on clayey soils, the significance of understanding their behavior, and the limitations of laboratory experiments, this study investigates soil behavior via numerical modeling of cone penetration tests in saturated clay with undrained conditions. In this study, the effect of the coefficient of lateral earth pressure and initial effective vertical stresses on pore water pressure has been investigated. Additionally, the correlations between excess pore water pressures at points u2 and u1, as well as u2 and u3, have been outlined. Modified Cam-Clay constitutive model was employed in all numerical analyses using FLAC2D software. The validation of proposed relationships was also addressed using the database of field tests available in the literature provided by different researchers. The obtained results indicated that as each parameter of lateral pressure coefficient and vertical effective stress increased, the excess pore water pressure also increased at all three locations where pore water pressure is measured.

In this research, numerical simulation using the finite element method and PLAXIS numerical software (version 8.2) were used. Also, the calculation point of the road settlement, which is the criterion for comparing different models, is selected in the loading center on the road, which is considered as the representative of the road settlement in the output results of the vertical displacement. The results of the numerical investigation of the effect of the tensile strength of geosynthetics on the road settlement show that this parameter did not have a significant effect on the road settlement. Also, from the numerical modeling of the effect of the length of geosynthetics on the road body, it is determined that the settlement of the road in modeling with geogrid is the same size as the width of the road (which is equal to 7 meters in this model) equal to 3.65 mm and with geogrid 9 meters wide. It is equal to 3.5 mm. The results showed that if the amount of friction between the geosynthetic element and the soil is considered equal to the internal friction angle of the soil, the settlement of the road at the loading center of the model has decreased by 12%. Finally, the investigation of the effect of geosynthetic element placement on the road settlement shows that by moving the geosynthetic layer from the sub-base-substrate boundary to the top-base boundary, the road settlement decreased by 0.9 mm.

Baffled aprons or Chutes have been in use on irrigation projects for many years. The fact that many of these structures have been built and have performed satisfactorily indicates that they are practical and that in many cases they are an economical answer to the problem of dissipating energy. Baffled chutes are used to dissipate the energy in the flow at a drop and are most often used on channel waste ways or drops. During the past 2 decades, heuristic and metaheuristic optimization techniques have emerged as a promising solution, offering several benefits and possibilities. (Saberi et al., 2021; Sedaghat et al., 2019).

In urban environments, due to the existence of structures in the city such as buildings and, more importantly, the presence of people in them, as well as existing underground structures such as service spaces including sewage tunnels, aqueducts, and adjacent tunnels, there have been always concerned about damages to these structures and their interactions existed as a result of tunneling. Significant interaction effects can occur when a new tunnel is dug in the vicinity of an existing tunnel. For example, the construction of a new tunnel could impose unauthorized deformations or bending moments on the existing structural support system. This interaction depends on parameters such as the distance of the tunnels, the size of both tunnels, the rigidity of the support system and the method used to locate the second tunnel, and the geotechnical characteristics of the excavation site.Aqueducts are underground structures and excavating new tunnels can have special interaction effects on these structures. An aqueduct is a subterranean canal with a gentle slope, which connects water-rich zones at high altitudes to the fields where cultivation takes place.According to studies, the interaction between underground structures is one of the critical factors that affect ground displacement and subsidence. The effect of the interaction between the tunnels as well as the amount of face pressure on the ground subsidence has been investigated using methods such as physical modelling, numerical modelling, and local measurements. In this paper, the effect of face pressure has been investigated in excavating the 2nd tunnel Line of Tabriz Metro on existing aqueducts. It is worth noting that for 3D modelling, FLAC3D software is used in this paper.

Weir is one of the most common artificial hydraulic structures that are used to measure flow in canals, divert flow, store water, change the flow regime in canals and control floods during rainfall. Free weirs are divided into two categories: linear and non-linear. One of the most important advantages of piano key weirs compared to linear weirs is the improvement of flow transfer capacity by increasing the length of the crest and as a result, increasing the length of the water passage in a fixed width of the construction without increasing the upstream water load.The purpose of this research is to numerically model the flow and investigate the effect of simultaneous changes in the number of cycles and the angle of the weir on the flow coefficient by trying to keep the total length of the weir crest and other geometric parameters constant for all models. After the investigations, it was found that increasing the weir angle of the piano key at a fixed length for all models increases the flow coefficient, while increasing the number of cycles at a fixed length for all models due to the reduction of the inlet key water tank area, increasing the contraction of the current stream lines and then intensifying the local submergence in the outlet key, the current permeability coefficient will decrease significantly

The advancement of technology with an increasing population has led to the requirement for high-speed mobility trains. High-speed transportation by trains requires passing through soft soil conditions, which requires stability. High-speed trains are used nowadays in developed countries to reduce travel time. When the train moves at a critical speed, it can significantly increase the dynamic responses of the components on the railway lines. The present study examines the results of 3D numerical modeling, considering the impact of the high-speed train passing through the mechanical earth wall stabilized by plate anchors. Numerical modeling was carried out using Plaxis 3D finite element software. The impact of various factors such as the speed of the train (180, 200 & 250 Km/h), the number of plates (single, double, and triple), and the number of train tracks (1 & 2 tracks) have been investigated. The Hardening soil with small strain model has been used for modeling the behavior of the backfill soil. In this study, the geometrical characteristics of the Thalys high-speed train were used to model the train passing through the walls of 6 meters that were stabilized with plate anchors. From the results, it was concluded that Increasing train speed from 160 to 250 Km/h increases the settlement under the rails by 11% and increases the horizontal displacement of the wall by 13%. It was confirmed that increasing train speed will result in an increase in the settlement under the rails and increases the horizontal displacement of the wall in all investigated cases. Increasing the number of plates along with decreasing their dimensions has a positive effect on the wall’s performance with regard to the horizontal displacement of the wall. Also, it should be mentioned that by increasing the number of train tracks from 1 to 2, the settlement under the rails increased by 5%, and the horizontal displacement of the wall increased by 20%.

 In this research, comprehensive studies have been carried out by laboratory and numerical modeling methods on the variables affecting soil improvement with soil-cement columns under different conditions of overhead and seismic loading. experimental studies are aimed at evaluating the performance of soil-cement columns in soft ground stabilization under two conditions of rigid footing and embankment fill, and based on the results, the numerical modeling was defined and validated (numerical modeling error less than 8%).
The results of experimental studies showed that the stabilization by using soil-cement column under embankment fill condition caused more stabilization of soft soil compared to the condition of rigid footing and the amount of settlement decreased by 75% and 55% respectively. The results of numerical modeling showed that the use of soil-cement column has improved the seismic behavior of soft soil and the average of settlement under the loading of 5 major earthquakes has decreased by 54.13% under rigid footing conditions and 71.63% under embankment fill.

The use of structural elements such as piles are considered as an effective solution in improving the overall performance of an embankment system in terms of stability and settlement control. In recent years using helical piles has been considered due to their proper performance. This research presents a numerical investigation to compare the performance of embankments rested on concrete and helical piles. A 3D finite element models are developed separately in ABAQUS software for embankments based on helical and concrete piles while the length and diameter of their pile shafts are the same. The model was validated via comparing the obtained numerical results with the field and laboratory measurements (observation). The results show that the helical piles have significantly reduced the settlement in the embankments and the soft foundation soil and controlled lateral embankment displacement. Also, the distribution of axial force along the embedment depth of the pile indicates that the helical pile has higher bearing capacity than the concrete pile and behaves frictionally. The presence of the cap on the helical pile was also examined and the results show that it causes adequate control of the settlement in the embankment system and increases the bearing capacity of the piles. In addition, adding the blade to the pile body at different distances does not have a significant effect on improving the performance of the pile-supported embankment system while it could lead to embankment settlement and lower load transmission.

Numerical simulation has increasingly become a very important tool for solving complex phenomena in fluid mechanics. Today, computational fluid dynamics (CFD), which uses numerical simulation to solve fluid flow problems, has become a major tool in many scientific and engineering studies. So far, most simulations have been performed using network-based Euler methods. The main problem with using such methods is the presence of sharp and mobile joints as well as free surface cells that require complex behaviors. In recent years, a new generation of numerical methods called mesh-free particle methods (Lagrangian) has been developed to solve computational fluid dynamics (CFD) problems. In these methods, the domain of the fluid is represented by a set of moving particles in the Lagrangian system. Mesh-free Lagrangian methods, including SPH and MPS, allow numerical modeling of flow in the face of large deformations or Discontinuity of boundaries. Due to the importance of the subject, the purpose of this study is to simulate the hydrodynamics of flow on the overflow of Dahan Ghaleh dam using a mesh-free Lagrangian method based on weakly compressible moving particle semi-implicit formulation (WC-MPS).

In Lagrangian methods, unlike the Eulerian method, instead of networking the solution field and discrete the equations on the nodes, the solution field is divided into a number of particles and the discrete equations are solved on these particles. In fact, the governing equations are transformed into particle interaction equations using different operators. In the WC-MPS method, the system is considered as a system with weakly compressibility and calculates the pressure of each particle using the state equation. The MPS method uses particle density to track the free surface. Because there are no particles outside the free surface, the density of the particles on the free surface decreases severely. A particle is known as a free surface particle whose density is somewhat lower than the standard particle density. The value of this limit may be selected from 80% to 99% depending on the problem. Therefore, the pressure of this particle on the free surface will be set to zero in each time step and there is no need to apply any additional conditions for the free surface. For solid (impermeable) boundaries, such as walls or beds, In the vicinity of solid boundaries, the particle density decreases, which can lead to computational disturbances. Therefore, a number of ghost particles are located outside the boundaries to prevent this density reduction. In order to model the inlet and outlet flow, the particle recycling method at the inlet and outlet boundaries, which was developed by Jafari Nodoushan et al. (2016) was used.

In this study hydraulic parameters of the flow on the broad crested weirs, chute, and flip bucket of Dahan Ghaleh dam are investigated. At first, the free surface profile was compared at times t = 1, 5, 10, 15, 30 seconds for three flow rates of 461, 600, and 904 m3/s. when the discharge is 600 m3/s, the depth and velocity of the flow at the beginning of the channel will be 1.1 m and 9.1 m/s, respectively. The value of the depth and velocity of the flow at the beginning of the channel in WCMPS modeling is 1.191 m and 8.420 m/s, respectively, which shows the accuracy of the model in predicting the depth and velocity of the flow. In this research, the pressure is simulated in the form of pressure contour at different points in terms (pa) for three different flow rates. The highest pressure is near the bed in the approach channel and no part of the broad crested weirs, chute, and flip bucket is under negative pressure. Simulation of cavitation index has been done in broad crested weirs, chute, and flip bucket. the results showed that the cavitation index in the range of 110m to 140m has approached the critical value and the possibility of creating cavitation phenomenon in this area is more than in other places, but considering the cavitation index value in this area is greater than 1.8, according to the recommendation Falvey (1990) it does not need to be protected against cavitation. At the end, the height and length of the jump from the edge of the bucket for different discharges have been investigated.

In this study, the hydraulic parameters of the flow on the broad crested weirs, chute, and flip bucket of Dahan Ghaleh dam are investigated. The desired model has simulated the depth and velocity of the flow at the beginning of the channel after of the overflow, depth, velocity, and Froude number of the flow in the bucket floor with an error of less than 10%, and the jump length per discharge 600 (m3/s) with a maximum error of 12% has simulated. The comparison of the results indicates the accuracy and reliability of the results of the developed model.

In tunnel drilling operations using tunnel boring machine (TBM), a relatively large concentrated load is applied by the device jacks to the prefabricated parts or segments of the tunnel cover. This load leads to significant tensile stresses in the segments. One of the most important parameters affecting the tensile stresses in the segments is the geometry of the loading plates of the trust jacks. In this study, with the aim of reduction of the values of tensile stresses in the segments, the innovative changes in the geometry of the loading plates of the propulsion jacks have been evaluated experimentally and numerically.

The purpose of this paper is to evaluate the behavior of vulnerable joints of substandard RC frames, improved by Shear and flexural retrofit of beam-column joints using FRP sheets. For this purpose, the behavior of the retrofitted joints is compared with the control joints with and without special seismic details. Considering the main focus of previous studies on two-dimensional joints and not considering the real conditions including the effect of slab and transverse beam in the joints, in order to apply geometric conditions and constructional limitations, in this study the behavior of joints with slab and transverse beam effect has been extracted by experimental study. For this purpose, 2 experimental specimens of concrete exterior beam-column joint with a scale of 1/2 are made and subjected to a cyclic load. The specimens include one control specimen, without special seismic details, and the other retrofitted specimen include a joint without seismic detail, which has been improved with FRP sheets. Finally, the studied joints were modeled using OpenSees software and compared with the experimental results of the research. The results of the retrofitted joint behavior show no strength drop, stable cyclic behavior, reduced pinching effects, improved cyclic behavior due to change of the failure mode from shear failure of the joints to the formation of flexural plastic hinges in the beam. This performance can be attributed to the effectiveness of the proposed retrofit methods in promoting the behavior of vulnerable joints with real geometric conditions