جستجوی مقالات مرتبط با کلیدواژه « numerical modeling » در نشریات گروه « عمران »

Environmental vibrations can have a significant impact on noise pollution and the health of the residents of buildings adjacent the vibration sources. Therefore, the studies conducted in the last two decades on reducing vibrations have attracted a lot of attention from researchers. In this study, the effect of different types of improved trenches with Leca lightweight aggregate, including single and double-walled trenches in both active and passive modes, has been investigated, using the combination of Plexis3D finite element software and Python programming language, and the models with the results of other researches. It has been validated and also, a parametric study has been done to evaluate the effect of geometrical factors including depth, width and length for both systems. The obtained results indicate that in order to achieve an acceptable amount of trench efficiency, the depth of 0.8λr and 1λr is sufficient as the optimal depth for single and wall systems, respectively, and considering the effect of the width of the trench filled with Leca, a width equal to 0.2λr and 0.15λr are enough to reach the optimal width for single-wall and double-wall systems, respectively. Also, for passive design, the role of depth can be ignored for single and double-walled barriers, because trench width plays a more important role compared to trench depth. Moreover, to achieve an acceptable single-wall system, the normal width should be increased to about 0.2λr.

In this research, the seismic behavior of the back-to-back MSE walls has been assessed in a probabilistic approach using the fragility curves and the effect of the overlapping length of the metal strips on the vulnerability of this type of walls has been investigated. To this end, the back-to-back MSE walls are simulated using FLAC2D finite difference program, and validated with a shaking table physical model test. So, using the results of nonlinear incremental analysis, fragility curves are analytically extracted based on PGA and PGV intensity measures under far-field and near-fault earthquakes. The obtained results, in addition to providing the possibility of predicting the vulnerability of the wall in different seismic intensities, indicate that increasing the length of the metal strips from 0.65 to 0.85 of the wall height (increasing the overlapping length from 0.3 to 0.7wall height), reduces the probability of seismic damage up to 35% in the far-field and by about 50% in the near-fault earthquakes, respectively.

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 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.

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%.

The retrofitting plan is effective when, in addition to being cost-effective, it minimizes casualties, reduces infrastructure damage, and limits the extent and scope of damages as much as possible. The design and construction of most explosion-resistant barriers in all types of structures are not optimal due to the high cost on the one hand and the low probability of explosion during the life of the structure on the other hand. In this research, the proposal of using the combined method of restraining net along with the blast wave absorber panel as a new model in protecting the building against external explosions has been studied. The rocket is restrained at a certain distance from the main structure by a resistant net and the panel absorbs the wave caused by the explosion. By conducting studies and experiments on various absorbent materials, the selected panel was introduced and its behavior against threats at different distances was evaluated numerically and in the field. The results of the simulations were in good agreement with the field tests, which can be generalized for different amounts of charge.

 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.

In today’s world, roads are considered the main arteries of the global community. One of the most typical methods to build these routes is stabilizing the excavations on two sides of the roads. Using multiple helical anchors in excavation stabilization is one of the means recently used by many road and geotechnical engineers. The increasing use of multiple helical anchors has led to several laboratories, numerical, and field studies. Therefore, this study employed the FLAC 3D software also a three-dimensional numerical investigation of bearing capacity under different inclination angles in sandy soil. In the present study, the effect of soil installation, which is caused by installing helical anchors in the soil, has been studied on the load-bearing capacity of these helical anchors. For this purpose, first, a verification test is done to validate the modeling approach. Then, by performing a parametric analysis, the effect of different inclination angles, as well as the installation effect on the bearing capacity of the multiple helical anchors, are studied. The present study results show that the maximum bearing capacity of the helical anchors is achieved by the angle of 5 and 10 degrees. In addition, by investigating the installation effect, the bearing capacity of the helical anchors has been significantly reduced with respect to the number of helical plates and the density of soil.

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.

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.

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

In this article, seismic vulnerability of one of the ancient monuments ‎in Iran, Falakol aflak Castle, located in ‎Lorestan, is evaluated. In this ‎regard, by conducting field surveys, the damages in different parts of ‎the ‎building were categorized. The results of these investigations ‎indicated erosion and cracking in the ‎construction of the building, ‎settlements of parts of the building that caused cracks in some parts ‎of the building, ‎and rising dampness due to the presence of water ‎flow in the foundation of the building. Next, by modeling the ‎building ‎in Abaqus software, the seismic vulnerability of the building was ‎studied through incremental analysis. The ‎results of this analysis ‎indicated the vulnerability of different parts of the building, which ‎indicated the necessity of ‎presenting a seismic improvement plan. By ‎using in-situ piles and micro piles in the soil as well as vertical ‎reinforced ‎cores in the walls, the results of numerical analysis showed ‎that a significant improvement in the seismic ‎performance of the ‎building has occurred. The intensity of the original maximum plastic ‎strains and its extent were ‎much less compared to the unretrofitted ‎building. Also, the force-displacement diagrams of the building in ‎different ‎directions indicated a significant decrease in the ‎deterioration of the building's stiffness, which indicates the ‎reduction ‎of its vulnerability due to the addition of the proposed improvement ‎system. ‎

Some excavations need to be designed for a long time or sometimes they are left for a long time. Stabilization of most of the excavations has been done using anchors. Field surveys of these excavations show that in some cases, deformation of the excavations increases over time, and the locking force of anchors decreases, leading to dangers. Therefore, it is very important to know the long-term behavior of stabilization systems by an anchor and reduce the anchor load. The main purpose of this study is to evaluate the changes in anchor load in excavations. Numerical modeling of the long-term behavior of soils has many complexities and may not correspond to reality. Therefore, in this study, data on the long-term behavior of an excavation project in Tehran were collected and then numerical modeling in finite difference software was used to study the long-term behavior of this system. Also, using the back analysis method, the input creep variables of the rheological model of the time function in the numerical model were determined and used. Comparison of the results of this research and field survey results confirms the time function behavior of the numerical model performed in software. The results of this research show that in an anchor installed in the middle depth of the excavation project, a 7% reduction in load occurs one year after prestressing. Also, during the creep time, the maximum horizontal deformation of the excavation walls increases by 13% during one year.

Groundwater is an essential source of fresh water, which is less prone to pollution in comparison to surface water, and access to this valuable resource is affordable. These issues make groundwater a viable source during surface water shortages such as drought, especially in arid and semi-arid countries. In this research, the equation of contamination transport in groundwater is modeled by a novel dual discrete finite volume method (DDFVM). Using this numerical method, the contamination concentrations are obtained at the center and vertices of each element. This model has been applied to an unstructured triangular mesh that could be fitted to complex geometric boundaries. For the transient flow regimes, the flow equation has been coupled with the contaminant transport problem, and the results of the numerical model are validated with the model of Modflow. Finally, the flow and transport FV coupled model has been applied in a porous media with strong heterogeneity. The free-oscillation results for the two parameters of head and concentration demonstrate the stability of the model.

Analysis of structural components under fatigue loading due to the complexity of the loading is one of the most challenging problems in civil and structural engineering field. In order to find the fatigue life of a structural member, the costly and time-consuming experiments must be conducted while the collected data is very scattered and cannot be used for other conditions and problems. Therefore, finding effective numerical models to analyze a member subjected to fatigue load, could reducing time and expenses while could offer a systematic and general solution in variety of conditions. In this research, using the findings of a previous experimental study, the behavior of CFRP retrofitted and unretrofitted notched steel beams under fatigue loading has been studied by finite element by numerical modeling in a commercial finite element software. In this study, 11 notched CFRP retrofitted and unretrofitted steel beams (hot-rolled W5×10 made of A36 steel) were modeled and fatigue loaded until failure with stress range between 207 and 379 MPa under frequency of 5 to 10 Hz. The results of numerical modeling were compared with the results of previous experimental study and several equations were presented to estimate the fatigue life of unretrofitted and retrofitted specimens. The normalized stiffness losses of specimens were investigated as well. The verifications showed that numerical models and extracted equations have good agreement with the experimental results.

The stone columns, as a method of soil improvement, significantly reduce soil settlement due to incoming loads and increase soil load-bearing capacity. Adding geotextile as a stone column encasement has a considerable impact on this relationship. In this study, the amount of loose sandy soil settlement was investigated by numerical modelling of stone columns with the Plaxis 3D Foundation software, and the results were validated by using laboratory modelling,. For this purpose, a single stone column was modelled in two modes of rainfall density and compacted states and continuously the group mode in the soil was investigated. Also, the effect of adding geotextile encasement to the inner part of stone column investigated as a central core. So, a 6 centimetre diameter of central core that surrounded with geotextile encasement has considered inside of a 10 centimetre diameter of stone column in both rainfall density and compacted state. The results of experimental and numerical modelling were well-matched with each other. Also, it was clear that the increasing of stone column number and compaction can enhance soil bearing capacity, considerably. The adding of central core has had considerable effect on soil bearing capacity, too. This is due to the increase of all-round stress in the interior of the stone columns. The results showed that the stone column with a diameter of 10 cm increased the bearing capacity compared to unreinforced soil by 36%, while in the stone column with central core in rainfall density and compacted states, this amount is 43% and 54%, respectively. Also by evaluation of appearance deformations in stone columns after loading showed that increasing the density and adding geotextile encasement to the central core has a considerable effect on the created deformations and prevention of local ruptures and the process of deformation becomes more favorable.