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Showing 12 results for Numerical Simulation

Sabagh Yazdi S.r., Mohammad Zadeh Qomi M.,
Volume 2, Issue 2 (6-2004)
Abstract

A numerical model is introduced for solution of shallow water flow equations with negligible physical dissipations due to canal roughness and turbulence effects. Two-dimensional velocity distribution and water depth of the flow field are computed by solving the depth average equations of continuity and motion. The equations are converted to discrete form using cell vertexfinite volume method on triangular unstructured mesh. The formulation of the added numericalviscosity is chosen in such a way that preserves the accuracy of numerical results. The accuracy ofthe model is assessed by computing the challenging case of inviscid frictionless flow in a canal with a 1800 bend. The computed results are compared with analytical solution which is obtainedfrom potential flow theory. Simulation of frictionless free surface flow in a constant width meandering sinusoidal canal is considered as an application of the model. The algorithm produced encouraging results.
D. P. Chen, C. X. Qian, C. L. Liu,
Volume 8, Issue 4 (12-2010)
Abstract

 Concrete deformation due to temperature and moisture condition will always develop simultaneously and interactively. The environmentally (hygral and thermally) induced stress and deformation are essential to concrete durability. To simulate the deformation of concrete caused by the coupling effect of temperature and moisture, a numerical simulation approach is proposed comprising analytical process and finite element analysis is proposed based on the mechanism of heat and moisture transfer in porous medium. In analytical method, Laplace transformation and transfer function were used to simplify and solve the coupled partial differential equations of heat and moisture transfer. The hygro-thermal deformation of concrete is numerically simulated by finite element method (FEM) based on the obtained temperature and moisture stress transformed from the solved moisture distribution. This numerical simulation approach avoids the complex eigenvalues, coupling difficulty and low accuracy in other solving method, and also effectively calculates the moisture induced shrinkage which is almost impossible using familiar FEM software. Furthermore, a software named Combined Temperature and Moisture Simulation System for concrete (CTMSoft) was represented and developed by a mix programming of Visual Basic, Matlab and ANSYS. CTMSoft provided a simple and more intuitive interface between user and computer by providing a graphical user interface (GUI). The validity of the numerical simulation approach was verified by two cases analysis.


Kabir Sadeghi,
Volume 9, Issue 3 (9-2011)
Abstract

An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structurechr('39')s force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.


K. Sadeghi,
Volume 12, Issue 3 (9-2014)
Abstract

An analytical nonlinear stress-strain model and a microscopic damage index for confined and unconfined concretes together with a macroscopic damage index for reinforced concrete (RC) structures under cyclic loading are proposed. In order to eliminate the problem of scale effect, an adjustable finite element computer program was generated to simulate RC structures subjected to cyclic loading. By comparing the simulated and experimental results of tests on the full-scale structural members and concrete cylindrical samples, the proposed stress-strain model for confined and unconfined concretes under cyclic loading was accordingly modified and then validated. The proposed model has a strong mathematical structure and can readily be adapted to achieve a higher degree of precision by modifying the relevant coefficients based on more precise tests. To apply the proposed damage indices at the microscopic and macroscopic levels, respectively, stress-strain data of finite elements (confined and unconfined concrete elements) and moment-curvature data of critical section are employed. The proposed microscopic damage index can easily be calculated by using the proposed simple analytic nonlinear stress-strain model for confined and unconfined concretes. The proposed macroscopic damage index is based on the evaluation of nonlinear local degradation of materials and taking into account the pseudo-plastic hinge produced in the critical section of the structural element. One of the advantages of the macroscopic damage index is that the moment-curvature data of the critical section is sufficient in itself and there is no need to obtain the force-displacement data of the structural member.
M. Heidarzadeh, A. A. Mirghasemi, H. Niroomand,
Volume 13, Issue 1 (3-2015)
Abstract

We report engineering experiences from the critical task of relief well installation under high artesian flow conditions at the downstream toe of the Karkheh earth dam, Iran. Due to the establishment of excessive uplift pressure at the downstream toe of the Karkheh dam, installation of a series of new relief wells was considered to permanently relieve part of these pressures. The mentioned uplift pressure, as high as around 30 m above the ground level, was produced in a confined conglomerate aquifer bounded above and below by relatively impervious mudstone layers which reduced the safety factor of the dam toe to below 1.0. Investigations on the shortcomings of the old relief wells installed at the dam site showed that the main problems were: insufficient well numbers, insufficient well diameters, irregular well screens causing their blockage by time passing, and insufficient total opening area. Despite engineering difficulties and associated risk of downstream toe instability, installation of new relief wells was successfully completed under high artesian flow conditions” was successfully completed. The employed technique for the construction of the new relief wells under flowing artesian conditions was based on: 1) cement grouting and casing of the well, 2) telescopic drilling, 3) application of appropriate drilling fluid, and 4) controlling the artesian flow by adding a long vertical pipe to the top of the relief wells. Numerical modeling of seepage for the Karkheh dam foundation showed that, as a result of the installation of the new relief wells, the safety factor of the downstream toe increased to the safe value of 1.3 for the normal reservoir water level.
D.p. Chen, C.w. Miao, J.p. Liu, M.s. Tang,
Volume 13, Issue 3 (9-2015)
Abstract

This paper presents theoretical and numerical state-of-the-art information in the field of hygro-thermo-mechanical deformation simulation in structural concrete. The aspects discussed include coupled hygro-thermo-mechanical performance of porous materials including concrete, multi-scale simulation of concrete properties especially the volumetric and structural deformation performance, and the multi-scale simulation of concrete under the coupling effect of multi-physics fields. The multi-scale simulation section includes the multi-scale simulation of composition and structure in concrete, the multi-scale simulation of concrete’s mechanical performance, and the multi-scale simulation of durability concerned performance of concrete. This paper presents an overview of the work, of which data from early 80 recent studies, carried out on the multiscale simulation of hygro-thermo-mechanical deformation performance of structural concrete. The relating previous studies and analysis showed that sufficient data have been obtained to give confidence in simulating hygro-thermo-mechanical performance of concrete based on the theory of heat and mass transfer in porous media, and the clear relationships have been obtained between moisture-heat transfer and hygro-thermal distribution at different scale. It is necessary to make further systematic multi-scale research on the relationship between micro-structure and property parameters of cement paste, threephase basic properties at meso level of concrete and the performance of concrete structures, which makes important practical significance to solve the crack of large-area and mass concrete structure and improve the durability of concrete structures
R. Abbasnia, M. Aslami,
Volume 13, Issue 3 (9-2015)
Abstract

A new model is proposed for two-dimensional simulation of the concrete fracture in compression. The model generated by using the Voronoi diagram method and with considering random shape and distribution of full graded aggregates at the mesoscopic level. The aggregates modeled by combining irregular polygons, which then is placed into the concrete with no intersection between them. By this new modeling approach, the simulation of high-strength concretes with possible aggregates fracture is also feasible. After generation of the geometrical model, a coupled explicit discrete element method and a modified rigid body spring model have been used for solution. In this method, all the neighboring elements are connected by springs. The mortar springs have Elasto-plastic behavior and considering normal concrete, the aggregate springs behave only elastically without any fracture. The proposed model can accurately predict the mechanical behavior of concrete under compression for small and large deformations both descriptively and quantitatively
Shuai Li, Jian-Min Zhang, Wei-Lin Xu, Jian-Gang Chen, Yong Peng, Jun-Ning Li, Xiao-Long He,
Volume 14, Issue 1 (1-2016)
Abstract

The cavitation erosion induced by high flow velocities is very prominent in high head and large unit discharge tunnel. Air entrainment is an effective technology to solve this problem. In this study, numerical simulation and physical model test are applied to the comparative study of air-water flows on bottom and lateral aerator in tunnel. The flow pattern, aeration cavity, air concentration and pressure distribution were obtained and there is a close agreement between the numerical and physical model values. The hydraulic characteristic and aeration effect of anti-arc section are analyzed. The results indicated that added lateral aeration facilities on 1# and 2# aerator can weaken backwater and increase the length of the bottom cavity, but it is limited to improve the air concentration and protect sidewall downstream of the ogee section. Air concentration improved on side walls downstream of anti-arc section when added lateral aeration facility on 3# aerator. The black water triangle zone disappeared and the floor and side walls well protected.


Kabir Sadeghi,
Volume 14, Issue 5 (7-2016)
Abstract

A fast converging and fairly accurate nonlinear simulation method to assess the behavior of reinforced concrete columns subjected to static oriented pushover force and axial loading (sections under biaxial bending moment and axial loading) is proposed. In the proposed method, the sections of column are discretized into “Variable Oblique Finite Elements” (VOFE). By applying the proposed oblique discretization method, the time of calculation is significantly decreased and since VOFE are always parallel to neutral axis, a uniform stress distribution along each oblique element is established. Consequently, the variations of stress distribution across an element are quite small which increases the accuracy of the calculations. In the discretization of section, the number of VOFE is significantly smaller than the number of “Fixed Rectangular Finite Elements” (FRFE). The advantages of using VOFE compared to FRFE are faster convergence and more accurate results. The nonlinear local degradation of materials and the pseudo-plastic hinge produced in the critical sections of the column are also considered in the proposed simulation method. A computer program is developed to calculate the local and global behavior of reinforced concrete columns under static oriented pushover and cyclic loading. The proposed simulation method is validated by the results of tests carried out on the full-scale reinforced concrete columns. The application of the “Components Effects Combination Method” (CECM) is compared with the proposed “Simultaneous Direct Method” (SDM). The obtained results show the necessity of applying SDM for nonlinear calculations. Especially during the post-elastic phase, which occurs frequently during earthquake loading.


Kabir Sadeghi,
Volume 15, Issue 1 (1-2017)
Abstract

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Biaxial Bending Moment and Axial Loading (CBBMAL). In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of the columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE). The basic equilibrium is justified over a critical hypothetical cross-section assuming the Kinematics Navier’s hypothesis with an average curvature. The method used qualifies as a “Strain Plane Control Process” that requires the resolution of a quasi-static simultaneous equations system using a triple iteration process over the strains in each section. In order to reach equilibrium, three main strain parameters (the strains in the extreme compressive point, the strains in the extreme tensile point and the strains in another corner of the section) are used as three main variables. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns. The application of the Components Effects Combination Method (CECM) is also compared with the proposed Simultaneous Direct Method (SDM). The results obtained show the necessity of applying SDM for the post-elastic phase, which occurs frequently during earthquake loading.


Xilin Lu,
Volume 15, Issue 6 (9-2017)
Abstract

This paper presents numerical and theoretical studies on the stability of shallow shield tunnel face found in cohesive-frictional soil. The minimum limit support pressure was determined by superposition method; it was calculated by multiplying soil cohesion, surcharge load, and soil weight by their corresponding coefficients. The varying characteristics of these coefficients with soil friction angle and tunnel cover-to-diameter ratio were obtained by wedge model and numerical simulation. The face stability of shallow shield tunnel with seepage was studied by deformation and seepage coupled numerical simulation; the constitutive model used in the analysis was elastic-perfectly plastic Mohr–Coulomb model. The failure mode of tunnel face was shown related to water level. By considering the effect of seepage on failure mode, the wedge model was modified to calculate the limit support pressure under seepage condition. The water head around the tunnel face was fitted by an exponential function, and then an analytical solution to the limit support pressure under seepage condition was deduced. The variations in the limit support pressure on strength parameters of soil and water lever compare well with the numerical results. The modified wedge model was employed to analyze the tunnel face stability of Qianjiang cross-river shield tunnel. The influence of tide on the limit support pressure was obtained, and the calculated limit support pressure by the modified wedge model is consistent with the numerical result.



Volume 15, Issue 6 (9-2017)
Abstract

It is vital to control the settlement of ultra-high voltage and long span tower foundation because of the difficult construction and strict deformation control. Based on the thinking of deformation compatibility, the mechanical model of deformation compatibility between pile and soil is established. Relying on the long span tower project Lingzhou–Shaoxing ±800 kV DC transmission lines across the Yangtze River, through checking ultimate bearing capacity of existing pile foundation, it can be obtained that the present design foundation can effectively meet the upper 200–220 t load, but it cannot meet the load requirements about 300 t in the construction. The failures of tower foundation mainly display that piles cut into the soil with penetration type in the early condition. With the load increasing, the shallow soil and infrastructure gradually damage with the whole cap sinking, cushion layer destruction and the surrounding soil uplifting. As a result, tower foundation is unable to withstand the effect of upper overload and the whole tower becomes shear failure. The treatment scheme was proposed that it can improve the cushion thickness and strength combined with grouting consolidation to soil around the piles. Thus, the stability of tower foundation improves significantly and settlement was controlled within the permitted range of below 10 mm, which can meet the structure requirements. The results of numerical simulation based on deformation compatibility between pile and soil coincide well with field measured results.



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