numerical modeling

Triaxial soil test is one of the most important and widely used experiments to identify the soil behavior and determination of soil shear strength parameters. Thorough study of the soil behavior requires numerous experiments that require time and cost. The alternative solution is the use of numerical modeling. Numerical modeling requires constitutive soil model to provide a qualitative description of soil behavior using behavioral parameters and provide the relationship between stress-strain in different states and under different loads. In this research, numerical modeling undrained triaxial test with finite element method by Midas GTS NX software under different confining pressures have been done. Validation of the numerical modeling has been done with the data available in the technical literature. The hardening soil model shows the most agreement with the stress-strain behavior of the soil compared to the conventional Mohr-Coulomb model. Therefore, better results can be observed in geotechnical engineering modeling by having hardening soil model parameters. Therefore, in this paper, the behavioral parameters of the hardening soil for the standard Urmia lake sand are determined using repeated numerical modeling using the finite element method and compared with the laboratory results. The matching between these results demonstrates the ability of the present modeling method to determining the required behavioral parameters of all types of soils.

Estimating the cavitation damage to morning-glory spillways is quite important due to the uncertainties that affect cavitation (e.g., high velocity, negative flow pressure, etc.). This paper aims to develop the model uncertainties to address the reliability assessment of the cavitation damage to different points of the Haraz Dam morning-glory spillway in Iran. As an explicit limit state function was lacking to determine the cavitation reliability, 35 samples were produced based on the statistical features, probability distribution and inter-correlation of the uncertainties. Using the Latin Hypercube Simulation (LHS) method and Shapiro-Wilk Test, the cavitation response was found for them through the ANSYS Fluent-3D numerical model analyses, and the implicit LSF was created for 4 critical points on the morning-glory spillway. To do so, the Response Surface Method (RSM) was utilized to generate the explicit LSF and the reliability of the cavitation damage was estimated using the Monte Carlo and first and second order reliability methods. The obtained results show that P4, with pf > 80%, is the most critical overflow point whereas the lowest RMSE is between SORM and MCS method.

One of the most important challenges facing mechanical parts that are exposed to dynamic loads in various industries, such as automotive and aerospace, is their failure due to fatigue. Al-2024 series alloys are widely used due to their high strength-to-weight ratio and high fatigue resistance. Therefore, increasing the fatigue life of structures made of these types of alloys is always one of the most important design issues. In this study, the impact of changes in laser pulse pressure parameters as well as the percentage of overlap of laser effect points in the laser shock process, its effect on the fracture and fatigue behavior of aluminum alloy with the help of numerical modeling methods and also experimental tests were carried out and then evaluated. they got. After examining the results of the fracture tests, it was observed that the fracture toughness of the shocked samples increases by 38%. Also, the fatigue life of the samples treated with this method has been improved by 10-32% in different conditions, and in general, the shock process has been effective in improving the fracture and fatigue behavior of aluminum alloy.

In this article, the laminar flow of an incompressible and viscoelastic fluid inside a channel with porous walls has been investigated using optimal asymptotic homotopy method (OHAM). The flow inside the channel is considered steady and the Darcy model is used to simulate the effects of drag on the flow caused by the porous medium. The governing equations of the problem are converted into non-linear ordinary differential equations and solved. To prove the correctness of the solution, some of the results have been compared with the obtained numerical results. The effects of Darcy number, Deborah number and Reynolds number on the velocity distribution are analyzed. Based on the comparison, the ability and high accuracy of this method to solve the problem has been determined. Finally, it can be concluded that this method can be used as a reliable method to solve the internal flow of fluid inside a channel with a porous wall.

The mountainous areas that cover most of Iran have always been threatened by slope instabilities and landslides. This phenomenon causes a lot of damage to the roads and lands used by humans in these areas every year. The predisposing factors of slope instability such as slope, soil layers and land use cause a lot of damage to natural resources such as rapid soil loss, destruction of agricultural lands, forests and roads. The purpose of this study is to reach the position, role and application of numerical modeling in predicting landslides. Therefore, for this purpose and in FLAC software environment, modeling and numerical analysis were performed by reverse analysis method for seismic landslide in Latian dam watershed and considering all geotechnical criteria (laboratory and field experiments and factors affecting its occurrence). The results were reviewed and evaluated.Reliability calculations for slope stability as well as measuring the displacement of assumed points on the slope, which was performed on accurate geometric modeling and application of physical and mechanical properties of soil layers; showed that the reduction of soil resistance parameters in the region for reasons such as weathering of soil layers and rainfall have been the main causes of this landslide in which the role of water in reducing resistance (severe reduction of adhesion and internal friction angle) and increasing shear force from The pore water pressure is very prominent due to soil saturation.

The environmental pollution crisis caused by the excessive use of fossil fuels and the risk of the destruction of natural resources and reserves, as well as the excessive production of greenhouse gases and, consequently, global warming, led many energy researchers to use renewable energy As a fossil fuel alternative. Solar chimneys are one of the types of renewable energies that have been taken into consideration by researchers over the past decade. Solar chimney power plants are such plants which include solar collectors, chimney and turbines that are placed at the entrance of the chimney. The aim of this study is numerical modeling of a solar chimney power plant prototype model built in Tehran University and investigation of the affecting parameters on enhancement the air velocity within it. The two dimensional numerical modeling based on finite volume method is conducted using  standard wall function turbulence modeling through an optimum mesh. The numerical results show good agreement with experimental data with maximum 6 percent difference in magnitude. Comparing with similar studies, modeling the power plant without using the energy storage properties of the earth by using constant heat flux on the collector regardless of the environmental radiation conditions has been conducted in the present research. The results show that increasing the chimney height, collector radius and collector height and decreasing the radius of the  chimney would result in increasing 76 percent in air velocity through the chimney (from 1.7 m/s in the experimental model to 3m/s) and consequently improving the model efficiency. Furthermore, among the effective parameters, collector and chimney radius play greater roll on increasing the air velocity through the chimney. The results of this research may play significant role on optimizing the constructed solar chimney power plant model.

The study of earth dams behavior during the construction, completion and also the first impoundment as one of the most critical times during the life time of the dam because of the stress and water pure pressure in the core and also water level in this period has special importance. For this purpose, the behavior of the Chahchahe dam was studied by using of obtained results from monitoring recorded data and back analysis was done by GeoStudio finite element software. This dam is an earth dam with core clay and its maximum height is 47 meters from the natural bed of river. Chahchahe dam which has been constructed on Chahchahe river is located in the Kalat basin watershed, in 95 kilometers northeast of Mashhad. In order to consider the parameters in design process and simulate as real conditions of dam construction, back analysis was done base on the results of monitoring to can be predict the behavior of dam. In this study, the comparison of numerical model and monitoring results show acceptable and suitable accordance, so that the amount of settlement in the clay core was obtained 65 cm from monitoring result and evaluated 66 cm by numerical model. Also, the maximum stress at the 530 meter level in the core was read 820 kPa, which was calculated 950 kPa based on the numerical model at the same level, and in all of cases, the obtained values from numerical models are as confidence.

Solar pond technology is the easiest and the most economical system for converting and storing the solar heat energy. In this study, the effect of various parameters such as thickness of various layers, heat loss from the pond’s surface, the wall-shading effect and the pond size on the temperature of the storage zone were numerically investigated. The validity of the model is tested against experimental data for a small square pond constructed and tested in Urmia university under Urmia climate conditions, and a good agreement between theoretical and experimental data for the temperature in the storage zone has been obtained. According to the results it was observed that the thickness of the surface layer should be as thin as possible and that the gradient layer thickness plays a primary role in storing the heat in the pond and its thickness should be selected appropriately. In addition, the results indicated that the heat loss from the pond’s surface occurs mostly by evaporation rather than radiation and convection. It was indicated through case studies that the wall-shading effect is very high in small ponds but in larger ponds the shading effect does not exert a high influence on the storing layer temperature.

Increasing energy cost and reduction of fossil fuel resources have been resulted in increasing demand of renewable energy, such as micro biomass particles in small scale Stirling engines to generate combined heat and power. In such Stirling engines, biomass particles are burnt in external combustion chamber and then, the generated heat is transferred to the working fluid of the engine cycle. Therefore, combustion of fine particle plays basic role in operation and effectiveness of these Stirling engines. Simulation of combustion chambers of those engines using computational fluid dynamics, as a first step of engine design, can reveal more insight to optimization process. In this study, combustion chamber of 55 kW combined heat and power Stirling engine has been simulated and the effects of some parameter have been investigated. The numerical results show good agreement with experiments. Increasing secondary air mass flow rate yields hotter flue gas and higher Stirling engine efficiency. The smaller particles yield to more evaporation and combustion rate of particles which cause to increase outlet temperature. Increasing particle injection velocity causes to decrease burning rate of particle, because some particles leave out the combustor before evaporation and burning.

In this research, the GPR method has been employed to identify subsurface in-homogeneities along Isfahan main power line tunnel as an application in geotechnical engineering practices. To this goal, the GPR response of common 2D synthetic models including horizontal cylinder, 2D prism and arbitrary polygon corresponding to targets encountered in usual geotechnical practices were simulated first. To achieve this objective, an improved 2D finite difference algorithm developed for forward modeling in frequency domain, was used in MATLAB programming environment. Next, the GPR response of 3D synthetic models containing vertical cylinder and sphere (representing usual form of cavities) was produced by means of GPRMAX3D software for more detailed and realistic interpretations. To detect probable subsurface in-homogeneities including different types of manmade buried installations, subsidence and buried wells along the Isfahan main electric power line tunnel, 14 longitudinal GPR profiles covering more than 1200 meters along the tunnel axis were surveyed. The data were collected using a 250 MHz GPR system equipped with shielded antennas. The interpretation of final radargrams after applying different filters revealed that the GPR method is capable of detecting the location and type of subsurface in-homogeneities. In order to verify the performance and ability of GPR method in solving geotechnical problems encountered in real geological conditions and in particular the results obtained in current case study, a vertical borehole was drilled at one of in-homogeneities found on the radargrams which had been interpreted as a buried abandoned well. The result was in agreement with the respective interpreted radargram.