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Maximum entropy based finite element analysis of porous media

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Frontiers of Structural and Civil Engineering 2019年第2期13卷 364-379页

作者： Emad NOROUZI Hesam MOSLEMZADEH soheil mohammadi High Performance Computing Laboratory School of Civil EngineeringFaculty of EngineeringUniversity of TehranTehranIran

The maximum entropy theory has been used in a wide variety of physical, mathematical and engineering applications in the past few years. However, its application in numerical methods, especially in developing new shape functions, has attracted much interest in recent years. These shape functions possess the potential for performing better than the conventional basis functions in problems with randomly generated coarse meshes. In this paper, the maximum entropy theory is adopted to spatially discretize the defonnation variable of the governing coupled equations of porous media. This is in line with the well-known fact that higher-order shape functions can provide more stable solutions in porous problems. Some of the benchmark problems in deformable porous media are solved with the developed approach and the results are compared with available references.

关键词： maximum entropy FEM fully coupled multi-phase system porous media

Numerical analysis of rock fracturing by gas pressure using the extended finite element method

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Petroleum Science 2015年第2期12卷 304-315页

作者： Majid Goodarzi soheil mohammadi Ahmad Jafari Department of Civil Engineering and Geoscience University of Newcastle School of Civil Engineering University of Tehran School of Mining Engineering University of Tehran

High energy gas fracturing is a simple approach of applying high pressure gas to stimulate wells by gen- erating several radial cracks without creating any other damages to the wells. In this paper, a numerical algorithm is proposed to quantitatively simulate propagation of these fractures around a pressurized hole as a quasi-static phenomenon. The gas flow through the cracks is assumed as a one-dimensional transient flow, governed by equations of conservation of mass and momentum. The fractured medium is modeled with the extended finite element method, and the stress intensity factor is calculated by the simple, though sufficiently accurate, displacement ex- trapolation method. To evaluate the proposed algorithm, two field tests are simulated and the unknown parameters are determined through calibration. Sensitivity analyses are performed on the main effective parameters. Considering that the level of uncertainty is very high in these types of engineering problems, the results show a good agreement with the experimental data. They are also consistent with the theory that the final crack length is mainly determined by the gas pressure rather than the initial crack length produced by the stress waves.

关键词： Gas fracturing Numerical modeling Extended finite element Fracture mechanics

Micromechanics of breakage in sharp-edge particles using combined DEM and FEM

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Particuology 2008年第5期6卷 347-361页

作者： Ahad Bagherzadeh-Khalkhali Ali Asghar Mirghasemi soheil mohammadi School of Civil Engineering University College of EngineeringUniversity of Tehran

By combining DEM （Discrete Element Method） and FEM （Finite Element Method）, a model is established to simulate the breakage of twodimensional sharp-edge particles, in which the simulated particles are assumed to have no cracks. Particles can, however, crush during different stages of the numerical analysis, if stress-based breakage criteria are fulfilled inside the particles. With this model, it is possible to study the influence of particle breakage on macro- and micro-mechanical behavior of simulated angular materials. Two series of tests, with and without breakable particles, are simulated under different confining pressures based on conditions of biaxial tests. The results, presented in terms of micromechanical behavior for different confining pressures, are compared with macroparameters. The influence of particle breakage on microstructure of sharp-edge materials is discussed and the related confining pressure effects are investigated. Breakage of particles in rockfill materials are shown to reduce the anisotropy coefficients of the samples and therefore their strength and dilation behaviors.

关键词： DEM FEM Particle breakage Rockfill Micromechanics Anisotropy Confining pressure

Wavelet-based iterative data enhancement for implementation in purification of modal frequency for extremely noisy ambient vibration tests in Shiraz-Iran

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Frontiers of Structural and Civil Engineering 2020年第2期14卷 446-472页

作者： Hassan YOUSEFI Alireza TAGHAVI KANI Iradj MAHMOUDZADEH KANI soheil mohammadiA High Performance Computing Lab Schoo of Civil EngineeringFaculy of EngineeringUniversity of TehranTehranIran School of Civil Engineering Faculty of EngineeringUniversity of TehranTehranIran

The main purpose of the present study is to enhance high-level noisy data by a wavelet-based iterative filtering algorithm for identification of natural frequencies during ambient wind vibrational tests on a petrochemical process *** of denoising methods fail to filter such noise *** the signal-to-noise ratio and the peak signal-to-noise ratio are ***-based one-step and variational-based filtering methods fail to denoise properly with thresholds obtained by theoretical or empirical *** to the fact that it is impossible to completely denoise such high-level noisy data,the enhancing approach is used to improve the data quality,which is the main novelty from the application point of view *** this iterative method,a simple computational approach is proposed to estimate the dynamic threshold ***,different thresholds can be obtained for different recorded signals in one ambient *** is in contrast to commonly used approaches recommending one global threshold estimated mainly by an empirical *** the enhancements,modal frequencies are directly detected by the cross wavelet transform(XWT),the spectral power density and autocorrelation of wavelet *** frequencies are then compared with those of an undamaged-model,simulated by the finite element method.

关键词： ambient vibration test high level noise iterative signal enhancement wavelet cross and autocorrelation of wavelets

Dynamic Adaptive Finite Element Analysis of Acoustic Wave Propagation Due to Underwater Explosion for Fluid-structure Interaction Problems

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Journal of Marine Science and Application 2015年第3期14卷 302-315页

作者： Seyed Shahab Emamzadeh Mohammad Taghi Ahmadi soheil mohammadi Masoud Biglarkhani Islamic Azad University Kangan Branch Kangan *** Iran Department of Civil Engineering Tarbiat Modares University Tehran 14115-143 Iran School of Civil Engineering University of Tehran Tehran 4563-11155 Iran Department of Civil Engineering University of Hormozgan Hormozgan 3995 Iran

In this paper, an investigation into the propagation of far field explosion waves in water and their effects on nearby structures are carried out. For the far field structure, the motion of the fluid surrounding the structure may be assumed small, allowing linearization of the governing fluid equations. A complete analysis of the problem must involve simultaneous solution of the dynamic response of the structure and the propagation of explosion wave in the surrounding fluid. In this study, a dynamic adaptive finite element procedure is proposed. Its application to the solution of a 2D fluid-structure interaction is investigated in the time domain. The research includes：a） calculation of the far-field scatter wave due to underwater explosion including solution of the time-depended acoustic wave equation, b） fluid-structure interaction analysis using coupled Euler-Lagrangian approach, and c） adaptive finite element procedures employing error estimates, and re-meshing. The temporal mesh adaptation is achieved by local regeneration of the grid using a time-dependent error indicator based on curvature of pressure function. As a result, the overall response is better predicted by a moving mesh than an equivalent uniform mesh. In addition, the cost of computation for large problems is reduced while the accuracy is improved.

关键词： adaptive mesh fluid-structure interaction acoustic wave finite element analysis underwater explosion

Light Scattering and SAXS Study of AOT Microemulsion at Low Size Droplet

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Soft Nanoscience Letters 2012年第1期2卷 8-12页

作者： soheil Sharifi Masoud Amirkhani Jahanbakhsh Mashaiekhy Asla Mohamad Reza mohammadi Othmar Marti 不详

We study collective diffusion coefficient (Dc) of Water-in-oil nanoemulsions (L2 phase) stabilized by AOT and dispersed in n-Decane oils by dynamic light scattering (DLS). At constant water concentration we vary the oil concentration and there is clear evidence for a changing collective diffusion coefficient of the droplets in AOT nanoemuslion. The collective diffusion coefficient in AOT nanoemulsions is studied from relaxation investigations with dynamic light scattering. Also, we study the collective diffusion coefficient (Dc) of droplets with add the TBAC to the droplets of AOT nanoemulsion. We discuss the results with study structural investigations with small-angle x-ray scattering. The results of this study suggest that the formation of non-spherical aggregates at low concentration of droplets can describe the behavior of the collective diffusion coefficient at AOT nanoemulsion.

关键词： Nano-droplet Microemulsions Light scattering SAXS Diffusion

Efficacy and safety of ivermectin in patients with mild and moderate COVID-19:A randomized controlled trial

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Asian Pacific Journal of Tropical Medicine 2023年第1期16卷 3-8页

作者： Alireza Malektojari Sara Ghazizadeh Mohammad Hamed Ersi Elham Brahimi soheil Hassanipour Mohammad Fathalipour Mehdi Hassaniazad Evidence Based Medicine Center Hormozgan University of Medical SciencesBandar AbbasIran Clinical Research Development Center of Shahid mohammadi Hospital Hormozgan University of Medical SciencesBandar AbbasIran Infectious and Tropical Diseases Research Center Hormozgan Health InstituteHormozgan University of Medical SciencesBandar AbbasIran Gastrointestinal and Liver Diseases Research Center Guilan University of Medical SciencesRashtIran Department of Pharmacology and Toxicology Faculty of PharmacyHormozgan University of Medical SciencesBandar AbbasIran

Objective:To evaluate the effectiveness and safety of ivermectin in patients with mild and moderate ***:This study was a single-center,randomized,open-label,controlled trial with a 2-arm parallel-group design on 68 patients with *** to the 1:1 ratio between the study groups(ivermectin group and standard treatment group),patients were randomly admitted to each intervention ***:The mean age of the participants in the ivermectin group was(48.37±13.32)*** of them were males(54.5%)and the participants in the control group had a mean age of(46.28±14.47)years,with nineteen of them being males(59.4%).As a primary outcome,after 5 days of randomization,there was no significant difference between the ivermectin group and the control group in the length of stay in the hospital(P=0.168).ICU admission(P=0.764),length of stay in ICU(P=0.622),in-hospital mortality(P=0.427),adverse drug reactions,and changes in the mean difference of laboratory data had not any significant difference between the two groups(except for urea change).In addition,the radiologic findings of the two groups of patients were not significantly *** regression analysis showed that for every 10 years increase of age,0.6 day of hospitalization duration was *** was no statistically significant association between other variables and clinical ***:Among adult hospitalized patients with moderate to severe COVID-19,there was no significant relationship between the administration of ivermectin single dose in a five-day course and clinical improvement,and mortality of the participants.

关键词： COVID-19 Randomized controlled trial Ivermectin Hospitalization Mechanical ventilation Clinical symptoms