An overview on advances in computational fracture mechanics of rock

Mohammadnejad Mojtaba,Liu Hongyuan,Chan Andrew,Dehkhoda Sevda,Fukuda Daisuke 한국자원공학회 2021 Geosystem engineering Vol.24 No.4

Due to its complexities, rock fracturing process still poses many pressing challenges despite intense research efforts. With the rapid development of computational mechanics, numerical techniques have gradually become robust tools for the investigation of rock fracture. Nevertheless, not all of the devised methods are capable of adequately modelling the rock fracture process. For an accurate simulation of the process, a numerical method needs to be capable of modelling crack initiation, propagation, bifurcation, coalescence and separation. This paper provided a review of recent advances in computational analysis of the rock fracture process, which is built upon a number of literature on numerical modelling of mechanics of failure in rock and other brittle materials. After briefly discussing the fundamentals of rock fracture mechanisms, the basic structure of the existing and recently developed numerical techniques such as finite element method, boundary element method, distinct element method, combined methods and multi-scale coupled method are illustrated. Finally, the strengths and weaknesses of these numerical techniques are discussed and the most promising methods are highlighted.

Optimization of lateral resisting system of framed tubes combined with outrigger and belt truss

Mohammadnejad, Mehrdad,Kazemi, Hasan Haji Techno-Press 2022 Advances in computational design Vol.7 No.1

In this paper, the optimum location of the belt truss-outrigger for a combined system of framed tube, shear core and outrigger-belt truss is calculated. The optimum location is determined by maximization of the first natural frequency. The framed tube is modeled using a non-prismatic cantilever beam with hollow box cross section. The governing differential equation is solved using the weak form integral equations and the natural frequencies of the structure are calculated. The graphs are introduced for quick calculation of the first natural frequency. The location of the belt truss-outrigger that maximizes the first natural frequency of the structure is introduced as an optimum location. The structure is modeled using SAP-2000 finite elements software. In the modelling, the location of the belt truss-outrigger is changed along the height of the structure. With various locations of the outrigger, the lateral deflection of the all stories and axial force in the columns of the outer tube are calculated. The analysis is repeated by locating the outrigger-belt truss at the optimum location. The analysis results are compared and effect of the optimum location on the lateral deflection and the shear lag phenomena are investigated.

A new and simple analytical approach to determining the natural frequencies of framed tube structures

Mohammadnejad, Mehrdad,Kazemi, Hasan Haji Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.1

This paper presents a new and simple solution for determining the natural frequencies of framed tube combined with shear-walls and tube-in-tube systems. The novelty of the presented approach is based on the bending moment function approximation instead of the mode shape function approximation. This novelty makes the presented solution very simpler and very shorter in the mathematical calculations process. The shear stiffness, flexural stiffness and mass per unit length of the structure are variable along the height. The effect of the structure weight on its natural frequencies is considered using a variable axial force. The effects of shear lag phenomena has been investigated on the natural frequencies of the structure. The whole structure is modeled by an equivalent non-prismatic shear-flexural cantilever beam under variable axial forces. The governing differential equation of motion is converted into a system of linear algebraic equations and the natural frequencies are calculated by determining a non-trivial solution for the system of equations. The accuracy of the proposed method is verified through several numerical examples and the results are compared with the literature.

Tunable band gap energy of single-walled zigzag ZnO nanotubes as a potential application in photodetection

Mohammadnejad Shahram,Ahadzadeh Shabnam,Rezaie Mahdiyar Nouri 한국물리학회 2021 Current Applied Physics Vol.29 No.-

ZnO nanotubes play a substantial role in various optoelectronic applications such as light-emitting diodes, solar cells and photodetectors. In this study, the structural, electronic, and optical effects of (n,0) single-walled ZnO nanotubes with different radius are discussed. An ab-initio approach of density functional theory with the generalized gradient approximation has been done by Quantum ESPRESSO software on nanotubes with n = 3 to 6. All simulated ZnO nanotubes illustrate semiconducting behavior, which due to the quantum confinement effect, the band gap value decreases by the increase in diameter. Moreover, optical characteristics including dielectric function ε(ω), refractive index n(ω), optical absorption coefficient α(ω), conductivity σ(ω), energy loss spectrum L(ω) and reflectivity R(ω) have been analyzed and compared. The predicted optical features show that the mentioned nanotubes transmit light in perpendicular polarization better than parallel one and present superior reflect characters. Additionally, ZnO NTs act as a good absorbent in the visible wavelength which they can absorb various colors of the visible spectrum or even UV emission by altering the number of n. This ability turns ZnO NTs into remarkable photodetectors. Furthermore, according to optical characteristics like energy loss spectrum and dielectric function, it is obvious that results are approximately similar for different nanotubes and despite the miner red-shift of the position of the main peak, their appearance is close to each other. Therefore, ZnO NTs can be utilized in various applications such as optical filters, polarizers, and UV shields.

Flapwise and non-local bending vibration of the rotating beams

Mehrdad Mohammadnejad,Hamed Saffari 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.2

Weak form integral equations are developed to investigate the flapwise bending vibration of the rotating beams. Rayleigh and Eringen nonlocal elasticity theories are used to investigate the rotatory inertia and Size-dependency effects on the flapwise bending vibration of the rotating cantilever beams, respectively. Through repetitive integrations, the governing partial differential equations are converted into weak form integral equations. The novelty of the presented approach is the approximation of the mode shape function by a power series which converts the equations into solvable one. Substitution of the power series into weak form integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of the non-trivial solution for resulting system of equations. Accuracy of the proposed method is verified through several numerical examples, in which the influence of the geometry properties, rotatory inertia, rotational speed, taper ratio and size-dependency are investigated on the natural frequencies of the rotating beam. Application of the weak form integral equations has made the solution simpler and shorter in the mathematical process. Presented relations can be used to obtain a close-form solution for quick calculation of the first five natural frequencies of the beams with flapwise vibration and non-local effects. The analysis results are compared with those obtained from other available published references.

A new analytical approach for determination of flexural, axial and torsional natural frequencies of beams

Mehrdad Mohammadnejad 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.3

In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.

A new and simple analytical approach to determining the natural frequencies of framed tube structures

Mehrdad Mohammadnejad,Hasan Haji-Kazemi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.1

This paper presents a new and simple solution for determining the natural frequencies of framed tube combined with shear-walls and tube-in-tube systems. The novelty of the presented approach is based on the bending moment function approximation instead of the mode shape function approximation. This novelty makes the presented solution very simpler and very shorter in the mathematical calculations process. The shear stiffness, flexural stiffness and mass per unit length of the structure are variable along the height. The effect of the structure weight on its natural frequencies is considered using a variable axial force. The effects of shear lag phenomena has been investigated on the natural frequencies of the structure. The whole structure is modeled by an equivalent non-prismatic shear-flexural cantilever beam under variable axial forces. The governing differential equation of motion is converted into a system of linear algebraic equations and the natural frequencies are calculated by determining a non-trivial solution for the system of equations. The accuracy of the proposed method is verified through several numerical examples and the results are compared with the literature.

Free vibration analysis of non-prismatic beams under variable axial forces

Saffari, H.,Mohammadnejad, M.,Bagheripour, M.H. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.5

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

Gene Co-expression Network Analysis Associated with Acupuncture Treatment of Rheumatoid Arthritis: An Animal Model

Dea Louise Ravn,Afsaneh Mohammadnejad,Kemal Sabaredzovic,Weilong Li,Jesper Lund,Shuxia Li,Anders Jørgen Svendsen,Veit Schwämmle,Qihua Tan 대한침구의학회 2020 대한침구의학회지 Vol.37 No.2

Background: Classical acupuncture is being used in the treatment of rheumatoid arthritis (RA). To explore the biological response to acupuncture, a network-based analysis was performed on gene expression data collected from an animal model of RA treated with acupuncture.Methods: Gene expression data were obtained from published microarray studies on blood samples from rats with collagen induced arthritis (CIA) and non-CIA rats, both treated with manual acupuncture. The weighted gene co-expression network analysis was performed to identify gene clusters expressed in association with acupuncture treatment time and RA status. Gene ontology and pathway analyses were applied for functional annotation and network visualization.Results: A cluster of 347 genes were identified that differentially downregulated expression in association with acupuncture treatment over time; specifically in rats with CIA with module-RA correlation at 1 hour after acupuncture (-0.27; <i>p</i> < 0.001) and at 34 days after acupuncture (-0.33; <i>p</i> < 0.001). Functional annotation showed highly significant enrichment of porphyrin-containing compound biosynthetic processes (<i>p</i> < 0.001). The network-based analysis also identified a module of 140 genes differentially expressed between CIA and non-CIA in rats (<i>p</i> < 0.001). This cluster of genes was enriched for antigen processing and presentation of exogenous peptide antigen (<i>p</i> < 0.001). Other functional gene clusters previously reported in earlier studies were also observed.<br>Conclusion: The identified gene expression networks and their hub-genes could help with the understanding of mechanisms involved in the pathogenesis of RA, as well understanding the effects of acupuncture treatment of RA.

Application of Organized Media for Rapid Spectrofluorimetric Determination of Trace Amounts of Cr(VI) in the Presence of Cr(III)

Madrakian, Tayyebeh,Afkhami, Abbas,Mohammadnejad, Masoumeh Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.6

A simple, selective and sensitive fluorescence quenching method was developed to the determination Cr(VI). The method is based on the oxidation of $I^-\;to\;{{I_3}^-}$ by Cr(VI) in sulfuric acid solution followed by immediate formation of ion association compound between I3 − and rhodamine 6G in Tween-80 micellar media at room temperature. The influence of several surfactants on rhodamine 6G fluorescence signal was studied; particular attention was paid in the aggregation behavior of rhodamine 6G–Tween-80 system. The experimental parameters (e.g., type of surfactant, reagent concentration) were studied and the optimal conditions were established. The linear calibration graph was obtained in the range 2.0 - 100.0 ng m$L^{-1}$ Cr(VI). The detection limit of the method was 0.37 ng m$L^{-1}$. The relative standard deviation (R.S.D.) is less than 5% (n = 5). The efficiency of the method for the determination of Cr(VI) in the presence of Cr(III) in the sample was investigated. The method was applied successfully to the determination of Cr(VI) and total Cr in water, and liver tissue samples.