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Comparative assessment of passive scattering and active scanning proton therapy techniques using Monte Carlo simulations
, Article Journal of Instrumentation ; Volume 17, Issue 9 , 2022 ; 17480221 (ISSN) ; Hosseini, S. A ; Akhavanallaf, A ; Vosoughi, N ; Zaidi, H ; Sharif University of Technology
Institute of Physics
2022
Abstract
Background: in this study, two proton beam delivery designs, i.e. passive scattering proton therapy (PSPT) and pencil beam scanning (PBS), were quantitatively compared in terms of dosimetric indices. The GATE Monte Carlo (MC) particle transport code was used to simulate the proton beam system; and the developed simulation engines were benchmarked with respect to the experimental measurements. Method: A water phantom was used to simulate system energy parameters using a set of depth-dose data in the energy range of 120-235 MeV. To compare the performance of PSPT against PBS, multiple dosimetric parameters including Bragg peak width (BP W50), peak position, range, peak-To-entrance dose ratio,...
Continuous model for flexural vibration analysis of Timoshenko beams with a vertical edge crack
, Article Archive of Applied Mechanics ; 2014 ; ISSN: 09391533 ; Ebrahimi, A ; Behzad, M ; Sharif University of Technology
Abstract
In this paper, a continuous model for flexural vibration of beams with a vertical edge crack including the effects of shear deformation and rotary inertia is presented. The crack is assumed to be an open-edge crack perpendicular to the neutral plane. A quasi-linear displacement filed is suggested for the beam, and the strain and stress fields are calculated. The governing equation of motion for the beam has been obtained using Hamilton principle. The equation of motion is solved with a modified weighted residual method, and the natural frequencies and mode shapes are obtained. The results are compared to the results of similar model with Euler–Bernoulli assumptions and finite element model...
Analysis of twisted laser beam focusing and defocusing in plasma
, Article Physica Scripta ; Volume 88, Issue 3 , August , 2013 ; 00318949 (ISSN) ; Bahrampour, A. R ; Sharif University of Technology
2013
Abstract
Using the source dependent expansion method and paraxial approximation, the evolution of the beam spot size (BSS) in laser plasma interaction is investigated. Considering a collisionless mechanism, the self-focusing of a Laguerre-Gaussian (LG) light beam in a plasma medium is studied and the evolution of the BSS is solved analytically for the non-saturating nonlinearity state, and numerically for the saturating state. The self-focusing of a doughnut beam depends on the initial BSS, in which if the initial BSS gets bigger, the beam in the medium will be focused faster. We show that if the nonlinear effect of the plasma medium is saturated, the LG beam profile can remain stable and the BSS...
Forced vibration of delaminated Timoshenko beams subjected to a moving load
, Article Science and Engineering of Composite Materials ; Volume 19, Issue 2 , June , 2012 , Pages 145-157 ; 0334181X (ISSN) ; Ahmadian, M. T ; Jafari-Talookolaeia, R. A ; Sharif University of Technology
Abstract
A composite beam with single delamination under the action of moving load has been modeled accounting for the Poisson's effect, shear deformation, and rotary inertia. The existence of the delamination changes the stiffness of the structure, and this affects the dynamic response of the structure. We have used a constrained mode to simulate the behavior between the delaminated surfaces. Based on this mode, eigensolution technique is used to obtain the natural frequencies and their corresponding mode shapes for the delaminated beam. Then, the Ritz method is adopted to derive the dynamic response of the beam subjected to a moving load. The obtained results for the free and forced vibrations of...
Continuum models calibrated with atomistic simulations for the transverse vibrations of silicon nanowires
, Article International Journal of Engineering Science ; Volume 100 , 2016 , Pages 8-24 ; 00207225 (ISSN) ; Afsharmanesh, B ; Tajaddodianfar, F ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
We have conducted Molecular Dynamics (MD) simulations with the Environment-Dependent Interatomic Potential (EDIP) to obtain the natural frequency of ultra-thin Silicon Nanowires (SiNWs) with various crystallographic structures, boundary conditions and dimensions. As expected, results show that the mechanical properties of SiNWs are size-/orientation-dependent. The observed phenomena are ascribed to the surface effects which become dominant due to the large surface-to-volume number of atoms at the investigated range of dimensions. Due to their accuracy, atomistic simulations are widely accepted for the investigations of such nano-scaled systems; however, they suffer from high computational...
Dynamics of a generally layered composite beam with single delamination based on the shear deformation theory
, Article Science and Engineering of Composite Materials ; Volume 22, Issue 1 , 2015 , Pages 57-70 ; 0334181X (ISSN) ; Abedi, M ; Kargarnovin, M. H ; Ahmadian, M. T ; Sharif University of Technology
Walter de Gruyter GmbH
2015
Abstract
The free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented using the finite element method (FEM). The effect of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia, and Poisson's effect are taken into account. To verify the validity and the accuracy of this study, the numerical solutions are presented and compared with the results from available references and very good agreement observed. Furthermore, the effects of some parameters such as slenderness ratio, the rotary inertia, the shear deformation, material anisotropy, ply configuration, and delamination...
Parametric analyses of multispan viscoelastic shear deformable beams under excitation of a moving mass
, Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 131, Issue 5 , 2009 , Pages 0510091-05100912 ; 10489002 (ISSN) ; Nikkhoo, A ; Mehri, B ; Sharif University of Technology
2009
Abstract
This paper presents a numerical parametric study on design parameters of multispan viscoelastic shear deformable beams subjected to a moving mass via generalized moving least squares method (GMLSM). For utilizing Lagrange's equations, the unknown parameters of the problem are stated in terms of GMLSM shape functions and the generalized Newmark-β scheme is applied for solving the discrete equations of motion in time domain. The effects of moving mass weight and velocity, material relaxation rate, slenderness, and span number of the beam on the design parameters and possibility of mass separation from the base beam are scrutinized in some detail. The results reveal that for low values of beam...
An improvement on the Brinson model for shape memory alloys with application to two-dimensional beam element
, Article Journal of Intelligent Material Systems and Structures ; Volume 25, Issue 15 , 1 October , 2014 , Pages 1905-1920 ; ISSN: 1045389X ; Arghavani, J ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
Abstract
In this article, the one-dimensional phenomenological constitutive model originally proposed by Brinson for shape memory alloys is improved to predict asymmetric behavior in tension and compression. We propose an approach that decomposes stress-induced martensite volume fraction into two parts, one in tension and one in compression. Results of numerical examples show reasonable agreement with experimental data. Moreover, we implement the proposed model in a user-defined material subroutine in the nonlinear finite element software ABAQUS/Standard as a two-dimensional Euler-Bernoulli beam element. We simulate several beam problems and a shape memory alloy staple. Regarding the results, the...
Slope variation effect on large deflection of compliant beam using analytical approach
, Article Structural Engineering and Mechanics ; Volume 44, Issue 3 , 2012 , Pages 405-416 ; 12254568 (ISSN) ; Ganji, D. D ; Roshan, N ; Moheimani, R ; Hatami, M ; Hasanpour, A ; Sharif University of Technology
2012
Abstract
In this study the investigation of large deflections subject in compliant mechanisms is presented using homotopy perturbation method (HPM). The main purpose is to propose a convenient method of solution for the large deflection problem in compliant mechanisms in order to overcome the difficulty and complexity of conventional methods, as well as for the purpose of mathematical modeling and optimization. For simplicity, a cantilever beam of linear elastic material under horizontal, vertical and bending moment end point load is considered. The results show that the applied method is very accurate and capable for cantilever beams and can be used for a large category of practical problems for the...
Dynamic green function solution of beams under a moving load with different boundary conditions
, Article Scientia Iranica ; Volume 16, Issue 3 B , 2009 , Pages 273-279 ; 10263098 (ISSN) ; Davar, A ; Rahmani, O ; Sharif University of Technology
2009
Abstract
This paper presents the linear dynamic response of uniform beams with different boundary conditions excited by a moving load, based on the Elder-Bernouli beam theory. Using a dynamic green function, effects of different boundary conditions, velocity of load and other parameters are. assessed and some of the numerical results are compared with those given in the. references. © Sharif University of Technology, June 2009
Development and validation of an optimal GATE model for double scattering proton beam delivery
, Article Journal of Instrumentation ; Volume 16, Issue 2 , 2021 ; 17480221 (ISSN) ; Vosoughi, N ; Mahani, H ; Sharif University of Technology
IOP Publishing Ltd
2021
Abstract
Proton therapy (PT) is an emerging external beam radiation therapy characterized by superior dose distribution compared to conventional modalities. In the present study, an optimal GATE model was developed and then validated for a double scattering proton nozzle based on the previously constructed model. To this aim, a double scattering treatment nozzle was modeled in the GATE platform. To accelerate the GATE simulations, a virtual range modulation wheel (vRMW) and a variance reduction technique (VRT) were implemented. Proton beam flatness, symmetry, and delivery efficiency, secondary neutron dose, and dosimetric performance were characterized through a set of GATE simulations. The findings...
A timoshenko beam element based on the modified couple stress theory
, Article International Journal of Mechanical Sciences ; Vol. 79, issue , 2014 , pp. 75-83 ; ISSN: 00207403 ; Asghari, M ; Ahmadian, M. T ; Sharif University of Technology
Abstract
Since the classical continuum theory is neither able to evaluate the accurate stiffness nor able to justify the size-dependency of micro-scale structures, the non-classical continuum theories such as the modified couple stress theory have been developed. In this paper, a new comprehensive Timoshenko beam element has been developed on the basis of the modified couple stress theory. The shape functions of the new element are derived by solving the governing equations of modified couple stress Timoshenko beams. Subsequently, the mass and stiffness matrices are developed using energy approach and Hamilton's principle. The formulations of the modified couple stress Euler-Bernoulli beam element...
Analysis of large amplitude free vibrations of clamped tapered beams on a nonlinear elastic foundation
, Article Applied Mathematical Modelling ; Volume 38, Issue 3 , 1 February , 2014 , Pages 1176-1186 ; ISSN: 0307904X ; Mazaheri, H ; Salarieh, H ; Sharif University of Technology
Abstract
The purpose of this paper is to present efficient and accurate analytical expressions for large amplitude free vibration analysis of single and double tapered beams on elastic foundation. Geometric nonlinearity is considered using the condition of inextensibility of neutral axis. Moreover, the elastic foundation consists of a linear and cubic nonlinear parts together with a shearing layer. The nonlinear governing equation is solved by employing the variational iteration method (VIM). This study shows that the second-order approximation of the VIM leads to highly accurate solutions which are valid for a wide range of vibration amplitudes. The effects of different parameters on the nonlinear...
Dynamic green function for response of timoshenko beam with arbitrary boundary conditions
, Article Mechanics Based Design of Structures and Machines ; Volume 42, Issue 1 , 2 January , 2014 , Pages 97-110 ; ISSN: 15397734 ; Mofid, M ; Sharif University of Technology
Abstract
This paper presents the dynamic response of uniform Timoshenko beams with arbitrary boundary conditions using Dynamic Green Function. An exact and direct modeling technique is stated to model beam structures with arbitrary boundary conditions subjected to the external load that is an arbitrary function of time t and coordinate x and the concentrated moving load. This technique is based on the Dynamic Green Function. The effect of different boundary conditions, load, and other parameters is assessed. Finally, some numerical examples are shown to illustrate the efficiency and simplicity of the new formulation based on the Dynamic Green Function
A numerical investigation on the free vibration of carbon nanopeapods as variable frequency beam resonators
, Article Modern Physics Letters B ; Volume 27, Issue 21 , August , 2013 ; 02179849 (ISSN) ; Alavi, S. M ; Sharif University of Technology
2013
Abstract
This study aims at investigation of the resonance frequencies of carbon nanopeapods constructed by a single wall carbon nanotube and encapsulated buckyball molecules (C60). A nanopeapod can be used as a nanoscale variable frequency beam resonator according to the number and positions of the encapsulated fullerenes. Using the molecular structural mechanics method the covalence bonds are simulated by equivalent beam elements and the van der Waal interactions between the buckyballs and nanotube are modeled as linear springs. Also, an equivalent beam model is proposed for the nanopeapod with sectional properties which are obtained by the molecular structural mechanics model. The beam-like modes...
Vibration analysis of delaminated Timoshenko beams under the motion of a constant amplitude point force traveling with uniform velocity
, Article International Journal of Mechanical Sciences ; Volume 70 , 2013 , Pages 39-49 ; 00207403 (ISSN) ; Jafari Talookolaei, R. A ; Ahmadian, M. T ; Sharif University of Technology
2013
Abstract
A composite beam with single delamination traveled by a constant amplitude moving force is modeled accounting for the Poisson's effect, shear deformation and rotary inertia. The mechanical behavior between the delaminated surfaces is modeled using a piecewise-linear spring foundation. The governing differential equations of motion for such system are derived. Primarily, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes of such beam. Then, the Ritz method is employed to derive the dynamic response of the beam due to the moving force. The obtained results for the free and forced vibrations of beams are verified against reported similar...
A size-dependent beam element based on the modified couple stress theory
, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011, Denver, CO ; Volume 8 , 2011 , Pages 591-597 ; 9780791854945 (ISBN) ; Khajehpour, M ; Ahmadian, M. T ; ASME ; Sharif University of Technology
Abstract
In this paper, the modified couple stress theory is employed to develop a size-dependent beam element able to predict the size-dependency observed in microbeams. The stiffness matrix is obtained for the aforementioned beam element. As an example, the deflection of a microcantilever is evaluated using the proposed beam elements and the results of the finite element method are compared to the analytical results obtained by the classical beam theory. The maximum deflection of the beam is depicted versus the ratio of the beam thickness to the material length scale parameter, the parameter appearing in non-classical continuum theories. The results show that when the characteristic size of the...
Application of homotopy and homotopy perturbation methods to differential equations of heat transfer and shear deformation of beams
, Article Applied Mathematical Sciences ; Volume 5, Issue 21-24 , Apr , 2011 , Pages 1051-1063 ; 1312885X (ISSN) ; Rohi, E ; Marzabadi, F. R ; Vaziry, M. A ; Sharif University of Technology
2011
Abstract
In this paper, different physical differential equations related to heat transfer and shear deformation of beams are solved by new but powerful analytical methods: Liao's Homotopy method (H.M), Homotopy method with Pade approximation and the He's Homotopy-Perturbation Method (HPM). Nonlinear convective-radiative cooling equation, nonlinear heat equation with cubic nonlinearity and the shear deformation of sandwich beams are used as examples to illustrate the solution procedures. Comparison of the applied methods with exact solutions reveals that both methods are greatly effective
Implementation of microplane model into three-dimensional beam element for shape memory alloys
, Article International Journal of Applied Mechanics ; Volume 7, Issue 6 , December , 2015 ; 17588251 (ISSN) ; Arghavani, J ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2015
Abstract
In this study, a three-dimensional (3D) beam element based on Timoshenko beam theory is introduced for shape memory alloys (SMAs). Employing the microplane approach, we use a 3D SMA constitutive model extended from a 1D model proposed by Brinson. The SMA model is implemented into a user-defined subroutine (UMAT) in the nonlinear finite element software ABAQUS/Standard. Results of numerical examples show reasonable agreement with experimental data in proportional and non-proportional loadings. Furthermore, several applications (staple, spring, structure) are simulated and the results are compared with those of continuum elements. According to the results, the 3D SMA beam element can be used...
Cyclic behaviour of interior reinforced concrete beam-column connection with self-consolidating concrete
, Article Structural Concrete ; Volume 17, Issue 4 , 2016 , Pages 618-629 ; 14644177 (ISSN) ; Kazemi, M. T ; Attari, N. K. A ; Sharif University of Technology
Wiley-Blackwell
Abstract
A significant amount of research on self-consolidating concrete (SCC) technology has been devoted to evaluating the suitability of the material for its use in structural applications. However, more research is required to confirm the adequacy of SCC structural members for resisting gravity and seismic loads. This study focuses on the experimental investigation of the seismic performance of interior reinforced concrete beam-column connections with SCC. Four beam-column connection specimens, three with SCC and one with normally vibrated concrete (NC), were designed for this experimental study. Factors such as concrete type (SCC or NC) and axial load ratio (0, 7.5 and 15 % of column section...