Mohammad Rahimian

University of Tehran | UT · School of Civil Engineering

This paper analytically investigates the indentation problem of a 3m trigonal piezoelectric half-plane under a frictionless insulating punch for the first time. To this end, the general solutions of the governing equations are determined for an x-cut 3m piezoelectric half-plane using Fourier transform. The mixed value boundary problem of contact is...

This paper presents an analytical formulation for deriving the three-dimensional (3D) elastodynamic Green’s functions of functionally graded transversely isotropic tri-material composite under time-harmonic loading. With the aid of a complete set of displacement potentials, Fourier expansions, and Hankel integral transforms, displacement and stress...

In this paper, a numerical approach based on a three-dimensional (3D) standard coupled boundary element method-finite element method (BEM-FEM) formulation in the frequency domain is presented. The approach allows studying the dynamics response of a structure bonded to the surface of a layered transversely isotropic half-space subjected to time-harm...

Piezoelectric materials have a wide range of industrial applications in different branches of engineering due to their electromechanical coupling. So, investigating their responses to either mechanical or electric loadings helps engineers for efficient design of smart systems. However, most of the studies have assessed the well-known 6 mm piezoelec...

Vertical vibration of a rigid disk embedded in a multi-layered poroelastic medium is considered in this paper, for the first time. The whole medium is underlying a liquid layer with finite depth to evaluate the submarine structures. Extended reflection and transmission matrix are introduced for layered porous media. The governing differential equat...

In this paper, an analytical method is developed for the axisymmetric dynamic response of a finite thickness liquid layer overlying a transversely isotropic porous solid half-space due to body waves. Potential functions and integral transforms are used together to handle the equations of wave motion in two media. The time-harmonic excitation with a...

In this document, Iran digital national plan consisted of vision, goals, objectives, strategies, policies and projects is presented. For this matter, concerning the design science paradigm, the exhaustive framework has been prepared consisted of 3 layers, including enabler, application, and impact. The enabler layer is comprised of six constructs i...

Wave propagation in a multi-layered transversely isotropic porous medium has been considered in this paper, which consists of n parallel layers overlying on a half-space. Potential functions are used to solve elastodynamic differential equations of the poroelastic medium. Time-harmonic excitation is assumed and the procedure of solution is performe...

The equations of wave motion are considered in this article for three-layered medium which consists of liquid and porous layers with finite depth and solid half-space such as ocean bed. By virtue of scalar potential functions for each layer, complicated differential equations of layers are reduced to ordinary differential equations. An analytical m...

This research focuses on finite element model updating and damage assessment of structures at element level based on global nondestructive test results. For this purpose, an optimization system is generated to minimize the structural dynamic parameters discrepancies between numerical and experimental models. Objective functions are selected based o...

In this study an innovative mobile Tuned Mass Damper (TMD) system is proposed which enables the TMD device to move along the cable and optimize its position. A three dimensional model of an inclined cable with sag is created using OpenSees. A mobile TMD device incorporating a semi-active Magnetorheological (MR) damper is implemented. Nine different...

An analytical treatment is presented for bonded contact of a rigid disk inclusion embedded in a penny-shaped crack in a transversely isotropic full-space. Theoretical analysis is carried out using a complete potential function method, and with the aid of Hankel transforms. Boundary conditions propel the problem toward a set of triple integral equat...

Trapezoidal prestressed unbonded retrofit (TPUR) systems have been recently developed and tested. The authors have already developed a comprehensive and accurate analytical solution for the TPUR system that takes many system parameters into account. The main aim of this paper is to develop a simplified analytical solution for predicting the behavio...

Machine learning algorithms, both supervised and unsupervised learning approaches, have matured vibration-based structural damage detection methods in recent years. Unlike supervised methods, there is no need for labeled data of damage states in unsupervised techniques. One of the challenges in the process of detecting structural damages is separat...

Structural damage detection using machine learning algorithms deals with the data gathered from the sensors mounted on the structure rather than investigating the dynamic properties of the structure using direct analyses. The features extracted from the data of the sensors can also be modal dynamic properties. However, in this paper, a combination...

The acoustic wave velocity depends on elasticity and density at most materials, but because of anisotropy and especially piezoelectric coupling effect, the acoustic wave propagation at piezoelectric based crystalloacoustic materials, is an applied and challenging problem. In this paper, using modified Christoffel's equation based on group velocity...

In this paper, a new family of single-parameter exponentially gradient elements (EG-elements) are introduced, which can be used in various numerical procedures such as boundary and finite element methods. These elements have the ability to accurately interpolate the unknown values in regions, where either high gradient or singularity of the unknown...

By introduction of two scalar potentials, an analytical method is developed for the solution of poroelastodynamic boundary value problems in transversely isotropic fluid-saturated poroelastic media. The governing equations of motion are considered in the framework of Biot's complete model without any assumption or simplification. As a case of appli...

In this paper, an analytical formulation is presented to study an exponentially graded transversely isotropic tri-material under applied axisymmetric point-load and patchload with the aid of Hankel transform and use of a potential function. The given formulation is shown to be reducible to the special cases of (1) an inhomogeneous finite layer on a...

This paper aims at proposing a novel type tunable acoustic metamaterials with complete band gap composed of piezoelectric rods (Lithium Niobate) with square array as inclusion embedded polyimide aerogel background. The plane wave expansion method and the principles of Bloch-Floquet method used to get a band frequency and study the pass band for noi...

The asymmetric three-dimensional radiation pattern and resultant elastodynamic response of stress waves in a model comprising a compressible water column overlying a transversely isotropic seabed in which a time-harmonic source acts is theoretically investigated. The use of potential functions, the Hankel transform, and a Fourier series expansion a...

This paper aims at proposing a novel type of acoustic metamaterials with complete band gap composed of piezoelectric rods with square array as inclusions embedded in an air background (matrix). A modified plane wave expansion method accompanied with the principles of the Bloch–Floquet method with electromechanical coupling effect and also impedance...

In the framework of linear elastic continuum mechanics, an analytical formulation is presented for the axisymmetric axial interaction of a rigid disk in frictionless contact with the face of a penny-shaped crack in a transversely isotropic solid. The problem is reduced to an integral equation and is shown to be degenerated to the formulation of iso...

Surface waves dispersion is studied in a two-layer half-space consisting of a finite liquid layer overlying a transversely isotropic solid half-space. A couple of complete potential functions are utilized to uncouple the equation of motion of the transversely isotropic solid along with a displacement potential for the liquid. The frequency equation...

In this paper, closed-form integral expressions are derived to describe how surface gravity waves (tsunamis) are generated when general asymmetric ground displacement (due to earthquake rupturing), involving both horizontal and vertical components of motion, occurs at arbitrary depth within the interior of an anisotropic sub-sea solid beneath the o...

The eastern part of the Iranian plateau is characterized by large and infrequent earthquakes with recurrence intervals of more than several hundred years. Given that previous observations and paleoseismological studies are insufficient for forecasting large earthquakes, we have developed a physics-based synthetic seismicity model for the fault syst...

A theoretical investigation is presented for the dynamic interaction of a rigid circular disc and its surrounding space, which is a trimaterial transversely isotropic full-space, and the disc is undergoing a prescribed horizontal harmonic vibration. Because the equations of motion form a system of coupled partial differential equations in a cylindr...

In this paper, an attempt is made to optimize the location and design procedure of the backfill stopes according to the some geotechnical parameters. In this regard, a large number of numerical models were made using FLAC 2D software, because of the plane strain condition. So shallow, semi-deep and deep individual stopes has been defined. Since all...

NW Iran is a region of active deformation in the Eurasia-Arabia collision zone. This high strain field has caused intensive faulting accompanied by several major (M 6> 6.5) earthquakes as it is evident from historical records. Whereas seismic data (i.e. instrumental and historical catalogs) are either short, or inaccurate and inhomogeneous, physics...

A rigorous formulation is presented for the frictionless axisymmetric interaction of a rigid disk with a two-layered inhomogeneous medium. The materials are considered to be linearly elastic transversely isotropic materials and the exponential variation of properties along the depth of each layer is assumed in order to model the effect of inhomogen...

By virtue of a pair of scalar potentials for the displacement of the solid skeleton and the pore fluid pressure field of a saturated poroelastic medium, an alternative solution method to the Helmholtz decomposition is developed for the wave propagation problems in the framework of Biot's theory. As an application, a comprehensive solution for three...

In this paper, the axisymmetric dynamic response of a finite thickness liquid layer overlying a transversely isotropic solid half-space is developed. The use of potential functions accompanied by the integral transform method is applied to handle the equations of motion of the two media. Closed form expressions are derived for stress and displaceme...

Stay cables are crucial elements that greatly influence the structural behavior of cable structures such as cable stayed bridges, suspension bridges, and other cable structures. Cable elements are susceptible to external excitations due to their high flexibility and low inherent damping. In this study, first, a primary two dimensional (2-D) model o...

The dispersion of interface waves is studied theoretically in a model consisting of a liquid layer of finite thickness overlying a transversely isotropic solid layer which is itself underlain by a transversely isotropic solid of dissimilar elastic properties. The method of potential functions and Hankel transformation was utilized to solve the equa...

Stay cables are crucial elements that greatly influence the structural behavior of cable stayed bridges. Cable elements are susceptible to external excitations due to their high flexibility and low inherent damping. Though traditional mechanical dampers, with one end connected to the cable and the other end to the deck, are useful for vibration red...

Cables are widely used in different structures such as cable stayed bridges, suspension bridges, and other cable structures. The dynamic behavior of an inclined sagged cable as an individual structural element, is highly complicated due to its high tension and geometrical nonlinearity. Moreover, the high flexibility and low inherent structural damp...

Cables are widely used in different structures such as cable stayed bridges, suspension bridges, and other cable structures. The dynamic behavior of an inclined sagged cable as an individual structural element, is highly complicated due to its high tension and geometrical nonlinearity. Moreover, the high flexibility and low inherent structural damp...

Stay cables are crucial elements that greatly influence the structural behavior of cable stayed bridges. Cable elements are susceptible to external excitations due to their high flexibility and low inherent damping. Though traditional mechanical dampers, with one end connected to the cable and the other end to the deck, are useful for vibration red...

A theoretical formulation is presented for the determination of the dynamic interaction of a horizontally loaded inextensible circular membrane embedded at the interface of a transversely isotropic bi-material full-space, using cylindrical co-ordinate system and applying Hankel integral transforms in the radial direction and Fourier series, the pro...

By virtue of the representations of displacements, stresses, and temperature fields in terms of two scalar potential functions and the use of correspondence principle, an analytical derivation of fundamental Green's functions for bi-material half-space composed of a transversely isotropic thermo-elastic layer and an isotropic thermo-visco-elastic h...

A horizontal layer between two transversely isotropic half-spaces forms a trimaterial full-space, involved in this paper. A mathematical formulation is presented to determine the response of a rigid circular membrane, which is laid down at an interface of the tri-material transversely isotropic full-space and is considered to be under a prescribed...

This investigation is concerned with a mathematical analysis of an elastic circular cylindrical pile embedded in a transversely isotropic half-space under lateral dynamic excitations. A combination of time-harmonic horizontal shear force and moment are applied at the top end of the pile. The boundary value problem is formulated by decomposing the p...

An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring (FVSS), can be widely used, especially in tuned mass dampers (TMDs) with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper...

In this paper, solution of inverse problems in elastostatic fields is investigated. For this purpose, we propose a qualitative inverse approach based on linear sampling method (LSM) for cavity/inclusion detection in a two-dimensional (2D) isotropic linear elastic body using measurement of data on the boundary. The LSM is an effective approach to im...

A linear thermoelastic isotropic material is considered. A complete solution in terms of three scalar potential functions for the coupled displacement-temperature equations of motion and heat equation is presented, where the governing equations for the potential functions are the wave, heat, or a repeated wave-heat equation. The completeness theore...

In the framework of elastostatics, a mathematical treatment is presented for the boundary value problem of the interaction of a flexible cylindrical pile embedded in a transversely isotropic half‐space under transverse loadings. Taking the pile region as a stiffened subdomain of an extended half‐space, the formulation of the interaction problem is...

With the aid of a complete set of two scalar potential functions, the transient responses of an isotropic thermoelastic half-space subjected to time dependent tractions and heat flux applied to a finite patch at an arbitrary depth below a free surface are derived. Using the displacements-and temperature-potential function relationships, the coupled...

With the aid of a complete set of two scalar potential functions, the transient responses of an isotropic thermoelastic half-space subjected to time dependent tractions and heat flux applied to a finite patch at an arbitrary depth below a free surface are derived. Using the displacements-and temperature-potential function relationships, the coupled...

A horizontally multilayered Green elastic transversely isotropic half-space is considered as the domain of the boundary value problem involved in this paper, such that the axes of material symmetry of different layers are parallel to the axis of material symmetry of the lowest half-space, which is depthwise. The domain is assumed to be affected by...

A theoretical formulation is presented for the determination of the dynamic interaction of a vertically loaded rigid disc embedded at the interface of a transversely isotropic bi-material full-space. With the aid of Hankel integral transforms, a relaxed treatment of the mixed-boundary value problem is formulated as dual integral equations, which ca...

By virtue of the representations of displacements, stresses, and temperature fields in terms of two scalar potential functions and the use of correspondence principle, an analytical derivation of fundamental Green's functions for bi-material half-space composed of a transversely isotropic thermo-elastic layer and an isotropic thermo-visco-elastic h...

For the first time, a theoretical formulation is presented for the load-transfer analysis of an elastic cylindrical thin-walled pile immersed in a transversely isotropic half-space under axisymmetric excitations. By generating a set of weakly singular Green's functions for the embedding medium and using a shell theory for the pile, it is shown that...

A complete set of potential functions consisting of three scalar functions is presented for coupled displacement-temperature equations of motion and heat equation for an arbitrary x3-convex domain containing a linear thermoelastic transversely isotropic material, where the x3-axis is parallel to the axis of symmetry of the material. The proof of th...

A half-space containing transversely isotropic thermoelastic mate-rial with a depth-wise axis of material symmetry is considered to be under the effects of axisymmetric transient surface thermal and forced excitations. With the use of a new scalar potential function, the coupled equations of motion and energy equation are uncoupled, and the governi...

تحلیل سازههاي زیرزمینی تحت شرایط محیطی مختلف و بارهاي مکانیکی مملو از عدم قطعیت میباشد. با توجه به وجود ناهمگنی ذاتی مصالح زمینشناسی انتخاب فرض همگنی چندان واقعی نخواهد بود و از طرف دیگر روابط دقیق نه به لحاظ تئوري و نه به لحاظ عملی امکان پذیر میباشد، در چنین حالتی مطابق عرف مسائل عملی از تئوري احتمال و روش اغتشاش جهت لحاظ نمودن اثر غیر قطعی ناهمگن...

An innovative design for an adaptive configuration tuned mass damper (ACTMD) is proposed. An ACTMD is a semiactive dynamic vibration absorber by which the undesirable rotational vibrations of a structure can be greatly suppressed. It can also be used to attenuate translational vibrations that are converted into rotation by means of an appropriate m...

By virtue of a new complete scalar potential function, an analytical formulation is presented to determine displacements, stresses, and temperature in an axisymmetric linear thermoelastic transversely isotropic half-space affected by time harmonic surface axisymmetric ver-tical traction and/or surface heat flux. With the use of only one scalar pote...

SUMMARYA boundary integral equation method is presented for a rigid cylindrical pipe‐pile of finite length embedded in a transversely isotropic half‐space under lateral loads. In the framework of three‐dimensional elastostatics, the complicated soil‐structure interaction problem is shown to be reducible to three coupled Fredholm integral equations....

With the aid of a new complete scalar potential function, an analytical formulation for thermoelastic Green's functions of an axisymmetric linear elastic isotropic half-space is presented within the theory of Biot's coupled thermoelasticity. By using the potential function, the governing equations of coupled thermoelasticity are uncoupled into a si...

In this article, an innovative base isolation system based on steel–polytetrafluoroethylene sliding bearings equipped with shape memory alloy is proposed. This isolation system employs superelastic Ni–Ti alloy cables as recentering components and dissipates input energy through the friction and additional damping of shape memory alloy. As a case st...

With the aid of a new complete scalar potential function, an analytical formulation for thermoelastic Green's functions of an axisymmetric linear elastic isotropic half-space is presented within the theory of Biot's coupled thermoelasticity. By using the potential function, the governing equations of coupled thermoelasticity are uncoupled into a si...

A half-space containing transversely isotropic thermoelastic mate-rial with a depth-wise axis of material symmetry is considered to be under the effects of axisymmetric transient surface thermal and forced excitations. With the use of a new scalar potential function, the coupled equations of motion and energy equation are uncoupled, and the governi...

By virtue of a new complete scalar potential function, an analytical formulation is presented to determine displacements, stresses, and temperature in an axisymmetric linear thermoelastic transversely isotropic half-space affected by time harmonic surface axisymmetric ver-tical traction and/or surface heat flux. With the use of only one scalar pote...

This paper deals with the stability of time domain dual boundary element method (DBEM). A time-weighted time domain DBEM is presented in this study and used for the first time in order to improve the stability of the standard time domain dual boundary element method. In this research a time weighting function with a prediction algorithm based on co...

A rigorous integral equation formulation is presented for the axisymmetric load-transfer analysis of a thin-walled pile embedded in a transversely isotropic half-space under axial load. By virtue of a set of ring-load Green’s functions for the pile and one for the half-space, the problem is shown to be reducible to a pair of Fredholm integral equat...

An innovative design for a semiactive variable stiffness (SAVS) device is presented in this paper. This beamlike device is capable of altering its stiffness in a smooth manner between minimum and maximum levels by using the variations of moment of inertia of an area as it rotates around a normal axis passing through its centroid. Analytical express...

Present study addresses the effectiveness of viscous dampers (VDs) in reducing the seismic responses of Izadkhast Bridge under earthquake ground motions. With the length of 485 m, Izadkhast Bridge is the longest box girder bridge in Iran and is located in Isfahan-Shiraz railway. The bridge is installed with VDs at the two ends. The Finite element m...

With the aid of a method of displacement potentials, an efficient and accurate analytical derivation of the three-dimensional dynamic Green’s functions for a transversely isotropic multilayered half-space is presented. Constituted by proper algebraic factorizations, a set of generalized transmission–reflection matrices and internal source fields th...

A rigorous mathematical formulation is presented for the analysis of a thin cylindrical shell embedded in a transversely isotropic half-space under vertically incident P-wave excitation. By virtue of a set of ring-loads Green's functions for the shell and a group of dynamic fundamental solutions for the half-space under arbitrary interfacial dynami...

In this research, an enhanced flexibility-(force-) based formulation is developed for a shear deformable beam-column element by using force interpolation functions. The development is derived from Reissner's exact stress resultant theory and its finite strain field for a Timoshenko frame element. Here, the state-space approach is applied, and the d...

The increasing application of plane-strain testing at the (sub-) micron length scale of materials that comprise elastically anisotropic cubic crystals has motivated the development of an anisotropic two-dimensional discrete dislocation plasticity (2D DDP) method. The method relies on the observation that plane-strain plastic deformation of cubic cr...

This paper deals with the interaction of a embedded rigid circular disc with a transversely isotropic layer underlain by a transversely isotropic half-space. The disc is assumed to be under a system of loads which causes it to undergo a rigid body translation equal to Δ in the vertical direction. With the aid of Hankel transforms and a method of po...

A consistent flexibility matrix is presented for a large displacement equilibrium-based Timoshenko beam-column element. This development is an improvement and extension to Neuenhofer-Filippou [1] (1998. ASCE J. Struct. Eng. 124, 704-711) for geometrically nonlinear Euler-Bernoulli force-based beam element. In order to find weak form compatibility a...

An enriched collocation method with the modified equilibrium on line method (ELM) for imposition of Neumann boundary conditions is presented for solving the two-dimensional elastic fracture problems. In the modified ELM, equilibrium over the lines on the Neumann boundary is satisfied as Neumann boundary condition equations. In this paper, two diffe...

In this paper, three-dimensional amplification of plane harmonic SH, SV, and P waves in multilayered alluvial valleys is investigated by using a boundary element method in frequency domain. It is shown that in order to achieve real responses, the problem must be analyzed and modeled three-dimensionally. Also, for exact evaluation of surface ground...

In this paper, a collocation technique with the modified equilibrium on line method (ELM) for imposition of Neumann (natural) boundary conditions is presented for solving the two-dimensional problems of linear elastic body vibrations. In the modified ELM, equilibrium over the lines on the natural boundary is satisfied as Neumann boundary condition...

This research is to offer a higher-order approximation method for a planar curved beam with enhanced formulation accuracy in state space. Here, the differential equations along with algebraic ones are formed and solved simultaneously, having no problem with element state determinations. The flexibility-based method, in which force interpolation fun...

We present a wavelet based adaptive scheme and investigate the efficiency of this scheme for solving nearly singular potential PDEs over irregularly shaped domains. For a problem defined over Ω∈ℜd, the boundary of an irregularly shaped domain, Γ, is defined as a boundary curve that is a product of a Heaviside function along the normal direction and...

A common difficulty in applying radial basis function (RBF) methods to nearly singular problems is either convergence failure or a very slow convergence rate. Motivated by the close connection between RBFs and wavelets, we have demonstrated the efficiency of adaptive distributions based on multiresolution wavelet decomposition for the RBF approxima...

With a height of 435 m, Milad Tower, situated in north-west of Tehran, Iran, would be the fourth highest telecommunication tower of the world. This tower has the largest head structure among its counterparts. Preliminary studies demonstrate that the upper part of the tower has excessive wind-induced acceleration-related vibrations beyond human comf...

Analysis of the dynamic response of a three-dimensional arch dam is conducted taking into account the effects of dam-reservoir and dam-foundation interactions. The Karaj arch-dam in Iran is considered as a case study. The dam, fluid, and foundation domains are treated as substructures and modeled with boundary elements. The foundation domain is ass...

A theoretical formulation is presented for the determination of the interaction of a vertically loaded disc embedded in a transversely isotropic half-space. By means of a complete representation using a displacement potential, it is shown that the governing equations of motion for this class of problems can be uncoupled into a fourth-order partial...

We present a wavelet based adaptive scheme and investigate the efficiency of this scheme for solving nearly singular potential PDEs. Multiresolution wavelet analysis (MRWA) provides a firm mathematical foundation by projecting the solution of PDE onto a nested sequence of approximation spaces. The wavelet coefficients then were used as an estimatio...

With a height of 435 m, Milad tower would be the fourth highest TV and telecommunication tower of the world. The tower is situated in north-west of Tehran, few kilometers from the known "North Tehran" and "Ray" active faults. Therefore, taking into account the near field aspects of strong motion in the design of such an important structure is neces...

The meshfree local integration on line method (MLILM) is presented for solving two-dimensional problems in linear elasticity. For this purpose, local unsymmetric weak forms (LUWF) are developed using weighted residual method locally from the equilibrium equations. In this method, local domains are quadrangles and the test functions are pyramids cen...

In this paper, the main characteristics of Frank–Read (F–R) sources used in a mechanism-based discrete dislocation plasticity (M-DDP) analysis are estimated by employing a recently developed non-singular continuum elastic theory of dislocations. The critical nucleation stress, τnuc, is determined more accurately because the dislocation core effects...

By virtue of a complete representation using two displacement potentials, an analytical derivation of the elastodynamic Green’s functions for a linear elastic transversely isotropic bi-material full-space is presented. Three-dimensional point-load Green’s functions for stresses and displacements are given in complex-plane line-integral representati...

By virtue of a complete representation using two displacement potentials, an analytical derivation of the elastodynamic Green's functions for a transversely isotropic layer underlain by a transversely isotropic half-space is presented. Three-dimensional point-load and patch-load Green's functions for stresses and displacements are given in the comp...

With the aid of a complete representation using two displacement potentials, an efficient and accurate analytical derivation of the fundamental Green’s functions for a transversely isotropic elastic half-space subjected to an arbitrary, time-harmonic, finite, buried source is presented. The formulation includes a complete set of transformed stress-...

In the present study, the theory of coupled thermoelastodynamic is applied to determine the displacement, temperature and stress (DTS) fields of a torsionless axisymmetric transversely isotropic half-space under a surface loading. The basic equations of coupled thermoelasticity consist of the equations of motion and the energy equation, which forms...