Ghodrat Karami - Academia.edu (original) (raw)
Papers by Ghodrat Karami
Computational Mechanics, 1994
A combined finite element evaluation of hydrodynamic pressure and boundary element calculation of... more A combined finite element evaluation of hydrodynamic pressure and boundary element calculation of film thickness is presented. The viscosity and the density of the oil are assumed to vary with pressure, however the isothermal condition is assumed to prevail. The technique is based on an iterative procedure by assuming an initial hydrodynamic pressure. The iteration cycle will then be followed by the calculation of the film thickness and hydrodynamic pressure to arrive at a converged solution. The bearings have been treated realistically as finite domain bodies and their deformations are evaluated by boundary element method. The accuracy of the technique is illustrated in elastohydrodynamic lubrication (EHL) of inclined slider and line contact problems.
Computers & Structures, 1993
ABSTRACT
Computer Methods in Biomechanics and Biomedical Engineering, 2009
This paper proposes a micromechanics algorithm utilising the finite element method (FEM) for the ... more This paper proposes a micromechanics algorithm utilising the finite element method (FEM) for the analysis of heterogeneous matter. The characterisation procedure takes the material properties of the constituents, axons and extracellular matrix (ECM) as input data. The material properties of both the axons and the matrix are assumed to have linear viscoelastic behaviour with a perfect bonding between them. The results of the modelling have been validated with experimental data with material white input from brainstem by considering the morphology of brainstem in which most axons are oriented in longitudinal direction in the form of a uniaxial fibrous composite material. The method is then employed to examine the undulations of axons within different subregions of white matter and to study the impact due to axon/matrix volume fractions. For such purposes, different unit cells composed of wavy geometries and with various volume factions have been exposed to the six possible loading scenarios. The results will clearly demonstrate the undulation and axon volume fraction impacts. In this respect, undulation affects the material stiffness heavily in the axon longitudinal direction, whereas the axons' volume fraction has a much greater impact on the mechanical properties of the white matter in general. Also the results show that the created stresses and strains in the axons and matrix under loading will be impacted by undulation change. With increase in undulation the matrix suffers higher stresses when subjected to tension, whereas axons suffer higher stresses in shear. The axons always exhibit higher stresses whereas the matrix exhibits higher strains. The evaluated time-dependent local stress and strain concentrations within a repeating unit cell of the material model are indicative of the mechanical behaviour of the white tissue under different loading scenarios.
Journal of The Mechanical Behavior of Biomedical Materials, 2009
Computational Materials Science, 2008
International Journal of Impact Engineering, 2009
Annals of Biomedical Engineering, 2010
A mechanized and integrated computational scheme is introduced to determine the human brain respo... more A mechanized and integrated computational scheme is introduced to determine the human brain responses in an environment where the human head is exposed to explosions from trinitrotoluene (TNT), or other high-yield explosives, in military applications. The procedure is based on a three-dimensional (3-D) non-linear finite element method (FEM) that implements a simultaneous conduction of explosive detonation, shock wave propagation, blast–head interactions, and the confronting human head. The processes of blast propagation in the air and blast interaction with the head are modeled by an Arbitrary Lagrangian–Eulerian (ALE) multi-material FEM formulation, together with a penalty-based fluid/structure interaction (FSI) algorithm. Such a model has already been successfully validated against experimental data regarding air-free blast and plate–blast interactions. The human head model is a 3-D geometrically realistic configuration that has been previously validated against the brain intracranial pressure (ICP), as well as shear and principal strains under different impact loadings of cadaveric experimental tests of Hardy et al. [Hardy W. N., C. Foster, M. Mason, S. Chirag, J. Bishop, M. Bey, W. Anderst, and S. Tashman. A study of the response of the human cadaver head to impact. Proc. 51 st Stapp. Car Crash J. 17–80, 2007]. Different scenarios have been assumed to capture an appropriate picture of the brain response at a constant stand-off distance of nearly 80 cm from the core of the explosion, but exposed to different amounts of a highly explosive (HE) material such as TNT. The overpressures at the vicinity of the head are in the range of about 2.4–8.7 atmosphere (atm), considering the reflected pressure from the head. The methodology provides brain ICP, maximum shear stresses and maximum principal strain within the milli-scale time frame of this highly dynamic phenomenon. While focusing on the two mechanical parameters of pressure, and also on the maximum shear stress and maximum principal strain to predict the brain injury, the research provides an assessment of the brain responses to different amounts of overpressure. The research also demonstrates the ability to predict the ICP, as well as the stress and strain within the brain, due to such an event. The research cannot identify, however, the specific levels of ICP, stress and strain that necessarily lead to traumatic brain injury (TBI) because there is no access to experimental data regarding head–blast interactions.
Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2009
A major role for the cerebrospinal fluid (CSF) is to provide effective damping against sudden int... more A major role for the cerebrospinal fluid (CSF) is to provide effective damping against sudden intracranial brain motions during dynamic head impact. This paper examines the roles of CSF properties on human brain responses under certain impact loadings. The brain is assumed to have a hyperviscoelastic material behaviour, while CSF is considered to be fluid-like elastic, viscoelastic, and nearly incompressible elastic with a low shear modulus and a high bulk modulus. A finite element parametric investigation on a head model under different scenarios of impact is conducted. In the study, the CSF material parameters are varied within the expected range of change, while other components of the head model are kept constant. The results indicate that the solutions from the modelling of CSF by a fluid-like medium are more realistic and support the findings of the experiment. The results also indicate that varying CSF properties did not have a major impact on the peak intracranial pressures but the impact on brain principal and shear strains are relatively significant. A sizeable impact on the relative motion of the brain, with respect to the skull, can also be observed.
Journal of Composite Materials, 2008
ABSTRACT: An efficient computational algorithm is proposed to evaluate the viscoelastic propertie... more ABSTRACT: An efficient computational algorithm is proposed to evaluate the viscoelastic properties of fibrous composites. A repeating unit cell (RUC) based on a pre-determined fiber packing is assumed to represent the microstructure of the composite. Finite element analysis of this ...
Engineering Structures, 2003
Computational Mechanics, 2003
A differential quadrature element method (DQEM) based on first order shear deformation theory is... more A differential quadrature element method (DQEM) based on first order shear deformation theory is developed for free vibration analysis of non-uniform beams on elastic foundations. By decomposing the system into a series of sub-domains or elements, any discontinuity in loading, geometry, material properties, and even elastic foundations can be considered conveniently. Using this method, the vibration analysis of general beam-like structures is to be studied. The governing equations of each element, natural compatibility conditions at the interface of two adjacent elements and the external boundary conditions are developed in a systematic manner, using Hamilton's principle. The present DQEM is to be implemented to Timoshenko beams resting on partially supported elastic foundations with various types of boundary conditions under the action of axial loading. The general versality, accuracy, and efficiency of the presented DQEM are demonstrated having solved different examples and compared to the exact or other numerical procedure solutions.
Computer Methods in Applied Mechanics and Engineering, 2004
... plates. Bert and Malik [17] and [18] used semi-analytical DQM for free vibration analysis of ... more ... plates. Bert and Malik [17] and [18] used semi-analytical DQM for free vibration analysis of rectangular thin plates. ... DQM. Also, a review of the early developments of DQM can be referenced to the papers by Bert and Malik [21] and [22]. ...
Composite Structures, 2006
Engineering Structures, 2004
International Journal for Numerical Methods in Engineering, 2003
A new methodology is introduced in the differential quadrature (DQ) analysis of plate problems. T... more A new methodology is introduced in the differential quadrature (DQ) analysis of plate problems. The proposed approach is distinct from other DQ methods by employing the multiple boundary conditions in a different manner. For structural and plate problems, the methodology employs the displacement within the domain as the only degree of freedom, whereas along the boundaries the displacements as well as the second derivatives of the displacements with respect to the co-ordinate variable normal to the boundary in the computational domain are considered as the degrees of freedom for the problem. Employing such a procedure would facilitate the boundary conditions to be implemented exactly and conveniently. In order to demonstrate the capability of the new methodology, all cases of free vibration analysis of rectangular isotropic plates, in which the conventional DQ methods have had some sort of difficulty to arrive at a converged or accurate solution, are carried out. Excellent convergence behaviour and accuracy in comparison with exact results and/or results obtained by other approximate methods were obtained. The analogous DQ formulation for a general rectangular plate is derived and for each individual boundary condition the general format for imposing the given conditions is devised. It must be emphasized that the computational efforts of this new methodology are not more than for the conventional differential quadrature methods. Copyright © 2002 John Wiley & Sons, Ltd.
Engineering Structures, 2006
... behavior of thin, isotropic rhombic plates with clamped and simply supported edges by using a... more ... behavior of thin, isotropic rhombic plates with clamped and simply supported edges by using a high precision conforming triangular plate bending element ... 8] studied the large deflection of isotropic simply supported thin rhombic plates ... 9] presented a finite element analysis of the ...
Composite Structures, 2003
Energy Conversion and Management, 2006
Engineering Structures, 2005
... The applications of PDQ for thin beams and plates and also for rectangular thick plates have ... more ... The applications of PDQ for thin beams and plates and also for rectangular thick plates have been carried out by the authors [21], [22], [23], [24 ... Liew and Han [29] employed the DQ method to present the bending analysis of simply supported thick skew plates based on ...
Numerical Heat Transfer Part A-applications, 2006
Home >> Numerical Heat Transfer Part A: Applications, Volume 49, Number 5. A Differential Q... more Home >> Numerical Heat Transfer Part A: Applications, Volume 49, Number 5. A Differential Quadrature Element Method for Nonlinear Transient Heat Transfer Analysis of Extended Surfaces. Authors: Malekzadeh, P. 1 ; Rahideh, H. 2 ; Karami, G. 3. ...
Computational Mechanics, 1994
A combined finite element evaluation of hydrodynamic pressure and boundary element calculation of... more A combined finite element evaluation of hydrodynamic pressure and boundary element calculation of film thickness is presented. The viscosity and the density of the oil are assumed to vary with pressure, however the isothermal condition is assumed to prevail. The technique is based on an iterative procedure by assuming an initial hydrodynamic pressure. The iteration cycle will then be followed by the calculation of the film thickness and hydrodynamic pressure to arrive at a converged solution. The bearings have been treated realistically as finite domain bodies and their deformations are evaluated by boundary element method. The accuracy of the technique is illustrated in elastohydrodynamic lubrication (EHL) of inclined slider and line contact problems.
Computers & Structures, 1993
ABSTRACT
Computer Methods in Biomechanics and Biomedical Engineering, 2009
This paper proposes a micromechanics algorithm utilising the finite element method (FEM) for the ... more This paper proposes a micromechanics algorithm utilising the finite element method (FEM) for the analysis of heterogeneous matter. The characterisation procedure takes the material properties of the constituents, axons and extracellular matrix (ECM) as input data. The material properties of both the axons and the matrix are assumed to have linear viscoelastic behaviour with a perfect bonding between them. The results of the modelling have been validated with experimental data with material white input from brainstem by considering the morphology of brainstem in which most axons are oriented in longitudinal direction in the form of a uniaxial fibrous composite material. The method is then employed to examine the undulations of axons within different subregions of white matter and to study the impact due to axon/matrix volume fractions. For such purposes, different unit cells composed of wavy geometries and with various volume factions have been exposed to the six possible loading scenarios. The results will clearly demonstrate the undulation and axon volume fraction impacts. In this respect, undulation affects the material stiffness heavily in the axon longitudinal direction, whereas the axons' volume fraction has a much greater impact on the mechanical properties of the white matter in general. Also the results show that the created stresses and strains in the axons and matrix under loading will be impacted by undulation change. With increase in undulation the matrix suffers higher stresses when subjected to tension, whereas axons suffer higher stresses in shear. The axons always exhibit higher stresses whereas the matrix exhibits higher strains. The evaluated time-dependent local stress and strain concentrations within a repeating unit cell of the material model are indicative of the mechanical behaviour of the white tissue under different loading scenarios.
Journal of The Mechanical Behavior of Biomedical Materials, 2009
Computational Materials Science, 2008
International Journal of Impact Engineering, 2009
Annals of Biomedical Engineering, 2010
A mechanized and integrated computational scheme is introduced to determine the human brain respo... more A mechanized and integrated computational scheme is introduced to determine the human brain responses in an environment where the human head is exposed to explosions from trinitrotoluene (TNT), or other high-yield explosives, in military applications. The procedure is based on a three-dimensional (3-D) non-linear finite element method (FEM) that implements a simultaneous conduction of explosive detonation, shock wave propagation, blast–head interactions, and the confronting human head. The processes of blast propagation in the air and blast interaction with the head are modeled by an Arbitrary Lagrangian–Eulerian (ALE) multi-material FEM formulation, together with a penalty-based fluid/structure interaction (FSI) algorithm. Such a model has already been successfully validated against experimental data regarding air-free blast and plate–blast interactions. The human head model is a 3-D geometrically realistic configuration that has been previously validated against the brain intracranial pressure (ICP), as well as shear and principal strains under different impact loadings of cadaveric experimental tests of Hardy et al. [Hardy W. N., C. Foster, M. Mason, S. Chirag, J. Bishop, M. Bey, W. Anderst, and S. Tashman. A study of the response of the human cadaver head to impact. Proc. 51 st Stapp. Car Crash J. 17–80, 2007]. Different scenarios have been assumed to capture an appropriate picture of the brain response at a constant stand-off distance of nearly 80 cm from the core of the explosion, but exposed to different amounts of a highly explosive (HE) material such as TNT. The overpressures at the vicinity of the head are in the range of about 2.4–8.7 atmosphere (atm), considering the reflected pressure from the head. The methodology provides brain ICP, maximum shear stresses and maximum principal strain within the milli-scale time frame of this highly dynamic phenomenon. While focusing on the two mechanical parameters of pressure, and also on the maximum shear stress and maximum principal strain to predict the brain injury, the research provides an assessment of the brain responses to different amounts of overpressure. The research also demonstrates the ability to predict the ICP, as well as the stress and strain within the brain, due to such an event. The research cannot identify, however, the specific levels of ICP, stress and strain that necessarily lead to traumatic brain injury (TBI) because there is no access to experimental data regarding head–blast interactions.
Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2009
A major role for the cerebrospinal fluid (CSF) is to provide effective damping against sudden int... more A major role for the cerebrospinal fluid (CSF) is to provide effective damping against sudden intracranial brain motions during dynamic head impact. This paper examines the roles of CSF properties on human brain responses under certain impact loadings. The brain is assumed to have a hyperviscoelastic material behaviour, while CSF is considered to be fluid-like elastic, viscoelastic, and nearly incompressible elastic with a low shear modulus and a high bulk modulus. A finite element parametric investigation on a head model under different scenarios of impact is conducted. In the study, the CSF material parameters are varied within the expected range of change, while other components of the head model are kept constant. The results indicate that the solutions from the modelling of CSF by a fluid-like medium are more realistic and support the findings of the experiment. The results also indicate that varying CSF properties did not have a major impact on the peak intracranial pressures but the impact on brain principal and shear strains are relatively significant. A sizeable impact on the relative motion of the brain, with respect to the skull, can also be observed.
Journal of Composite Materials, 2008
ABSTRACT: An efficient computational algorithm is proposed to evaluate the viscoelastic propertie... more ABSTRACT: An efficient computational algorithm is proposed to evaluate the viscoelastic properties of fibrous composites. A repeating unit cell (RUC) based on a pre-determined fiber packing is assumed to represent the microstructure of the composite. Finite element analysis of this ...
Engineering Structures, 2003
Computational Mechanics, 2003
A differential quadrature element method (DQEM) based on first order shear deformation theory is... more A differential quadrature element method (DQEM) based on first order shear deformation theory is developed for free vibration analysis of non-uniform beams on elastic foundations. By decomposing the system into a series of sub-domains or elements, any discontinuity in loading, geometry, material properties, and even elastic foundations can be considered conveniently. Using this method, the vibration analysis of general beam-like structures is to be studied. The governing equations of each element, natural compatibility conditions at the interface of two adjacent elements and the external boundary conditions are developed in a systematic manner, using Hamilton's principle. The present DQEM is to be implemented to Timoshenko beams resting on partially supported elastic foundations with various types of boundary conditions under the action of axial loading. The general versality, accuracy, and efficiency of the presented DQEM are demonstrated having solved different examples and compared to the exact or other numerical procedure solutions.
Computer Methods in Applied Mechanics and Engineering, 2004
... plates. Bert and Malik [17] and [18] used semi-analytical DQM for free vibration analysis of ... more ... plates. Bert and Malik [17] and [18] used semi-analytical DQM for free vibration analysis of rectangular thin plates. ... DQM. Also, a review of the early developments of DQM can be referenced to the papers by Bert and Malik [21] and [22]. ...
Composite Structures, 2006
Engineering Structures, 2004
International Journal for Numerical Methods in Engineering, 2003
A new methodology is introduced in the differential quadrature (DQ) analysis of plate problems. T... more A new methodology is introduced in the differential quadrature (DQ) analysis of plate problems. The proposed approach is distinct from other DQ methods by employing the multiple boundary conditions in a different manner. For structural and plate problems, the methodology employs the displacement within the domain as the only degree of freedom, whereas along the boundaries the displacements as well as the second derivatives of the displacements with respect to the co-ordinate variable normal to the boundary in the computational domain are considered as the degrees of freedom for the problem. Employing such a procedure would facilitate the boundary conditions to be implemented exactly and conveniently. In order to demonstrate the capability of the new methodology, all cases of free vibration analysis of rectangular isotropic plates, in which the conventional DQ methods have had some sort of difficulty to arrive at a converged or accurate solution, are carried out. Excellent convergence behaviour and accuracy in comparison with exact results and/or results obtained by other approximate methods were obtained. The analogous DQ formulation for a general rectangular plate is derived and for each individual boundary condition the general format for imposing the given conditions is devised. It must be emphasized that the computational efforts of this new methodology are not more than for the conventional differential quadrature methods. Copyright © 2002 John Wiley & Sons, Ltd.
Engineering Structures, 2006
... behavior of thin, isotropic rhombic plates with clamped and simply supported edges by using a... more ... behavior of thin, isotropic rhombic plates with clamped and simply supported edges by using a high precision conforming triangular plate bending element ... 8] studied the large deflection of isotropic simply supported thin rhombic plates ... 9] presented a finite element analysis of the ...
Composite Structures, 2003
Energy Conversion and Management, 2006
Engineering Structures, 2005
... The applications of PDQ for thin beams and plates and also for rectangular thick plates have ... more ... The applications of PDQ for thin beams and plates and also for rectangular thick plates have been carried out by the authors [21], [22], [23], [24 ... Liew and Han [29] employed the DQ method to present the bending analysis of simply supported thick skew plates based on ...
Numerical Heat Transfer Part A-applications, 2006
Home >> Numerical Heat Transfer Part A: Applications, Volume 49, Number 5. A Differential Q... more Home >> Numerical Heat Transfer Part A: Applications, Volume 49, Number 5. A Differential Quadrature Element Method for Nonlinear Transient Heat Transfer Analysis of Extended Surfaces. Authors: Malekzadeh, P. 1 ; Rahideh, H. 2 ; Karami, G. 3. ...