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Volume 27 (2022): Issue 4 (December 2022)

Volume 27 (2022): Issue 3 (September 2022)

Volume 27 (2022): Issue 2 (June 2022)

Volume 27 (2022): Issue 1 (March 2022)

Volume 26 (2021): Issue 4 (December 2021)

Volume 26 (2021): Issue 3 (September 2021)

Volume 26 (2021): Issue 2 (June 2021)

Volume 26 (2021): Issue 1 (March 2021)

Volume 25 (2020): Issue 4 (December 2020)

Volume 25 (2020): Issue 3 (September 2020)

Volume 25 (2020): Issue 2 (June 2020)

Volume 25 (2020): Issue 1 (March 2020)

Volume 24 (2019): Issue 4 (December 2019)

Volume 24 (2019): Issue 3 (September 2019)

Volume 24 (2019): Issue 2 (June 2019)

Volume 24 (2019): Issue 1 (March 2019)

Volume 23 (2018): Issue 4 (November 2018)

Volume 23 (2018): Issue 3 (August 2018)

Volume 23 (2018): Issue 2 (May 2018)

Volume 23 (2018): Issue 1 (February 2018)

Volume 22 (2017): Issue 4 (December 2017)

Volume 22 (2017): Issue 3 (August 2017)

Volume 22 (2017): Issue 2 (May 2017)

Volume 22 (2017): Issue 1 (February 2017)

Volume 21 (2016): Issue 4 (December 2016)

Volume 21 (2016): Issue 3 (August 2016)

Volume 21 (2016): Issue 2 (May 2016)

Volume 21 (2016): Issue 1 (February 2016)

Volume 20 (2015): Issue 4 (December 2015)

Volume 20 (2015): Issue 3 (August 2015)

Volume 20 (2015): Issue 2 (May 2015)

Volume 20 (2015): Issue 1 (February 2015)

Volume 19 (2014): Issue 4 (December 2014)

Volume 19 (2014): Issue 3 (August 2014)

Volume 19 (2014): Issue 2 (May 2014)

Volume 19 (2014): Issue 1 (February 2014)

Volume 18 (2013): Issue 4 (December 2013)

Volume 18 (2013): Issue 3 (August 2013)

Volume 18 (2013): Issue 2 (June 2013)

Volume 18 (2013): Issue 1 (March 2013)

Journal Details
Format
Journal
eISSN
2353-9003
First Published
19 Apr 2013
Publication timeframe
4 times per year
Languages
English

Search

Volume 22 (2017): Issue 2 (May 2017)

Journal Details
Format
Journal
eISSN
2353-9003
First Published
19 Apr 2013
Publication timeframe
4 times per year
Languages
English

Search

17 Articles
Open Access

Analytical Solution of Mixed Boundary Value Problems Using the Displacement Potential Approach for the Case of Plane Stress and Plane Strain Conditions

Published Online: 09 Jun 2017
Page range: 269 - 291

Abstract

Abstract

Two elastic plate problems made of duralumin are solved analytically using the displacement potential approach for the case of plane strain and plane stress conditions. Firstly, a one end fixed plate is considered in which the rest of the edges are stiffened and a uniform load is applied to the opposite end of the fixed end. Secondly, a plate is considered in which all of the edges are stiffened and a uniform tension is applied at its both ends. Solutions to both of the problems are presented for the case of plane stress and plane strain conditions. The effects of plane stress and plane strain conditions on the solutions are explained. In the case of stiffening of the edges of the plate, the shape of the plate does not change abruptly, which is clearly observed in both of the cases. For the plane strain condition, the plates become stiffer in the loading direction as compared to the plane stress condition. For the plane strain condition, there is a significant variation of the normal stress component, σzz at different sections of the plate. The graphical results, clearly identify the critical regions of the plate for the case of the plane stress and plane strain condition.

Keywords

  • analytical solution
  • displacement potential approach
  • plane stress and plane strain conditions
  • mixed boundary value problems
Open Access

On Some Mechanical Properties and Wear Behavior of Sintered Bronze Based Composites Reinforced with Some Aluminides Microadditives

Published Online: 09 Jun 2017
Page range: 293 - 302

Abstract

Abstract

In the paper, the changes in some mechanical properties and wear behavior of CuSn10 sintered bronze and MMCs based on this bronze reinforced with composite ultrafine aluminide powders FeAl/15 % Al2O3, NiAl/15 % Al2O3 and Ti-46Al-8Cr are described. It was observed that the presence of aluminides in the MMCs leads to an increase in the hardness, but the flexural strength may increase or decrease depending on the type of aluminide. The presence of aluminides in the MMC reduces the wear rate considerably. It is decreased in the direction of FeAl/15 % Al2O3 → NiAl/15 % Al2O3 → Ti-46Al-8Cr aluminides and for the best MMC composition the advantage is about 20 times. In the MMCs wear process, micro-craters are formed on the contact surface and it is the principal reason of a decrease in the wear rate.

Keywords

  • metal-matrix composites (MMCs)
  • mechanical properties
  • surface analysis
  • wear
Open Access

Effect of Hall Current in Thermoelastic Materials with Double Porosity Structure

Published Online: 09 Jun 2017
Page range: 303 - 319

Abstract

Abstract

The present investigation is concerned with one dimensional problem in a homogeneous, isotropic thermoelastic medium with double porosity structure in the presence of Hall currents subjected to thermomechanical sources. A state space approach has been applied to investigate the problem. As an application of the approach, normal force and thermal source have been taken to illustrate the utility of the approach. The expressions for the components of normal stress, equilibrated stress and the temperature change are obtained in the frequency domain and computed numerically. A numerical simulation is prepared for these quantities. The effect of the Hartmann number is depicted graphically on the resulting quantities for a specific model. Some particular cases of interest are also deduced from the present investigation.

Keywords

  • Hall current
  • double porosity
  • thermoelasticity
  • state space approach
  • thermomechanical sources
Open Access

Effect of Relative Velocity Between Rough Surfaces: Hydrodynamic Lubrication of Rotary Lip Seal

Published Online: 09 Jun 2017
Page range: 321 - 332

Abstract

Abstract

Since the sixties, most of numerical studies that model the rotary lip seal lubrication have been restricted by assuming that one of the two opposing surfaces is smooth: either the lip or the shaft. This hypothesis, although it is verified only for a shaft roughness ten times smaller than that of the seal, is the best solution to avoid the transient term “∂h/∂t” in the deterministic approach. Thus, the subject of the present study is twofold. The first part validates the current hydrodynamic model with the international literature by assuming the asperities on the lip and shaft as a two-dimensional cosine function. In the second part the Reynolds equation for rough surfaces with relative motion is solved. The numerical results show that the relative motion between rough surfaces impacts significantly the load support and the leakage rate, but affects slightly the friction torque.

Keywords

  • hydrodynamic lubrication
  • roughness
  • relative velocity
  • Reynolds equation
  • finite differences
Open Access

Simulating Progressive Damage of Notched Composite Laminates with Various Lamination Schemes

Published Online: 09 Jun 2017
Page range: 333 - 347

Abstract

Abstract

A three dimensional finite element based progressive damage model has been developed for the failure analysis of notched composite laminates. The material constitutive relations and the progressive damage algorithms are implemented into finite element code ABAQUS using user-defined subroutine UMAT. The existing failure criteria for the composite laminates are modified by including the failure criteria for fiber/matrix shear damage and delamination effects. The proposed numerical model is quite efficient and simple compared to other progressive damage models available in the literature. The efficiency of the present constitutive model and the computational scheme is verified by comparing the simulated results with the results available in the literature. A parametric study has been carried out to investigate the effect of change in lamination scheme on the failure behaviour of notched composite laminates.

Keywords

  • damage mechanics
  • user-defined subroutine
  • composite laminates
  • finite element
  • strength
  • degradation
Open Access

Exact Solution of the Harmonic Problem for a Rectangular Plate in Flat Deformation by the Method of Initial Functions

Published Online: 09 Jun 2017
Page range: 349 - 361

Abstract

Abstract

A wide range of applications is based nowadays on analytical developments which allow a precise and effective approach and short time of computations compared with the time required for numerical methods; in this way these developments are suitable for calculations in real time. This work proposes an approach for solving a two-dimensional harmonic problem of a rectangular plate under local surface loading using Vlasov’s symbolic method of initial functions and a general solution of the harmonic equation for a rectangle. Substituting the harmonic functions in symbolic form for the corresponding solutions allows us to give the exact solution of the problem in trigonometric form.

Keywords

  • harmonic functions
  • initial functions
  • flat deformation
Open Access

Unsteady MHD Mixed Convection Flow of a Micropolar Fluid Over a Vertical Wedge

Published Online: 09 Jun 2017
Page range: 363 - 391

Abstract

Abstract

An analysis is presented to investigate the unsteady magnetohydrodynamic (MHD) mixed convection boundary-layer flow of a micropolar fluid over a vertical wedge in the presence of thermal radiation and heat generation or absorption. The free-stream velocity and surface temperature are assumed to be oscillating in magnitude but not in the direction of the oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the finite difference method for the entire frequency range, and the series solution for low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions provide a good agreement with the series solutions. The amplitudes of skin friction and couple stress coefficients are found to be strongly dependent on the Richardson number and the vortex viscosity parameter. The Prandtl number, the conduction-radiation parameter, the surface temperature parameter and the pressure gradient parameter significantly affect the amplitudes of skin friction, couple stress and surface heat transfer rates. However, the amplitudes of skin friction coefficient are considerably affected by the magnetic field parameter, whereas the amplitudes of heat transfer rate are appreciably changed with the heat generation or absorption parameter. In addition, results are presented for the transient skin friction, couple stress and heat transfer rate with the variations of the Richardson number, the vortex viscosity parameter, the pressure gradient parameter and the magnetic field parameter.

Keywords

  • micropolar fluid
  • unsteady flow
  • radiation
  • heat generation
Open Access

Fem and Experimental Analysis of Thin-Walled Composite Elements Under Compression

Published Online: 09 Jun 2017
Page range: 393 - 402

Abstract

Abstract

Thin-walled steel elements in the form of openwork columns with variable geometrical parameters of holes were studied. The samples of thin-walled composite columns were modelled numerically. They were subjected to axial compression to examine their behavior in the critical and post-critical state. The numerical models were articulately supported on the upper and lower edges of the cross-section of the profiles. The numerical analysis was conducted only with respect to the non-linear stability of the structure. The FEM analysis was performed until the material achieved its yield stress. This was done to force the loss of stability by the structures. The numerical analysis was performed using the ABAQUS® software. The numerical analysis was performed only for the elastic range to ensure the operating stability of the tested thin-walled structures.

Keywords

  • thin-walled structures
  • finite element method
  • numerical and experimental investigations
  • buckling
Open Access

Transport of MHD Couple Stress Fluid Through Peristalsis in a Porous Medium Under the Influence of Heat Transfer and Slip Effects

Published Online: 09 Jun 2017
Page range: 403 - 414

Abstract

Abstract

An attempt has been made to examine the effects of magnetohydrodynamic couple stress fluid in peristaltic flow with porous medium under the impact of slip, heat transfer and wall properties. The expressions are obtained for temperature, coefficient of heat transfer and velocity. Influences of different parameters, the Hartmann number, Brinkman number and adaptability parameters on the temperature and warmth trade coefficient are discussed through outlines.

Keywords

  • peristaltic flow
  • couple stress fluid
  • Darcy number
  • slip parameter
  • compliant walls
Open Access

Mathematical Modeling of Torsional Surface Wave Propagation in a Non-Homogeneous Transverse Isotropic Elastic Solid Semi-Infinite Medium Under a Layer

Published Online: 09 Jun 2017
Page range: 415 - 426

Abstract

Abstract

The present paper deals with the mathematical modeling of the propagation of torsional surface waves in a non-homogeneous transverse isotropic elastic half-space under a rigid layer. Both rigidities and density of the half-space are assumed to vary inversely linearly with depth. Separation of variable method has been used to get the analytical solutions for the dispersion equation of the torsional surface waves. Also, the effects of nonhomogeneities on the phase velocity of torsional surface waves have been shown graphically. Also, dispersion equations have been derived for some particular cases, which are in complete agreement with some classical results.

Keywords

  • non-homogeneous media
  • torsional surface waves
  • rigidity
Open Access

Curvilinear Squeeze Film Bearing with Porous Wall Lubricated by a Rabinowitsch Fluid

Published Online: 09 Jun 2017
Page range: 427 - 441

Abstract

Abstract

The present theoretical analysis is to investigate the effect of non-Newtonian lubricant modelled by a Rabinowitsch fluid on the performance of a curvilinear squeeze film bearing with one porous wall. The equations of motion of a Rabinowitsch fluid are used to derive the Reynolds equation. After general considerations on the flow in a bearing clearance and in a porous layer using the Morgan-Cameron approximation the modified Reynolds equation is obtained. The analytical solution of this equation for the case of a squeeze film bearing is presented. As a result one obtains the formulae expressing pressure distribution and load-carrying capacity. Thrust radial bearing and spherical bearing with a squeeze film are considered as numerical examples.

Keywords

  • non-Newtonian fluid
  • Rabinowitsch model
  • curvilinear squeeze film bearing
  • porous layer

Brief Note

Open Access

Essential Factors For The Changes In Concrete During Electrochemical Extraction

Published Online: 09 Jun 2017
Page range: 443 - 450

Abstract

Abstract

The objective of the article is to present one of the most significant factors affecting electrochemical removal of chloride ions from concrete. Based on the literature findings, tests were carried out on specimens containing chloride admixtures introduced to the cement grout, on elements subjected to chloride penetration from the solution in laboratory conditions and on fragments of constructions penetrated by chlorides as a result of a long-term exposure to seawater.

Keywords

  • chloride ion penetration
  • electrochemical extraction
  • conrete
  • seawater
Open Access

Natural Frequencies of Axisymmetric Vibrations of Thin Hyperbolic Circular Plates with Clamped Edges

Published Online: 09 Jun 2017
Page range: 451 - 457

Abstract

Abstract

A free vibration analysis of homogeneous and isotropic circular thin plates with nonlinear thickness variation and clamped edges is considered. The limited independent solutions of differential Euler equation were expanded in the power series based on the properties of integral equations. The analytical frequency equations as power series were obtained using the method of successive approximations.

Keywords

  • circular plates
  • power series
  • clamped edge
Open Access

Reversed Robin Hood Syndrome in the Light of Nonlinear Model of Cerebral Circulation

Published Online: 09 Jun 2017
Page range: 459 - 464

Abstract

Abstract

The brain is supplied by the internal carotid and vertebro-basilar systems of vessels interconnected by arterial anastomoses and forming at the base of the brain a structure called the Circle of Willis (CoW). An active intrinsic ability of cerebral vascular bed maintains constant Cerebral Blood Flow (CBF) in a certain range of systemic pressure changes. This ability is called autoregulation and together with the redundant structure of the CoW guarantee maintaining CBF even in partial occlusion of supplying arteries. However, there are some situations when the combination of those two mechanisms causes an opposite effect called the Reversed Robin Hood Syndrome (RRHS). In this work we proposed a model of the CoW with autoregulation mechanism and investigated a RRHS which may occur in the case of Internal Carotid Artery (ICA) stenosis combined with hypercapnia. We showed and analyzed the mechanism of stealing the blood by the contralateral side of the brain. Our results were qualitatively compared with the clinical reports available in the literature.

Keywords

  • cerebral blood flow
  • autoregulation
  • steal syndrome
  • Circle of Willis
  • Computational Fluid Dynamics
Open Access

Mechanical Parameters of the Curvilinear Squeeze Film Bearing Lubricated by a Gecim-Winer Fluid

Published Online: 09 Jun 2017
Page range: 465 - 473

Abstract

Abstract

Based upon a Gecim-Winer fluid flow model, a curvilinear squeeze film bearing is considered. The equations of motion are given in a specific coordinates system. After general considerations on the Gecim-Winer fluid flow these equations are used to derive the Reynolds equation. The solution of this equation is obtained by a method of successive approximation. As a result one obtains formulae expressing the pressure distribution and load-carrying capacity. The numerical examples of the Gecim-Winer fluid flow in gaps of two simple bearings: radial and spherical are presented.

Keywords

  • modified Reynolds equation
  • Gecim-Winer fluid
  • squeeze film
  • mechanical parameters of bearing
  • additives

Technical Note

Open Access

Identification Damage Model for Thermomechanical Degradation of Ductile Heterogeneous Materials

Published Online: 09 Jun 2017
Page range: 475 - 481

Abstract

Abstract

The failure of ductile materials subject to high thermal and mechanical loading rates is notably affected by material inertia. The mechanisms of fatigue-crack propagation are examined with particular emphasis on the similarities and differences between cyclic crack growth in ductile materials, such as metals, and corresponding behavior in brittle materials, such as intermetallic and ceramics. Numerical simulations of crack propagation in a cylindrical specimen demonstrate that the proposed method provides an effective means to simulate ductile fracture in large scale cylindrical structures with engineering accuracy. The influence of damage on the intensity of the destruction of materials is studied as well.

Keywords

  • damage
  • manufacturing
  • thermal and mechanical fatigue
Open Access

Comparative Numerical Analysis of Different Strengthening Systems of Historical Brick Arches

Published Online: 09 Jun 2017
Page range: 483 - 491

Abstract

Abstract

The article presents a comparative numerical analysis of various ways to strengthen historical brick arches. Five ways of strengthening brick arches with steel tie-rods have been proposed. Two of these involve the use of braces wrapped around pillars supporting the arch connected with a tie-rod; the other two ways involve the use of the tie-rods with welded metal sheets of different sizes; the latter involves the use of a tie-rod glued with the use of an epoxy adhesive. The collected data were compared with the reference model of the arch left without any interference. The results make it possible to evaluate the effectiveness of the methods by comparing displacements in the vertical and horizontal direction and stresses. The article indicates the direction of proper planning and design of the arch strengthening in brick structures in historical buildings.

Keywords

  • historical buildings
  • brick arches
  • tie-rod
  • modal analysis
  • FEM
17 Articles
Open Access

Analytical Solution of Mixed Boundary Value Problems Using the Displacement Potential Approach for the Case of Plane Stress and Plane Strain Conditions

Published Online: 09 Jun 2017
Page range: 269 - 291

Abstract

Abstract

Two elastic plate problems made of duralumin are solved analytically using the displacement potential approach for the case of plane strain and plane stress conditions. Firstly, a one end fixed plate is considered in which the rest of the edges are stiffened and a uniform load is applied to the opposite end of the fixed end. Secondly, a plate is considered in which all of the edges are stiffened and a uniform tension is applied at its both ends. Solutions to both of the problems are presented for the case of plane stress and plane strain conditions. The effects of plane stress and plane strain conditions on the solutions are explained. In the case of stiffening of the edges of the plate, the shape of the plate does not change abruptly, which is clearly observed in both of the cases. For the plane strain condition, the plates become stiffer in the loading direction as compared to the plane stress condition. For the plane strain condition, there is a significant variation of the normal stress component, σzz at different sections of the plate. The graphical results, clearly identify the critical regions of the plate for the case of the plane stress and plane strain condition.

Keywords

  • analytical solution
  • displacement potential approach
  • plane stress and plane strain conditions
  • mixed boundary value problems
Open Access

On Some Mechanical Properties and Wear Behavior of Sintered Bronze Based Composites Reinforced with Some Aluminides Microadditives

Published Online: 09 Jun 2017
Page range: 293 - 302

Abstract

Abstract

In the paper, the changes in some mechanical properties and wear behavior of CuSn10 sintered bronze and MMCs based on this bronze reinforced with composite ultrafine aluminide powders FeAl/15 % Al2O3, NiAl/15 % Al2O3 and Ti-46Al-8Cr are described. It was observed that the presence of aluminides in the MMCs leads to an increase in the hardness, but the flexural strength may increase or decrease depending on the type of aluminide. The presence of aluminides in the MMC reduces the wear rate considerably. It is decreased in the direction of FeAl/15 % Al2O3 → NiAl/15 % Al2O3 → Ti-46Al-8Cr aluminides and for the best MMC composition the advantage is about 20 times. In the MMCs wear process, micro-craters are formed on the contact surface and it is the principal reason of a decrease in the wear rate.

Keywords

  • metal-matrix composites (MMCs)
  • mechanical properties
  • surface analysis
  • wear
Open Access

Effect of Hall Current in Thermoelastic Materials with Double Porosity Structure

Published Online: 09 Jun 2017
Page range: 303 - 319

Abstract

Abstract

The present investigation is concerned with one dimensional problem in a homogeneous, isotropic thermoelastic medium with double porosity structure in the presence of Hall currents subjected to thermomechanical sources. A state space approach has been applied to investigate the problem. As an application of the approach, normal force and thermal source have been taken to illustrate the utility of the approach. The expressions for the components of normal stress, equilibrated stress and the temperature change are obtained in the frequency domain and computed numerically. A numerical simulation is prepared for these quantities. The effect of the Hartmann number is depicted graphically on the resulting quantities for a specific model. Some particular cases of interest are also deduced from the present investigation.

Keywords

  • Hall current
  • double porosity
  • thermoelasticity
  • state space approach
  • thermomechanical sources
Open Access

Effect of Relative Velocity Between Rough Surfaces: Hydrodynamic Lubrication of Rotary Lip Seal

Published Online: 09 Jun 2017
Page range: 321 - 332

Abstract

Abstract

Since the sixties, most of numerical studies that model the rotary lip seal lubrication have been restricted by assuming that one of the two opposing surfaces is smooth: either the lip or the shaft. This hypothesis, although it is verified only for a shaft roughness ten times smaller than that of the seal, is the best solution to avoid the transient term “∂h/∂t” in the deterministic approach. Thus, the subject of the present study is twofold. The first part validates the current hydrodynamic model with the international literature by assuming the asperities on the lip and shaft as a two-dimensional cosine function. In the second part the Reynolds equation for rough surfaces with relative motion is solved. The numerical results show that the relative motion between rough surfaces impacts significantly the load support and the leakage rate, but affects slightly the friction torque.

Keywords

  • hydrodynamic lubrication
  • roughness
  • relative velocity
  • Reynolds equation
  • finite differences
Open Access

Simulating Progressive Damage of Notched Composite Laminates with Various Lamination Schemes

Published Online: 09 Jun 2017
Page range: 333 - 347

Abstract

Abstract

A three dimensional finite element based progressive damage model has been developed for the failure analysis of notched composite laminates. The material constitutive relations and the progressive damage algorithms are implemented into finite element code ABAQUS using user-defined subroutine UMAT. The existing failure criteria for the composite laminates are modified by including the failure criteria for fiber/matrix shear damage and delamination effects. The proposed numerical model is quite efficient and simple compared to other progressive damage models available in the literature. The efficiency of the present constitutive model and the computational scheme is verified by comparing the simulated results with the results available in the literature. A parametric study has been carried out to investigate the effect of change in lamination scheme on the failure behaviour of notched composite laminates.

Keywords

  • damage mechanics
  • user-defined subroutine
  • composite laminates
  • finite element
  • strength
  • degradation
Open Access

Exact Solution of the Harmonic Problem for a Rectangular Plate in Flat Deformation by the Method of Initial Functions

Published Online: 09 Jun 2017
Page range: 349 - 361

Abstract

Abstract

A wide range of applications is based nowadays on analytical developments which allow a precise and effective approach and short time of computations compared with the time required for numerical methods; in this way these developments are suitable for calculations in real time. This work proposes an approach for solving a two-dimensional harmonic problem of a rectangular plate under local surface loading using Vlasov’s symbolic method of initial functions and a general solution of the harmonic equation for a rectangle. Substituting the harmonic functions in symbolic form for the corresponding solutions allows us to give the exact solution of the problem in trigonometric form.

Keywords

  • harmonic functions
  • initial functions
  • flat deformation
Open Access

Unsteady MHD Mixed Convection Flow of a Micropolar Fluid Over a Vertical Wedge

Published Online: 09 Jun 2017
Page range: 363 - 391

Abstract

Abstract

An analysis is presented to investigate the unsteady magnetohydrodynamic (MHD) mixed convection boundary-layer flow of a micropolar fluid over a vertical wedge in the presence of thermal radiation and heat generation or absorption. The free-stream velocity and surface temperature are assumed to be oscillating in magnitude but not in the direction of the oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the finite difference method for the entire frequency range, and the series solution for low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions provide a good agreement with the series solutions. The amplitudes of skin friction and couple stress coefficients are found to be strongly dependent on the Richardson number and the vortex viscosity parameter. The Prandtl number, the conduction-radiation parameter, the surface temperature parameter and the pressure gradient parameter significantly affect the amplitudes of skin friction, couple stress and surface heat transfer rates. However, the amplitudes of skin friction coefficient are considerably affected by the magnetic field parameter, whereas the amplitudes of heat transfer rate are appreciably changed with the heat generation or absorption parameter. In addition, results are presented for the transient skin friction, couple stress and heat transfer rate with the variations of the Richardson number, the vortex viscosity parameter, the pressure gradient parameter and the magnetic field parameter.

Keywords

  • micropolar fluid
  • unsteady flow
  • radiation
  • heat generation
Open Access

Fem and Experimental Analysis of Thin-Walled Composite Elements Under Compression

Published Online: 09 Jun 2017
Page range: 393 - 402

Abstract

Abstract

Thin-walled steel elements in the form of openwork columns with variable geometrical parameters of holes were studied. The samples of thin-walled composite columns were modelled numerically. They were subjected to axial compression to examine their behavior in the critical and post-critical state. The numerical models were articulately supported on the upper and lower edges of the cross-section of the profiles. The numerical analysis was conducted only with respect to the non-linear stability of the structure. The FEM analysis was performed until the material achieved its yield stress. This was done to force the loss of stability by the structures. The numerical analysis was performed using the ABAQUS® software. The numerical analysis was performed only for the elastic range to ensure the operating stability of the tested thin-walled structures.

Keywords

  • thin-walled structures
  • finite element method
  • numerical and experimental investigations
  • buckling
Open Access

Transport of MHD Couple Stress Fluid Through Peristalsis in a Porous Medium Under the Influence of Heat Transfer and Slip Effects

Published Online: 09 Jun 2017
Page range: 403 - 414

Abstract

Abstract

An attempt has been made to examine the effects of magnetohydrodynamic couple stress fluid in peristaltic flow with porous medium under the impact of slip, heat transfer and wall properties. The expressions are obtained for temperature, coefficient of heat transfer and velocity. Influences of different parameters, the Hartmann number, Brinkman number and adaptability parameters on the temperature and warmth trade coefficient are discussed through outlines.

Keywords

  • peristaltic flow
  • couple stress fluid
  • Darcy number
  • slip parameter
  • compliant walls
Open Access

Mathematical Modeling of Torsional Surface Wave Propagation in a Non-Homogeneous Transverse Isotropic Elastic Solid Semi-Infinite Medium Under a Layer

Published Online: 09 Jun 2017
Page range: 415 - 426

Abstract

Abstract

The present paper deals with the mathematical modeling of the propagation of torsional surface waves in a non-homogeneous transverse isotropic elastic half-space under a rigid layer. Both rigidities and density of the half-space are assumed to vary inversely linearly with depth. Separation of variable method has been used to get the analytical solutions for the dispersion equation of the torsional surface waves. Also, the effects of nonhomogeneities on the phase velocity of torsional surface waves have been shown graphically. Also, dispersion equations have been derived for some particular cases, which are in complete agreement with some classical results.

Keywords

  • non-homogeneous media
  • torsional surface waves
  • rigidity
Open Access

Curvilinear Squeeze Film Bearing with Porous Wall Lubricated by a Rabinowitsch Fluid

Published Online: 09 Jun 2017
Page range: 427 - 441

Abstract

Abstract

The present theoretical analysis is to investigate the effect of non-Newtonian lubricant modelled by a Rabinowitsch fluid on the performance of a curvilinear squeeze film bearing with one porous wall. The equations of motion of a Rabinowitsch fluid are used to derive the Reynolds equation. After general considerations on the flow in a bearing clearance and in a porous layer using the Morgan-Cameron approximation the modified Reynolds equation is obtained. The analytical solution of this equation for the case of a squeeze film bearing is presented. As a result one obtains the formulae expressing pressure distribution and load-carrying capacity. Thrust radial bearing and spherical bearing with a squeeze film are considered as numerical examples.

Keywords

  • non-Newtonian fluid
  • Rabinowitsch model
  • curvilinear squeeze film bearing
  • porous layer

Brief Note

Open Access

Essential Factors For The Changes In Concrete During Electrochemical Extraction

Published Online: 09 Jun 2017
Page range: 443 - 450

Abstract

Abstract

The objective of the article is to present one of the most significant factors affecting electrochemical removal of chloride ions from concrete. Based on the literature findings, tests were carried out on specimens containing chloride admixtures introduced to the cement grout, on elements subjected to chloride penetration from the solution in laboratory conditions and on fragments of constructions penetrated by chlorides as a result of a long-term exposure to seawater.

Keywords

  • chloride ion penetration
  • electrochemical extraction
  • conrete
  • seawater
Open Access

Natural Frequencies of Axisymmetric Vibrations of Thin Hyperbolic Circular Plates with Clamped Edges

Published Online: 09 Jun 2017
Page range: 451 - 457

Abstract

Abstract

A free vibration analysis of homogeneous and isotropic circular thin plates with nonlinear thickness variation and clamped edges is considered. The limited independent solutions of differential Euler equation were expanded in the power series based on the properties of integral equations. The analytical frequency equations as power series were obtained using the method of successive approximations.

Keywords

  • circular plates
  • power series
  • clamped edge
Open Access

Reversed Robin Hood Syndrome in the Light of Nonlinear Model of Cerebral Circulation

Published Online: 09 Jun 2017
Page range: 459 - 464

Abstract

Abstract

The brain is supplied by the internal carotid and vertebro-basilar systems of vessels interconnected by arterial anastomoses and forming at the base of the brain a structure called the Circle of Willis (CoW). An active intrinsic ability of cerebral vascular bed maintains constant Cerebral Blood Flow (CBF) in a certain range of systemic pressure changes. This ability is called autoregulation and together with the redundant structure of the CoW guarantee maintaining CBF even in partial occlusion of supplying arteries. However, there are some situations when the combination of those two mechanisms causes an opposite effect called the Reversed Robin Hood Syndrome (RRHS). In this work we proposed a model of the CoW with autoregulation mechanism and investigated a RRHS which may occur in the case of Internal Carotid Artery (ICA) stenosis combined with hypercapnia. We showed and analyzed the mechanism of stealing the blood by the contralateral side of the brain. Our results were qualitatively compared with the clinical reports available in the literature.

Keywords

  • cerebral blood flow
  • autoregulation
  • steal syndrome
  • Circle of Willis
  • Computational Fluid Dynamics
Open Access

Mechanical Parameters of the Curvilinear Squeeze Film Bearing Lubricated by a Gecim-Winer Fluid

Published Online: 09 Jun 2017
Page range: 465 - 473

Abstract

Abstract

Based upon a Gecim-Winer fluid flow model, a curvilinear squeeze film bearing is considered. The equations of motion are given in a specific coordinates system. After general considerations on the Gecim-Winer fluid flow these equations are used to derive the Reynolds equation. The solution of this equation is obtained by a method of successive approximation. As a result one obtains formulae expressing the pressure distribution and load-carrying capacity. The numerical examples of the Gecim-Winer fluid flow in gaps of two simple bearings: radial and spherical are presented.

Keywords

  • modified Reynolds equation
  • Gecim-Winer fluid
  • squeeze film
  • mechanical parameters of bearing
  • additives

Technical Note

Open Access

Identification Damage Model for Thermomechanical Degradation of Ductile Heterogeneous Materials

Published Online: 09 Jun 2017
Page range: 475 - 481

Abstract

Abstract

The failure of ductile materials subject to high thermal and mechanical loading rates is notably affected by material inertia. The mechanisms of fatigue-crack propagation are examined with particular emphasis on the similarities and differences between cyclic crack growth in ductile materials, such as metals, and corresponding behavior in brittle materials, such as intermetallic and ceramics. Numerical simulations of crack propagation in a cylindrical specimen demonstrate that the proposed method provides an effective means to simulate ductile fracture in large scale cylindrical structures with engineering accuracy. The influence of damage on the intensity of the destruction of materials is studied as well.

Keywords

  • damage
  • manufacturing
  • thermal and mechanical fatigue
Open Access

Comparative Numerical Analysis of Different Strengthening Systems of Historical Brick Arches

Published Online: 09 Jun 2017
Page range: 483 - 491

Abstract

Abstract

The article presents a comparative numerical analysis of various ways to strengthen historical brick arches. Five ways of strengthening brick arches with steel tie-rods have been proposed. Two of these involve the use of braces wrapped around pillars supporting the arch connected with a tie-rod; the other two ways involve the use of the tie-rods with welded metal sheets of different sizes; the latter involves the use of a tie-rod glued with the use of an epoxy adhesive. The collected data were compared with the reference model of the arch left without any interference. The results make it possible to evaluate the effectiveness of the methods by comparing displacements in the vertical and horizontal direction and stresses. The article indicates the direction of proper planning and design of the arch strengthening in brick structures in historical buildings.

Keywords

  • historical buildings
  • brick arches
  • tie-rod
  • modal analysis
  • FEM

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