Journal & Issues

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
ISSN
1734-4492
First Published
19 Apr 2013
Publication timeframe
4 times per year
Languages
English

Search

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

Journal Details
Format
Journal
eISSN
2353-9003
ISSN
1734-4492
First Published
19 Apr 2013
Publication timeframe
4 times per year
Languages
English

Search

20 Articles
Open Access

Evaluation of the Influence of Wind-Driven Rain on Moisture in Cellular Concrete Wall Boards

Published Online: 09 Sep 2017
Page range: 509 - 519

Abstract

Abstract

The non-stationary moisture level of a cellular concrete wall board in a heated utility building located in the northern part of the town of Brest (Belarus), depending on the climatic influence, was assessed in this work. The results were obtained both in a calculation experiment and a physical test. It was observed that the main reason for the high moisture levels in cellular concrete is wind-driven rain intensifying the process of free capillary moisture transfer. A comparative analysis of the results of the physical test and the calculation experiment showed that the THSS software elaborated by the authors was able to predict the actual moisture levels of the shielding structure under study accurately enough when precise data concerning the thermal and physical characteristics of the materials as well as the occurring climatic influences were submitted.

Keywords

  • cellular concrete
  • wind-driven rain
  • capillary transfer
  • water sorption coefficient
  • moisture content
Open Access

Effect of Initial Stress on the Dynamic Response of a Multi-Layered Plate-Strip Subjected to an Arbitrary Inclined Time-Harmonic Force

Published Online: 09 Sep 2017
Page range: 521 - 537

Abstract

Abstract

The forced vibration of a multi-layered plate-strip with initial stress under the action of an arbitrary inclined time-harmonic force resting on a rigid foundation is considered. Within the framework of the piecewise homogeneous body model with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies (TLTEWISB), a mathematical modelling is presented in plane strain state. It is assumed that there exists the complete contact interaction at the interface between the layers and the materials of the layer are linearly elastic, homogeneous and isotropic. The governing system of the partial differential equations of motion for the considered problem is solved approximately by employing the Finite Element Method (FEM). Further, the influence of the initial stress parameter on the dynamic response of the plate-strip is presented.

Keywords

  • multi-layered plate-strip
  • finite element method
  • initial stress
  • time-harmonic force

MSC 2010

  • 74H15
  • 74S05
Open Access

Conjugate Heat and Mass Transfer on Fluctuating Mixed Convection Flow along a Vertical Wedge with Thermal Radiation

Published Online: 09 Sep 2017
Page range: 539 - 565

Abstract

Abstract

We study the boundary layer characteristics of heat and mass transfer flow past a vertical wedge in the presence of thermal radiation. The surface temperature and the species concentration are assumed to be oscillating in the magnitude but not in the direction of oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the straightforward finite difference method for the entire frequency range, and the series solution for the low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions have been presented in terms of the amplitudes and phase angles of the skin friction, the rate of heat transfer and the mass transfer with the variations of Richardson’s number, the Prandtl number, the conduction–radiation parameter, the surface temperature parameter and the Schmidt number. Furthermore, the effects of these parameters are examined in terms of the transient skin friction, heat transfer and mass transfer.

Keywords

  • mixed convection
  • thermal radiation
  • vertical wedge
Open Access

Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel

Published Online: 09 Sep 2017
Page range: 567 - 582

Abstract

Abstract

The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.

Keywords

  • microchannel
  • transverse magnetic field
  • induced magnetic field
  • velocity slip
  • temperature jump
Open Access

Axisymmetric Vibration for Micropolar Porous Thermoelastic Circular Plate

Published Online: 09 Sep 2017
Page range: 583 - 600

Abstract

Abstract

The present investigation is concerned with a two dimensional axisymmetric problem in a homogeneous isotropic micropolar porous thermoelastic circular plate by using the eigen value approach. The Laplace and Hankel transform are used to solve the problem. The expression of displacements, microrotation, volume fraction field, temperature distribution and stresses are obtained in the transformed domain subjected to thermomechanical sources. A computer algorithm is developed for numerical computations. To obtain the resulting quantities in a physical domain, a numerical inversion technique is used. The resulting quantities are depicted graphically for a specific model. Some special cases are also deduced.

Keywords

  • micropolar porous thermoelasticity
  • eigen value
  • Laplace and Hankel transforms
  • thermomechanical sources
Open Access

Digital Materials – Evaluation of the Possibilities of using Selected Hyperelastic Models to Describe Constitutive Relations

Published Online: 09 Sep 2017
Page range: 601 - 612

Abstract

Abstract

The authors tried to identify the parameters of numerical models of digital materials, which are a kind of composite resulting from the manufacture of the product in 3D printers. With the arrangement of several heads of the printer, the new material can result from mixing of materials with radically different properties, during the process of producing single layer of the product. The new material has properties dependent on the base materials properties and their proportions. Digital materials tensile characteristics are often non-linear and qualify to be described by hyperelastic materials models. The identification was conducted based on the results of tensile tests models, its various degrees coefficients of the polynomials to various degrees coefficients of the polynomials. The Drucker’s stability criterion was also examined. Fourteen different materials were analyzed.

Keywords

  • digital materials
  • hyperelastic
  • identification of models
  • FEM
  • 3D printing
  • PolyJet Matrix technology
Open Access

Numerical Solutions by EFGM of MHD Convective Fluid Flow Past a Vertical Plate Immersed in a Porous Medium in the Presence of Cross Diffusion Effects via Biot Number and Convective Boundary Condition

Published Online: 09 Sep 2017
Page range: 613 - 636

Abstract

Abstract

In this investigation, the numerical results of a mixed convective MHD chemically reacting flow past a vertical plate embedded in a porous medium are presented in the presence of cross diffusion effects and convective boundary condition. Instead of the commonly used conditions of constant surface temperature or constant heat flux, a convective boundary condition is employed which makes this study unique and the results more realistic and practically useful. The momentum, energy, and concentration equations derived as coupled second-order, ordinary differential equations are solved numerically using a highly accurate and thoroughly tested element free Galerkin method (EFGM). The effects of the Soret number, Dufour number, Grashof number for heat and mass transfer, the viscous dissipation parameter, Schmidt number, chemical reaction parameter, permeability parameter and Biot number on the dimensionless velocity, temperature and concentration profiles are presented graphically. In addition, numerical results for the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are discussed through tabular forms. The discussion focuses on the physical interpretation of the results as well as their comparison with the results of previous studies.

Keywords

  • thermal diffusion
  • diffusion thermo
  • MHD
  • porous medium
  • EFGM
Open Access

Role of Slip Velocity in a Magneto-Micropolar Fluid Flow from a Radiative Surface with Variable Permeability: A Numerical Study

Published Online: 09 Sep 2017
Page range: 637 - 651

Abstract

Abstract

An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

Keywords

  • slip velocity
  • chemical reaction
  • micropolar fluid
  • MHD
  • heat and mass transfer
  • FDM
Open Access

A Numerical Simulation for Prediction of Infrared Radiation Emitted from Plain Surfaces with Different Geometries

Published Online: 09 Sep 2017
Page range: 653 - 664

Abstract

Abstract

In this paper, infrared radiation exiting plain surfaces with different geometries is numerically simulated. Surfaces under consideration are assumed to have steady uniform heat generation inside. Moreover, the boundaries of the surfaces are considered to be at the surroundings temperature. Infrared radiation is calculated based on the temperature profile determined for the surface. The temperature profile of the surface is determined assuming the two dimensional heat conduction equations to govern the problem. The physical domain is transformed into the appropriate computational domain and the governing equation is mapped into the suitable forms in the new coordinate system of variables. After that the temperature profile of the surface is computed, the infrared radiation distribution of the surface is evaluated based on the equations given in the manuscript. The temperature profile as well as the IR images are given in the results section. It is concluded that the maximum value of infrared radiation of the surface occurs at the center. Moreover, it is concluded that among surfaces with equal areas, the one having the largest perimeter has the least value of IR at its center.

Keywords

  • numerical simulation
  • infrared radiation
  • plain surfaces
Open Access

Non-Newtonian Momentum Transfer past an Isothermal Stretching Sheet with Applied Suction

Published Online: 09 Sep 2017
Page range: 665 - 674

Abstract

Abstract

The paper discusses the flow of an incompressible non-Newtonian fluid due to stretching of a plane elastic surface in a saturated porous medium in the approximation of boundary layer theory. An exact analytical solution of non-linear MHD momentum equation governing the self-similar flow is given. The skin friction co-efficient decreases with an increase in the visco-elastic parameter k1 and increase in the values of both the magnetic parameter and permeability parameter.

Keywords

  • non-Newtonian fluid
  • magnetic field
  • permeability
  • effect of viscoelasticity
Open Access

Reynolds Number Effects in the Flow of a Vočadlo Electrorheological Fluid in a Curved Gap

Published Online: 09 Sep 2017
Page range: 675 - 695

Abstract

Abstract

Many electrorheological fluids (ERFs) as fluids with micro-structure demonstrate a non-Newtonian behaviour. Rheometric measurements indicate that some flows of these fluids may by modelled as the flows of a Vočadlo ER fluid. In this paper, the flow of a Vočadlo fluid – with a fractional index of non-linearity – in a narrow gap between two fixed surfaces of revolution with a common axis of symmetry is considered. The flow is externally pressurized and it is considered with inertia effect. In order to solve this problem the boundary layer equations are used. The Reynolds number effects (the effects of inertia forces) on the pressure distribution are examined by using the method of averaged inertia terms of the momentum equation. Numerical examples of externally pressurized flows in the gap between parallel disks and concentric spherical surfaces are presented.

Keywords

  • inertia effects
  • fixed surfaces of revolution
  • Vočadlo ER fluid
  • pressurized flow
Open Access

Curvilinear Squeeze Film Bearing Lubricated with a Dehaven Fluid or with Similar Fluids

Published Online: 09 Sep 2017
Page range: 697 - 715

Abstract

Abstract

In the paper, the model of a DeHaven fluid and some other models of non-Newtonian fluids, in which the shear strain rates are known functions of the powers of shear stresses, are considered. It was demonstrated that these models for small values of material constants can be presented in a form similar to the form of a DeHaven fluid. This common form, called a unified model of the DeHaven fluid, was used to consider a curvilinear squeeze film bearing. The equations of motion of the unified model, given in a specific coordinate system are used to derive the Reynolds equation. The solution to the Reynolds equation is obtained by a method of successive approximations. As a result one obtains formulae expressing the pressure distribution and load-carrying capacity. The numerical examples of flows of the unified DeHaven fluid in gaps of two simple squeeze film bearings are presented.

Keywords

  • DeHaven fluid
  • modified Reynolds equation
  • squeeze film
  • mechanical parameters of the bearing
Open Access

Influence of Wall Porosity and Surfaces Roughness on the Steady Performance of an Externally Pressurized Hydrostatic Conical Bearing Lubricated by a Rabinowitsch Fluid

Published Online: 09 Sep 2017
Page range: 717 - 737

Abstract

Abstract

In the paper, the influence of both the bearing surfaces roughness as well as porosity of one bearing surface on the pressure distribution and load-carrying capacity of a curvilinear, externally pressurized, thrust bearing is discussed. The equations of motion of a pseudo-plastic 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 and Christensen theory of hydrodynamic lubrication with rough bearing surfaces the modified Reynolds equation is obtained. The analytical solution is presented; as a result one obtains the formulae expressing the pressure distribution and load-carrying capacity. Thrust radial and conical bearings, externally pressurized, are considered as numerical examples.

Keywords

  • pseudo-plastic fluid
  • Rabinowitsch model
  • curvilinear and conical thrust bearings
  • porous layer
  • Christensen roughness
Open Access

Modeling of Two-Wheeled Self-Balancing Robot Driven by DC Gearmotors

Published Online: 09 Sep 2017
Page range: 739 - 747

Abstract

Abstract

This paper is aimed at modelling a two-wheeled self-balancing robot driven by the geared DC motors. A mathematical model consists of two main parts, the model of robot’s mechanical structure and the model of the actuator. Linearized equations of motion are derived and the overall model of the two-wheeled self-balancing robot is represented in state-space realization for the purpose of state feedback controller design.

Keywords

  • self-balancing robot
  • inverted pendulum
  • DC gearmotor
  • state space model
Open Access

Study on the Size Effect of Auxetic Cellular Materials

Published Online: 09 Sep 2017
Page range: 749 - 757

Abstract

Abstract

The objective of this paper is to investigate the effects of scale of an auxetic cellular material sample on the evaluation of elastic properties. Size and boundary effects are studied in detail. This is achieved by conducting computer simulations of the auxetic structure under the typical loading exerted by the compression and simple shearing test performed by means of ABAQUS FEA. The material microstructure is discretized by the plane network of Timoshenko beam elements. The results of the studies give insight to the scale effects. Structures with designed properties can be potentially used for engineering applications.

Keywords

  • negative Poissons ratio
  • auxetic structures
  • size effect
Open Access

Inertia and Couple-Stress Effects in a Curvilinear Thrust Hydrostatic Bearing

Published Online: 09 Sep 2017
Page range: 759 - 767

Abstract

Abstract

The flow of a couple-stress lubricant in a clearance of a curvilinear thrust hydrostatic bearing with impermeable walls is considered. The flow in the bearing clearance is considered with inertia forces. The equations of motion are solved by an averaged inertia method. As a result, the formulae for pressure distributions without and with inertia effects were obtained. Radial thrust bearings and spherical bearings are discussed as numerical examples. It is shown that inertia effects influence the bearing performance considerably.

Keywords

  • couple-stress lubricant
  • inertia effects
  • hydrostatic thrust bearing
Open Access

Measurements of Temperature of CNC Machine Tool Ball Screw Utilising IR Method

Published Online: 09 Sep 2017
Page range: 769 - 777

Abstract

Abstract

In numerous papers it is proposed to use IR measurements of feed axis ball screw temperature distribution in order to compensate CNC machine tool thermal errors. The paper aims to validate reliability of the IR measurements in application to the feed axes ball screws. The identification of key factors influencing the accuracy of the IR measurements of ball screw temperature distribution has been conducted. A test-bench utilizing a ball screw assembly with built-in temperature sensors was introduced and the experimental data are presented along with conclusions.

Keywords

  • thermography
  • ball screws
  • CNC machine tools
  • thermal error
Open Access

Influence of Cooling Lubricants on the Surface Roughness and Energy Efficiency of the Cutting Machine Tools

Published Online: 09 Sep 2017
Page range: 779 - 787

Abstract

Abstract

The Technical University of Liberec and Brandenburg University of Technology Cottbus-Senftenberg investigated the influence of cooling lubricants on the surface roughness and energy efficiency of cutting machine tools. After summarizing the achieved experimental results, the authors conclude that cooling lubricants extensively influence the cutting temperature, cutting forces and energy consumption. Also, it is recognizable that cooling lubricants affect the cutting tools lifetime and the workpiece surface quality as well. Furthermore, costs of these cooling lubricants and the related environmental burden need to be considered. A current trend is to reduce the amount of lubricants that are used, e.g., when the Minimum Quantity Lubrication (MQL) technique is applied. The lubricant or process liquid is thereby transported by the compressed air in the form of an aerosol to the contact area between the tool and workpiece. The cutting process was monitored during testing by the three following techniques: lubricant-free cutting, cutting with the use of a lubricant with the MQL technique, and only utilizing finish-turning and finish-face milling. The research allowed the authors to monitor the cutting power and mark the achieved surface quality in relation to the electrical power consumption of the cutting machine. In conclusions, the coherence between energy efficiency of the cutting machine and the workpiece surface quality regarding the used cooling lubricant is described.

Keywords

  • machining
  • turning
  • milling
  • process fluids
  • minimum quantity lubrication
Open Access

Comparative Analysis of Buckling Load of Circular and Corrugated Tubes by Utilizing Key Performance Indicators

Published Online: 09 Sep 2017
Page range: 789 - 797

Abstract

Abstract

The performance of buckling load of tubular structures under quasi-static axial loading is quite appreciable, numerous tubes of various cross-section have been extensively investigated and corrugated sections have been designed to further improve the performance. In this paper, a carefully designed set of key performance indicators (KPIs) is utilized to assess and compare the buckling load of circular and corrugated tubes. A series of diagrams related to KPIs with various parameters of tubes are presented to demonstrate the influence of sectional configuration on the performance of tubes as well as the effect of the material on the potential of the same. The work is inestimable to engineering designs and applications, and further studies on the buckling load of other configurations.

Keywords

  • buckling load
  • tubular structures
  • quasi-static
  • key performance indicators (KPIs)
  • circular and corrugated sections
Open Access

Erratum to: R. Goraj

Published Online: 09 Sep 2017
Page range: 799 - 799

Abstract

20 Articles
Open Access

Evaluation of the Influence of Wind-Driven Rain on Moisture in Cellular Concrete Wall Boards

Published Online: 09 Sep 2017
Page range: 509 - 519

Abstract

Abstract

The non-stationary moisture level of a cellular concrete wall board in a heated utility building located in the northern part of the town of Brest (Belarus), depending on the climatic influence, was assessed in this work. The results were obtained both in a calculation experiment and a physical test. It was observed that the main reason for the high moisture levels in cellular concrete is wind-driven rain intensifying the process of free capillary moisture transfer. A comparative analysis of the results of the physical test and the calculation experiment showed that the THSS software elaborated by the authors was able to predict the actual moisture levels of the shielding structure under study accurately enough when precise data concerning the thermal and physical characteristics of the materials as well as the occurring climatic influences were submitted.

Keywords

  • cellular concrete
  • wind-driven rain
  • capillary transfer
  • water sorption coefficient
  • moisture content
Open Access

Effect of Initial Stress on the Dynamic Response of a Multi-Layered Plate-Strip Subjected to an Arbitrary Inclined Time-Harmonic Force

Published Online: 09 Sep 2017
Page range: 521 - 537

Abstract

Abstract

The forced vibration of a multi-layered plate-strip with initial stress under the action of an arbitrary inclined time-harmonic force resting on a rigid foundation is considered. Within the framework of the piecewise homogeneous body model with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies (TLTEWISB), a mathematical modelling is presented in plane strain state. It is assumed that there exists the complete contact interaction at the interface between the layers and the materials of the layer are linearly elastic, homogeneous and isotropic. The governing system of the partial differential equations of motion for the considered problem is solved approximately by employing the Finite Element Method (FEM). Further, the influence of the initial stress parameter on the dynamic response of the plate-strip is presented.

Keywords

  • multi-layered plate-strip
  • finite element method
  • initial stress
  • time-harmonic force

MSC 2010

  • 74H15
  • 74S05
Open Access

Conjugate Heat and Mass Transfer on Fluctuating Mixed Convection Flow along a Vertical Wedge with Thermal Radiation

Published Online: 09 Sep 2017
Page range: 539 - 565

Abstract

Abstract

We study the boundary layer characteristics of heat and mass transfer flow past a vertical wedge in the presence of thermal radiation. The surface temperature and the species concentration are assumed to be oscillating in the magnitude but not in the direction of oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the straightforward finite difference method for the entire frequency range, and the series solution for the low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions have been presented in terms of the amplitudes and phase angles of the skin friction, the rate of heat transfer and the mass transfer with the variations of Richardson’s number, the Prandtl number, the conduction–radiation parameter, the surface temperature parameter and the Schmidt number. Furthermore, the effects of these parameters are examined in terms of the transient skin friction, heat transfer and mass transfer.

Keywords

  • mixed convection
  • thermal radiation
  • vertical wedge
Open Access

Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel

Published Online: 09 Sep 2017
Page range: 567 - 582

Abstract

Abstract

The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.

Keywords

  • microchannel
  • transverse magnetic field
  • induced magnetic field
  • velocity slip
  • temperature jump
Open Access

Axisymmetric Vibration for Micropolar Porous Thermoelastic Circular Plate

Published Online: 09 Sep 2017
Page range: 583 - 600

Abstract

Abstract

The present investigation is concerned with a two dimensional axisymmetric problem in a homogeneous isotropic micropolar porous thermoelastic circular plate by using the eigen value approach. The Laplace and Hankel transform are used to solve the problem. The expression of displacements, microrotation, volume fraction field, temperature distribution and stresses are obtained in the transformed domain subjected to thermomechanical sources. A computer algorithm is developed for numerical computations. To obtain the resulting quantities in a physical domain, a numerical inversion technique is used. The resulting quantities are depicted graphically for a specific model. Some special cases are also deduced.

Keywords

  • micropolar porous thermoelasticity
  • eigen value
  • Laplace and Hankel transforms
  • thermomechanical sources
Open Access

Digital Materials – Evaluation of the Possibilities of using Selected Hyperelastic Models to Describe Constitutive Relations

Published Online: 09 Sep 2017
Page range: 601 - 612

Abstract

Abstract

The authors tried to identify the parameters of numerical models of digital materials, which are a kind of composite resulting from the manufacture of the product in 3D printers. With the arrangement of several heads of the printer, the new material can result from mixing of materials with radically different properties, during the process of producing single layer of the product. The new material has properties dependent on the base materials properties and their proportions. Digital materials tensile characteristics are often non-linear and qualify to be described by hyperelastic materials models. The identification was conducted based on the results of tensile tests models, its various degrees coefficients of the polynomials to various degrees coefficients of the polynomials. The Drucker’s stability criterion was also examined. Fourteen different materials were analyzed.

Keywords

  • digital materials
  • hyperelastic
  • identification of models
  • FEM
  • 3D printing
  • PolyJet Matrix technology
Open Access

Numerical Solutions by EFGM of MHD Convective Fluid Flow Past a Vertical Plate Immersed in a Porous Medium in the Presence of Cross Diffusion Effects via Biot Number and Convective Boundary Condition

Published Online: 09 Sep 2017
Page range: 613 - 636

Abstract

Abstract

In this investigation, the numerical results of a mixed convective MHD chemically reacting flow past a vertical plate embedded in a porous medium are presented in the presence of cross diffusion effects and convective boundary condition. Instead of the commonly used conditions of constant surface temperature or constant heat flux, a convective boundary condition is employed which makes this study unique and the results more realistic and practically useful. The momentum, energy, and concentration equations derived as coupled second-order, ordinary differential equations are solved numerically using a highly accurate and thoroughly tested element free Galerkin method (EFGM). The effects of the Soret number, Dufour number, Grashof number for heat and mass transfer, the viscous dissipation parameter, Schmidt number, chemical reaction parameter, permeability parameter and Biot number on the dimensionless velocity, temperature and concentration profiles are presented graphically. In addition, numerical results for the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are discussed through tabular forms. The discussion focuses on the physical interpretation of the results as well as their comparison with the results of previous studies.

Keywords

  • thermal diffusion
  • diffusion thermo
  • MHD
  • porous medium
  • EFGM
Open Access

Role of Slip Velocity in a Magneto-Micropolar Fluid Flow from a Radiative Surface with Variable Permeability: A Numerical Study

Published Online: 09 Sep 2017
Page range: 637 - 651

Abstract

Abstract

An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

Keywords

  • slip velocity
  • chemical reaction
  • micropolar fluid
  • MHD
  • heat and mass transfer
  • FDM
Open Access

A Numerical Simulation for Prediction of Infrared Radiation Emitted from Plain Surfaces with Different Geometries

Published Online: 09 Sep 2017
Page range: 653 - 664

Abstract

Abstract

In this paper, infrared radiation exiting plain surfaces with different geometries is numerically simulated. Surfaces under consideration are assumed to have steady uniform heat generation inside. Moreover, the boundaries of the surfaces are considered to be at the surroundings temperature. Infrared radiation is calculated based on the temperature profile determined for the surface. The temperature profile of the surface is determined assuming the two dimensional heat conduction equations to govern the problem. The physical domain is transformed into the appropriate computational domain and the governing equation is mapped into the suitable forms in the new coordinate system of variables. After that the temperature profile of the surface is computed, the infrared radiation distribution of the surface is evaluated based on the equations given in the manuscript. The temperature profile as well as the IR images are given in the results section. It is concluded that the maximum value of infrared radiation of the surface occurs at the center. Moreover, it is concluded that among surfaces with equal areas, the one having the largest perimeter has the least value of IR at its center.

Keywords

  • numerical simulation
  • infrared radiation
  • plain surfaces
Open Access

Non-Newtonian Momentum Transfer past an Isothermal Stretching Sheet with Applied Suction

Published Online: 09 Sep 2017
Page range: 665 - 674

Abstract

Abstract

The paper discusses the flow of an incompressible non-Newtonian fluid due to stretching of a plane elastic surface in a saturated porous medium in the approximation of boundary layer theory. An exact analytical solution of non-linear MHD momentum equation governing the self-similar flow is given. The skin friction co-efficient decreases with an increase in the visco-elastic parameter k1 and increase in the values of both the magnetic parameter and permeability parameter.

Keywords

  • non-Newtonian fluid
  • magnetic field
  • permeability
  • effect of viscoelasticity
Open Access

Reynolds Number Effects in the Flow of a Vočadlo Electrorheological Fluid in a Curved Gap

Published Online: 09 Sep 2017
Page range: 675 - 695

Abstract

Abstract

Many electrorheological fluids (ERFs) as fluids with micro-structure demonstrate a non-Newtonian behaviour. Rheometric measurements indicate that some flows of these fluids may by modelled as the flows of a Vočadlo ER fluid. In this paper, the flow of a Vočadlo fluid – with a fractional index of non-linearity – in a narrow gap between two fixed surfaces of revolution with a common axis of symmetry is considered. The flow is externally pressurized and it is considered with inertia effect. In order to solve this problem the boundary layer equations are used. The Reynolds number effects (the effects of inertia forces) on the pressure distribution are examined by using the method of averaged inertia terms of the momentum equation. Numerical examples of externally pressurized flows in the gap between parallel disks and concentric spherical surfaces are presented.

Keywords

  • inertia effects
  • fixed surfaces of revolution
  • Vočadlo ER fluid
  • pressurized flow
Open Access

Curvilinear Squeeze Film Bearing Lubricated with a Dehaven Fluid or with Similar Fluids

Published Online: 09 Sep 2017
Page range: 697 - 715

Abstract

Abstract

In the paper, the model of a DeHaven fluid and some other models of non-Newtonian fluids, in which the shear strain rates are known functions of the powers of shear stresses, are considered. It was demonstrated that these models for small values of material constants can be presented in a form similar to the form of a DeHaven fluid. This common form, called a unified model of the DeHaven fluid, was used to consider a curvilinear squeeze film bearing. The equations of motion of the unified model, given in a specific coordinate system are used to derive the Reynolds equation. The solution to the Reynolds equation is obtained by a method of successive approximations. As a result one obtains formulae expressing the pressure distribution and load-carrying capacity. The numerical examples of flows of the unified DeHaven fluid in gaps of two simple squeeze film bearings are presented.

Keywords

  • DeHaven fluid
  • modified Reynolds equation
  • squeeze film
  • mechanical parameters of the bearing
Open Access

Influence of Wall Porosity and Surfaces Roughness on the Steady Performance of an Externally Pressurized Hydrostatic Conical Bearing Lubricated by a Rabinowitsch Fluid

Published Online: 09 Sep 2017
Page range: 717 - 737

Abstract

Abstract

In the paper, the influence of both the bearing surfaces roughness as well as porosity of one bearing surface on the pressure distribution and load-carrying capacity of a curvilinear, externally pressurized, thrust bearing is discussed. The equations of motion of a pseudo-plastic 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 and Christensen theory of hydrodynamic lubrication with rough bearing surfaces the modified Reynolds equation is obtained. The analytical solution is presented; as a result one obtains the formulae expressing the pressure distribution and load-carrying capacity. Thrust radial and conical bearings, externally pressurized, are considered as numerical examples.

Keywords

  • pseudo-plastic fluid
  • Rabinowitsch model
  • curvilinear and conical thrust bearings
  • porous layer
  • Christensen roughness
Open Access

Modeling of Two-Wheeled Self-Balancing Robot Driven by DC Gearmotors

Published Online: 09 Sep 2017
Page range: 739 - 747

Abstract

Abstract

This paper is aimed at modelling a two-wheeled self-balancing robot driven by the geared DC motors. A mathematical model consists of two main parts, the model of robot’s mechanical structure and the model of the actuator. Linearized equations of motion are derived and the overall model of the two-wheeled self-balancing robot is represented in state-space realization for the purpose of state feedback controller design.

Keywords

  • self-balancing robot
  • inverted pendulum
  • DC gearmotor
  • state space model
Open Access

Study on the Size Effect of Auxetic Cellular Materials

Published Online: 09 Sep 2017
Page range: 749 - 757

Abstract

Abstract

The objective of this paper is to investigate the effects of scale of an auxetic cellular material sample on the evaluation of elastic properties. Size and boundary effects are studied in detail. This is achieved by conducting computer simulations of the auxetic structure under the typical loading exerted by the compression and simple shearing test performed by means of ABAQUS FEA. The material microstructure is discretized by the plane network of Timoshenko beam elements. The results of the studies give insight to the scale effects. Structures with designed properties can be potentially used for engineering applications.

Keywords

  • negative Poissons ratio
  • auxetic structures
  • size effect
Open Access

Inertia and Couple-Stress Effects in a Curvilinear Thrust Hydrostatic Bearing

Published Online: 09 Sep 2017
Page range: 759 - 767

Abstract

Abstract

The flow of a couple-stress lubricant in a clearance of a curvilinear thrust hydrostatic bearing with impermeable walls is considered. The flow in the bearing clearance is considered with inertia forces. The equations of motion are solved by an averaged inertia method. As a result, the formulae for pressure distributions without and with inertia effects were obtained. Radial thrust bearings and spherical bearings are discussed as numerical examples. It is shown that inertia effects influence the bearing performance considerably.

Keywords

  • couple-stress lubricant
  • inertia effects
  • hydrostatic thrust bearing
Open Access

Measurements of Temperature of CNC Machine Tool Ball Screw Utilising IR Method

Published Online: 09 Sep 2017
Page range: 769 - 777

Abstract

Abstract

In numerous papers it is proposed to use IR measurements of feed axis ball screw temperature distribution in order to compensate CNC machine tool thermal errors. The paper aims to validate reliability of the IR measurements in application to the feed axes ball screws. The identification of key factors influencing the accuracy of the IR measurements of ball screw temperature distribution has been conducted. A test-bench utilizing a ball screw assembly with built-in temperature sensors was introduced and the experimental data are presented along with conclusions.

Keywords

  • thermography
  • ball screws
  • CNC machine tools
  • thermal error
Open Access

Influence of Cooling Lubricants on the Surface Roughness and Energy Efficiency of the Cutting Machine Tools

Published Online: 09 Sep 2017
Page range: 779 - 787

Abstract

Abstract

The Technical University of Liberec and Brandenburg University of Technology Cottbus-Senftenberg investigated the influence of cooling lubricants on the surface roughness and energy efficiency of cutting machine tools. After summarizing the achieved experimental results, the authors conclude that cooling lubricants extensively influence the cutting temperature, cutting forces and energy consumption. Also, it is recognizable that cooling lubricants affect the cutting tools lifetime and the workpiece surface quality as well. Furthermore, costs of these cooling lubricants and the related environmental burden need to be considered. A current trend is to reduce the amount of lubricants that are used, e.g., when the Minimum Quantity Lubrication (MQL) technique is applied. The lubricant or process liquid is thereby transported by the compressed air in the form of an aerosol to the contact area between the tool and workpiece. The cutting process was monitored during testing by the three following techniques: lubricant-free cutting, cutting with the use of a lubricant with the MQL technique, and only utilizing finish-turning and finish-face milling. The research allowed the authors to monitor the cutting power and mark the achieved surface quality in relation to the electrical power consumption of the cutting machine. In conclusions, the coherence between energy efficiency of the cutting machine and the workpiece surface quality regarding the used cooling lubricant is described.

Keywords

  • machining
  • turning
  • milling
  • process fluids
  • minimum quantity lubrication
Open Access

Comparative Analysis of Buckling Load of Circular and Corrugated Tubes by Utilizing Key Performance Indicators

Published Online: 09 Sep 2017
Page range: 789 - 797

Abstract

Abstract

The performance of buckling load of tubular structures under quasi-static axial loading is quite appreciable, numerous tubes of various cross-section have been extensively investigated and corrugated sections have been designed to further improve the performance. In this paper, a carefully designed set of key performance indicators (KPIs) is utilized to assess and compare the buckling load of circular and corrugated tubes. A series of diagrams related to KPIs with various parameters of tubes are presented to demonstrate the influence of sectional configuration on the performance of tubes as well as the effect of the material on the potential of the same. The work is inestimable to engineering designs and applications, and further studies on the buckling load of other configurations.

Keywords

  • buckling load
  • tubular structures
  • quasi-static
  • key performance indicators (KPIs)
  • circular and corrugated sections
Open Access

Erratum to: R. Goraj

Published Online: 09 Sep 2017
Page range: 799 - 799

Abstract

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