AUT Journal of Mechanical Engineering | AmirKabir University Of Technology (original) (raw)

Papers by AUT Journal of Mechanical Engineering

In this paper, the behavior of one chain of small heat shock protein based on molecular dynamic s... more In this paper, the behavior of one chain of small heat shock protein based on molecular dynamic simulation is modeled by the nonlinear identifier. Molecular dynamic simulation is timeconsuming due to the high load of calculations, and providing a model of system behavior facilitates utilizing protein as a bio nano robot in a shorter time. The ARC1 is a molecular Chaperone with swarm structure containing 12 chains. Each chain of small heat shock protein contains two sections; arm and the central cavity which is introduced as a bionanorobot for their special biological structure and their reaction to external forces. The conformational changes of protein with one chain due to external excitation have been analyzed. In addition to system identification of one chain of small heat shock protein, the eﬀect of temperature, pH, and content of solvent are examined on the behavior of bionanorobot arm and a central cavity in a wide range of variation. The results show that minimum number of error is relevant to the adaptive neuro fuzzy system identifier. Modeling the behavior of one chain provides a suitable condition to control the central cavity and bionanorobot arm in a shorter period of time compared to the molecular dynamic simulation.

In this paper, the pull-in phenomenon is suppressed using a range of values of amplitude and freq... more In this paper, the pull-in phenomenon is suppressed using a range of values of amplitude
and frequency of high-frequency voltage excitations in the post pull-in condition of the cracked microelectromechanical systems. These specified ranges are named as stable zones. It is investigated the effects of the crack parameters (depth and location) on changes of these zones, in the post pull-in condition. It is shown that these zones have different areas for different crack parameters. The cracked micro-beam is
modeled as a single-degree-of-freedom systems consist of mass-spring-damper and the motion equation
of the cracked micro-beam is extracted. The method of direct partition of motion is used to split the fast
and slow dynamics. By means of slow dynamic part, the effects of the crack on the averaged position of
vibration of cracked micro-beam are investigated versus voltage amplitude and frequency of the highfrequency AC. By approaching the crack to the fixed end or increasing the depth of crack, the stability
zone reduced. Therefore, the pull-in instability can be suppressed in the lower range of amplitude and
frequency. This method can be used in sensors’ health-monitoring and one can predict the parameters of
the crack using this method.

In this research, rubber pad forming process of metallic bipolar plates made of stainless steel 3... more In this research, rubber pad forming process of metallic bipolar plates made of stainless
steel 316L with a thickness of 0.1 mm has been studied. In addition, a rubber pad made of polyurethane
with the hardness number of shore A 85 and a thickness of 25mm is used in order to apply pressure to
the plate to form the sheets. In order to study the effect of die clearance on depth filling, two die sets with
different clearances were made. The results showed that when clearance is applied between punch die
and matrix, the amount of uniformity becomes more in the depth of stuffed channel. But, the rubber pad
is destroyed after some forming operation and plastic deformation occurs in it. Also, in the die set with
the lower clearance, the amount of rubber pad life has been increased and the amount of flow channel
depth gets greater. In the research results, it was determined that when the channel depth is small and a
rubber pad is used with a higher hardness, the die set with a clearance has more favorable results due to
uniformity in the flow channels’ depth. However, by increasing the depth of bipolar plate channels, using
die sets with lower clearance are better due to the increasing the rubber pad life

In layered structures, the interface of layers is not always perfect and the analysis of problems... more In layered structures, the interface of layers is not always perfect and the analysis of
problems which have imperfect interfaces is of the high level of importance. In this paper, an analytical
approach is used to study the behavior of a layered functionally graded spherical vessel under thermal
and mechanical loadings at the inner and outer surfaces. The interfaces of the layers in the vessel are
considered to be imperfect and a viscoelastic layer of negligible thickness is assumed between any
two layers. The behavior of these viscoelastic layers is modeled by means of Kelvin-Voigt model. In
order to solve the problem, the governing equations of each layer are extracted via the thermoelasticity
theory and by applying the appropriate boundary conditions at the interface of the layers, the overall
displacement and stress fields are found in the vessel and numerical results are presented for different
parameters. The obtained results show that the stiffness of the viscoelastic layer affects the value of the
displacements and the stresses as well as the stabilization time of the system. However, changing the
damping parameter of the Kelvin-Voigt model only changes the stabilization time and not the values of
the displacements and stresses.

Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. This pape... more Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. This
paper describes the improvement of the transient thermal fatigue life of gas turbines casings through the
application of pins. The repair technology under consideration involved drilling a number of holes in
the gas turbines casing along the crack and inserting pins into them. The crack position and direction
were determined using non-destructive tests. A series of finite element models were developed and
tested in AStM-A395 elastic-perfectly plastic ductile cast iron. In some specimens, holes were drilled
near the crack tips. Pins were inserted into the holes in some cases. Abaqus software finite element
package and Zencrack fracture mechanics code were used for modeling. The efficiency of crack repair
by the installation of pins was investigated along with the effect of the number of pins on crack repair
efficiency. The result shows that the insertion of pins into holes drilled in the vicinity of the crack tips is
an effective method of retarding crack growth in a gas turbine casing.

In this study, a novel design paradigm is presented to obtain some geometry-related electrochemic... more In this study, a novel design paradigm is presented to obtain some geometry-related electrochemical and physical properties of an infiltrated SOFC electrode. A range of digitally realized microstructures with different backbone geometric properties and virtual electro-catalyst particle loadings under various deposition conditions are generated. Triple Phase Boundary (TPB), the active surface density of particles and gas transport factor are evaluated in those realized models based on selected infiltration strategy. Based on this database, a neural network is trained to relate the desired range of input geometric parameters to a property hull. The effect of porosity and geometric anisotropy in backbones in addition to the loading, distribution and aggregation behavior of particles is systematically investigated on those performance indicators. The results indicated that microstructures with very high amount of TPB and contact surface density of particle have a relatively low gas diffusion factor, meanwhile increasing these parameters does not involve a sensible contradiction. Also, by adding particles, the TPB density variation is changed as a function of backbone porosity and the average shape of aggregated particles. A direct search into the microstructure and property hull is applied to find the best parameters in modeling approach aiming the maximum effective geometric properties. Finally, a genetic algorithm is employed to detect appropriate geometric factors getting the maximum acquirable performance in infiltrated SOFC electrodes.

This article aims to investigate the effects of various parameters on the thermal load. The gover... more This article aims to investigate the effects of various parameters on the thermal load. The governing equations include continuity and Navier-Stokes equations for the flow field and the energy equation for the temperature distribution in transient mode. Numerical simulation of the thermoacoustic refrigerator by taking the non-zero thickness of the plate stack into account, that is a conjugate heat transfer problem, in a form of 2D has been performed in FLUENT software. Real simulation of thermoacoustic refrigerators needs a consideration of both heat exchangers, whereas in most simulations one or both heat exchangers have been neglected. Results are influenced by the steady state. Input dynamic pressure should be adjusted according to the temperature of the heat exchanger. The results demonstrate the effect of the distance of the plates on the average thermal load suggesting that the distance between the plates should be four times of the thickness of the plates so that the device works properly. By increasing the distance of the plates thermal load decreases. This is mainly because of pressure amplitude reduction induced by an increase in the distance between the plates.

This article aims to study the thermal performances of four different natural draft cooling tower... more This article aims to study the thermal performances of four different natural draft cooling
towers under crosswind condition. The windbreakers and the oblique exit plane have been simultaneously
included in the structure of the new cooling tower. A finite volume method using SIMPLE algorithm was
used to simulate the flow field around each cooling tower. The thermal performance of the new geometry
has been compared with those of others for the generally investigated wind velocity profile for 10 m/s,
and also two uniform wind velocities for 3 and 7 m/s. The cooling capacity of the cooling tower utilizing
windbreakers and the oblique exit plane was predicted as 98.3% of the design value in the presence of
generally studied wind velocity profile of 10 m/s, while that of the cooling tower utilizing windbreakers
was predicted as 93.5%. Of course, the percentage of the thermal improvements of the different restoring
strategies are sensitive to the profile of an approaching wind. The uniform wind velocity decreases the
thermal efficiency of the cooling tower more than the distributed one, while the restoring strategies using
windbreakers provide a higher percentage of thermal improvements in the presence of uniform wind
velocity.

In this research, Large Eddy Simulation of in-cylinder flow during suction and compression stroke... more In this research, Large Eddy Simulation of in-cylinder flow during suction and compression stroke in an axisymmetric engine is performed. A computer code using Smogorinsky subgrid model is developed to solve the governing equations of the flow. A proper understanding of flow during suction and compression strokes, gives better information for fuel/air mixture and combustion. The results show that the advantage of LES model is the ability of computing turbulence characteristics in various crank angles of engine cycle. This advantage of model is highlighted by calculating RMS values of axial velocity in comparison with experimental ones. The results show that axial velocity fluctuations during intake reaches to a higher level than in compression stroke because of the inlet jet to the cylinder and intensive gradient of variables. In this regard, the flow in 100 degree ATDC during intake stroke reaches the maximum level of turbulence intensity and then turbulence generated during intake stroke decays rapidly. During intake stroke, three main vorticities are generated inside the cylinder. In the compression stroke these three vorticities are merged together to establish a new vorticity with direction of rotation opposite to the intake flow. Some smaller recirculating regions are also generated at 90 degree BTDC.

Subcooling degree and surface roughness are two major parameters that have a considerable effect ... more Subcooling degree and surface roughness are two major parameters that have a considerable effect on boiling heat transfer. In the present study, the effects of subcooling degree on pool boiling heat transfer coefficient and surface temperature distribution are investigated experimentally. Tests are conducted for saturated and subcooled water with different subcooling degrees in the local atmospheric pressure (863 mbar) around a horizontal stainless steel cylinder with specific surface roughness. The test section is a pool with dimensions of 120×400×550 mm and test case is a circular cylinder with 80 mm length, 9 mm diameter and 0.794 μm average surface roughness. In this research, experiments are performed for the degrees of subcooling between 5.5°C to 45.5°C and for the heat fluxes between 0.31 kW/m32 to 125.62 kW/m. Results show that by increasing the degree of subcooling for a specific average surface roughness, average surface temperature is decreased and due to changes in the mechanism of heat transfer from nucleate boiling to natural convection, heat transfer coefficient is also decreased. In the region of natural convection, the variation of heat transfer coefficient with heat flux is low and when boiling process begins, this variation is more considerable. Furthermore, for lower heat fluxes (less than 5 kW/m), the temperature difference between upper and lower sides of the test case is less than 1°C which increases for higher heat fluxes so that for more than 100 kW/m2,it reaches to 6°C.

The aim of this paper is to study the deposition and dispersion of nano particles in fully develo... more The aim of this paper is to study the deposition and dispersion of nano particles in fully developed laminar pipe flows numerically. To simulate particle transport and to locate the position of particles, the Eulerian - Lagrangian method is used under the conditions of one-way coupling. Due to studied range of particle diameters from 5 nm to 100 nm, the main effective force for particle deposition is the Brownian diffusion force. After studying the mesh independency and validating results, time history analysis of particle transport is also performed by injecting the particles from the inlet surface and tracking them at each moment. Furthermore, the effective parameters, i.e. particle diameter, pipe length and diameter, temperature and particle density are studied comprehensively. The results of time history analysis of particle transport show that nano particles with less diameters are more deposited in less time. Furthermore, maximum number of escaped particles from the pipe occurred at 0.035 s after injecting the particles for all studied particle diameters due to the studied flow rate and length of the pipe. The output of this study can provide a guideline for evaluating nano particle transport and deposition in fully developed laminar pipe flows.

In this paper, we conduct a numerical study of mixed electro-osmotic/Poiseuille slip flows of vis... more In this paper, we conduct a numerical study of mixed electro-osmotic/Poiseuille slip flows of
viscoelastic fluids in microchannels with rectangular cross sections by means of second order finite difference
method. In this regard, the complete form of the PTT-constitutive equation is used to describe the rheological
behavior of the fluid. The numerical results being validated by the same simplified theoretical study reveal an
excellent accuracy with relative error less than 0.3%. Afterward, the extended numerical study is used to investigate the 2D velocity distribution and volumetric flow rate in the presence of wall surface hydrophobicity through rectangular microchannels. In addition, in this investigation, the exact solution of unidirectional electroosmotic flow of PTT-viscoelastic fluids is derived for slit hydrophobic microchannels, and after validating, the solution is used to investigate the rheological behavior of viscoelastic fluids in the range of operating parameters. The results exhibit a uniform effect of hydrophobicity in increasing the profile of 1D velocity distribution in slit microchannels. Finally, in order to determine the stability of the grid network, various under relaxation factors are applied to determine the speed of convergence of finite difference method, and then, by using the analytical procedure, the critical Weissenberg number is introduced as a function of velocity scale ratio and Debye–Hückel parameter. The evaluation of the numerical method in the critical area indicates the stability of viscoelastic fluid flow for the values of the Weissenberg number less than the corresponding critical value in the theoretical analysis.

In this paper, a new phase field method for the interaction between martensitic phase transformat... more In this paper, a new phase field method for the interaction between martensitic phase
transformations and dislocations is presented which is a nontrivial combination of the most advanced
phase field methods to phase transformations and dislocation evolution. Some of the important points in
the model are the multiplicative decomposition of deformation gradient into elastic, transformational and
plastic parts, defining a proper energy to satisfy thermodynamic equilibrium and instability conditions,
including phase-dependent properties of dislocations. The system of equations consists of coupled
elasticity and phase field equations of phase transformations and dislocations. Finite element method
is used to solve the system of equations and applied to study the growth and arrest of martensitic plate
and the evolution of dislocations and phase in a nanograined material. It is found that dislocations play
a key role in eliminating the driving force of the plate growth and their arrest which creates athermal
friction. Also, the dual effect of plasticity on phase transformations is revealed; due to dislocations
pile-up and its stress concentration, the phase transformation driving force increases and consequently,
martensitic nucleation occurs. On the other hand, the dislocation nucleation results in decreasing the
phase transformation driving force and consequently, the phase transformation is suppressed.

Three-dimensional simulation of a red blood cell deformation in a shear flow is performed using i... more Three-dimensional simulation of a red blood cell deformation in a shear flow is
performed using immersed boundary lattice Boltzmann method for the fluid flow simulation, as well as
finite element method for membrane deformation. Immersed boundary method has been used to model
interaction between fluid and membrane of the red blood cell. Red blood cell is modeled as a biconcave
discoid capsule containing fluid with an elastic membrane. Computations are performed at relatively
small and large shear rates in order to study the dynamic behavior of red blood cell, especially tumbling
and swinging modes of its motion. A rigid-body-like motion with the constant-amplitude oscillation
of deformation parameter and continuous rotation is observed for red blood cell at its tumbling mode.
However, at a relatively large shear rate, red blood cell follows a periodic gradual deformation and
elongation with a final ellipsoidal shape. The effect of different initial orientations of red blood cell is
also investigated in the present paper. Results show that the dynamic response of red blood cell is not
sensitive to this parameter.

Unsteady compressible flows over a stationary 60-degree swept delta wing with a sharp leading edg... more Unsteady compressible flows over a stationary 60-degree swept delta wing with a sharp
leading edge were computationally simulated at different Mach numbers and moderate angles of the
attack. An unstructured grid, Spalart-Allmaras Detached Eddy Simulation turbulence model, and a
dual-time implicit time integration were used. Vortical flow structures associated with various freestream
conditions are displayed and their variations versus time are studied. Variations of flow field
parameters, such as u velocity component and pressure coefficient with the flow time are demonstrated
at several point probes in the flow field. A Power Spectral Density frequency analysis is performed for
such unsteady behaviours to identify the dominant frequencies which exist in each flow condition. The
frequency analyses show that low frequencies associated with vortex breakdown oscillation are the most
dominant frequencies in all cases where vortex breakdown occurs. Dominant frequencies associated with
helical mode instability are also present at the probes downstream of breakdown. Dominant frequencies
related to the shear layer instabilities were observed for the low subsonic regime.

In this article, the buckling load of an axisymmetric cylindrical shell with a variable thickness... more In this article, the buckling load of an axisymmetric cylindrical shell with a variable
thickness is determined analytically by using the perturbation method. The loading is axial and the
material properties are defined by the Hooke’s law. The displacement field is predicted by using the
first order shear deformation theory and the nonlinear von-Karman relations are used for the kinematic
description of the shell. The stability equations, which are the system of nonlinear differential equations
with variable coefficients, are derived by the virtual work principle and are solved using the perturbation
technique. Also, the buckling load is determined by using the finite element method and it is compared
with the analytical solution results, the classical shell theory, and other references. The effects of linear
and nonlinear shell profiles variation on the axial buckling load are investigated. Also, we studied the
effects of geometric parameters on the buckling load results. The results show that the first order shear
deformation theory is more useful for buckling load determination of thicker shells.

In this paper, supersonic flutter analysis of cantilevered trapezoidal plates composed of two fun... more In this paper, supersonic flutter analysis of cantilevered trapezoidal plates composed of
two functionally graded face sheets and an isotropic homogeneous core is presented. Using Hamilton’s
principle, the set of governing equations and external boundary conditions are derived. A transformation
of coordinates is used to convert the governing equations and boundary conditions from the original
coordinates into the new dimensionless computational ones. Generalized differential quadrature method
(GDQM) is employed as a numerical method and critical aerodynamic pressure and flutter frequencies
are derived. Convergence, versatility, and accuracy of the presented solution are confirmed using
numerical and experimental results presented by other authors. The effect of power-law index, thickness
of the core, total thickness of the plate, aspect ratio and angles of the plate on the flutter boundaries are
investigated. It is concluded that any attempt to increase the critical aerodynamic pressure leads to a
decrease in lift force or rise in total weight of the plate.

In this study, free vibration analysis of laminated composite skew plates with embedded shape mem... more In this study, free vibration analysis of laminated composite skew plates with embedded
shape memory alloys under thermal loads is presented. The plates are assumed to be made of NiTi/Graphite/
Epoxy with temperature-dependent properties. The thermo-mechanical behavior of shape memory alloy
wires is predicted by employing one-dimensional Brinson’s model. The governing equations are derived
based on first-order shear deformation theory and solved using generalized differential quadrature
technique as an efficient and accurate numerical tool. Some examples are provided to show the accuracy
and efficiency of the applied numerical method by comparing the present results with those available
in the literature. A parametric study is carried out to demonstrate the influence of skew angle, pre-strain
and volume fraction of shape memory alloys, temperature, and stacking sequence of layers on the natural
frequencies of the structure. Results represent that shape memory alloys can change the vibrational
characteristics of shape memory alloy hybrid composite skew plates by a considerable amount. The
numerical results also reveal that the effect of shape memory alloy wires on natural frequencies of
composite plates with simply supported boundaries is higher than those with clamped boundaries.

The present paper studies the whole body vibration of a three-axle dump truck during various oper... more The present paper studies the whole body vibration of a three-axle dump truck during
various operational conditions in Zonuz Kaolin Mine of Iran. At first, the root mean square of vibrations
at different speeds, as well as in payloads and distribution qualities of materials in the truck dump body
and also on different haul road qualities are experimentally obtained. Then, the vibrational health risk
in all operational conditions is statistically analyzed based on ISO 2631-1 standard. As a result of this
analysis, an optimization problem is constructed and solved to obtain the optimum operating conditions
of the truck. In the proposed problem, at first, regression analysis in terms of RMS of vibrations
and truck speed is applied. Then, the total RMS at the consequential working phases of the truck is
minimized in the presence of some constraints related to the health risk and productivity levels. Solving
the proposed constrained optimization problem determines the optimum payload and truck speed in
various conditions to keep materials hauling at the lowest possible vibrational health risk level while the
mine productivity at the planned level remains.

Numerous studies have been conducted for failure criteria of fiber reinforced composites. The aim... more Numerous studies have been conducted for failure criteria of fiber reinforced composites.
The aim of this study is to present a new computational and mathematical method to analyze the
progressive damage and failure behavior of composite plates containing initial geometric imperfections
under uniaxial in-plane compression load. A new methodology is presented based on collocation method
in which the interested domain is discretized with Legendre-Gauss-Lobatto nodes. In order to avoid an
excessive number of nodes, an appropriate weight coefficient is considered for each node. The method is
based on the first order shear deformation theory and small displacement theory. Several failure criteria,
including Maximum stress, Hashin and Tsai-Hill, are used to predict the failure mechanisms. The stiffness
degradation is carried out by instantaneous and complete ply degradation model. Two different types of
boundary conditions are considered in this study. The effects of thickness, initial imperfections, and
boundary conditions are studied, as well. The results are compared with the previously published data.
It is found that the boundary conditions have significant effects on the ultimate strength of imperfect
composite plates.