Abstract: In this paper, modeling of an acoustic enclosed
vehicle cabin has been carried out by using boundary element
method. Also, the second purpose of this study is analyzing of linear
wave equation in an acoustic field. The resultants of this modeling
consist of natural frequencies that have been compared with
resultants derived from finite element method. By using numerical
method (boundary element method) and after solution of wave
equation inside an acoustic enclosed cabin, this method has been
progressed to simulate noise inside a simple vehicle cabin.
Abstract: The management of the health-care wastes is one of
the most important problems in Istanbul, a city with more than 12
million inhabitants, as it is in most of the developing countries.
Negligence in appropriate treatment and final disposal of the healthcare
wastes can lead to adverse impacts to public health and to the
environment. This paper employs a fuzzy multi-criteria group
decision making approach, which is based on the principles of fusion
of fuzzy information, 2-tuple linguistic representation model, and
technique for order preference by similarity to ideal solution
(TOPSIS), to evaluate health-care waste (HCW) treatment
alternatives for Istanbul. The evaluation criteria are determined
employing nominal group technique (NGT), which is a method of
systematically developing a consensus of group opinion. The
employed method is apt to manage information assessed using multigranularity
linguistic information in a decision making problem with
multiple information sources. The decision making framework
employs ordered weighted averaging (OWA) operator that
encompasses several operators as the aggregation operator since it
can implement different aggregation rules by changing the order
weights. The aggregation process is based on the unification of
information by means of fuzzy sets on a basic linguistic term set
(BLTS). Then, the unified information is transformed into linguistic
2-tuples in a way to rectify the problem of loss information of other
fuzzy linguistic approaches.
Abstract: In the paper we discuss the influence of the route
flexibility degree, the open rate of operations and the production type
coefficient on makespan. The flexible job-open shop scheduling
problem FJOSP (an extension of the classical job shop scheduling) is
analyzed. For the analysis of the production process we used a
hybrid heuristic of the GRASP (greedy randomized adaptive search
procedure) with simulated annealing algorithm. Experiments with
different levels of factors have been considered and compared. The
GRASP+SA algorithm has been tested and illustrated with results for
the serial route and the parallel one.
Abstract: This paper describes Nano-particle based Planar Laser
Scattering (NPLS) flow visualization of angled supersonic jets into a
supersonic cross flow based on the HYpersonic Low TEmperature
(HYLTE) nozzle which was widely used in DF chemical laser. In
order to investigate the non-reacting flowfield in the HYLTE nozzle, a
testing section with windows was designed and manufactured. The
impact of secondary fluids orifice separation on mixing was examined.
For narrow separation of orifices, the secondary fuel penetration
increased obviously compared to diluent injection, which means
smaller separation of diluent and fuel orifices would enhance the
mixing of fuel and oxidant. Secondary injections with angles of 30, 40
and 50 degrees were studied. It was found that the injectant
penetration increased as the injection angle increased, while the
interfacial surface area to entrain the freestream fluid is largest when
the injection angle is 40 degree.
Abstract: A numerical study of flow in a horizontally channel
partially filled with a porous screen with non-uniform inlet has been
performed by lattice Boltzmann method (LBM). The flow in porous
layer has been simulated by the Brinkman-Forchheimer model.
Numerical solutions have been obtained for variable porosity models
and the effects of Darcy number and porosity have been studied in
detail. It is found that the flow stabilization is reliant on the Darcy
number. Also the results show that the stabilization of flow field and
heat transfer is depended to Darcy number. Distribution of stream
field becomes more stable by decreasing Darcy number. Results
illustrate that the effect of variable porosity is significant just in the
region of the solid boundary. In addition, difference between constant
and variable porosity models is decreased by decreasing the Darcy
number.
Abstract: In this paper, a new approach is introduced to solve
Blasius equation using parameter identification of a nonlinear
function which is used as approximation function. Bees Algorithm
(BA) is applied in order to find the adjustable parameters of
approximation function regarding minimizing a fitness function
including these parameters (i.e. adjustable parameters). These
parameters are determined how the approximation function has to
satisfy the boundary conditions. In order to demonstrate the
presented method, the obtained results are compared with another
numerical method. Present method can be easily extended to solve a
wide range of problems.
Abstract: The significant effects of the interactions between the
system boundaries and the near wall molecules in miniaturized
gaseous devices lead to the formation of the Knudsen layer in which
the Navier-Stokes-Fourier (NSF) equations fail to predict the correct
associated phenomena. In this paper, the well-known lattice
Boltzmann method (LBM) is employed to simulate the fluid flow and
heat transfer processes in rarefied gaseous micro media. Persuaded
by the problematic deficiency of the LBM in capturing the Knudsen
layer phenomena, present study tends to concentrate on the effective
molecular mean free path concept the main essence of which is to
compensate the incapability of this mesoscopic method in dealing
with the momentum and energy transport within the above mentioned
kinetic boundary layer. The results show qualitative and quantitative
accuracy comparable to the solutions of the linearized Boltzmann
equation or the DSMC data for the Knudsen numbers of O (1) .
Abstract: A numerical investigation of surface heat transfer
characteristics of turbulent air flows in different parallel plate
grooved channels is performed using CFD code. The results are
obtained for Reynolds number ranging from 10,000 to 30,000 and for
arc-shaped and rectangular grooved channels. The influence of
different geometric parameters of dimples as well as the number of
them and the geometric and thermophysical properties of channel
walls are studied. It is found that there exists an optimum value for
depth of dimples in which the largest wall heat flux can be achieved.
Also, the results show a critical value for the ratio of wall thermal
conductivity to the one of fluid in which the dependence of wall heat
flux to this ratio almost vanishes. In most cases examined, heat
transfer enhancement is larger for arc-shaped grooved channels than
rectangular ones.
Abstract: The performance of Advection Upstream Splitting
Method AUSM schemes are evaluated against experimental flow
fields at different Mach numbers and results are compared with
experimental data of subsonic, supersonic and hypersonic flow fields.
The turbulent model used here is SST model by Menter. The
numerical predictions include lift coefficient, drag coefficient and
pitching moment coefficient at different mach numbers and angle of
attacks. This work describes a computational study undertaken to
compute the Aerodynamic characteristics of different air vehicles
configurations using a structured Navier-Stokes computational
technique. The CFD code bases on the idea of upwind scheme for the
convective (convective-moving) fluxes. CFD results for GLC305
airfoil and cone cylinder tail fined missile calculated on above
mentioned turbulence model are compared with the available data.
Wide ranges of Mach number from subsonic to hypersonic speeds are
simulated and results are compared. When the computation is done
by using viscous turbulence model the above mentioned coefficients
have a very good agreement with the experimental values. AUSM
scheme is very efficient in the regions of very high pressure gradients
like shock waves and discontinuities. The AUSM versions simulate
the all types of flows from lower subsonic to hypersonic flow without
oscillations.
Abstract: The Spalart and Allmaras turbulence model has been
implemented in a numerical code to study the compressible turbulent
flows, which the system of governing equations is solved with a
finite volume approach using a structured grid. The AUSM+ scheme
is used to calculate the inviscid fluxes. Different benchmark
problems have been computed to validate the implementation and
numerical results are shown. A special Attention is paid to wall jet
applications. In this study, the jet is submitted to various wall
boundary conditions (adiabatic or uniform heat flux) in forced
convection regime and both two-dimensional and axisymmetric wall
jets are considered. The comparison between the numerical results
and experimental data has given the validity of this turbulence model
to study the turbulent wall jets especially in engineering applications.
Abstract: In this study, we used shape memory alloys as
actuators to build a biomorphic robot which can imitate the motion of
an earthworm. The robot can be used to explore in a narrow space.
Therefore we chose shape memory alloys as actuators. Because of the
small deformation of a wire shape memory alloy, spiral shape memory
alloys are selected and installed both on the X axis and Y axis (each
axis having two shape memory alloys) to enable the biomorphic robot
to do reciprocating motion. By the mechanism we designed, the robot
can increase the distance as it moves in a duty cycle. In addition, two
shape memory alloys are added to the robot head for controlling right
and left turns. By sending pulses through the I/O card from the
controller, the signals are then amplified by a driver to heat the shape
memory alloys in order to make the SMA shrink to pull the mechanism
to move.
Abstract: A measurement apparatus is designed and fabricated to
measure the effective thermal conductivity (keff) of a VIP (vacuum
insulation panel) core specimen under various vacuum states and
external loads. The apparatus consists of part for measuring keff, and
parts for controlling external load and vacuum condition. Uncertainty
of the apparatus is validated by measuring the standard reference
material and comparing with commercial devices with VIP samples.
Assessed uncertainty is maximum 2.5 % in case of the standard
reference material, 10 % in case of VIP samples. Using the apparatus,
keff of glass paper under various vacuum levels is examined.
Abstract: Thermoacoustic instabilities in combustors have
remained a topic of investigation for over a few decades due to the
challenges it posses to the operation of low emission gas turbines.
For combustors burning liquid fuel, understanding the cause-andeffect
relationship between spray combustion dynamics and
thermoacoustic oscillations is imperative for the successful
development of any control methodology for its mitigation. The
paper presents some very unique operating characteristics of a
kerosene-fueled diffusion type combustor undergoing limit-cycle
oscillations. Combustor stability limits were mapped using three
different-sized injectors. The results show that combustor instability
depends on the characteristics of the fuel spray. A simple analytic
analysis is also reported in support of a plausible explanation for the
unique combustor behavior. The study indicates that high amplitude
acoustic pressure in the combustor may cause secondary breakdown
of fuel droplets resulting in premixed pre-vaporized type burning of
the diffusion type combustor.
Abstract: The results of an experimental study of the process of
convective and boiling heat transfer in the vessel with stirrer for
smooth and rough ring-shaped pipes are presented. It is established
that creation of two-dimensional artificial roughness on the heated
surface causes the essential (~100%) intensification of convective
heat transfer. In case of boiling the influence of roughness appears on
the initial stage of boiling and in case of fully developed nucleate
boiling there was no intensification of heat transfer. The similitude
equation for calculating convective heat transfer coefficient, which
generalizes well experimental data both for the smooth and the rough
surfaces is proposed.
Abstract: Among all mechanical joining processes, welding has
been employed for its advantage in design flexibility, cost saving,
reduced overall weight and enhanced structural performance.
However, for structures made of relatively thin components, welding
can introduce significant buckling distortion which causes loss of
dimensional control, structural integrity and increased fabrication
costs. Different parameters can affect buckling behavior of welded
thin structures such as, heat input, welding sequence, dimension of
structure. In this work, a 3-D thermo elastic-viscoplastic finite
element analysis technique is applied to evaluate the effect of shell
dimensions on buckling behavior and entropy generation of welded
thin shells. Also, in the present work, the approximated longitudinal
transient stresses which produced in each time step, is applied to the
3D-eigenvalue analysis to ratify predicted buckling time and
corresponding eigenmode. Besides, the possibility of buckling
prediction by entropy generation at each time is investigated and it is
found that one can predict time of buckling with drawing entropy
generation versus out of plane deformation. The results of finite
element analysis show that the length, span and thickness of welded
thin shells affect the number of local buckling, mode shape of global
buckling and post-buckling behavior of welded thin shells.
Abstract: Study of the vibration cylindrical shells made of
a functionally gradient material (FGM) composed of stainless
steel and nickel is important. Material properties are graded in
the thickness direction of the shell according to volume
fraction power law distribution. The objective is to study the
natural frequencies, the influence of constituent volume
fractions and the effects of boundary conditions on the natural
frequencies of the FG cylindrical shell. The study is carried
out using third order shear deformation shell theory. The
governing equations of motion of FG cylindrical shells are
derived based on shear deformation theory. Results are
presented on the frequency characteristics, influence of
constituent volume fractions and the effects of clampedclamped
boundary conditions.
Abstract: This study offers a new simple method for assessing
an axial part-through crack in a pipe wall. The method utilizes simple
approximate expressions for determining the fracture parameters K,
J, and employs these parameters to determine critical dimensions of a
crack on the basis of equality between the J-integral and the J-based
fracture toughness of the pipe steel. The crack tip constraint is taken
into account by the so-called plastic constraint factor C, by which the
uniaxial yield stress in the J-integral equation is multiplied. The
results of the prediction of the fracture condition are verified by burst
tests on test pipes.
Abstract: This article considers the positional buckling of
composite thick plates under thermal loading . For this purpose , the
complex finite strip method is used . In analysis of complex finite
strip, harmonic complex function in longitudinal direction , cubic
functions in transversal direction and parabola distribution of
transverse shear strain in thickness of thick plate based on higherorder
shear deformation theory are used . In given examples , the
effect of angles of stratification , number of layers , dimensions ratio
and length – to – thick ratio across critical temperature are
considered.
Abstract: Cavitation in pumps is known as the formation of
vapor bubbles due to pressure drop and collapsing these bubbles. In
some conditions, it has been observed that the formation of bubbles
occurs at the pressure side of centrifugal pump blades. In this study,
the formation of bubbles at the pressure side of blades has been
investigated. Water is used in this study as the fluid and performance
curves were depicted for different flow rates in an approximately
constant speed. The results show that when a centrifugal pump works
in low flow rates, a secondary flow namely recirculation starts to
begin. In this condition, separation of flow increases which causes
vortex formation and local pressure drop and eventually the
formation of vapor bubbles starts.
Abstract: In this paper a numerical technique is used to predict
the metal temperature of a gas turbine vane. The Rising combustor
exit temperatures in gas turbine engines necessitate active cooling for
the downstream turbine section to avoid thermal failure. This study is
performed the solution of external flow, internal convection, and
conduction within the metal vane. Also the trade-off between the
cooling performances in four different hole shapes and configurations
is performed. At first one of the commonly used cooling hole
geometry is investigated; cylindrical holes and then two other
configurations are simulated. The average temperature magnitude in
mid-plan section of each configuration is obtained and finally the
lower temperature value is selected such as best arrangement.