Abstract: Solid fan blades and discs in aero engines are subjected to high combined low and high cycle fatigue loads especially around the contact areas between blade and disc. Therefore, special coatings (e.g. dry film lubricant) and surface treatments (e.g. shot peening or laser shock peening) are applied to increase the strength with respect to combined cyclic fatigue and fretting fatigue, but also to improve damage tolerance capability. The traditional deterministic damage tolerance assessment based on fracture mechanics analysis, which treats service damage as an initial crack, often gives overly conservative results especially in the presence of vibratory stresses. A probabilistic damage tolerance methodology using crack initiation data has been developed for fan discs exposed to relatively high vibratory stresses in cross- and tail-wind conditions at certain resonance speeds for limited time periods. This Monte-Carlo based method uses a damage databank from similar designs, measured vibration levels at typical aircraft operations and wind conditions and experimental crack initiation data derived from testing of artificially damaged specimens with representative surface treatment under combined fatigue conditions. The proposed methodology leads to a more realistic prediction of the minimum damage tolerance life for the most critical locations applicable to modern fan disc designs.
Abstract: We present a method to set up system functions
through a near filed communication (NFC) of a smartphone. The
short communication distance of the NFC which is usually less
than 4 cm could prevent any interferences from other devices and
establish a secure communication channel between a system and the
smartphone. The proposed set-up method for system function values
is demonstrated for a blacbox system in a car. In demonstration,
system functions of a blackbox which is manipulated through NFC
of a smartphone are controls of image quality, sound level, shock
sensing level to store images, etc. The proposed set-up method for
system function values can be used for any devices with NFC.
Abstract: At present, vibrations of rotors of gas transmittal unit evade sustainable forecasting. This paper describes elastic oscillation modes in resilient supports and rotor impellers modeled during computational experiments with regard to interference in the system of gas-dynamic flow and compressor rotor. Verification of aeroelastic approach was done on model problem of interaction between supersonic jet in shock tube with deformed plate. ANSYS 15.0 engineering analysis system was used as a modeling tool of numerical simulation in this paper. Finite volume method for gas dynamics and finite elements method for assessment of the strain stress state (SSS) components were used as research methods. Rotation speed and material’s elasticity modulus varied during calculations, and SSS components and gas-dynamic parameters in the dynamic system of gas-dynamic flow and compressor rotor were evaluated. The analysis of time dependence demonstrated that gas-dynamic parameters near the rotor blades oscillate at 200 Hz, and SSS parameters at the upper blade edge oscillate four times higher, i.e. with blade frequency. It has been detected that vibration amplitudes correction in the test points at magnetic bearings by aeroelasticity may correspond up to 50%, and about -π/4 for phases.
Abstract: Adult mesenchymal stem cells (MSCs) have been investigated using preclinical approaches for tissue regeneration. Porcine MSCs (pMSCs) are capable of growing and attaching to plastic with a fibroblast-like morphology and then differentiating into bone, adipose, and cartilage tissues in vitro. This study was conducted to investigate the proliferating abilities, differentiation potentials, and multipotency of miniature pig adipose tissue-derived MSCs (mpAD-MSCs) with or without long-term cryopreservation, considering that cryostorage has the potential for use in clinical applications. After confirming the characteristics of the mpAD-MSCs, we examined the effect of long-term cryopreservation (> 2 years) on expression of cell surface markers (CD34, CD90 and CD105), proliferating abilities (cumulative population doubling level, doubling time, colony-forming unit, and MTT assay) and differentiation potentials into mesodermal cell lineages. As a result, the expression of cell surface markers is similar between thawed and fresh mpAD-MSCs. However, long-term cryopreservation significantly lowered the differentiation potentials (adipogenic, chondrogenic, and osteogenic) of mpAD-MSCs. When compared with fresh mpAD-MSCs, thawed mpAD-MSCs exhibited lower expression of mesodermal cell lineage-related genes such as peroxisome proliferator-activated receptor-g2, lipoprotein lipase, collagen Type II alpha 1, osteonectin, and osteocalcin. Interestingly, long-term cryostoraged mpAD-MSCs exhibited significantly higher cell viability than the fresh mpAD-MSCs. Long-term cryopreservation induced a 30% increase in the cell viability of mpAD-MSCs when compared with the fresh mpAD-MSCs at 5 days after thawing. However, long-term cryopreservation significantly lowered expression of stemness markers such as Oct3/4, Sox2, and Nanog. Furthermore, long-term cryopreservation negatively affected expression of senescence-associated genes such as telomerase reverse transcriptase and heat shock protein 90 of mpAD-MSCs when compared with the fresh mpAD-MSCs. The results from this study might be important for the successful application of MSCs in clinical trials after long-term cryopreservation.
Abstract: The collapse of the infamous Rana Plaza, a multi-storeyed commercial building in Savar, near Dhaka, Bangladesh has brought with it a plethora of positive and negative consequences. Bangladesh being a key player in the export of clothing, found itself amidst a wave of economic upheaval following this tragic incident that resulted in numerous Bangladeshis, most of whom were factory workers. This paper compares the consequences that the country’s Ready Made Garments (RMG) sector is facing now, two years into the incident. The paper presents a comparison of statistical data from study reports and brings forward perspectives from all dimensions of Labour, Employment and Industrial Relations in Bangladesh following the event. The paper brings across the viewpoint of donor organizations and donor countries, the impacts of several initiatives taken by foreign organizations like the International Labour Organization, and local entities like the Bangladesh Garment Manufacturers and Exporters Association (BGMEA) in order to reinforce compliance and stabilize the shaky foundation that the RMG sector had found itself following the collapse. Focus of the paper remains on the stance taken by the suppliers in Bangladesh, with inputs from buying houses and factories, and also on the reaction of foreign brands. The paper also focuses on the horrific physical, mental and financial implications sustained by the victims and their families, and the consequent uproar from workers in general regarding compliance with work safety and workers’ welfare conditions. The purpose is to get across both sides of the scenario: the economic impact that suppliers / factories/ sellers/ buying houses/exporters have faced in Bangladesh as a result of complete loss of reliability on them regarding working standards; and also to cover the aftershock felt on the other end of the spectrum by the importers/ buyers, particularly the foreign entities, in terms of the sudden accountability of being affiliated with non- compliant factories. The collapse of Rana Plaza has received vast international attention and strong criticism. Nevertheless, the almost immediate strengthening of labourrights and the wholesale reform undertaken on all sides of the supply chain, evidence a move of all local and foreign stakeholders towards greater compliance and taking of precautionary steps for prevention of further disasters. The tragedy that Rana Plaza embodies served as a much-needed epiphany for the soaring RMG Sector of Bangladesh. Prompt co-operation on the part of all stakeholders and regulatory bodies now show a move towards sustainable development, which further ensures safeguarding against any future irregularities and pave the way for steady economic growth.
Abstract: In this paper, we present an analytical method for
analysis of nano-scale spherical shell subjected to thermo-mechanical
shocks based on nonlocal elasticity theory. Thermo-mechanical
properties of nano shpere is assumed to be temperature dependent.
Governing partial differential equation of motion is solved
analytically by using Laplace transform for time domain and power
series for spacial domain. The results in Laplace domain is
transferred to time domain by employing the fast inverse Laplace
transform (FLIT) method. Accuracy of present approach is assessed
by comparing the the numerical results with the results of published
work in literature. Furtheremore, the effects of non-local parameter
and wall thickness on the dynamic characteristics of the nano-sphere
are studied.
Abstract: The source of the jet noise is generated by rocket exhaust plume during rocket engine testing. A domain decomposition approach is applied to the jet noise prediction in this paper. The aerodynamic noise coupling is based on the splitting into acoustic sources generation and sound propagation in separate physical domains. Large Eddy Simulation (LES) is used to simulate the supersonic jet flow. Based on the simulation results of the flow-fields, the jet noise distribution of the sound pressure level is obtained by applying the Ffowcs Williams-Hawkings (FW-H) acoustics equation and Fourier transform. The calculation results show that the complex structures of expansion waves, compression waves and the turbulent boundary layer could occur due to the strong interaction between the gas jet and the ambient air. In addition, the jet core region, the shock cell and the sound pressure level of the gas jet increase with the nozzle size increasing. Importantly, the numerical simulation results of the far-field sound are in good agreement with the experimental measurements in directivity.
Abstract: This paper outlines the development of an
experimental technique in quantifying supersonic jet flows, in an
attempt to avoid seeding particle problems frequently associated with
particle-image velocimetry (PIV) techniques at high Mach numbers.
Based on optical flow algorithms, the idea behind the technique
involves using high speed cameras to capture Schlieren images of the
supersonic jet shear layers, before they are subjected to an adapted
optical flow algorithm based on the Horn-Schnuck method to
determine the associated flow fields. The proposed method is capable
of offering full-field unsteady flow information with potentially
higher accuracy and resolution than existing point-measurements or
PIV techniques. Preliminary study via numerical simulations of a
circular de Laval jet nozzle successfully reveals flow and shock
structures typically associated with supersonic jet flows, which serve
as useful data for subsequent validation of the optical flow based
experimental results. For experimental technique, a Z-type Schlieren
setup is proposed with supersonic jet operated in cold mode,
stagnation pressure of 4 bar and exit Mach of 1.5. High-speed singleframe
or double-frame cameras are used to capture successive
Schlieren images. As implementation of optical flow technique to
supersonic flows remains rare, the current focus revolves around
methodology validation through synthetic images. The results of
validation test offers valuable insight into how the optical flow
algorithm can be further improved to improve robustness and
accuracy. Despite these challenges however, this supersonic flow
measurement technique may potentially offer a simpler way to
identify and quantify the fine spatial structures within the shock shear
layer.
Abstract: Escherichia coli (E. coli) is the most isolated bacteria
from blood circulation of septicemic calves. Given the prevalence of
septicemia in animals and its economic importance in veterinary
practice, better understanding of changes in clinical signs following
disease, may contribute to early detection of disorder. The present
study has been carried out to detect changes of clinical signs in
induced sepsis in calves with E. coli. Colisepticemia has been
induced in 10 twenty-day old healthy Holstein- Frisian calves with
intravenous injection of 1.5 X 109 colony forming units (cfu) of
O111:H8 strain of E. coli. Clinical signs including rectal temperature,
heart rate, respiratory rate, shock, appetite, sucking reflex, feces
consistency, general behavior, dehydration and standing ability were
recorded in experimental calves during 24 hours after induction of
colisepticemia. Blood culture was also carried out from calves four
times during experiment. ANOVA with repeated measure is used to
see changes of calves’ clinical signs to experimental colisepticemia,
and values of P≤ 0.05 was considered statistically significant. Mean
values of rectal temperature and heart rate as well as median values
of respiratory rate, appetite, suckling reflex, standing ability and feces
consistency of experimental calves increased significantly during
study (P 0.05). The
results of present study showed that total score of clinical signs in
calves with experimental colisepticemia increased significantly,
although score of some clinical signs such as shock did not change
significantly.
Abstract: In this article, we used the residual correction method
to deal with transient thermoelastic problems with a hollow spherical
region when the continuum medium possesses spherically isotropic
thermoelastic properties. Based on linear thermoelastic theory, the
equations of hyperbolic heat conduction and thermoelastic motion
were combined to establish the thermoelastic dynamic model with
consideration of the deformation acceleration effect and non-Fourier
effect under the condition of transient thermal shock. The approximate
solutions of temperature and displacement distributions are obtained
using the residual correction method based on the maximum principle
in combination with the finite difference method, making it easier and
faster to obtain upper and lower approximations of exact solutions.
The proposed method is found to be an effective numerical method
with satisfactory accuracy. Moreover, the result shows that the effect
of transient thermal shock induced by deformation acceleration is
enhanced by non-Fourier heat conduction with increased peak stress.
The influence on the stress increases with the thermal relaxation time.
Abstract: The development of composite materials and the
related design and manufacturing technologies is one of the most
important advances in the history of materials. Composites are
multifunctional materials having unprecedented mechanical and
physical properties that can be tailored to meet the requirements of a
particular application. Some composites also exhibit great resistance
to high-temperature corrosion, oxidation, and wear. Polymers are
widely used indoors and outdoors, therefore they are exposed to a
chemical environment which may include atmospheric oxygen, acidic
fumes, acidic rain, moisture heat and thermal shock, ultra-violet light,
high energy radiation, etc. Different polymers are affected differently
by these factors even though the amorphous polymers are more
sensitive. Ageing is also important and it is defined as the process of
deterioration of engineering materials resulting from the combined
effects of atmospheric radiation, heat, oxygen, water, microorganisms
and other atmospheric factors.
Abstract: In this study, failure analysis of pipe system at a micro
hydroelectric power plant is investigated. Failure occurred at the pipe
system in the powerhouse during shut down operation of the water
flow by a valve. This locking had caused a sudden shock wave, also
called “Water-hammer effect”, resulting in noise and inside pressure
increase. After visual investigation of the effect of the shock wave on
the system, a circumference crack was observed at the pipe flange
weld region. To establish the reason for crack formation, calculations
of pressure and stress values at pipe, flange and welding seams were
carried out and concluded that safety factor was high (2.2), indicating
that no faulty design existed. By further analysis, pipe system and
hydroelectric power plant was examined. After observations it is
determined that the plant did not include a ventilation nozzle (air
trap), that prevents the system of sudden pressure increase inside the
pipes which is caused by water-hammer effect. Analyses were carried
out to identify the influence of water-hammer effect on inside
pressure increase and it was concluded that, according Jowkowsky’s
equation, shut down time is effective on inside pressure increase. The
valve closing time was uncertain but by a shut down time of even one
minute, inside pressure would increase by 7.6 bar (working pressure
was 34.6 bar). Detailed investigations were also carried out on the
assembly of the pipe-flange system by considering technical
drawings. It was concluded that the pipe-flange system was not
installed according to the instructions. Two of five weld seams were
not applied and one weld was carried out faulty. This incorrect and
inadequate weld seams resulted in; insufficient connection of the pipe
to the flange constituting a strong notch effect at weld seam regions,
increase in stress values and the decrease of strength and safety
factor.
Abstract: Traditional mechanical control systems in thrust
vectoring are efficient in rocket thrust guidance but their costs
and their weights are excessive. The fluidic injection in the nozzle
divergent constitutes an alternative procedure to achieve the goal. In
this paper, we present a 3D analytical model for fluidic injection
in a supersonic nozzle integrating an orifice. The fluidic vectoring
uses a sonic secondary injection in the divergent. As a result, the
flow and interaction between the main and secondary jet has built in
order to express the pressure fields from which the forces and thrust
vectoring are deduced. Under various separation criteria, the present
analytical model results are compared with the existing numerical
and experimental data from the literature.
Abstract: Numerical studies have been carried out using a
validated two-dimensional standard k-omega turbulence model for
the design optimization of a thrust vector control system using shock
induced self-impinging supersonic secondary double jet. Parametric
analytical studies have been carried out at different secondary
injection locations to identifying the highest unsymmetrical
distribution of the main gas flow due to shock waves, which produces
a desirable side force more lucratively for vectoring. The results from
the parametric studies of the case on hand reveal that the shock
induced self-impinging supersonic secondary double jet is more
efficient in certain locations at the divergent region of a CD nozzle
than a case with supersonic single jet with same mass flow rate. We
observed that the best axial location of the self-impinging supersonic
secondary double jet nozzle with a given jet interaction angle, built-in
to a CD nozzle having area ratio 1.797, is 0.991 times the primary
nozzle throat diameter from the throat location. We also observed
that the flexible steering is possible after invoking ON/OFF facility to
the secondary nozzles for meeting the onboard mission requirements.
Through our case studies we concluded that the supersonic self-impinging
secondary double jet at predesigned jet interaction angle
and location can provide more flexible steering options facilitating
with 8.81% higher thrust vectoring efficiency than the conventional
supersonic single secondary jet without compromising the payload
capability of any supersonic aerospace vehicle.
Abstract: Complex lifting entry was selected for precise landing
performance during the Mars Science Laboratory entry. This study
aims to develop the three-dimensional numerical method for precise
computation and the surface panel method for rapid engineering
prediction. Detailed flow field analysis for Mars exploration mission
was performed by carrying on a series of fully three-dimensional
Navier-Stokes computations. The static aerodynamic performance was
then discussed, including the surface pressure, lift and drag coefficient,
lift-to-drag ratio with the numerical and engineering method.
Computation results shown that the shock layer is thin because of
lower effective specific heat ratio, and that calculated results from both
methods agree well with each other, and is consistent with the
reference data. Aerodynamic performance analysis shows that CG
location determines trim characteristics and pitch stability, and certain
radially and axially shift of the CG location can alter the capsule lifting
entry performance, which is of vital significance for the aerodynamic
configuration design and inner instrument layout of the Mars entry
capsule.
Abstract: Hypersonic flows around spatial vehicles during their reentry phase in planetary atmospheres are characterized by intense aerothermodynamics phenomena. The aim of this work is to analyze high temperature flows around an axisymmetric blunt body taking into account chemical and vibrational non-equilibrium for air mixture species and the no slip condition at the wall. For this purpose, the Navier-Stokes equations system is resolved by the finite volume methodology to determine the flow parameters around the axisymmetric blunt body especially at the stagnation point and in the boundary layer along the wall of the blunt body. The code allows the capture of shock wave before a blunt body placed in hypersonic free stream. The numerical technique uses the Flux Vector Splitting method of Van Leer. CFL coefficient and mesh size level are selected to ensure the numerical convergence.
Abstract: This study presented to reduce earthquake damage and
emergency rehabilitation of critical structures such as schools, hightech
factories, and hospitals due to strong ground motions associated
with climate changes. Regarding recent trend, a strong earthquake
causes serious damage to critical structures and then the critical
structure might be influenced by sequence aftershocks (or tsunami)
due to fault plane adjustments. Therefore, in order to improve seismic
performance of critical structures, retrofitted or strengthening study
of the structures under aftershocks sequence after emergency
rehabilitation of the structures subjected to strong earthquakes is
widely carried out. Consequently, this study used composite material
for emergency rehabilitation of the structure rather than concrete and
steel materials because of high strength and stiffness, lightweight,
rapid manufacturing, and dynamic performance. Also, this study was
to develop or improve the seismic performance or seismic retrofit of
critical structures subjected to strong ground motions and earthquake
aftershocks, by utilizing GFRP-Corrugated Infill Panels (GCIP).
Abstract: This paper examines the effect of the volatility of oil
prices on food price in South Africa using monthly data covering the
period 2002:01 to 2014:09. Food price is measured by the South
African consumer price index for food while oil price is proxied by
the Brent crude oil. The study employs the GARCH-in-mean VAR
model, which allows the investigation of the effect of a negative and
positive shock in oil price volatility on food price. The model also
allows the oil price uncertainty to be measured as the conditional
standard deviation of a one-step-ahead forecast error of the change in
oil price. The results show that oil price uncertainty has a positive
and significant effect on food price in South Africa. The responses of
food price to a positive and negative oil price shocks is asymmetric.
Abstract: Fluid viscous damping systems are well suited for
many air vehicles subjected to shock and vibration. These damping
system work with the principle of viscous fluid throttling through the
orifice to create huge pressure difference between compression and
rebound chamber and obtain the required damping force. One
application of such systems is its use in aircraft door system to
counteract the door’s velocity and safely stop it. In exigency
situations like crash or emergency landing where the door doesn’t
open easily, possibly due to unusually tilting of fuselage or some
obstacles or intrusion of debris obstruction to move the parts of the
door, such system can be combined with other systems to provide
needed force to forcefully open the door and also securely stop it
simultaneously within the required time i.e. less than 8 seconds. In
the present study, a hydraulic system called snubber along with other
systems like actuator, gas bottle assembly which together known as
emergency power assist system (EPAS) is designed, built and
experimentally studied to check the magnitude of angular velocity,
damping force and time required to effectively open the door.
Whenever needed, the gas pressure from the bottle is released to
actuate the actuator and at the same time pull the snubber’s piston to
operate the emergency opening of the door. Such EPAS installed in
the suspension arm of the aircraft door is studied explicitly changing
parameters like orifice size, oil level, oil viscosity and bypass valve
gap and its spring of the snubber at varying temperature to generate
the optimum design case. Comparative analysis of the EPAS at
several cases is done and conclusions are made. It is found that
during emergency condition, the system opening time and angular
velocity, when snubber with 0.3mm piston and shaft orifice and
bypass valve gap of 0.5 mm with its original spring is used, shows
significant improvement over the old ones.
Abstract: Universal modeling method well proven for industrial
compressors was applied for design of the high flow rate supersonic
stage. Results were checked by ANSYS CFX and NUMECA Fine
Turbo calculations. The impeller appeared to be very effective at
transonic flow velocities. Stator elements efficiency is acceptable at
design Mach numbers too. Their loss coefficient versus inlet flow
angle performances correlates well with Universal modeling
prediction. The impeller demonstrates ability of satisfactory operation
at design flow rate. Supersonic flow behavior in the impeller inducer
at the shroud blade to blade surface Φ des deserves additional study.