Abstract: Bianchi type cosmological models have been studied
on the basis of Lyra’s geometry. Exact solution has been obtained by
considering a time dependent displacement field for constant
deceleration parameter and varying cosmological term of the
universe. The physical behavior of the different models has been
examined for different cases.
Abstract: This paper presents the data of a series of two-dimensional Discrete Element Method (DEM) simulations of a large-diameter rigid monopile subjected to cyclic loading under a high gravitational force. At present, monopile foundations are widely used to support the tall and heavy wind turbines, which are also subjected to significant from wind and wave actions. A safe design must address issues such as rotations and changes in soil stiffness subject to these loadings conditions. Design guidance on the issue is limited, so are the availability of laboratory and field test data. The interpretation of these results in sand, such as the relation between loading and displacement, relies mainly on empirical correlations to pile properties. Regarding numerical models, most data from Finite Element Method (FEM) can be found. They are not comprehensive, and most of the FEM results are sensitive to input parameters. The micro scale behaviour could change the mechanism of the soil-structure interaction. A DEM model was used in this paper to study the cyclic lateral loads behaviour. A non-dimensional framework is presented and applied to interpret the simulation results. The DEM data compares well with various set of published experimental centrifuge model test data in terms of lateral deflection. The accumulated permanent pile lateral displacements induced by the cyclic lateral loads were found to be dependent on the characteristics of the applied cyclic load, such as the extent of the loading magnitudes and directions.
Abstract: Fragility analysis is an effective tool for the seismic vulnerability assessment of civil structures in the last several years. The design of the expansion joints according to various bridge design codes is almost inconsistent, and only a few studies have focused on this problem so far. In this study, the influence of the expansion joint clearances between the girder ends and the abutment backwalls on the seismic fragility assessment of continuous integral bridge frames is investigated. The gaps (ranging from 60 mm, 150 mm, 250 mm and 350 mm) are designed by following two different bridge design code specifications, namely, Caltrans and Eurocode 8-2. Five bridge models are analyzed and compared. The first bridge model serves as a reference. This model uses three-dimensional reinforced concrete fiber beam-column elements with simplified supports at both ends of the girder. The other four models also employ reinforced concrete fiber beam-column elements but include the abutment backfill stiffness and four different gap values. The nonlinear time history analysis is performed. The artificial ground motion sets, which have the peak ground accelerations (PGAs) ranging from 0.1 g to 1.0 g with an increment of 0.05 g, are taken as input. The soil-structure interaction and the P-Δ effects are also included in the analysis. The component fragility curves in terms of the curvature ductility demand to the capacity ratio of the piers and the displacement demand to the capacity ratio of the abutment sliding bearings are established and compared. The system fragility curves are then obtained by combining the component fragility curves. Our results show that in the component fragility analysis, the reference bridge model exhibits a severe vulnerability compared to that of other sophisticated bridge models for all damage states. In the system fragility analysis, the reference curves illustrate a smaller damage probability in the earlier PGA ranges for the first three damage states, they then show a higher fragility compared to other curves in the larger PGA levels. In the fourth damage state, the reference curve has the smallest vulnerability. In both the component and the system fragility analysis, the same trend is found that the bridge models with smaller clearances exhibit a smaller fragility compared to that with larger openings. However, the bridge model with a maximum clearance still induces a minimum pounding force effect.
Abstract: In this paper we presented a new method for tracking
flying targets in color video sequences based on contour and kernel.
The aim of this work is to overcome the problem of losing target in
changing light, large displacement, changing speed, and occlusion.
The proposed method is made in three steps, estimate the target
location by particle filter, segmentation target region using neural
network and find the exact contours by greedy snake algorithm. In
the proposed method we have used both region and contour
information to create target candidate model and this model is
dynamically updated during tracking. To avoid the accumulation of
errors when updating, target region given to a perceptron neural
network to separate the target from background. Then its output used
for exact calculation of size and center of the target. Also it is used as
the initial contour for the greedy snake algorithm to find the exact
target's edge. The proposed algorithm has been tested on a database
which contains a lot of challenges such as high speed and agility of
aircrafts, background clutter, occlusions, camera movement, and so
on. The experimental results show that the use of neural network
increases the accuracy of tracking and segmentation.
Abstract: The Metropolitan Region of Sao Paulo (MRSP) has suffered from serious water scarcity. Consequently, the most convenient solution has been building wells to extract groundwater from local aquifers. However, it requires constant vigilance to prevent over extraction and future events that can pose serious threat to the population, such as subsidence. Radar imaging techniques (InSAR) have allowed continuous investigation of such phenomena. The analysis of data in the present study consists of 23 SAR images dated from October 2007 to March 2011, obtained by the ALOS-1 spacecraft. Data processing was made with the software GMTSAR, by using the InSAR technique to create pairs of interferograms with ground displacement during different time spans. First results show a correlation between the location of 102 wells registered in 2009 and signals of ground displacement equal or lower than -90 millimeters (mm) in the region. The longest time span interferogram obtained dates from October 2007 to March 2010. As a result, from that interferogram, it was possible to detect the average velocity of displacement in millimeters per year (mm/y), and which areas strong signals have persisted in the MRSP. Four specific areas with signals of subsidence of 28 mm/y to 40 mm/y were chosen to investigate the phenomenon: Guarulhos (Sao Paulo International Airport), the Greater Sao Paulo, Itaquera and Sao Caetano do Sul. The coverage area of the signals was between 0.6 km and 1.65 km of length. All areas are located above a sedimentary type of aquifer. Itaquera and Sao Caetano do Sul showed signals varying from 28 mm/y to 32 mm/y. On the other hand, the places most likely to be suffering from stronger subsidence are the ones in the Greater Sao Paulo and Guarulhos, right beside the International Airport of Sao Paulo. The rate of displacement observed in both regions goes from 35 mm/y to 40 mm/y. Previous investigations of the water use at the International Airport highlight the risks of excessive water extraction that was being done through 9 deep wells. Therefore, it is affirmed that subsidence events are likely to occur and to cause serious damage in the area. This study could show a situation that has not been explored with proper importance in the city, given its social and economic consequences. Since the data were only available until 2011, the question that remains is if the situation still persists. It could be reaffirmed, however, a scenario of risk at the International Airport of Sao Paulo that needs further investigation.
Abstract: While the need for equal access to civil, political as well as economic, social and cultural rights is clear under the international law, the adoption of the Convention on the Elimination of all forms of Discrimination against women in 1979 made this even clearer. Despite this positive progress, the abuse of refugee women's rights is one of the basic underlying root causes of their marginalisation and violence in their countries of asylum. This paper presents a critical review on the development of refugee women's rights at the international levels and national levels. It provides an array of scholarly literature on this issue and examines the measures taken by the international community to curb the problem of violence against women in their various provisions through the instruments set. It is cognizant of the fact that even if conflict affects both refugee women and men, the effects on women refugees are deep-reaching, due to the cultural strongholds they face. An important aspect of this paper is that it is conceptualised against the fact that refugee women face the problem of sexual and gender based first as refugees and second as women, yet, their rights are stumbled upon. Often times they have been rendered "worthless victims" who are only in need of humanitarian assistance than active participants committed to change their plight through their participation in political, economic and social participation in their societies. Scholars have taken notice of the fact that women's rights in refugee settings have been marginalized and call for a need to incorporate their perspectives in the planning and management of refugee settings in which they live. Underpinning this discussion is feminism theory which gives a clear understanding of the root cause of refugee women's problems. Finally, this paper suggests that these policies should be translated into action at local, national international and regional levels to ensure sustainable peace.
Abstract: Soil improvement using vibro stone column techniques consists of two main parts: (1) the installed load bearing columns of well-compacted, coarse-grained material and (2) the improvements to the surrounding soil due to vibro compaction. Extensive research work has been carried out over the last 20 years to understand the improvement in the composite foundation performance due to the second part mentioned above. Nevertheless, few of these studies have tried to quantify some of the key design parameters, namely the changes in the stiffness and stress state of the treated soil, or have consider these parameters in the design and calculation process. Consequently, empirical and conservative design methods are still being used by ground improvement companies with a significant variety of results in engineering practice. Two-dimensional finite element study to develop an axisymmetric model of a single stone column reinforced foundation was performed using PLAXIS 2D AE to quantify the effect of the vibro installation of this column in soft saturated clay. Settlement and bearing performance were studied as an essential part of the design and calculation of the stone column foundation. Particular attention was paid to the large deformation in the soft clay around the installed column caused by the lateral expansion. So updated mesh advanced option was taken in the analysis. In this analysis, different degrees of stone column lateral expansions were simulated and numerically analyzed, and then the changes in the stress state, stiffness, settlement performance and bearing capacity were quantified. It was found that application of radial expansion will produce a horizontal stress in the soft clay mass that gradually decrease as the distance from the stone column axis increases. The excess pore pressure due to the undrained conditions starts to dissipate immediately after finishing the column installation, allowing the horizontal stress to relax. Changes in the coefficient of the lateral earth pressure K ٭, which is very important in representing the stress state, and the new stiffness distribution in the reinforced clay mass, were estimated. More encouraging results showed that increasing the expansion during column installation has a noticeable effect on improving the bearing capacity and reducing the settlement of reinforced ground, So, a design method should include this significant effect of the applied lateral displacement during the stone column instillation in simulation and numerical analysis design.
Abstract: Reinforced concrete (RC) shear wall system of residential buildings is popular in South Korea. RC walls are subjected to axial forces in common and the effect of axial forces on the strength loss of the fire damaged walls has not been investigated. This paper aims at investigating temperature distribution on fire damaged concrete walls having different axial loads. In the experiments, a variable of specimens is axial force ratio. RC walls are fabricated with 150mm of wall thicknesses, 750mm of lengths and 1,300mm of heights having concrete strength of 24MPa. After curing, specimens are heated on one surface with ISO-834 standard time-temperature curve for 2 hours and temperature distributions during the test are measured using thermocouples inside the walls. The experimental results show that the temperature of the RC walls exposed to fire increases as axial force ratio increases. To verify the experiments, finite element (FE) models are generated for coupled temperature-structure analyses. The analytical results of thermal behaviors are in good agreement with the experimental results. The predicted displacement of the walls decreases when the axial force increases.
Abstract: Reinforced earth structures are generally subjected to cyclic loading generated from earthquakes. This paper presents a summary of the results and analyses of a testing program carried out in a large-scale multi-function geosynthetic testing apparatus that accommodates soil samples up to 1.0 m3. This apparatus performs different shear and pullout tests under both static and cyclic loading. The testing program was carried out to investigate the controlling factors affecting soil/geogrid interaction under cyclic loading. The extensibility of the geogrids, the applied normal stresses, the characteristics of the cyclic loading (frequency, and amplitude), and initial static load within the geogrid sheet were considered in the testing program. Based on the findings of the testing program, the effect of these parameters on the pullout resistance of geogrids, as well as the displacement mobility under cyclic loading were evaluated. Conclusions and recommendations for the design of reinforced earth walls under cyclic loading are presented.
Abstract: Many embankment dams have suffered failures during
earthquakes due to the increase of pore water pressure under seismic
loading. After analyzing of the behavior of embankment dams under
severe earthquakes, major advances have been attained in the
understanding of the seismic action on dams. The present study concerns numerical analysis of the seismic
response of earth dams. The procedure uses a nonlinear stress-strain
relation incorporated into the code FLAC2D based on the finite
difference method. This analysis provides the variation of the pore
water pressure and horizontal displacement.
Abstract: For several hundred years, the design of railway tracks
has practically remained unchanged. Traditionally, rail tracks are
placed on a ballast layer due to several reasons, including economy,
rapid drainage, and high load bearing capacity. The primary function
of ballast is to distributing dynamic track loads to sub-ballast and
subgrade layers, while also providing lateral resistance and allowing
for rapid drainage. Upon repeated trainloads, the ballast becomes
fouled due to ballast degradation and the intrusion of fines which
adversely affects the strength and deformation behaviour of ballast.
This paper presents the use of three-dimensional discrete element
method (DEM) in studying the shear behaviour of the fouled ballast
subjected to direct shear loading. Irregularly shaped particles of
ballast were modelled by grouping many spherical balls together in
appropriate sizes to simulate representative ballast aggregates. Fouled
ballast was modelled by injecting a specified number of miniature
spherical particles into the void spaces. The DEM simulation
highlights that the peak shear stress of the ballast assembly decreases
and the dilation of fouled ballast increases with an increase level of
fouling. Additionally, the distributions of contact force chain and
particle displacement vectors were captured during shearing progress,
explaining the formation of shear band and the evolutions of
volumetric change of fouled ballast.
Abstract: The floor beams of steel buildings, cold-formed steel
floor joists in particular, often require large web openings, which may
affect their shear capacities. A cost effective way to mitigate the
detrimental effects of such openings is to weld/fasten reinforcements.
A difficulty associated with an experimental investigation to establish
suitable reinforcement schemes for openings in shear zone is that
moment always coexists with the shear, and thus, it is impossible to
create pure shear state in experiments, resulting in moment
influenced results. However, Finite Element Method (FEM) based
analysis can be conveniently used to investigate the pure shear
behaviour of webs including webs with reinforced openings. This
paper presents the details associated with the finite element analysis
of thick/thin-plates (representing the web of hot-rolled steel beam,
and the web of a cold-formed steel member) having a large
reinforced opening. The study considered simply-supported
rectangular plates subjected to in-plane shear loadings until failure
(including post-buckling behaviour). The plate was modelled using
geometrically non-linear quadrilateral shell elements, and non-linear
stress-strain relationship based on experiments. Total Langrangian
with large displacement/small strain formulation was used for such
analyses. The model also considered the initial geometric
imperfections. This study considered three reinforcement schemes,
namely, flat, lip, and angle reinforcements. This paper discusses the
modelling considerations and presents the results associated with the
various reinforcement schemes under consideration.
Abstract: The objective of this work is to carryout critical
comparison of different actuation mechanisms like electrostatic,
thermal, piezoelectric, and magnetic with reference to a micro
cantilever. The relevant parameters like force generated,
displacement are compared in actuation methods. With these results,
helps in choosing the best actuation method for a particular
application. In this study, Comsol/Multiphysics software is used.
Modeling and simulation is done by considering the micro cantilever
of same dimensions as an actuator using all the above mentioned
actuation techniques. In addition to their small size, micro actuators
consume very little power and are capable of accurate results. In this
work, a comparison of actuation mechanisms is done to decide the
efficient system in micro domain.
Abstract: Internal circulation two-platen clamping system for
injection molding machine (IMM) has many potential advantages on
energy-saving. In order to estimate its properties, experiments were
carried out in this paper. Displacement and pressure of the components
were measured. In comparison, the model of hydraulic clamping
system was established by using AMESim. The related parameters as
well as the energy consumption could be calculated. According to the
analysis, the hydraulic system was optimized in order to reduce the
energy consumption.
Abstract: In this work, repaired crack in 6061- T6 aluminum
plate with composite patches presented, firstly we determine the
displacement, strain and stress, also the first six mode shape of the
plate, secondly we took the same model adding central crack
initiation, which is located in the center of the plate, its seize vary
from 20 mm to 60 mm and we compare the first results with second.
Thirdly we repair various cracks with composite patch (carbon/
epoxy) and for (2 layers, 4 layers). Finally the comparison of stress,
strain, displacement and six first natural frequencies between un-cracked
specimen, crack propagation and composite patch repair.
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: In this article, the radial displacement error correction
capability of a high precision spindle grinding caused by unbalance
force was investigated. The spindle shaft is considered as a flexible
rotor mounted on two sets of angular contact ball bearing. Finite
element methods (FEM) have been adopted for obtaining the
equation of motion of the spindle. In this paper, firstly, natural
frequencies, critical frequencies, and amplitude of the unbalance
response caused by residual unbalance are determined in order to
investigate the spindle behaviors. Furthermore, an optimization
design algorithm is employed to minimize radial displacement of the
spindle which considers dimension of the spindle shaft, the dynamic
characteristics of the bearings, critical frequencies and amplitude of
the unbalance response, and computes optimum spindle diameters
and stiffness and damping of the bearings. Numerical simulation
results show that by optimizing the spindle diameters, and stiffness
and damping in the bearings, radial displacement of the spindle can
be reduced. A spindle about 4 μm radial displacement error can be
compensated with 2 μm accuracy. This certainly can improve the
accuracy of the product of machining.
Abstract: During machining process, chatter is an unavoidable
phenomenon. Boring bars possess the cantilever shape and due to
this, it is subjected to chatter. The adverse effect of chatter includes
the increase in temperature which will leads to excess tool wear. To
overcome these problems, in this investigation, Cartridge brass (Cu –
70% and Zn – 30%) is passively fixed on the boring bar and also
clearance is provided in order to reduce the displacement, tool wear
and cutting temperature. A conventional all geared lathe is attached
with vibrometer and pyrometer is used to measure the displacement
and temperature. The influence of input parameters such as cutting
speed, depth of cut and clearance on temperature, tool wear and
displacement are investigated for various cutting conditions. From
the result, the optimum conditions to obtain better damping in boring
process for chatter reduction is identified.
Abstract: This study, tries to suggest a design method based on
displacement using finite difference numerical modeling in
reinforcing soil retaining wall with steel strip. In this case, dynamic
loading characteristics such as duration, frequency, peak ground
acceleration, geometrical characteristics of reinforced soil structure
and type of the site are considered to correct the pseudo static method
and finally introduce the pseudo static coefficient as a function of
seismic performance level and peak ground acceleration. For this
purpose, the influence of dynamic loading characteristics,
reinforcement length, height of reinforced system and type of the site
are investigated on seismic behavior of reinforcing soil retaining wall
with steel strip. Numerical results illustrate that the seismic response
of this type of wall is highly dependent to cumulative absolute
velocity, maximum acceleration, and height and reinforcement length
so that the reinforcement length can be introduced as the main factor
in shape of failure. Considering the loading parameters, geometric parameters of the
wall and type of the site showed that the used method in this study
leads to efficient designs in comparison with other methods, which
are usually based on limit-equilibrium concept. The outputs show the
over-estimation of equilibrium design methods in comparison with
proposed displacement based methods here.
Abstract: Environmental and functional conditions, sometimes,
necessitate the architectural plan of the building to be asymmetric,
and this result in an asymmetric structure. In such cases finding an
optimal pattern for locating the components of lateral load bearing
system, including shear walls, in the building’s plan is desired. In
case of shear wall in addition to the location the shape of the wall
cross-section is also an effective factor. Various types of shear walls
and their proper layout might come effective in better stiffness
distribution and more appropriate seismic response of the building.
Several studies have been conducted in the context of analysis and
design of shear walls; however, few studies have been performed on
making decisions for the location and form of shear walls in multistory
buildings, especially those with irregular plan. In this study, an
attempt has been made to obtain the most reliable seismic behavior of
multi-story reinforced concrete vertically chamfered buildings by
using more appropriate shear walls form and arrangement in 7-, 10-,
12-, and 15-stoy buildings. The considered forms and arrangements
include common rectangular walls and L-, T-, U- and Z-shaped plan,
located as the core or in the outer frames of the building structure.
Comparison of seismic behaviors of the buildings, including
maximum roof displacement and particularly formation of plastic
hinges and their distribution in the buildings’ structures, have been
done based on the results of a series of nonlinear time history
analyses, by using a set of selected earthquake records. Results show
that shear walls with U-shaped cross-section, placed as the building
central core, and also walls with Z-shaped cross-section, placed at the
corners give the building more reliable seismic behavior.