Abstract: This paper presents a method to detect multiple cracks
based on frequency information. When a structure is subjected to
dynamic or static loads, cracks may develop and the modal
frequencies of the cracked structure may change. To detect cracks in a
structure, we construct a high precision wavelet finite element (EF)
model of a certain structure using the B-spline wavelet on the interval
(BSWI). Cracks can be modeled by rotational springs and added to the
FE model. The crack detection database will be obtained by solving
that model. Then the crack locations and depths can be determined
based on the frequency information from the database. The
performance of the proposed method has been numerically verified by
a rotor example.
Abstract: In the present paper, an improved initial value
numerical technique is presented to analyze the free vibration of
symmetrically laminated rectangular plate. A combination of the
initial value method (IV) and the finite differences (FD) devices is
utilized to develop the present (IVFD) technique. The achieved
technique is applied to the equation of motion of vibrating laminated
rectangular plate under various types of boundary conditions. Three
common types of laminated symmetrically cross-ply, orthotropic and
isotropic plates are analyzed here. The convergence and accuracy of
the presented Initial Value-Finite Differences (IVFD) technique have
been examined. Also, the merits and validity of improved technique
are satisfied via comparing the obtained results with those available
in literature indicating good agreements.
Abstract: The V-notches are most possible case for initiation of cracks in parts. The specifications of cracks on the tip of the notch will be influenced via opening angle, tip radius and depth of V-notch. In this study, the effects of V-notch-s opening angle on stress intensity factor and T-stress of crack on the notch has been investigated. The experiment has been done in different opening angles and various crack length in mode (I) loading using Photoelasticity method. The results illustrate that while angle increases in constant crack-s length, SIF and T-stress will decrease. Beside, the effect of V-notch angle in short crack is more than long crack. These V-notch affects are negligible by increasing the length of crack, and the crack-s behavior can be considered as a single-edge crack specimen. Finally, the results have been evaluated with numerical finite element analysis and good agreement was obvious.
Abstract: To date, theoretical studies concerning the Carbon
Fiber Reinforced Polymer (CFRP) strengthening of RC beams with
openings have been rather limited. In addition, various numerical
analyses presented so far have effectively simulated the behaviour of
solid beam strengthened by FRP material. In this paper, a two
dimensional nonlinear finite element analysis is presented to validate
against the laboratory test results of six RC beams. All beams had the
same rectangular cross-section geometry and were loaded under four
point bending. The crack pattern results of the finite element model
show good agreement with the crack pattern of the experimental
beams. The load midspan deflection curves of the finite element
models exhibited a stiffer result compared to the experimental beams.
The possible reason may be due to the perfect bond assumption used
between the concrete and steel reinforcement.
Abstract: The process for predicting the ballistic properties of a liquid rocket engine is based on the quantitative estimation of idealized performance deviations. In this aim, an equilibrium chemistry procedure is firstly developed and implemented in a Fortran routine. The thermodynamic formulation allows for the calculation of the theoretical performances of a rocket thrust chamber. In a second step, a computational fluid dynamic analysis of the turbulent reactive flow within the chamber is performed using a finite volume approach. The obtained values for the “quasi-real" performances account for both turbulent mixing and chemistryturbulence coupling. In the present work, emphasis is made on the combustion efficiency performance for which deviation is mainly due to radial gradients of static temperature and mixture ratio. Numerical values of the characteristic velocity are successfully compared with results from an industry-used code. The results are also confronted with the experimental data of a laboratory-scale rocket engine.
Abstract: This paper is concerned with the permanence and extinction problem of enterprises cluster constituted by m satellite enterprises and a dominant enterprise. We present the model involving impulsive effect based on ecology theory, which effectively describe the competition and cooperation of enterprises cluster in real economic environment. Applying comparison theorem of impulsive differential equation, we establish sufficient conditions which ultimately affect the fate of enterprises: permanence, extinction, and co-existence. Finally, we present numerical examples to explain the economical significance of mathematical results.
Abstract: Effective cooling of electronic equipment has emerged
as a challenging and constraining problem of the new century. In the
present work the feasibility and effectiveness of jet impingement
cooling on electronics were investigated numerically and
experimentally. Studies have been conducted to see the effect of the
geometrical parameters such as jet diameter (D), jet to target
spacing (Z) and ratio of jet spacing to jet diameter (Z/D) on the heat
transfer characteristics. The values of Reynolds numbers considered
are in the range 7000 to 42000. The results obtained from the
numerical studies are validated by conducting experiments. From the
studies it is found that the optimum value of Z/D ratio is 5. For a
given Reynolds number, the Nusselt number increases by about 28%
if the diameter of the nozzle is increased from 1mm to 2mm.
Correlations are proposed for Nusselt number in terms of Reynolds
number and these are valid for air as the cooling medium.
Abstract: This research aims at modeling and simulating the effects of nanofluids on cylindrical heat pipes thermal performance using the ANSYS-FLUENT CFD commercial software. The heat pipe outer wall temperature distribution, thermal resistance, liquid pressure and axial velocity in presence of suspended nano-scaled solid particle (i.e. Cu, Al2O3 and TiO2) within the fluid (water) were investigated. The effect of particle concentration and size were explored and it is concluded that the thermal performance of the heat pipe is improved when using nanofluid as the system working fluid. Additionally, it was observed that the thermal resistance of the heat pipe drops as the particle concentration level increases and particle radius decreases.
Abstract: In this study a two dimensional axisymmetric, steady state and incompressible laminar flow in a rotating single disk is numerically investigated. The finite volume method is used for solving the momentum equations. The numerical model and results
are validated by comparing it to previously reported experimental data for velocities, angles and moment coefficients. It is
demonstrated that increasing the axial distance increases the value of axial velocity and vice versa for tangential and total velocities. However, the maximum value of nondimensional radial velocity
occurs near the disk wall. It is also found that with increase rotational Reynolds number, moment coefficient decreases.
Abstract: PCMs have always been viewed as a suitable
candidate for off peak thermal storage, particularly for refrigeration
systems, due to the high latent energy densities of these materials.
However, due to the need to have them encapsulated within a
container this density is reduced. Furthermore, PCMs have a low
thermal conductivity which reduces the useful amount of energy
which can be stored. To consider these factors, the true energy
storage density of a PCM system was proposed and optimised for
PCMs encapsulated in slabs. Using a validated numerical model of
the system, a parametric study was undertaken to investigate the
impact of the slab thickness, gap between slabs and the mass flow
rate. The study showed that, when optimised, a PCM system can
deliver a true energy storage density between 53% and 83% of the
latent energy density of the PCM.
Abstract: A numerical analysis of wave and hydrodynamic models
is used to investigate the influence of WAve and Storm Surge
(WASS) in the regional and coastal zones. The numerical analyzed
system consists of the WAve Model Cycle 4 (WAMC4) and the
Princeton Ocean Model (POM) which used to solve the energy
balance and primitive equations respectively. The results of both
models presented the incorporated surface wave in the regional
zone affected the coastal storm surge zone. Specifically, the results
indicated that the WASS generally under the approximation is not
only the peak surge but also the coastal water level drop which
can also cause substantial impact on the coastal environment. The
wave–induced surface stress affected the storm surge can significantly
improve storm surge prediction. Finally, the calibration of wave
module according to the minimum error of the significant wave height
(Hs) is not necessarily result in the optimum wave module in the
WASS analyzed system for the WASS prediction.
Abstract: In the context of sensor networks, where every few
dB saving counts, the novel node cooperation schemes are reviewed
where MIMO techniques play a leading role. These methods could be
treated as joint approach for designing physical layer of their
communication scenarios. Then we analyzed the BER performance
of transmission diversity schemes under a general fading channel
model and proposed a power allocation strategy to the transmitting
sensor nodes. This approach is then compared to an equal-power
assignment method and its performance enhancement is verified by
the simulation. Another key point of the contribution lies in the
combination of optimal power allocation and sensor nodes-
cooperation in a transmission diversity regime (MISO). Numerical
results are given through figures to demonstrate the optimality and
efficiency of proposed combined approach.
Abstract: In this paper, a generalized synchronization scheme, which is called function synchronization, for chaotic systems is studied. Based on Lyapunov method and active control method, we design the synchronization controller for the system such that the error dynamics between master and slave chaotic systems is asymptotically stable. For verification of our theory, computer and circuit simulations for a specific chaotic system is conducted.
Abstract: The development and extension of large cities induced
a need for shallow tunnel in soft ground of building areas. Estimation
of ground settlement caused by the tunnel excavation is important
engineering point. In this paper, prediction of surface subsidence
caused by tunneling in one section of seventh line of Tehran subway
is considered. On the basis of studied geotechnical conditions of the
region, tunnel with the length of 26.9km has been excavated applying
a mechanized method using an EPB-TBM with a diameter of 9.14m.
In this regard, settlement is estimated utilizing both analytical and
numerical finite element method. The numerical method shows that
the value of settlement in this section is 5cm. Besides, the analytical
consequences (Bobet and Loganathan-Polous) are 5.29 and 12.36cm,
respectively. According to results of this study, due tosaturation of
this section, there are good agreement between Bobet and numerical
methods. Therefore, tunneling processes in this section needs a
special consolidation measurement and support system before the
passage of tunnel boring machine.
Abstract: In working mode some unexpected changes could
be arise in inner structure of electromagnetic device. They
influence modification in electromagnetic field propagation map.
The field values at an observed boundary are also changed. The
development of the process has to be watched because the arising
structural changes would provoke the device to be gone out later.
The probabilistic assessment of the state is possible to be made.
The numerical assessment points if the resulting changes have
only accidental character or they are due to the essential inner
structural disturbances.
The presented application example is referring to the 200MW
turbine-generator. A part of the stator core end teeth zone is
simulated broken. Quasi three-dimensional electromagnetic and
temperature field are solved applying FEM. The stator core state
diagnosis is proposed to be solved as an identification problem on
the basis of a statistical criterion.
Abstract: The objective of this work is to investigate the
turbulent reacting flow in a three dimensional combustor with
emphasis on the effect of inlet swirl flow through a numerical
simulation. Flow field is analyzed using the SIMPLE method which is
known as stable as well as accurate in the combustion modeling, and
the finite volume method is adopted in solving the radiative transfer
equation. In this work, the thermal and flow characteristics in a three
dimensional combustor by changing parameters such as equivalence
ratio and inlet swirl angle have investigated. As the equivalence ratio
increases, which means that more fuel is supplied due to a larger inlet
fuel velocity, the flame temperature increases and the location of
maximum temperature has moved towards downstream. In the mean
while, the existence of inlet swirl velocity makes the fuel and
combustion air more completely mixed and burnt in short distance.
Therefore, the locations of the maximum reaction rate and temperature
were shifted to forward direction compared with the case of no swirl.
Abstract: In this paper, creep constitutive equations of base
(Parent) and weld materials of the weldment for cold-drawn 304L
stainless steel have been obtained experimentally. For this purpose,
test samples have been generated from cold drawn bars and weld
material according to the ASTM standard. The creep behavior and
properties have been examined for these materials by conducting uniaxial
creep tests. Constant temperatures and constant load uni-axial
creep tests have been carried out at two high temperatures, 680 and
720 oC, subjected to constant loads, which produce initial stresses
ranging from 240 to 360 MPa. The experimental data have been used
to obtain the creep constitutive parameters using numerical
optimization techniques.
Abstract: Applicability of tuning the controller gains for Stewart manipulator using genetic algorithm as an efficient search technique is investigated. Kinematics and dynamics models were introduced in detail for simulation purpose. A PD task space control scheme was used. For demonstrating technique feasibility, a Stewart manipulator numerical-model was built. A genetic algorithm was then employed to search for optimal controller gains. The controller was tested onsite a generic circular mission. The simulation results show that the technique is highly convergent with superior performance operating for different payloads.
Abstract: The entropy of intuitionistic fuzzy sets is used to indicate the degree of fuzziness of an interval-valued intuitionistic fuzzy set(IvIFS). In this paper, we deal with the entropies of IvIFS. Firstly, we propose a family of entropies on IvIFS with a parameter λ ∈ [0, 1], which generalize two entropy measures defined independently by Zhang and Wei, for IvIFS, and then we prove that the
new entropy is an increasing function with respect to the parameter λ. Furthermore, a new multiple attribute decision making (MADM) method using entropy-based attribute weights is proposed to deal with the decision making situations where the alternatives on attributes are expressed by IvIFS and the attribute weights information is unknown. Finally, a numerical example is given to illustrate the applications of the proposed method.
Abstract: The necessity of updating the numerical models inputs, because of geometrical and resistive variations in rivers subject to solid transport phenomena, requires detailed control and monitoring activities. The human employment and financial resources of these activities moves the research towards the development of expeditive methodologies, able to evaluate the outflows through the measurement of more easily acquirable sizes. Recent studies highlighted the dependence of the entropic parameter on the kinematical and geometrical flow conditions. They showed a meaningful variability according to the section shape, dimension and slope. Such dependences, even if not yet well defined, could reduce the difficulties during the field activities, and also the data elaboration time. On the basis of such evidences, the relationships between the entropic parameter and the geometrical and resistive sizes, obtained through a large and detailed laboratory experience on steady free surface flows in conditions of macro and intermediate homogeneous roughness, are analyzed and discussed.