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In the present paper, Molecular Dynamics Simulation (MDS) is performed for Poiseuille flow of liquid Argon in a nanochannel by embedding the fluid particles in an external force with different potential functions. Three types of Lennard-Jones (LJ) potentials are used as interatomistic or molecular models for evaluations of interactions and density, velocity profiles across the channel are investigated. The interatomic potentials are LJ 12-6 potential, LJ 9-6 potential and LJ-Smooth potential. Density and velocity profiles across the channel are investigated. Obtained results show that hydrodynamic characteristics and behavior of flow depends on the type of interaction potential. It is shown that the LJ 9-6 predictions for velocity and temperature are larger than those of LJ12-6 and LJ-Smooth potentials. Also, applying LJ 9-6 results in further calculations time. The results show the effect of interaction force model on the understanding and analyzing of nanoscale flows.

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In this study, generated entropy of mixed convection of Al2O3–water nano fluids in a vertical channel with sinusoidal walls under a constant and uniform magnetic field was numerically investigated. The effects of various parameters such as volume fraction of nanoparticles, amplitude of sine wave, Reynolds, Grashof and Hartman numbers were studied. This study was carried out by assuming the laminar, steady state and incompressible flow. Also, the thermo physical properties of nanoparticles were assumed constant. The Boussinesq approximation was used to calculate the variations of the density caused by buoyancy force and the finite volume method and two phase mixture model were used to simulate the flow. The results showed that the entropy generation due to heat transfer and viscous effects increase by adding nanoparticles to the base fluid. Also, the results showed that the entropy generation due to heat transfer increases by increasing the Grashof number and decreasing the Reynolds number, while a reverse trend is observed for entropy generation due to viscous effects. By increasing the Hartman number, the entropy generation due to heat transfer increases at first and then decreases and entropy generation due to viscous effects reduces. For all studied intensities of magnetic fields, the entropy generation decreases using corrugated channels.

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Catastrophic failures due to corrosion are among the most common phenomena in pre-stressed concrete pipeline, which has been reported in Iran, as well. Structural health monitoring, quick assessment and timely detection of corrosion in its early stages with active in-situ sensors is could prove vital in avoiding such hazards. Acoustic emission is a non-destructive technique that can be used to give a better insight on the structural state of such concrete structures. However, the interpretation of the AE measurements is quite challenging and may actually be even more difficult when the concrete is cracked, which would affect the material and structural properties of concrete pipes. The amplitude distribution of the acquired signals is very sensitive to micro-cracking. This paper presents the results of an experiment conducted in the laboratory of Middle East Technical University on pre-stressed concrete pipe for determining the amplitude attenuation and path of acoustic wave propagation and frequency spectrum before and after corrosion using Hsu-Nielsen pencil-lead break source and applying accelerated corrosion. The results from the laboratory tests indicate that since the changing in amplitude and wave propagation path is negligible before and after corrosion, the AE measurements can be used as an accurate method for tackling the problem mentioned above. Then the performed AE measurements are reported and results discussed.

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Corrosion in spiral steel prestressed wires tensioned around core are one of the major weaknesses of prestressed concrete pipes which their untimely detection can cause sudden failure and damages. To date, these kinds of pipes are used and produced in Iran and their abrupt failure due to corrosion has been experienced. In this study acoustic emission monitoring in prestressed concrete was used to investigate the corrosion. An approximately full-scale experimental sample pipe is made in Middle East Technical University laboratory. The pipe is loaded by internal water pressure and accelerated corrosion applied to the sample and the resulted acoustic emission signals are recorded using piezoelectric sensors during corrosion. The sample is tested under wetting and drying cycles frequently for corrosion detection in which during the experiment, pipe inside pressure was fluctuated and Kaiser Effect was studied in different conditions. Experimental results show significant changes in some gained acoustic emission parameters as the pipe work pressure increases to higher amounts. It is shown that the changed AE parameters can be used for damage prediction, condition assessment and corrosion detection of prestressed concrete pipelines.

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In this paper, ferrofluid flow in a closed cooling loop without any mechanical pump has been simulated. The flow of the ferrofluid in the closed loop is resulted from applying a non-uniform magnetic field and the thermo-magnetic effect of the ferrofluids. The ferrofluid consist water and different volume fractions of iron oxide nanoparticles with nanoparticle diameter of 13nm. The two phase mixture model and the control volume technique have been used in the present study. The applied non-uniform magnetic field is resulted from an electromagnetic solenoid and the steady and also the transient modeling of the flow in the cooling loop from start point (stagnant ferrofluid in loop) have been carried out. The obtained results show that by applying magnetic field and also by taking advantage of temperature dependent property of the magnetic susceptibility, a flow of ferrofluid is created in the loop and by increasing the heat input (heater power) in the loop, the flow rate in the loop is increased. Moreover, the results show that by having a cold source (for rejection of produced heat) with higher constant temperature, the flow rate in the loop increases. Furthermore, the flow rate in the cooling loop is increased as the volume fraction of the nanoparticles in the base fluid increases. The mentioned cooling loop can be used in the electronic cooling systems.

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In recent years, a new approach called transmissibility based operational modal analysis has been propounded.The new approach is able to identify the modal parameters of structural systems based on the transmissibility functions, where, unlike conventional methods of operational modal analysis, there is no limiting assumption about the input excitations. In this paper, an effective form of transmissibility called power spectral density transmissibility is used in order to identify the dynamic characteristics of a 5DOF system. The dynamic system that is modeled using MATLAB/Simulink is excited by the different earthquakes such as El Centro, Northridge and Loma Prieta, and white Gaussian noise is also added to its responses with different signal to noise ratios. The modal parameters (natural frequencies and mode shapes) of the numerical model are calculated and extracted based on the singular values and vectors obtained from singular value decomposition of the power spectral density transmissibility matrix. This matrix, unlike the Fourier spectral transmissibility matrix, can be created based on the transferring outputs obtained from just one loading condition; therefore, there is no need to use the outputs of multiple loading conditions, so that it is possible to identify the dynamic characteristics with only one dynamic test. In this research, the modal identification results are evaluated through comparison with the values obtained from exact solution of the system. The comparison shows that the modal parameters extracted from the system responses with different noise levels have a good agreement with the exact values.

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Recently, a new approach called Transmissibility based Operational Modal Analysis (TOMA) has been presented in order to identify the dynamic characteristics of structural systems that determines the modal parameters of structures using the concept of transmissibility. In the TOMA approach, unlike OMA methods that use the assumption of white noise input, no limiting assumption is considered for the input excitations, and the modal parameters of structural systems are extracted based on the features of transmissibility matrix. The transmissibility methods, like other frequency domain methods, do not present very satisfactory results in identifying the damping values. Therefore, in the present paper, a new combined method called Fourier Spectral Transmissibility-Wavelet Transform (FST-WT) is proposed which, in addition to determining the natural frequencies and mode shapes of the system, also addresses the exact detection of damping values based on the features of wavelet transform. In this research, the capability of the FST-WT method in identifying and extracting the modal parameters of a 5-DOF system under free vibration is investigated using the responses obtained from the MATLAB Simulink model. For this purpose, the frequencies and mode shapes are respectively extracted from the inverse of the second singular value and the first left singular vector of transmissibility matrix, and the damping values are also determined using the single frequency signals (wavelet coefficients) obtained from wavelet transform based on the minimal Shannon entropy criterion. The comparison of the identification results shows a good agreement with the exact values.