MODAL IDENTIFICATION AND DAMAGE DETECTION USING THE DATA-DRIVEN STOCHASTIC SUBSPACE AND ARMAV METHODS

This paper presents results of modal identification and damage detection on the Steel-Quake structure using the autoregressive moving average vector and data-driven stochastic subspace methods. The methods directly work with the recorded time signals and allow to analyse linear systems where only the system output is measured, while the input is unknown but produced by uncorrelated random signals. These techniques can also be used directly to analyse data obtained from the free response of linear systems.     

Fuel characteristics of gasified coconut shell in a fluidized and a spouted bed reactor

In this study, an attempt has been made to gasify coconut shell in a fluidized and a spouted bed reactor. The effects of the gasification temperature on individual gas components, their yields and heating values for both types of beds have also been studied. The fluidized bed appears slightly superior to the spouted bed both in respect to heating value and gas yield over the temperature range studied.     

Analysis of flows driven by a torsionally–oscillatory lid in a fluid-saturated porous enclosure with thermal stable stratification

The convection flow caused by a torsionally–oscillatory lid with thermal stable stratification in an enclosure filled with porous medium is studied in this paper. The governing continuity, momentum and energy transport equations are solved by a semi-implicit projection finite element method. The Grashof number and Reynolds number for ranges 10⁴⩽Gr⩽10⁶, 10²⩽Re⩽10³ are involved in this research for Darcy number 10⁻², 10⁻⁴, 10⁻⁶ and porosity 0.4, 0.6. The results present that the permeability of porous medium deeply dominates the flow field and diminishes the flow strength as the permeability is decreased. The increase in the value of Gr/(Re²·Da) retards the stable stratification from the top surface to extend into the interior domain. The influence of oscillatory frequency is so serious in heat flux variation at some particular frequency corresponding to the resonant frequency. There is an evident resonant frequency at Da=10⁻² condition; however, this phenomenon is not clear for Da⩽10⁻⁴ at different oscillatory frequencies.     

Discretization error estimator for transcient dynamic simulations

In this paper, we demonstrate that the concept of error in constitutive relation provides an answer to the problem of error estimation in transient dynamic analysis.The construction of our error measure is based on a reformulation of the transient dynamic problem. From the solution to the discretized model, we build a set of fields, which satisfy the kinematic constraints, the initial conditions and the equilibrium equation exactly. The quality of this numerical solution depends on the extent to which the constitutive relations are satisfied.Our error estimator can be used with explicit as well as implicit time integration schemes. Here, it is first calculated on a simple single-degree-of-freedom linear dynamic problem. Its satisfactory behavior is demonstrated by different tests. Moreover, it is compared with several other indicators from the literature.Next, we explain how this error measure can be applied to problems involving both time and space. Then, preliminary one-dimensional test results for a bar fixed at one end are presented and discussed.Finally, we introduce a new error indicator which turns out to be an indicator of the error on the time integration for the initial reference problem. This indicator enables us to extract from the global error estimation the main contribution, which is relative to the time integration scheme chosen. Then, this quantity is calculated in order to evaluate the error due to the lumped mass assumption for problems solved by the explicit central difference method.     

The Modeling of CO2 Removal From a Gas Mixture by 2-amino-2-methyl-1-propanol (AMP) Using the Modified Kent Eisenberg Model

In this paper, the solubility of CO₂ in AMP solution has been measured at temperature range of 293, 303, 313, and 323 K. The amine concentration ranges studied are 2.0, 2.8, and 3.4 M. A solubility apparatus was used to measure the solubility of CO₂ in AMP solution on samples of flue gases from thermal and central power plants of Esfahan Steel Company. The modified Kent Eisenberg model was used to correlate and predict the vapor-liquid equilibria of the (CO₂ + AMP + H₂O) system. The model predicted results are in good agreement with the experimental vapor-liquid equilibrium measurements.     

A 7th–grade science project casts doubt on the standard explanation of the Gaussian plume model for seepage through soil

The Gaussian plume model is traditionally used to describe the movements of contaminants through carrier media. In two dimensions, the model is mathematically derived from a stochastic representation of sequential collisions between contaminant particles and the particles of the carrier medium. The corresponding model for three dimensions is derived by analogy. We show with a simple experimental system that this deduction by analogy is faulty.     

Kinetic study of methane hydrate formation in the presence of carbon nanostructures

The effect of synthesized nanostructures,including graphene oxide,chemically reduced graphene oxide with sodium dodecyl sulfate(SDS),chemically reduced graphene oxide with polyvinylpyrrolidone,and multi-walled carbon nanotubes,on the kinetics of methane hydrate formation was investigated in this work.The experiments were carried out at a pressure of 4.5 MPa and a temperature of 0 ℃ in a batch reactor.By adding nanostructures,the induction time decreases,and the shortest induction time appeares at certain concentrations of reduced graphene oxide with SDS and graphene oxide,that is,at a concentration of 360 ppm for reduced graphene oxide with SDS and 180 ppm for graphene oxide,with a 98% decrease in induction time compared to that in pure water.Moreover,utilization of carbon nanostructures increases the amount and the rate of methane consumed during the hydrate formation process.Utilization of multi-walled carbon nanotubes with a concentration of 90 ppm showes the highest amount of methane consumption.The amount of methane consumption increases by 173% in comparison with that in pure water.The addition of carbon nanostructures does not change the storage capacity of methane hydrate in the hydrate formation process,while the percentage of water conversion to hydrate in the presence of carbon nanotubes increases considerably,the greatest value of which occurres at a 90 ppm concentration of carbon nanotubes,that is,a 253% increase in the presence of carbon nanotubes compared to that of pure water.     

Preparation of TiO2 nanoparticles by using tripodal tetraamine ligands as complexing agent via two-step sol–gel method and their application in dye-sensitized solar cells

The effect of different tripodal tetraamine ligands was investigated on the particle size, agglomeration level, optical and photovoltaic properties of TiO₂ nanoparticle prepared via a two-step sol–gel method. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results showed that the symmetry of ligands has a crucial effect on the size and agglomeration level of the products. The optical and photovoltaic properties of the products were studied, as well. The reflectivity property of the samples due to different agglomeration sizes is shown to be very important factor in increasing conversion efficiency of DSSC.     

Fractional differential equations in electrochemistry

Electrochemistry was one of the first sciences to benefit from the fractional calculus. Electrodes may be thought of as “transducers” of chemical fluxes into electricity. In a typical electrochemical cell, chemical species, such as ions or dissolved molecules, move towards the electrodes by diffusion. Likewise, other species are liberated into solution by the electrode reaction and diffuse away from the electrode into the bulk solution. It is demonstrated in this paper that the electric current is linearly related to the temporal semiderivative of the concentrations, at the electrode, of the species involved in the electrochemical reaction. More usefully, the semiintegral of the current provides immediate access information about concentrations.     

Selecting critical clinical features for heart diseases diagnosis with a real-coded genetic algorithm

In clinic, normally a lot of diagnostic features are recorded from a patient for a certain disease. It will be beneficial for the prompt and correct diagnosis of the disease by selecting the important and relevant features and discarding those irrelevant and redundant ones. In this paper, a real-coded genetic algorithm (GA)-based system is proposed to select the critical clinical features essential to the heart diseases diagnosis. The heart disease database used in this study includes 352 cases, and 40 diagnostic features were recorded for each case. Using the proposed genetic algorithm, 24 critical features have been identified, and their corresponding diagnosis weights for each heart disease of interest have been determined. The critical diagnostic features and their clinic meanings are in sound agreement with those used by the physicians in making their clinic decisions.