farzad shafiei dizaji - Academia.edu (original) (raw)

Papers by farzad shafiei dizaji

Active and Passive Smart Structures and Integrated Systems XVI, Apr 20, 2022

Engineering Computations, 2022

PurposeThe purpose is to reduce round-off errors in numerical simulations. In the numerical simul... more PurposeThe purpose is to reduce round-off errors in numerical simulations. In the numerical simulation, different kinds of errors may be created during analysis. Round-off error is one of the sources of errors. In numerical analysis, sometimes handling numerical errors is challenging. However, by applying appropriate algorithms, these errors are manageable and can be reduced. In this study, five novel topological algorithms were proposed in setting up a structural flexibility matrix, and five different examples were used in applying the proposed algorithms. In doing so round-off errors were reduced remarkably.Design/methodology/approachFive new algorithms were proposed in order to optimize the conditioning of structural matrices. Along with decreasing the size and duration of analyses, minimizing analytical errors is a critical factor in the optimal computer analysis of skeletal structures. Appropriate matrices with a greater number of zeros (sparse), a well structure and a well con...

Neural Processing Letters, 2022

ArXiv, 2021

Five new algorithms were proposed in order to optimize well conditioning of structural matrices. ... more Five new algorithms were proposed in order to optimize well conditioning of structural matrices. Along with decreasing the size and duration of analyses, minimizing analytical errors is a critical factor in the optimal computer analysis of skeletal structures. Appropriate matrices with a greater number of zeros (sparse), a well structure, and a well condition are advantageous for this objective. As a result, a problem of optimization with various goals will be addressed. This study seeks to minimize analytical errors such as rounding errors in skeletal structural flexibility matrixes via the use of more consistent and appropriate mathematical methods. These errors become more pronounced in particular designs with ill-suited flexibility matrixes; structures with varying stiffness are a frequent example of this. Due to the usage of weak elements, the flexibility matrix has a large number of non-diagonal terms, resulting in analytical errors. In numerical analysis, the ill-condition of...

Scientia Iranica

Organic dust flames deal with a field of science in which many complicated phenomena like pyrolys... more Organic dust flames deal with a field of science in which many complicated phenomena like pyrolysis or devolatization of solid particles and combustion of volatile and char particles take place. One-dimensional flame propagation in the cloud of fuel mixture has been analyzed in which flame structure is divided into three zones: preheat zone, reaction zone and post flamezone.It is assumed that particles pyrolyze first to yield a fuel mixture consisting of gaseous and charry fuel. In this research, the effect of char content on pyrolysis process has taken into account and a novel non-linear burning velocity correlation is obtained.Our results are in a reasonable agreement with experimental data.

Combustion, Explosion, and Shock Waves, 2014

The kinetics of devolatilization of some foodstuff materials like white wheat flour, sugar, and c... more The kinetics of devolatilization of some foodstuff materials like white wheat flour, sugar, and cocoa powders are studied by using thermogravimetric analysis, in order to measure their pyrolysis rate. The mean pyrolysis rate of these materials is used as a criterion to predict their explosivity. A comparison of the mean pyrolysis rates shows that the sugar powder is the most explosive material among others. Wheat flour explosivity is very close to sugar, and cocoa powder has the least tendency to explode. Our results are completely compatible with National Fire Protection Association reports.

Journal of Earthquake Engineering, 2010

... However, in contrast to the FR frames, the PR frames were designed to utilize every beam-to-c... more ... However, in contrast to the FR frames, the PR frames were designed to utilize every beam-to-column connection in the building in resisting the lateral ... Both frames utilized A572 Grade 50 steel for the girders and the columns. ... Performance of PR moment frame buildings in UBC ...

A software has been developed to use artificial neural networks (ANNs) for the modelling of nonli... more A software has been developed to use artificial neural networks (ANNs) for the modelling of nonlinear hysteretic response of concrete gravity dams under earthquake loading when reservoir and foundation interactions are included. The neural network which is designed for a given dam has been called the "Neuro-modeller" of that dam. Pine flat dam has been studied as example problem. Firstly using an analysis software, the dam has been analyzed under different earthquakes to collect a large number of data for training the "Neuro-modeller" which has then been used for the analysis of the dam under other earthquakes. Numerical tests using other earthquakes have been done to verify the capabilities of the neuro- modeller, all of which have been successful.

Designing structures to withstand dynamic environmental hazards such as earthquakes, strong winds... more Designing structures to withstand dynamic environmental hazards such as earthquakes, strong winds, and hurricanes is of primary concern for civil engineers. In addition, recent advances in architectural forms, structural systems, and high performance materials have enabled the design of very slender and lightweight structures. These flexible structures are susceptible to be exposed to high levels of vibrations under strong winds and earthquakes, which may lead to structural damage and potential failure. Over the past two decades, shape memory alloys (SMAs) have emerged as a smart material that can be used in passive vibration control devices for energy dissipating and re-centering purposes. However, the quantity of equivalent viscous damping provided by superelastic NiTi SMA wires or bars is not sufficient to render the use of SMAs as the sole damping device implemented in a tall structure subjected to severe dynamic loadings. This study explores the performance of recently develope...

This research proposes and evaluates a superelastic memory alloy re-centering damper system for i... more This research proposes and evaluates a superelastic memory alloy re-centering damper system for improving the reaction of steel frame buildings that have been exposed to several levels of seismic threat. The planned superelastic memory alloy re-centering damper (SMARD) relies on high-performance shape memory alloy (SMA) bars for its abilities of recentering and augments its deformation potential with friction springs. To begin, this study investigates the superelastic reaction of NiTiHfPd SMAs under a variety of conditions and shows how they can be used in seismic applications. To gather experimental results, uniaxial experiments on superelastic NiTiHfPd SMAs are performed at temperatures ranging from -35 to 25 oC and loading frequencies ranging from 0.05 to 1 Hz with four distinct strain amplitudes. We explore the impact of loading rate and temperature on the superelastic properties of NiTiHfPd SMAs. The complex answer of 6-floor and 9floor steel special moment frame buildings with...

The goal of this paper is to classify objects mapped by LiDAR sensor into different classes such ... more The goal of this paper is to classify objects mapped by LiDAR sensor into different classes such as vehicles, pedestrians and bikers. Utilizing a LiDAR-based object detector and Neural Networks-based classifier, a novel real-time object detection is presented essentially with respect to aid self-driving vehicles in recognizing and classifying other objects encountered in the course of driving and proceed accordingly. We discuss our work using machine learning methods to tackle a common high-level problem found in machine learning applications for self-driving cars: the classification of pointcloud data obtained from a 3D LiDAR sensor.

ArXiv, 2020

Hysteresis phenomena have been observed in different branches of physics and engineering sciences... more Hysteresis phenomena have been observed in different branches of physics and engineering sciences. Therefore, several models have been proposed for hysteresis simulation in different fields; however, almost neither of them can be utilized universally. In this paper by inspiring of Preisach Neural Network which was inspired by the Preisach model that basically stemmed from Madelungs rules and using the learning capability of the neural networks, an adaptive universal model for hysteresis is introduced and called Extended Preisach Neural Network Model. It is comprised of input, output and, two hidden layers. The input and output layers contain linear neurons while the first hidden layer incorporates neurons called Deteriorating Stop neurons, which their activation function follows Deteriorating Stop operator. Deteriorating Stop operators can generate non-congruent hysteresis loops. The second hidden layer includes Sigmoidal neurons. Adding the second hidden layer, helps the neural net...

Journal of Engineering Mathematics

Dust flames are associated with two-phase combustion phenomena where flame characteristics depend... more Dust flames are associated with two-phase combustion phenomena where flame characteristics depend on interactions between solid and gas phases. Since organic dust particles can be effectively utilized in energy production systems, investigation of this phenomenon is essential. In this study, an analytical model is presented to simulate the combustion process of moist organic dust. The flame structure is divided into three zones: preheat zone, reaction zone, and postflame zone. To determine the effects of moisture content and volatile evaporation, the preheat zone is also divided into four subzones: first heating subzone and drying subzone, second heating subzone, and volatile evaporation subzone. The results obtained from the presented model are in reasonable agreement with experimental data for lycopodium particles. An increase in moisture content causes a reduction in burning velocity owing to moisture evaporation resistance. Consequently, the effects of some important parameters,...

ABSTRACT In this paper a model is presented in which thermal radiation is taken to account in ord... more ABSTRACT In this paper a model is presented in which thermal radiation is taken to account in order to predict initiation of flame instability. One dimensional model is used to evaluate the flame characteristics. In order to analyze the flame structure, it is divided into three zones: preheat zone, reaction zone and post-flame zone. Preheat zone is also divided into four subzones: first heating subzone and drying subzone, second heating subzone and volatile evaporation subzone. Then governing equations are written and they are made dimensionless by using space-time coordinates. Then these equations are solved. By considering thermal radiation amount of induced heat from reaction zone into the preheat zone increases. This plays a significant role in the improvement of vaporization process and burning velocity of organic dust mixture, compared with the case in which the thermal radiation factor is neglected. According to results, burning velocity and initiation of flame instability strongly depend on radiative heat transfer. By considering thermal radiation effect, obtained burning velocity has better agreement with experimental data, and consequently our model is more reliable to use.

There are several different mechanisms for creating a restoring force to return a building struct... more There are several different mechanisms for creating a restoring force to return a building structure to plumb after an earthquake. One approach is to allow structure to undergo controlled rocking at discrete locations such as column-base joint or beam-column joints. Another approach is to employ braces or seismic control devices with self-centering capabilities. Due to its inherent nonlinear elastic behavior, shape memory alloys (SMAs) have been considered to develop self-centering braces or devices. Recently, NiTiHfPd alloys that have very high strength (up to 2000 MPa), high dissipation/damping capacity, good cyclic stability and large operating temperature have been developed. This study explores the superelastic response of NiTiHfPd SMAs under various conditions and illustrates their application into seismic applications. In order to collect experimental data, uniaxial tests are conducted on superelastic NiTiHfPd SMAs in the temperature range of-35 ºC to 25 ºC, and at the loading frequencies of 0.05 Hz to 1 Hz with four different strain amplitudes. The effects of loading rate and temperature on superelastic characteristics of NiTiHfPd SMAs are examined. A numerical model that reliably simulates the response of NiTiHfPd SMAs is developed. Then, a four-story moment resisting frame with and without supplementary SMA damping elements is designed and modeled. Nonlinear response history analyses are conducted to assess the performance of NiTiHfPd SMAs in mitigating seismic response and limiting residual drifts of steel frames subjected to strong ground motions.

ABSTRACT In order to develop application of Stirling engines which is using micro-scale biomass p... more ABSTRACT In order to develop application of Stirling engines which is using micro-scale biomass particle, it is essential to study combustion of organic particles. In this article, we study flame instability to calculate effect of various prominent parameters on initiation of instability in organic dust combustion. Effective parameters on initiation of instability, which are investigated in this article, are moisture content, Damköhler number, Lewis number and Zeldovich number. To calculate effect of these parameters, a one dimensional model is used. The flame structure is divided into three zones: preheat zone, reaction zone and post-flame zone. Governing equations are also rewritten in dimensionless space-time coordinates, conseq-uently a new set of equations are appeared. By solving these newly achieved governing equations and combining them, a new expression, dispersion equation, is obtained. By solving this equation it is possible to predict effect of different parameters on initiation of instability in organic dust flame.

In addition to reducing the size and time of analyses, reduction of analytical errors is one of t... more In addition to reducing the size and time of analyses, reduction of analytical errors is one of the most important considerations in ideal analysis of skeletal structures by computer. Appropriate matrixes with more zeros (sparse), well structure, and well condition are helpful for this aim. Therefore, an optimizing problem with multiple objectives will be considered.The objective of this research is reducing the analytical errors such as rounding errors in flexibility matrixes of skeletal structures by performing more constant and proper algorithm. These errors increase in special structures with unsuitable flexibility matrixes; the structures with different stiffnesses are one of the most prevalent examples for this case.Use of weak elements leads into high non-diagonal terms in flexibility matrix, which result in analytical errors. In numerical analysis, ill-condition of a matrix is soluble by movement or substitution of the rows; then specification and implementation of these cha...