A Preconditioner for the LSQR algorithm

Saeed Karimi,Davod Khojasteh Salkuyeh,Faezeh Toutounian 한국전산응용수학회 2008 Journal of applied mathematics & informatics Vol.26 No.1

Iterative methods are often suitable for solving least squares problems min∥Ax − b∥₂, where A ∈ Rm×n is large and sparse. The well known LSQR algorithm is among the iterative methods for solving these problems. A good preconditioner is often needed to speedup the LSQR convergence. In this paper we present the numerical experiments of applying a well known preconditioner for the LSQR algorithm. The preconditioner is based on the ATA-orthogonalization process which furnishes an incomplete upper-lower factorization of the inverse of the normal matrix ATA. The main advantage of this preconditioner is that we apply only one of the factors as a right preconditioner for the LSQR algorithm applied to the least squares problem min∥Ax − b∥₂. The preconditioner needs only the sparse matrix-vector product operations and significantly reduces the solution time compared to the unpreconditioned iteration. Finally, some numerical experiments on test matrices from Harwell-Boeing collection are presented to show the robustness and efficiency of this preconditioner. Iterative methods are often suitable for solving least squares problems min∥Ax − b∥₂, where A ∈ Rm×n is large and sparse. The well known LSQR algorithm is among the iterative methods for solving these problems. A good preconditioner is often needed to speedup the LSQR convergence. In this paper we present the numerical experiments of applying a well known preconditioner for the LSQR algorithm. The preconditioner is based on the ATA-orthogonalization process which furnishes an incomplete upper-lower factorization of the inverse of the normal matrix ATA. The main advantage of this preconditioner is that we apply only one of the factors as a right preconditioner for the LSQR algorithm applied to the least squares problem min∥Ax − b∥₂. The preconditioner needs only the sparse matrix-vector product operations and significantly reduces the solution time compared to the unpreconditioned iteration. Finally, some numerical experiments on test matrices from Harwell-Boeing collection are presented to show the robustness and efficiency of this preconditioner.

Designing and optimizing of composite and hybrid drive shafts based on the bees algorithm

Saeed Karimi,Alireza Salamat,Sirus Javadpour 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.4

The main aim of this work is to introduce a novel approach to design and optimize of composite drive shafts based on Bees algorithm (BA). BA was performed on a specific filament wound composite drive shaft which was supposed to be installed in a cooling tower. Three different composite laminates were optimized by BA to evaluate their final mass to cost ratio. The laminates were Glass fiber reinforced epoxy (GFRE), Carbon fiber reinforced epoxy (CFRE) and a hybrid of them. The conduction of BA led to just one optimum output for GFRE and CFRE; however, a cost-mass diagram including various acceptable solutions was the end result for the hybrid drive shaft. At the end, the BA predictions of the lowest cost optimized hybrid drive shaft were compared with the results of ANSYS simulations.

A PRECONDITIONER FOR THE LSQR ALGORITHM

Karimi, Saeed,Salkuyeh, Davod Khojasteh,Toutounian, Faezeh Korean Society of Computational and Applied Mathem 2008 Journal of applied mathematics & informatics Vol.26 No.1

Iterative methods are often suitable for solving least squares problems min$||Ax-b||_2$, where A $\epsilon\;\mathbb{R}^{m{\times}n}$ is large and sparse. The well known LSQR algorithm is among the iterative methods for solving these problems. A good preconditioner is often needed to speedup the LSQR convergence. In this paper we present the numerical experiments of applying a well known preconditioner for the LSQR algorithm. The preconditioner is based on the $A^T$ A-orthogonalization process which furnishes an incomplete upper-lower factorization of the inverse of the normal matrix $A^T$ A. The main advantage of this preconditioner is that we apply only one of the factors as a right preconditioner for the LSQR algorithm applied to the least squares problem min$||Ax-b||_2$. The preconditioner needs only the sparse matrix-vector product operations and significantly reduces the solution time compared to the unpreconditioned iteration. Finally, some numerical experiments on test matrices from Harwell-Boeing collection are presented to show the robustness and efficiency of this preconditioner.

Association of White Blood Cell Counts, Leukocyte Ratios, and Serum Uric Acid with Clinical Outcome of Intravitreal Bevacizumab in Diabetic Macular Edema

Saeed Karimi,Amir Arabi,Toktam Shahraki,Sare Safi 대한안과학회 2022 Korean Journal of Ophthalmology Vol.36 No.3

Implementation of magnetic Fe3O4@ZIF-8 nanocomposite to activate sodium percarbonate for highly effective degradation of organic compound in aqueous solution

Saeed Sajjadi,Alireza Khataee,Reza Darvishi Cheshmeh Soltani,Nafiseh Bagheri,Afzal Karimi,Amirali Ebadi Fard Azar 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.68 No.-

Here, as-synthesized Fe3O4 nanoparticles were incorporated into the zeolitic imidazolate framework (ZIF-8) lattice to activate sodium percarbonate (SPC) for degradation of methylene blue (MB). The reaction rate constant of Fe3O4@ZIF-8/SPC process (0.0632 min−1) at acidic conditions (pH = 3) was more than six times that of the Fe3O4/SPC system (0.009 min−1). Decreasing the solute concentration, along with increasing SPC concentration and Fe3O4@ZIF-8 nanocomposite (NC) dosage, favored the catalytic degradation of MB. The Fe3O4@ZIF-8 NC after fifteen consecutive treatment processes showed the excellent stability with a negligible drop in the efficiency of the system (<10%). The reaction pathway was obtained via GC–MS analysis.

Analysis of the Influence of Electrical Discharge Machining Parameters on Surface Roughness of CK45

Abedi, Esmail,Daneshmand, Saeed,Karimi, Iman,Neyestanak, A. A. Lotfi The Korean Electrochemical Society 2015 Journal of electrochemical science and technology Vol.6 No.4

Electrical discharge machining is an unconventional machining process in which successive sparks applied to machine the electrically conductive materials. Any changes in electrical discharge machining parameters lead to the pieces with distinct surface roughness. The electrical discharge machining process is well applied for high hardness materials or when it is difficult to use traditional techniques to do material removing. Furthermore, this method is widely applied in industries such as aerospace, automobile, molding, and tool making. CK45 is one of the important steels in industrial and electrical discharge machining can be considered as a proper way for its machining because of high hardness of CK45 after thermal operation of the electrical discharge machining process. Optimization of surface roughness as an output parameters as well as electrical discharge machining parameters including current, voltage and frequency for electrical discharge machining of CK45 has been studied using copper tools and kerosene as the dielectric. For such a purpose and to achieve the precise statistical analysis of the experiment results design of experiment was applied while non linear regression method was chosen to assess the response of surface roughness. Then, the results were analyzed by means of ANOVA method and machining parameters with more effects on the desired outputs were determined. Finally, mathematical model obtained for surface roughness.

Viscous fluid induced vibration and instability of FG-CNT-reinforced cylindrical shells integrated with piezoelectric layers

Mahmood Rabani Bidgoli,Mohammad Saeed Karimi,Ali Ghorbanpour Arani 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.3

In this paper, viscous fluid induced nonlinear free vibration and instability analysis of a functionally graded carbon nanotube-reinforced composite (CNTRC) cylindrical shell integrated with two uniformly distributed piezoelectric layers on the top and bottom surfaces of the cylindrical shell are presented. Single-walled carbon nanotubes (SWCNTs) are selected as reinforcement and effective material properties of FG-CNTRC cylindrical shell are assumed to be graded through the thickness direction and are estimated through the rule of mixture. The elastic foundation is modeled by temperature-dependent orthotropic Pasternak medium. Considering coupling of mechanical and electrical fields, Mindlin shell theory and Hamilton's principle, the motion equations are derived. Nonlinear frequency and critical fluid velocity of sandwich structure are calculated based on differential quadrature method (DQM). The effects of different parameters such as distribution type of SWCNTs, volume fractions of SWCNTs, elastic medium and temperature gradient are discussed on the vibration and instability behavior of the sandwich structure. Results indicate that considering elastic foundation increases frequency and critical fluid velocity of system.

Simultaneous Multi‑area Economic‑Environmental Load Dispatch Modeling in Presence of Wind Turbines by MOPSO

Farzad Habibi,Farshad Khosravi,Saeed Kharrati,Shahram Karimi 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.3

Multi-objective particle swarm optimization (MOPSO) algorithm was proposed in this paper to solve the load dispatch problem among thermal and wind turbines considering the environmental factors in multi-area power systems. The unpredictable nature of wind generations has resulted in the higher complexity of the economic load dispatch (ELD) problem. As the wind farm’s generation is very difcult to predict, the extra cost during the evaluation of the ELD are taken into account as well. In the developed method, the storage and additional cost are defned in the objective function of the ELD problem, using the mean value of wind energy density. The operational constraints among multi-areas, including the transmission lines capacity limit and generation-demand balance constraints as well as the constraints of generation limit of generators are considered in the economic-environmental load dispatch (EELD) problem. The efciency of the proposed method was evaluated based on the simulation results on IEEE 118 bus test system, considering twelve thermal power plants, two wind farms and three areas.

An experimental study and new correlations of viscosity of ethylene glycol-water based nanofluid at various temperatures and different solid concentrations

Mahmood Rabani Bidgoli,Reza Kolahchi,Mohammad Saeed Karimi 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.58 No.1

This article presents an experimental study on the effect of temperature and solid volume fraction of nanoparticles on the dynamic viscosity for the CuO/EG-water nanofluid. Nanoparticles with diameter of 40 nm are used in the present study to prepare nanofluid by two-step method. A “Brookfield viscometer” has been used to measure the dynamic viscosity of nanofluid with solid volume fraction up to 2% at the temperature range between 20 to 60°C. The findings have shown that dynamic viscosity of nanofluid increases with increasing particle volume fraction and decreasing temperature. Nine different correlations are developed on experimental data point to predict the relative dynamic viscosity of nanofluid at different temperatures. To make sure of accuracy of the proposed correlations, margin of deviation is presented at the end of this study. The results show excellent agreement between experimental data and those obtained through the correlations.

Transient thermoelastic analysis of carbon/carbon composite multidisc brake using finite element method

Ghashochi-Bargh, Hadi,Goodarzi, Mohammad-Saeed,Karimi, Masoud,Salamat-Talab, Mazaher Techno-Press 2020 Advances in aircraft and spacecraft science Vol.7 No.2

In the current paper, a generalization of the results of Zhao et al. (2008) on a new design of C/C composite multidisc brake system is presented. The purpose of this paper is to study the effect of thermal sensitivity of Carbon/Carbon (C/C) composite material on the temperature distributions, deformation, and stress during braking. In this regard, a transient temperature-displacement coupled analysis for C/C composite brake discs with frictional heat generation under simulated operating conditions is performed. An axisymmetric model for brake system is used for the finite element analysis according to the theory of energy transformation and transportation. The transient temperature distributions on the friction surfaces, deformation, and stress are obtained. To check the validity, the results are corroborated with other solutions available in the literature, wherever possible. The current study could be used as a guide in the initial design of a high performance multidisc brake system.