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RISS 인기검색어
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- 저자 : Keivani, Afram (검색결과 8 건)
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Forced vibration analysis of a dam-reservoir interaction problem in frequency domain
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2014 Coupled systems mechanics Vol.3 No.4
In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.
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A closed-form solution for a fluid-structure system: shear beam-compressible fluid
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2013 Coupled systems mechanics Vol.2 No.2
A closed-form solution for a fluid-structure system is presented in this article. The closed-form is used to evaluate the finite element method results through a numeric example with consideration of high frequencies of excitation. In the example, the structure is modeled as a cantilever beam with rectangular cross-section including only shear deformation and the reservoir is assumed semi-infinite rectangular filled with compressible fluid. It is observed that finite element results deviate from the closed-form in relatively higher frequencies which is the case for the near field earthquakes.
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Forced vibration analysis of a dam-reservoir interaction problem in frequency domain
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2013 Interaction and multiscale mechanics Vol.6 No.4
In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.
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Shamshirband, Shahaboddin,Keivani, Afram,Mohammadi, Kasra,Lee, Malrey,Hamid, Siti Hafizah Abd,Petkovic, Dalibor Elsevier 2016 RENEWABLE & SUSTAINABLE ENERGY REVIEWS Vol.59 No.-
<P><B>Abstract</B></P> <P>The prime aim of this study is appraising the suitability of adaptive neuro-fuzzy inference framework (ANFIS) to compute the monthly wind power density. On this account, the extracted wind power from Weibull functions are utilized for training and testing the developed ANFIS model. The proficiency of the ANFIS model is certified by providing thorough statistical comparisons with artificial neural network (ANN) and genetic programming (GP) techniques. The computed wind power by all models are compared with those obtained using measured data. The study results clearly indicate that the proposed ANFIS model enjoys high capability and reliability to estimate wind power density so that it presents high superiority over the developed ANN and GP models. Based upon relative percentage error (RPE) values, all estimated wind power values via ANFIS model are within the acceptable range of −10% to 10%. Additionally, relative root mean square error (RRMSE) analysis shows that ANFIS model has an excellent performance for estimation of wind power density.</P>
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Max<sub>R</sub>(M) AND ZARISKI TOPOLOGY
ANSARI-TOROGHY, H.,KEIVANI, S.,OVLYAEE-SARMAZDEH, R. 호남수학회 2006 호남수학학술지 Vol.28 No.3
Let R be a commutative ring and let M be an R-module. Let X = $Spec_R(M)$ be the prime spectrum of M with Zariski topology. In this paper, by using the topological properties of X, we will obtain some conditions under which $Max_R(M)=Spec_R(M)$.
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Mahmoud Abbasi,Behrouz Bagheri,Rasoul Keivani 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2
Friction stir welding (FSW) as an efficient solid state joining process has numerous applications in industries. Temperature distributionanalysis through simulation not only brings the possibility to characterize the microstructure of different zones, but also enables one tosave cost and energy as optimum welding variables are obtained with less concern. In the present study, the temperature distributionduring the friction stir welding (FSW) process of AA6061-T6 was evaluated using finite element method (FEM). Since experimentalmeasurements cannot be readily made in the weld region, it is difcult to understand physics in the stir zone of the welds without simulation. Abaqus software was applied to model the parts and simulate the process of welding, while Johnson-Cook law utilized to evaluatethe effect of strain rate and generated heat. FE-results were verified by experimental results. The comparisons revealed a good compatibilitybetween the results. The effect of probe shape on temperature distribution was also studied. It was found that spherical pins result inthe highest temperatures at workpieces with respect to cylindrical and tapered pins. Additionally, it was concluded that more heat is generatedin workpieces as pin angle increases.
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Somayeh Sadeghi,Maryam Nasirian,Elaheh Keivany,Peiman Nasri,Maryam Sadat Mirenayat 대한혈액학회 2021 Blood Research Vol.56 No.4
Background Since the emergence of coronavirus disease 2019 (COVID-19), various clinical manifestations ranging from asymptomatic to severe, life-threatening courses have been presented. It is well known that COVID-19 patients are at an increased risk of pulmonary thromboembolism (PTE) development; however, the associated demographic, medical, and clinical factors for developing PTE remain unknown. The current study aimed to assess the characteristics of patients with PTE. Methods This case-control study was derived from an ongoing population-based investigation of hospitalized patients with COVID-19 pneumonia. The case group included 99 patients with PTE confirmed by computed tomography pulmonary angiography (CTPA), and the controls (N=132) were age-matched patients selected from the PTE-suspected patients with a negative CTPA. The demographic, medical, and clinical characteristics of the study population were entered into the study checklist and compared. A logistic regression test was used to determine the factors associated with PTE development. Results Among the 13,099 admitted patients, 690 (5.26%) were suspected of having PTE according to their clinical manifestations. CTPA was performed for suspected cases, and PTE was confirmed in 132 patients (19.13%). Logistic regression assessments revealed that male gender (OR, 2.39; 95%CI, 1.38‒4.13), decreased oxygen saturation (OR, 2.33; 95%CI, 1.27‒4.26), and lower hemoglobin (OR, 0.83, 0.95), and albumin (OR, 0.31; 95%CI, 0.18‒0.53) levels were associated with PTE development. Conclusion PTE was confirmed in one-fifth of suspected patients who underwent CTPA imaging. Male sex, decreased oxygen saturation, and lower levels of hemoglobin and albumin were independent predictors of PTE in patients with COVID-19 pneumonia.
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