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Investigation on the performance of a new pure torsional yielding damper
Shahram Lotfi Mahyari,Hossein Tajmir Riahi,Mahmoud Hashemi Esfahanian 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.5
A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%.
Mahdi N. Mahyari,Hasan Karimi,Hasan Naseh,Mehran Mirshams 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.10
The focus of the present study is to investigate the effectiveness of installing vortex breakers at the outlet of launch vehicle tanks on postponing vortex formation and decreasing the critical height of propellants while discharging. Analytical results in the absence of a vortex breaker show that the effects of the Weber and Reynolds numbers in the flow field can be ignored for values greater than 720 and 1.1 × 105, respectively; and critical height can be considered as a function of Froude number under aforementioned conditions. The analytical criteria are verified by two-dimensional, axis symmetrical, transient and two-phase numerical model. Eventually, some experiments are conducted to examine the effectiveness of the applied vortex breakers in reduction of the critical height of propellant. Experimental results show that a 30% decrease can be achieved in critical height by using a particular type of vortex breaker. Additionally, the carried out simulations for an existing two-stage launch vehicle indicate a 13% increase in orbital altitude, which in turn proves the considerable improvement in launch vehicle mass/energetic capabilities.
Ghasem Oskueyan,Moslem Mansour Lakouraj,Mojtaba Mahyari 한국탄소학회 2021 Carbon Letters Vol.31 No.2
In recent years, special attention of energy researchers has been paid to application of polymer–carbon dots composite in energy storage systems. In this work, for the first time, we introduced a combination of polyaniline, carbon dots, polypyrrole and graphene as high performance supercapacitor. Synergistic effect of conductive polymers combined with specific properties of graphene and carbon dots improved the electrochemical performance of supercapacitor. Carbon dots was prepared from carrot juice hydrothermally as a biomass carbon source and polyaniline–carbon dots was synthesized via in-situ polymerization. Electrochemical performance of polyaniline with different carbon dots content was investigated and nanocomposite of polyaniline with 10 wt% carbon dots was selected to mix with polypyrrole–graphene to obtain a high potential window supercapacitor. The as-prepared composite was characterized by several spectroscopic and microscopic techniques. The electrochemical properties of this electrode were studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy techniques. A polyaniline–carbon dots (10%)/polypyrrole–graphene has showed the maximum specific capacitance of 396 F g? 1. Value of specific capacity remained at 62% under the current density of 5 A g? 1.
Khoobi, Mehdi,Ramazani, Ali,Foroumadi, Alireza,Souldozi, Ali,Ś,lepokura, Katarzyna,Lis, Tadeusz,Mahyari, Amir,Shafiee, Abbas,Joo, Sang Woo WILEY‐VCH Verlag 2013 Helvetica chimica acta Vol.96 No.5
<P><B>Abstract</B></P><P>Dialkylammonium dicyano(7‐methyl‐6‐oxo‐6<I>H</I>‐dibenzo[<I>b</I>,<I>d</I>]pyran‐9‐yl)methanides <B>4a</B>–<B>4j</B> are obtained in good yields <I>via</I> a simple reaction between 3‐acetylcoumarins (=3‐acetyl‐2<I>H</I>‐1‐benzopyran‐2‐ones) <B>1</B> and malononitrile (<B>2</B>) in EtOH (<I>Table 1</I>). In this reaction, a charge‐separated zwitterionic salt is formed.</P>