فهرس المقالات Scale parameter

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  1 - Natural Frequency of Rotating Single-Walled Carbon Nanotubes with Considering Gyroscopic Effect
  A Fatahi-Vajari Z Azimzadeh
  10.22034/jsm.2019.1866624.1424
  This paper investigates the bending vibration of rotating single-walled carbon nanotubes (SWCNTs) based on nonlocal theory. To this end, the rotating SWCNTs system modeled as a beam with a circular cross section and the Euler-Bernoulli beam theory (EBT) is applied with أکثر

  This paper investigates the bending vibration of rotating single-walled carbon nanotubes (SWCNTs) based on nonlocal theory. To this end, the rotating SWCNTs system modeled as a beam with a circular cross section and the Euler-Bernoulli beam theory (EBT) is applied with added effects such as rotary inertia, gyroscopic effect and rotor mass unbalance. Using nonlocal theory, two coupled sixth order partial differential equations that govern the vibration of rotating SWCNTs are derived. To obtain the natural frequency and dynamic response of the nanorotor system, the equation of motion for the rotating SWCNTs are solved. It is found that there are two frequencies in the frequency spectrum. The positive rootintroduced as forward whirling mode, while the negative root represents backward whirling mode. The detailed mathematical derivations are presented while the emphasis is placed on investigating the effect of the several parameters such as, tube radius, angular velocity and small scale parameter on the vibration behavior of rotating nanotubes. It is explicitly shown that the vibration of a spinning nanotube is significantly influenced by these effects. To validate the accuracy and efficiency of this work, the results obtained herein are compared with the existing theoretical and experimental results and good agreement is observed. To the knowledge of authors, the vibration of rotating SWCNTs considering gyroscopic effect has not investigated analytically yet and then the results generated herein can be served as a benchmark for future works. تفاصيل المقالة
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  2 - Coupled Axial-Radial Vibration of Single-Walled Carbon Nanotubes Via Doublet Mechanics
  Z Azimzadeh A Fatahi-Vajari
  10.22034/jsm.2019.665256
  This paper investigates the coupled axial-radial (CAR) vibration of single-walled carbon nanotubes (SWCNTs) based on doublet mechanics (DM) with a scale parameter. Two coupled forth order partial differential equations that govern the CAR vibration of SWCNTs are derived أکثر

  This paper investigates the coupled axial-radial (CAR) vibration of single-walled carbon nanotubes (SWCNTs) based on doublet mechanics (DM) with a scale parameter. Two coupled forth order partial differential equations that govern the CAR vibration of SWCNTs are derived. It is the first time that DM is used to model the CAR vibration of SWCNTs. To obtain the natural frequency and dynamic response of the CAR vibration, the equations of motion are solved and the relation between natural frequencies and scale parameter is derived. It is found that there are two frequencies in the frequency spectrum and these CAR vibrational frequencies are complicated due to coupling between two vibration modes. The advantage of these analytical formulas is that they are explicitly dependent to scale parameter and chirality effect. The influence of changing some geometrical and mechanical parameters of SWCNT on its CAR frequencies has been investigated, too. It is shown that the chirality and scale parameter play significant role in the CAR vibration response of SWCNTs. The scale parameter decreases the higher band CAR frequency compared to the predictions of the classical continuum models. However, with increase in tube radius and length, the effect of the scale parameter on the natural frequencies decreases. The lower band CAR frequency is nearly independent to scale effect and tube diameter. The CAR frequencies of SWCNTs decrease as the length of the tube increases. This decreasing is higher for higher band CAR frequency. To show the accuracy and ability of this method, the results obtained herein are compared with the existing theoretical and experimental results and good agreement is observed. تفاصيل المقالة
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  3 - Study on the Pull-In Instability of Gold Micro-Switches Using Variable Length Scale Parameter
  M Fathalilou M Sadeghi G Rezazadeh M Jalilpour A Naghilou S Ahouighazvin
  In this paper, the size dependent behavior of the gold micro-switches has been studied. This behavior becomes noticeable for a structure when the characteristic size such as thickness or diameter is close to its internal length-scale parameter. The size dependent effect أکثر

  In this paper, the size dependent behavior of the gold micro-switches has been studied. This behavior becomes noticeable for a structure when the characteristic size such as thickness or diameter is close to its internal length-scale parameter. The size dependent effect is insignificant for the high ratio of the characteristic size to the length-scale parameter, which is the case of the silicon base micro-beams. On the other hand, in some types of micro-beams like gold base, the size dependent effect cannot be overlooked. In such cases, ignoring this behavior in modeling will lead to incorrect results. Some previous researchers have applied classic beam theory on their models and imposed a considerable hypothetical value of residual stress to match their theoretical results with the experimental ones. In this study, by obtaining the equilibrium positions or fixed points of the gold micro-beam, a considerable difference between the obtained fixed points using classic beam theory and modified couple stress theory has been shown. In addition, it has been shown that the calculated pull-in voltages using modified couple stress theory are much closer to the experimental results than those obtained by classic beam theory. Finally, it has been shown that considering a unique value of length scale parameter, especially for the smallest values of the beam thicknesses, may leads to inaccurate results and variable length scale parameter should be considered. تفاصيل المقالة
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  4 - Thermo-elastic Damping in a Capacitive Micro-beam Resonator Considering Hyperbolic Heat Conduction Model and Modified Couple Stress Theory
  M Najafi G Rezazadeh R Shabani
  In this paper, the quality factor of thermo-elastic damping in an electro-statically deflected micro-beam resonator has been investigated. The thermo-elastic coupled equations for the deflected micro-beam have been derived using variational and Hamilton principles based أکثر

  In this paper, the quality factor of thermo-elastic damping in an electro-statically deflected micro-beam resonator has been investigated. The thermo-elastic coupled equations for the deflected micro-beam have been derived using variational and Hamilton principles based on modified couple stress theory and hyperbolic heat conduction model. The thermo-elastic damping has been obtained discretizing the governing equations over spatial domain and applying complex frequency approach. The effects of the applied bias DC voltage, playing simultaneously role of an external force and softening parameter, on the quality factor have been studied. The obtained results of the modified couple stress and classic theories are compared and the effects of the material internal length-scale parameter on the differences between results of two theories have been discussed. In addition, the effects of different parameters such as beam length and ambient temperature on the quality factor have been studied. تفاصيل المقالة
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  5 - Lateral Vibrations of Single-Layered Graphene Sheets Using Doublet Mechanics
  A Fatahi-Vajari A. Imam
  This paper investigates the lateral vibration of single-layered graphene sheets based on a new theory called doublet mechanics with a length scale parameter. After a brief reviewing of doublet mechanics fundamentals, a sixth order partial differential equation that gove أکثر

  This paper investigates the lateral vibration of single-layered graphene sheets based on a new theory called doublet mechanics with a length scale parameter. After a brief reviewing of doublet mechanics fundamentals, a sixth order partial differential equation that governs the lateral vibration of single-layered graphene sheets is derived. Using doublet mechanics, the relation between natural frequency and length scale parameter is obtained in the lateral mode of vibration for single-layered graphene. It is shown that length scale parameter plays a significant role in the lateral vibration behavior of single-layered graphene sheets. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However with increasing the length of the plate, the effect of scale parameter on the natural frequency decreases. For validating the results of this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement with the latter is observed. تفاصيل المقالة
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  6 - اثرات پارامترهای بزرگ‌مقیاس حوضه آبریز بر رودخانه سیمینه‌رود
  فرشید بستان منش راد صادق پرتانی روح اله نوری
  در این پژوهش میزان اثر و همبستگی کمی پارامترهای بزرگ‌مقیاس (کاربری اراضی، تراکم جمعیت، ساختار زمین‌شناسی و فرسایش) به عنوان شاخص‌‌های جغرافیایی بزرگ‌مقیاس مورد توجه و بررسی قرار گرفته است. روند تغییرات متغیر‌های کیفی رودخانه به عنوان متغیرهای کوچک‌مقیاس و میزان تاثیر شا أکثر

  در این پژوهش میزان اثر و همبستگی کمی پارامترهای بزرگ‌مقیاس (کاربری اراضی، تراکم جمعیت، ساختار زمین‌شناسی و فرسایش) به عنوان شاخص‌‌های جغرافیایی بزرگ‌مقیاس مورد توجه و بررسی قرار گرفته است. روند تغییرات متغیر‌های کیفی رودخانه به عنوان متغیرهای کوچک‌مقیاس و میزان تاثیر شاخص‌های بزرگ‌مقیاس در این تحقیق توسط آزمون‌های آماری چند متغیره کنترل و بررسی شده است. آمار کیفی رودخانه سیمینه‌رود به عنوان مطالعه موردی مورد استفاده قرار گرفته است. داده‌های کیفی سه فصل بهار 1387، پاییز 1387، بهار 1388 شامل متغیرهای NSF و تعدادی دیگر از متغیرهای کیفی مهم درحوضه مورد تحلیل قرار گرفته است. فرایندهای نرمال‌سازی و متناظر‌سازی کمی و کیفی داده‌های جغرافیایی، داده‌های سطحی و متغیر‌های کیفی آب به عنوان اولین گام برای شروع تحلیل‌ها در نظر گرفته شد. نتایج ارتباط مستقیم و موثر پارامترهای بزرگ‌مقیاس بر متغیر‌های کیفی آب را نشان داد. متغیرهای بزرگ‌مقیاس زراعت‌دیم و زراعت‌آبی با متغیرهای کوچک‌مقیاس (PO4، TDS، TUR) و همچنین متغیرهای کاربری شهر و فرسایش سطح یک با متغیرهای BOD5 (BOD در روز پنجم)، EC، TDS ارتباط مستقیم نشان دادند. همچنین در این پژوهش ساختار زمین‌شناسی با پتانسیل خطر آلودگی متوسط (B) به طور مستقیم بر فسفر(PO4) و متغیرهای قیزیکی آب (EC،TDS ،TS ) اثر دارد. با استفاده از این نتایج می‌توان به تخمین کیفیت آب و مقایسه‌ تطبیقی متغیرهای کیفی بر مبنای شاخص‌های بزرگ‌‌مقیاس در میان چند حوضه آبریز پرداخت. استخراج شاخص‌های بزرگ‌مقیاس که بتواند به عنوان یک مقیاس در پیش‌بینی کیفیت رودخانه برای حوضه‌ها و زیر‌حوضه‌های مختلف استفاده گردد، از نتایج کاربردی این پژوهش است. تفاصيل المقالة
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  7 - A new method for determination of natural frequency in bending vibration mode of single-walled carbon nanotubes
  علیرضا فتاحی واجاری
  This paper investigates the bending vibration of single-walled carbon nanotubes based on a new theory called doublet mechanics with a scale parameter. A sixth order partial differential equation that governs the bending vibration for such nanotubes is derived. Euler-Ber أکثر

  This paper investigates the bending vibration of single-walled carbon nanotubes based on a new theory called doublet mechanics with a scale parameter. A sixth order partial differential equation that governs the bending vibration for such nanotubes is derived. Euler-Bernoulli beam model is used in this paper. Using doublet mechanics, the relation between natural frequency and scale parameter is derived in the bending vibration mode. It is proven that scale parameter plays significant role in the vibration behavior of such nanotubes in lateral direction. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However, with increasing the tube length, the scale effect on the natural frequency decreases. To validate this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement is observed. It is the first time that DM is used to model the bending vibration of carbon nanotube. تفاصيل المقالة