Dynamic stability

دسترسی آزاد مقاله

1 - Theoretical Investigation of Hyper-coordinate Planar Si Clusters in [SiMnHn]q (M = Cu, Ni and n = 4, 5, 6)
Maryam Ahangari-Givi Jamshid Najafpour Khadijeh Kalateh

In this study, the geometries of the [SiNinHn]q and [SiCunHn]q clusters, (n = 4,5,6 and q = 0,+1,-1) complexes have been optimized to form complexes with four, five and six planar and nonplanarsubstituents, with negative, neutral or positive atomic charge, using Density چکیده کامل

In this study, the geometries of the [SiNinHn]q and [SiCunHn]q clusters, (n = 4,5,6 and q = 0,+1,-1) complexes have been optimized to form complexes with four, five and six planar and nonplanarsubstituents, with negative, neutral or positive atomic charge, using Density FunctionalTheory (DFT) at B3LYP/6-311+G (3df, p) computational level and then their thermodynamicstability were investigated by studying the obtained smallest vibrational frequencies andbinding energy. پرونده مقاله

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2 - Analysis of Off-road Performance for a Tracked Vehicle
MohamadReza Elhami

Suspension system is one of the most important factors in provision of ride comfort and dynamic stability in any vehicle. However, the suspension system for the tracked vehicle has more particular specifications in compare with the other vehicles. Due to its continuous چکیده کامل

Suspension system is one of the most important factors in provision of ride comfort and dynamic stability in any vehicle. However, the suspension system for the tracked vehicle has more particular specifications in compare with the other vehicles. Due to its continuous track, these specifications can help the tracked vehicles possess an improved dynamic stability in off-road maneuvers compared to the vehicles with discrete tiers. In this paper, off-road performance of the tracked vehicle has been thoroughly investigated. In this regard, firstly the mathematical model of a tracked vehicle suspension system with governing dynamic equations are derived and the state-space representation are represented. After on, the off-road inputs such as hill inputs, passing over Belgian block and irregular terrain are applied to the dynamic model and the system outputs, especially body hull vertical acceleration as one of the most important criteria of stability, are reviewed. The results show that the responses are in range of acceptable overshoot and there suggest the related critical speed of the vehicle. Furthermore, for model validation the results are compared with ACMP reference model in response to the standard off-road inputs and the results are satisfactory. پرونده مقاله

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3 - Dynamic Response of Bi-Directional Functionally Graded Materials (BDFGMs) Beams Rested on Visco-Pasternak Foundation Under Periodic Axial Force
A.A Ghorbanpour Arani S Niknejad A.A Abbasian Arani

10.22034/jsm.2020.678358

Since the temperature or stress distribution in some advanced machines such as modern aerospace shuttles and craft develops in two or three directions, the need for a new type of FGMs is felt whose properties vary in two or three directions. On the other hand, dynamic b چکیده کامل

Since the temperature or stress distribution in some advanced machines such as modern aerospace shuttles and craft develops in two or three directions, the need for a new type of FGMs is felt whose properties vary in two or three directions. On the other hand, dynamic buckling behavior of structures is a complicated phenomenon which should be investigated through the response of equations of motion. In this paper, dynamic response of beams composed of bi-directional functionally graded materials (BDFGMs) rested on visco-Pasternak foundation under periodic axial force is investigated. Material properties of BDFGMs beam vary continuously in both the thickness and longitudinal directions based on the two types of analytical functions (e.g. exponential and power law distributions). Hamilton's principle is employed to derive the equations of motion of BDFGMs beam according to the Euler-Bernoulli and Timoshenko beam theories. Then, the generalized differential quadrature (GDQ) method in conjunction with the Bolotin method is used to solve the differential equations of motion under different boundary conditions. It is observed that a good agreement between the present work and the literature result. Various parametric investigations are performed for the effects of the gradient index, length-to-thickness ratio and viscoelastic foundation coefficients on the dynamic stability region of BDFGMs beam. The results show that the influence of gradient index of material properties along the thickness direction is greater than gradient index along the longitudinal direction on the dynamic stability of BDFGMs beam for both exponential and power law distributions. پرونده مقاله

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4 - Static and Dynamic Stability Analysis of Thick CNT Reinforced Beams Resting on Pasternak Foundation Under Axial and Follower Forces
M Hosseini A Ghorbanpour Arani M karamizadeh Sh Niknejad A Hosseinpour

10.22034/jsm.2019.585582.1401

In this paper, a numerical solution is presented for static and dynamic stability analysis of carbon nanotube (CNT) reinforced beams resting on Pasternak foundation. The beam is considered to be exposed to compressive axial and follower forces at its free end. The beam چکیده کامل

In this paper, a numerical solution is presented for static and dynamic stability analysis of carbon nanotube (CNT) reinforced beams resting on Pasternak foundation. The beam is considered to be exposed to compressive axial and follower forces at its free end. The beam is modeled based on the Reddy’s third order shear deformation theory and governing equations and external boundary conditions are derived using Hamilton’s principle. The set of governing equations and boundary conditions are solved numerically using differential quadrature method. Convergence and accuracy of results are confirmed and effect of various parameters on the stability region of the beam is investigated including volume fraction and distribution of CNTs, width and thickness of the beam and elastic and shear coefficients of the foundation. پرونده مقاله

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5 - Dynamic Stability Analysis of Bi-Directional Functionally Graded Beam with Various Shear Deformation Theories Under Harmonic Excitation and Thermal Environment
A Ghorbanpour Arani Sh Niknejad A Mihankhah I Safari

10.22034/jsm.2019.583270.1375

In this article, dynamic stability analysis of bi-directional functionally graded materials (BDFGMs) beam rested on visco-Pasternak foundation under harmonic excitation is studied. Also, BDFGMs beam is subjected to a transversely uniformly distributed temperature rising چکیده کامل

In this article, dynamic stability analysis of bi-directional functionally graded materials (BDFGMs) beam rested on visco-Pasternak foundation under harmonic excitation is studied. Also, BDFGMs beam is subjected to a transversely uniformly distributed temperature rising and it is assumed that the material properties to be temperature-dependent. According to the exponential and power law distributions, thermo-mechanical properties of BDFGMs beam vary continuously in both the thickness and longitudinal directions. Based on various shear deformation theories (e.g. Euler-Bernoulli, Timoshenko, third order shear deformation and sinusoidal shear deformation theories), the stability equations of BDFGMs beam is derived by applying the Hamilton's principle. The generalized differential quadrature method (GDQM) in conjunction with the Bolotin method is utilized to solve the differential stability equations under SS, SC and CC boundary conditions. To validate the present analysis, a comparison study is carried out with the results found in the literature and a good agreement is observed compared to the reported results. Finally, numerical results are presented to study the influences of the gradient index, length-to-thickness ratio, temperature rise and foundation parameters on the dynamic stability region of BDFGMs beam. The results of presented paper can be used to the optimal design and assessment of the structural failure. پرونده مقاله

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6 - Dynamic Stability of Functionally Graded Beams with Piezoelectric Layers Located on a Continuous Elastic Foundation
N Omidi M Karami Khorramabadi A Niknejad

This paper studies dynamic stability of functionally graded beams with piezoelectric layers subjected to periodic axial compressive load that is simply supported at both ends lies on a continuous elastic foundation. The Young’s modulus of beam is assumed to be gra چکیده کامل

This paper studies dynamic stability of functionally graded beams with piezoelectric layers subjected to periodic axial compressive load that is simply supported at both ends lies on a continuous elastic foundation. The Young’s modulus of beam is assumed to be graded continuously across the beam thickness. Applying the Hamilton’s principle, the governing dynamic equation is established. The effects of the constituent volume fractions, the influences of applied voltage, foundation coefficient and piezoelectric thickness on the unstable regions are presented. پرونده مقاله

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7 - تحلیل پایداری ارتعاشات عرضی ورق‌های مستطیلی شکل تحت عبور متناوب جرم‌های متحرک
احسان ترکان مصطفی پیرمرادیان محمد هاشمیان

در این پژوهش، پایداری ارتعاشات عرضی ورق مستطیلی شکل نازک با شرایط مرزی تکیه گاه های ساده که تحت عبور متناوب جرم های متحرک یکسان قرار دارد، با در نظر گرفتن تمامی ترم های اینرسی جرم های متحرک در تحلیل، مورد بررسی قرار گرفته است. در اثر عبور متناوب جرم ها از روی سطح ورق، ی چکیده کامل

در این پژوهش، پایداری ارتعاشات عرضی ورق مستطیلی شکل نازک با شرایط مرزی تکیه گاه های ساده که تحت عبور متناوب جرم های متحرک یکسان قرار دارد، با در نظر گرفتن تمامی ترم های اینرسی جرم های متحرک در تحلیل، مورد بررسی قرار گرفته است. در اثر عبور متناوب جرم ها از روی سطح ورق، یک مسأله ی پریودیک خطی حاصل می شود. از روش گالرکین، برای تبدیل معادله دیفرانسیل پاره ای ارتعاشات عرضی ورق به مجموعه ای از معادلات دیفرانسیل معمولی، استفاده گردیده است. در این تحقیق از تئوری فلاکه به عنوان یک روش تحلیلی عددی، برای بدست آوردن نواحی پایدار و ناپایدار صفحه ی پارامترها استفاده شده است. همچنین با بکارگیری روش پارامترهای فشرده به عنوان روشی نیمه تحلیلی، علاوه بر صحه گذاری بر نتایج حاصل از تئوری فلاکه، وجود پدیده ی پاسخ هم زمان برای سیستم ورق-جرم متحرک اثبات و نشان داده شده است. شبیه سازی های عددی انجام شده برای یافتن جابجایی نقطه میانی ورق، صحیح بودن نتایج تحلیلی حاصل از دو روش را به خوبی نشان می دهد. پرونده مقاله

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8 - A PSO-Based Static Synchronous Compensator Controller for Power System Stability Enhancement
Meisam Mahdavi Ali Nazari Vahid Hosseinnezhad Amin Safari

In this paper Power system stability enhancement through static synchronous compensator (STATCOM)based controller is investigated. The potential of the STATCOM supplementary controllers to enhance thedynamic stability is evaluated. The design problem of STATCOM based da چکیده کامل

In this paper Power system stability enhancement through static synchronous compensator (STATCOM)based controller is investigated. The potential of the STATCOM supplementary controllers to enhance thedynamic stability is evaluated. The design problem of STATCOM based damping controller is formulatedas an optimization problem according to the eigenvalue based objective function that is solved by a particleswarm optimization (PSO) algorithm. The controllers are tuned to simultaneously shift the lightly dampedand un-damped electro-mechanical modes of machine to a prescribed zone in the s-plane. The resultsanalysis reveals that the designed PSO based STATCOM damping controller has an excellent capability indamping the power system low frequency oscillations and enhance greatly the dynamic stability of thepower system. پرونده مقاله

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9 - FACTS Control Parameters Identification for Enhancement of Power System Stability
Ali Ahmadian Masoud Aliakbar Golkar

The aim of this paper is to investigate a novel approach for output feedback damping controller design ofSTATCOM in order to enhance the damping of power system low frequency oscillations (LFO). The design ofoutput feedback controller is considered as an optimization pr چکیده کامل

The aim of this paper is to investigate a novel approach for output feedback damping controller design ofSTATCOM in order to enhance the damping of power system low frequency oscillations (LFO). The design ofoutput feedback controller is considered as an optimization problem according with the time domain-basedobjective function which is solved by a honey bee mating optimization algorithm (HBMO) that has a strongability to find the most optimistic results. The effectiveness of the proposed controller are tested anddemonstrated through nonlinear time-domain simulation studies over a wide range of loading conditions. Thesimulation study shows that the designed controller by HBMO has a strong ability to damping of power systemlow frequency oscillations. Moreover, the system performance analysis under different operating conditionsshow that the φ based controller is superior to the C based controller. پرونده مقاله

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10 - A New Robust Control Design Based on Feedback Compensator for Sssc
علی عجمی احد چهاندیده شندی

In this paper, the modified linearized Phillips-Heffron model is utilized to theoretically analyze asingle-machine infinite-bus (SMIB) installed with SSSC. Then, the results of this analysis are used forassessing the potential of an SSSC supplementary controller to impr چکیده کامل

In this paper, the modified linearized Phillips-Heffron model is utilized to theoretically analyze asingle-machine infinite-bus (SMIB) installed with SSSC. Then, the results of this analysis are used forassessing the potential of an SSSC supplementary controller to improve the dynamic stability of apower system. This is carried out by measuring the electromechanical controllability through singularvalue decomposition (SVD) analysis. This controller is tuned for simultaneously shifting theundamped electromechanical modes to a prespecifed area in the s-plane. The issue of designing arobustly SSSC- based controller is considered and formulated as an optimization problem accordingto the eigenvalue-based multi-objective function consisting of the damping ratio of the undampedelectromechanical modes and the damping factor. Next, considering its high capability to find themost optimistic results, the Gravitational Search Algorithm (GSA) is used to solve this optimizationproblem. Wide ranges of operating conditions are considered in design process of the proposeddamping controller in order to guarantee its robustness. The effectiveness of the proposed controlleris demonstrated through eigenvalue analysis, controllability measure, nonlinear time-domainsimulation and some performance indices studies. The results show that the tuned GSA based SSSCcontroller which is designed by using the proposed multi-objective function has an outstandingcapability in damping power system low frequency oscillations, also it significantly improves thepower systems dynamic stability. پرونده مقاله

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11 - Improvement of Power System Stability with Salp ‎Swarm Algorithm and Fuzzy Type II
Payam Rokni Nakhi Salman Amirkhan Javad Safaei Kuchaksaraei Fatemeh Hamedani

The use of renewable resources in the power system is increasing day by day. Wind energy is one of the forms of renewable energy sources that has been widely available to humans due to the common nature of renewable energy with low concentration (low density). Due to th چکیده کامل

The use of renewable resources in the power system is increasing day by day. Wind energy is one of the forms of renewable energy sources that has been widely available to humans due to the common nature of renewable energy with low concentration (low density). Due to the constant changes of wind and as a result of changes in the power produced by wind farms, uncertainty in the power of the power system will become an integral part. Now, if the permeability of these resources increases, they can directly affect the dynamic stability of the system and the margin of stability of the system will change in power systems expansion, instability was often due to a lack of synchronizing torque. Issues such as the small perturbation stability of local oscillation modes and low-frequency inter-zone oscillation modes became apparent with a significant improvement in power system performance. The paper presents an optimal and coordinated power oscillation damper based on a wind turbine and power system stabilizer (PSS) to maintain the stability of power system and damp inter-area oscillations. The optimal and coordinated design of the PSS located at the generator site and the damper installed in the control section of the doubly-fed induction generator (DFIG) is defined as an optimization problem. پرونده مقاله

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12 - بررسی پایداری دینامیکی ریزشبکه‌ی اینورتری با در نظر گرفتن مجموعه‌ی بارهای دینامیکی و استاتیکی
سعید زمانیان سجاد سعدی رضا غفارپور آرام مهدویان

عملکرد مناسب و پایدار هر سیستم الکتریکی تا حد زیادی مرتبط با شناخت طراحان از ماهیت آن سیستم است؛ بنابراین لزوم ارائه ی مدلی دقیق و مبتنی بر رفتار واقعی سیستم از اهمیت فوق العاده ای برخوردار است. درزمینه‌ی ریزشبکه های اینورتری با توجه به نبود گشتاور همگام ساز کافی فرآیند چکیده کامل

عملکرد مناسب و پایدار هر سیستم الکتریکی تا حد زیادی مرتبط با شناخت طراحان از ماهیت آن سیستم است؛ بنابراین لزوم ارائه ی مدلی دقیق و مبتنی بر رفتار واقعی سیستم از اهمیت فوق العاده ای برخوردار است. درزمینه‌ی ریزشبکه های اینورتری با توجه به نبود گشتاور همگام ساز کافی فرآیند طراحی باید با حداکثر دقت انجام پذیرد. به این منظور ابتدا باید مدل دینامیکی کاملی از ریزشبکه به دست آورد. یکی از مهم ترین بخش های ریزشبکه های اینورتری بخش بار است، به این دلیل که رفتار بار در خروجی بخش تولید توان، بر تمامی ارکان سیستم تأثیرگذار است؛ بنابراین تمرکز مقاله ی حاضر بر بررسی تأثیر مدل سازی بار در فرآیند طراحی سیستم خواهد بود.ابتدا با ارائه ی معادلات اجزای ریزشبکه مدل فضای حالت آن به‌دست‌ آمده و در حضور مدل بار استاتیکی پایداری سیستم بررسی خواهد شد. سپس با قرار دادن مجموعه ی بارهای مدل دینامیکی بازیابی نمایی و استاتیکی چندجمله ای، صحت نتایج حاصل از طراحی مبتنی بر مدل استاتیکی مورد تحقیق قرار می‌گیرد. در این مسیر روش مکان ریشه ها و مشاهده ی عملکرد ریزشبکه معیار پایداری سیستم خواهد بود. به‌منظور دست یابی به اهداف پایدارسازی و بهبود عملکرد سیستم، ضرایب مشارکت متغیرهای حالت استخراج و پارامترهای تأثیرگذار مورد مطالعه قرار خواهند گرفت. پرونده مقاله

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13 - Novel Adaptive Recurrent Neural Controller based on VSC HVDC Damping Controller to Improve Power System Stability
Naser Taheri

10.30495/ijsee.2022.1963367.1216

The use of high voltage direct current (HVDC) transmission lines in power systems not only increase the capacity of electrical power transmission systems, but also strengthen the stability of the power network. In order to optimize the HVDC influences on voltage-frequen چکیده کامل

The use of high voltage direct current (HVDC) transmission lines in power systems not only increase the capacity of electrical power transmission systems, but also strengthen the stability of the power network. In order to optimize the HVDC influences on voltage-frequency stability, it is necessary to design supplementary controllers in the most optimal path between input-output signals of the whole power system. The supplementary controllers are added to the local control loop of HVDC to improve active-reactive power flow. In this paper, an optimized method based on the controllability concept is proposed for the coupling of the input-output (IO) signals of the power system equipped with voltage source converter (VSC)-based HVDC. Then, the optimal path is used for supplementary damping controller design based on a novel adaptive recurrent neural network (ARNN). The ARNN is trained online Using a new training algorithm. The simulation results, which are carried on using MATLAB software, show the effectiveness of the control strategy to improve the voltage profile and dynamic stability of the power system. پرونده مقاله

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14 - A New Method for Simplification and Reduction of State Estimation’s Computational Complexity in Stability Analysis of Power Systems
Ebadollah Amouzad Mahdiraji Seyed Mohammad Shariatmadar

The dynamic stability problem is one of the challenges that is constantly being discussed in power systems. Meanwhile, one of the most important factors which will have a direct impact on its determination is the system state estimation. To monitor the stability of the چکیده کامل

The dynamic stability problem is one of the challenges that is constantly being discussed in power systems. Meanwhile, one of the most important factors which will have a direct impact on its determination is the system state estimation. To monitor the stability of the power system, one of the determinative factors is the accuracy and speed of the state estimation equations’ input data. Therefore, in this paper, the Factorized Load Flow Method was used as a method for estimating input data of the system stability analysis. In this study, factorized load flow method was presented in full details in terms of theoretical relations and simulation results, and in order to prove its performance efficiency a comparison was made between its results with the results of the Newton-Raphson method. The conducted comparisons and investigations showed that the proposed method can determine the needed inputs for state estimation with high speed and precision. The proposed method was simulated using coding environment of MATLAB software and it was shown that this idea enjoyed an appropriate quality for reducing the computational complexity and increasing the accuracy and speed of state estimation. پرونده مقاله

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15 - Online Aggregation of Coherent Generators Based on Electrical Parameters of Synchronous Generators
Farkhondeh Jabari Heresh Seyedi Sajad Najafi Ravadanegh

This paper proposes a novel approach for coherent generators online clustering in a large power system following a wide area disturbance. An interconnected power system may become unstable due to severe contingency when it is operated close to the stability boundaries. چکیده کامل

This paper proposes a novel approach for coherent generators online clustering in a large power system following a wide area disturbance. An interconnected power system may become unstable due to severe contingency when it is operated close to the stability boundaries. Hence, the bulk power system controlled islanding is the last resort to prevent catastrophic cascading outages and wide area blackout. Meanwhile, the aggregation of the coherent generators is the most important step in large power grids intentional defensive splitting to guarantee the dynamic stability of the created islands and reduce the computational burden of the huge initial search space. The proposed method of this paper determines the coherent machines based on the electrical parameters of the synchronous generators instead of the dynamical parameters such as rotor angle or speed curves, speed participation factors, etc. The stator and excitation windings flux, excitation voltage and current have been proposed as coherency indices. The proposed coherency based aggregation has been carried out on New England 39-bus test system. The time-domain simulation results demonstrate the effectiveness and capability of the proposed method to identify the coherent machines following a severe contingency. پرونده مقاله

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16 - Coordinated Design of PSS and SSSC Damping Controller Considering Time Delays using Biogeography-based Optimization Algorithm
Javad Gholinezhad Mahmoud Ebaadian Mohammad R. Aghaerrahimi

In this paper, a consistent pattern with the optimal coordinated design of PSS and SSSC controller to improve the damping of low frequency oscillations is shown. In this design, sensing and signal transmission time delays are considered as effectiveness parameters. The چکیده کامل

In this paper, a consistent pattern with the optimal coordinated design of PSS and SSSC controller to improve the damping of low frequency oscillations is shown. In this design, sensing and signal transmission time delays are considered as effectiveness parameters. The design problem has been considered an optimization problem and biogeography-based optimization (BBO) algorithm is used for searching the optimal controller parameters. The proposed controller is employed for a single machine and two-machine power systems. The results are displayed in different load conditions to present the efficiency of the proposed method. The proposed controller provides sufficient damping for power system oscillations, in different operating conditions and disturbances. Results analysis shows that the use of biogeography-based optimization algorithm has a higher efficiency in damping oscillations of the power system, compared with the PSO algorithm, and increases the dynamic stability more. پرونده مقاله

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17 - Thermodynamic, spectral and antimicrobial activity of inclusion complexes of acridone and its oxime with β-cyclodextrin
Swapna Sankar Nayak Sunakar Panda

One of the methods to enhance bio-accessibility of drugs like Acridone and its oxime is toform inclusion complexes with β-cyclodextrin. The formation of such complexes has beenconfirmed by changes in spectral characteristics and melting point data. The aqueous phas چکیده کامل

One of the methods to enhance bio-accessibility of drugs like Acridone and its oxime is toform inclusion complexes with β-cyclodextrin. The formation of such complexes has beenconfirmed by changes in spectral characteristics and melting point data. The aqueous phasesolubility studies reveal 1:1 stoichiometry between the compound and, β-cyclodextrin. The studyof thermodynamic parameters like ΔG, ΔH, ΔS indicates the inclusion complex formation to beexothermic and spontaneous. The study of antimicrobial activity of these compounds indicatesthat the microbes like E. coli and P. aeruginosa are susceptible and the susceptibility increasessignificantly after formation of inclusion complex. پرونده مقاله

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18 - Dynamic stability analysis of functionally graded Euler-Bernoulli nanobeams under a sequence of moving nanoparticle based on nonlocal elasticity theory
Rahman Khanahmadi Mohammad Hashemian Mostafa Pirmoradian

This study investigates the dynamic stability of the Euler-Bernoulli functionally graded (FGM) nanobeam based on the nonlocal elasticity theory while considering surface effects. Nanoparticles pass over nanobeam sequentially with a constant velocity, and the nanoparticl چکیده کامل

This study investigates the dynamic stability of the Euler-Bernoulli functionally graded (FGM) nanobeam based on the nonlocal elasticity theory while considering surface effects. Nanoparticles pass over nanobeam sequentially with a constant velocity, and the nanoparticle inertia is also considered. A thermal gradient with constant temperature changes is applied to this nanobeam. The functionally graded nanobeam properties, including Young’s modulus, density, surface residual stress, and surface modulus are taken by the power law. The classical equations of motion are obtained by applying the Hamilton’s principle according to the energy method. The governing equations are extracted using nonlocal elasticity theory, and the surface effects are taken by Gurtin-Murdoch theory. The dynamic stability graphs will be presented on nanoparticle mass-velocity coordinates. This article investigated the small scale effect parameter, temperature changes, Pasternak environment shearing and elastic constants, and the volume fraction parameter in power law. The results show that increasing Pasternak foundation constants increase the functionally graded nanobeam stability, and increasing small scale parameter reduces its stability. Increasing nanobeam temperature shifts the functionally graded stability region of nanobeam towards faster nanoparticle velocity, which indicates a higher dynamic stability for the nanobeam. پرونده مقاله

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19 - The influence of various boundary conditions on dynamic stability of a beam-moving mass system
Ramin Motiei Mostafa Pirmoradian Hossein Karimpour

In this paper, the effect of different boundary conditions on dynamic stability of a beam located on a viscoelastic medium stimulated by moving masses and periodic axial force is studied. Partial differential equations governing the system are derived using Hamilton's m چکیده کامل

In this paper, the effect of different boundary conditions on dynamic stability of a beam located on a viscoelastic medium stimulated by moving masses and periodic axial force is studied. Partial differential equations governing the system are derived using Hamilton's method and based on Euler-Bernoulli beam theory. Then, equations are converted into a set of ordinary differential equation with time-varying coefficients using Galerkin method along with trigonometric shape functions. The time-varying position of moving loads causes these time-varying coefficients in the governing equations. By applying Floquet's theory to the obtained equations, the conditions of parametric resonance are analyzed for different values of mass and velocity of passing loads. The results obtained from this research show that the stiffness and viscosity of the elastic medium have positive effects on the stability of the beam under moving and fluctuating axial loads. So, with a suitable choice for these values in practical applications, it is possible to prevent unexpected vibrations of the structure. In addition, the use of fixed supports for the two ends of the beam exposed to the mentioned loadings has high reliability in the discussion of dynamic stability. پرونده مقاله

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20 - Dynamic Stability of Single Walled Carbon Nanotube Based on Nonlocal Strain Gradient Theory
فرشید آقاداودی محمد هاشمیان

This paper deals with dynamic Stability of single walled carbon nanotube. Strain gradient theory and Euler-Bernouli beam theory are implemented to investigate the dynamic stability of SWCNT embedded in an elastic medium. The equations of motion were derived by Hamilton چکیده کامل

This paper deals with dynamic Stability of single walled carbon nanotube. Strain gradient theory and Euler-Bernouli beam theory are implemented to investigate the dynamic stability of SWCNT embedded in an elastic medium. The equations of motion were derived by Hamilton principle and non-local elasticity approach. The nonlocal parameter accounts for the small-size effects when dealing with nano- size structures such as single-walled carbon nanotubes. Influences of nonlocal effects, modulus parameter of elastic medium and aspect ratio of the SWCNT on the critical buckling loads and instability regions are analyzed. It is found that the difference between instability regions predicted by local and nonlocal beam theories is significant for nanotubes. پرونده مقاله

دسترسی آزاد مقاله

21 - Dynamic Stability Analysis of a Beam Excited by a Sequence of Moving Mass Particles
مصطفی پیرمرادیان

In this paper, the dynamic stability analysis of a simply supported beam carrying a sequence of moving masses is investigated. Many applications such as motion of vehicles or trains on bridges, cranes transporting loads along their span, fluid transfer pipe systems and چکیده کامل

In this paper, the dynamic stability analysis of a simply supported beam carrying a sequence of moving masses is investigated. Many applications such as motion of vehicles or trains on bridges, cranes transporting loads along their span, fluid transfer pipe systems and the barrel of different weapons can be represented as a flexible beam carrying moving masses. The periodical traverse of masses over the beam results a linear time periodic problem. Floquet theory and Incremental Harmonic Balance (IHB) method are used to obtain the boundary of stable and unstable regions in the plane of moving mass parameters. Results of IHB method do verify the boundary curve separating the stable and unstable regions generated by Floquet theory. Also the result of numerical simulations confirms the result of the applied semi-analytical methods. پرونده مقاله

دسترسی آزاد مقاله

22 - Dynamic Stability of Nano FGM Beam Using Timoshenko Theory
شهاب صفاری محمد هاشمیان

Based on the nonlocal Timoshenko beam theory, the dynamic stability of functionally gradded (FG) nanoeams under axial load is studied in thermal environment, with considering surface effect. It is used power law distribution for FGM and the surface stress effects are co چکیده کامل

Based on the nonlocal Timoshenko beam theory, the dynamic stability of functionally gradded (FG) nanoeams under axial load is studied in thermal environment, with considering surface effect. It is used power law distribution for FGM and the surface stress effects are considered based on Gurtin-Murdoch continuum theory. Using Von Karman geometric nonlinearity, governing equations are derived based on Hamilton’s principle. The developed nonlocal models have the capability to interpret small scale effects. Winkler and Pasternak types elastic foundation are employed to represent the interaction of the nano FG beam and the surrounding elastic medium. A parametric study is conducted to investigate the influences of the static load factor, temperature change, nonlocal elastic parameter, slenderness ratio, surface effect and springs constant of the elastic medium on the dynamic stability characteristics of the FG beam, with simply-supported boundary conditions. It is found that the difference between instability regions predicted by local and nonlocal beam theories is significant for nanobeams with lower aspect ratios. Moreover, it is observed that in contrast to high temperature environments, at low temperatures, increasing the temperature change moves the origins of the instability regions to higher excitation frequencies and leads to further stability of the system at lower excitation frequencies, considering surface stress effect shifts the FG beam to higher frequency zone پرونده مقاله

فهرست مقالات Dynamic stability

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