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دسترسی آزاد مقاله
1 - A New Numerical Study Method of Thermal Stress Distribution and Tortuosity Effectiveness in an Anode Porous Electrode for a Planar Solid Oxide Fuel Cell
I.E Fahs M GhasemiA fuel cell is an electro-chemical tool capable of converting chemical energy into electricity. High operating temperature of solid oxide fuel cell, between 700oC to 1000oC, causes thermal stress. Thermal stress causes gas escape, structure variability and cease operati چکیده کاملA fuel cell is an electro-chemical tool capable of converting chemical energy into electricity. High operating temperature of solid oxide fuel cell, between 700oC to 1000oC, causes thermal stress. Thermal stress causes gas escape, structure variability and cease operation of the SOFC before its lifetime.The purpose of the current paper is to present a method that predicts the thermal stress distribution in an anisotropic porous anode of planar SOFC. The coupled governing non-linear differential equations, heat transfer, fluid flow, mass transfer, mass continuity, and momentum are solved numerically. A code based oncomputational fluid dynamics (CFD), computational structural mechanics and finite element method (FEM) is developed and utilized. The code uses the generated data inside the porous anode in order to detect the temperature and the stress distribution using the Darcy’s law and the Navier-Stokes equations. The numerical results used to govern the areas of high values of stresses were higher than the yield strength of materials. The results show that a highest thermal stress occurs at lower corners of the anode. The concentrated temperature occurs at the middle of the electrolyte-anode whereas the maximum pressure occurs at the middle of the upper and lower section of the anode. پرونده مقاله -
دسترسی آزاد مقاله
2 - Thermoelastic Behaviour in a Multilayer Composite Hollow Sphere with Heat Source
S.P Pawar J.J Bikram G.D KedarThis paper deals with the mathematical approach to discuss the radially varying transient temperature distribution in a multilayer composite hollow sphere subjected to the time independent volumetric generation of heat in each layer. Initially the layers are at arbitrar چکیده کاملThis paper deals with the mathematical approach to discuss the radially varying transient temperature distribution in a multilayer composite hollow sphere subjected to the time independent volumetric generation of heat in each layer. Initially the layers are at arbitrary temperature and the analysis assumes all the layers of the body are thermally isotropic and having a perfect thermal contact. It is novel to obtain the exact solution for temperature field by the separation of variables by splitting the problem into two parts homogeneous transient and non-homogeneous steady state. The set of equations obtained are solved by using the rigorous applications of analytic techniques with the help of eigen value expansion method. The thermoelastic response is studied in the context of uncoupled Thermoelasticity. The results obtained pointed out that the magnitude and distribution of the temperature and thermal stresses are greatly influenced by the layered heat generation parameter. The accuracy and feasibility of the proposed model is demonstrated by an example of three layered hollow sphere of Aluminium, Copper and Iron subjected to given conditions. The results presented in this article could be found hardly in an open literature despite of extensive search. پرونده مقاله -
دسترسی آزاد مقاله
3 - Thermoelastic Analysis of Annular Sector Plate Under Restricted Boundaries Amidst Elastic Reaction
A Mahakalkar V VargheseAn analytical framework is developed for the thermoelastic analysis of annular sector plate whose boundaries are subjected to elastic reactions. The exact expression for transient heat conduction with internal heat sources is obtained using a classical method. The fourt چکیده کاملAn analytical framework is developed for the thermoelastic analysis of annular sector plate whose boundaries are subjected to elastic reactions. The exact expression for transient heat conduction with internal heat sources is obtained using a classical method. The fourth-order differential equation for the thermally induced deflection is obtained by developing a new integral transformation in accordance with the simply supported elastic supports that are subjected to elastic reactions. Here it is supposed that the movement of the boundaries is limited by an elastic reaction, that is, (a) shearing stress is proportional to the displacement, and (b) the reaction moment is proportional to the rate of change of displacement with respect to the radius. Finally, the maximum thermal stresses distributed linearly over the thickness of the plate are obtained in terms of resultant bending momentum per unit width. The calculation is obtained for the steel, aluminium and copper material plates using Bessel's function can be expressed in infinite series form, and the results are depicted using a few graphs. پرونده مقاله -
دسترسی آزاد مقاله
4 - Effect of Thermosensitivity on Heat Conduction and Stresses of a Multilayered Annular Disk
G.D. Kedar V.B. Srinivas V.R ManthenaThis paper deals with the analysis of temperature, deflection and thermal stresses of a multilayered annular disk. The thermo-mechanical properties of the disk are taken to be temperature dependent. Using Kirchhoff’s variable transformation, the non-linear heat co چکیده کاملThis paper deals with the analysis of temperature, deflection and thermal stresses of a multilayered annular disk. The thermo-mechanical properties of the disk are taken to be temperature dependent. Using Kirchhoff’s variable transformation, the non-linear heat conduction equation is reduced to a linear form. Finite integral transform, Fourier series and Fourier transform techniques are used to solve the heat conduction equation and the desired solution is obtained in series form. Deflection, thermally induced resultant moments and the corresponding thermal stresses are determined. Numerical analysis is carried out for a three layered annular disk and the results are depicted graphically. Thermosensitivity plays a vital role in the thermal profile of the multilayered disk. In the temperature dependent case, the radial stress suddenly becomes compressive in the middle region, whereas it is tensile throughout all the regions in the temperature independent case. Due to the inhomogeneous thermal conductivity considered in the form of exponential function, the temperature and the corresponding thermoelastic quantities shows the lag along radial direction. پرونده مقاله -
دسترسی آزاد مقاله
5 - Thermal Stress Analysis of a Composite Cylinder Reinforced with FG SWCNTs
A Ghorbanpour Arani S Amir V Sadooghi M MohammadimehrThermal stress analysis of a thick-walled cylinder reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) is considered in radial direction. Thick-walled cylinder is subjected to a thermal field. Two layouts of variations in the volume fraction چکیده کاملThermal stress analysis of a thick-walled cylinder reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) is considered in radial direction. Thick-walled cylinder is subjected to a thermal field. Two layouts of variations in the volume fraction of SWCNTs were considered in the composite cylinder along the radius from inner to outer surface, where their names are incrementally decreasing (Inc Dec) and incrementally increasing (Inc Inc). Micromechanical models based on the Mori-Tanaka is used to define effective macroscopic properties of the nano composite shell. Using equations of motion, stress-strain and their corresponding constitutive correlations of a polystyrene vessel, a second order ordinary differential equation was proposed based on the radial displacement. The higher order governing equation was solved in order to obtain the distribution of displacement and thermal stresses in radial, circumferential and axial directions. The results indicate that FG distributions of SWCNTs have significant effect on thermal stresses and displacements in axial, radial and circumferential directions, so that in Inc Inc layout, the radial and circumferential stresses are lower than of other FG structures. پرونده مقاله -
دسترسی آزاد مقاله
6 - Mathematical Modeling of Thermoelastic State of a Thick Hollow Cylinder with Nonhomogeneous Material Properties
V. R Manthena N.K Lamba G.D KedarThe object of the present paper is to study heat conduction and thermal stresses in a hollow cylinder with nonhomogeneous material properties. The cylinder is subjected to sectional heating at the curved surface. All the material properties except for Poisson’s ra چکیده کاملThe object of the present paper is to study heat conduction and thermal stresses in a hollow cylinder with nonhomogeneous material properties. The cylinder is subjected to sectional heating at the curved surface. All the material properties except for Poisson’s ratio and density are assumed to be given by a simple power law in the axial direction. A solution of the two-dimensional heat conduction equation is obtained in the transient state. The solutions are obtained in the form of Bessel’s and trigonometric functions. For theoretical treatment, all the physical and mechanical quantities are taken as dimensional, whereas we have considered non-dimensional parameters, for numerical analysis. The influence of inhomogeneity on the thermal and mechanical behaviour is examined. The transient state temperature field and its associated thermal stresses are discussed for a mixture of copper and tin metals in the ratio 70:30 respectively. Numerical calculations are carried out for both homogeneous and nonhomogeneous cylinders and are represented graphically. پرونده مقاله -
دسترسی آزاد مقاله
7 - Stress Analysis in Thermosensitive Elliptical Plate with Simply Supported Edge and Impulsive Thermal Load
V Varghese P Bhad L KhalsaThe paper concerns the thermoelastic problems in a thermosensitive elliptical plate subjected to the activity of a heat source which changes its place on the plate surface with time. The solution of conductivity equation and the corresponding initial and boundary condit چکیده کاملThe paper concerns the thermoelastic problems in a thermosensitive elliptical plate subjected to the activity of a heat source which changes its place on the plate surface with time. The solution of conductivity equation and the corresponding initial and boundary conditions is obtained by employing a new integral transform technique. In addition, the intensities of bending moments, resultant force, etc. are formulated involving the Mathieu and modified functions and their derivatives. The analytical solution for the thermal stress components is obtained in terms of resultant forces and resultant moments. پرونده مقاله -
دسترسی آزاد مقاله
8 - One-Dimensional Transient Thermal and Mechanical Stresses in FGM Hollow Cylinder with Piezoelectric Layers
S.M Mousavi M Jabbari M.A KianiIn this paper, an analytical method is developed to obtain the solution for the one dimensional transient thermal and mechanical stresses in a hollow cylinder made of functionally graded material (FGM) and piezoelectric layers. The FGM properties are assumed to depend o چکیده کاملIn this paper, an analytical method is developed to obtain the solution for the one dimensional transient thermal and mechanical stresses in a hollow cylinder made of functionally graded material (FGM) and piezoelectric layers. The FGM properties are assumed to depend on the variable r and they are expressed as power functions of r but the Poisson’s ratio is assumed to be constant. Transient temperature distribution, as a function of radial direction and time with general thermal boundary conditions on the inside and outside surfaces, is analytically obtained for different layers, using the method of separation of variables and generalized Bessel function. A direct method is used to solve the Navier equations, using the Euler equation and complex Fourier series. This method of solution does not have the limitations of the potential function or numerical methods as to handle more general types of the mechanical and thermal boundary conditions. پرونده مقاله -
دسترسی آزاد مقاله
9 - Estimation of Thermoelastic State of a Thermally Sensitive Functionally Graded Thick Hollow Cylinder: A Mathematical Model
V. K Manthena N.K Lamba G.D KedarThe object of the present paper is to study temperature distribution and thermal stresses of a functionally graded thick hollow cylinder with temperature dependent material properties. All the material properties except Poisson’s ratio are assumed to be dependent چکیده کاملThe object of the present paper is to study temperature distribution and thermal stresses of a functionally graded thick hollow cylinder with temperature dependent material properties. All the material properties except Poisson’s ratio are assumed to be dependent on temperature. The nonlinear heat conduction with temperature dependent thermal conductivity and specific heat capacity is reduced to linear form by applying Kirchhoff’s variable transformation. Solution for the two dimensional heat conduction equation with internal heat source is obtained in the transient state. The influence of thermo-sensitivity on the thermal and mechanical behavior is examined. For theoretical treatment all physical and mechanical quantities are taken as dimensional, whereas for numerical computations we have considered non-dimensional parameters. A mathematical model is constructed for both homogeneous and nonhomogeneous case. Numerical computations are carried out for ceramic-metal-based functionally graded material (FGM), in which alumina is selected as ceramic and nickel as metal. The results are illustrated graphically. پرونده مقاله -
دسترسی آزاد مقاله
10 - Analysis of Motion of Micro-Gripper Exposed to the Electric Field and Thermal Stresses for Using in Micro-Robotics
shahram abbaspour ghiyam eslamiMicro system technology is a relatively new scientific research that deals with the development and study of properties of materials in micro dimensions. Micro-grippers are widely used in switching, positioning, and assembling micron sized components in micro-robotics. چکیده کاملMicro system technology is a relatively new scientific research that deals with the development and study of properties of materials in micro dimensions. Micro-grippers are widely used in switching, positioning, and assembling micron sized components in micro-robotics. In this study, the static and dynamic behavior of visco-elastic Micro-Tweezers under the thermal and electrostatic field is studied numerically. In order to consider more realistic assumptions, the visco-elastic behavior is investigated and thermal effects are simulated by considering both linear and nonlinear models. Considering Euler-Bernoulli beam theory, governing differential equation of motion are derived. Finally, the effect of different parameters such as the parameter of visco-elastic parameters, the effects of temperature and intensity of the electrostatic field on the dynamic and static characteristics of the Micro-Tweezers have been investigated. The results show that visco-elastic behavior has a significant effect on the dynamic behavior of Micro-Tweezers, and with its increase, the damping of the system increases and the amplitude of the Micro-Tweezers oscillations decreases. The system's damping increases from 0.01 to 0.08, the maximum amplitude of Micro-Tweezers decreases from 0.9 to 0.66. پرونده مقاله -
دسترسی آزاد مقاله
11 - اثر حرارت بر رفتار پوشش مرکب پلهای بزرگ راه آهن ( مطالعه موردی: پل پروژه قطعه دوم راه آهن میانه- بستان آباد- تبریز)
علیرضا سعیدی احمد ملکیپل های بزرگ مسیر جدید راه آهن میانه - تبریز در منطقه ای با خطر نسبی زلزله بسیار زیاد و تپه ماهورهای متشکل از خاک های سست مستعد لغزش واقع شده است. با توجه به شرایط خاص کاربری، شناسایی عوامل مخرب و جلوگیری از خرابی پیشرونده به سادگی امکان ندارد. با توجه به سیکل تغییرات دم چکیده کاملپل های بزرگ مسیر جدید راه آهن میانه - تبریز در منطقه ای با خطر نسبی زلزله بسیار زیاد و تپه ماهورهای متشکل از خاک های سست مستعد لغزش واقع شده است. با توجه به شرایط خاص کاربری، شناسایی عوامل مخرب و جلوگیری از خرابی پیشرونده به سادگی امکان ندارد. با توجه به سیکل تغییرات دمایی روزانه و فصلی، تحمیل صدمات جبرانناپذیر در اثر ایجاد موانع انبساط حرارتی مابین کوله و عرشه به طور اتفاقی یا عمدی در سازه محتمل است. بنابراین جهت شناسایی رفتار حرارتی پل و جلوگیری از عواملی مخرب احتمالی، پل با نرم افزارCSI Bridge مورد بررسی قرار گرفته و نتایج حاصل از اعمال تغییرات حرارت تحلیل شده است. نتایج نشان می دهد که با افزایش دما به صورت تدریجی، تنش، نیروهای محوری و برشی و لنگر تا 60 درجه سانتیگراد به طور یکنواخت افزایش می یابد. با رسیدن دما به مرز 65 درجه سانتیگراد تنش ناشی از تغییرات حرارت به مقدار 17.7 درصد افزایش می یابد. با اعمال دمای 800 درجه سانتیگراد در دهانه میانی ضمن تغییرات شدید نیروهای محوری و برشی به مقدار 9833 تن و لنگر خمشی به مقدار 2074 تن بر متر و مقدار جابجایی 24.34 سانتی متر محاسبه گردید. پرونده مقاله -
دسترسی آزاد مقاله
12 - Experimental Study on Effective Parameters for Thermal Cutting of Glass Sheets
سید محمدرضا خلیلیThe new non-conventional cutting process by the use of thermal shock is a convenient procedure for cutting the brittle materials such as glasses and ceramics. This method is based on the application of localized thermal shock to brittle materials by the use of hot air j چکیده کاملThe new non-conventional cutting process by the use of thermal shock is a convenient procedure for cutting the brittle materials such as glasses and ceramics. This method is based on the application of localized thermal shock to brittle materials by the use of hot air jet, which induces thermal stresses at the tip of an existed pre-crack. Due to the thermo-elastic behavior of materials, the pre-crack is propagated in the material. By the use of this process, the glass and brittle materials can be cut to any shape without the use of cutting tools. In this paper, based on the presented phenomena and the induced time-dependent thermal shock, the tip of an existed pre-crack in a glass sheet is heated by a moveable point heat source. The effect of parameters such as cutting speed, nozzle orifice diameter, cutting temperature, macroscopic quality of cutting surface on cutting the brittle materials were studied. The results indicated that as far as a pre-defined distance is developed between the moveable heating point and the tip of the existed pre-crack, the crack is propagated in stable manner and under complete control, and hence better cutting surface quality. Based on this distance, the effective cutting parameters are investigated and set to get better cutting process. پرونده مقاله -
دسترسی آزاد مقاله
13 - اثر تنش سرما بر محتوای کلروفیل، فلورسانس کلروفیل و فعالیت آنزیمهای اکسیداتیو سه رقم جو (Hordeum vulgare L.)
علی بشیرزاده خانلار عبدالهاف زمان محمودوفسرما یکی از مهمترین تنشهای غیرزیستی است که رشد و عملکرد محصول را در سراسر جهان محدود میکند. به منظور بررسی چگونگی سازگاری گیاهچههای 20 روزه جو با تنش سرمای کوتاه مدت، مطالعه حاضر بهصورت فاکتوریل با چهار تکرار در آزمایشگاه بذر مؤسسه تحقیقات اصلاح و تهیه نهال و بذر ک چکیده کاملسرما یکی از مهمترین تنشهای غیرزیستی است که رشد و عملکرد محصول را در سراسر جهان محدود میکند. به منظور بررسی چگونگی سازگاری گیاهچههای 20 روزه جو با تنش سرمای کوتاه مدت، مطالعه حاضر بهصورت فاکتوریل با چهار تکرار در آزمایشگاه بذر مؤسسه تحقیقات اصلاح و تهیه نهال و بذر کرج، انجام شد. فاکتورهای آزمایش شامل ارقام جو (رقم کارون حساس به سرما، فصیح نیمه متحمل به سرما و ماکویی متحمل به سرما) و سه سطح تنش سرما شامل 4، 8 و 22 (شاهد) سلسیوس، بود که تیمارهای دمایی بهمدت 48 ساعت بر گیاهچههای جو اعمال شد. نتایج تجزیه واریانس نشان داد که برهمکنش سرما و رقم بر روی اغلب صفات اندازهگیری شده در این مطالعه معنیدار بود. مقایسه میانگین نیز نشان داد بیشترین مقدار F0 در رقم کارون و فصیح در 8 درجه و در رقم ماکویی در 4 درجه مشاهده شد در حالیکه در هر سه رقم با کاهش دما مقدار Fv و محتوای کلروفیل a کاهش یافت. نسبت Fm/Fv در رقم ماکویی و فصیح با کاهش دما کاهش یافت اما در رقم کارون تغییر معنیداری در این نسبت مشاهده نشد. علاوه بر این با کاهش دما میزان مالوندیآلدهید و پراکسید هیدروژن و نیز فعالیت آنزیم پراکسیداز در هر سه رقم بهویژه رقم کارون افزایش یافت اما فعالیت آنزیم کاتالاز و سوپراکسید دیسموتاز تحت تاثیر رقم قرار نگرفت و بیشترین فعالیت کاتالاز و پراکسیداز به ترتیب در دمای 8 و 4 درجه بهدست آمد. نتایج بهدست آمده نشان داد ارقام متحملتر نسبت به رقم حساس (کارون) در دماهای پایین با محدود کردن تولید ترکیباتی مانند H2O2 و مالوندیآلدهید ، محتوای کلروفیل و کارایی فتوسنتزی بالاتری داشته که احتمالاً منعکس کننده سازگاری بیشتر به سرما است. پرونده مقاله
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