One of the common methods of structural damage detections and identification of location and severity of the damage in structures is investigation of changes in modal parameters before and after damage. These methods which are mostly based on optimization techniques use More
One of the common methods of structural damage detections and identification of location and severity of the damage in structures is investigation of changes in modal parameters before and after damage. These methods which are mostly based on optimization techniques use an objective function based on natural frequencies and mode shapes. This paper reviews previous researches in damage detection techniques based on modal parameters and common objective functions used in the optimization stage in the damage detection process. To this end, damage detection methods based on natural frequency, mode shape, curvature mode shape and both of mode shape and natural frequency are reviewed. In the following, due to high importance of objective function in the damage detection process, objective functions based on modal assurance criterion, flexibility matrix and natural frequency and mode shapes are compared
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One of the common methods of structural damage detections in structures is investigation of changes in modal parameters before and after damage. These methods which are mostly based on optimization techniques use an objective function based on natural frequencies and mo More
One of the common methods of structural damage detections in structures is investigation of changes in modal parameters before and after damage. These methods which are mostly based on optimization techniques use an objective function based on natural frequencies and mode shapes. Success in detection of location and severity of the damage in these methods is severely a function of sensitivity of the objective function to the damage. As the objective function itself is function of natural frequencies or mode shapes or both of them, it is necessary that the sensitivity of modal parameters to damage location and severity is investigated. To this end, a cantilever beam is simulated numerically in this paper. Changing the location and severity of the damage, the effect of them on natural frequencies and mode shapes is studied. The results show that by increasing damage severity, natural frequencies decrease. On the other hand, moving the crack from the fix end to the free end of the cantilever beam, changes in the natural frequencies does not obey a specific pattern and for a crack of constant severity, decrement of natural frequencies from intact beam depends on the location of crack on the beam. Also it is observed that as the cracks approaches to the fix end, decrement of natural frequencies increased. The results show that the sensitivity of mode shapes to crack is low in beam. Therefore it is recommended to use natural frequencies or both natural frequencies and mode shapes together in objective functions.
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Choosing appropriate objective function is necessary for detection of damage location and severity. To this end, objective functions based on modal parameters such as mode shapes and natural frequencies are combined with other objective functions capable to detect damag More
Choosing appropriate objective function is necessary for detection of damage location and severity. To this end, objective functions based on modal parameters such as mode shapes and natural frequencies are combined with other objective functions capable to detect damage location. Then the location and severity of damage is obtained using optimization techniques. In this paper a cantilever beam is simulated numerically in MATLAB software using finite element method and then single and multi-objective genetic algorithms with different objective functions based on modal parameters are used to detect damage location and severity. To compare different objective functions, the effect of coordinate incompleteness, frequency range of interest and also environmental noise on the obtained results is studied.
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The Adomian decomposition method is employed in this paper to investigate the free vibration of cable consisting of two uniform sections. Each section is considered a substructure which can be modeled using ADM. applying boundary and continuity conditions, the dimension More
The Adomian decomposition method is employed in this paper to investigate the free vibration of cable consisting of two uniform sections. Each section is considered a substructure which can be modeled using ADM. applying boundary and continuity conditions, the dimensionless natural frequencies and corresponding mode shapes can be easily obtained simultaneously. The computed results for different boundary conditions are presented. The computed results agree well with those analytical and numerical results given in the literature. These results indicate that the present analysis is accurate and provides an efficient, reliable and systematic procedure which is simple and more straightforward than the other modal analysis. Also the effect of amount of mass and spring stiffness at the boundary on variation of natural frequencies is obtained and an effective procedure is suggested for encountering these kinds of problems.
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Thin wall shell structure has low weight and high resistance. The load capacity, buckling behavior and post buckling behavior of steel tanks thin wall, is very sensitive to geometric imperfections. Due to the small wall thickness of the shell structures enabling t More
Thin wall shell structure has low weight and high resistance. The load capacity, buckling behavior and post buckling behavior of steel tanks thin wall, is very sensitive to geometric imperfections. Due to the small wall thickness of the shell structures enabling the creation of any deformation and there is a disturbance on the surface of the wall. Considering the types of errors occurred when build or assembled these structures, are not built these structure, ideally. This imperfections may be in the process of rolling, removable panels, installation or welding arise. Incomplete reports about the negative impact of the effect of welding on the axial bearing capacity. Comprehensive research on the effects of imperfection of initial geometrical shape on the steel tank vibration modes, and its effect on the bearing capacity steel storage tanks that considerable research It's not done. In this research, the actual behavior of cylindrical shells with initial geometric imperfections on mode shapes steel tanks in the pre-buckling and post-buckling. And the effect of initial geometric imperfections on steel tanks slashing been paid. Using finite element software, ABAQUS, and verification of the results of the analysis and nonlinear analysis with experimental results. Been paid. Imperfect geometric shape has changed mods. The effect of these changes on slashing are very small.
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برای شناسایی و تحلیل ارتعاشی سازهها اندازه گیری حداقل چند فرکانس طبیعی اول و شکل مودهای مربوطه ضروری است. اندازهگیری چند شکل اصلی مودها مستلزم نصب چند حساسه در نقاط شکمی سازه و تحریک یک نقطه از سازه و یا نصب یک حساسه و تحریک همزمان چند نقطه مشخص است More
برای شناسایی و تحلیل ارتعاشی سازهها اندازه گیری حداقل چند فرکانس طبیعی اول و شکل مودهای مربوطه ضروری است. اندازهگیری چند شکل اصلی مودها مستلزم نصب چند حساسه در نقاط شکمی سازه و تحریک یک نقطه از سازه و یا نصب یک حساسه و تحریک همزمان چند نقطه مشخص است. هر دو روش مستلزم داشتن تعداد زیادی حساسه شتاب و یا نیرو است. تحریک سازه میتواند توسط ضربه چکش، تحریککنندههای الکترو مغناطیس، آکوستیک و یا لیزری باشد. روش دیگر در اندازهگیری شکل مودهاکه نیازمند فقط یک حساسه نیرو و یک حساسه شتاب است، تحریککننده متحرک برای اعمال انواع بارهای متحرک است. اعمال نیرو در تحریک کننده متحرک میتواند از انواع الکترومغناطیس، هیدرولیک و یا پنوماتیک باشد. روش پنوماتیکی به علت پاکی و دقت میتواند از کارایی خوبی برخوردار بوده و برای ایجاد تحریک غیر تماسی مورد استفاده قرار گیرد. این نوع اعمال کننده نیرو که برای تحلیل سازههای حساس و شکننده که انواع دیگر تحریک کنندهها نظیر تحریک با چکش و تحریک تماسی الکترومغناطیس عملکرد مناسبی ندارند از اهمیت ویژهای برخوردار است. در این مقاله، طراحی و ساخت دستگاه تحریک کننده پنوماتیک متحرک برای تحریک یک تیر با اعمال نیروهای ضربهای، بار ثابت پلهای یا شیب ویا هارمونیک در سرعتهای متغیر ارائه و عملکرد تحریک کننده با ایجاد تحریک بر روی یک تیر بررسی و با نتایج نظری مقایسه شده است
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اهمیت داشتن توانایی برای نظارت بر سلامت سازه و شناسایی آسیب در سریعترین زمان ممکن، یکی از مهمترین دغدغه­های مهندسان بهویژه در رشته­های مکانیک و هوافضاست. این اهمیت ناشی از آن است که آسیب و تخریب یک سازه در حین خدمت میتواند خسارات مالی و جانی بسیار شدید و بعضاً More
اهمیت داشتن توانایی برای نظارت بر سلامت سازه و شناسایی آسیب در سریعترین زمان ممکن، یکی از مهمترین دغدغه­های مهندسان بهویژه در رشته­های مکانیک و هوافضاست. این اهمیت ناشی از آن است که آسیب و تخریب یک سازه در حین خدمت میتواند خسارات مالی و جانی بسیار شدید و بعضاً جبرانناپذیری را به دنبال داشته باشد. یکی از روش­های مورد توجه در این عرصه، روش عیب­یابی با استفاده از تغییرات در خصوصیات ارتعاشی سازه است. هدف از تحقیق حاضر عیب­یابی پوسته استوانه­ای کامپوزیتی از طریق انجام آنالیز مودال تجربی و به کمک روش­های عیب­یابی بر پایه شکل مود و بررسی حساسیت آن­ها در برابر شدت­های مختلف آسیب است. نتایج حاصل بیانگر آن است که تکنیک­های عیب­یابی بر پایه شکل مود از آنجا که مستقیماً از دادههای خام تست مودال استفاده نمی­کنند، قابلیت اطمینان کمتری نسبت به تکنیک عیب­یابی دیگر دارند و کارامدی روش­های ذکر شده شدیداً به دقت تست و داده­های مودال استخراج شده وابسته است. بهطور کلی اکثر روش­های مورد استفاده به جز در مرحله اول آسیب یعنی حفره­ای با ضخامت 4 میلیمتر، در دیگر مراحل قادر به تشخیص موقعیت آسیب هستند.
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