یک مدل استوکستیکی خوردگی سازه های فولادی در معرض آب دریا

نوع مقاله: پژوهشی

نویسنده

دانشگاه امام حسین (ع)

چکیده

بمنظور آنالیز قابلیت اعتماد سازه های فولادی که در دریا بکار گرفته می شوند و بالتبع درمعرض خوردگی ناشی از اثرات آب خورنده دریا هستند ضرورت دارد که یک مدل فیزیکی که نمایشگر رفتار عمومی خوردگی فولاد در معرض آب دریا باشد و نیزیک مدل استوکستیکی که فرآیند خوردگی را بلحاظ رفتار احتمالاتی آن توصیف کند بکار گرفته شوند. دراین مقاله از مدل خوردگی ملچرز بمنظور توصیف رفتار فیزیکی خوردگی برای فولادهای دریایی استفاده می گردد.  همچنین یک مدل احتمالاتی پیشنهاد می شود که درآن فرآیند خوردگی بصورت پلکانی مدل شده و هر پله آن یک پرش در مقدار خوردگی را نمایش می دهد. طول زمانی این پله ها ثابت و تعیینی گرفته می شوند اما پرش آنان متغیر های تصادفی مستقلی مدل می شوند که از توزیع گاما پیروی می کنند. در این نوشتار برخلاف فرآیند معمول گاما، پارامتر های شکل و مقیاس توزیع های گاما در هر پله متفاوت گرفته شده و بنابراین خوردگی تجمعی در هر زمان دلخواه در طول عمر سازه جمع n متغیر تصادفی با مشخصات احتمالاتی متفاوت خواهد شد. در این تحقیق پس از ارائه مدل احتمالاتی این فرآیند، شیوه ای جدید از کاربردروش تخمین پارامترهای "احتمال حداکثر" با استفاده از داده های خوردگی در کانال پاناما ارائه می گردد و در پایان از این مدل برای آنالیز قابلیت اعتماد سازه های دریایی در معرض خوردگی در مناطقی شبیه وضعیت اقلیمی کانال پاناما استفاده می گردد. نتایج اعمال مدل پیشنهادی در خصوص داده های موجوی نشان می دهند که مدل انعطاف پذیری مناسبی را برای نمایش میانگین و واریانس فرآیند  خوردگی دارا می باشد.  

کلیدواژه‌ها


عنوان مقاله [English]

A stochastic corrosion model for structural steels subject to sea waters

نویسنده [English]

  • Mohammad Reza Moarefzadeh
چکیده [English]

In order to perform reliability analysis of steel structures subject to sea waters and thus to corroding marine environments, it is necessary to use: a) a model describing physical behavior of corrosion in structures placed in these circumstances and b) a stochastic model describing probabilistic behavior of corrosion phenomenon along time. In this study, Melchers' model is employed as a physical corrosion model. Furthermore, a probabilistic model is proposed in which the corrosion process is discretized into a few steps each of which representing a jump/an increment in corrosion quantity. Despite having a pre-defined deterministic small duration, each step is modeled with an independent random variable following a gamma distribution. In this paper, in contrast to the conventional gamma process, the shape and scale parameters of the involving gamma distributions are different for each step. This will result in an accumulating corrosion process which is a sum of n different gamma distributed random variables in any arbitrary point of time. Herein, in addition, a new application of "maximum likelihood method" for estimating of model parameters is proposed. Panama Canal data for carbon and low-alloyed steels is used for the purpose of parameter estimation. Reliability analysis of a structure subjected to an environment similar to that of Panama Canal is then investigated. Implementation of the model proposed herein to data available indicates that it could be sufficiently flexible to show the mean and variance of the marine corrosion processes. 

 





 





 

کلیدواژه‌ها [English]

  • marine corrosion
  • structural reliability
  • carbon steels/low-alloyed steels
  • gamma random variable
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