كشف آسيب در سازه ها توسط آناليز موجك با استفاده از داده هاي آناليز مودال

Damage Detection in Structures by Wavelet Analysis using Modal Analysis Data

كشف آسيب در مراحل اوليه‌ي شكل‌گيري در سازه هاي مهندسي بسيار مهم است. تقريباً تمام روش هايي كه تاكنون پيشنهاد شده‌اند، متكي به مقايسه‌ي سازه‌ي سالم اوليه و سازه‌ي موجود هستند. با وجود اين، روش مذكور هميشه قابل اجرا نيست، زيرا رفتار سازه‌ي اوليه در بيشتر حالات در دسترس نيستند. روش آناليز موجك، كه اخيراً معرفي شده است، به اين مشكل غلبه كرده است؛ زيرا به اطلاعاتي از سازه‌ي سالم نياز ندارد. اين روش از شكل هاي مودي تجربي، كه از سيستم هاي پايش به‌دست مي آيند، استفاده مي كند. سپس با يك تبديل رياضي، ناپيوستگي هاي شكل هاي مودي، كه معمولاً بسيار ناچيز هستند، برجسته و به‌راحتي شناسايي مي شوند. در اين مطالعه، امكان كاربرد اين روش براي سه نوع سازه شامل: يك تير ساده، يك قاب و يك پل كابلي معلق بررسي شده است. نتايج نشان مي دهند كه اين روش توانايي بسيار بالايي در تشخيص محل آسيب دارد.

Over the past few decades, the methods of damage detection in civil and mechanical structures have drawn much attention from various fields in structural health monitoring (SHM) systems. Structural health monitoring (SHM) is related to damage monitoring, with operational loads playing a significant role in terms of fatigue life and damage accumulation prognostics. Many different techniques, like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves, are nowadays investigated in terms of efficient and user-friendly damage identification systems. This paper proposes a new approach for damage detection in structures with minor damage in the early growth stages. Wavelet analysis, a relatively new mathematical tool, has been used increasingly in recent years. This rather new method has been applied to various fields including civil, mechanical and aerospace engineering. Damage detection in early stages is very crucial in engineering structures. Almost all proposed methods, so far, rely merely on comparison of the structural behavior of the present structure with that of the original intact structure. However, this method is not always applicable, as either the behavior of the original structure is not available, in most cases, or the impact of damage is too negligible in the early stages to be identified. The newly introduced method of Wavelet Analysis has overcome these problems, as it does not require data of the intact structure. The method utilizes experimental mode shapes obtained from data acquisition systems. Then, with a mathematical transformation, the discontinuities of the mode shapes, which are normally very negligible, are highlighted and, therefore, easily identified. Throughout the present study, the applicability of the method for three types of structure, including a simple beam, a frame and a suspended cable bridge, is verified. The obtained results show the great potential of the method in discernment of damage location with great accuracy.