تعیین پارامترهای کیفیتی یک مهار کننده با استفاده از اندازه گیری های لرزشی محیط

ABSTRACT Modal parameter identification of a containment using ambient vibration measurements

As energy needs around the world coupled with rising oil and gas prices along with environmental constraints and concerns about energy supply security persistently grow, the expectations on nuclear energy, which can provide clean and economic energy, rise. According to IAEA (IAEA, 2008), there were 439 nuclear power reactors in operation worldwide by the end of 2007, which provide about 15% of the world’s electricity. However, more than 70% of them are more than 20 years old, and thus, assuming the 40 years of design life, majority of the operating nuclear power plants will face decommission or extension of operating licenses. One of the major concerns in extending operating licenses is the integrity of safety-related structures including the containment, since, unlike mechanical and electrical equipments, the replacement of the containment and many other safety-related structures would be economically unfeasible (Naus et al., 1996).

To date, the structural integrity of the containment has been evaluated periodically via visual inspections along with chemical tests, nondestructive strength tests, etc. However, these methods can only provide local information on the structural condition and require considerable time and cost to estimate overall structural integrity (Park and Choi, 2008). One of the more effective methods that have gained attention for evaluating the structural condition of the whole structure is the structural integrity monitoring (SIM) method, which utilizes measured dynamic responses from a structural system to assess the physical properties of the structure (Salawu, 1997; Choi et al., 2006). Usually the SIM method comprises the measurement technique for recording dynamic responses, the data processing technique for extracting dynamic characteristics, e.g., resonant frequencies, damping, and mode shapes, and the system identification technique for relating extracted dynamic characteristics to physical properties of the structural system (Doebling et al., 1996). For large-scale structures such as high rise buildings and long-span bridges,measuring dynamic responses appropriately would be the most important task.

There are two test methods available in measuring the dynamic response of a structure: the forced vibration test and ambient vibration test. Until the late 1990s, the forced vibration tests were preferred due to the accuracy of the corresponding system identification techniques. However, during the last two decades more attention was paid to ambient vibration tests because of their low cost and convenience (Michel et al., 2008). For forced vibration test, a challenging issue is the excitation of large civil engineering structures, which leads to huge reaction mass shakers or impact testing using a falling weight (Peeters et al., 2001). Especially for such a structure as the containment to which applying appropriate excitation is a difficult task, the ambient vibration test is the reasonable choice without interrupting normal operation.