جستجوی مقالات مرتبط با کلیدواژه « تابع همبستگی » در نشریات گروه « فنی و مهندسی »

In this paper, an innovative finite element updating method is presented based on the sensitivity of wavelet transform coefficients of correlations function structural parameters is proposed to identify the damage. The Quasi-linear sensitivity of the wavelet coefficients of the WTCF concerning the structural parameters is evaluated based on incomplete measured structural responses. This WTCF sensitivity is more sensitive to local structural changes than the wavelet transform function response sensitivity. The model is updated by the wavelet transform coefficients achieved in the frequency range in the vicinity of the resonances, in which damping and incomplete measurements have no significant effect on the results of the parameter estimation. The proposed algorithm is used to estimate the structural parameters of the frame model. By the solution of the sensitivity equation through Least-squares method, the finite element model of the structure is updated for estimation of the location and severity of structural damages, simultaneously. The proposed method was successfully applied to a 2D frame model using simulated data contaminated by measurement and modeling errors. The robustness of the method against modeling and mass measurement errors is investigated by adding random errors to the mass parameters of the frame model.

As underground hidden facilities are used for various applications, imaging systems are requiredfor the detection and recognition of these facilities. In this paper, imaging by mechanical wavepropagation in the soil is investigated. Most underground facilities can be considered as airchambers located in the middle of the soil. Air and soil have a large difference in acousticimpedance, so underground facilities can produce a large reflective signal because the amplitudeof the reflected signal depends on the difference in impedance of the two materials. Seismic andnon-destructive concrete testing systems also use the process of propagation of mechanicalwaves in the material. Although seismic systems have been successful in the detection issue,they require several meters of space for equipment layout, and transportation complexity is alsoone of their problems. They are unsuitable for urban space because they are inherently designedto detect water sources at depths of several hundred meters. On the other hand, while thenon-destructive concrete testing system equipment have suitable dimensions, they have lowpenetration depth which is impractical for this purpose. Seismic and non-destructive testingsystems of concrete operate in the range of subsonic and ultrasonic waves, respectively. Thisresearch project proposes the idea that by choosing an operating frequency between the twomentioned ranges, it is possible to obtain equipment with the appropriate dimensions forimaging underground facilities. In this project we managed to image an undergroundconstructed cylindrical cavity with the diameter of 1 meter and the depth of 4 meters. Theaccuracy of this method depends on the sound propagation speed in the material. Since there areaccurate relationships for the propagation speed of sound in air, the diameter of the cylinder wasestimated with an accuracy of about 4%, but with the measurement of propagation speed beinginfeasible in this project, leading to the ambiguity in the value of propagation speed of sound insoil, the values cited in several reference sites were used, giving the accuracy of 4 to 20%.