ارزیابی آزمایشگاهی و عددی سامانه کم‌هزینه شناسایی پارامترهای مودال مبتنی بر حسگرهای MEMS

Modal analysis is a fundamental method for identifying the dynamic characteristics of structures and for evaluating their behavior in structural health monitoring systems. Accurate identification of modal parameters, such as natural frequencies and mode shapes, plays a crucial role in understanding the structural response and in providing reliable information for condition assessment and damage detection. However, the precise laboratory equipment commonly required for this purpose is often expensive, which restricts its widespread use, particularly in low-budget experimental studies and practical monitoring applications. Therefore, developing a low-cost yet sufficiently accurate alternative has become an important research need in the field of structural health monitoring. In this study, with the aim of providing an economical and efficient alternative, a vibration monitoring system based on an MPU6050 MEMS sensor and an ESP32 processing unit was designed, implemented, and evaluated. The proposed system was developed to offer a practical and affordable solution for capturing vibration responses while maintaining acceptable accuracy for modal identification purposes. In the first stage, the theoretical analysis of a cantilever beam was carried out in order to extract the natural frequencies and mode shapes of the structure as analytical reference values. These reference results were used as a basis for evaluating the performance of the proposed measurement system and for assessing the consistency of the experimental and numerical findings. Then, considering the target modes and with the aim of improving the accuracy of vibration recording, the arrangement of sensors in the laboratory environment was determined using the E-optimality sensor placement algorithm. This step was particularly important because the quality of the measured modal information is strongly affected by sensor locations, especially when a limited number of low-cost sensors is used. Based on the optimal layout, the measurement system was developed through a low-cost approach and applied in the experimental program. After data acquisition, preprocessing steps were performed, including the removal of unwanted components, signal conditioning, and appropriate filtering, in order to improve the quality of the recorded responses and reduce the effect of noise and irrelevant signal content. The processed data were then analyzed using the FFT and FDD methods to identify the dominant frequencies and extract the modal characteristics of the tested structure. Subsequently, the experimental natural frequencies and mode shapes were obtained, and for validation purposes, a corresponding numerical model was developed in Abaqus and subjected to modal analysis. Comparison of the results showed that the difference in natural frequencies between the experimental and numerical models in the first four modes was less than 4.3%, while the numerical model showed a difference of less than 0.3% compared with the theoretical results, indicating the high accuracy of the numerical modeling. In addition, the MAC values between the experimental and numerical models were greater than 97% for all modes, and those between the numerical and theoretical models were greater than 99%, demonstrating a very strong correlation between the identified mode shapes. The results of this study show that the proposed low-cost system, when optimal sensor placement and proper data processing are applied, has acceptable accuracy for extracting modal characteristics in the laboratory specimen studied. These results indicate the potential of using the proposed approach as a basis for future studies and developments of low-cost systems for measuring and monitoring the dynamic characteristics of structures.