| Abstract:Concrete pump truck is a specialty vehicle with the pump transport mechanism used for pumping conceret and boom used for distributing conceret integrated on automobile chassis. It has the advantages of high efficiency, good pouring quality and high flexibility. Due to the interaction of the poor working conditions, difficult to maintenance, materials aging, environmental erosion, fatigue, other long-term effects and disaster factors, the structural damage and failure of concrete pump truck has the propoety of gradient and sudden. Improper operation and not timely maintenance are likely to cause significant economic and life-safety issues.The work in this thesis was supported by the National "863" Plan essential project of China "Remote Monitoring and Maintenance of Key Technologies and Unit System"(2008AA042801) and "Concrete Pump Truck Remote Monitoring and Maintenance Application System Development"(2008AA042802). Using theoretical studies, simulation modeling and experimental analysis as research tools, the key technology of health monitoring for concrete pump truck structure, such as structural health monitoring method, sensor optimal placement, monitoring signal acquisition and processing, characteristic parameter extraction and health status evaluation method are studied in this thesis. The main contents are as follows:The structure and load characteristics of concrete pump truck was described. The statistics analysis of the common failure of the concrete pump truck structural was done. The static and dynamic characteristics of concrete pump truck boom structure were studied by simulation and experimental analysis. The health monitoring strategy of concrete pump truck boom structure based on strain parameter was proposed.The determination of sampling frequency in spectrum analysis, amplitude analysis and damage analysis was studied. The relationship between sampling frequency and damage analysis accuracy was deduced. A signal sampling strategy based on error contral was proposed. This method was applied to the strain signal sampling frequency determination of pump truck boom structure health monitoring. By examples, it is verified the sampling frequency can not only met the accuracy requirements of damage analysis, but also save data storage and increase the data treatment efficiency. Based on theory and methods of wavelet multi-resolution analysis, the noise reduction and abnormal value elimination of the structure monitoring strain signal were processed, and the distribution characteristics and the cumulative damage of different scale response signal was analyzed.Based on comprehensive evaluation method, a method of optimal monitoring strain sensor placement was proposed. According to the characteristics of concrete pump truck boom structure, working environment, damage and health monitoring content, the factor set affecting sensor placement was determinded. And the weight of each factor was determined based on Analytical Hierarchy Process (AHP). The fuzzy support matrix was constructed by using the correlation coefficient of strain signal of the proposed measuring points, and the comprehensive support degree of each proposed measured points was also calculated. Based on fuzzy mathematics methods, factors such as the stress level, the measuring point security, the sensor installation performance and the stress gradient, were classified and standardized. At last, the selected monitoring points of a concrete pump truck boom were optimized according to comprehensive evaluation method.The cumulative damage theory and the method of damage characteristic parameter extraction were researched. Based on fatigue damage theory, the influence mechanism of signal segment on the damage calculation accuracy was studied. A optimal load spectrum extraction method based on the real-time monitoring data of pump truck boom structure was proposed. The method can reduce the truncation of long-time stress cycles and frequent signal reorganization, which can improve the accuracy of load spectrum extraction and fatigue damage calculation.Based on damage index, the health evaluation system of boom structural was established, which introduced the fatigue damage into structure health status assessment of running condition, structure periodical check and life assessment. The evaluation result can provide the basis for health maintenance and management of the pump truck boom structure. Using fatigue damage as the evaluation index, and combining with wavelet multi-resolution analysis theory and method, the cumulative damage of different scale stress response was analyzed. The study reveals the influence of different scale stress response on the boom structure damage. |
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