| With the rapid growth of transportation and logistics industry, large special vehicle are used more and more in transportation of heavy equipments and structures. Special vehicle manufacturers should not only consider increasing vehicle speed, loading coefficient and reducing transportation cost, but also consider improving transport safety, ride comfort and a lightweight structure, which have become the development trend of the whole industry in the design and application process. Hydraulic modular assembly trailer (HMAT) is a specialized large, heavy goods land transportation. Due to the heavy weight and large structure size of the trailer’s bogie frame, the natural frequency characteristics and the rigid-flexible coupling phenomenon of the elastic bogie frame directly affect the dynamic response properties of the vehicle system. However, there are few researches on dynamic response of HMAT system today, mainly due to the fact that this type of vehicle is made of multi-structural components, mechanisms and systems with large and complex multi-body system. The past studies of HMAT structural strength problems focused primarily on static analysis method, which cannot fully reflect the structure response under random dynamic load. Therefore, the combination of the finite element analysis, multi-body dynamics simulation and structure fatigue analysis, and their application to the study of HMAT system dynamic response and its structure fatigue strength have engineering significance and academic value. Main contents and conclusions of this thesis are as follows:(1) When investigating the dynamic response properties of the15axle HMAT system, after considering the dynamic characteristics of bogie frame’s elastic structure, the finite element models of the bogie frame were built using ANSYS software. And with reasonable selection of master degrees of freedom of the model, modal analysis method based on the reduced degree of freedom of the substructures was used to solve the natural frequencies and mode shapes of the bogie frame. The analysis results show that the first20modes of the bogie frame calculated using the reduced degree of freedom method are able to meet the accuracy requirements of the model calculations, while improving the computational efficiency.(2) The establishment methods of the kinematic and dynamics equations of rigid and flexible body in multi-body systems were explored. The dynamics equation of the hydraulic cylinder of hydraulic suspension system is established based on the mechanical differential equations and fluid flow equations of the liquid. By combining the dynamic equations of multi-body system, the dynamic equations of the mixed multi-body and hydraulic suspension system model of trailer were derived.(3) Based on ADAMS software, the multi-rigid body and rigid-flexible coupling multi-body system models of the15axle HMAT were established with considering the elastic dynamic characteristics of the bogie frame and effect of hydraulic suspension system on the dynamic response properties of trailer. There models were simulated with excitation signal generated by road roughness, and was verified by trailer vibration experiment. The results show that, the measuring points in simulation of rigid-flexible coupling multi-body system model and experiments have the same variation trend of frequency spectrum, the relative difference of modal frequency value is small, and thus the established rigid-flexible coupling multi-body system model is accurate. (4) Aiming at the loading scheme design of HMAT with bracket structures, the effects of the number and bracketlocations and the balance support methods of the hydraulic circuit system on the load capacity of the bogie frame were analyzed based on stress level and vertical deformation, as the result of finite element static analysis of the bogie frame. With the least of brackets number, a loading scheme with three brackets was chosen to meet the frame static strength requirements.(5) Based on HMAT multi-body system dynamic model of the reasonable loading scheme that was chosen, the effects of trailer’s operation conditions on the dynamic response of trailer were studied under different road roughness and various speeds. The simulation results show that, the root-mean-square value of the vertical acceleration of trailer parts and the dynamic load between parts increase with the augmentation of road roughness and trailer speed. Under the impact of sinusoidal uneven road excitation, the vertical acceleration of the swing-arm and the dynamic loads of trailer axle increase sharply. The established hydraulic circuit system could achieve the basic functions of a hydraulic suspension system, with trailer wheels of each hydraulic cylinder group bearing equal load and dynamic load acting on bogie frame reduced. The vertical acceleration of left, right, front and rear parts of the bogie frame is greater than those of longitudinal plane of symmetry or close to bracket positions, owing to the effect of bracket stiffness and hydraulic suspension system.(6) When studying the effect of trailer’s operation conditions on the fatigue life of swing-arm and bogie frame structures, the stress time histories of these structures were obtained using finite element quasi-static superposition analysis in discrete time points. The fatigue life prediction model of swing-arm was established basing on local stress-strain method. The calculation results show that, the stress concentration positions of swing-arm appear at the cross section of fracture failure location where its stress level has entered into plastic state. With operational conditions of trailer running on ordinary B grade, C grade and D grade roads, the fatigue life of risk points are greater than the service life of trailer. However, on sinusoidal uneven roads, its fatigue life decreases significantly with the intensification of sinusoidal amplitude and the increase of trailer speed. The calculation results are also in line with the logistics company’s operation records:the swing-arm fracture failure often occurs in complex rugged roads.(7) The fatigue life prediction model of bogie frame’s welded structure was established based on the hot spot stress method of Recommendations for Fatigue Design of Welded Joints and Components standard of International Institute of Welding (IIW). The calculation results show that, with operational conditions of trailer running on the class S2of sinusoidal uneven roads and5.55m/s being the trailer speed, the shortest fatigue life of risk points is13.5years and is less than the service life of trailer, but greater than the retirement life of trailer. According to the results of structural fatigue life prediction, the applicable operation conditions were proposed with fatigue life of swing-arm and bogie frame are considered. |
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