Research On Structural Stability And Complex Motion Dynamic Of Telescopicboom System In Construction Crane

Construction crane is a kind of hoisting machinery that can lift and move heavy things by multi-action in a specific domain, which play a significant role in all kinds of engineering. Wheel crane has many desirable features such as flexible, stable and efficient, thereby being widely used in structure, transportation, hydroelectric project and military industry. The telescopic boom is the most important working component of the wheel crane because it may bear quite large loads, both axially and transversely, and sometime the impact loads as well. Therefore, the exact analysis of the static and dynamic stability and the motion of the boom are necessary in order to prove that the crane can work in safety. These are also the objects of this thesis. Besides, the effect of the supporting cylinder, friction force between the different sections of the telescopic boom and the pull-rope or drawbar on the out-of-plane stability of the boom. Also, based on the flexible multibody system dynamics, a method that takes both accuracy and efficiency into consideration has been introduced and implemented on the typical flexible boom of the engineering crane in this investigation.In the crane design role GB/T3811-2008, a multi-stepped column model is used to compute the out-of-plane stability of the telescopic boom, in which the effect of the supporting cylinder and the friction force between the different sections of the boom are omitted. However, these effects should be considered. To this end, two kinds of models are introduced to simulate the instability of the boom. One model only takes the supporting cylinder into consideration, while the other one takes supporting cylinder and the friction force both. Begin with the accurate differential equations of the critical buckling, different recursive formulations of the Euler critical force are derived based on three models, which are the conventional model and the two new models introduced in this thesis, respectively. After this, the different Euler critical forces are compared. Finally, the effort of the non-directional force caused by the drawbars on the out-of-plane stability is discussed. The analysis shows that the multi-stepped column model used in the crane design role is more likely to be safe and the non-directional force caused by the pull-ropes or drawbars can improve the out-of-plane stability of the telescopic boom in quite a large extent.In order to analysis the dynamic stability of the telescopic boom which undergo a small deformation, the finite element method and Lagrange equations are used to build up the parametrical vibration equations of the complex beam-rod structure under a axial periodic load, resulting in the critical frequency equations of the dynamic instability boundary. Using these equations, the first and second dynamic instability regions are obtained. Besides, the effect of the damping on the instability regions is discussed. The results show that the nonlinear finite element method is an efficient and accurate method to solve the parametric vibration problems. The dynamic instability areas become smaller when the damping grows up. What more, the effect on the second area is more significant. After this, because of the low accuracy of the traditional two-node beam element in the stability analysis, a new kind of nonlinear Euler-Bernoulli beam element with three node is created through the interpolation theory, which takes the second order effect into consideration. The successful application of this new element in the structural dynamic stability demonstrates that it has much higher accuracy than the traditional two-node beam element does. Specifically, three or four traditional elements are needed to guarantee the same accuracy as the new one, which means the calculation efficient has been improved.The kinetic equations of the flexible multibody system are a set of highly coupling and nonlinear differential-algebraic equations which are very difficult to solve. Therefore the application in the engineering is quite inconvenient. Based on the theory of the flexible multibody system dynamics, preserving the features of the KED method and with the use of some suitable assumptions, the kinetic equation of the beam-bar element are built up and the explicit formulation of the coefficient matrixes are given in this thesis. Besides, the additional matrix caused by the lumped parameters has also been taken into consideration. According to the transformation between the nodal position, velocity and acceleration in the floating and the global reference coordinates, the motion equations of the spatial beam-bar system in the global reference coordinates are obtained. Finally, the solving strategy and the organization of the procedure are discussed and the corresponding finite element procedure of the flexible beam-rod system is programmed. The numerical results coming from the flexible dynamic analysis of the typical slider-crank mechanism demonstrate that the high-efficiency method presented in this thesis has quite high accuracy and an appropriate calculation amount which is close to the KED method’s, which means that the solving efficiency of the flexible multibody system dynamics has been improved by this method.The telescopic boom of QAY500all terrain crane is chosen to test the method presented in this thesis. Some multiple working conditions are analyzed such as revolution, lifting and changing amplitude. The main purpose is to obtain the dynamic respond of the flexible telescopic boom in the complex nonlinear motions and the deformation and the changing process of the strain of every key point or structural body, which are important basis of the structural design and analysis of the crane.