Papers by Author: Nian Li Lu

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Authors: Li Xia Meng, Nian Li Lu, Shi Ming Liu
Abstract: The exact stiffness matrix of a tapered Bernoulli-Euler beam is proposed, whose profile is assumed linear variation. Classical finite element method to get stiffness matrix through interpolation theory and the principle of virtual displacement is abandoned. Starting from the governing differential equation with second-order effect, the exact stiffness matrix of tapered beam can be obtained. In the formulation of finite element method, the stiffness matrix derived has the same accuracy with the solution of exact differential equation method. As is demonstrated in the numerical examples, the presented method can yield, in a very efficient way, accurate results for single tapered beam or structures consisting of tapered elements.
1968
Authors: Nian Li Lu, Wei Gang Zhan
Abstract: Fatigue is the most common failure mechanisms in many engineering structures with inherent defects under variable amplitude loading, Such as lifting structures, airplanes, bridges and so on have to endure for a long term cycle loadings in the actual service. For such structures, fatigue life is dominantly predicted by crack growth analysis, using the stress intensity factor range. In this paper, an improved extend finite element method is proposed for stress intensity factor calculation, which can overcome the limitation of the level set method in judge the element types. Numerical experiment is provided to demonstrate the utility and robustness of the proposed method.
1728
Authors: Peng Lan, Teng Fei Wang, Nian Li Lu
Abstract: The out-of-plane stability of crane jib is studied considering the lateral flexibility of the fixed joint. The analytical expression of the out-of-plane buckling characteristic equation for the crane jib with single cable is obtained by establishing the bending deflection differential equation of jib under the instability critical state with the method of differential equation. The equilibrium equation of the fixed point in the lateral direction is introduced to solve the differential equation besides the boundary conditions. The analytical results obtained agree very well with the finite element method (FEM) results. To consider the lateral flexibility of the cable fixed joint, a dimensionless stiffness coefficient measuring the lateral constraint was introduced to derive the out-of-plane buckling characteristic equation. The degeneration forms of the characteristic equation under the limit cases of zero lateral stiffness, infinite lateral stiffness are further discussed. And the influence of the lateral stiffness of fixed joint on the stability of jib is investigated. It is shown that the increase of the lateral stiffness will significantly improve the buckling load of the crane jib especially when the lateral stiffness is very small.
240
Authors: Teng Fei Wang, Peng Lan, Nian Li Lu
Abstract: The analysis model is built to investigate the out-of-plane stability of crane jib with auxiliary bracing. Considering the second-order effect, the analytical expression of the out-of-plane buckling characteristic equation for the crane jib with auxiliary bracing is obtained by establishing the bending deflection differential equation of jib under the instability critical state with the method of differential equation. The equilibrium equation of the cable converging point in the lateral direction is introduced to solve the differential equation besides the boundary conditions and deformation compatibility equations. With the characteristic equation, the critical compression or the critical lifting load can be easily obtained. The characteristic equation is analytically expressed and the analytical results obtained agree very well with the finite element method (FEM) results. The validity of the characteristic equation is verified.
201
Authors: Liang Du, Peng Lan, Nian Li Lu
Abstract: To analyze the stability of stepped telescopic booms accurately, using vertical and horizontal bending theory, this paper established the deflection differential equations of stepped column model of arbitrary sectioned telescopic boom, the stability were analyzed, and obtained the precise expression of the buckling characteristic equation; Took certain seven-sectioned telescopic booms as example, by comparing the results with ANSYS, the accuracy of the equations deduced in this paper was verified. Presented the equivalent component method for the stability analysis of multi-stepped column, the equivalent cross-sectional moment of inertia was deduced by energy method, thus the stability of stepped column equivalent to that of constant section component. By comparing the results with exact value, the precision of equivalent component method was verified which was convenient for stability analysis of telescopic boom.
871
Authors: Nian Li Lu, Wei Gang Zhan, Yan Mei Wang
Abstract: Fatigue is the most common failure mechanisms in structures of construction machinery with inherent defects under variable amplitude loading, which have to endure for a long term cycle loadings in the actual service. In the present investigation an exponential model is proposed for fatigue life prediction with retardation caused by a single spike under constant amplitude loading. Comparisons between the predicted life and the experimental data are provided to demonstrate the utility and robustness of the proposed model.
240
Authors: Wei Gang Zhan, Jia Wang, Nian Li Lu
Abstract: This paper presents an analysis in attachment spacing of tower cranes. Both the support spacing under the rigid support and the flexible support are obtained for this purpose. For deriving the rigid support spacing, differential equation is used. The principle is used for calculating the support spacing, which the extended segment has the same Euler critical force with the independent segment. The flexible support distance is obtained by setting the integrated stiffness matrix zero, which is equivalent to structural instability. The order of the overall stiffness matrix is big when the tower crane is attached many times. In order to calculate more convenient for solving the matrix determinant, a transfer matrix method is adopted. To verify the influence of the flexibility caused by the support device, an example is carried out by both rigid and flexible support situations for this purpose, and the support spacing is computed numerically. Numerical results for the support distances of a tower crane will be presented and discussed.
499
Authors: Liang Du, Peng Lan, Nian Li Lu
Abstract: To proceed on dynamic analysis of folding boom system in its range changing case with high precision and convenience, conditionally decoupled the nonlinear flexible system dynamic equations, obtained motion equation of rigid system and flexible element kinematic equation considering rigid flexible coupling effect, an efficient dynamic analysis method for planer link system was given. Based on Lagrange equation, basic formulations of flexible and rigid multi-body dynamic for open link mechanism were established. By introducing equivalent rigid virtue element, the unified pattern of multi-sectioned rigid body system dynamic equation was obtained. Took the rigid body dynamic analysis as precondition and borrowed the thought of KED method, a high-efficiency elastokinetics method was given for planer link system. Took the range changing case of certain overhead working truck arm as example, analyzed by the elastokinetics method, obtains the dynamic response considering rigid-flexible coupling effect. Results show that the elastokinetics method for planer link system is of high efficiency and accuracy.
171
Authors: Liang Du, Peng Lan, Nian Li Lu
Abstract: Based on the spatial beam-column differential equations, the slope deflection equations considering second-order and bend-torsion coupling effect are established. The additional moment caused by torsion and bend deflection are taken into account. Then the finite element pattern of spatial beam-column considering the couple effect of torsion and bend is given. The tangent stiffness matrix and relevant program for nonlinear analysis are further obtained. By the nonlinear calculation and stability analysis of single component which has high accuracy or precise solution, the precision of the FEM model given in this paper is verified by comparing the results with that given in references.
73
Authors: Yuan Xue, Jun Li, Nian Li Lu, Da Qi Wu
Abstract: Luffing jib cranes are large flexible complex truss structure, and their mechanical property is nonlinearity. So the Precise analysis method for the stiffness and stability problem has been paid attention to by the researchers. To solve this problem, the equivalent mechanical model of luffing jib crane was established by taking the lifting load, counter weight and dead weight into consideration. The stiffness and stability of luffing jib crane was analyzed by using the differential equation of deflection based on second-order effect. The calculating formulas of lateral deflection, amplification factor of deflection and stability was derived. Taking a luffing jib tower crane for example, the lateral stiffness was calculated respectively by the formula given by this paper, the traditional linear method and the finite element method, and show that the result calculated by the formula given by this paper is identical to that by finite element software ANSYS, the error is 1.8%. and the error of traditional method is 7.6%, It is clear that calculation expression of lateral deflection, deflection amplification factor and the stability in this paper are accuracy. This method can be applied to the analysis of calculation of luffing jib tower crane stiffness and stability.
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