Simultaneously evolutionary optimization of several natural frequencies of a two dimensional structure

Zhao, Chongbin,Steven, G.P.,Xie, Y.M. Techno-Press 1999 Structural Engineering and Mechanics, An Int'l Jou Vol.7 No.5

This paper presents a solution method, which can be regarded as the further extension of the generalized evolutionary method (Zhao et al. 1998a), for the simultaneous optimization of several different natural frequencies of a structure in general and a two dimensional structure in particular. The main function of the present method is to optimize the topology of a structure so as to simultaneously make several different natural frequencies of interest to be of the corresponding different desired values for the target structure. In order to develop the present method, the new contribution factor of an element is proposed to consider the contribution of an element to the gaps between the currently calculated values for the different natural frequencies of interest and their corresponding desired values in a weighted manner. Using this new contribution factor of an element, the most inefficiently used material can be detected and removed gradually from the design domain of a structure. Through applying the present method to optimize two and three different natural frequencies of a two dimensional structure, it has been demonstrated that it is possible and applicable to use the generalized evolutionary method for tackling the simultaneous optimization of several different natural frequencies of a structure in the structural design.

General evolutionary path for fundamental natural frequencies of structural vibration problems: towards optimum from below

Zhao, Chongbin,Steven, G.P.,Xie, Y.M. Techno-Press 1996 Structural Engineering and Mechanics, An Int'l Jou Vol.4 No.5

In this paper, both an approximate expression and an exact expression for the contribution factor of an element to the natural frequency of the finite element discretized system of a structure in general and a membrane in particular have been derived from the energy conservation principle and the finite element formulation of structural eigenvalue problems. The approximate expression for the contribution factor of an element is used to predict and determine the elements to be removed in an iteration since it depends only on the quantities associated with the old system in the iteration. The exact expression for the contribution factor of an element makes it possible to check whether the element is correctly removed at the end of an iteration because it depends on both the old system and the new system in the iteration. Thus, the combined use of the approximate expression and the exact expression allows a considerable number of elements to be removed in a single iteration so that the efficiency of the evolutionary structural optimization method can be greatly improved for solving the natural frequency optimization problem of a structure. A square membrane with different boundary supports has been chosen to investigate the general evolutionary path for the fundamental natural frequency of the structure. The related results indicated that if the objective of a structural optimization is to raise the fundamental natural frequency of the structure to an optimal value, the general evolutionary path during its optimization is that the elements are gradually removed along the direction from the area surrounded by the contour of the highest value to that surrounded by the contour of the lowest value.

Analytical solutions for crack initiation on floor-strata interface during mining

Zhao, Chongbin Techno-Press 2015 Geomechanics & engineering Vol.8 No.2

From the related engineering principles, analytical solutions for horizontal crack initiation and propagation on a coal panel floor-underlying strata interface due to coal panel excavation are derived in this paper. Two important concepts, namely the critical panel width of horizontal crack initiation on the panel floor-underlying strata interface and the critical panel width of vertical fracture (crack) initiation in the panel floor, have been presented. The resulting analytical solution indicates that: (1) the first criterion can be used to express the condition under which horizontal plane cracks (on the panel floor-underlying strata interface or in the panel floor because of delamination) due to the mining induced vertical stress will initiate and propagate; (2) the second criterion can be used to express the condition under which vertical plane cracks (in the panel floor) due to the mining induced horizontal stress will initiate and propagate; (3) this orthogonal set of horizontal and vertical plane cracks, once formed, will provide the necessary weak network for the flow of gas to inrush into the panel. Two characteristic equations are given to quantitatively estimate both the critical panel width of vertical fracture initiation in the panel floor and the critical panel width of horizontal crack initiation on the interface between the panel floor and its underlying strata. The significance of this study is to provide not only some theoretical bases for understanding the fundamental mechanism of a longwall floor gas inrush problem but also a benchmark solution for verifying any numerical methods that are used to deal with this kind of gas inrush problem.

Study on Residual Stress Releasing of 316L Stainless Steel Welded Joints by Ultrasonic Impact Treatment

Xiao-Dong Hu,Chongbin Ma,Yicheng Yang,Qingliang Zeng 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.3

In this paper, the eff ect of ultrasonic impact treatment (UIT) on the residual stress of 316L welded butt-joint was investigated. Firstly, the temperature fi eld distribution in the welded joint was simulated based on the double-ellipsoidal heat source model, and the residual stresses were calculated by a sequential coupling thermo-mechanical fi nite element method. Subsequently, based on the theory of transient contact mechanics, the eff ects of UIT on releasing of the welding residual stress was analyzed. The microstructure of the weld metal before and after the UIT treatment was compared to study the infl uence of UIT. The results show that the maximum residual stresses in the weld metal and heat aff ected zones are released due to the dislocation multiplication during the UIT, and this eff ect on the weld metal is more remarkable than that on the heat aff ected zones. The results of numerical simulation of UIT are consistent with the corresponding experimental results. After UIT, the transverse and longitudinal tensile stresses near the fusion line are changed to compressive stresses.

Seismic performance of precast assembled bridge piers with hybrid connection

Shuang Zou,Heisha Wenliuhan,Yanhui Liu,Zhipeng Zhai,Chongbin Zhang 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.85 No.3

Precast assembled bridge piers with hybrid connection (PASP) use both tendons and socket connections. To study the seismic performance of PASP, a full-scale in-situ test was performed based on an actual bridge project. The elastic-plastic fiber model of PASP was established using finite element software, and numerical analyses were performed to study the influence of prestress degree and socket depth on the PASP seismic performance. The results show that the typical failure mode of PASP under horizontal load is bending failure dominated by concrete cracking at the joint between the column and cushion cap. The cracking of the pier concrete and opening of joints depend on the prestress degree and socket depth. The prestressing tendons and socket connection can provide enough ductility, strength, restoration capability, and bending strength under small horizontal displacements. Although the bearing capacity and post yield stiffness of the pier can be improved to some extent by increasing the prestressing force, ductility is reduced, and residual deformation is increased. Overall, there are reasonable minimum socket depths to ensure the reliability of the socket connection.