Nonlinear Dynamic Finite Element Method Research Articles

Non-bracket oblique traction-hoisting construction strategy for cable-truss structures

This study describes the non-bracket oblique traction-hoisting construction strategy for cable-truss structures, which is to assemble the upper and lower radial cables, hoop cables, sling cables, and compression rods without stress at a low altitude, then hoist the cable-strut system to a high altitude by oblique traction of the upper radial cables through the jack fixed on the upper radial anchorage nodes, and finally actively tension the lower radial cables to achieve the designed shape and prestress level of the entire structure. This strategy assembles at a low altitude, requires simple operations, results in high tensioning efficiency, and does not require brackets, which could guarantee both quality and quantity in terms of completing the construction of cable-truss structures. The semilune-shaped canopy of Yueqing Stadium is constructed using this strategy. The construction simulation and disturbance stability analyses of the structure in the traction-hoisting state and prestress tensioning state are conducted using a nonlinear dynamic finite element method. In the traction-hoisting stage, the deformation changes sharply, and the hoop cables and upper radial cables make up the primary bearing substructure, while the lower radial cables are in a suspended hanging state. In the forming process, the forces of the radial and hoop cables increase gradually, and the structure finally reaches the designed state. For cable-trusses with crossed upper and lower radial cables, the additional stabilizing tooling ropes should be tied at the top of the middle rods to ensure geometric stability because they are susceptible to excessive out-of-plane displacement or even overturning, which is the least desirable at the beginning of traction hoisting.

Research on Key Technologies of the Non-Bracket Construction Method for an Annular Cable Supported Grid Structure

A cable strut structure uses a tension cable net as the main load-bearing system, which can allow full play of the high-strength material characteristics of the cables, greatly reduce the burden on the lower supporting system, and increase the span in an economic and effective manner. The annular cable supported grid structure is a new type of cable strut structure, which uses rigid grids to replace the flexible cables at the top chord of the spoke cable truss to meet the requirements of laying a heavy rigid roof. In this paper, first the structural mechanical characteristics of the annular cable supported grid structure are introduced, showing that the structural characteristics derived from the cable truss are the basis of non-bracket construction, while the presence of the upper grid results in difficulties with structure installation configuration control. Second, considering the characteristics of the cable supported grid structure and the difficulties in construction, the non-bracket construction method for annular cable supported grid structure with the commonly used nonlinear dynamic finite element method (NDFEM) in construction simulations is proposed. Finally, a numerical example is given and analyzed to verify the accuracy and feasibility of this method. The results indicate that the non-bracket construction technology proposed in this paper is suitable for the construction of a cable supported grid structure, and has the advantages of convenient prestress flow control, no need for brackets, simple and economical construction equipment, flexible arrangement of construction period, safe and reliable construction, and high construction accuracy.

Analysis of Seismic Isolation Performance of X-Shaped Rubber Bearings (XRBs)

A detailed analysis of the seismic safety performance of building structures using X-shaped rubber bearings (XRBs) under seismic action at different seismic levels of intensity were carried out in this study. The horizontal mechanical properties of XRB were studied by analytical methods. To reveal the failure prevention and control capability of XRBs under strong ground motions, a detailed comparative analysis was conducted of the seismic performances of three-story buildings using XRBs, typical rubber bearings (TRBs), and TRBs with retaining wall protection (RWP). A nonlinear dynamic finite element method was used to analyze the displacement, velocity, and acceleration responses of the seismically isolated structures at different ground motion intensity levels. The results show that the failure of the seismic isolation layer occurs in the building using TRBs under seismic intensity with a 1‱ probability of exceedance (PE) in one year. When the RWP is set around the seismic isolation layer, the superstructure will collide with the wall, which leads to a dramatic increase in superstructure acceleration, while the overall seismic isolation performance of the structure is affected. Nevertheless, XRBs can effectively prevent deformation failure of the seismic isolation layer of a building, reduce the seismic response of a superstructure, and can improve the seismic safety level of a building.

Development of a fully coupled numerical hydroelasto-plastic approach for offshore structure

Offshore structure encountering large waves could generate structural collapsed accident which is a problem of nonlinear fluid–structure interaction sometimes called hydroelasto-plasticity in which structural nonlinearities involving plasticity and buckling and wave load nonlinearities are generated. A viscous-flow numerical approach is put forward to study the hydroelasto-plastic problem in this paper. The viscous-flow hydroelasto-plastic approach combines CFD(Computational Fluid Dynamics) and nonlinear FEM(Finite Element Method) to realize one-way and two-way coupling. CFD platform uses VOF(Volume of Fluid) to models air-wave two-phase flow to make numerical waves which are compared to theory results, and uses DFBI(Dynamic Fluid–Body Interaction) and overlapping grid to calculate offshore structure motion and wave loads. Nonlinear FEM uses explicit nonlinear dynamic FEM to calculate offshore structural collapse responses considering plasticity and buckling. Radial basis function is used to interpolate wave pressures and structural motion and deformation on common surface of hydrodynamic model and FEM model. The viscous-flow hydroelasto-plastic approach is used to simulate an experiment model. Simulation results from both one-way and two-way coupling approaches are compared with experiments. Comparison shows that the two-way coupling provides a better numerical simulation of the experimental model. This paper proposes the viscous-flow hydroelasto-plastic approach coupling CFD and nonlinear FEM as new numerical means to study the offshore structural collapse problem caused by waves.

Study on the calculation method for dynamic wind deflection of transmission line in strong wind area

In order to improve the design and early-warning accuracy for wind deflection of transmission line in strong wind area, it is necessary to calculate the dynamic wind deflection of transmission line in consideration of fluctuating wind effect. In this paper, the generation method for fluctuating wind velocity in consideration of spatial correlation is discussed, then the wind load on every element node of conductor is determined on the basis of the calculation formula for wind load, and finally the dynamic wind deflection angle of insulator and the dynamic wind deflection displacement of conductor is calculated by using the nonlinear dynamic finite element method.

Proposal of Failure Mode Map Under Dynamic Loading—Ratcheting and Collapse

Ratcheting, collapse, and fatigue are the probable failure modes which can occur under alternate dynamic loading like seismic loading. The objective of this study is to propose a failure mode map for rectangular beams by determining the conditions of occurrence of the ratcheting and collapse failure modes. The paper considers the analogy between thermal ratcheting and dynamic ratcheting. The nonlinear dynamic finite element method was used to analyze a rectangular beam model for different loading conditions. The results were plotted on a nondimensional primary and secondary stress parameter graph similar to the Bree diagram for thermal ratcheting. The similarity between thermal load and dynamic load was observed. The main difference between thermal and dynamic loading is the effect of the frequency of dynamic loading on the occurrence of ratcheting and collapse. Experimental observations of ratcheting have been obtained and are used for comparison to validate the analytical predictions. From the above results, a failure mode map has been proposed which can evaluate the occurrence conditions of ratcheting and collapse under dynamic loadings.

Numerical investigation of nonlinear fluid–structure interaction dynamic behaviors under a general Immersed Boundary-Lattice Boltzmann-Finite Element method

A numerical approach based on the immersed boundary (IB), lattice Boltzmann and nonlinear finite element method (FEM) is proposed to simulate hydrodynamic interactions of very flexible objects. In the present simulation framework, the motion of fluid is obtained by solving the discrete lattice Boltzmann equations on Eulerian grid, the behaviors of flexible objects are calculated through nonlinear dynamic finite element method, and the interactive forces between them are implicitly obtained using velocity correction IB method which satisfies the no-slip conditions well at the boundary points. The efficiency and accuracy of the proposed Immersed Boundary-Lattice Boltzmann-Finite Element method is first validated by a fluid–structure interaction (F-SI) benchmark case, in which a flexible filament flaps behind a cylinder in channel flow, then the nonlinear vibration mechanism of the cylinder-filament system is investigated by altering the Reynolds number of flow and the material properties of filament. The interactions between two tandem and side-by-side identical objects in a uniform flow are also investigated, and the in-phase and out-of-phase flapping behaviors are captured by the proposed method.

Strength of a Container Ship in Extreme Waves Obtained by Nonlinear Hydroelastoplasticity Dynamic Analysis and Finite Element Modeling

Extreme waves have caused a lot of ship accidents and casualties. In this paper, a two-dimensional (2D) hydroelastoplasticity method is proposed to study the nonlinear dynamic responses of a container ship in extreme waves. On the one hand, the traditional ultimate strength evaluation is mainly performed using a quasi-static assumption without considering the dynamic wave effect. On the other hand, the dynamic response of a ship induced by a wave is studied based on hydroelasticity theory, which means the ship structural response to large waves is linear. Therefore, a 2D hydroelastoplasticity method that accounts for the coupling between the time-domain wave and ship beam for nonlinear vertical bending moment (VBM) is proposed. In addition, a nonlinear dynamic finite element method (FEM) is also applied for the nonlinear VBM of ship beam. The computational results of the FEM, including the nonlinear VBM and deformational angle, are compared with the results of the 2D hydroelastoplasticity and hydroelasticity. A number of numerical extreme wave models are selected for computations of hydroelasticity-plasticity, hydroelasticity, and FEM. A difference is observed between the nonlinear VBM calculated by FEM and linear VBM calculated by hydroelasticity, and conclusions are drawn.

Integral tow-lifting construction technology of a tensile beam-cable dome

A cable dome is a form of cable-strut tensegrity structure, which is popular for long span membrane roof structures. However, there is an opportunity for its major development for a wider range of applications if rigid roof cable dome structures can be achieved. In this paper, we propose the tensile beam-cable dome (TBCD), a new type of space structure based on the features of the cable dome. By changing the ridge cables to hinged tensile beams, a structure can easily be covered with a rigid roof. We introduce its configuration and mechanical characteristics, and put forward four categories of this structure with hinges set at different locations on the tensile beams. In addition to achieving the aims of tow-lifting and tensioning construction, the integral tow-lifting method is presented for TBCD, and the nonlinear dynamic finite element method (NDFEM) of form-finding analysis is introduced for the overall construction analysis. For integral tow-lifting construction, the mechanism hinges should be set at the middle of the tensile beams to make the tensile beam grid into a mechanism system. Through construction analysis of seven mechanism hinge distribution modes, the modes with mechanism hinges set only on the middle or inner tensile beams were optimal.

Finite Element Analysis of Bullet Penetration Circular Sandwich Plate

A nonlinear dynamic finite element method based on ANSYS/LS-DYNA is used to simulate the physical process of a bullet penetrating circular sandwich plate at a speed of about 400 m/s. In the simulation, Lagrange algorithm, Johnson-Cook and Crushable-foam constitutive model are choosed. Energy time history curve, impact force time history curve, Von-Mises stress nephogram and displacement nephogram are obtained. At the same time, stress time history curve of the maximum stress element and displacement time history curve of the maximum displacement node are obtained. Compared with the non-sandwich plate, it is found that the use of sandwich plate can reduce the total mass, inner plate stress and displacement, and can protect inner plate well.

The Damage Evolution of Concrete Structure under Earthquake

Theoretical study on earthquake damage under seismic load about of concreate structure，in order to better study the damage evolution mechanism of reinforced concrete frame structure in earthquake. The two-parameter seismic damage factor model,which is based on deformation and dissipation,was improved using the theoretical analysis method in this study .Using the three-level earthquake-resistant design damaging index based on the importance of structure as the collapse criteria for evaluation. Using the nonlinear dynamic finite element method and do a collapse numerical simulation analysis of a three layers concrete frame. Calculate the dynamic response and damaging factor of each time step, and study the damage evolution.The results show that the improved damage index calculating model can calculate both on the maximum damage index and structure damage index quantificationally and continuously and describe the process of collapse damage of the integral structure.

Application of the Improved Immune Algorithm to Structural Design Support System

Genetic algorithms (GAs), based on a multipoint search method and a crossover operation, are useful search procedures for combinatorial optimization problems. They also are applied to many kinds of practical optimization problem. However, in general, the GAs have a tendency to decrease rapidly of population diversities in processes of searching. In order to address this drawback, some researchers have proposed new algorithms for maintaining the population diversity. On the other hand, immune algorithms (IAs) are optimization techniques that imitate immune systems in an organism. The IAs are able to obtain a multiple quasi-optimum solution while maintaining the population diversity compared with GAs. In this paper, in order to consider the application of the IAs to optimum structural design problems, we developed a useful design support system for reinforced concrete (RC) slabs by combining a three-dimensional (3D) nonlinear dynamic finite element method (FEM) and an improved immune algorithm (IA). For the analysis of impact failure behavior of RC slabs, layered nonlinear FEM models with thin plate bending elements, and 3D elastoplastic FEM models with eight-node isoparametric hexahedral elements were used. First, an existing IA was modified to make it suitable for RC slab design, and both genetic and immune algorithms were applied to optimization problems with multiple optimum solutions. This modified IA was also applied to quasi-optimization problems with multiple maximum values. By comparing the above two approaches, the usefulness of the IA for design problems with discrete parameters was verified. Next, indices for evaluating impact resistance were discussed, and design simulation was conducted, based on these indices, by combining the layered nonlinear FEM and the IA. From results obtained, the accuracy and usefulness of the IA-based design support system were discussed. For obtaining a more practical design support system, shear reinforcement will be taken into account by combining the IA with the 3D elastoplastic FEM. Furthermore, the effectiveness and future potential of the design support system were confirmed by investigating an effect of introducing a database of design plans.

Impact-Resistant Design of RC Slabs Using Immune Algorithms

A three-dimensional nonlinear dynamic finite-element method (FEM) was applied to evaluate the ultimate behavior and failure modes of reinforced concrete (RC) slabs subjected to soft impact loads. In order to propose a practical impact-resistance evaluation method for RC slab structures, computer graphics (CGs) were used as a visualization technique to simulate impact-failure behavior of RC slabs until postfailure range was reached on the analytic results during impact loading. Immune algorithms are combined with a three-dimensional nonlinear dynamic FEM analysis for the purpose of proposing the design of RC slabs subject to soft impact loads. The results give evidence that presents complicated failure modes, and immune algorithms can be applied to the design of RC slabs effectively.

Computational studies on path independent integrals for non-linear dynamic crack problems

Recently the authors have derived various new types of path independent integrals in which the theoretical limitations of the so-calledJ integral are overcome. First, for elastodynamic crack problems, a path independent integralJ′ which has the physical meaning of energy release rate was derived. Later, more general forms of path independent integralsT * andT were derived, which are valid for any constitutive relation under quasi-static as well as dynamic conditions. This paper presents the theoretical and computational aspects of these integrals, of relevance in non-linear dynamic fracture mechanics. An efficient solution technique is also presented for non-linear dynamic finite element method in which a factorization of the assembled stiffness matrix is done only once throughout the computation for a given mesh pattern. Finite element analyses were carried out for an example problem of a center-cracked plate subject to a uniaxial impact loading. The material behavior was modeled by three different constitutive relations such as linear-elastic, elastic-plastic, elastic-viscoplastic cases. The applicability of theT * integral to non-linear dynamic fracture mechanics was shown with the numerical results.

Analysis of path independent T* integral in elastoplastic dynamic fracture testing.

Recently, the authors have derived new types of path independent integrals in which the theoretical limitations of the so-called J integral are overcome. For elastodynamic crack problems, a path independent J' integral which has the physical meaning of the energy release rate was derived. Later, the J' integral was extended to a more general form of path independent integral T* which is valid for any constitutive relation under quasi-static as well as dynamic conditions. In this paper, the T* integral in a compact tension (CT) specimen for elastoplastic dynamic fracture testing was analysed using an efficient nonlinear dynamic finite element method. The T* integral exhibits excellent path independency despite the impact loading and large plastic deformations. This indecates the validity of the T* integral as a fracture parameter in nonlinear dynamic fracture mechanics. This paper also shows the possibility of experimental measurement of the T* integral.