Computers & Structures最新文献

In this study, a semi-analytical model is developed to investigate the fluid-structure coupling characteristics of liquid sloshing in an elastic rectangular container subjected to horizontal external excitation based on the scaled boundary finite element method (SBFEM) for the first time. The fluid inside the container is assumed to be incompressible, inviscid and irrotational, with the hydrodynamic pressure chosen as independent nodal variable in the governing equations. The container walls are considered as cantilever beams. The coupled fluid-structure system is initially divided into the structural domain and fluid domain, after which the SBFEM is employed to obtain the governing equations for each sub-domain. In the framework of the SBFEM, only the boundary of each sub-domain, rather than the entire computational domain, needs to be meshed and discretized. This method reduces the spatial dimension of the problem by one and offers an efficient approach to model the computational domain, while allowing for analytical formulations to be derived for the internal of the domain, resulting in an accurate description of the field variables. The fundamental equation of the entire coupled fluid-structure system is then assembled by performing the equilibrium condition and compatibility condition to ensure the balance of interaction forces at the interface between container walls and the liquid. The free vibrations analysis of the fluid-structure coupling system is solved by utilizing the generalized eigenvalue problem, and the transient dynamic response is determined using the synchronous solution algorithm in conjunction with the implicit-implicit scheme of the Newmark method. To validate the excellent accuracy and stability of the proposed formulation, several numerical examples are presented to investigate the free vibration and transient dynamic characteristics for the fluid-structure coupling problem. The obtained results show good agreement with reference solutions available in the literature. Additionally, the effects of geometrical and material parameters on the system responses are examined and discussed.

Ultrasonic guided waves are widely applied in health monitoring of slender structures. Being different from the well-known semi-analytical finite element method (SAFE), the global-discretized semi-analytical formulation (GDSA) exactly satisfies all the continuity and boundary conditions accurately while has improved computational efficiency, but is only applicable to the plate-like problems described in the Cartesian coordinate system currently, which is not applicable to the cylindrical waveguide. In the present work, the polar coordinate system is therefore introduced into the GDSA formulation to improve the computational efficiency of calculating the dispersion relation in a multi-layer cylindrical waveguide without loss of accuracy. The characteristic equations of the unit layer are derived from the principle of virtual work. The involved matrices are explicitly derived in the form of Kronecker product to reduce the dimension of the matrices to be evaluated and a reduced Boolean matrix is introduced to avoid the singularity problem caused by the trivial radial displacement of the central point. The dispersion curves of a steel wire are firstly analyzed and are verified in comparison with the analytical solutions solved from the Pochhammer-Chree equations. Taking the steel wire having a surface corrosion as a two-layer case example, the dispersion curves are obtained based on the quadratic eigenvalue equation. It is found that the cut-off frequency of the F(1,2) mode is sensitive to corrosion, having potential to detect corrosion of hidden cable wires.

This paper presents insights into the finite element (FE) simulation of semi-buried box structures under combined blast and fragment loads. Semi-buried box structures are important military protective structures of national and strategic importance and must withstand extreme loading threats from weapon detonations. Herein, the dynamic response of a semi-buried box structure with a blast door subjected to cased explosive charge detonations is investigated using the finite element simulation technique considering both blast and fragment loading. A series of analyses are performed using FE simulation software LS DYNA to estimate the intricate effects of two simultaneous cased charge detonations on the semi-buried box structure by varying the cased loading and point of fragment impact. At first, a comparative study of the semi-buried box structure with and without the protective sand layer is performed under different cased loading. Thereafter, the response of the semi-buried box structure with the protective sand layer is studied under different cased loading along with different points of fragment impacts. Results indicate that the present simulation technique is proficient in estimating the response of the semi-buried box structure under cased loading.

This paper proposes a nonlinear interval finite element method for elastic–plastic analysis of structures with spatially uncertain parameters. The spatially uncertain parameters are described by the interval field, and the variation bounds of the elastic–plastic structural responses can be calculated effectively. Quantified by the interval field, the spatially uncertain parameters are represented by the interval Karhunen–Loève (K-L) expansion, based on which the nonlinear interval finite element equilibrium equation is formulated. An interval iterative method is then presented to solve the equilibrium equation and obtain an outer solution of the variation bounds of structural responses such as displacement. In this method, the Newton-Raphson iterative method is used to transform the nonlinear problem into a linear one, and then the interval iterative method is introduced to solve the interval linear equations. Three numerical examples are employed to illustrate the feasibility and accuracy of the proposed method.

The aim of the present work consists in investigating the nonlinear behavior of porous beams reinforced with graphene platelets (GPL) and supported carbon nanotubes (CNT), termed functionally graded graphene platelets reinforced composite beam (FG-GPLRC) and functionally graded nanotube carbon reinforced composite beam (FG-CNTRC), respectively. Notably, the distribution of GPL/CNT is explored in both uniform and non-uniform patterns across the beam's thickness. What sets this research apart is its utilization of a refined beam model as enhanced FSDT incorporating nonlinear shear terms which is a crucial advancement in accurately capturing the post-buckling response in certain boundary conditions, a feature lacking in the existing FSDT literature. Innovatively, the post-buckling load-deflection relationship is derived through the solution of governing equations incorporating cubic nonlinearity. This is achieved by employing Galerkin's method alongside a non-iterative high-order continuation technique based on the asymptotic numerical method coupled with the Tchebychev-radial point interpolation method (TRPIM), using a path-following where the solutions are obtained branch-by-branch by eliminating the need for iterative processes. In essence, this research underscores the pivotal role of porosity and GPL/CNT reinforcement in shaping the post-buckling configuration of both perfect and imperfect nanocomposite beams, thereby advancing our understanding of structural behavior in porous nanocomposite materials. The findings of this study illuminate the significant influence of parameters such as porosity coefficient, porosity distribution, GPL/CNT distribution, and GPL-weight/CNT-volume fraction on the nonlinear buckling behavior of porous beams.

This paper introduces an advanced computational method for assessing the biaxial bending capacities of arbitrary-shaped reinforced concrete and steel–concrete composite cross-sections under fire conditions. The proposed approach involves a strain-driven iterative method coupled with an adaptive plastic centroid providing a “fail-safe” methodology by combining the bisection and damped Newton methods to improve its global convergence properties. Several key computational issues are addressed: (1) strength assessment criteria and its impact on computational outcomes, (2) the pathological behavior of local convergent iterative methods causing divergence or spurious solutions in stress-resultant space, (3) the softening behavior of concrete in compression affecting solution uniqueness and interaction diagram convexity, (4) non-planar vertical interaction diagrams induced by a mobile centroid, and (5) computational challenges related to solution non-uniqueness or non-existence in M-M stress resultant space when axial force falls outside the iso-load contour. An additional notable feature and novelty of the proposed method lie in its unique capability to assess true plane vertical interaction diagrams enabling also both ultimate and nominal strength assessment. Validation includes comparisons with other numerical results and experimental data from international literature, extending the benchmark results for the strength capacity assessment of composite cross-sections exposed to high temperatures.

This paper presents an energy-based homogenization method (EBHM) to calculate the equivalent elastic properties of lattice structures with generalized periodicity. Unlike the traditional implementation of the homogenization method, expressions of closed-form are derived for the equivalent elastic matrix, equivalent coefficients of thermal stress and thermal expansion in terms of the elastic strain energy of the unit cell so that the tedious numerical solution and programming are avoided. It is shown that the elastic strain energy can easily be calculated by mapping the unit cell with the imposition of specific periodic boundary conditions. The implementation can resort to any available finite element tools. Numerical examples are used to compare the EBHM with the homogenization mapping method, classical homogenization method and direct finite element analysis (FEA). The computational accuracy is investigated to show the effectiveness of the EBHM.

Multi-material phononic crystals hold promise for manipulating elastic wave propagation, enhancing the rigidity of the host structure, and realizing multifunctionality, including electric conduction, sound insulation, and heat diffusion. This paper presents a multi-material topology optimization pipeline for phononic crystal design, incorporating both isotropic and anisotropic materials. First, the dispersion theory for elastic wave propagation in periodic structures is presented. Then a novel interpolation function is proposed for multi-material topology optimization by using a variant of the projection operator. Finally, both isotropic and anisotropic materials are utilized to demonstrate the effectiveness of the proposed method for multi-material phononic crystal design when compared with SIMP-based structures. The numerical analysis indicates that the proposed method performs well in optimizing the phononic structure with metal composite materials.

Although various structural optimization techniques have a sound mathematical basis, the structural robustness and practical constructability of optimal designs pose a great challenge in the manufacturing stage. This paper presents an automated novel approach stemming from structural optimization and engineering principles, where discrete members of the structurally optimized designs are driven towards optimal utilization. The developed workflow unifies topology, layout and size optimization in a single parametric platform, which subsequently outputs a ready-to-manufacture CAD skeletal model which can be manufactured either additively or by assembly. All such outputs are checked and validated for structural requirements; strength, stiffness and stability in accordance with standard codes of practice. In the implementations, first, a topology-optimal model is generated and converted to a one-pixel-wide chain model using skeletonization. Herein, this paper uses a novel efficient method to extract the skeleton by using pixel-padding near the domain borders. Secondly, a spatial frame is extracted from the skeleton for its member size and layout optimization. Finally, the CAD model is generated using constructive solid geometry trees and the structural integrity of each member is assessed to ensure structural robustness prior to manufacturing. Various examples presented in the paper showcase the validity of the presented workflow across various structural engineering applications.

This study presents a new topology optimization method for transient two-phase fluid-structure interaction (FSI) problem. From a topology optimization point of view, it is formidable challenging to consider the mutual coupling with structure and two-phase flow and the evolution of sharp interface between two-phase flow (tracking interface). To tackle these formidable issues, the monolithic design approach incorporating with the deformation tensor is applied and the simulation of the two-phase flow is carried out with the volume of fluid (VOF). The spatially varying design variables in topology optimization determines whether the corresponding domains or elements are solid or fluid (two-phase flow) to maximize or minimize objective function. To simplify the coupling procedure and maintain the numerical convergence, the one-way coupling between two-phase fluid and structure is assumed rather than the two-way coupling. To carry out the topology optimization, the Darcy's force determined by the design variable is added to the Navier-Stokes equation and the Young's modulus and the structural density are also interpolated with respect to the design variables. In addition, the phase-field equation in the VOF method is also modified to take into account the evolution of the design variable and the front of the phase field value. To investigate the effect of the two-phase fluid-structure interaction, several transient two-dimensional problems are considered.