Computers & Structures最新文献

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.

In large-scale structural fire resistance tests, the interaction between the individual elements and the surrounding structure causes discrepancies in behaviour compared to single-element fire tests. Large-scale tests of real structures are challenging due to financial and time limitations. To bridge this gap, the concept of “Hybrid Fire Testing (HFT)” emerges, where a portion of the structural system (i.e., physical substructure) is experimentally tested while the remaining structure (i.e., numerical substructure) is analyzed numerically. The primary challenges in HFT involve ensuring stability throughout the analysis by considering the varying stiffness of the fire-exposed element during the test and establishing a versatile communication platform between the physical substructure (PS) and numerical substructure (NS) components. This paper presents a comprehensive HFT framework, implemented within a user-friendly software interface, facilitating both virtual and experimental testing. The software incorporates a new method addressing stability concerns by predicting PS stiffness during the test, achieving convergence within a limited number of iterations. Additionally, the framework includes a communication platform utilizing internet protocols (IP) and COM ports for rapid and easy connection to diverse experimental control systems and finite element software packages. The functionality of the developed software is validated through its successful application in an HFT conducted on a 3-story steel structure within a simulated environment. Both force-controlled and displacement-controlled approaches confirm the method’s adaptivity to the employed test procedures.

The paper presents a new type of weakly nonlinear two-scale model of controllable periodic porous piezoelectric structures saturated by Newtonian fluids. The flow is propelled by peristaltic deformation of microchannels which is induced due to piezoelectric segments embedded in the microstructure and locally actuated by voltage waves. The homogenization is employed to derive a macroscopic model of the poroelastic medium with effective parameters modified by piezoelectric properties of the skeleton. To capture the peristaltic pumping, the nonlinearity associated with deforming configuration must be respected. In the macroscopic model, this nonlinearity is introduced through homogenized coefficients depending on the deforming micro-configurations. For this, linear expansions based on the sensitivity analysis of the homogenized coefficients with respect to deformation induced by the macroscopic quantities are employed. This enables to avoid the two-scale tight coupling of the macro- and microproblems otherwise needed in nonlinear problems. The derived reduced-order model is implemented and verified using direct numerical simulations of the periodic heterogeneous medium. Numerical results demonstrate the peristaltic driven fluid propulsion in response to the electric actuation and the efficiency of the proposed treatment of the nonlinearity. The paper shows new perspectives in homogenization-based computationally efficient modelling of weakly nonlinear problems where continuum microstructures are perturbed by coupled fields.

This paper presents a new optimization framework in which the structural analyzer (isogeometric analysis–IGA) and data-driven surrogate model (deep neural network–DNN) are sequentially and repeatedly employed as the evaluation function in the optimization process of the computationally heavy problem of three-dimensional material distribution optimization in functionally graded (FG) plates. The optimization process starts with IGA normally, and the key point is to collect the evaluated candidates as data to build DNNs as surrogates predicting the plate behavior. Then, in the surrogate-assisted phase, based on the best predicted value, one more IGA analysis could be performed to find a new truly best candidate solution. This is also to track the surrogates' accuracy, which is another key feature of the proposed framework. When the prediction becomes less accurate, the optimization process is back to using IGA, more data is collected, and the whole procedure is repeated. Compliance minimization in FG plates under static bending is considered with various plate geometries. Numerical results confirm that the proposed recurrent optimization framework reduces up to 38% computational time whilst ensuring that the best candidate solution is always exact and of highest optimality.

To improve accuracy and convergence of biaxial wheel fatigue simulation with coupled nonlinearity, we propose a two-stage approach based on a composite tire model. The tire model is calibrated through an identification procedure, wherein the actual tire stiffness characteristics are matched, effectively addressing the difficulty in lack of tire structure and materials information. Based on the identified tire model, restart analysis algorithm is employed to decouple the biaxial simulation into a two-stage analysis, where wheel deformability is sequentially considered. At the first stage, large deformation of the loaded tire is calculated by modeling the wheel as a rigid part. Then the deformation and stress states of tire are maintained at the second stage, and the wheel elasticity is recovered for stress calculation. Compared to a single-stage direct method, the proposed method significantly reduces computational costs, while exhibiting only a minor stress discrepancy on the wheel rim. Finally, experimental results show that the present method not only ensures high accuracy in predicting stresses of the wheel disc, but also effectively reduces errors on the wheel rim region. It is convinced that the proposed method provides an efficient and reliable means for the comprehensive evaluation of wheel strength in biaxial fatigue tests.

The use of Reduced Dimensional Models (RDM) discretized like beams, plates and shell elements drastically decreases the computational cost of solving a full 3D elastic problem with a Finite Element Method (FEM). However, its kinematic assumptions are only applicable to bodies with regular sections or continuous layouts. For the correct analysis of irregular regions, it is necessary to rely on bi-dimensional or solid models that fully reproduce the geometry of the body and its behavior but have a much higher computational cost. The Mixing Dimensional Coupling (MDC) technique allows linking models discretized with elements of different topologies, allowing the possibility of considering the most cost-effective model in each region. This coupling takes place at the interface that delimits both models and relies on the equilibrium of work and reactions on its two faces. In this paper, the formulation is presented for coupling beams with laminar sections and 2D Plane-Stress (PS) models demonstrating its proper behavior. Finally, this coupling is used for defining a new beam element, the Beam-Like Reduced Order Model (BLROM), which is obtained from a Plane-Stress model of their longitudinal section.