Global Finite Element Model Research Articles

Hybrid modular construction system “INNO3DJOINTS”: Experimental behaviour and numerical modelling of isolated sub-frames

With the growing demand for sustainable, cost-effective and overall-efficient building solutions, the need for dependable modular construction systems is steadily on the rise. In the present paper a novel hybrid modular construction system named INNO3DJOINTS is introduced, employing cold-formed welded steel tubular columns, fabricated according to EN 10219, and cold-formed steel thin-wall section based truss-girders, joined by the innovative plug-and-play (P&P) connector, designed to provide ease-of-assembly and -disassembly. The experimental investigation conducted on isolated sub-frame configurations of the novel system is presented, where 6 full-scale specimens were subjected to horizontal and vertical loading. The test configurations differed in the P&P joint socket thickness and the absence/presence of the light steel framing (LSF) wall, encased with oriented strand board (OSB). In addition, a numerical model for predicting the system's global behaviour is proposed, developed in SAP2000. Initially, the behaviour of the employed P&P joint configurations, categorized as partial-strength, is characterized using experimental and validated ABAQUS finite element model (FEM) data, resulting in a spring model implemented into the global FEM. Finally, the numerical and experimental results are compared and discussed, leading to conclusions regarding the system's 2D structural performance, identified behaviour governing phenomena, P&P joint influence, LSF wall and OSB contribution, as well as the capabilities of the developed FEM.

Temperature behavior of long-span cable-stayed bridges by using unified analysis

Varying temperatures significantly affect long-span cable-stayed bridges. However, previous studies on the temperature behavior of bridges were either limited by finite sensors, failing to capture the accurate relation between the temperature and responses, or constrained to a “divide-and-conquer” strategy, requiring considerable manual intervention. This study develops a unified approach to the investigation of thermal behaviors of cable-stayed bridges by integrating heat-transfer analysis and structural analysis based on the same refined global 3D finite element model. A navigation channel bridge of Hong Kong‒Zhuhai‒Macao Bridge is used as the testbed. First, the heat-transfer analysis is conducted based on thermal boundary conditions carefully determined from real-time ambient temperature, wind, and solar radiation, which are tailored for each surface to reflect the influence of the geometric configuration and temperature difference. Then, the detailed temperature distribution results are automatically converted to thermal loads, and thermal elements are changed to structural elements to calculate the temperature-induced responses. Results show that temperature has a significant effect on the structural responses of the bridge. The calculated temperatures and temperature-induced responses are in good agreement with their measured counterparts, verifying the effectiveness of the proposed unified approach to investigating the temperature behavior of cable-stayed bridges.

Global temperature behavior monitoring and analysis of a three-tower cable-stayed bridge

Varying temperature is a major load of long-span cable-stayed bridges. The temperature effect on the structural behavior may mask the influences of other loads. Conventional studies on the thermal behavior of bridges are limited to regression analyses based on measurement or numerical studies of 2D or local 3D models. This study investigated the global 3D temperature behaviors of a three-tower cable-stayed bridge through the integration of field monitoring and unified numerical simulation. A 3D refined model of the bridge with thermal elements was built, and the thermal boundary conditions were determined from environmental field monitoring data for the global 3D heat-transfer analysis. The calculated temperatures agreed well with the field monitoring counterparts. The temperatures were then input into the same global finite element model with mechanical elements for structural analysis. The temperature-induced structural responses, including the structural displacements and forces, agreed well with the measurement counterparts. The temperature-induced structural response variation pattern and sensitivity were summarized and quantified. This unified numerical simulation enables an efficient and accurate analysis of the global 3D thermal behavior of bridges, as compared with the conventional 2D or local 3D simulation.

Crack propagation analysis of slewing bearings in wind turbines applying a modified sub-model technology

As slewing bearings in wind turbines are exposed to complex operational environments, they are prone to crack initiation, propagation and evolution that can lead to contact fatigue problems. Reliable crack extension prediction is a critical requirement. With the goal of obtaining more accurate crack characteristics, this study proposes a crack initiated contact finite element model (CI-CFEM) targeted at the raceway of slewing bearings by introducing a modified sub-model. In the application of the global finite element model (G-FEM) to the slewing bearing system, the rolling displacements of the ball and the boundary displacements are employed in CI-CFEM to take account of external ring deformations and the support conditions. The crack is embedded using FRANC3D, and the stress intensity factor distribution and propagation characteristics of the crack front are investigated. Furthermore, the effect of external load and the design parameters of the slewing bearing on crack propagation are explored, providing insight for optimizing the design of slewing bearings to extend service life. The results reveal that changing external loads and bearing parameters are an effective means of retarding crack propagation rate, while have relatively minor influence on crack growth angle.

Structural efficiency evaluation of innovative reusable launch vehicles

This work is focused on evaluating the structural design of the innovative reusable micro launcher MESO, originated from the RRTB, a funded project by EU. The structural efficiency of MESO is evaluated in association with its mass budget, which is based on project’s early adopted requirements. In this particular design loop, the reusability concept is intergraded by implementing the fail-safe design approach, considering the exclusive use of high TRL aluminum alloys. The main objective of this work is achieved by developing a global Finite Element Model (FEM), comprising a set of sub-models, which represent the primary structure, the secondary structures, the equipment and their interfaces as well.The paper proceeds with the description of the modelling approach regarding mesh development and the connections created between the sub-models for assembling the integrated Global FEM of the launcher. The first iteration of the load analysis loop resulted in the extraction of the Design Limit Loads (DLL). The DLL investigated in both ground and flight cases, which comprise the most severe combination of quasi-static loads. The FEM is verified and subjected to various types of preliminary structural analysis, taking into consideration the required ECSS design and safety factors for static strength and stability assessment.The analyses results indicated the order of magnitude and the location of all weak areas of the launcher. Subsequently a preliminary sizing procedure is performed in order to prevent all failure modes according to the structural design requirements. The conclusions derived from the structural analysis of the first design loop influence the design modifications to be considered for the next design loop, where the same steps are going to be followed until the structural design requirements are satisfied once again.

Preliminary nonlinear analysis of a scaled masonry building under shaking test for the blind prediction of the SERA AIMS project

Experimental tests performed on scaled masonry buildings provide key information to improve the knowledge under seismic actions. Masonry buildings behavior is strongly influenced by their physical and mechanical parameters under dynamic actions. In fact, the actual structural behavior is very complex to predict due to the significant variability of the input parameters and the strong heterogeneity of masonry. Furthermore, the behavior of masonry buildings is often influenced by the interaction with adjacent building units. In this context, the SERA AIMS project aims to improve knowledge on the interaction between adjacent buildings. In order to assess the seismic capacity of masonry structures and their damage evolution, nonlinear models often require a numerical calibration of nonlinear parameters. Simplified Finite Element (FE) models, with some very simple assumptions, can be more suitable for complex problems like as the interaction between adjacent building aggregates. The low initial knowledge level in the SERA AIMS blind competition favored simple assumptions. The availability of simple models allowed to perform consecutive time histories including the cumulative effects of previous signals. In fact, the tested prototype was subjected to many replicas. The masonry structure and the crucial interfaces between the units have been modelled by means of nonlinear elements according to the reduced knowledge level at the blind prediction stage. The main goal was to estimate the key information of a masonry building under seismic action like as: triggering and the type of damage at the most stressed areas and therefore the load threshold at which evident damage is expected. Global FE model provides information on the global behaviour (in plane behaviour), while, according to the failure models typically found in masonry buildings, kinematic analyses have been performed to assess the out of plane (local) behaviour, too. The numerical results obtained by the preliminary analysis have been compared with the experimentally detected damages. The simplified approach, based on limited information without calibration, discussed in this paper, represents a useful support tool to design dynamic tests on full-scale or scaled masonry buildings, but also to assess the vulnerability of real masonry structures.

Impact of Airframe–Propulsion System Modeling Strategies on Key Structural Performance Metrics

Whole-aircraft coupled aerodynamics, flight dynamics, and structural dynamics models are commonly employed during the aircraft design process, generally increasing in fidelity, and associatively accuracy, as the design matures. While literature acknowledges the impact of explicitly representing the propulsion system in such models, it does not address the impact of structural idealizations on key metrics that inform early conceptual design. This paper investigates the impact of a range of propulsion system structural modeling strategies and their attendant idealizations on the accuracy with which key structural performance metrics may be acquired. A conventional tube-and-wing airframe with under-wing-mounted, high-bypass-ratio, turbofan propulsion systems is employed as a verification case. The lowest-fidelity modeling strategies defined herein are capable of acquiring airframe loads and vertical power plant center-of-mass inertial loads within . Higher-fidelity, predominantly 2D strategies are necessary for acquisition of propulsion system displacements, deformations, and power plant swing frequency within of a global finite element model. However, sufficient data must be available to allow the construction of higher-fidelity strategies during early design stages.

Buckling and Bearing Capacity Variation Caused by Local Corrosion at Support in Steel Bridge

The local corrosion of steel plate girder bridges at supports is a major issue affecting the safety. To clarify its effect on the buckling characteristics and bearing capacity, the static tests were carried out. The bearing capacities and local deformation were compared. The local buckling characteristics were refined by stress testing. To further investigate the effect mechanism of corrosion, the global finite element models (FEMs) of bridge were established. Separate corrosion of each component was considered. By comparing the strength and ultimate loads, the key member on bearing capacity reduction was specified. The influence of corrosion scope including the parameters of length, height, and depth on the bearing capacity was clarified. The results show the effect mechanisms of different-member corrosion on bearing capacity reduction were completely diverse. The web corrosion was the main cause of the bearing capacity reduction, which was the first to buckle. The relative position between corrosion scope and the support should also be considered during the evaluation of bearing capacity.

Further Development of the W7-X Magnet System Finite Element Global Model in Preparation for Enhanced Operation Phase

The Wendelstein 7-X (W7-X) stellarator equipped with a large cryogenic magnet system (MS) has been enhanced for the long pulse operation at the Max-Planck-Institute for Plasma Physics in Greifswald, Germany. In parallel with the process, the MS global finite element model (GM) has been developed further to consider two interrelated issues: i) the effect of winding pack (WP) embedding (EB) process and ii) planar coil case pins and bolts plastification. The procedure of implementing the EB effect in ANSYS is based on the death/birth feature of particular elements, special fixation algorithm and careful check of the unavoidable artificial stress level. The approach to get a refined prediction of plastic strain/ stress levels for multiple pins and bolts uses the detailed local pin/bolt models to check the GM stiffness representation and to deliver the target values using an interpolation procedure. If the main focus during first two experimental campaigns, for roughly 13 months, was on the static structural strength of the MS, the issue of cyclic behavior is addressed in the updated GM post-processing procedure. The post-processing routine predicts how many electromagnetic cycles and cool down-warm up cycles with particular loading patterns could be safely withstood with required margins by the system components. This paper is focusing on the structural cyclic behavior modelling of the W7-X magnet system components. Several related issues are addressed, such as: 1) Specific features of winding pack embedding modelling, 2) Reasonably simplified modeling of multiple pins and bolts in the GM, 3) Preliminary assessment of coil case pin failure. In addition, lessons learned so far regarding the gradual modifications of the GM are also summarized briefly.

Fracture mechanics and hot spot stress‐based fatigue life calculation: Case study for a crane runway girder

AbstractThis work presents the case study of a welded overhead crane runway girder. A full‐shell global finite element model was developed and validated using strain measurements. The global model drives solid submodels of different scales. Using load spectra based on real operational data, hot spot stress and XFEM‐based fracture mechanics simulations are performed to assess the fatigue properties of two critical joints. For the fracture mechanics‐based approach, it is shown that small cracks quickly converge to the same aspect ratio. Hence, the choice of the initial crack aspect ratio was found to be inconsequential. But the aspect ratio must not be assumed to be constant during the fatigue crack growth simulations. Finally, it is shown that the size at which a crack is transferred from one submodel to a subsequent is critical for the accuracy of the fatigue crack growth simulations.

Maxwell force analysis of CN HCCB TBM based on preliminary design

The Chinese (CN) Helium Cooled Ceramic Breeder (HCCB) Test Blanket Module (TBM) will be tested in ITER according to the ITER TBM program. In order to well achieve the test goals and to meet the ITER technical requirements, the design of CN HCCB TBM is continuously updating since 2004 and it is currently in preliminary design (PD) phase. As an in-vessel component of ITER, TBM will be exposed to strong magnetic field. Consequently, large electromagnetic (EM) loads may generate on TBM structures and should be quantitatively evaluated to provide input for the structural integrity assessment of TBM. In this paper, the Maxwell force (MF), one of the EM loads, is numerically calculated and discussed. To improve the calculation efficiency, the finite element (FE) model is simplified by ignoring the cooling channels. Hence, the corrected B-H curve based on effective volume ratio of ferrite material is adopted to exclude the influence caused by absence of cooling channels. Current obtained results are comparable with those in previous work and agree well with analytical ones also, which indicates that the global FE model developed here is acceptable and the analytical equation derived in this paper can be used to approximately predict the MF on TBM.

Proposal of analysis method of global-local finite element method for finite strain elastic-plastic fracture mechanics analysis

The purpose of this study is to make it possible to perform a large number of paratric analyzes on the position and shape of cracks under finite elasto-plastic deformation. In this report, we propose a one-way coupled analysis method using displacement interpolation between a global finite element method analysis model created without assuming cracks and a local finite element method analysis model assuming cracks. The proposed method is based on the superconvergent patch recovery, and uses the least-squares method to apply the nodal displacements of the global finite element model to the nodes of the local finite element model as displacement boundary conditions. In addition, we will create an merged finite element method analysis model assuming a crack directly in the global finite element method analysis model and identify the application conditions that can be applied to the problem without loss of accuracy through relative comparison by J-integral calculation at the crack tip which is nonlinear fracture mechanics parameter.

Investigation of Adhesive Joining Strategies for the Application of a Multi-Material Light Rail Vehicle.

To meet the high demand for lightweight energy-efficient and safe structures for transport applications, a current state-of-the-art light rail vehicle structure is under development that adopts a multi-material design strategy. This strategy creates the need for advanced multi-material joining technologies. The compatibility of the adhesive with a wide range of material types and the possibility of joining multi-material structures is also a key advantage to its success. In this paper, the feasibility of using either epoxy or polyurethane adhesive joining techniques applied to the multi-material vehicle structure is investigated. Importantly, consideration is given to the effect of variation in bond thickness for both families of structural adhesives. Multi-material adhesively bonded single lap joints with different adhesives of controlled bond thicknesses were manufactured and tested in order to experimentally assess the shear strength and stiffness. The torsional stiffness and natural frequency of the vehicle were modelled using a global two-dimensional finite element model (FEM) with different adhesive properties, and the obtained vehicle performances were further explained by the coupon-level experimental tests. The results showed that the vehicle using polyurethane adhesive with a target bond thickness of 1.0 mm allowed for optimal modal frequency and weight reduction.

A Finite Element Method for Predicting Equivalent Properties of 14T MRI Main Coil

In 2017,The Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) has announced a project to develop a 14 T MRI for the research of brain science and neurology. A type of conductor like 11.7 T MRI Magnet is developed for main coil of 14T MRI, which is called Rutherford cable in channel (RIC). Conductor of 14 T MRI magnet is subjected to huge electromagnetic loads and mechanical load during the operational period. During the design, the material properties of conductor must be obtained to predict the stress-strain behavior accurately to simplify the finite element (FE) model. This paper proposes a finite element method for predicting equivalent properties of 14 T MRI main coil. Then a global finite element model of a small model coil is built to verify the effectiveness and accuracy of this method.

Dynamic Behavior of a Suspended Steel Space Frame-Glass Composite Floor

This study investigates the dynamic performance of a large-span suspended steel space frame-glass composite floor (SSSF-GCF). Both the ambient vibration and the human-induced vibration of the floor were experimentally measured to identify vertical dynamic characteristics and evaluate vibration serviceability of the floor. Although vertical dynamic characteristics of the floor based on the global simplified finite element (FE) model of the structure agree well with those identified via experimental modal analysis, the global simplified FE model significantly underestimates vertical vibration amplitudes of the floor due to the coupled effect between two layers. Accordingly, an equivalent local FE model of the floor system was proposed and updated via adjusting the vertical stiffness of the interstory hanging pillars. It is shown that the equivalent local FE model can well predict both the dynamic characteristics and human-induced vibration response of the floor. Finally, the effect of the damping ratio on the acceleration response of the floor was numerically demonstrated with the verified local FE model.

A two-stage finite element based method for the study of stiffness and failure load of osteoporotic spines

Abstract A two-step method for investigating the stiffnesses and failure loads of vertebral bodies is presented. It is based on the representation of the spine in a global finite element model of structural elements. A detailed model of two interconnected vertebrae and an intervertebral disc was implemented. Calculations on this model are shown which illustrate the dependencies of structural stiffnesses on vertebral body properties. These structural stiffnesses can then be used to represent the spine in the global model.

Investigation on Plastic Flow Behaviors of FCC Polycrystalline Aluminum under Pre-Cyclic Tension-Compression Loading: Experiments and Crystal Plasticity Modeling.

The plastic flow behaviors of FCC polycrystalline aluminum after pre-cyclic tension-compression deformation are mainly investigated in tension–torsion stress space by the physically based crystal plasticity model introducing a back-stress. A global finite element model (GFEM) constructed of sufficient grains was established to simulate the same-size thin-walled tube specimen constrained and loaded as the experiments of yield surfaces. The computational results showed that the shape of subsequent yield surfaces and the plastic flow directions directly depended on the given offset strain levels and the applied re-loading paths under different pre-cyclic deformations. The angle deviation between the plastic flow direction and the theoretical orthogonal direction further indicated that there was a large difference between them in the inverse pre-straining direction, but the difference was negligible in the pre-straining direction. From the influence of the anisotropic evolution of the subsequent yield surfaces on plastic flow, we found that the plastic normality rule followed the smooth yield locus; conversely, the significant non-associated flow was attributed to the distorted yield locus. Furthermore, it was also demonstrated that the anisotropic evolution and the plastic flow trend of the subsequent yield surfaces obtained by experiments can be better reproduced by the crystal plasticity model.

Comparison of structural model reduction methods applied to a large-deformation wing box

AbstractIn this paper, the accuracy and practical capabilities of three different reduced-order models (ROMs) are explored: an enhanced implicit condensation and expansion (EnICE) model, a finite element beam model, and a finite volume beam model are compared for their capability to accurately predict the nonlinear structural response of geometrically nonlinear built-up wing structures. This work briefly outlines the different order reduction methods, highlighting the associated assumptions and computational effort. The ROMs are then used to calculate the wing deflection for different representative load cases and these results are compared with the global finite element model (GFEM) predictions when possible. Overall, the ROMs are found to be able to capture the nonlinear GFEM behaviour accurately, but differences are noticed at very large displacements and rotations due to local geometrical effects.

Multidisciplinary Optimisation of Aircraft Structures with Critical Non-Regular Areas: Current Practice and Challenges

The design optimisation of aerostructures is largely based on Multidisciplinary Design Optimisation (MDO), which is a set of tools used by the aircraft industry to size primary structures: wings, large portions of the fuselage or even an entire aircraft. The procedure is computationally expensive, as it must account for several thousands of loadcases, multiple analyses with hundreds of thousands of degrees of freedom, thousands of design variables and millions of constraints. Because of this, the coarse Global Finite Element Model (GFEM), on which the procedure is based, cannot be further refined. The structures represented in the GFEM contain many components and non-regular areas, which require a detailed modelling to capture their complex mechanical behaviour. Instead, in the GFEM, these components are represented by simplified models with approximated stiffness, whose main role is to contribute to the identification of the load paths over the whole structure. Therefore, these parts are kept fixed and are not constrained during the optimisation, as the description of their internal deformation is not sufficiently accurate. In this paper, we show that it would nevertheless be desirable to size the non-regular areas and the overall structures at once. Firstly, we introduce the concept of non-regular areas in the context of a structural airframe MDO. Secondly, we present a literature survey on MDO with a critical review of several architectures and their current applications to aircraft design optimisation. Then, we analyse and demonstrate with examples the possible consequences of neglecting non-regular areas when MDO is applied. In the conclusion, we analyse the requirements for alternative approaches and why the current ones are not viable solutions. Lastly, we discuss which characteristics of the problem could be exploited to contain the computational cost.

Benchmark of wrinkling formulae and methods for pre-sizing of aircraft lightweight sandwich structures

Sandwich structures are widely used in many industrial applications and especially in light aviation. The local buckling phenomenon named “wrinkling” is one of the primary causes of compressive failure of such structures. Its calculation is a difficult practical problem since this phenomenon cannot be captured by the GFEM (Global Finite Element Model) classically used for aircraft structure sizing. Therefore, pre-sizing involves the use of a wrinkling model, which can be found in the literature. In practice, such models are used with high safety factors by the industry. This paper proposes an evaluation of analytical wrinkling formulas in an industrial setting. Realistic applications involve a framework (3D stress state, orthotropy, skin asymmetry) far from the assumptions on which most of the analytical formulations are based. The case study is a sandwich composite beam subjected to uni-axial compressive load. Limitations and assumptions of the analytical wrinkling models studied are quantified and a discussion on the relevance of using simple formulas for the design of sandwich structured composites is developed.