Full-scale Finite Element Model Research Articles

Advanced piezoelectric fluid energy harvesters by monolithic fluid–structure–piezoelectric coupling: A full-scale finite element model

A full-scale finite element model is presented for monolithic fluid–structure interaction (FSI) simulations of thin-walled piezoelectric fluid energy harvesters (PFEHs). Unlike widely used beam/plate-based models, our model employs a solid finite element discretization to precisely represent the complex PFEH designs involving microstructured transducers and non-uniform cantilevers. These features, plus the local FSI effects, are often ignored by simplified models. We applied the Galerkin method to formulate the weak form of the mixed equation system, integrating the flow dynamics, the geometrically nonlinear cantilever, the piezoelectric components, the electrode, and the output circuit within a closed-circuit electro-mechanical coupled system. The coupling of the multiple domains is achieved through boundary-fitted discretization within a monolithic scheme, using shifted-Crank–Nicolson temporal integration. This work explored implementing piezoelectric FSI systems within the FEniCS-based TurtleFSI library, and experimented techniques such as employing penalty functions for achieving electrode components with uniform electric potentials. We investigated various advanced PFEH features, including the baseplate design, the arrangement and microstructure of the piezoelectric components, and their influence on the system's dynamic and energy output behavior. The results confirmed the model's key advantages: full-scale modeling allows the integration of complex base structures and transducer microstructures in PFEH design. Combined with monolithic FSI coupling, it offers greater versatility, supporting a wider range of fluid environments and configurations in both wind and hydropower harvesting. Additionally, the modeling strategy can be intended not only to enhance power output, but also to minimize material usage, reduce mechanical fatigue, and extend the operational lifespan of PFEH systems.

Experimental and numerical validation of high strain rate impact response and progressive damage of 3D orthogonal woven composites

Advanced three-dimensional (3D) woven composites for aerospace and automotive applications are commonly subjected to complex dynamic environments involving vibrations and impacts, resulting in examining their impact properties is extremely important. This paper first experimentally discussed the influences of strain rates, weft yarn densities and loading directions on the impact performances and failure mechanisms of 3D orthogonal woven composites (3DOWCs). Secondly, full-scale finite element models were developed to predict the stress distribution and interfacial damage evolution process. The predictions were well in agreement with the experimental results. This research revealed that the impact characteristics exhibited strain rate sensitivity. With increasing weft yarn densities, the high strain rate impact behaviors also improved. Particularly, the warp impact strength of 3DOWCs with a weft yarn density of 2 yarn/cm (W5-2) at 812 s−1 was 17.4% and 24.0% higher than that of 3DOWCs with a weft yarn density of 1.5 yarn/cm (W5-1) at 822 s−1. Meanwhile, warp impact strength consistently exceeded to that of the weft impact strength. Additionally, strain rates, weft yarn densities, and loading directions dramatically affected the stress distribution and interfacial damage evolution process of 3DOWCs. Significant warp yarns fracture and matrix cracking were the principal failure patterns in the warp impact, whereas the damage in the weft impact was dominated by localized fracture of weft yarns and interfacial debonding.

On the application of hybrid deep 3D convolutional neural network algorithms for predicting the micromechanics of brain white matter

Background:Material characterization of brain white matter (BWM) is difficult due to the anisotropy inherent to the three-dimensional microstructure and the various interactions between heterogeneous brain-tissue (axon, myelin, and glia). Developing full scale finite element models that accurately represent the relationship between the micro and macroscale BWM is however extremely challenging and computationally expensive. The anisotropic properties of the microstructure of BWM computed by building unit cells under frequency domain viscoelasticity comprises of 36 individual constants each, for the loss and storage moduli. Furthermore, the architecture of each unit cell is arbitrary in an infinite dataset. Methods:In this study, we extend our previous work on developing representative volume elements (RVE) of the microstructure of the BWM in the frequency domain to develop 3D deep learning algorithms that can predict the anisotropic composite properties. The deep 3D convolutional neural network (CNN) algorithms utilizes a voxelization method to obtain geometry information from 3D RVEs. The architecture information encoded in the voxelized location is employed as input data while cross-referencing the RVEs’ material properties (output data). We further develop methods by incorporating parallel pathways, Residual Neural Networks and inception modulus that improve the efficiency of deep learning algorithms. Results:This paper presents different CNN algorithms in predicting the anisotropic composite properties of BWM. A quantitative analysis of the individual algorithms is presented with the view of identifying optimal strategies to interpret the combined measurements of brain MRE and DTI. Significance:The proposed Multiscale 3D ResNet (M3DR) algorithm demonstrates high learning ability and performance over baseline CNN algorithms in predicting BWM tissue properties. The hybrid M3DR framework also overcomes the significant limitations encountered in modeling brain tissue using finite elements alone including those such as high computational cost, mesh and simulation failure. The proposed framework also provides an efficient and streamlined platform for implementing complex boundary conditions, modeling intrinsic material properties and imparting interfacial architecture information.

Numerical modeling of the effects of impact conditions, foundation stiffness, and cable pretension on the behavior of high-tension guard cable systems

Cable barriers are one type of road restraint system commonly used on highways across the United States to contain and redirect errant vehicles and to prevent crossover accidents. These systems are typically tested under the provisions from safety manuals considering standard crash conditions (e.g., vehicle speed and impact angle). To understand the performance of cable barriers, it is important to evaluate the effects of non-standard crash and system conditions, including various vehicle speeds, impact angles, foundation material stiffness, and cable pretension loads. For that purpose, we created a set of full-scale finite element models in LS-DYNA to assess the effects of these non-standard conditions on the performance of high-tension cable barrier systems. The results from the models show that soft soils and under-tensioned systems yield higher cable deflections. Moreover, the results indicate that speeding vehicles colliding at non-standard angles increase cable tensions by up to 91% and cable deflections by up to 318%. These findings highlight the importance of evaluating cable barrier performance under more severe scenarios, which could lead to system failure and more severe collision consequences.

Periodic tetrahedral auxetic metamaterial

In this work, we introduce a novel three-dimensional auxetic mechanical metamaterial consisting of rotating tetrahedra connected by ideal hinges at their vertices, arranged to form a periodic framework structure. Through analytical and kinematic approaches, we evaluated the deformation behavior of the proposed idealized model, revealing Poisson’s ratios ranging between −0.36 and −2.72 and a transverse isotropic response as a result of its geometry. A specimen of the proposed metamaterial concept is designed by introducing deformable ribs between the solid units, and fabricated via additive manufacturing in polymeric material. Auxetic behavior of the prototype was assessed through a compression test and accurately predicted by a full-scale Finite Element model. We envisage that this new metamaterial design can have a significant impact on a wide range of engineering applications, particularly as bone substitute biomaterial.

Experimental evaluation and numerical investigation on the anti-collapse performance of beam-to-column connections in the minor-axis direction

This study examined the effects of structural resistance in both major- and minor-axis directions on the anti-collapse performance of a fully bolted composite frame. Current research in the field has focused predominantly on the anti-collapse performance of H-columns in the major-axis direction, potentially hindering accurate determination of anti-collapse transmission path within a structure. Herein, monotonic static loading experiments were conducted on two substructures in the minor-axis direction: one equipped with welded flange and bolted web connections and the other with fully bolted connections. The ductility development curve, dynamic collapse response curve, and resistance mechanism correlation curve were employed to evaluate the test results. Fully bolted connections exhibited superior nonlinear rotation capacity, which is essential for the development of a structure's catenary resistance The failure mechanisms and resistance development processes of the structures were reproduced using the ABAQUS/Explicit dynamic quasi-static modeling technique. A full-scale finite element model was developed for the frame with fully bolted connections loaded in the minor-axis direction. This research will contribute to the robust design of fully bolted structural frames that considers the effects of the column stiffness, thickness of the splicing cover plate, number of bolt rows, and bolt apertures of flange connections on deformation and resistance to loading in the minor-axis direction.

Parametric study, finite element analysis, and load capacity calculation for flexural behaviour of seawater and sea sand concrete beams reinforced with GFRP bars

This study sought to enhance the understanding of seawater sea sand concrete (SWSSC) structures reinforced with glass fiber-reinforced polymer (GFRP) bars. To achieve this, an experimental investigation was conducted involving the production and testing of 6 GFRP bar-reinforced SWSSC beams (GFRP beams) alongside 3 ordinary seawater sea sand concrete (OSWSSC) beams (Ordinary beams) to evaluate their flexural performance. Additionally, a subsequent analysis comprised the establishment of 11 full-scale finite element models aimed at parameter assessment on GFRP beams. The experimental and numerical findings revealed that an increase in sea sand replacement ratio in SWSSC beams, with a shear-span ratio of 2.2, led to varying degrees of shear-compression failure. Notably, owing to the superior crack resistance of SWSSC, the beams demonstrated outstanding structural coordination. Compared to OSWSSC beams, GFRP beams with a 100 % replacement ratio of sea sand or an increased in concrete strength to C55 had initial stiffness values that were 150 % and 106 % larger, respectively. Further investigation unveiled that a reduction in the shear-span ratio from 2.5 to 1.0 or an increase in the longitudinal reinforcement ratio from 1.27 % to 2.53 % significantly augmented the ultimate load-carrying capacity, resulting in increases of 88.0 % and 37.7 %, respectively. Based on these findings, several design recommendations are proposed: 1. Establish a deflection limit at l0/500 or implement more stringent measures for GFRP beams. 2. Consider reducing the diameter of GFRP bars while maintaining a 50 % sea sand replacement rate to mitigate crack formation. 3. An excessive longitudinal reinforcement ratio hampers the enhancement of specimen load-carrying capacity. 4. Consider utilizing Chinese specifications for flexural capacity calculations.

A new method for obtaining the in situ interfacial shear strength of the 3D woven composite

The interfacial strengths have significant effects on the accuracy of numerical simulations for the 3D woven composite (3DWC). However, obtaining the in situ interfacial strengths of the 3DWC currently presents substantial challenges. Furthermore, it remains questionable whether the interlaminar strength of laminate composites can represent the interfacial strength of the 3DWC. This paper proposes an in situ experiment-simulation (ISES) method to determine the shear strength of the interface within the 3DWC. For this purpose, several novel off-axis tensile specimens were designed with a simplified and continuous interface structure. A corresponding full-scale finite element (FE) model based on the mesoscale structure of the specimen was established, employing the cohesive zone model to describe the interface mechanical behavior. The in situ interfacial shear strength of the 3DWC was then obtained using the proposed ISES method.

Characterization of electric field distribution in valve-side casing of 500 kV converter transformer considering AC and DC mixed voltage

The converter transformer, as one of the indispensable core devices in the ultra-high voltage direct current (UHVDC) transmission system, exhibits highly complex electric field distribution characteristics within the valve-side bushing. In-depth research into the electric field distribution characteristics and variation patterns of the valve-side bushing under both alternating current (AC) and direct current (DC) voltage conditions is crucial for ensuring the reliable operation of the transmission system. This study focuses on investigating the electric field distribution of the valve-side bushing under AC and DC voltage excitations. A full-scale finite element model of the valve-side bushing of the converter transformer is constructed using finite element simulation software for modeling and research purposes. The results indicate that the internal electric field distribution of the bushing is generally similar under both AC and DC voltage excitations. However, in the SF6-filled region, a steeper voltage drop is observed under DC excitation compared to AC. The space charges generated in the DC electric field due to field polarization have a significant impact on the distortion of the electric field on the inner and outermost layer electrode plates. These conclusions provide theoretical guidance for the insulation design of the valve-side bushing in converter transformers at the 500 kV voltage level and similar ratings.

Dynamic response and energy absorption of aluminum foam sandwich under low-velocity impact

Aluminum foam sandwich (AFS) are widely used in energy absorption because of their light weight and excellent energy dissipation capabilities. In this study, energy absorption, deformation modes, and dynamic response of AFS under low-velocity impact are investigated using experimental and numerical approaches. Dynamic impact tests are performed utilizing a drop hammer impact test on AFS with different core densities, face sheet thicknesses, and impact energy. Based on the 3D Voronoi foam model, a full-scale finite element model (FEM) is developed to simulate the mechanical response of AFS under low-velocity impact, and verified by experimental results. The contributions of different AFS components to energy absorption at various impact velocities are further analyzed, along with the effects of face sheet thickness distribution. The results indicate that the performance of the face sheet and core and the impact energy have a remarkable influence on the low-velocity impact response and damage modes of the AFS. The type of structure configuration, “thin top and thick bottom,” enables the AFS better play its energy absorption while ensuring the overall light weight. This study provides a reference for the design and optimization of the face sheet thickness of AFS when it is used as an energy-absorbing member and improves their design efficiency.

Effect of slab dimensions on the maximum stress and ultimate vertical load of a 15-story flat slab building

The research of flat slab structures requires more investigation into the full-scale analysis of steel flat slab structures under vertical loads. The impact of slab dimensions on the maximum stress of slabs and columns, as well as the ultimate vertical load at the linear elastic stage, has been examined using full-scale finite element models. The particular structures selected for the analysis are 15-story steel flat slab structures with various slab dimensions under the static vertical load and standard earth gravity. This research also involves: (1) the verification of stress singularity at the corner of cubic columns in the finite element model; (2) the discussion about the variation of maximum stress of slabs and columns as the floor changes, and the interaction of columns and slabs; (3) the validation of the vulnerability of slab-column connection.

Experimental and numerical investigations on seismic behavior of spiral stirrup-confined square concrete-filled steel tubular columns

To investigate the seismic behavior of spiral stirrup-confined square concrete-filled steel tubular (SS-CFST) columns, ten square CFST columns, including eight SS-CFST columns and two ordinary CFST columns were experimentally studied through the cyclic loading tests. The critical test variables included the axial load ratio, spiral pitch, and longitudinal reinforcement ratio. First, the seismic behavior of the SS-CFST columns was herein discussed and clarified based on the failure modes, hysteretic response, skeleton curves, load-bearing capacity, strength and stiffness degradation, ductility and energy dissipation. Then, a total of 53 full-scale finite element (FE) models were established for parameter analysis of SS-CFST columns. The experimental and numerical results showed that the expansion deformation, necking and fracture of spiral stirrup were not formed when the SS-CFST columns were damaged, but the confinement effect effectively reduced the concrete fragmentation, alleviated the buckling of steel tube and longitudinal rebar, and limited the expansion of internal cracks. In the range of n=0.20–0.50, the ductility of SS-CFST columns significantly decreased with an increase in the axial load ratio, despite the stable bearing capacity and good energy dissipation of the columns. Moreover, unlike SS-CFST columns with high axial load ratio, spiral stirrup can only slightly improve the load-bearing capacity of SS-CFST columns with small axial load ratio (nt≤0.35). Compared with ordinary CFST columns, the strength degradation, ductility, collapse resistance, and energy dissipation of SS-CFST columns were significantly improved except for lateral stiffness, and the ultimate drift ratio of all SS-CFST columns in the test was greater than 3.00%. Furthermore, for SS-CFST columns, increasing the longitudinal reinforcement ratio can improve the lateral load-bearing capacity and stiffness. Finally, the formulas established in this paper can be adopted to assess the lateral load-bearing capacity of SS-CFST columns.

Bending study of submarine power cables based on a repeated unit cell model

Predicting the bending behaviours of a submarine power cable (SPC) is always a tough task due to its complex geometry and inner layer contact, not to mention the stick–slip mechanism. A full-scale finite element model is cumbersome during the early design stage and a more efficient model for practical use is required. Therefore, in this paper, a repeated unit cell (RUC) technique-based FE model is developed, which simplifies the bending analysis of SPCs using a short-length representative cell with periodic conditions. The verification of this RUC model is conducted from cable and component levels, respectively. The cable overall response is validated by the curvature-moment relationships from our cable bending tests regarding four cable samples whose material properties are obtained through a set of material tests. As for the component level, the behaviours of particular components are studied and compared with the results from a full-scale numerical model. Discrepancy is observed between the RUC model and the test, which can be explained by the distinctions of boundary conditions between these two methods. The proposed Cable-RUC model has been found robust and computationally efficient for studying SPCs under bending.

An improved equivalent beam model of large periodic beam-like space truss structures

Space truss structures are essential components for space-based remote sensing loads with high spatial and temporal resolutions. To achieve high-precision vibration control, an accurate and efficient dynamics model is essential. In addition to the current equivalent beam model (EBM) based on the classical continuum theory, an improved equivalent beam model (IEBM) is proposed that considers the impact of the distinction between trusses and beams on torsional and shear deformations, as well as the impact of shear deformation on flexural rigidity. According to the displacement expressions of spatial beams, torsional, shear, and bending correction coefficients are introduced to derive expressions of strain energy and kinetic energy. The energy equivalence principle is then utilized to calculate the elasticity and inertia matrices, and dynamics equations are established using the finite element method. Subsequently, an IEBM is constructed by employing the particle swarm optimization approach to determine the correction coefficients with the truss natural frequency as the optimization target. The natural vibration characteristics of the structure are estimated for various material properties. Compared with the full-scale finite element model, the EBM reaches a maximum error of 80% for a low modulus of elasticity, while the maximum error of the IEBM is less than 2% for any given parameters, indicating its superior accuracy to the EBM.

An energy-based method for predicting the peak displacement of steel casing composite pile under lateral impact loading

Effective and convenient prediction of the peak displacement of piles under collision conditions facilitates the design framework preparation and pile damage evaluation. Hence, an energy-based method was proposed to predict the peak displacement of the widely used steel casing composite (SCC) piles under impact loading. The pile deformation energy was first calculated based on its deformation characteristics and the relationship between the sectional bending moment and curvature. The pile deformation energy and pile–soil energy distribution ratio were then employed to determine the relationship between the total absorbed impact energy and pile head displacement, which was represented by curves. The peak pile displacement under lateral impact loading was finally obtained by interpolating the absorbed impact energy curves. By conducting sectional analysis of the pile considering the strain rate effects and using a structural pushover procedure, the peak pile head displacements for various collision cases were predicted with reasonable accuracy. The effectiveness and reliability of the proposed method were verified by comparing its results with those of previous reduced-scale impact tests and validated full-scale finite element models.

Experimental and numerical study on the dynamic response of aluminum alloy wood sandwich panels under high-velocity impact

The purpose of this study was to investigate the high-velocity impact response and failure modes of three-layer sandwich panels consisting of aluminum alloy sheets and plywood. The energy absorption mechanism and interaction between the plywood core and aluminum alloy panels were investigated by a high-velocity impact test. Different types of bullets were used in the impact test, and impact velocity parameters were obtained using a high-velocity camera to assess damage patterns. A full-scale finite element model was established to simulate the response mode of plywood sandwich under high-velocity impact. After the finite element model was verified by the experimental results, the energy absorption of the sandwich structure was further discussed. The results showed that the sandwich structure provided better protection than the double-layer structure. The analysis and predictions were in good agreement with the experimental results and numerical calculations. The experimental and numerical studies proposed in this paper are expected to provide new references and ideas for the design of multilayer structures with better impact resistance and lightweight characteristics.

On the compressive properties of aluminum and magnesium syntactic foams: Experiment and simulation

The influence of the materials of Al and Mg-based syntactic foams on the compressive behavior was investigated. Two different kinds of foams of cp-Al and cp-Mg in combination with ceramic hollow spheres (Al2O3 or Al2O3/SiO2/mullite) were manufactured by infiltration technique. A full-scale finite element model was established to explain the experimental results and to explore the effect of matrix and hollow sphere properties up to the peak strain. In this full-scale model, the ceramic hollow spheres’ effective elastic and fracture properties were used, determined from compression tests and micromechanical model of single hollow spheres. The finite element model predicted the compression curve with high precision in the investigated deformation range for the highly ductile foams with Al matrix, indicating that fracture becomes the dominant failure mode only near the peak stress. The model of Mg matrix syntactic foams showed that fracture in the early stage of compression did not change the strength of the material; however, it significantly lowered the stiffness in the case of Al2O3 hollow sphere having a diameter of ∼4 mm and thin (150 µm) wall. If significant reactions occurred between the matrix and hollow spheres during manufacturing, the model could estimate the formed complex interface’s effect on the syntactic foams’ strength.

Finite Element Model Updating of RC Bridge Structure with Static Load Testing: A Case Study of Vietnamese ThiThac Bridge in Coastal and Marine Environment.

Diagnostic load testing refers to the use of the measured historical responses of the structure in the field data to better understand its dynamic and static structural behaviours. It is important and necessary to predict the health state, load capacity, and aging of the structure by updating the finite element (FE) model, which can give useful information to aid the design of retrofits and the maintenance of the existing bridge in the future. The paper presents an update of the full-scale FE model for the reinforced concrete (RC) bridge structure over the seawater river based on the experimental strains under the static load testing in which the representative FE model of the actual structure is determined from the optimisation procedures. The optimisation variables are applied, including the cross-sectional properties and concrete material calibrated through the genetic algorithm (GA) optimisation in the MATLAB software, which interfaces with the FE modelling in the scripting of the SOFISTIK TEDDY software automatically. The bending moments at the mid-span of the RC girders are determined in the FE modelling to compute stresses, which are compared with the measured stresses through optimisation scenarios with a percentage error of the objective function less than 10%. The measured data of concrete strains are recorded from reusable strain transducers installed on the mid-span girders for every bridge span, which are used to calibrate the bridge model in static load testing. The novelty of the solution is to implement innovative techniques using field data as an improved approach for calibrating automatically the analytical FE model parameters of all RC spans of the bridge until its static behaviours are very similar to those of the actual bridge. The final updated FE modelling is used to apply truck load configurations according to bridge design standards such as the AASHTO specifications, which can predict the load limits of the existing bridge structure more accurately and reliably. These proposed approaches can be applied to large bridges as well as complex structures with supporting FE analysis software and data processing software.

Field test and probabilistic vulnerability assessment of a reinforced concrete bridge pier subjected to blast loads

Bridge piers have a high risk of being attacked in wartime, which has the potential to trigger progressive bridge collapse. This study aims to predict the failure probability of reinforced concrete (RC) piers exposed to military attack scenarios. Field explosion test and axial compression test were conducted to investigate the damage and post-blast performance of the RC pier first. Then, the uncertainties sourcing from the weapon accuracy were investigated. A performance-based (PB) vulnerability probabilistic assessment framework is developed which combines the Monte Carlo simulation (MCS) with a full-scale finite element (FE) model which was verified with test results. A probabilistic vulnerability assessment of a typical RC pier subjected to stochastic blast loading is conducted, and the vulnerability curve corresponding to three performance levels is developed. In addition, the damage modes and post-blast performance of the RC pier under blast loading are analyzed. Results show that the blast-induced damage to an RC pier had a significant influence on the axial bearing capacity, and the pier presents different damage modes at different scaled distances, which has a critical value of 0.65 m/kg1/3 between local and global damage modes. The failure probability of the pier corresponding to different performance levels increased with an increase in the TNT charge. The pier’s probability of collapse is less than 20 % when the TNT charge weight does not exceed 500 kg.

An aircraft accident reconstruction by numerical simulation method and investigations of impact force

Numerical simulation method is wildly used and proved to be efficient in accident reconstruction, and in-depth conclusions might be derived from reliable simulation results. An aircraft accident reconstruction of MU5735 is carried out in this paper on the basis of public information from the Internet, as an example of application of numerical simulation method in accident reconstruction. Impact point, velocity and weight of the aircraft are firstly estimated by technical methods. Then 17 cases of numerical simulations are conducted with a refined full-scale finite-element model of Airbus A320, and several factors are further discussed, i. e., penetration depth, impact load and impact force. It indicates that, (1) according to the penetration depth in public report, the aircraft probably impacted almost vertically to the ground with a velocity of around 250 m/s; (2) there is a peak of thousands of times the gravity acceleration in fuselage’s structural dynamic response and lasts for a long time, which might lead to the malfunction of the airborne equipment; (3) maxima of impact forces against different targets are mainly influenced by the materials of targets, and the peak of impact force against rigid ground is about 1.74 times larger than that against soil ground.