Full-scale Finite Element Model Research Articles

Evaluation of the need for negative moment reinforcing in prestressed concrete bridges in the view of service loads

It is common practice to put additional longitudinal reinforcement (b2 bars) over intermediate supports to resist any negative moment induced by the superimposed dead loads and live loads on bridges. However, little research has been conducted on the performance of the additional negative reinforcing steel. Requirements for the termination of the additional negative moment reinforcing steel have largely been based upon the engineering judgement, previous performance, and existing practice. The main objective of the research is to evaluate the effect of different amounts of b2 bars on resisting the negative moment over the pier on a continuous prestressed concrete girder bridge when it subject to the live load generated moment and secondary moment. To achieve this objective, a live load field test was performed on a bridge designed with different amounts of b2 bars to allow for comparison of the varying levels of negative moment reinforcement present. A full-scale finite element model was developed and validated against the field-collected data to study the b2 bar performance subjected to live loads. An evaluation was performed, utilizing an analytical approach by calculating the time-dependent secondary moment using mRESTRAINT and loading the beam-line FE model with the maximum negative moment. It was found that the negative moment induced by the live load and secondary moment does appear through the service life of the bridge. The high differential shrinkage rate between the fresh deck concrete and the girder concrete is the main source of the negative moment over the supports. The magnitude of the secondary moment was found to be highly influenced by the time when the continuity established. The results also indicated that the additional longitudinal reinforcing steel provides minimal effect on resistance to the negative moment prior to the formulation of deck cracking, regardless of whether the negative moment was induced by live loads or secondary moment. The current design approach determines the b2 bars requirement for the strength level based on the live load, it may be necessary to include the secondary moment in the design.

A Computational Biomechanics Human Body Model Coupling Finite Element and Multibody Segments for Assessment of Head/Brain Injuries in Car-To-Pedestrian Collisions.

It has been challenging to efficiently and accurately reproduce pedestrian head/brain injury, which is one of the most important causes of pedestrian deaths in road traffic accidents, due to the limitations of existing pedestrian computational models, and the complexity of accidents. In this paper, a new coupled pedestrian computational biomechanics model (CPCBM) for head safety study is established via coupling two existing commercial pedestrian models. The head–neck complex of the CPCBM is from the Total Human Model for Safety (THUMS, Toyota Central R&D Laboratories, Nagakute, Japan) (Version 4.01) finite element model and the rest of the parts of the body are from the Netherlands Organisation for Applied Scientific Research (TNO, The Hague, The Netherlands) (Version 7.5) multibody model. The CPCBM was validated in terms of head kinematics and injury by reproducing three cadaveric tests published in the literature, and a correlation and analysis (CORA) objective rating tool was applied to evaluate the correlation of the related signals between the predictions using the CPCBM and the test results. The results show that the CPCBM head center of gravity (COG) trajectories in the impact direction (YOZ plane) strongly agree with the experimental results (CORA ratings: Y = 0.99 ± 0.01; Z = 0.98 ± 0.01); the head COG velocity with respect to the test vehicle correlates well with the test data (CORA ratings: 0.85 ± 0.05); however, the correlation of the acceleration is less strong (CORA ratings: 0.77 ± 0.06). No significant differences in the behavior in predicting the head kinematics and injuries of the tested subjects were observed between the TNO model and CPCBM. Furthermore, the application of the CPCBM leads to substantial reduction of the computation time cost in reproducing the pedestrian head tissue level injuries, compared to the full-scale finite element model, which suggests that the CPCBM could present an efficient tool for pedestrian brain-injury research.

Data‐driven models for temperature distribution effects on natural frequencies and thermal prestress modeling

In vibration-based damage detection, it is fundamentally important to distinguish between changes in the dynamics of a structure and those related to environmental effects. Modal properties of structures are widely used as damage-sensitive features and indicate changes in physical properties due to structural damage or degradation. However, civil structures such as bridges are influenced by various operational and environmental conditions (such as traffic, wind, humidity, and, most importantly, temperature), and these variables also alter the modal properties of structures. Changes in modal properties caused by environmental effects can mask the effect of structural damage, resulting in unreliable structural damage assessments. It is thus fundamentally important to understand the relationship between environmental effects and modal properties. In this paper, a full-scale finite element (FE) model is used in a simulation-based study to investigate the effects of temperature distribution on natural frequencies. Two approaches for modeling the temperature effects on natural frequencies (thermal prestress imposed at an element level and temperature-dependent Young's modulus) are implemented in the FE model, and results are compared. Then, temperature profiles of the model are hypothetically simulated. These simulation results are used to develop a linear model and the three most popular machine learning models to reproduce the effects of temperature distribution on natural frequencies. Finally, a comprehensive comparison is made between the performances of these data-driven models.

Investigation of wind effect reduction on square high-rise buildings by corner modification

Although empirical formulas have been provided in relevant design code for estimating wind loads and wind-induced responses on square high-rise buildings, the effects of corner modification treatments on wind loads and wind-induced responses of square high-rise buildings need to be evaluated quantitatively. In this study, wind pressure measurements for a benchmark square high-rise building and three corner modified square high-rise buildings were first carried out to acquire the spatial-temporal varying pressure distributions. Moreover, the corresponding full-scale finite element models were established in ANSYS software to get their dynamic properties. Combined with wind tunnel test results and modal analysis, wind loads and wind-induced responses of the four square high-rise buildings were calculated and compared for designing the best aerodynamic treatment of reducing wind effects on square high-rise buildings. This article aims to provide visual comparisons of wind effect reduction for structural designers and owners of square high-rise buildings.

High-Fidelity Sensitivity Analysis of Modal Properties of Mistuned Bladed Disks Regarding Material Anisotropy

A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using full-scale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems (CS) used in industry for description of the blade anisotropy orientations. The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.

Evaluation of displacements by means of 3D laser scanning in a mechanically loaded replica of a hull section of the Vasa ship

For a development of full-scale finite-element models of large objects in cultural heritage, it can be useful to mechanically test replicas of key parts to identify structural properties which would otherwise not be available. This paper presents full scale tests on a replica of a section of the hull of the 17th century warship Vasa in three load configurations. We focus on determining a displacement of the loaded replica from 3D laser measurements. Two measures were found useful: (i) 3D displacements at well-defined intersections of the wooden replica, and (ii) normal displacements of larger surfaces. Wood surfaces were preferred to steel parts of the rig since the latter showed more scatter in displacement values in their point clouds caused by their reflective properties. The measurements were verified with draw-wire sensors. Some of these sensors were attached to the steel rig supporting the replica and, therefore, measured relative displacements. The scanning data was also useful to quantify the absolute movement of the steel rig supporting the replica, which improved the precision of the measurements of replica deformation. Finally, it is discussed how the replica test results can be used in a model of the entire museum ship.

Analysis of the Effect of Tungsten Inert Gas Welding Sequences on Residual Stress and Distortion of CFETR Vacuum Vessel Using Finite Element Simulations

The as-welded sectors of China Fusion Engineering Testing Reactor (CFETR) vacuum vessel (VV) have very tight tolerances. However, it is difficult to investigate the welding stress and distortion without the production of a full-scale prototype. Therefore, it is important to predict and reduce the welding stress and distortion to guarantee the final assembly by using an accurately adjusted finite element model. In this paper, a full-scale finite element model of the 1/32 VV mock-up was built by ABAQUS which is a powerful finite element software for engineering simulation, and three different tungsten inert gas (TIG) welding sequences were simulated to study the effect of welding sequences on the welding stress and distortion. The results showed that the main welding stress happened on the weld zone, and the maximum distortion occurred on the shell near the welding joints between the inboard segment (PS1) and the lower segment (PS4). The inboard segment (PS1), upper segment (PS2), and lower segment (PS4) distorted to inside of the shell perpendicularly, while the equatorial segment (PS3) distorted to outside of the shell perpendicularly. According to the further analysis, the maximum welding stresses in sequence 1, sequence 2, and sequence 3 were 234.509 MPa, 234.731 MPa, and 234.508 MPa, respectively, and the average welding stresses were 117.268 MPa, 117.367 MPa, and 117.241 MPa, respectively, meanwhile, the maximum welding displacements in sequence 1, sequence 2, and sequence 3 were 1.158 mm, 1.157 mm, and 1.149 mm, respectively, and the average welding displacements were 1.048 mm, 1.053 mm, and 1.042 mm, respectively. Thus, an optimized welding sequence 3 was obtained and could be applied to the practical assembly process of the 1/32 VV mock-up.

Lightweight and crashworthiness design of an electric vehicle using a six-sigma robust design optimization method

ABSTRACTDesign optimization plays an important role in electric vehicle (EV) design. However, fluctuations in design variables and noise factors during the forming process affect the stability of optimization results. This study uses six-sigma robust design optimization to explore the lightweight design and crashworthiness of EVs with uncertainty. A full-scale finite element model of an EV is established. Then, multi-objective design optimization is performed by integrating optimal Latin hypercube sampling, radial basis functions and non-dominated sorting genetic algorithm-II to achieve minimum peak acceleration and mass. Finally, six-sigma robust optimization designs are applied to improve the reliability and sigma level. Robust optimization using adaptive importance sampling is shown to be more efficient than that using Monte Carlo sampling. Moreover, deformation of the battery compartment and peak acceleration of the B-pillar are greatly decreased. The EV’s safety performance is improved and the lightweight effect is remarkable, validating the strong engineering practicability of the method.

A Model for the Design of a Pomelo Peel Bioinspired Foam

The structure of pomelo peel arouses research interest in recent years because of the outstanding damping and energy dissipating performance of the pomelo peel. Researchers found that pomelo peel has varying pore size through the peel thickness; the pore size gradient is one of the key reasons leading to superior energy dissipation performance of pomelo peel. In this paper, we introduce a method to model pomelo peel bioinspired foams with nonuniform pore distribution. We generate the skeletal open cell structure of the bioinspired foams using Voronoi tessellation. The skeleton of the bioinspired foams is built as three-dimension (3D) beam elements in a full-scale finite element model. The quasi-static and dynamic mechanical behaviors of the pomelo peel bioinspired foams could be derived through a finite element analysis (FEA). We illustrate our method using a case study of pomelo peel bioinspired aluminum foams under quasi-static compression and free fall impact circumstances. The case study results validate our method and demonstrate the superior impact resistance and damping behavior of bioinspired foam with gradient porosity for designers.

Numerical And Experimental Investigations of Nonlinearity Behaviour In A Slender Cantilever Beam

Nonlinear problem is always occur in slender structures that are usually characterized by large displacements and rotations but small strains. Linear design assumption could lead to premature failure if the structure behaves nonlinearly. In this paper, the static displacement of a slender beam subjected to point load is investigated numerically by incorporating the large amplitude of the displacement. Two types of numerical analyses are performed at a full-scale finite element model which is linear static and geometric nonlinear implicit static. the results of the FEA linear static analysis are compared with the results from the FEA geometric nonlinear implicit static analysis. It shows that very high different load-displacement value response. Experimental static displacement test has been performed to validate both numerical results.

On the effective Young’s modulus of metal matrix syntactic foams

ABSTRACTThe effective Young’s modulus of aluminium matrix syntactic foams was determined by modal analysis. Two different matrix materials (Al99.5 and AlSi12) were used, and they were reinforced by Globocer grade ceramic hollow spheres. In order to validate the results, a full-scale finite element model was also created. A new algorithm was developed to place the spheres in a proper, probabilistic spatial distribution. Finite element simulations were carried out in modal analysis and compression test senses. In addition, three different analytical methods were studied to estimate the effective Young’s modulus. The measured values were compared with the finite element and analytical results. The determined effective Young’s moduli showed good agreement.This paper is part of a thematic issue on Light Alloys.

Inverse problem-based analysis on non-uniform thermo-mechanical behaviors of slab during continuous casting

A full-scale finite element model of a slab and its mold was developed to reveal the complex thermo-mechanical behaviors of slab in a vertical caster during continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mold. The model was validated by comparing the calculated temperature with the measured ones. The results show that the thermal and mechanical states of the slab are not symmetric, reflecting the non-uniform nature of thermo-mechanical behaviors and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving and optimizing the operation parameters for continuous casting slab.

Biomimetic idealization of a mechanically coupled acoustic sound sensing mechanism

This paper presents the idealization of a mechanically coupled acoustic sensor mechanism for directivity with the use of polysilicon, which has ideal mechanical and electrical material properties in terms of micro-fabrication. A mathematical model related to mechanical sensitivity is developed as a function of the material properties and geometry of the sensor, which evaluates the characteristics of a two-degree-of-freedom-based lumped parameter model. A challenge in such a study is that the model needs to be simple but sufficiently sophisticated to capture the characteristics of the sensor mechanism. Eigen modes and frequencies of the mechanically coupled acoustic sensor mechanism are determined by an energy method using mode functions applicable to the complete system that are from admissible the mode functions chosen for the component elements of the system. The synthesis is accomplished by using equations of constraint that follow conditions imposed by force equilibrium and deflection compatibility at the junctions. Finally, the results are compared with those obtained by a full-scale finite element model developed in a commercial software package. The predicted first and second natural frequencies differed by less than 10% and 3%, respectively, in all test cases.

Novel Frame Model for Mistuning Analysis of Bladed Disk Systems

The work investigates the application of a novel frame model to reduce computational cost of the mistuning analysis of bladed disk systems. A full-scale finite element (FE) model of the bladed disk is considered as benchmark. The frame configuration for a single blade is identified through structural identification via an optimization process. The individual blades are then assembled by three-dimensional (3D) springs, whose parameters are determined by means of a calibration process. The dynamics of the novel beam frame assembly is also compared to those obtained from three state-of-the-art FE-based reduced order models (ROMs), namely: a lumped parameter approach, a Timoshenko beam assembly, and component mode synthesis (CMS)-based techniques with free and fixed interfaces. The development of these classical ROMs to represent the bladed disk is also addressed in detail. A methodology to perform the mistuning analysis is then proposed and implemented. A comparison of the modal properties and forced response dynamics between the aforementioned ROMs and the full-scale FE model is presented. The case study considered in this paper demonstrates that the beam frame assembly can predict the variations of the blade amplitude factors, and the results are in agreement with full-scale FE model. The CMS-based ROMs underestimate the maximum amplitude factor, while the results obtained from beam frame assembly are generally conservative. The beam frame assembly is four times more computationally efficient than the CMS fixed-interface approach. This study proves that the beam frame assembly can efficiently predict the mistuning behavior of bladed disks when low-order modes are of interest.

Prediction of Longitudinal Cracks Based on a Full-Scale Finite-Element Model Coupled Inverse Algorithm for a Continuously Cast Slab

A full-scale finite-element model of a slab and its mold is developed to predict the appearance of longitudinal cracks during continuous casting, in which the measured data are combined with the model through an inverse algorithm. The simulation results show that the stress distributions in the slab are not symmetrical, reflecting the non-uniformity of the thermo-mechanical behavior. The longitudinal crack sensitivity index is highest at 60–100 mm below the meniscus, and the position of an actual longitudinal crack agrees well with the calculated result. This illustrates the validity of the proposed method for predicting longitudinal cracks, and hence demonstrates the necessity of building the full-scale model integrated with measured data.

Bayesian model updating of a full-scale finite element model with sensitivity-based clustering

Model updating based on vibration response measurements is a technique for reducing inherent modeling errors in finite element (FE) models that arise from simplifications, idealized connections, and uncertainties with regard to material properties. Updated FE models, which have relatively fewer discrepancies with their real structural counterparts, provide more in-depth predictions of the dynamic behaviors of those structures for future analysis. In this study, we develop a full-scale FE model of a major long-span bridge and update the model to improve an agreement between the identified modal properties of the real measured data and those from the FE model using a Bayesian model updating scheme. Sensitivity-based cluster analysis is performed to determine robust and efficient updating parameters, which include physical parameters having similar effects on targeted natural frequencies. The hybrid Monte Carlo method, one of the Markov chain Monte Carlo sampling methods, is used to obtain the posterior probability distributions of the updating parameters. Finally, the uncertainties of the updated parameters and the variability of the FE model's modal properties are evaluated.

Model order reduction in design of parameterized structures under different load configurations

In structural design of mechanical systems a dynamic analysis is carried out in the time domain or in the frequency domain which implies solving the equation of motion several times. Usually the systems depend on a set of parameters which influence their responses. Thus the design process includes numerical simulations using a full-scale finite element (FE) model for each set of parameters which is computationally demanding and time consuming. In this contribution the response in the frequency domain due to different load configurations is investigated by using a mixed approach of two related methods for parametric model order reduction (MOR) based on interpolation in matrix manifolds of the reduced order models (ROMs) and by using a global basis over the parametric space. Furthermore an approach based on interpolation of the reduced solution is presented. These approaches of MOR permit the computational efficient evaluation of different load configurations and avoid the generation of a new FE model for each case. A numerical example illustrates the capability of those methods. The respective results using parametric MOR (pMOR) approaches are compared with the solution obtained by using the corresponding full-scale FE model and the direct application of the Krylov subspace method (KSM).

Behavior of concrete-filled round-ended steel tubes under bending

The objective of this paper is to investigate the flexural behavior of concrete-filled round-ended steel tubes (CFRTs) under bending. Beam specimens were tested to investigate the mechanical behavior of the CFRTs, including four CFTs with different concrete strengths and steel ratios, and three CFRTs with varied aspect ratios. The load vs. deflection relationships and the failure modes for CFRTs were analyzed in detail. The composite action between the core concrete and steel tube was also discussed and examined based on the experimental results. In addition, ABAQUS program was used to develop the full-scale finite element model and analyze the effect of different parameters on the moment vs. curvature curves of the CFRTs bending about the major and minor axis, respectively. Furthermore, design formulas were proposed to estimate the ultimate moment and the flexural stiffness of the CFRTs, and the simplified theoretical model of the moment vs. curvature curves was also developed. The predicted results showed satisfactory agreement with the experimental and FE results. Finally, the differences of the experimental, FE and predicted results using the existing codes were illustrated.

Analysis of non-uniform thermal behaviour of special steel during slab continuous casting

A full-scale finite-element model of a slab and its mould was developed to reveal the complex thermal behaviour of special steel in a vertical caster during slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mould. The model was validated by comparing the calculated temperature with the measured ones. The temperature distribution of the slab is not symmetric, reflecting the non-uniform nature of heat transfer and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving the casting parameters and operations for special steel.

Application of projection-based model reduction to finite-element plate models for two-dimensional traveling waves

A finite element (FE) model simulates an unconstrained aluminum thin plate to which four macro-fiber composites are bonded. This plate model is experimentally validated for single and multiple inputs. While a single input excitation results in the frequency response functions and operational deflection shapes, two input excitations under prescribed conditions result in tailored traveling waves. The emphasis of this article is the application of projection-based model reduction techniques to scale-down the large-scale FE plate model. Four model reduction techniques are applied and their performances are studied. This article also discusses the stability issues associated with the rigid-body modes. Furthermore, the reduced-order models are utilized to simulate the steady-state frequency and time response of the plate. The results are in agreement with the experimental and the full-scale FE model results.