Fidelity Finite Element Research Articles

Effect of three-dimensional space on progressive collapse resistance of reinforced concrete frames under various column removal scenarios

In this study, high fidelity finite element (FE) model was adopted to investigate the progressive collapse resistance of reinforced concrete (RC) frame structures under various column removal scenarios. The validity of the numerical model was verified by comparing with the existing experimental results. Afterwards, to facilitate the research on possible simplified boundary conditions served for further various column removal scenarios, the effect of multi-span continuous beams was firstly evaluated and the simplified methods were compared. Then, the effect of various column removal scenarios addressing the three-dimensional effect on the progressive collapse resistance of RC frame structures with and without slab was systematically evaluated. The analysis results showed that the continuous span beams increased the internal compressive force of the beam section at compressive arch action (CAA) stage, which effectively improved the CAA strength of the substructure. For simple modeling, the use of horizontal constraints at the end of the beam could replace the continuous span beams. The presence of transverse beams and slab provided additional load transfer paths for collapse resistance. The compressive membrane action (CMA) and tensile membrane action (TMA) of the slab significantly improved the progressive collapse resistance of the substructure in the small and large deformation stages, respectively. The location of the removed column significantly affected the contribution ratio of transverse beams and slab to the progressive collapse resistance of the substructure, which was quantitatively evaluated for practical design.

Simultaneous Regression and Selection in Nonlinear Modal Model Identification

High fidelity finite element (FE) models are widely used to simulate the dynamic responses of geometrically nonlinear structures. The high computational cost of running long time duration analyses, however, has made nonlinear reduced order models (ROMs) attractive alternatives. While there are a variety of reduced order modeling techniques, in general, their shared goal is to project the nonlinear response of the system onto a smaller number of degrees of freedom. Implicit Condensation (IC), a popular and non-intrusive technique, identifies the ROM parameters by fitting a polynomial model to static force-displacement data from FE model simulations. A notable drawback of these models, however, is that the number of polynomial coefficients increases cubically with the number of modes included within the basis set of the ROM. As a result, model correlation, updating and validation become increasingly more expensive as the size of the ROM increases. This work presents simultaneous regression and selection as a method for filtering the polynomial coefficients of a ROM based on their contributions to the nonlinear response. In particular, this work utilizes the method of least absolute shrinkage and selection (LASSO) to identify a sparse set of ROM coefficients during the IC regression step. Cross-validation is used to demonstrate accuracy of the sparse models over a range of loading conditions.

Dynamic characteristics of single door electrical cabinet under rocking: Source reconciliation of experimental and numerical findings

Seismic qualifications of electrical equipment, such as cabinet systems, have been emerging as the key area of nuclear power plants in Korea since the 2016 Gyeongju earthquake, including the high-frequency domain. In addition, electrical equipment was sensitive to the high-frequency ground motions during the past earthquake. Therefore, this paper presents the rocking behavior of the electrical cabinet system subjected to Reg. 1.60 and UHS. The high fidelity finite element (FE) model of the cabinet related to the shaking table test data was developed. In particular, the first two global modes of the cabinet from the experimental test were 16 Hz and 24 Hz, respectively. In addition, 30.05 Hz and 37.5 Hz were determined to be the first two local modes in the cabinet. The high fidelity FE model of the cabinet using the ABAQUS platform was extremely reconciled with shaking table tests. As a result, the dynamic properties of the cabinet were sensitive to electrical instruments, such as relays and switchboards, during the shaking table test. In addition, the amplification with respect to the vibration transfer function of the cabinet was observed on the third floor in the cabinet due to localized impact corresponding to the rocking phenomenon of the cabinet under Reg.1.60 and UHS. Overall, the rocking of the cabinet system can be caused by the low-frequency oscillations and higher peak horizontal acceleration.

A Friction-Enhanced Tuned Ring Damper for Bladed Disks

Abstract This paper introduces a new type of damper for turbomachinery blisks. The major pitfalls of the damper concepts currently employed are two: the low level of relative motion that is available at the damper attachment location, and the inability to control the preload at the frictional interface. To address these issues, the proposed damper is designed as a tuned vibration absorber (TVA), which allows energy transfer from the blades to the damper provided that the natural frequency of the damper is close to that of the host structure. Thanks to the enhanced energy transfer, the damper can experience increased relative motion. Frictional contacts are then included to dissipate the energy transferred to the damper. The damper structure must be stiff enough to withstand centrifugal loading without affecting the preload too much. However, it also must be compliant to make sure that its natural frequencies can match the ones of the host structure. For this reason, the proposed damper involves a complex geometry that is stiff in the radial direction and softer in the circumferential direction, which is the direction of the relative motion. A model of the damper is created to damp the vibration of a realistic blisk. The effectiveness of the damper is investigated using high fidelity finite element (FE) models. The frequency response of the system is obtained to analyze the effectiveness of the proposed design. Preliminary results show the potential of this technology for structures with such low damping.

Numerical investigation on load redistribution capacity of flat slab substructures to resist progressive collapse

To study the load redistribution capacity of reinforced concrete (RC) flat slab structures subjected to a middle column loss scenario, high fidelity finite element (FE) models were built using commercial software LS-DYNA. The numerical models were validated by experimental results. It is found that the continuous surface cap model (CSCM) with an erosion criterion considering both the maximum principal and shear strain could effectively predict the punching shear failure at slab-column connections. The validated FE models were employed to investigate the effect of boundary conditions, amount of integrity reinforcement, and slab thickness on the load redistribution capacity of flat slab structures. Furthermore, multi-story RC flat slab substructures were built to capture the load redistribution behavior of different floors. Parametric studies indicate that ignoring the constraints from surrounding slabs may underestimate the load redistribution capacity of the flat slab substructures. Therefore, it is suggested that in future numerical or experimental studies, rigid horizontal constraints should be applied at the slab edge of the substructure to well represent the constraints from surrounding slabs. In addition, it is also found that the amount of integrity reinforcement would significantly affect the post-punching performance of flat slab structures. It is suggested that the minimum integrity reinforcement ratio should be 0.63%.

A critical assessment of design tools for stress analysis of adhesively bonded double lap joints

Despite the proliferation of high fidelity finite-element (FE) models, lower fidelity models remain commonly used in adhesively bonded joint design. These design models can save both computational and user time due to their simplicity and ease of use. This study presents a detailed assessment of local stress fields predicted by five design models: A4EI, HyperSizer, Joint Element Designer, Carrera Unified Formulation, and a Continuum Solid Shell FE model. All models were compared with a high fidelity, dense mesh FE model. Six double lap joint cases with different combinations of features like different adhereds, a core, and tapers were compared.

Stick-slip behavior of reversing the tubular woven bag covering a rigid tube-theoretical and numerical studies

Abstract A tubular woven bag covering a rigid tube, known as a crucial component in flexible tube coring system adopted for future lunar soil coring missions, which dynamic performance, especially the stick-slip behavior, might largely affect the reliability and quality of the lunar soil coring, should be explored in depth. In this study, we have developed analytical formulation and high fidelity finite element (FE) model to investigate the stick-slip behavior of the tubular woven bag covering a rigid tube in the turning inward process. The theoretical model is established via dividing the whole process into the unfolding and the detaching periods. The FE model is efficiently established and solved by using nonlinear finite element code LS-DYNA. Results demonstrate that good agreement can be realized between the numerical results and the theoretical ones. Moreover, based on the developed theoretical model, parametric analysis of the stick-slip process is performed to quantify the effects of the key parameters, including the mass, damping and stiffness of the woven bag, the driving velocity, the pressure on the bag, and the initial wrinkle ratio, on the stick-slip behavior. The findings from this study can provide practical and important guidance for designing the deep lunar soil coring system with high stability and reliability.

Computational Framework for Online Estimation of Fatigue Damage using Vibration Measurements from a Limited Number of Sensors

This study proposes a computational framework for the online estimation of fatigue damage using operational vibration measurements from a limited number of sensors. To infer the stress response time histories required for fatigue prediction, the measured structural response is driven to a high fidelity finite element (FE) model, which is reconciled using appropriate model updating techniques that minimize the discrepancy between the experimental and analytical frequency response functions (FRFs). Fatigue is accordingly estimated via the Palmgren-Miner rule, while the available FE model allows for stress estimation at unmeasured spots. The method is successfully validated and assessed through an experimental study that pertains to a linear steel substructure supporting the entire body of a pre-beater assembly at a PPC power plant.

Damage Assessment of Two-Way RC Slab Subjected to Blast Load Using Mode Approximation Approach

Significant research efforts have been invested on studying the response and damage of structures subjected to blast loads for better life and property protections. The single-degree-of-freedom (SDOF) approach has been widely adopted to simplify the structural response analysis for engineering design purpose. However, such an approach under certain circumstances oversimplifies the structural behavior and might not give reliable predictions of structural responses to blast loads. On the other hand, although detailed high fidelity finite element (FE) approach is able to give relatively accurate predictions of structural response, it is unfortunately not straightforward for application and very time-consuming, which impedes its application among engineers. Therefore, a method that can assure not only reliability but also efficiency is highly needed for design practice. In the present study, mode approximation method with Pressure–Impulse (P-I) diagrams is applied to analyze response and damage of RC slab due to blast load. Slab under analysis is assumed rigid-plastic and simply supported. Shear failure, bending failure and combined failure modes are considered based on different failure modes. Critical equations for structural shear and bending failures are derived respectively with appropriate failure criteria. P–I diagrams are then developed for quick damage assessments. The analytical results are verified by comparing with high fidelity numerical simulations. The reliability and efficiency of using this approach for design and analyzing RC slab response under blast loads are demonstrated.

Improved human-computer interaction for mechanical systems design through augmented strain/stress visualisation

It is difficult to obtain realistic stress and strain estimates for mechanical designs due to unknown operational conditions, input forces and/or parameters. This limits a designer in evaluating whether a certain product meets all design specifications. This work presents an extended Kalman filter to obtain accurate strain and stress estimates of a structure under operational loading. An augmented reality application allows visualisation of these strains and stresses on a real component. This leads to an effective human-computer interface to evaluate a physical prototype. The developed approach exploits parametric reduced order models based on high fidelity finite-element design models to obtain an efficient formulation. This paradigm is validated on a flexible beam with unknown input forces and length. The proposed approach permits a more natural visualisation and interpretation of operational conditions. Our results encourage the adoption of this approach in applications ranging from design validation to online monitoring of structural components.

Finite Element Analysis of Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK) Surgery Allograft to Predict Endothelial Cell Loss

ABSTRACTPurpose: To develop high fidelity finite element (FE) models of the Descemet’s stripping automated endothelial keratoplasty (DSAEK) allograft to estimate the stress distributions generated on the allograft during its deformed state in popular allograft insertion configurations and qualitatively correlate the stress distributions to postsurgical endothelial cell (EC) loss.Materials and Methods: Corneal allograft simulation was performed using ANSYS (Canonsburg, PA, USA) utilizing isotropic nonlinear hyperelastic corneal material properties to evaluate the stress distributions generated on the DSAEK allograft during popular allograft insertion configurations, namely forceps, taco, and double-coil insertion configurations. The gathered FE simulation results were qualitatively compared with published clinical studies to verify the simulation results.Results: The FE simulation results demonstrate that high stress regions predicted by FE model results correctly predict the areas of postsurgical EC loss as published in the studies available in open literature. The FE simulation stress magnitude results suggest that highest EC loss due to mechanical bending trauma occurs in double-coil configuration followed by forceps and then taco configuration.Conclusions: The results of the presented FE simulation study highlight that allograft regions with high stress distribution demonstrate postsurgical EC loss in clinical studies. The modeling procedures presented in this research can be utilized to develop novel surgical devices/techniques that can modulate the postsurgical EC loss due to mechanical bending trauma and facilitate allograft unfolding inside the AC, thereby improving the results of the DSAEK surgical procedure.

Effect of structural parameters on design of variable-stiffness composite cylinders made by fiber steering

A variable stiffness composite cylinder made by fiber steering is optimized for maximum buckling load due to pure bending. A multistep design optimization procedure is developed to get the maximum potential improvement in structural performance. To improve the computational efficiency, low-cost and computationally inexpensive surrogate models based on radial basis functions (RBF) are used as approximate for the high fidelity finite element (FE) analyzes. Different RBF formulations are also studied and compared with each other in terms of their accuracy.The effects of radius (R) and aspect ratio (L/R), as two structural parameters, on the structural improvement of the variable stiffness cylinders are also investigated. Keeping the thickness (t) constant, radius (R) is shown to have no considerable effect on the buckling load improvement of the variable stiffness cylinders whereas the aspect ratio (L/R) has a substantial effect on the buckling load improvement. Improvements up to 38.5% are obtained for cylinders with low aspect ratio.