Fidelity Finite Element Model Research Articles

Development of blade tip timing signal simulator based on a novel model reduction method of bladed disks

In order to improve the calculation efficiency of high fidelity finite element model (FEM) and solve the problem of the high BTT test cost, a blade tip timing (BTT) data simulator of rotating bladed disk based on reduced order model (ROM) is developed in this paper. Firstly, the ROM of rotating mistuned bladed disk is constructed by using the proper orthogonal decomposition (POD) method. Then, a construction method of BTT data simulator based on the ROM is proposed, which considers the influence of rotation effect, mistuned and speed fluctuation. Finally, the simulator is constructed based on an academic bladed disk, and the vibration parameters are identified by using the traditional vibration parameter identification methods to verify the effectiveness of the simulator. This study provides a new data generation method for effectively verifying the effectiveness of vibration parameter identification algorithm.

Stochastic reduced order modelling and analysis of rotating bladed discs

A computational finite-element (FE)-based technique is proposed for developing a stochastic reduced order model for rotating bladed disc with spatial random inhomogeneities. The spatial inhomogeneities imply the system to be randomly mistuned. The formulation assumes the availability of a high fidelity FE model for the tuned system. The corresponding FE matrices are antisymmetric on account of the Coriolis forces due to rotation. The spatial inhomogeneities, available from limited point measurements on the blades, are modelled as non-Gaussian random fields with arbitrary distributions. A low order stochastic computational model is developed by projecting the FE model onto a reduced dimensional state space defined in terms of specified observable nodal points and expressing the stochasticity through an arbitrary polynomial chaos (aPC) basis. This model enables probabilistic quantification of the variabilities in the system response and estimating failure probabilities. The methodology enables drastic reduction in the state space and stochastic dimensions, addresses the practical difficulties with having limited measurable data points, antisymmetric FE matrices, aPC representation in complex irregular geometries and carrying out probabilistic analyses on industrial systems, at significantly reduced computational costs. The methodology is illustrated through an academic rotor and an industrial rotor blade.

MEM vs. FEM: practical crashworthiness insights for macro element modelling applied to sub-assembly and full vehicle automotive structures

This paper proposes a modelling approach for integral vehicle structures, applied to frontal crash loading, based on the Macro element approach. Addressing the idealisation of complex sub-structures and full vehicle was through identification of critical parameters for conversion of validated FEM into MEM equivalents through sensitivity analyses. Two examples of impact onto rigid barriers are presented; 1). Frontal crash energy management system (consisting crush-can and longitudinal engine rail), impacting at 8.6 m/s and 2). A complete vehicle impact at 56 km/hr (15m/s). Both case studies predict key features of collapse, with force-time histories agreeing within ±10–15% against FEM. Case study 1 required a 3 second solution time versus 1.5 h (8CPUS) mass-scaled FEM (105k element). For Case study 2, MEM required 7.5mins versus 16.5 hrs for a 3 M element FEM vehicle. For all simulations, LS-DYNA R10.0 and Visual Crash Studio R4.0 used. Developing a framework to overcome accuracy/stability problems, together with issues related to robustness and error reduction is discussed. Model complexity was progressive, involving a-priori knowledge of collapse and/or analysing several sub-assemblies to guide idealisation. The level of agreement demonstrates the advantages of MEM as a complementary method to support conceptual vehicle design and offers significant advantages for design exploration, particularly across multiple crash certification cases. Highlights Idealisation of complex sub-structures into Macro element modelling (MEM) equivalents using high fidelity finite element models (FEM) Methodology based on critical parameters for conversion of validated FEM into MEM Proposed MEM conversion for complete vehicle frontal impact onto a rigid barrier Correlation of critical parameters with structural behaviour through sensitivity analyses MEM error in force-time histories within 10–15%, relative to high fidelity FEM FEM Solution times reduced from several hours to several minutes for MEM equivalents

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.

Vibration response prediction of coated blisks under multi-point non-contact excitations using mistuning identification data

The mistuning and excitations of the real engineering coated blisk are very complex and it is difficult to predict the vibration response. In this study, a numerical method of response prediction for coated blisks under multi-point non-contact excitations is proposed. The purpose of applying multi-point non-contact excitations to the blades is to get closer to the actual excitations condition of coated blisks. A non-rotating coated academic blisk is used as the research object, the component mode mistuning (CMM) reduced-order technique focusing on blade mistuning is improved to establish the response prediction model of the coated blisk, which includes quantized parameters of the blade substrate mistuning and the mistuning caused by coating. Meanwhile, the effects of the mass, stiffness and damping mistuning of the blisk substrate and the coating on the response are comprehensively considered in the model. In order to preserve the simulation accuracy of the response prediction model, the blade substrate mistuning and the mistuning caused by coating are identified, and the reduced-order model (ROM) is updated by the identification results of mass and stiffness mistuning. The response predictions of the numerical case and actual case of the non-rotating simplified coated academic blisk are carried out respectively. For the numerical case, the results of response prediction are in good agreement with the response calculation results of the high fidelity finite element model (FEM). Compared with the numerical case, the error between the predicted response and the tested response is larger, but this error level is sufficient to meet the requirements of engineering applications. All the results show that the proposed method is effective for predicting the response of the non-rotating coated academic blisks under multi-point excitations.

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%.

Applications of SPDM in aircraft structural analysis at Embraer

Aircraft structural analysis is a process that involves several engineers working concurrently to analyze in detail all structural elements of an airframe, as well as the behavior of the aircraft structure as a whole. The airframe has to be decomposed in its major components such as fuselage sections, wings and control surfaces to allow the distribution of the analyses among the engineers. Finite element models (FEM) are created for each major component and used in the analyses. The major components, such as the wing, are further decomposed into its constituent parts, such as spars, ribs, and stringers; which might be modeled in more detail using dedicated FEMs. It’s a great challenge to manage the evolution of the structural modifications that happen during the course of these analyses. Design changes originated from stress analysis using higher fidelity FEMs have to be transferred to the lower fidelity FEMs and an assembly of the whole airframe FEM needs to be created and analyzed once again, using the correct versions of all the FEMs of the major parts. The objective of this paper is to present the results of the solution implemented by Embraer to overcome these challenges, by using the Simulation Process and Data Management (SPDM) technology. Embraer embarked on the SPDM journey eight years ago and during past years has matured various aspects of their SPDM implementation. The focus of the paper is on explaining applications of the SPDM system in the area of structural analysis at Embraer with a couple of representative business processes as examples, including the rapid generation and evaluation of aircraft assemblies and the consolidation and standardization of various simulation methods across the organization, by making those available over the SPDM platform. Key enablers for increasing simulation throughput and data traceability at Embraer are described. In addition, the approach that Embraer took for ongoing additions of new business processes to the SPDM system is presented. The results of the SPDM implementation at Embraer are encouraging, showing qualitative and quantitative gains of productivity and management of engineering data. The standardization and automation of engineering processes and the proper management of data generated by these processes are becoming an integral part of any competitive engineering department nowadays.

Effect of resin-rich zones on the failure response of carbon fiber reinforced polymers

We study the impact of size and spatial arrangement of resin-rich zones on the failure response of a carbon fiber reinforced polymer (CFRP) subject to loadings applied in the direction transverse to the fibers. An automated computational framework is utilized for the finite element (FE) modeling and simulation of damage process. The proposed approach relies on a packing-optimization algorithm to virtually reconstruct three large Statistical Volume Elements (SVEs) of CFRP with varying size and distribution of resin-rich zones, as observed in the imaging data. A parallel, non-iterative mesh generation algorithm is then employed to create high fidelity FE models. The failure analyses are carried out considering the ductile damage response of the polymer matrix, as well as cohesive debonding and contact along fiber-matrix interfaces. The study shows that although the presence of resin-reach zones does not highly affect the failure response under transverse tensile and shear loads, it has a notable impact on the strength and toughness under transverse compression. Further, we show that using different boundary conditions and changing the compressive load direction (i.e., parallel versus perpendicular to the lamina) have a notable impact on the failure response of SVE.

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.

Bayesian estimation of tension in bridge hangers using modal frequency measurements

The tension of an arch bridge hanger is estimated using a number of experimentally identified modal frequencies. The hanger is connected through metallic plates to the bridge deck and arch. Two different categories of model classes are considered to simulate the vibrations of the hanger: an analytical model based on the Euler-Bernoulli beam theory, and a high-fidelity finite element (FE) model. A Bayesian parameter estimation and model selection method is used to discriminate between models, select the best model, and estimate the hanger tension and its uncertainty. It is demonstrated that the end plate connections and boundary conditions of the hanger due to the flexibility of the deck/arch significantly affect the estimate of the axial load and its uncertainty. A fixed-end high fidelity FE model of the hanger underestimates the hanger tension by more than 20 compared to a baseline FE model with flexible supports. Simplified beam models can give fairly accurate results, close to the ones obtained from the high fidelity FE model with flexible support conditions, provided that the concept of equivalent length is introduced and/or end rotational springs are included to simulate the flexibility of the hanger ends. The effect of the number of experimentally identified modal frequencies on the estimates of the hanger tension and its uncertainty is investigated.

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.

Development and Validation of a High Anatomical Fidelity FE Model for the Buttock and Thigh of a Seated Individual.

Current practices for designing new cushions for seats depend on superficial measurements, such as pressure mapping, which do not provide sufficient information about the condition of sub-dermal tissues. Finite element (FE) modelling offers a unique alternative to integrate assessment of sub-dermal tissue condition into seat/cushion design and development processes. However, the development and validation of such FE models for seated humans requires accurate representation of the anatomy and material properties, which remain challenges that are yet to be addressed. This paper presents the development and validation of a detailed 3D FE model with high anatomical fidelity of the buttock and thigh, for a specific seated subject. The developed model consisted of 28 muscles, the pelvis, sacrum, femur, and one layer of inter-muscular fat, subcutaneous fat and skin. Validation against in vivo measurements from MRI data confirmed that the FE model can simulate the deformation of soft tissues under sitting loads with an accuracy of (mean±SD) 4.7±4.4mm. Simulation results showed that the maximum strains (compressive, shear and von-Mises) on muscles (41, 110, 79%) were higher than fat tissues (21, 62, 41%). The muscles that experienced the highest mechanical loads were the gluteus maximus, adductor magnus and muscles in the posterior aspect of the thighs (biceps femoris, semitendinosus and semimembranosus muscles). The developed FE model contributes to the progression towards bio-fidelity in modelling the human body in seated postures by providing insight into the distribution of stresses/strains in individual muscles and inter-muscular fat in the buttock and thigh of seated individuals. Industrial applications for the developed FE model include improving the design of office and household furniture, automotive and airplane seats and wheelchairs as well as customisation and assessment of sporting and medical equipment to meet individual requirements.

Development of Evolutionary Method for Optimizing a Roll Forming Process of Aluminum Parts

This paper presents the development of the knowledge-based neural network (KBNN) and genetic algorithm (GA) in modeling and optimization of the roll forming (RF) process of aluminum parts. The idea of a KBNN using multifidelity finite element (FE) models was developed to model the mechanical behaviors of the aluminum sheet. Initially, the less costly but less accurate FE model was used to build the response surface functions for the knowledge path of the KBNN. After that, a small number of the more accurate but expensive finite element analysis (FEA) of the high fidelity FE model were utilized in a multilayer perceptron (MLP) neural network with the prior knowledge to produce the KBNN prediction results. Two powerful optimization algorithms, the Levenberg–Marquadrt (LM) and GA, were applied to train the KBNN. The trained KBNN was used to perform the parametric study for investigating the effects of process parameters on the part quality. After that, the optimization of the process parameters was carried out by employing the combination of the GA and KBNN. The optimization objective was minimizing the overall damage in the aluminum part while keeping the longitudinal strain and spring back angle less than allowable limits to prevent the existence of defects. The modeling and optimization results by using the KBNN and GA were compared with the results from other methods to prove the advantages of the developed one against others.