Generated Finite Element Models Research Articles

X-ray with finite element analysis is a viable alternative for MRI to predict knee osteoarthritis: Data from the Osteoarthritis Initiative.

Magnetic resonance imaging (MRI) offers superior soft tissue contrast compared to clinical X-ray imaging methods, while also providing accurate three-dimensional (3D) geometries, it could be reasoned to be the best imaging modality to create 3D finite element (FE) geometries of the knee joint. However, MRI may not necessarily be superior for making tissue-level FE simulations of internal stress distributions within knee joint, which can be utilized to calculate subject-specific risk for the onset and development of knee osteoarthritis (KOA). Specifically, MRI does not provide any information about tissue stiffness, as the imaging is usually performed with the patient lying on their back. In contrast, native X-rays taken while the patient is standing indirectly reveal information of the overall health of the knee that is not seen in MRI. To determine the feasibility of X-ray workflow to generate FE models based on the baseline information (clinical image data and subject characteristics), we compared MRI and X-ray-based simulations of volumetric cartilage degenerations (N = 1213) against 8-year follow-up data. The results suggest that X-ray-based predictions of KOA are at least as good as MRI-based predictions for subjects with no previous knee injuries. This finding may have important implications for preventive care, as X-ray imaging is much more accessible than MRI.

Buckling resistance of hot‐finished CHS beam‐columns using FE modelling and machine learning

AbstractThe use of circular hollow sections (CHS) has increased in recent years owing to its excellent mechanical behaviour including axial compression and torsional resistance as well as its aesthetic appearance. They are popular in a wide range of structural members, including beams, columns, trusses and arches. The behaviour of hot‐finished CHS beam‐columns made from normal‐ and high‐strength steels is the main focus of this article. A particular attention is given to predict the ultimate buckling resistance of CHS beam‐columns using the recent advancement of the artificial neural network (ANN). Finite element (FE) models were established and validated to generate an extensive parametric study. The ANN model is trained and validated using a total of 3439 data points collected from the generated FE models and experimental tests available in the literature. A comprehensive comparative analysis with the design rules in Eurocode 3 is conducted to evaluate the performance of the developed ANN model. It is shown that the proposed ANN‐based design formula provides a reliable means for predicting the buckling resistance of the CHS beam‐columns. This formula can be easily implemented in any programming software, providing an excellent basis for engineers and designers to predict the buckling resistance of the CHS beam–columns with a straightforward procedure in an efficient and sustainable manner with least computational time.

Artificial neural network model for strength predictions of CFST columns strengthened with CFRP

This paper presents an optimised Artificial Neural Network (ANN) model for predicting the ultimate axial strengths of concentrically loaded Concrete-Filled Steel Tubular (CFST) short and slender columns strengthened with Carbon Fibre-Reinforced Polymer (CFRP). Since experimental data on CFRP strengthened CFST columns is limited, an accurate Finite Element (FE) model is developed and used to provide additional numerical data. A multi-layered feed-forward back-propagation network is proposed, optimised, and trained using the results of 76 experimental tests and 450 generated FE models. The accuracy of the ANN model is assessed through comparing its computed results with experimental data. A reliability analysis is performed using Monte Carlo Simulation (MCS) to evaluate the safety of the solutions computed by the ANN model. ANN-based equations and Graphical User Interface (GUI) are developed based on the trained ANN model for the determination of the ultimate axial strengths of CFST columns. The results show that the developed ANN model is capable of accurately predicting the ultimate axial strengths of CFRP strengthened CFST columns with a high degree of accuracy.

Automatic 3D image based finite element modelling for metallic foams and accuracy verification of digital volume correlation

3D image-based finite element (FE) modelling provides the feasibility to explore how the subtle structural features inside metallic foams affect their complex deformation and mechanical responses. But the modelling currently includes frequent manual modifications, which makes it a time and labor consuming task. The quality of generated model depends heavily on experienced creator. This paper demonstrates an automatic procedure to extract structure information from 3D images and generate reliable geometric models for meshing. With self-adaptive algorithms that fit local features of grayscale distribution and internal structure, high-fidelity FE models can be established efficiently without interference from subjective judgments. The generated FE models well reproduce the stress-strain relation and inhomogeneous deformation of aluminium foams, compared with experimental results. Using the simulation with a high-fidelity FE model as “ground truth”, the accuracy of digital volume correlation (DVC) in the deformation measurement of complex cellular materials is for the first time evaluated quantitatively and precisely, based on the definition of an equivalent displacement vector bridging the results obtained by FE simulation and by DVC.

Study of the Mechanical Properties of Wood under Transverse Compression Using Monto Carlo Simulation-Based Stochastic FE Analysis

Wood is an anisotropic material, the mechanical properties of which are strongly influenced by its microstructure. In wood, grain compression strength and modulus are the weakest perpendicular to the grain compared to other grain directions. FE (finite element) models have been developed to investigate the mechanical properties of wood under transverse compression. However, almost all existing models were deterministic. Thus, the variations of geometry of the cellular structure were not considered, and the statistical characteristic of the mechanical property was not involved. This study aimed to develop an approach to investigate the compression property of wood in a statistical sense by considering the irregular geometry of wood cells. First, the mechanical properties of wood under radial perpendicular to grain compression was experimentally investigated, then the statistical characteristic of cell geometry was extracted from test data. Finally, the mechanical property of wood was investigated using the finite element method in combination with the Monte Carlo Simulation (MCS) techniques using randomly generated FE models. By parameter sensitivity analysis, it was found that the occurrence of the yield points was caused by the bending or buckling of the earlywood axial tracheid cell wall in the tangential direction. The MCS-based stochastic FE analysis was revealed as an interesting approach for assessing the micro-mechanical performance of wood and in assisting in understanding the mechanical behavior of wood based on its hierarchical structure.

Probability density functions of the DoB in tubular KT-joints of jacket-type platforms under out-of-plane bending loads

The degree of bending (DoB) has a profound effect on the fatigue behavior of tubular joints commonly found in offshore jacket structures. Probability density functions (PDFs) of the involved random variables are necessary for the fatigue reliability analysis of jacket structures. The objective of present research was the derivation of PDF for the DoB in tubular KT-joints commonly found in jacket-type platforms. A total of 243 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB at the saddle positions of the central and outer braces in tubular KT-joints subjected to three types of OPB moment loading.

Effects of geometrical parameters on the local joint flexibility (LJF) of three-planar tubular T-joints in offshore structures

ABSTRACT In this paper, the results of a parametric study conducted on the local joint flexibility (LJF) of three-planar tubular T-joints are presented and discussed. A set of finite element (FE) analyses were carried out on 81 FE models subjected to two types of axial loading in order to study the effects of geometrical characteristics of three-planar T-joint on the LJF factor (f LJF). Generated FE models were verified against available experimental data and parametric equations. The f LJF values in three-planar and uniplanar T-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar T-joints to calculate the f LJF in three-planar T-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to develop a new parametric formula for the prediction of the f LJF in axially loaded three-planar T-joints.

Simulation of Thin-Walled Members with Arbitrary-Shaped Cross-Sections for Static and Dynamic Analyses

The main objective of this paper is to validate a finite-element (FE) modeling protocol to simulate thin-walled members for static and dynamic analyses. Arbitrary-shaped cross-sections, including open, closed, and multicellular sections can be efficiently modeled for further advanced study. The framework is thoroughly validated and verified using the existing analytical and closed-form solutions, as well as experimental results available in literature. This work is motivated by the higher accuracy of the shell FE-based modeling to capture the local and global complex behaviors of thin-walled members with asymmetric sections. Higher computational expenses, however, are required for such sophisticated shell finite element models (SFEM). Accordingly, a framework hosted in MATLAB and implementing the python scripting technique in ABAQUS, is developed, which includes eigen buckling, static nonlinear, modal frequency and dynamic time-history analyses. For a more modeling convenience, various parameters are incorporated such as imperfections, residual stresses, material definitions, element choice, meshing control, and boundary conditions. Several examples are provided to illustrate the application of the proposed framework, and to prove the robustness and accuracy of the generated FE models. This paper concludes with the efficiency of implementing SFEMs for simulating thin-walled members; thereby, establishing a more accurate and advanced structural analysis.

Degree of bending (DoB) in offshore tubular KT-joints under the axial, in-plane bending (IPB), and out-of-plane bending (OPB) loads

Through-the-thickness stress distribution characterized by the degree of bending (DoB) has a major effect on the fatigue behavior of tubular joints commonly found in steel offshore structures. The determination of DoB values is essential for improving the accuracy of fatigue life estimation using the stress-life (S–N) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. In the present research, data extracted from 648 finite element (FE) analyses carried out on 81 tubular KT-joint models was used to study the effects of geometrical parameters on the DoB values in KT-joints subjected to eight different types of loading including two types of axial loading, three types of in-plane bending (IPB) moment loading, and three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop 21 parametric design formulas for the calculation of the DoB in tubular KT-joints under the axial, IPB, and OPB loadings.

Computational efficient method for assessing the influence of surgical variability on primary stability of a contemporary femoral stem in a cohort of subjects.

Finite element (FE) modelling can provide detailed information on implant stability; however, its computational cost limits the possibility of completing large numerical analyses into the effect of surgical variability in a cohort of patients. The aim of this study was to develop an efficient surrogate model for a cohort of patients implanted using a common cementless hip stem. FE models of implanted femora were generated from computed tomography images for 20 femora (11 males, 9 females; 50-80years; 52-116kg). An automated pipeline generated FE models for 61 different unique scenarios that span the femur-specific range of implant positions. Peak hip contact and muscle forces for stair climbing were scaled to the donors' body weight and applied to the models. A cohort-specific surrogate for implant micromotion was constructed from Gaussian process models trained using data from FE simulations representing the median and extreme implant positions for each femur. A convergence study confirmed suitability of the sampling method for cohorts with 10+ femora. The final model was trained using data from the 20 femora. Results showed very good agreement between the FE and the surrogate predictions for a total of 1036 alignment scenarios [root mean squared error (RMSE) < 20µm; [Formula: see text] = 0.81]. The total time required for the surrogate model to predict the micromotion range associated with surgical variability was approximately one-eighth of the corresponding full FE analysis. This confirms that the developed model is an accurate yet computationally cheaper alternative to full FE analysis when studying the implant robustness in a cohort of 10+ femora.

A Probability Distribution Model for the Degree of Bending In Tubular KT-Joints of Offshore Jacket-Type Platforms Subjected To IPB Moment Loadings

The objective of present research was the derivation of probability density functions (PDFs) for the degree of bending (DoB) in tubular KT-joints commonly found in jacket-type platforms. A total of 243 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to three types of in-plane bending (IPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, the Generalized Extreme Value model was proposed as the governing probability distribution function for the DoB. After substituting the values of estimated parameters, nine fully defined PDFs were presented for the DoB at the crown, toe, and heel positions of the central and outer braces in tubular KT-joints subjected to three types of IPB moment loading.

Probabilistic analysis of the DoB in axially-loaded tubular KT-joints of offshore structures

The degree of bending (DoB) characterizing the through-the-thickness stress distribution has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Probability density functions of the involved random variables are necessary for the fatigue reliability analysis of offshore structures. The objective of present research was the derivation of probability density function (PDF) for the DoB in tubular KT-joints commonly found in jacket-type offshore platforms. A total of 162 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to two types of axial loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, the Generalized Extreme Value model was proposed as the governing probability distribution function for the DoB. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB in tubular KT-joints subjected to two types of axial loading.

Effects of geometrical parameters on the degree of bending (DoB) in two-planar tubular DT-joints of offshore jacket structures subjected to axial and bending loads

The fatigue life of tubular joints commonly found in offshore structures is not only dependent on the value of hot-spot stress (HSS), but is also significantly influenced by the through-the-thickness stress distribution characterized by the degree of bending (DoB). In the present research, data extracted from the finite element (FE) analyses carried out on 81 two-planar tubular DT-joint models was used to study the effects of geometrical parameters on the DoB values in DT-joints subjected to six different types of loading including two types of axial loading, two types of in-plane bending (IPB) moment loading, and two types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using available parametric equations. The determination of DoB values in a tubular joint is essential for improving the accuracy of fatigue life estimation using the stress-life (SN) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop three DoB parametric formulas for the fatigue analysis and design of two-planar DT-joints.

Probabilistic analysis of the local joint flexibility in two-planar tubular DK-joints of offshore jacket structures under in-plane bending loads

Tubular DK-joints are among the most common joint types in jacket substructure of offshore wind turbines (OWTs) and oil/gas production platforms. The local joint flexibility (LJF), as an intrinsic feature of a tubular joint, is one of the factors affecting the global static and dynamic responses of an offshore structure. In the present paper, a total of 324 finite element (FE) analyses were carried out on 81 FE models of two-planar tubular DK-joints under four types of in-plane bending (IPB) moment loads. Generated FE models were validated based on the available experimental data, FE results, and parametric equations. FE analysis results were used to develop a set of probability density functions (PDFs) for the LJF factor (fLJF) in IPB-loaded DK-joints. Based on a parametric FE investigation, a sample database was prepared for the fLJF values and density histograms were generated for respective samples. Nine theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov and chi-squared tests were used to assess the goodness of fit. Finally, the Birnbaum-Saunders model was proposed as the governing probability distribution function for the fLJF. After substituting the values of estimated parameters, four fully defined PDFs were presented for the fLJF in two-planar tubular DK-joints under four types of IPB loading.

Development of a probability distribution model for the LJF factors in offshore two-planar tubular DK-joints subjected to OPB moment loading

Probability distribution models are essential for the reliability-based analysis and design of offshore structures. The objective of the present research was developing a probability distribution model for the local joint flexibility (LJF) factor, fLJF, in two-planar tubular DK-joints commonly found in jacket-type offshore wind turbines and oil/gas production platforms. A total of 324 finite element (FE) analyses were carried out on 81 FE models of DK-joints subjected to four types of out-of-plane bending (OPB) moment loads. Generated FE models were validated using the available experimental data, FE results, and design formulas. Based on the results of parametric FE study, a sample database was prepared for the fLJF values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Nine theoretical probability density functions (PDFs) were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov and chi-squared tests were used to evaluate the goodness of fit. Finally, the lognormal model was proposed as the governing probability distribution function for the fLJF. After substituting the values of estimated parameters, four fully defined PDFs were presented for the fLJF in tubular DK-joints subjected to four types of OPB moment loads.

Comparative studies for failure pressure prediction of corroded pipelines

Abstract The Finite Element (FE) Method is one of the most efficient approaches to quantify reliably the remaining strength of corroded pipes, by allowing the direct simulation of the physical phenomena involved in the failure of the pipe. In this paper, the results of failure pressure of corroded pipelines obtained using nonlinear FE analyses of the models generated by a computer system called PIPEFLAW will be presented. This system integrates several tools to automatically generate FE models and to perform FE analysis using a friendly interface. A set of cases considering colonies of idealized corroded defects is analyzed. The results are compared to experimental burst tests presented in the literature, numerical results obtained via FE models generated manually and results obtained using semi-empirical methods. The results obtained using the PIPEFLAW automatic and flexible procedures show good agreement with those given by handmade FE models and experimental tests. Some highly conservative predictions given by the semi-empirical methods are also observed.

The development of a computational tool for generation of high quality FE models of pipelines with corrosion defects

Corrosion is one of the most common causes of accidents involving pipelines. Unfortunately, the semi-empirical methods currently available are overly conservative for the assessment of some types of corrosion defects in pipelines. Fortunately, the computational simulations through finite element (FE) method are a very efficient and reliable approach to quantify the remaining strength of corroded pipes. However, the process of computational modeling demands intense manual labor from the engineer, and it is also slow and extremely repetitive, especially in cases of multiple defects. The main purpose of this work was to describe an original methodology for the automatic generation of FE models of pipes with corrosion defects (single or multiple). The model discretization uses semi-structured mesh and specific mesh transitions, which demanded even more manual labor. Also, the computational modeling process needs to be robust and efficient to ensure accuracy without excessive number of degrees of freedom. Thus, the tool allows the pre-configuration of mesh transitions and other parameters related to the mesh refinement. This program, called PIPEFLAW, is built-in as a software extension into the MSC.PATRAN commercial software and is written with Patran Command Language. The PIPEFLAW program has a friendly graphical user interface, which allows the user to provide the main parameters of the pipe and defect (or a series of defects), considering several different configurations and geometries. This paper is focused on the automatic generation of 3D FE models of pipelines with a single or a colony of idealized defects with rectangular or elliptical shapes. As result, some examples of FE pipe models with defects generated automatically by the program are shown and some element shape tests were performed to evaluate the final mesh quality of the FE pipe model. The methodology is validated through the comparison of the internal failure pressure of a pipeline with two rectangular defects, obtained using experimental burst test, manually generated FE models, semi-empirical methods and PIPEFLAW generated model. The developed tools lead to a reduction in the modeling procedure in the case presented from 2 weeks, using non-automatic standard procedure normally used in the industry, to 1 min.

Effect of Occlusal Splints on the Stress Distribution on the Temporomandibular Joint Disc.

Conservative approach, including occlusal splint therapy, is the first option to treat temporomandibular disorders (TMD), because of its reversibility. The present study analyzed the effect of the articular disc position and occlusal splints use on the stress distribution on this disc. A two-dimensional (2D) finite element (FE) model of the temporomandibular joint with the articular disc at its physiologic position was constructed based on cone-beam computed tomography. Three other FE models were created changing the disc position, according to occlusal splint use and anterior disc displacement condition. Structural stress distribution analysis was performed using Marc-Mentat package. The equivalent von Mises stress was used to compare the study factor. Higher stress concentration was observed on the intermediate to anterior zone of the disc, with maximum values over 2MPa. No relevant difference was verified on the stress distribution and magnitude comparing disc positions and occlusal splint use. However, there was stress reduction arising from the use of the occlusal splints in cases of anterior disc displacement. In conclusion, based on the generated FE models and established boundary conditions, the stress increased at the intermediate zone of the TMJ disc during physiological mandible closure. The stress magnitude was similar in all tested situations.

A study on the Local Joint Flexibility (LJF) of two-planar tubular DK-joints in jacket structures under in-plane bending loads

In the present paper, results of a parametric study conducted on the Local Joint Flexibility (LJF) of two-planar tubular DK-joints under In-Plane Bending (IPB) loads are presented. DK-joints are among the most common joint types in jacket substructure of Offshore Wind Turbines (OWTs). A total of 324 finite element (FE) analyses were carried out on 81 FE models under four types of IPB loading in order to investigate the effect of the DK-joint’s geometrical parameters on the LJF factor (fLJF). Based on the results of parametric study, the factors leading to the LJF reduction were introduced. Generated FE models were verified using the existing experimental data, FE results, and parametric equations. The effect of the weld profile was also considered. The fLJF in two-planar DK- and uniplanar K-joints were compared. Results indicated that the effect of multi-planarity on the LJF is quite significant and consequently the use of the equations already available for uniplanar K-joints to calculate the fLJF in two-planar DK-joints may lead to highly under-/over-predicting results. To handle this issue, the FE results were used to derive a set of parametric equations for the prediction of the fLJF in IPB-loaded two-planar DK-joints. The proposed equations were checked against the acceptance criteria recommended by the UK DoE and can be reliably used for the analysis and design of tubular joints in OWTs.

Geometrical effects on the local joint flexibility of two-planar tubular DK-joints in jacket substructure of offshore wind turbines under OPB loading

The local joint flexibility (LJF) of two-planar tubular DK-joints in offshore jacket structures under the out-of-plane bending (OPB) loads is studied in the present paper. Altogether, 81 finite element (FE) models were generated and analyzed by ANSYS in order to investigate the effects of DK-joint's geometrical parameters on the LJF factor (fLJF) under four types of OPB load cases. Generated FE models were validated against the existing experimental data, FE results, and parametric equations. After the parametric study of geometrical effects, the fLJF in two-planar DK- and uniplanar K-joints were compared. Results showed that the effect of multi-planarity on the fLJF values is considerable. Hence, the application of the equations already available for uniplanar K-joints to determine the fLJF in two-planar DK-joints might result in highly under-/over-predicting outputs. To suggest a solution for this issue, results of 324 analyses carried out on generated FE models were used to develop a new set of parametric formulas for the calculation of the fLJF in OPB-loaded two-planar DK-joints. Applicability of proposed formulas was assessed based on the UK DoE acceptance criteria.