Structural Finite Element Research Articles

Characterising variability and regional correlations of microstructure and mechanical competence of human tibial trabecular bone: An in-vivo HR-pQCT study.

Quantifying spatial distribution of trabecular bone mechanical competence and microstructure is important for early diagnosis of skeletal disorders and potential risk of fracture. The objective of this study was to determine a spatial distribution of trabecular mechanical and morphological properties in human distal tibia and examine the contribution of regional variability of trabecular microarchitecture to mechanical competence. A total of 340 representative volume elements at five anatomic regions of trabecular bone - anterior, posterior, lateral, medial and centre - from ten white European-origin postmenopausal women were studied. Region-specific trabecular parameters such as trabecular volume fraction, trabecular thickness, trabecular number, trabecular surface area, trabecular separation, plate-like structure fraction and finite element analysis of trabecular stiffness were determined based on in-vivo high resolution peripheral quantitative computed tomographic (HR-pQCT) images of distal tibiae from ten postmenopausal women. Mean values were compared using analysis of variance. The correlations between morphological parameters and stiffness were calculated. Significant regional variation in trabecular microarchitecture of the human distal tibia was observed (p < 0.05), with up to 106% differences between lowest (central and anterior) and highest (medial and posterior) regions. Higher proportion of plate-like trabecular morphology (63% and 53%) was found in medial and posterior regions in the distal tibia. Stiffness estimated from finite element models also differed significantly (p < 0.05), with stiffness being 4.5 times higher in the highest (medial) than lowest (central) regions. The bone volume fraction was the strongest correlate of stiffness in all regions. A novel finding of this study is the fact that significant regional variation of stiffness derived from two-phased FEA model with individual trabecula representation correlated highly to regional morphology obtained from in-vivo HR-pQCT images at the distal tibia. The correlations between regional morphological parameters and mechanical competence of trabecular bone were consistent at all regions studied, with regional BV/TV showing the highest correlation. The method developed for regional analysis of trabecular mechanical competence may offer a better insight into the relationship between mechanical behaviour and microstructure of bone. The findings provide evidence needed to further justify a larger-cohort feasibility study for early detection of bone degenerative diseases: examining regional variations in mechanical competence and trabecular specifications may allow better understanding of fracture risks in addition to others contributing factors.

Structure design of six-component strain-gauge-based transducer for minimum cross-interference via hybrid optimization methods

Cross-interference is an important performance index for multi-channel strain-gauge-based transducer. In this study, a comprehensive optimization model for minimum cross-interference while satisfying constraints of principal sensitivity and cross-sensitivity is presented for a six-component wheel force transducer (WFT) structure design. The WFT structure has a “T”-type elastic body other than the conventional Maltese cross-type. Based on structure finite element analysis and circuit analysis, the quantified principal sensitivity, cross-sensitivity, and cross-interference are discussed. Then, a mechanical-electrical multidisciplinary optimization model is constructed which has a complex objective function and many constraints. Trial computations show that this model has multiple local optimal points. Hybrid optimization methods including simulated annealing (SA) algorithm and sequence quadratic programming (SQP) algorithm are then adopted to obtain a better design. The optimization results reveal that, for the studied “T”-type transducer structure, relatively stronger lateral beam and weaker longitudinal beam are helpful to achieve low cross-interference. The performance of the optimized structure is verified by comparison with the benchmark structure and by stepwise loading. The presented comprehensive optimization model has good generality applicable to different-type multi-channel strain-gauge-based transducer structure design.

Meso-scale modelling and failure analysis of kenaf fiber reinforced composites under high strain rate compression loading

This paper presents a multi-scale structure finite element modelling scheme to analyse the damage behaviors of Kenaf fiber reinforced composite materials subjected to high strain rate compressions. The proposed modelling framework includes a micro-scale structure model with periodic boundary conditions for homogenizing the heterogeneous fiber/resin system into a unit cell, and a meso-scale model with established constitutive relationship for the constituents integrated with failure criterion to account for the stiffness degradation and subsequent element removal. The finite element results from the model provide the localities of stress propagation, the stress distribution, and the progressive failure behaviour within the Kenaf fiber reinforced composite materials. The results which are stress-strain behaviour and developed damages are found to be in fair agreement with the available test data.

Study on Optimization Model of Truss Structure under Different Constraints

The paper takes the real jacket offshore platform as an example. The structural finite element software structural analysis was used to establish the structural section optimization, shape optimization and shape optimization model based on component reliability. The results reflect that the shape optimization efficiency based on component reliability is high under the premise of guaranteeing the reliability of the structure. Therefore, preference should be given to the structural shape optimization considering reliability in the engineering.

A New Traction Motor System With Integrated-Gear: A Solution for Off-Road Machinery

Off-road traction applications require extremely high torque, especially, at low speeds. Such a high torque can be reached by gearing up the torque of an electrical machine. A tooth-coil permanent magnet synchronous machine with an integrated planetary gear is proposed as a solution for heavy off- and on-road traction applications. The key benefits of tooth-coil permanent-magnet synchronous machine (PMSM) in the proposed drive system and its integration with a planetary gearbox are explained in detail. A multi-objective optimization is performed to determine the slot/pole combination of the PMSM and the design process of the proposed drive system is entirely clarified. The proposed tooth-coil PMSM is investigated by electromagnetic and structural finite element analysis to obtain the final design and highlight the machine performance. A prototype is built to validate the proposed system. The results show that the traction drive system works well in laboratory and offers means to serve as a traction system in heavy off- and on-road applications.

Effects of model uncertainty in nonlinear structural finite element model updating by numerical simulation of building structures

Uncertainties in finite element (FE) model updating arise from two main sources: measurement noise and modeling errors. The latter includes model parameter uncertainty and model uncertainty itself. Among these sources of uncertainty, model uncertainty has been proven to be the most influential source of error in FE model updating, which is particularly important when using the updated model for damage identification (DID) purposes. This paper investigates the effects of model uncertainty when updating mechanics-based nonlinear FE models of building structures subjected to earthquake excitation. To solve the parameter estimation problem, the unscented Kalman filter is used as parameter estimation tool. Numerically simulated response data of two state-of-the-art nonlinear FE models of building structures designed according to modern design codes are used as application examples. A two-dimensional steel building and a three-dimensional reinforced concrete building, both subjected to seismic base excitation, are analyzed for different types and levels of model uncertainty. The results show that model uncertainty may have significant detrimental effects when using the updated FE model for DID, chiefly in the case of large modeling uncertainty. Although a good match between the measured (observed) and FE predicted responses is usually achieved, unobserved responses at global and local levels often show significant errors.

Experimentally validated structural finite element method analysis of a tibial intramedullary nail: Optimal choice of the contact settings.

This article focuses on the static structural analysis of a tibial intramedullary nail, carried out by the finite element method. The investigated subject is concerned with the issue of frictional contacts that, generating a non-linear problem, play an important role in numerical analyses. Experimental tests were also developed on tibial intramedullary nail specimens. The experimental results, in terms of force-displacement, were used to calibrate and validate the finite element analysis, by tuning the contact parameters available in the software.

An improved spectral decomposition flexibility perturbation method for finite element model updating

Finite element analysis is the most powerful tool to predict the behavior of a structure in engineering practice. Generally, the initial finite element model must be corrected with experimental data due to its complexity. Thus, it is very necessary to study a finite element model updating method with high precision and high efficiency. To this end, this article presented an improved spectral decomposition flexibility perturbation method for structural finite element model updating. The improvements of the proposed method lie in two aspects. First, using the uniform correction model, the proposed method is more economical in computation than the initial method because the spectral decomposition and reorganization of elemental stiffness matrices can be avoided. Second, using the twice singular-value-truncation method, the proposed method has better performance than the initial method in combating data noise. A beam structure is employed to demonstrate the proposed method for model updating in a noisy environment. It was found that the result obtained by least squares estimate is seriously distorted and the result obtained by the first singular value truncation is also not entirely satisfactory. Only the result obtained by the second singular value truncation is the most stable and accurate. Overall, the improved spectral decomposition flexibility perturbation method is robust and effective in small modification case, large modification case, adjacent modification case, and multiple modifications case. The proposed method may be very useful for structural finite element model updating in the noisy environment.

Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90's in favor of horizontal axis wind turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfill this gap, a structural finite element analysis (FEA) model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the lifting line free vortex wake (LLFVW) method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34 m rotor. In this work, some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small-scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1 kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a one-dimensional beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade. Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a blade element momentum (BEM) simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.

Noise comparison of centrifugal pump operating in pump and turbine mode

Investigations regarding the relation of noise performance for centrifugal pump operating in pump and turbine modes continue to be inadequate. This paper presents a series of comparisons of flow-induced noise for both operation modes. The interior flow-borne noise and structure modal were verified through experiments. The flow-borne noise was calculated by the acoustic boundary element method (ABEM), and the flow-induced structure noise was obtained by the coupled acoustic boundary element method (ABEM)/structure finite element method (SFEM). The results show that in pump mode, the pressure fluctuation in the volute is comparable to that in the outlet pipe, but in turbine mode, the pressure fluctuation in the impeller is comparable to that in the draft tube. The main frequency of interior flow-borne noise lies at blade passing frequency (BPF) and it shifts to the 9th BPF for interior flow-induced structure noise. The peak values at horizontal plane appear at the 5th BPF, and at axial plane, they get the highest sound pressure level (SPL) at the 8th BPF. Comparing with interior noise, the SPL of exterior flow-induced structure noise is incredibly small. At the 5th BPF, the pump body, cover and suspension show higher SPL in both modes. The outer walls of turbine generate relatively larger SPL than those of the pump.

Assumption of Constraining Force to Explain Distortion in Laser Additive Manufacturing.

Distortion is a common but unrevealed problem in metal additive manufacturing, due to the rapid melting in metallurgy and the intricate thermal-mechanical processes involved. We explain the distortion mechanism and major influencing factors by assumption of constraining force, which is assumed between the added layer and substrate. The constraining force was set to act on the substrate in a static structural finite element analysis (FEA) model. The results were compared with those of a thermal-mechanical FEA model and experiments. The constraining force and the associated static structural FEA showed trends in distortion and stress distribution similar to those shown by thermal-mechanical FEA and experiments. It can be concluded that the constraining force acting on the substrate is a major contributory factor towards the distortion mechanism. The constraining force seems to be primarily related to the material properties, temperature, and cross-sectional area of the added layer.

RF02 ANOMALOUS AORTIC CORONARY ARTERY ORIGIN: A PARAMETRIC STRUCTURAL FINITE ELEMENT ANALYSIS AND COMPUTATIONAL SIMULATION.

Background and aim: In anomalous aortic origin of coronary arteries (AAOCA) underlying ischemic mechanism during high stress conditions have still to be elucidated. The study aims to understand the biomechanics of such a condition and in particular how the lumen of the AAOCA may narrow during aortic expansion. Methods: We create a parametric computer-aided designed (CAD) model of the aortic root and AAOCA origin and perform a static finite element analysis (FEA) on 10 models with different angles of take-off and intramural penetration at three different loading conditions (i.e. stress condition). The model is defined by twenty-three parameters describing aortic root geometry and allows to vary coronary position, take-off angle, degree of intramural penetration, and length of the intramural course to simulate the pathological conditions of AAOCA. Results: We show that the AAOCAs experience a reduced luminal expansion (LE) (LE = 1.85%, 5.98%, 10.42%) compared to the healthy ones (LE = 11.9%, 22.43%, 36.66%,) at 120-150-180 mmHg of aortic root pressure respectively. Acute angles of take-off lead to elongated ostia, with an eccentricity (e) that increases with aortic expansion (i.e. e = 0.72-0.69-0.66 at 120-150-180 mmHg, take-off angle = 35’ and 50% penetration). Conclusions: The study describes for the first time an idealized geometrical model as a proof of concept for static structural finite element simulations to assess the role of specific geometrical features on AAOCA physiopathology. The possible mechanism of lumen reduction in AAOCA can rely on biomechanical reasons and computational simulations may allow patient specific predictive model in future.

The flank wear prediction in micro-milling Inconel 718

PurposeCutting tool wear is known to affect tool life, surface quality, cutting forces and production time. Micro-milling of difficult-to-cut materials like Inconel 718 leads to significant flank wear on the cutting tool. To ensure the respect of final part specifications and to study cutting forces and tool catastrophic failure, flank wear (VB) has to be controlled. This paper aims to achieve flank wear prediction during micro-milling process, which fills the void of the commercial finite element software.Design/methodology/approachBased on tool geometry structure and DEFORM finite element simulation, flank wear of the micro tool during micro-milling process is obtained. Finally, experiments of micro-milling Inconel 718 validate the accuracy of the proposed method for predicting flank wear of the micro tool during micro-milling Inconel 718.FindingsA new prediction method for flank wear of the micro tool during micro-milling Inconel 718 based on the assumption that the wear volume can be assumed as a cone-shaped body is proposed. Compared with the existing experiment techniques for predicting tool wear during micro-milling process, the proposed method is simple to operate and is cost-effective. The existing finite element investigations on micro tool wear prediction mainly focus on micro tool axial wear depth, which affects size accuracy of machined workpiece seriously.Originality/valueThe research can provide significant knowledge on the usage of finite element method in predicting tool wear condition during micro-milling process. In addition, the method presented in this paper can provide support for studying the effect of tool flank wear on cutting forces during micro-milling process.

Reliability-based alarm thresholds for structures analysed with the finite element method

Civil engineering structures are commonly monitored to assess their structural behaviour, using alarm thresholds to indicate when contingency actions are needed to improve safety. However, there is a need for guidelines on how to establish thresholds that ensure sufficient safety. This paper therefore proposes a general computational algorithm for establishment of reliability-based alarm thresholds for civil engineering structures. The algorithm is based on Subset simulation with independent-component Markov chain Monte Carlo simulation and applicable with both analytical structural models and finite element models. The reliability-based alarm thresholds can straightforwardly be used in the monitoring plans that are developed in the design phase of a construction project, in particular for sequentially loaded structures such as staged construction of embankments. With the reliability-based alarm thresholds, contingency actions will only be implemented when they are needed to satisfy the target probability of failure.

Nonlocal Analysis of Natural Vibrations of Carbon Nanotubes

When the atomic level is considered, the dynamic properties have a major influence on nanostructures behavior because of their ultrahigh or very high natural frequencies. Vibrations are essential in the analysis of resonators, oscillators, and sensors for carbon nanotube-based devices. The present paper is dedicated to the eigenfrequencies analysis of single-walled carbon nanotubes. In the analysis, the small-scale coefficient is introduced, and the nonlocal elasticity theory is applied in the modal analysis of the carbon nanotubes. The correlation between nonlocal small-scale parameter and the vibrational behavior of the carbon nanotubes is studied. The determination of nonlocal parameter is based on the structural finite element model of the nanotube. A detailed parametric study is realized to investigate the effects of the length-to-diameter ratio L/D, nonlocal coefficient, the influence of boundary conditions on eigenfrequencies of carbon nanotubes. The main contribution of this work is the evaluation of the nonlocal parameter for single-walled carbon nanotubes based on the finite element approximation in modeling the dynamic behavior instead of commonly used MD simulations. It was clearly displayed that the application of the nonlocal beam models involves analysis of the small-scale parameter, whose value determines the final eigenfrequencies. The highest values of eigenfrequencies were observed for the local beam model. It was presented that the eigenfrequencies for carbon nanotubes decrease when the nanotube length increases for all analyzed modes. On the other hand, when the diameter of carbon nanotubes increases, the eigenfrequency values rise. The numerical validation of the nonlocal parameter revealed the high dependence on the boundary conditions and the mode number. However, the influence of the mode number and the boundary conditions is vanishing for long single-walled carbon nanotubes.

Finite element modeling assumptions impact on seismic response demands of MRF-buildings

Recent seismic events have raised concerns over the safety and vulnerability of reinforced concrete moment resisting frame “RC-MRF” buildings. The seismic response of such buildings is greatly dependent on the computational tools used and the inherent assumptions in the modelling process. Thus, it is essential to investigate the sensitivity of the response demands to the corresponding modelling assumption. Many parameters and assumptions are justified to generate effective structural finite element (FE) models of buildings to simulate lateral behaviour and evaluate seismic design demands. As such, the present study focuses on the development of reliable FE models with various levels of refinement. The effects of the FE modelling assumptions on the seismic response demands on the design of buildings are investigated. the predictive ability of a FE model is tied to the accuracy of numerical analysis; a numerical analysis is performed for a series of symmetric buildings in active seismic zones. The results of the seismic response demands are presented in a comparative format to confirm drift and strength limits requirements. A proposed model is formulated based on a simplified modeling approach, where the most refined model is used to calibrate the simplified model.

Damage Detection of 2D Frame Structures using Incomplete Measurements by Optimization Procedure and Model Reduction

The article presents an effective method for damage assessment of 2D frame structures using incomplete modal data by optimization procedure and model reduction technique. In this proposed method, the structural damage detection problem is defined as an optimization problem, in which a hybrid objective function and the damage severity of all elements are considered as the objective function and the continuous design variables, respectively. The teaching-learning-based optimization (TLBO) algorithm is applied as a powerful optimization tool to solve the problem. In addition, owing to the use of incomplete measurements, an improved reduction system (IRS) technique is adopted to reduce the mass and stiffness matrices of structural finite element model. The efficiency and robustness of the proposed method are validated with a 4-storey (3 bay) steel plane frame involving several damage scenarios without and with measurement noise. The obtained results clearly demonstrate that even the incompleteness and noisy environment of measured modal data, the present method can work properly in locating and estimating damage of the frame structure by utilizing only the first five incomplete modes' data. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Influence of Small Teeth on Vibration for Dual-Redundancy Permanent Magnet Synchronous Motor

The dual-redundancy permanent magnet synchronous motor (DRPMSM) has high reliability in its applications. Compared with the traditional permanent magnet synchronous motor (PMSM), small teeth were added to the stator in DRPMSM and its vibration has new characteristics. This paper derived the analytic expression of the radial electromagnetic force for PMSM in the air gap based on the Maxwell stress equation and summarized its sources. The simplified stator teeth model of the traditional PMSM and DRPMSM were established in 12-slot/10-pole (12s10p), and the analytical expression and Fourier expansion of radial electromagnetic force on the teeth were given. The electromagnetic and structural finite element models of the motor were established, and analyses of modal and harmonic response were carried out. The simulation results show that the stator vibration amplitude of DRPMSM is smaller than that of traditional PMSM at no-load and is also bigger under rated load. Furthermore, in order to guarantee the low amplitude of stator vibration under rated load for DRPMSM, the width of the small teeth should be smaller.

Performance comparison of Kalman−based filters for nonlinear structural finite element model updating

Finite element (FE) model updating has emerged as a powerful technique for structural health monitoring and damage identification of civil structures. Updating mechanics-based nonlinear FE models allows for a complete and comprehensive damage diagnosis of large and complex structures, but it is computationally demanding. This paper first introduces an Iterated Extended Kalman filter (IEKF) to update mechanics-based nonlinear FE models of civil structures. Different model updating techniques using the Extended Kalman filter (EKF), Unscented Kalman Filter (UKF) and IEKF, are then compared for their performance in terms of convergence, accuracy, robustness, and computational demand. Finally, a non-recursive estimation procedure is presented and its effectiveness in reducing the computational cost, while maintaining accuracy and robustness, is demonstrated. An application example is presented based on numerically simulated response data for a three-dimensional 5-story 2-by-1 bay reinforced concrete (RC) frame building subjected to bi-directional earthquake excitation. Excellent estimation results are obtained with the EKF, UKF, and IEKF used in conjunction with the proposed non-recursive estimation approach. Because of the analytical linearization used in the EKF and IEKF, abrupt and large jumps in the estimates of the model parameters are observed with these filters, which may lead to divergence of the nonlinear FE model solution procedure. The UKF slightly outperforms the EKF and IEKF, but at a higher computational cost.

In situ thermoelastic stress analysis – an improved approach to airframe structural model validation

ABSTRACTThe recent adaptation of uncooled infrared imaging technology to thermoelastic stress analysis (TSA) offers an opportunity to improve the validation basis for structural finite element modelling of complex airframe components. Uncertainties in modelling can lead to inaccurate airframe lifing predictions and premature test failures that delay and add cost to aircraft full-scale durability test programs. Traditional model validation practice relies on data drawn primarily from discrete strain gauge, structural deflection and load-cell measurements. Supplementing this data with full-field stress imagery is shown to lead to a significantly improved model validation capability. After reviewing the fundamentals of TSA and its application using uncooled infrared detectors this article describes an experimental study conducted on an F-35 full-scale durability test airframe. It is shown that small low-cost microbolometers installed on the airframe provide a rapid and unobtrusive means of obtaining high-fidelity full-field stress imagery of complex airframe components. Such data enables a direct and rapid assessment of model accuracy in areas of potentially life-limiting stress concentration where predictive accuracy needs to be most assured but has traditionally been difficult to verify using the established model validation approach. Issues of general relevance to the application of TSA to full-scale durability testing are also discussed.