Finite Element Model For Analysis Research Articles

Research on Modal Behavior of Large Francis Turbine Runner

The water-added-mass can affect the modal behavior of the Francis turbine runner largely. The sealing rings in the band-chamber and the crown-chamber outside of the runner are utilized to prevent leakage of water around the Francis turbine. The sealing rings and the chambers filled with water can also affect the modal behavior of the turbine. When the turbine runner operates in the power plant at various operating conditions, the seal clearances of the band-chamber and the crown-chamber filled with water may change the modal behavior of the large Francis turbine runner. Firstly, the 3D geometrical structure of the studied large-scale Francis turbine runner was constructed, and then the CAD model was meshed to establish the finite-element model for numerical analysis. Next, the modal shapes and the natural-frequencies of runners in the air were calculated, which is the traditional method used for the structural modal behavior analysis of the turbine runners. Finally, this paper investigates the modal behavior of a large-scale Francis runner prototype with the combined effects of sealing rings and water added-mass by direct water-structure coupled analysis via the finite element method (FEM) to obtain more realistic results. The results reveal that the effects of water-added-mass and sealing rings cause a significant decrease in the natural-frequency of the large Francis turbine runner, which may lead to an increase in the amplitude of vibrations and even cracks. Technical suggestions are proposed to improve the monitoring and maintenance in the power stations to maintain the safe and efficient operation of the large Francis turbine units.

Computational modelling of built-up cold-formed steel columns and parametric studies

The paper develops a detailed finite-element model for the reliable nonlinear collapse analysis of built-up cold-formed steel columns with discrete fastener connections. First, the main components of the computational model are discussed, including their available options and comparison between their results, followed by a rational justification for the options chosen in this study. Specifically, a detailed theoretical background is provided with conclusive comparisons of the options for enforcing end support conditions, applying contact conditions between the constituent plates, selecting connection elements for representing intermediate screw fasteners, and finally, the incremental load stepping and nonlinear solution schemes. The accuracy and performance of the proposed FE modelling strategy are verified against the experimental data, contributing to the calibration of the influencing parameters. The predictions of the proposed methodology are shown to be in excellent agreement with the test data in terms of the failure mode and the inelastic capacity curve up to ultimate capacity and beyond. Upon its successful calibration, the FE model is utilised to perform extensive parametric studies into the effects of various design parameters on the ultimate strength of built-up columns. This includes practical variations of cross-section dimensions, sectional slenderness, built-up section geometry, and fastener spacing. The parametric study results suggest a meaningful dependency of the ultimate capacity of built-up sections on the fastener spacing ratio, the critical buckling half-wavelength of the built-up section and the relative number of restrained components in the built-up configuration undergoing sectional buckling.

BIO-PRINTING OF FEMUR MODEL: A BONE SUBSTITUTE FOR BIOMEDICAL RESEARCH

This paper deals with the development of a medical support model that can be used as a prototype to study the anatomy of the femur and for biomechanical research experimentation related to bone plates. CT scan data of the femur bone are converted into a 3D model using MIMICS software and imported into a finite-element model for analysis. The materials selected for the fabrication of the femur model were PEEK and CF PEEK (infused with chopped carbon fibre). The femur bone model was analysed using ANSYS® WORKBENCH® 2021 R2 with different material properties. By conducting a subsequent FE analysis, the optimal material was finally arrived at. Using 3D-printing technology, the 3D model of the femur was fabricated by using a material spool with better properties suited for the femur bone. The FE results were compared with the experimental results of the fabricated femur model and the results of the CF PEEK bone model closely matched the properties of real human femur, and it can be used as a femur bone substitute for biomechanical investigations of bone plates instead of using a real femur.

Damage identification of seismic-isolated structure based on CAE network using vibration monitoring data

Seismic-isolated systems have been investigated and practiced globally to prevent the destruction of existing structures, and vibration-based structural health monitoring is important for maintaining the functionality of the isolation systems. Given the recent boom in computational science and machine learning algorithms, this paper deployed a structural health monitoring system for a rubber bearing-isolated gymnasium in an area with high seismic fortification intensity and introduced an unsupervised deep learning network named convolutional autoencoder (CAE) to identify damage from vibrations of the isolation layer. The CAE network is first trained by operational monitoring vibrations and tested by new data. The vibration assessment results indicate that the CAE network can accurately reconstruct daily data and effectively detect unexpected ground motion. Thereafter, to further test the network's damage identification and localization performance, an analytical finite element model of the gymnasium structure is established, and the undamaged and damaged datasets are generated for network verification and updating. The verification results demonstrate that the CAE network leads to reliable feature extraction power in global and local damage detection of the isolation layer. The proposed vibration assessment method is beneficial to building administrators in making accurate and timely decisions with the assistance of the score result provided by the CAE network.

Finite Element Model Updating of RC Bridge Structure with Static Load Testing: A Case Study of Vietnamese ThiThac Bridge in Coastal and Marine Environment.

Diagnostic load testing refers to the use of the measured historical responses of the structure in the field data to better understand its dynamic and static structural behaviours. It is important and necessary to predict the health state, load capacity, and aging of the structure by updating the finite element (FE) model, which can give useful information to aid the design of retrofits and the maintenance of the existing bridge in the future. The paper presents an update of the full-scale FE model for the reinforced concrete (RC) bridge structure over the seawater river based on the experimental strains under the static load testing in which the representative FE model of the actual structure is determined from the optimisation procedures. The optimisation variables are applied, including the cross-sectional properties and concrete material calibrated through the genetic algorithm (GA) optimisation in the MATLAB software, which interfaces with the FE modelling in the scripting of the SOFISTIK TEDDY software automatically. The bending moments at the mid-span of the RC girders are determined in the FE modelling to compute stresses, which are compared with the measured stresses through optimisation scenarios with a percentage error of the objective function less than 10%. The measured data of concrete strains are recorded from reusable strain transducers installed on the mid-span girders for every bridge span, which are used to calibrate the bridge model in static load testing. The novelty of the solution is to implement innovative techniques using field data as an improved approach for calibrating automatically the analytical FE model parameters of all RC spans of the bridge until its static behaviours are very similar to those of the actual bridge. The final updated FE modelling is used to apply truck load configurations according to bridge design standards such as the AASHTO specifications, which can predict the load limits of the existing bridge structure more accurately and reliably. These proposed approaches can be applied to large bridges as well as complex structures with supporting FE analysis software and data processing software.

Microstructural analysis and multiscale modeling for stiffening and strengthening of consolidated earthen-site soils

While experimental explorations to consolidate earthen-site soils using composite materials have obtained desirable reinforcing effect, few modeling efforts were conducted to reveal how microstructures of consolidated soils affect their effective stiffness and strength. The current study develops a multiscale modeling technique to quantify the stiffening and strengthening effects of consolidants to earthen-site soils. Specifically, a micromechanics-based finite element method is applied to simulate the homogenized constitutive relations of the untreated and consolidated soils, based on the microstructures from scanning electron microscopy images and image-processing procedures. Multiscale models are used to examine the influence of input properties of consolidants on the sensitivity of mechanical properties of the earthen-site samples. Comparison between modeling and experimental results shows a satisfactory agreement. The macroscopic mechanical properties of soils are remarkably affected by their microstructures. This study demonstrates the feasibility of integrating scanning electron microscopy and image processing technology into the finite-element modeling for stiffening and strengthening analysis of consolidated earthen-site soils.

Application of refined mixed finite element model for analysis of laminated composite beams

Analysis of laminated composite members is always a critical phenomenon. To address this issue, the authors developed the six nodes two dimensional refined mixed finite element model (r-MFEM) for accurate analysis of laminated composite beam. This model has transverse stress σZ and τxz as primary variables along with displacement u and w. Equilibrium equations are used to refine the variation of primary variables in the formulation. In the present paper, various laminated composite beams have been analysed by the six nodes two-dimensional r-MFEM element to show the model’s versatility. The results obtained has been compared with the other author’s work.

Design analysis of electro-adhesive mechanism for wall-climbing robot

Electro-adhesive mechanism (EAM) has recently been considered for research studies to be used in a wall-climbing robot. The EAM has the advantage over other adhesion mechanisms due to its suitability to work on various wall surface materials. The main challenges associated with the electro-adhesion are achieving high payload, precise fabrication and integration with the robot locomotion. In the present work, electro-adhesive mechanisms have been considered for analysis, simulation and experimental validation under different design parameters for their suitability in the wall-climbing robot. Design parameters such as shape of the electrode, insulating material and high input voltage for the EAM have been evaluated from the analytical model and finite element model using EMWorks software. These studies show that the different design parameters have a major influence on the generated adhesion force. Simulation and experimental studies have been done for the comparison of two cases, namely simple and comb shape electrode pair design with different insulating materials. The results show that the comb shape electrode pair design of the electro-adhesion mechanism exhibits more adhesion force as compared to the simple electrode pair design. The study also suggests low thickness with high relative permittivity material of the insulating layer can be preferred for the design of the mechanism. An analytical study has been carried out for the suitability of EAM application for wall-climbing robots.

Finite element model for analysis of vibration damping characteristics of isotropic surface structures

In this paper, a finite element (FE) model was developed to predict the vibration response of isotropic beams, involving several modes of resonance. The cantilever beam model was employed in the FE model in line with Timoshenko’s bending theory. The FE analysis has been carried out using the modal analysis and harmonic analysis tools of Ansys R19.0. The FE model was subjected to a grid independence study to minimize the computational time without sacrificing accuracy. The resonant frequencies were utilized to compute the damping modulus of the material for both the FE and experimental results. The frequency response functions from the finite element analysis were compared with the experimental results of the cantilever beam subjected to impulse hammer excitation. Aluminium alloy AA6061-T6 was taken up as the homogeneous and isotropic beam material for both the experimental and the FE model. The effect of the magnitude and location of the excitation load, the geometry of the FE model on the vibration response was analyzed in detail. The FE model validation with the experimental results shows that the FE model is effective in predicting the damping response of any isotropic material.

Numerical modeling on deformation of viscous stringers in deforming salt bodies under a compressive environment—a case study from the South Oman Salt Basin

Salt deposits are extremely potent seals for hydrocarbon reservoirs present in the sedimentary basins worldwide. Large rock inclusions (stringers) encased within various salt bodies may adopt diverse modes of deformation and displacement. Analyzing the movement and segmentation of these elastic and viscous stringers provides a comprehensive understanding of the intricate internal deformation mechanisms in the associated salt diapirs. The difference in viscosity between the stringers and the surrounding salt deposit yields a massive impact on the internal complexity of the salt structures. An analytical finite element model was built in combination with an adaptive remeshing process in this study, to achieve a suitable downbuilding simulation. The standard model setup is regulated with observations from South Oman Salt Basin. In this paper, the evaluation of parameter sensitivity concerning the dynamics of viscous stringers in salt diapirs was carried out, especially the sensitivity study pertaining to varied salt and stringer viscosities, which contribute to the distinct pattern of the internal structure in salt diapirs. The results of the study establish that viscous stringers exhibit characteristic extension and folding. When the viscosity contrast between the salt and the stringer is 1000:1, strong folding of stringers dominates the internal structure of the salt diapirs, and when the viscosity contrast between the two is 10:1, only small-scale minor folding of the stringers takes place. This variation in the viscosity contrast causes disparate internal stress distribution of the stringers. In addition, the location of the stringers and the thickness of salt deposit between the stringers as well as between the stringers and the base also govern the deformation pattern of the internal structure of the salt domes.

Modeling and Analysis of Polarized Couplers under Misalignment for Electric Vehicle Wireless Charging Systems

Wireless power transfer (WPT) is becoming popular increasingly in stationary electric vehicle (EV) charging. Various coil structures were proposed to improve the coupling characteristics, and polarized couplers have been proven to have better performance. Considering the varying spatial scales of transmitting and receiving, coils will alter the mutual inductance, further affecting the output power and transmission efficiency; therefore, it is crucial to calculate the mutual inductance of polarized couplers with variable offset for WPT system design. However, given the complex structure and the various excitation conditions of polarized couplers, the solving process based on the finite element model is time-consuming and resource intensive, therefore it is necessary to develop analytical models of mutual inductance for polarized couplers under misalignment. In this paper, the analytical models of the two commonly used polarized couplers with a Double-D polarized coil (DDP) or a Bipolar polarized coil (BP) on both sides under misalignment along any direction under different excitation conditions are proposed based on dual Fourier transformation. The mutual inductance characteristics of the two polarized couplers under misalignment can be investigated based on the proposed analytical models and finite element models, respectively. The results show that the mutual inductance of BP-BP coupler with in-phase current excitation mode is greater and more stable, and the method based on the analytical model is timesaving. Finally, the prototype of the WPT system with the two polarized couplers has been built, and experiments have also been carried out to verify the accuracy of the analytical models.

Finite element model updating of metallic and composite structures-A state of the art review

<abstract> Finite element model updating (FEMU) is a technique to improve the analytical finite element (FE) model of any structure from its experimental modal test data. The main purpose to apply FEMU on structures is to remove the uncertainties or errors present in the analytical FE model. The main objective of this paper is to present a review on the various FEMU techniques which can be applied to remove the uncertainties present in the FE model of the actual engineering structures. Applications of various FEMU techniques on the metallic and the composite structures have been discussed in this review paper. FEMU is applied on the metallic and the composite structures to remove the error present in their FE models. The main objective of the FEMU is to accurately predict the modal analysis characteristics such as the spatial-model, modal-model and the response model of the structures. The uncertainties present in the analytical or simulated FE model of any structure may be due to its material properties, dimensions and most probably due to the uncertainties present in the boundary conditions of the structure. However, to provide a sufficient strength to this review paper, the different updating methods are applied on the three degree of freedom spring mass system, on a 1-D aluminum beam, 2-D aluminum panel and on a graphite-epoxy composite material laminate. It is found that the updating algorithms are fast and reliable enough to remove error present in the numerical or simulated FE model of the structures and deliver the accurate estimation of the spatial-model, modal-model and response model of the different material structures. </abstract>

Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects

Modern developments of biomedical applications demand a better understanding of mechanical behaviour of soft biological tissues. As human soft tissues demonstrate a significant structural and functional diversity, characterisation of their mechanical behaviour still remains a challenge. Limitations related with implementation of mechanical experiments on human participants lead to a use of finite-element models for analysis of mechanical responses of soft tissues to different loads. This study focuses on parameters of numerical simulation considered for modelling of indentation of a human lower limb. Assessment of the effect of boundary conditions on the model size shows that at a ratio of its length to the tissue’s thickness of 1.7 for the 3D model this effect vanishes. The numerical results obtained with models employing various sets of mechanical parameters of the first-order Ogden scheme were compared with original experimental data. Furthermore, high sensitivity of the resulting reaction forces to the indenting direction is demonstrated for cases of both linear and angular misalignments of the indenter. Finally, the effect of changes in material parameters and their domain on their contribution to the reaction forces is discussed with the aim to improve our understanding of mechanical behaviour of soft tissues based on numerical methods. The undertaken research with its results on minimal requirements for finite-element models of indentation of soft tissues can support inverse analysis of their mechanical properties and underpin orthopaedic and medical procedures.

Finite element modeling for analysis of electroluminescence and infrared images of thin-film solar cells

Sheet resistance losses and local defects are challenges faced in solar module fabrication and upscaling processes. Commonly used investigation tools are non-invasive optical and thermal imaging techniques, such as electroluminescence, photoluminescence as well as illuminated and dark infrared imaging. Here, we investigate the potential of computationally efficient finite element simulation of solar cells and modules by considering planar electrodes coupled by a local current–voltage coupling law. Sheet resistances are determined by fitting current simulation results of an OPV solar cell to electroluminescence imaging data. Moreover, a thermal model is introduced that accounts for Joule heating due to an electrothermal coupling. A direct comparison of simulated temperature maps to measured infrared images is therefore possible. The electrothermal model is successfully validated by comparing measured and simulated temperature profiles across four interconnected organic solar cells of a mini-module. Furthermore, the influence of shunts on the thermal behavior of OPV modules is investigated by comparing electrothermal simulation results to dark lock-In IR thermography images.

A Steel-Concrete Composite Beam Element for Structural Damage Identification

The composite action between the layers of steel and concrete is governed by the shear connection. Because of the complicated interconnection behavior of these composite layers, it is difficult to detect damage in the composite structures, especially, the interfacial integrity of the two layers. In this paper, anovel method has been developed for structural damage identification of composite structures based on a steel-concrete composite beam element with bonding interface. In displacement-based finite element (FE) formulation, three damage indicators have been embedded into stiffness matrix of the composite beam that are defined as a stiffness reduction in the concrete, steel and interface layers. An algorithm-based on recursive quadratic programming has been proposed to identify structural damage in the composite beam from static measurements. The analytical FE model is validated by adapting its static responses in undamaged state with those obtained from an equal experimental model as well as a FE model developed in commercial software ABAQUS. A convergence study is conducted to determine the number of the composite beam FEs. To verify the proposed method, the static responses of the FE model with different damage cases at a given loading are calculated, and the measurements are simulated by adding different levels of white noise. Then, the proposed algorithm is applied to identify damage of the composite beam. The effects of measurement noise, loading location and amplitude, measurement numbers and the sizes of FE mesh on the identified results have been investigated. The numerical results show that this method is efficient and accurate to separately identify small damage in the concrete slab, and the steel girder and bonding interface of the composite beam.

Convergence studies of finite element model for analysis of steel-concrete composite beam using a higher-order beam theory

The finite element model based on a higher-order beam theory (HBT) is the most favourable modelling technique for an accurate prediction response of steel-concrete composite beams. The higher-order beam model is achieved by taking a third-order variation of the longitudinal displacement over the beam depth for the steel and concrete layers separately. The deformable shear studs used for connecting the concrete slab with the steel girder are modelled as distributed shear springs along with the interface between these two material layers. For the implementation of finite element formulation, the field consistent technique and full numerical integration of the stiffness matrix is carried out in order to avoid any shear locking and stress oscillation problem. There are four different types of beam elements incorporated to develop models to observe an optimal number of beam element required for good convergence. The proposed model is assessed through validation and verification using existing published results and numerical results produced by detailed 2D finite element modelling of steel-concrete composite beams. The validation and verification show a very good performance of the proposed finite element models.

Encoding multiple permanent shapes in 3D printed structures

Conventional methods of programmed shape change in polymers are one-way and one-time only. We introduce a new method of combining a bioinspired, hierarchical architecture with the pre-strain generated by extrusion-based 3D printing to encode multiple permanent shapes in thermoplastic polymer shell structures. At high temperature, these structures are multistable and can snap repeatedly between all encoded permanent shapes without reprogramming. At low temperature, the structures are monostable with increased stiffness; the multistability can be switched on and off via temperature. Characterization studies are performed to determine how to control the level of pre-strain and the deflection behavior of the structure to enable finite element modeling for analysis and design. This pre-straining technique may be thought of as a virtual mold: printed structures are initially flat but have multiple permanent shapes encoded. Taking advantage of the geometric freedom of 3D printing, complex geometries, and pre-strain fields may be used to create highly tailored snapping structures. Thermoplastic filaments with added particles may be used to impart additional multifunctionality to the structures, such as magnetic responsiveness, to enable remote actuation. These switchable multistable structures have potential applications in fields including robotics, aerospace, and smart buildings.

A Novel Algorithm for the Determination of Walker Damage in Loaded Disc Springs.

In this paper, a novel algorithm for the determination of Walker damage in loaded disc springs is presented. The algorithm takes a 3D-scan of a disc spring, measured residual stresses, material parameters, and spring loads as inputs. It outputs a distribution of Walker damage over the surface area of the input disc spring. As the algorithm allows a fully automated determination of the Walker damage, it can be used by disc spring manufacturers to reduce the working time spent on this task by specialized engineers significantly. Compared to spreadsheet applications using analytical formulas and finite element models using idealized geometry, this approach offers a superior description of the stress states in disc springs.

Blind, simultaneous identification of full-field vibration modes and large rigid-body motion of output-only structures from digital video measurements

Abstract Many operating structures undergo vibration associated with significant rigid-body motion, such as earthquake-excited structures which vibrate while moving (and/or rocking) along with the shaking ground, rotating structures such as the blades of helicopter, aircraft, wind turbine, and in UAV’s measurements (images/videos) of infrastructure response which is coupled with the motion of the UAV itself. In many such cases, the rigid motion is very dominant; measurement and identification of the relatively subtle deformation (flexible) motion of the structure in their operations is very challenging, especially when high-resolution vibration measurement and high-fidelity dynamics modeling are required to capture and characterize spatially local and temporally transient dynamics behaviors and features of the structure. Traditional contact-type wired or wireless sensors, such as accelerometers, strain gauges, and LVDT’s, are discrete point-wise sensors that only allow instrumentations at a limited number of places, providing very low spatial resolution vibration measurements. Non-contact interferometry-based optical measurement techniques using laser beams such as laser Doppler vibrometers, electronic speckle pattern interferometry (ESPI) and holographic interferometry, can provide high spatial resolution vibration measurement without the need to install sensors on the structure. However, they are very vulnerable to ambient vibration and rigid-body motion. As an alternative non-contact optical measurement method, photogrammetry uses white-light imaging of digital video cameras that are relatively low-cost, agile, and provides simultaneous measurements with very high spatial resolution where every pixel effectively becomes a sensing unit. Furthermore, it is robust to rigid-body motion. Using image processing algorithms such as optical flow and image correlation, photogrammetry has been successfully used for vibration measurements and experimental modal analysis of structures (including rotating-type) where full-field (or as many points as the pixel number of the image frame on the structure) modal parameters (mode shapes) can be obtained. However, existing such methods typically rely on installing and tracking the optical markers or speckle paints on the structure’s surface, which becomes less applicable for large measurement area or in harsh environment (high temperature and corrosion). In addition, they are computationally extensive. Aiming to alleviate these challenges, this study presents the development of adapting a recently-proposed video-based method for output-only, simultaneous identification of both the subtle, full-field deformation modes and the dominant rigid-body motion from only the video of the vibrating while moving structure. Full-field dynamic parameters (deformation modes) of structure, as well as its rigid-body motion can be efficiently estimated, respectively. Laboratory experiments were conducted on a bench-scale building structure with “free-free” boundary condition. Comparisons were made with an analytical finite element model. Results demonstrate that the method can efficiently and accurately extract the full-field, (total) motion of the structure and further identify or separate the subtle deformation modes and large rigid-body motion, respectively. Furthermore, videos reconstructed by the method (provided in the supplementary materials) show that it enables realistic visualization of the subtle deformation modes of the structure in presence of large rigid-body motion. Several practical limitations for implementing the method are also discussed.

Design of Ultrasonic Longitudinal-Torsional Vibrator Based on Waveguide Principle for Manufacturing and Medical Applications

This paper presents a new design of an ultrasonic vibrator that transforms longitudinal vibration into torsional vibrations for both manufacturing and medical applications. Conventional design methods of the ultrasonic vibrators are difficult to achieve complex hybrid vibration due to the limit of traditional straight shape and the tedious machining processes in fabrication. To overcome the disadvantages, this paper presents a new design of a hybrid longitudinal-torsional (L&T) ultrasonic vibrator. The hybrid L&T vibrator was designed using the acoustic waveguide principle and successfully transform the longitudinal vibration into a harmonic torsional vibration on the sample plane. An analytical finite element modeling was conducted for optimizing the hybrid L&T design parameters. Due to the complex design geometry, the new L&T design is difficult to be manufactured by conventional machining processes. Selective laser melting additive manufacture (SLM-AM) was used to fabricate the new hybrid L&T vibrator design. The designed hybrid longitudinal-torsional (L&T) vibrator was driven by axially polarized piezo-ceramic stacks for ultrasonic vibration applications. The experiments validate that the developed L&T vibrator is able to deliver high-energy efficiency vibration in both the longitudinal and the torsional directions. The presented new design of L&T ultrasonic vibrators can be used for applications of ultrasonic machining, surgical bone drilling, high efficient ultrasonic motors, or vibrational needle insertions or surgical tools for medical treatments.