Structural Finite Element Research Articles

Topology and FEA modeling and optimization of a patient-specific zygoma implant

Additive manufacturing has proven to be a very beneficial production technology in the medical and healthcare industries. While existing for over four decades, recent work has seen great improvements in the quality of products; particularly in medical devices such as implants. Improved customization reduced operating time and increased cost-effectiveness associated with Metal AM for these products offers a new value proposition. This paper investigates and evaluates modelling methods for the zygoma bone (human jawbone) and explores the most suitable material and optimum design for this critical biomedical implant. This paper proposes an innovative and efficient pre-process methodology that includes modelling, design validation, topological optimization, and numerical analysis. The method includes the generation of the model using reverse engineering of CT scan data and a topology optimization technique which makes the implant lightweight without causing excessive stress concentration. Static structural Finite Element Analysis was conducted to test three different biocompatible materials (Ti6Al4V, stainless steel 316L and CoCr alloys) which are commonly available for metal additive manufacturing. The stresses and conditions in the analysis were that of the human mastication process and all the implant design were tested with the three material types. The Taguchi method was used to determine the optimum design which was found to result in the highest mass reduction of 25% with Ti6Al4V as the implant material.

The CFD-Based Simulation of a Horizontal Axis Micro Water Turbine

A horizontal axis micro water turbine generator has been designed for use as a source of power generation where the reservoir construction has only a low head. It uses the natural flow rate of water to generate a specific power output. The power is, however, limited by the flow rate of water which has to be sufficient to keep operating a suitable number of revolutions per minute for the blades. Tis research aimed to introduce a new blade can be disassembled and modular on the wheel blade and developing for optimum design of the horizontal axis micro water turbine generator. A 3D model of the wheel blade in the horizontal axis micro water turbine generator was created by using Autodesk Inventor Professional 2018 software. Computational Fluid Dynamics (CFD) analysis and structural Finite Element Analysis (FEA) are presented in this paper. CFD analysis was performed to obtain the velocity and pressure difference between the concave and convex regions of the wheel blade while FEA was used to obtain the structural response of the wheel blade due to the water velocity load applied in terms of stresses and displacements.

Structural Finite Element Evaluation of Twisted Stacked-Tape Cable Under Cyclic Lorentz Loads

Structural finite element analysis (FEA) was performed on a straight 40-tape Twisted Stacked-Tape Cable (TSTC) surrounded with a solid copper core to investigate the stress state of the tape-stack under cyclic transverse compressive Lorentz loads up to the tenth cycle. Two worst-case stack orientations, 45 degree and 90 degree, were investigated. In addition, the stack was modeled as simply placed into the core or soldered to the core. Since annealing of the copper core can occur during machining; the stress state of the stack was studied as a function of yield strength of the copper. The results showed that if the copper was strong enough, the stress state of the stack remained unaltered and low up to 300 kN/m cyclic transverse compressive loading. However, when the copper was fully annealed, the plastic deformation accumulated from cyclic loading more significantly affected the stress distribution in the stack. If the tape-stack was simply placed into the core, the tapes can move and slide after each loading cycle. The averaged stress went down for the first few cycles, and then plateaued. However, when the stack was soldered to the core, the stack had less room to move, and therefore the stress state remained at higher values and was less affected by cyclic loading. Additionally, when producing the stack, the tapes at the edge may not align perfectly, and this would introduce additional stress concentration. The misalignment of the stack was studied, and the results showed that this effect caused higher stress in the stack. The numerical modeling presented provides a technique to simulate cyclic loading of TSTC cable. Besides, the information on the stress state of the tape-stack can be used to investigate the behavior of more recently developed cable designs and optimize future configurations.

Flutter Analysis of Last Stage Steam Turbine Power Plant Blade Through Transient Blade Row Simulation

Flutter phenomena becomes significant in response with turbomachinery design trends that prioritize efficiency. Especially in later stages of steam turbines, the slender profile of the blade becomes more prone to unstable dynamic aeroelasticity. Predicting the potential of flutter on a turbine blade can be done by constructing aeroelastic stability curve with evaluation of aerodynamic damping value under different rotor blade position, relative to the stator blade (inter blade phase angle). In this study, combination of steady Computational Fluid Dynamics (CFD), structural Finite Element Analysis (FEA) and transient blade row CFD was carried out using ANSYS 2019 R2 with the end goal of constructing aeroelastic stability curve and analysing the flutter risk of a 350 MW last stage steam turbine blade. At inter blade phase angle position of -180°, -70°, 0°, 77° and 180°, the system are exhibits positive aerodynamic damping values which indicates low to none flutter potential.

A substructure method for underground structure-dry soil-saturated soil–bedrock interaction under obliquely incident earthquake and its application to groundwater effect on tunnel

This study presents a substructure method with good accuracy and excellent efficiency for seismic underground structure-dry soil-saturated soil–bedrock interaction problem under obliquely incident earthquake. A combined zigzag-paraxial on-surface condition attached on structural surface is proposed to provide the dynamic stiffness of structural surrounding media including dry soil, saturated soil and underlying half space bedrock. The on-surface boundary condition can be implemented to any desired degree of accuracy and is compatible with numerical method such as the finite element method and the finite difference method. The condition is then coupled with structural finite element scheme and seismic wave input method to establish a substructure method. The reliability and accuracy of the proposed substructure method are verified by applying it in two degenerated interaction problems and comparing with other solutions. Finally, the proposed substructure method is employed to establish a lined tunnel-dry soil-saturated soil–bedrock interaction model for evaluating the seismic response of a lined tunnel embedded in the layered half space rich in groundwater, with an emphasis on the effects of changing groundwater levels on seismic response of tunnel lining.

Stabil: An educational Matlab toolbox for static and dynamic structural analysis

AbstractThe capability to analyze structures under static and dynamic loads is an essential skill for structural engineers. Structural analysis therefore is a key component in civil and architectural engineering education, where analytical methods are traditionally complemented by the use of (commercial) software packages. The latter are often closed source, which may obscure the links to the underlying matrix structural analysis or finite element formulation. To stimulate active, cooperative, and solution‐oriented learning, we developed Stabil, an electronic learning environment implemented as a Matlab toolbox. Stabil has an open structure to elucidate the links between theory and implementation and is presently used throughout the curricula of Civil and Architectural Engineering at KU Leuven. This paper explains the main principles of Stabil and discusses teaching experiences over the past 15 years. Stabil can be downloaded from http://bwk.kuleuven.be/bwm/stabil.

Improving efficiency and robustness of enhanced assumed strain elements for nonlinear problems

AbstractThe enhanced assumed strain (EAS) method is one of the most frequently used methods to avoid locking in solid and structural finite elements. One issue of EAS elements in the context of geometrically nonlinear analyses is their lack of robustness in the Newton–Raphson scheme, which is characterized by the necessity of small load increments and large number of iterations. In the present work we extend the recently proposed mixed integration point (MIP) method to EAS elements in order to overcome this drawback in numerous applications. Furthermore, the MIP method is generalized to generic material models, which makes this simple method easily applicable for a broad class of problems. In the numerical simulations in this work, we compare standard strain‐based EAS elements and their MIP improved versions to elements based on the assumed stress method in order to explain when and why the MIP method allows to improve robustness. A further novelty in the present work is an inverse stress‐strain relation for a Neo‐Hookean material model.

Impeller Optimization in Crossflow Hydraulic Turbines

Crossflow turbines represent a valuable choice for energy recovery in aqueducts, due to their constructive simplicity and good efficiency under variable head jump conditions. Several experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines have already been proposed, but all of them assume that structural safety is fully compatible with the sought after geometry. We show first, with reference to a specific study case, that the geometry of the most efficient impeller would lead shortly, using blades with a traditional circular profile made with standard material, to their mechanical failure. A methodology for fully coupled fluid dynamic and mechanical optimization of the blade cross-section is then proposed. The methodology assumes a linear variation of the curvature of the blade external surface, along with an iterative use of two-dimensional (2D) computational fluid dynamic (CFD) and 3D structural finite element method (FEM) simulations. The proposed methodology was applied to the design of a power recovery system (PRS) turbine already installed in an operating water transport network and was finally validated with a fully 3D CFD simulation coupled with a 3D FEM structural analysis of the entire impeller.

Aeroelastic prediction and analysis for a transonic fan rotor with the “hot” blade shape

This paper focuses on aeroelastic prediction and analysis for a transonic fan rotor with only its “hot” (running) blade shape available, which is often the case in practical engineering such as in the design stage. Based on an in-house and well-validated CFD solver and a hybrid structural finite element modeling/modal approach, three main aspects are considered with special emphasis on dealing with the “hot” blade shape. First, static aeroelastic analysis is presented for shape transformation between “cold” (manufacturing) and “hot” blades, and influence of the dynamic variation of “hot” shape on evaluated aerodynamic performance is investigated. Second, implementation of the energy method for flutter prediction is given and both a regularly used fixed “hot” shape and a variable “hot” shape are considered. Through comparison, influence of the dynamic variation of “hot” shape on evaluated aeroelastic stability is also investigated. Third, another common way to predict flutter, time-domain method, is used for the same concerned case, from which the predicted flutter characteristics are compared with those from the energy method. A well-publicized axial-flow transonic fan rotor, Rotor 67, is selected as a typical example, and the corresponding numerical results and discussions are presented in detail.

Sustainability evaluation for early design (SEED) framework for energy use, embodied carbon, cost, and daylighting assessment

ABSTRACT Given climate change and rapid global development, buildings must meet increasingly stringent environmental performance goals. Although numerous building simulation software assess energy performance, few inform the early stages of design when critical decisions impacting energy use and carbon footprint are made. Underrepresented early design simulation software could potentially significantly improve the environmental performance of buildings. This paper presents the SEED Framework for multi-objective early design decision-making that utilizes EnergyPlus-based building energy, structural finite element analysis, and Radiance-based daylighting simulations. When furnished with basic inputs, the SEED Framework generates numerous design options ranked by energy use, embodied carbon, construction cost, and daylighting metrics. A case study of a hypothetical mid-sized office building modelled in the Boston, Washington D.C., and Phoenix, USA climates demonstrates how the framework can guide decisions throughout pre- and schematic design phases. This framework aims to assist architects in designing high performance buildings within project and budgetary constraints.

Revealing the nanoindentation response of a single cell using a 3D structural finite element model

Changes in the apparent moduli of cells have been reported to correlate with cell abnormalities and disease. Indentation is commonly used to measure these moduli; however, there is evidence to suggest that the indentation protocol employed affects the measured moduli, which can affect our understanding of how physiological conditions regulate cell mechanics. Most studies treat the cell as a homogeneous material or a simple core–shell structure consisting of cytoplasm and a nucleus: both are far from the real structure of cells. To study indentation protocol-dependent cell mechanics, a finite element model of key intracellular components (cortex layer, cytoplasm, actin stress fibres, microtubules, and nucleus) has instead been developed. Results have shown that the apparent moduli obtained with conical indenters decreased with increasing cone angle; however, this change was less significant for spherical indenters of increasing radii. Furthermore, the interplay between indenter geometry and intracellular components has also been studied, which is useful for understanding structure-mechanics-function relationships of cells.

Rapid Computational Analysis of DNA Origami Assemblies at Near-Atomic Resolution

Structural DNA nanotechnology plays an ever-increasing role in advanced biomolecular applications. Here, we present a computational method to analyze structured DNA assemblies rapidly at near-atomic resolution. Both high computational efficiency and molecular-level accuracy are achieved by developing a multiscale analysis framework. The sequence-dependent relative geometry and mechanical properties of DNA motifs are characterized by the all-atom molecular dynamics simulation and incorporated into the structural finite element model successfully without significant loss of atomic information. The proposed method can predict the three-dimensional shape, equilibrium dynamic properties, and mechanical rigidities of monomeric to hierarchically assembled DNA structures at near-atomic resolution without adjusting any model parameters. The calculation takes less than only 15 min for most origami-scale DNA nanostructures consisting of 7000-8000 base-pairs. Hence, it is expected to be highly utilized in an iterative design-analysis-revision process for structured DNA assemblies.

Energy-decaying and momentum-conserving schemes for transient simulations with mixed finite elements

We present the four-field (of displacements, velocities, stresses and strains) and the three-field (of displacements, velocities and stresses) mixed variational formulations for structural dynamics, which can be used to derive in an elegant way the energy-decaying and momentum-conserving (EDMC) time-stepping schemes for transient simulations with mixed solid and structural finite elements. These mixed variational formulations are in this work applied for the derivation of EDMC schemes for the geometrically exact, recently proposed, mixed-hybrid, shell finite elements (with excellent performance), which combine mixed interpolations of the Hu–Washizu type or the Hellinger–Reissner type with the assumed natural strain concept. To this end, the first-order and the second-order accurate EDMC schemes are designed. The superior properties of the considered mixed-hybrid shell finite elements, which are reflected in statics by excellent convergence properties, ability to take very large solution steps, and low-sensitivity to mesh distortion, are in this manner extended for (long-term) transient simulations. Numerical examples, which illustrate transient simulations with the EDMC schemes and mixed-hybrid shell finite elements, show (among other effects) that the underlying structure of the shell motion is numerically preserved even for very large time steps.

Structural Performance and Finite Element Modeling of Roller Compacted Concrete Dams: A Review

There is no doubt that concrete is one of the most consumed materials all over the world. It is a composite mix widely used for constructing structures and infrastructures to sustain environmentally induced stresses such as thermal and seismic. As the mainstream of construction industry is tended to find out feasible solutions, Roller Compacted Concrete (RCC) was introduced to play an essential role in the development of dams and pavements, where over 550 RCC dams were created by the end of 2012. In fact, this material has the same basic constituents of conventional concrete with a zero-slump and a significant difference in the placing process. The majority of available studies in the literature are composed of numerical investigations to assess the thermal and seismic behavior of RCC dams and to provide a clear view on how to improve its performance under various loading conditions. This paper summarizes and compares the general conclusions of recent works on evaluating the structural performance of RCC dams.

Effect of Thickness of Various Restorative Materials and Hybrid Layer on Stress Distribution of Direct Cervical Restorations of Teeth using a Three Dimensional Structural Finite Element Analysis

Simulation of effect of thickness of restorative materials and hybrid layer on stress distribution of direct cervical restorations is critical to evaluate the best option for a bi-layered restoration in the cervical cavity.

Microstructure simulation using self‐consistent clustering analysis

AbstractTo capture all the individual microstructural effects of complex and heterogeneous materials in structural finite element simulations, a two‐scale simulation approach is necessary. Since the computational effort of such two‐scale simulations is extremely high, different methods exist to overcome this problem. In terms of a FFT‐based microscale simulation, one possibility is to use a reduced set of frequencies leading to a reduced numerical solution of the Lippmann‐Schwinger equation [?]. In a post‐processing step, highly resolved microstructural fields may then be reconstructed by using the compressed sensing technique [?]. Since the stress evaluation of this method is in real space and therefore not reduced, it is most beneficial in terms of linear elastic material behavior. Another very recent method to reduce the computational effort of a microscale simulation is the self‐consistent clustering analysis [?,?]. Such a self‐consistent clustering analysis is split into an offline and an online stage. Within the offline stage, the material points of the high‐fidelity representation of the unit cell are grouped into clusters with similar material behavior. Thereafter, in the online stage, a self‐consistent clustering analysis is used to solve the boundary value problem by a clustered Lippmann‐Schwinger equation. Since the generation of clusters may be based on linear elastic simulations, we propose to use a reduced set of frequencies for these simulations to improve the efficiency of the total algorithm. Elastic and elasto‐plastic composites are investigated in a small strain setting as representative simulation examples.

Crownwall Failure Analysis through Finite Element Method

Several failures of recurved concrete crownwalls have been observed in recent years. This work aims to get a better insight within the processes underlying the loading phase of these structures due to non-breaking wave impulsive loading conditions and to identify the dominant failure modes. The investigation is carried out through an offline one-way coupling of computational fluid dynamics (CFD) generated wave pressure time series and a time-varying structural Finite Element Analysis. The recent failure of the Civitavecchia (Italy) recurved parapet is adopted as an explanatory case study. Modal analysis aimed to identify the main modal parameters such as natural frequencies, modal masses and modal shapes is firstly performed to comprehensively describe the dynamic response of the investigated structure. Following, the CFD generated pressure field time-series is applied to linear and non-linear finite element model, the developed maximum stresses and the development of cracks are properly captured in both models. Three non-linear analyses are performed in order to investigate the performance of the crownwall concrete class. Starting with higher quality concrete class, it is decreased until the formation of cracks is reached under the action of the same regular wave condition. It is indeed shown that the concrete quality plays a dominant role for the survivability of the structure, even allowing the design of a recurved concrete parapet without reinforcing steel bars.

Sound transmission loss of plate-type metastructures: Semi-analytical modeling, elaborate analysis, and experimental validation

Recent studies on plate-type metastructures have shown promising applications in low-frequency sound insulation, as they possess a low-frequency sound transmission loss (STL) that is considerably higher than that derived from the mass law. To design a plate-type metastructure for a sound insulation application, three problems are worth exploring: 1) how to predict efficiently the STL of the metastructure, 2) how to understand its unusual STL behavior, and 3) how to design its parameters to obtain a high STL at a target frequency and achieve a broad frequency band of high STL without increasing the mass. The purpose of this work is to address these problems by investigating a plate-type metastructure that is simply constructed using a periodic array of mass blocks attached to a thin host plate. For the first problem, a semi-analytical method is proposed for efficient prediction of normal, oblique, and diffuse STL based on fast retrieval of dynamic surface mass density using a considerably reduced structural finite element model and without having to include the acoustic field. This method is validated based on comparisons with an existing numerical method and reported experimental data. For the second problem, the mechanisms of unusual STL behavior are revealed by analyzing dynamic surface mass density as well as Bloch wave dispersion and Bloch modes. The third problem is addressed by conducting an elaborate parametric analysis that provides straightforward guidelines for adjusting structural parameters to tune the STL peak frequency as well as offering general guidelines for designing multiple parameters to achieve a broader frequency band of high diffuse STL with a given surface mass density. A design guideline for improving STL bandwidth is experimentally validated through measurements of two specimens designed and fabricated with identical surface mass densities. Because the considered plate-type metastructure is simple yet instructive, these investigations and findings are of fundamental and practical interest to the design of sound insulation metastructures.

Semi-Analytical and Finite Element Investigations of the Vibration of a Stepped Beam on an Elastic Foundation

In this study free vibration behavior of a stepped beam on an elastic foundation is considered. The vibration of uniform beams on an elastic foundation has been previously studied extensively and various solutions are available in the literature. However, the problem considered in current study appears not to have been widely covered in the literature and analytical solutions are strictly limited. To this aim, semi-analytical solutions are obtained first by using Adomian decomposition method, then finite element solutions are computed via structural finite element analysis software (SAP 2000). The free vibration analysis of stepped beam considering the combinations of different support conditions at each end are performed employing semi-analytical and finite element methods. The findings of the analysis are compared and discussed in detail.

Convergence Characteristics of Geometrically Accurate Spatial Finite Elements

Abstract The convergence characteristics of three geometrically accurate spatial finite elements (FEs) are examined in this study using an eigenvalue analysis. The spatial beam, plate, and solid elements considered in this investigation are suited for both structural and multibody system (MBS) applications. These spatial elements are based on geometry derived from the kinematic description of the absolute nodal coordinate formulation (ANCF). In order to allow for an accurate reference-configuration geometry description, the element shape functions are formulated using constant geometry coefficients defined using the position-vector gradients in the reference configuration. The change in the position-vector gradients is used to define a velocity transformation matrix that leads to constant element inertia and stiffness matrices in the case of infinitesimal rotations. In contrast to conventional structural finite elements, the elements considered in this study can be used to describe the initial geometry with the same degree of accuracy as B-spline and nonuniform rational B-spline (NURBS) representations, widely used in the computer-aided design (CAD). An eigenvalue analysis is performed to evaluate the element convergence characteristics in the case of different geometries, including straight, tapered, and curved configurations. The frequencies obtained are compared with those obtained using a commercial FE software and analytical solutions. The stiffness matrix is obtained using both the general continuum mechanics (GCM) approach and the newly proposed strain split method (SSM) in order to investigate its effectiveness as a locking alleviation technique.