Finite Element Simulation Research Articles

Effect of Water-added-mass on Modal Behavior of Shaft-line of Large Hydroelectric Generator Unit

The water-added-mass to a hydro turbine-shaft-line can significantly affect its modal behavior including the vibration modes and their natural frequencies. So it is of great significance to consider the effect of added water mass on the modal behavior of a hydro turbine to assure the safe and efficient operation of the hydro turbine-shaft-line system. In this investigation, the effect of water-added-mass on the shaft-line of one large prototype hydroelectric generator unit has been investigated in detail via the finite element tool. First, a CAD model of the shaft-line was created based on actual dimensions. Then a finite element model of the entire shaft-line was generated with high-quality hexahedral and tetrahedral cells. A first round of finite element simulation of the shaft-line in the air was performed without considering the effect of surrounding water, but the results were not realistic. On this basis, a finite element-based water-structure coupling simulation was carried out to analyze the effect of water-added-mass on the modal behavior of the shaft-line of the large hydroelectric generator unit. The result is more realistic to reality than that in the air. The results of this study show that when the water surrounding the turbine runner is added to the hydro-turbine shaft-line, it increases the overall mass of the shaft-line system, thereby reducing the natural frequencies of the system. The decrease in natural frequencies can cause the shaft-line to approach its critical speed during operation, vibrate at higher amplitudes than usual, and even lead to potential damage to the shaft-line system. According to the results calculated with the finite element water-structure coupling method, the countermeasures to improve the evaluation of the water-added-mass effect on the structural modal behavior of the shaft-line for the hydroelectric generator units have been provided. The conclusion can also apply to other hydraulic turbine and pump units.

Analysis of the correlation between GIS partial discharge current waveform and charge quantity with UHF signals

The Ultra-High Frequency (UHF) method, as a crucial technology for online GIS monitoring, struggles with the issue of being unable to accurately reflect the number of partial discharges, which poses a significant challenge for this technique. To examine the relationship between partial discharge waveforms, charge quantity, and UHF signals, a physical field model of partial discharge is developed using finite element simulation software, allowing a comparison of the peak-to-peak values of UHF signals with the parameters of the partial discharge current. Research demonstrates a roughly linear relationship between the peak-to-peak values of UHF signals and the magnitude of the partial discharge current but no definitive connection with the discharge quantity. These significant findings guide the quantitative detection of partial discharges in electrical equipment using the UHF method.

Synergy of Modulating In-Plane Pores and Zincophilic Sites On the Flexible Graphene Paper for Efficient and Dendrite-Free Hosted Zn Anode

The practical advancement of Zn-ion batteries (ZIBs) in the portable/wearable electronics field is still hindered by the notorious Zn dendrites formation and the lack of an appropriate host to construct a highly effective flexible Zn anode. Herein, we present a three-dimensional (3D) N-doped graphene paper framework with abundant in-plane pores (rHGP-N) as an efficient Zn plating/stripping scaffold. Remarkably, the rHGP-N paper electrode exhibits an unprecedentedly low Zn nucleation overpotential of 5.2 mV and maintains a high average Coulombic efficiency (∼99.3%) over a superior long Zn plating/stripping cycling of 1400 h. DFT calculation results demonstrate that pyrrolic-nitrogen on graphene possess the strongest adsorption energy for Zn2+, serving as zincophilic sites to guide Zn uniform nucleation. Moreover, the finite elements simulation results illustrate that flexible graphene paper with abundant in-plane pores can mitigate structural stress and inhibit the formation of Zn dendrites by spatially homogenizing Zn2+ ions flux throughout the entire electrode. The assembled ZIBs full cell (rHGP-N@Zn//rHGP-N@Mn3(PO4)2) demonstrates an impressive volumetric energy density of 77 mWh cm-3, as well as excellent flexibility and mechanical stability with negligible capacity decay under harsh deformation conditions. Our approach can be potentially utilized in designing dendrite-free metal-based flexible anodes for Mg, Ca, or Al-ion batteries.

A domain decomposing reduced-order method for solving the multi-domain transient heat conduction problems

In this article, a domain decomposition algorithm combined with a reduced-order model (ROM) is proposed to deal with the transient heat conduction problems in multi-domain structures. Using the domain decomposition algorithm and the finite element method (FEM), the original problem is decomposed into multiple non-overlapping subdomains, which can be solved independently under appropriate boundary conditions. However, additional inter-regional connected calculation will be brought through the simple geometry decomposition. Thus, the proper orthogonal decomposition (POD), a projection-based ROM technique, is utilized to further reduce the number of unknowns and the calculation time for each subdomain. To be more specific, the local POD bases of each subdomain are obtained by decomposing a snapshot matrix that gathered according to time by the application of the virtual boundary conditions on interfaces of the adjacent subdomains and other boundaries. Furthermore, the problems under different boundary conditions can be linked by the variable condensation technique on the interfaces, which enhances the efficiency of the numerical solver dramatically. Finally, the accuracy and efficiency of the proposed method are demonstrated by comparing the results calculated using both the proposed algorithm and the direct finite element simulation.

Three-dimensional mechanical characteristics analysis of double-shoulder tool joint under complex loads

Taking a new type of special threaded drill pipe joint as the research object, a 3D nonlinear finite element model of the double-shoulder tool joint (DSJ) including the engage and retract groove structure is established by considering the factors of structural asymmetry and contact of each engaging surface. ABAQUS/Explicit finite element method (FEM) is used to study the stress and contact pressure distribution characteristics of the critical structure of DSJ under complex loads. The accuracy of the finite element model was verified by combining with the physical test, and the connection strength and sealing performance of DSJ are evaluated. The results show that the stress concentration occurs at the key structure of DSJ under the make-up torque. The geometry size and structural discontinuity at the transition fillet of the double-shoulder structure have a significant effect on the stress and contact pressure distribution on the shoulder. Under axial tension, the stress level and stress concentration area of the whole joint and the key structure change, especially in the thread section. The sealing performance on the shoulder decreases significant, while that of the thread section increases slightly. The test results are consistent with the finite element simulation results, and this joint shows good mechanical properties, which can meet the design requirements of drilling tool manufacturers and provide data support for its optimal design and application.

Simulation and design optimization of embedded steam baking integrated machine bottom plate structure

To address the challenges related to excessive deformation of the bottom plate during the opening and closing of the steam-baking integrated machine door, a comprehensive approach that incorporates finite element simulation and experimental testing was employed to investigate the plate’s deformation characteristics. Various structural parameters influencing the bottom plate were evaluated, and a series of enhancement strategies for the bottom plate structure were proposed. Following the optimization process, subsidence deformation of the bottom plate was reduced by 64%, and warpage deformation was reduced by 13.6%. Thus, a solid groundwork was established for subsequent structural stiffness analysis and optimization endeavors in the realm of embedded steam-baking integrated machines.

Modeling of crack tip fields and fatigue crack growth in fcc crystals

Predicting the mechanical behavior of polycrystalline materials containing a crack under both monotonic and cyclic loading conditions is crucial for accurately assessing the integrity of engineering materials. This study focuses on the deformation characteristics of face-centered cubic (fcc) grains within the crack tip field and their significant role in governing the driving force for fatigue crack growth during cyclic loading. We employ a cyclic crystal plasticity finite element (CPFE) model to analyze the mechanical response of austenitic 316L stainless steel polycrystals by accounting for nonlinear kinematic hardening effects. Through CPFE simulations, we investigate the deformation fields in 316L grains at the crack tip, considering two different grain orientations under plane strain conditions. Our CPFE results under monotonic loading align consistently with previous theoretical and experimental findings, particularly in comparing CPFE-simulated and experimentally observed plastic sectors consisting of different slip traces on the specimen surface near the crack tip. Based on a critical plastic work criterion for crack advancement, cyclic CPFE simulations are used to determine the fatigue crack growth rate as a function of stress intensity factor range for the two crack tip grain orientations in stainless steel. The simulated Paris law exponent matches experimental values. Furthermore, we compare cyclic CPFE results with those from cyclic J2 plasticity finite element simulations. This study demonstrates a cyclic CPFE approach for determining crack tip fields, accounting for crystallographic effects on plastic deformation of crack tip grains. Our approach can be applied to effectively evaluate fatigue crack growth rates in fcc polycrystalline metals.

Design and time-domain finite element simulation of multi-functional transformation optical device

In this paper, we first proposed mathematical model equations for wave propagation in a multi-functional transformation optical device, namely, an electromagnetic rotation concentrator. This device can concentrate electromagnetic energy while rotating electromagnetic waves. We also demonstrate the stability of the model equation in the continuous case. Next, we designed the multi-functional device with multiple layers. We then proposed a time-domain finite element method for simulating wave propagation in this device and conducted a stability analysis of the model equations in the discrete case. Finally, we implemented the proposed algorithm and obtained numerous numerical results that demonstrate the validity of our model equations. To the best of our knowledge, this is the first work on time-domain modeling and analysis of multi-functional electromagnetic devices.

Accelerating H* desorption of hollow Mo2C nanoreactor via in-situ grown carbon dots for electrocatalytic hydrogen evolution

Molybdenum carbide (Mo2C) is a promising non-noble metal electrocatalyst with electronic structures similar to Pt for hydrogen evolution reaction (HER). However, strong H* adsorption at the Mo sites hinders the improvement of HER performance. Here, we synthesized monodisperse hollow Mo2C nanoreactors, in which the carbon dots (CD) were in situ formed onto the surface of Mo2C through carburization reactions. According to finite element simulation and analysis, the CD@Mo2C possesses better mesoscale diffusion properties than Mo2C alone. The optimized CD@Mo2C nanoreactor demonstrates superior HER performance in alkaline electrolyte with a low overpotential of 57 mV at 10 mA cm−2, which is better than most Mo2C-based electrocatalysts. Moreover, CD@Mo2C exhibits excellent electrochemical stability during 240 h, confirmed by operando Raman and X-ray diffraction (XRD). Density functional theory (DFT) calculations show that carbon dots cause the d-band center of CD@Mo2C to shift away from Fermi level, promoting water dissociation and the desorption of H*. This study provides a reasonable strategy towards high-activity Mo-based HER eletrocatalysts by modulating the strength of Mo–H bonds.

Spatial sensitivity distribution assessment and Monte Carlo simulations for needle-based bioimpedance imaging during venipuncture using the finite element method.

Despite being among the most common medical procedures, needle insertions suffer from a high error rate. Impedance measurements using electrode-equipped needles offer promise for improved tissue targeting and reduced errors. Impedance visualization usually requires an extensive pre-measured impedance dataset for tissue differentiation and knowledge of the electric fields contributing to the resulting impedances. This work presents two finite element simulation approaches for both problems. The first approach describes the generation of a multitude of impedances with Monte Carlo simulations for both, homogeneous and inhomogeneous tissue to circumvent the need to rely on previously measured data. These datasets could be used for tissue discrimination. The second method describes the simulation of the spatial sensitivity distribution of an electrode layout. Two singularity analysis methods were employed to determine the bulk of the sensitivity within a finite volume, which in turn enables consistent 3D visualization. The modeled electrode layout consists of 12 electrodes radially placed around a hypodermic needle. Electrical excitation was simulated using two neighboring electrodes for current carriage and voltage pickup, which resulted in 12 distinct bipolar excitation states. Both, the impedance simulations and the respective singularity analysis methods were compared with each other. The results show that the statistical spread of impedances is highly dependent on the tissue type and its inhomogeneities. The bounded bulk of sensitivities of both methods are of similar extent and symmetry. Future models should incorporate more detailed tissue properties such as anisotropy or changing material properties due to tissue deformation to gain more accurate predictions.

Homogenization Model for Multistable Honeycomb Metastructures with Beam-like Behavior

Reduced order models facilitate initial design space investigations and enable assessing the benefits of compliant structures utilized for shape adaptability. This work presents a simple model to determine the flexural rigidity of a beam-like, multistable metastructure used as a spar in a hybrid spanwise morphing wing. The model considers the more complex metabeam as a homogeneous beam described by Euler-Bernoulli beam theory with an equivalent flexural rigidity. The analytical model's validity is established by comparing the obtained static and dynamic responses to finite element simulations. A closed-form expression of the flexural rigidity is then given, drawing from the multistable honeycomb's material properties and the metabeam’s geometry. The model's limitations are addressed by examining several specific cases of the metabeam’s morphed configurations and a more complex metabeam structure.

The Evaluation of Explicit Parameters on Eulerian-Lagrangian Simulation of Wave Impact on Coastal Bridges

Simply supported bridges along the United States Gulf Coast are highly vulnerable to extreme wave conditions and water elevations. A better understanding of the loading demands on the bridges under these extreme events will lead to improved designs and enhanced resiliency. Nonetheless, analyses through numerical models pose difficulties in terms of reliability and computational burden. On the other hand, experimental models for large-scale bridge superstructures are subject to limited space allocation and related scaling challenges. Hence, optimized Finite Element (FE) models that can simulate Wave-Superstructure Interaction (WSI) are a preferred viable solution to estimate loads experienced by these bridge superstructures. Nonetheless, the results of the FE simulations are highly dependent on the numerical parameters and configurations implemented in the model; thus, the implications of parameter selection must be assessed to help scholars and engineers develop reliable FE models. In this paper, an experimental scaled model was used to calibrate numerical models following the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. This explicit approach solves the Navier-Stokes equations to simulate fluid flow, and the dynamics response of the structure depends on analysis parameters (mass scaling factor, damping hourglass control, displacement hourglass scaling factor, and bulk viscosity scaling factors) and configurations (mesh size). The results provide a platform to compare numerical outputs and find the best parameters that suit WSI models. Moreover, the force signals applied to the superstructure experience high oscillations due to WSI. Different digital filter designs have been used to remove unwanted oscillations and provide researchers with recommendations on generating models that deliver optimal results.

Modeling Particle-Doped Materials for Performance Improvement of Contact-Separation Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) are an attractive energy harvesting technology due to their high efficiency and vast applications in self-powered sensors. In this work, dielectric–dielectric contact-separation TENGs were modeled with time-dependent finite element simulations with the objective of improving TENG’s performance by enhancing the relative permittivity (εr).To achieve this, the chosen material (PDMS, εr=2.75) was doped with SrTiO3 (εr = 300) particles. The open-circuit voltage (VOC) and short-circuit current (ISC) remained constant as ϵr increased, as predicted by existent models, but in contradiction with available experimental data. Thus, we introduced a charge correction model relating ϵr and surface charge density, allowing us to observe an increase in TENG performance output (VOC and ISC). This work shows that finite element simulations are suitable for better understanding and optimizing TENGs’ performance.

Numerical simulation of the hydrogen charging process in an adsorption storage tank

Adsorption storage utilizing activated carbon is acknowledged as a promising approach for hydrogen storage duo to its high efficiency. This study compares the activated carbon adsorption storage method with the conventional empty tank storage approach. Finite element simulation is conducted to analyze the hydrogen charging process. Results reveal that under conditions with an initial temperature of 281 K and a storage pressure of 50 MPa, the adsorption tank exhibits a higher system volumetric capacity compared to the empty tank, with an increase of 12.6%. Furthermore, the influence of activated carbon's macroporosity and adsorption performance on storage capacity is investigated. It is indicated that increasing macroporosity effectively enhances storage capacity. Additionally, a comparison between the hydrogen storage performance of AX-21 activated carbon and carbon nanotubes (CNTs) highlights the significant impact of adsorption performance of the adsorbent materials on the storage capacity and temperature distribution.

Research on the Support Performance of Internal Feedback Hydrostatic Thrust and Journal Bearing Considering Load Effect

This study aims to analyze the impact of uniform and eccentric load conditions on the performance of internal feedback hydrostatic thrust and journal bearing. Two distinct models are established: a three-degrees-of-freedom uniform load model and a five-degrees-of-freedom eccentric load model. The support stiffness, overturning stiffness, and flow rate for both thrust and journal bearings are calculated. Additionally, numerical analysis is conducted to examine the influence of oil film thickness, inlet pressure, and restrictor size on the operational characteristics of the bearings, revealing the interplay between an eccentric load and journal bearing speed. The validity of the theoretical algorithm is verified through finite element simulation. The research outcomes hold significant guiding implications for the design and application of internal feedback hydrostatic bearings.

Finite element simulation and experimental investigation of in-situ laser-assisted diamond turning of monocrystalline silicon

While the effectiveness of in-situ laser-assisted diamond turning (In-LAT) for promoting the ductile machinability of monocrystalline silicon has been demonstrated, the underlying cutting mechanisms remain inadequately understood. In this study, we investigate the fundamental mechanisms involved in the In-LAT of monocrystalline silicon by finite element (FE) simulations and experiments. Specifically, a FE model of In-LAT of monocrystalline silicon is developed, which incorporates a Drucker–Prager constitutive model to address the brittle fracture of the material, as well as temperature-dependent materials properties to address the thermal softening effect. Furthermore, experiments of In-LAT of monocrystalline silicon are conducted with the self-developed In-LAT device, including tapering cutting and end face cutting. Simulation results demonstrate that In-LAT significantly increases the critical depth of cut for the brittle-to-ductile transition of monocrystalline silicon in tapering cutting mode by 72.2% compared to conventional cutting, accompanied with significantly reduced cutting forces, continuous chip profile and reduced surface brittle damage. The promotion of ductile machinability of monocrystalline silicon under In-LAT is attributed to the reduction and dispersion of stress in the cutting zone, which is in contrast to the significant stress concentration at the rake face and cutting edge in conventional cutting. And simulation results also provide an optimal temperature field of 900 K for the In-LAT of monocrystalline silicon, above which the excessive plastic flow accompanied by thermal accumulation results into deteriorated surface roughness. These findings provide valuable insights for understanding the cutting mechanisms of In-LAT and the parameter optimization for In-LAT application.

Fidelity of Finite Element–Based Virtual Tire Assembly Models Used for Vehicle Noise, Vibration, and Harshness Structural-Borne Noise Performance Considering Vibrational Modal and Steady-State Dynamic Simulation

ABSTRACT The increasing presence of battery electric vehicles brings about new challenges to the noise, vibration, and harshness performance of tires. One of the new challenges involves the expansion of frequency range for structural-borne noise virtual predictions. Current standard virtual tire simplifies the tire geometry as an axisymmetric body, neglecting the effect of complex tread pattern. It is perceived that this simplification can lead to prediction error for a tire’s structural-borne noise performance at mid-frequency range (250∼500 Hz). This study investigates how different tread pattern representation affects the structural-borne noise prediction. This study uses linear, steady-state dynamics finite element simulations of a modified SAE J2710 test and traveling sinusoid test. The resulting frequency responses of the virtual tires and the computational time to obtain each frequency response are compared. The comparison shows that while including the 3D tread pattern does show some differences under certain conditions, it is not necessary to use this technique for every case, especially during the early evaluation stage.

Electroelastic wave dispersion in the rotary piezoelectric NEMS sensors/actuators via nonlocal strain gradient theory

This article introduces a computational means for investigating the electroelastic nonlinear wave dispersion traits of the nano-dimension sandwich pipe, which is composed of a core formed of a bi-directional functionally graded (Bi-FG) material, together with a piezoelectric sensor/actuator. A combination of Hamilton’s principle, first-order shear deformation, along with Von-Karman nonlinearity, is used for modeling and obtaining the nonlinear governing equations of the nano-sized sandwich pipe connected to a piezoelectric part. The nonlinear governing equations to obtain the nonlinear phase velocity of the current system are determined using a combination of analytical and multiple scales approaches. Due to some computational cost for choosing the precise values of both the nonlocality factor and length scale of the nanopipe in the laboratory, for the first time in this research, with the aid of COMSOL multi-physics finite element simulation, the results are verified, and new outcomes for obtaining the exact functions for nonlocal and length scale factors is presented. In addition, an artificial neural network (ANN) is utilized in this study for the prediction of the results. The mathematical and finite element results were used to train the ANN. A newly presented optimization algorithm is exploited for the first time for optimizing the ANN parameters concluding higher accuracy of the ANN predictions. Consequently, to explore the influences of the location of the piezoelectric patch, nonlocality and length scale factors, and applied voltage parameter on the phase velocity characteristics of the nano-dimension sandwich pipe made of a Bi-FG core and electrically patch, an effort is performed. As an applicable result that can be useful in the related nano-industries, the current work presents exact nonlocal and length scale functions for different conditions.

EFFECT OF SEGMENT DISLOCATION ON THE MECHANICAL PROPERTIES OF LINED TUNNELS IN A COMPLEX ENVIRONMENT

In complex environments, tunnels with a lined structure are more affected by the dislocation of a segment. This study uses finite element simulations to further investigate the relationship between environmental changes and segments in lined tunnels. Tunnels with and without a lining are simulated under varying strata resistance, buried depth, and water level conditions. The horizontal and vertical displacements and stress changes in the two tunnels are compared when segment dislocation occurs. The results show that the lateral displacement of the tunnel is relatively stable and less influenced by external loads. However, the longitudinal displacement change is the opposite, and it increases significantly when the displacement exceeds 10 mm. When the lined tunnel is subjected to a large external load and misalignment occurs, the performance of the tube sheet joint bolts deteriorates, resulting in a stress decrease. Furthermore, the lined tunnel exhibits an increased ability to resist deformation and does not exactly follow the law of small displacements from small misalignments. When a large misalignment occurs, the lined tunnel may be damaged by elliptical deformation along the 45° direction, and its internal forces would be much larger than those of the unlined tunnel.

Research on Symmetrical Flexible Clamping Conveyor for Scallion Harvester

Aiming at the problems of low conveying efficiency, poor adaptability of conveying Scallion poles of different diameters, and little innovation of the mechanism that exist in the existing clamping conveyor device, a symmetrical flexible clamping conveyor device suitable for Scallion harvesting was innovatively designed. The design and analysis of the overall structure of the clamping conveyor, the clamping mechanism, the clamping pulley and other key mechanisms were carried out, and finally the finite element simulation analysis of the clamping conveyor was carried out, and the analysis of the deformation cloud and stress cloud showed that the designed clamping conveyor could meet the requirements of the working strength. The designed symmetric flexible clamping and conveying device can automatically adjust the clamping force according to the diameter of Scallion stalks to realize efficient and lossless clamping, which is more innovative than the existing clamping and conveying devices.