Finite Element Method Calculations Research Articles

The design and simulation of a MOSFET-based MEMS pressure sensor using an integrated simulation approach

A novel integrated design and simulation approach is applied to analyze the performance of a metal–oxide–semiconductor field-effect transistor (MOSFET)-based microelectromechanical systems (MEMS) pressure sensor circuit while varying circuit and CMOS parameters, viz. the supply voltage and threshold voltage (Vt), respectively. For effective mechanical pressure sensing, a sensor MOSFET is integrated near the fixed edge of a deformable silicon diaphragm for maximum stress exposure. The stress value where the sensor MOSFET is located on the diaphragm surface is calculated using the finite-element method (FEM). Additionally, the threshold voltage required to activate the sensor MOSFET is also extracted using the FEM. The extracted value of Vt along with the corresponding gate oxide thickness are used to design and simulate the sensor circuit in the SPICE tool. The FEM-based multiphysics simulation is linked to a standard direct-current (DC) model SPICE simulation using our proposed carrier mobility model for a MOSFET under mechanical stress. All the FEM computations are performed using COMSOL Multiphysics, all the electrical simulations are performed using LT-SPICE, and the full sensor circuit is designed and simulated by integrating COMSOL Multiphysics and LT-SPICE via a MATLAB script. The validity of the design is confirmed by comparing these results with analytical computations. The results obtained using the integrated simulation approach confirm that the design is reliable and enable the sensor performance to be examined in terms of its sensitivity, yielding a value of 30 mV/MPa.

Acoustic modes of locally resonant phononic crystals: Comparison with frequency-dependent mass models

Locally resonant acoustic materials were proposed to control sound using structures with feature size orders of magnitude smaller than the acoustic wavelength in air. We analytically derive the effective, frequency-dependent mass densities of resonant oscillators consisting of a heavy mass within a light shell, embedded in foam, in two dimensions, using a rigid core-shell approximation. The effective mass is expressible in closed form by elementary functions, enabling a mapping of the low-frequency physics to a simple one-dimensional model involving a point mass harmonically coupled within a box. The acoustic band structure of a two-dimensional square lattice of these oscillators is evaluated in the effective, frequency-dependent mass density model and compared with the exact solution. For the out-of-plane oscillation within this two-dimensional phononic crystal, the nonlinear eigenvalue equation resulting from the frequency-dependent density is solved with the Cutting Surface Method to yield the acoustic band structure. This agrees with the exact band structure obtained by finite element method calculations within $2%$ numerical error. For the in-plane oscillations involving internal translations or rotations within the core-shell resonators, the one-dimensional mass-in-a-box model recaptures the exact acoustic modes at only certain high-symmetry points of the two-dimensional Brillouin zone. The description of more complex resonances within acoustic metamaterials requires a fundamental generalization of current effective mass models.

Real-Time Numerical Dosimetry of Low-Frequency Electromagnetic Fields by Using Multipoles

Computation of the internal electric field induced in the human body by low-frequency power systems is time-consuming. We compute an approximate solution in nearly real time by using a reduced basis for the internal field. The basis is computed once (off-line) by approximating the source by multipoles, the coefficients of which can be computed for any position of the human body due to analytic translation and rotation formulas. The results are validated with respect of finite element method (FEM) computation.

SHM System and a FEM Model-Based Force Analysis Assessment in Stay Cables.

The Rędziński Bridge in Wrocław is the biggest Polish concrete cable-stayed bridge. It is equipped with a large structural health monitoring (SHM) system which has been collecting the measured data since the bridge opening in the year 2011. This paper presents a comparison between the measured data and the finite element method (FEM) calculations, while taking into account 7 years of data collection and analyses. The first part of this paper concerns the SHM application. In the next part, which contains comparisons between forces in cables and temperature changes throughout the structure, the measured data are presented. The third part includes SHM-based calculations and simulations with a complex FEM model to check the measured data and to estimate future measurements. The last part contains a durability assessment calculation for the cable stays.

Influence of Boundary Conditions on Numerical Homogenization of High Performance Concrete.

Concrete is the most widely used construction material nowadays. We are concerned with the computational modelling and laboratory testing of high-performance concrete (HPC). The idea of HPC is to enhance the functionality and sustainability of normal concrete, especially by its greater ductility as well as higher compressive, tensile, and flexural strengths. In this paper, the influence of three types (linear displacement, uniform traction, and periodic) of boundary conditions used in numerical homogenization on the calculated values of HPC properties is determined and compared with experimental data. We take into account the softening behavior of HPC due to the development of damage (micro-cracks), which finally leads to failure. The results of numerical simulations of the HPC samples were obtained by using the Abaqus package that we supplemented with our in-house finite element method (FEM) computer programs written in Python and the homogenization toolbox Homtools. This has allowed us to better account for the nonlinear response of concrete. In studying the microstructure of HPC, we considered a two-dimensional representative volume element using the finite element method. Because of the random character of the arrangement of concrete’s components, we utilized a stochastic method to generate the representative volume element (RVE) structure. Different constitutive models were used for the components of HPC: quartz sand—linear elastic, steel fibers—ideal elastic-plastic, and cement matrix—concrete damage plasticity. The numerical results obtained are compared with our own experimental data and those from the literature, and a good agreement can be observed.

Evaluation of crack propagation behavior of porous polymer membranes

This study experimentally and numerically investigated the crack propagation behavior of porous polymer membranes in order to identify the criterion for crack propagation. A notch was introduced into the membrane as an initial crack (pre-crack), and a uniaxial loading was applied to produce stable crack propagation. During the test, crack propagation was observed using a CCD camera and the digital image correlation (DIC) method. The strain around the pre-crack tip at the onset of crack propagation was measured experimentally using the DIC method. We found that large-scale yielding developed before crack propagation. Stable crack propagation was observed for all tensile tests. In parallel, a homogeneous model that mimicked the porous polymer membrane was created using the finite element method (FEM) to investigate the stress/strain distribution around the crack tip. This study adopted the yield criterion proposed by Deshpande and Fleck. The computed strain distribution was compared with the experimental results, and the distributions were found to be similar. The strain distribution obtained by the DIC method and FEM computation yielded a J-integral value, which could be used to investigate the criterion for crack propagation. Regardless of the initial crack length, the J-integral value at the onset of crack propagation was a constant value for all tests. We concluded that we successfully determined the criterion for crack propagation in the porous polymer membrane. Our comprehensive study using DIC experiments and FEM computations is useful for identifying the crack propagation behavior of a porous polymer membrane and for determining the criterion for crack propagation.

NUMERICAL SIMULATION OF LATERALLY LOADED PILE GROUPS ADJACENT TO A SLOPE

This paper is a numerical study based on a number of numerical model tests of pile groups, subjected to static lateral loading. Tests were conducted on single, (2x1), and (2x3) pile groups at three-diameter (3D) spacing. The model piles studied is concrete piles with 25 cm diameter and 10m length founded in loose sand (Dr=25%). The model is developed to study the effect of the number of piles in group on its lateral capacity on level ground and adjacent to a slope of inclination (3H:2V). The behavior of the piles was analyzed using a 3-D elasto-plastic finite element method (FEM) computer program Plaxis 3D ver. 2020, which represents a realistic model to simulate the problem. The response of the piles in the group was compared with the response of the single pile. It was found that the behavior of laterally loaded pile group depends largely on the arrangement of piles in group with respect to direction of load. In case of a slope it was found that the behavior of pile groups depends on the distance of lead row of pile groups from the slope crest (B/D) and arrangement of piles in group corresponding to load direction. &nbsp

Application of Inverse Neural Networks for Optimal Pretension of Absorbable Mini Plate and Screw System

Mandibular fractures are common facial lesions typically treated with titanium plate and screw systems; nevertheless, this material is associated with secondary effects. Absorbable material for implants is an alternative to titanium, but there are also problems such as incomplete screw insertion and screw breakage due to high pretension in the screw caused by the insertion torque. The purpose of this paper is to find the optimal screw pretension (SP) in absorbable plate and screw systems by means of artificial neural network (ANN) and its inverse (ANNi). This optimal SP must satisfy a desired maximum von Mises strain (MVMS). For training the ANN, a database was generated by means of a design of experiments (DOE). Each DOE configuration was solved by means of finite element method (FEM) calculations. To obtain the optimal value for (SP) in the mini absorbable screw for fracture fixation, a strategy to invert the ANN is developed. Using the ANN coefficients, a sensitive study was performed to identify the influence of the design parameters in the MVMS. The optimal SP obtained was 14.9742 N. The MVMS condition was satisfied with an error less than 1.1% in comparison with FEM and ANN results. The screw shaft length is the most influencing MVMS parameter.

Parameters Identification of the Anand Material Model for 3D Printed Structures.

Currently, there is an increasing use of machine parts manufactured using 3D printing technology. For the numerical prediction of the behavior of such printed parts, it is necessary to choose a suitable material model and the corresponding material parameters. This paper focuses on the determination of material parameters of the Anand material model for acrylonitrile butadiene styrene (ABS-M30) material. Material parameters were determined using the genetic algorithm (GA) method using finite element method (FEM) calculations. The FEM simulations were subsequently adjusted to experimental tests carried out to achieve the possible best agreement. Several experimental tensile and indentation tests were performed. The tests were set up in such a way that the relaxation and creep behaviors were at least partially captured. Experimental tests were performed at temperatures of 23 °C, 44 °C, 60 °C, and 80 °C. The results obtained suggest that the Anand material model can also be used for ABS-M30 plastic material, but only if the goal is not to detect anisotropic behavior. Future work will focus on the search for a suitable material model that would be able to capture the anisotropic behavior of printed plastic materials.

Mechanical Properties of Atomically Thin Tungsten Dichalcogenides: WS2, WSe2, and WTe2.

Two-dimensional (2D) tungsten disulfide (WS2), tungsten diselenide (WSe2), and tungsten ditelluride (WTe2) draw increasing attention due to their attractive properties deriving from the heavy tungsten and chalcogenide atoms, but their mechanical properties are still mostly unknown. Here, we determine the intrinsic and air-aged mechanical properties of mono-, bi-, and trilayer (1-3L) WS2, WSe2, and WTe2 using a complementary suite of experiments and theoretical calculations. High-quality 1L WS2 has the highest Young's modulus (302.4 ± 24.1 GPa) and strength (47.0 ± 8.6 GPa) of the entire family, overpassing those of 1L WSe2 (258.6 ± 38.3 and 38.0 ± 6.0 GPa, respectively) and WTe2 (149.1 ± 9.4 and 6.4 ± 3.3 GPa, respectively). However, the elasticity and strength of WS2 decrease most dramatically with increased thickness among the three materials. We interpret the phenomenon by the different tendencies for interlayer sliding in an equilibrium state and under in-plane strain and out-of-plane compression conditions in the indentation process, revealed by the finite element method and density functional theory calculations including van der Waals interactions. We also demonstrate that the mechanical properties of the high-quality 1-3L WS2 and WSe2 are largely stable in air for up to 20 weeks. Intriguingly, the 1-3L WSe2 shows increased modulus and strength values with aging in the air. This is ascribed to oxygen doping, which reinforces the structure. The present study will facilitate the design and use of 2D tungsten dichalcogenides in applications such as strain engineering and flexible field-effect transistors.

A Plane Stress Failure Criterion for Inorganically-Bound Core Materials.

Inorganically-bound core materials are used in foundries in high quantities. However, there is no validated mechanical failure criterion, which allows performing finite-element calculations on the core geometries, yet. With finite-element simulations, the cores could be optimised for various production processes from robotic core handling to the decoring process after the casting. To identify a failure criterion, we propose testing methods, that enable us to investigate the fracture behaviour of inorganically-bound core materials. These novel testing methods induce multiple bi-axial stress states into the specimens and are developed for cohesive frictional materials in general and for sand cores in particular. This allows validating failure criteria in principal stress space. We found that a Mohr-Coulomb model describes the fracture of inorganic core materials in a plane stress state quite accurately and adapted it to a failure criterion, which combines the Mohr-Coulomb model with the Weakest-Link theory in one consistent mechanical material model. This novel material model has been successfully utilised to predict the fracture force of a Brazilian test. This prediction is based on the stress fields of a finite element method (FEM) calculation.

Analysis of Lateral Displacement Law of Deep Foundation Pit Support in Soft Soil Based on Improved MSD Method

Foundation pit envelope and foundation pit excavation solution design is a multidisciplinary problem that could be linked to a series of safety issues in the geotechnical engineering of an actual construction project. Moreover, the construction of large deep foundation pit in soft soil often faces greater risks and challenges as the support structure deforms more easily and unpredictably. In order to improve the deformation prediction of deep foundation pit engineering precision and efficiency and to ensure that the construction of deep foundation pit engineering is safe and efficient, in this article the traditional MSD (mobilizable strength design) theory research and analysis, combined with the Jinan formation characteristics of a tunnel in JInan, and new parameters were introduced to the original MSD method theory: the wall itself within the bending strain energy U and support compression elastic potential energy of V. A new law of conservation of energy is constructed, and finally, an optimized MSD method has been proposed, this method is shown in the article. Finally, the results of foundation pit deformation calculation were compared among the optimized MSD method, finite element calculation method, and field monitoring data analysis method, so as to demonstrate the reliability of the prediction system of optimized MSD method and finite element analysis method. The results show that, by optimizing the MSD calculation method, the horizontal displacement of the retaining wall varies depending on the excavation depth of the foundation pit and the form of internal support with the overall peak value of displacement between 0∼0.2% H (H being the excavation depth); the deformation of retaining wall increases gradually with the increase of excavation depth of the foundation pit, and the peak position of deformation gradually moves down with the excavation of foundation pit. The trend of these changes is consistent with the results of the finite element method and field data analysis method, proving that the optimized MSD method is reliable in predicting the deformation of the foundation pit under specific stratum conditions.

An improved continuous medium technique for three-dimensional analysis of tall building structures

This paper presents a three-dimensional analysis of tall building structures using an improved continuous medium technique model in which consistent global column bending and column longitudinal deformation are considered along with a decoupling technique for the resulting system of differential equations. A numerical example shows that although the proposed methodology is very simple and suitable for hand calculations, it presents very good accuracy in comparison with finite element method computations.

Analysis of Pure Bending Vertical Deflection of Improved Composite Box Girders with Corrugated Steel Webs

Steel bottom plates are applied as replacements for the concrete bottom plates in order to reduce the dead weight of the composite box girders with corrugated steel webs and steel bottom plates (CSWSB). Due to the change in the material, the previous analytical calculation methods of vertical deflection of composite box girders with corrugated steel webs (CSWs) cannot be directly applied to the improved composite box girders. The shear lag warpage displacement function was derived based on the shear deformation laws of the upper flange and the bottom plates of the improved composite box girders. The equations for the calculation of the shear deformation and the additional deflection due to the shear lag of continuous and simply supported composite box girders with CSWSB under concentrated and uniformly distribution loads were derived by considering the double effects of the shear lag and the shear deformations of the top and the bottom plates with different elastic moduli. The analytical solutions of the vertical deflection of the improved composite box girders include the theory of the bending deflection of elementary beams, shear deformation of CSWs, and the additional deflection caused by the shear lag. Based on the theoretical derivation, an analytical solution method was established and the obtained vertical deflection analytical solutions were compared with the finite element method (FEM) calculation results and the experimental values. The analytical equations of vertical deflection under the two supporting conditions and the two load cases have verified the analyses and the comparisons. Further, the additional deflections due to the shear lag and the shear deformation are found to be less than 2% and 34% of the total deflection values, respectively. Moreover, under uniform distributed load conditions, the deflection value was found to be higher than that of the under concentrated load condition. It was also found that the ratio of the deflection caused by the shear lag or the shear deformation to the total deflection decreased gradually with the increase in the span width ratio. When the value of the span width ratio of a single box and single chamber composite box girder with CSWSB was equal to or greater than 8, the deflections caused by the shear lag and the shear deformation could be ignored.

Levitas

We received and we gladly publish this contribution by distinguished designer and theorist Ian Ritchie, as an example of that bridging research and practice which our journal intends to promote and disseminate. [MS] ABSTRACT - The design and engineering development of two apex connected square woven flat surfaces, each constrained at ground level by three anchors and lifted to form a 3D gridshell whose theoretical geometry is modified by the small sectional profile of the rectangular members made of wood. The warp and weft of the weave are of identical section and made from Italian red oak. The process of artistic investigation is explained and then taken into theoretical designs, computed, and is then tested iteratively through choice of wood, a 33% physical model which is laser surveyed and fed back into the computer model and FEM (Finite Element Method) analysis, and finally followed by a partial full scale mock up, before realising the sculpture at the Arte Sella environmental art park.

STATIC ECCENTRICITY FAULT DETECTION METHOD FOR ELECTRICAL ROTATING MACHINES BASED ON THE MAGNETIC FIELD ANALYSIS IN THE AIR GAP BY MEASURING COILS

Electrical rotating machines have a great economic significance as they enable conversion of energy between mechanical and electrical state. Reliability and operation safety of these machines can be greatly improved by implementation of continuous condition monitoring and supervisory systems. Especially important feature of such systems is the ability of early fault detection. For this reason, several methods for detection and diagnosis of the machine faults have been developed and designed. As fault detection methods can largely differ in the types of detectable faults, machine adoptability and price of the system, a novel method was developed that can be used for cost-effective detection of various faults of electrical machine. Machine fault detection technique presented in this paper is based on the measurement of magnetic field in the air gap. Numerous studies have proven that crucial information about the machine condition can be determined based on measurement and analysis of the magnetic field in the air gap. It has also been confirmed that analysis of the air gap magnetic field can be used to detect, diagnose and recognize various electrical faults in their very early stage. Proposed method of positioning and installation of the measuring coils on ferromagnetic core parts within the air gap region of the machine enables differentiation of various faults. Furthermore, different faults can be detected if measuring coils are placed on the stator teeth then when placed on the rotor side. The paper presents method on how to analyse and process the measured voltages acquired from measuring coils placed within the machine, especially in the case of rotor static eccentricity detection. The methodology is explained by means of finite element method (FEM) calculations and verified by measurements that were performed on the induction machine. FEM calculation model was used to predict measurement coil output of the induction motor for healthy and various faulty states (at different amounts of static eccentricity). These results were then confirmed by measurements performed in the laboratory on the induction traction motor that was specially modified to enable measurements of faulty operation states of the machine. Measurements comprised of several machine fault conditions broken one rotor bar, broken multiple rotor bars, broken rotor end ring and various levels of rotor static eccentricity.
 Other methods used for faults detection are primarily based on the monitoring of quantities such as current and vibration and their harmonic analysis. This new system is based on the tracing the changes of induced voltage of the measuring coils installed on the stator teeth. Faults can be detected and differentiated based on RMS value of these voltages and the number of voltage spikes of voltage waveform i.e. without the need of harmonic analyses. If these coils are installed on the rotor it is possible to detect the stator winding faults in a similar manner.

Heat Transfer Coefficient Determination during FC-72 Flow in a Minichannel Heat Sink Using the Trefftz Functions and ADINA Software

This work focuses on subcooled boiling heat transfer during flow in a minichannel heat sink with three or five minichannels of 1 mm depth. The heated element for FC-72 flowing along the minichannels was a thin foil of which temperature on the outer surface was measured due to the infrared thermography. The test section was oriented vertically or horizontally. A steady state heat transfer process and a laminar, incompressible flow of the fluid in a central minichannel were assumed. The heat transfer problem was described by the energy equations with an appropriate system of boundary conditions. Several mathematical methods were applied to solve the heat transfer problem with the Robin condition to determine the local heat transfer coefficients at the fluid/heated foil interface. Besides the 1D approach as a simple analytical method, a more sophisticated 2D approach was proposed with solutions by the Trefftz functions and ADINA software. Finite element method (FEM) calculations were conducted to find the temperature field in the flowing fluid and in the heated wall. The results were illustrated by graphs of local heated foil temperature and transfer coefficients as a function of the distance from the minichannel inlet. Temperature distributions in the heater and the fluid obtained from the FEM computations carried out by ADINA software were also shown. Similar values of the heat transfer coefficient were obtained in both the FEM calculations and the 1D approach. Example boiling curves indicating nucleation hysteresis are shown and discussed.

A plasmonic lens based on coordinate transformation

With the development and maturity of nanofabrication technology, many nanostructures with specific electromagnetic characteristics and optical functions have been designed and demonstrated. Artificial materials with these special optical properties are known as metamaterials. In this paper, a metamaterial lens is proposed and characterized. After using the space transformation approach based on the coordinate transformation principles, the lens becomes anisotropic and inhomogeneous, thus realizing the regulation of electromagnetic waves. The electromagnetic wave transformation characteristics of the superlens are numerically analysed by irradiating a plane transverse wave with a wavelength of 300 nm onto a rectangular slab. The results show that the waveform of the incident light changes from plane waves to cylindrical after passing through the superlens. The validity of the superlens is verified by finite element method calculations.

Use of Maraging Steel 1.2709 for Implementing Parts of Pressure Mold Devices with Conformal Cooling System

In this paper, we present the results of experimental tests and numerical calculations for parts of foundry mold devices made by selective laser melting (SLM). The main aim of this research was to compare the heat conduction efficiency of the conformal and the traditional channel arrangement. The infusion spreader with a conformal channel arrangement and the test material were made with an M2 Concept Laser Cusing machine using 1.2709 steel powder. Temperature changes in the spreaders were compared between conventional and conformal cooling channels using finite element method (FEM) calculations. The position of the so-called “thermal equilibrium isotherm” was determined for both sprue spreaders, which separate the area of the mold with a constant temperature from the zone of cyclic temperature changes. The components of the sprue spreaders in a stress state caused by temperature changes during the operation of the pressure machine were determined using the FEM model. It was found that the cooling system shortened the time of solidification and cooling of the alloy. Based on the analysis of the strength test results and the fracture surface of the samples, the relationship between heat treatment parameters and the strength, hardness, and elongation of the tested material was determined. The sprue spreaders were installed under a pressure machine and tested under production conditions. The use of a sprue spreader with a conformal cooling system shortened the time of a single cycle of the casting machine compared to the conventional solution.

Electric field enhancement control in active junction of IGBT power module

Dielectric liquids are incompressible, able to fill voids and have selfhealing effect and hence are being considered as alternative encapsulation materials to establish power electronics at ambient high pressure at subsea conditions. In a long-term endurance test, insulated-gate bipolar transistor (IGBT) chips subjected to 6.5 kV DC stress in dielectric oil environment was reported to have failed after less than one week in operation. A critical look at the failed objects revealed contamination fibres at the surface and around the high field regions. This paper presents the numerical simulation of field distribution around a conducting fibre at the surface of the IGBT chip. It also evaluates the influence of the nature of the encapsulation material on the integrity of power electronic modules using a long-term experiment at a medium elevated temperature for high and low relative humidity operated close to service load using IGBT relevant chips. Finite element method (FEM) calculations show how the high field region can be shielded from impurities that can easily trigger partial discharge (PD) and breakdown. The simulation suggests that coating the surface of the module with a thin polymer layer with a thickness of 20 μm or more could be sufficient to improve the reliability of the encapsulation system. Additional polymer coat with thickness 27 μm on the chip made the system survive without failure for 67 weeks under test and dry operating condition. Meanwhile, thick coating such as silicone gel protected the object longer under higher relative humidity.