Finite Element Computer Model Research Articles

Electrodynamic Force, Casimir Effect, and Stiction Mitigation in Silicon Carbide Nanoelectromechanical Switches.

Logic switches enabled by nanoelectromechanical systems (NEMS) offer abrupt on/off-state transition with zero off-state leakage and minimal subthreshold swing, making them uniquely suited for enhancing mainstream electronics in a range of applications, such as power gating, high-temperature and high-voltage logic, and ultralow-power circuits requiring zero standby leakage. As NEMS switches are scaled with genuinely nanoscale gaps and contacts, quantum mechanical electrodynamic force (EDF) takes an important role and may be the ultimate cause of the plaguing problem of stiction. Here, combined with experiments on three-terminal silicon carbide (SiC) NEMS switches, a theoretical investigation is performed to elucidate the origin of EDF and Casimir effect leading to stiction, and to develop a stiction-mitigation design. The EDF calculation with full Lifshitz formula using the actual material and device parameters is provided. Finite element modeling and analytical calculations demonstrate that EDF becomes dominant over elastic restoring force in such SiC NEMS when the switching gap shrinks to a few nanometers, leading to irreversible stiction at contact. Artificially corrugated contact surfaces are designed to reduce the contact area and the EDF, thus evading stiction. This rational surface engineering reduces the EDF down to 4% compared with the case of unengineered, flat contact surfaces.

Seismic response of the elevated concrete water tower considering liquid–solid–soil interaction

In the present study, the elevated concrete water tower is used as the research object. In order to investigate the ground motion response law of the elevated concrete water tower with the near-field Chichi wave, the near-field no-pulse Tehachapi Pump wave and the far-field long-period Tianjin waves when the liquid–solid–soil interaction (LSSI) is considered. And the finite element calculation model of the elevated concrete water tower and foundation with different liquid storage rate was established and the dynamic time history analysis was also conducted. The calculation results demonstrate that when considering LSSI, the elevated concrete water tower exhibits different response characteristics under the action of three types of seismic waves. Under the action of pulsed seismic waves in the near field, the seismic response of the elevated water tower structure is the most intense, followed by the far-field long-period seismic wave, and the response in the near-field no-pulse seismic wave remains the least.

An Inductive Force Sensor for In-Shoe Plantar Normal and Shear Load Measurement

Diabetic foot ulcers (DFUs) are a severe global public health issue. Plantar normal and shear load are believed to play an important role in the development of foot ulcers and could be a valuable indicator to improve assessment of DFUs. However, despite their promise, plantar load measurements currently have limited clinical application, primarily due to the lack of reliable measurement techniques particularly for shear load measurements. In this paper we report on the design and evaluation of a novel tri-axis force sensor to measure both normal and shear load on the foot’s plantar surface simultaneously. The sensor consists of a group of inductive sensing coils above which a conductive target is placed on a hyperelastic elastomer. Movement of the target under load affects the coil inductances which are measured and digitized by an embedded system. Using a computational finite element model, we investigated the influence of sensing coil form and configuration on sensor performance. A sensor configured with four-square coils and maximal turns provided the best performance for plantar load measurements. A prototype was fabricated and calibrated using a neural network to map the non-linear relationship between the sensor output and the applied tri-axis load. Experimental evaluation indicates that the tri-axis sensor can effectively detect shear load of ±16 N and normal load up to 105 N (RMS errors: 1.05 N and 1.73 N respectively) with a high performance. Overall, this sensor provides a promising basis for plantar normal and shear load measurement which are crucial for improved assessment of DFU.

Research on Open Cut Blasting Technology of Reservoir Diversion Tunnel

In order to study the andesitic porphyrite failure rule of open-cut blasting in diversion tunnel of reservoir, taking the Qianping reservoir project as an example through blasting test and vibration detection, field observation, statistical analysis and numerical simulation, the blasting technology of open cut diversion tunnel of reservoir is studied. Finite element method software ANSYS was used to establish the finite element calculation model of open cut diversion tunnel of Qianping reservoir. The andesitic porphyrite blasting process is simulated by using the dynamic analysis module LS-DYNA in ANSYS. The simulation results are compared with the test results, determining the optimal design scheme for open cut blasting of diversion tunnel. Numerical analysis and test results show that andesitic porphyrite blasting excavation is suitable for blasting parameters in I-2 area. The three-dimensional numerical model, firstly established in this paper, can be used to guide similar blasting schemes. The research results are of guiding value to similar projects.

Ground penetrating radar survey for structural assessment of a heritage sport building

In order to prevent seismic damage on building heritage built before Seismic Standards, constructions require to be assess to verify the structural response in the case of multi-level intensity seismic actions. This problem especially concerns those buildings with a social function as schools, hospitals, etc., or with historical and architectural value as that designed by important builders of the past.This is the case of the bar-restaurant building of “Bellariva” Sport Centre, designed and built in Florence by the World-famous Italian engineer Pier Luigi Nervi in the Sixty years. Its structure is characterized by reinforced concrete frames and hosts the locker rooms of the swimming pool and a bar on the first floor, a restaurant on the second, where a long crack was observed. The presence of a large balcony with heavy perimeter planters near the cracked zone motivated the execution of on-site tests finalized to determine the steel bars connecting the restaurant floor to the balcony. A Ground Penetrating Radar survey was performed in order to determine the internal structure of the floor, dimensions and disposition of steel bars, and to gather information about the connections between perimeter beams and balcony at the level of the restaurant. The experimental campaign allowed to refine a computational Finite Element Model that was utilized for the performance analysis of the structure in the current state. The paper presents the main results of a preliminary seismic analysis carried out on the structure, on the basis of which some retrofit intervention are suggested.

The crashworthiness performance of integrally woven sandwich composite panels made using natural and glass fibers

As a way to save petroleum resources, considerable efforts were made in the last three decades to develop green composites. Green composites are a category of composite materials in which at least one phase (reinforcement or matrix) is made from renewable resources. An attempt was made to present a simple fabrication process to produce hollow integrally woven sandwich composites. In addition, the potential of jute fibers to be utilized as piles in the core of an integrally woven sandwich composite was assessed and compared to the counterparts made using glass fibers. The crashworthiness performances of integrally woven sandwich composite samples considering the effect of relative density, pile material and the presence of polyurethane foam were investigated through performing quasi-static flat-wise compression tests. Based on the findings, the foam-filled integrally woven sandwich composites exhibited stable compression load-displacement response and better energy absorption properties over pure foam, which make them appropriate for automobile interior components. Moreover, a computational cost-efficient finite element modeling was presented and subsequently validated with experimental results.

Influence of wind loads on façade scaffolds covered with different types of nets

In the process of the structural design of the working and façade scaffolds, the self-weight of the elements, the service load and the wind load should be taken into account. The wind load on a covered façade scaffold is determined by many factors, including the wind velocity, the solidity ratio of the building’s façade, the geometric characteristics of the scaffold’ components and the type of cladding – netting or sheeting. The paper investigates the effects of wind loads on both types of façade scaffolding – with and without claddings. A computational finite element model was developed to study the specifics of the scaffoldings in the function of the nets permeability and the solidity ratio of the façade. Load combinations, according to the requirements in EN 12811-1, were considered to obtain the internal forces and stresses of the scaffold elements subject to wind actions. Based on the numerical analyses, it was found that the porosity and air permeability of the nets have a significant effect on the internal forces and stresses of the façade scaffolds elements, which also depend on the anchorage patterns and solidity ratio of the façade. In conclusion, recommendations are given regarding the application of specific structural schemes and anchoring patterns, depending on the permeability of the different façade scaffold nets.

Influence of Comprehensive Joint Loads on Tibial Implant Micromotion in Total Ankle Arthroplasty

Category:AnkleIntroduction/Purpose:Biologic fixation of total joint replacements by bone ingrowth requires minimal bone-implant micromotion [1]. Computational finite element (FE) models used to evaluate the interaction between implant and bone typically only consider simplified loading conditions based on the peak compressive force which occurs near toe-off [2,3]. However, a previous study focused on cementless knee replacements demonstrated that peak micromotion during activity cycles occurred with sub-maximal forces and moments [4]. Our objective was to calculate multi-axial loading at the ankle joint throughout level walking and evaluate tibial fixation of ankle replacements under these loading conditions. We hypothesized that peak micromotion would occur with sub-maximal loads and moments instead of at the instant of peak compressive load.Methods:Our validated six-degree-of-freedom robotic simulator utilizes in vivo data from human subjects to replicate the individual bone kinematics in cadaveric specimen throughout activity [5]. We rigidly fixed retro-reflective markers using bone pins to the tibia, talus, and calcaneus bones of three cadaveric specimens to record individual bone kinematics using motion capture cameras. We recorded the ground reaction and muscle-tendon forces during the simulated stance phase of level walking.Musculoskeletal models were then developed in OpenSim using the specimen-specific morphology and implant position from CT- scans and from the simulator outputs to determine the loading profile at the ankle joint during stance. The calculated loads were then applied to specimen-specific finite element models to evaluate the bone-implant interaction. Peak micromotion at each time point of loading was measured and compared to the loading profile to determine if it corresponded with the peak compressive load.Results:For all specimens, the peak compressive load at the ankle joint was accompanied by multi-axial moments and relatively small shear forces (Figure 1). The peak compressive load for each specimens was between 750 N and 850 N and occurred during 75-80% of gait. The largest moment experienced by all specimens was an internal moment late in stance. The peak micromotion for each specimen did not correspond to the instance of peak compressive load, as indicated in Figure 1. Instead, peak micromotion occurred at 54%, 88%, and 96% of gait. For each specimen, these instances corresponded to the combination of a sub-maximal compressive load with high eversion and internal moments.Conclusion:We have developed a workflow to calculate ankle joint loads corresponding to cadaveric simulations that reproduce a daily activity based on in vivo data. The specimen-specific, multi-axial loading profile at the ankle for our initial results suggests that peak micromotion at the bone-implant interface of the tibial implant does not coincide with the peak compressive force. The instant of peak compressive load may not capture the worst-case scenario for the interaction between the implant and the bone. Instead, the multi-axial forces and moments at the ankle joint throughout activity should be considered when evaluating implant fixation.

Reconstruction design of a turbine generator foundation

The key to the reconstruction of turbine foundation is the dynamic performance control and the anti fatigue performance and durability of the new and old concrete interface. Based on the finite element analysis method, the natural vibration analysis of the steam turbine foundation before the reconstruction is carried out, and the calculation data of the natural vibration frequency and mode are compared with the field dynamic test data to verify the rationality of the finite element calculation model. On this basis, the natural vibration analysis and the harmonic response analysis of the reconstruction scheme are carried out, and the vibration line displacement of the key points of the disturbance force of the steam turbine foundation meets the vibration displacement control standard within the frequency range of 0 ∼ 62.5Hz. The static analysis is carried out for the transformation scheme, and the prestressed reinforcement is arranged to ensure the compression of the new and old interface; the project abandoned bonded rebars with limited service life and adopted self-locking anchors with the same life as the original structure to connect old and new concrete bonding surface. The low cycle fatigue test of self-locking bolt and concrete base material is carried out. The test results show that there is no fatigue failure, which shows that the reinforcement scheme can meet the requirements of fatigue resistance and durability.

A generalized strain energy function using fractional powers: Application to isotropy, transverse isotropy, orthotropy, and residual stress symmetry

In this paper, we propose a generalized strain energy density function based on invariants of stretch tensor with arbitrary exponents. We employ polynomial, logarithmic and exponential functions of these invariants to develop the strain energy functions. We also study characteristics and applications of the proposed model for isotropy, transverse isotropy, orthotropy with a special focus on initial/residual stress symmetry. The proposed invariants generalize the existing strain energy potentials constructed with invariants of Cauchy stretch. We construct generalized strain energy functions for initial stress problems using initial stress symmetries. We obtain objectivity of strain energy for initially stressed transversely isotropic solids to derive the invariants and study resulting symmetry. By extending Dunford–Taylor integration based approach and tensor diagonalization approach, we obtain stress through differentiation of anisotropic scalar invariants with respect to a tensor. These approaches are usually applicable for derivative of isotropic tensor functions with respect to tensors. Using initial stress compatibility, we derive constraint equations for material parameters by evaluating the limits of Cauchy stress in the reference configuration. In order to apply the proposed model for initial stress problems, we further investigate bending and unbending of hyperelastic structures. We study bending of a rectangle to a cylinder and unbending of a cylinder to a rectangle in presence of initial/residual stress and observe both magnifying and moderating effects of initial stress for stress distribution and flexural characteristics. Using experimental data we substantiate the proposed model for seat foam, bovine pericardium and rabbit skin which represent compressible isotropic and incompressible orthotropic materials. For demonstration, we use both polynomial and exponential functions of these invariants. Furthermore, we develop a nonlinear finite element computational model for thermo-hyperelastic structure where thermal stress represents the initial stress. We corroborate this stress–strain data with the proposed model for initial stress symmetry and observe nice agreements.

Bayesian calibration of hysteretic reduced order structural models for earthquake engineering applications

Seismic risk assessment entails frequently a large number of nonlinear time-history analyses. The use of high-fidelity Finite Element Models (FEMs) in this context, though supports high accuracy predictions, involves a substantial computational burden. This has incentivized researchers to explore the use of calibrated Reduced Order Models (ROMs) to replace the computational expensive FEMs, with the calibration process established so that the ROM can match the desired FEM characteristics. Recent studies have explicitly examined this calibration for hysteretic, multi-degree-of-freedom ROMs utilizing FEM time-history response data. This calibration has been posed as a least-squares optimization problem for the configurable ROM parameters, considering the discrepancy between the ROM and FEM responses for a selected number of excitations, for different output quantities of interest (QoIs). This work extends these efforts to examine a Bayesian calibration framework of ROMs for earthquake engineering applications. The entire posterior distribution of the ROM parameters is identified, instead of solely the point estimate that the current least-squares optimization provides. This facilitates a quantification of the uncertainty in the calibrated ROM parameters. For formulating the likelihood function different assumptions are discussed, impacting, ultimately, how the different earthquake excitations and QoIs are effectively combined. Comparisons to the objective function utilized in the established least-squares approach are drawn. Furthermore, a model class selection is advocated to compare different candidate ROMs in order to choose the most appropriate one given the available data. Finally, a hierarchical Bayesian inference approach is examined, treating independently the ROM calibration for each earthquake excitation, but unifying the ROM parameters under a common prior, updated using data from all excitations. Different challenges are discussed for implementing such a multilevel Bayesian framework for the current application. The illustrative implementation considers two different structures, corresponding to different materials and heights, with the FEMs developed in OpenSees. The different calibration approaches are evaluated by utilizing the calibrated ROMs for seismic risk assessment for different seismicity scenarios.

Research on the Simplified Calculation Model of Large Phased Array Radar Reflector Mechanics Based on NASTRAN

there are many plates and beams on the radar array. In the process of finite element calculation, choosing the appropriate shell mesh finite element model to replace the solid finite element model can reduce the calculation amount. In this paper, the finite element solid mesh model is established based on the reflection panel model of a radar antenna array, and the simulation results are obtained. Secondly, the shell grid is used to perform finite element modeling and correction calculations on the reflective panel. The results show that the modified shell grid calculation results are very close to the solid grid model results, and can replace the solid grid to simplify the calculation of the array.

Study in deep shale gas well to prevent shoulder protruding packer with high pressure sealing

Shale gas is a kind of unconventional oil and gas resources that can be exploited in shale strata. According to the evaluation of oil and gas resources carried out by the ministry of land and resources of China, the geological resources of shallow shale gas with a depth of 4500 m are 122 trillion cubic meters. However, the overall geological conditions of shale gas in China are complex and the buried depth is too large. For deep shale gas wells with vertical depth of more than 3500 m, problems such as shoulder protruding, tearing, crushing and insufficient sealing performance of rubber tube are caused by high-pressure fracturing. Aiming at the above problems, proposes a high-pressure sealed preventing shoulder protruding (HPS-PSP) structure packer. Based on the deformation theory of rubber tube, the finite element calculation model of packer tube under the setting condition was established. The influence of the thickness of the prevent shoulder protruding ring and the height of the trapezoidal ring groove and the length of the trapezoidal upper base on the sealing performance of the rubber tube were analyzed. The results show that: The HPS-PSP packer can effectively solve the problems of protrusion of rubber tube shoulder and insufficient sealing performance, and the contact pressure increases by 60.1% compared with the conventional one. The research work provides a method to improve the sealing performance of packer rubber, which is of great significance to improve the applicability of packer in deep shale gas fracturing operation.

Fluid-structure interaction modeling of the abrasive waterjet drilling of carbon fiber reinforced polymers

Abstract The major challenges facing engineers while fabricating high precision components from carbon fiber reinforced polymers (CFRP) especially when using an abrasive waterjet (AWJ) include the predominant interlaminar delamination and tapered kerfs. Therefore, in the present work, a comprehensive 3-D transient fluid-structure interaction (FSI) model is developed and numerically simulated to investigate mechanisms leading to delamination and hole-geometric defects while drilling autoclave cured aerospace grade multidirectional CFRP laminates. The FSI model comprised a two-way interaction between the computational fluid dynamics (CFD) flow model and structural finite element (FE) model. The CFD model explored the dynamic jet characteristics while impinging the anisotropic CFRP surface. The resulting forces from the CFD domain acted as loads in the transient FE model to predict the initiation of cracks and delamination. Subsequently, extensive experiments were conducted to validate the proposed numerical model. The results illustrated that during abrasive waterjet drilling of CFRP, delamination was initiated by the hydraulic impact as the abrasive waterjet penetrated the workpiece. Additionally, the study revealed that an increase in abrasive waterjet pressure and abrasive particle size resulted in a higher inter-ply debonding and crack propagation. Correspondingly, an increase in the standoff distance (SoD) resulted in reduced crack propagation and delamination. Further, the liquid-solid interface exhibited asymmetric cracks. The present findings not only provide requisite guidelines to achieving high-precision drilling of multidirectional CFRP but also provide technical guidelines to improving the performance characteristics of the abrasive waterjet machining (AWJM) process.

The biomechanical efficacy of a dressing with a soft cellulose fluff core in prophylactic use.

In this work, we developed an experimental-computational analysis framework which facilitated objective, quantitative, standardised, methodological, and systematic comparisons between the biomechanical efficacies of two fundamentally different dressing technologies for pressure ulcer prevention: A dressing technology based on cellulose fibres used as the core matrix was evaluated vs the conventional silicone-foam dressing design concept, which was represented by multiple products which belong in this category. Using an anatomically-realistic computer (finite element) model of a supine female patient to whom the different sacral dressings have been applied virtually, we quantitatively evaluated the efficacy of the different dressings by means of a set of 3 biomechanical indices: The protective efficacy index, the protective endurance, and the prophylactic trade-off design parameter. Prior rigorous experimental measurements of the physical and mechanical behaviours and properties of each tested dressing, including tensile, compressive, and friction properties, have been conducted and used as inputs for the computer modelling. Each dressing was evaluated for its tissue protection performances at a new (from the package) state, as well as after exposure to moisture conditions simulating wet bedsheets. Our results demonstrated that the dressing with the fluff core is at least as-good as silicone-foams but importantly, provides the best balance between protective performances at its "new" condition and the performance after being exposed to moisture. We conclude that preventative dressings are not equal in their prophylactic performances, but rather, the base technology, the ingredients, and their arrangement in the dressing structure shape the quality of the delivered tissue protection.

Vocal Tradeoffs in Anterior Glottoplasty for Voice Feminization.

Anterior (Wendler) glottoplasty has become a popular surgery for voice feminization. However, there has been some discrepancy between its theoretical pitch-raising potential and what is actually achievable, and downsides to shortening the glottis have not been fully explored. In addition, descriptions of the surgery are inconsistent in their treatment of the vocal ligament. This study aimed to determine 1) how fundamental frequency (fo ) is expected to vary with length of anterior glottic fixation, 2) the impact of glottic shortening on sound pressure level (SPL), and 3) the effect of including the ligament in fixation. Computational simulation. Voice production was simulated in a fiber-gel finite element computational model using canonical male vocal fold geometry incorporating a three-layer vocal fold composition (superficial lamina propria, vocal ligament, and thyroarytenoid muscle). Progressive anterior glottic fixation (0, 1/8, 2/8, 3/8, etc. up to 7/8 of membranous vocal fold length) was simulated. Outcome measures were fo , SPL, and glottal flow waveforms. fo increased from 110 Hz to 164 Hz when the anterior one-half vocal fold was fixed and continued to progressively rise with further fixation. SPL progressively decreased beyond 1/8 to 1/4 fixation. Inclusion of the vocal ligament in fixation did not further increase fo . Any fixation increased aperiodicity in the acoustic signal. The optimal length of fixation is a compromise between pitch elevation and reduction in output acoustic power. The simulation also provided a potential explanation for vocal roughness that is sometimes noted after anterior glottoplasty. NA Laryngoscope, 131:1081-1087, 2021.

A New Calculation Method of the Lightning Electromagnetic Field Considering Variable Return Stroke Velocity

The article proposes an improved method for the calculation of the electromagnetic field radiated by a lightning return stroke over a perfectly conducting ground. Specifically, the proposed time domain expressions allow a closed-form solution for the field produced by an impulse-current propagating upward along a vertical path with a given velocity. The expressions are valid for a wide class of engineering return stroke models and can be adopted also in case the return stroke velocity varies along the channel. The solution for an arbitrary current waveform can be obtained by the convolution of the current at the channel base with the electromagnetic field due to the impulse-current along the channel. The accuracy and advantages of the method are assessed by the comparison with those obtained by a finite-element method computer model. The expressions are implemented in the LIOV-EMTP-RV code for the calculation of the induced voltages in an overhead distribution line.

Dynamic Behaviour Analysis of Turbocharger Rotor-Shaft System in Thermal Environment Based on Finite Element Method

The stable operation of a high-speed rotating rotor-bearing system is dependent on the internal damping of its materials. In this study, the dynamic behaviours of a rotor-shaft system with internal damping composite materials under the action of a temperature field are analysed. The temperature field will increase the tangential force generated by the internal damping of the composite material. The tangential force will also increase with the rotor speed, which can destabilise the rotor-shaft system. To better understand the dynamic behaviours of the system, we introduced a finite element calculation model of a rotor-shaft system based on a 3D high-order element (Solid186) to study the turbocharger rotor-bearing system in a temperature field. The analysis was done according to the modal damping coefficient, stability limit speed, and unbalance response. The results show that accurate prediction of internal damping energy dissipation in a temperature field is crucial for accurate prediction of rotor dynamic performance. This is an important step to understand dynamic rotor stress and rotor dynamic design.

Finite element calculation model of the piled rafts

Finite element model for calculating piled rafts in difficult geological conditions.

Venous Biomechanics of Angioplasty and Stent Placement: Implications of the Poisson Effect

PurposeTo characterize the Poisson effect in response to angioplasty and stent placement in veins and identify potential implications for guiding future venous-specific device design. Materials and MethodsIn vivo angioplasty and stent placement were performed in 3 adult swine by using an established venous stenosis model. Iron particle endothelium labeling was performed for real-time fluoroscopic tracking of the vessel wall during intervention. A finite-element computational model of a vessel was created with ADINA software (version 9.5) with arterial and venous biomechanical properties obtained from the literature to compare the response to radial expansion. ResultsIn vivo angioplasty and stent placement in a venous stenosis animal model with iron particle endothelium labeling demonstrated longitudinal foreshortening that correlated with distance from the center of the balloon (R2 = 0.87) as well as adjacent segment narrowing that correlated with the increase in diameter of the treated stenotic segment (R2 = 0.89). Finite-element computational analysis demonstrated increased Poisson effect in veins relative to arteries (linear regression coefficient slope comparison, arterial slope 0.033, R2 = 0.9789; venous slope 0.204, R2 = 0.9975; P < .0001) as a result of greater longitudinal Young modulus in veins compared with arteries. ConclusionsClinically observed adjacent segment narrowing during venous angioplasty and stent placement is a result of the Poisson effect, with redistribution of radially applied force to the longitudinal direction. The Poisson effect is increased in veins relative to arteries as a result of unique venous biomechanical properties, which may be relevant to consider in the design of future venous interventional devices.