Axisymmetric Finite Element Model Research Articles

Study of the acoustic attenuation of 2D axisymmetric models of the human ear equipped with hearing protection

The ear is the organ responsible for auditory perception. Its role is to amplify, transmit, and convert an acoustic wave present in the environment into an electrical pulse that the brain can interpret via the auditory nerve. The objective of this study was to develop two axisymmetric 2D finite element models of the human ear to predict insertion loss when a porous earplug is introduced into the ear canal. In these models, the structure-acoustic interaction was resolved by finite element analysis. For a better representation, assumptions and boundary conditions (such as fixe boundary condition, spring-mass-damping boundary condition, etc...) are considered. The tympanic ring and the earplug are assumed to be fixed, and a load of what comes after the posterior part of the tympanic ring (the ossicular chain) has been replaced by an equivalent mechanical impedance mass-spring-damper system. The first model has a regular geometry, and the second model is obtained by reconstructing a 3D model. These two models were inspired by our previous work. For each model, the insertion loss (IL) is predicted and the results obtained are compared with those of the sound attenuation measurements of hearing protection performed in the laboratory.

Study on the 2D equivalent nonlinear dynamics simulation model related to high speed precision bearing and spindle

The stiffness and contact stress of the bearing spindle system are the key factors affecting its machining accuracy and service life under the condition of high-speed service, which will be affected by different structural parameters and service conditions. It is essential to establish an efficient and accurate computational simulation model to understand the influence of complex factors on the nonlinear dynamic characteristics of the bearing spindle system. Firstly, in the paper, a 2D axisymmetric finite element model of the bearing, aims at the relationship between stiffness and contact stress of the bearing under high-speed service, has been built based on a classical dynamic analysis model and the reversed method of material parameters of equivalent rolling balls. Additionally, for the BT30 spindle, the 2D axisymmetric finite element model of the bearing spindle system also has been built and applied in mechanical analysis of spindle under different conditions of assembly and service, based on the bearing model. The results show that the axial force of bearings decreases as the rotational speed increases, and an augmentation in speed will result in a reduction in the axial stiffness of the BT30 spindle. In addition, the maximum contact stress exhibits a slight decline as the rotational speed increases. Furthermore, with an escalating preload, the stiffness and contact stress of the spindle undergo substantial increments, however, these parameters will cease to alter once a certain threshold is reached.

Numerical prediction of ground-borne vibrations due to continuous vibratory driving of circular closed-ended piles

Various types of pile driving work may induce high-intensity ground-borne vibrations. Predicting vibration intensity before adopting mitigation measures is vital for minimizing the impact of vibration on nearby structures and occupants. Vibratory pile driving is a commonly applied foundation construction method. However, numerical simulation models for ground vibrations during a complete process of vibratory driving have rarely been studied. This study introduces an axisymmetric finite element model that utilizes the arbitrary Lagrangian-Eulerian technique to simulate the continuous vibratory driving of a circular closed-ended pile penetrating from the ground surface to a target depth. The model validity was confirmed by assessing the calculated ground vibrations against the findings documented in earlier research. The results showed that the critical penetration depth of piles, at which the maximum peak particle velocity (PPV) occurs, varied with the radial distance and depth of points of interest, contradicting a common preconception. Moreover, the maximum PPV did not always occur on the ground surface across all radial distances. Parametric analysis revealed that an increase in the soil cohesion strength, pile diameter, or soil-pile friction, or a decrease in the driving frequency or soil damping ratio would increase ground vibrations due to vibratory pile driving.

Structural Optimization of a Giant Magnetostrictive Actuator Based on BP-NSGA-II Algorithm

This study introduces an integrated structural optimization design method based on a BP neural network and NSGA-II multi-objective genetic algorithm. Initially, a two-dimensional axisymmetric finite element model of the Giant Magnetostrictive Actuator (GMA) was established, and the coupling simulation of the electromagnetic field, structural field, and temperature field was conducted to obtain the GMA’s performance parameters. Subsequently, the structural parameters of the GMA magnetic circuit, including the magnetic conducting ring, magnetic conducting sidewall, magnetic conducting body, and coil, were used as inputs, and the axial magnetic induction intensity, uniformity of axial magnetic induction intensity, and coil loss on the Giant Magnetostrictive Material (GMM) rod were used as outputs to establish a back propagation (BP) neural network model. This model delineated the nonlinear relationship between structural parameters and performance parameters. Then, the BP-NSGA-II algorithm was applied to perform multi-objective optimization on the actuator’s structural parameters, resulting in a set of Pareto optimal non-dominated solutions, from which a set of optimal solutions was obtained using the entropy weight method. Finally, simulation analysis of this optimal solution was conducted, indicating that under a 5 A power supply excitation, the maximum axial magnetic induction intensity on the optimized GMM rod increased from 0.87 T to 1.12 T; the uniformity of axial magnetic induction intensity improved from 93.1% to 96.5%; and the coil loss decreased from 7.79 × 104 W/m3 to 4.97 × 104 W/m3. Based on the optimization results, a prototype actuator was produced, and the test results of the prototype’s output characteristics proved the feasibility of this optimization design method.

A multiobjective optimization framework based on FEA, ANN, and NSGA-II to optimize the process parameters of tube-to-tubesheet joint

This study presents a multiobjective optimization framework that integrates Artificial Neural Network (ANN) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) for the optimization of rolling process parameters of tube-to-tubesheet joint (TTT-joint). During the rolling process, both beneficial contact pressure and detrimental tensile residual stress are generated within the joint. The primary objective of this framework is to minimize the tensile residual stress while maximizing the contact pressure in the TTT-joint. To achieve this, a backpropagation ANN model is trained to rapidly estimate the residual stress and contact pressure for various sets of rolling process parameters. For training purposes, a series of nonlinear elastoplastic finite element (FE) simulations are performed to generate the input database for the neural network. A detailed parametric study is performed based on the axisymmetric FE model of the TTT-joint. The trained neural network is then incorporated into the NSGA-II optimization algorithm to find the fitness function and optimized process parameters. The contact pressure and residual stress predicted by the proposed ANN-NSGA-II framework are validated by finite element analysis (FEA) using the optimized parameters. The present analysis established that the proposed methodology can be applied in practical engineering problems to obtain the process parameters that yield the maximum contact pressure and minimum tensile residual stress in the TTT-joint.

Fire Endurance of Spherical Concrete Domes Exposed to Standard Fire

Fire is considered a common hazard for civil structures. Public and administrative buildings are commonly designed by considering the standard fire rating and, in many cases, contain large compartments with central domes, in which fire growth can be significant. Moreover, tanks and underground fortified structures may be constructed as domes to support the heavy soil above. This paper numerically addressed such a case. First, an axisymmetric finite element model was developed and validated to predict the dome’s transient, thermal, structural, and thermal-structural behavior. Next, the model was used to conduct a parametric study to investigate the effects of the dome ring reinforcement, thickness, stiffness, central angle, base restraints, load type (external pressure or gravitational), and load ratio on the fire endurance of the dome. Design recommendations to increase the fire endurance of concrete domes were formulated based on the parametric study.

A numerical and experimental study on mechanical behaviours of type III composite vessels with different lay-up sequences

ABSTRACT 5 % .There are various factors that have impact on the burst pressure and the failure mechanism of filament wound composite pressure vessels. The sequence of lay-up was less considered because previous researchers paid little attention on the mechanical performance of the whole vessel. In this paper, a 2D axisymmetric finite element model was proposed to predict the damage evolution, failure strength and failure mode of the composite overwrapped pressure vessels. UMAT subroutine based on Hashin failure criteria was introduced to simulate the progressive damage properties of the composite material. The FE models were validated by comparison with the experimental results, and the error between the numerical simulation results and the experimental results was near 5%. In addition, two schemes were performed to evaluate the effects of different lay-up sequence on the ultimate strength and obtain the optimized scheme of lay-up sequence.

Plastically Deformed Tubes Subjected to Mechanical Expansion Processes.

In engineering, the stress state of expanded tubes is crucial for ensuring structural integrity and preventing stress corrosion cracking. The analysis of stresses and strains in tubes subjected to mechanical expansion using an ogive bullet is essential, yet existing theoretical methods for estimating the stress distributions, especially with spherical and ogive shapes, are sparse. This study explores the expansion of 3/8 inch copper and stainless-steel tubes using an expanding bullet, where tangential and longitudinal strains are measured. A novel analytical approach is introduced to evaluate the stresses and strains, segmenting the tube into three zones, each analyzed with a distinct theory. Validation is achieved through an axisymmetric finite element model that employs a multi-linear kinematic hardening material behavior. The analytical model also estimates the expanding mandrel's push force, which is then compared with the results from numerical simulations and experimental data, showing good agreement across methods.

Miniaturized acoustic concentrators for ultrafast 3D ultrasound imaging

Ultrafast 3D ultrasound imaging is a rapidly growing research field that enables real-time imaging at a high frame rate and in a non-invasive manner. Currently, to achieve ultrafast 3D ultrasound, plane or diverging waves from virtual sources are used. These virtual sources can be considered as focal points during emission, allowing for improved transmission of ultrasonic energy. However, they have limitations in terms of transmitted energy, complex electronics, and timing issues, which impact the quality of the resulting images. To address this, a study was conducted to design and experiment with new miniaturized ultrasound transmitters based on cylindrical waveguides with tapered sections. These transmitters, with a diameter of approximately 100 μm, can replace the virtual sources. A numerical study based on 2D axisymmetric Finite Element Modeling (FEM) is first performed to model the transmission and reflection of longitudinal ultrasonic waves through various cylindrical rods. The results demonstrated that the transmission depends on the diameter ratio, frequency and longitudinal mode order (L0, L1, L2, etc.). An experimental study is then conducted on a stainless steel waveguide instrumented with 6mm piezo discs. The mechanical energy, estimated using Laser Doppler Vibrometer is transmitted through a 150 μm diameter rod, allowing mechananical focusing in the frequency range between 0.5 and 5 MHz. The application of this method to separate emission/reception transducers is then demonstrated for 3D ultrafast imaging.

Effect of shielding of eddy current probes on the sensitivity for sweep frequency measurements

Eddy current measurements are prone to edge effects when measurements are carried out near a sample boundary. In order to reduce these edge effects, typically ferrite shields are used which constrain the magnetic field within the shield volume. However, their effects on sensitivity towards changes in conductivity for Sweep Frequency Eddy Current (SFEC) measurements have not been investigated. A 2D axisymmetric Finite Element Model (FEM) has been developed to predict the frequency response of impedance of SFEC probes. The model predicted that the addition of shields minimized edge effect but with reduced sensitivity. A simulation study is carried out to optimize the probe design to increase the sensitivity of shielded ferrite probes. Based on these results, a probe is constructed with a custom ferrite shield and its shielding efficiency and probe sensitivity are compared experimentally with those for the probe with conventional ferrite shields.

Embankments Reinforced by Vertical Inclusions on Soft Soil: Numerical Study of Stress Redistribution

Constructing embankments over soft soils is a challenge for geotechnical engineers due to large settlements. Among diverse ground-improvement methods, combining piles and geosynthetics (e.g., geosynthetic-reinforced piles, deep cement mixing columns, geotextile-encased columns) emerges as a reliable solution for time-bound projects and challenging ground conditions. While stress distribution within pile-supported embankments has been extensively studied, the load transfer efficiency of piled solutions with geosynthetic reinforcement remains less explored. The novelty in this study lies in the investigation of three different inclusion solutions from a common control case in the numerical model considering the role of geosynthetic reinforcement. This study investigates the load transfer mechanisms in embankments supported by various techniques including geosynthetic-reinforced piles, deep cement mixing columns, and geosynthetic-encased granular columns. Two-dimensional axisymmetric finite element models were developed for three cases of embankments supported by vertical inclusions. Numerical findings allow clarification of the soft ground and embankment characteristics which influence the arching and membrane efficiencies. Rigid piles outperform deep cement mixing (DCM) columns and geotextile-encased columns (GEC) in reducing settlements of soft ground. Geosynthetic reinforcements are particularly helpful for rigid pile solutions in high embankments due to their load transfer capability. Additionally, physical properties of fill soil can impact the inclusion solutions, with high shear resistance enhancing the arching effect and lower modulus subsoils showing better arching performance.

Effects of rotation on the rolling noise radiated by wheelsets in high-speed railways

Railway rolling noise is produced by the vibration of both the wheelsets and the track; the wheelsets dominate the high frequency noise and become increasingly important at high speed. The effect of rotation on the wheelset vibration and noise radiation is investigated using different wheelset models in a rolling noise prediction model for a wide range of speeds. Each wheelset model takes account of the rotation to a different extent. An axisymmetric finite element model of a flexible rotating wheelset is implemented based on a complex exponential formulation and expressed in either an inertial or a non-inertial frame of reference. The model can include the inertial Coriolis and centrifugal forces and is also extended to include stress stiffening. Modes of the rotating wheel with non-zero number of nodal diameters are split into co- and counter-rotating waves with separated natural frequencies. The extent of the frequency separation depends on the shape of the mode and its dominant component of vibration. At common train speeds the frequency shifts due to stress-stiffening and spin-softening effects are found to be small compared with the gyroscopic effects due to the Coriolis forces. The effect of including the inertial Coriolis and centrifugal forces on the overall A-weighted sound power level is less than 0.3 dB below 400 km/h, while for higher train speeds, differences may exceed 1 dB in some one-third octave bands. Overall, these differences are small compared with other sources of uncertainty in rolling noise modelling, confirming that representing the wheel rotation with a moving load approach provides a suitable approximation for use in rolling noise predictions.

On the re-evaluation of the clamped members stiffness of bolted joints

To address the structural integrity of bolted joints and verify their capacity to withstand external loads and relaxation resulting from thermal expansion difference and creep, proper evaluation of the axial stiffnesses of bolt and clamped members are of vital importance. A number of finite element (FE) based methods are available for the calculation of the stiffnesses of joint elements, most of which rely on the displacement of arbitrarily selected nodes that has led to the improper evaluation of joint stiffness values. In this paper, the stiffness of clamped members is evaluated by a simple FE methodology using a known bolt stiffness evaluated separately. Two load cases, one based on the application of external force (mechanical loading) and the other on temperature (thermal loading), are conducted using the FE method to validate the obtained results. The proposed methodology is also compared with other FE models and analytical methods obtained from the literature. The new technique is based on axisymmetric FE modeling and is applied to bolted joints with bolts ranging from M6 to M36 having various grip lengths. Finally, the stiffnesses of the bolt and clamped members can be determined accurately, and a general formula is proposed to evaluate the stiffness of clamped members.

Numerical Modelling and Predicting Performance of Geogrid-Reinforced Low-Volume Unpaved Roads over Soft Subgrades

AbstractPavement performance is usually predicted by large-scale laboratory experiments, expensive field tests and/or comparatively cheaper numerical modelling alternative. In this study, a finite element limiting strain model has been developed to investigate the strain response of both unreinforced and geogrid-reinforced pavements on unpaved roads where the geogrid is placed at the bottom of the unbound granular base layer. A two-dimensional (2D) axisymmetric finite element model (FEM) is used to analyse the behaviour of both unreinforced and geogrid-reinforced granular base. The critical pavement responses (vertical surface deformation, compressive strain and compressive stress at the top of subgrade, etc.) are simulated numerically using ABAQUS. These critical responses are used to develop the pavement performance models (strain limiting models) and to predict long-term service life of pavement or the reduction of thickness of granular base for equivalent service life or a combination of both. The parametric results are then used to develop design charts to aid practitioners to use directly in designs. The numerical model is verified using published literature-based information and found to be reasonable. The results show that the traffic benefit ratio (TBR) of 3.1 at a 20 mm rut depth can be achieved for a thin granular base built over soft subgrade using a medium stiff geogrid.

Airfield pavement resiliency assessment against extreme dynamic events by explicit axisymmetric finite element models

Infrastructure resiliency has become an essential element in ensuring community recovery after unexpected events. In airfield pavement, resilience can be achieved through an improved design approach by understanding the fundamental elements of damage mitigation and thus allowing rapid recovery. The objective of this study was to numerically evaluate easy-to-implement alternatives for mitigating damage in rigid airfield layered pavement systems when subjected to dynamic events such as blasts or high-velocity impacts. This was accomplished by developing an efficient axisymmetric explicit finite element model, which served as an analytical tool for the study. The model was developed in LS-DYNA and the methodology consisted of a comprehensive parametric analysis. The results showed that the concrete pavement layer parameters—mass density and compressive strength—have the most significant effect on the damage to the pavement when subjected to extreme dynamic events. The material parameters for the pavement layers were optimized to minimize the damage, caused by dynamic loads, achieving more than 70% damage mitigation. Furthermore, adding a granular base layer to the rigid airfield pavement design reduces the concrete pavement layer damage by almost 40%. An asphalt concrete overlay reduces the concrete pavement layer damage by about 55%. Moreover, adding an asphalt concrete overlay to the optimized rigid airfield pavement design reduces the damage by 10%. In contrast, adding a granular base layer to the optimized rigid airfield pavement design is ineffective.

Numerical investigation of effects of nickel-base alloy overlay size on the welding residual stresses in an austenite stainless steel narrow-gap girth weld

Based on the experimental measurement of the residual stress in the nickel-based alloy overlaid stainless-steel narrow-gap girth weld, an axisymmetric finite element (FE) model was established to simulate the residual stress in the girth weld to verify the model. Then a large number of numerical simulations were carried out with the verified FE model to study the effects of the size (height and length) of the nickel-based alloy weld overlay on the residual stress in the girth weld. The optimal overlay sizes to achieve sufficient depth of the compressive stress were investigated. The results show that as the overlay height increases, the hoop compressive stress depth from the inner wall at the weld centerline increases, while the range of the axial compressive stress distribution decreases. The hoop and axial compressive stress depths at the weld centerline increase as the overlay width increases, while the depth of the hoop compressive stress remains unchanged when the overlay width reaches a critical value. The effect of the overlay height on the hoop stress is greater than that of the overlay width, and it is more difficult to mitigate the axial stress by increasing the width of the overlay layer with a large overlay height. For the narrow-gap 304 stainless-steel pipe girth weld with a size of Ø273 mm × 28 mm, the optimum nickel-based alloy overlay is 14 mm in height and 210 mm in width, which can cause both hoop and axial stresses at the inner wall to be compressive, and the hoop compressive stress depth from the inner wall reaches 88 % of the pipe wall thickness and axial compressive stress depth reaches 78 % of the wall thickness.

Thermal stress analysis of laser cleaning ofaluminum alloy oxide film.

In this paper, a theoretical model for laser cleaning of aluminium alloy oxide film is presented from the perspective of thermal stress. Additionally, we developed a two-dimensional axisymmetric finite element model for calculation. Thermal stresses result from thermal expansion. Using thermodynamic equations, numerical calculations enablethe determination of a theoretical cleaning threshold by comparing the thermal stresses to the adhesion between the oxide film and the substrate. Through theory and experiments, it is known that the greater the laser fluence, the better is the cleaning effect. The findings indicate that cleaning of the oxide film on aluminum alloys can be achieved under appropriate parameters. The cleaning threshold for laser cleaning of the oxide film is determined to be 3629.47J/c m 2 (continuous laser fluence is 3628.73J/c m 2; nanosecond laser fluence is 0.74J/c m 2). The thermal stress model of laser cleaning is highly useful for selecting the appropriate laser flux in practical applications. Both a simulation and experimental results can provide an explanation for the mechanism of interaction between the laser and the aluminum alloy oxide film, demonstrating that thermal stress is one of the cleaning mechanisms during the laser cleaning process of the oxide film.

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

A numerical model for stress relaxation analysis of sealing systems in nonbonded pipe end fittings

Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures, which ultimately affects the sealing performance of end sealing systems. To assess stress relaxation curves under varying temperatures and pre-strains, this paper conducts both tensile and stress relaxation tests on PVDF materials. To describe the stress relaxation characteristics of these materials, the Prony series is utilized. In order to identify the parameters of the series, the paper employs the Levenberg-Marquardt method of nonlinear regression. A finite element model is established to verify the accuracy of the parameter identification method. Subsequently, the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting, while taking into account fluid pressure inside the pipeline using a pressure penetration method. The impact of stress relaxation on the sealing performance is then discussed. Finally, the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.

Numerical Fatigue Life Evaluation With Experimental Results for Type III Accumulators

Abstract Type III accumulator is widely used in hydrogen stations. A high-cost pressure cycle test is mandatory to ensure the safety of the accumulator in present regulations. To reduce the high cost, the aim is to develop a methodology of numerical fatigue life prediction, where an axisymmetric finite element model for the Type III accumulator is created precisely and actual loading process including autofrettage pressure is simulated. The alternating stress intensity is evaluated based on the instructions in KD-3 of 2015 ASME Boiler & Pressure Vessel Code, Section VIII, Division 3. By comparing stress amplitude distributions with the leak positions after the pressure cycle test, and plotting the results in the design fatigue curve, it could be shown that fatigue life prediction of Type III accumulator can be done by precise finite element analysis of the liner including dome part, where the principal axes of stress change in pressure cycle.