Axisymmetric Finite Element Analysis Research Articles

Two-Dimensional FEA-Based Iron Loss Calculation Method for Linear Oscillating Actuator Considering the Circumferential Segmented Structure

Linear compressors have a simpler mechanical structure and higher efficiency than the rotary compressors because they have lower frictional loss. Therefore, the linear oscillating actuator (LOA) is an attractive option for compressors owing to its high power density and efficiency. However, the complex structure of LOA such as segmented outer stator and mover leads to conduct 3-D finite element analysis (FEA) for calculating accurate iron loss, but it requires high computation cost. Thus, we proposes a method to calculate iron loss only using 2-D axisymmetric FEA considering the permeance in stator core. To compensate for the alterations in the magnetic flux density resulting from the structure of the mover and outer stator of the LOA, two equivalent coefficients are applied in permanent magnets in mover to correct the induced voltage and outer stator to correct the magnetic flux density. Through the utilization of these two equalization methods, iron loss can be accurately calculated using only 2-D axisymmetric FEA. The proposed method can be used to accurately determine the efficiency of the LOA without 3-D FEA, thus, making the LOA design process more efficient.

Analysis of the geotechnical behavior of a piled raft in tropical lateritic soil based on long-term monitoring of columns, piles, and raft–soil interface

This paper aims to analyze and describe the geotechnical behavior of a piled raft foundation of a tall building (53 floors, 172.4 m high) through the monitoring of strains in the building’s columns and piles, the stresses at the raft–soil interface, and the foundation settlements. Field and laboratory tests were performed, and associated with axisymmetric and three-dimensional finite element analysis to the assessment of the measured data. The monitoring of the pile strains suggests the occurrence of soil expansion, caused by the raft excavation process, up to approximately 6 months after the excavation was completed. The presence of different soil profiles under the raft, with different mechanical properties, affected the distribution of the foundation settlements and the pile loads. Initially, the average pile loads were concentrated in the perimeter elements, but, as the construction of the building evolved, they tended to become more uniform. The effect of the superstructure stiffness caused successive load redistributions in the columns, which contributed to the maintenance of the maximum angular distortion of the building within the allowable values and reduced the load difference between the piles positioned in opposite soil profiles.

Numerical modeling of the effect of loading rate on the tensile load capacity of offshore caisson foundations

Suction caissons are skirted foundations frequently used in offshore environments supporting various structures. Among those lie the offshore wind turbines (OWT), which are currently one of the most common renewable energy systems. In this paper we study the tensile capacity of caisson foundations of OWT in dense sands, where the generation of excess pore pressure is analyzed. The tensile capacity of suction buckets under various loading rates is investigated using a series of quasi-static axisymmetric finite element analyses with coupled flow-deformation formulation. DeltaSand model is utilized for the soil, which is an elasto-plastic state-dependent model capturing the response of sands at varying relative densities. Numerical results are validated with available test data of scaled physical model experiments. Particular emphasis is placed on the interaction between suction-bucket and the soil. Parameters governing the soil-caisson interface playing a key role in the uplift response are identified. Lastly, a case study that can be observed in offshore foundations is simulated. Results show that the developed numerical model is applicable to capturing the uplift response of bucket in an ocean environment. The outcome of this study will contribute to closing the gap in the design of suction caissons of OWT in existing standards.

Methodology of estimation of temperature mode in the 2xBgu type railway braking system

The article presents finite element models of the 2xBgu type tread brake for the simulation of extended repeated frictional heating carried out on a full-scale inertia dynamometer. The numerical calculations were conducted for the brake blocks made of two organic composite materials newly developed specifically for this study. The transient temperature changes obtained from the 2D axisymmetric and 3D finite element analyses and experimental data agreed well during continuous process of about 1200 s. Simulation of such a long period of braking sequence required introducing simplifications in the boundary conditions in the contact area, convection cooling, arrangement of the model (2D axisymmetric, 3D). The focus was laid on representation of variation of the coefficient of friction and the temperature dependence of the properties of the friction materials during braking. The carried out research indicates limitations in the finite element analysis and directions of necessary improvements in modelling as well as measurements with the use of embedded thermocouples.

Size effects on spheroidal voids by Finite Fracture Mechanics and application to corrosion pits

AbstractThe present work aims at investigating the failure size effect of a spheroidal void in an infinite linear elastic solid under remote tension by means of the coupled Finite Fracture Mechanics (FFM) approach. The opening stress field and the stress intensity factor (SIF) of an annular crack surrounding the cavity —necessary for the FFM implementation— are obtained numerically through parametric axisymmetric finite element analyses (FEAs): The spheroid aspect ratio is varied between 0.1 and 10 and Poisson's ratio between 0.1 and 0.5. Accordingly, semi‐analytical functions approximating the stress concentration factor and the SIF are put forward. Finally, the failure size effect on spheroidal voids is reported, and FFM predictions are compared with experimental results on the fatigue limit arising from corrosion pits, showing a fairly good agreement.

Evaluation of capacity of power hammer machine foundation from high strain dynamic load test: Field test and axisymmetric numerical modeling

The power hammer machines induce harmful vibrations in different parts of the foundation which may result in excessive dynamic settlement. While designing the hammer machine foundation, variety of static and repetitive impact load tests are generally conducted to ensure both the stability and serviceability of the foundation system. The static load test (SLT) is performed in the case of such foundations to obtain the ultimate capacity. However, the SLT is unable to predict the reliable response of the machine foundation. Hence, the current study is aimed to investigate the static and dynamic resistance of power hammer machine foundation by employing the high strain dynamic load test (DLT). The test procedure involves measuring the acceleration, axial force and settlement at the top of the machine foundation. Additionally, the soil resistance pertaining to damping is assumed to disappear with the zero-velocity at the first moment, which is identical to the unloading point method (UPM). Also, the field test and axisymmetric finite element analysis by considering the nonlinear soil model were performed to evaluate the stress settlement curve (SSC) from both SLT and DLT. The results reveal that the capacity of the machine foundation subjected to repetitive dynamic loads increases gradually and then tend to remain stable in case of additional impact loads. The SLTs showed 3–4 % higher static resistance than the first DLT and 8–9 % reduction in contrast to the second DLT. Moreover, the residual plastic deformation of the soil beneath the machine foundation was recorded to rapidly increase at the beginning of hammer tamping while it decreased steadily with further increasing of the hammer blows.

The Determination of Downhole Dynamic Compaction Paramaters Based on Finite Element Analysis

Downhole dynamic compaction (DDC) has been commonly used in China to stabilize collapsible soil through the application of construction and demolition waste material (CDW). DDC basically forms a column inside the soil stratum which is similar to a stone column except DDC materials are put in sequence and then compacted by using DDC hammer. Due to its attractive features such as its big diameter, feasibility of using oversized material particles, rapid and simple construction technique, it is used as one of the ground improvement methods for an airport project in Indonesia. Despite of all the advantages provided by DDC, it is difficult to obtain DDC parameters from laboratory tests as it is difficult to replicate the compaction effort induced by the DDC hammer and laboratory tests are not commonly employed for oversized materials. Hence, alternative method is required to evaluate DDC parameters. In this study, static load test is conducted to determine load-deformation curve of the DDC pile. Soil parameters are first determined through soil test data such as standard penetration test (SPT), laboratory test and also pressure meter tests. Correlation between pressure meter tests and SPT test result is also carried in order to interpret the soil parameter at the site. Axisymmetric finite element analysis is then carried by using MIDAS GTS NX in order to back analyses DDC parameters by matching the simulation curve with load settlement curve of the DDC. In this paper, it is shown that back analysis using hardening soil model for DDC material can be used to match simulation curve with the load-deformation curve.

Određivanje trajnih deformacija savitljivih kolničkih konstrukcija pomoću metode konačnih elemenata

The unbound granular material used in flexible road pavements exhibits an elastoplastic behaviour under repetitive traffic loads. Permanent deformation occurring on pavement surface under traffic load is one of the main road pavement problems affecting road performance. Therefore, many permanent deformation models for calculating road pavement rutting have recently been developed by researchers. Most of these studies involve performance of dynamic triaxial tests. In this study, deformation characteristics of unbound granular materials are determined using the resonant column test. Then, instead of determining the total permanent deformation by summing up the calculated permanent deformations obtained in each pavement layer, dynamic 2D axisymmetric finite element analyses are performed for four different pavement cross sections to predict the total permanent deformation occurring on pavement surface under certain load cycles. The first modelled cross section of unbound granular material consists of natural aggregate. The base and/or subbase of remaining three cross sections consists of steel slag waste material. The permanent deformation versus load cycle is presented for four multi-layer road cross sections using semi logarithmic graphs. Finally, the permanent deformation model equation is developed for each pavement cross section using their fitting curves.

Model validation for estimating taper microgroove deformation during total hip arthroplasty head-neck assembly

Total hip arthroplasty (THA) failure and the need for revision surgery can result from fretting-corrosion damage of the head-neck modular taper junctions. Prior work has shown that implant geometry, such as microgrooves, influences damage on retrieved implants. Microgroove deformation within the modular taper junction occurs when the female head taper meets the male stem taper during THA surgical procedure. The objective of this work was to validate microgroove deformation after head-neck THA assembly as calculated by finite element analysis (FEA). Four 28 mm CoCrMo head tapers and four Ti6Al4V stem tapers were scanned via white light interferometry. Heads were assembled onto stem tapers until 6kN reaction force was achieved, followed by head removal using a cut-off machine. The stem tapers were then rescanned and analyzed. Simultaneously, a 2D axisymmetric FEA model was developed and assembled per implant geometries and experimental data. For experiments and FEA, the mean change in microgroove height was 1.23 µm and 1.40 µm, respectively. The largest microgroove height change occurred on the proximal stem taper due to the conical angles of the head and stem tapers. FEA showed that the head-stem assembly induced high stresses and microgroove peaks flattening. 76–89% and 91–100% of the microgrooves in the experiments and FEA, respectively, showed height changes along the contact length of the stem taper. A validated FEA model of THA head-neck modular junction contact mechanics is essential to identifying implant geometries and surface topographies that can potentially minimize the risk of fretting and fretting-corrosion at modular junctions.

Crystallographic Anisotropy Dependence of Interfacial Sliding Phenomenon in a Cu(16)/Nb(16) ARB (Accumulated Rolling Bonding) Nanolaminate.

Nanolaminates are extensively studied due to their unique properties, such as impact resistance, high fracture toughness, high strength, and resistance to radiation damage. Varieties of nanolaminates are being fabricated to achieve high strength and fracture toughness. In this study, one such nanolaminate fabricated through accumulative roll bonding (Cu(16)/Nb(16) ARB nanolaminate, where 16 nm is the layer thickness) was used as a test material. Cu(16)/Nb(16) ARB nanolaminate exhibits crystallographic anisotropy due to the existence of distinct interfaces along the rolling direction (RD) and the transverse direction (TD). Nanoindentation was executed using a Berkovich tip, with the main axis oriented either along TD or RD of the Cu(16)/Nb(16) ARB nanolaminate. Subsequently, height profiles were obtained along the main axis of the Berkovich indent for both TD and RD using scanning probe microscopy (SPM), which was later used to estimate the pile-up along the RD and TD. The RD exhibited more pile-up than the TD due to the anisotropy of the Cu(16)/Nb(16) ARB interface and the material plasticity along the TD and RD. An axisymmetric 2D finite element analysis (FEA) was also performed to compare/validate nanoindentation data, such as load vs. displacement curves and pile-up. The FEA simulated load vs. displacement curves matched relatively well with the experimentally generated load–displacement curves, while qualitative agreement was found between the simulated pile-up data and the experimentally obtained pile-up data. The authors believe that pile-up characterization during indentation is of great importance to documenting anisotropy in nanolaminates.

A simplified analytical model to simulate martensite reorientation and plasticity in shape memory alloy ring couplers

Recent studies on Shape Memory Alloy rings have been undertaken at the European Organization for Nuclear Research (CERN) to develop smart and leak-tight couplers for Ultra High Vacuum systems of particle accelerators. A special thermo-mechanical process (training) is needed to provide SMA rings with proper functional properties, that is to allow thermal mounting, dismounting, and leak tight coupling within a given service temperature window. Low temperature ring expansion is a crucial part of the training process as it gives suitable size, shape recovery properties, and thermal stability range to the SMA element. An analytical model, based on simplified elastic-plastic axisymmetric concepts, has been developed and implemented in a commercial software to simulate isothermal SMA rings expansions. It is particularly useful to predict the final size of a martensitic SMA coupler as a function of the initial dimensions and of the pre-deformation parameters. The effectiveness of the model has been demonstrated by analyzing the stress/deformation field occurring in a wide range of ring geometries for different load cases including martensite reorientation and plasticity. The predictions of the analytical model have been systematically compared with those obtained by axisymmetric finite element (FE) analyses based on elastic-plastic constitutive models and experimental measurements.

Numerical Simulation of the Water Vapor Separation of a Moisture-Selective Hollow-Fiber Membrane for the Application in Wood Drying Processes.

In this study, a simplified two-dimensional axisymmetric finite element analysis (FEA) model was developed, using COMSOL Multiphysics® software, to simulate the water vapor separation in a moisture-selective hollow-fiber membrane for the application of air dehumidification in wood drying processes. The membrane material was dense polydimethylsiloxane (PDMS). A single hollow fiber membrane was modelled. The mass and momentum transfer equations were simultaneously solved to compute the water vapor concentration profile in the single hollow fiber membrane. A water vapor removal experiment was conducted by using a lab-scale PDMS hollow fiber membrane module operated at constant temperature of 35 °C. Three operation parameters of air flow rate, vacuum pressure, and initial relative humidity (RH) were set at different levels. The final RH of dehydrated air was collected and converted to water vapor concentration to validate simulated results. The simulated results were fairly consistent with the experimental data. Both experimental and simulated results revealed that the water vapor removal efficiency of the membrane system was affected by air velocity and vacuum pressure. A high water vapor removal performance was achieved at a slow air velocity and high vacuum pressure. Subsequently, the correlation of Sherwood (Sh)–Reynolds (Re)–Schmidt (Sc) numbers of the PDMS membrane was established using the validated model, which is applicable at a constant temperature of 35 °C and vacuum pressure of 77.9 kPa. This study delivers an insight into the mass transport in the moisture-selective dense PDMS hollow fiber membrane-based air dehumidification process, with the aims of providing a useful reference to the scale-up design, process optimization and module development using hollow fiber membrane materials.

Critical length of encased stone columns

Encased stone columns are vertical inclusions in soft soils formed by gravel wrapped usually with a geotextile. Their critical length is the one where further lengthening of the column provides a negligible improvement and it is therefore not effective to build columns longer than it. This paper aims to obtain common values of the critical length using simplified two-dimensional axisymmetric and full three-dimensional finite element analyses. A uniform soft soil layer with a linear elastic perfectly plastic behaviour is considered for the sake of simplicity. For the studied cases, the critical column length is around 1.3–2.5 times the footing diameter for encased stone columns, and slightly lower for ordinary stone columns, namely around 1.1–1.9. The critical length of the encasement is found to be slightly lower than the critical column length. The value of the critical column length is related to the extent of plastic deformation and that may be used to decide the column length in the design phase without the need of parametric analyses. As a first approximation, a general value of the critical column length of 2 and 2.5 times the footing diameter may be considered for ordinary and encased stone columns, respectively.

Coupling hardening soil model and Ménard pressuremeter tests to predict pile behavior

This paper presents a simple method to apply the Ménard Pressuremeter Test (PMT) results for the calibration of the soil stiffness due to primary deviatoric loading used in the Hardening Soil (HS) Model. A hyperbolic extension is used to rebuild the PMT pressure-expansion curve at small-strain values. The method was applied to simulate a series of PMT tests using axisymmetric finite element analysis (FEA) and was compared with the conventional HS model calibration using consolidated drained triaxial tests with reasonable accordance. Finally, the method was used in axisymmetric FEA of two static load tests in instrumented piles, performed in different sites. The results indicate good agreement between predicted and measured values of pile load-settlement behavior, average shear stresses at pile shaft and pile base pressure considering usual pile working loads. For highly mobilized piles, the numerical simulations indicated that an increase in soil cohesion was able to match the predictions of pile failure, in order to consider in a simplified way the effects of soil suction and pile execution procedure, which were not simulated herein.

Effective modeling of spiral wound gasket with graphite filler in gasketed flange joint subjected to bending loads

Abstract The flange joints with gasket are used in automobile, aircraft, pressure vessel and pipelines. The gasket deformation behavior controls the leakage phenomenon of the joint. The stress in spiral wound gasket with graphite filler is analyzed using micromechanical approach and axisymmetric finite element analysis. The material characteristics of individual constituents in gasket are modeled using their elasto-plastic behavior. The uniaxial compressive behavior of gasket is observed to be in good agreement with experimental values. The flange joint is analyzed for leakage by using 3D finite element model with individual constituents of gasket. A realistic distribution of contact stress in gasket is obtained using micromechanical approach. The contact stress distribution in the compression and tension side, when subjected to external bending load is also evaluated. The effective gasket width for sealing is contributed by filler tape alone, rather than combination of metal and filler tape in spiral wound gasket.

Framework for probabilistic leakage resistance envelopes of casing connections

Probabilistic well casing design is a recent trend in Oil & Gas exploration, especially for ultra-deep and HPHT wells. Reliability-based design allows safety margins to be optimized, while managing the corresponding risks. Statistics for pipe body geometry and strength are today widely available, but most reported incidents are related to connection failures. In this context, a methodology is proposed herein to construct probabilistic leakage resistance envelopes for casing connections. The methodology is based on extensive axisymmetric Finite Element analysis, considering geometric variabilities resulting from manufacturing tolerance. Maximum internal pressure is found for different values of axial load. Multi-dimensional response surfaces are constructed to take into account individual effects, and cross-effects for the most relevant variables. Regression analysis is used to construct failure envelopes for pre-defined probability levels. These are also converted into probabilistic envelopes for arbitrary combinations of axial load and internal pressure. The API 8 Round 5½ J55 14 lb/ft LTC connection is employed as study object, but the methodology can be readily extended to other connections with metal-to-metal seal. To the best of our knowledge, this is the first time such a probabilistic framework for leakage resistance of casing connections is presented in the literature. This framework, and the resulting models, are fundamental for the proper reliability-based design of well casing.

3D bending simulation and mechanical properties of the OLED bending area

AbstractDue to the poor mechanical properties of traditional simulation models of the organic light-emitting device (OLED) bending area, this article puts forward a finite element model of 3D bending simulation of the OLED bending area. During the model construction, it is necessary to determine the viscoelastic and hyperelastic mechanical properties, respectively. In order to accurately obtain the stress changes of material deformation during the hyperelasticity determination, a uniaxial tensile test and a shear test were used to obtain data and thus to characterize the hyperelastic properties. In order to measure the viscoelasticity, a stress relaxation test was used to draw the stress relaxation curve, so as to characterize the viscoelastic properties. Then, the plane or axisymmetric stress–strain analysis was achieved, and the material parameters of the 3D model of the OLED bending area were obtained. Finally, the 3D model was applied to the 3D bending of the OLED bending area. Combined with the axisymmetric finite element analysis method, the 3D bending simulation finite element model of the OLED bending area was constructed by dividing the finite element mesh. Experimental results show that the mechanical properties of the proposed model are better than those of traditional OLED bending simulation models. Meanwhile, the proposed model has stronger application advantages.

Bending induced wrinkling and creasing in axially crushed aluminum tubes

Concertina folding of tubes used for impact mitigation bends the tube section to tight curvatures that can lead to failures on the tensioned side of the folds. This paper reports results from such axial crushing experiments on Al-6061-T6 circular tubes in which cleft-like features were also observed on the compressed sides of folds. Microscopic examination of the compressed sides of sectioned folds at different stages of bending revealed the following. Compression leads to surface wrinkles that are initiated by small initial surface roughness. Further bending increases the amplitude of the wrinkles, and at even higher bending the wrinkles morph into folds, creases, and sharp discontinuities. Metallographic examination of these surface undulations revealed that surface wrinkles encompass several grains, which deform conforming to the imposed local geometric changes. With this in mind, the axial crushing was simulated at the continuum level via an axisymmetric finite element analysis coupled with a suitably calibrated non-quadratic elastic–plastic constitutive model. A sufficiently refined mesh and representative initial surface imperfections enabled monitoring of the evolution of surface instabilities on the compressed sides of folds. Surface wrinkles appear at compressive strains of about 50%. As the local bending increases, their amplitude grows, and subsequently they evolve into local folds, and creases that resemble surface features observed in the experiments.

Failure analysis of an exploded large-capacity liquid storage tank using finite element analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.

Failure Analysis of an Exploded Large-Capacity Liquid Storage Tank Using Finite Element Analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.