Three-dimensional Finite Element Method Model Research Articles

Surrogate numerical prediction method of TBM position via FEM simulation and machine learning

The position of the tunnel boring machine (TBM) during tunnel construction is critical and must be precisely controlled. Owing to the geological uncertainty and complexity of the interaction between the ground and the TBM, controlling the position of the TBM is challenging. Hence, a surrogate numerical method is proposed to predict the position of the TBM using the finite element method (FEM) and machine learning method. First, a refined three-dimensional FEM model was established. Different values of the property parameters of the ground and the thrust force of the TBM were input into the FEM model, generating a database that includes 1000 cases. Subsequently, the database is used to train a gradient boosting regression (GBR) model. The GBR model learns from the database and establishes the relationship between the construction parameters, ground parameters, and TBM position as a surrogate model. The surrogate model exhibited high accuracy on the test set. With a geological survey and a construction parameter monitoring system, the TBM position could be predicted quickly and precisely using a surrogate model. The construction parameters were adjusted if the TBM position did not satisfy the requirements.

Finite element analysis of the influence of dowel angle on CFRP anchors

In current retrofitting design guidelines, carbon fiber reinforced polymer (CFRP) anchors are recognized as an efficient and minimally invasive approach to delaying delamination. Recent research has demonstrated the capability of Finite Element Method (FEM) models to accurately reproduce the behavior of experimentally tested CFRP anchors. Among the various design parameters of CFRP anchors, the dowel angle is one of the least studied, yet it is a crucial factor. There is limited experimental data available for this parameter and there are no numerical models focused on its influence on anchor behavior. This article reports the results of a comprehensive three-dimensional FEM model for CFRP anchors, with a particular emphasis on varying dowel angles. The model accuracy is verified against direct shear joint tests drawn from the literature, including aspects such as the maximum load, load-slip curves, and the distribution of strains along the CFRP. Subsequently, the model is used to conduct a sensitivity analysis of the dowel angle in conjunction with other important parameters for the design of CFRP anchors. These parameters are the length of the CFRP ply behind the anchor, the number of anchors within the joint, the fiber content, and the depth of the dowel. The results obtained from the modeling show an important influence of the dowel angle on the effective use of carbon fibers and the enhancement of joint strength. By offering insights into the interactions between the dowel angle and other design parameters, this research contributes information that can guide the development of design guidelines for the optimization of CFRP anchor systems.

Rapid Identification of Material Defects Based on Pulsed Multifrequency Eddy Current Testing and the k-Nearest Neighbor Method.

The article discusses the utilization of Pulsed Multifrequency Excitation and Spectrogram Eddy Current Testing (PMFES-ECT) in conjunction with the supervised learning method for the purpose of estimating defect parameters in conductive materials. To obtain estimates for these parameters, a three-dimensional finite element method model was developed for the sensor and specimen containing defects. The outcomes obtained from the simulation were employed as training data for the k-Nearest Neighbors (k-NN) algorithm. Subsequently, the k-NN algorithm was employed to determine the defect parameters by leveraging the available measurement outcomes. The evaluation of classification accuracy for different combinations of predictors derived from measured data is also presented in this study.

Analysis of proto-type Tarim Basin in the late Precambrian and the dynamic mechanism of its evolution.

Tarim Basin has undergone an intricate tectonic evolution history ever since its formation from two discrete terranes in Neoproterozoic rather than in the Paleoproterozoic. More precisely, the amalgamation is assumed to happen during 1.0-0.8 Ga based on plate affinity. As the beginning of a unified Tarim block, studies of Tarim Basin in the Precambrian are basic and important. After the amalgamation of south and north paleo-Tarim terranes, Tarim block was experiencing a complicated tectonic process of being affected by mantle plume related to the breakup of Rodinia supercontinent in the south, and compressed by the Circum-Rodinia Subduction System in the north. The breakup of Rodinia supercontinent finished in the late Sinian Period, leading Kudi Ocean and Altyn Ocean to open and separating Tarim block from itself. According to the residual strata thickness, drilling data, and lithofacies distribution, the proto-type basin and tectono-paleogeographic maps of Tarim Basin in the late Nanhua Period and Sinian Period are reconstructed. With these maps, the characteristics of the rifts are revealed. Two rift systems were developed inside the unified Tarim Basin in the Nanhua Period and Sinian Period, one back-arc rift system in the northern margin and the other aulacogen system in the southern margin. The azimuth distribution of the rifts in Quruqtagh showed a predominant NE-SW trend, and the rifts in Aksu trended mainly NW-SE, while the rifts in Tiekelike trended SW-NE. With a three-dimensional elastic FEM (Finite Element Method) model that includes all rifts and deposited areas in Tarim Basin, applying the southern subduction and northern mantle upwelling properly to get the paleotectonic mian stress axes and the differential stress field, the dynamic mechanisms of rifts evolution are proved to be related to the peripheral tectonic environment mentioned above.

Linear extrapolation method based on multiple equiproportional models for thermal performance prediction of ultra-large array.

Strong demand for developing the photothermal (PT) and electrothermal devices with ultra-large array is increasing. Thermal performance prediction is vital to optimize the key properties of the devices with ultra-large array. Finite element method (FEM) provides a powerful numerical approach for solving complex thermophysics issues. However, for calculating the performance of devices with ultra-large array, it is very memory-consuming and time-consuming to build an equal scale three-dimensional (3D) FEM model. For an ultra-large periodic array irradiated with a local heating source, the use of periodic boundary conditions could lead to considerable errors. To solve this problem, a linear extrapolation method based on multiple equiproportional models (LEM-MEM) is proposed in this paper. The proposed method builds several reduced-size FEM models to carry out simulation and extrapolation, which avoids dealing with the ultra-large arrays directly and greatly reduces the computation consumption. To verify the accuracy of LEM-MEM, a PT transducer with beyond 4000 × 4000 pixels is proposed, fabricated, tested and compared with the prediction results. Four different pixel patterns are designed and fabricated to test their steady thermal properties. The experimental results demonstrate that LEM-MEM has great predictability, and the maximum percentage error of average temperature is within 5.22% in four different pixel patterns. In addition, the measured response time of the proposed PT transducer is within 2 ms. The proposed LEM-MEM not only provides design guidance for optimizing PT transducers, but is also very useful for other thermal engineering problems in ultra-large array that requires facile and efficient prediction strategy.

Examination of the Partial Discharge Behaviour Within a Spherical Cavity in Insulation Paper of Transformer

This paper investigates the behaviour of partial discharge (PD) in transformer insulation paper based on the Finite Element Method (FEM). The three-dimensional (3D) FEM model consists of conductor and insulation paper, representing part of a transformer’s high voltage winding. The conductor’s width, height, and length used in this study were 2.4 mm, 11.5 mm, and 16 mm. An insulation paper thickness of 1 mm was modelled around the conductor. An internal cavity with a diameter of 0.5 mm cavity was introduced within the insulation paper. This study introduced two locations of the spherical cavities at the centre and left corner of the insulation paper: Location 1 (L1) and Location 2 (L2). An AC voltage of 33 kV, 50 Hz, was applied to the conductor while the bottom of the insulation paper was grounded. The model was used to study the electric field distribution within the insulation paper and its effect on PD current and charge magnitude. The influence of cavity location on the charge magnitude was also examined. It is found that the electric field distribution is influenced by the conductor configuration as well as the location of the cavity. The electric field in the cavity is the highest at L1 compared to L2. The first PD occurs faster for the cavity with a high electric field. Due to the PD occurrence at the same inception field, the real PD current and charge magnitude is similar at different locations. The apparent PD current and charge magnitude induced at the ground electrode is slightly higher at L1 than at L2.

Effects of tool angles and uncut chip thickness on consumption of plastic deformation energy during machining process

Research on the underlying mechanism that controls the chip deformation and energy consumption is a basis to instruct the cutting process planning and improve the machining efficiency. The metal cutting process can be treated as purposeful separation of workpiece material, and the stress state located at the tool tip has great effect on the fracture of material being removed. Through studying the relationship between the stress triaxiality and chip formation process, this paper aims to reveal the effects of tool rake angle, inclination angle and uncut chip thickness on chip deformation behavior and associated energy consumption during machining of 1045 steel based on finite element method (FEM). A two-dimensional FEM model for orthogonal cutting is developed to study the effect of tool rake angle and uncut chip thickness on chip deformation, while a three-dimensional FEM model for oblique cutting is developed to investigate the effect of tool inclination angle. The parameter of chip compression ratio (CCR) is adopted to assess the chip plastic deformation and energy consumption under varied machining conditions. The cutting force component calculated based on CCR is compared with the total cutting force to demonstrate the dominant role of chip plastic deformation in cutting energy consumption. The results indicate that larger rake angle and smaller inclination angle of cutting tools as well as larger uncut chip thickness lead to increase of stress triaxiality near the tool tip, which can reduce the material fracture strain and be beneficial for the separation of material being removed from the bulk workpiece. This paper will be attractive from both practical and fundamental perspectives devoted to instructing the optimization of cutting parameters to improve the processing efficiency and reduce the energy consumption.

A three-dimensional numerical model for evaluation of eddy current effects on electromagnetic forces of HTS electrodynamic suspension system

Magnetic levitation (Maglev) train has the advantages of high speed, low noise, low carbon emission and low operation costs, which meets the demands of future transportation systems. The high temperature superconducting (HTS) ElectroDynamic Suspension (EDS) system with on board HTS magnets and null-flux ground suspension coils is one of the most promising schemes for commercial operation. The numerical model of the electromagnetic forces in the HTS EDS system is well established through the dynamic circuit approach. However some realistic behavior including the eddy current induced in the metal vessel cannot be easily described as simple circuit components like a coil. The analysis of these issues is easier with a finite element method (FEM). In this paper, a three-dimensional FEM model is built to simulate the electromagnetic behavior of the null-flux coils – HTS magnet mechanism in motion. Especially, the electromagnetic interaction forces between the ground null-flux coils and HTS magnets mechanism are studied. Moreover, effects of framed vessel structures on electromagnetic forces of the HTS EDS system is discussed.

Applicability of Proportional Damping for Seismic Response Evaluation Using Three-Dimensional Finite Element Method Model Consisting of Structures with Multiple Damping Properties

The purpose of this study is to investigate the applicability of proportional damping to reduce the computational load, which is a common issue for seamless structural integrity evaluation with a 3D-FEM model. When the proportional damping is applied, it is necessary to compare this method with current design method (strain energy proportional damping) regarding on the seismic response calculation precision. Therefore, the research target is to construct a modeling method of proportional damping that realizes the same calculation precision as current design method. The ratios of the maximum stresses in strain energy proportional damping and proportional damping were confirmed using the 3D-FEM model with multiple damping properties, and the applicability of the proportional coefficients setting method based on the magnitude of the effective mass ratio was examined. As a result, it was confirmed that the proportional damping method can calculate the same stress distribution as current design method by setting the proportional coefficients for vibration modes with large effective mass ratios and for the upper limit frequency of the target frequency range.

Temperature Rise at the Pulp-Dentin Junction for a Multi-Layered Composite Restoration using the Finite Element Method

Objectives: During the light-curing process of composite restoration, excessive heat can be produced, which can potentially lead to pulp necrosis (death). In this study, we aimed, based on the Finite Element Method (FEM), to assess the risk of pulp damage during the light-curing process by investigating the influence of light-curing devices, under various irradiation regimes, on the temperature increase at the pulp-dentin junction, during a one-layer or multi-layered deep composite restoration. Methods: A Three-dimensional finite element method model of typical geometry and material properties, as commonly reported in the literature, was employed in COMSOL Multiphysics simulations in order to determine the temperature increase in the pulp. Various combinations of light intensities, durations, and irradiation regimes were investigated for the two cases, of shallow and deep multi-layered composite restoration. Results: Results of light-curing composite resins within enamel; indicate that the temperature rise during the curing process was within the safety margins. Results of light-curing composite resin restorations closer to the pulp with thin remaining dentin, indicate a temperature increase that could be sufficient to cause thermal injury in the pulp. Modulating the light output marginally, reduced the temperature rise while reducing the intensity and increasing the curing duration which was consistently more effective in this respect. Conclusion: The results clearly demonstrate that with currently adopted standard procedures, there exists a risk of thermal injury during multi-layered composite restorations with thin remaining dentin; it is thus important to establish appropriate curing regimes that would lead to minimal temperature increase during deep composite restorations and hence reduce the risk of thermal injury to the pulp.

Simulation and experimental investigation of multi-walled carbon nanotubes/aluminum composite fabrication using friction stir processing

Multi-walled carbon nanotube/aluminum composites are fabricated on Al–Si cast alloy employing friction stir processing. First, the microstructure of the stir zone, as well as the effect of process parameters on the size of silicon particles, is investigated. Then, the process is numerically simulated using a thermo-mechanically coupled three-dimensional finite element method model. Material flow, as the primary reason for the dispersion of reinforcing particles, is considered in the numerical model, and proper conditions to obtain a uniform dispersion of multi-walled carbon nanotubes are determined. Scanning electron microscope analysis is carried out to consider the particle distribution in the texture of the stir zone. The results show that the particle distribution improves significantly by changing the tool rotation direction between the friction stir processing passes. The hardness test is accomplished on the cross-section of the friction stir processed specimens, and finally, the wear test is performed to compare the wear resistance of the composites with the base alloy. The results show that the wear resistance and hardness of the produced composites are considerably enhanced compared to the base alloy.

Impacts of Mode Mixity on Controlled Spalling of (100)-Oriented Germanium

Controlled spalling is a technology to prepare single-crystal thin films of semiconductors by fracture with a subsurface crack propagating nearly parallel to the substrate surface. Practical applications require uniform thickness and a smooth surface across the whole film. Both wafer-scale and patterned-stressor-defined small-area spalling of germanium substrates are conducted experimentally and numerically. River line features are observed on spalled surfaces close to lateral edges of the spall, regardless of the spall direction and the size of the spalled area. Three-dimensional finite element method modeling shows the river lines are caused by mixed mode I + III loading near the lateral edges of spall and predicts a spall depth variation near the lateral edges of spall due to mixed mode I + II loading. The absolute range of river lines increases with lateral size of spall, while the relative range of river lines decreases, consistent with variations in mode mixity.

Improved two-temperature modeling of ultrafast thermal and optical phenomena in continuous and nanostructured metal films

In this work, a pump-probe experiment is used to study the ultrafast dynamics of heat transfer in thin gold films and gold nanostructures on glass substrates, following local heating by ultrashort laser pulses. Full spectrotemporal differential reflectivity and transmission maps were obtained for different film thicknesses (30, 50, 80, 150, and 200 nm) and different laser fluences $(0.38 \mathrm{to} 9.5\phantom{\rule{0.16em}{0ex}}{\mathrm{Jm}}^{\ensuremath{-}2})$. For arrays of gold nanorods, the two orthogonal probe polarizations were also acquired. We propose an improved model for these phenomena based on a modified two-temperature model that integrates thermal conduction and the three-dimensional finite element method model to link the spatiotemporal temperature maps to the spectrotemporal optical response maps. The impact of an underlying titanium adhesion layer is reported. Excellent agreement between numerical and experimental data for both the gold films and the nanostructures is shown.

Noninvasive Measurements and FEM Analyses for Estimating the Rotor Bar-Lamination Contact Resistance

This research work investigates the phenomenon of interbar currents in induction motors equipped with die-cast aluminum cages. Flowing in the lamination and distorting the bar current distributions, the interbar currents cause additional stray losses as well as an increase of the joule loss in the cage bars. The contact resistance between the bars and the rotor laminations is the key modeling element for a correct prediction of the interbar currents and the related extra losses. The study presents a new noninvasive method to obtain a reliable estimation of the contact resistance. The proposed hybrid approach is based on a mix of experimental data and Finite Element method (FEM)-based simulation results. A reliable three-dimensional FEM model of a four-pole 15-kW induction motor with closed rotor slots has been used to investigate the impact of variable contact resistance on the interbar currents, rotor joule losses, and the voltage drops along the bars, opening a new perspective for this complex phenomenon and its impact on the stray losses. Finally, the proposed methodologies are critically discussed and the obtained results compared with other relevant research works.

An Analysis of Temperature Distribution and Ablated Volume in the 3-D FEM Tissue Model with Blood Vessel during Radio-Frequency Ablation

The current treatment for a brain tumor has many methods such as surgery or chemotherapy but often the treatments may affect the patient or treatment is still limited in some aspects. A promising technique for brain tumor treatment is radio-frequency ablation. Radio-frequency ablation utilizes alternating current (AC), typically at about 500 kHz, to destroy unwanted tissues by heating to temperatures exceed 45°C to 50 °C. The objective of this research is to study the treatment of brain tumor during radio-frequency ablation with computer simulation through finite element method (FEM) for solving the problem. A three-dimensional FEM model of brain tissue with a brain tumor and blood vessel is considered. Three types of blood vessels i.e. aorta, main veins and terminal veins are studied. The electric current equation and time-dependent bioheat transfer equation coupled with time-dependent convective blood vessel heat transfer equation are solved to predict temperature distribution and ablated volume within brain tissue model. The simulation results are compared with the simulation results from previous work to verify the accuracy of the presented model. The effects of the blood vessel are included and not included in the brain tissue model, types of blood vessel and treatment time during radio-frequency ablation on the temperature distribution and ablated volume are investigated. The outcomes indicated that size of blood vessel results in heat sink effects which increase with the velocity of blood flow. The aorta causes more heat sink effects than main veins and terminal veins, respectively; thereby the ablated area and ablated volume in case of the aorta is higher than one in case of main veins and terminal veins, respectively. In addition, the temperature value increases with greater treatment time. The results from this study provide the basis for planning the radio-frequency ablation of brain tumor, leading to approaches of medical practice process improvement.

Strain Measurement on Quasi-Isotropic HTS Strand at 77 K by Fiber Bragg Grating and Extensometer Sensor

This article measures the strain response of quasi-isotropic strand at 77 K when subjected to uniaxial tensile loads by using extensometer sensor and simultaneously verifies the possibility of utilizing Fiber Bragg grating (FBG) sensor for the same measurements. Through matching the measured data from the two sensors, strain sensitivity of FBG sensor is calibrated and fitted to be 1.21 pm/ μ ϵ. In elastic deformation region, the stress–strain curve of the strand captured by FBG sensor coincides well with that from the extensometer sensor, but the range it could reach is only 0.31% strain ( ϵ tens ∼0.31%) due to the limitation of the elongation. Through fitting the stress–strain curve obtained by the extensometer, elastic modulus 115.5 GPa and yield stress 471 MPa of the strand are, respectively, determined. Then, depending on the measured stress–strain results and the equation on critical current as a function of tensile strain, critical stress of the strand is estimated to be 464 MPa. Furthermore, a three-dimensional finite element method model of the strand established by Comsol software is employed to understand the testing results.

Three-dimensional stress-transfer mechanism and soil arching evolution induced by shield tunneling in sandy ground

Tunnel excavation inevitably causes variations in stress and displacement fields in soil, which could affect the serviceability and safety of the adjacent underground structures. Change of the earth pressure acting on the existing structures is closely related to soil arching effect caused by a new tunnel excavation, but it is still lack of full understanding. In this study, a finite element method (FEM) model was first verified by field measurements based on a case history of Metro Line 2 construction in Changsha, China. Then, a series of simplified three-dimensional (3D) FEM models were established to investigate the stress redistribution and the soil arching evolution induced by earth pressure balance shield (EPBS) tunneling. The changes of the earth pressure, the coefficient of lateral earth pressure, and the settlement of soil mass above the tunnel during tunneling were analyzed and the soil arching zone was determined. 3D stress-transfer mechanism in soil arching zone during tunneling was revealed. In addition, the influences of shield-driving parameters (i.e. support pressure, grouting pressure) on soil arching evolution were also investigated. The results show that the loosened zone extends to nearly 0.73D (D = tunnel diameter) above the tunnel crown in vertical direction. The height of the arch zone above the loosened zone is about 1.27D. The horizontal soil arching in front of EPBS occurs near the ground surface. With EPBS advancing, the horizontal soil arching gradually transforms into the vertical soil arching. After the installation of lining, the earth pressure is finally mainly transferred by vertical soil arching in the transverse section. The proper combination of shield-driving parameters for controlling the expansion of the loosened zone is support pressure of 0.6P1 − 2.2P1 and grouting pressure of 1.0P2 − 1.8P2, where P1 is initial horizontal stress at the tunnel axis and P2 = 1.2P1.

Numerička simulacija ponašanja uzoraka od lakoagregatnog betona u slučajevima laboratorijskog ispitivanja

This paper presents the numerical modelling of the experimental determination of the compressive strength and the static modulus of elasticity of the lightweight concrete using the finite element method (FEM). In the theoretical review, a concrete damage plasticity (CDP) model of the concrete behaviour is described. Numerical modelling and nonlinear static (incremental-iterative) analyses were performed for two different configurations using the Abaqus © software. The first configuration of the model considers the experimental determination of the concrete compressive strength of the concrete cube, and the second one the determination of the static modulus of elasticity on the concrete cylinder. Steel plates in the three-dimensional FEM models located on the upper and lower sides of the specimens, which serve as the support or for the load application, thus capturing the contact conditions of concrete specimens with testing equipment more realistically, have also been taken into account.

Numerical Investigation of Differently Formed Steel Circular Columns under Axial Compression

A finite-element method (FEM) model was used to numerically investigate the overall buckling behaviours of hot-rolled (HR), submerged arc welded (SAW) and high-frequency welded (HFW) steel circular columns under axial compression. A three-dimensional FEM model of circular hollow sections was developed by using shell elements considering material non-linearities, geometric imperfections and residual stress. The FEM model was used to simulate experimental studies carried out by past researchers. Good agreement was found between the numerical and experimental results, which validate the FEM model for further research. The validated FEM model was used to analyse 180 numerically generated HR, SAW and HFW steel circular columns with various section sizes and slenderness values. The numerical results were then compared with existing column design curves in Chinese, European and American codes. To further improve the design efficiency, new column design curves for steel circular columns are recommended based on the formulas given in GB 50017-2003 and Eurocode 3.

Obtaining the thermal resistance of air enclosed at the interface of multilayer fabrics by simulation

An air layer enclosed at the interface was largely responsible for the insulation results of multilayer fabrics obtained from experiments. In this study, a three-dimensional finite element method model, in which the air layer enclosed at the interface of multilayer fabrics was ignored, was developed to calculate the fabric thermal resistance, and the result obtained from the fabric model was independent of the air. A Thermolab II Tester KES-F7 was also used to measure the thermal resistance of fabrics, and the experimental results were influenced by the air layer. By comparing the simulation and experimental result, the air layer thermal resistance was determined, and then an estimating equation, which can be used to estimate the fabric and air layer thermal resistance for multilayer fabrics, was proposed. The results suggested that the surface roughness of fabrics was strongly related to the air layer thermal resistance, with a linear relationship between them. Moreover, for multiple layers stacked by different fabrics, the air layer thermal resistance at the interface was mainly decided by the fabric with the rougher surface. An estimating equation was also developed to predict the thermal resistance of multilayer fabrics and good correlation between predicted and experimental values was observed.