Fine Mesh Model Research Articles

Finite element mesh transition for local–global modeling of composite structures

This study presents an automatic mesh generation algorithm designed to address computational challenges in simulating small-scale defects within large composite structures. The algorithm seamlessly transitions from a coarse mesh, corresponding to the global structure, to a highly refined mesh in targeted local regions of interest. The transition element number and shape can be adjusted by the specified parameters. Tailored to complement this method for non-homogeneous composite models, which include multiple materials such as cohesive layers representing interlayer properties, a volume fraction calculator is integrated to automatically assign the mixture material property in each transition element. Entire processes are fully automated using a MATLAB script, eliminating the need to open the FEA software interface. The validation studies of the reconstructed two-dimensional models, assembled with the wrinkle-defect model, demonstrate their feasibility. The performance of the model is examined in terms of strain and displacement at the connecting boundaries, load–displacement curve, and interlayer failure prediction. The mesh transition model achieves agreeable results compared to a fully fine mesh model, and a 92% reduction in computational time in stress analysis, showing the efficiency of the mesh transition for local–global modeling of composite structures.

Assessment of the CTF subchannel code for modeling a large-break loss-of-coolant accident reflood transient

With increased industry interest in extending reactor operating cycles, the neams! (neams!) program has been investigating the behavior of high-burnup fuel during design basis accidents such as the lbloca! (lbloca!) with consideration for risk of ffrd! (ffrd!). As part of that activity, the neams! subchannel th! (th!) code, CTF, is being used for modeling of lbloca! and to determine the impact of subchannel resolution on results. Although CTF includes a wide range of models for lbloca! conditions, the code has not been used for this application while maintained at ornl! (ornl!) until now. Therefore, in this work, a preliminary assessment of several of these models was performed using openly available reflood experimental data from the feba! (feba!) tests. One coarse mesh and one fine mesh model were set up in CTF for high and low flooding rate tests performed in the unblocked feba! facility. A coarse TRACE model was set up to be as consistent as possible with the coarse CTF model to allow for code-to-code benchmarking. The assessment shows a tendency of the codes to over-predict pct! (pct!) near the top of the bundle and to quench early. Advanced spacer grid models were shown to improve upper bundle predictions in CTF. The resolved CTF model over-predicted pct! by a larger degree in the center channels in the low-flooding rate test, and it is believed that the radiative heat transfer model, which was not used in this study, may be needed to correct this over-prediction. Finally, this work demonstrates the importance of the droplet model in determining quench time and vapor temperature and pct! prediction, which necessitates a more in-depth validation of these models in the future.

Thermal performance augmentation of honeycomb metal matrix embedded phase change material in shell-tube latent heat storage unit

Due to the global warming challenge, there is a transition from the utilization of fossil fuels to harvesting new and renewable energy sources globally. Solar energy, being the infinite source with easy accessibility, leads the race among other allied sources. However intermittent nature of it demands an efficient thermal energy storage system. In the present experimental study, an innovative heat transfer augmentation technique i.e. aluminium honeycomb grill and fine mesh embedded in PCM is demonstrated. Both visualization of PCM melt fraction and capture of temperature contour complemented each other to identify the honeycomb version (HC-LHSU) as substantially better (43 % improvement in charge period) than the base model (BM-LHSU). On the other side, due to fine pores (porosity = 95 %), the fine meshmodel (FM-LHSU) yielded poorer results than BM-LHSU. Even the temperature gradient that exists during the charge or discharge period is gauged and recognized HC-LHSU as the best, followed by BM-LHSU and FM-LHSU. Since the onset of the phase transition zone reflects heat storage rate, the same is identified, and the charge period (sensible heat + latent heat) assessed to be 8000 s, 10000 s, and 12,000 s for HC-LHSU, BM-LHSU, and FM-LHSU, respectively. Further, an improvement in the average Nusselt number by 74 % and 67 % during the charge and discharge period respectively compared to the base model justified the honeycomb grill's role in augmenting the energy storage unit's performance.

A Mesh Space Mapping Modeling Method with Mesh Deformation for Microwave Components.

In this study, a low-cost space mapping (SM) modeling method with mesh deformation is proposed for microwave components. In this approach, the coarse-mesh model with mesh deformation is developed as the coarse model, and the fine-mesh model is simulated as the fine model. The SM technique establishes the mapping relationship between the coarse-mesh model and the fine-mesh model. This approach enables us to combine the computational efficiency of the coarse model with the accuracy of the fine model. The automatic mesh deformation technology is embedded in the coarse model to avoid the discontinuous change in the electromagnetic response. The proposed model consisting of the coarse model and two mapping modules can represent the features of the fine model more accurately, and predict the electromagnetic response of microwave components quickly. The proposed mesh SM modeling technique is applied to the four-pole waveguide filter. The value for the training and test errors in the proposed model is less than 1%, which is lower than that for the ANN models and the existing SM models trained with the same data. Compared with HFSS software, the proposed model can save about 70% CPU time in predicting a set of 100 data. The results show that the proposed method achieves a good modeling accuracy and efficiency with few training data and a low computational cost.

Numerical simulation of residual stress of butt-welded joint involved in complex column-beam welded structure

The objective of this work is to clarify the effect of the structural restraint and the adjacent welded joints in column-beam welded structure on the final residual stress distribution and its evolution process of the butt-welded joint between the diaphragm and the flange through numerical simulation method. Based on ABAQUS software, a three dimensional thermal-mechanical coupled method was developed to predict the residual stress distribution for multi-pass welded joints. To improve calculation efficiency, an effective computational approach that combines a relatively coarse mesh design and an instantaneous heat source model was proposed to analyze the residual stress distribution for complex welded structures. Firstly, both a fine mesh model with moving heat source and a relatively coarse mesh model with instantaneous heat source were employed to predict the residual stress distribution in the same thick-plate butt-welded joint made of high strength low alloy steel. The computational accuracy of the proposed computational method was verified through comparing the results of the fine mesh model with moving heat source and the corresponding experimental data. Then, the residual stress distributions of the column-beam welded structure, the butt-welded joint under structural restraint condition and free state were calculated using the proposed computational approach. Results suggest that the structural restraint and the adjacent welded joints in the structure have a significant effect on the residual stress distribution.

Modeling of Preload Bolted Flange Connection Structure for Loosening Analysis and Detection

The specified finite element model is proposed for preload bolted flange connection structure widely used in aerospace and rocket design. A fine hexahedral mesh model of the bolt is used to predict the dynamic response of the structure accurately. The tightening process, which is ignored in the traditional I-shaped simplified model of bolted flange connection structure, can be simulated well based on the proposed model. After the vibration analysis and stress analysis of the bolted flange connection structure under impact load, it is found that the change of contact state of the flange surface results in a larger sticking contact area. And the reduction of the contact area at the thread causes slippage when the bolt is loose. As bolt loosening leads to changes in the time and frequency domain of response, a new loosening detection method for the preload bolted flange connection is provided. The index for identifying the loosening is designed using empirical mode decomposition and discrete integral in the high-frequency domain. The experiment of the preload bolted flange connection structure under impact load shows the efficiency of the proposed method which can identify loosening based on acceleration signal quickly and nondestructively.

A movable boundary model for helical coiled once-through steam generator using preconditioned JFNK method

Helical coiled once-through steam generator (H-OTSG) is the largest and the most complicated heat exchanger in the high-temperature gas-cooled reactor (HTGR), whose performance plays an important role in the nuclear power plant design and dynamic behavior analysis. A mathematical model of H-OTSG is developed based on the movable boundary method and solved by the advanced fully implicit Jacobian-free Newton-Krylov algorithm. The physical-based preconditioners are proposed and analyzed in this work, which achieves high-performance in solving the nonlinear steam generator system. In order to evaluate the performance of the movable boundary model, the fixed fine mesh model is also considered. The comparison is made between these two models from the perspective of the computational efficiency and accuracy. The simulation results are validated by the HTR-10 steam generator design data, showing that both models agree well with the design data, but have their own features. The fixed fine mesh model has its advantages in the accuracy, while the movable boundary model can realize the high computational efficiency.

Study of Crater in the Gobi Desert Induced by Ground Explosion of Large Amounts of TNT Explosive up to 10 Tons

Explosion craters on the ground surface induced by contact or near-field explosions have important implications, which can be used to assess blast consequences, guide the design of the explosion, or develop a protective strategy. In this study, to understand the crater characteristics induced by the contact explosion of large weight explosives, four field contact explosion tests were conducted on the surface of the Gobi Desert with large TNT charge weights of 1 ton, 3 tons, and 10 tons (test conducted twice). Cratering on the ground surface generated by large amounts of explosives was measured and evaluated, including the shape, depth, and diameter. A fine-mesh numerical model was developed and validated on the AUTODYN software platform, and a detailed parametric study was performed on the resulting craters. The effects of sand and gravel density, initiation method, shear modulus, and failure criteria were analyzed and discussed. An energy conversion coefficient was determined, and the corresponding theoretical equations were derived to predict the dimensions of the craters resulting from the large weight contact explosion. The calculated cratering characteristics were consistent with previous data and hence can be used in future engineering applications.

Active Learning Based 3D Semantic Labeling From Images and Videos

3D semantic segmentation is one of the most fundamental problems for 3D scene understanding and has attracted much attention in the field of computer vision. In this paper, we propose an active learning based 3D semantic labeling method for large-scale 3D mesh model generated from images or videos. Taking as input a 3D mesh model reconstructed from the image based 3D modeling system, coupled with the calibrated images, our method outputs a fine 3D semantic mesh model in which each facet is assigned a semantic label. There are three major steps in our framework: 2D semantic segmentation, 2D-3D semantic fusion, and batch image selection. A limited annotation image set is first used to fine-tune a pre-trained semantic segmentation network for obtaining the pixel-wise semantic probability maps. Then all these maps are back-projected into 3D space and fused on the 3D mesh model using Markov Random Field optimization, thus yield a preliminary 3D semantic mesh model and a heat model showing each facet’s confidence. This 3D semantic model is used as a reliable supervisor to select the parts that are not well segmented for manual annotation to boost the performance of the 2D semantic segmentation network, as well as the 3D mesh labeling, in the next iteration. This Training-Fusion-Selection process continues until the label assignment of the 3D mesh model becomes steady. By this means, we significantly reduce the amount for annotation but not the labeling quality of 3D semantic models. Extensive experiments demonstrate the effectiveness and generalization ability of our method on a wide variety of datasets.

Modelling and validation of fluid flow inside a dissipative ladle shroud and a continuous casting tundish

Fluid flow plays a significant role in the continuous casting of molten steel. In this paper, two Reynolds Averaged Naiver-Stokes (RANS) models and a Large Eddy Simulation (LES) model were comparatively employed to characterize the fluid flow inside a dissipative ladle shroud and a tundish. LES model was proved to be powerful to characterize the turbulence structure inside the ladle shroud. The effect of meshing density on the computational accuracy was considered using the LES model. The fine-mesh model can capture multiscale vortices inside the ladle shroud; while, the coarse-mesh model disables the LES to obtain the detailed flow information. The experiment of particle image velocimetry (PIV) was used to verify the flow field obtained by the LES model inside the tundish. The PIV and the LES results agree well in terms of flow pattern and velocity vector.

Conversion of the geological model (fine-mesh) to a dynamic (coarse-mesh) hydrocarbon model with the nature approach in the simulation of thermal recovery in a fractured reservoir

The operation and proper management of reservoirs requires the prediction of reservoir performance. This prediction is generally done by computer simulation. Since simulation software generates static models in the number of millions and even billions, dynamic simulation on these models is difficult and sometimes impossible; therefore, multi-scale block generation is necessary. In this study, we introduce a methodology that was inspired by Earth’s pattern to generate multi-scale grids on a multi-phase, heterogeneous reservoir, where the enhanced oil recovery process is steam injection. From a reservoir engineer’s point of view, Earth is equivalent to a multi-scale grid model that could be a pattern for multi-scale grid generation in a hydrocarbon reservoir to minimize central processing unit time for dynamic simulation. The principle of multi-scale grid generation in hydrocarbon reservoirs is as follows: regions with a high Darcy’s velocity should be fine-scale and other segments with low intensity of heterogeneity regions could resize into the up-scale. The intersection of latitude and longitude lines means that Earth’s model could be a practical pattern for dynamic simulation. This intersection creates segments with fine-size blocks, like the South and North Poles, that are equal to the injection and production wells in the reservoir model and other segments that have different intensities of coarse-size blocks. Earth’s magnetic field, which enters from South and exits from the North Pole, leads us to could consider Earth as a hydrocarbon model. The results of the multi-scale grid generation method, which was inspired by Earth’s pattern, were compared with the fine-mesh (geological) model; the results show that the proposed method predicts with high accuracy and less run-time compared with the fine-mesh model.

A dual-mesh method for efficient thermal stress analysis of large-scale welded structures

Transient thermo-mechanical analysis of welding problem requires tremendous computation cost. To accelerate the thermal analysis of large-scale welded structures, an efficient computation scheme based on heat transfer localization and dual meshes was proposed. The computation accuracy is guaranteed by a local fine mesh model with size determined by a theoretical solution and a global coarse mesh model with equivalent heat input. The validity and accuracy of the dual-mesh method were verified using an experimental bead-on-plate model. By extending the weld length, the computation time of the proposed method was proved to be almost linearly dependent on the model scale. The thermal analysis of fillet welding of a large panel structure with 6-m-long weld was accelerated by 10 times over conventional finite element analysis and 2.2 times over adaptive mesh method. Meanwhile, the physical memory consumption was also greatly reduced by the dual-mesh method. Such efficient computation method enables fast evaluation of welding stress and distortion which are vital for manufacturing process and structure performance.

직접구조강도 평가를 위한 선체 국부구조 상세요소분할모델 자동생성

Under the circumstances of Common Structure Rules for Bulk Carrier and Oil Tanker (CSR-H; Harmonized Common Structure Rules) which is on effective from July 2015, the modeling area for finite element (FE) has been extended to forward and afterward cargo hold regions of a ship, more design man-hours are required in the FE modeling than that of previous rules. In addition, it is mandatorily required to generate the fine-mesh model for hot spot zones, but the target area has been extended so extensively, more design man-hours are required for fine-mesh modeling than that of coarse mesh modeling. Moreover, the local area for fatigue analysis should be modeled with very fine-mesh. However, these kinds of FE modeling for different level of detail and different purpose of analysis are time consuming and repetitive works. In this research, we would like to introduce the auto fine mesh modeling functionality that can generate fine-mesh and very-fine mesh model from the coarse mesh model, and retrieve and restore them to coarse mesh for certain purpose by re-mesh functionality. Through this process, FE model can be managed and reused with a consistent FE model from the initial design stage to detailed design stage of a ship.

Finite Element Modeling and Experimental Verification of Nitriding Process in S30C Steel

A mathematical model has been developed to simulate the nitriding process of plain carbon steel, considering the simultaneous diffusion of nitrogen in different iron-nitrogen (Fe-N) phases and the precipitation dynamics of γ’e and iron-nitride. The model can predict the distribution of nitrogen concentration, volume fraction of Fe-N phases and hardness. Furthermore, a finite element method (FEM) post-process technology is presented to avoid the limit of FEM mesh improvement and time-saving. The uniform-sum-division algorithm is adopted as local refinement algorithm (LRA) of meshes. The modified inverse distance weighting (IDW) method is used to interpolate the FEM simulated results. Then, the nitriding model and post-process technology are incorporated within the framework of the developed FEM code COSMAP (COmputer Simulation of MAnufacturing Process) based on metallo-thermo-mechanical theory. In order to validate the nitriding model and FEM post-process technology, the nitriding process of S30C steel is modeled by COSMAP software. The simulated distributions of nitrogen content and hardness are consistent with the measured ones. In addition, the simulated results at different mesh size are compared for two-dimensional model. It is indicated that the interpolated results agree well with the simulated results of fine mesh model and the experimental ones.Keywords: finite element, nitriding, S30C, iron nitride, inverse distance weighting

A framework for the upscaling of the electrical conductivity in the quasi-static Maxwell’s equations

Electromagnetic simulations of complex geologic settings are computationally expensive. One reason for this is the fact that a fine mesh is required to accurately discretize the electrical conductivity model of a given setting. This conductivity model may vary over several orders of magnitude and these variations can occur over a large range of length scales. Using a very fine mesh for the discretization of this setting leads to the necessity to solve a large system of equations that is often difficult to deal with. To keep the simulations computationally tractable, coarse meshes are often employed for the discretization of the model. Such coarse meshes typically fail to capture the fine-scale variations in the conductivity model resulting in inaccuracies in the predicted data. In this work, we introduce a framework for constructing a coarse-mesh or upscaled conductivity model based on a prescribed fine-mesh model. Rather than using analytical expressions, we opt to pose upscaling as a parameter estimation problem. By solving an optimization problem, we obtain a coarse-mesh conductivity model. The optimization criterion can be tailored to the survey setting in order to produce coarse models that accurately reproduce the predicted data generated on the fine mesh. This allows us to upscale arbitrary conductivity structures, as well as to better understand the meaning of the upscaled quantity. We use 1D and 3D examples to demonstrate that the proposed framework is able to emulate the behavior of the heterogeneity in the fine-mesh conductivity model, and to produce an accurate description of the desired predicted data obtained by using a coarse mesh in the simulation process.

Comparison of 3DSIM thermal modelling of selective laser melting using new dynamic meshing method to ANSYS

Selective laser melting (SLM) is an additive manufacturing (AM) process in which parts are fabricated by selectively melting regions of the surface of a metallic powder bed in a layer-by-layer fashion. Various thermal phenomena such as heat conduction, convection, radiation, melting and solidification, dynamic phase changes, and evaporation occur during the SLM process. In addition, laser intensity and powder bed scan speeds during processing complicate understanding of the process due to complex dynamic interactions between the powder bed and laser. In order to study these dynamic interactions, a finite element model has been developed which uses a dynamic mesh with spatial non-linear thermal properties to track the point of laser exposure on the powder bed to study thermal evolution during SLM. The model is able to achieve a refined, localised mesh in the melt zone and heat affected zone (HAZ), surrounded by a relatively coarse mesh outside of the HAZ regions. The dynamic meshing for this implementation is achieved using both the sub-modelling functionality in ANSYS and a new set of algorithms being commercialised by 3DSIM, LLC. It was found that dynamic meshing reduces the model size and computational burden. In this paper, the use of the sub-modelling approach for dynamic meshing was verified by comparing it against a uniform fine mesh model. The results of the two models match within an acceptable tolerance. Also, a mesh sensitivity analysis was carried out in order to show solution convergence as a function of increasing mesh density. The results of this analysis were also validated using experiments to show a match between experimental and simulated melt pools. Finally, the ANSYS solution was compared with a new set of dynamic meshing finite element analysis algorithms running in Matlab. It was found that these new algorithms were significantly faster than their ANSYS counterparts for solving problems using a dynamic mesh.

Experimental modelling of transverse oscillations in aquaculture netting parallel to the flow — Sounds baffling

Numerous studies have been undertaken to improve the viability, durability and suitability of materials and methods used for aquaculture enclosures. While many of the previous studies considered macro-deformation of nets, there is a paucity of information on netting micro-deformation. When aquaculture pens are towed, industry operators have observed the motion described as “baffling” — the transverse oscillation of the net planes parallel and near parallel to the flow. The difficulty to observe and assess baffling motion in a controlled experimental environment is to sufficiently reproduce netting boundary conditions and the flow environment experienced at sea. The focus of the present study was to develop and assess experimental methods for visualisation and quantification of these transverse oscillations. Four net-rig configurations with varied boundary conditions and model-netting properties were tested in a flume tank. While the Reynolds number was not equivalent to full-scale, usage of the pliable and fine mesh model netting that enabled baffling to develop at low flow velocities was deemed to be of a larger relevance to this initial study. Baffling was observed in the testing frame that constrained the net sheet on the leading edge, similarly to a flag attachment onto a pole. Baffling motion increased the hydrodynamic drag of the net by 35%–58% when compared to the previously developed formula for taut net sheets aligned parallel to the flow. Furthermore, it was found that the drag due to baffling decreased with the increasing velocity over the studied Reynolds numbers (below 200); and the drag coefficient was non-linear for Reynolds numbers below 120. It is hypothesised that baffling motion is initially propagated by vortex shedding of the netting twine which causes the netting to oscillate; there after the restoring force causes unstable pressure differences on each side of the netting which excites the amplitude of the netting oscillations.

Packaging Parameters Analysis for the Fatigue Reliability of Stacked Chip Ball Grid Array by Using the Optimal Equivalent Solder Balls

A global/local method with the modified sub‐modeling approach of the two‐parametric optimal equivalent volume solder balls is introduced to predict the deformation and reliability of the package. The equivalent solder balls as exhibit in this method can obviously reduce the required elements/nodes quantities to enhance computing efficiency. A package model of wire‐bonded stacked chip ball grid array under cyclic thermal loading is used as a test vehicle to verify the influences of design factors by fatigue life indicator. Comparing the proposed method with the global fine mesh model, it is found that the difference in the accumulated strain energy density is merely 5.77%, but the optimal equivalent model has highly saved 90% finite element analysis required elements, which means the adopted method can effectively replace the global fine mesh model because both results are in accordance with each other. Using design of experiments to efficiently verify each factor influence with their cross‐coupling effects, this paper adopts two kinds of response surface methods that confirm the fatigue life of the proposed approach can be improved by as much as 123.7% for the dual response surface method and 126.3% for the mixed response surface method when comparing with the baseline model. In addition, the optimization of generic algorithm for both response surface methods is demonstrated in this study. From the reviews of factor coupling effects, it is concluded that the response surface method is eligible to achieve the optimum design for package reliability improving. Copyright © 2013 John Wiley & Sons, Ltd.

Structural Stress Analysis of Trough to Deck Plate Weld in Orthotropic Steel Bridge Decks

A comparative study among five methods to calculate the structural stress of the trough to deck plate joint in orthotropic steel deck was carried out. The five methods used are surface stress extrapolation method (SSE), Haibach method, Xiao and Yamada method and CAB method. FEM analysis shows the five methods are mesh sensitive. Structural stress calculated using element type solid95 is larger than that of solid45. For fine and medium mesh model, structural stress calculated by Haibach method is larger than other methods, which means a lower fatigue life. Structural stress calculated by Yamada method is lower than other methods, which means a higher fatigue life than that calculated by other methods. For coarse mesh model, structure stress calculated by quadratic extrapolation method is larger than other methods, and, structural stress calculated by Yamada method is much lower than other methods.

Prediction of flow field and aerodynamic noise of jet fan using large eddy simulation

To conduct a product development of turbomachinery continuously and developmentally, an approach using large eddy simulation (LES) should be one of the mainstream, because it is already essential to utilize computational fluid dynamics (CFD) using Reynolds averaged Navier–Stokes Simulation in industrial field. In recent years, the demand for a high-efficiency and low-noise jet fan, which is used for ventilation of a tunnel of a carriage way, is getting higher and higher. However, to conduct noise prediction of the jet fan with high accuracy, it needs the high-performance computing technique using a supercomputer. In this study, CFD of the jet fan is conducted using LES. Noise simulation is also conducted using the LES result. Moreover, the fine mesh model is generated by refining a coarse mesh, and LES is conducted using the Earth Simulator. The result of surface pressure using the fine mesh is clearer than the one using the coarse mesh.