Full 3D Geometry Research Articles

Digital bead modeling for wire-arc directed energy deposition

Prediction of 2D cross-section and full 3D geometry for stacked weld beads is critical for the outcome of wire-arc directed energy deposition (DED) parts; however, most additive path planning software packages model beads as extrusions of a rectangle. Weld beads are not rectangular, and the resulting shape is dependent upon physics effects at the moment of deposition. Physics phenomena such as the geometry of the underlying surface, the heat input of the welding mode, and the direction of gravity contribute to bead shape. This paper presents a novel implicit modeling method that discretizes a 2D area or 3D volume of space into pixels or voxels and constructs fields based on these physics phenomena. The fields are combined using a weighting scheme trained on 3D scan measurements of welds and wire-arc DED prints. Pixels or voxels are added until the known amount of deposited volume has been achieved. Thereby, a strong conservation of mass principle is applied to the process. Utilizing machine learning techniques, the present model can be trained on a database of scans allowing for the representation of a wide variety of prints. Results show that this method can produce predictions with realistic bead morphology and sub-millimeter form error.

Effect of symmetry-breaking on the MHD edge stability limit of tokamak plasmas

We demonstrate for the first time that symmetry-breaking in tokamak plasmas reduces the window of stable edge operational space, leading to a lower achievable edge pressure gradient. Predictive simulations with the linear magnetohydrodynamic stability code CASTOR3D show a reduction of the critical pressure gradient by up to 30%, in agreement with experimental observations. The analysis has been extended to experimental plasmas considering, for the first time, ion diamagnetic drift effects in realistic non-axisymmetric (3D) tokamak geometry. The 3D geometry in plasmas with edge localised modes (ELMs) increases the growth rate of edge instabilities compared to the axisymmetric case. Further reducing the edge pressure gradient eliminates the instabilities corresponding to an experiment with suppressed ELMs, reproducing the empirically observed threshold for ELM suppression. Our findings highlight the importance of predictions of the ELM occurrence in full 3D geometry for future tokamak devices with intentionally and unintentionally broken axisymmetry.

Three-dimensional particle-in-cell simulations of laser-driven multiradiation sources based on double-layer targets.

Double-layer targets (DLTs), made of a low-density foam on top of a solid substrate, can efficiently convert the energy of a high-intensity laser to provide sources of photons and protons. We investigate a 30-fs pulse with a peak intensity of I∼8.7×10^{20}W/cm^{2} and a peak power of ∼120 TW interacting with a DLT using three-dimensional (3D) particle-in-cell simulations. We focus on providing quantitative results in full 3D geometry on the foam thickness dependence; on the competition between two photon-generating processes in DLTs, i.e., nonlinear inverse Compton scattering (NICS) and bremsstrahlung (BS); and on the acceleration of protons via enhanced target-normal sheath acceleration. We discuss conversion efficiency, average energy, and angular distributions of such multiradiation sources. We find that NICS can prevail over BS if the DLT's substrate is thin enough (∼µm) and that the optimal foam thickness that maximizes the conversion efficiency in NICS and BS photons and the proton cutoff energy, among those considered, is the same (15µm). These results show that DLTs constitute an excellent tool for developing relatively compact and optimized laser-driven multicomponent radiation sources.

Potential of Radioactive Isotopes Production in DEMO for Commercial Use

There is widespread use of nuclear radiation for medical imagery and treatments. Worldwide, almost 40 million treatments are performed per year. There are also applications of radiation sources in other commercial fields, e.g., for weld inspection or steelmaking processes, in consumer products, in the food industry, and in agriculture. The large number of neutrons generated in a fusion reactor such as DEMO could potentially contribute to the production of the required radioactive isotopes. The associated commercial value of these isotopes could mitigate the capital investments and operating costs of a large fusion plant. The potential of producing various radioactive isotopes was studied from material pieces arranged inside a DEMO equatorial port plug. In this location, they are exposed to an intensive neutron spectrum suitable for a high isotope production rate. For this purpose, the full 3D geometry of one DEMO toroidal sector with an irradiation chamber in the equatorial port plug was modeled with an MCNP code to perform neutron transport simulations. Subsequent activation calculations provide detailed information on the quality and composition of the produced radioactive isotopes. The technical feasibility and the commercial potential of the production of various isotopes in the DEMO port are reported.

Numerical Analysis of Oil Lubrication and Cooling of Roller Thrust Bearing in High-Performance Mixed-Flow Pump

This article deals with the numerical simulation of an oil–air multiphase flow inside the thrust bearing of a high-performance mixed-flow pump, including both the lubrication effects and the cooling of the oil by the water-cooling system based on spiral piping. The bearing is lubricated by the oil bath method with partially submersed rollers. Very complex full 3D geometry is modelled in all details, but for modelling purposes, the impacts of some model simplifications on the results are tested. The comprehensive CFD analysis is based on fully transient simulations, taking into account the different rotational speeds and different coordinate systems of all rotating components. The oil distribution on the bearing ring and roller walls as well as the oil temperature are discussed in detail. The results demonstrate that the designed cooling system is efficient in keeping the bearing and oil temperatures at safe values to guarantee bearing rating life even at extreme climatic conditions. The simulations present a comprehensive way of solving complex problems of the bearing and its cooling system applicable to engineering practice. The results of the simulations indicate also that the complexity of the computational domain and bearing clearances have a significant impact on the obtained results.

A Parametric Thoracic Spine Model Accounting for Geometric Variations by Age, Sex, Stature, and Body Mass Index

<div>In this study, a parametric thoracic spine (T-spine) model was developed to account for morphological variations among the adult population. A total of 84 CT scans were collected, and the subjects were evenly distributed among age groups and both sexes. CT segmentation, landmarking, and mesh morphing were performed to map a template mesh onto the T-spine vertebrae for each sampled subject. Generalized procrustes analysis (GPA), principal component analysis (PCA), and linear regression analysis were then performed to investigate the morphological variations and develop prediction models. A total of 13 statistical models, including 12 T-spine vertebrae and a spinal curvature model, were combined to predict a full T-spine 3D geometry with any combination of age, sex, stature, and body mass index (BMI). A leave-one-out root mean square error (RMSE) analysis was conducted for each node of the mesh predicted by the statistical model for every T-spine vertebra. Most of the RMSEs were less than 2 mm across the 12 vertebral levels, indicating good accuracy. The presented parametric T-spine model can serve as a geometry basis for parametric human modeling or future crash test dummy designs to better assess T-spine injuries accounting for human diversity.</div>

Advanced 3D analysis of fibrotic ring-like pattern in non-ischemic cardiomyopathy predicts major arrhythmic events

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): This work was supported by the National Institute for Health Research Biomedical Research Centre at Guy’s and St. Thomas’ Trust and King’s College, the Centre of Excellence in Medical Engineering funded by the Wellcome Trust and Engineering and Physical Sciences Research Council (EPSRC; WT088641/Z/09/Z). M.J.B. is supported by a Medical Research Council New Investigator Grant (MR/N011007/1) and British Heart Foundation (Project grant PG/18/74/34077). This work was supported by EPSRC 2018/19 DTP - EP/R513064/1 grant. This work was supported by a National Heart and Lung Institute Foundation grant awarded to Professor Sanjay Prasad and Dr Richard Jones. This work was supported by a National Heart and Lung Institute Foundation grant awarded to SKP, DJH, REJ, UT and BPH. Additionally, the study was supported by an Intermediate Clinical Research Fellowship awarded to BPH (FS/ICRF/21/26019). Background The presence of ring-like patterns of mid-wall fibrosis identified on late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) is associated with an increased risk of major arrhythmic events (MAE) in non-ischemic cardiomyopathy (NICM). Analysis of tissue bordering core fibrosis and healthy myocardium (Gray Zone [GZ]) has been suggested as an important pro-arrhythmic substrate in this population. Purpose To investigate refined anatomical definitions of the fibrotic ring pattern, including the importance of GZ inclusion in the association with MAE in NICM. Methods LGE CMR data from 292 NICM patients were analysed to delineate both core and GZ fibrosis. Fibrosis quantification masks for each 2D image slice were used, along with AHA 17-segment maps, to identify fibrotic ring patterns: defined by fibrosis extending by 3 or more continuous AHA-segments for any individually-contiguous fibrotic component within each slice (Fig 1A). Ring patterns were assessed separately for core fibrosis and core + GZ, as well as individually in basal, mid-basal and mid-apical regions. In separate analysis, LGE contours were aligned, interpolated, and used to generate 3D computational volumetric models (Fig 1B). Individually-connected scar components were extracted and the 3D circumferential angular variation (3DCAV) of each separate fibrotic structure quantified as a continuous variable (Fig 1C). Association of the presence of ring patterns and 3DCAV with a composite MAE were investigated. Results Of 292 patients, 67(23%) had core fibrotic ring patterns (54 basal, 28 mid-cavity level, 6 apical). Over a median(IQR) of 6(4) years, 16(24%) patients experienced MAE. On univariate Cox analysis, ring pattern core fibrosis was a strong predictor of MAE (Hazard ratio [HR] 2.2, 95% confidence interval [CI] 1.13-4.31, p=0.021). Apical-basal region analysis showed that basal ring pattern was associated with MAE (HR 2.25, 95%CI, 1.13-4.51, p=0.022). Multivariate Cox analysis including raised NYHA Class and severely reduced LVEF, overall ring (HR 2.14, 95%CI, 1.05-4.33, p=0.035) and basal ring pattern (HR 2.9, 95%CI 1.39-6.02, P=0.004) continued to show independent association with the MAE. Analysis of the full 3D geometry of the individual scar components also showed that our novel 3DCAV metric was associated with the MAE on both univariate (HR 1.31, 95%CI 1.08-1.59, P=0.007) and multivariate (HR 1.3, 95%CI, 1.06-1.60, P=0.013). Analysis of core ring patterns outperformed analysis of core+GZ patterns in all cases. Conclusions Our study confirms that ring-like patterns of fibrosis in NICM are strongly associated with MAE in NICM, with patterns predominantly at the basal regions conferring enhanced risk relative to mid-basal and mid-apical regions. Inclusion of GZ quantification in ring-pattern analysis did not enhance risk prediction. Our novel 3D analysis of circumferential fibrosis patterns may provide a more robust quantitative metric for stratification.

Direct numerical simulation of the two-dimensional speed bump flow at increasing Reynolds numbers

The Speed Bump flow model was designed by Boeing to provide a mildly three-dimensional flow with separation from a very smooth surface, strongly controlled by the turbulence. Experiments are conducted by several teams, as are simulations, over a range of Reynolds numbers. Direct Numerical Simulations (DNS) are not possible for the full 3D geometry of width L, leading several groups to conduct DNS over a two-dimensional geometry, in other words the cross-section of the full geometry, with periodic lateral conditions and a typical domain width of 0.04L. This does not allow precise comparisons with experiment, but code-to-code comparison is instructive. A shallow separation bubble is present, as intended. The domain width becomes marginal after reattachment, where the boundary layer is much thicker. The Reynolds number based on L has been 106, so far in the literature, which causes partial relaminarization and tends to defeat the purpose of testing turbulence models. Flow visualisation is clear on this. Here, we present results at the Reynolds number 106 and 1.4 × 106, and the higher value essentially eliminates relaminarization. Detailed results are shown, including studies of domain width, grid resolution, and numerical dissipation. The turbulence models give inaccurate results for skin friction, already in the intense favourable pressure gradient, which causes the formation of an internal boundary layer; the separation prediction on the other hand is reasonable. The wall curvature seems to play a role. The present results also provide trustworthy data to test Large-Eddy Simulation (LES), especially if using a Wall Model (WMLES). The comparisons will have a preliminary character until the results of the ongoing detailed experiments and of DNS at even higher Reynolds number and with a wider domain are available and carefully compared.

Numerical Homogenization of Multi-Layered Corrugated Cardboard with Creasing or Perforation.

The corrugated board packaging industry is increasingly using advanced numerical tools to design and estimate the load capacity of its products. This is why numerical analyses are becoming a common standard in this branch of manufacturing. Such trends cause either the use of advanced computational models that take into account the full 3D geometry of the flat and wavy layers of corrugated board, or the use of homogenization techniques to simplify the numerical model. The article presents theoretical considerations that extend the numerical homogenization technique already presented in our previous work. The proposed here homogenization procedure also takes into account the creasing and/or perforation of corrugated board (i.e., processes that undoubtedly weaken the stiffness and strength of the corrugated board locally). However, it is not always easy to estimate how exactly these processes affect the bending or torsional stiffness. What is known for sure is that the degradation of stiffness depends, among other things, on the type of cut, its shape, the depth of creasing as well as their position or direction in relation to the corrugation direction. The method proposed here can be successfully applied to model smeared degradation in a finite element or to define degraded interface stiffnesses on a crease line or a perforation line.

Complex geometries in additive manufacturing: A new solution for lattice structure modeling and monitoring

The production of novel types of complex shapes is nowadays enabled by new manufacturing paradigms such as additive manufacturing, also known as 3D printing. The continuous increase of shape complexity imposes new challenges in terms of inspection, product qualification and process monitoring methodologies. Previously proposed methods for 2.5D free-form surfaces are no longer applicable in the presence of this kind of new full 3D geometries. This paper aims to tackle this challenge by presenting a statistical quality monitoring approach for structures that cannot be described in terms of parametric models. The goal consists of identifying out-of-control geometrical distortions by analyzing either local variations within the part or changes from part to part. The proposed approach involves an innovative solution for modeling the deviation between the nominal geometry (the originating 3D model) and the real geometry (measured via x-ray computed tomography) by slicing the shapes and estimating the deviation slice by slice. 3D deviation maps are then transformed into 1D deviation profiles enabling the use of a profile monitoring scheme for local defect detection. The feasibility and potential of this method are demonstrated by focusing on a category of complex shapes where an elemental geometry regularly repeats in space. These shapes are known as lattice structures, or metamaterials, and their trabecular shape is thought to provide innovative mechanical and functional performance. The performance of the proposed method is shown in real and simulated case studies.

Laser-driven ion acceleration from near-critical Gaussian plasma density profile

In this paper, we report on multiple phases of efficient laser-driven ion acceleration from near-critical density plasma of Gaussian density profile. Tracking of high-energy accelerated ions in multidimensional particle-in-cell simulations reveals the development of accelerating fields affecting the particles and the contribution of each acceleration phase to final ion energies. While the acceleration of ions occurs in a short time interval when a steep (infinite) density gradient is present, the accelerating field affecting the most energetic ions has unexpected local maxima about 50 fs after the moment when ultrashort (30 fs) laser pulse completely left the target with smooth density gradients. This field can be attributed to the apex of electron filament created behind the transmitted laser pulse. Full 3D simulation confirms the observations in 2D simulations in terms of ion acceleration mechanisms. However, it shows a substantial reduction of maximum achievable ion energies and a larger angular spread of accelerated ions compared with 2D approach, which demonstrates the necessity of using computationally demanding full 3D geometry for similar numerical studies.

About the Influence of Eco-Friendly Fluids on the Performance of an External Gear Pump

This paper wants to investigate the effects of eco-friendly fluids on the thermo-fluid-dynamic performance of external gear pumps in order to provide a first response to the increasingly urgent demands of the green economy. A computational fluid dynamics (CFD) approach based on the overset mesh technique was developed for the simulation of the full 3D geometry of an industrial pump, including all the characteristic leakages between components. A sensibility analysis of the numerical model with respect to different fluid properties was performed on a commonly used mineral oil, showing the key role of the fluid compressibility on the prediction of the pump volumetric efficiency. Moreover, the influence of temperature internal variations on both fluid density and viscosity were included. The BIOHYDRAN TMP 46 eco-friendly industrial oil and olive oil were further considered in this work, and the results of the simulations were compared for the three fluid configurations. A slightly lower volumetric efficiency was derived for the olive oil application against the other two conditions, but suggestive improvements were produced in terms of pressure and temperature distributions. Therefore, based on the obtained results, this paper encourages research activity towards the use of eco-friendly fluids in the hydraulic field.

Potential design problems for ITER fusion device

The international thermonuclear experimental reactor (ITER) is a worldwide project currently being built in France for the demonstration of the feasibility of thermonuclear technologies for future realization of successful commercial fusion energy. ITER is of the tokamak based design using strong magnetic fields to confine the very hot plasma needed to induce the fusion reaction. Tokamak devices are currently the front leading designs. Building a successful magnetic fusion device for energy production is of great challenge. A key obstacle to such design is the performance during abnormal events including plasma disruptions and so-called edge-localized modes (ELMs). In these events, a massive and sudden release of energy occurs quickly, due to loss of full or partial plasma confinement, leading to very high transient power loads on the reactor surface boundaries. A successful reactor design should tolerate several of these transient events without serious damages such as melting and vaporization of the structure. This paper highlights, through comprehensive state-of-the-art computer simulation of the entire ITER interior design during such transient events, e.g., ELMs occurring at normal operation and disruptions during abnormal operation, potential serious problems with current plasma facing components (PFCs) design. The HEIGHTS computer package is used in these simulations. The ITER reactor design was simulated in full and exact 3D geometry including all known relevant physical processes involved during these transient events. The current ITER divertor design may not work properly and may requires significant modifications or new innovative design to prevent serious damage and to ensure successful operation.

Validation of high-fidelity ion cyclotron range of frequencies antenna coupling simulations in full 3D geometry against experiments in the ASDEX Upgrade tokamak

We address the validation of finite elements ion cyclotron range of frequencies (ICRF) antenna coupling simulation against experiments performed in the ASDEX Upgrade tokamak. Measurements of the loading resistance in ICRF-heated, magnetically-perturbed 3D plasma discharges are compared against numerical predictions of the RAPLICASOL code. To this end, the 3D induction field and the 3D density profile are modeled by concatenating the PARVMEC, BMW and EMC3-EIRENE codes. The 3D density is input to RAPLICASOL, where full-wave simulations are performed on a finite element mesh retaining full 3D geometry in the ICRF antenna model and the plasma description. The results are further compared with RAPLICASOL simulations using a 1D density profile as measured at the outboard midplane in the same experiments. We find that simulations using a 1D density profile overestimate the change in loading resistance by a factor of ∼197 − 248%, while simulations using the full 3D density profile are in agreement with experiments within a factor ∼16%.

Explaining the winds of AGB stars: Recent progress

AbstractThe winds observed around asymptotic giant branch (AGB) stars are generally attributed to radiation pressure on dust, which is formed in the extended dynamical atmospheres of these pulsating, strongly convective stars. Current radiation-hydrodynamical models can explain many of the observed features, and they are on the brink of delivering a predictive theory of mass loss. This review summarizes recent results and ongoing work on winds of AGB stars, discussing critical ingredients of the driving mechanism, and first results of global 3D RHD star-and-wind-in-a-box simulations. With such models it becomes possible to follow the flow of matter, in full 3D geometry, all the way from the turbulent, pulsating interior of an AGB star, through its atmosphere and dust formation zone into the region where the wind is accelerated by radiation pressure on dust. Advanced instruments, which can resolve the stellar atmospheres, where the winds originate, provide essential data for testing the models.

DLGAN: Depth-Preserving Latent Generative Adversarial Network for 3D Reconstruction

Although deep networks based methods outperform traditional 3D reconstruction methods which require multiocular images or class labels to recover the full 3D geometry, they may produce incomplete recovery and unfaithful reconstruction when facing occluded parts of 3D objects. To address these issues, we propose Depth-preserving Latent Generative Adversarial Network (DLGAN) which consists of 3D Encoder-Decoder based GAN (EDGAN, serving as a generator and a discriminator) and Extreme Learning Machine (ELM, serving as a classifier) for 3D reconstruction from a monocular depth image of an object. Firstly, EDGAN decodes a latent vector from the 2.5D voxel grid representation of an input image, and generates the initial 3D occupancy grid under common GAN losses, a latent vector loss and a depth loss. For the latent vector loss, we design 3D deep AutoEncoder (AE) to learn a target latent vector from ground truth 3D voxel grid and utilize the vector to penalize the latent vector encoded from the input 2.5D data. For the depth loss, we utilize the input 2.5D data to penalize the initial 3D voxel grid from 2.5D views. Afterwards, ELM transforms float values of the initial 3D voxel grid to binary values under a binary reconstruction loss. Experimental results show that DLGAN not only outperforms several state-of-the-art methods by a large margin on both a synthetic dataset and a real-world dataset, but also predicts more occluded parts of 3D objects accurately without class labels.

Three-dimensional particle shape characterizations from half particle geometries

Many three-dimensional (3D) imaging techniques, such as 3D laser scanner, stereophotography, and structured light techniques, can only capture upper half particle geometries in the camera view, and lower half particle geometries are occluded from the camera. This research aims to evaluate the accuracy of using half particle geometries to compute 3D particle shape descriptors. Computational geometry techniques are developed to compute eight commonly used particle shape descriptors automatically. Five coarse sand specimens are scanned by X-ray computed tomography and structured light to generate full 3D and half particle geometries, respectively. The convexity, diameter sphericity, and surface area sphericity computed from half particles overestimate these values computed from full 3D particles, which are corrected by statistical equations. The circularity, volume sphericity, intercept sphericity, sphere ratio sphericity, and roundness computed from half particles agreed excellently with these values computed from 3D particles.

Design and CFD analysis of an industrial fan for a concentrating high-temperature solar powerplant

The increasing request for the use of renewable energy sources leads to the study of different types of new alternative powerplants, one of them being the electricity generation by means of solar concentration powerplants with open volumetric receiver, using non-pressurized air as the heat transfer fluid. Due to the poor heat transfer characteristics of the fluid, a large air mass flowrate is needed in the solar tower to transfer a sufficient amount of heat to a conventional steam cycle. The aim of this study is to design a machine with 5 MW electrical power output and 1.125 compression ratio that is able to work in this severe environment. The compression needed by the forced convection circuit, requires verification of the relevance of the compressibility phenomena. The design start from the machine type selection and the sizing of the compressor, based on the standard mono-dimensional turbomachinery theory, and continue with the verification of the fluid dynamic performance of the fan, based on a commercial CFD code (ANSYS-FLUENT). A first 2D case is evaluated to ensure that the geometry is working correctly, then the full 3D geometry is simulated to quantify the real performance of the compressor. A preliminary structural analysis of the blade is also performed to verify the structural integrity of the chosen configuration.

Quantitative analysis of elemental depth on Wendelstein 7-X divertor baffle screws by picosecond laser-induced breakdown spectroscopy

Analysis of elemental distributions in plasma-facing components (PFCs) is vital for the study of material erosion, deposition, and fuel retention in Wendelstein 7-X (W7-X) stellarator operating in full 3D geometry. In this work, we report the results on the application of picosecond laser-induced breakdown spectroscopy (ps-LIBS) combined with laser-induced ablation quadrupole mass spectrometry (LIA-QMS) to quantitatively investigate the elemental depth distribution and fuel retention on the screws PFCs from the divertor baffle of W7-X. Depth profiles of H, C, Ti and Mo intensities on the screws with specific multilayer structures have been achieved by LIBS combined with LIA-QMS. A linear correlation approach has been applied for identifying the interface between the C layer and the Ti layer and shows that a laser ablation rate of (82.9 ± 0.9) nm/shot can be achieved on C layer thickness measurement by a laser energy density of 6.5 J/cm2. Moreover, quantitative H retention content on the surface of the screws with stellarator discharge plasma exposure is approximately 1.1 × 1021 atoms/m2 which is higher than approximately 3.5 × 1020 atoms/m2 on the surface of the new screw without plasma exposure. The studies well demonstrate the ability to determine elementary resolved layer thicknesses and H retention measurements by depth analysis of LIBS on PFCs exposed in W7-X.

Geometrical Details Matter for Mechanical Modeling of Cell Morphogenesis

Morphogenesis of wavy epidermal pavement cells in plants has fascinated researchers for decades. A mechanical mechanism had been proposed in which the anticlinal cell walls, forming the in-plane cell borders, feature contiguous stiff and soft zones that generate waves upon stretching. We replicated this model as designed and also expanded on it to test its validity for three-dimensional (3D) cell geometry. Our results suggest that both the assumptions going into and the predictions arising from this hypothesis do not stand closer scrutiny and may misguide experimentalists. Unlike what the published data seem to suggest, we observed that only waves of negligible magnitude can be formed by this anticlinal stretch model and that these are virtually eliminated when full 3D geometry of the cell is considered. Further, the model produces cell wall stresses that do not match the experimental evidence.