Pool Volume Research Articles

Modelling the influences of powder layer depth and particle morphology on powder bed fusion using a coupled DEM-CFD approach

Optimising the quality of metal parts produced by additive manufacturing requires an understanding of how the powder characteristics impact both layer spreading and the subsequent powder melting. Here we present a simulation study which couples models of powder spreading (by the Discrete Element Method) and powder bed fusion by laser beam (by CFD). Previous simulations of these processes have mostly assumed idealised smooth surfaces, spherical particles and a single laser track. Here we seek a more realistic description by spreading over a previously-melted (rough) surface and by melting a number of tracks laid side-by-side to mimic the crosshatched scans typically used during part production. The effects of powder morphology (via a range of particle shapes including spheres, disks, ellipsoids and cuboids) and layer depth on spreading and subsequent melting have been investigated. We find that the fraction of laser energy transferred to the part and the melt pool volume both increase rapidly with the volume of powder deposited, due to the combined effects of multiple laser reflections and the insulating nature of the powder layer. In contrast, particle shape has very little effect on the overall melting behaviour of the powder, with the volume deposited and uniformity of coverage being the key determining factors. These observations suggest that the use of cheaper non-spherical powders is feasible provided that a sufficiently uniform coverage can be achieved at small layer depths.

Two-stage radiosurgery for large brain metastases: a systematic review and meta-analysis of clinical outcomes.

Brain metastases (BMs) are the most common intracranial tumors. In several cases, they present as large masses, which are related to a worse prognosis and more complex therapeutic alternatives. Staged radiosurgery is reported to achieve local control with minimal radiation-related adverse events in BMs. However, no methodological consensus has been achieved in its use for large brain metastases (LBMs; > 2 cm). Therefore, the authors aimed to determine the effectiveness and safety of 2-stage Gamma Knife radiosurgery (GKRS) for LBMs, in order to optimize patients' postoperative course. A systematic review of available literature was run in PubMed/MEDLINE, Scopus, Web of Science, Cochrane (OvidSP), and Google Scholar for works published up to December 14, 2022. Nonrandomized clinical trials, case series, and cohort studies were included. The risk of bias was assessed using the Risk of Bias in Nonrandomized Studies-of Interventions (ROBINS-I) and Joanna Briggs Institute tools. Pooled mean difference and rates estimates were calculated by a random-effects model meta-analysis. The degree of heterogeneity was expressed using the I2 statistic. A subgroup analysis was performed. Ultimately, the certainty of evidence was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) assessment. Fourteen studies met the eligibility criteria (cohorts, case series, and nonrandomized clinical trials), including 958 patients. A total pooled mean volume reduction of 6.27 cm3 (95% CI 5.67-6.88 cm3) and 54.36% (95% CI 39.92%-68.79%) after 2-stage GKRS was reported. Pooled rates of complete response (44.63%; 95% CI 26.50%-64.31%), neurological mortality (16.19%; 95% CI 7.68%-30.98%), and all-cause mortality (47.92%; 95% CI 28.04%-68.49%) were calculated. Overall certainty of evidence ranged from very low to moderate. Two-stage GKRS is an effective and safe approach for the treatment of LBMs. Nevertheless, the lack of available literature and the weak methodological approaches used determine a low to very low certainty of evidence and cannot provide robust evidence to recommend this intervention. Therefore, it is necessary to conduct higher-quality primary studies.

Exploring Less Invasive Visual Surveys to Assess the Spatial Distribution of Endangered Mediterranean Trout Population in a Small Intermittent Stream.

Monitoring the conservation status of endangered freshwater fish using less invasive methods poses challenges for ecologists and conservationists. Visual surveys have been proposed as an alternative to electrofishing, which is a standard methodology that can cause injuries, physiological stress and post-release mortality in organisms. To test the efficacy of visual methods, a study was conducted in an intermittent stream of Sardinia (Italy). Two visual methods were employed: a visual survey from streambanks (VSS) and an underwater visual survey (UVS) using cameras. The aims of this study were (1) to compare the effectiveness of these methods in detecting patch occupancy patterns and (2) to investigate the effect of environmental variables on the detection probability of Mediterranean native trout. Environmental variables characterizing pool habitats were recorded, and generalized linear models (GLMs) were employed to assess the correlation between these variables and trout presence/absence. GLM analysis revealed that UVS had higher detection probability with larger pool volume, whereas submerged macrophytes negatively affected detection probability. Detection from streambanks (VVS) was negatively affected by a high turbulence rate. In conclusion, our study suggests the utility of visual methods to describe patterns of patch occupancy of Mediterranean trout. However, methods can be differently affected by environmental variables. Therefore, monitoring programs using these methods should consider these factors to ensure a reliable description of within-stream trout distribution in intermittent streams.

Impact of Dam Materials and Hydraulic Properties on Developing the Breaching Dimensions

Dam safety is an important issue as it directly influences environmental and life losses. Embankment material and embankment core are important factors that contribute to determining the size and hydraulic characteristics of the breach that occurs due to dam failure. The current topic is to present the analysis of the impact of the dam materials properties and hydraulic characteristics on breach dimensions due to overtopping failure using 2D-HEC-RAS software with the aid of RAS-Mapper. The analysis was made by Digital Elevation Model (DEM) conversed to a Triangular Irregular Network (TIN), then the 2D area of the dam was determined and the storage area boundary was calculated. Mosul dam in Iraq, considered one of the big dams that consist of different materials in the core and body, was selected as a case study to simulate the dam breach development due to overtopping failure. Six scenarios of dam failure were carried out for three types of dam materials (dam with corewall, concrete-face dam, and homogeneous zoned fill dam), each with high and medium erodibility. All scenarios were made for the reservoir elevation of 341 m which is considered the probable elevation for failure occurrence. The results showed that the minimum and maximum values of breach width were found to be 542 m and 1118 m, respectively in both cases of concrete-face dam type with a high erodibility and homogeneous zoned fill dam with medium erodibility rate. It has been illustrated that the medium erodibility in each scenario gives a smaller width for a long time, especially in homogeneous zoned fill dam type which is a good indication in engineering design. The analysis of sensitivity was carried out to examine the impact of pool volume at failure on breaching time and width of the breach. It showed that the breach width is more sensitive to reservoir fill capacity and there is a linear relationship between water volume reduction ratios and the breach width. Finally, tests of the six cases reveal that the proposed model is sensitive to soil conditions.

Effect of salt modulators on the elution behavior of insulin and the separation of product-related impurities in reversed-phase chromatography

In this work, the effect of the salt modulators potassium chloride, ammonium chloride, ammonium sulfate, and potassium sulfate on the elution behavior of insulin in reversed-phase chromatography with ethanol as the organic modifier was investigated. Without the addition of salt modulators, insulin shows the formation of multiple peaks under non-linear loading conditions, presumably due to an aggregate formation equilibrium. Flow rate and temperature did not influence the appearance of multiple peaks. The addition of chloride and sulfate salt modulators changed the monomer-multimer equilibrium, and multi-peak formation no longer occurred. Chloride salts induce a Langmuirian elution behavior, whereas sulfate salts induce additional insulin-insulin interactions resulting in an anti-Langmuirian elution behavior. The elution behavior can be influenced by the combination of both chloride and sulfate salts and by varying the concentration ratio. The separation with respect to two product-related impurities also showed significant differences under Langmuirian and anti-Langmuirian elution conditions and the purification of insulin could be optimized. Induced anti-Langmuirian elution by lowering the chloride/sulfate ratio suppresses an observed tag-along effect of one variant resulting in a slightly smaller pool volume with increased insulin concentration and a significantly increased insulin recovery.

Effect of powder properties on mesoscale thermal FEM simulations of powder bed additive manufacturing

Numerous studies have used FEM simulations to assess the effects of the heat source parameters on the melt pool volume during metal powder bed additive manufacturing. However, considerable debate still exists on how to incorporate the evolution of the thermophysical properties used to describe the powder as it undergoes heating, melting, consolidation and finally solidification. For single layer studies, since powder volume is much smaller compared to the substrate volume, highly detailed, computationally expensive powder property descriptions may not provide a commensurate increase in accuracy of simulation results. This study aims to quantify the effect of powder properties on the melt pool volume created during electron beam melting of Ti6Al4V powder using predictions from a FEM-based heat conduction model. The dependence of thermal conductivity, specific heat, and density of the powder on temperature and beam power density will be studied. Additionally, the relevance of the powder properties with changing layer height and beam power and speed will also be quantified.

A point field driven approach to process metrics based on laser powder bed fusion additive manufacturing models and in situ process monitoring

The widespread adoption of additive manufacturing (AM) in different industries has accelerated the need for quality control of these AM parts. Some of the complex and labor-intensive challenges associated with qualification and certification of AM parts are addressed by modeling and monitoring process conditions. Quantifying melt-track process conditions remains a significant computational challenge due to the large-scale differential between melt pool and part volumes. This work explores a novel point field (PF) driven AM model-based process metric (AM-PM) approach for calculating melt track resolved process conditions with maximal computational speed. A cylindrical Ti-6Al-4V test article with 16 equiangular zones having varied process parameters was built. The melt-track resolved AM-PMs were calculated and mapped to porosity existence for the 5.8-million-point PF of the test article. AM-PMs were calculated in 6.5 min, ~ 665 × faster than a similarly sized finite element calculation. This approach enables efficient prediction, assessment, and adjustment of AM builds.Graphical abstract

Predicting biomass of resident kōkopu (Galaxias) populations using local habitat characteristics.

With the global decline of freshwater fishes, quantifying the body size-specific habitat use of vulnerable species is crucial for accurately evaluating population health, identifying the effects of anthropogenic stressors, and directing effective habitat restoration. Populations of New Zealand's endemic kōkopu species (Galaxias fasciatus, G. argenteus, and G. postvectis) have declined substantially over the last century in response to anthropogenic stressors, including habitat loss, migratory barriers, and invasive species. Despite well-understood habitat associations, key within-habitat features underpinning the reach-scale biomass of small and large kōkopu remain unclear. Here, we investigated whether the total biomass of large (> 90 mm) size classes of each kōkopu species and the composite biomass of all small (≤ 90 mm) kōkopu were associated with components of the physical environment that provided refuge and prey resources across fifty-seven 50-m stream reaches. Because kōkopu are nocturnal, populations were sampled by removal at night using headlamps and hand-nets until reaches were visually depleted. Based on Akaike's information criterion, greater large banded kōkopu biomass was most parsimoniously explained by greater pool volume and forest cover, greater large giant kōkopu biomass by greater bank cover and pool volume, and greater large shortjaw kōkopu biomass by greater substrate size and pool volume. In contrast, greater composite small kōkopu biomass was best explained by smaller substrate size, reduced bank cover, and greater pool volume. Local habitat associations therefore varied among kōkopu species and size classes. Our study demonstrates the importance of considering the ontogenetic shift in species' habitat use and provides an effective modelling approach for quantifying size-specific local habitat use of stream-dwelling fish.

Pool Formation and The Role Of Instream Wood In Small Streams In Predominantly Second-growth Forests.

Extensive and intensive forest harvesting during the 20th century often had, and continues to have, negative impacts on stream structure and ultimately fish. Loss of instream wood and pools has been identified as a pathway by which riparian forest management can negatively impacts salmonids. Passive riparian restoration (allowing forests and streams to recover through natural processes) through the use of riparian buffers when conducting forest harvests has often been employed to promote stream habitat recovery. In this study, we evaluate the effects of 25 years of passive restoration on instream wood and pool recovery in 74 reaches in small streams (1st through 3rd order) across three channel types (pool-riffle, step-pool, and cascade) in a predominantly second-growth forest. Gradient and stream size were the most important variables for determining pool density, while stream size was the most important variable for determining pool depth. Instream wood formed 39% of pools in pool-riffle, 30% of pools in step-pool and 25% of pools in cascade channels types. Instream wood volume had a significant (R2 = 0.261, P ≤ 0.001) positive relationship with pool volume in wood-formed pools. Dimensions of individual wood pieces were associated with their likelihood of pool formation: for each additional 1 meter length within the bankfull channel the odds of forming a pool increased by 25.6%, and for each additional centimeter in diameter the odds of pool formation increased by 2.0%. When compared with studies conducted in both second- and old-growth forests, we concluded that streams associated with second-growth forests hadve both reduced densities and sizes of instream wood and pools. Young forests are likely continuing to negatively impact stream habitat and fish populations. Because riparian zones in many forests are now dominated by relatively young forest stands, and given the timeline for recovery using passive restoration alone (e.g., 100 s of years in Pacific Coastal forests), active restoration could be explored to accelerate instream wood and pool recovery.

Can angiographic Flat Detector Computed Tomography blood volume measurement be used to predict final infarct size in acute ischemic stroke?

Introduction and purposeFlat detector computed tomography (FD-CT) technology is becoming more widely available in the angiography suites of comprehensive stroke centers. In patients with acute ischemic stroke (AIS), who are referred for endovascular therapy (EVT), FD-CT generates cerebral pooled blood volume (PBV) maps, which might help in predicting the final infarct area. We retrospectively analyzed pre- and post-recanalization therapy quantitative PBV measurements in both the infarcted and hypoperfused brain areas of AIS patients referred for EVT. Materials and methodsWe included AIS patients with large vessel occlusion in the anterior circulation referred for EVT from primary stroke centers to our comprehensive stroke center. The pre- and post-recanalization FD-CT regional relative PBV (rPBV) values were measured between ipsilateral lesional and contralateral non-lesional areas based on final infarct area on post EVT follow-up cross-sectional imaging. Statistical analysis was performed to identify differences in PBV values between infarcted and non-infarcted, recanalized brain areas. ResultsWe included 20 AIS patients. Mean age was 63 years (ranging from 36 to 86 years). The mean pre- EVT rPBV value was 0.57 (±0.40) for infarcted areas and 0.75 (±0.43) for hypoperfusion areas. The mean differences (Δ) between pre- and post-EVT rPBV values for infarcted and hypoperfused areas were respectively 0.69 (±0.59) and 0.69 (±0.90). We found no significant differences (p > 0.05) between pre-EVT rPBV and ΔrPBV values of infarct areas and hypoperfusion areas. ConclusionAngiographic PBV mapping is useful for the detection of cerebral perfusion deficits, especially in combination with the fill run images. However, we were not able to distinguish irreversibly infarcted tissue from potentially salvageable, hypoperfused brain tissue based on quantitative PBV measurement in AIS patients.

Aquatic Systems of the Wichita State University Biological Field Station: Youngmeyer Ranch, Elk County, Kansas

Intermittent streams and rivers account for over half of the world's waterways and yet they are still vastly understudied compared to permanent streams and rivers. Wichita State University Biological Field Station: Youngmeyer Ranch presents an opportunity to study intermittent streams and stream pools across 1902 hectares of Flint Hills tall grass prairie ecosystems. We used a freely available satellite imagery program (Google Earth Pro©) to map and provide an initial inventory of streams, intermittent stream pools, and cattle ponds. We also used historic images to create connectivity (percent of downstream length with water) and hydroperiod indices (number of years out of four that pools held water). In total, we mapped 58.2 km of major (2nd to 3rd order) and minor (1st order) streams, and 13 cattle pond impoundments on the property. We used a systematic random sample to select a subset of seven stream reaches (out of 83) within the property for on-the-ground surveys of intermittent stream pools. Within selected streams, a subset of 117 stream pools were sampled in the summer of 2020 and data was collected on the average stream pool width, max depth, length, volume, and biological communities. Stream pools averaged 6.5 ± 9.7 m3 (mean ± SD) in volume, 12.50 ± 9.3 m in length, 2.97 ± 1.7 m in width, and 0.38 ± 0.26 m in depth. Stream and stream pool permanence varied widely across the landscape with pools holding water 3.2 ± 0.8 out of the four years with high resolution satellite imagery. We provided an initial baseline of aquatic systems at Youngmeyer Ranch and characterized representative intermittent stream pools in the Flint Hills and the Great Plains. We also demonstrated the viability of using Google Earth Pro© for mapping and taking inventory of aquatic systems without proprietary software or on-site access.

Resultant physical properties of as-built nitinol processed at specific volumetric energy densities and correlation with in-situ melt pool temperatures

In this study, direct comparisons between the properties of three groups of as-built nitinol (NiTi) samples fabricated using three pre-determined volumetric energy densities (VED) as calculated based on hatch spacings (VEDH = 40, 80, and 120 J/mm3), were examined. The additive manufacturing technique adopted is the powder bed fusion using a laser beam (PBF-LB), and the powder feedstock is Ni50Ti50. Although the three VEDH's increased by 100% for each sample group, each VEDH value was within the range of those recommended in the literature, as well as equivalent to 100 J/mm3 (VEDf), VED as calculated based on laser spot size. Significant differences were found between the thermal profiles and normalised thermal gradients, resulting in compositional differences, defects, phase, and phase transformation behaviour, Young's modulus, hardness, and microstructure. Thermal gradients and full-wave amplitude of the in-situ melt pool thermal radiation waveforms increased as VEDH increased. Higher VEDH's resulted in more martensitic NiTi samples with larger melt pool volume and >98% sample relative density. Austenite transformation temperatures increased with an increase in at.% Ti for each increase in VEDH, consequent on the higher normalised average melt pool temperatures. The calculated thermal gradient (normalised) was correlated to higher thermal stresses as VEDH increased, resulting in residual stress-induced weld-metal liquation microcracks. This work has demonstrated the potential of post-processed in-situ melt pool thermal radiation data, in providing insights into the physical property variations of as-built nitinol samples fabricated via PBF-LB.

Spatial variations and pools of non-structural carbohydrates in young Catalpa bungei undergoing different fertilization regimes.

Despite the importance of non-structural carbohydrates (NSC) for growth and survival in woody plants, we know little about whole-tree NSC storage. Here, Catalpa bungei trees fertilized using different schedules, including water and fertilizer integration, hole application, and no fertilization, were used to measure the spatial variations of sugar, starch, and NSC concentrations in the leaf, branch, stem, bark, and root. By calculating the volume of whole-tree NSC pools and the contribution of distinct organs, we were also able to compare the storage under various fertilization regimes. We found that the spatial distribution patterns of each organ undergoing different fertilization regimes were remarkably similar. Height-related increases in the sugar and NSC concentrations of the leaf and bark were observed. The concentrations of sugar and NSC in the branch did not appear to vary longitudinally or horizontally. The sugar and NSC concentrations in the stem fluctuated with height, first falling and then rising. The coarse root contained larger amounts of NSC components in comparison to fine root. Contrary to no fertilization, fertilization enhanced the distribution ratio of the leaf, branch, and stem NSC pools while decreasing the distribution ratio of the root NSC pool. Particularly, the addition of fertilizer and water significantly increased the biomass of the organs, enhancing the carbon sink of each organ and whole-tree in comparison to other fertilization regimes. Our main goal was to strengthen the empirical groundwork for comprehending the functional significance of NSC allocation and stock variations at the organ-level of C. bungei trees.

The Effect of Reporting Opacity on Trading Opacity: New Evidence from American Depositary Receipt Trades in Dark Pools*

ABSTRACTTrading volume is increasingly shifting to dark venues, and the causes of this move are not well understood. We examine whether a firm's reporting opacity affects its dark pool trading and provide robust evidence that (partly) explains this volume migration. Exploiting the exogenous variation in home‐country reporting opacity in a sample of American Depositary Receipts (ADRs) and using multiple metrics for reporting opacity, we find that greater opacity associates with increased dark pool trading. This relation holds after controlling for firms' information environments, country‐specific governance issues, observable differences between ADRs and other securities that trade in dark pools (matched sample analysis), volume migration to dark pools during earnings announcements, informed trading in lit versus dark venues, ADR levels, IFRS reporting requirements, and the possible endogenous determination of home‐country reporting opacity and dark pool volume. The positive relation is stronger for ADRs held by (quasi‐indexing) institutions with low turnover and diversified holdings and weaker for ADRs favored by (transient) institutions that trade frequently and (dedicated) institutions that hold concentrated portfolios. Bid‐ask spreads are greater for higher opacity ADRs that trade in dark pools, indicating that reporting opacity is associated with the negative effect of dark pool trading on market quality. Our findings help inform the current debate on off‐exchange trading by showing how reporting regimes affect the trading venue choice.

New heat source model for accurate estimation of laser energy absorption near free surface in selective laser melting

As the absorption energy distribution is mainly determined by the heat source modelling, a heat source model capable of estimating precisely the distribution of absorbed laser energy is essential for the accuracy and reliability of computational simulations. In most existing mesoscale selective laser melting (SLM) modelling with ray tracing technology, laser energy has been treated as a surface heat source and laser energy absorption only occurs at reflection points in surface elements, leading to unphysical absorption energy distribution and localized temperature overestimation with extremely high peak. Here we propose a new heat source model incorporating both laser penetration and ray tracing, and accurately estimate the absorption energy distribution by calculating the laser energy attenuation during laser propagation in metal. The modified ray tracing scheme constructed here is capable of tracing ray propagation through different media and across interfaces. Computational simulations on SLM with different powder bed densities are carried out. Compared to the conventional surface heat source model in SLM simulations, our new heat source model reduces the high peak temperature of elements with low liquid volume fraction, guarantees the simulation success and eliminates the overestimation of the evaporation heat loss. Melt pool volume and depth as well as the recoil pressure is also characterized. A comparison between simulations and experimental results indicate that the proposed new heat source model is also capable of simulating the surface temperature of metal substrates upon heating pulse. In addition, keyhole morphologies from experimental observation and numerical simulations based on the proposed model are in good agreement.

A mean platelet volume in inflammatory bowel disease: A systematic review and meta-analysis.

BackgroundInflammatory bowel disease (IBD) is a chronic gastrointestinal tract inflammatory state, which is affecting millions of individuals in the world. It can affect alimentary canals such as colon, rectum, ileum and other parts. In IBD, platelet parameters underwent several changes. Therefore, the aim of this review was determining the estimated pooled mean platelet volume and mean difference in inflammatory bowel disease to elucidate its potential diagnostic value.MethodsArticles were extensively searched in bibliographic databases using Medical Subject Heading and entry phrases or terms. In addition, articles were directly searched in Google Scholar to account for the studies omission in searching bibliographic databases. Observational (cohort, cross-sectional and case-control) studies, published in English language and conducted on IBD were included. For studies meeting the eligibility criteria, the first author’s name, publication year, population, study design, study area, sample size, mean platelet volume and standard deviation were extracted and entered in to Microsoft-excel. The analysis was done by Stata version 11. In order to estimate the pooled mean platelet volume and mean difference, random effect model was done. The heterogeneity was quantified using Higgin’s I2 statistics. Publication bias was determined using Egger’s test statistics and funnel plot. Sub-group analysis based on population carried to reduce heterogeneity.ResultsA total of 17 relevant articles with 2957 participants (1823 IBD cases and 1134 healthy controls) were included to this study. The pooled estimated MPV was 9.29fl; 95% CI: 9.01–9.57 and 9.50fl; 95% CI: 8.81–10.20 in IBD and control groups, respectively. The standardized pooled estimate of mean difference in mean platelet volume was -0.83fl; 95% CI: -1.15, -0.51; I2: 93.1%; P-value < 0.001. In subgroup analysis based on population, the highest estimated mean difference in MPV was observed among patients of CD; -2.30; 95% CI: -3.46, -1.14; I2: 97.8%; P-value < 0.001.ConclusionAccording to the current systematic review and meta-analysis, mean platelet volume was lower in IBD compared to control. The decreased mean platelet volume could be attributed to platelet consumption or sequestration associated with the progression of IBD. As a result, in IBD, mean platelet volume can provide diagnostic and prognostic information.

An effective method for large-scale temperature simulation in SLM based on the finite difference

Numerical simulation is an effective approach to analyze the selective laser melting (SLM) process and reduce the production development cost. Based on the finite difference method (FDM), the nonuniform grid algorithm (NUGA) is developed to simulate the thermal behavior in SLM process concerning the variable thermophysical parameters of materials with different status. The NUGA can effectively improve computing efficiency, and the calculation speed using NUGA is 610 times than that without using NUGA. Different heat transfer strategies are used on each side of the two critical scanning speeds, 68.95 mm/s and 6895 mm/s, respectively, and the results of temperature calculations are highly consistent. The correctness of the heat transfer strategy under different speeds is analyzed using the NUGA. The effects of processing parameters (laser power, scanning speed and building height) on the shape and volume of the molten pool are investigated. As the scanning speed ranged from 100 mm/s to 500 mm/s, the width and depth of the molten pool decrease, while the length increases. As the laser power ranged from 100 W to 500 W, the length, width and depth of molten pool all increase. The length of the molten pool increases 11.68% from 264.94 of layer 1 to 295.88 of layer 5. The molten pool volume decreases, then increases and decreases finally from the start to the end of single molten path. The molten pool volume increases with increasing laser power and building height, while decreases with increasing scanning speed in general. The NUGA is an effective method for temperature simulation of large-size parts, which expands the application range of temperature simulation in SLM process.

A thermophysical modelling of electric discharge coating process

This research paper presents a thermophysical model development and simulation of the electric discharge coating process (EDC). Many literature are available for the electric discharge coating process from an experimental perspective. A 2-D axisymmetric model was initially developed with the realistic assumption with multispark overlap conditions considered in this work. The melt pool volume of the tool material is estimated from the 2D model. The 3D coating model was developed using COMSOL Multiphysics 5.4. This model predicts the temperature distribution on the green compact tool electrode and coating thickness on the substrate. To validate the simulation model, the experimental result from the literature is compared with the simulation result. The simulation and validation trials results reveal that the present developed coating model can predict the coating thickness with minimum error (4%–14%). The developed multispark model for the EDC process can be referenced to understand the coating mechanism for various tools and workpiece materials.

Экспериментальное и численное исследование теплообмена при выращивании тонкостенных деталей методом коаксиального лазерного плавления

Computer modeling of the thermal behavior of a thin-walled part made of austenitic 316L stainless steel, grown by coaxial laser melting with variable and constant laser power, has been simulated. The conducted work was aimed at investigating the effect of the number of weld deposit layers and studying the influence of bending radius in heat patterns of the growing zone, taking into account a molten pool volume.

Sensing and characterization of backside weld geometry in surface tension transfer welding of X65 pipeline

With the exploitation of marine oil and gas resources, steel catenary risers (SCR) have been widely used worldwide, which has promoted the development of automatic pipeline welding technology. Root-pass welding is critical in the pipeline welding process, since the resulting backside weld geometry largely affects the corrosion resistance and fatigue properties of the pipeline. STT (surface tension transfer) welding has been one of the main methods of root-pass welding for pipeline, in which the short-circuiting period, peak current period and base current period can be identified clearly. A signal sensing method based on the change in arc voltage during the peak current period (ΔU¯) was proposed to characterize the backside weld pool geometry with the help of heat amount inputted to the pipe in 1 s (J). Unlike pulsed gas metal arc welding (GMAW-P), the peak arc force of the short-circuiting transfer was not large enough or was not with sufficient time to excite the weld pool oscillation with a large amplitude, further to affect the backside weld height and width to a great extent. Thus, J, which has a great influence on the weld pool volume (that will determine the backside weld pool geometry to some extent when full penetration occurs) in the low current range, was introduced and was included to corresponding models to characterize the backside weld pool geometry jointly with ΔU¯. The results showed that the models were accurate under the welding parameters and conditions in the present work, which could be applied in the subsequent prediction and control of backside weld geometry in the STT welding.