High Energy Content Research Articles

Successive variational nonstationary mode decomposition for bearing multi-fault diagnosis undertime-varying speed conditions

Rolling bearings are important components in mechanical machinery, and their failure will directly affect the normal operation of the machine. Therefore, the analysis of mechanical machinery vibration signals is crucial for ensuring the normal operation of the machinery. Successive variational mode decomposition (SVMD) is an important technique for decomposing a bearing stationary signal into its characteristic modes with a priori penalty factor. Therefore, it cannot handle nonstationary bearing signals. To tackle the above problems, a novel method, named successive variational nonstationary mode decomposition (SVNMD), is developed in this article. First, a new decomposition framework is proposed by adopting the constructed resampling operator to modify the optimization function of the SVMD, which eliminates the influence of frequency mixing. Second, in order to automatically determine the optimal penalty factor, an iterative selection scheme is developed, which is free from prior knowledge. Third, an instantaneous frequency estimation theory is proposed to obtain the common trend function of the signal. Finally, a time-frequency representation with high-energy concentration is obtained to accurately identify the fault characteristics of rolling bearings. Both the simulation and experimental verification have confirmed the productiveness of the SVNMD in diagnosing multiple faults of bearings under time-varying speed conditions.

Unlocking the Ultrafast Deposition Kinetics within Bi‐Tailored Core‐Shell Structured Carbon Nanofibers for Highly Efficient and Ultrastable Sodium Metal Batteries

Sodium metal anodes (SMA), featuring high energy content, low electrochemical potential and easy availability, are a compelling option for sustainable energy storage. However, notorious sodium dendrite and unstable solid‐electrolyte interface (SEI) have largely retarded their widespread implantation. Herein, porous amorphous carbon fiber embedded with Bi nanoparticles in nanopores (Bi@NC) was rationally designed as a 3D host for SMA. In‐situ and ex‐situ characterizations, along with theoretical simulations unlock that the in‐situ formed Na‐Bi alloy significantly accelerates sodium metal nucleation and sodium ion diffusion kinetics, enabling uniform sodium plating within the void spaces and a stable SEI outside the carbon fiber. Particularly, the Bi@NC electrode achieved a high Coulombic efficiency of 99.99% at 3 mA cm‐2 and 3 mAh cm‐2 in half‐cell tests, a cycle life of 1000 hours at 5 mA cm‐2 and 10 mAh cm‐2, and sustained performance over 600 cycles under harsh conditions under 30 mA cm‐2 and 3 mAh cm‐2 within symmetrical cells. The full battery assembled with a Na3V2(PO4)3@C cathode and Bi@NC anode delivered long‐term cyclability over 800 cycles, demonstrating its potential for flexible application of sodium‐based energy storage systems. This work highlights the Bi@NC electrode as a promising candidate for high‐performance and flexible sodium metal batteries.

Unlocking the Ultrafast Deposition Kinetics within Bi-Tailored Core-Shell Structured Carbon Nanofibers for Highly Efficient and Ultrastable Sodium Metal Batteries.

Sodium metal anodes (SMA), featuring high energy content, low electrochemical potential and easy availability, are a compelling option for sustainable energy storage. However, notorious sodium dendrite and unstable solid-electrolyte interface (SEI) have largely retarded their widespread implantation. Herein, porous amorphous carbon fiber embedded with Bi nanoparticles in nanopores (Bi@NC) was rationally designed as a 3D host for SMA. In-situ and ex-situ characterizations, along with theoretical simulations unlock that the in-situ formed Na-Bi alloy significantly accelerates sodium metal nucleation and sodium ion diffusion kinetics, enabling uniform sodium plating within the void spaces and a stable SEI outside the carbon fiber. Particularly, the Bi@NC electrode achieved a high Coulombic efficiency of 99.99% at 3 mA cm-2 and 3 mAh cm-2 in half-cell tests, a cycle life of 1000 hours at 5 mA cm-2 and 10 mAh cm-2, and sustained performance over 600 cycles under harsh conditions under 30 mA cm-2 and 3 mAh cm-2 within symmetrical cells. The full battery assembled with a Na3V2(PO4)3@C cathode and Bi@NC anode delivered long-term cyclability over 800 cycles, demonstrating its potential for flexible application of sodium-based energy storage systems. This work highlights the Bi@NC electrode as a promising candidate for high-performance and flexible sodium metal batteries.

Study of the Combustion Characteristics of a Compression Ignition Engine Fueled with a Biogas–Hydrogen Mixture and Biodiesel

Increasing the use of renewable energy sources is essential to reduce the use of fossil fuels in internal combustion engines and to reduce greenhouse gas emissions. An experimental and numerical simulation study of the combustion process of a compression ignition engine was carried out by replacing fossil diesel with a dual fuel produced from renewable energy sources. In conventional dual-fuel applications, fossil diesel is used to initiate the combustion of natural gas or petroleum gas. In the present study, fossil diesel was replaced with advanced biodiesel – hydrotreated vegetable oil, and natural gas was replaced with biogas. In the experimental study, a gas mixture of 60% natural gas (by volume) and 40% carbon dioxide (by volume) was used to replicate the biogas while maintaining a 40%, 60%, and 80% gas energy share in the fuel. It was observed that using fossil diesel and biogas in the dual-fuel engine significantly slowed down the combustion process, which normally resulted in poorer energy performance. One way to compensate for the lack of energy (due to the presence of carbon dioxide) in the cylinder is to use a gas such as hydrogen, which has a high energy content. To analyze the effect of hydrogen on the dual-fuel combustion process, hydrogen gas was added to the replicated biogas at 10%, 20%, and 30% of the natural gas volume, maintaining the biogas at a (natural gas + hydrogen)-to-carbon dioxide volume ratio of 60%/40% and the expected gas energy share. The combustion process analysis, which was conducted using the AVL BOOST software (Austria), determined the heat release rate, temperature, and cylinder pressure rise in the dual-fuel operation with different renewable fuels and compared the results with those of fossil diesel. It was found that when the engine was operated at medium load and with the flammability of the biogas approaching the limit, the addition of hydrogen significantly improved the combustion characteristics of the dual-fuel engine.

Generalized reassigning transform: Algorithm and applications

Time-frequency analysis (TFA) has attracted the attention of many scholars and engineers for analyzing nonstationary signals in the field of condition monitoring of rotating machinery. For complex mechanical equipment, measured signals always contain both harmonic and impulsive components, which presents a challenge for current TFA methods. To concurrently characterize harmonic and impulsive components, a novel TFA algorithm, called generalized reassigning transform (GRT) is developed in this paper. First, the time-frequency fusion extraction criterion (TFFEC), which includes time-frequency data fusion (TFDF) and time-frequency data extraction (TFDE), is designed to calculate time-frequency representation (TFR) from short-time Fourier transform (STFT) results under different window sizes, which improves time-frequency resolution and eliminates noise influence. Furthermore, the chirp rate (CR)-based postprocessing strategy is constructed to characterize nonstationary signals with both harmonic-like and impulsive-like components. Specifically, the CR discrimination criterion is introduced to classify the TFFEC result into two distinct types: harmonic-like component and impulsive-like component, and then, the TFR with high energy concentration and strong readability is obtained by advanced postprocessing TFA including the synchro-reassigning transform (SRT) and horizontal reassigning transform (HRT). The effectiveness of the GRT in condition monitoring and fault diagnosis is validated through numerical and experiment verification.

Nutritional value and quality indicators of bulk feed in the Vologda region according to the requirements of new State National Standards

The main requirements for the quality of bulk feed when feeding dairy cattle have been provided in the article. Silage and silazhe are succulent feeds that form the basis of the ration in dairy farming, they account for up to 80 % of its structure. The relevance of the research lies in the need to test succulent feeds and study their nutritional value, chemical composition, quality indicators for modeling and adjusting the feeding rations of highly productive dairy cows under the new State National Standard requirements. The purpose of the work was to study the nutritional value and quality indicators of succulent feed in the Vologda region according to the requirements of the new State National Standard. The studies were carried out in 2019–2023 at agricultural enterprises of the Vologda region. The object of the research was succulent feed (silage and silazhe) prepared on farms. When studying the dynamics of the nutritional value and chemical composition of succulent feed used in the Vologda region, general trends have been observed. Over a number of years, the harvested feed has consistently high crude protein and metabolic energy content, and consistently low crude fiber and crude ash levels. The content of metabolic energy in dry matter of silage during the study period was 9.9–10.7 MJ/kg, crude protein 9.5–16.8 %, crude fiber 13.8–28.5 %, dry matter 203.1–257.9 g/kg. In order to improve the quality of harvested feed, it is necessary to strengthen measures to increase the proportion of dry matter in all types of silage, and also to pay special attention to the technology of harvesting silage from corn.

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

AbstractDiarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens up an entire new structure and property space expanding the versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached in up to 87 % upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state also serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of our aza‐diarylethene in a materials application.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Numerical study on inter-particle effects for multiple reacting biomass and coal particles based on Micro-CT morphology

Co-firing of biomass with coal combines the environmental benefits of renewable biomass with the high energy content of coal. Although the common numerical simulation treats the biomass and coal particles with ideal morphology, real particles often demonstrate nonsmoothed surface and irregular shape. To understand the impact of particle morphology in a group of biomass and coal particles co-firing together and to inform simple models appropriate, this study investigated the interparticle effects among particles using realistic particle morphology, focusing on fluid dynamics such as temperature distribution, flow patterns and drag coefficients. Particle-scale computational fluid dynamics (CFD) simulations using micro-CT imaging showed that realistic particle shapes resulted in nonuniform flow fields and temperature distributions with different reaction intensities due to the species transportation. It is in contrast to traditional ideal shape models, which often rely on simplified spherical representations of particles and cannot capture the intricacies of real particle shapes. Realistic models revealed more complex surfaces, highly irregular particle structures, and varied reaction zones that affected the overall dynamics. In addition, changing the orientation of one particle affects the combustion characteristics of neighboring particles. This effect is also not captured while using the spherical structure. These differences underscore the critical impact of particle morphology on drag and heat transfer, thereby challenging conventional spherical models. The findings of this study advocate for a paradigm shift in CFD modeling approaches, emphasizing the importance of realistic particle representation to improve the accuracy of predictions and enhance the co-firing system efficiency.

To investigate the effect of discharge energy and addition of nano-powder on processing of micro slots using EDM assisted µ-milling operation

ABSTRACT Micro-electric Discharge-Milling (µ-ED-M) is a non-contact process that uses an electrical spark to remove the material from a submerged workpiece with an electrode in a dielectric. The present paper focuses on optimizing process energizing (Capacitor, Voltage) and process stabilizing (Tool Travel Speed, Nano-Powder) parameters for controlling the size and surface characteristics of micro-crater. The present work focuses on the effect of nano-powder concerning dimensional aspects and surface characteristics at high and low capacitance levels. A µ-slot has been generated on the copper material by a tungsten carbide electrode. The experimentation is performed with two capacitor levels and three voltage and tool travel speed levels using full factorial design technique using with and without mixing of nano-powder in dielectric. The desirability functional multi-objective optimization approach is used to analyze the MRR, TWR, Width, and Depth. Field emission scanning electron microscopy (FESEM), non-contact optical profilometer, and x-ray diffraction (XRD) techniques are used to analyze the surface morphology of machined surfaces. The ANOVA is used to optimize the results; at low discharge energy, tool travel speed contributes 41% and promotes a higher thickness of recast layer 12.7 µm, whereas high discharge energy and nano-powder concentration contribute approx.—36% with 8.56 µm of recast layer.

Association of ultra-processed food consumption with cardiovascular risk factors among patients with type-2 diabetes mellitus

BackgroundUltra-processed foods mainly have high energy content and density and low nutrients. Unhealthy lifestyles mainly develop cardiovascular diseases and, as a result, unhealthy food patterns.ObjectiveThis study aimed to investigate the relationship between the consumption of ultra-processed foods (UPFs) and the risk of novel cardiovascular disease (CVDs) in type-2 diabetes mellitus patients (T2DM).MethodThis is a cross-sectional study that was conducted on 490 type-2 diabetes mellitus patients. A validated 168-item food frequency questionnaire evaluated food intake. Ultra-processed foods were assessed according to NOVA classification. Cardiovascular risk factors such as Castelli risk index 1 and 2 (CRI-I and II), atherogenic index of plasma (AIP), lipid accumulation product (LAP), and cholesterol index (CI) were assessed by traditional CVD risk factors. The anthropometric indices predicting CVD, such as a body shape index (ABSI), body roundness index (BRI), and abdominal volume index (AVI), were assessed.ResultsEach 20-gram increase in UPF consumption was associated with a significant elevation in serum level of TC [B (SE): 1.214 (0.537); 95% CI: 0.159–2.269] and lower HDL serum concentration [B (SE): −0.371 (0.155); 95% CI: −0.675 to −0.067]. The crude model for CRI 1 [B (SE): 0.032 (0.012); 95% CI: 0.009–0.056], CRI 2 [B (SE): 0.022 (0.009); 95% CI: 0.004–0.040], and AIP [B (SE): 0.006 (0.003); 95% CI: 0.000–0.012] showed significant adverse effects.ConclusionsOur study showed that higher consumption of UPFs is associated with higher chances of developing cardiovascular diseases in T2DM patients.

Assessment of Fuel Wood Consumption and Its Effect on Forest Depletion in Dry Deciduous Forest of Haliyal Taluk, Uttar Kannada District, India

Forest plays a significant role in extending wood and non-wood resources around the world, Forests provide ecosystem services, such as timber, food, fuel, fodder, non-wood products and shelter, which are essential for human well-being. However the increasing demand and pressure on forest resources majorly like fuel wood lead to degradation of forests. Hence it is important to assess the fuel wood consumption pattern and its impact on the forest for sustainable management of resources. In the present study, Haliyal taluk was selected, the area which is under rapid urbanization, surrounded by dry deciduous forest and the people living in that area depend on forest for fuel wood consumption. The study examined fuel wood collection among different farmer categories: large, medium, small, and landless. Results from the semi structured questioner survey revealed that medium farmers collected the most fuel wood. The total fuel wood consumption in Haliyal taluk was 5232.2 tonnes, with an average household consumption of 2.60 quintals of fuel wood per year. Major preferred tree species for fuel wood were Xylia xylocarpa, Terminalia tomentosa and Lagerstroemia lanceolata, which are valued for their high energy content, favourable burning characteristics and availability. For estimation of forest degradation Randomized Block Design was used and the study classified the forest vegetation into four crown density classes: Very Dense Forest (T1), Moderately Dense Forest (T2), Open Forest (T3), and Scrub (T4). Data was collected from 20 plots (20 x 20 m each) across these classes to measure forest depletion. The results showed that statistically significant differences in degradation levels, with the highest depletion (31.56 m³/ha) in very dense forests followed by moderate depletion (6.75 m³/ha) in moderately dense forests and the lowest (2.4 m³/ha) in scrub forests. This pattern reflects greater anthropogenic pressures and higher fuel wood availability in more dense forest types.

Medium-chain fatty acid receptor GPR84 deficiency leads to metabolic homeostasis dysfunction in mice fed high-fat diet.

Overconsumption of food, especially dietary fat, leads to metabolic disorders such as obesity and type 2 diabetes. Long-chain fatty acids, such as palmitoleate are recognized as the risk factors for these disorders owing to their high-energy content and lipotoxicity. In contrast, medium-chain fatty acids (MCFAs) metabolic benefits; however, their underlying molecular mechanisms remain unclear. GPR84 is an MCFA receptor, particularly for C10:0. Although evidence from invitro experiments and oral administration of C10:0 in mice suggests that GPR84 is related to the metabolic benefits of MCFAs via glucose metabolism, its precise roles invivo remain unclear. Therefore, the present study investigated whether GPR84 affects glucose metabolism and metabolic function using Gpr84-deficient mice. Although Gpr84-deficient mice were lean and had increased endogenous MCFAs under high-fat diet feeding conditions, they exhibited hyperglycemia and hyperlipidemia along with lower plasma insulin and glucagon-like peptide-1 (GLP-1) levels compared with wild-type mice. Medium-chain triglyceride (C10:0) intake suppressed obesity, and improved plasma glucose and lipid levels, and increased plasma GLP-1 levels in wild-type mice; however, these effects were partially attenuated in Gpr84-deficient mice. Our results indicate that long-term MCFA-mediated GPR84 activation improves the dysfunction of glucose and lipid homeostasis. Our findings may be instrumental for future studies on drug development with GPR84 as a potential target, thereby offering new avenues for the treatment of metabolic disorders like obesity and type 2 diabetes.

Laboratory study of energy transformation characteristics in breaking wave groups

The spilling-breaking waves that appear in chirped wave packets are studied in a two-dimensional wave channel. These waves are produced by superposing waves with gradually decreasing frequencies. The analysis focuses on the nonlinear characteristics, energy variation, and energy transformation during the evolution and breaking of wave groups. Ensemble empirical mode decomposition is used to analyze the non-breaking and breaking energy variations of the intrinsic mode functions (IMFs). It is found that the third-order IMF component is a source of non-breaking energy dissipation and the second-order IMF, which represents a short wave group with a relatively higher energy content, is a primary source of the energy loss caused by wave breaking. Additionally, the findings reveal that among the three waves preceding the maximum crest, the wave closest to the maximum crest carried most of the energy. When wave breaking occurs, the energy dissipation caused by the wave breaking primarily originates from that wave. After wave breaking, whether it is the first breaker or subsequent breakers, the main energy dissipation occurs in a frequency range higher than the dominant frequency. This energy loss plays a significant role in increasing the energy of free waves. Moreover, a potential link between the number of carrier waves and wave breaking phenomena has been found. As the number of carrier waves increased, both the nonbreaking and breaking energy dissipation rates exhibited an overall increasing trend. The amount of nonbreaking energy dissipation was generally more than twice the breaking energy dissipation rate. For wave groups with more carrier waves, the modulation instability plays a significant role in generating larger waves. Furthermore, an analysis of the dominant frequency variations of the wave group before wave breaking suggests that wave breaking is not a sufficient condition for a frequency downshift in the wave spectra.

Analysis of Energy Transfer in the Ignition System for High-Speed Combustion Engines

In order to produce reliable and reproducible ignition of lean fuel–air mixtures and highly stratified mixtures, it is necessary to ensure a high concentration of spark discharge energy and to provide a strong energy impulse for the triggering of chain processes of chemical decomposition of fuel molecules. For this reason, studies have been undertaken on the flow of electrical energy from the ignition system to the spark plug and on the formation of an electric discharge arc with a high concentration of thermal energy. The experimental results were obtained using an ignition coil energy test stand and a constant volume chamber with high-speed spark discharge recording capability. It was confirmed that increasing the charging time of the ignition coil from 0.5 ms to 5.0 ms increases the energy delivered to the coil from 9.5 mJ to 330 mJ. In the same range, the energy generated by the coil was recorded to range from 4.2 mJ to 70 mJ. The coil’s efficiency was found to decrease with increasing charging time from 45% up to 20.5%. Further energy losses were presented when the spark discharge energy was analyzed. In the paper, the results of investigations concerning electric discharge arc development have been presented, illustrated by a few exemplary photos, and discussed. The mathematical interpretation of the electrical energy flux in the ignition system resulting from the energy of the discharge arc has been conducted and illustrated by some functional independences and relationships.

A novel route to produce metal or ceramic parts in space: local debinding and sintering of powdered filaments

AbstractIn-space manufacturing of polymer feedstocks has already been shown using the widely investigated filament extrusion additive manufacturing (AM) technology. Yet, polymers are only a small piece of the puzzle, and there is a growing demand to locally source metal and ceramic parts. In this manuscript, we propose a cost-effective method for in-orbit manufacturing of metal and ceramic multi-material components using highly packed powdered filaments, which need to be shaped, debinded, and sintered in sequential steps. Traditional debinding and sintering of material extrusion (MEX) AM parts are known to be time-consuming and require complex post-processing, often involving toxic debinding agents. To overcome this, a low-intensity infrared diode laser and an induction heater are coupled to a hybrid MEX system to allow full processing in situ, within the same volume. The results show that the main binder matrix can be removed across the 3D volume of the part via laser ablation of the polymeric mass, even for multi-material metal–ceramic composites. The sintered geometries further densify efficiently within the bulk due to the high-energy concentration of the induction sintering treatment, providing short processing times. Debinding and sintering locally, in the same machine, offer a simple and effective way to produce space hardware in situ, avoiding the use of consumables or part transportation to bulky equipment.

Analyzing the combustion characteristics of Thar coal block XI: A comprehensive study

Coal is a key energy resource in the world that is available at low cost and the high energy content in coal makes it a fuel of choice in many developed and developing countries. Regardless of massive reserves, Thar coal of Pakistan is low-rank lignite coal with high moisture contents and has very limited use. The proximate analysis, ultimate analysis and X-ray diffractometry analysis were performed to investigate the combustion characteristics, morphological and mineral characteristics of Thar coal block XI. Thar coal samples in this study are characterized as low-rank lignite coal. The proximate analysis showed a significant difference in moisture content, volatile content, fixed carbon content and ash residue. The ultimate analysis provided the details of elemental contents (Carbon, Hydrogen, Nitrogen and Sulfer) in coal. The combustion characteristics such as combustion performance of lignite at high temperatures (950 °C) was investigated in thermogravimeter and the results showed the variations in the ignition temperature, burnout tempearature, combustion index and burnout index. The marphological characteristic were determined by X-ray diffraction. The mineral congregations, ash yields, major and minor elements (SiO2, Al2O3, CaO,MgO, Fe2O3) varied significantly in the coal. These analyses integrate various results for assessing major monitoring parameters of coal reactivity, its temperature ranges and combustion products.

Floating particles transport through the free surface vortex technique: A novel numerical study to assess the interaction among different scales of vortex structures

Fat, oil, and grease (FOG) floating particles in the sump of sewage pumping stations will accumulate together to form rigid layers, resulting in failure for pump device. To overcome this, the free surface vortex (FSV) technique has been considered and applied to transport floating particles toward the submerged suction pump inlet. This paper investigates the potential of vortices as a means of downward motion of FOG. The entrainment capacity of FSV is investigated by numerical simulations using a coupled level-set and volume-of-fluid method. Two coherent structures are decomposed by proper orthogonal decomposition: FSV represented by the first two orders with high energy content and spiral vortex bands represented by low energy and high order models. The extracted ridges of the finite-time Lyapunov exponent (FTLE) delineate different regions of the flow field and effectively capture the evolution of Lagrangian coherent structures. The floating particles in the sump are first caught by the dividing line formed by the FTLE ridges, mixed in the entrainment zone, and then merged into the vortex. The enstrophy production term dominates the development of vorticity. Subject to the influence of flow velocity gradients, both radial and tangential vortices undergo a transition into axial vortices. This transformation enhances the vortex's capacity to entrain particles within the vortex core area, leading to their rapid inward spiraling toward the vortex center and eventual expulsion due to the vortex's entrainment effect.

Simulation and experimental study of femtosecond laser ablation mechanisms of NiCoCrAlY coatings

To enhance the adhesion of turbine blade thermal barrier coating systems using the LST method, a thorough understanding of the ablation mechanism of NiCoCrAlY bond coat material by femtosecond laser systems is essential for producing high-quality textured grooves. This study systematically investigates the ablation mechanisms of NiCoCrAlY material, exploring the effects of laser energy density, laser scanning speed, and the number of laser scans on the ablation of NiCoCrAlY. Numerical simulations based on the two-temperature model were conducted, providing a comprehensive analysis of thermal effects, heat accumulation, and material response during the laser ablation process. The experimental results indicate that 1) the ablation phenomenon caused by heat accumulation becomes evident as the laser energy density increases from 1.948 J/cm2 to 4.521 J/cm2, with the accumulated heat reaching 1525.2 K, leading to distinct melting residues and heat-affected zones on the groove walls. 2) The change in laser scanning speed also affects heat accumulation. Using a laser scanning speed of 800 mm/s results in a high material removal rate, smooth machined walls, and a uniform surface with no significant heat-affected zones. 3) Excessively high numbers of laser scans shift the laser focus to the bottom of the groove. The high concentration of laser energy causes intense localized ablation, forming sharp bases with numerous cracks and melting residues. To achieve efficient and high-quality laser ablation, it is necessary to ensure that the number of scans remains below 40.

Natural Hydrogen, the Ultimate Green Energy: Current Status and Prospects

Natural hydrogen is green hydrogen that is naturally produced on Earth, that is, an energy source that does not emit carbon without using additional energy for production. Since carbon is emitted from the existing gray hydrogen and blue hydrogen, green hydrogen with perfect eco-friendliness has been required. Natural hydrogen is produced through four mechanisms: serpentinization, radioactive decomposition, magma gas removal, and rock destruction and can exist in the dissolved ․ content of fluid mammals. Representative sites discovered to date include Mali, Africa, Brazil, and Australia, and each topography has different characteristics. Although reserves are estimated using geochemical and geophysical exploration technologies, the reliability is not high because the deep hydrogen flow in various geological environments is not considered. Based on this, this study drew the following conclusions. 1) Hydrogen can realize carbon neutrality with high energy content and independence, but 2) economic feasibility cannot be evaluated due to the uncertainty of the reserves and current reserves of natural hydrogen. Therefore, 3) for commercial use, leakage detection technology is required along with an understanding of the mechanism for generating natural hydrogen.