Search Results (116)

Powder Bed Fusion-Laser Beam/Metals (PBF-LB/M) enables the layer-by-layer fabrication of complex parts; however, non-uniform thermal transients during the process induce high stresses. Geometric constraints dominate stress–relaxation behavior, which is the primary mechanism leading to part distortion. Therefore, the printing structure serves as a major factor influencing the distortion of PBF-LB/M-fabricated components, of which the forming angle and support structure parameters are the two key factors affecting the printing structure. This study investigates the effects of forming angles and support parameters on the distortion behavior of oral stents manufactured via PBF-LB/M. The results indicate that the magnitude of distortion varies significantly with the forming angle, with the minimum distortion of 0.667 mm occurring at 75°, while the maximum distortion reaches 1.706 mm at 30°. Combined stiffness theory and thermal stress analysis reveal that the thermal stress peaks at a forming angle of 30°, which is governed mainly by the printed cross-sectional area per layer and the cumulative build height. Meanwhile, structural stiffness gradually decreases as the forming angle increases. The study also confirms that support parameters significantly affect distortion, confirming that larger support mesh size and spacing directly contribute to increased maximum distortion. Based on stiffness theory and thermal stress analysis, it is concluded that support structures reduce distortion primarily through two mechanisms: enhancing the overall structural stiffness and facilitating force transmission. Full article

Coal serves as a cornerstone and stabilizer for China’s energy security; utilizing it in a clean and efficient manner aligns with the current national energy situation. The moisture content of coal is a crucial factor affecting its calorific value and separation efficiency. Therefore, enhancing the drying rate while simultaneously reducing the moisture content in coal is essential to improve separation efficiency. This paper primarily investigates the drying and separation characteristics of wet fine coal particles within a gas–solid fluidized bed system. A hot gas–solid fluidized bed was employed to study the particle fluidization behavior, heat–mass transfer, and agglomeration drying properties under varying airflow temperatures. The results indicate that as the airflow temperature increases, the minimum fluidization velocity tends to decrease. Additionally, with an increase in bed height, the particle temperature correspondingly decreases, leading to weakened heat exchange capability in the upper layer of the bed. Faster heating rates facilitate rapid moisture removal while minimizing agglomeration formation. The lower the proportion of moisture and magnetite powder present, the less force is required to break apart particle agglomerates. The coal drying process exhibits distinct stages. Within a temperature range of 75 °C to 100 °C, there is a significant enhancement in drying rate, while issues such as particle fragmentation or pore structure collapse are avoided at elevated temperatures. This research aims to provide foundational insights into effective drying processes for wet coal particles in gas–solid fluidized beds. Full article

Underground pressurized pipe leakage can induce sand fluidization, leading to ground collapses in urban areas. Additionally, the defluidization process is one of the main causes of sinkholes. In this study, a physical model test was conducted to examine sand bed fluidization and defluidization through a slot, which allowed precise control of the water flow rate in increments of 10 mL/s. The sand layer movement during the experiments was recorded, and the pressure field was accurately measured. The fluidization and defluidization processes were classified into five stages: fluidization static bed, internal fluidization, surface fluidization, internal defluidization, and defluidization static bed. Subsequently, the static bed stage included slow fluidization and fast fluidization, with the former driven by seepage and the latter involving densification and upward movement of sand particles above the orifice. Fluidization initiated at 240 mL/s when the sand particles near the orifice were compressed to approximately minimum porosity 0.37. The head losses comprised orifice head loss, seepage head loss, and vortex head loss, each exhibiting different variation patterns with the water flow rate. Hysteresis was observed in the cavity height curve, attributed to the arching effect. The findings of this study contribute to a more comprehensive understanding of effective strategies for preventing ground collapse. Full article

The article is focused on the quantitative assessment of the thermal impact of polar mesospheric clouds (PMCs) on the mesopause caused by the emission of absorbed solar and terrestrial infrared (IR) radiation by cloud particles. For this purpose, a parameterization of mesopause heating by PMC crystals has been developed, the main feature of which is to incorporate the thermal properties of ice and the interaction of cloud particles with the environment. Parametrization is based on PMCs zero-dimensional (0-D) model and uses temperature, pressure, and water vapor data in the 80–90 km altitude range retrieved from Solar Occultation for Ice Experiment (SOFIE) measurements. The calculations are made for 14 PMC seasons in both hemispheres with the summer solstice as the central date. The obtained results show that PMCs can make a significant contribution to the heat balance of the upper atmosphere, comparable to the heating caused, for example, by the dissipation of atmospheric gravity waves (GWs). The interhemispheric differences in heating are manifested mainly in the altitude structure: in the Southern Hemisphere (SH), the area of maximum heating values is 1–2 km higher than in the Northern Hemisphere (NH), while quantitatively they are of the same order. The most intensive heating is observed at the lower boundary of the minimum temperature layer (below 150 K) and gradually weakens with altitude. The NH heating median value is 5.86 K/day, while in the SH it is 5.24 K/day. The lowest values of heating are located above the maximum of cloud ice concentration in both hemispheres. The calculated heating rates are also examined in the context of the various factors of temperature variation in the observed atmospheric layers. It is shown in particular that the thermal impact of PMC is commensurate with the influence of dissipating gravity waves at heights of the mesosphere and lower thermosphere (MLT), which parameterizations are included in all modern numerical models of atmospheric circulation. Hence, the developed parameterization can be used in global atmospheric circulation models for further study of the peculiarities of the thermodynamic regime of the MLT. Full article

Standalone tsunami defense structures have demonstrated limitations in mitigating wave energy during the 2011 Japan tsunami. In order to mitigate future tsunamis in Japan, multi-layered protective mechanisms have been suggested or implemented after the incident. These include heightening the destroyed or existing embankment with concrete or stones, protecting embankments with concrete blocks, compacting the landward soil, elevating the ground following the coastal embankment, and incorporating green belts. Despite extensive research on the mitigation effects of such multiple countermeasures, the optimal structural configuration remains uncertain. In this study, we evaluated the performance of a multiple mitigation system consisting of a landward forest (F) on an elevated mound (M) following a seaward embankment (E) under a range of supercritical flow conditions using a flume experiment. Several mound heights and lengths were selected to determine the optimum mound for installing the forest. The combination of E and F of 12 rows of trees on M with a minimum height of 1.8 cm (Case EMF_R12) created the greatest water cushion depth between E and M. When M was positioned without F, the water cushion between E and M was created by raising the height of the mound rather than its length. Conversely, a mound with a minimum height and length with a forest was found to be effective in creating the largest water cushion and maximum reduction of the flow energy. The highest energy reduction was between 45 and 70% in this experiment. These findings provide useful insights for developing multiple tsunami mitigation strategies that combine artificial and natural approaches. Full article

A numerical analysis model for sand-mudstone interbedded fracturing based on field application in South China is presented in this paper. The proposed model can analyze the influence laws of different longitudinal lithology changes, stress difference changes, different interlayer positions, and fracturing fluid construction parameters on fracture characteristics. Based on the study of fracture characteristics of low-modulus mudstone, a set of layered stress loading experimental devices was independently designed and developed. Experimental analysis shows that the stress difference has a limited limiting effect on the interlayer propagation of hydraulic fracturing fractures in the Weizhou Formation, and the fracture height is prone to interlayer propagation. The injection of high-rate and high-viscosity fracturing fluid has a significant impact on the hydraulic fracture surface penetration. Numerical simulation analysis shows that the smaller the elastic modulus of the mudstone interlayer and the lower the minimum horizontal principal stress compared to the sandstone layer, the more favorable it is for fracture propagation. Field application showed that the highest injection rate of the fracturing pump in well A was 7 m³/min for south-west Weizhou oilfield shale oil. The interpretation results of the acoustic logging after fracturing showed obvious response characteristics of the formation fractures, and the farthest detection fracture response well distance was 12 m, indicating a good fracturing transformation effect and providing technical support for subsequent offshore shale oil fracturing construction. Full article

Deepening the understanding of composite and metal joint methodologies applied in the aerospace industry is crucial for minimizing operational expenditures. Current investigations are focusing on innovative joining techniques that incorporate additive manufactured rivet pins. This research aims to analyze the mechanical strength of these joints for the effective optimization of pin profiles. Through extensive study of the impact of pin geometry on joint performance, we derived the optimal pin design, considering various initial parameters with the objective of minimizing stress concentration in the pin structure. The joint configurations of metal to composite interfaces were systematically examined using finite element analysis and lap shear testing, which included a singular pin and an adhesive-bonding layer. Numerical simulations reveal that the maximum shear stress in the pin is located at the junction between the base of the pin and the metal plate. By optimizing the shape and dimensions of the pin, both the shear and axial stresses can be significantly mitigated. Following the numerical optimization process, a series of enhanced pins have been produced via additive manufacturing techniques to facilitate mechanical testing. The experimental data obtained align closely with the simulation results, thereby reinforcing the validity of the optimization. The optimal configuration for a single pin, involving a 60° angle and a total height of 3.43 mm, achieves the minimum shear stress. Based on these findings, further investigations are underway to explore optimized designs utilizing multiple pins. This paper presents the results of the single pin study, whereas the findings pertaining to the ongoing investigation on the multi-pin configuration will be disseminated in subsequent publications. Full article

Scientific management and environmental regulation of facility strawberries depends on the level of accurate prediction and forecasting of low temperature freezes in plastic greenhouses during winter and spring strawberry cultivation. Accurate identification of potential factors affecting layer-by-layer minimum temperatures in plastic greenhouses and selection of optimal forecasting methods are important for safe strawberry production. However, the identification of important drivers of minimum temperatures in plastic greenhouses and the prediction of potential drivers of use are still unclear. In this study, we used Classification and Regression Tree (CART) to identify the importance of the potential factors affecting the minimum temperatures at different depths and different heights of plastic greenhouses. Random forest (RF), back-propagation (BP), and multiple linear regression (MLR) were used to establish the minimum temperature prediction models for plastic greenhouses at different depths and heights, respectively. The results showed that T_smin10, T_smin25, T_amin150, T_amin320, and T_amin150 were the most important variables explaining the changes in minimum temperatures at heights T_smin25, T_smin10, T_smin2, T_amin150, and T_amin320 respectively. RF, BP performed much better than MLR, as it showed much lower error indices (AE and RMSE) and higher R² than MLR. The superiority of RF and BP in predicting minimum temperatures is related to their ability to deal with non-linear and hierarchical relationships between minimum temperatures and predictors. The low-temperature frost protection and fine management of strawberries in the Changfeng area can be related to the prediction method of minimum temperature in plastic greenhouses constructed in this study. Full article

The urbanization effect (UE) on local or regional climate is a prominent research topic in the research field of urban climates. However, there is little research on the UE of Urumqi, a typical arid region city, concerning various climatic factors and their spatio–temporal characteristics. This study quantitatively investigates the UE of Urumqi on multiple climatic factors in summer based on a decade-long period of WRF–UCM (Weather Research and Forecasting model coupled with the Urban Canopy Model) simulation data. The findings reveal that the UE of Urumqi has resulted in a reduction in the diurnal temperature range (DTR) within the urban area by causing an increase in night-time minimum temperatures, with the maximum decrease reaching −2.5 °C. Additionally, the UE has also led to a decrease in the water vapor mixing ratio (WVMR) and relative humidity (RH) at 2 m, with the maximum reductions being 0.45 g kg⁻¹ and −6.5%, respectively. Furthermore, the UE of Urumqi has led to an increase in planetary boundary layer height (PBLH), with a more pronounced effect in the central part of the city than in its surroundings, reaching a maximum increase of over 750 m at 19:00 Local Solar Time (LST, i.e., UTC + 6). The UE has also resulted in an increase in precipitation in the northern part of the city by up to 7.5 mm while inhibiting precipitation in the southern part by more than 6 mm. Moreover, the UE of Urumqi has enhanced precipitation both upstream and downstream of the city, with a maximum increase of 7.9 mm. The UE of Urumqi has also suppressed precipitation during summer mornings while enhancing it in summer afternoons. The UE has exerted certain influences on the aforementioned climatic factors, with the UE varying across different directions for each factor. Except for precipitation and PBLH, the UE on the remaining factors exhibit a greater magnitude in the northern region compared to the southern region of Urumqi. Full article

Bound metal deposition (BMD) additive manufacturing technique was used to fabricate gears of PH 17-4 stainless steel material. The gears were fabricated with different layer heights (namely 150 μm and 50 μm) and also subjected to post-fabrication machining. Each gear was tested against commercially available gear in a high-precision control test rig. The operational temperature and noise level were measured during the test, while the material loss due to wear was evaluated at the end of the test. The 50 μm layer height gear performed the best with the least wear loss, minimum noise generation, and temperature rise. The 150 μm layer height gear, which was mechanically polished, performed very similarly to it (50 μm layer height gear) and cost 33% less to print; thus, it was considered the best performing when cost was incorporated. The conclusions found that post machining of printed parts greatly impacts their performance, and thus, the post-print conditions should be considered just as much as the printing conditions. Full article

A study was undertaken at Lake Apopka in Florida to assess the minimum water depth required to contain a wind-induced episodic rise of fluid mud. In a year-long investigation, measurements were made at the mean water depth of 1.3 m to record the variation of suspended sediment concentration due to bed erosion and settling of the flocculated matter. The height of rise is defined as the elevation above the bed at which the mud floc volume fraction is at the threshold between the so-called flocculation settling and hindered settling regimes. The rise, which is considered significant when fluid mud occupies the 0.2 m high benthic boundary layer (BBL), occurs when the threshold wind exceeds about 9 m s⁻¹ corresponding to a 4% cumulative probability of occurrence. Predictive modeling suggests that in 2 m water depth the required wind would be about 14 m s⁻¹ with a low probability of 2%. Moreover, a transition occurs from wave-dominant resuspension at low depths to current-dominance in deeper water, which likely influences BBL dynamics with potential effects on the benthic biota. Provided a higher than present depth can be sustained in the large lake, the deduced relationship between fluid mud rise, wind speed, and water depth makes it feasible to select the depth at which the frequency of fluid mud occupying the BBL remains acceptably low. The developed protocol is general enough to be applicable to other similar shallow lakes where fluid mud rise must be contained. Full article

This study investigates the use of cotton ropes (CRs) as a sustainable and cost-effective substitute for synthetic fiber-reinforced polymers for concrete confinement, offering significant environmental benefits such as lower CO₂ emissions and reduced energy consumption. The work evaluates the effectiveness of CR strips for confining concrete, including scenarios with recycled concrete aggregates (ReCA). Compressive strength improvements varied among specimens, with Specimen I-3F showing a 140.52% increase and Specimen II-3F achieving a 46.67% improvement. Strip configurations for Type I recycled aggregate concrete (RAC) outperformed full wraps on Type II RAC, exemplified by Specimen I-3S’s 84.51% improvement. Ultimate strain enhancements ranged from 915% to 4490.91%, driven by the significant rupture strain of cotton rope confinement. For Type I RAC, complete wrapping significantly outperformed strip configurations by 56%, 50%, and 32% in ultimate strength improvement for 1, 2, and 3 layers, respectively. The confinement ratio, varying from 0.10 to 0.70, greatly influenced the compressive behavior, with compressive strength normalized by unconfined strength increasing consistently with the confinement ratio. A minimum confinement ratio of roughly 0.40 is required to achieve an increasing second part in the compressive behavior. The initial parabolic branch was modeled using Popovics’ formulation, revealing an elastic modulus approximately 20% lower than ACI 318-19 predictions. The second branch was described using a linear approximation, and nonlinear regression analysis produced expressions for key points on the idealized compressive curve, enhancing model accuracy for CR-confined RAC. The $R^2$ values for the nonlinear regression analysis performed on experimental results were greater than 0.90. This study highlights the effectiveness of neural network expressions to predict the compressive strength of CR-confined concrete. A strength reduction (ratio of full wrap and strip wrap height CRs) factor of 0.67 was proposed and used for strip-wrapped specimens. It was seen that the neural network models also predicted the compressive strength of partially wrapped specimens with reasonable accuracy using the strength reduction factor. Full article

The biodegradability and comparatively less harmful degradation of polylectic acid (PLA) make it an appealing material in many applications. The composite material is used as a feed for a 3D printer, consisting of PLA as a matrix and graphene (3 wt.%) as reinforcement. The composite is extruded in the form of wires using a screw-type extruder machine. Thus, prepared wire is used to 3D print the specimens using fused deposition modeling (FDM) type additive manufacturing technology. The specimens are prepared by varying the different process parameters of the FDM machine. This study’s primary objective is to understand the tribological phenomena and surface roughness of PLA reinforced with graphene. Initially, pilot experiments are conducted to screen essential factors of the FDM machine and decide the levels that affect the response variables, such as surface roughness and wear. The three factors, viz., layer height, printing temperature, and printing speed, are considered. Further experiments and analysis are conducted using the Box–Beheken method to study the tribological behavior of 3D-printed composites and the effect of these parameters on surface roughness and wear loss. It is interesting to note that layer height is significant for surface roughness and wear loss. The optimum setting for minimum surface roughness is layer height at 0.16 mm, printing temperature at 180 °C, and printing speed at 60 mm/s. The optimum setting for minimum wear loss is layer height at 0.24 mm, printing temperature at 220 °C, and printing speed at 90 mm/s. The desirability function approach is used to optimize (multiobjective optimization) both surface roughness and wear loss. The layer height of 0.16 mm, printing temperature of 208 °C, and printing speed of 90 mm/s are the optimum levels for a lower surface roughness and wear loss. The SEM images reveal various wear mechanisms, viz., abrasive grooves, micro-fractures, and the presence of wear debris. The work carried out helps to make automobile door panels since they undergo wear due to excessive friction, aging, material degradation, and temperature fluctuations. These are taken care of by graphene addition in PLA with an optimized printing process, and a good surface finish helps with proper assembly. Full article

OGFC (open-graded friction course) steel slag ultra-thin wearing courses are a drainage-type layer used in preventive maintenance and have been successfully applied in road construction in China. However, research on the use of steel slag in ultra-thin wearing courses has mainly focused on macroscopic volumetric indicators and performance, often overlooking the impact of internal mesoscopic void characteristics. This study utilized X-ray CT to scan OGFC ultra-thin wearing course steel slag asphalt mixtures with varying void ratios. A custom digital image processing program was developed to comprehensively and quantitatively characterize the mesoscopic void features of the mixtures from multiple perspectives, analyzing their influence on macroscopic performance. The results show that the surface void ratio and void number exhibited opposite trends with respect to specimen height. Compared to conventional asphalt mixtures, the OGFC steel slag mixtures had a higher average surface void number; the maximum difference between the maximum and minimum surface voids rate reached up to 14.2%. As the equivalent void radius and fractal dimension increased, both the stability and dynamic stability of the mixtures decreased, and the maximum reduction in Marshall stability reached 32.4%. Previous macroscopic-scale studies have struggled to identify these internal mesoscopic void characteristics, and this research provides a deeper understanding of the mesoscopic void structure in OGFC ultra-thin wearing course steel slag asphalt mixtures. Full article

The construction of high rockfill dams on deep overburden in seismically active regions poses significant challenges. Currently, there are no standardized guidelines for defining the computational domain range in seismic analysis, necessitating the establishment of a universally applicable computational domain range that optimizes the balance between computational accuracy and efficiency. This has critical engineering implications for the seismic analysis of rockfill dams on deep overburden. This study employed the seismic wave input method to consider the dynamic interaction between the dam, overburden, and infinite domain. A systematic investigation was conducted on a concrete-faced rockfill dam (CFRD) constructed on deep overburden, considering the influences of overburden thickness, dam height, overburden properties, soil layer configuration, ground motion intensity, and the frequency content of the seismic waves. The acceleration response and seismic deformation of the dam were analyzed. Subsequently, the computational domain range corresponding to various levels of acceptable engineering precision was established. The results indicated that the lateral boundary length should extend a minimum distance equal to the sum of 3 times the overburden depth and 1.2 times the maximum dam height. Additionally, the depth below the overburden–bedrock interface should extend at least 1.2 times the maximum dam height. This study provides a crucial foundation for determining the optimal computational domain range in the seismic analysis of rockfill dams constructed on deep overburden. Full article