Increase In Depth Research Articles

Patterns of tree regeneration and their implications for succession in Himalayan pine-oak forests, India

Factors affecting successional processes are critical determinants of the structural and compositional changes in a plant community. The present study examines the role of plant traits, such as seed size and dispersal mode, habitat factors such as canopy closure, leaf litter, soil moisture, disturbance, fire frequency, and landscape forest cover, in arrival and establishment of tree species in the oak-pine forests of the Western Himalayas. For this, we compared the regeneration, abundance, and composition of tree species in pine forests (pioneer stage) with that in oak-dominated hardwood forests (climax stage). The microsite factors and landscape forest cover varied significantly between the two stages. While species diversity was comparable across seedling, sapling, and pole stages, density of regenerating individuals was relatively lower in oak forest sites. The extent of overlap in species composition between oak and pine forest sites was also found to be low for both regeneration and adult stages. The amount of forest cover surrounding the study sites (landscape forest cover) did not significantly impact regeneration. Instead, factors related to establishment were determined to be more important. Regeneration density decreased with an increase in canopy closure (light environment) and litter depth, implying their crucial role in driving the successional trajectories. When plant traits were considered, all three regeneration stages of large-seeded and animal-dispersed species were of comparable densities in pine and oak forests, suggesting an absence of dispersal or arrival limitation. However, anthropogenic disturbance was found to negatively impact density of zoochorous species while fire frequency negatively influenced the diversity of large-seeded species. Control of extractive pressures, reducing incidence of fire, and retention of protected oak stands may be necessary to enable regeneration of zoochorous and of large-seeded species and thereby, natural succession to oak-dominated hardwood forest in this human-dominated landscape.

Investigation on friction pressure of oil storage and brine discharge in underground salt caverns

The design and control of oil injection and brine removal constitute a crucial task in the construction of salt cavern oil storage (SCOS). In this article, the innovation is that the SCOS pressure governing equations were established, and the impacts of salt cavern depth, crude oil viscosity, as well as injection rate on pipeline friction pressure and wellhead injection pressure were calculated and assessed. Besides, the selection principle of varying viscosity crude oil in different depths of salt caverns, as well as the implementation of an optimal oil injection rate, were proposed. The findings indicated that within the depth range of 500 ∼ 2,000 m, there was a nearly linear correlation between the increase in salt cavern depths and the corresponding rise in injection pressures. The friction pressure generated by the injection pipe constituted the predominant proportion among them, and the range of oil injection pressure was 3.4 ∼ 23.0 MPa. Additionally, the injection pressure and friction pressure were primarily influenced by the viscosity of crude oil, with cavern depth and injection displacement following suit. Shallow salt caverns are optimal for storing high-viscosity crude oil, whereas deep salt caverns are better suited for low-viscosity crude oil storage.

Analysis of the Influence of Contact Stress on the Fatigue of AD180 High-Carbon Semi-Steel Roll

In this study, to investigate the problem of contact fatigue and the damage mechanism of an AD180 high-carbon semi-steel roll, rolling contact fatigue tests were conducted using specimens cut from the periphery of a roll ring. These specimens were characterized under different contact stresses using SEM, a profile system, an optical microscope, and a Vickers hardness tester. The results indicates that the main forms of fatigue damage of an AD180 high-carbon semi-steel roll are peeling, pitting corrosion, and plowing. Moreover, the surface of the roll exhibits delamination and plastic deformation characteristics under high contact stress. Meanwhile, the size and depth of peeling, as well as the amount of pitting corrosion, increase with the contact stress. Peeling is mainly caused by a crack that originates at the edge of the specimen surface and propagates along the pearlite structure and the interface between pearlite and cementite. High contact stress can lead to an increase in the crack propagation depth and angle, resulting in the formation of larger peeling. Under cyclic loading, the near-surface microstructure of the specimen hardens due to grain refinement and dislocation strengthening, and the depth of the hardened layer increases with the increase in contact stress. When the contact stress reaches 1400 MPa, the near surface structure of the specimen changes from pearlite to troostite.

Impact of Hydrostatic Pressure on Molecular Structure and Dynamics of the Sodium and Chloride Ions in Portlandite Nanopores.

In order to address the issues of energy depletion, more resources are being searched for in the deep sea. Therefore, research into how the deep-sea environment affects cement-based materials for underwater infrastructure is required. This paper examines the impact of ocean depth (0, 500, 1000, and 1500 m) on the ion interaction processes in concrete nanopores using molecular dynamics simulations. At the portlandite interface, the local structural and kinetic characteristics of ions and water molecules are examined. The findings show that the portlandite surface hydrophilicity is unaffected by increasing depth. The density profile and coordination number of ions alter as depth increases, and the diffusion speed noticeably decreases. The main cause of the ions' reduced diffusion velocity is expected to be the low temperature. This work offers a thorough understanding of the cement hydration products' microstructure in deep sea, which may help explain why cement-based underwater infrastructure deteriorates over time.

286 Impact of feeding strategies on bodyweight and body condition in mature AI boars

Abstract The objective of this experiment was to determine how varying feeding strategies for boars impacts body weight (BW), backfat depth, loin muscle depth, Knauer caliper measurements, flank to flank tape measurement, body condition score (BCS), and scrotal width and length. This experiment was conducted over two 9-wk periods. Boars were weighed and measurements were taken every 3 wk during the study. Boars (n = 28; Acuity and Topig Norvsin) from two age groups (9 and 15 mo) and two genetic lines (maternal and terminal) were used during this experiment. Boars were blocked by breed and age and randomly allocated to receive one of the three feed intake (FI) levels of a corn-soybean meal-based diet (met NRC 2012 nutrient requirements) using the NRC (2012) maintenance equation [ME for maintenance = (100*kg BW0.75) + 15 kcal for sperm production]. Treatments were: HIGH (150% of maintenance, n = 9), MAIN (100% of maintenance, n = 10), LOW (80% of maintenance, n = 9) for the first 9-wk period. During the second 9-wk period remaining HIGH and LOW boars were crossed-over to opposite treatments (HIGH-LOW, n = 9; LOW-HIGH, n = 7) and maintenance remained unchanged (MAIN-MAIN, n = 8). Data were analyzed using PROC MIXED in SAS 9.4. Boar was the experimental unit with main effects of feed intake and age, and week serving as a repeated measure. Significance was determined at P < 0.05 and a trend at 0.05 < P ≤ 0.10. Three-way interactions of FI*Age*Week were observed during the first 9-wk period. Young boars fed HIGH had a greater increase in BW (P = 0.002), caliper (P = 0.011), backfat depth (P = 0.003), BCS (P = 0.003), and scrotal width (P = 0.004) than old boars fed HIGH and young boars fed LOW had a greater reduction in these variables then old LOW boars. Boars fed LOW for the first 9-wk period had reduced scrotal length (P = 0.004), greater reduction in BW change (P < 0.001), and reduced tape change (P = 0.021) compared with HIGH and MAIN fed boars. Two-way interactions for the second 9-wk period were observed. HIGH-LOW fed boars had decreased BW (FI*Week; P < 0.001), tape (FI*Week; P = 0.019), caliper (FI*Week; P = 0.012), BCS (FI*Week; P < 0.001), and scrotal width (FI*Week; P = 0.047) while LOW-HIGH boars had increased measurements for these variables over time. Additional two-way interactions during the second 9-wk period included Tape (FI*Age; P = 0.046) and BCS (FI*Age; P = 0.028). Overall young boars had more adverse reactions to the varying feeding strategies than old boars, this included larger changes in BW and composition measures. Young and old boars fed MAIN level lost BW and condition indicating the equation for maintenance energy requirement is not accurate for modern genetics working boars. Future research is needed with varying ages and feed intakes in the boar stud to better understand the impacts of growth, development, and maintenance energy for the modern AI boar.

Influence of heat storage on performance of multi-borehole mid-deep borehole heat exchangers

Storing heat underground is an effective method to solve the problem of apparent ground temperature decrease due to long-term operation of a multi-borehole mid-deep borehole heat exchanger (MMBHE), which will cause heating capacity decrease and even heating failure. To understand the influence of heat storage on the MMBHE operation performance, based on the proposed model considering heat storage and extraction, this research comprehensively analyzes the influence of heat storage on the MMBHE heat extract capacity, ground temperature distribution, fluid temperature variation along flow path. The influential factors analyzed include borehole layout, borehole amount, borehole spacing, and borehole depth. The results indicate that adopting heat storage in non-heating seasons significantly improves the ground temperature and the heat extraction capacity of the MMBHE. The MMBHE can extract more heat with heat storage than that without heat storage when the heat storage fluid temperature is higher than the critical heat storage temperature which is much less the borehole bottom temperature. As the case discussed in this paper, the mean heat extraction capacity with heat storage is 24.25 % higher than that without heat storage. As the borehole depth increases, there is a substantial increase in the heat extraction capacity of the MMBHE with no heat storage, and the heat storage effect is weakened when heat storage adopted in non-heating period. Less borehole number and larger borehole spacing make larger mean borehole heat extraction capacity of an MMBHE with no heat storage. However, when the borehole layout, borehole amount, borehole spacing, and borehole depth change, fluctuation of the mean borehole heat extraction capacity with heat storage is much smaller compared to those with no heat storage. When the borehole spacing increases from 25 m to 45 m with no heat storage, the mean heat extraction capacity of the MBHE is increased by 27.67 kW, while that is 11.88 kW with heat storage. This research can provide some inherent understanding of the heat storage on MMBHE performance and reference for designing MMBHE with heat storage systems.

Snow depth has greater influence on moss biocrusts' soil multifunctionality than the number of freeze-thaw cycles

Continued global warming and changes in precipitation patterns, especially regarding snow depth and freeze-thaw cycles (FTCs), have significantly affected the hydrothermal environment in winter at mid- and high-latitudes. In this study, we assessed the effects of changes in snow depth and FTCs, on the biogeochemical cycling of biological soil crusts. We collected moss crust soil samples from a temperate desert in northwest China, and measured the changes in the amount of snow (65 % snow removal, ambient snow, and 65 % snow increase) and FTCs (FT0, FT5, and FT15) under an artificial environment simulation, to determine the nutrient content and enzyme activities related to soil carbon, nitrogen, and phosphorus cycles. In terms of how snowfall and FTCs affect soil multifunctionality (SMF) of desert moss crusts, the research findings demonstrated that snow depth, FTCs, and their interplay have a significant influence on the carbon, nitrogen, phosphorus contents, enzyme activities, and SMF of moss crusts. Compared to snow removal, an increase in snow depth corresponded to a significant increase in the soil water content, and an improvement in soil carbon and nitrogen cycling and SMF. The number of FTCs increased, which led to enhancements in soil phosphorus cycling, soil total phosphorus, and available phosphorus content, together with a reduction in inorganic nitrogen content and the activities of certain enzymes involved in carbon and nitrogen cycling. The structural equation model indicated that snow depth had the greatest effect (total effect of 0.165) on SMF in moss crusts compared to FTCs (total effect of 0.048). Therefore, it is necessary to consider snow depth when examining the effects of climate change on nutrient cycling in the biological soil crusts of temperate deserts.

Soil column-experimental research on the migration pattern of petroleum pollutant in the soil

In the process of oilfield exploitation and production, harmful pollutants, such as Crude oil that falls to the ground (generally refers to crude oil that leaks to the ground during oil production or transportation), production wastewater and oil-bearing mud are produced. In this contribution, the soil and crude oil from Daqing area are adopted as experimental materials to make a soil column-experimental device. The results show that the maximum migration depth of petroleum pollutants is 25 cm, most of the pollutants exist above 10 cm. The components of pollutants in disturbed soil column are complex, and the peak area of each component is large, mainly distributed in C12–C28, while in undisturbed soil column, the content of pollutants is small, and the peak area of each component is also small, mainly distributed in C12–C22. With the increase of depth, the relative content of aromatic hydrocarbons increases. The migration ability of low carbon component is weaker than the other components in crude oil. The components with high carbon number are significantly higher in shallow part. The relative contents of each component from high to low are saturates, aromatic hydrocarbons, resin and asphaltene in the soil. Compared with disturbed soil columns, the structure of undisturbed soil is complex, and the migration rate of pollutants in undisturbed soil is slower than that in disturbed soil. With the increase of depth, the light components of disturbed soil columns gradually decrease, and the relative content of heavy components changes little. The light components of the undisturbed soil column also gradually decreased, and the heavy components greater than C22 did not migrate to the depth of the soil column.

Fatigue characteristics of deep excavation-disturbed Jinping marble

Deep rocks encountered in underground engineering are frequently in complex in situ environments and experience both excavation disturbance during construction and cyclic loading throughout the long-term operation. Understanding the fatigue behavior of excavation-disturbed rocks in complex stress environments is critical for assessing the long-term stability of deep rock structures. Hence, an experimental method has been developed to capture the fatigue damage process of rocks while considering the in situ environment and excavation disturbance. Using this method, a series of triaxial fatigue damage experiments were conducted on Jinping deep marble samples from various in situ environments of 100 m, 1000 m, 1800 m, and 2400 m to better understand the variation in fatigue characteristics at different depths. With increasing depth, the samples experienced more cycles and greater fatigue deformation before failure. Further insights were gained into the fatigue damage behavior in terms of stiffness degradation, energy dissipation and irreversible strain accumulation. A decrease in the elastic modulus and an increase in the dissipated energy and irreversible strain exhibit an evolution pattern of initial→stabilization→acceleration, reflecting the nonlinear fatigue process that occurs inside marble. With increasing depth, marble samples have longer fatigue lives but exhibit more significant stiffness loss, energy dissipation and irrecoverable deformation accumulation; thus, evaluating the instability of deep rock structures solely using fatigue life alone is inadequate. Moreover, the previously reported inverted S-shaped evolution of fatigue damage was observed, and it was found that an increase in depth leads to an earlier onset of the accelerated fatigue damage stage with greater dominance of fatigue failure. Based on the nonlinear strain, loading cycle variable and fatigue life, a highly accurate nonlinear fatigue model was developed to describe the complete inverted S-shaped evolution pattern of fatigue damage, which demonstrated excellent practical implications for the theoretical characterization of anisotropic fatigue damage in disturbed Jinping marble.

Effect of Rubber Cup Rotational Speeds during Tooth Polishing on Sound, Early Caries, and Cracked Tooth Surfaces

High-speed rubber cup polishing can exacerbate tooth surface damage, especially when preexisting conditions such as early caries or cracks exist. This study aimed to quantify the extent of damage to sound teeth based on rotating rubber cup speed and assess the damage in relation to the tooth surface condition. Using a rubber cup, 36 sound teeth were polished at 100, 3000, and 10,000 rpm, and 24 teeth with early carious lesions and 24 cracked teeth were polished at 3000 and 10,000 rpm. Polishing was performed using a rubber cup and prophylaxis paste, applying an on–off method (3.0 N force for 3 s). Damage depth was quantified using a surface profilometer and examined using scanning electron microscopy. Polishing at 10,000 rpm caused significantly more damage to sound teeth than polishing at lower speeds (depth increase: 71.45 ± 15.12 µm at 100 rpm; 61.91 ± 17.82 µm at 3000 rpm; p < 0.001). Teeth with early carious lesions or cracks demonstrated more damage after polishing than sound teeth (p < 0.05). Therefore, the rotational speed of the rubber cup has a critical impact on the extent of enamel damage. Higher speeds can increase the damage depth in both sound and damaged tooth surfaces.

Effect of process parameters on the roughness and tensile behavior of parts manufactured by the metals LPBF process

AbstractThe laser powder bed fusion process for metals (LPBF‐M) results in the development of stochastic surface features that significantly influence the interactions between parts and their surrounding environment, as well as their mechanical properties. The process parameters influence the surface quality, which is quantified by the surface roughness. Therefore, customizing the surface roughness during the build process can significantly contribute to obtaining ready‐to‐use parts, reducing the need for extensive surface posttreatments. This paper utilizes theoretical estimations of melt pool depth under iso‐linear energy density, iso‐power, and iso‐temperature manufacturing process parameter conditions. These estimations are then compared with experimental evaluations of surface roughness and tensile strength in upright‐built specimens to extract the trends in terms of the input energy versus roughness, and the input energy versus tensile behavior. The results show that iso‐energy values yield similar roughnesses due to the consistent expected melt pool depth. Moreover, an increase in melt pool depth generates higher surface roughness, while smaller melt pool dimensions result in improved roughness. Additionally, a comparison between the melt pool size and tensile test performance reveals a detrimental impact on the tensile strength for specimens estimated to have smaller melt pool depths.

Comparative Analysis of Influencing Factors on Heat Extraction Performance of Multi-Type Shallow Borehole Heat Exchangers

In this paper, the influence of design parameters and geological parameters on the heat extraction capacity of common coaxial type, single U-type, and double U-type borehole heat exchangers(BHEs) in shallow ground source heat pump system is analyzed, and the heat extraction performance of different types of BHEs is further compared. The results show that with the increase in borehole depth and ground temperature gradient, the outlet temperature of the three types increases at the end of the heating season, and the single U-type BHE increases most significantly. The increase in inlet flow rate will decrease the outlet temperature of the three BHEs, and the U-type is the most obvious decrease. The increase in inlet temperature will reduce the temperature difference between inlet and outlet of the three types BHEs. Given the same design parameters, coaxial-type BHE obtains the maximum heat.

Finite Element Analysis Study of Buried Crack Defects in B-Sleeve Fillet Welds

Finite Element Analysis Study of Buried Crack Defects in B-Sleeve Fillet Welds

Open-access digital elevation model (DEM) selection for flood inundation modelling using HEC-RAS in Capital City of Nusantara

Flood is a classic but complex issue in most regions of Indonesia. Nusantara, the future capital of Indonesia, is now undergoing construction but the site continues to experience flooding due to high intensity rainfall. To overcome this challenge, identification of flood points in those areas needs to be done. Digital Elevation Models (DEM) are the most important component in modeling flood inundation in data-sparse areas. High-accuracy DEMs have been found to give better flood estimation but the availability of such data is very limited. Therefore, open-access DEMs, such as SRTM, DEMNAS, and MERIT-Hydro, are the most common choices used in modeling flood inundation in Indonesia. Each data set may provide varying model outcomes, due to different data processing methods. These results often lead to confusion as to which result should be used in subsequent studies. In this study, flood inundation in Nusantara will be generated using different DEMs and HEC-RAS hydraulic modeling with 25-, 50-, and 100-year return period rainfall events. The return period rainfall was obtained by calibrating Global Precipitation Measurement (GPM) satellite rain data. The results provide various flood inundation conditions, MERIT-Hydro tends to present higher flood depths. Followed by DEMNAS and SRTM which have lower flood depths. On the other hand, the use of return period variation gives a linear increase in flood depth for the DEMNAS model. While a decline in increment occurred in the SRTM and MERIT-Hydro models when the two big year return periods were applied. This research can be considered for the Nusantara development planning.

Effects of cover crops and nitrogen fertilization on soil physical properties, carbon and nitrogen fractions, and winter wheat yield in the Chinese loess plateau: A 4-year field experiment

Context or problemLone-term application of chemical fertilizers in farmland ensure adequate or profitable crop yields but may damage soil structure. Cover crops (CCs) have great potentials to improve soil quality and promote sustainable crop production. However, the combined impacts of CCs with nitrogen fertilization on soil quality and crop yields are not clear. Objective or research questionWe aimed to examine the effects of CCs combined with N fertilization rates on soil physical properties, C and N fractions in both bulk soils and aggregates, and crop yields, and to find the best management practice that improve both soil quality and crop yields synthetically. MethodsA 4-year summer CCs - winter wheat field experiment was conducted in the Loess Plateau of China. CCs with different species and combinations (CC) were soybean (SB), sudan grass (SG), a mixture of both (SS), and no cover crop (CK) and N fertilizer (NR) were applied to winter wheat at rates of 0 (N0), 60 (N60), and 120 (N120) kg N ha−1. Soil physical properties and C and N fractions in both bulk soils and aggregates were evaluated at 0–10, 10–20, and 20–40 cm soil depths. ResultsSoil total porosity (TP), saturated water content (SWC), capillary water capacity (CWC), and C and N fractions decreased while bulk density (BD) increased with the increase of soil depth. The CC, NR, and their interaction (CC×NR) had significant effects on soil BD, aggregate size distribution and stability (MWD), and C and N fractions and only CC and CC×NR had significant effects on other physical properties. The incorporation of CCs significantly increased the proportions of > 5 mm aggregates and C and N fractions in both bulk soils and aggregates, especially in 0–10 and 10–20 cm. And SB and SS improved soil other physical properties more than SG, especially in 0–10 cm, which decreased BD by 13.2% and 12.6% while increased TP by 6.5% and 8.3%, SWC by 14.3% and 15.3%, CWC by 13.9% and 14.2%, MWD by 16.6% and 14.4%, respectively, compared to CK. Additionally, soil physical properties improved more with N60 while the C and N fractions in both bulk soils and aggregates increased more with N120. However, BD increased by 2.6% and 3.3% in N60 and N120 than N0, respectively. The correlations between the proportion of macro-aggregates and soil C and N fractions at 0–10 and 10–20 cm indicated the positive effects of CCs on improving soil structure and fertility simultaneously. Aggregated-associated C and N fractions decreased firstly and then increased with the reduced aggregate sizes, and were higher in micro-aggregates than in other size classes. N60-SB increased wheat yields by 98.7% compared with N0-CK. ConclusionsOverall, the incorporation of soybean residue was the best management practice for winter wheat yield and soil fertility under the reduced N fertilization. Implications or significanceThe selection of CCs species should depend on farmland managements, and the appropriate CCs with N fertilizer rates would target the improvements in soil quality, the sequestration of soil organic carbon, and crop yields synergistically.

Dynamic tensile properties of a novel high strength and high toughness bolt steel: Constitutive models and microstructures

With the continuous increase of depth in underground engineering, rock bursts or rock explosions can cause instantaneous shock load and result in rock engineering disasters. To solve these problems, a novel high strength and high toughness (HSHT) bolt steel with constant resistance and large deformation is proposed. This study aims to investigate the dynamic constitutive models and microstructure of HSHT steel under extreme loading conditions. A series of dynamic tension tests were conducted using a Split Hopkinson Tensile Bar (SHTB) system with a high-speed camera. The results revealed that the HSHT steel exhibited a positive strain rate effect. As the strain rate increased from 1000 s−1 to 5000 s−1, the yield strength and ultimate strength of the HSHT steel increased gradually. However, no obvious changes in the uniform elongation. Specifically, the yield strength, tension strength, and uniform elongation of strain rate at 5000 s−1 were 1100 MPa, 1170 MPa, and 30%, respectively. According to the results of the SHTB tests, a modified Johnson-Cook model was proposed. Additionally, we investigated the microstructure of HSHT steel at a high strain rate through microscopic characterization techniques. A large number of fine and deep dimples were observed near the fracture of HSHT steel under dynamic loading. Moreover, the HSHT steel demonstrates a significant presence of nano-twins, which effectively impedes crack propagation both within the grain interior and along grain boundaries. The above findings reveal the relationship between mechanical behavior and microstructure in HSHT steel within dynamic loading conditions, providing valuable insights for the design of HSHT steel in underground engineering.

Changes in the physical and mechanical properties and structure of rocks depending on the depth of mining operations in iron ore quarries

The trend of the activity of open-quarry mining enterprises of iron ore raw materials is an increase in depth quarries. It is investigated in the work, changes in physical and mechanical properties and rock structure depending on the depth of mining operations in quarries. Natural geophysical and laboratory methods of research were applied. It was established that the angle of internal friction, Poisson’s ratio and rock density practically do not depend on depth of mining operations. But with an increase in the depth of iron ore quarries, there is an increase in the compressive and tensile strength of rocks. Indicator of specific adhesion has significant dynamics of fluctuations depending on the mineral composition of rocks and can either increase or decrease in deep horizons, which must be taken into account in each specific calculation. For example, by determining marginal angles of slopes of sides and ledges. According to the data of geophysical studies, it is established a characteristic increase in the intensity of creep shear processes and surface deformations rocks when the quarry depth increases. The results of research are recommended to be taken into account when organizing the mining and technological process in deep iron ore quarries.

Effect of wear on the dynamic characteristics of a rigid rotor supported by journal bearings

The purpose of this work is to examine the effects of wear severity on the static and dynamic characteristics of journal bearings, and on the vibration response of a rigid rotor supported by journal bearings. Numerical simulations using MATLAB was conducted for three different operating regimes, namely low loaded operating regime (ϵ0=0.15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\epsilon _0 = 0.15$$\\end{document}), moderately loaded operating regime (ϵ0=0.45\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\epsilon _0 = 0.45$$\\end{document}) and highly loaded operating regime (ϵ0=0.75\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\epsilon _0 = 0.75$$\\end{document}) with wear depth parameter ratio (δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta$$\\end{document}) varied from 0 to 0.5 at increments of 0.1. Numerical results showed that the vibration response of the rotor generally increases with the increase of the wear depth for all cases of low, moderately and highly loaded operating regimes of the bearings. For the values of parameters considered in this work, it was shown that the vibration response amplitude of the rotor in worn journal bearings may be six times larger compared to the response amplitude of the rotor in non-worn bearings.

Method for Pressure Relief in Deep Coal Mine Roadways Using Borehole Groups and Its Application to Guqiao Coal Mine

Abstract With the increase in the mining depth of coal mines in China, the problem of large deformation of roadways owing to high-ground pressure has become prominent even under enhanced support systems. To reduce the high pressure on the surrounding rock, this study investigates a pressure-relief method for deep roadways using drilling borehole groups. Based on a deep roadway in the Huainan mining area of China, the influences of drilling parameters, such as borehole diameter, length, and arrangement were investigated. The results indicate that the fan-shaped arrangement of the borehole group can compensate for the dilatancy deformation of the surrounding rock. The peak stress of the surrounding rock is reduced and transferred to the inner part of the surrounding rock. Furthermore, a field experiment was conducted on an experimental roadway. The deformation of the roadway was monitored and compared with that of an adjacent roadway that did not apply the pressure-relief method. The monitoring results indicated that the deformation of the experimental roadway was significantly reduced.

Surface Integrity of Binderless WC Using Dry Electrical Discharge Assisted Grinding

AbstractBinderless tungsten carbide (WC) is preferred for manufacturing tools, mould, and wear-resistant components. However, due to its high brittleness and hardness, the machined binderless WC surface is prone to generate microcracks and the machining efficiency is extremely low. Aiming at this difficulty, a clean and eco-friendly dry electrical discharge assisted grinding (DEDAG) method without any liquid medium was proposed for the processing of binderless WC. DEDAG principle was revealed and the DEDAG platform was first developed. A series of DEDAG, conventional dry grinding (CDG), and conventional wet grinding (CWG) experiments were conducted on binderless WC under different processing parameters. The current and voltage waveforms during the DEDAG process were observed, and the discharge properties were analyzed. The chip morphologies, surface hardness, residual stress, as well as surface and subsurface morphologies were analyzed. The results show that the surface hardness and roughness obtained by DEDAG are smaller than that by CDG or CWG. The measured residual tensile stress after CDG is larger against DEDAG. The ground surface by DEDAG has better crystal integrity than that by CDG. DEDAG can soften/melt workpiece material and diminish grinding chips, thereby promoting plastic removal and increasing processing efficiency. The influences of DEDAG parameters on the ground surface quality are also investigated, and the optimal DEDAG parameters are determined. With the increase of open-circuit voltage or grinding depth, the surface quality improves first and then worsens. The optimal open-circuit voltage is 40 V and the grinding depth ranges from 10 µm to 15 µm. This research provides a new idea for promoting the efficient and low-damage processing of binderless WC.