Equivalent Diameter Research Articles

Mitigating urban heat island through neighboring rural land cover

Globally, the deteriorating Urban Heat Island (UHI) effect poses a significant threat to human health and undermines ecosystem stability. UHI mitigation strategies have been investigated and utilized extensively within cities by the provision of green, blue or gray infrastructures. However, urban land is precious and limited for these interventions, making it challenging to address this issue. Neighboring rural land cover may serve as a cooling source and have a great potential to mitigate UHI through processes such as heat absorption and circulation. This study aims to address the following questions: (1) what is the location of neighboring rural land cover to effectively mitigate UHI for the entire city and (2) what are the key parameters of the landscape. We investigated the quantitative and qualitative relationships between rural land cover and UHI, drawing on geographical and environmental data from 30 Chinese cities between 2000 and 2020. We found that the rural land cover extending outward from the urban boundary, approximately half of the equivalent diameter of city, had the most pronounced impact on UHI mitigation. The number and adjacency of landscape patches (a patch is a homogeneous and nonlinear basic unit of a landscape pattern, distinct from its surroundings) emerged as two key factors in mitigating UHI, with their individual potential to reduce UHI by up to 0.5 °C. The proposed recommendations were to avoid fragmentation and enhance shape complexity and distribution uniformity of patches. This work opens new avenues for addressing high-temperature urban catastrophes from a rural perspective, which may also promote coordinated development between urban and rural areas.

Numerical simulation of the effects of toothed structure on the flow boiling characteristics of micro-fin tubes

Abstract The numerical simulation of R141b flow boiling in micro-fin tubes (MFTs) with a 1 mm equivalent diameter is conducted using the VOF and the Lee models. An analysis of the boiling heat transfer (HT) characteristics has been performed, considering impacts of the four factors. The most suitable correlation of boiling HT has also been evaluated. The summarized findings are as follows: the BHT coefficient within the MFTs consistently rises with increased mass velocity, heat flux, and saturation temperature. However, there is a presence of a partially dry-out region inside the MFTs at high heat flux. Additionally, the enhancement of boiling HT by elevating saturation temperature is not prominent in the low vapor quality range. HT coefficients of the MFTs with various fin structures ranked in magnitude are as follows: tapered MFTs > trapezoidal MFTs > circular MFTs. The model proposed by Wu is identified as the best predictor for flow boiling HT performance in horizontal MFTs, although its prediction accuracy is limited in the low vapor quality range.

Расчет порозности и эквивалентного диаметра насадки тепломассообменного аппарата с регулярной вращающейся насадкой

The use of modernized irregular stationary nozzles, regular stationary nozzles, movable (suspended, gushing and circulating) and regular movable nozzles in heat and mass transfer devices is considered. It is established that the gas movement is carried out along tortuous channels formed by regularly placed nozzle elements. Equations for calculating the porosity of the rotating nozzle in the cross-section of the apparatus, volume porosity and equivalent diameter, taking into account the structural components of rotating nozzle elements with rectangular blades and the steps of placing the nozzle elements in the vertical and radial directions, have been obtained. The influence of arrangement steps of the nozzle elements on the equivalent diameter on the basis of the obtained graphical dependences is considered and analysed. It is determined that the equivalent diameter depends on the steps of rotating elements arrangement in vertical and radial directions in direct proportion. It allows to assume that at average values of steps of arrangement of the nozzle elements it is possible to reduce energy consumption.

Lattice Boltzmann simulation of flow boiling heat transfer process in a horizontal microchannel with rectangular cavities

Bubble nucleation, growth and separation from cavities on the bottom of a microchannel for subcooled flow boiling are investigated by pseudo-potential lattice Boltzmann method. The influence of subcooling temperature, wall superheat, wettability, cavity size, and cavity number on the flow boiling heat transfer is systematically studied. The results show that the bubble equivalent diameter is 1.9 times larger at subcooling temperature 0.05Tc than that at 0.15Tc, and the heat flux is also 8 % higher at subcooling temperature 0.05Tc than that at 0.15Tc. It is found that the flow boiling changes from nucleate boiling to film boiling with the increase of wall superheat. When the wall wettability changes from the hydrophobic wall (θ = 120°) to the hydrophilic wall (θ = 30°), the average Nusselt number (Nuav) is reduced by 23 %. We also optimize cavity height and the uniformly distributed cavity number in the microchannel. It is found that the Nuav is increased by 9.7 % when the cavity height changes from h = 20lu (lattice unit) to h = 60lu. However, there exists an optimal cavity height about h = 60lu, where the heat transfer performance cannot be improved with the cavity height over this value. In addition, the number of cavities in the microchannel can improve the boiling heat transfer. When the cavity number changes from 1 to 4, the Nuav is increased by 10 %.

The structural evolution of undisturbed loess due to water infiltration

Loess structure is the physical key factor that determines its stability and consists of macro-pores, loose texture, and water sensitivity. The structural change characteristics and effects of the undisturbed loess before and after water infiltration are studied using mechanical CT and simulation tests in order to study the structural change process within the undisturbed loess caused by water infiltration. The change in particle state is as follows: the peak frequency point of the equivalent diameter of the loess particles after infiltration ranged from 16.75 to 23.76 μm, and the eroded fine particles consisted primarily of fine particles. The smaller loess particles are removed by water infiltration resulting in coarsening of soil particles. The sphericity of the loess particles gradually changes from spherical pores to angular and dendritic pores. The particle inclination angle transitions to a range greater than 70°, and its proportion is approximately 61%. The change in pore structure is as follows: The loess porosity after infiltration increased by approximately 20%, and the increase in the pore area ratio of the mesopores and the macropores was higher than that of the micropores. Additionally, the small pores increased by more than 5 times the original state of the undisturbed loess. The connected pores expanded less than 60% of the initial state to more than 90% after infiltration, thus, increasing the dominant seepage channel of the undisturbed loess. These changes in particle and porosity further increase the water filtration intensity and promote the migration of fine particles (mainly silt particles), linking loess catastrophes and are the leading cause of loess settlement and slope instability. The process of water infiltration into the loess, the mechanism of loess collapsibility, and the influence of salinity on the loess structure and strength are discussed in this study.

Effect of gradation on macro-meso shear properties of the alluvial-diluvial soil-rock mixture (ADSRM)

Alluvial-diluvial soil-rock mixture (ADSRM) is a unique geological material primarily consisting of pebbles, gravel, and soil. Gradation design significantly enhances the shear strength of ADSRM, offering significant implications for sustainable construction of transportation infrastructure in mountainous regions. Hence, the N-method of gradation theory was employed for the gradation design of ADSRM fillers in this study. Macro-mechanical testing reveals that the graded sample exhibits significantly higher shear strength, equivalent cohesion, and friction angle compared to the ungraded sample, with more pronounced shear dilatancy. Meso-shear properties suggest that the graded sample has a lower percentage of pore area compared to the ungraded sample, but a higher percentage of small pores relative to total pores, and more crushed rock blocks under the same normal stress conditions. Pore abundance indicates that the majority of pores on the shear plane are oblate in shape. The findings from the equivalent diameter and fractal dimension of the rock block contour suggest improved grinding roundness of rock blocks in the graded sample post-shearing. In summary, the quantity of pores and broken rock blocks primarily impacts the strength and equivalent cohesion of the filler, while the abundance, roundness, shape coefficient, and fractal dimension of rock block contour mainly affects the internal friction angle.

Characterizing the Stoichiometry of Individual Metal Sulfide and Phosphate Colloids in Soils, Sediments, and Industrial Processes by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Size and purity of metal phosphate and metal sulfide colloids can control the solubility, persistence, and bioavailability of metals in environmental systems. Despite their importance, methods for detecting and characterizing the diversity in the elemental composition of these colloids in complex matrices are missing. Here, we develop a single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS) approach to characterize the elemental compositions of individual metal phosphate and sulfide colloids extracted from complex matrices. The stoichiometry was accurately determined for particles of known composition with an equivalent spherical diameter of ≥∼200 nm. Assisted by machine learning (ML), the new method could distinguish particles of the copper sulfides covellite (CuS), chalcocite (Cu2S), and chalcopyrite particles (CuFeS2) with 75% (for Cu2S) to 99% (for CuFeS2) accuracy. Application of the sp-icpTOF-MS method to particles recovered from natural samples revealed that iron sulfide (FeS) particles in lake sediment contained ∼4% copper and zinc impurities, whereas pure pyrite (FeS2) was identified in hydraulic fracturing wastewater and confirmed by selected area electron diffraction. Colloidal mercury in an offshore marine sediment was present as pure mercury sulfide (HgS), whereas geogenic HgS recovered from an industrial process contained ∼0.08 wt % silver per Hg, enabling source apportionment of these colloids using ML. X-ray absorption spectroscopy confirmed that Hg was predominantly present as metacinnabar (β-HgS) in the industrial process sample. The determination of impurities in individual colloids, such as zinc and copper in FeS, and silver in HgS may enable improved assessment of their origin, reactivity, and bioavailability potential.

Optimizing Rolling Strategies for API 5L X80 Steel Heavy Plates Produced by Thermomechanical Processing in a Reversible Single-Stand Mill

This study focuses on advancing the production of predominantly bainitic heavy plates to meet the API 5L X80 standard. The investigation involves a thorough evaluation of the influence of rolling parameters and austenite conditioning on both microstructural characteristics and mechanical properties. Accurate specifications for chemical composition, processing temperatures, and mean deformations were established using mathematical models and bibliographical references. Four rolling conditions were performed in a reversible single-stand mill, allowing for comprehensive comparison and critical analysis. Microstructural and mechanical characterizations were performed utilizing several techniques, including optical microscopy (OM), scanning electron microscopy (SEM), tensile tests, Charpy impact tests, and hardness tests to ensure adherence to API 5L standards. Additionally, the SEM-EBSD (electron backscattered diffraction) technique was employed for a complementary analysis. The EBSD analysis included crystallographic misorientation maps, mean kernel misorientation parameters (ϑ), low- and high-angle grains boundaries, mean equivalent diameter, and evaluation of the contribution of different strengthening mechanisms to yield strength. Results underscored the significant influence of austenite conditioning on both microstructure and mechanical properties. Considering the specificities of a reversible single-stand mill, it was concluded that, unlike the classic approach for ferritic or ferritic–pearlitic HSLA (high-strength low-alloy steel), when a product with a predominantly bainitic microstructure is required, the accumulated deformation in the austenite during the finishing rolling stage, as well as its temperature, must be meticulously controlled. It was shown that the greater the deformation and the lower the temperature, the more favorable the scenario for the undesired polygonal ferrite formation, which will deteriorate the material’s performance. Furthermore, an optimized production route was identified and adapted to the specificities of the employed rolling mill. The presented data have great importance for researchers, manufacturers, and users of API 5L X80 heavy plates.

Numerical study on the growth characteristics of bubble in a petal-shaped fuel rod channel

Based on the VOF multiphase flow model and bubble growth model, a numerical analysis model of bubble growth of subcooled flow boiling in a petal-shaped fuel rod channel was established. The growth characteristics of a single bubble and the influence of thermal parameters were analyzed. Firstly, the growth rate, shape, and trajectory of the bubble were investigated under typical working conditions. Secondly, the influences of inlet subcooling, inlet velocity, and wall superheat on the bubble growth characteristics were clarified. Finally, the existing bubble growth rate prediction correlation was evaluated based on the results of numerical calculations. The results show that the bubble growth rate is fast at the early stage of bubble growth when the evaporation heat flow from the microlayer plays a major role. With the disappearance of microlayer evaporation, the bubble diameter increases slowly. The bubble diameter decreases continuously when the evaporation heat flow in the overheating layer is less than the condensation heat flow after the bubble lift-off. Compared to the rectangular channel, the bubble diameter in a petal-shaped fuel rod channel has a larger equivalent diameter and more obvious lateral movement. With the increase of inlet flow velocity and inlet subcooling, the total evaporation heat flow of the bubble decreases, while the condensation heat flow increases, which results in the decrease of bubble diameter. The influence of increasing wall superheat on bubble diameter is opposite to that of increasing inlet flow velocity and inlet subcooling. Based on the numerical results, a new prediction correlation for bubble growth rate in a petal-shaped fuel rod channel was developed, whose prediction error is within ±20 %. The related research results help to further reveal the subcooled boiling heat transfer mechanism in a petal-shaped fuel rod channel.

Flow and heat transfer mechanism and optimization design of spirally corrugated tubes

Abstract Spirally corrugated tubes are widely used as high-efficiency heat transfer tubes in various industrial production fields due to their simple manufacturing, low cost, and bi-directional enhanced heat transfer ability. In this study, numerical simulations were conducted on the flow in multi-start spirally corrugated tubes with an equivalent inner diameter of Di=20 mm. The effects of starts value of 1-8, pitch ratio p/Di of 1.5-3.0, ripple depth ratio e/Di of 0.05-0.20, and Reynolds number Re of 5000-3000 on the heat transfer and resistance characteristics of the multi-start spirally corrugated tubes were studied, and the mechanism of heat transfer enhancement was demonstrated by field synergy theory. In addition, through the performance evaluation standard PEC, the optimization design of the multi-start spirally corrugated tube was achieved. The research results indicate that increasing the start value and ripple depth improves heat transfer performance, despite higher flow resistance. As the pitch increases, the heat transfer performance decreases, and the flow resistance correspondingly decreases. When the start value is 8, p/Di=1.5, e/Di=0.20, and Re=20000, it is the optimal performance evaluation criteria (PEC) value, equal to 1.764. This will be of great significance for the design, manufacturing, and practical application of spirally corrugated tubes.

Model for fracture conductivity considering particle size redistribution caused by proppant crushing

Clarifying the dynamic evolution and control mechanisms of fracture conductivity is crucial for optimizing hydraulic fracturing design. Previous studies on fracture conductivity mechanisms in deep shale reservoirs have been insufficient, particularly when considering proppant crushing, rendering existing models inapplicable. Therefore, in this study, the coupled effects of particle size redistribution caused by proppant crushing were considered. A particle crushing model based on fractal theory was introduced. It was combined with the Kozeny–Carman equation, and equations were derived for the evolution of the equivalent diameter of the proppant pile gradation curve and permeability, establishing a new model for predicting the fracture conductivity considering the particle size redistribution caused by proppant crushing. Furthermore, it provides an optimized chart of conductivity that matches the supply conductivity of the reservoir. The results of the study reveal that the fracture conductivity decreases owing to proppant rearrangement, compaction, and crushing, with a more significant decline in the initial compression stage, where the rate of conductivity reduction is 2.5 times that of the compaction stage. Proppant crushing shifts the gradation curve leftward, reducing the equivalent particle diameter and, consequently, the fracture conductivity. By adjusting the crushing ratio, apparent Young's modulus, looseness factor, and proportion of large-particle components of the proppant, the fracture conductivity can be controlled. This provides a theoretical basis for the development of proppant properties and fracturing optimization in deep shale reservoirs.

Deformation behavior and microstructure evolution of Al-Zn-Mg-Cu alloy under low-frequency vibration-assisted compression: Considering the relative amplitude

The effect of superimposed low-frequency vibration (LFV) during deformation is somewhat similar to that of ultrasonic-vibration, however its mechanism is still unclear. In order to clarify the mechanism of LFV, the LFV-assisted compression experiments of Al-Zn-Mg-Cu alloy with different amplitudes were conducted. The length of the elastic deformation zone (LE) of the material was considered when selecting the relative amplitude parameters. The macro-mechanical response, distribution of secondary phases, dislocation evolution and microhardness were determined. The results show that LFV with different amplitudes exerted different effects on the material. LFV at vibration amplitude <LE exerted a superimposed effect on the elastic stress. The proportion of micron-diameter secondary phases with an equivalent diameter < 3 μm increased by 16.67 % and dislocation proliferation was promoted. LFV at amplitude >LE exerted the coupling effects of elastic stress superposition and plastic vibration softening. The proportion of micron-diameter secondary phases with an equivalent diameter < 3 μm increased by 42.77 %, the proportion of nanoscale precipitates with an equivalent diameter < 2.5 nm decreased by 63.21 %, and dislocation annihilation was accelerated. This study reveals the amplitude correlation to LFV mechanism and provides a new idea for the application of vibration-assisted forming.

Exposures to particulate matters and childhood sleep disorders—A large study in three provinces in China

ObjectivesEvidence on the link between long-term ambient particulate matter (PM) exposures and childhood sleep disorders were scarce. We examined the associations between long-term exposures to PM2.5 and PM1 (PM with an aerodynamic equivalent diameter <2.5 μm and <1 μm, respectively) with sleep disorders in children. MethodsWe performed a population-based cross-sectional survey in 177,263 children aged 6 to 18 years in 14 Chinese cities during 2012–2018. A satellite-based spatiotemporal model was employed to estimate four-year annual average PM2.5 and PM1 exposures at residential and school addresses. Parents or guardians completed a checklist using the Sleep Disturbance Scale for Children. We estimated the associations using generalized linear mixed models with adjustment for characteristics of children, parents, and indoor environments. ResultsLong-term PM2.5 and PM1 exposures were positively associated with odds of sleep disorders for almost all domains. For example, increments in PM2.5 and PM1 per 10 μg/m3 were associated with odds ratios of global sleep disorder of 1.24 (95 % confidence interval [CI]: 1.14, 1.35) and 1.31 (95 %CI: 1.18, 1.46), respectively. Similar results were observed for subtypes of sleep disorder. These associations were heterogeneous regionally, with stronger associations among children residing in southeast region than in northeast and northwest regions. Moreover, larger estimates of PM1 were found than that of PM2.5 in southeast region. ConclusionLong-term PM2.5 and PM1 exposures are independently associated with higher risks of childhood sleep disorders, and these associations vary by geographical region.

An Experimental Performance Assessment of a Passively Controlled Wind Turbine Blade Concept: Part A—Isotropic Materials

This paper is the first part of a two-part series, which presents preliminary findings on a novel flexible curved wind turbine blade designed for passive control, comparing its aerodynamic performance and behavior against a conventional straight blade. Characterized by its ability to twist around its longitudinal axis under bending loads, the flexible curved blade is engineered to self-regulate in response to varying wind speeds, optimizing power output and enhancing operational safety. This design utilizes inherent elasticity and specific geometric configurations to develop torsional loads, resulting in continuous adjustment of the blade’s pitch angle via twist–bend deformation. The study focuses on a comparative analysis conducted in a wind tunnel, testing both a small-scale model of the conventional blade and the flexible curved blade of equivalent diameter. Results indicate that the flexible curved blade concept successfully moderates its rotational speed and power output at higher wind speeds and demonstrates the capability to start generating power at lower wind speeds and stabilize power effectively, aligning with sustainability goals by potentially reducing reliance on active control systems. Despite promising outcomes, passive control mechanisms did not activate at the designed wind speeds, revealing a misalignment between expected and actual performance and underscoring the need for further refinements in blade design and control settings. Additionally, the power coefficient (Cp) versus tip speed ratio (TSR) comparison showed that flexible curved blades operate within a lower TSR range and exhibit controlled capping of power under high wind conditions, marked by a distinctive ‘hook-like’ feature in Cp behavior. This study confirms the feasibility of designing and manufacturing passively controlled wind turbine blades tailored to specific performance criteria and underscores the potential of such technology. Future work, to be detailed in a subsequent paper, will explore further optimizations and the use of Glass Fiber-Reinforced Polymer (GFPR) composite materials to enhance blade flexibility and performance.

Risk assessment of soil compaction due to machinery traffic used in infield transportation of sugarcane during mechanized harvesting

Soil stress imposed by tire-soil contact from transshipment vehicles used in mechanized sugarcane harvesting results in increase in the degree of compactness. In this study we aimed to: (i) estimate the magnitude and propagation of vertical stress into soil caused by sugarcane transshipment wheeling; and (ii) assess the risk and occurrence of soil compaction in an Oxisol of southeastern Brazil. Three tractor-trailers with a carrying capacity of 10, 21, and 30 Mg, and an autonomous truck-trailer with a carrying capacity of 20 Mg were evaluated as field traffic treatments. For each treatment, magnitude and distribution of vertical soil stress (σz) and soil strength (precompression stress, σp) were predicted by modeling estimation and risk of compaction was assessed by σp/σz relationship. The occurrence of soil compaction was evaluated based on measured changes in the bulk density and macroporosity (equivalent pore diameter > 50 μm) up to 0.70 m deep after wheeling. Estimates indicated that the autonomous truck applied stresses that reached 595 kPa at the soil surface beneath the centerline of the tire, imposing the greatest risk of compaction up to a depth of 0.35 m depth. The stresses at the soil surface beneath the centerline from the tractor-towed trailer tires ranged from 275 to 279 kPa, imposing a risk of compaction that did not exceed 0.29 m depth. All assessed transshipment configurations promoted soil compaction, detected by increases in the soil bulk density and decreases in the macroporosity, even at greater depths where risk prediction had not alerted to the soil compaction. The most significant impact on soil compaction was observed for the autonomous truck-trailer and the tractor-towed trailer with a carrying capacity of 30 Mg, also affecting subsoil, as evidenced by a relative increase in soil bulk density of 5 % and 7 % in the 0.30−0.50 m and 0.50−0.70 m layers, respectively, and a relative reduction in macroporosity of 40 % and 50 % in these same soil layers.

Study on the influence of void evolution of porous asphalt concrete on acoustic absorption performance under high-temperature loading

This paper investigated the void evolution in porous asphalt concrete (PAC) under high-temperature loading and the resulting decay in acoustic absorption performance. The specimen of PAC-13 with a void content of 20.2 % was designed and loaded with MMLS3 for 0–100,000 cycles at 60℃. Computed tomography techniques were employed to extract the distribution characteristics and structural parameters of voids. Subsequently, the acoustic absorption coefficients were measured at different loading stages. The results indicate that PAC experienced both rapid and gradual reduction phases in air void content under high-temperature loading. After 100,000 cycles of loading, the air void content decreased by 5.44 %, void connectivity decreased by 4.32 %, and the average number of voids in section reduced by 8.30 %. The distribution range of nearly 90 % of void sizes shifted from below 7 mm to below 6 mm after 100,000 cycles. At different loading stages, the void content, average number and average equivalent diameter of connected voids exhibited a positive correlation and similar trends with the absorption capacity of PAC for small vehicle noise. This study provides novel insights and perspectives into the acoustic performance degradation of PAC due to void evolution under high-temperature loading.

Numerical modeling and experiment for isothermal selective external oxidation behavior of Fe-Mn binary alloys

This paper described work undertaken to the selective external oxidation of Fe-Mn binary alloys during isothermal recrystallization annealing. The effect of different peak temperature, soaking time, dew point conditions on external oxidation of Fe-Mn alloys were investigated. Based on an image segmentation technology, external oxidation behavior was evaluated by the equivalent diameters and coverage fraction of external oxides. A numerical kinetics model of the coupled selective internal-external oxidation during isothermal annealing of Fe-Mn binary alloys was proposed. The model allowed the case of internal and external oxidation simultaneously occurred. Based on the assumptions of oxidation reaction at the steel/atmosphere interface reached an instantaneously local thermodynamic equilibrium, the coupled relationship was described by two interactions. The surface dissolved oxygen content could be controlled by both the annealing atmosphere and the coverage fraction of external oxides on the surface, while the diffusion of oxidant and oxygen inside the steel were blocked by the precipitation behavior of internal oxides. Therefore, the model achieved predict quantitatively the coverage of oxides on the external surface of the steel and the mass fraction profiles of Mn after annealing. The correctness of the calculation results was verified experimentally.

Potential of Miscanthus × giganteus as fuel in a suspended furnace

ABSTRACT Miscanthus is one of the potential bioenergy crops in the world. This non-woody biomass can grow almost anywhere and does not require high cultivation costs. Its energy content is approximately 525 GJ/ha/year, the highest among other non-woody biomass. This research aims to study the potency of Miscanthus × giganteus as fuel in a suspended furnace. Some combustion characteristics of Miscanthus particles were determined experimentally and numerically. At a 40°C/min heating rate, the particle's initial and active decomposition temperatures are 197 and 352°C, respectively. The study also reveals that the combustion mode of the Miscanthus particles was affected by the furnace temperature. At furnace temperatures of 300–400°C, the combustion mode of the Miscanthus particles refers to the simultaneous combustion model. While, at temperatures 450–600°C, its combustion produces extensive flames and is called the sequential combustion model. The extensive flames are useful in cyclone furnaces to maintain combustion stability. Under cold modelling, the average drag time of the representative particles with an equivalent diameter of 1384 µm, in a typical furnace, is 26.82 s, much higher than its combustion time of 11.25 s. This indicates that the particles can be burned out in a suspended state.

Ultrasonic pulse velocity as a non-destructive measure for the projectile impact resistance of cementitious composites across a wide range of mix compositions

This paper presents an investigation on the applicability of using ultrasonic pulse velocity (UPV) as a non-destructive measure for characterizing high velocity projectile impact (HVPI) resistance as well as physical/mechanical properties of cementitious composites across a wide range of mix compositions. Ultra-high performance concretes (UHPCs), engineered cementitious composites (ECCs), concretes, mortars and cement pastes with compressive strengths ranging from 34.2 MPa to 220.2 MPa and elastic moduli ranging from 17.1 GPa to 104.2 GPa are considered for investigation. Projectile impact resistance of cementitious composites is evaluated in terms of the depth of penetration (DOP) and equivalent crater diameter (ECD). Physical/mechanical properties, including compressive strength, static and dynamic moduli of elasticity, density, hardness, splitting tensile strength, compressive and flexural toughnesses, are investigated. The UPV is found to be a promising non-invasive and non-destructive measure for the DOP characterization, since both the UPV and DOP are governed by the weighted properties of underlying constituent materials (e.g. matrix and fine/coarse aggregate). In comparison to the DOP, the correlation between the ECD and UPV is relatively weak. The results indicate that there exists a strong correlation between the UPV and the elastic modulus/density/hardness of cementitious composites. It is also found that commonly used two-phase composite models can predict the UPV of concrete with good accuracy.

Study on phase resonance risk coefficient of pumped-storage units

Abstract In this paper, 48 pumped-storage units (rated output of a single unit is not less than 100MW) put into operation or under construction in China were taken as the research object, and the risk of phase resonance caused by pressure wave propagation in the spiral casing of the unit was studied. The risk coefficient of phase resonance under the matching relationship between different rotational speeds and the number of guide vanes and blades was analyzed, and the advantages and disadvantages of the matching relationship between different rotational speeds and the number of guide vanes and blades were compared. The fitting formulas of the circumferential Mach number with rated head due to the pressure wave propagating along the spiral casing under two equivalent diameters were proposed, which provided references for the optimal hydraulic design of pumped-storage units.